Abstract
The effects of cyanidation conditions (pH, time, particle size of the ore, additives to the leach, and oxidative pre-treatments) at ambient temperatures on the extraction of platinum, palladium and gold from samples from the Coronation Hill deposit, Australia, were studied. Three ore lithologies were investigated: a diorite, a green tuffaceous siltstone, and a quartz-feldspar porphyry. Coarse and fine native gold, native platinum and palladium, stibiopalladinite and platinum-palladium selenides were identified in the samples. Coarse gold, but no platinum or palladium, was recovered by amalgamation. Cyanidation at pH 11.5 for 48 h of ore ground to 80% − 74 μm (standard cyanidation conditions) extracted 6–18% of the platinum, 20–50% of the palladium (the values depending on the ore type), and over 95% of the gold. Lowering the cyanidation pH to 9.5 resulted in extraction of up to 85% of the palladium, although the platinum extractions were usually less than 20%. Final grinding increased the palladium extractions but had little effect on platinum extractions, and decreased gold extractions by a few percent. The high gold extractions were obtained by 24 h cyanidation, but longer times were required for extraction of platinum and palladium. Addition of thallium salts at pH 9.5 increased the platinum extraction values to 30–35%. Addition of sodium chloride, sodium sulphite, sodium thiosulphate, lead salts and hydrogen peroxide had little effect on the extraction of the precious metals. Pre-treatment with sodium chloride/hydrogen peroxide solution at pH 1, and filtration before the subsequent cyanidation at pH 9.5, increased the platinum extraction from 20% to 37%. However, the palladium extraction was reduced to 25%.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have