Boron Isotope Enrichment by Multistage Countercurrent Stripping Based on [A336]+[C272]− Ionic Liquid Extraction System

Abstract

The development of separation and enrichment processes for boron isotopes (¹⁰B and ¹¹B) presents significant challenges due to their minimal differences. Previous studies have demonstrated that ¹¹B can be enriched in the raffinate through multistage countercurrent extraction, based on the synergistic extraction of H₃BO₃ using trioctylamine and tartaric acid. However, the nonrecyclability of tartaric acid and the complexity of the process hinder the industrial application of this system. In this study, a multistage countercurrent extraction and stripping process was constructed based on an ionic liquid extraction system. The efficiency and mechanism of H₃BO₃ extraction using the [A336]⁺[C272]⁻ was investigated. Subsequently, the boron isotope enrichment efficiency was studied during a 5-stage countercurrent alkaline stripping process. The results show that H₃BO₃ is extracted by [A336]⁺[C272]⁻ into the organic phase through hydrogen bonding, with an average stoichiometric ratio of 1:1. Since the trigonal planar structure (B₍₃₎–O) is preserved before and after extraction, no isotope exchange occurred between ¹⁰B and ¹¹B during extraction. Alkaline stripping facilitates the conversion of the extracted H₃BO₃ into borate and polyborate species with tetrahedral structure (B₍₄₎–O) in the aqueous phase, which enables isotope exchange between ¹⁰B and ¹¹B. As a result, ¹¹B is enriched in the organic phase. Using a 5-stage countercurrent stripping, the ¹¹B/¹⁰B ratio is increased from the natural abundance value of 4.0011 to 4.1349 . The enrichment efficiency is found to be positively correlated with the stripping efficiency, owing to the decreasing proportion of molecular H₃BO₃ in the stripping solution as the stripping efficiency increases. This work proposes a novel process for the enrichment of boron isotopes, laying the foundation for potential industrial applications.