The liquid–liquid equilibria for low pH aqueous acid solution + tri-octylamine (or tri-butylphosphate) + 1-decane and the binary and ternary excess molar volumes and deviations of the refractive indices

Liquid–liquid phase equilibria (LLE) for the ternary system containing water + tri-octylamine (TOA) or tri-butylphosphate (TBP) + 1-decane were reported in a previous paper. These ternary combinations can be used as selective solvents and diluents in the molybdenum (Mo) extraction process. In the interest of industrial applicability, the LLE for the system containing aqueous sulfuric acid solution (pH 1.0) + TOA or TBP + 1-decane has been discussed at the temperature of 298.15 K and a normal atmospheric pressure. The solubility of TOA and TBP in water was a little decreased with the addition of sulfuric acid. Nonrandom two-liquid (NRTL) and universal quasichemical (UNIQUAC) models were used for the description of the determined LLE data. In addition, the density (ρ) and the refractive index (nD) for the systems TOA + 1-decane and TBP + 1-decane at 298.15 K were determined. These data were used to calculate the binary excess molar volume (VE) and the deviations of the refractive indices (ΔR) over the entire composition range. The ternary VE and ΔR prediction for the TOA + TBP + 1-decane system was determined from the binary data with the Radojkovič equation.

► Liquid–liquid equilibria were measured for the ternary system containing selective solvents and diluents in the molybdenum extraction process.
► NRTL and UNIQUAC models were used for the description of the determined LLE data.
► The density and the refractive index for the systems TOA + 1-decane and TBP + 1-decane at 298.15 K were determined.
► The ternary VE and ΔR prediction for the TOA + TBP + 1-decane system was determined from the binary data with the Radojkovič equation.
► TBP could be a more useful solvent than TOA when TBP and TOA have the same selectivity for Mo because of the lower solubility of TBP in an aqueous solution.