Humic acid is extracted from the municipal sludge of Zhengyang Sewage Treatment Plant in Jinzhong city,Shanxi province,China,and used to leach the Pb-Cr compound contaminated soil collected from a smelting plant in Yunnan province and a mining area in Hubei province,respectively.The effects of the mass ratio of soil to humic acid at 1∶10,1∶20,and 1∶30,respectively on the removal of lead and chromium from the contaminated soil are studied.The humic acid extracted from the sludge is characterized by means of SEM and FT-IR,and the contents,distribution forms and enzyme activities of heavy metals in the soil before and after leaching are measured by means of ICP-MS and UV spectrophotometer.Results show that the sludge-derived humic acid can reduce the available content of heavy metals in the soil,the removal effect of Pb in red soil reaches the best when the ratio of soil to humic acid is 1∶20,and that in black soil reaches the best when the ratio is 1∶30.The removal effect of humic acid on Cr in red soil and black soil increases with the increasing ratio of humic acid to soil.This is because humic acid contains a large number of functional groups,which can provide active sites for heavy metal complexation reaction,thus reducing the content of heavy metals in soil.
humic acidelutingCrPbspeciation distribution of heavy metals
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