有机质和铁氧化物对水稻土吸附Cd~(2+)的贡献

采用等温吸附和吸附动力学方法研究了2种水稻土对Cd2+的吸附特征。结果表明,水稻土对Cd2+的吸附符合Freundlich等温吸附方程,单独去除土壤有机质后,河南伊川水稻土(HN)的吸附能力增加了15%,而四川邛崃水稻土(SC)则降低了33%;去除铁氧化物后对Cd2+吸附能力均显著降低。在去除铁氧化物条件下去除有机质或者在去除有机质条件下去除铁氧化物,HN和SC的Cd2+吸附能力均明显降低。与一级动力学一点模型比较,两点模型更适合拟合HN和SC对Cd2+的吸附动力学。去除有机质后,HN快吸附速率常数降低,而SC则有所增加;去除铁氧化物后,HN和SC的快吸附速率常数均明显降低。HN中铁氧化物对Cd2+吸附贡献均大于有机质,SC中铁氧化物与有机质的贡献量基本一致。对HN中Cd2+吸附过程中起主导作用的是铁氧化物和黏土矿物,其对吸附量的贡献率分别为61%~76%和21%~36%,而SC中起主导作用的是黏土矿物,贡献率可达85%,其次是有机质和铁氧化物。

Contribution of Organic Matter and Iron Oxides to Adsorption of Cd2+ on Paddy Soils

Isothermal adsorption and adsorption dynamics methods were employed to study the characte-ristics of Cd2+ adsorption on 2 paddy soils.The obtained results showed that,the sorption of Cd2+ 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 Cd2+ 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 Cd2+ sorption respectively.The dominant constituents of SC was clay minerals,which contributed 85% to the sorption,followed by organic matter and iron oxides.