Hydrometallurgy

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

 i) Leaching
 ii) Ion Exchange
 iii) Electrometallurgy
 iv) Precipitation

Leaching

An aqueous solution containing a lixiviant is added to the ore. The oxidation potential and pH of the solution is often manipulated in order to promote the leaching of an ore component to the liquid phase.

Ion Exchange

Chelating agents, natrally forming zeolites, activated carbon, resins and liquid orgaincs impregnated with chelating agents are all used to exchange cations or anions from the solution. Selectivity and recovery are a funtion 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 contaminants from aqueous solutions. Precipitation will proceed when through reagent addition, evapouration, pH change or temperature manipulation, any given species exceeds its limit of solubility. In order to improve efficiency in downstream processes, seeding crystalization is often used. The thermodynamic tendancy towards precipitation is shown using Pourbaix diagrams, however these do not show the kinetic or speed at which the salt or metal will be precipitated. Cementation is a type of precipitation.