Investigations have revealed the permeation performance of electrolytes in the separation process by nanofiltration membranes in single salt solutions. However, there is still not much information about the separation process of mixed electrolyte solutions, and by now most of the investigations have been on solutions containing three kinds of ions, in which anions are mostly NO-3, Cl- and SO 2-4, and cations are mostly Na+,Ca 2+ and Mg 2+. In this work, permeation experiments of three kinds of nanofiltration membranes（ESNA 1-LF, ESNA 1 and LES 90） for binary electrolyte solutions（NaNO3, Ca（NO3）2; NaCl, NaNO3; NaCl, Ca（NO3）2; etc.） were carried out, and the interactions between co-ions and counter-ions were investigated.The result showed that the ion with better permeation performance would permeate first,thus depressing the rejection of itself and enhancing the rejection of the co-ion with poor permeation performance. Interaction between co-ions with similar permeation performance was not obvious. Counter-ions influenced each other mainly through the electroneutrality principle.
