The determination of the two species of uranium(VI and IV) present in 6 uranium ores was studied in relation to the chemical and mineralogical composition, humidity, and pH of the samples taken over from the mine. X-ray diffraction studies, performed on the uranium ores in powder form allowed to establish their mineralogical composition. Thechemical analysis pointed out Quite numerous monographic studies and reviews have been devoted to the distribution of the U VI and U IV chemical species present in the composition of the minerals forming the uranium ores [1Ϫ3]. Up to the ratio between the two uranium species in several ores it is seen as varying with the conditions characterizing the mining sites from which the samples under analysis had been extracted. One of the remarks done was that the H и and HO и primary radiolysis products, resulted from the decomposition of the ground water under the influence of the α-rays emitted by uranium nuclei, as well as those associated to chain nuclear fission reactions for the Oklo-Gabon zone, induced major transformations in the ratio established between the two uranium species [4Ϫ6].Raman spectrometric measurements in gaseous phase performed on the samples of uranium ores with different mineralogical composition pointed out the presence of certain H 2 O-salt-H 2 -O 2 and H 2 O-salt-H 2 ± CH 4 inclusions of organic origin, resulted from micro organisms, in the holes microcraks.
The possibility of bioaccumulation of uranium and thorium species in the blue-green algae Azolla caroliniana Willd. was investigated. The behavior of the Azolla caroliniana-* M n+ (* M n+ = UO 2 2+ , Th 4+) system was studied versus contact time, pH and anion nature with no ionic competition. The effective UO + 2 2 and Th 4+ ions removal from low radioactive waste waters was demonstrated. The analysis of the data revealed the following optimum working conditions: for uranium: contact time 20 hours, pH = 6.0, t = 28 o C and 2⋅10-3 M UO 2 (CH 3 COO) 2 solution as uranium source; as result, the maximum of K d is obtained for a value of nearly 600 mL/g, and a ratio V/M=100 mL/g; for thorium: contact time 30 hours, pH = 5.5, t = 26 o C and 10-3 M Th(NO 3) 4 solution as thorium source; the maximum of K d is about 900 mL/g, for the same ratio V/M.
The present work is focused on an electrochemical method of uranium extraction. The basic principle of the method is the electrolytic one. Using platinum electrodes it was generated a potential dependence of the uranium concentration on the redox potential. Knowing the potential, the time dependence of uranium extraction from UO 2 (NO 3 )*H 2 O salt and uranium ore solid suspension was studied with good results. Therefore, this method can be considered as clean and in consequence appropriate for uranium decontamination of some solid and/or liquid media. Moreover, the method can be used in extraction -decontamination of sand (ore or spent fuel).
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