As utilization of critical metals such as lithium, cobalt and nickel become essential for energy storage and battery manufacturing, providing resource security is of crucial importance. For countries with limited natural resources, finding cost effective and environmentally sustainable recycling processes motivates the need for enhanced separation processes. For critical metal recycling, where hydrometallurgical processes are selected, solvent extraction remains the most efficient separation and purification technique employed1,2.
Improvements of the solvent extraction process can be realized focusing on two independent aspects: (i) the formulation of the extracting organic phase based on the chemical affinity between the extractant molecule and the target metal, and (ii) the process setup driving the contact and mixing of the two immiscible phases as well as their separation. Nowadays, solvent extraction benefits from numerous chemical formulations to facilitate the separation of dissimilar metals. However, only few efficient process setups are available such as mixer settlers, pulse columns, or centrifugal extractors. These technologies promote the metal transfer either through vigorous mixing in a mixing cell, or through long phase contact time in columns. Nevertheless, they required several steps to reach considerable separation performance, thus leading to high cost and/or space requirements.
Recently, through research developed in the context of lanthanide separation 3 at the Japan Atomic Energy Agency, it was found that at a certain stage during mixing using a specific device configuration, the aqueous and organic phases formed an emulsion which can efficiently and rapidly contact the two phases but also to separate them with an unprecedented high velocity. Focusing on this specific liquid-liquid contact regime new separation technology was developed now known as Emulsion Flow Technology (EFT). We aim to provide an overview of EFT in comparison with the standard mixer settler by comparing it through performance criteria such as size, extraction efficiency, cost and versatility.
As a result of its highly efficient contact and phase-separating aspects one of the advantages was the ability to downsize and modularize the design and process leading to space reductions by 4 to10 times when compared to conventional mixer settlers. Furthermore, we will present the current commercialisation status where development of this new technology is now being applied to critical metal separation, extraction and recovery of lithium, cobalt and nickel from spent lithium-ion batteries.