Selective removal of zinc, lead, and arsenic from zinc production sludge via roasting and room-temperature leaching

Abstract

Hydrometallurgical zinc production generates large quantities of iron-rich sludges that pose a hazardous waste challenge due to their heavy metal content. This study presents a method for the selective removal of heavy metals from jarosite-type sludge through optimized roasting followed by a three-step leaching process using water, sodium chloride solution, and sodium hydroxide solution, at ambient conditions. Nearly 100% of zinc was selectively extracted by water leaching (L/S = 10, 1 h) after roasting at 700 °C for 1 h, while iron remained in the solid residue. Subsequently, ∼85% of lead was removed using sodium chloride solution (300 g/L NaCl, L/S = 10, 2 h), followed by >90% extraction of arsenic and residual lead via alkaline leaching (2 M NaOH, L/S = 10, 4 h), resulting in >98% total lead removal. The final solid residue contained 55 wt% iron, with the total heavy metal content reduced to below 1 wt%. Small-scale batch leaching experiments were validated by a continuous five-month column leaching experiment, which demonstrated comparable efficiency and selectivity for the removal of zinc, lead, and arsenic, while cumulative iron leaching remained as low as 0.06%. A 24-h batch leaching (shaking) test of the final residue showed a significant reduction in the leachability of cadmium, copper, nickel, lead, and zinc compared to the initial sludge to below their legal limit values for classification as hazardous waste. By enabling the recovery of valuable metals (zinc, lead) and a critical raw material (arsenic), this approach reduces the amount of hazardous waste and transforms a hazardous industrial residue into a potential secondary resource for the ironmaking industry and/or construction industry.