Analysis of solidification behavior and roasting isothermal kinetics of free-alkali in Bayer red mud

Abstract

Red mud is difficult to be used directly in building material due to its strong alkalinity, especially the free-alkali. Recent studies have found that roasting can effectively solidify the free-alkali in red mud. However, the alkali-solidification kinetics of red mud have not been studied. In this paper, thermal analysis and isothermal kinetics of alkali-solidification process of red mud by roasting were systematically investigated. The results showed that high temperatures above 800 ℃ were conducive to improving the reaction rate of alkali-solidification. The most probable mechanism function was the D₆ model in diffusion models, which indicated that three-dimensional diffusion was the limiting link of the alkali-solidification process. According to the determined mechanism function, the corresponding preexponential factor A was calculated to be 19.36 min⁻¹, the apparent activation energy E_a was 97.62 kJ·mol⁻¹. Meanwhile, SEM-EDS analyses verified the alkali-solidification mechanism. This research provides important insight into the efficient solidification of free-alkali in red mud.