Effects of Volatilization on Groundwater Chemistry
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II11.7.1
Effects of Volatilization on Groundwater Chemistry A.L. Pulvirenti,1 K.M. Needham,1 M.A. Adel-Hadadi,1 E.J. Bishop,1 and A. Barkatt1 C.R. Marks2 and J.A. Gorman2 1 2
The Catholic University of America, Washington, D.C. 20064 Dominion Engineering, Inc.,11730 Plaza America Drive, Reston, VA 20190
ABSTRACT Both concentrated and dilute simulated solutions of saturated J13 and unsaturated UZ pore water were concentrated through distillation of the solutions under atmospheric pressure. It was observed that condensed vapors from the pH of J13 waters steadily rose during the distillations to a value of 10, while the pH of UZ waters remained steady until 90% of the volume of the solution had been distilled, after which the pH of the condensed vapors dropped precipitously, often below 1. Residual solutions analyzed when most of the solution had been distilled away were also found to be extremely acidic. The temperature of these residual solutions was around 144oC due to their high solute content causing boiling point elevation. All experiments were performed with the condenser open to ambient air at atmospheric pressure. The pH drop during the distillation of UZ water is attributed largely to the presence of large amounts of magnesium. Specimens of Alloy 22 tested in the residual solutions of at their boiling temperature (around 144oC) showed significant rates of general corrosion over a broad range, often approaching 1 mm/year. Similarly high corrosion rates were also observed in tests on Alloy 22 specimens in condensates obtained during the late stages of the distillation. These tests were performed either in situ at 75-80oC using a Soxhlet extractor, or in separate pressure vessels at temperatures between 90 and 130oC. INTRODUCTION In current testing of Alloy 22 as a candidate for waste package containers for the Yucca Mountain geologic waste repository, reference groundwaters used have been based on J13 reference water from the saturated zone, which is a primarily sodium bicarbonate-based water[1]. The analysis of the recently collected pore water, squeezed from the unsaturated (vadose) zone above the repository horizon (UZ), showed that it was a calcium chloride and magnesium sulfate-based water[1]. Thermal concentration experiments[1] on both waters showed that during concentration the pH of residual J13 waters rose (from 8 – 10-10.5 when concentrated to a factor of 1000), while UZ waters exhibited a pH drop (from 7.5 to 5-6 at a concentration factor of 1243.) The UZ pore water of Ref. 1 is one of a broad range of water chemistries observed in samples of water recovered from the unsaturated zone[2,3]. There is no reason to expect that thermal evaporation of waters in the environment will stop at concentration factors on the order of 1000. Therefore, in the current study, the evolution of the chemical compositions of J13 and UZ during extreme concentration was explored. In addition, the vapor phase released from the solutions was collected as condensate by standard distillation techniques and analyzed. Finall
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