不锈钢电极对重金属污染土壤的强化电动修复及电极腐蚀结晶现象与机制

电极腐蚀和盐分结晶是制约土壤电动修复技术工程化应用的重要难题.本研究选择不锈钢作为电极,采用去离子水(DW)、柠檬酸(CA)和聚天冬氨酸(PASP)作为电解液,对Pb、Cu污染土壤进行强化电动修复,考察了重金属去除作用及影响因素,探讨了电极腐蚀和盐分结晶现象与机制.结果表明,在电场作用下,土壤中的Ca会迁向阴极在碱性条件下形成CaCO_3和Ca(OH)_2晶体,降低了电极的导电性;PASP对不锈钢电极有明显的缓蚀作用,CA和PASP都能明显地破坏CaCO_3晶体的形成,但无法对Ca(OH)_2晶体形成有效的破坏;CA和PASP都能促进土壤中Pb的去除,但PASP对Cu去除强化作用不明显,而CA对Cu的去除强化作用非常显著;不锈钢配合不同的缓蚀剂、增强剂联合使用,可以作为电动修复技术工程化应用的电极选择.

Enhanced Electrokinetic Remediation of Heavy Metals Contaminated Soils by Stainless Steel Electrodes as well as the Phenomenon and Mechanism of Electrode Corrosion and Crystallization

Electrode corrosion and salt crystallization are important challenges that restrict the engineering application of electrokinetic technology. In the present study, using stainless steel as an electrode, and deionized water (DW), citric acid (CA) and polyaspartic acid (PASP) as electrolytes, Pb/Cu-contaminated soil was remediated by electrokinetic. All of the EK experiments were conducted in a 2 L soil cell reactor with a moisture level of about 35% blended with 1000 mg·g^-1 of Pb and 778 mg·g^-1 of Cu under a constant voltage gradient (1 V·cm^-1, 2 V·cm^-1) for 150 h. The removal efficiency of heavy metals and influencing factors, as well as the phenomenon and mechanism of electrode corrosion and salt crystallization were explored. The experimental results showed under the action of electric field, the Ca in the test soil would move to the cathode, and the crystal was formed in the alkaline condition. Additionally, the conductivity of the electrode was reduced. During the EK process, water at the anode was primarily oxidized, undergoing a reduction reaction at the cathode. Because H⁺ and OH^- were transported through the soil by electromigration and electro-osmotic flow (EOF), changes in soil pH could occur. The concentrations distribution of Pb-Cu appeared to be related to the distribution of soil pH in the cell, which might be associated with the desorption and hydroxide precipitation of Pb-Cu. PASP resulted in obvious inhibitory effect on the corrosion of stainless steel electrode, CA and PASP could clearly destroy the formation of CaCO₃ crystal, while barely effectively disrupted the formation of Ca (OH)₂ crystal. Both CA and PASP could promote the removal of Pb, but the influence of PASP on the removal of Cu was not obvious, and the effect of CA was very significant. Combined with different corrosion inhibitor and reinforcing agent, stainless steel can be chosen as the engineering application electrode in electrokinetic remediation.