Abstract
The sorption behavior of traces Sr(II) toward β-Ca3(PO4)2 (TCP) depending on the concentration of the cation, pH, and concentrations of humic acids (HA) in the solution was udied. Thermodynamic analysis of the solubility of TCP (1) was performed taking into account the formation of Ca(OH)2 (CH, 2), Ca(H2PO4)2 (MCPA, 3), CaHPO4·2H2O (DCPD, 4), Ca5(PO4)3OH (hydroxyapatite, OHAp, 5), and Ca2P2O7 (DCPP, 6). It is shown that, depending on the pH of the solution, the main equilibrium phases with the solution are phases (4) and (5). X-ray di raction analysis, Raman spectroscopy, and 31P NMR data of the phase (1) samples after contact with a solution of 0.01 mol/L NaNO3 for about 10 days showed the presence of only the phase (1). The solubility of (1) regarding the concentration of Ca2+, PO43- ions and the stoichiometric ratio (Ca/P) in solutions, depending on pH, corresponds to the presence of surface phases (4) or (5). The model of surface complexation in the Henry region adequately describes the mechanism of sorption of Sr(II) by the surface phase (5) on TCP particles in the form of the SrHPO40 complex. The formation of the HA complex Sr(II) in solution does not a ect distribution coe cient K d(Sr) in the range of HA concentrations of 0-150 mg/L due to the competitive e ect of hydrogen phosphate ions on strontium complexes.
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