Fe3O4 Surface Research Articles

Photocatalytic debromination enhancement of Ph-C≡C-Cu by Fe3O4 modification

A series of Fe3O4/Ph-C≡C-Cu magnetic hybrids were synthesized by a repeatable photothermal method in this work. The structure and morphology studies proved that Ph-C≡C-Cu grow on the surface of Fe3O4 in a different way, which significantly affected its physical properties and photocatalytic performance. With 4% Fe3O4 modification, the photocatalytic degradation rate of high concentration of pentabromophenol (PBP, 3 ×10−4 M) achieved the highest, which is 6 times higher than those of pure Ph-C≡C-Cu and Fe3O4. The degradation of hexabromobenzene (HBB) over Ph-C≡C-Cu was also improved to be twice higher. The excellent photocatalytic activity of Fe3O4/Ph-C≡C-Cu can be attributed to the big surface area, high carrier generation, transfer and separation efficiency. The TONs exceed 1 of both PBP and HBB degradation demonstrates real photocatalytic processes.

Effective stabilization of pickering emulsion using a smart material with V-shaped surface structure via controlled polymerization: Its multi-responsive behavior, recyclable process and applications

Poly (2-(dimethylaminoethyl methacrylate)-b-(glycidyl methacrylate)-b-(acrylic acid)) blocks prepared by RAFT polymerization were grafted to the surface of Fe3O4 to obtain four-responsive nanocomposite particles (P(DMAEMA-b-GMA-b-AA)/Fe3O4) with V-shaped surface structure. Subsequently, the structure and properties of the P(DMAEMA-b-GMA-b-AA)/Fe3O4 nanoparticles were characterized by FT-IR, TEM and TGA. Moreover, various factors on P(DMAEMA-b-GMA-b-AA)/Fe3O4 Pickering emulsion stability were investigated including pH, nanoparticle concentration, water–oil ratio and oil phase polarity. Notably, its superiority was demonstrated by the formation of the Pickering emulsion that underwent CO2, temperature, magnetic and pH-induced reversible emulsification/demulsification for at least 10 cycles without obvious performance decay or even morphology changes. It was demonstrated that the emulsification/demulsification mechanisms under the action of temperature, CO2, and temperature might be related to the surface wettability of nanoparticles by measuring zeta potential, interfacial tension and contact angle. Furthermore, the P(DMAEMA-b-GMA-b-AA)/Fe3O4 nanoparticles exhibited environmentally friendly behavior and could be easily recycled and further utilized through magnetic force. They were also found to stabilize diverse real oil phases. Therefore, the developed nanoparticles have significant potential for applications in oily wastewater treatment, oil transfer, and design of crude oil delivery systems.

Polyphenol‐Mediated Synthesis of Superparamagnetic Magnetite Nanoclusters for Highly Stable Magnetically Responsive Photonic Crystals

AbstractAchieving high stability and excellent optical performance in complex environments is crucial for practical applications of magnetically responsive photonic crystals (MRPCs). It, however, remains a great challenge. This study demonstrates a polyphenol‐mediated strategy for synthesizing size‐controllable superparamagnetic magnetite (Fe3O4) colloid nanocrystal clusters (CNCs) that can be stably dispersed in various polar solvents to form MRPCs with brilliant structural colors for a long term. As tannic acid (TA) functions as a linker to robustly bind polyvinylpyrrolidone (PVP) chains to Fe3O4 surfaces, the MRPCs can maintain nearly constant diffraction wavelength and high reflectance for up to 4 years. The strong coordination between TA and Fe3+ inhibits crystal growth, ensuring the small primary crystal size and superparamagnetism of Fe3O4@TA‐PVP CNCs. Partial oxidation of TA accelerates the crystal nucleation and growth, reducing the overall CNC particle size, which can be utilized for controlling the particle size. Additionally, enhancing the dissolution of PVP before the solvothermal reaction improves the size monodispersity of the products, making the as‐constructed MRPCs ideal for practical applications in color display, sensors, anti‐counterfeiting, and camouflage. The Fe3O4@TA‐PVP CNCs with high stability and versatility for surface‐functionalization are also promising for magnetic resonance imaging, targeting drug delivery, recyclable catalysis, and magnetic nanomotors.

The overlooked role of electrostatic repulsion between nanoparticle catalysts in ligand-enhanced heterogeneous Fenton-like reactions

Chelating agents are now frequently used to facilitate Fenton and Fenton-like reactions by building complexes with iron. A series of advantages can be exemplified, such as fast circulation of Fe(Ⅲ)/Fe(Ⅱ), enhanced catalytic performance of Fe-ligand, and iron precipitation inhibition, etc. However, few studies explored whether electrostatic repulsion between nanoparticle catalysts had an influence on catalytic performance in ligand-enhanced Fenton-like reactions. In this study, we discovered that the coexistence of 0.1 mM EDTA and 10 mM phosphate dramatically accelerated diclofenac (DCF) degradation by Fe3O4/Air (∼95% within 20 h). In-depth explorations demonstrated the enhanced electrostatic repulsion between Fe3O4 caused by the addition of EDTA and phosphate played a key role in the promoted DCF degradation. The enhanced electrostatic repulsion between Fe3O4 led to a notable increase in the percentage of Fe-EDTA, which benefited O2 activation and DCF degradation. Reactive oxygen species (ROS) were mainly generated through one-electron activation mechanism of O2 and •OH were confirmed to be predominant active species responsible for DCF degradation. Fe(Ⅱ)-EDTA on Fe3O4 surface was evidenced to be served as main sites for O2 and H2O2 activation. During the degradation reaction, sufficient surface Fe(Ⅱ) on Fe3O4 was maintained with the assistance of EDTA. Toxicity analysis showed that DCF was transformed into less toxic intermediates, demonstrating the feasibility of this technology in practical applications. This work for the first time reveals the importance of electrostatic repulsion between nanoparticle catalysts in ligand-enhanced Fenton-like reactions, providing a low-cost and effective advanced oxidation process for contaminants degradation.

Preparation of curcumol-loaded magnetic metal-organic framework using supercritical solution impregnation process

A metal-organic frameworks (MOFs)-based drug delivery system was prepared by supercritical solution impregnation (SSI) technology. Firstly, core-shell structured Fe3O4@UiO-66 composite was synthesized by in situ growth of MOFs layers on the surface of carboxy-functionalized Fe3O4. The composite exhibited superparamagnetic properties with a magnetization saturation of 5.51 emu/g, allowing magnetic targeting and MR imaging along with effective drug loading and controlled release. A hydrophobic anti-cancer drug, curcumol (CUR) was encapsulated into the synthesized composite using the SSI process and ethanol impregnation. The effects of impregnating solvent, impregnation time, impregnation temperature and impregnation pressure on the drug loading content were investigated. In SSI process, the drug load reached impregnation equilibrium within 2 h. In the range of pressure 10–20 MPa and temperature 40–60 °C, the drug loading content was varied from 1.09 wt% to 5.72 wt% by adjusting the impregnation conditions. The optimal impregnation conditions were 50 °C and 20 MPa. SSI was more efficient and faster compared to conventional ethanol impregnation, and the final product can be obtained without further purification. In in vitro drug release experiment, Fe3O4@UiO-66 exhibited a sustained controlled drug release for up to 36 h. Overall, SSI technology proves to be a promising strategy to maximize the drug loading capacity of Fe3O4@UiO-66.

The effect of Artemisia annua L. extract on microbiologically influenced corrosion of A36 steel caused by Pseudomonas aeruginosa

The protective effect of A. annua against microbiologically influenced corrosion (MIC) of A36 steel caused by P. aeruginosa (PA) in a simulated marine environment was investigated using electrochemical, spectroscopic, and surface techniques. PA was found to accelerate the local dissolution of A36 which led to the formation of a porous α-FeOOH and γ-FeOOH surface layer. 2D and 3D profiles of treated coupons, obtained by optical profilometer, revealed the formation of crevices in the presence of PA. On the contrary, adding A. annua to the biotic medium led to the formation of a thinner, more uniform surface without significant damage. Electrochemical data showed that the addition of A. annua prevented the MIC of A36 steel with an inhibition efficiency of 60%. The protective effect was attributed to the formation of a more compact Fe3O4 surface layer, as well as the adsorption of phenolics, such as caffeic acid and its derivatives on the A36 steel surfaces, as detected by FTIR and SEM-EDS analysis. ICP-OES confirmed that Fe and Cr species more readily diffuse from A36 steel surfaces incubated in biotic media (Fe; 1516.35 ± 7.94 μg L-1 cm−2, Cr; 11.77 ± 0.40 μg L-1 cm−2) compared to the inhibited media (Fe; 35.01 ± 0.28 μg L-1 cm−2, Cr; 1.58 ± 0.01 μg L-1 cm−2).

Mixed-Phase Fe2O3 Derived from Natural Hematite Ores/C3N4 Z-Scheme Photocatalyst for Ofloxacin Removal

Abatement of pharmaceutical pollutants from aquatic systems is crucial but remains a challenge. Semiconductor photocatalysis has emerged as an eco-friendly technique that utilizes renewable solar energy to address environmental issues. Naturally occurring and earth abundant hematite (Fe2O3) ores can be incorporated as a suitable component of a photocatalyst. Herein, Brazilian hematite was partially phase transformed into heterophase (consisting of α/γ-Fe2O3) by a simple single-stage heat treatment procedure. The method of synthesis was simple and economical, requiring neither solvents nor concentrated acids. The existence of α/γ-phases in the produced Fe2O3 (FO) was confirmed by X-ray diffraction analysis. After the phase transformation process, the local structure surrounding the Fe atoms was varied as evidenced from X-ray absorption spectroscopy. Given its low toxicity, narrow bandgap, and chemical stability, FO was further combined with g-C3N4 (CN) to form composites. The optical properties of the synthesized CNFO composites confirmed that the visible light harvesting ability of CN was enhanced after combining with FO. The CN sheets were grown uniformly over the surface of FO as evidenced from scanning electron microscopy. The prepared composites could degrade an aqueous solution of ofloxacin (OFX, 10 ppm) under visible light with remarkable efficacy. The performance of CNFO-5% was 4.8 times higher when compared to pure CN. The initial rate constant value for the photocatalytic degradation of OFX by CNFO-5% was 0.1271 min−1. The catalyst was stable even after five repeated cycles of photodegradation. The photoluminescence spectra and electrochemical measurements confirmed the efficient separation and transfer of the photogenerated charges across their interface. The investigations on different scavengers demonstrated that superoxide anion radicals and holes played a significant role in the degradation of OFX. The mechanism for the charge transfer was proposed to be a Z-scheme heterojunction. These results point to the potential of using inexpensive, abundant, and recyclable natural hematite ores as state-of-the-art photocatalysts for the elimination of pharmaceuticals in wastewater.

Experimental and theoretical studies of natural mineral attapulgite supported iron-based oxygen carriers in chemical looping hydrogen production

The low-priced and efficient oxygen carrier is the key to the successful operation of chemical looping hydrogen production (CLH) technology, and also the premise and foundation of its large-scale application. In this study, a novel iron-based oxygen carrier based on natural mineral attapulgite (ATP) was first applied to CLH. The effects of support on the performance of iron-based oxygen carrier and its mechanism in the CLH process were investigated. The results showed the Fe2O3 with ATP as support had more superior activity and stability than those supported by expanded perlite, kaolin or Al2O3. In particular, Fe6ATP4 exhibited a high hydrogen yield at 850 °C which was twice as high as that of Fe2O3/Al2O3. The excellent reaction performance of Fe2O3/ATP was validated by both experimental and theoretical methods. Density functional theory (DFT) calculations revealed that the electrons in Fe2O3/ATP system have stronger delocalization than those of Fe2O3/Al2O3. Moreover, XPS showed there were more defect oxides or hydroxyl groups on the surface of ATP-supported Fe2O3, which further facilitated the reduction reaction.

Enhancing the Potentiometric H2 Sensing of Pr0.1Ce0.9O2−δ Using Fe2O3 Surface Modification

Monitoring the concentration of hydrogen is very important as it is a flammable and explosive gas. Non-Nernstian potentiometric hydrogen sensors hold promising potentials for the sensitive detection of hydrogen. This paper reports the improved H2-sensing performance of a mixed oxide ion-electron conducting (MIEC) Pr0.1Ce0.9O2−δ (PCO) electrode using Fe2O3 surface modification. The Fe2O3-modified PCO exhibited a high response of −184.29 mV to 1000 ppm H2 at 450 °C. The response values exhibited a linear or logarithmic dependence on the H2 concentration for below or above 20 ppm, respectively. A sensitivity of −74.9 mV/decade in the concentration range of 20–1000 ppm was achieved, and the theoretical limit of detection was calculated to be 343 ppb. Moreover, a power-law relationship between the response time and the concentration value was also found. Electrochemical impedance analyses revealed that the excellent H2-sensing performance may be attributed to the large ratio of the electrochemical activity of the hydrogen oxidation reaction (HOR) over the oxygen exchange reaction (OER). In addition, the distribution of relaxation time (DRT) results reveal that the enhanced electrochemical kinetics caused by H2 presence in air is mainly related to acceleration of the electrode surface processes.

Green synthesis of magnetically separable and reusable Fe3O4/Cdots nanocomposites photocatalyst utilizing Moringa oleifera extract and watermelon peel for rapid dye degradation

This study focused on green-synthesized magnetite/carbon dots nanocomposites (GS-Fe3O4/Cdots) utilizing Moringa oleifera leaf extract and watermelon peel waste for rapid degradation of methylene blue (MB) dye. Co-precipitation and hydrothermal method were used to synthesize GS-Fe3O4 and Cdots, respectively. In addition, the sonication method was used to link Cdots on Fe3O4 surface. X-ray diffraction spectrum of GS-Fe3O4/Cdots inform the cubic inverse spinel and has crystallite size in the range of 10.1–7.2 nm. The crystallite size also decreased with the increase of Cdots concentration. The transmission electron microscope showed the most uniform size of nanocomposites at around 13.4 nm. The functional group of Fe-O was detected on the nanocomposites, proof that Fe3O4 still exists after fabrication. The presence of C = C, C-O, and C-O-C also indicates the existence of Cdots on the surface of Fe3O4. The addition of Cdots affected the saturation magnetization and coercivity value in the range of 29.2 – 38.3 emu/g and 59–65 Oe, respectively, which showed a good magnetic properties. As an organic dye, MB was used for a photocatalytic process under UV irradiation. The degradation efficiency was raised to 98% for 30 min photocatalytic process. The magnetically separable capability makes nanocomposites could be recycled and reused three times with high degradation. Furthermore, GS-Fe3O4/Cdots potential as a low-cost and environmentally friendly reusable photocatalyst for rapid wastewater degradation.

Chemistry of the Interaction and Retention of TcVII and TcIV Species at the Fe3O4(001) Surface.

The pertechnetate ion TcVIIO4 - is a nuclear fission product whose major issue is the high mobility in the environment. Experimentally, it is well known that Fe3O4 can reduce TcVIIO4 - to TcIV species and retain such products quickly and completely, but the exact nature of the redox process and products is not completely understood. Therefore, we investigated the chemistry of TcVIIO4 - and TcIV species at the Fe3O4(001) surface through a hybrid DFT functional (HSE06) method. We studied a possible initiation step of the TcVII reduction process. The interaction of the TcVIIO4 - ion with the magnetite surface leads to the formation of a reduced TcVI species without any change in the Tc coordination sphere through an electron transfer that is favored by the magnetite surfaces with a higher FeII content. Furthermore, we explored various model structures for the immobilized TcIV final products. TcIV can be incorporated into a subsurface octahedral site or adsorbed on the surface in the form of TcIVO2·xH2O chains. We propose and discuss three model structures for the adsorbed TcIVO2·2H2O chains in terms of relative energies and simulated EXAFS spectra. Our results suggest that the periodicity of the Fe3O4(001) surface matches that of the TcO2·2H2O chains. The EXAFS analysis suggests that, in experiments, TcO2·xH2O chains were probably not formed as an inner-shell adsorption complex with the Fe3O4(001) surface.

Simultaneous removal of Cs(I) and U(VI) by a novel magnetic AMP@PDA@Fe3O4 composite

The development and use of clean energy produced by nuclear power plants is becoming a major international trend, but it will inevitably lead to the problem of radionuclide pollution. Radioactive nuclear wastewater containing Cs and U and produced as a byproduct of coastal nuclear power production can cause substantial environmental pollution. In order to simultaneously remove radioactive cesium and uranium, polydopamine (PDA) inlaid ammonium phosphomolybdate (AMP) has established a hydrophilic functional structural film on the surface of Fe3O4, forming AMP@PDA@Fe3O4 (APF) which is used to simultaneous remove Cs(I) and U(VI). Using the pH sensitive range of APF adsorption in the process of adsorbing Cs(I) and U(VI), synergistic adsorption can be achieved under the condition of weak acidity to neutral. The effects of temperature, and common cations on Cs(I) and U(VI) adsorption by APF were investigated, the adsorption was found to be sensitive to the presence of K+. The efficiency of Cs(I) and U(VI) adsorption by APF was 99.88% and 98.39%, respectively. The Cs(I) adsorption process was primarily ion exchange with NH4+ within APF composite, whereas that for U(VI) was primarily C-O complexation. Both the Cs(I) and U(VI) adsorption reactions were consistent with second-order kinetic and Langmuir isothermal adsorption models. After five cycles of experiments the removal efficiency of Cs(I) and U(VI) can reach 64.88% and 79.81%, respectively. APF was also found to have high selectivity for Cs and U in seawater with high salt content at pH 6.0–7.0. In mimic contaminated seawater, the efficiency of Cs(I) and U(VI) removal was 97.65% and 84.63%, respectively. These findings provide references for the remove of Cs(I) and U(VI) from radioactive wastewater, making the process of energy production safer.

Intercalation of Well-Dispersed Fe2 O3 with SnO2 toward Durable Peroxymonosulfate Activation to Eliminate Antibiotics: Performance and Mechanism.

Sustainable Fe2 O3 /SnO2 with fine interfacial feature derived from FeSnO(OH)5 was prepared and employed for elimination contaminants. The synergistic effect between Fe2 O3 and SnO2 endowed a remarkable degradation performance for tetracycline degradation. Well dispersed SnO2 can function as fine protective layer to enhance the anchoring of iron ions. In addition, SnO2 with excellent conductivity can accelerate electron transfer on the surface of Fe2 O3 , further activation PMS. Approximately 89.3% of tetracycline (TC) was removed in Fe2 O3 /SnO2 /PMS system, which was higher than alone Fe2 O3 /PMS (73.2%) and SnO2 /PMS (39.7%) systems. The operating parameters were evaluated and studied. Electron paramagnetic resonance (EPR) and quenching tests manifested that 1 O2 was primary active specie, and ⋅OH, ⋅SO4 - and ⋅O2 - were participated in the degradation process. Besides, degradation pathways were proposed by identifying the intermediate products. This work is expected to offer a potential design for construction eco-friendly heterogeneous catalyst toward wastewater treatment.

First-principles computational study on adsorption and inhibition mechanism of kinetic hydrate inhibitors

Kinetic hydrate inhibitors (KHIs) have been used in the oil and gas industry as a cost-effective hydrate mitigation strategy, but the intrinsic inhibition mechanisms are less conclusive and require further verification. In this study, we have focus on the adsorption of KHIs on the metal surfaces to understand the inhibition performance by performing the first-principles computational method. The results show that KHIs are preferentially adsorbed onto the Fe surface than the Fe3O4 surface, and they accept electrons from the Fe surface, but donate electrons to the Fe3O4 surface. The hydrophobic interaction plays a dominate role in the adsorption affinity, and the electron transfer between KHIs and the surface enhances the adsorption stability. In addition, the adsorption affinity of four poly(N-vinyl lactam)s with 5–8-membered rings is compared, and PVCap that has a 7-membered ring shows the strongest adsorption strength on the Fe surface.

Synthesis of magnetic Fe3O4@SiO2-(-NH2/-COOH) nanoparticles and their application for the removal of heavy metals from wastewater

In this work, Fe3O4@SiO2-(-NH2/-COOH) nanoparticles were synthesized for the removal of Cd2+, Pb2+ and Zn2+ ions from wastewater. The results of characterization showed that Fe3O4@SiO2-(-NH2/-COOH) was superparamagnetic with a core–shell structure. The surface of Fe3O4 was successfully coated with silica and modified with amino groups and carboxyl groups through the use of a silane coupling agent, polyacrylamide and polyacrylic acid. The dispersion of the particles was improved, and the surface area of the Fe3O4@SiO2-(-NH2/-COOH) nanoparticles was 67.8 m2/g. The capacity of Fe3O4@SiO2-(-NH2/-COOH) to adsorb the three heavy metals was in the order Pb2+ > Cd2+ > Zn2+, and the optimal adsorption conditions were an adsorption dose of 0.8 g/L, a temperature of 30°C and concentrations of Pb2+, Cd2+ and Zn2+ below 120, 80 and 20 mg/L, respectively. The maximum adsorption capacities for Pb2+, Cd2+ and Zn2+ were 166.67, 84.03 and 80.43 mg/g. The adsorption kinetics followed a pseudo-second-order model and Langmuir isotherm model adequately depicted the isotherm adsorption process. Thermodynamic analysis showed that the adsorption of the three metal ions was an endothermic process and that increasing the temperature was conducive to this adsorption.

Improving the Oxygen Evolution Reaction on Fe3O4(001) with Single-Atom Catalysts.

Doping magnetite surfaces with transition-metal atoms is a promising strategy to improve the catalytic performance toward the oxygen evolution reaction (OER), which governs the overall efficiency of water electrolysis and hydrogen production. In this work, we investigated the Fe3O4(001) surface as a support material for single-atom catalysts of the OER. First, we prepared and optimized models of inexpensive and abundant transition-metal atoms, such as Ti, Co, Ni, and Cu, trapped in various configurations on the Fe3O4(001) surface. Then, we studied their structural, electronic, and magnetic properties through HSE06 hybrid functional calculations. As a further step, we investigated the performance of these model electrocatalysts toward the OER, considering different possible mechanisms, in comparison with the pristine magnetite surface, on the basis of the computational hydrogen electrode model developed by Nørskov and co-workers. Cobalt-doped systems were found to be the most promising electrocatalytic systems among those considered in this work. Overpotential values (∼0.35 V) were in the range of those experimentally reported for mixed Co/Fe oxide (0.2-0.5 V).

Synergistic lubrication of organic friction modifiers in boundary lubrication regime by molecular dynamics simulations

The synergistic effect of organic friction modifiers (OFMs) combining glycerol monolaurate (GML) and tri-n-octylamine (N888) in base oil is studied by molecular dynamics simulations. The adsorption and shear behaviors indicate that the triple-chains N888 molecules intersperse among the long-chain GLM molecules to form an intercoordination adsorption film. The system with a number ratio of 3:1 of GML to N888 shows a better synergistic lubrication with the lowest friction coefficient. The chemisorption of GML molecules on Fe2O3 surface is verified by density function theory. High shear velocity accompanying friction heat causes adsorption film breakage and high friction, while contact pressure conduces to friction reduction. The synergistic lubrication is attributed to the interface slip between base oil and OFM films, rather than the interlaminar shear caused by an imbalanced combination or high shear velocity.

Understanding the mechanism for initial deposition under the coupling effect of sodium and calcium during boiler operation: The first-principles study and thermodynamic analysis

During the boiler operation, ash deposition can result in a decrease in boiler efficiency and an enhanced release of pollutants. To relieve these issues, the formation mechanism for initial deposition triggered by the coupling effect of sodium and calcium was investigated by the first-principles study in this paper. The results indicated that the binding of sodium and calcium deposited on Fe3O4(001) surface is non-covalent interaction. Furthermore, |V|/G values of different particles on the surface are less than 2 and closed to 1. So the reactions of sodium and calcium deposited on the Fe3O4(001) are mainly closed-shell interactions accompanied by partial covalent interaction by Atom-in-Molecule theory. Additionally, the position and form of weak interaction also be further clarified by the independent gradient model. The thermodynamic calculation results showed that Gibbs free energy change is more affected to the change of the temperature under the existence of sodium and calcium. The reaction equilibrium constants is larger than 1, indicating that sodium and calcium are easily combined with Fe3O4(001). Moreover, calcium is more likely to promote a positive reaction than sodium.

Clean recycling of low-grade refractory limonitic waste using suspension magnetization roasting coupled with magnetic separation: A semi-industrial approach towards a waste utilization plan

Efficient utilization and clean recycling of low-grade refractory iron ore are essential to deal with the fast depletion of high-grade iron ore. A semi-industrial test of suspension magnetization roasting (SMR) for a low-grade refractory limonite waste with a grade of 32.46% by using reducing gases of CO and H2 mixture was conducted. The optimal experiments conditions were determined at a temperature of 550 °C, a reducing gas flow of 3.3 m3/h, a reductant concentration of 30% and a total gas volume of 14.0 m3/h. The iron grade of 59.27% and a recovery of 96.30% were obtained in the semi-industrial continuous and stable operation experiment. The iron transformation was mainly in the order of mFe2O3·nH2O to Fe3O4, which was detected by X-ray diffraction and the relative resonance area of magnetite and γ-Fe2O3 phase was 93.90% according to the result of 57Fe Mössbauer spectral analysis. The peak of Fe3+ shifted to 710.11 eV and the area increased constantly, showing that the surface of Fe3O4 occurred in the X-ray photoelectron spectroscopy. The magnetic magnetization transformed from 0.1 to 27.71 A·m2·kg−1 using the vibrating sample magnetometer (VSM). Cracks and a large number of holes in the roasted ores could be discovered by scanning electron microscopy (SEM) and the enrichment of iron elements could be reserved by mapping scan using energy dispersive spectrometry (EDS). The environmental protection methods of the SMR was investigated by discussing the carbon emissions challenges and exhaust pollution emission problems. This study demonstrates that the SMR is a green and effective technology for low-grade limonite waste utilization.

Understanding the effect of dolomite additive on corrosion characteristics of straw biomass ash through experiment study and molecular dynamics calculations

Experiments and molecular dynamics calculations were conducted to study the corrosion characteristics of straw biomass ash with dolomite as an additive. The results showed that the corrosion of metal by straw ash followed a parabolic law with respect to time, and this corrosion gradually reduced after adding dolomite. At 650 °C, the surface of straw ash almost completely sintered and melted and was composed of SiO2, KCl, K2Si4O9 and K2CrO4. The corrosion layer contained cracks and many acicular Fe–Cr oxides. After adding 5% dolomite, the corrosion rate decreased by 57.74%. The ash layer loosened and was mainly composed of CaMgSi2O6, CaSiO3 and MgSiO3. No evident cracks were observed in the corrosion layer. As the temperature increased, the absolute value of the binding energy of KCl on the Fe2O3 and dolomite surfaces increased. Moreover, stronger chemical interactions were observed between the K+, Cl−, and dolomite. On the same surface, the diffusion coefficient of K+ was higher than that of Cl−. At the same temperature, the diffusion coefficient of K+ and Cl− on the dolomite was greater than on the Fe2O3. KCl was more likely to combine with dolomite than with the metal surface, alleviating the metal corrosion caused by biomass ash.