HfB2-SiC-MoSi2 oxidation resistance coating fabricated through in-situ synthesis for SiC coated C/C composites

A brand new HfB2-SiC-MoSi2 coating was fabricated to protect carbon/carbon (C/C) composites with inner SiC coating from oxidation, which was prepared by in-situ synthesis. In this paper, the C/C substrate with the protection of the HfB2-SiC-MoSi2/SiC coating could resist oxidation in 1773 K air for 408 h. The double coating also presented expected oxidation protection performance at dynamic oxidation environment. In the test process, the surface coating was oxidized to form a self-sealing silicate glass layer containing HfO2 and HfSiO4, which could hinder crack propagation in coating

Green remediation of Cd and Hg contaminated soil using humic acid modified montmorillonite: immobilization performance under accelerated ageing conditions

Solidification/Stabilization (S/S) is an effective way to immobilize toxic metals in contaminated soil. However, utilization of ordinary Portland cement (PC) in this process has raised environmental concerns owing to the high carbon footprint from PC manufacturing and the risk of toxic element leaching in the long term. Hence there is an urgent need to seek for “green” immobilization approaches with long-term stability. In this study, a clay-based material, humic acid modified montmorillonite (HA-Mont) was applied to a Cd and Hg contaminated soil. Field emission scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (FESEM/EDS), N2 adsorption-desorption, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analyses were performed to investigate the characteristics of this material. Compared to the soil without any treatment, dosage of 5% HA-Mont could effectively reduce Cd and Hg concentrations by 94.1% and 93.0%, respectively and to below the regulatory limits in the TCLP (Toxicity Characteristic Leaching Procedure) leachates. Compared to the soil treated with virgin montmorillonite, HA modification resulted in the reduction of leachate concentrations of Cd and Hg by 69.5% and 65.9%, respectively. Long-term immobilization performance of the HA-Mont treatment was examined using a quantitative accelerated ageing method. In order to examine the ageing features, a novel method based on conditional probability was developed, and the reliability of HA-Mont immobilization was found to fit the Weibull model well, as the ageing rate of immobilization effect increased with time. After 120 years of ageing, reliability of both metals could still remain above 0.95. Cd concentration in TCLP leachates at 120th year could still remain below the regulatory limit (294 μg/L vs 1000 μg/L), while Hg concentration reached the regulatory limit of 200 μg/L in 96th year. This is the first attempt developing a green S/S method of Cd and Hg contaminated soil using HA-Mont and examining the long-term ageing characteristics of the stabilized soil using a probability-based approach

Electrophoretic deposition and laser cladding of bioglass coating on Ti

Bioglass coatings derived from electrophoretic deposition method were fused on Ti surface by laser cladding process using a continuous CO laser. The specimens were studied by field-emission scanning electron microscopy, X-ray diffraction and bonding tests. Titanium oxide layer with hierarchical structures consisting of submicron rows of leaf-like embossments and nano-pores was obtained by combining acid etching and anodization processes, which increased the surface roughness of Ti. When heat-treatment temperature was 700 °C and high, CaSiO phase began to crystallize from the bioglass matrix and the crystallinity reached its maximum at 700 °C. During the electrophoretic deposition process, porous bioglass coatings composed of bioglass particles and fibers were deposited on Ti surface. Bioglass coatings with similar hierarchical structure containing submillimeter bioglass beads and microfibers were synthesized on Ti surface by laser fusion. There are no obvious microcracks at the interface of the Ti-coating, which revealed the good bonding between Ti-porcelain. With the laser scanning distance decreased, the bond strength increased accordingly. After only one day immersion in SBF, calcium phosphate began to precipitate on the bioglass coating's surfaces. The thickness of the calcium phosphate precipitation and the amount of microparticles increased with immersion time

Green remediation of Cd and Hg contaminated soil using humic acid modified montmorillonite: Immobilization performance under accelerated ageing conditions

Solidification/Stabilization (S/S) is an effective way to immobilize toxic metals in contaminated soil. However, utilization of ordinary Portland cement (PC) in this process has raised environmental concerns owing to the high carbon footprint from PC manufacturing and the risk of toxic element leaching in the long term. Hence there is an urgent need to seek for “green” immobilization approaches with long-term stability. In this study, a clay-based material, humic acid modified montmorillonite (HA-Mont) was applied to a Cd and Hg contaminated soil. Field emission scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (FESEM/EDS), N2 adsorption-desorption, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analyses were performed to investigate the characteristics of this material. Compared to the soil without any treatment, dosage of 5 % HA-Mont could effectively reduce Cd and Hg concentrations by 94.1 % and 93.0 %, respectively and to below the regulatory limits in the TCLP (Toxicity Characteristic Leaching Procedure) leachates. Compared to the soil treated with virgin montmorillonite, HA modification resulted in the reduction of leachate concentrations of Cd and Hg by 69.5 % and 65.9 %, respectively. Long-term immobilization performance of the HA-Mont treatment was examined using a quantitative accelerated ageing method. In order to examine the ageing features, a novel method based on conditional probability was developed, and the reliability of HA-Mont immobilization was found to fit the Weibull model well, as the ageing rate of immobilization effect increased with time. After 120 years of ageing, reliability of both metals could still remain above 0.95. Cd concentration in TCLP leachates at 120th year could still remain below the regulatory limit (294 μg/L vs 1000 μg/L), while Hg concentration reached the regulatory limit of 200 μg/L in 96th year. This is the first attempt developing a green S/S method of Cd and Hg contaminated soil using HA-Mont and examining the long-term ageing characteristics of the stabilized soil using a probability-based approach

Sustainable in situ remediation of recalcitrant organic pollutants in groundwater with controlled release materials : a review

The removal of recalcitrant organic pollutants in groundwater is a challenge being faced around the world. Achieving effective long-term remediation of contaminated aquifers faces a variety of significant issues such as back diffusion, tailing, and rebound. In recent years, some researchers have proposed the use of controlled release materials (CRMs) as a new approach to counteracting such issues. The novelty of CRMs lies in that they release their active products slowly, over prolonged periods of time, in order to sustain in situ treatments and long-term effectiveness. Here we review the main constituents of CRMs, analyze their production, characterization, and applications, with a focus on reaction mechanisms, effectiveness, and secondary effects. This review shows that the reactive components of CRMs most commonly involve either: (i) chemical oxidants to treat contaminants such as TCE, PCE, BTEX, and 1,4-Dioxane; (ii) sources of dissolved oxygen to stimulate aerobic biodegradation of contaminants such as BTEX and 1,4-Dioxane; or, (iii) substrates that stimulate reductive dechlorination of contaminants such as TCE and 1,2-DCA. It was found that in some studies, CRMs provided sustained delivery of CRM treatment reagents over several years, and achieved complete contaminant removal. However, lower removal rates were apparent in other cases, which may be ascribed to insufficient dispersion in the subsurface. There are a relatively limited number of field-scale applications of CRMs in contaminated land remediation. Those conducted to date suggest that CRMs could prove to be an effective future remediation strategy. Lessons learned from field applications, suggestions for future research directions, and conclusions are put forward in this review

Risk Transmission of Trade Price Fluctuations from a Nickel Chain Perspective: Based on Systematic Risk Entropy and Granger Causality Networks

Nickel is a strategic mineral resource, with 65% of nickel being used in stainless steel. The situation in Ukraine starting in February 2022 has led to significant fluctuations in nickel prices, with prices of nickel products along the same chain affecting and passing through each other. Using systematic risk entropy and granger causality networks, we measure the volatility risk of trade prices of nickel products using the nickel industry chain trade data from 2000–2019 and explore the transmission patterns of different volatility risk prices from the industry chain perspective. The findings show that: (1) Nickel ore has the highest risk of import trade price volatility and a strong influence, but low risk transmission. Stainless steel has the highest trade price impact but is also subject to the strongest passive influence. (2) The Americas have a higher risk of trade price volatility but a weaker influence. The influence and sensitivity of trade prices is stronger in Asia and Europe. (3) Indonesia’s stainless steel export prices have a high rate of transmission and strong influence. Germany’s ferronickel export prices are highly susceptible to external influences and can continue to spread loudly. Russian nickel ore export prices are able to quickly spread their impact to other regions

Green synthesis of layered double hydroxides (LDH) for the remediation of As and Cd in water and soil

Layered double hydroxides (LDH) show great promise for the remediation of heavy metals and metalloids in aqueous media and soils. In this study, we propose a green synthesis approach for LDH utilizing industrial waste granulated ground blast furnace slag (GGBS) and readily available magnesium oxide (MgO), and applied these green synthesized LDH for As and Cd remediation in both water and soil. The synthesized LDH were characterized via multiple approaches including SEM, HRTEM-EDS, TGA, XRD, and FTIR, demonstrating that the addition of 20% MgO in the raw materials (LDHb) substantially improved the stability of LDH compared to LDH synthesized solely from pure GGBS (LDHa). Batch adsorption experiments were conducted to evaluate the adsorption efficiency of LDHa and LDHb for Cd(II) and As(V) under varying initial solution pH conditions. Results showed that as the pH increased, calcium leaching remained high while aluminum leaching gradually increased. The adsorption isotherms and kinetic studies further revealed that LDHb displayed better adsorption performance for As(V) across different pH conditions, while both LDH showed a 100% removal rate of Cd(II) at pH ranging from 6 to 9. Both LDHa and LDHb exhibited promising immobilization effects on As and Cd in contaminated soils, with LDHa showing superior stabilization performance toward As, immobilizing 83.8% of bioavailable As in the farmland soil and 78.7% in the industrial site soil, compared to LDHb's 54.8% and 50.6%, respectively. The findings of this study hold promise for the practical application of LDH as an efficient and environmentally friendly remediation material for contaminated water and soils containing toxic metal(loid)s

Green and Size-Specific Synthesis of Stable Fe–Cu Oxides as Earth-Abundant Adsorbents for Malachite Green Removal

Many challenges remain for the mass production of nanoparticles for the removal of contaminants from water, primarily due to the complexity of the synthetic protocols involved and the use of hazardous reagents. Although the development of phytosynthetic methods for the green fabrication of nanomaterials have seen keen interest, there remains much scope for improvement in terms of maximizing adsorption capacity and controlling the size of the nanoparticles produced. A green and sustainable pathway is described using Virginia creeper (<i>Parthenocissus quinquefolia</i>) leaf extract in the presence of oxalic acid for the synthesis of earth abundant Fe,Cu-based nanoparticle adsorbents. This optimized green method could produce Fe,Cu-based nanoparticles with a remarkably high maximum adsorptive capacity (1399 mg g^–1) for aqueous Malachite Green (MG) removal. Furthermore, various particle sizes (between 160 and 1000 nm) were attained by simply varying the amount of oxalic acid. The synthesized adsorbent displayed other excellent characteristics, including (i) maintaining a high adsorption capacity over a wide range of pH conditions, (ii) remaining chemically stable under an ambient storage environment, and (iii) having good recycling potential, with consistent removal efficiency observed over four adsorption/desorption cycles. This work not only promotes the use of natural, earth-abundant, and renewable resources in synthesizing novel and efficient absorbents but also provides a simple, convenient, and cost-effective strategy for the purification of dye-laden wastewater