Remediation Of Heavy Metal-contaminated Soil Using Organic Acid Washing And Solidification/Stabilization

The remediation of heavy-metal contaminated soil receives much more concern. In-situ washing remediation technology has advantages of simple conduction, efficient, and less cost, which has a potential in soil remediation. Solidification/stabilization remediation technology is also a popular soil remediation technology at present in our country. In this study, copper, nickel, chromium contaminated soil were washed by organic acids, and suitable washing reagents, concentration of washing reagent, washing volume, washing mode were tested in the washing experiment. Furthermore, suitable curing agent and stabilizer, optimizing remediation conditions were tested in the solidification/stabilization experiment. The results obtained are as follows:(1) Compared with different washing efficiency of four kinds of organic acid, citric acid and tartaric acid were the better washing reagents. After the washing conditions experiment, we found that 5 soil pore volume of 0.6 mol/L tartaric acid in intermittent washing gave the higher removal, in which conditions the removal of Cu, Ni and Cr could reach 92.12%,95.73% and 52.03%, respectively. In addition, the analysis for the existing forms of heavy metals in contaminated soil before and after washing showed that the removal of five existing forms of heavy metals was influenced by two factors, one was the initial content of the existing forms in the soil, the other was the properties of the existing forms. Finally, Copper, nickel, chromium in soil after washing were mainly existed as residual forms, which account for 71.77%, 61.48% and 82.07% of the total respectively. Therefore, the washing greatly reduced the migration ability and biological availability of three kinds of heavy metals.(2) The results of solidification/stabilization experiment showed that ferrous sulfate and cement were ideal reducing agent and curing agent respectively. Considering the economic and efficiency factors, the best addition amount of ferrous sulfate was 3 times of theory demand, and the best addition amount of cement was 10% of dry sludge quantity. After the orthogonal experiments, we found that cement in the solidification/stabilization remediation played a leading role, while ferrous sulfate had little effect on the remediation. At the same time, the concentration of hexavalent chromium and total chromium in sludge leaching solution after treatment of 10% of cement addition (dry sludge quantity) could meet to "landfill pollution control standard" (GB16889-2008). Considering the mixed intensity in the practical engineering, the addition of 15%～20% (calculated by dry matter of sludge) of cement to the contaminated sludge was suggested.