CO₂ sequestration via carbonation of widely available low-cost minerals, such as olivine, can permanently dispose of CO₂ in an environmentally benign and a geologically stable form. We report the results of studies of the mechanisms that limit aqueous olivine carbonation reactivity under the optimum sequestration reaction conditions observed to date:  1 M NaCl + 0.64 M NaHCO₃ at T ≈ 185 °C and P_CO2 ≈ 135 bar. A reaction limiting silica-rich passivating layer (PL) forms on the feedstock grains, slowing carbonate formation and raising process cost. The morphology and composition of the passivating layers are investigated using scanning and transmission electron microscopy and atomic level modeling. Postreaction analysis of feedstock particles, recovered from stirred autoclave experiments at 1500 rpm, provides unequivocal evidence of local mechanical removal (chipping) of PL material, suggesting particle abrasion. This is corroborated by our observation that carbonation increases dramatically with solid particle concentration in stirred experiments. Multiphase hydrodynamic calculations are combined with experiment to better understand the associated slurry-flow effects. Large-scale atomic-level simulations of the reaction zone suggest that the PL possesses a “glassy” but highly defective SiO₂ structure that can permit diffusion of key reactants. Mitigating passivating layer effectiveness is critical to enhancing carbonation and lowering sequestration process cost.

Title

Environ. Sci. Technol., 2006, 40 (15), pp 4802–4808 DOI: 10.1021/es0523340 Publication Date (Web): June 15, 2006

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Publisher Country

Palestine

Publication Type

Both (Printed and Online)

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Year

2006

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