| Summary and Recommendation | WNP Processing Plant Air Discharge Assessment | 4397169-66885702-113 | 16/06/2022 | 26 Sensitivity: General Precious metals recovery The pregnant eluate is passed through a series of electrowinning cells, containing cathodes in the form of steel wool. The gold and silver migrates and attaches to the stainless steel cathodes. The cathodes are then rinsed, yielding a muddy sludge. The muddy sludge is dried, and the powder that remains is mixed with fluxes and put into the furnace. The furnace attains a high temperature of 1200°C and after several hours the molten material is poured into a cascade of moulds to produce doré bullion bars. The fluxes form a slag of impurities which is removed, leaving a bar which is a 99% pure melt of gold and silver. Each bar of doré bullion contains around 75% – 90% silver and 10% – 25% gold and weighs approximately 20 kg. The bullion is sent to the Western Australian Mint in Perth, where it is further refined to separate the gold from the silver. After refining, the gold and silver is credited to the OceanaGold mint account and the precious metals are sent to the international market.
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