Environmental Aspects of Phosphate and Potash Mining United ...

The Environmental Approach of the Phosphate Rock and Potash Mining Industry
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Pit Wall Erosion Control
Heavy weathering of the overburden and orebody at
the Catalão phosphate rock mine of Copebras S.A.
means the pit walls are extremely prone to erosion
creating concern about the stability of the 80 metre
high final pit walls. The company has implemented a
number of measures in response.
Temporary internal pit walls are designed and excavated
to a steeper overall slope. As excavation occurs
against the designed pit limits, the pit wall slopes are
flattened to enhance long-term stability. Final pit walls
are designed with an overall slope of 34o, consisting
of five metre wide catch berms placed every five
metres vertically, with an intervening wall slope of
60o. The catch berms are sloped back into the pit wall
to capture any rainfall and prevent erosion of the pit
wall by run-off. Excess water collecting on the berms is
transferred to the bottom of the pit through a series of
pipe drains constructed from 44-gallon drums welded
together. The berms are vegetated to enhance stability.
The approach leaves a final pit wall that resists the
erosion effects of rainfall, enhancing establishment of
vegetation and long-term stability.
Final pit wall with drains - Copebras S.A., Brazil
Beneficiation waste disposal impoundments, dams,
and ponds may contain materials that may present an
ongoing threat to the environment if not rehabilitated
effectively.
At some operations, the clay fines generated during
beneficiation of phosphate rock are drained and
allowed to consolidate. Landscaping is required to
establish suitable drainage. The clay fines may be suitable
for conversion to agricultural land due to the
elevated phosphate levels and good water retention
properties, grassland or forest.
Potash salt tailings present an ongoing issue due to the
potential for dissolution of the salt by rain. In
response to this, a number of rehabilitation methods
have been implemented including dissolution of the
salt, disposal of the resulting brines and capping of the
salt pile with impermeable layers.
Commonly, the surface of shafts are capped to prevent
humans or wildlife falling into them. In potash mines,
shafts are sealed just above the orebody to prevent
water from overlying aquifers entering, dissolving ore,
and presenting a future water contamination issue.
Sealing of Decommissioned Shafts
Kali und Salz GmbH in Germany has conducted
research into the sealing of disused potash mine
shafts, in partnership with a local University. The purpose
of the shaft sealing is to prevent water from
entering the orebody and dissolving salts from the
evaporite beds. If this occurs the overlying aquifers
may become contaminated with salt.
Research has focused on the use of bentonite clay
plugs placed in the shaft above the evaporite horizons.
Water coming into contact with the bentonite
will cause it to swell, sealing any possible paths of
ingress.
Vegetated pit wall - Copebras S.A., Brazil
Revegetation
Revegetation is typically conducted to stabilize the disturbed
areas and prevent wind and water erosion. This
can vary from planting or seeding with a single grass
species, conversion to agricultural or forestry purposes,
through to the establishment of quite complex
ecosystems involving upland forests, grasslands and
wetlands. Where natural ecosystems are being reestablished,
native species tend to be used, but faster
growing non-native grass species are sometimes used