Probing for pollution

Australian scientists have developed a network of small oxygen probes that could potentially avert acid damage to the environment and save mining companies millions of dollars.

The probe, developed by the Commonwealth Scientific and Industrial Research Organisation (CSIRO), is said to be poised to revolutionise the way mining companies monitor the rehabilitation of Australia’s mine sites, especially where acidic mine wastes are present.

The presence of oxygen in sulphidic mine wastes results in oxidation of the sulphide minerals, and with water forms sulphuric acid. The resultant acid mine drainage causes contamination of surface and groundwater.

To reduce or eliminate this contamination, the mineral wastes are commonly covered with earth or synthetic covers.

CSIRO say that their probe has successfully provided a detailed and accurate assessment of the long-term stability and effectiveness of these covers to prevent oxygen reaching the mineral wastes.

The instrument achieves this by continually monitoring oxygen levels in mine waste sealed under the covers.

‘Acid mine drainage caused by the oxidation of sulphidic mining waste is one of the biggest environmental problems faced by the mining industry,’ said Dr Brad Patterson, an environmental chemist with CSIRO Land and Water who has worked on the probes for over five years.

‘Currently, managing these wastes costs the Australian mining industry around $60 million a year,’ he said.

Despite concerns about the long-term effectiveness of the earth coverings, this method is, at present, said to be one of the few cost-effective solutions to preventing acid leaching from the mine waste into the environment.

Placed at various depths in the earth cover and buried waste, the oxygen probes monitor the effectiveness of the cover by detecting the amount of oxygen present. No oxygen means the covers are doing their job.

Conventional sampling of the tailings for oxygen is done manually and infrequently. In remote locations, this sampling may only occur two or three times a year.

‘The CSIRO probes constantly monitor oxygen levels, giving an accurate interpretation of any changes in oxygen concentration over time,’ said Dr Patterson. ‘Any failings of the earth cover can be immediately discovered and action taken.’

The probe has so far been successfully tested at a site in Western Australia.

‘The probe performed successfully under aggressive conditions such as high acidity and the data confirmed the cover was doing its job in preventing oxygen getting to the waste underneath,’ Dr Patterson said. ‘We are confident the probes are sufficiently robust to withstand conditions found in most mine sites around the world.’

CSIRO has also developed a probe to detect and monitor volatile organic compounds like benzene and trichlorethene, compounds that are common contaminants found as a result of petroleum and solvent spills, in groundwater and soil environments.

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