Geochemical results of leaching shale at ambient temperature and 1000C

Oak Ridge National Laboratory is conducting research for the U.S. DOE to evaluate the potential for sedimentary rocks to serve as a repository for high level nuclear waste. The work reported in this paper of these efforts and represents an attempt to characterize the geochemical behavior of various shale types at high temperatures. Experiments were designed to analyze the mineralogical alterations and the changes in the pore water chemistry which occur when the temperature is increased. This study centered on the batch leaching of different shale types for several weeks in distilled water at ambient temperature at 1000C. The composition of the water after leaching and the resulting mineralogy were determined. These data were used for mineral equilibria calculations by the thermodynamic computer code, PHREEQE. The geochemical reactions that occur with a temperature increase and the mineral equilibria that control the aqueous chemistry were inferred from the relationships in the analytical data set and the results from PHREEQE. Shales were chosen to represent the various compositional parameters thought to be important in the geochemical alterations of shales at high temperature: clay mineralogy, calcite, pyrite, and organic material