Efficient extraction of rhenium through demulsification of imidazolium ionic liquid-based microemulsions from aqueous solution

Abstract

Rhenium has important applications in metallurgy, military, aviation, chemical, and petrochemical industries and related fields. Because the average concentration of rhenium in the Earth’s crust is just one part per billion (ppb), it is necessary to research the separation and extraction of rhenium from its associated minerals or related solutions. In this study, rhenium extraction through demulsification of an alkyl imidazolium ionic liquid-based microemulsion was explored. Alkyl chain length, components of microemulsion, temperature, acid concentration, and competitive ions affecting rhenium extraction were thoroughly considered. The components of the microemulsion had a significant effect on the extraction process. Extraction efficiency improved with the increase in the alkyl chain length, but it decreased with the rising concentration of nitric acid. The concentration of alkyl imidazole cations in the continuous phase had obvious effects on extraction efficiency. Thermodynamic studies showed the process was endothermic and spontaneous. The extraction mechanisms were an anion exchange and electrostatic attraction between the two N atoms of the imidazole ring and water (H2O) or perthenate (ReO4−) forming the complex ([Omim]ReO4)•(HReO4). Thus, the extraction efficiency of the microemulsion system was about 1.6 times greater than that of the performance of ionic liquids alone. A microemulsion system can be damaged by a strong electrostatic repulsion and steric hindrance effect between the adjacent imidazole rings on the interface of the microemulsion droplet after rhenium extraction. The extraction system is a potential application for the selective separation and extraction of rhenium from simulated radionuclide liquid waste through adjustments to the acidity concentration. Findings of this study provide some basic data regarding the technology for separating and extracting rhenium in future.