渤海湾表层沉积物重金属在不同粒级有机-矿质复合体中的分布

采用超声分散法分离沉积物中不同粒级有机-矿质复合体,研究了渤海湾沉积物中Pb,Cd,Cr等重金属的污染及其在不同粒级有机-矿质复合体中的分布.结果表明,3种重金属含量总体上随着复合体粒径增大而减小.X射线衍射(XRD)结果显示,随着沉积物粒径的增大,主要来自原生矿物的石英和长石等岩石结构物质的含量增加,但这些物质中的重金属含量较低.渤海湾表层沉积物中重金属污染主要发生在以次生硅酸盐矿物及硅、铁、铝等氧化物或氢氧化物为主的细粒沉积物上,细粒样品由于其较大的比表面积和富含有机质的特性,通过吸附、沉淀、离子交换等,导致所含重金属含量较高.粘粒复合体中Pb含量是粗砂中的2.3倍,Cd是粗砂的3.8倍,而Cr是粗砂的2.8倍.

Distribution of Heavy Metals in Different Fractions of Organo-Mineral Aggregates in Surficial Sediment of Bohai Bay

Based on the organo-mineral aggregates in various fractions from surficial sediments by ultrasonic dispersion in water followed by sedimentation,the distribution of heavy metals Pb,Cd and Cr in the organo-mineral aggregates of the sediment has been investigated.It is shown that the amounts of the three metals generally decrease with the increase of grain sizes of sediment.The X ray diffraction(XRD) analysis shows that the amount of quartz and feldspar increases when the grain size of sediment increases,and the heavy metals remain in a relatively low level,which mainly comes from the primary mineral.It is indicated that the heavy metals in surficial sediments of Bohai Bay mainly exist in secondary silicate mineral and fine fraction deposits,which primarily consist of oxide or hydroxide of Si,Fe and Al.The fine fraction samples have relatively large specific areas and rich organic matter content,which results in high levels of heavy metals through adsorption,deposition and ion exchange activities.The levels of Pb,Cd and Cr in clay aggregate are respectively 2.3,3.8 and 2.8 times higher than that of coarse aggregates.