Study On Extraction And Separation Of Molybdenum (?) With Polyethylene Glycol-sodium Sulfate Aqueous Two-phase Systems

The extraction and separation performance of molybdenum?VI?was studied by polyethylene glycol-sodium sulfate aqueous two-phase systems without any extractant in order to providing a green,environmentally friendly approach according with sustainable development for future industrial applications.Firstly,the effect of temperature,system composition and PEG molecular weight on the phase equilibria of PEG-Na₂SO₄ aqueous two-phase systems was studied by the tie-line method.The results showed that the tie-line length increases,the composition difference in two phases increases and the phase separation ability strengthens as increasing temperature,system composition and molecular weight of PEG.The reliability of the experimental data was proved by fitting the phase equilibrium tie-line data by empirical equations.Secondly,the effect of aqueous pH,molybdenum concentration,Na₂SO₄concentration,PEG concentration and temperature on the distribution properties of molybdenum?VI?was studied by PEG-Na₂SO₄ aqueous two-phase systems.The results indicated that the extraction efficiency of molybdenum?VI?is the best at pH=2.00;the partition coefficient and extraction rate of molybdenum?VI?increase with the increase of molybdenum concentration,Na₂SO₄ concentration,PEG concentration and PEG molecular weight;the partition coefficient of molybdenum?VI?increases with increasing temperature,showing that the phase transfer process of molybdenum?VI?is endothermic.The stripping performance of molybdenum?VI?was studied by?NH₄?₂SO₄ aqueous solution for the molybdenum loaded PEG-rich phase,the results showed that the stripping effect of molybdenum?VI?is better under higher temperature and lower phase ratio.The analysis on thermodynamic properties of molybdenum?VI?phase transfer process showed that the phase transfer process of molybdenum?VI?conforms to nonlinear van't Hoff equation,and the phase transfer?G°is negative,indicating that the phase transfer process is spontaneous,and both phase transfer?H°and?S°are positive values,indicating that the phase transfer process of molybdenum?VI?is driven by entropy.The analysis on extraction mechanism of molybdenum?VI?showed that polyacid anion of molybdenum?VI?is extracted into hydrophilic area in PEG-rich phase by electrostatic attraction between polyacid anion and protonated PEG quasi cation.Finally,the fabrication process of MoO₃ from roasted low-grade molybdenum concentrate was studied by leaching with NaClO₃ and Na₂CO₃,extraction and stripping by aqueous two-phase system,evaporation,cooling crystallization and roasting and the qualified MoO₃ product was obtained.The results showed that the effect of leaching temperature on leaching rate is more significant than the effect of leaching speed,indicating that the leaching process is mainly controlled by chemical reaction rate;with the increase of NaClO₃ and Na₂CO₃ concentration,the leaching rate of molybdenum increases.XRD and SEM analysis showed that the obtained MoO₃ product is monoclinic with good crystallinity and large crystallites.