Μm Size Fraction Research Articles

Analyzing the Mineralogy and Space Weathering Characteristics of the Finest Fraction in Apollo Core Sample 73002

AbstractApollo 17 core sample 73001/2 was recently made available to researchers for analysis using state‐of‐the‐art techniques in the framework of a modern understanding of lunar surface processes. In this work, we employ transmission electron microscopic analysis to observe the mineralogy, microstructural, and chemical characteristics of space weathering and solar energetic particle (SEP) track distribution in soil grains in the <20 μm size fraction in core sample 73002. The modal mineralogy and stratigraphic space weathered grain abundance suggests that a geologically recent mixing event affected the top 3 cm of 73002. Surface exposure age distributions derived from SEP tracks demonstrate that individual regolith grains rarely reside on the surface for longer than ∼4 million years. The abundance of surface exposed monomineralic fragments with respect to depth correlates well with bulk measurements of space weathered soils using other techniques, such as ferromagnetic resonance. Exposure age distributions suggest the presence of two unique in situ reworking zones spanning the top 8 cm of the core and median exposure ages decrease with increasing depth for both reworking zones, albeit at different rates. These rates were compared to reworking models and suggest a relationship between median exposure age and reworking rate with respect to depth. Applications of modern transmission electron microscopy to core sample 73001/2 have proven useful in understanding lunar regolith evolution both within the context of the Apollo 17 field site and more broadly via in situ reworking.

Methodological assessment for efficient collection of Schistosoma mansoni environmental DNA and improved schistosomiasis surveillance in tropical wetlands

Schistosomiasis, caused by trematodes of genus Schistosoma, is among the most seriously neglected tropical diseases. Although rapid surveillance of risk areas for Schistosoma transmission is vital to control schistosomiasis, the habitat and infection status of this parasite are difficult to assess. Environmental DNA (eDNA) analysis, involving the detection of extra-organismal DNA in water samples, facilitates cost-efficient and sensitive biomonitoring of aquatic environments and is a promising tool to identify Schistosoma habitat and infection risk areas. However, in tropical wetlands, highly turbid water causes filter clogging, thereby decreasing the filtration volume and increasing the risk of false negatives. Therefore, in this study, we aimed to conduct laboratory experiments and field surveys in Lake Victoria, Mbita, to determine the appropriate filter pore size for S. mansoni eDNA collection in terms of particle size and filtration volume. In the laboratory experiment, aquarium water was sequentially filtered using different pore size filters. Targeting >3 µm size fraction was found to be sufficient to capture S. mansoni eDNA particles, regardless of their life cycle stage (egg, miracidia, and cercaria). In the field surveys, GF/D (2.7 µm nominal pore size) filter yielded 2.5-times the filtration volume obtained with a smaller pore size filter and pre-filtration methods under the same time constraints. Moreover, a site-occupancy model was applied to the field detection results to estimate S. mansoni eDNA occurrence and detection probabilities and assess the number of water samples and PCR replicates necessary for efficient eDNA detection. Overall, this study reveals an effective method for S. mansoni eDNA detection in turbid water, facilitating the rapid and sensitive monitoring of its distribution and cost-effective identification of schistosomiasis transmission risk areas.

Spatial distribution, sources, and health risk assessment of elements in road dust (

This research delves into the spatial distribution of 17 elements (Al, B, Ba, Bi, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb, Sr, Te, and Zn) within the < 20 μm size fraction of road dust samples collected from 177 locations within 65 grid cells (each 5×5 km2) throughout Delhi in February 2021. Notably, Fe and Al emerge as the predominant elements in the road dust samples. Using Principal Component Analysis (PCA), Absolute Principal Component Score (APCS), and Multiple Linear Regression (MLR) techniques, it is observed that crustal sources (58%), non-exhaust vehicular emissions (21%), and two distinct industrial origins (2% and 19%) are major contributors to the road dust composition. Bi and Te exhibited the highest geo-accumulation indices, indicating significant pollution levels, with notably high contamination factors, surpassing a contamination degree of 24. Elements like Cd posed the highest potential ecological risk, dominating 95% of the risk assessment. The hazard index analysis highlighted that urban populations, especially children, face the greatest risk through ingestion, followed by dermal exposure, and least through inhalation. Notably, Cd, Pb, Cr, and Ni were identified as elements posing a very high carcinogenic risk to the general populace.

Minimizing entrainment recovery of ultrafine silicate minerals in pentlandite flotation using carboxymethyl cellulose

The presence of silicate minerals is a common occurrence in various ore types, including nickel sulphide ores. These silicate minerals dilute the grade of flotation concentrates through recovery by entrainment which leads to poor flotation performance and subsequently loss of values. Flotation by entrainment is further enhanced as the particle size of the feed becomes finer. The present work investigates the entrainment characteristics of silicate minerals in the flotation of pentlandite. Within the context of the selective flotation of pentlandite from silicate gangue minerals, the influence of different particle sizes on entrainment flotation was also carried out. PAX was used as a collector for recovering pentlandite, whereas carboxymethyl cellulose (CMC) was employed as a dispersant for the silicate gangue mineral. Microflotation experiment was conducted on a pentlandite-quartz mixture of different particle sizes including − 106 + 75 µm, − 75 + 38 µm, − 38 + 20 µm, and − 20 µm. Electroacoustic zeta potential measurements, Fourier-Transform Infrared (FTIR) Spectroscopy, and Ultraviolet–Visible (UV–Vis) spectroscopy were used to characterise the interaction between pentlandite and quartz and in the presence of PAX and CMC. It was observed during the mixed minerals flotation tests that flotation by entrainment increased with a decrease in feed particle size irrespective of the dosage of CMC. Notwithstanding, the addition of CMC led to notable reduction in entrained silica flotation from 58 % to 38 % in the −20 µm size fraction attributed to improved particle drainage from the froth layer in the presence of CMC. Furthermore, UV–Vis spectroscopy and FTIR results gave further evidence that PAX adsorbed onto pentlandite and quartz minerals surfaces in the presence of CMC, which is consistent with the flotation response observed. Overall, this study confirms entrainment of gangue species is dominant within fine or ultra-fine mineral particles and proposes the use of CMC as a dispersant to limit gangue flotation by entrainment.

Assessment of fine and coarse tyre wear particles along a highway stormwater system and in receiving waters: Occurrence and transport

Tyre wear has been identified as a major road-related pollutant source, with road runoff transporting tyre wear particles (TWP) to adjacent soil, watercourses, or further through stormwater systems. The aim of this study was to investigate the occurrence and transport of TWP along a stormwater system. Water and sediment have been sampled at selected points (road runoff, gully pots, wells, outlet to a ditch, and stream) through a stormwater system situated along a highway in Sweden during November and December 2022, and March 2023. As there is limited data on the size distribution of TWP in different environmental media, especially in the size fraction <20 μm, the samples were fractioned into a fine (1.6–20 μm) and a coarse (1.6–500 μm) size fraction. The samples were analysed using a combination of marker compounds (benzene, α-methylstyrene, ethylstyrene, and butadiene trimer) for styrene-butadiene rubbers with PYR-GC/MS from which TWP concentration was calculated. Suspended solids were analysed in the water samples, and organic content was analysed in the sediment samples. TWP was found at nearly all locations, with concentrations up to 17 mg/L in the water samples and up to 40 mg/g in the sediment samples. In the sediment samples, TWP in the size fraction 1.6–20 μm represented a significant proportion (20–60%). Correlations were found between TWP concentration and suspended solids in the water samples (r = 0.87) and organic content in the sediment samples (r = 0.72). The results presented in this study demonstrate that TWP can be transported to the surrounding environment through road runoff, with limited retention in the studied stormwater system.

Tectonic and erosional controls of sediment residence time in small catchments draining an active mountain range: Evidence from uranium comminution age

Sediment residence time (SRT) is a key parameter of the Earth’s surface system, bridging the realms of sediment transport, biogeochemical cycles, sedimentary archives, and watershed management. SRT in mountainous catchments includes the time particles have spent in the subsurface weathering zone, which has been challenging to measure thus limiting our understanding of the magnitude and controlling factors of SRT in steep terrains. In this study, we apply the 234U/238U activity ratio, (234U/238U), which reveals particle comminution age, to estimate SRTs in 32 catchments (drainage area of 6.79–143.67 km2) draining an active mountain range at the eastern margin of the Tibetan Plateau. The uranium comminution age allows us to account for the time that particles have spent in the weathering zone. The sampled catchments span a range of erosional, topographic, climatic and lithologic conditions, providing a unique opportunity to explore the controlling factors on SRTs. We measured the (234U/238U) of the 20–25 µm size fraction of the collected riverbed sediment samples and used the results to calculate particle comminution ages, which are used to approximate SRTs of fine sediment in the catchment. We then investigated the relationships between estimated SRTs and denudation rates, topography, climate, and lithology to assess controls on SRTs. The estimated SRTs range from 5.0 to 149.2 ka, and exhibit strong negative correlations with the 10Be-derived denudation rates and metrics for landscape steepness (relief, gradient, and channel steepness), with weak-to-moderate correlations with climatic and lithologic conditions. By combining the SRTs and denudation rates and assuming a steady-state weathering zone, we estimate a catchment-average comminution depth of 1.98 to 28.7 m, comparable to the depth of weathering zone estimated from modeling studies. Considering a topographic steady-state where denudation rates are in equilibrium with uplift rates, our results suggest that tectonic uplift exerts a primary control on the SRT in active mountain ranges, such that faster uplift rates shorten SRTs. Our findings suggest that tectonic uplift could regulate the temporal duration of chemical weathering by limiting the SRTs of fresh minerals in mountainous regions, sustaining a ‘kinetically-limited’ weathering scenario.

Impact of power input in pulp conditioning on coal flotation and real-time characterization by focused beam reflectance measurement (FBRM)

ABSTRACT Pulp conditioning is a necessary procedure in the coal flotation industry, and optimizing the power input of such processes is in favor of improving flotation efficiency and reducing costs. This paper applied a pulp conditioning system combined with the focused beam reflectance measurement (FBRM) to investigate the impact of power input on coal flotation. Under the same energy input, the highest flotation efficiency of 50.09% was achieved in a pulp conditioning pattern of 1800 rpm-3 min, but the flotation efficiency reached only 36.13% in 1200 rpm-7.2 min. The kerosene collector can disperse into large numbers of droplets that exceed 2000 counts/s at size fractions of −10 μm and 20–50 μm in high power input and achieve better adsorption on coal. In the pulp conditioning process, the coal particle numbers of −50 μm size fraction decreased significantly from 15,000 counts/s to nearly 8000 counts/s at 32.3 W power input and coarse aggregates of 50–1000 μm size were detected. Under high power input conditions caused by high agitation speed, extra energy contributed validly to the kinetic energy of coal particles/collector droplets and the generation of oil-water and oil–coal interfaces. The shear flocculation behavior induced by the high power inputs in pulp conditioning is favorable for the flotation recovery of fine and ultra-fine particles.

Physical Mechanisms Sustaining Silica Production Following the Demise of the Diatom Phase of the North Atlantic Spring Phytoplankton Bloom During EXPORTS

AbstractEach spring, the North Atlantic experiences one of the largest open‐ocean phytoplankton blooms in the global ocean. Diatoms often dominate the initial phase of the bloom with succession driven by exhaustion of silicic acid. The North Atlantic was sampled over 3.5 weeks in spring 2021 following the demise of the main diatom bloom, allowing mechanisms that sustain continued diatom contributions to be examined. Diatom biomass was initially relatively high with biogenic silica concentrations up to 2.25 μmol Si L−1. A low initial silicic acid concentration of 0.1–0.3 μM imposed severe Si limitation of silica production and likely limited the diatom growth rate. Four storms over the next 3.5 weeks entrained silicic acid into the mixed layer, relieving growth limitation, but uptake limitation persisted. Silica production was modest and dominated by the &gt;5.0 μm size fraction although specific rates were highest in the 0.6–5.0 μm size fraction over most of the cruise. Silica dissolution averaged 68% of silica production. The resupply of silicic acid via storm entrainment and silica dissolution supported a cumulative post‐bloom silica production that was 32% of that estimated during the main bloom event. Diatoms contributed significantly to new and to primary production after the initial bloom, possibly dominating both. Diatom contribution to organic‐carbon export was also significant at 40%–70%. Thus, diatoms can significantly contribute to regional biogeochemistry following initial silicic acid depletion, but that contribution relies on physical processes that resupply the nutrient to surface waters.

Globorotalia truncatulinoides as indicator of Subtropical Convergence and thermocline change during the late Quaternary in the Southeast Atlantic

Planktic foraminifera in biogenic sediments are widely applied as palaeoceanographic tools and the abundances of Globorotalia truncatulinoides have been used over the past few decades as indicators of upper water column changes over geologic time. The two morphological coiling directions of this species (sinistral and dextral) can provide valuable insight into how the upper water masses of the South Atlantic vary in response to climate change. This study aims to document and analyse the abundances of the planktic foraminiferal species G. truncatulinoides and its two morphological coiling directions in two cores from the continental slope of western South Africa at >3500 m water depth to assess the response of upper water masses to Quaternary climate change. The relative abundances of total G. truncatulinoides in the >125 μm size fraction, abundances of the dextral and sinistral forms in the >212 μm fraction and the division into further size fractions (212 μm, 250 μm, 300 μm, 355 μm, >400 μm) were analysed and considered to determine whether these abundances can be related to oceanographic regime shifts in the eastern South Atlantic during the late Pleistocene from MIS 6 to MIS 1. It was found that the Subtropical Convergence was located at a more southern location during MIS 5 and MIS 1, which allows for warmer subtropical species to increase in abundance with increasing Agulhas leakage around the southwestern margin. The thermocline is interpreted to have deepened during glacial terminations and interglacial periods when productivity was relatively lower and temperatures increased. The size fraction of the sinistral form in the >355 μm is dominant in MIS 5, MIS 3 and MIS1, indicating implications for the use of this species at certain size ranges. This study therefore indicates that G. truncatulinoides is a useful tracer of past Quaternary oceanographic changes along the western margin of South Africa, particularly when the coiling directions at the larger size fraction is taken into account.

347 Aerodynamic Size Distribution of SARS-CoV-2 Aerosol Shedding

OBJECTIVES/GOALS: We designed the Biocascade Exhaled Breath Sampler (BEBS) to characterize viral aerosol shedding among individuals with influenza and other respiratory virus infections. We first aimed to test the BEBS on volunteer COVID-19 cases and report the aerodynamic size distribution of exhaled breath aerosol particles carrying SARS-CoV-2 RNA. METHODS/STUDY POPULATION: From June 15 through December 15, 2022, we recruited 27 PCR-confirmed COVID-19 cases from a college campus and the surrounding community to provide 30-minute breath samples into a well-validated Gesundheit-II (G-II) exhaled breath aerosol sampler. Among these individuals, 17 provided an additional exhaled breath sample into the newly designed BEBS. We quantified samples for viral RNA using reverse transcription digital polymerase chain reaction (RT-dPCR) and determined the viral RNA copies collected within two aerosol size fractions (≤5 µm and &gt;5 µm in diameter) from the G-II, and four aerosol size fractions (&lt;1.15 µm, 1.15–3.2 µm, 3.3–8.2 µm, and &gt;8.2 µm) from the BEBS. RESULTS/ANTICIPATED RESULTS: Individuals with a SARS-CoV-2 Omicron BA.4 or BA.5 infection shed virus in aerosols at an average rate of 7.5x103 RNA copies per 30-minute G-II sample, with 78% of the total RNA in aerosols ≤5 µm in diameter. Among the BEBS samples, 10% of the total viral RNA was detected in aerosols &lt;1.15 µm, 43% in 1.15–3.2 µm, 37% in 3.3–8.2 µm, and 10% in the &gt;8.2 µm size fraction. Based on viral RNA loads, our results indicate that exhaled aerosols ≤3.2 µm contribute the majority of SARS-CoV-2 inhalation exposure. DISCUSSION/SIGNIFICANCE: Our data provide additional evidence that respirable aerosols contribute to the spread of SARS-CoV-2. Thus, our data suggest that mitigation measures designed to reduce infectious aerosol inhalation, such as ventilation and the use of air cleaners and respirators, are needed to control the spread.

Preserved particulate organic carbon is likely derived from the subsurface sulfidic photic zone of the Proterozoic Ocean: evidence from a modern, oxygen-deficient lake.

Biological processes in the Proterozoic Ocean are often inferred from modern oxygen-deficient environments (MODEs) or from stable isotopes in preserved sediment. To date, few MODE studies have simultaneously quantified carbon fixation genes and attendant stable isotopic signatures. Consequently, how carbon isotope patterns reflect these pathways has not been thoroughly vetted. Addressing this, we profiled planktonic productivity and quantified carbon fixation pathway genes and associated organic carbon isotope values (δ13 CPOC ) of size-fractionated (0.2-2.7 and >2.7 μm) particulate matter from meromictic Fayetteville Green Lake, NY, USA. The high-O2 Calvin-Benson-Bassham (CBB) gene (cbbL) was most abundant in the <2.7 μm size fraction in shallow oxic and deep hypoxic waters, corresponding with cyanobacterial and eukaryote algal populations. The low-O2 CBB gene (cbbM) was most abundant near the lower oxycline boundary in the larger size fraction, coincident with purple sulfur bacteria populations. The reverse citric acid cycle gene (aclB) was equally abundant in both size fractions in the deepest photic zone, coinciding with green sulfur bacteria populations. Methane coenzyme reductase A (mcrA), of anaerobic methane cyclers, was most abundant at the lower oxycline boundary in both size fractions, coinciding with Methanoregula populations. δ13 CPOC values overlapped with the high-O2 CBB fixation range except for two negative excursions near the lower oxycline boundary, likely reflecting assimilation of isotopically-depleted groundwater-derived carbon by autotrophs and sulfate-reducers. Throughout aphotic waters, δ13 CPOC values of the large size fraction became 13 C-enriched, likely reflecting abundant purple sulfur bacterial aggregates. Eukaryote algae- or cyanobacteria-like isotopic signatures corresponded with increases in cbbL, cbbM, and aclB, and enrichment of exopolymer-rich prokaryotic photoautotrophs aggregates. Results suggest that δ13 CPOC values of preserved sediments from areas of the Proterozoic Ocean with sulfidic photic zones may reflect a mixture of alternate carbon-fixing populations exported from the deep photic zone, challenging the paradigm that sedimentary stable carbon isotope values predominantly reflect oxygenic photosynthesis from surface waters.

Grazing by nano- and microzooplankton on heterotrophic picoplankton dominates the biological carbon cycling around the Western Antarctic Peninsula

Over the past 40 years, the significance of microzooplankton grazing in oceanic carbon cycling has been highlighted with the help of dilution experiments. The ecologically relevant Western Antarctic Peninsula (WAP) ecosystem in the Southern Ocean (SO), however, has not been well studied. Here we present data from dilution experiments, performed at three stations around the northern tip of the WAP to determine grazing rates of small zooplankton (hetero- and mixotrophic members of the 0.2–200 µm size fraction, SZP) on auto- and heterotrophic members of the < 200 µm plankton community as well as their gross growth. While variable impacts of SZP grazing on carbon cycling were measured, particulate organic carbon, not the traditionally used parameter chlorophyll a, provided the best interpretable results. Our results suggested that heterotrophic picoplankton played a significant role in the carbon turnover at all stations. Finally, a comparison of two stations with diverging characteristics highlights that SZP grazing eliminated 56–119% of gross particulate organic carbon production from the particulate fraction. Thus, SZP grazing eliminated 20–50 times more carbon from the particulate fraction compared to what was exported to depth, therefore significantly affecting the efficiency of the biological carbon pump at these SO sites.

Optimizing liberation of phosphate ore through high voltage pulse fragmentation

This study investigates the selective high voltage pulse (HVP) fragmentation and its role in enhancing the metallurgical performance in phosphate ore processing. We have adapted the use of HVP fragmentation to enable the complete comminution of the considered ore, without the need for additional grinding steps. The efficiency of the HVP process strongly depends upon two parameters – the discharge ratio and the electric field, which, combined, allow for an improved liberation. Furthermore, for the same feed, the high voltage pulse fragmentation provides a coarser product with fewer fines. This study also emphasizes an improved liberation of the target mineral, carbonate fluorapatite, in the 100–315 μm fraction, while concentrating gangue minerals in the <100 μm size fraction. These findings are supported by X-ray tomography, validating the principle of pre-weakening induced by high voltage pulses on phosphate ore and further confirming the significance of our research.

Unusual sources of fossil micrometeorites deduced from relict chromite in the small size fraction in ~467 Ma old limestone

ABSTRACTExtraterrestrial chrome spinel and chromite extracted from the sedimentary rock record are relicts from coarse micrometeorites and rarely meteorites. They are studied to reconstruct the paleoflux of meteorites to the Earth and the collisional history of the asteroid belt. Minor element concentrations of Ti and V, and oxygen isotopic compositions of these relict minerals were used to classify the meteorite type they stem from, and thus to determine the relative meteorite group abundances through time. While coarse sediment‐dispersed extraterrestrial chrome‐spinel (SEC) grains from ordinary chondrites dominate through the studied time windows in the Phanerozoic, there are exceptions: We have shown that ~467 Ma ago, 1 Ma before the breakup of the L chondrite parent body (LCPB), more than half of the largest (&gt;63 μm diameter) grains were achondritic and originated from differentiated asteroids in contrast to ordinary chondrites which dominated the meteorite flux throughout most of the past 500 Ma. Here, we present a new data set of oxygen isotopic compositions and elemental compositions of 136 grains of a smaller size fraction (32–63 μm) in ~467 Ma old pre‐LCPB limestone from the Lynna River section in western Russia, that was previously studied by elemental analysis. Our study constitutes the most comprehensive oxygen isotopic data set of sediment‐dispersed extraterrestrial chrome spinel to date. We also introduce a Raman spectroscopy‐based method to identify SEC grains and distinguish them from terrestrial chrome spinel with ~97% reliability. We calibrated the Raman method with the established approach using titanium and vanadium concentrations and oxygen isotopic compositions. We find that ordinary chondrites are approximately three times more abundant in the 32–63 μm fraction than achondrites. While abundances of achondrites compared to ordinary chondrites are lower in the 32–63 μm size fraction than in the &gt;63 μm one, achondrites are approximately three times more abundant in the 32–62 μm fraction than they are in the present flux. We find that the sources of SEC grains vary for different grain sizes, mainly as a result of parent body thermal metamorphism. We conclude that the meteorite flux composition ~467 Ma ago ~1 Ma before the breakup of the LCPB was fundamentally different from today and from other time windows studied in the Phanerozoic, but that in contrast to the large size fraction ordinary chondrites dominated the flux in the small size fraction. The high abundance of ordinary chondrites in the studied samples is consistent with the findings based on coarse extraterrestrial chrome‐spinel from other time windows.

The Spectral Characteristics of Lunar Agglutinates: Visible–Near‐Infrared Spectroscopy of Apollo Soil Separates

AbstractThe lunar surface evolves over time due to space weathering, and the visible–near‐infrared spectra of more mature (i.e., heavily weathered) soils are lower in reflectance and steeper in spectral slope (i.e., darker and redder) than their immature counterparts. These spectral changes have traditionally been attributed to the space‐weathered rims of soil grains (and particularly nanophase iron therein). However, understudied thus far is the spectral role of agglutinates—the agglomerates of mineral and lithic fragments, nanophase iron, and glass that are formed by micrometeoroid impacts and are ubiquitous in mature lunar soils. We separated agglutinates and non‐agglutinates from six lunar soils of varying maturity and composition, primarily from the 125–250 μm size fraction, and measured their visible–near‐infrared reflectance spectra. For each soil, the agglutinate spectra are darker, redder, and have weaker absorption bands than the corresponding non‐agglutinate and unsorted soil spectra. Moreover, greater soil maturity corresponds to darker agglutinate spectra with weaker absorption bands. These findings suggest that agglutinates (rather than solely the space‐weathered rims) play an important role in both the darkening and reddening of mature soils—at least for the size fractions examined here. Comparisons with analog soils suggest that high nanophase iron abundance in agglutinates is likely responsible for their low reflectance and spectrally red slope. Additional studies of agglutinates are needed both to more comprehensively characterize their spectral properties (across size fractions and in mixing with non‐agglutinates) and to assess the relative roles of agglutinates and rims in weathering‐associated spectral changes.

Development and validation of an acid/alkaline digestion method for efficient microplastic extraction from wastewater treatment plant effluents: Sulfuric acid concentration and contact time do matter

Accurate analysis of microplastic particles (MPs) in environmental samples requires removal of interferences during sample preparation. Wastewater samples are interference-rich and thus particularly challenging, with concentrated sulfuric acid currently deemed impractical as a reagent. Therefore, this study aimed to establish a straightforward, effective, and safe method employing concentrated sulfuric acid and potassium hydroxide to eliminate interferents from effluent samples obtained from wastewater treatment plants (WWTPs). We found that 80 % sulfuric acid at room temperature with a brief contact time of 5 min was viable through a qualitative spot test involving 37 plastics categorized into three types (I, II, and III) based on their polymer structure's oxygen position. A quantitative assessment revealed that treatments involving H2SO4 and KOH (20 %, 24 h, 48 °C), either separately or in combination, had no discernible physical impact on the overall plastics, except for a subtle one for Type III plastics (e.g., nylon and PMMA) known to be labile under harsh pH conditions. This acid/alkaline digestion (AAD) method, incorporating such conditions for H2SO4 and KOH treatments, yielded a high mass removal efficacy (97.8 ± 2.4 %, n = 13) for eliminating natural particle interferents for primary, secondary, and tertiary effluent samples. Furthermore, the AAD method allowed for the determination of MPs in effluents with high surrogate particle recoveries (e.g., 95.1 % for larger than 500 μm size fraction). This method is readily adaptable to create appropriate protocols for different types of environmental matrices.

Occurrence, characterization, and transport mechanism of welding fumes particles emitted during the welding process

In metalworking processes, welding fumes are a prevalent type of particle aerosols. Particle characteristics, physical factors, and the generation process influence the transport of welding fumes in the air. This research delves into the investigation of welding fumes particles during two types of currents: low current (60A) and high current (130A). The study encompasses the determination of the occurrence and characterization of these particles, as well as estimating their transport mechanisms during the welding process. Direct reading instruments were utilized to measure the mass concentration and the number concentration of welding fumes particles alongside environmental parameters such as relative humidity, air velocity, and air temperature. The size distribution and morphology of the particles were collected through a sampling pump and subsequently analyzed using a Field Emission Scanning Electron Microscope (FESEM). Welding fumes particle transport was predicted by employing variables such as Reynolds number (Re), settling velocity, mechanical velocity, and stopping distance. The welding process’s high current (130 A) generates a higher mass concentration (0.122mg/m3) than the low current (60 A) (0.064mg/m3). Notably, for particle size fractions ranging from 0.5μm to 2.0μm, the number of particles generated during high current surpassed that of low current, except for the 0.3μm size fraction. Analysis of the size distribution through FESEM revealed particle sizes of 2.25μm, 2.33μm, and 2.63μm for welding fumes collected during 130A. In contrast, fumes collected during 60A exhibited sizes of 0.45μm, 0.61μm, and 0.60μm. Notably, accumulation of particles were observed, indicating that the fumes collected during 60A consisted of smaller particles classified as fine particles. The particle counts for high and low currents were 283,232,661 count/m3 and 300,604,341 count/m3, respectively. The observed particle shapes appeared agglomerate, comprised of primary spherical particles adhering together through Van Der Waals forces. Reynolds number values (Re=0.0046-0.0223, less than 1) indicated that the motion of fume particles occurred within a laminar flow regime. Furthermore, the movement of particles was influenced by their diameter, with larger particles exhibiting higher settling velocities, smaller mechanical mobility, and shorter travelled distances. In summary, this research sheds light on the intricate transport mechanisms of welding fumes, providing insights into their occurrence, characterization, and transport during the metalworking process.

Gas atomization of fully-amorphous Ni62Nb38 powder

In this study, close-coupled gas atomization is explored to produce the binary metallic glass-former Ni62Nb38. The alloy is noteworthy due to its yield strength exceeding 3GPa, glass transition above 900 K, and considerable ductility when quenched from the melt. Ni62Nb38 is the best glass former in the Ni-Nb system, possessing an extraordinarily high glass-forming ability for a binary alloy. Yet, its critical casting thickness remains below 2 mm. Hence, Ni62Nb38 becomes a potential candidate for additive manufacturing to overcome size constraints for engineering applications. Our results reveal that spherical, fully amorphous powder with a high yield in the 20–63 µm size fraction and an oxygen level below 900wppm can be successfully produced by close-coupled gas atomization. This paves the way for using binary Ni-Nb alloy powders in additive manufacturing of large, intricate parts with very high strength.

On the selection of the coarsest size class in flotation rate characterizations

This paper studies size-by-size batch flotation kinetics for the separation of Cu at particle sizes +75 μm, investigating the responses in the -150/+75 μm, -212/+150 μm, -300/+212 μm, -355/+300 μm and +355 μm size fractions. The kinetic results were analyzed to identify classes limited by the maximum achievable recovery or low flotation rates. Combinations of these classes were investigated, emulating the selection of the coarsest size in a kinetic study. The impact of compositing size classes was discussed, emphasizing implications in the identification of difficult-to-float components. The -212/+75 μm classes reached steady recoveries at long flotation times, whereas the -355/+212 μm classes presented sustained increasing recoveries at extended flotation times. Flotation rate distributions in the -212/+75 μm classes exhibited mound-shaped distributions, indicating low fractions of rate constants close to zero (R∞-limited case). Conversely, the -355/+212 μm classes presented reverse J-shaped distributions, with a high fraction of valuable minerals with flotation rates close to zero (rate-limited case). Combining several size classes in the definition of the coarsest size fraction in kinetic characterizations proved to hide the flotation patterns of the less massive constituents (+212 μm classes). The +75 μm and +150 μm cumulative retained classes trended towards steady recoveries, consistently leading to mounded flotation rate distributions. This study highlighted the need for reliable methodologies to select size fractions in kinetic characterizations, as their arbitrary definitions may lead to a misinterpretation of the mineral losses when compositing classes with different flotation responses.

Aquatic invertebrate mandibles and sclerotized remains in Quaternary lake sediments

Subfossil remains of aquatic invertebrates found in lacustrine sediments are useful paleoenvironmental indicators. Strongly scleroticized chitinous body parts from the exoskeleton or exuviae from invertebrates are often the most resistant to degradation during syn- and post-depositional processes. Invertebrate mandibles and body parts that superficially resemble mandibles, such as claw-like appendages and pygopodia, are frequently found in sieved Quaternary lacustrine, palustrine, and deltaic sediments. Guides, catalogs and atlases have been published that are well suited for the identification of subfossil remains for several invertebrate groups, such as chironomids, cladocerans, and ostracods, among others. However, aquatic invertebrate remains of several ecologically important invertebrate groups continue to be underused in paleoenvironmental studies, in part, because there are few visual keys or other documentation sources (e.g. descriptions, catalogs or atlases) that increase awareness and facilitate identification. Here we present sets of digital photomicrographs of pre-identified aquatic invertebrate specimens collected from streams, lakes and ponds that have been chemically cleared to preserve structures that are observed in subfossil remains in sieved sediment samples, commonly the > 100 μm size fractions. In addition, we present examples of these structures from Quaternary lake-sediment samples and cite the dispersed literature that demonstrate that these remains are preserved and remain identifiable in the fossil record. We document mandibles from several taxonomic groups that include Crustacea: Amphipoda, Isopoda, Ostracoda, and Notostraca; and Insecta orders: Coleoptera, Diptera, Ephemeroptera, Hemiptera, Odonata, Lepidoptera, Megaloptera, Plecoptera, and Trichoptera. The compilation of microphotographs also includes pygopodia and claw appendages of Plecoptera and Trichoptera, with additional images of other common invertebrate mouthpart and head remains. We describe several types of fossilizing structures that are, to our knowledge, not previously described in the paleoecological literature (e.g. mandibles of amphipods or plecopterans) but also show that some structures are considerably more variable than expected based on available descriptions, such as the mandibles of Ephemeroptera or Trichoptera, and that these can potentially be separated into different morphotypes useful for identification of subfossil material. We also discuss the potential of analyzing and interpreting the additional remains together with the remains of more commonly analyzed invertebrate groups (e.g. Chironomidae) to contribute to paleoenvironmental interpretations, which will allow assessments of functional groups (e.g. predators, shredders, grazers) or habitat types (e.g. littoral, profundal or lotic environments) that aquatic invertebrate remains originate from.