Coarse Fraction Research Articles

Untargeted analysis of environmental contaminants in surface snow samples of Svalbard Islands by liquid chromatography-high resolution mass spectrometry

In recent years, there is increasing attention on the contaminants of emerging concern (CECs), which include plasticizers, flame retardants, industrial chemicals, pharmaceuticals, and personal care products, since they have been detected even far away from pollution sources. The polar regions are not exempt from the presence of anthropogenic contaminants, and they are employed as a model for understanding the pollutant fate and impact.During the 2021 spring campaign, sixteen surface snow samples were collected close to the research station of Ny-Ålesund located on the Spitsbergen Island of the Norwegian Svalbard Archipelago. The samples were extracted by solid-phase extraction and analyzed by liquid chromatography-high-resolution tandem mass spectrometry (LC-HRMS/MS) following an untargeted approach. Compound tentative identification was obtained with the aid of the software Compound Discoverer, using both mass spectral database search and manual validation. Among the 114 compounds identified with a high confidence level in the snow samples, >80 have some commercial or industrial use (drugs, plasticizers, fragrances, etc.), therefore they could be of anthropogenic origin. Nonetheless, a clear contamination trend did not appear in the snow samples collected on eight different days during one month. The comparison with aerosol samples collected in the same area did not help identifying the source, either, since only a few compounds were in common, and they were mainly of natural origin. As such, the analysis of aerosol sample did not support possible long-range transport, also considering that compounds were detected mostly in the coarse fraction.

Prolonged Drought Enhances Northwest China Dust Storm Activity

AbstractThe patterns and forcing mechanism of dust storms in arid Northwest China remain unclear and debated due to lack of reliable long‐term geological records. Here we present a ∼1,600‐year dust storm history in Northwest China based on the sedimentary coarse fraction (>63 μm) retrieved from Lake Hurleg and Lake Qinghai on the northeastern Tibetan Plateau (NETP). The NETP dust storm history, which agrees well with those from North China, shows two prolonged intervals of high dust storm occurrences during the Medieval Warm Period and the past century, and two prolonged weakened dust storm intervals from ∼400 to 700 CE and during the Little Ice Age. The temporal variation in NETP dust storm activities is out‐of‐phase with moisture records over central Asia, with enhanced dust storms corresponding to warm‐dry intervals, and vice versa. The prolonged centennial warm‐dry climates over arid Northwest China to arid central Asia could have led to decreased soil moisture, deteriorated vegetation cover, and increased dust particle supply and dust storm activities; while the prolonged centennial cold‐wet climates could have increased soil moisture, vegetation cover, and decreased dust storm activities. We contend that whilst human impact could be responsible for the obviously increased eolian dust flux in the most recent century, it is most likely that the prolonged natural hydroclimatic conditions regulate the global dust storm activity before the Anthropocene.

An Alternative Technology to Obtain Dewatered Mine Tailings: Safe and Control Environmental Management of Filtered and Thickened Copper Mine Tailings in Chile

An alternative process to obtain a high degree of dewatering tailings that produces a high-density product is presented in this article. This technology involves the combination of tailings particle grain size classification by hydrocyclones (HC) and tailings dewatering by horizontal vibratory screens (HVS). It makes it possible to dewater tailings to a high grade of performance. This alternative technology (HC-HVS) involves the recovery of water from the coarse fraction of tailings (sands) through two hydrocycloning stages, followed by a dewatering stage of cycloned tailings sands on horizontal vibratory screens, to reduce moisture content and turn it into a “cake”. The resulting coarse fraction tailings are easily transported to a dry stack tailings storage facility (TSF). The fine fraction of tailings (slimes) can be dewatered on thickener equipment to recover part of the process water. Finally, this article describes the main benefits of this alternative dewatered tailings technology with an emphasis on (i) dewatering technology evolution over the last 17 years; (ii) process stages features; (iii) pilot test results; (iv) tailings properties analysis (such as particle grain size distribution, fines content) and (v) lessons learned about the experience gained in the operation of Mantos Blancos case study with dry stack tailings storage facility.

Increasing the content of coarse fractions in the mined coal mass by a combine using paired cuts

The main volume of coal is mined underground using shearers. In modern shearers, auger actuators are mainly used, which are distinguished by the simplicity of design, manufacturability and reliability. However, in the process of separating coal from mass by cutting, the yield of fine grades is 40-50 % of the total production volume. Therefore, the search and development of technical solutions that provide an increase in the yield of large fractions in the process of coal mining with auger shearers is an urgent task. Traditionally, this problem is solved by increasing the thickness of the slices, which is achieved by installing cutters with a larger radial reach and increasing the shearer feed rate. An unconventional way to increase the cross section of slices by forming energy-efficient paired and group slices with mutual superposition of stress fields in the mass from the action of neighboring cutters is considered. The results of modeling the process of cutting coal confirm that an increase in the efficiency of destruction of the rock mass by the cutters of the auger executive bodies of the shearer can be achieved by a complex technical solution, including the formation of paired cuts and combined stress zones in the rock mass. As a result, the output of large fragments when cutting with paired cutters increases by 1.3-1.8 times compared with cutting with a single cutter.

Optimised dry processing of protein concentrates from Australian pulses: A comparative study of faba bean, yellow pea and red lentil seed material

AbstractMilling and air classification settings were optimised for production of protein concentrates from Australian faba bean, yellow pea and red lentil seed material. Pulses were milled to flour of three progressively finer particle size distributions (D50 of 23–25, 16–18 and 13–14 μm) and air classified at classifier wheel speeds of 7080, 9600 and 10,200 rpm. Maximum protein concentration was reported for pulse flours (D50 of 13–14 μm) at 9600 rpm. Protein concentrations of 61.4, 58.1 and 61.0 g/100 g (db.), reflecting a fold increase in protein content of 1.9, 2.3 and 2.1, were reported for faba bean, yellow pea and red lentil, respectively. Protein, ash, fat and total dietary fibre contents were significantly higher in fine fractions (p < 0.05), compared with coarse fractions, resulting in protein concentrates with enhanced nutritional properties. Amino acid score (AAS) of protein concentrates highlighted deficiencies in sulphur‐containing amino acids, methionine and cysteine (MET + CYS), and tryptophan. Based on the lowest AAS (MET + CYS), protein concentrates were ranked highest for yellow pea (0.75), followed by faba bean (0.58) and red lentil (0.51). Phytochemical analysis demonstrated that bioactive constituents also co‐concentrated with protein (fine fraction), potentially leading to protein concentrates with enhanced health benefits. Shelf‐life assessment for the original flours and protein concentrates indicated the onset of rancidity after 3 months of storage. As fat content co‐concentrated with protein, the rancidity (%) scores were higher for protein concentrates compared with the original flours. This demonstrates the importance of developing effective treatments, suitable for dry processing, which can extend shelf‐life and stability of protein concentrate ingredients for domestic and export markets. The objective of this study was to increase the knowledge available on dry processing of protein concentrates from Australian pulses. The information generated from this study will look to inform future commercial scale processing operations.

Milk Thistle Oilseed Cake Flour Fractions: A Source of Silymarin and Macronutrients for Gluten-Free Bread.

The utilization of plant by-products as functional food ingredients has received increasing attention in the last decade. One such by-product generated during milk thistle oil pressing is oilseed cakes, which could be used as a novel food ingredient. Therefore, the study aimed at investigating the effects of the addition of milk thistle oilseed cake (MTOC) flour fractions obtained via dry sieving, differing in particle size (unsieved; coarse: >710 µm; medium: 315–710 µm; and fine: <315 µm), on the quality of gluten-free bread and stability of silymarin during breadmaking. The 10% addition of the fractions into gluten-free bread increased the protein, fibre, fat, ash and silymarin content. The breads with the coarse fraction had the highest content of fibre, whereas the breads with the fine fraction excelled in protein, fat and ash content. The medium fraction was characterized as the richest source of silymarin, whilst the fine fraction was the poorest. Silymarin constituents were slightly released during dough rising but also partially decomposed during baking; moreover, silydianin was the most susceptible and degraded the most. The enriched breads had better sensory and textural properties compared to the control bread. The results suggest that MTOC flour fractions can improve the potential health benefits and nutritional profile of gluten-free bread.

Chemical and Mineralogical Characterization of Montevive Celestine Mineral

The Montevive celestine mineral deposit, set in the Granada Basin in a marine evaporitic uppermost Tortonian–lowermost Messinian sequence, is the largest reserve in Europe of this economically important strontium ore. Currently, the mine has a large amount of tailings resulting from the rejection of a manual dry screening of high-grade celestine mineral. This visual and density screening was carried out in the early days of mining (1954–1973). Concentrating the celestine mineral and increasing the ore recovery rate would reduce mine operation costs and the generation of new tailings, reducing the impact on the environment. In order to define more adequate concentration methods, we have used complementary analytical techniques such as optical (OM) and scanning and transmission electron microscopy (SEM and TEM), energy-dispersive X-rays (EDXs), X-ray fluorescence (XRF), and X-ray diffraction (XRD) to fully characterize the morphology, microstructure, chemistry, and mineralogy of the celestine mineral. The low-grade mineral is made of prismatic celestine crystals that are replacing a matrix of micro sparry calcite. Other minority minerals are strontianite, dolomite, quartz, and clays (kaolinite, paragonite, and illite). There is also a certain amount of iron oxides and hydroxides (mainly magnetite) associated with clays. We showed that the concentration of low-grade celestine mineral can be achieved through a low-cost and eco-friendly method based on grinding and size separation. The coarser fractions (&gt;5 mm) have more celestine (up to 12 percent units higher than the starting unprocessed mineral) due to the selective loss of calcite and minority minerals (quartz, clays, and iron oxides) that are mainly found in the finer fraction (&lt;1 mm). This process can make mine exploitation more sustainable, reducing the generation of residues that negatively impact the environment.

CHARACTERIZATION OF SIZE-RESOLVED PARTICLES AND CHEMICAL COMPOSITION AT TWO ELEMENTARY SCHOOLS IN HANOI, VIETNAM

Indoor and outdoor ultrafine, accumulation mode, and coarse fractions collected at two elementaryschools (S1 and S2) in Hanoi capital, Vietnam were characterized in terms of mass, numberconcentrations, particle morphology, and chemical composition to assess the indoor air quality atthe examined schools. The sampling campaigns were performed simultaneously indoors andoutdoors for three consecutive weeks at each school. Indoor average concentrations of CO2 and COat both schools were below the limit values recommended by the American Society of Heating,Refrigerating and Air-Conditioning Engineers (1000 ppm for CO2) and World Health Organization(7 mg/m3 for CO). Indoor mass concentrations of PM10 and CO2 at S1 and S2 were stronglyinfluenced by the presence of children and their activities indoors whereas the numberconcentration of particlesseemed not to be impacted by occupants’ activities. Water-soluble ionscommonly presented unimodal distribution for indoor and outdoor airborne particles at S1 and S2,which accounted for typically a proportion of around 3.5-5% of the total mass of particles. Oxygen(O) was the most abundant element in all fractions, followed by carbon (C) for indoor and outdoorparticles.

Lithium-Ion Battery Recycling─Influence of Recycling Processes on Component Liberation and Flotation Separation Efficiency

Recycling is a potential solution to narrow the gap between the supply and demand of raw materials for lithium-ion batteries (LIBs). However, the efficient separation of the active components and their recovery from battery waste remains a challenge. This paper evaluates the influence of three potential routes for the liberation of LIB components (namely mechanical, thermomechanical, and electrohydraulic fragmentation) on the recovery of lithium metal oxides (LMOs) and spheroidized graphite particles using froth flotation. The products of the three liberation routes were characterized using SEM-based automated image analysis. It was found that the mechanical process enabled the delamination of active materials from the foils, which remained intact at coarser sizes along with the casing and separator. However, binder preservation hinders active material liberation, as indicated by their aggregation. The electrohydraulic fragmentation route resulted in liberated active materials with a minor impact on morphology. The coarse fractions thus produced consist of the electrode foils, casing, and separator. Notwithstanding, it has the disadvantage of forming heterogeneous agglomerates containing liberated active particles. This was attributed to the dissolution of the anode binder and its rehardening after drying, capturing previously liberated particles. Finally, the thermomechanical process showed a preferential liberation of individual anode active particles and thus was considered the preferred upstream route for flotation. However, the thermal treatment oxidized Al foils, rendering them brittle and resulting in their distribution in all size fractions. Among the three, the thermomechanical black mass showed the highest flotation selectivity due to the removal of the binder, resulting in a product recovery of 94.4% graphite in the overflow and 89.4% LMOs in the underflow product.

A strontium isoscape of inland southeastern Australia

Abstract. The values and distribution patterns of the strontium (Sr) isotope ratio 87Sr/86Sr in Earth surface materials are of use in the geological, environmental, and social sciences. Ultimately, the 87Sr/86Sr ratios of soils and everything that lives in and on them are inherited from the rocks that are the parent materials of the soil's components. In Australia, there are few large-scale surveys of 87Sr/86Sr available, and here we report on a new, low-density dataset using 112 catchment outlet (floodplain) sediment samples covering 529 000 km2 of inland southeastern Australia (South Australia, New South Wales, Victoria). The coarse (&lt;2 mm) fraction of bottom sediment samples (depth ∼ 0.6–0.8 m) from the National Geochemical Survey of Australia were milled and fully digested before Sr separation by chromatography and 87Sr/86Sr determination by multicollector-inductively coupled plasma mass spectrometry. The results show a wide range of 87Sr/86Sr values from a minimum of 0.7089 to a maximum of 0.7511 (range 0.0422). The median 87Sr/86Sr (± median absolute deviation) is 0.7199 (± 0.0071), and the mean (± standard deviation) is 0.7220 (± 0.0106). The spatial patterns of the Sr isoscape observed are described and attributed to various geological sources and processes. Of note are the elevated (radiogenic) values (≥∼ 0.7270; top quartile) contributed by (1) the Palaeozoic sedimentary country rock and (mostly felsic) igneous intrusions of the Lachlan geological region to the east of the study area; (2) the Palaeoproterozoic metamorphic rocks of the central Broken Hill region; both these sources contribute radiogenic material mainly by fluvial processes; and (3) the Proterozoic to Palaeozoic rocks of the Kanmantoo, Adelaide, Gawler, and Painter geological regions to the west of the area; these sources contribute radiogenic material mainly by aeolian processes. Regions of low 87Sr/86Sr (≤∼ 0.7130; bottom quartile) belong mainly to (1) a few central Murray Basin catchments; (2) some Darling Basin catchments in the northeast; and (3) a few Eromanga geological region-influenced catchments in the northwest of the study area; these sources contribute unradiogenic material mainly by fluvial processes. The new spatial Sr isotope dataset for the DCD (Darling–Curnamona–Delamerian) region is publicly available (de Caritat et al., 2022; https://dx.doi.org/10.26186/146397)​​​​​​​.

Geochemical characteristics of surface aeolian sand in the Badain Jaran Desert, northwestern China: Implications for weathering, sedimentary processes and provenance

Knowledge of the provenance of the aeolian sand in deserts is crucial for revealing their development and the corresponding driving mechanisms. As the second-largest desert in China, the Badain Jaran Desert (BJD) has developed the tallest megadunes on Earth. However, the material source of these dunes, especially the provenance of different particle size fractions, is debated. Here, we address these issues using new geochemical data, consisting of the major, trace, and rare earth elemental signatures of different particle-size fractions of dune sands in the BJD and sediments from potential source areas. The source area sediments are from the rivers originating in the Qilian Mts., the Gobi regions between the Heihe River and the BJD, the piedmont of the Gobi-Altay Mts., and the alluvial fan of the Beida Mts. The results show that the dune sands of the BJD are mainly derived from felsic source rocks subjected to weak chemical weathering in the source area. The fine fraction (<63 μm) of the aeolian sand in the BJD has experienced some degree of sedimentary sorting and recycling, despite its mineralogical immaturity. Furthermore, comparison of the immobile trace elements and rare earth element (REE) ratios of the samples from the BJD with those from the potential source regions, together with the results of multidimensional scaling and principal component analysis, shows that the coarse fraction (63–250 μm) of the dune sand in the BJD originated mainly from fluvial and Gobi deposits eroded from the Qilian Mts.; whereas the fine fraction has a mixture of provenances, including the Qilian Mts. and the Gobi-Altay Mts., although the latter contribution is of limited significance.

Fine particles and pyrogenic carbon fractions regulate PAH partitioning and burial in a eutrophic shallow lake

Aquatic particles and organic carbon (OC) regulate the occurrence and transport of hydrophobic organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) in water-suspended particle-sediment interfaces. Conventional studies on the mechanisms regulating the relationships between PAHs and total particles/OC have ignored micro-scale regulatory factors such as particle size and OC composition. Field research in the eutrophic shallow Lake Taihu, China, revealed that the fine particle fractions 2.7–10 μm in diameter had stronger PAH adsorption capacity and significantly regulated PAH particle size distribution and water-particle partitioning. Selective PAH biodegradation by planktonic microorganisms probably significantly weakened the capacity of the coarse fractions to regulate PAHs. OC fragments at different temperature gradients had markedly different influences on the particle size distribution of PAHs. High-temperature pyrogenic OC fractions (part of black carbon) were the principal OC regulatory factors for medium-to high-molecular-weight PAHs. However, the OC fragments did not directly affect the particle distribution of low-molecular-weight PAHs. During particle deposition and burial, microbial PAH utilization and efficiency probably regulated the burial potential of various hydrophobic PAH species. Biodegradation of relatively less hydrophobic PAHs with octanol-water partition coefficients (log Kow) < 5.8 showed an increasing trend with decreasing PAH hydrophobicity. Biological pump action of the relatively higher hydrophobic PAH species (log Kow > 5.8) showed a decreasing trend with increasing PAH hydrophobicity. The discoveries of the present work further clarified the mechanisms of PAH partitioning and burial in a eutrophic shallow lake and collectively provides a valuable reference for modeling the transport and dispersal mechanisms of hydrophobic, particle-bound organic contaminants in other aquatic ecosystems.

Bioaccessibility of Pb in health-related size fractions of contaminated soils amended with phosphate

Lead (Pb) contamination is one of the most significant exposure hazards to human health. Contaminated soil particles may be eroded and transferred either to the atmosphere (<10 μm) or to streams; or they may be incidentally ingested (<200 μm). Among strategies for the long-term management of this risk, one of the most cost-effective is the reduction of Pb mobility and bioavailability via amendment with phosphorus-containing materials.To clarify the effectiveness of P amendment in reducing Pb mobility and bioaccessibility in different soil size fractions, an experiment was performed by adding a soluble P compound to a historically contaminated urban soil (RO), a mining soil (MI), and an uncontaminated spiked soil (SP) at different P:Pb molar ratios (2.5:1, 5:1, and 15:1).In the <10 μm fraction of soils, P addition reduced bioaccessible Pb only in the SP soil at the highest dose, with little to no effect on RO and MI soils. Similarly, in the coarse fraction, Pb was immobilized only in the SP soil with all three P doses. These results were probably due to the higher stability of Pb in historically contaminated soils, where Pb dissolution is the limiting factor to the formation of insoluble Pb compounds.The bioaccessible proportion of Pb (using SBET method) was higher than 70 % of the total Pb in all soils and was similar in both fine and coarse particle fractions. Due to the enrichment of Pb in finer particles, this implies possible adverse effects to the environment or to human health if these particles escape from the soil. These results call for increasing attention to the effect of remediation activities on fine soil particles, considering their significant environmental role especially in urban and in historically low or moderately contaminated areas.

Potential of air-currents assisted particle separation (ACAPS) technology for hybrid fractionation of clean-label faba bean (Vicia faba L.) protein

Air-currents assisted particle separation (ACAPS) of faba beans prior to wet separation was evaluated for its impact on chemical composition, yield and recovery of protein, starch and dietary fibre, and protein secondary structural changes. The protein and dietary fibre contents of faba bean cultivars Snowbird and Athena were positively correlated (r = 0.9, P < 0.0001) with the increasing particle size, which was offset by starch contents. ACAPS treatment of faba bean dehulled bean flours resulted in both protein- and dietary fibre-rich coarse fractions (75–500 μm). Subjecting the ACAPS-treated protein-rich (Snowbird: 38.96 ± 0.33% and Athena: 37.54 ± 0.20%) coarse fractions (250–500 μm) to micellization resulted in protein isolates (Snowbird: 97.74 ± 0.18% and Athena: 94.30 ± 0.29%). This method also resulted in starch isolates (Snowbird: 94.05 ± 1.67% and Athena: 94.33 ± 0.53%) and dietary fibre concentrates (Snowbird: 54.41 ± 1.87% and Athena: 44.89 ± 1.40%) as co-products, which were “clean label” ingredients. FTIR data confirmed that hybrid fractionation had minimal impact on protein secondary structures with β-sheets as the major structures.

Revealing the mechanism of stability loss of a two-fraction granular flow in a rotating drum

The qualitative nature and quantitative parameters of motion instability of a two-fraction granular filler of a rotating drum were determined. The factors of motion instability and key parameters of the oscillating system were identified and their influence on the self-excitation of pulsed self-oscillations was estimated. Two continuous and one periodic steady-state modes of filler motion were found. Periodic self-oscillations due to the development of instability during the transition from continuous circulation mode to the wall layer mode were revealed. As factors of motion instability, filler dilatancy and damping effect of fine fraction particles on the pulsed interaction of coarse fraction particles were taken. It turned out that the main key parameter of the oscillating system is the drum speed, which determines a change in dilatancy. The increase in instability is realized as a reduction of the bifurcation values of speed and dilatancy. Other key parameters are the content of the fine fraction in the filler κff and the filling degree of the chamber κlf, the growth of which increases the self-oscillating instability. The features of the oscillatory system are the relaxation type, discontinuous nature of self-oscillations and hard self-excitation mode under bistability. The discontinuous character and oscillatory hysteresis increase with decreasing κff and κlf. The limit values of the dynamic motion parameters corresponding to the conditions of self-excitation of self-oscillations in the absence and presence of fine fraction were determined: 0.96–1.11 and 0.218–0.382 for the bifurcation value of relative speed, 0.745–0.855 and 0.24–0.322 for the bifurcation value of dilatancy. The effects found make it possible to substantiate the parameters of the self-oscillating process of processing polygranular materials in drum-type machines.

Sustainable use of different size fractions of municipal solid waste incinerator bottom ash and recycled fine aggregates in cement mortar

The demand for recycled fine aggregates (RFA) is increasing daily, and researchers are continuously looking for cheaper and local alternative fine aggregates. The increasing growth of municipal solid waste (MSW) incineration plants has led to the accumulation of incinerated bottom ash in the vicinity of cities. There can be a possibility to utilize this municipal solid waste incinerated bottom ash (MSW-BA) as a partial replacement of recycled fine aggregated to achieve sustainable and economical mortars. This study analyzed the feasibility of incorporating different grain sizes, fine fraction (0.15–0.3 mm), medium fraction (0.3–0.6 mm), and coarse fraction (0.6–4.75 mm)) of MSW-BA and RFA in sustainable cement mortars with replacement amounts of 10 %, 20 % and 30 %, respectively. In addition to assessing the mechanical properties of the sustainable mortar, Mercury Intrusion Porosimetry was carried out. Based on the filler effect combined with its mineralogy and pozzolanic properties of MSW-BA, a medium fraction at 10 % replacement showed the highest compressive and flexural strength of 31.05 MPa and 5.07 MPa, respectively. After exposure to the 1 mol/liter sodium hydroxide (NaOH) solution, the largest reduction of compressive strength by 7.92 MPa was found in 10 % medium fraction replacement of MSW-BA. Porosity was also reduced when smaller grain sizes of MSW-BA was replaced with RFA, and leaching tests have confirmed leaching of heavy metal are under limits. Results showed that adding MSW-BA can improve the compressive strength of concrete up to a certain extent, but over-addition of MSW-BA can lead to a detrimental effect on strength.

Influence of Processing Parameters on Fibre Properties during Twin-Screw Extrusion of Poplar Wood Chips

For sustainable agriculture, the contentious input of peat in growing media needs to be replaced by a substitute with the best possible water-holding capacity (WHC). Wood from fast growing poplar trees, cultivated in short rotation coppices (SRC), is a suitable alternative if it is processed correctly in a twin-screw extruder. The processing parameters, such as the aperture setting of the extruder, moisture content, and specific energy demand (SED), during twin-screw extrusion, as well as their influence on fibre properties such as WHC and particle size distribution, are investigated. SRC-poplar wood chips from clone Max3 are the raw material used for this research. As a result, the best volume-based WHC (75%) at −1 kPa suction tension was achieved for dry extruded wood chip fibre at an aperture setting of 15 mm and an SED of 340 kWh*t−1. The smallest SED of 140 kWh*t−1 was measured at apertures of 35 mm and 40 mm, which resulted in a volume-based WHC of approximately 30% and a dry matter mass flow during processing of 0.289 t*h−1 (40 mm). The particle size distribution of semi-dry wood chips has the highest fine fraction as well as the smallest coarse fraction. Conclusively, poplar wood can be processed fresh and dry into fibre at an acceptable SED, which results in an acceptable WHC.

Sources and temporal dynamics of suspended sediment transport along the middle Paraná River

The Paraná River is one of the world's largest fluvial systems due to its discharge. During the last 30 years, water discharge has averaged 18,389 m3 s−1 downstream of the Paraguay-Paraná confluence, where its most important tributaries, the Paraguay and the upper Paraná rivers contribute 22% and 78% of its total discharge, respectively. However, the sedimentological dynamics of this system behaves peculiarly due to the influence of the Bermejo River, a tributary of the Paraguay River. Even though the contribution of the Bermejo River discharge represents only 2% of the Paraná River discharge, its input of suspended sediments is significant due to the erosive processes in the upper Bermejo basin.Most earlier studies have primarily focused on the contributions and dynamics of the wash load (silt and clay) from the Bermejo River through the Paraguay River to the Paraná River, and neglected the relevance of fine and very fine sands (coarser than 63 μm). These sediment fractions play a key role in bed sediment composition, roughness, and bed forms, ultimately modifying the flow resistance and the morphodynamic processes, among other environmental and biological parameters.This study seeks to quantify the suspended sediment contribution of the main tributaries of the middle Paraná River during the last three decades. In particular, water discharge, sediment transport and grain size data measured at gage stations located at the Paraguay River upper reach, the Bermejo River, and the upper and middle reaches of the Paraná River are analyzed. Focus is placed on the coarse suspended sediment fraction. Additionally, the authors collected sediment samples at different river cross-sections and water discharges.The temporal analysis revealed the dynamic behavior of the sediments along the system. The results show different behaviors of the wash load and suspended sand transport provided by the Bermejo River. Along the middle Paraná reach, results suggest a significant suspended coarse fraction deposition during the highest sediment input period. Bed sediments, in turn, are re-suspended during the months with low contributions from the Bermejo and/or during the high water levels stages of the Paraná. This sediment dynamics produces a complex pattern of coarse sediment transport in the Paraná River at its middle reach, also modifying the sedimentological characteristics of the river bed.

Gravity beneficiation of low quality gibbsite-kaolinite bauxite

The current study deals with preliminary chemical activation, which allows transforming the phase composition before gravitational concentration and effective removal of silicon during subsequent alkaline treatment, in order to obtain a raw material suitable for the production of alumina by the Bayer method. Electron-microscopic analysis of the original bauxite showed that the coarse-crystalline fraction was tightly pressed by the fine one. Silicon modulus of the averaged bauxite sample is 3.65. After chemical activation of bauxite in a sodium bicarbonate solution, the fine fraction got separated from the coarse fraction and the phase composition changed i.e. the calcium silicate phase disappeared and the calcite phase was formed. Preliminary chemical activation at temperatures of 90 and 120 оС for 20 min resulted in the increase of the bauxite beneficiation degree by 12.1 and 15.2%. In order to obtain a quality bauxite concentrate with a silica modulus of more than 7, the coarse-grained bauxite fraction separated after gravity concentration should be subjected to chemical beneficiation in an alkaline solution at a second stage.

Reuse of Powders and Recycled Aggregates from Mixed Construction and Demolition Waste in Alkali-Activated Materials and Precast Concrete Units

This article describes the recycling of coarse and fine fractions and powder from construction and demolition waste (CDW) using alkaline activation technology (geopolymerization). The CDW sample used corresponds to a mixture (mixed waste) of concrete (Co), ceramics (Ce) and masonry (M). Co, Ce and M (CDW-Mixed) powders were used as geopolymer precursors. As an alkaline activator, a mixture of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) was used. From CDW-Mixed, a hybrid cement added with 10% ordinary Portland cement (OPC) was synthesized to promote curing at room temperature (25 °C). From the alkali-activated hybrid cement and the incorporation of mixed recycled aggregates (gravel and sand), applications of mortars, concretes, fiber-reinforced materials and prefabricated units, such as solid blocks, perforated (hollow) blocks and pavers, were produced. The results of the physical–mechanical characterization validate the application potential of these CDW-based materials in the construction sector. Compressive strengths of up to 40.5 MPa for mortar and 36.9 MPa for concrete were obtained after 90 days of curing at room temperature ≈ 25 °C. Similarly, a life cycle analysis (LCA) associated with raw materials demonstrated the environmental sustainability (44% lower carbon footprint) of mixed alkali-activated CDWs compared to conventional materials based on OPC.