Gold smelting is a metallurgical process used to separate metal from ore, rocks that contain gold. The ore is ground and treated with chemicals to remove some impurities before being heated at high temperatures with a flux that triggers a chemical reaction, causing the metal to precipitate out of the mixture. After gold has been smelted, it needs to be refined to purify it so it can be used in production of a variety of products, from jewelry to electronic components.
The discovery of ores and smelting marked an important point in human development, as people could access previously inaccessible metals bound in ores to use in metalworking projects. Early humans built furnaces for their gold smelting, controlling temperatures with bellows and combustible materials to reach the necessary high heat. Similar equipment is used in modern processing facilities, although temperature controls are far tighter.
This process causes an actual chemical change in the ore; it doesn’t just melt the gold. Once gold has been smelted, it cannot be returned to ore form. Facilities that perform gold smelting start with processed ore that has been carefully inspected to grade the quality and estimate how much usable metal it will yield. It is mixed in smelting crucibles so it can be heated, and when the flux is added, the metal starts to flow to the bottom, while slag rises to the top. Slag can be skimmed off, leaving metal behind.
After gold smelting, the metal still has impurities. These include other metals along with some mineral content in some cases. In refining, it is further processed to remove these impurities and yield a product that is between 95 and 99% pure in most cases. Higher purity requires more work, making it more expensive, but it may be necessary for some products. It can also be alloyed with other metals to develop specific traits like gold with a particular color or a stronger metal for use in projects where pure gold is too soft.
Pollution is a concern with the smelting process. Mining and processing ore tends to generate pollution in the form of chemicals and disruption to the natural environment, while slag can also be hazardous for the environment if it is not handled responsibly. Companies with concerns about the environment control their supply chain and may use a variety of measures to keep metallurgical pollution to a minimum in their production processes.