1. Reduction with Reducing Agents:
- This method involves using a reducing agent, such as sulfur dioxide (SO2), ferrous sulfate (FeSO4), or sodium thiosulfate (Na2S2O3), to reduce auric chloride (AuCl3) to metallic gold.
- The reaction with sulfur dioxide can be represented as:
2AuCl3 + 3SO2 + 3H2O → 2Au + 6HCl + 3H2SO4
2. Electrowinning:
- Electrowinning is a process that uses electrolysis to extract gold from auric chloride.
- In this method, a cathode (usually made of stainless steel) and an anode (made of inert material like platinum) are immersed in an auric chloride solution.
- When an electric current is passed through the solution, gold ions (Au3+) are reduced to metallic gold and deposited on the cathode.
3. Cementation:
- Cementation involves the displacement of gold from auric chloride by a more reactive metal, such as iron or zinc.
- Iron nails or zinc shavings are added to the auric chloride solution, and the gold ions in the solution react with the metal to form metallic gold and the corresponding metal chloride.
- The reaction with iron can be represented as:
2AuCl3 + 3Fe → 2Au + 3FeCl3
4. Precipitation:
- Gold can also be extracted from auric chloride through precipitation reactions.
- Certain reagents, such as oxalic acid (H2C2O4) or sodium borohydride (NaBH4), can cause gold ions to precipitate as gold metal.
- The reaction with oxalic acid can be represented as:
2AuCl3 + 3H2C2O4 → 2Au + 6HCl + 6CO2
After extraction, the obtained gold is often subjected to further purification steps to remove any impurities and obtain pure gold metal.
