Bayer red mud (RM) occupies a large amount of land, which excessive Na+ seriously damages groundwater resources. In this research, a RM based cementitious material (RMC) composed of RM and ordinary ...Portland cement (OPC) was developed. It is interesting to find that a binary reaction consisting of cement hydration and geopolymer reaction in RMC. The mechanical and Na+ consolidation rate of RMC were improved by the synergistic effect of binary reaction. The results indicated that the compressive strength of RMC is the highest and reaches 32.5R OPC when the mass ratio of CaO/(SiO2+Al2O3) is 1.37, and the Na+ leaching concentration is environmentally acceptable. The 7 days compressive strength of RM-based cementitious material No.2 (RMC2) can reach 93.80% of that of 28 days. As the predominant hydration products, cement hydration product (Ca5(SiO4)2(OH)2) and geopolymer (CaAl2Si2O8·2H2O and Na3Al3Si3O12·2H2O) were principally responsible for the strength development of RMC2 at 7 days. The optimal densification microstructure and SiO4 polymerization structure was presented in RMC2. The supreme Na+ consolidation rate was 99.23% in RMC2 due to the cooperation of physical fixation and Si(Al)O4 charge balance principle. This paper provides a fresh theoretical guidance for the utilization of RM and its Na+ in building materials.
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•The binary reaction in red mud based cementitious material has been studied clearly.•Cement hydration and geopolymer reaction constitute a binary reaction.•The cooperation of cement hydration and geopolymer reaction has enhanced effect.•Hydration products based on binary reaction have highly dense polymer structure.•Na+ in red mud was utilized to form geopolymer to improve early strength of RMC.
•This study progresses a state-of-the-art review of red mud and fly ash for the production of geopolymer composites.•The physical and chemical properties of RM-FAGPC is reviewed.•The fresh and ...hardened properties of RM-FAGPC is discussed.•The durability and microstructure properties of UHP-GPC is reviewed.•Recommendations and observations are advanced for future research.
Cement manufacturing emits a lot of CO2, which adds to negative environmental effects, including global warming and climate change. These phenomena have reignited interest in using a range of industrial waste products to make geopolymer composites and alkali activated binders, with the goal of reducing the use of regular Portland cement in building construction. One of these toxic radioactive waste substances is red mud (RM), which is produced as a byproduct of Bayer's aluminium (Al) production process. The objective of this study is to undertake a state-of-the-art review of the literature on the usage of red mud and fly ash (FA) in the production of red mud-fly ash geopolymer composites (RM-FAGPC). The environmental and economic implications, physical and chemical characteristics, manufacturing, distribution, categorization, and prospective uses of red mud are all discussed. Furthermore, current advances in the use of red mud and FA for geopolymer synthesis in terms of physical, mechanical, durability, and microstructure characteristics are highlighted. Furthermore, this research aims to design a path toward a realistic valorisation that considers both actual and perceived problems, including leaching, radioactivity, and the life cycle evaluation of red mud geopolymer composites (RM-GPC). The potential usage of RM-FAGPC manufacturing highlights the need for more research into the combination and proportion of these two raw materials with other cement-based materials, which might lead to novel, cost-effective, and energy-saving construction processes and products. It is also suggested that investigative efforts be focused on ecological, economic, and life cycle analyses.
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•Red mud and MSWIFA are used for synthesis of RGM.•Aluminosilicate is effectively activated by mechanical activation.•The activator reacts adequately with activated aluminum.•RGM can ...be potentially used as a supplementary cementitious material.
A novel method to activate red mud was proposed in this study. Municipal solid waste incineration fly ash (MSWIFA) and red mud were utilized to prepare red mud-based geopolymer materials (RGM). The hydration characteristics of RGM were studied by X-ray diffraction, scanning electronic microscopy, and Fourier transform infrared spectroscopy. The long-term stability and physical properties of RGM were tested by freeze–thaw cycle, European Community Bureau reference (BCR) and unconfined compressive strength (UCS) tests. Results showed that mechanical activation can not only effectively activate red mud, but also effectively improve the reaction of MSWIFA and red mud. When 14% sodium silicate was added to the binder, the UCS reached 12.75 MPa at 28 days. In the RGM, aluminosilicate was effectively activated by mechanical activation and reacted with calcium ion to form complex hydration products. The activator reacts adequately with activated aluminum to form a high-strength geopolymer. The freeze–thaw cycles and BCR test results also showed that the RGM had long-term stability and the characteristics satisfied the requirements of MU10 fly ash bricks. This study demonstrated that RGM may be utilized in cement composites.
Directing to unwieldiness NOx emitted by the industry, the removal of NOx was implemented using yellow phosphorus (P4) emulsion and red mud slurry as composite absorbent. Where yellow phosphorus is ...considered to stimulate formation of the ecological ozone (O3) from O2, the oxidation of insoluble NO into water-soluble NOx species by O3, and the red mud as a pH buffer can be used to maintain the pH of the absorption liquid in a range that better absorbs NOx. NO is finally converted into NO2− and NO3−, whereas the yellow phosphorus is mainly PO43−. Single-factor influencing on the efficiency of denitration include the concentration of yellow phosphorus, reaction temperature, stirring intensity, gas flow rate, O2 content, and red mud solid-liquid ratio were investigated. Response surface methodology (RSM) was used to optimize the process parameters. It was indicated that the removal rate of NOx can reach 99.3% under the optimal conditions. Moreover, the possible denitration reaction mechanism was also discussed.
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•A novel denitration method of yellow phosphorus emulsion coupled with red mud was developed.
•The influence factors on NOx removal efficiency were systematically investigated.
•The possible denitration reaction mechanism and the absorption products were discussed.
•The composite absorbent has better oxidation absorption ability to NO in flue gas.
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•A new kind of economical explosion suppression powders were successfully fabricated.•The NaHCO3/red-mud composite powders exhibit better inhibition performance compared to each pure ...component.•The composite powders have a unique core-shell structure, which can contribute to the synergistic suppression effect.
The NaHCO3/red-mud (RM) composite powders were successfully prepared by the solvent-anti-solvent method for methane explosion suppression. The RM was used as a carrier, and the NaHCO3 was used as a loaded inhibitor. The NaHCO3/RM composite powders showed a special core-shell structure and excellent endothermic performance. The suppression properties of NaHCO3/RM composite for 9.5% CH4 explosion were tested in a 20L spherical explosion vessel and a 5L Perspex duct. The results showed that the NaHCO3/RM composite powders displayed a much better suppression property than the pure RM or NaHCO3 powders. The loading amount of NaHCO3 has an intensive influence on the inhibition property of NaHCO3/RM composite powders. The best loaded content of NaHCO3 is 35%. It exhibited significant inhibitory effect that the explosion max-pressure declined 44.9%, the max-pressure rise rate declined 96.3% and the pressure peak time delayed 366.7%, respectively.
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•A catalyst containing FeAl2O4 phase was prepared using rice husk red mud.•The phase change of iron in red mud during pyrolysis was studied.•FeAl2O4 generates cavities which ...preferentially form 1O2 with PDS in the presence of light.•Red mud-based biochar showed high TCH degradation and mineralization activity.
Heterogeneous photocatalytic activation of persulfate (PDS) attracted much attention due to its positive environmental impact and efficacy in wastewater treatment. In this paper, a number of photocatalysts (RHRMX) were successfully synthesized by co-pyrolysis with rice husk (RH) using red mud (RM) as a precursor of Fe. Among them, RHRM50 exhibited excellent catalytic performance, with a high degradation rate of 99.5% for 20 mg/L tetracycline hydrochloride (TCH) in 60 min and its mineralization rate of 85.1% under the synthesized photocatalytic coupled PDS activation. In addition, the degradation efficiency under light conditioned remained above 95% after 5 cycles. The combination of the photoelectric properties and the Mott-Schottky spectrum of RHRM50 suggested that the photocatalysis was mainly attributable to FeAl2O4, with the energy band gap was determined to be 1.782 eV. Electron spin resonance (ESR) and burst experiments showed that under light, the FeAl2O4 generated holes mainly reacted with PDS to form 1O2, which was the main factor leading to the increase in the degradation rate. Based on density functional theory (DFT) calculations and identification of intermediates by liquid chromatography-mass spectrometry (LC-MS), hypothetical four potential pathways for TCH degradation were proposed. In addition, the potential ecotoxicity of TCH and its intermediates was evaluated using the ecological conformational relationship (ECOSAR). In conclusion, the green strategy of using RM to prepare RHRMX had a broad application prospect in the field of wastewater treatment and environmental protection.
Red mud is a solid waste in aluminum industry and has been proven to be an efficient alternative to NOx selective catalytic reduction (SCR) catalysts. Acid washing treatment to red mud can improve ...its alkalinity and surface properties, and increase the conversion rate of NOx. In this paper, Cu, Ce, and Cu/Ce was supported on acid washed red mud and NOx catalytic conversion performance on metal modified red mud catalysts was studied. The research results indicate that Cu+ and Cu2+ in the Cu supported catalyst effectively promote NO conversion rate of red mud in low-temperature (200–300 °C) flue gas, reaching a maximum of 90.7%; Ce3+ and Ce4+ in Ce supported catalysts effectively promote the NO conversion rate of red mud in flue gas at 200–400 °C, reaching a maximum of 94.0%; Cu/Ce supporting exhibits better NO conversion rate than single metal supported catalysts at low-temperatures, the optimal Cu:Ce ratio for supporting is 1:1; and also exhibits better NO conversion rate than Cu supported catalysts at high-temperature (300–400 °C), reaching a maximum of 95.5%. The reason may be that under the synergistic effect of Cu/Ce, ACRM-Cu1Ce1 has stronger low-temperature redox ability, higher weak acidic peaks, higher average oxidation state of Fe ions, and higher Cu+ content.
Red mud (RM) is the major waste material with strong alkaline discharged which is during the alumina extraction process. The global stock of RM has exceeded 4 billion tons and its disposal as a solid ...waste has always been a thorny environmental problem. However, RM is widely considered to be a potential resource due to its high content of valuable metal components such as iron. High-iron RM is rich in iron and can potentially become a valuable resource if the iron can be extracted effectively. It is of great research value and profound significance to recover iron from high-iron RM. This paper systematically reviews the iron recovery methods for resource utilization of high-iron RM, and divides the technology of iron recovery from high-iron RM into three aspects: physical separation method, pyrometallurgy method (reduction smelting and reduction roasting) and hydrometallurgy method (acid leaching). The basic principles and effect of iron extraction of the above technologies are summarized respectively, and the advantages and disadvantages of different technologies are compared. It is pointed out that the feasibility and economic cost are the main factor restricting the industrial application of these technologies. Therefore, it is of great significance to overcome various problems and difficulties, and develop innovative processes and technologies, which can realize the recycling and utilization of iron in high-iron RM and realize the reduction of RM emission at the same time.
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•The hazards caused by red mud and trends in red mud research were presented.•The research status of iron recovery methods from high-iron red mud is reviewed.•The advantages and disadvantages of several iron recovery methods are compared.•Technologies suitable for industrial production needs to be studied in the future.
•A novel RM/CdS S-scheme photocatalysis-self-Fenton system was constructed.•Combining in-situ H2O2 with industrial waste RM boost photocatalytic activity.•S-scheme heterojunction promotes the spatial ...separation of charge carriers by IEF.
The photo-Fenton process is recognized as an effective water treatment method due to its superior efficiency and technical feasibility, but the application of photo-Fenton is limited by the addition of Fe2+/Fe3+ and hydrogen peroxide (H2O2). Herein, we construct a red mud/cadmium sulfide (RM/CdS) S-scheme heterojunction photocatalysis-self-Fenton system with decorating Aluminum oxide plant waste RM particles on the surface of CdS nanospheres, which can generate H2O2 in situ and simultaneously activate H2O2 to produce hydroxyl radicals (OH) active species, exhibiting efficient degradation of amoxicillin (AMX) antibiotic pollutant under visible light irradiation. Moreover, the formation of RM/CdS S-scheme heterojunction promotes the spatial separation of the charge carriers by the built-in electric field (IEF) at the interface between RM and CdS. This research presents a novel design route for the construction of S-scheme photocatalysis-self-Fenton system in the efficient treatment of wastewater based on the industrial wastes.
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•A novel method for high-performance simultaneous removal of NOx and SO2 is developed.•The influence factors on NOx and SO2 removal efficiency were systematically investigated.•The ...main product was identified as gypsum (CaSO4·2H2O) after desulfurization and denitration.•The mechanism of catalytic oxidation absorption reaction was studied.
This study develops a novel method for simultaneously removing NOx and SO2 from coal-fired flue gas via coupling yellow phosphorus emulsion with red mud. The effects of different factors on the synergistic purification of sulphur-nitric acid were investigated in this study. The achieved removal efficiencies of NOx and SO2 were as high as 97.9% and 100%, respectively, under optimized conditions. This indicates that the yellow phosphorus emulsion coupled with red mud as a composite absorbent is favorable for simultaneous removal effect on NOx and SO2. The samples before and after the reaction were characterized using X-ray diffraction, X-ray fluorescence, inductively coupled plasma, scanning electron microscopy, and other methods, and the main product was identified as gypsum (CaSO4·2H2O) after desulfurization and denitrification. Adsorption kinetics, isotherm adsorption, and breakthrough curve models of NOx and SO2 adsorption on red mud were established. Moreover,the mechanism of multiphase oxidation and absorption reactions for simultaneous desulfurization and denitrification was also speculated.
