[Effect of Butyl Xanthate on Pb²⁺ and Cd²⁺ Adsorption by Soil Around a Dressing Plant]

Flotation agents can enter the soil and water environment around mining areas through beneficiation wastewater discharge and overflow from tailings ponds. The adsorption of Pb²⁺ and Cd²⁺ on soil around a lead-zinc dressing plant was investigated in the presence of potassium butyl xanthate (PBX). Batch experiments were conducted with different initial pH, PBX, Pb²⁺, and Cd²⁺solution concentrations. The fractions of lead and cadmium were altered after treatment with different concentrations of PBX. The results showed that adsorption of Pb²⁺and Cd²⁺ on soil was seriously inhibited by PBX. When PBX concentration was 40 mg·L^-1, the adsorption capacity of Pb²⁺ and Cd²⁺ decreased from 3540 mg·kg^-1 and 387 mg·kg^-1 to 3085 mg·kg^-1 and 100 mg·kg^-1, respectively. The Pb²⁺ and Cd²⁺ adsorption kinetic process was best fitted by the quasi-second-order kinetic model, which indicated that the adsorption process of Pb²⁺ and Cd²⁺ on soil was mainly chemical adsorption. The formation of a hydrophobic and insoluble complex and competitive adsorption between PBX, Pb²⁺, and Cd²⁺ on the soil surface was the main reason for reducing the adsorption capacity. The results showed that PBX could increase the mobility of Pb²⁺ and Cd²⁺ on soil. The degree of impact improved with increasing initial concentration of PBX and pH but decreased with increasing initial concentration of Pb²⁺ and Cd²⁺, and the adsorption isotherms conformed to the Freundlich isotherm. Under low PBX content (100 mg·kg^-1), exchangeable and reducible cadmium contents in the soil increased, which could lead to the activation of cadmium in soil. However, the addition of PBX to the treated soil could reduce the content of exchangeable and reducible lead. As the concentration of PBX increased, the reduction effect also increased, which was related to the stronger complex stability of Pb(C₄H₉OCS₂)₂ than that of Cd(C₄H₉OCS₂)₂. The results showed that residual flotation reagents in beneficiation wastewater may increase the potential ecological risk of heavy metals such as Pb and Cd in soil, and the prevention and control of the potential ecological risk should be strengthened.