Migration Of Cr Research Articles

Fe (hydr)oxides and organic colloids mediate colloid-bound chromium mobilization in Cr(VI) contaminated paddy soil

The association of chromium (Cr) with colloidal particles transport in contaminated sites can affect hexavalent chromium (Cr(VI)) migration and transformation, which is an important mechanism for Cr pollutants in soil and groundwater systems. Here, we investigated colloid and particle-bound Cr migration and transformation effects on rice Cr accumulation during different rice growth stages and different redox conditions in Cr(VI) contaminated soil by pot experiment. Results showed that 13–29% of soil Cr was water dispersible colloid-bound (100–1000 nm) form during rice growth. Using transmission electron microscopy - energy dispersion spectroscopy and asymmetric flow field - flow separation, we identified colloid-bound organic matter (OM) and iron (Fe), most likely in the form of Fe (hydr)oxides - clay composites, as the primary Cr carrier. Specifically, colloid-bound Cr was mainly associated with 125–350 nm soil particle size. Under different redox conditions, colloid- and nanoparticle-bound Cr concentration decreased with increasing nanoparticles zero-valent iron (nZVI) dose. Soil reoxidation promoted the colloid- and nanoparticle-bound Cr release due to the weakly crystalline Fe-(hydr)oxides reprecipitation. Further quantitative analysis showed that colloid-bound Cr concentrations were positively correlated with colloid-bound Mn concentrations during the whole rice growth soils. Most important of all, Cr content in rice grain was positively correlated with colloid-bound Cr significantly. This study provides a quantitative and size-resolved understanding of particle-bound Cr in paddy soils, highlighting the importance of colloid-bound Cr and Fe interactions in Cr geochemical cycle of paddy soil.

A transformation and auxiliary extraction of Cr during electrokinetic removal of Cr-contaminated multilayer composite soil chamber.

Multilayer composite soil chamber was proposed to extract the Cr of contaminated site soil and insight into transformation of Cr fractionation associated with valence states. The variations of current, soil pH and moisture content were explored, as well as the migration of Cr fractionation and redistribution of Cr. Results indicated that duration of half peak current could be used to adjust treatment time and it varied among different composite ways. Moreover, extraction efficiency of Cr in soil near cathode was relatively higher and reached 60% when citric acid was used. Citric acid could promote the transformation between different Cr fractionations or different valence states. It could also improve the desorption of Cr, and could prevent excessive fluctuations of moisture content at the same time. Cr redistributed acrossed the soil chamber after extraction. When deionized water was used, Cr(VI) significantly migrated toward anode mainly in the form of exchangeable fractionation (EXC) while Fe-Mn oxides fractionation (Fe-Mn) which may be in the form of cationic Cr(III) hydroxides migrated toward cathode. When using citric acid, fractionations that were difficult to migrate of Cr, especially for Fe-Mn in site soils could be activated and became EXC and carbonate fractionation (CAR), then migrated to the anode or cathode. The migration of exchangeable Cr(III) was dramatically enhanced. But the use of citric acid could cause Cr(VI) transformation to Cr(III) near anode. In addition, during the migration process, EXC could go back to Fe-Mn again or transform to residue fractionation (RES).

Hydrothermal carbonization of Chinese medicine residue from licorice: Effects of pore and chemical structures on chromium migration

The Chinese medicine residue (CMR) is composed of wet substances, so using hydrothermal carbonization (HTC) to recover renewable energy from the residue is a suitable treatment method. Chromium (Cr), a kind of heavy metal element, is enriched in hydrochar and severely restricts its effective utilization. An in-depth analysis of the migration path and mechanism of Cr in hydrochar is helpful in promoting energy utilization for CMR. Here, licorice, a significant Chinese medicine, was selected as the example to analyze the evolutions of its pore and chemical structures and their effects on the migration mechanism of Cr during the HTC process. The products obtained under various HTC conditions were analyzed using nitrogen adsorption, FTIR, and 13C NMR. The results show that, considering reaction time and relevant reactions as the primary factors during the HTC process, the migration pathway of Cr in hydrochar undergoes two stages, and they are the accompanying migration stage and the recovery aggregation stage. Active adsorption sites for Cr may exist within the pore structure of hydrochar. In the HTC process, hydrolysis, decarboxylation, and decarbonylation reactions are the direct drivers of Cr migration, while aromatization is the underlying cause of Cr recovery and aggregation. It is hypothesized that Cr catalyzes the acetylene cyclotrimerization reaction, thereby promoting the formation of aromatic structures in hydrochar and integrating into the hydrochar carbon skeleton.

Microstructural evolution and diffusion mechanism of MCrAlY coated nickel-based superalloy turbine blades after serviced for 47,000 h

The large-sized industrial gas turbine blades exhibit non-uniform microstructural degradation in various parts due to ultra-long term service in high-temperature and high-pressure environments. Determination of degradation behavior at critical locations is important for the safety of gas turbine and blades refurbishment program. The microstructure characterization on the surface and interface of MCrAlY coated Ni-based superalloy blades have been studied. The microstructure evolution near the coating/ substrate interface was studied by scanning electron microscope (SEM) and the difference in degradation of the main precipitates at several locations were quantified. Surface oxidation and interfacial diffusion were analyzed through energy dispersive spectrum (EDS) and electron probe microanalyzer (EPMA) to clarify the influence of elemental diffusion on microstructure. The results indicated that regional microstructure evolution influenced by the spatial structural characteristics of the blades. The migration of Ni, Al, Cr, and Co dominated the diffusion mechanism during service, and reconstructed the microstructure of the coating/substrate interface and surface.

Elucidating the role of Cr migration in Ni-Cr exposed to molten FLiNaK via multiscale characterization

Structural materials used in nuclear reactor environments are subjected to coupled extremes such as high temperature, irradiation, and corrosion which act in concert to degrade their functional performance. Connecting alloy microstructure such as grain boundaries, and accumulating point defects with corrosion attack and pore morphology is critical to understanding underlying mechanisms. We uncover the compositional variations and morphology at multiple length scales in corrosion-damaged Ni-Cr alloy after exposure to oxidants in molten fluoride salts. A complex network of dense corrosion pores is detected by surface-level SEM observations. The corrosion pores take on a 1-dimensional morphology and are enriched with Ni and depleted of Cr 1–5 µm from the pore surface. STEM-EDS and 4D-STEM strain maps acquired simultaneously highlight the local variations in composition and structure of a ≤ 200 nm Cr-rich layer identified from a cross-section taken at the bottom of an isolated corrosion pore between the Ni-Cr alloy matrix and the embedded salt. However, the absence of an observed interface between the Ni-Cr alloy matrix and the FCC-structured Cr-rich layer suggests that Cr plating from the salt did not transpire. These findings support a proposed Cr lattice diffusion mechanism rather than Cr-precipitation from the salt to accommodate temperature transient conditions during sample cooling. Through the development of a 1D phase field model, these results are rationalized by formation energies for the Ni- and Cr-oxidation into the molten salt. This study reveals the locally altered microstructure caused by high temperature corrosion in non-steady-state molten salt nuclear reactor environments.

Effects of ionic strength and bentonite ratio on the migration of Cr(VI) in clayey soil-bentonite engineered barrier.

Soil-bentonite (S-B) barriers have been widely used for heavy metal pollution containment. This study conducted batch adsorption tests and diffusion-through tests to evaluate how ionic strength and bentonite ratio influence the migration of Cr(VI) in natural clay-bentonite mixtures. The test results indicated that the adsorption of Cr(VI) exhibited an obvious anion adsorption effect, the pH of the soil mixture increased with the addition of bentonite, resulting in a decrease in the positive surface charge. This change led to a decrease in Cr(VI) adsorption capacity, from 775.19 mg/kg for pure clay to 378 mg/kg for mixture samples with excessive bentonite. Furthermore, as the ionic strength increases from 0 to 0.1 M, the Cr(VI) adsorption capacity increases slightly due to the weakening of electrostatic repulsion on the clay particle surface, but the effective diffusion coefficient (De) increases by 21.97%. The compression of the diffusion double layer (DDL) under high ionic strength conditions enlarges the diffusion path and enhances the migration of Cr(VI) through the pore flow paths. Moreover, hydrated bentonite effectively fills the interaggregate pores of natural clay, thus creating narrower and more tortuous flow paths. However, excessive bentonite increases the pH value and pore volume, resulting in changes to the soil microstructure and disrupting the continuous skeleton of natural clay, which is unfavorable for Cr(VI) containment. Based on the study of the Cr(VI) contaminated site, a bentonite ratio of 2:10 is recommended for optimal natural performance of the natural clay-bentonite barrier.

Effects of nZVI on the migration and availability of Cr(VI) in soils under simulated acid rain leaching conditions

Hexavalent chromium, Cr(VI), is a ubiquitous toxic metal that can be reduced to Cr(III) by nano-zero-valent iron (nZVI). Finding out effects of continuous rainfall leaching on the Cr(VI) release and availability remains a problem, needing to be addressed. Whether the Cr(VI) reduction by nZVI and continuous rainfall leaching lead to localized heterogeneity in soil is unclear. Therefore, two in situ high-resolution (HR) techniques of the diffusive gradients in thin-films (DGT) and planar optode were combined with ex situ sampling experiments here. Results demonstrate that nZVI decreased Cr(VI) leaching by 5.60–8.50 % compared to control soils. DGT-measured concentrations of Cr(VI), CDGT-Cr(VI), ranged from 7.31 to 19.4 μg L-1 in the control soils, increasing with depth while CDGT-Cr(VI) in nZVI-treated soils (2.41–6.18 μg L-1) decreased or remained stable with depth. However, simulated acid-rain leaching increases CDGT-Cr(VI) by 1.61-fold in nZVI-treated soils, negatively affecting the remediation. DGT measurements in bulk soils using disc devices are better at capturing the change of Cr(VI) availability at different conditions, whereas 2D-HR DGT mappings did not characterize significant mobilization of Cr(VI) at the micro-scale. These findings emphasize the importance of monitoring Cr(VI) release and availability in remediated soil under acid-rain leaching conditions for effective environment management.

Effects of woodland slope on heavy metal migration via surface runoff, interflow, and sediments in sewage sludge application

Sewage sludge (SS) application to forest plantation soils as a fertilizer and/or soil amendment is increasingly adopted in plantation forest management. However, the potential risks of SS-derived heavy metals (HMs) remain a concern. Many factors, including woodland slope may affect the risks, but the understanding of this issue is limited. This research evaluated the HMs migration via surface runoff, interflow, and sediments when SS was applied in woodlands of varying slopes. We conducted indoor rainfall simulations and natural rainfall experiments to clarify the effect of slope on the migration of HMs via runoff (including surface and interflow) and sediments. In the simulated rainfall experiment, HMs lost via sediments increased by 9.79–27.28% when the slope increased from 5° to 25°. However, in the natural rainfall experiment, when the slope of forested land increased from 7° to 23°, HMs lost via surface runoff increased by 2.38% to 6.13%. These results indciate that the surface runoff water on a high slope (25°) posed high water quality pollution risks. The migration of HMs via surface runoff water or interflow increased as the steepness of the slope increased. The total migration of Cu, Zn, Pb, Ni, Cr and Cd via sediment greatly exceeded that via surface runoff and interflow. Particles ≤ 0.05 mm contributed the most to the ecological risks posed by sediments. Cd was the main source of potential ecological risks in sediments under both experimental conditions.

Characteristics and numerical simulation of chromium transportation, migration and transformation in soil–groundwater system

Understanding chromium (Cr) migration and dispersion patterns in the soil-groundwater system is critical for the control and remediation of subsurface Cr contamination. In this study, a typical Cr-contaminated site from the Pearl River Delta (PRD) in China was simulated with a three-dimensional (3D) sandbox experiment to investigate the migration and transformation behavior of Cr. Results revealed that under the combined influence of rainfall and groundwater flow, a complex flow field favorable for 3D migration and solute dispersion was formed. The flow field characteristics were influenced by water-table depth, which in turn affected Cr behavior in the system. Moreover, downward flow field expansion under low water-table conditions led to Cr vertical migration range expansion, causing greater contamination in the deep soil. The migration process was accompanied with Cr(VI) reduction, during which approximately 75 % of the total Cr was immobilized in soils. The reactive transport model achieved a good fit for Cr retention and morphological distribution in the solid phase. The model indicates that Cr is more readily transported and dispersed with groundwater, and Cr migrated and spread downstream by 15 m during the eighth year. Therefore, managing water-table depth could be a strategy to minimize the Cr vertical migration and contamination.

Reduction and transformation of Cr(VI)-associated ferrihydrite by Shewanella oneidensis MR-1: Kinetics and secondary minerals

Hexavalent chromium (Cr(VI)) could be sequestrated by soils via microbial reduction to Cr(III) and association with minerals, however, quantitative understanding of metal reducing bacteria on the coupled kinetics of Cr and Fe minerals is still lacking. Here, microbial-mediated ferrihydrite transformation and reductive sequestration of Cr(VI) were investigated with Shewanella oneidensis MR-1 under varying Cr/Fe ratios. Quantitative results depicted that the contents of magnetite from ferrihydrite transformation decreased from 70 % to 22 % after 288 h as Cr/Fe ratios increased from 0 to 8 × 10−3, and reductive transformation rates increased with decreasing Cr/Fe ratio. Elemental mapping and line scan analyses at nano-scale revealed that Cr(VI) was evenly combined within fresh ferrihydrite, and a part of produced Cr(III) was doped into the crystal lattice of magnetite and goethite. Cr may be sequestrated by secondary Fe minerals via structural substitution, surface complexation, and physical encapsulation. Microscopy-based results exhibited that more Fe minerals adsorbed on the surface of cell and less cells were lysed at low Cr/Fe ratios. Confocal laser scanning microscopy depicted that less cells were alive at high Cr/Fe ratios. The amplification of extracellular electron transfer-associated genes was downregulated as Cr/Fe ratios increased. The Cr/Fe ratios could affect cell activity, the combination with Fe minerals, and Mtr gene expression, thus controlling the reductive sequestration of Cr(VI) and phase transformation of ferrihydrite. A kinetic model has been established by combining elementary reductions, and it could well describe Cr(VI) reduction and Cr(III) incorporation under various Cr/Fe ratios during dissimilatory Fe reduction process. These findings could broaden our knowledge of quantifying the migration and transport of Cr in anoxic Cr-contaminated soil environments, and could be useful for simulating Cr dynamic behaviors in the natural soil, aquatic, and sediment environments.

Cr(VI) Reduction and Sequestration by FeS Nanoparticles Formed in situ as Aquifer Material Coating to Create a Regenerable Reactive Zone.

Remediation of large and dilute plumes of groundwater contaminated by oxidized pollutants such as chromate is a common and difficult challenge. Herein, we show that in situ formation of FeS nanoparticles (using dissolved Fe(II), S(-II), and natural organic matter as a nucleating template) results in uniform coating of aquifer material to create a regenerable reactive zone that mitigates Cr(VI) migration. Flow-through columns packed with quartz sand are amended first with an Fe2+ solution and then with a HS- solution to form a nano-FeS coating on the sand, which does not hinder permeability. This nano-FeS coating effectively reduces and immobilizes Cr(VI), forming Fe(III)-Cr(III) coprecipitates with negligible detachment from the sand grains. Preconditioning the sand with humic or fulvic acid (used as model natural organic matter (NOM)) further enhances Cr(VI) sequestration, as NOM provides additional binding sites of Fe2+ and mediates both nucleation and growth of FeS nanoparticles, as verified with spectroscopic and microscopic evidence. Reactivity can be easily replenished by repeating the procedures used to form the reactive coating. These findings demonstrate that such enhancement of attenuation capacity can be an effective option to mitigate Cr(VI) plume migration and exposure, particularly when tackling contaminant rebound post source remediation.

Comprehensive distribution characteristics and factors affecting the migration of chromium in a typical chromium slag-contaminated site with a long history in China.

The contamination of abandoned chromium slag-contaminated sites poses serious threats to human health and the environment. Therefore, improving the understanding of their distribution characteristics and health risks by multiple information is necessary. This study explored the distribution, accumulation characteristic, and the role in the migration process of chromium. The results showed that the contents of total Cr and Cr (VI) ranged from 12.00 to 7400.00mg/kg, and 0.25 to 2160.00mg/kg, respectively. The average contents of both total Cr and Cr (VI) reached the highest value at the depth of 7-9m, where the silt layer retaining total Cr and Cr (VI) was. The spatial distribution analysis revealed that the total contamination area percentages of total Cr and Cr (VI) reached 7.87% and 90.02% in the mixed fill layer, and reduced to 1.21% and 34.53% in the silty layer, and the same heavily polluted areas were located in the open chromiumresidue storage. Soil pH and moisture content were the major factors controlling the migration of total Cr and Cr(VI) in soils. Results of probabilistic health risk assessment revealed that carcinogenic risk was negligible for adults and children, and the sensitive analysis implied that the content of Cr(VI) was the predominant contributor to carcinogenic risk. The combination of chemical reduction and microbial remediation could be the feasible remediation strategy for soil Cr(VI) pollution. Overall, this study provides scientific information into the chromium post-remediation and pollution management for various similar chromium-contaminated sites.

The Release and Migration of Cr in the Soil under Alternating Wet-Dry Conditions.

In recent decades, chromium contamination in soil has emerged as a serious environmental issue, demanding an exploration of chromium's behavioral patterns in different soil conditions. This study aims to simulate the release, migration, and environmental impact of chromium (Cr) in contaminated soils under natural rainfall conditions (wet-dry cycles). Clean soils sourced from Panzhihua were used to cultivate chromium-containing soils. Simulated rainfall, prepared in the laboratory, was applied to the cultivated chromium-containing soils in indoor simulated leaching experiments. The experiments simulated three years of rainfall in Panzhihua. The results indicate that soils with higher initial Cr contents result in higher Cr concentrations in the leachate, but all soils exhibit a low cumulative Cr release. The leachate shows similar patterns in total organic carbon (TOC), pH, electrical conductivity, and Cr content changes. An analysis of the speciation of Cr in the soil after leaching reveals a significant decrease in the exchangeable fraction for each Cr species, while the residual and oxidizable Cr fractions exhibit notable increases. The wet-dry cycle has the following effects on the soil: it induces internal reduction reactions in the soil, leading to the reduction of Cr(VI) to Cr(III); it alters the binding of Cr ions to the soil, affecting the migration of chromium; and it involves microorganisms in chemical processes that consume organic matter in the soil. After three years of rainwater leaching, chromium-containing soils released a relatively low cumulative amount of total chromium, resulting in a reduced potential risk of groundwater system contamination. Most of the chromium in the chromium-containing soil is fixed within the soil, leading to less biotoxicity.

Spatial Distribution and Migration of Heavy Metals in Dry and Windy Area Polluted by Their Production in the North China

We explored the migration and distribution of heavy metal pollution in a dry and windy area in northern China. We collected soil, atmospheric deposition, and water samples, and measured heavy metal concentrations. Cu, Zn, As, and Pb in the 0–10 cm soil layer had a fan-shaped distribution, consistent with their atmospheric deposition fluxes. This indicates that the distribution of these heavy metals was driven by strong winds. The concentration of Cd in the river increased from 0.257 mg/L upstream to 0.460 mg/L downstream, resulting in the same distribution trends as soil near the river. Surface runoff may therefore drive Cd migration. The concentration of Pb in the river exceeded the pollution threshold, resulting in accumulation in the 5–10 cm soil layer. Atmospheric deposition fluxes were consistent with the soil distribution results, and principal component analysis showed that the contribution of surface runoff was high. This suggests that the migration of Pb and Cr is driven by both wind and surface runoff. Six heavy metals showed different migration behaviors, suggesting specific control strategies should be implemented for individual heavy metals.

Investigation of high‐entropy alloy derived spinel‐based layer for SOFC cathode‐side contact application

AbstractA simulated interconnect/contact/cathode/cathode support test cell is fabricated to investigate the effectiveness of the high‐entropy alloy as the contact material on the microstructure and the performance of the converted spinel‐based layer. Although the CuMnNiFeCo alloy powder is selected as the contact precursor, it showed good sinterability after sintering at 900°C for 2 h in air. The electrical performance of the contact layer is evaluated by the area‐specific resistance measurement, including isothermal exposure and thermal cycling. The compatibility of the contact layer with adjacent components is investigated through observing the cross‐sectional view of the test cell. Furthermore, the effectiveness of the contact layer in inhibiting Cr migration is also assessed.

Migration and transformation pathways of Cr(Ⅵ) in ferrihydrite-humic acid-Cr(Ⅵ) coprecipitation induced by Shewanella putrefaciens: Combination of adsorption and reduction

Adsorption and bio-reduction are preferred methods for the Cr(VI) removal due to its toxicity and carcinogenicity. However, the migration and transformation mechanisms of Cr(VI) in the natural ferrihydrite (Fh)-humic acid (HA)-Cr(VI) (Fh-HA-Cr) coprecipitation ternary system in the presence of Shewanella putrefaciens remain unclear. Fh-HA-Cr coprecipitations were synthesized by regulating OC/Fe and cultured in the presence of S. putrefaciens while controlling pH and Fe(II). Results revealed that the fate and speciation of Cr(VI) involve the following pathways. Firstly, acidic conditions accelerate Cr(VI) adsorption by coprecipitation, which diminishes in the presence of S. putrefaciens. Meanwhile, exogenous HA promotes redox on the surface of Fh-HA-Cr co-precipitates under acidic conditions, facilitating Cr(VI) conversion into Cr(III). Secondly, HA and Fe(II) jointly mediate the Cr(VI) reduction in the presence of S. putrefaciens under neutral conditions. Thirdly, the adsorbed Cr(VI) and reduced Cr(III) are incorporated into coprecipitation in the presence of S. putrefaciens, inhibiting Cr desorption under neutral conditions. Our findings highlight the significant roles of S. putrefaciens in the adsorption and reduction of Cr(VI) during Fh-HA-Cr coprecipitation transformation, providing a theoretical basis for Cr(VI) removal.

Emission of nitrogen/sulfur pollutants and migration of heavy metals during combustion of oily sludge from the oil refining process in fluidized bed

Oily sludge is a kind of hazardous waste due to the enrichment of nitrogen, sulfur, and heavy metals. In this work, the combustion of oily sludge from an oil refining factory in a fluidized bed reactor at 850–1050 °C and 0.8–1.2 excess air ratios were studied, with a focus on emission of nitrogen and sulfur pollutants and migration of Cr, Ni, Cu, Zn, Cd, Pb. The emission characteristics of nitrogen and sulfur pollutants were exhibited through monitoring the flue gas. The migration characteristics of heavy metals were clarified by analyzing their retention in bottom and fly ash. Moreover, the BCR (European Community Bureau of Reference) sequential extraction of the heavy metals in bottom ash was also carried out to obtain the migration of heavy metals in different forms. The contents of NOx and SO2 in the flue gas increased with temperature and excess air ratio increasing. High temperature led to less heavy metal retention in the bottom ash. The strong oxidizing atmosphere can weaken the volatilization of heavy metals. The stabilities of the heavy metal in different forms were in the following order: F4 (residual fraction) > F3 (oxidizable fraction) > F2 (reducible fraction) > F1 (exchangeable and acid soluble fraction). F4 was the dominant fraction of heavy metals in the bottom ash. The >60 % content of F3 and F4 led to the high stability of Cu and Ni while the >57 % content of F1 and F2 led to the high volatility of Cd and Pb in bottom ash. The differences in the component map of F1-F4 for the six heavy metals gave rise to their different migration characteristics during combustion.

Superior reduction and immobilization of Cr(VI) in soil utilizing sulfide nanoscale zero-valent iron supported by phosphoric acid-modified biochar: Efficiency and mechanism investigation

A novel strategy was proposed to remediate Cr(VI)-contaminated soil via phosphoric acid-modified biochar supported sulfide nanoscale zero-valent iron (SnZVI@PBC). Results of characterizations revealed that FeSX shell existed in outer layer of nZVI to prevent its oxidation after sulfidation modification, and SnZVI was effectively dispersed owing to the support of PBC, accelerating the electron transport for Cr(VI) reduction. The SnZVI@PBC presented pH-dependence and fast capture for Cr(VI) with outstanding binding amount of 335.55 mg/g. More importantly, the Cr(VI) content declined from 1300.75 to 223.30 mg/kg with conversion into stable Cr(III) in soil after 42 d of remediation with 2.0 % SnZVI@PBC under 60 % moisture content. Furthermore, leaching experiments showed that SnZVI@PBC could effectively immobilize Cr(VI), decreasing its migration and harmful risks to plants and human. Particularly, the fractions of exchangeable and carbonate-bound Cr decreased by 96.77 % and 83.60 %, which transformed to relatively stable fractions. Interestingly, the presence of humic acid, and the freezing-thawing/wetting-drying process promoted the immobilization performance of SnZVI@PBC for Cr(VI). SnZVI@PBC could alleviate the migration and poisonousness of Cr(VI) in soil primarily via reduction, co-precipitation, pore filling, and electrostatic attraction. Overall, SnZVI@PBC could be considered as a feasible amendment with superior reducing capacity and immobilization performance for Cr(VI)-contaminated soil.

Effect of hydrogen on the passivation for ultra-thin 316 L SS foil

The reformation and characterisation of the passive film formed on ultra-thin 316 L after hydrogen charging is investigated by combining EBSD, TMDS, XRD, Synchrotron-based XPS, and electrochemical experiments. The results show that ultra-thin foil reforms a passive film after 12 h of hydrogen release in NaCl solution. The reformed passive film is half the thickness of the as-received passive film and is dominated by Cr oxides/hydroxides. The lattice extension caused by residual hydrogen accelerates Cr migration to form Cr2O3; while the diffusible hydrogen occupies the cation vacancies and results in high defect density for the reformed passive film within 12 h.

Migration and transformation of trace elements during sewage sludge and coal slime Co-combustion

Co-combustion of sewage sludge (SS) and coal slime (CS) could improve the combustion properties of the two materials, however, high levels of trace elements (TEs) can be released from the two wastes, resulting in secondary pollution. The migration and transformation behavior of As, Cr, Pb, Zn, and Mn during co-combustion is explored in current research. The results showed co-combustion could inhibit the emission of Zn, As, Pb, and Mn, and the effect was more pronounced for Zn, As and Mn. Meanwhile, minerals like kaolinite and gypsum were found to generated in the ash from co-combustion but not solo-combustion. Model experiments demonstrated that kaolinite captured As, Pb and Mn, while gypsum captured Zn, As and Mn but facilitated the emission of Pb and Cr. This well explained the distinct TEs emission characteristics between co-combustion and solo combustion. As the temperature elevated, kaolinite in co-combustion ash decomposed and the generation of gypsum was promoted. In this way, the emission ratios of Zn, As, and Mn initially increased but subsequently decreased between 700 and 1300 °C, whereas Pb and Cr emission ratios increased by twofold within the same temperature range. Leaching characteristics and risk assessment code on co-combustion ashes were also conducted in this study. The results indicated a marginal elevation in the risk associated with trace elements (TEs) following co-combustion, provided that all five TEs remained within the limits of national standards.