Fluid Phase Equilibria 363 (2014) 199–206 Contents lists available at ScienceDirect Fluid Phase Equilibria j ourna l ho me page: www.elsevier.com/locate/fluid Liquid–liquid equilibrium of the CuSO 4 + PEG 4000 + H 2 O system at different temperatures Martha Claros, María Elisa Taboada, Héctor R. Galleguillos, Yecid P. Jimenez ∗ Department of Chemical and Mineral Process Engineering, Universidad de Antofagasta, Av. Angamos 601, Antofagasta, Chile a r t i c l e i n f o Article history: Received 29 August 2013 Received in revised form 27 November 2013 Accepted 28 November 2013 Available online 11 December 2013 Keywords: Aqueous two-phase system Liquid–liquid equilibrium Polyethylene glycol Copper sulfate a b s t r a c t Phase diagram and liquid–liquid equilibrium (LLE) data for the CuSO 4 + polyethylene glycol 4000 (PEG 4000) + H 2 O system were determined experimentally at T = 288.15, 298.15 and 308.15 K. The effect of temperature on the binodal curves and tie-lines was studied and it was found that an increasing in temperature caused the expansion of two-phase region. The Chen-NRTL and modified Wilson models were used to correlate the experimental tie-line data. The results show that the quality of fitting is better with the modified Wilson model. © 2013 Elsevier B.V. All rights reserved. 1. Introduction An alternative of liquid/liquid separation process is by aqueous two phase systems (ATPS), which are usually formed by combining incompatible polymer/polymer, polymer/salt or salt/salt dissolved above a certain critical concentration [1]. These systems have been widely studied [2–5] and are recognized as an economical and efficient downstream processing method and they offer many advantages such as short process time, low energy consumption and are environmentally friendly [6]. Poly(ethylene glycol) (PEG), which is a hydrophilic polymer, is the most common polymers used with kosmotropic (water struc- turing) salt to form the polymer–salt ATPSs. The applications of the polymer based ATPS includes separation, concentration and fractionation of biological solutes and particles such as cells and proteins [7–9]. Also, they are used in selective distribution and separation of metal ion species [10,11]. Currently, organic solvents are the most widely used in cop- per hydrometallurgical process, but unfortunately these solvents are highly volatile and pollutants. Whereby, the ATPS represent an alternative to the traditional solvent extraction process, where the organic solvents are used. As part of a long-term study, the liquid–liquid equilibrium data for the ATPS formed by CuSO 4 + PEG 4000 + H 2 O at T = 288.15, 298.15 and 308.15 K are reported. In future ∗ Corresponding author. Tel.: +56 55 2637902. E-mail address: yecid.jimenez@uantof.cl (Y.P. Jimenez). works, these liquid–liquid equilibrium (LLE) data will allow to plan the partition experiences of metal ions. Mohsen-Nia et al. [12] reported the phase diagram of the CuSO 4 + PEG 20000 + H 2 O system at T = 290.15, 299.15, 308.15, and 317.15 K and the UNIQUAC model was used to correlate the exper- imental data. de Oliveira et al. [13] reported the equilibrium data of the poly(ethylene oxide) 4000 + copper sulfate + water system at T = 278.15, 283.15, 308.15, and 318.15 K. In both works, there is not report about physical properties in the equilibrium and in the last work the binodal curves neither were determined. Regarding to the phase diagram of CuSO 4 + PEG 4000 + H 2 O sys- tem, there is no report of this at T = 288.15, 298.15 and 308.15 K. Moreover, the refractive index, density and kinematic viscosity of each phase in the equilibrium at T = 288.15, 298.15 and 308.15 K were measured. Over the years, the LLE phase diagrams of polymer–salts ATPS were modeling with models based on the lattice theories, the Flory–Huggins theory, and on the local composition concepts and their modifications [14–18], the latter being the most familiar ones used to represent this kind of LLE phase diagram. In the present work the Chen-NRTL [19] and modified Wilson [20] mod- els were applied for the correlation of experimental LLE data of the aqueous CuSO 4 + PEG 4000 + H 2 O system at T = 288.15, 298.15 and 308.15 K. The entropy of mixing molecules of different sizes was represented by the Flory–Huggins expression [21] and to account for the long-range electrostatic interactions of the ions the Pitzer–Debye–Hückel equation [22] was used. Additionally, the effect of temperature on the LLE of the system above mentioned was also study. 0378-3812/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2013.11.038