18.EN_CN 浅析影响我矿卤水净化絮凝剂效果的因素

浅析影响卤水净化絮凝沉降效果的因素
荀春
（云南盐化股份有限公司650011）
摘要：通过对昆明盐矿卤水净化澄清效果进行实验研究，从理论和实际分析总结影响卤水净化澄清效果的内外部因素,为今后解决类似问题提供一定的理论和实际依据。

关键词：卤水净化絮凝沉降因素
卤水净化是真空制盐工艺过程中的关键工序之一。

其目的和意义在于除去或降低卤水中的杂质，提高制盐设备的生产能力，保证产品的质量，为化工生产和综合利用提供优质合格的原料。

昆明盐矿20万吨制盐装置系引进瑞士苏尔寿.埃塞维舍公司的先进生产工艺及关键设备，是现代化制盐企业之一。

原料卤水属于芒硝型岩盐卤水。

在真空蒸发制盐工艺中，对卤水质量要求极高，生产的精卤中Ca2++Mg2+控制在10PPm以下。

如果卤水净化效果不佳，将直接影响生产的正常进行，会导致加热室管壁形成硬质垢层，甚至堵管，传热效率降低，洗刷罐频率增加，制盐设备寿命缩短等危害，从而影响产品的质量和产量，将导致整个企业的经济效益受到严重影响。

昆明盐矿自93年6月试车投产以来，曾经几度出现卤水澄清效果不佳的问题，尤其在98年下半年出现的情况最为严重，持续周期长达半年左右，净化后的卤水在罐内透光率极低，以反应罐内楼梯台数观察，总楼梯台数20台，效果最差时几乎一台都看不到，最好时也只能看到10台左右，与净化效果正常时的清可见底形成极大的反差。

当时好在卤水净化过滤装置已建好使用，才勉强得以维持生产的顺利进行。

公司对此情况非常重视，成立了卤水净化澄清效果项目攻关小组。

通过努力，基本找到了可能影响卤水澄清效果的因素。

现将之归纳总结如下，与同行们进行探讨，并为今后出现类似的情况提供一定的理论依据。

1、昆明盐矿卤水净化的基本情况：
1.1卤水中的杂质存在形式：
昆明盐矿卤水属于芒硝型卤水，卤水中主要含Ca2+ 、Mg2+ 、AL、P、有机物、少量粘土等杂质。

1.2卤水净化的方法：
采用石灰—纯碱一步法。

1.3卤水净化反应的基本原理：
Mg2++CaO+H2O→Mg（OH）2↓+Ca2+
Ca2++Na2Co3→CaC03↓+2Na+
1.4絮凝剂的选择使用：
絮凝剂类型对絮凝沉降效果影响很大,多数情况下往往是决定因素。

一般情况下,非离子型的聚丙烯酰胺（PAM）类絮凝剂适用的pH 值范围为1～6;阴离子PAM适用的pH值范围为6～10;阳离子型PAM适用的pH 值范围为0～10 ,在处理废水中作用很大,适用于极难处理的一些悬浮体系。

絮凝剂类型的选择除了考虑沉降效果因素外，还要考虑沉降物的过滤性能，只有满足这两方面的要求，方能满足生产需求。

通过多次实验室小试和大生产的实验，确定使用阴离子部分水解型聚丙烯酰胺（PH-PAM）作为助沉剂，固含量为2.5%，平均分子量为1000万左右,水解度为30%。

2、卤水净化工艺流程简图见附图：
3、影响卤水净化澄清效果的因素分析
3.1卤水悬浮体系中固形物的化学组成与表面电性的改变而产生的影
响。

具体描述表面电性的参数是δ-电位。

δ-电位的大小直接与整个卤水悬浮体系的稳定性有直接关系（见附表）。

由表一可看出，只有δ-电位介于±20-30mv的粒子才容易凝聚。

我矿采用部分水解型聚丙烯酰胺（PH-PAM）作为助沉剂，而PH-PAM通常只与δ-电位大于0的悬浮体系产生絮凝作用。

高分子末端固着在颗粒表面上，伸入溶液中的链节再吸附在相邻颗粒的空白部位上，互相拉紧，形成“桥”。

PH-PAM吸附在正电荷部位上，酰胺基与粒子表面上的羟基或氢原子之间形成氢键产生絮团，从而凝聚，加速固液分离速度。

通过实验和查阅相关资料，导致整个卤水悬浮体系δ-电位变化的原因有以下几个方面：
3.2不同水解度絮凝剂的长期累积，导致悬浮体系δ-电位的改变。

PH-PAM官能团荷负电。

在改性过程中，曾经过高地提高水解度（理论计算约在50-70%），而实际改性过程并不完全，导致NaOH过量，加大了活性官能团的位阻。

而NaOH本身就是一种无机阴离子混凝剂，最终使卤水悬浮体系的δ-电位向负方向移动。

3.2.1卤水净化采用石灰-纯碱法。

石灰和纯碱的含量不高，极有可能带入其他电解质，影响悬浮颗粒表面电性和双电层的厚度、组成，影响絮凝剂穿透双电层在颗粒表面的吸着。

此外，石灰、纯碱在某种意义上也是阴离子混凝剂，如果投加过量太多，日久天长也会产生累积，使整个悬浮体系的δ-电位发生变化，从而影响卤水的澄清效果。

3.2.2由于矿层的变化，卤水的成份也会发生变化，从而使卤水悬浮体系的δ-电位发生变化。

在此方面应对不同采区的卤水进行抽样全分析、收集资料，以便将来有据可寻。

附表如下：
3.3卤水悬浮体系的温度对絮凝剂效果的影响
原卤通过加入CaO、Na2CO3产生化学反应,生成CaC03、Mg（OH）2沉淀，还有极少部分生成MgCO3沉淀，而MgCO3容易沉积在CaC03表面形成[CaMg3（CO3）4]矾花状沉淀物。

当体系温度低于15℃时，随着温度升高，粘度逐渐下降，絮凝时絮团的沉降速率渐快。

但温度过高时，矾花的水和作用增强，影响PH-PAM在颗粒表面的吸附，从而影响净化沉降效率；温度较低时，会减少悬浮颗粒间的碰撞机会，降低PH-PAM与颗粒间的架桥机会。

所以温度过高、过低都会影响卤水净化的絮凝效果，实验证明温度在15-30℃有利于絮团的絮凝沉降。

3.4卤水悬浮体系固形物的粒度与比重对絮凝效果的影响
固形物粒度太大或太小均不利于絮凝效果。

只有当固相粒度适中时，才有利于絮凝沉降。

粒度太小时，不利于絮凝剂捕捉悬浮粒子；而粒子太大时，则不利于絮凝剂
长链的粘接搭桥作用。

所以在卤水反应时间的控制上，添加絮凝剂时机选择上应进一步摸索、实验，特别是在固形物粒度分布的定量检测上，对于卤水净化絮凝效果的因素分析很重要。

3.5卤水悬浮液固相浓度对絮凝效果的影响
悬浮体系中悬浮物的含量（固相浓度）会影响絮凝效果。

过大的固含量（>30%），絮团的自由沉降受阻；过小的固含量（低于0.1%），粒子的碰撞机会会减少，影响絮团的形成。

所以在卤水净化工艺过程中，在抽泥浆的次数、停产清理泥浆的数量上应进行多观察，寻找经验数据，以利于指导生产。

3.6絮凝剂分子量对絮凝效果的影响
按照絮凝剂架桥作用原理，PH-PAM必须有足够长的柔性分子链才能在粒子间架桥，其絮凝效果应随分子量的增加而递增，然而事实并非如此分子量太大（M>1X107），絮团凝聚速度太快，沉降速度也加快，会导致细小颗粒仍悬浮在上清液层中，而这些残留的细小颗粒表面形成了一层絮凝膜，因粒径太小而处于稳定状态，存在于卤水悬浮体系中，导致卤水透光率不好。

所以掌握卤水中悬浮粒子的粒径范围，对选择絮凝剂分子的分子量有很大作用。

3.7反应罐搅拌时间和搅拌强度对絮凝效果的影响
PH-PAM主要借助于酰胺基与悬浮粒子吸附，其键合能仅几十千卡/克分子。

作用力较弱，所以机械搅拌的强度要适中，否则絮团容易被搅碎，从而影响絮凝效果。

PH-PAM与悬浮粒子的作用十分迅速，所以搅拌时间不易太长，否则絮团也容易被搅碎，从而影响卤水的澄清效果。

3.8在卤水悬浮体系中，如果卤水含量过高，导致Na+含量升高，而部
分水解型聚丙烯酰胺[CH2-CH]X [CH2- CH]Y中的-COONa-
CONH2 COONa
离解成-COO-和Na+平衡移动受到影响，使有效官能团的键合效率降低，影响卤水净化的絮凝效果。

此外，卤水含量的升高，密度增大导致体系内悬浮粒子浮力增加，沉降速度受阻，从而影响沉降效果。

4、结语
影响卤水净化絮凝效果的因素很多,还有在絮凝剂的配制、用量等方面的因素，具体情况应该具体分析。

以上所述因素有可能几种因素共同作用，也可能只有某种因素单独作用。

出现此类情况，应进行综合分析，排除干扰因素，有的放矢的处理问题。

当然，要做好这些工作，原始资料的积累相当重要，只有通过一定的实验手段和经验数据来进行判断，最终找出其关键因素，发现问题，解决问题，保证生产顺利进行。

参考文献
〔1〕王春梅，胡啸林，章忠秀. 工业用水与废水,V ol.3 No.1 2002,33-35.
〔2〕徐初阳，罗慧，聂容春，李振奇. 煤炭技术,V ol.23 No.1 Jan.,2004,63-65.
〔3〕郑红. 在废水处理中影响聚丙烯酰胺絮凝效果的若干因素〔J〕青海环境，2002，（12）：68-69。

作者简介：荀春（1972—），男，云南曲靖人，毕业于上海轻工业高等专科学校化工系香料香精专业，现在云南盐化股份有限公司工作，副经理、工程师，主要从事生产、质量和标准化管理工作。

地址：昆明市拓东路石家巷10号邮编：650011
电话：（0871）3120848 传真：（0871）3162767
Analysis of Factors Influencing Flocculating and Sedimentation
in Brine Purification
Chun Xun
(Yunnan Salt & Chemical Industry Co., Ltd., 650011)
Abstract: Through the experimental study on the clarification effect of the brine purification of Kunming Salt Mine, both internal and external factors influencing the clarification effect of the brine purification are analyzed theoretically and practicality and summarized, providing theoretical and practical evidences for resolving similar problems in the future.
Keywords: brine purification, flocculation, settlement, factors
Brine purification is one of the key processes in the vacuum salt manufacturing technology. Its aim and significance are to remove or reduce impurities in brine to increase the productive capacity of salt producing equipment, ensure the quality of products and provide high-quality and qualified raw materials for chemical production and comprehensive utilization. Kunming Salt Mine introduced the advanced production technology and key equipment for its 200,000-ton salt production apparatus from the Sulzer Company of Switzerland which makes Kunming Salt Mine one of the modernized salt production enterprises. The feed brine is a kind of mirabilite type rock salt brine. In the technology of vacuum evaporation for producing salt, it is required that brine must have extremely high quality. The content of Ca2++Mg2+ in the refined brine should be below 10ppm. The poor effect of brine purification will exert direct influence on the normal production and lead to hard scaling on pipe wall of the heating chamber, or even blocking the pipe. Therefore, a series of harms will be caused, such as the reduction of heat transfer efficiency, the increase of tank washing frequency and the cut-down of the life of the equipment. These problems will affect the quality and output of products, thus exerting serious influence on the economic efficiency of the enterprise.
Since Kunming Salt Mine was put into operation after commissioning in June 1993, the problem of poor effect of clarification of brine occurred several times. Particularly at the later half of 1998, the problem became most severe, lasting for about half a year. The light transmittance of the brine after purification is extremely low in the tank. Tests were made by observing total 20 steps through the reaction tank containing brine. However, almost no steps could be seen in the worst case and about 10 steps could be seen in the best case. In the case with the normal purification effect, the bottom can be seen clearly, which is an extremely great contrast. At that time, it was fortunate that the filtering devices for brine clarification had been completed and could be used so that production could be maintained. The company attached great importance to this
situation and organized a team to tackle the issue of brine purification and clarification effect. Through efforts, factors possibly influencing the effect of clarification in brine purification have been basically found. Now I hereby sum up as follows to have a discussion with people in this field and provide some theoretical evidences for reference for the similar situation in the future.
1. BASIC SITUATION OF BRINE PURIFICATION IN KUNMING SALT MINE
1.1 Forms of impurities in brine
The brine of Kunming Salt Mine belongs to Glauber’s salt brine, mainly containing Ca2+, Mg2+, AL, P, organic matters, a small quantity of clay, and etc.
1.2 Method of brine purification
Lime-soda ash one-step method is adopted.
1.3 Basic principle of brine purification reaction
Mg2++CaO+H2O→Mg (OH)2-
↓+Ca2+
Ca2++Na2CO3→CaCO3↓+2Na+
1.4 Selection and use of flocculating agent
The type of flocculating agent has great influence on the effect of flocculating sedimentation and it is usually a decisive factor in most cases. In general, the range of the applicable pH values of flocculant of non-ionic polyacrylamide (PAM) category is between 1 and 6. The range of the applicable pH values of anion PAM is between 6 and 10 and that of cationic PAM is between 0 and 10. The cationic PAM plays an important role in the treatment of waste water, and is suitable for some suspension systems which are extremely difficult to be treated. In the selection of the flocculant type, not only the factors of sedimentation effect should be considered, but also the filtration performance of sediment should be taken into consideration. Only when requirements in these two aspects are satisfied, the demand of production can be met.
Through small-scale experiment in the laboratory and large-scale pilot production for many times, the use of partially hydrolyzed polyacrylamide (PH-PAM) of anion type as a sedimentation aid has been decided. The content of solid substances is 2.5%, with average molecular weight of about 10,000,000 and hydrolysis degree is 30%.
2. Schematic diagram of brine purification process (see the diagram attached below)
Chinese characters in the figure above: 原卤— Raw brine; 过滤池—Filtering basin;
精卤池— Refined brine basin; 2000系统— System 2000
3. ANALYSIS OF THE FACTORS INFLUENCING CLARIFICATION EFFECT OF BRINE PURIFICATION
3.1 The results of the changes of chemical constitution and electrical property on surface in the suspension system of brine. The parameter used for describing electrical property on surface is δ-potential. The value of δ-potential has a direct relation with the stability of the whole suspension system of brine (see attached table). It can be seen from Table 1 below that only when the δ-potential of particles is between ±20mV-30mV, it is easy to coagulate. The partially hydrolyzed polyacrylamide (PH-PAM) anion type is used as a sedimentation aid in Kunming Salt Mine. However, PH-PAM generally has flocculation effect only when the δ-potential of the suspension system is higher than 0. The end of the polymer chain is fixed on the surface of particles and the polymer segment that extends into the solution absorbs the blank part of adjacent particles. The polymer chain is stretched by the two particles linked by the polymer and forms a “bridge”. The PH-PAM absorbs onto the part of positive charges and amido forming hydrogen bond with hydroxyl on the particle surface or between atoms of hydrogen and flocculi produced, thus beginning to coagulate to accelerate the speed of solid-liquid separation. Through experiments and literature research, I sum up the reasons resulting in the change of the δ-potential in the entire suspension system of brine as follows:
3.2 The long-term accumulation of flocculants with different hydrolysis degrees will result in the change of
δ-potential in the suspension system. Functional groups of PH-PAM have negative charge. During the process of modification, the hydrolysis degree has been excessively increased (about 50%~70% according to theoretical calculation). However, the process of actual modification is not complete, which leads to the excessive increase of NaOH and the increase of the steric hindrance of activated functional groups. Since sodium hydroxide (NaOH) itself is a kind of inorganic anion coagulant, thus it makes the δ-potential of the suspension system of brine move towards negative direction.
3.2.1 The lime-soda ash method is used for the brine purification. The content of lime and soda ash is not high, thus it is extremely possible to bring in other electrolytes and influence the electrical property on the surface of suspended particles and the thickness and the composition of the double electrical layer so as to influence the sorption process of the flocculant on the particle surface when they penetrate the double layer. Furthermore, lime and soda ash are also negative ion coagulants in some senses. If adding too much, they will accumulate day by day, thus making the δ-potential of the entire suspension system have a change so as to influence the clarification effect of brine.
3.2.2 Due to the change of ore bed, the composition of brine will also change, and consequently the δ-potential of the suspension system of brine changes. In this aspect, it is necessary to make full analysis of samples for brine from different extracting areas, and collect data for future reference. Table 1 is hereby attached:
3.3 Influence of Temperature of Brine Suspension System on Flocculant Effect Chemical reaction will occur by adding CaO and Na2CO3into raw brine, and the precipitate of CaCO3, Mg(OH)2 is produced. There is also a trace of precipitate of MgCO3. However, MgCO3 is easy to deposit on the surface of CaCO3to form alum grain-like precipitate [CaMg3 (CO3)4]. When the system temperature is lower than
the viscosity will gradually decrease and the sedimentation rate of flocculation will gradually increase when flocculating. However, when the temperature is excessively high, the hydration of alum grain will increase, thus influencing the absorption of PH-PAM on the particle surface so as to affect the effect of settlement of purification. When temperature is lower, the chance of collision among suspended particles will decrease,
and the bridging chance between PH-PAM and particles decreases. Therefore, excessive high or low temperature will influence the flocculation effect in brine purification. Experiments prove that the temperature at 15~30℃ is beneficial to the settlement of flocculation.
3.4 Influence of Graininess and Specific
Gravity of Solid Substances in Brine Suspension System on Flocculation Effect
Excessively large or small graininess of solid content is not beneficial to flocculation. Only moderate graininess of solid phase will be beneficial to the settlement of flocculation. Too small graininess is not favorable for flocculant to catch suspended particles, but too large graininess is not beneficial to the bonding and bridging functions of the long chain of flocculant. Therefore, it is important to control the time of reaction of brine, and tests should be further carried out to select better time for adding flocculant. Particularly, the quantitative test of graininess distribution for solid content is very important for the analysis of factors influencing the flocculation effect in brine purification.
3.5 Influence of Solid Phase
Concentration of Brine Suspension
on Flocculation Effect
The content of suspending particles in the suspension system (solid phase concentration) will affect the effect of flocculation. Excessively large solid content (>30%) will hinder the free settlement and excessively small solid content (<1%) will reduce the chance of collision of particles and influence the formation of flocculi. Therefore, in the process of brine purification, the times of slurry pumping and the quantity of slurry cleaning during shutdown should be carefully observed in order to find out empirical data to guide production.
3.6 Influence of Molecular Weight of Flocculant on Effect of Flocculation According to the principle of flocculant bridging, PH-PAM must have enough flexible molecular chain for bridging among particles. Its flocculating effect should increase with the increase of molecular weight. However, it is not the case. Excessively high molecular weight (M>1×107) and too high speed of flocculi coacervation will increase the velocity of sedimentation and result that fine particles suspend at the upper part of the supernatant liquor. A layer of flocculating film formed on the surface of these fine residual particles, thus being in a stable state due to their excessively small particles and existing in the suspension system of brine so as to lead to poor light transmittance. Therefore, it is very important to master the particle range of suspended grains of brine for the correct selection of the molecular weight of flocculant.
3.7 Influence of Agitating Time and Intensity on of Flocculation Effect
PH-PAM mainly depends on the absorption between amido and suspended particle, in which the linkage energy is only dozens of kcal/mol with weak force. Therefore, the strength of mechanical agitation should be moderate. Otherwise, the flocculi will be easy to become broken by agitation and influence the flocculation effect. Because PH-PAM acts with suspended particles in a very fast way, the time for agitation should not be too long to eliminate the breaking of
the flocculi and depress the influence on the clarification effect of brine.
3.8 In the suspension system of brine, the excessively high concentration of brine will lead to the increase of the content of Na+. However, the -COONa- in PH-PAM dissociates into -COO- and equilibrium movement of Na+ will be affected, thus reducing the linkage efficiency of effective functional group and influencing the effect of flocculation. In addition, the increase of the content and density of brine will result in the increase of the buoyancy of suspended particles in the system and the decrease of the settlement velocity so as to influence the sedimentation effect.
4. CONCLUSION
There are many factors influencing the flocculation effect in the brine purification. In addition, some factors come from the preparation of flocculants, dosage, etc. Special analysis is required for particular conditions. For the above-mentioned factors, several factors may work together and sometimes only one factor independently plays its role in such influence. For such conditions, comprehensive analysis should be made to eliminate factors of interference and treat problems with a definite purpose in mind. Of course, it is very important to collect primary data; hence the analysis can be carried out well. Judgment should be made through certain experimental means and empirical data to finally find out critical factors and existing problems so as to timely solve the problems and ensure the smooth implementation of production. References
1.Chunmei Wan, Xiaolin Hu, Zhongxiu
Zhang. Industrial Water & Waste Water, V ol. 3, No.1, 2002, 33-35.
2.Chuyang Xu, Hui Luo, Rongchun Nie,
Zhenqi Li. Colliery Engineering. V ol. 23, No.1, Jan. 2004, 63-65.
3.Hong Zheng. Several Factors
Influencing Flocculating Effect of PAM in Wastewater Treatment. [J] Qinghai Environment. 2002, (12)：68-69.
_________________________
About the Author
Xun Chun (1972~), male, born in Qujing, Yunnan, graduated from the Perfume & Essence Faculty, Chemical Engineering Department of Shanghai Light Industry College. He is now working for Yunnan Salt & Chemical Industry Co.,Ltd. as deputy manager, engineer, mainly undertaking administrative work of production, quality and standardization. Add: 10 Shijiaxiang, Tuodong Road, Kunming Postal Code: 650011
Tel:86-871-3120848
Fax: 86 871 3163767
11。