Thin-Layer Modeling and Determination of Effective Moisture Diffusivity and Activation Energy for Drying of Red Mud from Filter Presses

Abstract

Red mud is generated during alumina production through Bayer process; it is the insoluble product obtained after bauxite digestion with sodium hydroxide at elevated temperature and pressure. In recent years, various attempts have been made to exploit red mud for the extraction of its valuable components or its usage in the fabrication of cement, ceramics, and other minor products; in all such cases, red mud drying constitutes a major preliminary processing stage that has not been studied in depth. In the current study, drying kinetics and energetics of red mud obtained from filter presses of Aluminum of Greece are studied. Drying experiments were performed under isothermal condition over a wide temperature range (50–250 °C) and 10 thin-layer models were employed for simulation of temporal evolution of moisture removal. Three statistical error factors were implemented in order to test models’ accuracy, and it was found that Midilli et al.'s equation showed the best fit (R2 > 0.99). Effective moisture diffusivity was estimated by diffusion model based on the Fick’s second law and found to vary from 0.3510 × 10−9 to 21.3951 × 10−9 m2 s−1 at a drying temperature ranging from 50 to 250 °C, respectively. The activation energy of red mud drying was found to have a value of 28.133 kJ mol−1.