Electro-Enhanced Membrane Sorption: A New Approach for Selective Ion Separation and Its Application to Phosphate and Arsenic Removal

Abstract

We describe a new electro-enhanced sorption approach, where an electric field is applied across an ion-selective nanocomposite membrane. Unlike capacitive deionization, here, the membrane rather than the electrode functions as the sorbent, whereas the electrodes are inert. This electrode-sorbent decoupling extends the space of suitable sorption materials, currently constrained to conductive materials. Here, we synthesized ferric oxyhydroxide (FeO) nanocomposite membranes (FeOm) using diffusion-controlled growth of FeO nanoparticles within porous track-etched membranes, resulting in a high-capacity sorbent. The use of FeOm to study the electro-enhanced sorption of phosphate revealed that the electric potential (5−15 V) accelerates both the adsorption and desorption steps. Furthermore, desorption at pH ∼10−11much lower than the current practice for FeO regeneration (pH 13−14)was demonstrated, potentially enabling 2−3 orders of magnitude savings on chemical consumption. Lastly, a highly selective uptake of arsenate from simulated groundwater was demonstrated, pointing at the potential of the new approach to intensify sorption processes.

Current Density Dependence of Transport Selectivity of Metal Ions in the Electrodriven Process across the Cation Exchange Membrane

“…Selective transport of cations across cation exchange membranes (CEMs) is vital in multiple applications like desalination and energy production by electrodriven transport (ED), reverse electrodriven transport, electrodeionization, capacitive deionization, etc. ,− Transport selectivity (i.e., ability to preferentially transport one cation over another) between multi- and monovalent cations is a prerequisite in processes like water softening, , metal ion extraction, , NaCl production from seawater, , etc., whereas the preferential transport among the monovalent cations is utilized in the process like recovery of Cs + from nuclear waste. , Along with the cationic composition and membrane characteristics, operation parameters are also known to affect the cation transport in CEMs . Therefore, an empirical understanding of the transport phenomena under various working conditions is necessary to improve the process efficiency. , In this regard, the working current/voltage is a crucial parameter in electrodriven processes.…”

Ion-capture electrodialysis using multifunctional adsorptive membranes

“…Adsorptive membranes are an emerging class of materials with improved separation performance compared to conventional membranes (4,(10)(11)(12)(13)(14). However, limited tunability, capacities, and selectivities remain major challenges in their development (4).…”

“…Adsorptive membranes are an emerging class of materials that have been shown to exhibit improved performance in numerous separations when compared with conventional membranes, including for water purification (4,(9)(10)(11)(12)(13). However, improvements are needed in the capacities, selectivities, and regenerabilities achievable with these materials to enable their wide-scale use, which is also currently hindered by the limited structural and chemical tunability of most adsorptive membranes (4).…”