Ionic liquid-based polymer inclusion membranes for metal ions extraction and recovery: Fundamentals, considerations, and prospects

Heavy metal removal from wastewater and valuable metal recovery from electronic waste are of critical environmental and economic significance. Separation based on the use of polymer inclusion membranes (PIMs) with the advantage of simultaneous extraction and stripping has emerged as a promising approach for efficient and selective metal ion removal and/or recovery from wastewaters or electronic waste. However, the conventional extractants used in PIMs are often not selective to certain metal ions, and are highly volatile and toxic, leading to low extraction efficiency and significant environmental concerns. Ionic liquids (ILs) have negligible vapor pressure and can be purposely designed for extraction of specific ions. In addition, ILs can be multifunctional by purpose design, for instance, having the functions of both extractants and plasticizers. Therefore, the marriage of PIMs and ILs (i.e., IL-based PIMs) has been highly attractive for selective extraction and recovery of various metal ions. In this review, we discuss the fundamentals of PIMs, explore the key considerations of ILs for PIMs, and provide an overview of IL-based PIMs for different applications. By leveraging the advantages of ILs, the marriage of PIMs and ILs offers new possibilities for efficient and sustainable metal ion extraction and recovery. This review offers a state-of-the-art assessment of the previous efforts and strategies as well as future research directions for the recovery of metal ions through the application of ILs-based PIMs.