Desalination 163 (2004) 323–332 0011-9164/04/$– See front matter © 2004 Elsevier B.V. All rights reserved Presented at PERMEA 2003, Membrane Science and Technology Conference of Visegrad Countries (Czech Republic, Hungary, Poland and Slovakia), September 7–11, 2003, Tatranské Matliare, Slovakia. *Corresponding author. Influence of ionic strength and pH of dispersed systems on microfiltration Dagmar Šmídová a *, Petr Mikulášek a , Richard J. Wakeman b , Pavlína Velikovská a a University of Pardubice, Faculty of Chemical Technology, Department of Chemical Engineering, nám. Cs. legií 565, 532 10 Pardubice, Czech Republic Tel. +420 (46) 603-7282; Fax +420 (46) 603-7068; email: dagmar.smidova@upce.cz b Loughborough University, Department of Chemical Engineering, Loughborough, Leics. LE11 3TU, UK Received 25 July 2003; accepted 31 October 2003 Abstract The influence of particle shape, ζ-potential and size with change of pH and ionic strength on permeate flux during the microfiltration of model dispersions (two different china clays with mean particle sizes of 3.5 μm and 1.5 μm) on flat sheet ceramic membranes (ZrO 2 , mean size of pores 0.2 μm) have been studied. The experiments include measurement of the basic characteristics of model dispersions. The description of the experimental system is also presented. The results of the experiments show that the ζ-potential of particles has indispensable impact on the permeate flux. This phenomenon is especially pronounced during the microfiltration of dispersion in the area close to the isoelectric point of dispersion, when the value of permeate flux increased to double value of non-treated dispersion. This phenomenon has caused the particle interaction. In the area close to the isoelectric point the dispersion had a tendency to instability, and particles tend to aggregate. It resulted in a higher porosity of the filter cake and thereby to a higher value of the permeate flux and a lower value of the filter cake resistance. Keywords: Microfiltration; pH; Ionic strength; ζ-potential 1. Introduction The influence of particle properties on the filtration of dispersion has long been recognised [1–6]. Studies of many different aqueous dispersions have established that the characteristic properties of the feed such as particle charge [7–9], particle size distribution [10] and particle shape [11–14] can all influence filterability. Cross-flow mem- brane processes for liquid feed streams are com- plicated by membrane fouling and concentration