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Gold cyanidation (also known as the cyanide process or the MacArthur–Forrest process) is a hydrometallurgical technique for extracting gold from low-grade ore through conversion to a water-soluble coordination complex. It is the most commonly used leaching process for gold extraction. [1]
Sodium thiosulfate and ammonium thiosulfate have been proposed as alternative lixiviants to cyanide for extraction of gold from ores [8] and printed circuit boards. [9] The complex [Au(S 2 O 3) 2] 3-is assumed to be the principal product in such extractions. Presently cyanide salts are used on a large scale for that purpose with obvious risks. [8]
Ammonium thiosulfate (ammonium thiosulphate in British English) is an inorganic compound with the formula [NH 4] 2 S 2 O 3. It is white crystalline solid with ammonia odor, readily soluble in water , slightly soluble in acetone and insoluble in ethanol and diethyl ether .
Cyanide leaching "heap" at a gold mining operation near Elko, Nevada. On top of the large mounds of ore, are sprinklers dispensing a solution of cyanide. 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 ...
Leaching is a process widely used in extractive metallurgy where ore is treated with chemicals to convert the valuable metals within the ore, into soluble salts while the impurity remains insoluble. These can then be washed out and processed to give the pure metal; the materials left over are commonly known as tailings .
Biological substances can experience leaching themselves, [2] as well as be used for leaching as part of the solvent substance to recover heavy metals. [6] Many plants experience leaching of phenolics, carbohydrates, and amino acids, and can experience as much as 30% mass loss from leaching, [5] just from sources of water such as rain, dew, mist, and fog. [2]
Bioleaching is the extraction or liberation of metals from their ores through the use of living organisms.Bioleaching is one of several applications within biohydrometallurgy and several methods are used to treat ores or concentrates containing copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt.
After leaching, the leach liquor must normally undergo concentration of the metal ions that are to be recovered. Additionally, undesirable metal ions sometimes require removal. [1] Precipitation is the selective removal of a compound of the targeted metal or removal of a major impurity by precipitation of one of its compounds.