THE MICROFILTRATION OF VERY DILUTE COLLOIDAL SUSPENSIONS

The deposition mechanism of colloidal gold particles of two different sizes on microfiltration (MF) membranes has been investigated under a range of pressure, electrolyte concentrations, pH, and polarization co nditions. Unlike the smaller particles which gave the greater flux in the absence of stirring, the larger particles showed a greater flux un der conditions of stirring. The smaller particles showed a flux signif icantly lower and a flux decline greater than those of the larger part icles. Evidence of aggregation due to concentration polarization is co nfirmed using electron microscopy of membrane surface and cross sectio ns. Addition of salt can vary the particle rejection and flux by reduc ing particle-particle repulsion as well as particle-membrane repulsion . The results with gold sols are compared with those previously obtain ed for silver sols. Colloidal gold sols appear to be more adsorptive o n the membrane surface than silver particles of comparable size, resul ting in lower flux and higher rejection. Charge titration of silver an d gold sols indicates higher charge density on silver sols and unusual titration curves for gold due to the presence of citrate ions and des tabilization of the sols. (C) 1994 Academic Press, Inc.