Article

Overview On Extraction and Separation of Rare Earth Elements from Red Mud: Focus on Scandium

Authors:
  • Center of Earth Science, Metallurgy and Ore Benefication, Kazakhstan, Almaty
  • CSIR-National Metallurgical Laboratory, Jamshedpur, India
To read the full-text of this research, you can request a copy directly from the authors.

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.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... During alumina production using the Bayer process, a solid waste known as red mud is generated (Akcil et al. 2018). The annual production of red mud is estimated to be around 100 to 150 million tons (Evans 2016). ...
... One of the most common methods of disposing of red mud is storing it in open-air dams or discharging it into the ocean (Borra et al. 2017). The high pH of red mud (11 to 12.5) makes its proper disposal a major environmental challenge (Chun et al. 2014;Xue et al. 2016;Akcil et al. 2018;Narayanan et al. 2018). Besides its environmental risks, the disposal of red mud is costly and occupies large land areas (Lockwood et al. 2015;Wen et al. 2016;Swain et al. 2020). ...
... The presence of Fe, especially in the form of ferric, can significantly reduce the final purity of the Ti product. Solvent extraction is a widely used method for the concentration and recovery of REEs (Akcil et al. 2018). Organophosphorus-based extractants are the most common extractant group used for the solvent extraction of REEs. ...
Article
Full-text available
In this study, a combination of physical and chemical separation processes was used to recover the metallic components of red mud. At first, the impact of carbothermal reduction on magnetic separation of iron was studied. Low magnetic properties of iron minerals resulted in insignificant separation of iron from other components in the non-carbothermally reduced sample. Various carbothermal reduction parameters were optimized to maximize iron separation from other components. The optimum conditions were found T = 1350 °C, t = 120 min, coal/red mud ratio of 3, reaction time of 120 min, and the soda ash/red mud ratio of 0.2. Under the optimum condition, the iron recovery of the magnetic product was observed 91% with 81% Fe content, while the non-magnetic product has contained 90% of Ti and Al and 80% of rare earth elements (REEs). Following the physical separation of iron, the chemical separation of remaining red mud components was investigated using leaching with sulfuric, hydrochloric, and nitric acids. The leaching experiments were performed on two samples, treated red mud with carbothermal reduction and an untreated sample. The untreated sample had a higher dissolution efficiency for Ti and REEs than the carbothermally reduced sample. Different dissolution behavior of the red mud components was explained by samples’ mineralogy. In the end, considering the obtained results, various scenarios for the recovery of red mud components were evaluated from technical and environmental aspects.
... Red mud also contains a concentrated amount of rare earth elements. Akcil et al (2018) found that red muds around the world can contain total rare earth concentrations up to 1700 ppm. This puts red mud in a unique position to be able to produce critical materials that are necessary for the independence of the economy from China, who controls more than 95% of current rare earth element production (Akcil et al, 2018). ...
... Akcil et al (2018) found that red muds around the world can contain total rare earth concentrations up to 1700 ppm. This puts red mud in a unique position to be able to produce critical materials that are necessary for the independence of the economy from China, who controls more than 95% of current rare earth element production (Akcil et al, 2018). This dissertation will investigate methods to reduce the amount of red mud as well as reduce its hazardous properties. ...
... The predominant methods for rare earth extraction have been in ion exchange methods, extraction with organic solvents, and precipitation of low soluble compounds (Akcil et al, 2018). Most rare earth elements exhibit very similar chemical properties, which makes the separation of rare earths from each other uniquely difficult. ...
Article
Red mud is an industrial slurry waste that is produced as a byproduct of the Bayer process for alumina. The waste is generated in large quantities, up to a ratio of 2:1 against the valued product alumina. Red mud exhibits many chemical and physical properties that categorize it as a hazardous material. Due to the addition of sodium hydroxide in processing, the pH is typically at values close to 13. Small particle size discourages separation from water for disposal, so drying red mud happens over many years. The pH of red mud can be reduced with inexpensive reagents. Carbon dioxide is a greenhouse gas that is finding a great deal of research into potential sinks to reduce the footprint on the atmosphere. Combining carbon dioxide with red mud can effectively reduce the pH while also providing a sink for the greenhouse gas. Carbon dioxide is able to reduce the pH of red mud from 13 to 10 over long periods of time. Red mud can be utilized to produce a variety of value-added products. Most red muds around the world contain a large quantity of iron, titanium, aluminum, and rare earth elements. One method of removing the iron is through the iron nugget process which reduces iron and removes impurities in a single step. The iron nugget process is able to produce blast furnace quality pig iron (over 90% iron purity) with the addition of a carbonate flux material. Rare earth elements are concentrated in the slags from the iron nugget process and can be removed with acid leaches. The current view of red mud as a waste material is misleading. The proposed work will investigate methods to reduce the hazardous nature of red mud by reducing the pH and also remove valuable minerals. This will effectively give value to the waste product while simultaneously reducing the overall amount of red mud waste that needs to be disposed.
... Considering the high amount of RM generated every year, and the risk in REE supply worldwide, there has been increasing interest in recovering REE from RM (Akcil et al., 2018;Swain et al., 2020;Ujaczki et al., 2018). Nonetheless, conventional mining techniques are hardly suitable for REE recovery from RM. Pyrometallurgy, which is the most well-established method for metal extraction from ores, requires a temperature range within 900 • C -3000 • C (Priya and Hait, 2017) and its use for metal extraction from RM is not cost-effective (Swain et al., 2020). ...
... ambient pressure and temperature can be applied), and eco-friendly (Das and Das, 2013;Işıldar et al., 2019). However, due to the low selectivity of the bioleaching processes, a combination of more than one separation step might be required (Akcil et al., 2018). Fig. 3 shows the mechanisms of three bio-based processes e.g. ...
... Thus, RE recovery from secondary resources has been gaining attention in order to meet the growing demand (Borra et al., 2015). The composition and concentrations of REEs in RM is reliant on the original bauxite ore found in various countries and as per prior information, the major REEs that can be recovered from RM consist of La, Ce, Nd, Y and Sc (Akcil et al., 2018). Considering the metal prices, 99% of the overall value of REEs in the bauxite reside is accounted to Sc followed by Nd (Reid et al., 2017). ...
Article
The growing demand for rare earth elements (REEs) confronted with a parallel supply risk, draws major interest to utilize secondary resources bearing higher REE content than the primary resources. The European Commission has recently identified bauxite as a Critical Raw Material (CRM). In particular, unexploited bauxite residues have invited due attention owing to their abundance (worldwide generation at 120 – 150 million tons/yr) and presence of REEs (0.5 - 1.7 kg/ton) and scandium (Sc) in particular, with Fe: 14–45%, Al: 5–14%, Si: 1–9%, Na: 1–6% and Ti: 2–12%. Nevertheless, it has also to be taken into consideration that higher amassing of this waste is turning into a global concern due to its hazardous impacts and disposal issues owing to its high alkalinity, fine particle size and metal content. Industrial valorization of REEs from stockpiled bauxite residues could possibly unlock approximately a 4.3 trillion-dollar economy globally. This review foresees bauxite as a potential resource for REEs and identifies the problems associated with disposal of bauxite residues. Considering the recycling potential of bauxite residues for supplying valuable metals for technology, biotechnology is seen as a promising alternative to the conventional methods. Comprehensive details including role and challenges of biotechnology in green recovery of REEs from bauxite residues, their scale-up and environmental issues are critically discussed. Furthermore, w.r.t. the bauxite residues, the REE market potential is presented with discussions into future prospects, following the current impact of COVID-19 pandemic on the demand and supply of REE to industrial sectors.
... At present, the source of scandium is comprehensively recovered from titanium dioxide waste liquid, red mud (bauxite residue), tungsten acid slag, and so on, the production, and application of scandium is also greatly restricted (Xiao et al. 2020b;Chenna et al. 2015;Akcil et al. 2018). The development of effective methods of separation and extraction of scandium from poorer raw materials should be considered as a strategy for metals' circular economy that also diminish the environmental impact of these residues. ...
... Red mud is a by-product of bauxite processing through the Bayer process (Zhao, Miller and Wang 2010). Throughout production of alumina by the Bayer process, 95-100% of the scandium contained in bauxite remains in red mud (Akcil et al. 2018). The scandium content of the red mud varies between 15 and 170 ppm, depending on the source of bauxite, which is a potentially valuable scandium resource (Avdibegovic, Regadío and Binnemans 2017). ...
... Secondary resources such as optical glass, glass polish, cracking catalysts, red mud, bottom ash and e-wastes, do serve as an important resource to supplement the deficit of critical metals. 14,14,15,41,[59][60][61] In this section, particular emphasis is given to highlight and discuss the hydrometallurgical strategies applied for the recovery of REEs from four different but selective CE-Scrap [spent fluorescent lamps (SFLs), NiMH batteries, computer monitor scraps and scrap neodymium-iron-boron (NdFeB) magnets], the recycling and resource recovery potential of which could have significant application in the development of clean/green energy technologies and/or in hi-tech applications. 3,62 Spent fluorescent lamp and recovery of yttrium The global consumption of Y has been estimated to be 7650 Mg. ...
... Secondary resources such as optical glass, glass polish, cracking catalysts, red mud, bottom ash and e-wastes, do serve as an important resource to supplement the deficit of critical metals. 14,14,15,41,[59][60][61] In this section, particular emphasis is given to highlight and discuss the hydrometallurgical strategies applied for the recovery of REEs from four different but selective CE-Scrap [spent fluorescent lamps (SFLs), NiMH batteries, computer monitor scraps and scrap neodymium-iron-boron (NdFeB) magnets], the recycling and resource recovery potential of which could have significant application in the development of clean/green energy technologies and/or in hi-tech applications. 3,62 Spent fluorescent lamp and recovery of yttrium The global consumption of Y has been estimated to be 7650 Mg. ...
Article
The global demand for rare earth elements (REEs) with respect to hi‐tech applications is on a constant rise; however, their supply is a matter of concern. To the rescue, the urban wastes e.g. the consumer electronic scraps (CE‐Scraps) are seen to have a remarkable potential to meet the growing demand for metals. In line with the circular economy principles, these secondary resources are considered as the potential source of REEs. Globally, their commercial extraction and recovery are yet to be adopted as less than 1% of the REE is recycled from the CE‐Scrap products, with the rest removed from the materials cycle. Considering the economic importance and industrial applicability of REEs, the current status of the potential CE‐Scrap resources for REEs recycling is presented herein. The summarized availability of all REEs, their mode of occurrence, and the prospects of relevant recycling processes, typically by the hydrometallurgical route, is discussed. The feasibility of using established REE extraction and recovery technologies is discussed concerning the CE‐Scraps such as spent fluorescent lamps, spent NiMH hybrid batteries, computer monitor scraps, and scrap NdFeB magnets. Furthermore, the pros and cons associated with their separation are discussed along with the future directions of research and policies to be envisaged in urban resource recycling. This article is protected by copyright. All rights reserved.
... Bauxite residue, also known as red mud, is a waste generated during alumina production from bauxite ore through the Bayer process (Akcil et al., 2018). It is estimated that per tonne of alumina produced, 1 to 2.5 tonnes of red mud is generated (Lu et al., 2018;Zhou et al., 2018). ...
... The management of red mud has always been a significant challenge because of its high alkalinity, fine particle size, and its large production volume (Borra et al., 2017). The disposal of the red mud can impose serious environmental challenges due to its high pH nature (11 to 12.5) and complex composition (small particle size, polymetallic composition, readily soluble species and etc.) (Akcil et al., 2018;Narayanan et al., 2018). Red mud is considered as an interesting resource for the extraction of several major metals, such as titanium, aluminum, and several other minor metals, including rare earth elements (REEs) (Alkan et al., 2017). ...
Article
Red mud is a waste generated during the Bayer process in the production of alumina. Recovery of metallic components of the red mud has both environmental and economic benefits. In this study, the effect of carbothermal reduction on the physical and chemical separation of red mud components, namely Ti, REEs, Fe, and Al, were investigated. At first, the impact of carbothermal reduction on the efficiency and selectivity of iron separation from the bulk material through magnetic separation was studied. At the optimum conditions of T = 1350 °C, using a ring-shaped mixing regime of coal and red mud, coal/red mud ratio of 3, t = 120 mins, and soda ash/red mud ratio of 0.2, the iron content of the red mud was effectively metalized and separated from Ti, REEs, and Al. Recovery of iron in the magnetic separation concentrate was 91%, with Fe content of 81%, while about 90% of Ti and Al and 80% of REEs were retained in the non-magnetic product. For the untreated sample, however, iron separation was insignificant mostly due to the low iron metallization. Finally, the dissolution behavior of Ti, REEs, Fe, and Al for both treated and untreated samples using H2SO4, HCl, and HNO3 were studied. Different dissolution behavior of the REEs and Ti were observed and correlated to the mineralogical composition of the sample. Overall, carbothermal reduction has shown to positively affect the magnetic separation of iron but negatively affected the Ti and REEs dissolution efficiency.
... It is important to note that Sc content in red mud is in the range of 0.013-0.039% [9] that is quite significant. The actual composition of red mud depends on the bauxite mineralogy and different technological parameters of the Bayer process [10]. ...
... Many processes were proposed for recovery of valuable components from red mud [8,12,13]. In last years, there is a high interest for selective recovery of scandium [9,14,15]. Direct leaching processes using different lixiviants such as alkaline solutions [16,17], hydrochloric and sulfuric acids [18][19][20][21][22][23][24], organic acids [25,26] and ionic liquids [27,28] were thoroughly investigated. However, the direct leaching methods are either non-selective or ineffective for the extraction of titanium and REEs. ...
Preprint
Red mud is a hazardous waste of alumina industry that contains high amounts of iron, aluminum, titanium and REEs. One of the promising methods for the extraction of iron from red mud is car-bothermic reduction with the addition of sodium salts. This research focuses on the process of hy-drochloric high-pressure acid leaching using 10–20% HCl of two samples of non-magnetic tailings obtained by 60-minute carbothermic roasting of red mud at 1300 °C and the mixture of 84.6 wt. % of red mud and 15.4 wt. % Na2SO4 at 1150 °C, respectively, with subsequent magnetic separation of metallic iron. An influence of temperature, leaching duration, solid-to-liquid-ratio and acid con-centration on dissolution behavior of Al, Ti, Mg, Ca, Si, Fe, Na, La, Ce, Pr, Nd, Sc, Zr were studied. Based on the investigation of the obtained residues, mechanism of passing of valuable elements into the solution was proposed. It has shown that 90% Al, 91% Sc and above 80% of other REEs can be dissolved under optimal conditions; Ti can be extracted into the solution or the residue depending on the leaching temperature and acid concentration. Based on the research results, novel flowsheets for red mud treatment were developed.
... Scarce Sc deposits are monopolized worldwide which drives prices up and threatens global technological and sustainable development. Therefore, the development of effective, profitable, and eco-friendly Sc mining technologies is an urgent challenge of modern science [8,9]. ...
... Sc purification is a many-stage process, which makes it expensive and difficult to obtain in high amounts. Furthermore, the separation of REEs from each other is a very difficult process because of their highly similar physicochemical properties, ionic radii, valence, and magnetic properties [8,46]. However, biosorption of Sc by different biological systems is marginally better than that of other REEs. ...
Article
Full-text available
Scandium (Sc) plays a special role in high-tech industries because of its wide application in green, space, and defense technologies. However, Sc mining and purification are problematic due to political, technological, and environmental difficulties. The deficit of this element limits global technological development. One sustainable solution to this problem is to use microorganisms to extract Sc from ore and waste, as well as to concentrate and separate it from other elements. Sc also demonstrates attractive metabolic effects on microbes that is of great interest in white biotechnology. Sc increases the production of proteins and secondary metabolites and activates poorly expressed genes. This review offers a comprehensive analysis of current knowledge on the application of Sc–microorganism interactions in promising biotechnologies, its perspectives, and future challenges.
... Approximately 2.7 billion tons of red mud is generated globally since 2007, with a yearly increase of 120 million tons (Ujaczki et al. 2017;Erçağ and Apak 1997). Red mud contains a high percentage of Fe, among other elements, in addition to REEs, which range from 500 to 1700 ppm (Akcil et al. 2018). A few studies have been conducted on the removal of these REEs from red mud in various countries, such as India, Greece, China, and Turkey (Akcil et al. 2018). ...
... Red mud contains a high percentage of Fe, among other elements, in addition to REEs, which range from 500 to 1700 ppm (Akcil et al. 2018). A few studies have been conducted on the removal of these REEs from red mud in various countries, such as India, Greece, China, and Turkey (Akcil et al. 2018). Although red mud, produced in vast quantities every year, presents a valuable source for REE recovery, there is a lot of unexplored areas of study about this topic. ...
Article
Full-text available
Rare earth elements or REEs are a vital and irreplaceable part of our modern technological and digital industries. Among the REEs that are the most critical to be recovered are Ce, La, and particularly, Nd, and Y, due to high demand and at a potential future supply risk. Innovative techniques must be considered to recover REEs from secondary resources. In this study, REEs are extracted from iron mining sludge from Central Anatolia in Turkey. Two different acid solutions were compared, one with a higher acid content (120 ml HCl and 80 ml HNO3 per liter) and one with lower acid content (20 ml HNO3 per liter). Nanofiltration, as a process to concentrate the acidic leachate and increase the REE concentration, was carried out at pH levels of 1.5, 2.5, and 3.5 and under 12, 18, and 24 bar operating pressures. SLM studies had been carried out using a PVDF membrane with a pore diameter of 0.45 μm, with three different carriers to separate the REEs from other major elements in the concentrated leachate. Through this analysis, the optimum operating conditions for nanofiltration are at pH 3.5 at 12 bar, using the leach with low acidity, achieving about 90% recovery efficiency of the REEs. SLM studies using 0.3M D2EHPA, with a 3-h reaction time, showed the highest mass flux values for the REEs. Nanofiltration and SLM represent novel methods of REE concentration and extraction from iron mining sludge.
... In spite of all their contributions to the mitigation of environmental impacts, their production is resource and pollution intensive, creating a dissonance between the environmentally damaging supply of rare earths and their use in environmentally friendly technologies [5]. In the current scenario, improved extraction/separation strategies to achieve a sustainable and green circular economy of rare earths from residual wastes, like red mud, are an absolute necessity [6,7]. The chemical composition of red mud varied widely, which might be attributed to the origin of native ore and/or operational conditions during the Bayer process [8][9][10]. ...
Article
Full-text available
The present work was conducted to evaluate the bioleaching feasibility of red mud with Penicillium chrysogenum strain KBS3 in the presence of glucose, sawdust, and molasses as a substrate and in various leaching modes. The one-step bioleaching system involved 12 mM citric acid, 2.5 mM oxalic acid, 1.8 mM tartaric acid, and 1162 mM gluconic acid, with glucose as the substrate. The biogenic acid production in the two-step bioleaching system involved 15 mM, 1 mM, 0.5 mM, and 152 mM, respectively, and in the spent-medium bioleaching system, it was 63 mM, 29 mM, 23 mM, and 3 mM, respectively, using glucose as the substrate and a pulp density of 3%. The concomitant bio-mobilization of rare earths investigated under different modes were observed to be: 79% Y, 28% La, and 28% Ce in one-step (mode 1) bioleaching; 63% Y, and 28% both La and Ce in the spent-medium (mode 2) bioleaching; and 67% Y, 20% La, and 15% Ce in a two-step (mode 3) bioleaching. On the other hand, the bio-mobilization of rare eaths with molasses as the substrate was found to be: 57% Y, 13.5% La, and 12.7% Ce in mode 4 bioleaching; 57% Y, 14% La, and 12% Ce in mode 5 bioleaching; and 49% Y, 6.3% La, and 2.9% Ce in mode 6 bioleaching of the red mud. Insignificant results were observed using sawdust as the substrate.
... These residues are harmful due to its alkalinity, but also are rich in valuable rare earth metals as to be economically treated. Scandium represents about 95% of the economic value of the REEs present in red mud containing between 130 and 390 ppm [44]. ...
Chapter
Rare earth elements (REEs) are critical raw materials and are attracting interest because of their applications in novel technologies and green economy. Biohydrometallurgy has been used to extract other base metals; however, biole-aching studies of REE mineral extraction from mineral ores and wastes are yet in their infancy. Mineral ores have been treated with a variety of microorganisms. Phosphate-solubilizing microorganims are particularly relevant in the bioleaching of monazite because transform insoluble phosphate into more soluble form which directly and/or indirectly contributes to their metabolism. The increase of wastes containing REEs turns them into an important alternative source. The application of bioleaching techniques to the treatment of solid wastes might contribute to the conversion towards a more sustainable and environmental friendly economy minimizing the amount of tailings or residues that exert a harmful impact on the environment.
... The presence of other components and its physical characteristics are drawbacks for using red mud as a raw material for steelmaking. A number of studies as described in Akcil et al. (2018) have focused on the extraction of iron and titanium (as oxides) from red mud. But the majority of them lacks an appealing economics. ...
Article
The aim was to study bioleaching of rare earth elements from red mud by a chemoorganotrophic microorganism, and to investigate the microbe-mineral interactions. Red mud is a promising resource for scandium, whose concentration was 92 and 54 mg/kg in two samples from Germany and India, respectively; however, both showed appreciably high concentration of zirconium. A gluconic acid-producing bacterium, Gluconobacter oxydans (DSMZ 46616), was used in the bioleaching experiments under parametric variation of inoculum concentration, pulp density, and culture adaptation. At a solid load of 10% (w/v) red mud with 10% (v/v) bacterial inoculum at 37 °C, a maximum solubilisation of 83% and 94% Sc was observed after 18–20 d of incubation for Indian and German red mud, respectively. The total amount of gluconic acid excreted by the bacteria increased with an increase in pulp density up to 10% (w/v). After bioleaching, SEM-EDAX analysis of the solid residue depicted enrichment of zirconium associated with the silicate matrix, and the bacterial cells were adhered to the major mineral matrix.
... In the last few decades, the increasing use of Sc and other REEs in high tech, aerospace, and defense applications have resulted in a higher demand for these elements and their classification as critical raw materials (CRMs) by the European Commission due to their supply risk [4]. The utilization of BR as a secondary source, especially for Sc and REEs, has been studied by several researchers [5][6][7]. Hydrometallurgical methods were mainly investigated using different mineral acids, such as nitric [3], hydrochloric [7], and sulfuric acid [2], under different leaching conditions [7,8]. ...
Article
Full-text available
The disposal of voluminous, highly alkaline, bauxite residue (BR), the industrial by-product of alumina production by the Bayer process, constitutes an intricate global environmental problem. BR, containing valuable metals such as rare-earth elements (REEs)—in particular, scandium (Sc)—can be used as a secondary source for REE extraction. The scope of this study was the investigation of bioleaching as an innovative and environmentally friendly approach for the extraction of Sc from BR. The bioleaching parameters were studied on Greek BR and experiments were performed using different microbial cultures and solid to liquid ratios (S/L). The maximum extraction of Sc was 42% using Acetobacter tropicalis in a one-step bioleaching process at 1% S/L. The main organic acids produced were acetic, oxalic, and citric. The bioleaching data indicated a probable synergistic effect of the different organic acids produced by microorganisms along with a more targeted leaching mechanism.
... Generally, Sc is obtained as a by-product of the processing of various ores, or it is extracted from previously processed tailings or residues, such as RM (Anawati and Azimi, 2019). Scandium accounts for approximately 90% of the commercial worth of the REEs found in RM, and its high concentration (50-120 mg/kg) makes it a suitable ore for this element (Reid et al., 2017;Akcil et al., 2018). These concentrations are significant when compared to that of the natural element in the Earth's crust of 23 mg/kg and more than that detected in bauxite ore Botelho Junior et al., 2020). ...
Article
Full-text available
The aim of this study was to recover Sc as the main product and Fe as a by-product from Hungarian bauxite residue/red mud (RM) waste material by solvent extraction (SX). Moreover, a new technique was developed for the selective separation of Sc and Fe from real RM leachates. The presence of high Fe content (∼38%) in RM makes it difficult to recover Sc because of the similarity of their physicochemical properties. Pyrometallurgical and hydrometallurgical methods were applied to remove the Fe prior to SX. Two protocols based on organophosphorus compounds (OPCs) were proposed, and the main extractants were evaluated: bis(2-ethylhexyl) phosphoric acid (D2EHPA/P204) and tributyl phosphate (TBP). The results showed that SX using diethyl ether and tri-n-octylamine (N235) was efficient in extracting Fe(III) from the HCl leachate as HFeC14. Over 97% of Sc was extracted by D2EHPA extractant under the following conditions; 0.05 mol/L of D2EHPA concentration, A/O phase ratio of 3:1, pH 0–1, 10 min of shaking time, and a temperature of 25 °C. Sc(OH)3 as a precipitate was efficiently obtained by stripping from the D2EHPA organic phase by 2.5 mol/L of NaOH with a stripping efficiency of 95%. In the TBP system, 99% of Sc was extracted under the following conditions: 12.5% vol of TBP, an A/O phase ratio of 3:1, 10 min of shaking time, and a temperature of 25 °C. The Sc contained in the TBP organic phase could be efficiently stripped by 1 mol/L of HCl with a stripping efficiency of 92.85%.
... (continued on next page) (continued on next page) treatment. For example, Mondillo et al. (2019) showed that FeO/OHs in bauxite can incorporate various amounts of Sc, V, Cr, Co, Ni, and REE and that these concentrations can be detected within FeO/OHs contained in red muds (Logomerac, 1971;Borra et al., 2015;Borra et al., 2016a;Borra et al., 2016b;Deady et al., 2016;Zhang et al., 2016;Davris et al., 2016;Davris et al., 2017;Reid et al., 2017;Akcil et al., 2018;Bolanz et al., 2018;Rivera et al., 2018;Tóth et al., 2019). Iron oxidehydroxides in Zn-nonsulfide deposits also contain variable amounts of valuable metals such as Ge, Zn, and Pb Mondillo et al., 2018a;Mondillo et al., 2018b;Santoro et al., 2013;Santoro et al., 2014;Santoro et al., 2015;Santoro et al., 2020). ...
Article
Iron-(oxy)-hydroxide (FeO/OH) phases are abundant in all supergene ore deposits. The most common FeO/OH phase in supergene environments is goethite, although hematite, lepidocrocite, ferrihydrite, and maghemite can also occur. Natural FeO/OHs are rarely chemically pure, as a range of metal cations can be readily incorporated into their mineral structure. Although an extensive body of literature exists on the scavenging action of synthetic FeO/OHs, there is a general lack of studies of natural systems and, more specifically, of studies dealing with the geochemistry of trace elements in FeO/OHs associated with supergene ores. Furthermore, although it is known that FeO/OHs in supergene ore systems typically contain elevated levels of useful metals like REE, Sc, V, Co, Mn, Cr, and Ni, in most cases, these phases are considered as gangue and hence, the metals are not recovered. Only in the case of Ni(Co)-laterite deposits the FeO/OHs are often exploited for Ni and Co, and sometimes for Sc. Most previous works on Ni(Co)-laterite deposits have focused on the lateritization process of the parent rocks and the mineralogy of the resulting Ni(Co)-bearing minerals. Only rarely have published studies focused on REE, V, Sc, and PGE deportment within FeO/OHs. In this study, we describe new mineralogical and chemical data (XRPD, SEM-EDS, EPMA, ICP-AES, LA-ICP-MS, and TEM-HRTEM) obtained from a range of natural FeO/OH samples collected from four important Ni(Co)-laterite deposits, namely Wingellina (Western Australia), Piauí (Brazil), Karaçam and Çaldağ (Turkey). In the course of this study, we investigated the geochemistry of goethite and hematite within the oxidation zone of the respective laterite profiles, evaluating the deportment of minor metals such as Ti, Sc, Cr, Ni, Co, V, Zn, and Mn. Although derived from different parent rocks located in different geographic areas, the FeO/OH samples collected share a number of common features. In particular, there are commonalities in ore textures, mineralogy, and metal deportment. Based on multivariate statistical analysis, the chemistry of the studied FeO/OHs define three major elemental associations: i) Mn–Al–Ti–Sc–V as evident in goethite samples from Wingellina; ii) Mg–Ni–Si–Zn as exemplified by samples from Karaçam and Piauí, and iii) Cr–V as illustrated by the Çaldağ samples. These contrasting geochemical footprints can be explained in terms of first- and second-order controls with the chemical composition of the parent rock representing the first-order, and favorable pH conditions for the fixation of trace elements within FeO/OHs representing the second-order control. Seasonality and maturation may be additional factors influencing FeO/OHs mineralogy, as periods of arid climate may have favored the dehydration of some FeO/OHs to form more stable species (such as goethite to hematite) over time. In summary, our observations have helped to better understand the ore deposition model relating to surficial weathering systems and have also established the parameters that control the distribution of economically relevant by-product metals in FeO/OHs in diverse conditions during the formation of Ni(Co)-laterites.
... Many processes have been proposed for the recovery of valuable components from red mud [9,13,14]. In the last years, there has been a high interest for the selective recovery of scandium [10,15,16]. Direct leaching processes using different lixiviants such as alkaline solutions [17,18], hydrochloric and sulfuric acids [19][20][21][22][23][24][25], organic acids [26,27] and ionic liquids [28,29] have been thoroughly investigated. ...
Article
Full-text available
Red mud is a hazardous waste of the alumina industry that contains high amounts of iron, aluminum, titanium and rare-earth elements (REEs). One of the promising methods for the extraction of iron from red mud is carbothermic reduction with the addition of sodium salts. This research focuses on the process of hydrochloric high-pressure acid leaching using 10 to 20% HCl of two samples of non-magnetic tailings obtained by 60 min carbothermic roasting of red mud at 1300 °C and the mixture of 84.6 wt.% of red mud and 15.4 wt.% Na2SO4 at 1150 °C, respectively, with subsequent magnetic separation of metallic iron. The influence of temperature, leaching duration, solid-to-liquid-ratio and acid concentration on the dissolution behavior of Al, Ti, Mg, Ca, Si, Fe, Na, La, Ce, Pr, Nd, Sc, Zr was studied. Based on the investigation of the obtained residues, a mechanism for passing valuable elements into the solution was proposed. It has shown that 90% Al, 91% Sc and above 80% of other REEs can be dissolved under optimal conditions; Ti can be extracted into the solution or the residue depending on the leaching temperature and acid concentration. Based on the research results, novel flowsheets for red mud treatment were developed.
... On the other hand, RM contains several interesting minor or trace elements, including rare earth elements (REEs) [13,14], of which gallium (60-80 g t -1 ), yttrium (60-150 g t -1 ), uranium (50-60 g t -1 ), and thorium (20-30 g t -1 ) are the most common [15]. Given the significant rise in the price of REEs and RE metal oxides, which began at $300 per kilogram in 2010 and rose to $3600 per kilogram in 2011, RM has been extensively researched for the recovery of these important elements [16]. The separation and purification of REEs is the biggest chal-lenge owing to the similar physicochemical properties of Sc, Y, and La [17,18]. ...
Article
In this article, we provide an overview of the methods used to enhance the recovery of rare‐earth elements (REEs) from bauxite residue or red mud (RM). RM is a byproduct of the Bayer alumina production process. Storage is an issue with regard to both space and the environment. The composition of the RM varies depending on the original bauxite source and digestion protocol. Apart from its major components, RM contains various REEs. Our study aimed at developing and improving technological steps to recover REEs such as scandium (Sc), lanthanum (La), and yttrium (Y) from the RM, which is considered to be a waste material. RM samples were collected from the Hungarian red mud storage facility in Ajka (MAL Company). Different parameters such as leaching agents, contact time, temperature, and solid‐to‐liquid ratio (S/L) were investigated to achieve optimum REE recovery from the RM. The recovery procedure of REEs includes cross‐breeding of hydrometallurgical technological steps such as acid digestion, ion exchange, and solvent extraction (SX). Digestion with different mineral acids was studied herein. Sulfuric acid (H2SO4), hydrochloric acid (HCl), nitric acid (HNO3), and acid mixtures were used for digestion. The process followed here was selected by considering its efficiency for the selective recovery of Sc, La, and Y and its suitability for the subsequent solvent extraction and ion exchange of the leaching solution for the separation of the individual lanthanides. The results obtained using the ICP‐OES technique showed that the extraction of REEs was high for leaching by using HCl and aqua regia as leaching agents under a microwave digestion system compared to other acids. The REE concentrations in the leachate were as follows: Sc = 30–86 ppm, La = 158–190 ppm, and Y = 50–93 ppm.
... The high concentration of major metals in leached solution of the waste strongly interferes with the extraction of REEs as their separation is problematic [66]. Ion exchange is used for the separation however, cationic contamination of the resins by species such as Fe 3+ , Al 3+ , Ca 2+ decrease the sorption or selectivity of REEs [61]. ...
Article
Full-text available
Bauxite Residue (BR) is an industrial waste generated by the extraction of alumina through the Bayer process. It is usually stored in specially constructed sedimentation ponds. Long term storage notoriously leads to severe environmental issues due to its high alkalinity which affects neighboring communities. It contaminates phreatic and surface waters through the infiltration of metal laden caustic solution and radionuclides. The air also gets polluted through dispersion of particles which threatens surrounding biodiversity. To manage these environmental concerns, it is necessary to engineer the waste residue into value added products. This paper systematically reviews the mineralogical and chemical characterization of the waste and techniques developed for its recycling.
... However, a large number of studies are aimed to find additional scandium resources (Wang et al., 2011). The most promising of which are bauxite ores processing wastes i.e. red mud (Akcil et al., 2018;Ujaczki et al., 2018), vanadium mud (Wang et al., 2013;Cao et al., 2020), and Nb-Ta ores (Purcell et al., 2018;Molchanova et al., 2019). ...
Article
This study contains research on the sorption separation of scandium, zirconium, and titanium from acidic sulfate solutions by a novel monofunctional Purolite RUA21207 ion exchange resin with primary amino groups. The kinetic and equilibrium performance of Sc, Zr, Ti sorption has been investigated. The results revealed that sorption favored at 25 g L⁻¹ H2SO4 in solution when the initial scandium concentration had been no more than 0.9 g L⁻¹. Zirconium and titanium could be selectively eluted from the loaded resin with the solutions of 150 g L⁻¹ KHF2 and 50 g L⁻¹ HCl, respectively. In this work, the scandium concentrate generated from acid waste of titanium white production has been dissolved in 25 g L⁻¹ H2SO4. Then, the solution has been passed through a column loaded with Purolite RUA21207 resin. Purification of scandium by 147 times that of zirconium and more than twice that of titanium have been achieved. Purolite RUA21207 resin has high potential application in the purification of scandium concentrate from Zr and Ti by sorption and definitely can be used for providing high purity scandium oxide.
... Various acids are used to dissolve multiple elements (iron, aluminum, titanium, and rare earth elements [REEs]) in red mud in accordance with the acid dosage, leaching time, and temperature [13,14]. However, multielement dissolution complicates and increases the cost of downstream separation processes [15,16]. In addition, the high-pressure hydrochemical treatment of red mud has been performed [17]. ...
Article
Full-text available
A combined low-temperature sodium salt-assisted roasting and water leaching process was investigated as a cleaning method for the treatment of Al-goethite-containing red mud (AGRM), which is conducive to aluminum recycling and iron mineral enrichment in leaching residue. In this work, the mineralogical characteristics and phase transformation of AGRM roasted at low temperature were evaluated by using an advanced mineral identification and characterization system, thermogravimetric analysis and differential scanning calorimetry, X-ray diffractometry, and backscatter scanning electron microscopy/energy dispersive spectrometry. In addition, the main factors, such as roasting temperature, sodium hydroxide dosage, leaching temperature, and time were investigated. Results revealed that the fraction of aluminum in Al-goethite is up to 73.59% of the total aluminum content in AGRM. The transformation of Al-goethite into Al-hematite occurred at approximately 360 °C, and adding sodium hydroxide can promote the conversion due to the formation of sodium aluminate. Compared with AGRM after roasting at 400 °C for 30 min followed by water leaching at 30 °C for 10 min, the leaching rate of aluminum increased from 0.36% to 90.21% and the grade of TFe in the leaching residue increased from 45.63 wt% to 54.09 wt% after roasting with 25 wt% sodium hydroxide under the same conditions. Given that the enhanced transformation of Al-goethite significantly improved aluminum recovery and the obtained iron-rich leaching residue can be easily co-disposed in the steel industry, thus may achieve the almost zero-waste discharge of AGRM from the Bayer process.
... Rare earth elements (REEs) are expensive in general due to their scarcity and difficult extraction and separation processes [6], and scandium is one of the most expensive REEs [7]. To illustrate the point, with the average crustal abundance of 22×10 −6 [8], it is the 31st element in the earth's crust. ...
Article
Raffinate copper leach solution of the Iran Sarcheshmeh copper complex has up to 3 mg/L scandium (Sc), which is significantly better than many existing sources, making it a possible source for the recovery of Sc using the ion exchange method. Visual Minteq software was employed to ascertain the ionic species likely to be formed under operational conditions in the mine and for selecting the suitable ion exchange resin. The cationic resin thus chosen was employed statically with ions-bearing synthesized solutions and statically/dynamically for actual copper mining raffinate solution. Room temperature and pH of 1.5 showed the highest Sc adsorption. The dynamic tests established the full saturation of the resin at 450 BV of the raffinate solution flow. Using sodium carbonate for elution, desorption of Sc, Y and Ce from the resin during static elution tests at constant duration was higher than that of Fe, Al and Cu. The results from the dynamic tests followed similar trends for the priority and the extent of the elution process. Desorption results from specimens of dynamic tests show a 60:1 concentration ratio leading to a 186 mg/L Sc-rich solution.
... Commonly, hydrometallurgical methods are based on dissolving raw product in an acidic or alkaline solution followed by separation of the target components and compounds from the liquid phase using precipitation, sorption or extraction. Scandium is one of the most interesting trace elements presenting in red mud (Akcil et al., 2018). ...
Article
Bauxite residue (red mud) is a promising anthropogenic source of scandium because only at the aluminum plants of Ural region (Russia) nearly 150 tons of this trace metal appears in the waste dumps annually. This work describes a method of red mud carbonization by carbon dioxide that results on the one hand to scandium leaching and on the other hand decrease of toxicity of the red mud due to conversion of hydroxides to carbonates and decrease of pH value from 12 to less than 9. The ways of increase of scandium leaching degrees based on ultrasonic treatment and mechanical activation were evaluated. It was supposed that carbonated red mud had high sorption activity being the main cause of secondary loss of scandium in the carbonate treatment process.
... Despite the works reported in the literature, none explored the recovery of scandium and zirconium by the leachingsolvent extraction process. The rare earth element is the most valuable, representing up to 95% of the economic value in the residue [60,61]. After the acid leaching of the bauxite residue, zirconium is the second most valuable element, more than the other rare earth elements present in the leaching solution. ...
Article
The separation of scandium from the solution generated in acid leaching is one of the main challenges for the hydrometallurgical processing of bauxite residue. Several organic extractants were evaluated, being the most prominent phosphine acids, while amine-based compounds have shown great results for separating metallic ions. The present study aims at the separation of scandium and zirconium from the Brazilian bauxite residue. The acid leaching was carried out using 20% of H2SO4, S/L ratio equals 1/10, for 8 h at 90 °C. Further, solvent extraction experiments were carried out using D2EHPA, Cyanex 923, and Alamine 336 diluted in kerosene, evaluating the effect of pH, temperature, extractant concentration, synergism with TBP and A/O ratio. After optimizing various process parameters, Alamine 336 has obtained separation factors of Zr/Al, Zr/Fe, and Zr/Ti equal to 15150, 45054, and 19713, respectively, at pH 1.0, A/O ratio equals to 1:1 and 25 °C. The stripping rate achieved 92% using Na2CO3 0.25 mol/L. The scandium separation ratio reached higher values for 10% of Cyanex Cyanex 923 than D2EHPA 10% + TBP 5%. Scrubbing for contaminants removal may be carried out using HCl 5 mol/L with 0.1% of scandium losses, and all scandium was stripped by H3PO4 5 mol/L. Despite the works reported in the literature, there a few of them exploring the recovery of scandium and zirconium by the leaching-solvent extraction process. The flowchart proposed is strictly connected to the sustainable development goals 7, 8, 9, and 12.
Article
Full-text available
Bauxite residue, known as red mud, is a by-product of alumina production using the Bayer process. Currently, its total global storage amounts to over 4.6 billion tons, including about 600 million tons in Russia. The total global storage of red mud occupies large areas, leading to environmental damage and increasing environmental risks. Moreover, it contains a significant amount of sodium, which is easily soluble in subsoil water; therefore, a sustainable approach for comprehensive recycling of red mud is necessary. The bauxite residue contains valuable elements, such as aluminum, titanium, and scandium, which can be recovered using liquid media. In recent years, many methods of recovery of these elements from this waste have been proposed. This paper provides a critical review of hydrometallurgical, solvometallurgical, and complex methods for the recovery of valuable components from red mud, namely, aluminum, titanium, sodium, and rare and rare-earth elements. These methods include leaching using alkaline or acid solutions, ionic liquids, and biological organisms, in addition to red mud leaching solutions by extraction and sorption methods. Advantages and disadvantages of these processes in terms of their environmental impact are discussed.
Article
Full-text available
In this study, a magnetic separation–shaking table gravity separation process was used to treat Sc-bearing V–Ti magnetite tailings, and the Sc2O3 content in the Sc concentrate was enhanced from 0.0039 to 0.0061%. The majority of the Sc in the Sc concentrate originates from augite, hornblende, and aluminosilicate. Magnesium chloride and the Sc concentrate were placed in a roasting furnace for chloridizing roasting, causing the partial chlorination of Sc to ScCl3. Sc was extracted from the roasted ore using hydrochloric acid leaching. Sc extraction indices demonstrated 95.12% Sc2O3 leaching efficiency and 0.0011% Sc2O3 content in the acid leaching residue, clearly indicating the extraction of Sc. No noticeable peak of Sc was observed in the spectrum of the acid leaching residue. Most of the Sc in the roasted ores was dissolved as Sc3+, and it entered the liquid phase. The main minerals in the acid leaching residue were Mg2SiO4, CaTiO3, and Fe2SiO4.
Article
Red mud contains large amounts of rare and valuable minerals. Specifically, rare earth elements are present at a concentrated amount in many red mud samples around the world. There is currently only one ore source in the United States that can produce rare earth elements. Pursuing avenues to extract rare earths from red mud is highly advantageous to reduce the amount of red mud being stockpiled, give value to red mud as a waste, and utilize a source for producing rare earths. The iron nugget process effectively increases the concentration of rare earth elements by removing iron. Slag from the iron nugget process upgraded the concentration of rare earth elements by 100%, which makes this a desirable feed for processing. Hydrochloric acid was used to dissolve the rare earth oxides present in the nugget slags, rare earths were then precipitated as a solid using oxalic acid. HCl leach can recover 170 grams of rare earths per ton of red mud nugget slag and oxalic acid precipitation can recover 45 grams per ton.
Article
In this work, we studied the effect of microwave treatment of red mud briquettes containting more than 48% of Fe on the process of iron reduction under various conditions of heat treatment. Research samples were collected from red mud formed during the production of alumina from bauxite at the Ural Aluminum Smelter. The chemical composition of mud samples was examined by X-ray fluorescence analysis. The composition of initial mud and that of agglomerates obtained after treatment in microwave and muffle furnaces was studied using the X-ray diffraction method. Phase transitions and structural changes occurring under the effect of heating were studied by scanning electron microscopy. The experimental briquettes comprising red mud and charcoal were treated at 850°C and 1000°C in a microwave furnace (under the frequency of 2.45 GHz and the power of 900 W). For reference, briquettes of analogous composition were heat-treated in a muffle furnace under the same conditions. It was found that, under the conditions of microwave heating to 1000°C for 10 min, hematite is completely reduced to metallic iron after the addition of wustite. An analysis of the m i-crostructure of the samples after microwave treatment showed that the particles of metallic iron in the as-obtained pellet-agglomerates have a larger size than in those after conventional thermal heating in a muffle furnace. The metallized phases of reduced iron at the end of heat treatment in a microwave furnace create a stable durable body of agglomerates. The evidence-based parameters of the process can become a basis for designing a technology for recycling such an industrial material as red mud. The obtained high-strength pellets from red mud with a high content of reduced iron (up to 85%) may be used as an alternative charge material for ferrous metallurgy. The proposed technology for recycling red mud into pellet-agglomerates can be applied in various industries to reduce environmental impact on the production areas of alumina plants.
Article
Full-text available
Storage of red mud – bauxite processing waste – leads to serious environmental problems due to its high alkalinity and particle dispersity. Full or partial utilization or recycling of red mud could reduce the harmful effect on the environment. Scandium is the most valuable ingredient of red mud, yet it's extraction is poorly commercialized due to its high cost. The new efficient extraction technologies promise an ensured supply of scandium and a significant drop in cost. Here, scandium concentrate, extracted from leachate after carbonate treatment of red mud, was subjected to sulfatisation by H2SO4 to separate silica from water-soluble sulfates. To recover and selectively separate scandium from other impurity metals, the crystallization of two complex scandium and ammonium sulfates – NH4Sc(SO4)2 and (NH4)3Sc(SO4)3 – is proposed. The solubilities of these sulfatoscandiates in water, established by isothermal method, are 33.4 and 72.4 g/L, respectively. For the less soluble NH4Sc(SO4)2 a further considerable reduction of solubility has been observed in H2SO4 solutions of concentration above 3.5 М in the presence of 0.5 М NH4Cl at 20 ± 1 °C. More than 99% of scandium in the form of micron-sized NH4Sc(SO4)2 crystals has been recovered from a multicomponent liquid at 5–6 М H2SO4 and 0.5 М NH4Cl. The product contains extremely low levels of impurities. The precipitation of NH4Sc(SO4)2 offers a much higher selectivity in separation of Sc from the other main constituents, as demonstrated by the large separation coefficients between scandium and other metals βSc/M (e.g., for the couple with aluminum βSc/Al = 4280). The recrystallization product after calcination at 1000°С contains 99% Sc2O3.
Article
REEs are essential materials for modern technology due to their unmatched physical and chemical properties. This paper reviews the potential and types of rare earth elements (REE) in 32 different secondary sources that contain water, wastewater, and slime/solid wastes originating from Turkey. Secondary sources were classified into five different categories as mining wastes (M), combustion residuals (C), sediments and sludges (S), e-waste (E), and wastewater (WW). After pre-processing and acidic digestion of solid samples, elemental concentrations of wastewaters and acidic leachates were measured. The highest total REE (REEtotal) concentration was obtained in a combustion residue sample coded as C5 with 379 mg/kg. Besides, the highest critical REE (REEcritical) content was found in an e-waste sample including 346 mg/kg total REE and 76% critical REE. In addition, boron mine wastewater (W5) with a total REE concentration of 110 μg/L was evaluated as a significant important secondary source in terms of yttrium. The association, between scandium and total REE concentrations of category M and S, was evaluated and correlation coefficients of 0.86 and 0.69, respectively were calculated. E-waste and thermal power plant (TPP) ashes were evaluated as the secondary sources with the highest REE potential among the whole type of waste/wastewater.
Conference Paper
Full-text available
With escalating demand for metals, an increasing global population and rapid technology development, there is a worldwide challenge to secure a sustainable metal supply for industry. Current recycling rates for such metals are extremely low, mainly due to a lack of feasible recovery technologies. As a consequence, valuable metal resources are being landfilled each year from sources such as municipal and industrial solid wastes and leachates. The practice of landfilling these valuable resources not only impacts the environment due to the potential leaching of metal rich toxic liquids, but also represents a significant long term loss to the economy. Recovery of metals from industrial process wastes, such as bauxite residue and incinerator ashes potentially offers significant quantities of metals to the benefit of the environment and economy alike. The difficulty with their recovery, however is that metals of concern tend to be present in low concentrations within complex matrices and can be technically difficult to extract. Here the extent of unrecovered metals in leachates from bauxite residue and incinerated bottom and fly ashes from municipal solid wastes are quantified and their potential economic value assessed. Additionally the potential of sawdust modified biochar and KOH modified hydrochar to remove Vanadium (V) from aqueous solutions in batch study experiments are assessed, with measured optimum uptakes of 16.5 and 12.3 mg g-1 respectively at a solution pH 4. Finally consideration is given to future research needs to improve the overall performance of biosorption of leachate metals
Article
Red mud is a polymetallic waste generated during Bayer's process of alumina production. High alkalinity (pH > 11), multiple elements, and micron-sized particles make red mud recycling energy-intensive and challenging. The following work presents a hydrometallurgical flowsheet for separation of different red mud elements and recovery of high purity Fe (II) product using cost-effective reagents, energy-efficient processes, and minimal waste generation. Red mud preprocessing was carried out by mild hydrochloric acid wash (1 M, 13 pct pulp density, 40 °C 15 minutes), followed by leaching of hematite from neutralized red mud in oxalic acid (2 M, 10 pct pulp density, 95 °C, 2.5 hours). UV light-assisted photochemical reduction of oxalic leach solution of red mud separated more than 98 pct Fe in the form of ferrous oxalate (purity more than 99 pct) within 5 hours. The process's material balance shows a overall recovery of more than 85 pct Fe value as solid ferrous oxalate of high purity and concentrating titanium oxide in the residue and aluminum in the leaching solution.
Article
Full-text available
Bauxite residue, known as “red mud,” is a potential raw material for extracting rare-earth elements (REEs). The main REEs (Sc, Y, La, Ce, Nd, Nb, and Sm) from the raw bauxite are concentrated in RM after the Bayer leaching process. The earlier worldwide studies were focused on the scandium (Sc) extraction from RM by concentrated acids to enhance the extraction degree. This leads to the dissolution of major oxides (Fe2O3 and Al2O3) from RM. This article studies the possibility of selective Sc extraction from alkali fusion red mud (RMF) by diluted nitric acid (HNO3) leaching at pH ≥ 2 to prevent co-dissolution of Fe2O3. RMF samples were analyzed by X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and inductively coupled plasma mass spectrometry (ICP-MS). It was revealed that Sc concentration in RMF can reach up to 140–150 mg kg−1. Sc extraction was 71.2% at RMF leaching by HNO3 at pH 2 and 80 °C during 90 min. The leaching solution contained 8 mg L−1 Sc and a high amount of other REEs in the presence of relatively low concentrations of impurity elements such as Fe, Al, Ti, Ca, etc. The kinetic analysis of experimental data by the shrinking core model showed that Sc leaching process is limited by the interfacial diffusion and the diffusion through the product layer. The apparent activation energy (Ea) was 19.5 kJ/mol. The linear dependence of Sc extraction on magnesium (Mg) extraction was revealed. According to EPMA of RMF, Sc is associated with iron minerals rather than Mg. This allows us to conclude that Mg acts as a leaching agent for the extraction of Sc presented in the RMF in an ion-exchangeable phase.
Article
The reduction kinetics of serial phase transitions of iron oxides during reduction to a metallized state with different modes of technical hydrogen supply has been studied and substantiated. The results of the pellets formation when 3-5 % molasses is added to the red mud as a binding reagent are presented. The dependences of the reduction rate of iron oxides on the hydrogen flow rate are obtained. Based on the results of the experiments, a kinetic model was constructed, and with the help of X-ray phase and spectral analysis, it was proved that the agglomerates formed after heat treatment received high strength due to the adhesion of reduced iron particles with red mud particles. The use of a new type of charge materials in melting units will reduce the amount of emissions and dust fractions, as well as increase the metal yield.
Article
A comprehensive process flowsheet is investigated to recover metallic values from red mud with high-purity products such as alumina, silica, ferrous oxalate, titania, and Sc-Ga containing purified solution. The carbonated red mud leached in 1 M hydrochloric acid at 50 °C for 1 h dissolves 44.5% Al and 51% Si, followed by 2 M oxalic acid leaching at 90 °C for 2.5 h yielding 61% Fe and 46–48% Sc and Ga dissolution. High-purity ferrous oxalate product is retrieved from the leach solution, and the Sc and Ga ions report to the solution. Titanium enriched residue is baked with 1 mL/g sulfuric acid at 300 °C for 1 h, forming TiOSO4, Fe2(SO4)3, and Al2(SO4)3 phases, followed by water leaching. 64.5% Ti and ∼ 27% Fe dissolution is attained, and solution contains Fe (7.47 g/L), Ti (3.09 g/L), Al (2.44 g/L), Si (0.17 g/L), Sc (2 mg/L), and Ga (3 mg/L) ions. Thermal hydrolysis of solution recovers titania precipitate (96.9% purity), and the solution after hydrolysis contains Fe, Sc, and Ga values. The overall metal extraction (84% Fe, 79% Ti, 92% Al, 78% Sc, 89 % Ga) in the proposed flowsheet is higher compared to direct acid baking process (51% Fe, 65% Ti, 89% Al, 51% Sc, 48 % Ga). Products recovered include high-purity silica (4.8 wt%), alumina (9.3 wt%), Fe(II) oxalate (20.7 wt%), titania (8.9 wt%), and a final residue yield of 12.6 wt%. Microwave exposure at 2 kW for 7 min improves the dissolution of the Sc (84%) and Ti (85.5%). H2 reduction at 450 °C, 30 min converted hematite to magnetite and increased Fe dissolution to 90%. Red mud's mineralogical and composition modification by magnetic separation, reduction, and microwave exposure were ineffective to improve selective dissolution.
Article
Increasing disruption in the rare earth supply chain creates an urgency to develop alternative resources, in which utilization of coal-based materials presents great potential. Nevertheless, environmental control is a significant challenge in rare earth extraction processes. This study was conducted to contribute to the limited information on removing thorium and uranium from rare earths while coal-based products are used as feedstock. The laboratory studies suggested that the selective precipitation and solvent extraction approach yields the most favorable separation performance. Complete thorium precipitation was achieved around a pH value of 4.8. Due to the close precipitation pH ranges of uranium and rare earths, further separation by solvent extraction was applied to achieve an enhanced separation. Based on a Box-Behnken experimental design, the effect of extractant concentration, pH, strippant concentration, and O/A ratio was investigated. Best separation performance was achieved using 50 v% TBP at a pH of 3.5 with an O/A ratio of 3 and 1 mol/L H2SO4, which resulted in 1.8% uranium and 73.4% rare earth extraction. The extraction and precipitation behavior of the elements were further assessed with the distribution ratio, separation factor, thermodynamic parameters, and species distribution diagrams to provide a thorough understanding of the separation mechanisms. The results were statistically analyzed, and a model was developed to predict uranium recovery. The developed experimental protocol was validated using a rare earth oxalate sample produced at the pilot-scale processing facility. Finally, a conceptual process flowsheet was developed to effectively separate radionuclides while producing rare earth oxide products.
Article
Full-text available
Bauxite residue (BR), simultaneously an environmental challenge as well as known to be a secondary resource for resources various valuable metals like Ti, V, Ga, and rare earth metal (REM). Lack of understanding and technology detects BR to be stockpiled which is counterproductive considering the environment, land scarcity, and management of BR inventories. As BR remains unexploited, significant amounts of REMs in BR remain unlocked, which are critical metals from green energy, environmental sustainability, and supply chain bottleneck perspective. Our current investigation analyses the potential of BR as secondary resources and quantity and worth of REM being remains unlocked. The quantitative content of global bauxite, alumina, and BR production during the last 5 decades have been analyzed. Also, plausible BR generation in the next 3 decades has been estimated. Considering the content of REM in BR amount of REM either stockpiled or to be stockpiled along with BR has been analyzed. Our study indicated about 9.14 million tons of REM remain locked in the stockpiled BR, 31.24 million tons of REM remain locked in the bauxite reserve. The worth of worldwide REM oxide remains unexploited in bauxite reserves and locked in stockpiled BR could be approximately $5000 billion, potentially can meet current and project demand of REM abundantly.
Article
Full-text available
The recovery of scandium (Sc) from wastes and various resources using solvent extraction (SX) was discussed in detail. Moreover, the metallurgical extractive procedures for Sc recovery were presented. Acidic and neutral organophosphorus (OPCs) extractants are the most extensively used in industrial activities, considering that they provide the highest extraction efficiency of any of the valuable components. Due to the chemical and physical similarities of the rare earth metals, the separation and purification processes of Sc are difficult tasks. Sc has also been extracted from acidic solutions using carboxylic acids, amines, and acidic β-diketone, among other solvents and chemicals. For improving the extraction efficiencies, the development of mixed extract-ants or synergistic systems for the SX of Sc has been carried out in recent years. Different operational parameters play an important role in the extraction process, such as the type of the aqueous phase and its acidity, the aqueous (A) to organic (O) and solid (S) to liquid (L) phase ratios, as well as the type of the diluents. Sc recovery is now implemented in industrial production using a combination of hydrometallurgical and pyrometallurgical techniques, such as ore pre-treatment, leaching, SX, precipitation, and calcination. The hydrometallurgical methods (acid leaching and SX) were effective for Sc recovery. Furthermore, the OPCs bis(2-ethylhexyl) phosphoric acid (D2EHPA/P204) and tributyl phosphate (TBP) showed interesting potential taking into consideration some co-extracted metals such as Fe(III) and Ti(IV).
Article
Full-text available
Bauxite residue, also known as red mud (RM), from alumina production is the most promising technogenic material for the production of scandium (Sc) and other rare earth elements (REEs). Conveniently, RM is processed by using a strong acid (pH < 2.5), which lead to co-dissolution of iron and other undesirable major components. In this work, for the first time, the possibility of selective extraction of scandium from red mud by using highly diluted acid (pH > 4) in the presence of MgSO4 was shown. The effect of temperature (40–80 °C), time (0–60 min), pH (2–5), and the MgSO4 concentration (12–36 g L−1) on Sc extraction efficiency was evaluated. It was shown that Sc extraction was higher than 63% even at a pH of 4, at 80 °C, after 1 h, while more than 80% could be extracted at a pH of 2. Iron extraction reduced from 7.7 to 0.03% by increasing the pH from 2 to 4. The kinetics study using the shrinking core model (SCM) has shown that diffusion through a product layer is a rate-limiting stage of the process at high temperatures (>60 °C) and low pH (<3), whereas, at lower temperatures and higher pH values, the leaching rate is limited by diffusion through the liquid film.
Article
The mineral deposits in the Kachchh region of Gujarat contain bauxite of all different grades, with a huge amount of low-grade bauxite. The low-grade bauxite from Kachchh is characterized in detail using different physicochemical techniques like X-ray diffraction (XRD), wavelength dispersive X-ray fluorescence (WD-XRF), field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray (EDX) detector, nitrogen adsorption/desorption isotherm at 77 K, and inductive coupled plasma-mass spectrophotometer (ICP-MS). The different mineral phases present in the low-grade bauxite were identified from the X-ray diffraction studies. The different elements present in the mineral were identified and quantified using WD-XRF and EDX measurements. The quantification of rare-earth elements particularly scandium is carried out by ICP-MS analysis. The digestion method has been optimized for the complete mineral digestion and precise measurement of scandium. The low-grade Kachchh bauxite is explored for the possible extraction of alumina and scandium. The ICP-MS analysis shows the presence of approximately 80 ppm of scandium in the low-grade bauxite. The low-grade bauxite has approximately 39% alumina, which is predominantly gibbsite in nature. The alkali digestion conditions were optimized for the maximum dissolution and extraction of gibbsite.
Article
Full-text available
In an effort to identify new sources of critical raw materials (CRMs) possibility of recovering selected CRMs from Polish coals, chars, and ashes resulting from the combustion of coals and chars was investigated. The samples were collected from pilot fluidized bed gasification systems. The search for CRMs in coal gasification wastes has not been widely reported before. The study used 2 bituminous coal and 1 lignite sample; the concentration of individual critical raw materials (CRMs) was analyzed using the ICP-MS method. The obtained results were compared with Clarke values in coal ash and in the Earth’s crust, and with the adopted cut-off grade. As shown by the analysis, the highest concentrations of CRMs can be found in fly ash, mainly in samples from the eastern part of the Upper Silesian Coal Basin. This applies mostly to Be, Cs, or Sb due to the fact that their concentrations were found to be higher than the Clarke value in the Earth’s crust; the mentioned fly ashes could be used as potential sources of critical elements if appropriate recovery technologies are developed. In addition, the tested materials have elevated Se, Pb, Ni concentrations, but their recovery is currently not economically viable. Compared to the currently adopted cut-off grade levels, there are no critical elements in the analyzed coal gasification waste that could be recovered.
Article
Full-text available
Rare earth elements (REEs) are becoming more and more significant as they play crucial roles in many advanced technologies. Therefore, the development of optimized processes for their recovery, whether from primary resources or from secondary sources, has become necessary, including recovery from mine tailings, recycling of end-of-life products and urban and industrial waste. Ionic solvents, including ionic liquids (ILs) and deep-eutectic solvents (DESs), have attracted much attention since they represent an alternative to conventional processes for metal recovery. These systems are used as reactive agents in leaching and extraction processes. The most significant studies reported in the last decade regarding the recovery of REEs are presented in this review.
Conference Paper
Full-text available
With escalating demand for metals, an increasing global population and rapid technology development, there is a worldwide challenge to secure a sustainable metal supply for industry. Current recycling rates for such metals are extremely low, mainly due to a lack of feasible recovery technologies. As a consequence, valuable metal resources are being landfilled each year from sources such as municipal and industrial solid wastes. The practice of landfilling these resources not only impacts the environment due to potential leaching of metal rich toxic liquids, but also represents a significant long term loss to the economy. Recovery of metals from industrial process wastes, such as bauxite residue and incinerator ashes potentially offers significant quantities of metals to the benefit of the environment and economy alike. The difficulty with their recovery, however is that metals of concern tend to be present in low concentrations within complex matrices and can be technically difficult to extract. Here the extent of unrecovered metals in leachates from bauxite residue and incinerated bottom and fly ashes from municipal solid wastes are quantified and their potential economic value assessed. The potential of saw dust modified biochar and KOH modified hydrochar to remove Vanadium (V) from aqueous solutions in batch study experiments are also assessed, yielding optimum uptakes of 16.5 and 12.3 mg g⁻¹ respectively at a solution pH 4. Finally consideration is given to future research needs to improve the sustainability and overall performance of biosorption of leachate metals.
Book
Full-text available
Heavy metals (HMs) are natural environmental constituents, but their geochemical processes and biochemical equilibrium have been altered by indiscriminate use for human purposes. Due to their toxicity, persistence in the environment and bioaccumulative nature; HMs are well-known environmental contaminants. As result, there is excess release into natural resources such as soil and marine habitats of heavy metals such as cadmium, chromium, arsenic, mercury, lead, nickel, copper, zinc, etc. Their natural sources include the weathering of metal-bearing rocks and volcanic eruptions, while mining and other industrial and agricultural practices include anthropogenic sources. Prolonged exposure and increased accumulation of such heavy metals may have detrimental effects on human life and aquatic biota in terms of health. Finally, the environmental issue of public health concern is the pollution of marine and terrestrial environments with toxic heavy metals. Therefore, because of the rising degree of waste disposal from factories day by day, it is a great concern. Pollution of HMs is therefore a problem and the danger of this environment needs to be recognized.
Article
Full-text available
Biohydrometallurgy recovers metals through microbially mediated processes and has been traditionally applied for the extraction of base metals from low-grade sulfidic ores. New investigations explore its potential for other types of critical resources, such as rare earth elements. In recent times, the interest in rare earth elements (REEs) is growing due to of their applications in novel technologies and green economy. The use of biohydrometallurgy for extracting resources from waste streams is also gaining attention to support innovative mining and promote a circular economy. The increase in wastes containing REEs turns them into a valuable alternative source. Most REE ores and industrial residues do not contain sulfides, and bioleaching processes use autotrophic or heterotrophic microorganisms to generate acids that dissolve the metals. This review gathers information towards the recycling of REE-bearing wastes (fluorescent lamp powder, spent cracking catalysts, e-wastes, etc.) using a more sustainable and environmentally friendly technology that reduces the impact on the environment.
Article
Global demand for rare earth elements (REEs) has been on the rise due to recent rapid technological advancements. Even though most REEs are mainly recovered from rich ores and mineral deposits, recovery of REEs from secondary sources has attracted attention. However, low metal concentration, complex matrices and high levels of other impurities in mine wastes and tailings have remained the toughest challenges to overcome. The presence of low amount of valuable metals such as Sc requires utilization of very selective separation techniques such as ion exchange. A series of ion exchange resins (chelating, solvent impregnated and strongly acidic) were studied in the recovery of Sc from synthetic and actual pregnant leach solutions obtained from acid-leaching of coal fly ash. To the best of our knowledge, this paper exhibits the first attempt in selective recovery (from other REEs as well as major Fe and Al contaminations) of Sc in coal fly ash using ion exchange separation technique. With maximum capacity of ∼24 mg Sc/g resin, Sc was adsorbed quickly on phosphorus containing Lewatit® VP OC 1026 and TP 272 resins even in the presence of high levels of potentially interfering Fe³⁺ and Al³⁺ ions. Full elution of the adsorbed REEs from VP OC 1026 was achieved with 5 M H2SO4, with only minor Sc removal. While elution of Sc from these chelating resins has been reported to be challenging, Sc could be eluted almost completely with 2 M NH4F. Recovery of REEs with 5 M H2SO4 from TP 272 resulted in co-elution of only 7% of the adsorbed Sc while the rest could be eluted efficiently with 6 M HNO3.
Article
The leaching behavior of scandium (Sc) from bauxite residues can differ significantly when residues of different geological backgrounds are compared. The mineralogy of the source rock and the physicochemical environment during bauxitization affect the association of Sc in the bauxite i.e., how Sc is distributed amongst different mineral phases and whether it is incorporated in and/or adsorbed onto those phases. The Sc association in the bauxite is in turn crucial for the resulting Sc association in the bauxite residue. In this study systematic leaching experiments were performed on three different bauxite residues using a statistical design of experiments approach. The three bauxite residues compared originated from processing of lateritic and karstic bauxites from Germany, Hungary, and Russia. The recovery of Sc and Fe were determined by ICP-OES measurements. Mineralogical changes were analyzed by X-ray-diffraction and subsequent Rietveld refinement. The effects of various parameters including temperature, acid type, acid concentration, liquid-to-solid ratio and residence time were studied. A response surface model was calculated for the selected case of citric acid leaching of Hungarian bauxite residue. The investigations showed that the type of bauxite residue has a strong influence. The easily leachable fraction of Sc can vary considerably between the types, reaching ~20–25% in German Bauxite residue and ~50% in Russian bauxite residue. Mineralogical investigations revealed that a major part of this fraction was released from secondary phases such as cancrinite and katoite formed during Bayer processing of the bauxite. The effect of temperature on Sc and Fe recovery is strong especially when citric acid is used. Based on the exponential relationship between temperature and Fe-recovery it was found to be particularly important for the selectivity of Sc over Fe. Optimization of the model for a maximum Sc recovery combined with a minimum Fe recovery yielded results of ~28% Sc recovery at <2% Fe recovery at a temperature of 60 °C, a citric acid normality of 1.8, and a liquid-to-solid ratio of 16 ml/g. Our study has shown that detailed knowledge about the Sc association and distribution in bauxite and bauxite residue is key to an efficient and selective leaching of Sc from bauxite residues.
Article
Red mud is a hazardous waste of alumina production by the Bayer method, which can be used for recovery of valuable elements such as iron, aluminum, titanium, and scandium. In this study, carbothermic roasting of red mud followed by dry or wet magnetic separation was applied with addition of alkaline salts to enhance iron extraction. A comparative influence of the use of sodium and potassium carbonates and sulfates, as well as the effects of roasting temperature and amounts of the additives on iron recovery and the iron concentrate grade were studied experimentally on two industrial red mud samples. The general mechanism of the roasting process in the presence of alkali metals was proposed in terms of temperature and iron extraction. Influence of the grinding fineness of the roasted samples and magnetic field strength during wet magnetic separation on iron extraction was also studied. It was shown that the addition of sodium and potassium carbonates and sulfates during carbothermic roasting of red mud improves the magnetic separation of metallic iron. The composition and microstructure of the separation products were examined, and their possible application was discussed.
Article
Red mud is an industrial waste generated during alumina production containing residual minerals of bauxite ore. Significant metallic values with appreciable concentration make it a potential polymetallic source. The current red mud management involves storage in artificial ponds/dams or dry stacked in open areas, which poses an environmental risk, and disposal processes are costly. Recently, red mud is utilized for cement production; however, it results in the loss of valuable minerals, which could be strategically advantageous for resource-deficient nations. Red mud utilization for producing concentrate can significantly improve process efficiency of alumina production, reduce industrial liability and environmental impact. The globally generated red muds are compared according to the mineralogy, composition, and associated values. Hematite is the chief constituent in the red mud, with anatase, gibbsite, goethite, quartz, and desilication phases such as cancrinite, sodalite, and olivine in a significant amount. Red mud originated from karst bauxites containing higher rare-earth content as adsorbed ions on the mineral surfaces, isomorphous substitution, and discrete rare-earth minerals such as bastnaesite, xenotime, chuchite, and allanite. Scandium holds 95% of the rare-earth economic value in the red mud and is associated with hematite, goethite, and anatase. The paper presents a critical overview of the laboratory, pilot, and commercial processes employed to recover iron, aluminum, titanium, scandium, and REEs from various red muds. The response parameters such as alumina-to-silica ratio, iron grade, total rare-earth elements were used to determine the appropriate processing route for recovery of metals from red mud. An integrated process is proposed to recover metallic values from the red mud while ensuring minimal waste generation.
Article
Full-text available
A nonwoven fabric adsorbent loaded with 2-ethylhexyl hydrogen-2-ethylhexylphosphonate (EHEP) was developed for the separation and recovery of dysprosium (Dy) and neodymium (Nd) from an aqueous solution. The adsorbent was prepared by the radiation-induced graft polymerization of a methacrylate monomer with a long alkyl chain onto a nonwoven fabric and the subsequent loading of EHEP by hydrophobic interaction and chain entanglement between the alkyl chains. The adsorbent was evaluated by batch and column tests with a Dy (III) and Nd (III) aqueous solution. In the batch tests, the adsorbent showed high Dy (III) adsorptivity close to 25.0 mg/g but low Nd (III) adsorptivity below 1.0 mg/g, indicating that the adsorbent had high selective adsorption. In particular, the octadecyl methacrylate (OMA)-adsorbent showed adsorption stability in repeated tests. In the column tests, the OMA-adsorbent was also stable and showed high Dy (III) adsorptivity and high selectivity in repeated adsorption–elution circle tests. This result suggested that the OMA-adsorbent may be a promising adsorbent for the separation and recovery of Dy (III) and Nd (III) ions.
Article
Full-text available
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.
Article
Full-text available
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.
Conference Paper
Full-text available
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).
Conference Paper
Full-text available
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.
Article
Full-text available
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.
Article
Full-text available
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.
Article
Full-text available
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.
Article
Full-text available
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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).
Article
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.
Article
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.
Article
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.
Article
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.
Article
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 he