Colour and turbidity removal with reusable magnetic particles—III immobilized metal hydroxide gels

Abstract

A novel, reusable, magnetic coagulant-adsorbent was prepared and used for removing colour and turbidity from surface water. The adsorbent was made by deposition of ferric hydroxide gel onto fine magnetite. The surface charge of such a composite particle is pH dependent, and the amphoteric properties of the ferric hydroxide gel coating can be exploited in the clarification process. At pH < 6, the surface is positively charged and adsorption of negatively charged particles occurs. Conversely, the adsorbed impurities can be released by increasing the pH to above pH 10. The reactivated particles can then be reused. The particles have high sedimentation rates and are easy to handle magnetically. The magnetic gel was successfully employed to treat a number of waters. It was especially effective in treating a highly coloured reservoir water. It was possible to reuse the gel after regeneration for many cycles with a gradual deterioration in performance.