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Updated: Dec 26, 2025

Calcium Carbonate Formation in the Presence of Biopolymeric Additives
Published on: May 14, 2019
Solubility of CaHPO4 · 2H2O in the Quaternary System Ca(OH)2 - H3PO4 - NaCl - H2O at 25 °C
P R Patel1, T M Gregory1, W E Brown1
1Institute for Materials Research, National Bureau of Standards, Washington, D.C. 20234.
Abstract:
Solubility of CaHPO4 · 2H2O was determined in the quaternary system Ca(OH)2 - H3PO4 - NaCl - H2O at 25 °C in the pH range 4.39-6.38; ionic strengths of the saturated solutions varied from 0.00485 to 0.545, Satisfactory constancy in the solubility product, ( ) was obtained when (i) the ion activity coefficients, γ , were calculated with the Debye-Hückel equation, ; the value 0.0626 for the coefficient in the linear term was derived from the solubility data by utilizing a statistical procedure, and (ii) formation of an ion pair was taken into account; a statistically derived value for the stability constant of this ion pair is 7.0 ± 2.4 1 × mol-1. The ion pair appears to have significant concentrations in physiological fluids.
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