Environmental risk of mining - Environmental Deterioration and Contamination: Problems and their Management - page 116

hard minerals, mainly those containing metals (De la Vergne, 2003) such as ore con-
taining gold, silver, iron, copper, zinc, nickel, tin and lead, but also involves using the
same techniques for excavating ores of gems such as diamonds. In contrast, soft rock
mining refers to a group of underground mining techniques used to extract coal, oil
shale and other minerals or geological materials from sedimentary (“soft'') rocks.
Solution or fluid mining is a relatively new but rapidly growing field (Bartlett,
1998) for the extraction of metals, minerals and materials from the earth through
leaching and fluid recovery. Solution or fluid mining covers

- Recovery of water-soluble minerals, by dissolving the minerals with water (e.g.

minerals such as salt, potash, trona, and magnesium salts may be produced by
pumping saturated fluid from underground caverns. The caverns are created by
pumping out the saturated brine while pumping in fresh water as a controlled
production process. The minerals are then recovered from the saturated fluid by
recrystallization);

- Recovery of acid-soluble minerals/metals from solutions by dissolving under-

ground materials and pumping them to the surface (e.g. acidic leaching solution
injected into the deposit to dissolve the acid-soluble minerals-in situ leaching);

- Melting underground materials with hot water and pumping them to the surface;

- Washing insoluble material by underground jets and pumping the slurry to the

surface;

- Driving material from well to well by gas drive, water drive, or combustion;

- Extracting the metals from hydrothermal fluid vents from under the ocean.

Except the last one, solution mining is done by wells. Both solution and fluid
mining result in a solution enriched in the minerals, which is then retrieved and sent
to a solvent extraction or electrowinning plant. This method is used for copper and
potash mining.

2.2.2 Mineral processing

After the ore containing the desired material has been extracted, it is generally necessary
to separate the wanted constituents from the unwanted ones, and to create a more uni-
formly sized material for subsequent processing. Such operations, collectively referred
to as mineral processing, are often carried out near the extraction site (mine) to min-
imize transport of low-value materials. Mineral processing primarily directed toward
resizing includes milling (crushing, grinding), sizing (screening, centrifugation), con-
solidation (sintering, pelletizing, briquetting). Beneficiation processes carried out with
the objective of removing impurities or concentrating desired material include wet pro-
cesses (washing, leaching, flotation, dissolution or solvent extraction, followed by crys-
tallization or precipitation, filtration, electrowinning, ion exchange), thermal processes
(calcining, roasting, autoclaving, drying), magnetic and electrostatic separation.

3 ENVIRONMENTAL IMPACTS

Mining operations have an impact on the environment through the extraction and
processing of the raw material, using large amounts of water and hazardous chemi-
cals. Transportation of huge amounts of run-of-mine ore and processed material or