Recovery of boron from unacidified salt lake brine by solvent extraction with 2,2,4-trimethyl-1,3-pentanediol

Abstract

In this work, the extraction of boron from salt lake (SL) brine using 2,2,4-trimethyl-1,3-pentanediol (TMPD) was investigated. Factors affecting boron recovery during the solvent extraction process, including feed pH, concentrations of extractant and H3BO3, phase ratio of organic to brine (O/A), and temperature, were investigated. Increasing feed pH initially resulted in a high boron extraction rate, but there was a limitation, as further increasing feed pH resulted in rapid formation of B[OH]4− having a low capacity to complex with TMPD, and therefore lower boron extraction. Boron recovery increased as the TMPD concentration and O/A increased. Salting-out effect experiment indicated that the addition of magnesium chloride showed two opposite effects on boron extraction. The combination of pH <7, O/A = 1 & TMPD/H3BO3 molar ratio = 2:1 was ideal for boron recovery, resulting in single-stage boron extraction efficiency of >85% and three-stage of 99.79%. To investigate the extraction mechanism, the slope ratio method was combined with Raman spectroscopy and infrared spectroscopy to characterize the structure of TMPD and boron complex in organic extraction solvent. Furthermore, under the optimal conditions, a three-stage extraction and two-stage stripping process was performed, resulting the extraction and stripping efficiency of boron were 97.12% and 88.98%, respectively. The results of the study reveal a promising strategy of boron recovery from SL brine without acidification.