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Dockrey J.W.,University of British Columbia | Dockrey J.W.,Lorax Environmental Services Ltd. | Lindsay M.B.J.,University of Saskatchewan | Mayer K.U.,University of British Columbia | And 5 more authors.
Minerals | Year: 2014

Microbial populations and microbe-mineral interactions were examined in waste rock characterized by neutral rock drainage (NRD). Samples of three primary sulfide-bearing waste rock types (i.e., marble-hornfels, intrusive, exoskarn) were collected from field-scale experiments at the Antamina Cu–Zn–Mo mine, Peru. Microbial communities within all samples were dominated by neutrophilic thiosulfate oxidizing bacteria. However, acidophilic iron and sulfur oxidizers were present within intrusive waste rock characterized by bulk circumneutral pH drainage. The extensive development of microbially colonized porous Fe(III) (oxy)hydroxide and Fe(III) (oxy)hydroxysulfate precipitates was observed at sulfide-mineral surfaces during examination by field emission-scanning electron microscopy-energy dispersive X-ray spectroscopy (FE-SEM-EDS). Linear combination fitting of bulk extended X-ray absorption fine structure (EXAFS) spectra for these precipitates indicated they were composed of schwertmannite [Fe8O8(OH)6–4.5(SO4)1–1.75], lepidocrocite [γ-FeO(OH)] and K-jarosite [KFe3(OH)6(SO4)2]. The presence of schwertmannite and K-jarosite is indicative of the development of localized acidic microenvironments at sulfide-mineral surfaces. Extensive bacterial colonization of this porous layer and pitting of underlying sulfide-mineral surfaces suggests that acidic microenvironments can play an important role in sulfide-mineral oxidation under bulk circumneutral pH conditions. These findings have important implications for water quality management in NRD settings. © 2014 by the authors; licensee MDPI, Basel, Switzerland. Source

Jeen S.-W.,Chonbuk National University | Mattson B.,Lorax Environmental Services Ltd.
Environmental Technology (United Kingdom) | Year: 2016

Laboratory column tests for passive treatment systems for mine drainage from a waste rock storage area were conducted to evaluate suitable reactive mixture, system configuration, effects of influent water chemistry, and required residence time. Five columns containing straw, chicken manure, mushroom compost, and limestone (LS), in either layered or mixed configurations, were set up to simulate the treatment system. The results showed that all of the five columns removed metals of concern (i.e. Al, Cd, Co, Cu, Fe, Ni, and Zn) with a residence time of 15 h and greater. Reaction mechanisms responsible for the removal of metals may include sulfate reduction and subsequent sulfide precipitation, precipitation of secondary carbonates and hydroxides, co-precipitation, and sorption on organic substrates and secondary precipitates. The results suggest that the mixed systems containing organic materials and LS perform better than the layered systems, sequentially treated by organic and LS layers, due to the enhanced pH adjustment, which is beneficial to bacterial activity and precipitation of secondary minerals. The column tests provide a basis for the design of a field-scale passive treatment system, such as a reducing and alkalinity producing system or a permeable reactive barrier. © 2016 Informa UK Limited, trading as Taylor & Francis Group Source

Simpson S.,University of Manitoba | Simpson S.,Lorax Environmental Services Ltd. | Sherriff B.L.,University of Manitoba | Gulck J.V.,ARKTIS Solutions Inc. | And 4 more authors.
Applied Geochemistry | Year: 2011

This study was to investigate the source, mobility and attenuation of As at the New Britannia Mine, Snow Lake, Manitoba. One major source of As contamination was determined to be an arsenopyrite residue stockpile (ARS) containing refractory Au in a waste rock impoundment. It appears that As is still moving through glacial clay at the base of the ARS into a confined aquifer even though the pile was capped in the year 2000. Arsenic is also being mobilized from a deposit of tailings, which formed following spills by previous owners, Nor Acme. Arsenic from the tailings is being mobilized by oxidation of arsenopyrite and reduction of arsenate to the more mobile arsenite by arsenate-reducing bacteria. This contamination is affecting a shallow unconfined aquifer and surface water flowing from the tailings through wetlands towards Snow Lake. Arsenic is being attenuated by adsorption to hydrated ferric oxides (HFO) in the tailings, wetland soils and aquatic plants. Although As in surface water, soils and plants along the flow path from the mine to Snow Lake are above Canadian drinking water guidelines, efficient natural attenuation by HFO in soils and plants of the wetlands have limited the concentration in Snow Lake to below drinking water standards. © 2011 Elsevier Ltd. Source

Martin A.J.,Lorax Environmental Services Ltd. | Simpson S.,Lorax Environmental Services Ltd. | Fawcett S.,Lorax Environmental Services Ltd. | Wiramanaden C.I.E.,University of Saskatchewan | And 6 more authors.
Environmental Science and Technology | Year: 2011

The biogeochemical mechanisms of Se exchange between water and sediments in two contrasting lentic environments were assessed through examination of Se speciation in the water column, porewater, and sediment. High-resolution (7 mm) vertical profiles of <0.45 μm Se species across the sediment-water interface demonstrate that the behavior of dissolved Se(VI), Se(IV), and organo-Se are closely linked to redox conditions as revealed by porewater profiles of redox-sensitive species (dissolved O2, NO 3 -, Fe, Mn, SO4 2-, and ΣH 2S). At both sites Se(VI) is removed from solution in suboxic near-surface porewaters demonstrating that the sediments are serving as diffusive sinks for Se. X-ray absorption near edge spectroscopy (XANES) of sediments suggests that elemental Se and organo-Se represent the dominant sedimentary sinks for dissolved Se. Dissolved Se(IV) and organo-Se are released to porewaters in the near-surface sediments resulting in the diffusive transport of these species into the water column, where between-site differences in the depths of release can be linked to differences in redox zonation. The presence or absence of emergent vegetation is proposed to present a dominant control on sedimentary redox conditions as well as on the recycling and persistence of reduced Se species in bottom waters. © 2011 American Chemical Society. Source

Wanless V.D.,Woods Hole Oceanographic Institution | Behn M.D.,Woods Hole Oceanographic Institution | Shaw A.M.,Woods Hole Oceanographic Institution | Shaw A.M.,Lorax Environmental Services Ltd. | Plank T.,Lamont Doherty Earth Observatory
Contributions to Mineralogy and Petrology | Year: 2014

We present major element, trace element, and volatile concentrations from 66 naturally glassy, olivine-hosted melt inclusions erupted along the Eastern Volcanic Zone (EVZ) of the ultraslow-spreading Gakkel Ridge. Melt inclusion compositions suggest that there are systematic variations in the mantle source composition and melting dynamics from the eastern to the western end of the EVZ. This includes increasing water contents and highly incompatible trace element concentrations (e.g., Ba and Nb) and decreasing light and middle rare earth element concentrations. Ratios of light to heavy rare earth elements in the easternmost melt inclusions are relatively homogeneous, but become more variable to the west. To determine the source of the geochemical variability observed along the EVZ, we model trace elements associated with mantle melting in one- and two-component systems. We consider four possible mantle sources and a range of melting regime shapes, from a full melting triangle to a vertical melting column centered beneath the ridge axes. The observed geochemical variations can be explained by melting of a heterogeneous mantle source composed of depleted MORB mantle plus a metasomatized mantle, where the proportion of the metasomatized component and the extent of melting increases toward the west. Lower rare earth element concentrations and trace element ratios in the westernmost sites also suggest inefficient melt focusing from the outer edges of the melting region. Our results indicate that despite variations in the size of the melting zone and the composition of the mantle source along the ridge axis, the region over which the melts are pooled back to the ridge axis is relatively constant (~10-20 km), suggesting that there is a limit to the distance melts can be transported from off-axis in ultraslow-spreading environments. © 2014 Springer-Verlag Berlin Heidelberg. Source

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