Separation of liquid-liquid dispersions in deep-layer gravity settler .1. Experimental study of the separation process

The separation of liquid-liquid dispersions is a crucial operation in the solvent extraction of metals because very often the throughputs of solvent extraction plants are limited by phase separation characteristics rather than mass transfer rates in the mixer. The separation of phases in a laboratory scale mixer-settler has been investigated in a system consisting of 10% Acorga M5640 in Escaid 103-0.25 M Na2SO4 solution. The thickness of the dispersion band, the local dispersed phase hold-up, and the droplet size distribution at different positions in the dispersion band were determined for various operational conditions. Based on the flow pattern of the dispersion, two well defined zones were identified in the band: a narrow distribution zone just above the passive interface characterized by a horizontal velocity of the drops, and above it a dense zone where the drops have essentially vertical movement. The drop size measurements indicated little variation in size in the horizontal direction but a dramatic increase in the vertical direction of the dispersion band. The thickness of the band was found to be a function of the specific flow rate of the dispersed phase, and independent of the phase ratio.