【作者】 杨素珍；

【导师】 沈照理； 郭华明；

【作者基本信息】 中国地质大学（北京） ， 地下水科学与工程， 2008， 博士

【摘要】 本文选择浅层地下水砷异常较为严重的内蒙古河套平原作为研究区,在资料分析、野外调研和室内实验测试的基础上,开展了对研究区水文地球化学和高砷地下水形成机理的研究,主要内容如下:1.分析了研究区地下水环境演化过程。河套盆地是一个新生代断陷盆地,自更新世早期以来经历了由湿冷-湿冷/暖-全新世干旱的古气候变化,盆地的发展经历了湖泊全盛期-收缩期-消亡期-河流发育期,沉积环境演化为湖积/河积交错沉积。根据14C年龄测试结果,9～23m地层属于上更新统上部地层,而这个时期,气候趋于干旱,湖水退缩,残留湖泡形成。湖泊在消亡过程中,高度浓缩的富含砷的湖水被埋藏、保存到沉积物的空隙中,成为区域地下水的一部分,经长期演化形成了今天的高砷水,也是当地居民的取水层位。2.揭示了高砷地下水的水化学特征。平原浅层地下水中砷的浓度范围为0.6～572μg/L。高砷水以高浓度的Fe、Mn、HCO3-和S2-,以及低浓度的NO3-、SO42-为特征。pH值介于7.01～8.43,大部分为弱碱性水,氧化还原电位为-153～98 mV,As(III)是As的主要形态,平均达到As总量的75%,Fe含量较高,最高达5.90 mg/L。3.综合研究了3个代表性钻孔资料,得出:高砷地下水通常埋藏于由灰黑色细砂构成的强还原的冲湖积含水层中。沉积物中总As含量为7.3～73.3 mg/k(g平均值为18.9 mg/kg)。与总As和总S含量的弱相关性相比,总As与Fe、Mn的总量表现出稍强的相关性。系列提取试验表明具化学活性的As主要吸附于Fe/Mn氧化物上,达到3500μg/kg。还原条件下As的迁移取决于Fe/Mn氧化物的还原性溶解和As还原性解吸。4.首次进行了关于地下水颗粒物对砷行为影响的研究。43个地下水水样的化学分析结果显示未经过滤的水样中大多数元素(Ba、Co、Mn、Mo、Ni、V、Sr、Mg、Ca、Na、K)的浓度与经0.45μm滤膜过滤的水样中的基本一致,两者比率接近1.00。尽管SI方解石、SI白云石大于零,但在地下水中它们也可以小型胶体颗粒形式存在。在经0.45μm膜过滤的水样中Cd、Pb、Fe及Al的浓度明显小于未经过滤水样。尽管少量As、Cu、Zn可被大颗粒无机胶体吸附,但是这些元素主要还是与粒径小于0.45μm的有机配位胶体结合。5.对研究区有代表性的36个地下水样的27个化学成分指标进行了R型聚类分析。建立了As与其他化学成分之间的多元线性回归模型,并进行了相关性分析。对As(III)和Eh进行了曲线回归分析。更多还原

【Abstract】 The Hetao Basin of Inner Mongolia is a typical endemic arseniasis area, where high As groundwater has universally been found since 1990s. This study has investigated hydrogeochemistry and mechanism of As mobilization in the shallow aquifers, based on intensive data analysis, field works and lab experiments. The main achievements having been reached are shown as follows.1. The basin is one of the Cenozoic rift basins, which has experienced a series of paleo-climate change since Early Pleistocene, including wet cold, wet-warm, and arid (Holocene). A former lake was believed to develop at the early stage of late Pleistocene (around 120 ka BP), and vanish during the Holocene. With the vanishment of the lake, the early Yellow River occurred. It results in a complex sedimentary environment with fluvial and lacustrine sediments interlacing each other. 14C dating shows that shallow aquifer sediments (9-23 m below land surface) developed during late stage of late Pleistocene, during which climate was arid and the lake shrank. The lake water became a part of pore water in the sediment and is gradually evolved into modern shallow groundwater, which is the main supply water for residents’living.2. Chemical characteristics of high As groundwater have been evaluated. Arsenic concentrations in shallow groundwaters from the Hetao Basin of Inner Mongolia range between 0.6 and 572μg/L. They are characterized by high concentrations of dissolved Fe, Mn, HCO3-, and S2?, and low concentrations of NO3- and SO42-. Groundwater pH is near-neutral to weak alkaline (7.01-8.43). Redox potentials range from ?153 to 83 mV. In the reducing groundwaters, inorganic As(III) accounts for around 75% of total dissolved As. Fe concentrations are up to 5.90 mg/L3. Systemically investigation has been carried out for three representative boreholes. It indicates that high As groundwaters usually occur in shallow aquifers with dark grey or black fine sand, which deposited in the lacustrine reductive environment. Total As contents in the sediments are observed to be 7.3–73.3 mg/kg (average of 18.9 mg/kg). The total As is mildly-strongly correlated with total Fe and total Mn, while a quite weak correlation exists between total As and total S. It is found in the sequential extraction that chemically active As is mainly bound to Fe-Mn oxides, up to 3500μg/kg. The mobilization of As under reducing conditions is believed to include reductive dissolution of Fe-Mn oxides and reduction of adsorbed As.4. Effect of groundwater particles on As behavior has been performed. Chemical analysis of 43 groundwater samples shows concentrations of most elements (Ba, Co, Mn, Mo, Ni, V, Sr, Mg, Ca, Na, K) in unfiltered samples are well correlated with those in <0.45μm fraction, and the ratios between them are close to 1.00. Although saturation indices for calcite and dolomite are greater than 0, they would possibly exist as small size colloids in groundwater. Concentrations of Cd, Pb, Fe, and Al in <0.45μm fraction are mostly less than those in unfiltered fraction. Arsenic, Cu, Zn and Cr are grouped into another species. These elements could mainly be associated with organic-complexing colloids with particle size less than 0.45μm, although As, Zn and Cu would partially be carried by large-size inorganic colloids.5. R cluster analysis has been carried out in terms of 27 chemical compositions of 26 representative groundwater samples. Multiple linear regression was established between As and other components. Curve regression analysis shows that As(III) is a negative exponential of Eh.更多还原