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1.
Hg mobilization from contaminated soils and mine wastes was the source of environmental contamination in the Valle del Azogue mining area. We researched solid-phase speciation and aqueous mobility of Hg through Scanning electron microscopy-energy dispersive X-ray spectroscopy and electron probe microanalysis analysis, solid-phase-Hg-thermo-desorption (SPTD) and laboratory column experiments. We found that in contaminated soils and mine wastes, the predominant Hg species was cinnabar (HgS), mainly formed from the weathering of Hg-rich pyrite, and metallic Hg (0) in the matrix, whereas in calcines and tailings the dominant species was metallic Hg (0). The mobilization of Hg in the aqueous phase seems to have originated from the dissolution of elemental Hg (0) present in soils and wastes, reaching concentrations of up to 67 μg l−1, and showing a higher long-term environmental potential risk, in addition to atmospheric emissions.  相似文献   

2.
《Applied Geochemistry》2000,15(3):281-294
Mercury has been used in some mineralizing hydrothermal systems as a significant pathfinder of Au and other elements. In addition, its geochemical behaviour reflects some characteristics related to the transport mechanism of metal-bearing fluids. In this work the authors analyse the geochemical aspects and the environmental impact of Hg mobilization from the old mining area of Valle del Azogue (VA), from smelting slags, mining waste and the partially exploited mineralization that remains a few metres underground. The main pathway of Hg is the transport of vapor from different foci, therefore a mathematical simulation of the process of Hg vapor transport was carried out in the Valle del Azogue (VA) mineral deposit. This is one of the two sites in Spain (the other being the famous district of Almaden), where Hg vapor emissions have been cited. The results obtained by means of mathematical simulation were compared with both the real Hg concentration values detected in the field (upper part of the mining area), and with the geochemical distribution patterns of Au and other elements related to the mineralization. A close relationship between the simulated Hg vapor distribution and soil gas concentrations was identified. It is proposed that the transport of Hg emissions from this old mining area could be the cause of present contamination of marine sediments in the area.  相似文献   

3.
《Applied Geochemistry》2004,19(3):379-393
The speciation of Hg is a critical determinant of its mobility, reactivity, and potential bioavailability in mine-impacted regions. Furthermore, Hg speciation in these complex natural systems is influenced by a number of physical, geological, and anthropogenic variables. In order to investigate the degree to which several of these variables may affect Hg speciation, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to determine the Hg phases and relative proportions of these phases present in Hg-bearing wastes from selected mine-impacted regions in California and Nevada. The geological origin of Hg ore has a significant effect on Hg speciation in mine wastes. Specifically, samples collected from hot-spring Hg deposits were found to contain soluble Hg-chloride phases, while such phases were largely absent in samples from silica-carbonate Hg deposits; in both deposit types, however, Hg-sulfides in the form of cinnabar (HgS, hex.) and metacinnabar (HgS, cub.) dominate. Calcined wastes in which Hg ore was crushed and roasted in excess of 600 °C, contain high proportions of metacinnabar while the main Hg-containing phase in unroasted waste rock samples from the same mines is cinnabar. The calcining process is thought to promote the reconstructive phase transformation of cinnabar to metacinnabar, which typically occurs at 345 °C. The total Hg concentration in calcines is strongly correlated with particle size, with increases of nearly an order of magnitude in total Hg concentration between the 500–2000 μm and <45 μm size fractions (e.g., from 97–810 mg/kg Hg in calcines from the Sulphur Bank Mine, CA). The proportion of Hg-sulfides present also increased by 8–18% as particle size decreased over the same size range. This finding suggests that insoluble yet soft Hg-sulfides are subject to preferential mechanical weathering and become enriched in the fine-grained fraction, while soluble Hg phases are leached out more readily as particle size decreases. The speciation of Hg in mine wastes is similar to that in distributed sediments located downstream from the same waste piles, indicating that the transport of Hg from mine waste piles does not significantly impact Hg speciation. Hg LIII-EXAFS analysis of samples from Au mining regions, where elemental Hg(0) was introduced to aid in the Au recovery process, identified the presence of Hg-sulfides and schuetteite (Hg3O2SO4), which may have formed as a result of long-term Hg(0) burial in reducing high-sulfide sediments.  相似文献   

4.
Mercury accumulation in the food chain, as a consequence of gold recovery in Brazil, has been an issue of concern. Reactions of Hg in the environment are quite complex, and can involve various Hg chemical species. Laboratory experiments were carried out on Hg0 solubility, Hg complexation and sorption on river sediments from a gold mining region in Brazil. The reactivity and the mobility of Hg species were considered. Results indicate that methyl mercury is more mobile than ionic mercury, and that the presence of humic acid enhances drastically the solubility of Hg0. The soluble complex formed has a relatively lower interaction at the sediment/water interface and is more prone to spread through the aquatic environment.  相似文献   

5.
Five hundred years of mercury (Hg) mining activity in Idrija, Slovenia caused widespread Hg contamination. Besides Hg emissions from the ore smelter, tailings have been found to be the major source of river sediment contamination. In the present study, solid phase binding forms and the aqueous mobility of Hg have been investigated in tailings of the Idrija Hg mine by means of a pyrolysis technique and aqueous Hg speciation. Results show that Hg binding forms differ with the age of the tailings due to the processing of different ores with different roasting techniques. In older tailings, the predominant Hg species is cinnabar (HgS), due to incomplete roasting, whereas in tailings of the 20th century the amount of cinnabar in the material decreased due to a higher efficiency of the roasting process and the increasing use of ores bearing native Hg. In younger tailings, metallic Hg (Hg0) sorbed to mineral matrix components such as dolomite and Fe-oxyhydroxides became the predominant Hg binding form in addition to unbound Hg0 and traces of HgO. Leaching tests show that in younger tailings high amounts of soluble Hg exist in reactive form. In older tailings most of the soluble Hg occurs bound to soluble complexes. It might be assumed that in the long term, matrix-bound Hg0 could be bound to humic acids derived from soils covering the tailings. This means that, despite the lower total Hg concentrations found in the younger tailings, the long-term risk potential of its mobile matrix-bound Hg0 is higher than that of older tailings bearing mostly immobile cinnabar.  相似文献   

6.
Considerable fractions of the Hg content of lake and river systems in Scandinavia are discharged from the soil of the catchments. An important soil type in Scandinavia is the iron–humus podzol. The sorption characteristics of this soil type for inorganic Hg(II) and monomethyl mercury were investigated by batch experiments. The solubility of Hg2+ and CH3Hg+ in the soil horizons containing organic matter increases with increasing pH of the soil solution by favoring the formation of solute organic matter–mercury complexes. While the solubility of Hg2+ is strongly dependent on complexation to dissolved organic matter, the solubility of CH3Hg+ is more dependent on ion exchange. The concentration of solute inorganic Hg(II) increased with increasing temperature probably because of an increase in the concentration of dissolved organic carbon. There was no effect of temperature on the concentration of solute CH3Hg+. At pH values where inorganic mercury–hydroxo complexes are formed, inorganic Hg(II) is efficiently sorbed to the metal oxides of the mineral soil. The soil–water distributions of inorganic Hg(II) in the different soil horizons were described by Freundlich isotherms or linear isotherms for common and contaminated mercury contents in the soils.  相似文献   

7.
Aqueous production and water-air exchange of elemental mercury (Hg0) are important features of the environmental cycling of Hg. We investigated Hg0 cycling in ten Arctic Alaskan lakes that spanned a wide range in physicochemical characteristics. Dissolved gaseous Hg (DGM, dominated by Hg0) varied from 40 to 430 fM and averaged 200 fM. All surface waters were supersaturated relative to the atmosphere. DGM averaged 3 ± 2% of dissolved (i.e., filter passing) dissolved total mercury (DTM) and 15 ± 6% of dissolved labile Hg (DLM). In-lake DGM profiles generally followed the vertical distribution of light, indicating photoreduction of Hg(II) complexes as a source of Hg0. Additionally, DGM correlated linearly with DLM (r2 = 0.82, p < 0.0001) in the lake surface, signifying that Hg complexes (mostly organic Hg associations) in dissolved phase are photoreducible and contribute to production of DGM. Further, a positive relation between DGM/DTM and both Ka (light attenuation coefficient; r2 = 0.73, p < 0.02) and DOC (r2 = 0.60, p = 0.02) suggests that solar radiation and dissolved organic matter control DGM production and its cycling. An average rate of DGM formation (0.6 ± 0.2% of DTM d−1; range, 0.20.8) was estimated by assuming steady state with the evasional rate. In-lake DGM formation occurs at lower rates in waters with greater suspended particulate matter and dissolved organic carbon (DOC), pointing to the significant role of organic matter plays in controlling DGM formation in these aquatic systems. Estimated evasional fluxes of Hg0 (average, 140 ± 50 pmol m−2 d−1; range, 60-200) were comparable to those of temperate lakes (e.g., Wisconsin, Michigan). In arctic lakes, the rate of evasion during ice-free periods (7 ± 3 nmol m−2 yr−1) is similar to the atmospheric input of Hg (wet + dry) to the lakes based on levels in summertime precipitation but not including additional sources, e.g., springtime depletion.  相似文献   

8.
《Applied Geochemistry》1999,14(2):147-158
This study evaluates several southern Appalachian Piedmont mining districts for Hg contamination in surface waters and determines potential relationships between Hg discharged from historical mining operations and site-specific physical factors. Water samples were collected from 3 fluvial systems that drain areas where Hg was used to amalgamate Au from ore during the 19th century. Each of the fluvial systems exhibit similar physical characteristics such as climate, vegetation, and rock type. Total Hg (HgT) determinations were made using cold vapour atomic fluorescence spectroscopy techniques. Concentrations of HgT in the southern Appalachian Piedmont range from 1–3 ng l−1 in waters of the Arbacoochee, Alabama, and South Mountains, North Carolina, Mining Districts to 13 ng l−1 in waters of the Dahlonega Mining District in Georgia. The correlation between HgT and total suspended solids (TSS) at the southern Appalachian sites was good with a coefficient of determination (r2) of 0.82. A clear trend between environmentally-available Fe (FeE) and HgT (r2=0.86) was also evident. The correlation between HgT and FeE most likely reflects similarities in the mechanisms that control the aqueous concentrations of both metals (i.e., the particle-reactive nature of the two elements), allowing for the sorption of Hg onto Fe-oxyhydroxides. Hence, increased loads of TSS from erosional events are probably responsible for higher stream water HgT concentrations. Vegetation at these sites, which is heavy due to the warm, humid climate of the SE, may help reduce the total amount of Hg released from contaminated mining sites to the rivers by controlling erosion, hence, decreasing the input of contaminated particles into streams and rivers.These southern Appalachian mining sites used Hg amalgamation techniques similar to those used in other precious metals mining districts, such as the highly contaminated Comstock Au–Ag district in Nevada, yet HgT concentrations are orders of magnitude lower; This difference in concentration between the southern Appalachian districts and the Comstock district may correlate to the relative amounts of Hg that were used in each. However, other variables were evaluated to determine if physio-chemical differences such as climate could influence HgT concentrations in surface waters of the two areas.  相似文献   

9.
The Wanshan Hg mining area in Guizhou, China, was one of the world’s largest Hg producing regions. Numerous mine-waste and calcines still remain, leaching Hg to local rivers and streams and potentially impacting the local population. Several studies have been published on local environmental impacts of these mining and retorting residues, but a comprehensive, regional survey on the distribution of Hg in the rivers in the region, as presented in this paper, has not previously been conducted. This study focuses on the regional distribution and temporal variation of aqueous Hg fractions in the five main watercourses draining the Wanshan Hg mining and retorting area, covering more than 700 km2. Three sampling campaigns were carried out in 2007 and 2008, covering high flow, normal flow and low flow periods. Total (THg), particulate (PHg), dissolved (DHg) and reactive (RHg) Hg fractions were determined. All rivers had the highest Hg concentrations at sample sites about 100–500 m downstream of the mine wastes. Total Hg concentrations ranged from extremely high (up to 12,000 ng L−1) at the sample site just 100 m below mine wastes, to quite low in tributary streams (1.9 ng L−1, about 14 km downstream of the mine wastes). Total Hg and PHg concentrations were usually highest during high flow periods in the Hg-contaminated areas (i.e. THg ? 50 ng L−1), while in the less-impacted downstream areas (with THg < 50 ng L−1) the Hg concentrations were usually lowest during high flow periods. Although highly elevated concentrations of Hg in water samples were found just downstream of the mine wastes, the concentrations decreased sharply to well below 50 ng L−1 (US EPA Hg concentration standard for protection of fresh water), within only 6–8 km downstream. Concentrations of THg were highly dominated by and correlated with PHg (R2 = 0.996–0.999, P < 0.001); PHg constituted more than 80% of THg in Hg-contaminated areas, and could account for 99.6% of the THg close to the mine wastes.  相似文献   

10.
贵州万山汞矿尾矿堆及地表水的环境地球化学特征   总被引：5，自引：0，他引：5  
对贵州万山汞矿区尾渣堆(主要为炉渣组成)、地表水及河流沉淀物的汞迁移进行了研究。由于赋矿岩石为白云岩，高温煅烧的炉渣中含CaO等碱性物质，炉渣的风化作用释放出汞以及碱性水．流经尾渣堆的地表水碱性强(pH10．6-11．8)、电导率高，且具有明显不同的主要离子组成．万山汞矿矿石单一，主要为辰砂，其他矿石极少，因此炉渣及其渗滤水中除汞外的重金属含量很低．尾渣堆中的汞及碱性物质是对周围环境的主要威胁．在尾渣堆下游汞含量很快降低，约300n，范围内水中的溶解汞从300—1900，ng/L降至72ng／L，而且水的碱性也被中和．但是，由于尾渣堆中的汞及碱性物质含量高，尾渣堆的长时间风化及水流的溶解会将大量汞搬运到周围的土壤及水体并对生物产生不利影响．  相似文献   

11.
Quantifying mercury (Hg) emissions from active volcanoes is of particular interest for better constraining the global cycle and environmental impact of this highly toxic element. Here we report on the abundance of total gaseous (TGM = Hg0(g) + HgII(g)) and particulate (Hg(p)) mercury in the summit gas emissions of La Soufrière andesitic volcano (Guadeloupe island, Lesser Antilles), where enhanced degassing of mixed hydrothermal-magmatic volatiles has been occurring since 1992 from the Southern summit crater. We demonstrate that Hg in volcanic plume occurs predominantly as gaseous mercury, with a mean TGM/Hg(p) mass ratio of ~ 63. Combining the mean TGM/H2S mass ratio of the volcanic plume (~ 3.2 × 10− 6), measured close to the source vent, with the H2S plume flux (~ 0.7 t d− 1), determined simultaneously, allows us to estimate a gaseous mercury emission rate of 0.8 kg yr− 1 from La Soufrière summit dome. Somewhat lower TGM/Stot mass ratio in fumarolic gases from the source vent (4.4 × 10− 7) suggests that plume chemical composition is not well represented by the emission source (fumaroles) due to chemical processes prior to (or upon) discharge. Current mercury emission from La Soufrìere volcano represents a very small contribution to the estimated global volcanic budget for this element.  相似文献   

12.
We present here the first mercury speciation study in the water column of the Southern Ocean, using a high-resolution south-to-north section (27 stations from 65.50°S to 44.00°S) with up to 15 depths (0-4440 m) between Antarctica and Tasmania (Australia) along the 140°E meridian. In addition, in order to explore the role of sea ice in Hg cycling, a study of mercury speciation in the “snow-sea ice-seawater” continuum was conducted at a coastal site, near the Australian Casey station (66.40°S; 101.14°E). In the open ocean waters, total Hg (HgT) concentrations varied from 0.63 to 2.76 pmol L−1 with “transient-type” vertical profiles and a latitudinal distribution suggesting an atmospheric mercury source south of the Southern Polar Front (SPF) and a surface removal north of the Subantartic Front (SAF). Slightly higher mean HgT concentrations (1.35 ± 0.39 pmol L−1) were measured in Antarctic Bottom Water (AABW) compared to Antarctic Intermediate water (AAIW) (1.15 ± 0.22 pmol L−1). Labile Hg (HgR) concentrations varied from 0.01 to 2.28 pmol L−1, with a distribution showing that the HgT enrichment south of the SPF consisted mainly of HgR (67 ± 23%), whereas, in contrast, the percentage was half that in surface waters north of PFZ (33 ± 23%). Methylated mercury species (MeHgT) concentrations ranged from 0.02 to 0.86 pmol L−1. All vertical MeHgT profiles exhibited roughly the same pattern, with low concentrations observed in the surface layer and increasing concentrations with depth up to an intermediate depth maximum. As for HgT, low mean MeHgT concentrations were associated with AAIW, and higher ones with AABW. The maximum of MeHgT concentration at each station was systematically observed within the oxygen minimum zone, with a statistically significant MeHgTvs Apparent Oxygen Utilization (AOU) relationship (p < 0.001). The proportion of HgT as methylated species was lower than 5% in the surface waters, around 50% in deep waters below 1000 m, reaching a maximum of 78% south of the SPF. At Casey coastal station HgT and HgR concentrations found in the “snow-sea ice-seawater” continuum were one order of magnitude higher than those measured in open ocean waters. The distribution of HgT there suggests an atmospheric Hg deposition with snow and a fractionation process during sea ice formation, which excludes Hg from the ice with a parallel Hg enrichment of brine, probably concurring with the Hg enrichment of AABW observed in the open ocean waters. Contrastingly, MeHgT concentrations in the sea ice environment were in the same range as in the open ocean waters, remaining below 0.45 pmol L−1. The MeHgT vertical profile through the continuum suggests different sources, including atmosphere, seawater and methylation in basal ice. Whereas HgT concentrations in the water samples collected between the Antarctic continent and Tasmania are comparable to recent measurements made in the other parts of the World Ocean (e.g., Soerensen et al., 2010), the Hg species distribution suggests distinct features in the Southern Ocean Hg cycle: (i) a net atmospheric Hg deposition on surface water near the ice edge, (ii) the Hg enrichment in brine during sea ice formation, and (iii) a net methylation of Hg south of the SPF.  相似文献   

13.
Selenium (Se) is an important co-existing elemental component of the mineral matrix of mercury (Hg) ore deposits. The hazards associated with Se contamination of the aquatic ecosystems in Hg mining areas; however, are often overlooked by environmental researchers due to a preoccupation with Hg. Selenium may also pose a long-term risk to the local ecosystem, and further complicate the situation as Se may also play an important antagonistic role against Hg. Furthermore, most studies on Se pollution have focused only on total Se, whereas the toxicity, bioavailability, and bioaccumulation of Se in aquatic ecosystems is primarily determined by its site-specific individual species. In this study, the concentrations of total Se, inorganic Se (tetravalent and hexavalent), and organic Se were determined in water samples collected from 41 typical sites selected in rivers, tributaries, and springs in Wanshan, China, where Hg and Se co-occur due to historic Hg mining and retorting activities. Se concentrations were observed to decrease with distance from mine-waste calcines, which indicated that mine-waste calcines may be significant sources of the elevated Se in the rivers, especially in downstream areas within 8 km from the mine-waste calcines. The concentration of total aqueous Se throughout the study area was highly variable (3.8 ± 6.0 μg L−1) and on average was one order of magnitude greater than that in natural river systems worldwide (0.1–0.3 μg L−1). The majority of the Se was hexavalent (3.1 ± 4.9 μg L−1; 65%), followed by tetravalent (0.53 ± 0.86 μg L−1; 15%) and organic forms (0.85 ± 1.5 μg L−1; 20%), possibly due to the generally alkaline conditions. Se concentrations in some sampling sites exceeded certain recommended limit of values. However, the existing criteria for Se in aquatic system are mainly based on total Se and the recommended limit of values in different countries or organizations are inconsistent with one another. Therefore, the need to consider Se speciation rather than only total Se is highlighted for future studies.  相似文献   

14.
汞易挥发且通常以气态形式在大气环境中迁移转化,检测汞在气相中的含量可为汞的治理工作提供依据,但检测气相汞的技术并不成熟。该项工作需要准确地对气相元素汞量进行测定,而测定的前提是必须具备准确、可靠的标定方法。本研究提出以Hg~(2+)离子为前驱体标定煤热解气中气相元素汞量的方法。该方法是基于水溶液中Hg~(2+)可被还原剂定量还原成元素汞蒸汽的原理,实现对气相元素汞量的标定。与传统的基于饱和蒸汽原理的标定方法相比,该方法的优点是取样时不易受温度影响,易于精确控制汞量,且避免了实验室内储存汞蒸汽所造成的汞污染。以测定四种煤在热解过程中元素汞的释放量为例考察了本方法的准确性,结果表明本方法具有较好的重复性和适应性。与美国Ontario-Hydro方法分析的结果进行对比,两种方法的相对标准偏差均小于3.0%,说明本研究的标定方法的可靠性较高。  相似文献   

15.
Hg in hydrothermal systems is generally thought to be transported as Hg-S complexes. However, the abundance of Hg0vap, in geothermal emissions suggests that Hg0eq, is present in the liquid phase of geothermal systems. Calculations for reducing fluids (HS? dominant over SO=4) in equilibrium with cinnabar indicate that Hg0eq, can be quite abundant relative to other species at temperatures above 200°C. Increasing pH and temperature, and decreasing total S, ionic strength, and pO2 all promote the abundance of Hg0eq. When a vapor phase develops from a geothermal liquid, Hg partitions strongly into the vapor as Hg0vap. Vapor transport at shallow level then results in the formation of Hg halos around shallow aquifers as well as in a flux of Hg to the atmosphere. Hg deposition may occur in response to mixing with oxidizing or acidic water, turning Hg0eq, into Hg++, with subsequent cinnabar precipitation. When pyrite is the stable Fe-sulfide, cinnabar solubility is at its lowest, so cinnabar + pyrite assemblages are common. Cinnabar + hematite ± pyrite can precipitate from more oxidized or S-poor water. Hg0liq, can occur as a primary mineral, in coexistence with all common Fe-sulfides and oxides. Cinnabar ± Hg0liq cannot coexist with pyrrhotite or magnetite at temperatures between 100° and 250°C. Evidence from Hg deposits indicates that many formed from dilute hydrothermal fluids in which Hg probably occurred as Hg0eq. In S-rich systems, Hg may occur as Hg-S complexes, and in saline waters it can occur as Hg-Cl complexes.  相似文献   

16.
Methylmercury cation (CH3Hg+) is known to have a strong affinity for organic matter in soil, sedimentary, and aquatic environments. The objective of this study is to determine the dominant ligands binding CH3Hg+ in humic acids by evaluating several CH3Hg+-ligand complexation models, using mercury LIII-edge extended X-ray absorption fine structure (EXAFS). The model CH3Hg+ binding ligands examined in this study include thiol (-SH), hydrogen polysulfide (-SSH or -SSSH), sulfide (-S-), disulfide (-SS-), carboxyl (-COOH), and amine (-NH2). Based on the atomic geometry around mercury in each model structure, we distinguished CH3Hg+-binding ligands in two different humic acids (soil and aquatic). We observed CH3Hg+ preferentially binds to thiol ligands. After saturating reactive thiol ligands, the majority of CH3Hg+ binds to carboxyl ligands rather than to amine or other reduced sulfur ligands than thiol. We found no evidence of significant CH3Hg+-sulfide/disulfide or CH3Hg+-hydrogen polysulfide complexes in any samples. When CH3Hg+ binds to a humic ligand, the C-Hg bond in CH3Hg+ remains intact. Some heavy atoms are proximately coordinated around the mercury atom in the sample containing the highest CH3Hg+ levels used in this study.  相似文献   

17.
The main carrying phases of mercury (Hg) were analyzed in a 120 cm sediment core taken at the Laguna del Plata (LP), a small lake connected to the main water body of Laguna Mar Chiquita (LMC) during highstands. LMC is considered to be one of the largest saline lakes in the world representing a sensitive climatic indicator due to its frequent lake level variations at millennial and interdecadal scale like the last ones that started early in the 1970s and after 2004. Total particulate Hg (HgTP) concentrations vary between ∼13 and ∼131 μg kg−1 indicating a system with low pollution. Selective extractions with ascorbate, HCl and H2O2 were performed in the sediments and they revealed that Hg is associated mainly to reactive sulphides in the base of the core, while in the middle and upper part the organic matter seems to be the main Hg-bearing phase. The highest and most important peak was found in sediments accumulated between 1991 and 1995. More than a punctual source of pollution, this peak is likely related to two eruptive events occurred in the Andean Cordillera in this period: the eruption of Hudson volcano in southern Patagonia that occurred in 1991 and the one of the Láscar volcano in northern Chile that occurred in 1993. In both cases, the respective ash plumes were documented to have reached the Laguna del Plata region.  相似文献   

18.
Pristine water bodies in the Negro River basin, Brazilian Amazon, show relatively high concentrations of mercury. These waters are characterized by acidic pH, low concentrations of suspended solids, and high amounts of dissolved organic matter and are exposed to intense solar radiation throughout the year. This unique environment creates a very dynamic redox chemistry affecting the mobility of mercury due to the formation of the dissolved elemental species (Hg0). It has been shown that in this so-called black water, labile organic matter from flooded forest is the major scavenger of photogenerated H2O2. In the absence of hydrogen peroxide, these black waters lose their ability to oxidize Hg0 to Hg2+, thus increasing Hg0 evasion across the water/atmosphere interface, with average night time values of 3.80 pmol m?2 h?1. When the dry period starts, labile organic matter inputs gradually diminish, allowing the increasing concentration of H2O2 to re-establish oxidative water conditions, inhibiting the metal flux across the water/atmosphere interface and contributing to mercury accumulation in the water column.  相似文献   

19.
Mercury (Hg) and methylmercury (CH3Hg+) concentrations in streambed sediment and water were determined at 27 locations throughout the Sacramento River Basin, CA. Mercury in sediment was elevated at locations downstream of either Hg mining or Au mining activities where Hg was used in the recovery of Au. Methylmercury in sediment was highest (2.84 ng/g) at a location with the greatest wetland land cover, in spite of lower total Hg at that site relative to other river sites. Mercury in unfiltered water was measured at 4 locations on the Sacramento River and at tributaries draining the mining regions, as well as agricultural regions. The highest levels of Hg in unfiltered water (2248 ng/l) were measured at a site downstream of a historic Hg mining area, and the highest levels at all sites were measured in samples collected during high streamflow when the levels of suspended sediment were also elevated. Mercury in unfiltered water exceeded the current federal and state recommended criterion for protection of aquatic life (50 ng/l as total Hg in unfiltered water) only during high streamflow conditions. The highest loading of Hg to the San Francisco Bay system was attributed to sources within the Cache Creek watershed, which are downstream of historic Hg mines, and to an unknown source or sources to the mainstem of the Sacramento River upstream of historic Au mining regions. That unknown source is possibly associated with a volcanic deposit. Methylmercury concentrations also were dependent on season and hydrologic conditions. The highest levels (1.98 ng/l) in the Sacramento River, during the period of study, were measured during a major flood event. The reactivity of Hg in unfiltered water was assessed by measuring the amount available for reaction by a strong reducing agent. Although most Hg was found to be nonreactive, the highest reactivity (7.8% of the total Hg in water) was measured in the sample collected from the same site with high CH3Hg+ in sediment, and during the time of year when that site was under continual flooded conditions. Although Hg concentrations in water downstream of the Hg mining operations were measured as high as 2248 ng/l during stormwater runoff events, the transported Hg was found to have a low potential for geochemical transformations, as indicated by the low reactivity to the reducing agent (0.0001% of the total), probably because most of the Hg in the unfiltered water sample was in the mercury sulfide form.  相似文献   

20.
Zusammenfassung Die röntgenographische Neubestimmung der Kristallstruktur des kubischen Quecksilberminerals Eglestonit [a o=16,036(3) Å, RaumgruppeIa3d-O h 10 ,R=0,039 für 185 beobachtete Reflexe] führte auf den Zellinhalt Hg96Cl48O32. Die Anordnung des Quecksilbers in Hg2-Gruppen weist auf eine reine Hg(I)-Verbindung hin, was mit dieser Formel in Widerspruch steht. Aufgrund der H2O-Bestimmung von synthetischem Eglestonit und in Übereinstimmung mit einem kurzen O–O-Abstand, welcher eine Wasserstoffbrücke anzeigt, muß man annehmen, daß die Elementarzelle zusätzlich 16 röntgenographisch nicht nachweisbare H-Atome enthält. Die chemische Formel lautet folglich [Hg2]3Cl3O2H. Eglestonit kann aus Kalomel durch Hydrothermalbehandlung in alkalischem Medium synthetisiert werden.
Reexamination of the mercury mineral eglestonite: Crystal structure, chemical composition, and synthesis
Summary The reexamination of the crystal structure of the cubic mercury mineral eglestonite [a o=16.036(3) Å, space groupIa3d-O h 10 ,R=0.039 for 185 observed X-ray reflections] has led to a cell content of Hg96Cl48O32. The arrangement of mercury in Hg2-groups indicates a pure Hg(I) compound in contradiction to this formula. Based on the H2O determination of synthetic eglestonite and in agreement with the observation of a short O–O distance as characteristic for a hydrogen bond, one must assume that the unit cell also contains 16 H-atoms which cannot be specifically located by X-ray methods. The chemical formula therefore reads [Hg2]3Cl3O2H. Eglestonite can be synthesized by hydrothermal treatment of calomel in alkaline media.

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