The recovery of boron from salt lake brines has become an effective way to meet the increasing demand, particularly in China. In this study, nine commercially available monohydric alcohols with different structures were selected for boron extraction from a salt lake brine with high magnesium content. Passing through the optimization, isodecanol was finally selected for the detailed study on boron recovery from brine due to its moderate viscosity, lower solubility water entrainment and high extraction efficiency. Parameter effects on boron extraction were systematically studied, including equilibrium pH, organic concentration, phase ratio, temperature, and salting-out effect. A McCabe–Thiele diagram was established to determine the boron extraction and stripping stages. An organic solution containing 2.5 mol L⁻¹ isodecanol was used for a simulated three-stage counter-current extraction test under optimized extraction conditions, and the boron extraction reached 99.07%. A simulated four-stage counter-current stripping test was carried out with water with the stripping efficiency of 98.71%. In total the boron recovery reached 97.79%. Additionally, the mechanism of boron extraction by isodecanol was investigated using both slope analysis method and Fourier transform infrared spectroscopy (FTIR). The stoichiometric ratio of isodecanol to boron required to form boric acid ester was found to be 1.268. These results indicate that the extraction system has great potential for commercial application in boron recovery from salt lake brines with high magnesium content.

Both Cyanex 272 (bis (2,4,4-trimethylpentyl) phosphinic acid) and Ionquest 801 (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) are commonly used for metal extraction and separation, particularly for zinc, cobalt, and nickel, which are often found together in processing solutions. Detailed metal extractions of zinc, cobalt, and nickel were studied in this paper using Cya-nex 272, Ionquest 801, and their mixtures. It was found that they performed very similarly in zinc selectivity over cobalt. Cyanex 272 performed much better than Ionquest 801 in cobalt separation from nickel. However, very good separation of them was also obtained with Ionquest 801 at its low concentration with separation factors over 4000, indicating high metal loading of cobalt can significantly suppress nickel extraction. Slop analysis proved that two moles of dimeric extractants were needed for one mole extraction of zinc and cobalt, but three moles were needed for the extraction of one mole nickel. A synergistic effect was found between Cyanex 272 and Ionquest 801 for three metal extractions with the synergistic species of M(AB) determined by the Job’s method.

The poor operational stability of electrolytes is a persistent impediment in building redox flow battery technology; choosing suitable stability additives is usually the research direction to solve this problem. The effects of five phosphate containing additives (including 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), hexamethylene diamine tetramethylene phosphonic acid (HDTMPA), amino trimethylene phosphonic acid (ATMPA), sodium ethylenediamine tetramethylene phosphonate (EDTMPS), and diethyl triamine pentamethylene phosphonic acid (DTPMP)) on the thermal stability and electrochemical performance of the positive electrolyte of vanadium redox flow battery were investigated. With 0.5 wt% addition, most of the selected additives were able to improve the thermal stability of the electrolyte. HEDP and HDTMPA extended the stability time of the pentavalent vanadium electrolyte at 50 °C from 5 days (blank sample) to 30 days and 15 days, respectively. The electrochemical performance of the electrolyte was further investigated by cyclic voltammetry, steady state polarization, and electrochemical impedance spectroscopy tests. It was found that most of the additives enhanced the electrochemical activity of the positive electrolyte, and the diffusion coefficients, exchange current densities, and reaction rate constants of V(IV) species became larger with the addition of these additives. It is verified that the thermal stability and electrochemical stability of the electrolyte are significantly improved by the combination of ATMPA + HEDP or ATMPA + HDTMPA. This study provides a new approach to improve the stability of the positive electrolyte for vanadium redox flow battery.