Effect of Thermal Treatment of Bauxite Ore on Carbon (Organic and Inorganic) Content and Solubility in Bayer Process Liquor

Bauxite inputs into the Bayer process at a Jamaican refinery were found to contain approximately 0.4% inorganic carbon (or 3.2% CaCO3) and 0.2% organic carbon. Thermal treatment or heating of 10 g bauxite samples for 30 min at temperatures ranging from 300 to 1000 °C was shown to significantly reduce levels of both organic (up to 93%) and inorganic carbon (up to 100%); however, there was an accompanying noticeable decrease in solubility of bauxite ore calcined at temperatures above 300 °C based on predigestion alumina/caustic (A/C) ratios in spent liquor at 99 °C. X-ray diffraction and X-ray database (XDB) spectral analysis of the calcined bauxite (>600 °C) demonstrated the appearance of corundum (α-alumina), a form of aluminum oxide much less soluble than boehmite or gibbsite.