Mechanically enhanced leaching of selenium and mercury in acid sludge from lead-zinc smelting process

Acid sludge, a hazardous waste from lead (Pb)-zinc (Zn) smelting process, typically contains selenium (Se) and mercury (Hg), both of which have high economic value. Recovering these elements contributes to resource reuse and environmental pollution reduction. However, designing an efficient recovery process for Se and Hg is a key technical challenge in the disposal of Se/Hg-containing acid sludge. In this study, we proposed a highly efficient wet recovery method for Se and Hg, which involves mechanical ball milling pretreatment of acid sludge followed by an oxidizing acid leaching process. Through single-factor experiment and response surface methodology (RSM) optimization, the leaching efficiencies of 99.69 % for Se and 99.64 % for Hg within 11 min were achieved. The thermodynamics and kinetics of the leaching process were thoroughly investigated to elucidate the conversion mechanisms of Se and Hg and the rate-controlling step from chemical reaction. Notably, the mechanical pretreatment significantly enhanced the leaching efficiencies of Se and Hg in less time compared to direct leaching process, owing to the reduced particle size, more scattered distribution and decreased crystallinity. This research offers valuable insights into the efficient leaching of Se and Hg species from acid sludge, potentially addressing the issues of resource wastage and environmental pollution from large stockpiles of acid sludge.