Heini Ervanne

Soluble and particle-bound 234,238U, 226Ra and 210Po in ground waters

Summary Water of five drilled wells was filtered with three membranes (pore size 0.45 µm-5 kD) to determine the soluble and particle-bound forms of 234,238U, 226Ra and 210Po. Three of the waters were of Ca-HCO3 type and two of Na-Cl type. Some of the waters also exhibited high concentrations of Fe, Mn and humic substances. 234,238U was present entirely in soluble form in all waters, probably as uranyl ion (UO22+) in soluble carbonate complexes. 226Ra was in soluble form in the waters with low concentrations of Fe and Mn, but 10% of the total 226Ra activity was bound to particles in the Fe-Mn-rich waters. The behaviour of Po varied with water composition. Particle-bound 210Po was observed to correlate with the combined concentration of iron and manganese in the raw waters. In the two of waters of Na-Cl type, in which the concentrations of Fe, Mn and humic substances were high, salinity of the waters did not enhance the solubility of polonium. Polonium was present in both soluble and particle-bound forms in all the ground waters.

Redox Chemistry in Uranium-rich Groundwater of Palmottu Uranium Deposit, Finland

Groundwater redox conditions and oxidation states of dissolved uranium were studied in natural water samples from a uranium deposit. Consistently good correlations were observed between the dissolved U(IV)/U(VI) ratio and the measured redox potential value. Dissolved redox pairs in a uranium-rich groundwater sample were studied by monitoring the Eh-change caused by acid/base addition. The results have been compared with the theoretical redox behaviour of uranium.

Interferences in uranium oxidation states during dissolution of solid phases

The effects of iron on uranium oxidation states during sample dissolution were studied. A mineral acid mixture in anaerobic conditions was used for the dissolution the sample and the uranium oxidation states were determined by ion exchange. The first experiments were performed with pure iron chloride compounds. In the second stage, study was made of common iron-containing minerals. Uranium oxidation states were affected when the content of iron compound was as low as 10-5M. In the case of the natural minerals, pyrite caused uranium to change to an increasingly reduced state, whereas goethite caused it to change to an increasingly oxidized state as the amount of mineral was increased. The interferences of the silicates fell between those of pyrite and goethite. The results indicate that a wide range of common bulk rocks with less than 20 wt% of iron-containing minerals can be reliable chemically analyzed for uranium oxidation state.

Dating of fluvial sediments from the Amazon lowland in Peru

Abstract TL dating was attempted on sediments from surficial alluvial formations of the Peruvian Amazon, a huge area for which there are few Pleistocene age determinations. The samples were collected from several locations of erosional banks carved in older alluvial deposits in order to date the Quaternary stratigraphy. The major part of the time-scale falls beyond the range of the radiocarbon method. A complex resedimentation also makes the use of this method difficult. Here TL dating can provide an approximate idea of the age and history of sedimentation. Some preliminary results are presented and problems due to sample characteristics are discussed.

Uranium mineral - groundwater equilibration at the Palmottu natural analogue study site, Finland

The redox-potential, pH, chemical composition of fracture waters, and uraninite alteration associated with the Palmottu uranium mineralization, have been studied. The data have been interpreted by means of thermodynamic calculations. The results indicate equilibrium between uraninite, ferric hydroxide and groundwater in the bedrock of the study site. Partially oxidized uraninite (UO{sub 2.33}) and ferric hydroxide are in equilibrium with the fresh, slightly acidic and oxidized water type, while primary uraninite is stable with deeper waters that have a higher pH and lower Eh. Measured Eh-pH values of groundwater cluster within a relatively narrow range indicating buffering by heterogeneous redox-processes. A good consistency between measured Eh and analyzed uranium oxidation states was observed.

Modelling of niobium sorption on clay minerals in sodium and calcium perchlorate solutions

Abstract The sorption behaviour of niobium on kaolinite and illite minerals in sodium and calcium perchlorate solutions was evaluated with use of the mass distribution coefficient, Rd, obtained in batch sorption experiments. Very high distribution coefficient values, about 100 m3/kg, were obtained for both minerals in the neutral pH range between 6 and 8. Values were somewhat lower at pH 5. In NaClO4 solution, the sorption of niobium starts to decrease at pH higher than 8. This is in agreement with the increase, with pH, in the proportion of anionic niobate species, which are presumed to be low or non-sorbing. A similar decrease was not observed in Ca(ClO4)2 solution, probably owing to the influence of Ca on niobium solution speciation and surface species. The surface complexation model was applied to model the Rd values. The model fitted well for the NaClO4 solution but only at pH below 9 for the Ca(ClO4)2 solution. The discrepancy between the strong sorption of niobium in calcium-bearing solution at high pH and the calculated speciation is due in part to the non-inclusion of calcium niobate solution species and Ca-Nb compounds in the present NEA and other similar thermodynamic databases.