Modeling extraction separation of Nd(III) and La(III) from nitrate media in hollow-fiber modules



The use of two microporous hollow-fiber modules for simultaneous extraction and stripping of binary Nd(III) and La(III) from nitrate media with a kerosene solution of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) to a HNO3 solution was investigated. Experiments were carried out at different feed pH values (2–6), total metal concentrations (2–24 g-mol/m3), metal concentration ratios (0.25–4), and dimeric PC88A concentrations (17–137 g-mol/m3). A kinetic model was presented that takes into account the resistances of diffusion in the aqueous stagnant layer, membrane pore, and organic stagnant layer as well as interfacial reactions. It was shown that the calculated time changes of the feed- and strip-phase metal concentrations were in acceptable agreement with the measured data (standard deviation, 8%). The extraction process was dominated by membrane diffusion under the conditions studied, whereas the stripping process was primarily governed by combined membrane and aqueous strip-layer diffusion. Effective separation of Nd(III) over La(III) by PC88A in such continuous NDSX process could be achieved, mainly by selective stripping, at high feed pH values or low organic PC88A concentrations. © 2007 American Institute of Chemical Engineers AIChE J, 2007