Study On Extraction And Separation Of Tungsten And Molybdenum By Aqueous Two-phase Systems

There is similar physicochemical properties and high separation difficulty of tungsten and molybdenum so the separation of both metals has been challenging topics for scientific researchers.The extraction and separation performance,the mechanism of extraction and the thermodynamic properties of phase transfer process of tungsten(VI)and molybdenum(VI)in aqueous solution were studied by aqueous two-phase systems formed by polyoxyethylene nonionic surfactant and sodium sulfate,which is supposed to provide a new theoretical guidance for future industrial application.Firstly,the phase equilibrium properties of the aqueous two-phase systems consisting of nonionic surfactant and sodium sulfate were studied,and the influence of the system composition and temperature on the phase equilibrium was investigated.The results indicated that the phase separation ability strengthens as increasing system composition and temperature.The phase equilibrium data were correlated,which proved the reliability of the experimental data.Secondly,the separation performance of tungsten and molybdenum was studied by aqueous two-phase system consisting of alkylamine polyoxyethylene ether,such as AC1205,AC1210,AC1215,AC1810,AC1815 and AC1830,and sodium sulfate under the nearly neutral condition.The effect of aqueous pH,initial concentration of tungsten and molybdenum,concentration of surfactants and sodium sulfate and temperature on the separation of both metals was experimented.The results showed that the aqueous pH and temperature were the greatest influence on the extraction performance of both metals and the optimum pH was 6.8 and temperature was 353.15 K.The effect of the concentration of tungsten,molybdenum,sodium sulfate and surfactant had a certain influence on the separation performance of both metals.Under the optimal conditions for the AC1205 system,the extraction rate of tungsten was 96.5%,while the extraction rate of molybdenum was 16.5%,and the maximal separation factor of tungsten and molybdenum reached 95.1.Thirdly,the separation performance of tungsten and molybdenum was studied by aqueous two-phase systems consisting of sodium sulfate and surfactants,such as PEG4000,PEG2000 and L35 under acidic condition.The effect of aqueous pH,concentration of complexing agent,surfactant and sodium sulfate,initial concentration of tungsten and molybdenum and temperature on the separation of both metals was experimented.The results indicated that complexing agent of molybdenum was the key factor for the separation of both metals.There was greater effect of aqueous pH value on the separation of both metals and the optimum pH was 2.0 and temperature was 353.15 K.The order of separation efficiency of both metals for non-ionic surfactants from high to low was: PEG4000,PEG2000 and L35.The effect of concentration of tungsten,molybdenum and sodium sulfate on the separation performance of both metals was slight.Under the optimal extraction conditions for the PEG4000 system,the extraction of tungsten was more than 93%,while the extraction of molybdenum was less than 13%,and the maximal separation factor of both metals reached 73.1.Finally,the extraction mechanism of tungsten and molybdenum was studied by ultraviolet spectrum,infrared spectrum,Raman spectrum and dynamic light scattering,and the phase transfer process of tungsten was analyzed thermodynamically.The results revealed that the phase transfer process of paratungstate B depended on the electrostatic attraction between the anion of paratungstate B and the protonated pseudo-cation in surfactant molecules.Tungsten partitioning process was spontaneous and driven by entropy.