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The Wohlwill process is an industrial-scale chemical procedure used to refine gold to the highest degree of purity (99.999%). [1] The process was invented in 1874 by Emil Wohlwill . This electrochemical process involves using a cast gold ingot , often called a doré bar , of 95%+ gold to serve as an anode .
The resulting gold is 99.5% pure, but of lower purity than gold produced by the other common refining method, the Wohlwill process, which produces gold of up to 99.999% purity. [1] [2] The Wohlwill process is commonly used for producing high-purity gold, such as in electronics work, where exacting standards of purity are required.
16th century cupellation furnaces (per Agricola). Cupellation is a refining process in metallurgy in which ores or alloyed metals are treated under very high temperatures and subjected to controlled operations to separate noble metals, like gold and silver, from base metals, like lead, copper, zinc, arsenic, antimony, or bismuth, present in the ore.
With the karat gold this low (6K), and over medium high heat, the dilute nitric acid will dissolve the Sterling silver (and other base metals in the karat gold) starting on the outside surface of the 6K gold alloy, working its way into the gold alloy, forming a honeycomb structure as it works its way into the metals.
Gold occurs principally as a native metal, i.e., gold itself.Sometimes it is alloyed to a greater or lesser extent with silver, which is called electrum.Native gold can occur as sizeable nuggets, as fine grains or flakes in alluvial deposits, or as grains or microscopic particles (known as colour) embedded in rock minerals.
In metallurgy, refining consists of purifying an impure metal. It is to be distinguished from other processes such as smelting and calcining in that those two involve a chemical change to the raw material, whereas in refining the final material is chemically identical to the raw material. Refining thus increases the purity of the raw material ...
Pressure oxidation is a process for extracting gold from refractory ore. The most common refractory ores are pyrite and arsenopyrite , which are sulfide ores that trap the gold within them. Refractory ores require pre-treatment before the gold can be adequately extracted. [ 1 ]
The specifications of bullion are often regulated by market bodies or legislation. In the European Union, the minimum purity for gold to be referred to as "bullion", which is treated as investment gold with regard to taxation, is 99.5% for gold bullion bars and 90% for bullion coins. [2]