- © The Mineralogical Society Of America
Recent years have seen the growing development and application of reactive transport models to describe, at different spatial and temporal scales, natural and industrial processes involving water-rock interactions such as continental weathering and its impact on ocean chemistry and climate, cycling of metals and the formation of ore deposits, porosity formation/reduction and oil migration in sedimentary basins, transport and geological sequestration of CO2, and geothermal power generation. The successful application of these models requires a comprehensive and robust kinetic data base of mineral-water interactions. To address this need significant efforts have been made over the past two decades to i) measure in the laboratory mineral dissolution/crystallization rates and ii) develop robust rate laws which could be incorporated in reactive transport algorithms. The aim of this chapter is to review the mechanisms which control the kinetics of mineral dissolution and precipitation and show that accurate knowledge of aqueous chemistry and thermodynamics is essential for quantifying the available kinetic data of mineral water interaction.
REACTIVE TRANSPORT AND THE CONTROL OF FLUID-MINERAL INTERACTIONS
The main processes involved in reactive transport in a porous and/or fractured media: advection, molecular diffusion, mechanical dispersion and fluid-solid reactions (dissolution and crystallization) are illustrated in Figure 1⇓. Crystal dissolution and growth proceed via the transport of aqueous reactants and products to and from the surface coupled to chemical reactions occurring at the surface. The overall rate of dissolution or crystallization is controlled by the slowest of these coupled processes, either surface reaction or transport of aqueous species. When surface reactions are fast relative to molecular diffusion, dissolved species are depleted at the solid surface; the reaction is “transport” controlled1. If transport is fast relative to surface reactions, no depletion is observed; the overall reaction rate is “surface reaction” controlled. The rotating disk reactor method (Gregory and Riddiford 1956) allows discrimination …