The process for separating and purifying lithium in brines based on electrodialysis with monovalent selective ion exchange membranes was investigated in our previous work. The migration of coexisting cations in brines was competitive with lithium ions, especially monovalent cations (Na+ and K+). The aim of this study was to examine the influence of major coexisting cations in brines on lithium recovery in the selective-electrodialysis (S-ED) process. Considering the factors of coexisting cations, such as concentration and type, some migration laws of lithium ion were found as follows: the concentration of coexisting cations had negative effect on the migration of lithium ion; the influence order of coexisting cations on lithium migration was contrary to their hydrated radius sequence: K+>Na+>Ca2+>Mg2+. In order to characterize the migration process of cations through monovalent selective cation exchange membrane in microcosmic theory, a partial dehydration conceptual model based on charge capillary column theory and ionic potential was proposed. And the model was used to characterize the ions migration process. Simultaneously, considering the hydration potential which indicates how strongly an ion would attract water molecules, the influence sequence of coexisting cations was explained legitimately. These observations might provide some theoretical basis and technological support for the relevant research of recovering lithium from brines. A partial dehydration conceptual model of ion migration in the cation exchange membrane. Display omitted •Selective-electrodialysis (S-ED) was used to recover lithium from brine.•Effect of coexisting cations concentration on lithium recovery by S-ED was investigated.•The influence sequence of coexisting cations on lithium migration was K+>Na+>Ca2+>Mg2+.•A partial dehydration model was proposed to discuss the separation mechanism of cations in S-ED process.