Addition Of Red Mud Research Articles

Enhancing short-chain fatty acids production from waste activated sludge anaerobic fermentation with addition of red mud: Performance and mechanisms

Red mud (RM) as hazardous waste produced from aluminum refining industry has threatened the environment and human health. In this study, RM was added into the fermenter to promote short chain fatty acids (SCFAs) production from waste activated sludge (WAS) anaerobic fermentation. Results showed that the addition of RM could effectively improve the SCFAs production, especially, acetic acid. In particular, the production of total SCFAs and acetic acid in 20 g/L RM added fermenter were 1108.1 mg COD/L and 415.5 mg COD/L, which were 116.0% and 1308.0% higher than that in control fermenter. Batch experiment revealed that RM could enhance the hydrolysis and acidification process. Further study indicated that the activity of enzyme related to hydrolysis-acidification, abundance of fermentative bacteria for SCFAs production and functional metabolism genome were all improved with the addition of RM. The potential mechanism maybe that the RM promoted the hydrolysis-acidification process with the contained varies Fe(Ⅲ) oxides as electron acceptor, and the produced Fe2+ could serve as necessary trace elements to synthesize enzyme and then stimulate the expression of enzyme genes.

Investigation on Erosion Resistance in Polyester-Jute Composites with Red Mud Particulate: Impact of Fibre Treatment and Particulate Addition.

This research investigates the manufacturing and characterisation of polyester-based composites reinforced with jute fibres and red mud particulates. The motivation stems from the need for sustainable, high-performance materials for applications in industries, like aerospace and automotive, where resistance to erosion is critical. Jute, a renewable fibre, combined with red mud, an industrial byproduct, offers an eco-friendly alternative to conventional composites. The composites were fabricated using compression moulding with varying red mud contents (10, 20, and 30 wt.%) and a fixed 40 wt.% of jute fibre. Fibre treatments included sodium hydroxide (NaOH) and silane treatments to improve bonding and performance. Erosion tests were performed using an air-jet erosion tester, examining the effects of the red mud content, fibre treatment, and impact angles. Scanning Electron Microscope (SEM) analysis provided insights into the erosion mechanisms. A distinctive reduction in erosion rates at higher impact angles (30°-60°) was observed, attributed to the semi-ductile nature of the composites. The addition of red mud enhanced erosion resistance, although an excess of 30 wt.% reduced resistance due to poor surface bonding. Silane-treated composites showed the lowest erosion rates. This study provides new insights into the interplay among material composition, fibre treatment, and erosion dynamics, contributing to the development of optimised, eco-friendly composite materials.

Synergistic action and effect mechanism of coal gangue powder and red mud on the properties of concretes

Red mud and coal gangue powder were employed as substitutes for cement to prepare red mud concrete, coal gangue concrete, and red mud-coal gangue concrete. The effects of red mud and coal gangue powder on the physical properties, workability, and mechanical properties of concretes were evaluated, and the hydration reaction mechanisms were elucidated through microanalysis. Furthermore, the reaction process was investigated through thermogravimetric analysis. The results indicated that the individual addition of red mud and coal gangue powder had negative effect on the strength, workability, and porosity of concretes. However, the combination of red mud and coal gangue powder significantly improved the strength and porosity of the concrete compared to red mud concrete and coal gangue concrete. The red mud-coal gangue concrete with 15 % red mud and 15 % coal gangue powder had lower porosity, and comparable compressive strength with the cement concrete. The microscopic results and thermogravimetric analyses indicated that the synergistic effect of red mud and coal gangue led to the improvement of the strength of red mud-coal gangue concrete. The red mud exhibited the promotion effect on the hydration of coal gangue powder to generate new C-S-H, filling the pores. The denser structure in the red mud-coal gangue concrete was formed, thereby improving the pore space and mechanical properties of the concretes.

Performances enhancing of supersulfated cement (SSC) using waste alkaline activators: Red mud and carbide slag

Supersulfated cement (SSC), since its invention, showed lower early-age strength gain, which has limited its practical applications. The urgent issue is how to regulate and enhance its early-age performance. In this context, solid waste materials such as bauxite residue-red mud (RM) and carbide slag residue (CS) from acetylene production by calcium carbide hydrolysis were used to improve the hydration and performance of SSC. By utilizing a range of analytical techniques such as isothermal calorimetry (IC), X-ray diffraction (XRD), backscatter scanning electron images (BSE), and thermogravimetric analysis (TGA), the hydration process, phase assemblages and microstructure of CS/RM-modified SSC were systematically investigated. It’s found that CS, as a calcareous alkaline activator, act as a regulator for adjusting the two main hydration reactions of C-A-S-H deposition and ettringite formation in SSC. The alkaline activator induces the hydration of slag and promotes the formation of hydration products. However, an excessively high dosage of carbide slag delays the primary ettringite formation reaction because it inhibits the dissolution of slag and promotes the formation of outer products. It leads to a looser and more porous paste matrix, resulting in higher expansion strain and poor strength gain at full curing ages. In contrast, red mud improves the hydration rate and enhances the hydration degree of SSC within the studied content (up to 30 wt%). With addition of red mud, SSC hydration is significantly advanced and deepened, resulting in more hydrates, particularly inner products. Red mud facilitates the depolymerization of the slag glass network and promotes the forming of nuclei and growth of hydration products. However, an excessively high red mud content would lead to a looser and more porous paste matrix due to the characteristics of red mud particle itself. An optimal red mud content has been identified as 20 wt%.

Performance and microstructure of red-mud-blended concrete under different aqueous environments

The effects of aqueous environments on the performances of red-mud-blended concretes (RMCs) were evaluated by measuring their compressive strength, water absorption, and porosity. The pH value, electrical conductivity, and heavy metal concentrations of the immersion solutions were measured to determine the effects of RMCs on the aqueous solutions. The hydration products and microstructures of RMCs were analyzed to determine the effect mechanisms. The results showed that the addition of red mud to concretes increases the apparent porosity and water absorption and decreases the compressive strength. Acidic environments exhibited the most significant effect on the performances of RMCs. In a neutral environment, C–S–H gel generation and a high Si/Ca ratio resulted in enhanced corrosion resistance for the RMC with 35 % red mud, and its compressive strength decreased by 15.07 % after 28 d of immersion. The pH value and electrical conductivity showed a rapid increase, indicating the leaching of soluble alkalis and a large number of ions during soaking. The electrical conductivity showed a rapid increase with the immersion time within 60 d, indicating the leaching out of a large number of ions. The heavy metal concentration and pH value were within the range specified by Chinese standard (DZ/T 0290–2015), which provides many references for evaluating the interaction between RMCs and the aqueous environment.

Properties of Red-Mud-Modified Basic Magnesium Sulfate Cement.

This study aimed to decipher the influence of red mud on the mechanical properties, pore structure, and microstructure of basic magnesium sulfate cements (BMSCs). The results showed that BMSC prepared with an appropriate addition of red mud exhibited improved mechanical properties and yielded the highest compressive strength of 94.54 MPa after curing for 28 days. Adding red mud reduced the total porosity and optimized the pore structure of BMSC. The microstructure and hydration products of the specimens were examined using X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The results illustrate that the addition of 50% red mud did not affect the amount of the main strength phase 5-1-7 produced in BMSC. It could also reduce the residual amount of MgO and the generation of Mg(OH)2. The red mud and the M-S-H gel generated by the reaction between active SiO2 and α-MgO in the red mud together filled the pore structure of BMSC, making its microstructure denser and higher-strength. This study aims to improve the comprehensive use of red mud, and the results show that red mud can improve the mechanical properties of BMSCs, protecting the environment and simultaneously reducing BMSC production costs to create good economic benefits.

Preparation and Research on Mechanical Properties of Eco-Friendly Geopolymer Grouting Cementitious Materials Based on Industrial Solid Wastes.

Red mud (RM), a hazardous solid waste generated in the alumina production process, of which the mineral composition is mainly hematite, is unable to be applied directly in the cement industry due to its high alkalinity. With the rise of geopolymers, RM-based grouting materials play an essential role in disaster prevention and underground engineering. To adequately reduce the land-based stockpiling of solid wastes, ultrafine calcium oxide, red mud, and slag were utilized as the main raw materials to prepare geopolymers, the C-R-S (calcium oxide-red mud-slag) grouting cementitious materials. The direct impact of red mud addition on the setting time, fluidity, water secretion, mechanical properties, and rheological properties of C-R-S were also investigated. In addition, a scanning electron microscope (SEM), X-ray diffraction (XRD), three-dimensional CT (3D-CT), Fourier transform infrared spectroscopy (FT-IR), and other characterization techniques were used to analyze the microstructure and polymerization mechanism. The related results reveal that the increase in red mud addition leads to an enhanced setting time, and the C-R-S-40 grouting cementitious material (40% red mud addition) exhibits the best fluidity of 27.5 cm, the lowest water secretion rate of 5.7%, and a high mechanical strength of 57.7 MPa. The C-R-S polymer grout conforms to the Herschel-Bulkley model, and the fitted value of R2 is above 0.99. All analyses confirm that the preparation process of C-R-S grouting cementitious material not only substantially improves the utilization rate of red mud, but also provides a theoretical basis for the high-volume application of red mud in the field of grouting.

Insights into mechanisms of red mud promoting biogas production from waste activated sludge anaerobic digestion

Anaerobic digestion of waste activated sludge is usually limited by the low overall methane yield. The addition of exogenous materials is considered to be a potential method to improve anaerobic methane production. In this study, red mud was added into waste activated sludge anaerobic digester and its effects on anaerobic digestion were investigated. Results showed that methane production was improved with the addition of red mud, and almost reached maximum in 10 g/L red mud added reactor (124.4 mL/g VSS), which was about 24.0 % higher than control. Further investigation indicated that the key genes related to methane metabolism, the activity of the corresponding coenzymes and the rate of extracellular electron transfer were also increased in red mud added reactor. Batch experiments on the effects of red mud in each stage of waste activated sludge anaerobic digestion showed that red mud could improve solubilization, hydrolysis, and acidification processes, but inhibit the methanogenesis process. The potential mechanism behind the enhancement of methane production during whole waste activated sludge anaerobic digestion is that the addition of red mud can intensify the hydrolysis and acidification processes, thereby providing more substrates for methanogens and subsequently enhancing the activity of coenzymes related to methane production.

Simulation study on basic road performance and modification mechanism of red mud modified asphalt mixture

Abstract In order to study the basic road performance and the mechanism of red mud modified asphalt, Marshall test, rut test, freeze-thaw splitting test, and immersion Marshall test were carried out for matrix asphalt mixture and red mud modified asphalt mixture, and molecular simulation technology was introduced to study the mechanism of red mud modified asphalt. The results showed that the penetration rate of red mud modified asphalt was lower than that of the matrix asphalt, and the softening point of asphalt was significantly improved after the addition of red mud, and the mixing of red mud reduced the asphalt ductility greatly. The intensity ratio (test strength ratio; TSR) of the freeze-thaw test of red mud modified asphalt under 3, 5, 7, 9, and 11% was increased by 13.18, 11.22, 13.54, 12.01, and 8.45%, respectively, compared with the matrix asphalt mixture, and the dynamic stability value increased by 127.23, 176.87, 200.99, 96.23, and 12.95%; the residual stability value of the immersion Marshall test increased obviously. Generally, the research of red mud modified asphalt is quite worthy, it can solve the problem of aluminum ore slag and reuse of resources, and provide a new way to extend the industrial chain.

Enhancing High Solid Anaerobic Digestion of Kitchen Waste with Red Mud Addition: Performance and Microbial Community

Enhancing High Solid Anaerobic Digestion of Kitchen Waste with Red Mud Addition: Performance and Microbial Community

Red mud application as filler in asphalt mixtures production

Red mud is the solid waste from bauxite processing during aluminium production. Its inadequate disposal causes social, economic and environmental prejudices. The industrial solid waste insertion evaluation in the production chain is beneficial and necessary. This work aims to evaluate the mechanical performance of asphalt mixtures produced with red mud as filling material. Asphalt mixtures with 5% and 7% red mud were produced, and permanent deformation and moisture-induced damage tests were carried out. A mixture without red mud addition (control) was produced for comparison. The results showed that the mixtures with red mud presented permanent deformation resistance greater than the control one, with more than 40% reduction in rutting deformation. The moisture damage did not significantly affect the mixtures tested. The red mud application as a filler in asphalt mixtures is viable and can be an alternative to reduce the damage such a waste can cause to the environment.

Ash fusion characteristics of iron‐rich coal in Xinjiang under different atmospheres and the influence mechanism of adding red mud and pipeline scale

AbstractTo realize the high‐efficiency utilization of iron‐rich coal, it is necessary to conduct in‐depth research on the ash fusion characteristics and regulation mechanism. In this paper, the ash fusion temperature test of iron‐rich coal in Xinjiang (ZC) under different atmospheres was first carried out. Then, red mud (HJ) from Huajin Aluminum Industry and black water pipe scale (GDG) were selected as the additives. After the same ashing procedure, the two additives were mixed with iron‐rich coal ash in different proportions to realize the regulation of the chemical composition of the coal ash to improve the ash fusion characteristic. The ash fusion temperature (AFT) experiment was carried out in the automatic ash melting point analyzer, and high‐temperature ash melting slags at different temperatures were prepared. The mineral phases of coal ash and slag were characterized by XRD and compared with the Factsage simulation calculation results to reveal the influence mechanism of coal ash fusion temperature. The result shows that the fusion temperature of ZC iron‐rich coal ash is significantly different between oxidizing atmosphere and weak reducing atmosphere. Compared with the oxidizing atmosphere, the four characteristic temperatures of ZC iron‐rich coal ash are significantly lower under weak reducing conditions, and the difference is about 150°C. The addition of red mud and pipeline scale increased the fusion temperature of ZC coal ash to varying degrees. The addition of HJ ash has little effect on the deformation temperature of ZC coal ash, while the addition of different proportions of HJ ash significantly increases the flow temperature of ZC coal ash. When the addition ratio of HJ ash is 40%, the flow temperature FT of ZC coal ash increases most obviously, which is about 50°C. The addition of HJ ash and GDG ash will lead to an increase in the content of iron‐containing spinel, thereby increasing the ash flow temperature.

Properties of red mud blended magnesium phosphate cements: Workability and microstructure evolution

Alumina and iron oxide which constitute significant components of red mud can participate in the hydration reaction with phosphate. This paper partially replaced magnesia with red mud in the preparation of magnesium phosphate cement (MPC) and investigated the effects of red mud substitution on the performance of fresh and hardened properties of the MPC. The fresh properties of MPC were analyzed by measuring the setting time, fluidity, early hydration heat release and rheological properties, while the hardened mechanical properties were characterized by compressive strength measurement. The phase composition and micro-morphology were examined by XRD, SEM, EDS, and TG-DTA. The experimental results demonstrated that the incorporation of red mud prolonged the setting time, and postponed the occurrence of the peak temperature, and reduced the hydration reaction intensity. Regarding to the rheological properties, an increase in the dynamic yield stress was followed by a decline with gradually addition of red mud. Conversely, the plastic viscosity increased consistently. Concerning hardened properties, adding appropriate amount of red mud powders to MPC can significantly improve the compressive strength of hardened MPC mortars. The samples containing 15 % red mud yield the highest compressive strength, especially in the early strength, it was even more pronouncedly improved by 14.8 % comparing to the controlled samples at 3 h. Furthermore, detailed information about the modification effects of red mud on the MPC microstructure has been studied. The density of the MPC matrix was improved, microcracks and gaps appeared less, and some new hydrates could be determined, which is responsible for the improvement of the MPC’s mechanical properties.

Effect of red mud on combustion behavior and heavy metal stabilization of Refuse Derived Fuel (RDF)

Refused Derived Fuel (RDF) from municipal solid waste has become a promising and effective approach for waste storage and utilization. However, the poor combustion performance and heavy metals (HMs) emission limit the development of this technology. In this study, red mud (RM), an industrial waste from the alumina extraction process, was used as an additive to improve the combustion behavior of RDF. The results show that 10 wt% of red mud addition can increase the flammability index (F) and the comprehensive combustion characteristic index (S) by 91% and 156%, respectively. It significantly reduced the burnout temperature of RDF by 59 °C. Moreover, RM also promoted the transformation of HMs into more stable forms. The proportion of F4 speciation for Cr, Ni, Cu, Zn Cd, and Pb in ash residues increased by 6.42%, 50.91%, 92.48%, 43.77%, 15.77%, and 4.53%, respectively, while the leaching rate of Cr, Ni, and Cd decreased by 1.7%, 0.99%, and 1.31%. The findings proved that RM could serve as an efficient additive for enhancing RDF combustion and stabilizing the HMs in ash residues, which would provide new insight into the co-utilization of wastes and the contribution to the clean combustion of RDF.

Effect of Red Mud Addition on Electrical and Magnetic Properties of Hemp-Derived-Biochar-Containing Epoxy Composites

Waste stream valorization is a difficult task where the economic and environmental issues must be balanced. The use of complex metal-rich waste such as red mud is challenging due to the wide variety of metal oxides present such as iron, aluminum, and titanium. The simple separation of each metal is not economically feasible, so alternative routes must be implemented. In this study, we investigated the use of red mud mixed with hemp waste to produce biochar with high conductivity and good magnetic properties induced by the reduction of the metal oxides present in the red mud through carbothermal processes occurring during the co-pyrolysis. The resulting biochar enriched with thermally-reduced red mud is used for the preparation of epoxy-based composites that are tested for electric and magnetic properties. The electric properties are investigated under DC (direct current) regime with or without pressure applied and under AC (alternating current) in a frequency range from 0.5 up to 16 GHz. The magnetic measurements show the effective tailoring of hemp-derived biochar with magnetic structures during the co-pyrolytic process.

Effect of TiO2 inoculants on the wear conduct of the aluminium AA 6061/red mud high performance hybrid composite

The current work focuses on the manufacturing of aluminium AA 6061 composites and its tribological characterization. This is achieved by reinforcing the matrix with red mud. However, the uniform dispersion of red mud requires ultrasonic assisted stir casting and the use of optimum wt.% of TiO2 inoculants. In this regard, the composition of red mud is fixed at 2 wt.%, since the addition of red mud beyond 2 wt.% results in the agglomeration, while the wt.% of TiO2 inoculants is varied from 2 wt.% to 6 wt.%. The wear tests are conducted as per the L9- Orthogonal Array (OA) for a load range of 10 N to 30 N, sliding distance of 500 m to 2500 m, disk rotation speed of 200 RPM to 600 RPM. The regression coefficients are more than 0.9 and close to unity and the error between the experimental outcomes and statistical values are within the tolerance band. The SWR and COF is minimized for 2 wt.% of red mud, 4 wt.% of TiO2, beyond which there is a slight increase in the wear of the composites attributed to the agglomeration of the reinforcments in certain localized regions and the presence of voids in other regions.

The Effect of Bayer Red Mud Blending on the Mechanical Properties of Alkali-Activated Slag-Red Mud and the Mechanism

In this paper, Bayer red mud and ground granulated blast furnace slag were formed into three different ratios (7:3, 5:5 and 3:7) of alkali-activated cementitious materials (AASR) using a water glass solution as the alkali activator. By studying the compressive strength of different red mud content, the effect of Bayer red mud content on the mechanical properties of AASR was analyzed. The influence mechanism of red mud content on the mechanical properties of AASR was revealed by the variation of micro-porosity, connected porosity, Isothermal calorimetry, XRD, FTIR, and BSE/EDS testing techniques. The results show that the compressive strength of the specimens at the same age decreases with the increase of red mud content. On one hand, the addition of red mud makes the connected porosity in the AASR system increase, and the densification of the slurry structure decreases; on the other hand, the inert minerals in red mud participate in the hydration reaction to a lesser extent, the overall hydration reaction process becomes lower, and the generation of hydration products providing strength decreases.

Study on the mechanism and reaction characteristics of red-mud-catalyzed pyrolysis of corn stover

With catalytic pyrolysis gradually becoming the most efficient thermal treatment for biomass, the search for catalysts with high economic and catalytic performances has attracted widespread attention from scholars. In this study, the use of red mud as a catalyst for the pyrolysis of biomass to produce high-quality pyrolysis gas was investigated. The effects of the three components of red mud (Fe2O3, Al2O3, and CaCO3) on pyrolysis and the catalytic effect and mechanism of red mud on pyrolysis were analyzed. Fe2O3 was the most dominant catalytically active ingredient in red mud, which had a good contribution to the improvement of carbon conversion and hydrogen yield. Specifically, Fe2O3-catalyzed corn stover pyrolysis at a 40 % addition ratio increased the hydrogen yield by 82 %. Because of the stable pore structure provided by Al2O3 and SiO2 as carriers and the chimeric structure of the catalyst particles, the specific surface area of the red mud reached 25.88 m2/g, and the specific surface area of the magnetic separation product reached 42.41 m2/g, which greatly improved the catalytic performance. Red-mud-catalyzed corn stover pyrolysis with a red mud addition ratio of 40 wt% could achieve an H2 yield of 108 ml/g, representing a rise of 79 %. The phase composition and crystal structure of the red mud and magnetic separation products were analyzed; the components in the red-mud catalyst doped with each other at the lattice level in the form of a solid solution, which improved the catalytic activity.

Co-utilization of zinc contaminated soil and red mud for high-strength ceramsite: Preparation, zinc immobilization mechanism and environmental safety risks

In this research, high strength ceramsite was sintered by zinc contaminated soil and red mud. In addition, the influence of sintering temperature and red mud addition on ceramsite properties and Zn immobilization were investigated, and the Zn immobilization mechanisms were determined. The X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM-EDS), and BCR sequential extraction technique were used to determine the crystal phases, microstructures, and Zn immobilization. Under the optimum synthesis conditions (sintering temperature of 1150 °C and the red mud addition of 5%), the sintered ceramsite exhibited a Zn loss rate of 10.31%, Zn leaching concentration of 0.13 mg/L (performed by rotating vibration device), bulk density of 1052.6 kg/m3, 1 h water absorption of 1.06%, and cylindrical compressive strength of 27.06 MPa, implying that the ceramsite obtained under this conditions not only meets the Chinese National Standards and has no environmental risk. High temperature and the addition of red mud were beneficial to the immobilization of Zn in ceramsite. The main immobilization mechanism of Zn in ceramsite was the formation of ZnFexAl2−xO4 spinel and the encapsulation of glass phase. Thus, Zn can be immobilized effectively by ceramsite prepared from zinc contaminated soil and red mud at high temperature.

Analysis of Chemical Stabilizer on the Behavior of Expansive Soil

Abstract: Rapid growth in industrialization and urbanization in developing countries like India, leads to increasing scarcity of land which forces us to utilize the available land even though it is problematic. Problematic soils are those having low bearing capacity, high compressibility and high swelling/shrinkage and as such they are not suitable for any geotechnical application. In most geotechnical engineering projects, increase in concentration of Red mud, Maximum dry density of mixture increases. The mix containing 30% Red Mud + 67% Soil + 3% Fly Ash has good bearing strength characteristics. The bearing strengths of Red Mud were increased to 7.354% on addition of Red Mud and Fly Ash in the ratios of 30% and 3% respectively. With increase in concentration of red mud, California bearing ratio increase up to a fixed concentration of Red mud. With increase in percentage concentration of Red Mud, Optimum moisture content of the mixture (Red Mud + Fly Ash + Soil) increases. With increase in concentration of Red mud, Maximum dry density of mixture increases.