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Review
. 2021 Dec 8;60(48):17285-17302.
doi: 10.1021/acs.iecr.1c02287. Epub 2021 Nov 19.

Nonaqueous Solvent Extraction for Enhanced Metal Separations: Concept, Systems, and Mechanisms

Zheng Li  1 , Brecht Dewulf  1 , Koen Binnemans  1
Affiliations
Review

Nonaqueous Solvent Extraction for Enhanced Metal Separations: Concept, Systems, and Mechanisms

Zheng Li et al. Ind Eng Chem Res. .

Abstract

Efficient and sustainable separation of metals is gaining increasing attention, because of the essential roles of many metals in sustainable technologies for a climate-neutral society, such as rare earths in permanent magnets and cobalt, nickel, and manganese in the cathode materials of lithium-ion batteries. The separation and purification of metals by conventional solvent extraction (SX) systems, which consist of an organic phase and an aqueous phase, has limitations. By replacing the aqueous phase with other polar solvents, either polar molecular organic solvents or ionic solvents, nonaqueous solvent extraction (NASX) largely expands the scope of SX, since differences in solvation of metal ions lead to different distribution behaviors. This Review emphasizes enhanced metal extraction and remarkable metal separations observed in NASX systems and discusses the effects of polar solvents on the extraction mechanisms according to the type of polar solvents and the type of extractants. Furthermore, the considerable effects of the addition of water and complexing agents on metal separations in terms of metal ion solvation and speciation are highlighted. Efforts to integrate NASX into metallurgical flowsheets and to develop closed-loop solvometallurgical processes are also discussed. This Review aims to construct a framework of NASX on which many more studies on this topic, both fundamental and applied, can be built.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Comparison of (left) conventional solvent extraction and (right) nonaqueous solvent extraction (NASX) systems.
Figure 2
Figure 2
Structures of typical extractants.
Figure 3
Figure 3
Separation of REEs by Cyanex 923 from aqueous and ethylene glycol solutions. [Adapted from Batchu et al.]
Figure 4
Figure 4
Extraction of Nd(III) and Dy(III) by Cyanex 923 from a mixture of PEG and water solutions. [Adapted from Dewulf et al.]
Figure 5
Figure 5
Extraction of Ni(II) from aqueous and methanolic solutions by Alamine 336. Data were taken from Florence and Farrar.
Figure 6
Figure 6
Extraction of La(III) and Ni(II) by Aliquat 336 from various polar molecular organic solvents. [Adapted from Li et al.]
Figure 7
Figure 7
Water activity in Ca(NO3)2·nH2O, as a function of water mole fraction at 70 °C. [Data were taken from Yamana et al.]
Figure 8
Figure 8
Hydration number of Eu(III) and Dy(III) in Ca(NO3)2nH2O at 50 °C. [Adapted from Fujii et al.]
Figure 9
Figure 9
Transformation of lanthanides extraction sequence from positive to negative by addition of water. [Adapted from Li and Binnemans.]
Figure 10
Figure 10
Addition of TEAC to EG solution enhances the separation of Co(II) and Sm(III). [Adapted from Li et al.]
Figure 11
Figure 11
Flowsheet of a solvometallurgical process.
See this image and copyright information in PMC

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