Applied Geochemistry (v.23, #12)
Roman road pollution assessed by elemental and lead isotope geochemistry in East Belgium by Virginie Renson; Nathalie Fagel; Nadine Mattielli; Serge Nekrassoff; Maurice Streel; François De Vleeschouwer (3253-3266).
The ability of inorganic geochemistry to record environmental change and especially human impact has been evidenced by several studies across Europe, especially in peat, where it is possible to record the impact of agriculture, mining and other industries. However, despite the numerous investigations on the impact of ancient human activities such as ore mining and smelting, little attention has been paid to geochemistry as a tool to solve problems of palaeopollution in the surroundings of archaeological sites. This paper presents geochemical evidence of the impact of a possible early Roman road built in SE Belgian peatland. Increased Zn and Pb concentrations suggest that Pb–Zn ores were transported on the road. Lead isotope analyses suggest that these ores are locally derived, being compatible with those found in the nearby Pb–Zn ore deposits from East Belgium. Present results provide direct evidence that East Belgian Pb–Zn ores were already being mined during Roman times, i.e. earlier than previously suspected (i.e. 14th century) and that Zn appears to be relatively immobile here. On a broader scale, it also demonstrates that such an early road already had an impact on the environment in terms of metal pollution. This paper enlarges on the range of possibilities offered by geochemistry in the field of geoarchaeology.
Effect of indigenous bacteria on geochemical behavior of arsenic in aquifer sediments from the Hetao Basin, Inner Mongolia: Evidence from sediment incubations by Huaming Guo; Xiaohui Tang; Suzhen Yang; Zhaoli Shen (3267-3277).
Incubation studies were carried out using 5 freshly collected sediments from shallow aquifers of the Hetao Basin, Inner Mongolia. The aquifer sediments covering a range of redox conditions, as indicated by their deep grey to yellow color were mixed with degassed artificial As solution or degassed deionized water at a ratio of solid to water of about 1:10 (wt./wt.). Suspensions which were either amended with glucose or autoclaved, were incubated in parallel with unamended suspensions. Five microcosm cultures of unamended sediments gradually release the equivalent of 0.03–0.30 μg/g As to the dissolved phase. The addition of glucose as a potential electron donor results in a marked stimulation in the mobilization of As (0.71–3.81 μg/g) in the amended incubations for all sediments. The quantity of As released accounts for 60–70% of As bound to Fe/Mn oxides in the original sediments. The microbially mediated mobilization of As with the organic nutrient as an electron donor is strongly associated with the As bound to Fe/Mn oxides, as well as the exchangeable As. During the incubations amended with glucose, 2–4% of the sediment Fe is released. The results suggest that the introduction of labile dissolved organic C into the yellowish sediment aquifers with As-free groundwater would reduce a significant proportion of the Fe(III) oxyhydroxides mediated by anaerobic bacteria respiration and increase groundwater As concentrations.
Origins of high pH mineral waters from ultramafic rocks, Central Portugal by José M. Marques; Paula M. Carreira; Maria Rosário Carvalho; Maria J. Matias; Fraser E. Goff; Maria J. Basto; Rui C. Graça; Luís Aires-Barros; Luís Rocha (3278-3289).
This paper reviews the geochemical, isotopic (2H, 18O, 13C, 3H and 14C) and numerical modelling approaches to evaluate possible geological sources of the high pH (11.5)/Na–Cl/Ca–OH mineral waters from the Cabeço de Vide region (Central-Portugal). Water–rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the Cabeço de Vide mineral waters, which was corroborated by numerical modelling approaches. The local shallow groundwaters belong to the Mg–HCO3 type, and are derived by interaction with the local serpentinized rocks. At depth, these type waters evolve into the high pH/Na–Cl/Ca–OH mineral waters of Cabeço de Vide spas, issuing from the intrusive contact between mafic/ultramafic rocks and an older carbonate sequence. The Cabeço de Vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization. Magnesium silicate phases (brucite and serpentine) seem to control Mg concentrations in Cabeço de Vide mineral waters. Similar δ 2H and δ 18O suggest a common meteoric origin and that the Mg–HCO3 type waters have evolved towards Cabeço de Vide mineral waters. The reaction path simulations show that the progressive evolution of the Ca–HCO3 to Mg–HCO3 waters can be attributed to the interaction of meteoric waters with serpentinites. The sequential dissolution at CO2 (g) closed system conditions leads to the precipitation of calcite, magnesite, amorphous silica, chrysotile and brucite, indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth. The apparent age of Cabeço de Vide mineral waters was determined as 2790 ± 40 a BP, on the basis of 14C and 13C values, which is in agreement with the 3H concentrations being below the detection limit.
Rivers of North-Rhine Westphalia revisited: Tracing changes in river chemistry by Andrea Stögbauer; Harald Strauss; Julia Arndt; Victoria Marek; Florian Einsiedl; Robert van Geldern (3290-3304).
Three rivers in North-Rhine Westphalia, Germany, were investigated for their hydrochemical properties including their stable isotopic composition of water (δ 2H, δ 18O) and dissolved river compounds (δ 13CDIC, δ 34SSO4 and δ 18OSO4, and δ 15NNO3 and δ 18ONO3). The study focused on two objectives: an assessment of potential sources for river solutes (anthropogenic vs. natural sources), and the quantification of changes in river chemistry over the past 15 a (for the rivers Lippe and Ruhr). Decreasing concentrations were found for most of those river constituents that are commonly linked to anthropogenic activities, such as [ NO 3 - ] , [Cl−], [K+], and [Na+]. An observed increase in [ SO 4 2 - ] for the river Lippe reflects most likely varying discharges from mining activities. Variations in the isotopic composition of water display the influence of ocean water (river Ems) or of evaporation that occurred either in channels (river Ems), in reservoirs (river Ruhr) or due to the use of river water for cooling purposes (river Lippe). δ 13CDIC values around −11‰ point to carbonate dissolution by carbonic acid as the major source for dissolved inorganic C. Modifications of this average δ 13CDIC resulted from enhanced agricultural use, sewage inputs, and gas exchange with the atmosphere in reservoirs and channels. The isotopic composition of dissolved SO 4 2 - reveals atmospheric deposition and sulphide oxidation as its major sources. Sulphate from sulphide oxidation in parts reflects the local geology (river Ruhr); in the Kreidebecken leaching of sulphide seems to be linked to agriculture and drainage (rivers Lippe and Ems). However, SO 4 2 - introduced from mining activities into the Lippe and the Ems does not alter the isotopic composition of riverine SO 4 2 - , despite rather high discharges. Nitrogen and O isotopes reveal that manure and sewage are major sources of NO3 in most parts of the river Ruhr. Only a single value from the headwaters displays the signature of soil NO3. Downstream increasing δ 15NNO3 and δ 18ONO3 values (both by 2‰ on average) point to denitrification and to additional inputs from atmospheric deposition.
Correlation between dissolved 4He concentration and 36Cl in groundwater at Äspö, Sweden by Yasunori Mahara; Takuma Hasegawa; Kimio Miyakawa; Tomoko Ohta (3305-3320).
Tunnel excavation at Äspö Island, Sweden, has caused severe groundwater disturbance, gradually extending deeper into the tunnel as present-day Baltic seawater intrudes through fractures connecting to the surface. However, the paleo-hydrogeochemical conditions have remained in the deep highly saline waters that have avoided mixing. A correlation has been observed between dissolved 4He concentration and Cl− ion concentration, measured every two years from 1995 to 2001 at Äspö. Groundwater mixing conditions can be examined by the correlations between 1/Cl, 36Cl/Cl, and 3H concentrations. Subsurface production is responsible for the majority of the 36Cl and excess dissolved 4He of interstitial groundwater in fractures. The secular equilibrium ratio of 36Cl/Cl in rock was theoretically estimated to be (5.05 ± 0.82) × 10−14 based on the neutron flux intensity, a value comparable to the measured 36Cl/Cl ratio in rock and groundwater. The degassing crustal 4He flux was estimated to be 2.9 × 10−8 ∼ 1.3 × 10−6 (ccSTP/cm2a) using the HTO diffusion coefficient for the Äspö diorite. The 4He accumulation rate ranges from 6.8 × 10−10 (for the in situ accumulation rate) to 7.0 × 10−9 (ccSTP/(gwater · a) considering both 4He in situ production and the degassing flux, assuming 4He is accumulated constantly in groundwater. By comparing the subsurface 36Cl increase with 4He concentrations in groundwater, the 4He accumulation rate was determined from data for groundwater arriving at the secular equilibrium of 36Cl/Cl. The 4He accumulation rate was found to be (1.83 ± 0.72) × 10−8 ccSTP/(gwater · a) without determining the magnitude of degassing 4He flux.
Classification of distinct eruptive phases of the diamondiferous Star kimberlite, Saskatchewan, Canada based on statistical treatment of whole rock geochemical analyses by E.C. Grunsky; B.A. Kjarsgaard (3321-3336).
Discrete eruptive events of the Star kimberlite, Saskatchewan, Canada have been classified into five distinctive clusters using statistical methods applied to whole rock geochemical data. The data set consists of 270 kimberlite samples from 38 drill holes that were analysed for whole rock major- and trace-element geochemistry. The data set was analysed by multivariate statistical techniques after a log-ratio transformation, including principal component analysis and linear discriminant analysis. Data analysis using principal component analysis recognized five distinct classes, confirmed by petrographic study, which correspond to unique mineralogical compositions. Based on relationships from detailed drill core logging results, these five geochemical classes are the Cantuar, Pense, early Joli Fou (eJF), mid Joli Fou (mJF) and late Joli Fou (lJF) equivalent age eruptive phases of the Star kimberlite. Subsequent statistical analysis utilizing linear discriminant analysis supports the distinctions between the classes. For the four kimberlite eruptive phases (Pense, early Joli Fou, mid Joli Fou and late Joli Fou) for which there is macrodiamond data from bulk sampling, there is an excellent correlation between the amount of lithospheric mantle contamination (as defined by the geochemistry) and the diamond grade.
Biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of Opalinus Clay and Posidonia Shale in northern Switzerland by Marcel Elie; Martin Mazurek (3337-3354).
Samples from two argillaceous formations (Opalinus Clay and Posidonia Shale) of near-identical maturity from northern Switzerland were subjected to a geochemical characterisation of organic matter and to confined-system pyrolysis experiments. Throughout the study area, the characteristics of organic matter are similar, indicating a spatially homogeneous sedimentary facies. Posidonia Shale contains marine organic matter deposited in a reducing environment, while a predominantly terrigenous source and a more oxidising environment of deposition was identified for Opalinus Clay. In the western and central parts of the study area, organic maturity is close to the onset of oil generation. In the easternmost part, a higher maturity has been reached due to a deeper burial below thick Tertiary Molasse deposits.Isothermal pyrolysis experiments were conducted at temperatures between 250 and 390 °C over 24 h. Bitumen yields increase along similar pathways for both Opalinus Clay and Posidonia Shale, but the maximum values are displaced by 10–20 °C. Data pertaining to maturity were determined from GC–MS analyses of saturated hydrocarbons, and specific attention was given to C29-sterane and C32-hopane isomerisation ratios. The evolution of these parameters with rising temperature is slightly different in the two formations, which is attributed to the contrasting organic facies. The pyrolysis data, together with literature data from natural basins, were used to calculate kinetic parameters for C29-sterane and C32-hopane, assuming a single-step isomerisation scheme according to the Arrhenius law. The resulting values based on pyrolysis data alone are very similar to those based on the combination of pyrolysis and natural data. Activation energies are similar in both formations, while the frequency factors are up to one order of magnitude higher for Posidonia Shale when compared to Opalinus Clay. For the Benken site, maximum temperature during Cretaceous burial was calculated on the basis of the kinetic data, using the TTI approach. The resulting temperatures of 75–80 °C are 5–10 °C below those derived in the literature from apatite fission-track analysis, vitrinite reflectance and basin modelling.
Dissolved and labile concentrations of Cd, Cu, Pb, and Zn in the South Fork Coeur d’Alene River, Idaho: Comparisons among chemical equilibrium models and implications for biotic ligand models by Laurie S. Balistrieri; Richard G. Blank (3355-3371).
In order to evaluate thermodynamic speciation calculations inherent in biotic ligand models, the speciation of dissolved Cd, Cu, Pb, and Zn in aquatic systems influenced by historical mining activities is examined using equilibrium computer models and the diffusive gradients in thin films (DGT) technique. Several metal/organic-matter complexation models, including WHAM VI, NICA-Donnan, and Stockholm Humic model (SHM), are used in combination with inorganic speciation models to calculate the thermodynamic speciation of dissolved metals and concentrations of metal associated with biotic ligands (e.g., fish gills). Maximum dynamic metal concentrations, determined from total dissolved metal concentrations and thermodynamic speciation calculations, are compared with labile metal concentrations measured by DGT to assess which metal/organic-matter complexation model best describes metal speciation and, thereby, biotic ligand speciation, in the studied systems. Results indicate that the choice of model that defines metal/organic-matter interactions does not affect calculated concentrations of Cd and Zn associated with biotic ligands for geochemical conditions in the study area, whereas concentrations of Cu and Pb associated with biotic ligands depend on whether the speciation calculations use WHAM VI, NICA-Donnan, or SHM. Agreement between labile metal concentrations and dynamic metal concentrations occurs when WHAM VI is used to calculate Cu speciation and SHM is used to calculate Pb speciation. Additional work in systems that contain wide ranges in concentrations of multiple metals should incorporate analytical speciation methods, such as DGT, to constrain the speciation component of biotic ligand models.
A new tool for in situ monitoring of Fe-mobilization in soils by Mohamad Fakih; Mélanie Davranche; Aline Dia; Bernd Nowack; Patrice Petitjean; Xavier Châtellier; Gérard Gruau (3372-3383).
The aim of this study was to design and test a new tool for (i) the quantitative in situ monitoring of Fe(III) reduction in soils and (ii) the tracking of the potential mineralogical changes of Fe-oxides. The tool consists of small (2 × 2 × 0.2 cm) striated polymer plates coated with synthetic pure ferrihydrite or As-doped ferrihydrite (Fh–As). These slides were then inserted within two different horizons (organo-mineral and albic) located in a wetland soil with alternating redox conditions. Dissolution was quantified by X-ray fluorescence (XRF) analyses of total metal contents before and after insertion into the soil. The crystallographic evolution of Fe-oxides was characterized by scanning electron microscope equipped with an energy-dispersive spectrometer (SEM–EDS). Over the months, the ferrihydrite progressively disappeared, at rates comparable to those previously measured in laboratory studies, i.e. in the 1–10 × 10−12 mol Fe m−2 s−1 range. SEM observations indicate that the supports were highly colonized by bacteria and biofilms in the organo-mineral horizon, suggesting a biological-mediated process, while the albic horizon appeared to be characterized by a mostly chemical-mediated process. In the albic horizon, Fe-sulphide and other micro-precipitates were formed after 7 months of incubation in balance with a quasi dissolution of initial Fe-oxides.
Tracing groundwater flow and sources of organic carbon in sandstone aquifers using fluorescence properties of dissolved organic matter (DOM) by D.J. Lapworth; D.C. Gooddy; A.S. Butcher; B.L. Morris (3384-3390).
The fluorescence properties of groundwaters from sites in two UK aquifers, the Penrith Sandstone of Cumbria and the Sherwood Sandstone of South Yorkshire, were investigated using excitation–emission matrix (EEM) fluorescence spectroscopy. Both aquifers are regionally important sources of public supply water and are locally impacted by pollution. The Penrith Sandstone site is in a rural setting while the Sherwood Sandstone site is in suburban Doncaster. Fluorescence analysis of samples from discrete sample depths in the Penrith Sandstone shows decreasing fulvic-like intensities with depth and also shows a good correlation with CFC-12, an anthropogenic groundwater tracer. Tryptophan-like fluorescence centres in the depth profile may also provide evidence of rapid routing of relatively recent applications of organic slurry along fractures. Fluorescence analysis of groundwater sampled from multi-level piezometers installed within the Sherwood Sandstone aquifer also shows regions of tryptophan-like and relatively higher fulvic-like signatures. The fluorescence intensity profile in the piezometers shows tryptophan-like peaks at depths in excess of 50 m and mirrors the pattern exhibited by microbial species and CFCs highlighting the deep and rapid penetration of modern recharge due to rapid fracture flow. Fluorescence analysis has allowed the rapid assessment of different types and relative abundances of dissolved organic matter (DOM), and the fingerprinting of different sources of organic C within the groundwater system. The tryptophan:fulvic ratios found in the Penrith Sandstone were found to be between 0.5 and 3.0 and are characteristic of ratios from sheep waste sources. The Sherwood Sandstone has the lowest ratios (0.2–0.4) indicating a different source of DOM, most likely a mixture of terrestrial and microbial sources, although there is little evidence of pollution from leaking urban sewage systems. Results from these two studies suggest that intrinsic fluorescence may be used as a proxy for, or complementary tool to, other groundwater investigation methods in helping provide a conceptual model of groundwater flow and identifying different sources of DOM within the groundwater system.
Growing up green on serpentine soils: Biogeochemistry of serpentine vegetation in the Central Coast Range of California by Christopher Oze; Catherine Skinner; Andrew W. Schroth; Robert G. Coleman (3391-3403).
Serpentine soils derived from the weathering of ultramafic rocks and their metamorphic derivatives (serpentinites) are chemically prohibitive for vegetative growth. Evaluating how serpentine vegetation is able to persist under these chemical conditions is difficult to ascertain due to the numerous factors (climate, relief, time, water availability, etc.) controlling and affecting plant growth. Here, the uptake, incorporation, and distribution of a wide variety of elements into the biomass of serpentine vegetation has been investigated relative to vegetation growing on an adjacent chert-derived soil. Soil pH, electrical conductivity, organic C, total N, soil extractable elements, total soil elemental compositions and plant digestions in conjunction with spider diagrams are utilized to determine the chemical relationships of these soil and plant systems. Plant available Mg and Ca in serpentine soils exceed values assessed in chert soils. Magnesium is nearly 3 times more abundant than Ca in the serpentine soils; however, the serpentine soils are not Ca deficient with Ca concentrations as high as 2235 mg kg−1. Calcium to Mg ratios (Ca:Mg) in both serpentine and chert vegetation are greater than one in both below and above ground tissues. Soil and plant chemistry analyses support that Ca is not a limiting factor for plant growth and that serpentine vegetation is actively moderating Mg uptake as well as tolerating elevated concentrations of bioavailable Mg. Additionally, results demonstrate that serpentine vegetation suppresses the uptake of Fe, Cr, Ni, Mn and Co into its biomass. The suppressed uptake of these metals mainly occurs in the plants’ roots as evident by the comparatively lower metal concentrations present in above ground tissues (twigs, leaves and shoots). This research supports earlier studies that have suggested that ion uptake discrimination and ion suppression in the roots are major mechanisms for serpentine vegetation to tolerate the chemistry of serpentine soils.
Laboratory and field evaluation of a flushable oxic limestone drain for treatment of net-acidic drainage from a flooded anthracite mine, Pennsylvania, USA by Charles A. Cravotta (3404-3422).
This paper demonstrates the use of dissolution-rate data obtained in the laboratory to indicate the potential quality of effluent from a field-scale oxic limestone drain (OLD) treatment system for neutralization of dilute acidic mine drainage (AMD). Effluent from the Reevesdale Mine South Dip Tunnel, a large source of AMD and base flow to the Wabash Creek and Little Schuylkill River in the Southern Anthracite Coalfield of east-central Pennsylvania, is representative of AMD with low concentrations but high loadings of dissolved Fe, Al and other metals because of a high flow rate. In January 2003, rapid neutralization of the AMD from the Reevesdale Mine was achieved in laboratory tests of its reaction rate with crushed limestone in closed, collapsible containers (Cubitainers). The tests showed that net-alkaline effluent could be achieved with retention times greater than 3 h and that effluent alkalinities and associated dissolution rates were equivalent for Fe(OH)3-coated and uncoated limestone. On the basis of the laboratory results, a flushable OLD containing 1450 metric tons of high-purity calcitic limestone followed by two 0.7-m deep wetlands were constructed at the Reevesdale Mine. During the first year of operation, monthly data at the inflow, outflow and intermediate points within the treatment system were collected (April 2006–2007). The inflow to the treatment system ranged from 6.8 to 27.4 L/s, with median pH of 4.7, net acidity of 9.1 mg/L CaCO3, and concentrations of dissolved Al, Fe and Mn of 1.0, 1.9 and 0.89 mg/L, respectively. The corresponding effluent from the OLD had computed void-volume retention times of 4.5–18 h, with median pH of 6.6, net acidity of −93.2 mg/L CaCO3, and concentrations of dissolved Al, Fe and Mn of <0.1, 0.08 and 0.52 mg/L, respectively. The wetlands below the OLD were effective for retaining metal-rich solids flushed at monthly or more frequent intervals from the OLD, but otherwise had little effect on the effluent quality. During the first year of operation, approximately 43 metric tons of limestone were dissolved and 2 metric tons of Al, Fe and Mn were precipitated within the OLD. However, because of the accumulation of these metals within the OLD and possibly other debris from the mine, the effectiveness of the treatment system declined. Despite the installation of a flush-pipe network at the base of the OLD to remove precipitated solids, the limestone bed clogged near the inflow. Consequently, a large fraction of the AMD bypassed the treatment system. To promote flow through the OLD, the flush pipes were open continuously during the last 4 months of the study; however, this effluent was only partially treated because short-circuiting through the pipes decreased contact between the effluent and limestone. A reconfiguration of the flow path through the limestone bed from horizontal to vertical upward could increase the limestone surface area exposed to the metal-laden influent, increase the cross-sectional area perpendicular to flow, decrease the flow path for solids removal, and, consequently, decrease potential for clogging.
Corrosion-induced gas generation in a nuclear waste repository: Reactive geochemistry and multiphase flow effects by Tianfu Xu; Rainer Senger; Stefan Finsterle (3423-3433).
Corrosion of steel canisters, stored in a repository for spent fuel and high-level nuclear wastes, leads to the generation and accumulation of H2 gas in the backfilled emplacement tunnels, which may significantly affect long-term repository safety. Previous studies have used H2 generation rates based on the volume of the waste or canister material and the stoichiometry of the corrosion reaction. However, Fe corrosion and H2 generation rates vary with time, depending on factors such as amount of Fe, water availability, water contact area and aqueous and solid chemistry. To account for these factors and feedback mechanisms, a chemistry model was developed related to Fe corrosion, coupled with two-phase (liquid and gas) flow phenomena that are driven by gas-pressure buildup associated with H2 generation and water consumption. Results indicate that by dynamically calculating H2 generation rates based on a simple model of corrosion chemistry, and by coupling this corrosion reaction with two-phase flow processes, the degree and extent of gas-pressure buildup could be much smaller compared to a model that neglects the coupling between flow and reactive transport mechanisms. By considering the feedback of corrosion chemistry, the gas pressure increases initially at the canister, but later decreases and eventually returns to a stabilized pressure that is slightly higher than the background pressure. The current study focuses on corrosion under anaerobic conditions for which the coupled hydrogeochemical model was used to examine the role of selected physical parameters on H2 gas generation and corresponding pressure buildup in a nuclear waste repository. The developed model can be applied to evaluate the effect of water and mineral chemistry of the buffer and host rock on the corrosion reaction for future site-specific studies.
A preliminary study of the Hg flux from selected Ohio watersheds to Lake Erie by T.O. Fitzgibbon; W. Berry Lyons; Christopher B. Gardner; Anne E. Carey (3434-3441).
New measurements of riverine dissolved and particulate Hg fluxes into Lake Erie from 12 northern Ohio watersheds have been determined from samples collected in April 2002 and analyzed using ultra-clean techniques with cold-vapor atomic fluorescence spectrometry. Total Hg concentrations ranged through 2.5–18.5 ng L−1, with a mean of 10.4 ng L−1 with most Hg in particulate form. Dissolved Hg concentrations ranged through 0.8–4.3 ng L−1, with a mean of 2.5 ng L−1. Highest total Hg concentrations were observed in western rivers with primarily agricultural land use and eastern rivers with mixed land use in their watersheds. Total suspended solid concentrations ranged through 10–180 mg L−1 with particulate Hg concentrations ranging through 47–170 ng g−1, with a mean of 99 ng g−1. Particulate Hg was similar to published data for central Lake Erie bottom sediments but much lower than for bottom sediments in western Lake Erie. Total Hg concentrations were positively correlated with suspended sediment concentrations and negatively with dissolved N O 3 - concentrations. The total estimated annual Hg fluxes from these rivers into Lake Erie is estimated to be 85 kg, but because only one event was sampled during high flow conditions, this may be an overestimate. This is much lower than previous published estimates of riverine Hg input into Lake Erie.
Effectiveness of sulfate-reducing passive bioreactors for treating highly contaminated acid mine drainage: I. Effect of hydraulic retention time by Carmen-Mihaela Neculita; Gérald J. Zagury; Bruno Bussière (3442-3451).
Sulfate-reducing passive bioreactors have proved to be an effective technology for the treatment of acid mine drainage (AMD) contaminated waters over relatively short periods of time (1–5 a). However, long-term efficiency can be limited by several factors including problems related to the hydraulic properties of the reactive mixture. In this study, the effect of two hydraulic retention times (HRTs) of 7.3 d and 10 d on the performance of passive bioreactors was evaluated over an 11-month period for the treatment of a highly contaminated AMD. Evolution of the porosity and hydraulic conductivity of the reactive mixture was also evaluated during the 15-month operation of two bioreactors. Results indicated that bioreactors were effective at both HRTs for increasing the pH and alkalinity of contaminated water and for SO4 and metal removal (60–82% for Fe and up to 99.9% for Cd, Ni and Zn). Although the quality of treated effluent was significantly improved with the 10 d HRT compared to the 7.3 d HRT, results showed that the higher HRT reduced the porosity and the permeability of the reactive mixture which might lead to hydraulic related problems and, eventually, to limited efficiency in long-term operation compared to a shorter HRT. The choice of HRT for a passive bioreactor must therefore consider both the desired quality of treated effluent and the potential for deterioration of hydraulic properties in the reactive mixture.
Use of sequential extraction procedure for assessing the environmental impact at regional scale of the São Domingos Mine (Iberian Pyrite Belt) by Rafael Pérez-López; Antonio M. Álvarez-Valero; José Miguel Nieto; Reinaldo Sáez; João X. Matos (3452-3463).
São Domingos is one of the most emblematic Portuguese mining districts in the Iberian Pyrite Belt (IPB). The beginning of mining exploitation in the area has been dated back to pre-Roman times, remaining in activity until 1966 when it was definitely halted. The intense mining labours are reflected in the presence of a huge amount of sulphide-mining wastes and downstream production of acid mine drainage (AMD). The mining wastes in the area are highly heterogeneous, and numerous different types may be recognized, including slags, iron oxides, smelting ashes, brittle and blocks of pyrite, leaching tank refuses, industrial landfill and other residues coming from ore extraction (gossan wastes and country rocks). The chemical speciation of potentially toxic elements (As, Cd, Cr, Cu, Fe, Mn, Pb, S, Sb and Zn) in all mine wastes from São Domingos was determined by modified BCR-sequential extraction procedure (European Community Bureau of Reference) and combined with the mass/volume proportions of each waste to quantify the potential risk of this mining district at regional scale. Analytical recoveries by sequential extraction, with respect to a pseudo-total metal content digestion, were generally acceptable (100 ± 17%). The oxidizable fraction corresponds with metals bound to sulphides and released easily under oxidizing conditions in AMD production processes. This is the most polluting fraction for the environment in this type of residues. Part of this fraction is retained by precipitation of soluble secondary minerals in warm periods, moving to the bio-available fraction that is dissolved in rainy periods. Just considering the bio-available fraction, all mine wastes from São Domingos may leach up to 172514 ton of Fe, 10564 ton of S, 6644 ton of Pb, 2610 ton of Zn, 1126 ton of Mn, 1032 ton of Cu, 183 ton of Cr, 109 ton of As, 34 ton of Sb and 0.9 ton of Cd. The process of precipitation and re-dissolution of efflorescent salts formed directly by oxidation of the oxidizable fraction is seasonally repeated, which causes an annual self-feeding and releasing of the bio-available fraction. Thus, the present study shows the pollutant potential of this IPB mining district and explains the spoiled state of the fluvial courses in the region.
Sedimentary record of black carbon in the Pearl River estuary and adjacent northern South China Sea by Xuesong Sun; Ping’an Peng; Jianzhong Song; Gan Zhang; Jianfang Hu (3464-3472).
The concentrations of black carbon (BC) and δ13CBC were determined in sediments of three dated cores from the Pearl River estuary (core PR-3) and adjacent northern South China Sea (cores SS-30, E2). For comparison, the total organic C (TOC) contents and δ13CTOC in the sediments were also measured. Relatively higher concentrations and fluxes of BC were found in sedimentary core PR-3, taken in the Pearl River estuary. The BC concentration profiles or fluxes correlated well with fossil-fuel usage in the Pearl River Delta. Maximum BC fluxes occurred in the late 1970s to early 1980s as recorded in core PR-3, and in the 1950s (core SS-30), reflecting the maximum BC emission in the Pearl River Delta and Hong Kong region, respectively. After the 1980s, a rapid decrease of BC fluxes and a light δ13CBC excursion were presumably due to improvements in combustion and pollution-control technologies and a shift of energy structure from biomass and coal to a mixture of coal, gas, oil and biomass. The fossil BC that contributed to total BC in core PR-3 increased from 20–30% to 70–80% during the last five decades. The study also shows that BC correlates well with terrestrial organic matter and that the ratio of BC to TOC is a good pollution indicator in relation to anthropogenic activities.
Rare earth element fractionation during the precipitation and crystallisation of hydrous ferric oxides from anoxic lake water by Elke Bozau; Jörg Göttlicher; Hans-Joachim Stärk (3473-3486).
An enrichment of light rare earth elements (LREE) is characteristic for most of the acidic, Fe- and SO4-rich pit lakes and groundwaters in the lignite mining area of Lower Lusatia (Germany). One of these acidic lakes – the pit lake “RL 1223” – has a strong thermal and chemical stratification. The upper water layer (0–9 m) shows pH values of about 3 during all seasons. The monimolimnion (10–17 m) of the lake is anoxic and has pH values of about 7. The rare earth element (REE) patterns of the upper lake water show enriched LREE (LaN/YbN = 1.6) whereas the opposite patterns (depletion of LREE, LaN/YbN = 0.4) are found in the anoxic water of the monimolimnion. Experiments were conducted to observe the behaviour of REE during Fe oxidation in water from the monimolimnion (depth 14 m). The sampled monimolimnion water was placed in plastic bottles, and the changing water chemistry was observed for 40 weeks after sampling. Due to the initial anoxic conditions almost all Fe precipitated in the investigated water, and the pH value decreased from about 7 to 3 during the oxidation. The Fe precipitates are identified as ferrihydrite which is transformed into goethite within the oxidation process. Stable pH conditions (pH 3.0) were reached after about 10 weeks of oxidation.The original REE patterns of the investigated water are generally reflected in the Fe precipitates collected at the beginning of the experiment as well as after up to 40 weeks of oxidation. However, in the corresponding water LREE were temporally enriched with a maximum LaN/YbN ratio of 1.0 and a maximum LaN/SmN ratio of 2.3 after 6 weeks of oxidation time (pH 3.8–4.9). Although complex geochemical changes took place between the start and the end of the experiment REE patterns observed at these points in time are nearly identical. These differences of the REE pattern can be explained by the sampling procedure. The experimental findings can be transmitted to the mining dump aquifers of the study area where geochemical conditions comparable to the experimental oxidation time from 3 to 6 weeks are found and hydrous ferric oxides are precipitating. Groundwater passing through the mining dumps can preferentially desorb LREE from the Fe precipitates and display the typical LREE enrichment and carry it to the epilimnion of the acidic pit lakes in Lower Lusatia.
Pesticides and lipids occurrence in Tangier agricultural soil (northern Morocco) by H. El Bakouri; A. Aassiri; J. Morillo; J. Usero; M. Khaddor; A. Ouassini (3487-3497).
This study evaluates pesticide occurrence in Tangier agricultural soil (northern Morocco). Soil samples were measured for alpha endosulfan, beta endosulfan, endosulfan sulfate, alpha HCH, beta HCH, gamma HCH, aldrin, dieldrin, endrin, o,p′ DDT, p,p′ DDD, p,p′ DDE and p,p′ DDT. The analyses were performed by gas chromatography coupled with mass spectrometry (GC/MS). Endosulfan isomers (alpha and beta) and endosulfan sulfate were detected in soil samples, in which the beta isomer showed the highest concentrations. Some DDT metabolites (o,p′ DDT and p,p′ DDE) and alpha HCH were also detected in the analyzed soil. The lipid fraction of the soil samples was extracted by accelerated solvent extraction and fractionated using chromatographic techniques. The principal biomarkers obtained were alcohols, esters, ketones, aldehydes, fatty acids and hydrocarbons. Lipid biomarkers were characterized to determine soil organic matter sources. Experimental results showed that the organic matter was mainly of plant origin, although the bacterial contribution was significant.
River system recovery following the Novaţ-Roşu tailings dam failure, Maramureş County, Romania by Graham Bird; Paul A. Brewer; Mark G. Macklin; Dan Balteanu; Mihaela Serban; Basarab Driga; Sorin Zaharia (3498-3518).
The River Vişeu catchment in Maramureş County, northwestern Romania, has a long history of base and precious metal mining. Between 1994 and 2003 waste from mining activity at Baia Borşa was stored in the Novaţ-Roşu tailings pond in the upper Vişeu catchment. However, in March 2000, the tailings dam failed releasing approximately 100,000 m3 of contaminated water and 20,000 t of mineral-rich solid waste, which was routed downstream through the Rivers Novaţ, Vaser and Vişeu into the River Tisa. Following the accident metal (Cd, Cu, Pb, Zn) concentrations in river water and river channel sediment were assessed in samples collected annually (July 2000, 2001, 2002 and 2003) from 29 sites in the Vişeu catchment, downstream of the tailings pond. Additionally, the speciation of sediment-associated metals was established using a 4-stage sequential extraction procedure (SEP) and Pb isotope analysis (206/204Pb and 207/204Pb) was carried out to establish the provenance of contaminated sediments. Metal concentrations in river water were found to comply with EU directive ‘target’ values within four months of the failure. However, the impact of the spill upon river channel sediments was found to be much longer-lasting, with evidence of the delayed downstream remobilization of tailings stored within the narrow Novaţ valley following the dam failure, as well as continued inputs of contaminated sediment to the River Vişeu from the River Tisla, another mining-affected tributary. Comparison with data from other recent tailings dam failures, indicates that river system recovery rates depend upon local geomorphological conditions, hydrological regimes, and the nature and scale of post-spill clean-up operations.
Conceptual model of recharge to southeastern Badain Jaran Desert groundwater and lakes from environmental tracers by John B Gates; W Mike Edmunds; W George Darling; Jinzhu Ma; Zhonghe Pang; Adam A Young (3519-3534).
Sources of groundwater recharge to the Badain Jaran Desert in China have been investigated using geochemical and isotopic techniques. Stable isotope compositions (δ18O and δ2H) of shallow groundwater and surface water from oasis lakes evolve from a starting composition considerably depleted compared to local unsaturated zone moisture, confirming inferences from chloride mass balance that direct infiltration of precipitation is not a volumetrically important source of recharge to the shallow aquifer in the study area. Shallow phreatic and deeper confined groundwater bodies appear unconnected based on chemical composition and radiocarbon activities. Hydrogeologic evidence points toward a bordering mountain range (Yabulai) as a likely recharge zone, which is consistent with tracer results. A mean residence time in the range of 1–2 ka for the desert’s southeastern margin is inferred from radiocarbon. These results reveal that some replenishment to the desert aquifer is occurring but at a rate much lower than previously suggested, which is relevant for water resources planning in this ecologically sensitive area.
Geochemistry of the upper Han River basin, China, 1: Spatial distribution of major ion compositions and their controlling factors by Siyue Li; Quanfa Zhang (3535-3544).
The upper Han River basin (approximately 95,200 km2) is the water source area of China’s South-to-North Water Transfer Project. Over the period from 2005 to 2006, a total of 292 grab samples collected from 47 sites in the upper Han River were analyzed for major ions (Cl−, NO 3 - , SO 4 2 - , HCO 3 - , Na+, K+, Ca2+ and Mg2+), Si, T, pH, EC and TDS. Correlation matrix and principal component analysis were used to quantify the geochemical and anthropogenic processes and identify factors influencing the ionic concentrations. The results reveal that the waters are slightly alkaline with low ionic strength, and all ions show remarkable spatial variations. The lowest solute concentrations are observed in catchment with higher vegetation cover, with higher Cl−, NO 3 - and SO 4 2 - concentrations occur in catchments with industrial establishments. The major ion chemistry of the upper Han River basin is mainly controlled by rock weathering with HCO 3 - and Ca2− dominating the major ion composition. The spatial variation in overall water quality as well as comparison with WHO and Chinese standards for drinking water indicates that the basin has high-water quality, yet it is possible that NO 3 - enrichment will occur in the near future. This research will help water conservation in the basin for the interbasin water transfer project.
Keywords: Upper han river; Major ion chemistry; Geochemistry; Water quality;
Effectiveness of sulfate-reducing passive bioreactors for treating highly contaminated acid mine drainage: II. Metal removal mechanisms and potential mobility by Carmen-Mihaela Neculita; Gérald J. Zagury; Bruno Bussière (3545-3560).
Column bioreactors were used for studying mechanisms of metal removal, assessment of long-term stability of spent reactive mixtures, as well as potential metal mobility after treating highly contaminated acid mine drainage (AMD; pH 2.9–5.7). Several physicochemical, microbiological, and mineralogical analyses were performed on spent reactive mixtures collected from 4 bioreactors, which were tested in duplicate for two hydraulic retention times (7.3d and 10d), with downward flow over an 11-month period. Consistent with the high metal concentrations in the AMD feed, and with low metal concentrations measured in the treated effluent, the physicochemical analyses indicated very high concentrations of metals (Fe, Mn, Cd, Ni, and Zn) in the top and bottom layers of the reactive mixtures from all columns. Moreover, the concentrations of Fe (50.8–57.8 g/kg) and Mn (0.53–0.70 g/kg) were up to twice as high in the bottom layers, whereas the concentrations of Cd (6.77–13.3 g/kg), Ni (1.80–5.19 g/kg) and Zn (2.53–13.2 g/kg) were up to 50-times higher in the top layers. Chemical extractions and elemental analysis gave consistent results, which indicated a low fraction of metals removed as sulfides (up to 15% of total metals recovered in spent reactive mixtures). Moreover, Fe and Mn were found in a more stable chemical form (residual fraction was 42–74% for Mn and 30–77% for Fe) relative to Cd, Ni or Zn, which seemed more weakly bound (oxidisable/reducible fractions) and showed higher potential mobility. Besides identifying (oxy)hydroxide and carbonate minerals, the mineralogical analyses identified metal sulfides containing Fe, Cd, Ni and Zn. Metal removal mechanisms were, therefore, mainly adsorption and other binding mechanisms with organic matter (for Cd, Ni and Zn), and the precipitation as (oxy)hydroxide minerals (for Fe and Mn). After 15 months, however, the column bioreactors did not lose their capacity for removing metals from the AMD. Although the metals were immobile during the bioreactor treatment, their mobility could increase from spent reactive mixtures, if stored inappropriately. Metal recovery by acidic leaching of spent substrates at the end of bioreactor operation could be an alternative.
Spring water trace element geochemistry: A tool for resource assessment and reconnaissance mineral exploration by Marie-Eve Caron; Stephen E. Grasby; M. Cathryn Ryan (3561-3578).
Geochemical data from 151 spring locations within the 37,000 km2 South Nahanni River Basin of the Mackenzie Mountains, Northwest Territories, were analysed as part of a reconnaissance assessment of mineral potential in this large and remote region. Statistical data analyses, graphical methods and strategic grouping of springs according to geochemistry, pH and temperature, were used to identify regions with higher mineralization potential quickly and efficiently. Testing of internal consistency indicates that known world class deposits within the basin are readily detected, but by different methods. As different deposit types have different geochemical signatures a new 3-component approach was developed to analyze trace element data for signatures of mineralisation. Estimation of circulation depth, and therefore maximum potential ore depth, further refines the assessment of economic potential. The depth of circulation of the spring waters ranged from 4.7 km to less than 200 m for the entire dataset. In total, 62 spring locations were identified as having anomalous trace metal content by one or more method (approximately 40% of the dataset). Specifically, 11 spring locations were classified as anomalous by all three methods, and 17 by at least two methods, and 34 by only one method.
The passivation of calcite by acid mine water. Column experiments with ferric sulfate and ferric chloride solutions at pH 2 by Josep M. Soler; Marco Boi; José Luis Mogollón; Jordi Cama; Carlos Ayora; Peter S. Nico; Nobumichi Tamura; Martin Kunz (3579-3588).
Column experiments, simulating the behavior of passive treatment systems for acid mine drainage, have been performed. Acid solutions (HCl or H2SO4, pH 2), with initial concentrations of Fe(III) ranging from 250 to 1500 mg L−1, were injected into column reactors packed with calcite grains at a constant flow rate. The composition of the solutions was monitored during the experiments. At the end of the experiments (passivation of the columns), the composition and structure of the solids were measured. The dissolution of calcite in the columns caused an increase in pH and the release of Ca into the solution, leading to the precipitation of gypsum and Fe–oxyhydroxysulfates (Fe(III)–SO4–H+ solutions) or Fe–oxyhydroxychlorides (Fe(III)–Cl–H+ solutions). The columns worked as an efficient barrier for some time, increasing the pH of the circulating solutions from 2 to ∼6–7 and removing its metal content. However, after some time (several weeks, depending on the conditions), the columns became chemically inert. The results showed that passivation time increased with decreasing anion and metal content of the solutions. Gypsum was the phase responsible for the passivation of calcite in the experiments with Fe(III)–SO4–H+ solutions. Schwertmannite and goethite appeared as the Fe(III) secondary phases in those experiments. Akaganeite was the phase responsible for the passivation of the system in the experiments with Fe(III)–Cl–H+ solutions.
The speciation of iodine in the salt impacted Black Butte soil series along the Virgin river, Nevada, USA by Spencer M. Steinberg; Brenda Buck; Janice Morton; James Dorman (3589-3596).
Salt-impacted soils occur in floodplains, wetlands and backswamps in arid climates. These soils become sinks or temporary storage sites for soluble salts and contaminants including agricultural chemicals, industrial pollutants and radionuclides such as 129I. The vertical distribution of I in the Black Butte soil series along the Virgin river was assessed and the distribution of I between I−, IO 3 - and organically bound I was determined. The speciation of I was compared to the organic C content, specific components of the organic C, and clay content. This study indicates that organic I was the most abundant form of I in these soil samples and that the content of organic I generally correlated to total organic matter and lignin (as measured by chemolysis) of the samples.
Environmental isotopes (N, S, C, O, D) to determine natural attenuation processes in nitrate contaminated waters: Example of Osona (NE Spain) by Laura Vitòria; Albert Soler; Àngels Canals; Neus Otero (3597-3611).
Nitrate-contaminated groundwater from an aquifer in the Osona region (NE Spain) was chemically and isotopically ( δ 15 N NO 3 , δ 18 O NO 3 , δ 34 S SO 4 , δ 18 O SO 4 , δD, δ 18 O H 2 O and δ 13 C DIC ) characterized. Diffuse- NO 3 - contamination reached values of 366 mg/L. Nearly 75% of the 37 sampled sites had higher concentrations than the 50 mg/L in NO 3 - limit for drinking water. To identify the source of pollution δ 15 N NO 3 and δ 18 O NO 3 were used with results, for most samples, in the range of pig manure NO 3 - . Nitrification processes were evaluated by means of the δ 18O of NO 3 - and water. Isotopic data suggested that natural attenuation of NO 3 - was taking place. This process was confirmed using the δ 18 O NO 3 coupled with the NO 3 - / Cl - ratio, avoiding the influence of continuous NO 3 - inputs. A further insight on denitrification processes was obtained by analyzing the ions involved in denitrification reactions. Although the role of organic matter oxidation could neither be confirmed nor discarded, this approach showed a link between denitrification and pyrite oxidation. Therefore, in areas with no adequate infrastructure (e.g. multipiezometers), such as the one studied, this approach could be useful for implementing better water management.
Diffusion of iodide and iodate through Opalinus Clay: Monitoring of the redox state using an anion chromatographic technique by Martin A. Glaus; Werner Müller; Luc R. Van Loon (3612-3619).
The through- and out-diffusion behaviour of 125I− and 125 IO 3 - were separately studied in an intact sample of Opalinus Clay (OPA) from the Benken drilling site (Switzerland) using purified tracer solutions. The concentrations of the two radioactive I species, 125I− and 125 IO 3 - , were monitored using a high performance anion exchange chromatographic technique. An effective diffusion coefficient, D e = (4.5 ± 0.5) × 10−13 m2 s−1, and a rock capacity factor, α = 0.04 ± 0.01, were measured in the through-diffusion experiments with 125I−. The latter result shows that no sorption of I− takes place on OPA because in previous work the same rock capacity factor was measured for the non-sorbing Cl− tracer. The out-diffusion of 125I− was characterised by an unexpectedly high flux from the surface adjacent to the high concentration reservoir in the through-diffusion experiment. The present experiments resolved former inconsistencies with respect to the sorption of I− on OPA, where unpurified tracers were used. However, they confirmed the inconsistencies with respect to the observed D e values between through- and out-diffusion experiments. No break-through of 125 IO 3 - could be observed in the through-diffusion experiment with 125 IO 3 - as the source species. Instead a flux of 125I− into the target reservoir was substantiated. This observation, together with the speciation analysis in the feed reservoir, showed that IO 3 - was rapidly converted to I− upon contact with OPA. The transformation was presumably mediated by unidentified reducing components of OPA because such fast reactions are not observed in homogeneous aqueous solutions. The rapid conversion of IO 3 - to I− in the OPA sample was corroborated in the profile analysis performed after the through-diffusion experiment, where a strongly one-sided distribution of the tracer ion was observed.
Geochemistry and stable sulfur and oxygen isotope ratios of the Podwiśniówka pit pond water generated by acid mine drainage (Holy Cross Mountains, south-central Poland) by Zdzisław M. Migaszewski; Agnieszka Gałuszka; Stanisław Hałas; Sabina Dołęgowska; Józef Dąbek; Ewa Starnawska (3620-3634).
The paper presents the results of a geochemical and isotopic study of acidic pond water in the abandoned Podwiśniówka quarry (Poland). The scope of investigations also encompassed mineralogical and isotopic studies of pyrite and related supergene minerals. Compared to similar sites throughout the world, the pit pond water examined is characterized by a very low pH averaging 2.64 ± 0.33 and simultaneously very low concentrations of SO 4 2 - (geometric mean of 237 ± 57 mg L−1), Fe(II) (4.8 ± 3.4 mg L−1), Fe(III) (10.0 ± 6.2 mg L−1) and other trace elements. This acidity has been generated by complex processes of As-rich pyrite oxidation combined primarily with hydrolysis, precipitation, and transformation of Fe oxyhydroxysulfates and oxyhydroxides into goethite. The specific mineralogy of ore and gangue minerals, but especially the lack of acid–buffering constituents, has additionally contributed to the very low pH and element concentrations. Of the toxic elements, the high content of As (1111–1879 mg kg−1) in the western part of pit pond sediment may be of great concern, especially when using lime as a neutralizing agent of the acidic water. The δ34S of soluble SO4 varied from −19.8‰ to −11.1‰ and was different from that of efflorescent sulfates (−25.7‰ to −25.4‰) and host pyrite (−25.4 ± 2.5‰). The comparison of the δ18O– SO 4 2 − (−2.0 ± 1.2‰) and δ18O–H2O (−6.2 ± 3.5‰) values indicated that the pyrite underwent bacterially catalyzed oxidation by two natural oxidants, primarily by Fe3+ and to a lesser extent O2.
Modeling the diffusion of Na+ in compacted water-saturated Na-bentonite as a function of pore water ionic strength by Ian C. Bourg; Garrison Sposito; Alain C.M. Bourg (3635-3641).
Assessments of bentonite barrier performance in waste management scenarios require an accurate description of the diffusion of water and solutes through the barrier. A two-compartment macropore/nanopore model (on which smectite interlayer nanopores are treated as a distinct compartment of the overall pore space) was applied to describe the diffusion of 22Na+ in compacted, water-saturated Na-bentonites and then compared with the well-known surface diffusion model. The two-compartment model successfully predicted the observed weak ionic strength dependence of the apparent diffusion coefficient (D a) of Na+, whereas the surface diffusion model did not, thus confirming previous research indicating the strong influence of interlayer nanopores on the properties of smectite clay barriers. Since bentonite mechanical properties and pore water chemistry have been described successfully with two-compartment models, the results in the present study represent an important contribution toward the construction of a comprehensive two-compartment model of compacted bentonite barriers.
Speciation of Cu in MSWI bottom ash and its relation to Cu leaching by S. Arickx; T. Van Gerven; E. Boydens; P. L’hoëst; B. Blanpain; C. Vandecasteele (3642-3650).
In Flanders, recycling of bottom ash is mainly inhibited by the high leaching of Cu. Although it has been proved that dissolved organic C plays a major role in the Cu leaching, the possible role of inorganic Cu mineral speciation has never been experimentally examined. In this study the speciation of Cu is investigated using a combination of optical microscopy and electron microprobe –WDX/EDX. Several Cu species were determined. Metallic Cu (with or without an oxide shell), CuO and Cu2O were the most abundant. These particles were most likely present in wire-like structures. Copper also occurred as alloy (brass, bronze, zamak), and was found frequently together with typical elements such as Ca, Cl and S. Finally, small metallic Cu particles seemed to be trapped in or precipitated on oxides and silicates. Based on this Cu speciation study, pure Cu minerals were selected and leached as a function of time. The solubility after equilibrium of all studied Cu minerals never exceeded 20 μg/L (which equals 10% of the total Cu leaching).The effect of heating (2 h at 400 °C) on the speciation of Cu was investigated using the same combination of techniques. Results show that metallic Cu seemed to be converted to Cu oxide (mostly CuO) and that the particles were more porous after heating. These conclusions were verified by XRD analysis of the heated pure Cu minerals. After heating, the Cu minerals were also leached as a function of time, to study the impact on Cu leaching. Results indicate that their leaching had slightly increased in comparison with the non-heated Cu minerals. However, the major decrease in Cu leaching in heated bottom ash, more than neutralizes this effect and thus can be attributed to the destruction of organic matter and not to the (small) change in Cu speciation.
The normative mineralogy of 10 soil profiles in Fennoscandia and north-western Russia by R. Salminen; V. Gregorauskiene; T. Tarvainen (3651-3665).
The mineralogical composition of soil horizons in different soil types of different ages was estimated by applying the NORMA software, which was developed originally for calculating the normative mineralogical composition of young podsols. Ten soil profiles from six sites in NW Russia, two in Finland, and one in NE Norway were sampled in 1999 as a part of the pilot phase of a large geochemical mapping project. Total element concentrations were determined from the <2 mm fraction by XRF from powdered pellets for Al, Ca, Cr, Fe, K, Mg, Mn, Na, P, S, Si, Ti, and Zr, and for Ba by ICP-AES after HF+HClO4 extraction. Extractable concentrations for Al, Ca, Cr, Fe, K, Mn, Mg, Na, P, S, Ti, Zr, and Ba were determined by ICP-MS or ICP-AES after aqua regia (a 1:3 mixture of strong HCl and HNO3) extraction. Total C was determined using a thermal conductivity detector from a sample burned in an O2 stream. The NORMA software was used to calculate the percentage of normative soluble minerals pyrite, apatite, titanite, calcite, biotite, chlorite, weathered albite, hydrous Al-silicate, goethite and soluble residue. The percentages of non-soluble normative minerals rutile, hornblende, K-feldspar, albite, anorthite, tremolite, wollastonite, kaolinite, magnetite, zircon, quartz, carbon (graphite), and non-soluble residue were calculated after soluble minerals.The calculated mineralogical composition of C-horizon samples in each profile reflected the known geological composition of the bedrock from which the soil parent material was derived during geological processes. Secondary minerals including goethite and hydrous Al-silicates, were detected in upper soil horizons reflecting the development of soils. Rather than age, the local bedrock geology together with the mineralogical composition and chemical properties of the parent material proved to be the controlling factor in the formation of secondary minerals. The results showed that the NORMA method can be used in defining the mineralogy of soil horizons in a large variety of soil types.
The chemical characteristics of acid mine drainage with particular reference to sources, distribution and remediation: The Witwatersrand Basin, South Africa as a case study by H. Tutu; T.S. McCarthy; E. Cukrowska (3666-3684).
Water quality in the immediate vicinity of mine tailings in and around Johannesburg, South Africa was investigated. Pollution is derived primarily from Au mine tailings dumps that are disused or are undergoing retreatment to extract remaining Au, and is dispersed by way of groundwater plumes. These discharge into perennial streams in the area. Pollution manifests itself in the form of low pH (>2) and high SO 4 2 - concentrations (exceeding 7,000 mg L−1 in some cases). Water quality improves away from the tailings area. Pollution loads were found to be higher at the end of the rainy season, due to a rise in the water table and hence increased groundwater seepage. Polluted groundwater usually has low Eh (300 mV) and pH (2–3), and high EC (up to 8 mS cm−1 in some instances). Oxidation of Fe occurs as the groundwater emerges on surface, further lowering pH, and establishing an Fe(III)-Fe(OH)3 redox equilibrium, which operates for many kilometres downstream. Various processes that occur increase compositional heterogeneity in the water, amongst which are evaporation, dissolution of efflorescent crusts and dilution by unpolluted water. Wetland environments are characterised by high pH and low Eh, and appear to be influenced by a sulfide–sulfate redox system, under which SO 4 2 - and metals are removed, and pH increased. Lakes in the mining area have normal water quality, which arises from a combination of metal removal by wetlands (most lakes have wetlands at their inlets) and dilution by rain and unpolluted groundwater. They offer a potential method for passively treating polluted water arising from tailings dumps.
Sources and transport of carbon and nitrogen in the River Sava watershed, a major tributary of the River Danube by Nives Ogrinc; Roland Markovics; Tjaša Kanduč; Lynn M. Walter; Stephen K. Hamilton (3685-3698).
Carbon and nitrogen dynamics were examined throughout the River Sava watershed, a major tributary of the River Danube, in 2005 and 2006. The River Sava exported 2.1 × 1011 mol C/yr as dissolved inorganic carbon (DIC), and emitted 2.5 × 1010 mol C/yr as CO2 to the atmosphere. Stable carbon isotope ratios indicate that up to 42% of DIC originated from carbonate weathering and ∼23% from degradation of organic matter. Loads of dissolved and particulate organic carbon increased with discharge and export rates were calculated to be 2.1 × 1010 mol C/yr and up to 4.1 × 109 mol C/yr, respectively. Isotopic compositions (δ13C and δ15N) and C/N ratios indicated that soil organic matter was the dominant source of particulate organic matter for 59% of the samples. Eighteen percent of the samples were dominated by plankton, 12% by periodic inputs of fresh terrestrial plant detritus with C/N > 15, and about 11% of the samples were dominated by the contribution of aquatic vascular plants. Nitrate inputs were controlled by land use in the River Sava watershed. δ 15 N NO 3 values <6‰ were found in predominantly forested watersheds, while values >6‰ typically represented watersheds with a higher percentage of agricultural and/or urban land use. Elevated δ 15 N NO 3 values (up to +25.5‰) at some sites were probably due to the combined effects of low-flow and inputs from sewage and/or animal waste.
Leaching of lead metallurgical slags and pollutant mobility far from equilibrium conditions by Nicolas Seignez; Arnaud Gauthier; David Bulteel; Denis Damidot; Jean-Luc Potdevin (3699-3711).
Lead metallurgical slags are partially vitrified materials containing residual amounts of Zn, Pb, Cr, Cd and As. These hazardous materials are generally buried on heaps exposed to weathering. In this study, leaching behavior of lead blast furnace slags has been tested using pure water and open flow experiments. It appears that in such far from equilibrium and slightly acidic conditions, the main phase to be altered is the vitreous phase. As for lunar, basaltic and nuclear glasses, alkalis/proton exchanges prevail and lead to the formation of a non-protective altered layer enriched in Si, Fe and Al. The composition of the altered layer is quite constant except for Si whose concentration decreases towards the leachate interface. Owing to their sizes, micrometric Pb droplets are not always totally dissolved at the slag surface. Nevertheless, nanometric Pb droplets are instantaneously dissolved while a surrounding altered layer is formed. This leads to high Pb releases in open flow systems. Leachate chemistry and dissolution rates of the vitreous phase are closely comparable to previous leaching tests with basaltic and nuclear glasses in conditions far from equilibrium. Moreover, this study confirms that Fe is a stable element in such conditions.
Geochemistry of the headwaters of the Yangtze River, Tongtian He and Jinsha Jiang: Silicate weathering and CO2 consumption by Weihua Wu; Jiedong Yang; Shijin Xu; Hongwei Yin (3712-3727).
Water and sediment samples were collected from the headwaters of the Yangtze River, Tongtian He and Jinsha Jiang (upstream of the Yangtze River which flows on the eastern Qinghai-Tibet Plateau). A detailed geochemical study of the river system was carried out to determine: (i) temporal and spatial variations of the major ions and their implications; (ii) contribution of carbonate, silicate and evaporite to the river dissolved load and (iii) CO2 consumption via silicate weathering. Results show that cations derived from evaporite dissolution account for 44.7–82.8% of the total cations in the headwaters of the Yangtze River and increasing from SE to NW of the drainage basin. The contribution from silicate weathering gradually increases from the headwaters due to exposure of intrusive rocks and volcanic rocks in the Jinsha Jiang suture belt. Proportion of cations derived from silicate weathering to the total cations in river waters reaches a maximum at Panzhihua City, which is consistent with the abundant exposure of Cenozoic granitoids and Precambrian high-grade metamorphic rocks around Panzhihua. The Jinsha Jiang basin has higher silicate weathering rates but lower carbonate weathering rates than the middle and lower reaches of the Yangtze River. The calculated enrichment factors of potentially harmful metals in the river sediments are within the range of 0.33–2.59, indicative of level 1 or 2 contamination. The highest enrichment factor for Co, Cr and V is found in Panzhihua City, indicating that it has been influenced by anthropogenic sources.
Seasonal variations of microbial sulfate and iron reduction in alkaline Pb–Zn mine tailings (Ontario, Canada) by T. Praharaj; D. Fortin (3728-3740).
Several studies have shown that SO4-reducing bacteria (SRB) are active in acidic sulfide-rich mine tailings and sediments impacted by mining activities. SRB activity in acidic tailings has been shown to vary with seasons as a result of fluctuating in situ physico-chemical conditions. Iron-reducing bacteria (FeRB) also play an important role in Fe cycling in sediments impacted by mining activities, but their activity in mine tailings is poorly understood, despite the fact that geochemical evidence indicates that they might be active. The present study was undertaken to assess the seasonal changes in SRB and FeRB abundance and activity in alkaline Pb–Zn mine tailings (Calumet tailings) located near Ottawa, ON, Canada. Results showed that FeRB and SRB populations were present throughout the year at two different sampling sites at the Calumet tailings, but SO4 reduction rates (SRR) were lower in the spring than in the summer, indicating that SRB activity was affected by organic C availability and/or temperature. Surface agricultural runoff at one site provided ample nutrients and organic C to the tailings, but SRB activity remained lower than the site not impacted by nutrient runoff, suggesting that the type of organic C was different between the two sites and that less labile organic substrates were available to SRB in the organic-rich site. High SRB activity in the site containing low organic C inhibited the abundance of FeRB, and possibly their activity, as a result of abiotic reduction of Fe(III)-rich minerals by biogenic sulfides, which lowered the pool of final electron acceptors. The abiotic reduction pathway was consistent with the porewater data which showed that sulfide was consumed and SO4 produced, along with Fe(II). These results show a strong interdependence between SRB and FeRB activity, as observed in other environments, such as saltmarsh sediments. Low temperature did not appear to hinder FeRB abundance in alkaline tailings. Finally, despite evidence that SRB populations were active at both sites, the |S isotopic composition of the AVS and CRS fractions were not representative of biogenic sulfides, indicating that the overall S-isotope signature of mine tailings is more representative of abiotic sulfides originating from the ore body.
Natural attenuation of uranium and formation of autunite at the expense of apatite within an oxidizing environment, south Eastern Desert of Egypt by Hamdy H. Abd El-Naby; Yehia H. Dawood (3741-3755).
X-ray diffraction (XRD), back scattered electron imaging (BSE), wavelength-dispersion spectral scan (WDS), X-ray compositional mapping and quantitative electron probe micro analyses (EPMA) have been used to examine a natural attenuation of U during low temperature alteration of the Sela granite, south Eastern Desert of Egypt. The data confirmed that a pre-existing hydroxyapatite was transformed to autunite through an unidentified intermediate phase. The boundaries between these three phases are not sharp and are generally interfering indicative of the replacement of Ca by U. The hydroxyapatite, intermediate phase and autunite show similar chondrite normalized rare earth elements (REE) patterns suggesting a genetic relationship. Alteration processes have enriched the three phases with heavy rare earth elements (HREE) and Eu and caused Ce, Dy and Yb negative anomalies. Based on the pH of the aqueous solutions, two mechanisms may explain the conversion of hydroxyapatite to autunite: (1) the dissolution of hydroxyapatite and precipitation of autunite which would happen when the uranyl bearing solutions were acidic enough (pH = 3–6.8) to be able to dissolve the pre-existing hydroxyapatite and (2) sorption of the uranyl ion on the surface of hydroxyapatite followed by substitution of ( UO 2 ) 2 + at the expense of Ca2+. The latter mechanism would have happened if the pH of the aqueous solutions were near neutral and at low dissolved concentrations of uranyl ion. The genesis of uranyl mineralization in the Sela area supports the use of apatite-based technologies for U remediation in an oxidizing environment.
Impact of human activities on the central Mediterranean offshore: Evidence from Hg distribution in box-core sediments from the Ionian Sea by Rossella Di Leonardo; Adriana Bellanca; Massimo Angelone; Marcella Leonardi; Rodolfo Neri (3756-3766).
Total Hg concentrations have been measured for five box-core sediments collected seawards of the Augusta industrial area (SE Sicily). In more coastal sediments, upcore increasing Hg concentrations, exceeding the Hg background concentration estimated for the Strait of Sicily, indicate Hg contamination over time due to the industrial area development. Strong correlation between total organic C (TOC) and Hg concentrations was found only for core BX2, that displays organic C to total N (C/N) ratios indicative of autochthonous organic matter. For other sediments, high Hg enrichment factors with respect to TOC indicate, in addition to Hg trapping by TOC, other factors as responsible for Hg accumulation. In the presence of some contribution of detrital organic matter, Hg is mainly adsorbed onto the mineral component of the bottom sediments probably because TOC is saturated by Hg excess. Contaminant impact affected also the open sea environment. Main drivers of Hg flux towards the offshore were dredged materials, which repeatedly discharged sediment, resulting in substantial increases in TOC contents and high C/N ratios. Consistent with the geochemistry of recent turbidites, these anomalous sedimentary inputs induced sediment redox environment modifications, constrained by Mn peaks, which affected Hg distribution.
Geochemistry of peat over kimberlites in the Attawapiskat area, James Bay Lowlands, northern Canada by Kéiko H. Hattori; Stewart Hamilton (3767-3782).
The James Bay Lowlands, which is the SE part of the Hudson Bay Lowlands, Canada, and within the Paleozoic limestone terrane, is covered mostly by peatlands. Peat samples were examined in the Attawapiskat area, a region of discontinuous permafrost, where more than 19 kimberlite pipes have been found beneath a cover of peat (2–4 m thick) and Quaternary sediments (up to 20 m thick) of Tyrell Sea clay beds and glacial tills. Pore water at a depth of 40 cm in the peat has a consistently low pH, <4, and high Eh, ∼290 mV, in the areas over limestones far from kimberlites. On the other hand, peat pore water close to kimberlites has a high pH, up to 6.7, and low Eh, down to 49 mV; the values of pH and Eh are inversely correlated. The high pH and low Eh close to kimberlites suggest active serpentinization of olivine in the underlying kimberlites. The bulk compositions of peat indicate precipitation of secondary CaCO3 and Fe–O–OH. The secondary carbonate contains high concentrations of kimberlite pathfinder elements, such as Ni, rare earth elements (REE) and Y. The ratios of metal concentrations extracted by ammonium acetate solution at pH 5 (AA5) to those in a total digestion confirm that a majority of the divalent cations are hosted by the secondary carbonate, whereas tri-, tetra- and penta-valent cations are not. As these charged cations are not leached in Enzyme Leach, they are most likely adsorbed on Fe–O–OH.The compositions of peat show spatial variation with the distribution of kimberlites, suggesting that they are influenced by the underlying rocks even through there are thick layers of tills and sediments between the bedrocks and peat. However, elevated concentrations of pathfinder elements of kimberlites in bulk peat samples and AA5 leach are not necessarily directly above kimberlites. The diffused metal anomalies around kimberlites are attributed to the dissolution–precipitation of secondary phases (carbonates and Fe–O–OH) in acidic and reduced waters in peat, and the movement of waters through peat. This pilot study suggests that peat compositions do reflect the underlying bedrock compositions. For kimberlite exploration, a geochemical survey of peat is useful to discriminate concealed kimberlites from other anomalies defined by geophysical and other techniques; however, such a geochemical survey is not suitable for delineating the shapes of the concealed kimberlites due to broad dispersed anomalies.
The impact of pyrite variability, dispersive transport and precipitation of secondary phases on the sulphate release due to pyrite weathering by Claus Kohfahl; Paul L. Brown; Claire M. Linklater; Kai Mazur; Parviz Irannejad; Asaf Pekdeger (3783-3798).
The objective of this study was to investigate the impact of flow, transport and geochemical parameters in the unsaturated and saturated zones on the release of SO4 from overburden lignite spoil piles into the adjacent lake. A vertical one-dimensional model was set up using the reactive transport simulator SULFIDOX in order to account for the unsaturated zone. The SULFIDOX model was calibrated for effective diffusion using measured O2 in the gas phase and SO4 concentrations in the liquid phase from the unsaturated zone of the heap. The results show high sensitivity to O2 supply and initially present gypsum, but the inclusion of secondary mineral precipitation in equilibrium is of minor importance for the results. To account for the transport of released SO4 from the saturated zone into the surface water, scenarios were performed by using SULFIDOX results as input concentration for a two-dimensional vertical model set up with PROCESSING MODFLOW and MT3D. These scenarios indicate a rising discharge of SO4 into the adjacent lake due to continued pyrite weathering for 80 a. Results are highly sensitive to dispersivity, whereas the spatial variability of pyrite distribution did not show any influence on the results. The consideration of initially present gypsum shows a major effect on the modelled SO4 release.
Capillary geochemistry in non-saturated zone of soils. Water content and geochemical signatures by Marie Pettenati; Lionel Mercury; Mohamed Azaroual (3799-3818).
The unsaturated zone (UZ) retains aqueous solutions against gravity by capillary forces. This suction state corresponds to a decreasing internal pressure of the water, which modifies its thermodynamic properties. Accordingly, the speciation of solutes and the solubility of solids and gases in such capillary solutions change. The volumetric capillary water content of the soil at high suction can be calculated extrapolating the water retention curves (WRC) with the Rossi–Nimmo model. Interestingly, several tens of liters per cubic meter of soil can be thus suctioned, a sufficiently large volume to support that: (1) capillary water is not restricted to nanosized pores, which means it disobeys the Young–Laplace law and is metastable with respect to vapor (superheating); and (2) the geochemistry of capillary solutions might significantly influence the subsurface mass transfer. Two field situations are here interpreted using the capillary thermodynamic properties: (1) the trapping of sand grains during the growth of desert roses (gypsum), and (2) the development of abnormal paragenetic sequences in some saprolites.The capillary approach is extended to the soil solids, so that the micro-mineralogy can be explicitly (though sketchily) integrated in the calculations. The key conclusion is that capillarity changes the saturation indexes (and so the reaction rates) at given solution composition, in a way consistent with the field observations. This perspective amounts to geochemically distinguishing the capillary and percolating solutions, which is interestingly analogous to the immobile and mobile water distinction already often integrated in UZ flow models.
Long term mobilisation of chemical elements in tephra-rich peat (NE Iceland) by François De Vleeschouwer; Brigitte Van Vliët Lanoé; Nathalie Fagel (3819-3839).
This paper presents geochemical profiles of a tephra-bearing minerotrophic peat column from NE-Iceland obtained using various elemental analyses of the solid phase and the pore water. The influence of tephra grain size, thickness and composition of each tephra on the peat geochemistry was investigated. Interpretations are supported by a statistical approach, in particular by autocorrelation, and by microscopy observations. Minerotrophic peat geochemistry may be strongly dependent upon post-depositional mobilization and possible leaching of elements as demonstrated by Fe and trace metal concentration profiles. Chemical elements, and more specifically potentially harmful metals, can be slowly leached out of volcanic falls during their weathering and re-accumulate downwards. It is emphasised that a tephra deposit can act as an active geochemical barrier, blocking downward elemental movements and leading to the formation of enriched layers. In this study, the formation of poorly amorphous Fe phases above the Hekla 3 tephra is shown. These poorly crystalline Fe phases scavenged Ni.
Self-diffusion of water and its dependence on temperature and ionic strength in highly compacted montmorillonite, illite and kaolinite by Fátima González Sánchez; Luc R. Van Loon; Thomas Gimmi; Andreas Jakob; Martin A. Glaus; Larryn W. Diamond (3840-3851).
The effect of temperature and ionic strength on the diffusion of HTO parallel to the direction of compaction through 5 highly compacted clay minerals (bulk dry density, ρ b,d = 1.90 ± 0.05 Mg/m3), namely montmorillonite (Na- and Ca-form), illite (Na- and Ca-form), and kaolinite, was studied. The diffusion experiments were carried out at temperatures between 0 °C and 60 °C and at ionic strengths of 0.01 M and 1 M NaCl for the Na-form clays and kaolinite, and of 0.005 M and 0.5 M CaCl2 for the Ca-form. The ionic strength had an insignificant influence on the values of the effective diffusion coefficient (variation by less than 10%) for the clays under study at this degree of compaction. The effective diffusion coefficients followed the order Na-montmorillonite < Ca-montmorillonite < Ca-illite < Na-illite ⩽ kaolinite. It is thought that the differences between Na- and Ca-montmorillonite originate from the larger size particles, and thus the lower tortuosity of the latter; whereas the differences between Na- and Ca-illite are related to the different degree of solvation of the Na and Ca cations. The activation energies were successfully calculated using the Arrhenius law. Swelling clays (Na- and Ca-montmorillonite) had slightly larger activation energy values (20 kJ/mol) compared to bulk water (17 kJ/mol); Ca-illite (16 kJ/mol), Na-illite (13 kJ/mol) and kaolinite (14.4 kJ/mol) lower values than that of bulk water. The low activation energies of the last three clays may be related to weaker H-bonds between water and the clay surfaces compared to those in bulk water.
Comment on “Anthropogenic influences on the input and biogeochemical cycling of nutrients and mercury in Great Salt Lake, Utah, USA” by D. Naftz, C. Angeroth, T. Kenney, B. Waddell, N. Darnall, S. Silva, C. Perschon and J. Whithead by Mae Gustin (3852-3853).
Reply to the comment on “Anthropogenic influences on the input and biogeochemical cycling of nutrients and mercury in Great Salt Lake, Utah, USA”, by Mae Gustin by David Naftz; Cory Angeroth; Terry Kenney; Bruce Waddell; Nathan Darnall; Steven Silva; Clay Perschon; John Whitehead (3854-3855).
Editor’s comment by Ron Fuge (3856).