Abstract: In order to remove cadmium (Cd) from contaminated soil, magnetic nano hydroxyapatite (nHAP@Fe₃O₄) was synthesized by co-precipitation method under the soil water ratio of 1∶1 precursor. 0, 0.1%, 5%, 1.0% and 3.0% nHAP@Fe₃O₄ were then added to soil, respectively. After 21, 30 and 45 days of remediation, magnetic separation was used to separate nHAP@Fe₃O₄ from soil, and the removal rates of Cd in soil, the recovery effect of materials and the changes of soil physical and chemical properties after remediation were then investigated. The results show that the average Cd removal rate and the material (nHAP@Fe₃O₄) recovery rate of heavy polluted paddy soil (containing 2.510 mg·kg^-1 of Cd) with the addition of 1% nHAP@Fe₃O₄ were 16.45% and 85.33%, respectively. The nHAP@Fe₃O₄ can significantly reduce the exchangeable and carbonate bound forms of soil Cd, and promote its transformation to a more stable form. After the remediation by nHAP@Fe₃O₄, the pH of the soil was increased, while the CEC decreased and the pore size between soil particles was increased. The removal of Cd from soil could be realized by using magnetic method to separate nHAP@Fe₃O₄ and adsorb Cd from the soil, which has little effect on soil physico-chemical properties. It is suitable for the remediation of severely polluted agicultural soil.

Key words: nano hydroxyapatite, magnetic material, cadmium pollution, soil remediation