Kinetic Study on the Chemical and Isotope Exchange Reactions Between Aqueous Solutions and Solid Compounds.

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The primary objective of this research was to develop a new experimental method for studies of the kinetics of reactions between minerals and solutions over a wide range of temperature and pressure. We have developed three new experimental methods and facilities, which are far superior to those used by previous investigators. The first one is an in situ observation method using a differential interference microscope and the principle of chemical titration ; the newly developed experimental facility is applicable to studies on reactions between a variety of solids (both organic and in organic) and solutions (both aqueous and non-aqueous) at temperatures upto-300^ﾟC and pressures up to-200 bars. The new experimental facility was used to determine the various kinetic parameters (reaction rates, mechanisms, solubility, etc.) governing the dissolution/growth of gypsum, barium nitrate, K-alum, and CdI_2 in aqueous solutions at 25^ﾟC, and barite in aqueous solutions at 25^ﾟ-200^ﾟC. The second … More new development is a high temperature photospectroscopic method for determination of the speciation of aqueous solutions during reactions with a solid compound. This method was successfully applied to the PbS-NaCI-H_2O system in the temperature range of 25^ﾟ to 350^ﾟC. The third new development is an application of the sulfur hydrolysis reaction to control the redox state of fluids, which is essential for studies on reaction kinetics of a mneral and solution involving redox reactions. This method was successfully applied to determine the reaction rates and the solubilities of gold and pyrite in aqueous solutions at 250^ﾟ-350^ﾟC. The reaction products from these experiments were analyzed for the sulfur isotopic compositions ; these data were used to obtain kinetic information on the redox reactions among aqueous species at high temperatures. The results of investigations described above, and those obtained from other studies in this project, are important steps toward establishing the principles governing the migration and accumulation of important elements in the Earth's crust and in the hydrosphere. Less