Organic compounds in the processing of lateritic bauxites to alumina: Part 1: Origins and chemistry of organics in the Bayer process

This review is the first of a series examining the history and current state of knowledge of the science related to organic compounds in the Bayer process for the extraction of alumina from lateritic bauxites. Part 1 covers the origins, nature and chemistry of organic compounds in Bayer liquors. It provides a compilation of the information available from the public literature, and critical analysis of the research that has been carried out in this area in the past 50 years. It points the way to future opportunities for research to assist in mitigating the high costs that organics impose on the industry globally ($500 Mpa in Australia alone).

Research Highlights
► This article provides a comprehensive review of the origins, nature and chemistry of organic compounds in Bayer process liquors;
► Organics impose a major economic cost on the industry globally ($500 Mpa in Australia alone);
► The bauxite is the main source of organics in the Bayer process;
► Over 90% of the organic compounds in Bayer liquor have molecular weights of less than 500 Da: aliphatic acid anions (66%), aromatic anions (31%), and nitrogen-containing compounds (3%);
► Compounds containing multiple hydroxyl groups are largely absent due to removal by ongoing reaction, adsorption and incorporation into scales;
► Organic molecules participate in both sides of redox processes in Bayer digestion, leaving the oxidized forms (organic acids) in the liquors; the reduced forms (hydrogen, ammonia and amines, hydrocarbons, alcohols and carbonyls) enter the gas phase.