ヒドロキシアパタイトに対するシュウ酸イオンの吸着とその吸着量におよぼす添加物の影響

抄録

Adsorption of oxalate ion (Ox^2-) in aqueous solutions (30°C, pH 7.5-12.0) to hydroxyapatite (HAP) was confimed to be reversible and of Langmuir type. The amount (x_Ox) of adsorbed Ox^2- from Na₂Ox was larger than that from K₂Ox through the size effect of the counter ion. As the thermodynamic activity (ionic activity product) of adsorbate (Na₂Ox or K₂Ox) increases with an increase in concentration of the counter ion, x_Ox increased with an increase in the amount of added NaCl or KCl. But the amount of adsorption, x_Ox, increased with a decrease in pH because of competitive adsorption with OH^-. It was also suggested that Ox^2- competes with Cl^- for the adsorption sites on HAP. Therefore, the amount of adsorption, x_Ox, increased apparently by the addition of L-lysine HCl or glycine, but it was concluded that the increase was due to the decrease of pH and these substances do not affect x_Ox after pH-correction. On the other hand, x_Ox was decreased by the addition of Na₂HPO₄, NaHCO₃ or sodium L-aspartate even after pH-correction owing to the competitive adsorption between Ox^2- and these anions. It was concluded that Ox^2- is adsorbed to HAP by electrostatic force and that some portion of adsorbed Ox^2- is subjected to the ion-exchange with orthophosphate ion on the HAP surface. Some properties of renal calculus formation was explained on the basis of the results presented here.