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

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.