Paired electrolysis for simultaneous electrochemical water softening and production of weak acid solutions

In this work, a new paired electrolysis procedure is successfully introduced. This is a combination of two different processes: electrochemical water softening (EWS) and electrochemical production of weak acid solutions (EPWA). This paired electrolysis method is tested for hardness removal in a simulated solution of concentrates, such as that produced by the electrodialysis of brackish water. The use of a divided electrochemical cell makes it possible to achieve removal efficiencies higher than 90% in optimum conditions. The good performance and stability of the cathode are also demonstrated by long-term experiments. Simultaneously, weak acids are obtained by protonation of their conjugate bases in the anodic compartment. Lactic acid is obtained from lactate with a purity of no less than 80% in this work without significant loss of efficiency in hardness removal. The main interest lies in the commercial value of weak acids such as lactic acid, citric acid or gluconic acid, among others. The methodology makes it possible to benefit from both cathodic and anodic processes, which may contribute to decreasing the final EWS treatment costs for a cost-effective desalination application. [Display omitted] •Electrochemical water softening and production of weak acid solutions as coupled processes•A new approach based on obtaining suitably pure weak acids solutions is tested.•Lactic acid solutions with purity around 80% are obtained without efficiency loss.•Lactic acid is used due to its commercial value and possibility of valorisation.•Long-term experiments evaluate the system behaviour with time.