Hydrometallurgy

Hydrometallurgy involves the use of aqueous chemistry to purify metals or mineral concentrates. Typically hydrometallurgy can be separated into the following processes:

• Leaching
• Ion Exchange
• Electrometallurgy
• Precipitation

Leaching

Leaching utilizes an aqueous solution containing a lixiviant which is added to the ore. 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.

Ion Exchange

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 tendancy 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.