Phenomenological Kinetics of the Carbonation Reaction of Lithium Hydroxide Monohydrate: Role of Surface Product Layer and Possible Existence of a Liquid Phase

This article describes the physico-geometrical mechanism and overall kinetics for the carbonation of lithium hydroxide monohydrate (LHMH). The constituent reactions of thermal dehydration of LHMH and carbonation of as-produced anhydrous lithium hydroxide (LH) were investigated using thermogravimetry and morphological observations. On the basis of the kinetic information of the constituent reactions, the overall reaction of carbonation of LHMH under conditions of different CO 2 concentrations and heating rates was kinetically deconvoluted into separate processes of thermal dehydration and reaction of the as-produced LH with CO 2 . The kinetic results were interpreted, with reference to the morphological characteristics of the partially reacted sample particles at different reaction stages, as the consecutive processes of the thermal dehydration of LHMH and the carbonation of as-produced LH starting at room temperature, which is geometrically controlled by shrinkage of the reaction interface, LHMH–LH–lithium carbonate (Li 2 CO 3 ). The possible existence of a liquid phase at the reaction interface is deduced from the kinetic behavior and microscopic evidence. Variations in overall carbonation behavior as a function of heating rate and CO 2 concentration are explained by the changes in the gaseous diffusion behaviors for H 2 O evolution and CO 2 uptake via the surface product layer of Li 2 CO 3 and the evaporation rate of the liquid phase.