Extraction of boric acid from high-magnesium brine using ionic liquids and alcoholic solvents

Abstract

This study ultimately identifying isooctanol as the most effective extraction agent when using ethyl chloroacetate as the solubilizing medium. The research examined how factors such as extraction time, brine pH, the volume ratio of organic to aqueous phases (O/A ratio), number of extraction stages, and ionic strength impacted the efficiency of boric acid extraction, and discussed critical parameters in the re-extraction phase. Experimental results indicated that with a composition of 50 % isooctanol and 20 % ethyl chloroacetate, and an O/A ratio of 2, a single extraction from a boric acid solution containing 1.5 mol/L MgCl₂ at pH 5.5 achieved an extraction efficiency of 44 %. By maintaining the organic phase composition and adjusting the O/A ratio to 1 for a single extraction from a boric acid solution with 4 mol/L MgCl₂ at pH 4.16, the extraction efficiency increased to 60 %. Utilizing water as the re-extraction solvent and an O/A ratio of 1.5, the re-extraction rate of boric acid reached 99.6 %. Density Functional Theory (DFT) calculations revealed that the oxygen and hydrogen atoms in boric acid are strong reactive sites, and the hydroxyl groups in isooctanol can interact with these to facilitate extraction. The weak interaction forces between boric acid and isooctanol, primarily hydrogen bonds and van der Waals forces, play a crucial role, with the strength of hydrogen bonds being particularly decisive in the extraction process. The study successfully established an efficient boric acid extraction system and demonstrated its excellent reusability and stability through cyclic extraction experiments.