Thermodynamic Model for BiPO 4(cr) and Bi(OH)3(am) Solubility in the Aqueous Na+–H+–H2PO- 4 –HPO 2- 4 –PO 3- 4 –OH- –Cl- –H2O System
Journal Article
·
· Journal of Solution Chemistry
- Rai Enviro-Chem, Yachats, OR (United States)
- Japan Atomic Energy Agency (JAEA), Tokai (Japan)
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Prior to this study no data for the solubility product of BiPO 4(cr) or the complexation constants of Bi with phosphate were available. The solubility of BiPO 4(cr) was studied at 23 ± 2 °C from both the over- and under-saturation directions as functions of a wide range in time (6–309 days), pH values (0–15), and phosphate concentrations (reaching as high as 1.0 mol·kg-1). HCl or NaOH were used to obtain a range in pH values. Steady state concentrations and equilibrium were reached in <6 days. The data were interpreted using the SIT model. These extensive data provided a solubility product value for BiPO 4(cr) and an upper limit value for the formation of BiPO 4(aq). Because the aqueous system in this study involved relatively high concentrations of chloride, reliable values for the complexation constants of Bi with chloride were required to accurately interpret the solubility data. Therefore as a part of this investigation, existing Bi–Cl data were critically reviewed and used to obtain values of equilibrium constants for various Bi–Cl complexes at zero ionic strength along with the values for various SIT ion interaction parameters. Predictions based on these thermodynamic quantities agreed closely with our experimental data, the chloride concentrations of which ranged as high as 0.7 mol·kg-1. The study showed that BiPO 4(cr) is stable at pH values <9.0. At pH values >9.0, Bi(OH)3(am) is the solubility controlling phase. Reliable values for the Bi(OH)3(am) solubility reactions involving Bi(OH)3(aq) and Bi(OH) - 4 and the formation constants of these aqueous species are also reported.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 991579
- Report Number(s):
- PNNL-SA--75194
- Journal Information:
- Journal of Solution Chemistry, Journal Name: Journal of Solution Chemistry Journal Issue: 7 Vol. 39; ISSN 0095-9782; ISSN JSLCAG
- Country of Publication:
- United States
- Language:
- English
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