Radionuclides behavior in natural water estimate based upon determination physicochemical state of their stable chemical analogs

¹ Institute of Solid State Chemistry, UB RAS, 91 Pervomajskaya ul., 620041 Ekaterinburg, Russian Federation
² Institute of Plant and Animal Ecology, UB RAS, 624250, Biophysical Station, POB 18, Zarechny, Sverdlovsk Reg., Russian Federation
³ Institute of Mineralogy UB RAS, 456301 Miass, Chelyabinsk Reg., Russian Federation
⁴ Scientific Engineering Co. ECSORB, 8th March ul., 620014 Ekaterinburg, Russian Federation

Abstract

The physicochemical state of radionuclides of Sr, U, REE and Th(IV) and their natural analogs in the river Techya (Chelyabinsk reg., RF) is analyzed in connection with seasonal variations of the chemical composition of water. It is shown that the chemical state of Sr(II) and U(VI) strongly depends on the level of CO₂ in the river water. A high level of soluble carbonate leads to co-precipitation of to 10–15% Sr(II) and to 20% U(VI) on the surface of mineral (Ca - Si - Al - O + Fe - O phase mixture) and biological suspensions with the size of >3 micron. The rest of Sr(II) exists in the river water in the form of aqua-cations. Uranium (VI) is present in the water as a set of hydroxo- and carbonate complexes which do not interact with the cation-exchanger and in the form of Ca₂UO₂(CO₃)₃ which may be involved in the ion-exchange interaction. Th(IV) and La (III) are found to exist in the water as hydroxo-complexes (<80%) and in the form of suspension (<20%). When the concentration of CO₂ in the river water decreases to the level typical of the autumn period, the suspended CaCO₃ vanishes and the fraction of Ca₂UO₂(CO₃)₃ in the water changes.