High Metal Content Research Articles

Novel approach to recycling of steel swarf using hydrometallurgy

Steel swarf is a hazardous waste which is challenging to recycle due to its high content of heavy metals and cutting fluids and is today commonly landfilled. The swarf can contain up to 80% iron and represents a potential secondary raw material for production of reagents like ferric chloride, which can be utilized in wastewater treatment. This work presents a novel hydrometallurgical approach for recycling steel swarf and production of ferric chloride by selective separation of iron from heavy metals. Swarf containing 69% iron was leached with hydrochloric acid. A leachate containing 24.600 mg/L Fe with 150 mg/L Mn, 12 mg/L Ni and <1 mg/L Cr and Mo was obtained. The oil-based cutting fluids largely remained in the solid residue with only 1% dissolution in the aqueous phase. These findings showed that ferric chloride solutions of 99% purity can be produced from steel swarf in a single leaching step.

ВЛИЯНИЕ УСЛОВИЙ ФОРМИРОВАНИЯ ВОДОНЕФТЯНЫХ ЭМУЛЬСИЙ НА ИХ СТРУКТУРНО-МЕХАНИЧЕСКИЕ СВОЙСТВА

Abstract. The Republic of Kazakhstan is one of the leaders in the production of hydrocarbons. However, the oil produced in Kazakhstan, especially from the Severnye Buzachi oil and gas field, has a high viscosity and, therefore, belongs to the category of unconventional resources with a high content of metals associated with asphalt-resinous components. This problem is common to all countries producing oil in the Caspian basin. Analysis of the development of the Severnye Buzachi oil and gas field indicates a sharp increase in water availability at the initial stage of development, which is due to an excessively large difference in the rheological characteristics of reservoir oil and water. As a result, an oil-water emulsion is formed at the bottom of the well and in the trunk, which can acquire many different states with various physical, mechanical and technological properties. A significant number of works have been devoted to the study of the properties of oil-water emulsions. Oil in the Caspian basin is characterized as viscous and heavy with a high content of metals, especially vanadium and nickel, which interact in oil with asphalt-resinous components. These properties of oil reduce oil recovery. These properties and methods of optimizing oil production were considered on the basis of the North Buzach oil and gas region of the Republic of Kazakhstan. The structural and mechanical properties of water-oil emulsions of crude oil have been experimentally studied. Based on the measured parameters, the shear stress values were calculated at the shear rate of the walls, and then flow curves were constructed for different temperatures and oil-water ratios. As a result, the regularities of changes in rheological properties depending on the water content and temperature were revealed and a formula was obtained that allows determining the values of the effective viscosity complex of oil-water emulsions. Based on the results obtained, optimization of technological modes of oil preparation for further transportation and processing in different periods of operation can be carried out in this area. Keywords: oil-water emulsion, demulsification, rheology, heavy oil, oil and gas field, Northern Buzachi, resins, asphaltenes, emulsifier, reagent, turbulence, flow, experimental studies, viscosity.

Full and Hollow Metal–Ceramic Beads Based on Tantalum and Alumina Produced by Alginate Gelation

Metal–ceramic composite beads containing different amounts of tantalum and alumina, particularly 100 vol% tantalum and 60–40 vol% tantalum/alumina, are produced by the alginate gelation process. Sodium alginate is used as gelling agent in the metal–ceramic suspension, while a calcium chloride solution is prepared to trigger the consolidation process. As in the previous study, different nozzles are used in order to obtain beads of three different sizes. The largest beads result to be hollow, and hence require a freeze‐drying step in order to prevent their collapse. After debinding in air, the composite beads are sintered at 1600 °C under inert atmosphere. Samples in green and sintered state are analyzed by digital light microscopy and scanning electron microscopy. Investigations by mercury intrusion porosimetry reveal that composite beads feature smaller pores compared to pure tantalum beads, as well as lower open porosity. The fracture strength is evaluated on single beads. Despite the high metallic content, both composite and pure tantalum beads show a brittle behavior. X‐ray powder diffraction (XRD) analyses reveal the presence of , , and alongside pure Ta in the samples prepared from pure tantalum. The impurities are due to reactions with Na, C, and Ca from the used additives.

Heavy Metal Contamination and Health Risk of Soils and Vegetables Grown Near a Gold Mine Area: A Case Study of Barberton, South Africa

Pollution from mining operations has a direct impact on agricultural production and can lead to potential health risks because of the accumulation of heavy metals in vegetables. Vegetables and soil samples collected from Thaba Nchu farm located near a gold mining site were analysed to determine the concentration of heavy metals. Soil and vegetable samples were digested using the wet method and heavy metals were analysed using the inductively coupled plasma-mass spectrometry technique. The soil-to-plant Transfer Factors (TF) and Health Risk Index (HRI) were calculated. The highest mean levels of Fe, Mn, Ni, Pb, and Cu were detected in spinach while the highest mean level of Zn was found in onion. Iron levels in lettuce, spinach, beetroot, onion, and carrot ranged from 2203 to 3404 mg/kg which was above the permissible limits (450 mg/kg) recommended by the Food and Agriculture Organization–World Health Organization (FAO/WHO). The concentration of Pb (0.4 mg/kg) and Cr (13.8 mg/kg) in spinach exceeded the permissible level recommended by FAO/WHO of 0.3 mg/kg and 1.3 mg/kg, respectively. The metal transfer factors in vegetables were in the order: Cd&gt;Pb&gt;Cu&gt;Fe&gt;Ni&gt;Co&gt;Zn&gt;Cr&gt;Mn. The daily intake and HRI of Mn and Fe in vegetables were above safe levels. There was no obvious heavy metal contamination in the soil and irrigation water. These results suggest that the consumption of vegetables grown on the study site could pose danger to human health. High heavy metal content in crops was attributed to the accumulation of Fe and Mn, which are the major ores extracted from the mining activities in the study area. Given the potential health risks, regular monitoring of heavy metal contamination in the soils and crops is recommended.

Optimizing the gasification reactivity of biochar: The composition, structure and kinetics of biochar derived from biomass lignocellulosic components and their interactions during gasification process

Biochar can become a renewable substitute to coal in the future’s energy mix. This work aims to investigate the optimization of reactivity of biochar samples derived from biomass (Miscanthus) and its lignocellulosic components (i.e. cellulose, hemicellulose and lignin) by studying the material characteristics, composition, thermal behavior and interaction during the CO2 gasification process. For biochar production, the yield increased with lignin content in the biomass, but high lignin content reduced biochar’s porous structure. The conversion characteristic was gradually stimulated by increasing the gasification temperature and heating rate, and the lignin biochar (LB) reactivity was the most promoted. High lignin content was favorable for improving the biochar reactivity. The reactivity of the xylan biochar (XB) was attributed to the high content of alkali and alkaline earth metals, while the activity of the cellulose biochar (CB) was due to the rich porous structure. The activation energy of biochar samples gasification reaction ranged from 109.8 to 196.1 kJ/mol, and the values decreased with the increase of carbon conversion rate. Modelled biomass with 32.5% cellulose, 15% xylan and 52.5% lignin was considered the optimal feedstock to make biochar because of the its low activation energy and high gasification reactivity.

Hydrophobicity and efflorescence of lightweight fly ash geopolymer incorporated with calcium stearate

Lightweight concrete is a porous material that is growing in demand because of its attractive properties. However, because of the high porosity of this lightweight material, moisture can fill pores causing cracks and facilitating algal and fungal growth. Calcium stearate (CS) is hydrophobic and could provide a water-repellent layer on the walls of capillary pores. A high dosage of CS increases air content and reduces the density of the concrete, and so this research proposed using CS to create a lightweight fly ash geopolymer. CS was used as a pore generator and water-repellent material in a geopolymer system, replacing fly ash at dosages of 0, 1, 2.5, 5, and 10% by weight. The physical and chemical properties of geopolymers were investigated. Given the high content of soluble alkali metal in the geopolymer system, efflorescence was also studied.The results show that the incorporation of CS increases the hydrophobicity of the geopolymer surface and reduces efflorescence. Calcium silicate hydrate forms in the pores and matrix of the geopolymer, as indicated by the detection of calcium silicate hydrate in the XRD pattern and the Ca–O–Si peak in the FTIR spectra. The use of CS in fly ash geopolymer also results in lower thermal conductivity of the material compared with the control. The K value was 0.13–0.62 W/m·K, depending on the CS content and density. Compressive strengths varied from 18 to 55 ksc. Efflorescence was not observed for mixes with 5 and 10% CS content. In addition, a hydrophobic surface was achieved with a mix with 5% CS, as indicated by the high contact angle of 96.67°. The test results thus confirm that a hydrophobic lightweight fly ash geopolymer without efflorescence can be fabricated with the incorporation of CS.

M-type (22) Kalliope: A tiny Mercury

Context. Asteroid (22) Kalliope is the second largest M-type asteroid in the main belt and is orbited by a satellite, Linus. Whereas the mass of Kalliope is already well constrained thanks to the presence of a moon, its volume is still poorly known, leading to uncertainties on its bulk density and internal structure. Aims. We aim to refine the shape of (22) Kalliope and thus its diameter and bulk density, as well as the orbit of its moon to better constrain its mass, hence density and internal structure. Methods. We acquired disk-resolved observations of (22) Kalliope using the VLT/SPHERE/ZIMPOL instrument to reconstruct its three-dimensional (3D) shape using three different modeling techniques. These images were also used together with new speckle observations at the C2PU/PISCO instrument as well as archival images from other large ground-based telescopes to refine the orbit of Linus. Results. The volume of (22) Kalliope given by the shape models, corresponding to D = 150 ± 5 km, and the mass constrained by its satellite’s orbit yield a density of ρ = 4.40 ± 0.46 g cm−3. This high density potentially makes (22) Kalliope the densest known small body in the Solar System. A macroporosity in the 10–25% range (as expected for this mass and size), implies a grain density in the 4.8–5.9 g cm−3 range. Kalliope’s high bulk density, along with its silicate-rich surface implied by its low radar albedo, implies a differentiated interior with metal contributing to most of the mass of the body. Conclusions. Kalliope’s high metal content (40–60%) along with its metal-poor mantle makes it the smallest known Mercury-like body. A large impact at the origin of the formation of the moon Linus is likely the cause of its high metal content and density.

Catalysts Derived from Nickel-Containing Layered Double Hydroxides for Aqueous-Phase Furfural Hydrogenation

Changes in the structural and textural properties of NiAl-layered double hydroxides (LDHs) (with 2–4 molar ratios of metals) and state of nickel that occur in different steps of the synthesis of nickel catalysts were studied using XRD, thermal analysis, TPR, low-temperature nitrogen adsorption, XANES, EXAFS, and electron microscopy methods. Relations between nickel content, catalyst reduction conditions, state of nickel, and its catalytic properties were revealed. It was shown that the use of NiAl LDH as the catalyst precursor even at a high content of active metal allows for the obtaining of the dispersed particles of supported nickel that are active in the aqueous-phase hydrogenation of furfural. The catalyst activity and conversion of furfural were found to increase with elevation of the catalyst reduction temperature and the corresponding growth of the fraction of reduced nickel. However, a lower reduction temperature (500 °C) makes it possible to form smaller nickel particles with the size of 4–6 nm, and a high Ni content (Ni:Al = 4) can be used to obtain the active Ni@NiAlOx catalyst. Under mild reaction conditions (90 °C, 2.0 MPa), the furfural conversion reached 93%, and furfuryl alcohol was formed with the selectivity of 70%. Under more severe reaction conditions (150 °C, 3.0 MPa), complete conversion of furfural was achieved, and cyclopentanol and tetrahydrofurfuryl alcohol were the main hydrogenation products.

THE MANUFACTURING PRODUCTS AND PARTS BY 3D-PRINTING METHOD FROM COMPOSITE FILAMENTS WITH HIGH METAL CONTENT

It is established that one of the most promising areas of development of modern engineering is the development of new technologies for rapid production (rapid manufacturing), the essence of which is the layered design of powder products based on CAD model, ie model whose three-dimensional geometry is described digitally by using solid modeling programs (AutoCAD, SolidWorks, Compas-3D, CATIA, ProE, etc.). The main advantages of using additive technologies, including 3D printing with filaments containing metals. The types of 3D printers that print metal are considered. The use of metal powders in 3D printing technologies is described. The main characteristics and properties of such metals, TI titanium, stainless steel SS, aluminum Al, copper Cu, FE iron and alloys based on them can be used as materials or additives in additive technologies. The advantages of their use over traditional technologies (casting, rolling, etc.) are described. The scheme of technological process of manufacturing products of industry mechanical engineering by a 3D printing with a high metal content is given. Each of the stages of the technological process is considered and described. Stainless steel metal powder was selected for the manufacture of filament and its chemical composition is investigated. Experimental studies have been conducted to determine the mechanical, thermophysical and rheological characteristics of polymeric materials used for the manufacture of 3D prints. On the basis of the studies, it is proposed to use Plastic powder as a connecting element in the filament. The design of the auger for supplying the material of the extrusion machine is designed and manufactured. The form of the extrusion head is developed and selected, which sets the diameter of the filament being made. A 3D printer for printing products and parts with a high metal content was selected and improved. Experimental studies of the wear of the 3D printer’s extruder nozzle on contact with the abrasive thread.

Chemical structure and nanomechanics relevant electrochemistry of solid-phase humic acid along a typical forest-river-paddy landscape section in eastern China and its environmental implications

Solid-phase humic acid (HAsolid) plays a critical role in global carbon cycle and redox biogeochemistry of topsoil, because of its unique physicochemical properties, including electrochemical property. In this study, topsoil HAsolid along a typical forest-river-paddy landscape section in eastern China was investigated in the aspects of electrochemical property, chemical structure and nanomechanics, and their relationship. Nano-size HAsolid particles were extracted from topsoil of paddy soil (PS-HAsolid), forest soil (FS-HAsolid) and riverside sediment (RS-HAsolid). Results showed that all the HAsolid were conductive and played an important role in conductivity of topsoil suspension. HAsolid contained both reversible and irreversible redox peaks, with redox activity of PS-HAsolid > RS-HAsolid > FS-HAsolid. Owing to limited humification, electron exchange capacity (EEC) values of topsoil HAsolid suspensions were modest (3.18–4.45 μmol e−g−1 HAsolid). Compared with RS-HAsolid and FS-HAsolid, PS-HAsolid showed higher aromaticity and higher degree of humification with simple and even nanomechanical property. Long-term cultivation (human activities) as well as high content of polyvalent metals in paddy soil were supposed to facilitate formation of aromatic carbon and improve humification of HAsolid. The results suggested that aromatic carbon and high humification degree of PS-HAsolid contributed to simple and even nanomechanics, which further optimized its electrochemical property. This study not only provides novel insight into the mechanism of HAsolid mediating electron transfer, but also inspires ideas for soil and environmental management with different purposes based on regulation of HAsolid.

Soil sodium, magnesium and potassium contents contribute to metals uptake and accumulation in leaves of Atriplex halimus in tailings ponds

Accumulation of tailings results in environmental risks due to the transfer of toxic elements through erosion and/or leaching. The most common reclamation strategy has been phytotechnologies application. Atriplex halimus is a species adapted to the soils developed over tailings. This study aimed to assess: i) the efficacy of A. halimus in phytoremediation of contaminated salt-affected soils, ii) how soil properties, especially macronutrients, affect metal uptake by A. halimus and iii) A. halimus ability to change soil characteristics. Four tailings ponds were sampled where A. halimus grew: three were reclaimed by marble waste, pig slurry and pig manure owing to lack of vegetation, and the other was spontaneously colonized. Different soil properties, metal fractions of rhizospheric and non-rhizospheric soils and metals absorption by A. halimus tissues were analyzed. Rhizosphere showed higher total organic carbon (TOC), inorganic carbon (IC), and soluble and total K than the non-rhizospheric soils. A. halimus had an accumulation capacity of metals mostly in leaves, followed by stems, with bioaccumulation factors for metals > 1. Our findings showed that besides the general soil properties, including pH, IC and TOC, electrical conductivity and the soil soluble fractions of Na, Mg and K were the key factors contributing to the metals accumulation in A. halimus leaves. A. halimus has been previously used and encouraged in phytoremediation strategies. However, owing to its high accumulation of metals in shoots, this species should be avoided in soils with high content of salts and heavy metals, since it could contribute to their spread.

Dielectric and optical evaluation of high-emissivity coatings for temperature measurements in microwave applications

In this work, several commercial high-emissivity coatings have been characterized in terms of emissivity, chemical composition and dielectric properties as a function of temperature, under microwave irradiation. Accurate knowledge of their response under exposure to microwaves provides new and crucial information about their practical usability for non-contact temperature measurements in microwave environments. Due to their high metallic content, some of the studied coatings exhibited unexpected microwave-triggered reactions that hindered their use up to the maximum temperature specified by the manufacturers. Emissivity and chemical analyses before and after the heating cycles confirmed the degradation of some of the samples predicted by dielectric measurements. This work illustrates how a careful characterization of optical and dielectric properties under representative operating conditions (temperature range, microwave exposure) is vital in order to select the appropriate reference coating to obtain reliable temperature measurements in microwave applications.

Influences of summer monsoon variations on the terrigenous influx, bioproductivity and early diagenetic changes in the southwest Bay of Bengal during Late Quaternary

The sediment core (MGS11/02), collected from the lower boundary of the Bay of Bengal (BoB) oxygen minimum zone (890 m) is studied to understand the influences of summer monsoon variations on the terrigenous sediment influx and its relation to bioproductivity and early diagenetic changes in the southwest BoB during the Late Quaternary. The high content of terrigenous controlled metals increased, kaolinite/chlorite increased, and K/Rb decreased after 19 cal kyr BP, indicating a simultaneous increase in the terrigenous influx and intensity of chemical weathering during this period. The variations in summer monsoon and land influx observed in the core sediments are also reflected in the sources of organic matter. High values of δ13C observed at 40 to 19 cal kyr BP suggests higher influence of marine organic matter and/or presence of C4 terrestrial plant. The negative shift of δ13C between 19 and 6 cal kyr BP could be the result of the change in terrestrial plant biomass to C3 photosynthesis and increased marine organic matter. Rock magnetic properties and redox-sensitive metals distribution suggests the prevalence of reduced environment during 52 to 19 cal kyr BP and oxic condition during 19 cal kyr BP to present. The low sedimentation during glacial period allowed sufficient time for pyritization which resulted in the low magnetic signals during 52 to 20 cal kyr BP and led to reducing conditions in the sediment interval. The δ15N values in the core sediments are suggesting the absence of denitrification in the water column during last 52 cal kyr BP. Previous studies suggest that the BoB is a geochemical ‘tipping point’ because the slight changes in water column denitrification by anthropogenic or climatic impact can accelerate BoB nitrogen contribution to the global nitrogen budget. This study indicates the absence of water column denitrification signals during last 52 cal kyr BP even though drastic climatic changes happened in the BoB in the Late Quaternary.

Micro- and Macroelements Content of Plants Used for Landfill Leachate Treatment Based on Phragmites australis and Ceratophyllum demersum

One of the key problems associated with the functioning of landfills is the generation of leachate. In order to reduce their negative impact on the environment, various treatment technologies are applied. Among them, solutions based on the use of phytotechnology deserve special attention. The aim of this study was to evaluate the impact of landfill leachate on the content of micro- and macroelements in plant material. The research was carried out in four municipal waste landfills located in Poland. Emergent macrophytes (P. australis) and submergent macrophytes (C. demersum) were used in this research. The migration and distribution of pollutants reaching the roots and shoots of P. australis from water solutions were also studied. The concentrations of heavy metals in the studied plants were low in all analysed cases. Higher metal contents could often be observed in roots rather than in shoots, but these differences were insignificant. The chemical composition of the studied plant samples was primarily related to the source of origin of the treated leachate (landfill), as clearly demonstrated by cluster analysis. In the conducted studies, no important differences were noted in the accumulation of the studied components between submergent plants (C. demersum) and emergent macrophytes (P. australis).

A Static Balance Model and Analysis of 430 Stainless Steel Produced by Basic Oxygen Furnace–Argon Oxygen Decarburization Furnace Process

Herein, a static mass and energy balance model of 430 stainless steel (SS) produced by the basic oxygen furnace (BOF)–argon oxygen decarburization furnace (AOD) process is established and verified by plant data. It is found that in the AOD, the energy input is efficiently utilized, the heat available for other uses is relatively low (4.0%), and the addition of SS scrap is limited. The high carbon content of dephosphorization hot metal (DPHM) and post‐combustion ratio (PCR) in AOD are conducive to promoting the recycling of SS scrap. In contrast, when the carbon content of DPHM and PCR is low, it is necessary to add an exothermic agent to the furnace. Due to the saving of nickel‐containing raw materials and China's high proportion of thermal power, the carbon emissions and energy consumption per ton 430 SS produced by the BOF–AOD process are 3131 kg‐CO2 and 24 161 MJ, which is much lower than per ton 304 SS produced by the electric arc furnace (EAF)–AOD process. Meaning the former is more conducive to the promotion of energy conservation and emission reduction.

Metals in green mussels: is there any effect on their reproduction? A preliminary study of Muara Angke, Jakarta Bay

Water pollution and its impacts on ecosystems in Jakarta Bay have been extensively studied over the years. Muara Angke is known anecdotally as one of the most heavily polluted parts of Jakarta Bay. In the context of the ongoing debate regarding contamination in the area, we present data on the concentration of metals in green mussels Perna viridis, one of the most popular edible commodities in Jakarta Bay. Histological examination of P. viridis gonads was also performed to demonstrate the direct effects of possible contamination on reproduction in this organism. The concentration of arsenic (As), copper (Cu), nickel (Ni), zinc (Zn), and mercury (Hg) exceeded the upper limits of heavy metal contents in marine biota, whilst only As exceeded the maximum limits of heavy metal contents in processed food, both limits set by Indonesian government. Although the histological observation of gonad tissue after being stained with hematoxylin and eosin revealed some pathologies, high contents of metals in mussels collected in Muara Angke seemed not to affect their reproduction. Ecologically, direct impacts on the tissue of P. viridis will provide vital information needed to predict the health of the species in Muara Angke and the sustainability of the population.

NEW HORIZONS PROCESSING OF TECHNOGENIC WASTE OF THE COPPER INDUSTRY

At the present time, in the mining and metallurgical industry, there are trends in the processing of man-made waste that have accumulated over the course of many years. Since the world's reserves of ore deposits with a high initial content of non-ferrous metals and easily processed ores are currently practically depleted. This is due to a decrease in the volume of processing of conditioned ores and the involvement in the development of industrial waste, refractory ores and off-balance from low-grade dumps. High prices for metals on the world market create a favorable environment for the development of technologies for the extraction of precious metals involving the processing of mineral resources of technogenic origin. The work studies the mineralogical composition of industrial waste from the copper industry in the conditions of JSC "Almalyk MMC", determined the effectiveness of methods for the selective extraction of platinoids and paid attention to the methods of dissolution, reduction of platinum metals and methods of their purification from various impurities. Based on the study of this topic and the analysis of the results of the research, the authors proposed an optimal technology and complex methods for extracting platinum, palladium and rhodium from industrial waste using selective methods suitable for each metal separately using hydrometallurgy and pyrometallurgy. Hydrometallurgical methods have been developed for the purification of palladium, platinum and rhodium with treatment, respectively, with formic, citric and nitric acids. As a result of the developed technologies, the possibility of complex extraction of platinum group metals from industrial waste has been achieved. In this case, the end-to-end extraction of all platinoids is over 80%.

Effects of S and Al on K Migration and Transformation during Coal and Biomass Co-combustion.

The co-combustion of biomass and coal has both environmental and economic benefits in terms of pollutants and greenhouse gas emissions. However, one of the key factors affecting the feasibility of this technology is the ash deposition and corrosion caused by the high alkali metal content of biomass, especially K. After the addition of elemental S to corn stalk/Xiaolongtan lignite blended fuel and Al2O3 to corn stalk/Datong lignite, combustion experiments were carried out in a tubular furnace to explore the effects of S and Al in coal on K migration and transformation. The experimental results show that when S/K < 6, an increase in the S/K ratio inhibited the release of K. When S/K > 6, the sulfation become saturated, and an increase in S promoted the release of K. When S/K = 6, the higher the temperature was, and the more obvious the inhibitory effect on the release of K was. Increasing the S/K ratio not only increased the CaSO4 content of the ash but also increased the content of water-soluble K compounds, such as K2SO4, and decreased the contents of acid-soluble K compounds and insoluble K compounds, such as KAlSi3O8. After Al2O3 was added, as the Al/K ratio increased, the K release rate gradually decreased. When the sample with Al/K = 2.5 and the original samples were burned at 600–700 °C, the difference in the K release rates of the two samples was relatively small. When the temperature was higher than 700 °C, the higher the temperature was, and the greater the difference in the K release rates of the samples was, which indicates that a high temperature promotes the formation of aluminosilicates containing K.

Confined transformation of trifunctional Co2(OH)2CO3 nanosheet assemblies into hollow porous Co@N-doped carbon spheres for efficient microwave absorption

Carbonaceous-magnetic composites are the most appealing candidates for electromagnetic wave absorption, and creating hollow interiors and nanopores in the composites is commonly recognized as an essential strategy to reinforce their overall performances. Herein, we propose a spatial confinement strategy mediated by Co2(OH)2CO3 nanosheet assemblies for achieving highly dispersed Co nanoparticles into hollow porous N-doped carbon shells (HP-Co@NCS). Systematic multi-technique characterizations indicate that the Co2(OH)2CO3 nanosheet assemblies simultaneously play a trifunctional role during the synthesis, including Co source, template of the hollow interior cavities, and micro-/mesopore porogen. The chemical composition can be modulated by simply varying the ratio of Co2(OH)2CO3 and carbon source (dopamine). The optimized HP-Co@NCS absorber exhibits a well-defined hollow structure and unprecedented high porosity (specific surface area of 742 m2 g−1) even with a high metallic Co content of 35.8 wt%. These profitable structural characteristics can facilitate incident EM waves penetrating the absorber's interior and promoting multiple reflections and scattering. Therefore, the HP-Co@NCS absorber exhibits efficient microwave absorption ability with a minimum reflection loss of −39.0 dB at a thin thickness of 2.5 mm and an effective absorption bandwidth up to 5.5 GHz (12.5–18.0 GHz) at a thin thickness of 2.0 mm. This work provides a new methodology to design advanced carbonaceous-magnetic composite materials with hollow porous structures for microwave absorption.

Plant community data from a statewide survey of paired serpentine and non-serpentine soils in California, USA.

Soils derived from ultramafic parent materials (hereafter serpentine) provide habitat for unique plant communities containing species with adaptations to the low nutrient levels, high magnesium : calcium ratios, and high metal content (Ni, Zn) that characterize serpentine. Plants on serpentine have long been studied in evolution and ecology, and plants adapted to serpentine contribute disproportionately to plant diversity in many parts of the world. In 2000-2003, serpentine plant communities were sampled at 107 locations representing the full range of occurrence of serpentine in California, USA, spanning large gradients in climate. In 2009-2010, plant communities were similarly sampled at 97 locations on nonserpentine soil, near to and paired with 97 of the serpentine sampling locations. (Some serpentine locations were revisited in 2009-2010 to assess the degree of change since 2000-2003, which was minimal.) At each serpentine or nonserpentine location, a north- and a south-facing 50 × 10 m plot were sampled. This design produced 97 "sites" each consisting of four "plots" (north-south exposure, serpentine-nonserpentine soil). All plots were initially visited three or more times over two years to record plant diversity and cover, and a subset were revisited in 2014 to examine community change after a drought. The original question guiding the study was how plant diversity is shaped by the spatially patchy nature of the serpentine habitat. Subsequently, we investigated how climate drives plant diversity at multiple scales (within locations, between locations on the same and different soil types, and across entire regions) and at different levels of organization (taxonomic, functional, and phylogenetic). There are no copyright restrictions and users should cite this data paper in publications that result from use of the data.