[in Japanese]

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The enthalpies as well as the amount of interaction of Pb²⁺, Cu²⁺, Hg⁺ and Ag⁺ ions in the aqueous nitrate solution were studied with calcium hydroxyapatite (HAp) surfaces of different Ca/P atomic ratio by means of flow adsorption microcalorimetry. Pb²⁺ ion interacted with HAp surface almost irreversibly with a large heat of reaction. The amount of Pb²⁺ interacted with HAp surface corresponds to about 2 ionic surface layers of Ca²⁺ ions of HAp. The interaction behaviour of Hg²⁺ with HAp was similar to that of Pb²⁺. The enthalpies of ion exchange interaction of Cu²⁺ and Ag⁺ were smaller than that of Pb²⁺. The mechanism of interaction of these ions was discussed in view of the heat of interaction.

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A general formula of hydrotalcite like Mg-Al layered double hydroxide (LDH) is expressed as [Mg_1-x²⁺Al_x³⁺ (OH) ₂] ^x+ [An_x/n^n-] ·yH₂O. An oxidative decomposition method of EDTA-Metal chelate with hydrogen peroxide was investigated in order to prepare LDH. Effects of H₂O₂ concentrations and Mg/Al mole ratio (R₁) in the reaction solution on the Mg/Al mole ratio (R_s) in LDH were investigated to find an optimum synthesis conditions. LDH was successfully obtained by allowing to react the solution with R₁=6 and pH = 10 for 6 h. The R_s values were influenced with the R₁ value. The R_s values were the range of 1.4-2.3. The (003) basal spacing of the products was spread to the range of 0.758 nm to 0.770 nm with increasing R_s The (003) basal spacing of the ethylene glycol-intercarated LDH was 1.36-1.40 nm. However, it spread only to 0.78 nm on the R_s value being 2.3.

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