The liquid surfactant membrane has advantages superior to those of other types of liquid membranes, but its biggest bottleneck lies in the demulsification process for separating the stripping solution from the organic phase containing surfactant and carrier. This paper is concerned with the electrostatic coalescence of the W/O emulsion stabilized with surfactant in an a.c. high-voltage current applied between two insulated flat electrodes. Effects of the dispersed phase hold-up, the applied voltage and the frequency on the phase separation rate were studied.The separation rate was larger for lower initial hold-up of the dispersed phase. When the initial hold-up was less than 40%, the coagulation stage preceded the coalescence stage and the separation rate decreased. The separation rate increased approximately with the second order of the applied voltage. It also increased with frequency and tended to become constant at frequencies in the range of 1000 to 2000 Hz. The water content of the separated oil phase decreased with increase in frequency.
Recently, interest has increased in the practical application of solvent extraction technology for the mutual separation and purification of rare earth metals. 2-Ethylhexyl phosphonic acid mono-2-ethylhexyl ester (henceforth EHPNA) has recently been developed, and was found to have high capacity of lanthanoid extraction.This paper reports the extraction rate of praseodymium and neodymium with EHPNA in toluene from hydrochloric acid solution by use of a stirred transfer cell of Lewis type at 298 K. The experimental results suggested the existence of chemical reaction resistance at the interface at low extractant concentration and high pH value in the forward extraction, in addition to the film mass transfer resistances in the aqueous and the organic phases. The time course change of the extraction from mixed lanthanoid aqueous solution was satisfactorily predicted by the extraction model presented.
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