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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
Biokolproduktion i fluidiserad bädd reaktörer
No full textThis study explores the production of biocarbon from forest biomass through pyrolysis in fluidized bed reactors, emphasizing the relationship between the operating conditions, ash behavior, and physicochemical properties of the resulting solid biocarbon. Fluidized bed reactors offer distinct advantages for biocarbon production, including efficient heat transfer, isothermal operation, and scalability. These characteristics make them particularly suitable for integration into existing energy infrastructures. A key strategy investigated in this study is the use of a weakly oxidizing atmosphere composed of recycled flue gases from combustion processes as the fluidization medium. This approach enables heat integration with fluidized bed boilers and reduces the need for external inert gases, thereby lowering operational costs and improving the overall energy efficiency and circularity of the system. The impact of this atmosphere on biocarbon yield and composition was studied in detail, particularly regarding its influence on the behavior of ash-forming elements and textural properties. Special attention is given to the transformation and retention of ash-forming elements, such as potassium and phosphorus, which affect the suitability of biocarbon for industrial applications. The experimental and modeling results show that fluidized bed conditions favor the selective removal and distribution of these elements. Analytical techniques, including inductively coupled plasma (ICP), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and thermodynamic equilibrium calculations (TECs), were used to assess the mechanisms of ash transformation. In parallel, the evolution of particle properties, such as size, density, porosity, and surface area, was evaluated under different conversion regimes. Structural degradation owing to attrition and fragmentation was found to play significant roles in carbon retention and fines generation. Preliminary pilot-scale tests conducted with a different woody feedstock showed trends similar to those observed at the laboratory scale when comparable devolatilization severities were applied, reinforcing the transferability of key process–property relationships. Overall, these findings support the development of integrated and sustainable fluidized bed systems for biocarbon production, offering practical pathways to reduce fossil carbon use and improve resource efficiency in biomass valorization processes
The Effectiveness of Environmental Regulations: Design, Implementation and Institutional Context
No full textThis doctoral thesis consists of an introductory preface and five independent papers, which all address the effectiveness of environmental regulations. The focus is on how regulatory design and implementation as well as institutional context could influence the outcomes of industrial pollution control. Paper I investigates the impact of performance standards on the Chemical Oxygen Demand (COD) discharges from Swedish pulp and paper mills over a four-decade long period. The analysis employs an instrumental variable estimation of the fixed effects panel data model and data for 22 individual mills. The results show that these COD standards have led to significant reductions in water pollution from the mills. However, the magnitudes of this effect differ across two regulatory regimes in Sweden, thus highlighting the role of the institutional context in which the environmental regulations have been embedded. Paper II focuses on how the adoption of compliance periods, i.e., granting industry extended deadlines to comply with new standards, has affected pollution reductions. This regulatory tool is discussed conceptually, and the empirical analysis relies on an extended version of the above data set, and a Panel Vector Autoregressive model. The results illustrate that the combination of COD discharge standards and compliance periods has been effective in reducing water pollution. High regulatory capacity will improve the effectiveness of this type of regulation. Paper III investigates the factors that help explain the duration of environmental licensing processes and devotes particular attention to the role of incomplete license applications. Theoretically, the industrial actors might have an incentive to submit environmental impact assessments (EIAs) that have a high risk of being deemed inadequate by the authorities. The analysis relies on an Accelerated Failure Time (AFT) model and data covering 1606 environmental licensing processes in Sweden, and that reached a final decision during the time-period 2018-2022. The results confirm that the high prevalence of incomplete applications has been strongly correlated with prolonged environmental licensing processes. The purpose of Paper IV is to investigate how environmental licensing procedures can be implemented, and the regulatory requirements designed, to regulate pollution without jeopardizing investments in novel zero-carbon or digital projects. This is achieved in the context of two licensing processes: Northvolt’s battery factory in the city of Skellefteå and Facebook’s data center in Luleå. The empirical analysis builds on an analytical framework, which provides the conceptual anchor for 20 semi-structured interviews with key persons involved in these two processes. The findings are consistent with the notion that well-functioning licensing processes will be characterized by three general attributes: flexibility, predictability and knowledge. These can be attained within the realms of existing legislation, in turn suggesting that successful green and digital transitions are likely not contingent on comprehensive legal reforms. Finally, Paper V provides a brief and conceptual discussion of the choice between economic instruments, e.g., taxes, and performance standards in environmental policy. This paper questions the claim that the former unequivocally represents a superior policy approach for mitigating pollution. Based on recent research, it is argued that the zero-carbon transition involves specific challenges that tend to strengthen the case for the use of standards. Moreover, standards-based regulations are not necessarily implemented as crudely as some economic models assume, and efforts could be undertaken to reduce compliance costs and encourage green technological change. Overall, the findings in this thesis are consistent with the notion that such efforts ought to acknowledge the entire set-up of the regulatory system, including knowledge generation and information-sharing as well as the nature of the relationship between regulators and industry
Röntgensjuksköterskor i interprofessionella traumateam : Att navigera inom professionella roller, teamdynamik och organisatoriska strukturer
No full textTrauma care is a highly complex and time-critical setting that demands rapid decision-making and synchronised interprofessional collaboration. In trauma units, teams are assembled ad hoc, bringing together multiple professionals who must work in synchrony under pressure to ensure patient safety and effective clinical outcomes. Within ad hoc trauma teams, radiographers operate under complex and time-critical conditions, providing diagnostic imaging that is critical to clinical decision-making and patient outcomes. Despite this complexity, their professional role, agency, and collaborative integration remain underexplored in trauma care research. Addressing this gap, this thesis explores how radiographers’ professional roles and positioning are shaped within interprofessional trauma teams, with particular attention to team dynamics, organisational processes, and interprofessional practice. The thesis is based on four qualitative studies: (I) a focus group study exploring radiographers’ experiences of interprofessional collaboration during trauma alerts; (II) a study using critical incident technique to examine team behaviours from radiographers’ perspectives; (III) a study combining interviews and observations to investigate interdependencies and interactions between radiographers and other team members; and (IV) a grounded theory study exploring organisational processes for collaboration, based on interviews, focus group discussions, and document analysis. Together, these studies provide a multifaceted understanding of radiographers’ roles and the dynamics of trauma team collaboration. Based on these studies, the findings demonstrate how radiographers navigate inclusion and exclusion within trauma team decision-making processes, as revealed through multiple professional perspectives, observational insights, and analysis of trauma manuals. Visibility, role clarity, and shared awareness emerge as key conditions for effective collaboration. Team behaviours and hierarchical structures shape interprofessional dynamics, with relational and cultural barriers influencing workflow and mutual understanding. Leadership is essential for recognising radiographers’ competencies and promoting ethical, inclusive collaboration. Interdependence within teams is necessary but unevenly distributed. Trust, communication, and shared goals support adaptable teamwork, while limited daily collaboration hampers relational understanding, especially between radiographers and trauma leaders. Organisational conditions, including decision-making structures, team composition, and clinical guidelines, are affected by broader structural, cultural, and relational factors, which in turn impact practical collaboration and raise implications for patient safety. The findings further suggest that radiographers’ professional positioning is continuously negotiated within organisational boundaries. Structural conditions, spatial arrangements, and situated learning practices influence how visibility, inclusion, and agency are enacted in practice. These insights underscore the need for organisational strategies that promote ethical, inclusive, and effective interprofessional collaboration in acute care settings. Recommended strategies include spatial arrangements that foster proximity and informal communication, shared platforms for knowledge exchange that support inclusive decision-making, and interprofessional education that strengthens collaboration and coordination. These strategies address key needs in the studies: clearer role definitions, enhanced visibility of radiographers’ expertise, and leadership that supports interprofessional integration within trauma teams
Modeling and Analysis of Rotorcraft Airfoil Aerodynamics Under Martian Atmospheric Conditions
No full textThroughout history, human curiosity and the desire to explore have driven advancements in engineering capabilities and technologies. These efforts have extended our reach beyond Earth, with Mars emerging as one of the most important targets for planetary exploration. While rovers and landers have traditionally been used to study planetary surfaces, rotorcraft and other aerial vehicles have recently shown great promise for exploring the Red Planet. Such vehicles can access diverse terrains that are difficult or impossible for conventional landers and rovers to reach. However, the unique characteristics of the Martian atmosphere present significant aerodynamic challenges that must be overcome to enable sustained and efficient flight. Successful operation under these conditions requires a deep understanding of low Reynolds number aerodynamics, due to the rarefied atmosphere, and the influence of environmental factors such as pervasive Martian dust. The combination of low Reynolds number flows and suspended dust particles creates unique challenges for rotorcraft aerodynamics on Mars. This thesis investigates these challenges through Computational Fluid Dynamics (CFD) simulations, focusing on the performance of a cambered plate airfoil with 6% camber and 1% thickness, which is well suited to the Martian environment. The research addresses both fundamental aerodynamic phenomena and environmental effects, providing insights into model selection for accurate flow prediction, sensitivity of performance to Reynolds number variations, and the long-term impact of dust accumulation on airfoil behavior. This work presents a comprehensive overview of the evolution of drone designs for planetary exploration, emphasizing the main aerodynamic and control challenges involved. Operating in planetary atmospheres introduces unique difficulties, particularly due to the low chord-based Reynolds numbers and the presence of floating dust particles that can affect both aerodynamics and system reliability. The aerodynamic behavior at Reynolds numbers on the order of 104 is investigated, focusing on the effect of increasing the rotor or chord dimension. Results show that increasing the Reynolds number from 20,000 to 50,000 does not significantly improve performance, as the formation of Laminar Separation Bubbles (LSBs) on the surface still occurs. The transition model used, γ–Reθ, is able to accurately capture bubble formation. However, its limitations are also identified through comparison with other models, among which γ–Reθ is found to be the most reliable transition RANS model for these flows, since k-kL-ω fails to reproduce the correct post-stall behavior. Unsteady Navier–Stokes (UNS) simulations exhibit the same inability due to the absence of turbulence modeling; however, their lower computational cost makes them suitable for preliminary studies and acceptable for low angles of attack. The accumulation of dust particles on the airfoil surface is also examined, showing that particle deposition alters the airfoil geometry and leads to measurable changes in aerodynamic performance. While the effect is modest in the short term, it could become significant over long exposure times. The results are obtained under simplifying assumptions, such as a smooth surface and no detachment of particles. Further refinement is achieved by simulating particle deposition on an airfoil exposed solely to wind, where the wind velocity is modeled using a simple stochastic approach. The simulations account for both particle accumulation and instantaneous detachment during the run, and additional detachment is evaluated in a post-processing step. The resulting surface modification is then used to study its effect on the aerodynamic performance, providing a more complete understanding of how dust environments influence drone operation in planetary exploration. Overall, the findings contribute to a deeper understanding of low Reynolds number aerodynamics and environmental degradation mechanisms relevant to Martian rotorcraft. The results offer guidance for aerodynamic model selection, design optimization, and long-term operational strategies for future aerial exploration missions on Mars
Tribological performance of novel bio-based polymer composites
No full textVarious industrial and societal developments in recent times are connected to climate change, sustainability, and green technology. Among these are legislations and directives from governing bodies and institutions, as well as research efforts and investments from academia and industry. One major example of an institution getting involved is that of the United Nations (UN) who published their UN Sustainable Development Goals (SDG) in 2015, in which they define pathways to a more sustainable future. A number of these goals are directly associated with the adaptation and development of sustainable engineering solutions, including enhanced resource and energy efficiency. The selection of materials in a tribological context (i.e. the study of surfaces in contact and motion) plays a major role in achieving these objectives, directly impacting resource efficiency. Frictional losses in machines and equipment and the wear of their constituents have a direct impact on the energy efficiency and sustainability of systems. An important class of tribo-materials are polymeric components. Especially thermoplastic polymers and their composites have gained significant importance in sectors like green energy production or transportation over the last few decades due to their favourable strength-to-weight ratio, corrosion resistance and, in many cases, self-lubricity, as well as their overall tailorable properties. However, they are mostly produced from ecologically undesirable fossil-based resources. Bio-based options both for reinforcements and matrix polymers to this day often lack strength or consistency of properties. In the spirit of these aspects, this thesis explores the development and characterisation of high-performing thermoplastic composites containing or consisting of bio-based materials, focusing on their thermal and mechanical properties, morphology, and tribological performance. Polyoxymethylene (POM) and polyamide 11 (PA11) were selected as matrix materials in this work as they are already widely employed in tribological applications, but often in combination with fossil-based reinforcements. They possess appreciable mechanical strength, temperature stability, and chemical resistance. Their higher hydrophilicity compared to other common engineering thermoplastics, furthermore, makes them favourable choices for combining with natural-based materials. PA11 moreover contributes to the aspect of sustainability by virtue of being fully bio-based. Short regenerated cellulose fibres and cellulose nanocrystals (CNC) were selected as reinforcements based on their outstanding mechanical strength and higher thermal stability compared to other bio-based fillers. The short cellulose fibres were added to POM, while the CNCs were incorporated into PA11, both via melt-mixing processes leading to homogeneously dispersed systems in both cases. The gathered results on the POM composites showed a significant increase in strength under tension and flexion at the highest fibre content as well as a rise in crystallinity upon introduction of the reinforcements. Tribological evaluations have shown that the fibre addition led to an in individual cases substantial and in general noticeable reduction of the wear coefficient at a wide range of conditions, both in preliminary tests and in the subsequent p · v range assessment. The effect on the coefficient of friction, however, was on average detrimental, especially at the lower tested speed of 0.5 m · s−1. Nevertheless, the short cellulose fibres stabilised the friction behaviour of POM at harsher p · v conditions. A main reason for these improvements was the change in tribofilm formation towards a higher coverage of the wear track, protecting the polymer samples from the asperities of the countersurface discs. Using CNC, notable improvements of the crystallinity, compressive strength and thermal stability of the polymer and its properties were achieved. The CNC also reduced the wear coefficient of PA11 by close to 90 % and was instrumental for the tribofilm formation on the countersurfaces. Additionally, the coefficient of friction decreased as well, most likely explained through the increased presence of polymeric material on the countersurface discs, while also crystallinity further increased through possible strain-induced crystallisation. Raman spectroscopy, moreover, was proven to be a capable non-destructive evaluation method for tribofilm morphology, providing highly valuable insights for understanding wear and friction mechanisms that are otherwise often difficult to obtain. The effect of annealing at different parameters on the PA11-based composites was evaluated as well and found to be an important influence factor for crystallinity, crystal structure and tribological properties. Further improvements of especially the wear coefficient were obtained, leading to a total reduction of more than an order of magnitude when compared to the as-processed neat PA11. Reducing the coefficient of friction by thermal post-processing was successful as well, which again is assumed to be rooted in the aforementioned change in tribofilm formation and appearance as well as adjustments of the crystal structure, as proven by X-ray diffraction (XRD) experiments. Overall, the cellulosic materials at both size scales improved the wear resistance of either matrix polymer significantly, while also in certain circumstances providing a lower coefficient of friction. In conclusion, this work shows the potential of bio-based reinforcements and composites to be successfully employed as engineering composite materials for load-bearing applications
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
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