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Limitations of Alkali Leaching in Coal Purification: A Case Study of the Bogovina Basin
No full textCoal is the most abundant and cheapest fossil fuel in the world [1]. It is the second most crucial energy source worldwide,
accounting for about 40% of global primary energy consumption [2]. Due to the increasing need to reduce the amount of
waste generated during coal combustion, there are various methods to solve these problems through chemical coal cleaning.
This study investigates the effect of alkali leaching on low-rank coal. Investigations were based on experimental conditions
that were tested, including various operational conditions, such as concentration of leaching reagents and temperatures, in
order to determine the optimal treatment parameters.
This research evaluates the effect of alkali leaching on the reduction of sulfur and ash content in coal. The results were
compared with the effects of acid leaching. However, the analysis of the leached residues showed that alkali leaching of
coal has limited efficiency, particularly in terms of demineralisation and desulfurization.
The coal sample used in this study was collected from the East field deposit, Bogovina Basin (Eastern Serbia). This coal
belongs to the bright brown coal group (the Low-rank A) [3]. The coal was ground to a fine particle size of <250 microns.
The alkali leaching process was performed under the following conditions: reagent concentration of 10 % sodium hydroxide
solution NaOH, temperature of 60 °C, and treatment duration of 30 minutes. The content of sulfur and ash in the initial coal
sample was 6.03 wt. %, and 17.52 wt. %, respectively [4]. After the leaching process, alkali leaching reduces sulfur and ash
content only slightly, and the concentrations were reduced to 5.49 wt. % for sulfur, and 15.74 wt. % for ash. These results
indicate the extent of removal achieved under the applied conditions. On the other hand, treatment with organic and
inorganic acids has demonstrated better results after the leaching process [4]. Based on the obtained results, it can be
concluded that alkali reagents are not adequate for optimal cleaning of coal. Alkali coal leaching showed low efficiency in
both deashing and desulfurization. These studies highlight the importance of selecting chemical methods that are compatible
with coal content, coal type, and the aim of the investigation. This contributes to the further development of the
environmentally friendly use of fossil fuels
Transforming volcanic rocks from Lichadonisia Island, Greece, into advanced luminescent nanostructures for potential solar concentrator applications
No full textAs the demand for environmentally sustainable materials rises, particularly in applications like luminescent solar concentrators (LSCs) for urban environments, this study investigates the potential of volcanic rock-derived nanostructures from Lichadonisia Island, Greece. These
nanostructures are designed to absorb sunlight and convert it to longer wavelengths efficiently. By grinding volcanic rocks and inducing nanostructure formation, followed by enrichment with FeO, enhanced luminescent properties were achieved. Comprehensive characterization using X ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Field Emission Scanning
Electron Microscopy (FESEM), and Energy Dispersive X-ray Spectroscopy (EDS) confirmed the crystalline nature of the volcanic rocks and the presence of FeO in an amorphous state. FTIR analysis revealed characteristic peaks of volcanic rocks and additional vibrations from FeO, as well as modifications of Si-O-Al vibrations. FESEM-EDS observations indicated plate-like nanoparticle structures with FeO nanoforms on modified surfaces. Luminescence properties,
assessed via Photoluminescence Excitation-Emission (PLE-PL) spectroscopy, showed that while pure nanostructures exhibited luminescence at 470 nm, FeO-enriched nanostructures demonstrated enhanced intensity and an additional emission peak at approximately 425 nm. These findings suggest that volcanic rock-derived nanostructures, particularly when enriched
with FeO, offer significant potential for use in eco-friendly LSCs
Interactive effects of microplastics and toxic metals pollution in Serbian urban environments
No full textMicroplastics (MPs) represent a global threat to soil biota, food chain, and human health [1]. Although
MPs and toxic metals are ubiquitous contaminants, little is known about the hazardous nature of their
coupled co-contamination effects [2]. This study examined the prevalence of MPs in Serbian (sub)urban
soils and investigated the intricate relationship between MPs and accompanied toxic metals Cd, As, and
Pb. MPs abundance was assessed by an optimized density separation method. Cd, As, and Pb
contents in soil and model plant were determined using inductively coupled plasma optical emission
spectroscopy (ICP-OES). On average, urban soils contained 489 ± 281 MPs per kg, whereby
polystyrene (PS) was the main contributor (28.57%). The highest contents of MPs (600 MPs kg-1), Cd
(2.23 μg g-1), As (36.92 μg g-1) and Pb (64.83 μg g-1) were found in soils from Bor. Spearman
correlation analysis revealed the connection between MPs abundance, soil physicochemical
parameters, and toxic metals mobility. MPs in soils negatively correlated with soil pH (-0.63). Significant
positive correlations identified between soil MPs and bioavailable contents of Cd (0.82), As (0.95), and
Pb (0.63) indicated that MPs presence may promote toxic metals mobility. In addition, Cd content in
roots and shoots positively correlated with MPs in soils (0.61 and 0.65), suggesting that MPs in soils
might improve toxic metal uptake by plants. These findings demonstrated that soil MPs could intensify
the migration of toxic metals in the soil-plant system, increasing the risks to the environment and human
health
Application of flotation tailings as a substitute for cement in concrete structures for environmental protection and sustainable development – Part I: Sulfide neutralization
No full textFlotation tailings (FT), as a product of the exploitation and processing of copper ore, represent a significant environmental and health risk due to the high content of heavy metals and sulfide compounds. Contemporary concepts of sustainable development and circular economy increasingly emphasize the need for rational use of resources and minimization of all types of waste, including mining waste. In this context, the reuse of flotation tailings in the construction industry represents a significant step towards closing the material flow in the mining and construction sectors. In order to reduce the negative impact of FT on the environment, the possibility of its application as a substitute for a portion of cement in the production of concrete was investigated. The main challenge is to reduce the negative impact of sulfides, originating from sulfide compounds, in order to achieve the desired concrete quality. Limestone aggregates of different size fractions (0/4, 4/8, 8/16 mm) were used for sulfide neutralization. Pyrite concentrate was used as a sulfide source, which together with FT provides the mixtures FT-7, FT-14, FT-25, and FT-40, with sulfur contents of 7.56, 13.84, 25.02, and 39.82%, respectively. FT mixtures were used as a substitute for Portland cement (PC) in the preparation of concrete. Test methods included XRD (X-ray diffraction), XRF (X-ray fluorescence), SEM (scanning electron microscopy), LP (leaching procedure), TCLP (toxicity characterization leaching procedure), assessment of acid eluate generation potential (AP—acid potential, NP—neutralization potential, and NNP—net neutralization potential), NEN (determination of heavy metals in cured concrete eluate), and UCS (uniaxial compressive strength of cured concrete). The results showed that the chemical characteristics of FT, as well as the chemical and mechanical properties of hardened concrete, allow the efficient use of these tailings in concrete mixes, which significantly utilizes FT, reduces the generation of mining waste, and contributes to the reduction of the negative impact on the environment and achieving sustainable development in mining
Potential of recycling and reuse mining waste in Serbia: challenges and prospect
No full textWaste materials from mining activities are increasingly used as secondary raw materials, which
reduces the need to extract new resources from nature and mitigates the negative impact on the environment.
This paper examines sustainable industrial practices in Serbia's mining and energy sector, focusing on flotation
tailings and fly ash, constituting 95% of disposed waste in 2023. The study investigates metal recovery potential
from copper mining regions such as Bor and Majdanpek and the utilization of fly ash from thermal power plants
in construction and other industries. By reviewing existing state and legislation, the paper discusses the
potential to provide the foundation for increased circularity in these sectors
Material flows and environmental consequences in Serbian mining practices
No full textBased on gold and copper processing, Serbia's mining sector faces significant challenges due to outdated
practices, existing regulations, and a lack of investment in sustainable technologies. Economically important,
the industry unfortunately causes severe environmental degradation, resulting in air, water, and soil pollution,
which is compounded by resource overexploitation and poor waste management. Serbia's material flow
indicators show high raw material consumption and hazardous waste production, with per capita Raw Material
Consumption (RMC) exceeding the EU average. The country ranks low in resource productivity and struggles
to align its practices with modern European standards. Serbia's mining royalty rates remain relatively low
compared to other countries, limiting state revenue and enabling resource overexploitation. Additionally, the
lack of local processing of raw materials reduces the sector's economic contribution. While foreign investors
bring capital and technology, concerns about environmental impacts and equitable benefit distribution persist.
To address these issues, Serbia must enforce strict environmental standards, and adopt new technologies while
incorporating material flow analysis into policy-making to achieve better resource management and minimize
environmental damage. Promoting local processing and increasing mining royalties could enhance economic
contributions while fostering sustainability. Collaborative efforts among government entities, investors, and
the public are essential to balancing different aspects of the development of the Serbian mining sector by
transitioning to more acceptable mining practices while preserving ecological integrity
Development of novel high-temperature alumina-based ceramic adhesive as a sealing material for IT-SOFC with the addition of wastewater sludge
No full textIn recent years, the tendency of modern society toward "green" technologies, which might solve concerns regarding the growing consumption of fossil fuels, is rising. Furthermore, the adoption of so-called waste-to-wealth concepts in industry has become a primary focus of forthcoming scientific research. Accordingly, in the present study, we investigated the potential application of an innovative alumina-based ceramic adhesive material with a partial addition of waste sludge as perspective sealant for IT-SOFCs. The extensive characterization was intended to determine whether the material possesses specific properties most relevant to sealing applications. The coefficient of thermal expansion (CTE), an important property of the sealant samples, was determined using dilatometry. The results were within the optimal range. A leaching test was performed to confirm its ecological friendliness. In addition, the sealant's sealing performance and thermomechanical stability in a single cell under operating conditions were validated via open circuit voltage (OCV) measurements. Good cell hermeticity and stable operating voltages in the intermediate temperature range were provided, indicating the potential applicability of IT-SOFC technology. In the upcoming research, further optimization of the material composition and properties will be carried out to achieve higher efficiency and better robustness
Comparative Study of Natamycin Encapsulation in Liposomes: Thin-Film vs. Proliposome Methods for Enhanced Stability, Controlled Release, and Efficacy Against Milk Spoilage and Pathogenic Microorganisms
No full textThe aim of this study was to evaluate liposomal particles as a potential delivery system for natamycin, a widely known antimicrobial agent used in the food industry. The goal was to prolong its diffusion into the surrounding medium. Natamycin-loaded liposomes were prepared using two methods (proliposome and thin-film) and two different phospholipid mixtures. The characterization of natamycin-loaded liposomes was performed in terms of their chemical composition (FT-IR analysis), encapsulation efficiency (EE), and antimicrobial potential against spoilage and pathogenic microorganisms that can be found in milk and milk products. During the 60-day storage period, their size, polydispersity index (PDI), and zeta potential were measured. The in vitro release kinetics of natamycin from liposomes were also assessed, and the results showed a significantly lower release rate of the drug when it was encapsulated. EE showed a high level of natamycin encapsulation (>80%), which was confirmed with FT-IR analysis. The stability study indicated that these systems were stable over a 60-day storage period, as the zeta potential of all formulations was ~−25 mV. Satisfactory antimicrobial performance of the developed liposomes against Listeria monocytogenes, Yersinia enterocolitica, Candida tropicalis, Candida parapsilosis, and Aspergillus flavus (MIC values from 0.00625 to 4 mg/mL) indicates that loading of natamycin into liposomal carriers was an adequate method for their encapsulation and delivery in the milk industry
Recovery of Cu and Fe from a Sphalerite Concentrate by the MnO2–KI Leaching Oxidation System
No full textThis study examined the leaching behavior of copper and iron from a sphalerite concentrate
in sulfuric acid utilizing an ensemble MnO2–KI oxidizing system. The temperature
was shown to significantly influence the leaching kinetics, with the efficiency notably
improving between 40 ◦C and 80 ◦C. The introduction of KI affected the balance between
sulfur passivation and oxidant availability, facilitating increased leaching efficiencies. At
3 wt% KI, maximum recoveries of 82.1% Cu and 85.3% Fe were achieved, which indicates a
notable decrease in surface passivation. Kinetic study analysis revealed low activation energies
of 28.90 kJ mol−1 for copper and 18.94 kJ mol−1 for iron, indicating that both processes
proceed readily at moderate temperature regimes. Despite being diffusion-controlled, the
mechanisms of dissolution are different: iron leaching is more complicated, involving
pyrite oxidation, sulfur layer formation, transformation to marcasite, and ultimately iron
(III) release, whereas copper leaching involves direct interaction of chalcopyrite with the
oxidants, similar to the behavior of sphalerite