Sugar-Derived Causticization Additives for the Bayer Process

BauxiteBauxite digestion in the Bayer processBayer process results in a buildup of sodium carbonate in the caustic liquor, which reduces the efficiency of aluminaAlumina production. This effect is mitigated by limeLime causticisation, during which carbonate is removed, preferably as calcium carbonate. The extent and efficiency of causticisation in Bayer liquors are limited by the formationFormation of tricalcium aluminate (TCA) and alumino-carbonates, which also reduce overall plant productivityProductivity due to the consequent loss of aluminaAlumina from the liquor. We demonstrate that TCA formationFormation can be minimized or eliminated by using sugar-derived molecules, specifically gluconic acid, a mixture of gluconic and glucaric acids, and sodium gluconate. This reduction in TCA formationFormation improves the efficiency of causticisation by three to four times as determined by the rate constants for carbonate consumption or by the relative increase of C/S ratio. This in turn reduces aluminaAlumina and caustic losses in the causticiser, with the potential to improve the plant liquor C/S and hence the overall productivityProductivity of the Bayer circuit.