Hydrometallurgy
Encyclopedia : H : HY : HYD : Hydrometallurgy
Hydrometallurgy involves the use of aqueous chemistry to purify metals or mineral concentrates. Typically hydrometallurgy consists of several specific processes.
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Leaching
Leaching uses an aqueous solution containing a lixiviant which is added to the ore. This is usually an acid. The oxidation potential and pH of the solution is often manipulated in order to promote the leaching or dissolving of an ore component into the aqueous phase. For refractory ore and minerals, leaching may require high-temperature and high-pressure treatment.In-Situ Leaching
In-situ leaching utilised the same processes as normal heap leaching and leaching. However, in this case, no ore is physically mined. In stead, holes are drilled into the deposit and explosives or hydraulic fracturing used to create open space. Lixiviant is pumped down into the deposit and extracted from other holes and the metals removed. The Beverley uranium deposit is an example of in-situ leaching.Solvent extraction
Here a mixture of an extractant in a diluent is used to extract a metal from one phase to another.Ion Exchange
Chelate|Chelating agents, natural zeolites, activated carbon, resins, and liquid organics impregnated with chelating agents are all used to exchange cations or anions with the solution. Selectivity and recovery are a function of the reagents used and the contaminants present.Electrometallurgy
Electrowinning and electrorefining involve the recovery and purification of metals using electrodeposition of metals at the cathode, and either metal dissolution or a competing oxidation reaction at the anode.Precipitation
Precipitation in hydrometallurgy involves the chemical precipitation of either metals and their compounds or of the contaminants from aqueous solutions. Precipitation will proceed when, through reagent addition, evaporation, pH change or temperature manipulation, any given species exceeds its limit of solubility. In order to improve efficiency in downstream processes, seeding to initiate crystallization is often used.The thermodynamic tendency towards precipitation is shown using Pourbaix diagrams, however these do not show the kinetics or speed at which the salt or metal will be precipitated. Cementation is a type of precipitation.
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