水动力条件下重金属在沉积物上的吸附及其形态分布与转化

以北京近郊通州凉水河底泥沉积物为研究对象,利用环流槽(annular flume)模拟河流水力学条件,研究了重金属(Cr、Cu、Zn和Pb)在上覆水、悬浮颗粒物(SPMs)以及底泥中的交换、分配、形态分布与转化特征。结果表明,在动态水流环境条件下,加入到上覆水体中的重金属离子(5 mg/L)很快被吸附到SPMs上,模拟运行1 h后,上覆水中重金属的浓度(低流速条件下Zn除外),均不到初始值的3%;而SPMs中重金属的浓度在实验初期随着运行时间而降低,并且其浓度在低流速(0.2 m/s)时较高流速(0.35 m/s)条件下高,这是由于"颗粒物浓度效应"所致。在整个模拟运行周期(35 d)内,表层底泥中重金属形态发生了改变。其中,重金属的F4(硫化物+有机物)形态由于其与硫化物结合的形态被氧化而逐渐释放出来,并最终剩下不易氧化的有机物结合形态。与此同时,释放出的重金属通过再分配作用以易解析的F1～F3形态吸附于SPMs及底泥沉积物中,从而导致这3种形态浓度有所升高。

Adsorption and speciation distribution of heavy metals in sediments under hydrodynamic conditions

The transport and distribution of heavy metals (Cr, Cu, Zn and Pb) in water column, suspended particulate matters (SPMs) and the sediment collected from Liangshui River, Beijing were investigated under hydrodynamic conditions using an annular flume. It is found that all heavy metals in soluble phase except for Zn at lower velocity would be less than 3% of their initial concentrations, indicating that heavy metals introduced into the overlying water can be quickly immobilized by SPMs via adsorption under the hydrodynamic conditions. Heavy metal contents in SPMs decreased with time and were measured higher at lower velocity than those at higher velocity, which is probably due to "particle concentration effect". It is found that the F4 phase (sulphidic/organic) of heavy metals decreased as the AVS binding forms were gradually oxidized under the hydrodynamic conditions. At the same time, the released sulfide binding fractions of heavy metals would be redistributed as labile forms (F1~F3) via adsorption onto SPMs, leading to the increase of their respective content during the hydrodynamic experiment.