Preg-robbing verification and prevention in gold chloride-bromide leaching

The use of cyanide is becoming more challenging due to the related environmental risks, increasing the interest in cyanide-free gold leaching. Chloride-bromide leaching is one of the widely investigated alternative lixiviants for gold recovery. However, gold is known to adsorb or precipitate readily on the carbonaceous matter present in the ore, being one of the challenges in chloride process development. The current study presents an equation indicating gold loss due to preg-robbing into solids in chloride-bromide media. The equation was verified using a naturally preg-robbing gold concentrate. It was shown that the graphite naturally present in gold ore can be an equally active preg-robbing agent for gold chloride complex as industrially manufactured and commercially available activated carbon. In order to study preg-robbing prevention during gold leaching in chloride-bromide media, carbon blinding, and Cl₂-pretreatment were applied. Blinding with ShellSol D70 was shown to improve gold recovery only slightly whereas Cl₂-pretreatment was shown to increase gold recovery from 2% to 45% for a naturally preg-robbing gold concentrate.