To develop an activity coefficient model for aqueous multielectrolyte systems, ion-specific NRTL parameters were applied to the electrolyte-NRTL model. In total, 132 ion-specific NRTL parameters for 21 ionic species (K+, Na+, Mg2+, H+, Ca2+, Zn2+, Al3+, NH4+, Cd2+, Co2+' Cu2+, Pb2+, Mn2+, Ni2+, Cr3+, Cl-, SO42-, NO3-, OH-, ClO4-, CrO42-) were determined from the binary activity coefficient data of aqueous electrolytes and used to predict the activity coefficients of electrolytes in aqueous multieletrolyte solutions without any additional parameters. Furthermore, solubilities of inorganic salts including heavy metals in aqueous mixed electrolyte systems and the distribution ratio of Cu in a solvent extraction process containing HCl and CuCl2 were predicted using the activity coefficients derived from our ion-specific electrolyte-NRTL model. The results showed that the NRTL parameters obtained in this study accurately predict phase equilibria of systems involving inorganic salts such that this model can be used in the design of recovery processes such as crystallization and solvent extraction.