Search Results (28)

The limestone quarrying and processing industry generates huge amounts of waste, with limestone sludge being one of the most prevalent and challenging by-products. This study aims to evaluate the potential of limestone sludge as a sustainable secondary raw material for the mechanochemical synthesis of bioceramics, specifically hydroxyapatite (HA), for high-added-value applications in bone tissue engineering. High-energy milling is innovatively used as the processing route: dry sludge (functioning as the calcium source), a phosphate source, and water were milled with the aim of producing calcium phosphates (in particular, hydroxyapatite) via mechanosynthesis. The industrial sludge was thoroughly analyzed for chemical composition, heavy metals, and mineral phases to ensure suitability for biomedical applications. The mixture of reagents was tailored to comply with Ca/P = 1.67 molar ratio. Milling was carried out at room temperature; the milling velocity was 600 rpm, and milling time ranged from 5 to 650 min. Characterization by XRD, Raman spectroscopy, and SEM confirmed the progressive transformation of calcite into hydroxyapatite through a metastable DCPD intermediate, following logarithmic reaction kinetics. The resulting powders are fine, homogeneous, and phase-pure, demonstrating that mechanosynthesis provides a low-cost and environmentally friendly pathway to convert limestone waste into functional bioceramic materials. This suggests that Moleanos sludge is a viable and sustainable source to produce tailored calcium phosphates and confirms mechanosynthesis as a cost-effective and reliable technology to activate the low-kinetics chemical reactions in the CaCO₃-H₃PO₄–H₂O system. This work highlights a novel circular economy approach for the valorization of industrial limestone sludge, turning a difficult waste stream into a high-value, sustainable resource. Full article

The growing demand for sustainable waste management practices has prompted interest in the land application of paper sludge as an alternative to landfilling and incineration. This study evaluates the environmental potential of paper sludge derived from recycled hygienic paper production by investigating its effects on soil respiration, seed germination, and seedling development. A comprehensive set of respirometric tests using the OxiTop^® system assessed microbial activity in soil amended with various concentrations of paper sludge (1–100%). Concurrently, bioassays using Lepidium sativum L. and Pisum sativum L. seeds examined the phytotoxicity and physiological response during germination. The results show that low to moderate sludge concentrations (1–20%) stimulated microbial activity and enhanced germination parameters, with a germination index (GI) up to 150% at 1%. However, higher concentrations (>40%) led to oxygen depletion, microbial stress, and decreased plant growth, indicating potential phytotoxicity and the need for application thresholds. For certain intermediate concentrations (e.g., 30–40%), a delay of approximately 21 days before sowing is recommended to allow microbial communities to stabilize and avoid initial stress conditions for plants. This study demonstrates that controlled application of paper sludge in soil systems can serve as a viable and sustainable disposal method, supporting circular economy principles and reducing the environmental burden of paper industry by-products. Full article

The persistent pharmaceutical diclofenac (DCF) presents a significant environmental challenge due to its widespread presence and biological activity in water systems. This study aimed to develop and characterize a novel, low-cost biosorbent by modifying waste guava seeds (GS) with the cationic surfactant cetyltrimethylammonium bromide (CTAB) to enhance the removal of DCF from aqueous solutions. GS and seeds modified with CTAB at 2 mmol/L (MGS-2) and 10 mmol/L (MGS-10) were prepared and characterized using FTIR, SEM-EDS, TGA, and Zeta Potential measurements. Batch adsorption experiments were conducted to assess the effects of contact time, biosorbent dosage, and solution pH. CTAB modification changed the biosorbent’s surface charge from negative to positive, thereby enhancing DCF removal. The MGS-10 biosorbent demonstrated the fastest kinetics. Critically, an intermediate level of surfactant modification (MGS-2) proved optimal, achieving a maximum adsorption capacity of 38.0 mg/g at 45 °C. This capacity significantly surpassed both the GS (29.7 mg/g) and the MGS-10 (32.7 mg/g). This superior performance is attributed to a favorable multi-stage adsorption mechanism, which combines electrostatic attraction and hydrophobic interactions, and is determined to be an endothermic and entropy-driven process. While highly effective, the biosorbents showed poor regenerability with NaOH, indicating a need to explore alternative regeneration methods. This work demonstrates that optimally modified guava seeds are a promising and sustainable material for remediating pharmaceutical contaminants from water. Full article

Some of nuclear power’s primary detractors are the unique environmental challenges and impacts of radioactive wastes generated during fuel cycle operations. Key benefits of spent fuel reprocessing (SFR) are reductions in primary high active waste (HAW) masses, volumes, and lengths of radiotoxicity at the expense of secondary waste generation and high capital and operational costs. By employing advanced waste management and resource recovery concepts in SFR beyond the existing standard PUREX process, such as minor actinide and fission product partitioning, these challenges could be mitigated, alongside further reductions in HAW volumes, masses, and duration of radiotoxicity. This work assesses various current and proposed SFR and fuel cycle options as base cases, with further options for fission product partitioning of the high heat radionuclides (HHRs), rare earths, and platinum group metals investigated. A focus on primary waste outputs and the additional energy that could be generated by the reprocessing of high-burnup PWR fuel from Gen III(+) reactors using a simple fuel cycle model is used; the effects of 5- and 10-year spent fuel cooling times before reprocessing are explored. We demonstrate that longer cooling times are preferable in all cases except where short-lived isotope recovery may be desired, and that the partitioning of high-heat fission products (Cs and Sr) could allow for the reclassification of traditional raffinates to intermediate level waste. Highly active waste volume reductions approaching 50% vs. PUREX raffinate could be achieved in single-target partitioning of the inactive and low-activity rare earth elements, and the need for geological disposal could potentially be mitigated completely if HHRs are separated and utilised. Full article

The disposal of low-level and intermediate-level radioactive solid waste has aroused widespread concern. In this work, the pyrolysis characterizations of simulated radioactive solid waste, cotton gloves (CG), stain removal cloths (SRC), plastic bags (PB), shoe covers (SC), and ion exchange resins (IER), were analyzed using thermogravimetric analysis, Thermogravimetric–Fourier Transform Infrared Spectrometry–Mass Spectrometry (TG-FTIR-MS) and Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS). The main mass loss stages of CG, SRC, PB, SC, and IER were 240–500 °C, 210–500 °C, 400–550 °C, 180–610 °C, and 25–700 °C, respectively. The average activation energies calculated by three iso-conversional methods were 184.09–211.46 kJ/mol, 172.33–180.85 kJ/mol, 264.63–268.01 kJ/mol, 150.49–184.36 kJ/mol, and 150.72–151.66 kJ/mol, respectively. Pyrolysis of CG and SRC mainly produced CO₂ and oxygenated compounds. SC generated large amounts of HCl during pyrolysis. Combined with rapid pyrolysis analysis, it was shown that CG and SRC mainly produced carbohydrates, aliphatic hydrocarbons, and aromatics. The pyrolysis products of SC mainly consisted of aliphatic hydrocarbons, aromatics, and acids. The pyrolysis products of PB were mainly olefins and alcohols. IER produced large amounts of aromatics during rapid pyrolysis. Specifically, the pyrolysis of IER generated some SO₂. This work provides a theoretical basis and data support for the treatment of mixed combustible radioactive waste. Full article

This study presents a comprehensive analysis of the microstructural characteristics and chemical composition of base and weld materials from reactor pressure vessels in the first (units 1 and 2) and second (unit 8) generations of Russian VVER 440 reactors at the Greifswald nuclear power plant. We measured the specific activities of ⁶⁰Co and ¹⁴C in activated samples from units 1 and 2. ⁶⁰Co, with its shorter half-life (t_1/2 = 5.27 a), is a key dose-contributing radionuclide during decommissioning, while ¹⁴C (t_1/2 = 5700 a) plays an important role in a geological repository for low- and intermediate-level radioactive waste. Our findings reveal differences in the proportions of trace elements between the base and weld materials as well as between the two reactor generations. Microstructural analysis identified Mo-rich precipitates and (Mn, S)-rich inclusions containing secondary micro-inclusions in the unit 1 and 2 samples. Raman spectroscopy confirmed iron oxides (γ-Fe₂O₃, Fe₃O₄), silicates (Mn-SiO₃), and Cr₂O₃/NiCr₂O₄ in the base metal as well as MnFe₂O₃ in the weld metal. X-ray photoelectron spectroscopy identified Mn inclusions as MnS, MnS₂, or mixed Mn, Fe sulfides, and the Mo precipitates as MoSi₂. These findings offer valuable insights into the speciation of elements and the potential release of radionuclides through corrosion processes under repository conditions. Full article

The degradation of polystyrene (PS) represents a significant challenge in plastic waste management due to its chemical stability and low biodegradability. In this study, the catalytic degradation mechanisms of PS were investigated by density functional theory (DFT)-based calculations using the hybrid functional B3LYP and the 6-311G++(d,p) basis in Gaussian 16. The influence of acidic (AlCl₃, Fe₂(SO₄)₃) and basic (CaO) catalysts was evaluated in terms of activation energy, reaction mechanisms, and degradation products. The results revealed that acid catalysts induce PS fragmentation through the formation of carbocationic intermediates, promoting the selective cleavage of C-C bonds in branched chains with bond dissociation energies (BDE) of 176.8 kJ/mol (C1-C7) and 175.2 kJ/mol (C3-C8). In contrast, basic catalysts favor β-scission by stabilizing carbanions, reducing the BDE to 151.6 kJ/mol (C2-C3) and 143.9 kJ/mol (C3-C4), which facilitates the formation of aromatic products such as styrene and benzene. Fe₂(SO₄)₃ was found to significantly decrease the activation barriers to 328.12 kJ/mol, while the basic catalysts reduce the energy barriers to 136.9 kJ/mol. Gibbs free energy (ΔG) calculations confirmed the most favorable routes, providing key information for the design of optimized catalysts in PS valorization. This study highlights the usefulness of computational modeling in the optimization of plastic recycling strategies, contributing to the development of more efficient and sustainable methods. Full article

In most countries, low- and intermediate-level wastes (LILWs) are cemented in carbon steel drums for later disposal. The durability of waste packages is determined by the chemical environment generated by both cement-based engineered barrier systems and the aggressive species present in the waste. Decontamination sludges are challenging wastes that are currently not accepted for final disposal due to their acidic nature and high concentrations of organic species and complexants. Thus, it was proposed to use electrochemical measurements to study the corrosion of steel sheets, simulating drums embedded in new alkali-activated slag (AAS) formulations with surrogate decontamination liquids, and determine their viability for use as confining matrices in order to increase the service life of the drums. The carbon steel coupon embedded in the Portland cement reference (R-L) paste showed the best corrosion resistance, followed by that of steel embedded in sodium silicate-activated slag (BFS-S-L) paste. This behaviour may be related to an improvement in the protective nature of the surface film. However, in sodium carbonate-activated slag (BFS-C-L) paste, the effect of the sludge in the matrix seemed to be more intense, leading to a pH decrease in the paste porewater, an effect that could hinder the formation of a passive layer on the surface of the carbon steel. Under such conditions, the initiation of the corrosion process seems to be favoured, resulting in the formation of a non-protective scale consisting mainly of hematite. Full article

Glutathione transferases (GSTs) are the primary catalysts protecting from reactive electrophile attack. In this review, the quantitative levels and distribution of glutathione transferases in relation to physiological function are discussed. The catalytic properties (random sequential) tell us that these enzymes have evolved to intercept reactive intermediates. High concentrations of enzymes (up to several hundred micromolar) ensure efficient protection. Individual enzyme molecules, however, turn over only rarely (estimated as low as once daily). The protection of intracellular protein and DNA targets is linearly proportional to enzyme levels. Any lowering of enzyme concentration, or inhibition, would thus result in diminished protection. It is well established that GSTs also function as binding proteins, potentially resulting in enzyme inhibition. Here the relevance of ligand inhibition and catalytic mechanisms, such as negative co-operativity, is discussed. There is a lack of knowledge pertaining to relevant ligand levels in vivo, be they exogenous or endogenous (e.g., bile acids and bilirubin). The stoichiometry of active sites in GSTs is well established, cytosolic enzyme dimers have two sites. It is puzzling that a third of the site’s reactivity is observed in trimeric microsomal glutathione transferases (MGSTs). From a physiological point of view, such sub-stoichiometric behavior would appear to be wasteful. Over the years, a substantial amount of detailed knowledge on the structure, distribution, and mechanism of purified GSTs has been gathered. We still lack knowledge on exact cell type distribution and levels in vivo however, especially in relation to ligand levels, which need to be determined. Such knowledge must be gathered in order to allow mathematical modeling to be employed in the future, to generate a holistic understanding of reactive intermediate protection. Full article

Amino acids, particularly the ones that cannot be synthesised during fermentation, are reportedly to be key nutrients for anaerobic fermentation processes, and some of the acids are also intermediate products of anaerobic fermentation of protein-rich waste. To date, particularly, there is a lack of research on the effects of some amino acids, such as cysteine, glycine, aspartic acid, and valine, on lactic production from the fermentation of food waste and also the mechanisms involved in the process. Thus, this study investigated the effects of the four different amino acids on lactic acid production during the acidic anaerobic fermentation of food waste. Firstly, batch experiments on synthetic food waste at different pHs (4.0, 5.0, and 6.0) were executed. The results harvested in this study showed that higher LA concentrations and yields could be obtained at pH 5.0 and pH 6.0, compared with those at pH 4.0. The yield of lactic acid was slightly lower at pH 5.0 than at pH 6.0. Furthermore, caustic consumption at pH 5.0 was much lower. Therefore, we conducted batch experiments with additions of different amino acids (cysteine, glycine, aspartic acid, and valine) under pH 5.0. The additions of the four different amino acids showed different or even opposite influences on LA production. Glycine and aspartic acids presented no noticeable effects on lactic acid production, but cysteine evidently enhanced the lactic acid yield of food waste by 13%. Cysteine addition increased α-glucosidase activity and hydrolysis rate and simultaneously enhanced the abundance of Lactobacillus at the acidification stage as well as lactate dehydrogenase, which also all favoured lactic acid production. However, the addition of valine evidently reduced lactic acid yield by 18%, and the results implied that valine seemingly inhibited the conversion of carbohydrate. In addition, the low abundance of Lactobacillus was observed in the tests with valine, which appeared to be detrimental to lactic acid production. Overall, this study provides a novel insight into the regulation of lactic acid production from anaerobic fermentation of food waste by adding amino acids under acidic fermentation conditions. Full article

The total amount of cellulose from paper, wood, food, and other human activity waste produced in the EU is in the order of 900 million tons per year. This resource represents a sizable opportunity to produce renewable chemicals and energy. This paper reports, unprecedently in the literature, the usage of four different urban wastes such as cigarette butts, sanitary pant diapers, newspapers, and soybean peels as cellulose fonts to produce valuable industrial intermediates such as levulinic acid (LA), 5-acetoxymethyl-2-furaldehyde (AMF), 5-(hydroxymethyl)furfural (HMF), and furfural. The process is accomplished by the hydrothermal treatment of cellulosic waste using both Brønsted and Lewis acid catalysts such as CH₃COOH (2.5–5.7 M), H₃PO₄ (15%), and Sc(OTf)₃ (20% w:w), thus obtaining HMF (22%), AMF (38%), LA (25–46%), and furfural (22%) with good selectivity and under relatively mild conditions (T = 200 °C, time = 2 h). These final products can be employed in several chemical sectors, for example, as solvents, fuels, and for new materials as a monomer precursor. The characterization of matrices was accomplished by FTIR and LCSM analyses, demonstrating the influence of morphology on reactivity. The low e-factor values and the easy scale up render this protocol suitable for industrial applications. Full article

Spent ion-exchange resins (SIERs) generated yearly in large volumes in nuclear power plants (NPPs) require particular predisposal handling and treatment with the primary objectives of waste volume reduction and lowering the disposal class. Deep decontamination of the SIERs using solution chemistry is a promising approach to reduce the amount of intermediate-level radioactive waste (ILW) and, thus, SIER disposal costs. However, the entrapment of nonexchangeable radionuclides in poorly soluble inorganic deposits on SIERs significantly complicates the implementation of this approach. In this work, the elemental and radiochemical compositions of inorganic deposits in an intermediate-level-activity SIER sample with an activity of 310 kBq/g have been analyzed, and a feasibility study of SIER decontamination using solution chemistry has been conducted. The suggested approach included the magnetic separation of crud, removal of cesium radionuclides using alkaline solutions in the presence of magnetic resorcinol-formaldehyde resin, removal of cobalt radionuclides using acidic EDTA-containing solutions, and hydrothermal oxidation of EDTA-containing liquid wastes with immobilization of radionuclides in poorly soluble oxides. The decontamination factors for ¹³⁷Cs, ⁶⁰Co, and ⁹⁴Nb radionuclides were 3.9 × 10³, 7.6 × 10², and 1.3 × 10², respectively, whereas the activity of the decontaminated SIER was 17 Bq/g, which allows us to classify it as very low-level waste. Full article

Renewable source-derived carbon is found to be a green alternative catalyst to zeolite for the pyrolysis of plastics. However, only polyethylene (PE) catalytic pyrolysis over biomass-derived carbon has been extensively studied. In this work, carbon was produced from industrial organic solid waste using different activation agents, and their catalytic performance on the thermal degradation of typical polymers, namely PE, polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) were investigated. The degradation mechanisms and the roles of different active sites of the carbons are discussed. Steam failed to activate the carbon, which has a low specific surface area (6.7 m²/g). Chemical activation using H₃PO₄ and ZnCl₂ produces carbons with higher specific surface area and more porosity. The pyrolysis characteristics of LDPE, PP, PS, and PET catalyzed by the carbons were studied using TGA and a fixed-bed reactor. The thermogravimetric results indicate that all three carbons reduce the pyrolysis temperature. The analysis of the products shows that the P- and Zn-involved acid sites on the AC-HP and AC-ZN change the reaction pathway of plastics and promote: (1) C-C cracking and aromatization of polyolefins; (2) the protonation of phenyl carbon of PS to yield higher benzene, toluene, and ethylbenzene; and (3) the decarboxylation of the terephthalic acid intermediate of PET, resulting in higher CO₂ and benzene. In addition, the high-value chemicals, long-chain alkylbenzenes, were found in the liquids of AC-ZN and AC-HP. The long-chain alkylbenzenes are probably formed by acid-catalyzed alkylation of aromatic hydrocarbons. This study provides basic data for the development of a cheap catalyst for plastic pyrolysis. Full article

Sustainable management of coal waste is one of the major environmental concerns for coal mining, whether active or legacy, worldwide. Coal dump deposits demand a large physical area or footprint for disposal of solid waste, change the topography, and generate both pyritic dust and acid rock drainage (ARD) where pyritic coal waste is deposited. The beneficiation of dump deposits or, preferably, of coal waste prior to its dumping can reduce or even eliminate the liabilities related to coal waste management. In this work, dense medium separation studies of coal discards, using heavy liquids, resulted in three pooled fractions from typical South African coal waste discards from the Mpumalanga region for future use: (a) a fraction of low density with increased calorific value; (b) a fraction of intermediate density, rich in ash and acid neutralizing minerals and lower in sulfur; and (c) a fraction of high density, rich in sulfidic minerals including pyrite. The fractions were characterized using particle size analysis, sink-float studies, static tests to predict ARD potential, proximateand ultimate analysis, and gross calorific value. The results showed that approximately 70% of this discard coal is composed of a material of sufficient quality for energy generation in conventional power stations. A pyrite-rich concentrate made up 2% of the total discard mass; comprising more than 45% of the sulfidic mineral present in the feed and displaying no acid neutralizing capacity (ANC). The remaining discard fraction, with intermediate density, presented potential to be used for several ends including soil fabrication, co-disposal or as aggregate material in civil engineering; additional testing to ensure applicability for the selected re-purposing option should be chosen based on proposed use. Full article

There are many regulations related to the radiological control of NORMs (Naturally Occurring Radioactive Materials) in activities such as mining, industry, etc. Consequently, it is necessary to apply fast and accurate methods to measure the activity concentrations of long-lived natural radionuclides (e.g., ²³⁸U, ^{234,232,230,228}Th, ^228,226Ra, ²¹⁰Pb, ²¹⁰Po, and ⁴⁰K) in samples characterized by a wide variety of compositions and densities, such as mining samples (wastes, minerals, and scales). Thus, it is relevant to calculate the radioactive index (RI), which summarizes for all radionuclides the ratio between the activity concentration and its respective threshold activity concentration as established by regulations, in order to classify a material as a NORM. To proceed with the determinations of these radionuclides, two spectrometric techniques based on both alpha-particle and gamma-ray detections should be employed. In the case of gamma-ray spectrometry, it is necessary to correct the full-energy peak efficiency (FEPE) obtained for the calibration sample, ${\epsilon }_c$, due to self-attenuation and true coincidence summing (TCS) effects. The correction is especially significant at low gamma emission energies, that is, $E_{\gamma }$ < 150 keV, such as 46 keV (²¹⁰Pb) and 63 keV (²³⁴Th). On the other hand, in samples which contain radionuclides that are in secular disequilibrium with others belonging to the same series (²³⁸U or ²³²Th series), like wastes or intermediate products, it is necessary to measure some pure-alpha emitters (²³²Th, ²³⁰Th, ²¹⁰Po) by employing alpha-particle spectrometry. A practical and general validated procedure based on both alpha and gamma spectrometric techniques and using semiconductor detectors is presented in this study. Full article