9:45 AM - 10:00 AM
[MIS13-03] Carbon mineralization using acid mine drainage: crystal growth from multicomponent solution
Keywords:carbon mineralization, Carbon Dioxide Removal, enhanced rock weathering, mine drainage, calcite
Carbon mineralization, in which carbonate minerals crystallize from CO2 gas by artificially promoting rock weathering, is considered against global warming. In particular, adding natural rocks to acid mine drainage is expected to remediate and neutralize the drainage, so demonstration tests are underway to implement this in society. The remediated drainage is released into the ocean after merging with a river. We are investigating how to crystallize carbonate minerals artificially during these processes from the viewpoint of crystal growth theory.
Four main factors change the composition of mine drainage: (1) rock addition, (2) crystallization except for calcite, (3) dissolution of atmospheric CO2 into the solution, and (4) confluence with river water or seawater. We estimated the supersaturated conditions of calcite by combining these factors using chemical equilibrium calculations. However, since predicting the nucleation process is difficult for chemical equilibrium calculations, we performed nucleation experiments from various solution conditions. In addition, since natural rocks containing impurities are added, unintended secondary minerals will be formed, so we performed dissolution experiments on natural rocks.
In this study, we investigated the Shojigawa Mine in southwestern Hokkaido as a model case. The Shojingawa mine discharges drainage with a pH of 2-3 [1], whereas pH of seawater is about 8.1. Therefore, dealing with a wide range of pH solutions is necessary. The ratio of anions involved in calcite crystallization (Dissolved Inorganic Carbon: CO32-, HCO3-, H2CO3*) changes significantly depending on the pH, and the solubility changes by more than five orders of magnitude. Furthermore, natural solutions have multiple components. Therefore, we used the geochemical code PHREEQC [2] to calculate the chemical equilibrium of the solution.
When we performed a dissolution experiment of natural rock powder (basalt) in collected the Shojingawa mine drainage, we found that gypsum (CaSO4・2H2O) was easily formed. This is because the drainage contains a lot of sulfate ions, and gypsum solubility is lower than calcite at pH 6 or less. Hence, the gypsum becomes supersaturated due to the increase in Ca ions caused by basalt dissolution. To avoid this, it is necessary not to increase the Ca ions over the solubility of gypsum or to increase the Ca ions after raising the pH to 6 or higher. The change in concentration and pH due to rock addition is under investigation because it depends not only on the type of rock addition, but also on the rock's dissolution rate, the rock grain size, and the drainage flow rate. In the presentation, we will introduce experimental data on calcite nucleation from solutions with various pH and previous research [3]. We will discuss comparisons between the theory of the interfacial tension dependence of solubility [4] and our data.
[1] Noroda et al. (2023), Journal of MMIJ 139 (4-8) 21.
[2] https://www.usgs.gov/software/phreeqc-version-3
[3] Bergwerff et al. (2021), Crystals 11, 1318. etc.
[4] Kashchiev et al. (2003) Cryst. Res. Technol. 38 (7–8) 555. etc.
Four main factors change the composition of mine drainage: (1) rock addition, (2) crystallization except for calcite, (3) dissolution of atmospheric CO2 into the solution, and (4) confluence with river water or seawater. We estimated the supersaturated conditions of calcite by combining these factors using chemical equilibrium calculations. However, since predicting the nucleation process is difficult for chemical equilibrium calculations, we performed nucleation experiments from various solution conditions. In addition, since natural rocks containing impurities are added, unintended secondary minerals will be formed, so we performed dissolution experiments on natural rocks.
In this study, we investigated the Shojigawa Mine in southwestern Hokkaido as a model case. The Shojingawa mine discharges drainage with a pH of 2-3 [1], whereas pH of seawater is about 8.1. Therefore, dealing with a wide range of pH solutions is necessary. The ratio of anions involved in calcite crystallization (Dissolved Inorganic Carbon: CO32-, HCO3-, H2CO3*) changes significantly depending on the pH, and the solubility changes by more than five orders of magnitude. Furthermore, natural solutions have multiple components. Therefore, we used the geochemical code PHREEQC [2] to calculate the chemical equilibrium of the solution.
When we performed a dissolution experiment of natural rock powder (basalt) in collected the Shojingawa mine drainage, we found that gypsum (CaSO4・2H2O) was easily formed. This is because the drainage contains a lot of sulfate ions, and gypsum solubility is lower than calcite at pH 6 or less. Hence, the gypsum becomes supersaturated due to the increase in Ca ions caused by basalt dissolution. To avoid this, it is necessary not to increase the Ca ions over the solubility of gypsum or to increase the Ca ions after raising the pH to 6 or higher. The change in concentration and pH due to rock addition is under investigation because it depends not only on the type of rock addition, but also on the rock's dissolution rate, the rock grain size, and the drainage flow rate. In the presentation, we will introduce experimental data on calcite nucleation from solutions with various pH and previous research [3]. We will discuss comparisons between the theory of the interfacial tension dependence of solubility [4] and our data.
[1] Noroda et al. (2023), Journal of MMIJ 139 (4-8) 21.
[2] https://www.usgs.gov/software/phreeqc-version-3
[3] Bergwerff et al. (2021), Crystals 11, 1318. etc.
[4] Kashchiev et al. (2003) Cryst. Res. Technol. 38 (7–8) 555. etc.