Kinetics and Reusability of Hydrophobic Eutectic Solvents in Continuous Extraction Processes in a Pilot Setting

Hydrophobic eutectic solvents (HES) show significant promise as extractants for metal ions. At their current stage of development, however, they have many disadvantages, such as high costs, limited data on reusability and, often, lower extraction efficiency when compared with traditional extraction systems. This study investigates the physico-chemical properties of five HES formulations based on 1-octanol in combination with camphor, 2′-hydroxypropiophenone, menthol, 1-octanoic acid, and thymol. The 1-octanol/camphor HES exhibited substantially higher extraction efficiency for Fe(III) ions than a solution of 1-octanol in toluene at the same concentration. Furthermore, it showed stability when used in a mixer-settler type extractor. The 1-octanol/camphor HES achieved a rapid extraction and re-extraction rate, with phase contact time reduced to just 2 min, without loss of extraction efficiency. Using the supported liquid membrane method, the proposed Oct/Cam HES enabled a threefold concentration of iron ions in the raffinate phase under continuous operation, confirming its potential for reusability.