Hydrophobic deep eutectic solvents for the recovery of gallium from zinc mine tailings

Global demand for gallium is rapidly increasing, due to its applications in electronic devices. Challenges in gallium supply are caused by the lack of gallium ore; this metal is recovered as a secondary element from mine tailings of other metal industries, chiefly aluminium, although recovery from zinc mine tailings is also possible. 90% of UK's gallium supply comes from China, 8% from Russia and only 2% from UK, posing a serious threat to the supply chain. While China and Russia use aluminium tailings to produce gallium, secure supply for the UK/EU markets would be best served by leveraging on UK/EU zinc mines.
Our group developed a family of hydrophobic DES based on a metal-extracting agent, trioctylphosphine oxide (TOPO), some of them efficient in selective separation of very dilute gallium from the zinc leachate (waste from zinc mining). The best performance was achieved with DES comprised of TOPO and malonic acid, in contrast to a very similar formulation of TOPO and levulinic acid.
Here, we propose the study of these two hydrophobic DES formulations based on TOPO, with and without gallium chloride, in order to understand the difference between the structure of the two DES, and its influence on the mechanism governing selective separation.