Production of zinc and lead concentrates from lean oxidized zinc ores by alkaline leaching followed by two-step precipitation using sulfides

An integrated hydrometallurgical process for the production of zinc and lead concentrates from lean oxidized zinc ores by alkaline leaching, followed by two-step sulfide precipitation of lead and zinc sulfides, is developed. The lean zinc oxidized ore was firstly ground to a size below 0.2 mm, followed by alkaline leaching at 90 °C for 120 min in NaOH solution, in which both zinc and lead are effectively extracted. Lead concentrates were then highly selectively and quantitatively produced from the leach solution by adding sodium sulfide as precipitant. Zinc concentrates were obtained in the same way from the Pb-free solution. Optimum conditions of lead precipitation were found to be 1.8 Na2S·9H2O/Pb weight ratio, 90 °C, 60 min and those for zinc precipitation were 2.4 Na2S·9H2O/Zn weight ratio, 90 °C, 180 min. Finally, a scale-up experiment was carried out and found that the lead and zinc total extraction both reached above 80% calculated from the ores and the quality of lead and zinc concentrates can meet industrial requirements for roasting processes. Meanwhile, it was found that the loss of NaOH is negligible and the main consumption of chemicals was that of sodium sulfide.