There are several methods used for gold refining and processing of gold dore bars. The choice of method depends on various factors, including the composition of the dore bars, the desired level of purity, the quantity of material being processed, and the available equipment and resources.
Here are some common methods:
Aqua Regia Refining: This method involves the use of a mixture of nitric acid and hydrochloric acid (known as aqua regia) to dissolve and purify gold. Aqua regia is capable of dissolving most impurities, leaving behind purified gold.
Miller Process: The Miller process is a widely used method for refining gold dore bars. It involves melting the dore bars in a furnace and then selectively precipitating impurities by introducing chlorine gas into the molten metal. The impurities form a slag that can be removed, leaving behind purified gold.
Wohlwill Process: The Wohlwill process is another common method for gold refining. It uses electrolysis to separate impurities from gold. The gold dore bars are dissolved in a suitable electrolyte, and an electric current is passed through the solution, causing impurities to settle as anode sludge while pure gold deposits on the cathode.
Electrolytic Refining: In electrolytic refining, a similar principle to the Wohlwill process is applied. The dore bars are dissolved in an electrolyte solution, and an electric current is passed through it. Impurities migrate to the anode, forming a sludge, while pure gold is deposited on the cathode.
Chlorination Process: Chlorination is a refining method where chlorine gas is passed through molten gold, effectively separating impurities. The impurities combine with chlorine to form volatile compounds that are removed, leaving behind purified gold.
Acidless Separation: Acidless separation is a relatively newer method that uses specialized equipment to separate impurities from gold without the use of chemicals. It involves a combination of mechanical processes and electrolysis to achieve purification.
It’s important to note that the choice of refining method may vary based on the specific requirements and capabilities of the refinery. Some refineries may employ a combination of methods or variations of these processes to achieve the desired level of purity and quality in the refined gold.