High Concentrations Of Cr Research Articles

Geochemical Assessment of Some Trace Elements in Selected Locations at Thi-Qar Governorate Soil, Southeast Iraq

Trace elements (Co, Cr, Mn, Mo, Ni, Rb, Th, U, and V) in surface soil of Al-Aslah (NH1), Nasiriyah refinery (NH2), Gharraf (NH3), and Tall Al-Laham (NH4) at Thi-Qar governorate, southeast Iraq, were studied. The study aims to detect their distribution and pollution levels to reduce the subtracted from industrial sources and avoid using contaminated areas for agricultural purposes before the soil treatment process. Inductivity Coupled Plasma Mass Spectrometry (ICP-MS) technique was used to determine the concentrations of these elements, and the results showed that there is a high concentration of Cr, Ni, Mo, and Mn in the soil of the study area, which exceeded the international levels compared with other elements (Co, Th, U, and V). The Geo accumulation index (I geo) values showed that the soil area was classified as low contamination in all sites and for all trace elements except for Mo, which is polluted in Al-Gharraf and strongly polluted in Tall Al-Laham. The values of the enrichment factor (EF) were indicated to be minimal enrichment of (Mn and V) in all sites and moderate enrichment of (Co) in all sites except in the Gharraf soil sample, which is considered as minimal enrichment. At the same time, it suffers from significant enrichment of (Cr) in all sites. The values of contamination factor (CF) showed extreme contamination of Cr and Ni in all sites due to the oil industry (Nasiriyah refinery), except for Ni in the Gharraf soil sample, which is considered as high contamination and moderately contamination with Co in all sites, and low contamination with Mn and V. The main cause of the increasing trace element concentrations in the study area that the samples located in industrial sites where trace elements are one of the waste products from fuel combustion from the oil fields and the waste of the brick factories near the study area, also the nature of the study area soil which is clay soil that absorb the trace elements on its surfaces.

Soil and environment quality in artisanal small-scale mining areas in western Côte d’Ivoire

Artisanal small-scale gold mining activities grow in different regions of Côte d’Ivoire, causing enormous soil and environmental damages. This study was conducted in the vicinity of illegal artisanal small-scale gold mining zones to investigate soil quality using environmental assessment tools, mainly pollution and geochemical accumulation indexes. The mining spoil from artisanal pits was sampled directly between 0 and 20 cm, collecting 500 g of soil per sampling point. Sub-samples of soil were analyzed for multi-element using X-ray fluorescence technique. The results of the XRF analysis revealed higher trace element levels at some sampling points than the recommended levels. High arsenic concentrations were identified at three sampling sites: cavally sites with 7.09 and 16.08 mg kg-1 and Zérégbo with 9.57 mg kg-1. Moreover, significant concentrations of Cu and Pb were found at the Cavally site whilst Singouiné and Zérégbo showed high concentrations of Co and Cr. The study, globally, revealed the environmental hazards caused by the organized artisanal mining.

Characterization of Red, Pink, Orange, and Purple Gem-Quality Spinel from Four Important Areas

Spinel is a precious stone with a long history. In ancient societies spinel was considered to be an imitation of ruby. With the depletion of ruby mineral resources, gem—grade spinel has attracted more and more attention from consumers. In the last decade, as the popularity of spinel in the global colored gem market continues to rise, plenty of domestic and foreign jewelry brands have launched spinel based jewelry. This study takes spinels from Burma, Vietnam, Sri Lanka, and Tanzania as its research objects and performs a series of tests to obtain their gemological characteristics, spectral characteristics, and chemical composition, with the aim of comparing the differences between spinels with different colors from different areas and exploring the chromogenic mechanism of spinels. Only Burmese red spinels have a typical Cr spectrum. The types of inclusions and the contents of trace elements are the main differences between spinels from the four areas. Burmese spinel is characterized by an octahedral negative crystal filled with dolomite or a mixture of dolomite and calcite. Magnesite is present in Sri Lankan spinels, and dolomite is present in Tanzanian spinel. Dislocation systems and the presence of titanite and talc inclusions are strongly indicative features of Vietnamese spinel. Sri Lankan spinel is characterized by abundant gas–liquid inclusions, such as the beaded healing fissure. The trace element contents of the four areas are different. Burmese spinel is poor in Fe and Zn (Fe: 135.68–3925 ppm; Zn: 338.58–1312 ppm), while Burmese red spinel is rich in Cr (up to 7387 ppm). Vietnamese spinel is rich in Fe (3669.63–19,425 ppm) and poor in Ti content (<89 ppm), while Tanzanian spinel is rich in Zn (5129.96–7008 ppm). High content of Cr + V can lead to the red color in spinel, and the contents of Cr and V change obviously with color. Spinels appear red when Cr content is higher than V, while spinels appear orange when V content is higher than Cr. The red, pink, and orange spinels are colored by Cr3+ and V3+, showing a wide absorption band centered at 400 nm and 550 nm. Fe plays a dominant role in purple spinels. The purple spinel is colored by Fe3+ and Fe2+.

Distribution and migration of uranium, chromium, and accompanying metal(loid)s in soil-plants system around a uranium hydrometallurgical area

The extraction and utilization of uranium (U) ores have led to the release of significant amounts of potentially toxic metal(loid)s (PTMs) into the environment, constituting a grave threat to the ecosystem. However, research on the distribution and migration mechanism of U, chromium (Cr), and their accompanying PTMs in soil-plant system around U hydrometallurgical area remains insufficient and poorly understood. Herein, the distribution, migration, and risk level of PTMs were evaluated in soil and plant samples around U hydrometallurgical area, Northern Guangdong, China. The results demonstrated that the maximum content of U and Cr found in the analyzed soils were up to 84.2 and 238.9 mg/kg, respectively. These values far exceed the soil background values in China and other countries. The highest content of U (53.6 mg/kg) was detected in Colocasia antiquorum Schott, and the highest content of Cr (349.5 mg/kg) was observed in Pteridium aquilinum, both of which were enriched in their roots. The risk assessment of PTMs demonstrated that the study area suffered from severe pollution (PN > 3), especially from U, Cr, Th, and As, suggesting the non-negligible anthropogenic impacts. Hence, in light of the significant ecological hazard posed by the U hydrometallurgical area, it is imperative to implement appropriate restoration measures to ensure the human health and maintain the stability of the ecosystem.

An investigation on nitrogen uptake and microstructure of equimolar quaternary FeCoNiCr high entropy alloy after active-screen plasma nitriding

Under nitrogen diffusion treatments, N-expanded austenite (γN) can form at the surface of self-passivating Fe-Cr, Ni-Cr, and Co-Cr alloys at low temperatures, which provides beneficial hardening and enhancements in wear resistance without reducing corrosion resistance. Given the wide research interests in multicomponent equimolar alloys, an equimolar quaternary FeCoNiCr high entropy alloy (HEA) was investigated after active-screen plasma nitriding at 430–480 °C in this study. Firstly, the formation of γN-FeCoNiCr case at 430 °C was demonstrated with the bright case appearance after metallographic etching, the lattice expansion under XRD, the FCC electron diffraction patterns and the shear bands under TEM. Secondly, the thick treatment cases at ∼9–16 μm first indicated that N interstitial diffusion was not sluggish in the FeCoNiCr surface. Thirdly, analogous to stainless steels, the onset of dark regions in the etched γN-FeCoNiCr case was owing to the formation of a cellular mixture of CrN + γ-(Fe, Co, Ni) nano-lamellae at elevated treatment temperatures. The residual bright regions in γN-FeCoNiCr at 480 °C showed ∼1–3 nm CrN nanoprecipitates with no substantial Cr segregation. Additionally, a significant nanocrystalline layer was seen at the topmost surface at 480 °C, which is most likely associated with the high substrate Cr content.

Hydrophobic deep eutectic solvents as the green media for highly efficient extraction of Cr(VI) over a broad pH range and low oil-water ratio

The occurrence of Cr(VI) ions in aquatic ecosystems poses serious public health risks, making the development of effective removal technology for Cr(VI) ions urgent. This study presents a green and effective method for extracting Cr(VI) ions using hydrophobic deep eutectic solvents (HDESs) composed of tetran-octyl ammonium bromide and carboxylic acids. The results show that the extraction efficiency of [N8888][Br]-C6OOH(1:2) for Cr(VI) is as high as 98.2 % for high concentration of Cr(VI) (500 mg⋅g−1) with a low oil–water ratio of 1:66. Surprisingly, these HDESs demonstrate remarkable efficacy in extracting Cr(VI) ions over a broad pH range and at a low oil–water ratio, even in the presence of multiple competing ions. A serious of kinetic, thermodynamic, and spectroscopic experiments suggested that the extraction mechanism of Cr(VI) ions is a synergistic dissolution diffusion and ion exchange. As a proof of concept, we have successfully demonstrated the application of prepared HDESs for extracting trace amounts of Cr(VI) ions from H3PO4 solutions with varying mass fractions, and the extraction process resulted in a Cr(VI) removal rate that achieved 99.7 %. Furthermore, the extraction performance HDESs for Cr(VI) ions remained nearly unchanged after eight cycles of continuous extraction and regeneration. Impressively, a precipitation method was also employed to convert the isolated Cr(VI) ions into valuable BaCrO4. The research findings provide valuable insights for the development of highly efficient Cr(VI) extractants.

Reduction and Removal Mechanism of Cr(VI) by a Novel Penicillium Rubens LR6

Bioreduction of Cr(VI) is an efficient and environmentally friendly remediation method. In this study, we isolated and screened a strain of Penicillium rubens LR6 that could tolerate to Cr(VI) and investigated its mechanism for removing Cr(VI). We ascertained the factors affecting the ability of strain to remove Cr(VI) through batch experiments. The results revealed that the strain could effectively remove high concentrations of Cr(VI) and exhibit excellent removal efficiency under different environmental conditions. The removal of Cr(VI) by the strain could be accurately explained by the exponential decay equation, where approximately 9.45% of the Cr was immobilized on the microorganisms. We further investigated the ability of different cell fractions to remove Cr(VI) and found that bioreduction was the primary mechanism involved. This was supported by SEM and TEM analyses, which showed the presence of Cr on the surface and inside the cells. Additionally, XPS analysis confirmed the presence of both Cr(VI) and Cr(III) on the cell surface, and FTIR analysis suggested the involvement of amino, carboxyl, and hydroxyl groups in the reduction and fixation of Cr(VI) on the cell surface. The findings offer a novel technique for bioremediation of Cr(VI)-contaminated wastewater in weakly acidic to weakly alkaline and high salinity environments, providing potential solutions for remediating chromium-contaminated environments.

Probabilistic Assessment of the Intake of Trace Elements by Consumption of Red Deer (Cervus elaphus) and Wild Boar (Sus scrofa) Meat

The aim of this work was to study the nutritional value of game meat through the fulfillments of Dietary Reference Intakes (DRI) for trace elements (Co, Cr, Cu, Fe, Ni, Se, and Zn). A probabilistic model (@Risk) was developed based on the consumption data of hunter-consumers obtained from a previously published survey. Two game species widely consumed in Europe were selected: red deer (Cervus elaphus) and wild boar (Sus scrofa). Red deer muscle had the highest content of Cr (0.25 mg/kg) and Zn (44.3 mg/kg) and wild boar muscle recorded the highest Cu (2.23 mg/kg), Ni (0.60 mg/kg), and Se (0.19 mg/kg), showing statistically significant differences between the two species for these elements. No statistically significant differences were found for Fe between both game species (red deer: 52.9 mg/kg and wild boar: 53.3 mg/kg). Co content in this kind of meat was negligible for both species. The results obtained from the simulation of the probabilistic model with red deer indicated that a consumption once per week of this meat fulfills Cr, Fe, and Zn DRIs for the 95th percentile in hunter-consumers. Regarding wild boar, the values obtained also fulfill the Fe DRI and were between 61 and 75% for the rest of the trace elements analyzed.

Ten-Year Recycling of Vanadium Alloy in Fusion Reactors

Low-activation characteristics and dominant radioactive isotopes limiting materials recycling were analyzed for a fusion-reactor-grade vanadium alloy, NIFS-HEAT-2. In order to reduce contact dose rate after use in fusion reactors, purification of the base metal vanadium was examined by chemical aqueous separation, electron-beam vacuum melting and zone refining, focusing on the removal of the dominant high-activation impurities, such as Co, Cu, Fe, Nb, Ni and Mo. Based on the measured impurity levels, remote recycling of vanadium alloy is possible within ten years after use in fusion reactors under operation condition with 100 dpa irradiation. Early quasi-hands-on recycling requires further purification and re-design of alloy composition especially with low Ti and high Cr content. The present paper discusses status of material R&Ds for the ten-year recycling and impact on operation of fusion reactors.

Enhanced mechanical properties and strengthening mechanism of Cu-Ni-Si alloy with trace chromium addition

Cu-3Ni-0.7Si-xCr-0.05Mg (x = 0.1 and 0.4) (wt% nominal composition) alloys were fabricated to investigate the effect of Cr contents on properties evolution and precipitation behavior of Cu-Ni-Si alloy. The results of the property analysis show that trace addition of 0.1 wt% Cr element contributes a better strength (ultimate tensile strength of 823 MPa) after single cold rolling and aging treatment. The precipitation behavior is characterized by transmission electron microscopy. It is found that nanoscale FCC structural Cr precipitates shift into submicron Cr3Si particles with Cr content increasing from 0.1 wt% to 0.4 wt%. Meanwhile, such superior formation of Cr3Si particle decreases the fraction of δ-Ni2Si owing to quick consumption of Si element from Cu matrix. Further quantitative analysis of various strengthening mechanisms reveals that the changed precipitation behavior notably affects their strengthening contribution to Cr contained alloys, resulting in an increase of more than 5.6% in the Orowan-Ashby mechanism. Surprisingly, in the case of the aging state at a temperature of 460 °C for a duration of 2 h, it is confirmed that although a much larger strengthening effect origins from nanosized δ-Ni2Si precipitate, the strength variation relies more on the Cr precipitation. That is, the lower strength at higher Cr content is mainly caused by the lower strengthening effect from Cr element related phases. In addition, the effect of the addition of trace Cr element on the operating mechanism on conductivity is also clarified. The results are expected to provide an appropriate content of Cr element and a dependable processing theory guidance for improving the comprehensive properties of the Cu-Ni-Si alloys.

Petrological and Geochemical Constraints on the Origin of Strongly Peraluminous Granitoids from the Triassic Guangtoushan Pluton in South Qinling

AbstractAs an important part of the early Mesozoic granites in the South Qinling tectonic belt (SQTB), the Guangtoushan pluton provides a material basis for research on the composition of magma sources and the effects of peritectic assemblage entrainment (PAE) on the changes in the granite composition. As shown by the results of LA‐ICP‐MS zircon U‐Pb dating, the Guangtoushan pluton was emplaced during the Late Triassic (214–212 Ma) and was formed in the post‐collision stage between the SQTB and the Yangtze plate. The collected samples had high SiO2 content and low Cr and Ni contents, indicating that the magmas did not undergo significant crust‐mantle mixing during their evolution. The Guangtoushan granitoids were distributed along the trend line of magmatic fractional crystallization in the F–An–Or diagram. This result, combined with the relatively homogeneous Sr‐Nd isotopic composition, implies that the Guangtoushan pluton underwent slight assimilation and contamination. As can be inferred from the comparison between the compositions of the Guangtoushan granitoids and various fluid‐absent experimental melts, the magma sources of the Guangtoushan granitoids contain a variety of materials, such as graywackes, pyroclastic graywackes, and pelites and are not derived from lower crustal mafic rocks. The correlation between the maficity and the major and trace elements further indicates that the strongly peraluminous granitoids from the Guangtoushan pluton was formed by the partial melting of biotite‐bearing crustal rocks and its magmatic evolution was accompanied by the entrainment of clinopyroxenes and accessory minerals.

Efek Pre-Roasting Terhadap Parameter Kinetika Leaching Cr dari Limonit

Hydrometallurgical processes such as leaching of limonite ore to extract valuable metals including Ni and Co are often non-selective, including other metals in the leachate product. The leaching behavior of Cr from the chromite mineral contained in limonite ore is of concern due to the high Cr content of the leachate effluent. The pre-roasted process is frequently used to pre-treat limonite to increase the precious metal content. This study aims to determine the leaching behavior of Cr and the effect of pre-roasting on its kinetic parameters. The pre-roasting process was carried out at 280 and 610 oC for 4 hours. Observation of Cr leaching behavior was carried out in the leaching temperature range of 30-90 oC for 0-120 minutes using sulfuric acid solvent. The highest Cr recovery was achieved in pre-roasted ore leaching at 610 oC with leaching operating conditions of 2 M sulfuric acid, solid-liquid ratio of 5 g/50 mL, 200 rpm, for 120 minutes, at a leaching temperature of 90 oC, under these conditions Cr recovery reached 53.16%. The higher the roasting temperature, the lower the activation energy required for the leaching process. Cr leaching from raw and pre-roasted ore is controlled by the diffusion process through the ash layer with activation energies (EA) of 21.41, 18.64, and 14.71 kJ/mol for raw ore, pre-roasted ore 280 oC, and pre-roasted ore 610 oC, respectively. The comparison of kinetics data from several roasting products for atmospheric leaching feeds will provide industry with information to integrated pyro-hydrometallurgical process to increase Cr production from laterite.

Eoarchean ultramafic rocks represent crustal cumulates: A case study of the Narssaq ultramafic body, southern West Greenland

Several ultramafic enclaves found within the Eoarchean Itsaq Gneiss Complex (IGC) in southern West Greenland have previously been interpreted as representing mantle relicts. However, as Archean ultramafic rocks are frequently overprinted by metamorphism and late-stage metasomatism, it can be difficult to distinguish between peridotites representing mantle residues or primitive crustal cumulates. Therefore, detailed evaluation of individual Eoarchean peridotite occurrences is required to better constrain their origin. Here, we present new petrological observations and geochemical data for the >3.8 Ga Narssaq Ultramafic Body (NUB) in the IGC of SW Greenland. The NUB ultramafic rocks have high FeOt and Cr contents with flat chondrite-normalized trace element patterns and positive Cr-Mg correlations, which distinguish them from mantle rocks. In addition, the variations in olivine and spinel compositions are consistent with a fractional crystallization process. The above geochemical features suggest that the ultramafic rocks of NUB cannot be explained as mantle residues. Instead, their major element compositions are related to the spatially associated tholeiitic amphibolites, indicating that these ultramafic rocks likely represent crustal cumulates derived from high-Mg magmas. This interpretation is supported by thermodynamic modeling using MELTS, which shows that the compositions of the ultramafic rocks in the NUB can be reproduced via fractional crystallization of local high-Mg tholeiitic basalts, involving the accumulation of olivine, spinel, and possibly clinopyroxene, in conjunction with trapped melt. The NUB ultramafic rocks can thus form as a natural consequence of fractional crystallization of regular highly magnesian tholeiitic magmas, making a cumulate origin the simplest explanation for Eoarchean peridotites in general. This also implies that the formation of the NUB did not involve refertilization of subduction-like components as previously assumed, and thus did not require subduction to have taken place in the Eoarchean.

Bulk composition and O–C isotope constraints on the petrogenesis of Richat carbonatites (Mauritania)

In the northwestern Mauritanian Taoudeni Basin, the famous Richat structure is the only occurrence known of carbonatite. Despite several studies on this unique geological feature, the mineralogy and petrogenesis of the Richat dome carbonatites are underdocumented.Major, trace element whole rocks and carbon-oxygen isotope data are reported for Cretaceous carbonatites from Richat dome in Mauritania. More than 45 carbonatite dykes have been mapped, they are oriented N°15-N°80. Based on color, four groups have been identified, dark, gray, red breccia, and brown carbonatites. They exhibit different mineralogical and texture characteristics. The studied carbonatites are mainly composed of dolomite, calcite, and ankerite, with lesser amounts of apatite and quartz. Accessory minerals such as pyrochlore, spinel, pyrite, chalcopyrite, magnetite, hematite, baryte, phlogopite, and zircon are also present. Other REE-bearing minerals (britholite, monazite, and bastnaesite) were revealed by X-ray diffraction.Three types of carbonatites are identified: magnesiocarbonatites (dominants), ferrocarbonatites and calciocarbonatite. The presence of spinel and pseudomorphed olivine, as well as high contents of Ni (380 ppm), Co (34 ppm), and Cr (840 ppm) in the dark and brown carbonatites, suggests that these rocks are the result of the low-degree partial melting of a spinel-bearing peridotite. Furthermore, the Zr/Hf (48–80) and Nb/Ta (26–48) ratios show significantly higher values than those observed in the primitive mantle, they are interpreted as formed by partial melting of the metasomatized mantle. The high values of δ18O in addition to the presence of baryte, ankerite, and quartz in the Richat carbonatites suggest that they are the result of secondary processes involving a low-temperature fluid-rock interaction.The carbonatites from the Richat dome are enriched in LREE (La = 258–1070 ppm) and LILE as Sr, Ba, Th, U, and depleted in HREE (Yb = 2–14 ppm) and HFSE such as Zr, Hf, Ti. These characteristics are like those of Cretaceous peri-atlantic alkaline carbonatites such as Barra do Itapirapua in Brazil, Ondurakorume and Kalkfeld in Namibian, lupangola in Angola, and Twihinate in Morocco. Reactivation of a deep pan-African NNE-SSW lineament would have been a fundamental factor in the formation of the Richat carbonatites.

Biosorption potential of Purpureocillium lilacinum biomass for chromium (VI) removal: isolation, characterization, and significance of growth limiting factors

Chromium (VI) is known to be harmful element that commonly found industrial waste, mining activities, and wastewater discharges from various industries. When released into the environment, Cr (VI) can contaminate soil, water, and air, posing a serious threat to living organisms. Aiming to Cr decontamination, this work was framed to isolate the fungal species having high Cr tolerance capacity and to exploit as bio-sorbent for the removal of Cr (VI) from aqueous solutions by biosorption. Among the fungal species isolated from the Cr (VI) contaminated soil sample, the filamentous fungus of Ophiocordycipitaceae family, Purpureocillium lilacinum was identified using molecular sequencing technique, showed maximum tolerance against Cr (VI) with a tolerance index of 1.19 ± 0.23. Further, Plackett Burman Design was applied to investigate for ascertaining the significance of different carbon and nitrogen sources on P. lilacinus growth, as well as the influence of environmental factors, such as pH, temperature, and Cr (VI) concentration. The results explicated that glucose was the most preferred carbon source for P. lilacinus, while yeast extract was the most preferred for nitrogen source. The optimum pH value and temperature were found to be 6.0 and 26 °C, respectively. In addition, P. lilacinus isolate was identified to survive in high concentrations of Cr (VI), indicating its potential for employing effective bioremediation of chromium-contaminated site.

Sigma‐Phase Distribution in 2507 Super Duplex Stainless Steel Continuous Casting Slabs

The sigma‐phase distribution in a 2507 super duplex stainless steel continuous casting slab is analyzed using microstructural analyses and thermodynamic calculations. The sigma phase contains high Cr and Mo contents, and precipitates along the phase boundary between austenite and ferrite and grows toward the interior of the ferrite phase in the continuously cast slab. The sigma‐phase fraction at the center of the width direction is higher than that in the one fourth width. Furthermore, the sigma‐phase fraction at the center of the thickness direction is higher than those at the upper and lower surfaces, which is due to the lower cooling rate at the center. The Brinell hardness (HB) at the center increases to 313 HB with an increasing sigma‐phase fraction. The sigma‐phase fraction at the one fourth thickness near the lower surface is higher than that at the one fourth thickness near the upper surface at the same cooling rate. Additionally, Mo and Ni are severely segregated in this zone. A higher Mo content influences the precipitation and stabilization of the sigma phase. Furthermore, Scheil–Gulliver calculations indicate that compositional segregation results in an increase in the sigma‐phase precipitation temperature range.

Use of agro-industrial wastes for the removal of chromium(VI) from contaminated water: an electrochemical exploration

Bioadsorption with agro-industrial wastes is a viable technique for the removal of heavy metals from wastewater. This work assessed the capacity as removal agent chromium(Cr)(VI) of walnut, coffee, and moringa shells. Three equilibrium experiments were carried out, the effect of Cr(VI) concentration, changes in pH solution, and desorption degree; the Cr(VI) content was determined by UV–vis spectroscopy; and an electrochemical analysis was performed. The biomaterials showed an adsorption capacity from highest to lowest as follows: walnut > coffee > moringa, recording up to 31 mg/g. At slightly acidic pH the materials presented their highest adsorption capacity with 98% of Cr(VI) retained; and, the lowest desorption of Cr(VI) was recorded with CaCl2, while the highest Cr concentration in moringa was desorbed with HCl, while NaOH had its maximum desorption with coffee and walnut shells. Electrochemically, the three biomaterials presented a high potential to be used as biosorbents because they present the Cr(VI)/Cr(III) redox couple, although coffee presented the highest efficiency, followed by walnut and moringa shells.

Unravelling the Impact of Metal Dopants and Oxygen Vacancies on Syngas Conversion over Oxides: A Machine Learning-Accelerated Study of CO Activation on Cr-Doped ZnO Surfaces.

As a critical component of the OX-ZEO composite catalysts toward syngas conversion, the Cr-doped ZnO ternary system can be considered as a model system for understanding oxide catalysts. However, due to the complexity of its structures, traditional approaches, both experimental and theoretical, encounter significant challenges. Herein, we employ machine learning-accelerated methods, including grand canonical Monte Carlo and genetic algorithm, to explore the ZnO(1010) surface with various Cr and oxygen vacancy (OV) concentrations. Stable surfaces with varied Cr and OV concentrations were then systematically investigated to examine their influence on the CO activation via density functional theory calculations. We observe that Cr tends to preferentially appear on the surface of ZnO(1010) rather than in its interior regions and Cr-doped structures incline to form rectangular islands along the [0001] direction at high Cr and OV concentrations. Additionally, detailed calculations of CO reactivity unveil an inverse relationship between the reaction barrier (Ea) for C-O bond dissociation and the Cr and OV concentrations, and a linear relationship is observed between OV formation energy and Ea for CO activation. Further analyses indicate that the C-O bond dissociation is much more favored when the adjacent OVs are geometrically aligned in the [1210] direction, and Cr is doped around the reactive sites. These findings provide a deeper insight into CO activation over the Cr-doped ZnO surface and offer valuable guidance for the rational design of effective catalysts for syngas conversion.

Arbuscular mycorrhizal fungi alter rhizosphere fungal community characteristics of Acorus calamus to improve Cr resistance.

To investigate changes in fungal community characteristics under different Cr(VI) concentration stresses and the advantages of adding arbuscular mycorrhizal fungi (AMF), we used high throughput sequencing to characterize the fungal communities. Cr(VI) stress reduced rhizosphere soil SOM (soil organic matter) content and AMF addition improved this stress phenomenon. There were significant differences in fungal community changes under different Cr(VI) concentrations. The fungal community characteristics changed through inhibition of fungal metabolic ability, as fungal abundance increased after AMF addition, and the fungal diversity increased under high Cr(VI) concentration. The dominant phyla were members of the Ascomycota, Basidiomycota, Mortierellomycota, and Rozellomycota. Dominant groups relevant to Cr resistance were Ascomycota and Basidiomycota fungi. Moreover, Fungal community characteristics were analyzed using high-throughput sequencing of the cytochrome c metabolic pathway, NADH dehydrogenase, and NADH: ubiquinone reductase and all these functions were enhanced after AMF addition. Therefore, Cr(VI) stress significantly affects fungal community structure, while AMF addition could increase its SOM content, and metabolic capacity, and improve fungal community tolerance to Cr stress. This study contributed to the understanding response of rhizosphere fungal community in AMF-assisted wetland phytoremediation under Cr stress.

Effect of Cr and Y on the microstructure and mechanical properties of Fe-Cr-Al alloys during corrosion-aging in superheated steam at 500 °C

The α-α’ phase separation of Fe-Cr-Al alloys during long-term service at 475–500 °C may lead to the increase of strength and hardness and the decrease of ductility, which will limit the application of Fe-Cr-Al alloys as accident tolerant fuel (ATF) cladding material. The mechanical behavior and microstructure evolution of Fe-12Cr-5Al, Fe-12Cr-5Al-0.01Y, Fe-20Cr-5Al and Fe-20Cr-5Al-0.02Y (wt%) alloys in 500 °C superheated steam for 2000 h have been investigated by tensile test, Vickers hardness measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), three-dimensional atom probe (3DAP) and thermodynamic calculations. Results show that increasing the Cr content may refine the grain and improve tensile strength of the alloy, while adding trace Y has negligible effect on the grain size and tensile strength of the alloy; the corrosion-aging hardening of 20CrY and 20Cr alloys is attributed to the α-α’ phase separation, which is closely related to the high content of Cr in the alloy. The addition of trace Y promotes the nucleation and growth of α’ phase in alloys with the content of 20%Cr during the corrosion-aging process but has insignificant influence on the mechanical properties of the alloy.