Mass transfer studies in RDC column by the coupling effects of perforated structure and reactive extraction of Mo(VI) and W(VI) from sulfate solution

Abstract

Solvent extraction of molybdenum (VI) and tungsten (VI) by synergism of the mixture of D2EHPA and TBP were conducted in the RDC extractor with perforated structure. The initial aqueous pH, extractant concentration, ammonium hydroxide concentration as a stripping agent, and synergistic enhancement factor were optimized in the initial experiments before collecting column data. In the RDC column, the influence of agitation rate and inlet phase velocities were examined on the hydrodynamic velocities, mass transfer data, and distribution coefficients. The finding data indicated that the impact of agitation speed on the distribution coefficients of molybdenum and tungsten is considerable in comparison the inlet phase flow rates. Published empirical models for estimating the slip and characteristic velocities were compared with the solvent extraction data, and the modified models were presented by considering the reactive extraction. Mass transfer performance based on the dispersed phase was studied by applying the axial dispersion model. Column performance enhances the increment of the operational variables such as agitation speed, inlet solvent phase flow rate, and inlet aqueous phase flow rates, but the variations of agitation speed and solute transfer direction have a high impact on this phenomenon. The previous models for estimating the mass transfer coefficients were compared with the present work. The published models failed to acceptable estimate the mass transfer evaluation due to column geometry and reactive extraction systems. Finally, the new models were proposed by using the dimensionless analysis methods for obtaining the enhancement factor in both extraction and stripping stages.