NH_4VO_3在NH_4H_2PO_4-H_2O和(NH_4)_3PO_4-H_2O体系中的溶解度

Solubility of NH_4VO_3 in NH_4H_2PO_4-H_2O and (NH_4)_3PO_4-H_2O Systems

采用等温溶解法测定了偏钒酸铵NH_4VO_3在NH_4H_2PO_4-H_2O和(NH_4)_3PO_4-H_2O体系中T=298.15-328.15 K时的溶解度以及溶液的密度和p H值。结果表明,NH_4VO_3的溶解度随着(NH_4)_3PO_4或NH_4H_2PO_4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,NH_4VO_3分别在NH_4H_2PO_4-H_2O、(NH_4)_2HPO_4-H_2O和(NH_4)_3PO_4-H_2O体系中溶解度,发现在相同的磷酸盐浓度下NH_4VO_3的溶解度在NH_4H_2PO_4-H_2O体系中最大,在(NH_4)_3PO_4-H_2O体系中居中,在(NH_4)_2HPO_4-H_2O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(NH_4)_2HPO_4-H_2O体系中最大,在(NH_4)_3PO_4-H_2O体系中居中,在NH_4H_2PO_4-H_2O体系中最小,与溶解度规律一致。

The solubility of ammonium metavanadateNH4VO3 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 p H values of the solutions were also determined. The solubility of NH4VO3 decreased at first and then increased with increasing NH4H2PO4or（NH4）3PO4concentrations. 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^-1using the p H 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.