OVERVIEW OF THE IMPACT OF MINING ON THE ... - IIED pubs

Where the available moisture exceeds the losses due to evaporation, AMD can be
expected to “move” away from its source and pose a larger problem for a mining
operation. This tendency is reflected in the use of the Weinert N weathering
index. Physical or mechanical weathering processes dominate in areas with a
high Weinert N index experience; available moisture levels are low and AMD is
seldom a problem. The converse holds for moister areas with a low Weinert N
index. Whilst this understanding will not resolve existing AMD problems, it
provides useful information as to the most suitable types of effluent processing
and control processes that will be needed for new mines in specific areas.
• No universal or permanent “cure” for the AMD “problem” has yet been found, though temporary, site-specific
solutions have been demonstrated in several southern African mining operations. It is therefore possible
that AMD problems will continue to persist for the foreseeable future despite the enormous expenditures
and concerted attention paid to the problem so far. However, despite this somewhat gloomy outlook, the
collaborative COALTECH 2020 initiatives in South Africa have shown real promise in devising innovative
ways to manage the AMD problem. This initiative involves representatives of all the major mining houses,
as well as scientists, engineers and academics, and seems to offer the greatest opportunity of dealing with
the AMD issue successfully.
6.1.2 Impacts due to the release of potentially toxic metals
No mining operation is ever fully successful in recovering every part of the metal or metals that it seeks to
extract. Residual metals that pass through the mining processes enter the external environment where they
have the potential to pose varying types of problem to the biophysical environment. The most noticeable
problems concern the toxicity of nearly all metals when they are present as metal ions in solution. Almost every
metal has the potential to cause some form of harm to aquatic life if it is present in sufficiently high
concentrations. The more important “problem” metals are mercury, cadmium, chrome, vanadium, zinc, copper,
and, to a lesser extent, iron and manganese, because these metals exert toxic effects at relatively low
concentrations if they are present in specific oxidation states or forms.
Specific areas of concern around potentially toxic metals are:
• The release of hexavalent chrome from chrome mining operations and from ferroalloy smelters and
refineries in South Africa and Zimbabwe. If discharged to the aquatic environment, hexavalent chrome can
be extremely toxic to aquatic life.
• The persistent use of mercury to concentrate gold by artisan gold miners poses toxicity risks to the aquatic
environment and to the health of the miners. It appears that almost every artisan gold mining operation in
Malawi, Mozambique, South Africa, Tanzania, Zambia and Zimbabwe uses mercury extraction methods
• Vanadium and chrome contamination of ground and surface waters by vanadium and chrome mines located
on the Bushveld Igneous Complex in South Africa, particularly the Steelpoort Valley and the region around
Rustenburg in the Crocodile sub-catchment.
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