The dissolution of UO2 in carbonate-bicarbonate solutions containing sodium hypochlorite as an oxidant has been investigated. The effect of temperature, sodium hypochlorite concentration and stirring speed was examined. In the temperature range of 303 to 318 K, the leaching reaction displayed linear kinetics. Apparent activation energy obtained from the differential approach was found to be 57 kJ mol–1. This relatively high activation energy value indicates a chemically controlled behavior of UO2 dissolution. The order of reaction with respect to sodium hypochlorite concentration was found to be unity.
The extraction behavior of uranium, thorium and nitric acid has been investigated for the TEHDGA/isodecyl alcohol/n-dodecane
solvent system. Conditional acid uptake constant (KH) of TEHDGA/n-dodecane and the ratio of TEHDGA to nitric acid were obtained as 1.72 and 1:0.96, respectively. The extracted
species of uranium and thorium in the organic phase were found to be UO2(NO3)2·2TEHDGA and Th(NO3)4·2TEHDGA. A workable separation factor (DTh/DU) of the order of 300 was observed between thorium and uranium in the nitric acid range of 0.5M to 1.5M. Similar separation
factor was also achieved at higher acidity when thorium was present in large concentration compared to uranium. These results
indicate that TEHDGA solvent system could be a potential candidate for separation of thorium from uranium.