Luleå University of Technology Publications
Not a member yet
39356 research outputs found
Sort by
Catalytic conversion of carbon dioxide into fuels
No full textHeterogeneous catalysis offers one of the sustainable solutions to the global warming challenge by converting greenhouse gases, particularly carbon dioxide (CO2), into valuable chemicals, notably methane (CH4). The CO2 methanation is a thermodynamically favorable and scalable process, typically carried out using nickel (Ni) based catalysts. However, the intense exothermicity of the methanation reaction poses challenges, including sintering of Ni nanoparticles and carbon deposition, which critically undermine the catalyst's stability. Resilience of the catalyst can be enhanced by tuning the metal-support interaction (MSI) and regulating the dispersion of Ni nanoparticles. The aim of this thesis was to develop stable and robust Ni catalysts by tuning the MSI and dispersion of Ni nanoparticles supported over the hierarchical zeolite 13X (h13X). Preliminary experiments demonstrated that Ni loading, activity, and instability of the catalyst are correlated. Under optimized synthesis conditions, grafting functional groups onto the support resulted in a stronger MSI and preferentially deposited Ni nanolayers, thereby enhancing the activity and stability of the catalyst. The addition of the cobalt cocatalyst strengthened the MSI and stabilized the catalyst's performance, notably during the initial stages of CO2 methanation. The synergistic effect of surface modification and cocatalyst resulted in lower activation energy, higher activity, and increased stability of the catalyst. Additionally, the influence of oxide promoters (La, Ca, Mg, Ce) proved to be dependent on their specific characteristics, with a notable increase in surface basicity, MSI, and catalyst stability. Based on the outcomes of surface modification and traditional catalyst design, a metal-chelation strategy was explored to regulate the size of Ni nanoparticles. The Ni was coordinated to the amine-based ligands, including pyridine, bipyridine, diethylenetriamine, and oleylamine, followed by their impregnation on the support. Remarkable differences were observed in the characteristics of the catalysts depending upon the type of ligand. A broader Ni distribution was observed for the heterocyclic ligand, whereas better textural properties were achieved by the aliphatic amines, which were attributed to the coordination of Ni in the metal-chelate complexes and the strength of interaction with the support. Besides the catalyst’s design, the process parameters, including temperature, pressure, H2/CO2 ratio, gas hourly velocity, and gas composition, showed a profound impact on the CO2 conversion, CH4 selectivity, and stability of the catalysts. overall, this thesis offers insights into regulating the catalyst's MSI, dispersion, distribution, activity, and stability
Adsorption and Separation in Small-Pore Zeolites : From fundamental studies to membrane process design for biogas and natural gas upgrading
No full textZeolites are crystalline aluminosilicates with well-defined 3D porous structures consisting of tetrahedral units of aluminate (AlO45-) and silicate (SiO44-) ions. They can be classified by pore size, with small-pore zeolites featuring 8-membered rings and pore openings around 3.0-4.5 Å, medium-pore zeolites with 10-membered rings and pore sizes of 4.5-6.0 Å, large-pore zeolites with 12-membered rings and pore sizes between 6.0-8.0 Å, and extra-large pore zeolites (>12-ring). Zeolites are used in catalysis, adsorption, and separation processes in the industry. Small-pore zeolite membranes, such as CHA (0.37 nm pore size) and DDR (0.36 nm pore size), have been extensively evaluated for a variety of separations, due to their suitable pore sizes, which enable separation of small molecules from larger molecules, along with their excellent thermal stability and chemical resistance. Particularly in gas separation, these membranes have demonstrated exceptional performance for a range of industrially relevant gas pairs, such as CO2/CH4, CO2/N2, N2/CH4, and H2/CH4, highlighting their strong potential for biogas and natural gas upgrading. Nevertheless, further fundamental studies are needed in order to improve the membrane materials, deepen our understanding of the mass transfer mechanisms in zeolites, and optimize their performance in practical applications. In this thesis, the adsorption isotherms of the common components of natural gas and biogas, CO2, CH4, N2, and He were experimentally measured over wide temperature ranges on large, all-silica, CHA, DDR, and MFI zeolite crystals. The Toth equation was fitted to the measured adsorption data and adsorption parameters were estimated, such as adsorption capacity at saturation (Csat), affinity constant (b), Toth heterogeneity parameter (t), enthalpy of adsorption (ΔHads), and adsorption entropy (ΔSads). The estimated adsorption parameters presented in this work are accurate, primarily due to the large crystals used for the adsorption measurements and the recording of low-temperature adsorption isotherms. These data are invaluable for understanding adsorption and mass transfer in zeolite materials, as well as for advancing the development of zeolite membranes for gas separation. The second part of this thesis evaluates highly permeable DDR disc membranes under various conditions for the separation of CO2/CH4 and H2/CH4, gas pairs that are particularly relevant for natural gas and biohydrogen upgrading. For CO2/CH4 separation, the exceptionally high selectivity of 2325 paired with a high CO2 permeance of 34 × 10-7 mol/(m2·s·Pa) was observed for an equimolar mixture at a feed pressure of 3 bar and a temperature of -30 °C. The highest CO2 permeance was recorded at the same feed pressure and a temperature of +10 °C with a value of 44 × 10-7 mol/(m2·s·Pa), while the selectivity remained remarkably high at 1118. For H2/CH4 separation, a H2 permeance of 7.2 × 10-7 mol/(m2·s·Pa) was recorded for a feed of a 1/1 H2/CH4 mixture at room temperature and pressure of 3 bar. The high permeance was paired with a H2/CH4 selectivity of 207, markedly higher than previously reported for DDR membranes. Furthermore, a mass transfer model accounting for adsorption, surface barrier, and surface diffusion was fitted to the experimental data. Results showed that the model could accurately describe the mass transfer in the zeolite pores and that the surface barrier was the limiting mass transfer step. Based on the separation results, one-stage membrane processes were designed for upgrading biogas to biomethane using DDR membranes at three different operating pressures. The processes displayed a significantly low membrane area, methane slip, and need of electricity power, compared to a polymeric membrane process. The final part of this thesis investigates CHA membranes for the upgrading of a synthetic natural gas mixture with a composition that is typical after a Joule Thompsson process in the industry. The membranes exhibited high flux at a feed pressure of 30 bar while the selectivity for the gas pairs of CO2/N2, CO2/CxHy, and N2/CxHy were also excellent. The optimal temperature for CO2 removal was found to be around 25 °C, where a great CO2 flux of 1.2 mol/(m²·s) was observed coupled with a CO2 permeance of 13 × 10-7 mol/(m²·s·Pa). Under these conditions, high selectivity for CO2/CH4, CO2/C2H6, and CO2/C3H8 of 68, 101, and 190, respectively, were observed. The optimal temperature for N2 removal was around 35 °C; at this temperature high N2 flux of 2.5 × 10-3 mol/(m²·s) was observed, with the N2 permeance reaching 1 × 10-7 mol/(m²·s·Pa). Finally, a membrane process, designed based on the separation data, showed that a membrane area of only 13.6 m2 is sufficient for the upgrading of 1000 Nm3/h natural gas to pipeline gas at a feed pressure of 30 bar, which is approximately 100 times smaller than the membrane area needed for a polymeric membrane process. Overall, the findings in the thesis suggest that small-pore zeolite membranes hold great potential for the upgrading of biogas and natural gas
A Penny for the Environment : Perceptions, Signalling and Bias in Crowdfunding
No full textThis doctoral thesis consists of an introductory preface and four independent papers, addressing and examining different aspects of crowdfunding. The papers focus on the role of perceptions, signalling and gender effects in influencing the outcomes for environmentally oriented crowdfunding initiatives. Paper 1 investigates how an average backer's perceptions of a crowdfunding project's environmental characteristics impact funding outcomes. The empirical analysis is based on data from 406 projects, and four individuals' independent assessments of each project's degree of different environmental characteristics. There is partial evidence that projects perceived as environmentally beneficial are more successful than others in securing funding. However, evidence shows that signalling a project as environmentally beneficial negatively affects crowdfunding outcomes, regardless of whether the project is perceived as genuinely environmentally beneficial or as using greenwashing tactics. Thus, project owners ought to be cautious with making environmental claims to market their projects. In Paper 2, voluntary crowdfunding donations are used as a payment vehicle to examine the attitudes for restoring the aurochs, an extinct keystone species. By reintroducing the aurochs, some ecosystem services could be restored. However, de-extinction could be viewed as "unnatural" by the general public, potentially harmful for the legitimacy of conservation policy. The paper investigates whether attitudes towards restoring the aurochs are dependent on the de-extinction technique: breeding or gene editing. The empirical data are based on a split-sample contingent valuation survey of over 2000 individuals, and the findings indicate that while the de-extinction technique does not affect crowdfunding donations on average, women are more reluctant than men to donate to the project if it employs a gene-editing technology. Additionally, the results indicate large heterogeneity in willingness to pay; however, in general, higher willingness to pay is found amongst younger individuals and within members of environmental organisations. Paper 3 focuses on gender effects in donation crowdfunding for an environmentally oriented initiative. Specifically, the study investigates potential gender bias against the project owner, as well as gender differences amongst backers. The results are based on a split-sample contingent valuation survey of over 1600 respondents, where half of the respondents were presented with a male project owner, and the other half was presented with a female project owner. The results suggest there is no gender bias in funding decisions: both project owners were equally likely to secure funding for their initiatives. Additionally, there was little evidence of gender differences between respondents. Instead, other respondent and project characteristics, such as age, latent environmental attitudes and requested donation amount, affect the decision to contribute to the environmental crowdfunding project. Paper 4 also investigates gender biases against the project owner, however, in a lending crowdfunding setting. The study employs a split-sample choice experiment, presenting an energy technology demonstration project. While such projects are generally led by men, the split-sample survey allows for alternating the gender of the project owner. The study investigates whether risk signals and project attributes are interpreted differently based on the gender of the entrepreneur. The results are based on responses from 2000 individuals, and indicate little evidence of gender bias. However, male respondents are more likely to invest in a project in which a female project owner has established a network to collaborate with, but are also more negative towards a project with a female leader who has no such collaboration.Individuellt engagemang och teknologisk utveckling: gräsrotsfinansieringens roll i övergången till ett fossilfritt samhälleAttityder till användande av bioteknik för återställande av artbestån
Eldriven in situ-sanering av jord förorenad med arsenik och PAH
No full textContaminated soil is a global problem due to its association with environmental and health risks. The wood impregnation industry is one example that has left many sites co-contaminated with polycyclic aromatic hydrocarbons (PAH) and metal(loid)s, such as arsenic. Despite the negative environmental and economic aspects of landfilling, this is the most common soil remediation technology in Sweden and Europe. This study sought to investigate the effects of an electricity driven remediation on soil contaminated with arsenic and PAH, to contribute to the knowledge about using it as an alternative to landfilling. The technology can be practiced in situ, since it uses electricity applied over electrodes inserted into the soil. Novel for this study was the intentionally corroding iron rod electrodes, which sought to amend the soil with iron. This was done to allow for formation of iron oxides in the soil, which could immobilise arsenic by chemical adsorption, thereby reducing the risk of spreading of arsenic and lowering of its toxicity. Simultaneously, the intention was to degrade PAH with hydroxyl radicals, forming from hydrolysis of water molecules in the soil. What also stood out in this study is that a pulsating current was used instead of chemical additives for PAH desorption, prior degradation. To test the effects of the technology on arsenic immobilisation and PAH degradation in sand and peat, experiments were set up on laboratory and intermediate scales. An additional experiment was performed in microcosms to test how varying redox conditions affect arsenic immobilisation in treated soil. Results showed that the concentrations of arsenic and PAH decreased in both soil and soil solution. However, low redox conditions and high organic matter content were two factors reducing the remediation effect. During anoxic conditions, an increase was shown in the exchangeable arsenic fraction. Moreover, the treatment was more effective in sand than in peat, most likely due to its lower organic matter content. However, the treated soil performed better under oxidizing conditions in terms of promoting arsenic immobilisation, and under reducing conditions in terms of preventing arsenic remobilisation, compared to untreated soil. This study showed that electricity driven remediation can be suitable for arsenic immobilisation and simultaneous PAH degradation. It could be a potential alternative to landfilling, especially when taking site-specific conditions into account, and when combining it with other remediation techniques. However, more studies are needed to confirm that, and the exchangeable arsenic fraction needs to be reduced prior industrial implementation.Förorenad mark är ett globalt problem på grund av dess påverkan på hälsa och miljö. Träimpregneringsindustrin är ett exempel som har lämnat många platser samförorenade med polycykliska aromatiska kolväten (PAH) och metall(oid)er, såsom arsenik. Trots de negativa miljömässiga och ekonomiska aspekterna av deponering är detta den vanligaste marksaneringstekniken i Sverige och Europa. Denna studie syftade till att undersöka effekterna av en eldriven saneringsteknik på mark förorenad med arsenik och PAH, för att bidra till kunskapen om att använda den som ett alternativ till deponering. Tekniken kan användas in situ, eftersom den är eldriven och elektricitet appliceras över elektroder som förs ner i jorden. Innovativt för denna studie är de avsiktligt korroderande järnelektroderna, som syftade till att tillsätta järn till jorden, för att möjliggöra bildandet av järnoxider. Dessa järnoxider skulle kunna immobilisera arsenik genom kemisk adsorption och därigenom minska arsenikföroreningens toxicitet samt minska risken för dess spridning. Avsikten var att samtidigt bryta ner PAH med hydroxylradikaler, bildade genom hydrolys av vattenmolekyler i jorden. Originellt för denna studie är också användningen av en pulserande ström för den PAH-desorption som föregick nedbrytningen, istället för kemiska lösningsmedel. För att testa teknikens påverkan på immobilisering av arsenik och nedbrytning av PAH i sand och torv, genomfördes experiment på laboratorie- och mellanstor skala. Ytterligare ett experiment utfördes i mikrokosmer för att testa hur varierande redoxförhållanden påverkar immobilisering av arsenik i behandlad jord. Resultaten visade att koncentrationerna av arsenik och PAH minskade i både jord och grundvatten. Låga redoxförhållanden och hög halt organiskt material var dock två faktorer som minskade saneringseffekten. Under anoxiska förhållanden ökade den utbytbara arsenikfraktionen. Dessutom var behandlingen mer effektiv i sand än i torv, mest troligen på grund av sandens lägre innehåll av organiskt material. Den behandlade jorden uppvisade dock en större motståndskraft mot remobilisering under reducerande förhållanden och främjade immobilisering under oxiska förhållanden, jämfört med obehandlad jord. Studien visade att eldriven sanering kan vara lämplig för immobilisering av arsenik och samtidig nedbrytning av PAH. Den skulle kunna vara ett potentiellt alternativ till deponering, särskilt när man tar hänsyn till platsspecifika förhållanden och när man kombinerar den med andra saneringstekniker. Fler studier behövs dock för att bekräfta detta och den utbytbara arsenikfraktionen behöver reduceras före industriell implementering
Geology, magmatic evolution, and Cu-Au sulfide genesis of the Mundonguara deposit, Manica Greenstone Belt, Mozambique
No full textThis thesis presents an integrated geological study of the Mundonguara Cu-Au deposit, located within the Archean Manica Greenstone Belt of western Mozambique, which forms part of the eastern Zimbabwe Craton. The research combines petrography, lithogeochemistry, U-Pb geochronology, mineralogy, mineral chemistry, and stable isotope analysis (S, C, and Oisotopes) to develop a comprehensive genetic model and contribute to the understanding of metallogenic processes in Archean greenstone terranes. Fieldwork and geochemical analyses reveal that the Macequece Formation, which hosts the Mundonguara Cu-Au deposit, comprises Al-undepleted peridotitic komatiites, pyroxenitic komatiites, ultramafic cumulates, and intrusive mafic to felsic rocks. These units show evidence of a mantle plume origin and were emplaced in a continental rift setting. U-Pb zircon ages from intrusive and extrusive units constrain the timing of a major magmatic event to 2.94-2.91 Ga, placing the Macequece Formation within the Lower Greenstones of the Bulawayan Supergroup. A major unconformity separates it from the overlying M'Beza-Vengo Formation, recording a temporal gap of ca. 170 Ma and indicating a craton-wide tectonic transition. Additional Neoproterozoic ages (578-846 Ma) reveal overprinting by later tectono-thermal events, including those associated with the Rodinia breakup and the Pan-African orogeny. Sulfur isotope compositions of sulfides (δ³⁴S: -0.40‰ to +4.02‰) support a dominantly magmatic source, with minor crustal input. Carbon and oxygen isotope ratios in gangue carbonates (δ¹³C: -9.61‰ to -4.32‰; δ¹⁸O: +4.93‰ to +13.05‰) define multiple stages of fluid-rock interaction, from early carbonate alteration of komatiites to later Cu-Au mineralization. These isotope signatures reflect the involvement of hybrid fluids of predominantly magmatic-hydrothermal character and with minor crustal contributions. Mineral chemistry data further support this model. Chalcopyrite trace element patterns are consistent with medium-temperature hydrothermal systems (e.g., IOCG, skarn), while Ni enrichment indicates interaction with komatiitic host rocks. Pyrite compositions define two groups with contrasting Co/Ni ratio, pointing to mixing between magmatic and metamorphic fluid sources. Sphalerite Fe content yields ore formation temperatures between 280 and 335 °C, consistent with low- to medium-temperature hydrothermal systems and overlapping withorogenic gold deposits. Altogether, the data supports a hybrid genetic model for the Mundonguara deposit, involving dominantly magmatic-hydrothermal fluids, minor metamorphic contributions, and metal input from both mantle-derived and local ultramafic rocks. The system differs from classical IOCG-and orogenic gold deposits and is best interpreted as an orogenic gold deposit with atypical metal association hosted in komatiitic rocks
Continuous Change Through Professionalization : Fragmentation, Digitalization and Sustainabilization in Construction from the Perspective of Swedish Architects
No full textIn this thesis I discuss how change in the construction sector affects and is affected by individuals’ perceptions and actions. Previous research has shown that behavioral change at the individual level is needed to achieve change at the macro level. This thesis therefore highlights continuous change from a professional perspective. Specifically, it focuses on the change phenomena of fragmentation, digitalization, and sustainabilization,and is thus connected to ongoing debates in research on how to ‘manage fragmentation’ or ‘achieve digitalization and sustainability’. Some previous studies in these areas rely on assumptions that are problematized and presented in a new light in this thesis. By focusing on professionalization, the thesis unveils the complex and reciprocal relationship between these change phenomena. Previous research has rarely analyzed fragmentation, digitalization, and sustainabilization together, especially from a professionalization perspective. The thesis therefore fills a research gap while simultaneously addressing highly relevant issues that are discussed daily at individual, organizational, and sectoral levels.The thesis focuses particularly on the architectural profession. This is partly because increasing fragmentation has significantly altered the role of architects in construction projects, not least because they are seen as central actors in driving digitalization and sustainability efforts. However, the focus on architects is also motivated by their under-representation in existing research. The theoretical points of departure are institutional theory (with a focus on agency) as well as sociological concepts related to professional identity and professional roles.Methodologically, the thesis builds on interpretive qualitative studies at the individual level, where focus groups, interviews, and shadowing have been used. In total, 41 architects participated in these studies, sharing their perceptions of themselves and their everyday practices in construction projects.By focusing on the professionalization underpinning larger structural changes—fragmentation, digitalization, and the sustainability transition—the thesis explores new perspectives. It discusses: the nature of fragmentation (from static to dynamic); the impact of fragmentation on digital and sustainability change (from barrier to enabler); how fragmentation can be managed (from the architect’s perspective); professional roles (from fixed to flexible); the profession (from uniformity to diversity); agency (from “cultural dopes” via entrepreneurs to implicit agents); professional identity (from partly unexplored to a central source of institutional change); as well as how digitalization and the sustainability transition can be understood as institutional movements.The thesis contributes empirically to theoretical fields such as research on professions and institutional theory (especially concerning agency and institutional work). It also offers new perspectives on long-standing challenges within construction research. For example, the results show the significance of professional identity for achieving institutional change in the construction sector, as well as how professionals cope with, navigate, and adapt to continuous change—insights that are central for understanding and practically managing fragmentation.Finally, with this thesis I hope to contribute to a renewed discussion about the development and future of the architectural profession, as well as the need to consider individual experiences to understand larger structural phenomena
Utilization and Reactivity Enhancement of Wood Ash in Cement–Based and Alkali–Activated Materials
No full textConcrete is the most widely used construction material worldwide due to its good mechanical properties, durability, and affordability. However, Portland cement production contributes approximately 5–8% of global anthropogenic CO₂ emissions. Supplementary cementitious materials (SCM), which can partially replace Portland cement, present the greatest potential for reducing the environmental impact of the construction industry. Recently, there has been increasing interest in research on the potential use of wood ash (WA) as an SCM. Utilization of WA in concrete promotes waste reuse and offers a sustainable option for SCM. However, since the characteristics of WA can vary significantly depending on its source and production conditions, further research is needed to optimize its effective use. This study aims to investigate the potential use of WA as an SCM and compare it with coal fly ash (FA), focusing on enhancing its reactivity and performance in both cement-based and alkali-activated materials through mechanochemical activation (MCA; high-energy grinding). The properties of WAs and the effect of MCA were examined, including Strength Activity Index (SAI), Frattini, R3 test, TGA/DTG, XRD and SEM-EDS analysis. WA was used to replace 10 wt.% and 20 wt.% of Portland cement in concrete and of ground granulated blast furnace slag (GGBFS) in alkali-activated mortars. Workability, strength, hydration behaviour, and microstructural properties were evaluated. The leaching behavior of WA was evaluated through batch tests, and the environmental performance of selected concrete mixes containing WA was further investigated using dynamic surface leaching tests (DSLT) on monolithic concretes. The frost durability of these concrete mixes was examined using the de-icing salt frost scaling test. MCA significantly increased the fineness and specific surface area of WA significantly, resulting in enhanced reactivity. Depending on their chemical composition, some WAs exhibited predominantly pozzolanic behavior, while others showed latent hydraulic properties. The use of WA after MCA in concrete and alkali-activated mortars led to improvements in strength, cumulative heat release and microstructure compared to unground WA. At lower replacement levels, the compressive strength improved compared with the control sample in certain mixes. In air-entrained concrete, it improves frost durability by reducing surface scaling. MCA improved the environmental compatibility by reducing the leaching of most heavy metals, despite stainless-steel grinding media increasing Cr and Ni concentrations. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) showed that, after MCA, WAs with higher pozzolanic oxide contents clustered more closely with FA
Textural and chemical characterization of sulfide minerals for improved beneficiation and exploration, Skellefte district, Sweden
No full textVolcanogenic massive sulfide (VMS) deposits belong to the most significant sources of base and precious metals such as Zn, Cu, Pb, Ag, and Au, as well as critical elements such as In, Ga, Ge, Sb, and Bi. Deformation and metamorphism of VMS deposits complicate their exploration and beneficiation. Examples are found in the Skellefte district, northern Sweden, where VMS deposits formed and underwent polyphase deformation (D1, D2, D3) during the 2.0–1.8 Ga Svecokarelian orogeny, imparting structural and mineralogical complexity at various scales. Presence of highly conductive graphitic strata in the host succession complicates direct detection using conventional electromagnetic geophysical techniques, necessitating a larger emphasis on geological and geochemical criteria to guide exploration. This study addresses these challenges by providing an integrated mineralogical, chemical, and textural characterisation of the Rävliden North Zn–Cu–Pb–Ag VMS deposit in the Skellefte district. Rävliden North is hosted at the transition between 1.89–1.88 Ga metavolcanic rocks of the Skellefte group and overlying 1.88–1.87 Ga, predominately metasedimentary rocks of the Vargfors group. Massive to semi-massive sphalerite, pyrrhotite, galena, pyrite occurs structurally and stratigraphically above chalcopyrite, pyrrhotite, pyrite-dominated mineralisation. Petrographic and structural analysis reveals textural evidence of sulfides hosted in ductile to brittle structures (e.g. foliations, boudinage, durchbewegt ore, piercement veins, tension gashes, breccia, and veinlets), indicative of polyphase remobilisation. Microanalysis show that sphalerite and chalcopyrite retain a zonation comparable with unmetamorphosed VMS, with enrichment of Cu, Co, and In in chalcopyrite-rich mineralisation. Limited syn-metamorphic redistribution of trace elements occurred beyond partitioning between coexisting sulfides. In-situ δ34S analyses indicate limited isotopic fractionation, with δ³⁴S values tightly constrained at 0 ± 2‰, consistent with a volcanic sulfur source. Meanwhile, variable δ114Cd, δ66Zn, δ56Fe and Zn/Cd ratios in sphalerite suggest an importance of mass-dependent kinetic fractionation with lighter isotopes precipitating near a high-temperature source, albeit volcanic source rocks akin to the Skellefte group can be pinpointed based on Pb isotopes. Overprinting, late-Svecokarelian sulfide assemblages (sphalerite, galena, Ag-rich sulfosalts) occur in quartz veins and sulfide-cemented breccia that crosscut ductile fabrics in the hanging wall. These host sphalerite and galena enriched in Cd, Ag, and Sb, and exhibit δ34S values consistent with recycling of syn-sedimentary sulfides, originally formed via sulfate reduction under anoxic deep-ocean conditions. Post-Svecokarelian mineralisation associated with calcite or zeolite (laumontite, heulandite and wairakite) veins and breccia crosscut all ductile fabrics. Distinctive colour-zoned sphalerite with oscillatory trace-element distribution in twins (enriched in Ga, Ge, Cu, Sb) together with δ114Cd, δ66Zn, δ56Fe, Zn/Cd, δ34S, δ15C and δ18O indicate a low-temperature (~150 °C) system involving reduced meteoric to connate water. Mineralogical and Pb isotopic similarities to nearby vein- and breccia-type Zn-Pb deposits indicate derivation from a juxtaposed mineral system at c. 0.5 Ga, linked to far field effects during opening of the Iapetus Ocean or the Timanian orogeny. Future research should test exploration vectors derived from hanging wall mineralisation, perhaps by correlating bulk-rock geochemical proxies with mineral-scale chemistry. The classification of Rävliden North’s VMS mineralisation based on dominant sulfides, host lithology, and textures allowed the investigation of mineral processing performance. Massive sphalerite-rich mineralisation hosted in amphibole and mica rich rocks differ markedly in grindability and flotation response compared to chalcopyrite-rich veinlets in more quartz-rich rocks. Recovery and concentrate quality for Zn, Cu, and Pb are controlled by mineralogy, liberation and grain size, while trace and critical elements (Ag, Sb, Bi, Cd, Hg, Tl, As) recovery depends on liberation and inter-locking associations with sulfides and sulfosalts. The results allow optimisation of blending protocols that could help enhance recoveries, mitigate deleterious elements, and facilitate exploitation of future by-products such as Bi and Sb. Future research should develop geometallurgical models that capture deposit-scale variability and strategies to recover critical metals as by-products
Geochemistry and Mineralogy of Acid Sulfate Soils in northern Sweden: Elemental distribution and groundwater chemistry
No full textAcid sulfate soils (AS-soils) refer to soils or fine-grained sulfide-bearing sediments that can produce acidity through sulfide oxidation. AS-soils do not pose a risk under waterlogged conditions; however, when exposed to oxygen, they can cause significant environmental and economic impacts. AS-soils oxidation results in sulfuric acid production, acidification of water bodies, element mobilization within the soil and into aquatic systems, adverse effects on biota, infrastructure damage, and potential deleterious effects on human health. Studying AS-soils presents a significant challenge due to their widespread impacts, highlighting the need for efforts to mitigate their environmental consequences. This doctoral thesis investigated the geochemical and mineralogical characteristics of AS-soils in northern Sweden, aiming to enhance understanding of their characteristics and weathering processes and thus contribute to developing environmental management strategies. AS-soils represent a global concern due to their extensive distribution, mainly in coastal areas that were once covered by saline or brackish water. In Sweden, AS-soils are distributed along the coastline and are derived from post-glacial sediments enriched with Fe sulfides. In the Baltic Sea, sulfide-bearing sediments are exposed to oxygen due to post-glacial isostatic uplift or groundwater table lowering. In Sweden, AS-soils are already oxidized, posing environmental risks that are further intensified in northern regions due to a greater rate of isostatic uplift. AS-soils are characterized by the accumulation of elements in a transition zone (TZ) between oxidized and reduced sediments. The oxidized zone (OZ) is distinguished by low pH values (< 4), element depletion, and the precipitation of Fe (oxy)hydroxide and Fe hydroxysulfate secondary minerals as common products of sulfide oxidation. In contrast, the reduced zone (RZ) represents the AS-soil parent material and consists of unoxidized black, fine-grained laminated sediments, characterized by a high total organic carbon content, high S content, and abundance of primary Fe sulfide minerals. Groundwater fluctuations influence soil redox conditions and pH, causing the transformation of unoxidized sediments into oxidized ones. This zone transformation induces the dissolution and reprecipitation of minerals, leading to element mobilization. This study analyzed AS-soils in Luleå, northern Sweden, from a geochemical and mineralogical perspective. Research on soil and groundwater was conducted in one waterlogged (SW) and one oxidized (SN) AS-soil profile located in Södra Sunderbyn, in the vicinity of the Lule River. Elemental distribution over the different zones was analyzed, identifying depletion and accumulation zones, and assessing the mobilized elements as potential contaminants in soil and water bodies. Mineralogical analyses were conducted through techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and microprobe, which were applied with the aim of identifying primary and secondary minerals, their composition, textures, morphologies, and distribution over the zones, and their impact on soil chemistry under weathering conditions. Furthermore, sequential extraction experiments were performed to associate the elements with each of the soil fractions and to quantify the potential elements released under oxidation. Additionally, interactions between groundwater and subsoil were evaluated, identifying sources and element mobilization pathways, acting as potential contaminants. The results demonstrated that both AS-soil profiles have the potential to generate acidity and mobilize elements upon exposure to oxygen, posing a negative environmental impact. Different S species were identified across the soil profiles. In unoxidized samples, S mainly occurs as primary Fe sulfide, metastable Fe sulfide, and organic S. Framboidal pyrite, the most abundant sulfide mineral and the primary acidity contributor, precipitated under anoxic-euxinic conditions through microbial sulfate reduction (MSR), as evidenced by negative δ³⁴S values. In contrast, oxidized samples predominantly contain S in secondary Fe hydroxysulfate minerals, such as jarosite or schwertmannite, which display negative δ³⁴S values indicative of sulfide oxidation processes, associated with their precursor sulfide. Incubation experiments over the profiles showed that pH decreases the most in samples with high S content, but not necessarily with high TOC content. In this research, it is demonstrated that framboidal pyrite is highly reactive and prone to rapid oxidation even with short periods of exposure to oxygen. Compositional maps obtained by microprobe analysis indicated that framboidal pyrite is a source of Cu, Mn, Mo, and Ni. These trace elements are typically distributed within the framboids, except for Mn, which surrounds the framboids, creating a Mn-rich rim. The labile and more stable organic fraction is strongly associated with Cu, Mo, and S, which are susceptible to mobilization during weathering. Despite past oxidation and element mobilization occurring in the OZ, this zone still exhibited a high percentage of elements with potential to be removed, as shown in the extraction experiments. The most soluble phases and pore water contribute with high concentrations of Cd, Cu, Mn, Mo, and S, indicating their high potential for environmental release. Seasonal variations result in groundwater fluctuations exposing the sulfide-bearing sediments to oxygen as the water table decreases, leading to oxidation and acidification. In contrast, during high water table periods, secondary mineral dissolution and element mobilization take place. These fluctuated redox conditions were evidenced by variations in δ⁵⁶Fe groundwater values, due to dissolution and transformation of Fe phases. The SN well registered high concentrations of Al, Co, Fe, Mn, Ni, S, and Zn in May and October, during low groundwater table periods. In contrast, the SW well remained waterlogged, preventing oxidation and acidity generation. The difference between the wells is evident in δ³⁴S values, with the SW well exhibiting strong ³⁴S enrichment from active MSR, while the SN well reflects dominant sulfide oxidation and limited MSR activity. This study shows the environmental risks associated with sulfide oxidation in northern Sweden and demonstrates that maintaining sulfide-bearing sediments under waterlogged conditions is essential to limit oxygen exposure, reduce acid generation, maintain alkaline pH levels, and minimize the release of dissolved elements, thereby mitigating negative environmental impacts
Reliability-based assessment of concrete dams considering combined sliding and overturning
No full textThis thesis aims to improve the assessment of dam safety through the formalization of an identified failure mode that combines the sliding and overturning failure mechanisms. The failure mode is relevant to dams with geometrical variations and large-scale asperities in the rock-concrete interface and represents the behavior observed in finite element analyses (FEA) and scale model tests. Dams are vital infrastructure, providing services such as water storage for hydropower and irrigation, flood control, and containment of industrial byproducts. However, storing large volumes of water carries the risk of potentially catastrophic consequences in the event of failure, making safety assessments essential throughout a dam’s service life. Regulatory rules and guidelines prescribe methods for performing such dam safety assessments, in which a dam’s safety against global failure modes such as sliding and overturning is commonly evaluated. However, these failure modes rely on assumptions that may not be consistent with the actual behavior of dams when large-scale asperities are present along the rock-concrete interface, which may cause the dam to exhibit a failure mode that combines both sliding and overturning. Furthermore, these regulatory rules and guidelines typically employ deterministic assessment approaches, providing general safety factors that must be calibrated for specific cases to achieve the desired level of safety. Given that dams are unique structures with inherent uncertainties, this approach is unlikely to produce consistent safety levels. The failure mode presented in this thesis, referred to as combined sliding and overturning (CSO), addresses the limitations of the traditional failure modes and reflects the failure behavior observed in concrete dams with large-scale asperities along the rock-concrete interface. Having been identified in FEA of concrete buttress dams, the failure mode was formalized and an analytical formulation was developed, providing results almost identical to those of FEA. The assumptions behind the failure mode and analytical formulation were compared with twelve scale model tests on concrete buttress dams, which included a monitoring system to validate these assumptions. The tests confirmed the assumptions and also evaluated the influence of factors such as rock bolts, reinforcement, and rock joints on load capacity and behavior, which primarily affected the load capacity. By relying solely on equilibrium equations, like traditional failure modes, the analytical formulation provides a simple alternative to methods such as FEA and can be readily applied with reliability analysis to assess a dam’s safety while accounting for its unique uncertainties. This is exemplified by a study on the reliability and sensitivity analysis of concrete buttress dams, in which a population of buttress dam monoliths, varying in height, width, and other characteristics, is generated and assessed for sliding, overturning, and CSO under two load cases, involving either overtopping or ice load. As such, influential factors for a dam’s reliability, including the basic friction angle, the dilation angle, the monolith height, and the inclinations of the front plate and the large-scale asperities, were identified. By introducing original methods to assess a dam’s load capacity while highlighting which factors impact the reliability of concrete dams, this thesis contributes to improved concrete dam safety assessment