Platinum, palladium, and gold extraction from Coronation Hill ore by cyanidation at elevated temperatures

The effects of cyanidation conditions (pH, time, temperature and particle size of the ore) on the extraction of platinum, palladium, and gold from a quartz-feldspar porphyry sample from the Coronation Hill deposit, Australia, were studied. The main precious metal minerals in the sample were identified as coarse and fine native gold, native platinum and palladium, stibiopalladinite and palladium-platinum-iron alloy phases.Coarse gold, but no platinum or palladium, was recovered by amalgamation. At ambient temperature, for material 80% - 74 μm and a cyanidation time of 48 h, reducing the cyanidation pH from 11.5 to 9.5 increased the palladium extraction from 22.7 to 66.4% and the platinum extraction from 5.7 to 25.7%. Total gold extractions were not affected and were over 98%. Finer grinding increased the palladium extractions but had little effect on platinum extractions, and decreased gold extractions by a few percent.Cyanidation at elevated temperatures of up to 150°C under an overpressure of nitrogen, air, or oxygen increased the palladium and platinum extraction values. The optimum temperature range was 100–125°C. At 100°C under air, 87–92% of the palladium, 73–79% of the platinum, and 95–97% of the gold were extracted in 4–6 h at pH 9.5–11.5.Possible treatment options involving cyanidation at ambient and elevated temperatures, with or without flotation, for recovery of gold, platinum, and palladium are discussed.