Recovery of desalination brines: separation of calcium, magnesium and sulfate as a pre-treatment step

Abstract

Sustainable treatment of reverse osmosis (RO) desalination brines should be focused on achieving the highest global recovery of freshwater combined with the recovery of the valuable compounds. In this line of investigation, an integrated process where NaCl is transformed into chemical stuff based on the use of bipolar membrane electrodialysis was developed and reported previously. The efficiency of the membrane recovery step relies among other variables on the concentration and purity of the fed brines, making the application of different pre-treatment steps necessary. The objective of this study is to evaluate the viability of removing calcium, magnesium and sulfate from RO brines in order to obtain a purified solution rich in NaCl. The proposed system consists of a set of ion-exchange resins combining cationic- and anionic-exchange stages. Removal of calcium and magnesium using the weakly acid-resin Lewatit TP208 was evaluated. Whereas, the strong basic resin Lewatit Monoplus M600 was used for sulfateremoval working in fixed bed columns.