Removal of the unwanted materials (e.g., sand, clays, etc.) from the ore is known as concentration, dressing or benefaction. Before proceeding for concentration, ores are graded and crushed to reasonable size. Concentration of ores involves several steps and selection of these steps depends upon the differences in physical properties of the compound of the metal present and that of the gangue. The type of the metal, the available facilities and the environmental factors are also taken into consideration. Some of the important procedures for concentration of ore are:

(i) Hydraulic washing

(ii) Magnetic separat

(iii)Froth-floatation process

(iv) Leaching

Which of the following cannot be concentrated by electromagnetic separation?

Zinc blende

Electromagnetic separation is used to concentrate an ore when either the particles of the ore or the impurities present in it are magnetic in nature. This technique is used to separate the magnetic chromite, magnetite, and pyrolusite minerals from the non-magnetic gangue particles. Either froth flotation or electrostatic separation are used to concentrate zinc blende.