Transport of impurities and water during potassium nitrate synthesis by electrodialysis metathesis

•KNO3 obtained by electrodialysis metathesis: NaNO3+K2SO4→KNO3+Na2SO4.•Both products current efficiency close to 100%, purity >99%.•Negligible osmosis and back diffusion.•Electroosmosis prevents products concentration.•Complex mechanism of contaminants transport. The applicability of KNO3 synthesis by electrodialysis metathesis (ED-M) following: NaNO3+K2SO4→KNO3+Na2SO4 reaction scheme using Ralex PP membranes was examined. The effects of operating parameters: current density, feed concentration and composition on a current efficiency, solute and solvent transport were investigated. Current efficiencies observed were close to 100% and purity of the products exceeded 99%. It was found that electroosmosis contributed to water transport the most. At the same time, osmosis and solute back diffusion did not influence the process.