渭河杨凌—兴平段表层沉积物中重金属的环境地球化学研究

【作者】 翟萌；

【导师】 卢新卫；

【作者基本信息】 陕西师范大学 ， 环境科学， 2010， 硕士

【摘要】 渭河杨凌—兴平段位于渭河陕西流域中游,是陕西重要的工农业城镇。近年来随着经济的发展,渭河资源与区位优势愈显突出。由于环保力度的加大,许多高污染、高耗能企业从一线大城市向杨凌、武功、兴平这些中小城镇转移,更加重了这里的环境压力。本文采集了渭河杨凌—兴平段9个采样段面的表层沉积物样品,通过实验得出了该区域表层沉积物的理化特征；运用X-Ray荧光光谱仪分析了沉积物中主要重金属的含量水平；采用修正的BCR四步连续提取法揭示了各重金属的赋存形态；通过机械筛分实验详细研究了沉积物的粒径组成及不同粒径范围内重金属的富集和形态特征差异,并探讨了沉积物理化指标、重金属含量水平、赋存形态之间的相互关系,以此来研究渭河杨凌—兴平段表层沉积物的环境地球化学特征,以期为合理利用渭河资源,有针对性的治理渭河污染提供科学合理的理论依据。本研究的主要结论如下：(1)渭河杨凌—兴平段表层沉积物的各项理化指标分别为：pH值为7.972,电导率值为404μs/cm,烧失量平均值为1.96%,低频磁化率、高频磁化率和频率磁化率分别为60.7×10-8m3/kg、59.3×10-8m3/kg和2.45%,粒度分析结果显示,该河段沉积物主要以粉粒、沙粒为主。沉积物常量元素组成与地壳丰度基本一致,这说明了河流沉积物主要来源于地壳岩石的风化作用,反映了地壳原始矿物组成。(2)渭河杨凌—兴平段表层沉积物重金属含量均值分别为Cu 17.7 mg/kg, Pb 18.9 mg/kg, Zn 72.7 mg/kg, Cr 100.2 mg/kg, Ni 21.1 mg/kg, Co 33.9 mg/kg, Mn 484 mg/kg。其中Cr、Co和Zn的均值含量明显超出了陕西土壤背景值。从重金属的空间分布特征来看,距离工业密集分布近的断面重金属含量相对偏高,城镇区域断面重金属含量高于偏远乡村地区,以工业为主的区域重金属含量高于新兴高科技农业区域。(3)渭河杨凌—兴平段表层沉积物重金属都以残余态为主要存在方式,重金属的直接危害性(主要指弱酸提取态)大小为：Co (42.47%)>Mn(36.09%)>Pb(24.40%)>Ni(11.69%)> Zn(9.35%)>Cu(6.13%)>Cr(2.85%)>Fe(2.25%);重金属的潜在危害性(主要指可氧化态与可还原态之和)大小为：Fe(39.37%)＞Pb(38.60%)> Cu(28.66%)> Zn(22.49%)> Ni(21.73%)> Mn(17.66%)>Co(14.57%)>Cr(9.66%);重金属的环境生态风险(主要指弱酸提取态、可还原态与可氧化态之和)大小为：Pb(62.99%)＞Co(57.04%)> Mn(53.75%)> Fe(41.62%)> Cu(34.79%) >Ni(33.41%)＞Zn(31.84%)>Cr(12.51%)。(4)渭河杨凌—兴平段表层沉积物主要集中在<75μm的给范围内,pH值和烧失量随着粒径的减小有略微增大的趋势；电导率值在较大粒径沉积物中含量较高；沉积物较高的磁化率值出现在小粒径<50μm和大粒径>900μm的范围中。沉积物重金属总含量主要集中在<75μm的粒径范围中。Cr在细小沉积物中浓度含量较高,Pb、Mn、Ni、Cu、As、Fe的较大值都分别分布在<50μm、150-300μm和>900μm这三个粒径范围内；Co元素浓度含量在较小粒径和较大粒径范围含量较高,在中等粒径含量较低。(5)渭河杨凌—兴平段沉积物重金属形态在不同粒径上的分布差异不明显,Cu、Pb、Cr、Ni和Mn在不同粒径范围内同一形态所占比例基本一致,Zn元素随着粒径的增大“非稳态”含量逐渐减小；Co元素在<75μm的细小颗粒中主要以“稳定态”存在,而在75-150μm和>150μm的较大颗粒中则主要以“非稳态”存在。(6)渭河杨凌—兴平段表层沉积物重金属间的相关性表明：Fe、Mn与其它各种重金属都有较好的相关性,Pb、Cu、Zn和Ni之间的相关性较高；Cr和Co与其它元素相关性较弱,而且呈现出负相关趋势。Pb、Cu、Zn、Ni、Mn、Fe、As都与CaO、K2O、MgO、A12O3呈现出显著的相关关系;与Na2O、SiO2和pH多呈现出负相关关系；聚类分析显示：在B1、B2和B3态中,Cu、Pb、Cr、Ni的聚类关系均最近,在B4态中Mn和Zn与其它各重金属分别各为一类。(7)通过对比渭河各城市段表层沉积物重金属环境地球化学特征,结果表明Cu、Pb、Ni和Mn元素含量空间分布规律一致,即在杨凌兴平段浓度最低,而在宝鸡、咸阳和西安等区域浓度相对较高。Cr与Zn元素的分布规律相同,即最大值都出现在杨凌兴平段,其它各段含量水平基本一致。渭河不同河段所受重金属危害程度大小顺序为宝鸡段>西安段>咸阳段>杨凌兴平段。总体而言,重金属高含量多出现在工业密集分布、人口众多的大城市河段,但个别重金属元素在偏僻地区的异常含量应引起高度重视。更多还原

【Abstract】 Yangling-Xingping Section of Wei River Located the Middle reaches of Shaanxi, which is an important industrial and agricultural town . In recent years, With the development of economic, resources and geographical advantages about Wei River are shown more and more prominent. Because of increasing the degree of environmental protection, many high-polluting and high energy-consuming enterprises move from the bigger cities to the smaller ones, such as Yangling、Wugong、Xingping and increase the environment pressure of these Region. This article collected 9 Sampling profile of surface mixed sediments, By experiment shows the physical and chemical characteristics of surface sediments, using X-Ray Fluorescence Spectrometer analyse the levels of main heavy metals in the sediments, making use of a modified four-step BCR sequential extraction method reveals the chemical speciation of heavy metals, adopting mechanical sieving experiments study the size component and the diversity of heavy metals enrichment and morphological characteristics in different size sediments. Discussing the relationship about the physical and chemical indicators, heavy metal concentration levels and the chemical speciation.These provided a scientific basis for making use of resources and targeted treatment pollution about Wei River. The main conclusions of this study are as follows:(1) Physical and chemical indicators of Yangling-Xingping section in the surface sediments are that, the average of pH value, conductivity, loss on ignition,_low-frequency magnetic susceptibility, high-frequency magnetic susceptibility and frequency magnetic susceptibility are 7.972,404μs/cm, 60.7×10-8m3/kg,59.3×10-8m3/kg and 2.45%. The results of size analysis show that the main compositions of sediments are silt and sand. Constant element is consistent with crustal abundance. This shows that the river sediments are derived from the weathering of crustal rocks and reflects the original mineral composition of the crust.(2) The average content of heavy metals, such as Cu, Pb, Zn,Cr, Ni,Co and Mn are 17.7 mg/kg, 18.9 mg/kg,72.7 mg/kg,100.2 mg/kg,21.1 mg/kg,,33.9 mg/kg and 484 mg/kg. Where Cr, Co and Zn were significantly exceed the mean soil background value in Shaanxi Province. From the view of the spatial distribution about heavy metals, the high content of heavy metals are found in Industrial concentration areas, the heavy metals content of sediments from Urban area were higher than those in remote rural areas, Industrial areas were higher than high-tech agricultural zone.(3) The heavy metals mainly exist by residual speciation in the surface sediments from Yangling-Xingping section in Wei River. The direct harmful of heavy metals(Weak acid extraction speciation) are in the following order:Co(42.47%)> Mn (36.09%)>Pb (24.40%)>Ni(11.69%)>Zn(9.35%)>Cu(6.13%)>Cr(2.85%)>Fe(2.25%);The potentially harmful of heavy metals(reducible and oxidable speciation) are in the following order: Fe (39.37%) >Pb(38.60%)>Cu(28.66%)>Zn(22.49%)>Ni(21.73%)>Mn(17.66%)>Co(14.57%)>Cr(9.66%); Environmental and ecological risks of heavy metals(Weak acid, reducible and oxidable speciation) are in the following order: Pb(62.99%)> Co(57.04%)>Mn(53.75%)> Fe(41.62%)>Cu(34.79%)> Ni(33.41%)>Zn(31.84%)>Cr(12.51%).(4) Sediments are mainly concentrated in the range of<75μm._pH value and loss on ignition with decreasing particle size has a slightly increasing trend. Higher levels of the conductivity Concentrate in the bigger size. Higher magnetic susceptibility values appear in the small particle size of< 50μm and the large size of>900μm. The total content of heavy metals in sediments concentrate in the size range of< 75μm. High density of Cr focus on the small size, The larger values of Pb, Mn, Ni, Cu, As and Fe are distributed in the size range of<50μm,150-300μm and>900μm.The higher density of Co concentrate on the smaller and larger size range, but the lower density of Co concentrate on the medium size range.(5) Heavy metals chemical speciation are no significant difference in different size.The same speciation of Cu, Pb, Cr, Ni and Mn appear the same scale in the different size range. With the increasing size of sediments, the "Non-steady speciation "of Zn becomes decrease. Co mainly exists by "steady speciation"in the size of<75μm, but the "Non-steady speciation " mainly exists in the size range of 75-150μm and>150μm.(6) The correlation of heavy metals in the surface sediments show that Fe, Mn and other heavy metals have a good correlation, Pb, Cu, Zn and Ni have a higher correlation, the correlation of Cr, Co and other elements are not only week, but the trend shows a negative correlation. Pb, Cu, Zn, Ni, Mn, Fe, As show a significant correlation with CaO, K2O, MgO, Al2O3 and show a negative correlation with Na2O, SiO2 and pH value. Cluster analysis showed that Cu, Pb, Cr and Ni have a nearest clustering relations in the speciation of B1,B2 and B3. Mn and Zn are different with other heavy metals in the speciation of B4.(7) By comparing Environmental geochemistry with different city sections in the surface sediments of Wei River, the results show that there are the same spatial distribution rule with Cu, Pb, Ni and Mn, that means The lowest concentration appear in Yangling- Xingping section while the higher concentration appear in the city of Xi’an, Xianyang and Baoji. There are the same distribution rule with Cr and Zn, that means the maximum level appears in the Yangling-Xingping section and the other sections keep the same level. The Harmful of heavy metals in the different sections of Wei River are in the following order: Baoji> Xi’an> Xianyang>Yangling-Xingping._Overall, high levels of heavy metals always appear in the big cities where the industry is concentrated and the population are numerous. However, the unusual content of individual heavy metals in the remote areas should be high regarded.更多还原