Selectrodialysis: Fractionation of divalent ions from monovalent ions in a novel electrodialysis stack

In view of wastewater recycling and industrial requirements to valorize nutrients and other valuable ions from waste streams, as well as to refine the product streams, a novel electrodialysis stack, denoted as selectrodialysis, was designed and used for ion fractionation. In this work, separation of sulphate from a NaCl/Na2SO4 mixture is investigated. Prior to the investigation, the selectrodialysis stack was qualitatively tested on a synthetic wastewater to study the potential of ion fractionation by using this novel configuration. Different approaches including changing of pH and current density were used to evaluate the effects on the stack selectivity, the current efficiency and the product (sulphate) purity. Furthermore, the optimized parameters were applied to produce a sulphate-enriched stream from sulphate-free solutions (NaCl solution) in the product stream. The results show that the sulphate purity can reach over 85% with the current efficiency of over 50%. It is proved that selectrodialysis is feasible and effective for chloride/sulphate fractionation. (C) 2011 Elsevier B.V. All rights reserved.