1. Enhancing strength and ▫$CO_2$▫ uptake in lignite-based fly ash geopolymer mortar through supercritical carbonationTinkara Marija Podnar, Željko Knez, Gregor Kravanja, 2025, izvirni znanstveni članek Opis: This study demonstrates the potential of supercritical CO₂ curing to enhance the performance and sustainability of lignite-based fly ash geopolymer mortar offering a promising approach to reducing CO₂ emissions in the construction industry while improving material properties. The research comprehensively compared conventional curing (GEO-REF) with supercritical CO₂ curing (GEO-CO₂), revealing that GEO-CO₂ samples exhibited higher compressive and flexural strengths, achieving peak performance almost immediately after curing. Supercritical CO₂ exposure resulted in enhanced carbonation, with a depth of up to 7.6 mm and a carbonation rate of up to 67 %. XRD confirmed phase changes due to CO₂ curing, with GEO-CO₂ showing additional calcium carbonate-calcite, calcium carbonate-aragonite, and calcium silicate hydroxide compared to GEO-REF. Nitrogen adsorption/desorption studies indicated larger pore diameters but a reduced BET surface area in GEO-CO₂ samples, suggesting structural changes due to CO₂ exposure. TGA analysis revealed that supercritical CO₂ curing reduced water retention and enhanced carbonation, resulting in increased CaCO₃ content and changes in Ca(OH)₂ levels.
Ključne besede: geopolymer, fly ash, carbonation, CO2 fixation, supercritical CO2, high pressure reactor
Objavljeno v DKUM: 25.07.2025; Ogledov: 0; Prenosov: 4
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2. Towards circularity in Serbian mining: unlocking the potential of flotation tailings and fly ashNela Vujović, Vesna Alivojvodić, Dragana Radovanović, Marija Štulović, Miroslav Sokić, Filip Kokalj, 2025, izvirni znanstveni članek Opis: This paper examines sustainable industrial practices in Serbia, particularly in the mining and energy sector, focusing on the potential of flotation tailings and fly ash, as materials with the largest share in disposed waste in Serbia in 2023 (95%). It highlights the environmental challenges of mining waste and explores innovative approaches to waste management within the circular economy framework. The study analyzes the current state of mining waste in Serbia, particularly in copper mining regions in the east of the country. It discusses the potential for metal recovery from waste and its reuse in various industries. The research also investigates the use of fly ash from thermal power plants as a valuable resource in the construction industry and other sectors. The paper reviews existing initiatives and legislation in Serbia in order to promote sustainable mining practices and waste utilization. By presenting case studies and potential applications, the study demonstrates how implementing circular economy principles in the mining sector can contribute to environmental protection, resource conservation, and economic growth in Serbia. The comprehensive overview of the current state in Serbia provides a solid foundation for establishing a higher degree of circularity in the mining and energy sectors.
Ključne besede: mining, flotation tailings, fly ash, Serbia, circular economy
Objavljeno v DKUM: 17.03.2025; Ogledov: 0; Prenosov: 8
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3. Thermal, mechanical, and microstructural properties of novel light expanded clay aggregate (LECA)-based geopolymer concretesTinkara Marija Podnar, Gregor Kravanja, 2025, izvirni znanstveni članek Opis: The construction sector’s reliance on traditional cement significantly contributes to CO2 emissions, underscoring the urgent need for sustainable alternatives. This study investigates fine (0–4 mm), rounded, uncoated, porous-surfaced lightweight expanded clay aggregate (LECA)-based geopolymers, which combine the low-carbon benefits of geopolymers with LECA’s lightweight and insulating properties. Geopolymers were synthesized using lignite-rich fly ash with varying ratios of LECA to aggregate. Mechanical testing revealed that the reference mixture without LECA (REF-GEO) achieved the highest compressive strength of 37.89 ± 0.75 MPa and flexural strength of 7.62 ± 0.11 MPa, while complete substitution of the aggregate with LECA (LECA-100%) reduced the compressive strength to 17.31 ± 0.88 MPa and flexural strength to 3.41 ± 0.11 MPa. The density of the samples decreased from 2.06 g/cm3 for REF-GEO to 1.31 g/cm3 for LECA-100%, and thermal conductivity dropped significantly from 1.15 ± 0.07 W/mK to 0.38 ± 0.01 W/mK. Microstructural analysis using XRD and SEM-EDX highlighted changes in the material’s internal structure and the increase in porosity with higher LECA content. Water vapor permeability increases over time, particularly in samples with higher LECA content. These findings suggest that LECA-based geopolymers are suitable for low-load or non-structural elements. They are ideal for sustainable, energy-efficient construction that requires lightweight, insulating, and breathable materials.
Ključne besede: geopolymers, LECA, fly-ash, sustainable composites
Objavljeno v DKUM: 12.02.2025; Ogledov: 0; Prenosov: 22
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4. Formation of meso- and micro-pores in fly-ash zeolites using a three-step activationBhagwanjee Jha, D. N. Singh, 2014, izvirni znanstveni članek Opis: Researchers have comprehensively characterized alkali- activated fly-ash (the residue) and ascertained its highly zeolitic nature. In order to evaluate its potential for application as an adsorbent for the decontamination of waste water, the decisive parameters have mostly been the cation-exchange capacity, the mineralogy and the morphology of the residue. However, a study of the pore characteristics (e.g., the size and volume) of such residues is still warranted to anticipate their contaminant transport and the diffusion phenomena as a type of geotechnical engineering material. In this situation, the present study demonstrates the evolution of pores in the fly-ash after alkali activation up to three steps, and simultaneously, its effects` on other characteristics (e.g., the specific gravity, specific surface area and the cation-exchange capacity) of three types of similarly synthesized residues (the first, produced by using a NaOH aqueous solution and the other two residues, the result of alkali activation using a NaOH spent solution, the filtrates). Based on N2 gas absorption isotherms and infrared transmittance spectra, residues obtained from the second and third steps, each involving 24 hours of treatment using filtrates of 1.5-M NaOH, are established to be significantly enriched in the finer meso- and micro-pores, respectively, in comparison with a pure and macro-porous zeolite 4A.
Ključne besede: fly-ash, hydrothermal treatment, three-step activation, pore characteristics
Objavljeno v DKUM: 14.06.2018; Ogledov: 1066; Prenosov: 329
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5. Zeolitization characteristics of fly ashes from wet- and dry- disposal systemsBhagwanjee Jha, D. N. Singh, 2012, izvirni znanstveni članek Opis: The fly ash disposal at thermal power plants is either through wet- or dry-disposal systems. As these disposal practices result in different characteristics for the fly ashes, their interaction with alkalis, and hence the zeolitization potential, will be different. In order to demonstrate this, investigations were conducted to study the physical, chemical, mineralogical and morphological characteristics of the residues of the fly ashes collected from the lagoons and hoppers of the same thermal power plant, after their hydrothermal treatment. Field-emission-gun scanning electron microscopy and X-ray diffraction analysis of these residues demonstrated that the hopper ash attains an exceptionally high cation-exchange capacity and $SiO_2/Al_2O_3$ ratios (SAR), which correspond to the formation of major fly ash zeolites as compared to its counterpart. In other words, the study presented here helps to establish the superiority of hopper ash over lagoon ash for synthesizing fly ash zeolites and their enhanced quantity and quality.
Ključne besede: alkali activation, lagoon ash, hopper ash, fly ash zeolites
Objavljeno v DKUM: 13.06.2018; Ogledov: 1136; Prenosov: 118
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