BACKGROUNDBrines from the drainage of potash mine tailings and from seawater reverse osmosis (SWRO) desalination were previously evaluated as sources of NaCl for the chlor-alkali industry. Valorisation of NaCl as raw material is required to meet the membrane electrolysis specifications of NaCl saturation and control of interferences (Ca, Mg and sulphate). Brines concentration in NaCl was previously achieved for SWRO brines using electrodialysis (ED). In this work, valorisation of Ca and Mg by-products via selective recovery was evaluated. RESULTSRecovery of Ca(II) and Mg(II) using chemical precipitation with Na2CO3 and NaOH was evaluated at 25 degrees C and 65 degrees C using one single reagent and mixtures of reagents. The excess of reactants needed to achieve the maximum removal efficiency ranged from 0.35 to 14 g L-1 Na2CO3 and 0.85 g L-1 NaOH. Selective concentration of SWRO brines by ED benefited the purification, as it slightly diluted the antiscalants. The increase of temperatures also benefited their removal process. CONCLUSIONSTotal chemical analysis of Ca and Mg by-products showed the presence of mixed salts of Ca and Mg when Na2CO3 was used and more pure precipitates of Mg when NaOH was used. In both cases, small amounts of minor traces initially present in the brines were found. (c) 2014 Society of Chemical Industry.