【作者】 闫倩；

【导师】 戴霜；

【作者基本信息】 兰州大学 ， 环境工程， 2011， 硕士

【摘要】 土壤是人类环境的重要组成部分,也是地表环境系统中物质与能量迁移和转化的重要载体,在维护和保持地球表层环境系统的自然平衡和环境质量中起着重要作用。钢铁厂排放的废水、废气、废渣严重污染周围的土壤,因此对钢铁厂造成的土壤污染的监测与研究引起了广泛关注。本文通过测定兰州某钢铁厂附近的土壤Pb、Zn、Cu、Fe和Mn金属元素含量及磁化率,结合岩石磁学参数(等温剩磁、热磁曲线、磁滞回线)分析,取得了如下成果：1.Pb、Zn、Cu、Fe和Mn元素含量变化趋势大致相同,并且均在最表层土壤中含量最大。金属元素之间显著相关,相关系数为0.6～0.86,表明金属元素来源相同。金属污染现状评价结果显示：垂直方向上,污染主要集中在2cm以上土壤；水平方向上,污染程度受主导风向和污染源影响,钢铁厂上风向属轻度污染,下风向2km范围内多属中度污染(其中污染物落地最大浓度点位于采点A9附近(距炼钢炉1.2km),属重度污染),2km至最远采点(3.7km)属轻度污染。2.高、低频磁化率值变化趋势一致,均从下向上升高,在深度20-5 cm,磁化率值基本不变,在5～2 cm,磁化率值逐渐升高,2 cm处磁化率值快速升高,达5 cm处的1.45倍,而在2～0 cm,磁化率值骤然增大,在0.5～0cm处最大,是5 cm深度以下样品的3.5倍,表明深度2cm以上的土壤中有外来磁性矿物的输入。磁化率在水平方向上的变化与金属元素的变化特征一致。磁化率和频率磁化率呈负相关关系,表明表层土壤的磁化率增高是钢铁厂排放污染物造成的,而且主要集中在深度2～0cm；岩石磁学测量表明外来输入的磁性矿物主要为假单畴-多畴粒级的磁铁矿,而背景土壤中磁性矿物则为赤铁矿和磁铁矿。3.磁化率和重金属元素含量显著相关,指示磁性矿物和金属元素具有类似的来源。基于环境磁学方法比常规化学方法相对简便、快速、经济、不破坏样品且无二次污染,本文提出了磁化率浓集因子(S)这一新的土壤污染监测评价参数,并按照金属元素污染判断指标和磁化率变化特征,提出了判断污染程度的磁化率浓集因子指标体系(分别为Si≤1属无污染、1<Si≤10属轻度污染、10<Si≤20属中度污染、Si>20属重度污染),为快速而经济地进行土壤污染监测与评价提供新的指标。更多还原

【Abstract】 Soil is an important part of environment, it plays an important role in migration and transformation of matter and energy. However, waste which comes from steel factories pollutes the air, water and soil seriously. Therefore studying the soil pollution adjacent the steel factory is practically significant. With the advantage of simple, fast, inexpensive, non-destructive measurement, environmental-magnetic methods have been widely used in environmental pollution studies. Based on the measurement of the contents of Pb, Zn, Cu, Fe, Mn and magnetic susceptibility of the soils adjacent a steel factory near Lanzhou city, together with the rock-magnetism parameters of representative samples (including isothermal remanent magnetization (IRM), magnetic remanent coercivity (Bcr), saturation magnetization (Ms) and saturation remanent magnetization (Mrs), magnetization unblocked temperature), this paper evaluates the pollution of the soils in this region, and proposes a new indicator-the magnetic susceptibility concentration.The contents of the measured heavy metals are significantly increased in the topsoil. And the similar fluctuant trend depth-dependent for each measured heavy metal with a correlation coefficient of 0.66～0.86 is found in the measured profile. All these show that the anthropogenic dust input into the topsoil. This suggests that the steel factory is probably the predominant cause for strong metal signals. Pollution is mainly found in the downwind direction area, of which the strongest part is in a range of 2 km and a depth of 2 cm. All the individual pollution indexes and Nemerow indexes of heavy metals of topsoil are higher than 1, pollution indexes of sampling A9 of topsoil are higher than 3, which show that the topsoil is contained seriously.The magnetic susceptibility in uppermost soil horizons (0～2cm) increases significantly relative to the deep soil, and gradually decrease at 2～5 cm. The magnetic susceptibility of soils below 5 cm has not been disturbed, thus it can refer to the background values of soil here. Negative correlation between magnetic susceptibility and frequency indicates that high susceptibility values of the topsoil are caused by the steel factory emissions. The variation of the susceptibility is consistent with the measured heavy metals, indicating that the pollution area estimated by the magnetic susceptibility corresponds to that by the heavy metals. Rock-magnetism measurement show that magnetite and hematite exist in the deep soils (below 5cm levels) and the magnetite predominates in the polluted topsoil samples. The plot of Day indicates the grain sizes of magnetite are mainly pseudo-domain and a few of multi-domain.A strong correlation between the magnetic susceptibility and metals indicates they have the same source. Here we propose magnetic susceptibility concentration factor (S) as a new indicator to evaluate the magnitude of the soil pollution, whose criteria calculated from the correspondent index system of Nemerow, i.e. Si≤l referring to non-pollution,1<Si≤10 to slight pollution,10<Si≤20 to moderate pollution and Si>20 to heavy pollution. It is expected that the S would be used as an effective indicator to monitor and evaluate the magnitude of soil pollution instead of the chemical parameters.更多还原