Thermodynamic Study On The Molybdenum Extraction And Competitive Extraction Of Tungsten And Molybdenum By Primary Amine

Due to the lack of the theoretical basis of research on the process of tungsten and molybdenum extraction by primary amine,a study on the experiments and thermodynamic model of tungsten and molybdenum extraction have been carried out.The following innovative results were obtained:?1?This study has reported Pitzer parameters of Na₂WO₄ at 293.15 K by modeling for tungstic precipitation from Na₂WO₄-Na₂SO₄-H₂ O SLE system and the mean ionic activity coefficients for Na₂WO₄ were calculated with Pitzer parameters.These data were consistent with other available data in literature at 298.15 K by isopiestic method.Therefore the accuracy of the Pitzer parameters of Na₂WO₄ was proved.After regression with GAMS software in LLE system at 293.15 K,the average absolute relative deviation?AARD?was reduced,compared with previous work.This study has also predicted the equilibrated concentration of WO₄2-in the LLE system.The values of lnK at different conditions were calculated.The obtained results indicated that the ln K values approximately kept constant,which confirmed the advantage of thermodynamic model with Pitzer parameters.?2?The LLE data of molybdenum extraction from sodium molybdenate solution in sulfuric acid by primary amine N1923 were obtained at 293.15 K.The extraction reactions were determined with the slope method at 293.15 K within different molality ranges based on the molybdenum phase diagram.It was assumed that there are mainly two extraction complexes generated in the organic phase,and the stoichiometric ratios are 1 and 4 for H₂MoO₄?RNH₂ and H6Mo7O24??RNH₂?4,respectively.Thermodynamic parameters were obtained with Pitzer-Pitzer and Pitzer-Margules models.The prediction for equilibrium molality and equilibrium pH in aqueous phase and the calculated lnK values excellently verified the parameters.Then the mean ionic activity coefficients for Na₂MoO₄ and Na6Mo7O24 were calculated and compared with similar ionic species.Finally,the microstructures of the complexes were proposed to demonstrate the reaction mechanism in molybdenum extraction.?3?The LLE data of tungsten and molybdenum co-extraction in sulfuric acid by primary amine N1923 were obtained at 293.15 K.The ionic species in aqueous phase were determined by phase diagrams and further verified by the relationship between distribution coefficients and equilibrium pH.Combined with the E-pHe diagram,the extraction priority was explained elaborately.The parameters obtained in sole extraction of tungsten,molybdenum by primary amine were used in competitive extraction data.The Pitzer parameters for the interaction between different extraction complexes were regressed subsequently,and these parameters had an excellent prediction on the equilibrium pH of the raffinate solution.