Magazine article Ecos

A Red Mud Remedy

Magazine article Ecos

A Red Mud Remedy

Article excerpt

Following years of diligent research, scientists at Alcoa Western Australia have developed an effective way to deal with 'red mud', an undesirable bauxite residue generated in large quantities by alumina refineries.

For every tonne of alumina produced in Alcoa's Western Australian refineries, two tonnes of residue result. Half of this is a fine-grained material known as red mud and half is a coarser, sand-sized material.

The red mud contains residual caustic material, despite being washed in the refinery, and it therefore needs to be securely stockpiled (dry-stacked) in lined storage areas designed to protect surface and ground waters. Its high alkalinity has been one of the main obstacles to recycling it into other products.

The new process, called residue carbonation, is a high-speed industrial adaptation of a natural chemical process that not only reduces the alkalinity of the waste mud (from a pH of about 13.5 to 10.5), but also locks up carbon dioxide that would otherwise contribute to global warming.

'We see this as a double coup,' says Program Manager at Alcoa, Mr David Cooling. 'Stockpiling refinery residue has ongoing environmental and land-use implications and incurs significant storage costs, but carbonation makes the waste product more friendly to the environment and potentially re-usable, as well as offering the bonus of reducing industry greenhouse gas emissions.'

Alcoa's Technology Development Group, based at Kwinana, WA, has led the research and development work on residue carbonation in collaboration with Hatch Engineering, CSIRO Minerals and several universities. Dr Peter Smith and his CSIRO colleagues at the CRC for Hydrometallurgy conducted the early research on the mechanisms behind the reduction of red mud alkalinity using C[O.sub.2] gas.

Alcoa's small-scale field trials led to construction of a full-scale prototype carbonation facility at its Kwinana refinery, one of the company's three alumina refineries in WA. …

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