New Insights into Digestion Kinetics of Gibbsite in the Bayer Process: High-Pressure DSC

Research on the digestion kinetics of gibbsite in the Bayer process contributes to understanding the reaction mechanism and promoting the reaction process. In this work, the non-isothermal kinetics of synthesized pure gibbsite digestion in NaOH solution was studied at the heating rates of 2.5 K min⁻¹, 5 K min⁻¹, 7.5 K min⁻¹, and 10 K min⁻¹ by high-pressure differential scanning calorimetry (HP-DSC). The apparent activation energy was calculated using the Ozawa method and the Kissinger method, then the most probable mechanism function of the reaction was determined using the Coats–Redfern method. The apparent activation energies calculated from the Ozawa and Kissinger methods were 62.56 kJ mol⁻¹ and 61.86 kJ mol⁻¹, respectively, indicating that the digestion of gibbsite was controlled by chemical reactions. The integral and differential forms of the most probable mechanism function were G(α) = 1 − (1 − α)^1/3 and f(α) = 3(1 − α)^2/3, which accorded with systolic spherical models. Furthermore, the kinetics equation of the gibbsite digestion in NaOH solution has been proposed.