Gold is primarily purified, rather than filtered in the traditional sense, using chemical processes to separate it from impurities. The two main methods are the Miller process and the Wohlwill process.
Miller Process
The Miller process uses gaseous chlorine to remove impurities from gold.
- Method: Gold is heated to its melting point (1064 °C or 1947 °F), and chlorine gas is bubbled through the molten gold.
- Mechanism: Virtually all impurities react with the chlorine more readily than gold. These impurities form chloride compounds that either volatilize (evaporate) or separate as a slag on the surface of the molten gold.
- Result: This process leaves behind gold of approximately 99.5% purity.
- Advantages: It's a relatively quick and simple process.
- Disadvantages: It doesn't produce gold of very high purity compared to other methods. It also poses environmental risks due to the release of chlorine gas and other potentially hazardous byproducts.
Wohlwill Process
The Wohlwill process uses electrolysis to achieve a higher level of gold purity.
- Method: Gold is dissolved in a hydrochloric acid solution containing gold chloride (an electrolyte).
- Mechanism: An electric current is passed through the solution. Gold ions are deposited on the cathode (negative electrode) as pure gold, while impurities remain in the solution or form a sludge at the bottom of the electrolytic cell.
- Result: This process yields gold with a purity of up to 99.999%.
- Advantages: Achieves a very high level of purity.
- Disadvantages: It's a more complex and time-consuming process than the Miller process and is also more expensive.
In summary, gold "filtering" is more accurately described as refining or purification, and it primarily involves chemical processes rather than physical filtration methods like using a filter paper. The Miller and Wohlwill processes are the most common methods for achieving this.
