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Concept
Hydrometallurgy
Summary
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 involves the use of aqueous solutions to extract metal from metal-bearing materials which are brought into contact with them. In China in the 11th and 12th centuries, this technique was used to extract copper; this was used for much of the 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. By using chelating agents, one can selectively extract certain metals. These agents are typically amines of Schiff bases.
The five basic leaching reactor configurations are in-situ, heap, vat, tank and autoclave.
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. The solution is then collected and processed. The Beverley uranium deposit is an example of in-situ leaching.
In heap leaching processes, crushed (and sometimes agglomerated) ore is piled in a heap which is lined with an impervious layer. Leach solution is sprayed over the top of the heap, and allowed to percolate downward through the heap.
Official source
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