Carbon Dissolution Research Articles

A self-sustaining effect induced by iron sulfide generation and reuse in pyrite-woodchip mixotrophic bioretention systems: An experimental and modeling study

Dual electron donor bioretention systems have emerged as a popular strategy to enhance dissolved nitrogen removal from stormwater runoff. Pyrite-woodchip mixotrophic bioretention systems showed a promoted and stabilized removal of dissolved nutrients under complex rainfall conditions, but the sulfate reduction process that can induce iron sulfide generation and reuse was overlooked. In this study, experiments and models were applied to investigate the effects of filler configuration and dissolved organic carbon (DOC) dissolution rate on treatment performance and iron sulfide generation in pyrite-woodchip bioretention systems. Key parameters govern that DOC dissolution and microbe-mediated processes were obtained by experiments. The water quality models that integrate one-dimensional constant flow, sorption and microbial transformation kinetics were used to predict the performance of bioretention systems. Results showed that the mixotrophic bioretention system with woodchip mixed in the vadose zone and pyrite in the saturated zone achieves a better performance in both nitrogen removal efficiency and by-product control. Comparably, woodchip and pyrite mixed in the saturated zone could encounter a high secondary pollution risk. The sensitivity coefficients of oxic/anoxic DOC dissolution rates to total nitrogen removal are 0.36 and -2.43 respectively. Iron sulfide generation was affected by DOC distribution and the competition between heterotrophic denitrifiers, autotrophic denitrifiers, and sulfate-reducing bacteria (SRB). DOC accumulation has an antagonistic effect on iron production and sulfate reduction. Extra DOC accumulation favors sulfate reduction while high DOC concentration inhibits pyrite-based denitrification and reduces Fe(III) production. The recycling of iron sulfide can improve the robustness and sustainability of bioretention systems.

Feasibility assessment and underlying mechanisms of metabisulfite pretreatment for enhanced volatile fatty acids production from anaerobic sludge fermentation

Employing chemical pretreatment for waste activated sludge (WAS) fermentation is crucial to achieving sustainable sludge management. This study investigated the feasibility of metabisulfite (MS) pretreatment for enhancing volatile fatty acids (VFAs) production from WAS. The results show that after 24-h MS pretreatment, the content of soluble organic matter and loosely bound extracellular polymeric substances (LB-EPS), especially proteins, increased significantly. During the fermentation, MS pretreatment under alkaline conditions was more efficient, with VFA peaking on the fifth day, showing a 140 % increase compared to the alkaline control group. Correlation analysis suggests that the dosage of MS, rather than pH, is closely related to the levels of soluble protein, polysaccharides, LB-EPS, and subsequential VFAs production, while alkaline conditions facilitate the dissolution of total organic carbon. Furthermore, sulfite radicals (SO3•−) are attributed to cell inactivation and lysis, while alkaline conditions initially reduce the size of the flocs, further promoting MS for attacking flocs, thereby improving the performance of fermentation. The study also found that MS pretreatment reduced microbial community diversity, enriched hydrolytic and fermentation bacteria (Actinobacteriota and Firmicutes), and suppressed methanogens (Methanobacteriaceae and Methanosaetaceae), making it a safe, viable, and cost-effective chemical agent for sustainable sludge management.

Sources of limestone dissolution from surface water-groundwater interaction in the carbonate critical zone

Dissolution of carbonate minerals in karst aquifers has long been recognized to result from recharge of surface water undersaturated with respect to calcite from carbonic acid produced by hydration of dissolved atmospheric and respired CO2. However, dissolution also results from additional acids produced by reactions of redox sensitive solutes in the subsurface, which may represent a source of CO2 to Earth's atmosphere. Because the magnitude of dissolution by these additional acids is poorly constrained, we compare here fractions of dissolution from initial surface water undersaturation and subsurface redox reactions. Estimates are based on chemical mixing and geochemical (PHREEQC) modeling of time series measurements of water compositions at a spring vent that receives surface water during stream flooding and a stream sink-rise system in north-central Florida. During a single spring reversal, 9.2 × 105 kg of limestone dissolved. At the stream sink-rise system, where subsurface residence times are shorter than during the spring reversal, both limestone dissolution (102–104 kg) and precipitation (102–105 kg) occur as water flows through the conduits with residence times ranging from 10 to 70 h. At both sites, maximum calcite dissolution rates of ∼10 μM hr−1 occurs at subsurface residence times between 30 and 50 h. For subsurface residence time > ∼20–60 h, the models indicate that production of additional acid in the subsurface is required for ∼53 ± 7% of dissolution. Oxidation of organic carbon, ammonium, pyrite, iron, and/or manganese produce sufficient acid for additional dissolution, but dissolved oxygen is insufficient for these reactions, indicating some acidity is generated under anerobic conditions. Dissolution caused by subsurface reactions in our samples represents mobilization of 20 × 104-30 × 104 kg of CO2 via remineralization of organic carbon or carbonate dissolution by nitric and sulfuric acids. Acid produced by subsurface redox reactions during surface water-groundwater interactions, including non‑carbonic acids, are important in conduit development and carbon cycling in the carbonate critical zone.

Promotion of manganese on Fe-based catalyst for the production of carbon nanotubes (CNTs) from plastics

Manganese (Mn) is an effective promoter of Fe-based catalysts to increase the production of carbon nanotubes (CNTs) from waste plastics but suffers from the lack of insights into how Mn affects the catalytic performance of CNTs production. Herein, we systematically investigate the promotion mechanism of Mn in Fe-based catalysts by varying the adding order of Mn and Fe during one or two-step impregnation methods. The results show that α-(Fe1-xMnx)2O3 is formed and uniformly distributed in Fe crystals when Mn and Fe are simultaneously added by the one-step impregnation method ((Mn + Fe)/MgO), resulting in the highest gas (66.3 mmol/gplastic), and CNTs (235 mg/gplastic) yields. While α-(Fe1-xMnx)2O3 in FeMn/MgO (Fe is added first and followed by Mn by two-step impregnation method) exhibited a poor distribution resulting in reduced gas and CNTs yields compared to (Mn + Fe)/MgO. For MnFe/MgO prepared by the two-step impregnation method and Mn is added first, the formed α-(Fe1-xMnx)2O3 is entirely not inserted into Fe crystals, and the corresponding catalyst exhibits lower gas and CNTs yields. The best catalytic performance of (Mn + Fe)/MgO is owing to the well-dispersed α-(Fe1-xMnx)2O3, which increases the carbon solubility capacity of the Fe crystals and regulates the equilibrium of carbon dissolution and precipitation, promoting the thermal cracking and carbon formation reactions, thereby improving the catalytic performance of CNTs and gas production.

Investigation of interstitial carbon in the disordered bcc FeCr alloys

The solution enthalpy of interstitial carbon in the ferromagnetic bcc Fe-Cr disordered alloys was calculated. It was found that the enthalpy depends on the number of chromium atoms in the octahedron constituting the octahedral pore and their positions, as well as on the magnetic states of the lattice atoms (Fe/Cr) surrounding the interstitial atom. The lowest cell energy corresponds to the configuration in which only chromium atoms are in the first coordination sphere of the carbon atom. The magnetic moments of the carbon and the nearest lattice atoms show dependency from their distances. For the most energetically favorable configurations, the values of the enthalpy of carbon dissolution in Fe-Cr alloy and in α-Fe are close to each other. It is found that these configurations correspond to the states in which the local magnetic moment on the interstitial carbon atom is close to zero. Also the elastic constants of the Fe-Cr-C alloy were calculated, and it is shown that alloying with carbon slightly increases the elastic properties of Fe-Cr alloys.

Preparation and interfacial microstructure of high thermal conductivity diamond/SiC composites

Diamond/SiC composites offer valuable applications in thermal management because of their exceptional thermal properties. Currently, the predominant method employed for crafting diamond/SiC composites is the reaction sintering approach. However, it encounters the challenge of a high residual silicon content. In this study, we introduced techniques such as bimodal diamond particles and high-density carbon sources (submicron diamond powder) to enhance the diamond content and reduce the residual silicon, optimizing the phase composition. The results indicated the diamond/SiC composite demonstrated a thermal conductivity of 666 W/m·K, a thermal expansion coefficient of 2.73 × 10−6 K−1, and an elastic modulus of 753 GPa. Furthermore, the meticulous assessment of the interface microstructure of diamonds in the diamond/SiC composite was conducted using transmission electron microscopy. The formation of nanocrystal-SiC and interface defects were elucidated by the mechanism of carbon dissolution saturation.

Groundwater‐surface water interaction, dissolved organic carbon oxidation and dissolution in carbonate aquifers

AbstractThe high primary porosity and permeability of eogenetic karst aquifers permit water recharged through secondary dissolution features to be temporarily stored in aquifer matrix porosity. The recharged water contains elevated dissolved organic carbon (DOC) concentrations that, when oxidized, enhance limestone dissolution and impact carbon cycling. We evaluate the relationship between DOC oxidation and limestone dissolution using observations at a stream sink‐rise system and reversing spring in the Floridan aquifer, north‐central Florida, USA, where subsurface residence times of recharged water are days and months, respectively. We estimate water chemical compositions during surface water‐groundwater interactions at these two systems with mixing models of surface water and groundwater compositions and compare them with measured DOC, dissolved inorganic carbon (DIC), Ca2+ and dissolved organic nitrogen (DON) concentrations. Differences between measured and modelled concentrations represent net changes that can be attributed to calcite dissolution and redox reactions, including DOC oxidation. DOC losses and Ca2+ gains exhibit significant (p < 0.01) inverse linear correlations at both the reversing spring (slope = −0.9, r2 = 0.99) and the sink‐rise system (slope = −0.4, r2 = 0.72). DOC oxidation in both systems was associated with decreases in the molar C:N ratio (DOC:DON). Significant (p < 0.01) positive linear correlations between increases in Ca2+ and DIC concentrations after correcting for DIC derived from calcite dissolution occurred at both the reversing spring (slope = 1.3, r2 = 0.99) and the sink‐rise system (slope = 1.61, r2 = 0.75). Greater deviations from the expected slope of −1 or +1 at the sink‐rise system than at the reversing spring indicate DOC oxidation contributes less dissolution at the sink‐rise system than at the reversing spring, likely from shorter storage in the subsurface. A portion of the deviation from expected slope values can be explained by the dissolution of Mg‐rich carbonate or dolomite rather than pure calcite dissolution. Despite this, slope values reflect kinetic effects controlling incomplete consumption of carbonic acid during dissolution reactions.

Wettability Characteristics of Nanoporous Carbon Bricks Incorporated with Al2O3 Phase and Molten Iron in Sustainable and Low‐Carbon Blast Furnace

Analyzing the wetting behavior between carbon brick and molten iron in a blast furnace is crucial for understanding prolonging the furnace's lifespan. This study investigates the wetting behavior between microporous carbon brick and molten iron. The contact angle between the carbon brick and molten iron is measured at various temperatures and carbon saturation conditions, while the microscopic morphology of the reacted interface is examined. Furthermore, the wetting mechanism of molten iron on the carbon brick surface is elucidated. The findings reveal that both the microporous carbon brick and molten iron remain in a never‐wetting state within the furnace. As the temperature rises from 1150 to 1450 °C, the contact angle decreases from 138° to 128°, whereas the initial carbon content in the molten iron increases from 2.6 wt% to 4.1 wt%. Additionally, the initial contact angles gradually increase from 128.3° to 133.6°, with final equilibrium contact angles of 119.2° to 127.0°, indicating a nonwetting state. The carbon dissolution reaction occurs within the carbon matrix region of the microporous carbon brick prior to carbon saturation in the molten iron. Conversely, the presence of a ceramic phase in the ceramic area hampers both chemical erosion and physical penetration of the molten iron.

Active CO2 emissions from thermal springs in the Karakoram fault system and adjacent regions, western Tibetan Plateau

Large-scale intra-continental strike-slip faults provide the pathways for groundwater circulation and the release of CO2-rich fluids through thermal springs, which is a significant type of deep CO2 emissions into the atmosphere and hydrosphere. India-Asia collision created numerous strike-slip faults and thermal springs in the Tibetan Plateau and adjacent regions, but their CO2 origins and fluxes are still not well understood. Here, we present a quantitative study on CO2 emissions from thermal springs in the Karakoram fault system (KKFS) and adjacent regions, western Tibetan Plateau, with the aim of revealing the origins of CO2-rich fluids and estimating the dissolved and gaseous CO2 fluxes. Hydrogen and oxygen isotopic data show that the geothermal waters were recharged by local precipitation (e.g., rainfall and snow-melt water) and experienced variable degrees of water-rock interaction, giving rise to the dominant Na–HCO3 type and minor Na–Cl and Ca–HCO3 type waters discharging from thermal springs. Spatially, the thermal springs within or close to the KKFS (Group 1 and Group 2) have larger circulation depths of 1.3–5.1 km, while those away from the KKFS (Group 3) exhibit shallow (0.6−0.8 km) groundwater circulation. Mass balance calculations reveal high deeply-sourced carbon inputs (60.4−94.3%) to dissolved inorganic carbon (DIC) of the Group 1 and Group 2 samples, while the Group 3 samples have higher shallow carbon contributions (50.4−60.9%) to DIC via dissolution of carbonate and organic carbon. This is consistent with higher Δ14CDIC values (−788.6‰ to −692.1‰) in Group 3 samples and the lack of radioactive 14C in Group 1 and Group 2 samples (Δ14CDIC = −999.9‰ to −985.9‰). Based on chemical compositions and fluxes of spring water and bubbling gases, the total CO2 output from thermal springs (including dissolved and gaseous CO2) in the KKFS is estimated to be ∼2332 t a−1, in which the endogenic carbon such as metamorphic CO2 accounts for ∼1863 t a−1. Our results provide the first estimate of deep CO2 flux for the KKFS and would contribute to a better understanding of active CO2 emissions facilitated by strike-slip faulting processes in continental collision zone.

Nitrification inhibitor 3,4-dimethylpyrazole phosphate alleviates the dissolution of soil inorganic carbon caused by nitrogen fertilization

In carbonate soils, soil inorganic carbon (SIC) dissolves and releases CO2 due to exogenous application of nitrogen fertilizer, which makes the soil an important carbon source. Application of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is likely to be an effective measure to alleviate SIC dissolution. A 5-year field experiment was conducted to observe SIC dynamics under three treatments: No N fertilizer (CK), N fertilizer (NF), and N fertilizer combined with DMPP (N + NI). Soil samples were collected from 0 to 20, 20–40, 40–60, 60–80, and 80–100 cm in depth, and soil organic carbon (SOC), SIC, total carbon (TC), total nitrogen (TN), and carbon isotope composition (δ13C) of the soil were analyzed. The proportion of pedogenic carbonate (PIC) in SIC was estimated using an isotopic mass balance equation. Results showed that: (1) compared with the application of N only, DMPP had no significant effect on SOC content and δ13CSOC in the 0–100 cm soil profile; (2) the application of N fertilizer significantly reduced the SIC content by 10.0 g·kg−1 (58.3 %) in the 0–80 cm soil profile. In the 0–20, 20–40, and 60–80 cm soil layers, the SIC content was reduced by 2.9, 1.9, and 3.8 g·kg−1, respectively. However, the SIC content significantly increased by 3.2 g·kg−1 (58.9 %) in the 80–100 cm soil layer. DMPP application significantly increased the SIC content in the 0–20 and 20–40 cm soil layers by 1.3 g·kg−1 (50.9 %) and 1.2 g·kg−1 (48.2 %), respectively; (3) DMPP combined with N significantly alleviated PIC dissolution in the 0–40 cm soil layers and increased PIC stock in 0–100 cm soil by 6.2 Mg·ha−1 (64.6 %). Applying DMPP to farmland soil containing carbonate significantly alleviated the dissolution of N fertilizer on PIC, which may decrease CO2 emissions in the field.

Innovative cation exchange-driven carbon migration and recovery patterns in anaerobic fermentation of waste activated sludge

Despite numerous treatments have been developed to enhance anaerobic fermentation of waste activated sludge, the innovative cation exchange (CE) approach has been rarely reported, little attempt was conducted to revealcarbon source fate. The interphase carbon balance was illustrated to clarify endogenous carbon dissolution, biotransformation,and recovery patterns. By CE-mediated divalent cation removal, almost 34.72 % of particulate carbon sources were dissolved in 2-day treatment, corresponding to soluble carbon content of 1165.58 mg C/L. Most of the originally dissolved carbon sources (58.01–66.81 %) were bio-transformed to volatile fatty acids with high bioavailability, while the further transformation to biogas was inhibited, contributing to recoverable carbon source accumulation. Overall, 21.38 % of total solid carbon sources were recovered through 8-day fermentation, the carbon extraction was implemented by solid–liquid separation with carbon loss of 14.21–22.91 %, manifesting the valid carbon recovery of 85.05–87.96 mg C/g VSS. Such CE-driven carbon recovery provided negentropy benefits in sustainable cycle economy.

New Data on the Expression of the Early Eocene Hyperthermals in Northern Bulgaria: Riben Section Revisited

We present new lithologic, nannofossil biostratigraphic and benthic carbon and oxygen isotope records for a marly-rich, 11 m thick Paleocene-Eocene section, now exposed at an old quarry at Riben Village, northern Bulgaria. The occurrence of NP9, NP10 and NP11 nannofossil zones is evidenced by detailed high-resolution nannofossil biostratigraphy. The carbon dissolution interval is marked by the abrupt drop of CaCO3 content and deposition of a clay interval at the onset of the Paleocene-Eocene Thermal Maximum (PETM). Stable isotope analyses of δ13C and δ18O were performed on benthic-foraminiferal tests. An unusual two-fold carbon isotope excursion (CIE) in the PETM interval is documented (total negative shift of 2.89‰). Moreover, three paired negative excursions: two in the Paleocene within the PETM interval, upper NP9 zone, and one within the early Eocene, NP11 zone are identified. The most prominent negative carbon isotope excursion (4.90‰ negative shift) is related with ETM3 (or “X” event), 52.84 Ma ago.
 Integration of nannofossil biostratigraphy, benthic stable isotope data sets and lithology unravel two separate early Eocene hyperthermal events: the PETM (= ETM1) and the ETM3 (= “X” event), recorded at Riben section.

Synergistic catalytic biomass-H2O gasification for H2 production and biochar etching mechanism: Experimental and DFT studies

Biomass-H2O gasification facilitated by multi-metal synergistic catalysis for H2 production. Oxygen transfer, carbon dissolution, lateral/vertical etching mechanism, and hydrogen production capacity of biomass self-contained K and added Ni catalytic gasification were studied through biomass loaded with K and Ni pyrolysis, biochar gasification experiments, and DFT calculations. The H2 yield from KNi catalytic gasification was 67.09 mmol/g (increased by 13.51%). Driven by *OH, K migrates and transforms from the inside of the carbon matrix to form active sites (CK), increasing carbon defects (40–50%) and reactivity. The vertical etching ability of Ni on biochar is enhanced from outside to inside (forming NiC and CK to reduce carbon dissolution energy barrier) and the gasification reaction rate is increased. The competition between the strong attraction of Ni on OH and the van der Waals force of K on OH leads to a 7.7% increase in the energy barrier of the rate-determining step (H transfer). The work enhances the understanding of the multi-metal catalytic gasification of rich H2 and provides a foundation for developing catalytic gasification technology.

Reductive roasting of red mud with carbon and sulfuric acid dissolution of iron and aluminum: Transformation phases and leaching characteristics

A novel approach is proposed, combining pyrometallurgical and hydrometallurgical processes, to enhance the recovery of Fe and Al while effectively breaking down the mineral composition of red mud. The study delves into the roasting reduction behavior and conversion mechanism of red mud, utilizing thermodynamic analysis and conducting roasting experiments. Extensive investigations were conducted to analyze the impact of roasting temperature and time on the carbothermal reduction of red mud. The results indicate that the most favorable leaching effect of iron and aluminum from red mud was achieved after roasting at 1000 °C for 45 min. The behavior of roasted red mud during acid leaching was meticulously explored. During the roasting process, the majority of hematite in the red mud underwent reduction to wustite (FeO) and zero-valent iron, while the aluminum-bearing minerals melted and decomposed to form NaAlSiO4 and Ca2Al2SiO7, along with other substances. The formation of low-valent and independently present iron products played a role in achieving high Fe leaching efficiency. The presence of Ca and Al-containing compounds such as Ca2Al2SiO7 in the product of roasting proved difficult to leach, leading to poor Al leaching efficiency. The acid leaching process exhibited promising results, with maximum leaching efficiency of iron and aluminum reaching 95.7% and 72.5%, respectively. This success can be attributed to the control over experimental conditions, which allowed for the generation of desired iron oxides with various valence states.

Comparison of residual carbon content and morphology of B4C powders synthesized under different conditions

In this article, the impact of different B4C synthesis methods on the amount of residual carbon and the final morphology of the prepared ceramic particles was investigated. The main materials for the synthesis of B4C were glucose and boric acid, and the effects of adding tartaric acid and performing mechanical activation were studied. For this purpose, two methods of carbon dissolution and boron carbide oxidation were used to determine the amount of residual carbon in the ceramic products. The results of the investigations on the sample synthesized in optimal conditions showed that if additives and mechanical activation are not used, about 7 wt% of carbon will remain in the synthesized powder. The amount of carbon decreased to 5.7 wt% with mechanical activation, but the best result was obtained with the addition of tartaric acid, in which the amount of impurity dropped to 3.3 wt%. Finally, the size and morphology of B4C particles and carbon impurities were observed and compared using a scanning electron microscope.

Interfacial phenomenon and Marangoni convection of Fe–C melt on coke substrate under in situ observation

The interfacial phenomenon between liqiuid iron and coke is important for determining the melting efficiency in the blast furnace iron-making process. In this study, the interaction observed in the case of the iron-carbon (Fe–C) melt on coke substrate was investigated using a high-temperature vacuum wettability test equipment. The Fe–C melt did not wet and spread on the coke substrate with different graphitization degrees (r0) at a high temperature of 1450 °C. The contact angles changed from 124.5° to 105.3°, and the r0 increased from 9.30 to 50.00%, thus indicating a nonwetting state. The deepening of graphitization decreased the contact angle. Thereby, increasing the contact area between liquid iron and the carbonaceous material, which facilitated carbon dissolution. The irregular movements of Fe–C melt were observed in situ during the wetting process. The horizontal force of the droplet caused by interfacial tension and the contact angle; the Marangoni convection owing to the gradient of carbon concentration; and the impulse force caused by the generation, aggregation, and release of SiO bubbles at the interface were attributed to the driving force.

Wetting and spreading of NiTi melt on graphite and carbon felt

Experiments were carried out on the wetting and spreading of the nitinol melt over the polished surface of high-density pure graphite. The furnace heater and the dispenser from which the melt was extruded were also made of graphite of the same quality. The measurements were carried out in vacuum of 10−3 Pa at a temperature close to the melting point and higher, up to 1430 °C. High-speed filming of the transferred drop was used simultaneously with high-speed thermal imaging. As a result, the kinetics of the spreading of the nitinol melt over the graphite surface was obtained, and the surface tension was also measured by the pendant drop method. The dissolution of carbon in the melt prevents the formation of a barrier layer of titanium carbide. Electron microscopic studies confirmed the formation of a dense layer of titanium carbide on the contact surface. An experiment was carried out on the melting of nitinol on carbon felt at a temperature of 1350 °C. It is shown that nitinol's drop on felt with a density of about 100 kg/m3 (porosity 93%) does not impregnate into the felt, retains volume and shape for more than 15 min. This indicates that carbon felt or cloth may be good candidates for lining materials.

Phosphate-Induced Reaction to Prepare Coal-Based P-Doped Hard Carbon with a Hierarchical Porous Structure for Improved Sodium-Ion Storage

The use of coal as a precursor for producing hard carbon is favored due to its abundance, low cost, and high carbon yield. To further optimize the sodium storage performance of hard carbon, the introduction of heteroatoms has been shown to be an effective approach. However, the inert structure in coal limits the development of heteroatom-doped coal-based hard carbon. Herein, coal-based P-doped hard carbon was synthesized using Ca3(PO4)2 to achieve homogeneous phosphorus doping and inhibit carbon microcrystal development during high-temperature carbonization. This involved a carbon dissolution reaction where Ca3(PO4)2 reacted with SiO2 and carbon in coal to form phosphorus and CO. The resulting hierarchical porous structure allowed for rapid diffusion of Na+ and resulted in a high reversible capacity of 200 mAh g−1 when used as an anode material for Na+ storage. Compared to unpretreated coal-based hard carbon, the P-doped hard carbon displayed a larger initial coulombic efficiency (64%) and proportion of plateau capacity (47%), whereas the unpretreated carbon only exhibited an initial coulombic efficiency of 43.1% and a proportion of plateau capacity of 29.8%. This work provides a green, scalable approach for effective microcrystalline regulation of hard carbon from low-cost and highly aromatic precursors.

Interfacial reaction mechanism and high temperature stability of heat-resistant steel and SiC under a vacuum environment

The physical and chemical stabilities of SiC and heat-resistant steel were assessed by the diffusion couple method under vacuum at 1200 °C, which is a commonly used condition in magnesium metallurgy. High-temperature visualization instruments were used and Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermodynamic analyses were performed to verify the relevant mechanism. The reaction between SiC and heat-resistant steel can be divided into two stages: solid–solid and solid–liquid reactions. The solid–solid interfacial reaction produces graphite, which hinders the interfacial reaction. The interfacial reaction simultaneously generates silicides (NiSi, Ni2Si, and Ni3Si) with low melting points and transforms the reaction interface into a solid–liquid interface. The formation of the liquid phase promotes the dissolution and diffusion of carbon, leading to the accelerated corrosion of SiC and low-temperature melting of steel. Supersaturated carbon precipitates in the melt in the form of nanowires or nanotubes are catalyzed by Fe/Ni. Herein, a general model describing the direct interfacial reaction mechanism of SiC and heat-resistant steel is proposed to explain the reaction process under vacuum.

Effects of vegetation restoration on distribution characteristics of heavy metals in soil in Karst plateau area of Guizhou.

In southwest China, vegetation restoration is widely used in karst rocky desertification control projects. This technology can effectively fix the easily lost soil, gradually restore the plant community and improve soil fertility. However, the change law of soil heavy metals in the restoration process remains to be further studied. Therefore, in this work, Guizhou Caohai Nature Reserve as a typical karst area was taken as the research object to investigate the influence of vegetation restoration technology on repairing soil heavy metal pollution. The spatial distribution characteristics of soil heavy metals (chromium, nickel, arsenic, zinc, lead) before and after vegetation restoration in karst area were studied by comparative analysis and linear stepwise regression analysis. The main influencing factors and spatial distribution characteristics of heavy metals in karst area were further discussed. The results showed that: (1) heavy metals in karst soils are affected by surface vegetation, root exudates, microorganisms and leaching. Only heavy metals nickel (Ni) and lead (Pb) showed the tendency of surface enrichment and bottom precipitation enrichment in non-karst soils. Path analysis suggested that non-metallic soil factors such as soil bulk density (BD), total nitrogen (TN) and ammonium nitrogen (NH4 +-N) had direct effect on the content of heavy metals in soil. (2) The proportion of 0.25-2 mm aggregates in the surface soil of vegetation restoration belt was more than 40%, and the proportion of surface soil ≤2 mm aggregates in this increased to 83% and 88%, respectively, which could improve the soil structure and properties effectively. (3) Vegetation restoration effectively restored the nutrient elements such as carbon and nitrogen in the soil, and enhanced the soil material circulation. Furthermore the content of heavy metals in the surface soil higher than that in the 10-20 cm soil layer. Plant absorption, biosorption mechanism of microorganisms, coupling of root exudates, dissolution of soil soluble organic carbon and pH make the contents of heavy metals Cr, Ni and Pb in vegetation restoration belt slightly lower than those in karst soil. At the same time, affected by vegetation coverage, residual heavy metals in soil are further leached by surface runoff. Therefore, the content of heavy metals in soil could reduce combined heavy metal enrichment plants for extraction with remediation. This study elucidates the advantages and remedy mechanism of vegetation restoration in the remediation of heavy metal contaminated soils in Caohai area of Guizhou, and this plant activation and enrichment extraction remediation technology would be popularized and applied in the remediation of heavy metal contaminated soils in other karst areas.