活性炭电吸附处理水中氯仿的研究

【作者】 郭亚萍；

【导师】 袁星； 全燮；

【作者基本信息】 东北师范大学 ， 环境科学， 2002， 硕士

【摘要】 氯仿为可疑性致癌物，国内外自来水中均检测到以氯仿为主的三卤甲烷的存在。有研究表明此物质的来源是饮用水氯化消毒后，腐殖质与含氯物质反应生成。由于氯仿等对饮用水、人体的危害很大，各国对其很为重视，美国EPA把氯仿划入优先控制污染物一列。 卤代烃的处理方法是研究热点，对水中三氯甲烷最有效的处理是活性炭吸附。但常规的活性炭处理成本高，需再生。若能人为地提高活性炭吸附力，则可有效地去除水中氯仿，并推广活性炭的应用。 本论文用电化学方法，从吸附动力学与吸附热力学这两方面考查了外加电场对活性炭吸附水中氯仿的影响。并进行了机理分析。 实验用恒电位仪作控制电源，调节工作电极电位（相对于参比电极电位）来控制加在活性炭上的电场，用顶空进样法测定水中氯仿的剩余浓度，参照方法与依据都是国家标准方法或国外先进方法。 实验结果表明：在实验所加电场范围中，活性炭量与所加的电位之间存在一定的关系，从-500mV，-300mV，-100mV，0mV，100mV，300mV到500mV，活性炭吸附量随之逐渐提高，吸附速度加快，即阳极极化有利于活性炭吸附量提高，阴极极化则对活性炭吸附起抑制作用。本研究中，活性炭在电场下吸附量与其平衡浓度之间的关系符合Freundlich方程Q=kC^1/n，其中n=1，显示线性吸附特征。吸附等温方程中的系数k与控制电位V相关，其相关关系为k=0.001V+0.92。 文章对所得结果进行了机理分析与探讨。吸附剂和吸附质的性质是影响水溶液中吸附的主要因素。从电化学角度分析，活性炭是导电颗粒，覆盖在工作电极表面的活性炭相当于工作电极的扩展，在通电条件下表面电荷过载；从吸附质的性质分析，氯仿为弱极性分子。用MOPAC2000软件中的PM3计算法计算氯仿分子的结构与表面净电荷分布可知：氯仿分子的结构呈四面体。因此，工作电极上活性炭对氯仿的最终吸附量是吸附与电荷作用力的共同作用结果。阳极极化时，活性炭表面带正电荷，吸附点增加，吸附量与吸附速率提高；相反，阴极极化则活性炭表面的负电荷与氯仿异性相斥，吸附量减小。另外，氯仿的电解氧化还原电位大于500mV，因此，此电场范围不会分解氯仿，回收率实验与色谱分析也证明了电场只对活性炭的吸附起催化作用，而不改变吸附剂与吸附质的内部性质。更多还原

【Abstract】 THMs, mostly chloroform, are motored in drinking water in many countries including China, Japan, and America. Some researches indicated that THMs are carcinogen, and they resulted from the reaction of humus with chlorinate, which is from the drinking water being chlorinated. THMs must be preferentially removed for their carcinogen.Many people take in the researches on methods of removal such chemicals. Adsorption on activated carbon is a better and effective way for chloroform. However, the usual adsorption on activated carbon is costly and activated carbon need regenerated. If we can find a way to artificially enhance the adsorption of activated carbon, its benefits on economy and environment will be considerable.It is the aim of this work to investigate electrosorption of chloroform in water on granular activated carbon. The potentials on working electrode are controlled by potentiostat and the concentration of chloroform is measured by headspace gas chromatography. Adsorption isotherm and adsorption kinetics of granular activated carbon are measured in order to obtain specific information about the influence of the charge on the absorbability of chloroform. The influence of the bed potential on the adsorption equilibria shows a dependence on applied potential in electrolyte of approximately O.lmol/L ionic strength. With electrosorption from aqueous solution, 60% enhancement of the concentration in one controlled potential is achievable. The valve of PH is hardly changed during the process of electrosorption and adsorption. Potentials anodic to EPZC increase the amount adsorption and the rate of adsorption. However, potentials catholic to EPZC decrease the adsorption capacity of the granular activated carbon. That is to say, with the increase of controlled potentials from -SOOmV. -SOOmV, -lOOmV, OmV, lOQmV, 300mV,to SOOmV vs.Sat.RE, the amount adsorption and the rate of adsorption is increased.The fundamentals of electrosorption on granular activated carbon for water treatment are discussed. The configuration and net atomic charges of chloroform are calculated with PM3 calculation by MOPAC2000. On the whole, the surface charge of chloroform is negative. Thus, both the adsorption capacity of granular activated carbon and attractive or repulsive forces of charge influence the electrosorption of chloroform on granular activated carbon.The redox potentials of chloroform are more than 500mV and electrosorption is only controlled by electric field and adsorption of granular activated carbon. The tests of adsorptions also testify it. The Freundlich isotherm equation Q=KC n is used for fitting the data. Here, n=l. In all cases, the adsorption equilibria show a strong dependence on the applied potentials, K= 0.001V+0.92,K is the consistent of Freundlich isotherm equation; V is the controlled potentials WE vs. RE.更多还原