Early Results on Uranium and Thorium Distribution in the Natural Waters of the Baydar Valley (the Crimean Peninsula)
D. A. NOVIKOV1,2, T. V. KORNEEVA1, YU. G. KOPYLOVA3, A. V. CHERNYKH1, F. F. DULTSEV1, A. A. KHVASHCHEVSKAYA3
1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
3Tomsk Polytechnic University, Tomsk, Russia
Keywords: natural waters, uranium, thorium, migration forms, the Crimean Peninsula
Pages: 449-459
Abstract
The early data on the distribution and the forms of uranium and thorium migration in different geochemical types of natural waters of the Baydar Valley (the Crimean Peninsula) are obtained. Fresh and ultrafresh waters, mainly with hydrocarbonate calcium composition with total dissolved solids from 208 to 1269 mg/dm3, widely occur in the region. Fracture-karst waters, which are best protected from the continental salination, relate to weakly alkaline (pH 7.7), fresh with total dissolved solids 444 mg/dm3, and not very high Si concentrations (2.23 mg/dm3), hydrocarbonate calcium by composition. The waters of the zone of regional fracturing and fissure-vein waters are prone to the influence of continental salination processes and anthropogenic load. They are characterized by pH from neutral to alkaline (7.1-8.6); they are mainly fresh (269-1269 mg/dm3), with average Si content of 4.61-4.70 mg/dm3, their composition is hydrocarbonate calcium with increased concentrations of SO42-, Mg2+ and Na+. The surface waters are prone to continental salination; they are weakly alkaline (рН 8.3), moderately fresh (207-364 mg/dm3), with the average Si concentration of 1.18 mg/dm3, hydrocarbonate calcium composition and increased concentrations of Cl-, Mg2+ and Na+. The determined concentrations of uranium (238U) vary within the range from 2.64 • 10-5 to 2.25 • 10-3 mg/dm3, thorium (232Th) - from 2.04 • 10-7 to 2.50 • 10-5 mg/dm3. The nature of radioactivity of the studied objects is due to 238U, because the waters are characterized by the oxidative parameters of the geochemical environment with pH 7.1-8.9, Eh 67.2-209.3 mV and the concentration of dissolved oxygen 3.19-12.25 mg/dm3. The ratio 232Th/238U is (1.09 • 10-3)-0.71. Waters enriched with 238U to the highest extent are the waters of regional fracturing zone, mainly related to sodium aluminosilicates, subjected to continental salination under the conditions of anthropogenic impact, and waters enriched with 232Th are those of the regional fracturing zone, mainly related to sodium silicates (long-term interaction in the water - rock system) subjected to continental salination. 238U migrates in the form of anion complexes UO2(CO3)34- and UO2(CO3)22-, to a lower extent (<1 % of the total content) in the form of Ca2UO2(CO3)3(aq) and CaUO2(CO3)32-. Results of calculations over 232Th revealed its presence only in the form of complex Th(OH)3CO3-.
DOI: 10.15372/CSD2021322
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