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Overview On Extraction and Separation of Rare Earth Elements from Red Mud: Focus on Scandium
Abstract
The paper provides an overview of the methods used for processing of red mud to extract rare earth elements (REEs). Red mud is a toxic and highly alkaline waste. Several methods have been adopted and being practiced all over the world for the processing of red mud. Complex processing of red mud is cost-effective since red mud contains iron, aluminum, titanium, calcium, rare earth metals etc. It has been observed that the acid leaching of red mud can almost completely recover the rare earth elements in the solution with various individual techniques and also a combination of them. Therefore, the choice of extraction method depends on the form in which the element occurs in the solution. However, relatively low concentrations of rare earth in the solution and significant amount of impurities increase the cost of getting the final commercial products. To ensure the cost-effectiveness of the process involving rare earth’s extraction from red mud, it is necessary to increase their content by several times. This article presents the various studies that have been carried out in these aspects and the possibility of making this resource a sustainable one for REE extraction with a special focus on scandium replenishment.
... According to Bayer's process, for every ton of alumina, 1 to 1.5 tons of red mud and 5-20 g/L caustic is generated [1]. It has been estimated that the annual global production of red mud exceeds 150 million tonnes [2]. In India, the annual production of red mud is more than 4 million tonnes [3]. ...
... The dominant constituents in red mud are Al 2 O 3 , Fe 2 O 3 , TiO 2 , SiO 2 , Na 2 O, and CaO, with small quantities of V, Ga, P, B, Pb, Zn, Cd, K, Sr, Mg, Th, Zr, Hf, As, Sb, Bi, Mn, Cu, Ni, Co, W, Nb, Ta and others [1][2][3]. The concentration of iron is very high (more than 40%) in the deposits of countries like Greece, Hungary, the UK, and India. ...
... The concentration of iron is very high (more than 40%) in the deposits of countries like Greece, Hungary, the UK, and India. However, Chinese red mud has lower Fe content [17,18], whereas, the content of titanium (TiO 2 ) is high in Indian (18%) and French (16%) red mud [2]. Titanium (Ti) extraction from red mud is done by both pyrometallurgical and hydrometallurgical techniques. ...
To ensure the complete utilization of red mud and parallel reduction in carbon footprints from alumina production, it is very important to tackle the alkalinity in red mud which poses problems in the processing of bauxite residue. Despite various methods, this article stresses the use of CO2 neutralization which has been employed to address alkalinity (2176 ppm) and simultaneously recovers the alkali under atmospheric pressure, which assisted in improved scandium extraction. Under conditions of particle size < 50 μm, 20% pulp density, 3-4 atm pressure, room temperature, in 30 min brought down the pH from 9.99 to 6.26, with 36–37% alkali recovery and capturing 28.8 g CO2/kg red mud. The neutralized red mud serves as an excellent feed for acid leaching to extract Ti and REEs. With 2 M sulfuric acid at 10% pulp density and 90 oC, 96% La, 95% Ce, and ~ 90% Sc were recovered in 2 h. The residue after the second stage operation was rich in Fe, Al and Si and thus can be processed by a hybrid pyro-hydro-metallurgical process, for achieving complete valorization of red mud while recovering critical metals.
Graphical Abstract
... Red mud's mineralogical composition comprises aluminum oxide as diaspore and boehmite, ferrous minerals as hematite, limonite and goethite, anatase, rutile, calcite, dolomite, and pyrite. In addition, the extra phases produced during the Bayer process, namely sodalite and gibbsite, contribute to the red mud's composition [47]. ...
... It has been shown that red mud contains 500 to 1700 ppm of REEs. It is worth noting that the Sc percentage in red mud is considerable, ranging from 130 to 390 ppm [47]. The REE concentrations in red mud are more significant when compared to the currently mined bastnäsite (carbonate-fluorides) and monazite (phosphates) ores, where the average REE levels range from 3000 to 13,000 g/ton [51]. ...
... About 133,000 metric tons of REEs were used globally in 2010, and it was predicted that the amount would increase to 350,000 metric tons by the end of 2023 [54]. REEs have a wide range of uses in different sectors, such as industrial, medicinal, petroleum, glass, alloys, biological, automotive, permanent magnets, automobile catalytic converters, and other applications, as well as metallurgical additives, glass polishing, alloys, ceramics, and other products [47,55,56]. China has produced the great majority of the world's rare-earth metals and its market share was around 90%. China, however, has started a campaign to impose restrictions and has established a system of export quotas for rare-earth products. ...
Aluminum is produced from its primary bauxite ore through the Bayer process. Although Al is important nowadays in the development of humanity, its production leads to the generation of a huge amount of waste, called red mud. Globally, the estimation of the stock of red mud is about 4 billion tons, with about 10 million tons located in Turkey. The presence of rare-earth elements (REEs) in crucial materials such as red mud makes it a major source of these elements. A number of methods have been developed for treating red mud, which are employed globally to recover valuable products. The application of a suitable method for REE extraction from red mud is a way to overcome the supply risk, contributing to reducing the environmental issues linked to red mud pollution. The current review summarizes the research on red mud processing and examines the viability of recovering REEs from red mud sustainably, utilizing hydrometallurgy and biohydro-metallurgy.
... The typical scandium deposit is found as small isolated pockets in pegmatite formations and is not easy to exploit in an industrial way, even if they supply beautiful mineral samples. The dominating source of scandium is secondary extraction, from waste products after bauxite processing (Akcil et al. 2018;Altinsel et al. 2018). A smaller amount comes from scandium mining and from extraction from laterite soils (Altinsel et al. 2018;Botelho et al. 2020). ...
... The Norwegian and Madagascan deposits are associated with gabbro and pegmatite formations, but are not used for production (Kristiansen 2003, Rosing-Schow 2020. Scandium is currently produced by calcio-thermic reduction of ScF 3 , which is obtained by fluorination of the oxide (Akcil et al., 2018). These are two reactions: ...
... The ranges found are for uranium 1-10 ppm in the ore, corresponding to 110-200 per uranium content. For tinstone, a scandium content of 125-200 ppm is given, for zirconium about 50-120 ppm, 12 ppm in ilmenite or about 22 ppm per titanium content (Akcil et al. 2018;Botelho et al. 2020, Borra et al. 2016). An estimated 12,000 ton of scandium is believed to be present in primary Australian deposits that would support scandium mining. ...
The scandium production rate and price data for scandium oxide and scandium metal was extracted from various sources. Data for extractable resources of scandium were found and evaluated by application of estimated yields. The feasible extractable resource is about 6.1 million ton, and with present technology, about 676,000 ton scandium appear as potentially extractable. The potential for scandium extraction is about 1500 ton/year at present, but only about 45 ton per year was produced in 2022. With improved extraction and access yields, production could be increased to about 450 ton per year, and the scandium resource would increase to about 1.5 million ton. The investigation suggests that there will be an increased demand for scandium metal in the future, but that it is limited by the high price and the lack of a properly functioning market and by a lack of production infrastructure. The scandium market show signs of being disorganized and unstructured. Modelling of future scandium production was done using the WORLD7 integrated assessment model, after development of a scandium module. Simulations show that the price will remain relatively high, but lower than in the past. The most uncertain factor for predicting the price is the size of the demand. The main limitation for making scandium metal is high energy costs and low extraction yields.
... Red mud is an environmental liability due to its high alkalinity, complex composition, fine particle size, and large production volume [5][6][7][8]. Red mud slurry has a pH value typically in a range of 10 to 12 [7,8]. Owing to its high alkalinity, red mud is considered hazardous waste. ...
... Red mud is an environmental liability due to its high alkalinity, complex composition, fine particle size, and large production volume [5][6][7][8]. Red mud slurry has a pH value typically in a range of 10 to 12 [7,8]. Owing to its high alkalinity, red mud is considered hazardous waste. ...
... According to Fig. 1-a, Fe, Al, Ca, and Ti containing compounds constituted the major phases of the sample. Iron is mostly observed as hematite (Fe 2 O 3 ) and chamosite ((Fe 2+ , Mg) 5 Al (AlSi 3 O 10 ) (OH) 8 ). Most of the Ti of the sample was in the form of TiO 2 as two different forms of anatase and rutile. ...
... The rare earths are the fifteen metallic elements of the lanthanide series, together with yttrium and scandium [60]. They have many applications, especially in the electronic industry, where they are used in many devices such as mobile phones, screens, high-capacity batteries, permanent magnets for wind power stations, ceramics, etc. [61]. The concentration of these elements in bauxite residues varies, but (for example) atypical Jamaican residue (which can be 5-10 times higher in REEs than bauxites from other regions) contains (in ppm): scandium 135, lanthanum 500, cerium 650, neodymium 250, samarium 65, europium 15, terbium 10, ytterbium 30, lutetium 5, tantalum 10 [7]. ...
... The recovery of REEs from red mud mainly focuses on hydrometallurgical methods [8], with acid-leaching technology as the predominant method [14]. The choice of extraction method depends on the forms of existence of the REEs in the solution [61]. ...
Red mud, a voluminous industrial waste produced during the Bayer process in the alumina industry, has numerous application possibilities across various fields. Its potential uses are diverse, ranging from the construction industry and metallurgy to environmental protection and agriculture. There are three main aspects of red mud utilization. First, it can be analyzed from the point of view of resource utilization, where it could be applied as raw material mostly in the construction industry. Second, it could be a useful source of valuable components, such as rare earths and metals, especially iron. Third, red mud could have different environmental applications, in wastewater treatment, soil remediation, etc.The paper summarizes current data on red mud utilization methods and aims to emphasize the potential for red mud utilization in various fields.
... Researchers have also reported red mud as a potential secondary source for REE recovery (Liu & Li, 2015;Rayzman, 1998). Red mud is a waste generated after extracting alumina from bauxite ores (Akcil et al., 2018). It was reported by Binnemans et al. (2013) that the scandium concentration in red mud is significant and ranges between 130 and 390 ppm. ...
... At the same time, the red mud contains a noticeable amount of gangue materials such as iron, aluminum, calcium, silicon, and titanium; thus, it is crucial to separate REEs with a high purity. The common separation methods after the leaching of REEs from red mud include ion exchange methods (Akcil et al., 2018;Ohsenkühn-Petropulu et al., 1995). Acid leaching of red mud by sulfuric, hydrochloric, or nitric acid can recover above 80% of the REEs from the solution. ...
Rare earth elements (REEs) are critical in emerging clean energy, advanced technologies, and military defense applications due to their unique physical, chemical, optical, and luminescent properties. Given the potential supply chain restrictions imposed by one country's dominance in the global REE market and the consistently growing demand for REEs, developing the US domestic REE supply chain is imperative. Thus, alternative sources are crucial to supply the demand and prevent interruption in manufacturing products that consume REEs. Concurrently, acid mine drainage (AMD) is a long-standing and widespread global challenge the mining industry encounters. AMD is generated in large volumes and continuously when the sulfidebearing minerals, typically pyrite, are exposed to air and water and then oxidized. The highly acidic nature of AMD dissolves high concentrations of heavy metals, which imposes severe risks to receiving waters and soil due to its high acidity and elevated concentrations of metals.
Past and ongoing research has suggested that AMD and its treatment sludge are promising sources of critical minerals, including rare earth elements (REEs). Therefore, by developing a new AMD processing strategy, AMD and its treatment byproducts can be turned from mine waste to a feedstock of strategic, critical elements. This study characterized various coal-based AMD and their treatment sludge samples for REEs and major metal elements. Characterization study results indicated that several AMD sludge materials contain a significantly high content of critical minerals. For example, around 356.76 ppm of REEs, 226.01 ppm of cobalt, 2.63% aluminum, 1.11% magnesium, and 0.55% manganese were detected on a dry basis in one sludge sample collected from a coal-based AMD treatment facility.
Following identifying promising feedstock, a separation process was developed to recover REEs. The main challenge facing AMD sludge processing was the presence of significant amount of impurities, such as aluminum, iron, calcium, and silicon, compared to a low REE content. Firstly, parametric leaching tests were conducted to determine the optimum leaching recovery. Then, stage-wise precipitation tests were performed to study the precipitation behaviors of various groups of elements, including REEs and other major metals, at different pH regions and the feasibility of selectively recovering REEs by targeting one particular pH region. The results revealed that selectively recovering REEs by targeting one specific pH region was not feasible for the studied AMD sludge feedstock. However, the impurities, specifically iron and silicon, could be selectively removed from REEs at a pH set-point of 3.5.
Afterward, separation approaches were investigated to further remove the impurities while selectively extracting REEs. First, the effect of different organic-to-aqueous (O:A) ratios on solvent extraction was studied, and the O:A ratio of 1 was found to be optimum. Then, three different solvent extraction methodologies, including regular solvent extraction with DEHPA, solvent extraction with a phase modifier of TBP, and post-oxidation solvent extraction, were evaluated to enhance the purity of produced rare earth oxides (REO). The final process selected for REE recovery consists of (a) sulfuric acid leaching at a pH of 0.5 with a leaching time of 8 minutes, (b) selective oxidation precipitation at pH 3.5 using hydrogen peroxide, (c) post-oxidation solvent extraction with 0.5 M DEHPA at an O:A ratio of 1, (d) two-stage stripping with hydrochloric acid, (e) oxalic acid precipitation at a pH of 1.5 to produce REE oxalate, (f) roasting to convert REE oxalates to oxides, and finally (g) washing. As a result of the developed process, a mixed REO product with a purity up to 80% by weight was produced from the AMD treatment byproduct.
... The red mud is dissolved in an acidic solution, commonly hydrochloric acid (HCl), sulfuric acid (H 2 SO 4 ), phosphoric acid, nitric acid, oxalic acid, and organic acids (Liu et al. 2021), to dissolve iron in the pregnant leach solution (PLS). Regarding iron extraction, it is established that acid leaching of red mud is an effective method for extracting rare earth elements (REEs), enabling substantial recovery of these elements from the solution (Akcil et al. 2018). The PLS, which contains iron and other metal ions, is subsequently purified by ion exchange, solvent extraction, and precipitation. ...
... For example, increasing the concentration of HNO 3 from 0.5-1.5 N to 1.0-1.5 N can potentially enhance the recovery rates of iron and titanium. Nevertheless, such an increase may also result in recovering 40-45% of scandium in the leach solution (Akcil et al. 2018). Additionally, using acidic solvents with low pH poses a potential risk of environmental pollution if not properly managed due to the possibility of leaks. ...
Red mud is a residual substance generated as a waste in the refining of bauxite to produce alumina. The handling and disposal of red mud present significant challenges for the alumina industry due to its large volume of production and associated environmental risks, which include high pH, slow settling, and prolonged stabilization time in Tailings Storage Facilities (TSFs). Currently, annual red mud production levels are estimated to range between 0.1 and 0.15 billion tons, depending on the specific bauxite variety and the parameters employed during the digestion process. In general, red mud is composed of several constituents, including silica (SiO₂), gibbsite (Al(OH)₃), boehmite and diaspore (AlO(OH)), anatase and rutile (TiO₂), calcite (CaCO₃), and various iron-bearing minerals such as goethite (FeOOH), hematite (Fe₂O₃), and magnetite (Fe₃O₄). Iron concentrations in red mud demonstrate significant variability, with a range extending from 6% to 60%. These components present potential for further utilization. Owing to the generally fine particle size of red mud, selective flocculation has been proposed as a viable method for the treatment of stockpiled red mud or as an iron separation technique. Compared to chemical extraction methods, selective flocculation is more effective in managing fine particles and offers a less complicated approach. Current research efforts are focused on enhancing the selectivity of the process to yield higher iron content in the concentrates. One such technique involves the development of novel reagents. Bioreagents, derived from living organisms, are being designed to provide an environmentally friendly alternative. Certain microorganisms, such as bacteria and fungi, produce substances that are analogous to the chemical compounds commonly employed in conventional selective flocculation processes or other compounds that are suitable for selective bioflocculation applications. The objective of this review is to provide an overview of the current status of iron concentrations and extraction techniques from red mud, as well as the advancements in iron-selective bioflocculation research to date. It is expected that a comprehensive understanding of the selective bioflocculation method for iron extraction from red mud will be achieved, thereby facilitating the potential for further development of the method.
... The REEs contained in bauxite residues are at a content of 500-1700 mg/kg [7,8], and the primary REEs are lanthanum(La), cerium(Ce), neodymium(Nd), praseodymium(Pr), scandium(Sc), and yttrium(Y) [9]. Bauxite residues have provided potential opportunities for the production of REEs apart from the use of ion adsorption clay deposits [10]. The REEs in bauxite residues are generally extracted through acid leaching followed by a solvent extraction process. ...
... In the actual extraction process, both an ion exchange reaction and a solvation process could occur. The reaction can be represented by Equation (10). The equilibrium constant K was calculated according to Equation (11) and further transferred into Equation (12). ...
Bauxite residue is a hazardous solid waste produced in the alumina production process and has also become a significant rare earth resource. The extraction behaviors of La, Ce, Sc and Y solubilized in the phosphoric acidic leachate of bauxite residue were investigated in this study with di-(2-ethylhexyl) phosphoric acid as the extractant. With a relatively low concentration of 2% at an aqueous solution pH of 1.5, 90% Sc and 98% Y were extracted by di-(2-ethylhexyl) phosphoric acid. Less than 5% La and Ce and impurities of Fe, Al, Ti and Ca were extracted in this situation. As the concentration of di-(2-ethylhexyl) phosphoric acid increased to 20%, almost all the Sc and Y were extracted and the extraction ratios of La and Ce were 87% and 95%, respectively. A good separation of REEs against impurities was simultaneously obtained in the solvent extraction process and their separation coefficients were much higher than 1. A stepwise extraction process was proposed and established to extract Sc/Y and La/Ce sequentially from the phosphoric acidic leachate. It was further revealed that the Sc and Y in the acidic leachate were extracted by di-(2-ethylhexyl) phosphoric acid through an ion exchange process, and that the extraction of La and Ce was due to an antagonistic process where both an ion exchange reaction and a solvation reaction occurred.
... The possibility of using middlings products from bauxite, nepheline, apatite, phosphate rock, kaolinite clays, etc. as additional REM raw materials is being studied [3][4][5]. According to statistics published by the U.S. Geological Survey (USGS) in 2022, global kaolin production in 2020 was estimated at about 46 million tons. ...
... At this stage, the raw material was the clay of the Alexeevskoe deposit. 3 and HCl solutions with concentrations of 5-20% were used to determine the dependence of the degree of extraction on the type of mineral acid. Leaching was carried out at temperature 20 • С, ratio L:S = 3 and duration of 40 min (Fig. 3a-c). ...
Currently, due to the high rate of development of the rare-earth industry, new sources of raw materials are being mastered and new technologies for obtaining rare-earth metals (REM) are being developed. Studies have shown that REM in kaolinite clays of Alexeevskoe deposit in Kazakhstan and Egypt deposits in Sinai Peninsula (K-Watt, K-Tech) and in Aswan region (KB,KPL) are mainly represented by erbium (Er). Production of Er concentrate is considered as a by-product in a comprehensive middlings processing of kaolinite clays to produce alumina and building materials. The possibility of obtaining Er concentrate by sulfuric acid leaching and sorption concentration methods has been determined. Optimal technological conditions of kaolinite clays leaching is the use of 5% solution of H2SO4, at temperature 50 °C, duration 60 min and L:S ratio = 5. Under these conditions the separation of REM from the main components Fe2O3, Al2O3, SiO2 is achieved. Concentrates were obtained with the content of the sum of REM oxides from 91.3 to 93.4%, in which the relative content of Er was from 64.89 to 90.82%. The results showed that the developed technology can be used for processing of erbium-containing kaolinite clays of various deposits.
... Such mentioned materials include slags from iron production but also other iron-containing carrier ores, such as those from zinc or aluminium production. This explains why small amounts of REE can also be found in iron-containing residues from non-ferrous metallurgy, such as red mud from the aluminium industry, or in iron precipitation residues from the zinc industry [15][16][17]. The last column is an important factor because it decides how willing the industry is to build new infrastructure for its extraction or change the production quantity of the base metal and thus the supply side of the market leading to price volatility, to counteract shortages of hitch-hiker metals. ...
In the context of the European Critical Raw Materials Act, this work attempts to demonstrate the potential of residual material flows from non-ferrous metallurgy and their possible contribution to the supply security of metals by locally available new secondary resources, assuming technically and economically viable processing. Based on the aluminium, zinc, copper and lead industries, the resulting waste streams are discussed and, in particular, the complex process consisting of physical, chemical and metallurgical steps is described. Their diversity, be it slags, dusts or even sludges, has a wide variety of morphologies and compositions due to the process of generation. In the past, many concepts for reprocessing were investigated, but the goal was usually only the recovery of one target element or to avoid landfilling by using it, for example, as a building material, whereby the metals contained are completely lost. If the target is the extraction of valuables, the required interdisciplinary process development must be based on an in-depth characterization to understand the behaviour of metals and trace elements in possible extraction steps and also to develop suitable strategies for influencing the behaviour of target elements with the aim of extraction. This starts with an in-depth comprehension of the formation process, which is the subject of this article and has a direct influence on the composition and morphology of the materials, thus forming the basis for understanding the behaviour in potential recycling processes. Furthermore, typical compositions of the residual material streams, sources and, if available, quantities are shown and, in summary, an attempt is made to evaluate the materials in a SWOT analysis and to address the challenges in developing extraction steps for processing. While mine tailings are mostly found outside of Europe, the potential of the residual materials from metallurgy is local due to the processing of the concentrates in Europe. This leads to several potential advantages in a possible reprocessing, such as no or shorter transport routes, which is linked to lower quantity of emissions, defined volume and known composition, no geopolitical risk, conservation of primary resources, and increasing Europe’s sustainability through a more comprehensive use of the raw materials.
This article is part of the discussion meeting issue ‘Sustainable metals: science and systems’.
... Disposal of RM causing serious hazards. Utilization of RM as construction material such as backfilling, road construction, cement production, brick & concrete, tiles, aggregates and recovery of rare earth & valuable metal, etc. seems inevitable (Kalkan, 2006;Yarbaşı et al., 2007;Nadaroglu et al., 2010;Nadaroglu, H., Kalkan, E., 2012;Cozzolino et al., 2023;Borges et al 2011;Ashok and Sureshkumar, 2014;Agrawal et al., 2015;Borra et al., 2016;Kim et al., 2017;Nikbin et al., 2018;Akcil et al., 2018;Khairul et al., 2019;Mukiza et al., 2019a). Table 2 presented the resource status and inventory of eight major bauxite producer country. ...
Red mud (Bauxite residue) is an industrial by-product (IBP) generated as a vast volume, mainly from aluminum industries. Disposal of red mud in open land leads to serious environmental hazards, occupies a vast land area, and incurs enormous economic and social costs. Storage and maintenance of red mud dumps are also costly, and their failures frequently flood vast areas, killing people and cattle and disrupting the ecosystem. Conversely, research data shows that the red mud has enormous potential to transform its valuable resources. Due to the growing demand for bauxite ore for aluminum industries, the volume of red mud has been increasing rapidly, causing an inevitable multidirectional consequence in the context of environmental and sustainability issues. On the other hand, the rising demand and resource crises continue to deplete natural resources; the gap of enormous resource availability has become a severe challenge for scientists, researchers, and institutional R&D to develop a process technology to re-generate resources through the recycling of wastes. Using red mud through the circular economy concept can replenish the depletion of virgin resources (mainly the construction sector) and extract valuable materials and metals from red mud. Recycling RM through the circular business model can increase the sustainability of natural resources, reduce environmental pollution, water contamination, and land pollution, increase land area, replenish the depletion of natural resources, enhance economic growth, and mitigate global warming and climate change.
... The large inventory of BR and its complicated and hazardous properties (alkalinity, high sodium, fine particles, soluble metals, radioactivity, etc.) attract many researchers to work on the treatment and utilization of BR. Some of the most attractive areas include the utilization or modification of BR for manufacturing cement, (Hertel et al., 2021;Pontikes and Angelopoulos, 2013) construction (Arroyo et al., 2020;Tang et al., 2018), or advanced materials (Huang et al., 2008;Peng et al., 2023b;Wang et al., 2008Wang et al., , 2023b, and recovery of iron (Cardenia et al., 2019;Jovičević-Klug et al., 2024), aluminium (Urík et al., 2015;Uzun and Gülfen, 2007), titanium (Agatzini-Leonardou et al., 2008;Alkan et al., 2017;Mishra et al., 2002), silica (Piga et al., 1993), rare earth elements (REEs) (Abhilash et al., 2014;Akcil et al., 2018;Davris et al., 2016;Salman et al., 2021;Wang et al., 2023a). Among them, the valorization of BR by mineral and metal recovery is the most cost-effective and sustainable solution and attracts many researchers to work in this field. ...
... As previously mentioned, red mud has become a source of scandium based on hydrometallurgical recovery . Considering the scarcity of scandium as a mineral source and the high cost of scandium and/or scandium-oxide, several studies have been proposed for this purpose [62][63][64][65][66][67][68][69]. The main researches are centered on leaching with sulfuric acid followed by extraction of specific organic solvents; calcination, acid leaching and recovery with ion exchange resins, among others. ...
This work aims to demonstrate the importance of knowledge for the formulation of clean technologies in the production of materials and chemical products, which do not go against the interests of society and are centered on environmental preservation. Most chemical processes were conceived at the beginning of the century or in the 1950s, where the principles of preservation of man, the environment and industrial safety were not fundamental requirements in the implementation of these large basic industries. The origin of the raw materials and the multiple industrial technologies adopted in the manufacture of various products and the recovery of industrial waste or other origins are fundamental factors that dictate the quality of the final product. Several industrial processes were presented where the level and type of contaminant is inseparably linked to its origins and the industrial processes imposed. In addition, it is concluded that it is important to develop a critical technical awareness in society, especially in the University, which aims to understand the manufacturing routes of the products and the contaminants generated and/or aggregated during industrial processing, especially in relation to the quality of the products and environmental preservation.
... REEs are present in bauxite residue in various amounts, with Sc accounting for >95% of the commercial value. Bauxite residue has been discovered to contain a tiny fraction of REEs, varying from 500 ppm to 1700 ppm (Akcil et al., 2018). It is worth noting that the % age of scandium in bauxite residue is fairly high, varying from 130 to 390 ppm. ...
... [5,6] Despite its utility, Sc is often found in trace amounts, typically coexisting with other elements in the crust rather than in concentrated mineral deposits. [7][8][9] As a result, Sc is primarily recovered as a byproduct during metal processing or derived from industrial waste, such as the red mud waste generated during electrolytic aluminum production [10,11] or from Tungsten mine waste. [12] Sc's global supply shortage, which stands at just 15-25 t/year, has contributed to its exorbitant pricing. ...
This paper investigates the synergistic extraction performance of Scandium using a mixture of Cyanex572 and Cyanex923 in sulfuric acid medium. The results show that the best synergistic effect is achieved when the pH value of the aqueous phase is 2 and the mole fraction of Cyanex572 is 0.5, with a synergy coefficient value R of 4.78. In addition, the extraction mechanism of this synergistic system is discussed, and the extracted complex is determined to be [Sc(SO4)0.5(HL2)2B2] by slope analysis. The loaded Scandium can be stripped within two times by 2 mol/L sulfuric acid to obtain a stripping efficiency of 99.4 %. Finally, this synergistic system was applied to extract Scandium, demonstrating the potential application in separation of Scandium from the leachate of laterite nickel ore.
... Red mud is deficient in vanadium and other valuable metals, such as titanium and even rare earth elements. Despite this, efforts are continued to recover these metals from red mud because of the high economic value, which may involve a series of mineral processing techniques, attributed to the low concentration of non-ferrous metals (Akcil et al. 2018;Swain, Akcil, and Lee 2020). ...
Vanadium is a critical metal that has been widely used in a broad variety of applications with almost no metal substitutes. However, the limited availability of its (vanadium) primary resources has raised concerns of supply security. In view of the criticality, recycling vanadium from secondary resources has been identified as a vital supply alternative. This article thus presents a comprehensive overview of metallurgical processes used in the recycling of vanadium from a variety of secondary resources, including spent HDS catalyst, spent SCR catalyst, fly ash, red mud, Bayer’s sludge, alloy scrap, tailings, etc. First, the physicochemical characteristics of these secondary resources are emphasized. Understanding the characteristics of vanadium-bearing secondary resources is important as it determines the recycling route. The metallurgical recycling processes of vanadium, which include aqueous- and thermal processes are discussed in depth, along with the theoretical backgrounds and fundamentals of each process. Also discussed are the industrial-scale processes and trend in research and development (R&D) for the respective secondary resources. Besides highlighting the status of recycling processes, the article also provides prospective directions for such resources.
... Thus, extracting REEs and vanadium is an inevitable approach to realize the resourceful and valuable utilization of RM. The contents of neodymium, lanthanum and cerium in RM is 2-6 times than those in earth's crust (Akcil et al., 2018). REEs are mainly present as symbiotic (Lu et al., 2018). ...
As a bulk solid waste with high alkalinity, red mud (RM) not only occupies a large amount of land and requires high maintenance costs, but also unavoidably generates serious hazards to the surrounding ecological environment. The comprehensive treatment of RM has become an enormous challenge for the green, low-carbon and high-quality development of the global alumina industry. To minimize the RM destruction to the ecology and the waste of secondary resources, the sustainable utilization of RM was widely investigated in the past decades, especially for the recovery of valuable metals. This paper systematically summarized the research status of recycling valuable metals (Al, Fe, Na, Ti, Sc, Ga, V and RE) from RM in recent years. The recycling technology mainly includes physical beneficiation, hydrometallurgy, pyrometallurgy and electrodialysis. The technical principles and characteristics as well as the current problems of various recovery processes from RM were comprehensively introduced, and the future development directions of sustainable utilization were also prospected. The advantages and disadvantages based on the different aspects of recovery efficiency, energy consumption and environmental impact were also discussed. The proposal of new technologies for the harmless, high-value and full utilization of RM is beneficial to the future research on the comprehensive utilization of bulk industrial solid wastes.
... Therefore, there has been numerous research on the extraction of REEs and titanium from red mud. Literature reviews indicate that most of the extractions of REEs from red mud have been experimentally investigated using hydrometallurgy methods involving leaching in acid solution followed by retrieval of REEs from the solution using precipitation, solvent extraction or ion exchange adsorption (Zhang et al. 2016;Akcil et al. 2018;Archambo and Kawatra 2021). Recovery of titanium and gallium from red mud have also been experimentally investigated via the hydrometallurgy route (Mehta and Patel 1951;Kasliwal and Sai 1999;Agatzini-Leonardou et al. 2008;Ghorbani and Fakhariyan 2013;Abdulvaliyev et al. 2015;Huang et al. 2016;Alkan et al. 2018;Xue et al. 2019). ...
The Western Indonesia Bauxite Province in Kalimantan forms a lateritic bauxite region with a complex history and poorly known sustainable metal contents within the bauxite residue. Bauxite residue produced using the Bayer process contains notable scandium. We present new geochemistry, mineralogical, and geological data from the lateritic bauxite and red mud from the active mine and deposit, which aims to investigate the behavior of critical elements during weathering. The geochemical analysis and translated isocon results have shown that the content of scandium in red mud is higher than the average concentration of crustal rocks and is concentrated in the ferrite layer and bauxite residue. A positive correlation between the existence of iron oxyhydroxide mineral in residual iron-rich layer and red muds with the rare earth elements (REE) and scandium concentrations may be interpreted as a scavenging effect of mobile REE. The weathering and leaching processes in bauxite allows the adsorption of the trivalent scandium cation (Sc ³⁺ ) on goethite and are followed by the ionic substitution with other trivalent cations in the crystal of hematite. The study illustrates the importance of understanding processes during weathering and laterization for geochemical processes and rare earth elements exploration in tropical areas.
Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits
Supplementary material: https://doi.org/10.6084/m9.figshare.c.6689139
... Similar results can be facilitated using microwaves (Agrawal et al., 2019) or pre-washing with sulphuric acid (H 2 SO 4 ) or sulphate solutions (Meng et al., 2020). From further sintering J o u r n a l P r e -p r o o f processes (Akcil et al., 2018) and alkaline leaching, REEs can also be recovered (Borra et al., 2015). ...
Bauxite residues known as “Red Mud” (RM) are the principal waste of caustic digestion of bauxite from the Bayer Process, whose costs of disposal are expensive and cover 5% of the total costs of extraction and processing for aluminium production. Nevertheless, this material can be considered an important source of high-value elements, such as rare earths (REEs) and metals, Fe, Ti, Al and others. In this work, the focus has been on the recovery of iron in the form of the compound Fe(II) oxalate. Four types of acids have been used (HCl, H2SO4, H3PO4, H2C2O4) for iron extraction from RM coming from Montenegro. Hydrochloric acid shows a higher iron extraction capacity, reaching an iron extraction yield in solution of 22.6%. Sulfuric and phosphoric acid, instead, interacted with RM leading to the formation of sulfonate and phosphate species, inhibiting the leaching ability of individual species. Oxalic acid showed the least amount of iron ions extracted but formed a stable ionic complex in solution, Fe2(C2O4)3∙2H2O. Starting from this complex it was possible to recover the corresponding salt by a reduction and precipitation process. Through a pre-treatment with HCl and a subsequent treatment with oxalic acid, it was possible to obtain a better yield of iron oxalate. Starting from the laboratory scale, a CHEMCAD plant was conceptualized with a yield higher than 16% per pass (repeatable 3 times with a global iron yield >50%) and obtaining iron(II) oxalate dihydrate with purity up to 96%wt. In a holistic view of the problem, the proposed process can operate in parallel with other procedures proposed in the literature for the recovery of other valuable substances from red mud.
... In addition to REE-containing orebodies, there are potential alternative sources of REEs that could address the current lack of local supplies while enabling waste valorization. Some of these sources include products of coal combustion (coal fly ash and bottom ash), phosphogypsum [55], red mud (aluminum processing residue) [2], and electronic waste [3]. Among these potential sources, coal fly ash has received the most research attention over the past 20 years for a variety of reasons [57,37,43,59]. ...
... Largely dispersed but not actually rare, Sc is the first, lightest and the most expensive transition metal, and with 20-30 µg/g natural abundance in earth's crust is ranked the 50th most abundant element (Altinsel et al., 2018). However, Sc does not often occur as a single deposit (USGS, 2010) and it can be recovered from secondary sources such as mine tailings including bauxite residue (Akcil et al., 2018;Li et al., 2018;Zhu et al., 2017). Since Sc does not bind to common oreforming anions, it is found in more than 100 minerals at low concentrations (USGS, 2020). ...
... Al and Ti are recovered using hydrometallurgy, here different leaching and digesting agents are used to extract metals, and after that, concentration/precipitation steps are commenced (Ghorbani and Fakhariyan 2013). Likewise, valuable rare earth elements like Sc have a remarkably higher concentration in red mud than in their natural ore (Akcil et al. 2018;Lei et al. 2021). European Commission classified Sc as a critical raw material (CRM) due to high demand and low availability (Ochsenkuehn-Petropoulou et al. 2018;Cusack et al. 2019). ...
The mining industry has powered the human endeavor to make life more innovative, flexible, and comfortable. However, it has also led to concerns due to the increasing amount of mining and associated industrial waste. Special attention is highly desired for its proper management and safe disposal in the environment. The problem has only augmented with the increase in the mining costs because of the investments needed for ecological remediation after the mining operation. It is pertinent that the targeted technologies need to be developed to utilize mining and associated industrial waste as a secondary resource to ensure sustainable mining operations. Every perceived waste is a valuable resource that is needed to be utilized to create additional value. In this review, the case of alkaline bauxite residue (red mud)—alumina refinery waste has been discussed at length. The highlight of the proposed work is to understand the importance of alkaliphile-assisted biomining—a sustainable alternative to conventional metal recovery processes. Along with the recovery of metals, pH reduction of red mud is possible through biomining, which ultimately paves the way for its complete utilization. The unique adaptation strategies of alkaliphiles make them more suitable for biomining of red mud through bioleaching, biosorption, and bioaccumulation, which have been discussed here. Furthermore, we have focused on the potential of the indigenous microflora of red mud for metal recovery in addition to its neutralization. The study of indigenous alkaliphiles from red mud, including its isolation and propagation, is crucial for the industrial-scale application of alkaliphile-based technology and has been emphasized.
... Meanwhile, red mud is a typical secondary resource, containing Fe, Al, Na, Ti, Cr, Sc, V, Ga, and other valuable elements [10]. Unfortunately, it is difficult to conduct red mud effectively by conventional beneficiation methods (i.e., gravity separation, magnetic separation, floatation, and their combination process) because of its complex material composition, micro-fine grain size, and high alkalinity [11][12][13][14][15]. The reduction, recycling, harmlessness and full component utilization of red mud can not only solve the serious environmental pollution caused by the above-mentioned red mud stockpiling, but also alleviate the resource guarantee dilemma of China's high dependence on imports of iron ore under the current serious shortage of domestic iron ore resources, reduce China's dependence on foreign iron ore, and promote the sustainable, healthy and coordinated development of China's national economy [16]. ...
In order to simulate the pre-reduction behavior of ore powder by coal gas produced by smelting reduction of coal-based electric furnace, an efficient and clean utilization technique for red mud based on fluidized bed carbon monoxide reduction was developed in the present study. Experimental results indicated that a metallization rate of 68.08 % and reduction degree of 78.72 was obtained under the optimal conditions of reduction temperature of 800 °C, CO concentration of 85 %, and reduction time of 30 min. Pre-reduced materials can be used as raw materials for electric furnace melting reduction. The order in which iron oxides were reduced is only related to temperature, and at 800 °C, iron oxides were reduced in the order of Fe2O3 to Fe3O4 to FeO to Fe. During different stages of prereduction, the surface structure of ore particles changes, which is related to the metallization rate of iron oxides in red mud.
Nitrogen oxides (NOx) have numerous negative effects on both the environment and human health. They are major contributors to photochemical smog and acid rain. As a result, researchers are increasingly focused on developing de-NOx technologies. One effective method for removing NOx from the environment is selective catalytic reduction (SCR), with ammonia serving as the reductant (NH3–SCR). Rare earth-based catalysts have emerged as viable options for low-temperature NH3–SCR. Currently Ce-based NH3–SCR catalysts, such as CeO2–TiO2, CeO2–WO3, CeO2–MoO3, Ce–Mn–TiO2, CeO2–MnO2, Ce0.67Zr0.33O2, and CeO2–Fe2O3 have focused significant attention from researchers. The 4f orbitals of rare earth elements (REEs) are devoid of full electron occupancy. This attribute contributes to their distinct catalytic efficacy when employed as catalyst substrates. The oxygen storage capacity of Ce-based catalysts has further enhanced their popularity. Various methods, including microwave, hydrothermal, precipitation and sol–gel techniques, have been used by researchers to prepare catalysts in order to reduce the NOx emission. The paper has covered the impact of the preparation technique on rare earth catalyst performance and the NH3–SCR reaction mechanism to achieve a wide operating temperature. The global production and reserves of rare earth elements (REEs) worldwide have been thoroughly examined, and catalysts for the reduction of NOx emissions in automobiles by Ce and La have been explored.
Hidrometalurji metal ekstraksiyonunda sıkça kullanılan etkin ve bilinen bir yöntemdir. Ancak bu sistemlerde kullanılan yüksek miktarda su ve açığa çıkan atık asit miktarı sebebiyle, bilim dünyasında alternatif metot araştırma faaliyetleri her geçen gün artmaktadır. Bu noktada literatür incelendiğinde yeşil kimya ve solvometalurji kavramının ön plana çıktığı görülmektedir. Bu çalışmada solvometalurjik yöntemlerde kullanılan yeşil çözücüler tanımlanmış, iyonik sıvılar ve ötektik altı çözücüler hakkında bilgiler verilmiştir. Solvometalurjik yöntemlerin birincil hammaddelere uygulandığı örneklere yer verilmiş, bu bağlamda nadir toprak elementlerinin ve bakırın solvometalurjik yöntemlerle eldesi üzerine detaylı açıklamalarda bulunulmuştur. İkincil kaynaklardan hareketle; atık lityum iyon pillerin, floresan lamba atıklarının, hurda NdFeB ve SmCo mıknatısların, maden atıklarından solvometalurjik yöntemler kullanılarak metallerin geri kazanılması hakkında detaylı bilgiler verilmiştir. Sonuç olarak; solvometalurjinin hidrometalurjik temelli yöntemlere göre daha az su kullanımı başta olmak üzere üretimde kaynak kullanımını azaltma iddiası taşıdığı, solvometalurjik yöntemlerin uygulandığı birçok proseste gerek çözümlendirme verimleri, gerekse çözelti saflaştırma ve zenginleştirme oranlarının daha yüksek olduğu, bu yöntemlerin oda sıcaklığında çalışma olanağı ve geleneksel yöntemlerle karşılaştırıldığında çok daha düşük enerji tükettiği ifade edilmiştir. Solvometalurjik yöntemlerin araştırıldığı akademik çalışmaların önümüzdeki dönemlerde de artarak devam edeceğinin beklendiği, bununla birlikte yöntemin laboratuvar ölçeğinden yarı-endüstriyel hatta endüstriyel boyuta taşınmasına yönelik çalışmaların kısa-orta vadede artarak devam edeceğinin öngörüldüğü belirtilmiştir.
The increasing importance of recycling end-of-life photovoltaic modules is demonstrated by the rising quantity of discarded crystalline silicon solar cells that contain valuable metals. Despite advanced recycling methods, the surplus of broken Si wafers poses challenges for reintegration into new module manufacturing. The present study introduces a novel recycling process that addresses this issue and promotes sustainable waste processing, focusing on the untapped resources of Si wafer breakage and environmentally harmful red mud. The proposed method uses these two critical waste materials to enable a silicothermal reduction, yielding ferrosilicon-based alloys. To comprehensively analyze the influence of the iron oxide source on alloy composition, a readily available iron oxide pigment (Bayferrox 110) is implemented as a reference material. Fe–Si-based alloys containing 15 to 65 wt % Si are produced by the silicothermal reduction with soda ash as a flux, at a temperature of 1600 °C. The use of Bayferrox as an iron oxide source facilitates the production of Fe–Si alloys that are free from additional impurities. Moreover, the use of red mud as the source of iron oxide leads to the production of Fe–Si–Ti alloys, containing up to 8.6 wt % of Ti. The inclusion of Ti in the ferrosilicon-based alloy elevates the market value of the resulting products, emphasizing the commercial viability of the suggested recycling process. By simultaneously utilizing two critical waste materials, namely, red mud and Si wafer breakage, this novel recycling strategy demonstrates significant potential, especially in view of a circular and holistic waste management.
Rare earth elements (REE) are increasingly critical resources in technological applications, but the current understanding of their separation by uptake into minerals remains limited. Here, we examined the adsorption and solubilization of scandium (Sc), yttrium (Y), and lanthanum (La) into aluminum hydroxide (gibbsite, Al(OH)3). Based on spectroscopic investigations such as inductively coupled plasma-optical emission spectroscopy (ICP-OES) and time of flight-secondary ion mass spectrometry (ToF-SIMS), only Sc exhibited favorable incorporation and adsorption (0.66 and 0.06 atom%, respectively). Analysis of solid state 45Sc magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR) indicated that Sc exhibits an octahedral coordination consistent with isolated substitutions for Al in the gibbsite structure, leading to a decrease in the long-range order detectable by X-ray diffraction. Density functional theory (DFT) calculations reinforced this interpretation by reproducing the detected structural distortion as well as demonstrating the relatively favorable energetic basis for Sc incorporation into gibbsite by substitution.
The efficient extraction recovery of scandium (Sc(iii)) is crucial for its application in high-end technology. Two novel hydrophobic carboxylic acid ionic liquids (ILs), namely, [lauryl betaine][bis(trifluoromethanesulphonyl)imide] ([Laur][Tf2N]) and [cocamidopropyl betaine][bis(trifluoromethanesulphonyl)imide] ([Coca][Tf2N]), were synthesized using two inexpensive amphoteric surfactants as cation sources. [Laur][Tf2N] (257 °C) and [Coca][Tf2N] (251 °C) exhibited good thermal stability and strong hydrophobicity. The viscosity of [Coca][Tf2N] (4.29 × 10³ mP s) was higher than that of [Laur][Tf2N] (2.55 × 10³ mPa s) at 25 °C. The optimal extraction conditions were an extraction equilibrium time of 40 min, an initial Sc(iii) concentration of 0.001 mol L⁻¹, a sodium nitrate concentration of 0.5 mol L⁻¹, and a pH of 3. The extraction efficiency of [Laur][Tf2N] and [Coca][Tf2N] could even exceed 98.7% and 96.0%, respectively. The cation exchange extraction mechanism was studied by slope analysis, IR spectroscopy and ¹³C NMR spectroscopy. Sc(iii) extracted using [Laur][Tf2N] and [Coca][Tf2N] could be completely stripped with 0.1 mol L⁻¹ and 0.2 mol L⁻¹ HNO3 once, respectively. The structure of the ILs was not broken after stripping, and the extraction efficiency of the ILs remained almost unchanged after five cycles. In addition, the extraction differences at different pH levels made it possible to separate Sc(iii) from other rare earths using ionic liquids [Laur][Tf2N] and [Coca][Tf2N].
Industry represents a fundamental component of modern society, with the generation of massive amounts of industrial waste being the inevitable result of development activities in recent years. Red mud is an industrial waste generated during alumina production using the Bayer process of refining bauxite ore. It is a highly alkaline waste due to the incomplete removal of NaOH. There are several opinions in both the literature and legislation on the hazards of red mud. According to European and national legislation, this mud is not on the list of hazardous wastes; however, if the list of criteria are taken into account, it can be considered as hazardous. The complex processing of red mud is cost-effective because it contains elements such as iron, manganese, sodium, calcium, magnesium, zinc, strontium, lead, copper, cadmium, bismuth, barium and rare earths, especially scandium. Therefore, the selection of an extraction method depends on the form in which the element is present in solution. Extraction is one of the prospective separation and concentration methods. In this study, we evaluated the kinetic modelling of the solid–liquid acid extraction process of predominantly scandium as well as other elements present in red mud. Therefore, three acids (HCl, HNO3 and H2SO4) at different concentrations (10, 20 and 30%) were targeted for the extraction of Sc(III) from solid red mud. Specific parameters of the kinetics of the extraction process were studied, namely the solid:liquid ratio, initial acid concentration, contact time and temperature. The extraction kinetics of Sc(III) with acids was evaluated using first- and second-order kinetic models, involving kinetic parameters, rate constants, saturation concentration and activation energy. The second-order kinetic model was able to describe the mechanism of Sc(III) extraction from red mud. In addition, this study provides an overview on the mechanism of mass transfer involved in the acid extraction process of Sc(III), thereby enabling the design, optimization and control of large-scale processes for red mud recovery.
The scandium production rate and price data for scandium oxide and scandium metal was extracted from various sources. Data for extractable resources of scandium were found and evaluated by application of estimated yields. The feasible extractable resource is about 6.1 million ton, and with present technology, about 676,000 ton scandium appear as potentially extractable. The potential for scandium extraction is about 1,500 ton/year at present, but only about 45 ton per year was produced in 2022. With improved extraction and access yields, production could be increased to about 450 ton per year, and the scandium resource would increase to about 1.5 million ton. The investigation suggests that there will be an increased demand for scandium metal in the future, but that it is limited by the high price and the lack of a properly functioning market and by a lack of production infrastructure. The scandium market show signs of being disorganized and unstructured. Modelling of future scandium production was done using the WORLD7 integrated assessment model, after development of a scandium module. Simulations show that the price will remain relatively high, but lower than in the past. The most uncertain factor for predicting the price is the size of the demand. The main limitation for making scandium metal is high energy costs and low extraction yields.
Bioleaching exhibits high potential for the processing of low-grade complex mineral resources. With the development of the economy and an increase in demand, rare earth elements (REEs) in secondary resources, such as phosphogypsum, red mud and coal-related resources, are gaining more and more attention. In this review, the bioleaching performance of diverse microorganisms is summarized and compared for primary (mainly monazite) and secondary REE resources, based on publications from the past decade. The mineral characteristics of these REE resources are different, as they can be found in phosphate, sulfate, or silicate forms. Correspondingly, microbial species suitable for use in bioleaching differ. The most efficient bioleaching microbe for monazite is Paecilomyces sp., while Acidianus manzaensis is effective in processing red mud. Acidophilic sulfur oxidizers are suitable for processing acidic phosphogypsum. Acidithiobacillus thiooxidans could recover a significant amount of REEs from coal fly ash. In particular, monazite has a high REE content but extremely low bioleaching efficiency compared to that of secondary resources, supporting the understanding that bioleaching approaches are more competitive for minerals with low REE contents. Overall, great progress has been made over the last decade, as considerable REE recovery rates have been achieved, and the main metabolites of microbes were identified. However, numerous challenges still exist. Future efforts should focus on improving biorecovery efficiency, reducing the cost of cell-culture media, and exploring the interaction mechanism between cells and minerals, with an emphasis on mineralogical phase transformations and the molecular regulation mechanisms inside cells during the bioleaching process.
The growing stockpiles of bauxite residueBauxite residue and associated environmental hazards require a sophisticated process flowsheet for sustainable residue management and value recoveryRecovery. Considering the association of multiple elements (Fe, Al, Si, Ca, Ti, V, Sc) within bauxite residueBauxite residue, metal extraction is of prime interest. The complex association of different elements and physical and chemical characteristics makes the extraction and purification process expensive and challenging. The present study focuses on developing a novel hydrometallurgical flowsheet for the subsequent recoveryRecovery of base metals and critical elements from bauxite residueBauxite residue. The major elements present in bauxite residueBauxite residue are recovered as high-purityPuritymagnetiteMagnetite, titaniumTitanium dioxide, and aluminaAlumina. At the same time, critical elements (such as V and Sc) are recovered in the liquid stream generated after the recoveryRecovery of base metals.
Rare earths are classified as most important and critical material for US economy and defense by Congress, and a mandate has been set to increase their in-house production, domestic resource utilization and decrease reliance on foreign resources and reserves. They are widely available in earth crust as ore (bastnaesite (La, Ce)FCO3, monazite, (Ce, La, Y, Th)PO4, and xenotime, YPO4), but their so-called economic reserves are sparsely located geographically. They may be produced by various means such as beneficiation (physical, chemical, mechanical, or electrical), reduction (direct or indirect), electrolysis (of aqueous or molten/fused single or mixed salt systems) at high temperature or hydrometallurgy. Out of these, direct reduction, also known as metallothermic reduction (La and Ca reduction), is mostly utilized. Its variant, high temperature electrowinning of fused salts, is also practiced widely. These processes are material- and application-specific. In this study, the author will employ thermodynamics (Ellingham diagrams, free energy of formation, reduction potential, Nernst equation, Pourbaix (Eh-pH) diagrams, E-pO⁻² diagrams), kinetics, and energetic of a chemical reaction (chemical metallurgy) to reduce rare earth oxide/salt to rare earth metals (REO/RES – REM). It is shown that materials and energy requirement vary greatly depending on the type of mineral ore, production facility, and beneficiation/mineral processing method selected. The aim is to reduce dependence on coal deposits. It is anticipated this route will be able to produce rare earths with >35% yield and >98% purity which will be described in subsequent studies and patents.
The main components of metallurgical slags are iron compounds, which are extracted by reduction smelting. There are several types of this process with obtaining various products based on iron and slags of various compositions (aluminum-calcium self-disintegrating), etc. The mode of smelting and cooling of alumocalcium slag, formed during melting in the furnace, should ensure the most complete spontaneous crumbling of it, as well as high rates of extraction of REM from it. Synthetic slags similar in phase composition to industrial samples after smelting of iron-containing ores were selected for the experiments. The simulated samples correspond to the region of primary crystallization of bicalcium silicate on the triple state diagram of CaO – SiO 2 – Al 2 O 3 system. The slag after crumbling was subjected to a sieve analysis using a mechanical sieve. In the experiments, slags with a silicon module k = 2.0 were used, which actively crumbled during their cooling. With an increase in the silicon module, the crumbling deteriorates. It was established that it is impossible to precisely limit the areas of compositions of crumbling slags at certain cooling rates. The conducted studies showed that the crumblability of slags improves as it approaches the center of the bicalcium silicate region. The composition of slags close to composition of the intersection points of the lines 2CaO·SiO 2 – 2CaO·Al 2 O 3 and 2CaO·SiO 2 – 12CaO·7Al 2 O 3 with the lines of the permanent silicon module granulometric composition almost does not depend on the cooling rate. The temperature mode from smelting to cooling affects the slags crumblability. The most promising are slags with a silicon module in the range of 2.85 – 3.00, close to the phase triangle 12CaO·7Al 2 O 3 – 2CaO·SiO 2 – 2CaO·Al 2 O 3 .
This chapter covers a comprehensive overview for recycling of different secondary resources, their generation, metal content, and recycling processes. This chapter depicts the prominence of the various processes for metal extraction from anthropogenic wastes (aluminium cans, e-wastes, LCD screens), and industrial wastes (ferrous and non-ferrous metal wastes, catalysts, effluents, mine tailings, and metallurgical slags. Alongside, the underlying issues like material collection, treatment, and mode of operations have been discussed.KeywordsMaterial recyclingAnthropogenicIndustrialResourcesExtractionEfficiency
Red mud produced from the Bayer process was used for the high temperature metallurgical processing of ilmenite. The major components of the red mud were Fe2O3, Al2O3, Na2O, and TiO2, which play important roles in the flux material. The process temperature of ilmenite slag was lowered from 1794 K (1521°C) to 1687 K (1414°C), as a preliminary study by a high-temperature microscope. Thermochemical calculations using FactSageTM 7.0 confirmed the effect of red mud on the lowered melting temperature of ilmenite slag. The discrepancy between the observed results of the microscope and the calculated phase diagram was due to the slag viscosity, which was significantly affected by Al2O3 in red mud. The reduction of ilmenite at lower temperatures by the addition of red mud was investigated at 1723 K (1450°C). Ilmenite, pseudobrookite, and associated clay minerals were the major phases in the reduced ilmenites which was confirmed by X-ray diffraction (×RD) analysis. Microscopic images obtained by scanning electron microscopy (SEM) showed variations in the pseudobrookite phases according to the amount of fluxed red mud. The benefits of red mud utilization are discussed with regard to the lower energy consumption and recovery of resources.
The current study deals with preliminary chemical activation, which allows transforming the phase composition before gravitational concentration and effective removal of silicon during subsequent alkaline treatment, in order to obtain a raw material suitable for the production of alumina by the Bayer method. Electron-microscopic analysis of the original bauxite showed that the coarse-crystalline fraction was tightly pressed by the fine one. Silicon modulus of the averaged bauxite sample is 3.65. After chemical activation of bauxite in a sodium bicarbonate solution, the fine fraction got separated from the coarse fraction and the phase composition changed i.e. the calcium silicate phase disappeared and the calcite phase was formed. Preliminary chemical activation at temperatures of 90 and 120 оС for 20 min resulted in the increase of the bauxite beneficiation degree by 12.1 and 15.2 %. In order to obtain a quality bauxite concentrate with a silica modulus of more than 7, the coarse-grained bauxite fraction separated after gravity concentration should be subjected to chemical beneficiation in an alkaline solution at a second stage.
Despite their significance in numerous applications, many critical minerals and metals are still considered minor. Since most of them are not found alone in mineral deposits, their co- or by-production depends on the production of base metals and other major commodities. In many cases, the concentration of the minor metals is low enough not to be considered part of the production. Hence, their supply is not always secured, their availability decreases, and their criticality increases. Many researchers have addressed this issue, but no one has set actual impact factors other than economic ones that should determine the production of these minor commodities. This study identified several parameters, the number and diversity of which gave birth to developing a computational tool using a multi-criteria-decision analysis model based on the Analytical Hierarchical Process (AHP) and Python. This unprecedented methodology was applied to evaluate the production status of different commodities in a polymetallic deposit located in Chovdar, Azerbaijan. The evaluation outcomes indicated in quantifiable terms the production potentials for several commodities in the deposit and justified the great perspectives of this tool to evaluate all kinds of polymetallic deposits concerning the co- and by-production of several minor critical raw materials.
Herein, tartaric acid (TA) was used as a binder to prepare red mud pellets. The effect of TA on the compressive strength and induration mechanism of the pellets containing TA was analyzed via the changes in crystal structure, functional groups, and valence states of the constituent elements. The induration mechanism of TAPE is likely the chemical reaction between TA and partial calcite along with complexation of TA with minerals containing Ca(II), Al(III), and Fe(III). The density functional theory calculation results revealed that the TA-Ca(II) complexation products in red mud were more stable than those of Al(III) and Fe(III).
In the light of an expected supply shortage of rare earth elements (REE) measures have to be undertaken for an efficient use in all kinds of technical, medical, and agricultural applications as well as—in particular—in REE recycling from post-use goods and waste materials. Biologically- based methods might offer an alternative and supplement to physico-chemical techniques for REE recovery and recycling. A wide variety of physiologically distinct microbial groups have the potential to be applied for REE bioleaching form solid matrices. This source is largely untapped until today. Depending of the type of organism, the technical process (including a series of influencing factors), the solid to be treated, and the target element, leaching efficiencies of 80 to 90% can be achieved. Bioleaching of REEs can help in reducing the supply risk and market dependency. Additionally, the application of bioleaching techniques for the treatment of solid wastes might contribute to the conversion towards a more sustainable and environmental friendly economy.
It has been said that 'where there's muck there's brass' and now a former Soviet Union scientist is claiming to have demonstrated that some red mud residues are rich in scandium and that chemical beneficiation may make its recovery worthwhile. Scandium has been shown to have significant alloying potential for aluminium particularly in welding applications. And as millions of tonnes of red mud is dumped each year - at great expense - and scandium is worth upwards of $10000/kg there may be sense in the proposal. Aluminium Today publishes this article in the hope that it may generate discussion and welcomes readers comments on the subject.
The world economy is confronted with an increasing supply risk of critical raw materials. In the search for alternative sources, red mud may offer potential in particular for rare earth elements (REEs). Red mud is a by-product resulting from alumina extraction. Depending on the bauxite's origin, red mud may contain considerable amounts of REEs. The extraction of REEs from red mud by selective acid leaching was explored in this study. Hydrochloric (HCl), sulphuric (H 2 SO 4) and nitric (HNO 3) acid were applied for leaching. Citric (C 6 H 8 O 7) and oxalic (C 2 H 2 O 4) acid as small molecular weight organic chelators that can be biologically produced were studied as green alternative to mineral acids. After acidic extraction, REEs were purified by liquid-liquid extraction using di-(2-ethylhexyl)phosphoric acid (D2EHPA).
During direct acid leaching of bauxite residue, high amounts of iron also dissolve at high REEs recovery. In this paper, a sulphation-roasting-leaching process was developed to selectively leach the REEs. The bauxite residue was mixed with water and concentrated H2SO4 followed by roasting and then leaching of the calcined product with water. Several parameters including roasting temperature, duration of roasting, amount of acid were studied under optimised conditions, about 60 wt% of scandium and more than 90 wt% of other REEs can be dissolved with very small amounts of iron (< 1 wt%) and other major elements reporting to the solution.
During acid leaching of bauxite residue (red mud), the increase in dissolution of rare earth elements (REEs) is associated with an increase in iron dissolution, which poses problems in the downstream processing. Therefore, it would be beneficial to remove iron from bauxite residue by smelting reduction. The slag generated in the smelting reduction process could then be further processed for recovery of REEs. Smelting experiments were carried out at temperatures between 1500 °C and 1600 °C. Wollastonite (CaSiO3) was used as a flux and graphite as a reducing agent. Addition of wollastonite decreases the slag melting temperature and the viscosity, facilitating slag-metal separation, whereas a graphite content higher than the optimum level alters the slag chemistry and hinders the slag-metal separation. The optimum conditions were found to be for heating at 1500 °C: 20 wt% of wollastonite and 5 wt% of graphite. More than 85 wt% of the iron was separated from the slag in the form of a nugget. A further 10 wt% of the iron could be extracted from the slag by subsequent grinding and magnetic separation. The slag obtained after iron removal was treated with HCl, HNO3 and H2SO4 acids to extract REEs. Room temperature leaching was found to be not beneficial for REEs extraction. High-temperature leaching enhanced the recovery of REEs. More than 95% of scandium, >70% of REEs and about 70% of titanium could be leached at 90 °C. The selectivity of REEs over iron during slag leaching was clearly improved.
A method for leaching rare earth elements from coal ash in the presence of elemental sulfur-oxidizing communities of acidophilic chemolithotrophic microorganisms was proposed. The optimal parameters determined for rare element leaching in reactors were as follows: temperature, 45°C; initial pH, 2.0; pulp density, 10%; and the coal ash to elemental sulfur ratio, 10 : 1. After ten days of leaching, 52.0, 52.6, and 59.5% of scandium, yttrium, and lanthanum, respectively, were recovered.
A pilot-plant process has been developed based on an innovative laboratory-scale method for the recovery of scandium that exists in economically interesting concentrations in red mud, the main byproduct of alumina production. This method includes acid leaching of the red mud pulp, ion-exchange separation of scandium and lanthanides from the co-leached main elements such as iron, and subsequent liquid−liquid extraction of the eluate for further scandium purification and enrichment. In this work, experimental and theoretical investigation of the pilot-scale leaching process was performed. The following parameters were tested: mode of agitation, solid-to-liquid ratio, acidity of the leachate, number of stages in the process, and pretreatment of red mud with concentrated acids in order to achieve optimum scandium recovery combined with low iron dissolution. Furthermore, by theoretical interpretation of the experimental data, a predictive correlation for the scandium leaching efficiency was developed.
Laboratory-scale research has focused on the recovery of titanium from red mud, which is obtained from bauxite during the Bayer process for alumina production. The leaching process is based on the extraction of this element with diluted sulfuric acid from red mud under atmospheric conditions and without using any preliminary treatment. Statistical design and analysis of experiments were used, in order to determine the main effects and interactions of the leaching process factors, which were: acid normality, temperature and solid to liquid ratio. The titanium recovery efficiency on the basis of red mud weight reached 64.5%. The characterization of the initial red mud, as well as this of the leached residues was carried out by X-ray diffraction, TG-DTA and scanning electron microscopy.
According to European Commission reports published between 2010 - 2013, the development of European economy depends crucially on access to critical raw materials. Following the analysis performed by experts at European level, in 2011 was compiled and published a list of 14 critical raw materials, the so-called EU-14. In 2014 the list was updated with several new elements and one element (tantalum), was withdrawn from the list. The current list, being renamed EU-20, covers 20 critical raw materials including several high tech critical metals. Traditional mine exploitations are concentrated on using the deposits of ore extracted and processed by conventional techniques. The efficiency of metal recovery was variable over time and as a result, a significant amount of metal was discarded, most concentrations exceeding the current minimal permissible threshold. On the other hand, it is necessary the recovery of recyclable waste for reducing the risk of shortage of high tech critical metals. Therefore, it is necessary to develop new technologies for obtaining high tech critical metals, which is applicable to both primary and secondary sources of raw materials. Recovery of high-tech critical metals by processing ore, tailings or mine wastes, and recyclable materials can be successfully done with help of consortia or individual isolates of microorganisms, bacteria or fungi. Microorganisms interact with metals thus altering their physical and chemical condition. Isolation of individual strains and identification of microbial consortia that can be used in the design and development of effective biotechnological processes for the extraction of high tech critical metals is a current challenge of the scientific research in Europe.
In this study, the recovery of gallium (Ga) and aluminum (Al) from the by-product of Bayer process, the electrofilter dust of a calcination plant, was studied. Factorial leaching tests were also designed based on the results of the preliminary tests. Effects of factors and their interactions on the extraction of Ga and Al were demonstrated using Analysis of Variance of the findings. In the factorial design, nitric acid (HNO3) leaching tests up to 43.4% Ga and 35.2% Al were leached from the electrofilter dust. The addition of oxalic acid (H2C2O4) significantly enhanced the sulphuric acid (H2SO4) leaching of the dust with up to 48.3% Ga and 39.6% Al extractions.
Bauxite residue (or red mud) is a waste generated during the Bayer process of alumina production. Its storage is a spatial and environmental concern. Currently, there are no bulk applications of bauxite residue except for minor use in cements and ceramics. Nonetheless, some types of bauxite residues are rich in rare-earth elements (REEs), and the extraction of scandium in particular is of special interest. Leaching experiments on Greek bauxite residue were performed with different acids at different concentrations, liquid-to-solid ratios, leaching times and temperatures. Extraction of the REEs was high for leaching in HCl solutions compared to other acids, but the dissolution of iron was high as well (~60%). The maximum extraction of the REEs was around 80%. Sodium and calcium were completely dissolved during leaching. Dissolution of aluminium, silicon and titanium was between 30 and 50%. The leaching data show a very close association of scandium with the iron oxide phases.
In this study, recovery of vanadium and gallium from solids waste by-products (vanadium sludge and electrofilter dust of calcination plant) of Bayer process was investigated. An efficient purification process wasdevelopedbased on the removal of impurities such as phosphate by water leaching, neutralisation using CO2-enriched air and addition of aluminate solution. Recovery of V2O5 from the purified solution via the precipitation of ammonium metavanadate, its conversion into polyvanadate by the addition of ammonium sulphate and sulphuric acid, respectively, and then the ignition of the latter at 560°C was demonstrated. Effects of various parameters on the purification and precipitation processes were shown. A treatment process involving sintering and two-stage of carbonisation was also demonstrated to produce a Ga-rich precipitate. A gallate solution suitable for electrolysis of Ga was also shown to be prepared from this precipitate. A complete flowsheet was proposed for the treatment of vanadium sludge and electrofilter dust.
Leach solutions and wastes of Bayer process are important resources for metals such as aluminum and vanadium. Despite the fact that vanadium cake is precipitated and removed in the Seydisehir Eti Aluminum Facility (Turkey), it cannot be used due to low metal content and impurities it contains. Within the scope of this study, research and development of environmentally acceptable, technically sound and low-cost chemical leaching and recovery methods were conducted for the recovery of vanadium from the by-product cake of the Bayer process. In the conducted studies, a sample of vanadium cake was used after its detailed characterization. Roasting tests were performed in order to remove the arsenic in the vanadium cake; however, it was found that roasting was not effective in removing the arsenic from the cake. The performance of different reagents were examined in chemical leaching tests (H2O and H2SO4 leaching, H2SO4 leaching with the addition of NaSO3, and NH4F); in the H2SO4 leaching tests performed with the addition of Na2SO3, the concentration of the reagents and the effect of temperature on the efficiency of vanadium recovery (max. 93.09%) were determined with the full factorial experimental design method, the outcomes were evaluated with ANOVA (variance analysis) method, and empirical models were formed. In lab and semi-pilot scale leaching tests, vanadium recoveries were 96.34% and 94.76% respectively. Vanadium was precipitated with NaOH and FeSO4 and almost all vanadium (95.8%) was obtained as Fe3(VO4)2. Cost analysis and economic evaluation have shown the economic feasibility of the leaching and recovery processes proposed.
Bauxite residue (red mud) is a hazardous waste generated from alumina refining industries. Unless managed properly, red mud poses significant risks to the local environment due to its extreme alkalinity and its potential impacts on surface and ground water quality. The ever-increasing generation of red mud poses significant challenges to the aluminium industries from management perspectives given the low proportion that are currently being utilized beneficially. Red mud, in most cases, contains elevated concentrations of iron in addition to aluminium, titanium, sodium and valuable rare earth elements. Given the scarcity of iron supply globally, the iron content of red mud has attracted increasing research interest. This paper presents a critical overview of the current techniques employed for iron recovery from red mud. Information on the recovery of other valuable metals is also reviewed to provide an insight into the full potential usage of red mud as an economic resource rather than a waste. Traditional hydrometallurgy and pyrometallurgy are being investigated continuously. However, in this review several new techniques are introduced that consider the process of iron recovery from red mud. An integrated process which can achieve multiple additional values from red mud is much preferred over the single process methods. The information provided here should help to improve the future management and utilization of red mud.
With an increase in number of waste nickel-metal hydride batteries, and because of the importance of rare earth elements, the recycling of rare earth elements is becoming increasingly important. In this paper, we investigate the effects of temperature, hydrochloric acid concentration, and leaching time to optimize leaching conditions and determine leach kinetics. The results indicate that an increase in temperature, hydrochloric acid concentration, and leaching time enhance the leaching rate of rare earth elements. A maximum rare earth elements recovery of 95.16% was achieved at optimal leaching conditions of 70 °C, solid/liquid ratio of 1:10, 20% hydrochloric acid concentration, −74 μm particle size, and 100 min leaching time. The experimental data were best fitted by a chemical reaction-controlled model. The activation energy was 43.98 kJ/mol and the reaction order for hydrochloric acid concentration was 0.64. The kinetic equation for the leaching process was found to be: 1−(1−x)1/3=A/ρr0[HCl]0.64exp−439,8008.314Tt. After leaching and filtration, by adding saturated oxalic solution to the filtrate, rare earth element oxalates were obtained. After removing impurities by adding ammonia, filtering, washing with dilute hydrochloric acid, and calcining at 810 °C, a final product of 99% pure rare earth oxides was obtained.
Calcium and iron removal from a bauxite ore by Bacillus polymyxa has been demonstrated. Within a period of 7 days, the above organism could remove all the calcium and about 45% of iron from the ore in the presence of 2% sucrose in a Bromfield medium. The highest removal of calcium and iron corresponded with the maximum in extracellular polysaccharide production by the organism. Scanning electron microscopy of the biobeneficiated bauxite surfaces indicated tenacious attachment of the bacteria onto the ore particle. Some calcium and iron removal was observed even in the presence of bacterial metabolites such as polysaccharides, organic acids and slime. However, the calcium removal in the absence of microorganism (by metabolites alone) was found to be 50% of that obtained in its presence. These observations clearly indicate that both a direct mechanism through bacterial attachment to the ore and an indirect mechanism through leaching with metabolites are involved in the biobeneficiation process.
Laboratory-scale experiments were conducted to recover lanthanum and cerium from Indian red mud in sulphuric acid medium. The method includes acid leaching of red mud pulp and subsequent liquid –liquid extraction of the leached metals with different organic extractants, in order to establish the technical feasibility of extraction and separation simultaneously. Maximum Recovery of lanthanum (99.9%) was recorded with 3 M H2SO4 at ambient (35 °C) temperature, S/L ratio of 10 g/L and agitation rate of 200 rpm in 1 h time. Whilst 99.9% cerium recovery was achieved at 75 °C and solid/liquid ratio of 10 g/L in 3 M H2SO4. Significant specificity for complete extraction of lanthanum, cerium and scandium by Cyanex 301 was noted as compared to the solvents such as DEHPA and Cyanex 272.
The extraction of scandium from an Australian red mud by selective acid leaching was explored and preliminary leaching tests showed that diluted sulphuric acid can be used to leach scandium from the red mud. The recovery of scandium from a synthetic leach solution of the red mud using solvent extraction was studied. A number of extractants were investigated for the extraction of scandium and its separation from the other metals in the synthetic leach solution. It was found that amongst the three acidic organophosphorus extractants studied, D2EHPA performed best. With the organic system consisting of 0.05 M D2EHPA and 0.05 M TBP in Shellsol D70 under an A/O ratio of 5:1 at pH 0.25 and 40 °C, over 99% scandium was extracted and almost no iron and aluminium were co-extracted. The scandium extracted can be stripped from the D2EHPA/TBP system with 5 M NaOH to obtain Sc(OH)3 product. A conceptual flowsheet for the recovery of scandium from red mud is proposed.
Supply of some critical raw materials by European industry is becoming more and more difficult. After the case of natural textile fibres, in particular cotton, and timber, over the last few years the problem of rare earths (REs) availability has also risen. The 97% of the global supply of rare earth metals (REMs) is produced by China, that has recently done copious cuts of its exports, apparently in order to protect its environment. This fact has greatly increased the REs prices, causing tension and uncertainty among the world hi-tech markets. Many of these materials, in fact, have very few effective substitutes and low recycling rates too. In addition, their natural reserves of rare earths are concentrated in a small number of countries (China, Brazil, US, Russia, Democratic Republic of Congo). REMs are a group of 17 elements particularly used in many new electronic and advanced components: such as fuel cells, mobile phones, displays, hi-capacity batteries, permanent magnets for wind power generation, green energy devices, etc. Many analysts foresee much more requests in the next decades.
The article reviews the cathodic process of gallium ion reduction in alkaline solutions. The solution composition influence on the gallium anion reduction kinetics was analyzed by measuring the polarization curves on a dropping mercury electrode. Itwas found that the cathodic process rate is proportional to the specific adsorption of background cations in the sequence Na+ b K+ b Li+ b Cs+ b La3+. A higher rate of reduction of gallium anion present in alkaline solution of lithiumcation is a result of participation of thewatermolecules fromthe hydration shell of Li+ as a proton donor. In the presence of polyvalent lanthanum cations in alkaline solution, the gallium anion reduction rate increases sharply. This is related to a shift in the ƒÕ1-potential and participation of hydrated cations La(H2O)3 + n. The presence of surface-active agents,which have no proton.donor properties, in the solution, complicates the reduction reaction. Certain patterns of themechanism of the galliumion discharge reaction in alkaline solutions allowqualifying it as the second group of anions, and the slowstage of the reduction reaction comes down to simultaneous transfer of an electron and proton to the discharging anion. The estimated charge of the discharging gallium anion, which is equal to .0.24 in the transition state of the reaction, is indicative of formation of associates with background electrolyte cations [Me+ c GaO2], [Me+ c GaO(OH)2] by gallate anions in alkaline solutions („‚„N 12).
Red mud is the major waste material produced during alumina production following the Bayers process. Depending on the quality of the raw material processed, 1–2.5 tons of red mud is generated per ton of alumina produced. The treatment and disposal of this residue is a major operation in an alumina plant. A lot of research and developmental activities are going on throughout the world to find effective utilization of red mud, which involves various product developments. This article attempts to review these developments.
A process is described for the enrichment of titanium dioxide in red mud. The procedure employed is leaching the red mud with hydrochloric acid followed by roasting the leached residue with sodium carbonate. The kinetics of leaching of various constituents of red mud were obtained experimentally in a stirred batch reactor. The variables include acid to mud ratio and temperature. The data obtained were analysed using the shrinking core model and Jander's equation. The effect of roasting time and temperature on percentage dissolution of alumina in leached residue was studied using a full factorial search and optimized conditions were obtained.
By using X-ray microanalysis, the mechanism of sorption of rare earth elements (REE) and their localization in cells of Candida utilis were found to depend on the metal ion speciation in solution, the permeability of the cytoplasmic membrane (CPM), and elemental composition of cells. Sorption capacity of the yeast cells increased with the increase in the pH of solution, which is connected with the extent of metal hydrolysis. Cells with native permeability of CPM did not sorb either scandium at pH values below 4.5 or lanthanum and samarium at pH values below 5.0. Such cells accumulate rare earth elements on surface structures. Only the cells with impaired CPM could sorb REE from the acid solutions. In this case, REE were accumulated inside the cells due to the interaction with phosphorus-containing compounds; the amount of sorbed REE depended on the content of phosphorus in the yeast cells. The yeast cells were shown to have extremely high affinity to scandium which thus can be selectively sorbed from solutions containing other REE, iron, and aluminum.
The aim of this work is to investigate biological leaching of rare earth elements (REEs) and radioactive elements from red mud, and to evaluate the radioactivity of the bioleached red mud used for construction materials. A filamentous, acid-producing fungi named RM-10, identified as Penicillium tricolor, is isolated from red mud. In our bioleaching experiments by using RM-10, a total concentration of 2% (w/v) red mud under one-step bioleaching process was generally found to give the maximum leaching ratios of the REEs and radioactive elements. However, the highest extraction yields are achieved under two-step bioleaching process at 10% (w/v) pulp density. At pulp densities of 2% and 5% (w/v), red mud processed under both one- and two-step bioleaching can meet the radioactivity regulations in China.
This study presents a rapid and selective method for the recovery of lanthanides and yttrium, existing in economically interesting concentrations, from red mud, the byproduct of the alumina production. The leaching process is based on the extraction of these elements with diluted nitric acid from red mud under moderate conditions and without using any preliminary treatment. Several parameters such as leaching agents, contact time, temperature, pressure and solid to liquid ratio were investigated in order to achieve an optimum recovery. The process followed here was selected taking into account its efficiency for the selective recovery of yttrium and lanthanides, but also its suitability for the subsequent liquid-liquid extraction of the leaching solution for the separation of the individual lanthanides. The achieved recovery percentages were for Y about 90%, for the investigated heavy lanthanides (Dy, Er, Yb) up to 70%, for the middle ones (Nd, Sm, Eu, Gd) up to 50% and for the group of light lanthanides (La, Ce, Pr) up to 30%. Most of the main elements of the red mud and especially iron are hardly dissolved by this leaching process, leading to an interference free determination of the lanthanides and yttrium in the leachate by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).
Scandium, existing in economically interesting concentrations, in red mud, the byproduct of the alumina production, could be selectively separated from the main and minor elements, as well as from yttrium and the lanthanides by the development of a combined ion exchange-solvent extraction method. After a suitable borate/carbonate fusion of red mud, the sample solution was passed through the ion exchanger Dowex 50W-X8 and the main elements, such as Fe, Al, Ca, Si, Ti, Na as well as the minor ones Ni, Mn, Cr, V were removed by elution with 1.75 M HCl. Sc, Y and the lanthanides were quantitatively obtained by a subsequent elution with 6 M HCl. Using as extractant di(2-ethylhexyl)phosphoric acid in hexane, scandium could be selectively and nearly quantitatively extracted in the organic phase, while yttrium and the lanthanides remained in the aqueous phase. By suitable backstripping of the organic phase, scandium was finely quantitatively recovered in high purity in the aqueous phase. Experimental conditions, including the pH of the extracted solutions, the ratio of aqueous to organic phase and the contact time were investigated in order to achieve high distribution ratios and a selective extraction. In this way all spectral interferences for the inductively coupled plasma atomic emission spectrometric determination of scandium were eliminated and a very low detection limit in the ng/g range was achieved, allowing the determination of very low levels of scandium in complex matrices. The validity of the described process was tested on the bauxitic reference material BX-N from ANRT (Association Nationale de la Recherche Technique, France) and the procedure was applied on red mud samples coming from the Greek alumina production.
Activated carbon (AC) was modified by tri-butyl phosphate (TBP) for selectively extracting scandium from red mud and characterized by BET (Brunauer-Emmett-Teller) surface area. The modified AC had a preferential adsorption to scandium. The influences of adsorbent dosage, adsorption temperature, and time on adsorption capacity and selectivity to scandium were examined. An optimum adsorbent dosage (∼6.25 g/L), adsorption temperature (308 K), and adsorption time (40 min) were figured out. A pseudo-second-order kinetics model was employed for describing the adsorption process of scandium.
India has fairly rich reserves of rare and refractory metals. Abundant sources of ilmenite, rutile, zircon and rare earths are found in the placer deposits of the southern and eastern coasts of the country. Columbite-tantalite occur in mica and the mining belts of Bihar and cassiterite deposits are found in Bastar (Madhya Pradesh). Vanadium as a minor associate occurs in bauxites and in the vast deposits of titaniferrous magnetites.
Over the years, research and development and pilot plant works in many research organisations in India have built up a sound technological base in the country for process metallurgy of many refractory and rare earth metals starting from their indigenous sources. The present paper provides a comprehensive view of the developments that have taken place till now on the processing of various refractory and rare earth metals with particular reference to the extensive work carried out at the Department of Atomic Energy. The coverage includes mineral beneficiation, separation of individual elements, preparation of pure intermediates, techniques of reduction to metal and final purification. The paper also reviews some of the recent developments that have been taken place in these fields and the potential application of these metals in the foreseeable future.
An analytical procedure for the rapid, accurate and reproducible determination of lanthanides, yttrium and scandium in iron-aluminum rich matrices as bauxites and red mud from alumina production was developed. After a suitable dissolution, the samples were directly analysed for these elements by inductively coupled plasma atomic emission spectroscopy (ICP-AES), without using any separation or preconcentration step. Some of the investigated elements were also directly determined in the solid samples by x-ray fluorescence analysis (XRF). The optimum conditions and analytical wavelengths were selected by both methods for each investigated element, after detailed studying of the spectral interferences from the major elements from the matrix and the interlanthanide-interferences. In the unique reference bauxitic material BX-N, for which only some proposed values exist, the concentration of nearly all lanthanides, yttrium and scandium Sc could be determined. The precision and accuracy of the described ICP-AES and XRF methods for these elements were tested on the geological standard materials SY-2, SY-3 (Canadian syenites) and the proposed values of BX-N. In this study the enrichment factor of the above mentioned elements in red mud were also determined in comparison to the feed bauxites and the constancy of the concentration level in productions samples, followed up over three years. The obtained results for the lanthanides were evaluated on the basis of chondrite normalized distribution patterns.
The extraction of scandium and uranium from red mud resulting from alumina production with the ampholite resins AFI-21 and AFI-22 was studied. These resins are of great interest due to their high ability to form complexes and their good specific sorption selectivity. The aspects studied include loading capacity, kinetics and elution. The ion-exchange technology for the treatment of red mud was developed and tested at a pilot plant scale. The prospects for developing an industrial process are discussed.
The future availability of rare earth elements (REEs) is of concern due to monopolistic supply conditions, environmentally unsustainable mining practices, and rapid demand growth. We present an evaluation of potential future demand scenarios for REEs with a focus on the issue of comining. Many assumptions were made to simplify the analysis, but the scenarios identify some key variables that could affect future rare earth markets and market behavior. Increased use of wind energy and electric vehicles are key elements of a more sustainable future. However, since present technologies for electric vehicles and wind turbines rely heavily on dysprosium (Dy) and neodymium (Nd), in rare-earth magnets, future adoption of these technologies may result in large and disproportionate increases in the demand for these two elements. For this study, upper and lower bound usage projections for REE in these applications were developed to evaluate the state of future REE supply availability. In the absence of efficient reuse and recycling or the development of technologies which use lower amounts of Dy and Nd, following a path consistent with stabilization of atmospheric CO(2) at 450 ppm may lead to an increase of more than 700% and 2600% for Nd and Dy, respectively, over the next 25 years if the present REE needs in automotive and wind applications are representative of future needs.
A chromatographic method has been developed for separation and determination of scandium (Sc) and rare earth elements (REEs) in samples from a red mud (RM)-utilization process. Reversed-phase high-performance liquid chromatography (RP-HPLC) with post-column derivatization using 4-(2-pyridylazo)-resorcinol (PAR) and UV–visible detection at 520 nm was tested using different gradient elution profiles and pH values to optimize separation and recovery, primarily for Sc but also for yttrium and the individual lanthanides, from iron present in the samples. The separation was performed in less than 20 min by use of a mobile phase gradient. The concentration of α-hydroxyisobutyric acid (α-HIBA), as eluent, was altered from 0.06 to 0.4 mol L–1 (pH 3.7) and 0.01 mol L–1 sodium salt n-octane sulfonic acid (OS) was used as modifier. Very low detection limits in the nanogram range and a good resolution for Sc and REEs except for Y/Dy were achieved. Before application of the method to the red mud samples and to the corresponding bauxites, Sc and REEs were leached from red mud with 0.6 mol L–1 HNO3
and mostly separated, as a group, from the main elements by ion exchange/selective elution (6 mol L–1
HNO3) in accordance with a pilot-plant process developed in this laboratory. After evaporation of the eluent to dryness the extracted elements were re-dissolved in the mobile phase. By use of this chromatographic method Sc, which is the most expensive of the elements investigated and occurs in economically interesting concentrations in red mud, could be separated not only from co-existing Fe but also from Y/Dy, Yb, Er, Ho, Gd, Eu, Sm, Nd, Pr, Ce and La. All the elements investigated were individually recovered. Their recoveries were found to be nearly quantitative.
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Red mud: A secondary resource for rare Earth elements
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Rare Earth elements in Karst-bauxites: A novel untapped European resource?
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The behavior of scandium and lanthanum on the red mud processing