LAUSR

Abstract In this study, potassium hydroxide leaching as pretreatment before cyanide leaching of a flotation concentrate of an antimonial refractory gold-silver ore was investigated. The ore assaying 1157 g/t Ag and 3.96 g/t Au was found to be composed of predominantly quartz, barite, kaolinite, clay, mica/chlorite, and dolomite/ankerite. Electrum, pyrargyrite, acanthite, and tetrahedrite were identified to be the most important silver-bearing phases in the ore. A flotation concentrate with a high silver grade (0.6% Ag) at 94.8% silver recovery, as well as high recoveries of antimony (86.8%), zinc (98.6%), and lead (84.7%), was produced in flotation tests. Gold recovery to the concentrate was limited to be 74.4%. The cyanide leaching of the concentrate has yielded consistently low extractions of silver (≤13.8%) confirming the refractory nature of the ore. Alkaline pretreatment of the concentrate was performed in which effects of potassium hydroxide concentration (0.05–3 mol/L) and temperature (20–80 °C) on the removal of antimony and subsequent cyanide leaching of silver were investigated. Extraction of antimony was substantially enhanced from 11.5 to 93.8% with increasing the concentration of KOH and temperature. The activation energy (Ea) for leaching of antimony was calculated to be ≈17 kJ/mol with the implication of a diffusion-controlled leaching reaction. Silver extraction in the cyanidation improved from 13.8% to 95.7% as a consequence of the removal of antimony (i.e. 93.8%) by the alkaline pretreatment. This improvement in the silver extraction can be attributed to the decomposition of silver-bearing antimonial minerals i.e. pyrargyrite, and tetrahedrite in the concentrate. These findings confirm that potassium hydroxide leaching is a suitable approach for the pretreatment of antimonial refractory silver ores.