THE COMALCO BAUXITE ACTIVATION PROCESS

Thermal treatment of bauxite for removal of organic material has been attempted on numerous occasions in the past, but for reasons of deactivation of dehydrated alumina phases under otherwise economically attractive processing conditions there has been no commercial implementation of such processes. In recent work it has been surprisingly found that thermal treatment of bauxite can simultaneously achieve the extinction of crystalline alumina bearing phases, the destruction of extractable organic carbon and the avoidance of deactivation of alumina by water vapour. The thermal processing conditions are such that the process can be conducted with low energy consumption and high intensity. The outcome is a commercially viable process for converting boehmitic high temperature digestible bauxite to low temperature digestible bauxite. The process has been piloted at a scale of one tonne per hour.

The properties of the product are such that in low temperature digestion alumina reversion effects are almost undetectable and very high liquor alumina loadings can be achieved, particularly in double digestion scenarios. Other advantages in the Bayer process include extinction of carbonate and oxalate, very high purity liquors, reduced scaling rates from liquor, improved product purity (especially in relation to soda and silica). Quartz digestion can be almost completely avoided. The liquor productivity that can be achieved with the activated bauxite product is such that a significant expansion of output from existing digestion and precipitation circuits can be expected.

Activated bauxite rehydrates with a heating and liquor dehydrating effect in the Bayer process, and in combination with the enhanced liquor productivity and enabled cogeneration, results in a neutral overall energy effect.