Concentration of Ores: Chemical Methods

(a) Calcination: Calcination is a process in which the ore are usually carbonate or hydrated oxide is subjected to the action of heat in order of expel water from hydrated oxide and carbon dioxide from a carbonate.

Examples: ZnCO3 —> ZnO + CO2

CaCO3 —> CaO + CO2

Al2O3.2H2O —> Al2O3 + 2H2O

2Fe2O3.3H2O —> 2Fe2O3 + 3H2O

Calcination is generally done in a reverberatory furnace.

(b) Roasting: Roasting is a process in which ores (usually sulphide ores) either alone or along with some other materials are subjected to the action of heat and air at temperatures below their melting points in order to bring about chemical changes in them. Calcination is also roasting but in this case we are concerned mainly with the changes due to the expulsion of some ingredients such as water, carbon dioxide and no other chemical change occurs. But during roasting chemical changes like oxidation, chlorination etc. takes places. The following equations represent roasting:

2PbS + 3O2 —> 2PbO + 2SO2

PbS + 2O2 —> PbSO4

2ZnS + 3O2 —> 2ZnO + 2SO2

ZnS + 2O2 —> ZnSO4

CuS + 2O2 —> CuSO4

2Cu2S + 3O2 —> 2Cu2O + 2SO2

Roasting is generally carried out in a reverberatory furnace or in a blast furnace.

(c) Leaching: It involves the treatment of the ore with a suitable reagent as to make it soluble while impurities remain insoluble. The ore is recovered from the solution by suitable chemical method. e.g. bauxite ore contains ferric oxide, titanium oxide and silica as impurities. When the powdered ore is digested with an aqueous solution of sodium hydroxide at about 150°C under pressure, the alumina dissolves forming soluble sodium meta aluminate while ferric oxide, TiO2 and silica remains as insoluble part.

Al2O3 + 2NaOH —> 2NaAlO2 + H2O

Next Page →

← Back Page

Leave a Reply