『Abstract
　This paper explores how dissolution and precipitation reactions are coupled in batch reactor experimental systems at elevated temperatures. This is the fourth paper in our series of “Coupled Alkali Feldspar Dissolution and Secondary Mineral Precipitation in Batch Systems”. In our third paper, e demonstrated via speciation-solubility modeling that partial equilibrium between secondary minerals and aqueous solutions was not attained in feldspar hydrolysis batch reactors at 80-300℃ and that a strong coupling between dissolution and precipitation reactions follows as a consequence of the slower precipitation of secondary minerals (Zoo and Lo, 2009). Here, we develop this concept further by using numerical reaction path models to elucidate how the dissolution and precipitation reactions are coupled. Modeling results show that a quasi-steady state was reached. At the quasi-steady state, dissolution reactions proceeded at rates that are orders of magnitude slower than the rates measured at far from equilibrium. The quasi-steady state is determined by the relative rate constants, and strongly influenced by the function of Gibbs free energy of reaction (ΔGo) in the rate laws.
　To explore the potential effects of fluid flow rates on the coupling of reactions, we extrapolate a batch system (Manor et al., 2007) to open systems and simulated one-dimensional reactive mass transport for oligoclase dissolution and kaolinite precipitation in homogeneous porous media. Different steady states were achieved at different locations along the one-dimensional domain. The time-space distribution and saturation indices (SI) at the steady states were a function of flow rates for a given kinetic model. Regardless of the differences in SI, the ratio between oligoclase dissolution rates and kaolinite precipitation rates remained 1.626, as in the batch system case (Ganor et al., 2007). Therefore, our simulation results demonstrated coupling among dissolution, precipitation, and flow rates.
　Results reported in this communication lend support to our hypothesis that slow secondary mineral precipitation explains part of the well-known apparent discrepancy between lab measured and field estimated feldspar dissolution rates (Zhu et al., 2004). Here we show how the slow secondary mineral precipitation provides a regulator to explain why the systems are held close to equilibrium and show how the most often-quoted “near equilibrium” explanation for an apparent field-lab discrepancy can work quantitatively. The substantiated hypothesis now offers the promise of reconciling part of the apparent field-lab discrepancy.』

1. Introduction
2. Conceptual models and assumptions
　2.1. Standard state thermodynamic data
　2.2. Rate laws
　2.3. Reactive surface area
3. Modeling results and analyses
　3.1. Albite dissolution-sanidine preparation experiments
　　3.1.1. Congruent dissolution stage (0-7 h)
　　3.1.2. Steady state dissolution of albite and precipitation of sanidine (〜672-1848 h)
　　3.1.3. Albite incongruent dissolution with initiation of sanidine precipitation (7-504 h)
　　3.1.4. Sanidine precipitation (7-672b h)
　　3.1.5. Simulation of the entire experiment period (0-1848 h) and beyond
　3.2. Feldspar hydrolysis batch experiments at 200℃ and 300 bars
4. Discussions
　4.1. The influence of f(ΔGr) and Sj on the coupling of reactions
　4.2. Influences from fluid flow rates
5. Conclusions and remarks
Acknowledgments
References