Optimization of antigorite heat pre-treatment via kinetic modeling of the dehydroxylation reaction for CO2 mineralization

This contribution describes a predictive framework expedient to the thermal processing of serpentinites for the mineralization of CO2. We demonstrate the optimization of heat treatment of antigorite, providing a benchmark of an extreme case of activation among serpentine minerals. Antigorite was investigated non-isothermally via thermogravimetry-mass spectrometry and in situ X-ray powder diffraction, its thermal reaction sequence elucidated, and reaction kinetics subsequently modeled. Based on the thermally induced structural changes, preferred content of residual hydroxyls in the dehydroxylated antigorite amounts to 10-40% of those present initially. This degree of dehydroxylation minimized the transformation of antigorite into new crystalline phases maximizing the amorphization of the new structure. The thermal reaction sequence provided both the explanation for the observed kinetic behavior and the basis for this optimization strategy. The optimal time for heat activation corresponds to <= 30 min, including the heat-up period at a rate of 30 degrees C min(-1) and an iso-thermal stage at 730 degrees C. This was successfully modeled using a three-dimensional phase boundary reaction model (R3), with activation energy E-a of 160 kJ mol(-1) and a frequency factor A of 5.7 +/- 4.1 x 10(5) s(-1) (5.7 x 10(5) s(-1) for dynamic and 1.6 x 10(5) s(-1) for static stage). This strategy translates to a fast and efficient thermal processing in an optimally sized calcining vessel. Furthermore, these results imply that activation of the more common serpentine minerals lizardite and chrysotile would be significantly faster as their dehydroxylation proceeds at lower temperatures than that of antigorite. (C) 2011 Society of Chemical Industry and John Wiley & Sons, Ltd