Ionic liquid-based aqueous two-phase systems offer an attractive alternative to volatile organic solvents in liquid-liquid extraction. In this work, the phase diagrams of the 1-alkyl-3-methyl imidazolium tetrafluoroborate ([C(2)mim]BF4/[C(4)mim]BF4)+ZnSO4/MgSO4/Li2SO4+ H2O ATPSs were determined at 298.15 K. Three empirical equations were used to correlate the binodal data and the optimum equation was selected. The effective excluded volume (EEV) values obtained from the binodal model for these systems were determined. The EEV and the binodal curves plotted in molality both indicate that the salting-out abilities of the three salts follow the order: ZnSO4> MgSO4> Li2SO4, while the phase-separation abilities of the investigated ILs are in the order of [C(4)mim]BF4>[C(2)mim]BF4. Finally, the liquid-liquid equilibrium data were successfully correlated by the Othmer-Tobias and Bancroft equations, meanwhile the slope of tie line increased with an increase in cation alkyl chain length. (C) 2013 Elsevier B.V. All rights reserved.