Pore-scale study of the effect of secondary carbonate precipitation on the dissolution of primary minerals using the lattice Boltzmann method
Abstract
Reactive transport processes involving dissolution and/or precipitation are pervasive in Earth, energy, and environmental systems. One typical example is geologic sequestration of carbon dioxide. Among these reactive processes, it is commonly encountered that a second phase precipitates while the primary phase dissolves, and the precipitation and dissolution reactions are fully coupled with each other. In the case of mineral trapping of CO2, the primary silicate mineral dissolves due to a decrease of pH caused by the dissolution of CO2 into the solution; meanwhile the dissolved CO2 can react with cations to form a secondary precipitate of carbonate mineral. Although the effect of precipitation of secondary solid phase on the dissolution of the primary solid phase has been studied extensively, the results reported in the literature are often inconclusive and sometimes even contradict one another. The reason is that the coupled dissolution and precipitation processes are controlled by several factors whose contribution is difficult to ascertain, including the dissolution and precipitation reaction kinetics, temperature and pressure, pH and species concentration of the solution, physicochemical properties of the primary and secondary minerals, as well as the nucleation and crystal mechanisms of the precipitates, etc. In this study, a pore-scale (mesoscopic) model based on the lattice Boltzmann method (LBM) is developed to investigate the effects of secondary precipitation on the dissolution of the primary mineral. The model can predict coupled multiple physicochemical processes including fluid flow, mass transport, chemical reaction, dissolution, precipitation consisting of nucleation and crystal growth, as well as dynamical evolution of pore geometries. Effects of dissolution and precipitation reaction kinetics, molar volumes of primary and secondary minerals, initial powder size and surface roughness of the primary mineral, as well as nucleation and crystal growth mechanisms on the dissolution and precipitation processes are investigated in terms of rate and amount of dissolution and precipitation. Several types of dissolution and precipitation processes are identified based on the morphology and structure of the precipitates and on the extent to which the precipitates affect the dissolution of the primary mineral. Simulation results are also compared with existing experimental results. Depending on the conditions, the effect of the precipitates spans the full range of possible behavior from trivial changes to enhanced or reduced dissolution rates of the primary phase.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.V34A..02K
- Keywords:
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- 1009 GEOCHEMISTRY Geochemical modeling;
- 1042 GEOCHEMISTRY Mineral and crystal chemistry;
- 1012 GEOCHEMISTRY Reactions and phase equilibria