Separation of boron and lithium from aqueous solutions by bipolar membrane electrodialysis (BMED)

In this study, the feasibility of bipolar membrane electrodialysis (BMED) method for recovery of boron and lithium from aqueous solutions has been investigated. For this purpose, experiments were carried out with model solutions containing boron and lithium. Three different BMED systems containing different ion exchange membranes were used and some parameters affecting the process performance were investigated. ASTOM ACILYZER BMED system, MEGA BMED system and PC-Cell BMED system were used in studies. The influences of type and of acid base solutions in acid base chambers and the electrical potential applied were investigated using ASTOM ACILYZER and MEGA BMED systems. In addition, the influence of the feed flow rate and the pH of the feed solution on process were investigated using the MEGA BMED system. Once the process parameters have been optimized, the optimum conditions for the MEGA BMED system and the ASTOM ACILYZER BMED system have been determined. Optimal conditions were different for these two BMED systems. This result showed that the optimum conditions could change according to the BMED system used. Optimum conditions for MEGA BMED system and ASTOM ACILYZER BMED system were applied to PC-Cell BMED system. As a result of BMED experiments, the highest recoveries of lithium and boron were obtained as 71% and 66% respectively under 25 V of electrical potential with MEGA BMED system while initial concentrations of acid and base were 0.003 M HCl-0.003 M NaOH, feed flow rate was 50 L/h and pH value of the sample solution was 10. The highest recoveries of lithium and boron were obtained as 62% and 50%, respectively under electrical potential of 30 V of with ASTOM ACILYZER model BMED system while initial acid base concentrations were 0.05 M HCl-0.05 M NaOH. However, when three different BMED systems were compared and the experimental conditions were kept constant (0.05 M HCl-0.05 M NaOH), the highest recoveries of lithium and boron were achieved by PC-Cell BMED system as 76% and 49% under 20 V electrical potential. Keywords: Boron, lithium, electrodialysis (ED), bipolar membrane, recovery.