REMEDIATION PRACTICE OF HEXAVALENT CHROMIUM AND CYANIDE CONTAMINATED SOIL AT THE ORIGINAL SITE OF A MACHINERY PLANT IN ZHANGJIAKOU,CHINA

The electroplating wastewater generated during the electroplating process of the machinery factory will cause soil hexavalent chromium and cyanide pollution. Relying on the long-term use of the electroplating process of contaminated site remediation projects, the remediation target and the amount of work were determined through the preliminary site environmental investigation and risk assessment results, and the site soil pollution degree and pollution scope analysis; synthesis of site features and pollution characteristics, conduction of remediation technology screening determined that chemical oxidation, chemical reduction and solidification or stabilization was the core remediation technology for the project. The optimal composition and appending proportion of repairing agents were obtained by conducting small-scale and pilot-scale experiments, and used to implement the project. The results showed that after the chemical oxidation, chemical reduction and solidification or stabilization processing procedure of the hexavalent chromium and cyanide compound contaminated soil, the maximum exceeded concentration was reduced from the original 37.3, 186.0 mg/kg to below the corresponding standard limits of 3.0, 22 mg/kg, respectively; the leaching concentration of hexavalent chromium was lower than 0.5 mg/L, meeting the remediation requirements. The successful practice of the remediation project could provide reference for the design and implementation of remediation projects of other compound contaminated sites.