西辽河不同粒级沉积物对重金属镉的富集特征

为估算随泥沙颗粒迁移的重金属镉(Cd)的质量分数,采用平衡吸附法研究了西辽河不同粒级沉积物对Cd的富集特征。结果表明,不同粒级沉积物对Cd的富集系数从大到小依次为黏粒(6.65)、粉粒(4.13)、细砂(0.92)、粗砂(0.90)。黏粒级沉积物对Cd属于重度富集,粉粒级沉积物对Cd属于中度富集。其原因有二:细粒级沉积物中腐殖质含量明显高于粗粒级;细粒级沉积物中稳结态腐殖质比例较高,稳结态腐殖质的腐殖酸组成以胡敏酸为主,胡敏酸在复合体表面形成了S-HA-Cd三元配合物,增加了黏土矿物表面吸附位。西辽河沉积物在汛期黏粒级和粉粒级冲泻质泥沙所携载的吸附态镉质量分数可分别按沉积物原样的6.65和4.13倍估算。

Enrichment effects of cadmium on the deposits of different size particles in the Western Liao River

The paper is engaged in a study of the enrichment effects of cadmium on the deposits of different size particles in the Western Liao River.As a matter of fact,the river is the main source of heavy metal pollution in the estuaries and continental shelf whereas the heavy metal contaminants are usually existing in the water in the form of dissolved particles for such heavy metals mainly account for the main input form by the rivers.To estimate the mass fraction of cadmium (Cd) on the sediment particles in the River,we have divided the river into five sections,which are respectively located in Yutiangao,Hailasu,Tongliao,Shuangliao,Sanyanjing.In our investigative experiments,we have collected our study samples from the surface sediments (0-10 cm) of the above mentioned sections,and divided them into the following four groups:the clay group,the slit group,the fine and coarse sand groups in accordance with their diameters.And,then,we have done batch experiments of equilibrium adsorption to explore the enrichment features of the different size particle sediments on Cd in the River.The results of our study show that the adsorption behaviors of such sediments on Cd follow the Langmuir isothermal adsorption equation with the enrichment coefficients on Cd various with the difference of the sizes.Nevertheless,while the clay particles exhibit the highest enrichment coefficient (6.65),the other particles of different sizes tend to follow by the groups of slit (4.13),fine sand (0.92),and the coarse sands (0.90).The identification and discrimination results of the organic components in the sediment have shown that the background concentrations of humus tend to be significantly higher in the fine sized sediments than that in the coarse ones.Furthermore,the former prove to contain greater proportion of stable humus than the latter.And,in turn,the humic acid can display a S -HA-Cd structure on its complicated surface with the main components forming stably combined humus.Therefore,the above said features can suggest that fine size sediments may be endowed with greater adsorption face areas for Cd than the coarse ones,but,in contrast,the adsorption capacity of fine size sediment to Cd turn to be much higher than that of the coarse ones.And,finally,the mass percentages of the adsorption state Cd brought about by the clay and silt groups should be estimated equivalent to 6.65,that is,4.13 times of the original sample sediments.