Water desalination by neutralization dialysis with ion-exchange membranes: Flow rate and acid/alkali concentration effects

• Kinetics of surface water desalination by neutralization dialysis was studied.
• The ND process feasibility was evaluated.
• ND process costs and its possibility of optimization were evaluated.
• Ion-transport control was discussed and roles of DBLs and IEMs have been clarified.
• Calculated and experimentally measured fluxes of batch operation were very close.

Kinetics of surface water desalination by neutralization dialysis (ND) was studied in a three-compartment stack with ion-exchange membranes, and the process feasibility was evaluated. The pH and the ionic conductivity of a model saline solution (0.02 M NaCl) were measured during different ND operations in batch mode. The influence of the flow rate, the solution concentration in the alkali and acid compartments was investigated. It was found that, at the beginning of the operation, the ion-exchange kinetics was mainly controlled by the membrane diffusion. The maximal fluxes of exchanging ions (Jmax) (Na+ and H+ across CMX membrane, and Cl− and OH− across AMX membrane) were theoretically evaluated. The calculated and the experimentally measured fluxes at the beginning of batch operation were close. However, after some minutes of solution desalination, the salt concentration decreased, which involved diffusion boundary layer controlled kinetics. Hence, with time, the fluxes decreased and were considerably smaller than Jmax. The increase/decrease in the acid and alkali solution concentration resulted in corresponding increase/decrease in the ion-exchange rate. Recommendations have been provided to reduce the desalination duration.