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  • 1.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Project: Kolarctic ENBI EnviMIne2014Other (Other (popular science, discussion, etc.))
    Abstract [en]

    The objectives of the project are to develop a methodology for environmentally safe mine closure under specific conditions in the Barents region by cross border cooperation, exchange experiences and scientific knowledge.

  • 2.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Sulphide oxidation and geochemical processes in mine tailings2003Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The generation of acid mine drainage (AMD) from oxidation of sulphide- bearing waste is a world wide problem, due to low pH levels and the release of metals to recipients. It is therefore important to understand the fundamental geochemical processes occurring in mine waste. The geochemistry of the drainage water from the tailings at the abandoned Laver copper mine in Northern Sweden was studied in 2001 and compared with a previous study performed in 1993. All drainage water is collected in a brook, which means that Laver is a favourable site for mass balance studies. The results show a decrease in the amount of sulphide-associated elements such as S, Cu and Zn in the drainage water, and an increase of the pH level. It has been suggested that this is due to the decrease in the sulphide oxidation rate in the tailings. Modelling the oxidation front movement using the shrinking core model gives similar results. This indicates that the sulphur transported in the drainage water could relatively well reflect the oxidation rate in the tailings. Oxygen sampling was also performed in 2001- 2002 to evaluate whether the flux of oxygen into the tailings was restricted by a vegetation cover. The results show that vegetation does not limit oxygen diffusion into the tailings. There is an atmospheric concentration throughout a profile through oxidised grass covered tailings during the whole sampling period. Oxygen concentrations at depths where sulphide oxidation occurs show seasonal variations, probably due to varying water saturation. Cemented layers were sampled at two locations in the Laver impoundment tailings, where they had been formed in spite of the low sulphide content and lack of carbonates. The aim of the study was to determine the effects of cemented layer formation on metal mobility in the tailings. The cementing agents are jarosite and Fe-oxyhydroxides. Arsenic is strongly enriched and somewhat higher concentrations of Pb, V, Mo and Hg, compared to those in unoxidised tailings, occur in these layers. Sequential extraction shows that these metals are mostly adsorbed/co-precipitated with crystalline iron oxyhydroxides. The enriched metals will probably be remobilised if changes towards more reducing conditions occur, for instance as a result of remediation of the tailings impoundment. An attempt was made to use LA-ICP-SMS to quantify the role of pyrite surfaces as scavengers of metals in oxidising mine tailings. Pyrite grains were collected from a profile through the pyrite-rich tailings at the Kristineberg mine in Northern Sweden. At each spot hit by the laser, the surface layer was analysed in the first shot, and a second shot on the same spot indicated the chemical composition of the pyrite immediately below. The crater diameter for a laser shot is known, and by estimating the crater depth and total pyrite surface, the total enrichment on pyrite grains was calculated. Results are presented for As, Cd, Co, Cu, Ni and Zn. The results clearly show that there is an enrichment of As, Cd, Cu and Zn on the pyrite surfaces below the oxidation front in the tailings, but not of Co and Ni. Arsenic is also enriched on the pyrite grains that survived in the oxidised zone. However, only 1.4 to 3.1% of the Cd and Zn released by sulphide oxidation in the oxidised zone had been enriched on the pyrite surfaces in the unoxidised tailings, but for As and Cu the corresponding figures are about 64 and 43%, respectively. The results should not be taken too literally but allow the conclusion that scavenging to pyrite surfaces is an important process for retention of As and Cu below the oxidation front in pyrite-rich tailings. Although only pyrite grains that appeared to be fresh, without surface coatings, were used in this study, the possibility of a thin layer of Fe-hydroxides occurring must be considered. Both adsorption to the pyrite directly, or to Fe-oxyhydroxides, may explain the enrichment of As, Cd, Cu and Zn on the pyrite surfaces, and, in the case of Cu, also replacement of Fe (II) by Cu(II) in pyrite.

  • 3.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Sulphide oxidation, oxygen diffusion and metal mobility in sulphide-bearing mine tailings in Northern Sweden2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Large quantities of sulphide-bearing mining wastes produced from ore processing are deposited throughout the world. Sulphide oxidation in the wastes may release acidic water with high concentrations of metals to the environment. Remediation strategies are usually site specific, since the physical and chemical properties of the wastes vary. Therefore, sulphide oxidation, oxygen diffusion and metal mobility in unoxidised and oxidised, remediated and unremediated wastes have been studied in the present work. The efficiency of different cover systems on unoxidised tailings from Kristineberg, were studied in pilot-scale test cells (5*5*3 m3)under field conditions. Clayey till, sewage sludge, apatite and Trisoplast were used as sealing layers and unspecified till as a protective cover. In one cell tailings were left uncovered. Unoxidised tailings in the test-cells in the initial stage after deposition showed relatively low sulphur release (600- 800 mg/l)in leachate waters, which probably was an effect of high moisture content in the tailings prior to deposition. Near-neutral pH found in the leachates was an effect of neutralisation by carbonate minerals present and lime (Ca(OH)2) added prior to deposition. Similar sulphur concentrations were found also in the uncovered tailings. The sulphide oxidation rate increased with time in the uncovered tailings, and decreased in the covered. The lowest oxygen concentrations were observed below the cover system with sewage sludge, which was the most effective barriar against oxygen in a short-term perspective. The oxygen fluxes through the clayey till and apatite layers were within the same magnitude and varied between 0.5 and 4 mole/year,m2. The Trisoplast layer seemed to have failed as a barrier against oxygen. Tailings studied at field scale at Laver and Kristineberg had oxidised for more than 50 years. The tailings at Kristineberg have high pyrite content (c.25% and 50%) and those at Laver have low grade of pyrrhotite (2-3%). The Laver tailings are unremediated, while at Kristineberg the tailings were remediated in 1996. The transport of metals in the drainage water at Laver decreased during a study period of 8 years. The transport of dissolved sulphur indicated a declining trend of sulphide oxidation rate in the tailings, which was confirmed by oxygen measurements in the tailings and weathering rate estimations. The decline was considered to be natural as a result of the increased distance that oxygen has to travel to reach unoxidised sulphide grains. The major part of the amounts of metals released by sulphide oxidation were secondarily retained in the tailings, and to a small extent in layers cemented by jarosite and Fe-(oxy)hydroxides. Sequential extraction of these layers showed that metals such as Cu and Pb were mostly associated with crystalline Fe-(oxy)hydroxides. Most important retention mechanism was, however, sorption onto minerals surfaces below the oxidation front. The studied Impoundment 1 at Kristineberg was remediated by two different methods; on one part a dry cover consisting of a sealing layer and a protective cover were applied, and the groundwater table was raised and a single dry cover applied on the other part. When the groundwater table was raised in oxidised tailings, secondarily retained metals such as Fe, Mg, Mn, S and Zn were remobilised resulting in increased concentrations in the groundwater. The concentrations declined with time, due to dilution by inflowing uncontaminated water. Decreased concentrations of Fe, Mg, Mn, S and Zn were observed also in the groundwater below the dry cover as the amount of percolating water decreased. The concentrations of trace elements such as Cd, Co, Cr, Cu, Ni and Pb were almost depleted in the groundwater, since these metals were retained within the tailings by mechanisms such as co-precipitation, precipitation and sorption. Analysis of pyrite grains by LA-ICP-SMS showed that pyrite surfaces were important for retention of As and Cu, in particular, but also for Cd and Zn. This study shows that the physico-chemical conditions expressed by pH and redox potential have a large impact on element mobility’s. For example, As was mobilised as a result of remediation, while the concentrations of most metals decreased in the drainage waters.

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  • 4.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Andersson, Elin
    Vectura Consulting AB.
    Mueller, Seth
    Boliden Mineral AB.
    Neutralization/prevention of acid rock drainage using mixtures of alkaline by-products and sulfidic mine wastes2013In: Environmental Science and Pollution Research, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 20, no 11, p. 7907-7916Article in journal (Refereed)
    Abstract [en]

    Backfilling of open pit with sulfidic waste rock followed by inundation is a common method for reducing sulfide oxidation after mine closure. This approach can be complemented by mixing the waste rock with alkaline materials from pulp and steel mills to increase the system’s neutralization potential. Leachates from 1 m3 tanks containing sulfide-rich (ca.30 wt %) waste rock formed under dry and water saturated conditions under laboratory conditions were characterized and compared to those formed from mixtures. The waste rock leachate produced an acidic leachate (pH < 2) with high concentrations of As (65 mg/L), Cu (6 mg/L), and Zn (150 mg/L) after 258 days. The leachate from water-saturated waste rock had lower concentrations of As and Cu (<2 μg/L), Pb and Zn (20 μg/L and 5 mg/L), respectively, and its pH was around 6. Crushed (<6 mm) waste rock mixed with different fractions (1–5 wt %) of green liquid dregs, fly ash, mesa lime, and argon oxygen decarburization (AOD) slag was leached on a small scale for 65 day, and showed near-neutral pH values, except for mixtures of waste rock with AOD slag and fly ash (5 % w/w) which were more basic (pH > 9). The decrease of elemental concentration in the leachate was most pronounced for Pb and Zn, while Al and S were relatively high. Overall, the results obtained were promising and suggest that alkaline by-products could be useful additives for minimizing ARD formation

  • 5.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bark, Glenn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Ericsson, Magnus
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Söderholm, Patrik
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences.
    Wanhainen, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Widerlund, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Norrbottens malm- och mineralresurs och dess potentiella betydelse för innovation, samhälle och miljö2014Report (Other academic)
    Abstract [sv]

    Gruvindustrins betydelse för samhällsutveckling och infrastruktur i Sverige och inte minst i Norrbottens län är mycket stor. De geologiska förutsättningarna att hitta nya brytvärda förekomster i Norrbotten är goda. Länet är tillsammans med Västerbotten en av Europas viktigaste regioner för utvinning av metaller. Det syns också i den nyligen framtagna regionala mineralstrategin för Norrbotten och Västerbotten. Visionen för den regionala mineralstrategin: ”Genom långsiktigt hållbart nyttjande av Norrbottens och Västerbottens läns mineralresurser har ytterligare tillväxt skapats i regionen och hela Sverige. Vi har utvecklat och stärkt vår ställning som ledande gruv- och mineralnation.”Eftersom framtidspotentialen för gruvnäringen är mycket god men okunnigheten hos både allmänhet och beslutsfattare om näringens betydelse för innovation och samhällsutveckling är stor, kopplat med en utbredd oro för miljöpåverkan, måste dessa viktiga framtidsfrågor belysas. Med finansiering från Länsstyrelsen i Norrbotten bedrevs därför under första hälften av 2014 en förstudie som syftade till att sammanfatta kunskapsläget om framtidens gruvindustri i Norrbotten. Resultaten av förstudien redovisas i den här rapporten. En viktig slutsats är att det under nästa strukturfondsperiod (med start 2015) behövs ett framtidsinriktat forskningsprogram för att belysa de möjligheter som finns. Denna förstudie utgör grund för en kommande ansökan till strukturfonderna. Kompetensen som finns vid Luleå tekniska universitet, Sveriges centrum för gruvrelaterad forskning och utbildning, bör användas för att studera troliga framtidsmöjligheter och hur de ska kunna användas för att få en så positiv utveckling som möjligt för länet. Projektet bör innehålla följande tre huvudinriktningar, som naturligtvis hör ihop:Vilka malm- och mineralresurser finns det potential för i Norrbotten, och vilka kommer sannolikt att exploateras i framtiden?Vad kommer den exploateringen att ha för betydelse för innovation och samhällsutveckling?Vad kommer den exploateringen att få för miljöeffekter och hur ska man göra för att minska miljöbelastningen?En annan slutsats är att nedlagda gruvområden inte måste ses som förstörd natur. Betydande mervärden som gruvturism skulle kunna skapas om vilja, kreativitet och beslutsamhet finns. Detta är ett givet utvecklingsområde där småföretag och entreprenörer kan göra stor insats om de politiska och myndighetsmässiga förutsättningarna finns. Dessa aspekter skulle också kunna belysas i det föreslagna forskningsprogrammet eller i ett eget projekt.

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  • 6.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Dagli, Deniz
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Knutsson, Sven
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Literature review on potential geochemical and geotechnical effects of adopting paste technology under cold climate conditions2013Report (Other academic)
    Abstract [en]

    The purpose of this literature review is to summarize the recent research regarding geochemical and geotechnical stability of paste tailings, identify knowledge gaps and future research needs. The present study has been conducted by the Division of Geosciences and Environmental Engineering together with the Division of Mining and Geotechnical Engineering at Luleå University of Technology on behalf of Boliden Mineral, LKAB and Outotec.A survey conducted by MEND (Mine Environment Neutral Drainage) in 2006 on the environmental effects related to the use of paste tailings summarizes that only a few studies had been performed about long-term effects on the surface and groundwater quality. Instead, the focus had been on the additives and the strength of the paste. It is still uncertain how the paste technology affects the long-term environmental stability from a geochemical point of view. Concerns regarding the stability of paste with high sulphide content are still relevant. Studies performed indicate that sulphide oxidation occurs within cemented paste as well as on the surface of non-cemented paste and cracks formed on the surfaces could induce oxidation. For cemented paste, metals released by sulphide oxidation might be sequestered due to high pH induced by the alkaline additives, but anion such as Se has been shown to be mobilized. The leachate has been shown to be near-neutral initially, but the neutrality decreases with time and probably metals sequestered in the matrix will also be released. Again, it should be noted that no long term study was performed on leaching of paste, cemented or uncemented. The longest leaching study was performed for one year. Arsenic has been proven to be retained in Ca-arsenates in cemented paste, but the long term stability of these precipitates is relatively unknown. Expanded secondary phases e.g. gypsum and ettringite have been observed to form when there is sulphate in the process or drainage of water. These phases could crack the paste, but, on the other hand, can also fill former cracks when deposited in layers. The effects of the formation of these phases are relatively uncertain in a long-term perspective. Presence of different elements such as ammonium, sulphates and metals in the water has been shown to negatively affect the curing process and therefore water is suggested to be treated before use. The presence of carbon dioxide during the paste formation could also affect the curing process, but could sequester metals in carbonate phases.Geotechnical and rheological properties of paste is well defined and documented. Several case studies have been found in literature providing valuable information about the details of the works being carried out. However, a difficulty has been noted during the investigation of the effects of cold climate conditions when current practice is applied in the colder parts of the world. It is not certain how some specific and vital parameters are going to be affected by cold temperatures. Parameters such as deposition slopes and deposition scheme, strength development of the paste are expected to be responsive to cold climate conditions. There are predictions about which properties are going to be affected in what way, but there is also a need to establish a scientific base for discussion. These have been highlighted as research needs and information gaps at the end of the report.

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  • 7.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Hamberg, Roger
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Project: ERA-MIN project "Tools for sustainable gold mining in EU"2014Other (Other (popular science, discussion, etc.))
    Abstract [en]

    This research identifies and evaluates environmental impacts and economical challenges of gold mining in Finland, Sweden, Portugal, Romania, Poland and Ireland. The focus of this project is in gold exploration, mineral processing, water treatment, waste management, environmental monitoring, risk assessment and socio-economic impacts of gold mining. Finasieras av Vinnova

  • 8.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Hanna, Kaasalainen
    Sweco.
    Maurice, Christian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nyström, Elsa
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nigéus, Susanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    StopOx: Utilization Of Industrial Residuals For Prevention Of Sulfide Oxidation In Mine Waste2019Report (Other academic)
    Abstract [en]

    This report is the outcome of the SIP STRIM project

    StopOx-Utilization of industrial residuals for prevention of sulfide oxidation in mine waste implemented at Applied geochemistry, Luleå University of Technology running from 2015 to 2018. Boliden Mineral has been partner and co-funder of the project. Other partners in the project were Cementa, Dragon Mining, MEROX, Nordkalk, and SP Processum. The overall aim of the project was to develop prevention technologies to reduce the sulfide oxidation in mine waste, during and after operation, and thereby reduce the generation of acid mine drainage. The StopOx project has been focusing on sulfidic mine waste from the Boliden area which were disposed of and are causing acid mine drainage or have the potential. Industrial residues/products were supplied by BillerudKorsnäs, Cementa, MEROX, and Nordkalk. The report consists of chapters based on three subprojects.

    Chapter 1. Introduction

    Chapter 2. Inhibition technology with aim to minimize waste rock oxidation during operations by using residues from other industries (passivation of sulfidic surfaces by the formation of secondary minerals)

    Chapter 3. The suitability of green liquor dregs as substitutes for or additives to till in a sealing layer as part of a cover system

    Chapter 4. Weathering of waste rock under changing chemical conditions

    The research described in chapters 2 and 3 was performed by Ph.D. students and will continue until 2021, while the subproject in chapter 2 ended in 2018.

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  • 9.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Lundberg, Angela
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nason, Peter
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Simulation of pyrite oxidation in fresh mine tailings under near-neutral conditions2012In: Journal of Environmental Monitoring, ISSN 1464-0325, E-ISSN 1464-0333, Vol. 14, no 8, p. 2245-2253Article in journal (Refereed)
    Abstract [en]

    Sulphidic residual products from ore processing may produce acid rock drainage, when exposed to oxygen and water. Predictions of the magnitude of ARD and sulphide oxidation rates are of great importance in mine planning because they can be used to minimize or eliminate ARD and the associated economic and environmental costs. To address the lack of field data of sulphide oxidation rate in fresh sulphide-rich tailings under near-neutral conditions, determination and simulation of the rate was performed in pilot-scale at Kristineberg, northern Sweden. The quality of the drainage water was monitored, along with oxygen and carbon dioxide concentrations. The chemical composition of the solid tailings was also determined. The field data were compared to predictions from simulations of pyrite oxidation using a 1-D numerical model. The simulations' estimates of the amount of Fe and S released over a seven year period (52 kg and 178 kg, respectively) were in reasonably good agreement with those obtained by analysing the tailings (34 kg and 155 kg, respectively). The discrepancy is probably due to the formation of secondary precipitates such as iron hydroxides and gypsum; which are not accounted for in the model. The observed mass transport of Fe and S (0.05 and 1.0 kg per year, respectively) was much lower than expected on the basis of the simulations and the core data. Neutralization reactions involving carbonates in the tailings result in a near-neutral pH at all depths except at the oxidation front (pH < 5), indicating that the dissolution of carbonates was too slow for the acid to be neutralized, which instead neutralized deeper down in the tailings. This was also indicated by the reduced abundance of solid Ca at greater depths and the high levels of carbon dioxide both of which are consistent with the dissolution of carbonates. It could be concluded that the near-neutral pH in the tailings has no decreasing effect on the rate of sulphide oxidation, but does reduce the concentrations of dissolved elements in the drainage water due to the formation of secondary minerals. This means that sulphide oxidation rates may be underestimated if determined from drainage alone.

  • 10.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Lundberg, Angela
    Öhlander, Björn
    Changes of groundwater quality in sulphide-bearing mine-tailings as a result of remediation at Kristineberg, northern Sweden2007In: Mining and the Environment International Conference: proceedings, Centre for Environmental Monitoring, Laurentian University , 2007Conference paper (Refereed)
    Abstract [en]

    At the Kristineberg mine in northern Sweden, sulphide-rich tailings left open for 50 years were remediated in 1996 by applying double dry cover on one part of an impoundment, and raised groundwater level combined with simple till cover on the other part. Groundwater pipes installed in the impoundment were sampled from 1998 during a period of 6 years. The results showed that the groundwater quality varied considerably in the impoundment, even under the same type of cover. Secondarily retained Fe, S, Mg, Mn and Z were remobilised when the groundwater was raised. In the part with raised groundwater level, the average concentration of Fe ranged from 2700 to 9000mg/l in 1998, and the range for S was 2200 to 7000mg/l. During 2003 the average concentrations had decreased and ranged between 150 and 900 mg/l for Fe and between 130 and 900 mg/l for S. The improvement of the water quality was caused by inflow of less contaminated groundwater and decreasing sulphide oxidation rate. The redox potential generally decreased and pH increased. The concentrations of Cd, Cu and Pb in groundwater decreased rather rapidly all over the impoundment after remediation. In areas with relatively high pH and low redox potential, Al, Cd, Co, Cr, Cu, Fe, Ni, Pb and Zn were almost depleted.

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  • 11.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Lundberg, Angela
    Öhlander, Björn
    Pilot scale studies of different dry covers on sulphide-rich tailings in northern Sweden, oxygen diffusion2005In: Securing the future: international conference on mining and the environment, metals and energy recovery : proceedings, Stockholm: SweMin , 2005, p. 9-18Conference paper (Other academic)
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  • 12. Alakangas, Lena
    et al.
    Lundberg, Angela
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pilot-scale studies of different covers on unoxidised sulphide-rich tailings, northern Sweden: oxygen diffusion2010In: Mine Water and the Environment: proceedings of the 10th IMWA Congress 2008 : 2-5 June, 2008 - Karlovy Vary, Czech Republic / [ed] Nadia Rapantova; Zbyněk Hrkal, Ostrava: VSB - Technical University Ostrava, Faculty of Mining and Geology, Institute of Environmental Engineering , 2010, p. 347-350Conference paper (Refereed)
    Abstract [en]

    The efficiency of five cover systems to decrease oxygen intrusion into sulphide-rich tailings was studied in pilot-scale test cells (5x5x3 m(3)). The covers consisted of clayey till, sewage sludge, fine-grained apatite concentrate or Trisoplast (a mixture of a polymer, bentonite and tailings sand) as sealing layers and unspecified till as protective cover. In one reference cell, tailings were uncovered. Oxygen concentrations below the entire covers were highest below the Trisoplast and apatite layers, and lowest below the sewage sludge layer. Effective diffusion coefficients (D-eff) and oxygen fluxes were estimated in the covers with non-oxygen-consuming sealing layers (clayey till and apatite). For the protective covers the Deff ranged between E-09 and E-07 m(2)/s, and for the sealing layers between E-10 and E-09 m(2)/s, and for the entire covers between E-10 and E-08 m(2)/s. Seasonal variations in D-eff were larger within the covers than between the different cover systems. Oxygen fluxes through the entire covers with clayey till and apatite ranged between 0.2 and 4 mole m(2)/year, which was a reduction of more than 99% compared to uncovered dry tailings.

  • 13.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maurice, Christian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Projekt: Användning av restprodukter för förhindrande sulfid oxidation i reaktivt gruvavfall- en förstudie2014Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    En inventering av lämpliga restmaterial för efterbehandling och behandling av gruvavfall har genomförts och resulterat i en rapport

  • 14.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maurice, Christian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Macsik, Josef
    Strategic services & Sustainable Development at Ecoloop AB, Sweden.
    Nyström, Elsa
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Sandström, Nadia
    Luleå University of Technology.
    Andersson-Wikström, Alexandra
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Hällström, Lina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kartläggning av restprodukter för efterbehandling och inhibering av gruvavfall: Funktion, tillgång och logistik2014Report (Other academic)
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  • 15.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maurice, Christian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nyström, Elsa
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Siren, Susanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Project: Utilization of Industrial Residuals for Prevention of Sulphide Oxidation in Mine Wastes2014Other (Other (popular science, discussion, etc.))
  • 16.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nason, Peter
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Declining element concentrations in groundwater after remediation in sulphide-rich tailings at Kristineberg, northern Sweden2010In: Mine Water & Innovative Thinking / [ed] Ch. Wolkersdorfer; A. Freund, Cape Breton University Press , 2010, p. 323-327Conference paper (Refereed)
  • 17.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Torklid Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Project: Development, Evaluation and Optimization of Measures to Reduce the Impact on the Environment from Mining Activities in Northern Regions2016Other (Other (popular science, discussion, etc.))
    Abstract [en]

    Min-North is a transnational project financed by the Interreg Nord program and coordinated by LTU. The project is a cooperation between Geological survey of Finland, GTK, Oulo University (Finland), The Arctic University of Norway, UiT and several (>17) small and large enterprises and mining companies in the northern region with expertise within geology, waste management, geophysics and geochemistry. The overall goal is to reduce the environmental impacts of mining in the northern regions by developing, evaluating, optimizing environmental techniques. In Sweden, geophysical and geochemical techniques will be integrated to develop a 4D model for tracing pollution transport in the mine waste, mine areas and in(to) the surroundings.

  • 18.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Salifu, Musah
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Heino, Neea
    Geological Survey of Finland, Finland.
    Hyvönen, Eija
    Geological Survey of Finland, Finland.
    Karlsson, Teemu
    Geological Survey of Finland, Finland.
    Panttila, Hannu
    Geological Survey of Finland, Finland.
    Pietilä, Raija
    Geological Survey of Finland, Finland.
    Tornivaara, Anna
    Geological Survey of Finland, Finland.
    Turunen, Kaisa
    Geological Survey of Finland, Finland.
    Lu, Jinmei
    UiT The Arctic University of Norway, Norway.
    Fu, Shuai
    UiT The Arctic University of Norway, Norway.
    Bui, Minh Tuan
    UiT The Arctic University of Norway, Norway.
    Heiderscheidt, Elisangela
    University of Oulu, Finland.
    Postila, Heini
    University of Oulu, Finland.
    Leiviskä, Tiina
    University of Oulu, Finland.
    Ronkanen, Anna-kaisa
    University of Oulu, Finland.
    Kujala, Katharina
    University of Oulu, Finland.
    Khan, Uzair
    University of Oulu, Finland.
    Gogoi, Harshita
    University of Oulu, Finland.
    Min-North: Development, Evaluation and Optimization of Measures to Reduce the  Environmental Impact of Mining Activities in Northern Regions2019Report (Other academic)
    Abstract [en]

    The Min-North (Development, Evaluation and Optimization of Measures to Reduce the Environment Impact of Mining Activities in Northern Regions) project was a trans-national cooperative project, with participants from the Geological Survey of Finland (GTK), University of Oulu (UO), UiT The Arctic University of Norway (UiT), Luleå University of Technology (LTU) and SMEs from Sweden, Finland and Norway. The project was funded by Interreg Nord and Norrbottens länsstyrelse. The participants have expertise in mine waste management, mine water treatment and geophysics. The overall aim of the project was to enhance the development of environmental protection technologies. An associated goal was to deepen cross-border cooperation by creating a larger critical mass of researchers in mine waste management and local SMEs in the Northern regions with greater capacities to disseminate and implement new methods, products and services. The project ran for 36 months from the 1st of January 2016 to the end of December 2018.

     

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  • 19.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Rosenkranz, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Martinsson, Olof
    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.
    Project: Improve Resource Efficiency and Minimize Environmental Footprint2016Other (Other (popular science, discussion, etc.))
    Abstract [en]

    The REMinE project is organized in five work packages that comprise: detailedcharacterization and risk assessment of the mine wastes selected (WP2), identification of new processing methods for mine waste (WP3), characterization and risk assessment of the remaining residuals (WP4), outlining business opportunities and environmental impact in a conceptual model for sustainable mining (WP5). The project comprises case studies of historical mine wastes from three different European countries, namely Portugal, Romania and Sweden. The interdisciplinary research collaboration in this project is innovative in the sense that separation of minerals and extraction of metals not only are basedon technical and economic gain but also considers the environmental perspective.

  • 20.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Öhlander, Björn
    Formation and composition of cemented layers in low-sulphide mine tailings, Laver, northern Sweden2006In: Environmental Geology, ISSN 0943-0105, E-ISSN 1432-0495, Vol. 50, no 6, p. 809-819Article in journal (Refereed)
    Abstract [en]

    Cemented layers (hardpans) are common in carbonate or sulphide-rich mine tailings and where pyrrhotite is the predominating Fe-sulphide. Laver, northern Sweden, is an abandoned Cu-mine where the tailings have low pyrrhotite content, almost no pyrite and no carbonates. Two cemented layers at different locations in the Laver tailings impoundment were investigated, with the aim to determine their effects on metal mobility. The cementing agents were mainly jarosite and Fe-oxyhydroxides in the layer formed where the tailings have a barren surface, whereas only Fe-oxyhydroxides were identified below grass-covered tailings surface. Arsenic was enriched in both layers which also exhibit high concentrations of Mo, V, Hg and Pb compared to unoxidised tailings. Sequential extraction indicates that these metals and As were mainly retained with crystalline Fe-oxides, and therefore potentially will be remobilised if the oxic conditions become more reducing, for instance as a result of remediation of the tailings impoundment.

  • 21.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Öhlander, Björn
    Pilot-scale studies of different covers on unoxidised sulphide-rich tailings in northern Sweden: the geochemistry of leachate waters2006In: Mine Water and the Environment, ISSN 1025-9112, E-ISSN 1616-1068, Vol. 25, no 3, p. 171-183Article in journal (Refereed)
    Abstract [en]

    Leachate water quality from covered and uncovered unoxidised sulphide-rich tailings in six pilot-scale (5x5x3 m3) test cells was monitored during 2004 and 2005. The covers consisted of a layer of clayey till, sewage sludge, apatite or Trisoplast (a commercial mixture of tailings, bentonite, and a polymer). All layers were protected by an unspecified till except in one reference cell, where the tailings were left open. All leachate waters showed near-neutral pH as a result of neutralization by calcite in the tailings and by Ca(OH)2 added prior to deposition. Average dissolved sulphur concentrations in the leachates were ≈ 600 mg L-1, except in the cell with sewage sludge (300 mg L-1). The source of sulphur was mainly pyrite oxidation, but residual sulphur probably remained from the enrichment process. The near-neutral pH favoured precipitation of metal-(oxy)hydroxides with subsequent removal of trace elements such as Cd, Cu and Pb (< 15 μg L-1) from the solutions. High concentrations of Co, Mn, Ni, and Zn were found in leachates from the apatite, Trisoplast, and uncovered tailings cells. High As concentrations were found in the leachates in the sewage sludge and clayey till cells. The lowest metal concentrations, redox potential, and highest pH were found in the sewage sludge cell. Decreased elemental metal concentrations during 2004 suggest improved performance over time.

  • 22.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Öhlander, Björn
    The effect of vegetation on mine tailings2003In: Program with Abstracts : Joint Annual Meeting, Geological Association of Canada; Mineralogical Association of Canada , 2003, Vol. 28Conference paper (Other academic)
    Abstract [en]

    One of the major aims with passive remediation of sulfide-bearing mine tailings is to minimize or exclude oxygen diffusion through the tailings and decrease the oxidation of sulfides. A vegetation cover could potentially decrease the oxygen flux by oxygen consumption during decay of organic matter. The abandoned Cu mine at Laver in northern Sweden has not been remediated except for establishment of vegetation, and this offers the opportunity to investigate the effect of a vegetation cover on tailings.Whole-year sampling of surface drainage water from the tailings impoundment was performed during 1993 and 2001. The release of metals was only 5-10 % of the estimated weathering rate in the tailings during 1993 because of secondary retainment within the tailings. Results from 2001 show decreasing concentrations of several elements and increasing pH, indicating decreasing oxidation rate.Pore-gas measurement in two vertical profiles shows that vegetation on the tailings has no effect as a barrier for oxygen diffusion in comparison with barren parts.Cemented layers, which have formed at various depths in the tailings, have decreased the flux of oxygen to deeper parts; this could be an explanation of the decreased oxidation rate. The different cemented layers in the tailings differ in chemical composition and physical characteristics. There are two major types, both of which both contain iron oxides and carbon. The origin of the carbon is possibly the vegetation cover. None of the cemented layers acts as a trap for heavy metals, but As is enriched.The effect of vegetation as a oxygen barrier is negligible, but vegetation could act as a source for organic matter that could increase aggregation of iron oxides and clay minerals, thereby enhancing the formation of cemented layers or increasing metal-organic complexes which decrease the mobility of metals.

  • 23.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Öhlander, Björn
    Lundberg, Angela
    Changes of sulphide oxidation rates over time in mine tailings, Laver, Northern Sweden2009In: 8th International Conference on Acid Rock Drainage (ICARD) and Securing the Future: Mining, Metals & the Environment in a Sustainable Society 2009: Skelleftea, Sweden, 22 - 26 June 2009, Red Hook, NY: Curran Associates, Inc., 2009Conference paper (Refereed)
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  • 24.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Öhlander, Björn
    Lundberg, Angela
    Estimation of temporal changes in oxidation rates of sulphides in copper mine tailings at Laver, Northern Sweden2010In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 408, no 6, p. 1386-1302Article in journal (Refereed)
    Abstract [en]

    Tailings containing pyrrhotite were deposited in an impoundment at a copper mine at Laver, Northern Sweden, which operated between 1936 and 1946. Since then the oxidation of sulphides has acidified recipient water courses and contaminated them with metals. Measurements from surface water sampled in 1993, 2001 and 2004-05 from a brook into which the tailing impoundment drains indicate that the amounts of sulphide-associated elements such as Cu, S and Zn released into the brook have decreased over time, while pH has increased. The mass transport of S in the brook during 1993 and 2001 corresponded well with the amount of S estimated to be released from the tailings by oxidation. Secondary precipitates such as covellite and gypsum, which can trap sulphur, were shown in earlier studies to be present in only low amounts. The annual release of elements from the tailings was estimated from the volume of tailings assumed to oxidise each year, which depends on movement of the oxidation front with time. The results indicate that the oxidation rate in the tailings has decreased over time, which may be due to the increased distance over which oxygen needs to diffuse to reach unoxidised sulphide grains, or their cores, in the tailings.

  • 25.
    Ban, Jiaxing
    et al.
    School of Water Resource and Environmental, Research Center of Environmental Science and Engineering, China University of Geosciences (Beijing), Beijing, 100083, China; Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, 999077, Hong Kong, China.
    Sun, Keke
    Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, 999077, Hong Kong, China.
    Yao, Jun
    School of Water Resource and Environmental, Research Center of Environmental Science and Engineering, China University of Geosciences (Beijing), Beijing, 100083, China.
    Sunahara, Geoffrey
    School of Water Resource and Environmental, Research Center of Environmental Science and Engineering, China University of Geosciences (Beijing), Beijing, 100083, China; Department of Natural Resource Sciences, McGill University, Montreal, Quebec, H9X3V9, Canada.
    Hudson-Edwards, Karen
    Environment and Sustainability Institute and Camborne School of Mines, University of Exeter, Penryn, Cornwall, TR10 9FE, UK.
    Jordan, Gyozo
    Department of Applied Chemistry, Szent István University, Budapest, 1118, Hungary; State Key Laboratory for Environmental Geochemistry, China Academy of Sciences, Guizhou, 550081, China.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Ni, Wen
    State Key Laboratory of High-Efficient Mining and Safe of Metal Mines, University of Science and Technology Beijing, Ministry of Education, Beijing, 100083, China.
    Poon, Chi-Sun
    Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, 999077, Hong Kong, China.
    Advances in the use of recycled non-ferrous slag as a resource for non-ferrous metal mine site remediation2022In: Environmental Research, ISSN 0013-9351, E-ISSN 1096-0953, Vol. 213, article id 113533Article, review/survey (Refereed)
    Abstract [en]

    The growing global demand for non-ferrous metals has led to serious environmental issues involving uncovered mine site slag dumps that threaten the surrounding soils, surface waters, groundwater, and the atmosphere. Remediation of these slags using substitute cement materials for ordinary Portland cement (OPC) and precursors for alkali-activated materials (AAMs) can convert hazardous solid wastes into valuable construction materials, as well as to attain the desired solidification and stabilization (S/S) of heavy metal(loid)s (HM). This review discusses the current research on the effect of non-ferrous slags on the reaction mechanisms of the OPC and AAM. The S/S of HM from the non-ferrous slags in AAM and OPC is also reviewed. HM can be stabilized in these materials based on the complex salt effect and isomorphic effects. The major challenges faced in AAMs and OPC for HM stabilization include the long-term durability of the matrix (e.g., sulfate attack, stability of volume). The existing knowledge gaps and future trends for the sustainable application of non-ferrous slags are also discussed.

  • 26.
    Filcenco-Olteanu, Antoneta
    et al.
    Research and Development National Institute for Metals and Radioactive Resource.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Fiuza, Antoio
    University of Porto, Engineering Faculty.
    Zlǎgnean, Marius
    Research and Development National Institute for Metals and Radioactive Resource.
    Tomuş, Nicolae
    Research and Development National Institute for Metals and Radioactive Resource.
    Physical chemical characterization of historical mining waste and ARD prediction tests2017In: E3S Web of Conferences, E-ISSN 2267-1242, Vol. 18, no 4, article id 01031Article in journal (Refereed)
    Abstract [en]

    There are thousands of historical mine tailings and metallurgical residues present on inactive metal mining sites which have been abandoned. However, the potential release of dissolved metals, acidity, or suspended particulates from mine-waste dumps can be a serious and long-lasting problem. A variety of environmental impacts may occur at this abandoned mine sites and leading the list is acid generation, which is one of the main problems from metal mining. The objective of the present study was to characterize and evaluate the Romanian historical tailing of Sasar-Red Valley, near Baia Mare. This involved physical and chemical characterization of the materials and its acid generating potential. Sasar tailing impoundment contains 8.5 million m3 of tailings and occupies an area of 32.5 hectares. Tailings samples were collected from different depths in three sampling points, and characterized by grain size, chemical elements concentration, elements distribution of elements in depth, paste pH, acid-base account and net acid generation tests. Acid base accounting (ABA) tests in conjunction with net acid generation (NAG) tests classified the samples into the category of 'potentially acid generating'. This paper presents a synthesis of works performed in the Improve Resource Efficiency and Minimize Environmental Footprint (REMinE) project.

  • 27.
    Hamberg, Roger
    et al.
    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.
    Maurice, Christian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Cementation of cyanidation tailings: Effects on the release of As, Cu, Ni and Zn2018In: Proceedings of the 11th ICARD | IMWA | MWD Conference: “Risk to Opportunity” / [ed] Christian Wolkersdorfer, Lotta Sartz, Anne Weber, Jo Burgess, Gilles Tremblay, International Mine Water Association (IMWA) , 2018, Vol. 2, p. 617-622Conference paper (Refereed)
    Abstract [en]

    Maintaining saturated conditions in two cemented paste backfill (CPB)-mixtures (1-3 wt.% of binders) based on cyanidation tailings was vital for reducing the pyrrhotite oxidation rate and the release of Cu, Ni and Zn. The opposite was true for As, that desorbed from Fe-precipitates and formed soluble Ca-arsenates. Flooding of CPB-fillings could be a long-term process, where unsaturated zones can form within CPB-masses. At this stage, leachates from CPBs (1 wt. %), became acidic, causing As-release to decrease but the opposite for Cu. In CPBs (3wt. %), As-release was unaltered but the Zn-release increased as binder-related Zn-phases dissolved in alkaline conditions.

  • 28.
    Hamberg, Roger
    et al.
    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.
    Maurice, Christian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The release of arsenic from cyanidation tailings2016In: Arsenic Research and Global Sustainability: Proceedings of the 6th International Congress on Arsenic in the Environment, AS 2016 / [ed] Bhattacharya, Prosun; Vahter, Marie; Jarsjo, Jerker; Kumpiene, Jurate; Charlotte, Sparrenbom, London: CRC Press, 2016, p. 201-202Conference paper (Refereed)
    Abstract [en]

    Tailings from a gold mine containing 1000 mg/kg of As were used to predict the release of As over an extended period of time. Post-cyanide mine processes were aiming to form arsenates and Fe-hydrates for effective As-immobilization. Speciation of the As in ore and tailings samples revealed that mining processes have dissolved the majority of the arsenopyrite in the ore, causing secondary As phases to co-precipitate with newly formed Fe-hydrates. Weathering Cell Tests (WCT) were conducted to assess the effect of weathering on the stability of As in the tailings. As-bearing Fe-hydrates remained intact during the early stages of the WCT. During later stages of the WCT, the release of As, Fe and S increased due to pyrrhotite oxidation and the destabilization of As-bearing Fe-hydrates. Low proportions of As was released in WCT, but additional pyrrhotite oxidation as pH falling to < 3 could further destabilize As-bearing Fe-hydrates

  • 29.
    Hamberg, Roger
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bark, Glenn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maurice, Christian
    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.
    Release of arsenic from cyanidation tailings2016In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 93, p. 57-64Article in journal (Refereed)
    Abstract [en]

    At a gold mine in northern Sweden, gold occurring as inclusions in pyrrhotite and arsenopyrite is leached by cyanidation of the ore. The main sulphide minerals in the ore are pyrrhotite and arsenopyrite. Effluents from the cyanidation process are treated with Fe2(SO4)3 to form Fe-precipitates suitable for the co-precipitation of As. The aim of this study was to perform static and kinetic leaching tests on the ore and tailings to define geochemical processes governing As mobility. Sequential leaching tests suggested that the majority of dissolved As deriving from the sulphide fraction in the ore was incorporated in newly formed Fe-precipitates in the tailings. The mobility of As in the tailings was therefore mainly dependent on the stability of these As-bearing Fe-precipitates. Weathering cell tests (WCT) involving 31 weekly cycles of wetting and air exposure were conducted to assess the stability of the As in the tailings under accelerated weathering conditions. The first stage of the WCT was characterized by a pH ≈ 5 and low As leaching, probably driven by the dissolution of amorphous Fe-As species. In the second stage of the WCT, leaching of Fe, S and As increased and the pH decreased to <3.5. An increase of the leachate’s molar Fe/S-ratio suggested that pyrrhotite oxidation was occurring. The falling pH destabilized As-bearing Fe-precipitates, causing further As release. The total As release during the WCT corresponded to only a small proportion of the tailings’ total As content. The accelerated As-leaching observed towards the end of the WCT could thus indicate that its release could increase progressively over time.

  • 30.
    Hamberg, Roger
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maurice, Christian
    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.
    Lowering the water saturation level in cemented paste backfill mixtures: Effect on the release of arsenic2017In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 112, p. 84-91Article in journal (Refereed)
    Abstract [en]

    The Cemented Paste Backfill (CPB) method allows the mixing of dewatered tailings slurries with cementitious binders to backfill excavated underground workings. After mine closure, CPB workings are permanently flooded by rising groundwater. This flooding is considered beneficial for reducing the risk of acid generation associated with CPB containing sulphide minerals. In general, CPB workings are slowly flooded and the process may lead to regions with a low degree of water saturation to form within the CPB. This in turn, may increase oxygen ingress in the CPB, thereby prolonging oxidation of the minerals. To investigate the environmental impact of this oxidation, tailings containing elevated concentrations of arsenic (As) and pyrrhotite were handled via CPB. In this study, CPB mixtures containing 1–3 wt.% of cementitious binders and tailings was studied. The water saturation level in the CPB-mixtures was lowered as curing time extended. In mimicked flooded conditions, the mobility of As in the CPB mixtures was correlated with As-bearing cementitious phases that are sensitive to a reduction in the pH. In CPB-mixtures with lower proportions of binders, cementitious As-phases dissolved while the water saturation level decreased to form more stable As-phases. Increasing binder fractions, most of the cementitious As-phases persisted in the CPB while water saturation levels were lowered and release of As increased. Regardless of curing conditions, managing these tailings via the CPB method yielded increased mobility of As compared with that in the unmodified tailings; this resulted possibly from the formation of less acid-tolerant As species.

  • 31.
    Hamberg, Roger
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maurice, Christian
    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.
    The formation of unsaturated zones within cemented paste backfill mixtures: Effects on the release of copper, nickel, and zinc2018In: Environmental Science and Pollution Research, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 25, no 21, p. 20809-20822Article in journal (Refereed)
    Abstract [en]

    Flooding of cemented paste backfill (CPB) filled mine workings is, commonly, a slow process and could lead to the formation of unsaturated zones within the CPB-fillings. This facilitates the oxidation of sulfide minerals, and thereby increases the risk of trace-metal leaching. Pyrrhotitic tailings from a gold mine (CT), containing elevated concentrations of Ni, Cu and Zn, were mixed with cement and/or fly ash (1-3 wt. %) to form CT-CPB-mixtures. Pyrrhotite oxidation progressed more extensively during unsaturated conditions, where acidity resulted in dissolution of the Ni, Cu, and Zn associated with amorphous Fe-precipitates and/or cementitious phases. The establishment of acidic, unsaturated conditions in CT-CBP:s with low fractions (1 wt. %) of binders increased the Cu-release (to be higher than that from CT), owing to the dissolution of Cu-associated amorphous Fe-precipitates. In CT-CPB:s with relatively high proportions of binder, acidity from pyrrhotite oxidation was buffered to a greater extent. At this stage, Zn-leaching increased due the occurrence of fly ash-specific Zn-species soluble in alkaline conditions. Irrespective of binder proportion and water saturation level, the Ni- and Zn-release were lower, compared to that in CT. Fractions of Ni, Zn, and Cu associated with acid-soluble phases or amorphous Fe-precipitates, susceptible to remobilization under acidic conditions, increased in tandem with binder fractions. Pyrrhotite oxidation occurred irrespective of the water saturation level in the CPB-mixtures. That in turn, poses an environmental risk, whereas a substantial proportion of Ni, Cu and Zn were associated with acid-soluble phases.

  • 32.
    Hamberg, Roger
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maurice, Christian
    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.
    The use of low binder proportions in cemented paste backfill: Effects on As-leaching2015In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 78, p. 74-82Article in journal (Refereed)
    Abstract [en]

    Gold is extracted by cyanide leaching from inclusions in arsenopyrite at a mine in the north of Sweden. The major ore mineral assemblage consists of pyrrhotite and arsenopyrite–loellingite. Arsenopyrite is assumed to be oxidized during cyanidation and the stability of secondary As-phases needs to be assessed. One way of managing such tailings is to convert them into a monolithic mass by using a method called cemented paste backfill (CPB). In CPB, tailings are traditionally mixed with water (typically 25% by weight) and small amounts (3–7%) of binders, and backfilled into excavated underground areas. To investigate the release of arsenic (As) from CPB prepared from As-rich tailings, tailings containing approx. 1000 ppm of As, mainly in the form of As-bearing iron (Fe)-precipitates (FEP), were mixed with small quantities (1–3%) of biofuel fly ash (BFA), ordinary cement, and water to produce monolithic CPB masses. CPB-recipes were designed to meet the strength demand of 200 kPa, stated by the mine operators. Tank leaching tests (TLT) and the weathering cell test (WCT) were used to compare the leaching behavior of As in unmodified tailings and CPB-materials. Results from the leaching tests (TLT and WCT) showed that the inclusion of As-rich tailings into a cementitious matrix increased leaching of As. This behavior could partially be explained by an increase of pH where As sorbed to FEPs becomes unstable. In the CPB mixtures, small (>1%) proportions of the total As in the solid material was released from less acid-tolerant species (i.e. Ca-arsenates and As bonded to cementitious phases). Unmodified tailings generated an acidic environment in flooded conditions at which As-bearing FEPs were stable. Acid was added to the crushed CPB materials during later stages of the WCTs to mimic the effects of weathering. This increased the leaching of Fe and had minor effects on that of As but did not affect S-leaching.

  • 33.
    Hällström, Lina
    et al.
    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.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geochemical characterization of W, Cu and F skarn tailings at Yxsjöberg, Sweden2018In: Journal of Geochemical Exploration, ISSN 0375-6742, E-ISSN 1879-1689, Vol. 194, p. 266-279Article in journal (Refereed)
    Abstract [en]

    Little attention has been paid to tailings from skarn ore deposits and their environmental impact, even though they can contain elevated concentrations of elements of potential concern together with sulfides and fluorite. Historical skarn tailings at Yxsjöberg, Sweden, containing e.g. Be, Bi, Cu, F, Sn, S, W, and Zn were geochemically characterized as a first step to evaluate the environmental impact and the potential to re-mine the tailings. The tailings were deposited between 1897 and 1963 in the Smaltjärnen Repository without dams or a complete cover, and have been in contact with the atmosphere for >30 years. Four vertical cores throughout the tailings were taken and divided into 134 subsamples, which were analyzed for total concentrations and paste pH. Selected samples from different depths were mineralogically characterized using optical microscopy, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), Raman vibrational spectroscopy, and X-ray diffraction (XRD). Minerals, hand-picked from drilled rock cores, were analyzed for the element content, and a modified Element to Mineral Conversion (EMC) that pinpoints the quantitative distribution of elements between the minerals in the tailings was carried out. The average concentrations of Be, Bi, Cu, Sn, Zn, W, F and S in the tailings were 284, 495, 946, 559, 301, and 960 ppm, and 1.9 and 1.2 wt%, respectively. The tailings has reached a late stage development due to pyrrhotite oxidation resulting in low pH (<4) in the uppermost tailings, and formations of secondary minerals such as gypsum, hydrous ferric oxides (HFO) and orthogonal calcite. Secondary pyrite and magnetite, formed from monoclinic pyrrhotite was detected, and different weathering rates of secondary pyrite, hexagonal and monoclinic pyrrhotite was indicated, with secondary pyrite as the most stable and monoclinic pyrrhotite as the least. The rare and easily-weathered mineral danalite (Fe4Be3(SiO4)3S) was found in the drilled rock cores and by XRD in the tailings. However, the mineral could not be found by optical microscopy or SEM-EDS. This suggests that the mineral has been weathered to a great extent, which poses a high risk of releasing elements of potential concern to the groundwater since danalite contains approximately 40% of the total Be and Zn concentrations in the tailings. Fluorine was mainly found in fluorite, Cu in chalcopyrite, and Bi in bismuthinite; which all showed signs of weathering in acidic condition in the uppermost part, subsequent with decreased concentrations, followed by accumulation peaks deeper down in the tailings correlated with Al. Tungsten was mainly found in scheelite; most grains were unweathered, but a few grains had altered rims or HFO on the mineral surfaces. Tin was mainly found in ferrohornblende, hedenbergite and grossular. Beryllium, Cu, F, and Zn has high potential to be released to the surrounding environment from the Smaltjärnen Repository, while W, Bi and Sn are relatively stable in the tailings. Most of the scheelite is intact and re-mining could, therefore, be a suitable remediation method that would both reduce the environmental impact and simultaneously support the supply of critical raw materials in the EU.

  • 34.
    Hällström, Lina
    et al.
    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.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Metal Release from Acidic and Near-Neutral pH-Conditions in Historical W, Cu and F Skarn Tailings at Yxsjöberg, Sweden2018In: 11th ICARD | IMWA | WISA MWD 2018 Conference: Risk to Opportunity / [ed] Wolkersdorfer, Ch.; Sartz, L.; Weber, A.; Burgess, J.; Tremblay, G., 2018, Vol. 1, p. 351-356Conference paper (Refereed)
    Abstract [en]

    Weathering products stored in the pore water and/or as easily soluble salts in historical skarn tailings containing Be, Bi, Cu, W, and Zn, were released in water soluble fraction in the upper-most acidic tailings, at the visual oxidation front (1.5m), and/or below 2.5m (pH>7). Thus, there is a risk that these metals can pollute receiving waters by neutral mine drainage. Re-mining the tailings could be a suitable remediation method that would both reduce the environmental impact and simultaneously support the supply of metals.

  • 35.
    Hällström, Lina
    et al.
    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.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Scheelite weathering and tungsten (W) mobility in historical oxidic-sulfidic skarn tailings at Yxsjöberg, Sweden2020In: Environmental Science and Pollution Research, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 27, no 6, p. 6180-6192Article in journal (Refereed)
    Abstract [en]

    More knowledge of the geochemical behavior of tungsten (W) and associated contamination risks is needed. Therefore, weathering of scheelite (CaWO4) and secondary sequestration and transport of W to groundwater in historical skarn tailings and surface water downstream of the tailings were studied. The tailings contained 920 mg/kg W, primarily in scheelite. Mineralogical and geochemical analyses were combined to elucidate the geochemical behavior of W in the tailings, and water samples were taken monthly during 2018 to monitor its mobility. In the tailings, a large peak of W was found at 1.5 m depth. There, 30 wt%. of W was present in easily reducible phases, indicating former scheelite weathering. Currently, W is being released from scheelite to water-soluble phases at 2.5 m depth. The release of WO42− is hypothetically attributed to anion exchange with CO32− released from calcite neutralizing acid produced from pyrrhotite oxidation in the upper tailings and transported downwards to pH conditions > 7. Higher concentrations of dissolved W were found in the groundwater and particulate W in downstream surface water than in reference water, but they were lower than current contamination thresholds. Tungsten showed correlations with hydrous ferric oxides (HFO) in both the tailings and surface water.

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  • 36.
    Hällström, Lina P.B.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Salifu, Musah
    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.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The geochemical behaviour of Be and F in historical mine tailings of Yxsjöberg, Sweden2020In: Journal of Geochemical Exploration, ISSN 0375-6742, E-ISSN 1879-1689, Vol. 218, article id 106610Article in journal (Refereed)
    Abstract [en]

    The speciation, mobility, transport, and fate of beryllium (Be) in the terrestrial environment is poorly studied even though it is considered to be one of the most hazardous elements in the periodic table. Historical tailings containing the unusual mineral danalite [Be3(Fe4.4Mn0.95Zn0.4)(SiO4)3.2S1.4] together with Fe-sulfides and fluorite has been stored open to the atmosphere for more than 50y. Environmental mineralogy, which combines geochemical and mineralogical techniques, was used to elucidate the weathering of danalite and fluorite. Danalite is unstable in oxic conditions due to the occurrence of Fe(II) and S-(II) in the crystal lattice and has oxidized at the same pace as pyrrhotite in the tailings. The acidic conditions generated from sulfide oxidation and the release of F from fluorite weathering have most likely enhanced Be mobility in the tailings. Secondary gypsum, hydrous ferric oxides and Al-oxyhydroxides are hypothesized to have played an important role regarding the mobility of Be in the tailings. The results indicate that Be released from danalite was first scavenged by these secondary minerals through co-precipitation. However, the dissolution of secondary gypsum due to changing geochemical conditions has also released Be to the groundwater. The groundwater at the shore of the tailings revealed the highest Be concentrations measured anywhere in the world (average: 4.5 mg/L) even though the water has a circumneutral pH. This extraordinary finding can be explained by high concentrations of F (73 mg/L), as F and Be have been shown to form strong complexes. The weathering of danalite and fluorite will continue for hundreds of years if remediation measures are not taken. Re-mining the tailings could be an appropriate remediation method.

  • 37.
    Jia, Yu
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nason, Peter
    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.
    Maurice, Christian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Degradation of digested sewage sludge residue under anaerobic conditions for mine tailings remediation2014In: Environmental Earth Sciences, ISSN 1866-6280, E-ISSN 1866-6299, Vol. 72, no 9, p. 3643-3654Article in journal (Refereed)
    Abstract [en]

    Previous studies showed that 85 % of total organic matter (TOM) in digested sewage sludge (biosolids) used as a sealing layer material over sulfide tailings at the Kristineberg Mine, northern Sweden had been degraded 8 years after application, resulting in a TOM reduction from 78 % to 14 %. To achieve a better understanding of the field observations, laboratory studies were performed to evaluate biodegradation rates of the TOM under anaerobic conditions. Results reveal that the original biosolid consisted of ca. 60 % TOM (48.0 % lignin and 11.8 % carbohydrates) that had not been fully degraded. The incubation experiments proved that 27.8 % TOM in the biosolid was further degraded anaerobically at 20-22 C during the 230 d incubation period, and that a plateau to the biodegradation rate was approached. Based on model results, the degradation constant was found to be 0.0125 (day-1). The calculated theoretical gas formation potential was ca. 50 % higher than the modeled results based on the average degradation rate. Cumulated H2S equated to 0.65 µmoL*g-1 of biosolid at 230 d. However, the large sulfurous compounds reservoir (1.76 g SO42- kg-1 biosolid) together with anaerobic conditions, can generate high concentrations of this gas over a long-term perspective. Due to the rate of biodegradability identified via anaerobic processes, the function of the biosolid to serve as an effective barrier to inhibit oxygen migration to underlying tailings, may decrease over time. However, a lack of readily degradable organic fractions in the biosolid and a large fraction of organic matter that was recalcitrant to degradation suggests a longer degradation duration, which would prolong the biosolid material’s function and integrity.

  • 38.
    Jia, Yu
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nason, Peter
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maurice, Christian
    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.
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Investigation of biosolids degradation under flooded environments for use in underwater cover designs for mine tailing remediation2015In: Environmental Science and Pollution Research, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 22, no 13, p. 10047-10057Article in journal (Refereed)
    Abstract [en]

    To evaluate the potential suitability of digested sewage sludge (frequently termed biosolids) for use as underwater cover material for mine waste tailings, the degradability of biosolids at 20 − 22 °C under flooded anaerobic conditions was evaluated during incubation for 230 days. Leaching of elements from the flooded anaerobic system was also evaluated. Biosolid degradation was confirmed by the generation and accumulation of CH4 and CO2. Specifically, approximately 1.65 mmoL gas/g biosolids was generated as a result of incubation, corresponding to degradation of 7.68 % of the organic matter, and the residue was stable at the end of the laboratory experiment. Under field conditions in northern Sweden, it is expected that the degradation rate will be much slower than that observed in the present study (Nason et al. Environ Earth Sci 70:30933105, 2013). Although the majority of biosolid fractions (>92 %) were shown to be recalcitrant during the incubation period, long-term monitoring of further degradability of residue is necessary. The leaching results showed that most of the metals and metalloids leached from the biosolids at day 230 were below the limit value for non-hazardous waste, although Ni was the only element approximately three times higher than the limit value for inert material at the landfill site. In conclusion, biosolids have potential for use as covering material for underwater storage of tailings based on their biodegradability and leaching of elements.

  • 39.
    Kaasalainen, Hanna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Sweco Environment, Luleå, Sweden.
    Lundberg, Paula
    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.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Impact of declining oxygen conditions on metal(loid) release from partially oxidized waste rock2019In: Environmental Science and Pollution Research, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 26, no 20, p. 20712-20730Article in journal (Refereed)
    Abstract [en]

    The best available technology for preventing the formation of acid drainage water from the sulfidic waste rock at mine closure aims to limit the oxygen access to the waste. There is, however, a concern that contaminants associated with secondary minerals become remobilized due to changing environmental conditions. Metal(loid) mobility from partially oxidized sulfidic waste rock under declining and limited oxygen conditions was studied in unsaturated column experiments. The concentrations of sulfate and metal(loid)s peaked coincidently with declining oxygen conditions from 100 to < 5 sat-% and to a lesser extent following a further decrease in the oxygen level during the experiment. However, the peak concentrations only lasted for a short time and were lower or in the similar concentration range as in the leachate from a reference column leached under atmospheric conditions. Despite the acid pH (~ 3), the overall quality of the leachate formed under limited oxygen conditions clearly improved compared with atmospheric conditions. In particular, the release of As was two orders of magnitude lower, while cationic metals such as Fe, Cu, Mn, and Zn also decreased, although to a lesser extent. Decreased sulfide oxidation is considered the primary reason for the improved water quality under limited oxygen conditions. Another reason may be the immobility of Fe with the incorporation of metal(loid)s in Fe(III) minerals, in contrast to the expected mobilization of Fe. The peaking metal(loid) concentrations are probably due to remobilization from solid Fe(III)-sulfate phases, while the relatively high concentrations of Al, Mn, and Zn under limited oxygen conditions were due to release from the adsorbed/exchangeable fraction. Despite the peaking metal(loid) concentrations during declining oxygen conditions, it is clear that the primary remediation goal is to prevent further sulfide oxidation.

  • 40.
    Karlsson, Teemu
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Circular Economy Solutions Unit, Geological Survey of Finland, P.O. Box 1237, 70211, Kuopio, Finland.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kauppila, Päivi
    Circular Economy Solutions Unit, Geological Survey of Finland, P.O. Box 1237, 70211, Kuopio, Finland.
    Räisänen, Marja Liisa
    Industrial Environments and Recycling Unit, Geological Survey of Finland, P.O. Box 1237, 70211, Kuopio, Finland.
    A Test of Two Methods for Waste Rock Drainage Quality Prediction: Aqua Regia Extraction and Single-addition Net-acid Generation Test Leachate Analysis: [两种废矿石排水质量预测方法: 王水提取法和单添加净产酸实验 (NAG) 滤出液分析法] [Ein Test von zwei Methoden zur Qualitätsvorhersage von Haldensickerwässern: Königswasseraufschluss und Sickerwasseranalyse über den Nettosäurebildungspotentialtest bei einmaliger Zugabe]2021In: Mine Water and the Environment, ISSN 1025-9112, E-ISSN 1616-1068, Vol. 40, no 3, p. 736-751Article in journal (Refereed)
    Abstract [en]

    The mobility of contaminants from mine waste can be assessed using different extraction methods. Aqua regia (AR) extraction is the most commonly used method in Finland. Another method is the analysis of leachate from net acid generation (NAG) tests, which is primarily designed for acid production potential assessment. We investigated the performance of single-addition NAG test leachate analysis and AR extraction in drainage quality prediction, using waste rock and drainage water samples from several Finnish waste rock sites. Our objective was to improve interpretation of the AR and single-addition NAG test leachate analysis results in drainage quality prediction. The AR extraction effectively reflected elements that occurred in elevated concentrations in drainage water, though it over-predicted Al, As, Cd, Co, Cu, and Ni in some circumneutral drainages, and Cr in general. The single-addition NAG test leachate analysis also performed well in assessing the mobility of contaminants including Al and Cr at acid mine drainage sites. As the contaminants tend to precipitate in neutral NAG test solution, the usability of the method in neutral mine drainage cases should be further investigated. Furthermore, the conclusions presented in this study are limited to waste rock samples collected from the surface of piles; future work will examine waste rock history, dump cores, drainage quality changes, etc. in more detail.

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  • 41.
    Karlsson, Teemu
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Circular Economy Solutions, Geological Survey of Finland, Neulaniementie 5, FI-70211 Kuopio, Finland.
    Kauppila, Päivi
    Circular Economy Solutions, Geological Survey of Finland, Neulaniementie 5, FI-70211 Kuopio, Finland.
    Lehtonen, Marja
    Circular Economy Solutions, Geological Survey of Finland, Vuorimiehentie 2, FI-02151 Espoo, Finland.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kauppila, Tommi
    Circular Economy Solutions, Geological Survey of Finland, Neulaniementie 5, FI-70211 Kuopio, Finland.
    Sulfur analyses and mineralogical data in the preliminary mine waste characterization2022In: Environmental Monitoring & Assessment, ISSN 0167-6369, E-ISSN 1573-2959, Vol. 194, article id 437Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to investigate the use of the acid production potential (AP) calculation factor and seven different S analysis methods in the preliminary mine waste characterization by analyzing and comparing 48 Finnish mine waste samples. Special attention was paid on mineralogical aspects and data produced in the exploration phase of a mining project.

    According to our results, the abundance of sulfide species other than pyrite in Finnish mine waste suggests that the factor to calculate the AP should be considered based on mineralogy and would often be below 31.25. Therefore, the mineralogy-based determination of S should be preferred. However, the determination of S based on scanning electron microscope (SEM) mineralogy includes some uncertainties. Underestimation of S content may appear if not all S-bearing mineral particles have been detected, or if the amount of S is low in general. This uncertainty appears to be especially related to the samples containing elevated (> 9 wt%) amounts of serpentine, diopside, augite, and/or hornblende. Risk of overestimating AP is related to samples containing high amounts (> 4.13 wt%) of S-bearing minerals. These uncertainties can be reduced by inspecting that the SEM mineralogy-based S concentrations are in line with the energy dispersive X-ray spectrometer data. The aqua regia extractable S concentrations, which are often available in the exploration phase, appeared to be usable in the preliminary waste rock AP assessment and often comparable with the analytical total S values in the Finnish waste rock samples, especially when the samples did not contain any sulfate minerals. In contrast, the analytical sulfide S and the X-ray fluorescence methods may lead to an underestimation of AP.

  • 42.
    Karlsson, Teemu
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Industrial Environments and Recycling Unit, Geological Survey of Finland, Kuopio, Finland.
    Räisänen, Marja Liisa
    Industrial Environments and Recycling Unit, Geological Survey of Finland, Kuopio, Finland.
    Lehtonen, Marja
    Mineral Processing and Materials Research Unit, Geological Survey of Finland, Espoo, Finland.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Comparison of static and mineralogical ARD prediction methods in the Nordic environment2018In: Environmental Monitoring & Assessment, ISSN 0167-6369, E-ISSN 1573-2959, Vol. 190, no 12, article id 719Article in journal (Refereed)
    Abstract [en]

    Acid rock drainage (ARD) is a major problem related to the management of mining wastes, especially concerning deposits containing sulphide minerals. Commonly used tests for ARD prediction include acid–base accounting (ABA) tests and the net acid generation (NAG) test. Since drainage quality largely depends on the ratio and quality of acid-producing and neutralising minerals, mineralogical calculations could also be used for ARD prediction. In this study, several Finnish waste rock sites were investigated and the performance of different static ARD test methods was evaluated and compared. At the target mine sites, pyrrhotite was the main mineral contributing to acid production (AP). Silicate minerals were the main contributors to the neutralisation potential (NP) at 60% of the investigated mine sites. Since silicate minerals appear to have a significant role in ARD generation at Finnish mine waste sites, the behaviour of these minerals should be more thoroughly investigated, especially in relation to the acid produced by pyrrhotite oxidation. In general, the NP of silicate minerals appears to be underestimated by laboratory measurements. For example, in the NAG test, the slower-reacting NP-contributing minerals might require a longer time to react than is specified in the currently used method. The results suggest that ARD prediction based on SEM mineralogical calculations is at least as accurate as the commonly used static laboratory methods.

  • 43.
    Karlsson, Teemu
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Circular Economy Solutions, Geological Survey of Finland, 70211 Kuopio, Finland.
    Räisänen, Marja Liisa
    Industrial Environments and Recycling, Geological Survey of Finland, 70211 Kuopio, Finland.
    Myöhänen, Timo
    Eurofins Labtium Oy, 70211 Kuopio, Finland.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Lehtonen, Marja
    Circular Economy Solutions, Geological Survey of Finland, 02151 Espoo, Finland.
    Kauppila, Päivi
    Circular Economy Solutions, Geological Survey of Finland, 70211 Kuopio, Finland.
    Hydrogen Peroxide Ammonium Citrate Extraction: Mineral Decomposition and Preliminary Waste Rock Characterization2021In: Minerals, E-ISSN 2075-163X, Vol. 11, no 706Article in journal (Refereed)
    Abstract [en]

    A commonly-used method in ore exploration is hydrogen peroxide ammonium citrate (HA) extraction, which has not typically been used in waste rock characterization. In this study, the sulfide specificity and leaching of other minerals in HA extraction was evaluated and its performance was compared with the aqua regia (AR) extraction for preliminary assessment of harmful element mobility. Samples collected from several different mine sites in Finland were utilized. The waste rock sample S contents ranged from 0.3% to 5.3%, and sums of the AR extractable elements As, Cd, Co, Cu, Ni and Zn range from 120 to 8040 mg/kg. The drainage types ranged from acid high-metal to neutral low-metal, with pH’s of 3.3–7.7. Mineralogical changes that took place in the HA solution were investigated by the field emission scanning electron microscope (FE-SEM) equipped with an energy-dispersive X-ray spectroscopy analyzer (EDS) and X-ray diffraction (XRD) methods. Results of the study showed that the HA extraction appears to be a more specific method for sulfide decomposition compared with AR extraction. Sulfide minerals, especially base metal sulfides pentlandite, chalcopyrite and sphalerite, decomposed efficiently in HA extraction. However, the Fe-sulfides pyrrhotite and pyrite only decomposed incompletely. The study showed that the HA extraction results can be used in the preliminary prediction of element mobility. Based on the results, the elevated As, Cd, Co, Cu, Ni, S and Zn leachability in the HA extraction appears to predict elevated drainage concentrations. If the HA-extractable sum of As, Cd, Co, Cu, Ni and Zn is >750 mg/kg, there is an increased risk of high-metal (>1000 µg/L) drainage. Therefore, the HA extraction data, e.g., produced during ore exploration, can be utilized to preliminary screen the risks of sulfide related element mobilities from waste rock material.

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  • 44.
    Liu, Jian-li
    et al.
    University of Science and Technology Beijing, Beijing, China.
    Yao, Jun
    China University of Geosciences (Beijing), China.
    Wang, Fei
    University of Science and Technology Beijing, Beijing, China.
    Min, Ning
    China University of Geosciences (Beijing), China.
    Gu, Ji-hai
    China University of Geosciences (Beijing), China.
    Li, Zi-fu
    University of Science and Technology Beijing, Beijing, China.
    Sunahara, Geoffrey
    China University of Geosciences (Beijing), China; McGill University, Montreal, Quebec,Canada.
    Duran, Robert
    China University of Geosciences (Beijing), China; Université de Pau et des Pays de l’Adour, Pau Cedex, France.
    Solevic-Knudsen, Tatjana
    University of Belgrade, Belgrade, Serbia.
    Hudson-Edwards, Karen A.
    University of Exeter, Penryn, Cornwall, UK.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bacterial diversity in typical abandoned multi-contaminated nonferrous metal(loid) tailings during natural attenuation2019In: Environmental Pollution, ISSN 0269-7491, E-ISSN 1873-6424, Vol. 274, p. 98-107Article in journal (Refereed)
    Abstract [en]

    Abandoned nonferrous metal(loid) tailings sites are anthropogenic, and represent unique and extreme ecological niches for microbial communities. Tailings contain elevated and toxic content of metal(loid)s that had negative effects on local human health and regional ecosystems. Microbial communities in these typical tailings undergoing natural attenuation are often very poorly examined. The diversity and inferred functions of bacterial communities were examined at seven nonferrous metal(loid) tailings sites in Guangxi (China), which were abandoned between 3 and 31 years ago. The acidity of the tailings sites rose over 31 years of site inactivity. Desulfurivibrio, which were always coupled with sulfur/sulfide oxidation to dissimilate the reduction of nitrate/nitrite, were specific in tailings with 3 years abandonment. However, genus beneficial to plant growth (Rhizobium), and iron/sulfur-oxidizing bacteria and metal(loid)-related genera (Acidiferrobacter and Acidithiobacillus) were specific within tailings abandoned for 23 years or more. The increased abundance of acid-generating iron/sulfur-oxidizing and metal(loid)-related bacteria and specific bacterial communities during the natural attenuation could provide new insights for understanding microbial ecosystem functioning in mine tailings. OTUs related to Sulfuriferula, Bacillus, Sulfurifustis, Gaiella, and Thiobacillus genera were the main contributors differentiating the bacterial communities between the different tailing sites. Multiple correlation analyses between bacterial communities and geochemical parameters indicated that pH, TOC, TN, As, Pb, and Cu were the main drivers influencing the bacterial community structures. PICRUSt functional exploration revealed that the main functions were related to DNA repair and recombination, important functions for bacterial adaptation to cope with the multi-contamination of tailings. Such information provides new insights to guide future metagenomic studies for the identification of key functions beyond metal-transformation/resistance. As well, our results offers novel outlooks for the management of bacterial communities during natural attenuation of multi-contaminated nonferrous metal(loid) tailings sites. 

  • 45.
    Liu, Jian-li
    et al.
    School of Energy and Environment Engineering, University of Science and Technology Beijing.
    Yao, Jun
    School of Water Resource and Environment Engineering, China University of Geosciences, Beijing.
    Wang, Fei
    School of Energy and Environment Engineering, University of Science and Technology Beijing, Beijing.
    Ni, Wen
    School of Civil and Resource Engineering, University of Science and Technology Beijing.
    Liu, Xing-yu
    National Engineering Laboratory of Biohydrometallurgy, General Research. Institute for Nonferrous Metals .
    Sunahara, Geoffrey
    Department of Natural Resource Sciences, McGill University, Montreal, Quebec.
    Duran, Robert
    Equipe Environnement et Microbiologie, MELODY group, Université de Pau et des Pays de l’Adour, IPREM UMR CNRS.
    Jordan, Gyozo
    Department of Applied Chemistry, Szent István University.
    Hudson-Edwards, Karen A.
    Environment & Sustainability Institute and Camborne School of Mines, University of Exeter.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Solevic-Knudsen, Tatjana
    Institute of Chemistry, Technology and Metallurgy, University of Belgrade.
    Zhu, Xiao-zhe
    School of Energy and Environment Engineering, University of Science and Technology Beijing.
    Zhang, Yi-yue
    School of Energy and Environment Engineering, University of Science and Technology Beijing.
    Li, Zi-fu
    School of Energy and Environment Engineering, University of Science and Technology Beijing.
    China's most typical nonferrous organic-metal facilities own specific microbial communities2018In: Scientific Reports, E-ISSN 2045-2322, Vol. 8, no 1, article id 12570Article in journal (Refereed)
    Abstract [en]

    The diversity and function of microorganisms have yet to be explored at non-ferrous metal mining facilities (NMMFs), which are the world's largest and potentially most toxic sources of co-existing metal(loid)s and flotation reagents (FRs). The diversity and inferred functions of different bacterial communities inhabiting two types of sites (active and abandoned) in Guangxi province (China) were investigated for the first time. Here we show that the structure and diversity of bacteria correlated with the types of mine sites, metal(loid)s, and FRs concentrations; and best correlated with the combination of pH, Cu, Pb, and Mn. Combined microbial coenobium may play a pivotal role in NMMFs microbial life. Arenimonas, specific in active mine sites and an acidophilic bacterium, carries functions able to cope with the extreme conditions, whereas Latescibacteria specific in abandoned sites can degrade organics. Such a bacterial consortium provides new insights to develop cost-effective remediation strategies of co-contaminated sites that currently remain intractable for bioremediation.

  • 46.
    Lu, Jinmei
    et al.
    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.
    Jia, Yu
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Gotthardsson, Jenny
    Boliden Mineral AB.
    Evaluation of the application of dry covers over carbonate-rich sulphide tailings2013In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 244-245, p. 180-194Article in journal (Refereed)
    Abstract [en]

    In this study, four ten years test areas with covered tailings were geochemically evaluated. Three areas were covered with a fly ash and an overlying sludge layer, and one only with a sludge cover, originating from paper mills. The accumulation of As, Fe and Pb in sludge layers, originating from air-borne dust and the depletion of K, Na and P from both cover layers were observed. High release of elements from tailings was observed in the comparison profile due to oxidation and weathering of tailings. In only sludge covered area, the leaching of elements from tailings decreased. In the profiles with thin ash (20 cm and 30 cm), most elements were retained in tailings with pH 7-9. In the profile with the thickest ash (50 cm), elements such as As, Cd, Cu, Mg, Mn, Pb, S and Zn were depleted in the uppermost tailings with pH above 11 and retained deeper in the zone with pH 7-8, which implied that large quantities of fly ash increased the oxidation and weathering of tailings and mobility of elements. Elements excluding K, never reached the groundwater in high concentrations in the covered areas, while the comparison area had high Ca, K, Mn and S concentrations

  • 47.
    Lu, Jinmei
    et al.
    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.
    Wanhainen, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Metal mobilization under alkaline conditions in ash-covered tailings2014In: Journal of Environmental Management, ISSN 0301-4797, E-ISSN 1095-8630, Vol. 139, p. 38-49Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to determine element mobilization and accumulation in mill tailings under alkaline conditions. The tailings were covered with 50 cm of fly ash, and above a sludge layer. The tailings were geochemically and mineralogically investigated. Sulfides, such as pyrrhotite, sphalerite and galena along with gangue minerals such as dolomite, calcite, micas, chlorite, epidote, Mn-pyroxene and rhodonite were identified in the unoxidized tailings. The dissolution of the fly ash layer resulted in a high pH (close to 12) in the underlying tailings. This, together with the presence of organic matter, increased the weathering of the tailings and mobilization of elements in the uppermost 47 cm of the tailings. All primary minerals were depleted, except quartz and feldspar which were covered by blurry secondary carbonates. Sulfide-associated elements such as Cd, Fe, Pb, S and Zn and silicate-associated elements such as Fe, Mg and Mn were released from the depletion zone and accumulated deeper down in the tailings where the pH decreased to circum-neutral. Sequential extraction suggests that Cd, Cu, Fe, Pb, S and Zn were retained deeper down in the tailings and were mainly associated with the sulfide phase. Calcium, Cr, K and Ni released from the ash layer were accumulated in the uppermost depletion zone of the tailings

  • 48.
    Nason, Peter
    et al.
    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.
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Assessing the impact of sewage sludge on a formally remediated tailings impoundment in relation to the transport of metals in groundwater2011In: Mine Water - managing the Challenges: 11th Congress of the International Mine Water Association / [ed] Thomas R. Rüde; Antje Freund; Christian Wolkersdorfer, Aachen, Germany: RWTH Aachen University, Institute of Hydrogeology , 2011, p. 429-434Conference paper (Refereed)
    Abstract [en]

    In 2009 sewage sludge was applied to an already successfully remediated saturated and dry covered sulphide tailings impoundment in northern Sweden as a vegetation substrate. The aim of this study was to identify the dispersion, magnitude and duration of sludge-borne constituents released. Readily leachable sludge-borne constituents (DOC, Fe, Co, Cr, Ni, Pb and Zn) created a contamination plume which affected the impoundment groundwater within the first year of application. The majority of the plume originated from the water-saturated area of the impoundment that was only covered with a 10% surface area of sludge. The dry-composite covered area of the impoundment, which contained a 70% sludge cover, did not contribute to the contamination plume due to the efficiency of the cover at reducing water infiltration and contamination dispersal. The constituents were transported along the dominant groundwater flow direction, underneath the dry covered area of the impoundment, to the effluent of the impoundment groundwater system due to inflowing uncontaminated groundwater from an adjacent till slope. All metal and DOC concentrations in the impoundment groundwater returned to pre-sludge application concentrations within two years, due to successful plant establishment on the sludge.

  • 49.
    Nason, Peter
    et al.
    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.
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Impact of Sewage Sludge on Groundwater Quality at a Formerly Remediated Tailings Impoundment2014In: Mine Water and the Environment, ISSN 1025-9112, E-ISSN 1616-1068, Vol. 33, no 1, p. 66-78Article in journal (Refereed)
    Abstract [en]

    Sewage sludge can be a suitable, organic-rich substrate to promote vegetation ofsulfide-mine tailings, but it may contain contaminants, that, when oxidized, canadversely affect underlying groundwater systems. The geochemical impact of asurface application of 12,000 metric tons of anaerobically-digested sewage sludge on the groundwater quality of a remediated sulfide-tailings impoundment in northern Sweden was evaluated to determine if sludge-borne metals and nitrate were released to the underlying groundwater system. Two years of data from a field-scale groundwater monitoring programme initiated just before the sludge application was compared to groundwater data from 1998-2006. Grass was successfully established within two years. However, until that occurred, elevated concentrations of sludge-borne metals (Cu, Ni, Pb, Zn) were released to the underlying groundwater. In addition, the release of nitrate likely exacerbated metal concentrations by providing an oxidant for pyrite in the underlying tailings. The release was periodic due to the establishment of the grass, which immobilized metals and nitrate in the sludge. Metals bound asorgano-metallic complexes, due to dissolved organic carbon released from the sludge, migrated across the tailings impoundment. Model simulations indicate that the plume will take six years to exit the groundwater environment. Though the impacts are relatively short-term, this type of application should be reconsidered in the future.

  • 50.
    Nason, Peter
    et al.
    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.
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Sewage sludge as a sealing layer for the remediation of sulphide-bearing mine tailings: ageing and degradation of the barrier material2011Conference paper (Other academic)
    Abstract [en]

    Using sewage sludge as an organic barrier to mitigate oxygen diffusion to underlying sulphidic tailings was performed in experimental pilot-scale test cells, northern Sweden and was proved to be successful over an 8 year period (Nason et al., 2010). However, degradation and ageing of the sewage sludge may limit its function in the long-term as indicated by surface applications of sewage sludge, as the exposure of the material to atmospheric oxygen may cause aerobic degradation of the organic matter fraction (Peppas et al., 2000), nitrification (Cravotta, 1998) and subsequent structural disintegration (Ahlberg, 2006). A pilot-scale test cell with a 0.3m sewage sludge sealing layer capped by a 1.2m protective layer of glacial till was used to cover tailings. Quantification of the changing properties of the sewage sludge after an 8 year period occurred using temperature data and solid sludge and leachate geochemistry. It was found that all layers were frozen between December to April and that a perched water table formed above the sealing layer from April to August (Shcherbakova, 2006). The subsequent lack of contact of the sludge with oxygen minimised aerobic degradation of the organic fraction, prevented nitrification and created an anoxic environment in the sludge. Nitrate in the leachate was <1mg/l and the subsequent lack of acidification created a neutral pH in the sludge and underlying tailings. Elevated alkalinity (360-600 mg/l) and low sulphate (9-67 mg/l) in the leachate indicated that sulphate reduction by anaerobic degradation of the organic matter had occurred in the sludge. On average, the organic fraction was reduced by 80%, but was most prevalent at the sludge to tailings interface where 92% of the organic matter had been lost since deposition. Mass balance calculations of the sludge revealed a 19.6% total loss of volume due to the organic matter degradation and leaching of Cd, Cu, Hg, Zn and P that were elevated in the original sludge material. No structural degradation as experienced by surface applications such as shrinkage or cracking occurred as the barrier was not exposed to oxygen. The integrity and function of the sub-surface sewage sludge layer was less compromised compared to a surface layer as degradation was dominated by anaerobic processes. However, organic degradation rates were high and it is recommended that this type of application is effective only as a medium-term solution for mitigating oxygen diffusion to underlying sulphidic tailings and for preventing acid rock drainage. Ahlberg, G. (2006). Göteborg University. Doctoral Thesis: 20. Cravotta, C. A. 1998. Ground Water 36(1): 9-19. Nason et al., 2010. IMWA 2010: Nova Scotia, Canada, Cape Breton University Press. Peppas et al., 2000. Minerals Engineering 13(5): 563-574. Shcherbakova, E. 2006. Luleå University of Technology. Doctoral Thesis

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