Heavy metal removal from aqueous solution by wasted biomass from a combined AS-biofilm process

合集下载

Magnetite nanoparticles for removal of heavy metals

Magnetite nanoparticles for removal of heavy metals from aqueous solutions:synthesis and characterizationLiliana Giraldo •Alessandro Erto•Juan Carlos Moreno-Piraja´n Received:29September 2012/Accepted:29December 2012/Published online:12January 2013ÓSpringer Science+Business Media New York 2013Abstract Fe 3O 4magnetic nanoparticles were synthesized by co-precipitation method.The structural characterization showed an average nanoparticle size of 8nm.The syn-thesized Fe 3O 4nanoparticles were tested for the treatment of synthetic aqueous solutions contaminated by metal ions,i.e.Pb(II),Cu(II),Zn(II)and Mn(II).Experimental results show that the adsorption capacity of Fe 3O 4nanoparticles is maximum for Pb(II)and minimum for Mn(II),likely due to a different electrostatic attraction between heavy metal cations and negatively charged adsorption sites,mainly related to the hydrated ionic radii of the investigated heavy metals.Various factors inﬂuencing the adsorption of metal ions, e.g.,pH,temperature,and contacting time were investigated to optimize the operating condition for the use of Fe 3O 4nanoparticles as adsorbent.The experimental results indicated that the adsorption is strongly inﬂuenced by pH and temperature,the effect depending on the dif-ferent metal ion considered.Keywords Magnetite ÁNanoparticles ÁIsotherms ÁMetal ions1IntroductionAdsorption processes are worldwide adopted in the ﬁeld of environmental protection,thanks to the ability of certain solids to preferentially concentrate onto their surface spe-ciﬁc substances,such as heavy metals and organics.A wide range of adsorbents have been developed and tested,including several activated carbons for the removal of pollutants from wastewaters (Faur-Brasquet et al.2002;Mohan and Singh,2002;Puziy et al.2004;Di Natale et al.,2009;Moreno-Piraja´n and Giraldo 2012).During the last 10years,extensive researches have been carried out to ﬁnd low-cost and high capacity adsorbents for water remedia-tion.A large number of low-cost agricultural wastes,mud (Keith and McKay 2008;Purevsuren et al.2004),tire rubber and ﬂy ash (Jiang 2001;Wilson et al.2003;Wu et al.2005;Nasiruddin Khan and Farooq Wahab 2007;Balsamo et al.2011)have been used for the removal of metal ions from polluted water.Several natural resources have been also studied including tree fern (Pattanayak et al.2000;Moreno et al.2010),peat,chitosan,coal and bone char (Pattanayak et al.2000)or minerals such as sodium and calcium bentonite (Liu et al.2007).The efforts to ﬁnd alternative low-cost materials and the recent progress of nano-techniques have led to the devel-opment of new classes of nanoparticles for the treatment of contaminated water.Nanoparticles,often characterized by large speciﬁc surface area,have attracted great interest because of their unique properties and potential applications.Metal oxide nano-adsorbents have been extensively studied as they show very attractive properties compared to their bulk form,such as high adsorption capacity,enhanced catalytic activity,high dispersion degree and superparamagnetism behavior (Banﬁeld and Zhang 2001;L.GiraldoDepartamento de Quı´mica,Universidad Nacional de Colombia,Bogota ´,ColombiaA.ErtoDipartimento di Ingegneria Chimica,Universita`degli Studi di Napoli Federico II,Naples,ItalyJ.C.Moreno-Piraja´n (&)Departamento de Quı´mica,Universidad de los Andes,Bogota ´,Colombiae-mail:jumoreno@.coAdsorption (2013)19:465–474DOI 10.1007/s10450-012-9468-1Niemeyer2001;Roco2003;Savage and Diallo2005; Waychunas et al.2005;Perez,2007;Nassar et al.2011a, b).These properties offer novel applications for nano-adsorbents in manyﬁelds such as electronics,biotech-nology,medicine,heavy oil upgrading,air pollution control and,in particular,for water treatment(Goya et al. 2003;Hua et al.2009;Kang et al.2005;Pankhurst et al. 2003;Portet et al.2001;Reimer and Weissleder1996; Ha¨feli et al.1997).For an instance,magnetic iron oxide (Fe3O4)nanoparticles have been investigated not only in theﬁeld of magnetic recording but also in the areas of medical care and magnetic sensing in the recent decades (Shen et al.2009;Sun et al.2000;Xie et al.2007; Pankhurst et al.2003).It is believed that these magnetic nanoparticles exhibit amphoteric surface activity,easy dispersion ability and,thanks to their very small dimen-sions,a high surface-to-volume ratio,resulting in a high metal adsorption capacity(Shen et al.2009;Nassar,2011; Tratnyek and Johnson2006;Sun and Zeng2002;Si et al. 2004;Wan et al.2006).The use of magnetic nanoparticles for separation and preconcentration in analytical chemistry provides a new methodology that is faster,simpler and more precise than those used traditionally.The greatest advantage of this method is that desired materials are separated from solution by a simple and compact process while fewer secondary wastes are produced.Other advantages are represented by a large active surface area for given mass of particles and the ability to process solution that contains suspended solids (Khajeh and Khajeh2009).In addition,an easy separation of the metals loaded on the magnetic adsorbent from solution can be achieved using an external magneticﬁeld. Thus,an efﬁcient,economic,scalable and non-toxic syn-thesis of Fe3O4nanoparticles is highly desired for practical applications and fundamental research.A possible appli-cation of this sorbent should start from a thorough analysis of the main parameters inﬂuencing the adsorption of heavy metals on magnetite nanoparticles.Moreover,the individ-uation of the main adsorption mechanisms should take into account a quite large number of metal ions,so to allow a comparative analysis too.At the moment,there is still a lack of this information in the pertinent literature.In this work,the feasibility of Fe3O4nano-adsorbents for the removal of different metal ions,i.e.lead,zinc, copper,and manganese from aqueous solutions has been investigated.An accurate preparation procedure and a thorough characterization of the Fe3O4nanoparticles has been provided.Adsorption tests have been carried out by varying solution pH,contact time and temperature.A critical interpretation of the experimental results allowed the identiﬁcation of theﬁeld of potential application of iron oxide nano-adsorbents for metal adsorption from industrial wastewater.2Experimental2.1Sample preparationFe3O4magnetite nanoparticles were synthesized by co-precipitation method(Shen et al.2009).The procedure followed for the preparation is here speciﬁed,indicating the actual quantity of reagents used in the present work.A volume of100mL of ferric chloride(0.5M)was added to 200mL of ferrous chloride solution(0.5M)and150mL of ammonium hydroxide(1M).300mL of deionized water was deoxygenated by bubbling N2gas for30min in a1000mLﬂask and then added to the solution.Subse-quently,50mL of ammonium chloride was added and the mixture was stirred magnetically for10min under a nitrogen atmosphere.Afterwards,50mL of ferrous chlo-ride0.5M and50mL of ferric chloride0.5M were added and then the resultants were aged for10min before being separated.Below it is reported the reaction for the forma-tion of Fe3O4particles(Palacin et al.1996):Fe2þþ2Fe3þþ8NH3ÁH2O¼Fe3O4#þ8NHþ4þ4H2Oð1ÞFinally,the Fe3O4product was separated by a centrifugal pump and washed twice with deionized water and ethanol.The obtainedﬁne Fe3O4nanoparticles were dried at60°C for8h(Shen et al.2009).2.2Sample characterizationFourier transform infrared spectroscopy(FTIR)spectra was performed on previously dried magnetite sample using a FTIR spectrophotometer(Model NICOLET5700,USA) in wave range of3,500–400cm-1with a resolution of 4cm-1.The dried sample was placed on a silicon substrate transparent to infrared,and the spectra were measured according to the transmittance method.In addition,a GL-16A high-speed centrifuge(Shanghai)was used for separating the solid from the liquid during the sample preparation.The micrographs of prepared nanoparticles were obtained using a JSM-7001F scanning electron microscopy(SEM)and a Tecnai G220transmission electron microscopy(TEM)was used for the character-ization of nanoparticle size.Speciﬁc(BET)and external nanoparticle surface areas were measured by nitrogen adsorption and desorption at77K,using a Autosorb3B (Quantachrome,MI,FL,USA)analyzer.The samples were degassed at423K under N2ﬂow overnight before analysis. Surface area was calculated using the BET equation.The total pore volume,V pore,was evaluated from nitrogen uptake at a relative pressure of ca.0.97,using the adsorption branch.N2adsorption measurements were per-formed in duplicate to check the proper functioning of theequipment and the entire technique,and the average values have been presented.The crystallographic phase was also determined by analyzing the X-ray powder diffraction taken with a PW1830diffractometer(Rigaku PDLX, Japan),using a monochromatized X-ray beam with nickel-ﬁltered CuK a radiation(k=0.154021nm).2.3AdsorbatesThe following chemicals were used as precursor salts for the metal cations used in the experimental tests, namely Cu(NO3)2Á5H2O(99.9985%,Merck,Germany), Pb(NO3)2(99,9%,Fisher Scientiﬁc,Toronto,ON,Canada) Zn(NO3)2Á5H2O(99%,Fisher Scientiﬁc)and Mn(NO3)2Á4H2O(Merck,Germany).Individual stock solutions were prepared by dissolving a speciﬁed amount of the corre-sponding metal salt in250mL of deionized water,subse-quently diluted to the required concentration.All metal salts were used without further puriﬁcation(Shen et al. 2009).2.4Adsorption procedureThermodynamic and kinetic adsorption tests were per-formed in batch-mode;for all the experimental runs the procedure described by Nassar(2011)was followed.In a typical experiment,200mg of Fe3O4nanoadsorbent were weighed into a100mL vial containing50mL of metal ion solution.Metals concentration ranged from10to 600mg L-1,in order to investigate a broad spectrum of concentrations.Tests aimed at the analysis of pH effect were conducted at298K and the initial pH of the solution was adjusted without a signiﬁcantly change in the initial concentration of metal ions in solution.Standard0.1M HCl and0.1M NaOH solutions were used for pH adjustment.The effect of temperature was investigated as well,and adsorption tests were carried out at288,293,313and 323K.When adsorption equilibrium was reached,the nanoad-sorbent was conveniently separated via external magnetical ﬁeld and the solution wasﬁltered to allow metal concen-tration measurements.For the adsorption kinetic studies,metal ion initial concentration was set to150mg L-1for each metal,and the experiments were carried out in a temperature incubator at298K,200rpm and solution pH5.5.In order to deter-mine the time required to reach the adsorption equilibrium, samples were analyzed for metal ion concentration at predetermined time intervals.To assure the accuracy, reliability,and reproducibility of the collected data,all batch tests were performed in triplicate and average values only were reported.Blank tests were run in parallel on metal solutions without addition of sorbent,showing that the experimental procedure does not lead to any reduction of metal concentration and pH variation unrelated to sor-bent effects.For all the tests,the concentration of metal ions in the supernatant was measured by a plasma-atomic emission spectrometer(ICP-AMS,Optima3000XL,PerkinElmer)in accordance with the Standard Methods for water(Ameri-can Public Health Association1995).The adsorbed amount of metal ions(mg of metal ion g-1of Fe3O4nanoadsorbent)was determined by the mass balance reported in Equation(2):Q e¼C oÀC emVð2Þwhere C o is the initial metal ion concentration in the supernatant(mg L-1),V is the sample volume(L),and m is the mass of Fe3O4nanoadsorbent(g).For time-dependent data,C replaces C e and Q replaces Q e in Equation(2).3Results and discussion3.1Fe3O4magnetite nanoparticles characterizationFTIR spectrum in Fig.1shows that the H–O–H bending vibration at about1,000–1,600cm-1,typical of the H2O molecule,has very low intensity.Additionally,the sec-ond absorption band,between900and1,000cm-1,cor-responds to bending vibration associated to the O–H bond.The O–H in plane and out of plane bonds appear at 1,583.45–1,481.23and935.41–838.98cm-1,respec-tively(Nassar et al.2011b).For strong hydrogen bridges, its maximum lies at about900–1000cm-1.Theseﬁrst two bands correspond to the hydroxyl groups attached to the hydrogen bonds in the iron oxide surface,as well as the water molecules chemically adsorbed to the magnetic particle surface.In the spectrum showed(Fig.1),the sample exhibits two intense peaks,respectively at582 and640cm-1bands,that are due to the stretching vibration mode associated to the metal–oxygen absorp-tion band(Fe–O bonds in the crystalline lattice of Fe3O4) (Ahn et al.2003).They are characteristically pronounced for all spinel structures and for ferrites in particular.This occurs because of the contributions,in these regions, deriving from the stretching vibration bands related to the metal in the octahedral and tetrahedral sites of the oxide structure.Moreover,the FTIR spectrum shows an absorption band at1,706cm-1,which corresponds to the stretching vibration of the carboxyl group(C=O),asso-ciated to the oleic acid molecule,adsorbed onto the surface of the crystallites.Summarizing,magnetite nanoparticles have crystalline structure of inverse spineltype,and FTIR absorption spectroscopy allowed identi-fying characteristic features of the spinel structure,as well as a presence of certain types of chemical substances adsorbed on the surface of nanoparticles(Ahn et al.2003; Farmer1974,1982).The magnetite sample was characterized by X-ray powder diffraction(XRD)with the corresponding results displayed in Fig.2.The diffraction pattern and the rela-tive intensities of all the diffraction peaks are typical of the magnetite and match those synthesized in this research.Furthermore,the sample shows some of the character-istics of the bulk magnetite crystallite phase,with the broad peaks suggesting the nano-crystallite nature of the mag-netite particles(Gonza´lez et al.2010).The resulting mean particle diameter of magnetite nanoparticles,as calculated from the Scherrer equation, was ca.10nm.This was in agreement with the result obtained from the TEM image(Fig.3).From this image and from the corresponding electron diffraction pattern,it was determined that the magnetite particles are spherical with an average diameter of8nm.The corresponding BET speciﬁc surface area of the particles was95.5m2g-1,as determined by conventional method.The SEM analysis shown in Fig.4almost conﬁrmed the results of the TEM analysis,as particle sizes in the range 10–70nm were measured.3.2Adsorption tests:effect of contact timeThe adsorption efﬁciency(g)can be deﬁned as:g¼C iÀC fC iÂ100ð3Þwhere C i and C f represent initial andﬁnal metal ion con-centration,respectively.In order to determine the effect of contact time on Pb(II),Mn(II),Cu(II)and Zn(II)ions adsorption efﬁciency and to determine the time required to reach equilibrium, experimental tests were carried out using200mg Fe3O4 nanoparticles and1:4liquid to solid ratio(L/S)at298K and pH5.5,with a contact time varied in the range of 2–48h.Figure 5shows the effect of contact time on the adsorption efﬁciency of Pb(II),Cu(II),Zn(II)and Mn(II).It is clear that the adsorption efﬁciency of Zn(II)and Mn(II)were highly time dependent,i.e.,a longer contact time resulted in higher adsorption efﬁciency.It can also be observed that a contact time of 24h is sufﬁcient to reach the equilibrium for all the investi-gated ions.Very interestingly,the adsorption efﬁciency of Pb(II)and Cu(II)were extremely high for very low time (\10h)and remained constant in the whole range of the time investigated.3.3Adsorption kineticsIn order to better analyze the rates of Mn(II),Zn(II),Cu(II)and Pb(II)adsorption on Fe 3O 4magnetite nanoparticles,two simple kinetic models were tested.The pseudo-ﬁrst order rate expression,popularly known as the Lagergren equation,is generally described by the following equation (Lagergren,1898):dqdt¼k ad q e Àq ðÞð4Þwhere,q e is the amount of the metal ions adsorbed at equilibrium per unit weight of sorbent (mg g -1);q is the amount of metal ions adsorbed at any time (mg g -1).Besides,k ad is the rate constant (min -1).Integrating with appropriate boundary conditions (q =0for t =0and q =q t for t =t ),Eq.4takes the form:ln q e Àq ðÞ¼ln q e Àk ad tð5ÞHowever,if the intercept does not equal the natural logarithm of equilibrium uptake of metal ions,the reaction is not likely to follow a ﬁrst-order path even if experimental data have high coefﬁcient of determination (Lagergren,1898).The coefﬁcients of determination for all metal ions adsorption kinetic tests were found to be between 0.9434and 0.9765and were reported in Table 1together with the Lagergren rate constants calculated from the slope of Eq.5(Ho and McKay,1998).The adsorption data was also analyzed in terms of a pseudo-second order mechanism given by (Hou et al.2003;Marmier et al.2000).dqdt¼k 2q e Àq ðÞ2ð6Þwhere,k 2is the rate constant (mg g -1min -1).Integrating the above equation and applying boundary conditions (i.e.q =0for t =0and q =q t for t =t),gives:t q t ¼1h o þ1q et ð7Þhere,h o is the initial adsorption rate.If the second-order kinetics is applicable,the plot of t/q against t in Eq.7should give a linear relationship from which theconstantsFig.3Transmission electron microscope (TEM)imagen for mag-netic Fe 3O 4nanoparticlessynthesizedFig.4SEM of image magnetic Fe 3O 4nanoparticlessynthesizedFig.5Effect of contact time on the adsorption of Pb(II),Mn(II),Cu(II)and Zn(II)ions using magnetic Fe 3O 4nanoparticles.T =298K,pH 5.5,adsorbent dosage =200mg,V solution =50mL,Initial metal ions concentration =150mg L -1q e and h o can be determined.Linear model gave a good ﬁt to the experimental data.This means that the adsorption can be described by a pseudo-second order rate equation,hence q e and h o were evaluated and presented in Table 1.R 2values are approximately the same for all the 4metal ions,with values of about 0.999.In the limit at initial adsorption time,h o is deﬁned as (Ho and McKay 1998;Horsfall and Spiff 2004):h o ¼k 2q 2eð8Þh o was calculated for the 4metal ions and the values are reported in Table 1.The results obtained are similar to previous studies (Lagergren 1898;Ho and McKay 1998;Horsfall and Spiff 2004).For all the regressions,the residual sum of squares (SSE),as the difference between the predicted values and the experimental data,can be calculated by the following equation:Xnq e exp Àq e calc ðÞ2ð9Þwhere the subscripts exp and calc refer to the experimental and the calculated q values,respectively.A lower SSE value indicates a lower discrepancy between the experi-mental and the estimated parameters,allowing to deter-mine the best ﬁtting model.Hence,the higher correlation coefﬁcients (R 2)and lower SSE values for pseudo-second-order kinetic model indicated that the sorption followed a pseudo-second order mechanism,likely controlled by chemisorption (Araneda et al.2008).3.4Effect of pHThe pH of the aqueous solution is an important controlling parameter in heavy metal ion adsorption processes,as reported by several authors in the literature.Fig.6showsthe effect of solution pH in the range 2–7on the removal ofPb(II),Cu(II),Zn(II)and Mn(II)ions from aqueous solu-tions by magnetite nanoparticles.As a matter of fact,at higher pH the determination of reliable adsorption capacity is not possible,due to the possible precipitation of cations as hydroxides.Experiments were carried out at 298K with a contacting time of 24h.The adsorption efﬁciency increases by increasing the pH,for all the investigated cations.As an example,Pb(II)adsorption efﬁciency gradually increases from 75.7%to 92.3%when the pH increases from 2to 7.The results demonstrate that the cations removal was mainly dependent on the proton concentration in the solution.This has been previously attributed to the for-mation of surface complexes between the functional groups (:FeOH)of the sorbent and,for example,the Pb(II)ions,Table 1Lagergren rate equation constants and pseudo second-order rate equation constants for Mn(II),Zn(II),Cu(II)and Pb(II)adsorption on Fe 3O 4magnetite nanoparticles Metal ions Pseudo ﬁrst-order rate equation constants q e (exp.)SSE R 2k ad (9min)(g mg -1)Mn(II)0.02411.50.5410.9654Zn(II)0.02612.40.5230.9434Cu(II)0.03114.50.5560.9687Pb(II)0.03316.40.5830.9765Metal ions Pseudo second-order rate equation constants q e (exp)SSE R 2h o (9min g mg -1)(g mg -1)Mn(II)1234.522.50.0170.9996Zn(II)1298.524.60.0140.9994Cu(II)1345.625.60.0080.9999Pb(II)1445.627.80.0070.9999Fig.6The effect of pH on the adsorption of Pb(II),Cu(II),Zn(II)and Mn(II)ions onto magnetic Fe 3O 4nanoparticles.T =298K,t =24h,adsorbent dosage =200mg,V solution =50mL,Initial metal ion concentration =150mg L -1with the possible reaction being expressed as follows(Hou et al.2003):sH2Oþq FeOHþrPb2þ) FeOðÞq Pb r OHðÞ2ÀqÀsðÞsþs+qðÞHþð10Þwhere(:FeO)q Pb r(OH)s(2–q–s)corresponds to the surface complexes and s,q and r are the stoichiometric coefﬁcients. When pH increases,this equilibrium shifts in such a manner that a greater number of sites are present in the more reactive deprotonated form,thereby leading to a higher uptake of Pb(II).The results show very similar trends for Zn(II),Cu(II) and the Mn(II)adsorption efﬁciency;this pH dependency has been attributed to the formation of surface complexes similar to those reported in the equation(10)for Pb(II) cations.Furthermore,from measured zeta potential of magnetite solution at different pH values,it appears that the magne-tite surface has a positive charge at pH below6.0and a negative charge when pH is higher than6.0(Hou et al. 2003).This result is consistent with experimental data reported in Fig.6.Furthermore it should be noted that magnetite is an amphoteric solid,which can develop charges in the pro-tonation(Fe–OH?H?$Fe–OH2?)and deprotonation (Fe–OH$Fe–O-?H?)reactions of Fe–OH sites on surface(Wang et al.2011).The reactions can be written as: FeOH) FeOÀþHþK s a1ð11Þ FeOHþ2) FeOHþHþK s a2ð12Þand the corresponding acidity constants,asK s a1¼Hþ½ FeOÀf gFeOf gð13ÞK s a2¼Hþ½ FeOHf gFeOHþ2ÈÉð14Þwhere[]is the solution species concentration in mol L-1 and{}is the solid surface concentration in mol/g. According to the pH of the solution,the surface is charged differently and could behave as an anion or cation exchanger.It is important to realize that negative,positive, and neutral functional groups can coexist on magnetite surface.At pH\pH zpc,the FeOH2?groups predominate over the FeO-groups,i.e.,although the surface has a net positive charge,some FeO-groups are still present.At the pH zpc,the number of FeOH2?groups equals the number of FeO-groups and as the pH increases,the number of FeO-groups increases(pH zpc have been calculated but not reported here).It follows that magnetite particles may adsorb either negatively or positively charged species by electrostatic attraction depending on pH,even if,as pre-viously reported,a complete analysis of all the pH interval is not possible dealing with cations.Figure6shows that a magnitude of adsorption can be deﬁned according to the following order:Mn\Zn\Cu \Pb.The uptake of Mn(II),Zn(II),Cu(II)and Pb(II)ions onto magnetite nanoparticles occurs by physico-chemical interactions,likely represented by electrostatic attractions. In particular,the size of hydrated ionic radii seems to inﬂuence the interactions with the negative charged adsorption site,as the greater the ion’s hydration,the far-ther it is from the adsorbing surface and the weaker its adsorption(hydrated ionic radii:Pb2?:4.01A˚\Cu2?: 4.19A˚\Zn2?:4.30A˚\Mn2?:4.43A˚)(Ko et al.,2004). Hence,Pb(II)has the lowest hydrated ionic radius and the highest capability to compete with proton and,hence,the highest comparative adsorption capacity.The results obtained in this work in terms of metal adsorption capacity are of the same order of magnitude of those reported by other authors in the literature on the same sorbent(Wang et al.2011;Yuan et al.2009;Boddu et al. 2008;Yean et al.2005).Although many different sorbents can be used for the same purpose,magnetic nanosorbents possess a number of unique physical and chemical properties and they are easily dispersed in aqueous solutions.A large number of their atoms are superﬁcial atoms which are unsaturated and,hence,can determine high adsorption capacity towards several metal ions(Kalfa et al.2009;Zhang et al.2008;Liu et al.2005).Magnetic particles can be removed very quickly from a matrix using a magneticﬁeld, but they do not retain their magnetic properties when the ﬁeld is removed(Wang et al.2011).This system has also several advantages compared with conventional or other nano-adsorbents such as the absence of secondary wastes and the possible recycling of the materials involved on an industrial scale.Furthermore,the magnetic particles can be tailored to separate speciﬁc metal species in water,wastes or slurries(Yantasee et al.2007;Ngomsik et al.2006;Liu et al. 2008).However,from a practical point of view,there is a major drawback in the application of such nanomaterials for treating wastewater.Because the treatment of wastewater is usually conducted in a suspension of these nanoparticles,an additional separation step is required to remove them from a large volume of solution,resulting in increased operating costs.3.5Adsorption isothermsAdsorption isotherms of Mn(II),Zn(II),Cu(II)and Pb(II) onto magnetite nanoparticles are reported in Fig.7.Under the above-mentioned conditions,the maximum adsorption capacity resulted to be0.180mmol g-1for Pb(II),0.170mmol g-1for Cu(II),0.160mmol g-1for Zn(II),and0.140mmol g-1for Mn(II),respectively.Theuptake of Mn(II),Zn(II),Cu(II)and Pb(II)ions onto magnetite nanoparticles occurs by physico-chemical interactions,likely represented by electrostatic attractions and the comparative adsorption magnitude is conﬁrmed on the entire equilibrium concentration range.A basic modelling analysis was carried out in order to determine the isotherm model that better describes the experimental data.In Table 2,Langmuir and Freundlich model parameters were reported,as derived from the regression analysis.The Freundlich equation frequently gives an adequate description of adsorption data over a restricted range of concentration;it is usually suitable for a highly heteroge-neous surface and an adsorption isotherm lacking of a plateau,indicating a multi-layer adsorption (Lagergren 1898).Values of 1/n less than unity indicate that a sig-niﬁcant adsorption takes place at low concentration but the increase in the amount adsorbed with concentration becomes less signiﬁcant at higher concentration and vice versa (Ho and McKay 1998).The essential characteristic of the Langmuir isotherms can be expressed in terms of a dimensionless constant separation factor or equilibrium parameter,R L ,which is deﬁned as (Farmer 1974):R L ¼11þb C o ðÞð15Þwhere b is the Langmuir constant and C o is the initial metal ion concentration.The value of R L indicates the type of the isotherm to be either favorable (0\R L \1),unfavorable (R L [1),linear (R L =1)or irreversible (R L =0).From our study,an initial metal ion concentration of 600mg L -1,R L values for Pb(II),Cu(II),Mn(II)and Zn(II)ions adsorption ranged from 2.09to 1.67,therefore,adsorption process is unfavorable.As can be observed from data reported in Table 2,Langmuir model shows the highest comparative value of the coefﬁcient of determination (R 2)and the lowest value for SSE,indicating a better approximation of model parameters to the experimental counterparts.In Fig.7the ﬁtting of experimental data by Langmuir model was reported.3.6Effect of the temperatureFor all the investigated ions,adsorption experiments were conducted varying the temperature between 15°C and 40°C under the following conditions:L/S =1:4and pH 5.5.Figures 8a and b show the curves obtained for the adsorption tests at different time and temperature for Pb(II)and Zn (II)taken as example,respectively.As can be observed,for both ions,the adsorption capacity is greater for lower temperatures,as expected being adsorption an exothermic process.Moreover,the increase in adsorption capacity is higher for lowest values of temperature.The temperature has an effect also on the time necessary to reach the equilibrium;a higher temperature,in fact,determines a lower equilibriumtime.Fig.7Mn(II),Zn(II),Cu(II)and Pb(II)adsorption isotherms onto Fe 3O 4magnetite nanoparticles.T =25°C,pH =5.5Comparison between experimental data and Langmuir model.V solution =50mL,Initial metal ion concentration =150mg L -1Table 2Estimated parameters for the Langmuir and Freundlich models for isotherm of Mn(II),Zn(II),Cu(II)and Pb(II)adsorption on Fe 3O 4magnetite nanoparticles.T =25°C IonsFreundlich model q ¼K F c 1n eq Langmuir model q ¼q maxb ceqð1þb c eq ÞK F (mmol g -1)(L mmol -1)1/n1/nR 2q max (mg g -1)b (L g -1)R L (L mmol -1)R 2Mn(II)0.144±0.0060.175±0.0020.95870.149±0.007 1.37±0.04 1.670.9987Zn(II)0.160±0.0090.178±0.0040.96430.177±0.008 1.47±0.05 1.770.9988Cu(II)0.173±0.0110.123±0.0030.97450.184±0.005 1.68±0.03 1.990.9988Pb(II)0.185±0.0130.112±0.0060.98760.189±0.0031.89±0.042.090.9999。

HEAVY-METAL REMOVAL METHOD AND HEAVY-METAL REMOVAL

专利名称：HEAVY-METAL REMOVAL METHOD AND HEAVY-METAL REMOVAL DEVICE发明人：NAKAI, TAKAYUKI,MATSUBARA,SATOSHI,NAKAI, OSAMU,KYODA, YOJI申请号：EP13862448申请日：20131122公开号：EP2933234A4公开日：20160511专利内容由知识产权出版社提供摘要：Provided are a heavy-metal removal method and a heavy-metal removal device, which are capable of reducing the amount of a neutralizing agent to be used. In a neutralization tank provided with a vertical-type cylindrical reaction vessel 110, stirring blades 120 arranged in the reaction vessel 110, and an annular aeration tube 130 having a large number of air outlets 131 and being arranged to a bottom part of the reaction vessel 110, aeration is performed by introducing gas for oxidation from a large number of air outlets 131 of the aeration tube 130 while stirring an aqueous solution containing at least one kind of ion of a divalent ferrous ion and a divalent manganese ion as a heavy metal element by rotation of the stirring blades 120, and the aqueous solution is subjected to a neutralization treatment.申请人：SUMITOMO METAL MINING CO., LTD.更多信息请下载全文后查看。

微生物絮凝剂处理重金属废水的研究进展

微生物絮凝剂处理重金属废水的研究进展摘要：我国工业随着经济的飞速发展，各种废水尤其是工业废水的排放量显著增加。

如何高效处理重金属废水，保护水资源成为了目前广泛讨论的热点话题。

通过对重金属废水处理方式的对比，发现利用微生物絮凝剂处理重金属废水的效果好且不易产生二次污染，作为一种天然的高分子新型水处理剂，价格低廉，对生态环境友好，且对人体及生态环境无毒。

微生物絮凝剂具有高效、无二次污染的特性，目前已成为绿色净水剂研究的热点之一。

本文主要介绍目前处理重金属的方法以及微生物絮凝剂特点及其对重金属废水的处理，并对利用微生物絮凝剂处理重金属废水的研究发展进行展望。

关键词：水处理；微生物絮凝剂；重金属；无污染微生物絮凝剂属新型的天然高分子水处理剂，可以克服其他絮凝剂所存在的缺陷[1]。

利用微生物发酵产生代谢产物来制备的微生物絮凝剂，具有高效、无二次污染的特点[2]。

微生物絮凝剂的使用效果比有机高分子絮凝剂以及无机絮凝剂更为显著，并且无毒无味，有着非常可观的市场空间与发展前景[3-4]。

重金属废水对生态环境以及人体健康都会造成严重危害。

废水中的重金属污染物不能被轻易降解，且毒性长期存在，只能改变其状态通过吸附，或与阴离子配体形成配合物或螯合物，从水体中分离出来。

絮凝剂通过将废水中的重金属离子转移到絮凝物质中的方式去除污染物，而有的絮凝剂由于本身性质容易造成二次污染。

因此，在综合考虑环境和生态效益的基础上，选用生态友好型微生物絮凝剂处理重金属废水，通过微生物絮凝剂对重金属离子的吸附性，实现重金属废水的处理[5]。

2 重金属废水2.1 重金属废水的危害由于社会的经济飞速发展，工业化水平快速提高，一些工业产生的重金属废水对水体的污染日益严重。

重金属污染物具有潜在危害性，不易被水中的微生物降解，对生态环境和人类健康有危害严重。

重金属可以通过诸多方式和途径进入到水体中，受重金属污染水体的底泥也会因重金属的沉降而污染。

重金属在水体内受到条件影响发生独特理化反应，与水体中的物质进一步相互作用。

Adsorption of heavy metal ion from aqueous single metal solution by chemically

Adsorption of heavy metal ion from aqueous single metal solutionby chemically modiﬁed sugarcane bagasseOsvaldo Karnitz Jr.a ,Leandro Vinicius Alves Gurgel a ,Ju´lio Ce ´sar Perin de Melo a ,Vagner Roberto Botaro a ,Taˆnia Ma ´rcia Sacramento Melo a ,Rossimiriam Pereira de Freitas Gil b ,Laurent Fre´de ´ric Gil a,*aDepartamento de Quı´mica,Instituto de Cie ˆncias Exatas e Biolo ´gicas,Universidade Federal de Ouro Preto,35400-000Ouro Preto,Minas Gerais,BrazilbDepartamento de Quı´mica,Instituto de Cie ˆncias Exatas,Universidade Federal de Minas Gerais,31270-901Belo Horizonte,Minas Gerais,BrazilReceived 22November 2005;received in revised form 28April 2006;accepted 2May 2006Available online 14July 2006AbstractThis work describes the preparation of new chelating materials derived from sugarcane bagasse for adsorption of heavy metal ions in aqueous solution.The ﬁrst part of this report deals with the chemical modiﬁcation of sugarcane bagasse with succinic anhydride.The carboxylic acid functions introduced into the material were used to anchor polyamines,which resulted in two yet unpublished modiﬁed sugarcane bagasse materials.The obtained materials were characterized by elemental analysis and infrared spectroscopy (IR).The sec-ond part of this reports features the comparative evaluation of the adsorption capacity of the modiﬁed sugarcane bagasse materials for Cu 2+,Cd 2+,and Pb 2+ions in aqueous single metal solution by classical titration.Adsorption isotherms were studied by the Freundlich and Langmuir models.Ó2006Elsevier Ltd.All rights reserved.Keywords:Adsorption;Modiﬁed sugarcane bagasse;Polyamines;Isotherm;Heavy metals1.IntroductionWater pollution is a major environmental problem faced by modern society (Baird,1995)that leads to eco-logical disequilibrium and health hazards (Kelter et al.,1997).Heavy metal ions such as copper,cadmium,lead,nickel,and chromium,often found in industrial waste-water,present acute toxicity to aquatic and terrestrial life,including humans.Thus,the discharge of eﬄuents into the environment is a chief concern.The methods commonly used to remove toxic heavy metal from municipal and industrial wastewater are based on the adsorption of ions onto insoluble compounds and the separation of the sed-iments formed.Many eﬀorts have been made recently toﬁnd cheaper pollution control methods and materials(Panday et al.,1985;Ali and Bishtawi,1997;Acemiog˘lu and Alma,2001).The new material world trends point to the importance of using industrial and agricultural residues as production starting materials.Reusing and recycling these residues can minimize the environmental problems associated with their build-up and reduce the use of noble starting materi-als.This trend has contributed to the reconsideration of the use of traditional biomaterials such as natural lignocellu-losic ﬁbers to substitute synthetic polymers,for example,since in many cases they have a better performance.Brazil is the world leading producer of sugarcane for both the alcohol and the sugar industries.These industries produce a large amount of sugarcane bagasse and although it is burned to produce energy for sugar mills,leftovers are still signiﬁcant.Thus,on account of the importance of0960-8524/$-see front matter Ó2006Elsevier Ltd.All rights reserved.doi:10.1016/j.biortech.2006.05.013*Corresponding author.Tel.:+553135591717;fax:+55315511707.E-mail address:laurent@iceb.ufop.br (L.F.Gil).Bioresource Technology 98(2007)1291–1297bagasse sugar as an industrial waste,there is a great interest in developing chemical methods for recycling it.Sugarcane bagasse has around50%cellulose,27%polyoses,and23% lignin(Caraschi et al.,1996).These three biological poly-mers have many hydroxyl and/or phenolic functions that can be chemically reacted to produce materials with new properties(Xiao et al.,2001;Navarro et al.,1996).Despite the many studies of the chemical modiﬁcation of cellulose published around the world in this area(Gurnani et al.,2003;Gellerested and Gatenholm,1999),only a few have investigated the modiﬁcation of bagasse sugar(Krish-nan and Anirudhan,2002;Orlando et al.,2002).This work describes the preparation and the evaluation of new chelating materials from sugarcane bagasse to adsorb heavy metal ions in aqueous solution.In a prelimin-ary study,it has been chosen to study the adsorption of Cu2+,Cd2+,and Pb2+.Theﬁrst part of this work describes the modiﬁcation of sugarcane bagasse with succinic an-hydride to introduce carboxylic functions to sugarcane bagasse and the chemical introduction of commercial linear polyamine via the formation of amide functions.It is well known that polyamines have powerful chelating properties, mainly towards ions such as Cu2+,Zn2+,and Pb2+(Bian-chi et al.,1991;Martell and Hancock,1996).The second part of this work evaluates the adsorption of Cu2+,Cd2+,and Pb2+onto three modiﬁed sugarcane bag-asses(MSBs)from aqueous single metal ion solutions by classical titration.The results were analyzed by the Lang-muir and Freundlich models(Ho et al.,2005).2.Methods2.1.MaterialsPolyamines ethylenediamine3and triethylenetetramine 4were used in this work.Succinic anhydride,1,3-diiso-propylcarbodiimide(DIC),and triethylenetetramine,from Aldrich,were used without puriﬁcation.Ethylenediamine and dimethylformamide were distilled before use.Pyridine was reﬂuxed with NaOH and distilled.2.2.Sugarcane bagasse preparationSugarcane bagasse was dried at100°C in an oven for approximately24h and nextﬁber size was reduced to pow-der by milling with tungsten ring.The resulting material was sieved with a4-sieve system(10,30,45,and60mesh). Then,the material was washed with distilled water under stirring at65°C for1h and dried at100°C.Finally,it was washed anew in a sohxlet system with n-hexane/ ethanol(1:1)as solvent for4h.2.3.Synthesis of MSBs1and2Washed and dried sugarcane bagasse(5.02g)was trea-ted with succinic anhydride(12.56g)under pyridine reﬂux (120mL)for18h.The solid material wasﬁltered,washed in sequence with1M solution of acetic acid in CH2Cl2, 0.1M solution of HCl,ethanol95%,distilled water,and ﬁnally with ethanol95%.After drying at100°C in an oven for30min and in a desiccator overnight,MSB1(7.699g) was obtained with a mass gain of53.4%.MSB2was obtained by treatment of1with saturated NaHCO3solu-tion for30min and afterwards byﬁltering using sintered ﬁlter and washing with distilled water and ethanol.2.4.Synthesis of MSBs5and6The process used to introduce amine functions was the same as that used to prepare MSB5and6.MSB1was trea-ted with5equiv of1,3-diisopropylcarbodiimide(DIC)and 6equiv of polyamine in anhydrous DMF at room tempera-ture for22h under stirring.Afterﬁltration,the materials were washed with DMF,a saturated solution of NaHCO3, distilled water,andﬁnally with ethanol.Next,they were dried at80°C in an oven for30min and in a desiccator overnight.2.5.Kinetic study of metal ion adsorption of MSBs2,5,and6Experiments with each material and metal ion were per-formed to determine the adsorption equilibrium time from 10to90min in10min intervals.The amount of100mg MSB was placed in a250-mL Erlenmeyer with100.0mL metal ion solution with concentration of200mg/L under stirring.The experiments were done at pHs5.8for Cu2+, 7.0for Cd2+,and6.2for Pb2+,optimal values to obtain the best adsorption.To adjust pH values,was added NaOH solution(0.01mol/L)into metal solutions with MSB.Afterﬁltration,metal ion concentration was deter-mined by EDTA titration.2.6.pH study of metal ion adsorption of MSBs2,5,and6Experiments with each material and metal ion were per-formed to determine the eﬀect of pH on ion adsorption.An amount of100mg MSB was placed into a250-mL Erlen-meyer with100.0mL of metal ion solution200mg/L under stirring.pH was calibrated with HCl or NaOH solutions (0.1–1.0mol/L).The reaction times used were30min (MSB2)or40min(MSB5and6)for Cu2+and Cd2+, and40min(MSB2)or50min(MSB5and6)for Pb2+. Metal ion concentration was determined afterﬁltration by EDTA titration.No signiﬁcative variation of pH was observed at the end of each experiment.2.7.Adsorption isotherms of MSBs2,5,and6Experiments were performed for each material and metal ion to determine adsorption isotherms.In each experiment,100mg of MSB was placed into a250-mL Erlenmeyer with100.0mL of metal ion solution in speciﬁc concentrations(between200mg/L and400mg/L)under stirring.Each experiment was performed at the pH of1292O.Karnitz Jr.et al./Bioresource Technology98(2007)1291–1297larger ion adsorption during the time necessary for equilib-rium (Tables 3and 4).After ﬁltration,the metal ion con-centration was determined by EDTA titration.2.8.Characterization of the new obtained materials MSB 1,2,5,and 6were characterized by IR spectro-scopy in a Nicolet Impact 410equipment with KBr.Elemental analyses were accomplished in Analyzer 2400CHNS/O Perkin Elemer Series II.3.Results and discussion3.1.Synthesis of MSBs 1,2,5,and 6The synthesis route used to prepare MSBs 1,2,5,and 6are presented in Scheme 1.Prewashed sugarcane bagasse was succinylated for various periods of time.The degree of succinylation of the bagasse ﬁbers was determined by measuring the quantity of acid function.The results are shown in Fig.1.The concentration of carboxylic functions per mg of bagasse was determined by retro titration.For this,MSB 1was initially treated with an excess solution of NaOH (0.01mol/L)for 30min.Soon afterwards the material was ﬁltered and the obtained solution was titrated with an HCl solution (0.01mol/L).The highest degree of succinylation was reached after 18-h ing this reaction time,sugarcane bagasse was succinylated to pro-duce MSB 1,which presented a weight gain of 54%and a concentration of carboxylic acid function per mg of 3.83·10À6mol.Next,MSB 1was treated with a saturated NaHCO 3solution to produce MSB 2.Starting from MSB 1,two polyamines were introduced:ethylenediamine 3and triethylenetetramine 4.The method-ology used to introduce the polyamines was the same for the two MSBs 5and 6,as shown in Scheme 1.Concentra-tions of 2.4·10À6mol (5)and 2.6·10À6mol (6)of amine function per mg of material were determined by back titra-tion with excess HCl solution.The introduction of the amine functions was also veriﬁed by IR spectroscopy (Table 1)and elemental analysis (Table 2).3.2.Characterization of MSBs 1,5,and 6Characterization of carboxylated MSB 1was accom-plished by IR spectroscopy.The spectrum of unmodiﬁed sugarcane bagasse and MSB 1are presented in Fig.2.The spectrum of MSB 1displayed two strong bands at 1740and 1726cm À1in relation to that of unmodiﬁed sug-arcane bagasse.This demonstrated the presence of two types of carbonyl functions,one relative to carboxylic acid and another relative to the ester.The acid and ester IR bands indicate that succinic anhydride acylated theO.Karnitz Jr.et al./Bioresource Technology 98(2007)1291–12971293hydroxy group of bagasse to generate an ester bond with consequent release of a carboxylic acid functional group.The spectra of MSBs5and6(Figs.3and4,respectively) showed three new strong bands at1550–1650cmÀ1(see data in Table1)corresponding to the presence of amide and amine functions,and one band at1060cmÀ1 corresponding to C–N stretch.The bands at1635and 1650cmÀ1(Fig.3)correspond to the axial deformation of the carbonyl of the amide function and the angular deformation of the N–H bond of the amine function.The band at1575cmÀ1corresponds to the angular deformation of the N–H bond of the amide function.The band at 1159cmÀ1(Fig.4)corresponds to the asymmetric stretch of C–N–C bond.The main bands observed in all MSBs are presented in Table1.MSB elemental analysis data presented in Table2show a modiﬁcation in the carbon and hydrogen composition of MSB1and a larger proportion of nitrogen as the number of amine functions in the used polyamine increases.3.3.Study of adsorption of Cu2+,Cd2+and Pb2+on MSBs2,5,and6The study of the MSB adsorption properties was accom-plished for each material and metal ion.A kinetic study and an adsorption study as a function of pH wereﬁrst carried out.3.3.1.Eﬀect of contact timeThe kinetic study of MSB2with Cu2+,Cd2+,and Pb2+ ions in aqueous solution is presented in Fig.5.Adsorption equilibrium was reached after20min for Cd2+ions.A time of30min was chosen for all studies of MSB2with Cd2+. The adsorption equilibrium times chosen for pH and con-centration dependent experiments are presented in Table3.Similar studies were accomplished for MSBs5and6for Cu2+,Cd2+,and Pb2+.The results are presented in Table3.3.3.2.pH EﬀectThe removal of metal ions from aqueous solutions by adsorption is dependent on solution pH as it aﬀects adsor-Table1Main IR spectrum bands observed in MSBs1,5,and6MSB Main bands observed(cmÀ1)11740,172651745,1650,1635,1575,1423,1060 61738,1651,1635,1560,1400,1159,1060 Table2Elemental analysis of MSBs1,2,5,and6C(%)H(%)N(%) Sugarcane bagasse43.98 6.020.13MSB145.41 5.620.10MSB238.04 5.140.01MSB544.01 6.51 2.21MSB646.88 6.65 3.431294O.Karnitz Jr.et al./Bioresource Technology98(2007)1291–1297bent surface charge,the degree of ionization,and the species of adsorbates.The study of adsorption of Cd 2+,Cd 2+,and Pb 2+on MSB 2as a function of pH was accom-plished with the reaction times given in Table 3;the results are presented in Fig.6.The adsorption of the three metal ions increases with the increase in pH.Maximum removal of Cd 2+was observed above pH 6and in the case of Pb 2+and Cu 2,above pH 5and 5.5.Similar studies were accomplished for MSBs 5and 6and Cu 2+,Cd 2+and Pb 2+with similar results,as shown in Table 4.3.3.3.Adsorption isothermsThe Langmuir (Ho et al.,2005)(Eq.(1))and Freundlich (Eq.(2))isotherms were evaluated by adsorption experi-ments as a function of the initial metal ion concentrations in aqueous solution under equilibrium time and pH condi-tions given in Tables 3and 4.The results of each material and metal ion are presented in Fig.7(Langmuir)and Fig.8(Freundlich)and Table 5.c q ¼1Q max Âb þc Q maxð1Þln q ¼ln k þ1nln cð2ÞTable 3Adsorption equilibrium times of MSBs 2,5and 6MSB Equilibrium time (min)Cu 2+Cd 2+Pb 2+230304054040506404050Table 4pH of largest adsorption of MSBs 2,5and 6MSB pH of largest adsorption Cu 2+Cd 2+Pb 2+2 5.5–6.0 6.5–7.5 5.0–6.05 5.5–6.0 6.5–7.5 5.0–6.065.5–6.06.5–7.55.0–6.0O.Karnitz Jr.et al./Bioresource Technology 98(2007)1291–12971295where q(mg/g)is the concentration of adsorbed metal ions per gram of adsorbent,c(mg/L)is the concentration of metal ion in aqueous solution at equilibrium,Q max and b are the Langmuir equation parameters and k and n are the Freundlich equation parameters.High correlation coeﬃcients of linearized Langmuir and Freundlich equations indicate that these models can explain metal ion adsorption by the materials satisfactorily. Therefore,both models explained metal ion adsorption by MSBs2,5,and6as can be observed in Table5,with the exception of the Freundlich model for Pb2+adsorption by MSB2.The Langmuir isotherm parameter Q max indicates the maximum adsorption capacity of the material,in other words,the adsorption of metal ions at high concentrations. It can be observed in Table5that MSB5presents the larg-est Cu2+adsorption capacity while MSB6adsorbs Cd2+ and Pb2+the ngmuir parameter b indicates the bond energy of the complexation reaction of the material with the metal ion.It can be observed that MSB2presents the largest bond energy for Cu2+and Cd2+,while three materials do not diﬀer signiﬁcantly for Pb2.The Freundlich isotherm parameter k indicates the adsorption capacity when the concentration of the metal ion in equilibrium is unitary,in our case1mg/L.This parameter is useful in the evaluation of the adsorption capacity of metal ions in dilute solutions,a case closer to the characteristics of industrial eﬄuents.The values of k of MSB2and5are much similar for Cu2+and Cd2+ and much higher than that for MSB6.This shows the superiority of both materials in the adsorption of these metal ions in low concentrations.MSB5has a higher k value for Pb2+when compared to those of the other materials.These results were compared with those of Vaughan et al.(2001)for a commercial macroreticular chelating resin with thiol functional groups,Duolite GT-73.The Q max of Duolite GT-73for Cu2+,Cd2+,and Pb2+were 62mg/g,106mg/g,and122mg/g,respectively.Duolite GT-73exhibited Q max lower than those of MSBs(Table5).4.ConclusionsThrough a fast,eﬀective,and cheap methodology,it was possible to devise a strategy to introduce chelating func-tions(carboxylic acid and amine)to sugarcane bagasse. Modiﬁed sugarcane bagasses presented a good adsorption capacity for Cu2+,Cd2+,and Pb2+ions with maximum adsorption capacity observed for MSB6.It has been dem-onstrated that metal ion adsorption eﬃciency is propor-tional to the number of amine functions introduced into the material.MSB2,which contained only carboxylate functions,showed an eﬃciency similar to that of MSB5, a material of much more complex synthesis. AcknowledgementsWe thank FAPEMIG forﬁnancial support,CAPES and UFOP.Table5The Langmuir and Freundlich parameters for Cu2+,Cd2+and Pb2+ adsorptionMetalion MSB Langmuir FreundlichQ max (mg/g)b(L/mg)r2k(mg/g)n r2Cu2+21140.431191.623.90.919351390.1730.999898.315.80.906161330.0140.992722.8 3.640.9635Cd2+21960.1030.993459.4 4.160.977351640.0680.995762.8 5.490.983463130.0040.9528 5.15 1.630.9856Pb2+21890.1100.994566.0 4.660.757951890.1250.999914724.510.98163130.1210.9994121 5.210.8771296O.Karnitz Jr.et al./Bioresource Technology98(2007)1291–1297ReferencesAcemiog˘lu,B.,Alma,M.H.,2001.Equilibrium studies on adsorption of Cu(II)from aqueous solution onto cellulose.Journal of Colloid and Interface Science243,81–83.Ali,A.A.,Bishtawi,R.,1997.Removal of lead and nickel ions using zeolite tuﬀ.Journal of Chemical Technology and Biotechnology69, 27–34.Baird,C.,1995.Environmental Chemistry.W.H.Freeman and Company, New York.Bianchi,A.,Micheloni,M.,Paoletti,P.,1991.Thermodynamic aspects of the polyazacycloalkane complexes with cations and anions.Coordi-nation Chemistry Reviews110,17–113.Caraschi,J.C.,Campana,S.P.,Curvelo, A.A.S.,1996.Preparac¸a˜o e Caracterizac¸a˜o de Polpas Obtidas a Partir de Bagac¸o de Cana de Ac¸u´car.Polı´meros:Cieˆncia e Tecnologia3,24–29.Gellerested,F.,Gatenholm,P.,1999.Surface properties of lignocellulosic ﬁbers bearing carboxylic groups.Cellulose6,103–121.Gurnani,V.,Singh,A.K.,Venkataramani,B.,2003.2,3-Dihydroxypyri-dine-loaded cellulose:a new macromolecular chelator for metal enrichment prior to their determination by atomic absorption spectrometry.Analytical and Bioanalytical Chemistry377,1079–1086. Ho,Y.S.,Chiu,W.T.,Wang,C.C.,2005.Regression analysis for the sorption isotherms of basic dyes on sugarcane dust.Bioresource Technology96,1285–1291.Kelter,P.B.,Grundman,J.,Hage,D.S.,Carr,J.D.,Castro-Acun˜a,C.M., 1997.A discussion of water pollution in the United States and Mexico;with High School Laboratory Activities for the analysis of lead, atrazine,and nitrate.Journal of Chemical Education74,1413–1421. Krishnan,K.A.,Anirudhan,T.S.,2002.Removal of mercury(II)from aqueous solutions and chlor-alkali industry eﬄuent by steam activated and sulphurised activated carbons prepared from bagasse pith:kinetics and equilibrium studies.Journal of Hazardous Materials92,161–183. Martell, A.E.,Hancock,R.D.,1996.Metal complexes in aqueous solutions.Plenum,New York.Navarro,R.R.,Sumi,K.,Fujii,N.,Matsumura,M.,1996.Mercury removal from wastewater using porous cellulose carrier modiﬁed with polyethyleneimine.Water Research30,2488–2494.Orlando,U.S.,Baes,A.U.,Nishijima,W.,Okada,M.,2002.Preparation of chelating agents from sugarcane bagasse by microwave radiation as an alternative ecologically benign procedure.Green Chemistry4,555–557.Panday,K.K.,Gur,P.,Singh,V.N.,1985.Copper(II)removal from aqueous solutions byﬂy ash.Water Research19,869–873. Vaughan,T.,Seo,C.W.,Marshall,W.E.,2001.Removal of selected metal ions from aqueous solution using modiﬁed corncobs.Bioresource Technology78,133–139.Xiao,B.,Sun,X.F.,Sun,R.,2001.The chemical modiﬁcation of lignins with succinic anhydride in aqueous systems.Polymer Degradation and Stability71,223–231.O.Karnitz Jr.et al./Bioresource Technology98(2007)1291–12971297。

Adsorption of heavy metal ions from aqueous solutions by activated carbon prepared

Short CommunicationAdsorption of heavy metal ions from aqueous solutions byactivated carbon prepared from apricot stoneM.Kobya a ,E.Demirbasb,*,E.Senturk a ,M.InceaaDepartment of Environmental Engineering,Gebze Institute of Technology,41400Gebze,TurkeybDepartment of Chemistry,Gebze Institute of Technology,41400Gebze,TurkeyReceived 17July 2004;received in revised form 24November 2004;accepted 10December 2004Available online 25February 2005AbstractApricot stones were carbonised and activated after treatment with sulphuric acid (1:1)at 200°C for 24h.The ability of the acti-vated carbon to remove Ni(II),Co(II),Cd(II),Cu(II),Pb(II),Cr(III)and Cr(VI)ions from aqueous solutions by adsorption was investigated.Batch adsorption experiments were conducted to observe the eﬀect of pH (1–6)on the activated carbon.The adsorp-tions of these metals were found to be dependent on solution pH.Highest adsorption occurred at 1–2for Cr(VI)and 3–6for the rest of the metal ions,respectively.Adsorption capacities for the metal ions were obtained in the descending order of Cr(VI)>Cd(II)>Co(II)>Cr(III)>Ni(II)>Cu(II)>Pb(II)for the activated carbon prepared from apricot stone (ASAC).Ó2005Elsevier Ltd.All rights reserved.Keywords:Apricot stone;Adsorption;Heavy metals;Aqueous solution;pH1.IntroductionHeavy metal ions such as cobalt,copper,nickel,chro-mium and zinc are detected in the waste streams from mining operations,tanneries,electronics,electroplating and petrochemical industries,as well as in textile mill products (Patterson and Passino,1987).Heavy metals have a harmful eﬀect on human physiology and other biological systems when they exceed the tolerance levels.Heavy metals are not biodegradable and tend to accu-mulate in living organisms,causing various diseases and disorders.The most widely used methods for removing heavy metals from wastewaters include ion exchange,chemical precipitation,reverse osmosis,evaporation,membrane ﬁltration and adsorption.Most of these methods suﬀer from some drawbacks,such as high capital and opera-tional cost or the disposal of the residual metal sludge,and are not suitable for small-scale industries.Many reports have appeared on the development of low cost activated carbon from cheaper and readily available materials (Bailey et al.,1999).Activated carbons,with their high surface area,micro porous character and chemical nature of their surface,have made them poten-tial adsorbents for the removal of heavy metals from industrial wastewater.Studies on the adsorption of heavy metals by acti-vated carbon and various low-cost materials have been reported in the literature.These include activated car-bon prepared from peat,coconut shells,coal (Paajanen et al.,1997),anthracite (Petrov et al.,1992),hazelnut shell activated carbon (Cimino et al.,2000;Demirbas,2003;Kobya,2004),kaolinite (Yavuz et al.,2003),coir-pith (Kadirvelu and Namasivayam,2003),bambara nut and rice husks (Ajmal et al.,2003),almond shells,olive and peach stones (Ferro-Garcia et al.,1988),and vari-ous commercially activated carbons (Netzer and0960-8524/$-see front matter Ó2005Elsevier Ltd.All rights reserved.doi:10.1016/j.biortech.2004.12.005*Corresponding author.Fax:+902627542385.E-mail address:erhan@.tr (E.Demirbas).Bioresource Technology 96(2005)1518–1521Hughes,1984)which have been used for removal of heavy metals from aqueous solutions.The purpose of this study was to remove selected heavy metals,namely Ni(II),Co(II),Cd(II),Cu(II), Pb(II),Cr(III)and Cr(VI)from aqueous solutions and to evaluate the inﬂuence of pH on activated carbon pre-pared from apricot stone(ASAC).2.MethodsChemical activation utilizes chemicals,such as H2SO4,H3PO4,ZnCl2,KOH and CaCl2,that have dehydration and oxidation characteristics(Kim et al., 2001).Carbonisation and activation are usually carried out simultaneously in the chemical activation process.Apricot stones were obtained from Malatya in Turkey.The material was ground in a micro hammercutter mill(Glen Mills)and sieved to a size range of 2.0mm·0.5mm particle size prior to activation.Chem-ical activation using H2SO4at moderate temperatures produces a high surface area and high degree of micro-porosity(Demirbas,2003).The materials were mixed in a1:1wt ratio with concentrated H2SO4,placed in an oven and heated to200°C for24h.After this,the sam-ples were allowed to cool to room temperature,washed with distilled water and soaked in1%NaHCO3solution to remove any remaining acid.The samples were then washed with distilled water until pH of the activated carbon reached6,dried at105°C for5h and sieved to obtain the desired particle size(1.00–1.25mm).The sur-face area of the activated carbons was measured by BET (Brunauer-Emmett-Teller nitrogen adsorption tech-nique).Characteristics of the carbon are presented in Table1.Higher surface area(>642m2/g)and lower mes-oporosity are obtained with H3PO4for carbonisation of apricot stone at higher temperature(Philip and Girgis, 1996)when it is compared with H2SO4,but H2SO4is al-most as eﬃcient as H3PO4in the carbonisation process.The size distribution of micropores of activated carbon is understood to be one of the critical factors determining its applicability(Blacher et al.,2000).The microstructures of the carbon were observed by SEM (Philips XL30S-FEG)and are shown in Fig.1.The sample was gold coated prior to SEM observation.This ﬁgure shows that the adsorbent had an irregular and porous surface,indicating relatively high surface areas. This observation is supported by the BET surface area of the activated carbon.The pore size distributions were calculated using t-plots(Gregg and Sing,1982).The porosity of the carbon was around74%.Batch experiments were conducted to investigate the eﬀect of pH on adsorption of metals on ASAC.All reagents used were of AR grade(Sigma-Aldrich,Ger-many).Salts used were cadmium sulphate for Cd(II), nickel sulphate for Ni(II),copper sulphate for Cu(II), cobalt nitrate for Co(II),lead nitrate for Pb(II),chro-mium nitrate for Cr(III)and potassium dichromate for Cr(VI).Samples were prepared by dissolving each metal salt at a known concentration in deionised water to obtain a stock solution.The initial pH of the solution was adjusted by using either0.1M NaOH or0.05M H2SO4.50ml solution of known concentration(C0) and initial pH was placed in a100ml screw-cap conical ﬂask with0.1g of adsorbent and was agitated at a speed of200rpm in a thermostatic shaker bath at25°C for 48h.The initial concentration of metal ions and corre-sponding concentrations afterﬁxed time periods were measured by atomic absorption spectrophotometry (Perkin Elmer SIMAA6000).Chromium was deter-mined spectrophotometrically using diphenylcarbazide. The solution pH was measured using a Mettler Toledo 340pH meter.The metal concentration retained in the adsorbent phase(q e,mg/g)was calculated by using the following equationqe¼ðC0ÀC eÞVW sð1Þwhere C0and C e are the initial andﬁnal concentrations of metal ion in solution(mg/l),V is the volume ofTable1The characteristics of the activated carbonParameters Value Bulk density(g/ml)0.43 Ash content(%) 2.21 pH 6.00 Moisture content(%)7.18 Surface area(m2/g)566 Solubility in water(%)0.85 Solubility in0.25M HCl(%) 1.22 Decolorising power(mg/g)22.8 Iodine number(mg/g)548 Particle size(mm)1.00–1.25Fig.1.SEM image of ASAC.M.Kobya et al./Bioresource Technology96(2005)1518–15211519solution(l)and W s is the mass of the adsorbent(g). Each experiment was carried out in duplicate and the average of two values was used in the calculations. The maximum diﬀerence between the two values was less than3%of the mean.3.Results and discussionThe pH of the solution is an important factor in determining the rate of surface reactions.The variation in adsorption capacity in this pH range is largely due to the inﬂuence of pH on the surface adsorption character-istics of ASAC.The eﬀect of pH on the adsorption of metal ions on the adsorbent is presented in Table2.For Cr(VI),the amount adsorbed decreased from 34.70to7.86mg/g as the pH increased from1to6. For the rest of the metal ions,the amount adsorbed increased from3.08to33.57mg/g for Cd(II),7.74to 30.07mg/g for Co(II),2.83to29.47mg/g for Cr(III), 2.50to27.21mg/g for Ni(II),4.86to24.21mg/g for Cu(II)and6.69to22.85mg/g for Pb(II),respectively, as the pH increased from1to6.The pH experiments also showed maximum removalof99.99%for Cr(VI)at pH1,99.86%for Pb(II)at pH3, 99.67%for Cd(II)at pH5,99.11%for Co(II)at pH6, 98.56%for Cr(III)at pH4,97.59%for Ni(II)at pH4 and96.24%for Cu(II)at pH4,respectively.Chromium exists mostly in two oxidation states which are Cr(VI)and Cr(III)and the stability of these forms is dependent on the pH of the system(Cimino et al.,2000;Selomulya et al.,1999).It is well known that the dominant form of Cr(VI)at pH2is HCrOÀ4.Increas-ing the pH will shift the concentration of HCrOÀ4toother forms,CrO2À4and Cr2O2À7.Maximum adsorptionat pH1.0indicates that it is the HCrOÀ4form of Cr(VI) which is the predominant species between pHs1and2.At pH values lower than3,there is excessive proton-ation of the carbon surface resulting in a decrease in the adsorption of Ni2+,Co2+,Cd2+,Pb2+and Cu2+(=M) ions.This is consistent with the results obtained by Petrov et al.(1992).On increasing the pH of M(II) solutions from3,the percentage removal increased and become quantitative over the pH range3–6.The increase in metal removal as pH increased can be explained on the basis of a decrease in competition between proton(H+)and positively charged metal ion at the surface sites,and by decrease in positive charge which results in a lower repulsion of the adsorbing metal ion.The removal eﬃciencies of metal ions are aﬀected by the initial metal ion concentration with the removal decreasing as the concentration increases at constant pH.In addition to that,at solution pH above3the pre-ponderance of OHÀgenerates a competition between the carbon surface and the solution OHÀions for M(II)ions,which causes a decrease in the adsorption of M(II)ions on the carbon surface.In other words, the increase in M(II)removal above pH3for the carbon may be due to the retention of M(OH)2species into pores of the carbon particles.A change in pH at the end of the adsorption experi-ments indicates that a lowerﬁnal pH was reached for higher adsorbent concentration(Table2).The increase in adsorbent concentration results in greater removal of metal ions from the solution,leading to a higher H+concentration and accounting for the decrease in theﬁnal pH value.As solution pH was increased,the onset of metal hydrolysis and precipitation began at a pH of3for all metal ions and precipitation was dominant at higher pHs(P5).This indicated that the adsorption capacity of the adsorbent is clearly pH dependent.4.ConclusionActivated carbon prepared from apricot stone,an agricultural waste,could be used as potential adsorbentTable2Adsorption of the metal ions onto ASAC at various pH valuesMetal Adsorptionparameters pH123456Nickel C e(mg/l)50.2533.65 6.66 1.33 1.100.20q e(mg/g) 2.5010.8024.3026.9626.9727.21Removal(%)9.0539.1087.9597.5997.6398.51pHﬁnal 1.09 1.91 3.46 4.73 6.00 6.15Cobalt C e(mg/l)45.2033.2711.40 2.09 1.240.54q e(mg/g)7.7413.7024.6429.3029.7230.07Removal(%)25.5145.1781.2196.5697.9699.11pHﬁnal 1.18 2.13 3.60 4.91 5.02 5.24Cadmium C e(mg/l)61.2031.627.457.580.220.22q e(mg/g) 3.0817.8729.9629.8933.5733.57Removal(%)9.1553.0688.9488.7599.6799.68pHﬁnal 1.03 2.08 3.58 4.33 5.65 5.47Lead C e(mg/l)32.3516.680.0620.0280.0400.034q e(mg/g) 6.6914.5222.8322.8522.8422.85Removal(%)29.2563.5299.8699.9499.9199.93pHﬁnal 1.02 2.12 4.36 5.73 6.53 6.50Copper C e(mg/l)39.9722.40 3.17 1.87 1.51 1.25q e(mg/g) 4.8613.6423.2623.9124.0824.21Removal(%)19.5554.9193.6196.2496.9697.48pHﬁnal 1.07 1.98 3.34 4.59 4.62 4.87Cr(III)C e(mg/l)53.8838.03 4.740.860.940.60q e(mg/g) 2.8310.7527.4029.3429.3029.47Removal(%)9.4936.1292.0498.5698.4298.99pHﬁnal 1.06 2.04 3.12 4.08 5.02 5.98Cr(VI)C e(mg/l)0.007 2.1028.2031.8757.1962.81q e(mg/g)34.7033.3020.5018.7011.357.86Removal(%)99.9996.9959.7154.4718.3010.27PHﬁnal 1.02 2.01 3.22 4.42 5.01 6.021520M.Kobya et al./Bioresource Technology96(2005)1518–1521for the removal of heavy metal ions from aqueous solu-tions.Batch experiments were conducted to assess the eﬀect of pH on ASAC.Adsorptions of the metal ions were found to be highly pH dependent and the results indicated that the optimum pH for removal was1for Cr(VI)while that for the rest of the metal ions varied from3to6.Cost analysis for the preparation of acti-vated carbon was not carried out,but as apricot stone is found in abundance in Turkey,carbon cost is expected to be economical.ReferencesAjmal,M.,Rao,R.A.K.,Anwar,S.,Ahmad,J.,Ahmad,R.,2003.Adsorption studies on rice husk:removal and recovery of Cd(II) from wastewater.Bioresour.Technol.86,147–149.Bailey,S.E.,Olin,T.J.,Bricka,R.M.,Adrian,D.D.,1999.A review of potentially low-cost sorbents for heavy metals.Water Res.33, 2469–2479.Blacher,S.,Sahouli,B.,Heinrichs,B.,Lodewyckx,P.,Pirard,R., Pirard,J.P.,2000.Micropore size distributions of activated ngmuir16,6754–6756.Cimino,G.,Passerini,A.,Toscano,G.,2000.Removal of toxic cations and Cr(VI)from aqueous solution by hazelnut shell.Water Res.34, 2955–2962.Demirbas,E.,2003.Adsorption of cobalt(II)from aqueous solution onto activated carbon prepared from hazelnut shells.Adsorpt.Sci.Technol.21,951–963.Ferro-Garcia,M.A.,Rivera-Utrilla,J.,Rodriguez-Gordillo,J., Bautista-Toledo,I.,1988.Adsorption of zinc,cadmium and copperon activated carbons obtained from agricultural by-products.Carbon26,363–373.Gregg,S.J.,Sing,K.S.W.,1982.Adsorption Area and Porosity,second ed.Academic Press Inc.,New York,USA,p.303.Kadirvelu,K.,Namasivayam, C.,2003.Activated carbon from coconut coirpith as metal adsorbent:adsorption of Cd(II)from aqueous solution.Adv.Environ.Res.7,471–478.Kim,J.W.,Myoung,H.S.,Dong,S.K.,Seung,M.S.,Young,S.K., 2001.Production of granular activated carbon from waste walnut shell and its adsorption characteristics for Cu2+ion.J.Hazard.Mater.B85,301–315.Kobya,M.,2004.Adsorption,kinetic and equilibrium studies of Cr(VI)by hazelnut shell activated carbon.Adsorpt.Sci.Technol.22,51–64.Netzer,A.,Hughes,D.E.,1984.Adsorption of Cr,Pb and Co by activated carbon.Water Res.18,927–933.Paajanen,A.,Lehto,J.,Santapakka,T.,Morneau,J.P.,1997.Sorption of cobalt on activated carbons from aqueous solution.Sep.Sci.Technol.32,813–826.Patterson,J.,Passino,R.,1987.Metal Speciation,Separation,and Recovery.Lewis Publishers,Inc.,Chelsea,MI,USA.Petrov,H.,Budinova,T.,Khovesov,I.,1992.Adsorption of zinc, cadmium,copper and lead ions on oxidised anthracite.Carbon30, 135.Philip,C.A.,Girgis,B.S.,1996.Adsorption characteristics of micro-porous carbons from apricot stones activated by phosphoric acid.J.Chem.Technol.Biotechnol.67,248–254.Selomulya,C.,Meeyoo,V.,Amal,R.,1999.Mechanisms of Cr(VI) removal from water by various types of activated carbons.J.Chemical Technol.Biotechnol.74,111–122.Yavuz,O.,Altunkaynak,Y.,Guzel,F.,2003.Removal of copper, nickel,cobalt and manganese from aqueous solution by kaolinite.Water Res.37,948–952.M.Kobya et al./Bioresource Technology96(2005)1518–15211521。

黑曲霉的固定化

Removal of heavy metals from industrial wastewater by free and immobilized cells of Aspergillus nigerK.Tsekova a ,*,D.Todorova a ,S.Ganeva ba Stephan Angeloff Institute of Microbiology e Bulgarian Academy of Sciences,Acad.G.Bonchev,Str.,bl.26,1113So ﬁa,Bulgaria bFaculty of Chemistry e So ﬁa University,1164So ﬁa,Bulgariaa r t i c l e i n f oArticle history:Received 24March 2010Received in revised form 5May 2010Accepted 9May 2010Available online 7June 2010Keywords:Biosorption Heavy metals Wastewater Immobilization Aspergillus nigera b s t r a c tAspergillus niger ,strain B 77,was immobilized by inclusion in two different polymers:polyvinyl e alcohol hydrogel (PVA)and Ca e alginate.The biomass/polymer matrices were formed into equal size unites of the cubes and spheres,and the resulting biomass/polymer matrices were used to remove heavy metals (Cu 2þ,Mn 2þ,Zn 2þ,Ni 2þ,Fe 3þ,Pb 2þ,Cd 2þ)from wastewater in shake ﬂask experiments.Total biosorption capacities of the biosorbents were in the following order:free cells (33.3mg/g)<PVA e biomass (39.8mg/g)<Ca alginate e biomass (44.6mg/g).The metal removal ef ﬁciencies of the beads Ca alginate e biomass were 96.2%for Cd 2þ;90.0%for Pb 2þ;80.0%for Fe 3þ;72.8%for Cu 2þ;55.4%for Zn 2þ;54.4%for Ni 2þand 52.3%for Mn 2þ,while the removal ef ﬁciencies of cubes PVA e biomass for the same heavy metals ions were:95.0%;88.0%;80.0%;67.1%;58.5%;48.9%and 44.6%,respectively.The results obtained from these experiments,were compared with those using dispersed biomass as a sorbent.Promising results were obtained in the laboratory,as effective metal removals were observed.Ó2010Elsevier Ltd.All rights reserved.1.IntroductionThe increase use of heavy metals in difference industrial activ-ities causes their existence in wastewater.The discharge of heavy metal ions in industrial ef ﬂuent is of great concern because of their toxic effect on living species,even at very low concentrations.The detoxi ﬁcation of metal ions from industrial ef ﬂuent using biosorption processes is an area of extensive research during the last years (Volesky and Holan,1995;Tripathi et al.,2007).Biosorption is an innovative and low cost effective method for the removal of toxic substances from wastewaters (Zouboulis et al.,2003;Silva et al.,2009;Chatterjee et al.,2010).Fungi are recognized for their superior ability to produce a large variety of extra cellular proteins,organic acids,enzymes and other metabolites,and their waste biomass may be used as effective biosorbent for removal,reduction and detoxi ﬁcation of industrial ef ﬂuents ingredients (Gupta and Mukerji,2001;Christian et al.,2005).Various fungal species under the genus Aspergillus ,Penicil-lium and Rhizopus have been shown to be effective in biosorption of heavy metals from polluted ef ﬂuents both as immobilized cells and in the mobilized state (Kapoor and Viraraghvan,1995;Leitão,2009;Tsekova et al.,2010a,b ).During the last decade many research works have been focused on the development of immobilized systems of microorganisms into polymeric matrices suitable for metal ions uptake applications (Zouboulis et al.,2003;Tsekova et al.,2008;Mata et al.,2009).Biosorption has been considered as a promising technology for the removal of low levels of toxic metals from industrials ef ﬂuents and natural waters.In view of potential applications in remediation of heavy metals from aqueous solutions the immobilization of the biomass is generally necessary.Immobilized cells are usually easier to handle,require less complex separation systems,allow a high biomass density to be maintained and provide a greater opportu-nity for reuse and recovery.Despite the current interest in microbial detoxi ﬁcation of ef ﬂuents,relatively little work has been concerned with charac-terization of metal uptake by ﬁlamentous fungi,particularly when the heavy metals present at different and low concentrations.The purpose of this study was to determine the ability of Aspergillus niger (free and immobilized biomass)to remove toxic metals from an industrial wastewater by batch system.2.Materials and methods 2.1.Sample collection siteWastewater samples were from copper production factory in Pirdop,Bulgaria.The samples were collected for a relative long*Corresponding author.Tel.:þ35929793167;fax:þ35928700109.E-mail addresses:ktsekova@microbio.bas.bg (K.Tsekova),sganeva@chem.uni-so ﬁa.bg (S.Ganeva).Contents lists available at ScienceDirectInternational Biodeterioration &Biodegradationjou rn al homepage:/locate/ibiod0964-8305/$e see front matter Ó2010Elsevier Ltd.All rights reserved.doi:10.1016/j.ibiod.2010.05.003International Biodeterioration &Biodegradation 64(2010)447e 451period of time(April e November2009)in high e grade plastic bottles of1.5l capacity and stored in a refrigerator at4 C.From all taken wastes a representative sample was prepared mixing150ml from each separate bottle.2.2.Determination of heavy metal concentrationsThe initial concentration of the metals in the wastewater and samples after biosorption treatment were determined using an Atomic Absorption Spectrophotometer Perkin Elmer Analyst400, air-acetyleneﬂame.Cadmium and lead after biosorption were determined using electrothermal atomic absorption spectrom-eter Zeeman Perkin Elmer3030,pyrolytically coated graphite tubes and optimized temperature program for modiﬁer freeETAAS.2.3.Preparation of biosorbents2.3.1.Microorganisms,medium and cultivationThe mutant strain A.niger B77(A.niger),an industrial producer of glucoamylase(N 65/1980,National Bank of Industrial Micro-organisms and Cell Cultures,Bulgaria)was used in this study. Spores from established culture(6e7days old)incubated on potato glucose agar slants at30 C were used for the preparation of inocula.The liquid growth medium consisted of(g/L):glucose30 and corn steep liqueur45;pH adjusted to4.8.Cultivation of A.niger was carried out in500e ml Erlenmeyer ﬂasks with75ml growth medium on a rotary shaker at30 C.After 48h of cultivation,the mycelium was harvested byﬁltration from the medium,washed twice with distilled water and stored at4 C until use.The dry weight of the free fungal biomass(FC)was determined after drying at85 C for48h.2.3.2.Immobilizing materials and techniquesPoly(vinyl)alcohol(PVA)hydrogel was obtained as describe earlier(Tsekova et al.,2008).The PVA e hydrogel used for immo-bilization was cut into small pieces(4Â4Â4mm in size).They were washed with distilled water and than submerged in500-ml Erlenmeyerﬂasks containing75ml growth medium(previously autoclaved for20min at120 C).The carrier pieces were inoculated with10ml A.niger spores suspension(1Â106/ml)were cultivated as described above.After48h of incubation,the PVA e immobi-lized biomass of A.niger was harvested from the medium,washed twice with distilled water and stored at4 C until used as a bio-sorbent.The dry weight of PVA e biomass was determined as described for FC.Method described by El e Naggar et al.(2006)was used to prepare Ca alginate beads the spore suspension(10ml,1Â106/ml) was mixed with Na e alginate prior to its stabilization.Beads of approximately4mm diameter were obtained by selecting an appropriate oriﬁce size through which the polymer/spores mixed passed.The cultivation was carried out as described above.After 48h of incubation,the Ca alginate e immobilized biomass of A.niger was harvested from the medium,washed twice with distilled water and stored at4 C until used as a biosorbent.The dry weight of Ca alginate e biomass was determined as described for FC.2.4.Batch biosorption studiesBatch biosorption experiments were carried out in500ml Erlenmeyerﬂasks,as follows:preweighed biosorbent samples (wet or immobilized biomass)with concentration varying from0.1 to0.5g/l(dry weight)were examined.Each sample was added to 100ml of real wastewater,containing heavy metal ions.Biosorption studies were performed at different initial pH from5.5to7.5using 0.1N NaOH.The mixtures were then agitated at120rpm on a rotary shaker up to30min at25 C.Then the content of theﬂasks was separated byﬁltration using a Whatman N 1ﬁlter paper.2.5.Metal uptake(q)Uptake of metal ions was calculated from a metal mass balance yielding:q¼VðC iÀC fÞ(1) where:q is mg metal ions per g dry biosorbent;V is the reaction volume(l),C i and C f are the initial and residual metal concen-trations(mg/l),respectively,and m is the amount of dry bio-sorbent(g).The concentration of the metal ions in theﬁltrates was deter-mined using atomic absorption spectrophotometer with an air/ acetyleneﬂame(model2380;Perkin Elmer,Uberlingen,Germany).Aliquots of wet biomass as well as of immobilized biomass, followed by drying for48h at85 C,were considered as dry biosorbent to calculate the uptake.The efﬁciency of heavy metal removal was calculated from the amount of metal ions adsorbed on the biosorbent and the amount of metal ions available in the wastewater,as the following equation:%removal¼mg heavy metal ions removedmg heavy metal ions availableÂ100(2)2.6.ReproducibilityAll the experiments were run in triplicates and controls were also run on same pattern without addition of biosorbent.The data shown are average from three separate experiments.Table1Characteristics of the biosorption process for removal of heavy metals from waste-water using free biomass as a sorbent.Performance of biosorbentof A.niger biomassHeavy metals in mixed solution,mg/lCu Zn Ni Fe Pb Cd Mn Initial concentrations mg/l7 1.30.90.20.050.0813 Equilibrium concentrations mg/l 2.8 1.10.460.060.0060.0048.1 Equilibrium time min20151555520 Heavy metal uptake mg/g140.66 1.50.460.150.2516.3 Removal efﬁciency%6015.448.970889537.7 Free biomass(m)0.3g/l;pH e6.5;number of parallels:(n)3;relative standard deviation(RSD)3e8%.Table2Characteristics of the biosorption process for removal of heavy metals from waste-water:PVA e biomass m¼0.3g/l;pH e6.5.Performance of biosorbent Heavy metals in mixed solution,mg/lCu Zn Ni Fe Pb Cd Mn Initial concentrations mg/l7 1.30.90.20.050.0813 Equilibrium concentrations mg/l 2.30.540.460.040.0060.0047.2 Equilibrium time min1510555515 Heavy metal uptake mg/g15.6 2.5 1.50.530.140.2519.3 Removal efﬁciency%67.158.548.980889544.6 Number of parallels:(n)3;relative standard deviation(RSD)3e8%.K.Tsekova et al./International Biodeterioration&Biodegradation64(2010)447e451 4483.Results and discussion3.1.Sorption of heavy metals from wastewater by freeand immobilized cells of A.niger3.1.1.Sorption of heavy metals from industrial wastewater by free biomass of A.niger (FC)A.niger biomass absorbed Fe 3þ,Pb 2þand Cd 2þions from industrial wastewater more rapidly than other ions (Table 1)within 15e 20min.Experiments indicated that sorption equilibrium reached much faster in case of industrial wastewater sample (up to 20min)in comparison to single ions solution (up to 30min)using same biosorbent (Tsekova et al.,2010a ).These results are impor-tant,as equilibrium time is one of the important parameters for selecting a wastewater treatment system.This may be due to the presence of co e metal ions in the industrial ef ﬂuents as well as to the differences in the heavy metal ions concentrations (Muhammad et al.,2009;Chatterjee et al.,2010).The removal percentages order at equilibrium was:Cd 2þ(95%)>Pb 2þ(88%)>Fe 3þ(70%)>Cu 2þ(60%)>Ni 2þ(48.9%)>Mn 2þ(37.7%)>Zn 2þ(15.4%)3.1.2.Sorption of heavy metals by immobilized biomass of A.nigerThe effect of immobilization of A.niger on PVA e hydrogel as well as on Ca alginate on the removal of heavy metal ions by adsorption was investigated.The metal removal study,illustrated in Tables 2,3showed that their removals were affected by immobilization of A.niger in comparison to the removal ef ﬁciency by free biomass (Table 1).In general,the both immobilized biosorbents displayed higher bio-sorption capacities for Mn 2þand Cu 2þ,presented in the ef ﬂuent at higher initial concentrations.There was however considerabledifference in total biosorption capability of the test fungal bio-sorbents.Immobilized on Ca alginate cells of A.niger showed highest total biosorption capacity of 71.6mg/g for all heavy metal ions (Table 3),followed by PVA immobilized cells(68.9mg/g,Table 2)and free cells(59.3mg/g j ,Table 1),respectively.Meanwhile,the superior biosorption potential of Ca alginate e immobilized cells (22.6mg/g and 17mg/g)over PVA e immobilized ones (19.3mg/g and 15.6mg/g)was observed in the case of Mn 2þand Cu 2þions,respectively.In general,removal ef ﬁciency of the test biosorbents,for available metal ions,was observed to follow the sequence in following mode:FC (59.3%)<PVA e biomass (68.9%)<Ca alginate e biomass (71.6%).The both immobilized biosorbents displayed high removal potential for Cd 2,Pb 2þ,Fe 3þ,in comparison to other heavy metal ions from the industrial ef ﬂuent.At the same time the immobilized biomass in Ca alginate exhibited the highest biosorption potency toward Mn 2þand Cu 2þions,that ’s why it was chosen for the following investigations.3.1.3.Effect of pHFig.1shows the effect of pH on the biosorption of different metals by A.niger immobilized biomass.Removal ef ﬁciency was analyzed over a pH range 5.5e 7.5.The results show that the metal sorption was a function of pH,as the pH increased from 5.5to 6.5,adsorption capacity increased at ﬁrst for all metals.Maximum adsorption occurs at pH 6.5for Fe 3þ,Cu 2þ,Pb 2þand Cd 2þ,and at pH 7.5for Zn 2þ,Ni2þand Mn 2þ.The maximum removal ef ﬁciencies (%)for the different metals by Ca alginate e biomass were 96.3%for Cd 2þ(at pH 7.5)>90%for Pb 2þ(at pH 7.5)>80%for Fe 3þ(at pH 6.5)>72.8%for Cu 2þ(at pH 6.5)>61.5%for Mn 2þ(at pH 7.5)>59.7%for Zn 2þ(at pH 7.5)>58.9%for Ni 2þ(at pH 7.5).After pH 7.5the ef ﬁciency of the metal removal process increases drastically due to the formation of metal hydroxides with their respective metal ions (Zouboulis et al.,2003).This is mostly due to the metal precipitation as hydrox-ides which depend on the pH and ion concentration,but not due to the biosorption (Al e Qodah,2006;AjayKumar et al.,2009).pH value is one of the main factors in biosorption ef ﬁciency of different biosorbents.The different pH binding pro ﬁles for different metal ions are due to the nature of the chemical interactions of metal ions with the biosorbent.Solution pH in ﬂuences surface metal binding sites of the biosorbents and the chemistry of the cell walls,as well as physicochemistry and hydrolysis of the metals.Table 3Characteristics of the biosorption process for removal of heavy metals from waste-water:Ca alginate e biomass m ¼0.3g/l;pH e 6.5.Performance of biosorbentHeavy metals in mixed solution,mg/l CuZnNiFePbCdMn Initial concentrationsmg/l 7 1.30.90.20.050.0813Equilibrium concentrations mg/l 1.90.580.410.040.0050.003 6.2Equilibrium time min 1510555515Heavy metal uptake mg/g 17 2.4 1.60.530.150.3022.6Removal ef ﬁciency%72.855.454.4809096.252.3Number of parallels:(n)3;relative standard deviation (RSD)3e 8%.102030405060708090100Cu Zn Ni Fe Pb Cd Mnr e m o v a l , %pH - 6.5pH - 7.5Fig.1.Effect of pH on metal ions removal from wastewater using Ca alginate e immobilized cells of Aspergillus niger as a biosorbent.(m 0.3g/l dry weight).Vertical bars show standard error of means of three replicates.K.Tsekova et al./International Biodeterioration &Biodegradation 64(2010)447e 4514493.1.4.Effect of adsorbent weight (g/l)The effect of adsorbent weight (g/l)on the adsorption ef ﬁciency of the best fungal biosorbent (Ca alginate e immobilized cells)is shown on Fig.2.Adsorption experiments were carried out at different biosorbent doses ranging from 0.1to 0.5g/l in mixed ions solution.It was observed as a general trend that there is an increase of the removal percentage with increase in adsorbent weight from 0.1to 0.3g/l.The maximum removal of the most heavy metal ions was attained at an adsorbent dose of 0.3g/l with no further signi ﬁcant increase in the removal percentage at higher biosorbent concentration tested was observed.In the case of Fe 3þ,Mn 2þand Ni 2þmaximum removal was attained at 0.5g/l of adsorbent weight.Removal ef ﬁciency increases for Fe 3þfrom 80%till 90%,Mn 2þfrom 52.3%till 61.5%,and for Ni 2þfrom 58.9%till 79%when the sorbent mass increases from 0.3g/l to 0.5g/l.These results are in agreement with previously studies on many other adsorbents (Yu et al.,2001;Dakiky et al.,2002).As the biosorbent mass increases the number of available binding sites or surface area for the heavy metal ions also increased.However,the removal ef ﬁciency of Pb 2þand Cd 2þretained constant when the biosorbent weight increased.Accord-ing to the previous works,higher biosorbent dose could produce a “screening ”effect on the binding sites,thus resulting in lower heavy metal uptake (Yahaya et al.,2009;Tsekova et al.,2010a,b ).3.1.5.Secondary chemical treatment of the ﬁltrate after biosorptionTo the ﬁltrate obtained after biosorption 5ml 2%sodium diethyldithiocarbamate (NaDDTC)solution and 4g activated char-coal were added,mixed for 10min and ﬁltered through Whatman N 1ﬁlter paper.In this second ﬁltrate the concentration of all the examined heavy metals was below the detection limit of the measurement method.Such successful procedure for completely removing of heavy metals from ef ﬂuents has been not reported in the literature yet.4.ConclusionThe ability of A.niger biomass to bind and remove heavy metals,i.e.Cu 2þ,Zn 2þ,Ni 2þ,Pb 2þ,Cd 2þ,Fe 3þ,Mn 2þfrom real wastewater was investigated.To overcome the separation problems of using freely suspended biomass form,as well as,mass loss after regen-eration of the biosorbent,the biomass was immobilized in the polymer matrixes (PVA and Ca alginate gels).Biosorption studies of Ca alginate e A.niger beads have been found to be effective in removing of relatively low concentrations of these seven heavy metals from wastewater.The process was mainly in ﬂuenced by pH and biosorbent dose.At pH 6.5and biosorbent dose of 0.5g/l dry weight the removal ef ﬁciencies obtained for Ca alginate e biomass beads were:for Cd 2þe 96.2%;for Pb 2þe 90%;for Fe 3þe 90%;for Cu 2þe 73.5%;for Ni 2þe 70.9%for Zn 2þe 60.9%and Mn 2þe 61.5%.The results obtained showed that immobilized biomass of A.niger ,appears as a possible biosorbent to be used for treatment of metal e polluted industrial wastewaters.The secondary chemical treatment with NaDDTC-activated charcoal showed complete removal of all the studied heavy metals.AcknowledgementsThis work was supported by the National Science Fund at the Ministry of Education and Science of Republic of Bulgaria (Grant DOO2-185/2008)and Operative Program Human Resources (Grant BG051PO001e 3.3.04/32).ReferencesAjayKumar,A.V.,Darwish,N.A.,Hilal,N.,2009.Study of various parameters in thebiosorption on heavy metals on activated sludge (Special Issue for Environ-ment).World Applied Sciences Journal 5,32e 40.Al e Qodah,Z.,2006.Biosorption of heavy metal ions from aqueous solutions byactivated sludge.Desalination 196,164e 176.Chatterjee,S.K.,Bhattacharjee,I.,Chandra,G.,2010.Biosorption of heavy metalsfrom industrial waste water by Geobacillus thermodenitri ﬁcans .Journal of Hazardous Materials 175,117e 125.Christian,V.,Shrivastava,R.,Shukla,D.,Modi,H.A.,Vyas,B.R.M.,2005.Degradationof xenobiotic compounds by lignin e degrading white e rote fungi:enzy-mology and mechanism involved.Indian Journal of Experimental Biology 43,301e 312.Dakiky,M.,Khamis,M.,Manassra,A.,Mer ’eb,M.,2002.Selective adsorption ofchromium (VI)in industrial wastewater using low e cost abundantly available adsorbents.Advance Environmental Research 6(4),533e 540.El e Naggar,M.Y.,El e Assar,S.A.,Youseff,A.Y.,El e Sersy,N.A.,Beltagy,E.A.,2006.Extracellular b e mannanase production by the immobilization of the locally isolated Aspergillus niger .International Journal of Agriculture &Biology 8(1),57e 62.Gupta,R.,Mukerji,K.G.,2001.Bioremediation:Past,present and future.In:Tewari,R.,Mukerji,K.G.,Gupta,J.K.,Gupta,L.K.(Eds.),Role of microbes in the management of environmental pollution.A.P.H.Publishing Corp,New Delhi,pp.73e 81.Kapoor, A.,Viraraghvan,T.,1995.Fungal biosorption:an alternative treatmentoption for heavy metal bearing wastewater:a review.Bioresource Technology 53,195e 206.Cu Zn Ni Fe Pb Cd Mnr e m o v a l , %m - 0.1g/l m - 0.3g/l m - 0.5g/lFig.2.Effect of sorbent dose on metal ions removal from wastewater using Ca alginate e immobilized cells of Aspergillus niger as a biosorbent.(pH 6.5).Vertical bars show standard error of means of three replicates.K.Tsekova et al./International Biodeterioration &Biodegradation 64(2010)447e 451450Leitão, A.L.,2009.Potential of Penicillium species in the bioremediationﬁeld.International Journal of Environmental Research and Public Health6, 1393e1417.Mata,Y.N.,Blázquez,M.L.,Ballester,A.,González,F.,Munoz,J.A.,2009.Biosorption of cadmium,lead and copper with calcium alginate xerogels and immobilized Fucus vesiculosus.Journal of Hazardous Materials163,555e562. Muhammad,R.,Nadeem,R.,Hanif,M.A.,Ansari,T.M.,Rehman,K.U.,2009.Pb(II) biosorption from hazardous aqueous streams using Gossypium hirsutum (Cotton)waste biomass.Journal of Hazardous Materials161,88e94.Silva,R.M.P.,Rodriguez,A.Á.,De Oca,J.M.G.M.,Moreno,D.C.,2009.Biosorption of chromium,copper,manganese and zinc by Pseudomonas aeruginosa AT18 isolated from a site contaminated with petroleum.Bioresource Technology100, 1533e1538.Tripathi,A.K.,Harsh,N.S.K.,Gupta,N.,2007.Fungal treatment of industrial efﬂu-ents:a mini e review.Life Science Journal4(2),78e81.Tsekova,K.,Christova,D.,Todorova,D.,Ivanova,S.,2008.Biosorption of ternary mixture of heavy metals by entrapped in PVA e hydrogel biomass of Penicillium cyclopium.Comptes rendus de l`Academie bulgare des Sciences61(9),1175e1180.Tsekova,K.,Todorova,D.,Dencheva,V.,Ganeva,S.,2010a.Biosorption of copper(II)and cadmium(II)from aqueous solutions by free and immobilized biomass ofAspergillus niger.Bioresource Technology101,1727e1731.Tsekova,K.,Christova,D.,Dencheva,V.,Ganeva,S.,2010b.Biosorption of binarymixture of copper and cobalt by free and immobilized biomass of Penicilliumptes rendus de l`Academie bulgare des Sciences63(1),85e90.Volesky,B.,Holan,Z.R.,1995.Biosorption of heavy metals.Biotechnology Progress11(3),235e250.Yahaya,Y.A.,Don,M.M.,Bhatia,S.,2009.Biosorption of copper(II)onto immobilizedcells of Pycnoporus sanguineus from aqueous solution:equilibrium and kineticstudies.Journal of Hazardous Materials161,189e195.Yu,B.,Zhang,Y.,Shukla,S.S.,Dorris,K.L.,2001.The removal of heavy metals fromaqueous solutions by sawdust adsorption:removal of lead and comparison ofits adsorption with copper.Journal of Hazardous Materials84,83e94.Zouboulis,A.I.,Matis,K.A.,Loukidou,M., Sebesta,F.,2003.Metal biosorption by PAN e immobilized fungal biomass in simulated wastewaters.Colloids andSurfaces212,185e195.K.Tsekova et al./International Biodeterioration&Biodegradation64(2010)447e451451。

HEAVY-METAL REMOVAL METHOD AND HEAVY-METAL REMOVAL

专利名称：HEAVY-METAL REMOVAL METHOD ANDHEAVY-METAL REMOVAL DEVICE发明人：Takayuki NAKAI,Satoshi MATSUBARA,OsamuNAKAI,Yoji KYODA申请号：US14651354申请日：20131122公开号：US20150315046A1公开日：20151105专利内容由知识产权出版社提供专利附图：摘要：Provided are a heavy-metal removal method and a heavy-metal removal device,which are capable of reducing the amount of a neutralizing agent to be used. In aneutralization tank provided with a vertical-type cylindrical reaction vessel , stirring blades arranged in the reaction vessel , and an annular aeration tube having a large number of air outlets and being arranged to a bottom part of the reaction vessel , aeration is performed by introducing gas for oxidation from a large number of air outlets of the aeration tube while stirring an aqueous solution containing at least one kind of ion of a divalent ferrous ion and a divalent manganese ion as a heavy metal element by rotation of the stirring blades , and the aqueous solution is subjected to a neutralization treatment.申请人：SUMITOMO METAL MINING CO., LTD.地址：Tokyo JP国籍：JP更多信息请下载全文后查看。

Removal of heavy metals from aqueous solution by sewage

a
Abstract The removal of binary mixed metal ions [Hg(II), Pb(II), Cu(II) and Cr(III)] from water was investigated. Two different sewage sludge-based adsorbents were produced and used for this purpose: PS, obtained by pyrolysis of sewage sludge, and AS, by ZnCl2 chemical activation of sewage sludge followed by pyrolysis. The AS products showed a better development of surface and porosity (472 m2/g of BET surface, 0.05 and 0.22 cm3/g of micro- and mesopore volume, respectively) than the PS. Results on the adsorption of the above metal ions in competition were found and compared with single adsorption results. In competition, as with single systems, AS showed a higher adsorption capacity than PS. The amount of metal adsorbed, differed depending on the binary system. Both PS and AS equilibrium data were well suited to the Langmuir model and showed the capacity order: Hg(II)> Pb(II)> Cu(II)> Cr(III). Moreover, for both PS and AS, the Langmuir maximum adsorption capacity showed that each metal adsorption was diminished by the presence of a competitive metal ion. Once PS and AS were saturated in the binary systems, metal recovery by desorption showed that, except for Cu(II) desorption from AS, recuperation was quite low in all cases, especially for Pb(II). Keywords: Heavy metals; Purification; Competition; Desorption; Sewage sludge

heavy metals

1Abstract Discharge of waste contaminated with heavy metals and related elements is known to have an adverse effect on the environment and solving this problem has for long been presented as a challenge. Nowadays, continuing demand for and increasing value of high-tech metals and rare earth elements makes efficient recy-cling technologies of utmost importance. In solving these tasks, the biosorption—sequestration of heavy metals, radionuclides and rare earth elements usually by non-living biomass—can be a part of the solution.Keywords Decontamination • Bacterial biosorbent • Fungal biosorbent • Algal biosorbent • Mechanism of biosorption • Modeling of biosorption1.1 B rief View on Conventional Waste Stream TreatmentsIndustrialization has long been accepted as a hallmark of civilization. The Boul-ton and Watt steam engine, the synonym of industrial revolution, propelled huge changes in mining, metallurgical technology, manufacturing, transport and agricul-ture. Since then, progressive metallurgy and the use of metals and chemicals in nu-merous industries have resulted in a generation of large quantities of liquid effluent loaded with high levels of heavy metals, often as bioavailable mobile and thus toxic ionic species (Calderón et al. 2003; Peakall and Burger 2003; Gadd 1992a ). Due to their elemental non-degradable nature, heavy metals always and regardless of their chemical form, pose serious ecological risk, when released into the environment. Not only is there the demand for cleanup of contaminated waste water to meet regulatory agency limits, but there is also increasing value of some metals which place a call for efficient and low-cost effluent treatment and metal recuperation technologies.P. Kotrba et al. (eds.), Microbial Biosorption of Metals, DOI 10.1007/978-94-007-0443-5_1, © Springer Science+Business Media B.V . 2011Chapter 1Microbial Biosorption of Metals—General Introduction Pavel KotrbaP. Kotrba ( )Department of Biochemistry and Microbiology, Institute of Chemical Technology Prague, Technicka 3, 166 28 Prague, Czech Republic e-mail: pavel.kotrba@vscht.cz2P. Kotrba Conventional procedures for heavy metal removal from aqueous industrial ef-fluents involve precipitation, ion exchange, electrochemical methods and reverse osmosis. Another promising approach is solvent extraction. Conversion of metal ions to insoluble forms by chemical precipitation is the most common method, reducing the metal content of solution to the levels of mg l−1. The cheapest pre-cipitation technique relies on alkalization of the metal solution (usually with lime) to achieve formation of insoluble metal species, namely of hydroxides. Chemical precipitation could also be achieved by the addition of other coagulants, such as of potash alum, sodium bisuphite, sulphide or iron salts. Though it is cost effec-tive; such precipitation lacks the specificity, produces large volumes of high water content sludge and has low performance at low metal concentrations. Although adsorption using activated carbon is generally expensive (and not suitable for many metal species), it is an efficient method for the removal of metallic mercury following chemical reduction (e.g., with hydrazine) of mercuric ions in heavily contaminated process waters.Ion exchange employing manmade synthetic organic resins is the most common method. It becomes the method of choice especially for its capacity to reduce the metal contents to μg l−1 levels in relatively large volumes of effluent, some possi-bility to formulate metal-selective resin and well established procedures for metal recovery from and reuse of the ion exchanger. This method is, however, relatively expensive, which therefore makes the processing of concentrated metal solutions cost intensive. Precautions should also be taken to prevent the poisoning of ion exchanger by organics and solids in solution.Electro-winning, employing electro-deposition of metals on anodes is popu-larly used for the recuperation of metals in mining and metallurgical operations as well as in electrical industries and electronics. Electrodialysis involves the use of ion selective semi-permeable membranes fitted between the charged electrodes attracting respective ions (in the case of metal cations, the anode compartment is smaller to concentrate the metal in). The main disadvantage of electrodialysis operation is clogging of the membrane by metal hydroxides formed during the process. Like electrodialysis, reverse osmosis and ultrafiltration employ semi-permeable membranes which allow water to pass, while solutes, including heavy metals, remain contained in retentate. The advantages of membrane-based pro-cesses involve some selectivity of metal separation and tolerance to changes in pH. One disadvantage of membrane-based approaches is that they are cost intensive.Reactive two-phase extraction complexing extractants specifically (or preferen-tially) dissolved in organic solvents has been suggested as another technological alternative (Schwuger et al. 2001). This approach may provide a viable method for the selective recuperation of metals, e.g., of platinum group metals from spent cata-lysts (Marinho et al. 2010). Suitable extractants for platinum involve organophos-phorus compounds, aliphatic amines and ammonium quaternary salts. The main disadvantages of this process are the difficult recovery of metals from organic phase and the toxicity of extractants.3 1 Microbial Biosorption of Metals—General Introduction1.2 B io-based Methods for Waste Water Treatment and Environment RestorationThe natural capacity of microrganisms, fungi, algae and plants to take up heavy metal ions and radionuclides and, in some cases, to promote their conversion to less toxic forms has sparked the interest of (micro)biologists, biotechnologists and environmental engineers for several decades. Consequently, various concepts for “bio-removal” of metals from waste streams and bioremediations of contami-nated environment are being proposed, some of which were brought to pilot or industrial scale (Bargar et al. 2008; Macek et al. 2008; Muyzer and Stams 2008; Singh et al. 2008; Chaney et al. 2007; Sheoran and Sheoran 2006; Volesky 2004; Lloyd et al. 2003; Ruml and Kotrba 2003; Baker et al. 2000; Gadd 1992b; see also Chap. 2). The “bio” prefix refers to the involvement of biological entity, which is living organisms, dead cells and tissues, cellular components or products. The ultimate goal of these efforts is to provide an economical and eco-friendly tech-nology, efficiently working also at metal levels below 10 mg l−1. These are the features that living as well as dead biomass could be challenged for. There are generally three routes to follow considering “bio-removal” of metallic species from solutions. The first two rely on properties of living cells and involve active metal uptake—bioaccumulation (i.e., plasma membrane mediated transport of metal ion into cellular compartment) and eventual chemical conversion of mobile metal to insoluble forms. The later may occur in the cytoplasm, at the cell surface or in the solution by precipitation of metal ion with metabolites, via redox reac-tions or by their combination. The effectiveness of the process will depend on the (bio)chemistry of particular metal and on metabolic activity of eligible organism, which is in turn affected by the presence of metal ions. To this point, the use of metallotolerant species or physical separations of the production of metal-pre-cipitating metabolite from metal precipitation in contaminated solution produce viable methods. For their importance in the treatment of industrial liquid streams as well as of the environmental pollution are some of these approaches discussed in Chap. 9. Several of them are to various extents dependent on or involve the metabolism-independent metal uptake event at the cell wall by polysaccharides, associated molecules, and functional groups. This metal sequestration capacity is commonly known as biosorption, which itself represents the third potent way of “bio-removal” of metals from solution.Biosorption is a general property of living and dead biomass to rapidly bind and abiotically concentrate inorganic or organic compounds from even very di-luted aqueous solutions. As a specific term, biosorption is used to depict a method that utilizes materials of biological origin—biosorbents formulated from non-living biomass—for the removal of target substances from aqueous solutions. Biosorp-tion “traditionally” covers sequestration of heavy metals as well as rare earth ele-ments and radionuclides or metalloids, but the research and applications extended to the removal of organics, namely dyes (Kaushik and Malik 2009; see also some examples with magnetic biocomposite biosorbents in Chap. 13), and biosorption is4P. Kotrba being proposed for the recovery of high-value proteins, steroids, pharmaceuticals and drugs (V olesky 2007).Decades of biosorption research provided a solid understanding of the mecha-nism underlying microbial biosorption of heavy metals and related elements. It in-volves such physico-chemical processes as adsorption, ion-exchange, chelatation, complexation and microprecipitation. These depend on the type and ionic form of metal, the type of metal binding site available from microbial biomass, as well as on various external environmental factors (see Chap. 3). Accumulated knowledge resulted in the development of suitable modelling approaches comprehensively described in Chap. 4. When properly used, these models explain the equilibrium biosorption data, the kinetics in batch reactors and the dynamics in biosorption col-umns both for single and multimetal systems and provide a powerful tool for the de-sign and development of the actual biosorption process. It should be noted here that it was due to a poor understanding of mechanisms and kinetics of AlgaSORB TM and AMT-Bioclaim TM processes commercialized in the early 1990s that hindered the adequate assessment of process performance and limitations, and thus the expected widespread industrial application of biosorption.Biosorbents are derived from raw biomass selected for its superior metal-sequestering capacity. Investigated biomass types are of such diverse origins as bacterial, cyanobacterial, fungal (including filamentous fungi and unicellular yeasts), algal, plant or even animal (chitosan). This book covers development in major areas exploiting bacterial biomass (Chap. 5), fungal biomass (Chap. 6) and algal biomass (including macroalgae; Chap. 7) for the biosorption of heavy metal and radionuclides as well as for the sequestration of precious and rare earth elements (Chap. 8). It is noteworthy to add that the potential of plant-based biosorbents formulated from agricultural waste is attaining growing attention (Demirbas 2008; Sud et al. 2008; a few examples with magnetic biocomposite biosorbents are given in Chap. 13). The cheapest microbial biomass could be procured from selected fermentation industries as waste by-product or could be harvested from its natural habitat when it is produced in sufficient quantity there (e.g., marine macroalgae). Independent propagation of biomass under specific conditions optimizing its metallosorption properties is another option. Some ef-forts have been also devoted to modifications of yeast (Chap. 10) and bacterial (Chap. 11) cell walls through their genetic engineering, resulting in a surface display of particular amino acid sequences providing additional (even selective) metal-binding sites.When derived from dead raw biomass featuring high metal uptake, the biosor-bent for its practical application should exhibit some additional characteristics im-proving its stability and favoring hydrodynamic process conditions. To this end, biosorbent particle size, density and porosity, hardness, resistance to a broad range of physical and chemical conditions could be tailored by an appropriate immo-bilization method. Conventional strategies of biosorbent formulation from differ-ent types of microbial biomass are described in respective chapters as well as in Chap. 12. Chapter 13 further sets the biosorbent design forward to “smart materi-als”, the magnetically responsive biocomposites improving biosorbents applicabil-1 Microbial Biosorption of Metals—General Introduction5 ity by enabling their selective magnetic separation even from solutions containing suspended solids.1.3 F uture Thrusts in BiosorptionCompared with conventional or some biological methods for removing metal ions from industrial effluents, the biosorption process offers the advantages of low op-erating cost, minimization of the use of chemicals, no requirements for nutrients or disposal of biological or inorganic sludge, high efficiency at low metal concen-trations, and no metal toxicity issues. The operation of biosorption shares many common features with ion-exchange technology and, despite shorter life cycle and less selectivity options, biosorbents could be considered direct competitors of ionex resins. The high cost of the ion-exchange process limits its application. Not all industries producing metal bearing effluents have financial resources for such sophisticated treatment and most opt only for basic decontamination techniques to meet regulation limits. The accumulated knowledge already provides a solid basis for the commercial exploitation of biosorption processes. Huge markets already exist (V olesky 2007) and they may even grow with progressively stricter legisla-tion worldwide and increase demand on metal resources. Future efforts to improve selectivity and shelf life of biosorbents, further information on biosorption mecha-nisms and reliability and performance of biosorption models as well as more pilot scale demonstrations should bring convincing marketing arguments for large-scale applications. Biosorption also has the potential to find an industrial application in the future separation technologies with renewable biosorbents complementing con-ventional methods in hybrid or integrated installations.ReferencesBaker AJM, McGrath SP, Reeves RD, Smith JAC (2000) Metal hyperaccumulator plants: a review of the ecology and physiology of a biological source for phytoremediation of metal-polluted soil. In: Terry N, Bañuelos GS (eds) Phytoremediation of contaminated soil and water. CRC Press, Boca Raton, pp 85–107Bargar JR, Bernier-Latmani R, Giammar DE, Tebo BM (2008) Biogenic uraninite nanoparticles and their importance for uranium remediation. Elements 4:407–412Calderón J, Ortiz-Pérez D, Yáñez L, Díaz-Barriga F (2003) Human exposure to metals. Pathways of exposure, biomarkers of effect, and host factors. Ecotoxicol Environ Saf 56:193–103 Chaney RL, Angle JS, Broadhurst CL, Peters CA, Tappero RV, Sparks DL (2007) Improved under-standing of hyperaccumulation yields commercial phytoextraction and phytomining technolo-gies. J Environ Qual 36:1429–1443Demirbas A (2008) Heavy metal adsorption onto agro-based waste materials: a review. J Hazard Mater 157:220–229Gadd GM (1992a) Metals and microorganisms: a problem of definition. FEMS Microbiol Lett 79:197–203P. Kotrba 6Gadd GM (1992b) Microbial control of heavy metal pollution. In: Fry JC, Gadd GM, Herbert RA, Jones CW, Watson-Craik IA (eds) Microbial control of pollution. Cambridge University Press, Cambridge, pp 59–87Kaushik P, Malik A (2009) Fungal dye decolourization: recent advances and future potential. En-viron Int 35:127–141Lloyd JR, Lovley DR, Macaskie LE (2003) Biotechnological application of metal-reducing micro-organisms. Adv Appl Microbiol 53:85–128Macek T, Kotrba P, Svatoš A, Demnerová K, Nováková M, Macková M (2008) Novel roles for GM plants in environmental protection. Trends Biotechnol 26:146–152Marinho RS, Afonso JC, da Cunha JW (2010) Recovery of platinum from spent catalysts by liq-uid–liquid extraction in chloride medium. J Hazard Mater 179:488–494Muyzer G, Stams AJ (2008) The ecology and biotechnology of sulphate-reducing bacteria. Nat Rev Microbiol 6:441–454Peakall D, Burger J (2003) Methodologies for assessing exposure to metals: speciation, bioavail-ability of metals, and ecological host factors. Ecotoxicol Environ Saf 56:110–121Ruml T, Kotrba P (2003) Microbial control of metal pollution: an overview. In: Fingerman M, Nagabhushanam R (eds) Recent advances in marine biotechnology, vol 8. Science Publishers Inc., Enfield, pp 81–153Schwuger MJ, Subklew G, Woller N (2001) New alternatives for waste water remediation with complexing surfactants. Colloid Surface A 186:229–242Sheoran AS, Sheoran V (2006) Heavy metal removal mechanism of acid mine drainage in wet-lands: a critical review. Mineral Eng 19:105–116Singh S, Kang SH, Mulchandani A, Chen W (2008) Bioremediation: environmental clean-up through pathway engineering. Curr Opin Biotechnol 19:437–444Sud D, Mahajan G, Kaur MP (2008) Agricultural waste material as potential adsorbent for se-questering heavy metal ions from aqueous solutions—a review. Biores Technol 99:6017–6027 V olesky B (2004) Sorption and biosorption. BV-Sorbex Inc., St. LambertV olesky B (2007) Biosorption and me. Water Res 4017–4029。

heavy metal ions with continuous aluminum electrocoagulation

Removing heavy metal ions with continuous aluminum electrocoagulation:A study on back mixing and utilization rate of electro-generated AlionsJun Lu ⇑,Yan Li,Mengxuan Yin,Xiaoyun Ma,Shengling LinSchool of Environmental and Chemical Engineering,Jiangsu University of Science and Technology,Zhenjiang,Jiangsu 212003,Chinah i g h l i g h t sThe mass transfer of species in continuous electrocoagulation channel was discussed. The back mixing is dependent on both ﬂuid dynamics and mass transfer. Increasing current density or residence time could intensify the back mixing.The molar ratio of M/Al could be used to quantify the utility of electro-generated Al ions well. The optimization and reactor design could be based on the optimization of M/Al ratio.a r t i c l e i n f o Article history:Received 11October 2014Received in revised form 17December 2014Accepted 3January 2015Available online 13January 2015Keywords:Continuous electrocoagulation Mass transfer Back mixing Heavy metal ion Adsorptiona b s t r a c tElectrocoagulation (EC)technology is based on rapid in situ dissolution of sacriﬁcial anode to generate precipitates and ﬂocs capable of removing heavy metal ions.The lack of mechanism-based approach to reactor optimization has limited its implementation.The continuous EC process for treating heavy metal ions (Ni 2+)was studied.Effects of some experimental parameters on the heavy metal ions removal were investigated.The back mixing was investigated through the concentration distribution at the direction of streamline.In continuous EC process characterized by in situ generation of absorbents,the degree of back mixing is dependent on both ﬂuid dynamics and mass transfer.The degree of back mixing increases with the increment of current density or residence time.A new universal parameter named as molar ratio of M/Al (M is the heavy metal ions)was introduced to quantify the utilization rate of electro-generated Al ions (or Fe ion)in EC process.The M/Al ratio is found to decrease with the increment of current density and residence time.Further,the relationship between the ratio and traditional parameters (removal efﬁ-ciency and the consumption of energy and electrode)was discussed in this article.The optimization and reactor design could be based on the optimization of M/Al ratio.Ó2015Elsevier B.V.All rights reserved.1.IntroductionIndustrial wastewaters with heavy metals are directly or indi-rectly discharged into the environment,especially with the devel-opment of industries.Most of the metals such as copper,nickel,lead and chromium are not biodegradable and tend to accumulate in living organisms.Some of them are known to be toxic or carcin-ogenic [1,2].Thus,it is harmful when they are discharged without careful treatment.Due to their high toxicity,industrial wastewa-ters are strictly regulated and have to be treated before being discharged.Various techniques have been applied to the treatment of heavy metals,such as chemical precipitation [3],adsorption [4],ion-exchange [5],and reverse osmosis [6].Among these techniques chemical precipitation is widely used for heavy metal removal from wastewaters.This method has many disadvantages like excessive coagulant material and large amounts of sludge,which could lead to secondary pollution.In recent years,an electrochemical method named electrocoag-ulation (EC)has attracted signiﬁcant attention for heavy metal removal owing to its easy operation,less amount of added chemi-cals and sludge and no second-pollution particularly,etc.[7].The main chemical reactions occurring in EC cells with the aluminum electrodes are as follows [8]:/10.1016/j.cej.2015.01.0111385-8947/Ó2015Elsevier B.V.All rights reserved.⇑Corresponding author.Tel.:+8651184401181.E-mail address:jluabc@ (J.Lu).电凝（EC ）技术是基于在牺牲阳极溶出度快速生成并能去除重金属离子的絮凝沉淀。

removalofheavyme...

GENERAL PAPERSOrganized byG. CoimbatoreSymposia Papers Presented Before the Division of Environmental ChemistryAmerican Chemical SocietySan Francisco, CA September 10-14, 2006REMOVAL OF HEAVY METALS FROM WATER WITH FOREST BASED MATERIALS James D. McSweeny1, Roger M. Rowell1, George C. Chen1,Thomas L. Eberhardt2 and Soo-Hong Min31U.S. Department of Agriculture, Forest ServiceForest Products Laboratory, Madison, WI 537262Southern Research Station, USDA Forest Service, Pineville, LA 71360 3Samsung Corporation, Sungnam-si, Gyonggi-Do, Korea 463-824IntroductionFor 1.5 to 2.5 billion people in the world, clean water is a critical issue (Lepkowski 1999). In the U.S., it is estimated that 90% of all Americans live within 10 miles of a body of contaminated water (Hogue, 2000). The development of filters to clean our water supply is big business. It is estimated that global spending on filtration (including dust collectors, air filtration, liquid cartridges, membranes and liquid macro-filtration) will increase from $17 billion in 1998 to $75 billion by 2020 (Noble, 2000). The fastest-growing non-industrial application area for filter media is for the generation of clean water.One of the prevalent contaminates in our water is metal ions that come from a wide variety of sources including abandoned hard rock and coal mines, highways and large parking lot runoff and natural erosion of minerals. Most methods to remove metal ions from solution are expensive. However, it has been shown that wood and bark are effective in removing metal ions from water (Bryant et al., 1992; Kumar and Dara, 1980; Laszlo and Dintzis, 1994; Randall, 1977).Materials and MethodsTwo methods are presented here that modify wood to increase the sorption of metal ions from contaminated water by increasing the carboxyl content of the cell wall polymers, thus increasing the negatively charged sites that participate in ion exchange with cations. One technique involves grafting citric acid to wood by esterification of a wood hydroxyl group with one of two adjacent carboxylic acid groups of a citric acidmolecule. The other technique involves a two-step oxidation process: First using sodium periodate to selectively cleave adjacent polysaccharide hydroxyl groups, resulting in the formation of a dialdehyde. A second oxidation step with sodium hypobromite converts aldehydes to carboxylates. All treatments were conducted at room temperature. Citric AcidTen ml of 200 g/l ACS Reagent citric acid (anhydrous) was added to 2 g of milled aspen wood and allowed to soak for ½ h. The excess water was removed by oven drying 4 h at 60°C. The dry sample was thermochemically reacted by elevating oven temperature. Separate samples were reacted for 2, 4 and 6 h at 110, 120 and130°C. Reacted samples were water-rinsed to remove unreacted citric acid and then vacuum oven dried for 16 h at 45°C.Sodium PeriodateTwenty-five g of milled southern pine wood was mixed in 500 ml solutions containing ACS Reagent sodium periodate (99%). Three concentrations of periodate were used, with separate wood samples, consisting of 1, 2 and 3 % (w/v). Samples were reacted for 24 h, water-rinsed and vacuum oven dried for 16 h at 45°C.Sodium HypobromiteACS Reagent bromine (99.5%) was used to prepare the sodium hypobromite solution immediately before each use. Bromine and sufficient NaOH to yield pH 11 were combined in a 300 ml aqueous solution. Ten g of periodate treated wood was added to three separate concentration levels of the hypobromite. The 1, 2, and 3% (w/v) sodium periodate treated samples were added to 0.3, 0.6 and 0.8% (w/v) solutions of bromine as sodium hypobromite, respectively. Samples were reacted for 24 h, water-rinsed and vacuum oven dried for 16 h at 45°C.Cu Copper ion Sorption Testing2+ ion was used as standard to determine the efficiency of each modification in removing metal ions from aqueous solutions. The test method involved a 0.1g test sample in 50ml of 50 ppm and a 24 hour equilibrium batch test protocol (pH range 4.6 to5.2). The wood sorbent was filtered from each standard solution and was analyzed for remaining Cu 2+ ion with a Jobin Yvon, Ultima, inductively coupled plasma-atomic emission spectrometer instrument.FTIR SpectoscopyA Nicolet Nexus 670 spectrometer equipped with a Thermo Nicolet Smart Golden Gate MKII Single Reflection ATR accessory was used to monitor changes to carboxylate and ester carbonyl regions of the modifed wood, compared with the unmodified wood. Results and DiscussionBoth modification methods resulted in substantial increases to sorption capacity of the wood calculated as Cu 2+ ion/wood (mg/g). In addition, changes in the FTIR/ATR spectra reflected increases to carboxyl and with citric acid treated, ester carbonyl regions of the modified wood, from that of the unmodified wood.The greatest increase in sorption capacity with the citric acid method was a 2 h reaction at 130°C, 20% (w/v) citric acid reaction with aspen wood. Weight gain of the wood from the grafted citric acid for this treatment condition was 28.5% and resulted in a 236.6 % increase in Cu2+ ion sorption capacity (mg/g). At treatments longer than 2 h, decreases to Cu2+ ion sorption capacity and increases to 1,730 cm-1 absorbance, may be due to ester cross-links formed between wood hydroxyls and free carboxyls of the bound citrate (see Figures 1 and 2).Figure 1.Cu2+ ion sorption capacity (mg/g) of citric acid treated aspen wood as a function of treatment time at 110°C, 120ºC and 130ºC using 0.01 M sodium acetate buffered standard with initial pH of 5.1. Y-axis values are an average of three replicates. The point at zero hours treated is untreated wood.Figure 2. FTIR scans of 1,730 cm-1 (ester) carbonyl region with baselines normalized to 1320 cm1. Samples are treated with 0.1 M NaOH. Scans are of untreated (control) aspen wood and wood reacted with citric acid for 2, 4 and 6 hours at 130°C.The results in Table 1 show the periodate/hypobromite method applied to southern pine wood. The greatest increase was with a 24 hour reaction at room temperature, 3% (w/v) sodium periodate reaction followed by a 24 hour at room temperature, 0.8% (w/v) Br2 (as hypobromite) reaction. The total weight loss to the wood for this reaction was 12.6% and resulted in a 148.4% increase in Cu2+ ion sorption capacity (mg/g). Figure 3 shows increases to the carboxylate region with increasing concentration of periodate/ hypobromite.Table 1. Sodium periodate and sodium hypobromite treatments of southern pine wood.Treatment1,2(%)ChangeinOxidant(%)WeightChangeaftertreatmentq eCu2+(mg/g)Sorption pH rangeUntreated 3.14.6-5.21% Periodate for 24hrs, 0.3% Br2 for 24 hrs -29.2,-82.6-1.9,-3.44.7 4.6-4.72% Periodate for 24hrs, 0.6% Br2 for 24 hrs -29.2,-85.3-2.6,-5.67.0 4.6-4.73% Periodate for 24hrs, 0.8% Br2 for 24 hrs -18.1,-87.7-2.5,-10.17.8 4.6-4.81 % oxidant is w/v;2 qesorption values an average of 3 replicates.Figure 3. FTIR scans of 1,604 cm-1 (carboxylate) carbonyl region with baselines normalized to 1,317 cm1. Scans are of untreated (control) southern pine wood and the following treatments: a = 1% Periodate for 24hrs, 0.3% Br2 for 24 hrs; b = 2% Periodate for 24hrs, 0.6% Br2 for 24 hrs; c = 3% Periodate for 24hrs, 0.8% Br2 for 24 hrs.ReferencesBryant, P.S., Petersen, J.N, Lee, J.M. and Brouns, T.M. (1992). Sorption of heavy metals by untreated red fir sawdust. Appl. Biochem. Biotechnol 34-35:777-778. Hogue, C. (2000). Muddied waters. Chemical and Engineering News, 19-20, August. Kumar, P. and Dara, S.S. (1980). Modified barks for scavenging toxic heavy metal ions.Indian J. Envir. Health, 22:196.Laszlo, J.A. and Dintzis, F.R. (1994). Crop residues as ion-exchange materials.Treatment of soybean hull and sugar beet fiber (pulp) with epichlorohydrin to improve cation-exchange capacity and physical stability. J. Applied Polymer Sci., 52:521-528.Lepkowski, W. (1999). Science meets policy in shaping water’s future. Chemical and Engineering News, 127-134, December.Noble, T. Filtration makes solid gains. Chemical and Engineering News, 13-15, October (2000).Randall, J.M. (1977). Variations in effectiveness of barks as scavengers for heavy metal ions. Forest Products Journal 27(11):51.McSweeny, J.D., Rowell, R.M., Chen, G.C., Eberhardt, T.L., & Min, S.H. (2006). Removal of heavy metals from water with forest based materials. 232nd ACS National Meeting and Exposition. September 10-14. (San Francisco, CA.). Preprints of Extended Abstracts, vol.46, No.2, paper No.206, pp. 283-288.。

Method of removing heavy metals from silicate sour

专利名称：Method of removing heavy metals fromsilicate sources during silicate manufacturing 发明人：Yung-Hui Huang,John V. Offidani申请号：US11282073申请日：20051117公开号：US07201885B1公开日：20070410专利内容由知识产权出版社提供摘要：Methods for the removal of lead from a metal silicate during the process of manufacturing of such a material are provided. With the reliance upon lower cost starting silicon dioxide starting materials that are known to exhibit elevated amounts of heavy metal therein for the purpose of producing metal silicates (such as sodium silicate, as one example), it has been realized that removal of significant amounts of such heavy metals is necessary to comply with certain regulatory requirements in order to provide a finished material that exhibits the same low level of heavy metal contamination as compared with finished materials that are made from more expensive, purer starting silicon dioxides. Two general methods may be followed for such decontamination purposes. One entails the introduction of a calcium phosphate material, such as dicalcium phosphate, tricalcium phosphate, and/or hydroxyapatite, to a formed metal silicate solution but prior to filtering. The other requires the introduction of calcium phosphate material (again, hydroxyapatite, tricalcium phosphate, and/or dicalcium phosphate) in a silicon dioxide, caustic, and water slurry with said dicalcium phosphate thus present throughout the overall reaction steps of metal silicate formation and is removed by filtering. In each situation, the hydroxyapatite, tricalcium phosphate, or dicalcium phosphate actually aidsin rendering immobile the heavy metals therein, such as lead, cadmium, and the like, thereby preventing release of high amounts of bioavailable amounts of such heavy metals from products for which the target metal silicates are considered reactants. Thus, the heavy metal-containing metal silicates may then be utilized to produce precipitated silicas, as one example, that exhibit much lower levels of bioavailable heavy metals as compared with the original silicon dioxide source.申请人：Yung-Hui Huang,John V. Offidani地址：Bel Air MD US,Havre de Grace MD US国籍：US,US代理人：William Parks,Carlos Nieves更多信息请下载全文后查看。