Study on thermodynamics of anions′ dynamic exchange of tungsten metallurgy system by ion chromatography

Aiming at the controversy over affinity between anions and quaternary ammonium resin in tungsten metallurgy, the study investigated into the influences of NaOH, Na₂CO₃ and NaHCO₃ on anions elution in quaternary ammonium type column at different temperatures by ion chromatograph. Thus, order of affinity between the anions and the column, and the thermodynamic parameters of dynamic exchange were obtained. The results showed that with NaOH as eluent, the affinity order between anions and quaternary ammonium column was: MoO₄^2- > WO₄^2- > AsO₄^3- > PO₄^3- > SO₄^2- > Cl^- > F^-. When Na₂CO₃ or NaHCO₃ was used as eluent, phosphorus and arsenic were converted into the form of HPO₄^2- and HAsO₄^2-, respectively, resulting in a decrease of their affinity for the chromatographic column. Furthermore, the capability to elute anions ranked: NaOH > Na₂CO₃ > NaHCO₃. When NaOH was used as eluent, temperature had a significant effect on the peak time of each anion. Besides, when NaOH and Na₂CO₃ were used as eluents, the corresponding thermodynamic parameters could be calculated by Van′t Hoff equation, and the order of relative Gibbs free energy changes was consistent with that of affinity between anions and quaternary ammonium column.