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1.
Natural zeolitic rocks consisting mainly of chabazite-phillipsite, clinoptilolite, and volcanic glass have been evaluated by means of batch methods to remove arsenic from waters with different mineralization degree (from deionized water to natural water with a specific conductivity of 1,600 μS cm− 1). Arsenic was previously spiked in the studied waters at concentrations of about 100 µg l− 1 to simulate actual cases. The compositional range of natural waters is representative of large hydrogeochemical regions around the world. The experiments were focussed on the application of natural common zeolitic rocks to water treatment for human consumption. The removal efficiency observed rises, in the better cases, 60–80% for chabazite-phillipsite raw materials whereas is 40–60% for clinoptilolite-bearing ones. The arsenic removal tends to increase with water mineralization degree, independently of the zeolitic rock type. A large zeolitic content in the chabazite-phillipsite raw materials increase the removal. Instead, the inverse situation is observed in the clinoptilolite-bearing rocks. The relevance of the quantitative mineralogical analysis, determining also the content of volcanic glass, as well as the use of natural waters in the removal tests has been demonstrated.  相似文献   

2.
Iron-hydroxide-rich and plant litter-containing sediments from natural sites contaminated with uranium mine tailing leachates were examined for their ability to adsorb arsenic. The samples with high contents of iron hydroxides (Fetotal concentration, >300 g kg−1) exhibited remarkable fixation of arsenic (up to 40 g As kg−1). This value corresponded approximately to the supersaturation point for natural iron hydroxides under the present conditions, and it was significantly lower than the value found for synthetic iron hydroxides. There was a strong correlation (R=0.8999) between the concentration of iron and that of arsenic at low arsenic contents, indicating adsorption on strong binding sites. Although all the samples had noticeable contents of organic carbon (plant litter), calcium, and manganese, no obvious effect of these elements on arsenic fixation could be detected. The amount of iron hydroxides was found the only fixation-controlling parameter immediately below a leaching water source.  相似文献   

3.
Activated carbon is the adsorbent commonly used to remove arsenic from contaminated water. However, the problem is that it is not always available everywhere and considered expensive in developing countries. An inexpensive alternative to activated carbon can therefore aid the adequate treatment of contaminated water. Tea waste, water hyacinth and banana peel are investigated extensively in this study as the inexpensive alternative. Tea waste treated with a right proportion of aqueous FeCl3 reagent is found to have substantially higher arsenic removing capacity (which is quantified by arsenic concentrations measured employing Double Beam Atomic Absorption Spectrophotometer) than the other two. The comparison made subsequently between tea waste and activated carbon reveals the feasibility of the utilization of tea waste. The arsenic removing capacity of tea waste treated with the right proportion of aqueous FeCl3 reagent is found to be equal to that of the activated carbon treated with the same reagent over the continuous operative time of 2 h. The tea waste treated rightly with the same reagent also removes arsenic at acceptable capacities over extended operative times such as 4–6 h. It is therefore proposed to consider tea waste as the inexpensive alternative to activated carbon in treating arsenic contaminated water.  相似文献   

4.
New major, trace and isotopic geochemical results from a regional study of springs discharging from the major carbonate rock aquifer in the Interlake Region of Manitoba, Canada, are used to understand water–rock reactions, timing of recharge/discharge, tufa formation processes, and as baseline data. Spring waters are fresh with total dissolved solids (TDS) concentrations ranging from 150 to 880 mg/L. Waters discharging in the northern part of the study area have lower TDS, are dominantly Ca–Mg–HCO3 waters with low SO4 concentrations (<< 50 mg/L), and appear to have interacted primarily with Silurian carbonate lithologies. In contrast, waters in the southeastern part of the study area have higher TDS and have elevated SO4 concentrations (up to 210 mg/L). Spring waters have elevated Mg/Camolar (1.23 ± 0.23), typically greater than congruent dissolution of dolomite. Ca and Mg concentrations and Mg/Camolar indicate that groundwater residence times were sufficient to allow equilibration with bedrock dolomite lithologies; elevated tritium in northern waters indicates a significant recharge component in the 1960's and 1970's. Tufa precipitates that have formed from many of the spring waters are low-Mg calcite (MgO = 1.70 to 5.80 wt.%). Sr concentrations are variable (57 to 657 ppm) and tufa Sr/Camolar ratios appear to be entirely controlled by spring water Sr/Camolar. Empirically determined Sr distribution coefficients (DSr = 0.389 ± 0.083) indicate rapid crystallization following CO2 degassing, consistent with heavier δ13CVPDB compared to spring waters. Sulfate concentrations are generally too low for calcitization (dedolomitization) reactions driven by anhydrite dissolution to be the dominant control on the elevated groundwater Mg/Camolar, implying either extensive sulfate reduction along the flow paths (however, δ13CDIC suggests the elevated SO4 is more consistent with Fe-sulfide oxidation), or that other processes are involved. Major ion ratios suggest that the waters in the southern part of the study area are more consistent with interaction with siliciclastic rocks than with anhydrite dissolution. We suggest that calcitization (dedolomitization) reactions driven by anhydrite dissolution may not dominate all carbonate aquifers and that mixing of waters in karst conduits combined with ion exchange reactions are important controls on water chemistry in these systems.  相似文献   

5.
Mining and processing of arsenopyrite ore at the Mole River mine in the 1920–1930s resulted in abandoned mine workings, waste dumps and an arsenic oxide treatment plant. Weathering of waste material (2.6–26.6 wt% As) leads to the formation of water soluble, As‐bearing mineral salts (pharmacolite, arsenolite, krautite) and sulfates which affect surface waters after rainfall events. Highly contaminated soils, covering about 12 ha at the mine, have extreme As (mean 0.93 wt%) and elevated Fe, Ag, Cu, Pb, Sb and Zn values compared with background soils (mean 8 ppm As). Regionally contaminated soils have a mean As content of 55 ppm and the contaminated area is estimated to be 60 km2. The soils have acquired their metal enrichments by hydromorphic dispersion from the dissolution of As‐rich particulates, erosion of As‐rich particulates from the dumps, and atmospheric fall‐out from processing plant emissions. Stream sediments within a radius of 2 km of the mine display metal enrichments (62 ppm to 27.5 wt% As) compared with the mean background of 23 ppm As. This enrichment has been caused by erosion and collapse of waste‐dump material into local creeks, seepages and ephemeral surface runoff, and erosion and transportation of contaminated soil into the local drainage system. Water samples from a mine shaft and waste‐dump seepages have the lowest pH (4.1) and highest As values (up to 13.9 mg/L), and contain algal blooms of Klebsormidium sp. The variable flow regime of the Mole River causes dilution of As‐rich drainage waters to background values (mean 0.0086 mg/L As) within 2.5 km downstream. Bioaccumulation of As and phytotoxicity to lower plants has been observed in the mine area, but several metal‐tolerant plant species (Angophora floribunda, Cassinia laevis, Chrysocephalum apiculatum, Cymbopogon refractus, Cynodon dactylon, Juncus subsecundus and Poa sieberiana) colonise the periphery of the contaminated site.  相似文献   

6.
The arsenic content of geothermal hot springs and their sediments in the north-central Andean region of Ecuador has been investigated. The area of study is located between parallels 1°11′N and 1°30′S and includes five provinces. The area is rich in geothermal surface manifestations that are mainly used for medicinal baths in recreational complexes. Unfortunately, water residuals without treatment are released from the recreational facilities to surrounding water bodies. The results indicate that total arsenic in geothermal waters in this region has a range of 2–969 μg As/L, and sediments contain arsenic ranging from 1.6 to 717.6 mg/kg. Chemical analyses of sediment samples show the presence of sulfur, iron, aluminum and calcium. A high concentration of natural organic matter was also found in some samples (20–29.5%); thus sorption and coprecipitation can be the main mechanisms of As immobilization on mineral phases and natural organic matter.  相似文献   

7.
Arsenic sequestration by sorption processes in high-iron sediments   总被引：3，自引：0，他引：3  
High-iron sediments in North Haiwee Reservoir (Olancha, CA), resulting from water treatment for removal of elevated dissolved arsenic in the Los Angeles Aqueduct system, were studied to examine arsenic partitioning between solid phases and porewaters undergoing shallow burial. To reduce arsenic in drinking water supplies, ferric chloride and a cationic polymer coagulant are added to the aqueduct upstream of Haiwee Reservoir, forming an iron-rich floc that scavenges arsenic from the water. Analysis by synchrotron X-ray absorption spectroscopy (XAS) showed that the aqueduct precipitate is an amorphous hydrous ferric oxide (HFO) similar to ferrihydrite, and that arsenic is associated with the floc as adsorbed and/or coprecipitated As(V). Arsenic-rich floc and sediments are deposited along the inlet channel as aqueduct waters enter the reservoir. Sediment core samples were collected in two consecutive years from the edge of the reservoir along the inlet channel using 30- or 90-cm push cores. Cores were analyzed for total and extractable arsenic and iron concentrations. Arsenic and iron speciation and mineralogy in sediments were examined at selected depths by synchrotron XAS and X-ray diffraction (XRD). Sediment-porewater measurements were made adjacent to the core sample sites using polyacrylamide gel probe samplers. Results showed that sediment As(V) is reduced to As(III) in all cores at or near the sediment-water interface (0-4 cm), and only As(III) was observed in deeper sediments. Analyses of EXAFS spectra indicated that arsenic is present in the sediments mostly as a bidentate-binuclear, inner-sphere sorption complex with local atomic geometries similar to those found in laboratory studies. Below about 10 cm depth, XAS indicated that the HFO floc had been reduced to a mixed Fe(II, III) solid with a local structure similar to that of synthetic green rust (GR) but with a slightly contracted average interatomic Fe-Fe distance in the hydroxide layer. There was no evidence from XRD for the formation of a crystalline GR phase. The release of dissolved iron (presumably Fe2+) and arsenic to solution, as monitored by in situ gel probes, was variable but, in general, occurred at greater depths than arsenic reduction in the sediments by spectroscopic observations and appears to be near or below the depth at which sediment GR was identified. These data point to reductive dissolution of the sorbent iron phase as the primary mechanism of release of sorbed arsenic to solution.  相似文献   

8.
Arsenic in soil, vegetation and water of a contaminated region   总被引：2，自引：1，他引：1  
Arsenic concentrations of surface waters, soils and plants were surveyed in three contaminated villages of Bijar County. Total arsenic in water samples (4.5 to 280 μg/L) was correlated with electrical conductivity, total dissolved solid, total hardness, alkalinity, chloride, sulphate, bicarbonate, calcium and sodium (p<0.001). Total arsenic in the soils ranged from 105.4 to 1500 mg/kg. Some of the soil factors play an important role in soil arsenic content and its bioavailability for organisms. In general, the arsenic concentrations in plants were low, especially in the most common wild species. Among 13 plant species, the highest mean arsenic concentration was found in leaves of Mentha Longifolia (79.4 mg/kg). Arsenic levels in soils and plants were positively correlated, while the ability of the plants to accumulate the element, expressed by their biological accumulation coefficients and arsenic transfer factors, was independent of the soil arsenic concentration. Relationships between the arsenic concentrations in plants, soils and surface water and the environmental aspects of these relationships have been discussed in comparison with literature data. The accumulation of arsenic in environmental samples (soil, sediment, water, plant, etc.) poses a potential risk to human health due to the transfer of this element in aquatic media, their uptake by plants and subsequent introduction into the food chain.  相似文献   

9.
The Furtei gold mine in Sardinia (Italy) exploits a volcanic-hosted high-sulphidation epithermal deposit. Large amounts of materials derived from exploitation are present in open pits, waste rock dumps and cyanidation tailings impoundment. Mineralized rocks in outcrops and waste dumps contain significant amounts of sulphides (mainly pyrite and enargite). These materials have a high potential for acid drainage generation and release of toxic elements (notably Cu and As, but also Al, Ni, Co and Cd) as pointed out by laboratory leaching tests and in agreement with chemical composition of waters draining the mining area, that show pH as low as 2, up to 180 mg/L Cu, up to 5 mg/L As, and up to 788 mg/L Al. On the other hand, leaching solutions and waters interacting with mineral assemblages of the propylitic alteration zone (mainly composed of chlorite, quartz, and calcite, with relic magmatic plagioclase) show higher pH, and lower metal loads. Leachates from cyanidation tailings show variable pH (between 6.2 and 9.7, depending on sulphide content in tailings); cyanide concentration varies between 110 µg/L and about 3 mg/L, whereas contents of toxic elements in leachates are, with the exception of Hg, within the limits of Italian regulations for non-dangerous industrial wastes. Reclamation plans provide for confinement of tailings within specific repositories. This measure should effectively reduce the environmental impact of these materials. Reclamation plans should also include an adequate management of other high-sulphide wastes.  相似文献   

10.
Twenty-two bottled mineral and spring waters from Norway, Sweden, Finland and Iceland have been analysed for 71 inorganic chemical parameters with low detection limits as a subset of a large European survey of bottled groundwater chemistry (N = 884). The Nordic bottled groundwaters comprise mainly Ca–Na–HCO3–Cl water types, but more distinct Ca–HCO3, Na HCO3 and Na–Cl water types are also offered. The distributions for most elements fall between groundwater from Fennoscandian Quaternary unconsolidated aquifers and groundwater from Norwegian crystalline bedrock boreholes. Treated tap waters have slightly lower median values for many parameters, but elements associated with plumbing have significantly higher concentrations in tap waters than in bottled waters. The small dataset is able to show that excessive fluoride and uranium contents are potential drinking water problems in Fennoscandia. Nitrate and arsenic displayed low to moderate concentrations, but the number of samples from Finland and Northern Sweden was too low to detect that elevated concentrations of arsenic occur in bedrock boreholes in some regions. The data shows clearly that water sold in plastic bottles is contaminated with antimony. Antimony is toxic and suspected to be carcinogenic, but the levels are well below the EU drinking water limit. The study does not provide any health-based arguments for buying bottled mineral and spring waters for those who are served with drinking water from public waterworks. Drinking water from crystalline bedrock aquifers should be analysed. In case of elevated concentrations of fluoride, uranium or arsenic, most bottled waters, but not all, will be better alternatives when treatment of the well water is not practicable.  相似文献   

11.
The mobility of subsurface arsenic is controlled by sorption, precipitation, and dissolution processes that are tied directly to coupled redox reactions with more abundant, but spatially and temporally variable, iron and sulfur species. Adjacent to the site of a former pesticide manufacturing facility near San Francisco Bay (California, USA), soil and groundwater arsenic concentrations are elevated in sediments near the prior source, but decrease to background levels downgradient where shallow groundwater mixes with infiltrating tidal waters at the plume periphery, which has not migrated appreciably in over two decades of monitoring. We used synchrotron X-ray absorption spectroscopy, together with supporting characterizations and sequential chemical extractions, to directly determine the oxidation state of arsenic and iron as a function of depth in sediments from cores recovered from the unsaturated and saturated zones of a shallow aquifer (to 3.5 m below the surface). Arsenic oxidation state and local bonding in sediments, as As-sulfide, As(III)-oxide, or As(V)-oxide, were related to lithologic redox horizons and depth to groundwater. Based on arsenic and iron speciation, three subsurface zones were identified: (i) a shallow reduced zone in which sulfide phases were found in either the arsenic spectra (realgar-like or orpiment-like local structure), the iron spectra (presence of pyrite), or both, with and without As(III) or As(V) coordinated by oxygen; (ii) a middle transitional zone with mixed arsenic oxidation states (As(III)–O and As(V)–O) but no evidence for sulfide phases in either the arsenic or iron spectra; and (iii) a lower oxidized zone in the saturated freshwater aquifer in which sediments contained only oxidized As(V) and Fe(III) in labile (non-detrital) phases. The zone of transition between the presence and absence of sulfide phases corresponded to the approximate seasonal fluctuation in water level associated with shallow groundwater in the sand-dominated, lower oxic zone. Total sediment arsenic concentrations showed a minimum in the transition zone and an increase in the oxic zone, particularly in core samples nearest the former source. Equilibrium and reaction progress modeling of aqueous-sediment reactions in response to decreasing oxidation potential were used to illustrate the dynamics of arsenic uptake and release in the shallow subsurface. Arsenic attenuation was controlled by two mechanisms, precipitation as sulfide phases under sulfate-reducing conditions in the unsaturated zone, and adsorption of oxidized arsenic to iron hydroxide phases under oxidizing conditions in saturated groundwaters. This study demonstrates that both realgar-type and orpiment-type phases can form in sulfate-reducing sediments at ambient temperatures, with realgar predicted as the thermodynamically stable phase in the presence of pyrite and As(III) under more reduced conditions than orpiment. Field and modeling results indicate that the potential for release of arsenite to solution is maximized in the transition between sulfate-reduced and iron-oxidized conditions when concentrations of labile iron are low relative to arsenic, pH-controlled arsenic sorption is the primary attenuation mechanism, and mixed Fe(II,III)-oxide phases do not form and generate new sorption sites.  相似文献   

12.
Wetlands are significant sources and sinks for arsenic (As), yet the geochemical conditions and processes causing a release of dissolved arsenic and its association with the solid phase of wetland soils are poorly known. Here we present experiments in which arsenic speciation was determined in peatland mesocosms in high spatiotemporal resolution over 10 months. The experiment included a drought/rewetting treatment, a permanently wet, and a defoliated treatment. Soil water content was determined by the TDR technique, and arsenic, iron and sulfate turnover from mass balancing stocks and fluxes in the peat, and solid phase contents by sequential extractions. Arsenic content ranged from 5 to 25 mg kg−1 and dissolved concentrations from 10 to 300 μg L−1, mainly in form of As(III), and secondarily of As(V) and dimethylated arsenic (DMA). Total arsenic was mainly associated with amorphous iron hydroxides (R2 > 0.95, α < 0.01) and deeper into the peat with an unidentified residual fraction. Arsenic release was linked to ferrous iron release and primarily occurred in the intensely rooted uppermost soil. Volumetric air contents of 2-13 % during drought eliminated DMA from the porewater and suppressed its release after rewetting for >30 d. Dissolved As(III) was oxidized and immobilized as As(V) at rates of up to 0.015 mmol m−3 d−1. Rewetting mobilized As(III) at rates of up to 0.018 mmol m−3 d−1 within days. Concurrently, Fe(II) was released at depth integrated rates of up 20 mmol m−3 d−1. The redox half systems of arsenic, iron, and sulfur were in persistent disequilibrium, with H2S being a thermodynamically viable reductant for As(V) to As(III). The study suggests that rewetting can lead to a rapid release of arsenic in iron-rich peatlands and that methylation is of lesser importance than co-release with iron reduction, which was largely driven by root activity.  相似文献   

13.
Concern about arsenic is increasing throughout the world, including areas of the United States. Elevated levels of arsenic above current drinking-water regulations in ground and surface water can be the result of purely natural phenomena, but often are due to anthropogenic activities, such as mining and agriculture. The current study correlates arsenic speciation in acid mine drainage and mining-influenced water with the important water-chemistry properties Eh, pH, and iron(III) concentration. The results show that arsenic speciation is generally in equilibrium with iron chemistry in low pH AMD, which is often not the case in other natural-water matrices. High pH mine waters and groundwater do not always hold to the redox predictions as well as low pH AMD samples. The oxidation and precipitation of oxyhydroxides deplete iron from some systems, and also affect arsenite and arsenate concentrations through sorption processes.  相似文献   

14.
Groundwater arsenic survey in Cachar and Karimganj districts of Barak Valley, Assam shows that people in these two districts are drinking arsenic-contaminated (max. 350 μg/l) groundwater. 66% of tubewells in these two districts have arsenic concentration above the WHO guideline value of 10 μg/l and 26% tubewells have arsenic above 50 μg/l, the Indian standards for arsenic in drinking water. 90% of installed tubewells in these two districts are shallow depth (14–40 m). Shallow tubewells were installed in Holocene Newer Alluvium aquifers are characterised by grey to black coloured fine grained organic rich argillaceous sediments and are mostly arsenic contamination in groundwater. Plio-Pleistocene Older Alluvium aquifers composed of shale, ferruginous sandstone, mottle clay, pebble and boulder beds, which at higher location or with thin cover of Newer Alluvium sediments are safe in arsenic contamination in groundwater. 91% of tubewell water samples show significantly higher concentrations of iron beyond its permissible limit of 1 mg/l. The iron content in these two districts varies from 0.5 to as much as 48 mg/l. Most of the arsenic contaminated villages of Cachar and Karimganj districts are located in entrenched channels and flood plains of Newer Alluvium sediments in Barak-Surma-Langai Rivers system. However, deeper tubewells (>60 m) in Plio-Pleistocene Older Alluvium aquifers would be a better option for arsenic-safe groundwater. The arsenic in groundwater is getting released from associated Holocene sediments which were likely deposited from the surrounding Tertiary Barail hill range.  相似文献   

15.
A fluid inclusion investigation of the polymetallic mineralization at Yinshan from the Le–De metallogenic belt in Jiangxi Province of China has been carried out using petrographic and microthermometric techniques. The data obtained here indicate that three major types of fluids were involved during the formation of the deposit. They are type I vapor-rich, type II liquid-rich and type III halite-bearing inclusions within the H2O–NaCl system. The high salinity fluids represented by type III inclusions, being unusual to the distal part of an intrusion-centered ore-forming system such as Yinshan, have been interpreted as the product of direct exsolution of a crystallizing magma, rather than a result of fluid immiscibility from a low salinity fluid. Evidence used to support such an interpretation includes the mode of homogenization of type III inclusions exclusively via halite dissolution, spatial separation of type I and type III inclusions on microscopic scale, the consistent phase ratios within the inclusions concerned, and considerable deviation in homogenization temperature for both type I and type III inclusions. Trapping conditions for type I inclusions were estimated to be around 440 °C and 260 bars, while type III inclusions were constrained to be trapped at least above 900 bars and > 500 °C. The formation temperatures for type II inclusions range from 270 to 390 °C if a lithostatic pressure of 260 bars is assumed. Pressure fluctuation determined by this fluid inclusion study coupled with decreases in salinity and temperature as result of the potential fluid mixing are supposed to have played an important role in triggering the precipitation of ore minerals from the hydrothermal solution.  相似文献   

16.
Arsenic occurrence in groundwater near the Cimino-Vico volcanoes (central Italy) was analysed considering the hydrostratigraphy and structural setting and the shallow and deep flows interacting within the Quaternary volcanics. Groundwater is the local source of drinking water. As documented in the past, arsenic in the groundwater has become a problem, and the European maximum allowable contaminant level was recently lowered to 10 μg/L. Chemical analyses of groundwater were conducted, sampled over an area of about 900 km2, from 65 wells and springs representative of the volcanic aquifer and thermal waters. Considering the type of aquifer, the nature of the aquifer formation and its substratum, the hydrochemical data highlight that the arsenic content of the groundwater is mainly connected with the hydrothermal processes in the volcanic area. Thermal waters (54–60°C) fed from deep-rising fluids show higher arsenic concentrations (176–371 μg/L). Cold waters sampled from the volcanic aquifer are characterized by a wide variability in their arsenic concentration (1.6–195 μg/L), and about 62% exceed the limit of 10 μg/L. Where the shallow volcanic aquifer is open to deep-rising thermal fluids, relatively high arsenic concentrations (20–100 μg/L) are found. This occurs close to areas of the more recent volcano-tectonic structures.  相似文献   

17.
The study area covers an about 100 km2 of the middle Ganga plain in Uttar Pradesh, experiencing intensive groundwater extraction. In order to recognize the arsenic contamination zones of the Varanasi environs, sixty eight groundwater samples have been collected and analyzed for major ions, iron and arsenic. Twenty one sediment samples in the four boreholes were also collected to deduce the source of arsenic in the groundwater. The preliminary survey reports for the first time indicates that part of rural and urban population of Varanasi environs are drinking and using for irrigation arsenic contaminated water mostly from hand tube wells (<70 m). The study area is a part of middle Ganga plain which comprises of Quaternary alluvium consists of an alternating succession of clay, clayey silt and sand deposits. The high arsenic content in groundwater samples of the study area indicates that 14% of the samples are exceeding the 10 μg/l and 5% of the samples are exceeding 50 μg/l. The high arsenic concentration is found in the villages such as Bahadurpur, Madhiya, Bhojpur, Ratanpur, Semra, Jalilpur, Kateswar, Bhakhara and Kodupur (eastern side of Ganga River in Varanasi), situated within the newer alluvium deposited during middle Holocene to Recent. The older alluvial aquifers situated in the western side of the Ganga River are arsenic safe (maximum As concentration of 9 μg/l) though the borehole sediments shows high arsenic (mean 5.2 mg/kg) and iron content (529 mg/kg) in shallow and medium depths. This may be due to lack of reducing conditions (i.e organic content) for releasing arsenic into the groundwater. Rainfall infiltration, organic matter from recently accumulated biomass from flood prone belt in the newer alluvium plays a critical role in releasing arsenic and iron present in sediments. The main mechanism for the release of As into groundwater in the Holocene sandy aquifer sediments of Varanasi environs may be due to the reductive dissolution of Fe oxyhydroxide present as coatings on sand grains as well as altered mica content. The high societal problems of this study will help to mitigate the severity of arsenic contamination by providing alternate drinking water resources to the people in middle Ganga plain and to arrange permanent arsenic safe drinking water source by the authorities.  相似文献   

18.
A mesophilic iron oxidizing bacterium, Acidithiobacillus ferrooxidans, has been isolated (33 °C) from a typical, chalcopyrite concentrate of the Sarcheshmeh copper mine in the region of Kerman located in the south of Iran. In addition, a thermophilic iron oxidizing bacterium, Sulfobacillus, has been isolated (60 °C) from the sphalerite concentrate of Kooshk lead and zinc mine near the city of Yazd in the center point of Iran. Variation of pH, ferrous and ferric concentration on time and effects of some factors such as temperature, cell growth, initial ferrous concentration and pH on bioleaching of low-grade complex zinc–lead ore were investigated. The results obtained from bioleaching experiments indicate that the efficiency of zinc extraction is dependent on all of the mentioned variables; especially the temperature and initial Fe(II) concentration have more effect than other factors for these microorganisms. In addition, results show that the maximum zinc recovery was achieved using a thermophilic culture. Zinc dissolution reached 58% with Sulfobacillus while it was 51% with A. ferrooxidans at pH = 1.5, initial Fe(II) concentration = 7 and 9 g/L for A. ferrooxidans and Sulfobacillus, respectively, after 30 days.  相似文献   

19.
Peculiar magmatic rocks were erupted and emplaced at depth at the margin of the Gondwana supercontinent during the Cambro-Ordovician transition. These rocks are characterized by high contents in silica and iron but they do not have equivalents in the high-silica members of the calc-alkaline series. They have particular geochemical signatures, with Al saturation index, ASI > 1, FeO > 2.5 wt.%, MgO > 0.8 wt.% for very low contents in calcium (CaO < 2.0 wt.%), supporting a derivation from near-total melting (> 80 vol.% melt) of metagreywackes. The results from inverse experiments indicate that the most plausible conditions are within the range 1000 °C (excess water) and 1100–1200 °C (subsaturated and dry) at pressures of 1.5 to 2.0 GPa. A tectonic scenario implying melting of subducted sediments within an ascending mantle-wedge plume is suggested for the generation of primary ferrosilicic melts at the Gondwana continental margin during Upper Cambrian to Lower Ordovician times.  相似文献   

20.
Groundwater is a significant water resource in India for domestic, irrigation, and industrial needs. By far the most serious natural groundwater-quality problem in India, in terms of public health, derives from high fluoride, arsenic, and iron concentrations. Hydrogeochemical investigation of fluoride contaminated groundwater samples from Kolar and Tumkur Districts in Karnataka are undertaken to understand the quality and potability of groundwater from the study area, the level of fluoride contamination, the origin and geochemical mechanisms driving the fluoride enrichment. Majority of the groundwater samples did not meet the potable water criteria as they contained excess (>1.5 mg/L) fluoride, dissolved salts (>500 mg/L) and total hardness (75–924 mg/L). Hydrogeochemical facies of the groundwater samples suggest that rock weathering and evaporation–crystallization control the groundwater composition in the study area with 50–67% of samples belonging to the Ca–HCO3 type and the remaining falling into the mixed Ca–Na–HCO3 or Ca–Mg–Cl type. The saturation index values indicated that the groundwater in the study area is oversaturated with respect to calcite and under-saturated with respect to fluorite. The deficiency of calcium ion concentration in the groundwater from calcite precipitation favors fluorite dissolution leading to excess fluoride concentration.  相似文献   

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