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1.
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been applied to determine the elemental composition of the surface layer, as well as of the first interior layer, of quartz grains from the mine tailings from Kristineberg (northern Sweden) in order to determine concentration gradients between these two layers. The quartz grains were collected from the oxidized and unoxidized zones within the tailings. The aim of this study is to assess the role of quartz surfaces as sites for the attenuation of solutes from the mine-tailings porewater. Concentrations of Cu, Ag, Sb, Pb and Bi are highest near the surface of each grain and decrease towards the interior. The surface concentration of Cu, Zn and Pb is more pronounced within the unoxidized than within the oxidized zone of the tailings. Cu exhibits a distinct concentration peak at the surface of the quartz grains below the pre-remediation oxidation front. For Zn and Ce the trend of high surface concentration is less pronounced than for Cu or Pb. Silver, Bi and As are preferably adsorbed within the uppermost layers of the oxidized zone where the pH is as high as 6.2. The conversion of intensity signals of the elements to concentration values in ppm was done by using external standards (NIST silicate glass). 相似文献
2.
Field and laboratory studies of the sulphide-bearing tailings at Laver, northern Sweden, show that the present release of
metals from the tailings is low, especially with regard to Cu. A large part of the Cu released by sulphide oxidation is enriched
in a distinct zone just below the oxidation front. The enrichment zone occurs almost all over the tailings area except in
areas with a shallow groundwater table. The Cu enrichment is caused by formation of covellite and adsorption onto mineral
surfaces. The transport of Zn, Co, Cd, Ni and S seems to be controlled mainly by adsorption. No secondary zone or secondary
minerals containing these metals have been found. Just below the groundwater table, metals are released into solution when
the enrichment zone reaches the groundwater due to the low pH. An increased release of metals, especially Cu, can be expected
in the future, since the enrichment zone is moving towards the groundwater table.
Received: 4 December 1997 · Accepted: 17 December 1998 相似文献
3.
This study evaluates the pollution load on a creek based on the physicochemical and mineralogical properties of old tailings. The Sanggok mine is one of the largest lead–zinc producers in the Hwanggangri mining district, Republic of Korea. The vertical profile of the old tailings in the mine area can be divided into three units based on color change, and mineralogical and textural variations, as well as physical and chemical properties. Unit I (surface accumulation and oxidized heterogeneous tailing soil) has lower pH and higher Eh than unit II (originally unoxidized dumped tailing soil) and unit III (pebble-bearing bottom soil). The conductivity data indicates that unit I and II have very high values compared to unit III and basement. The mine area consists mainly of carbonate rocks; however, mineral constituents of tailing soil and sediments near the mine were mainly composed of quartz, mica, feldspar, amphibole, calcite, dolomite, magnesite, and clay minerals. Units I and II are characterized by high abundances of siderite, locally pyrite, and dolomite. Precipitates in the mining drainage mainly included: smectite, illite, berthierine, quartz, siderite, hexahydrite, and Ca-ferrate. Among the separated metallic minerals, tailing soils and sediments of highly concentrated toxic metals are found: some pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, malachite, goethite, various hydroxide, and uncertain secondary minerals. Units I and II are characterized by relatively high concentrations of Ca, Fe, Mn and low contents of Al, Mg, K, Na, Ti, rare earth elements (REEs) that correlated with the proportion of secondary minerals. Potentially toxic elements such as Ag, As, Cd, Cu, Pb, Sb, and Zn are highly enriched in the upper two units. This metal concentration can be influenced by changes in the depth because of oxic and suboxic zonal distribution. The removal zone (unit I) has probably migrated below the elevation of the maximum enrichment layer due to deepening of the oxic/suboxic boundary. In most of the materials, the enrichment index is higher than 3.62. The highest value of 42.55 is found in the oxidation surface soils of the tailing pile. An average enrichment index of the profiles and precipitates are 27.62 and 22.62, respectively. Rocky basement soils have an average enrichment index of 6.63, which is influenced by overlying the tailing pile. The water quality and habitat of the Sanggok creek are severely polluted. Polluted surface water may also negatively impact the agricultural soil and groundwater. 相似文献
4.
Pyrite and pyrrhotite are the principal minerals that generate acid drainage in mine wastes. Low-pH conditions derived from Fe-sulfide oxidation result in the mobilization of contaminant metals (such as Zn, Cd, Ni and Cr) and metalloids (such as As) which are of environmental concern. This paper uses data from detailed mineralogical and geochemical studies conducted at two Canadian tailings impoundments to examine the mineralogical changes that pyrite, pyrrhotite, sphalerite and magnetite undergo during and after sulfide oxidation, and the subsequent release and attenuation of associated trace elements. The stability of sphalerite in tailings impoundments generally is greater than that of pyrrhotite, but less than pyrite. Dissolved Ni and Co derived from Fe sulfides, and to a lesser extent, dissolved Zn and Cd from sphalerite, are commonly attenuated by early-formed Fe oxyhydroxides. As oxidation progresses, a recycling occurs due to continued leaching from low-pH pore waters and because the crystallinity of Fe oxyhydroxides gradually increases which decreases their sorptive capacity. Unlike many other elements, such as Cu, Pb and Cr, which form secondary minerals or remain incorporated into mature Fe oxyhydroxides, Zn and Ni become mobile. Magnetite, which is a potential source of Cr, is relatively stable except under extremely low-pH conditions. A conceptual model for the sequence of events that typically occurs in an oxidizing tailings impoundment is developed outlining the progressive oxidation of a unit of mine waste containing a mixed assemblage of pyrrhotite and pyrite. 相似文献
5.
The potential to use the alkaline residue products fly ash, green liquor dregs, and lime mud originating from paper mills as dry cover materials to seal tailings has been investigated. Metals concentration in lime mud and fly ash had the lowest and highest contents, respectively. The tailings (<1 % sulfur content, primarily pyrite) were disposed about 50 years ago and originated from the former Rönnskär mine site in Sweden. The results of chemical composition analysis show that the raw unoxidized tailings are active toward oxidation, while the components of the adjacent oxidized tailings are not. To quantify the release of metals from the tailings and to evaluate the effect of a sealing layer on oxidation and weathering of the tailings, batch leaching tests were conducted in which leachate from alkaline residue materials was fed to the tailings. The results show that a higher concentration of most trace elements is leached from the unoxidized tailings than from the oxidized tailings. Except As and Cr, the rest of analyzed metals (Cd, Cu, Ni, Pb) became immobilized in response to the increased pH as a consequence of the amendment. The three tested alkaline amendments show a similar potential for preventing the release of metals (with the exception of As and Cr) from the tailings. Under either aerobic or anaerobic conditions, microbial activity was found to be of minor importance. XRD analysis of the field samples revealed that it was feasible to use alkaline residue products in covering tailings, and that it was advantageous to use ash as a cover material more than dregs. 相似文献
6.
Environmental geochemistry of the derelict Webbs Consols mine,New South Wales,Australia 总被引：3，自引：3，他引：0
Small-scale mining and mineral processing at the Webbs Consols polymetallic PbZnAg deposit in northern New South Wales, Australia has caused a significant environmental impact on streams, soils and vegetation. Unconfined waste rock dumps and tailings dams are the source of the problems. The partly oxidised sulphidic mine wastes contain abundant sulphides (arsenopyrite, sphalerite, galena) and oxidation products (scorodite, anglesite, smectite, Fe-oxyhydroxides), and possess extreme As and Pb (wt% levels) and elevated Ag, Cd, Cu, Sb and Zn values. Contemporary sulphide oxidation, hardpan formation, crystallisation of mineral efflorescences and acid mine drainage generation occur within the waste repositories. Acid seepages (pH 1.9–6.0) from waste dumps, tailings dams and mine workings display extreme As, Pb and Zn and elevated Cd, Cu and Sb contents. Drainage from the area is by the strongly contaminated Webbs Consols Creek and although this stream joins and is diluted by the much larger Severn River, contamination of water and stream sediments in the latter is evident for 1–5 km, and 12 km respectively, downstream of the mine site. The pronounced contamination of local and regional soils and sediments, despite the relatively small scale of the former operation, is due to the high metal tenor of abandoned waste material and the scarcity of neutralising minerals. Any rehabilitation plan of the site should include the relocation of waste materials to higher ground and capping, with only partial neutralisation of the waste to pH 4–5 in order to limit potential dissolution of scorodite and mobilisation of As into seepages and stream waters. 相似文献
7.
Acid Mine Drainage and Heavy Metal Pollution from Solid Waste in the Tongling Mines, China 总被引：2，自引：0，他引：2
Based on investigation of the characteristics of solid waste of two different mines, the Fenghuangshan copper mine and the Xinqiao pyrite mine in Tongling, Anhui province in central-east China, the possibility and the differences of acid mine drainage （AMD） of the railings and the waste rocks are discussed, and the modes of occurrence of heavy metal elements in the mine solid waste are also studied. The Fenghuangshan copper mine hardly produces AMD, whereas the Xinqiao pyrite mine does and there are also differences in the modes of occurrence of heavy metal elements in the railings. For the former, toxic heavy metals such as Cu, Pb, Zn, Cd, As and Hg exist mostly in the slag mode, as compared to the latter, where the deoxidization mode has a much higher content, indicating that large amounts minerals in the waste rocks have begun to oxidize at the earth surface. AMD is proved to promote the migration and spread of the heavy metals in mining waste rocks and lead to environmental pollution of the surroundings of the mine area. 相似文献
8.
铜陵矿山酸性排水及固体废弃物中的重金属元素 总被引：8，自引：0，他引：8
在调查中国铜陵凤凰山铜矿和新桥硫铁矿两种不同类型矿山固体废弃物特征的基础上,研究了矿山尾矿和废石产生酸性排水的可能性及其差异以及矿山固体废弃物中重金属元素的赋存形式。结果表明,凤凰山铜矿的尾矿基本不产生矿山酸性排水,而新桥硫铁矿采矿废石产生矿山酸性排水,并且凤凰山铜矿的尾矿和新桥硫铁矿采矿废石中重金属元素的赋存形式也有差异,前者重金属Cu、Pb、Zn、Cd、As、Hg主要赋存于硅酸盐态中,而后者在还原态中有较高的含量,这反映了在地表条件下尾矿中大量重金属元素已经发生了迁移,而采矿废石已经开始氧化,且酸性排水的存在更有利于废石中重金属元素的迁移和扩散,进而导致矿区周围环境的污染。 相似文献
9.
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
10.
Redistribution of potentially harmful metals and As was studied based on selective extractions in two active sulphide mine tailings impoundments in Finland. The Hitura tailings area contains residue from Ni ore processing, while the Luikonlahti site includes tailings from the processing of Cu–Co–Zn–Ni and talc ores. To characterize the element solid-phase speciation with respect to sulphide oxidation intensity and the water saturation level of the tailings, drill cores were collected from border zones and mid-impoundment locations. The mobility and solid-phase fractionation of Ni, Cu, Co, Zn, Cr, Fe, Ca, Al, As, and S were analysed using a 5-step non-sequential (parallel) selective extraction procedure. The results indicated that metal redistribution and sulphide oxidation intensity were largely controlled by the disposal history and strategy of the tailings (sorting, exposure of sulphides due to delayed burial), impoundment structure and water table, and reactivity of the tailings. Metal redistribution suggested sulphide weathering in the tailings surface, but also in unsaturated proximal areas beside the earthen dams, and in water-saturated bottom layers, where O2-rich infiltration is possible. Sulphide oxidation released trace metals from sulphide minerals at both locations. In the Hitura tailings, with sufficient buffering capacity, pH remained neutral and the mobilized metals were retained by secondary Fe precipitates deeper in the oxidized zone. In contrast, sulphide oxidation-induced acidity and rise in the water table after oxidation apparently remobilized the previously retained metals in Luikonlahti. In general, continuous disposal of tailings decreased the sulphide oxidation intensity in active tailings, unless there was a delay in burial and the reactive tailings were unsaturated after deposition. 相似文献
11.
Mobility and retention of trace elements in hardpan-cemented cassiterite tailings, north Queensland, Australia 总被引：1，自引：0，他引：1
This study reports on the mobility and retention of trace elements in cassiterite tailings at the inactive Jumna mill, tropical north Queensland. Since the 1980s, the uncapped tailings have developed laterally discontinuous Fe-rich hardpans, which are located in the higher parts of gently sloping tailings masses and at the top (<50 cm) of the tailings piles. Hardpan-cemented tailings comprise thin layers (typically ∼0.2–2 mm thick) of HFO (hydrous ferric oxides) and sulfate efflorescences cementing tailings grains. In comparison to the tailings, the hardpan-cemented tailings contain significantly higher median As, Ca, Cd, Co, Cu, Fe, In, Mn, Mo, Stotal, Th, U, Y and Zn values. Partial leaching studies of tailings and pond water analyses indicate that wetting and acidification of Fe-cemented tailings removes significant proportions of trace elements into pore and surface waters. Tin shows no mobility due to the presence of weathering-resistant cassiterite (SnO2) and, As and Pb display limited mobility possibly due to their coprecipitation with jarosite-type phases and HFO materials at the top of the tailings profile. By contrast, the trace elements Cd, Ce, Cu, La, Ni, Pb, U and Zn display the greatest mobility, possibly due to their incorporation in soluble sulfate efflorescences and sorption onto mineral and HFO surfaces. Hence, the Fe-rich hardpans do not protect the sulfidic tailings from further oxidation nor do they cause permanent sequestration of trace elements. 相似文献
12.
Acid neutralization mechanisms and metal release in mine tailings: a laboratory column experiment 总被引：1，自引：0，他引：1
Jasna Jurjovec Carol J. Ptacek David W. Blowes 《Geochimica et cosmochimica acta》2002,66(9):1511-1523
Mining and milling of base metal ore deposits can result in the release of metals to the environment. When sulfide minerals contained in mine tailings are exposed to oxygen and water, they oxidize and dissolve. Two principal antagonistic geochemical processes affect the migration of dissolved metals in tailings impoundments: sulfide oxidation and acid neutralization. This study focuses on acid neutralization reactions occurring in the saturated zone of tailings impoundments. To simulate conditions prevailing in many tailings impoundments, 0.1 mol/L sulfuric acid was passed continuously through columns containing fresh, unoxidized tailings, collected at Kidd Creek metallurgical site. The results of this column experiment represent a detailed temporal observation of pH, Eh, and metal concentrations. The results are consistent with previous field observations, which suggest that a series of mineral dissolution-precipitation reactions control pH and metal mobility. Typically, the series consists of carbonate minerals, Al and Fe(III) hydroxides, and aluminosilicates. In the case of Kidd Creek tailings, the dissolution series consists of ankerite-dolomite, siderite, gibbsite, and aluminosilicates. In the column experiment, three distinct pH plateaus were observed: 5.7, 4.0, and 1.3. The releases of trace elements such as Cd, Co, Cr, Cu, Li, Ni, Pb, V, and Zn were observed to be related to the pH buffering zones. High concentrations of Zn, Ni, and Co were observed at the first pH plateau (pH 5.7), whereas Cd, Cr, Pb, As, V, and Al were released as the pH of the pore water decreased to 4.0 or less. 相似文献
13.
Establishing a shallow water cover over tailings deposited in a designated storage facility is one option to limit oxygen diffusion and retard oxidation of sulfides which have the potential to form acid mine drainage (AMD). The Old Tailings Dam (OTD) located at the Savage River mine, western Tasmania contains 38 million tonnes of pyritic tailings deposited from 1967 to 1982, and is actively generating AMD. The OTD was constructed on a natural gradient, resulting in sub-aerial exposure of the southern area, with the northern area under a natural water cover. This physical contrast allowed for the examination of tailings mineralogy and geochemistry as a function of water cover depth across the OTD. Tailings samples (n = 144, depth: ≤ 1.5 m) were collected and subjected to a range of geochemical and mineralogical evaluations. Tailings from the southern and northern extents of the OTD showed similar AMD potential based on geochemical (NAG pH range: 2.1 to 4.2) and bulk mineralogical parameters, particularly at depth. However, sulfide alteration index (SAI) assessments highlighted the microscale contrast in oxidation. In the sub-aerial zone pyrite grains are moderately oxidized to a depth of 0.3 m (maximum SAI of 6/10), under both gravel fill and oxidized covers, with secondary minerals (e.g., ferrihydrite and goethite) developed along rims and fractures. Beneath this, mildly oxidized pyrite is seen in fresh tailings (SAI = 2.9/10 to 5.8/10). In the sub-aqueous zone, the degree of pyrite oxidation demonstrates a direct relationship with cover depth, with unoxidized, potentially reactive tailings identified from 2.5 m, directly beneath an organic-rich sediment layer (SAI = 0 to 1/10). These findings are broadly similar to other tailings storage facilities e.g., Fox Lake, Sherritt-Gordon ZnCu mine, Canada and Stekenjokk mine, Sweden where water covers up to 2 m have successfully reduced AMD. Whilst geotechnical properties of the OTD restrict the extension of the water cover, pyrite is enriched in cobalt (up to 2.6 wt%) indicating reprocessing of tailings as an alternative management option. Through adoption of an integrated mineralogical and geochemical characterization approach for tailings assessment robust management strategies after mine closure can be developed. 相似文献
14.
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
15.
In the old mining area of Rodalquilar, mine wastes, soil and sediments were characterized and the results revealed high concentration
of Au, Ag, As, Bi, Cu, Fe, Mn, Pb, Se, Sb and Zn in tailings and sediments. The contaminant of greatest environmental concern
is As. The mean concentration in the tailings was 679.9, and 345 mg/kg in the sediments of Playazo creek. The groundwater
samples from the alluvial aquifer showed high concentration of Al, As, Cd, Fe, Hg, Mn, Ni, Pb, Se, Sb and Zn and very high
concentration of chloride and sulfate, which were above the concentration defined in the European standards for drinking water.
The presence of As in groundwater may be caused by the oxidation of arsenian pyrite, the possible As desorption from goethite
and ferrihydrite and the jarosite dissolution. Groundwater concentrations of Cd, Fe, Mn, and possibly Cu, were associated
with low values of Eh, indicating the possible dissolution of oxy-hydroxides of Fe and Mn. The mobility of metals in the column
experiments show the release of Al, Fe, Mn, Cr, Cu, Ni, V and Zn in significant concentrations but below the detected values
in groundwater. However, As, Cd, Sb, Se Pb and Au, are generally mobilized in concentrations above the detected values in
groundwater. The possible mass transfer processes that could explain the presence of the contaminants in the aquifer and the
leachates was simulated with the PHREEQC numerical code and revealed the possible dissolution of the following mineral phases:
jarosite, natrojarosite, arsenian pyrite, alunite, chlorite, kaolinite and calcite. 相似文献
16.
Heavy metals pollution of aquatic ecosystems in the vicinity of a recently closed underground lead-zinc mine (Basque Country, Spain) 总被引：3，自引：0，他引：3
A presentation is made of the study of an underground polymetallic sulphide mine and the pollution caused by this in the adjoining aquatic ecosystems. Troya Mine is in the Basque Cantabrian region (northern Spain). The annual production of the ore deposit of over 3.7 million tons of Pb (0.9%), Zn (11.2%) and Cu (0.2%) was 300,000 t. It was open and producing from 1986-1993. The mineralization was made up of pyrite, marcasite, sphalerite, galena, chalcopyrite and arsenopyrite. Only the Zn and the Pb were mined. We studied the distribution and behaviour of the heavy metals Zn, Pb, Fe, Mn, Cu, Cr and Cd in the water column, dissolved and suspended fractions, and in the sediments of Estanda Stream and of Gezala Creek. Zn, Cd and Mn tend to be found in the water; Fe, Pb, Cu and Cr appear as an adsorbed fractionin the solid phases. Those of the second group are significantly linked to the fluvial sediments and present very high levels. The concentrations of the metals are conditioned by the waters from the mine galleries, by the leached waste, by the surface runoff, and by overflow from the spillway of the tailings pond. Our observations provide knowledge on the extent of the polluting power of the metals, the physico-chemical effects in play and the subsequent chances of recovering these highly affected environments. 相似文献
17.
P. C. S. Carvalho A. M. R. Neiva M. M. V. G. Silva I. M. H. R. Antunes 《Environmental Earth Sciences》2014,71(5):2029-2041
Tailings deposited over the Castanheira, a stream which flows through the old Ag–Pb–Zn Terramonte mine area, showed a great potential environmental risk due to sulphide weathering, facilitated by the tailings–water interaction. The high concentrations of Al, Fe, Pb and Zn in the tailings are associated with the exchangeable, reducible and sulphide fractions and suggest sphalerite and pyrite occurrences. Oxidation of pyrite is responsible for the low pH values (3.38–4.89) of the tailings. The water from the Castanheira stream is not suitable for human consumption due to high concentrations of SO4 2?, Mn, Al, Cd, Ni, and Pb. The lowest concentrations of metals and metalloids were detected in downstream stretches of the Castanheira. However, As, Fe and Zn in deeper sediments tend to increase downstream. Significant concentrations of trivalent forms of arsenic were detected in water samples. In downstream stretches of the Castanheira, some free ions (Fe2+, Mn2+ and Zn2+) also predominate and the water is saturated with ferrihydrite, goethite, hematite, lepidocrosite and magnetite. 相似文献
18.
The world‐class Poderosa‐Pataz district is famous for its gold endowment in vertically and laterally extensive quartz‐sulphide veins. Precipitating mechanisms are investigated to determine why gold is so laterally and vertically distributed. Micro‐XRF and LA‐ICP‐MS element mapping of pyrites surrounding gold grains reveals systematic enrichment of As around or near visible gold accumulations. These As‐enriched zones define discordant rims and corridors overprinting pyrites. LA‐ICP‐MS spot analyses performed within and outside the As enrichment zones indicate that As is enriched on average by two orders of magnitude in association with gold. Secondary pyrite transformation by hydrothermal fluids with elevated As‐Au induced a change in the semiconducting properties of pyrite grains, resulting in the precipitation of visible gold particles at the interfaces of As‐enriched zones. The electrochemical precipitation mechanism acted as a filter to extract gold in solution regardless of variations in pressure and temperature, hence explaining the vertically and laterally extensive gold mineralization. 相似文献
19.
T. L. Noble B. G. Lottermoser A. T. Townsend 《Australian Journal of Earth Sciences》2016,63(6):781-793
Remediation of a legacy tin-tailings site in northeast Tasmania, Australia was carried out by statutory authorities. This study evaluated the fate of As and other deleterious trace metals Cd, Cu, Fe and Zn (among others) following the application of lime and fertiliser. Arsenic concentrations in the tailings ranged from 86 mg/kg to 0.26 wt%. Surface application of lime resulted in a 100-fold reduction in dissolved As concentrations in on-site surface waters; from an average of 196 µg/L prior to lime addition, to between 2.0 and 7.4 µg/L post-amendment. The concentration of other deleterious elements, however, varied between dry and wet cycles. The concentrations of Cd, Cu and Zn in surface waters were high and similar to pre-remediation levels during dry conditions (0.4, 13.5 and 6.1 mg/L, respectively), and only below freshwater ecosystem protection values during wet conditions. Bioaccumulation of Cd was observed in the naturally occurring coloniser, Juncus pallidus, with 4–5 times more Cd in the above-ground biomass relative to the tailings. Ferric arsenate (scorodite) was the dominant source of As identified in the tailings mineralogy. Hydrous ferric oxides and Fe-bearing cassiterite were also identified as hosting As. The pH increase in the surface lime-amended tailings was inferred to result in precipitation of observed hydrous ferric oxides, hematite and goethite, providing high-surface area for adsorption of arsenate onto positively charged surfaces. Jarosite was observed in both the surface lime-amended and subsurface non-amended tailings and suggests a continued supply of acidity to the pore waters despite the application of lime. Leaching experiments showed that As was more mobile in the lime-dosed tailings than in subsurface non-amended tailings, likely owing to desorption in alkaline pH conditions. By contrast, the mobility of Cd, Cu and Zn in the surface lime-amended tailings was reduced by at least two orders of magnitude compared with subsurface non-amended tailings. Evaluation of the applied rehabilitation strategy highlights the limits of a single chemical remediation approach to a polymetallic (including metalloids) waste with complex mineralogy and large seasonal fluctuations. Rehabilitation of metalliferous mine sites requires a complete understanding of all environmentally significant elements and their pathways into local receptors. 相似文献
20.
以广西大厂镇鲁塘铅锌矿尾砂为研究对象,通过淋滤实验研究了不同氧化还原条件下尾砂中Cu、Cd、Zn、Pb和As等元素的活化和迁移规律。结果表明：经高浓度氧化、高浓度还原条件处理的尾矿表现为pH<7的酸性环境,经低浓度氧化环境条件处理的尾砂呈现pH>7的弱酸性至弱碱性环境;尾砂中Cu、Cd元素活化迁移受pH值的影响明显,即高浓度还原和高浓度氧化条件可以促进Cu和Cd元素的迁移,酸性条件对Cu和Cd元素的迁移起到促进作用;Zn与Cd元素存在竞争吸附关系,但二者仍有明显差别;Pb和As元素受到还原条件的影响,能有效促进Pb和As元素的释放迁移。在淋滤实验前期,铅锌矿的表面阻力较小,由于环境酸碱性的改变,初始尾砂对重金属元素的吸附位能发生变化,重金属元素初期迁移能力得到加强;淋滤后期,矿物颗粒表面由于发生氧化还原反应,促使颗粒表面的阻力增加,重金属元素的溶出量减少,迁移能力受到抑制。 相似文献