Simultaneous Stabilization of As, Zn, Pb and Cd in Lead Slag by Pyrolysis Residue of Oily Sludge

To address the problem of heavy metal contamination of lead smelting slag such as As, Zn, Pb and Cd in the Sishuizhuang area of Gejiu City, Yunnan Province, oily sludge pyrolysis residue was used to stabilize them to reduce the leaching toxicity of these heavy metals. The pyrolysis residue is a carbonaceous composite containing a large amount of nano-FeS, Fe_1-xS, CaS, etc., which has the potential to stabilize the heavy metals in lead slag. It was shown that heavy metals As, Zn, Pb and Cd in lead slag could be efficiently and synchronously adsorbed on the surface of pyrolysis residue, reducing the leaching toxicity of these heavy metals in lead slag. When the weight ratio of pyrolysis residueis is 4% and liquid-solid ratio is 10:100, the leaching concentrations of As, Zn, Pb and Cd in the lead slag can be reduced from 0.7202, 3.5120, 0.3800 and 0.0456 mg/L to 0.0714, 0.1668, 0.0262 and 0.0038 mg/L, respectively, which are lower than the surface water environmental quality standards (GB 3838—2002 ) in the Ⅳ level limit value. The reduction of leaching concentration of As, Zn, Pb and Cd in lead slag is due to the reaction of As in lead slag with Ca²⁺ and Fe²⁺ on the surface of pyrolysis slag to produce stable calcium arsenate and ferrous arsenate in situ, and the reaction of Zn²⁺, Pb²⁺ and Cd²⁺ in lead slag with S^2- on the surface of pyrolysis slag to produce stable ZnS, PbS and CdS in situ, which improves the stability of As, Zn, Pb and Cd in lead slag.