硫铁矿对Cr(Ⅵ)污染土壤的长效还原稳定化研究

针对酸溶态占比高的Cr(Ⅵ)污染土壤还原解毒不彻底、后期易返黄的问题,确定了水溶态Cr(Ⅵ)快速还原、酸溶态Cr(Ⅵ)长效缓释还原的修复思路。试验考察了单独添加硫铁矿对Cr(Ⅵ)处理的效果,并采用Fe SO4·7H2O、硫铁矿分步还原法探究处理后污染土壤的长效稳定性,进行了540 d的长期监测。结果表明:Fe SO4·7H2O还原药剂长效性较差,在自然环境中容易发生氧化,失去还原效能,无法完全还原缓慢释放的酸溶态Cr(Ⅵ),有必要加入长效还原缓释药剂对酸溶态Cr(Ⅵ)进行持续还原。硫铁矿单独修复水溶态Cr(Ⅵ)为主的污染土壤,在添加20%的硫铁矿,反应14 d的条件下,土壤中Cr(Ⅵ)浸出浓度降至30. 4 mg/L。采用Fe SO4·7H2O和硫铁矿分步还原酸溶态Cr(Ⅵ)污染土壤,先加入2%的Fe SO4·7H2O,养护3 d后再加入3%的硫铁矿反应27 d,Cr(Ⅵ)浸出浓度即降至0. 29 mg/L,加入5%的硫铁矿,反应4 d后Cr(Ⅵ)浸出浓度即可降至0. 43 mg/L,之后Cr(Ⅵ)浸出浓度保持稳定。经过540 d的长期监测未发现浸出浓度有上升情况。

LONG-TERM REDUCTION STABILIZATION OF HEXAVALENT CHROMIUM CONTAMINATED SOIL BY PYRITE

In order to solve the problems of hexavalent chromium contaminated soil with a high proportion of acid-soluble, incomplete reduction and detoxification, and easy recovery in the later period, remediation idea of water-soluble hexavalent chromium rapid reduction and acid-soluble hexavalent chromium long-term reduction was determined. The experiments were designed to investigate the effect of adding pyrite alone to the treatment of hexavalent chromium, and explored the long-term stability of contaminated soil by step reduction of using ferrous sulfate and pyrite, and a 540-day long-term monitoring was carried out. The results showed:FeSO₄·7H₂O reducing agent was prone to oxidation in the natural environment and loosed its reducing power, leading to its poor long-term performance, and inability to fully reduce slow-release acid-soluble hexavalent chromium. It was necessary to add a long-acting reduction slow-release agent to continuously reduce acid-soluble hexavalent chromium. Pyrite alone could remediate water-soluble hexavalent chromium-contaminated soil, the leaching concentration of hexavalent chromium in soil decreased to 30.4 mg/L in the mixing of 20% pyrite, 14 days of reaction. Using ferrous sulfate and pyrite to reduce the hexavalent chromium contaminated soil mainly in acid soluble state: add 2% ferrous sulfate curing for 3 days and then add 3% pyrite for 27 days, the leaching concentration of hexavalent chromium droped to 0.29 mg/L; adding 5% pyrite, the leaching concentration of hexavalent chromium could be reduced to 0.43 mg/L after 4 days of reaction, after which the leaching concentration of hexavalent chromium remained stable. According to 540 days of long-term monitoring data, the leaching concentration did not rise.