Effect of bridge height on airflow and aeolian sand flux near surface along the Qinghai-Tibet Railway, China.

In this work, we studied the near-surface flow field structure of railway bridges with different heights through field investigation and wind tunnel simulation experiments. Meanwhile, we simulated the distribution of sand accumulation around a bridge via CFD software based on the sand accumulation around the Basuoqu bridge in the Cuona Lake section of the Qinghai-Tibet Railway. Results show that the sand around this railway bridge is mainly from the lake sediment on the west side of the railway and the weathered detritus on the east side. The height of the railway bridge in the sandy area affects the distribution of the near-surface flow field and the variation in speed on both sides of the bridge. The wind speed trough on both sides of the 6 m high bridge is higher, and the horizontal distance between the wind speed trough and the bridge section is 1.5 times that of the 3 m high bridge. Wind speed attenuates in a certain range on the windward and leeward sides of the bridge, forming an aeolian area; under the beam body, it is affected by the narrow tube effect, forming a wind erosion area. The height of the bridge determines its sand transport capacity. Under certain wind conditions, the overhead area at the bottom of the 3 m high bridge and its two sides do not have the sand transport capacity, so sand accumulates easily. Nevertheless, the sand accumulation phenomenon gradually disappears with the increase in bridge clearance height. The objectives of this study are to reveal the formation mechanism of sand damage for railway bridges, provide theoretical support for the scientific design of railway bridges in sandy areas, and formulate reasonable railway sand prevention measures to ensure the safety of railway running, which have certain theoretical significance and practical value.

Activation of peroxydisulfate by zero valent iron-carbon composites prepared by carbothermal reduction: Enhanced non-radical and radical synergies.

Since its application in environmental remediation, nano zero-valent iron (nZVI) has gained wide attention for its environmental friendliness, strong reducing ability, and wide range of raw materials. However, its high preparation cost and difficulty in preservation remain the bottlenecks for their application. Carbothermal reduction is a promising method for the industrial preparation of nZVI. Micronized zero-valent iron/carbon materials (Fe0/CB) were produced in one step by co-pyrolysis of carbon and iron. The performance of the Fe0/CB is comparable to that of nZVI. In addition, Fe0/CB overcomed the disadvantages of agglomeration and oxidative deactivation of nZVI. Experiments on the Fenton-like reaction of its activated PDS showed that metronidazole (MNZ) was efficiently removed through the synergistic action of radicals and non-radicals, which were mainly superoxide radicals (·O2-), monoclinic oxygen (1O2), and high-valent iron (FeIVO). Moreover, the degradation process showed better generalization, making it suitable for a wide range of applications in the degradation of antibiotics.

Sodium salt promoted the generation of nano zero valent iron by carbothermal reduction: For activating peroxydisulfate to degrade antibiotic.

Carbothermal reduction is a promising method for the industrial preparation of nano-zero-valent iron. Preparing it also involves very high pyrolysis temperatures, which leads to a significant amount of energy consumption. The temperature required for the preparation of nano-zero-valent iron by carbothermal reduction was reduced by 200 °C by the addition of sodium salt. Carbon-loaded nano zero-valent iron (Fe0/CB-Na) was prepared by carbothermal reduction through the addition of sodium salt. The results showed that Fe0/CB-Na@700 had the same activation performance as Fe0/CB@900 and the newly prepared nano-zero-valent iron. The addition of sodium salt promoted the transfer of oxygen from the iron oxide to the carbon structure during the roasting process so that the iron oxide was reduced to as much Fe0 as possible. Thus, sodium salts were optimized for the preparation of nano-zero-valent iron by carbothermal reduction through interfacial amorphization and oxygen transfer, thus reducing the preparation cost.

Lanthanum-doped magnetic biochar activating persulfate in the degradation of florfenicol.

In this study, lanthanum-doped magnetic biochar (LaMBC) was synthesized from bagasse by co-doping iron salt and lanthanum salt, and it was characterized for its application in the activation of persulfate (PS) in the degradation of Florfenicol (FLO). The results indicated that the LaMBC/PS system consistently achieved a degradation efficiency of over 99.5 %, with a reaction rate constant 4.71 times as that of MBC. The mechanism of FLO degradation suggested that O2•- and •OH played dominant roles, contributing 40.92 % and 36.96 %, respectively, during FLO degradation. Through physicochemical characterization and quenching experiments, it can be concluded that the key reasons for the enhancement of MBC activation performance are as follows: (1) Lanthanum doping in magnetized biochar increased the Fe(II) content in MBC. (2) Lanthanum doping significantly improved the adsorption capacity of LaMBC, increased the concentration of pollutants on the catalyst surface and effectively enhancing the reaction rate. (3) Lanthanum doping effectively increased the surface Fe(II) content during the reaction process in LaMBC, promoted the generation of active oxygen species in PS. This study delves into synthesizing and applying LaMBC for PS activation and FLO removal. The emphasis is on comprehensively characterizing and experimenting to elucidate the mechanism, proposing an innovative approach for efficiently degrading antibiotic wastewater.

Simultaneous remediation of co-contaminated soil by ball-milled zero-valent iron coupled with persulfate oxidation.

The problem of co-contaminated soil at e-waste dismantling sites is serious and constitutes a critical threat to human health and the ecological environment. Zero-valent iron (ZVI) has been proven to be effective in the stabilization of heavy metals and the removal of halogenated organic compounds (HOCs) from soils. However, for the remediation of co-contamination of heavy metals with HOCs, ZVI has disadvantages such as high remediation cost and inability to take into account both pollutants, which limits its large-scale application. In this paper, boric acid and commercial zero-valent iron (cZVI) were used as raw materials to prepare boric acid-modified zero-valent iron (B-ZVIbm) through a high-energy ball milling strategy. B-ZVIbm coupled with persulfate (PS) to achieve simultaneous remediation of co-contaminated soil. The synergistic treatment of PS and B-ZVIbm resulted in the removal efficiency of 81.3% for decabromodiphenyl ether (BDE209) and the stabilization efficiencies of 96.5%, 99.8%, and 28.8% for Cu, Pb, and Cd respectively in the co-contaminated soil. A series of physical and chemical characterization methods showed that the oxide coat on the surface of B-ZVIbm could be replaced by borides during ball milling. The boride coat facilitated the exposure of the Fe0 core, promoted the corrosion of ZVI and the orderly release of Fe2+. The analysis of the morphological transformation of heavy metals in soils revealed that most of the heavy metals in the exchangeable, carbonate-bound state were transformed into the residue state, which was the key mechanism for the remediation of heavy metal-contaminated soils with B-ZVIbm. The analysis of BDE209 degradation products showed that BDE209 was degraded to lower brominated products and further mineralized by ZVI reduction and free radical oxidation. In general, B-ZVIbm coupled with PS is a good recipe for synergistic remediation of co-contaminated soils with heavy metals and HOCs.

Remediation of polybrominated diphenyl ethers contaminated soil in the e-waste disposal site by ball milling modified zero valent iron activated persulfate.

Hydrophobic organic compounds (HOCs) in e-waste disposal sites are difficult to remove effectively. There is little reported about zero valent iron (ZVI) coupled with persulfate (PS) to achieve the removal of decabromodiphenyl ether (BDE209) from soil. In this work, we have prepared the flake submicron zero valent iron by ball milling with boric acid (B-mZVIbm) at a low cost. Sacrifice experiments results showed that 56.6% of BDE209 was removed in 72 h with PS/B-mZVIbm, which was 2.12 times than that of micron zero valent iron (mZVI). The morphology, crystal form, atomic valence, composition, and functional group of B-mZVIbm were determined by SEM, XRD, XPS, and FTIR, and the results indicated that the oxide layer on the surface of mZVI is replaced by borides. The results of EPR indicated that hydroxyl radical and sulfate radical played the dominant role in the degradation of BDE209. The degradation products of BDE209 were determined by gas chromatography-mass spectrometry (GC-MS), accordingly, the possible degradation pathway was further proposed. The research suggested that ball milling with mZVI and boric acid is a low-cost means of preparing highly active zero valent iron materials. And the mZVIbm has promising applications in improving the activation efficiency of PS and enhancing the removal of the contaminant.

Influence of calcination temperature on the fluorescence and magnetic properties of Gd2O3:Tb3+, K+ nanoparticles.

Gd2O3:Tb3+ nanoparticles were synthesized by using diethylene glycol as a solvent and doped with 3 mol% K+ ions. Gd2O3:Tb3+, K+ nanoparticles were calcinated at 600°C, 700°C, 800°C, and 900°C and subjected to the analysis of x-ray diffractometer, transmission electron microscope, Fourier transform infrared spectrometer, fluorescence spectroscopy, and magnetization. The experimental results showed that as the calcination temperature increased from 600°C to 800°C, the morphology and particle size of the Gd2O3:Tb3+, K+ nanoparticles did not change significantly; whereas when the calcination temperature rose from 800°C to 900°C, the structure of Gd2O3 particles changed from cubic to monoclinic. As the temperature increased (below 800°C), the crystallinity of the cubic particles increased and the surface defects of the particles decreased, resulting in an increase in fluorescence intensity. For the monoclinic particles, the fluorescence intensity was significantly decreased and the magnetization was increased. The measured magnetic results confirmed the good paramagnetism of the synthesized nanoparticles.