Properties of new deep eutectic solvent based on salicylaldoxime and thymol

Oximes are one of the most common classes of extractants for non-ferrous metals. They possess high capacity and selectivity and are used industrially worldwide. However, oxime-based extractants are susceptible to degradation due to nitration, oxidation, and hydrolysis. In conventional liquid-liquid extraction, modifiers that protect the oxime group by forming hydrogen bonds and by increasing reactivity are used to mitigate these processes. Therefore, the development of new hydrophobic eutectic solvents based on oximes, in which the second component protects the hydrogen group through intermolecular hydrogen bonding, is promising.

This paper presents a study of the properties of a new hydrophobic eutectic solvent based on salicylaldoxime (SA) and thymol. Differential scanning calorimetry data revealed a negative deviation from thermodynamic ideality, allowing the system to be termed a deep hydrophobic eutectic solvent (HDES). A component ratio of 4 to 6 was selected for further experiments. 1H NMR and IR spectroscopy were used to further study the interactions between the components, confirming the formation of hydrogen bonds between them. The proposed solvent was tested as an extractant for Co(II) and Ni(II) from chloride solutions.

In summary, the promising use of HDES SA/thymol in the extraction of nonferrous metals from chloride solution was demonstrated. The obtained data can be used in the development of new, effective hydrometallurgical processes for the extraction of nonferrous metals from multicomponent solutions.