Deep eutectic solvents for separation and purification applications in critical metal metallurgy:Recent advances and perspectives

Solvent extraction,a separation and purification technology,is crucial in critical metal metallurgy.Organic solvents commonly used in solvent extraction exhibit disadvantages,such as high volatility,high toxicity,and flammability,causing a spectrum of hazards to human health and environmental safety.Neoteric solvents have been recognized as potential alternatives to these harmful organic solvents.In the past two decades,several neoteric solvents have been proposed,including ionic liquids(ILs)and deep eutectic solvents(DESs).DESs have gradually become the focus of green solvents owing to several advantages,namely,low toxicity,degradability,and low cost.In this critical review,their classification,formation mechanisms,preparation methods,characterization technologies,and special physicochemical properties based on the most recent advancements in research have been systematically described.Subsequently,the major separation and purification applications of DESs in critical metal metallurgy were comprehensively summarized.Finally,future opportunities and challenges of DESs were explored in the current research area.In conclusion,this review provides valuable insights for improving our overall understanding of DESs,and it holds important potential for expanding separation and purification applications in critical metal metallurgy.

Highly efficient and selective removal of vanadium from tungstate solutions by microbubble floating-extraction

Selective separation of dissolved tungsten and vanadium is of great significance for the utilization of the secondary resources of these elements.In this work,selective removal of vanadium from tungstate solutions via microbubble floating-extraction was systematically investigated.The results indicated that vanadium can be more easily mineralized over tungsten from tungstate solutions using methyl trioctyl ammonium chloride as mineralization reagent under weak alkaline conditions.Owing to the higher bubble and interface mass transfer rates,high-efficiency enrichment and deep separation of vanadium could be achieved easily.Additionally,the deep recovery of tungsten and vanadium from the floated organic phase could be easily realized using a mixed solution of sodium hydroxide and sodium chloride as stripping agents.The separation mechanism mainly included the formation of hydrophobic complexes,their attachment on the surface of rising bubbles,and their mass transfer at the oil–water interface.Under the optimal conditions,the removal efficiency of vanadium reached 98.5%with tungsten loss below 8%after two-stage microbubble floating-extraction.Therefore,the microbubble floating-extraction could be an efficient approach for separating selectively vanadium from tungstate solutions,exhibiting outstanding advantages of high separation efficiency and low consumption of organic solvents.