Environmental Aspects of Phosphate and Potash Mining United ...

The Environmental Approach of the Phosphate Rock and Potash Mining Industry
Other impacts may include: wind-generated dust
from fines tailings; adverse effects on wildlife; and the
visual disturbance resulting from large elevated dams
or tailings stacks.
Waste Disposal Methods
A wide variety of waste disposal methods are
employed, including:
Discharge of wastes to rivers and oceans. This may
be accompanied by treatment to remove contaminants;
Stacking wastes such as sand tailings and salt tailings
in piles;
Retention of wastes such as brines, sand tailings,
magnetite tailings, clays and process water in dams
or ponds for storage, settling and clarification;
Backfilling of solid and liquid wastes into minedout
underground openings;
Deep well injection of brines.
The methods used at a specific location are influenced
by the characteristics of the waste and the site, and the
regulating requirements.
In some instances, liquid wastes such as brines, tailings,
effluent or clay fines have been discharged to
rivers or oceans. This may be done in a controlled
manner using monitoring systems to ensure that levels
of contaminants do not rise above prescribed levels
and threaten the aquatic ecosystem. Treatment of
phosphate rock tailings effluent improves the quality
of the release.
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Riverine Brine Disposal
Kali und Salz GmbH operate three potash operations in
the Werra region of Germany: Hattorf; Unterbreizbach;
and Wintershall. The operations extract a complex mineralized
ore 'Hartsalz', that consists of a mixture of
sylvinite, carnallite, kieserite, and halite from a deeply
buried potash deposit.
The ore is beneficiated using both dry electrostatic separation
and wet thermal dissolution separation
processes to produce a variety of potassium and magnesium
products. For each tonne of ore beneficiated,
22% becomes product, while 78% becomes waste. The
waste consists predominantly of salt tailings and magnesium
chloride (MgCl 2 ) brines. The process employed
allows the salt to be largely separated dry from potash,
Figure 3.6.2
Control of salt concentration in Werra River.
Kali und Salz GmbH, Germany.
Chloride
content
mg/l
30000
25000
20000
15000
10000
5000
0
producing dry salt tailings. On the other hand, magnesium
chloride can only be separated from the potash in
solution. This results in significant quantities of brine
being produced.
The salt tailings are generally conveyed to a salt stack on
the surface for disposal. Some salt tailings are used to
backfill carnallite rooms produced at the
Unterbreizbach underground mining operation. Brines
are disposed of by either deep well injection into a suitable
pervious dolomite formation or discharged to the
Werra and Ulster river system.
Brine waste produced at each beneficiation plant is
pumped to a series of lined retention ponds from which
discharge occurs to the river system. The discharge is
monitored and controlled using a computer system to
ensure that the permitted salt concentration of 2.5
grams per litre of river water is not exceeded as the river
conditions and flow rate vary.
The system prevents adverse effects on the aquatic
ecosystem downstream.
Brine retention ponds for controlled release to Werra River -
Kali und Salz GmbH, Germany