采矿业污染河流底泥及河漫滩沉积物的粒径组成与砷形态分布特征

Particle size distribution and arsenic partitioning in sediments from a river polluted by mining

采用连续提取法分析了刁江底泥和河漫滩沉积物中砷的形态变化规律及其与沉积物粒径组成的关系.结果表明,刁江流域底泥和河漫滩沉积物中As含量分布存在差异,底泥中As主要赋存在63～170μm粒级颗粒中,河漫滩沉积物中As主要赋存在<63μm粒级颗粒中.底泥和河漫滩沉积物中砷主要以铁合态、钙合态和残渣态的形式存在,且残渣态比例相对较高,表现出典型的尾砂污染特征.底泥中残渣态砷(Res-As)组成比例总体较高,主要赋存在63～170μm粒级颗粒中,而洪水水位河漫滩沉积物中Res-As组成比例相对较低,这与不同沉积物中硫化态砷的氧化反应差异有关.对于中下游河段,底泥和中水水位河漫滩沉积物中Res-As总体上呈逐渐降低的趋势,铁合态砷(Fe-As)组成比例的分布与Res-As呈相反的趋势.

Sequential extraction was used to investigate arsenic（As） fractionation in sediments from the Diaojiang River,which has been polluted by mining.The particle size distribution of sediments and its effect on arsenic partitioning were also analyzed.Arsenic was found to be highly concentrated in the 63 ～ 170 μm size fraction in bottom sediment,while it was mainly hosted in the 63 μm size fraction in floodplain sediments.Arsenic sediments mainly present as Fe-As,Ca-As and residual As（Res-As） forms.A high proportion of Res-As in sediments showed the typical mining tailing contamination in the river.The bottom sediment had a relatively high proportion of Res-As,which was mainly concentrated in the 63 ～ 170 μm size fraction,while the proportion of Res-As in floodplain sediment at the flood water level was lower,possibly due to different sulfide As oxidation in different exposure environments between the sediments.In the middle and lower reaches of the river,the proportion of Res-As in sediments in the bottom and median water level floodplain declined downstream,while Fe-As showed the opposite pattern.