Insoluble organic compounds in the Bayer process

During the dissolution of bauxite in a high-temperature (250-255 degreesC) Bayer process, which separates aluminum hydroxide and oxide in the ore from iron oxide and other impurities, a number of insoluble materials are produced from organic material entering the refinery with the bauxite. These insoluble organic materials appear in the waste solids termed "red mud", in the shell side of the heat exchangers, on sodium oxalate crystals, aluminum hydroxide gibbsite precipitate, in a precipitation tank scale, and on oxalate-gibbsite coprecipitation fines. These materials have been analyzed by NMR and pyrolysis GC/MS techniques. The organic material on the bauxite and red mud were found to differ considerably from each other. The deposits on sodium oxalate released higher concentrations of alkenes and alkanes on pyrolysis. The results are interpreted using current host-guest concepts of humic materials and hydrophobicity.