【作者】 邓娅敏；

【导师】 王焰新；

【作者基本信息】 中国地质大学 ， 环境工程， 2008， 博士

【摘要】 内蒙古河套盆地位于我国西北部干旱一半干旱地区,是中国典型的地方性砷中毒病区之一,受威胁人口达30万之多。位于盆地西部的杭锦后旗,是内蒙古自治区最严重的砷中毒旗县,共涉及9个乡镇35个村,高砷暴露人数达七万六千余人,患病人数为1169人,重病区地下水中砷含量在0.35-1.74 mg/l,最高值超过国家生活饮用水卫生标准限定值100多倍。全旗未进行改水的地区继续饮用高砷、高氟及苦咸水的人数达到16.86万,占到全旗人口的半数之多。病区靠近阴山山前自西向东呈带状分布,村民祖祖辈辈饮用高砷水,多数人患有不同程度的砷中毒症状,无法从事正常的生产和生活活动。高砷地下水导致的砷中毒严重危害了老百姓的身体健康,制约了当地的经济和社会发展。国家和地方政府对此高度重视,国家将拿出200亿元解决农村人口的吃水难问题,尤其是砷、氟中毒病区。我国政府已提出,到2010年砷中毒病区要通过改水实现水质达到农村生活饮用水卫生标准。因此,查清高砷地下水成因机制,对于正确指导当前的改水工作、防治砷对环境和人类的危害,促进社会和谐发展,都具有重要的现实意义。地下水砷污染问题是世界性的环境问题,也是当今环境科学领域研究的热点。河套盆地是一个中新生代断陷盆地,经历了新生代以来的各种地质环境的变化,包括构造运动、气候变化、黄河的泛滥改道等。此外,引黄灌溉在该区也有近千年的历史。因此,河套地区的地下水系统受到上述各种天然和人类活动的共同影响,使得砷在含水层中的富集和迁移机制更为复杂。因此,开展河套地区高砷地下水系统地球化学过程的研究,查明水砷中毒区的水文地质背景,掌握高砷水的分布规律及砷在含水层中的赋存形态,分析影响砷迁移富集的各种自然和人为活动要素,对揭示该区高砷水的形成机制有着重要的科学意义。本文通过分析河套盆地的形成及构造演化历史,古气候及地质环境的变化,确定了河套盆地沉积环境演化的基本框架。河套盆地沉积环境的演变过程与地下水系统的形成演化具有重要的内在联系。河套盆地沉积环境的变化和更新世以来的气候变化直接影响了地下水循环和水化学场的演化。从构造活动、古气候变化及古水文地质等角度,在大的时间尺度下探讨地下水系统的结构及沉积环境的变化,了解地下水演化的总体格局对于科学认识地下水系统的地球化学过程,并合理解释地下水系统中As、B等微量元素的来源和富集原因提供重要的背景。以杭锦后旗作为典型研究区,通过大量的野外调查采样及地下水水化学资料的分析,掌握了区内的基本水化学特征:大多数地下水含盐量较高,阴离子以氯离子和重碳酸根离子为主,阳离子以钠离子为主。地下水水化学组成自研究区边缘向中心的低洼地带呈现显著的差异。沿研究区北面的阴山山前和接受黄河水补给的研究区南缘,地下水TDS一般小于1g/1,地下水以Na-（Mg）-HCO₃及Na-HCO₃-Cl型为主;在中部地区,大多为矿化度较高的Na-Cl-HCO₃或Na-Cl型水。值得注意的是,地下水中As、F、B和Br等元素相对富集,在局部地区Ba、U等元素的含量也较高,大大超过国家生活饮用水卫生标准限定值。在高砷地下水中,往往SO₄^2-和NO₃^-含量较低,而HPO₄^-、氨氮、硫化物及溶解性有机碳浓度较高,还伴随着一定浓度的V、Sb、Mo和W。结合研究区水文地质条件、沉积环境以及人为活动等因素,对研究区进行了浅层地下水水环境分区,即山前溶滤区（Ⅰ）、黄河侧渗区（Ⅱ）、采矿影响区（Ⅲ）、还原环境区（Ⅳ）混合叠加区（Ⅴ）、洼地浓缩区（Ⅵ）。其中,山前溶滤区（Ⅰ）处于地下水补给区,地下水水质较好;黄河侧渗区（Ⅱ）受南部黄河水的影响较大,地下水径流条件略好于水流滞缓蒸发强烈的中部地区,其含盐量明显低于盆地中部。采矿影响区（Ⅲ）的地下水靠近东升庙超大型硫化铁矿床一带,由于黄铁矿的氧化导致水中SO₄^2-含量异常。还原环境区（Ⅳ）在靠近山前的平原区,含水层以富含有机质的冲积机质湖积沉积物为主,地下水呈现出显著的还原环境特征。（Ⅴ）混合叠加区位于山前洪积扇的前缘向地形坡度较小的平原区过渡的区域,含水层沉积物变细,透水性变差,地下水的含盐量增加,同时灌渠分布于其中,黄河水通过灌渠渗入地下,淡化混合,水化学类型较为复杂。洼地浓缩区（Ⅵ）位于盆地中心,沉积物颗粒细,且含水层之间有粘土隔水,致使地下水水流不畅,在干旱气候下,强烈的蒸发浓缩作用,使得地下水中TDS及各宏量组分浓度均居全区最高,水质较差,多为氯化物型水和氯化物—硫酸盐型水。决定该区水化学特性的主要水文地球化学过程包括:水解过程、溶解沉淀过程、蒸发浓缩过程、氧化还原过程及混合过程。铝硅酸盐等原生矿物的水解过程（非全等溶解）形成了次生矿物高岭土,并使水中的K、Ca、Na、Mg、HCO₃^-等离子的增加;然而,随着水中TDS和Cl^-浓度的逐渐增加,Ca和Mg在水中富集受到了方解石和白云石或者蒙脱石沉淀过程的限制;干旱少雨的气候条件加上水流滞缓的地下水运动特征,使得蒸发浓缩作用成为水中盐度、Na⁺和Cl^-浓度增加的主要过程。在盆地中部,沉积物含淤泥质及粘土夹层,富含有机质,逐渐形成了还原性较强的地下水环境,地下水中多组氧化还原反应并存,有利于砷的富集。同时研究区内灌渠纵横交错,灌渠里的黄河水与地下水的混合或淡化,使得区内淡咸水错综分布,水化学环境较为复杂。通过微量元素和氢氧同位素地球化学的研究,对地下水系统中的地球化学过程有明显指示作用。表明蒸发浓缩过程对地下水中Na、Cl及微量元素B,Br,As,F的富集具有重要影响;多年的引黄灌溉历史导致地下水位的抬升,加速了表土及浅层地下水盐分的聚集;引黄灌溉对含水层沉积物中某些化学组分（如硼）的释放有重要影响,并与地下水产生明显的混合作用;苏打水环境有利于As、F、B同时富集。随着pH增加,砷会从矿物表面解吸从而进入水相;Ca离子浓度较低的碱性环境利于地下水中的羟基置换含氟矿物中可交换的氟,从而进入地下水:高浓度的HCO₃与硼竞争吸附,使硼从有机质、粘土矿物及金属氧化物表面解吸进入地下水。锶同位素的研究表明靠近山前的地下水受到阴山山前高⁸⁷Sr/⁸⁶Sr背景的基岩溶滤的影响,⁸⁷Sr/⁸⁶Sr比值明显高于其他地下水样。而远离山前的地下水受到灌渠水的混合作用和蒸发作用的共同影响。此外,锶同位素组成指示了区域和局部的水流方向,并证实来自阴山,尤其是靠近多金属硫化物矿床区域的基岩风化是区内地下水中砷的原始来源之一。研究通过对砷中毒病区的调查和高砷地下水水化学类型的系统分析发现:高砷病区靠近阴山山前由西南向东北呈条带状分布。病区居民取水的层位主要位于地下20～35米的深度范围内,砷浓度普遍较高的水化学类型为HCO₃型、Cl-HCO₃型、Cl型及HCO₃-Cl型。TDS平均含量在1500 mg/l,在含盐量更高的水中,砷的浓度不超过50μg/l。高砷地下水的水化学特征表现为:较高的pH和碱度,强的还原环境,水中砷以As（Ⅲ）为主,占溶解的As的比例平均值达到85%,随着地下水中溶解的砷的浓度增加,As（Ⅲ）所占的比例呈增加的趋势;从颗粒态砷占总砷的比例来看,一般都在10%左右,最高超过了30%。此外,地下水中的某些无机组分与砷的浓度分布有密切关系,如磷酸盐、重碳酸盐、Sb、U、W等。这些组分与砷或者有着共同的来源,或者受到某些相同的地球化学过程的控制,如吸附过程或者氧化还原过程等。通过因子分析方法对高砷水化学资料的分析提取出影响高砷地下水化学特征的“盐渍化因子”、“还原环境因子”、“碳影响因子”及“吸附因子”。其中“盐渍化因子”和“碳影响因子”对杭锦后旗高砷地下水水化学特征的影响是本研究与世界其他高砷含水层相比较为突出的特点。杭锦后旗浅层高砷地下水的形成与强烈的还原环境密切相关,表现为水中高浓度的DOC、HCO_3^-、NH_4⁺、硫化物,浓度较低的硝酸盐和硫酸盐,以及局部地区高含量的甲烷气体。局部地下水中甲烷最高达到5107.7μg/l,指示出地下水处于极强的还原环境,这与第四纪湖相沉积环境及盆地的快速下降直接相关。通过对地下水还原环境的表征发现,不同区域的地下水经历着不同的氧还还原过程,还原环境的主要驱动力是多样化的,不同的还原环境指示物可以在同一地区同时富集。多种氧化还原敏感组分在地下水中并存的证据表明地下氧化还原分带存在重叠,这可能与在Fe-S-C复杂的地下氧化还原体系中多种微生物群落在新陈代谢过程中电子供体和电子受体复杂的循环过程有关。通过对研究区高砷钻孔和对照区钻孔沉积物的岩性变化、矿物组成和化学组成的分析,表明二者有显著区别:高砷区沉积物表层都有约10米的粘土或亚粘土覆盖,主要含水层为黑色或黑灰色中细砂层,砂层之间都被数层粘土夹层隔开,细粒的粘土层中含砷量往往较高。沉积物矿物组成以石英、长石、粘土矿物（蒙脱石、绿泥石、伊利石）为主,含有少量的闪石和方解石。不同岩性的沉积物之间矿物组成差别很大。高砷区沉积物中砷的含量在6.8-58.5 mg/kg,平均值达到16 mg/kg,高砷的层位主要位于地下15-25米的位置。对照区沉积物砷含量3-21.8 mg/kg,平均值为9.9 mg/kg。沙海钻孔沉积物中As与Fe、Sb、B、V、总碳、总S在剖面变化规律上较为一致。通过对沉积物中砷赋存形态的表征,从草酸草酸铵和盐酸羟胺选择性提取结果来看,沉积物中约1/3的As与铁的氧化物结合,而与锰的氧化物结合的量较少,仅占2%左右。逐级提取砷形态结果表明除后三步强酸提取的与坚固矿物相结合的砷形态外,强烈吸附态砷（F2）、与无定形氢氧化铁结合的砷（F4）及与挥发性硫、碳酸盐等结合的砷（F3）占主要部分,三者之和占总砷额比例在50%以上。可交换态砷（F1）和与结晶氢氧化铁结合的砷（F5）所占比例很小。砷从矿物表面的解吸和氢氧化铁还原性溶解是控制研究区含水层砷释放的主要地球化学过程,但二者的相对贡献大小在局部地区存在差异。砷在地下水系统中的迁移释放是一个宏观—微观多因素综合作用的结果,其成因既受到宏观上区域地质构造背景、第四纪环境演化及局部水动力条件的影响,又受到微观上沉积物矿物表面特征和地下水环境中各种化学组分及氧化还原环境的控制。区域构造地质背景及沉积环境的演化是高砷地下水形成的先决条件,地下水系统中的水文地球化学过程是高砷地下水形成的控制因素,引黄灌溉对高砷地下水的形成有一定影响。本文的创新点体现在:（1）系统研究了河套盆地西部As、B、F等微量元素的地球化学行为,并阐述了引黄灌溉对研究区水化学场的影响;（2）通过区域地质构造、古沉积环境演化、水文地球化学过程的研究、地下水化学和沉积物特征及砷在含水层中的赋存形态分析,借助同位素技术,从宏观与微观相结合的角度有效揭示了高砷水的形成机制。更多还原

【Abstract】 Hetao Basin（the Great Bend of Yellow River）of Inner Mongolia is located in the arid-semiarid region of northwestern China,which is one of the representative arseniasis-affected areas in China,where more than 300,000 victims of arseniasis.Hangjinhouqi county at the western part of Hetao Basin is the most serious and representive endemic arseniasis area in Inner Mongolia.About 76,000 people exposured in arseniasis area in 35 villages from 9 towns,among them there have been 1169 arseniasis patients.Most groundwater from arseniasis area contained high As with the concentration from 0.35 to 1.74 mg/1,which exceeds maximum contaminant level（MCL）based on the health risk associated with arsenic in drinking water（10μg/l）more than 100 times.Up to date,about 50%residents are still using groundwater with high contents of arsenic,TDS or high fluoride as the only source of potable water.Geographically, arseniasis-affected areas stretch southwest-northeast along Yin Mountains front.Residents have taken high arsenic groundwater as their potable water from generation to generation,most of them suffer from the arseniasis to different extent,which affect their daily life and normal production activity.Long-term intake of the high arsenic groundwaters has caused waterborne arsenic poisoning,which seriously endanger the redients and impede the sustainable development of local economy and society.National and local government attach great importance to this problem,20 billion RMB will be spent to resolve the difficulty on safe potable water in rural area, especially the endemic arseniasis and fluorosis area.Therefore,better understanding the genesis of high As groundwater is of pratically significance in correctly guiding current water source transforming and removal of arsenic from groundwater.Arsenic contamination in groundwater is a serious environmental issue all over the world, which is also the hot topic in environmental study.Hetao basin is a fault basin formed in Mesozoic and Cenzoic,which experienced geological environment changes since Cenozoic, including tectonic movement,climate change,flowage and watercourse change of Yellow River and son on.Furthermore,irrigation using delivered Yellow River water has a long history for thousands of years at Hetao Plain.Groundwater system in Hetao was influenced by both natural conditions and anthropogenic activities,which makes the arsenic enrichment and mobilization more complicated.Thus,the study on major factors and geochemical processes controlling arsenic mobilization in shallow aquifers at Hetao Basin has important scientific meaning,based on the investigation of the regional hydrogeological background and distribution of high As groundwater in the arseniasis area,the speciation analysis of As in both groundwater and sediments,discussion on natural and anthropogenic factors affecting As enrichment and release.The framework of evolution of sedimentary environment in Hetao basin is discussed based on analysis of changes of tectonic movement,paleo-climate,paleo-geology environment.The form and evolution of groundwater in Hetao basin are internally associated with the evolution of sedimentary environment.The changes of sedimentary environment and corresponding climate process directly affect regional groundwater flow and hydrogeochemical evolution.Groundwater system evolution is discussed at long-time scale in view of paleo-climate,paleo-tectonic movement,paleo-geology environment and hydrogeology.The general pattern of groundwater evolution is the most important background for scientifically understanding the geochemical process occurred in groundwater system and for reasonably comprehending the origin and enrichment for some minor elements such as As,B in groundwater system.Hangjinhouqi is selected for our case study.According the analysis of regional hydrogeotogical setting and large amounts of groundwater chemical data,the basic hydrochemical characteristics is summarized as follows:Most water samples have high TDS, with Cl and HCO₃ as the dominant anions and Na as the dominant cation.The chemical composition of groundwaters varied from the margins towards the low-lying areas in the centre of the study area.Along the Yin Mountains front in the northern part of this area,as well as the southern part receiving recharge from the Yellow River,shallow groundwaters are generally of Na-HCO₃ or Na-HCO₃-Cl type,while in the central parts of Hangjinhouqi,mostly Na-Cl-HCO₃ or Na-Cl type.The study area is located in the Hetao fault depression basin and yellow river diverting irrigation plain with arid and semi-arid climate.Due to paleogeography,hydrology,geological Structure and human activity,with dissolution,mixture,evaporating concentration,ion exchange, oxidation and reduction,the components in groundwater transport and enrich,representing different chemical characteristics.Because of the yellow river’s rechannel and irrigation,the fresh water,salt water,high-arsenic water and high-fluorine water distribute interlacedly, hydrochemical enviroment is very complicated.Due to differences of groundwater flow condition and hydrogeological units, hydrochemical classification represents zonation in spatial variation.From fan margin to plain center,the flow condition weaken,water quality changes from fresh to salty,salinity increases gradually,and the groundwater types from fresh bicarbonate water turn to saline chloride-sulfate water.The study area affected by yellow river,salinity is relatively low（TDS＜1.5 g/l）,mainly belong to carbonate water with little bicarbonate-chloride water.According to hydrogeological condition,sedimentary environment and human activities,the shallow groundwater in Hang jinhouqi is classified into six zones:piedmont soluable-filter zone （Ⅰ）,yellow river lateral seepage zone（Ⅱ）,mining affecting zone（Ⅲ）,reductive environment zone（Ⅳ）,mixing zone（Ⅴ）,depression concentrated zone（Ⅵ）.Among them,piedmont soluable-filter zone locates in groundwater recharge region,with HCO₃ as main anion and Na⁺ as main cation in groundwater.Water quality in this zone is good;yellow river lateral seepage zone （Ⅱ）affected southern yellow river,flow condition is better than central part with slow flow and strong evaporation,with HCO₃^- still as main anion and lowest As and Fe contents;groundwater in mining affecting zone（Ⅲ）has abnormal SO₄^2-content,due to oxidation of pyrite,the highest amount could be 1550 mg/l,and the average TDS reaches 2313 mg/l.The hydrochemical type belongs to sulfate-chloride groundwater,reductive environment zone（Ⅳ）is close to piedmont plain,representing strong reductive environment from west to northeast,with the highest contents of DOC,ammonia-nitrogen,sulfide,HPO₄^- and Ba;mixing zone（Ⅴ）locates in transition region from front of proluvial fan to low-slope plain.With hydraulic gradient decreasing,sedimentary in aquifers becomes fine,permeability turns weak,yellow river infiltrates into ground,hydrochemical characteristics become complicated,with chloride-bicarbonate water and bicarbonate-chloride water as main types;depression concentrated zone（Ⅵ）is in depression zone of the plain centre and the front of proluvial fan, with lacustrine deposited fine sand and clay layers between aquifers,which made groundwater flow slow.In arid climate,strong evaporation results into highest contents of TDS and main components,the water type are mainly chloride type or chloride-sulfate type.The main hydrogeochemical process defining the hydrochemical characteristics of the study area includes:hydrolysis process,dissolution-precipitation process,evaporating concentration,ion exchange,mixture,oxidation and reduction.The primary mineral,such as aluminosilicate,hydrolysis process forms secondary mineral kaolinite,and increases the contents of K、Ca、Na、Mg、HCO₃^-;However,with the TDS and Cl^- increasing,the enrichment of Ca and Mg is limited by calcite and montmorillonite precipitation;drought climate with slow flow makes the evaporating concentration as the main process increase TDS,Na⁺ and Cl^-.In the middle of the plain,the sediment contains silt and clay interlayer,rich in organic components,forming strong reduction environment,which is helpful for arsenic enrichment.The mixture of yellow river and groundwater lead to complex hydrochemical environment.Hydrogeochemical behavior and accumulative mechanism of several important trace elements,such as B,Br,F was discussed,especially the genesis of groundwater salinization and the relationship between soda-water environment and high concentration of boron,arsenic and fluoride.With the stable isotope analysis（hydrogen oxygen isotopes and strontium isotope）,the dissertation identified the main factors controlling the hydrochemical characteristics of the study area,the ratio of strontium isotope revealed the flow direction and sources direction of regional groundwater.The main understandings are as follows:1).The study on hydrochemisty and hydrogen oxygen isotopes of the study area suggestes that evaporating concentration played an important role in accumulation of Na,Cl and some trace elements,such as B,Br,As,F.2).The genesis of groundwater salinization is associated with geological structure,evolution of paleoclimate,variation of quaternary sedimentary environment,groundwater flow condition and human activities.3).Sodawater environment is benefitfle for simutaneous accumulation of As,F, B.With pH increasing,arsenic will come into groundwater desorbing from minerals;alkaline condition with low concentration of Ca is helpful for hydroxy displacement in groundwater;high concentrtion of HCO₃ makes boron easier to desorbe from organic matters,clay minerals and metal oxide.4).Long-term irragation from yellow river leads to groundwater table increasing, which speeds up salinity accumulation in surface soil and shallow groundwater;besides, geochemical data of trace elements and isotopes verify that irrigation from yellow river playes a significant role in releasing some chemical element（such as boron）and mixing effect.5).The study on strontium isotope suggest that piedmont groundwater affected by bedrock lioxiviation with high ⁸⁷Sr/⁸⁶Sr background value,⁸⁷Sr/⁸⁶Sr value is higher that other samples,which may affected mainly by mixing process and evaporation effect.In addition,the components of strontium isotope reveal the regional flow direction and verify that the original source of arsenic in groundwater is bedrock weathering which is close to polymetallic sulfide deposit.The formation of high arsenic groundwater in Hang jinhouqi is relative to strong reductive environment,representing high level DOC,HCO₃^-,NH₄⁺,sulfide,methane gas in some region and low content of nitrates and sulfate.Forming reductive environment is inseparable with basin tectonic activities and change of sedimentary environment.Quaternary in Hetao basin is composited by river-lake sedimentary system.In middle pleistocene,giant thick lake sediments was formed in basin.Mudstone rich in organic matter and humus developed well in north of the basin,besides,a lot of buried herbaceous plants provied material sources for methane bacteria growth.Hetao basin experienced fault-developing stage and depression sedimentation stage, while Hang jinhouqi located in the centre of sedimentation,with 5000m-thick pliocene formation and 1.85 mm/a sedimentary speed.The fast sedimentation leaded to the geochemical environment which was helpful for accumulation and biochemical reaction of organic matter.High-arsenic groundwater mainly represent As（Ⅲ）,accounting to 41～98%of total soulable As,average value 85%.This also verified that the groundwater is in strong reduction environment.It should be mentioned that the particle arsenic in groundwater of the study area is up to 172.5μg/l,more than 1/3 water samples the particle arsenic over 50μg/l.The proportion of particle arsenic to total arsenic is about 10%,with the highest exceeding 30%.Based on quantitive hydrochemical data,using factor analysis method,the disstertation identified four factors controlling hydrochemical characteristics in high-arsenic groundwater: salinization factor,reducing environment factor,carbon effecting factor and absorption factor. Among them,the the first three factors affect obviously.Salinization factor and carbon effecting factor is theprominent characteristics different from other high arsenic aquifers.The hydrogeochemical characteristics are quite different from those from other high-As groundwater regions under reducing conditions,such as Bangladesh,West Bangal and Hungary,as well as Datong basin in Shanxi province and Huhhot Basin in Inner Mongonia of China,due to extremely strong evapotranspiration resulting from the arid climate,also affected by regional geology,sedimentology,palaeoclimate evolution,paleohydrogeology,water-rock interaction and human activities.The evolution of high-As shallow groundwater in Hangjinhouqi with high content of DOC、HCO₃^-、NU₄⁺、and sulfide,low content of nitrates and sulfates and highly concentrated methane in some area,which reaches 5107.7μg/l is closely correlated to the intense reducing environment caused by quaternary lacustrine sediments and rapid subsidence of the basin.According to the characterization of the reducing environment in groundwater,different districts have been through different oxidation-reduction processes.The driving force for reducing environment is varying and different indicators can concentrate in the same region at the same time.Two cored boreholes（Shahai and Tuanjie village）were drilled in hydrogeologically distinct areas with the depth of 50 m.The observed range of total As concentrations in sediments are 7.7-34.6 mg/kg and 6.8-58.5 mg/kg,respectively.The concentrations correlate positively with Fe oxides.High sulfur content is detected in the sediments of Shahai,up to 0.194%assocaiated with high As concentration（34.6 mg/kg）with the depth of 25 m.Another borehole was drilled for comparison in Erdaoqiao in the south of our study area,where the concentration of As in groundwater is quite low（2μg/l）.The range of As concentration in the sediments is 3-21.8mg/kg, with the average value of 9.9 mg/kg.Up to one third of arsenic is ammonium oxalate-extractable and taken to be associated largely with Fe oxides.Only 2%of arsenic is hydroxylamine hydrochloride-extractable and taken to be associated with Mn oxides.Selectively sequentical extraction procedure has been used to investigate sediment As associations.Results show that approximately 35%of total As extracted by PO₄（strongly absorbed As）in sediments,also higher percentage of Oxalate-extractable As（As incorporated in amorphous iron oxides）,concentrated HNO₃ and H₂O₂ extractable As（As associated with sulfides and organic matter）,HCl-extractable As （targeting acid volatile sulfides,carbonates and amorphous metal oxides）.The release of As into solution is believed to be by desorption coupled with reductive dissolution of the Fe oxide minerals.The release of As in groundwater system is an integration of macro-micro multifactor;its cause of formation is affected macrocosmically by regional geological structure,quaternary environment revolution and hydraulic dynamics,and also microcosmically by mineralogical properties of sediments and chemical constituents in groundwater.The former factor is the precondition for the formation of high-As groundwater and the latter is the controlling factor. Besides,irrigation using deliverd Yellow River water impose some influence on the formation of high-As groundwater to some extent.The major advances achieved in this dissertation are as follows:1)trace elements geochemical behavior in Hetao basin such as As,F,B was systematicly studied,the influence of irrigation using deliverd Yellow River exerting on the hydrogeochemistry was also discussed;2) the formation mechanism of high-arsenic groundwater was analyzed from macro to micro scope on the basis of hydrogeology,regional geological structure,paleosedimentary evolution, hydrogeochemical and sedimentary characteristics study and arsenic speciation analysis.更多还原