Kinetics of the Smectite-Illite Transformation: An Experimental Study

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A series of experiments will be undertaken on clays under differing silica, aluminum, and potassium concentrations, at temperatures from 25oC up to 300oC. The new experimental technique for the proposed research has been thoroughly tested. It incorporates the dual pumping of solutions through two feeder-bombs containing quartz or boehmite which provide, by their equilibrium solubilities at controlled temperatures, fixed but adjustable silica and aluminum concentrations in the input solutions. In the proposed experiments, the narrowly sized clay samples will be suspended as fluidized bed within the reactor. Samples of both the solid and the solutions will then be extracted during each run to track the reaction progress, and a variety of analytical techniques will be used to evaluate compositional changes in the fluids and solids and the structural state of the illite/smectite sample. The results of these experiments will be important in several respects. First, they will provide kinetic data for modeling fluid-flow and diagenesis on a basin scale. In such models the release of water, reduction in porosity, and change in fluid chemistry and pressure associated with illitization are important processes that have to date been highly parameterized. Secondly, they should resolve the mechanism of the smectite to illite transformation. An active controversy persists as to whether illitization proceeds via a solid-state or a dissolution-reprecipitation path. In our experiments, the ability to control the fluid composition and flow rate (hence "closedness" of the system) allows us to assess whether these factors affect the rates and energetics of the reaction and whether they are dominated by mass transport of surface kinetics through an elemental reaction or through multiple pathways. In addition to its significance to the kinetics of illitization, the work proposed here will extend the valuable equilibrium solubility results of May et al. (1986)and of Aja et al. (1991a, b) on the stabilities of phases in the K2O-MgO-Al2O3-SiO2-H2O system. The experimental results should also resolve whether the fundamental particle explanation is solution or a mixture of multiple phases (e.g., Tardy and Fritz, 1981; Aagaard and Helgeson, 1983; Nadeau et al., 1984; Garrels, 1984; and Altaner, 1988).