MINERAL PROCESSING

art of treating crude ores and mineral products in order to separate the valuable minerals from the waste rock, or gangue. It is the first process that most ores undergo after mining in order to provide a more concentrated material for the procedures of extractive metallurgy. The primary operations are comminution and concentration, but there are other important operations in a modern mineral processing plant, including sampling and analysis and dewatering. All these operations are discussed in this article. also called Ore Dressing, mechanical treatment of crude ores to separate out the valuable minerals. Mineral-processing techniques were at first applied only to ores of precious metals such as gold and silver, but they later came to be used to recover other metals and nonmetallic minerals. They are also used during coal preparation to enrich the value of raw coal. The primary operations of mineral processing are comminution and concentration. Comminution involves the liberation of valuable minerals from physical combination with the waste minerals. It is customarily carried out by large jaw crushers and by smaller cylindrical grinding mills. Mills may be operated either wet or dry. Concentration consists of separating the liberated minerals from the waste. The most common methods are gravity separation and flotation separation. Gravity methods utilize the difference in density between valuable minerals and waste materials. Separation can be accomplished by jigging, an operation in which ground ore is fed into a pulsating body of water so that the heavier mineral fractions settle to the bottom while the lighter wastes remain at the top. Gravity separation can also be conducted on inclined planes, the ground ore being washed down spirals or shaking tables in such a manner that mineral and waste fractions settle in different areas. In flotation (q.v.), separation is accomplished by treating ground ore with chemical reagents that cause one fraction to sink to the bottom of a body of water and the other fraction to adhere to air bubbles and rise to the top. Other important mineral-processing operations are dewatering, in which the concentrated minerals are dried and readied for transport; and sampling and analysis, in which the composition and properties of the raw materials or processed minerals are periodically characterized. Additional reading Comprehensive works on the separation and concentration of minerals are Errol G. Kelly and David J. Spottiswood, Introduction to Mineral Processing (1982), which explains the scientific principles behind the processes; B.A. Wills, Mineral Processing Technology: An Introduction to the Practical Aspects of Ore Treatment and Mineral Recovery, 4th ed. (1988), with details on common techniques and machinery as well as on automated and computerized methods; and Norman L. Weiss (ed.), SME Mineral Processing Handbook, 2 vol. (1985), which also contains a brief historical survey of the industry as a whole. Mineral Facts and Problems (quinquennial) is a massive review regularly published by the U.S. Bureau of Mines. Holger Gruner