The relationship between the stage efficiency and the volumetric overall mass transfer coefficient in a mixer-settler extraction column has been derived under an assumption of complete mixing within the mixer. Stage efficiencies measured with the extraction of iodine by heptane were in good agreement with the values estimated from the volumetric overall mass transfer coefficient. The latter was calculated with the interfacial area obtained from the drop diameter and the dispersed phase hold-up and the overall mass transfer coefficient determined from the mass transfer coefficients of the dispersed and the continuous phases. This indicates that the stage efficiency can be estimated for the liquid-liquid system where drop coalescence in the mixer play a minor role. The effects of both phase flow rates and the distribution ratio of solute on the stage efficiencies were discussed on the basis of the calculated results.
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