Ultrafiltration of silica sols

Abstract

Ultrafiltration of three laboratory made silica and two commercial silica sols was studied using Amicon YC membrane in a 200 ml capacity batch-cell. The effect of silica particle size, stirring conditions, pressure, pH and silica contents on ultrafiltration was investigated. The results obtained indicate that the smaller particles have, disregarding the stirring conditions, lower filtration flux. The differences observed in filtration flux are more pronounced in the conditions without stirring. The obtained value of the membrane resistance is independent of the conditions investigated (stirring, pressure, pH, silica contents and particle size). The values of the resistance of polarized solids, specific resistance, and the mass of gel per membrane surface unit were calculated for all experimental conditions.

Experimental analysis of a gel layer in dead-end ultrafiltration of a silica suspension

“…It appears that dependence of specific resistance on bulk feed concentration and applied pressure is due to the nature &the deposit and particle size distribution in suspension. Previous studies have suggested that specific resistance of silica gel depends on physiochemical properties of bulk solution and operating conditions [9][10][11][12]. The specific resistance of this gel was found to be dependent on applied feed pressure as well as bulk feed concentration.…”

“…Several studies [9,10,12,17] in the past have reported the relationship of operating conditions and specific resistance of deposited layers. An influence of applied pressure and bulk feed concentration on the deposit was reported in all of these studies.…”

“…According to filtration theory [10], the resistance of polarized solids could be related to specific resistance (a) as follows:…”

“…This particle build-up near the membrane surface is known as concentration polarization, which causes an increase in hydraulic resistance resulting in permeate flux decline with time. Generally, presence of suspended solids causes an instantaneous reduction in flux relative to the pure water flux of 0011-9164/05/$-See front matter © 2005 Elsevier B.V. All rights reserved doi: 10.1016/j.desal.2004.07.032 the membrane. There are several phenomena responsible for flux reduction.…”

“…They interpreted their results based on constant filtration theory and concluded that specific resistance provided by the solute is in accord with particle size and conformation, and are both pressure and concentration dependent. Stakic et al [ 10] studied filtration of laboratorymade and commercial silica using an Amicon cell. They reported effects of silica particle size, stirring conditions, pressure and pH on UF and concluded that, in the case of unstirred conditions, flux increases with particle size, while under stirred conditions particle size does not influence flux value, and also membrane resistance is independent of the condition of investigation.…”