Bauxite mineralogy

Anand, R.R. Gilkes, R.J. Roach, G.l.D. (1991) Geochemical and mineralogical characteristics of bauxites. Darling Range, Western Australia. Appl. Geochem. 6 233-248... 

Bauxitic Kaolins andMullites. Deposits of bauxitic kaolins, kaolins having aluminous minerals, have been discovered that have alumina contents between 50 and 70%. These materials are made into refractory aggregates called calcines, grog, clinker, or grain. In addition to sdectivdy mined deposits, synthetic compositions can be prepared from kaolin and alumina and other minerals to produce compositions of desired alumina and mineralogical content. These synthetic mullites are readily available in the form of sintered and fused aggregates. 

The mineralogy of laterites, bauxites and ferricretes is complex, with nearly 200 minerals having now been identified in lateritic materials alone (e.g. Bardossy, 1979 Aleva, 1994). This range derives, in part, from the variety of protolith and/or host-rock compositions, and the numerous transformations that can take place upon their mineral constituents (Tardy et al., 1973 Figure 3.9). Nevertheless, the majority of laterites and ferricretes consist of combinations of less than a dozen rock-forming minerals this assemblage is dominated by stable secondary minerals, and particularly iron and aluminium oxides and sesquioxides (Table 3.1). 

CAC require large industrial facilities, similar to those used to make ordinary Portland cement. The raw materials for CAC are typically bauxite and limestone, which are ball-milled and mixed together to form a feed of appropriate composition, which is fed into rotary kilns to form a calcium aluminate clinker. The clinker is ball-milled to produce the cement. Analysis for composition and mineralogy at various stages of manufacture are essential to ensure a consistent product, see for example Chakraborty and Chattopadhyay [32] for a discussion of the bulk processing of high alumina CAC. 

Synthetic materials made by sintering of bauxite and kaolinite clay. After processing, the final material mineralogical composition consists of a mixture of mullite and corundum. Sometimes less common ceramics are also used, e.g., carborundum, stabilized cubic zirconia, other oxides, and silicates. 

Calcine Calcination. Heat treatment intended to produce physical and/or chemical changes in a raw material. The calcination of bauxite, for example, eliminates water and yields a product that is relatively free from further firing shrinkage when kyanite is calcined, on the other hand, the change is not in chemical but in mineralogical composition, mullite and cristobalite being formed. 

Beneslavskii, S. I., 1963. Mineralogiya Boksitov (Mineralogy of Bauxites). Moscow Gosgeoltekhizdat. Bergman, I., and M. S. Paterson, 1961. Silica powders of respirable size. I. Preliminary studies of dissolution rates in dilute NaOH. J. Appl. Chem. 11 369. 

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