土壤中铁的氧化物和氢氧化物对砷的吸附

测定了加钠Ａｓｈａｎｔｉ矿区土壤中天然铁氧化物和氢氧化物的砷浓度，发现其变化范围为２￣３５ ６００ｍｇ／ｋｇ。在ｐＨ值中中性的 富氧化粘土的土壤中以及尾矿的表面氧化部分，砷在这两相中的浓度最高，达３５ ６００ｍｇ／ｋｇ。在高酸性土壤或处于还原条件的地方，缺氧化物和氢氧化物中砷的浓度较低（最高为４３３ｍｇ／ｋｇ）。还观测到富有机制土壤的矿物中这两个相的砷浓度更低。在所研究的样品中非晶质铁的氢氧化物中     

原子荧光光谱法测定土壤和水系沉积物国家标准物质中砷

用王水浸提法和硝酸-高氯酸-氢氟酸混合酸消解法处理样品,原子荧光光度光谱法测定土壤和水系沉积物国家标准物质样品中的砷。方法检出限为0.02 mg/kg。两种前处理方法砷的测定值与标准值相符,均可以满足土壤和水系沉积物样品中砷含量的测定要求。单纯测定样品中砷含量时,王水浸提法更好;如果在测定砷同时还要测定其他元素,则可以选用混合酸消解法。     

南韩两个废弃的尾矿中砷和重金属的浓度

未经过处理的废弃尾矿，由于有毒元素，诸如砷（As）和铅（Pb）的扩散，可能导致对生态系统的危害。植物修复是大型矿山废石堆治理使用的方法。采集植物种类样品是在南韩两个废弃的金矿（Au）中进行的。根据美国环保署3050方法（US-EPA，1996）对植物样品进行分类，然后用电感耦合等离子体质谱法（ICP-MS）进行分析。得出植物的浓度和生物累积因素并总结了含有一种以上金属的植物种类。建议生长在Myoungbong尾矿的白杨树是对大规模金尾矿治理具有再种植的潜力。从Duckum尾矿采集的欧洲蕨中得出，砷的累计远远低于记载的超量堆积的植物累积的量，但是，通过每天相关的饮食，可能会对居民的健康造成长期不利的影响。     

西南表层岩溶带土壤中砷的迁移规律实验与模拟

岩溶地下河是我国西南地区的重要水源,工业生产过程中产生的砷污染物,除通过落水洞等直接进入并污染地下水外,还会在表层岩溶带溶缝、溶隙内吸附、滞留及富集,并在特定条件下再次迁移,成为"稳定次生污染源".以广西某砷污染事件为例,采用窄缝槽物理模型装置进行砷的动态吸附、解吸实验,并结合地球化学模拟研究砷污染物在表层岩溶带土壤中的迁移规律.实验结果显示表层岩溶带对砷的吸附以物理吸附（扩散过程）为主,相比吸附过程而言解吸速率则显得缓慢,而酸溶液相比去离子水可促进砷的解吸过程.地球化学模拟结果表明土壤矿物中以针铁矿对砷的吸附贡献最大,而酸溶液通过溶蚀针铁矿等矿物削弱对砷的吸附能力.因此在西南岩溶地区,表层岩溶带系统一旦纳入砷污染物,则解吸过程缓慢,易形成砷污染物的滞留、富集;而酸雨作用下砷的解吸、迁移过程加快,则会提高地下水系统的污染风险.      

水介质中多金属海水矿瘤砷吸附的研究

本文详细报告了水介质中多金属海水矿瘤吸附砷（Ⅲ）和砷（Ⅴ）的研究结果。海水矿瘤的元素成分主要由铁、锰、硅（含有微量铝）、铜、钴和镍。海水矿瘤对砷（Ⅴ）的吸附取决于水介质的pH值，而砷（Ⅲ）的吸附不受水介质pH值的影响。砷吸附数据大体上符合兰米尔（Langmuir）等温线。砷（Ⅲ）和砷（Ⅴ）的动力学数据满足一种假定的二级动力学模型。海水矿瘤去除砷的效果取决于砷的初始浓度。当水介质中砷（Ⅲ）的初始浓度为0．34mg／L或砷（Ⅴ）的初始浓度为0．78mg／L时，海水矿瘤的最佳剂量为0．74mg／g。砷（Ⅲ）的吸附一般取决于离子环境。除PO4^3-以外，砷（Ⅲ）的吸附不受阴离子的影响，但受阳离子的影响显著。另一方面，砷（Ⅴ）的吸附受阴离子的影响显著，但不受阳离子的影响。试验结果表明，海水矿瘤吸附的砷（Ⅲ）主要为内部结核复合物，而吸附的砷（Ⅴ）为部分内部结核和部分外部结核复合物。当水介质的pH值为2-10时，吸附的砷（Ⅲ）和砷（Ⅴ）的解吸附较小。当水介质的pH值为6或更高时，海水矿瘤能被用于吸附地下水中的砷（Ⅲ）和砷（Ⅴ）物种。海水矿瘤被成功地用于去除采于印度西孟加拉邦的6种受砷污染地下水样中的砷（6种地下水样中砷的浓度范围为0．04-0．18mg／L）。     

土壤中不同形态砷的分析方法

选取磷酸作为提取剂,比较了超声和水浴两种方法辅助提取土壤中不同形态的砷,离子色谱一氢化物发生原子荧光光谱联用法(IC-HGAFS)测定砷的4种形态,即As(Ⅲ)、As(Ⅴ)、MMA (甲基胂酸)和DMA(二甲基胂酸)。从测定结果可以看出,水浴的提取效果明显高于超声的提取效果。土壤中砷以无机态为主,而无机态砷又以As(Ⅴ)为主,没有检测到有机砷。测定土壤中各种形态砷的加标回收率为72.0%～105.4%,相对标准偏差(RSD,n=5)为2.61%～8.19%。     

改性磁铁矿对水体中砷的吸附特性研究

经过酸化改性后的天然磁铁矿,由于比表面积和内部结构发生变化,从而表现出很好的除砷性能,进一步研究其对水体中砷的吸附特征,为实际工程应用提供数据是十分必要的。本文对经0.5 mol/L盐酸浸泡、150℃温度下灼烧10 min的改性磁铁矿吸附砷的特征进行了表征,绘制吸附速率曲线图。吸附影响因素实验结果显示:当初始pH为6~9时,吸附性能强;Cl~-、Ca~(2+)、Mg~(2+)、HCO_3~-、CO_3~(2-)离子与As(Ⅲ)、As(Ⅴ)不会产生竞争吸附,PO_4~(3-)、NO_3~-、SO_4~(2-)离子与As(Ⅲ)产生竞争性吸附,且PO_4~(3-)SO_4~(2-)NO_3~-;PO_4~(3-)、NO_3~-离子与As(Ⅴ)产生竞争性吸附。结合X射线衍射、扫描电镜等研究结果,初步探讨了改性磁铁矿的除砷机理,认为改性后的磁铁矿比表面积明显增大,表面生成物含有Fe(Ⅱ)和Fe(Ⅲ)是其吸附砷能力提高的主要原因。实验结果证实,改性天然磁铁矿是一种值得进一步研究并实际应用的水体除砷材料。     

淮北孟庄煤矿煤中砷的分布和赋存规律研究

以安徽省淮北煤田孟庄煤矿3,5和6煤层为研究对象,系统刻槽采取3个煤层的15个样品,采用仪器中子活化法(INNA)测试了煤中砷和稀土等元素的含量,研究了砷在3,5和6煤层的空间分布,分析了砷与灰分、稀土元素、硫以及含量之间的相关性。研究结果表明:孟庄煤矿煤中的砷的含量略高于与华北-石炭二叠纪煤中砷的算术平均含量,低于全国煤中砷的平均值;煤中的砷与灰分含量、稀土元素以及铝含量之间存在较好的相关性,表明研究区煤中的砷与陆源存在一定的关系,无机组分的砷可能主要被粘土矿物吸附。     

不同耕作类型下土壤-农作物系统中汞、砷含量与生态健康风险评价

针对废弃矿山遗留生态环境问题,选择贵州丹寨废弃金汞矿为研究区,基于野外系统样品采集,通过原子荧光法和电感耦合等离子体质谱法分析了区内土壤和农作物中的汞(Hg)、砷(As)浓度,采用单指标污染标准指数法、单因子污染指数法、潜在生态危害指数法和目标危险系数法评价了区内Hg、As污染程度及生态健康风险.结果显示:旱地土壤Hg...     

原子荧光光度法测定土壤样品中砷的不确定度评定

通过原子荧光光度法对土壤样品中砷重复测定6次，计算实验标准差，同时对测试过程系统效应产生的不确定度分量进行评估，从而评定其不确定度。     

Mathematical modeling of biologically mediated redox processes of iron and arsenic release in groundwater

A one dimensional reactive transport model was developed in order to illustrate the biogeochemical behavior of arsenic and iron reduction and release to groundwater that accounts for the reaction coupling the major redox elements under reducing environment. Mass transport equation and the method of characteristics were used considering fundamental geochemical processes to simulate transport processes of different pollutants in mobile phase. The kinetic sub-model describes the heterotrophic metabolisms of several microorganisms. To model a complete redox sequence (aerobic or denitrifiers, Fe(III)-reduction, respiration bacteria of iron and arsenic compounds, and As(V) reduction) four functional bacterial groups (X ₁, X ₂, X ₃, and X ₄) were defined. Microbial growth was assumed to follow Monod type kinetics. The exchange between the different phases (mobile, bio, and matrix) was also considered in this approach. Results from a soil column experiment were used to verify the simulation results of the model. The model depicts the utilization of oxygen, nitrate, iron oxide and arsenic as electron acceptors for oxidation of organic carbon (OC) in a column. The OC as electron donor is one of the most important factors that affect the iron and arsenic reduction bacterial activity.     

Behavior of arsenic and geochemical modeling of arsenic enrichment in aqueous environments

Arsenic is present in aqueous environments in +III and +V oxidation states. In oxidizing environments, the principle attenuation mechanism of As migration is its adsorption on Fe(III) oxide and hydroxides. The adsorption affinity is higher for As(V) under lower pH conditions and for As(III) under higher pH conditions. Ferric oxide and hydroxides can dissolve under low Eh and pH conditions releasing adsorbed As. Oxidation-reduction processes often involve high organic matter content in sediments and also contamination by organics such as BTEX. Arsenic may desorb under high pH conditions. Changes of pH can be related to some redox reactions, cation exchange reactions driving dissolution of carbonates, and dissolution of silicates. In very reducing environments, where SO₄ reduction takes place, secondary sulfide minerals like As-bearing pyrite and orpiment, As₂S₃, can incorporate As. Geochemical modeling can be divided into two principal categories: (a) forward modeling and (b) inverse modeling. Forward modeling is used to predict water chemistry after completion of predetermined reactions. Inverse modeling is used to suggest which processes take place along a flowpath. Complex coupled transport and geochemistry programs, which allow for simulation of As adsorption, are becoming available. A common modeling approach is based on forward modeling with surface complexation modeling (SCM) of As adsorption, which can incorporate the effect of different adsorbent/As ratios, adsorption sites density, area available for adsorption, pH changes and competition of As for adsorption sites with other dissolved species such as phosphate. The adsorption modeling can be performed in both batch and transport modes in codes such as PHREEQC. Inverse modeling is generally used to verify hypotheses on the origin of As. Basic prerequisites of inverse modeling are the knowledge of flow pattern (sampling points used in model have to be hydraulically connected) and information about mineralogy including As mineral phases. Case studies of geochemical modeling including modeling of As adsorption are presented.     

Mass balance of dissolved lithium in the oceans

A tentative mass balance of dissolved Li in the oceans suggests that basalt-seawater reactions play an important role in the Li cycle. However, removal of dissolved Li by basalt during reactions at low or moderate temperatures cannot compensate totally for inputs owing to basalt-seawater reactions at high temperatures and to continental run-off. We propose that the Li budget in the oceans is balanced by incorporation of Li into authigenic clay minerals. Li concentration profiles in the water column support this model. Basalt-seawater reactions at high temperatures seem to affect strongly the distribution of dissolved Li in interstitial waters of overlying sediments, suggesting that this element can be used as an indicator of hydrothermal reactions in the basaltic basement.     

Constitutive modeling of unsaturated aggregated soils

A coupled water retention–mechanical constitutive model for unsaturated aggregated soils is presented here. Based on the multi‐scale experimental results, the model incorporates the inter‐particle bonding, fabric and partial saturation effects in a single framework. It is formulated within the framework of hardening elasto‐plasticity and is based on the critical state concept. Prior to model validation, we evaluate the model parameters and propose determination procedures for the main new parameters. Finally, the model is examined for its capability in simulating the experimental results of aggregated and bonded soils. Results of these simulations show that the model addresses the most features arising from the combined effects of soil structure and partial saturation. Copyright © 2010 John Wiley & Sons, Ltd.     

Finite element simulation of freezing processes in soils

The finite element method, formulated for non-linear heat conduction, allows the solution of practically any ground freezing problem. Stabilization of wet soils by artificial freezing and freezing under roads induced by cold winter conditions are considered in this paper. Special features of the program used include parabolic isoparametric elements, a new time stepping scheme and an improved procedure for the estimation of thermal properties.     

土壤中可挥发性污染物清除的离心试验研究

土工离心模拟试验技术是研究环境岩土工程问题的有效手段。本文研究了非水相流体污染物在非饱和土中的迁移以及随后的抽气清除过程。 当离心机运行到要求的加速度时,汽油污染物从地下油罐中释放并在非饱和土中迁移一年,之后采用土壤通气法对污染土壤进行修复。对土壤取样分析,得到污染物在土体中的迁移规律和分布特征。试验结果表明,土壤通气法可以清除非饱和土体中的挥发性有机污染物,是一种有效的原位土壤修复技术。     

Natural arsenic attenuation via metal arsenate precipitation in soils contaminated with metallurgical wastes: II. Cumulative evidence and identification of minor processes

Accurate identification of individual As species in contaminated environments is critical because the toxicology, mobility and adsorptive properties of this element may vary substantially with its chemical forms and oxidation states. The goal of this work was to relate the geochemical behavior of As in soils contaminated by a lead smelter in Mexico, with its chemical speciation, and to achieve direct identification of low-solubility poorly-crystalline metal arsenates. Arsenic was identified as the most mobile trace element in the wastes from the smelting plant. Arsenic solubility in soils was significantly lower than its solubility in wastes, showing natural attenuation of this element. Its solubility in soil was quantitatively described in selected samples through thermodynamic equilibrium modeling. The results indicated that As solubility is controlled by solid Pb and Cu arsenate formation. The behaviors of the sequential chemical extractions were consistent with the presence of the predicted arsenates. Microscopic evidence of the formation of solid metal arsenates were obtained in fine soil fractions of selected samples with high As contents, by using the following complementary techniques: X-ray diffraction, scanning electron microscopy and transmission electron microscopy, both coupled with energy dispersive X-ray spectroscopy, and the latter with a high angle annular dark field detector. All results supported the formation of low-solubility Pb arsenates as controlling As mobility in the samples studied, in which As(V) adsorption to Fe (hydr)oxides was not the dominant process of natural attenuation.     

铜离子在非饱和土中迁移的离心模型试验研究

利用土工离心机考察了铜离子泄漏后6个月至3年的时间里非饱和土中铜离子的变化和污染物的迁移机理。通过4种黏性上的离心模型试验研究，总结出铜离子在这类土体中的扩散规律。铜离子在一年内，主要受重力影响和水力梯度的作用，随渗流运移，存在一个舌状竖向扩散峰，污染范围近似呈三角形；一年后扩散范围逐渐转变为近似的正方形。竖向扩散速度高于水半向。土体密实度对铜离予的扩散有较为明显的影响，有效的击实或者碾压有助下防止污染物迁移。黏粒含量对铜离子的迁移阻碍非常迅速而且有效，黏粒含量很小的变化都会对迁移范围和速度有较大的影响。     

Geochemical processes controlling arsenic mobility in groundwater: A case study of arsenic mobilization and natural attenuation

The behavior of As in the subsurface environment was examined along a transect of groundwater monitoring wells at a Superfund site, where enhanced reductive dechlorination (ERD) is being used for the remediation of groundwater contaminated with chlorinated solvents. The transect was installed parallel to the groundwater flow direction through the treatment area. The ERD technology involves the injection of organic C (OC) to stimulate in situ microbial dechlorination processes. A secondary effect of the ERD treatment at this site, however, is the mobilization of As, as well as Fe and Mn. The concentrations of these elements are low in groundwater collected upgradient of the ERD treatment area, indicating that, in the absence of the injected OC, the As that occurs naturally in the sediment is relatively immobile. Batch experiments conducted using sediments from the site inoculated with an Fe(III)- and As(V)-reducing bacterium and amended with lactate resulted in mobilization of As, Fe and Mn, suggesting that As mobilization in the field is due to microbial processes.     

Finite-element method in modeling geologic transport processes

Deterministic mathematical modeling of complex geologic transport processes may require the use of odd boundary shapes, time dependency, and two or three dimensions. Under these circumstances the governing transport equations must be solved by numerical methods. For a number of transport phenomena a general form of the convective-dispersion equation can be employed. The solution of this equation for complicated problems can be solved readily by the finite-element method. Using quadrilateral isoparametric elements or triangular elements and a computational algorithm based on Galerkin's procedure, solutions to unsteady heat flux from a dike and seawater intrusion in an aquifer have been obtained. These examples illustrate that the finite-element numerical procedure is well suited for solving boundary-value problems resulting from modeling of complex physical phenomena.