Liquid-liquid extraction of molybdenum(VI) using aqueous two-phase systems (ATPS) consisting of polyethylene glycol (PEG) and sodium, ammonium and copper(II) salts: Comparison with conventional solvent extraction

In this work, the stripping of molybdenum from aqueous two-phase aqueous systems (ATPS) formed by a mixture of polyethylene glycol (PEG) 4000, salt and water was studied at different operational conditions of pH (7, 8 and 9) and temperature (308.15, 323.15 and 338.15 K), using two molybdenum salts (Na2MoO4 and (NH4)6Mo7O24). These salts were used for the experimental tests of extraction and stripping of the two-phase aqueous system of PEG 4000, CuSO4 and water, to evaluate the best percentage of stripping using different stripping agents: NaOH, Na2CO3, CuSO4 and a mixture of (NH4)2SO4 and NH4OH (Khayati et al., 2011). According to the results, the best stripping agent was the 20% (NH4)2SO4 solution as phase former plus 25% NH4OH as pH modifier. The experimental results indicate that the increase in temperature is directly proportional to the percentage of stripping. For the system of PEG 4000, CuSO4, water, Na2MoO4, (NH4)2SO4 and NH4OH system (ATPS 1) the percentage of stripping was 96.3%. In the case of PEG 4000, CuSO4, (NH4)6Mo7O24, water (NH4)2SO4 and NH4OH (ATPS 2) the stripping was 99%, these being the maximum values of stripping at pH = 2 and T = 308.15 K. It was determined that for ATPS 1, as the pH increases the stripping efficiency tends to decrease, while as the pH increases in ATPS 2, the stripping efficiency increases; this behavior is attributed to the hydration energy of the ions. Finally, a pre-feasibility study of the studied processes, ATPS 1, ATPS 2 and traditional solvent extraction (SX), was carried out, which included calculation of the profit factors.