Comprehensive review of dispersed phase holdup in solvent extraction columns

This review provides a critical and comprehensive evaluation of dispersed phase holdup (DPH) in the liquid-liquid extraction columns. As the volume fraction of the dispersed phase, DPH plays a fundamental role in column design and operation, influencing droplet residence time, size distribution, interfacial area, mass transfer efficiency, and flooding behavior. DPH is influenced by various factors such as agitation intensity, pulse strength, phase flow rate, fluid properties, and column geometry. Previous studies have shown that increasing the pulse intensity or stirring rate increases DPH, interfacial surface area, turbulence, and mass transfer coefficient. However, DPH can be significantly altered by the presence of nanoparticles, surfactants, and reaction conditions. This review synthesizes a wide range of literature covering measurement methods, hydrodynamic parameters, empirical correlations, and emerging topics such as reactive extraction, nanoparticle effects, and Marangoni-induced interfacial phenomena. Key points of agreement and disagreement that remain in the literature are identified, especially regarding the influence of operating parameters versus physical properties. Finally, the review concludes with evidence-based conclusions and practical recommendations for future research.