Membranes (Dec 2021)
High-Efficiency Separation of Mg<sup>2+</sup>/Sr<sup>2+</sup> through a NF Membrane under Electric Field
Abstract
The efficient separation of Sr2+/Mg2+ through nanofiltration (NF) technology is a great challenge because Sr2+ and Mg2+ ions are congeners with the same valence and chemical properties. In this work, an NF membrane under an electric field (EF) was successfully employed to separate Mg2+ and Sr2+ ions for the first time. The effects of current densities, Mg2+/Sr2+ mass ratios, pH of the feed, and coexisting cations on separation performance were investigated. Dehydration of Sr2+ or Mg2+ ions under EF was proved by molecular dynamics simulation. The results showed that a high-efficient separation of Mg2+/Sr2+ was achieved: Mg2+ removal of above 99% and increase in Sr2+ permeation with increasing EF. A separation factor reached 928 under optimal conditions, far higher than that without EF. The efficient separation of Mg2+/Sr2+ ions was mainly due to rejection of most Mg2+ ions by NF membrane and in situ precipitation of partly permeated Mg2+ ions by OH− generated on the cathode under EF. Meanwhile, preferential dehydration of Sr2+ ions under EF due to lower hydration energy of Sr2+ compared with Mg2+ resulted in an increase of permeation of Sr2+ ions. This work provided a new idea for separation of congener ions with similar valence and chemical properties.
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