Study On Soil Chemical Remediation Technology Of Chromium Contaminated Sites

Remediation of soils contaminated by heavy metals is one of the focuses in the present.On the basis of the investigation of soil pollution in a chromium contaminated site,the study of reduction of Cr in chromium contaminated soil with chemical leaching method and reduetion-solidification/stabilization method was carried out and the soil remediation plan of chromium contaminated site was established,which could provide technical reference for its application in practical engineering.The main results are as follows.1)According to the relevant national standards and norms,the status of site contamination was investigated and evaluated for the Cr production characteristics and the workshop distribution of the contaminated site.The results showed that the highest total chromium concentrations and hexavalent chromium concentrations of the soil in the chromium contaminated sites was 69500 mg/kg and 68300 mg/kg,respectively.Based on the pollution status of different sites,chromium contaminated soils of high and low concentrations were remediated by chemical leaching method and reduetion-solidification/stabilization method for removing chromium,respectively.2)The results of high concentrations of chromium contaminated soil chemical leaching experiment showed that citric acid was selected as the best leaching eluent.The optimum leaching conditions of citric acid was 4h of washing time,0.50mol/L of citric acid concentration,2.0 of p H value,and 1:10 of the solid-liquid ratio.Under this conditions,hexavalent chromium and total chromium removal rate reached 100% and 93.03%,respectively,after being washed four times.And the total chromium residual concentration in soil reduced from 2630.0mg/kg to 183.4mg/kg.3)The results of low concentrations of chromium contaminated soil reduetion-solidification/stabilization showed that ferrous ammonium sulfate and cement was the best reducing agent and curing agent,respectively,of which the best addition amount was 5% and 10%,respectively.Hexavalent chromium and total chromium in chromium contaminated soil leaching solution were 1.65mg/L and 4.02mg/L,respectively,which below the leaching concentration limits of hexavalent chromium and total chromium(2.50mg/L and 12.00mg/L)of the "Hazardous waste landfill pollution control standards"(GB 18598-2001).4)According to the present situation of chromium contaminated sites and the experimental results of chromium removal of soils,and combining the relevant national standards and norms,a remediation technology for the chromium contaminated soil was formulated.Total volume of contaminated soil in the field was 46215m~3.The volume of the high concentrations of chromium contaminated soil in three main regions of chromium slag yard,leaching workshop and transformation workshop,was 18685m~3,which could be remediated by chemical leaching treatment remediation.And the treated soil with the six main low concentrations of chromium contaminated soil regions of the office,raw material stack,circulating pool,broken workshop,drains and construction waste,which could be remediated by reduetion-solidification/stabilization treatment remediation.The total investment and the processing cost of restoration project were calculated to RMB 29,060,500 and 628.81 RMB/m~3,respectively.