Mineral Processing and Extractive Metallurgy
2022-03-08 Xinhai (389)
2022-03-08 Xinhai (389)
Mineral processing is a major division in the science of Extractive Metallurgy. Extractive metallurgy has been defined as the science and art of extracting metals from their ores, refining them and preparing them for use. Within extractive metallurgy, the major divisions in the order they may most commonly occur are, Mineral Processing (or Beneficiation), Hydrometallurgy, Pyrometallurgy,and Electrometallurgy. The last steps in the winning of metals are in Physical Metallurgy where the composition and treatment of metals are varied to provide desired physical and mechanical properties.
In mineral processing, a number of unit operations are required to prepare and classify ores before the valuable constituents can be separated or concentrated and then forwarded on for use or further treatment. The field of mineral processing has also been given other titles such as mineral dressing, ore dressing, mineral extraction, mineral beneficiation, and mineral engineering. These terms are often used interchangeably.
Ore is a term used to describe an aggregate of minerals from which a valuable constituent,especially a metal, can be profitably mined and extracted. Most rock deposits contain metals or minerals, but when the concentration of valuable minerals or metals is too low to justify mining, it is considered a waste or gangue material. Within an ore body, valuable minerals are surrounded by gangue and it is the primary function of mineral processing, to liberate and concentrate those valuable minerals.
Generally, mineral processing begins when an ore is delivered from a mine, to a processing facility.At this point, the ore is called run-of-mine material because there has been no treatment performed on it.
There are three primary types of run-of-mine materials:
1. Run-of-mine consisting of useful materials. These could include granites, building sand,limestone, coal and clays. Note that materials in this category are not classified as minerals.
2. Run-of-mine containing useful minerals. The minerals in this category among others include fluorite, apatite, diamonds and gemstones, vermiculite, barite, wollanstonite and chromite and are often referred to as industrial minerals. Other examples are i) barite that is used as weighing agent in oil drilling mud and ii) vermiculite, which is used for sound and thermal insulation. The unit value of this class of minerals is low but the purity is high, approaching a chemical grade. The minerals in this class are used directly for industrial applications once they are separated from a gangue content that must be low to start with. The low unit value only allows for marginal treatment costs.
3. Run-of-mine containing value bearing minerals. This class of run-of-mine is similar to the previous descriptions. However in this case, the target mineral obtains its value from the
contained metal and these categories of deposits are referred to as metaliferrous. For example, an ore containing the mineral chalcopyrite (CuFeS2) derives its value from the contained copper. Chalcopyrite does not in and of itself have any direct use as a mineral.Once chalcopyrite is concentrated (separated from the gangue), it requires further treatment to extract copper via chemical (hydrometallurgical or pyrometallurcial) methods.
The general focus of this document will be on metaliferrous ores represented by run-of-mine material described in category 3 above. An exception to the above discussion of mineral
processing arises when the valuable component of the ore is extracted directly by chemical methods. The most common and notable example of this are precious metal values (gold, silver
etc.) where the beneficiation process is applied directly on run-of-mine ores followed by the extraction of gold and in some cases silver as a relatively pure metal within the mineral processing circuit.
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 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 only one mineral.
3. The third rule is a corollary of the second. It is impractical to recover all of the valuable minerals into the concentrate.
The flowsheet in Figure 1 shows diagrammatically the typical sequence of operations in the process plant. The various unit operations used for liberation and separation will be discussed in
the following sections.
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