Search Results (233)

Drilling fluids are essential in oil and gas operations for wellbore stability, cuttings transport, pressure control, and fluid-loss reduction. Water-based drilling fluids (WBDFs) are widely used because of their cost-effectiveness and lower environmental impact compared with oil-based systems; however, they often suffer from fluid loss into the formation and lower rheological performance. This laboratory-scale study investigates the feasibility of using rice and bread waste powders as bio-based additives for WBDFs to mitigate fluid loss. The collected food wastes were dried, milled, and sieved into three particle sizes of fine (150 µm), very fine (75 µm), and ultrafine (45 µm). The prepared powders were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). A total of 18 drilling-fluid formulations were prepared using rice and bread powders at concentrations of 1 wt%, 2 wt%, and 3 wt%. Filtration tests were conducted under low-pressure low-temperature (LPLT) conditions of 100 psi and 25 °C and high-pressure high-temperature (HPHT) conditions of 1500 psi and 70 °C, while rheological properties were measured using a rotational viscometer. The results showed that additive type, particle size, and concentration strongly influenced WBDF performance. The best-performing formulation was WBDF with added rice powder at 45 µm and 3 wt% (RC45-3), which reduced fluid loss from 19.5 mL to 6.1 mL, corresponding to a reduction of approximately 68.7% at LPLT. Under HPHT conditions, the same formulation reduced fluid loss from 36.5 mL to 11.4 mL, corresponding to a reduction of approximately 68.8%. RC45-3 also produced the thinnest measured filter cake, reducing filter-cake thickness from 5.0 mm for the base mud to 0.52 mm. The formulation maintained shear-thinning behavior and produced suitable gel strength values, indicating improved suspension capacity. The improved performance of rice powder is attributed to its fine particle size, favorable morphology, and ability to form a compact, low-permeability filter cake. Overall, the findings indicate that processed rice waste powder has potential as a low-cost, bio-based fluid-loss-control agent for WBDFs, although further testing in field-representative mud systems is required before practical application. Full article

This study investigates the potential of a Falcon Ultra-Fine (UF) concentrator for the recovery of ultrafine scheelite particles from a weathered tailing stockpile of an historical scheelite mine, as it could represent a valuable secondary tungsten resource. The tailings are characterized by a P80 of 17.2 µm, with scheelite grains exhibiting a finer size distribution (P80 = 9.3 µm) and a high liberation degree (82 wt%). A three-stage Falcon concentration circuit was tested under varying operating conditions, including feed tank design, concentration of solids, particle size fraction, G-force and the number of treatment stages. Results showed that separation efficiency is primarily governed by the tank design and the feed particle size distribution, while variations in G-force and concentration of solids produced only minor effects. Hydrocyclone desliming to remove particles finer than 10 µm prior to concentration enhanced the separation selectivity of the Falcon-based concentration flowsheet. However, such pre-treatment of the material will require the implementation of a dedicated process to recover scheelite from the overflow to limit losses. These findings highlight the challenges of effective scheelite separation due to the fineness of these tailings. Full article

With increasingly strict air quality standards and growing concerns about air pollution, fine and ultrafine particulate matter remains a major challenge for conventional air cleaning technologies. Due to their small size, these particles are difficult to remove using traditional filtration and separation methods. Acoustic agglomeration can be used as a pre-treatment technology to increase particle size in a high-intensity acoustic field and improve the efficiency of particle removal. This study investigates acoustic-induced agglomeration of solid aerosol particles in a dynamic airflow system. The effects of acoustic frequency were evaluated at 3, 5.5, 7.5, and 15 kHz under a sound pressure level of 135 dB and at two airflow velocities: 0.75 m/s and 1.5 m/s. These velocities corresponded to different particle residence times in the acoustic field. Arizona test dust was used as the test aerosol, and particle-number concentration and particle-size distribution were measured before and after the acoustic field. The results showed that acoustic agglomeration of fine and ultrafine particles was strongly affected by both acoustic frequency and particle residence time. The highest agglomeration efficiency, reaching up to 42%, was obtained at 3 kHz, 135 dB, and longer particle residence time. These findings indicate that acoustic agglomeration can promote particle-size redistribution in moving airflow and may be used as a pre-treatment method for improving particulate matter removal in air quality control systems. Full article

Anatase-bearing lateritic ores from Qinglong, Guizhou Province, China, are characterized by extremely low TiO₂ grade, high clay content, fine-grained dissemination, and complex intergrowths with iron oxides, which severely hinder efficient beneficiation. In particular, anatase commonly occurs as ultra-fine particles encapsulated by clay minerals or closely associated with iron oxides, and its surface is often covered by nanoscale goethite films, resulting in surface passivation and pseudo-magnetic behavior. These characteristics lead to a pronounced contradiction between mineral liberation and excessive slime generation during conventional grinding processes. To address these challenges, a high-efficiency pre-concentration flowsheet was developed based on selective desliming, stage grinding, intensive scrubbing, flotation, and weak magnetic separation. Selective desliming via hydrocyclones was adopted, which is inferred to preferentially discard true slimes finer than 10 μm while potentially retaining most fine anatase particles within the underflow. Stage grinding was then applied, which may promote the improved liberation of anatase and early rejection of coarse gangue, and may help reduce overgrinding. Intensive scrubbing was introduced, which is expected to weaken or partially remove iron oxide coatings from the anatase surface, thereby potentially restoring surface activity and reducing pseudo-magnetic interference. Subsequent flotation and low-intensity magnetic separation were optimized to increase the concentrate TiO₂ grade and cut iron impurities, which may be associated with improved surface selectivity and weakened pseudo-magnetic responses. Closed-circuit beneficiation tests demonstrated that a TiO₂ concentrate with a grade of 29.62% and a recovery of 65.4% could be obtained from an ore with an initial TiO₂ grade of only 4.39%. Moreover, approximately 40% of the feed mass was rejected at the pre-concentration stage, significantly reducing the load on downstream separation processes. The proposed process demonstrates promising potential as a technical route for the beneficiation of similar refractory anatase-bearing lateritic ores. Full article

This study presents a comprehensive evaluation of sorbent injection to mitigate sodium emissions in a 250 MW_e cyclone-fired boiler using lignite coal. Using historical boiler operational data, a computational fluid dynamics (CFD) model was validated and simulations were subsequently conducted to identify optimum sorbent injection locations for maximizing dispersion within the boiler cross-section and limiting sorbent temperatures to avoid deactivation. Data from the literature were used to guide sorbent injection rates and target sorbent particle sizes. Subsequent field demonstrations with the injection of a commercially available sorbent achieved a 60–80% reduction in the gas phase sodium, which was visually corroborated by reduced deposition on heat exchanger probes placed inside the boiler as well as by data on ash composition as a function of size. Furthermore, a diffusion-kinetic model, incorporating alkali vapor (NaOH) capture and subsequent sorbent deactivation, was developed and integrated into the CFD simulations as a post-processing tool and tested against the field demonstration data. Additional bench-scale testing was conducted with a range of sorbents as part of tool development for selecting from locally available sorbent sources. These bench-scale tests indicated a definite shift in the aerosol particle size distribution (PSD) toward a coarser range and depletion in the ultra-fine sizes, confirming the capture of vapor phase sodium species by the sorbents. Notably, in these tests, the sorbents remained effective even when they became molten, suggesting the potential for more convenient and cost-effective injection strategies. Full article

Haze Pollution in China arises from the rapid enlargement of ultrafine particles into light-absorbing fine particulate matter through adsorption processes under atmospheric stagnation conditions. This study focuses on the sources of ultrafine particles (UFPs), the most critical component of haze pollutants during severe pollution periods in China. Utilizing methods including the spatial Durbin model and statistical data for the 28 cities (the “2 + 26” cities) within the Beijing–Tianjin–Hebei air pollution transmission channel—suffering the most severe haze pollution—it investigates the impact of pollution-intensive industries on haze pollution. This study reveals several key findings regarding China’s haze pollution. First, the principal source of ultrafine particles within China’s haze stems from the desulfurization, denitrification, and dust removal processes of pollution-intensive industries (the direct effect of these industries on haze is 0.028 * according to the SDM regression results). Crucially, the specific operational factors driving the abrupt increase in atmospheric UFPs during severe haze periods in China are identified as extensive management practices in desulfurization, the progressive tightening and annual escalation of denitrification emission standards, and the reliance on electrostatic precipitation which is ineffective against ultrafine particles. Second, haze pollution predominantly occurs in regions characterized by concentrations of pollution-intensive industries coupled with weak atmospheric environmental self-purification capacity (this carrying capacity for pollution-intensive industries exerts a significant negative impact on haze, demonstrated by a direct effect of −0.020 **; further analysis reveals that this is caused by regional differences in atmospheric self-purification capacity). Third, regional air transport acts as a contributing source, introducing UFPs from neighboring areas into local haze pollution, reflected by an indirect effect of pollution-intensive industries of 0.151 ** stemming from such spatial spillovers. Based on these conclusions, the study proposes a set of policy recommendations: relocate pollution-intensive industries using a gradient approach based on atmospheric self-purification capacity differences; systematically upgrade wet flue gas desulfurization technologies for industrial emissions; effectively promote technological innovation in denitrification processes; implement scientific controls on ammonia emissions; strengthen R&D in core technologies for UFP removal; innovate dust removal technologies to enhance overall system efficiency; reinforce regional coordinated governance; implement targeted training programs and select qualified management personnel; systematically enhance the environmental management capabilities of staff; and effectively mitigate the spillover effects of haze pollution. Full article

This case study investigates the ageing behaviour of hydroxyl-terminated polybutadiene (HTPB)-based solid propellants, containing 0.5% iron oxide and a bimodal ammonium perchlorate (AP) distribution (300 µm coarse AP and 40 µm fine AP). To achieve higher burning rates in large solid rocket motors, burning-rate catalysts were preferred over ultra-fine oxidiser compositions due to processing advantages. Characterisation of the iron oxide burning rate catalyst, specific to its surface area, was attempted. The role of surface characteristics in burning rate augmentation and ageing reactions was studied. Particle size and surface area estimates were obtained, and propellant burning rates, pressure exponents, and propellant ageing behaviour were evaluated to support the study. Accelerated thermal ageing of composite solid propellant samples at three different temperatures is carried out. The Arrhenius equation was used to model the dependence of the initial modulus on ageing time and temperature. An activation energy of 68.18 kJ/mole was obtained, which is approximately 4–8% lower than previously reported values for conventional propellants. The study concludes that iron oxide with a specific surface area of 10 m²/g and proportions up to 0.5% by weight can be safely used in propellant formulations without a significant reduction in the propellant’s shelf life. Full article

The management of fine bauxite tailings, rich in clay minerals, represents an environmental and operational challenge for the aluminum industry. This study (Part 1) presents a pilot-scale investigation into the dewatering of these ultrafine tailings using a decanter centrifuge, 0.62 m in diameter, as an alternative to conventional wet storage. Tests were conducted at three bowl speeds, 1600 rpm, 1700 rpm, and 1800 rpm, corresponding to G-forces of 888, 1003, and 1124 G. The feed slurry behaved as a non-Newtonian, yield-pseudoplastic fluid, as confirmed by rheology tests. A comprehensive mass balance and performance analysis were conducted. The results demonstrated a monotonic improvement in key performance metrics with increasing bowl speed. Accordingly, increasing the G-force from 888 G to 1124 G improved the final cake solid content from 66.3% to 71.5% (by weight), together with an increase in the average solid recovery from 40.0% to 56.2%. Partition curve analysis revealed the primary limitation: while recovery of particles coarser than 20 µm was very high (>98%), recovery of particles finer than 20 µm remained low, ranging from 22.0% to 35.1%. Partition curve analysis using the Whiten model identified a mechanical cut size (d_50c) ranging from 9.72 µm to 12.0 µm. Hydraulic bypass increased from 8.35% to 14.9% with increasing bowl speed, indicating a significant non-size-selective component of separation. Rheological analysis further showed that the apparent viscosity at 100 s⁻¹ decreased from 0.332 to 0.111 Pa·s across the tested conditions, confirming enhanced slurry mobility and its contribution to increased ultrafine bypass. While overall solid recovery reached 56.2% at 1124 G, the mechanical capture of the ultrafine fraction (<5 µm) remains the primary bottleneck for industrial viability. It is concluded that while the decanter centrifuge is mechanically viable for producing a high-solid cake, the limited recovery of fines would create an unsustainable circulating load in an industrial plant. These results demonstrate that G-force alone, within the tested range, is insufficient to manage these tailings and provide the basis for the mathematical modeling required to design the process, as described in Part 2 of this investigation. Full article

The temperature sensitivity coefficient greatly affects the interior ballistic performance of propellant charges. Even under consistent loading conditions, variations in environmental temperature can lead to maximum chamber pressure fluctuations of 40–80 MPa, thereby compromising weapon efficiency and operational safety. In order to obtain a single-base propellant with a higher energy and lower temperature sensitivity coefficient, ultra-fine RDX particles were added into the single-base propellant. The difference in thermal expansion coefficients between RDX and the single-base propellant matrix leads to temperature-dependent microcracking. These microcracks increase the burning surface area at low temperatures, compensating for the reduced chemical reaction rate and thereby lowering the temperature sensitivity coefficient. A scanning electron microscope (SEM) was used to observe the inner structure of the single-base propellant with and without RDX particles. The thermal mechanical analysis (TMA) results, together with SEM observations, reveal that the interfaces between the propellant matrix and the RDX particles are temperature-dependent. As a result, the burning surface area of the modified single-base propellant varies with temperature, contributing to a reduced temperature sensitivity coefficient. Closed bomb tests were conducted to verify this inference, and the obtained curves and relevant quickness (RQ) values showed that the modified single-base propellant had stable burning behavior and lower temperature sensitivity. This study leverages the structural interactions between high-energy fillers and polymer matrices to provide a potential strategy for designing climate-resilient ammunition. Full article

Developing sustainable and fire-resistant infrastructure is a critical technological, economic, and environmental challenge for modern construction stakeholders. Traditional cementitious composites experience severe microstructural degradation under extreme temperatures and their high carbon footprint exacerbates global environmental concerns. While the individual high-temperature behaviors of supplementary cementitious materials and fibers have been widely studied, the long-term synergistic mechanisms of high-volume fly ash combined with steel fibers under extreme thermal shock remain critically underinvestigated. To address this urgent need and bridge this scientific gap, hybrid mortars incorporating high-volume fly ash (FA) and steel fibers (SF) were tested under prolonged curing (150 days) and extreme heat (up to 600 °C). In terms of engineering and construction effects, the optimal CFA50-F hybrid composite delivered the highest residual compressive and flexural capacities (retaining nearly 60% of its late-age compressive strength at 32.00 MPa), preserved acoustic continuity (restricting UPV loss to 41.4%), and severely restricted high-temperature capillary permeability (limiting the water absorption increase to 49.7%) compared to traditional plain matrices. Scientifically, this superior resistance is governed by a two-step protective mechanism. High-volume FA chemically stabilizes the matrix by consuming vulnerable portlandite and preventing the formation of expansive calcium oxide. Simultaneously, ultra-fine FA particles physically densify the interfacial transition zones, securely anchoring the steel fibers and preventing premature high-temperature pull-out, while enabling the fibers to bridge thermally induced macro-cracks successfully. Environmentally and economically, an annualized service-life Life Cycle Assessment (LCA) revealed that substituting 50% of the cement with FA completely subsidizes the production-stage carbon penalty of the metallic reinforcement. By extending the operational lifespan to 40 years, the CFA50-F composite achieves a net 27% reduction in annualized global warming potential, providing a highly sustainable and cost-effective material solution. Full article

The progressive phase-out of coal-fired power plants in Portugal has significantly reduced the availability of fly ash (FA) as a supplementary cementitious material (SCM), reinforcing the need for sustainable alternatives. Waste glass powder (WGP), characterized by its high amorphous silica content, has emerged as a promising candidate; however, most studies focus on ultrafine particles or isolated performance indicators, lacking an integrated technical, environmental, and economic assessment. This study evaluates cement pastes incorporating 25% WGP (by volume) with different particle size distributions, including fineness levels comparable to cement and FA. Mechanical performance, grinding energy demand, carbon footprint, and cost were systematically analyzed. The results indicate that WGP is technically viable as an SCM, with a median particle size (D₅₀) of approximately 48 µm providing the most balanced performance. Although finer particles enhance pozzolanic reactivity, the associated increase in grinding energy and economic cost offsets these gains. The findings demonstrate that optimizing particle size, rather than maximizing fineness, enables a technically robust and industrially realistic use of WGP. This approach supports circular economic strategies and contributes to the decarbonization of the construction sector by identifying an efficient replacement pathway for FA under resource-scarcity conditions. Full article

Airborne particulate matter (PM) poses a major health risk, yet species selection for vertical greening systems (VGS) is poorly quantified. We evaluated PM retention by seven commercially available shade-tolerant species grown in a modular living wall system (LWS) on a north-facing façade at Sapienza University of Rome. After 3 months of in situ exposure, leaves were analyzed via SEM (1000×), collecting 210 images, 30 per species. An automated FIJI/ImageJ pipeline segmented particles, computed equivalent circular diameters, and classified them into (PM < 0.5, PM [0.5, 1), PM [1, 2.5), PM [2.5, 10), and PM ≥ 10 µm). Across species, ultrafine and fine fractions dominated deposits, with the <0.5 µm class typically comprising 60–70% of counts. Vinca minor cv. albomarginata exhibited the highest densities in ultrafine and fine classes, closely followed by Fatsia japonica; Hedera helix captured more coarse particles (2.5–10 µm and >10 µm). Heuchera sanguinea consistently displayed the lowest densities across all size classes. Performance patterns aligned with leaf surface traits: wax-coated, moderately rough or gently structured cuticles favored adhesion, whereas highly irregular microrelief did not consistently enhance retention. Methodological considerations include thresholding sensitivity, use of equivalent circular diameter for irregular particles, and an upper area filter that may undercount large aggregates. The findings identify Vinca minor cv. albomarginata and Fatsia japonica as priority species for PM mitigation in shaded VGS, with Hedera helix complementing coarse PM capture. The results provide trait-based, design-oriented guidance for living wall species selection in Mediterranean urban and indoor contexts. Full article

Urban transport is a major contributor to particulate matter (PM) pollution, yet information on the spatial distribution of fine and ultrafine particle fractions remains limited in medium-sized tropical cities. This study examines the spatial variability of transport-related particulate matter across eleven urban districts in Padang, Indonesia, using Nano Sampler-based measurements. Size-segregated PM concentrations (PM₁₀, PM_2.5, PM₁, and PM_0.5) were obtained from 24 h sampling campaigns conducted between June and July 2025 at locations selected based on urban density, proximity to major roadways, and land-use characteristics. Descriptive statistics, correlation analysis, and principal component analysis were applied to evaluate spatial patterns and traffic-related influences. The results show pronounced spatial heterogeneity in PM concentrations. Traffic-intensive and mixed-use districts exhibited higher PM levels, particularly for coarse and ultrafine fractions, whereas coastal districts showed lower concentrations due to enhanced atmospheric ventilation. Strong correlations were observed between traffic volume and coarse PM fractions, with moderate associations for fine and ultrafine particles, indicating combined exhaust and non-exhaust emissions. These findings highlight the importance of district-specific mitigation strategies and size-resolved monitoring to support effective urban air-quality management. Full article

The use of aeolian sand as a fine aggregate in concrete production provides a sustainable pathway to valorize abundant aeolian resources while alleviating the global shortage of natural construction aggregates. However, the high ultrafine particle content of aeolian sand results in the formation of highly porous interfacial transition zones (ITZ) between sand particles and cement paste, which is the primary cause of the inherent brittleness and inferior mechanical performance of aeolian sand concrete. To overcome this critical limitation, an alkali-activated surface layer (ASL) was constructed on aeolian sand via 4 mol/L KOH activation. This process induced the surface micro-dissolution of minerals to create high-density active ion sites (specifically Ca²⁺, K⁺, Na⁺, and Fe³⁺). These sites facilitated the precise anchoring of carbon nanotubes (CNTs) through the chemical coordination of single-stranded deoxyribonucleic acid (ssDNA). The influence of the ASL and the ssDNA/CNTs nanocomposite on the ITZ was elucidated through macro-mechanical testing and multi-scale microstructural characterization. Experimental results demonstrated that compressive strength, flexural strength, and compressive energy dissipation increased by 48%, 67%, and 42%, respectively. Microstructurally, the modification promoted a pore refinement mechanism, reducing the proportion of harmful (pores > 0.1 μm) from 51% to 20% and narrowing the ITZ width from 20–40 μm to 10–15 μm (a 67% reduction). The observed performance enhancement is attributed to the synergistic effect of the ASL and ssDNA/CNTs, which transforms the inherently weak ITZ into a chemically reinforced interfacial phase via molecular-scale coordination bonding and optimized stacking of cement hydration products. Full article

Fire smoke, rich in toxic ultrafine particles and polycyclic aromatic hydrocarbons (PAHs), poses significant health risks to first responders and vulnerable populations. In this study, a reproducible combustion–smoke simulation platform was developed to mechanistically quantify fire behavior, particle emissions, and PAH toxicity under controlled heat flux and oxygen conditions. Consistent combustion and smoke emissions were achieved by measuring heat release rate, particle mass, particle number concentration, and PAH concentration, with an overall average coefficient of variation below 15%. Systematic experiments with representative biomass (pine, oak) and plastics (PVC, polystyrene) demonstrate that fuel composition, heat flux, and oxygen availability jointly govern particle formation and PAH partitioning. Regardless of the combustion factors, ultrafine particles dominated the particle number concentration (55.5–86.2%). Plastic combustion generated 7 to 59 times particle mass, up to 260 times higher PAH emissions, and up to 58,500 times greater PAH toxic equivalent quotient (PAH-TEQ) than wood. Oxygen-deficient and smoldering regimes shifted emissions toward fine and ultrafine particles enriched in high-molecular-weight PAHs, revealing a coupled physical–chemical hazard not captured by bulk PM metrics alone. These results establish a quantitative framework linking combustion regime, particle size, and PAH toxicity, providing critical insight for exposure assessment, PPE design, and mitigation strategies in ventilation-limited and mixed-fuel fire scenarios. Full article