Inhibition of CaCO 3 scaling on RO membranes by trace amounts of zinc ions

Abstract

Anti-scalants, which are widely used for scale control in desalination processes, are essentially impurities capable of inhibiting scale precipitation and weakening scale adhesion on a flow surface. Many basic studies indicate that metallic ion impurities, notably Zn ions, can hinder significantly CaCO 3 precipitation from hard waters and alter crystal morphology. Recent studies demonstrate a substantial potential for suppressing CaCO 3 scale formation in hard water heating systems by trace concentrations of Zn ions. The objective of the present work was to explore the possibility of controlling CaCO 3 scale formation in RO membrane systems by a similar technique. Results obtained with a tubular RO system are most promising. A Zn ++ concentration of the order of 2 PPM was able to exert a marked suppression effect on both bulk precipitation of CaCO 3 and on membrane scaling on waters of moderate hardness.