Chemical Extraction is the process of using chemical reagents — including acids, bases, solvents, or complexing agents — to selectively dissolve, mobilize, and separate valuable metals or minerals from their host rock or mineral matrix. It is a cornerstone of hydrometallurgy and is widely applied in bauxite, gold, and other mining operations where physical concentration methods alone are insufficient to economically recover the target metal. In the Bayer Process for alumina production from bauxite, chemical extraction involves the high-pressure, high-temperature digestion of crushed bauxite in hot concentrated sodium hydroxide (NaOH) solution. The caustic selectively dissolves aluminium hydroxide and aluminium oxide minerals (gibbsite, boehmite, diaspore) to form soluble sodium aluminate, while silica reacts to form desilication products (DSP) and iron oxides remain as insoluble residues (red mud). In gold mining, chemical extraction most commonly involves heap leaching or tank leaching of crushed or ground ore using dilute sodium cyanide (NaCN) solution in the presence of dissolved oxygen, forming the stable gold-cyanide complex [Au(CN)₂]⁻. Alternative extraction systems include thiosulfate leaching and glycine leaching for cyanide-sensitive ores. In some iron ore operations, chemical extraction using hydrochloric acid (HCl) is explored to produce iron chloride for further processing. Diamond mining does not typically rely on chemical extraction for the diamond mineral itself (which is inert), but chemical reagents are used in processing plant circuits for ore dissolution and slime treatment. The efficiency of chemical extraction depends on reagent concentration, temperature, residence time, particle size, and ore mineralogy.
