Serpentine Activation for CO2 Sequestration

Abstract

Serpentinite calcination currently represents a key step for its activation within ex situ aqueous mineral carbonation. However, the dehydroxylation kinetics that govern this process remain largely unresolved within literature. Available Arrhenius parameters (i.e. A and E) span a wide range of values and appear correlated in terms of a kinetic compensation effect (i.e. linear relationship between loge(A) and E). Following this observation, a revised model for dehydroxylation is presented, validated against a systematic investigation into the role of particle size on the dehydroxylation rate for both South West Oregon and New England Australia Serpentinite using non-isothermal TGA. Within these experiments, dehydroxylation occurs primarily through a particle size dependent mechanism, best described by the canonical spherical, retreating interface model (R3), with statistically equivalent Arrhenius parameters reported between specimens. Examining the processing side of activation, this thesis additionally explores the role of flash calcination, where dehydroxylation is achieved in extremely short residence times (<2 s) through the use of high temperatures (>1073 K) and rapid heating rates (>104 K/s). High temperatures required by this technique however, led to instant deactivation of the calcine through recrystallisation of the dehydroxylated phase to the high temperature product, forsterite. Investigation into this phase transition indicates magnesium leachability declines proportionally to the extent of forsterite content. Kinetic parameters for this transition are reported, allowing quantification of this deactivation process as a function of calcination temperature, time, and particle size. Closing this thesis, the dissolution of activated serpentinite within the CO2-H2O system is examined at conditions relevant to ex situ mineral carbonation (10 MPa, 423 K), with emphasis on reaction pressure, temperature, and particle size on the magnesium leaching rate.