Applied Geochemistry (v.59, #C)
Predictive modelling of pH and dissolved metal concentrations and speciation following mixing of acid drainage with river water by Luke M. Mosley; Rob Daly; David Palmer; Peter Yeates; Chris Dallimore; Tapas Biswas; Stuart L. Simpson (1-10).
Discharge of acidic drainage from mining operations or acid sulphate soils can create severe environmental impacts if not managed appropriately. We tested different hydro-geochemical models to predict pH and dissolved Al, Fe and Mn concentrations and speciation following discharge and mixing of acid drainage into receiving waters; (1) an end member mixing approach using the geochemical model PHREEQC could accurately predict (r 2 > 0.9) pH and dissolved metal concentrations at various dilutions over a pH range of 2–7, (2) dissolved inorganic and organic, and solid phase, Al and Fe speciation could be predicted using the geochemical model Visual MINTEQ (at 10% dilution), although poorer results were observed for Mn and drainage mixtures with lower metal concentrations, (3) PHREEQC gave similar results to a 3-D hydro-biogeochemical model (ELCOM-CAEDYM) when tested on a small-scale, and (4) ELCOM-CAEDYM successfully predicted dissolved metal concentrations (r 2 ⩾ 0.8), and to some extent pH (r 2 = 0.2), over a 5 month period in a 90 km reach of the River Murray (South Australia) with over ten acid drainage discharges. The 3-D model was also used to assess river management scenarios and this highlighted a risk for dissolved Mn exceeding (aesthetic) drinking water guidelines in the river water at low flows. Limitations of the various models are discussed and we conclude that geochemical modelling is a useful tool to predict water quality impacts following discharge of acidic drainage to natural waters.
Chemical effects of sulfur dioxide co-injection with carbon dioxide on the reservoir and caprock mineralogy and permeability in depleted gas fields by Panteha Bolourinejad; Rien Herber (11-22).
The most suitable candidates for subsurface storage of CO2 are depleted gas fields. Their ability to retain CO2 can however be influenced by the effect which impurities in the CO2 stream (e.g. H2S and SO2) have on the mineralogy of reservoir and seal. In order to investigate the effects of SO2 we carried out laboratory experiments on reservoir and cap rock core samples from gas fields in the northeast of the Netherlands. The rock samples were contained in reactor vessels for 30 days in contact with CO2 and 100 ppm SO2 under in-situ conditions (300 bar, 100 °C). The vessels also contained brine with the same composition as in the actual reservoir. Furthermore equilibrium modeling was carried out using PHREEQC software in order to model the experiments on caprock samples.After the experiments the permeability of the reservoir samples had increased by a factor of 1.2–2.2 as a result of dissolution of primary reservoir minerals. Analysis of the associated brine samples before and after the experiments showed that concentrations of K, Si and Al had increased, indicative of silicate mineral dissolution.In the caprock samples, composed of carbonate and anhydrite minerals, permeability changed by a factor of 0.79–23. The increase in permeability is proportional to the amount of carbonate in the caprock. With higher carbonate content in comparison with anhydrite the permeability increase is higher due to the additional carbonate dissolution. This dependency of permeability variations was verified by the modeling study. Hence, caprock with a higher anhydrite content in comparison with carbonate minerals has a lower risk of leakage after co-injection of 100 ppmv SO2 with CO2.
Tracing toxic elements sources using lead isotopes: An example from the San Antonio–El Triunfo mining district, Baja California Sur, México by Leopoldo Gutiérrez-Caminero; Bodo Weber; Jobst Wurl; Mariela Carrera-Muñoz (23-32).
Pollution of sediments and water bodies with toxic elements around the San Antonio–El Triunfo mining district, Baja California Sur, México is probably sourced from the tailings of abandoned mines that are hosted in mineralized Cretaceous granitoids. However, there is evidence to suggest local hot springs related to recent faults may be an additional source for contamination in the area. In this study, lead isotope signatures are applied to draw conclusions with regard to potential sources of toxic elements. Lead isotope ratios were analyzed from sulfides and scoria from the abandoned mines, fluvial sediments, and igneous rocks with secondary disseminated mineralization. To differentiate between superposed secondary and residual primary lead, leaching experiments were performed, and both leachate and residues were analyzed separately. Most of the residues from sediment samples have lead isotope ratios similar to those from the sulfides and scoria of the mining district, indicating that most of the lead in the detritus is related to the mineralized plutons. However, there is evidence of an additional detrital component. Lead isotope ratios from the leachates indicate a different source for the superimposed lead that is best explained by the contamination with the average Mexican industrial lead. Secondary disseminated mineralization that is related to younger, deep structures (hot springs) has different lead isotope ratios compared to massive vein sulfides and accounts for a significant amount in areas with high contamination levels. Thus, lead isotope systematics is a feasible method for tracing sources of toxic elements to distinguish between different natural, metallurgical, and anthropogenic inputs.
A combined geochemical and isotopic study of the fluids discharged from the Montecatini thermal system (NW Tuscany, Italy) by F. Capecchiacci; F. Tassi; O. Vaselli; G. Bicocchi; J. Cabassi; L. Giannini; B. Nisi; G. Chiocciora (33-46).
The thermo-mineral fluids discharges of Montecatini Terme (Northern Apennines, Tuscany, Italy) have been exploited since the Roman times and despite the fact that this thermal complex is one of the biggest in Europe, the most recent geochemical investigations were published almost 40 years ago. To fill this gap, in this paper a detailed geochemical and isotopic investigation on the main thermal springs and wells from the Montecatini thermal system (MTS) is presented.The chemical and isotopic features of the Montecatini waters suggested that they are mainly controlled by water–rock interaction processes between meteoric water, permeating at depth from the surrounding reliefs (up to 800 m a.s.l.), and the Triassic evaporites (Burano Formation) belonging to the Tuscan sedimentary series. The local stratigraphic and tectonic framework favors an efficient recharge of the hydrothermal reservoir by the meteoric precipitation from a large catchment area and this aspect plays a fundamental role for the longevity of the Montecatini thermal spas, notwithstanding the huge amount of thermal water exploited. The 3H values indicated that the thermal waters are likely related to a relatively long (>50 years) fluid circulation pattern. Approaching the surface, thermal and saline waters mix with cold and low TDS (Total Dissolved Solids) waters hosted in short, shallow aquifer(s), whose chemistry is dictated by the interaction of rain waters with silico-clastic rocks of low solubility. Geothermometric estimations in the F−–SO4 2−–HCO3 − system suggested the occurrence of a main fluid reservoir at T ⩾ 80–95 °C and PCO2 ∼0.5 bars. Such CO2 pressure is consistent with values estimated for other thermal springs from central-southern Tuscany, being CO2 basically supplied by a deep source. Nevertheless, δ13C-CO2 and δ13C-TDIC values were lower than those expected for a mantle/thermometamorphic CO2 source. This can be explained by: (i) isotopic fractionation occurring during calcite precipitation and/or (ii) mixing with biogenically derived gases, occurring at relatively shallow depth.
Chemical immobilization of metals and metalloids by phosphates by Erla G. Hafsteinsdóttir; Danielle Camenzuli; Amy L. Rocavert; James Walworth; Damian B. Gore (47-62).
Remediation of metal contaminated media using orthophosphate fixation forms insoluble and non-bioavailable salts from metal and phosphate sources. The main focus has been on fixation of Pb, where the formation of pyromorphite, the most insoluble lead phosphate, has shown the great potential of this remediation technique. Other metals (Ba, Cd, Co, Cu, Eu, Ni, U, Zn) also have potential for effective fixation by orthophosphate. We review the applicability of the treatment across wider environmental conditions, particularly in surface soil, its use with elements other than Pb, product stability and efficiency with mixed contaminants.
Geochemical associations for evaluating the availability of potentially harmful elements in urban soils: Lessons learnt from Athens, Greece by Efstratios Kelepertzis; Ariadne Argyraki (63-73).
The estimation of potentially harmful element (PHE) availability in urban soil is essential for evaluating impending risks for human and ecosystem health. In the present study five single extraction procedures were evaluated based on the analysis of 45 urban top-soil samples from Athens, Greece. The pseudototal (aqua regia), potentially phytoavailable (0.05 M EDTA), mobilizable (0.43 M HAc), bioaccessible (0.4 M glycine) and reactive pools (0.43 M HNO3) of PHEs were determined. In general, geogenic elements in Athens soil (Ni, Cr, Co, As) are relatively less available than typical tracers of anthropogenic contamination (Pb, Zn, Cu, Cd). Results of principal component analysis (PCA) indicate an association between available fractions of Pb, Cu, Zn, Cd and amorphous Fe oxides, whereas amorphous Mn oxides account for the available concentrations of Mn, Ni and Co. Empirical multiple linear regression models demonstrate that pseudototal concentration is the predominant explanatory factor of variability for the available pools of the anthropogenic elements. Major elemental composition and total organic carbon (TOC) improve the predictions for the geogenic group of elements, although the explained variability remains low. Dilute HNO3 is a better predictor of Zn, Ni, As and Mn availability, whereas Pb and Cu available fractions are predicted more accurately by the classical aqua regia protocol. This study contributes to the international database on the environmental behavior of PHEs and provides additional knowledge that can be used toward the harmonization of chemical extraction methodology in urban soil.
Ion exchange reactions of major inorganic cations (H+, Na+, Ca2+, Mg2+ and K+) on beidellite: Experimental results and new thermodynamic database. Toward a better prediction of contaminant mobility in natural environments by Valentin Robin; Emmanuel Tertre; Daniel Beaufort; Olivier Regnault; Paul Sardini; Michael Descostes (74-84).
To our knowledge, no thermodynamic database is available in the literature concerning ion-exchange reactions occurring in low-charge smectite with tetrahedral charge (beidellite). The lack of this information makes it difficult to predict the mobility of contaminants in environments where beidellite and major cations, which act as competitors with contaminants for sorption on the clay phase, are present. The present study proposes a multi-site ion exchange model able to describe experimental data obtained for H+ and the four major cations (Na+, Ca2+, Mg2+ and K+) found in natural waters interacting with a <0.3 μm size fraction of Na-beidellite. The nature of the sites involved in the sorption processes is assessed using qualitative structural data. Moreover, the effect of the charge location in the smectite on the selectivity coefficient values is discussed by comparison with the results reported in the literature for smectite characterized by octahedral charge (montmorillonite). The new thermodynamic database proposed in this study is based on the same total sorption site density and distribution of sites regardless of the cations investigated. This database is valid for a large range of physico-chemical conditions: a [1–7] pH range, a total normality higher than 5 × 10−3 mol/L corresponding to a flocculated state for water/clay systems, and when sorption of ions pairs can be neglected. Note that this study provides evidence that a thermodynamic database describing ion exchange reactions between H+ and the four major cations of natural water for smectite cannot be valid irrespective of the total normality of the aqueous phase because smectite can form different phases (e.g., floc, gel) when immersed in aqueous system. The model proposed can be easily included in reactive transport software and is applied in the present study to predict the evolution of beidellite surface composition toward major inorganic cations in the context of mining site remediation. Finally, the new thermodynamic database proposed could be used for a better understanding of ion-exchange reactions occurring in many environments where beidellite is present, from soils to smectite-bearing sedimentary formations.
A modified version of Archie’s law to estimate effective diffusion coefficients of radionuclides in argillaceous rocks and its application in safety analysis studies by Luc R. Van Loon; Jens Mibus (85-94).
Display OmittedBecause of the very low hydraulic conductivity of clay rocks, molecular diffusion is the main process responsible for the transport of radionuclides released from the waste matrix into the host rock. Diffusion values are thus important input parameters in safety analyses. Because diffusion measurements are very time consuming, it is impossible to measure diffusion coefficients for all radionuclides of interest. It is therefore important to develop procedures for doing reliable estimates of diffusion coefficients.Diffusion data of mainly tritiated water (HTO) and anions (I−, Cl−) measured in different sedimentary rocks were taken from the literature. The effective diffusion coefficient could be related to the transport porosity by an extended version of Archie’s law (e-Archie): D e = D w · ε m 1 + B · ε m 2 . The extended version deviates from the classical law at porosity values below ca. 0.1.Effective diffusion coefficients of HTO, 36Cl− and 22Na+ were measured for a series of Swiss clay rocks (“Brauner Dogger”, Effingen Member, Opalinus Clay and Helvetic Marls) and for one Hungarian rock (Boda Claystone Formation) and could be satisfactorily described by the extended version of Archie’s law, bounded by an upper and a lower curve.A method was developed based on e-Archie for estimating effective diffusion coefficients for a series of radionuclides. Important input parameters are the accessible porosity of the rock and the diffusion coefficient of the radionuclide in water. In case of cations showing surface diffusion, a correction term was introduced based on the work of Gimmi and Kosakowski (2011).
Effect of exopolymers on oxidative dissolution of natural rhodochrosite by Pseudomonas putida strain MnB1: An electrochemical study by Huawei Wang; Daoyong Zhang; Wenjuan Song; Xiangliang Pan; Fahad A. Al-Misned; M. Golam Mortuza (95-103).
Oxidative dissolution of natural rhodochrosite by the Mn(II) oxidizing bacterium Pseudomonas putida strain MnB1 was investigated based on batch and electrochemical experiments using natural rhodochrosite as the working electrode. Tafel curves and batch experiments revealed that bacterial exopolymers (EPS) significantly increased dissolution of natural rhodochrosite. The corrosion current significantly increased with reaction time for EPS treatment. However, the corrosion process was blocked in the presence of cells plus extra EPS due to formation of the passivation layer. Moreover, the scanning electron microscopy and the energy dispersive spectroscopy (SEM–EDS) results showed that the surface of the natural rhodochrosite was notably changed in the presence of EPS alone or/and bacterial cells. This study is helpful for understanding the role of EPS in bacterially oxidation of Mn(II). It also indicates that the Mn(II) oxidizing bacteria may exert their effects on Mn(II) cycle and other biological and biogeochemical processes much beyond their local ambient environment because of the catalytically dissolution of solid Mn(II) by EPS and the possible long distance transport of the detached EPS.
The stable isotope composition of vanadium, nickel, and molybdenum in crude oils by G. Todd Ventura; Louise Gall; Christopher Siebert; Julie Prytulak; Peter Szatmari; Martin Hürlimann; Alex N. Halliday (104-117).
Crude oils often have high concentrations of transition metals including vanadium (V), nickel (Ni), iron (Fe), and to a lesser extent molybdenum (Mo). Determining the conditions under which these metals enter into crude oil is of interest for the understanding of biogeochemical cycles and the pathways leading to oil formation. This study presents the first high precision measurements of V, Ni, and Mo stable isotopes determined for a set of globally distributed crude oils as a first examination of the magnitude of potential stable isotope fractionation. Vanadium stable isotope compositions are presented for crude oils formed from different source rocks spanning a range of geologic ages (Paleozoic–Tertiary) and are complemented by Ni and Mo stable isotope compositions on a subset of crude oils produced from lacustrine source rocks in the Campos Basin, Brazil. The crude oils span a wide range of V and Mo isotope compositions, and display more restricted Ni stable isotope signatures. Overall, the stable isotope composition of all three systems overlaps with previously determined values for igneous and inorganic sedimentary materials. Comparisons between vanadium concentration and stable isotope composition yield distinct clusters associated with crude oils predominantly derived from terrestrial/lacustrine or marine/carbonate source rocks. The Ni stable isotope signatures of studied crude oils are similar to that of carbonaceous shales. The Mo stable isotope signatures of the lacustrine sourced crude oils are similar to what is observed for rivers. This indicates trace metal stable isotopic composition of crude oils are unlikely to result from mass dependent fractionation associated with the generation, expulsion, and migration of petroleum and are instead primarily inherited from the initial sedimentary organic matter or metal bearing fluids present during metalation. In contrast, although Mo stable isotopes also span a wide range of values, they do not appear to be correlated with source rock lithology, perhaps suggestive of a greater role for secondary processes. Finally, both V and Ni stable isotope compositions co-vary with V/(V + Ni), a commonly used parameter in determining crude oil grade. Since V/(V + Ni) ratios reflect redox conditions, the correlation implies that stable V and Ni isotope compositions may also respond to the redox conditions of the depositional environment. The contrasting behavior of these three isotope systems in this initial dataset provides fundamental guidance for future investigation to fully exploit the potential of these new isotopic tracers. These isotope tracers can be developed to determine a broad range of factors fundamental to the formation and preservation of petroleum source rocks that spans from provenance evaluation to paleoredox chemistry.
High-frequency, long-duration water sampling in acid mine drainage studies: A short review of current methods and recent advances in automated water samplers by Thomas P. Chapin (118-124).
Hand-collected grab samples are the most common water sampling method but using grab sampling to monitor temporally variable aquatic processes such as diel metal cycling or episodic events is rarely feasible or cost-effective. Currently available automated water samplers are a proven, widely used technology and typically collect as many as 24 samples during a deployment. However, these automated water samplers are not well suited for long-term sampling in remote areas or in freezing conditions. There is a critical need for low-cost, long-duration, high-frequency water sampling technology to improve our understanding of the geochemical response to temporally variable processes. This review article will examine recent developments in automated water sampler technology and utilize selected field data from acid mine drainage studies to illustrate the utility of high-frequency, long-duration water sampling.
Oxidative release of chromium from Archean ultramafic rocks, its transport and environmental impact – A Cr isotope perspective on the Sukinda valley ore district (Orissa, India) by Cora Paulukat; Lasse N. Døssing; Sisir K. Mondal; Andrea R. Voegelin; Robert Frei (125-138).
This study investigates Cr isotope fractionation during soil formation from Archean (3.1–3.3 Ga) ultramafic rocks in a chromite mining area in the southern Singhbhum Craton (Orissa, India). The Cr-isotope signatures of two studied weathering profiles, range from non-fractionated mantle values to negatively fractionated values as low as δ53Cr = −1.29 ± 0.04‰. Local surface waters are isotopically heavy relative to the soils. This supports the hypothesis that during oxidative weathering isotopically heavy Cr(VI) is leached from the soils to runoff.The impact of mining pollution is observed downstream from the mine where surface water Cr concentrations are significantly increased, accompanied by a shift to less positive δ53Cr values relative to upstream unpolluted surface water. A microbial mat sample indicates that microbes have the potential to reduce and immobilize Cr(VI), which could be a factor in controlling the hazardous impact of Cr(VI) on health and environment.The positive Cr isotope signatures of the Brahmani estuary and coastal seawater collected from the Bay of Bengal further indicate that the positively fractionated Cr isotope signal from the catchment area is preserved during its transport to the sea. Isotopically lighter Cr(VI) downstream from the mine is probably back-reduced to Cr(III) during riverine transport leading to similar Cr-isotope values in the estuary as observed upstream from the mine.
Apatite weathering as a geological driver of high uranium concentrations in groundwater by Andre Banning; Thomas R. Rüde (139-146).
Uranium is a heavy metal with potential adverse human health effects when consumed via drinking water. Although associated quality regulations have been implemented, geological sources and hydrogeochemical behavior of uranium in groundwater used for drinking water supply remain little understood. This study presents a hydrogeochemical and mineralogical characterization of a Triassic sandstone aquifer on a macro- and micro-scale, and an evaluation of uranium remobilization into groundwater, also considering the paleoenvironment and the distribution of the affected aquifer itself. Syndiagenetic uraniferous carbonate fluorapatite inclusions within the aquifer sandstones (“active arkoses”) were found to show structurally (chemical substitution in the crystal structure) and radiatively (α-recoil damage from uranium decay) enhanced mineral solubility. Extraction experiments indicated that these inclusions release uranium to groundwater during weathering. In conclusion, apatite alteration was identified as the responsible mechanism for widespread groundwater uranium concentrations >10 μg L−1 in the region representing Germany’s most significant problem area in this respect. Therefore, results indicate that the studied sedimentary apatite deposits cause the regional geogenic groundwater uranium problem, and must be considered as potential uranium sources in comparable areas worldwide.
Geochemistry of mineral water and gases of the Razdolnoe Spa (Primorye, Far East of Russia) by George Chelnokov; Natalya Kharitonova; Ivan Bragin; Oleg Chudaev (147-154).
New isotopic and chemical data on the sodium bicarbonate water and associated gases from the Razdolnoe Spa located in the coastal zone of Primorsky Kray of the Russian Far East, together with previous stable isotope data (δ18O, δD, δ13C), allow elucidation of the origin and evolution of the groundwater and gases from the spa. The water is characterized by low temperature (12 °C), TDS – 2.5–6.0 g/L, high contents of B (∼5 mg/L) and F (4.5 mg/L) and low contents of Cl and SO4. Water isotopic composition indicates its essentially meteoric origin which may comply with an older groundwater that was recharged under different (colder) climatic conditions. Major components of bubbling gases are CH4 (68 vol%), N2 (28%) and CO2 (4%). The obtained values δ13C and δD for CO2 and CH4 definitely indicate the marine microbial origin of methane. Thus the high methane content in the waters relates to the biochemical processes and presence of a dispersed organic matter in the host rocks. Based on the regional hydrogeology and the geological structure of the Razdolnoe Spa, Mesozoic fractured rocks containing Na–HCO3 mineral water and gases are reservoir rocks, a chemical composition of water and gases originates in different environmental conditions.
Genesis of salinized groundwater in Quaternary aquifer system of coastal plain, Laizhou Bay, China: Geochemical evidences, especially from bromine stable isotope by Yao Du; Teng Ma; Liuzhu Chen; Huimei Shan; Cong Xiao; Yu Lu; Cunfu Liu; Hesheng Cai (155-165).
In the south coast of Laizhou Bay, due to intensive groundwater extraction since the 1970s, salt water intrusion has occurred seriously, which increased the stress on regional fresh water resources. It is of great importance to understand origin of salinity and salinization process in coastal aquifers. To trace source and transport of dissolved bromide as a perfect representative of salinity and reveal genesis of salinized groundwater in regional aquifer system, Br stable isotopes of the sampled waters were surveyed coupled with hydrochemistry and stable H/O isotopes along the direction from inland to shore. The results show that groundwater salinity, hydrochemistry and stable isotopes exhibit regular variation from inland to shore. The TDS values of the groundwater increase gradually ranging from 0.52 to 133.74 g/L, the chemical types transform from Cl–Ca and HCO3–Ca to Cl–Na, 2H and 18O are getting more and more enriched, and the δ81Br values decrease gradually, from inland to shore. Trends of major ions versus bromide and Br isotope signatures for brine indicate brine originated from seawater evaporation followed by some water–rock interaction processes. The hydrogen and oxygen isotope signatures of the brine indicate the dilution by fresh water of meteoric origin was a probable process during or after brine formation. The δ81Br values of brine samples show good anticorrelation to both δ2H and δ18O values, probably confirming the addition of fresh water. The potential contribution of evaporate dissolution as a primary process to the brine was ruled out based on their Br isotope signatures. Trends of major ions versus bromide and H/O stable isotopes for brackish water reveal brine intrusion has occurred and mixed with fresh water inland, and Br stable isotopic composition of brackish water indicates that marine aerosol input could enrich the dissolved bromide in brackish water except for brine intrusion. Other processes, such as diffusion, subaerial evaporation and anthropogenic activities may change the budget of dissolved Br−, but are not primary processes responsible for behavior of Br stable isotope in shallow brackish water. Major contribution of meteoric water in deep fresh water and more influence by brine in deep saline water were revealed based on the Br isotopic results.
An integrated study of fluid–rock interaction in a CO2-based enhanced geothermal system: A case study of Songliao Basin, China by Jin Na; Tianfu Xu; Yilong Yuan; Bo Feng; Hailong Tian; Xinhua Bao (166-177).
The reactive behavior of a mixture of supercritical CO2 and brine under physical–chemical conditions relevant to the CO2-based Enhanced Geothermal System (CO2-EGS) is largely unknown. Thus, laboratory experiments and numerical simulations were employed in this study to investigate the fluid–rock interaction occurring in the CO2-EGS. Rock samples and thermal–physical conditions specific to the Yingcheng Formation of Songliao Basin, China, an EGS research site, were used. Experiments were conducted by using of reactors at high temperature and pressure. Six batch reaction experiments injected with supercritical CO2 were designed at temperatures of 150–170 °C and a pressure of 35 MPa. Moreover, a separate experiment at the same experimental conditions without injection of CO2 was also conducted for comparison. Analyses of scanning electron microscopy (SEM) and X-ray diffraction (XRD) of the resulting solids were conducted to characterize changes in mineral phases. Numerical simulations were also performed under the same conditions as those used in the experiments. Significant mineral alterations were detected at the CO2-EGS reservoir, which may change the properties of fluid flow. The presence of supercritical CO2 led to an dissolution of primary minerals such as calcite and K-feldspar and precipitations of secondary carbonate such as calcite and ankerite. The numerical simulations were generally consistent with laboratory experiments, which provide a tool for scaling the time up for long period of reservoir simulations. The information currently available for the mineral alteration at high-temperature natural CO2 reservoirs is generally consistent with those of our lab experiments and numerical simulations.
Natural uranium in Forsmark, Sweden: The solid phase by Lindsay Krall; Björn Sandström; Eva-Lena Tullborg; Lena Z. Evins (178-188).
U-bearing solid phases from Forsmark, Sweden, a proposed host for radioactive waste repositories, have been identified and characterized. Elevated dissolved U was found in some groundwater samples during the site investigations, prompting a need to study the local U geochemistry. Previous hydrochemical and whole-rock geochemical studies indicated that U was derived from local pegmatites, and mobilized and re-deposited during several geological events. In this study, down-hole gamma logs guided sampling of local pegmatites, cataclasites, and fracture fillings. Back-scattered electron-imaging, petrographic microscopy, and electron microprobe analyses were used to find and analyze U phases in thin sections. The results show that the principal U sources at Forsmark include pegmatitic uraninite (PbO up to ∼22 wt%) and metamict uranothorite. These primary minerals show variable degrees of alteration such as enrichment in Ca and Al and/or replacement by secondary Ca–U(VI)-silicates, haiweeite and uranophane. The haiweeite contains up to ∼5 wt% Al2O3, a chemical signature reflecting early (Proterozoic) events of hydrothermal fluid migration. Coffinitized, secondary uraninite is found in association with FeAl-silicates or Palaeozoic sulfide/sulfate minerals, indicating remobilization-precipitation and/or a secondary, sedimentary source of U. It is inferred that U was oxidized during geologically early periods. Later, U(IV) phases formed in fractures open to fluid circulation during the Palaeozoic. This study establishes the phases available as local U sources and/or sinks, and which will be considered in future isotopic and hydrochemical studies aimed to constrain the mechanisms and timing of water–U phase interaction.
Predicting the uptake of Cs, Co, Ni, Eu, Th and U on argillaceous rocks using sorption models for illite by Maria Marques Fernandes; Nóra Vér; Bart Baeyens (189-199).
Reliable predictions of radiocontaminant migration are a requirement for the establishment of radioactive waste repositories. Parametrization of the necessary sorption models seems to be, however, extremely challenging given the multi-mineralic composition of the lithosphere. In this study it is shown for two argillaceous rocks – Boda and Opalinus Clay relevant for the Hungarian and Swiss repository concepts, respectively – that this task can be substantially simplified by taking into account only the most sorptive mineral fraction, namely the 2:1 clay minerals illite and illite/smectite mixed layers. Two different models were required to blind predict the sorption isotherms of Cs, Co, Ni, Eu, Th and UO2 measured on the two clay rock samples in a synthetic porewater. Cs sorption was modelled with the generalised Cs (GCs) sorption model and the sorption of the other cations with the 2 site protolysis non electrostatic surface complexation and cation exchange (2SPNE SC/CE) model. The 2SPNE SC/CE model for illite was extended with surface complexation reactions on weak sites for Co, Ni, Eu, UO2 and on strong sites for Eu-carbonato complexes. Complementary to the sorption measurements and modelling, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to probe the retention mechanism of Ni on illite, Boda and Opalinus Clay at higher loadings. The reliable blind predictions of the selected metal cations, which are representative for monovalent alkaline metals, divalent transition metals, lanthanides, and trivalent, tetravalent and hexavalent actinides, confirms the applicability of this simplified bottom up approach, and, renders the underlying sorption models particularly useful to predict sorption for the wide range of cations to be considered in the safety analysis of radioactive waste repositories in clay-rich environments.
Inorganic chemical quality of European tap-water: 1. Distribution of parameters and regulatory compliance by David Banks; Manfred Birke; Belinda Flem; Clemens Reimann (200-210).
579 tap water samples were collected at the European scale and analysed in a single laboratory for more than 60 parameters. This dataset is evaluated here in terms of the statistical distribution of the analysed parameters and compliance with EU and international drinking water regulations. For most parameters a 99% (or better) degree of compliance was achieved. Among the parameters with the higher rates of non-compliance are: arsenic (1% non-compliance in EU member states, 1.6% when samples from non-EU states are also considered) and sodium (0.6%/1.0%). The decision by the WHO to raise its provisional guideline from 15 μg/L (WHO, 2004) to 30 μg/L (WHO, 2011) has reduced non-compliance for uranium from 1.0% to 0.2%. Despite the fact that tap water (i.e. presumed treated water) was collected, many observations can still be interpreted in terms of hydrogeochemical processes. The dataset demonstrates the potential value of very cost-effective, low-density sampling approaches at a continental (European) scale.
Inorganic chemical quality of European tap-water: 2. Geographical distribution by B. Flem; C. Reimann; M. Birke; D. Banks; P. Filzmoser; B. Frengstad (211-224).
579 tap water samples were collected at the European scale and analysed at a single laboratory for more than 60 parameters. This dataset is analysed here in terms of the spatial and national distribution of the analysed inorganic chemical parameters. The distribution of most parameters is controlled by various artificial and natural factors (land use, distribution network, water source and treatment, geographical location and geology). The distribution of nitrate can be interpreted in terms of land use and climate. Water treatment affects the distribution of phosphorus in tap water; especially the policy of adding phosphate to potable water in the UK to suppress plumbosolvency. The distribution of alkalinity, Ca, Mg, Sr and Li appears to reflect both water source (low in surface waters) and the geological contrast between base-poor crystalline rock terrains and carbonate rich sedimentary rock. The Scandinavian nations’ tap water shows the highest concentrations of most of the rare earth elements, probably reflecting their geological availability and mobility in low pH raw water sources. The distribution of fluoride, uranium and arsenic also appear to exhibit geological and source (groundwater versus surface water) controls. Hungary returns several high As results, which may reflect As-rich reducing groundwaters of the Pannonian basin. Much Estonian tap water reflects a very specific hydrochemical environment, namely Palaeozoic near-coastal aquifers, which yield deep, reducing or saline groundwater (possibly influenced by marine intrusion), enriched in Ba, B, Br−, Cl−, Eu, F−, I, Li, K, Mn and Na.
W. Mike Edmunds (1941–2015) by Yousif Kharaka; Russell Harmon; George Darling (225-226).