Sorption characteristics of rocks in the Yenisei site of Nizhnekansky granitoid massif

The article give data on sorption characteristics of five samples of rocks intersected by well R12 at different depths (166 m, 417 m, 443 m, 459 m, 476 m) in the Yenisei site at the exo-contact of Nizhnekansky granitoid massif in the area of Mining-Chemical Integrated Works (MCIW, Krasnoyarsk Territory). Sorption characteristics of plagio-gneisses, plagiogranite gneisses, migmatized granite gneisses and metamorphized gabbro-diabases were determined with regard to various-nature long-lived radionuclides (135,137Cs, 226Ra, 79Se, 237,239Np, 239,240Pu, 241,243Am), for which distribution ratios and sorption kinetics were assessed. The sorption test conditions (compositions of solutions, values of pH and redox potential) corresponded with natural water in the designed location of an underground research laboratory, namely: anaerobic conditions (sealed glove cabinet with nitrogen atmosphere); redox potential about -200 nV; water solution pH 7–8 (in equilibrium with bentonite); total dissolved solids 200–300 mg/l; hydrocarbonate–calcic medium; initial content of separate radionuclides 10–9 mole/l. It has been found that sorption of metal cations runs more rapidly and reaches equilibrium in 1–4 h, whereas sorption of selenium in the form of selenate ion is insignificant. Values of distribution ratios of the studied radionuclides are consistent in terms of magnitude with the published data, including other types of granitoids. Computer-aided radioexamination shows nonuniform distribution of radionuclides over the surface of the samples of granitoids, which is related with the sorption characteristics of separate mineral phases. Grains of quartz and unaltered feldspar show zero sorption activity relative to the studied radionuclides. Average values of sorption are obtained in the zones of microbreccias, seritization and chloritization. The best sorptive are “dark-colored” phyllosilicate minerals: smektite, interstratified chlorite/smektite, micaceous minerals. The authors appreciate participation of A. E. Kashtanov (Moscow State University), V. A. Petrov and V. V. Poluektov (Institute of Geology of Ore Deposits, Petrography, Mineralogy and Biochemistry of the Russian Academy of Sciences), and J. Hammer (Federal Institute for Geosciences and Natural Resources in Hannover, Germany) in this study.