Applied Geochemistry (v.76, #C)
Acid/base and metal complex solution chemistry of sulfonated polyacrylate copolymer versus temperature and ionic strength by Fangfu Zhang; Zhaoyi Dai; Fei Yan; Gedeng Ruan; Narayan Bhandari; Zhang Zhang; Ya Liu; Amy T. Kan; Mason B. Tomson (1-8).
Sulfonated polyacrylate copolymer (also known as vinyl sulfonated co-polymer; VS-Co) have been widely used in mineral scale control. However, the speciation chemistry of such polymers in solution is not fully understood. In this paper, the acid-base and calcium complex solution chemistry of a VS-Co has been determined from 0.01 to 2 m ionic strength and from 25 to 90 °C by combining electrostatic theory with potentiometric titrations. To process the titration data, VS-Co is treated as a hypothetical, averaged monoacid, HA, with the same concentration of the active carboxylic functional groups of VS-Co. The acid and calcium dissociation reactions of this acid are simply considered as 1:1 type hypothetical reactions, namely HA↔H+ + A− and Ca(A⋯A)↔Ca2++ (A⋯A)2−, with (A⋯A)2− as an arbitrary combinations of two dissociated A− units. The microconstants of the acid dissociation reaction are fitted with a linear electrostatic model with p K a = p K a , intr + b e l e c θ A − , where pK a,intr is an intrinsic constant referring to the condition of zero dissociation, θ A − is the deprotonated fraction of carboxylic functional groups and b elec is an electrostatic factor based on polyelectrolyte theory. Similarly, the microconstants of the Ca2+ dissociation reaction are fitted with p K CaA 2 = p K CaA 2 , intr + 2 b elec θ A − with doubled electrostatic effect since the complexation of Ca2+ with the polymer is considered to neutralize two negative charges. To quantitatively describe the speciation of VS-Co at various conditions, the pK a,intr , p K CaA 2 , intr , and b elec values are fitted empirically as a function of temperature (T, K), and ionic strength (I, m): p K a , intr = 5.068 − 128.398 T − 0.924 × I 1 / 2 + 0.311 × I p K CaA 2 , intr = 5.754 − 888.644 T − 5.749 × I 1 / 2 + 2.221 × I b e l e c = 3.234 − 1.321 × I 1 / 2 + 0.399 × I . Fitted results suggests no significant effect of temperature on the electrostatic factorb elec , which is consistent with electrostatic theory. Results from this study can be used to predict the equilibria of VS-Co in a solution, at various temperature, ionic strength, pH, and metal concentrations.
Keywords: Mineral scale; Sulfonated polyacrylate copolymer (VS-Co); Acid/base chemistry; Metal complex solution chemistry; Electrostatic model;
Influence of a tundra freeze-thaw cycle on sulfide oxidation and metal leaching in a low sulfur, granitic waste rock by Jeff B. Langman; David W. Blowes; Richard T. Amos; Colleen Atherton; David Wilson; Leslie Smith; David C. Sego; Sean A. Sinclair (9-21).
Drill cuttings were collected at 1 m depths from an instrumented, low sulfur, experimental waste rock pile containing a 4C-pyrrhotite that had been exposed to the extreme freeze-thaw cycle of a tundra climate. Boreholes were drilled from the top to base in the center of the pile and near the core-batter transition. Waste rock samples were analyzed for carbon, sulfur, and metal concentrations; sulfur oxidation states; and variation in iron and nickel forms due to oxidative dissolution of pyrrhotite. Results from X-ray absorption spectroscopy and aqueous extraction experiments were used to relatively compare samples from various depths in the boreholes, which indicate sulfide weathering fronts that decrease in intensity from the top to core to base at the center of the pile and from the core-batter transition to the center of the pile. The tundra climate and waste pile configuration produce a permafrost base, a seasonally frozen core, and an atmospheric-like zone near the surface. The fluctuation of the freeze-thaw cycle caused the greatest sulfide weathering near the surface and lesser weathering in the core and base of the pile. Metal- and sulfur-rich leachate from the higher weathering zone likely is collecting on a variable and seasonal frozen surface beneath the surface layer that causes metals and S to precipitate and (or) sorb during a portion of the year. The accumulation of sulfur and metals with the flux of this frozen surface produces a nickel and possibly an iron and sulfur enrichment zone beneath the surface layer in the center of the pile. The weathering front from the top to core to base of the pile and from core-batter transition to the core corresponds to a previously formulated leachate model, but the enrichment zone below the surface zone is unique to this conceptual waste-rock weathering model for this tundra climate.
Keywords: Freeze-thaw cycle; Sulfide oxidation; Metal leaching; Differential weathering; Enrichment zone;
The role of pH in the vapor hydration at 175 °C of the French SON68 glass by Abdelouahed Ait Chaou; Abdesselam Abdelouas; Yassine El Mendili; Christelle Martin (22-35).
The French simulated nuclear waste SON68 glass was altered in the presence of water vapor at 175 °C and 98% of relative humidity under several atmospheres (NH3, H2S, CO2 and argon). The objectives were to study the role of pH on hydration kinetics and secondary phases formation. The hydration was followed by infrared spectroscopy and the nature and extent of alteration products were determined by characterizing the reacted glass surface with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), μ-Raman spectroscopy and X-ray diffraction (XRD). The glass hydration/alteration rate clearly increased with increasing pH, that is controlled by the gas atmosphere, as the following: NH3 > Ar > CO2 > H2S. This can directly be linked to the secondary phases precipitated on the glass surface. Hence, the major alteration products observed at high pH (under NH3 and Ar) are analcime and Ca-silicates hydrates (CSH) while at low pH (under CO2 and H2S) only a hydrated gel layer was identified.
Keywords: SON68 glass; Vapor hydration; Secondary phases; pH effect;
Experimental insights into geochemical changes in hydraulically fractured Marcellus Shale by Virginia Marcon; Craig Joseph; Kimberly E. Carter; Sheila W. Hedges; Christina L. Lopano; George D. Guthrie; J. Alexandra Hakala (36-50).
Hydraulic fracturing applied to organic-rich shales has significantly increased the recoverable volume of methane available for U.S. energy consumption. Fluid-shale reactions in the reservoir may affect long-term reservoir productivity and waste management needs through changes to fracture mineral composition and produced fluid chemical composition. We performed laboratory experiments with Marcellus Shale and lab-generated hydraulic fracturing fluid at elevated pressures and temperatures to evaluate mineral reactions and the release of trace elements into solution. Results from the experiment containing fracturing chemicals show evidence for clay and carbonate dissolution, secondary clay and anhydrite precipitation, and early-stage (24–48 h) fluid enrichment of certain elements followed by depletion in later stages (i.e. Al, Cd, Co, Cr, Cu, Ni, Sc, Zn). Other elements such as As, Fe, Mn, Sr, and Y increased in concentration and remained elevated throughout the duration of the experiment with fracturing fluid. Geochemical modeling of experimental fluid data indicates primary clay dissolution, and secondary formation of smectites and barite, after reaction with fracturing fluid. Changes in aqueous organic composition were observed, indicating organic additives may be chemically transformed or sequestered by the formation after hydraulic fracturing. The NaCl concentrations in our fluids are similar to measured concentrations in Marcellus Shale produced waters, showing that these experiments are representative of reservoir fluid chemistries and can provide insight on geochemical reactions that occur in the field. These results can be applied towards evaluating the evolution of hydraulically-fractured reservoirs, and towards understanding geochemical processes that control the composition of produced water from unconventional shales.Display Omitted
Keywords: Marcellus Shale; Hydraulic fracturing; Geochemical reactions; Barite; Organic acids;
Microbially mediated barite dissolution in anoxic brines by Bingjie Ouyang; Denise M. Akob; Darren Dunlap; Devon Renock (51-59).
Fluids injected into shale formations during hydraulic fracturing of black shale return with extraordinarily high total-dissolved-solids (TDS) and high concentrations of barium (Ba) and radium (Ra). Barite, BaSO4, has been implicated as a possible source of Ba as well as a problematic mineral scale that forms on internal well surfaces, often in close association with radiobarite, (Ba,Ra)SO4. The dissolution of barite by abiotic processes is well quantified. However, the identification of microbial communities in flowback and produced water necessitates the need to understand barite dissolution in the presence of bacteria. Therefore, we evaluated the rates and mechanisms of abiotic and microbially-mediated barite dissolution under anoxic and hypersaline conditions in the laboratory. Barite dissolution experiments were conducted with bacterial enrichment cultures established from produced water from Marcellus Shale wells located in northcentral Pennsylvania. These cultures were dominated by anaerobic halophilic bacteria from the genus Halanaerobium. Dissolved Ba was determined by ICP-OES and barite surfaces were investigated by SEM and AFM. Our results reveal that: 1) higher amounts of barium (up to ∼5 × ) are released from barite in the presence of Halanaerobium cultures compared to brine controls after 30 days of reaction, 2) etch pits that develop on the barite (001) surface in the presence of Halanaerobium exhibit a morphology that is distinct from those that form during control experiments without bacteria, 3) etch pits that develop in the presence of Halanaerobium exhibit a morphology that is similar to the morphology of etch pits formed in the presence of strong organic chelators, EDTA and DTPA, and 4) experiments using dialysis membranes to separate barite from bacteria suggest that direct contact between the two is not required in order to promote dissolution. These results suggest that Halanaerobium increase the rate of barite dissolution in anoxic and high ionic strength solutions. Additionally, the increase in rate occurs without direct microbe-mineral contact suggesting that metabolites secreted by the bacteria may be responsible for promotion of dissolution. The findings of this study have implications for understanding barium cycling in marine/hypersaline environments, release of barium (and associated radium) from waste solids generated from energy and mining industries, as well as potential for developing new anti-scaling chemicals.
Keywords: Barite; Barium; Halophilic bacteria; Hydraulic fracturing; Produced water; Mineral-microbe interactions;
Reactive transport modelling of shale-bentonite interactions in a hypersaline environment by James C. Wilson; Steven Benbow; Richard Metcalfe; Helen Leung (60-73).
Bentonite is a widely considered sealing material for radioactive waste repositories and its behaviour has been studied in a variety of settings. In Ontario Power Generation's Deep Geological Repository (DGR) design for low and intermediate level radioactive waste, a reference 70:30 bentonite/sand mixture is the most voluminous component of the proposed shaft sealing system, in addition to cement- and asphalt-based components. In this study, the long-term durability of the bentonite in contact with sedimentary wall rocks of the shaft and highly-saline porewater was assessed. The possible significance of reactions between bentonite and high-salinity, magnesium-rich porewater for the sealing properties of bentonite has hitherto received less attention than reactions such as smectite illitization, iron-bentonite interactions and cement-bentonite interactions.Fully-coupled reactive transport models were developed to simulate the evolution of the interface between the bentonite/sand mixture and the Georgian Bay Shale, which forms the wall rocks of the shaft overlying the Cobourg Formation (limestone), within which it is proposed to locate the repository. The highly saline nature of the shale porewater led to a Pitzer approach being used to model mineral solubilities. The ‘base case’ simulation suggests that there will be rapid partial replacement of Na―montmorillonite with Ca-montmorillonite in the bentonite/sand, with K-montmorillonite then replacing Ca-montmorillonite over longer timescales (tens of thousands of years). Over 100,000 years, minor alteration of the primary minerals at the shaft seal-rock interface occurred in this model, resulting in a reduced porosity alteration zone with a thickness of a few centimetres. The main alteration product in the bentonite/sand was saponite, whereas in the shale, it was analcime (which was included as a representative sodium-rich framework silicate). A number of variant cases were also developed that explored the effects of model discretisation and geochemical assumptions (controls on dissolved silica concentrations) on calculated system evolution. The variation in discretisation led to minor differences in the evolution of the system, especially with regard to porosity. The assumption that quartz buffers the initial dissolved silica concentrations instead of amorphous silica (the ‘base case’ assumption) resulted in kaolinite forming along with saponite in the bentonite/sand, and kaolinite forming in preference to analcime in the host rock. However, none of the simulations resulted in a significant increase in bentonite-sand porosity over 100,000 years and most of the thickness of the bentonite/sand shaft seal remained unaltered. Hence the models suggest that the performance of the DGR bentonite/sand shaft seals in contact with hypersaline porewater should not be detrimentally affected.
Keywords: Bentonite; Radioactive waste disposal; Hypersaline; Reactive transport modelling;
Geochemical fates and unusual distribution of arsenic in natural ferromanganese duricrust by Huan Liu; Xiancai Lu; Juan Li; Xiaoye Chen; Xiangyu Zhu; Wanli Xiang; Rui Zhang; Xiaolin Wang; Jianjun Lu; Rucheng Wang (74-87).
Preferential enrichment of arsenic in iron oxides relative to manganese oxides has been well documented. In this study, however, a distinct arsenic enrichment is revealed in natural ferromanganese duricrusts, which are commonly found in natural weathering profiles of manganese-bearing carbonate rocks. In the studied ferromanganese duricrust covering Carboniferous carbonates at Qixia Mountain in eastern China, stromotalite-like structures composed by hematite, goethite, pyrolusite and hetaerolite have been observed. Electron microprobe analysis (EMPA) mapping and synchrotron-based micro-scanning X-ray fluorescence (μ-XRF) analyses reveal that the arsenic content in manganese oxides is elevated with respect to iron oxide phases. For example, the arsenic content of pyrolusite is approximately 5 times as much as that of hematite or hetaerolite. However, the highest arsenic content (0.58 wt% As2O5) occurs in 2.75 (±0.96, ±σ) μm micro-bands of hematite ((FexMnIII 1-x)2O3, 0.75 < x < 0.83). Although arsenic contents in the Mn-rich hematite micro-bands are extraordinarily high, the amount of hematite with a high Mn content is very low in the duricrust. Hence manganese oxides are suggested to be the major arsenic sink in the ferromanganese duricrust. Extended X-ray absorption fine structure spectra (EXAFS) further shows that all arsenic is present as oxidized As(V) and are bound to Fe/Mn oxides in bidentate binuclear bridging complexes with As―Fe and As―Mn bond distances of 3.24 Å and 3.23 Å, respectively. In addition, it is found that zinc is also more enriched in Mn oxides (besides hetaerolite) than in Fe oxides. The fine hematite crust with low contents of heavy metals could act as a protective seal to separate Mn oxides core with high Zn and As from environmental fluids. This separation could reduce the interaction between them and decrease the release of Zn and As from this ferromanganese duricrusts, which ensures long-term sequestration of heavy metals. The unique structural and mineralogical constraints on the distribution of heavy metals can provide insights into novel strategies for environmental remediation of heavy metals contaminations.Display Omitted
Keywords: Ferromanganese duricrust; Arsenic; Spatial distribution; μ-XRF; EXAFS;
Nitrogen and sulphur cycling in the saline coastal aquifer of Ferrara, Italy. A multi-isotope approach by M. Caschetto; N. Colombani; M. Mastrocicco; M. Petitta; R. Aravena (88-98).
The origin of high ammonium and sulphate concentrations, characterizing the saline groundwater of the Po River floodplain coastal aquifer, are documented. A detailed understanding of the hydrogeochemical conceptual model is built up using a hydrochemical (major ions, DOC, DIC and methane) and isotopic (δ15NNO3, δ15NNH4, δ18ONO3, δ34SSO4, δ18OSO4 and δ13CDIC) approach. Based on previous hydrogeological investigations, two boreholes located in contrasting environments (urban and agricultural) have been sampled at high vertical resolution.Groundwater is mostly under reducing conditions, characterized by high DOC and DIC concentrations but low to moderate methane content. Dissolved ammonium, as high as 87.8 mgL−1, derives by the mineralization of N-organic rich fine sediments, as indicated by its N isotopic signatures (1÷3‰). Attenuation processes of ammonium are ruled by dilution and by partial nitrification, supported by the enrichment in δ15NNH4 (∼+7‰). Apart from dilution/oxidation processes, the positive correlation between δ15NNO3 and δ18ONO3 agreed with the occurrence of denitrification in the shallow part of the aquifer. δ34SSO4 and δ18OSO4 data highlight that oxidation of pyrite occurs but is not necessarily linked to nitrate removal. The isotope data showed that sulphate (>2500 mgL−1) is of marine origin. In the deeper part of the aquifer, sulphur and oxygen isotopes enrichment patterns, demonstrated that sulphate reduction (SR) occurs in the aquifer and it is also possible that SR occurred in the underlying clay units. δ13CDIC pattern toward depleted δ13CDIC values even as low as −40.4‰ documented the occurrence of SR mediated by organic carbon and SR coupled to oxidation of methane (AOM) are involved in the sulphur and carbon cycles. The present study shows the advantage of using stable isotopes complemented with geochemical data to characterize the solutes' origins, both natural and anthropogenic, and giving insights on biogeochemical transformations involving nitrogen, sulphur and carbon in coastal sediments.
Keywords: Coastal aquifer; Multilevel sampling; Stable isotopes; Reactive nitrogen; Sulphate reduction; Anaerobic oxidation of methane;
Terrestrial sedimentary pyrites as a potential source of trace metal release to groundwater – A case study from the Emsland, Germany by Georg J. Houben; Maria A. Sitnikova; Vincent E.A. Post (99-111).
Pyrite is a common minor constituent of terrestrial freshwater sediments and a sink for trace elements. Different amounts and morphological types (framboids and euhedral crystals) of sedimentary pyrites were found in the heavy mineral fraction of cores obtained from several drillholes located in the Emsland region, NW Germany. Their trace element contents were investigated to assess their potential for groundwater contamination after oxidation, e.g. induced by dewatering or autotrophic denitrification. Nickel, arsenic and cadmium were found in significant concentrations in pyrite. Geochemical modeling showed that elevated trace metal concentrations in groundwater, potentially exceeding drinking water standards, should preferentially occur in a less than 1 m thick zone situated around the depth of the redoxcline, where nitrate is reduced by pyrite. This was confirmed by depth-specific groundwater sampling in the Emsland and by previously published studies. The absolute concentration of released trace metals depends on their content in the pyrite but also strongly on the nitrate load of groundwater.
Keywords: Pyrite; Trace elements; Autotrophic denitrification; Nitrate; Nickel;
Assessing changes in the physico-chemical properties and fluoride adsorption capacity of activated alumina under varied conditions by Laura Craig; Lisa L. Stillings; David L. Decker (112-123).
Adsorption using activated alumina is a simple method for removing fluoride from drinking water, but to be cost effective the adsorption capacity must be high and effective long-term. The intent of this study was to assess changes in its adsorption capacity under varied conditions. This was determined by evaluating the physico-chemical properties, surface charge, and fluoride (F−) adsorption capacity and rate of activated alumina under conditions such as hydration period, particle size, and slow vs. fast titrations. X-ray diffraction and scanning electron microscopy analyses show that the mineralogy of activated alumina transformed to boehmite, then bayerite with hydration period and a corresponding reduction in adsorption capacity was expected; while surface area analyses show no notable changes with hydration period or particle size. The pH dependent surface charge was three times higher using slow potentiometric titrations as compared to fast titrations (due largely to diffusion into pore space), with the surface acidity generally unaffected by hydration period. Results from batch adsorption experiments similarly show no change in fluoride adsorption capacity with hydration period. There was also no notable difference in fluoride adsorption capacity between the particle size ranges of 0.5–1.0 mm and 0.125–0.250 mm, or with hydration period. However, adsorption rate increased dramatically with the finer particle sizes: at an initial F− concentration of 0.53 mmol L−1 (10 mg L−1), 90% was adsorbed in the 0.125–0.250 mm range after 1 h, while the 0.5–1.0 mm range required 24 h to achieve 90% adsorption. Also, the pseudo-second-order adsorption rate constants for the finer vs. larger particle sizes were 3.7 and 0.5 g per mmol F− per min respectively (24 h); and the initial intraparticle diffusion rate of the former was 2.6 times faster than the latter. The results show that adsorption capacity of activated alumina remains consistent and high under the conditions evaluated in this study, but in order to increase adsorption rate, a relatively fine particle size is recommended.Display Omitted
Keywords: Activated alumina; Fluoride; Adsorption; Surface complexation;
The role of natural biogeochemical barriers in limiting metal loading to a stream affected by mine drainage by Giovanni De Giudici; Claudia Pusceddu; Daniela Medas; Carlo Meneghini; Alessandra Gianoncelli; Valentina Rimondi; Francesca Podda; Rosa Cidu; Pierfranco Lattanzi; R.B. Wanty; B.A. Kimball (124-135).
Rio San Giorgio (Iglesiente, Sardinia, Italy), a stream affected by abandoned mine wastes, is characterized by dense vegetation in the streambed, mainly comprised of Phragmites australis and Juncus acutus. This vegetation creates natural biogeochemical barriers that drive mineralization processes and attenuate metals load in the stream. Several techniques, covering scales from micrometres to kilometres, were applied to investigate the biogeochemical processes: water chemistry, injected hydrologic tracer, mineralogy, microscopic investigation and X-ray spectroscopy. From this multiscale and multimethod approach, we recognized two predominant sets of biogeochemical processes: microbially driven metal sulphide precipitation, mainly resulting in pyrite formation; and plant uptake of metals that leads to formation of iron oxide-hydroxide and incorporation of Zn within the roots and aerial part (stem and leaves). The dense vegetation in the Rio San Giorgio streambed controls its morphology, velocity of streamflow, and, as reflected by observed bromide-tracer loss, enhanced water exchange between the streambed and the hyporheic zone. The combined effect of these vegetative controls is to establish biogeochemical barriers that greatly retard trace-metal mobility in the hyporheic zone. We estimated this effect can lead to an apparent decrease in Zn load up to 60%.
Keywords: Mine wastes; Water pollution; Hydrologic tracer; Hyporheic zone; Biogeochemical barriers;
Characterizing glacial meltwater sources in the Athabasca Glacier, Canada, using noble gases as tracers by Yi Niu; M. Clara Castro; Chris M. Hall; Sarah M. Aciego; Carli A. Arendt (136-147).
This study is the first comprehensive noble gas study in meltwater of an alpine glacier. It uses stable noble gases' (He, Ne, Ar, Kr, and Xe) concentrations and isotopic ratios from the Athabasca Glacier meltwater (AGMW), Canada, in an attempt to identify the original source location of ice melt and the relative contributions of modern surface melt versus basal melt and/or groundwater. It also estimates first order water residence times of the glacial meltwater (GMW) resulting from a mixture of modern surface and basal melt and/or groundwater. Two patterns are apparent with respect to noble gas concentrations: 1) a mass-dependent depletion pattern with stronger depletion of the heavier noble gases compared to the lighter ones, and 2) a pattern displaying a relative Ne depletion with respect to Ar. Ratios of noble gas concentrations suggest that different gases have different degrees of equilibration and samples are far from equilibration with the atmosphere at any temperature compatible with the glacial environment. Xe concentrations alone suggest that all AGMW samples equilibrated with the atmosphere at altitudes between 2500 m and 3400 m, altitudes that lie within the altitude range (1900 m–3500 m) of the Columbia Icefield. Most samples display Xe equilibration altitudes above the maximum altitude of the AG (∼2700 m), suggesting that a significant portion of the current AGMW originates in the Columbia Icefield which contributes to both the AG per se and current subglacial meltwater discharge. All AGMW samples are largely dominated by surface melt as opposed to basal melt with surface melt representing at least 71%–96% of the total GMW. Basal melt and/or groundwater represent at most 4%–29% of the total GMW. All AGMW samples exhibit tritiogenic 3He (3Hetrit) levels varying between 0 and 12 TU. Based on estimated 3Hetrit levels, 4He concentrations, and average U and Th concentrations in carbonates, we conclude that the bulk of our AGMW is likely a mixture between pre-bomb and present time GMW with a most likely average residence time of 160 ± 5 years with the exclusion of one present day sample.
Keywords: Athabasca Glacier; Columbia Icefield; Noble gases; Altitude equilibration conditions; Water residence times; Glacial meltwater discharge;
Geochemical characteristics of oil sands fluid petroleum coke by Jake A. Nesbitt; Matthew B.J. Lindsay; Ning Chen (148-158).
The geochemical characteristics of fluid petroleum coke from the Athabasca Oil Sands Region (AOSR) of northern Alberta, Canada were investigated. Continuous core samples were collected to 8 m below surface at several locations (n = 12) from three coke deposits at an active oil sands mine. Bulk elemental analyses revealed the coke composition was dominated by C (84.2 ± 2.3 wt%) and S (6.99 ± 0.26 wt%). Silicon (9210 ± 3000 mg kg−1), Al (5980 ± 1200 mg kg−1), Fe (4760 ± 1200 mg kg−1), and Ti (1380 ± 430 mg kg−1) were present in lesser amounts. Vanadium (1280 ± 120 mg kg−1) and Ni (230 ± 80 mg kg−1) exhibited the highest concentrations among potentially-hazardous minor and trace elements. Sequential extractions revealed potential for release of these metals under field-relevant conditions. Synchrotron powder X-ray diffraction revealed the presence of Si and Ti oxides, organically-complexed V and hydrated Ni sulfate, and provided information about the asphaltenic carbon matrix. X-ray absorption near edge structure (XANES) spectroscopy at the V and Ni K-edges revealed that these metals were largely hosted in porphyrins and similar organic complexes throughout coke grains. Minor differences among measured V and Ni K-edge spectra were largely attributed to slight variations in local coordination of V(IV) and Ni(II) within these organic compounds. However, linear combination fits were improved by including reference spectra for inorganic phases with octahedrally-coordinated V(III) and Ni(II). Sulfur and Fe K-edge XANES confirmed that thiophenic coordination and pyritic-ilmenitic coordination are predominant, respectively. These results provide new information on the geochemical and mineralogical composition of oil sands fluid petroleum coke and improve understanding of potential controls on associated water chemistry.
Keywords: Petroleum coke; Oil sands; Geochemistry; Mineralogy; Trace elements; X-ray absorption spectroscopy;
Fractionation of mercury stable isotopes during coal combustion and seawater flue gas desulfurization by Shuyuan Huang; Dongxing Yuan; Haiying Lin; Lumin Sun; Shanshan Lin (159-167).
In the current study, fractionation of mercury isotopes during coal combustion and seawater flue gas desulfurization (SFGD) in a coal-fired power plant using a SFGD system was investigated. Fourteen samples were collected from the power plant. The samples were pretreated with a combustion-trapping method and were analyzed with a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). Compared with the raw coal, the bottom ash was enriched with lighter mercury isotopes with δ202Hg values ranging from −0.45 to −0.03‰. The fly ash was enriched with lighter mercury isotopes with δ202Hg values ranging from −1.49 to −0.73‰ for Chinese coal and from −1.47 to −0.62‰ for Indonesian coal. The δ202Hg of fresh seawater and desulfurized seawater was found to be −1.32 and −0.32‰ respectively. These δ202Hg values indicated that the desulfurized seawater was enriched with heavier mercury isotopes. Based upon the calculated results obtained from the mass balance equation, it was suggested that the stack emissions were enriched with lighter mercury isotopes. Mass independent fractionation was observed in most of the samples with a Δ199Hg/Δ201Hg ratio of approximately 0.96. The results help in improving the understanding of mercury isotope fractionation during coal combustion and SFGD, and are also useful in tracing the mercury emissions from coal fired power plants.
Keywords: Mercury stable isotopes; Isotope fractionation; Coal-fired power plant; Coal; Fly ash;
Geochemical and isotopic study to determine sources and processes affecting nitrate and sulphate in groundwater influenced by intensive human activity - carbonate aquifer Gliwice (southern Poland) by Sabina Jakóbczyk-Karpierz; Sławomir Sitek; Rasmus Jakobsen; Andrzej Kowalczyk (168-181).
A multi-species, multi-stable-isotope approach (δ15NNO3, δ18ONO3, δ34SSO4, δ18OSO4, δ18OH2O and δ2HH2O) was used together with environmental tracers (Ar, Ne, CFC-11 and CFC-12) and geochemical modelling to characterize sources and processes controlling concentrations of NO3 − and SO4 2- in groundwater of the carbonate aquifer Gliwice (southern Poland). The study area represents a strongly transformed environment with a range of human activities i.a. Agriculture, urbanization and industry. The δ15NNO3 and δ18ONO3 indicated that most samples contained NO3 − of mixed sources: artificial fertilizers, municipal and industrial sewage, while very good correlation between NO3 − and CFC-12 suggested that nitrate originated primarily from residential and industrial sewage. Conversely, isotopic composition of sulphate in groundwater suggested agriculture as well as oxidation of sulphides as dominant. The conclusion was supported by the comparison of CFCs and sulphate concentrations which revealed no relevant correlation. Geochemical modelling confirmed the presence of sulphate reduction in areas where isotopic analyses were not possible due to undetectable sulphate. Thus, the integrated application of stable isotopes, environmental tracers, groundwater chemistry and geochemical modelling shows a complex origin of groundwater pollution in the study area as well as variety of geochemical processes controlling chemistry of groundwater in a triple-porosity aquifer influenced by different types of human activity.
Keywords: Environmental tracers; Stable isotopes; Nitrate; Sulphate; Geochemical modelling; Carbonate aquifer; Urban geochemistry;
Interplay of molecular size and pore network geometry on the diffusion of dissolved gases and HTO in Boom Clay by E. Jacops; M. Aertsens; N. Maes; C. Bruggeman; B.M. Krooss; A. Amann-Hildenbrand; R. Swennen; R. Littke (182-195).
Through-diffusion experiments in Boom Clay have been performed with uncharged molecules: tritiated water (HTO) and dissolved gases of different size (He, Ne, H2, Ar, CH4, Xe and C2H6), allowing information to be obtained on the relationship between the diffusion coefficient and the molecular size (characterized by a 'kinetic diameter' of the molecules). Experiments have been performed on both clayey and silty Boom Clay samples, to scope for the changes induced by grain size variations on the diffusion process. Experiments on clay cores taken perpendicular as well as parallel to the bedding plane have also been executed, providing additional information on the anistropy of the diffusion process.Empirical relations are proposed to capture the observed decrease of both the diffusion coefficient in water and the effective diffusion coefficient in the Boom Clay porous medium as a function of molecular size. In the same way, the behaviour of the geometric factor G as a function of size is estimated.Although silty samples have a noticeably higher hydraulic conductivity than clayey samples, the difference in diffusion coefficient is less obvious. The anisotropy factor is roughly the same for all investigated components, with an average value of 1.5.
Quaternary redox transitions in deep crystalline rock fractures at the western margin of the Greenland ice sheet by Henrik Drake; Juhani Suksi; Eva-Lena Tullborg; Yann Lahaye (196-209).
When planning for long term deep geological repositories for spent nuclear fuel knowledge of processes that will influence and change the sub-surface environment is crucial. For repositories in northern Europe and similar areas, influence from advancing and retreating continental ice sheets must be planned for. Rapid transport of meltwater into the bedrock may introduce oxic conditions at great depth, which may affect the copper canisters planned to encapsulate the spent fuel. The lack of direct observations has led to simplified modelling assumptions not reflecting the complexity of natural systems. As part of a unique field and modelling study, The Greenland Analogue Project, of a continental ice sheet and related sub-surface conditions, we here present mineralogical and U-series data unravelling the Quaternary redox history in the deep bedrock fracture system close to the margin of the Greenland ice sheet. The aim was to increase the understanding of circulation of potentially oxygenated glacial meltwater from the surface down to 650 m depth.Secondary mineral coatings were sampled from open fractures in cored boreholes down to 650 m, within and below the current permafrost. Despite continental ice sheet coverage and/or prevailing permafrost during large parts of the last 1 Ma, measured disequilibrium in the 238U-234U-230Th system shows that water has circulated in the bedrock fracture system at various occasions during this time span. In fractures of the upper 60 m, infiltration of oxygenated surface water has resulted in a prominent near-surface ”oxidised zone” with abundant FeOOH precipitation. However, this zone must be relict because it is currently within permafrost and the U-series disequilibrium signatures of most fracture coatings show evidence of deposition of U prior to the Holocene and even prior to the last glaciation maximum which occurred less than 100 ka ago. This U deposition is found both within and below the near surface “oxidised zone” indicating temporal redox variation within this zone during the last 1 Ma. Potential Holocene leaching of U is indicated by 230Th/238U≫1 and close to secular equilibrium for 234U/238U in some of the near surface fractures and also in a couple of deeper fractures. Indicated U-leaching in the talik within the last 200 ka is proposed to be the result of talik-related discharge of water with a capability of keeping U in solution. Circulation of oxidative water in the deep system beneath the permafrost is indicated only in a few fractures and solely by U-series disequilibrium (230Th/238U activity ratios up to 2.97 at 431 m depth), probably due to restricted, perhaps sporadic infiltration of oxidative water, potentially during the Holocene. In these fractures, the conditions have in general been more reducing than in the near surface system where oxidising conditions have prevailed and penetration of oxygenated waters may have been continuous.
Keywords: Redox transitions; Fracture coatings; U-series isotopes; Greenland ice sheet; Nuclear waste disposal;
Correlating NORM with the mineralogical composition of shale at the microstructural and bulk scale by Joseph D. Levinthal; Bryony Richards; Mathew S. Snow; Matthew G. Watrous; Luther W. McDonald (210-217).
Hydrocarbons produced via hydraulic fracturing of shale formations frequently contain elevated quantities of Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM) that are difficult to dispose of and can be harmful to the environment. This research investigates the elemental composition of seven major shale formations at the bulk and microstructural scale to better understand the relationship between major naturally occurring radioactive elements (NORM) and organic phases within shales. Bulk mineralogy analysis was performed via powder X-ray diffraction to identify which shales were ideal for hydraulic stimulation based on the content of ductile and brittle minerals. To complement the XRD, Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN ® ) was performed to identify non-crystalline phases and provide spatial mapping of the minerals through the shale samples. In addition, XRD and QEMSCAN were used to determine the total sulfur and carbonate content as this greatly contributes to the acidity of the shale and subsequently, U and Th migration. Select samples were characterized by scanning electron microscopy - energy dispersive x-ray spectroscopy (SEM/EDX) to reveal the presence of heavy metals (i.e. U, Pb) near hydrocarbon-rich regions of the shale. The NORM content and organic content were also correlated using gamma well logging.
Keywords: Shale; Hydraulic fracturing; Uranium; NORM; TENORM; QEMSCAN; XRD; Mass spectrometry;
The role of low-temperature organic matter diagenesis in carbonate precipitation within a marine deposit by Kazuya Miyakawa; Eiichi Ishii; Akinari Hirota; Daisuke D. Komatsu; Kosuke Ikeya; Urumu Tsunogai (218-231).
Carbonate minerals in veins can record paleo-hydrogeological information that enables the reconstruction of groundwater history. This paper investigates the cause of differences in the occurrence of carbonate veins in the Koetoi and Wakkanai formations, both Neogene mudstone units in northwestern Hokkaido, from the perspective of controls on CO2 supply from the alteration of organic matter. Carbonate veins are rare in the Koetoi Formation, but are widespread in the Wakkanai Formation. This area is a region of oil and gas accumulation where deep groundwater is saturated mainly with CH4 and CO2. The results show high δ13C values in co-existing CH4 (∼–32.6‰) and CO2 (∼+31.0‰) gases. An investigation of δ13C – δD systematics among these gases indicates that isotopic fractionation was caused by microbial CO2 reduction. Although total organic carbon content in the Koetoi Formation decreases with increasing depth, total organic content in the Wakkanai Formation remains roughly constant with depth. Furthermore, although δ13C values also show depth dependence, values from the Wakkanai Formation are higher than those from the Koetoi Formation. This 13C-enrichment could be explained by Rayleigh fractionation in a closed system.Based on these results, the processes behind the formation of the carbonate veins can be summarized as follows. Carbon dioxide behavior is thought to play an important role with respect to carbonate formation because CO2 abundance is closely linked to pH and pressure. In shallow sedimentary rocks such as the Koetoi Formation that have started to experience diagenetic alteration of organic matter, CO2 in groundwater is supplied by microbial decomposition of organic matter and is reduced to CH4 by methanogens. In deep sedimentary rocks such as the Wakkanai Formation that have undergone diagenesis but have only experienced moderate temperatures so that thermal decomposition of organic matter has not yet begun, microbial degradation of organic matter has proceeded too far for any more CO2 to be produced. Thus, carbonate precipitation is initiated when pH rises due to microbial CO2 reduction. The contrast between the occurrence of carbonate veins in the Koetoi and Wakkanai formations can be explained by our results, which can also be applied to general carbonate behavior in marine sedimentary rocks.
Keywords: Carbon isotope ratio; Methane; Carbon dioxide; Carbonate vein; Carbonate reduction;