Summary of Research Progress on the Separation and Extraction of Iron from Bayer Red Mud

Liu X., Liu X., Zhang Z.

Ding Z., Cheng Y., Jin L., Wang W., Yan S.

The residue generated during the production process of alumina, known as red mud, is a type of solid waste. The engineering properties of red mud can be significantly enhanced through the modification and solidification using inorganic materials. This study primarily utilized red mud as the raw material, supplemented with fly ash, lime, and clay, to conduct a solidification experiment of red mud. Orthogonal tests with three factors of two ash ratio (ratio of lime to fly ash), two ash content (total lime and fly ash), and red mud types were designed to study the changes of different ratios and maintenance conditions, etc., on the engineering properties of red mud. In addition, the micro-mechanisms of modified red mud were investigated by means of XRF, XRD, SEM and EDX. The results show that for optimum moisture content, red mud types are the most important influencing factor and for maximum dry density, two ash content is the most important influencing factor. For strength characteristics, the optimum two ash ratio was 1.5:1, the optimum two ash content was 50%, and the optimum red mud types were 70% CRM (red mud made of Chalco Shandong Co., Ltd) mixed with 30% clay. The addition of lime, fly ash, and clay improves the temperature shrinkage coefficient of the red mud. Through the analysis of microscopic composition and structure, it can be seen that goethite (α-FeO(OH)) and magnetite (γ-Fe2O3) in the red mud reacted with the modified materials to generate crystalline aluminosilicate and amorphous hydrated silicate gel, and these products together with the original calcium carbonate (CaCO3), tricalcium aluminate (Ca3Al2O6) and garnet (Ca3TiFeSi3O12) in the red mud which have certain strengths enhance the structural strength of the modified red mud. The optimum ratio obtained from the combined test results was lime: fly ash: CRM = 30:20:50. Therefore, using lime, fly ash and clay as modified materials can greatly enhance the engineering properties of red mud and realise the resourceful use of red mud.

Bulayani M.M., Raghupatruni P., Mamvura T., Danha G.

The beneficiation of low-grade iron ores is a key research and development topic in the mineral processing industry. The gradual exhaustion of high-grade iron ore reserves, and rising consumer iron and steel demand globally necessitate efficient low-quality iron ore beneficiation to meet steelmaking quality requirements. This comprehensive review explores various beneficiation techniques for low-quality iron ore, focusing on conventional methods including comminution, froth flotation and gravity separation. This article discusses the principles, processes, and equipment used in these techniques and highlights recent advancements and research efforts in the field. This review also emphasizes the importance of effective beneficiation processes in enhancing economic viability, sustainable resource management, and environmental conservation. Furthermore, it presents a case study of iron ore deposits in Botswana, highlighting the potential economic growth and sustainable development that can be achieved by maximizing resource utilization through reductive roasting, followed by magnetic separation of iron ore using semi-bituminous coal as a reductant. Overall, this review provides valuable insights into low-grade iron ore beneficiation techniques and their significance in meeting the growing demand for high-quality iron and steel products.

Zheng F., Zhao Y., Wang H., Hu B., Liu C.

Reduction roasting‒magnetic separation was adopted to extract iron in red mud containing 47.45% Fe and 11.58% Al2O3. The process mineralogy and phase transformation of red mud during reduction roasting with CaO were studied using advanced mineral identification and characterization system, X-ray diffraction, scanning electron microscope, and energy-dispersive spectrometer. Results show that the main Fe-bearing minerals in red mud are hematite and alumogeothite, with corresponding contents of 47.99% and 37.81%, respectively. After reduction roasting with CaO, red mud is converted into metallic iron and Ca–Al compounds, and the iron grain size increases with roasting temperature. After roasting at 1175 °C for 60 min, the iron grain size reaches 18.85 μm. Under the conditions of grinding size of − 44 μm of 86.57%, and magnetic intensity of 1000 Gs, a concentrate with Fe grade of 90.14% and Fe recovery of 85.68% is obtained. Meanwhile, there are 40.01% of CaO and 23.96% of Al2O3 in magnetic tailing, which can be used as cement raw materials. This study lays the foundation for the resource utilization of red mud.

Wu P., Liu X., Zhang Z., Wei C., Wang J., Gu J.

Red mud (RM) is an alkaline waste residue discharged in alumina production. RM accumulation harms the environment and human health, making it urgent to find harmless treatment methods. RM contains abundant iron resources and potential pozzolanic activity minerals. The industrial utilization of RM has a positive impact on low-carbon and sustainable development in the steel and cement industries. This paper reviews a large-scale and harmless treatment method for high-iron red mud (HRM) that involves recovering iron from HRM using pyrometallurgy and utilizing the tailings after iron extraction from high-iron red mud (HRMT) to prepare cementitious materials. The paper elaborates on the general principles of iron recovery from HRM by pyrometallurgy, the activating principle of RM's pozzolanic activity by pyrometallurgy, the mechanical performance enhancement principle of HRMT-cement-based cementitious materials (HRMT-CM), and the stable solidification principle of hazardous elements in HRMT-CM. Finally, suggestions and prospects are proposed for the industrial utilization of RM.

Jeremy E., Sanwani E., Chaerun S.K., Mubarok M.Z.

Cai T., Pan R., Yang M.

Red mud is a strong alkaline solid waste produced by the alumina industry. Although it has found frequent use in building applications, its sodium content causes unwanted effects like “Frost”, demanding the removal of Na+ from red mud. Effective removal of Na+ can result in improving the performance of red mud as a material and increase its applicability. However, the removal of Na+ remains a key problem that needs to be addressed. In this paper, a comprehensive and systematic study has been carried out on the commonly used method of sulfuric acid dealkalization and its influence on the physical properties of red mud has been investigated. The variation of mineral phase content species in red mud and the mechanism of Na+ removal during acid leaching has been studied by regulating the sulfuric acid concentration. The red mud residues have been characterized using a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Brunauer Emmett Teller (BET) based on nitrogen adsorption–desorption. The results show that the Na+ leaching yield gradually increases with the increase in sulfuric acid concentration. Further, the Na-H, Na-O, Si-O, and Ca-O bonds in the main Na+ assigned mineral phase cancrinite are broken in a certain order based on the differences of bond energies at different acid concentrations. The results of this study can help to successfully address the issue of treatment of Na+ in bauxite slag and lessen the environmental contamination brought on by the subsequent discharge of waste liquid. Additionally, after treatment, the discharged waste liquid might be converted into usable products. The findings of this work have crucial implications for future-focused research in addition to offering a plausible pathway for ion alterations throughout the red mud dealkalization process.

Liu A., Bai Y., Wang C., Lin X., Guo F.

Red mud is an environmental burden during the alumina production process. To mitigate the hazards associated with red mud storage, this study investigated the utilization of alkaline red mud as a treatment agent for acidic mine drainage (AMD) with high concentrations of Fe(II) and Mn(II). This study explored the influence of reaction times, addition amounts of red mud, and pH values on the removal efficiency of Fe (II) and Mn(II) from high-concentration AMD. Various parameters such as suspended solids levels, effluent pH, and zeta potentials were measured to meet discharge standards. The adsorption mechanism of red mud was examined using SEM, XRD, EDX, XPS, and 3D-EEM analysis. Optimal conditions were determined as a reaction time of 2 h, pH value of 5.01 and the addition of 100 g/L red mud, achieving effective removal of Fe(II) (reduced from 1000 to 0.224 mg/L) and Mn (II) (reduced from 20 to 1.03 mg/L). The treated AMD meets discharge standards with reduced suspended matter content of 37.4 mg/L. These findings provided valuable insights for the utilization of red mud waste in engineering applications.

Bao S., Chen B., Zhang Y., Ren L., Xin C., Ding W., Yang S., Zhang W.

In recent two decades, ultrasound has been broadly applied to the hydrometallurgical leaching process to recover valuable metals within raw materials, aiming to solve the shortcomings of the conventional leaching process, including relatively low leaching recovery, long leaching duration, high reagent usage, high energy consumption and so on. The present work focuses on a comprehensive overview of the ultrasound-enhanced leaching of various metals, such as common nonferrous and ferrous metals, rare metals, rare earth elements, and precious metals, from raw metal ores and secondary resources. Moreover, the enhanced leaching mechanisms by ultrasound are discussed in detail and summarized based on the improvement of leaching kinetics, enhancement of the mass transfer and diffusion of lixiviants, and promotion of the oxidative conversion of metals from insoluble to soluble states. Lastly, the challenges and outlooks of future research on the leaching recovery for valuable metals with the assistance of ultrasound irradiation are proposed.

Li X., Zhang T., Lv G., Wang K., Zhu Z.

The recovery of iron from high-iron red mud is an important method for the large-scale utilization of red mud. Traditional fossil energy sources such as coking coal are usually used as reducing agents in the smelt reduction process of high-iron red mud, but they are not conducive to the early achievement of carbon neutrality in China. Straw carbon is a clean energy source with over 65% carbon content. Thus, the feasibility of straw carbon as a reducing agent to recover iron from high-iron red mud was investigated. Pig iron was obtained under the optimal reduction conditions of experimental temperature of 1400°C, alkalinity of 0.8, reduction duration of 20 min, MCaF2/MCaO of 4%, and carbon matching ratio of 1.1. More than 99% of the iron was recovered, and the results showed that straw carbon, which could effectively replace coking coal, achieved good results in the recovery of iron from high-iron red mud.

Chen J., Wang Y., Liu Z.

Red mud, as a solid waste produced during the alumina production, can cause severe eco-environmental pollution and health risks to human. Therefore, the resourcing of this type of solid waste is an effective way for the sustainable development. This paper reviews the recent progress on red mud-based catalysts for the removal of typical air pollutants, such as the catalytic reduction of nitrogen oxides (NOx) by NH3 (NH3-SCR) and the catalytic oxidation of CO and volatile organic compounds (VOCs). The factors influencing the catalytic performance and the structure-activity relationship have been discussed. Future prospects and directions for the development of such catalysts are also proposed. This review would benefit for the high value-added utilizations of red mud in mitigating atmospheric pollutions.

Gu J., Liu X., Zhang Z.

The accumulation of industrial solid wastes has led to serious environmental pollution. Resources and large-scale utilization of industrial solid wastes is an effective way to solve the problem of solid waste accumulation in China. This paper reviews the feasibility of using coal-based solid waste, metallurgical slag, tailings, industrial byproduct gypsum and municipal garbage incineration waste as road base materials. The properties of road base materials prepared from industrial solid wastes are similar to those of traditional materials. In addition, the unconfined compressive strength of road base materials prepared from different industrial solid wastes was compared. It was found that the type of industrial solid wastes and the proportion of designed raw materials can be reasonably selected according to the actual road demand and the source of industrial solid wastes. Moreover, the composite synergistic effect has been reported between various industrial solid wastes. This will help to improve the performance of road base materials prepared from multi-industrial solid wastes. Therefore, applying industrial solid wastes to road base materials can accomplish the large-scale utilization of industrial solid wastes and broaden the range of road base material selection. Finally, critical suggestions are given for the preparation of road base materials from industrial solid wastes.

Agrawal S., Dhawan N.

The current study investigates alkali baking using sodium hydroxide followed by water and sulfuric acid leaching to extract Al, Fe, Ti, Sc, and Ga values. Water leaching of baked mass selectively dissolves Al. Subsequent, sulfuric acid leaching of water-leach residue dissolves Fe, Ti, Sc, Ga, and remaining Al and Si values. The alkali baking forms sodium metal oxide (NaFeO2, Na2TiO3, NaAlO2, NaAlSiO4) phases, which improves the dissolution in sulfuric acid compared to the oxide phases of metals. The alkali dose was a prominent factor in forming sodium metal oxides. Baking at 600 °C, 1 h, 75 wt% NaOH yielded 60% Al dissolution during water leaching and 82% Ti, 83% Fe, 97% Sc, and 64% Ga dissolution during acid leaching. Scandium dissolution strongly correlates with titanium during leaching, and TEM analysis confirms the apparent enrichment of scandium in the anatase and hematite matrix. Carbonation of water leach solution precipitates alumina and dawsonite (NaAlCO3(OH)2) phases with a product having 85–87% Al2O3 purity and 12 wt% yield. Thermal hydrolysis of acid leach solution generates Ti(OH)4 precipitate which is calcined to obtain anatase with a 95–97% TiO2 and 13 wt% yield. The leach residue contains unreacted hematite and anatase phases having

Qiu G., Ning X., Shen J., Wang Y., Zhang D., Deng J.

A major industrial solid waste, iron tailings occupy a large area and pose long-term pollution risks. The pyrolysis gas of biomass was used as reducing agent to suspension magnetize and roast iron tailings to recover iron in this study. The process conditions, phase transformation and microstructure evolution of the iron tailings, pyrolysis gas production, and reaction regulations were investigated to explain the mechanism of iron recovery by suspension magnetization roasting (SMR) under the action of biomass pyrolysis gas. These studies were conducted using X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer, thermo-gravimetric and differential scanning calorimetry, brunauer-emmett-teller specific surface area, and gas chromatography. The results showed that, after the grinding-magnetic separation process, the iron recovery rate was 93.32 %; the iron grade of the iron concentrate was 61.50 %. The optimal process conditions were determined as follows: fast pyrolysis temperature of 600 °C, SMR temperature of 700 °C, biomass dosage of 10 %, and SMR time of 4-5 min. The formation of Fe3O4 from the surface to the interior of the particles during the reduction process, and formation of pores and cracks led to an increase in the specific surface area. The SMR temperature not only improved the heat and mass transfer effect in the reduction process but also generated more CO and H2 through the reverse reaction of methanation, which work together to increase the saturation magnetisation of the unit sample. This method can be used to efficiently recover high quality iron from refractory iron ores.

Liu X., Zou Y., Geng R., Li B., Zhu T.

In this work, a collaborative strategy for the aluminum and iron industry based on red mud recycling through the hydrometallurgy method was proposed. In this method, Fe3+ and Al3+ were firstly separated from the red mud by using H2SO4 as a leaching agent, which was by-produced from the sintering process of an iron and steel industry. Multiple influence factors on the leaching process were investigated, with the H2SO4 addition amount showing the strongest influence on the leaching rates of Al and Fe. The main components of the filter residue were CaSO4, TiO2, and SiO2, which could be reused as additives in the building materials. Subsequently, the final Fe recovery product was obtained through the co-precipitation, Fe/Al separation, and Fe(OH)3 calcination. In the final product, the content of Fe2O3 reached 82.87%, and the iron grade was 58.01%, meeting the requirement being raw materials for sinter production.