American Chemical Society
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Structure of Silica Polymers and Reaction Mechanism for Formation of Silica-Rich Precipitated Phases in Direct Aqueous Carbon Mineralization

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journal contribution
posted on 2019-12-02, 16:56 authored by E. Benhelal, T. K. Oliver, F. Farhang, J. M. Hook, M. S. Rayson, G. F. Brent, M. Stockenhuber, E. M. Kennedy
This research aims to provide insight into the structure and reaction mechanism of silica-rich phases formed as byproducts in direct aqueous carbonation of heat-activated lizardite. In undertaking this work, we employed analytical techniques such as thermogravimetric analysis (TGA), X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), 29Si solid-state nuclear magnetic resonance (29Si SS NMR), inductively coupled plasma-optical emission spectrometry (ICP-OES), and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) to characterize carbonation products and to understand the mechanism of formation and the structure of silica-rich byproducts. Thermodynamic analysis predicts the formation of magnesite and amorphous silica in the process of direct aqueous carbonation of heat-activated lizardite under the experimental conditions studied. Characterization of carbonation products disclosed the presence of magnesite, amorphous silica, and magnesium silicate phases. Analysis of supernatant solutions obtained from direct aqueous carbonation by MALDI spectroscopy showed the presence of silica polymers, which precipitate during the carbonation experiments. The precipitated amorphous silica on the surface of reacting particles was found to subsequently adsorb the dissolved magnesium (Mg) from the solution to form a magnesium silicate phase.