Immobilization of Cu(II) and Zn(II) in simulated polluted soil using sulfurizing agent

• Immobilization effects of DDTCNa and Na2S on Cu(II) and Zn(II) in contaminated soil were investigated.
• Effect of leaching pH on stability of immobilized heavy metals was discussed.
• Immobilization mechanism of DDTCNa and Na2S on Cu(II) and Zn(II) were studied.

Potential immobilization of Cu(II) and Zn(II) in soil by using sodium sulfide (Na2S) and sodium diethyl dithiocarbamate (DDTCNa) were investigated in terms of immobilizing agent dosage and leaching pH by column leaching tests. The formation of metal sulfide products and the immobilization mechanism were systematically studied by XRD measurements and chemical equilibrium analysis. Leaching test results indicated that great reduction rate of heavy metals in polluted soil was obtained when sulfuring agent was used as immobilizing agent. Especially, DDTCNa showed better immobilization effect on heavy metals than Na2S. With the increase of immobilizing agent dosage, heavy metal concentrations in leachate decreased. When immobilizing agent dosage was higher than 45 g kg−1, the reduction rate of Cu(II) and Zn(II) enhanced slightly. Immobilization of Cu(II) and Zn(II) was strongly dependent on leaching pH. The optimal immobilization effects on Cu(II) and Zn(II) were obtained in alkaline and neutral pH range for Na2S and DDTCNa, respectively. XRD measurements and chemical equilibrium analysis indicated that Na2S and DDTCNa could immobilize heavy metals by the formation of metal sulfide precipitates.