Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. Processing techniques that complement hydrometallurgy are pyrometallurgy, vapour metallurgy, and molten salt electrometallurgy. Hydrometallurgy is typically divided into three general areas:

Leaching
Solution concentration and purification
Metal or metal compound recovery

Leaching
Leaching involves the use of aqueous solutions to extract metal from metal bearing materials which is brought into contact with a material containing a valuable metal. The first examples come from 11-12th centuries China where it was applied to extraction of copper and accounted for a significant share of total copper production. In the 17th century it was used for the same purposes in Germany and Spain.The lixiviant solution conditions vary in terms of pH, oxidation-reduction potential, presence of chelating agents and temperature, to optimize the rate, extent and selectivity of dissolution of the desired metal component into the aqueous phase. Through the use of chelating agents, one can selectively extract certain metals. Such chelating agents are typically amines of schiff bases.The five basic leaching reactor configurations are in-situ, heap, vat, tank and autoclave. In-situ leaching
In-situ leaching is also called "solution mining." This process initially involves drilling of holes into the ore deposit. Explosives or hydraulic fracturing are used to create open pathways within the deposit for solution to penetrate into. Leaching solution is pumped into the deposit where it makes contact with the ore.
Uremic pruritus is caused by chronic kidney failure and is the most common internal systemic cause of itching. : 52–3 Nalfurafine, an orally-administered, centrally-acting κ-opioid receptor agonist, is approved to treat the condition in Japan. See also
Pruritus
List of cutaneous conditions

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