The effificient separation of Sr2+/Mg2+ through nanofifiltration (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 fifield (EF) was successfully employed to separate Mg2+ and Sr2+ ions for the fifirst 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-effificient 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 effificient 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.