IMPACTS OF MINERAL SURFACE REACTIONS ON AQUEOUS VANADATE ATTENUATION

Accumulation of vanadium (V) in the environment has become a global concern due to increased anthropogenic activity. Release of V by fossil fuel emissions or leaching of mine waste materials can concentrate V in aquatic systems, where it may reach concentrations hazardous to organisms and humans. Similar to potentially-hazardous elements (e.g., Mo and W), V is a redox-sensitive trace metal that predominantly occurs in three oxidation states (+III, +IV, and +V) in near-surface environments. Therefore, pH, redox conditions, and V concentration ([V]T) strongly affect aqueous speciation and attenuation mechanisms at mineral surfaces. Adsorption onto Fe (oxyhydr)oxides and Fe sulfides are key controls on metal(loid) mobility in terrestrial and marine environments. However, few studies have examined fundamental attenuation mechanisms for V within these systems. The objective of this thesis is to determine rates and mechanisms of V adsorption and, more generally, to improve understanding of environmental V geochemistry. Laboratory experiments examined (i) potential for aqueous vanadate (H2VVO4−) removal by Fe(II)-bearing phases (i.e., magnetite, mackinawite, siderite, and pyrite) under anoxic conditions and (ii) uptake of polynuclear V(V) species by Fe(III) (oxyhydr)oxides. Kinetic batch experiments demonstrated the rapid uptake of V under anoxic conditions by siderite and mackinawite (≥ 90 %) after 3 h, whereas removal by magnetite reached ~50 % and was limited during reaction with pyrite. Further XAS analysis showed the reduction of V(V) to V(IV) and V(III) with the formation of bidentate edge- and corner-sharing surface complexes at magnetite, while only bidentate binuclear surface complexes were observed following reaction with siderite. In the case of mackinawite, data suggests the incorporation of V(IV) and V(III) into the tetragonal FeS structure. Investigation of (poly)vanadate adsorption at ferrihydrite and hematite surfaces was performed using in situ attenuated total reflectance – Fourier transform infrared spectroscopy. Results highlight the pH dependency of polymerization reactions and, consequently, the formation of surface polymers. Ferrihydrite exhibited limited capacity for polyvanadate uptake at pH 5 and 6, whereas polymers had a high affinity for hematite from pH 3 to 6. Overall, this research improves understanding of relationships between metal-mineral interactions, redox conditions, and aqueous speciation reactions that influence V mobility in natural and contaminated environments

Aqueous vanadate removal by iron(II)-bearing phases under anoxic conditions

Copyright © 2020 American Chemical SocietyFunding was provided by the Natural Sciences and Engineering Council of Canada (NSERC) through the Discovery Grants program (Grant No. RGPIN-2014-06589). Additional support awarded to CJV through NSERC – Canada Graduate Scholarship – Masters (NSERC CGS-M) Program. A portion of the research described was performed at the Canadian Light Source, which is supported by the Canada Foundation for Innovation, NSERC, the University of Saskatchewan, the Government of Saskatchewan, Western Economic Diversification Canada, the National Research Council, and the Canadian Institutes of Health Research.Peer ReviewedVanadium contamination is a growing environmental hazard worldwide. Aqueous vanadate (HxVVO4(3−x)− (aq)) concentrations are often controlled by surface complexation with metal (oxyhydr)oxides in oxic environments. However, the geochemical behaviour of this toxic redox sensitive oxyanion in anoxic environments is poorly constrained. Here we describe results of batch experiments to determine kinetics and mechanisms of aqueous H2VVO4− (100 μM) removal under anoxic conditions in suspensions (2.0 g L−1) of magnetite, siderite, pyrite, and mackinawite. We present results of parallel experiments using ferrihydrite (2.0 g L−1) and Fe2+(aq) (200 μM) for comparison. Siderite and mackinawite reached near complete removal (46 µmol g−1) of aqueous vanadate after 3 h and kinetic rates were generally consistent with ferrihydrite. Whereas magnetite removed 18 µmol g−1 of aqueous vanadate after 48 h and uptake by pyrite was limited. Uptake by Fe2+(aq) was observed after 8 h, concomitant with precipitation of secondary Fe phases. X ray absorption spectroscopy revealed V(V) reduction to V(IV) and formation of bidentate corner-sharing surface complexes on magnetite and siderite, and with Fe2+(aq) reaction products. These data also suggest that V(IV) is incorporated into the mackinawite structure. Overall, we demonstrate that Fe(II)-bearing phases can promote aqueous vanadate attenuation and, therefore, limit dissolved V concentrations in anoxic environments

Sodium transport and attenuation in soil cover materials for oil sands mine reclamation

0883-2927/ © 2018 Elsevier Ltd. All rights reserved.Funding was provided to MBJL by the Natural Sciences and Engineering Council of Canada (NSERC) and Syncrude Canada Ltd. through the Industrial Research Chairs program (Grant No. IRCPJ 450684−13). Additional support awarded to CVJ through the Brian and Elaine Russel Undergraduate Research Fund and the NSERC Canadian Graduate Scholarships – Master’s (NSERC CGS-M) Program.Peer ReviewedReclamation soil covers are used in oil sands mine closure to support vegetative growth over tailings. Geochemical processes within these covers may impact solute transport during upward migration of oil sands process-affected water (OSPW) from the underlying tailings. In this study, we examined the geochemical processes controlling Na transport and attenuation within the peat and clay-till cover soils at Sandhill Fen in northern Alberta, Canada. We analyzed soil core samples collected along transects of this 54-ha pilot-scale oil sands mine reclamation wetland. The geochemical (Na, Ca, Mg, K, Cl, SO4, HCO3) and isotopic (δ2H, δ18O) compositions of extracted pore water were analyzed statistically to identify OSPW and fresh surface water within the cover. Depth-dependent trends in pore water sodium concentrations were not apparent, suggesting that the soil cover had been fully flushed by a mixture of OSPW and fresh surface water used to flood the fen. Relative concentrations of Na, Ca and Mg were used to define the extent of cation exchange within the clay cover. Complementary laboratory column experiments showed that cation exchange removed up to 50% of dissolved Na as the first pore volume of simulated OSPW passed through the peat and till. However, Na attenuation by these materials declined rapidly and was limited after 4 (peat) to 7 (till) pore volumes of OSPW flushing. Reactive transport modeling confirmed that cation exchange was the dominant control on Na attenuation and corresponding Ca and Mg release within the till and peat columns. Mineral precipitation-dissolution reactions also influenced dissolved Ca and Mg concentrations and, therefore, indirectly impacted Na attenuation. Overall, this study helps constrain the geochemical processes controlling Na transport and attenuation in oil sands reclamation soil covers exposed to OSPW, and indicates that the attenuation of Na from OSPW by these covers is short-lived

Mineralogy and geochemistry of oil sands froth treatment tailings: Implications for acid generation and metal(loid) release

Copyright © 2019 Elsevier Ltd. All rights reserved.This research was supported by the Natural Sciences and Engineering Council of Canada (NSERC) and Syncrude Canada Ltd. through the Industrial Research Chairs Grants program (Grant No. IRCPJ 450684−13). Additional support for CJV was provided by the NSERC Canadian Graduate Scholarships – Master’s (NSERC CGS-M) Program.Peer ReviewedFroth treatment tailings (FTT) are one of three principal tailings streams generated during bitumen extraction at oil sands mines in northern Alberta, Canada. Unlike the coarse tailings and fluid fine tailings, FTT are enriched in sulfide-minerals content and exhibit the potential for acid generation and metal(loid) leaching. However, the mineralogical and geochemical characteristics of this sulfide-bearing tailings stream remain poorly constrained. We examined samples of fresh FTT (n = 3) and partially-weathered FTT collected from a sub-aerial beach deposit (n = 15). X-ray diffraction revealed that weathering-resistant silicates, phyllosilicates, and oxides dominated (85 ± 7.3 wt. %) the FTT mineral assemblage, while sulfides (6.2 ± 3.6 wt. %) and carbonates (8.9 ± 4.3 wt. %) were relatively minor phases. Pyrite [FeS2] was the principal sulfide in all samples, while minor amounts of marcasite [FeS2] occurred only in beach samples. Sulfide mineral textures were highly variable and included euhedral to subhedral pyrite crystals, discrete and clustered pyrite framboids, and marcasite replacements of pyrite framboids. Siderite [FeCO3] accounted for 55 to 90 % of all carbonates, while dolomite [CaMg(CO3)2], calcite [CaCO3] and ankerite [Ca(Fe,Mg,Mn)(CO3)2] accounted for the remainder. Statistical analysis of bulk geochemical compositions suggested that environmentally-relevant metal(loid)s, including As, Cu, Co, Fe, Mn, Ni, Pb and Zn, were likely associated with sulfides, carbonates and, to a lesser extent, phyllosilicates. Electron probe microanalyses revealed a wide range of As, Cu, Co, Mn, Ni and Zn concentrations in pyrite, with As and Cu concentrations elevated in framboids. Rare earth elements (REEs), Th and U also occurred at elevated concentrations and statistical analyses suggest they are associated with zircon and, potentially, monazite and xenotime. Static acid-base accounting (ABA) tests indicated that all FTT samples are potentially acid generating. Our study describes the mineralogical and geochemical characteristics of oil sands FTT, and indicates that oxidative weathering has the potential to generate acidic drainage containing elevated dissolved concentrations of several metal(loid)s

Adsorption of (Poly)vanadate onto Ferrihydrite and Hematite: An In Situ ATR–FTIR Study

Copyright © 2020 American Chemical SocietyFunding was provided by the Natural Sciences and Engineering Council of Canada (NSERC) through the Discovery Grants program (Grant no. RGPIN-2014-06589). Additional support awarded to C.J.V. was through the NSERC-Canada Graduate Scholarship-Master’s (NSERC CGS-M) Program. M.P.S. would like to acknowledge the Natural Sciences and Engineering Research Council Collaborative Research and Training Experience Sustainable Applied Fertilizer and Environmental Remediation (NSERC CREATE SAFER) program, as well as the NSERC Research and Development grant supported by Federated Cooperatives Limited for financial support.Peer ReviewedVanadium (V) has been a useful trace metal in describing Earth’s biogeochemical cycling and development of industrial processes; however, V has recently been recognized as a potential contaminant of concern. Although Fe (oxyhydr)oxides are important sinks for aqueous V in soils and sediments, our understanding of adsorption mechanisms is currently limited to mononuclear species (i.e., HxVO4(3–x)–). Here we use in situ attenuated total reflectance – Fourier transform infrared spectroscopy to examine sorption mechanisms and capacity for (poly)vanadate attenuation by ferrihydrite and hematite from pH 3 to 6. Adsorption isotherms illustrate the low affinity of polyvanadate species for ferrihydrite surfaces compared to hematite. Mononuclear V species (i.e., [HxVO4](3−x)− and VO2+) were present at all experimental conditions. At low surface loadings and pH 5 and 6, H2VO4− adsorption onto ferrihydrite and hematite surfaces results from formation of inner sphere complexes. At [V]T above 250 µM, adsorbed polynuclear V species in this study include H2V2O72− and V4O124−. Whereas, HV10O286−, H3V10O285−, and NaHV10O284− are the predominant adsorbed species at pH 3 and 4 and elevated [V]T. Surface polymers were identified on hematite at all experimental pH values, whereas polymeric adsorption onto ferrihydrite was limited to pH 3 and 4. These results suggest that hematite offers a more suitable substrate for polymer complexation compared to ferrihydrite. Our results demonstrate the pH and concentration dependant removal of (poly)vanadate species by Fe(III) (oxyhydr)oxides, which has implications for understanding V mobility, behaviour, and fate in the environment

Mortality in women given diethylstilbestrol during pregnancy

We used Cox regression analyses to assess mortality outcomes in a combined cohort of 7675 women who received diethylstilbestrol (DES) through clinical trial participation or prenatal care. In the combined cohort, the RR for DES in relation to all-cause mortality was 1.06 (95% CI=0.98–1.16), and 1.11 (95% CI=1.02–1.21) after adjusting for covariates and omitting breast cancer deaths. The RR was 1.07 (95% CI=0.94–1.23) for overall cancer mortality, and remained similar after adjusting for covariates and omitting breast cancer deaths. The RR was 1.27 (95% CI=0.96–1.69) for DES and breast cancer, and 1.38 (95% CI=1.03–1.85) after covariate adjustment. The RR was 1.82 in trial participants and 1.12 in the prenatal care cohort, but the DES–cohort interaction was not significant (P=0.15). Diethylstilbestrol did not increase mortality from gynaecologic cancers. In summary, diethylstilbestrol was associated with a slight but significant increase in all-cause mortality, but was not significantly associated with overall cancer or gynaecological cancer mortality. The association with breast cancer mortality was more evident in trial participants, who received high DES doses

Influence of Iron Substitution and Solution Composition on Brucite Carbonation.

Carbon neutral or negative mining can potentially be achieved by integrating carbon mineralization processes into the mine design, operations, and closure plans. Brucite [Mg(OH)2] is a highly reactive mineral present in some ultramafic mine tailings with the potential to be rapidly carbonated and can contain significant amounts of ferrous iron [Fe(II)] substituted for Mg; however, the influence of this substitution on carbon mineralization reaction products and efficiency has not been thoroughly constrained. To better assess the efficiency of carbon storage in brucite-bearing tailings, we performed carbonation experiments using synthetic Fe(II)-substituted brucite (0, 6, 23, and 44 mol % Fe) slurries in oxic and anoxic conditions with 10% CO2. Additionally, the carbonation process was evaluated using different background electrolytes (NaCl, Na2SO4, and Na4SiO4). Our results indicate that carbonation efficiency decreases with increasing Fe(II) substitution. In oxic conditions, precipitation of ferrihydrite [Fe10IIIO14(OH)2] and layered double hydroxides {e.g., pyroaurite [Mg6Fe2III(OH)16CO3·4H2O]} limited carbonation efficiency. Carbonation in anoxic environments led to the formation of Fe(II)-substituted nesquehonite (MgCO3·3H2O) and dypingite [Mg5(CO3)4(OH)2·∼5H2O], as well as chukanovite [Fe2IICO3(OH)2] in the case of 23 and 44 mol % Fe(II)-brucite carbonation. Carbonation efficiencies were consistent between chloride- and sulfate-rich solutions but declined in the presence of dissolved Si due to the formation of amorphous SiO2·nH2O and Fe-Mg silicates. Overall, our results indicate that carbonation efficiency and the long-term fate of stored CO2 may depend on the amount of substituted Fe(II) in both feedstock minerals and carbonate products