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Gold is one of the earliest metals known to man. It's property of malleability, not being tarnished and it's color have given it a high value in historical times. The same properties have also made it into an important industrial metal.
Gold can be found in many places, naturally as gold ores and placer deposits but in this modern time it can be found in a number of other places too.
- Gold ores
- Gold bullion, coins, bars
- Jewellery, carat gold, white gold, gold filled
- Scrap from jewellery manufacturing, filings, sweeps, floor mats, ...
- Electronic scrap, bond wires in chips, gold plating on contact surfaces
- Super alloys in jet engines, gold nickel brazes
- IR reflector on mirrors, IR lamps, IR-blocking window panes
- Painting on glass and porcelain
- Gold leaf for decoration
- Gold thread used in embroidery
- As a coloring agent in cranberry glass
- In the reflective layer of some CD:s
- In dentistry as gold fillings and other parts
- As sputtering targets in machines that deposits gold in a vacuum
- Some chemicals in photography uses gold chloride
- gold salts for plating baths
For the refiner the challenge is to bring the gold out of a lot of garbage material. Sometimes the trick is to concentrate the gold bearing material so far it can be worked with chemical methods, and from that refined into industry standard 99.95% pure gold.
Different methods used for concentrate the gold.
- Incineration, removes organic matter as carbon dioxide and removes volatile salts and acids.
- Panning, gold from placer deposits, bond wires from incinerated chips
- Trimming and mechanical removing barren material
- Smelting, creating a refiners bar or copper anode and use a copper cell while precious metals concentrate in the anode slime
- Dissolving unwanted base metals, using nitric acid on gold filled or Copper chloride method on gold plated.
- Reverse plating with sulfuric acid
- Cyanide leaching, both ores and gold plated objects
- Eco-Goldex, a commercial variation of cyanide leaching.
- Modern Electroplating 4 : Electrodeposition of Gold by Paul A. Kohl, a great article on gold, its chemistry and plating.