Leaching behaviour of base and precious metals during cyanide leaching of a pyrite concentrate

This study investigated the influence of cyanide concentration (1.5-7 g/L NaCN), particle size (d<sub>80</sub> = 28-55 µm), and solid-to-liquid ratio (40-60% w/w) on the leaching behaviour of gold, silver, copper, zinc, and iron from a concentrate containing predominantly sphalerite, pyrite, and chalcopyrite, as determined by XRD analysis. The concentrate, containing 10.6 g/ton Au, 42 g/ton Ag, 0.21% Cu, 3.57% Zn, and 31% Fe, exhibited refractory characteristics with a low gold extraction (37%) at 1.5 g/L NaCN over a 24-hour leaching period. Increasing the cyanide concentration to 7 g/L enhanced gold extraction to 73%, albeit with a 3.64-fold increase in cyanide consumption. Copper leaching varied moderately (25-32%), likely attributed to its predominant occurrence as chalcopyrite. Negligible zinc leaching was observed, suggesting the relative inertness of sphalerite in the cyanide leaching environment. While particle size variations (d<sub>80</sub> = 28-55 µm) had minimal impact on gold extraction, a lower solid-to-liquid ratio (40% w/w) demonstrated improved gold extraction (51%) compared to 60% w/w. The optimal leaching conditions for achieving the highest gold and silver extractions were found to be 7 g/L NaCN, a pulp density of 40%, and a particle size of 55 µm (d<sub>80</sub>). These findings indicate that the concentrate exhibits refractory behavior under conventional cyanide leaching conditions. Elevated cyanide concentrations and lower solid-to-liquid ratios are required to enhance gold extraction, albeit with increased cyanide consumption.