Abstract: In order to determine the passivation effect of natural Spanish river carbonatite（SRC） on heavy metal cadmium （Cd） contaminated soils, field and pot experiments were used to study the distribution of available Cd, Cd forms and Cd of different rice parts by adding SRC in soils exceeding the risk screening values （CG and LQ） and risk control values （JH）. The results showed that SRC significantly changed soil available Cd, pH, Cd forms and Cd content in different parts of rice in CG and LQ soils, but had little effect on JH soil. When SRC was added, soil pH of CG and LQ increased by about 0.2, significantly reduced the contents of CaCl₂-Cd（0.01 mol/L CaCl₂ extraction） in CG and LQ soils, and the reduction ranged from 27.3% to 38.9%. Forms analysis of Cd showed that SRC could change Cd from easily absorbed Cd by plants to hardly absorbed Cd in CG and LQ soil change. The content of acidic Cd decreased by 6%~14% and the content of iron-manganese oxidized Cd and organic bound Cd increased by 8%~9%, respectively. Under field conditions, SRC significantly inhibited Cd uptake by rice roots, straws and grains, with decreases of 53.7%, 69.8% and 54.6%, respectively. SRC can reduce the bioavailability of Cd in soils by increasing soil pH and adsorbing Cd by minerals, and inhibit the absorption of Cd by rice.

Key words: carbonate rocks, cadmium, heavy metal fraction, soil remediation, paddy rice