Intensified dissolution of uranium from graphite substrate using ultrasound

Cavitation-assisted decontamination of yttria from graphite of different densities

“…The graphite surface shows the presence of macroporous opening ( Fig. 3 (c)) after the ultrasound treatment similar to that observed in the case of uranium leaching [10] under similar conditions (30 kHz as frequency and 30 min as the time of treatment). However, the degree of pore opening in the case of yttria coating was less compared to that of uranium.…”

“…Such instances were also observed in the case of delignification of newspaper where the extent of treatment enhanced from 16% to 44% by increasing the temperature from 40 °C to 100 °C [22] . Similarly in the case of uranium, the dissolution rate changed by 20% over the temperature range of 45 °C to 70 °C for treatment of 30 min at 33 kHz frequency in 6 M acid solution [10] .

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“…As the concentration increases, the dissolution is favoured based on higher availability of the acid to generate radicals that initiate the reaction [10] .The increase was gradual between 6 M and 8 M. It is also interesting to note that a 10% jump in dissolution is seen from 8M to 10 M acid concentration. Beyond 10 M, the increase in dissolution was around 5% for every 2 M increase in concentration, till 16 M. Overall, the trend shows that increase in acid concentration from 6 to 16 M is instrumental in almost linearly increasing the extent of dissolution by 26%, exactly similar to the trend observed in the case of uranium dissolution under similar conditions [10] . It is also important to note that significantly higher acid concentration gives rise to problems during scale-up.…”

“…Ultrasound offers a useful process intensification alternative, especially for the porous substrates, as showed for uranium in our earlier work [10] . In the case study with uranium, Physical Vapour Deposition (PVD) technique was used to coat the graphite coupons.…”

“…Since the work mainly targeted at decontamination of yttria coated graphite crucibles that mainly process molten uranium and plutonium, nitric acid is considered as the best choice for the leachant. Rao et al confirmed the percolation of liquid uranium through microcracks during the peeling off of the yttria top coat and hence contaminated crucible may have uranium embedded in the yttria layer as well [10] . Yttria is soluble in molten uranium around 1400 °C, as also reported by Condon et al [21] .…”