阴极电解液对Cd污染红壤电动修复的影响

摘要

Increasing pH in the cathode electrolysis room during electrokinetic remediation has a detrimental effect on the removal of heavy metals.To resolve this problem,the effects of different cathode electrolytes (ferric nitrate,copper sulfate and citric acid) were systematically studied on the electrokinetic remediation of Cd-contaminated red soil based on the higher standard electrode potentials of Fe3+/Fe2+ and Cu2+/Cu.The experimental results indicated that after ten days of electrokinetic remediation with ferric nitrate,copper sulfate and citric acid,whose pH were all kept at 2-3,the removal efficiency of Cd in soil was above 87.27％ by adding ferric nitrate into the cathode.In addition,w(Cd) in soil decreased from 75.95 mg/kg around the cathode to 9.13 mg/kg around the anode.The removal efficiencies of Cd in soil decreased when adding copper sulfate and citric acid into the cathode.The addition of Cu2+ increased the risk of heavy metal pollution in the soil.In addition,the proportion of weak acid extractable Cd in the soil increased to a maximum of 92.69％ from the initial value of 74.57％ by adding ferric nitrate,which promoted the migration of Cd in the soil.The research suggests that when adding the ferric nitrate solution as the cathode,the pH of the cathode electrolysis chamber was controlled,and the desorption and migration of Cd in soil was significantly promoted.Eventually,the removal efficiency of Cd in soil was more significant.%针对土壤重金属电动修复过程中阴极电解室pH升高会对重金属的去除产生不利影响的问题,利用Fe3+/Fe2、Cu2+/Cu标准电极电位较高的优势,以人工模拟Cd污染红壤为研究对象,对不同阴极电解液[Fe(NO3)3、CuSO4柠檬酸]的电动修复效果进行系统分析.结果表明:分别将Fe(NO3)3、CuSO4、柠檬酸加入阴极电解室中,pH均控制在2～3,电动修复10 d后发现,将Fe(NO3)3溶液、CuSO4溶液和柠檬酸作为阴极电解液均可以有效控制阴极室的pH,CuSO4溶液、柠檬酸的加入对土壤中Cd的去除效果较差,而且Cu2的加入增加了土壤重金属二次污染的风险.相对于CuSO4、柠檬酸试验组,Fe(NO3)3试验组土壤中Cd的去除率较高(大于87.27％),Fe(NO3)3试验组对土壤中Cd的修复效果也最为明显,土壤中w(Cd)由阴极附近的75.95 mg/kg降至阳极附近的9.13 mg/kg.分析电动修复后各试验组中不同形态Cd在Cd总量中所占比例的分析,结果显示,w(弱酸提取态Cd)所占比例由初始的74.57％最高可达到92.69％[Fe(NO3)3试验组],表明Fe(NO3)3的加入有助于促进土壤中Cd的迁移.研究显示,相比于CuSO4溶液、柠檬酸,Fe(NO3)3溶液作为阴极电解液在控制阴极电解室pH升高的前提下,显著促进了土壤中Cd的解吸和迁移,并达到最佳修复效果.