Presentation Information
[S2-03]Compositional Variation of Carbonate Minerals Induced by Selective Dissolution of Minerals in an Andesite-CO2-Saturated Water System
*Jion Kubota1, Otgonbayar Dandar1, Tomohito Kameda1, Masaoki Uno2, Atsushi Okamoto1 (1. Tohoku University, 2. The University of Tokyo)
Keywords:
Carbon mineralizaiton,Andesite,Stirring batch experiment
Andesite contains abundant divalent cations, making it a promising candidate for CO2 mineral sequestration. However, experimental studies on CO2 mineralization using andesite are limited. Due to the presence of various Ca- and Mg-bearing minerals (e.g., plagioclase and pyroxene), the specific reaction pathways and resulting carbonate compositions remain unclear. Additionally, few experiments have reproduced how mineral dissolution and carbonate precipitation respond to chemical and physical conditions. This study aims to quantify CO2 fixation and investigate mineral reactions in andesite under flow conditions using stirring batch experiments.
The experiments used powdered andesite samples from Niigata and Miyagi, and basalt from Iceland. Each 2.0 g sample was reacted with 50 mL of water in sealed containers under 20 MPa CO2 pressure. Tests were run at 150℃ and 200℃ with stirring (80 rpm) for 10 days. Post-experiment analyses included ICP-OES, EPMA, TG, and TPD-MS.
TPD-MS analysis showed andesite samples contained 0.13–0.38 mmol CO2/g at 200°C, about one-tenth to one-quarter of the 1.54 mmol/g sequestered in basalt. Carbonate and smectite clay minerals formed in all samples, with carbonates precipitating on primary minerals. Andesite carbonates were Ca- and Mg-rich (calcite to dolomite), while basalt carbonates were Mg- and Fe-rich (ferromagnesite).
Previous static batch experiments with andesite showed Fe-rich magnesite formation over 60 days, while stirring experiments produced Mg-rich calcite and dolomite. Geochemical modeling suggested typical andesite favors magnesite, with calcite formation being unfavorable. Changing the plagioclase-to-pyroxene ratio in the model affected carbonate types: an 8:2 ratio led to Ca- and Mg-rich carbonates like in stirred tests, while 1:9 produced Mg- and Fe-rich carbonates like in static tests. This implies pyroxene dissolves selectively under static conditions, but stirring enhances plagioclase dissolution, resulting in Ca-rich carbonates.
This study suggests that fluid flow variability in andesitic rocks influences the dissolution of Ca- and Mg-bearing minerals, changing the composition of carbonate precipitates. This affects CO2 storage capacity and long-term stability.
The experiments used powdered andesite samples from Niigata and Miyagi, and basalt from Iceland. Each 2.0 g sample was reacted with 50 mL of water in sealed containers under 20 MPa CO2 pressure. Tests were run at 150℃ and 200℃ with stirring (80 rpm) for 10 days. Post-experiment analyses included ICP-OES, EPMA, TG, and TPD-MS.
TPD-MS analysis showed andesite samples contained 0.13–0.38 mmol CO2/g at 200°C, about one-tenth to one-quarter of the 1.54 mmol/g sequestered in basalt. Carbonate and smectite clay minerals formed in all samples, with carbonates precipitating on primary minerals. Andesite carbonates were Ca- and Mg-rich (calcite to dolomite), while basalt carbonates were Mg- and Fe-rich (ferromagnesite).
Previous static batch experiments with andesite showed Fe-rich magnesite formation over 60 days, while stirring experiments produced Mg-rich calcite and dolomite. Geochemical modeling suggested typical andesite favors magnesite, with calcite formation being unfavorable. Changing the plagioclase-to-pyroxene ratio in the model affected carbonate types: an 8:2 ratio led to Ca- and Mg-rich carbonates like in stirred tests, while 1:9 produced Mg- and Fe-rich carbonates like in static tests. This implies pyroxene dissolves selectively under static conditions, but stirring enhances plagioclase dissolution, resulting in Ca-rich carbonates.
This study suggests that fluid flow variability in andesitic rocks influences the dissolution of Ca- and Mg-bearing minerals, changing the composition of carbonate precipitates. This affects CO2 storage capacity and long-term stability.