Establishing forward mixing model to mass transfer overview in multi-impeller agitated column for rare Earth extraction process

Abstract The current study develops comprehensive mass transfer models to optimize the rare earth extraction. A plug flow, axial dispersion, backflow, forward mixing-based mass transfer model was created and solved numerically using the fitting technique. The investigated process is a multi-impeller agitated column designed to provide proper contact between organic and aqueous phases to extract rare-earth ions. Taking Sm(III)–Gd(III) separation as an application case, extraction efficiency in the agitation speed of 200 rpm was obtained equal to 95.14%, 76.67% by this column for Gd(III), and Sm(III) ions, respectively. The model's findings were compared with experimental data, and a significant agreement was achieved with the forward mixing model. The results indicated that the high agitation speed is beneficial to increasing the interfacial area while reducing the mass-transfer coefficient. On the contrary, the circulation within the larger droplet improves the transfer of mass, albeit at the expense of reducing the interfacial area. The results showed that the drop size distribution is a crucial factor as the droplet sizes significantly affect the droplet mass transfer. The mathematical models’ values of E c for mass transfer parameters showed that the operational variables significantly affect the mass transfer rate and can cause deviations from the ideal flow path. A reasonable and appropriate estimation of the organic-side volumetric overall mass transfer coefficient was provided, which can be applied to this contactor’s design and scale-up.