Geometric Mean Size Research Articles

An investigation on pyrite floatability using stable micro-nanobubble-assisted flotation

This study critically examines the impact of micro-nanobubble (MNB)-assisted flotation on pyrite recovery in bulk ore, and clarifies the intricate relationship between pyrite and its associated ore. The physicochemical properties of MNBs and the interaction mechanisms between xanthate collector and pure pyrite mineral were evaluated using advanced analytical techniques, including Dynamic Light Scattering (DLS), Field-Emission Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy (FESEM-EDX), and Ultraviolet-Visible Spectroscopy (UV-Vis), in the absence and the presence of MNBs. MNBs were created through hydrodynamic cavitation, and their characteristics revealed a size increase from 600 nm to 3 µm over 25 days. Notably, the zeta potential measurements indicated an increase from -2.5 to 0 mV at a constant pH of 8, correlating with the geometric mean size of MNBs coarsening from 600 nm to 2-3 µm. The FESEM and EDS analyses disclosed that ultrasonic treatment effectively dispersed ultrafine surface coatings on pyrite particles, increasing iron and sulfur purity by 8% and 6%, respectively, and significantly reducing surface oxygen by 53%. Micro-flotation and batch rougher kinetic flotation experiments were conducted with and without MNBs, leading to a 7% and 8% improvement in recovery for pyrite mono-minerals (-105+53 µm) and its ore (d<sub>80</sub>=150 µm), respectively. The sorption behavior of sodium isopropyl xanthate (SIPX) collector on the particle surface was also investigated at various concentrations (ca. 10-160 µM) in the presence and absence of stable MNBs and demonstrated that the presence of MNBs resulted in a 1.6-fold increase in collector absorption on the pyrite surface, confirming the findings obtained from micro-flotation. Moreover, adsorption behavior is up to 1.3 times compared to the scenario without MNBs. The adsorption process was controlled by a pseudo-second-order model, indicating a chemical sorption mechanism.

Grindability of Torrefied Camelina Straw and Microparticle Evaluation by Confocal Laser Scanning Microscopy for Use as Biofuel

This study examined the combined effect of torrefaction and microwave absorbers on improving biomass thermochemical characteristics and grindability for heat, power, and value-added products. Camelina straw in two grinds, ground (6.4 mm screen size) and chopped with biochar addition (0%, 10% and 20%), was torrefied in a bench-scale microwave reactor at torrefaction temperatures of 250 °C and 300 °C with residence times of 10, 15 and 20 min under inert conditions and nitrogen-activated. After torrefaction, the geometric mean particle and size distribution, moisture content, ash content, bulk and particle densities were determined, and the grinding performance values of torrefied ground and chopped with and without biochar were determined and compared with the raw camelina straw. The results showed that the geometric diameter decreased after torrefaction in both grinds. The specific energy required for grinding torrefied biomass decreased significantly with biochar addition, longer residence times, and increased torrefaction temperatures. Torrefied ground camelina straw with biochar after grinding had the lowest grinding energy of 34.30 kJ at 300 °C/20 min. The surface morphology by confocal laser scanning microscopy of torrefied camelina straw particles indicated that biochar addition (>10%) and a torrefaction temperature at 250 °C can create profound surface distortion, and beyond 300 °C, colossal surface damage and carbonized weight fractions were produced.

Performance characteristics of 76 mm dense medium cyclone to wash high ash high NGM coal

ABSTRACT The present paper describes the detailed experiments carried out using 76 mm dense medium cyclone to determine the extent of beneficiation, ash percent reduction, recovery of ash and non-ash components in clean coal product and the effects of design parameters (Vortex finder and Spigot diameters) on the performance of the two separators have been brought out critically. Under the heading qualitative studies, the recoveries of ash (RA) and non-ash (RNA) percentages achieved in the clean coal, have been related to outlet diameters through regression equations. Further to quantify the performance of the separators, the two performance parameters has been named the efficiency index (EI) and separation efficiency index (SE) have been considered in the analysis. The performance of the separator measured using dependent (EI and SI) and the independent (Tromp or partition curves) criteria have also been discussed in detail. From the plotted tromp curves, the two performance parameters SG50 and EP have been estimated and their dependence on outlet diameters and geometric mean sizes have been depicted here. Additionally, to predict the performances of the separators, the concept of plotting generalized partition curves has been adopted for the separation of bulk coal (−3 + 0.5 mm) and the individual size fractions of the coal (1.93 mm, 1.22 mm, 0.86 mm and 0.35 mm), which have been defined mathematically by Gottfried’s model. It has been found that the coarse fraction of feed separated at lower density, whereas finer fraction have indicated to get separated at higher density.

Scour around Bridge Pier by Providing New Hybrid Collar with Opening Design for Different Pier Particulars

Abstract: The scour around bridge piers is a very complex phenomenon. Before the designing of the bridge piers, information of the system of scour around a bridge pier is expected for any designer. For the most part disappointment of the bridge is happened because of the scouring peculiarities. In this proposal work scour around equal compound piers were experimentally studied using recirculating flume. To the satisfaction of the proposition objective, all software modelling and experimental tests run were conducted in clear water scour conditions utilization uniform non-cohesive sand with D50 (Geometric mean size of sand) equal to 1.30 mm was used with different geometry uniform piers. From openFOAM as well as experimental study analysis go for this study to reduced scouring impacts around bridge pier by providing new hybrid collar design with openings for different particulars, in the shape of a collar with openings, to be an improvement over existing FPC. New hybrid collar design with opening combination can reduced scour around 71% to 75% at upstream and 48 to 50% at downstream scour can be minimised from experimental analysis

Effects of bioturbation by the fiddler crabLeptuca speciosa(Ives, 1891) (Decapoda: Brachyura: Ocypodidae) on mangrove peat in Barnes Sound, Florida, USA

AbstractBioturbation, which includes burrowing and foraging behaviors, is an important component of the functional role of fiddler crabs (Brachyura, Ocypodidae) within mangrove forests because it modifies sediment properties and composition of mangrove substrates. In this study, fiddler-crab population density and burrow architecture were measured to evaluate the influence of bioturbation by the fiddler crab Leptuca speciosa (Ives, 1891) on mangrove peat from Barnes Sound, Florida, USA. Measurements of burrow architecture were used to estimate the contribution of fiddler-crab burrowing to the bioturbation of mangrove peat. Comparisons were made between the total organic matter in bioturbated sediments, including feeding and burrowing pellets. A population density of 12 burrows m–2 was measured with no significant trends in the spatial distribution of fiddler crabs within the site. Although the deepest burrow depth was 18 cm, results show the upper 5 cm of the peat surface was consistently burrowed by crabs. Fiddler crabs were estimated to increase the total below-ground air-peat surface area m–2 by 5% and accounted for 22% of the excavated volume of mangrove peat per year. Fiddler crabs will thus rework the entire peat substrate within five years. Because data on carapace geometric mean size suggested that a juvenile population of L. speciosa was sampled, the bioturbation rate of the peat substrate will accelerate once this population matures. Feeding pellets had significantly lower percentages of total organic matter (P < 0.01) than other bioturbated peat samples, suggesting that fiddler-crab foraging behaviors significantly (P < 0.01) decrease the organic composition of surficial peats. These results imply that fiddler crab burrowing extends the depth of the taphonomically active zone thus enhancing mangrove peat decomposition and changing the bioavailability and distribution of organic matter in mangroves.

Vertically Resolved Pelagic Particle Biomass and Size Structure Across a Continental Shelf Under the Influence of a Western Boundary Current

AbstractContinental shelves are key to societal interactions with the oceans, supporting >90% of the world's fisheries through highly productive ecosystems. Previous research has shown that phytoplankton biomass is generally higher on the inner continental shelves, often due to increased nutrient inputs from upwelling or coastal run‐off. However, consistency in observed vertical and horizontal gradients (in abundance, biomass or size) of larger particulates, including zooplankton, on continental shelves has not been established. Using an optical plankton counter and CTD mounted on an undulating towed body, we present high‐resolution vertically resolved profiles of pelagic particle size structure across a continental shelf. Biomass was highest inshore, declining with distance from shore and with depth in the top 100 m of the water column, although the presence of frontal zones can alter this pattern. In the region adjacent to the East Australian Current (EAC), uplift generated by either the EAC interacting with the continental slope or upwelling‐favorable winds, correlated with smaller geometric mean sizes and steeper size spectrum slopes, particularly in the presence of frontal features. South of the EAC separation, the continental shelf water mass was more homogenous but still displayed the same horizontal and vertical patterns in particulate biomass and mean size. By combining our observations in a global comparison, we demonstrate consistent particulate distributions on continental shelves where the inner shelf has higher biomass with a steeper size spectrum slope compared to offshore. The highly productive inner shelf supports zooplankton communities vital to temperate ecosystems and coastal fisheries, through their consistently high biomass.

Biosorption of chromium (VI+) using tamarind fruit shells in continuously mixed batch reactor

<p>The locally available tamarind fruit shells (TFS) pre-treated with 1N H3PO4 was used to remove the hexavalent chromium (Cr6+) from aqueous phase. The investigation was done by using continuously mixed batch reactor (CMBR) under room temperature. Few preliminary investigations was undertaken to optimize the system parameters of the Cr6+ PATFS system. The batch studies cover the important experiments such as biosorption kinetics, biosorption equilibrium isotherm, effect of pH, effect of ionic strength, and effects of the presence of other anions in the system on biosorption of Cr6+. From preliminary investigation, the PATFS revealed a highest efficacy (99.1%) in removing Cr6+ from aqueous phase, apart from other pre-treated TFS. It was revealed that the density and mechanical properties of the treated and untreated composites increased with the decrease in the particle size; whereas, the water absorption percentage and void content decreased for the same. (a) Effect of heavy metal concentration on the sorption capacity. (b) Effect of solution pH on the sorption capacity. (c) Effect of sorption temperature on the sorption capacity. (d) Effect of sorption time on the sorption capacity. At a concentration of 50 mg/l of Cr6+, more than 95% was appeared to be removed by 12 g/l of 0.13 mm (geometric mean size) of PATFS. The biosorption kinetics of Cr6+ was modeled by using integrated rate expression and second order rate constants were determined for different Cr6+concentrations. Uptake of Cr6+on PATFS was well described by Freundlich isotherm for different biosorbent sizes. UV-VIS spectrophotometer was used to measure the concentration of Hexavalent chromium in water. The desorption study was also carried out and it’s significant by 0.5H2SO4.</p>

Determination of some engineering properties of fresh and boiled oil 6 palm fruits

Palm fruit is a product of oil palm and consists of the nut, the kernel, the fibre, oil and water. These components are separated by way of processing to get the desired products. For rational design of the handling systems, the engineering properties of the products are very important. A research was carried out to determine some engineering properties of fresh and boiled palm fruits. The properties determined are moisture content, sphericity solid and bulk densities, porosity, angles of repose and coefficients of friction. One thousand samples of the products were selected, conditioned and used for the experiments. The geometric and arithmetic mean diameters, volume, size and spherisity were calculated from the axial dimensions. The moisture contents were determined using gravimetric method. The angles of repose and coefficients of friction were determined on wood, glass and metal surfaces. The solid and bulk densities, porosity and compressive strength were determined using standard procedure. Results gave average moisture content of the fresh fruits to be 24.63 % and that of the boiled as 15.25 %. For the arithmetic and geometric mean diameters, the results were 1.9 cm and 580.6 cm respectively (fresh); 2.05 cm and 965.77 cm respectively (boiled), The average sphericities were calculated to be 70.7 % (fresh), and 73.28 % (boiled),. The average solid and bulk densities were 1.66 g/cm3 and 0.00054 g/cm3 respectively for fresh fruits, 1.32 g/cm3 and 0.00054 g/cm3 for the boiled product. The porosities of the samples were 60.21 % (fresh), and 75.73 % (boiled), The average values for the angles of repose on wood were 20.8 0 (fresh), 22.81 0(boiled), On glass, the angles of repose were 18.09 0 (fresh), 21.99 0 (boiled), On the metal surface, the angles of repose were 19.45 0 (fresh), 21.7 0 (boiled), The coefficients of static friction on wood were 0.38 (fresh), and 0.42 (boiled), On glass surface, the coefficient of static friction were 0.33 (fresh), 0.44 (boiled) while that of metals surface gave the coefficient of static friction were 0.35 (fresh), 0.4 (boiled).

Pediatric Microbial Keratitis: Identification of Clinical Biomarkers for Prognosis and Outcome of 218 Cases From 2009 to 2019.

The aim of this study was to analyze the risk factors, microbiological profile, and treatment efficacy in pediatric microbial keratitis (MK) and to identify clinical biomarkers prognosticating outcome. A retrospective analysis was conducted from patients younger than 16 years with MK-excluding viral, marginal, or interstitial keratitis. Data pertaining to predisposing factors, symptom duration, prior treatment, ulcer characteristics, microbiological profile, time to resolution, and final outcome were recorded. Statistical analysis was performed. The mixed-effects linear regression model with random intercept was used to evaluate factors affecting time to resolution. Among 218 episodes of 215 pediatric patients with MK, the geometric mean of central [median 3 mm, interquartile range (IQR) 1-4.3 mm] and peripheral ulcers (median 1 mm, IQR 1-2.5 mm) was significantly different ( P < 0.0001). Organisms identified were bacteria (56.9%), fungi (31.5%), and acanthamoebae (2.3%). Of 172 cases (78.8%), which resolved in a median resolution time of 22 days (IQR, 11-44 days), 107 (81.6%) with absent/negative microbiology healed on empirical therapy. On multivariate analysis, peripheral ulcers and geometric mean ulcer size affected time to resolution. Significantly higher percentage of eyes, which worsened or perforated, were on topical steroids compared with those which healed (31.8% vs. 9.2%, P = 0.0061). Good outcome even in culture negative cases suggests empirical therapy may be instituted for nonsevere peripheral pediatric MK; however, the importance of a microbiological workup cannot be underscored enough. Ulcer location and geometric mean size of ulcer may be used as clinical prognostic markers for resolution.

Inductively coupled nonthermal plasma synthesis of aluminum nanoparticles

Metallic nanoparticles of aluminum (Al), a nontoxic and earth-abundant element, are relevant to plasmonic and energetic applications. However, monodisperse Al nanoparticles are difficult to synthesize using all gas-phase approaches, especially in the 10 to 20 nm size range; yet, many applications require particles of this size due to their enhanced properties. Here, an inductive nonthermal plasma reactor fed with aluminum trichloride (AlCl3) and Ar is used to synthesize single-crystal aluminum nanoparticles. The particles can be produced with or without hydrogen. Several reactor conditions such as AlCl3 vapor concentration, flow rates, and power are found to strongly influence particle properties such as the oxide shell thickness, particle mono-dispersity, and particle size. Significant quantities of Ar relative to AlCl3, short residence times of 10 s of ms, and pressures in excess of 4.7 Torr are required to form Al particles with geometric mean sizes of 10–20 nm and geometric standard deviations as low as 1.3. While the Al nanoparticles are covered with 2–4 nm thick oxide shells, the best synthesis conditions yield particle sizes determined by electron microscopy that are comparable to crystallite sizes determined from x-ray diffraction.

Spray-dried lactose-leucine microparticles for pulmonary delivery of antimycobacterial nanopharmaceuticals

Pulmonary delivery of nanocarriers for novel antimycobacterial compounds is challenging because the aerodynamic properties of nanomaterials are sub-optimal for such purposes. Here, we report the development of dry powder formulations for nanocarriers containing benzothiazinone 043 (BTZ) or levofloxacin (LVX), respectively. The intricacy is to generate dry powder aerosols with adequate aerodynamic properties while maintaining both nanostructural integrity and compound activity until reaching the deeper lung compartments. Microparticles (MPs) were prepared using vibrating mesh spray drying with lactose and leucine as approved excipients for oral inhalation drug products. MP morphologies and sizes were measured using various biophysical techniques including determination of geometric and aerodynamic mean sizes, X-ray diffraction, and confocal and focused ion beam scanning electron microscopy. Differences in the nanocarriers’ characteristics influenced the MPs’ sizes and shapes, their aerodynamic properties, and, hence, also the fraction available for lung deposition. Spay-dried powders of a BTZ nanosuspension, BTZ-loaded silica nanoparticles (NPs), and LVX-loaded liposomes showed promising respirable fractions, in contrast to zirconyl hydrogen phosphate nanocontainers. While the colloidal stability of silica NPs was improved after spray drying, MPs encapsulating either BTZ nanosuspensions or LVX-loaded liposomes showed the highest respirable fractions and active pharmaceutical ingredient loads. Importantly, for the BTZ nanosuspension, biocompatibility and in vitro uptake by a macrophage model cell line were improved even further after spray drying.Graphical abstract

Milling method affects the physical properties of black bean flour

AbstractBackground and objectivesDry bean milling has attracted interest due to the increased need for nonwheat ingredients available for food applications. The objective of this study was to examine the physical and flow properties of black bean flour produced using a variety of laboratory mills and mill settings.FindingsFlour from mills which utilized screens (cyclone mill, centrifugal mill, and hammer mill) showed significantly different characteristics than flour from mills without a screen (disk mill and stone mill). Geometric mean size of flour particles was negatively correlated with starch damage (r = −.92), L* (r = −.94), angle of repose (r = −.94), and angle of slide (r = −.80 to −.90, depending on surface material) and positively correlated with moisture content (r = .72) and loose bulk density (r = .72). Finely ground flour resulted in particles that tended to be less circular and more elongated and had high angles of repose and slide.ConclusionsMilling method significantly affected (p &lt; .05) physical and flow properties of black bean flour.Significance and noveltyThese findings can be used by food processors in selecting a milling method that favors the production of black bean flour with the desired physical properties.

Evaluation of fecal fermentation profile and bacterial community in organically fed dairy cows consuming forage-rich diets with different particle sizes

Organic cattle farming encourages the use of forage-rich diets, and the reduction of particle size has been suggested as an approach to improve forage utilization and enhance nutrient intake of cows. However, reducing forage particle size increases passage rate, as well as the flow of potentially fermentable nutrients out of the rumen, and the consequences for hindgut fermentation have not been evaluated yet. This study evaluated the effects of decreasing dietary forage particle size on the fecal short-chain fatty acid (SCFA) profile and the bacterial community structure of dairy cows fed forage-based rations. Twenty-one organically fed lactating Holstein cows (4 primiparous and 17 multiparous; mean and standard deviation 703 ± 65 kg body weight, 135 ± 104 days in milk) were divided into 2 groups and fed 1 of 2 diets for 34 d. Diets contained 20% concentrate and 80% forage (dry matter basis), and were fed either as a control with a forage geometric mean particle size of 52 mm (CON; 11 cows) or as a diet with the forage particle size reduced to a geometric mean size of 7 mm (RED; 10 cows). Fecal samples were collected at the end of the experiment, and samples were immediately frozen at -20°C. Samples were analyzed for SCFA, and the fecal bacterial community was evaluated using 16S rRNA sequencing. Data showed that the concentration of total SCFA was not affected by treatment, but the proportion of propionate, a key glucogenic precursor in cattle, tended to be greater for RED (13.3 and 13.8 ± 0.1%, respectively). The predominant bacterial phyla, including Firmicutes (58.0 ± 0.7%), Bacteroidetes (26.9 ± 0.4%), and Verrucomicrobia (4.0 ± 0.4%), were not affected by forage particle size. Family Lachnospiraceae increased in relative abundance when the RED diet was fed (12.1 and 13.9 ± 0.5% for CON and RED, respectively), and genera Acetitomaculum (1.1 and 1.8 ± 0.2%), Turicibacter (0.7 and 0.9 ± 0.1%), and Ruminobacter (0.1 and 0.4 ± 0.1%) increased in relative abundance when RED was fed. In addition, relative abundance of some fecal bacterial taxa was correlated with major fecal SCFA and pH. Reducing the particle size of forages, from 52 to 7 mm geometric mean particle size, maintained fecal concentration of total SCFA and tended to enhance propionate concentration, without risk of dysbiosis. Thus, results suggest that reduction of forage particle size represents an effective approach to optimizing forage utilization while maintaining hindgut fermentation and fecal bacterial diversity in dairy cows fed forage-rich diets.

Effects of Pluronic F127 on phase inversion and membrane formation of PAN hollow fibers for air filtration

Among various pore formers, Pluronic F127 (F127), an amphiphilic nonionic surfactant, is an attractive additive which has often been used to create surface pores on hollow fibers and improve the permeate flux. Even though F127 has been employed in polymer dopes for membrane fabrication in various applications, most studies mainly focused on the enhancements of membrane properties instead of its influences on the phase inversion process and membrane formation. Therefore, the objectives of this study were to investigate its effects on the phase inversion process of a polyacrylonitrile/dimethyl sulfoxide/H2O (PAN/DMSO/H2O) system and the formation of PAN hollow fiber membranes. It was found that the addition of F127 reduced the dope stability and facilitated the solvent-nonsolvent demixing, resulting in a faster phase inversion process. In addition, F127 formed micelles in polymer dopes and induced large pores at membrane surface. Moreover, F127 enhanced the N2 permeance and mechanical properties of the resultant hollow fibers. Finally, the PAN/F127 hollow fibers were tested for air filtration and showed excellent filtration performance of >99.999% against NaCl aerosols with a geometric mean size of 43 nm. The hollow fiber spun from the PAN/DMSO dope containing 3 wt% F127 possesses the most balanced filtration performance in terms of filtration efficiency, mechanical properties, and gas permeance. Its filtration performance is also superior to most hollow-fiber air filters in the literature. This study may provide useful insights of using F127 for membrane fabrication for various applications.

Development of lab scale pineapple fruit juicer

Pineapple is the third most important tropical fruit in the world after banana and citrus fruit. This fruit is highly perishable and seasonal.Juice extraction is the process by which the liquid potion of the fruit is been squeezed or forced out of the solid part of the fruit either by manual or mechanical.Automatic pineapple juicer machine can do all the process required to produce the pineapple juice that means core of the pineapple can be crushing by the machine and the pomace and juice is separated differently. In this machine we firstly cut the fruit by using rotating knife and these fruit cubes are passed through squeezing mechanism in this screw shaft rotating and juice separate and pomace are separate. In this determination of physical properties like dimensions (Length, Width, Thickness), Geometric mean diameter, sphericity, size shape, surface area and density were determined. Average length, width and thickness were 164.8 mm, 87.12 mm and 88.9 mm, respectively. Average weight of pineapple fruit was 898.8 g. Size, shape, density and sphericity of pineapple fruit were 109.68, 53.38, 1.394 and 0.64, respectively. The average is taken the weight of fruit (g), weight of waste (g), weight of juice (g) are 1191.5, 318.6 and 826.1, respectively. On this observation we come to know that juice yield (%), extraction efficiency (%), extraction loss (%), are 71.09, 70.15, and 3.91were taken, respectively. The RPM is 2800. Powered by a 0.35 HP single phase electric motor, the machine has a capacity of 18.90 kg/h.

Modeling of particle size distribution and energy consumption of wet milled maize at varying soaking period and method in the production of Ogi

ABSTRACTEnergy consumptions and particles size distribution of soaked maize grains at varying time were studied and modeled. Rosin–Rammler–Bennet (RRB) model well fitted first milling size distribution with a high coefficient of determination (R2) and low root mean square error (RSME). The milling energy of maize grains decreased significantly (p < 0.05) with increase in soaking time. The milling energy decrease from 32 to 8.72 kWh/kg and 32.00 to 9.00 kWh/kg for maize variety E9W at 24th hour soaking conditions of 28 and 65°C, respectively. Similar observations for A4W, B2Y and C3Y at 24 h of soaking were recorded. The Work index, Kick’s and Rittinger’s constants decreased with increase in soaking time. There was significant difference (p < 0.05) in values obtained for Bond work index, Rittinger’s and Kick’s constants; these decreased with increase in soaking time. Predicted energy consumption followed similar trend. The interaction effect between energy consumption, Moisture content, and Milling time showed a high R2 (0.8767–0.99349); while the regressed model for determining energy consumption from relationship between the mass, moisture content, milling time and the ratio of the geometric diameter mean and final size of the product were also established in this work with R2 ranging from 0.9355 to 0.967.

Green coffee been exposure and symptoms in dock workers in Trieste (Italy).

Green coffee workers can develop allergic symptoms due to green coffee beans (GCB) or to castor bean (CB) that can contaminate sacks used for the transportation. Data are limited in literature and a previous study performed in Trieste demonstrated allergic symptoms in 14.3% of dockworkers handling GCB. To evaluate symptoms and exposure to GCB ultrafine particles in Trieste dockworkers. Workers involved in GCB sacks transportation, storage and opening were asked to fill out a questionnaire on allergic respiratory symptoms. They performed a spirometry test and an evaluation of NO exhaled breath condensate. Inhalable and respirable dust exposures were evaluated by means of personal and environmental pumps. Ultrafine particles exposure was evaluated by means of portable particles counter DISCMini. Between the 40 dockworkers exposed to GCB, 28 participated in the study (70%). Five (17.9%) reported personal allergy symptoms and two workers (7.1%) reported allergic oculorhinitis during work. One subject had symptoms only with Tanzania sacks and he resulted sensitized to CB. Workplace dust evaluation demonstrated values below Threshold Limit Values, but some work tasks were associated with exposure to more than 40,000 ultrafine particles with a geometric mean size of 37.2±1.35 nm. Prevalence of allergic symptoms in GCB workers was low but the presence of peaks of ultrafine particles exposure suggests the need to protect workers from exposure, limiting powder dispersion, avoiding the unloading of sacks inside the container and suggesting personal protective equipment regular use (FFP3).

Design of high efficiency PVDF-PEG hollow fibers for air filtration of ultrafine particles

This study reveals as the first attempt to apply hollow fibers for air filtration of ultrafine particles. Different from symmetric nano-fiber filters and non-woven fabrics, asymmetric polyvinylidene fluoride – polyethylene glycol (PVDF-PEG) hollow fibers with high gas permeances have been developed by the dry-jet wet-spinning process. The addition of high molecular weight PEGs in spinning dopes facilitates the formation of loosely connected cross-section and porous outer skin, thus enhances the gas permeance for air filtration. Under the inside-out testing mode, all PVDF-PEG hollow fibers display excellent filtration efficiency of 99.999% against polydispersed NaCl particles with a geometric mean size of ~30nm. Since permeance increases with an increase in PEG molecular weight in spinning dope, the PVDF-PEG hollow fiber with a PEG molecular weight (MW) of 12,000Da possesses the highest quality factor because it has the highest permeance and lowest transmembrane pressure. However, the PVDF-PEG hollow fiber with a PEG MW of 8000Da has the best mechanical properties. Under the dead-end filtration, the filtration efficiency increases with an increase in air flow rate. This trend is contrary to the findings observed in the flat and symmetric fibrous filtration. The asymmetric structure in the cross-section of the newly developed hollow fibers may enhance aerosol deposition via direct impaction and Brownian motion at high flow rates. The dead-end filtration results also show that the quality factor is higher at a lower flow rate. Similarly, the cross-flow filtration results show that the hollow fiber modules operated at low cross-flow ratios have high quality factors. Therefore, it is preferred to operate the newly developed PVDF-PEG hollow fiber at a low flow rate or low cross-flow ratio. This study may provide useful insights for developing hollow fibers for air filtration with the optimal operation conditions.

Characterization of Particulate Fume and Oxides Emission from Stainless Steel Plasma Cutting.

Plasma cutting is a metal fabrication process that employs an electrically conductive plasma arc to cut metals. The metal fume emitted from stainless steel plasma cutting may consist of hexavalent chromium (Cr6+), which is a carcinogen, and other toxicants. Overexposure to plasma cutting fume may cause pulmonary toxicity and other health effects. This study was to evaluate the effects of operation parameters (arc current and arc time) on the fume formation rates, Cr6+ and other oxides concentrations, particle size distributions (PSD), and particle morphology. A fume chamber and high-volume pump were used to collect fume produced from cutting ER308L stainless steel plates with arc currents varying between 20 and 50 A. The amount of fume collected on glass fiber filters was gravimetrically determined and normalized to arc time. Cr6+ and other oxides in the fume were analyzed using ion chromatography. PSD of the fume was examined using a scanning mobility particle sizer and an aerodynamic particle sizer for fine and coarse fractions, respectively. The particle morphology was imaged through a transmission electron microscope (TEM). Total fume generation rate increased with arc current and ranged from 16.5 mg min-1 at 20 A to 119.0 mg min-1 at 50 A. Cr6+ emissions (219.8-480.0 µg min-1) from the plasma cutting were higher than welding fume in a previous study. Nitrogen oxides level can be an indicator of oxidation level and Cr6+ formation (R = 0.93). Both PSD measurement and TEM images confirmed a multimodal size distribution. A high concentration of a fine fraction of particles with geometric mean sizes from 96 to 235 nm was observed. Higher arc current yielded more particles, while lower arc current was not able to penetrate the metal plates. Hence, the worker should optimize the arc current to balance cut performance and fume emission. The findings indicated that arc current was the dominant factor in fume emission from plasma cutting. Appropriate ventilation and respiratory protection should be used to reduce workers' exposure.

Laboratory study of the generation of nanoparticles from tire tread

ABSTRACTAn experimental study was carried out to investigate the formation process of airborne nanoparticles from tire tread. The formation of nanoparticles by volatilization of the tire tread was simulated in a reaction chamber. The number concentration of nanoparticles in the reaction chamber suddenly increased when the tire tread surface temperature reached above 160°C. The generated nanoparticles have a unimodal distribution and the number of nanoparticles increased as the heating rate increased. The geometric mean diameter and size distribution of the generated particles can be controlled by adjusting the cooling rate since the cooling rate is directly related to the growth of particles. From the morphological and elemental analyses, the main components of the tire nanoparticles were C, O, S, and Si and the particles had an irregular shape. Based on these observations, we concluded that the formation mechanism of nanoparticles from the tire tread was volatilization and condensation of the organic mat...