Boron separation and concentration from pre-treated seawater reverse osmosis brines by selective ion-exchange resins and electrodialysis

Abstract

Seawater reverse osmosis (SWRO) desalination brines contain a wide range of elements, at concentrations higher than those in seawater. Typically, these brines are discharged into the ocean after the reverse osmosis process for drinking water production, resulting in a loss of their potential value. Thus, recent research has focused on recovering valuable elements, including boron, from SWRO brines. This study investigates the use of selective ion-exchange (IX) resins and electrodialysis (ED) at a lab-scale for the separation and concentration of boron from SWRO brines. Dynamic experiments were conducted to test selective IX resins for boron separation. Batch tests were conducted to determine the minimum eluent concentration required to recover boron from the IX resins. Results indicated that it was possible to separate boron from almost all other elements in the brine. However, after the elution step, the major element in the solution was the anion used in the elution acid (Cl from HCl), with a concentration higher than that of boron (5 g Cl/L vs 1 g B/L). Thus, ED at an acidic pH was used for the separation of boron from the elution anion. Results showed that this process was suitable for this separation, obtaining two main streams: Cl-rich and B-rich. The latter was a solution, mainly containing boron, and without decreasing the initial boron concentration (around 1 g/L). Subsequently, ED at a basic pH was employed to concentrate boron at different stages. In this case, the use of two stages was the optimum for concentrating boron up to 2.5 g/L.