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1.
Adsorption/desorption and oxidation/reduction of arsenic at clay surfaces are very important to the natural attenuation of
arsenic in the subsurface environment. Although numerous studies have concluded that iron oxides have high affinities for
the adsorption of As(V), very little experimental work has addressed the arsenic attenuation capacities of different clay
minerals and aging process affecting the transformation of arsenic. The abundance of clay minerals in a variety of geochemical
environments and their influence on adsorption of contaminants suggests a need for more experimental work to characterize
the adsorption desorption, and oxidation of arsenic on clay minerals. In this investigation three types of clay mineral were
studied: the 1 : 1 layer clays [halloysite (IN), sedimentary M-kaolinite, and weathered EPK-kaolinite]; the 2 : 1 layer clays
[illite (MT) and illite/montmorillonite (MT)]; the 2 :>: 1 layer clay [chlorite (CA)]. The halloysite and the chlorite had
much greater As(V) adsorption (25–35 folds) than the other clay minerals. The clay minerals had lower As(III) adsorption than
As(V) adsorption, and the adsorption was affected by pH. Desorption of arsenic from the clay minerals was significantly influenced
by the aging process. The quantities of extractable As(III) and As(V) decreased with increasing aging time. The results demonstrated
that oxidation of As(III) to As(V) occurred on the clay surfaces, whereas reduction of As(V) to As(III) was not found in any
of the clay minerals studied. The oxidation of As(III) was affected by the types of clay and aging time.
Received: 22 March 1999 · Accepted: 15 April 1999 相似文献
2.
The aim of this study was to investigate the accumulation of arsenic (As) in and on roots of Zea mays (maize) and Helianthus annuus (sunflower) by means of synchrotron-based micro-focused X-ray fluorescence imaging (μ-XRF). Plant and soil samples were collected from two field sites in the Hetao Plain (Inner Mongolia, China) which have been regularly irrigated with As-rich groundwater. Detailed μ-XRF element distribution maps were generated at the Fluo-beamline of the Anka synchrotron facility (Karlsruhe Institute of Technology) to assess the spatial distribution of As in thin sections of plant roots and soil particles. The results showed that average As concentrations in the roots (14.5–27.4 mg kg −1) covered a similar range as in the surrounding soil, but local maximum root As concentrations reached up to 424 mg kg −1 ( H. annuus) and 1280 mg kg −1 ( Z. mays), respectively. Importantly, the results revealed that As had mainly accumulated at the outer rhizodermis along with iron (Fe). We therefore conclude that thin crusts of Fe-(hydr)oxides cover the roots and act as an effective barrier to As, similar to the formation of Fe plaque in rice roots. In contrast to permanently flooded rice paddy fields, regular flood irrigation results in variable redox conditions within the silty and loamy soils at our study site and fosters the formation of Fe-(hydr)oxide plaque on the root surfaces. 相似文献
3.
The arsenic accumulation process in intertidal sediments of Iriomote Island, Japan, is analyzed as a naturally balanced arsenic-fixation system. Major and minor element chemistry is analyzed by X-ray fluorescence photometry, mineralogy is investigated by X-ray diffractometry, and four arsenic compounds are characterized by hydrogen-generated atomic absorption photometry. It is found that arsenic is accumulated by iron hydroxides/oxides precipitated following the decomposition of humic acids in the shallower sediment, and is subsequently incorporated into iron sulfide minerals at depth. The arsenic is immobile during incorporation into arsenic-bearing phases, suggesting that arsenic is unlikely to be released into the porewater under natural conditions in early diagenesis. The formation and decomposition of arsenic-bearing organic compounds appear to be associated with the formation and decomposition of arsenic in oxyhydroxides/oxides, suggesting that microbial activity may play an important role in controlling the behavior of arsenic and arsenic-bearing phases in the sediment column. 相似文献
4.
Microcosm experiments were conducted to understand the mechanism of microbially mediated mobilization of Fe and As from high
arsenic aquifer sediments. Arsenic-resistant strains isolated from aquifer sediments of a borehole specifically drilled for
this study at Datong basin were used as inoculated strains, and glucose and sodium acetate as carbon sources for the experiments.
In abiotic control experiments, the maximum concentrations of Fe and As were only 0.47 mg/L and 0.9 μg/L, respectively. By
contrast, the maximum contents of Fe and As in anaerobic microcosm experiments were much higher (up to 1.82 mg/L and 12.91
μg/L, respectively), indicating the crucial roles of microbial activities in Fe and As mobilization. The observed difference
in Fe and As release with different carbon sources may be related to the difference in growth pattern and composition of microbial
communities that develop in response to the type of carbon sources. 相似文献
5.
In the city of Ouro Preto (MG), water catchment for public supply originates from superficial drainage, springs, old abandoned
mines and some driven wells. In the rocks of the region, As is originally found in gold-enriched sulphide-bearing mineral
deposits. The weathering process introduces As into the hydrological system by dissolution of this element into the leachate.
Measurement of the As content in the groundwater of some catchments was carried out during 1 year and these measurements demonstrated
high As content—up to 224 μg L −1 of As(V)—during the rainy season (the maximum concentration limit according to World Health Organization is 10 μg L −1). Lower values were observed during the dry season and in some sampling stations, As was not even detected. The As concentration
variability during 1 year shows a strict and direct relationship to seasonal and hydrological conditions. For city authorities,
responsible for public water supply, it is necessary to perform a complete inventory of the water sources used and constantly
monitor the As content in the water. 相似文献
6.
Unlike the majority of the water in the flooded mine complex of Butte Montana, which includes the highly acidic Berkeley pit
lake, groundwater in the flooded West Camp underground mine workings has a circum-neutral pH and contains at least 8 μM aqueous
sulfide. This article examines the geochemistry and stable isotope composition of this unusual H 2S-rich mine water, and also discusses problems related to the colorimetric analysis of sulfide in waters that contain FeS (aq) cluster compounds. The West Camp mine pool is maintained at a constant elevation by continuous pumping, with discharge water
that contains elevated Mn (90 μM), Fe (16 μM), and As (1.3 μM) but otherwise low metal concentrations. Dissolved inorganic
carbon in the mine water is in chemical and isotopic equilibrium with rhodochrosite in the mineralized veins. The mine water
is under-saturated with mackinawite and amorphous FeS, but is supersaturated with Cu- and Zn-sulfides. However, voltammetry
studies show that much of the dissolved sulfide and ferrous iron are present as FeS (aq) cluster molecules: as a result, the free
concentration of the West Camp water is poorly constrained. Concentrations of dissolved sulfide determined by colorimetry
were lower than gravimetric assays obtained by AgNO 3 addition, implying that the FeS (aq) clusters are not completely extracted by the Methylene Blue reagent. In contrast, the clusters are quantitatively extracted
as Ag 2S after addition of AgNO 3. Isotopic analysis of co-existing aqueous sulfide and sulfate confirms that the sulfide was produced by sulfate-reducing
bacteria (SRB). The H 2S-rich mine water is not confined to the immediate vicinity of the extraction well, but is also present in flooded mine shafts
up to 3 km away, and in samples bailed from mine shafts at depths up to 300 m below static water level. This illustrates that
SRB are well established throughout the southwestern portion of the extensive (>15 km 3) Butte flooded mine complex. 相似文献
7.
The mobility and availability of arsenite, As(III), in anoxic environments is largely controlled by adsorption onto iron sulfides and/or precipitation of arsenic in solid phases. The interaction of As(III) with synthetic mackinawite (FeS m) in pH 5 and 9 suspensions was investigated using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM), STEM elemental mapping, high resolution TEM, and X-ray photoelectron spectroscopy (XPS). At pH 5, arsenic sulfide phases precipitate among the FeS m particles as discrete particles that are an amorphous hydrous phase of arsenic sulfide. The oxidation state of As in the surface layers of the arsenic sulfide precipitates is ‘realgar-like’ based on XPS results showing that > 75% of the As 3d peak area is due to As with oxidation states between 0 and 2+. Discrete, arsenic sulfide precipitates are absent at pH 9, but elemental mapping in STEM-EDX mode shows that arsenic is uniformly distributed on the FeS m, suggesting that uptake is caused by the sorption of As(III) oxyanions and/or the precipitation of highly dispersed arsenic sulfides on FeS m. XPS also revealed that the FeS m that equilibrated without As(III) has a more oxidized surface composition than the sample at pH 9, as indicated by the higher concentration of O ( three times greater than that at pH 9) and the larger fraction of Fe(III) species making up the total Fe (2p 3/2) peak. These findings provide a better understanding of redox processes and phase transitions upon As(III) adsorption on iron sulfide substrates. 相似文献
8.
Several experiments of arsenic (As) adsorption by aquifer material of the San Antonio-El Triunfo (SA-ET) mining area were
conducted to test the feasibility of this material acting as a natural control for As concentrations in groundwater. This
aquifer material is mineralogically complex, composed of quartz, feldspar, calcite, chlorite, illite, and magnetite/hematite.
The total iron content (Fe 2O 3) in the fine fraction is ∼12%, whereas Fe 2O 3 in the coarse fraction is <10 wt%. The experimental percent total As adsorbed vs. pH curves obtained match the topology of
total As adsorbed onto iron oxi-hydroxides surface (arsenate + arsenite; high adsorption at low pH, low adsorption at high
pH). A maximum of about 80% adsorbed in the experiments suggests the presence of arsenite in the experimental solutions. The
experimental adsorption isotherm at pH 7 indicates saturation of surface sites at high solute concentrations. Surface titration
of the aquifer material indicates a point of zero charge (PZC) for the adsorbent of about 8 to 8.5 (PZC for iron oxyhydroxides
=7.9–8.2). Comparison between experimental and modeled results (using the MICROQL and MINTEQA2 geochemical modeling and speciation
computer programs) suggests that As is being adsorbed mostly by oxyhydroxides surfaces in the natural environment. Based on
an estimated retardation factor ( R), the travel time of the As plume from the SA-ET area to La Paz and Los Planes is about 700 to 5000 years.
Received: 17 March 1997 · Accepted: 8 September 1997 相似文献
9.
Feasibility of electrokinetic (EK) process combined with Fenton-like reaction was investigated for the removal of phenanthrene in a two-dimensional cell. Sandy soil and bentonite were selected as a model soil and a filling material to inhibit the leak of electrolyte solution within the electrode reservoirs into the soil by hydraulic pressure difference, respectively. The effects of parameters including current, electroosmotic flow (EOF), electrolyte pH, and moisture content on the removal efficiency were examined under constant voltage. At the end of operation for 21 days, the concentration of phenanthrene near the anode was lower than the other positions of soil specimen and increased gradually towards the cathode because hydrogen peroxide solution was supplied from anode to cathode region following the direction of EOF. The concentration of phenanthrene at the bottom soil was lower than that at the top soil. Because capillary attraction in the sandy soil with high porosity was too low to maintain appropriate moisture at the top of the cell, EOF moved through the bottom soil with higher moisture content. Overall removal efficiency at 140 V was 81.6%, which was higher than 68.9% at 100 V because total EOF increased by a factor of 1.5 upon increase of the voltage from 100 to 140 V. In addition, power consumptions at 100 and 140 V were 7.2 and 19.4 kWh, respectively. 相似文献
10.
Riverbank sediment cores and pore waters, shallow well waters, seepage waters and river waters were collected along the Meghna Riverbank in Gazaria Upazila, Bangladesh in Jan. 2006 and Oct.–Nov. 2007 to investigate hydrogeochemical processes controlling the fate of groundwater As during discharge. Redox transition zones from suboxic (0–2 m depth) to reducing (2–5 m depth) then suboxic conditions (5–7 m depth) exist at sites with sandy surficial deposits, as evidenced by depth profiles of pore water (n = 7) and sediment (n = 11; diffuse reflectance, Fe(III)/Fe ratios and Fe(III) concentrations). The sediment As enrichment zone (up to ∼700 mg kg −1) is associated with the suboxic zones mostly between 0 and 2 m depth and less frequently between 5 and 7 m depth. The As enriched zones consist of several 5–10 cm-thick dispersed layers and span a length of ∼5–15 m horizontally from the river shore. Depth profiles of riverbank pore water deployed along a 32 m transect perpendicular to the river shore show elevated levels of dissolved Fe (11.6 ± 11.7 mg L −1) and As (118 ± 91 μg L −1, mostly as arsenite) between 2 and 5 m depth, but lower concentrations between 0 and 2 m depth (0.13 ± 0.19 mg L −1 Fe, 1 ± 1 μg L −1 As) and between 5 and 6 m depth (1.14 ± 0.45 mg L −1 Fe, 28 ± 17 μg L −1 As). Because it would take more than a few hundred years of steady groundwater discharge (∼10 m yr −1) to accumulate hundreds of mg kg −1 of As in the riverbank sediment, it is concluded that groundwater As must have been naturally elevated prior to anthropogenic pumping of the aquifer since the 1970s. Not only does this lend unequivocal support to the argument that As occurrence in the Ganges-Brahmaputra-Meghna Delta groundwater is of geogenic origin, it also calls attention to the fate of this As enriched sediment as it may recycle As into the aquifer. 相似文献
11.
This paper documents arsenic concentrations in 157 groundwater samples from the island of Ischia and the Phlegrean Fields, two of the most active volcano-hosted hydrothermal systems from the Campanian Volcanic Province (Southern Italy), in an attempt to identify the environmental conditions and mineral-solution reactions governing arsenic aqueous cycling. On Ischia and in the Phlegrean Fields, groundwaters range in composition from NaCl brines, which we interpret as the surface discharge of deep reservoir fluids, to shallow-depth circulating fluids, the latter ranging from acid-sulphate steam-heated to hypothermal, cold, bicarbonate groundwaters. Arsenic concentrations range from 1.6 to 6900 μg·l − 1 and from 2.6 to 3800 μg·l − 1 in the Phlegrean Fields and on Ischia, respectively. They increase with increasing water temperature and chlorine contents, and in the sequence bicarbonate groundwaters < steam-heated groundwaters < NaCl brines. According to thermochemical modeling, we propose that high As concentrations in NaCl brines form after prolonged water-rock interactions at reservoir T, fO 2 and fH 2S conditions, and under the buffering action of an arsenopyrite + pyrite + pyrrhotite rock assemblage. On their ascent toward the surface, NaCl brines become diluted by As-depleted meteoric-derived bicarbonate groundwaters, giving rise to hybrid water types with intermediate to low As contents. Steam-heated groundwaters give their intermediate to high As concentrations to extensive rock leaching promoted by interaction with As-bearing hydrothermal steam. 相似文献
12.
A waste rock pile with initial high sulfide (10–20 wt.%) and low carbonate content (1–2 wt.%) located at Dlouhá Ves in the Czech Republic has been investigated in two profiles (excavation and outcrop) using powder X-ray diffraction, electron microprobe analysis, bulk composition analysis and Mössbauer spectroscopy. The mobility of arsenic and other contaminants was evaluated by leaching experiments. The primary source of the arsenic was arsenopyrite, which was significantly oxidized in both profiles. The principal As-bearing phase at the excavation profile was goethite, located at the top of the profile, and minerals of the jarosite group which were found down to its base. Melanterite, rich in copper and zinc, was found in a sulfide-rich, lower part of the profile together with anglesite. At the outcrop profile, minerals of the jarosite–beudantite group, scorodite and kaňkite prevail and no Fe(II)-minerals were found. The paste pH was lower at the excavation profile (minimum about 1.9) than at the outcrop profile (minimum of about 2.8). Processes in the pile are affected by the pyrite/arsenopyrite ratio, where high pyrite content decreases the As/S ratio and results in the formation of jarosite group minerals and low pH conditions. Where arsenopyrite predominates, sulphides are coated by scorodite and other Fe–As phases like schwertmannite, which limit their further oxidation. 相似文献
13.
Geophysical surveys were carried out in an arsenic contaminated area, in the Ron Phibun District in southern Thailand. Here, tin and associated minerals, i.e. arsenopyrite and pyrite, have been extracted from granites and natural processes and the mining activities led to arsenic contamination in the environment. Electrical resistivity and self-potential (SP) were used to define the distribution of arsenic contamination in the groundwater. Resistivities of 25–100 Ωm and a positive SP anomaly of 66.0 mV were observed in an area where the arsenic content in auger water at 3.5–5.0 m depths was high, 0.5–5.0 mg/l. Integrated interpretation of resistivity, seismic refraction, GPR and gravity data gave a clear image of subsurface shallow structures (< 30 m depths). There was a good correlation between the resistivity and the gravity data. A subsurface rise was found, which possibly acts as a naturally buried dam, separating a high-contaminated area from a low contaminated area. 相似文献
14.
Heavy/toxic metals have been widely investigated in the Antarctic. However, there are rare reports on arsenic up to now. Here,
we analyzed a 1,800-year record of arsenic concentration in lake sediments affected by penguin droppings. We found that arsenic
enriches in the penguin dropping sediments with 12.41 ± 0.45 μg/g (on dry weight), which is about two times higher than the
one in the background sediments with absence of penguin. Historical change in arsenic concentration was found to significantly
correlate with the fluctuation of penguin number, indicating that penguin activity will result in the enrichment of arsenic
somewhere in the maritime Antarctic. 相似文献
15.
Geological and geochemical study has been carried out to investigate arsenic contamination in groundwater in Nawalparasi, the western Terai district of Nepal. The work carried out includes analyses of core sediments, provenance study by rare earth elements analyses, 14C dating, and water analyses. Results showed that distribution of the major and trace elements are not homogeneous in different grain size sediments. Geochemical characteristics and sediment assemblages of the arsenic contaminated (Nawalparasi) and uncontaminated (Bhairahawa) area have been compared. Geochemical compositions of sediments from both the areas are similar; however, water chemistry and sedimentary facies vary significantly. Extraction test of sediment samples showed significant leaching of arsenic and iron. Chemical reduction and contribution from organic matter could be a plausible explanation for the arsenic release in groundwater from the Terai sediments. 相似文献
16.
A comparative hydrogeochemical study evaluated arsenic release mechanism and differences in contamination levels in the shallow groundwater of two areas within the deltaic environment of West Bengal (i.e. Karimpur and Tehatta blocks of Nadia district) in India. Groundwaters from both the areas are Ca-Na(K)-Cl-HCO 3 type with highly reducing character (−110.16 ± 16.85 to −60.77 ± 16.93 mV). Low correlations among As, Fe, and Mn and the higher association between As and DOC are indicative of microbial decomposition of organic matter enhancing the weathering of shallow aquifer materials. Arsenic contamination in groundwater is higher in Karimpur (95 ± 81.17 μg/L) than that in Tehatta (43.05 ± 41.06 μg/L). The release mechanism of arsenic into groundwater is very complex. Low Fe (0.27–4.78 mg/L and 0.81–4.13 mg/L), Mn (0.08–0.2 mg/L and 0.03–0.22 mg/L), and SO 42− (3.82 ± 0.31 and 2.78 ± 0.40 mg/L) suggest that the mechanism of arsenic release is not a single mechanistic pathway. Clustering of redox-active parameters in the principal component planes indicate that the reductive dissolution, and/or weathering/co-precipitation of Fe/Mn-bearing minerals in the shallow aquifer sediments control the dominant mechanistic pathway of arsenic release. 相似文献
17.
Dissolved major ions and important heavy metals including total arsenic and iron were measured in groundwater from shallow
(25–33 m) and deep (191–318 m) tube-wells in southeastern Bangladesh. These analyses are intended to help describe geochemical
processes active in the aquifers and the source and release mechanism of arsenic in sediments for the Meghna Floodplain aquifer.
The elevated Cl − and higher proportions of Na + relative to Ca 2+, Mg 2+, and K + in groundwater suggest the influence by a source of Na + and Cl −. Use of chemical fertilizers may cause higher concentrations of NH 4+ and PO 43− in shallow well samples. In general, most ions are positively correlated with Cl −, with Na + showing an especially strong correlation with Cl −, indicating that these ions are derived from the same source of saline waters. The relationship between Cl −/HCO 3− ratios and Cl − also shows mixing of fresh groundwater and seawater. Concentrations of dissolved HCO 3− reflect the degree of water–rock interaction in groundwater systems and integrated microbial degradation of organic matter.
Mn and Fe-oxyhydroxides are prominent in the clayey subsurface sediment and well known to be strong adsorbents of heavy metals
including arsenic. All five shallow well samples had high arsenic concentration that exceeded WHO recommended limit for drinking
water. Very low concentrations of SO 42− and NO 3− and high concentrations of dissolved Fe and PO 43− and NH 4+ ions support the reducing condition of subsurface aquifer. Arsenic concentrations demonstrate negative co-relation with the
concentrations of SO 42− and NO 3− but correlate weakly with Mo, Fe concentrations and positively with those of P, PO 43− and NH 4+ ions. 相似文献
18.
Here we report on the different sampling strategies for almost seven years of sampling rocks/sediments for the determination of As within the Intermediate Aquifer System (IAS) and upper Floridan Aquifer System (FAS), a very large and productive limestone aquifer spanning from Georgia into Florida. In the FAS, As contamination has become a recurring problem during aquifer storage and recovery (ASR), particularly in central and south Florida.To investigate these phenomena, samples from solid drill cores and rock cuttings were collected from the Hawthorn Group, Suwannee Limestone, Ocala Limestone and Avon Park Formation. Samples were taken along drill cores and rock cuttings (referred to as ‘interval’ samples) or from particular drill core sections and rock cuttings (referred to as ‘targeted’ samples) likely to contain elevated concentrations of As as indicated by the presence of pyrite, hydrous ferric oxide, organic matter, clay minerals, fracture surfaces, and high permeable (moldic) zones.Arsenic was present in all of the stratigraphic units at low concentrations, close to the global average for As in limestone of 2.6 mg/kg. The highest As concentration was 69 mg/kg. In all units, however, the average bulk As concentration in the targeted samples was substantially higher than that in the interval samples. Based on direct spot measurements by electron microprobe and indirect calculations, pyrite was identified as the main source of As in the FAS. Concentrations in pyrite ranged from less than 100 mg/kg to more than 11,000 mg/kg. Because pyrite is heterogeneously distributed, both vertically and horizontally in the sampled stratigraphic units, the same was observed for the distribution of As. However, As concentrations generally decreased with depth, i.e., highest As values in the Hawthorn Group and lowest As values in the Ocala Limestone and Avon Park Formation. Compared to pyrite, other trace minerals contained much less As.The average As concentrations of the two types of sample media (solid cores and rock cuttings) were quite similar. These results indicate that if simply the average bulk rock As concentration of a geologic unit is the desired outcome of an investigation, either interval or targeted sampling of rock cuttings, seems to be sufficient. This is particularly important when time and money are a factor. This approach could work equally well for any other trace element. Structural sedimentary information, such as fractures, etc., is likely lost, however, when sampling rock cuttings. Thus, if this information is required, solid core samples need to be collected by hollow core diamond drilling. 相似文献
19.
Arsenic (As) content of sediments from the Rio Conchos and Rio San Pedro in northern Mexico were measured to determine if
this toxic metalloid had accumulated to unsafe levels to humans and aquatic life. The spatial distribution of As in each of
the six clusters of river and arroyo sediments was analyzed to determine variations with respect to background levels and
to infer about potential As sources and sinks. In the northern part of the study area, background concentrations varied little
throughout the area and concentrations in river sediments were close to background levels. In the southern part, however,
the content of As in arroyo sediment contained a wider range of values and anomalous concentrations. The latter could be traced
in part to the presence of mine tailings. As concentrations were below the limit in all studied river stretches and thus do
not pose an immediate threat to the river environment, but As content in reservoir sediments exceeded the guideline values.
Reservoirs seem to act as a sink for As, warranting closer observation and monitoring. 相似文献
20.
Geochemical study of the Holocene sediments of the Meghna River Delta, Chandpur, Bangladesh was conducted to investigate the distribution of arsenic and related trace and major elements. The work carried out includes analyses of core sediments and provenance study by rare earth element (REE) analysis. Results showed that the cores pass downward from silty clays and clays into fine to medium sands. The uppermost 3 m of the core sediments are oxidized [average oxidation reduction potential (ORP) + 230 mV], and the ORP values gradually become negative with depths (−45 to −170 mV), indicating anoxic conditions prevail in the Meghna sediments. The REE patterns of all lithotypes in the study areas are similar and are comparable to the average upper continental crust. Arsenic and other trace elements (Pb, Zn, Cu, Ni, and Cr) have greater concentrations in the silts and clays compared to those in the sands. Positive correlation between As and Fe was found in the sediments, indicating As may be adsorbed on Fe oxides in aquifer sediments. 相似文献
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