Applied Geochemistry (v.29, #C)
Identification of contamination in a lake sediment core using Hg and Pb isotopic compositions, Lake Ballinger, Washington, USA by John E. Gray; Michael J. Pribil; Peter C. Van Metre; David M. Borrok; Anita Thapalia (1-12).
► Hg and Pb concentration and isotopic compositions traced anthropogenic sources. ► Concentrations and metal loadings of Hg and Pb increased during the smelting period. ► Hg isotopic compositions changed during smelting compared to the pre-smelting period. ► Data indicate mass independent fractionation of Hg isotopes.Concentrations and isotopic compositions of Hg and Pb were measured in a sediment core collected from Lake Ballinger, near Seattle, Washington, USA. Lake Ballinger has been affected by input of metal contaminants emitted from the Tacoma smelter, which operated from 1887 to 1986 and was located about 53 km south of the lake. Concentrations and loadings of Hg and Pb in Lake Ballinger increased by as much as three orders of magnitude during the period of smelting as compared to the pre-smelting period. Concentrations and loadings of Hg and Pb then decreased by about 55% and 75%, respectively, after smelting ended. Isotopic compositions of Hg changed considerably during the period of smelting (δ202Hg = −2.29‰ to −0.38‰, mean −1.23‰, n = 9) compared to the pre-smelting period (δ202Hg = −2.91‰ to −2.50‰, mean −2.75‰, n = 4). Variations were also observed in 206Pb/207Pb and 208Pb/207Pb isotopic compositions during these periods. Data for Δ199Hg and Δ201Hg indicate mass independent fractionation (MIF) of Hg isotopes in Lake Ballinger sediment during the smelting and post-smelting period and suggest MIF in the ore smelted, during the smelting process, or chemical modification at some point in the past. Negative values for Δ199Hg and Δ201Hg for the pre-smelting period are similar to those previously reported for soil, peat, and lichen, likely suggesting some component of atmospheric Hg. Variations in the concentrations and isotopic compositions of Hg and Pb were useful in tracing contaminant sources and the understanding of the depositional history of sedimentation in Lake Ballinger.
Geochemical processes, evidence and thermodynamic behavior of dissolved and precipitated carbonate minerals in a modern seawater/freshwater mixing zone of a small tropical island by Chin Yik Lin; Baba Musta; Mohd Harun Abdullah (13-31).
► We identify major geochemical process in a tropical small island. ► Precipitation and dissolution processes predominate in the mixing zone. ► Outputs from PHREEQC and MSA have been successfully validated via analytical methods. ► PHREEQC does not accurately predict the occurrence of dolomite in shallow aquifer. ► MSA and analytical methods warrant great results in dealing complex geochemical data.The geochemical processes and thermodynamic behavior of dissolved and precipitated carbonate minerals controlling the hydrochemistry of an aquifer in the seawater/freshwater mixing zone of a small island are identified. Field and laboratory analyses, geochemical modeling (PHREEQC) and multivariate statistical analysis (MSA) provide a quantitative interpretation for the geochemistry of the carbonate-dominated aquifer. Geochemical analyses and modeling results show that dissolution and re-precipitation of CaCO3 are the prevalent processes governing geochemical reactions in the mixing zone. Furthermore, this was confirmed by coherent statistical output that incorporates Principle Component Analysis (PCA) and k-means Cluster Analysis (k-CA). Generally, the composition of the lowland sandy soil was rather homogeneous and was primarily composed of quartz, aragonite, calcite and Mg-calcite. Thermodynamic model calculations indicate that the carbonate minerals calcite, aragonite and dolomite are supersaturated in the mixing zone. Nevertheless, Powder X-ray Diffraction (PXRD) and Scanning Electron Microscope (SEM) examination verified the occurrence of low-Mg-calcite (LMC) and the absence of dolomite, attributed to thermodynamic/kinetic hindrance, cation disorder and the presence of dolomite crystal growth rate inhibitors (such as SO4). The results suggest that dissolution of aragonite and precipitation of LMC drives the solid phase geochemistry in the small tropical island aquifer.
Isotopic evidence of enhanced carbonate dissolution at a coal mine drainage site in Allegheny County, Pennsylvania, USA by Shikha Sharma; Andrea Sack; James P. Adams; Dorothy J. Vesper; Rosemary C. Capo; Angela Hartsock; Harry M. Edenborn (32-42).
► Coal mine discharge. ► Carbon, sulfur, oxygen and strontium isotopes track sources of carbon. ► Enhanced carbonate weathering due to sulfuric acid-enhanced dissolution and cation exchange. ► Carbon dioxide outgassing.Stable isotopes were used to determine the sources and fate of dissolved inorganic C (DIC) in the circumneutral pH drainage from an abandoned bituminous coal mine in western Pennsylvania. The C isotope signatures of DIC (δ13CDIC) were intermediate between local carbonate and organic C sources, but were higher than those of contemporaneous Pennsylvanian age groundwaters in the region. This suggests a significant contribution of C enriched in 13C due to enhanced carbonate dissolution associated with the release of H2SO4 from pyrite oxidation. The Sr isotopic signature of the drainage was similar to other regional mine waters associated with the same coal seam and reflected contributions from limestone dissolution and cation exchange with clay minerals. The relatively high δ34SSO4 and δ18OSO4 isotopic signatures of the mine drainage and the presence of presumptive SO4-reducing bacteria suggest that SO4 reduction activity also contributes C depleted in 13C isotope to the total DIC pool. With distance downstream from the mine portal, C isotope signatures in the drainage increased, accompanied by decreased total DIC concentrations and increased pH. These data are consistent with H2SO4 dissolution of carbonate rocks, enhanced by cation exchange, and C release to the atmosphere via CO2 outgassing.
Hydrogeochemistry and geochemical simulations to assess water–rock interactions in complex carbonate aquifers: The case of Aguadulce (SE Spain) by Linda Daniele; Ángela Vallejos; Mercé Corbella; Luis Molina; Antonio Pulido-Bosch (43-54).
► Active hydrogeological processes related to intensive groundwater exploitation. ► The combination of geochemical and GIS tools reveal aquifer compartmentalisation. ► Samples containing up to 7.3% of seawater must have an additional source of sulfate. ► The models cannot be solved without ionic exchange. ► Carbonate aquifer does not appear to behave homogeneously in complex tectonic areas.The hydrogeological unit of Aguadulce (Campo de Dalías aquifers, SE Spain) has a complex geometry. This fact, together with a continuous rise in water demand due to intensive agriculture and tourism create problems for groundwater quantity and quality. In this paper classic geochemical tools managed by means of GIS software and geochemical simulations are combined to delineate, identify and locate the possible physicochemical processes acting in the Aguadulce groundwater. Two main aquifers can be distinguished: the carbonate or lower aquifer of Triassic age, and the calcodetritic or upper aquifer of Plio-Quaternary age. Groundwaters from the latter are more saline and, assuming all chlorinity originates from seawater intrusion, the seawater contribution to their composition would be up to 7%. Nevertheless the carbonate aquifer appears not to be homogeneous: it is compartmentalised into 4 zones where different processes explain the different groundwaters compositions. Zone 4 samples (E margin of the carbonate aquifer) resemble those of the Plio-Quaternary aquifer, where calcite precipitation, dolomite and gypsum dissolution and some cation exchange (water–rock interaction) together with seawater–freshwater mixing occur. In contrast, water–rock interaction predominates in zones 1 and 3 of the carbonate aquifer. Moreover, zone 2 samples, located between zones 1 and 3, are explained by water–rock interaction in addition to mixing with Plio-Quaternary aquifer waters. The combination of geochemical simulations with GIS and hydrogeochemical analyses has proven to be effective in identifying and locating the different physicochemical processes in the aquifer areas, thus improving understanding of hydrogeochemistry in complex aquifers.
Stable isotopic composition of soil calcite (O, C) and gypsum (S) overlying Cu deposits in the Atacama Desert, Chile: Implications for mineral exploration, salt sources, and paleoenvironmental reconstruction by Matthew I. Leybourne; Eion M. Cameron; Martin Reich; Carlos Palacios; Kevin Faure; Karen H. Johannesson (55-72).
► We collected soils overlying two porphyry copper deposits and a pampa, Atacama Desert, Chile. ► δ18O for calcite over fracture zones at the Spence deposit suggests involvement of earthquake-induced groundwater. ► S isotopes in gypsum at Spence also indicates involvement of groundwater, consistent with elevated Cu, Se, I. ► At Gaby Sur and Tamarugal, S isotopes cannot distinguish sulfur of porphyry from redeposited sulfate from interior salars. ► The three sites studied have had different histories of salt accumulation and display variable influence of groundwater.Soils overlying two porphyry Cu deposits (Spence, Gaby Sur) and the Pampa del Tamarugal, Atacama Desert, Northern Chile were collected in order to investigate the extent to which saline groundwaters influence “soil” chemistry in regions with thick Miocene and younger sediment cover. Soil carbonate (calcite) was analyzed for C and O isotopes and pedogenic gypsum for S isotopes. Soil calcite is present in all soils at the Spence deposit, but increases volumetrically above two fracture zones that cut the Miocene gravels, including gravels that overlie the deposit. The C isotope composition of carbonate from the soils overlying fracture zones is indistinguishable from pedogenic carbonate elsewhere at the Spence deposit; all δ13CVPDB values fall within a narrow range (1.40–4.23‰), consistent with the carbonate having formed in equilibrium with atmospheric CO2. However, δ18OVPDB for carbonate over both fracture zones is statistically different from carbonate elsewhere (average δ18OVPDB = 0.82‰ vs. −2.23‰, respectively), suggesting involvement of groundwater in their formation. The composition of soils at the Tamarugal anomaly has been most strongly affected by earthquake-related surface flooding and evaporation of groundwater; δ13CVPDB values (−4.28‰ to −2.04‰) are interpreted to be a mixture of dissolved inorganic C (DIC) from groundwater and atmospheric CO2. At the Spence deposit, soils only rarely contain sufficient SO4 for S isotope analysis; the SO4-bearing soils occur only above the fracture zones in the gravel. Results are uniform (3.7–4.9‰ δ34SCDT), which is near the middle of the range for SO4 in groundwater (0.9–7.3‰). Sulfur in soils at the Gaby Sur deposit (3.8–6.1‰ δ34SCDT) is dominated by gypsum, which primarily occurs on the flanks and tops of hills, suggesting deposition from SO4-rich fogs. Sulfate in Gaby Sur deposit gypsum is possibly derived by condensation of airborne SO4 from volcanic SO2 from the nearby Andes. At the Gaby Sur deposit and Tamarugal anomaly, pedogenic stable isotopes cannot distinguish between S from porphyry or redeposited SO4 from interior salars.The three sites studied have had different histories of salt accumulation and display variable influence of groundwater, which is interpreted to have been forced to the surface during earthquakes. The clear accumulation of salts associated with fractures at the Spence deposit, and shifts in the isotopic composition of carbonate and sulfate in the fractures despite clear evidence of relatively recent removal of salts indicates that transfer from groundwater is an ongoing process. The interpretation that groundwaters can influence the isotopic composition of pedogenic calcrete and gypsum has important implications for previous studies that have not considered this mechanism.
The Werra cyclotheme (Upper Permian, Fore-Sudetic Monocline, Poland): Insights into fluctuations of the sedimentary environment from organic geochemical studies by Bartosz Kluska; Mariusz J. Rospondek; Leszek Marynowski; Philippe Schaeffer (73-91).
► Fluctuations of OM sources and palaeoenvironment are revealed basing on biomarkers. ► Unique aryl isoprenoids with lycopane carbon skeleton have been identified. ► These fresh/brackish water alga biomarkers occur in hypersaline deposits (anhydrites). ► To explain this, an estuary model with salt wedge water stratification is proposed. ► The OM maturity is in “oil window” in accordance with recognition of oil generation.A study of the extracts of samples recording a transgressive–regressive succession of the Werra cyclothem, Zechstein (Upper Permian), from the southern margin of the European Permian Basin (the Fore-Sudetic Monocline, Poland) provides an insight into major sources of organic matter and diagenetic processes. The studied cross-section comprises all lithologies representative for the European basin, including transgressive sandstones (Weissliegend) and organic-rich shales (Kupferschiefer) followed by carbonates as well as regressive anhydrites with intercalations of rock salt. Due to the variable influence of overlapping diagenetic processes that affected the organic matter, i.e. maturation and late diagenetic oxidation related to base metal mineralisation, a reliable comparison of the biomarker results is only possible for the major upper part of the section (ca. 38 m, including carbonates and evaporites) but not for the oxidised first 2–3 m from the base of the Kupferschiefer.The transition from carbonate to evaporate sedimentation is associated with a shift to predominant even C-numbered n-alkanes, increased abundance of carotanes and high homohopane index reflecting enhanced reducing conditions. The presence of the C25 regular isoprenoid, squalane, biphytane and the rapid decrease in the pristane/phytane ratio in the evaporites are mainly controlled by the important contribution from both halophilic and methanogenic archaea. The occurrence of gammacerane in the anhydrites suggests development of water column stratification at some stages of the sea regression. This is associated with appearance of specific aryl isoprenoids with a lycopane carbon skeleton most likely related to Botrycoccus braunii race L algae. Lycopane derivative occurrence suggests that such an algal race could have occurred since Permian (currently known Recent-Eocene). The presence of the abundant freshwater/brackish algal biomarkers in evaporititic deposits can be envisaged in the costal part of the Zechstein basin with temporary salt wedge estuary water stratification. The algae bloomed in the top fertile fresh/brackish water layer fed by rivers, and the algal biomass was deposited on the sea floor covered with evaporitic brine. The stratification periodically broke down during precipitation of the rock salt, presumably due to a decrease in riverine water input, as revealed by characteristic disappearance of gammacerane and hopane distributions similar to those observed for the carbonate rocks.The methylphenanthrenes/phenanthrene ratio was used together with methyldibenzothiophenes/ dibenzothiophene ratio to assess maturity. These maturity estimations indicate that the peak of oil window has been reached, which is confirmed by other biomarker maturity parameters based on sterane and hopane distributions. The maturity stage of oil generation and expulsion was further confirmed by the presence of solid bitumen as cements in the sandstone underlying Kupferschiefer and bitumen veins and lenses in the carbonates.
Spinifex biogeochemistry across arid Australia: Mineral exploration potential and chromium accumulation by N. Reid; S.M. Hill (92-101).
► Triodia pungens and T. scariosa delineate ore bodies at multiple scales with multiple elements at several sites. ► Spinifex species are shown to accumulate Cr to potentially toxic levels. ► This Cr is concentrated at the tip and is associated with opaline silica deposits. ► Cr uptake in spinifex is not shown to be regulated to low levels as with other plant species at the same sites.Spinifex (Triodia spp.) grasslands cover vast areas of arid Australia, across a variety of soils and landscapes. These grasses are deep rooted and long lived, hence have great potential as a biogeochemical sampling medium for mineral exploration. This study discusses the results of analyses of Triodia pungens and Triodia scariosa from field sites over buried Au mineralisation (Coyote, Oberon and Tunkillia Prospects). At each site there is a multi-element anomaly in the vegetation over the projected mineralisation, the haloes are of different scales depending on the local landscape setting and dispersion potential of each element associated with mineralisation. The magnitude of the anomalies is similar for each site independent of underlying substrate. Overall, spinifex chemical composition has the potential to act as a point indicator of substrate geochemistry with very minimal dispersion (hundreds of metres only) that can delineate the extent of a potential ore deposit.This study also discusses the Cr accumulation potential of T. pungens and T. scariosa, discovered during the mineral exploration studies, from several field sites (Coyote, Oberon, Tunkillia and North Miitel Prospects). Triodia species are shown to be able to accumulate Cr up to potentially toxic levels independent of substrate concentration. This could be due to accumulation (active transport) or the lack of a barrier mechanism (passive uptake) within the plant.
Simulating fluoride evolution in groundwater using a reactive multicomponent transient transport model: Application to a crystalline aquifer of Southern India by Marie Pettenati; Jérôme Perrin; Hélène Pauwels; Shakeel Ahmed (102-116).
► Simulation of F accumulation in Southern India groundwater under paddy field irrigation. ► A solute recycling model was constructed on measured field data. ► The model describes the F progressive enrichment in the irrigation return flow. ► F build-up is caused by evaporation and mineral dissolution processes.Overexploitation of crystalline aquifers in a semi-arid climate leads to a degradation of water quality, with the main processes responsible for the observed salt loads probably being irrigation return flow (IRF) and a high evaporation rate. The present study has focused on modelling the F− accumulation caused by IRF below rice paddy fields in the small endorheic Maheshwaram watershed (Andhra Pradesh, Southern India). The transient simulation was performed with a 1D reactive transport PHREEQC column and took into account IRF evaporation, kinetically controlled mineral dissolution/precipitation, ion adsorption on Fe hydroxides, and mixing with fresh groundwater. The results revealed the role of cationic exchange capacity (CEC) in Ca/Na exchange and calcite precipitation, both favouring a decrease of the Ca2+ activity that prevents fluorite precipitation. Iron hydroxide precipitation offers a not inconsiderable adsorption capacity for F− immobilization. The principal sources of F− are fluorapatite dissolution and, to a lesser extent, allanite and biotite dissolution. Anthropogenic sources of F−, such as fertilizers, are probably very limited. After simulating an entire dry-season irrigation cycle (120 days), the results are in good agreement with the observed overall increase of Cl− in the Maheshwaram groundwater. The model enables one to decipher the processes responsible for water-resource degradation through progressive salinization. It shows that F− enrichment of the groundwater is likely to continue in the future if groundwater overexploitation is not controlled.
Stability and leaching of cobalt smelter fly ash by Martina Vítková; Jiri Hyks; Vojtěch Ettler; Thomas Astrup (117-125).
► pH-dependent leaching of cobalt smelter fly ash from slag recycling was studied. ► Contaminant release from minor metallic phases and silicate or glassy fraction. ► Model predicts CoO and zincite to control the Co and Zn leaching. ► Sorption on hydrous ferric oxides as effective attenuation of Pb and Cu release. ► High risk of Co, Cu, Pb and Zn mobilisation in the acidic soils around the Co smelter.The leaching behaviour of fly ash from a Co smelter situated in the Zambian Copperbelt was studied as a function of pH (5–12) using the pH-static leaching test (CEN/TS 14997). Various experimental time intervals (48 h and 168 h) were evaluated. The leaching results were combined with the ORCHESTRA modelling framework and a detailed mineralogical investigation was performed on the original FA and leached solid residues. The largest amounts of Co, Cu, Pb and Zn were leached at pH 5, generally with the lowest concentrations between pH 9 and 11 and slightly increased concentrations at pH 12. For most elements, the released concentrations were very similar after 48 h and 168 h, indicating near-equilibrium conditions in the system. Calcite, clinopyroxenes, quartz and amorphous phases predominated in the fly ash. Various metallic sulfides, alloys and the presence of Cu, Co and Zn in silicates and glass were detected using SEM/EDS and/or TEM/EDS. The leaching of metals was mainly attributed to the dissolution of metallic particles. Partial dissolution of silicate and glass fractions was assumed to significantly influence the release of Ca, Mg, Fe, K, Al and Si as well as Cu, Co and Zn. The formation of illite was suggested by the ORCHESTRA modelling to be one of the main solubility-controlling phases for major elements, whereas Co and Zn were controlled by CoO and zincite, respectively. Sorption of metals on hydrous ferric oxides was assumed to be an important attenuation mechanism, especially for the release of Pb and Cu. However, there is a high risk of Co, Cu, Pb and Zn mobility in the acidic soils around the smelter facility. Therefore, potential local options for “stabilisation” of the fly ash were evaluated on the basis of the modelling results using the PHREEQC code.
Geochemical techniques to discover open cave passage in karst spring systems by Elizabeth A. Hasenmueller; Robert E. Criss (126-134).
Display Omitted► DO and pH data provide a novel means to detect air passages in karst springs. ► Phreatic springs rapidly degas on emergence, causing large variations in DO and pH. ► Cave springs have higher TSS, E. coli, and calcite saturation indices. ► Cave springs can undergo more evaporative isotopic enrichment.Dissolved O2 (DO) and pH data provide a novel, inexpensive field method to detect open cave passages in karst spring systems that can be complemented by laboratory measurements of major elements and nutrients, total suspended solids (TSS), Escherichia coli (E. coli) levels, and stable isotopes. Karst springs in east-central Missouri that have no known air-filled passages (“phreatic” springs) typically have low DO and pH values (<80% saturation and <7.7, respectively), which are characteristic of groundwaters that do not communicate with the atmosphere. In contrast, springs draining vadose cave passages have higher DO and pH values (>60% saturation and >7.7, respectively) that resemble surface waters due to the equilibration of DO with the overlying cave atmosphere and the simultaneous degassing of dissolved CO2. Traverses down phreatic spring branches show exchange with the atmosphere causes an increase in DO only a short distance downstream of the spring orifice, while the pH concurrently increases due to the degassing of CO2. Further downstream both parameters tend to level off reflecting a general approach to equilibrium under surface conditions, though this process is more rapid for DO than for pH. In contrast, the DO and pH along cave spring branches change little from values at the cave entrance. Additionally, (1) degassing processes affect the saturation state of calcite, with cave springs being the most saturated with respect to calcite, (2) phreatic springs typically have lower TSS and E. coli levels than open cave springs due to slower and less variable flow delivery, longer residence times, and less turbulent flow, and (3) phreatic springs tend to plot on the global meteoric water line (MWL), while waters from open cave systems tend to be enriched in 18O and D and can plot below the line due to evaporation and exchange of the water with the overlying cave atmosphere.
The use of diffuse reflectance mid-infrared spectroscopy for the prediction of the concentration of chemical elements estimated by X-ray fluorescence in agricultural and grazing European soils by J.M. Soriano-Disla; L. Janik; M.J. McLaughlin; S. Forrester; J. Kirby; C. Reimann (135-143).
► We used mid-infrared for the prediction of 31 elements using 4130 European soils. ► The concentration of 23 elements (e.g. Al, Ca, Fe, Mg, etc.) was successfully predicted. ► The concentration of eight elements (e.g. Cu, P, Pb, etc.) was not successfully predicted. ► Model success dependent on the relationships (direct or indirect) with MIR absorbers. ► Multivariate relationships between elements were tested through PCA plots.The aim of this study was to develop partial least-squares (PLS) regression models using diffuse reflectance Fourier transform mid-infrared (MIR) spectroscopy for the prediction of the concentration of elements in soil determined by X-ray fluorescence (XRF). A total of 4130 soils from the GEMAS European soil sampling program (geochemical mapping of agricultural soils and grazing land of Europe) were used for the development of models to predict concentrations of Al, As, Ba, Ca, Ce, Co, Cr, Cs, Cu, Fe, Ga, Hf, K, La, Mg, Mn, Na, Nb, Ni, P, Pb, Rb, Sc, Si, Sr, Th, Ti, V, Y, Zn and Zr in soil using MIR spectroscopy. The results were compared with those obtained where MIR models were developed with the same soils but using the concentration of elements extracted with aqua regia (AR).The PLS models were cross-validated against the experimental log-transformed XRF values of all the elements. The calibration models were derived from a set of 1000 randomly selected calibration samples. The rest of the samples (3130) were used as an independent validation set. According to the residual predictive deviation (RPD), predictions were classified as follows: “Good quality”, Ca (2.9), Mg (2.5), Al (2.3), Fe (2.2), Ga (2.2), Si (2.1), Na (2.0); “Indicator quality”, V (1.9), Ni (1.9), Sc (1.9), K (1.8), Ti (1.8), Rb (1.8), Zn (1.7), Co (1.7), Zr (1.6), Cr (1.6), Sr (1.6), Y (1.6), Nb (1.6), Ba (1.5), Mn (1.5), As (1.5), Ce (1.5); “Poor quality”, Cs (1.4), Th (1.4), P (1.4), Cu (1.4), Pb (1.3), La (1.2), Hf (1.1).Good agreement was observed between the RPD values obtained for the elements analysed in this study and those from the AR study. Despite the different elemental concentrations determined by the XRF method compared to the AR method, MIR spectroscopy was still capable of predicting elemental concentrations.
Pressure solution of electrically conductive minerals in shallow crust-galvanic processes: A case study from pyrite under differential stress by Qingyou Liu; Yanqing Zhang; Heping Li (144-150).
► The pyrite pressure dissolution process is a galvanic corrosion process. ► There is a negative linear relationship between the pyrite potential difference and the stress action. ► Three different electrochemical dissolution mechanisms of pyrite are revealed.The pressure dissolution behaviour of pyrite was investigated via its polarisation curve and using electrochemical impedance spectroscopy (EIS) in a FeCl3 solution under differential stress. The results showed that the pyrite pressure dissolution process is a galvanic corrosion process and that there is a negative linear relationship between the pyrite potential difference and the stress action. The EIS experiments confirm that the pyrite was in a passive state in a 0.0010 mol L−1 FeCl3 solution and that a thin surface layer of Fe1− y S2 was present. In a 0.010 mol L−1 FeCl3 solution, the pyrite was in a trans-passive state, in which the aforementioned passive layer became porous. In a 0.10 mol L−1 FeCl3 solution, the pyrite was in an active state, the surface layer dissolved completely, and a lattice layer of S 2 0 was created instead of a passive layer of S0. Under the present stress conditions, the stress action did not change the pyrite electrochemical dissolution mechanism; however, the conditions decreased the charge transfer resistance and passive resistance and increased the species diffusion capacitance.
Uranium-bearing phases in a U-mill disposal site in Northern Canada: Products of the interaction between leachate/raffinate and tailings material by Michael Schindler; Jennifer L. Durocher; Tom G. Kotzer; Frank C. Hawthorne (151-161).
► Uranyl-phases in an U-tailings site. ► Raffinate–tailings interaction. ► U-bearing gypsum. ► Ammonium-bearing autunite and zippeite.The Above Ground Tailings Management Facility (AGTMF) is a licensed tailings receiving facility at the Key Lake mine site, Northern Saskatchewan, Canada. Tailings within the AGTMF were deposited between 1983 and 1995 and are derived from mining and milling of the Gaertner and Deilmann ore-bodies at Key Lake. The tailings are primarily composed of quartz, phyllosilicate and clay gangue minerals, minor amounts of Ni–Co–S-arsenides, iron oxide minerals and gypsum. They typically contain U concentrations on the order of between 50 and 300 ug/g U. A small area of the AGTMF receives occasional mill-process upset solutions with an initial pH-range of 2–6. The solutions contain elevated activities of U-bearing aqueous-species and are rapidly buffered to neutral and sub-alkaline pH values during interaction with surroundings tailings solids having a pH of approximately 10. This buffering and neutralization process results in the precipitation of gypsum and minor amounts of uranyl minerals. Phases of the autunite-group (chernikovite, (H3O)[(UO2)(PO4)](H2O)3 and troegerite, (H3O)[(UO2)(AsO4)] (H2O)3 with minor NH 4 + ) occur predominantly in the gypsum matrix but can also occur as crusts on silicates. The occurrence of troegerite is due to elevated concentrations of As within the deposited tailings solids. Surface alteration on phyllosilicates within tailings affected by the mill process solutions results in elevated concentrations of K at the phyllosilicate–water interface, which are ideal nucleation sites for the formation of single crystals of zippeite, K3(H2O)3[(UO2)4(SO4)2O3(OH)]. Use of NH4-sulfates and ammonia in the extraction and yellow-cake precipitation cycles and subsequent entrainment of (NH4)+ species in the tailings results in the occurrence of (NH4)-bearing phases of the zippeite- and autunite-group. Literature data on dissolution features, dissolution kinetics and mineral solubilities suggests that the minerals of the autunite group control the mobility of U in the contact zone between the mill-process solutions and the tailings.
Groundwater composition and pollution due to agricultural practices at Sete Cidades volcano (Azores, Portugal) by J. Virgílio Cruz; M.O. Silva; M. Isabel Dias; M. Isabel Prudêncio (162-173).
► Hydrogeochemical study made in Sete Cidades volcano (São Miguel, Portugal). ► Coupled methodology to characterize soil–water at several depths and groundwater. ► Role of unsaturated and saturated zones in water chemical evolution. ► Higher nitrate in soil–water and groundwater due to agriculture pollution.Groundwater is a strategic resource of the Azores archipelago given that agriculture is a major economic activity. A field study was undertaken at Sete Cidades volcano (São Miguel, Portugal) to characterize the composition of soil water at several depths in two sites: one without anthropogenic pressure (village site) and the other pasture land (Pa I site), and groundwater in the saturated zone of both sites. The composition of groundwater from springs discharging on the volcano flanks and inside the summit caldera is similar, composed principally of poorly mineralized Na–HCO3 and Na–HCO3–Cl water types, as suggested by median electrical conductivity values. Samples of groundwater collected in seven piezometers spread inside the Sete Cidades caldera are characterized by a conductivity between 95 and 232 μS/cm and the dominant water type is Na–HCO3.Soil water at the Sete Cidades village site is of Na–Cl type and its compositional similiarity to rain water suggests control by evapotranspiration. The limited soil depth of the site, as well as the high precipitation and soil hydraulic conductivity, cause vertical homogenization of soil water composition. In contrast, soil water sampled at the pasture site (Pa1) shows greater mineralization when compared to the previous site, and waters are mainly HCO3 to HCO3–Cl types with a Mg–Ca trend for cations. A trend was indicated for the relative soil water composition at site Pa I, from the more superficial suction cup (G1) to the deeper G14–15. This is an evolution similar to perched-water bodies inside the Sete Cidades Caldera. The Mg–Ca-dominated composition at lower depth is explained by the application of fertilizers. Nevertheless, other processes are also influencing water chemistry evolution, and the observed relative decreases in Ca, Mg and K with depth may result from clay formation and the uptake by ion exchange of Ca2+ and Mg2+ for Na+. Although, the relative increase in Na could also result from silicate weathering. Besides contributing to the Na content, silicate dissolution may also explain the relative increase in HCO3, both being associated with silica in solution.The impact of the excessive application of fertilizers is reflected by the NO3 contents of soil water at Pa I and the village sites, as values are higher where agriculture is developed, with a similar trend being observed in the saturated zone.
Mechanisms of dissolved arsenic removal by biochemical reactors: A bench- and field-scale study by C. Kira Jackson; Iris Koch; Kenneth J. Reimer (174-181).
► A field scale anaerobic bioreactor removes 94% of arsenic from contaminated water. ► Zinc enhances arsenic removal in bench scale bioreactor experiments. ► XANES indicated amorphous orpiment as an arsenic removal product.A series of two biochemical reactors (BCRs) in Trail, British Columbia, removes dissolved As(V), Zn2+ and SO 4 2 - from leachate water collected from historic mine waste landfills. Each reactor cell is over 2000 m3 and contains a biosolid matrix which acts as a substrate for microbial activity. The current study used representative samples collected from the Trail BCRs as well as bench scale models of the first Trail BCR to demonstrate that As sulfide precipitation is a mechanism of As removal on both the bench- and field-scale and that the presence of Zn is important in As removal. Six reactors containing a matrix of biosolids were treated with an inlet solution containing 0.113 mM As(V) (8.5 mg L−1) and 0.812 mM SO 4 2 - (78 mg L−1) at a rate of 85 mL day−1; another six reactors containing biosolids and two reactors containing sand were treated with a similar inlet solution containing 0.352 mM Zn2+ (23 mg L−1) in addition to As(V) and SO 4 2 - . X-ray absorption near edge structure (XANES) results indicated the potential presence of a mixture of As(III)–O and disordered As2S3 compounds in the solid substrate from both sets of reactors containing biosolids following completion of the experiment as well as in the solid representative samples from the Trail BCRs, indicating As sulfide precipitation as a mechanism of As removal on both the bench- and field-scale. Based on other recent literature, soluble As(III)–S species may also be present in the samples, particularly in the samples collected from the field-scale BCRs, since the XANES peak for those samples is broad and slightly higher than that of the orpiment standard. Among the bench scale reactors containing biosolids, those treated with the inlet solution containing Zn2+ removed more As(V) than those not treated with Zn2+ (p < 0.001). The mechanism by which Zn enhances As removal is unclear, but several possibilities have been identified. Zinc may sequester excess free sulfide by forming Zn sulfides, thus preventing the dissolution of amorphous orpiment; Zn–As complexation may lower the solubility of As; and kottigite may form in the aerobic inlet area of the reactors. Reactors containing only sand also removed As from the inlet water, but XANES results showed that the main form of As in the sand matrix is As(V), indicating that the sand reactors likely work by As(V) adsorption to Fe oxyhydroxides and/or by the formation of Zn arsenate. Samples from all bench scale reactors and from the Trail BCRs were tested using the Toxicity Characterization Leaching Procedure (TCLP) and results indicated that the reactor contents are not considered hazardous waste.
Hydrogen and oxygen isotopic compositions of sedimentary kaolin deposits, Egypt: Paleoclimatic implications by Hassan Baioumy (182-188).
► Carboniferous and Cretaceous kaolin deposits have similar H and O isotopes. ► Both deposits were formed by meteoric water. ► The deposits were formed under warm-temperate to tropical conditions. ► Egypt located south to the equator during the Carboniferous. ► Egypt located north to the equator during the Cretaceous.The clay fractions of sedimentary kaolin deposits representing different ages (Carboniferous and Cretaceous), types (pisolitic flint and plastic), and localities (Sinai and Aswan) from Egypt were analyzed for their H and O isotopic compositions to examine the paleoclimate conditions during their formation. The δD values of the Carboniferous deposits in Sinai range between −67‰ and −88‰, while the values for the Cretaceous deposits in Sinai range between −59‰ and −75‰. The δ18O values of the Carboniferous deposits range from 17.9‰ to 19.4‰ and the values for the Cretaceous deposits range between 19.2‰ and 20.4‰. The relatively low δD and δ18O values of the Carboniferous deposit at the Abu Natash area (−67‰ and 17.9‰, respectively) compared to other Carboniferous deposits (averages of −83.3‰, and 18.8‰ for δD and δ18O, respectively) could be due to isotopic exchange between this deposit and the adjacent dolomite and/or the enclosed hydrothermally-formed Mn ores of the Carboniferous Um Bogma Formation. The δD and δ18O values of the Cretaceous pisolitic flint kaolin deposit from Aswan (averages of −65‰ and 20.3‰, respectively) and plastic kaolin from the same area (averages of −66‰ and 19.5‰, respectively) are almost identical. The differences in the δ18O values between the clay fractions of the pisolitic flint kaolin (20.3‰) and the previously analyzed bulk kaolin of the same deposit (average of 17.5‰) suggest a significant effect of non-clay minerals on the isotopic compositions of the kaolin deposits.The H and O isotopic compositions plot close to the kaolinite line that marks the isotopic composition of kaolinite in equilibrium with meteoric water at 20 °C. This indicates that the kaolinite from both the Carboniferous and Cretaceous deposits in Egypt formed by meteoric water weathering of the source rock(s). The δD and δ18O values also suggest that kaolinite of these deposits formed under warm-temperate to tropical conditions. The slight deviations of some samples from the kaolinite line suggest post-depositional modifications of the isotopic compositions of studied deposits probably due to the interaction between earlier-formed kaolinite and downward percolating meteoric water.The δD and δ18O values of the Cretaceous and Carboniferous deposits from all localities suggest that both deposits formed under similar climatic conditions due to the location of Egypt at almost the same distance from the equator either to the south during the Carboniferous or to the north during the Cretaceous.
Dating groundwater in the Bohemian Cretaceous Basin: Understanding tracer variations in the subsurface by J.A. Corcho Alvarado; T. Pačes; R. Purtschert (189-198).
► Tracer methods were used for dating groundwater in complex groundwater systems. ► Groundwater affected by large fluxes of gases near deep reaching faults. ► Periglacial climate and strong permafrost conditions prevailed during the LGM. ► 39Ar measurements were used to determine initial 14C for radiocarbon dating. ► 4He was used to validate and extent the dating range of 14C.The northern section of the Bohemian Cretaceous Basin has been the site of intensive U exploitation with harmful impacts on groundwater quality. The understanding of groundwater flow and age distribution is crucial for the prediction of the future dispersion and impact of the contamination. State of the art tracer methods (3H, 3He, 4He, 85Kr, 39Ar and 14C) were, therefore, used to obtain insights to ageing and mixing processes of groundwater along a north–south flow line in the centre of the two most important aquifers of Cenomanian and middle Turonian age. Dating of groundwater is particularly complex in this area as: (i) groundwater in the Cenomanian aquifer is locally affected by fluxes of geogenic and biogenic gases (e.g. CO2, CH4, He) and by fossil brines in basement rocks rich in Cl and SO4; (ii) a thick unsaturated zone overlays the Turonian aquifer; (iii) a periglacial climate and permafrost conditions prevailed during the Last Glacial Maximum (LGM), and iv) the wells are mostly screened over large depth intervals.Large disagreements in 85Kr and 3H/3He ages indicate that processes other than ageing have affected the tracer data in the Turonian aquifer. Mixing with older waters (>50 a) was confirmed by 39Ar activities. An inverse modelling approach, which included time lags for tracer transport throughout the unsaturated zone and degassing of 3He, was used to estimate the age of groundwater. Best fits between model and field results were obtained for mean residence times varying from modern up to a few hundred years. The presence of modern water in this aquifer is correlated with the occurrence of elevated pollution (e.g. nitrates).An increase of reactive geochemical indicators (e.g. Na) and radiogenic 4He, and a decrease in 14C along the flow direction confirmed groundwater ageing in the deeper confined Cenomanian aquifer. Radiocarbon ages varied from a few hundred years to more than 20 ka. Initial 14C activity for radiocarbon dating was calibrated by means of 39Ar measurements. The 14C age of a sample recharged during the LGM was further confirmed by depleted stable isotope signatures and near freezing point noble gas temperature. Radiogenic 4He accumulated in groundwater with concentrations increasing linearly with 14C ages. This enabled the use of 4He to validate the dating range of 14C and extend it to other parts of this aquifer. In the proximity of faults, 39Ar in excess of modern concentrations and 14C dead CO2 sources, elevated 3He/4He ratios and volcanic activity in Oligocene to Quaternary demonstrate the influence of gas of deeper origin and impeded the application of 4He, 39Ar and 14C for groundwater dating.
The effect of sulfide concentrate mineralogy and texture on Reactive Oxygen Species (ROS) generation by Gavin C. Jones; Megan Becker; Robert P. van Hille; Susan T.L. Harrison (199-213).
► Metal-containing sulfide mineral concentrates generate ROS (H2O2 + • OH). ► ROS generation linked to decreased thermophilic bioleaching performance. ► ROS generation consistently correlated to combined Py + Cp content. ► Sulfide liberation and association effects ROS generation under acidic conditions. ► Increased “micro-cracked” particle volume results in increased sample reactivity.The generation of Reactive Oxygen Species (ROS), H2O2 and • OH, has been observed from sulfide mineral containing particles in acidic solutions. The implications of this phenomenon, as a potential microbial stress-causing effect, have been studied previously with respect to thermophilic bioleaching performance in the presence of finely milled pyrite and chalcopyrite concentrates. In this study, the effect of sulfide mineralogy on ROS generation in the absence of microbes under physicochemical conditions typical for the bioleach environment was investigated. The mineralogical and elemental composition of eleven different samples containing sulfide mineral was obtained. These Au, Cu and other base metal-containing sulfide mineral concentrates as well as a milled whole ore of low Cu grade were tested for ROS generation. The whole ore sample and two refractory Au concentrates containing approximately 50% pyrite, generated significantly less ROS compared to the base metal-containing concentrates when compared on a constant surface area loading basis. Sulfide mineral-related variables were correlated with ROS generation. A significant difference was observed between FeS2 and CuFeS2 grades separately, whereas a combined measure of both minerals present in samples showed a consistently strong correlation to ROS generation. The Cu grade, total Cu-containing sulfides and the chalcopyrite content of Cu-containing samples correlated well with ROS generation. However, a common deterministic variable with a strong association to increased ROS generation was not found. A sub-set of samples were subjected to QEMSCAN® for textural analysis. Results suggested that a decrease in sulfide mineral liberation, caused by gangue silicate mineral occlusion to solution, resulted in decreased reactivity as shown in one of the Au-containing samples. Well-liberated chalcopyrite and pyrite phases corresponded to increased reactivity of samples. Pyrite, which was present in all of the reactive samples, was shown to be associated with other sulfide minerals, implicating its importance in galvanic interactions. Micro-analysis of chalcopyrite and pyrite phases from highly reactive samples showed an abundance of particles with extensive cracking and the possible presence of secondary transformation phases (szomolnokite). These results suggest that sulfide mineralogy, liberation and extent of physical processing affect sulfide mineral concentrate reactivity in acidic solutions.