A comparative review of the mineralogical and chemical composition of African major bauxite deposits

Abstract

Bauxite, which is the main raw material that aluminium is extracted from was discovered in Africa in the early 1900s. Currently, the production and export capacities of the African Bauxite ore are about a third of the World's total capacity. However, the processes leading to the final finished product of; surface mining of the ore, refining ore into alumina and finally extracting the pure aluminium metal in high energy consuming smelters that employ the Hall-Héroult electrolysis process; seldom take place inside Africa. The main goal of this work is to analyse the mineralogical and geochemical characteristics of bauxite deposits from some prominent bauxite producing and exporting countries of Africa in order to fashion out if a trend exist for the type of source rocks. Judging from the data obtained, gibbsite is found to be the main aluminium oxide in all the bauxite deposits with slight occurrence of boehmite in 3 out of the 13 deposits, while goethite is the main oxyhydroxide iron mineral. The compiled results of the various investigations highlighted the fact that the deposits are of diverse qualities with respect to world standard of major element content of bauxite; with average percentage concentration in the ranges as: Al2O3 (43.73–61.25), Fe2O3 (1.55–34.25), SiO2 (0.42–10.84); except two of the deposits with alumina content less than 40%. With evaluated silica moduli less than 8 for only two (2) of the deposits (4.76 and 6.94), the rest have higher moduli that ranges between (14.49 and 75.45). The higher percentage of iron oxide content (>20) in six (6) out of the 13 ore deposits, allowed the deposits to be grouped into three (3) categories of grades; high alumina ore, ferruginous ore, siliceous ore and combination of each. Source rock of the deposits were determined through geochemical and petrographic considerations of laterisation products of the rocks through evaluation of the weathering indices of; Chemical Index of Alteration which was in the range (97.16–99.98) while the Ruxton ratio ranged between (0.0133–0.2100); signifying the parent rock underwent intensive weathering process. This is indicative of the source rocks of the Bauxite deposits being either (i) anorthositic, (ii) argillite and dolerite, (iii) granulite and feldspathic gneiss, and/or, (iv) mafic-basaltic andesite igneous. Awareness of new and yet-to-commence emerging bauxite producing African countries was created, by highlighting the economic impact those respective countries will experience when that mining sector is developed for the aluminum industry at home and world at large.