有机质和铁氧化物对水稻土吸附Cd(上标 2+)的贡献

Isothermal adsorption and adsorption dynamics methods were employed to study the characteristics of Cd(superscript 2+) adsorption on 2 paddy soils. The obtained results showed that, the sorption of Cd(superscript 2+) on paddy soils in accordance with Freundlich adsorption isotherm function. Sorption capacity of HN increased 15%, while that of SC decreased 33% after soil organic matter removed alone. Both of them decreased significantly when iron oxides was removed. Under condition of iron oxides free, removal of organic matter could decrease sorption capacity of HN and SC obviously. Under condition of organic matter free, sorption capacity decreased as the same when iron oxides was removed. Compared to one-site model based on first order kinetic equation, two-site model was more pertain to fit the adsorption dynamics of Cd(superscript 2+) on the paddy soils. Quick adsorption rate constant of HN paddy soils decreased, while it increased in SC paddy soils when organic matter was removed, and the rate constants decreased totally after removal of iron oxides. Contribution of iron oxides to the sorption was 4 to 19 times that of organic matter in HN paddy soils, and the contribution of iron oxides was equal to organic matter in SC paddy soils. The dominant constituents of HN were iron oxides and clay minerals, which contributed 61%-76% and 21%-36% to total Cd(superscript 2+) sorption respectively. The dominant constituents of SC was clay minerals, which contributed 85% to the sorption, followed by organic matter and iron oxides.