Surface Leaching Research Articles

Beneficiation of High Sulfur Tertiary Coal of Assam with Burkholderia sp. GR 8-02. An Eco-Friendly Approach Toward Clean Coal Production

The high sulfur content in North-East Indian coal is one of the primary challenges with using it as an energy source. Therefore, the present study uses Burkholderia sp. GR 8-02 to explore coal beneficiation from the Tipong mine (T20 and T60) in Assam (North-East India). Various particle size fractions (−125 to +210 µm, −210 to +250 µm, −250 to +297 µm, −297 to +400 µm and −400 to +500 µm) were treated and subjected to petrographic and chemical analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS), Thermogravimetric analysis (TGA), and Raman spectral analysis. The results revealed a 39.04% and 32.43% reduction in total sulfur for T20 and T60 samples, respectively. The ash content decreased by 19.79% in the T20 coal sample and by 24.52% in the T60 coal samples, with a relative decrease in the mineral matter content of approximately 17.43%. Following beneficiation with Burkholderia sp. GR 8-02, the −125 to +250 µm coal fraction exhibited maximum ash removal. The T20 sample useful heating value increased from 8116 to 8203 kcal/kg and the T60 sample from 8060 to 8210 kcal/kg. X-ray diffraction and FTIR patterns showed mineral phases like quartz, kaolinite, and pyrite. The FTIR spectra indicated altered C-S, SO2, and C=O bonds. The thermal profile showed a 12.54% mass loss difference between untreated and treated coal samples, suggesting lower thermal stability post-treatment without affecting the useful heating value (UHV). The treated coal’s surface leaching and morphological structure changes were investigated using Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) images. Raman analysis revealed increased carbon crystallinity and molecular structure in treated coal. This study offers an environmentally friendly and efficient approach to clean coal production.

Main controlling factors and exploration enlightenment of aluminous rock series gas reservoirs in Ordos Basin, NW China

Based on the data of outcrop, core, logging, gas testing, and experiments, the natural gas accumulation and aluminous rock mineralization integrated research was adopted to analyze the controlling factors of aluminous rock series effective reservoirs in the Ordos Basin, NW China, as well as the configuration of coal-measure source rocks and aluminous rock series reservoirs. A natural gas accumulation model was constructed to evaluate the gas exploration potential of aluminous rock series under coal seam in the basin. The effective reservoirs of aluminous rock series in the Ordos Basin are composed of honeycomb-shaped bauxites with porous residual pisolitic and detrital structures, with the diasporite content of greater than 80% and dissolved pores as the main storage space. The bauxite reservoirs are formed under a model that planation controls the material supply, karst paleogeomorphology controls diagenesis, and land surface leaching improves reservoir quality. The hot humid climate and sea level changes in the Late Carboniferous–Early Permian dominated the development of a typical coal-aluminum-iron three-stage stratigraphic structure. The natural gas generated by the extensive hydrocarbon generation of coal-measure source rocks was accumulated in aluminous rock series under the coal seam, indicating a model of hydrocarbon accumulation under the source. During the Upper Carboniferous–Lower Permian, the relatively low-lying area on the edge of an ancient land or island in the North China landmass was developed. The gas reservoirs of aluminous rock series, which are clustered at multiple points in lenticular shape, are important new natural gas exploration fields with great potential in the Upper Paleozoic of North China Craton.

Durability and performance of wood flour/polyethylene composites containing fire retardants after weathering via ASTM D2565

Wood–plastic composites are composite materials consisting of wood particles, thermoplastic polymer, and small amounts of other performance additives to increase performance in exterior construction applications such as decking and siding. Three best-performing fire retardants, determined from a previous study, which were brominated, magnesium hydroxide, and ammonium polyphosphate, were selected for this weathering study and more detailed analysis with color analysis, thermogravimetric analysis/differential scanning calorimetry, and the cone calorimeter. With the rapid surface heating condition at cone calorimeter irradiance of 50 kW m−2, modest surface leaching of fire retardant was detected as caused by weathering via increased first peak heat-release rate and reduced time to ignition values. Otherwise, the weathering had minimal effect on the remaining heat-release rate profile, and results confirmed ammonium polyphosphate as top performing fire retardant, even better than Ipe wood, with magnesium hydroxide and brominated slightly worse than Ipe. This suggests that 35% high-density polyethylene content reduced fire retardant bulk leaching.

The effects of electrochemical pretreatment and curing environment on strength and leaching of stabilized/solidified contaminated sediment

Stabilization and solidification (S/S) is known to improve the structural properties of sediment and reduce contaminant mobility, enabling the utilization of dredged contaminated sediment. Further reduction of contaminants (e.g., tributyltin (TBT) and metals) can be done using electrochemical treatment prior to S/S and could potentially minimize contaminant leaching. This is the first study on how electrochemical pretreatment affects the strength and leaching properties of stabilized sediments. It also investigates how salinity and organic carbon in the curing liquid affect the stabilized sediment.The results showed that the electrolysis reduced the content of TBT by 22% and zinc by 44% in the sediment. The electrolyzed stabilized samples met the requirements for compression strength and had a reduced surface leaching of zinc. Curing in saline water was beneficial for strength development and reduced the leaching of TBT compared to curing in fresh water. The results indicate that pretreatment prior to stabilization could be beneficial in reducing contaminant leaching and recovering metals from the sediment. The conclusion is that a better understanding of the changes in the sediment caused by electrochemical treatment and how these changes interact with stabilization reactions is needed. In addition, it is recommended to investigate the strength and leaching behavior in environments similar to the intended in situ conditions.

Assessment and prediction of hexavalent chromium vulnerability in groundwater by Geochemical modelling, NOBLES Index and Random Forest Model

Unregulated chromite mining causes enrichment of hexavalent chromium in the groundwater. Due to unpredictable monsoonal recharge and anthropogenic dependencies on groundwater, the depth and extent of chromium pollution becomes extremely difficult to demarcate. For this specific objective, the present study was carried out in order to explore the potential of a coupled surface and sub-surface modelling approach in Sukinda valley, which accounts for 97–98 % of the total chromite reserve of India. Through ionic speciation, saturation state and clustering analysis, the most probable source and corresponding mineral stability state was investigated. In order to trace the extent, status and severity of the problem, both hydrogeologic parameters as well as the geogenic soil parameters were taken into account to develop DRASTIC, DRASTIC-L as well as NOBLES Index. While DRASTIC and DRASTIC-L model provided assessment of vulnerability due to surface leaching of contaminants, NOBLES index, speciation analysis and geochemical model provided sub-surface assessment of vulnerability due to chromium. MRSA and SPSA sensitivity analysis were applied in order to understand the most critical factor that can dominantly control the surface contamination in the groundwater. Random Forest (RF) based machine learning techniques were applied in order to integrate the sub-surface as well as surface characteristics for the purpose of prediction of chromium in the groundwater. The present study therefore presents a novel methodology of risk assessment for regions where either extensive mining activities are operational or in regions with abandoned mines with operative acid mine drainage.

Evaluation of sealants to mitigate the release of per- and polyfluoroalkyl substances (PFAS) from AFFF-impacted concrete: Characterization and forecasting

Per- and polyfluoroalkyl substances (PFAS) within concrete pads impacted by historical firefighting training using aqueous film-forming foam (AFFF) may be potential secondary sources of PFAS due to surficial leaching. This study aimed to (i) characterize the effectiveness of two commercially available sealants (Product A and Product B) in mitigating leaching of five PFAS (e.g., PFOS, PFOA, PFHxS, PFHxA, 6:2 FTS) from concrete surfaces at the laboratory-scale, and (ii) develop a model to forecast cumulative leaching of the same five PFAS over 20 years from sealed and unsealed concrete surfaces. Laboratory trials demonstrated that both sealants reduced the surficial leaching of the five PFAS studied, and Product B demonstrated a comparatively greater reduction in surface leaching than Product A as measured against unsealed controls. The cumulative PFOS leaching from an unsealed concrete surface is estimated by the model to be about 400 mg/m2 over 20 years and reached asymptotic conditions after 15 years. In contrast, the model output suggests asymptotic conditions were not achieved within the modeled time of 20 years after sealing with Product A and 85% of PFOS was predicted to have leached (∼340 mg/m2). Negligible leaching of PFOS after sealing with Product B was observed ( < 5 × 10−9 mg/m2). Results from modeled rainfall scenarios suggest PFAS leachability is reduced from sealed versus unsealed AFFF-impacted concrete surfaces.

Optimized Workflow Framework in Construction Projects to Control the Environmental Properties of Soil

To optimize the workflow of civil engineering construction in a harbour, this paper developed a framework of the contaminant leaching assessment carried out on the stabilized/solidified dredged soil material. The specimens included the sampled sediments collected from the in situ fieldwork in Arendal and Kongshavn. The background levels of the concentration of pollutants were evaluated to assess the cumulative surface leaching of substances from samples over two months. The contamination of soil was assessed using a structured workflow scheme on the following toxic substances, heavy metals—As, Pb, Cd, Cr, Hg, Ni, and Zn; organic compounds—PAH-16 and PCB; and organotin compounds—TBT. The numerical computation and data analysis were applied to the results of geochemical testing creating computerised solutions to soil quality evaluation in civil engineering. Data modelling enabled the estimation of leaching of the contaminants in one year. The estimated leaching of As is 0.9153 mg/m2, for Ni—2.8178 mg/m2, for total PAH-16 as 0.0507 mg/m2, and for TBT—0.00061 mg/m2 per year. The performance of the sediments was examined with regard to permeability through a series of the controlled experiments. The environmental engineering tests were implemented in the Swedish Geotechnical Institute (SGI) in a triplicate mode over 64 days. The results were compared for several sites and showed that the amount of As is slightly higher in Kongshavn than for Arendal, while the content of Cd, Cr, and Ni is lower. For TBT, the levels are significantly lower than for those at Arendal. The algorithm of permeability tests evaluated the safety of foundation soil for construction of embankments and structures. The optimized assessment methods were applied for monitoring coastal areas through the evaluated permeability of soil and estimated leaching rates of heavy metals, PHB, PACs, and TBT in selected test sites in harbours of southern Norway.

Assessment of Dynamic Surface Leaching of Monolithic Polymer Mortars Comprised of Wastes

Today, the reuse of waste in building materials occupies an important place in the approach to the circularity of materials. National and European environmental regulations require ensuring the environmental safety of material-incorporating waste. For this, there are specific tests to verify that there is no health risk when using these materials. Concretely, to check the environmental acceptability of construction materials, including wastes, the release of hazardous substances into water must be assessed. In this research, we performed a diffusion test with the sequential renewal of water during a 64-day period according to the NF EN 15863 specifications on polymer mortar monoliths, common construction products used in floor-covering applications and incorporating sediments. Polymer mortars were prepared at a laboratory scale by incorporating 30 or 50% of polluted sediment for various polymer concentrations (12, 14, 16, 18, 20 and 25%). It was shown that the release of inorganic substances is limited in these hydrodynamic conditions. Among trace elements, As, Cd, Cr, Ni, Pb and Zn are lower than quantification limits in most leachates, whereas Ba, Co, Cu and V are systematically quantified at low concentration levels. This is particularly true for samples displaying the highest polymer concentration (25%) and the lowest sediment incorporation rate (30%). This is because of the low water absorption level and low porosity of polymer mortar matrices. No adverse effect is to be expected for environmental health from the leachates of these construction materials, including waterways sediments, because all the measured parameters were below the Soil Quality Decree limits applied in the Netherlands for environmental assessment of construction products.

Investigating the ecotoxicity of construction product eluates as multicomponent mixtures

BackgroundThe release of hazardous compounds from construction products can harm human health and the environment. To improve the sustainability of construction materials, the leaching of substances from construction products and their potential environmental impact should be assessed. Twenty-seven construction products from different product groups were examined with a combination of standardized leaching tests (dynamic surface leaching test and percolation test) and biotests (algae, daphnia, fish egg, luminescent bacteria, umu and Ames fluctuation tests). To identify the released substances, extensive qualitative and quantitative chemical analyses were performed, including gas chromatographic and liquid chromatographic screening techniques.ResultsMany of the tested eluates caused significant ecotoxic effects. Particularly high ecotoxicities were observed for grouts (lowest ineffective dilution (LID) up to 16384) and cork granules (LID up to 24578). The results of ecotoxicity tests allow the prioritization of the eluates that should be subjected to detailed chemical analyses. Organic screening by different methods and ranking the identified substances based on recorded hazard classification is a suitable approach to identify the relevant toxic substances.ConclusionsDetermining the ecotoxicity of eluates from construction products records the summary effect of all leachable substances. This instrument is especially useful for construction products of complex and largely unknown composition. The ecotoxicological and the chemical–analytical approach complement each other in an ideal way to characterize the potential hazard of eluates from construction products and to identify the environmentally hazardous components in these eluates. Our results confirm that the proposed harmonized methods for testing eluate toxicity are an adequate and applicable procedure to move toward a more sustainable way of building and to reduce toxic effects of construction products in their use phase in the environment..

Desalination of saline fields by soil leaching in the Karkhehnur Watershed, Iran

Abstract Since large parts of agricultural fields are saline or subjected to salinity stress, practical and efficient methods may be used for recycling fields, worldwide. The effects of the type and amount of soil leaching on the quality of saline fields, in different parts of the world have yet to be investigated. The objectives were to investigate: (1) the optimum depth of water required to decrease soil salinity of saline fields to the levels, suitable for crop production in the Karkhehnur Watershed, Khuzestan province, Iran, and (2) the most suitable method of soil surface leaching. Four different regions were selected for the experiment, and a wide range of soil-related parameters as well as water properties was determined. Soil leaching was conducted by surface continuous irrigation (three regions), and surface alternative irrigation (one region). The depths of soil leaching were equal to 0–25, 25–50, 50–75, 75–100, 100–125, and 125–150 cm. The class of salinity was changed to S2 (EC = 24 dS/m) from an initial class of S4 (EC = 87 dS/m) using a water depth of 25–125 cm in different experimental regions. If soil is highly saline, continuous irrigation may be a more effective method, however, under less stressful conditions, alternative irrigation can also be recommendable.

Stabilization/solidification of lead- and cadmium-containing tailings for cemented paste backfill by using clinker-free binders

Clinker-free cementitious materials are essential for both lowering the costs of cemented paste backfill (CPB) and ensuring that the heavy metal leaching meets relevant standards. This study investigated the influence of Pb(Ⅱ) and Cd(Ⅱ) on the hydration and mechanical properties of slag-based low-carbon binders, as well as the solidification/stabilization (S/S) efficiency of Pb(Ⅱ)- and Cd(Ⅱ)-containing tailings. The presence of Pb(Ⅱ) not only retarded the binder hydration but also decreased the compressive strength, while such negative effects were relatively little when adding Cd(Ⅱ); besides, the addition of calcined quarry dust (CQD) reduced these adverse impacts. X-ray diffractometry and thermogravimetric analysis showed that both Pb(Ⅱ) and Cd(Ⅱ) can influence the phase assembles, and hydrocerussite was detected in the composites containing Pb(II). Moreover, a horizontal semi-dynamic surface leaching test revealed that the main mechanism of Pb(Ⅱ) and Cd(Ⅱ) leaching is diffusion and adding CQD reduces their leachability and mean effective diffusion coefficient. The resulting solidified/stabilized tailings fulfilled the heavy metal leachability and mechanical strength requirements for CPB; this demonstrates that low-carbon binders can be effectively used for the sustainable treatment of Pb(Ⅱ)- and Cd(Ⅱ)-containing tailings, for CPB applications.

Provenance change and continental weathering of Late Permian bauxitic claystone in Guizhou Province, Southwest China

Known as the Guadalupian-Lopingian boundary (GLB), the unconformity between the Guadalupian (Middle Permian) and Lopingian (Late Permian) is widespread in the South China Block. This boundary presents an important period with actives of the Emeishan Large Igneous Provenance (ELIP), the regression and the mass extinction. In Zunyi and Liupanshui areas of Guizhou Province, southwestern China, marine deposits of the Middle Permian Maokou Formation were covered by the terrigenous deposits of the Upper Permian Longtan Formation, the bauxitic claystone at the bottom of the Longtan Formation indicates the exposure during the Middle - Late Permian transition. The provenance of this bauxitic claystone in the South China is complicated, previous studies argue that the flood basalt and submarine volcanic rocks in the ELIP and the aeolian tuff in the Indochina Block are potential sources. In this study, new mineralogical, geochronological and geochemical data are got from the NW Guizhou, our new data constrain the age of bauxitic claystone in Zunyi and Liupanshui are 262.1 ± 1.5 Ma and 267.0 ± 2.7 Ma, respectively. Combined with trace element geochemical analysis, the source materials of bauxitic claystone in Zunyi is mainly derived from the intermediate-acid extrusive rocks in the ELIP, while the provenance of bauxitic claystone in Liupanshui is derived from the submarine volcanic activities during the initial stage of the ELIP. From the central area of ELIP to the outer area, the provenance of early Late Permian sediments transforms from the volcanic rocks of ELIP to Paleo-Tethys magmatic arc. Mass balance calculation and geochemical multivariate statistical methods show that the bauxitic claystone in Zunyi experienced two groundwater level variations in the land surface leaching stage, and Fe2O3、P2O5、HREE show similar geochemical behaviors. HREE is adsorbed by iron phase minerals and phosphate minerals, resulting in simultaneous migration. Our study also finds that paleogeographic location is an important factor for Late Permian bauxitization in South China. The different paleogeographic location determines the supply mode of provenance, provenance lithology, exposure time, leaching degree and other factors.

Influence of different silicone oils on properties of MWCNTs-OH/PDMS coatings

ABSTRACT To research the influence of different silicone oil on the properties of the coatings based on polydimethylsiloxane (PDMS) reinforced by hydroxylated multi-walled carbon nanotubes, phenylmethyl silicone oil (PSO), methyl silicone oil (MSO), and the blend of PSO and MSO were incorporated into the antifouling coatings. The surface properties and leaching of silicone oil were investigated by water and diiodomethane contact angle and confocal laser scanning microscopy (CLSM). The mechanical properties were investigated by tensile test, and the antifouling properties were tested via bacterial biofilms and the diatom Navicula tenera adhesion. Results revealed that leaching rate, hydrophobicity, and surface free energy with coating with the blend of MSO and PSO (P/M-PDMS) was between those of the coating with PSO (PSO-PDMS) and coating with MSO (MSO-PDMS). P/M-PDMS was better than MSO-PDMS in resisting fouling organisms. P/M-PDMS prolonged the leaching process of the blend of MSO and PSO and showed better antifouling performance.

Geochemical tests to study the effects of cement ratio on potassium and TBT leaching and the pH of the marine sediments from the Kattegat Strait, Port of Gothenburg, Sweden

Cement is a key construction material in civil and geotechnical engineering. However, its application for stabilization of marine sediments needs further investigation. This paper tests the effects of varied amounts of Portland cement added to soil samples on the leaching of tributyltin (TBT) from the contaminated marine sediments and evaluates the pH level. Identifying the best combinations of Portland cement / slag / Cement Kiln Dust (CKD) for effective treatment of soil samples is a central challenge in marine geotechnical investigations with major implications for stabilization of dragged coastal sediments. The paper aims to test the TBT leaching as well as pH level and potassium (K) content in soil samples. Materials included marine sediments collected from the seabed of the Port of Gothenburg, Kattegat Strait, southwest Sweden. The methodology applied the existing specifications of the Swedish Institute for Standards (SIS) for geochemical tests of soil stabilized by Portland cement/slag/CKD. Leaching in soil samples was examined for 2.25, 9 and 36 days. Variations in the speed of decline of TBT leaching were noted depending on the ratio of Portland cement. The methodology follows the SIS instructions regarding the procedure of leaching tests: SS-EN 15863. Mixtures with pure Portland cement and cement / CKD gave pH values between 11.5–12 in the surface leaching experiments. Mixing of slag / CKD or slag lowered the pH range to 11–11.5 and 10–10.5, respectively. The leaching of TBT was affected by the changed amounts of seawater in the surface leaching experiments. The study shows that leaching reduces over time when the mobile fraction is being washed away and replaced by other leaching mechanisms and processes. Furthermore, in models in which leaching of TBT and potassium were assessed, there were, on average, changes in behaviour on the 9th day during the experiment time treatment and stabilization afterwards.

Impact of Iron and Aluminum on the Aggregate Stability of Some Latosols in Central and Southern Liberia (West Africa)

Problem: Latosols of Liberia are marked by intense surface leaching, strong acidity, low soil organic matter (SOM) content, and low nutrients status, caused by low aggregate stability, which are limiting factors to crop production.&#x0D; Aim: to evaluate the effect of soil organic carbon (SOC) different forms of Fe and Al on the aggregate stability of latosols.&#x0D; Methodology: Composite surface (0-20 cm depth) samples of four latosols at different localities in Liberia (Lat1, Phebe; Lat2, Felela; Lat3, Salala; Lat4, Todee) were collected and analyzed for aggregate stability parameters and factors by standard laboratory methods.&#x0D; Results: the studied soils are sandy clayey, very acidic and poor in SOC. The cation exchange capacity (CEC) ranges from 10.28 to 14.80 mmol.kg−1. Dominant forms of Al and Fe are free Fe (Fed) and Al [1], followed by amorphous Fe (Feo) and Al (Alo) and chelated Fe (Fep) and Al (Alp). The highest levels of water dispersible clay (WDC) and clay dispersible index (CDI) in Lat1 and Lat2 implied that these two soils are less stable compared to Lat3 and Lat4. The Fe and Al in all forms seem to contribute to soil aggregate stability. The SOC, although very low, also contributes to soil aggregate stability. SOC correlated positively with WDC, CDI and ASC, indicating the impact of SOC both as an aggregating agent and as a dispersing agent, in contrast to previous studies.&#x0D; Conclusion: The study reveals that Fe, Al and SOC are cementing materials which impact the aggregate stability in Latosols.

Ecotoxicological evaluation of construction products: inter-laboratory test with DSLT and percolation test eluates in an aquatic biotest battery

BackgroundA European inter-laboratory test with 29 participating laboratories investigated whether a battery of four ecotoxicological tests is suitable for assessing the environmental compatibility of construction products. For this purpose, a construction product was investigated with the dynamic surface leaching test (DIN CEN/TS 16637-2) and the percolation test (DIN CEN/TS 16637-3). The eluates were produced centrally by one laboratory and were tested by the participants using the following biotests: algae test (ISO 8692), acute daphnia test (ISO 6341), luminescent bacteria test (DIN EN ISO 11348), and fish egg test (DIN EN ISO 15088). As toxicity measures, EC50 and LID values were calculated.ResultsToxic effects of the eluates were detected by all four biotests. The bacteria test was by far the most sensitive, followed by the algae test and the daphnia test; the fish egg test was the least sensitive for eluates of both leaching tests. The toxicity level of the eluates was very high in the bacteria, daphnia, and algae test, with lowest ineffective dilution values of LID = 70 to LID = 13,000 and corresponding EC50 values around or even below 1 volume percent. The reproducibility (approximated by interlaboratory variability) of the biotests was good (< 53%) to very good (< 20%), regardless of the toxicity level of the eluates. The reproducibility of the algae test was up to 80%, and thus still acceptable.ConclusionIt can be confirmed that the combination of leaching and ecotoxicity tests is suitable to characterize with sufficient reproducibility the environmental impact posed by the release of hazardous substances from construction products.

Leaching and VOC Emission Tests of Polymer Composites Produced from Post-Consumer Waste in Terms of Application in the Construction Sector.

One of the existing priorities of the European Union is to search for rational waste management and to keep such waste in the economic cycle, while meeting the highest safety requirements. The paper presents the results of environmental tests of composites based on the polyethylene (rPE) and polypropylene (rPP) matrix and reinforced with cellulose fibres (newsprint, NP). Raw materials were obtained by recycling post-consumer waste such as beverage bottles and newsprint. The composites were tested for their potential use as materials in cladding panels and acoustic barriers. Given that normative documents for these products do not define specific environmental requirements, the composites were tested for the release of dangerous substances, such as anions of inorganic compounds, heavy metals, volatile organic compounds (VOCs), and their impact on the environment. A detailed in-depth analysis of the mechanisms of release of substances (diffusion, dissolution, surface leaching and depletion) from the rPP/NP composite into surface water, groundwater and soil was carried out. In turn, emission of VOCs from the rPE (low-density:high-density (LD:HD)—50:50) and rPE (LD:HD—30:70) composites into indoor air was also carried out. Raw materials in the form of granulates and loose cellulose fibres, used to produce the composites, were also tested for their environmental impact.

Effect on electrical and magnetic behavior of Al–Cu–Fe quasicrystals during surface leaching

Effect on electrical and magnetic behavior of Al–Cu–Fe quasicrystals during surface leaching

P–nitrophenol degradation by hybrid advanced oxidation process of heterogeneous Fenton assisted hydrodynamic cavitation: Discernment of synergistic interactions and chemical mechanism

The present study has investigated p-nitrophenol (PNP) degradation by hybrid advanced oxidation process (AOP) of hydrodynamic cavitation with heterogenous Fe3O4 nanoparticles. 78.8 ± 1.2% of PNP degradation was obtained at optimum operational conditions: inlet pressure = 8 atm, pH = 3, initial concentration of PNP = 20 mg L−1, Fe3O4:H2O2 = 1:100. PNP degradation profiles were analyzed using a kinetic model based on the reaction network. The closest match between the simulated and experimental degradation profiles was obtained for the initial concertation of [H2O2] = 0.6 M, which was far higher than concentration of externally added H2O2. This was attributed to in-situ generation of H2O2 through transient cavitation. Intense shear and turbulence generated in cavitating flow caused surface leaching of Fe3O4 particles that released Fe2+/Fe3+ ions. The synergy in the hybrid AOP was in-situ Fenton reactions between leached Fe2+/Fe3+ ions and H2O2 present in the reaction mixture. The mechanism in •OH mediated oxidative degradation of PNP was further explored with Density Functional Theory (DFT) simulations. Both •OH addition on benzene ring and H–abstraction reactions were simulated to identify the possible pathways for the degradation. On the basis of activation free energy analysis, degradation pathways initiating with both •OH addition and H abstraction were determined to be feasible. The ortho−C of benzene ring was the most favourable site for •OH addition, while H atom of phenolic hydroxyl group was more susceptible (or more reactive) for H-atom abstraction route.

Benchmarking of oxygen evolution catalysts on porous nickel supports

Summary Active and inexpensive oxygen evolution reaction (OER) electrocatalysts are needed for energy-efficient electrolysis applications. Objective comparison between OER catalysts has been blurred by the use of different supports and methods to evaluate performance. Here, we selected nine highly active transition-metal-based catalysts and described their synthesis, using a porous nickel foam and a new Ni-based dendritic material as the supports. We designed a standardized protocol to characterize and compare the catalysts in terms of structure, activity, density of active sites, and stability. NiFeSe- and CoFeSe-derived oxides showed the highest activities on our dendritic support, with low overpotentials of η100 ≈ 247 mV at 100 mA cm–2 in 1 M KOH. Stability evaluation showed no surface leaching for 8 h of electrolysis. This work highlights the most active anode materials and provides an easy way to increase the geometric current density of a catalyst by tuning the porosity of its support.