Environmental Engineering Reference
In-Depth Information
ions to sulphides producing bicarbonate alkalinity and hydrogen sulphide, which reacts
with metals, forming insoluble sulphides.
Remediation
In many parts of the world, there are abandoned mine sites where active ARD is occur-
ring. In Canada, the Mine Environment Neutral Drainage Program in 1994, estimated the
cost of remediation of acid generating mine wastes in Canada to be $ 3 billion. (MEND
1995) While the total quantities of potentially acid generating materials in Australia are
comparable to those in Canada, the estimated remediation costs in Australia are consider-
ably lower, amounting to less than $ 50 million for the remaining unrehabilitated aban-
doned sites (Harries 1997). This i gure does not include the numerous sites in remote, arid
parts of Australia where high evaporation rates limit the potential damage from ARD.
It is also a fact that much of Australia's historic mining has taken place in the oxidized
zone where sulphide minerals have been absent.
The issues involved and the potential control measures are essentially the same as those
affecting operating mines. However, the costs may be much higher because:
In Canada, the Mine Environment
Neutral Drainage Program in
1994, estimated the cost of
remediation of acid generating
mine wastes in Canada to be
$ 3 billion.
Records of construction and operation are generally unavailable or inadequate, and
considerable effort is required to identify the issues and to characterize the mine
wastes, and extent of contamination;
Following abandonment, structures such as tailings embankments and retaining walls
may have failed, discharging their contents which may have been transported well
beyond their original storage area;
Plumes of contaminated groundwater may have migrated well beyond the sources of
contamination; and
The capacity for treatment of problems no longer resides at the site. Investigators and
designers need to be recruited from outside and require time to become familiar with
the situation. Similarly, equipment for remediation may need to be mobilized from a
distance. This contrasts with an operating mine situation where most of the personnel
and equipment are already available.
Remediation seldom produces saleable products, although there have been numerous
examples of tailings re-treatment where the income generated paid for the necessary ARD
controls that had not previously been implemented. Lack of funds constrains many reme-
diation efforts, particularly at 'orphan sites' where the previous owners no longer exist and
which therefore depend, for remediation, on public funds. Nevertheless, there are many
examples where ARD from abandoned mine sites has been substantially reduced (see
for example Case 17.1 ), or treated to the extent that the receiving environment has been
returned to a condition comparable to that which existed prior to mining.
Lack of funds constrains many
remediation efforts, particularly
at 'orphan sites' where the
previous owners no longer exist.
REFERENCES
Environment Australia (1997) Managing Sulphidic Mine Wastes and Acid Drainage,
Booklet in the series 'Best Practice Environmental Management in Mining.' Principal
contributors: John Johnston and Gavin Murray, May 1997.
Harries J (1997) Acid Mine Drainage In Australia - Its Extent and Potential Future
Liability. A joint initiative of the Ofi ce of the Supervising Scientist and the Australian
Centre for Minesite Rehabilitation Research. Supervising Scientist Report 125.
Supervising Scientist, Canberra, Australia.
 
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