Colour and turbidity removal with reusable magnetic particles—I. Use of magnetic cation exchange resins to introduce aluminium ions

Abstract

Clarification of hard, turbid surface water by Al 3+ ions introduced on a sulphonic acid ion exchanger is described. If the resin beads are sufficiently fine, they act as nuclei for floc formation and accelerate the subsequent settling of the flocs. Incorporation of magnetic iron oxide in the resin beads enables them to be conveniently separated from the clarified water. Acidification of the resin-containing sludge then results in partial reloading of the resin with Al 3+ ions. However, the regenerated resin proved ineffective as a coagulant, a result attributed chiefly to hydrolysis of Al 3+ ions within the resin. The findings of this work are significant for the theory of coagulation and also suggested the possibility of enhancing clarification by adding fine particles with an absorbing surface.