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 SO2-4

and cations are mostly Na+，Ca2+ and Mg2+. 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.