Investigation into the Effect of Ultra-Fine Grinding of Low-Grade Cyanide Tailings Pyrite Concentrate for the Recovery of Gold

This study investigates the influence of particle grind size on metal dissolution, with a specific focus on improving gold recovery from pyrite-bearing low-grade cyanide tailings. Gold often exists as fine inclusions within pyrite, making it complex to recover using conventional methods. To address this challenge, both ultra-finely milled and unmilled pyrite concentrates were experimented in a leaching solution containing 3 kg/ton of sodium cyanide. The leaching process was conducted under controlled conditions, with pH maintained above 9.5 using unslaked lime and atmospheric oxygen present to enhance the reaction environment. A pulp density of 1.45 kg/L was used during the 24-hour leaching test. Samples were collected at intervals of 6, 9, 12, and 24 hours from a well-agitated leach drum, and the resulting solutions were analyzed to assess gold recovery. The experimental results demonstrated a clear relationship between finer grind size and improved gold dissolution. Notably, reducing the concentrate grind size from 32 µm to 25 µm led to a significant increase in gold extraction efficiency. Furthermore, a comparison between mill feed and mill product revealed a gold recovery increase from 47% to 62%, emphasizing the importance of ultra-fine grinding in unlocking encapsulated gold. This enhanced recovery is attributed to the improved liberation of gold particles, which allows for more effective interaction with the leaching solution. Consequently, these findings confirm that grind size is a key variable influencing the success of leaching processes for pyrite-hosted gold. This study highlights the value of particle size optimization in maximizing recovery from low-grade refractory cyanide tailings.