Separation of vanadium and molybdenum from aqueous solution using PEG2000 + sodium sulfate + water aqueous two-phase system

The separation of vanadium (V) and molybdenum (VI) was studied by co-extraction with an aqueous two-phase system formed by PEG2000 + sodium sulfate + water and by selective stripping with another aqueous two-phase system formed by ammonium sulfate solution and PEG2000 phase loaded vanadium and molybdenum. The effect of aqueous pH, concentration of vanadium and molybdenum, temperature on the co-extraction and concentration of ammonium sulfate, temperature and phase ratio on selective stripping separation of vanadium and molybdenum was investigated. The experimental results on co-extraction of vanadium and molybdenum indicated that the co-extraction rate of both metals is sensitive to aqueous pH, and their extraction rate can achieve above 97.54% and 99.49%, respectively, when the pH value of aqueous solution is at 2.0, the molar ratio of vanadium to molybdenum is about 1.5, the concentration of PEG2000 is 20%, and the temperature is 313.15 K, respectively. The co-extraction rate of both metals decreases slightly with an increase in temperature from 313.15 to 343.15 K. The extraction isotherm and McCabe–Thiele method showed that two theoretical stages are needed when concentration of vanadium and molybdenum decreases from initial 12 g/L and 10 g/L to 0.1 g/L under the optimal conditions. The results on selective stripping of both metals from loaded PEG2000 phase to aqueous phase indicated that the stripping rate and precipitation rate of vanadium are evidently impacted by aqueous pH within 8.0 ~ 11.0 and then a little influenced by other parameters. The stripping rate of molybdenum is relatively lower than that of vanadium and is influenced by all kinds of stripping conditions. The stripping rate and precipitation rate of vanadium achieve 99.88% and 98.84%, respectively, and stripping rate of molybdenum achieves 81.99% under the optimal stripping conditions of O/A = 2:1, stripping temperature 343.15 K, (NH4)2SO4 (w/w) 40% and the pH of aqueous solution at 10.0.