首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Gold extraction at the Macraes gold mine in New Zealand involves concentration of pyrite and arsenopyrite, oxidation of those sulphides, then cyanidation. The ore concentrate is predominantly Otago Schist host rock (andesitic composition) with up to 15% sulphides. The oxidation step is conducted on ore concentrate slurry in an autoclave at 225°C and 3,800 kPa oxygen gas pressure with continuous feed. The slurry takes ca. 1 h to pass through the autoclave, during which time the sulphides are almost completely oxidised. Sulphide oxidation causes strong acidification of the slurry, which is maintained at pH of 1–2 by addition of CaCO3. Scales form on walls in the autoclave, with minerals reflecting progressive oxidation and alteration of the ore through the system. The schist in the ore feed has mineralogy similar to propylitically altered andesite: quartz, albite, muscovite, chlorite, and pyrite. Muscovite undergoes almost complete dissolution, with associated precipitation of quartz and alunite (KAl3(SO4)2(OH)6). Other principal minerals deposited and discharged include anhydrite (and/or gypsum), jarosite (KFe3(SO4)2(OH)6), hematite (and/or amorphous iron oxyhydroxide), and amorphous arsenates. Dissolved ferrous iron passes right through the autoclave, and variably hydrated Fe2+and Fe3+sulphate minerals, including rozenite and szomolnokite (both FeSO4.hydrate) and ferricopiapite (Fe5(SO4)6O(OH).hydrate), are formed along the way. The autoclave chemical system resembles acid–sulphate hydrothermal activity in geothermal systems and high-sulphidation epithermal mineral deposits formed in arc environments. These natural acid–sulphate systems are pervaded by volcanic vapours in the near-surface environment, where widespread dissolution of host rocks occurs and deposition of quartz, alunite, and anhydrite is common. Some of the volume loss associated with these natural systems may be due to dissolution of soluble sulphate minerals by later-stage groundwater incursion.  相似文献   

2.
《Applied Geochemistry》2001,16(7-8):947-961
During dry season baseflow conditions approximately 20% of the flow in Boulder Creek is comprised of acidic metals-bearing groundwater. Significant amounts of efflorescent salts accumulate around intermittent seeps and surface streams as a result of evaporation of acid rock drainage. Those salts include the Fe-sulfates — rhomboclase ((H3O)Fe3+(SO4)2·3H2O), ferricopiapite (Fe3+5(SO4)6O(OH)·20H2O), and bilinite (Fe2+Fe23+(SO4)4·22H2O); Al-sulfates — alunogen (Al2(SO4)3·17H2O) and kalinite (KAl(SO4)2·11H2O); and Ca- and Mg-sulfates — gypsum (CaSO4·2H2O), and hexahydrite (MgSO4·6H2O). The dissolution of evaporative sulfate salt accumulations during the first major storm of the wet season at Iron Mountain produces a characteristic hydrogeochemical response (so-called “rinse-out”) in surface waters that is subdued in later storms. Geochemical modeling shows that the solutes from relatively minor amounts of dissolved sulfate salts will maintain the pH of surface streams near 3.0 during a rainstorm. On a weight basis, Fe-sulfate salts are capable of producing more acidity than Al- or Mg-sulfate salts. The primary mechanism for the production of acidity from salts involves the hydrolysis of the dissolved dissolved metals, especially Fe3+. In addition to the lowering of pH values and providing dissolved Fe and Al to surface streams, the soluble salts appear to be a significant source of dissolved Cu, Zn, and other metals during the first significant storm of the season.  相似文献   

3.
《Applied Geochemistry》2005,20(3):639-659
The oxidation of sulfide minerals from mine wastes results in the release of oxidation products to groundwater and surface water. The abandoned high-sulfide Camp tailings impoundment at Sherridon, Manitoba, wherein the tailings have undergone oxidation for more than 70 a, was investigated by hydrogeological, geochemical, and mineralogical techniques. Mineralogical analysis indicates that the unoxidized tailings contain nearly equal proportions of pyrite and pyrrhotite, which make up to 60 wt% of the total tailings, and which are accompanied by minor amounts of chalcopyrite and sphalerite, and minute amounts of galena and arsenopyrite. Extensive oxidation in the upper 50 cm of the tailings has resulted in extremely high concentrations of dissolved SO4 and metals and As in the tailings pore water (pH < 1, 129,000 mg L−1 Fe, 280,000 mg L−1 SO4, 55,000 mg L−1 Zn, 7200 mg L−1 Al, 1600 mg L−1 Cu, 260 mg L−1 Mn, 110 mg L−1 Co, 97 mg L−1 Cd, 40 mg L−1 As, 15 mg L−1 Ni, 8 mg L−1 Pb, and 3 mg L−1 Cr). The acid released from sulfide oxidation has been extensive enough to deplete carbonate minerals to 6 m depth and to partly deplete Al-silicate minerals to a 1 m depth. Below 1 m, sulfide oxidation has resulted in the formation of a continuous hardpan layer that is >1 m thick. Geochemical modeling and mineralogical analysis indicate that the hardpan layer consists of secondary melanterite, rozenite, gypsum, jarosite, and goethite. The minerals indicated mainly control the dissolved concentrations of SO4, Fe, Ca and K. The highest concentrations of dissolved metals are observed directly above and within the massive hardpan layer. Near the water table at a depth of 4 m, most metals and SO4 sharply decline in concentration. Although dissolved concentrations of metals and SO4 decrease below the water table, these concentrations remain elevated throughout the tailings, with up to 60,600 mg L−1 Fe and 91,600 mg L−1 SO4 observed in the deeper groundwater. During precipitation events, surface seeps develop along the flanks of the impoundment and discharge pore water with a geochemical composition that is similar to the composition of water directly above the hardpan. These results suggest that shallow lateral flow of water from a transient perched water table is resulting in higher contaminant loadings than would be predicted if it were assumed that discharge is derived solely from the deeper primary water table. The abundance of residual sulfide minerals, the depletion of aluminosilicate minerals in the upper meter of the tailings and the presence of a significant mass of residual sulfide minerals in this zone after 70 a of oxidation suggest that sulfide oxidation will continue to release acid, metals, and SO4 to the environment for decades to centuries.  相似文献   

4.
Formation conditions of ammoniojarosite in system Fe2（SO4）3-（NH4）2SO4-H2O are investigated in this paper. The results show that ammoniojarosite can be formed rapidly under normal temperature and pressure by controlling suitable pH value and Fe2（SO4）3 and （NH4）2SO4 concentrations. The pH value, temperature and concentration of Fe2（SO4）3 medium are key factors influencing the formation of ammoniojarosite. Under normal temperature, precipitation of ammoniojarosite can be seen within 24 hours at pH values between 2.6-3.1, and a great quantity of ammoniojarosite is formed within 48 hours. At about 90℃, the pH value range forming ammoniojarosite extends to 1.2-3.1, and within this range the rise of pH value is advantageous to the formation of ammoniojarosite and high Fe2（SO4）3 concentration is also advantageous. Relative pure ammoniojarosite is synthesized under high Fe2（SO4）3 concentration （≥0.05 M） and ammoniojarosite containing melanterite and colloid amorphous hydroxide vitriol iron is formed at low Fe2（SO4）3 concentration. The deposition process of ammoniojarosite can be used to harness wastewater from mines and other industries and remove S, Fe and other toxic and harmful elements, such as As, Cr, Hg, Pb in water. Rapid formation of ammoniojarosite and other jarosite analogs under normal temperature and pressure has a good potential prospect for harnessing acid wastewater by means of precipitation of jarosite and its analogs.  相似文献   

5.
《Applied Geochemistry》2001,16(9-10):1241-1249
A two-column reactor was designed to remove dissolved As and Cd from contaminated water. The reactor functions by equilibrating the targeted water with CO2 and directing it via saturated flow through a column of crushed siderite. This results in siderite dissolution and an increase in dissolved Fe(II). The feedwater is then directed into the top of a second, aerated column of crushed limestone, where it passes by unsaturated flow. The Fe2+ ion oxidizes quickly to Fe3+ and precipitates as Fe(III) oxyhydroxide, which is an effective sorbent of AsO43−. The aeration that occurs in the second column also removes dissolved CO2 from the feedwater. This causes precipitation of Ca and Cd carbonates. Together, the two processes reduce As and Cd concentrations from 1 and 3 mg/l, respectively, to below detection (respectively <0.005 and <0.01 mg/l). A time-limited reduction in Cr concentration also occurred. Much of the As was removed in the first column of the reactor, because Fe(III) oxyhydroxides also formed there. This was due to oxidation of Fe(II) by Cr(VI) and other oxidants present in the input wastewater. Although As is removed in the reactor columns by a sorption mechanism, the sorbent responsible, Fe(III) oxyhydroxide, is continuously produced during the operation of the reactor. Thus, unlike attenuation in a system with a fixed amount of sorbent, breakthrough of the As contaminant should never occur.  相似文献   

6.
The knowledge of mineralogy and molecular structure of As is needed to better understand the stability of As in wastes resulting from processing of gold ores. In this study, optical microscopy, scanning electron microscopy, electron microprobe, X-ray diffraction and X-ray absorption fine structure (XAFS) spectroscopy (including both XANES and EXAFS regimes) were employed to determine the mineralogical composition and local coordination environment of As in gold ores and process tailings from bench-scale tests designed to mimic a common plant practice. Arsenic-bearing minerals identified in the ores and tailings include iron (III) oxyhydroxides, scorodite (FeAsO4·2H2O), ferric arsenates, arseniosiderite (Ca2Fe3(AsO4)3O2·3H2O), Ca-Fe arsenates, pharmacosiderite (KFe4(AsO4)3(OH)4·6-7H2O), jarosite (K2Fe6(SO4)4(OH)12) and arsenopyrite (FeAsS). Iron (III) oxyhydroxides contain variable levels of As from trace to about 22 wt% and Ca up to approximately 9 wt%.Finely ground ore and tailings samples were examined by bulk XAFS and selected mineral grains were analyzed by microfocused XAFS (micro-EXAFS) spectroscopy to reconcile the ambiguities of multiple As sources in the complex bulk EXAFS spectra. XANES spectra indicated that As occurs as As5+in all the samples. Micro-EXAFS spectra of individual iron (III) oxyhydroxide grains with varying As concentrations point to inner-sphere bidentate-binuclear arsenate complexes as the predominant form of As. There are indications for the presence of a second Fe shell corresponding to bidentate-mononuclear arrangement. Iron (III) oxyhydroxides with high As concentrations corresponding to maximum adsorption densities probably occur as nanoparticles. The discovery of Ca atoms around As in iron (III) oxyhydroxides at interatomic distances of 4.14-4.17 Å and the coordination numbers suggest the formation of arseniosiderite-like nanoclusters by coprecipitation rather than simple adsorption of Ca onto iron (III) oxyhydroxides. Correlation of Ca with As in iron (III) oxyhydroxides as determined by electron microprobe analysis supports the coprecipitate origin for the presence of Ca in iron (III) oxyhydroxides.The samples containing higher abundances of ferric arsenates released higher As concentrations during the cyanidation tests. The presence of highly soluble ferric arsenates and Ca-Fe arsenates, and relatively unstable iron (III) oxyhydroxides with Fe/As molar ratios of less than 4 in the ore and process tailings suggests that not only the tailings in the impoundment will continue to release As, but also there is the potential for mobilization of As from the natural sources such as the unmined ore.  相似文献   

7.
《Geochimica et cosmochimica acta》1999,63(19-20):3417-3427
In order to verify Fe control by solution - mineral equilibria, soil solutions were sampled in hydromorphic soils on granites and shales, where the occurrence of Green Rusts had been demonstrated by Mössbauer and Raman spectroscopies. Eh and pH were measured in situ, and Fe(II) analyzed by colorimetry. Ionic Activity Products were computed from aqueous Fe(II) rather than total Fe in an attempt to avoid overestimation by including colloidal particles. Solid phases considered are Fe(II) and Fe(III) hydroxides and oxides, and the Green Rusts whose general formula is [FeII1−xFeIIIx(OH)2]+x· [x/z A−z]−x, where compensating interlayer anions, A−, can be Cl−, SO42−, CO32− or OH−, and where x ranges a priori from 0 to 1. In large ranges of variation of pH, pe and Fe(II) concentration, soil solutions are (i) oversaturated with respect to Fe(III) oxides; (ii) undersaturated with respect to Fe(II) oxides, chloride-, sulphate- and carbonate-Green Rusts; (iii) in equilibrium with hydroxy-Green Rusts, i.e., Fe(II)-Fe(III) mixed hydroxides. The ratios, x = Fe(III)/Fet, derived from the best fits for equilibrium between minerals and soil solutions are 1/3, 1/2 and 2/3, depending on the sampling site, and are in every case identical to the same ratios directly measured by Mössbauer spectroscopy. This implies reversible equilibrium between Green Rust and solution. Solubility products are proposed for the various hydroxy-Green Rusts as follows: log Ksp = 28.2 ± 0.8 for the reaction Fe3(OH)7 + e− + 7 H+ = 3 Fe2+ + 7 H2O; log Ksp = 25.4 ± 0.7 for the reaction Fe2(OH)5 + e− + 5 H+ = 2 Fe2+ + 5 H2O; log Ksp = 45.8 ± 0.9 for the reaction Fe3(OH)8 + 2e− + 8 H+ = 3 Fe2+ + 8 H2O at an average temperature of 9 ± 1°C, and 1 atm. pressure. Tentative values for the Gibbs free energies of formation of hydroxy-Green Rusts obtained are: ΔfG° (Fe3(OH)7, cr, 282.15 K) = −1799.7 ± 6 kJ mol−1, ΔfG° (Fe2(OH)5, cr, 282.15 K) = −1244.1 ± 6 kJ mol−1 and ΔfG° (Fe3(OH)8, cr, 282.15 K) = −1944.3 ± 6 kJ mol−1.  相似文献   

8.
Mineral precipitates formed under conditions representative of acid mine drainage were prepared by oxidizing 0.1 M FeS04 · 7H20 solutions at 24°C and pH 2.3, 2.6, 3.0, 3.3 and 3.6 using a bioreactor and a strain ofThiobacillus ferrooxidans. The oxidation of dissolved Fe2+ was monitored colorimetrically and was completed within 90 to 120 h at all pHs. Schwertmannite, Fe8O8(OH)6SO4, was a major component of the precipitates and was the only phase formed at pH 3.0. Jarosite, (H,Na,K)Fe3(OH)6(SO4)2, increased in abundance with decreasing pH whereas goethite, α-FeOOH, appeared at pH 3.3 and 3.6. A similar relationship between pH and mineralogy has been reported in natural specimens of mine drainage ochres.  相似文献   

9.
《Applied Geochemistry》2004,19(2):201-214
Detailed hydrochemical measurements, δ34SSO4 and 3H analyses were performed on 37 groundwater samples collected during February 1999, January and March 2000 from 6 locations in eastern and southeastern Bangladesh to examine redox processes that lead to As mobilization in groundwater. The study sites were chosen based on available nation-wide As surveys to span the entire spectrum of As concentrations in Bangladesh groundwater, and to represent 3 of 5 major geological units of the Ganges-Brahmaputra Delta: uplifted Pleistocene terrace, fluvial flood plain and delta plain. Arsenic was found to be mobilized under Fe-reducing conditions in shallow aquifers (<35 m depth), presumably of Holocene age. It remained mobile under SO4-reducing conditions, suggesting that authigenic sulfide precipitation does not constitute a significant sink for As in these groundwaters. The redox state of the water was characterized by a variety of parameters including dissolved O2, NO3−, Mn2+, Fe2+ concentrations, and SO42−/Cl− ratios. High dissolved [As] (> 50 μg/l; or > 0.7 μM ) were always accompanied by high dissolved [HCO3−] (> 4 mM), and were close to saturation with respect to calcite. Groundwater enriched in As (200–800 μg/l; or 2.7–10.7 μM) and phosphate (30–100 μM) but relatively low in dissolved Fe (5–40 μM) probably resulted from re-oxidation of reducing, As and Fe enriched water. This history was deduced from isotopic signatures of δ34SSO4 and 3H2O (3H) to delineate the nature of redox changes for some of the reducing groundwaters. In contrast, As is not mobilized in presumed Pleistocene aquifers, both shallow (30–60 m) and deep (150–270 m), because conditions were not reducing enough due to lack of sufficient O2 demand.  相似文献   

10.
《Applied Geochemistry》2004,19(11):1837-1853
Iron monosulfide formation and oxidation processes were studied in the extensively drained acid sulfate soil environment of the Tweed River floodplain in eastern Australia. Porewater profiles of pH, Eh, SO42−, Fe2+, Fe3+, Cl−, HCO3−, and metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) were obtained using in situ dialysis membrane samplers (`peepers'). Concentrations of acid volatile S (AVS), pyrite, total S, reactive Fe, total and organic C, simultaneously extracted metals (SEMs) and total elemental composition by X-ray fluorescence, were determined on sediment samples. The oxidation of pyrite in the surrounding landscape provides a source of acidity, Fe, Al, SO4 and metals, which are exported into the drainage system where they accumulate in the sediments and porewaters. Negative porewater concentration gradients of SO42− and Fe2+, and large AVS concentrations in the sediments, indicate Fe monosulfides form rapidly under reducing conditions and consume acidity and metals. Oxidation of the sediments during previous drought episodes has resulted in the conversion of monosulfides and pyrite to oxidised Fe minerals and the release of acidity, SO42−, Fe3+, and metals to the surface waters. These formation and oxidation cycles show that Fe monosulfides play an important role in controlling water quality in the drainage system.  相似文献   

11.
《Applied Geochemistry》2004,19(6):863-886
Large scale redox processes were investigated in a river recharged aquifer in the Oderbruch polder alongside the river Oder in north-eastern Germany. Major hydraulic and hydrochemical processes were identified qualitatively. As a result of intensive drainage activities in the past 250 a, the groundwater level within the polder is situated below the river water level and a levee prevents flooding of the lowland. As a consequence, river water permanently infiltrates into the shallow confined aquifer. A sequence of redox reactions, driven by organic matter degradation, can be observed during infiltration of oxic river water into the groundwater. Up to 3 km from the river, reduction processes from O2 respiration to SO2−4 reduction dominate the groundwater chemistry. While reduction of Fe- and Mn(hydr)oxides is the source of the high amounts of dissolved Fe2+ and Mn2+, carbonate dissolution/precipitation reactions control the actual groundwater concentration of Mn2+. The first order rate constant for SO2−4 reduction was found to be −0.0169 a−1. Fe2+ is released into the groundwater at a rate of 0.0033 mmol l−1 a−1. The groundwater chemistry is strongly linked to the hydraulic conditions. Near the river, the groundwater is confined and recharged by bank-filtration only. In contrast, in the central polder the groundwater is unconfined and percolation of rainwater through the dried loam is possible because of texture changes such as shrinkage fissures. Geogenic pyrite present within the alluvial loam is oxidised and large amounts of SO2−4 are released into the groundwater.  相似文献   

12.
《Applied Geochemistry》2001,16(5):559-570
Fe(II)–Fe(III) layered double hydroxysalt green rusts, GRs, are very reactive compounds with the general formula, [FeII(1−x) FeIIIx (OH)2]x+·[(x/n) An−·(m/n) H2O]x−, where x is the ratio FeIII/Fetot, and reflects the structure in which brucite-like layers alternate with interlayers of anions An− and water molecules. Two types of crystal structure for GRs, GR1 and GR2, represented by the hydroxychloride GR1(Cl−) and the hydroxysulphate GR2(SO42−) are distinguished by X-ray diffraction due to different stacking. By analogy with GR1(Cl−) the structure of the fougerite GR mineral, [FeII(1−x) FeIIIx (OH)2]x+·[x OH−·(1−x) H2O]x-  Fe(OH)(2+x)·(1−x) H2O, is proposed displaying interlayers made of OH− ions and water molecules (in situ deprotonation of water molecules is necessary for explaining the flexibility of its composition). The space group of mineral GR1(OH−) would be R3̄m, with lattice parameters a≅0.32 and c≅2.25 nm. Stability conditions and the Eh-pH diagram of Fe(OH)(2+x) (the water molecules are omitted) are determined from hydromorphic soil solution equilibria with GR mineral in Brittany (France). Computed Gibbs free energies of formation from soil solution/mineral equilibrium fit well with a regular solid solution model: μ°[Fe(OH)(2+x)]=(1−x) μ°[Fe(OH)2]+x μ°[Fe(OH)3]+RT [(1−x) ln (1−x)+x ln x]+A0 x (1−x), where μ°[Fe(OH)2]=−492.5 kJ mol−1, μ°[Fe(OH)3]=−641 kJ mol−1 and A0=−243.9 kJ mol−1 at the average temperature of 9±1°C. The upper limit of occurrence of GR mineral at x=2/3, i.e. Fe3(OH)8, is explained by its unstability vs. α-FeOOH and/or magnetite; Fe(OH)3 is thus a hypothetical compound with a GR structure which cannot be observed. These thermodynamic data and Eh-pH diagrams of Fe(OH)(2+x) can be used most importantly to predict the possibility that GR minerals reduce some anions in contaminated soils. The cases of NO3−, Se(VI) or Cr(VI) are fully illustrated.  相似文献   

13.
《Applied Geochemistry》1998,13(4):509-520
A gravity-fed, battery-powered, portable continuously-stirred tank reactor has been developed to directly measure aqueous reaction rates in the field. Dye and tracer experiments indicate the reactor is well-mixed. Rates of Fe2+ oxidation at untreated and passively treated coal mine drainage sites in Pennsylvania were measured under ambient conditions and with the addition of either O2 gas or NaOH solutions. Rates at 5 sites ranged from below the detection limit for this technique (approximately 10−9 mol L−1 s−1) to 3.27±0.01×10−6 mol L−1 s−1. Uncertainties in rates ranged from 70% near the lower limit of measurement to as little as 1% at higher rates of reaction. Multiple linear regressions showed no universal correlations of rates to Fe2+, dissolved O2, and pH (Thiobacillus populations were not measured), although data for two more acidic sites were found to fit well for the model log rate=log K+a log [Fe2+]+b log [OH−]+c log [O2]. Field rates of Fe oxidation from this and other studies vary by 4 orders of magnitude. A model using the ambient field rate of Fe oxidation from this study successfully reproduced independently-measured Fe2+ concentrations observed in a passive wetland treatment facility.  相似文献   

14.
Iron sulfide oxidation and the chemistry of acid generation   总被引：3，自引：0，他引：3  
Acid mine drainage, produced from the oxidation of iron sulfides, often contains elevated levels of dissolved aluminum (AI), iron (Fe), and sulfate (SO4) and low pH. Understanding the interactions of these elements associated with acid mine drainage is necessary for proper solid waste management planning. Two eastern oil shales were leached using humidity cell methods. This study used a New Albany Shale (4.6 percent pyrite) and a Chattanooga Shale (1.5 percent pyrite). The leachates from the humidity cells were filtered, and the filtrates were analyzed for total concentrations of cations and anions. After correcting for significant solution species and complexes, ion activities were calculated from total concentrations. The results show that the activities of Fe3+, Fe2+, Al3+, and SO4 2− increased due to the oxidation of pyrite. Furthermore, the oxidation of pyrite resulted in a decreased pH and an increased pe+pH (redox-potential). The Fe3+ and Fe2+ activities appeared to be controlled by amorphous Fe(OH)3 solid phase above a pH of 6.0 and below pe+pH 11.0. The Fe3+, Fe2+, and SO4 2− activities reached saturation with respect to FeOHSO4 solid phase between pH 3.0 and 6.0 and below pe+pH 11.0 Below a pH of 3.0 and above a pe+pH of 11.0, Fe2+, Fe3+, and SO4 2− activities are supported by FeSO4·7H2O solid phase. Above a pH of 6.0, the Al3+ activity showed an equilibrium with amorphous Al(OH)3 solid phase. Below pH 6.0, Al3+ and SO4 2− activities are regulated by the AlOHSO4 solid phase, irrespective of pe+pH. The results of this study suggest that under oxidizing conditions with low to high leaching potential, activities of Al and Fe can be predicted on the basis of secondary mineral formation over a wide range of pH and redox. As a result, the long-term chemistry associated with disposal environments can be largely predicted (including trace elements).  相似文献   

15.
《Applied Geochemistry》2003,18(9):1373-1386
The Baccu Locci stream catchment (Sardinia, Italy) is affected by serious As contamination as a consequence of past mining. The presence of both point and widespread sources of contamination (waste-rock dumps and flotation tailings, respectively) strongly affects surface water chemistry, and produces high As concentrations (hundreds of μg l−1) in stream waters. Water chemistry of the Baccu Locci stream changes considerably over a distance of about 10 km as a consequence of various, locally concomitant, processes acting along the stream course: (1) mixing with metal-rich SO4 waters; (2) dissolution/precipitation of metal-bearing phases; (3) mixing with HCO3-dominated lake waters; (4) gypsum dissolution coupled with calcite precipitation; (5) mixing with dilute surface and/or ground waters. In contrast to metals (e.g. Pb, Cu, Zn and Cd), whose dissolved concentrations rapidly decrease downstream of the mined area through (co-)precipitation/adsorption mechanisms, As concentrations tend to gradually increase (up to 0.9 mg l−1) along the stream course as far as the alluvial plain, though significant variations are locally observed. This behaviour is mainly due to the higher mobility of As than metals under the near neutral-oxidative conditions occurring in the Baccu Locci stream waters. Results of a leaching test indicate that part of the As contained in the flotation tailings occurs as As(III), which is more mobile and less strongly sorbed than As(V). The As released to the waters by various mechanisms (i.e. release/desorption from the Fe(III)-hydroxides coatings of silicate grains, oxidation of residual arsenopyrite, decomposition of scorodite) tends to remain in solution and to be transported long distances. As a consequence of the widespread presence of highly As-contaminated flotation tailings all over the medium-lower Baccu Locci stream catchment, long-term As contamination is expected.  相似文献   

16.
《Geochimica et cosmochimica acta》1999,63(19-20):3171-3182
The oxidation rate of pyrite at pH 7, 25°C and at constant partial pressure of oxygen (0.21 and 0.177 atm) was measured in the presence of the Fe(III)-chelators NTA, oxalate, leucine, EDTA, citrate, IDA and the Fe(III)-reductant ascorbic acid. With the exception of leucine and EDTA, non-reducing Fe(III)-chelators increased the oxidation rate relative to the reference state of formation of the Fe(OH)2+ complex at pH 7. The rate increase was proportional to the logarithm of the conditional stability constant of the ligands for the complexation of Fe3+. No effect on the oxidation rate was observed in the presence of EDTA, which shifted the redox potential of the redox couple Fe2+/Fe3+ to a value below that in the absence of any ligand at pH 7. Ascorbic acid decreased the pyrite oxidation rate by a factor of 5 at ascorbic acid concentrations between 10−4 and 10−2 mol L−1. Comparison of the rate constants for the oxidation of ascorbic acid by surface bound Fe(III) in the absence and presence of pyrite shows that the pyrite surface accelerates this reaction by a factor of 10. The oxidation of both pyrite and ascorbic acid is of fractional order with respect to ascorbic acid (HAsc): rpy=0.55 c(HAsc)−0.35 rHAsc=3.6 c(HAsc)0.59. Both the results from experiments with Fe(III)-chelating ligands and the Fe(III)-reductant, suggest a very efficient interference in the electron cycling between Fe(II) and Fe(III) at the pyrite surface. The interference seems to be mainly related to the reductive side of the iron cycling. It is therefore concluded that the electron transfer between ferric iron and pyritic sulfur limits the pyrite oxidation rate at pH 7.  相似文献   

17.
《Geochimica et cosmochimica acta》1999,63(19-20):3407-3416
The apparent solubilities of schwertmannite and ferrihydrite were estimated from the H+, OH−, Fe3+, and SO42− activities of the natural stream waters in Korea and mine drainage in Ohio, USA. Both chemical composition of the stream waters and the mineralogy of the precipitates were determined for samples from two streams polluted by coal mine drainage. This study combines these new results with previous data from Ohio, USA to redetermine solubilities. The activities of the dissolved species necessary for the solubility determinations were calculated from the chemical compositions of the waters with the WATEQ4F computer code.Laboratory analyses of precipitates indicated that the main minerals present in Imgok and Osheep creek were schwertmannite and ferrihydrite, respectively. The schwertmannite from Imgok creek had a variable chemical formula of Fe8O8(OH)8−2x(SO4)x· nH2O, where 1.74 ≤ x ≤ 1.86 and 8.17 ≤ n ≤ 8.62. The chemical formula of ferrihydrite was Fe2O3· 1.6H2O. With known mineralogy of the precipitates from each stream, the activities of H+, OH−, Fe3+, and SO42− in the waters were plotted on logarithmic activity-activity diagrams to determine apparent solubilities of schwertmannite and ferrihydrite. The best estimate for the logarithm of the solubility product of schwertmannite, logKs, was 10.5 ± 2.5 around 15°C. This value of logKs constrains the logarithm of the solubility product of ferrihydrite, logKf, to be 4.3 ± 0.5 to maintain the stability boundary with schwertmannite observed in natural waters.  相似文献   

18.
  相似文献   

19.
《Applied Geochemistry》2000,15(9):1383-1397
Water pollution arising from base metal sulphide mines is problematic in many countries, yet the hydrogeology of the subsurface contaminant sources is rarely well-characterized. Drainage water pumped from an active F–Pb mine in northern England has unusual chemistry (alkaline with up to 40 mg.l−1 Zn) which profoundly impacts the ecology of the receiving watercourse. Detailed in-mine surveys of the quantity and quality of all ground water inflows to the mine were made. These revealed major, temporally persistent heterogeneities in ground water quality, with three broad types of water identified as being associated with distinct hydrostratigraphic units. Type I waters (associated with the Firestone Sill aquifer) are cool (<10°C), Ca–HCO3–SO4 waters, moderately mineralized (specific electrical conductance (SEC)≤410 μS.cm−1) with <4 mg.l−1 Zn. Type II waters (associated with the Great Limestone aquifer) are warmer (≈15°C), of Ca–SO4 facies, highly mineralized (SEC≤1500 μS.cm−1) with ≤40 mg.l−1 Zn. Type III waters (in the deepest workings) are tepid (>18°C), of Ca–HCO3–SO4 facies, intermediately mineralized (SEC≤900 μS.cm−1) with ≤13 mg.l−1 Zn, and with significant Fe (≤12 mg.l−1) and Pb (≤8 mg/l). Monotonic increases in temperature and Cl− concentration with depth contrast with peaks in total mineralization, SO4 and Zn at medium depth (in Type II waters). Sulphate, Pb and Zn are apparently sourced via oxidation of galena and sphalerite, which would release each metal in stoichiometric equality with SO4. However, molal SO4 concentrations typically exceed those of Pb and Zn by 2–3 orders of magnitude, which mineral equilibria suggest is due to precipitation of carbonate “sinks” for these metals. Contaminant loading budgets demonstrate that, although Type II waters amount to only 25% of the total ground water inflow to the mine, they account for almost 60% of the total Zn loading. This observation has important management implications for both the operational and post-abandonment phases of the mine life cycle.  相似文献   

20.
《Applied Geochemistry》2004,19(7):995-1009
Published literature on preservation procedures for stabilizing aqueous inorganic As(III/V) redox species contains discrepancies. This study critically evaluates published reports on As redox preservation and explains discrepancies in the literature. Synthetic laboratory preservation experiments and time stability experiments were conducted for natural water samples from several field sites. Any field collection procedure that filters out microorganisms, adds a reagent that prevents dissolved Fe and Mn oxidation and precipitation, and isolates the sample from solar radiation will preserve the As(III/V) ratio. Reagents that prevent Fe and Mn oxidation and precipitation include HCl, H2SO4, and EDTA, although extremely high concentrations of EDTA are necessary for some water samples high in Fe. Photo-catalyzed Fe(III) reduction causes As(III) oxidation; however, storing the sample in the dark prevents photochemical reactions. Furthermore, the presence of Fe(II) or SO4 inhibits the oxidation of As(III) by Fe(III) because of complexation reactions and competing reactions with free radicals. Consequently, fast abiotic As(III) oxidation reactions observed in the laboratory are not observed in natural water samples for one or more of the following reasons: (1) the As redox species have already stabilized, (2) most natural waters contain very low dissolved Fe(III) concentrations, (3) the As(III) oxidation caused by Fe(III) photoreduction is inhibited by Fe(II) or SO4.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号