Revolution in treating contaminated mines

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

Bauxol^TM technology to prevent such

an event ever occurring again. The

results surprised independent

observers including former EU mining

executive, Folmer BangHansen.

‘We found this [Bauxol^TM] 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 Bauxol^TM

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. Bauxol^TM 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

explains: ‘Bauxol

^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

^TM technology

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

with Bauxol

^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

discharge catchment.

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.

Bauxol

^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.