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  • 1.
    Benaiges-Fernandez, Robert
    et al.
    Department of Genetics, Microbiology and Statistics, Universitat de Barcelona, Barcelona, Catalonia, Spain. Institute of Environmental Assessment and Water Research (IDAEA, CSIC), Barcelona, Catalonia, Spain.
    Palau, Jordi
    Institute of Environmental Assessment and Water Research (IDAEA, CSIC), Barcelona, Catalonia, Spain. Department of Mineralogy, Petrology and Applied Geology, Universitat de Barcelona, Barcelona, Catalonia, Spain.
    Offeddu, Francesco G.
    Institute of Environmental Assessment and Water Research (IDAEA, CSIC), Barcelona, Catalonia, Spain.
    Cama, Jordi
    Institute of Environmental Assessment and Water Research (IDAEA, CSIC), Barcelona, Catalonia, Spain.
    Urmeneta, Jordi
    Department of Genetics, Microbiology and Statistics, Universitat de Barcelona, Barcelona, Catalonia, Spain. Biodiversity Research Institute (IRBio), Universitat de Barcelona, Barcelona, Catalonia, Spain.
    Soler, Josep M.
    Institute of Environmental Assessment and Water Research (IDAEA, CSIC), Barcelona, Catalonia, Spain.
    Dold, Bernhard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Sustainable Mining Research & Consultancy EIRL, San Pedro de La Paz, Chile.
    Dissimilatory bioreduction of iron(III) oxides by Shewanella loihica under marine sediment conditions2019In: Marine Environmental Research, ISSN 0141-1136, E-ISSN 1879-0291Article in journal (Refereed)
    Abstract [en]

    Shewanella is a genus of marine bacteria capable of dissimilatory iron reduction (DIR). In the context of deep-sea mining activities or submarine mine tailings disposal, dissimilatory iron reducing bacteria may play an important role in biogeochemical reactions concerning iron oxides placed on the sea bed. In this study, batch experiments were performed to evaluate the capacity of Shewanella loihica PV-4 to bioreduce different iron oxides (ferrihydrite, magnetite, goethite and hematite) under conditions similar to those in anaerobic sea sediments. Results showed that bioreduction of structural Fe(III) via oxidation of labile organic matter occurred in all these iron oxides. Based on the aqueous Fe (II) released, derived Fe(II)/acetate ratios and bioreduction coefficients seem to be only up to about 4% of the theoretical ones, considering the ideal stoichiometry of the reaction. A loss of aqueous Fe (II) was caused by adsorption and mineral transformation processes. Scanning electron microscope images showed that Shewanella lohica was attached to the Fe(III)-oxide surfaces during bioreduction. Our findings suggest that DIR of Fe(III) oxides from mine waste placed in marine environments could result in adverse ecological impacts such as liberation of trace metals in the environment.

  • 2.
    Murray, Jesica
    et al.
    Instituto de Bio y Geo Ciencias del Noroeste Argentino, Universidad Nacional de Salta - CONICET, 4405 Rosario de Lerma, Argentina. Laboratoire d'Hydrologie et de Géochimie de Strasbourg, Université de Strasbourg, EOST, CNRS, Strasbourg, France.
    Nordstrom, Darrell Kirk
    United States Geological Survey, Boulder, CO, United States of America.
    Dold, Bernhard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Orué, Maria Romero
    Instituto de Bio y Geo Ciencias del Noroeste Argentino, Universidad Nacional de Salta - CONICET, Rosario de Lerma, Argentina.
    Kirschbaum, Alicia
    Instituto de Bio y Geo Ciencias del Noroeste Argentino, Universidad Nacional de Salta - CONICET, Rosario de Lerma, Argentina.
    Origin and geochemistry of arsenic in surface and groundwaters of Los Pozuelos basin, Puna region, Central Andes, Argentina2019In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 697, article id 134085Article in journal (Refereed)
    Abstract [en]

    Los Pozuelos is a closed basin in the Puna region of NW Argentina, Central Andes. This is a semi-arid region where closed basins are the most important feature for the hydrologic systems. The center of the basin is occupied by a fluctuating playa lake called Los Pozuelos lagoon, which constitutes a UNESCO Biosphere Reserve. This is one of the most populated closed basins in the Argentinian Puna and residents use groundwater for drinking and cooking. Lowest concentrations of As and dissolved solids are in the headwaters of the rivers (1.46–27 μg/L) and the highest concentrations are in the lagoon (43.7–200.3 μg/L). In groundwater, arsenic concentrations increase from the outer ring aquifer (3.82–29.7 μg/L) composed of alluvial-alluvial fan sediments to the inner lacustrine aquifer (10–113 μg/L) that surround the playa lake. Moreover, high concentrations of As during the dry season (90.2 and 113 μg/L), Na/K mass ratios (0.2 and 0.3), and formation of Na-rich efflorescent salts suggest that high evaporation rates increases As concentration, while rainwater dilutes the concentration during the wet season. As(V) is the dominant species in all the water types, except for the lagoon, where As(III) occasionally dominates because of organic matter buildup. There are at least three potential sources for As in water i) oxidation of As sulfides in Pan de Azúcar mine wastes, and acid mine drainage discharging into the basin; ii) weathering and erosion of mineralized shales; iii) weathering of volcanic eruptive non-mineralized rocks. Because it is a closed basin, the arsenic released from the natural and anthropogenic sources is transported in solution and in fluvial sediments and finally accumulates in the center of the basin where the concentration in water increases by evaporation with occasional enhancement by organic matter interaction in the lagoon.

  • 3.
    Roebbert, Y.
    et al.
    Leibniz Universität Hannover, Institut für Mineralogie.
    Rabe, K.
    Leibniz Universität Hannover, Institut für Mineralogie.
    Lazarov, M.
    Leibniz Universität Hannover, Institut für Mineralogie.
    Schuth, S.
    Leibniz Universität Hannover, Institut für Mineralogie.
    Schippers, A.
    Bundesanstalt für Geowissenschaften und Rohstoffe.
    Dold, Bernhard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Weyer, S.
    Leibniz Universität Hannover, Institut für Mineralogie.
    Fractionation of Fe and Cu isotopes in acid mine tailings: Modification and application of a sequential extraction method2018In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 493, p. 67-79Article in journal (Refereed)
    Abstract [en]

    Sulfidic mine tailings have a high potential for contamination of the environment by triggering acid mine drainage. Hence, it is crucial to understand metal mobilization processes and to develop monitoring tools. Metal isotope fingerprinting as a potential monitoring tool for metal sulfide oxidation processes was in the focus of this study by using stable isotope signatures of Cu and Fe. For Fe, a six-step sequential extraction method was applied, in order to separate potential Fe-bearing minerals (water-soluble, exchangeable fraction, Fe(III)(oxyhydr)oxides, Fe-oxides, sulfides and organic compounds and residual/silicates). For Cu, this method was modified into a four step extraction method (water-soluble, exchangeable fraction, oxalate fraction/bound to Fe-oxides and sulfides/residual). To verify accuracy and precision of the sequential extraction method for metal isotope analysis, isotope fractionation during the extraction procedure was investigated employing minerals for which the mineral composition and the isotopic composition was known. The developed procedure is suitable to separate target minerals with only a small loss in the elemental budget. No significant isotope fractionation was observed during the extraction procedure.

    Application of this method on two sites of porphyry copper mine tailings in the Atacama Desert in Chile (Chañaral bay) revealed several implications about the mobilization of Fe and Cu in an environmental setting. Iron contents and Fe isotope compositions are homogeneous with depth (0–61 cm; δ56Fe ~0.2–0.3‰) for the bulk and the Fe(hyr)oxide fraction and only the deepest samples at ~60 cm exhibited lower δ56Fe values (~0‰), which are likely related to the occurrence of an alluvium at this depth. The Fe silicate fraction shows higher δ56Fe values (0.6–0.9‰), most likely because of preferential leaching of the light Fe isotopes. This consequently indicates a more pronounced Fe isotope fractionation with depth, as is expected from longer weathering. The Fe sulfide fraction is isotopically lighter compared to the Fe(hydr)oxide fraction, because during sulfide oxidation the heavy Fe isotopes prefer the oxidized forms and oxidative precipitation results in an enriched Fe isotopic signature for Fe(hydr)oxides. The Cu isotope compositions of all bulk samples and individual fractions (except the Cu sulfides) of one site (Ch1) exhibited a decrease of the δ65Cu values from the depth towards the surface, i.e. in agreement with the capillary water rise in the arid climate. A correlation of δ65Cu with pH indicates preferential adsorption of 65Cu on Fe(oxy)hydroxides at site Ch1, which is evident by a change of δ65Cu from 0.5‰ to −0.7‰ in the water-soluble fraction. At another site (Ch12), where pH at depths was potentially not high enough for the formation of Fe-minerals that could adsorb Cu, only minor Cu isotope fractionation was observed in the water-soluble fraction. The Cu sulfide fraction at site Ch1 exhibits higher δ65Cu values with an increase from the bottom (0.42‰) to the surface (0.92‰), which might be related to preferential leaching of the light isotopes, e.g. by microorganisms.

  • 4.
    Salifu, Musah
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Aiglsperger, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Hällström, Lina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Billström, Kjell
    Department of Geological Sciences, Swedish Museum of Natural History, Frescativagen 40, Box 50007, 104 05, Stockholm, Sweden.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Dold, Bernhard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Strontium (87Sr/86Sr) isotopes: A tracer for geochemical processes in mineralogically-complex mine wastes2018In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 99, p. 42-54Article in journal (Refereed)
    Abstract [en]

    Interpretation of geochemical data based primarily on elemental concentrations often lead to ambiguous results due to multiple potential sources including mineral weathering, atmospheric input, biological cycling, mineral precipitation and exchange processes. The 87Sr/86Sr ratio is however not fractionated by these processes. In this study, Sr isotope (87Sr/86Sr) ratios have been coupled with chemical data of Sr and Rb-bearing minerals, tailings and leachates (water-soluble) to gain insight into the geochemical processes occurring within the Yxsjöberg Cu-W mine tailings, Sweden. The tailings have been exposed to oxidizing conditions resulting in three geochemical zones namely (i) oxidized, (ii) transition and (iii) unoxidized zones. Leachates from the oxidized zone are acidic (pH = 3.6–4.5) and contain elevated concentrations of metals (e.g. Fe, Cu and Zn) and SO4. The low pH has also led to subsequent weathering of most silicates, releasing Al, Ca, Mg and Na into solution. The 87Sr/86Sr ratio in the tailings ranges from 0.84787 to 1.26640 in the oxidized zone, 0.92660–1.06788 in the transition zone, whilst the unoxidized zone has values between 0.76452 and 1.05169. For the leachates, the 87Sr/86Sr ratio ranges from 2.44479 to 5.87552 in the oxidized zone, 1.37404–1.68844 in the transition zone and 1.03697–2.16340 in the unoxidized zone. Mixing (between mineral weathering and atmospheric sources) was identified as the major process regulating the Sr composition of the tailings and leachates. The highly radiogenic signatures of the leachates in the oxidized zone suggests weathering of biotite, K-feldspar and muscovite. Despite the very radiogenic signatures in the oxidized zone, increments in Ca/K ratios, Be, Ce, Tl, Al, Fe and SO4 concentrations in the water-soluble phase were recorded in its lower parts which suggests the dissolution of amphibole, pyroxene, plagioclase, fluorite, gypsum, Al and Fe –(oxy) hydroxides as well as cation exchange by clay minerals. Presence of clay minerals has led to the partial retainment of radiogenic 87Sr/86Sr resulting in increased 87Sr/86Sr in the solid tailings material at these depths. The 87Sr/86Sr ratios of the water-soluble phase in the transition zone is similar to that of helvine and could indicate its dissolution. In the upper part of the oxidized zone, the 87Sr/86Sr ratios and trends of Be, Ca, SO4, Tl and Zn in the water-soluble phase suggest the dissolution of gypsum which precipitated from a leachate with the isotopic signature of helvine. In the lower part of the unoxidized zone, elevated concentrations of W were recorded suggesting scheelite weathering. But the 87Sr/86Sr ratios are higher than that expected from dissolution of scheelite and indicates additional processes. Possible sources include biotite weathering and groundwater. This study reveals that when interpreting geochemical processes in mine waste environments, 87Sr/86Sr should be considered in addition to chemical constituents, as this isotopic tracer offers better insights into discriminating between different solute sources.

  • 5.
    Dold, Bernhard
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pooler, Robert
    SGS Minerals Chile, Geometallurgy Area, Puerto Madero 130, Pudahuel, Santiago.
    Optimization and quality control of automated quantitative mineralogy analysis for acid rock drainage prediction2017In: Minerals, ISSN 2075-163X, E-ISSN 2075-163X, Vol. 7, no 1, article id 12Article in journal (Refereed)
    Abstract [en]

    Low ore-grade waste samples from the Codelco Andina mine that were analyzed in an environmental and mineralogical test program for acid rock drainage prediction, revealed inconsistencies between the quantitative mineralogical data (QEMSCAN®) and the results of geochemical characterizations by atomic absorption spectroscopy (AAS), LECO® furnace, and sequential extractions). For the QEMSCAN® results, biases were observed in the proportions of pyrite and calcium sulfate minerals detected. An analysis of the results indicated that the problems observed were likely associated with polished section preparation. Therefore, six different sample preparation protocols were tested and evaluated using three samples from the previous study. One of the methods, which involved particle size reduction and transverse section preparation, was identified as having the greatest potential for correcting the errors observed in the mineralogical analyses. Further, the biases in the quantities of calcium sulfate minerals detected were reduced through the use of ethylene glycol as a polishing lubricant. It is recommended that the sample preparation methodology described in this study be used in order to accurately quantify percentages of pyrite and calcium sulfate minerals in environmental mineralogical studies which use automated mineralogical analysis

  • 6.
    Dold, Bernhard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Acid rock drainage prediction: A critical review2016In: Journal of Geochemical Exploration, ISSN 0375-6742, E-ISSN 1879-1689, Vol. 172, p. 120-132Article in journal (Refereed)
    Abstract [en]

    Acid rock drainage (ARD) prediction is a very important issue in order to predict and prevent environmental pollution associated with mining activities. Nowadays, simple tests are widely applied and established in the mining and consulting business for ARD prediction. These tests have many known errors and problems, as that they do not account for the complexity of the mineral assemblage of an ore deposit, and therefore are not able to predict the geochemical behavior accurately. This critical review has the aim of first, highlighting the geochemical processes associated to the problems of ARD prediction. Secondly, the errors and limitations of the standard static and kinetic tests are highlighted. The currently applied calculation factor of 31.25 for sulfide acid potential calculation overestimates the carbonate neutralization potential by 100% in its geochemical assumptions. Thus, the calculation factor 62.5, based on the effective carbonate speciation at neutral pH, is recommended. Additionally, standard ABA procedure ignore the acid potential of Fe(III) hydroxides and/or sulfates and do not distinguish between different carbonate minerals. This can be critical, as for example siderite can be a net acid producing carbonate. Therefore, it is crucial to count on accurate quantitative mineral data in order to be able to accurately predict ARD formation and potential liberation of hazardous trace elements to the environment.

    In many modern mining operations, quantitative mineral data is nowadays produced in order to enhance the recovery of the extraction process by the incorporation of geometallurgical information (e.g. quantitative mineralogy, mineral liberation, textural information, grain size distribution). Thus, the use of this very same existing data for ARD prediction can increase importantly the precision of ARD prediction, often without additional costs and testing. The only requirement is the interdisciplinary collaboration between the different divisions and data exchange in a modern mining operation.

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