Uranium in groundwaters of North Kazakhstan

Abstract

Relevance. The need to dentify the characteristics of the distribution of radioactive elements in the groundwater of Northern Kazakhstan. Aim. Generalization of available data on the geochemistry of groundwater and uranium and radon distribution in them using the example of the northern regions of the Republic of Kazakhstan. Methods. Generalization of long-term hydrogeochemical research and compilation of an electronic data bank on the territory of Northern Kazakhstan. A laboratory study of the chemical composition of groundwater was carried out at the Research Laboratory of Hydrogeochemistry of the School of Natural Resources Engineering of Tomsk Polytechnic University. Measurements of 222Rn contents in waters were carried out using the Alfarad Plus complex in the Laboratory of Hydrogeology of Sedimentary Basins of Siberia, Institute of Geology and Geography, Siberian Branch, Russian Academy of Sciences. Results. The groundwater of aquifers of different ages, distributed in the territory of Northern Kazakhstan (North Kazakhstan uranium province), was studied. Two geochemical sets of groundwater were identified. The first is characterized by the dominance of HCO3– and Mg2+ in the water composition, and the second by Cl– and Na+. A change in composition and an increase in the value of total mineralization from 0,1 to 49 g/dm3, in the direction from north to south, indicate the development of continental salinization. In natural waters of the first group, uranium content varies from 0.065 to 16000 μg/dm3 and radon activity from 4 to 3885 Bq/dm3. For sodium chloride waters of the second set, concentrations can reach 32500 μg/dm3, and radon activity is 6–59 Bq/dm3, since the emanating reservoir (granitoids) is located to the north – at a distance of 80–100 km. Naturally, granitoid massifs of the studied region are sources of uranium. Their drainage by the river network leads to its removal and concentration on geochemical barriers in the groundwater of the Neogene-Quaternary aquifer. This distribution of radioactive elements is associated with the high migration ability of uranium in solution in the form of uranyl ion in oxidizing geochemical conditions.

Keywords

• Radon waters
• uranium-238
• radon-222
• Northern Kazakhstan
• Ob-Zaisan folded region