| Summary: | This paper focus on how to treat the wastewater after soil washing since water pollution is a severe threat to the water security of China. Ca (OH)<sub>2</sub> and two kinds of biochars (biochar and ZnCl<sub>2</sub> modified biochar) were tested to treat the waste FeCl<sub>3</sub> washing effluent. Two kinds of biochars (biochar and ZnCl<sub>2</sub>-modified biochar) were prepared from maize straws. Soil samples were collected near a smelter for adsorption experiments. ICP-OES was used to determine the concentration of metal ions in the samples, as well as calculating their adsorption capacity and removal rate. As to Ca(OH)<sub>2</sub> treatment, the maximum removal rates of Cd, Pb, Cu, and Zn could exceed 99%, and the concentrations of Cd, Pb, Cu, and Zn in solution could reduce to 0.08, 0.018, 0.15, 0.44 mg/dm<sup>3</sup>, respectively. However, both of the two biochars had relatively low removal rates compared with Ca (OH)<sub>2</sub> treatment. The wastewater shows significantly lower environmental implications after the two treatments, and the lime precipitation method has better effects than biochar adsorption. The activated carbon adsorption method discussed can significantly improve the environmental pollution caused by soil washing wastewater, which is suitable for environmental treatment projects.
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