Membrane-free electrodeionization using phosphonic acid resin for nickel containing wastewater purification

Abstract

Membrane-free elctrodeionization (MFEDI) is a technology in which ion exchange resins can be electrically regenerated in situ. It allows the purification of nickel containing wastewater, as well as the production of concentrated nickel solution, which could be recycled. However, proper choice of packed ion exchange resins is crucial to MFEDI. In this study, emphasis was placed on improving the performance of MFEDI by the introduction of phosphonic acid resin. Much of this information was obtained by analyzing the characteristic of phosphonic acid resin, the stack configuration of packed ion exchange resin and the mechanism of electrical regeneration. The layered hybrid resin bed filled with both phosphonic acid resin and weak acid resin was found to be the most effective stack configuration for the adjustment of concentrate pH. The purification study demonstrated that, pure water with conductivity below 0.3 μS/cm was produced. The electrical regeneration study showed that, the average concentrate nickel concentration was over 95 mg/L, the concentrate pH was around 7.4, thus precipitation of nickel hydroxide was prevented. Moreover, in comparison to previous study, in which MFEDI was packed with hybrid strong acid and weak base resin and hybrid weak acid and strong base resin, the water recovery ratio was increased from 88.0% to 89.5%, the energy consumption was decreased from 5.6 to 4.1 kWh/m3 wastewater. The regeneration mechanism study revealed that, more than 72% of resin regeneration was attributed to the water splitting, and less than 28% of resin regeneration was contributed by the water electrolysis.