Experimental investigations of liquid–liquid disengagement in a continuous gravity settler

Several applications in chemical and hydrometallurgical industries involve separation of dispersed liquid–liquid flows. In the present work, experimental investigations of liquid–liquid disengagement are performed in a laboratory-scale continuous gravity settler for tri-butyl phosphate (TBP)–dodecane and nitric acid solution system that is used widely in hydrometallurgical solvent extraction processes. The effects of different operating parameters (total flow rate and inlet drop size distribution) and geometrical parameters (location of baffle inlet opening position and settling area) on the phase disengagement are investigated. The dispersion-band thickness, local dispersed-phase volume fraction and the drop size distribution within the dispersion band are measured. The results are analyzed using the order of magnitude estimates of the settler residence time, convective dispersion velocities, drop-rise velocities, rates of binary and interfacial coalescence processes. Based on the measurements performed in the present work and the data reported in the literature, an empirical correlation is proposed to predict the dispersion-band thickness as a function of dispersed phase flow rate, settling area, inlet drop size distribution, ratio of density of the dispersed phase to the continuous phase, ratio of inlet baffle opening position to the end plate height and inlet dispersed phase volume fraction.