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1.
Pyrite oxidation by Acidithiobacillus ferrooxidans at various concentrations of dissolved oxygen 总被引：1，自引：0，他引：1
《Chemical Geology》2006,225(1-2):16-29
Pyrite oxidation rates were examined at various concentrations of dissolved oxygen (DO) in the presence of the sulfur and iron oxidizer Acidithiobacillus ferrooxidans. Five different batch experiments were performed at room temperature for 75 days under various DO levels (273, 129, 64.8, 13.2, and ≤ 0.006 μM), containing pyrite grains (particle size 63–250 μm) and a modified 9K nutrient medium at pH 3. The reactors were inoculated with A. ferrooxidans. In all experiments, pH decreased with time and sulfur and iron were released to the solution, indicating pyrite oxidation at all DO levels. Pyrite oxidation rates (ca. 5 × 10− 10 mol m− 2 s− 1 at 273 μM DO) from all experiments showed positive correlation with DO, Fe(III), and bacterial concentration. These rates were significantly slower than rates presented in other published studies, but this is probably due to the significantly greater Fe(III) concentration at lower pH in these previous studies. The results obtained in this study suggest that ferric iron reduction at the pyrite surface is the primarily mechanism for microbial pyrite oxidation in the presence of DO. The results from our study support the indirect mechanism of sulfide oxidation, where A. ferrooxidans oxidizes ferrous iron in the presence of DO, which then oxidizes pyrite. 相似文献
2.
《Applied Geochemistry》2006,21(2):269-288
Reliable quantification of mineral weathering rates is a key to assess many environmental problems. In this study, the authors address the applicability of pure mineral laboratory rate laws for dissolution of mill tailings samples. Mass-normalised sulfide and aluminosilicate mineral dissolution rates, determined in oxygenated batch experiments, were found to be different between two samples from the same ∼50-year-old, carbonate-depleted mill tailings deposit. Consideration of difference in particle surface area and mineralogy between the samples resolved most of this discrepancy in rates. While the mineral surface area normalised dissolution rates of pyrite in a freshly crushed pure pyrite specimen and a sulfide concentrate derived from the tailings were within the range of abiotic literature rates of oxidation by dissolved molecular O2, as were rates of sphalerite and chalcopyrite dissolution in the tailings, dissolution rates of pyrite and aluminosilicates in the tailings generally differed from literature values. This discrepancy, obtained using a consistent experimental method and scale, is suggested to be related to difficulties in quantifying individual mineral reactive surface area in a mixture of minerals of greatly varying particle size, possibly due to factors such as dependence of surface area-normalised mineral dissolution rates on particle size and time, or to non-proportionality between rates and BET surface area. 相似文献
3.
《Applied Geochemistry》2003,18(2):221-239
The Aznalcóllar tailings dam at Boliden Apirsa's Aznalcóllar/Los Frailes Ag–Cu–Pb–Zn mine 45 km west of Seville, Spain, was breached on 25 April 1998, flooding approximately 4600 hectares of land along the Rı́os Agrio and Guadiamar with approximately 5.5 million m3 of acidic water and 1.3×106 m3 of heavy metal-bearing tailings. Most of the deposited tailings and approximately 4.7×106 m3 of contaminated soils were removed to the Aznalcóllar open pit during clean-up work undertaken immediately after the spill until January 1999. Detailed geomorphological and geochemical surveys of the post-clean-up channel, floodplain and valley floor, and sediment and water sampling, were carried out in January and May 1999 at 6 reaches representative of the types of river channel and floodplain environments in the Rı́o Guadiamar catchment affected by the spill. The collected data show that the clean-up operations removed enough spill-deposited sediment to achieve pre-spill metal (Ag, As, Cd, Cu, Pb, Sb, Tl, Zn) concentrations in surface sediment. These concentrations, however, are still elevated above pre-mining concentrations, and emphasise that mining continues to contaminate the Agrio-Guadiamar river system. Dilution by relatively uncontaminated sediment appears to reduce metal concentrations downstream but increases in metal and As concentrations occur downstream, presumably as a result of factors such as sewage and agriculture. River water samples collected in May 1999 have significantly greater dissolved concentrations of metals and As than those from January 1999, probably due to greater sulphide oxidation from residual tailings with concomitant release of metals in the warmer early summer months. These concentrations are reduced downstream, probably by a combination of dilution and removal of metals by mineral precipitation. Single chemical extractions (de-ionised water, CaCl2 0.01 mol l−1, CH3COONH4 1 M, CH3COONa 1 M and ammonium oxalate 0.2 M) on alluvial samples from reaches 1 and 6, the tailings, pre-spill alluvium and marl have shown that the order of sediment-borne contaminant mobility is generally Zn>Cd>Cu>Pb>As. Pb and As are relatively immobile except possibly under reducing conditions. Much of the highly contaminated sediment remaining in the floodplain and channel still contains a large proportion of tailings-related sulphide minerals which are potentially reactive and may continue to release contaminants to the Agrio–Guadiamar river system. Our work emphasises the need for pre-mining geomorphological and geochemical data, and an assessment of potential contributions of contaminants to river systems from other, non-mining sources. 相似文献
4.
Natural processes and anthropogenic activities may result in the formation and/or introduction of perchlorate (ClO4−) at elevated levels into the environment. Perchlorate in soil environments on Earth and potentially in Mars may modify the dynamics of metal release and their mobilization. Serpentine soils, known for their elevated metal concentrations, provide an opportunity to assess the extent that perchlorate may enhance metal release and availability in natural soil and regolith systems. Here, we assess the release rates and extractability of Ni, Mn, Co and Cr in processed Sri Lankan serpentine soils using a range of perchlorate concentrations (0.10–2.50 w/v ClO4−) via kinetic and incubation experiments. Kinetic experiments revealed an increase of Ni, Mn, Co and Cr dissolution rates (1.33 × 10−11, 2.74 × 10−11, 3.05 × 10−12 and 5.35 × 10−13 mol m−2 s−1, respectively) with increasing perchlorate concentrations. Similarly, sequential and single extractions demonstrated that Ni, Mn, Co and Cr increased with increasing perchlorate concentrations compared to the control soil (i.e., considering all extractions: 1.3–6.2 (Ni), 1.2–126 (Mn), 1.4–34.6 (Co) and 1.2–6.4 (Cr) times greater than the control in all soils). Despite the oxidizing capability of perchlorate and the accelerated release of Cr, the dominant oxidation state of Cr in solution was Cr(III), potentially due to low pH (<2) and Cr(VI) instability. This implies that environmental remediation of perchlorate enriched sites must not only treat the direct hazard of perchlorate, but also the potential indirect hazard of related metal contamination. 相似文献
5.
《Applied Geochemistry》2004,19(6):835-841
Experiments on dissolution kinetics of galena were performed in 1 mol l−1 NaCl solutions at pH 0.43–2.45 and 25–75 °C. When the dissolution reaction is far from equilibrium, a linear relation exits between the dissolution rate, r, and the H+ ion activity, [H+]. The rate law for galena dissolution is given by the following equation: r=k[H+]. With respect to H+, the dissolution reaction is in the first order. The apparent rate constant, k, has values of 2.34×10−7 mol m−2 s−1 at 25 °C, 1.38×10−6 mol m−2 s−1 at 50 °C, and 7.08×10−6 mol m−2 s−1 at 75 °C. The activation energy of dissolution reaction is 43.54 kJ mol−1. The mechanism of dissolution is suggested to be surface chemical reaction, and the rate determining step is the dissociation of the Pb–S bond of the surface complex, which releases Pb2+ into the solution. 相似文献
6.
《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
7.
《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
8.
C.G. Weisener J.W. Guthrie C.M. Smeaton D. Paktunc B.J. Fryer 《Journal of Geochemical Exploration》2011
Globally arsenic (As) is a ubiquitous trace element derived from the natural weathering of As-bearing rock. With the onset of reducing conditions, the prevalence of aqueous As(III) may be intensified through biotic and abiotic processes. Here we evaluate the stability of arsenic bearing Ca–Fe hydroxide phases collected from exposed tailings at Ketza River mine, Yukon, Canada, during the reductive dissolution of both acid treated and untreated samples by Shewanella putrefaciens 200R and Shewanella sp. ANA-3. Samples were acid treated in order to remove Ca–Fe oxide coatings and evaluate the influence of these coatings on the rates of microbial Fe(III) and As(V) reduction. Environmental scanning electron microscope (ESEM) micrographs of the solid phase show significant differences in the chemistry and physical morphology of the material by the bacteria over time and are especially evident in the acid treated samples. Moreover, while solution chemistry showed similar As(III) respiration rates of the inoculated acid treated samples for both ANA3 and 200R at ~ 1.1 × 10−6 μM·s− 1·m− 2, the Fe(II) respiration rates differed at 1.4 × 10− 7 and 9.5 × 10− 8 μM·s− 1·m−2 respectively, thus suggesting strain specific metal reduction metabolic pathways Additionally, the enhanced metal reduction observed in the acid treated inoculated samples suggests that the presence of the Ca–Fe hydroxide phase in the untreated samples acted as a barrier, inhibiting the bacteria from accessing the metals. This has implications for increased mobilization of metals by metal reducing bacteria within areas of increased acidity, such as acid mine drainage sites and industrial tailings ponds that can come into contact with surface and ground water sources. 相似文献
9.
《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
10.
34S/32S ratios have been measured in a suite of samples from the stratabound, volcanogenic massive sulphide deposit at Woodlawn, N.S.W. 34S values for the sulphides vary as follows: in the ore horizon, pyrite +6.7 to +9.2%. (mean +8.1‰), sphalerite +5.2 to +8.6‰. (mean +6.9‰), chalcopyrite +6.4 to +7.0‰ (mean +6.7‰) and galena +2.8 to +5.5‰ (mean +4.4‰); in the vein mineralization, the host volcanics—pyrite +8.7 to +11.4%. (mean +9.8‰), sphalerite +7.8 to + 10.3‰ (mean +9.2‰), chalcopyrite; +8.8 to +10.1‰ (mean +9.2‰) and galena +6.9 to +7.2‰ (mean +7.1‰). Barite from the upper ore horizon levels has an isotopic composition of +30.0‰, consistent with its having originated from Silurian ocean sulphate. The general order of 34S enrichment in the sulphides is pyrite > chalcopyrite ～ sphalerite > galena. Isotopic fractionations in the systems galena/sphalerite/pyrite and chalcopyrite/pyrite indicate an equilibration temperature of 275–300°C. This temperature is considered to represent that of sulphide deposition. 相似文献
11.
Bitumen recovery from Alberta oil sands generates fluid fine tailings, which are retained in tailings ponds where solids settle and release process water. The recovered water is recycled for bitumen extraction, while the resulting tailings are incorporated into various landforms for reclamation, with one option being conversion of tailings basins to viable end pit lakes. Tailings ponds commonly host diverse microbial communities, including SO4-reducing prokaryotes. The highly reducing nature of the hydrogen sulfide produced by these prokaryotes may impact the biogeochemical cycling of key nutrients. However, the behavioral dynamics of hydrogen sulfide production in ponds containing fluid fine tailings remain to be clearly explained. In this study, microcosms are used as analogues of the sediment–water interface of a tailings pond undergoing reclamation to determine sulfide generation patterns and the behavior of O2. In the microcosms, hydrogen sulfide fluxes correlated positively with biotic activity, reaching levels of over 2 × 103 nmol cm−2 s−1, leading to Fe sulfide formation. Depth-related hydrogen sulfide profiles in the microcosms were comparable to those encountered in situ, in Syncrude’s West In-Pit, an active tailing pond. Oxygen diffusion across the fluid fine tailing sediment–water interface was controlled to different degrees by both biotic and abiotic processes. The results have implications for quantitatively estimating the impact of hydrogen sulfide production, O2 availability, and biogeochemical cycling of key nutrients important for the success of life in fluid fine tailings-affected ecosystems. This paper shows that this production of hydrogen sulfide may be a self-limiting process, which will begin to decrease after a period of time. 相似文献
12.
文章以水口山矿田内的3个典型铅锌多金属矿床——康家湾铅锌金银矿床、老鸦巢铅锌金矿床和鸭公塘铅锌铁铜矿床的矿石为研究对象,通过野外地质调查、室内显微鉴定、电子探针分析和LA-ICPMS微量元素分析测试,研究了本区稀散元素的赋存状态、分布规律以及与主成矿元素(Pb、Zn、S、Fe)的关系等,总结出稀散元素在本区的富集规律.研究表明:本区矿石中闪锌矿、黄铁矿、黄铜矿、方铅矿主要富集Cd、In、Te3种稀散元素.康家湾铅锌金银矿床In/Zn比值为0.86,老鸦巢铅锌金矿床In/Zn比值为5.10,而鸭公塘铅锌铁铜矿床In/Zn比值为611.20,且w(In)为33.83×10-6～365.62×10-6,因此,康家湾铅锌金银矿床和老鸦巢铅锌金矿床矿石中的In是以类质同象赋存于闪锌矿和黄铜矿的晶格中,而鸭公塘铅锌铁铜矿床矿石中的In可能以硫铟铜矿的形式赋存.水口山矿田的Te主要有2种赋存形式:一种以类质同象形式赋存于硫化物(黄铁矿)中;另一种以矿石中形成其独立矿物辉碲铋矿(分子式为Bi2TeS2)和碲银矿(分子式为Ag2Te)存在. 相似文献
13.
Rumex acetosella and Minuartia verna are confined to mineralized ground in Macedonia. These plants contain relatively high concentrations of heavy metals such as copper, zinc, lead and manganese, and are to that extent, valuable indicators of sulphide mineralization, either pyrite + chalcopyrite or pyrite + chalcopyrite + sphalerite + galena. There is a direct relationship between the metal content of the plant ash and the metal content of the soils and mineralized substrate. 相似文献
14.
Copper–Gold Skarn Mineralization at the Karavansalija Ore Zone,Rogozna Mountain,Southwestern Serbia 
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下载免费PDF全文 Zhivko D. Budinov Kotaro Yonezu Thomas Tindell Jillian Aira Gabo‐Ratio Stanoje Milutinovic Adrian J. Boyce Koichiro Watanabe 《Resource Geology》2015,65(4):328-344
Karavansalija ore zone is situated in the Serbian part of the Serbo‐Macedonian magmatic and metallogenic belt. The Cu–Au mineralization is hosted mainly by garnet–pyroxene–epidote skarns and shifts to lesser presence towards the nearby quartz–epidotized rocks and the overlying volcanic tuffs. Within the epidosites the sulfide mineralogy is represented by disseminated cobalt‐nickel sulfides from the gersdorfite‐krutovite mineral series and cobaltite, and pyrite–marcasite–chalcopyrite–base metal aggregates. The skarn sulfide mineralization is characterized by chalcopyrite, pyrite, pyrrhotite, bismuth‐phases (bismuthinite and cosalite), arsenopyrite, gersdorffite, and sphalerite. The sulfides can be observed in several types of massive aggregates, depending on the predominant sulfide phases: pyrrhotite‐chalcopyrite aggregates with lesser amount of arsenopyrite and traces of sphalerite, arsenopyrite–bismuthinite–cosalite aggregates with subordinate sphalerite and sphalerite veins with bismuthinite, pyrite and arsenopyrite. In the overlying volcanoclastics, the studied sulfide mineralization is represented mainly by arsenopyrite aggregates with subordinate amounts of pyrite and chalcopyrite. Gold is present rarely as visible aggregate of native gold and also as invisible element included in arsenopyrite. The fluid inclusion microthermometry data suggest homogenization temperature in the range of roughly 150–400°C. Salinities vary in the ranges of 0.5–8.5 wt% NaCl eq for two‐phase low density fluid inclusions and 15–41 wt% NaCl eq for two‐phase high‐salinity and three‐phase high‐salinity fluid inclusions. The broad range of salinity values and the different types of fluid inclusions co‐existing in the same crystals suggest that at least two fluids with different salinities contributed to the formation of the Cu–Au mineralization. Geothermometry, based on EPMA data of arsenopyrite co‐existing with pyrite and pyrrhotite, suggests a temperature range of 240–360°C for the formation of the arsenopyrite, which overlaps well with the data for the formation temperature obtained through fluid inclusion microthermometry. The sulfur isotope data on arsenopyrite, chalcopyrite, pyrite and marcasite from the different sulfide assemblages (ranging from 0.4‰ to +3.9‰ δ34SCDT with average of 2.29 δ34SCDT and standard deviation of 1.34 δ34SCDT) indicates a magmatic source of sulfur for all of the investigated phases. The narrow range of the data points to a common source for all of the investigated sulfides, regardless of the host rock and the paragenesis. The sulfur isotope data shows good overlap with that from nearby base‐metal deposits; therefore the Cu–Au mineralization and the emblematic base‐metal sulfide mineralization from this metallogenic belt likely share same fluid source. 相似文献
15.
《Applied Geochemistry》2000,15(4):425-438
The dissolution of silica and diffusion of reactive dissolved Si in the porewaters of river sediments are investigated using sediments of different physical and chemical properties. Three sediments are considered: (a) from sectioned cores taken from a river-bed, (b) fine organic-rich surface sediment (<5 cm depth) installed in a fluvarium channel and, (c) coarse river sediment of low organic matter content also installed in a fluvarium channel. Dissolution rates of silica are measured at 10°C using batches of suspended material. The derived dissolution rate constants show large differences between the sediments. The river bed-sediment cores had vertical concentration profiles of dissolved Si that are consistent with the diffusion and dissolution of biogenic silica. Experiments in a fluvarium channel enabled Si fluxes to be calculated from a mass-balance of the overlying solution. The results are consistent with the attainment of a steady-state concentration profile of dissolved Si in the sediment. There are no discernible effects of water velocity over the sediment between 5 and 11 cm s−1. However, at 20 cm s−1, the flux increases as a result of either entrainment of fine particles at the surface or advective effects in the surface sediment. A fluvarium experiment with the fine sediment (<125 μm) over 61 days, produced a concentration profile with the highest concentration of 1025 μmol dm−3 at a depth of 4–5 cm in the sediment. A FORTRAN program is used to model the results of the increase in dissolved Si in the overlying water and development of a concentration profile in the porewater. This leads to a sediment diffusion coefficient of 1.21×10−9 m2 s−1 at 8.8°C at the beginning of the experiment and rate constant k=13.1×10−7 s−1 at pH=7.82 and average temperature of 7.6°C for the entire experiment. Fluxes measured at the sediment–surface interface and calculated assuming steady-state profiles had developed are typically 0.01–0.04 μmol m−2 (of river bed) s−1. The approach enables the efflux of dissolved Si from bottom-sediments to be estimated from dissolution rates measured using suspensions of bed-sediment. 相似文献
16.
《Geochimica et cosmochimica acta》2001,65(16):2633-2640
The role of methane clathrate hydrates in the global methane budget is poorly understood because little is known about how much methane from decomposing hydrates actually reaches the atmosphere. In an attempt to quantify the role of water column methanotrophy (microbial methane oxidation) as a control on methane release, we measured water column methane profiles (concentration and δ13C) and oxidation rates at eight stations in an area of active methane venting in the Eel River Basin, off the coast of northern California. The oxidation rate measurements were made with tracer additions of 3H-CH4.Small numbers of instantaneous rate measurements are difficult to interpret in a dynamic, advecting coastal environment, but combined with the concentration and stable isotope measurements, they do offer insights into the importance of methanotrophy as a control on methane release. Fractional oxidation rates ranged from 0.2 to 0.4% of ambient methane per day in the deep water (depths >370 m), where methane concentration was high (20–300 nM), to near-undetectable rates in the upper portion of the water column (depths <370 m), where methane concentration was low (3–10 nM). Methane turnover time averaged 1.5 yr in the deep water but was on the order of decades in the upper portion of the water column. The depth-integrated water column methane oxidation rates for the deep water averaged 5.2 mmol CH4 m−2 yr−1, whereas the upper portion of the water column averaged only 0.14 mmol CH4 m−2 yr−1; the depth-integrated oxidation rate for deep water in the 25-km2 area encompassing the venting field averaged 2 × 106 g CH4 yr−1. Stable isotope values (δ13C-CH4) for individual samples ranged from −34 to −52‰ (vs. PDB, Peedee belemnite standard) in the region. These values are isotopically enriched relative to hydrates in the region (δ13C-CH4 about −57 to −69‰), further supporting our observations of extensive methane oxidation in this environment. 相似文献
17.
Surface water samples from the Drake mining area show elevated metal concentrations, notably cadmium, iron and zinc. A detailed
study of a sphalerite /quartz vein from Strauss Pit and chalcopyrite and pyrite from the Adeline mine and Strauss Pit indicate
that micro-scale analyses of ores are necessary for environmental management of mine sites. Analyses show that Cd is elevated,
up to 2.1 % by weight, and is associated with sphalerite, replacing Zn, or to a lesser extent replacing Pb within small galena
grains. High concentrations of Cu are also associated with the Strauss Pit ore as small chalcopyrite grains along the margins
of the sphalerite vein, within the central quartz zone of the vein system, and as replacement rims on sphalerite grains. Chalcopyrite
from the Adeline mine area, is by comparison, metal poor, but still contains elevated heavy metal concentrations. Whereas,
pyrite and chalcopyrite, from Strauss Pit have variable heavy metal concentrations, with chalcopyrite from within sphalerite
veins having higher Cd and Zn concentrations than chalcopyrite distal to the veins. Cadmium and other heavy metals within
the ores are mobilised during sulphide weathering and enter the drainage network; precipitation of secondary oxidation minerals
act as temporary stores for many heavy metals. The complexity of the mineral and heavy metal associations at Strauss Pit suggest
that a detailed knowledge of these associations and distributions within ore bodies, and associated waste rocks, are needed
by environmental managers of mine sites because the presence of havy metals may greatly affect the decision making process,
and management strategies employed.
Received; 14 July 1999 · Accepted: 17 August 1999 相似文献
18.
《Geochimica et cosmochimica acta》1999,63(3-4):337-350
The paucity of weathering rates for quartz in the natural environment stems both from the slow rate at which quartz dissolves and the difficulty in differentiating solute Si contributed by quartz from that derived from other silicate minerals. This study, a first effort in quantifying natural rates of quartz dissolution, takes advantage of extremely rapid tropical weathering, simple regolith mineralogy, and detailed information on hydrologic and chemical transport. Quartz abundances and grain sizes are relatively constant with depth in a thick saprolite. Limited quartz dissolution is indicated by solution rounding of primary angularity and by the formation of etch pits. A low correlation of surface area (0.14 and 0.42 m2 g−1) with grain size indicates that internal microfractures and pitting are the principal contributors to total surface area.Pore water silica concentration increases linearly with depth. On a molar basis, between one and three quarters of pore water silica is derived from quartz with the remainder contributed from biotite weathering. Average solute Si remains thermodynamically undersaturated with respect to recently revised estimates of quartz solubility (<180 μM) but exceeds estimated critical saturation concentrations controlling the initiation of etch pit formation (>17–81 μM). Etch pitting is more abundant on grains in the upper saprolite and is associated with pore waters lower in dissolved silica. Rate constants describing quartz dissolution increase with decreasing depth (from 10−14.5–10−15.1 mol m−2 s−1), which correlate with both greater thermodynamic undersaturation and increasing etch pit densities. Unlike for many aluminosilicates, the calculated natural weathering rates of quartz fall slightly below the rate constants previously reported for experimental studies (10−12.4–10−14.2 mol m−2 s−1). This agreement reflects the structural simplicity of quartz, dilute solutes, and near-hydrologic saturation. 相似文献
19.
Sajjad Jannesar Malakooti Seyed Ziaedin Shafaei Tonkaboni Mohammad Noaparast Faramarz Doulati Ardejani Reza Naseh 《Environmental Earth Sciences》2014,71(5):2267-2291
Mineral processing operation at the Sarcheshmeh porphyry copper mine has produced huge quantities of tailings materials containing sulphide minerals in particular pyrite. These tailings materials were geochemically and mineralogically characterised to assess pyrite and chalcopyrite oxidation, acid mine drainage generation, and trace element mobility to lead development of a proper remediation plan. Five vertical trenches up to 4.2 m deep were excavated from the tailings surface, and 70 solid samples were taken in 0.3 m intervals. The samples were first mineralogically analysed. Pyrite was the main sulphide mineral found in the tailings. The gangue minerals include quartz ± muscovite–illite ± chlorite ± albite ± orthoclase ± halite. The samples were geochemically analysed for total concentrations of 62 elements, paste pH, SO4 2?, CO3 2?, and HCO3 ?. The maximum concentrations of SO4 2? (1,300, 1,170, 1,852, 1,960 and 837 mg/L) were observed at a depth of 0.9 m in profiles A, B, C, D and E, respectively. The tailings have a high acid-producing potential and low acid-neutralising potential (pyrite 4–6 wt %, calcite 1 wt %). Fe2(SO4)3, CuSO4, MgSO4 and MnSO4 were the dominant secondary sulphate minerals in the tailings. The lowest pH values (2.9, 3 and 3) were measured at a depth of 0.3 m in the profiles A, B and C, 3.9 at a depth of 0.6 m in the profile D and 3 at a depth of 0.9 m in the profile E. The upper portions of the profiles C (1.8 m) and D (2.1 m) were moderately oxidised, while oxidation in the profiles A, B and E did not extend more than 1.2, 1.2 and 1.5 m beneath the tailings surface. Zn, Pb, Rb, U, Hf, Nd, Zr and Ga show almost a constant trend with depth. Cd, Sr, Th, La and Ce increased with increasing depth of the tailings materials while, Co, V, Ti, Cr, Cu, As, Mn, Ag, Mo and Ni exhibit initially a decreasing trend from tailings surface to the depths that vary between 0.9 and 1.2. They then remained constant with the depth. The results show pyrite and chalcopyrite oxidation at surface layers of the tailings and subsequent leaching of the oxidation products and trace elements by infiltrated atmospheric precipitation. 相似文献
20.
A system is presented in which an atmosphere containing less than 10?6 mole fraction oxygen and water containing less than 5 ppb oxygen can be maintained. Flotation of chalcocite, chalcopyrite, galena, pyrite and sphalerite in this system reveals that these minerals are naturally floatable under these conditions. 相似文献