NH4VO3在NH4H2PO4-H2O和(NH4)3PO4-H2O体系中的溶解度

采用等温溶解法测定了偏钒酸铵(NH₄VO₃)在NH₄H₂PO₄-H₂O和(NH₄)₃PO₄-H₂O体系中T = 298.15-328.15 K时的溶解度以及溶液的密度和pH值。结果表明, NH₄VO₃的溶解度随着(NH₄)₃PO₄或NH₄H₂PO₄溶液浓度的增大,先降低后升高,这是由于同离子效应、化学反应平衡及离子活度的共同作用。比较T = 298.15K时, NH₄VO₃分别在NH₄H₂PO₄-H₂O、(NH₄)₂HPO₄-H₂O和(NH₄)₃PO₄-H₂O体系中溶解度,发现在相同的磷酸盐浓度下, NH₄VO₃的溶解度在NH₄H₂PO₄-H₂O体系中最大,在(NH₄)₃PO₄-H₂O体系中居中,在(NH₄)₂HPO₄-H₂O体系中最小。进一步地,在T = 298.15 K和磷酸盐浓度C = 0.5 mol·kg^-1时,结合pH值和反应溶度积常数K_SP等计算三个体系中的平均离子活度系数(γ_±),发现γ_±值在(NH₄)₂HPO₄-H₂O体系中最大,在(NH₄)₃PO₄-H₂O体系中居中,在NH₄H₂PO₄-H₂O体系中最小,与溶解度规律一致。

Solubility of NH4VO3 in NH4H2PO4-H2O and (NH4)3PO4-H2O Systems

The solubility of ammonium metavanadate (NH₄VO₃) in NH₄H₂PO₄-H₂O and (NH₄)₃PO₄-H₂O systems at T = 298.15-328.15 K was measured using the classic isothermal dissolution method. The densities and pH values of the solutions were also determined. The solubility of NH₄VO₃ decreased at first and then increased with increasing NH₄H₂PO₄ or (NH₄)₃PO₄ concentrations. This was considered to be caused by the common ionic effect, chemical reaction equilibrium and ionic activity. At T = 298.15 K, the solubility of NH₄VO₃ in the NH₄H₂PO₄-H₂O system was the highest, and was lower in the (NH₄)₃PO₄-H₂O system. The solubility in the (NH₄)₂HPO₄-H₂O system was the lowest. The mean ionic activity coefficients were calculated for the three phosphate solutions at C = 0.5 mol·kg^-1 using the pH values and dissolution reaction constant. The mean ionic activity coefficients were the largest for the (NH₄)₂HPO₄-H₂O system, and were smaller for the (NH₄)₃PO₄-H₂O system. The mean ionic activity coefficients were the smallest for the NH₄H₂PO₄-H₂O system, which agrees with the solubility variations of NH₄VO₃ in the three phosphate systems.