Mechanical treatment of crude ores to separate the valuable minerals. Mineral processing was at first applied only to ores of precious metals but later came to be used to recover other metals and nonmetallic minerals. It is also used during coal preparation to enrich the value of raw coal. The primary operations are comminution and concentration. Comminution is carried out by large jaw crushers and by smaller cylindrical grinding mills. Common methods of concentration are gravity separation and flotation separation. Gravity methods include jigging (ground ore is fed into a pulsating body of water so that the heavier mineral fractions settle out, leaving lighter wastes at the top) or washing the ore down inclined planes, spirals, or shaking tables so that mineral and waste fractions settle in different areas. Seealso beneficiation; mining.
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Many plants also incorporate hydrometallurgical or pyrometallurgical processes as part of an extractive metallurgical operation.
Mineral processing involves four general types of operations: comminution or particle size reduction, sizing or separation of particle sizes by screening or classification, concentration by taking advantage of physical and surface chemical properties, and dewatering or solid/liquid separation.
A number of auxiliary materials handling operations are also considered a branch of mineral processing such as storage (as in bin design), conveying, sampling, weighing, slurry transport, and pneumatic transport.
The simplest of sizing processes is screening, or passing the particles to be sized through a screen or number of screens. Screening equipment can include grizzlies, bar screens, and wire mesh screens. Screens can be static (typically the case for very coarse material), or they can incorporate mechanisms to shake or vibrate the screen.
Classification refers to sizing operations that exploits the differences in settling velocities exhibited by particles of different size. Classification equipment may include ore sorters, gas cyclones, hydrocyclones, rake classifiers, rotating trommels, or fluidized classifers. When the feed material contains particles of different densities as well as particles of different size, a degree of concentration takes place during classification because settling velocities are also dependent on particle density.