Particle Size Fractions Research Articles

Baseline concentrations and quantitative health risk assessment of polycyclic aromatic hydrocarbons (PAHs) in relation to particle grain size in street dust of Warsaw Poland.

Total concentrations, toxicity, and health risks of 16 polycyclic aromatic hydrocarbons (PAH) in street dust from Warsaw (Poland) in 6 granulometric fractions were investigated. Street dust was collected from 149 sampling points distributed among Area 1 (central districts, left bank of the Vistula River, mostly traffic-related pollution) and Area 2&3 (suburb area, mostly residential, right bank of the river). Street dust was investigated before ("all") and after separating into 5 size-dependent samples: (1-0.8mm) "0.8", (0.8-0.6mm) "0.6", (0.6-0.4mm) "0.4", (0.4-0.2mm) "0.2", and (below 0.2mm) " < 0.2". ΣPAH mean concentration was 3.21mg/kg for Area 1 and 0.89mg/kg for Area 2&3. ∑BaPTPE values calculated collectively for Area 1&2&3 were observed to be 318.3, 83.5, 131.1, 81.4, 164.3, and 339.7ng/g for "all", "0.6", "0.4", "0.2", and " < 0.2", respectively. Significant differences in ∑BaPTPE values were observed between fractions and specific areas. The cancer risk levels for children and adults, for all particulate size fractions, were comparable for dermal contact and by ingestion and ranged from 10-5 to 10-4, whereas the cancer risk levels via inhalation always ranged from 10-10 to 10-8. Therefore, inhalation of resuspended street dust is almost negligible compared to other pathways. Environmental implication. Street dust pollution in cities is one of the most important issues in the world and it negatively affects the quality of the environment and people's health. This study contributed to filling the gap in knowledge about the characteristics of PAH contaminants in the subject of the grain size of street dust from Poland and assessing the potential health risks. Therefore, our work has provided new significant information on PAH pollution, methods of measuring PAHs content and assessing the risk to human health, which may be useful to the scientific community, policymakers, and the general public.

The effect of different water types commonly applied during laser diffraction measurement on the particle size distribution of soils

It is expected in the future that soil particle size distribution (PSD) measurements by laser diffraction method (LDM) may replace sieve-pipette sedimentation methods (SPM) as they are faster, require less sample, and are accurate and reproducible. LDM measurement result is a continuous function of PSD, which can facilitate the conversion between the various limits (by countries, by scientific field) of the calculated particle size fractions (PSF – e.g. clay, silt, sand). Currently, there is no standard method for LDM PSD measurement. Many different types of instruments and preparation devices are currently used in laboratories, with various sample preparation, pre-treatment and measurement methods (duration, chemical and/or mechanical dispersion, settings, etc.). In soil LDM PSD measurements, researchers put relatively little emphasis on the choice of the type of aqueous media used. Thus, it is still questionable to what extent the results of the LDM measurement depend on the selection of the dispersion method and the aqueous media. For our research, eight soil samples with various physical and chemical properties were collected in Hungary. The particle size fractions (clay, silt, sand) determined with LDM (Malvern Mastersizer 3000) measured in three types of aqueous media (distilled, deionized and tap water), in different combinations of two dispersion methods (no treatment, ultrasonic or chemical dispersion with Calgon and their combination) were compared. For the comparison, PSF results of the conventional sieve pipette method (SPM) were used as a reference. Our results showed that LDM measurement can achieve various degrees of dispersion with different preparations, in many cases only partial dispersion, disaggregation, sometimes re-aggregation, and flocculation of soil particles were observed as compared to full preparation (in SPM). The “disaggregation pattern” of the soil samples also depended on the quality of the aqueous media and the properties of the soil investigated, because several types and degrees of interactions could occur in the various soil-liquid-dispersant/disaggregation effect systems.

Soil organic carbon and 13C changes when annual crops are replaced with perennial biomass crops in southwestern Ontario, Canada

Switchgrass (Panicum virgatum) and miscanthus (Miscanthus spp.) are C4 perennial biomass crops (PBCs) commonly cultivated in Ontario. The 13C natural abundance technique was used to assess the following: i) quantify the proportion of C4-derived soil organic carbon (SOC) stock (Mg C ha-1) within the SOC stocks of the whole soil, ii) determine the C4-derived SOC sequestration rate and iii) quantify C4-derived SOC stocks in soil particle size fractions. This was achieved by analyzing the δ13C values in SOC of both the whole soil and various soil particle size fractions in PBC fields that were converted from agriculture. At Guelph after 11 years of PBC, C4-derived SOC stock as a proportion of SOC stock in the whole soil accounted for 30% in switchgrass and 31% in miscanthus fields, while at Elora it comprised 41% in switchgrass and 50% in miscanthus. However, in Burlington after 4 years, C4-derived SOC represented 10-12% in PBC fields compared to 17% in agriculture fields. The C4 derived SOC sequestration rates were 0.8, 0.7 and 0.4 Mg C ha-1 y-1 in switchgrass, miscanthus and agriculture fields, respectively at the Guelph site. In miscanthus fields, lower C4-derived SOC stock in macro soil particles were observed, yet higher percentages were observed in micro soil particles and the silt plus clay fractions compared to switchgrass and agriculture fields. Agriculture fields had higher C4-derived SOC in macro soil particles, indicating lower SOC stability. Therefore, cultivating PBCs on low-productive agricultural lands could contribute to climate change mitigation practices due to increased SOC stability.

Soot particle morphology and polycyclic aromatic hydrocarbons formation molecular dynamics during diffusion combustion of three pentanol biofuels

Soot particles constitute a major pollutant in engine diffusion combustion, posing a serious threat to human health and the atmospheric environment. The employment of carbon-neutral biofuel, pentanol, in engines contributes to reducing soot emissions; however, its effectiveness is contingent upon the position of the OH functional group. This work investigated the soot morphology and microstructural parameters evolution of three pentanol isomers, and explored the influence mechanism of OH functional group positional isomerism on the entire process of PAHs formation at the atomic level. The results showed that the peak of primary particle size and soot volume fraction in pentanol flames showed a trend of 2-pentanol>3-pentanol>1-pentanol, and the initial formation time of soot in 1-pentanol flame is the latest, and the particle aggregate size is the smallest. The entire process of pentanol isomers soot formation can be divided into four stages: fuel pyrolysis forming initial ring, PAHs growing into initial soot, soot chain growth and structural evolution, soot morphology transformation and maturation. Among the three isomers, 2-pentanol has the fastest initial ring formation rate, the highest peak C-number in the largest molecule, and ultimately forms a more mature fullerene-like structure. 1-pentanol has the slowest initial ring formation rate, the lowest peak C-number in the largest molecule, ultimately forms a lower maturity layered structure. In terms of reaction pathways, H-atom abstraction and dehydroxylation reactions jointly dominate the initial decomposition pathway in 1-pentanol combustion, while in 2-pentanol, dehydroxylation becomes the main initial decomposition pathway due to the high stability of H atoms on β‑carbon. The dehydroxylation reaction tends to generate olefins, promoting the generation of C1-C4 hydrocarbon. The oxygen atom bonded on the α‑carbon site exhibits a stronger carbon fixation ability, and C1-C4 hydrocarbons are more inclined to participate in oxidation to form CO rather than promote the soot production.

Reducing segregation in vibrated binary-sized granular mixtures by excessive small particle introduction

We numerically examine binary-sized granular mixtures confined between two parallel walls subjected to vertical vibration using the discrete element method. For a size ratio of 3 between large and small particles, we study the structure of large particles in moderately dense regimes where the combined two-dimensional packing fractions of both particle sizes exceed 1. When the fraction of small particles is small, segregation of the large particles occurs. In contrast, as the fraction of small particles increases, an effective repulsion between the large particles emerges over distances greater than the large particle diameter, suppressing their segregation. The emergence of reduction in segregation is confirmed for another size ratio, vibrational acceleration, system size, and for a case of bidisperse size distribution. Additionally, at the size ratio of 3, the effective repulsion induces a hexagonal phase of the large particles at packing fractions lower than in mono-component systems. This work will provide a fresh insight into granular physics, prompting further experimental and theoretical study.Graphical This article numerically investigates the structures of quasi-two-dimensional binary-sized granular mixtures under vibration, and finds that segregation is reduced with increasing packing fraction of small particles

Determination of aggregate stability in kaolinitic subsoils using an energy-based, laser diffraction method

Traditional aggregate stability methodologies, such as wet sieving, rainfall simulation, and chemical dispersion, measure aggregate size, rather than stability. Sonication methods allow for energy-based measurements of aggregate stability, but most methods involve sieving to obtain gravimetric measurements of particle size fractions, which increases labor and variability compared to volumetric measurements by laser diffraction analyses. One criticism of energy-based methods is that ultrasonic devices are calibrated in a closed vessel containing water whereas the application of energy in routine analyses is commonly done in an open system containing soil and water, without considering the effects of soil mass and specific heat on sonication power or the energy lost from the system by conduction and/or other forces in an open system. Using texturally diverse subsoil samples with low carbon and similar clay mineralogy, we quantified 1) the effects of system type (thermodynamically closed versus open systems) and 2) the effect of assuming energy from calibrations in water versus measuring thermal energy in a soil–water system on soil dispersion curves. We found that these factors do not significantly affect soil dispersion curves of coarse- and medium-textured soils; however, fine samples are affected by system type and the method used to quantify energy. Overall, indices produced from soil dispersion curves are highly reproducible in both open and closed systems and correlate with soil physical properties that impact aggregate stability. These indices may streamline future measurements of aggregate stability and facilitate the inclusion of this important soil property in soil assessments.

Magnetic diagnosis model for heavy metal pollution in beach sediments of Qingdao, China

Magnetic techniques have been widely used in recent decades to determine heavy metal pollution in sediments due to their high sensitivity to magnetic particles and considerable measurement convenience. Beaches are usually greatly influenced by human activities, but pollution problems such as heavy metal pollution due to sewage discharge, nearby factories, and garbage disposal have reduced the tourism value and ecological environmental quality of beaches. In this study, three beaches in Qingdao city were chosen as examples, and a magnetic diagnostic model for heavy metal pollution in beach sediments was established using statistical methods. The results showed that beach No. 1 in Qingdao was not polluted, while the pollution level of beach No. 2 was lower than that of beach No. 3. Beach No. 2 exhibited slight Cr and Zn pollution and slight Fe enrichment, while beach No. 3 exhibited slight to severe Cr, Ni, and Zn pollution and severe Fe enrichment. The statistical model results indicated that χ, saturation isothermal remanent magnetization (SIRM), SOFT, and χARM are more suitable for establishing magnetic diagnostic models, and the pollution level, pollution source and diffusion range of heavy metal elements could be detected with this model. The main causes of pollution are sewage outlets and the disposal of artificial coal ash. When the magnetic susceptibility value of the 0.063–0.125 mm particle size fraction of Qingdao beach sediments is greater than 6000 × 10−8 m3kg−1, attention should be given to possible contamination by heavy metals. In this study, we revealed that environmental magnetic methods can be employed to effectively determine the pollution level, source, and diffusion of heavy metals in beach sediments, which can facilitate the management of heavy metals and other pollutants in beach sediments and ecological environmental protection.

Sandy soil spots in northwestern Paraná: approaches for identification and quantification

The predominance of sandy soils in the Northwest region of the state of Paraná, associated with the removal of natural vegetation, favored the development of patches of white sand on the surface without any aggregation. These spots are associated with the different types of land use existing in the region and the process of lateral soil transformation. As they constitute material without aggregation, they can be easily transported by wind and water and deposited in water bodies, causing severe environmental impacts. Thus, using thermal infrared satellite images, the objective of the present study was to map, determine the formation process of the spots and estimate the predominant particle size fractions. The model used and validated with field and laboratory information, allowed the identification of surfaces with patches of white sand present in the study region and estimating their percentage in different classes. After filtering the samples with vegetation cover during the product calculation period, an R² of 0.78 was obtained. The removal of natural vegetation has contributed to the formation and expansion of sandy patches and erosion in the northwest region of Paraná.

Structural and Textural Characteristics of Municipal Solid Waste Incineration Bottom Ash Subjected to Periodic Seasoning

The objective of this study was to determine the structural and textural description of municipal solid waste incineration (MSWI) bottom ash that was subjected to a six-month seasoning process. Bottom ash samples, with a particle size fraction of 0.063–0.1 mm, were seasoned in a closed landfill and collected for laboratory analyses at monthly intervals. The research focused on determining the structural parameters, using methods such as nuclear magnetic resonance spectroscopy (1H NMR), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), and the textural parameters, using low-pressure nitrogen adsorption (LPNA) at −196.15 °C. The analyses of the porous structure of the bottom ash samples revealed differences in texture of ASH 1 to ASH 6, specifically in the pore volume (micro- and mesopores), specific surface area, and pore size distribution. Changes in the structural and porous characteristics of the samples were attributed to the duration of the seasoning process. The results of the structural analysis of the bottom ash suggest its application in the concrete industry, potentially enhancing the long-term mechanical strength of concrete. The results of the textural analysis indicate the possible use of MSWI bottom ash in environmental applications, as the internal surface area could be further developed.

Mathematical Modeling of Fluidized Bed Magnetizing Roasting of Iron Ore Fines

The fluidized bed magnetizing roasting of low‐grade iron ore fines is employed as a beneficiation technique in iron‐making and steel‐making industries. In the present work, the unreacted shrinking core reaction kinetic model is coupled with the two‐fluid and kinetic theory of granular flow gas–solid flow model to simulate magnetizing roasting of hematite to magnetite in iron ore fines using a fluidized bed reactor. The model is validated with published experimental findings. Thereafter, the influence of different process parameters such as gas temperature, composition, velocity, and particle size on the reduction fraction and rate along with mass fraction and emission is studied. The reduction rate increases with gas temperature and mass fraction while it decreases with particle size. The emission increases with gas temperature, particle size, and mass fraction. However, the influence of gas velocity on these parameters is not significant. The reduction rate and time vary from 0.0010 to 0.0067 s−1 and 65 to 553 s, respectively, at a reduction fraction of 0.5. The mass fraction and emission range from 0.80 to 0.92 and from 0.63 to 4.14 g kg−1 ore, respectively.

A UV-resistant porous composite film for radiative cooling and enhanced hydrophobicity

Passive Daytime Radiative Cooling (PDRC) offers a promising strategy to reduce surface heat by reflecting solar radiation and emitting long-wave infrared radiation into space. However, the widespread application of PDRC is currently limited by challenges such as complex fabrication processes, high costs, and the materials’ susceptibility to outdoor aging. In this work, we fabricated a cost-effective, ultraviolet (UV)-resistant porous composite (UPC) film by phase separation technology. UPC films achieve high solar reflectance (0.92) and outstanding broadband longwave infrared thermal emissivity (0.975) by adjusting particle size and mass fractions of TiO2 particles embedded in Poly (methyl methacrylate) (PMMA). When applied to a drone, the films achieve a cooling effect of 12.6°C. Notably, the mid-infrared emissivity of UPC films remained stable after prolonged exposure to UV radiation (360 hours at an irradiance of 1 W/m2), with the reflectance decreasing by only 1.3 %. Software simulations were employed to evaluate the energy savings performance of UPC films in various urban environments, showing significant energy-saving benefits. Furthermore, after treatment with the modified solution, the surface contact angle of UPC films reaches 152.5°, providing excellent resistance to contamination. This work contributes to the advancement of low-cost, durable, and energy-efficient cooling solutions.

Influence of mixed particle sizes on shear yield stress of magnetorheological fluid

AbstractThis study investigated the effect of magnetic particle size and volume fraction on the shear yield stress and dynamic viscosity of magnetorheological fluids. Magnetorheological fluids with varying volume fractions of micro‐ and nanoscale magnetic particles were prepared. A plate‐on‐plate shear test bench was constructed to evaluate the fluids under a constant shear rate, with the applied current ranging from 0 A to 1.2 A. Results indicated that the shear yield stress initially increased and then decreased as the volume fraction of magnetic nanoparticles increased, reaching a maximum of 47 kPa at a volume fraction of 7 %. However, the excessive addition of magnetic particles or large‐diameter particles led to settling and reduced stability of the fluids. The findings suggest that optimizing the size and volume fraction of magnetic particles is crucial for maximizing the shear yield stress of magnetorheological fluids.

Obtaining Highly Efficient Radon Adsorbents by Adjusting the Pore Structure of Bamboo Charcoal with Particle Size Fractionated Activation.

To achieve highly efficient adsorbents for radon (Rn), this study prepared bamboo activated carbon (BAC) using bamboo charcoal as the precursor and KOH and NaOH as activators and employed a method of activation by adjusting the pore structure through particle size fractionation. Under the same activation conditions, KOH was consumed less and showed better Rn adsorption performance than NaOH, and the solid milling method saved more activator dosage compared to the liquid immersion method. After carbonizing the bamboo, the highest Rn adsorption coefficients of the bamboo charcoal activated with particle size fractionation (0.43-0.85, 0.25-0.43, 0.18-0.25, and <0.18 mm) were 8.41 ± 0.05, 10.03 ± 0.24, 9.31 ± 0.01, and 8.15 ± 0.21 L/g, respectively under N2 conditions (at a temperature of 25 °C and humidity of 35%), which were significantly greater than those of bamboo charcoal with overall activation (7.05 ± 0.23 L/g). After optimization, all of the bamboo charcoals with different particle sizes had the highest volume ratio for pores with a diameter of 0.77 nm. BC0.43-0.85K1.25 and BC0.25-0.43K0.75 maintained 95.74 and 92.36%, respectively, of the original adsorption coefficient after 5 cycles of regeneration under nitrogen. As the bamboo charcoal particle size decreased, the optimal mass ratio of alkali/carbon also decreased. This indicates that particle-size-fractionated activation can reduce the raw material and activator waste. The optimized BAC has a significantly higher Rn adsorption coefficient than the currently used coconut shell activated carbon (4.13 ± 0.51 L/g), making it an efficient and economical adsorbent with excellent application value for radon removal.

Beneficiation of High Sulfur Tertiary Coal of Assam with Burkholderia sp. GR 8-02. An Eco-Friendly Approach Toward Clean Coal Production

The high sulfur content in North-East Indian coal is one of the primary challenges with using it as an energy source. Therefore, the present study uses Burkholderia sp. GR 8-02 to explore coal beneficiation from the Tipong mine (T20 and T60) in Assam (North-East India). Various particle size fractions (−125 to +210 µm, −210 to +250 µm, −250 to +297 µm, −297 to +400 µm and −400 to +500 µm) were treated and subjected to petrographic and chemical analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS), Thermogravimetric analysis (TGA), and Raman spectral analysis. The results revealed a 39.04% and 32.43% reduction in total sulfur for T20 and T60 samples, respectively. The ash content decreased by 19.79% in the T20 coal sample and by 24.52% in the T60 coal samples, with a relative decrease in the mineral matter content of approximately 17.43%. Following beneficiation with Burkholderia sp. GR 8-02, the −125 to +250 µm coal fraction exhibited maximum ash removal. The T20 sample useful heating value increased from 8116 to 8203 kcal/kg and the T60 sample from 8060 to 8210 kcal/kg. X-ray diffraction and FTIR patterns showed mineral phases like quartz, kaolinite, and pyrite. The FTIR spectra indicated altered C-S, SO2, and C=O bonds. The thermal profile showed a 12.54% mass loss difference between untreated and treated coal samples, suggesting lower thermal stability post-treatment without affecting the useful heating value (UHV). The treated coal’s surface leaching and morphological structure changes were investigated using Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) images. Raman analysis revealed increased carbon crystallinity and molecular structure in treated coal. This study offers an environmentally friendly and efficient approach to clean coal production.

Composition and Biogeochemical Effects of Carbohydrates in Aerosols in Coastal Environment

We adopted a simple and rapid measurement method to analyze the concentrations of monosaccharides (MCHO) and polysaccharides (PCHO) in carbohydrates, a subset of organic carbon found in size-fractionated atmospheric particles. Seasonal and source-related factors influenced carbohydrate concentrations, with total water-soluble carbohydrates (TCHO) accounting for approximately 23% of the water-soluble organic carbon (WSOC) in spring when biological activity was high. We observed that the mode of aerosol transport significantly influenced the particle size distribution of carbohydrates, with MCHO exhibiting relatively high concentrations in fine particles (&lt;1 μm) and PCHO showing higher concentrations in coarse particles (&gt;1 μm). Moreover, our results revealed that MCHO and PCHO contributed 51% and 49%, respectively, to the TCHO concentration. This contribution varied by approximately ±19% depending on the season, suggesting the importance of both MCHO and PCHO. Additionally, through the combined use of principal component analysis (PCA) and positive matrix factorization (PMF), we determined that biomass burning accounts for 30% of the aerosol. Notably, biomass burning accounts for approximately 52% of the WSOC flux, with MCHO accounting for approximately 78% of the carbon from this source, indicating the substantial influence of biomass burning on aerosol composition. The average concentration of TCHO/WSOC in the atmosphere was approximately 18%, similar to the marine environment, reflecting the relationship between the biogeochemical cycles of the two environments. Finally, the fluxes of MCHO and PCHO were 1.10 and 5.28 mg C m−2 yr−1, respectively. We also found that the contribution of atmospheric deposition to marine primary productivity in winter was 15 times greater than that in summer, indicating that atmospheric deposition had a significant impact on marine ecosystems during nutrient-poor seasons. Additionally, we discovered that WSOC accounts for approximately 62% of the dissolved organic carbon (DOC) in the Min River, suggesting that atmospheric deposition could be a major source of organic carbon in the region.

Optical properties of La2O3 and HfO2 for radiative cooling via multiscale simulations

Abstract Radiative cooling materials have gained prominence as a zero-energy solution to mitigate global warming. However, a comprehensive understanding of atomic-scale optical properties and macroscopic optical performance of radiative cooling materials remains elusive, limiting insights into the underlying physics of their optical response and cooling efficacy. La2O3 and HfO2, representing rare earth and third/fourth subgroup inorganic oxides respectively, which show promise for radiative cooling applications. In this work, we employed multiscale simulations to investigate the optical properties of La2O3 and HfO2 across a broad spectrum. First-principles calculations revealed their dielectric functions and intrinsic refractive indices and the results indicated that the slightly smaller bandgap of La2O3 compared to HfO2 induces a higher refractive index in the solar band. Additionally, three-phonon scattering was found to provide more accurate infrared optical properties than two-phonon scattering, which enhances the emissivity in the sky window. Monte Carlo simulations were also used to determine the macroscopic optical properties of La2O3 and HfO2 coatings. Based on simulated results, we identified that particle size and particle volume fraction play the dominant role in optical properties. Our findings underscore the potential of La2O3 and HfO2 nanocomposites for environmentally friendly cooling and offer a new approach for high-throughput screening of optical materials through multiscale simulations.

A two-fluid multiphase flow model coupled with the population balance equations for the flow of a multidispersed particle system

SummaryWe present a two-fluid multiphase flow model that can be applied to the flow of polydisperse particle systems. In the model, the flow of polydisperse particle systems with different N particle sizes is considered only as two phases of fluid and particle phases, without considering the individual N phases, and the motion of particles with different diameters is represented by the motion characteristics of fluid and granular phases. The equations for the granular phase are obtained by averaging the Euler equations for the particles of different particle sizes. And the velocity of particles of different particle sizes is calculated by an explicit approximation, similar to determining the slip velocity in a mixed model of multiphase flow without solving the Eulerian momentum equation. Also, the conservation equation of particles of different particle sizes was obtained by adding the source term to the population balance equation, which is caused by the difference in the particle velocity of the particles with different particle sizes. The proposed method was compared with the results of experimental studies presented in the previous study to verify the validity of the method. The method has the advantage of not only visualizing the particle size fraction distribution but also of being stable in calculation and not increasing the computational effort significantly in studying the flow of polydisperse particle systems with particle size distribution.

Carbon Cycling in Marine Particles Based on Inorganic and Organic Stable Isotopes

The marine carbon cycle has a central role in biogeochemical cycling and a close interaction with the climate system. Here, we use the stable carbon isotope (δ13C) of particulate inorganic carbon (PIC) and particulate organic carbon (POC) in marine particles to diagnose carbonate dissolution and organic matter respiration processes in the ocean water column. We show PIC dissolution both in the euphotic zone, potentially driven by POC remineralization, and a preferential dissolution of coccoliths compared to foraminifera below the saturation horizon in the water column. Within the oxygen deficient zone (ODZ), POC remineralization and consequent respiration-driven PIC dissolution are both significantly diminished. We also demonstrate that POC remineralization preferentially removes a 13C-enriched component compared to isotopically-light bulk POC in both the large size fraction (LSF, > 51μ m) and small size fraction (SSF, 0.5 – 51μ m) of the pump particles, but exhibits a greater impact on the large particles because of its smaller inventory. Simultaneously, addition of a 13C-enriched heterotrophic or chemoautotrophic component to the SSF further increases the isotopic offset between SSF and LSF POC. Overall, this study uses δ13C to provide novel evidence for different biogeochemical processes in marine particles, and demonstrates carbonate dissolution in the ocean water column, both driven by bulk seawater chemistry and organic matter respiration within particles. The absence of O2 in the ODZ likely protects carbonate from dissolving by severely limiting organic matter respiration, thus reducing shallow PIC dissolution within the ODZs.

Size fraction characterisation of highly-calcareous and siliceous fly ashes

The properties of coal fly ash vary significantly depending on factors such as coal type, combustion conditions, and flue gas emission reduction methods. This study investigates the influence of particle size fractionation on the chemical composition, mineralogical structure, and thermal behaviour of two types of fly ash: high calcium ash derived from lignite (S1) and silica-rich ash from bituminous coal (S2). Dry aerodynamic separation was used to obtain distinct size fractions, which were then subjected to a comprehensive characterisation including X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and thermal analysis. The results reveal notable differences between the S1 and S2 ashes and between their size fractions. The finer fractions (< 20 μm) of S1 showed an increased calcium and sulphur content, while the coarser fractions (> 100 μm) contained more silica and alumina. The S2 ash exhibited a higher overall silica content, with alkali metals concentrated in finer fractions. Thermal analysis demonstrated distinct behaviours for each type and fraction of ash. Fine fractions of S1 ash showed SO2 emission at elevated temperatures, while S2 ash exhibited greater CO2 gas emission. After thermal treatment, the recrystallisation of the glassy phase was observed for S1, while the S2 ashes were more prone to melting and agglomeration. The study highlights the potential for the customised utilisation of specific ash fractions in various applications, such as geopolymer synthesis, adsorbent materials, and refractory products. This comprehensive characterisation contributes to a better understanding of fly ash properties and their dependence on particle size, providing valuable insights to optimise fly ash utilisation in various industries. The findings suggest strategies for a more efficient use of fly ash resources, particularly relevant in the context of decreasing fly ash availability due to the phase-out of coal power plants.

Power ultrasound-assisted enhancement of granulated blast furnace slag reactivity in cement paste

This paper introduces a first-time investigation into the impact of power ultrasound (PUS)-assisted preparation on the physicochemical and mechanical properties of cement-granulated blast furnace slag (GBFS) composite pastes. Pastes containing deposited GFBS with varying particle size fractions, partially replacing Portland cement, were prepared using PUS (ultrasonic horn tip, 20 kHz, 700 W) in pulse mode in a vertical jacketed glass sonoreactor with closed-circuit cooling. Cement paste incorporating 20 wt.% GBFS as mass substitution with varying particle size fractions was characterized by several physicochemical techniques at different curing ages. Exploring the cement and GBFS interaction induced by PUS, the compressive and flexural strength, the elastic modulus and indentation hardness, the heat of hardening, the mineral composition of hydration products, and the specific surface area BET were evaluated for a curing time of up to 28 days. The grain size distribution of GFBS and the reaction mixture's pH were measured. Both mechanical properties, heat of hydration and nanoporosity exhibited strong sensitivity to PUS treatment. Sonofragmentation of GBFS particles (especially the 125–250 μm fraction) increased with increasing sonication time, resulting in a relative increase of fraction <63 μm and a decrease of fraction >125 μm by 275 % and 60 %, respectively. Using the obtained SEM-EDS data, a simplified mechanism is proposed to explain the effects induced by PUS treatment.