Enhancement of the leaching rate of uranium in the presence of ultrasound

In the present work, experiments have been performed for leaching (recovery) of uranium from MgF2 (byproduct from the uranium ore recovery process) under various conditions of leach acid concentration with and without the presence of ultrasound, under different energy dissipation rates (different rotational speeds of conventional stirring by impeller), and on different MgF2 particle size distributions. The enhancement of the leaching rate due to ultrasound is found to occur in two steps: (1) MgF2 particle fragmentation leading to high specific solid-liquid interfacial area and by increase in the surface diffusional rate of the reactive species; (2) enhancement in the convective diffusivity of the leach acid solvent through micropores of the MgF2 agglomerate structure due to convective motion created by the cavitation phenomena (shock wave propagation, microjet formation) at the solid-liquid interface. Thus, the overall recovery has been increased by the application of ultrasound with several additional advantages such as low leach acid concentration and decrease in the leaching operation time. The energy dissipation rate with the use of ultrasound was very high, yet, at an equivalent energy dissipation rate in the form of conventional stirring, leaching rates or the final extent of the leaching could not be matched. This indicated that the scale (time and spatial) of energy dissipation has important effect on the overall leaching rate. Kinetics shows that the leaching operation can be explained as a classical shrinking core kinetics phenomenon with pore diffusion resistance as the rate-limiting step.