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1.
膨润土负载纳米铁去除地下水中六价铬研究   总被引：4，自引：1，他引：3  
李晨桦  陈家玮 《现代地质》2012,26(5):932-938
随着人民生活水平的提高和城市化进程的加快,有机污染物及重金属高强度场地污染对人类健康、生态环境及社会安全构成了严重威胁。地下水中的重金属Cr(Ⅵ)污染逐渐受到重视,纳米零价铁可以有效地将六价铬还原成三价铬,使其沉淀固定下来,从而将污染源区的污染物消减固定,防止其向周围扩散。然而由于纳米铁颗粒微小,易被氧化,极易团聚,自身活性受到限制,因此,纳米铁的分散性、稳定性、良好活性研究至关重要。采用低成本环境友好型粘土矿膨润土作为负载材料制备膨润土负载纳米铁（B-NZVI）,批实验和柱实验研究B NZVI去除模拟地下水中Cr(Ⅵ)。结果表明：(1)自制的膨润土负载纳米铁个体呈球形,呈分散状负载于膨润土;(2)相同铁含量的B-NZVI处理Cr(Ⅵ)的效率远大于纳米铁,还原反应符合伪一级反应动力学模型,表观速率常数K随着B NZVI初始浓度的减小而减小;(3)B NZVI在石英砂柱中基本无迁移,适用于点源污染,Cr(Ⅵ)穿透曲线为B-NZVI的实际应用提供了理论和实验基础。  相似文献   

2.
由于工业废物的不合理排放,大量的重金属污染物Cr(Ⅵ)进入地下环境,严重威胁着人类健康和生态环境。Cr(Ⅵ)在地下水环境中高度易迁移的特性,造成其污染修复上的困难,亟待一种绿色、经济、有效的阻截方式提高地下水对Cr(Ⅵ)的阻控能力。研究利用焦亚硫酸钠原位还原地下水中的Cr(Ⅵ),产生Cr3+作为黄原胶交联剂,形成凝胶阻截屏障,探究了各类成分对凝胶时间、黏度变化的影响及凝胶屏障对含水层的阻截效果,得到如下结论：(1)在Cr(Ⅵ)质量浓度达到200 mg/L的体系中,质量分数0.4%的黄原胶溶液在1.5 h内即可形成具有一定机械强度的凝胶;(2)凝胶具有耐盐性,适用于常见含水层,2.5～5 g/L的Na+和K+对凝胶起促进作用;(3)注入型凝胶阻截屏障能够大幅降低中砂介质的渗透系数至1×10-7 cm/s,满足地下水阻截需求。注入型凝胶屏障的形成无需引入有害物质,阻截结束后注入型屏障可经生物作用自然降解,不会长期改变含水层水力条件。研究成果可为Cr(Ⅵ)污染地下水中凝胶阻截屏障的构筑提供理论基础。  相似文献   

3.
León valley, located in the Mexican state of Guanajuato, has a long history (35+ a) of Cr contamination of groundwater and surface water. Here data are presented for Cr, major ion and trace element concentrations and Cr stable isotope measurements of groundwater in a heavily contaminated aquifer in Buenavista, where Cr ore processing residue piles (COPRPs) located in a chromate production factory are the main source of Cr. The aquifer directly beneath the factory still retains very high Cr(VI) concentrations (∼121 mg/L). Ongoing pump and treat remediation is keeping the high concentration plume confined to the factory area and immediate vicinity, though Cr is also detected at some distance away. Chromium isotope data of the aquifer directly under the factory show only a small increase in δ53Cr (+0.33‰ to +0.81‰) and indicates minimal reduction of Cr(VI) to Cr(III). Very high Cr(VI) concentrations have possibly overwhelmed natural reductants and furthermore fresh Cr(VI) was being leached into the groundwater from the COPRP. From just one year of Cr isotope data it is clear that more aggressive remediation techniques will be necessary to reduce or eliminate the contamination. The fringes of the Cr plume have substantially lower concentrations and can be partially explained by transport of the main plume or mixing between waters from the nearby landfill and highly contaminated waters from QC. While the source of Cr at the fringes of the plume could be attributed to a source from the nearby landfill instead of the main plume from the factory, the Cr stable isotope data show enrichment in the heavier isotopes and point to varying amounts of reduction. Isotopic enrichment seen between 2007 and 2008 along the fringe may indicate either reduction or less unreacted Cr(VI) is being transported to the fringes. In either case some potential for natural attenuation of Cr(VI) exists at the western margin of the plume with the landfill playing a role.  相似文献   

4.
通过对焦作地区浅层地下水中铬(Ⅵ)污染物分布特征进行调查,分析了研究区浅层地下水中铬(Ⅵ)的污染机理,并运用Visual MODFLOW建立地下水流模型及溶质运移模型,模拟预测了浅层地下水中铬(Ⅵ)的迁移规律。结果表明:研究区浅层地下水铬(Ⅵ)污染严重,污染源是位于老君庙西南方向的焦作某电厂堆灰场,主要原因是露天堆放的粉煤灰中的铬(Ⅵ)污染物在长期淋滤作用下下渗污染含水层。气候条件、包气带岩性、地下水化学环境以及人为因素等也间接使浅层地下水铬(Ⅵ)浓度升高;模拟结果显示在未来的五年时间内,受地形和地下水动力场的影响,浅层地下水中铬(Ⅵ)的迁移方向与地下径流方向一致,沿大沙河水流方向上扩散速度更快,污染区域面积逐渐增大。   相似文献   

5.
Tropical peat soils present higher ash content than those generated at temperate climate areas. Therefore, this study evaluated the characteristics of a Brazilian organic soil (OS), commercialized as peat, as well as its capacity in removing Cr(VI) from contaminated waters. The OS is composed of 35.5 wt% of organic matter and 56 wt% of inorganic fraction (ash), which is formed by minerals and phytoliths rich in silica (29.2 wt%) and alumina (23.6 wt%). The Cr(VI) removal tests were carried out in batch and column systems using OS and solutions of Cr(VI) prepared with distilled water and groundwater. Batch tests revealed that the organic substances in the OS caused the reduction of Cr(VI) to Cr(III), with an efficiency depending on solution pH. At pH 5.0 the Cr(VI) removal was 0.45 mg g?1 in 24 h; whereas at pH 2.0, this removal increased to 1.10 mg g?1. Since this redox reaction is very slow, the removal of Cr(VI) at pH 5.0 increased to around 2 mg g?1 after 5 days. The removal of Cr(VI) was more effective in the column tests than in the batch test due to the greater solid/solution ratio, and their half-lives were 4.4 and 26.2 h, respectively. Chemical analysis indicated that Cr(VI) was reduced by the humic substances of OS, followed by the precipitation and/or adsorption of Cr(III) into the organic and inorganic components, as anatase. The presence of Cr(III) increased the stability of anatase structure, avoiding its transformation into rutile, even after being heated at 800 °C/2 h.  相似文献   

6.
Hexavalent chromium is a soluble, mobile, and highly toxic metal ion in groundwater. Adsorption by permeable reactive barriers (PRBs) with special sorbent is a common method to remove hexavalent chromium. A series of experiments have been performed to remove hexavalent chromium in groundwater under PRB with modified chitosan. Therefore, in this paper, the authors first estimated adsorption characteristics of the modified chitosan in a column test, and then calibrated the PRB adsorption parameters in a sandbox test, and finally designed an optimal width, length, and depth of the PRB with the same reactive media in a three-dimensional aquifer. The results showed that the modified chitosan might be a potential adsorption medium. The design schemes can meet the water quality standard of 0.1 mg/L Cr(VI). Heterogeneity of dispersion is a crucial factor when designing the PRB. Therefore, the design of the PRB structures can be appropriate and serve as reference for groundwater remediation.  相似文献   

7.
Groundwater dominated lakes are an important feature of many landscapes. Their sediments are a particularly valuable source of paleoenvironmental information in semiarid regions where perennial lakes may otherwise be scarce. Where groundwater and lake composition are favorable, carbonate mineral precipitation, evaporative concentration of lake water, and microbial processes can combine to strongly deplete dissolved Ca relative to influent groundwaters. The authigenic carbonate flux (ACF) can then become limited by water column cation availability and thereby be coupled to groundwater inflow rates and aquifer recharge. Here we analyze sedimentary records from two marl-producing, groundwater-controlled lakes and demonstrate a link between one-dimensional ACF and the Palmer Drought Severity Index (PDSI), a measure of land surface wetness. In a restricted outflow lake with high-carbonate alkalinity, ACF is enhanced during historically wet climatic periods in response to increased aquifer recharge rates. ACF in this lake declines during droughts. A neighboring dilute lake with a high rate of groundwater outflow shows comparatively weak coupling between ACF and PDSI history. Ionic chemistry, carbonate mineral equilibria, and δ13C patterns of dissolved inorganic carbon show that the sensitivity of the ACF signal depends on the degree of evaporative evolution of lake water and the mineral saturation state of the water column under conditions of stratification and ice cover.  相似文献   

8.
The discharge of industrial effluents containing hexavalent chromium can be very harmful for the environment. Therefore, Cr(VI) should be removed from contaminated water, and especially from wastewater, to prevent its discharge into the environment. This study is aimed at analyzing the factors that affect the removal of Cr(VI) with the use of almond green hull and ash adsorbent. The effects of pH (2–10), adsorbent dose (2–24 g/L), Cr(VI) concentration (10–100 mg/L), exposure time (1–60 min), and temperature (5–50 °C) were examined. The surface morphology, pore size of adsorbent surfaces were characterized with SEM, EDX, FTIR. Maximum removal occurred at pH = 2. Results showed that the removal yield increased with the rise of exposure time and temperature. The data indicate that due to limited site on adsorbent surface, the removal efficiency decreased as initial Cr(VI) concentration increased. When the adsorbent dose was increased, the removal yield increased in the case of the bioadsorbent as well; however, in the ash adsorbent, there was an increase followed by a decreasing trend. The study highlights that almond green hull can be more efficient than its ash in the removal of Cr(VI) from aqueous solution. As a general result of study, it can be argued that almond green hull bioadsorbent and the obtained carbon are able to remove Cr(VI) from aqueous solutions; thus, they can be used as efficient and economical substitutes for existing adsorbents like activated carbon, for the removal of chromium from polluted aqueous solutions.  相似文献   

9.
The effective influence of industry or ultramafic rocks by natural processes to soil, plants and groundwater contamination by chromium, which is often a subject of debate, was investigated for the case of the Assopos basin, Greece. The Neogene Assopos basin, is mainly composed by Tertiary and Quaternary sediments of more than 400 m thick and is characterized by brittle type deformation (fault zones, faults). Chromium in soil, ranging from 67 to 204 ppm, is mostly hosted in chromite, Fe-chromite, Cr-bearing goethite and silicates.Special attention was given to the plants, which are a major source of organic matter that serves as the driving force for Cr(VI) reduction. The increase of the Fe, Mn and Ni contents, with the increasing Cr content in the plant-roots, in particular at the external parts of roots and those of bulb-type plants, suggest reduction and immobilization of Cr(VI) and that redox reactions play a significant role to the translocation processes from root to shoot.Groundwater samples from the Assopos aquifer showed a wide spatial variability, ranging from <2 to 180 ppb Crtotal content [almost same to the Cr(VI)-values] despite their spatial association. The presence of Cr(VI)-contaminated groundwater at depths >200 m is attributed to a direct injection of Cr(VI)-rich industrial wastes at depth rather than that Cr(VI) is derived from the Assopos river or by the interaction between water and Cr-bearing rocks. The heterogeneous distribution of Cr in groundwater may be related with the intense neotectonic deformation, as is exemplified by several sharp tectonic contacts between sediment types, while the Cr content in soil is mostly depend on the transported chromite grains.  相似文献   

10.
Highly reactive nano-scale biogenic magnetite (BnM), synthesized by the Fe(III)-reducing bacterium Geobacter sulfurreducens, was tested for the potential to remediate alkaline Cr(VI) contaminated waters associated with chromite ore processing residue (COPR). The performance of this biomaterial, targeting aqueous Cr(VI) removal, was compared to a synthetic alternative, nano-scale zero valent iron (nZVI). Samples of highly contaminated alkaline groundwater and COPR solid waste were obtained from a contaminated site in Glasgow, UK. During batch reactivity tests, Cr(VI) removal from groundwater was inhibited by ∼25% (BnM) and ∼50% (nZVI) when compared to the treatment of less chemically complex model pH 12 Cr(VI) solutions. In both the model Cr(VI) solutions and contaminated groundwater experiments the surface of the nanoparticles became passivated, preventing complete coupling of their available electrons to Cr(VI) reduction. To investigate this process, the surfaces of the reacted samples were analyzed by TEM-EDX, XAS and XPS, confirming Cr(VI) reduction to the less soluble Cr(III) on the nanoparticle surface. In groundwater reacted samples the presence of Ca, Si and S was also noted on the surface of the nanoparticles, and is likely responsible for earlier onset of passivation. Treatment of the solid COPR material in contact with water, by addition of increasing weight % of the nanoparticles, resulted in a decrease in aqueous Cr(VI) concentrations to below detection limits, via the addition of ⩾5% w/w BnM or ⩾1% w/w nZVI. XANES analysis of the Cr K edge, showed that the % Cr(VI) in the COPR dropped from 26% to a minimum of 4–7% by the addition of 5% w/w BnM or 2% w/w nZVI, with higher additions unable to reduce the remaining Cr(VI). The treated materials exhibited minimal re-mobilization of soluble Cr(VI) by re-equilibration with atmospheric oxygen, with the bulk of the Cr remaining in the solid fraction. Both nanoparticles exhibited a considerable capacity for the remediation of COPR related Cr(VI) contamination, with the synthetic nZVI demonstrating greater reactivity than the BnM. However, the biosynthesized BnM was also capable of significant Cr(VI) reduction and demonstrated a greater efficiency for the coupling of its electrons towards Cr(VI) reduction than the nZVI.  相似文献   

11.
天然成因的高氟地下水是世界范围内备受关注的环境问题和饮用水安全问题。前人对高氟地下水的形成过程已开展了大量研究,但是对于高原盆地复杂水文地质条件下不同类型含水层组(第四系松散层含水层、基岩裂隙或岩溶含水层以及新生代古近纪以来的碎屑岩含水层)高氟地下水的分布和形成过程尚不明确。本文以化隆—循化盆地为研究区,通过采集、测试研究区内的各类地下水样品,分析研究区内不同类型含水层中地下水的化学特征及同位素特征。结果表明,高氟地下水(1.007.73 mg/L)主要分布在沿黄河的河谷区域和巴燕低山丘陵区域的泉水和潜水中以及深部的承压水中,在垂向上高氟地下水无明显分布规律。接受黄河水入渗补给的河谷潜水中氟离子浓度较低,补给黄河的河谷潜水中氟离子浓度较高。贫钙富钠的弱碱性苏打型水有利于地下水中氟的富集。泉水和潜水中氟主要来源于萤石的溶解,而承压水中氟除了来源于萤石外,还来源于其他含氟矿物。对于潜水和第四系松散层泉水,蒸发浓缩作用促进了地下水中氟的富集。另外,阴离子竞争吸附作用、阳离子交换吸附作用是泉水(第四系松散层泉水和基岩裂隙泉水)和潜水中氟元素富集的主要原因,而承压水中氟离子浓度受竞争吸附作用影响较大,阳离子交换吸附作用影响较小。研究成果可为化隆—循化盆地低氟地下水的勘查和开发提供科学依据。  相似文献   

12.
Anomalous concentrations of Cr(VI) occur in groundwaters of the Adamantina Aquifer, in a large region in the western state of São Paulo, sometimes exceeding the potability limit (0.05 mg L−1). To identify the possible geochemical reactions responsible for the occurrence of Cr in groundwater in Urânia, borehole rock samples were collected in order to carry out mineralogical and chemical analyses. In addition, multilevel monitoring wells were installed and groundwater samples were analyzed. Analyses of the borehole rock samples show the occurrence of a geochemical anomaly of Cr in the quartzose sandstones (average concentrations of 221 ppm). Chrome-diopside is one of the main minerals contributing to this anomaly, having an average Cr content of 1505 ppm. Sequential extraction experiments indicated weakly adsorbed Cr in the order of 0.54 ppm, and this quantity is enough to provide the Cr concentrations observed in groundwater. Groundwaters from the monitoring wells proved to be stratified, with the highest concentrations of Cr(VI) (0.13 mg L−1) being associated with high redox and pH values (over 10) and high concentrations of Na. Geochemical reactions that may explain the release of Cr from the solid phase to groundwater involve the release of Cr(III) from minerals (like chrome-diopside and Cr-Fe hydroxide), followed by oxidation of Cr(III) to Cr(VI), probably related to the reduction of Mn oxides present in the aquifer. Then cation exchange occurs and dissolution of carbonates which increases the pH of groundwater, resulting in the desorption and mobilization of Cr(VI) into groundwater.  相似文献   

13.
李爽  文章  朱棋  刘慧  杨舒婷 《地球科学》2022,47(11):4176-4183
为使含水层中苯胺污染的原位修复过程高效安全且不产生二次污染,提出了一种电化学-水动力循环下的井内生物反应器修复地下水中苯胺的方法.在水动力循环系统的驱动下,评价了苯胺在水动力循环系统的挥发情况并且通过电化学手段提供氧气,井内生物反应器提供修复载体,在砂槽模拟的含水层体系中开展井内生物反应器降解苯胺的修复实验,并对生长曲线及含水层中苯胺修复进行了模拟.289 h的修复使体系内苯胺平均浓度从298 mg/L降低到132 mg/L,去除率为56.5%.运行过程中,监测点苯胺平均浓度在48 h内去除速率为1.10 mg/（L·h）,48~72 h内去除速率为0.85 mg/（L·h）,72 h到289 h内苯胺去除速率维持在0.65 mg/（L·h）,氧化降解逐步减弱.该过程符合Michaelis-Menten方程,反应速率为:-6.71×10-7/（15+t）2.该修复系统是基于地下水动力循环技术的改进,有望应用于有机污染地下水修复.   相似文献   

14.
以天然细砂为微生物来源,模拟研究了乳化植物油强化原位生物修复中高浓度Cr（Ⅵ）污染地下水的可行性,考察了修复效果及修复过程中地下水质变化及产物的稳定性。结果表明,反应77 d后,Cr（Ⅵ）质量浓度分别从20.0、30.0、50.0、80.0、110.0 mg/L降低到0.0、5.8、19.0、43.6、65.8 mg/L,去除率分别为100.0%、80.7%、61.9%、45.5%、40.2%。反应后介质中Cr形态分析表明,其主要以能在自然条件下稳定存在的铁锰结合态和有机结合态形式存在。此外,随反应进行,实验体系逐渐呈弱酸性环境,pH为5.80~6.70。当Cr被完全还原后,体系会发生异化铁还原,Fe（Ⅱ）质量浓度逐渐升高,最高可达117.0 mg/L,最终形成二价铁矿物。综上所述,天然细砂介质中的土著微生物能够利用乳化植物油强化并还原地下水中的中、高浓度Cr（Ⅵ）,且产物能够在自然状态下稳定存在,修复过程对地下环境的影响较小。  相似文献   

15.
Pannonibacter phragmitetus BB was utilized to treat hexavalent chromium [Cr(VI)] contaminated water. Cr(VI) concentration of the contaminated water (pH 10.85) was 534 mg/L. With the inoculum size ranging from 1 to 20 %, P. phragmitetus BB completely reduced Cr(VI) within 27 h when the initial medium concentration exceeded 20 g/L. The lag time of bio-reduction by Cr(VI)-induced cells was 24 h, which was longer than the non-Cr(VI)-induced cells. Under the agitation condition, an obvious bio-reduction lag phase existed and Cr(VI) was completely reduced within 24 h. However, the lag phase was not observed under the static condition, Cr(VI) was reduced continuously after inoculation and Cr(VI) was completely reduced after 27 h incubation. The main chromium components after Cr(VI) reduction were Cr(OH)3, Cr2O3 and CrCl3. The results of this study are fundamentally significant to the application of P. phragmitetus BB in the treatment of Cr(VI) contaminated water.  相似文献   

16.
A small-scale field test was initiated in September 1994 to evaluate the in situ remediation of groundwater contaminated with chromate using a permeable reactive barrier composed of a mixture of zero-valent Fe, sand and aquifer sediment. The site used was an old chrome-plating facility located on a U.S. Coast Guard air base near Elizabeth City, North Carolina. Dissolved chromate concentrations were reduced to less than 0.01 mg/L via reduction from Cr(VI) to Cr(III) as a result of the corrosion of the Fe. As the Fe corrodes, pH increases, oxidation-reduction potential declines, dissolved oxygen is consumed, and Fe(II) is generated. Mineral phases formed as a result of the Fe corrosion include ferrous sulfides and various Fe oxides, hydroxides, and oxyhydroxides.  相似文献   

17.
The possibility of using volcanic ash soils (VAS) or Andisols as a low-cost and natural adsorbent is investigated in this study for the removal of Cr (VI) from synthetic wastewater. Andisols can be used as adsorbent because they are characterized by the presence of non-crystalline secondary minerals such as allophane and imogolite that show variable charge characteristics and have the ability to retain cations and anions. The adsorption of Cr on to two VAS from Mt. Isarog and Mandalagan (B-Horizon), Philippines, was carried out at ambient temperature using batch adsorption studies. The effects of different parameters such as amount of adsorbent, contact time, initial Cr concentration and pH of the solution were investigated. The results showed that the VAS from Isarog is more effective in the removal of Cr than in Mandalagan. The maximum removal efficiency of the Isarog soil for a Cr concentration of 10mg/L reached 89% with a dose of 20 g/L at a moderately acidic pH of 3. The Mandalagan soil on the other hand could remove only 65% at the same pH conditions and parameters. The difference in the removal of the two soils may be attributed to their physico-chemical properties in which the Isarog soil has higher clay content, porosity and lower bulk density. Isarog soil has fine particles with higher surface area and more active non-crystalline minerals and thus has higher removal efficiency than Mandalagan soil. Based on the results, the use of VAS from Isarog appears to be economical and an alternative to commercially available adsorbents for the removal of Cr from contaminated wastewater.  相似文献   

18.
 The Hadejia–Nguru Wetlands are annually inundated flood plains in semi-arid northeastern Nigeria. The area has a unique ecosystem that forms a natural barrier against the encroachment of the Sahara desert. Both the rich wetland vegetation and local farmers using shallow tube wells depend on a groundwater mound (with a water table less than 6 m below the surface) that is present in the unconfined aquifer under the flood-plain area. Using well records (1991–97) and a hydrogeologic profile based on piezometers that were monitored for two years, it is shown that recharge through the annually inundated flood plains is the source of the groundwater mound. Maintenance of the groundwater-recharge function of the flood plains depends on wet-season releases from two large upstream dams. On the basis of a water-budget method, the mean (1991–97) wet-season unconfined groundwater recharge in the flood-plain area between Hadejia and Nguru and in the immediate vicinity (1250 km2) is estimated to be 132 mm (range, 73–197 mm). Outflow from the unconfined flood-plain aquifer to the unconfined upland aquifer is approximately 10% of the wet-season flood-plain recharge. The unconfined groundwater outflow from the flood-plain area can provide a significant contribution to the present-day rural water supply in the surrounding uplands, but it does not offer much potential for additional groundwater abstraction. In addition to outflow to the upland aquifer (∼14 mm), the distribution of the annually recharged water volume of the shallow flood-plain aquifer is (1) domestic uses (3 mm), (2) small-scale irrigation (∼15 mm), and (3) evapotranspiration ( 1 100 mm). Along the hydrogeologic profile, the recharge in the upland (i.e., outflow from the unconfined flood-plain aquifer and possibly diffuse rain-fed recharge) is in balance with the water uses (i.e., domestic uses, groundwater outflow, and evapotranspiration). The absence of a seasonal water-level trend in the two piezometers in the upland indicates that no rain-fed recharge occurs through preferential path-way (macropore) flow. Received, June 1998 / Revised, November 1998, January 1999 / Accepted, January 1999  相似文献   

19.
鲁西南地区高氟水分布规律与成因分析   总被引：1，自引：0，他引：1  
地方性氟中毒是我国北方地区最为典型的地方病之一,查明高氟地下水的空间分布及其成因是除氟改水、防治氟害的前提。通过对鲁西南地区不同层位地下水水质分析结果及水文地质、地质条件等多个环境影响因素的综合分析,查明了鲁西南地区高氟水的空间分布规律,并分析了影响浅层和深层高氟水形成的环境因素。浅层高氟水呈片状分布于洼地、缓平坡地等地势较低的区域,占鲁西南地区总面积的47%,大部分地区高氟水氟离子含量为1.2～2.0 mg/L,局部大于4.0 mg/L,其形成受气候、地质环境、地形地貌特征及水化学环境等多个因素的影响,成因类型为溶滤-蒸发浓缩型。深层高氟水具有水平分带性,占鲁西南地区总面积的65%,大部分高氟水氟离子含量为2.0～4.0 mg/L,氟离子含量分布与晚更新世沉积相带呈现很好的相似性,推测其为地质历史时期形成的古地下水。  相似文献   

20.
The present study was conducted to delineate the pollution vulnerability of the Quaternary aquifer in two areas, Imbaba and Shobra El-Khima, near Cairo, Egypt. Environmental isotopes combined with hydrochemistry were used for this purpose. The groundwater in the Imbaba area (average total dissolved solids about 900 mg/L; sodium/chloride, sulfate, and bicarbonate water types) is more mineralized than groundwater in the Shobra El-Khima area (average total dissolved solids 500 mg/L; calcium and sodium/bicarbonate water type). A high nitrate content and significant mineralization in the groundwater are probably due to contamination of recharge to the aquifer by irrigation drainage, deteriorated sewage networks, and septic tanks. The deuterium and oxygen-18 compositions of the groundwater are depleted compared to Nile River water, which is the main source of aquifer recharge. This less isotopically enriched water probably represents older Nile water recharge that flooded the region before construction of the Aswan High Dam in 1963, or it is a mixture of a young water and originally deposited paleowater that was in deeper horizons at a time of cooler and more humid climate. Intensive pumping has moved the paleowater higher in the aquifer. Groundwater in the Shobra El-Khima area has higher residence time, based on the tritium concentration, than groundwater in the Imbaba area. The percentage of the isotopically depleted water equals 75% in the Shobra El-Khima and 35% in Imbaba, and the thickness of the clay cap above the aquifer is 38 m in Shobra El-Khima and 20 m in Imbaba. These factors are indicative of the rate of recharge to the aquifer and were used to evaluate the pollution vulnerability in the two areas. Electronic Publication  相似文献   

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