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Borax is a crystal-forming mineral that can be reduced to a powder, in this case for use as a flux. The borax method is a technique of artisanal gold mining, which uses borax as a flux to purify gold concentrates. By using borax, no mercury flour is produced, hence gold recovery increases. [1] [2]
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.
Challenges include reagent cost and the efficiency of gold recovery, although some chlorination process using sodium hypochlorite (household bleach) have shown promise in terms or reagent regeneration. These technologies are at a pre-commercialisation stage and compare favourably to equivalent cyanidation methods, including gold recovery ...
The reaction with hydrochloric acid is an equilibrium reaction that favors formation of tetrachloroaurate(III) anions. This results in a removal of gold ions from solution and allows further oxidation of gold to take place. The gold dissolves to become chloroauric acid. In addition, gold may be dissolved by the chlorine present in aqua regia.
The Merrill–Crowe Process is a separation technique for removing gold from the solution obtained by the cyanide leaching of gold ores. It is an improvement of the MacArthur-Forrest process, where an additional vacuum is managed to remove air in the solution (invention of Crowe), and zinc dust is used instead of zinc shavings (improvement of Merrill).
Cyanidation was much more efficient and had a recovery rate of up to 90%. [5] Leading up to World War I, many new ideas for leaching processes were experimented. [4] This included using ammonia solutions for copper sulfides, and nitric acid for leaching sulfide ores. [4]
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Pressure oxidation has a very high gold recovery rate, normally at least 10% higher than roasting. [ 1 ] The oxidation of the iron sulfide minerals produces sulfuric acid , soluble compounds such as ferric sulfate, and solids such as iron sulfate or jarosite .