Removal of Uranium from Simulated Fly Ash by Chloride Volatilisation Method

Fly ash is generated from LWR nuclear power plant as a low-level waste, which is contaminated with a small amount of radioactive materials, composed mainly of uranium oxide. The constituents of the fly ash are similar to those of the ore; the major components of the ash are oxides of silicon, aluminum, sodium, magnesium, zinc, iron sodium and uranium. In this study, removal of uranium from the simulated fly ash, of which composition was U3O8: 10, CaO:25, SiO2: 25, Al2O3: 20, MgO: 10, ZnO:5, Fe2O3: 3 and Na2CO3: 2wt%, by chloride volatilisation method was examined. The simulated fly ash was chlorinated by the same manner as the dry way processing for the ore; namely, the ash was heated in a flow of chlorine in the presence of carbon at high temperatures. In the case of volatilisation of uranium from U3O8 and a simulated fly ash by chlorination using chlorine and carbon, it was seen that uranium of both samples showed similar volatilisation behaviour: The volatilisation ratio of uranium (VU) increased with increasing temperature from 800 to 1 100°C. The VU value attained 99.9% at 1 100°C. Iron, silicon and zinc showed similar behaviour to uranium, namely, they vaporised completely. The volatilisation ratio of aluminum, magnesium and sodium were still high in a range 80~90%. The volatilisation ratio of calcium was ~40% under the same chlorination condition, though it changed to chloride. For recovery of uranium from fly ash by chlorination using chlorine in the presence of carbon, high volatilisation ratio of uranium can be achieved at high temperatures. Volatilisation ratio of other components also increases, which decreases the amount of decontaminated residue resulting in the reducing of decontamination effect. Selection of heating condition is important.