白银矿山水体和沉积物中重金属及其化学形态分布特征

ANALYSIS ON SPECIATION AND TRANSPORTATION OF HEAVY METALS IN WATER AND SEDIMENT IN BAIYIN MINE

白银铜多金属矿山矿业活动产生的大量废水排入东大沟，对东大沟周围农田和黄河白银段水体造成了严重危害。采用等离子原子发射光谱（ICP—AES）和BCR法连续提取过程对东大沟水体和沉积物中重金属总量和各化学形态进行分析，结果表明水体和沉积物中Cd、Cu、Pb、Zn高度富集。水体中除Pb外，Cd、Cu、Zn含量超出国家标准的几倍到几十倍，随着河流流向呈显著降低趋势。沉积物中不同重金属化学形态分布有很大差异，尾矿坝坑底泥和黄河泥沙中重金属化学形态分布主要以弱酸提取态和残渣态为主，而东大沟沉积物中重金属化学形态呈现不同的分布特征，Pb以可还原态为主，Zn以残渣态为主，Cd以残渣态为主，其次为可氧化态，Cu以可氧化态为主。沉积物中Cd和Pb地积累指数均大于5，达到极强污染程度，Cu和Zn地积累指数在3～5之间，也不同程度达到强到极强污染。

Mining activities in the Baiyin copper-polymetallic ore deposit, which has been exploited for fifty years, have caused severe impact on the surrounding environment. The bulk waste water from the mining process containing such heavy metals as Cd, Cu, Pb and Zn has been drained into Dongdagou at Baiyin, which has contaminated the farmlands and the Yellow River in the Baiyin segment. The heavy metals in water and sediments in Dongdagou were analyzed using ICP-AES. The results showed that the concentrations of Cd, Cu, and Zn in water are a few to ten times higher than the background values. The concentrations of heavy metals in the sediments increased dramatically, and decreased in the flow direction. Analysis of the speciation of heavy metals in the sediments by the BCR sequence extraction procedure indicated that the distribution of chemical forms for each heavy metal was different, and even the distribution of different forms of the same metal were different. The distribution of the chemical forms of heavy metals are similar in both tailing dam and Yellow River, but different in Dongdagou, where Pb is mainly present in the reducible fraction, Zn is mainly in the residual fraction, Cd is mainly in the residual fraction and oxidizable fraction, and Cu is mainly in the oxidizable fraction. The contamination levels of Cd and Pb in the sediments are higher than those of Zn and Cu according to the results obtained by the geo-accumulation index method.