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Gold refineries process impure gold to generate pure gold for sale or alloy it with other metals. The process involves smelting, refining, and assaying the gold. Some refineries buy lots outright, while others pay based on the value of the assay. Environmentally conscious refineries control waste and use non-toxic materials.
A gold refinery receives gold with impurities and processes it to generate pure gold for sale or alloys it with other metals for specific purposes. Some refineries may accept lots directly from the public, while others only work with metal dealers. The facility has an assay station within the premises to assess the quality and value of the gold which works on behalf of clients. Some gold refineries buy lots outright, while others may pay people based on the value of the assay at the end of the process.
The first step in a gold refinery typically involves weighing the lot. Lots can include recycled gold jewelry and product components, scrap metal, etc. If the batch contains combustible impurities such as paper and cardboard, the refinery may place it in a low-temperature furnace to burn them off and make the batch easier to work with during the melting process. During smelting, the refinery adds a flux to the gold and melts it in a furnace. The gold will sink to the bottom of the furnace, while the impurities float to the top, tied up with the flow as slag.
At the end of the smelting, the gold refinery has a solid piece of gold bullion. It may still contain some impurities such as trace metals, requiring it to go through a final refining stage where the facility re-smelts the metal and processes it to force the silver and other materials upwards. One method, the Miller process, involves pumping bubbles of chlorine gas through molten gold to expel impurities, leaving behind a solid block of pure gold.
During the assay at the end of the process, the company will weigh the gold and test it to determine its level of purity. Pure gold fetches the highest prices, even if it’s intended for an alloy with another metal. The gold refinery can sell the gold to other companies such as recycled metal suppliers, jewelers and electronics manufacturers.
The processes in a gold refinery can vary. Processing precious metals requires the use of caustic and toxic chemicals, and pollution has historically been a problem for many refineries. Some companies pride themselves on environmentally conscious practices and may specifically advertise to customers interested in gold produced by environmentally conscious refineries. These companies control waste, use non-toxic materials whenever possible, and have independent audits to confirm they are operating cleanly and safely.
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