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Inorganic Chemistry

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28 Jan 2012 15:51:39 IST

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describe 3 physical method used to enrich metal ores.

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ratnesh mishra

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28 Jan 2012 16:27:45 IST

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Enrichment of ores means increasing the metal (or non-metal) content of an ore by removing as much of the minerals in the ore that do not contain the desired substance. This can be done by several means including screening, gravity separation, magnetic separation and fine grinding followed by froth flotation; to concentrate the metal-rich minerals and discard the non metallic ones (gangue).It is also known as ore dressing.1.froth flotation: Froth flotation commences by comminution (that is, crushing and grinding), which is used to increase the surface area of the ore for subsequent processing and break the rocks into the desired mineral and gangue in a process known as liberation, which then has to be separated from the desired mineral. The ore is ground into a fine powder and mixed with water to form a slurry. The desired mineral is rendered hydrophobic by the addition of a surfactant or collector chemical. The particular chemical depends on which mineral is being refined. As an example, SEX is added as a collector in the selective flotation of galena and sphalerite, after the addition of other flotation reagents. This slurry (more properly called the pulp) of hydrophobic particles and hydrophilic particles is then introduced to a water bath which is aerated, creating bubbles. The hydrophobic particles attach to the air bubbles, which rise to the surface, forming a froth. The froth is removed and the concentrate (con) is further refined.2.Gravity separation is an industrial method of separating two components, either a suspension, or dry granular mixture where separating the components with gravity is sufficiently practical: ie the components of the mixture have different specific weight. All of the gravitational methods are common in the sense that they all use gravity as the dominant force. Gravity separation is used in a wide variety of industries, and can be most simply differentiated by the characteristics of the mixture to be separated - principally that of 'wet' ie - a suspension versus 'dry' -a mixture of granular product. Often other methods are applied to make the separation faster and more efficient, such as flocculation, coagulation and suction. The most notable advantages of the gravitational methods are their cost effectiveness and in some cases excellent reduction.3.Magnetic separation is a process in which magnetically susceptible material is extracted from a mixture using a magnetic force. This separation technique can be useful in mining iron as it is attracted to a magnet.In mines where wolframite was mixed with cassiterite, such as South Crofty and East Pool mine in Cornwall or with bismuth such as at the Shepherd and Murphy mine in Moina, Tasmania, magnetic separation was used to separate the ores. At these mines a device called a Wetherill's Magnetic Separator (invented by John Price Wetherill, 1844?1906) was used. In this machine the raw ore, after calcination was fed onto a moving belt which passed underneath two pairs of electromagnets under which further belts ran at right angles to the feed belt. The first pair of electromagnets was weakly magnetised and served to draw off any iron ore present. The second pair were strongly magnetised and attracted the wolframite, which is weakly magnetic. These machines were capable of treating 10 tons of ore a day.It is also used in electromagnetic cranes that separates magnetic material from scraps.

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