High-Efficiency Separation of Mg2+/Sr2+ through a NF Membrane under Electric Field

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.Keywords:ENF process;congener ions;dehydration;efficient separation