How worthless mineral or earthy substance extracted from ore?

Concentration or Dressing or Benefaction is the process of removal of the Worthless mineral or earthy substance from the Ore. There are various methods of ore concentration but these methods are chosen on basis of the properties of the ore.

Methods of Ore Concentration

• Hydraulic Washing: In this method, extraction of Worthless mineral or earthy substance  from ore done by passing it through an upward stream of water whereby all the lighter particles of gangue are separated from the heavier metal ore. This is a type of gravity separation.
• Magnetic Separation: In this method, the Worthless mineral or earthy substance extracted from ore is separated by moving crushed or grind ore on the magnetic roller but it is possible only when either the ore or the gangue have magnetic properties. The ore is first ground to fine pieces and then passed on a conveyor belt passing over a magnetic roller. The magnetic ore remains on the belt and the gangue falls off the belt.
• Froth Flotation Method: This method is mainly used to remove gangue from sulphide ores. The ore is powdered and a suspension is created in water. To this are added, Collectors and Froth Stabilizers. Collectors (pine oils, fatty acids etc) increase the non-wettability of the metal part of the ore and allows it to form a froth. Froth Stabilizers (cresols, aniline etc) sustain the froth. The oil wets the metal and the water wets the gangue. Paddles and air constantly stir up the suspension to create the froth. This frothy metal is skimmed off the top and dried to recover the metal.
• Leaching: It is used when the ore is soluble in a solvent. The powdered ore is dissolved in a chemical, usually strong solution of NaOH. The chemical solution dissolves the metal in the ore and it can be extracted and separated from the gangue by extracting the chemical solution. Aluminium metal from Bauxite ore is extracted from this process.

Most of the large structures you see around you today have metallurgy to thank for their existence. What we learnt now is just the beginning in the extraction of metals.