Revolution in treating contaminated mines
A by-product of bauxite refining is proving invaluable as a method of cleaning up metal-rich, acid mine water.
Acid mine drainage (AMD),
failed tailings dams, sulphidic
mine wastes and
acidic soils blight the mining
industry year after year.
There is no more obvious
example of the impact the mining
industry can have on the environment
than the Baia Mare cyanide
spill of February 2000. In one of
Europe’s worst environmental
tragedies, toxic wastewater poured
from a failed tailings dam. Up to
100,000m³ of tailings water contaminated
with a lethal cocktail of
cyanide and heavy metals was discharged
from a Romanian tailings
pond when abnormally high winter
temperatures and precipitation
caused the dam to be breached.
Virotec International was called in
to demonstrate how it could use
BauxolTM technology to prevent such
an event ever occurring again. The
results surprised independent
observers including former EU mining
executive, Folmer BangHansen.
‘We found this [BauxolTM] to be one
of most effective methods for cleaning
up acid mine water and heavy
metal pollution,’ he said.
Baia Mare is just one case of the devastating potential of AMD. The combination
of heavy metals and high acidity can damage water resources, kill off eco-systems
and trigger disease. The cost to the mining industry in political and financial
terms is enormous. In the US around 2.7 million tonnes of acid rock drainage
is generated each year polluting more than 26,000km of waterways. Globally over
the past 50 years, there have been more than 250 recorded tailings dam failures.
The useful properties of BauxolTM
technology were first recognised by
scientists in Australia in the early
1990s. The technology has since
been developed following eight years
of environmental research and laboratory
testing. BauxolTM is produced
by chemically and physically modifying
the residue from alumina refining
enabling it to neutralise acid and
reduce the concentration of heavy
metals by up to 100,000 times.
The technology works by attacking
the dangerous components of
AMD. When Bauxol
TM is added to
metalladen mine water it triggers a
chemical reaction with the heavy
metal contaminants which are then
bound on to the fine grains as insoluble
minerals. Dr David McConchie,
professor of engineering and environmental
geochemistry at Southern
Cross University and a Virotec director
TM adsorbs on in
the first place but then the minerals
present recrystallise to form totally
new minerals with low solubilities.’
The new minerals are very stable.
We have found that the longer you
leave it after the metals have been
bound on, the more tightly they get
bound,’ says McConchie. ‘If you try
and leach them off a week after the
treatment, you get a small proportion
off but if you wait six months,
you get even less off.’
Bauxol TM grains settle within 48 hours to
form a thin layer of sediment. No more than 2-3mm thick, the sediment continues
to extract trace metals from the AMD water for up to 160 days.
McConchie, who leads Virotec’s
research team, is confident his company
has a product for remediating
AMD, acid sulphate soils, sulphidic
mine tailings, waste rock dumps and
a range of other environmental prob
lems. As well as a high trace metal
trapping potential, Bauxol
TM has a
high acidic neutralising capacity:
2.57.5 moles of acid per kg.
The potential of Bauxol
was first demonstrated on a large
scale in July 2000. Virotec applied it
to a 10m deep, 1,500Ml tailings dam
at Mount Carrington in northern
New South Wales. It was the largest
body of contaminated AMD water
ever treated by direct addition
methods. Red Bauxol
TM powder was
sprayed directly onto the dam. It dispersed,
settled within 48 hours and
left the water completely clear.
‘The Mount Carrington dam was
classified by the mines department
of New South Wales as the third
worst potential disaster in the state,’
says Virotec’s executive chairman
Brian Sheeran. But after treatment
TM, more than 99.99% of
the heavy metals were bound up and
converted into new and harmless
crystalline substances which quickly
settled out of the water. Also, the
acidic water was neutralised.
In little over a few weeks, Virotec
cleaned the toxic dam water to stringent
standards allowing it to be
released safely into the nearby
Plumbago Creek catchment over the
following 12 months at the rate of 1
to 2Ml per day. Discharge water has
bettered background levels in the
catchment over the period and
aquatic life has returned, not only to
the dam but also to the immediate
The results achieved in the 12
months following treatment show
that the water quality is maintained,
but treatment still occurs long after
active treatment ceases. Before treatment,
pH levels in the dam were 5.2.
Immediately after treatment, the pH
of the water increased to 7.3 and 12
months later stood at 8.1. Zinc levels
before treatment were in the region
of 11,570µg/l. After treatment, the
level dropped to 39µg/l and currently
stands at less than 1µg/l.
Similar reductions in other heavy
metals have been noted.
During the treatment process,
metal contaminants remain locked
in the Bauxol
TM sediment with no
evidence of redissolution.
The fine residue remaining after
treatment differentiates Bauxol
TM from traditional processes which can
leave a highly dispersed sludge. The
residue is inert and can be used as a
soil conditioner after it has captured
and bound up heavy metals. Treated
water can then be safely released and
sold on for irrigation, process or
drinking water purposes, or simply
released back into local ecosystems.
TM technology has been
used to remediate AMD at other
sites. Similar reductions in heavy
metals have been observed at Mount
Morgan, Queensland and Captains
Flat, NSW. Projects are being
planned for western Europe, which
is supplied with Bauxol
TM from an
alumina refinery on Sardinia.
Bauxol TM is also being applied to environmental
scalds such as acid sulphate soils and is helping to renew vital plant life.
Other applications of the technology include treating chromium-rich acidic tannery
effluent, treating leachates from domestic and industrial waste disposal sites,
removing arsenic from drinking water, phosphate removal to prevent blue green
algal blooms, improving plant growth in soils with poor water and nutrient holding
capacity, and treating sulphidic marine sediments.
In July 2001, Virotec started trading
on London’s Alternative
Investment Market (AIM) after a
$10.7M capital raising closed oversubscribed.
Later this year, the company
intends to apply for listing on
New York’s NASDAQ exchange.