The purpose of this paper was to study the oxidation of uranium species coming from some Romanian uranium ores at U(VI), in the presence of the following oxidizing agents: KMnO 4 /H 2 SO 4, H 2 O 2 and HCl+HNO 3. There was ascertained that the highest capacity of leaching is shown by KMnO 4 /H 2 SO 4 that achieved values of almost 100% after about 7 days. This fact was explained through the chemical and mineralogical composition of the studied ores.
It was investigated the bioleaching of uranyl ions from uranium ores, in aquatic medium with algae: Scenedesmus quadricauda and Nostoc linkia under different experimental conditions. The oxidation of U(IV) to U(VI) species, like uranyl ions was done by means of the atomic oxygen generated through photosynthesis by the aquatic medium from solution above of uranium ores. After almost 10 days of direct contact with the given microorganisms, it was observed a bioleaching degree between 10% and 20% in UO + 2 2 ions. The experiments were achieved at 30°C, in the presence of continuous illumination at 2×10 -7 J/cm 2 sec. The bioleaching results were observed spectrophotometrically in UV-VIS, measuring the absorbance of uranyl ions at 665 nm. After achieving the maximum bioleaching degree during 10 days, a process of bioaccumulation of uranyl ions was observed. This statement was confirmed by decreasing in time of absorbance in the UV-VIS spectra of solutions and also by means of IR spectra drawn on the alga microorganisms which retained former these cations.
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.
Abstract. The purpose of the present work was to study the oxidation of uranium species coming from different samples of some Romanian uranium ores at U(VI), in the presence of the following oxidizing agents: KMnO 4 /H 2 SO 4, H 2 O 2 and royal water. It was established that the highest capacity of leaching is shown by KMnO 4 /H 2 SO 4 that achieved values of ca. 100% in about seven days. This chemical reaction was explained through the chemical and mineralogical composition of the studied samples.
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