The Five Stages of Metal Refining: From Ore to Pure
The Royal Canadian Mint refines their gold using these five steps:
Doré bars in purities ranging from 5% to 95% are melted in a furnace. Dip samples are taken from the molten gold to determine its purity.
Chlorine gas is injected into the molten metal mix. All metals but gold float to the surface to form a slag of molten chloride. The resulting 995 fine gold is poured into an anode mould.
Soda ash is added to the molten chloride slag recovered from chlorination. The reaction causes gold particles to collect in a silver-gold alloy 'button' that settles at the bottom of the crucible.
This process brings gold to 9999 purity. The gold anode is placed in a bath containing a solution of hydrochloric acid and gold chloride. The anode is then subjected to an electric current. The anode dissolves, and the dissolved gold plates onto a titanium cathode. Impurities (mostly silver) fall to the bottom of the cell or form soluble chlorides.
5. Final pour
9999 fine gold is cast into bars of various sizes or turned into granulation gold.
The Gold Refining Process