Mineral processing refers to a number of interrelated procedures that are all aimed at extracting valuable material from ores. Many valuable minerals are mined as ores, which are rocks that contain useful substances. Mineral processing was done by hand in the past, though in modern times it is typically achieved through the use of heavy machinery. There are four main types of mineral processing, each of which uses a different method to separate valuable materials from ore gangue. The four different methods involve the reduction of ore particle sizes, the separation of particles by size, concentration of wanted minerals, and the removal of liquids from the solid minerals.
In broader terms, mineral processing consists of two functions. Firstly, it involves the preparation and liberation, of the valuable minerals from waste minerals and secondly, the separation of these values into two or more products, called concentrates. The term separation in this case is synonymous with concentration. These functions are carried out within the constraints of the following three rules.
1. The first rule deals with the conservation of mass. The total flow of the material into the process plant equals the total flow out.
2. The second rule relates to the quality or grade of the concentrate
product. In practice, it is impossible to produce a concentrate consisting of
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3. The third rule is a corollary of the second. It is impractical to recover all of the valuable minerals into the concentrate.
In order to separate the minerals from gangue (the waste minerals), it is necessary to crush and grind the rock to unlock, or liberate, valuable minerals so that they are partially or fully exposed. This process of size reduction is called comminution. The crushing and grinding process will produce a range of particles with varying degrees of liberation (Figure 2). Any particles that exceed a target size required for physical separation or chemical extraction are returned to the crushing or the grinding circuit.
The comminution process actually begins during the mining stage through the use explosives, excavators or scrapers for softer material. This is necessary in order to generate a material that is transportable by haul trucks or conveyors. Comminution in the mineral processing plant is carried out in a sequential manner using crushers and screens followed by grinding mills and classifiers. The various types of comminution equipment including their general application are described in detail below.
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