Carbonised red mud--a new water treatment product made from a waste material.

Proposals to use red mud, the waste produced by the extraction of alumina from bauxite ore in the Bayer process, as a material for treatment of heavy metal-contaminated water are limited by its inherent alkalinity and variability. Attempts to lower its pH have been largely unreliable. However, an alternative strategy is carbonisation of red mud by catalytic hydrocarbon cracking, which results in a magnetic material of greater surface area. The efficacy of this material has been compared with that of the untreated parent red mud and acidified red mud for the sorption of CrO(4)(2-), Cu(2+) and Pb(2+). Carbonised red mud does not remove CrO(4)(2-) from solution, but shows enhancement of Cu(2+) and Pb(2+) removal. There is an approximate ten-fold increase in removal of Cu(2+) and Pb(2+) by carbonised red mud compared with acidified red mud.