Concentration of Ores

Ores as mined are never pure: they are always associated with unwanted nonmetallic impurities, rocky material and siliceous matter, which are collectively called GANGUE (or matrix). Before any chemical extraction step can be carried out efficiently, this gangue must be removed as far as possible -- a preliminary physical/physico-chemical step called CONCENTRATION of the ore. Concentration raises the proportion of the metal of interest (or its compound) in the processed material, which makes every downstream step -- roasting/calcination, reduction, refining -- faster, cheaper and more effective, since less unwanted material has to be heated, reacted or handled. …