Pre-fractionation of potassium ions from brine/bittern by selective electrodialysis: Effect of crucial factors and its preliminary application

Abstract

The bittern from salt production process is an important potassium resource. The traditional extraction technology was complex and energy-intensive. A novel potassium extraction process based on monovalent ion exchange membrane separation technology was proposed in this research to reduce the mole ratio of magnesium to potassium (Mg2+/K+) in brine. The effects of Mg2+ concentration and operating conditions on the separation of K+ and Mg2+ were examined. The results showed that Mg2+ concentration was a key factor for the selectivity of ion exchange membrane, the increase of which would reduce the selectivity coefficient. The increase in operating voltage had little effect on the selectivity coefficient, but significantly increased the fluxes of K+ and Mg2+. The increase in temperature had a positive effect on the selectivity coefficient and ion flux. The effects of coexisting ions on the separation of K+ and Mg2+ were also explored. The increase in Na+ concentration will reduce the separation performance of K+ and Mg2+, while the increase of SO42- concentration could facilitate the separation performance. The extraction experiment results of potassium from sea salt bittern indicated that the Mg2+/K+ ratio decreased from 10.31 to 1.15 after 2.5 h. Potassium concentration was further increased and almost all the sulfates were rejected in the dilute solution, which was helpful to improve the purity of the KCl product.