Desiliconization kinetics of nickeliferous laterite ores in molten sodium hydroxide system

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Kinetic modelling of the adsorption of nitrates

Chemical Engineering Journal125(2006)111–117Kinetic modelling of the adsorption of nitratesby ion exchange resinM.Chabani a,A.Amrane b,∗,A.Bensmaili aa Facult´e de G´e nie des Proc´e d´e s et G´e nie M´e canique,U.S.T.H.B.BP32,El Allia,Bab ezzouar,Algeriab Equipe Chimie et Ing´e nierie des Proc´e d´e s-ENSCR/Universit´e de rennes1,UMR CNRS6226“Sciences chimiques de Rennes”,ENSCR,Campus de Beaulieu,av.du G´e n´e ral Leclerc,35700Rennes,FranceReceived21April2006;received in revised form17July2006;accepted6August2006AbstractThe capacity of ion exchange resins,Amberlite IRA400,for removal of nitrates from aqueous solution was investigated under different initial concentrations.The suitability of the Freundlich,Langmuir and Dubinin-Radushkevich adsorption models to the equilibrium data was investigated.The equilibrium data obtained in this study were found to follow Freundlich adsorption isotherm.The maximum sorption capacity was769.2mg/g at25◦C.Reversible-ﬁrst-order,intraparticle diffusion,ﬁlm diffusion and Bangham models were used toﬁt the experimental data. The adsorption of nitrates on Amberlite IRA400resin follows reversible-ﬁrst-order kinetics.The overall rate constants were estimated for different initial concentrations.Results of the intra-particle diffusion and theﬁlm diffusion models show that theﬁlm diffusion was the main rate-limiting step.The low correlation of data to the Bangham’s equation also conﬁrms that diffusion of nitrates into pores of the resin was not the only rate-controlling step.The thermodynamic constants of adsorption phenomena, H◦and S◦were found to be−26.122kJ/mol and−68.76J/mol in the range298–318K and+19.205kJ/mol and+68.76J/mol in the range318–343K,respectively.The negative values of the Gibbs free energy ( G)demonstrate the spontaneous nature of adsorption of nitrates onto Amberlite IRA400.©2006Elsevier B.V.All rights reserved.Keywords:Adsorption;Resin;Nitrates;Kinetics1.IntroductionSeveral nitrogenous compounds,including ammonia,nitrite and nitrate are frequently present in drinking water[1].Nitrates can cause several environmental problems.Nitrates and phos-phates can stimule eutrophication where pollution is caused in waterways by heavy algal growth,as they are both rate-limiting nutrients for process.A high concentration of nitrate-nitrogen in drinking water leads to the production of nitrosamine,which is related to cancer,and increases the risks of diseases such as methemoglobinemia in new-born infants[2,3].Several methods that serve to reduce nitrates in drinking water have been developed.The use of biological reactor seems to be the most promising technique in the treatment of high nitrate concentrations.However,maintaining biological processes at their optimum conditions is difﬁcult,and the problems of con-∗Corresponding author.Tel.:+33223235755;fax:+33223238120.E-mail address:abdeltif.amrane@univ-rennes1.fr(A.Amrane).tamination by dead-bacteria have to be solved to make such processes satisfactory for a safety use in drinking water treat-ment.Adsorption is a useful process for in situ treatment of underground and surface water,primarily due to it’s easy of use [3].Adsorbent resins are considered the most promising owing to their chemical stability and ability to control surface chemistry [4].The characteristics of adsorption behaviour are generally inferred in terms of both adsorption kinetics and equilibrium isotherms.They are also important tools to understand the adsorption mechanism,viz.the theoretical evaluation and inter-pretation of thermodynamic parameters[5,6].The objective of this study was to investigate equilibrium and kinetic parameters for the removal of nitrates from aqueous solutions by adsorption onto an ionized adsorbent,Amberlite IRA400.The Langmuir,Freundlich and Dubinin-Radushkevich (D-R)equations were used toﬁt the equilibrium isotherms.Ther-modynamic parameters were also evaluated through adsorption measurements.1385-8947/$–see front matter©2006Elsevier B.V.All rights reserved. doi:10.1016/j.cej.2006.08.014112M.Chabani et al./Chemical Engineering Journal125(2006)111–117Nomenclatureb Langmuir constant(cm3/mg)C0initial concentration in solution(mg/l)C e equilibrium concentration(mg/l)C t concentration at time t(mg/l)D p pore diffusion coefﬁcient(cm2/s)D fﬁlm diffusion coefﬁcient(cm2/s)E free energy of adsorption(kJ/mol)G Gibbs free energy(kJ/mol)H◦enthalpy of adsorption(kJ/mol)k overall rate constant of adsorption(min−1)k1forward rate constant(min−1)k2backward rate constant(min−1)k d distribution constant(l/g)k f Freundlich’s constant related to the sorptioncapacityk i intraparticle diffusion parameter(mg/g min0.5)m mass of adsorbent(g)n Freundlich’s constant related to the sorptionintensity of a sorbentq the amount of nitrates adsorbed or transferred(mg/l)q o maximum adsorption capacity(mg/g)q e adsorption capacity in equilibrium(mg/g)q t amount of adsorption at time t(mg/g)R ideal gas constant(8.314J/mol K)R p radius of the adsorbent(cm)S◦entropy of adsorption(J/mol K)t time(min)t1/2time for half adsorption(min)T temperature(K)v volume of solution(l)Greek letterεﬁlm thickness(cm)2.Materials2.1.Pre-treatment of resinBefore use,the resin was washed in distilled water to remove the adhering dirt and then dried at50◦C.After drying,the resin was screened to obtain a particle size range of0.3–0.8mm.2.2.The resin characteristicsThe main characteristics of the Amberlite IRA400(Merck, Darmstadt,Germany),a macroporous anion exchange resin,are given in Table1.2.3.Nitrate solutionsThe stock solution of NO3−used in this study was prepared by dissolving an accurate quantity of KNO3in distilled water.Table1Characteristics of Amberlite IRA400ion exchange resinPolymer matrix Polystyrene DVBFunctional group–N+R3Ionic form Cl−Exchange capacity 2.6–3eq kg−1of dry massAppearance Yellow to golden spherical beads,translucent Effective size0.3–0.8mmWater retention42–48%Visual density in wet state0.66–0.73g/mlTrue density in wet state 1.07–1.10g/mlA range of dilutions,1–18mg/l,was prepared from the stock solution.2.4.Sorption experimentsThe pH of the aqueous solutions of NO3−was approximately 6.8and did not varied signiﬁcantly with the dilution.The effect of temperature on the sorption rate of nitrates on Amberlite IRA400was investigated by equilibrating the sorption mix-ture(800ml)containing dried resin(2g)and nitrates(15mg/l) in a temperature range298–343K.The solutions were placed in ﬂasks and stirred for3h.Experiments were mainly carried out without initial adjustment of the pH.Preliminary tests showed that the adsorption was complete after1h.The concentration of residual nitrate ions was determined spectrophotometrically according to Rodier protocol[7].The sorption capacity at time t,q t(mg/g)was obtained as follows: q t=(C0−C t)vm(1) where C0and C t(mg/l)were the liquid-phase concentrations of solutes at the initial and a given time t,respectively,v(l)the volume of solution and m the mass resin(g).The amount of adsorption at equilibrium,q e was given by: q e=(C0−C e)vm(2) C e(mg/l)was the concentration of nitrates at equilibrium.The distribution constant k d was calculated using the follow-ing equation:k d=Amount of nitrates in adsorbentAmount of nitrates in solution×vm.(3) 3.Results and discussion3.1.Adsorption isothermsSorption equilibrium is usually described by an isotherm equation whose parameters express the surface properties and afﬁnity of the sorbent,at aﬁxed temperature and pH[8].An adsorption isotherm describes the relationship between the amount of adsorbate adsorbed on the adsorbent and the con-centration of dissolved adsorbate in the liquid at equilibrium. Equations often used to describe the experimental isotherm data are those developed by Freundlich[9],by Langmuir[10]and by Dubinin-Radushkevich[11].The Freundlich and LangmuirM.Chabani et al./Chemical Engineering Journal 125(2006)111–117113isotherms are the most commonly used to describe the adsorp-tion characteristics of adsorbent used in water and wastewater.3.1.1.Freundlich isotherm (1906)The empirical model can be applied to non-ideal sorption on heterogeneous surfaces as well as multilayer sorption and is expresses by the following equation:q e =k f C 1/ne(4)n and k f are the Freundlich constants.The ﬁt of data to Freundlich isotherm indicates the hetero-geneity of the sorbent surface.The magnitude of the exponent 1/n gives an indication of the adequacy and capacity of the adsor-bent/adsorbate system [12].In most cases,an exponent between 1and 10shows beneﬁcial adsorption.The linear plot of ln q e versus ln C e (Fig.1)shows that the adsorption obeys to the Fre-undlich model.k f and n were determined from the Freundlich plot and found to be 0.982and 1.074(Fig.1),respectively.n values above 1indicate favourable adsorption.ngmuir isotherm (1916)The Langmuir model is probably the best known and most widely applied sorption isotherm.It may be represented as fol-lows:q e =q o bC e1+bC e (5)The Langmuir constants q o and b are related to the adsorption capacity and the energy of adsorption,respectively.The linear plot of 1/q e versus 1/C e shows that the adsorption obeys to the Langmuir model (Fig.2),and gave the following values for q o and b ,769.2mg/g and 1.02cm 3/mg,respectively.3.1.3.Dubinin-Radushkevich (D-R)isothermRadushkevich [13]and Dubinin [14]have reported that the characteristic sorption curve is related to the porous structure of the sorbent.The sorption data were applied to the D-R model in order to distinguish between physical and chemical adsorption [15].The D-R equation was given by:ln q e =ln q o −βε2(6)Fig.1.Linearized Freundlich isotherm (Eq.(4))for nitrates adsorption by Amberlite IRA 400;T =25◦C,pH 6.8,adsorbent dose 1.25g/l.Fig.2.Linearized Langmuir isotherm (Eq.(5))for nitrates adsorption by Amber-lite IRA 400;T =25◦C,pH 6.8,adsorbent dose 1.25g/l.where βwas the activity coefﬁcient related to mean sorption energy and εthe Polanyi potential given by:ε=RT ln1+1e (7)where R was the gas constant (kJ/mol K)and T the temperature (K).The slope of the plot ln q e versus εgives β(mol 2/J 2)and the ordinate intercept yields the sorption capacity q o (mg/g).The mean sorption energy (E )is given by E =1/√−2β;for a magnitude of E between 8and 16kJ/mol,the adsorption process follows chemical ion-exchange [6,16],while values of E below 8kJ/mol characterize a physical adsorption process [17].The plot of ln q e against ε2for nitrate ions sorption on resin is shown in Fig.3.The E value was 40.8J/mol,which corresponds to a physical adsorption.The linear correlation coefﬁcients for Freundlich,Langmuir and D-R are shown in Table 2,and are always greater than 0.980.The Freundlich equation represents a better ﬁt of experimental data than Langmuir and D-Requations.Fig.3.Radushkevich-Dubinin isotherm (Eq.(6))for nitrates adsorption by Amberlite IRA 400;T =25◦C,pH 6.8,adsorbent dose 1.25g/l.114M.Chabani et al./Chemical Engineering Journal 125(2006)111–117Table 2Isotherm parameters collected for removal of nitrates by Amberlite IRA 400Freundlich constants k f 0.982n 1.074R 20.9951Langmuir constants q o (mg/g)769.2b (cm 3/mg) 1.02R 20.9933D-R constants q o (mg/g)76.5E (J/mol)40.8R 20.9873.2.Adsorption kinetics3.2.1.Effect of initial concentrationsPredicting the adsorption rate,in addition to the adsorbate residence time and the reactor dimensions,controlled by the system’s kinetics,are probably the most important factors in adsorption system design [18].Preliminary experiments showed high initial rates of adsorp-tion of nitrates followed by lower rates near equilibrium.Kinet-ics of nitrates removal at 298K showed high rates during the initial 15min,and decreased thereafter until nearly constant val-ues after 40min of adsorption (Fig.4).In batch adsorption processes the adsorbate molecules diffuse in porous adsorbent and the rate process usually depends upon t 1/2rather than the contact time,t [19,20]:q t =k i t 0.5(8)The plot of q t ,the amount of adsorbate adsorbed per unit weight of adsorbent versus square root of time has been com-monly used to describe an adsorption process controlled by diffusion in the adsorbent particle and consecutive diffusion in the bulk of the solution [21].Therefore,as can be observed in Fig.5,adsorption was linear and charaterized by extremelyfastFig.4.Time-courses of nitrates adsorption for different initial concentrations of nitricnitrogen.Fig.5.Effect of t 1/2on adsorption of nitrates by Amberlite IRA 400(Eq.(8)),adsorbent dose 1.25g/l,pH 6.8.uptake.During this phase,nitrates were adsorbed within a t 1/2value of about 10min;this behaviour can be attributed to the rapid use of the most readily available adsorbing sites on the adsorbent surface.After this phase,adsorption became negligi-ble.It may be attributed to a very slow diffusion of adsorbed nitrates from the ﬁlm surface into the micropores,which are the less accessible sites of adsorption [20,22,23].Fig.5shows two consecutive linear steps during the adsorption of nitrates on Amberlite IRA 400,and the deviation from the straight line indicates that the pore diffusion is not the only rate-limiting step.The slope of the linear portion from Fig.5was used to derive values for the rate parameter,k i ,for the intra-particle diffusion (Eq.(8)).The results show that intraparticle diffusion model was valid for the considered system.Kinetic parameters and correlation coefﬁcients obtained by the intra-particle model are given in Table 3.The values of k i increased for increasing initial concentrations.Kinetic data can further be used to check whether pore-diffusion was the only rate-controlling step or not in the adsorp-tion system using Bangham’s equation [24–26]:log log C 0C 0−qm =log k B m2.303v+a log t (9)As observed,the model did not match experimental data(Fig.6),showing that the diffusion in the pores of the sorbent wasTable 3Intraparticle diffusion (Eq.(8))kinetic parameters for adsorption of nitrates on Amberlite IRA 400resin at different concentrations Concentration of nitric nitrogen (mg/l)Intraparticle diffusion Correlation coefﬁcient R 2Kinetic parameters,k i (mg/g min 0.5)10.8740.5120.990 1.23.50.987 2.9150.990 3.93100.9038.75140.98211.7180.96615.5M.Chabani et al./Chemical Engineering Journal125(2006)111–117115Fig.6.Fit of adsorption kinetics at different initial concentrations of nitric nitro-gen by means of the Bangham’s model(Eq.(9)).not the only rate-controlling step.The correlation coefﬁcients given by the Bangham’s equation(Fig.6)conﬁrmed that the model did notﬁt satisfactory experimental data.Similar results were previously reported for4-CP adsorption by macroreticular resins[27]and for adsorption of4-chlorophenol by XAD-4[12].3.2.2.First-order reversible modelWhen a single species is considered to adsorb on a hetero-geneous surface,the adsorption of a solute from an aqueous solution follows reversible-ﬁrst-order kinetics[28,29].The het-erogeneous equilibrium between the solute in solution and the ion exchange resin may be expressed as:A k1k2B,(10)With k1the forward reaction rate and k2the backward reaction rate constant.If C0(mg/l)was the initial concentration of nitrates and q(mg/l)the amount transferred from the liquid phase to the solid phase at a given time t,then the rate was:d q d t =−d(C0−q)d t=k(C0−q)(11)where k(min−1)is the overall reaction rate constant.Since k1 (min−1)and k2(min−1)are the rate constants for the forward and the reverse processes,the rate can be expressed as:d qd t=k1(C0−q)−k2q(12)If X e(mg/l)represents the concentration of nitrates adsorbed at equilibrium,then at equilibrium:k1(C0−X e)−k2X e=0,d qd t=(k1+k2)(X e−q)(13) after integration,The above equation can be rearranged:ln(1−U t)=−(k1+k2)t=−kt(14) where U t=q/X e and k was the overall rate constant;U t,called the fractional attainment of equilibrium of nitrates,is givenby Fig.7.Fit of adsorption kinetics at different initial concentrations of nitric nitro-gen by means of the reversible-ﬁrst-order model(Eq.(14)).the following expression:U t=C0−C tC0−C e(15) where C0,C t and C e were the initial nitrates concentration,its concentration at a given time t and at equilibrium,respectively. The overall constant rate k for a given concentration corre-sponded to the slope of the straight line of the plot ln(1−U t) versus t(Fig.7).The equilibrium constant and the forward and backward constant rates k1and k2were calculated using Eq.(14)and are collected in Table4.The high correlation coefﬁcient values,if compared to that given in the available literature[30],conﬁrm the applicability of the model.It could be seen that the forward rate constants for the removal of nitrates were much higher than the backward rate constants for the des-orption process(Table4).The constant rates depend on the adsorption capacity,the diffusion coefﬁcient,the effective mass transfer area,the hydrodynamic of the system and other physico-chemical parameters.Ourﬁnding agreed with previous results [12].3.2.3.Diffusion processIn order to assess the nature of the diffusion process respon-sible for adsorption of nitrates on Amberlite IRA400,attempts were made to calculate the coefﬁcients of the process.Ifﬁlm dif-fusion was to be the rate-determining step in the adsorption of nitrates on the surface of the resin,the value of theﬁlm diffusion coefﬁcient(D f)should be in the range10−6to10−8cm2/s.If pore diffusion was to be rate limiting,the pore diffusion coefﬁ-cient(D p)should be in the range10−11to10−13cm2/s[31,32]. Assuming spherical geometry for the sorbent,the overall rate constant of the process can be correlated with the pore diffu-sion coefﬁcient and theﬁlm diffusion coefﬁcient independently according to[29]:Pore diffusion coefﬁcient:D p=0.03R2pt1/2,(16)andﬁlm diffusion coefﬁcient:D f=0.23R pε1/2q(17)116M.Chabani et al./Chemical Engineering Journal125(2006)111–117 Table4Constant rates for the removal of nitrates with Amberlite IRA400resin using reversible-ﬁrst-order model(Eq.(14))C0(mg/l)Correlationcoefﬁcients,R2Overall rate constant,k=k1+k2(min−1)Forward rate constant,k1(min−1)Backward rate constant,k2(min−1)10.9540.0860.0680.018 20.9940.0890.0770.012 3.50.9780.1160.1070.009 50.9850.1410.1290.011 100.9800.1370.1280.008 140.9750.1650.1510.013 180.9920.1630.1460.017 where R p was the radius of the adsorbent(R p=0.045cm),εtheﬁlm thickness(10−3cm)[19],q(mg/l)the amount of nitratesadsorbed and C0the initial concentration.By considering theappropriate data and the respective overall rate constants,poreandﬁlm diffusion coefﬁcients for various concentrations ofnitrates were determined(Table5).It clearly appeared thatnitrates removal on Amberlite IRA400resin was controlledbyﬁlm diffusion since coefﬁcient values were in the range10−6to10−8cm2/s.3.3.Thermodynamic studiesThe amounts of sorption of nitrates ions by Amberlite IRA400were measured in the range temperature298–343K.Ther-modynamic parameters were determined using the followingrelation[15,33–36]:ln k d= S◦R−H◦RT(18)where k d was the distribution coefﬁcient, H, S,and T the enthalpy,entropy and temperature(in Kelvin),respectively,and R was the gas constant.The values of enthalpy( H)and entropy ( S)were obtained from the slope and intercept of ln(k d)versus 1/T plot.Fig.8shows two linear parts in the temperature range explored.Aﬁrst decreasing part for a temperature range from 318to343K,and a second and increasing linear part for a tem-perature range from298to318K.Gibbs free energy( G)was calculated using the well-known equation:G= H−T S(19) The slope was positive in the temperature range298–318K and negative in a second step,from318to343K(Fig.8).The thermodynamic parameters are collected in Table6.Table5Diffusion coefﬁcients for the removal of nitrates by Amberlite IRA400resinC0(mg/l)Pore diffusion coefﬁcient,Eq.(16)(×10−7cm2/s)Film diffusion coefﬁcient, Eq.(17)(×10−8cm2/s)10.670.73 20.780.92 3.50.84 1.06 50.92 1.15 10 1.01 1.29 14 1.26 1.58 18 1.692.06Fig.8.Estimation of thermodynamic parameters(Eq.(18))for the adsorption of nitrates onto Amberlite IRA400.Table6Thermodynamic parameters for the adsorption of nitrates on Amberlite IRA400 298K308K318K318K333K343K G(kJ/mol)−5.631−4.944−4.256−2.66−3.692−4.38 H◦(kJ/mol)−26.122+19.205S◦(J/mol K)−68.76+68.76For theﬁrst range from298to318K,the negative value of enthalpy showed that the adsorption of nitrates was exother-mic.The negative values of adsorption entropy indicated that the adsorption process was reversible and demonstrated the sponta-neous nature of adsorption(Table6).In the range318–343K,Gibbs free energy( G)decreased for increasing temperatures,indicating that the reaction was spontaneous and favoured by higher temperatures.The positive value of enthalpy indicated that the adsorption was endothermic. The positive value of adsorption entropy showed the irreversibil-ity of the adsorption process and favoured complexation and stability of sorption.The resultant effect of complex bonding and steric hindrance of the sorbed species probably increased the enthalpy and the entropy of the system.4.ConclusionsThese results show that Amberlite IRA400is an effective adsorbent for the removal of nitrates from aqueous solution.TheM.Chabani et al./Chemical Engineering Journal125(2006)111–117117equilibrium between nitrates and resin was achieved in approx-imately60min,leading to96%removal of nitrates.The corre-lation coefﬁcient showed that Freundlich model gave a betterﬁt of experimental data than Langmuir and Dubinin-Radushkevich models.Adsorption kinetics was found to followﬁrst order reversible model expression.Theﬁlm diffusion was the main rate-limiting step.Temperature variations were used to evaluate enthalpy H, entropy S and Gibbs free energy G values.The negative value of G showed the spontaneous nature of adsorption.In the tem-perature range298–318K, H and S were negative,and the reaction was exothermic and reversible.From318to343K, H and S were positive,and the reaction was endothermic and irre-versible.In addition,positive S values favoured complexation and stability of sorption.References[1]N.¨Ozt¨u rk,T.Ennil Bektas,Nitrate removal from aqueous solution byadsorption onto various materials,J.Hazard.Mater.B112(2004)155–162.[2]H.Bouwer,Agricultural contamination:problems and solutions,WaterEnviron.Technol.(1989)292–297.[3]K.Mizuta,T.Matsumoto,Y.Hatate,K.Nishihara,T.Nakanishi,Removalof nitrate-nitrogen from drinking water using bamboo powder charcoal, Bioresour.Technol.95(2004)255–257.[4]N.I.Chubar,V.F.Samanidou,V.S.Kouts,G.G.Gallios,V.A.Kanibolotsky,V.V.Strelko,I.Z.Zhuravlev,Adsorption ofﬂuoride,chloride,bromide,and bromate ions on a novel ion exchanger,J.Colloid Interface Sci.291(2005) 67–74.[5]S.J.Allen,G.Mckay,J.F.Porter,Adsorption isotherm models for basicdye adsorption by peat in single and binary component systems,J.Colloid Interface Sci.280(2004)322–333.[6]A.¨Ozcan,A.S.¨Ozcan,S.Tunali,T.Akar,I.Kiran,Determination of theequilibrium,kinetic and thermodynamic parameters of adsorption of cop-per(II)ions onto seeds of Capsicum annuum,J.Hazard.Mater.B124(2005) 200–208.[7]J.Rodier,Water Analysis,seventh ed.,Dunod,Paris,1996(in French).[8]S.Sohn,D.Kim,Modelisation of Langmuir isotherm in solution systems-deﬁnition and utilization of concentration dependent factor,Chemosphere 58(2005)115–123.[9]H.M.F.Freundlich,¨Uber die adsorption in l¨o sungen,Zeitschrift f¨u rPhysikalische Chemie(Leipzig)57A(1906)385–470.[10]ngmuir,The constitution and fundamental properties of solids andliquids,J.Am.Chem.Soc.38(11)(1916)2221–2295.[11]M.M.Dubinin,E.D.Zaverina,L.V.Radushkevich,Sorbtsiyai strukturaaktivnykh uglei.I.Issledovanie adsorbtsii organicheskikh parov,Zhurnal Fizicheskoi Khimii21(11)(1947)1351–1363.[12]M.S.Bilgili,Adsorption of4-chlorophenol from aqueous solutions byXAD-4resin:isotherm,kinetic,and thermodynamic analysis,J.Hazard.Mater.137(2006)157–164.[13]L.V.Radushkevich,Potential theory of sorption and structure of carbons,Zhurnal Fizicheskoi Khimii23(1949)1410–1420.[14]M.M.Dubinin,Modern state of the theory of volumeﬁlling of microporeadsorbents during adsorption of gases and steams on carbon adsorbents, Zhurnal Fizicheskoi Khimii39(1965)1305–1317.[15]R.Donat,A.Akdogan,E.Erdem,H.Cetisli,Themodynamics of Pb2+andNi2+adsorption onto natural bentonite from aqueous solutions,J.Colloid Interface Sci.286(2005)43–52.[16]F.Helffrich,Ion Exchange,McGraw Hill,New York,1962.[17]M.S.Onyango,Y.Kojima,O.Aoyi,E.C.Bernardo,H.Matsuda,Adsorp-tion equilibrium modelling and solution chemistry dependence ofﬂuoride removal from water by trivalent-cation exchange zeolite F-9,J.Colloid Interface Sci.279(2004)341–350.[18]Y.S.Ho,Review of second-order models for adsorption systems,J.Hazard.Mater.136(2006)681–689.[19]W.J.Weber,J.C.Morris,Adsorption Processes for Water Treatment,But-terworth,London,1987.[20]Q.Feng,Q.Lin,F.Gong,S.Sugita,M.Shoya,Adsorption of lead andmercury by rice husk ash,J.Colloid Interface Sci.278(2004)1–8. 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青蒿素的经济效应英语作文

青蒿素的经济效应英语作文Artemisinin: An Economic Boon for Traditional MedicineThe discovery and application of artemisinin, a compound derived from the traditional Chinese herb Artemisia annua, has not only revolutionized the treatment of malaria but also had significant economic implications worldwide. This essay will explore the various economic effects of artemisinin, from its impact on the pharmaceutical industry to its influence on global health and trade.Firstly, the introduction of artemisinin-based combination therapies (ACTs) has been a game-changer in the pharmaceutical market. These treatments have proven to be highly effective against the Plasmodium parasite, which is responsible for malaria. The demand for ACTs has grown exponentially, leading to an increase in the production and trade of Artemisia annua. This has not only benefited the pharmaceutical companies involved in the development and distribution of these drugs but also stimulated the cultivation of the herb, particularly in countries where it is a native plant.Secondly, the economic benefits extend to theagricultural sector in regions where Artemisia annua is cultivated. Farmers have found a new cash crop that can be sustainably grown with relatively low inputs. The cultivation of artemisinin has provided an additional source of incomefor smallholders, contributing to poverty alleviation and improved livelihoods. Moreover, the cultivation techniques required for Artemisia annua are not labor-intensive, makingit an accessible option for communities with limited resources.The economic impact of artemisinin also includes its influence on global health. Malaria is a disease that disproportionately affects the world's poorest populations, with Sub-Saharan Africa bearing the highest burden. The availability of effective, affordable treatments has led to a decrease in malaria-related morbidity and mortality. This has significant economic ramifications, as healthier populations are more productive, leading to increased economic activity and improved standards of living.Furthermore, the success of artemisinin has shed light on the value of traditional medicines and has spurred interestin the research and development of other natural remedies.This has opened up new avenues for scientific exploration and economic investment in the field of ethnopharmacology. The potential for discovering new drugs from traditional sourcesis vast and could lead to a new wave of economic growth inthe pharmaceutical sector.However, the economic benefits of artemisinin are not without challenges. The threat of drug resistance to artemisinin is a major concern, as it could undermine the economic gains made in controlling malaria. Additionally, the price volatility of artemisinin in the global market canaffect the livelihoods of farmers who rely on its cultivation.Ensuring the sustainability of the artemisinin supply chain is crucial for maintaining its economic benefits.In conclusion, artemisinin has had a profound economic impact since its discovery. It has created new opportunities in the pharmaceutical and agricultural sectors, improved global health outcomes, and highlighted the potential of traditional medicines. The continued success of artemisinin as a treatment for malaria and its role in the economy will depend on ongoing research, sustainable farming practices, and the collective efforts to combat drug resistance.。

Opitcal Waves in Layered Media》(层状介质中的光波

《Opitcal Waves in Layered Media》简介一、出版情况《层状介质中的光波》（Optical Waves in Layered Media）是1998年由美国John Wiley & Sons 公司出版的，本书为2005年再版，全书406页。

二、作者情况叶伯琦(Pochi Yeh)目前是美国加州大学圣塔芭芭拉分校（University of California at Santa Barbara）电机电脑系教授与交大讲座教授（合聘）。

他1967年至1971年于国立台湾大学攻读物理系学士学位，1973至1975于美国加州理工学院物理系攻读硕士学位，1973至1977年于美国加州理工学院攻读物理系博士。

毕业后至1990年在美国洛克威尔国际科学中心光资讯部门任执行经理并在1985年至1990年任美国洛克威尔国际科学中心首席科学家。

1987年至今任台湾国立交通大学光电工程研究所兼任教授。

1990年被聘为加州大学圣塔芭芭拉分校电机电脑系教授。

曾荣誉美国光学学会会士（Optical Society of America Fellow）、电子电机工程学会会士（(IEEE Fellow）、洛克威尔科学中心达芬奇杰出工程师奖（Leonardo da Vinci Award, Engineering of the Year 1985）、国际光学工程学会金氏奖（Rudolf Kingslake Medal and Prize）等。

除本书外主要著作有晶体中的光波（Optical Waves in Crystals, Wiley l984）；非线性光折射简介（Introduction to Photorefractive Nonlinear Optics，Wiley l993）；液晶显示光学（Optics Of Liquid Crystal Displays, Wiley l999）；光子学：现代通信中的光电子学（Photonics: Optical electronics for modern communications，Oxford University Press 2006）。

The kinetics of desilication of synthetic spent Bayer liquor and sodalite crystal growth

Colloids and SurfacesA:Physicochemical and Engineering Aspects147(1999)283–295The kinetics of desilication of synthetic spent Bayer liquor andsodalite crystal growthM.C.Barnes,J.Addai-Mensah*,A.R.GersonIan Wark Research Institute,Uni6ersity of South Australia,The Le6els,Adelaide5095,AustraliaReceived30October1997;accepted15May1998AbstractThe kinetics of desilication of synthetic,sodium aluminosilicate solution(spent Bayer liquor)and growth of sodalite crystals have been studied under isothermal,batch crystallization conditions close to those prevailing in Bayer process heat exchangers.The desilication rate of the liquor via the formation and growth of sodalite scale on steel substrates was found to be independent of agitation rate.With sodalite seeding,the desilication rate was observed to increase dramatically due to seed crystal growth with the suppression of scale formation.An activation energy of30kJ mol−1 and a second order dependence of the desilication rate on relative supersaturation of SiO2were obtained for sodalite crystal growth.©1999Elsevier Science B.V.All rights reserved.Keywords:Desilication kinetics;Sodalite crystals;Sodium aluminosilicate scale;Spent Bayer liquor1.IntroductionThe presence of dissolved SiO2in sodium alumi-nate solutions,used for gibbsite precipitation dur-ing the Bayer process,causes an unwanted sodium aluminosilicate scale formation in alumina reﬁner-ies[1].The SiO2impurities originate from kaolin-ite and quartz present in the bauxite ores.The ore is digested at elevated temperatures(]150°C) with recycled sodium hydroxide solution to extract alumina hydrates(gibbsite and boehmite).Subse-quent to the precipitation of gibbsite at ca70°C the resulting liquor,which typically contains 0.6g dm−3SiO2,is recycled via a series of heat exchangers and evaporators for further bauxite digestion.Reheating the liquor from70to240°C after gibbsite precipitation results in the formation of sodium aluminosilicate scale due to the in-creased SiO2supersaturation caused by the low alumina content of the solution[1].The formation of sodium aluminosilicate scale in the heat exchangers is a costly phenomenon which results in a pressure drop,ﬂow restriction and energy consumption as well as serious foul-ing.Several studies have been carried out to un-derstand the mechanism of the formation of sodium aluminosilicate scale and desilication ki-netics of spent liquor[2–14].Most of these studies[3–5,7–10,13]investigated sodium alu-minosilicate precipitation kinetics in the presence of bauxite,red mud or sodium aluminosili-*Corresponding author.Tel:+61883023683;fax:+61883023673;e-mail:jonas.addai-mensah@.au0927-7757/99/$-see front matter©1999Elsevier Science B.V.All rights reserved. PII S0927-7757(98)00570-6M.C.Barnes et al./Colloids and Surfaces A:Physicochem.Eng.Aspects147(1999)283–295 284cate and their mixtures of complex mineralogyor ambiguously deﬁned crystallographic charac-teristics.Recent studies[14,19,20]carried out onthe mechanism of sodium aluminosilicate scalinghave shown that in heat exchangers,two sodiumaluminosilicate phases,sodalite and cancrinite,are formed from unseeded liquors.Sodalite hasbeen reported to be the less thermodynamicallystable phase and always precipitatesﬁrst.It thentransforms to cancrinite,at a rate which in-creases with increasing temperature.The authorshave observed that the time for transformationvaries from\350h at relatively low tempera-tures(B160°C)to ca4h at high temperatures(\240°C).Sodalite is cubic with space group P43n andhas AB–BA–AB layer packing.Cancrinite ishexagonal belonging to the space group P63withAB–AB type layer packing[15–18].The stoi-chiometry of the two dimorphs may be generi-cally written as Na6[AlSiO4]62NaX·n H2O,where X can be1/2CO2−3,1/2SO2−4,Cl−,OH−and NO−3[15–18].The SiO2equilibrium solubility of sodalite and cancrinite in spent Bayer liquors(solutions from which gibbsite has been precipitated)are signiﬁcantly different with that of the latter being lower[19,26].Hence,the solubility of SiO2may change from that relative to sodalite to that relative to cancrinite,as sig-niﬁcant phase transformation from sodalite to cancrinite occurs during aging of the crystalline products in situ.This may lead to a signiﬁcant change in the supersaturation of SiO2,the mech-anism of precipitation and hence,the desilication kinetics.Recent studies[14,21,27,28]have shown that the SiO2supersaturation which prevails in spent liquors is insufﬁcient to cause nucleation in the bulk solution.The desilication reaction which leads to sodalite scale formation was reported to be substrate mediated[14].It has been reported that seeding with sodalite or cancrinite greatly accelerates the desilication reaction rate[20]. However to date,the complete studies of spent liquor desilication kinetics for the sodalite or cancrinite seeded precipitation system have not yet been carried out.Only one desilication kinet-ics study which clearly speciﬁed sodalite as the seed crystals used has so far been reported in the literature[9].In other desilication kinetics studies[3–5,9–11,13]in which synthetic sodium aluminosilicate seeds were used,the crystallo-graphic phases and their equilibrium solubilities involved were not fully determined.When baux-ite,red mud or plant scale deposit was used as the seeding material in other studies[4,5,8,11], the mineralogical composition of the products and the effect of the impurities on the desilica-tion reaction rate were not reported.As a large proportion of reactive SiO2in bauxite is in the form of kaolin,it may react with the NaOH in the solution to change liquor composition and/ or act as a seed to promote desilication and additional reactions to seed growth[2,4,9,10]. Seeding with bauxite may also increase the solu-tion alumina concentration and thus change the liquor composition and driving force[1].Fur-thermore in some of the investigations,the sur-face areas of the seed and products were not taken into account during the analysis and cor-relation of the kinetic data[3,8,13].The above variations in the experimental methodologies used by the various investigators have resulted in a lot of uncertainties to be associated with the reported desilication mechanisms and kinetic parameters.To date it has not been clearly es-tablished whether the reported kinetics of spent liquor desilication were predominantly due to a nucleation mechanism and/or growth mechanism of a known sodium aluminosilicate phase.Con-sequently there has been a great deal of varia-tion in the kinetic parameters reported in the literature for the desilication of spent Bayer liquor.Activation energies in the range of38–92kJ mol−1and order of desilication reactions between1and3have been reported[3–5,8–11,13].The main aim of the present work was to determine the kinetics of desilication of self-nu-cleating and sodalite-seeded,synthetic spent Bayer liquors under conditions of which sodalite precipitation or crystal growth occurred.This was achieved by investigating the effect of SiO2 supersaturation,temperature,agitation rate and sodalite seeding on the rate of SiO2desupersatu-ration under isothermal,batch crystallization of sodalite crystals.M.C.Barnes et al./Colloids and Surfaces A:Physicochem.Eng.Aspects147(1999)283–2952852.MethodologyThe following chemicals,experimental proce-dures and analytical techniques were used.Syn-thetic spent Bayer liquors were prepared from: 179.9g dm−3gibbsite(C-31Hydrate,Alcoa Ar-kansas,U.S.A.)and216.7g dm−3sodium hy-droxide(Ajax Chemicals,Australia,97.5%pure, 2.5%Na2CO3).51.7g dm−3anhydrous sodium carbonate(BDH,Merck,Kilsyth,Australia, Analar,99.9%)and Milli-Q water(surface ten-sion of72.8mN m−1at20°C and a speciﬁc conductivity B0.5m S).To prepare a sodium aluminate solution,the required weight of sodium hydroxide was added to25%of theﬁnal volume of water in a stainless steel beaker.Af-ter complete dissolution,a known weight of alu-minium hydroxide was added.The mixture was then heated to105°C.After complete dissolu-tion,a known weight of sodium carbonate was dissolved in0.25dm−3of water and added to the sodium aluminate solution.Water was added to make up1litre of liquor.In order to bring the solution to the required experimental concentrations of154.8g dm−3 NaOH,128.5g dm−3Al(OH)3and40g dm−3 Na2CO3,0.25dm3of the liquor was placed in a 0.6dm3stainless steel autoclave operating at a 400rpm agitation rate at a constant tempera-ture.With unseeded experiments,0.10dm3of a solution containing0.741g of sodium metasili-cate(Ajax Chemicals,27.8–29.2%SiO2,28.1% Na2O,42–43%H2O by weight)was added to give aﬁnal volume of0.35dm3.With seeded experiments both a0.05dm3solution containing 0.741g of sodium metasilicate and0.05dm3of water containing0.645g of sodalite seed were added to the liquor sequentially once it had reached the required experimental temperature. The addition of the sodium metasilicate solution and seed slurry was carried out via a vertical, 0.1dm−3,high pressure steel tube whose bot-tom end is attached to the autoclave via a one-way valve.Discharge of the tube contents into the autoclave is achieved by metering com-pressed N2gas at a pressure exceeding the inter-nal pressure of the autoclave through the top end of the tube.As soon as the temperature required was achieved(typically within2min), the experimental time was set as zero.Each experiment was replicated at least three times.Samples were taken periodically during desilication.The solutions SiO2concentration was analysed by inductively coupled plasma (ICP,Spectro Analytical Instruments,Spectro SIM-SEQ ICP-OES).The error in SiO2analysis was determined experimentally to be B5%by both multiple ICP analysis of the same ICP so-lution and analysis of multiple preparations of ICP solutions prepared from the same replicate liquor sample.The errors given in the present work have been calculated on the basis of95% conﬁdence interval.In the seeded experiments,pure sodalite crys-tals were used as a seed.The seed was synthe-sized by adding75g of kaolin to a300g dm−3 sodium hydroxide solution and heating the mix-ture in an autoclave at160°C for12h.The re-sulting product was identiﬁed as sodalite with a unit cell parameter of8.85A˚by powder X-ray diffraction(XRD)analysis[17].The analysis also conﬁrmed that the sodalite seed crystals,as synthesized above,were not contaminated by aluminium trihydroxide(e.g.gibbsite).The crys-tals were washed in milli-Q water until they were neutral to litmus and the coarser fraction (1–40m m diameter)were allowed to settle for decantation of the unwantedﬁne crystals(B 1m m).The seed crystals were in the size range of1–40m m and had a BET(Brunauer,Emmett and Teller,[29])surface area of16.3m2g−1.A316stainless steel,high-pressure,Parr auto-claveﬁtted with an external heater and an inter-nal cooling system was used as the batch crystallizer.The vessel wasﬁtted with a central four blade,45°-pitch,two-tier impeller which provided constant agitation to within92rpm. Two,316stainless steel strips of dimensions 10mm×6mm were attached to the shaft of the impeller to provide scaling substrates for scan-ning electron microscopy(SEM)and X-ray powder diffraction analysis.The control of the heating rate,the agitation and the temperature of the autoclave was achieved through an auto-matic proportional,integral and derivative(PID) control system.M.C.Barnes et al./Colloids and Surfaces A:Physicochem.Eng.Aspects147(1999)283–295 286To prevent the solution from undergoing nu-cleate orﬁlm boiling,the autoclave was pre-pressurized,by using N2gas,to a pressure 100kPa higher than the estimated saturated va-pour pressure of the solution determined accord-ing to the experimental temperature and solution concentration.This also ensured that no signiﬁ-cant differences existed between the temperatures of the vessel surface,the bulk solution and satu-ration temperatures of the solution or suspen-sion to cause signiﬁcant solution water loss by vaporization.To ascertain whether or not sodium alumi-nosilicate scale formation occurred by nucleation in the bulk solution followed by adsorption of nuclei at the substrate surface or by a direct nucleation at the surface of the substrate,solu-tion samples were periodically removed and sub-jected to light scattering analysis(Brice Phoenix, Universal Light Scattering Photometer,Virtis Co.Gardiner,NY,USA).Light scattering analyses for sodalite seeded suspensions were carried out onﬁltrates obtained byﬁltering the sampled solution through a0.20m m membrane, to determine whether there were colloidal parti-cles present as a result of secondary nucleation. Dissymmetry ratios(DR),deﬁned as the ratio of intensity(I)of monochromatic light(u= 540nm)scattered at60°to that scattered at 120°(i.e.DR=I60°/I120°),were measured.DR= 1if there are no signiﬁcant number of particles in suspension of diameter\30nm,otherwise DR\1.All crystal samples were analysed using a par-ticle sizer(Malvern Mastersizer,Malvern,Eng-land),N2BET analysis(Coulter Omnisorp100, Hialeah,FL,USA),SEM(15kV on carbon coated samples by using a high resolutionﬁeld emission Cam Scan CS44FF,Cambridge,Eng-land)and XRD(Phillips PW1130/90).These lat-ter two techniques were used for crystal imaging and crystalline phase analysis,respectively.Parti-cle size analysis of product crystals were carried out on wet slurry samples subsequent toﬁltra-tion and washing.XRD patterns were collected on powdered samples in u/2u scanning mode us-ing Cu K a radiation(u=1.5418A˚).The scan speed was1°min−1between10°and70°2u.3.Results3.1.Isothermal,batch desilication kinetics3.1.1.The effect of supersaturationThe kinetic behaviour of unseeded spent liquors was investigated over4hours at three initial SiO2 supersaturation levels with solutions initially con-taining0.4,0.6and0.8g dm−3SiO2(with all other variables kept the same),in order to gain further understanding of the desilication mecha-nism and to establish the basis for comparison with seeded solutions.For analysis of the data, the driving force for desilication/sodalite precipi-tation has been expressed as a function of relative supersaturation of SiO2deﬁned as:|=C−C eqC eqwhere C and C eq are the respective solution SiO2 concentration at any time and at equilibrium.As sodalite has been observed to precipitateﬁrst,that is,prior to cancrinite formation,in present and previous studies[1,2,7,14,27],the supersaturation of the unseeded solutions has been deﬁned in terms of the sodalite equilibrium SiO2concentra-tions[26].Fig.1depicts typical SiO2desupersaturation curves of unseeded desilication process obtained for the three solutions at160°C.A very smallFig.1.The variation of relative supersaturation of SiO2with time during unseeded,batch desilication of spent sodium aluminate liquors at160°C:",0.4g dm−3; ,0.6g dm−3; and ,0.8g dm−3initial SiO2concentrations.M.C.Barnes et al./Colloids and Surfaces A:Physicochem.Eng.Aspects147(1999)283–295287 decrease in solution SiO2concentration occurredover4h at0.4and0.6g dm−3initial SiO2con-centrations.However,at0.8g dm−3SiO2concen-tration,desilication occurred rapidly after1h andcaused the relative SiO2supersaturation in theproduct solution to be lower than that obtainedfor the0.6g dm−3SiO2after4h.Similar obser-vations of increasing rate of desilication with in-creasing SiO2concentration were made at othertemperatures(90–220°C).The results suggest thatunder batch conditions,negligible desilication oc-curred over a4h period from supersaturated so-lutions which contained SiO2at concentrations inthe range of those experienced in plant spent liquors(0.3–0.6g dm−3SiO2).Thisﬁnding agrees with other literature reports for similar solutions [14,20].However,it must be noted that plant spent liquors have lower SiO2solubilities than synthetic spent liquors and may thus be slightly more supersaturated in general.All the solutions,including those from the ex-periments which contained0.8g dm−3SiO2ini-tially,sampled over the4h period were found to be optically clear with no crystal content upon ﬁltration through a0.20m m membrane.Light scattering analysis conﬁrmed that theﬁltrate did not contain any signiﬁcant number of colloidal size particles(of diameter\30nm).However, when a detectable decrease in SiO2concentration occurred,a layer of scale was always formed on the autoclave steel wall,regardless of the tempera-ture used.At temperatures up to220°C,XRD analysis identiﬁed the scale to be sodalite.3.1.2.The effect of temperatureFig.2shows the variation of relative supersatu-ration of SiO2as a function of time for solutions initially containing0.6g dm−3SiO2at the tem-perature range of90–240°C.The results show that between90and160°C,there was no signiﬁ-cant decrease in SiO2concentration over4h.At higher temperatures(\160°C),a sharp increase in the desilication rate was observed,although the initial relative supersaturation were only ca50–75%of those in the90–160°C temperature range. This observation suggests that at temperatures \160°C,increasing the temperature has a more profound effect on the desilication reaction than Fig.2.The relative supersaturation of SiO2as a function of time during unseeded,batch desilication of spent sodium aluminate liquors at90–240°C:",90°C; ,120°C; , 140°C;×,160°C; ,180°C; ,220°C;+,240°C. increasing SiO2relative supersaturation.At220°C the desilication reaction approached sodalite-seeded SiO2equilibrium solubility within4h.De-silication reactions using sodalite seeding showed that the SiO2concentration at180and220°C were the same as that for unseeded experiments at the same temperatures after4h.At240°C,the sodalite seeded SiO2solubility was exceeded after 3h,as the desilication curve crossed the zero relative supersaturation line established with so-dalite equilibrium solubility(Fig.2).XRD analy-sis of the scale product at240°C indicated that an almost complete transformation from the sodalite to cancrinite phase had occurred.Thus the forma-tion of cancrinite which has a lower equilibrium SiO2solubility[20,26],resulted in theﬁnal SiO2 concentration lower than was expected for a so-dalite contain system.This sodalite to cancrinite phase transformation is known to be sodalite dissolution-mediated[27].Hence in the determina-tion of the true solubility at240°C without signiﬁ-cant cancrinite contamination,a very high seed charge ofﬁne sodalite crystals for a predomi-nantly sodalite-solution interfacial area as well as strong agitation may be used to approach equi-librium over a short time(B3h).This approach was used to measure the equilibrium solubility of sodalite in spent liquors at temperatures up to 240°C and is reported elsewhere[26].M.C.Barnes et al./Colloids and Surfaces A:Physicochem.Eng.Aspects147(1999)283–295 288SEM images and XRD analysis of the stainless steel substrate surface obtained from the unseeded desilication experiments after4h,indicated that when signiﬁcant desilication occurred at higher temperatures(\160°C,Fig.2),there was a con-comitant formation of sodalite scale(Fig.3).The extent of scale coverage and size of the crystals increased with increasing temperature as shown in Fig.3.The primary particles of the scale were observed to be pseudo-hexagonal,prismatic crys-tals formed by twinning at an angle about the [001]axis in a characteristic manner as to produce a‘‘cauliﬂower-like’’stacking.The observed mor-phology of the scale particles are notably differentFig.3.SEM photomicrographs of316stainless steel substrates used in isothermal batch desilication of unseeded,spent sodium aluminate liquors,before experiment(A)and at:(B)90–160°C;(C and D)180°C;and(E and F)220°C.Images C–F show sodalite crystals formed on the surface as scale.M.C.Barnes et al./Colloids and Surfaces A:Physicochem.Eng.Aspects147(1999)283–295289Fig.4.The variation of relative supersaturation of SiO2with time at different rates of agitation during batch desilication of unseeded spent sodium aluminate liquors at160°C;", 100rpm; ,400rpm;and ,700rpm agitation rates.out under similar solution composition and tem-perature conditions[21].It was reported that un-der continuous,laminar plugﬂow precipitation of sodalite scale on stainless steel substrates,the extent of scale formation was independent of the solutionﬂow velocity for Reynolds numbers in the range of100–400.The results indicate that there is no signiﬁcant limitation of volume diffu-sion imposed on the solution scale forming species during transport to the reaction sites for precipitation.3.1.4.The effect of seeding with sodaliteA seed charge of0.645g to give30m2of sur-face area per1dm3of spent liquor was used.The effect of seeding on the extent of spent liquor desilication over4h was investigated at90,120, 140,160,180and220°C.Rapid desilication of the spent liquor occurred,the extent increasing with increasing temperature(Fig.5Table1).For exam-ple,at the higher temperatures(180and220°C), the solution SiO2concentration decreased to within0.1g dm−3of the equilibrium solubilities after4h.In Table1,the solution SiO2concentra-tions observed at140and180°C,for both seeded and unseeded spent liquors are given for compari-sons.The data clearly demonstrate that both seeding and temperature had a marked effect on the rate of SiO2desupersaturation of the spent liquor.from that of the scale-forming,globular or poorly faceted sodalite crystals precipitated at similar steel surfaces from spent liquors of lower Al(OH)3/NaOH molar ratio at160°C[14,20].The morphology is also different from the poorly faceted/globular sodalite seed crystals precipitated from the bulk solution at160°C(Fig.8).The exact crystallographic cause of the variation in the sodalite crystal morphology and their orientation on the steel surface is as yet unknown.3.1.3.The effect of agitationDetermining whether the desilication reaction and its concomitant scaling process are volume diffusion controlled,chemical reaction controlled or a combination of both is crucial to the under-standing of the mechanism of scale formation. This was investigated by varying the rate of agita-tion to give turbulentﬂow at constant tempera-ture and constant initial SiO2supersaturation. The SiO2desupersaturation curves obtained under turbulentﬂow at agitation rates of100,400and 700rpm(Reynolds numbers:7000–35000)at 160°C were found to be substantially similar, within the limits of uncertainty of SiO2concentra-tion determination(Fig.4).The lack of inﬂuence of the agitation rate on the kinetics of desilication of the unseeded spent liquors at160°C agrees with theﬁndings of a recent desilication study carried Fig.5.SiO2relative supersaturation of sodalite-seeded(30m2 crystal dm−3),spent sodium aluminate liquors as a function of time at90–220°C:",90°C; ,120°C; ,140°C;×, 160°C;*,180°C;and ,220°C.M.C.Barnes et al./Colloids and Surfaces A:Physicochem.Eng.Aspects147(1999)283–295290Table1Comparisons of solution SiO2concentrations obtained at various times during unseeded and sodalite-seeded,isothermal,batch desilication of spent sodium aluminate liquors140°C Seeded(g dm−3)180°C Unseeded(g dm−3)Time(min)140°C Unseeded(g dm−3)180°C Seeded(g dm−3)0.590.600.600.600.560.440.540.43300.400.550.420.54600.420.441200.570.360.380.351800.560.320.330.380.320.57240The size distribution of sodalite seed crystals used in the present work ranged from1–40m m (Fig.7).Size analyses of representative product crystal samples were carried out.At agitation rates of up to450rpm,gross breakage of these sodalite crystals does not occur during desilication [5,19].Hence the detection of colloidal size parti-cles(B1m m)would suggest secondary nucleation occurred.DRs of 1.090.1were observed for solutions obtained byﬁltering the slurries periodi-cally removed from the crystallizer vessel through a0.2m m membrane.This indicated the absence of colloidal size crystals that might have been formed as a result of secondary nucleation in the bulk solution.X-ray powder diffraction analysis of the seed and the products(Fig.6)showed that they did not undergo any phase transformation to can-crinite during the4h experiments carried out at temperatures B220°C.At220°C,however,a small amount of cancrinite was formed as a result of phase transformation,indicated after4h by the appearance of the cancrinite101diffraction peak at19°2u.Thus the desilication of the liquor was concluded to proceed by sodalite precipitation. The results of the crystal number and size anal-ysis(Fig.7)showed that there was an overall increase in average size of the crystals but no increase in their number and with no signiﬁcant smaller size fraction present in the product up to 4h.Therefore,the desilication occurred through growth of the seed crystals.This observation was supported by SEM imaging as demonstrated by the photomicrographs of the product crystals from experiments at140°C(Fig.8).Although the crystals appear to be composed of agglomerates,it can be seen that the individual primary particles became larger during the course of precipitation with noﬁne particle generation[Fig.8(B,D and F)].Similar observations of crystal growth only (of seeds)were made from the crystal size analysis at other plementary particle sizing,light scattering,SEM analysis of seed and products all lead to the conclusion that the addi-tion of sodalite seeds did not promote secondary nucleation but only mass deposition or growth on parent crystals.The seed and product crystals’surface area analysis by BET showed that al-though the speciﬁc surface area of the product crystals decreased with time,their total surface area remained substantially the same.The individ-ual,total surface areas were used in the desilica-tion kinetics analysis described below.SEM imaging of stainless steel substrates used in the seeded experiments showed that there were Fig.6.X-ray powder diffraction patterns of sodalite seed and product crystals obtained from the seeded desilication of spent sodium aluminate liquors at140–220°C over4h.M.C.Barnes et al./Colloids and Surfaces A:Physicochem.Eng.Aspects147(1999)283–295291Fig.7.Typical cumulative number-size distribution of sodalite crystals obtained during seeded desilication of spent sodium aluminate liquor at140°C.crystal growth,respectively.In the absence of signiﬁcant nucleation of any kind(i.e.secondary or heterogeneous nucleation),Eq.(1)simply re-duces to the form below for pure crystal growth.−d|d t=Ak g|g(2) With no seeding,the rate of desilication was extremely slow at temperatures below180°C.This did not allow accurate determination of the mech-anisms(i.e.nucleation and/or growth)and kinet-ics of the unseeded desilication reaction.With seeding,the rate of desilication was found to be sufﬁciently fast at all temperatures to enable the measurement of reliable kinetic data.The results shown in the preceding section demonstrated that the desilication reaction proceeds by sodalite crys-tal growth.As a result,the kinetic data and parameters presented here have been evaluated for the sodalite crystal growth mechanism.By plotting log((1/A)(−d|/d t))against log(|),g is obtained as the slope and log(k g)as the y-inter-cept from linear regression analysis.A typical plot is shown in Fig.9for seeded desilications carried out at140,180and220°C which indicates that a very goodﬁt of the kinetics data to Eq.(2)can be obtained.The rate constant k g and the reaction order g were estimated at each separate temperature.The analysis gave a reaction order of2.039 0.06for the temperatures and relative supersatu-ration used in this investigation.Consequently the overall reaction order for sodalite crystal growth was approximated to 2.The value of2is in agreement with some of the values found in the literature[8–10,13,28],although the values of1 and3have also been reported by some investiga-tors[3,4,11].The effect of temperature on the desilication or growth kinetics of sodalite crystals was further analysed by expressing the rate con-stants k g as a function of temperature using the Arrhenius relationship of the form:k g=k o exp(−E a/RT)(3) where k o is the pre-exponential factor (min−1m−2),E a is the activation energy for so-dalite crystal growth(kJ mol−1),T is the temper-ature(K),R is the gas constant (8.314Jmol−1K−1).no noticeable sodalite crystals(secondary nuclei) formed as scale on the steel surface.However,a few seed crystals were occasionally found to ad-here to the surfaces in a manner similar to the surface shown in Fig.3(B).The mechanism of adherence,either by van der Waals and electrical double layer or other chemical forces,has not yet been determined.3.2.The kinetics of desilication of seeded solutions and growth of sodaliteFor isothermal batch desilication of the SiO2-supersaturated sodium aluminate liquor,the su-persaturation may be dissipated by nucleation and crystal growth mechanisms.The kinetics of the two mechanisms may be quantiﬁed by a power law relationship of the form:−d|d t=k n|n+Ak g|g(1)where|is the relative supersaturation,(C−C eq)/ C eq;k n is the rate constant for nucleation (min−1);n is the order of the nucleation reaction; k g is the growth rate constant(min−1m−2);g is the order of crystal growth reaction;and A is the total surface area of crystals(m2).Theﬁrst and second terms on the right-hand side of Eq.(1)correspond to nucleation and。

科学艺术英语作文模板

科学艺术英语作文模板英文回答：Science and Artistic Expression。

Science and art, though often perceived as distinct domains, share an intimate relationship that has shaped human understanding and innovation for centuries. From the Renaissance masters who blended scientific principles with artistic representation to the modern-day collaborations between scientists and artists, the fusion of these disciplines has yielded groundbreaking discoveries and captivating masterpieces.Scientific Principles in Art。

Artists have long used scientific knowledge to enhance their craft. The study of human anatomy, for instance, aided the Renaissance masters in creating realistic depictions of the human form. Leonardo da Vinci, a polymathknown for his scientific prowess, famously dissected cadavers to understand muscle structure and proportions, which informed his iconic paintings such as the "Mona Lisa" and "The Last Supper."Moreover, artists have employed scientific techniques to create innovative effects. The Dutch Golden Age painter Johannes Vermeer utilized camera obscura to achieve precise perspective and light rendering in his interior scenes. In contemporary art, artists like Olafur Eliasson and Yayoi Kusama draw upon principles of physics, mathematics, and biology to create immersive and thought-provoking installations.Art as a Tool for Scientific Exploration。

Removal_of_iron_from_acidic_leach_liquor_of_lateritic_nickel_ore_by_goethite_precipitate

Removal of iron from acidic leach liquor of lateritic nickel ore by goethite precipitate ☆Yongfeng Chang ⁎,Xiujing Zhai,Binchuan Li,Yan FuNortheastern university of China,School of materials and metallurgy,Shenyang,110004,PR Chinaa b s t r a c ta r t i c l e i n f o Article history:Received 22July 2009Received in revised form 22November 2009Accepted 22November 2009Available online 27November 2009Keywords:LateriteMetallurgy of nickel Goethite precipitate Removing of ironThe separation of high levels of iron from acid leaching liquor is a dif ﬁcult task,especially in the atmosphere acid leaching process for laterite ore.In this paper the removal of iron by goethite precipitation from the leach liquor of reduced laterites is reported.The goethite precipitation process uses air as oxidation agent,that is,V.M.method,and does not need the pre-reduction of ferric iron since the soluble iron in leach liquor is mainly ferrous ion.The effects of pH value on the rate of iron removal and the loss of nickel to the residue were investigated.It was found the pH value had remarkable in ﬂuence on the nickel loss during goethite precipitation.By carefully controlling the pH value to less than 2.5the loss of nickel could be restricted to below 5%.Attempts of recover the nickel lost to the goethite residue through weak acid washing were unsuccessful,suggesting the retention of nickel by the goethite.©2009Elsevier B.V.All rights reserved.1.IntroductionNickel-bearing ores mainly exist in oxide form,laterites,which account for 72%of the world land-based nickel resource.The lateritic ores can be simply divided in two types,limonite and silicate-rich.The former is rich in ferric oxide and has low contents of magnesium,aluminum,and other acid consuming elements,thus is usually processed by hydrometallurgical methods,especially acid leaching methods,including high pressure acid leaching (HPAL)(Whittington and Muir,2000)and atmosphere acid leaching (AL)processes (McDonald and Whittington,2008).In nickeliferrous limonite,(Fe,Ni)O(OH)·nH 2O,nickel is mainly found in solid solution with the iron oxide.During acid leaching the nickel bound within the goethite can be released from the solid matrix by acid attack.The extent of nickel extraction is highly dependent upon the degree of decomposition of the host matrix,and not surprisingly,the operating cost is mainly dependent upon the net acid consumption per ton ore.HAPL is a proven economic method for the selective extraction of nickel from limonitic laterite.At high leaching temperature,normally 240–260°C,the leached iron and aluminum hydrolyze and precipitate as hematite and a range of mixed alunite/jarosite phase.This hydrolysis re-generates acid and reduces the overall acid consumption.But the expense of autoclaves and scaling problems are the key issues en-countered in HPAL practice (Queneau et al.,1984;Whittington,2000).Atmospheric leaching (AL)at lower temperature and in open vessels avoids the need for expensive HPAL autoclaves.However,twokey issues are the kinetics of nickel extraction and the ease with which the liquor can be processed subsequently.Speci ﬁcally,the leach liquor from AL is likely to contain signi ﬁcant concentrations of soluble iron and methods must be found to selectively reject these metals from solution (McDonald and Whittington,2008).These two issues and the higher acid consumption have hindered the application of AL technology to date.Various methods have been tested to improve the nickel extraction kinetics by AL and the selectivity over iron to decrease the acid consumption,which include using sulphur dioxide as reducing agent (Senanayake and Das,2004),adding chloride salt to assist leaching (Munroe,1997)and roasting pre-treatment to increase the porosity and surface area of the ores (Olanipekun,2000;Li et al.,2009;Landers and Gilkes,2007;Landers et al.,2009).Although the dissolution rate of nickel could be enhanced to some extent,the extraction degree of nickel is still near congruent to the iron,leading to a non-selective leaching to the nickel.All studies carried out to gain the high nickel extraction degree have common results:high acid consumption,high dissolved iron content in pregnant leach solution and high residual acid concentration.Due to the nature of the leaching process,most of the metals within the ore are dissolved during leaching,resulting in high acid consumption.Iron is the key element as it directly affects the acid consumption and also it creates major problems in selective recovery of metals from pregnant leach solution.To effective use the residual acid in the pregnant solution,two steps AL process were proposed.For the leaching solution of limonite ore,reactive nickel laterite ores with high-magnesia could be utilized as neutralizer to compensate the acid cost,and the iron in the liquor could be precipitated as jarosite.In HPAL case it has been well known as the BHP-Billiton enhanced HPAL (EPAL)process,which has been operated at Ravensthorpe for treating saprolite ore in parallel with HPAL for limonite (EPAL process).The AL of saprolite bene ﬁts from availability of “free ”acid from HPAL discharge.But the supply of lateriteHydrometallurgy 101(2010)84–87☆Presented at ICHM2009,Zhangjiajie,China.⁎Corresponding author.Tel.:+862483687729;fax:+862423906316.E-mail address:changyf@ (Y.Chang).0304-386X/$–see front matter ©2009Elsevier B.V.All rights reserved.doi:10.1016/j.hydromet.2009.11.014Contents lists available at ScienceDirectHydrometallurgyj o u r n a l h o me p a g e :w w w.e l s ev i e r.c o m/l o c a t e /hyd ro m e tores with high-magnesia,the reactivity of ores under AL conditions and the environmental issues caused by the disposal of jarosite are factors to be considered.Moreover,the high initial Fe/Ni ratio in the pregnant AL solution could result in excessive nickel and cobalt losses during the iron removal.No AL or multi step AL process stand alone commercial operations as yet.An alternative method to resolve the problems of the AL process is reduction pre-treatment,which changes the chemical nature of the ore before leaching.If the iron-bearing oxide laterite ore is reduced to low valence iron oxide,the AL can proceed at higher reaction rate and with selectivity to the nickel than for non-pretreated ore (Chang et al.,2008a,b ).Apostolidis and Distin (1978)found that the extraction of nickel had partial selectivity over magnesium from laterites contain-ing serpentine by reduction roasting followed by sulphuric acid leaching.De Graff and De Graff (1980)revealed that the leaching of reduced laterite ore by ferric chloride solutions with a little HCl to maintain the pH below 2gave very good extraction of nickel at temperatures from 25°C to 75°C.Purwanto et al.(2003)indicated that the in ﬂuence of selective reduction could speed up the nickel extraction and obstructed the iron dissolution.Thus pre-reducing makes the laterite ores more amenable to leaching.Though the extraction of nickel from the reduced laterite ores by sulphuric acid leaching showed partial selectivity over iron,a large part of the iron constituent in the reduced ores seemed to be wustite,and the solubility of the iron constituent under ambient pressure remained on a high level.In order to separate the high levels of iron from the solution,precipitation is the most widely used method,including jarotsite,goethite and hematite technique,which mainly came from the zinc industry.Mitsutomi et al.(1987)carried out the high-pressure –high-temperature leaching procedures with the auto-clave on the pre-reduced laterite ore to precipitate the soluble iron as hematite.But the need of expensive autoclave for the hematite precipitation departs from the original purpose of the AL process.To precipitate the soluble iron at atmosphere pressure the goethite and jarosite precipitation maybe the available choices.Advantages for the goethite precipitation compared to jarosite include no need for added alkalis,low volume and relatively stable residue for storage,thus in this study the goethite precipitation is adapted to remove the iron from the pregnant leaching solution of the pre-reduced laterite ore.Removal of iron via goethite precipitation process can be effected by the Vieille Montgane (V.M.)technique,which was developed somewhat later in the sixties by Societe de la Vieille Montgane,and then came into commercial application in the zinc industry (Dutrizac,1980).In the Vieille Montagne technique the iron-bearing solution is reduced to the ferrous state and is then oxidized by air to precipitate the iron as goethite.Since the leaching solution of the pre-reduced limonite laterite ore contains iron ion mainly as ferrous state,it is convenient to adopt V.M.technique by omitting the reduction step.This is another merit to reject the soluble iron as goethite precipitation from leaching solution of the pre-reduced limonite laterite ore compared to jarosite.Although reduction pre-roasting followed by sulphuric acid leaching of the laterite ore and the reductive leaching have been examined previously,little attention has been paid to the purify of leaching solution containing high levels of ferrous ions.The aim of this present study is to investigate the iron removal by goethite precipita-tion from the acidic leaching liquor of the pre-reduced limonite laterite ore,Particular interest was devoted to the factors that affect the nickel loss during iron precipitation process.2.ExperimentalMother liquor containing nickel for iron removal investigation was prepared by acid leaching reduced limonite laterite ore.The reduction procedure using microwave heating,and the leaching of reduced calcine,have been previously examined (Chang et al.,2008c ).The chemical composition of the ore is showed in Table 1and the XRD patterns of the ore and reduced calcine are presented in Fig.1.Acid leaching was performed at room temperature,and the concentration of nickel and iron (in ferrous form)were 0.63g L −1and 14.0g L −1,respectively.The liquor used for the iron removalTable 1Chemical composition of laterite ore (mass,%).Fe Ni Co Mg Ca Al Mn SiO 248.821.030.1370.4850.5923.461.092.47Fig.1.XRD patterns of laterite ore and reducedcalcine.Fig.2.Sketch map of the apparatus for the precipitation of iron by the goethite method.Table 2Effect of pH on iron precipitation rate and characteristic of the precipitate.pH valueTime for iron precipitation/minIron concentration of the ﬁnal liquor/(g L −1)Color of the precipitateFiltrationtime of the precipitate/min Ferrous ion oxidation rate/(mg L −1min −1)2.0–2.55500.453Yellow About 1.525.52.5–3.02600.352Brown About 1.553.83.0–4.02450.367Brown About 1.557.14.0–6.01750.271Brown reddish About2.080.07.0–8.0600.430Black(magnetic)About 10.0233.385Y.Chang et al./Hydrometallurgy 101(2010)84–87tests therefore had a Fe/Ni ratio of 22.2.For other tests requiring a low Fe/Ni ratio,the concentration of iron was maintained as constant and the concentration of nickel was increased to produce the desired ratio.The apparatus used for goethite precipitation is shown in Fig.2.Air was used as oxidation agent with the ﬂow rate at 1500mL min −1and 0.25g L −1copper ion was added to catalyze the oxidation of ferrousions.For all experiments the temperature were controlled at constant,95°C.The reactions during goethite precipitating are given as follows:Ferrous ion oxidation:2Fe 2þþ0:5O 2þ2H þ¼2Fe3þþH 2Oð1ÞFerric ion hydrolysis:Fe 3þþ2H 2O ¼FeOOH þ3Hþð2ÞTotal reaction:2Fe2þþ0:5O 2þ3H 2O ¼2FeOOH þ4Hþð3ÞThe total reaction is an acid generating process,thus a neutralizing agent must be used to ensure the reaction proceeds to completion.The pH value not only affects the oxidation rate of the ferrous ion but also affects the nickel loss in the goethite residue.So it is the key parameter in the precipitation process.The control of pH was achieved by adjusting the addition rate of basic magnesium carbonate,which neutralizes the acid released from the iron hydrolysis.The neutralization agent was added at stoichiometric ratio.Different pH values were selected to examine the effect on the ferrous oxidation rate and the nickel loss to the goethite residue.Due to the coating of precipitate onto the glass electrode of digital pH meter,the pH was directly measured by precision pH test paper.Ferrous iron content in the solution was determined by the titration method using K 2Cr 2O 7.Nickel content in the calcine and goethite precipitate were measured by the ICP-AES method.An X-ray diffractom-eter was utilized to analyze phase composition of samples obtained at different pH value.The morphology of the samples was examined by SEM.3.Results and discussion3.1.Effect of pH value on the iron precipitationThe effect of pH value on iron precipitation rate and characteristics of the precipitates are presented in Table 2.The iron content in the ﬁnal liquor is less than 1.0g L −1for all the tests,which con ﬁrmsnearlyFig.3.XRD patterns of precipitates formed at different pHvalues.Fig.4.SEM images of the precipitate morphology at different pH values.86Y.Chang et al./Hydrometallurgy 101(2010)84–87complete iron removal.The last column of Table2indicates the average rate of ferrous ion oxidation,which was calculated from the initial iron concentration and the precipitation time given in the third column of Table2.It can be seen that the oxidation rate of the ferrous ion increases with pH,and the color andﬁltration rate of the precipitate vary with pH. Both the color andﬁltration rate of the precipitate at pH7.0–8.0indicate distinguishing features;the oxidation rate of ferrous ion is markedly fast and the precipitate is magnetic in nature.To provide insight into the effect of pH value on the precipitation, XRD patterns and SEM images of the precipitates gained at different pH value are shown in Figs.3and4,respectively.At pH values of6.0or less,all the precipitates consist of goethite.As the pH increases,the XRD pattern indicates peak widening,which implies that the goethite crystallite sizes is decreasing.This was also conﬁrmed by the SEM images,as shown in Fig.4(a)to(c).The precipitate formed at pH7.0–8.0was not goethite,but magnetite,as shown in Fig.3.The morphology of the magnetite,shown in Fig.4(d),is clearly different to needle-like goethite crystallites.3.2.Nickel losses during the iron precipitatingDuring the iron removal process the loss of nickel to the precipitate was an issue of concern.The effects of pH value and Fe/Ni ratio on nickel loss are shown in Table3.At the same pH value range,e.g. pH2.5to3.0,the Fe/Ni ratio had little effect on the nickel content in the residue.But the higher initial Fe/Ni ratio induced more nickel loss to the residue,which was caused by the increase of the residue amount.Given the same initial Fe/Ni ratio at22.2,the pH value also showed remarkable inﬂuence on the nickel loss to the residue.When the pH value greater than3.0a larger portion of nickel was lost.In order to recycle the lost nickel to the residue,the weak acid washing tests were conducted.The results are shown in Table4.It can be seen that the nickel content in the residue changed little after washing.The loss of nickel in the precipitate may take place by two mechanisms,adsorption or co-precipitation(Carvalho-E-Silva et al.,2003;Singh et al.,2002),in through physical bonding or chemical bonding.Although extensive work have been done,it is still difﬁcult to determine whether the nickel retained by the solids is included into the mineral lattices,adsorbed onto the minerals,or precipitated out of solution(Beukes et al.,2000).But it has already been proven that surface area is a determining factor for nickel adsorption on the goethite.One possible model(Carvalho-E-Silva et al., 2003)to illustrate the loss of nickel in goethite is that substitution of Ni for Fe is accompanied by a proton capture resulting in NiO2(OH)4octahedra. The Fe3+for Ni2+substitution in goethite maybe is accompanied by a mechanism to compensate the charge imbalance.4.ConclusionsThe precipitation of iron from the leaching liquor of reduced laterite ore was demonstrated,using air as oxidation agent,that is, using V.M.method.The iron concentration in theﬁnal liquor can be lowered and decreased to below1.0g L−1.The pH value has remarkable effect on the rate of ferrous ion oxidation and the loss of nickel to the residue.Increasing pH value enhances the oxidation rate of ferrous ion but results in greater nickel loss to the residue.At a pH value of2.5–3.0the oxidation rate of ferrous ion is about53.8mg L−1min−1,and the loss of nickel is4.1%.In the precipitation process some nickel appears to co-precipitate with iron.This nickel could not be recovered by weak acid washing of the precipitate.AcknowledgementsThe authors gratefully acknowledge theﬁnancial support of the National Natural Science Foundation of China(Project No.50774020). ReferencesApostolidis,C.I.,Distin,P.A.,1978.The kinetics of the sulphuric acid leaching of nickel and magnesium from reduction roasted serpentine.Hydrometallurgy3,181–196. Beukes,J.P.,Giesekke,E.W.,Elliott,W.,2000.Nickel retention by goethite and hematite.Minerals Engineering13,1573–1579.Carvalho-E-Silva,M.L.,Ramos,A.Y.,Tolentino,H.C.N.,Enzweiler,J.,Netto,S.M.,Alves,M.D.C.M.,2003.Incorporation of Ni into natural goethite:an investigation by X-rayabsorption spectroscopy.American Mineralogist88,876–882.Chang,Y.F.,Zhai,X.J.,Fu,Y.,Li,B.C.,Zhang,T.A.,2008a.Sulphuric acid leaching kinetics of pre-reduced laterite ore.Journal of Molecular Science24(4),241–245in Chinese.Chang,Y.F.,Zhai,X.J.,Fu,Y.,Zhang,T.A.,2008b.Effect of iron reduction degree on leaching results of pre-reduced laterite ores with thin acid.Journal of Northeastern University:Natural Science29(12),1738–1741in Chinese.Chang,Y.F.,Zhai,X.J.,Fu,Y.,Ma,L.Z.,Li,B.C.,Zhang,T.A.,2008c.Phase transformation in reductive roasting of laterite ore with microwave heating.Transactions of Nonferrous Metals Society of China18(4),969–973.De Graff,De Graff,J.E.,1980.The treatment of lateritic ores—a further study of the Caron process and other possible improvements:Part2.Leaching studies.Hydrometal-lurgy5,255–271.Dutrizac,J.E.,1980.The physical chemistry of iron precipitation in the zinc industry.Lead–Zinc–Tin′80.Proceeding of a World Symposium on Metallurgy and Envirn-mental s Vegas,Nevada,pp.532–564.Landers,M.,Gilkes,R.J.,2007.Dehydroxylation and dissolution of nickeliferous goethite in New Caledonian lateritic Ni ore.Applied Clay Science35,162–172.Landers,M.,Gilkes,R.J.,Wells,M.,2009.Dissolution kinetics of dehydroxylated nickeliferous goethite from limonitic lateritic nickel ore.Applied Clay Science42, 615–624.Li,J.H.,Li,X.H.,Hu,Q.Y.,Wang,Z.X.,Zhou,Y.Y.,Zheng,J.C.,Liu,W.R.,Li,L.J.,2009.Effect of pre-roasting on leaching of laterite.Hydrometallurgy99,84–88.McDonald,R.G.,Whittington,B.I.,2008.Atmospheric acid leaching of nickel laterites review.Part1.Sulphuric acid technologies.Hydrometallurgy91,35–55. Mitsutomi,K.,Atmowidjojo, D.,Yusuf,1987.Some hydrometallurgical studies on Indonesian low-grade nickel laterite.International Journal of Mineral Processing19 (1–4),297–309.Munroe,N.D.H.,1997.The leaching of nickeliferous laterite with ferric chloride.Metallurgical and Materials Transactions B28B,995–1000.Olanipekun,E.O.,2000.Kinetics of leaching laterite.International Journal of Mineral Processing60,9–14.Purwanto,H.,Shimada,T.,Takahashi,R.,Yagi,J.I.,2003.Recovery of nickel from selectively reduced laterite ore by sulphuric acid leaching.ISIJ International43, 181–186.Queneau,P.B.,Doane,R.E.,Cooperrider,M.W.,Berggren,M.H.,Rey,P.,1984.Control of autoclave scaling during acid pressure leaching of nickeliferous laterite ore.Metallurgical Transactions B15B,433–440.Senanayake,G.,Das,G.K.,2004.A comparative study of leaching kinetics of limonitic laterite and synthetic iron oxides in sulfuric acid containing sulfur dioxide.Hydrometallurgy72,59–72.Singh, B.,Sherman, D.M.,Gilkes,R.J.,Wells,M.A.,Mosselmans,J.F.W.,2002.Incorporation of Cr,Mn and Ni into goethite(a-FeOOH):mechanism from extended X-ray absorptionﬁne structure spectroscopy.Clay Minerals37,639–649. Whittington,B.I.,2000.Characterization of scales obtained during continuous nickel laterite pilot-plant leaching.Metallurgical and Materials Transactions B31B, 1175–1186.Whittington,B.I.,Muir,D.,2000.Pressure acid leaching of nickel laterites:a review.Mineral Processing Extraction and Metallurgy Review21,527–600.Table3Effects of pH value and Fe/Ni ratio on nickel loss during the iron precipitation process. pH value Fe/Ni ratio a Ni in residue/%Loss of Ni/%2.5–3.022.20.1124.123.0–4.022.20.46715.97.0–8.022.2 2.0861.62.5–3.011.10.119 2.092.5–3.0 5.540.151 1.41a Refer to the concentration ratio in the initial liquor.Table4Variation of nickel concentration in the goethite precipitate before and after acid washing.Concentration of wash acid/mol L−1Ni content in the residue/%Before washing After washing0.50.1510.1541.00.1510.1600.50.4670.4791.00.4670.49487Y.Chang et al./Hydrometallurgy101(2010)84–87。

法布里珀罗基模共振英文

法布里珀罗基模共振英文The Fabryperot ResonanceOptics, the study of light and its properties, has been a subject of fascination for scientists and researchers for centuries. One of the fundamental phenomena in optics is the Fabry-Perot resonance, named after the French physicists Charles Fabry and Alfred Perot, who first described it in the late 19th century. This resonance effect has numerous applications in various fields, ranging from telecommunications to quantum physics, and its understanding is crucial in the development of advanced optical technologies.The Fabry-Perot resonance occurs when light is reflected multiple times between two parallel, partially reflective surfaces, known as mirrors. This creates a standing wave pattern within the cavity formed by the mirrors, where the light waves interfere constructively and destructively to produce a series of sharp peaks and valleys in the transmitted and reflected light intensity. The specific wavelengths at which the constructive interference occurs are known as the resonant wavelengths of the Fabry-Perot cavity.The resonant wavelengths of a Fabry-Perot cavity are determined bythe distance between the mirrors, the refractive index of the material within the cavity, and the wavelength of the incident light. When the optical path length, which is the product of the refractive index and the physical distance between the mirrors, is an integer multiple of the wavelength of the incident light, the light waves interfere constructively, resulting in a high-intensity transmission through the cavity. Conversely, when the optical path length is not an integer multiple of the wavelength, the light waves interfere destructively, leading to a low-intensity transmission.The sharpness of the resonant peaks in a Fabry-Perot cavity is determined by the reflectivity of the mirrors. Highly reflective mirrors result in a higher finesse, which is a measure of the ratio of the spacing between the resonant peaks to their width. This high finesse allows for the creation of narrow-linewidth, high-resolution optical filters and laser cavities, which are essential components in various optical systems.One of the key applications of the Fabry-Perot resonance is in the field of optical telecommunications. Fiber-optic communication systems often utilize Fabry-Perot filters to select specific wavelength channels for data transmission, enabling the efficient use of the available bandwidth in fiber-optic networks. These filters can be tuned by adjusting the mirror separation or the refractive index of the cavity, allowing for dynamic wavelength selection andreconfiguration of the communication system.Another important application of the Fabry-Perot resonance is in the field of laser technology. Fabry-Perot cavities are commonly used as the optical resonator in various types of lasers, providing the necessary feedback to sustain the lasing process. The high finesse of the Fabry-Perot cavity allows for the generation of highly monochromatic and coherent light, which is crucial for applications such as spectroscopy, interferometry, and precision metrology.In the realm of quantum physics, the Fabry-Perot resonance plays a crucial role in the study of cavity quantum electrodynamics (cQED). In cQED, atoms or other quantum systems are placed inside a Fabry-Perot cavity, where the strong interaction between the atoms and the confined electromagnetic field can lead to the observation of fascinating quantum phenomena, such as the Purcell effect, vacuum Rabi oscillations, and the generation of nonclassical states of light.Furthermore, the Fabry-Perot resonance has found applications in the field of optical sensing, where it is used to detect small changes in physical parameters, such as displacement, pressure, or temperature. The high sensitivity and stability of Fabry-Perot interferometers make them valuable tools in various sensing and measurement applications, ranging from seismic monitoring to the detection of gravitational waves.The Fabry-Perot resonance is a fundamental concept in optics that has enabled the development of numerous advanced optical technologies. Its versatility and importance in various fields of science and engineering have made it a subject of continuous research and innovation. As the field of optics continues to advance, the Fabry-Perot resonance will undoubtedly play an increasingly crucial role in shaping the future of optical systems and applications.。

《科学探究的精神与方法》高中生英语作文

《科学探究的精神与方法》高中生英语作文The Spirit and Methods of Scientific InquiryScientific inquiry is a systematic process that involves observing, asking questions, and conducting experiments to understand the natural world.It is a fundamental aspect of human progress and development, driving innovation and shaping our understanding of the universe.The spirit of scientific inquiry, which includes curiosity, skepticism, and perseverance, is essential for students to develop a deep appreciation for the scientific method and its applications.The first step in the scientific inquiry process is making observations.This involves using our senses to gather information about the world around us.Observations can be qualitative, describing qualities such as color or texture, or quantitative, involving measurements such as length or weight.It is important for students to learn how to make precise and accurate observations to ensure that their data is reliable.Once observations have been made, the next step is to ask questions.Questions are the foundation of scientific inquiry, as they inspire investigation and lead to further understanding.Students should be encouraged to ask questions about their observations, and to seek answers through research and experimentation.The scientific method is a structured approach to answering questions and testing hypotheses.It involves making a hypothesis, whichis an educated guess about the relationship between variables, and designing experiments to test the hypothesis.Students should learn how to design experiments that control for variables and use randomization to minimize bias.It is also important for students to learn how to analyze data and draw conclusions based on evidence.The spirit of scientific inquiry also includes skepticism, which is the willingness to question assumptions and challenge existing knowledge.Skepticism is crucial for preventing fraud and error in scientific research, and for promoting a culture of intellectual curiosity and open-mindedness.Students should be encouraged to question information and to seek multiple perspectives on any given topic.Finally, the scientific method requires perseverance and resilience.Scientific inquiry can be a lengthy and difficult process, involving many failed attempts and setbacks.Students should learn that failure is a natural part of the scientific process, and that perseverance and persistence are key to success in science and in life.In conclusion, the spirit and methods of scientific inquiry are essential for students to develop a deep appreciation for the scientific process and its applications.By fostering curiosity, skepticism, and perseverance, we can help students to become informed and engaged citizens, who are equipped to contribute to the ongoing development of scientific knowledge and understanding.。

遇事不决量子力学英语

遇事不决量子力学英语Quantum Mechanics in Decision-MakingIn the face of complex and uncertain situations, traditional decision-making approaches often fall short. However, the principles of quantum mechanics, a field of physics that explores the behavior of matter and energy at the subatomic level, can provide valuable insights and a new perspective on problem-solving. By understanding and applying the fundamental concepts of quantum mechanics, individuals and organizations can navigate challenging scenarios with greater clarity and effectiveness.One of the key principles of quantum mechanics is the idea of superposition, which suggests that particles can exist in multiple states simultaneously until they are observed or measured. This concept can be applied to decision-making, where the decision-maker may be faced with multiple possible courses of action, each with its own set of potential outcomes. Rather than prematurely collapsing these possibilities into a single decision, the decision-maker can embrace the superposition and consider the various alternatives in a more open and flexible manner.Another important aspect of quantum mechanics is the principle of uncertainty, which states that the more precisely one property of a particle is measured, the less precisely another property can be known. This principle can be applied to decision-making, where the decision-maker may be faced with incomplete or uncertain information. Instead of trying to eliminate all uncertainty, the decision-maker can acknowledge and work within the constraints of this uncertainty, focusing on making the best possible decision based on the available information.Furthermore, quantum mechanics introduces the concept of entanglement, where two or more particles can become inextricably linked, such that the state of one particle affects the state of the other, even if they are physically separated. This idea can be applied to decision-making in complex systems, where the actions of one individual or organization can have far-reaching and unpredictable consequences for others. By recognizing the interconnectedness of the various elements within a system, decision-makers can better anticipate and navigate the potential ripple effects of their choices.Another key aspect of quantum mechanics that can inform decision-making is the idea of probability. In quantum mechanics, the behavior of particles is described in terms of probability distributions, rather than deterministic outcomes. This probabilistic approach can be applied to decision-making, where the decision-maker canconsider the likelihood of different outcomes and adjust their strategies accordingly.Additionally, quantum mechanics emphasizes the importance of observation and measurement in shaping the behavior of particles. Similarly, in decision-making, the act of observing and gathering information can influence the outcomes of a situation. By being mindful of how their own observations and interventions can impact the decision-making process, decision-makers can strive to maintain a more objective and impartial perspective.Finally, the concept of quantum entanglement can also be applied to the decision-making process itself. Just as particles can become entangled, the various factors and considerations involved in a decision can become deeply interconnected. By recognizing and embracing this entanglement, decision-makers can adopt a more holistic and integrated approach, considering the complex web of relationships and dependencies that shape the outcome.In conclusion, the principles of quantum mechanics offer a unique and compelling framework for navigating complex decision-making scenarios. By embracing the concepts of superposition, uncertainty, entanglement, and probability, individuals and organizations can develop a more nuanced and adaptable approach to problem-solving. By applying these quantum-inspired strategies, decision-makers can navigate the challenges of the modern world with greater clarity, resilience, and effectiveness.。

化学动力学原理（第二版）说明书

Principles of Chemical KineticsPrinciplesofChemicalKinetics Second EditionJames E.HouseIllinoisStateUniversityandIllinois WesleyanUniversityAMSTERDAM • BOSTON • HEIDELBERG • LONDONNEW YORK • OXFORD • PARIS • SAN DIEGOSAN FRANCISCO • SINGAPORE • SYDNEY • TOKYOAcademic Press is an imprint of ElsevierAcademic Press is an imprint of Elsevier30Corporate Drive,Suite400,Burlington,MA01803,USA525B Street,Suite1900,San Diego,CA92101-4495,USA84Theobald’s Road,London WC1X8RR,UKThis book is printed on acid-freeCopyrightß2007,Elsevier Inc.All rights reserved.No part of this publication may be reproduced or transmitted in any form or by any means,electronic or mechanical,including photocopy,recording,or any information storage and retrieval system,without permission in writing from the publisher. Permissions may be sought directly from Elsevier’s Science&Technology Rights Department in Oxford,UK:phone:(þ44)1865843830,fax:(þ44)1865853333,E-mail:************************.You may also complete your request on-linevia the Elsevier homepage(http:==),by selecting‘‘Support&Contact’’then‘‘Copyright and Permission’’and then‘‘Obtaining Permissions.’’Library of Congress Cataloging-in-Publication DataHouse,J.E.Principles of chemical kinetics/James E.House.–2nd ed.p.cm.Includes index.ISBN:978-0-12-356787-1(hard cover:alk.paper) 1.Chemical kinetics.I.Title. QD502.H6820075410.394–dc222007024528 British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.ISBN:978-0-12-356787-1For information on all Academic Press publicationsvisit our web site at Printed in the United States of America07080910987654321Preface Chemical kinetics is an enormous W eld that has been the subject of many books,including a series that consists of numerous large volumes.To try to cover even a small part of the W eld in a single volume of portable size is a di Y cult task.As is the case with every writer,I have been forced to make decisions on what to include,and like other books,this volume re X ects the interests and teaching experience of the author.As with the W rst edition,the objective has been to provide an introduc-tion to most of the major areas of chemical kinetics.The extent to which this has been done successfully will depend on the viewpoint of the reader. Those who study only gas phase reactions will argue that not enough material has been presented on that topic.A biochemist who specializes in enzyme-catalyzed reactions may W nd that research in that area requires additional material on the topic.A chemist who specializes in assessing the in X uence of substituent groups or solvent on rates and mechanisms of organic reactions may need other tools in addition to those presented. In fact,it is fair to say that this book is not written for a specialist in any area of chemical kinetics.Rather,it is intended to provide readers an introduction to the major areas of kinetics and to provide a basis for further study.In keeping with the intended audience and purposes,derivations are shown in considerable detail to make the results readily available to students with limited background in mathematics.In addition to the signi W cant editing of the entire manuscript,new sections have been included in several chapters.Also,Chapter9‘‘Additional Applications of Kinetics,’’has been added to deal with some topics that do not W t conveniently in other chapters.Consequently,this edition contains substantially more material,including problems and references,than the W rst edition.Unlike the W rst edition,a solution manual is also available.As in the case of the W rst edition,the present volume allows for variations in the order of taking up the material.After the W rst three chapters,thevvi Prefaceremaining chapters can be studied in any order.In numerous places in the text,attention is drawn to the fact that similar kinetic equations result for di V erent types of processes.As a result,it is hoped that the reader will see that the assumptions made regarding interaction of an enzyme with a substrate are not that di V erent from those regarding the adsorption of a gas on the surface of a solid when rate laws are derived.The topics dealing with solid state processes and nonisothermal kinetics are covered in more detail than in some other texts in keeping with the growing importance of these topics in many areas of chemistry.These areas are especially important in industrial laboratories working on processes involving the drying, crystallizing,or characterizing of solid products.It is hoped that the present volume will provide a succinct and clear introduction to chemical kinetics that meets the needs of students at a variety of levels in several disciplines.It is also hoped that the principles set forth will prove useful to researchers in many areas of chemistry and provide insight into how to interpret and correlate their kinetic data.Contents1Fundamental Concepts of Kinetics11.1Rates of Reactions21.2Dependence of Rates on Concentration41.2.1First-Order51.2.2Second-Order81.2.3Zero-Order101.2.4N th-Order Reactions131.3Cautions on Treating Kinetic Data131.4E V ect of Temperature161.5Some Common Reaction Mechanisms201.5.1Direct Combination211.5.2Chain Mechanisms221.5.3Substitution Reactions231.6Catalysis27References for Further Reading30 Problems31 2Kinetics of More Complex Systems372.1Second-Order Reaction,First-Order in Two Components372.2Third-Order Reactions432.3Parallel Reactions452.4Series First-Order Reactions472.5Series Reactions with Two Intermediates532.6Reversible Reactions582.7Autocatalysis642.8E V ect of Temperature69References for Further Reading75 Problems75viiviii Contents3Techniques and Methods793.1Calculating Rate Constants793.2The Method of Half-Lives813.3Initial Rates833.4Using Large Excess of a Reactant(Flooding)863.5The Logarithmic Method873.6E V ects of Pressure893.7Flow Techniques943.8Relaxation Techniques953.9Tracer Methods983.10Kinetic Isotope E V ects102References for Further Reading107 Problems108 4Reactions in the Gas Phase1114.1Collision Theory1114.2The Potential Energy Surface1164.3Transition State Theory1194.4Unimolecular Decomposition of Gases1244.5Free Radical or Chain Mechanisms1314.6Adsorption of Gases on Solids1364.6.1Langmuir Adsorption Isotherm1384.6.2B–E–T Isotherm1424.6.3Poisons and Inhibitors1434.7Catalysis145References for Further Reading147 Problems148 5Reactions in Solutions1535.1The Nature of Liquids1535.1.1Intermolecular Forces1545.1.2The Solubility Parameter1595.1.3Solvation of Ions and Molecules1635.1.4The Hard-Soft Interaction Principle(HSIP)1655.2E V ects of Solvent Polarity on Rates1675.3Ideal Solutions1695.4Cohesion Energies of Ideal Solutions1725.5E V ects of Solvent Cohesion Energy on Rates1755.6Solvation and Its E V ects on Rates1775.7E V ects of Ionic Strength182Contents ix5.8Linear Free Energy Relationships1855.9The Compensation E V ect1895.10Some Correlations of Rates with Solubility Parameter191References for Further Reading198 Problems199 6Enzyme Catalysis2056.1Enzyme Action2056.2Kinetics of Reactions Catalyzed by Enzymes2086.2.1Michaelis–Menten Analysis2086.2.2Lineweaver–Burk and Eadie Analyses2136.3Inhibition of Enzyme Action2156.3.1Competitive Inhibition2166.3.2Noncompetitive Inhibition2186.3.3Uncompetitive Inhibition2196.4The E V ect of pH2206.5Enzyme Activation by Metal Ions2236.6Regulatory Enzymes224References for Further Reading226 Problems227 7Kinetics of Reactions in the Solid State2297.1Some General Considerations2297.2Factors A V ecting Reactions in Solids2347.3Rate Laws for Reactions in Solids2357.3.1The Parabolic Rate Law2367.3.2The First-Order Rate Law2377.3.3The Contracting Sphere Rate Law2387.3.4The Contracting Area Rate Law2407.4The Prout–Tompkins Equation2437.5Rate Laws Based on Nucleation2467.6Applying Rate Laws2497.7Results of Some Kinetic Studies2527.7.1The Deaquation-Anation of[Co(NH3)5H2O]Cl32527.7.2The Deaquation-Anation of[Cr(NH3)5H2O]Br32557.7.3The Dehydration of Trans-[Co(NH3)4Cl2]IO3 2H2O2567.7.4Two Reacting Solids259References for Further Reading261 Problems262x Contents8Nonisothermal Methods in Kinetics2678.1TGA and DSC Methods2688.2Kinetic Analysis by the Coats and Redfern Method2718.3The Reich and Stivala Method2758.4A Method Based on Three(a,T)Data Pairs2768.5A Method Based on Four(a,T)Data Pairs2798.6A Di V erential Method2808.7A Comprehensive Nonisothermal Kinetic Method2808.8The General Rate Law and a Comprehensive Method281References for Further Reading287 Problems288 9Additional Applications of Kinetics2899.1Radioactive Decay2899.1.1Independent Isotopes2909.1.2Parent-Daughter Cases2919.2Mechanistic Implications of Orbital Symmetry2979.3A Further Look at Solvent Properties and Rates303References for Further Reading313 Problems314 Index317。

DIELECTRIC HOLDER FOR QUANTUM DEVICES

专利名称：DIELECTRIC HOLDER FOR QUANTUMDEVICES发明人：Patryk Gumann,Salvatore BernardoOlivadese,Jerry M. CHOW申请号：US16173720申请日：20181029公开号：US20200136007A1公开日：20200430专利内容由知识产权出版社提供专利附图：摘要：A device includes a first substrate formed of a first material that exhibits a threshold level of thermal conductivity. The threshold level of thermal conductivity isachieved at a cryogenic temperature range in which a quantum circuit operates. In an embodiment, the device also includes a second substrate disposed in a recess of the first substrate, the second substrate formed of a second material that exhibits a second threshold level of thermal conductivity. The second threshold level of thermal conductivity is achieved at a cryogenic temperature range in which a quantum circuit operates. In an embodiment, at least one qubit is disposed on the second substrate. In an embodiment, the device also includes a transmission line configured to carry a microwave signal between the first substrate and the second substrate.申请人：International Business Machines Corporation地址：Armonk NY US国籍：US更多信息请下载全文后查看。

Kinetics of the Dimerization of Ethylene

Kinetics of the Dimerization ofEthyleneEthylene (C2H4) is a simple hydrocarbon molecule consisting of two carbon atoms and four hydrogen atoms. It is the second most important organic chemical after ammonia in terms of volume of production and economic value. Ethylene is widely used in the manufacture of plastics, synthetic rubber, and other organic compounds. Its dimerization process is one of the important chemical reactions used for producing hexene, octene, and other linear alpha olefins. The kinetics of the dimerization reaction of ethylene is the main focus of this article.IntroductionAs stated earlier, ethylene dimerizes to form linear alpha olefins, which are used as starting materials for detergents, lubricants, and other chemical products. The reaction is catalyzed by a transition metal complex, usually nickel or palladium. Ethylene dimerization is a simple yet important reaction, and its kinetics have been studied extensively.Reaction mechanismThe dimerization of ethylene proceeds via a coordination mechanism. The first step involves the formation of a nickel-ethylene complex, which is highly reactive. The complex is then oxidized to form a nickel ethylene radical, which is further oxidized to form a nickel ethylene dimer. The dimerization process is reversible, and the dimer can undergo a reverse reaction to form two molecules of ethylene.Rate expressionThe rate at which the dimerization reaction proceeds is determined by the rate of the forward reaction and the rate of the reverse reaction. The rate expression for the forward reaction is given by:rate = k [Ni-ethylene complex]where k is the rate constant and the [Ni-ethylene complex] is the concentration of the complex.The rate expression for the reverse reaction is given by:rate = k' [Ni-ethylene dimer]where k' is the rate constant and the [Ni-ethylene dimer] is the concentration of the dimer.The overall rate of reaction is the difference between the rates of the forward and the reverse reactions:rate = k [Ni-ethylene complex] - k' [Ni-ethylene dimer]The rate law indicates that the formation of the nickel-ethylene complex is the rate-determining step.Factors affecting the reaction rateSeveral factors can influence the rate of the ethylene dimerization reaction. These factors include temperature, pressure, and the presence of catalysts. Increasing the temperature and pressure of the reaction system increases the reaction rate. The presence of a catalyst, such as nickel or palladium, is necessary for the reaction to occur.Experimental methodsSeveral experimental techniques are available for measuring the kinetics of the ethylene dimerization reaction. These techniques include gas chromatography, mass spectrometry, and NMR spectroscopy. Gas chromatography is widely used to monitor the concentration of ethylene and the products formed during the reaction. Mass spectrometry is used to determine the molecular weight and composition of the reaction products. NMR spectroscopy can be used to study the reaction mechanism and monitor the formation of intermediate species during the reaction.ConclusionThe kinetics of the dimerization of ethylene is an interesting and important area of research. The reaction plays a crucial role in the production of linear alpha olefins, which are important raw materials for the chemical industry. The rate expression for the reaction is dependent on the concentration of the nickel-ethylene complex and the nickel-ethylene dimer. Several factors, such as temperature, pressure, and the presence of catalysts, can affect the rate of the reaction. Experimental techniques, such as gas chromatography, mass spectrometry, and NMR spectroscopy, can be used to study the kinetics and mechanism of the reaction.。

寒蝉效应英语

寒蝉效应英语The Cicada EffectThe cicada effect refers to a phenomenon where a large number of cicadas will emerge simultaneously after having spent years underground. With some cicada species, the entire population will live underground for 13 or 17 years before emerging together in a massive brood. When they finally come out en masse, the deafening "song" of the male cicadas calling out for mates creates a significant auditory effect.The cicada effect has become an analogy for major social or economic events with widespread simultaneous consequences. It reflects situations where a single initial trigger can lead to mass simultaneous collapse or change. Examples include financial crashes, political revolutions, power outages, and epidemics. The interdependence of factors makesprediction and isolation challenging.寒蝉效应寒蝉效应指的是大量寒蝉在地下生活多年后,集体出现的现象。

翻译

磁场条件对晶体质量增加的影响摘要从90世纪后期起，许多学者开始进行磁场对蛋白质结晶性能影响的研究。

研究发现，蛋白质结晶过程中，在均匀磁场或不均匀磁场（梯度不均匀）的条件下，蛋白质晶体质量都会增加。

晶体质量的增加取决于蛋白质晶体所在的磁场方向以及磁场对蛋白质溶液浮力对流的抑制。

磁场也影响蛋白质结晶动力学，并因此改变蛋白质结晶过程。

因此在这篇文献中，我们对磁场对蛋白质结晶性能的影响机理以及将来不可缺少的研究提出研究概要。

关键词：磁场晶体质量增加磁场方向磁场对流的抑制作用目录1、简介2、磁场条件下晶体质量的增加2.1在均匀磁场条件下2.2在不均匀磁场条件下（梯度不均匀）3、晶体质量增加的原因I：磁场方向4、晶体质量增加的原因II：浮力对流的抑制4.1洛伦兹力对流的抑制4.2磁力对流的抑制5、未解决的问题：流量与晶体质量6、磁场对蛋白质结晶的其他影响7、结论致谢参考文献1、简介在过去的十年里，由于同步辐射源的进步，X-射线进行结构分析时所需蛋白质晶体的大小明显减小了。

目前，关键问题是如何制备用于结构分析的高质量蛋白质晶体。

为了解决这个问题，许多学者尝试着在极端情况下控制蛋白质结晶，例如在微重力条件下（Delucas et al., 1989; Kundrot et al., 2001）或者在极大压力下（Suzuki et al., 2005; Visuri et al., 1990）。

运用磁场条件也是这样的尝试之一。

Rothgeb和Oldfieldwere是发表磁场对蛋白质结晶性能的影响报告的第一人（Rothgeb和Oldfieldwere，1981）。

他们发现，在核磁共振分光仪的磁体（8.5T,这里1T=10000G）中，血红素蛋白晶体可以随磁性进行调整。

但是，那时磁场对蛋白质结晶的影响没有得到关注，直到Rothgeb和Oldfieldwere推断出磁场方向的影响是由于金属离子与血红素蛋白结合的原因。

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