The surface chemistry of Bayer process solids: a review

The Bayer process is used for refining bauxite to smelting grade alumina (A l2O3), the precursor to aluminium. The process was developed and patented b y Karl Josef Bayer 110 years ago, and has become the cornerstone of the alu minium production industry worldwide. Production of alumina reached 46.8 me gatonnes (Mt) worldwide by the end of 1997, with Australia the worlds large st producer of bauxite and refiner of alumina with just under 30% of world production. Although the refining process is well established and the basic theories underpinning it are well defined, the fundamental chemistry of th e Bayer process is not well understood. Of particular interest to industria l and academic researchers alike, is the chemistry of the Bayer process sol ids-aluminium trihydroxide, 'red mud' and sodium oxalate. The surface chemi stry of these solids is of great industrial importance as the refining indu stry experiences significant restrictions due to limitations imposed on the process by surface chemical reactions. Of scientific interest is the conce ptual advancement of our knowledge and understanding of the nature of surfa ces under extreme (non-ideal) conditions. A review of the current literatur e relating to these important Bayer process solids is thus presented. While not exhaustive, the review is thorough and aims to familiarise the reader with current levels of understanding regarding the nature of Bayer process solids surfaces under Bayer process conditions, and the significant roles t hese solids play in the overall efficiency of the refining process. It is h oped that this review will provide a useful starting point for researchers new to the area of Bayer process research, whilst also stimulating further fundamental research in this economically and scientifically significant ar ea. (C) 1999 Elsevier Science B.V. All rights reserved.