Abstract
A pretreatment to remove and recover base metals present in complex sulfide refractory ores is proposed as a method to improve the extraction of precious metals with thiourea. Sodium citrate solutions at pH 8 and 5 were employed to extract lead and iron, respectively, from two concentrates: one having silver in a primarily galena matrix and the other, with gold associated with pyrite. The pretreatment solutions, containing the base metals, were subjected to electrolysis and pH adjustment, before being recycled back to the pretreatment stage. The results showed that citrate pretreatment successfully extracted lead and some iron, liberating the precious metals for thiourea leaching. The citrate pretreatment solution could be reutilized, after base metal removal, decreasing the reagent and water requirements. In all cases, the citrate pretreatment improved precious metal extraction.
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