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Advances in bio/chemical approaches for sustainable recycling and recovery of rare earth elements from secondary resources
... REE-bearing minerals are geographically unevenly distributed worldwide, with the majority of production originating from China ( Figure 2), that possesses reserves of monazite. Monazite deposits are also found in several other countries such as Australia, South Africa, Brazil, Malaysia, India, and Russia [46]. Markets and Markets predicts the REEs market growth USD 9.6 billion by 2026 [47], with a 12.3% CAGR from 2021 to 2026. ...
... Managing and disposing of hazardous chemical byproducts from production is challenging. Consequently, recycling rare earth elements from resources, such as end-of-life materials, is crucial to mitigating environmental impacts and ensuring a reliable domestic supply [46]. ...
... Different REE recycling methods are available, including commonly used techniques such as hydrometallurgy, pyrometallurgy, and selective electrochemical recovery. Aside from these conventional methods, alternative options like biometallurgy are gaining traction in the industry [46]. Currently, the primary methods employed for extracting REEs are pyrometallurgy and hydrometallurgy [87]. ...
Rare earth elements (REEs) are at the forefront of discussions, given their crucial role in cutting-edge and eco-friendly innovations that propel the industrial revolution towards a green economy. These elements have become indispensable to various modern technologies, such as smartphones, electronic devices, and renewable energy sources. Many different concepts and analyses have been introduced, such as the chemical similarities among REEs, health risks and ecological damages, the negative environmental impacts of current recovery processes, and strategies for advancing REE recovery towards a circular economy. Although these elements have been widely used in various applications over the last 20 years, the literature on these aspects is fragmented and spread across different research areas, shared by multiple branches and application fields. These fields include safety concerns, economic challenges, and technology. Summarizing and classifying this literature is challenging due to its fragmented nature, the variety of topics, and the different approaches used. The quest for cleaner recycling strategies necessitates a comprehensive assessment covering economic, technological, and environmental aspects. The primary goal of this review is to provide a holistic perspective on REEs, with a central focus on their economic, technological, and environmental dimensions, particularly emphasizing reuse, recycling, and occupational safety. The review begins by addressing complexities of REEs, highlighting the associated technologies, environmental concerns, and economic considerations. It further explores the aspects of reuse and recycling of REEs, shedding light on the advantages, drawbacks, hazards, and costs associated with recycling technologies for REE recovery. Additionally, the review summarizes occupational exposure and safety considerations related to REEs.
... In the basic research phase, many adsorbents have been studied and many reports are available. Examples include polymer-based adsorbents (ion-imprinted polymer-based adsorbents, impregnation of functional groups into adsorbents, etc.), carbon-based adsorbents (graphene oxide, carbon nanotubes, etc.), silica-based adsorbents (silica beads, zeolites, etc.), metal-organic frameworks (MOFs), clay minerals (kaolinite, halloysite, illite, expanded vermiculite, etc.), and biosorbents (cellulose-based adsorbents, chitosan-based adsorbents, etc.) [6][7][8][9][10][11]. Most of these adsorbents are designed to separate only REEs or REEs from other impurities such as Fe or Al. ...
The separation of adjacent rare earth elements (REEs) is a challenging issue due to their chemical similarity. We have investigated the separation of adjacent REEs using four types of adsorbents consisting of silica gel modified with diglycolamic acid with different functional groups at the amide position. For all the adsorbents, the adsorption ratio of REEs increased with the increase in atomic number from La to Sm and then became constant for heavy REEs. Among them, EDASiDGA, an adsorbent containing secondary and tertiary amides, showed a high separation factor for Nd/Pr of 2.8. The EDASiDGA-packed column was tested for individual recovery of Pr, Nd, and Sm. After the adsorption of these REEs from 0.10 M HCl, desorption tests were performed with 0.32 and 1.0 M HCl. As a result, Pr and Nd were eluted separately with 0.32 M HCl, and Sm was recovered with 1.0 M HCl. Since the EDASiDGA-packed column showed excellent separation of Pr/Nd/Sm without any chelating agent, it is promising for practical use.
... Traditional extraction methods often involve the use of harsh chemicals and can have significant environmental impacts. Bio-recovery, on the other hand, harnesses the metabolic capabilities of microorganisms to selectively leach and recover REEs (Danouche et al. 2024). Microorganisms active in bioleaching can be both autotrophic and heterotrophic. ...
Rare Earth Elements (REEs) are indispensable in contemporary technologies, influencing various aspects of our daily lives and environmental solutions. The escalating demand for REEs has led to increased exploitation, resulting in the generation of diverse REE-bearing solid and liquid wastes. Recognizing the potential of these wastes as secondary sources of REEs, researchers are exploring microbial solutions for their recovery. This mini review provides insights into the utilization of microorganisms, with a particular focus on microalgae, for recovering REEs from sources such as ores, electronic waste, and industrial effluents. The review outlines the principles and distinctions of bioleaching, biosorption, and bioaccumulation, offering a comparative analysis of their potential and limitations. Specific examples of microorganisms demonstrating efficacy in REE recovery are highlighted, accompanied by successful methods, including advanced techniques for enhancing microbial strains to achieve higher REE recovery. Moreover, the review explores the environmental implications of bio-recovery, discussing the potential of these methods to mitigate REE pollution. By emphasizing microalgae as promising biotechnological candidates for REE recovery, this mini review not only presents current advances but also illuminates prospects in sustainable REE resource management and environmental remediation.
... Bioleaching has emerged as a sustainable and green technology for metal recovery and is an alternative to conventional extractive processes with a reduced effect on climate change (Mohan and Joseph, 2020). This approach has been used commercially for the extraction of metals from low-grade ores and attracts attention for applying innovative methods to mobilize critical metals from secondary sources (Castro et al., 2020;Danouche et al., 2024), such as e-wastes (Baniasadi et al., 2019;Adetunji et al., 2023), spent catalysts (Moosakazemi et al., 2023), fly ash, red mud (Hedrich and Schippers, 2021), and scraps (Ilyas et al., 2013), to contribute to the development of a circular economy. ...
Microbial induced calcium carbonate precipitation (MICP) is considered as an environmentally friendly microbial-based technique to remove heavy metals. However, its application in removal and recovery of rare earth from wastewaters remains limited and the process is still less understood. In this study, a urease-producing bacterial strain DW018 was isolated from the ionic rare earth tailings and identified as Lysinibacillus based on 16S rRNA gene sequencing. Its ability and possible mechanism to recover terbium was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and fourier transform infrared spectroscopy (FTIR). The results showed that the urease activity of DW018 could meet the biomineralization requirements for the recovery of Tb³⁺ from wastewaters. The recovery rate was as high as 98.28% after 10 min of treatment. The optimal conditions for mineralization and recovery were determined as a bacterial concentration of OD600 = 1.0, a temperature range of 35 to 40°C, and a urea concentration of 0.5%. Notably, irrespective of CaCO3 precipitation, the strain DW018 was able to utilize MICP to promote the attachment of Tb³⁺ to its cell surface. Initially, Tb³⁺ existed in amorphous form on the bacterial surface; however, upon the addition of a calcium source, Tb³⁺ was encapsulated in calcite with the growth of CaCO3 at the late stage of the MICP. The recovery effect of the strain DW018 was related to the amino, hydroxyl, carboxyl, and phosphate groups on the cell surface. Overall, the MICP system is promising for the green and efficient recovery of rare earth ions from wastewaters.
Rare earth minerals (REMs) contain rare earth elements (REEs) that are important in modern technologies due to their unique magnetic, phosphorescent, and catalytic properties. However, REMs are not only non-renewable resources but also non-uniformly distributed on the Earth’s crust, so the processing of REE-bearing secondary resources via recycling is one potential route to ensure the long-term sustainability of REE supply. Flotation—a method that separates materials based on differences in their surface wettability—is a process applied for both mineral processing and recycling of REEs, especially when the particles are fine and/or a high-purity product is required. In this review, studies about rare earth flotation from 2012 to 2021 were systematically reviewed using the PRISMA guideline. It was found that most REM flotation research works focused on finding better collectors and depressants while, for recycling, studies on advanced flotation techniques like froth flotation, ion flotation, solvent sublation, electroflotation, and adsorbing colloid flotation with an emphasis on the recovery of dissolved REEs from aqueous solutions dominated.
Efficient and sustainable secondary sourcing of Rare-Earth Elements (REE) is essential to counter supply bottlenecks and the impacts associated with primary mining. Recycled electronic waste (E-waste) is considered a promising REE source and hydrometallurgical methods followed by chemical separation techniques (usually solvent extraction) have been successfully applied to these wastes with high REE yields. However, the generation of acidic and organic waste streams is considered unsustainable and has led to the search for “greener” approaches. Sorption-based technologies using biomass such as bacteria, fungi and algae have been developed to sustainably recover REE from e-waste. Algae sorbents in particular have experienced growing research interest in recent years. Despite its high potential, sorption efficiency is strongly influenced by sorbent-specific parameters such as biomass type and state (fresh/dried, pre-treatment, functionalization) as well as solution parameters such as pH, REE concentration, and matrix complexity (ionic strength and competing ions). This review highlights differences in experimental conditions among published algal-based REE sorption studies and their impact on sorption efficiency. Since research into algal sorbents for REE recovery from real wastes is still in its infancy, aspects such as the economic viability of a realistic application are still unexplored. However, it has been proposed to integrate REE recovery into an algal biorefinery concept to increase the economics of the process (by providing a range of additional products), but also in the prospect of achieving carbon neutrality (as large-scale algae cultivation can act as a CO2 sink).
Graphical abstract
As we enter the twenty-first century, the field of hydrometallurgy has emerged as a predominant force in extractive metallurgy, emphasizing the need for revitalization of various technologies applied to extractive metallurgy. As there have been numerous rethinking of the way we approach the field of extraction metallurgy, several developments have been introduced. In this paper, three areas of new developments in hydrometallurgy have been selected, and some impacts in metal extraction are discussed. (A) Thermodynamic calculations allow us to understand the effect of anions on the solubility of metal compounds. (B) Introduction of non-aqueous media, such as ionic liquids and deep eutectic solvents, may represent a paradigm shift in the broad sense of hydrometallurgy in the future. (C) A combination of two or more processes, such as electrochemical cell and membrane technologies, may induce a synergistic effect in the metal production and separation processes.
Phosphogypsum (PG) is an industrial by-product of the transformation of phosphate rocks. For decades, PG has been a source of environmental concern due to the massive amount produced thus far, i.e., 7 billion tons, with a current production rate of 200–280 million tons per year. Phosphate minerals contain various impurities that precipitate and concentrate within PG. These impurities hinder PG usability in various sectors. This paper aims to purify PG using an innovative process based on staged valorization of PG. Initially, PG dissociation by ethylenediaminetetraacetic acid (EDTA) was optimized. After screening of different parameters and monitoring the ionic conductivity of solutions, it was disclosed that a pH-dependent solubilization process in the presence of EDTA resulted in high solubility of PG, up to 11.82 g/100 mL at pH > 11. Subsequently, a recovery of the purified PG by selective precipitation of calcium sulfate dihydrate (CSD) from obtained filtrate through pH adjustment to 3.5 were investigated. An abatement of 99.34% Cr, 97.15% Cd, 95.73% P2O5, 92.75% Cu, 92.38% Al2O3, 91.16% Ni, 74.58% Zn, 72.75% F, 61.43% MgO, 58.8% Fe2O3, 56.97% K2O, and 55.41% Ba was achieved. The process relied on the variation of EDTA chelation properties towards monovalent, divalent, and trivalent cations at different pHs. According to the findings of this study, a staged purification process in the presence of EDTA is an effective method for removing impurities from the industrial PG.
Phosphogypsum (PG) waste is a by-product generated from wet-process phosphoric acid (H3PO4) manufacturing during phosphate rock decomposition. Worldwide, the annual production of PG ranges between 100 to 300 million tons, with only a few quantities utilized in several application domains (about 15%), the unused PG is usually discharged into the sea or stocked in large stockpiles with potential serious human and environmental risks. Therefore, in this review article we have studied and discussed the possible alternative ways for PG waste recycling and use. Indeed, this waste material could be considered as a mineral resource of secondary raw materials within the scope of a circular economy. An inclusive bibliographic search, dealing with our review’s objectives, was performed according to the two famous-databases: Web of Sciences and Scopus. After different selecting processes, about 153 articles are found. PG is used in several sectors, including agriculture, as well as in the brick and cement industry, and road construction. Other applications are reported in this study such as PG conversion to valuable products and rare earths elements (REEs) extraction. In the same context and in the sense of reducing greenhouse gasses emissions (GHGs), PG is often used as a calcium source for CO2 mineral sequestration. In addition, different methods of treatment and purification, techno�economic, life cycle and environmental assessment of the PG recycling, and valorization technologies are summarized and reported in this review. Finally, recent technologies used for extracting REEs from PG were investigated. The main results, conclusions, and recommendations reported here could considered as a guide for future studies, and also should be of benefit to scientists, chemists and engineers interested in the utilization/ treatment of PG.
PurposeThe present study was aimed to evaluate the fungal resistance level toward lanthanum as well as the influence of La on the development of fungi isolates also, assessing their biosorption and bioaccumulation capacity.Material and Methods
Spray technique of lanthanum was used for fungi growth, then testing each fungi tolerance index and biosorption capacity for lanthanum.ResultsOnly one fungi strain from three could tolerate until 3500 ppm La which undergoes a morphological, gene sequencing and phylogenetic analysis to be a strain MK457457.1 of Aspergillus niger. Aspergillus showed a high biosorption capacity in the synthetic concentrations with a removal percent of 99.89 and 84.70 at 200 and 3500 ppm respectively, this result was confirmed by scan electronic microscope (SEN) and energy dispersive X-ray (EDX) analysis. On testing Aspergillus on concentrated rare earth sample derivative from monazite from nuclear materials authority, Aspergillus showed a high removal percent even in the presence of many metals’ competition and interference, the removal percent activity of Aspergillus niger showed a high affinity in the REEs concentrated monazite sample for La, Ce, Nd and Dy recording 77.26, 64.29, 59.87 and 94.42 respectively.DiscussionFungi has a strong ability to adapt with the environmental stress as metal pollution with an improvement to mineral bioleaching, this may be due to the cell wall composition which includes 80–90% polysaccharides, proteins, lipids, polyphosphates, inorganic ions and other biosorption agents, accompanied with the extracellular biodegradative enzymes secretion and the siderophores or polymers, all this factor produce an excellent metal-binding and bioleaching-biosorption properties.Conclusion
Fungi were considered as a promising microorganism that helps in a great form in bioremediation and cleaning the environment and soil and from many metals to be able for its reuse.
The transition of the mineral processing sectors, which depend mainly on various petroleum-origin chemicals, to the green industry based on the production of greener materials and the reduction of carbon footprints, is mandatory due to the growing concerns regarding the extensive environmental impact of the mining industry. In this context, biological ore beneficiation is spurring increasing interest from scientists and industrials. The latest scientific developments in bio-metallurgy have allowed it to exploit biotechnologies in the flotation process as a novel/cleaner approach for separating gangue materials from valuables minerals. Current fundamental research projects have focused on the progress of biotechnology and the employment of biopolymers, microorganisms, and their metabolites, as well as plant-derived biosurfactants in the emerging field of bioprocessing, particularly bioflotation. Almost all studies on flotation have focused on chemical and physical parameters, and the role of natural biosurfactants remains little explored. This review presents a thorough understanding of the bioflotation concept by assessing previous research on several elements of bioflotation, including the impacts of biotechnology and operating factors (pH, biomass, and biosurfactants concentration), probable mechanisms, and unexplored areas, but from various pragmatic viewpoints. Recent studies are summarized by categorizing microorganisms, plants, and biopolymers based on their bioflotation performances. Furthermore, the most recent research investigations on biological flotation of specific minerals (salt-type sulphide and oxide) are reviewed. Finally, critical challenges of bioflotation are discussed, and novel perspectives are provided to contribute to solving the difficulties faced in its implementation.
Graphical abstract
Contemporary industrial processes and the application of new technologies have increased the demand for rare earth elements (REEs). REEs are critical components for many applications related to semiconductors, luminescent molecules, catalysts, batteries, and so forth. REEs refer to a group of 17 elements that have similar chemical properties. REE mining has increased considerably in the last decade and is starting an REE supply crisis. Recently, the viability of secondary REE sources, such as mining wastewaters and acid mine drainage (AMD), has been considered. A strategy to recover REEs from secondary water-related sources is through the usage of adsorbents and ion exchange materials in preconcentration steps due to their presence in low concentrations. In the
search for more sustainable processes, the evaluation of synthetic polymers and natural source materials, such as cellulose-based materials, for REE capture from secondary sources should be considered. In this review, the chemistry, sources, extraction, uses, and environmental impact of REEs are briefly described to finally focus on the study of different adsorption/ion exchange materials and their performance in capturing REEs from water sources, moving from commercially available ion exchange resins to cellulose-based materials.
The leaching of rare earth elements (REEs) from secondary resources is exponentially increasing to supply the widespread range of high-tech applications of these elements including phosphors lighting materials, catalysis and permanent magnets. Phosphate fertilizer byproducts including phosphogypsum (PG) were identified as a potential alternative resource of REEs, not only to face the expansion of market demand, but also to achieve a sustainable management of REE resources. This study reports the leaching of REEs from PG using methanesulfonic acid (MSA) as a green organo-sulfonic acid in comparison with other acids such as p-toluenesulfonic acid (PTSA) and hydrochloric acid (HCl). MSA achieved the highest leaching efficiency of 78% with low solubility of PG under the operating conditions of 3 M, solid to liquid ratio (S/L) of 1/8, 120 min and 25 °C. The optimized leaching process was also modeled using shrinking core theory to assess the kinetics behavior of the system and to enable the determination of the predominant mechanisms. It was demonstrated that the leaching is governed by a product layer diffusion-controlled model with an activation energy of 2.73 kJ mol−1. The cleaned PG after leaching could greatly meet the quality requirements of the building materials industry.
Rare earth elements (REEs) are metals including the 15 lanthanides together with Yttrium and Scandium. China is the leading country in their exploitation and production (∼90%). REEs are necessary for the production of several technological devices. This extended use of REEs has raised concerns about human health safety. In this review, we investigated the hazard of REEs to human health and the main gaps into the knowledge like as the need to develop further focused research activity. We categorized the research papers collected into eight main sections: environmental exposure, association of REEs with health problems, exposure to REEs due to lifestyle, REE exposure through the food chain, Gd contrast agents causing health problems, occupational REE exposure, and cytotoxicity studies of REEs. This review provided information about the exposome of REEs (the exposure of REEs to the human body), the existing research data, and the gaps that require attention and must be further investigated. More than one third of the literature about REE toxicity to human health concerns their cytotoxicity to human cell lines, while hair, blood serum and blood are the most studied matrices. The main results evidenced that REEs can enter human body via several routes, are associated with numerous diseases, can cause ROS production, DNA damage and cell death, and are more toxic to cancer cells than normal cells.
Research into the incorporation of cerium into a diverse range of catalyst systems for a wide spectrum of process chemistries has expanded rapidly. This has been evidenced since about 1980 in the increasing number of both scientific research journals and patent publications that address the application of cerium as a component of a multi-metal oxide system and as a support material for metal catalysts. This review chronicles both the applied and fundamental research into cerium-containing oxide catalysts where cerium’s redox activity confers enhanced and new catalytic functionality. Application areas of cerium-containing catalysts include selective oxidation, combustion, NOx remediation, and the production of sustainable chemicals and materials via bio-based feedstocks, among others. The newfound interest in cerium-containing catalysts stems from the benefits achieved by cerium’s inclusion, which include selectivity, activity, and stability. These benefits arise because of cerium’s unique combination of chemical and thermal stability, its redox active properties, its ability to stabilize defect structures in multicomponent oxides, and its propensity to stabilize catalytically optimal oxidation states of other multivalent elements. This review surveys the origins and some of the current directions in the research and application of cerium oxide-based catalysts.
Cladding-pumped erbium (Er3+)/ytterbium (Yb3+)-co-doped fiber amplifiers are more advantageous at high output powers. However, this amplification technique also has potential in telecom-related applications. These types of amplifiers have complex properties, especially when considering gain profile and a pump conversion efficiency. Such metrics depend on the doped fiber profile, absorption/emission spectra, and the input signal power. In this context, we design, build and characterize an inhouse prototype of cladding-pumped Er3+/Yb3+-co-doped fiber amplifier (EYDFA). Our goal is to identify the EYDFA configuration (a co-doped fiber length, pump power, input signal power) suitable for signal amplification in a multichannel fiber-optic transmission system with a dense wavelength allocation across the C-band (1530–1565 nm). Our approach involves experimentally determining the Er3+/Yb3+-co-doped fiber’s parameters to be used in a simulation setup to decide on an initial EYDFA configuration before moving to a laboratory setup. An experimental EYDFA prototype is tested under different conditions using a 48-channel dense wavelength division multiplexing (DWDM, 100 GHz) system to evaluate the absolute gain and gain uniformity. The obtained results allow the cladding pump amplifier’s suitability for wideband signal amplification to be assessed. The developed prototype provides >21 dB of gain with a 12 dB ripple within 1534–1565 nm. Furthermore, we show that the gain profile can be partially flattened out by using longer EYDF spans. This enhances signal amplification in the upper C-band in exchange for a weaker amplification in the lower C-band, which can be marginally improved with higher pump powers.
Supramolecular chemical strategies for Rare Earth (RE) element separations are emerging which amplify the small changes in properties across the series to bias selectivity in extraction or precipitation. These advances are important as the REs are crucial to modern technologies yet their extraction, separation, and recycling using conventional techniques remain challenging. We report here a pre-organised triamidoarene platform which, under acidic, biphasic conditions, uniquely and selectively precipitates light RE nitratometalates as supramolecular capsules. The capsules exhibit both intra- and intermolecular hydrogen bonds that dictate selectivity, promote precipitation, and facilitate the straightforward release of the RE and recycling of the receptor. This work provides a self-assembly route to metal separations that exploits size and shape complementarity and has the potential to integrate into conventional processes due to its compatibility with acidic metal feed streams.
We reconstruct paleoredox conditions in the Western Equatorial Atlantic (WEA) over the glacial-interglacial cycle (~130 ka) by using new high-resolution REEs data and their anomalies from a marine sediment core (GL-1248) collected from the equatorial margin off the continental shelf of NE Brazil. This approach aims to improve the understanding of the dynamics of paleoclimatic and sedimentary inputs on the coast of northeastern Brazil. Marine sediments were analyzed via Mass Spectrometry (ICP-MS) after total digestion with HF/HNO3. REEs proxies are a useful tool in understanding the transport and origin of sediments due to their physicochemical properties. Our data showed the Parnaíba River was the main source of REEs content in the western South Atlantic. Fe minerals (Fe-oxyhydroxides) produced via weathering of continental and tropical soils were the principal REE-carrier phase during transportation and ultimate deposition at core site GL-1248. Several regional climatic factors mainly rainfall changes contributed significantly to continental-REEs erosion of sedimentary layers of the Parnaíba Basin, and transport and deposition of the mobilized REEs from the continent to the study site. Furthermore, changes in the negative Ce-anomaly showed low variation along the core indicating a reduction in deep ocean oxygenation during the interglacial relative to the last glacial period. That variation, probably, was associated with glacial-interglacial variations in sea level with the exposure of the continental shelf. The origin of positive Eu anomalies in siliciclastic sediment, also observed in the core, was explained by preferential retention by feldspars such as plagioclases and potassium feldspars mostly from the assimilation of felspar during fractionation crystallization of felsic magma in the Parnaíba basin since the Last Interglacial.
The biomass of a yeast stain of Wickerhamomyces anomalus was evaluated as a natural biosorbent for the removal of Acid Red14 dye (AR14) in batch experiments. The outcome revealed a maximum biosorption capacity of 71.37 mg g⁻¹. Biosorption kinetic followed both the pseudo-second-order and intra-particle-diffusion model, while thermodynamic parameters showed a spontaneous and endothermic nature of the biosorption process. The Freundlich model was the best-fitting isotherms, suggesting a monolayer biosorption via chemisorption at homogeneous sites on the yeast surface. Next, the physicochemical characterization of W. anomalus biomass before and after biosorption using scanning electron microscopy coupled with X-ray spectroscopy, and the Fourier-transforms infrared spectroscopy indicated the involvement of various functional groups (amino, carboxyl, hydroxyl, and carbonyl groups) in AR14-biosorption. Also, the zeta potential of cells at a negative charge, and the acidic value of the zero-charge point confirmed the predominance of anionic groups in the cell wall. Hence, H-binding, π-π, and n-π interactions are likely to participate in the biosorption mechanism. Additionally, the influence of batch conditions on the decolorization capacity was statically screened and optimized using Plackett–Burman and Box–Behnken design, respectively. Results show that biomass dosage is the significant factor having a positive influence on the discoloration rate, while a negative correlation was found for dye concentration and high pH values. Maximum decolorization (77%) was achieved at pH level (3–4), with dye concentrations (50–75 mg L⁻¹) and yeast biomass 1.25 g L⁻¹. These results suggest that W. anomalus might be exploited as an effective, inexpensive, and environmentally friendly biosorbent.
Rare-earth element (REE) demand is expected to increase by a factor of up to 7 by 2040. Recycling avoids the significant hurdles associated with opening new mines, but collection and disassembly of REE-containing devices are barriers. Absolute and relative abundances of REEs and co-occurring constituents differ significantly in secondary compared to primary sources, presenting challenges and opportunities. REE concentrations are typically low, but manufactured devices include only the desired REE, avoiding the “REE balance problem” that besets natural ores. Fewer REEs need to be separated, as compared to separation of the entire lanthanide series. Co-recovery of precious (e.g., Au, Ag, Pt) or base metals (e.g., Cu, Sn, Zn) from e-wastes can offset recycling costs. Some examples of recently developed approaches for REE extraction and separation are presented here, with an emphasis on methods offering environmental benefits such as lower toxic chemical usage and reduced energy costs.
Graphical abstract
Rare earth elements (REEs) are important raw materials for green technologies. However, REE mining and production uses techniques that are often not environmentally sustainable. Life cycle assessment (LCA) is a well-recognized method for evaluating the environmental impacts of products and technologies. This article provides an overview of the environmental impacts based on published LCA results of primary REE production. Existing major REE deposits (Bayan Obo in China, Mountain Pass in the United States, Mount Weld in Australia, ion-adsorption deposits in several Chinese southern provinces) and currently possible production routes are compared. Alternative minerals, such as eudialyte, are also discussed. The article shows which environmental effects can be minimized by technology optimization and environmental safety strategies. Additionally, some of the environmental impacts discussed, may be difficult to mitigate, as they depend on the mineral type. Activities along the complex process chain of REEs production that have particularly high environmental impacts are identified.
Graphical abstract
The skyrocketing demand and progressive technology have increased our dependency on electrical and electronic devices.
However, the life span of these devices has been shortened because of rapid scientific expansions. Hence, massive volumes
of electronic waste (e-waste) is generating day by day. Nevertheless, the ongoing management of e-waste has emerged as
a major threat to sustainable economic development worldwide. In general, e-waste contains several toxic substances such
as metals, plastics, and refractory oxides. Metals, particularly lead, mercury, nickel, cadmium, and copper along with some
valuable metals such as rare earth metals, platinum group elements, alkaline and radioactive metal are very common; which
can be extracted before disposing of the e-waste for reuse. In addition, many of these metals are hazardous. Therefore, e-waste
management is an essential issue. In this study, we critically have reviewed the existing extraction processes and compared
among different processes such as physical, biological, supercritical fluid technologies, pyro and hydrometallurgical, and
hybrid methods used for metals extraction from e-waste. The review indicates that although each method has particular merits
but hybrid methods are eco-friendlier with extraction efficiency > 90%. This study also provides insight into the technical
challenges to the practical realization of metals extraction from e-waste sources.
This review explores the potential of separating and recycling rare earth elements (REEs) from different energy conversion systems, such as wind turbines, electric vehicles batteries, or lighting devices. The REEs include 17 elements (with global production of 242 kilometric tons in 2020) that can be found abundantly in nature. However, they are expensive and complicated to extract and separate with many environmental challenges. The overall demand for REEs is continuously growing (with a 10% yearly increase) and it is quite clear that recycling has to be developed as a supply strategy in addition to conventional mining. However, the success of both mining and recycling depends on appropriate separation and processing technologies. The overall REE recycling situation today is very weak (only 2% of REEs are recovered by recycling processes compared with 90% for iron and steel). The biggest recycling potentials rely on the sectors of lamp phosphors (17%), permanent magnets (7%), and NiMH batteries (10%) mainly at the end-of-life stage of the products. The profitability of rare earth recycling mostly depends on the prices of the elements to accommodate the processing costs. Therefore, end-of-life REE recycling should focus on the most valuable and critical REEs. Thus, the relevant processes, feed, and economic viability warrant the detailed review as reported here.
This study highlights the mechanisms of Pb(II)-phycoremediation using the Pb(II) tolerant strain of Scenedesmus obliquus. First, monitoring of cell growth kinetics in control and Pb(II)-doped medium revealed significant growth inhibition, while the analyses through flow cytometry and Zetasizer revealed no difference in cell viability and size. Residual weights of control and Pb(II)-loaded cells assessed by thermogravimetric analysis were 31.34% and 57.8%, respectively, indicating the uptake of Pb(II) into S. obliquus cells. Next, the use of chemical extraction to distinguish between the intracellular and extracellular uptake indicated the involvement of both biosorption (85.5%) and bioaccumulation (14.5%) mechanisms. Biosorption interaction of Pb(II) ions and the cell wall was confirmed using SEM-EDX, FTIR, zeta potential, zero-charge pH, and contact angle analyses. Besides, the biochemical characterization of control and Pb(II)-loaded cells revealed that the bioaccumulation of Pb(II) induces significant increases in the carotenoids and lipids content, while it decreases in the chlorophyll, carbohydrates, and proteins content. Finally, the metabolomic analysis indicated an increase in the relative abundance of fatty acid methyl esters, alkanes, aromatic compounds, and sterols. However, the alkenes and monounsaturated fatty acids decreased. Such metabolic adjustment may represent an adaptive strategy that prevents high Pb(II)-bioaccumulation in cellular compartments.
Rare earth elements (REE) have applications in various modern technologies, e.g., semiconductors, mobile phones, magnets. They are categorized as critical raw materials due to their strategic importance in economies and high risks associated with their supply chain. Therefore, more sustainable practices for efficient extraction and recovery of REE from secondary sources are being developed.
This book, Environmental Technologies to Treat Rare Earth Elements Pollution: Principles and Engineering: presents the fundamentals of the (bio)geochemical cycles of rare earth elements and which imbalances in these cycles result in pollution.overviews physical, chemical and biological technologies for successful treatment of water, air, soils and sediments contaminated with different rare earth elements.explores the recovery of value-added products from waste streams laden with rare earth elements, including nanoparticles and quantum dots.
This book is suited for teaching and research purposes as well as professional reference for those working on rare earth elements. In addition, the information provided in this book is helpful to scientists, researchers and practitioners in related fields, such as those working on metal/metalloid microbe interaction and sustainable green approaches for resource recovery from wastes.
ISBN: 9781789062229 (Paperback)
ISBN: 9781789062236 (eBook)
ISBN: 9781789062243 (ePUB)
Recently, demands for raw materials like rare earth elements (REEs) have increased considerably due to their high potential applications in modern industry. Additionally, REEs’ similar chemical and physical properties caused their separation to be difficult. Numerous strategies for REEs separation such as precipitation, adsorption and solvent extraction have been applied. However, these strategies have various disadvantages such as low selectivity and purity of desired elements, high cost, vast consumption of chemicals and creation of many pollutions due to remaining large amounts of acidic and alkaline wastes. Membrane separation technology (MST), as an environmentally friendly approach, has recently attracted much attention for the extraction of REEs. The separation of REEs by membranes usually occurs through three mechanisms: (1) complexation of REE ions with extractant that is embedded in the membrane matrix, (2) adsorption of REE ions on the surface created-active sites on the membrane and (3) the rejection of REE ions or REEs complex with organic materials from the membrane. In this review, we investigated the effect of these mechanisms on the selectivity and efficiency of the membrane separation process. Finally, potential directions for future studies were recommended at the end of the review.
The extraction and subsequent separation of individual rare earth elements (REEs) from REE-bearing feedstocks represent a challenging yet essential task for the growth and sustainability of renewable energy technologies. As an important step toward overcoming the technical and environmental limitations of current REE processing methods, we demonstrate a biobased, all-aqueous REE extraction and separation scheme using the REE-selective lanmodulin protein. Lanmodulin was conjugated onto porous support materials using thiol-maleimide chemistry to enable tandem REE purification and separation under flow-through conditions. Immobilized lanmodulin maintains the attractive properties of the soluble protein, including remarkable REE selectivity, the ability to bind REEs at low pH, and high stability over numerous low-pH adsorption/desorption cycles. We further demonstrate the ability of immobilized lanmodulin to achieve high-purity separation of the clean-energy-critical REE pair Nd/Dy and to transform a low-grade leachate (0.043 mol % REEs) into separate heavy and light REE fractions (88 mol % purity of total REEs) in a single column run while using ∼90% of the column capacity. This ability to achieve, for the first time, tandem extraction and grouped separation of REEs from very complex aqueous feedstock solutions without requiring organic solvents establishes this lanmodulin-based approach as an important advance for sustainable hydrometallurgy.
Phosphogypsum (PG) is generated annually from phosphoric acid production. This by-product contains 50% of sulfate (SO42−), which can be recycled biologically. Biorecovery of elemental sulfur (S0) involves firstly converting SO42− into biogenic sulfide using sulfate-reducing bacteria under anaerobic conditions, then oxidizing the sulfide produced into S0 using sulfur-oxidizing bacteria. This study focused on selecting and evaluating natural microbial consortia from SO42− rich biotopes for their application in the initial first step of S0 biorecovery. The PG sample was first comprehensively characterized using ICP-MS/OES, XRD, FTIR, and TGA analyses. Subsequently, SO42− leaching optimization was performed through a design of experiments approach. The analysis revealed that CaSO4 was the major component of the PG (78%), and the optimal parameters for leaching of SO42− from PG were at a NaOH concentration of 7.4% and PG concentration of 158 g.L−1. Furthermore, the MYC-consortium isolated from a hydrothermal niche demonstrated the highest reduction capacity among the studied consortia. It also exhibited the highest performance under SO42− concentrations up to 3.5 g.L−1, salinity levels up to 30 g.L−1, and in the presence of 60 ppm of Zn(II), 3 ppm of Cd(II), and 6 ppm of Pb(II). Moreover, this consortium showed a high capacity for reducing SO42− in the bioreactor (90% after 6 weeks) when utilizing SO42− from the PG-leached solution, as attested by the chemical analyses of the precipitate formed in the bioreactor. This research offers a comprehensive insight into the potential of MYC-consortium to convert leached SO42− from PG into sulfide, which is the most critical step in the S0-biorecovery.
Phosphogypsum (PG), a by-product of the phosphate industry, is high in sulfate, (SO42-), which makes it an excellent substrate for sulfate-reducing bacteria (SRB) to produce hydrogen sulfide. This work aimed to optimize SO42- leaching from PG to achieve a high biological reduction of SO42- and generate high sulfide concentrations for subsequent use in the biological recovery of elemental sulfur. Five SRB consortia were isolated and enriched from: IS (Industrial sludges), MS (Marine sediments), WC (Winogradsky column), SNV (petroleum industry sediments) and PG (stored Phosphogypsum). The five consortia showed reduction activity when using PG leachate (with water) as source of SO42- and lactate, acetate, or glucose as the electron donor. The highest reduction rate (81.5 %) was registered using lactate and the IS consortium (81.5 %) followed by MS (79 %) and PG (71 %). To enhance the concentration of leached SO42- from PG for future utilization with the isolated consortia, PG was treated with NaOH solutions (2 % and 5 %). SO42- release of 97 % was achieved with a 5 % concentration and the resulting leachate was further diluted to target a SO42- concentration of 12.4 g·L-1 for utilization with the isolated consortia. Compared to water leachate, a significantly higher reduction rate was registered (2 g·L-1 of SO42) using the IS consortium, demonstrating limited inhibition effect of sulfide- concentration on SRB functionalities. Moreover, metagenomic analysis of the consortia revealed that using PG as a source of SO42- increased the abundance of Deltaproteobacteria, including known SRB like Desulfovibrio, Desulfomicrobium, and Desulfosporosinus, as well as novel SRB genera (Cupidesulfovibrio, Desulfocurvus, Desulfococcus) that showed, for the first time, significant potential as novel sulfate-reducers using PG as a SO42- source.
The luminescent phosphor powder in the fluorescent lamp constitutes 2% of the lamp’s weight. It can be mentioned that fluorescent wastes are a crucial raw material to produce rare earth oxides. In the present study, microwave leaching process was conducted to dissolve rare earth elements yttrium (Y), europium (Eu), and remaining rare earth elements (REEs) present in the phosphor powder of the fluorescent lamp, and the yields were compared. In the microwave leaching process, the effects of the temperature (80–160 °C), acid type (hydrochloric acid (HCl), nitric acid (HNO3), sulphuric acid (H2SO4)), acid concentration (0.5–6 mol/L), solid to liquid ratio (0.1:10–0.5:10) and reaction time (5–90 min) parameters on leaching efficiencies of varying rare earth elements and calcium were investigated. The highest yield was obtained in the direct microwave leaching of fluorescent waste with the experimental conditions of 6 mol/L HCl, 160 °C, 0.1:10 solid-to-liquid ratio (S:L), and 90 min. Activation energy calculations were made, and kinetic models of the reactions were obtained, and it is observed that Y and Eu dissolution is diffusion-controlled, on the other hand, lanthanum (La), cerium (Ce), and terbium (Tb) were examined to be chemical reaction controlled. Moreover, calcium (Ca) and gadolinium (Gd) seem coherent with the mixed model. Concurrently, mathematical models of all experimental studies are created with the response surface Box-Behnken method and the correlation coefficients of all the models are over 90%.
Coal fly ash (CFA) as a potential resource for rare earth elements and yttrium (REY) has attracted extensive attention over the past few years. This paper focuses on studying microwave systems for the leaching of REY from CFA. Leaching parameters including hydrochloric acid (HCl) concentration, microwave heating time, microwave heating rate, and temperature were assessed. The optimal recovery of 74.91% REY, 86.77% light rare earth elements (LREY), and 34.79% heavy rare earth elements (HREY) are obtained at the conditions of 3 M HCl, T = 220°C, heating rate 39°C/min, and leaching time 30 min. The closed microwave system produces hydrogen chloride fluid or hydrogen chloride gas that is easier to react with CFA than hydrogen ions. It was revealed by the analysis of XRD, particle size, porosity, and SEM that fracture development benefits the entrance of leaching reagents into the inner layer of CFA. A positive linear correlation was found between leaching efficiency and REY³⁺ ionic radius. The stability of the REY-O bond also remains consistent with the ionic radius, leading to behavior differences during the leaching. This work was targeted to provide a theoretical and technological foundation for microwave-assisted HCl leaching for the extraction of REY in CFA.
There is a growing demand for advancing products and renewable technologies worldwide that rely on rare earth elements (REEs), including those directly necessary for a low-carbon energy transition, national security applications, and consumer electronics. This study focuses on current nature-based biological methods (i.e., bioleaching and biosorption) for REEs extraction from electronic wastes (e-wastes) and ore deposits. Comprehensive narrative and systematic reviews of bioleaching and biosorption extraction methods are performed to identify their sustainability challenges and benefits, and highlight the potential pathways that would address the existing gaps. From the narrative review, it is evident that biological methods for REEs extraction are more environmentally friendly than conventional methods currently used in the REE mining industry (e.g., acid leaching and solvent extraction). From the systematic review, it is clear that bioleaching and biosorption research has been a rapidly growing field of interest over the last 10 years, particularly for precious metals extraction (e.g., copper and gold). From both reviews, it is apparent that REEs extraction from domestic ore deposits alone is inadequate, and sustainable REEs recovery from e-wastes is also necessary to meet the growing REEs demand. It is concluded that targeted mixed REEs extraction for specific products can be a potential pathway for sustainable REEs extraction from both ore and e-wastes that would reduce separation costs and emissions from the associated use of harsh chemicals. It is further concluded that nature-based biological REE extraction solutions offer an opportunity to generate significant socio-economic and environmental benefits.
ABSRACT
A comparative study on the uptake of several rare earth element (REE) ions viz. La(III), Ce(III), Pr(III), Nd(III), Sm(III), Gd(III) and Dy(III) was carried out from nitric acid feeds using four extraction chromatography resins which contained the diglycolamide (DGA) ligands, N,N,N’,N’-tetra-n-alkyldiglycolamide with n-pentyl (TPDGA), n-hexyl (THDGA), n-octyl (TODGA) and n-decyl (TDDGA) groups taken in a room temperature ionic liquid (C4mim·NTf2). The uptake of the lanthanides followed the trend: the trend La(III) < Ce(III) < Pr(III) < Nd(III) < Sm(III) < Gd(III) < Dy(III), which is similar to their ionic potential values and the uptake trend of the resins was TPDGA > THDGA > TODGA > TDDGA. The uptake of the metal ions was very high (>10⁴ g/mL) for all the lanthanide ions and was found to increase with increasing nitric acid concentrations. Based on the encouraging batch data, column studies were carried out with all the four extraction chromatography resins with the lanthanide ions used in this work. The column studies were carried out with both individual lanthanide ions and their mixtures. While the loading studies were carried out with 80 mg/L solutions of the metal ions (with respect to each of those) in the mixture of REEs, the elution studies were carried out using a solution of 0.05 M EDTA in 1 M guanidine carbonate. For the column studies involving individual REEs, 550 mg/L solutions were used. The elution profiles appeared to be sharp as >95% elution of the metal ions was accomplished in only 3 mL of the eluent which amounted to only 1.6 bed volumes which is highly impressive. When the studies were carried for the mixture of lanthanide ions, the breakthrough of Dy(III) was last while that of La(III) was seen at much lower volumes which was dependent on the nature of the extractant in the resins.
Essential for smartphones, computers, batteries of hybrid and electric cars, medical scanners and weaponry, rare earth elements (REEs) play a pivotal role in every sphere of life globally. The race is on to develop alternative ways to utilize secondary sources, open new mines, reduce waste and recycle more. From being entirely dependent on China’s REE resources, the researchers and entrepreneurs globally are working towards development of alternative strategies to explore their indigenous resources to be self-sufficient. However, the existing strategies to extract these valuables rely on usage of mineral acids/alkalis. Continued effort on development of sustainable leaching methodologies led to the exploration of organic acids as a potential alternative. Low-molecular-weight carboxylic acids and organosulphonic acids have emerged as highly potent class of lixiviants for REE extraction. The knowledge of their variation in chemical structure and their complex potency towards lanthanides is essential towards development of an industrially viable process. In this review, the efficiency of the different organic acids in leaching REEs from various primary and secondary sources, along with their respective structural relevance has been summarized. This is expected to ameliorate the existing momentum of advancing nature-friendly industrial processes.
Rare earths and Yttrium (REY) are a group of critical metals essential for this electronic and digital era. China is the leading producer of REY with more than 90 % of global export. Mines of REY are limited and the need for green and efficient energies have augmented the demand of REY and it is putting enormous pressure on global production. REY market is predicted to grow from USD 5.3 billion in 2021 to USD 9.6 billion by 2026, at a CAGR of 12.3%. The need of permanent magnets is propelling the demand of the critical group REY and is expected to rise gradually in the coming years. In the present review, we have summarized the minable REY resources and their applications. The requirement for alternative resource is pivotal to meet our future needs. We have extensively reviewed the studies of REY in coal fly ash (CFA). A comprehensive analysis has been done for the REY resources worldwide for the last several decades in coal ash (CFA and bottom ash) and divulged into the application, speciation and distribution for major coal consuming countries like China, India, USA, Russia, UK, Poland etc. individually. We have also made a comparative global study and inferred potential extractable coal ash resources using various parameters such as global average, critical percentage (Cp), outlook coefficient (Cout) etc. for better understanding of economical exploitation.
The separation of rare earth elements by solid phase containing diglycolamide-type ligands is a hot topic. In this study, 2-[2-oxo-2-(1-pyrrolidinyl)ethoxy]acetic acid (PYRDGA) was synthesized and attached to the silica. The binding strength of SiO2@PYRDGA for rare earths showed a single increasing trend with the radius of rare earth atoms. IR and XPS spectra demonstrated that carbonyl oxygen and ether bond oxygen are binding sites for rare earth ions. SiO2@PYRDGA was used for the chromatographic separation of REEs, and the primary separation of 16 REEs was achieved at pH=2.0 using HNO3 solution as the eluent, and La, Ce, Pr, Nd, Sm, and Eu reached the baseline separation level.
Rare earth elements (REEs) are among the most important raw materials in developing new high-tech devices. There are many ways to recover REE ions from diverse sources. A new emerging sustainable technology is Magnetic Nanohydrometallurgy (MNHM). It combines nanotechnology with the hydrometallurgy process as the adsorption. It is one of the most promising due to its simplicity, high efficiency, low cost, environmentally friendly, and excellent efficiency for recovering metal ions. The MNHM uses functionalized-magnetic nano adsorbents (MNAs) with specific complexing agents to extract, concentrate, and separate metal ions as REEs from diluted leaching solutions. The MNAs have the main advantage possess superparamagnetism, easing their separation from aqueous media by an external magnetic field (magnetic separation). This paper compiles the recent results published in the literature on the current synthesis methods, types of assembly, and surface modification procedures for MNAs.
Furthermore, the REEs adsorption behavior onto MNAs is discussed in detail, as the factors affecting adsorption (pH, adsorbent dose, ionic strength, contact time, temperature, REEs concentration). The MNAs generally showed high REEs’ adsorption capacity, fast removal rates, excellent selectivity, and great reusability power. The adsorption process, which mostly follows the Langmuir isotherm, and the pseudo-second-order kinetic model, is typically endothermic, decreasing randomness and being spontaneous. The dominant adsorption mechanisms were surface complexation and electrostatic interaction. The MNHM is a promising cleaner technology compared to other more conventional technologies because it allows multiple reuses of MNAs, and eliminates consuming organic solvent. Most MNAs used in the REEs adsorption are environmentally friendly.
Strategical elements, such as rare earth elements, play a crucial role in the industry, especially in producing high-tech materials. Major global industries have developed a strong dependence on rare earth materials. Every year, there are innovations in industries such as modern technology, green energy, or communications technology, which need more strategic metals to improve investment profitability. This article reviews advances in rare earth separation methods and techniques to guide and recommend the best extractants, depending on leaching conditions and the final target product. Each method for separating and extracting agents is individually revised in terms of the mechanism and interaction of providing rare earth elements. This paper also evaluates past and current trends in these methods and technical extractants and identifies their strengths and weaknesses.
Replacement of conventional hydrometallurgical and pyrometallurgical process used in E-waste recycling to recover metals can be possible. The metallurgical industry has been considered biohydrometallurgical-based technologies for E-waste recycling. Biorecovery of critical metals from phosphor powder from spent lamps is an example of transition to a bio-based circular economy. E-waste contains economically significant levels of precious, critical metals and rare-earth elements (REE), apart from base metals and other toxic compounds. Recycling and recovery of critical elements from E-waste using a cost-effective technology are now among the top priorities in metallurgy due to the rapid depletion of their natural resources. This paper focuses on the perceptions of recovery of REE from phosphor powder from spent fluorescent lamps regarding a possible transition toward a bio-based economy. An overview of the worldwide E-waste and REE is also demonstrated to reinforce the arguments for the importance of E-waste as a secondary source of some critical metals. Based on the use of bioprocesses, we argue that the replacement of conventional steps used in E-waste recycling by bio-based technological processes can be possible. The bio-recycling of E-waste follows a typical sequence of industrial processes intensely used in classic pyro- and hydrometallurgy with the addition of bio-hydrometallurgical processes such as bioleaching and biosorption. We use the case study of REE biosorption as a new technology based on biological principles to exemplify the potential of urban biomining. The perspective of transition between conventional processes for the recovery of valuable metals for biohydrometallurgy defines which issues related to urban mining can influence the mineral bioeconomy. This assessment is necessary to outline future directions for sustainable recycling development to achieve United Nations Sustainable Development Goals.
Acid mine drainage (AMD) poses severe environmental pollution problems due to its high acidity, toxic metals and sulphate content. Current methods to tackle the problem are inadequate and those that work are costly. However, AMD contain the rare earth elements (REEs) which remain very important due to the growing increase in their demand because of their critical and indispensable use in many high-tech industries today. The growing demand of the REEs should be met by an increase in supply. The recovery of REEs from AMD is an important development that would cushion REEs materials supply challenges, thus requires significant consideration. There are several techniques that have been used to recover metal ions from wastewater including AMD. This paper gives a review of typical treatment techniques, innovative developments and examples of the various technologies used for the recovery of REEs from different process solutions, which could be applied in the recovery of REEs from AMD. These techniques include chemical precipitation, solvent extraction, cloud point extraction, ion flotation, ion-exchange, adsorption, molecular recognition technology, magnetic separation and membrane filtration methods. It is clear from the literature surveyed that chemical precipitation, solvent extraction, ion-exchange and adsorption are the most studied techniques for the recovery of REEs from dilute solutions. Precipitation, ion flotation and adsorption processes show significant potential in their application to recover REEs from AMD. However, the complex AMD chemistry with high concentration of heavy metals require development of integrated process flowsheets incorporating the removal of heavy metals prior to precipitation, ion flotation or adsorption to increase the purity of the REE product stream. On the other hand, these flowsheets should be developed with economic feasibility considerations.
Whereas solvent extraction is the preferred method for recovery of rare-earth ions from concentrated aqueous waste streams and pregnant leaching solutions, this method is not recommended for removal of rare-earth ions from diluted aqueous waste streams such as AMD because of the unavoidable contamination of the aqueous phase by organic solvents. Ion-exchange resins and chelating resins also show potential. However, despite ion-exchange being a cheap process, the slow kinetics, large volumes of AMD and the potential of resin poisoning from the impurities in AMD make the process challenging. This necessitates research into developing IX resin suitable for AMD chemistry. In addition, there is recognized prospect of the application of magnetic separation, ionic liquids and cloud point extraction in the recovery of REEs from dilute solutions, although these technologies have not been tested in treating huge volumes of process solutions.
The main objective of this work is to introduce a new green recycling process for recovering valuable metals from electronic waste. One of the fastest-growing electronic waste streams is end-of-life light emitting diodes (LEDs). Due to environmental risk and a worldwide shortage of metals, recycling and recovering their valuable metal is an urgent task. In this study, an innovative bio-hydrometallurgical method for the extraction of valuable metals from end-of-life LED lamps is proposed. The present study evaluated a direct multi-step regulation strategy of waste content to enhance the bio-acid leaching of LED at a high pulp density (40 g/L) using a culture of sulfur-oxidizing bacteria Acidithiobacillus thiooxidans (A. thiooxidans). Through a step-wise feeding strategy (10 g/d), the extraction of the metal was further improved due to balancing of A. thiooxidans population and stabilization of pH, ORP, and sulfuric acid concentration in the bioleaching solution. By comparing the results of multi-step and one-stage contact bioleaching, with multi-step contact bioleaching, Cu, Ni, and Ga extraction yields increased from 67%, 92%, and 39% to 100%, 100%, and 75%. Furthermore, this study demonstrates that the presence/addition of EPS did not only adsorb metal ions but also increased diffusion barriers, thus diminishing metal ion transfer from LED into bioleaching solution for an extended period of time. The multi-step non-contact bio-acid leaching method enhanced strategic critical element leaching yields to 100% from end-of-life LEDs. The final product, enriched in Au and Ag, could be used as a secondary source of precious metals.
The mineral economics of rare-earth elements (REEs) are a crucial factor in the development of new REE mineral exploration and mining projects as well as being defining factors in the security of supply and the determination of the criticality (vulnerability to supply restriction for a variety of factors that can cause supply–demand imbalances) of this group of elements. Production and, more importantly, refining of REEs remains focused in China, leading to a national monopoly that could cause future supply constraints and price volatility. Variations in the demand for individual REEs are demonstrated by December 2020 prices that varied between ~ USD$1.8/kg for samarium (Sm) oxides and ~ USD$2.15/kg for cerium (Ce) oxides to ~ $1305/kg for terbium (Tb) metal, reflecting lower supply and higher demand for Tb relative to Sm and Ce. Price variations between individual REEs are far greater than short-term fluctuations in the prices of an individual REE product. The higher prices for certain REEs, such as neodymium (Nd), dysprosium (Dy), and Tb, create further issues when compared with primary REE supply from orebodies, which is typically dominated by Lanthanum (La), Ce, and the other light REEs (LREEs). This balance problem is just one aspect of the lack of security of supply of REEs, with others including the small size and limited transformational growth potential of the sector relative to other parts of the minerals industry, volatile REE prices, and the geographical distribution of REE mining and (especially) processing and refining. These factors mean that long-term planning in this sector is difficult, especially relative to the ~ 10–20 years needed to bring a mineral exploration project into production. The range of problems affecting REE supply, including securing further domestic supplies within countries that either do not or only have limited current REE extraction or development of secondary resources of these elements, strongly suggests that policymaking and associated geopolitical approaches to secure imports of REEs will be vital tools in reducing the REE criticality and security of supply issues that face many countries who rely on secure access to primary REE supply.Graphical abstractGlobal mineral and metal production from 1956 to 2018 normalized to 1956 production (a) and in per capita terms normalized to 1956 production (b) showing the increase in global mineral and metal use per head of population with dashed lines indicate elements with lower normalized production in 2021 than in 1956. These diagrams effectively demonstrate the increase in the mineral and metal requirements for modern life, especially given the increase in recycling of a significant proportion of these commodities over the same period. The increase in demand for rare-earth elements (REEs) is especially visible, with modern society using ~ 12 times more REE per person in 2018 compared to 1956 and with primary REE production from mining some ~ 32 times higher in 2018 compared to 1956.
With the continuous improvement of technological level, the potential of rare earth elements (REEs) called "industrial gold" in various fields has been continuously explored, and some rare earth elements are regarded as very valuable additives in the high-tech field. With the rapid development of the rare earth industry in recent years, the demand for REEs has continued to rise. Because neighboring rare earth elements have extremely similar physical and chemical properties, in industrial applications, the purity of rare earth elements has high requirements, so the separation between rare earth elements is particularly important. Over time, people have developed a variety of techniques for the separation and recovery of rare earth elements, commonly used including chemical precipitation, ion exchange, solvent extraction, membrane separation, and adsorption, etc. At present, there are few reports on the comprehensive progress of all separation and purification technologies for a single rare earth element. This article mainly summarizes the latest developments in the separation of rare earth elements, evaluates the advantages and disadvantages of various process technologies, and prospects the development prospects of rare earth element separation technologies.
The rare earth elements, a group of metals consisting of the lanthanide series, together with yttrium and scandium, are increasingly important in high technology industries worldwide. Given the need to expand production of these elements, there is a search for processes to obtain them that are less environmentally damaging, since the rare earths production chain is associated with several environmental problems and concerns. Solvent extraction, one of the important steps involved in the obtaining of rare earth elements, is receiving much attention in the scientific and industrial community, with a renewed search for approaches that avoid the use of organic solvents. Among the various options, cloud point extraction and the use of aqueous two-phase systems are alternatives to the use of traditional organic solvents. This review considers these two more environmentally friendly techniques and their use for the extraction and/or separation of rare earth elements. The issues addressed include their potential to replace traditional liquid-liquid extraction, in terms of the efficiency, toxicity, and biodegradability of the components forming the systems, as well as their potential applications and future perspectives.
The ubiquitous and growing global reliance on rare earth elements (REEs) for modern technology and the need for reliable domestic sources underscore the rising trend in REE-related research. Adsorption-based methods for REE recovery from liquid waste sources are well-positioned to compete with those of solvent extraction, both because of their expected lower negative environmental impact and simpler process operations. Functionalized silica represents a rising category of low cost and stable sorbents for heavy metal and REE recovery. These materials have collectively achieved high capacity and/or high selective removal of REEs from ideal solutions and synthetic or real coal wastewater and other leachate source. These sorbents are competitive with conventional materials, such as ion exchange resins, activated carbon; and novel polymeric materials like ion-imprinted particles and metal organic frameworks (MOFs). This critical review first presents a data mining analysis for rare earth element recovery publications indexed in Web of science, highlighting changes in REE recovery research foci and confirming the sharply growing interest in functionalized silica sorbents. A detailed examination of sorbent formulation and operation strategies to selectively separate heavy (HREE), middle (MREE), and light (LREE) REEs from the aqueous sources is presented. Selectivity values for sorbents were largely calculated from available figure data and gauged the success of the associated strategies, primarily: (1) silane-grafted ligands, (2) impregnated ligands, and (3) bottom-up ligand/silica hybrids. These were often accompanied by successful co-strategies, especially bite angle control, site saturation, and selective REE elution. Recognizing the need to remove competing fouling metals to achieve purified REE “baskets,” we highlight techniques for eliminating these species from acid mine drainage (AMD) and suggest a novel adsorption-based process for purified REE extraction that could be adapted to different water systems.