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https://hdl.handle.net/2115/88886

Formation of magnesium silicate hydrate (M-S-H) at pH 10 and 50 degrees C in open-flow systems

英語

M-S-H

2023-01

Elsevier

Applied geochemistry

148

105544

Magnesium silicate hydrate (M-S-H) is a poorly crystalline Mg-silicate phase formed under alkaline conditions at low temperatures (T < 100 degrees C). Its formation has been studied in closed systems but not in open-flow systems, which better represent natural surface/subsurface environments. Here, MgO powder was used in reactions at pH similar to 10 and 50 degrees C in flow-through experiments to study the formation of M-S-H as a function of aqueous Si con-centration (1.5, 0.15, and 0 mM). Consumption of aqueous Si during precipitation of M-S-H resulted in an increase in the dissolution rate of the primary material (Mg hydroxide). Steady-state Si concentrations were used to calculate the dissolution rate of Mg hydroxide and the precipitation rate of M-S-H. Analyses of retrieved solids by electron microscopy and nuclear magnetic resonance spectroscopy confirmed the formation of M-S-H, although X-ray diffraction patterns pro-vided no clear evidence of the presence of M-S-H because of the small amount precipitated and its nano -crystallinity. The chemical composition (Mg/Si ratio) of the M-S-H varied with the aqueous Si concentration of the injected solution. Mg/Si ratios of 1.00 +/- 0.09 and 1.59 +/- 0.15 were obtained with Si concentrations of 1.5 and 0.15 mM, respectively. Results indicate that the formation of M-S-H is feasible under Earth surface condi-tions, with dissolved silica coexisting with Mg-bearing minerals at alkaline pH.

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© <2023>. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

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