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.