Material extracted from the earth is thoroughly processed in the mining process. Mining products used on a daily basis, such as metals, are the end result of a long series of transformations.
The series of transformations starts with the rock in the earth’s crust. Various minerals are formed in the earth’s crust as the result of different deposits and compound combinations. These mineral deposits are called ore. Most ore contains unnecessary minerals that are removed in the mineral process.
The type of mining process used depends on the type of mineral being processed. Minerals are usually categorized as rock materials, industrial minerals (e.g. clay), base metals (e.g. copper) and precious metals (e.g. gold). Other materials used by industry, such as coal, potash, iron ore and diamonds, are also mined.
Beginning of the process
Rock material is mined using explosives and quarrying. Large boulders are transported to big crushers that crush the rock material into smaller grain size.
Various sizes of crushers, both stationary and mobile, are used at mines. Among the types used are primary gyratory crushers, impact crushers, gyratory crushers, cone crushers and jaw crushers. The material to be crushed is fed into the crusher either via a conveyor, an excavator or a wheeled loader (reclaimer)
After crushing, the rock material is ground in grinding mills. There are a variety of different grinding mills, including rod and ball mills, semiautogenous (SAG) mills and autogenous mills. In the grinding mills, the impact of the minerals grinding against each other and against the steel balls in the mill breaks down the size of the minerals even further.
The mining process also includes a vibrating screen that sorts the crushed material into desired grain sizes.
Rock material is extremely hard and thus it wears down the crushers and grinders. Therefore the wear parts, like the various blades and rotors and the liners of grinding mills, must be replaced regularly.
In the mineral process valuable minerals are concentrated by removing unnecessary substances from the excavated rock material. The first phase of the process involves reducing the size of the mineral. This is done in crushers and grinding mills where the ore is broken down into smaller pieces.
When the fragments of ore are small enough, the pieces containing the most valuable minerals are separated from those containing mostly unneeded minerals. The separation process involves leaching, emission, gravity methods and magnetic separation. Emission chambers and pipes, coils and magnetic separation equipment are used in the separation process. Water must also be extracted from the concentrated product. Coils, filters, thickeners, sedimentation basins and dryers are used to do this.
In the next phase, metal is extracted from the mineral. Extraction methods vary depending on the product, but the main methods are pyrometallurgy (a metal production method employing high temperatures), hydrometallurgy (producing metal by leaching the raw material and flocculating the pure metal from the solution) and electrometallurgy (a metal production method applying electricity). Electrolysis, a forced oxidation-reduction reaction achieved using electric current, is an integral part of electrometallurgy. Electrolysis can be used to produce very pure elements.
After the extraction phase, the metals still contain impurities, so they must be purified. The refining process uses heat, chemicals and electricity. Electrowinning is used in gold refining.