Red Mud Research Articles

Environmental impact analysis of geopolymer based red mud paving blocks

Red mud is a by-product from alumina industry. Global production of red mud was around 369 million tons in 2023, and India contributed over 6% of total. Landfilling of red mud may leach out heavy metals to soil and water, which could have negative consequences for the ecosystem. Incorporating the red mud in a geopolymer matrix is a safe option. This paper aims to analyse the environmental impact of the 1.0 m3 red mud containing geopolymer paving blocks using GaBi (Indian extension database) software. The data used for the analysis was generated from the studies conducted in continuous geopolymer pilot plant (10 tons/day). The analysis shows the major contributions from alkali activators and electricity. Red mud paving blocks exhibit global warming potential (275 kg CO2 eq.), human toxicity (51.7 kg DCB eq.), and terrestrial ecotoxicity potential (0.441 kg DCB eq.). Red mud blocks have similar acidification (1.65 kg SO2 eq.) and abiotic depletion potential (fossil) (3080 MJ) on comparison with cement paving blocks. Red mud geopolymer paving blocks offer a sustainable alternative with the reduced environmental footprint compared to conventional methods.

An all solid waste CO2 sequestration material consist of multiple calcium silicate clinkers by carbide slag, copper tailing and red mud: Clinker crystal transformation and carbonation hardening properties

In this study, a CO2 sequestration material was obtained by all components solid wastes, i.e., carbide slag and copper tailing based on red mud (RM) as crystal regulator after a sintering and carbonation process. With the increasing dosage of RM, the mineral compositions of generated RM-modified clinkers were mainly γ-C2S (i.e., around 80 %) at low dosage RM (i.e., 3.0 %), and was gradually increased content of β-C2S (β-dicalcium silicate), C3S (tricalcium silicate) and C2AS (gehlenite) at high dosage RM (i.e., from 3.0 % to 10.0 %). Moreover, the compressive strength of various carbonated compacts made by RM-modified clinkers after CO2 curing were shows firstly increased and then decreased with a RM dosage inflection of 5.0 %. This compressive strength results should be attributed to their carbonation activity, i.e., higher carbonation activity, higher compressive strength. The obvious carbonation activity difference of various RM-modified clinkers were not simply depends on their only γ-C2S content, only β-C2S content, only C3S content or the sum of calcium silicate minerals, but more closely relate to their combined effect. This work provides a new utilization strategy of RM as crystal regulator according to its high alkaline and high Fe content composition characteristic for obtaining a CO2 sequestration materials. And also laid a new insight for a synergistic CO2 sequestration by multiple calcium silicate clinkers in the future.

A comprehensive review on phytoremediation of fly ash and red mud: exploring environmental impacts and biotechnological innovations.

Fly ash (FA) and red mud (RM) are industrial byproducts generated by thermal power plants and the aluminum industry, respectively. The huge generation of FA and RM is a significant global issue, and finding a safe and sustainable disposal method remains a challenge. These dumps contain harmful trace elements that have a significant impact on the environment and human health. It contributes to air, water, and soil pollution, disrupting the delicate balance of the ecosystems. It also introduces toxins into the food chain through biomagnification. Utilizing a vegetation cover can assist in addressing environmental health concerns associated with FA and RM dumps. Nevertheless, the presence of alkaline pH, toxic metals, the absence of soil microbes, and the pozzolanic properties of both FA and RM pose challenges to plant growth. Taking a comprehensive approach to the ecological restoration of these dumps through phytoremediation is crucial. This review examines the role of various factors in the ecological restoration of FA and RM dumps, specifically the use of naturally occurring plants. However, the issue of slow plant growth due to a lack of nutrients and microbial activities is being resolved through various advances, such as amendments in conjunction with organic matter, microbial inoculants, and the use of genetically modified plants. Research has demonstrated the benefits of using amendments to stimulate vegetation growth on FA and RM dumps. In this review, we explore various approaches to restoring FA and RM dumps and transforming them into productive sites that enhance the ecosystem services.

Influence of Red Mud on Swelling-shrinkage and Mechanical Performance of Compacted Expansive Soil

Influence of Red Mud on Swelling-shrinkage and Mechanical Performance of Compacted Expansive Soil

Preparation and performance optimization of fly ash- slag- red mud based geopolymer mortar: Simplex-centroid experimental design method

Cement production emits a large amount of CO2 into the atmosphere and consumes significant mineral resources, necessitating urgent green transformation in this traditional industry. To address carbon emissions in the building materials sector and effectively utilize industrial solid waste, this study presents the preparation of geopolymer mortar using a ternary mixture of fly ash (FA), slag (GGBS) and red mud (RM), making full use of the advantages of each component to optimize the mix proportion. The mix proportions are determined using the simplex-centroid experimental design method, with NaOH concentration (8 M, 10 M, 12 M) as the independent variable, aiming to meet multi-objective performance requirements including fluidity, setting time, flexural strength, and compressive strength. The microstructure and composition of hydration products are examined through scanning electron microscopy (SEM) and X-ray diffraction (XRD). Finally, the optimal mix proportion range is proposed. Results indicate that: (1) When the concentration of NaOH increases, the setting time is shortened, and the mechanical properties first increase and then decrease. The optimal alkali concentration is 10 mol/L. (2) RM and FA exhibit similar effects on mechanical properties, suggesting RM can replace FA in geopolymer material preparation. Besides, RM significantly reduces fluidity. (3) GGBS enhances mechanical properties and shortens setting time. The increase of GGBS content provides more CaO for the matrix and generates more compact C-S-H gel, and thus, the flexural strength and compressive strength of the geopolymer mortar are improved. When GGBS blending amount is 50 % and NaOH is 10 M, the flexural strength and compressive strength of mortar can reach 15.66 MPa and 69.06 MPa, respectively. (4) The simplex-centroid experimental design method provides a mix proportion design method that can meet the requirements of multiple properties at the same time.

Red mud enhanced biomass gasification to produce syngas: Mechanism, simulation and economic evaluation

Red mud (RM) has the potential to balance catalytic activity and recycling stability. To achieve the efficient utilization of RM, this study systematically explores the RM potential as the catalyst in biomass gasification through three aspects: catalytic experiment, simulation of biomass gasification coupled with solid oxide electrolysis cells for methanol and economic analysis. The catalytic experimental results indicate that RM has a positive effect on the biomass gasification, with a gas yield of 615.9 ml/gbiomass, representing an increment of 40.9 %. Fe2O3 and Al2O3 are the main catalytic components in RM. The simulation results on biomass gasification coupled with SOEC for methanol show that RM has increased the methanol yield to 381.83 kg/tonBiomass, with an increase of 23.9 %. The economic analysis indicates that the RM can reduce the methanol production cost, demonstrating a promising application prospect. This paper providing strong support for RM high-value synergistic utilization.

The influence of red mud filler on flexural strength in vinyl ester resin Hybrid composites with abaca fiber (Musa Textilies)

The influence of red mud filler on flexural strength in vinyl ester resin Hybrid composites with abaca fiber (Musa Textilies)

Kinetic research of red mud waste oxidative pyrolysis and comparison under different atmospheres

Red mud, as a solid waste with high alkalinity, had a detrimental impact on the environment and required urgent attention. Currently, the mass processing and consumption of red mud were typically conducted under thermal conditions, so it was essential to gain a comprehensive understanding of the oxidative pyrolysis process. The thermogravimetric experiments were conducted at multiple heating rates in air and exhibited three obvious stages. The activation energy and reaction mechanism of three oxidative pyrolysis stages were explored using model-free and model-fitting methods, revealing the activation energies of 162.2, 265.8, 214.1 kJ/mol and the most suitable reaction mechanisms of g(α)=[-ln(1-α)]³, g(α)=1-(1-α)1/⁴, g(α)=[-ln(1-α)]1/2 for each stage, respectively. Furthermore, the estimated kinetic parameters and reaction mechanisms were applied to extra heating rate to verify the accuracy. More important, the effect of air on the pyrolysis process of red mud was examined by comparing the results with those obtained from pure nitrogen pyrolysis. The obtained oxidative pyrolysis characteristics of red mud could provide valuable insights of its co-pyrolysis or combustion for resources recycling.

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.

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.

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.

Impact of red mud on soil properties and revegetation species growth in bauxite mining land reclamation

Bauxite mining, a key aluminum production process, can cause environmental degradation, soil erosion, and biodiversity loss. Reclamation measures like reforestation and water management can restore balance. Red mud, a by-product of alumina production, can enhance soil fertility and plant growth in post-bauxite mining reclamation areas. Its alkalinity and mineral composition reduce reliance on synthetic fertilizers, promoting sustainable soil management and addressing environmental challenges. This study aimed to examine the impact of red mud on soil characteristics and the growth of plants in areas during bauxite mining land reclamation. This study was conducted in the post-reclamation area of bauxite mining in West Kalimantan. The experiment involved two treatments: red mud application and a species of revegetation plant. Plant species consist of the plants Embeng, Forest Guana, Johar, and Rambutan. The study used a randomized block design with 24 experimental units. The parameters measured in the study included pH, organic carbon, nitrogen, phosphorus, exchangeable cations, cation exchange capacity, and base saturation, while growth parameters included a high percentage of plant growth and percentages of increased stem diameter. The findings showed that adding red mud to the planting hole increased soil pH and base saturation, improved nutrient availability, and enhanced plant growth in the areas post-mining bauxite at PT Antam, UBPB West Kalimantan. The Embeng Plant is highly regarded as a suitable plant species for re-vegetating areas after bauxite mining.

Preparation of Co-Ce@RM catalysts for catalytic ozonation of tetracycline.

In this work, a Co-Ce@RM ozone catalyst was developed using red mud (RM), a by-product of alumina production, as a support material, and its preparation process, catalytic efficiency, and tetracycline (TCN) degradation mechanism were investigated. A comprehensive assessment was carried out using the 3E (environmental, economic, and energy) model. The optimal production conditions for Co-Ce@RM were as follows: The doping ratio of Co and Ce was 1:3, the calcination temperature was 400°C, and the calcination time was 5h, achieving a maximum removal rate of 87.91% of TCN. The catalyst was characterized using different analytical techniques. Under the conditions of 0.4L/min ozone aeration rate, with 9% catalyst loading and solution pH9, the optimal removal rates and chemical oxygen demand by the Co-Ce catalytic ozonation at RM were 94.17% and 75.27%, respectively. Moreover, free radical quenching experiments showed that superoxide radicals (O2 -) and singlet oxygen (1O2) were the main active groups responsible for the degradation of TCN. When characterizing the water quality, it was assumed that TCN undergoes degradation pathways such as demethylation, dehydroxylation, double bond cleavage, and ring-opening reactions under the influence of various active substances. Finally, the 3E evaluation model was deployed to evaluate the Co-Ce@RM catalytic ozonation experiment of TCN wastewater. PRACTITIONER POINTS: The preparation of Co-Ce@RM provides new ideas for resource utilization of red mud. Catalytic ozonation by Co-Ce@RM can produce 1O2 active oxygen groups. The Co-Ce@RM catalyst can maintain a high catalytic activity after 20 cycles. The degradation pathway of the catalytic ozonation of tetracycline was fully analyzed. Catalytic ozone oxidation processes were evaluated by the "3E" (environmental, economic, and energy) model.

Novel red mud-based FeS2 composite used as an effective heterogeneous catalyst for the degradation of levofloxacin: Preparation, application and degradation mechanism

Red mud (RM), as industrial waste, was considered as the base material in this study. A heterogeneous catalyst of RM based-FeS2 (RM-FeS2) was prepared using a simple one-step calcination method. RM-FeS2, as an effective activator of peroxymonosulfate (PMS), was utilized in the levofloxacin (LVF) degradation progress. The effect of the preparation conditions on crystal structure and catalytic activity of RM-FeS2 was investigated. The systematic characterizations indicated that the surface area, electrical conductivity and the number of Fe(II) sites of RM were improved after compounding with FeS2. According to the investigation of catalytic performance of RM-FeS2, approximately 87% of LVF (10 mg/L) was degraded in 60 min with the reaction conditions: [RM-FeS2] = 0.2 g/L, [PMS] = 1 mmol/L and initial pH of 6.2. The RM-FeS2 possessed excellent stability and reusability. ·OH, SO4•−, 1O2 and Fe(Ⅳ) were the dominant active species in RM-FeS2/PMS system. Several possible degradation pathways of LVF were proposed. The toxicity of the treated LVF solution was effectively reduced in the RM-FeS2/PMS system. In a word, this study not only realized the resource utilization of RM, but also presented a novel perspective for the effective degradation of organic pollutants in wastewater.

Utilization of desilication products as efficient adsorbents for the removal of basic fuchsine

Desilication products (DSPs) are one of the main components of bauxite residue, which is currently discharged without further usage. The present study reports on the use of DSPs as adsorbents for basic fuchsine dye. Using artificial spent liquor, we synthesized not only neat DSP but also solids in the presence of various organics, to account for their likely occurrence during the Bayer process. The physico-chemical properties of all DSPs are similar, except for the specific surface area (SSA), which decreases as the organic content in the final product increases. Further, we compared the adsorption characteristics of DSP to those of Y-type faujasite (FAUY). Strikingly, both time-dependent adsorption measurements and adsorption isotherms showed that DSP, despite its 28-fold smaller SSA, binds 4–5 times more dye molecules. Computational modelling for sodalite (as a model for DSP) and FAUY indicates not only more favourable adsorbent-adsorbate interactions, but also more available free Si-OH sites for binding of fuchsine in the case of sodalite. Finally, we find that organic impurities present in the Bayer liquor do not alter the adsorption capacity of neat DSP to any significant degree; therefore, this adsorbent tolerates numerous organic contaminants without decreasing its affinity to the binding of fuchsine.

Transferring red mud to efficient adsorbent for the adsorption and immobilization of Ni(Ⅱ) from aqueous solution

Red mud, a solid waste produced in large quantities, possesses a high specific surface area and is rich in metal oxides, making it a promising material for adsorbent preparation. However, its practical application is constrained by its relatively low adsorption capacity and the potential environmental risks it poses. This study focused on the preparation of modified red mud (MRM) with enhanced adsorption performance for Ni2+ using a hydrothermal method involving sodium hydroxide and colloidal silica. The maximum adsorption capacity of MRM for Ni2+ reached 8.22 mmol·g–1, a substantial improvement compared to raw red mud (0.28 mmol·g–1) and sulfuric acid-activated red mud (0.46 mmol·g–1). The pseudo-second-order kinetic and Langmuir isotherm models accurately described the monolayer chemical adsorption process of Ni2+ on MRM. Additionally, leaching tests with simulated rainwater demonstrated that Ni-loaded MRM exhibited high stability, suggesting its potential for safe stockpiling or repurposing, such as in construction materials. Sequential extraction, XRD, FT-IR, and XPS results revealed that cation exchange was the primary mechanism in the adsorption process, with Ni2+ being immobilized within the zeolite framework structure of MRM, contributing to its strong adsorption stability. Inner-sphere complex formation also played a role in Ni2+ adsorption. In conclusion, this method offers an effective approach to both red mud utilization and heavy metal removal from wastewater, presenting a practical solution for waste management through resource recovery and environmental remediation.

Revealing the hydration mechanisms in iron-rich calcium sulfoaluminate cements with elevated bauxite residue content

The goal of the study was to investigate the reactivity at different Blaine, hydration behavior, and performance of calcium sulfoaluminate-ferrite cement (CSA-F). The raw meal incorporated bauxite residue (38 wt%) fired at 1260 °C and 1300 °C for 30 and 60 minutes. Based on multi-objective optimization, an optimum dosage of citric acid ranges between 0.4<x<0.6 wt% with a w/b ratio of 0.45 was chosen for the mortar evaluation and hydration studies. At an early age, monosulfates-AFm only started appearing for 1300_30. In the later age, an increase in ettringite formation was only reported at 1300°C for 60 min due to the dissolution of the Ternesite phase after 7d of hydration. Later-age studies after 28d reported ettringite, monosulfates, hydrogarnets (except for 1300_60), and strätlingite had formed. The 28d highest compressive strength was reported for 1300_60 corresponding to the highest bound water and amorphous content from the pore filling ettringite and amorphous stratlingite.

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%.

Unraveling the mechanism and the key role of amorphous structure C-O-Fe in tetracycline degradation by activation of persulfate in lotus leaf-based red mud-modified biochar

In the present study, red mud modified lotus leaf biochar was synthesized using a low-cost and concise method. The experimental results showed that when RM-HBC=0.4 g/L, PDS=4 mM, pH=5.0, the RM-HBC-PDS system exhibited the best degradation effect on TC, with the highest removal rate of 98.61 %, the highest degradation kinetics of 0.0229 min−1. Advanced characterization and density functional theory have demonstrated that the emergence of the C-O-Fe structure led to the redistribution of the surface charge of RM-HBC. This charge redistribution caused the electrons on the surface of RM-HBC to transfer from C to Fe through the C-O-Fe structure, forming an electron-rich center centered on Fe. The C-O-Fe structure facilitated the transformation of the Fe valence state within the RM-HBC while transmitting electrons, thus maintaining the regeneration of Fe(II). This further promoted the adsorption and activation ability of RM-HBC for PDS, thereby improving the degradation effect of TC in the system. XRD detection showed that the Fe3O4 crystal strength in RM-HBC after the reaction was significantly enhanced. This was due to the C-O-Fe present on the surface of RM-HBC in the process of degradation of TC, which accelerated sustained electron transfer at C-O-Fe, leading to structural fracture, recombination, and ultimately the formation of Fe3O4 crystals. Intermediate detection and toxicity prediction showed that the toxicity of TC was significantly reduced. All the above results confirmed that this study not only achieved the efficient treatment of antibiotic wastewater but also realized the rational utilization of lotus leaf and red mud resources.

Valorization of Glycerol to Glycerol Carbonate and Glycidol by Different Dialkyl Carbonates Utilizing Tricalcium Aluminate Hexahydrate as Transesterification Catalyst

AbstractIn this study, we report a base‐catalyzed transesterification reaction of glycerol, a waste product of the biodiesel industry, with various dialkyl carbonates, which act both as reactants and solvents, to convert glycerol carbonate into an industrially useful molecular building block. The catalyst, being used for the first time, is also a waste product from industry, present in bauxite residues and in the Portland cement, simply known as tricalcium aluminate. Despite being well‐known and readily available, this solid is only extremely poorly researched catalyst, nevertheless, using dimethyl and diethyl carbonate, glycerol conversion rates &gt;80% and glycerol carbonate yields &gt;60% could be achieved in just 1 h (under air atmosphere and reflux). In a comparison of the performance with other catalysts commonly researched today, as well as with other components of red mud and cements, the results showed that tricalcium aluminate is excellent, cheap, and largely environmentally friendly material for this purpose. Reusability studies of the catalysts have also shown that they provide high conversion and product yields even after repeated use, although different material characterization techniques showed intense glycerol‐catalyst surface interaction and intermediate product formation, the deactivating side effects of which could be avoided by catalyst regeneration steps.