Thermal Dehydration Kinetic Mechanism of Aluminum Sulfate Hydrates

Abstract

Thermal dehydration kinetics of aluminum sulfate hydrates was studied with TG/DTA under static open air environment. It was found that the thermal dehydration of the aluminum sulfate hydrates was a two-stage process. The first stage happened in the temperature range from 90 to 300°C with 13 water loss. The second stage happened in the temperature range from 300 to 380 °C with 2 water loss. Activation energy and former factor of each staged were obtained by regression the TG/DTA data with 19 differential and integral functions based on non-isothermal Achar method as well as Coats-Redfern method. The result indicated that the mechanism for the first stage dehydration was the proliferation of three-dimensional, spherical symmetry, 3D, D3, slow-α-t curve, n = 2, reaction is reaction 2. The mechanism of the second stage dehydration was random nucleation and subsequent growth, A3, S-shaped α-t curve, n=1/3, m = 3, reaction is reaction 1/3. Identified that the most likely mechanism of Al2(SO4)3•15H2O dehydration is 2 and 1/3 reactions two process.