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

Huan Liu,Feng Yan,Jianxin Li,Zhenyu Cui,Quan Li,Zhengguang Sun,Benqiao He

doi:10.3390/membranes12010057

Huan Liu, Feng Yan + Show 5 more

Open Access

https://doi.org/10.3390/membranes12010057

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Journal: Membranes	Publication Date: Dec 31, 2021
Citations: 2	License type: CC BY 4.0

Affiliation: Tianjin Polytechnic University, Hubei University

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.

Highlights

Strontium (Sr) is known as “metal monosodium glutamate” for the development of high-tech products, such as semiconductor substrates, electronics, medicines and magnetic materials [1,2]
There remains a great challenge in separating the congener ions of Sr2+ and Mg2+ due to the similar physical and chemical properties
The difference between RM and Rp is because the partially permeated Mg2+ ions reacted with OH− produced on our previous work due to positive-charge restructuring of the NF membrane surface and enhancement under electric field (EF) [24]

Summary

Introduction

Strontium (Sr) is known as “metal monosodium glutamate” for the development of high-tech products, such as semiconductor substrates, electronics, medicines and magnetic materials [1,2]. An electro-NF (ENF) process was employed to separate Mg2+ and Li+ from the MgCl2/LiCl feed solution, achieving an ultrahigh Mg2+ rejection due to positive-charge restructuring and enhancement under EF.

Results

Conclusion