Immobilization of Pb, Cu and Zn in contaminated soil using ball milling technique

Soil contamination caused by heavy metals has gained widespread attention from both government and public. In the present research, ball milling was utilized to remediate soil contaminated by Pb, Cu, and Zn and the influence of milling time on immobilization effectiveness was also investigated. The effectiveness of immobilization was evaluated by analyzing the leachable fraction of heavy metals from the ball-milled soil. When the milling time was 2 h, Pb, Cu, and Zn leaching concentrations decreased from 13.92 mg·L^-1, 2.83 mg·L^-1, and 114.42 mg·L^-1 to 0.027 mg·L^-1, 0.59 mg·L^-1, and 0.16 mg·L^-1, respectively; these values were all lower than the surface water Class III standard regulatory thresholds proposed by the Chinese Ministry of Ecology and Environment. Furthermore, the leaching characteristics of Pb, Cu, and Zn were investigated through pH-dependent tests and those results indicated that mechanical treatment improved the anti-acid ability of soil. In addition, the BCR sequential extraction procedure revealed that speciation shiftsof heavy metals are the root cause for the reduction of leaching concentrations; after ball milling of 4 h, the primary components of Pb, Cu and Zn in the soil were relatively stable (F₂ + F₃) and residual fraction (F₄), which accounted for 76.75%, 67.06% and 48.05% of total Pb, Cu and Zn, respectively.