Characterization of bauxite fines aiming to minimize their iron content

Samples of the fine and superfine bauxite products from Porto Trombetas were studied in order to make possible the evaluation of the occurrence of iron bearing minerals and to verify the possibilities of minimizing their content. These samples are constituted by gibbsite, 63–68% in weight, iron oxy-hydroxides, 23–21% (basically hematite and goethite), clay minerals, 3–4%, and minor amounts of quartz, anatase, zircon and bohemite. Microscopy studies indicated that the iron is associated with gibbsite as classical locked particles or is presenting a very intimate intergrowth; discrete particles of hematite–goethite are responsible for 50–60% of the iron content. Mineral separations made by both magnetic and heavy liquids with two cut points each were carried out; magnetic and gravity separability curves showed that is possible to achieve a very substantial reduction of the iron content in association with very high recovery levels. The study showed that for bauxite fine and superfine products, Fe2O3 grades of 8% and 6%, respectively (53–55% of total Al2O3), would be achieved with potential aluminum recoveries at about 90% by gravity concentration or magnetic separation.