Professional Items in Comminution Process
Most of the minerals are finely disseminated and intimately associated with the gangue so; they must be initially liberated before separation can be done. Comminution is the process in which the particle size of the ore is progressively reduced until the clean particles of mineral can be separated by such methods as are available. Comminution in its earliest stages can also be carried out in order to make the freshly excavated material easier to handle by scrapers, conveyors, and ore carriers, and in the case of quarry products to produce material of controlled particle size in the dryer machine.
Blasting can be described as the first stage of comminution carried out in the mine site in order to remove ores from their natural beds. Comminution in the mineral processing plant takes place in a sequence of crushing and grinding processes. Crushing reduces the particle size of run-of-mine ore to such a level that grinding mill can further grind it until the mineral and gangue is substantially produced as separate particles.
Crushing is accomplished by compression of the ore against rigid surfaces, or by impact against surfaces in a constrained motion path. Grinding is accomplished by abrasion and impact of the ore by the free motion of unconnected media such as rods, balls, or pebbles.
Crushing is usually a dry process, and is performed in several stages, reduction ratios being small, ranging from three to six in each stage. The reduction ratio of a crushing stage can be defined as the ratio of maximum particle size entering to maximum particle size leaving the crusher, although other definitions are sometimes used. There are a number of crushers available as jaw, gyratory, cone, roll, and impact crushers.Impact crusher:http://www.hx-china.com/3.html
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Grinding is usually performed wet to provide a slurry feed to the concentration process, although dry grinding has limited applications. There is an overlapping size area where it is possible to crush or grind the ore. From a number of case studies, it appears that at the fine end of crushing operations equivalent reduction can be achieved for roughly half the energy and costs required by grinding mills (Flavel, 1978).
Tumbling mills for size reduction with either steel rods (rod mills) or balls (ball mill), or sized ore (AG & SAG mills) as the grinding media used depending upon the size and energy considerations.
Ore grindability refers to the ease with which materials can be comminuted, and data from grindability tests are used to evaluate crushing and grinding efficiency. Most widely used parameter to measure ore grindability is the Bond work index Wi that is described in previous paragraph. Berry and Bruce (1966) developed a comparative method of determining the grindability of an ore. The method requires the use of a reference ore of known grindability. The reference ore is ground for certain time and the power consumption recorded. An identical weight of the test ore is then ground for a length of time such that the power consumed is identical with that of the reference ore.
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