Synergistic solvent extraction of boric acid by trioctylamine and 2-hydroxydodecanoic acid

A synergistic solvent extraction system comprising trioctylamine (TOA) and ligands with hydroxyl and carboxyl groups can efficiently recover boric acid (H₃BO₃) and separate boron isotopes. However, the structure of ligands might impact H₃BO₃ extraction, boron isotope separation, and solvent loss, which has not been thoroughly investigated. This study initially evaluated the influence of ligand's type, pK_a, and substituents on H₃BO₃ extraction efficiency, as well as the impact of the B₍₄₎-O structure (boron is bound to four oxygen atoms) in the organic phase on isotope separation efficiency. Subsequently, by synthesizing the highly hydrophobic 2-hydroxydodecanoic acid (HYA), the extraction performance and mechanism of the TOA/HYA system were investigated. The findings highlight the superior extraction efficiency when employing di-phenolic hydroxyl, phenolic hydroxyl + carbinol hydroxyl, and alcoholic hydroxyl + carboxyl ligands compared to phenolic hydroxyl + carboxyl, phenolic hydroxyl + ethanol hydroxyl, diol hydroxyl, and dicarboxylic ligands. The organic phase anion complex, exclusively comprising the B₍₄₎-O structure, enhances isotope separation effectiveness. The TOA/HYA system achieves an 80% single-stage extraction efficiency for H₃BO₃. H₃BO₃ and HYA are extracted into the organic phase at a ratio of 1:2, with the anion complex solely containing the B₍₄₎-O structure. This study paves the way for the construction of novel boric acid extraction and boron isotope separation systems.