氧化铁/水界面Cd吸附研究:CD-MUSIC模型模拟

The adsorption of Cd to iron oxide/water interface:The CD-MUSIC modeling

以针铁矿和赤铁矿为研究对象,研究p H、Cd浓度等对不同类型氧化铁Cd吸附行为的影响,构建氧化铁Cd吸附的CD-MUSIC模型,并分析氧化铁表面Cd的形态分布特征。结果表明:氧化铁表面Cd吸附量和吸附密度均随p H升高、Cd浓度增大而增大。针铁矿对Cd的吸附量和吸附密度显著高于赤铁矿。CD-MUSIC模型能准确模拟Cd在氧化铁/水界面的吸附特征,拟合结果表明Cd主要以(Fe OH)2Cd+1、(Fe OH)2Cd OH0两种形态吸附在氧化铁表面,其在针铁矿和赤铁矿表面亲和常数(lg KCd)分别是7.3、12.8和6.1、11.0。Cd的形态分布受p H的影响显著,但几乎不受Cd浓度的影响。p H 5.0和7.0时,针铁矿的Cd形态分布与赤铁矿相似,(Fe OH)2Cd+1是主要吸附形态。p H 9.0时,针铁矿上超过80%的Cd以(Fe OH)2Cd OH0形态存在。赤铁矿上,Cd浓度较低时,(Fe OH)2Cd+1是主要吸附形态;随Cd浓度增大,(Fe OH)2Cd+1和(Fe OH)2Cd OH0所占比例均逐渐接近50%。

In this study,the effect of pH and Cd concentration on the adsorption of Cd to the goethite and hematite was investigated by the pH-edge adsorption experiments and the CD-MUSIC modeling with the calculation of speciation distribution.The results showed that the amount and density of the Cd adsorption to the goethite was higher than that to the hematite,and with the increasing of the pH and Cd concentrations it increased for both goethite and hematite.The CD-MUSIC model taking into account the species(FeOH)2Cd+1 and(FeOH)2 CdOH0 could describe the adsorption of Cd to the iron oxide satisfactorily.The affinity constant of the(FeOH)2Cd^+1 and(FeOH)2CdOH0 were 7.3,12.8 and 6.1,11.0 for goethite and hematite,respectively.The calculation of the CD-MUSIC model indicated that the speciation distribution of Cd depended on the pH significantly.At pH 5.0 and 7.0,the speciation distribution of Cd for goethite was similar with that of the hematite.It was independent of the Cd concentrations and the(FeOH)2Cd^+1 was the primary species.At pH 9.0,higher than 80%of the Cd was bound by the goethite with the species(FeOH)2CdOH0.For the adsorption of Cd to the hematite,at low Cd concentration,the primary contribution of the species was the(FeOH)2Cd^+1.With the increasing of the Cd concentration,the fraction of these two species closed to 50%gradually and the contribution of the(FeOH)2CdOH0 become more important and dominate to the hematite.