Abstract
The presented paper is intended to study the chemical behaviour of combined geogenicanthropogenic uranium content in specific stream sediments. The sampling points have been chosen with respect to the natural conditions in the locality of groundwater outflow from a former uranium mine adit in Považský Inovec mountain range, near Kálnica village. Besides the total uranium determination and physical-chemical characterization of the relevant water- and sediment samples we carried out modified Tessier type sequential fractionation extractions of natural- and artificially contaminated sediment samples after time dependent agitation in air and in the atmosphere of argon. The obtained results have been compared with those fulfilled with montmorillonite K-10. The total uranium concentrations of the relevant groundwater samples as well as of stream sediments have been determined by ICP-MS using HP 4500. The determinations of uranium in extracts have been accomplished according STN757614, utilizing arsenazo III as a selective complex forming reagent for spectrophotometric determination of uranyl-ions at 650 nm. The total uranium concentration of the groundwater outflow and in the sediment taken in its immediate vicinity has been 31.75±0.35 μg dm-3 and 38.0±2.7 μg g-1 respectively. Unlike montmorillonit K-10, in which the carbonate-bound fraction of uranium after 1 week aeration and agitation in argon atmosphere represents 22.8% and 18.6% respectively, uranium in investigated sediments has been present predominantly in carbonate-bound fraction-reaching under similar conditions 38.6% and 26.6%, respectively.
Highlights
Uranium is an element of highly specific chemical, physical and biological properties
During sedimentation and diagenesis in the productive complex of strata occurred the accumulation of uranium and accompanying minerals and during the Alpine orogeny their concentration in the form of lenses
Sampling point 3 (N 48°44.81'; E 17°57.68) has been chosen directly at the groundwater outflow from the uranium mine, which flows to the stream Prostredný potok
Summary
Uranium is an element of highly specific chemical, physical and biological properties. Among basic features of uranium the following ones are crucial: it is a typical lithophilic natural radioactive component of the environment and contrary to its notoriety its radiotoxicity is negligible in comparison with chemical toxicity. The most prevalent form of uranium in aqueous solution is the light yellow, fluorescent uranyl ion ( UO22+ ). The trivalent U3+ can be formed by reduction of U(IV) but it is unstable as it oxidizes in aqueous solution (GREENWOOD and EARNSHAW, 1997). U(VI) concentrations in dependence of pe and pH introducing the following model conditions (Fig. 1-4): Total uranium: 0.00005 mmol dm-3; Alcalinity: 3.0 mmol dm-3; Calcium: 1.5 mmol dm-3; Temperature: 298.15 K; Thermodynamic data: U4+ + e- = U3+ (log K = -9.353; ΔH = 102.098 kJ)
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