EFFECTS OF CAUSTIC CONCENTRATION AND BAUXITE COMPOSITION ON ECONOMICSOF BAYER ALUMINA PLANTS

A study of the effect of caustic concentration and bauxite composition on the economics of the Bayer process was performed with the use of t he Aspen/SP software package. Flowsheets representing three variations of the process were simulated. The results indicate that changes in t he concentration of caustic (as Na2CO3) between 200 and 350 g/l have a significant effect on capital and operating costs. The total capital requirements of Bayer plants that employ gibbsite digestion or convent ional or double-digestion boehmite extraction methods decrease with in creasing caustic concentration in the digestion step. For all three pl ant types capital costs were found to decrease by an average of 8% whe n caustic concentrations were increased from 250 to 350 g/l caustic. I n most cases the double-digestion route was found to be the most attra ctive. The Aspen/SP software proved to be an appropriate tool for simu lating the Bayer process because of its flexibility, its ability to ha ndle solids and electrolytes and its costing facility.