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1.
We examined the solubility, mineralogy and geochemical transformations of sedimentary Fe in waterways associated with coastal lowland acid sulfate soils (CLASS). The waterways contained acidic (pH 3.26-3.54), FeIII-rich (27-138 μM) surface water with low molar Cl:SO4 ratios (0.086-5.73). The surficial benthic sediments had high concentrations of oxalate-extractable Fe(III) due to schwertmannite precipitation (kinetically favoured by 28-30% of aqueous surface water Fe being present as the FeIII species). Subsurface sediments contained abundant pore-water HCO3 (6-20 mM) and were reducing (Eh < −100 mV) with pH 6.0-6.5. The development of reducing conditions caused reductive dissolution of buried schwertmannite and goethite (formed via in situ transformation of schwertmannite). As a consequence, pore-water FeII concentrations were high (>2 mM) and were constrained by precipitation-dissolution of siderite. The near-neutral, reducing conditions also promoted SO4-reduction and the formation of acid-volatile sulfide (AVS). The results show, for the first time for CLASS-associated waterways, that sedimentary AVS consisted mainly of disordered mackinawite. In the presence of abundant pore-water FeII, precipitation-dissolution of disordered mackinawite maintained very low (i.e. <0.1 μM) S−II concentrations. Such low concentrations of S−II caused slow rates for conversion of disordered mackinawite to pyrite, thereby resulting in relatively low concentrations of pyrite (<300 μmol g−1 as Fe) compared to disordered mackinawite (up to 590 μmol g−1 as Fe). This study shows that interactions between schwertmannite, goethite, siderite, disordered mackinawite and pyrite control the geochemical behaviour of sedimentary Fe in CLASS-associated waterways.  相似文献   

2.
On the south-eastern edge of Russia, the chemical composition of rainwater is controlled by sea salts, terrestrial material, as well as volcanic (Kuril islands volcanic area) and anthropogenic emissions, mostly in the southern part of the area. The predominant major ions of the Primorye, Sakhalin and the Kuril Islands rainwaters were respectively HCO3−–SO42−, Ca–Na, and of Cl–Na. Concentration of trace elements changes within 1–2 orders of magnitude but some difference in the distribution of the elements between continental and island rainwater is found. The concentration of the chemical elements in the particulate fraction varies from < 10% to 90% of the total concentration (dissolved + particulate) with the following distribution: Tl, Na, Ca, Sr, Zn, Cd (< 10%)–Be, Th, Bi, Rb, U, K, Sc (10–20%)–Cu, Mn, Mg, Mo, Se, Ba, Ni, As, Ag, Cs, Co, Y, Ga, V (20–50%)–Sb, Pb, Ge, Cr, Fe, Al (50–90%).The concentration of elements of the particulate fraction of the rainwater usually is significantly different from concentrations in the crust, including both higher and lower concentrations. The terrestrial contribution to dissolved elements was evaluated and follows the decreasing order: Fe > K, Mg, Ca > Ba, Sr > Na (65–1%). Close order was found for total (dissolved and solid) concentrations. Sea salt contribution to dissolved element concentration in the rainwater decrease in the following order: Cl, Mg > K, SO4 > Ca > HCO3−, Ba, Fe (78–0.1%). Calculation of anthropogenic and volcanic inputs for two ions (Cl− and SO42−) shows that anthropogenic inputs for the Vladivostok and Yuzno-Sakhalinsk cities can be evaluated as 15–20% of Cl− and up to 80–90% of SO42−. Volcanic components in the Kuril Islands, where anthropogenic inputs are absent, can reach up to 76% of SO42− and 36% of Cl−.  相似文献   

3.
Cinnabar (α-HgS) and metacinnabar (β-HgS) dissolved at environmentally significant rates in oxygenated slurry experiments simulating a low-flow fluvial system. Based on SO42− production, cinnabar dissolution rates were 2.64 to 6.16 μmol (SO42−) m− 2 day− 1, and metacinnabar dissolution rates were 1.20 to 1.90 μmol (SO42−) m− 2 day− 1. Monodentate-bound thiosulfate (S2O32−) was identified as an oxidation product on the HgS surface by ATR-IR spectroscopy based on strong infrared absorption bands in the 1140–1145 cm− 1 and 1006–1014 cm− 1 regions. The presence of sulfide oxidation intermediates on the HgS surface indicates that SO42− concentration underestimates α-HgS and β-HgS dissolution in this setting. Mercury release rates during dissolution were more than two orders of magnitude less than SO42− production, but were significant: 0.47 mg (Hg) m− 2 y− 1 from cinnabar [6.45 nmol (Hg) m− 2 day− 1], and 0.17 mg (Hg) m− 2 y− 1 from metacinnabar [2.29 nmol (Hg) m− 2 day− 1]. The Hg mobilized during α-HgS and β-HgS dissolution is sufficient to form natural Au–Hg amalgam in downstream placer settings. The proportion of mercury that is not remobilized during α-HgS and β-HgS dissolution likely adsorbs to the dissolving mercuric sulfide. Adsorption of Hg2+ to cinnabar was detected in situ by anodic stripping voltammetry using a cinnabar-modified carbon paste electrode following accumulation of Hg2+ on the electrode at open circuit potential.  相似文献   

4.
Despite the common belief that AuI complexes with hydrogen sulfide ligands (H2S/HS−) are the major carriers of gold in natural hydrothermal fluids, their identity, structure and stability are still subjects of debate. Here we present the first in situ measurement, using X-ray absorption fine structure (XAFS) spectroscopy, of the stability and structure of aqueous AuI–S complexes at temperatures and pressures (T–P) typical of natural sulfur-rich ore-forming fluids. The solubility of native gold and the local atomic structure around the dissolved metal in S–NaOH–Na2SO4–H2SO4 aqueous solutions were characterized at temperatures 200–450 °C and pressures 300–600 bar using an X-ray cell that allows simultaneous measurement of the absolute concentration of the absorbing atom (Au) and its local atomic environment in the fluid phase. Structural and solubility data obtained from XAFS spectra, combined with quantum-chemical calculations of species geometries, show that gold bis(hydrogensulfide) Au(HS)2− is the dominant Au species in neutral-to-basic solutions (5.5  pH  8.5; H2O–S–NaOH) over a wide range of sulfur concentrations (0.2 < ΣS < 3.6 mol/kg), in agreement with previous solubility studies. Our results provide the first direct determination of this species structure, in which two sulfur atoms are in a linear geometry around AuI at an average distance of 2.29 ± 0.01 Å. At acidic conditions (1.5  pH  5.0; H2O–S–Na2SO4–H2SO4), the Au atomic environment determined by XAFS is similar to that in neutral solutions. These findings, together with measured high Au solubilities, are inconsistent with the predominance of the gold hydrogensulfide Au(HS)0 complex suggested by recent solubility studies. Our spectroscopic data and quantum-chemical calculations imply the formation of species composed of linear S–Au–S moieties, like the neutral [H2S–Au–SH] complex. This species may account for the elevated Au solubilities in acidic fluids and vapors with H2S concentrations higher than 0.1–0.2 mol/kg. However, because of the complex sulfur speciation in acidic solutions that involves sulfite, thiosulfate and polysulfide species, the formation of AuI complexes with these ligands (e.g., AuHS(SO2)0, Au(HS2O3)2−, Au(HSn)2−) cannot be ruled out. The existence of such species may significantly enhance Au transport by high T–P acidic ore-forming fluids and vapors, responsible for the formation of a major part of the gold resources on Earth.  相似文献   

5.
Study on the kinetics of iron oxide leaching by oxalic acid   总被引：2，自引：0，他引：2  
The presence of iron oxides in clay or silica raw materials is detrimental to the manufacturing of high quality ceramics. Although iron has been traditionally removed by physical mineral processing, acid washing has been tested as it is more effective, especially for extremely low iron (of less than 0.1% w/w). However, inorganic acids such as sulphuric or hydrochloric acids easily contaminate the clay products with SO42− and Cl−, and therefore should be avoided as much as possible. On the other hand, if oxalic acid is used, any acid left behind will be destroyed during the firing of the ceramic products. The characteristics of dissolution of iron oxides were therefore investigated in this study.The dissolution of iron oxides in oxalic acid was found to be very slow at temperatures within the range 25–60 °C, but its rate increases rapidly above 90 °C. The dissolution rate also increases with increasing oxalate concentration at the constant pH values set within the optimum range of pH2.5–3.0. At this optimum pH, the dissolution of fine pure hematite (Fe2O3) (105–140 μm) follows a diffusion-controlled shrinking core model. The rate expression expressed as 1 − (2 / 3)x − (1 − x)2 / 3 where x is a fraction of iron dissolution was found to be proportional to [oxalate]1.5.The addition of magnetite to the leach liquor at 10% w/w hematite was found to enhance the dissolution rate dramatically. Such addition of magnetite allows coarser hematite in the range 0.5–1.4 mm to be leached at a reasonable rate.  相似文献   

6.
We examined the transformations of Fe and S associated with schwertmannite (Fe8O8(OH)6SO4) reduction in acidified coastal lowlands. This was achieved by conducting a 91 day diffusive-flux column experiment, which involved waterlogging of natural schwertmannite- and organic-rich soil material. This experiment was complemented by short-term batch experiments utilizing synthetic schwertmannite. Waterlogging readily induced bacterial reduction of schwertmannite-derived Fe(III), producing abundant pore-water FeII, SO4 and alkalinity. Production of alkalinity increased pH from pH 3.4 to pH ∼6.5 within the initial 14 days, facilitating the precipitation of siderite (FeCO3). Interactions between schwertmannite and FeII at pH ∼6.5 were found, for the first time, to catalyse the transformation of schwertmannite to goethite (αFeOOH). Thermodynamic calculations indicate that this FeII-catalysed transformation shifted the biogeochemical regime from an initial dominance of Fe(III)-reduction to a subsequent co-occurrence of both Fe(III)- and SO4-reduction. This lead firstly to the formation of elemental S via H2S oxidation by goethite, and later also to formation of nanoparticulate mackinawite (FeS) via H2S precipitation with FeII. Pyrite (FeS2) was a quantitatively insignificant product of reductive Fe and S mineralization. This study provides important new insights into Fe and S geochemistry in settings where schwertmannite is subjected to reducing conditions.  相似文献   

7.
Twenty-eight samples of peat, peaty lignites and lignites (of both matrix and xylite-rich lithotypes) and subbituminous coals have been physically activated by pyrolysis. The results show that the surface area of the activated coal samples increases substantially and the higher the carbon content of the samples the higher the surface area.The adsorption capacity of the activated coals for NO, SO2, C3H6 and a mixture of light hydrocarbons (CH4, C2H6, C3H8 and C4H10) at various temperatures was measured on selected samples. The result shows a positive correlation between the surface area and the gas adsorption. In contrast, the gas adsorption is inversely correlated with the temperature. The maximum recorded adsorption values are: NO = 8.22 × 10− 5 mol/g at 35 °C; SO2 = 38.65 × 10− 5 mol/g at 60 °C; C3H6 = 38.9 × 10− 5 mol/g at 35 °C; and light hydrocarbons = 19.24 × 10− 5 mol/g at 35 °C. Adsorption of C3H6 cannot be correlated with either NO or SO2. However, there is a significant positive correlation between NO and SO2 adsorptions. The long chain hydrocarbons are preferentially adsorbed on activated lignites as compared to the short chain hydrocarbons.The results also suggest a positive correlation between surface area and the content of telohuminite maceral sub-group above the level of 45%.  相似文献   

8.
The interaction of organic compounds with the mineral phase is considered as one stabilization mechanism for organic carbon (OC) in soils. The objective of this study is to assess the role of mineral surfaces for the long-term stabilization of OC in arable soils, with special emphasis on iron oxides. Soil samples were taken from two contrasting treatment types, i.e. fertilized plots and C-depleted plots, in long-term agroecosystem experiments. The soil organic carbon pool of the C-depleted plots is considered to show a lower contribution of labile compounds and consequently to be relatively enriched in refractory compounds compared with the fertilized counterparts. In fractions <6 μm, OC was studied in relation to total mineral surface area, surface area contributed by oxides and silicates, and the content and type of iron oxides (dithionite and oxalate extractable iron, Fed and Feo). In two sandy soils, OC contents were linearly related to total mineral surface area and the content of the two iron oxide fractions (Fed and Feo). The surface area developed by the silicates was low and thus the surface area contribution from oxides was dominant in fractions <6 μm. In contrast to the sandy soils, in a loamy soil OC was not correlated with surface area or the iron oxide content. However, the different soils agreed with respect to the behavior of C in density fractions: losses of OC occurred mainly from the light fraction (2 g cm−3), whereas C in the heavy fraction (>2 g cm−3) proved to be stable. For the sandy soils, mineral surface area appears to control the storage of OC in fine fractions. Given the dominant surface area contribution from oxides, OC storage here primarily depends on the oxides. The C-depleted plots in particular show that surface area controls the accumulation of refractory C. The interaction of organic compounds with the mineral phase, mainly with the surface of oxides, seems to be a major mechanism for the long-term stabilization of OC in these sandy soils. An interaction with minerals seems to be important for stabilizing OC also in the loamy soil, although this is not reflected by a proportional relation between OC and surface area across the fractions.  相似文献   

9.
Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), Na–Ca–HCO3 type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has δ18O of − 8.3‰, δD of − 48.2‰,δ11B of 1.5‰, and 87Sr/86Sr of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5–8.0, mean 7.3), Na–Ca–Mg–Cl–SO4 type waters with moderate TDS (8.2 g/l–17.2 g/l, mean 9.3 g/l, brackish) and haveδ18O values in the − 5.8‰ to − 9.3‰ range (mean − 8.1‰), δD values in the − 20.8‰ to − 85.5‰ range (mean − 47.0‰),δ11B values in the + 9.5‰ to + 39.1‰ range (mean + 17.1‰), and 87Sr/86Sr values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH = 7.4), Na–Ca–Mg–Cl–SO4 type water with the highest TDS (249.1 g/l, brine) and has δ18O of − 2.8‰, δD of − 45.8‰,δ11B of 21.2‰, and 87Sr/86Sr of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and δ11B values along the pathway of groundwater migration which can only be interpreted in terms of water–rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water–rock interaction and mixing of meteoric water with connate waters contained in sediments.  相似文献   

10.
Individual and monthly precipitation samples from the polluted atmosphere of Bologna (Emilia-Romagna province) were collected during March 1996 to May 1997 and analyzed for major ions in solution and S isotopes in dissolved SO4.Weighted mean enrichment factors relative to seawater are found to be 1.0 for Na, 15.2 for K, 105 for Ca, 3.3 for Mg, 17.3 for SO4 and 663 for HCO−3. Very good positive correlations are observed for the Ca2+–Mg2+–HCO−3–SO2−4–NO−3 system, indicating that dissolution of Ca (±Mg)-carbonate particles by H2SO4 and HNO3 from combustion of oil and gas is a major process controlling the chemical composition of rain and snow. Na+ and Cl− in monthly precipitation derive essentially from sea spray, but the contribution of Na+ from continental sources is appreciable in a number of individual rains. NH+4 appears to be on average more abundant in spring and summer precipitation, its main sources being microbial activity in soils and application of fertilizers. K+ is probably of continental origin from soil dust.The S isotopic composition of SO4 is systematically positive, with mean δ34S values of +3.2±1.6‰ (n=40) in individual precipitation and +2.8±1.4‰ (n=12) in monthly precipitation. These isotopic compositions are interpreted in terms of a dominant contribution of S from anthropogenic emissions and subordinate contributions from biogenic and marine sources. Pollutant SO4 is estimated to have a δ34S value in the range +2.5 to +4.5‰, whereas a distinctive δ34S of −4.5‰ or lower indicates SO4 from oxidation of biogenic gases.The isotopic and chemical compositions of SO4 do not depend on wind direction, thus testifying to a mostly local source for pollutant S in the Bologna atmosphere.  相似文献   

11.
Values of overall Gibbs free energy of 144 organic oxidation (respiration) and disproportionation (fermentation) reactions are calculated at the temperatures and chemical compositions that exist in nine submarine vents, sediment seeps and geothermal wells in the hydrothermal system of Vulcano Island, Italy. The organic compounds considered here include four carboxylic acids (formic, acetic, propanoic and lactic), two C5 aldoses (arabinose and xylose), three C6 aldoses (galactose, glucose and mannose), and 15 protein-forming amino acids (Ala, Arg, Asp, Glu, Gly, His, Ile, Leu, Lys, Met, Phe, Ser, Thr, Tyr, and Val). Oxidation of these compounds is coupled to five redox pairs: O2/H2O, , S0/H2S, and Fe3O4/Fe2+. Energy yields from potential respiration reactions range from 6 to 118 kJ/mol of electrons transferred and show systematic behavior with respect to the terminal electron acceptor. Overall, respiration with O2 yields the most energy (98–118 kJ/mol e−), followed by reactions with (53– 86 kJ/mol e−), magnetite (29–91 kJ/mol e−), S0 (11–33 kJ/mol e−) and (6–34 kJ/mol e−). Energy yields show little correlation with organic compound family, but are correlated with fluid pH. Variability in energy yields across the nine sites is greatest for Fe(III) reduction and is primarily influenced by pH and the activity of Fe2+. In addition to the potential respiration reactions, the energetics of 24 potential fermentation reactions are also calculated. As expected, fermentation reactions generally yield much less energy than respiration. Normalized to the number of moles of carbon transferred, fermentation yields−8 to 71 kJ/mol C, compared with 16 to 531 kJ/mol C for respiration reactions. All respiration and fermentation reactions, except for methionine (Met) fermentation, are exergonic under the in situ hydrothermal conditions and represent a plethora of potential metabolisms for Vulcano’s diverse thermophilic heterotrophs.  相似文献   

12.
Several methods were evaluated and compared for the estimation of pyrite oxidation rates (POR) in waste rock at Mine Doyon, Quebec, Canada. Methods based on data collected in situ, such as the interpretation of temperature and oxygen concentration profiles (TOP) measured in the waste rock pile and pyrite mass balance (PMB) on solid phase samples were compared with the oxygen consumption measurements (OCM) in closed chamber in the laboratory. A 1-D analytical solution to a gas and heat transport equation used temperature and oxygen profiles (TOP) measured in the pile for the preliminary POR estimates at a site close to the slope of the pile (Site 6) and in the core of the pile (Site 7). Resulting POR values were 1.1 × 10− 9 mol(O2) kg− 1 s− 1 and 1.0 × 10− 10 mol(O2) kg− 1 s− 1 for the slope site and the core site, respectively. Oxidation rates based on pyrite mass balance (PMB) calculations for solid samples were 2.21 × 10− 9 mol(O2) kg− 1 s− 1 and 2.03 × 10− 9 mol(O2) kg− 1 s− 1, respectively, for the same slope and core sites, but the difference between sites was within the error margin. The OCM measurements in the laboratory on fresh waste rock samples yielded higher POR values than field methods, with average oxidation rate of 6.7 × 10− 8 mol(O2) kg− 1 s− 1. However, the OCM results on weathered and decomposed material from the rock stockpile (average oxidation rate 3.4 × 10− 9 mol(O2) kg− 1 s− 1) were consistent with results from the field-based estimates. When POR values based on fresh material are excluded, the remaining POR values for all methods range from 1.0 × 10− 10 to 3.4 × 10− 9 mol(O2) kg− 1 s− 1. The lowest estimated value (1.0 × 10− 10 mol(O2) kg− 1 s− 1) was based on TOP estimates in the interior of the pile where oxygen transport was limited by diffusion from the surface. These results suggest that small-scale OCM laboratory experiments may provide relatively representative values of POR in the zones of waste rock piles in which oxygen transport is not dominated by diffusion.  相似文献   

13.
The vertical distribution of reduced sulfur species (RSS including H2S/HS−, S0, electroactive FeS) and dissolved Fe(II) was studied in the anoxic water column of meromictic Lake Pavin. Sulfide concentrations were determined by two different analytical techniques, i.e. spectophotometry (methylene blue technique) and voltammetry (HMDE electrode). Total sulfide concentrations determined with methylene blue method (∑H2SMBRS) were in the range from 0.6 µM to 16.7 µM and were substantially higher than total reduced sulfur species (RSSV) concentrations determined by voltammetry, which ranged from 0.1 to 5.6 μM. The observed difference in the sulfide concentrations between the two methods can be assigned to the presence of FeS colloidal species.Dissolved Fe was high (> 1000 µM), whereas dissolved Mn was only 25 µM, in the anoxic water column. This indicates that Fe is the dominant metal involved in sulfur redox cycling and precipitation. Consequently, in the anoxic deep layer of Lake Pavin, “free” sulfide, H2S/HS−, was low; and about 80% of total sulfide detected was in the electroactive FeS colloidal form. IAP calculations showed that the Lake Pavin water column is saturated with respect to FeSam phase. The upper part of monimolimnion layer is characterized by higher concentrations of S(0) (up to 3.4 µM) in comparison to the bottom of the lake. This behavior is probably influenced by sulfide oxidation with Fe(III) oxyhydroxide species.  相似文献   

14.
Dissolution of the synthetic hydroxylapatite (HAP) and fluorapatite (FAP) in pure water was studied at 25 °C and 45 °C in a series of batch experiments. The XRD, FT-IR and SEM analyses indicated that the synthetic, microcrystalline HAP and FAP with apatite structure used in the experiments were found to have no obvious variation after dissolution except that the existence of OH groups in FT-IR spectra for FAP after 2880 h dissolution was observed. During the HAP dissolution (0–4320 h), the aqueous calcium and phosphate concentrations reached the maxima after 120 h and then decreased slowly with time. For the FAP dissolution in pure water, after a transient time of 1440 h (< 60 d), element concentrations and pH became constant suggesting attainment of a steady-state between the solution and solid. During early stages of the FAP dissolution reaction (< 72–120 h), mineral components were released in non-stoichiometric ratios with reacted solution ratios of dissolved Ca:P, Ca:F and P:F being lower than mineral stoichiometric ratios of Ca5(PO4)3F, i.e., 1.67, 5.0 and 3.0, respectively. This indicated that F were preferentially released compared to Ca from the mineral structure. The mean Ksp values were calculated by using PHREEQC for HAP of 10− 53.28 (10− 53.02–10− 53.51) and for FAP of 10− 55.71 (10− 55.18–10− 56.13) at 25 °C, the free energies of formation ΔGfo[HAP] and ΔGfo[FAP] were calculated to be − 6282.82 kJ/mol and − 6415.87 kJ/mol, respectively.  相似文献   

15.
The wetland constructed at the Big Five Tunnel in Idaho Springs, Colorado was designed to remove, passively, heavy metals from acid mine drainage. In optimizing the design of such a wetland, an improved understanding of the chemical processes operating there was required, particularly SO42− reduction and sulfide precipitation. For this purpose, field and laboratory data were collected to study the balance of S in the system. Field data collected included water analyses of the mine drainage and wetland effluents and measurements of H2S gas emissions from the wetland. The concentration of sulfide in the wetland effluent ranged from 10−4 to 10−3 mol/l. The average rates of H2S emission from the surface of the substrate were 150 nmol/cm2/d in the summer and 0.17 and 0.35 nmol/cm2/d in the winter. This maximum estimated loss of sulfide was not significant in reducing the amount of sulfide available for precipitation with metals. Sequential extraction experiments for S on wetland substrates showed that acid volatile sulfides (AVS) increased with time in the wetland substrate. A serum bottle experiment was conducted to study the S balance in the Big Five wetland by quantitatively measuring the amount of S in different phases as microbial SO42− reduction progressed. The increase in AVS reasonably balanced the decrease in SO42− concentration in the experiment, suggesting that the decrease in SO42− concentration represented the amount of SO42− reduced and that nearly all of the sulfide produced was precipitated as AVS. Sulfide precipitation was determined to be the primary metal removal process in the wetland system and amorphous FeS is the primary iron sulfide formed in the substrate.  相似文献   

16.
To study the geological control on groundwater As concentrations in Red River delta, depth-specific groundwater sampling and geophysical logging in 11 monitoring wells was conducted along a 45 km transect across the southern and central part of the delta, and the literature on the Red River delta’s Quaternary geological development was reviewed. The water samples (n = 30) were analyzed for As, major ions, Fe2+, H2S, NH4, CH4, δ18O and δD, and the geophysical log suite included natural gamma-ray, formation and fluid electrical conductivity. The SW part of the transect intersects deposits of grey estuarine clays and deltaic sands in a 15–20 km wide and 50–60 m deep Holocene incised valley. The NE part of the transect consists of 60–120 m of Pleistocene yellowish alluvial deposits underneath 10–30 m of estuarine clay overlain by a 10–20 m veneer of Holocene sediments. The distribution of δ18O-values (range −12.2‰ to −6.3‰) and hydraulic head in the sample wells indicate that the estuarine clay units divide the flow system into an upper Holocene aquifer and a lower Pleistocene aquifer. The groundwater samples were all anoxic, and contained Fe2+ (0.03–2.0 mM), Mn (0.7–320 μM), SO4 (<2.1 μM–0.75 mM), H2S (<0.1–7.0 μM), NH4 (0.03–4.4 mM), and CH4 (0.08–14.5 mM). Generally, higher concentrations of NH4 and CH4 and low concentrations of SO4 were found in the SW part of the transect, dominated by Holocene deposits, while the opposite was the case for the NE part of the transect. The distribution of the groundwater As concentration (<0.013–11.7 μM; median 0.12 μM (9 μg/L)) is related to the distribution of NH4, CH4 and SO4. Low concentrations of As (?0.32 μM) were found in the Pleistocene aquifer, while the highest As concentrations were found in the Holocene aquifer. PHREEQC-2 speciation calculations indicated that Fe2+ and H2S concentrations are controlled by equilibrium for disordered mackinawite and precipitation of siderite. An elevated groundwater salinity (Cl range 0.19–65.1 mM) was observed in both aquifers, and dominated in the deep aquifer. A negative correlation between aqueous As and an estimate of reduced SO4 was observed, indicating that Fe sulphide precipitation poses a secondary control on the groundwater As concentration.  相似文献   

17.
The Mapocho river, which crosses downtown Santiago, is one of the most important rivers in contact with a population of about six million inhabitants. Anthropogenic activities, industrialization, farming activities, transport, urbanization, animal and human excretions, domestic wastes and copper mining have affected the river, contaminating it and its sediments with heavy metals. Concentration and distribution of Cu, Zn, Pb and Cd were studied with the purpose of determining their bioavailability and their relation with the characteristics of the sediments. Freshly deposited seasonal sediments were collected from 0–8 cm depths from 6 locations (S1 to S6) along the 30-km long channel length, in the four seasons of year on the following dates: May 2001 (D1, autumn); August 2001 (D2, winter); October 2001 (D3, spring) and January 2002 (D4, summer). The dried samples were sifted to obtain the < 63-μm sediment fraction, since it has been shown that large amounts of heavy metals are bound in the fine-grained fraction of the sediment. Cu and Zn were analyzed by atomic absorption spectrophotometry and Pb and Cd by square wave anodic stripping voltammetry. The highest concentrations of Cu (2850 μg g− 1) were found in the northern part of the river (S1, average D1–D4), near the mountains and a copper mine, and then decreased downstream to 209 μg g− 1 (S6). Total Zn showed an irregular variation, with higher values at S1 (1290 μg g− 1) and high values in some winter sampling (1384 μg g− 1 S4, S5–D2). Pb showed different trends, increasing from S1 to S6 (17 to 61 μg g− 1), with the highest values in the summer samples (83 μg g− 1, S4–S6, D4), and total Cd increased slightly from mean values of 0.2 and 0.5 μg g− 1. Partition into five fractions was made using Tessier's analytical sequential extraction technique; the residue was treated with aqua regia for recovery studies, although this step is not part of the Tessier procedure. The results show that Cu, Zn and Pb in the sediments were dependent on the sampling places along the river, and variation in two years was low (D1–D4). The highest values of total organic matter, carbonate and conductivity were found in S6, which has the smallest size particles, while at S1 the sediments were predominantly sand and contain larger amounts of silica. Cu associated with carbonate decreased gradually from 58% (1771 μg g− 1, S1) to 16% (32 μg g− 1, S6); Cu bonded to reducible fraction was almost constant (33% to 37%), and Cu associated with oxidizable fraction increased from 7% (S1) to 34% (S6), but copper content was lower (214 to 68 μg g− 1). Zn had a similar fractionation profile. However, Pb bound to oxidizable fraction did not show significant percent variation along the river (20% to 19%), but the amount bounded was 4 to 12 μg g− 1. The residual fraction increased from 24% to 41% (5 to 25 μg g− 1, S1 to S6). The distribution of Cd in the sediment was almost independent of the sampling stations and was bound to carbonate, reducible and residual fraction in similar proportion. Cu and Zn at S1 were mainly bound to carbonates and reducible phases with 91% and 73% (2779 and 965 μg g− 1, respectively), and with a change in the pH and/or the redox potential of the sediment–water system, these contaminants could easily enter the food chain. In S6 the amount of Cu and Zn in these phases was 50% and 53% (100 to 313 μg g− 1, respectively).  相似文献   

18.
Literature data on the thermodynamics of complexation of Zr with inorganic species, at 25°C, have been critically reviewed. The preponderance of published complexation constants deal with F− and OH− ions. Stability constants for the complexation reactions are relatively independent of ionic strength and thus recomended values for each ligand type are averages of the most reliable data. Complexation constants under elevated conditions (T 250°C andPv = PH2O) have been predicted for various Zr complexes (F−, Cl−, SO42− and OH−) using Helgeson's electrostatic approach. Predominance diagrams (calculated for simple systems with these constants) suggest that, over a wide range of pH conditions, Zr(OH)4(aq) will dominate the aqueous geochemistry of Zr except under very high activities of competing ligands (e.g., F−, SO42−).The solubilities of vlasovite [Na2ZrSi4O11] and weloganite [Sr3Na2Zr(CO3)6·3H2O have been measured in KCI solutions (0.5–1.0 M) at 50°C. Weloganite dissolution is complicated by the predictable precipitation of strontianite (SrCO3) whereas vlasovite dissolves incongruently. Solubility products for the dissolution of welonganite and vlasovite are determined to be −28.96±0.14 and −20.40±1.18, respectively. Concentrations of Zr up to 10−3 m were present in the experimental solutions; the presence of large amounts of Zr in aqueous solutions support the possibility of extensive remobilization of Zr during hydrothermal mineralization.  相似文献   

19.
Cantilever torque magnetometry is utilized widely in physics and material science for the determination of magnetic properties of thin films and semiconductors. Here, we report on its first application in rock magnetism, namely the determination of K1 and K2 of single crystal octahedra of natural magnetite. The design of cantilever magnetometers allows optimization for the specific research question at hand. For the present study, a cantilever magnetometer was used that enables measurement of samples with a volume up to 64 mm3. It can be inserted into an electromagnet with a maximum field of 2 T. The cantilever spring is suitable for torque values ranging from 7.5 × 10− 7 N·m to 5 × 10− 6 N·m. The torque is detected capacitively; the measured capacitance is converted into torque by using a calibrated feedback coil. The magnetometer allows in-situ rotation of the sample in both directions and is, therefore, also suitable to analyze rotational hysteresis effects.The evaluation of the magnetite anisotropy constants involved Fourier analysis of the torque signal on the magnetite crystals' (001) and (110) planes. The absolute anisotropy constant has been computed using the extrapolation-to-infinite-field method. The value of K1 at room temperature is determined at − 1.28 × 104 [J m− 3] (± 0.13, i.e. 10%) and that of K2 at − 2.8 × 103 [J m− 3] (± 0.1, i.e. 2%). These values concur with earlier determinations that could not provide an instrumental error, in contrast with this work.The cantilever magnetometer performs four times faster than other torque magnetometers used for rock magnetic studies. This makes the instrument also suitable for magnetic fabric analysis.  相似文献   

20.
The possible contamination of a groundwater system with industrial wastewater originating from a paper mill factory has been investigated in Piteå, N. Sweden. Six samples were collected from the wastewater in the waste dump and twelve samples from the adjacent groundwater were analyzed for chemistry and sulfur isotopes. The industrial wastewater is a saline water consisting mainly of Na–HCO3–SO4, having a high pH and showing δ34S values between 7‰ and 9‰ affected by bacterial sulfate reduction. The groundwaters are relatively dilute, dominated by Na+, Ca2+ and HCO3−, but with varying concentrations as exemplified by sulfate with concentrations varying between 3 and 69 mg L− 1 while the δ34S values range from − 0.5‰ to 14.3‰. The data suggest that the main S sources in the waters are the bedrock sulfides and/or atmospheric deposition, which, sometimes, are overlapped by bacterial sulfate reduction. Contamination from the waste dump does not occur.  相似文献   

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