We have developed a process that lowers the cost of refining bauxite to alumina by treating the waste product generated—red mud—to recover a costly ingredient, caustic soda.
Economic processing of lower quality bauxite
Most of the world's bauxite (aluminium ore) resources include valuable alumina minerals mixed with alumino-silicate clays. Insoluble components of the bauxite are removed by digesting the ore with very hot caustic soda (sodium hydroxide) in what is known as the Bayer process.
In the Bayer process, the alumina and the silicate clays initially dissolve in the caustic soda solution. Sodium in the caustic soda then combines with reactive silica to form a residue waste product known as red mud, which falls out of the solution taking the sodium with it. The loss of sodium is at a significant cost.
This means that the higher the level of reactive silica in the ore, the more expensive it is to refine. Bauxite with more than about eight per cent reactive silica is generally considered to be uneconomic to process.
Australian, and global, reserves of high quality ore (with low levels of silica) are running out. However, Australia has vast reserves of bauxite containing eight per cent or more reactive silica. If we could make it economic to process this bauxite, we would increase our economic reserves significantly.
Recovering sodium from the residue
With funding from the Australian Government, we developed a patented process to recover the lost sodium by reprocessing the red mud by-product.
We treat the residue with sulphuric acid to neutralise it and scavenge the retained sodium in a solution.
This solution is then subjected to electrodialysis, producing recyclable sulphuric acid and sodium hydroxide that can be fed back into the Bayer process.
The process is 'bolted on' to the current refining process so it's simple in that it doesn't require costly changes upstream. It can be applied to some or all of the residue —even independently to reprocess red mud already stored.
Economic and environmentally friendly bauxite processing
Our process aims to maximise Australia's resources, by making lower-grade bauxite ores economic to mine. It's an opportunity for the bauxite processing industry in Australia and overseas.
As well as reducing bauxite processing costs, this process makes the remaining red mud less polluting and easier to handle – a significant benefit.
The process has been proven technically and economically at lab-scale. Now, we're planning to further test the process at a bauxite refining plant in the next step toward commercialisation.