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Hydrometallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. [1] [2] Processing techniques that complement hydrometallurgy are pyrometallurgy, vapour metallurgy, and molten salt electrometallurgy. Hydrometallurgy is typically divided into three general areas: Leaching
The solution drains from the tank, and is either recycled back into the vat or is pumped to the next step of the recovery process. Vat leach units are rectangular containers (drums, barrels, tanks or vats), usually very big and made of wood or concrete, lined with material resistant to the leaching media.
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]
The metal ore is either distilled in an electrolyte or acid solution, then magnetically deposited onto a cathode plate (electrowinning); or smelted then melted using an electric arc or plasma arc furnace (electrothermic reactor). [7] Another major difference in non-ferrous extraction is the greater emphasis on minimizing metal losses in slag.
Biomining is one of several applications within biohydrometallurgy with applications in ore refinement, precious metal recovery, and bioremediation. [2] The largest application currently being used is the treatment of mining waste containing iron , copper , zinc , and gold allowing for salvation of any discarded minerals.
There are many different types of beneficiation, with each step furthering the concentration of the original ore. Key is the concept of recovery, the mass (or equivalently molar) fraction of the valuable mineral (or metal) extracted from the ore and carried across to the concentrate.
Metallurgy: A process involving the separating and refining of metals from other substances; [4] Bioleaching: Using biological agents (bacteria) to extract metals or soils; [5] general term used to encompass all forms biotechnological forms of extraction (hydrometallurgy, biohydrometallurgy, biomining, etc)