Sedimentary Rock Program: A Summary of the Geochemical Characteristics of Shale Important to Waste Isolation

摘要

The geochemical characteristics of shales were investigated to evaluate their potential to serve as host media for the isolation of radioactive wastes. Four end-member shales for investigation were selected to represent smectite-rich, illite-rich, carbonate-rich, and organic-rich shales. The mineralogical differences between these shales were characterized and used to assess the potential behavior of these types of shales. The compositions of groundwaters associated with various shale terrains were obtained through a search of the literature and data bases. The ranges in groundwater composition can be summarized as follows: pH = 5.9-10.9, Na = 1.8-73,025 mg/L, Ca = 0. 7-2000 mg/L, mg = 0.2-559 mg/L, K = 0.2-349 mg/L, Cl = 0.5-120,008 mg/L, SO sub 4 = 0.2-5395 mg/L, and SiO sub 2 = 0.2-43 mg/L. Rock-water experiments and reaction path modeling were used to help interpret these results and perform sensitivity calculations. Sorption tests using Cs, Sr, U, Np, and Tc indicate that the shales have moderate to high affinity for ion-exchangeable cations. The behavior of redox-sensitive elements was somewhat more complicated, but mild sorption is suggested and may be related to the organic matter present in the shales, although the data do not support firm conclusions. 47 refs., 3 figs., 7 tabs. (ERA citation 14:014409)