Abstract— <p>Simultaneous Thermal Analysis (STA) in the heating rate range from 2 to 20°C/min was used to determine kinetic parameters of gibbsite dehydroxylation from bauxites of two genetic types: lateritic-sedimentary (India) and lateritic (Guinea). It is shown that the thermal behavior of gibbsite depends on particle size: a sample with a smaller crystal size exhibits a single-stage endothermic effect at 220–450°C, whereas a sample with relatively larger crystals had the effect split into three peaks, indicating formation of an intermediate boehmite phase. Kinetic parameters of dehydroxylation were calculated using model-dependent (Arrhenius) and isoconversion (Kissinger, Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose) methods. The effective activation energy values for fine-crystalline gibbsite (120–161 kJ/mol, depending on the method) significantly exceed those for coarse-crystalline gibbsite (78–131 kJ/mol), indicating its higher thermal stability. It was shown that with an increase in the heating rate, the activation energy decreases regularly due to the acceleration of diffusion processes. The obtained results have practical significance for optimizing the temperature-time regimes for processing bauxites of different genesis: fine-crystalline varieties require higher temperatures or longer holding times, whereas coarse-crystalline varieties, prone to boehmite formation, necessitate two-stage thermal treatment.</p>