Decreasing Yield and Alumina Content of Red Mud by Optimization of the Bauxite Processing Process

Bauxite produces 60-120 million tons of toxic red mud annually during its processing to alumina. Thus, in this work, the modeling of the bauxite processing process to reduce quantity of red mud produced and with low alumina content was envisaged. Bauxite from Minim-Martap was processed by adapting the Bayer process under laboratory conditions. This process was then optimized to obtain conditions that yield less red mud with reduced alumina content. This was done using the Doehlert experimental design with three factors: stirring time, sodium hydroxide concentration and temperature. X-ray diffraction (XRD) and X-ray fluorescence (XRF) were used to characterize obtained alumina, red mud and crushed bauxite. Model process equation obtained from optimization results shows that increasing the tested parameters lead to production of low amount of red mud (temperature and sodium hydroxide concentration were the main factors that influenced the process). The model obtained described the process adequately with a 92% coefficient of determination, low absolute average deviation of 0.004 and strong agreement between theoretical and experimental responses. The optimum conditions gave a red mud yield of 86% with 13% alumina compared to a non-optimized process with 98% red mud yield and 16% alumina content. The fact that increasing tested parameters reduced red mud yield however, implies high amount of alumina is produced, thus a significant economic and environmental advantage for the aluminum industry. It was concluded that optimization of bauxite processing process reduced red mud produced and its alumina content.