Solidification/stabilization of heavy metals and its efficiency in lead-zinc tailings using different chemical agents

Lead-zinc tailings are generated during the mining process which is considered as hazardous solid waste due to its high heavy metal content and leachability in the natural state. At present, the most effective technology for disposing heavy metals in solid wastes is the solidification/stabilization (S/S) technique. In terms of S/S technology, chemical stabilization is one of the most potential and practical method. This paper aims to investigate the S/S property of four typical chemical agents (Na₂S, NaH₂PO₄, TMT and Na₂EDTA) on the heavy metals in lead-zinc tailings. The results reveal that the heavy metals lead and zinc in tailings are stabilized more effectively by using chelating agents TMT than by using inorganic chemical agents Na₂S and NaH₂PO₄. When the dosage of TMT reaches 4%, the leaching concentration of lead and zinc is 0.18 and 14.60 mg/L according to toxicity characteristic leaching procedure (TCLP), and the stabilization efficiency of lead and zinc is 99.31% and 80.92%, respectively, while the leaching concentration of lead and zinc just drops to 0.41 and 16.00 mg/L with addition of 10% NaH₂PO₄. Furthermore, the leaching concentration of heavy metal lead in tailings treated by 4% Na₂EDTA increases to 53.44 mg/L which far exceeds the standard of pollution control. Therefore, considering stabilization efficiency and dosage, TMT is the preferred agent for solidifying heavy metals in lead-zinc tailings.