Thermodynamic analysis for separation of tungsten and molybdenum in W-Mo-H_2O system

The thermodynamic equilibrium diagrams for the distribution of species at different pH values,tungsten and molybdenum concentrations in W-H2O,Mo-H2O and W-Mo-H2O systems at 25 ℃ were drawn,and the variational regularities of species were also analyzed.The thermodynamic analysis shows that the tungsten and molybdenum are transformed from monomeric anions to heteropolyanions,then to isopolyanions during the acidification process in W-Mo-H2O system.The polymeric degree of tungsten is significantly higher than that of molybdenum in the pH range from 6.5 to 7.5,which indicates that the polymeric ability of monotunstates is stronger.At pH values of 3.0.6.5,the heteropolymolybdotungstate ions with higher concentration are formed,which is extremely unfavorable to the separation of tungsten and molybdenum.