Pyrometallurgical processing of red mud

Li X., Zhang T., Lv G., Wang K., Wang S.

Red mud is a highly alkaline solid waste discharged in the alumina production process. Because of its large amount of discharge and high alkalinity, it is mostly stored in dams, occupying a large number of land resources and posing a great safety hazard to the ecological environment. The large-scale consumption of red mud is a global technical problem. Different alumina production processes will produce different types of red mud, mainly Bayer process red mud. In addition to its overall utilization in the field of building materials, agriculture, the environment, and the chemical industry, red mud also contains valuable metal elements, such as titanium, iron, scandium, and aluminum, and is an important secondary mineral resource. This paper focuses on the principle and characteristics of red mud metallurgical treatment for the extraction of valuable components and looks forward to the prospect of large-scale, harmless, and high-value comprehensive utilization technology for red mud in China.

Zinoveev D., Pasechnik L., Grudinsky P., Yurtaeva A., Dyubanov V.

The main waste formed during the production of alumina by the Bayer method is red mud. This waste has a high content of iron, which can be effectively extracted by the carbothermic reduction and magnetic separation methods. The crucial factors affecting the commercial efficiency of this process are the iron reduction rate and the size of reduced iron particles. This study considers the influence of sodium sulfate addition to red mud on the kinetics of iron reduction and the iron grain growth process. The isothermal kinetics of the iron reduction process at 1000–1200 °C and 5–30 min of time was investigated for the red mud processing without additives and with 13.65% Na2SO4 addition. It was shown that the activation energy value for the reduction without additives was 65 kJ·mol−1, while it was 39 kJ·mol−1 for the reduction with Na2SO4 addition, respectively. Based on the microstructure study of the roasted samples, models were obtained for the calculation of the average diameter of iron grains without and with the additives. The iron grain growth process was thoroughly discussed, and its main mechanism was proposed.

Wei Z., Liu Q., Sun Z., Huang X., Gan M., Ji Z., Chen X., Fan X.

• Efficient method was developed to convert DR and RM into precursors for AAM synthesis. • The synthesized AAMs achieved excellent mechanical properties. • Main reaction products are gypsum, hydrotalcite and C-A S H gel. Disposal of flue gas desulphurization residue (DR) and red mud (RM) has been a focused problem due to the huge amounts and complicated compositions. In this work, an efficient co-disposal method was developed, through which DR and RM can be converted into solid precursors for the synthesis of high strength alkali activated materials (AAM). The effect of DR/RM mass ratio and calcination temperature on mineralogical composition of obtained precursors were investigated, together with the mechanical properties, microstructure, chemistry of reaction products of the synthesized AAM. Results show that the synthesized AAMs achieved excellent mechanical properties, with 3 d and 28 d compressive strength of 7.7–25.1 MPa and 30.1–58.8 MPa, respectively. Main reaction products include gypsum, hydrotalcite and C-A S H gel.

Pasechnik L.A., Skachkov V.M., Bibanaeva S.A., Medyankina I.S., Bamburov V.G.

Bauxites and red mud (RM) from alumina production facilities are distinguished by high contents of iron compounds and can be regarded a promising feedstock for magnetite production. The hydrothermal treatment of bauxites from the Severouralsk Bauxite Mine (SBM), red mud (RM), and hematite in an alkaline medium in the presence of FeSO4 or metal (Al, Fe, Ca, Mg, or 0.25Mg–0.25Al–0.5Fe) powders promotes the formation of magnetite in the products. The hydrothermal treatment parameters were dictated by bauxite leaching parameters at the production facility to provide high aluminum recovery. X-ray diffraction analysis, scanning electron microscopy, and magnetic measurements showed that the treatment of red mud in the presence of FeSO4 or metallic Al yielded highly disperse materials containing 32.4% or 23.7% Fe3O4, respectively. The presence of Fe or 0.25Mg–0.25Al–0.5Fe mixed powders in bauxite leaching provided for 40.8 or 67.9% Fe3O4, respectively, in the form of crystalline particles of sizes up to 5 μm. The higher magnetization values of the products owing to the formation of magnetic phases will ensure their efficient magnetic separation.

Yu J., Li Y., Lv Y., Han Y., Gao P.

• Suspension magnetization roasting and magnetic separation process treat red mud effectively. • Alumogoethite [Al x Fe (1- x ) ]OOH transformed into Fe-Al spinel phase Fe(Al,Fe) 2 O 4 . • Al-containing magnetite combined part of Fe(Al, Fe) 2 O 4 enter into the iron concentrate. • The saturation magnetization and specific magnetic susceptibility are enhanced via magnetization roasting. An innovative suspension magnetization roasting followed by magnetic separation process was developed to recover iron from high-iron red mud (HIRM), and the effects of roasting temperature, roasting time, CO concentration and grinding fineness on the recovery of iron were investigated. Under the optimized conditions, determined to be a roasting temperature of 560 ℃, reaction time of 15 min, CO concentration of 30% and total gas-flow rate of 500 mL/min, an iron concentrate assaying 55.44 wt% Fe with an iron recovery of 89.34% was prepared by magnetic separation. X-ray diffraction, chemical phase analysis, vibrating sample magnetometer, and scanning electron microscope were employed to assess the characteristics of red mud, roasted sample and magnetic separation products. The hematite in the red mud was transformed into magnetite during the suspension magnetization roasting, thus the magnetism was significantly enhanced. While, the alumogoethite was transformed into Fe-Al spinel phase Fe(Al,Fe) 2 O 4 , and entered the magnetic concentrate along with the magnetite. In addition, some fine-grained alumina particles were also easy to be wrapped by magnetic agglomerates and entered the magnetic concentrate, resulting in high aluminum content in the iron concentrate.

Khanna R., Konyukhov Y., Zinoveev D., Jayasankar K., Burmistrov I., Kravchenko M., Mukherjee P.S.

Managing red mud (RM), a solid waste byproduct of the alumina recovery process, is a serious ecological and environmental issue. With ~150 million tons/year of RM being generated globally, nearly 4.6 billion tons of RM are presently stored in vast waste reserves. RM can be a valuable resource of metals, minor elements, and rare earth elements. The suitability of RM as a low-grade iron resource was assessed in this study. The utilization of RM as a material resource in several commercial, industrial operations was briefly reviewed. Key features of iron recovery techniques, such as magnetic separation, carbothermal reduction, smelting reduction, acid leaching, and hydrothermal techniques were presented. RMs from different parts of the globe including India, China, Greece, Italy, France, and Russia were examined for their iron recovery potential. Data on RM composition, iron recovery, techniques, and yields was presented. The composition range of RMs examined were: Fe2O3: 28.3–63.2 wt.%; Al2O3: 6.9–26.53 wt.%; SiO2: 2.3–22.0 wt.%; Na2O: 0.27–13.44 wt.%; CaO: 0.26–23.8 wt.%; Al2O3/SiO2: 0.3–4.6. Even with a high alumina content and high Al2O3/SiO2 ratios, it was possible to recover iron in all cases, showing the significant potential of RM as a secondary resource of low-grade iron.

Liu X., Han Y., He F., Gao P., Yuan S.

Red mud (RM) is the major waste material with strong alkaline discharged which is during the alumina extraction process. The global stock of RM has exceeded 4 billion tons and its disposal as a solid waste has always been a thorny environmental problem. However, RM is widely considered to be a potential resource due to its high content of valuable metal components such as iron. High-iron RM is rich in iron and can potentially become a valuable resource if the iron can be extracted effectively. It is of great research value and profound significance to recover iron from high-iron RM. This paper systematically reviews the iron recovery methods for resource utilization of high-iron RM, and divides the technology of iron recovery from high-iron RM into three aspects: physical separation method, pyrometallurgy method (reduction smelting and reduction roasting) and hydrometallurgy method (acid leaching). The basic principles and effect of iron extraction of the above technologies are summarized respectively, and the advantages and disadvantages of different technologies are compared. It is pointed out that the feasibility and economic cost are the main factor restricting the industrial application of these technologies. Therefore, it is of great significance to overcome various problems and difficulties, and develop innovative processes and technologies, which can realize the recycling and utilization of iron in high-iron RM and realize the reduction of RM emission at the same time. • The hazards caused by red mud and trends in red mud research were presented. • The research status of iron recovery methods from high-iron red mud is reviewed. • The advantages and disadvantages of several iron recovery methods are compared. • Technologies suitable for industrial production needs to be studied in the future.

Agrawal S., Dhawan N.

• Red mud is evaluated as a polymetallic source for Fe, Ti , Al, Sc. • Scandium associated with Ti > Fe > Al and REEs occur as discrete phases or adsorbed on mineral surfaces. • Metallurgical application of red mud is important for the sustainable supply of critical metals. • This exhaustive review reports metal extraction by pyro- and hydro-metallurgical processes, from laboratory to pilot scale. • Proposed route for recovery of metallic values and valorization of red mud. Red mud is an industrial waste generated during alumina production containing residual minerals of bauxite ore. Significant metallic values with appreciable concentration make it a potential polymetallic source. The current red mud management involves storage in artificial ponds/dams or dry stacked in open areas, which poses an environmental risk, and disposal processes are costly. Recently, red mud is utilized for cement production; however, it results in the loss of valuable minerals, which could be strategically advantageous for resource-deficient nations. Red mud utilization for producing concentrate can significantly improve process efficiency of alumina production, reduce industrial liability and environmental impact. The globally generated red muds are compared according to the mineralogy, composition, and associated values. Hematite is the chief constituent in the red mud, with anatase, gibbsite, goethite, quartz, and desilication phases such as cancrinite, sodalite, and olivine in a significant amount. Red mud originated from karst bauxites containing higher rare-earth content as adsorbed ions on the mineral surfaces, isomorphous substitution, and discrete rare-earth minerals such as bastnaesite, xenotime, chuchite, and allanite. Scandium holds 95% of the rare-earth economic value in the red mud and is associated with hematite, goethite, and anatase. The paper presents a critical overview of the laboratory, pilot, and commercial processes employed to recover iron, aluminum, titanium, scandium, and REEs from various red muds. The response parameters such as alumina-to-silica ratio, iron grade, total rare-earth elements were used to determine the appropriate processing route for recovery of metals from red mud. An integrated process is proposed to recover metallic values from the red mud while ensuring minimal waste generation.

Wang S., Jin H., Deng Y., Xiao Y.

Red mud is a solid waste produced during the bauxite refining of alumina. In recent years, environmental problems caused by the accumulation of red mud have become increasingly serious. In order to understand the status of red mud recovery in recent years, this article uses a comprehensive literature database to classify and statistically analyze red mud-related publications from 2010 to 2019. The results show that research on the comprehensive utilization of red mud is mainly found in three fields: the construction and chemical industry, the environmental protection and agriculture industry, and the valuable elements extraction industry. A brief report is also made on the related research of red mud in the fields of cement, concrete, glass, ceramics, adsorbents, geopolymers, catalysts, composite materials, sewage treatment, waste gas treatment, soil improvement, and valuable element recovery. The current industrial consumption of red mud in China is measured, and some suggestions for solving the red mud problem are put forward.

Zhang J., Yao Z., Wang K., Wang F., Jiang H., Liang M., Wei J., Airey G.

• Red mud is a huge stock of industrial waste and causing serious environmental problems. • The physical–chemical behaviors of red mud were reviewed and its potential properties were analyzed. • The utilization of red mud in road bases and asphalt mixtures were reviewed and future research priorities were pointed out. Sustainable utilization of the bauxite residue (red mud) generated from the alumina refining has recently increased due to increased environmental concerns because of its high alkalinity and problematic pollutants when placed in landfills. This paper attempts to review recent research findings of utilizing red mud as a road material in pavement structures in literature, including road bases and asphalt mixtures. Previous laboratory investigations indicated that red mud is feasible to be used as a raw material in road bases with satisfactory unconfined compressive strength (UCS), frost resistance and durability performance, but their durability during the service life of the pavement is still unclear. The incorporation of red mud in asphalt mastics was found to be able to improve its stiffness, such as softening point, complex modulus, and viscosity. In terms of asphalt mixtures, replacing limestone filler in mixtures by red mud resulted in some positive effects on mechanical behaviors, high bulk density and good rutting resistance. However, the moisture susceptibility and raveling resistance of asphalt mixtures became relatively worse because of the addition of red mud. Referring to this overview, it is necessary to qualify the long-term service performance of road base materials prepared with red mud by using laboratory accelerating evaluation or road trials. For asphalt mixtures prepared with red mud, how to improve durability, in particular moisture resistance, will be a future research focus. In addition, the influence of red mud on cracking resistance at low temperature, fatigue properties and long-term durability of asphalt mixtures is still needed to be further explored.

Wei D., Jun-Hui X., Yang P., Si-Yue S., Tao C., Kai Z., Zhen W.

Red mud as the main byproduct generated during alumina extraction from bauxite. Owing to the high iron content in the red mud and the high correlation between iron and scandium during the leaching ...

Liu X., Gao P., Yuan S., Lv Y., Han Y.

High-iron red mud could potentially become a valuable resource if the iron could be extracted efficiently. A novel method for iron recovery from red mud using suspension magnetization roasting (SMR) followed by low-intensity magnetic separation has recently been developed. In this study, the effects of SMR operation parameters on its ability to extract iron from red mud were investigated. Under the optimized conditions, determined to be a roasting temperature of 540 °C, reaction time of 15 min, total gas-flow rate of 500 mL/min, and CO concentration of 30%, an iron grade of 56.41% and iron recovery of 88.45% was achieved. The saturation magnetization and specific magnetic susceptibility of the roasted sample under the optimal conditions studied were 37.17 A·m2/kg and 30.72 × 10−5 m3/kg, respectively. X-ray diffraction, chemical iron phase, and Mossbauer spectroscopy analyses were conducted on the raw and roasted samples, and the results indicate that hematite and goethite phases present in the raw red mud were transformed into magnetite and maghemite during the SMR process.

Ding W., Xiao J., Peng Y., Shen S., Chen T., Zou K., Wang Z.

Vasyunina N.V., Dubova I.V., Druzhinin K.E., Alekseev A.V., Gilmanshina T.R., Rudnitsky E.A.

This article summarizes the results of a systematic review of the literature in one particular application area – the extraction of valuable elements (Fe, Al, Na, Ti) from red mud. The analysis showed that depending on the composition of the bauxite being processed and the instrumentaltechnological scheme for producing alumina, the content of iron oxide (Fe2O3) varies from 7 to 70 % by weight, aluminum oxide (Al2O3) – from 2 to 33 % by weight, titanium oxide (TiO2) from 2.2 to 25 % wt., sodium oxide (Na2O) up to 12.5 % wt. The achieved maximum percentage of iron extraction is 97.5 %, aluminum – 89.7 %, sodium – 96.4 %, titanium – 97 %. It was noted that all practical studies were carried out in laboratory conditions only. As the most effective, technological proposals have been allocated for complex processing of red mud, including processes of smelting reduction, magnetic separation, leaching with mineral (HCl, H2SO4, HNO3) and organic (H2C2O4) acids. In modern studies, it is proposed to use microwave, ultrasound, or plasma technologies in recycling. As a result of the work, a systematic table was proposed on methods for extracting Fe, Al, Na, Ti from red mud. Suggestions are made on the criteria of technology that would have environmental, energy and economic benefits.

Archambo M., Kawatra S.K.

ABSTRACT Red mud is generated at a rate of up to 175.5 million tons per year. The global stockpile of red mud is near 4 billion tons. This material is hazardous with pH values from 11 to 13. Reduction of this waste is critical. Current industry practices for disposal of red mud involve different stockpiling techniques on valuable land area or disposing into critical bodies of water. This review studies processes which can reduce the negative environmental impact of red mud in an economic way. For instance, neutralization of red mud with CO2 can decrease the pH from 12.5 to 7. Treatment of red mud by this method lessens the negative environmental impact and prepares it for further processing for utilization. The current utilization rate of red mud is very low, only about 3 million tons per year are used as an additive for cement and construction. Red mud contains a large quantity of valuable minerals that can be extracted to both reduce the amount of red mud and provide value to the waste. This review investigates novel methods for treating red mud and extracting minerals like iron, titanium, and rare earth elements using a variety of smelting, direct reduction, and leaching processes. For example, the iron nugget process is a single step method to reduce iron oxides to metallic iron and separate them from red mud. Iron nuggets produced from red mud have an iron grade above 90%, which is comparable to pig iron generated by the blast furnace.