Assessment of leaching response and recovery enhancement factors of a gold refractory ore

Abstract

This research aimed to assess the leaching response and recovery enhancements on pyrite refractory gold ores from North Mara Gold Mine in Tanzania. Gold is found in a variety of geological settings and can occur in both its native, pure state and as part of other minerals. It is most found in quartz veins, typically formed by hydrothermal fluids, and in placer deposits, which are concentrations of heavy minerals eroded from source rocks and transported by water. Enhancing gold leaching involves optimizing various factors to increase gold dissolution rates and overall recovery. Key strategies include improving reagent efficiency, optimizing leaching conditions (like grind size, pH, cyanide level, temperature, and oxygen levels), and implementing pre-treatment methods to expose gold more effectively to the leach solution. Based on the grinding establishment results, a four-point milling curve showed that the optimal milling time for P80 <75 µm and P80 <150 µm was 18.4 and 9 min, respectively. The gravity test work conducted via Knelson concentrator for the P80 <150 µm grind showed that the decrease in pulp density from 38% to 25% resulted in an increase in the gravity concentrate mass pull from 121.65g to 126.14g indicating that at lower pulp density the gold bearing particles migrate much easier to the concentrate slots. Lower pulp density resulted in higher gold concentrate mass pull and higher concentrate grades in a Knelson concentrator. A grind of P80 <150 µm showed the best leaching results indicating that it is the optimum grind for effective liberation for the ore under investigation. An increase in the cyanide concentration from 0.023 - 0.025% to 0.030 - 0.035% resulted in a decrease in the gold recovery, indicating that higher leaching agent concentration does not necessarily increase the recovery considering the cyanide concentration range tested. Increase in dissolved oxygen (DO) from the range of 10-15 ppm to 15-20 ppm resulted in an increase in gold recovery, however, further increase in DO beyond 15-20 ppm led to approximately 30% decrease in gold recovery efficiency.