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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.
Gold extraction is the extraction of gold from dilute ores using a combination of chemical processes. Gold mining produces about 3600 tons annually, [1] and another 300 tons is produced from recycling. [2] Since the 20th century, gold has been principally extracted in a cyanide process by leaching the ore with cyanide solution.
The chemical reaction for the dissolution of gold, the "Elsner equation", follows: 4 Au + 8 NaCN + O 2 + 2 H 2 O → 4 Na[Au(CN) 2] + 4 NaOH. Potassium cyanide and calcium cyanide are sometimes used in place of sodium cyanide. Gold is one of the few metals that dissolves in the presence of cyanide ions and oxygen.
The borax method of gold extraction has been used by artisanal gold miners in the Benguet area north of Manila in the Philippines for more than 30 years. Some believe it was in practice as early as the 1900s. [who?] The method is increasingly being seen as a safe alternative to the widespread use of toxic mercury in artisanal gold mining today ...
Craddock, P. T. 2000a Historical Survey of Gold Refining: 1 Surface Treatments and Refining Worldwide, and in Europe Prior to AD 1500. In A. Ramage and P. T Craddock (eds) King Croesus' Gold; Excavations at Sardis and the History of Gold Refining. London: British Museum Press, 27–53. ISBN 978-0-674-50370-0, 0-674-50370-8
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.
Carbon in pulp (CIP) is an extraction technique for recovery of gold which has been liberated into a cyanide solution as part of the gold cyanidation process. [1]Introduced in the early 1980s, Carbon in Pulp is regarded as a simple and cheap process.
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