Applied Geochemistry (v.31, #C)

Coal deposits as promising sources of rare metals for alternative power and energy-efficient technologies by Vladimir V. Seredin; Shifeng Dai; Yuzhuang Sun; Igor Yu. Chekryzhov (1-11).
► There are many coal deposits worldwide with high content Ge, Ga, Se, Li, and REY. ► The rare metals are concentrated both coals and host- and basement-rocks. ► Genesis of the metal accumulations and their mode of occurrence may be different. ► Recovery of the metals from coal deposits is new way for clean energy development.This paper presents data on widespread abnormal accumulations in coal deposits of some rare metal(loid)s (Ge, Ga, Se, Li and REE + Y), which play a key role in energy-efficient technologies and alternative power development. It is shown that enrichment of these metal(loid)s may occur in coal seams in host- and basement-rocks of coal basins at comparable concentrations to those in conventional ores. Genesis of high concentrations of the rare metal(loid)s and their modes of occurrence in coal basins are reviewed. Moreover, utilization prospects of these metal(loid)s as byproduct coal deposits are evaluated. The extraction of these metal(loid) resources during coal exploitation and utilization would not only increase beneficial use of coal deposits themselves but also promote humanity’s further movement on the “green road”.

Effects on nutrient regime in two recipients of nitrogen-rich mine effluents in northern Sweden by Sara Chlot; Anders Widerlund; Eva Husson; Björn Öhlander; Frauke Ecke (12-24).
► Limiting nutrient in two recipients of mine effluents has been investigated. ► Total nitrogen and phosphorus in water, sediment and macrophytes have been analysed. ► Mining operations may result in elevated nitrogen and phosphorus concentrations. ► Nitrogen concentration in effluent influences prediction of nutrient limitation. ► Phytoplankton and macrophytes not always limited by the same nutrient.The question of the limiting nutrient(s) for production of phytoplankton and macrophytes was explored in two contrasting freshwater systems receiving N- and P-rich mine effluents from the Boliden and Kiruna mine sites, northern Sweden. For both sites, total N (TN), total P (TP) and TN:TP mass ratios in water, sediment and macrophytes were used to examine (1) spatial variations within the systems, (2) differences between the systems and (3) seasonal variations. The TN concentration from the discharge point at the Kiruna site was about seven times higher than at the Boliden discharge point, while the TP concentration was 10 times lower than in the discharge point at the Boliden site. The majority of the studied lakes showed elevated biomass of phytoplankton, with maximum values found in Lake Bruträsket (Boliden). Mining activities have affected the nutrient regime of the two recipients by contributing to elevated TN and TP concentrations and TN:TP mass ratios as well as elevated production of phytoplankton and macrophytes compared to the reference sites. Depending on the NH4 concentration in the effluent at the Boliden site, water column TN:TP mass ratios shifted from being >22, indicating P-deficiency, to between 9 and 22, indicating a transition from N- to P-deficiency (co-limitation). However, water column TN:TP mass ratios at the Kiruna site always indicated P-deficiency, while TN:TP mass ratios of macrophytes indicate that both sites may vary from N- to P-limitation. The study suggests that for the design of efficient monitoring programmes and remediation measures, it is important to consider the major N and P species in water, phytoplankton, sediment and macrophytes.

► Metal partitioning in sediment pore waters was assessed via tangential flow filtration. ► Five natural sediments were tested and TFF procedure was realised in anoxic conditions. ► A thorough cleaning procedure should be performed before running TFF on natural samples. ► Satisfying blanks and mass balance were obtained for Mn, Fe, Co, Zn and As. ► Metal affinity with the colloidal fraction in sediment pore waters was: Cu > Zn > Fe ≈ Co > As ≈ Mn.The partitioning of trace metal(oid)s between colloidal and “truly” dissolved fractions in sediment pore waters is often overlooked due to the analytical challenge; indeed, only small volumes are available and filtration membranes are rapidly clogged. Moreover, metal(oid)s are subject to co-precipitate with Fe. In this study, tangential flow filtration (TFF) was assessed for the fractionation of Fe, Mn, Cu, As, Co, Ni, Zn and Cd in sediment pore waters with a 5 kDa cut-off size membrane. Five natural sediments were collected and used for different tests. Results on blank samples showed that this technique was appropriate for Fe, Mn, Co, Zn, As and Cd. Although the applied concentration factors (CF) were low (<7.4) due to the small available volume of pore waters (50 mL), it was shown that colloidal concentrations obtained from the TFF procedure were similar whatever the applied concentration factor. The mass balance approach showed satisfying results (100 ± 25%) for Mn, Co, Zn and As. Mass balances were higher than 130% and highly variable for Cd, Ni and Cu. For Fe, mass balance was reproducible but low (71 ± 10%), probably due to sorption of positively charged Fe oxides on the membrane. Applying this method to five contrasting metal(oid)-contaminated sediments, it was shown that Mn, As, Co and Fe were mainly present in the “truly” dissolved phase (<5 kDa). This technique is a necessary step to assess sediment toxicity and bioavailability of metal(oid)s and could be of great interest for emergent pollutants such as nanometals.

Mobility and fluxes of trace elements and nutrients at the sediment–water interface of a lagoon under contrasting water column oxygenation conditions by Sylvain Rigaud; Olivier Radakovitch; Raoul-Marie Couture; Bruno Deflandre; Daniel Cossa; Cédric Garnier; Jean-Marie Garnier (35-51).
► Main constituents and trace elements concentration profiles in contaminated sediments. ► Contrasting oxygen concentrations in the overlying water column. ► Combination of thermodynamic calculations and inverse transport-reactions modelling. ► Identification and quantification of diagenetic reactions controlling trace elements mobility. ► Assessment of trace elements and nutrients fluxes at the sediment–water interface.The early diagenesis of the major carrier phases (Fe and Mn minerals), trace elements (As, Co, Cr, Hg, MeHg, Ni) and nutrients (ΣNO3, NH 4 + , ΣPO4) and their exchange at the sediment water/interface were studied in the Berre Lagoon, a Mediterranean lagoon in France, at one site under two contrasting oxygenation conditions (strictly anoxic and slightly oxic) and at an adjacent site with perennially well-oxygenated water. From the concentration profiles of the primary biogeochemical constituents and trace elements of the pore and bottom waters, as well as the total and reactive particulate phases, it was possible to locate and identify the diagenetic reactions controlling the mobility of trace elements in the sediments and quantify their rates by coupling one-dimensional steady-state transport-reaction modelling and thermodynamic speciation calculations.Under oxic conditions and in the absence of benthic organisms, the main redox reactions were well identified vertically in the surface sediments and followed the theoretical sequence of oxidant consumption: O 2 > Σ NO 3 / MnO 2 > Fe ( OH ) 3 > SO 4 2 - . However, under anoxic conditions, only MnO2, Fe(OH)3 and SO 4 2 - reduction were present, and they all occurred at the interface. The main biogeochemical controls on the mobility of As, Cr, Hg, MeHg and Ni in the surface sediments were identified as the adsorption/desorption on and/or coprecipitation/codissolution with Fe oxy-hydroxides. In contrast, Co mobility was primarily controlled by its reactivity towards Mn oxy-hydroxides. In sulphidic sediments, As, Hg and MeHg were sequestered along with Fe sulphides, whereas Co and Ni precipitated directly as metallic sulphides and Cr mobility was enhanced by complexation with dissolved organic ligands. The fluxes of trace elements at the sediment–water interface are essentially dependent on the localisation of their remobilisation and immobilisation reactions under the interface, which in turn is governed by the benthic water oxygenation conditions and kinetic competition among those reaction and diffusion processes. Under oxic conditions, the precipitation of Fe or Mn oxy-hydroxides in the surface sediments constitutes the most efficient mechanism to sequester most of the trace elements studied, thus preventing their diffusion to the water column. Under anoxic conditions the export of trace elements to the water column is dependent on the kinetic competition during the reductive dissolution of Fe and/or Mn oxy-hydroxides, diffusion and immobilisation with sulphides. It is also shown that benthic organisms in the perennially oxygenated site have a clear impact on this general pattern. Based on the extensive dataset and geochemical modelling, it is predicted that the planned re-oxygenation of the entire lagoon basin, if complete, will most likely limit or reduce the export of the trace elements from the sediments to the water column and therefore, limit the impact of the contaminated sediment.

► Hydrograph separation can be used to assess metal contamination in a watershed. ► Metal contaminants can be mobilized during storm events. ► We predict a release of metals when pH decreases through re-vegetation efforts.Water samples were collected continuously from perennial springs on a hillslope impacted by historical metal deposition to study the hydrologic and geochemical behavior of a watershed during storm events, and assess the natural attenuation of metals in soil. Water samples were collected throughout storm hydrographs for inorganic chemistry analyses, and a sequential extraction was performed on watershed soil samples. Despite 30 a of natural attenuation at the site, Zn is mobilized into streamwater during storm events, with concentrations ranging from 18 to 452 μg/L. While Cd and Pb concentrations in water samples remained relatively constant, Zn concentration increased corresponding with the peak in the hydrograph indicating this metal is being released from adsorption sites located in an unsaturated zone that is temporarily inundated during storm events. Zinc is held on exchangeable, water and acid soluble sites, and in the reducible fraction, further indicating Zn may be released as a result of the downward movement of water through the soil profile. Equilibrium geochemical modeling predicts Zn desorption with a decrease in pH, which may occur as a result of site re-vegetation. The long legacy of metal emissions from a historical smelting operation will continue to limit the attenuating ability of this site.

► A conceptual model of trace element behavior in the Bolivian Altiplano is proposed. ► Climate seasonal variability influences trace element sedimentary redistribution. ► Trace element sedimentary sequestration could be controlled by ENSO events.A combination of mineralogical (SEM–EDS, EMPA) and geochemical (redox dynamics, selective extractions) approaches was applied to mining- and smelting-impacted sediments from Lake Uru Uru and from the Cala Cala Lagoon, a non-impacted reference site, in the Bolivian Altiplano. The purpose was to assess the factors controlling the post-depositional redistribution (mobilization/sequestration) of trace metals and metalloids. As expected, trace metals and metalloids are less reactive at the reference site than in Lake Uru Uru. In the latter, trace metals and metalloids are principally hosted by Fe- and Mn-oxyhydroxides, authigenic sulfides and silicate particulates. Post-depositional redistribution is ascribed to early diagenetic processes driven by organic matter (OM) mineralization, including dissolution of trace metal-bearing phases and precipitation of authigenic sulfide and carbonate phases. Seasonal climate variability exerts a strong influence on these processes. Evaporation of surface water during the dry season in the northern part of Lake Uru Uru promotes large redox front oscillations in the sediments and, therefore, transient redox conditions, likely leading to the weakening of anoxia in near-surface sediments and to a ‘compressed’ redox zonation compared to the southern part of the lake. Seasonal disappearance of the water column in the Northern Lake Uru Uru entails an alternation of: (i) low trace element mobility in the dry season due to elemental precipitation; and (ii) an increase of trace element mobility via diffusive transport during the wet season due to release from OM, Fe- and Mn-oxyhydroxides and carbonates upon mineralization, reductive dissolution and destabilization processes, respectively. Reoxidation of authigenic Fe-sulfides likely following the re-instalment of the water column above the sediment at the end of the dry season and prior to the return of anoxia probably favors transport of trace elements to the water column. As a consequence of this intricate web of redox- and climate-related processes, both northern and southern sediments of Lake Uru Uru are a source of dissolved trace elements, particularly As and Cd, for the overlying water column via diffusive transport. However, much of the diffused As and Cd is likely to be removed from the dissolved phase by the redox loop through Fe-oxyhydroxide precipitation. Finally, it is suggested that long term sequestration of trace metals and metalloids in the sediments could be controlled by inter-annual climate variability such as ENSO events.

► Aluminium hydroxide sludge generated using poly-aluminium chloride adsorbs arsenic. ► XAS showed that arsenic is sorbed to the sludge through a strong bidentate–binucleate bond. ► The strong bonding indicates that the sorbed arsenic is chemically stable.Arsenic-contaminated waters can be remediated by adsorption of the As onto an amorphous Al(OH)3 sludge precipitated using poly-aluminium chloride, which is a widely used, very effective polymeric coagulant. Investigation of the atomic near-range order and structure of As adsorbed to this sludge using X-ray Absorption Spectroscopy showed that the EXAFS spectrum of the sludge samples is very similar to that of mansfieldite (AlAsVO4·2H2O), indicating that As in the sludge is present as AsV, and that the atomic near-range structure of As is similar in the two materials. In the sludge, the first As–O coordination shell is populated with ∼4 oxygen neighbours at 1.70 ± 0.01 Å, and As has ∼2 Al neighbours at 3.18 ± 0.02 Å, consistent with bidentate binuclear As–O–Al bonding (two O atoms from an AsO4 unit bonded individually to two Al atoms). Previous studies have shown that As bonding on crystalline Al oxides and hydroxides is also bidentate binucleate, contrasting with the variable As bonding on ferric oxy-hydroxides. In particular, the bidentate mononucleate bonding reported for As sorption on amorphous ferric oxy-hydroxide sludges suggests that As is more strongly bonded to Al(OH)3 sludges. The latter may, therefore, have an advantage over ferric oxy-hydroxide coagulants for treatment of As-enriched waters.

Diel variation of arsenic, molybdenum and antimony in a stream draining natural As geochemical anomaly by Petr Drahota; Barbara Nováková; Tomáš Matoušek; Martin Mihaljevič; Jan Rohovec; Michal Filippi (84-93).
► We examined diel (24-h) cycling of trace elements in a stream. ► As, Mo, and Sb varied in phase with the pH, water temperature, and streamflow. ► Trace anion element cycles were linked to temperature-dependent adsorption. ► Different mechanisms control the trace element variations on hourly and monthly scales.The Mokrsko Stream in the central Czech Republic is an oxic and slightly alkaline stream that drains a natural As geochemical anomaly. Although long-term monitoring has characterized the general seasonal trends in trace element concentrations (i.e., As, Mo, Cu, Zn) in this stream, little is known about solubility controls and sorption processes that influence diel cycles in trace element concentrations. Trace elements (including As species, Cu, Mn, Mo, Pb and Sb) and other parameters were monitored over two 24-h periods in unfiltered and filtered (0.1 μm) samples collected in August 2010 and June 2011. Copper and Pb were predominantly (>92% of the mass) associated with the particulate fraction (>0.1 μm). Arsenic, Mo and Sb were predominantly (>88% of the mass) in the “dissolved” (<0.1 μm) form. Particulate-associated elements displayed up to a factor of 13 differences between minimum and maximum concentrations, most likely due to increased streamflow related to rainfall events. Dissolved concentrations of the trace metal cations (Cu, Fe, Mn and Pb) were consistently low and displayed no diel trends. Dissolved As(V), Mo and Sb varied on a diel cycle, with increased concentrations (up to 36%) during the late afternoon and decreased concentrations during the nighttime. Diel trends in trace anionic elements are explained by temperature-dependent sorption, as the diel changes in pH during base flow were very small (0.07 std. units). Very low concentrations of As(III), which have been shown to vary in a diel cycle, were attributed to enhanced hydraulic exchange with As(III)-rich hyporheic water during rainfall events.

In situ investigations and reactive transport modelling of cement paste/argillite interactions in a saturated context and outside an excavated disturbed zone by Danièle Bartier; Isabelle Techer; Alexandre Dauzères; Philippe Boulvais; Marie-Madeleine Blanc-Valleron; Justo Cabrera (94-108).
► Sedimentary fluid introduction into the cement paste macroporosity. ► First results in a saturated context outside the excavated disturbed zone. ► Occurrence of a black rim in argillite with C–S–H, carbonates and illitization.The interactions between cementitious materials and a clayey deep formation were investigated by studying the specific in situ context of the Tournemire Underground Research Laboratory (URL) of the French Institute for Radioprotection and Nuclear Safety and by reactive transport modelling using the HYTEC code. The study forms part of the safety assessment framework for the deep geological disposal of high to intermediate level long-lived radioactive waste. The in situ context investigated in the Tournemire URL corresponds to an engineered cemented borehole crosscutting the Toarcian argillite formation. The argillite/CEM II cement paste contacts have been in place over 18 a and were sampled in a saturated context outside the excavated disturbed zone (EDZ). Studies of the mineralogy (XRD, carbonatometry, SEM and TEM), petrophysical properties (BET) and geochemistry (TOC, Sr contents, C, O and Sr isotopes, EDS analyses) were carried out both on the argillite and on the cement paste in contact. Alteration of the cement paste is clearly expressed by decalcification and the opening of macroporosity. These modifications are mainly due to the dissolution of portlandite. The neoformation of C–S–H phases was identified in the first few micrometre next to the argillite interface, along with secondary carbonates at the outermost contact. Geochemical measurements argue for the introduction of a sedimentary fluid into the macroporosity of the cement paste to explain the formation of part of these secondary phases. This hypothesis is considered and tested using the HYTEC code, which indicates that such transport could have occurred near the argillite/cement paste contact at a very early stage. After this stage, the transport was reversed and ‘cementitious’ fluids flowed from the cement paste to the argillite. The changes brought about by these fluids are observed over a thickness of 11–13 mm in a so-called ‘black rim’, in which carbonates and C–S–H secondary phases are identified in the matrix of the sediment. An illitization process may also be observed in this altered rim, reaching its maximum development towards the inner part. Geochemical analyses show that the argillite disturbances are strictly confined to the black rim. Theoretical mineralogical profiles based on thermodynamic equilibria defined by the HYTEC code are in good agreement with the observations, and are used to achieve a better understanding of transport processes.

Strontium isotope quantification of siderite, brine and acid mine drainage contributions to abandoned gas well discharges in the Appalachian Plateau by Elizabeth C. Chapman; Rosemary C. Capo; Brian W. Stewart; Robert S. Hedin; Theodore J. Weaver; Harry M. Edenborn (109-118).
► Abandoned oil and gas wells in the Appalachian region can be conduits for contaminated waters. ► Strontium isotopes and geochemistry show coal mine drainage infiltrated into aquifers and dissolved siderite. ► Iron-contaminated waters rose to the surface via leaking abandoned natural gas wells. ► Contributions from Devonian brine migration and mine spoil siderite were insignificant.Unplugged abandoned oil and gas wells in the Appalachian region can serve as conduits for the movement of waters impacted by fossil fuel extraction. Strontium isotope and geochemical analysis indicate that artesian discharges of water with high total dissolved solids (TDS) from a series of gas wells in western Pennsylvania result from the infiltration of acidic, low Fe (Fe < 10 mg/L) coal mine drainage (AMD) into shallow, siderite (iron carbonate)-cemented sandstone aquifers. The acidity from the AMD promotes dissolution of the carbonate, and metal- and sulfate-contaminated waters rise to the surface through compromised abandoned gas well casings. Strontium isotope mixing models suggest that neither upward migration of oil and gas brines from Devonian reservoirs associated with the wells nor dissolution of abundant nodular siderite present in the mine spoil through which recharge water percolates contribute significantly to the artesian gas well discharges. Natural Sr isotope composition can be a sensitive tool in the characterization of complex groundwater interactions and can be used to distinguish between inputs from deep and shallow contamination sources, as well as between groundwater and mineralogically similar but stratigraphically distinct rock units. This is of particular relevance to regions such as the Appalachian Basin, where a legacy of coal, oil and gas exploration is coupled with ongoing and future natural gas drilling into deep reservoirs.

► Multifractal modeling for delineation of mineralization phases in a deposit. ► Determination of four mineralization phases in the deposit for Au, Ag, As and Cu. ► Recognition of high and extreme gold mineralization in an epithermal deposit. ► Correlation of mineralization phases with geological phases based on field geology.The aim of this study is to delineate and separate mineralization phases based on surface lithogeochemical Au, Ag, As and Cu data, using the Concentration–Area (C–A) fractal method in the Touzlar epithermal Au–Ag (Cu) deposit, NW Iran. Four mineralization phases delineated by multifractal modeling for these elements are correlated with the findings of mineralization phases from geological studies. The extreme phase of Au mineralization is higher than 3.38 ppm, which is correlated with the main sulfidation phase, whereas Ag extreme phase (higher than 52.48 ppm) is associated with silicic veins and veinlets. The resulting multifractal modeling illustrates that Au and Ag have two different mineralization trends in this area. Extreme (higher than 398.1 ppm) and high mineralization phases of Cu from the C–A method correlate with hydrothermal breccias and main sulfidation stage in the deposit, respectively. Different stages of Au mineralization have relationships with As enrichment, especially in high and extreme (higher than 7.9%) phases. The obtained results were compared with fault distribution patterns, showing a positive correlation between mineralization phases and the faults present in the deposit. Moreover, mineralization phases of these elements demonstrate a good correlation with silicification and silicic veins and veinlets.

Metal species in a Boreal river system affected by acid sulfate soils by Miriam I. Nystrand; Peter Österholm (133-141).
► Acid sulfate soils release large amounts of metals in toxic forms as free ions and SO4-complexes. ► Colloidal organic carbon (OC) dominated, while dissolved OC was low and remarkably stable. ► OC had only a minor impact on metal complexation in these acidic waters. ► Mobility of Fe is limited and adsorption to its oxides is only found for As. ► The pH rise in the estuary will first cause precipitation of Al, Cu and U with OC.The bioavailability of metals and their potential for environmental pollution depends not simply on total concentrations but on their chemical form. Consequently, knowledge of aqueous metal speciation is essential in investigating potential metal toxicity and mobility. Dissolved (<1 kDa), colloidal (1 kDa–0.45 μm) and particulate (>0.45 μm) size fractions of sulfate, organic C (OC) and 18 metals/metalloids were investigated in the extremely acidic Vörå River system in Western Finland, which is strongly affected by acid sulfate (AS) soils. In addition, geochemical modelling was used to predict the formation of free ions and complexes in these acidic waters. The most important finding of this study is that the very large amounts of elements known to be released from AS soils (including Al, Ca, Cd, Co, Cu, Mg, Mn, Na, Ni, Si and U) occur and can prevail mainly in toxic forms throughout acidic river systems; as free ions and/or sulfate-complexes. This has serious effects on the biota and particularly dissolved Al can be expected to have acute effects on fish and other organisms. In the study area, only the relatively forested upstream area (higher pH and contents of OC) had significant amounts of a few bioavailable elements (including Al, Cu, Ni and U) due to complexation with the more abundantly occurring colloidal OC in the upstream area. It is, however, notable that some of the colloidal/particulate metals were most likely associated with metal bearing phyllosilicates eroded from clay soils. Moreover, the mobilisation of Fe and As was small and As was predicted to be associated with Fe oxides, indicating a considerable influence of Fe oxides on the mobilisation/immobilisation processes of As. Elements will ultimately be precipitated in the recipient estuary, where the acidic metal-rich river water will gradually be diluted/neutralised with brackish seawater in the Gulf of Bothnia. According to speciation modelling, such a pH rise may first cause precipitation of Al, Cu and U together with organic matters closest to the river mouth, in line with previous sediment studies from the estuary.

► We assess the groundwater quality in a region scale alluvial aquifer by 216 samples. ► We analyze a regional groundwater evolution using Stuyfzand classification and Piper plot. ► The major natural and anthropogenic processes occurring in the plain are identified as five PCs. ► The transformation relationships between NH4–N, NO2–N and NO3–N in the river delta are discussed. ► We evaluate the chemical compositions of groundwater affected by different land tillage practices.The lower Liaohe River Plain (LRP) is an economically and ecologically important area situated on an alluvial plain, where anthropogenic activities are very intensive. Field investigations were conducted in the LRP and 15 water quality parameters surveyed at 216 wells during September and October of 2009 and 2010. These showed significant variation in the hydrochemistry of groundwater throughout the plain. A Piper plot was used to identify the major geochemical processes occurring in the entire plain. Principal components analysis (PCA) was used to identify various underlying natural and anthropogenic processes that created these distinct water types. The Stuyfzand classification was used to subdivide and interpret the complex groundwater hydrochemistry of the Liaohe River delta. Five principal components (PCs) were extracted in terms of PCA, which can be invoked to explain 82% of the total variance in water quality parameters. The PCA results can be categorized by five major factors: (1) Holocene transgression and mixing; (2) surface water infiltration; (3) multi-factor processes; (4) rainfall and agricultural fertilizer contamination; and (5) Geogenic F enrichment. This study demonstrates that the great variation of groundwater hydrochemistry in the LRP should be attributed to both natural and anthropogenic processes.

Impact of iron on nuclear glass alteration in geological repository conditions: A multiscale approach by E. Burger; D. Rebiscoul; F. Bruguier; M. Jublot; J.E. Lartigue; S. Gin (159-170).
► Interactions between nuclear glass and iron were investigated in a clayey environment. ► A multiscale characterization was performed using SEM–EDS, TEM, Raman spectroscopy and STXM. ► Glass alteration increases with the iron content and the proximity between the glass and iron. ► Iron nanoprecipitates would be responsible of the consumption of dissolved silica coming from the glass.Interactions between nuclear glass and Fe were investigated in a clayey environment to better understand the mechanisms and driving forces controlling the long-term behavior of high-level waste glass in a geological repository. An integrated experiment involving a Glass–Iron–Clay (GIC) stack was run at a laboratory scale in anoxic conditions for 2 years and the interfaces were characterized by a multiscale approach using scanning electron microscopy coupled with energy dispersive spectroscopy, transmission electron microscopy, Raman microspectroscopy and scanning transmission X-ray microscopy at the SLS Synchrotron. The characterization of glass alteration patterns on cross sections revealed an increase in glass alteration with the Fe content and the proximity between the glass and Fe. The alteration layers are polyphase and stratified with an inner porous gel layer incorporating Fe and an outer layer composed of nanocrystalline Fe-silicates. Several mechanisms which could affect the glass alteration kinetics and the transport properties of the alteration layer are proposed to explain this pattern: (i) consumption of hydrolyzed silica by precipitation of Fe-silicates; (ii) penetration of Fe within the gel porosity probably as precipitates such as Fe oxyhydroxide or Fe-silicates. These new data may imply some consequences when considering the long-term behavior of glass in geological disposal conditions.

► First study from South Africa on mobilisation of iron from whole rocks in a fractured aquifer. ► Rate and extent of iron mobilisation does not depend on amount of iron present in rocks. ► Mineralogy, redox and organic acids are the main controls for mobilising iron in the aquifer. ► Secondary iron precipitates and not primary iron minerals are responsible for iron clogging in supply boreholes.Iron mobilisation from aquifer rocks in an important fractured aquifer system in South Africa is resulting in clogging of boreholes by Fe oxide minerals. Leach experiments using natural waters were conducted to determine the effects of redox conditions, pH lithology and presence of organic acids on the rate and extent of Fe dissolution from aquifer rocks, with the aim of clarifying the association of Fe clogging with geological formations that show Fe staining on weathering. The results indicate that the greatest amount of Fe (>30 mmol/kg rock) is leached from arenaceous rocks with low total Fe contents (49.0–75.0 mmol/kg) under anoxic conditions. Rocks with the highest Fe contents (>800 mmol/kg) generated low concentrations of Fe (<10 mmol/kg) even under favourable conditions of 0 mg/L DO and pH 3. The extent of Fe dissolution from the rocks was found to be most strongly dependent on the redox conditions, and the form of Fe present in the rock, with ascorbate-extracted amorphous Fe being the most mobile. The rate of dissolution is affected by pH and the presence of natural organic acids in the leachate. However, the effect of organic acids was only noticeable on arenaceous rocks.

Display Omitted► Daily Cl fluxes in upper Barwon River calculated for 1989–2011. ► Cl export exceeds rainfall input of Cl by up to 2230%. ► Catchment is not in geochemical balance. ► Geochemical balance reflects changes to landscape and hydrological system.Documenting whether surface water catchments are in net chemical mass balance is important to understanding hydrological systems. Catchments that export significantly greater volumes of solutes than are delivered via rainfall are not in hydrologic equilibrium and indicate a changing hydrological system. Here an assessment is made of whether a saline catchment in southeast Australia is in chemical mass balance based on Cl. The upper reaches of the Barwon River, southeast Australia, has total dissolved solids, TDS, concentrations of up to 5860 mg/L and Cl concentrations of up to 3370 mg/L. The high river TDS concentrations are due to the influxes of groundwater with TDS concentrations of up to 68,000 mg/L. Between 1989 and 2011, the median annual Cl flux from the upper Barwon catchment was 17.8 × 106  kg (∼140 kg/a/ha). This represents 340–2230% of the annual Cl input by rainfall to the catchment. Major ion and stable isotope geochemistry indicate that the dominant source of solutes in the catchment is evapotranspiration of rainfall, precluding mineral dissolution as a source of excess Cl. The upper Barwon catchment is not in chemical mass balance and is a net exporter of solutes. The chemical imbalance may reflect the transition within the last 100 ka from an endorheic lake system where solutes were recycled producing shallow groundwater with high TDS concentrations to a better drained catchment. Alternatively, a rise in the regional water table following land clearing may have increased the input of groundwater with high TDS concentrations to the river system.

► Spatial and temporal variations of Zn and Ni of the entire river were investigated. ► Six major source zones that represented different sources were identified. ► Differences of Zn and Ni between main channel and tributaries were discussed. ► Geochemical tracers were used to distinguish different reaches of the river. ► Annual net fluxes and relative contributions of each source zone were estimated.Dissolved and particulate Zn and Ni concentrations were determined at 76 locations along the Yangtze River basin from the headwaters to the estuary during flood and dry seasons. Spatial and temporal variations of Zn and Ni were investigated and six major source zones were identified. The Three Gorges Dam (TGD) blocked most of the suspended loads and extremely low concentration of Zn and Ni were observed downstream of the dam. Dissolved (ranging from 0.062 to 8.0 μg L−1) and particulate (ranging from 12 to 110 mg kg−1) Ni showed similar levels of concentrations during flood and dry seasons, whereas dissolved (ranging from 0.43 to 49 μg L−1) and particulate (ranging from 54 to 1100 mg kg−1) Zn were slightly and much lower in the flood season than dry season, respectively. This was attributed to the increased water discharge during the flood season causing a dilution effect and sediment resuspension. In the flood season, average concentrations of Zn and Ni were higher in the main channel than in tributaries, due to soil erosion and mining activities providing the dominant inputs. The situation was opposite in the dry season, attributed to the contribution of municipal sewage, industrial activities, and waste disposal. During the flood season, dissolved Zn and Ni concentrations were negatively correlated with pH. Water and suspended particulate matter (SPM) from the upper reaches, middle reaches, and lower reaches of the Yangtze River were characterized by their Zn and Ni concentrations. The Panzhihua, Nanling and Tongling mining areas were considered as the most important source zones of particulate Zn and Ni. The Chongqing region, Wuhan region and the Yangtze River Delta provided most of the dissolved Zn and Ni inputs into the river. Annual net flux of Zn (10–72 × 105  kg a−1) and Ni (5.0–19 × 105  kg a−1) in each source zone were estimated according to their respective influent and effluent fluxes. Contributions of the source zones to Zn and Ni transport decreased from the upper reaches to the lower reaches.

Long-term pCO2 dynamics in rivers in the Chesapeake Bay watershed by M. Bala Krishna Prasad; Sujay S. Kaushal; Raghu Murtugudde (209-215).
► Changes in land-use and terrestrial organic matter loadings regulate pCO2 dynamics in coastal ecosystem. ► The Anacostia River is more CO2 supersaturated than the Potomac River. ► Human activities make streams chimney for emitting CO2 to atmosphere unrealized hitherto. ► Using the regional model results, CO2 efflux could increase from streams in future.Streams and rivers are major exporters of C and other dissolved materials from watersheds to coastal waters. In streams and rivers, substantial amounts of terrigenous organic C is metabolized and degassed as CO2 to the atmosphere. A long-term evaluation of CO2 dynamics in streams is essential for understanding factors controlling CO2 dynamics in streams in response to changes in climate and land-use. Long-term changes in the partial pressure of CO2 (pCO2) were computed in the Anacostia River and the lower Potomac River in the Chesapeake Bay watershed. Long-term estimates were made using routine monitoring data of pH, total alkalinity, and dissolved nutrients from 1985 to 2006 at 14 stations. Longitudinal variability in pCO2 dynamics was also investigated along these rivers downstream of the urban Washington D.C. metropolitan area. Both rivers were supersaturated with CO2 with respect to atmospheric CO2 levels (392 μatm) and the highly urbanized Anacostia waters (202–9694 μatm) were more supersaturated than the Potomac waters (557–3800 μatm). Long-term variability in pCO2 values may be due to changes in river metabolism and organic matter and nutrient loadings. Both rivers exchange significant amounts of CO2 with the atmosphere (i.e., Anacostia at 0.2–72 mmol m−2  d−1 and Potomac at 0.12–24 mmol m−2  d−1), implying that waterways receiving organic matter and nutrient subsidies from urbanized landscapes have the potential to increase river metabolism and atmospheric CO2 fluxes along the freshwater–estuarine continuum.

An experimental model approach of biologically-assisted silicate dissolution with olivine and Escherichia coli – Impact on chemical weathering of mafic rocks and atmospheric CO2 drawdown by Bruno Garcia; Laurence Lemelle; Estelle Rose-Koga; Pascal Perriat; Romain Basset; Philippe Gillet; Francis Albarède (216-227).
► The mass balance of magnesium has been established. ► The presence of bacteria inhibits Mg release during weathering of olivine. ► The free-living Proteobacteria should decrease the amount of riverine Mg. ► Proteobacteria could play an inhibitor role in the drawdown of atmospheric CO2.Chemical weathering of Mg, Ca-silicates and alumino-silicates contributes significantly to the drawdown of atmospheric CO2 over long time scales. The present work focuses on how this mode of weathering may change in the presence of free-living bacteria in oligotrophic waters, which compose most of the surface freshwaters of the Earth. Forsterite (Fo90) was reacted for 1 week with a stable Escherichia coli population in water maintained at 37 °C and neutral pH in a batch reactor. Control samples with suspensions of pure olivine powders and E. coli cells in pure water were also used for reference. Olivine controls reproduce the Mg, Si and Fe release in solutions predicted from rates published in the literature with pH shifts of less than 0.5 unit. After 1 week, under abiotic conditions, weathered surfaces are enriched in Fe and Fe3+ relative to the initial composition of the mineral. Bacterial controls (without minerals) show decreasing Eh with increasing cell concentrations (−50 mV with 7 × 107  cells/mL and −160 mV with 8 × 108  cells/mL). Magnesium concentrations in bacterial control solutions are in the μg/L range and can be accounted for by the release of Mg from dead cells. More than 80% of the cells were still alive after 1 week. The solutions obtained in the experiments in which olivine reacts in the presence of cells show Mg and Si concentrations a few tens of percent lower than in the mineral control samples, with a prominent depletion of Fe(III) content of the mineral surfaces. Magnesium mass balance discounts both significant bacterial uptake and inhibition of the Mg dissolution rates as a consequence of changing pH and Eh. Coating by bacterial cell layers is also negligible. E. coli reduces the chemical weathering of olivine. This study infers that the presence of free-living Proteobacteria, a prevalent group of subsurface bacteria, should decrease the amount of riverine Mg released by chemical weathering of mafic rocks.

► Groundwater wells in the Madison aquifer are contaminated from acid mine drainage. ► Dissolved sulfate in mine drainage is isotopically distinct from Madison sulfate. ► A three-component mixing model is used to explain the range in isotopic values.The Stockett–Centerville area, south of Great Falls, Montana, was extensively mined for coal in the late 1800s through the early 1950s. After closure, the underground mine portals were sealed and the workings became partially flooded. The coal seams are rich in pyrite, and many of the mines have horizontal drains that are point sources of acid mine drainage (AMD) which flow into dry streambeds and soak into the ground. The Mississippian Madison Limestone is located stratigraphically below the coal and is an important source of drinking water. Twenty-six domestic water wells completed in the Madison near the former coal mines were sampled for water chemistry and stable-isotope analysis of water and dissolved SO 4 2 - . Madison aquifer groundwater plots close to the meteoric water line and reveals no clear evidence of mixing with water from the mine drains, the latter being slightly enriched in 18O by evaporation. In contrast, dissolved SO 4 2 - in the wells has isotopic compositions that suggest mixing from three end-member sources: (1) regional Madison aquifer groundwater with moderate SO 4 2 - concentrations (110–150 mg/L) that is isotopically enriched (δ34S = 20‰; δ18O = 14‰); (2) AMD water with very high SO 4 2 - concentrations (>1.9 g/L) that is isotopically depleted (δ34S = −15‰; δ18O = −11‰); and (3) local recharge water with low SO 4 2 - concentrations (<80 mg/L) and intermediate SO4-isotope characteristics (δ34S = −10‰; δ18O = −6‰). The percentage of SO 4 2 - derived from AMD is estimated to range from 0% to nearly 80%. Wells with the highest proportion of AMD SO 4 2 - have higher SO 4 2 - concentrations, but otherwise show no mining-associated water quality problems, such as low pH or elevated concentrations of trace metals, underscoring the ability of the Madison aquifer to buffer water quality. Most of the wells with evidence of AMD incursion are older wells that were not cased over their entire depth. It is possible that the open-hole method of completion has allowed some AMD-related water to infiltrate by gravity to the lower Madison aquifer. In this study, stable isotopes of SO 4 2 - proved to be a more powerful and sensitive tool to track AMD contamination compared to stable isotopes of water or conventional water-quality sampling.

Biomarkers in surface sediments from the Cross River and estuary system, SE Nigeria: Assessment of organic matter sources of natural and anthropogenic origins by Oliva Pisani; Daniel R. Oros; Orok E. Oyo-Ita; Bassey O. Ekpo; Rudolf Jaffé; Bernd R.T. Simoneit (239-250).
► Sources of organic matter to sediments from the SE Niger Delta region were assessed. ► A strong influence of point sources was observed along the river transects. ► Intermittent inputs of microbial OM are likely due to localized eutrophication. ► Anthropogenic inputs likely derive from oil production and/or urban activities. ► Other anthropogenic inputs are from untreated sewage waste and agricultural run-off.Herein, lipid biomarker analysis is applied to surface sediments from the southeastern Niger Delta region for the quantitative determination of aliphatic lipids, steroids and triterpenoids in order to differentiate between natural (autochthonous vs. allochthonous) and anthropogenic organic matter (OM) inputs to this deltaic environment. This ecosystem, composed of the Cross, Great Kwa and Calabar Rivers, is receiving new attention due to increased human and industrial development activities and the potential effects of these activities impacting its environmental health. While the presence of low molecular weight n-alkanes (<C22) and the fossil biomarkers pristane and phytane in all samples, are indicative of a minor petroleum related input, the total extractable organic component of the surface sediments of these rivers remains predominantly of a natural origin as characterized by the variety and predominance of lipid classes that are mainly derived from the epicuticular waxes of vascular plants and include n-alkanes, n-alkanols, n-alkan-2-ones, n-alkanoic acids, steroids and triterpenoids. In addition, recent OM inputs from microorganisms are indicated by the presence of lower molecular weight n-alkanoic acids (Cmax  = 16), while the major triterpenoids of the sediments, taraxerol and friedelin, and the major sterol, sitosterol, indicate recent OM inputs from vascular plants. Plankton-derived sterols, such as fucosterol and dinosterol, are also found in sediments from the Cross and Great Kwa Rivers and likely originate from autochthonous primary productivity. Furthermore, the coprosterols coprostanol and 24-ethylcoprostanol are present in most samples and indicate measurable anthropogenic contributions from domestic untreated sewage inputs and agricultural run-off, respectively. Of the three rivers studied, the Cross River system was excessively influenced by human and industrial development activities, including drivers such as urbanization and population center growth, land-use change to support agricultural production and animal husbandry, and petroleum exploration and production. These influences were found to be regionally specific as controlled by point sources of pollution based on the relative distributions measured and on the fact that the molecular characteristics of sedimentary OM were not distributed smoothly along a gradient.

► We report on mine water compositional evolution resulting from modern mining operations. ► The Sb/As ratio of mine drainage waters evolved from <1 to >1 with time. ► The rise in Sb/As ratio was enhanced by water treatment processes in the mine. ► Changes in mining methods had a dramatic effect on the mine drainage composition.The Globe-Progress gold mine has recently (since 2007) been developed as an open pit on the site of historic underground mine workings on an orogenic-type Au deposit. Historic mines followed auriferous quartz veins with arsenopyrite and low Sb content. Ore in the modern mine includes later-stage cataclasite with abundant stibnite. Hence, rock exposed in the area has evolved from Sb/As ratio <1 to Sb/As ratio near to or greater than 1, with locally high Sb contents. Water that has interacted with these rocks in the mine and processing system developed Sb/As ratios that were similar to those of the rocks, as indicated by compositions of pit waters and leachates from static leach tests. Mine drainage waters are circumneutral (pH 6–8) with high HCO 3 - and SO 4 - (both up to 300 mg/L). Dissolved As in drainage waters was typically near 0.5 mg/L or below, but reached ∼1 mg/L at times, and Sb reached ∼3 mg/L. The Sb/As ratio of mine drainage waters has evolved from <1 in historic mines, to ∼30 below the modern mine. The rise in Sb/As was enhanced by a ferric chloride treatment system for process waters that preferentially removed more As than Sb. Arsenic behaved conservatively during downstream dilution, and the As flux from the modern mine, ∼30 mg/s, is similar to As fluxes from historic mines. In contrast, the Sb flux has increased from ∼1 mg/s from historic mines to nearly 100 mg/s below the modern mine. Excavation of the modern open pit, combined with the addition of a water treatment system, removed Fe from the mine waters that historically produced abundant Fe oxyhydroxide precipitates. Hence attenuation of metalloids by adsorption, which was widespread in the historic mines, has ceased. Changing mining methods and contrasting ore types can have a dramatic effect on the metalloid contents of circumneutral mine drainage waters, and these metalloid contents evolve with time through the mining process.

Chemical weathering under mid- to cool temperate and monsoon-controlled climate: A study on water geochemistry of the Songhuajiang River system, northeast China by Baojian Liu; Cong-Qiang Liu; Gan Zhang; Zhi-Qi Zhao; Si-Liang Li; Jian Hu; Hu Ding; Yun-Chao Lang; Xiao-Dong Li (265-278).
► We made a systematic investigation on the Songhuajiang River water geochemistry. ► Total rock weathering rate of the Songhuajiang Basin is 7.78 t km−2  yr−1. ► The CO2 consumption rate by silicate weathering is 66.6 × 103  mol km−2  yr−1. ► Chemical weathering rates is dominated by climate and lithology in the study area. ► CO2 consumption by silicate weathering is comparable with that of Huanghe.For the first time, the river water geochemistry of the Songhuajiang Basin, the third largest river system in China, has been studied in order to understand chemical weathering and associated CO2 consumption rate in a mid- to cool temperate and monsoon-controlled climatic zone. The major ion compositions of the river waters are characterized by the dominance of Ca2+ and HCO 3 - , accounting for 46% and 74% of major cations and anions, respectively. The average total dissolved solids (TDS, 116 mg L−1) and total cation concentration (TZ+, 1388 μEq L−1) of the river waters are similar to those of global major rivers. The chemical weathering rates of carbonate, silicate and evaporites in the whole Songhuajiang Basin are estimated to be approximately 5.15, 2.23 and 0.40 t km−2  a−1, respectively. The total rock weathering rate for the whole Songhuajiang Basin is approximately 7.78 t km−2  a−1, which is at the lower end of the spectrum for global major rivers, and is comparable with that of the Amur and the Congo-Zaire River. The estimated CO2 consumption rates for the whole Songhuajiang Basin are 53.4 × 103  mol km−2  a−1 and 66.6 × 103  mol km−2  a−1 by carbonate and silicate weathering, respectively.As a sub-basin, the 2nd Songhuajiang has the highest (18.9 t km−2  a−1) while the Nenjiang River Basin has the lowest total rock weathering rate (5.03 t km−2  a−1), which indicates important controls of regional climate and lithology. Compared to the large rivers of China, total rock weathering rates increase from north to south, supporting the idea that the climate acts as major control on global chemical weathering. The CO2 consumption rate by silicate weathering within the whole Songhuajiang River Basin, though under mid- to cool temperate climate, is in the same order of magnitude as that of Huanghe (82.4 × 103  mol km−2  a−1) and is not much lower than that of Changjiang (112 × 103  mol km−2  a−1), which suggests that the role of Songhuajiang River weathering in long-term climate change cannot be neglected compared to those of the large rivers of China.

An experimental investigation of reaction zone controls on fluid flow and mass transport by J. Shi; U. Solpuker; Y. Kim; F.W. Schwartz (279-291).
► Hydraulic conductivity and calcite mineralogy determine reaction zone complexity. ► Dissolved constituents and reactions are coupled. ► A segmented zone of reaction evolves in time. ► Large scale heterogeneity controls reaction-zone dynamics. ► Eventually plugging eliminated the capability for injection.This study examines homogeneous and heterogeneous mass transport in porous media featuring a solid-phase reaction zone that evolves and influences mass transport. It uses both flow-tank experiments and 2D reactive transport modeling to elucidate plume and reaction-zone behavior in situations with inherent complexity due to flow and transport and geochemical variability. The system is created by pumping a dilute Fe(ClO4)3 solution through a medium of glass beads and crushed calcite. As pH increases through the dissolution of calcite, amorphous ferric oxyhydroxide precipitates. The distribution of Fe, dissolved carbonate species, and pH are strongly coupled to the reaction zone because of the dissolution of CaCO3 and the precipitation of Fe(OH)3. Plugging influences the transport of dissolved constituents because it promotes fingering, hydraulic fracturing and flow bypassing. With the homogeneous systems, differences in the fingering produced by changing CaCO3 contents produced a heterogeneous distribution of Fe(OH)3(s) and dissolved Fe. As a result, a reaction zone with a complex shape developed due to the heterogeneity in hydraulic conductivity and CaCO3 content.