Continuous ion exchange using magnetic shell resins. I. Dealkalisation-laboratory scale

A completely novel technique of continuous ion exchange has been developed, which uses ion exchangers prepared by grafting an active shell onto a magnetic polymeric core. In the magnetised form, the ion exchange resin beads clump together in the form of large flocs, with sedimentation velocities many times those of the individual beads. Small beads may then be used in fluidised or semi‐fluidised beds, at liquid flow rates equal to or greater than conventional ion exchange systems, but with the advantage of rapid reaction rates and attainment of equilibrium. A major practical advantage is that even as a settled bed the magnetised ion exchange resin remains semifluid, and can be pumped with practically no attrition. Utilising these properties, a truly continuous ion exchange system has been built for the process of dealkalisation, comprising a single stage fluidised adsorber and a compact moving bed regenerator which develops multistage contact. Transfer of ion exchanger between each vessel is effected by means of two peristaltic pumps. This paper summarises the results obtained in a laboratory sized apparatus, treating a hard, alkaline water at a superficial velocity of 30 m h −1 , and demonstrates the potential for a system utilising a fraction of the volume of ion exchange resin employed in a conventional system, in a simple robust plant with no valves, no screens, no pressure vessels and only one electrical level control.