Carbon used in the process is recycled. An electric current is passed through the new solution and the gold is deposited on a steel wool cathode. The gold laden cathode is treated with hydrochloric acid to dissolve any residual steel. The gold sludge is filtered and dried and is then ready for smelting. At this stage the gold-bearing material may still contain silver and base metals.
Gold is smelted in a crucible furnace to produce unrefined bullion.
In smelting, base metal impurities are oxidised and absorbed, leaving the precious metals to be poured into ingot moulds. Smelted gold is then refined. Refining Several refining processes are used in Australia chlorination, electrolytic and aqua regia. The gas reacts with silver and any remaining base metals to form chlorides, bubbles of which rise to the surface of the molten bullion and are removed. The molten, refined gold is cast into bars.