Abstract: Laboratory simulation tests were conducted to examine the effects of different washing reagents (distilled water, HCl, H₃PO₄, oxalic acid, and CaCl₂) in extracting the heavy metals from contaminated soils left by a chemical plant. The effects of reagent concentration, reaction time, and washing time on the washing efficiency were investigated, and the form variation of test heavy metals was determined before and after HCl washing. Distilled water, H₃PO₄, and CaCl₂ could remove less than 1% of most heavy metals, and the highest removal rate was only 3.58%; while 2 mol HCl·L^-1could obtain the highest washing efficiency under the optimal conditions, i.e., soil:liquid ratio was 1:3, reaction time was 1 hour, and the soils were washed twice by HCl solution. The removal rates of Cr, Pb, Zn, Cu, and Cd from test soils were 80.75%, 88.69%, 98.00%, 79.33%, and 95.52%, respectively. Among the washing reagents, HCl could effectively remove all forms of heavy metals.

Key words: washing, heavy metal, polluted soil, remediation, Kouhe River basin, water environmental capacity, ecological compensation, mechanism and policy.