A separation process is necessary for the recycling of the solvent and diluent from a molybdenum (Mo) acid leaching solution. Acetylacetone is a commercial Mo solvent and phosphonium-based ionic liquid (IL) that is a promising green selective solvent for Mo ions or dilutor based on the Mo extraction test. To develop a recycling process for the solvent, pseudo ternary liquid-liquid equilibria (LLE), a separation process design data set, was determined for several systems at 298.15 K: {Aqueous acid solution (AS-solution) + acetylacetone + tri-hexyltetradecyl phosphonium chloride ([P-666,P-14)[Cl]}, {AS-solution + acetylacetone + tri-hexyltetradecyl phosphonium bis(2,2,4-trimethylpentyl) phosphinate ([P-666,P-14][TMPP])} and {AS-solution + acetylacetone + tri-hexyltetradecylphosphonium dictanamide ([P-666,P-14[[DCA])}. The experiments were carried out at atmospheric pressure using stirred and thermo-regulated cells. The experimental LLE data for the aforementioned pseudo ternary systems were correlated using the non-random two liquid (NRTL) activity coefficient model. In addition, mixture properties, namely the excess molar volume (V-E) and deviations of the refractive indices (Delta R), were determined for the following binary systems at 298.15K: acetylacetone + [P-666,P-14][Cl]}, acetylacetone + [P-666.14][TMPP]} and {acetylacetone + [P-666,P-14][DCA]}. These binary data were correlated with the Redlich-Kister polynomial. (C) 2013 Elsevier B.V. All rights reserved.