Bauxite residue is a mixture of minerals that are left behind when alumina is removed from bauxite. Although it is thoroughly washed, the residue retains some alkaline liquor and requires long-term storage. By mixing CO2 into the bauxite residue, its pH level is reduced to levels found naturally in alkaline soils. A second sustainability benefit is that the improved environmental properties of the residue mean it also can be beneficially used as road base, building materials or to improve soil.
This program is expected to lock up 70,000 tons of CO2 a year, the equivalent of eliminating the emissions of 17,500 automobiles. Alcoa plans to deploy the technology to its nine alumina refineries worldwide. Deployment across Alcoa's operations in Australia alone could potentially save 300,000 tons of CO2 each year.
[Source: Alcoa via europapress.com]