Dissolution and precipitation kinetics of minerals

The chemical evolution of repository sites will necessarily involve the response of minerals to interactions with natural fluids. This water-rock interaction will lead to both the growth and the breakdown of a number of important mineral phases. These heterogeneous chemical reactions induce a strong and important coupling between the fluid flow dynamics and the minerals present in the geologic environment. The time-dependent dissolution or precipitation of solid phases in a repository environment will have direct effects on the porosity and permeability, on the mineralogy in the near field, and on the solution chemistry including the sorption and adsorption of radionuclides in the host rock. Therefore, to understand and accurately predict the long-term dissolution-precipitation behavior of phases in potential host rocks, a knowledge of a full rate law (that is, the rate law for both dissolution and precipitation) for individual phases is required. This rate law would include the possibility of attaining equilibrium (zero net rate) as a special case. Kinetic data are urgently needed for dissolution-precipitation of individual phases such as smectites, zeolites, natural glasses, silica phases (quartz, cristobalite, and tridymite), feldspars, and evaporative minerals (especially halite). The kinetic data on individual phases will then be combined with whole-rock experiments to provide a critical link and validation of the kinetic models that will be used to predict the chemical behavior of host rocks in the evolution of a repository site. These data needs are discussed in detail