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THE pH DEPENDENCE OF THE SURFACE CONCENTRATIONS OF CALCIUM AND PHOSPHORUS ON HYDROXYAPATITE IN AQUEOUS solUTIONS
Author(s) -
BELL L. C.,
MIKA H.
Publication year - 1979
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1979.tb00982.x
Subject(s) - stoichiometry , chemistry , adsorption , aqueous solution , dilution , desorption , solubility , calcium , inorganic chemistry , surface charge , analytical chemistry (journal) , nuclear chemistry , chromatography , organic chemistry , thermodynamics , physics
Summary A radioisotope dilution technique was used to measure the surface concentrations of Ca and P on hydroxyapatite equilibrated at pH values ranging from 5.19 to 8.81. The concentrations were rarely equal to those calculated for a stoichiometric surface. In general the molar surface Ca/P increased from a value less than the stoichiometric figure of 1.67 at low pH values to a value greater than 1.67 at high pH values. The solution Ca/P showed the opposite trend with pH. The deviations of the surface concentrations of Ca and P from stoichiometric values were attributed to adsorption and desorption of the elements at the solid surface. The extent of these reactions was influenced by both surface charge and the solution concentration of Ca and P. The relevance of the pH dependence of the surface composition of hydroxyapatite to the interpretation of solubility studies on the solid is discussed.