Environmental Aspects of Phosphate and Potash Mining United ...

Environmental Aspects of Phosphate and Potash Mining
Water Management and Treatment
The Foskor Ltd. operation at Phalaborwa is located in
the semi-arid northeast of South Africa, adjacent to the
Selati River and upstream from the Kruger National
Park.
The processing operation uses 250 million litres of
water per day, the majority of which is recirculated.
Excess water is transferred to the tailings dam before
release to the Selati River. The tailings water is high in
both total dissolved solids (TDS) and sulfates. The sulfates
are largely introduced with tailings sourced from
the adjacent Phalaborwa Copper mine, which currently
supplies about 40% of the phosphate ore feed for the
Foskor beneficiation plant.
Concerns by Kruger National Park management about
the potential effect of contaminated water on the
downstream aquatic ecosystem led to the implementation
of a water treatment system.
After consideration of the most suitable water treatment
processes on the market, the ‘Paques’ process was
selected. This bacterial process converts sulfates in the
tailings water to sulfur.The sulfur is subsequently recovered
and sold to the adjacent fertilizer processing
complex for use in the production of sulfuric acid.
The process is used to treat about 40 to 50 mega-litres
per day. Monitoring of the release is conducted as part
of a comprehensive surface and ground water monitoring
system for the site that includes biological
monitoring points located on the Selati River.
The water treatment system protects the downstream
aquatic ecosystem and the natural values of the Kruger
National Park. Additionally, the sulfur by-product can be
sold to recover a portion of the operating costs.
Selati River flowing adjacent to the tailings dam - Foskor
Ltd, South Africa
Water Contamination
Surface and ground water contamination may occur
through the release or seepage of tailings effluent and
brines from dams, ponds and stacks. Contaminants
might include clay fines, chemical reagents, sulfates,
salt and magnesium chloride. In addition, rainfall may
dissolve salt tailings or cause erosion and mobilize
fines.
Depending on the operation, water releases are
required to maintain the water balance of the operations
storage facilities. In most countries, this water
must meet established water quality standards. To
achieve this, excess water is treated through a system
of dams and wetlands to clarify and remove contaminants.
Where possible clean water and contaminated water
on the mine site are kept separate and handled
through different systems, to reduce the quantity of
water that must be treated before release.
Aquatic species are sometimes used as an indicator of
the performance of the waste management system.
Monitoring the biodiversity of aquatic species downstream
from release points provides an indicator of
environmental response.
The leakage of liquid wastes such as brines from storage
and disposal ponds is controlled to a large extent
by containment techniques such as plastic or clay liners,
ditches, drains and containment pumping wells.
Landscape Disturbance
The construction and operation of surface waste storage
facilities typically disturbs a significant area of
land. Some operations have reduced the area affected
by stacking wastes higher. In other cases, wastes are
disposed of to mined-out areas, avoiding impacts on
undisturbed areas.
Rehabilitation of disposal areas to mitigate environmental
effects is discussed in Sections 3.7 “Closure”
and 3.8 “Rehabilitation”.
Tailings Stability and Failure
The potential for accidental failure of waste disposal
dams and ponds is of concern. This can cause rapid,
extensive and widespread impacts on the surrounding
environment. The installation of monitoring systems,
preparation of emergency response plans and procedures,
and the regular auditing of performance assist