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It is a challenge to make thorough but efficient experimental designs for the coupled mineral dissolution and precipitation studies in a multi-mineral system, because it is difficult to speculate the best experimental duration, optimal sampling schedule, effects of different experimental conditions, and how to maximize the experimental outputs prior to the actual experiments. Geochemical modeling is an efficient and effective tool to assist the experimental design by virtually running all scenarios of interest for the studied system and predicting the experimental outcomes. Here we demonstrated an example of geochemical modeling assisted experimental design of coupled labradorite dissolution and calcite and clayey mineral precipitation using multiple isotope tracers. In this study, labradorite (plagioclase) was chosen as the reactant because it is both a major component and one of the most reactive minerals in basalt. Following our isotope doping studies of single minerals in the last ten years, initial solutions in the simulations were doped with multiple isotopes (e.g., Ca and Si). Geochemical modeling results show that the use of isotope tracers gives us orders of magnitude more sensitivity than the conventional method based on concentrations and allows us to decouple dissolution and precipitation reactions at near-equilibrium condition. The simulations suggest that the precise unidirectional dissolution rates can inform us which rate laws plagioclase dissolution has followed. Calcite precipitation occurred at near-equilibrium and the multiple isotope tracer experiments would provide near-equilibrium precipitation rates, which was a challenge for the conventional concentration-based experiments. In addition, whether the precipitation of clayey phases is the rate-limiting step in some multi-mineral systems will be revealed. Overall, the modeling results of multi-mineral reaction kinetics will improve the understanding of the coupled dissolution–precipitation in the multi-mineral systems and the quality of geochemical modeling prediction of CO2 removal and storage efficacy in the basalt systems. [ABSTRACT FROM AUTHOR]

Kyanite is an important and slow-dissolving mineral. Earlier work has measured its dissolution rate at high temperature and acidic pH, but experimental measurements at low temperature and near neutral pH were lacking. The rate equation by Palandri and Kharaka (A compilation of rate parameters of water–mineral interaction kinetics for application to geochemical modeling. US Geological Survey, Open File Report 2004-1068, 2004) indicates that the rate of kyanite dissolution at room temperature and near neutral pH is on the order of 10−17 mol m−2 s−1, orders of magnitudes slower than most common silicate minerals such as albite and quartz. This study used an externally-stirred mixed-flow reactor, which allows high solid:solution ratios, to measure the dissolution rate of kyanite at 0–22 °C and pH of 3.5–7.5. The measured dissolution rate of kyanite is 4.6–7.6 × 10−13 mol m−2 s−1 at 22 °C, and the apparent activation energy is 73.5 kJ mol−1. This dissolution rate is close to the rate of quartz dissolution and four orders of magnitude faster than the prediction by rate equation of Palandri and Kharaka (2004). Based on our new experimental data, we recommend the following rate equation for modeling the dissolution of kyanite at ambient temperatures. r = k e - E a R 1 T - 1 298.15 where k = 5.08 × 10−13 mol m−2 s−1, and Ea = 73.5 kJ mol−1. Review of literature data (Carroll in The dissolution behavior of corundum, kaolinite, and andalusite: a surface complex reaction model for the dissolution of aluminosilicate minerals in diagenetic and weathering environs. Dissertation, Northwestern University, 1989) led to a recommended rate equation for andalusite as for T = 25 °C and pH = 2–10: r = k 1 a H + n 1 + k 2 + k 3 a H + n 3 where k1 = 4.04 × 10−10 mol m−2 s−1, k2 = 7.95 × 10−10 mol m−2 s−1, k3 = 1.01 × 10−17 mol m−2 s−1, n1 = 1.2 and n3 = − 0.6. [ABSTRACT FROM AUTHOR]

Several important equilibrium Si isotope fractionation factors among minerals, organic molecules and the HSiO solution are complemented to facilitate the explanation of the distributions of Si isotopes in Earth's surface environments. The results reveal that, in comparison to aqueous HSiO, heavy Si isotopes will be significantly enriched in secondary silicate minerals. On the contrary, quadra-coordinated organosilicon complexes are enriched in light silicon isotope relative to the solution. The extent of Si-enrichment in hyper-coordinated organosilicon complexes was found to be the largest. In addition, the large kinetic isotope effect associated with the polymerization of monosilicic acid and dimer was calculated, and the results support the previous statement that highly Si-enrichment in the formation of amorphous quartz precursor contributes to the discrepancy between theoretical calculations and field observations. With the equilibrium Si isotope fractionation factors provided here, Si isotope distributions in many of Earth's surface systems can be explained. For example, the change of bulk soil δSi can be predicted as a concave pattern with respect to the weathering degree, with the minimum value where allophane completely dissolves and the total amount of sesqui-oxides and poorly crystalline minerals reaches their maximum. When, under equilibrium conditions, the well-crystallized clays start to precipitate from the pore solutions, the bulk soil δSi will increase again and reach a constant value. Similarly, the precipitation of crystalline smectite and the dissolution of poorly crystalline kaolinite may explain the δSi variations in the ground water profile. The equilibrium Si isotope fractionations among the quadra-coordinated organosilicon complexes and the HSiO solution may also shed light on the Si isotope distributions in the Si-accumulating plants. [ABSTRACT FROM AUTHOR]