Solute partitioning in a calcium carbonate-phosphoric acid-water system

A range of Ca phosphates form in a time-dependent process, when calcite interacts with a dilute orthophosphate solution. This study was conducted to ascertain the possible formation of a stable CaCO3-PO4 compound on calcite surfaces and to characterize its precursors. The solution's ionic speci...

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Bibliographic Details
Published inSoil Science Society of America journal Vol. 58; no. 6
Main Authors Salingar, Y. (Keren Kayemeth LeIsrael, Land Development Authority, Hayim, Israel), Kochva, M
Format Journal Article
LanguageEnglish
Published 01.11.1994
Subjects
ACIDE MINERAL
ACIDOS INORGANICOS
BICARBONATE
BICARBONATOS
CALCITA
CALCITE
CARBONATE DE CALCIUM
CARBONATO DE CALCIO
FOSFATOS
MINERALES
MINERAUX
PHOSPHATE
REACCIONES QUIMICAS
REACTION CHIMIQUE
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Summary:A range of Ca phosphates form in a time-dependent process, when calcite interacts with a dilute orthophosphate solution. This study was conducted to ascertain the possible formation of a stable CaCO3-PO4 compound on calcite surfaces and to characterize its precursors. The solution's ionic speciation provided evidence of the formation of a CaHCO3-PO4 compound (CBP) with a stoichiometric Ca/P ratio of 3 and a solubility product, Ksp, of (Ca2+)3(HCO3(-))3(PO4(-3) = 1O(-28.36). This hypothesis was also supported by electron spectroscopy analyses of the surface layers of the final solid product and scanning electron microscopy (SEM). Prior to the CBP formation, either a compound with the same Ca/P ratio as dicalcium phosphate (DCP, CaHPO4) formed, or CBP was in quasi-equilibrium at a Ca/P ratio of 1.5 to 2.3. Another possibility is that a poorly crystalline or amorphous Ca phosphate solid phase was formed. Finally, the newly formed CBP converted to hydroxyapatite (HAP, Ca5 (PO4)3OH)
Bibliography:P33
9534310
ISSN:0361-5995
1435-0661
DOI:10.2136/sssaj1994.03615995005800060007x