People at home can use the aqua regular method to refine gold, while refining on an industrial scale is done using the Wohlwill process. Safety measures are necessary to carry out the aqua regular method, as it involves high temperatures and chemicals.
For small scale refining, melt the gold in a crucible. An acetylene torch melts the gold, which is then separated into small portions and left to harden.
The gold is then transferred to a heavy plastic bucket or Pyrex container, where nitric acid is added to it. Thirty milliliters is required for each ounce of gold.
The nitric acid is left to react with the gold, and then hydrochloric acid is added. This mixture is left overnight.
A boiling mixture of urea and water is added to the acids to neutralize the nitric acid. Gold precipitant is added, and the gold is gradually separated from the acid once it forms.
After being rinsed with water, the gold mud is rinsed with aqua ammonia. It is then ready to be cleaned, dried and melted into an ingot.
The Wohlwill process uses acid and electricity to plate pure gold onto a cathode. It is used in industries where the highest possible purity of gold is required.