[B-BG02] Geo-Bio Interactions and its Applications

[BBG02-07] Initial dissolution behavior of crashed tremolite

*Haruto Nakayama¹, Keisuke Fukushi² (1.School of Geosciences and Civil Engineering, College of Science and Engineering, Kanazawa University, 2.Institute of Nature and Enviromental Technology, Kanazawa University)

Keywords:dissolution, Enhanced Rock Weathering, Initial dissolution behavior, Tremolite

Recently, Enhanced Rock Weathering (ERW) has been attracting attention as an effective and environmentally friendly CO₂ removal technology. ERW involves the application of finely crushed silicate rock to croplands. The silicate rock has an increased specific surface area, which promotes chemical weathering and removes atmospheric CO₂. Estimation of CO₂ removal potential by ERW requires mineral dissolution rates. Dissolution rates have been determined by laboratory experiments. The previous studies have used the steady-state dissolution rates for the estimation. On the other hand, it is important for CO₂ removal by ERW to consider not only steady-state dissolution rates but also initial mineral dissolution rates. In this study, the initial dissolution behavior of tremolite as a model Ca source in ERW was investigated in a batch reactor in the pH range of 6 - 10.5.
The initial dissolution behavior of Si, Mg, and Ca in tremolite obtained in this study showed non-stoichiometric dissolution behavior. A systematic change was observed for Si, where the dissolution rate increased with increasing pH. The initial dissolution rate of Si was about 100 times greater than the steady-state Si dissolution rate. Mg dissolved stoichiometrically to Si at pH 9 and 10.5, but preferentially to Si at pH 6. The amount of released Mg increased with decreasing pH, which is opposite trend with that of Si. It is considered that Mg is released by Mg²⁺-H⁺ ion exchange reaction at the mineral-water interface. Ca was released faster than Si and independent of pH. Thus, the mechanism of Ca releasing is different from that of Mg. The Na⁺ concentrations were 0.01 mol/L in all batch reactor systems. Therefore, Ca may have been released in large amounts by the Ca²⁺-Na⁺ ion exchange reaction. The initial release behavior of Ca in Tremolite may be beneficial to apply to ERW. Tremolite may supply Ca regardless of pH conditions of soil, at least in the first few hours after application. It may also release large amounts of Ca in high-salinity environments such as Mongolian alkaline lakes.