Recovery of gold from copper-rich ores using ion exchange resins

Abstract

In this study, the treatment of a refractory copper-rich gold ore was investigated. Initial studies focused on the characterization of the refractory behaviour of the ore, which yielded only 18.4% extraction in direct cyanide leaching. Diagnostic leaching tests have shown that 70% of gold which were recovered at HCl +NaCN and HNO3 +NaCN stages were linked with different mineral phases such as sulfide minerals. Ultrafine grinding did not offer extractions to the desired extent, even when cyanide concentration was increased up to 8 g/L as it only enhanced gold recoveries by 36% (from 18% to 54%). Chemical pretreatment of the ore using acid leaching and roasting proved to be the best treatment route as it offered 96% of gold recovery. In this study, adsorption tests on pregnant leach solutions obtained from cyanide leaching of copper-rich gold ore were also investigated. Activated Carbon (GAC 1240 M-1448), strong base resin (Purogold A194) and medium base resin (Purogold S992) were used as adsorbents for gold recovery from cyanide leaching solutions of the ore. In these tests effects of adsorbent type, dosage, cyanide concentration, process type (CIP/CIL/RIL/RIP) were also investigated. The experimental results showed that adsorbent dosage and cyanide concentration are important parameters affecting the extent of gold adsorption and its selectivity. Increasing cyanide concentration remarkably improved the selectivity allowing high recoveries even at low activated carbon/resin dosages. The adsorption tests have also demonstrated that the activated carbon has higher gold loading capacity than Purogold A194 and Purogold S992. Each adsorbent offered good selectivity for gold over copper. Purogold S992 appeared to be the most selective adsorbent that barely loaded copper. This distinctive trait makes the resin preferable for gold recovery from cyanide liquors containing a significant amount of copper values.