Extraction experiments of phosphoric and chloric acids from isoamyl alcohol by water were conducted in an impinging-stream reactor with thin films (Berman & Tamir (AIChE J. 46 (2000) 769; Can. J. Chem. Eng. 79 (2001) 305)). Phase separation was achieved in a regular gravity settler shown in Fig. 1.Extraction efficiency of about 100% was achieved, and mass transfer coefficients were higher by comparison to regular devices by a factor of 100-200. The limiting zone in the settler was the "sedimentation zone", typical to the present chemical system as well as similar ones.A model was established for the "sedimentation zone". It is based on known theories of droplets' motion in a liquid, on a special method which was developed here to determine the fractions of the dispersion phase moving upwards and downwards, as well as on a new approach to determine the droplets diameters. Experimental results substantiated the validity of the suggested model. (C) 2003 Elsevier Science Ltd. All rights reserved.