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

Abstract

Key words solubility, metastable zone width, impurity ions, phosphoric acid. PACS 61.72. 64.60.My, 64.70.dg, 64.75.Bc Effects of two typical impurity ions as Fe 2+ and SO 4 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 Fe 2+, SO 4 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.

Study of phosphoric acid crystallization using a focused beam reflectance measurement method

“…Kinetics of crystal growth Some researchers have studied thermodynamics and kinetics of phosphoric acid hemihydrate crystallization [8,11,12,15]. The stirring intensity of crystallization process has great influence on not only growth rate but also mechanism of crystal growth.…”

On the effect of impurities on the metastable zone width of phosphoric acid

“…It was observed that the solubility of phosphoric acid increases with an increase in temperature and decreases with an increase in the concentration c i of the impurities. The authors analyzed the data using Ný vlt's equation and obtained the value of nucleation order m [11]. It was found that m increases systematically from 3.5 to 4.68 and 4.85, respectively, with an increase in the concentration of Fe 2 + and SO 2À 4 ions to 250 ppm.…”

“…Recently, Ma et al [11] reported the results of an investigation of the effect of Fe 2 + and SO 2À 4 ions on the solubility and metastable zone width of phosphoric acid in the temperature range from 0 to 29.35 1C. The metastable zone width was measured by the laser intensity technique in the presence of 0.1 wt% crystal seeds.…”

“…1 shows the solubility of phosphoric acid and examples of supersolubility curves for two selected cooling rates R. The original data are taken from Ref. [11]. It may be seen that the maximum supercooling ratio DT max /T 0 increases with an increase in T 0 of the solution and the value of DT max /T 0 increases with increase in cooling rate R.…”

“…Recently, experimental data have been reported [10,11] on the solubility and metastable zone width of phosphoric acid in the presence of cationic and anionic impurities, which show an increase in DT max /T 0 with an increase in T 0 . From the literature published very recently on the metastable zone width for the crystallization from fluxes [12] and gels [13], it seems that the behavior of the T 0 -dependence of DT max /T 0 is not unusual.…”