The Ternary System H3PO4– Ca(OH)2–H2O Isotherms at 15 and 45 °C

Abstract

The solid-liquid phase equilibria of the system H3PO4-Ca(OH)2-H2O were studied under air pressure using a synthetic method based on conductivity measurements. Two isotherms at 15 and 45 °C were completely defined. The stable solid phases which appear in this range of temperature are hydroxyapatite (Ca10(PO4)6(OH)2), calcium hydrogen phosphate dihydrate (CaHPO4.2H2O), calcium hydrogen phosphate anhydrous (CaHPO4) and calcium dihydrogen phosphate monohydrate (Ca(H2PO4)2.H2O). These solid phases were characterized using X ray diffraction.

The Ternary System H3PO4-Ca(OH)2-H2O Isotherms at 15 and 45 °C

“…Indeed, on the Figure 3, we represented the X-ray diffraction diagram of the solid phase which derives from mixture N 1 . This diagram shows that Ca 10 (PO 4 ) 6 (OH) 2 has formed [1], with the existence of calcium carbonate, likely originating from contamination by atmospheric CO 2 trapped during separation.…”

“…To reach this objective, we approached, in the laboratory, the study of the phase equilibria of the various sub-systems of this quaternary. In a preceding work we established the isotherm 30 °C of the system H 3 PO 4 -Ca(OH) 2 -H 2 O [1]. In the present work, we established isotherms 15 and 45 °C of this system, by basing us on the conductivity measurement.…”

“…The Figure 4 represents the X-ray diffraction diagram of the solid phase resulting from mixture N 2 , which corresponds to the calcium hydrogen phosphate dihydrate (CaHPO 4 .2H 2 O) [1].…”

Study on Controlling the Dissolution of Calcium Dihydrogen Phosphate Using Ternary Phase Diagrams to Improve the Production Process of Phosphoric Acid

“…Furthermore, the solubility of Ca(H 2 PO 4 ) 2 decreases with the increasing of phosphoric acid concentration. 30 A high concentration of phosphoric acid leads to the precipitation of Ca(H 2 PO 4 ) 2 . In short, a phosphoric acid concentration that is too high will cause Ca(H 2 PO 4 ) 2 to precipitate out.…”

“…Promoting the generation of Ca­(H 2 PO 4 ) 2 is important to avoid the precipitation of phosphate and enhance the yield of phosphoric acid. Furthermore, the solubility of Ca­(H 2 PO 4 ) 2 decreases with the increasing of phosphoric acid concentration . A high concentration of phosphoric acid leads to the precipitation of Ca­(H 2 PO 4 ) 2 .…”