Experimental Study On The Treatment Of Cd, Pb And Cr-polluted Soil With Lime And Fly Ash

Developed countries and areas ,such as Europe, America and Japan carried out the research and remediation on heavy-metal contaminated soil since the 20th century, 60 to 70 . During the several decades , a relatively perfect legal policy, management systems and technical support system ,which will provide a reference for the integrated soil management for China ,has been establishedWith the development of industry and agriculture, soil pollution problem has become increasingly acute in China,so soil remediation is in urgent need. In the past 10 years, research on soil remediation has gone through a rapid increase in China. Looking at the research literature, methods of soil remediation included plants, microorganisms, physical , chemical, electrical, as well as some joint and multi-channel technologys , in which an extensive and in-depth research about the phyto-remediation mechanism and technologys of heavy-metal contaminated soil , has been done respectively.Solidification stabilization technology has lots of advantages, such as low-cost, short time, ability to handle a wide range of complex metal waste, easy-to-use, etc, which is a very effective method of remediation of heavy-metal contaminated soil.This experiment simulated Cd, Pb,Cr-contaminated soil, adding lime, fly ash etc.,and the results of their leaching toxicity tests show that: Cd has strong ablity of migration , for which it is not easy to be adsorbed in soil particles.After adding 5% lime,the leaching concentration of Cd reduced 85.5 % and was 0.25mg/l,close to 0.15mg/l,which is admission standard of Cd in general industrial solid waste into municipal solid waste landfill ,(GB16889-2008,Standard for Pollution Control on the Landfill Site of Municipal Solid Waste).Pb has strong ability of retention in the soil. After adding 5% lime,the leaching concentration of Pb reduced 45.2%, and was 0.34mg/l,close to 0.25mg/l,which is admission standard of Pb in general industrial solid waste into municipal solid waste landfill ,(GB16889-2008,Standard for Pollution Control on the Landfill Site of Municipal Solid Waste). It is a good way to add a few lime to Cd or Pb- polluted soil for pre-treatment before the landfill disposal.Cr⁶⁺ has strong ability of retention in the soil. It is a good way to add a few fly ash to Cr- polluted soil for pretreatment before the landfill disposal.As for lime and fly ash,Lime is the main factor of solidification &stabilization of Cd.When the amount of lime is large, the increase of lime is propitious to reduce leaching of Pb, besides, having larger molecular weightis,Pb has strong ability of retention in the soil,so the combined impression is obvious.The adsorption of fly ash should be a major factor of solidification &stabilization of Cr⁶⁺.In Addtion, pH values of extraction solutions affect the leaching results of Cd, Pb greatly. Between in the extraction solution 1# (pH 4.93±0.05) and in the extraction solution 2# (pH 2.64±0.05) , the leaching concentration of Cd, Pd, Cr make differences respectively about 30⁴0 times, 20³0times,1.8³.5 times.In conclusion, ability of acid neutralization or pH values, as well as the chemical reaction product of solidification &stabilization material is a major factor on the impact of solidification &stabilization. It should be considered in solidification &stabilization methods,which includes the physical and chemical characteristics of heavy metals, the selection of the material for solidification &stabilization, reaction product of solidification &stabilization.