The extraction of citric acid from its dilute solutions by means of emulsion liquid membranes (ELM) was studied. Alamine 336 added to the organic membrane was used as a carrier, the acceptor phase was a solution of sodium hydroxide whose concentration was in a stoichiometric excess with respect to that of the citric acid. The effect of the concentrations of carrier and modifier, the stirring rate of the emulsion in the external feed phase and the phase ratio between the external phase (F) and the emulsion was followed. The optimum composition of the membrane phase was found to be 40 vol.% Alamine 336, 8 vol.% chloroform and 4 vol.% emulsifier-C9232 Infineum Ltd. in alkanes, providing up to 97% removal of the citric acid from the feed solution. Using a volume ratio of 8.3:1 between the external phase and the emulsion (E) and a ratio of 1:1 between the two emulsion-forming phases S and A. a 15-fold preconcentration of citric acid as sodium citrate in the internal acceptor phase (A) was achieved. A mathematical model of the extraction of citric acid was developed on the basis of "shrinking-core" model proposed by Chaudhuri and Pyle for the extraction of lactic acid by means of ELM. The model was tested upon varying the system parameters and a good agreement between the calculated and experimental results was found. (C) 2004 Elsevier B.V. All rights reserved.