Extraction of metal from ore by dissolving the metal (as one of its salts ) and then recovering it from the solution.
The operations usually involved are leaching (dissolving in water), commonly with additional agents; separating the waste and purifying the leach solution; and precipitating the metal or one of its pure compounds from the leach solution by chemical or electrolytic means. Though hydrometallurgy originated in the 16th century, its principal development took place in the 20th century. The development of ion exchange, solvent extraction, and other processes now permits more than 70 metallic elements to be produced by hydrometallurgy, including most gold , much silver , and large tonnages of copper and zinc .