Abstract
New hydroxyapatite (HAp)-like compounds have been previously synthesized by reacting oyster shell powder (Oys) with (NH4)2HPO4 and Ca(OH)2 at 25–28°C (OyOHr) and 100°C (OyOHh). In this study, the effects of these compounds on the immobilization of cadmium (Cd) in soil were investigated as a function of their reaction time with soil. Oys, CaCO3, HAp, OyOHr, and OyOHh were each mixed well with soil and cadmium sulphate. They were then put into plastic pots and incubated at 15–30°C for 56 days with periodical watering. After 56 days, soils with OyOHr or OyOHh only leached 8–10% of the Cd added, whereas soils without addition leached 25%. The suppressive effect of the compounds on Cd uptake by lettuce (Lactuca sativa L.) was also examined using the soils with different reaction times with OyOHr or OyOHh for pot cultivation. In all the treatments, the Cd contents in shoots and roots decreased with soil incubation time with the Ca materials. In the soil incubated for 56 days, the Cd content in shoots was lowest with OyOHh where Cd uptake was suppressed by 48% compared with a control with no added Ca material.
