Investigation of Removal Possibilities of Colloidal Alumina from Aqueous Solution by the Use of Anionic Polyacrylamide

Abstract

Purification of drinking and industrial water required usage of high molecular weight polymer to cause flocculation process of dispersed suspension of contaminants. Polyelectrolytes, including ionic polyacrylamide are especially appropriate for these purposes, because in this case the suspension stability can be controlled by both steric and electrostatic forces. Thus the influence of solution pH and hydrolysis degree (carboxyl groups content) of anionic polyacrylamide (PAM) on the alumina (Al2O3) suspension stability were studied. The turbidimetry was applied for determination of the examined systems stability. The mechanism of suspension stabilization or destabilization in the polymer presence was proposed on the basis of determined parameters: adsorbed amount of PAM, its adsorption layer thickness, linear dimensions of macromolecules in the solution and zeta potential of alumina particles covered with the polyacrylamide layer. The greatest decrease of the alumina suspension stability in the polymer presence in comparison to that without the polymer was obtained at pH 6 after the addition of PAMs with higher molecular weight (i.e. 14 000 0000) and hydrolysis degrees 20 and 30% (efficient neutralization of solid surface charge). In turn, the most unstable alumina system proved to be that prepared at pH 9 containing PAM with the highest molecular weight and the greatest hydrolysis degree (causing the most effective bridging flocculation).