Nitric acid / Electrochemical destruction / Technetium electrodeposition SummaryPolarographic and cyclic voltammetry (CV) measurements in nitric solutions of Tc(VII) (HNO, + ΚΝ0 3 ; μ = 1.0, pH = 0.0-6.0) at hanging mercury drop electrode (HMDE) indicate two reduction processes occurring at pH dependent E in = 0.069 to -0.205 V/SCE and pH independent E, a = -0.71 V/SCE correspondingly. The first process is referred to Tc(VII)/Tc(III) diffusion controlled reduction. Observed high absolute values and dependence of the limiting current both on Tc(VII] and NOj concentration in the solution allow to account the second reduction process for NOi ions destruction, catalyzed by Tc(IV, III) ions. Electrochemical destruction of N0 3 ions in solutions 2.0-4.0 Μ HNO, containing (0.2-2.0)10" 3 Μ Tc(VII) has been examined, using potentiostatic electrolysis with graphite cathode. In 4 Μ HN0 3 electrolysis at the potentials Ε = -0.6 to -1.0 V has been found to result in partial (5-35%) Tc electrodeposition, accompanied by acceleration of electrochemical denitration process. Mechanism of N0 3~ ions electrochemical destruction, including catalysis by the Tc(IV, III) hydrated oxides deposited at the electrode surface is discussed.

The recent Russian results on technetium transmutation into ruthenium are summarized, including the first isolation of artificial stable ruthenium from irradiated technetium targets. To cite this article: V.

Technetium electrodeposition / Formate solutions / Electrochemical methods SummaryRecovery of technetium from aqueous formate buffer solutions of ionic strength n = 1.0 was studied in the pH interval from 1.6 to 7.5 at graphite cathode in an electrolytic cell with separated compartments was studied, using cyclic voltammetry (CV) and inverse Stripping voltammetry (ISV) techniques. It has been shown that Tc electrodeposition process becomes possible at the Potentials of graphite cathode < -0.6 V/SCE. Tc recovery from Solution was found to increase with the growth of the electrolyte pH and with the shift of the cathode potentials towards negative values. Using ISV technique the half-wave potential value of Tc electrodeposition process has been determined as Em = -0.72±0.02 V/SCE and was pH independent in the interval pH = 3.46-7.32. Mechanism of electrodeposition, including Tc(VII)/Tc(IV) reduction in the Solution followed by Tc(IV) hydrolysis at the electrode surface with formation of hydrated Tc oxide cathodic deposit has been proposed. The further precision of the Tc(VII) electrochemical reduction mechanism in formate buffer media and optimization of the electrodeposition process seems to be possible using additional analytical facilities except electrochemical methods.

Technetium / Stibnite / Natural water / SorptionSummary. The sorption of technetium by powdered and polished mineral stibnite Sb 2 S 3 has been investigated in simulated and natural underground waters from the Meuse/Haute-Marne region (France). The sorption by powdered stibnite has been found to be complete under both aerobic and anaerobic conditions in batch experiments. The sorption rate is higher in the absence of oxygen than under aerobic condition. Increasing the temperature from 30 • C to 60 • C results in a rise of the sorption rate by 9.1 and 27 times under anaerobic and aerobic conditions, respectively. The observed differences in sorption kinetics in the presence and in absence of oxygen are explained by the interaction of oxygen with sulfide ion in aerobic conditions and by the reduction of technetium(VII) by iron(II) and by other impurities present in natural water and in the mineral, and by the subsequent sorption of Tc(IV) on stibnite under anaerobic conditions. The sorption on a polished mineral surface resulted in the formation of a technetium film, probably Tc 2 S 7 , with a thickness of 1-3 µg Tc/cm 2 at pH 3-6 and 4-12 µg Tc/cm 2 at 9-12. The simultaneous formation of stibnite colloids with adsorbed technetium occurs at pH 9-12. The study of the technetium film on the mineral by proton induced X-ray emission analysis showed it to be at least one order of magnitude thinner on the SiO 2 impurities than on the main Sb 2 S 3 component and the iron impurities.

Technetium-99 / Ëlectrodeposition / Formate solutions / Kinetics SummaryThe kinetics of the Tc electrodeposition and the material balance of potentiostatic electrolysis of formate buffer solutions (pH = 1.79-8.5) containing 5*10 4 -1*1(T 2 M Tc(VII) at graphite cathode has been studied. The deposition of Tc from the solution was found to become possible at E < -0.6 V/SCE with the formation of hydrated oxides (Tc0,*yH 2 0 (x s 2, 1.5 < y < 2.0) at the electrode surface. The increase of electrolyte pH, the shift of the cathode potential (£ calh .) towards more negative values and the augmentation of the electrolyte surface/volume ratio (S/V) were found to increase the yield of the electrolysis and the rate of the electrodeposition process. A maximum technetium recovery of 92-95% has been observed in the electrolysis of neutral HCOONa solutions (pH = 6.0-7.5, μ = 1.0) containing up to 5 * 10"' M Tc(VII) at potentials of the graphite cathode E < -1.4 V/SCE. The electrode capacity to the Tc electrodeposition has been determined as 2.5 ±0.4 mg/cm 2 . A starting Tc concentration in the solution of [Tc(VII)] > 5 * 10"' M and the presence of more than 0.05 M NOT in the electrolyte were found to suppress the recovery of technetium from the solution.