Progress on the Industrial Applications of Red Mud with a Focus on China

Lyu F., Hu Y., Wang L., Sun W.

• The alkalinity formation and release processes of BR are introduced in detail. • The typical dealkalization methods are discussed and evaluated comprehensively. • Characteristics of BR and regional resources determine the appropriate process. • Financial efficiency should be well considered in the dealkalization process. Bauxite residue is a kind of strong alkaline waste produced in the production of alumina. Its long-term storage poses a potential threat to the environment. With the tightening of environment policies in various countries, the strong alkalinity of bauxite residue has become a bottleneck restricting the sustainable development of aluminum industry all over the world. This review covers the composition characteristics of bauxite residue, and describes the Bayer process in detail, where emphasis is put on the formation of alkaline substances in bauxite residue and its release process in long-term storage. This review focuses on several typical processes for the management of bauxite residue alkalinity in recent decades around the world. The phase transformation mechanisms, merits and limitations, as well as application status are discussed. The potential application values of these typical methods are evaluated based on process characteristics. The large amount and varied characteristics of bauxite residue determine that it is unrealistic to solve the dealkalization problem of all bauxite residue with one method. It is recommended that the appropriate dealkalization process of bauxite residue should be selected according to the characteristics of bauxite residue and regional resources, as well as the planning of subsequent application.

Li Y., Yue Q., He J., Zhao F., Wang H.

As the consumption of aluminum products in China continues to increase in recent years, the in-use stock of aluminum products is increasing. With the service life of aluminum products about to run out and the shortage of bauxite resources in China, recycling domestic aluminum scrap to produce secondary aluminum will become an inevitable trend. With reference to the development status of secondary aluminum in developed countries and the scenario we set, the future production and stock ratio of secondary aluminum in China are predicted. According to our selected scenarios, the research results include: (1) China's primary aluminum will reach its peak around 2025, and its production capacity will gradually decrease with the replacement of secondary aluminum in China; (2) With the increasing domestic aluminum stocks, China began to enter the era of scrap aluminum recycling after 2020, and the peak supply of aluminum scrap lagged behind the peak consumption of aluminum for 10–20 years. (3) The in-use stock of aluminum will peak around 2040 and the in-use stock of secondary aluminum will be saturated around 2060. (4) With the recycling of aluminum scrap, secondary aluminum will break through the production level of 10 million tons in 2023. The level of secondary aluminum in China will exceed the production level of primary aluminum for the first time around 2035. After 2050, secondary aluminum production will account for more than 60% of the total output and the secondary aluminum stock ratio (SASR) will account for more than 70%. Thus, there will be a rapid shifting in production capacity from primary to secondary routes. In this case, the relevant policies should pay more attention to the recovery of aluminum scrap and the production of secondary aluminum. As China's aluminum will maintain this strong consumption momentum and the shortage of bauxite in the country, research on China's future secondary aluminum will become increasingly important.

Ramos Huarachi D.A., Gonçalves G., de Francisco A.C., Canteri M.H., Piekarski C.M.

Life cycle assessment (LCA) is a solid tool to assess the potential environmental impacts in construction industry, an important material in this industry is the brick, along time several traditional and alternative bricks were developed and assessed environmentally by LCA. The purpose of this article is to review the literature related to LCA of bricks, responding important topics to characterize and guide future studies. Out of Traditional Bricks (TB), there are Alternative Bricks with Organic (ABO) and Inorganic (ABI) additives, that use wastes from several industries and differ of TB in the omission of firing for a stabilization process, however, to omit firing is hard and stabilization still needs further improvements. The principal system boundaries and tools for LCA were also reviewed. Regarding the most present impact categories, they were: Climate change (CC), Human Toxicity (HT) and Freshwater Ecotoxicity (FE), in every category, production is the stage of highest impact, and in the productive process, drying and burning processes have the highest potential impacts. Future searches could continue to study on new materials (wastes) for development of new ABO and ABI, to quantify the benefits of reusing wastes, and to study, either the replacement of firing with stabilizing processes, or the use of biomass as fuel source in firing, and to develop studies in different countries to create national datasets that will make future studies more representative.

Liu Y., Qin Z., Chen B.

• Novel magnesium phosphate cements were prepared with the solid waste-red mud. • The addition of red mud in MPC can improve the properties significantly. • The pore structure of MPC can be optimized by red mud. • The microstructures were observed and the new hydration products were analyzed. The main concern of this article is to understand the influences of red mud on the properties of magnesium phosphate cement (MPC), which were determined in terms of the fluidity, setting characteristic, temperature evolution during the hardening stage, mechanical properties, water resistance, hydration products, pore structure and microstructure. The results showed that the fluidity can increase to a value of 272.5 mm at a level of 20% red mud, and red mud was found to decrease the exothermic reaction intensity of the fresh mortar and to prolong the setting time to 25 min during the hardening stage. The mortar prepared with suitable addition of red mud presented with improved mechanical properties and enhanced water resistance during the whole ageing period, and the group containing 20% red mud yielded the highest compressive strength of 90.2 MPa at 28 days. Then, the pore structure was measured by low-field nuclear magnetic resonance (LF-NMR), which was found that adding red mud can reduce the total porosity and form more small pores. Moreover, the microstructure and the hydration products of the samples were tested by X-ray diffraction (XRD), scanning electron microscopy (SEM) along with energy dispersive spectrometer (EDS). The obtained results illustrated that red mud can fill in the microcracks, making the structure denser, and also formed with some new hydrates. The present work aimed at the utilization of red mud and the results illustrated that MPC can be modified by red mud significantly.

Das B., Mohanty K.

Conversion of wastes to energy and other value-added products is considered as a suitable method towards energy security. Wastes from various sources are becoming potential feedstocks for energy production through different techniques. The economy and sustainability of these processes demand the use of low-cost catalysts. Red mud (RM) is one of the most abundantly produced industrial wastes from aluminum industries. Such a huge production of RM, its alkaline nature and the presence of a small quantity of radioactive elements make it an environmental liability. Out of various utilization methods, RM as a catalyst for different chemical processes has been very successful. Presence of many valuable metals in RM, in particular, Fe makes it a suitable catalyst for energy production through processes such as pyrolysis, hydrotreating, transesterification and H2 production from biomass and other sources. This article critically reviews the advances in sustainable energy production through different processes mentioned above by RM based catalysts. Different characterization, activation and stability study of RM along with outcomes and mechanism of these processes are discussed. Furthermore, drawbacks associated with the low catalytic activity of RM and works that need to be carried out in the future for the improvement of its catalytic activity are discussed in detail.

Zeng H., Lyu F., Hu G., Tang H., Wang L., Sun W., Hu Y., Liu R.

Bauxite residue is a highly alkaline industrial solid waste generated through the alumina production process. Its high alkalinity causes serious environmental pollution. In this article, a fast, high-efficiency, low-cost dealkalization process was developed. Bauxite residue was dealkalized by sulfuric acid and CAM, a calcium-containing compound. The revegetation potential of dealkali bauxite residue was also studied. The dealkalization rate reached up to 94.31% when 18.4% sulfuric acid was added, and 2% CAM leaching occurred at room temperature for 10–30 min. The filtration speed increased by about 70 times with the addition of CAM up to 4.5%. The subsequent pot experiment showed that the dealkali bauxite residue met the growth requirements of plants. Scanning electron microscopy analysis showed that the particle size of neutralized bauxite residue was enlarged, thereby accelerating the soil formation process of the bauxite residue. This work provides technical support for ecologic restoration of a bauxite residue disposal area.

Lu G., Zhang T., Ma L., Wang Y., Zhang W., Zhang Z., Wang L.

Bayer red mud accounts for the largest proportion of solid waste produced in the non-ferrous metallurgy industry and is usually handled by stockpiling because of its high alkalinity. The calcification–carbonation method (CCM) was proposed to extract alumina and sodium oxide from red mud using a fully hydrometallurgical process in order to scale the valuable utilization of Bayer red mud. In this study, a modified CCM was applied, using calcium aluminate hydrate as the calcium source to recover alumina from a low-NaOH-concentration digested solution. Thermodynamic analysis revealed that the stable product of the calcification process was hydrogarnet with a high silicon saturation coefficient ( x , 3CaO·Al 2 O 3 · x SiO 2 ·6-2 x H 2 O), and a higher reaction temperature was beneficial for the formation of hydrogarnet with a high silicon saturation coefficient. Experimental results indicated that: (1) the calcification temperature was the most important determinant of the coefficient x of the hydrogarnet, which varied from 0.35 to 0.98 over a temperature range of 60–280 °C; (2) the x value and Na mass content in the calcified slag were 0.98 and 0.35%, respectively, under calcification conditions with an NaOH concentration of 200 g/L, a temperature of 260 °C, and a C/S of 2.5:1; (3) the Na mass content and A/S decreased to 0.03% and 0.52, respectively, in the new red mud structure due to the carbonation and digestion process. The Na mass content in the new red mud structure satisfies the raw material requirements for the cement industry, and approximately 74% of the alumina in the Bayer red mud was recovered by the CCM treatment. The primary phase in the new red mud structure was CaCO 3 , which can be used for preparing cement or other building materials. • A modified calcification–carbonation method (CCM) was proposed for treating Bayer red mud. • The effects of the calcification parameters on the structure of hydrogarnet were investigated. • The Na content and A/S of the red mud decreased to 0.03% and 0.52, respectively. • Alumina production could be achieved through the CCM by the Na and Al extraction.

Zhang Y., Hu Y., Sun N., Khoso S.A., Wang L., Sun W.

In the current study, a novel precipitant, sodium metasilicate nonahydrate, was investigated as a new magnesium precipitant for separating lithium from magnesium in brine with a high Mg/Li mass ratio. Various parameters and relative mechanisms of the precipitation process such as reaction time, agitation rate, sodium metasilicate nonahydrate dosage, and aging time were systematically studied. Sodium metasilicate nonahydrate exhibited superior performance in terms of precipitating magnesium and separating lithium from magnesium in brines with large ranges of initial Li+ and Mg2+ concentrations. It is demonstrated that appropriate agitation rate and aging time were beneficial for magnesium precipitation and enhancing the filtration capacity of the precipitates. The Li+ recovery in solution, Mg2+ precipitation rate, and mass ratio of Mg/Li reached approximately 86.73%, 99.94%, and 0.022, respectively, starting from an initial Mg/Li mass ratio of 30. The encouraging results suggest that Li can be recovered to a substantial degree from brines of different compositions via a precipitation method employing sodium metasilicate nonahydrate as the precipitant for Mg.

Zhang Y., Hu Y., Wang L., Sun W.

Lithium is one of the most important raw materials for the production of glass, ceramics, nuclear materials, pharmaceuticals, and batteries. Almost 80% of total land-based lithium reserves globally are salt-lake brines. Therefore, lithium should be extracted from salt-lake brines to meet the demand of various industries for lithium resources. Several approaches for lithium extraction have been developed in the past few decades, such as precipitation, ion exchange, adsorption, solvent extraction, and electrolysis. Among these methods, precipitation is the earliest studied and utilized in industrial plants. Furthermore, it has several advantages, such as low cost, green principle, and easy industrialization. This paper reviews the precipitation technology for lithium extraction and the relative mechanism proposed in literature to identify its important parameters. Precipitant dosage, pH value, temperature, and particle size of precipitate are important factors in the process. Economic viability and green principle of various methods are discussed, and potential technologies are suggested. Novel magnesium precipitants appear to be a prospective technology for lithium extraction from brines with high Mg/Li mass ratios. Magnesium precipitation technology also shows great potential in the comprehensive utilization of lithium and magnesium resources. Various precipitation approaches for lithium extraction from brines and perspectives for further investigation are proposed.

Xu X., Song J., Li Y., Wu J., Liu X., Zhang C.

As solid wastes in the alumina production of Bayer method, four kinds of Bayer red muds were successfully added to prepare ceramic tile samples for better waste utilization. The effects of four kinds of red muds on the properties of tile samples were discussed by XRD, SEM and EPMA analyses. Simultaneously, as by-products during the process of alumina production, Fe2O3 impurities were also investigated due to their high level ranging from 24 wt% to 36 wt% in the red muds. According to the radioactive inspection results, the four red muds were radioactive solid wastes which could be used for interior surface of class II civil buildings and exterior surface of buildings (GB6566-2010 China). The main phases of four red muds are boehmite, calcite, quartz and gibbsite. Preferable physical properties were obtained to be 0.12~9.92% in water absorption (belong to stoneware) and 30.57~60.96 MPa in bending strength, when the addition of red muds was 40 wt% (the addition of red muds was designed to be 40 wt% by the Method of Satisfied Chemical Compositions according to our previous experiments) and the firing temperatures were 940~1100 °C, 1080~1140 °C, 1080~1140 °C, 960~1120 °C, respectively. The main mechanism can be explained by the well-crystallized phases below 1100 °C with red muds as raw materials and non-excessive liquid phases at low firing temperatures that prompt the densification of samples. Although the liquid phases could lower the oxygen partial pressure around Fe2O3 and make unfavorable reduction of Fe2O3 into Fe3O4 and gas, they ultimately improved rather than decreased the performance of samples. Excellent properties of the samples make the four red muds appropriate to be used as raw materials for ceramic tiles, in accordance with Chinese National Standard (GB/T4100-2015), European Normalization (EN14411:2012), and American National Standard (ANSIA137.1-08).

Varghese V., K. A., Ramesh M.R., Chakradhar D.

The present study investigates the machining performance of AlCrN and AlTiN coated cemented carbide inserts during end milling of MDN 250 maraging steel. The mechanical and metallurgical characterization is carried out to determine the properties of the PVD coatings developed. The end milling experiments under dry, wet and cryogenic environment is carried out using coated uncoated inserts (UC) at different spindle speeds to evaluate the machining performance in terms of tool life, surface roughness and cutting forces. The coated inserts showed higher tool life, better surface finish, and low cutting forces during machining at different spindle speeds. It is found that the AlCrN coating had a better wear resistance and machining performance in comparison with AlTiN coating. The cryogenic environment reduced the surface roughness & cutting force and improved the tool life of the cutting tool compared to conventional dry and wet environment. It is revealed that coated tools along with cryogenic cooling can be employed for high-speed machining applications.

Wang L., Hu G., Lyu F., Yue T., Tang H., Han H., Yang Y., Liu R., Sun W.

Red mud (RM) is an industrial waste produced in large amounts during alumina extraction from bauxite. Its disposal generates serious environmental pollution due to high alkalinity. Therefore, a strategy for the effective utilization of RM must be developed. For instance, RM may be transformed into useful products, such as adsorbents. Given its high concentrations of aluminum oxides, iron oxides, titanium oxides, silica oxides, and hydroxides, RM may be developed as a cheap adsorbent for the removal of various ions from aqueous solution and soils (e.g., metal and non-metal ions, phenolic compounds, and dyes) and waste gas purification (sulfide and carbide). This review summarizes the background, properties, and applications of RM as an adsorbent. Proper approaches of removing metal and non-metal elements from wastewater are also systematically reviewed and compared. Emphasis is placed on the surface modification of RM to obtain high adsorption. Finally, the scope for future research in this area for RM is discussed in depth.

Sun C., Chen J., Tian K., Peng D., Liao X., Wu X.

A nationwide investigation was carried out to evaluate the geochemical characteristics and environmental impacts of red mud and leachates from the major alumina plants in China. The chemical and mineralogical compositions of red mud were investigated, and major, minor, and trace elements in the leachates were analyzed. The mineral and chemical compositions of red mud vary over refining processes (i.e., Bayer, sintering, and combined methods) and parental bauxites. The main minerals in the red mud are quartz, calcite, dolomite, hematite, hibschite, sodalite, anhydrite, cancrinite, and gibbsite. The major chemical compositions of red mud are Al, Fe, Si, Ca, Ti, and hydroxides. The associated red mud leachate is hyperalkaline (pH > 12), which can be toxic to aquatic life. The concentrations of Al, Cl−, F−, Na, NO32−, and SO42− in the leachate exceed the recommended groundwater quality standard of China by up to 6637 times. These ions are likely to increase the salinization of the soil and groundwater. The minor elements in red mud leachate include As, B, Ba, Cr, Cu, Fe, Ni, Mn, Mo, Ti, V, and Zn, and the trace elements in red mud leachate include Ag, Be, Cd, Co, Hg, Li, Pb, Sb, Se, Sr, and Tl. Some of these elements have the concentration up to 272 times higher than those of the groundwater quality standard and are toxic to the environment and human health. Therefore, scientific guidance is needed for red mud management, especially for the design of the containment system of the facilities.

Mukiza E., Zhang L., Liu X., Zhang N.

Red mud is highly alkaline slurry produced during alumina extraction from bauxite. Its disposal generates serious environmental pollution. The best way to solve red mud disposal issues is to develop economic utilization technologies that consume significant amounts of red mud. This paper reviews the possibility of utilizing red mud as a road base material, weak subgrade soil stabilizer as well as a subgrade material. Results showed that red mud can be used for those purposes. It was also found that the stabilizing content needed to meet a certain standard differs due to differences in requirements from one country to another. Therefore, there is a need to design proportions with UCS, CBR, leaching characteristics required by the country in which red mud is intended for use. The effect of various stabilizers on performance of red mud is discussed and it transpired that lime showed the best performance followed by dolime fine, ground granulated blast furnace slag, cement kiln dust and fly ash. Findings indicated that red mud shows better performance as a subgrade material than natural soil. Also the synergistic use of red mud and other wastes also improves the mechanical and durability properties of the material compared with using red mud alone. Based on mechanical, economic and environmental benefits, it is recommended to use red mud in road base structure rather than in subgrade despite higher red mud consumption in subgrade than in road base. The scope for future research in this area is also suggested.

Khairul M.A., Zanganeh J., Moghtaderi B.

Red mud or bauxite residue is a solid waste generated from the Bayer process. The disposal of red mud leads to a serious environmental threat because of its tiny particle size and high alkaline value. The utilisation and recycling of red mud is currently a crucial issue and needs to be addressed as soon as possible. This study demonstrates the different methods and techniques recently analysed or suggested for the consumption of bulk red mud to maintain a sustainable environment. The potential utilisations of red mud include valuable metal recovery, the preparation of construction materials and as an alternative catalyst for diverse processes, including hydrodechlorination, hydrogenation and hydrocarbon oxidation. In addition, the red mud can also be used to control environmental pollution, such as in wastewater treatment, soil remediation and the purification of flue gas. However, the proper utilisation and recycling of red mud has a number of shortcomings: pyro-metallurgical recovery involves high energy costs; large volumes of acid by-product needing to be neutralised after the leaching process; the fine particle size of red mud; and the necessity of pre-treatment in some methods. Although many studies have investigated the potential utilisation of red mud, most of them have concentrated on lab-scale studies. Therefore, a large-scale investigation of the recycling and utilisation of red mud needs to be explored. Moreover, an appropriate cost-benefit analysis of the existing technologies needs to be examined in the future because of the high cost of the transportation of a large amount of red mud from alumina refineries to the point of application.

Xue H., Lv G., Zhang T.

Rajković M., Jelić I., Janković M., Antonijević D., Šljivić-Ivanović M.

The increasing importance of waste materials utilization with the necessary modification to remove various pollutants from industrial wastewater has been a research focus over the past few decades. Using waste material from one industry to solve pollution problems in another ultimately leads toward sustainable and circular approaches in environmental engineering, solving waste management and wastewater treatment issues simultaneously. In contemporary research and industry, there is a notable trend toward utilizing industrial wastes as precursors for adsorbent formation with a wide application range. In line with this trend, red mud, a byproduct generated during alumina production, is increasingly viewed as a material with the potential for beneficial reuse rather than strictly a waste. One of the potential uses of red mud, due to its specific composition, is in the removal of heavy metal and radionuclide ions. This study summarizes red mud’s potential as an adsorbent for wastewater treatment, emphasizing techno-economic analysis and sorption capacities. An overview of the existing research includes a critical evaluation of the adsorption performance, factors influencing efficiency rather than efficacy, and the potential for specific pollutant adsorption from aqueous solutions. This review provides a new approach to a circular economy implementation in wastewater treatment while guiding future research directions for sustainable and cost-effective solutions.

Weng X., Haynes R., Zhou Y.

Ouda M., Sanad A.A., Krishna A., Kandah M., Kurdi J.

Ma J., Feng G., Han Y., Bai J., Wu G.

Baki V.A., Ke X.

Jiang X., Jiang X.M., Li N., Hu Z.G.

Red mud, a by-product of the aluminum industry, poses a threat to the environment with its high alkalinity and heavy metal content and may seep into the soil and groundwater, endangering ecology and health. Effective utilization of red mud can reduce pollution and achieve resource recycling. In this study, a metakaolin/red mud geopolymer was prepared by phosphoric acid excitation to investigate its adsorption capacity for lead ions. The ratio of metakaolin to red mud and the additions of phosphoric acid and water were optimized, and the optimal formulations were 3/7 mass ratio of metakaolin to red mud, 2.2 molar ratio of H3PO4/Al2O3, and 0.5 water-solid ratio, which demonstrated good stability and operability.

Weng X., Haynes R.J., Zhou Y.F.

Cheng F., Pang J., Berggren S., Tanvar H., Mishra B., Arlos M.J.

Harmaji A., Jafari R., Simard G.

Recycling and reusing industrial waste and by-products are topics of great importance across all industries, but they hold particular significance in the metal industry. Aluminum, the most widely used non-ferrous metal globally, generates considerable waste during production, including dross, salt slag, spent carbon cathode and bauxite residue. Extensive research has been conducted to recycle and re-extract the remaining aluminum from these wastes. Given their varied environmental impacts, recycling these materials to maximize residue utilization is crucial. The components of dross, salt slag, and bauxite residue include aluminum and various oxides. Through recycling, alumina can be extracted using processes such as pyrometallurgy and hydrometallurgy, which involve leaching, iron oxide separation, and the production of alumina salt. Initially, the paper will provide a brief introduction to the generation of aluminum residues—namely, dross, salt slag, and bauxite residue—including their environmental impacts, followed by an exploration of their potential applications in sectors such as environmental management, energy, and construction materials.

Ilahi K., Debbarma S., Mathew G., Inyang H.I.

Fu J., Chen Y., He J., Zhou H.

Geopolymers derived from solid waste can effectively remediate heavy metal polluted sites, achieving the ideal fusion of solid waste utilization and environmental remediation. Red mud and blast furnace slag were used to develop a geopolymer for the remediation of composite heavy metal-contaminated soils, focusing on Cd(II)-, Pb(II)-, Cu(II)-, and Zn(II)-contaminated soils. Uniaxial compressive strength tests, toxicity characteristic leaching procedures, pH change characteristics, and pH gradient tests were performed on the solidified/stabilized soil. The results showed that increasing the red mud-blast furnace slag content and curing age significantly enhanced the unconfined compressive strength. Furthermore, it suppressed the leaching of heavy metals in the solidified/stabilized soil. Notably, the treatment effectiveness of Cu(II) and Zn(II) was superior to that of Cd(II) and Pb(II). The leaching concentrations of Cd(II), Pb(II), and Zn(II) decreased in acidic to weakly alkaline environments but increased in strongly alkaline environments. However, the impact of curing age and initial heavy metal content on the pH of the solidified/stabilized soil was the opposite. In conclusion, red mud and blast furnace slag exhibited superior solidification/stabilization effects compared to cement. As environmental protection awareness grows and technology continues to evolve, geopolymers derived from red mud and blast furnace slag will play a greater role in pollution control and remediation, showcasing broad application prospects.

Ajeebi A.M., Alghamdi H.S., Sanhoob M.A., Aktary M., Abdul Aziz M., Alzahrani A.S., Alsayoud A.Q., Nasiruzzaman Shaikh M.

Reducing reliance on fossil fuels and mitigating industrial waste are two strategies for clean environmental management. An active research topic within this framework is to convert abundant bio-derived compounds, like furfural (FF), into a petroleum blend by employing industrial waste, like red mud (RM), as catalyst support. Here, we demonstrate that furfural can be chemoselectively converted in a single step into ethyl furfuryl ethers (EFE), which significantly enhance the blended petroleum's octane number. This is achieved in the presence of a recyclable Rh-impregnated RM catalyst. In this context, a range of valuable metals (M = Rh, Ir, and Ru) are impregnated into the RM (M@RM) and extensively characterized by SEM, EDS, XRD, FT-IR, TEM, and XPS. The 1 % Rh@RM composite, calcined at 400 °C (1 % Rh@RM-400), produced 75 % EFE selectivity with the > 99 % conversion of furfural. The prepared catalyst retains its stability for the multiple cycles of the furfural hydrogenation reactions.

Jin W., Chen Y., Lv Y., Jiang L., Bai W., Zhang K., Song C., Zhang X.

In order to reduce the negative impact on the environment caused by the massive accumulation of red mud (RM) and Yellow River sand (YRS), new alkali-excited granulated blast-furnace slag (GGBS)/RM/YRS (AGRY) geopolymer cementitious materials were prepared by combining RM and YRS with GGBS in different ratios and using sodium silicate as the alkali exciter. The effects of YRS dosage and different curing conditions on the mechanical properties, hydration products, and pore structure of cementitious materials were investigated and analyzed in terms of cost and carbon emissions. The results showed that when the dosage of YRS was 40%, the compressive strength of the prepared AGRY cementitious material could reach 48.8 MPa at 28 d under standard curing, which showed mechanical properties comparable to those of the cementitious material without YRS. The cementitious material has a more compact internal structure, and the combination of RM and YRS promotes the chemical reaction of Al and Si elements and generates the (N, C)-A-S-H gel products, which are the key to the strength enhancement of the cementitious material. In addition, the prepared cementitious material is only 90% of the cement cost for the same strength and has low carbon emission accounting for only 43% of the cement carbon emission. This study not only provides a new way for the resource utilization of RM and YRS, but also contributes an excellent new environmentally friendly material for the construction industry to achieve the goal of low carbon development.

Charan Nayak K., Pathania A., Radha Pathania A.

Aluminium plants generate a substance identified as red mud, which is an alkaline atrophy product. As the aluminium industry expands, the accumulation of red mud has become a more pressing concern. Various atrophy treatment technologies have been developed to utilize red mud as a material for environmental remediation. These substances, also identified as Red Mud Ecological Rehabilitation Ingredients (RM-ERMs), are created by stimulating red mud, fusing it in a complementary manner with additional compounds, or removing useful components from it. RM-ERMs find application in three main areas: purifying wastewater, treating atrophy gases, and remediating soil. The extremely alkaline nature of red mud is harnessed in the making of RM-ERMs, offering a window to perk up the environment through purification methods. The utility of RM-ERMs has shown promise as a potential method for simultaneously addressing various types of waste. This review provides an introduction to the physical and chemical characteristics of red mud, and summarizes the active mechanism of RM-ERMs in addressing specific contaminants in wastewater, atrophy gases, and soil. Additionally, a review of current challenges in the field of RM-ERMs offers crucial insights and recommendations for future research in this area.