Effects of impurity ions on solubility and metastable zone width of phosphoric acid

Effects of two typical impurity ions as Fe²⁺ and SO₄^2– in phosphoric acid on solubility and metastable zone width (MZW) had been studied. It was shown that polythermal method was suitable for solubility measurement in this study. The solubility experimental data was correlated with a polynomial equation. Being compared with Fe²⁺, SO₄^2– had a greater impact on the phosphoric acid solubility; and the variation in phosphoric acid MZW was just opposite. Phosphoric acid apparent secondary nucleation order was calculated to be 3.50 by means of modified regression method. And also the influence of impurity ions on apparent secondary nucleation order was investigated in this paper. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)