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BAUXITE EXTRACTABLE PHASES IN THE BAYER HIGH TEMPERATURE PROCESS: RE-ASSESSMENT OF BOEHMITE CONTENT AND ALUMINIUM SUBSTITUTION IN ALUMINO-GOETHITE

Authier-Martin, M. Fulford, G.D. Feret, F.

The exact quality of the bauxite that will feed Alcan alumina refineries beyond the year 2000 is a subject of significant interest to the process plants. Concern arises from the mining of lower grade bauxite and the potential of high variability within a single deposit. Alcan's traditional approach in bauxite characterization, using sound wet chemistry methods and semi-quantitative X-ray diffraction, has been successful for many years. Nevertheless, a number of alternative future bauxites have presented new challenges that have stretched Alcan's characterization methodology to its limits. More specifically, boehmite levels in low-boehmitic bauxites (< 4 % b.Al2O3) and aluminium substitution in alumino-goethite have received careful re-assessment. For example, accurate determination of boehmite levels in bauxites is critical to the appropriate choice of processing strategy; with lower and lower grade bauxite available, alumino-goethite from Jamaica and Boke bauxites presents an appealing potential source of additional alumina while it also raises a number of issues and possible problems.

Various analytical techniques, among them XDBTM, BQUANTTM, deuterated FT-IR, DSC and dithionite leach, were used to characterize boehmite and alumino-goethite in a series of Jamaica, Weipa, Ely and Boke bauxites. Typical results are presented in this paper and the mining and process implications are highlighted. Both the consistencies and the disparities of the data recorded from various analytical techniques are used to shed new light on the future bauxite quality and its processability.