Applied Geochemistry (v.23, #5)
Leaching mechanisms of oxyanionic metalloid and metal species in alkaline solid wastes: A review by Geert Cornelis; C. Anette Johnson; Tom Van Gerven; Carlo Vandecasteele (955-976).
An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility.
Mobility of arsenic in West Bengal aquifers conducting low and high groundwater arsenic. Part I: Comparative hydrochemical and hydrogeological characteristics by Bibhash Nath; Doris Stüben; Sukumar Basu Mallik; Debashis Chatterjee; Laurent Charlet (977-995).
The present study demonstrates the importance of hydrogeochemical characteristics (groundwater flow and recharge) of an aquifer in the release of As to groundwater. The study area (∼20 km2) is located in Chakdaha block, Nadia district, West Bengal, which hosts groundwaters of variable As content. The spatial distribution pattern of As is patchy with areas containing groundwater that is high in As (>200 μg L−1) found in close vicinity to low As (<50 μg L−1) groundwaters (within 100 m). The concentration of groundwater As is found to decrease with depth. In addition, the data shows that there is no conspicuous relationship between high groundwater As concentration and high groundwater abstraction, although the central cone of depression has enlarged over 2 a and is extending towards the SE of the study area. The river Hooghly, which forms the NW boundary of the study site, shows dual behaviour (effluent and influent during pre- and post-monsoon periods, respectively), complicating the site hydrogeology. The observed groundwater flow lines tend to be deflected away from the high As portion of the aquifer, indicating that groundwater movement is very sluggish in the As-rich area. This leads to a high residence time for this groundwater package, prolonging sediment–water interaction, and hence facilitating groundwater As release.
Mobility of arsenic in West Bengal aquifers conducting low and high groundwater arsenic. Part II: Comparative geochemical profile and leaching study by Bibhash Nath; Zsolt Berner; Debashis Chatterjee; Sukumar Basu Mallik; Doris Stüben (996-1011).
Aquifer sediments from areas of low- and high-As groundwater were characterized mineralogically and geochemically at a field site in the Nadia district of West Bengal, India. Leaching experiments and selective extraction of the sediments were also carried out to understand the release mechanism of As in the sub-surface. The correlation between measured elements (major, minor and trace) from low- and high-As groundwater areas are only significant for As, Fe and Mn. The borehole lithology and percentage of silt and clay fraction demonstrates the dominance of finer sediments in the high-As aquifer. Multivariate analysis of the geochemical parameters showed the presence of four different mineral phases (heavy-mineral fraction, phyllosilicates/biotite/Fe-oxyhydroxides, carbonates and sulphides) in the sediments. Selective extraction of sediment reveals that amorphous Fe-oxyhydroxide acts as a potential sink for As in the sub-surface. The result is consistent with microbially mediated redox reactions, which are controlled in part by the presence of natural organic matter within the aquifer sediments. The occurrences of As-bearing redox traps, primarily formed of Fe- and Mn-oxides/hydroxides, are also important factors that control the release of As into groundwater at the study site.
Immobilization of Se(VI) in mine drainage by permeable reactive barriers: column performance by K. Sasaki; D.W. Blowes; C.J. Ptacek; W.D. Gould (1012-1022).
The potential for immobilization of Se in mine drainage water using a permeable reactive barrier was investigated by a column study, in which the reactive components were zero valent Fe, municipal leaf compost, sawdust, and wood chips. These components were mixed with silica sand and gravel. Trace amounts of creek sediment were added to serve as a source of anaerobic bacteria. The influent concentration (40 mg L−1) of SeO 4 2 - decreased to less than 2 mg L−1 within one week and to less than 0.014 mg L−1 within 1 month during passage through the column. In the column, the concentrations of SO 4 2 - also were reduced from 620 to 220 mg L−1. After 2 months, cell populations of SO 4 2 - -reducing bacteria, estimated using the MPN method, were in the range of 106–107 cells g−1. Isotopic analysis of S showed δ 34S = −9.19‰ for the input solution, and δ 34S = −4.69‰ for the output solution. This change in isotopic ratio is attributed to the preferential utilization of 32 SO 4 2 - over 32 SO 4 2 - by SO4-reducing bacteria in the column. Geochemical calculations indicate that SeO 4 2 - is stable in the influent water, and that conditions within the column favour reduction of SeO 4 2 - to metallic Se or SeO 3 2 - , and the reduction of SO 4 2 - to S2−.
Composition and sources of extractable organic matter from a sediment core in Lake Kivu, East African rift valley by Khalid F. Al-Mutlaq; Laurel J. Standley; Bernd R.T. Simoneit (1023-1040).
Lake Kivu is a gas-charged East African rift lake with currently anoxic bottom water. The extractable compounds and residual organic matter of a short sediment core have δ 13C values typical of lacustrine microbial detritus. The total extracts consist primarily of polar compounds such as n-alkanoic acids, hydroxyalkanoic acids, triterpenoids, steroids and monosaccharides, with minor amounts of n-alkanes and n-alkanols. These tracer compounds and δ 13C values indicate that the organic matter in the surficial and deeper sedimentary record was dominated by bacterial sources. The sapropelic sediment between these horizons contains organic matter from primarily algal with lesser bacterial input. Terrestrial organic markers are minor in all samples. The major fractions of the compounds in the total extracts were oxidized in the upper water column prior to transit through the anoxic bottom water to sedimentary deposition. The sapropelic horizon may reflect lake water turnover with ventilation or hydrothermal activity and consequently increased algal blooms.
Thermal history of the unsaturated zone at Yucca Mountain, Nevada, USA by Joseph F. Whelan; Leonid A. Neymark; Richard J. Moscati; Brian D. Marshall; Edwin Roedder (1041-1075).
Secondary calcite, silica and minor amounts of fluorite deposited in fractures and cavities record the chemistry, temperatures, and timing of past fluid movement in the unsaturated zone at Yucca Mountain, Nevada, the proposed site of a high-level radioactive waste repository. The distribution and geochemistry of these deposits are consistent with low-temperature precipitation from meteoric waters that infiltrated at the surface and percolated down through the unsaturated zone. However, the discovery of fluid inclusions in calcite with homogenization temperatures (T h) up to ∼80 °C was construed by some scientists as strong evidence for hydrothermal deposition. This paper reports the results of investigations to test the hypothesis of hydrothermal deposition and to determine the temperature and timing of secondary mineral deposition. Mineral precipitation temperatures in the unsaturated zone are estimated from calcite- and fluorite-hosted fluid inclusions and calcite δ 18O values, and depositional timing is constrained by the 207Pb/235U ages of chalcedony or opal in the deposits. Fluid inclusion T h from 50 samples of calcite and four samples of fluorite range from ∼35 to ∼90 °C. Calcite δ 18O values range from ∼0 to ∼22‰ (SMOW) but most fall between 12 and 20‰. The highest T h and the lowest δ 18O values are found in the older calcite. Calcite T h and δ 18O values indicate that most calcite precipitated from water with δ 18O values between −13 and −7‰, similar to modern meteoric waters.Twenty-two 207Pb/235U ages of chalcedony or opal that generally postdate elevated depositional temperatures range from ∼9.5 to 1.9 Ma. New and published 207Pb/235U and 230Th/Uages coupled with the T h values and estimates of temperature from calcite δ 18O values indicate that maximum unsaturated zone temperatures probably predate ∼10 Ma and that the unsaturated zone had cooled to near-present-day temperatures (24–26 °C at a depth of 250 m) by 2–4 Ma. The evidence of elevated temperatures persisting in ash flow tuffs adjacent to parent calderas for as much as ∼8 Ma is a new finding, but consistent with thermal modeling. Simulations using the HEAT code demonstrate that prolonged cooling of the unsaturated zone is consistent with magmatic heat inputs and deep-seated (sub-water table) hydrothermal activity generated by the large magma body ∼8 km to the north that produced the 15–11 Ma ash flows and ash falls that make up Yucca Mountain. The evidence discussed in this and preceding papers strongly supports unsaturated zone deposition of the secondary minerals from descending meteoric waters. Although depositional temperatures reflect conductive (and possibly vapor-phase convective) heating of the unsaturated zone related to regional magmatic sources until perhaps 6 Ma, depositional conditions similar to the present-day unsaturated zone have prevailed for at least the past 2–4 Ma.
Trace elements in native gold by solution ICP-MS and their use in mineral exploration: A British Columbia example by Marty McInnes; John D. Greenough; Brian J. Fryer; Ron Wells (1076-1085).
An elegantly simple, aqua regia-based, ICP-MS analytical procedure is used to compare the trace element composition of density-separated alluvial native Au from seven stream silt samples with three samples of geographically-associated Au from a prospective ore deposit in central British Columbia. Not all of the alluvial Au could have come from the ore deposit based on present drainage. The silt sample Au, averaging four alluvial grains and totaling 12–250 μg per sample, generally yielded measurable concentrations for V, Fe, Cu, As, Pd, Ag, Sb, Pt and Bi. The bedrock Au samples represent the three dominant rock types in the showing. Their Au trace element compositions largely bracket the alluvial Au. Multidimensional scaling (exploratory statistics) shows that trace elements in the native Au form lithophile, chalcophile and siderophile groupings. This indicates that a small set of geochemical processes formed all the Au in one geologic environment. Previous work shows that Au from individual deposits has distinct assemblages of detectable elements. Given these observations and that detectable elements are the same in both the deposit and alluvial Au, and that concentrations in the former bracket those of the latter, it is concluded that the source of the alluvial Au has probably been identified. Apparently neither mineral inclusions nor weathering impaired fingerprinting of the Au. The simplicity of the approach indicates that this is a useful exploration tool for determining the bedrock source of alluvial Au. The study also shows that silt sample exploration in glaciated terrains must recognize that paleo-ice movement and paleo-stream directions can yield geographic distributions of alluvial Au that cannot be explained by present-day drainage patterns. Thus this simple analytical/exploration technique is potentially very useful to the exploration industry.
Arsenic and manganese in tube well waters of Prey Veng and Kandal Provinces, Cambodia by S. Sthiannopkao; K.W. Kim; S. Sotham; S. Choup (1086-1093).
Twenty-eight tube well water samples were collected in February, 2006, from households in the Cambodian provinces of Prey Veng and Kandal. Concentrations of total As in both provinces ranged from not detectable (ND) up to about 900 μg/L, with about 54% of all the samples collected exceeding the WHO drinking water guide value of 10 μg/L. In addition, about 32% of all samples contained concentrations of Mn exceeding the WHO drinking water guide value of 400 μg/L. It is interesting to note that more than half (about 56%) of tube wells with Mn over 400 μg/L had the non-detectable As. Barium, Sr and Fe were also detected in most of tube well samples, which were typically circum-neutral and reducing. Arsenic speciation was dominated (80%) by dissolved inorganic As(III). The occurrence and composition of the well waters is consistent with the As being mobilized from aquifer sediments by natural processes in a highly reducing environment. The highest estimated cumulative As intake for individuals using the sampled well waters as drinking water is estimated to be around 400 mg As/a – this is comparable to intakes that have resulted elsewhere in the world in serious As-related illnesses and highlights the possibility that such adverse health impacts may arise in Cambodia unless appropriate remedial measures are taken.
Study of the interaction between U(VI) and the anoxic corrosion products of carbon steel by Lara Duro; Souad El Aamrani; Miquel Rovira; Joan de Pablo; Jordi Bruno (1094-1100).
The objective of this study was to investigate the removal mechanism of U(VI) from groundwater by magnetite as the main product of anoxic steel corrosion. For this purpose, a systematic sequence of batch experiments was conducted to focus the active role of magnetite in the reduction of U under different conditions. Results indicated that under anoxic conditions U(VI) was sorbed at the magnetite surface, whereas under reducing conditions at different H2(g) pressures, U was present in tetravalent form as amorphous UO2.
Monomethylmercury sources in a tropical artificial reservoir by Bogdan Muresan; Daniel Cossa; Sandrine Richard; Yannick Dominique (1101-1126).
The distribution and speciation of mercury (Hg) in the water column, the inputs (wet deposition and tributaries) and the outputs (atmospheric evasion and outlet) of an artificial partially anoxic tropical lake (Petit-Saut reservoir, French Guiana) were investigated on a seasonal basis in order to appraise the cycling and transformations of this metal. The total mercury (HgT) concentrations in the oxygenated epilimnetic waters averaged 5 ± 3 pmol L−1 in the unfiltered samples (HgTUNF) and 4 ± 2 pmol L−1 in the dissolved (HgTD) phase (<0.45 μm). On average, the monomethylmercury (MMHg) constituted 8%, 40% and 18% of the HgT in the dissolved phase, the particulate suspended matter and in the unfiltered samples, respectively. Covariant elevated concentrations of particulate MMHg and chlorophyll a in the epilimnion suggest that phytoplankton is an active component for the MMHg transfer in the lake. In the anoxic hypolimnion the HgTUNF averages 13 ± 6 pmol L−1 and the HgTD 8 ± 4 pmol L−1. The averages of MMHgP and MMHgD in hypolimnetic waters were two and three times the corresponding values of the epilimnion, 170 ± 90 pmol g−1 and 0.9 ± 0.5 pmol L−1, respectively. In the long dry and wet seasons, at the flooded forest and upstream dam sampling stations, the vertical profiles of MMHgD concentrations accounted for two distinct maxima: one just below the oxycline and the other near the benthic interface. Direct wet atmospheric deposition accounted for 14 moles yr−1 HgTUNF, with 0.7 moles yr−1 as MMHgUNF, while circa 76 moles yr−1 of HgTUNF, with 4.7 moles yr−1 as MMHgUNF, coming from tributaries. Circa 78 moles (∼17% as MMHg) are annually exported through the dam, while 23 moles yr−1 of Hg0 evolve in the atmosphere. A mass balance calculation suggests that the endogenic production of MMHgUNF attained 8.1 moles yr−1, corresponding to a methylation rate of 0.06% d−1. As a result, the Petit-Saut reservoir is a large man-made reactor that has extensively altered mercury speciation in favor of methylated species.
Determination of the conditional interaction constant between colloidal technetium(IV) and Gorleben humic substances by K. Geraedts; A. Maes (1127-1139).
Varying pertechnetate (Tc(VII)) doses were reduced to Tc(IV) in the presence and absence of Gorleben humic substances with the aid of magnetite, a reducing Fe(II)-containing surface. In absence of humic substances dissolved Tc(IV) concentrations are over-saturated with respect to the known TcO2 · nH2O solubility and increase with increasing Tc(VII) dose due to the formation of a range of mononuclear to colloidal Tc(IV) species. In presence of dissolved humic substances, the Tc solubility is enhanced due to the additional interaction of dissolved Tc(IV) species with humic substances. Both in the absence and the presence of dissolved humic substances a sorption mechanism controls the distribution of the range of mononuclear to colloidal Tc(IV) species between the solid and the liquid phase. The proposed reaction mechanism between Tc(IV) and HS is represented by Σ[TcO(OH)2] n +HS = [TcO(OH)2] n − HS in which Σ[TcO(OH)2] n stands for the sum of monomeric and polynuclear (colloidal) Tc(IV) species present in the equilibrium solution. A log K-value of 2.9 (±0.3) was quantified from a modified Schubert approach which is based on the competition of HS and magnetite for all dissolved Tc(IV) species and was found independent of Tc–HS loading, Tc–magnetite loading and pH.
Evaluation of microwave-assisted acid extraction procedures for the determination of metal content and potential bioavailability in sediments by Cinzia Bettiol; Lorenzo Stievano; Mariangela Bertelle; Francesca Delfino; Emanuele Argese (1140-1151).
Acid extractions represent a simple and effective tool for the assessment of metal contamination, origin and bioavailability in the aquatic environment. Optimized microwave-assisted procedures utilizing two extractions (8 M HNO3 and 1 M HCl) were developed. Particular attention was given to the evaluation of efficiency and selectivity of the developed procedures. This involved an examination of the sediment and the extraction residues by Mössbauer spectroscopy and X-ray diffractometry. These instrumental approaches were used to identify the geochemical phases associated with acid decomposition. Microwave digestion with 8 M HNO3 produced an efficient solubilization of the most important metal-bearing phases and left unaffected only the minerals (quartz, feldspars, muscovite) with a negligible metal content, thus providing a good estimate of the total metal concentrations. The 1 M HCl extraction, despite the limitation due to the incomplete solubilization of pyrite and to the partial dissolution of sheet silicates, represents a simple and effective technique for providing an estimate of the bioavailable metal fraction in sediments. The combined use of the two microwave-assisted acid extractions can provide a rapid and simple approach for the risk assessment of metal-polluted sediments.
Soil alteration by continued oxidation of pyrite tailings by F. Martín; I. García; M. Díez; M. Sierra; M. Simon; C. Dorronsoro (1152-1165).
This work examines the alteration processes triggered after the oxidation of pyrite tailings deposited for 3 years over a carbonate soil. The infiltration of the acidic solution into the soil is causing important morphological, compositional and mineralogical changes in the profile. After 3 years of continued action of such alteration, a considerable degradation of the main soil properties was evident, the most notable being the decline in the cation-exchange capacity (caused by the decreases in clay and organic matter content), texture variation, greater electrical conductivity (10-fold greater than in unaffected soil), and the appearance of horizons with colorations strongly differing from those of the original soil (a discoloured layer with greyish tonalities in the first 5 mm, followed by a reddish-brown layer to a depth of 65–70 mm). At the same time, the carbonates have weathered, disappearing completely from the upper 35 mm and partially to 80 mm in depth. There has also been an intense acidification of the soil (with pH values close to 2.0 within the greyish layer) as well as a partial hydrolysis of the primary silicates (mainly feldspars and phyllosilicates), causing extreme infertility of the soil. The resulting products in this process give rise to intense neoformation of gypsum and hydroxysulphates of Fe and Al, which, together with the acidic conditions of the medium, determine the distribution of the main elements of the soil, both in their total and soluble forms.
Controls of δ 34S and δ 18O in dissolved sulphate: Learning from a detailed survey in the Llobregat River (Spain) by Neus Otero; Albert Soler; Àngels Canals (1166-1185).
The S and O isotopic composition of dissolved SO4, used as a tracer for SO4 sources, was applied to the water of the Llobregat River system (NE Spain). The survey was carried out at 30 sites where surface water was sampled on a monthly basis over a period of 2a. The concentration of dissolved SO4 varied from 20 to 1575 mg L−1. Sulphur isotopic compositions clustered in two populations: one – 93% of the samples – had positive values with a mode of +9‰; the other had negative values and a mode of −5‰. Data for δ 18OSO4 showed a mean value of +11‰, with no bi-modal distribution, though lower values of δ 18O corresponded to samples with negative δ 34S. These values can not be explained solely by the contribution of bedrock SO4 sources: that is, sulphide oxidation and the weathering of outcrops of sulphates, though numerous chemical sediments exist in the basin. Even in a river with a high concentration of natural sources of dissolved SO4, such as the Llobregat River, the δ 34S values suggest that dissolved SO4 is controlled by a complex mix of both natural and anthropogenic sources. The main anthropogenic sources in this basin are fertilizers, sewage, potash mine effluent and power plant emissions. Detailed river water sampling, together with the chemical and isotopic characterisation of the main anthropogenic inputs, allowed determination of the influence of redox processes, as well as identification of the contribution of natural and anthropogenic SO4 sources and detection of spatial variations and seasonal changes among these sources. For instance, in the Llobregat River the input of fertilisers is well marked seasonally. Minimum values of δ 34S are reported during fertilization periods – from January to March – indicating a higher contribution of this source. The dual isotope approach, δ 34S and δ 18O, is useful to better constrain the sources of SO4. Moreover, in small-scale studies, where the inputs are well known and limited, the mixing models can be enhanced and the contribution of the different sources can be quantified to some extent.
Coupled thermo-hydro-chemical models of compacted bentonite after FEBEX in situ test by Javier Samper; Liange Zheng; Luis Montenegro; Ana María Fernández; Pedro Rivas (1186-1201).
FEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project for the engineered barrier of a high-level radioactive waste (HLW) repository. FEBEX is based on the Spanish reference concept for radioactive waste disposal in crystalline rock according to which canisters are emplaced in horizontal drifts and surrounded by a compacted bentonite clay barrier. The project includes two main large-scale tests which started in February 1997: an in situ full-scale test performed at Grimsel, Switzerland, and a mock-up test operating at CIEMAT facilities in Madrid, Spain. Coupled thermal, hydrodynamic and chemical (THC) models for the engineered barrier have been developed from laboratory experiments and the mock-up test. Dismantling of section 1 of in situ test, which took place in the summer of 2002, provides a unique opportunity to test THC model predictions. Here a numerical THC model of FEBEX in situ test is presented. Predictions performed with three conceptual geochemical models are compared to measured temperature, water content and geochemical data obtained from aqueous extract tests of samples collected after dismantling of heater 1. These data require the use of inverse hydrogeochemical models for their interpretation in order to account for the geochemical processes suffered by bentonite samples during aqueous extraction. Model predictions reproduce temperatures and capture the trends of water content and most chemical species. However, there are some discrepancies near the heater which are especially significant for SO 4 2 - and HCO 3 - . The THC model could be improved by taking into account different types of water in bentonite, bentonite swelling, protonation/deprotonation by surface complexation, and CO2 degassing and dissolution processes.
Diagenetic processes on metals in hypersaline mudflat sediments from a subtropical saltmarsh (SE Gulf of California): Postdepositional mobility and geochemical fractions by M.F. Soto-Jiménez; F. Páez-Osuna (1202-1217).
To understand the biogeochemical cycles of trace metals (Cd, Cu, Fe, Mn, Ni and Zn) in a hypersaline subtropical marsh, geochemical studies of both interstitial and solid phases were conducted on sediment cores from Chiricahueto marsh, SE Gulf of California. The sequential extraction procedure proposed by Tessier was used to estimate the percentages of the metals present in each geochemical phase of the sediment. Metal concentrations in the solid phase were found to be enriched in the upper layers and mainly associated with reactive fractions such as organic matter, Fe–Mn oxyhydroxides and carbonates (46–74% of Ni, Mn and Cd, and 11–19% of Cu and Zn). Principal factor analysis (PFA) and Spearman correlation analysis revealed a strong positive association of metals and their reactive phases with OC (the diagenetic component), and a negative or non-association with the mud content, Al, Fe and Li (the lithogenic component). Diagenetically released metals are mainly mobilized within hypersaline sediments by buoyancy transport (>90% of total flux) in response to an extreme salinity gradient by input of fresh groundwater (3–6 psu cm−1). The molecular diffusion due to the gradient of metals in porewater (maximum and higher levels at 5–7 and below 20 cm depth, respectively) is significantly less important to the advective transport. Most of the metals mobilized by diffusion–advection processes are re-precipitated in the sediments by authigenic minerals, only <10% of most metals are extruded out to the overlying water column. Authigenic accumulation rates were estimated as 1.42–7.09 mg m−2 a−1 for Cd; 58.8–378 for Cu; 6922–17,985 for Fe; 38.2–345 for Mn; 20.8–263 for Ni; and 282–2956 mg m−2 a−1 for Zn. The Mn–Fe oxyhydroxides (40–85% of reactive metals) in the upper oxic–suboxic layers (<5 cm below surface) and sulfide minerals (75–97%) in anoxic sediment layers (7–18 cm) constitute the main scavengers for metals.
Direct versus indirect determination of suspended sediment associated metals in a mining-influenced watershed by Barbara A. Butler; James F. Ranville; Philippe E. Ross (1218-1231).
The differentiation between the concentration of metals associated with suspended sediments and those in the dissolved phase is often of importance in aquatic ecosystems, for such reasons as toxicity evaluation, total maximum daily load calculations, and a better understanding of metal transport. Often, published water quality data include only concentrations of total and dissolved metals, with particulate concentrations assumed equal to the difference between the two. The validity of this assumption for mining-influenced waters is addressed in this paper by comparing data determined from the subtraction of total (acid-soluble) and dissolved (operationally defined as less than 0.45-μm) metal concentrations (difference method) with data obtained from acid-digestion of the particles retained on the filters used for filtering the dissolved fraction (digestion method). Greater than fifty water samples containing suspended sediment were collected from each of three sites in the Clear Creek Watershed in Colorado during a two and one-half year study on the fate and transport of metals in the watershed. Volumes of water filtered ranged from 50 to 250 ml, representative of typical volumes used for the determination of dissolved metal concentrations. The particulate-associated concentrations of Al, Cu, Fe, Mn, and Zn determined from the difference method compared well with the concentrations determined by the digestion method. Statistical analyses indicated that there is not a statistically significant difference between the two methods at the 95% confidence level, with p-values of 0.65, 0.88, 0.39, 0.67, and 0.75, for Al, Cu, Fe, Mn, and Zn, respectively, over the three sites.
Metal extractability in acidic and neutral mine tailings from the Cartagena-La Unión Mining District (SE Spain) by Héctor M. Conesa; Brett H. Robinson; Rainer Schulin; Bernd Nowack (1232-1240).
Mine tailings are ubiquitous in the landscapes of mined areas. Metal solubilities were compared in two chemically distinct mine tailings from the old Mining District of Cartagena-La Unión (SE Spain). One of the tailings was acidic (pH 3.0) with 5400 mg/kg Zn, 1900 mg/kg As and 7000 mg/kg Pb. The other was neutral (pH 7.4) with 9100 mg/kg Zn, 5200 mg/kg Pb and 350 mg/kg As. In samples from the acidic tailings, more than 15% of the Zn and 55% of the Cd were extractable with 0.1 M NaNO3, and distilled water. In the neutral tailings, using the same reagents, less than 1% of the metals were extractable. A sequential extraction procedure revealed that the sum of the residual and the Fe oxide fractions of Cu, Zn and Pb comprised 80–95% in the acidic tailings and 70–90% in the neutral tailings. The acidic mine tailings had a higher metal solubility, resulting in more metal leaching in the short-term, but also a higher fraction of inert metal. In contrast, in the neutral tailings, the metals were evenly distributed between, oxides and the residual fraction. This implies lower metal mobility in the short-term, but that metal mobility may increase in the long-term. When applied to mine tailings, sequential extractions may provide misleading results because the strong cation exchange capacity of some extractants may induce pH changes and thereby significantly change metal solubility.
Impact of ancient metal smelting on arsenic pollution in the Pecora River Valley, Southern Tuscany, Italy by Pilario Costagliola; Marco Benvenuti; Laura Chiarantini; Sara Bianchi; Francesco Di Benedetto; Mario Paolieri; Luca Rossato (1241-1259).
A significant As anomaly has been reported in the literature for stream sediments and unlithified Quaternary deposits of the Pecora River valley in Southern Tuscany, extending from the “Colline Metallifere” pyrite-base metals district to the Tyrrhenian Sea. The As anomaly spreads over several square kilometers around a core that exceeds 500 ppm. Several source contributions (from natural to anthropogenic) have been invoked to explain the observed As distribution in the Pecora Valley, including the metal-working industry which was active in this area, particularly in Etrusco-Roman times and in the Middle Ages. In order to evaluate the contribution of ancient mining and metallurgical activities in the Pecora Valley to elevated As concentrations in the environment, a detailed mineralogical and geochemical survey of metallurgical slags and smelted ore minerals was undertaken from six different sites through the Pecora Valley: Poggio Butelli (Etrusco-Roman iron slags); Sata Creek, Arialla, Marsiliana, Forra and Cascata sites (all Medieval base metals slags). The As content of Etrusco-Roman slags is relatively low (few tens of ppm), whereas Medieval slags show variable, but higher amounts of base metals (±Ag) (ranging from tens to tens of thousands ppm) and As (up to 267 ppm, with average contents of about 40 ppm). Arsenic is mostly partitioned in sulfides disseminated through the glassy groundmass rather than in solid solution with the glassy matrix. Remnants of the ore used for base metal and Ag smelting during the Middle Ages had the highest As contents (up to about 1000 ppm).The overall As concentration in the slags, independent of age and type, is generally lower than that found in stream sediments and Quaternary alluvial deposit outcrops of the upper Pecora Valley. Textural observations indicate that exogenous alteration of slags is minor and mostly confined to superficial exposures of matte droplets or along fractures; metal particles embedded within the glassy groundmass, even those located a few micrometres from the surface, appear to be unaltered. It is suggested, therefore, that As and contaminant metal contributions to the Pecora valley by archaeometallurgical slags was minor, at least for slags from the last 2500 to 700 a BP. Similarly, based on gross mass balance calculations, airborne release of As due to smelting/roasting operations in the past cannot account for the observed extent of the As anomaly in stream sediments and Quaternary deposits. Although residues of unsmelted (or partially smelted) Fe–Cu–Pb–Zn charges or fluxes for base metal metallurgy contain much greater amounts of As than smelting slags, their relatively low abundance would limit the overall input of As into the Pecora river valley. On the other hand, concurrent research seems to indicate a major “geogenic” contribution to the As anomaly in the Pecora Valley.
The acidic mine pit lakes of the Iberian Pyrite Belt: An approach to their physical limnology and hydrogeochemistry by Javier Sánchez España; Enrique López Pamo; Esther Santofimia Pastor; Marta Diez Ercilla (1260-1287).
This study examines some relevant limnological and hydrogeochemical characteristics of 22 mine pit lakes of the Iberian Pyrite Belt (IPB). The studied pit lakes include some of the largest and historically most important mines of the IPB (including Corta Atalaya and Cerro Colorado in Riotinto, Filón Norte, Filón Centro and Filón Sur in Tharsis, Aznalcóllar, or San Telmo) and many other of minor size. As a whole, these lakes constitute, at present, a large volume of highly acidic and metal-polluted water. Some of these pit lakes are very recent (e.g., Corta Atalaya, 2.5 a; Los Frailes, 6 a) and present a continuous hydrological and geochemical evolution, although many others were abandoned decades ago and show nearly constant water volume. Depth profiles obtained in several pit lakes (e.g., San Telmo, Confesionarios, Cueva de la Mora, Concepción) indicate that many of them have developed meromixis and show, at present, a permanent thermal and chemical stratification with a well defined chemocline separating an anoxic, Fe(II)-rich monimolimnion, and a well mixed, oxygenated and Fe(III)-rich mixolimnion. In the upper layer, the bacterial oxidation of Fe(II) competes with photoreductive processes which take place in the surface water, thus provoking diel cycles of Fe(II) concentration. The observed water chemistry reflects the oxidation and dissolution of pyrite and other sulphides and gangue aluminosilicates from the country rock. The pit lakes of the IPB cover a wide range of water compositions, from circumneutral and relatively low-metal (e.g., Los Frailes, pH 7.2, 0.07 mg/L Fe, 3.8 mg/L Mn, 30 mg/L Zn), to extremely acidic and metal(loid)-rich (e.g., Corta Atalaya, pH 1.2, 36.7 g/L Fe, 6.7 g/L Zn, 1.3 g/L Cu, 159 mg/L As). Most pit lakes, however, are comprised within the pH range of 2.2–3.6 and appear to be strongly buffered by the hydrolysis and precipitation of Fe(III) in the form of schwertmannite, which forms colloids that can sorb trace elements from the aqueous phase.
Long-term interaction of wollastonite with acid mine water and effects on arsenic and metal removal by J.C. Fernández-Caliani; C. Barba-Brioso; R. Pérez-López (1288-1298).
This paper reports the results of a laboratory experiment conducted to investigate the effects of wollastonite dissolution on removal of potentially toxic trace elements from stream waters affected by acid mine drainage (AMD). Nearly pure wollastonite was treated with natural acid mine water (pH 2.1) for different lengths of time (15, 30, 50 and 80 days). The compositional and textural characterization of the solid reaction products suggests that wollastonite was incongruently dissolved leaving a residual amorphous silica-rich phase that preserved the prismatic morphology of the parent wollastonite. The release of Ca into solution resulted in a pH increase from 2.1 to 3.5, and subsequent precipitation of gypsum as well as poorly crystallized Fe–Al oxy-hydroxides and oxy-hydroxysulfates whose components derived from the AMD solution. A geochemical modeling approach of the wollastonite–AMD interaction using the PHREEQC code indicated supersaturation with respect to schwertmannite (saturation index = 10.7–15.7), jarosite (SI = 8.7–10.2), alunite (SI = 5.1), goethite (SI = 4.7) and jurbanite (SI = 2.2). These secondary phases developed a thin coating on the reacted wollastonite surface, readily cracked and flaked off upon drying, that acted as a sink for trace elements, especially As, Cu and Zn, as indicated by their enrichment relative to the starting wollastonite. At such low pH values, adsorption of As oxyanions on the positively charged solid particles and coprecipitation of metals (mainly Cu and Zn) with the newly formed Fe oxy-hydroxides and oxy-hydroxysulfates seem to be the dominant processes controlling the removal of trace elements.
Contamination of surface waters by mining wastes in the Milluni Valley (Cordillera Real, Bolivia): Mineralogical and hydrological influences by Matías Miguel Salvarredy-Aranguren; Anne Probst; Marc Roulet; Marie-Pierre Isaure (1299-1324).
This study is one of very few dealing with mining waste contamination in high altitude, tropical-latitude areas exploited during the last century. Geochemical, mineralogical and hydrological characterizations of potentially harmful elements (PHEs) in surface waters and sediments were performed in the Milluni Valley (main reservoir of water supply of La Paz, Bolivia, 4000 m a.s.l.), throughout different seasons during 2002–2004 to identify contamination sources and sinks, and contamination control parameters. PHE concentrations greatly exceeded the World Health Organization water guidelines for human consumption. The very acidic conditions, which resulted from the oxidation of sulfide minerals in mining waste, favoured the enrichment of dissolved PHEs (Cd > Zn ≫ As ≫ Cu ∼ Ni > Pb > Sn) in surface waters downstream from the mine. Stream and lake sediments, mining waste and bedrock showed the highest PHE content in the mining area. With the exception of Fe, the PHEs were derived from specific minerals (Fe, pyrite; Zn, Cd, sphalerite, As, Fe, arsenopyrite, Cu, Fe, chalcopyrite, Pb, galena, Sn, cassiterite), but the mining was responsible for PHEs availability. Most of the PHEs were extremely mobile (As > Fe > Pb > Cd > Zn ∼ Cu > Sn) in the mining wastes and the sediments downstream from the mine. pH and oxyhydroxides mainly explained the contrasted availability of Zn (mostly in labile fractions) and As (associated with Fe-oxyhydroxides). Unexpectedly, Pb, Zn, As, and Fe were significantly attenuated by organic matter in acidic lake sediments.Hydrological conditions highly influenced the behaviours of major elements and PHEs. During wet seasons, major elements were diluted by meteoric waters, whereas PHEs increased due to the dissolution of sulfides and unstable tertiary minerals that formed during dry seasons. This is particularly obvious at the beginning of the wet season and contributes to flushes of element transport downstream. The high altitude of the study area compensates for the tropical latitude, rendering the geochemical behaviour of contaminants similar to that of temperate and cold regions. These results might be representative of geochemical processes in ore deposits located in the high Andes plateau, and of their influence on PHE concentrations within the upper Amazon basin. Although mining activities in this region stopped 10 years ago, the impact of mining waste on water quality remains a serious environmental problem.
Chromium, chromium isotopes and selected trace elements, western Mojave Desert, USA by John A. Izbicki; James W. Ball; Thomas D. Bullen; Stephen J. Sutley (1325-1352).
Chromium(VI) concentrations in excess of the California Maximum Contaminant Level (MCL) of 50 μg/L occur naturally in alkaline, oxic ground-water in alluvial aquifers in the western Mojave Desert, southern California. The highest concentrations were measured in aquifers eroded from mafic rock, but Cr(VI) as high as 27 μg/L was measured in aquifers eroded from granitic rock. Chromium(VI) concentrations did not exceed 5 μg/L at pH < 7.5 regardless of geology. δ53Cr values in native ground-water ranged from 0.7 to 5.1‰ and values were fractionated relative to the average δ53Cr composition of 0‰ in the earth’s crust. Positive δ53Cr values of 1.2 and 2.3‰ were measured in ground-water recharge areas having low Cr concentrations, consistent with the addition of Cr(VI) that was fractionated on mineral surfaces prior to entering solution. δ53Cr values, although variable, did not consistently increase or decrease with increasing Cr concentrations as ground-water flowed down gradient through more oxic portions of the aquifer. However, increasing δ53Cr values were observed as dissolved O2 concentrations decreased, and Cr(VI) was reduced to Cr(III), and subsequently removed from solution. As a result, the highest δ53Cr values were measured in water from deep wells, and wells in discharge areas near dry lakes at the downgradient end of long flow paths through alluvial aquifers. δ53Cr values at an industrial site overlying mafic alluvium having high natural background Cr(VI) concentrations ranged from −0.1 to 3.2‰. Near zero δ53Cr values at the site were the result of anthropogenic Cr. However, mixing with native ground-water and fractionation of Cr within the plume increased δ53Cr values at the site. Although δ53Cr was not necessarily diagnostic of anthropogenic Cr, it was possible to identify the extent of anthropogenic Cr at the site on the basis of the δ53Cr values in conjunction with major-ion data, and the δ18O and δD composition of water from wells.
Comment on “Some numerical considerations in the geochemical analysis of distal microtephra” by A.M. Pollard, S.P.E. Blockley and C.S. Lane by Nicholas J.G. Pearce; Charles A. Bendall; John A. Westgate (1353-1364).
Reply to the comment on “Some numerical considerations in the geochemical analysis of distal microtephra”, by Nicholas J.G. Pearce, Charles A. Bendall and John A. Westgate by A.M. Pollard; S.P.E. Blockley; C.S. Lane (1365-1366).