Hydration kinetics of a calcination activated bauxite tailings-lime-gypsum ternary system

Abstract

To simulate the hydration process of bauxite tailings as supplementary cementitious material, the hydration kinetics of a calcination activated bauxite tailings-lime-gypsum ternary system was investigated. Hydration heat of the ternary system was measured at 50 °C by an isothermal calorimeter. Kinetics equations were used to simulate the hydration process of the ternary system. The Kinetics parameters, n, K, were calculated and discussed. XRD and TGA were used to characterise change of hydration products as the hydration was ongoing. Results demonstrate that the hydration kinetics equation can well simulate the hydration process of the calcination activated bauxite tailings-lime-gypsum system with 5% gypsum, but not suitable for the deceleration stage of the ternary system with 10% gypsum. When the content of bauxite tailings was increased, the ending time of induction period and the appearing time of second exothermic were decreased, but the value of second exothermic peak was increased. When the content of gypsum was decreased, similar results could be obtained. In the diffusion stage, the hydration rate and degree of hydration were extremely low due to the insufficient calcium hydroxide content, and the degree of hydration of the ternary system gradually decreased with the increasing of bauxite tailings content.