Environmental Aspects of Phosphate and Potash Mining United ...

Overview of Phosphate Rock and Potash Mining and Beneficiation
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Figure 2.2
Common potash mining processes and equipment
Extraction
Handling
Underground
Solution
Surface
Beneficiation / concentration
Size reduction
Desliming
Concentration
Dewatering
Drying
Compaction
Granulation
Storage
Continuous mining
machine
Longwall
Load-haul-dump (LHD) units
Drill and blast
Injection wells
Recovery wells
Evaporation ponds
Shuttle cars
Conveyors
Feed bins
Shaft or decline haulage
Brine pipelines
Cooling ponds
Crushing
Grinding
Screening
Hydrocyclones
Attrition scrubbing
Hydrocyclones
Flotation
Thermal dissolution-
-crystallization
Electrostatic separation
Heavy-media separation
Filters
Thickeners
Centrifuges
Rotary ovens
Fluidised bed dryers
Rotary compactor
Granulator
Conveyors
Sheds
Although it is not strictly mining, the concentration of
brine in solar evaporation ponds is another method of
producing potash ore. The method relies on the evaporation
of brine through a series of shallow ponds.
The initial ponds are used to precipitate halite (NaCl)
and concentrate the desired minerals, the brine is then
pumped into a second series of ponds in which the
potash ore, mostly carnallite, is precipitated. The carnallite
is harvested and pumped as a slurry to
beneficiation facilities for processing.
Potash Beneficiation
The processing of potash generally involves a series of
steps including:
Size reduction;
Desliming;
Separation;
Drying;
Compaction and granulation;
Disposal of the waste streams.
The specific process employed will depend on factors
such as the characteristics and constituents of the
potash ore and the market specifications.
Generally, the ore is reduced in size using a system of
crushing and grinding to liberate the different minerals
from each other. This is usually followed by
desliming by intense agitation followed by flotation or
hydrocyclones to separate the fines consisting of clays,
dolomite and sand from the potash ore.
Four basic techniques are used to separate the waste
minerals or by-products such as salt and concentrate
the potash; flotation, electrostatic separation, thermal
dissolution-crystallization, and heavy media separation.
Several of these may be used together to enhance
recovery.
Flotation is the most widely used technique, relying on
the difference in surface properties between minerals
to selectively float the desired mineral. Electrostatic
separation is a dry process in which the minerals are
separated using their different electrical conductivities.
Thermal dissolution-crystallization relies on the
same principle as solution mining, whereby a heated
brine preferentially dissolves potassium chloride.
Heavy media separation relies on the difference in specific
gravity between sylvite and halite to selectively
float and remove the lighter sylvite particles.