EK/PRB修复砷污染土壤影响因素及机理

Influencing Factors and Mechanism of Arsenic Removal from Soil by Electrokinetic Process Coupled with Permeable Reaction Barrier

为明确EK/PRB(电动联合渗透反应格栅)修复As污染土壤过程中各因素的影响机理、提高As的去除效率,以As污染高岭土为研究对象,考察PRB加入、PRB位置、pH调控及腐殖酸强化影响下,EK PRB系统中电流密度、土壤pH分布和土壤中As残余量、电渗透系数及电渗流的变化规律;探讨EK PRB修复后土壤中As形态的迁移转化规律.结果表明:①单独EK修复对土壤中As的去除效率较低,加入PRB后去除率为由42%增至57%,并且EK PRB修复可以将土壤中的As由不容易去除的可还原态转变成较容易去除的酸溶态.②采用盐酸调节阴极pH,可以将土壤中As的去除率由57%增至63%,但同时能耗也明显升高,由5.22 kW·h g升至39.38 kW·h/ g.③添加腐殖酸会促进土壤中As的迁移、提高As的去除效率,但也会增加土壤中难处理的可氧化态和残渣态As的占比.研究显示,EK PRB除As过程中以PRB的去除作用为主,阴极pH调控及腐殖酸强化均可以提高土壤中As的去除率.

Arsenic contamination caused by anthropogenic activities in soil and groundwater has created a strong legacy throughout the environment.Conventional off-site remediation technologies of soil replacement,solidification stabilization,and acid washing have been used to remediate As-contaminated soils,which were unsuccessful due to high labor and operating costs of the ex-situ technologies.Consequently,there is a need for an in-situ effective technique to remediate arsenic contamination that seriously impacts the subsurface environment.Hence,an innovative electrokinetic process coupled with permeable reaction barrier(PRB)of zero-valent iron was proposed for arsenic removal from soil.Batch tests were conducted to evaluate the variation of current density,soil pH,residual soil arsenic,electroosmosis coefficient and electroosmotic flow under the influence of PRB installed,electrode liquid pH control and humic acid reinforcement.Especially the migration and transformation of arsenic in soil after the remediation were discussed.The results showed that removal efficiency of arsenic was increased from 42%to 57%,and the arsenic were transformed from strong binding form,reducible to weak binding form,acid soluble,which was enhanced by a PRB system that was installed in an electrokinetic system.In the EK PRB process,arsenic removal was dominated by the PRB adsorption.The removal efficiency of arsenic could be increased from 57%to 63%but the energy consumption was obviously increased from 5.22 kW·h /g to 39.38 kW·h/ g when the pH of the cathode electrode was controlled by hydrochloric acid.The addition of humic acid could promote the migration of arsenic in soil and significantly increase arsenic removal efficiency,simultaneously the oxidizable and residual arsenic with strong binding forms were increased.The results revealed that the PRB played a dominated role in the remediation process of EK /PRB,and both the regulation of cathode pH and the enhancement of humic acid could improve the removal efficency of As.