Carbonation decomposition of hydrogarnet is a significant reaction of the calcification-carbonation new method for alumina production by using low-grade bauxite. In this work, non-isothermal decomposition kinetics of hydrogarnet in sodium carbonate solution was studied by high-pressure differential scanning calorimetry (HP-DSC) at different heating rates of 2, 5, 8, 10, 15 and 20 K.min(-1), respectively. The activation energy (Ea) was calculated with the help of isoconversional method (model-free), and the reaction mechanism was determined by the differential equation method. The calculated activation energy of this reaction was 115.66 kJ.mol(-1). Furthermore, the mechanism for decomposition reaction is Avrami-Erofeev (n = 1.5), and the decomposition process is diffusion-controlled. (C) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.