Beth MURRAY1, Emily BYRNE1, John HOLBREY1, Ma?gorzata SWAD?BA-KWA?NY1
1The QUILL Research Centre, School of Chemistry and Chemical Engineering, Queen's University Belfast, Belfast, United Kingdom
Global demand for gallium has rapidly increased over the past two decades, due to its applications in electronic devices. Challenges in its supply are exasperated by the lack of gallium ore, with this metal being recovered as a secondary element from mine tailings of other metal industries, chiefly aluminum, although recovery from zinc mine tailings is also potentially possible.1 Finally, gallium supply is endangered by geopolitical consideration, with the majority being supplied by China (80%).2
This work focuses on the separation of gallium from the zinc manufacturing industry, specifically from zinc leachate solution. In Northern Ireland, this route of recovery is of great interest, on account of Europe’s largest zinc mine being located in County Meath, Ireland.3
Our strategy relies on the use of hydrophobic deep eutectics solvents (DESs) as cost-effective, bifunctional solvents for the extraction of gallium. We have developed a family of DESs based on trioctylphosphine oxide (TOPO), due to its application as a metal extractant in industry, as well as it’s long alkyl chains which promote hydrophobicity.4 TOPO has been combined with a selection of benign and inexpensive small organic molecules, that can act as cooperative complexing agents and/or reducing agents. These mixtures have been tested for the extraction of gallium from a simulated zinc leachate solution, where small (36 ppm) quantities of gallium are present, accompanied by very large quantities of other metals.5 In several cases, very promising separation factors have been obtained.
References
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