Decreasing Size Fraction Research Articles

Mechanical Disintegration and Particle Size Sieving of Chondrus crispus (Irish Moss) Gametophytes and Their Effect on Carrageenan and Phycoerythrin Extraction.

To better understand the migration properties of hybrid carrageenan from the seaweed tissue during carrageenan extraction, the effect of increasing the seaweed surface area by the mechanical disintegration of gametophyte Chondrus crispus chips was studied under various temperature and time extraction conditions. Dried Chondrus crispus seaweed chips were milled by a rotor beater mill and classified into eight different size fractions by sieving with varying mesh sizes from 50 to 2000 μm. During extraction at 22 °C, the red color of the filtrate increased significantly with the decreasing particle size of the fraction, correlating with the increasing phycoerythrin concentration (from 0.26 mg PE/g dry seaweed in the >2000 μm size fraction to 2.30 mg PE/g dry seaweed in the <50 μm size fraction). On the other hand, under the same extraction conditions, only a small increase in carrageenan precipitate was obtained with the decreasing size fractions (from no recovery in the >2000 μm size fraction to 2.1 ± 0.1 g/kg filtrate in the <50 μm size fraction). This yield was significantly lower than the ones from extractions at 45 °C (5.4 ± 0.1 g/kg) or at 90 °C (9.9 ± 2.1 g/kg) for the same particle size and time conditions. It could be concluded that hybrid carrageenan extraction is not surface area dependent, while phycoerythrin is. Therefore, it seems that phycoerythrin and carrageenan extraction follow different mechanisms. This creates potential for the selective extraction of each of those two compounds.

‘Home’ and ‘away’ litter decomposition depends on the size fractions of the soil biotic community

The ‘home-field advantage’ (HFA) hypothesis predicts that litter decomposition is accelerated in its home environment (i.e. in conspecific soil). Soil organisms play a key role in driving such HFA effects. Soil biota have a large range of body sizes, referred to as size fractions, which may influence their roles in the decomposition process and in the generation of HFA effects. However, how HFA effects depend on the different size fractions of the soil biotic community is unknown. We conducted a microcosm decomposition experiment to examine how size fractions of the soil biotic community affected litter decomposition and HFA effects. In a semi-natural grassland in the Netherlands, we collected leaf litter and soil from two abundant forbs: Tanacetum vulgare and Jacobaea vulgaris. Watery extracts of the soils were sieved through differently-meshed sieves (ranging from 850 μm to 6 μm) to obtain soil communities of different size fractions. Microcosms were inoculated with these different size fractions of the soil biotic community and we examined their effects on microbial composition, litter mass loss and HFA effects. Three months after inoculation, the diversity of the fungal community in the inoculated pots decreased with decreasing size fractions of the soil biotic community. Similarly, litter mass loss also decreased with decreasing soil biotic community size. In contrast, the HFA effect increased with decreasing size fractions of the soil biotic community, but these differences disappeared after six months of decomposition. Our results indicate that soil microorganisms, mainly the smallest size fractions, are specialized to decompose specific resources and thus promote HFA effects, but that their effect is only apparent during specific stages of litter decomposition.

Vehicular contribution of PAHs in size dependent road dust: A source apportionment by PCA-MLR, PMF, and Unmix receptor models

This study focuses on the source apportionments of polycyclic aromatic hydrocarbons (PAHs) in road dust (RD) with four size fractions through three receptor models of principal component analysis with multiple linear regression (PCA-MLR), positive matrix factorization (PMF) and Unmix. The concentrations of total PAHs range from 0.45 to 2.03μgg−1. Results show that the concentrations of PAHs increased with a decreasing size fraction. Similar potential sources to PAHs in RD were extracted by three models with a little difference in numbers and percent load contributions of each identified sources. The overall proportion of the identified sources were ranked as vehicular emission>coke oven>surface pavement>others in each size fractions. In terms of risk assessment, the mean values of incremental lifetime cancer risk (ILCR) of the total cancer risk of PAHs in RD were lower than the baseline value of an acceptable risk. However, PAHs in smaller size fraction prone to have a higher adverse effect on children via ingestion. Furthermore, the ecological risk assessment of hazard quotients and mean hazard quotients indicated that PAHs in RD had a 9% probability of being toxic to the benthic organisms and aquatic environment.

Soil Development under Continuous Agriculture at the Morrow Plots Experimental Fields from X-ray Diffraction Profile Modelling

Impact of continuous cropping on clay mineralogy was assessed on a collection of unfertilized soil samples from the Morrow Plots experimental fields covering 110 years of long crop rotations. Evolution of mineralogy was quantitatively determined by fitting X-ray diffraction (XRD) patterns from four size fractions (50–2, 2–0.2, 0.2–0.05 and &lt;0.05 µm) of the surface horizon (0–20 cm). The mineralogy of the three clay subfractions (2–0.2 µm, 0.2–0.05 µm and &lt;0.05 µm) consists mainly of coexisting illite-smectite-chlorite whose compositions range from discrete illite (in the 2–0.2 µm subfraction) to discrete smectite (in the &lt;0.05 µm subfraction). Mixed layers of similar compositions were used to fit XRD data from all clay subfractions. With decreasing size fractions, both the size of the coherent scattering domains and the proportion of illite-rich mixed layers decrease, thus accounting for the higher cation exchange measured in the &lt;0.05 µm subfraction compared to other clay subfractions. The analysis of fine clay subfractions (&lt;0.2 µm or lower) provided key information and constraints to a complete and accurate description of the bulk &lt;2 µm fraction. Additional constraints derived from chemical treatments (K-saturation and heating) proved to be especially useful to propose a reliable structure model for these fine clay subfractions because of their weakly modulated diffraction signature. Mineralogy of all subfractions considered is essentially stable over the studied period (1904–2014), with the relative proportion of the different clay layer types (illite, smectite, kaolinite, chlorite) showing no significant evolution in the bulk &lt;2 µm fraction. A century of continuous cropping thus results essentially in an increase of fine clay particles (&lt;0.05 µm) and a decrease of the 0.2–0.05 µm subfraction, indicative of clay mineral dissolution and consistent with observed increase of cation exchange capacity with time. The relative proportion of the bulk &lt;2 µm fraction is nearly constant over the studied period, indicative of minimal export of clay phases.

Beneficiation of coarse particulate iron ore by using a dry density-based fluidized bed separator

A dry density-based fluidized bed separator was used to beneficiate coarse particulate iron ore. The atomized iron powder and zircon sand, with specific size fractions of 150–75 and 250–150μm, were mixed in certain proportion to form a binary dense media. The results indicated that the binary dense media efficiently formed stable fluidization within the fluidized bed for subsequent separation of iron ore particles. The theoretical separation density of 3.5–4.0g/cm3 was determined by investigating the relationships among particle size, density distribution, and total Fe-grade in the iron ore sample. The effects of static bed height, operational gas velocity, and weight proportion of the atomized iron powder in the binary dense media on the stability of bed density were studied to determine the appropriate operational conditions. The stability of bed density was maintained under the condition with a static bed height of 80–90mm, an operational gas velocity of 1.6–2.0Umf, and a weight proportion of the atomized iron powder in the binary dense media of 90%. The effects of static bed height, gas velocity, and size fraction of iron ore particles on the dry separation efficiency were also investigated to determine the optimum separation performance. The optimum total Fe-grade and satisfactory recovery were achieved at appropriate static bed height and gas velocity. The separation efficiency of coarse iron ore particles gradually decreased with decreasing size fraction. This study aims to provide an alternative approach for improving the quality of coarse particulate iron ore.

Size fractionation as a tool for separating charcoal of different fuel source and recalcitrance in the wildfire ash layer

Charcoal is a heterogeneous material exhibiting a diverse range of properties. This variability represents a serious challenge in studies that use the properties of natural charcoal for reconstructing wildfires history in terrestrial ecosystems. In this study, we tested the hypothesis that particle size is a sufficiently robust indicator for separating forest wildfire combustion products into fractions with distinct properties. For this purpose, we examined two different forest environments affected by contrasting wildfires in terms of severity: an eucalypt forest in Australia, which experienced an extremely severe wildfire, and a Mediterranean pine forest in Italy, which burned to moderate severity. We fractionated the ash/charcoal layers collected on the ground into four size fractions (>2, 2–1, 1–0.5, <0.5mm) and analysed them for mineral ash content, elemental composition, chemical structure (by IR spectroscopy), fuel source and charcoal reflectance (by reflected-light microscopy), and chemical/thermal recalcitrance (by chemical and thermal oxidation).At both sites, the finest fraction (<0.5mm) had, by far, the greatest mass. The C concentration and C/N ratio decreased with decreasing size fraction, while pH and the mineral ash content followed the opposite trend. The coarser fractions showed higher contribution of amorphous carbon and stronger recalcitrance. We also observed that certain fuel types were preferentially represented by particular size fractions. We conclude that the differences between ash/charcoal size fractions were most likely primarily imposed by fuel source and secondarily by burning conditions. Size fractionation can therefore serve as a valuable tool to characterise the forest wildfire combustion products, as each fraction displays a narrower range of properties than the whole sample. We propose the mineral ash content of the fractions as criterion for selecting the appropriate number of fractions to analyse.

Exploring the potential of clumped isotope thermometry on coccolith‐rich sediments as a sea surface temperature proxy

AbstractUnderstanding past changes in sea surface temperatures (SSTs) is crucial; however, existing proxies for reconstructing past SSTs are hindered by unknown ancient seawater composition (foraminiferal Mg/Ca and δ18O) or reflect subsurface temperatures (TEX86) or have a limited applicable temperature range ( ). We examine clumped isotope (Δ47) thermometry to fossil coccolith‐rich material as an SST proxy, as clumped isotopes are independent of original seawater composition and applicable to a wide temperature range and coccolithophores are widespread and dissolution resistant. The Δ47‐derived temperatures from &lt;63, &lt;20, &lt;10, and 2–5 μm size fractions of two equatorial Pacific late Miocene‐early Pliocene sediment samples (c1; c2) range between ∼18 and 29°C, with c1 temperatures consistently above c2. Removing the &gt;63 μm fraction removes most nonmixed layer components; however, the Δ47‐derived temperatures display an unexpected slight decreasing trend with decreasing size fraction. This unexpected trend could partly arise because larger coccoliths (5–12 μm) are removed during the size fraction separation process. The c1 and &lt;63 μm c2 Δ47‐derived temperatures are comparable to concurrent SSTs. The &lt;20, &lt;10, and 2–5 μm c2 Δ47‐derived temperatures are consistently cooler than expected. The Δ47‐ temperature offset is probably caused by abiotic/diagenetic calcite present in the c2 2–5 μm fraction (∼53% by area), which potentially precipitated at bottom water temperatures of ∼6°C. Our results indicate that clumped isotopes on coccolith‐rich sediment fractions have potential as an SST proxy, particularly in tropical regions, providing that careful investigation of the appropriate size fraction for the region and time scale is undertaken.

Chromium speciation and fractionation in ground and surface waters in the vicinity of chromite ore processing residue disposal sites.

Chromium concentrations of up to 91 mg l(-1) were found by ICP-OES for ground water from nine boreholes at four landfill sites in an area of S.E. Glasgow/S. Lanarkshire where high-lime chromite ore processing residue (COPR) from a local chemical works had been deposited from 1830 to 1968. Surface water concentrations of up to 6.7 mg l(-1) in a local tributary stream fell to 0.11 mg l(-1) in the River Clyde. Two independent techniques of complexation/colorimetry and speciated isotope dilution mass spectrometry (SIDMS) showed that Cr was predominantly (>90%) in hexavalent form (CrVI) as CrO4(2-), as anticipated at the high pH (7.5-12.5) of the sites. Some differences between the implied and directly determined concentrations of dissolved CrIII, however, appeared related to the total organic carbon (TOC) content. This was most significant for the ground water from one borehole that had the highest TOC concentration of 300 mg l(-1) and at which < 3% of Cr was in the form of CrVI. Subsequent ultrafiltration produced significant decreases in Cr concentration with decreasing size fractions, e.g. <0.45 microm, < 100 kDa, <30 kDa and < 1 kDa by the tangential-flow method. As this appeared related more to concentrations of humic substances than of TOC per se, horizontal bed gel electrophoresis of freeze-dried ultrafilter retentates was carried out to further characterise the CrIII-organic complex. This showed for the main Cr-containing fraction, 100 kDa-0.45 microm, that the Cr was associated with a dark brown band characteristic of organic (humic) matter. Comparison of gel electrophoresis and FTIR results for ultrafilter retentates of ground water from this borehole with those for a borehole at another site where CrVI predominated suggested the influence of carboxylate groups, both in reducing CrVI and in forming soluble CrIII-humic complexes. The implications of this for remediation strategies (especially those based on the addition of organic matter) designed to reduce highly mobile and carcinogenic Cr(VI)O4(2-) to the much less harmful CrIII as insoluble Cr(OH)3 are discussed.

K–Ar dating of magmatic sericite crystallites for determination of cooling paths of metamorphic overprints

A combined optical and X-ray characterisation of fine-grained micas in granodioritic to tonalitic dikes and intrusions of the Eastardennes–Eifel nappe (Linksrheinisches Schiefergebirge, Germany–Belgium) was completed with K–Ar dating of separated size fractions from these rocks. In each sample, the K–Ar ages decrease with decreasing size fraction, but the same size fractions of the different samples yield different ages. Application of the closure temperature concept to the K–Ar ages of the various size fractions indicates that the crystallite size expressed as CIS-FWHM ser001ad and coherent scattering domain (CSD) thickness acts as the effective radius of Ar diffusion. A linear model may describe the correlation between K–Ar ages and crystallite thickness. The ages younger than the model prediction are caused by the occurrence of microcline as an accessory K-bearing mineral phase. The obtained K–Ar ages were interpreted as representative of the cooling path of the magmatic components in the Eastardennes–Eifel nappe below 330°C. The K–Ar age of the largest size fraction of the tonalitic dike #V11 (313.6±7.2 Ma) is the closest value for the age of the Variscan cleavage development. The oldest age of the hydrothermally altered tonalitic dike (300.2±8.4 Ma) might represent an episode of hydrothermal fluid migration after cleavage development; it represents at least a minimum age. The microcline age (242.8±6.0 Ma) of the Hill intrusion may represent the closure temperature of this mineral at about 140°C.

Sheared-Root Inocula of Vesicular-Arbuscular Mycorrhizal Fungi

For efficient handling, vesicular-arbuscular mycorrhizal fungi should be processed into small and uniform inocula; however, processing can reduce the inoculum density. In this article we describe the preparation and use of sheared-root inocula of Glomus spp. in which inoculum densities were increased during processing. Our objectives were to determine inoculum viability and density after shearing and to ascertain if the sheared inocula could be pelletized or used with a gel carrier. Root samples were harvested from aeroponic cultures, blotted dry, cut into 1-cm lengths, and sheared in a food processor for up to 80 s. After shearing, the inoculum was washed over sieves, and the propagule density in each fraction was determined. Sheared inocula were also encapsulated in carrageenan or used in a gel carrier. Shearing aeroponically produced root inocula reduced particle size. Propagule density increased with decreasing size fraction down to a size of 63 mum, after which propagule density decreased. The weighted-average propagule density of the inoculum was 135,380 propagules g (dry weight) of sheared root material. Sheared roots were encapsulated successfully in carrageenan, and the gel served as an effective carrier. Aeroponic root inoculum was stored dry at 4 degrees C for 23 months without significant reduction in propagule density; however, this material was not appropriate for shearing. Moist roots, useful for shearing, began to lose propagule density after 1 month of storage. Shearing proved to be an excellent method to prepare viable root inocula of small and uniform size, allowing for more efficient and effective use of limited inoculum supplies.