Immobilization of Cadmium in Soil by Newly Developed Apatite-like Compounds Prepared from Oyster Shells

摘要

Oyster shell powder (an industrial waste) was reacted with diammonium phosphate with calcium to phosphate mole ratios of 5:5, 5:4, and 5:3 at both room (25–28°C) and high (100°C) temperatures to form apatite-like compounds. Oyster shell powder could react with the diammonium phosphate but crystallinity and the cadmium immobilizing effect were poor compared with commercially available hydroxyapatite. Calcium hydroxide was added to the oyster shell powder with an oyster shell to calcium hydroxide mole ratio of 6:4. When this mixture was reacted with 6 moles of diammonium phosphate under the same temperature conditions, a compound with crystallinity close to that of commercially available hydroxyapatite and a higher cadmium retention capacity could be synthesized. It was demonstrated that the cadmium immobilizing ability of this compound in soil is even larger than that of commercially available hydroxyapatite and also has an excellent soil neutralizing ability.