Search Results (996)

When it rains or snows over a city, water droplets capture airborne pollutants and transport them to the ground. Prolonged precipitation over the same area can remove a larger amount of pollution; however, rainfall systems vary in duration and tend to move rapidly across regions. Wet deposition sprinklers replicate this natural scavenging process. They can operate for extended periods as needed and can be installed at specific locations where pollution mitigation is most necessary. Despite encouraging experimental results and the widespread use of similar technologies in industrial sectors—such as mining, the construction industry, and waste management—very limited scientific research has focused on their application in urban environments. In particular, their use as an emergency measure during severe pollution episodes as a protective intervention for sensitive subjects, while awaiting the effects of long-term structural solutions, remain largely unexplored. In the present work, we systematically discuss the key elements required to design and implement a network of anti-smog cannons (ASC) to protect sensitive receptors from severe air pollution events in large cities. Based on this analysis, we established a generalized framework that can be applied to any urban context worldwide. We also examine the potential application of the proposed method to the city of Turin (≈850,000 inhabitants, north-western Italy), which is considered a representative case study for other cities in Western Europe. Our findings indicate that such a network is both technically feasible and economically sustainable for local government authorities. Full article

Mining activities have led to contamination of natural resources by heavy metals (HMs). Biomagnification studies of HMs within food webs are necessary for understanding the progressive increase in metal burdens across trophic levels and their potential ecotoxicological consequences. This study examined the trophic transfer of Cd, Cu, Pb, and Zn in a tri-trophic model involving maize plants (Zea mays), their herbivore, the grasshopper Sphenarium purpurascens, and their predator, the spider Neoscona oaxacensis, under controlled conditions. Samples from all individuals were collected in Huautla, Morelos, Mexico, where three tailing deposits are present, containing approximately 780,000 tons of waste rich in HMs. We evaluated the body biomass of the grasshopper and the percentage of maize leaf material consumed with and without HMs. HM bioaccumulation in maize, grasshopper, and spider tissues was analyzed, and the enrichment process, along with gender related effects on HM bioaccumulation in females and males of S. purpurascens, was studied. The results revealed enrichment of Pb, Cd, and Cu in maize leaf tissue, except for Zn. Grasshoppers exhibited biomagnification of the same metals, except for Cd. Metal bioaccumulation resulted in a reduced biomass of female and male grasshoppers, accompanied by an increased leaf consumption compared to grasshoppers fed maize leaves without HMs. The HMs’ bioaccumulation levels differed between genders, with males recording significantly higher concentrations of Zn and Pb. The excretion of HMs in feces and their bioaccumulation in exoskeletons are two efficient metal detoxification strategies in grasshoppers. This study revealed biomagnification in the spider N. oaxacensis, confirming metal biomagnification to higher trophic levels and providing critical insight into exposure pathways, risks to wildlife and humans, and how metal pollutants may disrupt ecosystem integrity. Full article

Nitrate contamination of water resources poses significant ecological and public health risks. This study developed a cobalt-immobilized microplastic catalyst (Co–MP) capable of activating peroxymonosulfate (PMS) and facilitating formic-acid-assisted catalytic denitrification of nitrate. Characterization via Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Energy-Dispersive X-ray Spectroscopy (EDX), and X-ray diffractometry (XRD) confirmed successful Co deposition, with the surface cobalt content reaching 5.2%. The system’s performance was optimized using Response Surface Methodology (RSM), identifying catalyst dosage and Co(II) concentration as the most significant factors. Under the optimized conditions (pH 5.5, reaction time 120 min, catalyst dosage 1.5 g L⁻¹, and Co(II) concentration 60 mg L⁻¹), the system achieved a nitrate removal efficiency of 90.6%, in excellent agreement with the model prediction (90.93%), along with an 86.7% reduction in total nitrogen, confirming stepwise denitrification to gaseous nitrogen species (N₂). The Co(II)/Co(III) redox cycle, sustained by PMS-assisted regeneration and driven by formic acid as the electron donor, ensured stable performance with minimal cobalt leaching (0.05 mg L⁻¹). This coupled oxidative–reductive system offers a sustainable dual-remediation strategy that simultaneously achieves selective nitrate conversion and valorizes microplastic waste for catalytic environmental applications. Full article

Corrosion induced by defective oxide scales severely compromises the durability of concrete structures. This study develops a dual-mechanism sol-gel protection strategy based on La³⁺/Ni²⁺/2-Methylimidazole (2-MI). First, 2-Methylimidazole-catalyzed epoxy ring-opening constructs defect-minimized Si–O–Si/C–O–C networks through 60 °C low-temperature curing, reducing microcrack formation and curing energy consumption compared to conventional 130 °C processing. Second, utilizing 400 °C waste heat from hot-rolled steel triggers pH-modulated La₂O₃/NiO co-deposition within oxide scale defects, enhancing corrosion resistance. After a 40-day immersion in SCP + 0.1 M NaCl, the coated reinforcement exhibits a low-frequency impedance modulus of 25.6 kΩ·cm², achieving a 10.4-fold increase over untreated steel. Specimens embedded in 3.5 wt% NaCl mortar demonstrate a 120-day impedance modulus of 74.63 kΩ·cm², exceeding the control by 8.03-fold. This strategy integrates efficient industrial waste heat utilization with energy-saving low-temperature curing, providing long-term corrosion protection for marine concrete structures. Full article

Additive manufacturing (AM) of hot-work tool steels such as H13 offers unique opportunities for producing complex, conformally cooled tools with reduced production time and material waste. In this study, five metal AM technologies—Fused Deposition Modeling and Sintering (FDMS, Desktop Metal Studio System and Zetamix), Binder Jetting (BJ), Laser Powder Bed Fusion (LPBF), and Directed Energy Deposition (DED)—were compared in terms of microstructure, porosity, and post-processing heat treatment response. The as-printed microstructures revealed distinct differences among the technologies: FDMS and BJ exhibited high porosity (6–9%), whereas LPBF and DED achieved near-full densification (<0.1%). Samples with sufficiently low porosity (BJ, LPBF, DED) were subjected to tempering and quenching treatments to evaluate hardness evolution and microstructural transformations. The satisfactory post-treatment hardness was observed in both tempered and quenched and tempered BJ samples, associated with secondary carbide precipitation, while LPBF and DED samples retained stable martensitic structures with hardness around 600 HV0.5. Microstructural analyses confirmed the dependence of phase morphology and carbide distribution on the thermal history intrinsic to each AM process. The study demonstrates that while FDMS and BJ are more accessible and cost-effective for low-density prototypes, LPBF and DED offer superior density and mechanical integrity suitable for functional tooling applications. Full article

Additive manufacturing (AM) technologies based on sintering, such as Powder Bed Fusion (PBF), Direct Energy Deposition (DED), Binder Jetting (BJT), and Material Extrusion (MEX), enable the production of complex metallic components with reduced material waste and design flexibility. However, the intrinsic porosity, microstructural anisotropy, and mechanical properties of sintered AM metals significantly influence their machinability, affecting tool wear, surface integrity, and cutting forces. This review explores the key material characteristics affecting the machining performance of sintered AM metals, focusing on conventional processes such as turning, milling, and drilling. The impact of microstructure, density, and mechanical properties on machining outcomes is analyzed, along with the challenges posed by the unique properties of sintered materials. Additionally, post-processing strategies, including heat treatments and surface finishing techniques, are discussed as potential solutions to enhance machinability. The review concludes by identifying future research opportunities, particularly in optimizing AM process parameters and developing hybrid manufacturing approaches to improve the industrial applicability of sintered AM metallic materials. Although previous studies focus on individual AM technologies, this review takes a novel approach by systematically comparing the machinability of metallic materials produced via PBF, DED, BJT, and MEX. By identifying commonalities and differences among these sintering-based AM processes, this work provides a comprehensive perspective on their machining behavior and post-processing requirements, offering valuable insights for industrial applications. Full article

Phosphate rock is a vital natural resource classified by the European Commission as a critical raw material (CRM), extensively mined for its agricultural, industrial, and technological applications. While primarily used in fertilizer production, phosphate deposits also contain significant concentrations of trace metals, notably rare earth elements (REE), which are essential for renewable energy, electronics, and defense technologies. In response to growing demand, the recovery of REE from phosphate ores and processing by-products, particularly phosphogypsum (PG), has gained international attention. This review provides a comprehensive analysis of the global phosphate industry, examining production trends, market dynamics, and the environmental implications of phosphate processing. Special focus is placed on the geochemical behavior and mineralogical associations of REE within phosphate ores and industrial residues, namely PG and purification sludge. Although often treated as waste, these by-products represent underexplored secondary resources for REE recovery. Technological advancements in hydrometallurgical, solvometallurgical, and bioleaching methods have demonstrated promising recovery efficiencies, with some pilot-scale studies exceeding 70%–80%. However, large-scale implementation remains limited due to economic, technical, and regulatory constraints. The circular economy framework offers a pathway to enhance resource efficiency and reduce environmental impact. By integrating innovative extraction technologies, strengthening regulatory oversight, and adopting sustainable waste management practices, phosphate-rich countries can transform environmental liabilities into strategic assets. This review concludes by identifying key knowledge gaps and suggesting future research directions to optimize REE recovery from phosphate deposits and associated by-products, contributing to global supply security, economic diversification, and environmental sustainability. Full article

In this work, we developed and characterized a hydroxyapatite (HA) ceramic coating derived from Ucides cordatus crab-shell waste and applied it onto Ti–Al–V titanium substrates for biomedical use. Substrate analysis confirmed an α + β two-phase microstructure and Rockwell C hardness of ~35 HRC; optical emission spectrometry indicated a non-conforming Ti–6Al–4V composition (Al slightly above and V slightly below ASTM F136-18 limits), with expected α-phase predominance. Aqueous synthesis of biogenic HA used CaO (from 800 °C calcined shells) reacted with β-tricalcium phosphate (β-Ca₃(PO₄)₂), followed by deposition onto Ti–Al–V surfaces prepared with or without a thermochemical treatment that homogenized roughness (Ra ≈ 0.587 µm). The coatings were continuous, ~95–98 µm thick, and showed good qualitative adhesion. Scanning Electron Microscopy (SEM) revealed porous, nanocrystalline, acicular morphologies typical of biogenic apatite’s. Energy-Dispersive X-ray Spectroscopy (EDS) yielded Ca/P ≈ 1.85–1.88, while X-ray Fluorescence (XRF) indicated Ca-enrichment relative to stoichiometric HA. X-ray Diffraction (XRD) confirmed a predominantly hexagonal HA phase with high crystallinity. These results demonstrate a technically and environmentally feasible route to bioactive coatings using marine biowaste, aligning low-cost, local waste valorization with functional performance on titanium implants. Full article

The burning of coal in thermal power plants throughout Serbia produces significant amounts of industrial waste, primarily in the form of fly ash, boiler ash, and slag. Given their annual production, availability, and fine grain structure, it is necessary that sustainable strategies are developed for their reuse, instead of depositing them directly in landfills. In this research, the possibility of using fly ash, slag, and diatomaceous earth as raw materials for the synthesis of geopolymers at low temperatures was examined, in order to replace cement in construction materials, with the aim of reducing carbon dioxide emissions. Special emphasis was put on the effect of addition of organic macromolecules—polyvinyl alcohol (PVA), chitosan, and starch—upon the structure and mechanical properties of the obtained materials. In addition, the behavior of the materials with regard to the leaching of heavy metals in different environmental conditions was examined. Chemometric methods of multivariate analysis were used to examine the correlations between the obtained physical–chemical parameters, while the dependence of mechanical properties on the composition of the raw mixture was analyzed using the Mixture Design of Experiments method. The results obtained indicate that the examined waste materials have potential to be used as an environmentally friendly alternative to cement. The addition of PVA and chitosan had a positive effect on the mechanical properties of the geopolymers, with the highest strength achieved in formulations based solely on fly ash, containing 2.5% PVA, which reached 12.6 MPa. It was also shown that the addition of 30% diatomaceous earth increases the density and compressive strength of the material, while reducing the number of microcracks present in its structure, with a compressive strength of 13 MPa. Full article

The limited availability of high-quality ore deposits and the environmental hazards of metallurgical wastes highlight the importance of developing resource-efficient metal recovery technologies. Zinc kiln slag (ZKS), also known as Waelz slag, a by-product material enriched in non-ferrous metals, was processed through oxidative HCl leaching with H₂O₂ as an oxidant. Thermodynamic simulation and laboratory experiments were applied to determine optimal leaching conditions to dissolve copper, zinc, and iron. Optimal leaching efficiency was achieved with consumptions of 0.8 g HCl and 0.1 g H₂O₂ per gram of ZKS, a liquid-to-solid (L/S) ratio of 5 mL/g, a temperature of 70 °C, and a duration of 180 min, which resulted in recoveries of 96.3% Cu, 93.6% Fe, and 76.8% Zn. The solid residue with 43.5 wt.% C is promising for reuse as a reductant material in pyrometallurgical processes. Copper and arsenic were separated from the leachate via cementation with iron powder, achieving recovery rates of 98.9% and 91.2%, respectively. A subsequent two-step iron precipitation produced ferric hydroxide with 52.2 wt.% Fe and low levels of impurities. As a result, the developed novel hydrochloric acid oxidative leaching and metal precipitation route for ZKS recycling provides an efficient and sustainable alternative to conventional treatment methods. Full article

A significant portion of coal mined in Kazakhstan is mainly used for fuel energy and metallurgy. Approximately 60% of electricity is generated by coal-fired power engineering. About 19 million tons of ash and slag waste (ASW) are annually sent to dumps. After coal combustion, in ASW not only are natural radioactive nuclides NRN (U²³⁸, Th²³², K⁴⁰) concentrated, but also rare and rare earth elements (REE). In this regard, ASW that essentially turns into quasi-technogenic deposits of NRN and REE, requires systemic measures for their utilization. The possibilities of extracting REE from coal power-industry waste are estimated based on the analysis of the concentration of REE (Ce, La, Nd, Sm, etc.), NRN (U²³⁸, Th²³² and their decay products, K⁴⁰) and the established significant correlations between rare earth and radioactive elements. The purpose of this paper is to study the natural radioactivity of coals and ash and slag waste as potential raw materials for assessing the quality and extracting rare earth metals. The stated purpose involves solving the following problems: studying the features of the NRN and REE distribution in coals and ash and slag waste; assessing the possibility of using ash and slag waste as a promising source of REE extraction based on nuclear radiometric studies; and studying the spectrometry of natural gamma radiation for assessing the quality of coals. Full article

In recent decades, the urban population of Ecuador has grown, increasing the need for wastewater sanitation in cities. Wastewater treatment in this country generates sewage sludge (SS), which is mainly deposited on land near wastewater treatment plants or in sanitary landfills, generating significant environmental impacts. In view of this, composting or vermicomposting of SS can be suitable treatments for this waste, and the final materials obtained can be used as organic amendments. The objective of this study was to compare the agronomic and economic aspects of composting and vermicomposting using the same SS mixtures with different plant residues. For this purpose, the evolution of various physicochemical and biological parameters of both processes, the quality of the materials obtained, and the costs of their production were evaluated. The results revealed that all the amendments presented characteristics suitable for safe agricultural use. The vermicomposts had significantly lower levels of salts and higher levels of most macro- and micronutrients than the composts, thus increasing their economic value. However, the average production cost of composts was lower than that of vermicomposts, with faster stabilization of organic matter. All of this indicates that both techniques could be suitable for treating SS, but in order to choose the most appropriate technique for the study area, further studies with other waste mixtures and agricultural validation of the composts and vermicomposts obtained, as well as control of possible contaminants, would be required. Full article

As cold spray additive manufacturing matures, significant efforts are being made to develop spray conditions for more challenging materials, thereby expanding the technology’s range of applications. One main challenge while using commercially available equipment is that, even under optimized conditions, deposition efficiency remains low for some materials. Powder particles that do not adhere are wasted, which can severely affect the process economics, especially in a mass production context and/or when expensive feedstocks are used. Powder recovery and reuse is a logical solution to mitigate this problem, yet few studies evaluate its feasibility and its impact on powder characteristics and ultimately coating performance. In this work, powder recovery was investigated for two cases: a Ni powder and a NdFeB-Al powder mix, used respectively for repair applications and for the fabrication of permanent magnets. A prototype recovery system was built, achieving a recovery efficiency of up to 75%. The powders were recovered after up to four spray runs, and their morphology and size distribution were characterized. The magnetic properties of both powders and coatings were evaluated using hysteresis measurements. Although the process affects the particle size distribution and their magnetic properties, powders remain suitable for re-deposition for both materials. In particular, it was shown that NdFeB-Al mix maintains 97% of its initial magnetic performance under industrial operating conditions. Full article

This study combines a multidisciplinary approach to Pyrenean and Alpine glacial lakes to characterize the sensitivity of Late Glacial to Holocene subaquatic flood deposits in deltaic environments to slope failures triggered either by earthquakes, rockfalls, or snow avalanches. To clarify the possible interactions between environmental changes and these natural hazards in mountain and piedmont lakes, we analyze the lacustrine sedimentary records of key historical events and discuss the recurrence of similar regional events in the past. High-resolution seismic profiles and sediment cores from large perialpine lakes (Bourget, Geneva, and Constance) and from small mountain lakes in the French Alps and the Pyrenees were used to establish a conceptual model linking environmental changes, tributary flood sedimentary processes, subaquatic deltaic depocenters, and potentially tsunamigenic mass-wasting deposits. These findings illustrate the specific signatures of the largest French earthquakes in 1660 CE (northern Pyrenees) and in 1822 CE (western Alps) and suggest their recurrence during the Holocene. In addition, the regional record in the Aiguilles Rouges massif near Mont Blanc of the tsunamigenic 1584 CE Aigle earthquake in Lake Geneva may be used to better document a similar Celtic event ca. 2300 Cal BP at the border between Switzerland and France. Full article

Pyrolysis has emerged as a commercially viable material recovery process that supports circularity in the tyre industry. Here, it is demonstrated that a high degree of control can be imparted over the UK tyre waste stream and that statistically different feedstocks can be used to produce different grades of rCB based on their ash contents. The lower ash content rCB produced from truck tyres had superior in-rubber properties, closely matching those of the N550 reference. Silica, when not paired with a coupling agent, is known to be less reinforcing than CB, lowering the reinforcing behaviour of the high ash content rCB variant produced from car tyres. This justifiably places ash content within the classification and specification development discussion. However, a proximate analysis of UK waste tyres suggests that the typical rCB ash specifications of <20 wt% are unrealistic. Such limits would force producers to consider modifying process conditions to allow the deposition of carbonaceous residues to artificially dilute the ash content. This study investigates this process philosophy but conclusively demonstrates that carbonaceous residue is more detrimental to rCB performance than ash content. As such, carbonaceous residue content demands far more attention from the industry than it is currently afforded. Full article