RE-USAGE OF DRY BAUXITE RESIDUE

Bott, R., Langeloh, T. and Hahn, J.

Bauxite residue is the main by-product of alumina refining requiring treatment and disposal, significantly influencing cost. Numerous attempts have been undertaken to improve the efficiency of residue disposal or to make it available for industrial re-usage.

Bauxite residue is characterised by parameters which can be seen as advantageous/disadvantageous for industrial re-usage like:

– a typical particle size distribution (×50 < 10 μm)

– a typical mineralogical composition consisting of Al2O3, Fe2O3, SiO2, TiO2 and others

– a pH-value in the original red mud of pH = 10–12 (soluble soda content of some 60 g/l)

– serious dewatering problems

For decades major alumina producers have undertaken research into alternatives to residue disposal and product development. This research has highlighted a large number of possible residue applications in different industries such as soil improvement, land reclamation for agriculture, regulator at cement production, sintering aids for iron and steel industry, catalyst for coal hydrogenation, top and bottom sealing of disposal areas, backfilling of underground mine etc.

To allow a further processing or a re-usage, it is required that bauxite residue is made available by the refinery with a very low soda content and a non-thixotropic and non-sticky behaviour to ensure secure transportation and problem free handling. However actual methods of filtration, washing and dewatering are not able to produce bauxite residue that is clean and dry enough to meet these requirements. This has to be seen against the background that thermal drying of wet bauxite residue is too energy and cost intensive and, therefore, not a feasible and profitable process alternative to produce dry bauxite residue for utilization. The Hi-Bar Steam Pressure Filtration is an innovative technology, which has now shown its capability to produce a really dry, easy to handle, bulk-like material.