Concentration of Ores

Once an ore is mined, crushed, and graded to a workable size, it still carries a load of unwanted material — sand, clay, and other earthy matter collectively called gangue. Stripping this away is called concentration (also called dressing or benefaction), and it's always the first real metallurgical step.

There's no single universal method

Which technique is used depends on:

• the physical-property difference between the valuable mineral and the gangue (density, magnetism, surface wettability, solubility — whichever property differs enough to exploit),
• the type of metal being sought,
• the facilities available, and
• environmental factors. …