Mineral processing is, in general, the most important downstream operation for mining engineers. This is because mostmined material—from hard-rock ores to coal to industrial minerals—is subjected to some type of comminution or beneficiationoperation. In most cases, several unit operations are performedsequentially in order to produce a marketable product or feed toan extraction operation such as leaching or smelting.
A tremendous number of unit operations are included under the broad heading of mineral processing. The breadth reflects the need to beneficiate everything from dense, competent hardrock ores to solid-fuel minerals like coal or oil shale to a wide range of industrial minerals that include hard, dense materials; soft, sticky clays; and light, fluffy minerals like vermiculite.
Comminution or size reduction is typically the first unit operation to which mined material is subjected. Crushing describes the breakage at coarse sizes, while grinding covers size reduction for fine particles. The run-of-mine ore is typically subjected to primary crushing in jaw or gyratory crushers , then secondary/tertiary crushing using cone crushers, roll crushers, hammer mills, or impactors. Crushing is generally followed by grinding. In this operation, material is reduced from about 12 to 25 mm (0.5 to 1.0 in.) down to very fine particle sizes.
The grinding may employ rod mills, ball mills, autogenous or semiautogenous mills, pebble mills, roller mills, fluid energy mills, or other types of grinding mills. Concurrent with crushing and grinding are the classification operations that sort and separate the crushed or ground particles on the basis of size and/or weight. The classification may be done by screening using stationary or vibrating screens or with sieve-bend screens. Hydrocyclones or mechanical classifiers (spiral, rake, or drag units) may also be used.
Comminution and classification are often followed by concentration. This is commonly done by flotation, a method that collects values, or less frequently, rejects gangue constituents in a stable froth. This involves use of aeration and/or agitation in conjunction with reagents that affect the surface chemistry of the fine particles.
Another approach to concentration involves gravity systems (heavy media separation, centrifugal specific gravity separation, jigging, tabling, and flowing film concentration). Gravity operations are less common than flotation, but are still widely used in coal preparation, beach sand processing, and placer operations.
Magnetic and electrostatic methods of concentration and separation also find some application in mineral processing, for example, magnetite concentration. Other operations of importance in mineral processing include mixing, thickening, clarifying, filtering, and drying. A wide range of mechanical equipment is used in these applications. Important ancillary operations include materials handling and feeding, particle agglomeration (pelletizing, briquetting, or sintering), and such activities as dust control, water treatment, and tailings disposal. The following segments are not intended to be comprehensive—there are the SME Mineral Processing Handbook and many other authoritative publications for this purpose.
However Comminution and classification are often followed by concentration. This is commonly done by flotation, a method thatcollects values, or less frequently, rejects gangue constituents ina stable froth. This involves use of aeration and/or agitation inconjunction with reagents that affect the surface chemistry ofthe fine particles. Another approach to concentration involvesgravity systems (heavy media separation, centrifugal specificgravity separation, jigging, tabling, and flowing film concentration). Gravity operations are less common than flotation, but arestill widely used in coal preparation, beach sand processing,and placer operations.
Magnetic and electrostatic methods ofconcentration and separation also find some application in mineral processing, for example, magnetite concentration.Other operations of importance in mineral processing includemixing, thickening, clarifying, filtering, and drying. A widerange of mechanical equipment is used in these applications.Important ancillary operations include materials handling andfeeding, particle agglomeration (pelletizing, briquetting, or sintering), and such activities as dust control, water treatment, andtailings disposal.The following segments are not intended to be comprehensive—there are the SME Mineral Processing Handbook andmany other authoritative publications for this purpose.
However the most universal operations are covered in order to give the miner some perspective on what happens to his ore once it leaves the mine. These key unit operations include crushing, grinding, screening, hydrocycloning, flotation, gravity concentration, and magnetic separation. Each of these topics is covered in sufficient depth to give the reader some feel for the principles and practices involved.
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Mineral processing industry and mineral mining industry
Mineral processing is, in general, the most important downstream operation for mining engineers. This is because mostmined material—from hard-rock ores to coal to industrial minerals—is subjected to some type of comminution or beneficiationoperation. In most cases, several unit operations are performedsequentially in order to produce a marketable product or feed toan extraction operation such as leaching or smelting.
A tremendous number of unit operations are included under the broad heading of mineral processing. The breadth reflects the need to beneficiate everything from dense, competent hardrock ores to solid-fuel minerals like coal or oil shale to a wide range of industrial minerals that include hard, dense materials; soft, sticky clays; and light, fluffy minerals like vermiculite.
Comminution or size reduction is typically the first unit operation to which mined material is subjected. Crushing describes the breakage at coarse sizes, while grinding covers size reduction for fine particles. The run-of-mine ore is typically subjected to primary crushing in jaw or gyratory crushers , then secondary/tertiary crushing using cone crushers, roll crushers, hammer mills, or impactors. Crushing is generally followed by grinding. In this operation, material is reduced from about 12 to 25 mm (0.5 to 1.0 in.) down to very fine particle sizes.
The grinding may employ rod mills, ball mills, autogenous or semiautogenous mills, pebble mills, roller mills, fluid energy mills, or other types of grinding mills. Concurrent with crushing and grinding are the classification operations that sort and separate the crushed or ground particles on the basis of size and/or weight. The classification may be done by screening using stationary or vibrating screens or with sieve-bend screens. Hydrocyclones or mechanical classifiers (spiral, rake, or drag units) may also be used.
Comminution and classification are often followed by concentration. This is commonly done by flotation, a method that collects values, or less frequently, rejects gangue constituents in a stable froth. This involves use of aeration and/or agitation in conjunction with reagents that affect the surface chemistry of the fine particles.
Another approach to concentration involves gravity systems (heavy media separation, centrifugal specific gravity separation, jigging, tabling, and flowing film concentration). Gravity operations are less common than flotation, but are still widely used in coal preparation, beach sand processing, and placer operations.
Magnetic and electrostatic methods of concentration and separation also find some application in mineral processing, for example, magnetite concentration. Other operations of importance in mineral processing include mixing, thickening, clarifying, filtering, and drying. A wide range of mechanical equipment is used in these applications. Important ancillary operations include materials handling and feeding, particle agglomeration (pelletizing, briquetting, or sintering), and such activities as dust control, water treatment, and tailings disposal. The following segments are not intended to be comprehensive—there are the SME Mineral Processing Handbook and many other authoritative publications for this purpose.
However Comminution and classification are often followed by concentration. This is commonly done by flotation, a method thatcollects values, or less frequently, rejects gangue constituents ina stable froth. This involves use of aeration and/or agitation inconjunction with reagents that affect the surface chemistry ofthe fine particles. Another approach to concentration involvesgravity systems (heavy media separation, centrifugal specificgravity separation, jigging, tabling, and flowing film concentration). Gravity operations are less common than flotation, but arestill widely used in coal preparation, beach sand processing,and placer operations.
Magnetic and electrostatic methods ofconcentration and separation also find some application in mineral processing, for example, magnetite concentration.Other operations of importance in mineral processing includemixing, thickening, clarifying, filtering, and drying. A widerange of mechanical equipment is used in these applications.Important ancillary operations include materials handling andfeeding, particle agglomeration (pelletizing, briquetting, or sintering), and such activities as dust control, water treatment, andtailings disposal.The following segments are not intended to be comprehensive—there are the SME Mineral Processing Handbook andmany other authoritative publications for this purpose.
However the most universal operations are covered in order to give the miner some perspective on what happens to his ore once it leaves the mine. These key unit operations include crushing, grinding, screening, hydrocycloning, flotation, gravity concentration, and magnetic separation. Each of these topics is covered in sufficient depth to give the reader some feel for the principles and practices involved.