Tracking the fate of nickel during transformation of nesquehonite to dypingite at 35°C
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The weathering of ultramafic rocks facilitates the formation of hydrated Mg- carbonate minerals. Carbon mineralization allows CO2 to be stored within solid, stable carbonates, by reacting CO2 with alkaline, earth metal-bearing hydroxide and silicate minerals. Engineered storage of CO2 in magnesium carbonate minerals is one method of offsetting greenhouse gas emissions. This method is favourable because carbonate minerals persist at Earth’s surface for thousands of years, and are considered permanent over geologic time. However, ultramafic rocks commonly contain transition metals that can be released during enhanced dissolution and are therefore of concern for accelerated carbon mineralization processes. Optimization of engineered Co2 requires knowledge of the fate of transition metals during the hydrated Mg-carbonate phases. In this study, we track the fate of Ni during the transformation of nesquehonite (MgCO3 · 3H2O), which can be used to store CO2, to dypingite (Mg5(CO3)4(OH)2·5H2O), a more stable carbonate. The transformation of nesquehonite to dypingite is temperature dependent, and was completed over 30 days at a temperature of 35°C. Transformation occurs through dissolution – repreciptation mechanisms. Our results demonstrate that nesquehonite readily sequestered Ni present in solution. Ni was immobilized, likely by substitution for Mg, or trapping, however it was partially released during the transformation to dypingite. These metals may be sequestered and stored rather than released during accelerated carbon mineralization, and may therefore not pose a risk to the environment.