The fate of the sulfide ion in galena leaching with neutral citrate media

Lead recovery from sulfides is traditionally associated with pyrometallurgical processes that involve elevated capital costs and the generation of harmful gases that, if not adequately treated, can cause severe environmental damage. For this reason, alternative methods are needed for lead recovery from this type of mineral. A hydrometallurgical approach could permit the use of environmentally friendly organic reagents, citrate in this case, to leach lead from galena in neutral media. The effects of pH, the mineral/solution ratio, and the hydrogen peroxide concentration as an oxidant in lead leaching at room temperature were studied. The results show that, at low citrate to lead ratios (similar to 2) and a H2O2/Pb ratio between 2.3 and 2.5, complete lead dissolution is possible, due to the formation of soluble sulfur oxyanion species (S4O62-, SO32-, S2O32-) in the near-neutral solutions. The proposed system limits the irreversible oxidation of sulfur species, liberated during galena leaching, to the sulfate ion (SO42-), which decreases the solubility of lead in solution.