Gold extraction, sometimes known as gold recovery, is the process of extracting the gold form the surrounding ores. This is can include any combination of certain procedures such as comminution, pyrometallurgical processes, mineral processing, and hydrometallurgical processing.
What these mean, in the same order, is crushing and grinding to reduce the size of the rocks, using heat and fire to remove the metals, different ways of crushing again, and using water to extract the gold.
Placer Mining Techniques for Gold Extraction
We know about the placer mining techniques discussed in other articles on this site, such as gold panning, dredging, sluicing, using trommels, wave tables, and cradles. The basic use of these methods is extracting the gold nuggets, flakes, and fine particles from the black sand that is found in placer deposits. These are formed when the velocity of water is slowed down enough for the heavier particles to drop from suspension, like gold.
This leaves a black sand, called alluvial soil which can be scooped out and filtered out using any of these placer mining techniques. The most beneficial would probably be the gold wave table and the gold panning techniques, which are best suited for fine particles.
Gold Extraction for High Concentration
Gold doesn’t always occur as just gold, but can be found as an alloy and mixed chemically with other elements. So sometimes concentration needs to be taken into account. Essentially what it is we are talking about getting all of the fine particles separated from the rest of the ore and getting them into a concentrated pile and recombining them into larger nuggets of gold.
This can be done using gold panning, wave tables, or other methods such as froth flotation. Once you get it all together you can smelt it into a coin, nugget, or bar. If it’s still mixed with other ores you will try a treatment process such as electrowinning, cyanidation leaching, etc.
There is so much more to this. You can go into so much detail about leaching and about refractory gold processes such as retreatment and roasting. We could talk about bio-oxidation, ultra fine grinding, and more, but it really is beyond the point for us hobbyists. You can do additional research if that portion interests you, but what has been written above are the basics of gold extraction, beyond that you don’t need to know much more.