Global demand for rare earth resources and strategies for green mining

Association between prenatal rare earth elements exposure and premature rupture of membranes: Results from a birth cohort study

BACKGROUND

The widespread exploitation and application of rare earth elements (REE) have led to the risk of human exposure and might result in the adverse health effect on pregnant women. However, no epidemiological studies have explored the associations between prenatal REE exposure and premature rupture of membranes (PROM).

OBJECTIVE

We aimed to investigate the associations of maternal urinary REE levels with the risk of PROM.

METHODS

A total of 4897 mother-newborn pairs were recruited from a birth cohort study in Wuhan, China. Urinary concentrations of REE were measured by inductively coupled plasma mass spectrometry (ICP-MS). The associations of prenatal REE exposure with PROM were evaluated using logistic regression models. False discovery rate (FDR) was applied to adjust for multiple testing. Weighted quantile sum (WQS) regression was used to estimate the association of urinary REE mixture with PROM.

RESULTS

With one unit increase (μg/g creatinine) in natural log-transformed urinary REE levels (Ce, Yb, La, Pr, Nd, Eu, Gd, Dy, Ho, Er, Tm), the adjusted ORs (95% CIs) for the PROM were from 1.143 (1.078, 1.211) to 1.317 (1.223, 1.419), and the associations were still observed after FDR adjustment (all P_FDRs < 0.05). The associations were stronger among male infants than female infants. Furthermore, the urinary REE mixture was also associated with the risk of PROM, a quartile increase in the WQS index of REE resulted in ORs (95% CI) for the PROM of 1.494 (1.356, 1.645) in the adjusted model.

CONCLUSIONS

Our findings suggested that prenatal exposure to REE (Ce, Yb, La, Pr, Nd, Eu, Gd, Dy, Ho, Er, and Tm) and REE mixture were associated with the increased risk of PROM. Further studies from different populations are needed to confirm the associations and to explore the mechanisms.

Characteristics of Some Selected Methods of Rare Earth Elements Recovery from Coal Fly Ashes

The article covers the issues related to the characteristics, application, and some methods of rare earth elements (REEs) recovery from coal fly ashes. REEs are elements with growing demand and a very wide range of application, especially when it comes to modern technologies. The conducted analysis and price forecast proved the existing upward tendency, and this confirmed the need to search for new REE sources, among industrial waste (proecological effect). The development of the REE recovery technology would involve solving several problems related to REE speciation, optimization of factors controlling their extractivity and selection of the REE separation method from obtained extraction solutions with a very extreme pH and complicated composition. The paper presented advantages and disadvantages of usually used methods of REE separation from coal fly ashes, like physical and acid–base leaching. It was also presented alternative REE recovery techniques in the form of membrane and biological methods and based on ion liquids (ILs) or chelating agents. The directions of further modifications, which will allow the efficient REE recovery were presented. The aim of this article was to propose specific solutions based on the creation of appropriate multistage method of REE recovery. It will be a combination of magnetic and size separation, acid–base leaching (including roasting in justified cases), removal of matrix elements with ILs (Al, Si, and Fe), and finally REE membrane separation, allowing one to obtain the appropriate process efficiency.

Silicon-hybrid carbon dots derived from rice husk: promising fluorescent probes for trivalent rare earth element ions in aqueous media

As a novel fluorescence probe, Si–CDs could not only be applied to distinguish four groups of different rare earth element ions (REEs) but also exhibit a rapid and sensitive response towards individual Tb3+,Eu3+ and Dy3+.

Copper at the crossroads: Assessment of the interactions between low-carbon energy transition and supply limitations

This article aims to assess the impact of copper availability on the energy transition and to determine whether copper could become critical due to the high copper content of low-carbon technologies compared to conventional technologies. In assessing copper availability through to 2050, we rely on our linear programming world energy-transport model, TIAM-IFPEN. We examine two climate scenarios (2 °C and 4 °C) with two mobility shape, implemented with a recycling chain. The penetration of low-carbon technologies in the transport and energy sectors (electric vehicles and low-carbon power generation technologies) is likely to significantly increase copper demand by 2050. To investigate how tension over copper resources can be reduced in the energy transition context, we consider two public policy drivers: sustainable mobility and recycling practices. Results show that in the most stringent scenario, the cumulative primary copper demand between 2010 and 2050 is found to be 89.4% of the copper resources known in 2010. They also pinpoint the importance of China and Chile in the future evolution of the copper market.

Ammonia nitrogen sources and pollution along soil profiles in an in-situ leaching rare earth ore

The ammonium sulphate ((NH₄)₂SO₄) in-situ leaching process is the most widely used extraction technology for weathered crust elution-deposited rare earth ores (WCED-REOs). Highly concentrated (NH₄)₂SO₄, a representative leaching agent, is often used in the leaching process of WCED-REOs. However, this in-situ leaching process causes nitrogen pollution in the soil, surrounding surface and ground water due to the high concentrations of (NH₄)₂SO₄ solutions used as a long term leaching agent. To date, the mechanism behind the variations in ammonia nitrogen (AN) in deep soil profiles is unclear. We conducted vertical and lateral soil sampling and analyzed the collected samples for soil moisture, pH, ammonia forms, and AN contents in soil profiles deeper than 500 cm in an in-situ leaching mining area of Ganzhou, Jiangxi Province, southern China. The results show that primary chemical pollutants in the soil are derived from residual leaching agents with high acidities and concentrations of AN. Twelve years after the mining process was completed, the mean pH values of the tailings in the mining area were 3.90 and 4.87 in its lower reaches. Due to the presence of chemical residues, the AN concentration was 12-40 times higher than that of the raw ore soil before it was mined. The percentages of different ammonium forms in the rare earth tailing soil were 65%, 30%, and 5% for the water-soluble, exchangeable, and fixed ammonium forms, respectively. The results of this study support effective prevention and remediation treatment of environmental problems caused by AN pollution of the soil in WCED-REOs.

Biological, biomolecular, and bio-inspired strategies for detection, extraction, and separations of lanthanides and actinides

Lanthanides and actinides are elements of ever-increasing technological importance in the modern world. However, the similar chemical and physical properties within these groups make purification of individual elements a challenge. Current industrial standards for the extraction, separation, and purification of these metals from natural sources, recycled materials, and industrial waste are inefficient, relying upon harsh conditions, repetitive steps, and ligands with only modest selectivity. Biological, biomolecular, and bio-inspired strategies towards improving these separations and making them more environmentally sustainable have been researched for many years; however, these methods often have insufficient selectivity for practical application. Recent developments in the understanding of how lanthanides are selectively acquired and used by certain bacteria offer the opportunity for a newer, more efficient take on these designs, as well as the possibility for fundamentally new designs and strategies. Herein, we review current cell-based and biomolecular (primarily small-molecule and protein-based) methods for detection, extraction, and separations of f-block elements. We discuss how the increasing knowledge regarding the selective recognition, uptake, trafficking, and storage of these elements in biological systems has informed and will continue to promote development of novel approaches to achieve these ends.

Emerging technologies for the recovery of rare earth elements (REEs) from the end-of-life electronic wastes: a review on progress, challenges, and perspectives

The demand for rare earth elements (REEs) has significantly increased due to their indispensable uses in integrated circuits of modern technology. However, due to the extensive use of high-tech applications in our daily life and the depletion of their primary ores, REE's recovery from secondary sources is today needed. REEs have now attracted attention to policymakers and scientists to develop novel recovery technologies for materials' supply sustainability. This paper summarizes the recent progress for the recovery of REEs using various emerging technologies such as bioleaching, biosorption, cryo-milling, electrochemical processes and nanomaterials, siderophores, hydrometallurgy, pyrometallurgy, and supercritical CO₂. The challenges facing this recovery are discussed comprehensively and some possible improvements are presented. This work also highlights the economic and engineering aspects of the recovery of REE from waste electrical and electronic equipment (WEEE). Finally, this review suggests that greener and low chemical consuming technologies, such as siderophores and electrochemical processes, are promising for the recovery of REEs present in small quantities. These technologies present also a potential for large-scale application.

Association of prenatal exposure to rare earth elements with newborn mitochondrial DNA content: Results from a birth cohort study

BACKGROUND

Rare earth elements (REE) have been widely used in industry and agriculture. Mitochondria are susceptible to environmental exposure and the change of mitochondrial DNA (mtDNA) content is a proxy indicator of mitochondrial response to damage. However, no study has explored the associations between prenatal repeated REE exposure and newborn mtDNA content.

OBJECTIVES

We aimed to investigate the trimester-specific associations between prenatal REE exposure and newborn mtDNA content.

METHODS

A total of 587 mother-newborn pairs were recruited from Wuhan Children's Hospital between November 2013 and March 2015 in Wuhan, China. Urinary concentrations of REE collected during 3 trimesters were measured by inductively coupled plasma mass spectrometry (ICP-MS). Quantitative real-time polymerase chain reaction (qPCR) was used to measure relative cord blood mtDNA content. We evaluated the trimester-specific associations between prenatal REE exposure and relative cord blood mtDNA content with multiple informant models. False discovery rate (FDR) was used to correct for multiple testing.

RESULTS

After adjustment for potential confounders, prenatal exposure to REE [gadolinium (Gd), dysprosium (Dy), erbium (Er), praseodymium (Pr)] during the third trimester were positively related to cord blood mtDNA content, and the positive associations with cord blood mtDNA content were still observed in Dy, Er, and Pr after FDR correction.

CONCLUSIONS

This prospective study demonstrated that maternal REE exposure during the third trimester was associated with the increased newborn mtDNA content, and the third trimester might be a potential window for sensitivity of newborn mtDNA content to REE exposure. The results might provide evidence of the potential health effects of environmental REE exposure.

An ultrasound-assisted sample preparation method of carbonatite rock for determination of rare earth elements by inductively coupled plasma mass spectrometry

RATIONALE

A method for the determination of rare earth elements in carbonatite rocks by inductively coupled plasma mass spectrometry (ICP-MS) was developed.

METHODS

An alkaline rock, carbonatite, was submitted to ultrasound-assisted extraction (USAE) using an ultrasound bath, a cup horn system or an ultrasound probe. The main USAE parameters were evaluated, such as extraction time (1 to 30 min), extraction temperature (20 to 100°C) and ultrasound amplitude (10 to 100%). For ICP-MS, a desolvation system (APEX-Q) was used to reduce interference in lanthanide determination. To evaluate if the effect of ultrasound improved extraction, experiments were carried out using magnetic stirring (500 rpm) for comparison.

RESULTS

The temperature and ultrasound amplitude optimized for the method were 70°C and 40%, respectively, using dilute nitric acid (3% v/v). Quantitative analyte recoveries were obtained using an ultrasound bath (25 kHz/100 W) which allowed for the simultaneous extraction of twelve replicates.

CONCLUSIONS

All the results obtained with the use of ultrasound systems were better than those obtained with mechanical stirring. The extracts were suitable for ICP-MS analysis and the results were in agreement with those obtained by the reference method (using wet acid digestion). Based on the results, the use of USAE can be considered an alternative method for sample preparation of carbonatite rocks, under milder conditions, for further ICP-MS analysis.

Probing the hydrophobic mechanism of N-[(3-hydroxyamino)-propoxy]-N-octyl dithiocarbamate toward bastnaesite flotation by in situ AFM, FTIR and XPS

HYPOTHESIS

Both hydroxamate and dithiocarbamate groups exhibit a unique bonding characteristic toward rare earth ions. A hydroxamic acid surfactant containing a dithiocarbamate group should possess a specific affinity to hydrophobize bastnaesite [(Ce, La)CO₃F] flotation.

EXPERIMENTS

N-[(3-hydroxyamino)-propoxy]-N-octyl dithiocarbamate (OAHD) was synthesized, and its flotation mechanism toward bastnaesite was investigated by in situ AFM, FTIR, XPS, micro-flotation and contact angle.

FINDINGS

In situ AFM clearly observed that OAHD aggregated on bastnaesite surface, which improved the contact angle and surface hydrophobicity of bastnaesite. FTIR spectra and XPS recommended that OAHD's dithiocarbamate and hydroxamate groups co-anchored on bastnaesite surface through strong chemisorption, which strengthened the bonding affinity of bastnaesite toward OAHD. UV spectra showed that both dithiocarbamate and hydroxamate groups exhibited weak affinity toward Ca²⁺ ions, which benefited OAHD's selective flotation separation of bastnaesite from calcite. The co-adsorption and special hydrophobic structure improved OAHD's flotation performance. As a result, OAHD returned higher flotation selectivity for bastnaesite than OHA (n-octyl hydroxamic acid) which chemisorbed on bastnaesite surface only through the hydroxamate group and used the heptyl as hydrophobic group.

A green method based on living macroalgae for the removal of rare-earth elements from contaminated waters

Low recycling rates of rare earth elements (REEs) are a consequence of inefficient, expensive and/or contaminating methods currently available for their extraction from solid wastes or from liquid wastes such as acid mine drainage or industrial wastewaters. The search for sustainable recovery alternatives was the motivation for this study. For the first time, the capabilities of 6 living macroalgae (Ulva lactuca, Ulva intestinalis, Fucus spiralis, Fucus vesiculosus, Osmundea pinnatifida and Gracilaria sp.) to remove REEs (Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy) from laboratory-prepared seawater spiked with REE solutions were evaluated. The assays lasted 72 h with REEs concentrations ranging from 10 to 500 μg L^-1. The link between REEs uptake and algal metabolism, surface morphology and chemistry were addressed. Kinetics varied among the species, although most of the removal occurred in the first 24 h, with no equilibrium being reached. Lack of mortality reveal that the algae maintained their metabolism in the presence of the REEs. Green alga U. lactuca stood out as the only capable of efficiently removing at least 60% of all elements, reaching removals up to 90% in some cases. The high bioconcentration factors, derived from mass balance analysis (c.a. 2500) support that the REEs enriched algal biomass (up to 1295 μg g^-1) may constitute an effective and environmentally friendly alternative source of REEs to conventional extraction from ores.

New insights on the impacts of e-waste towards marine bivalves: The case of the rare earth element Dysprosium

With the technological advances and economic development, the multiplicity and wide variety of applications of electrical and electronic equipment have increased, as well as the amount of end-of-life products (waste of electrical and electronic equipment, WEEE). Accompanying their increasing application, there is an increasing risk to aquatic ecosystems and inhabiting organisms. Among the most common elements present in WEEE are rare earth elements (REE) such as Dysprosium (Dy). The present study evaluated the metabolic and oxidative stress responses of mussels Mytilus galloprovincialis exposed to an increasing range of Dy concentrations, after a 28 days experimental period. The results obtained highlighted that Dy was responsible for mussel's metabolic increase associated with glycogen expenditure, activation of antioxidant and biotransformation defences and cellular damage, with a clear loss of redox balance. Such effects may greatly impact mussel's physiological functions, including reproduction capacity and growth, with implications for population conservation. Overall the present study pointed out the need for more research on the toxic impacts resulting from these emerging pollutants, especially towards marine and estuarine invertebrate species.

Hydration structure and water exchange kinetics at xenotime-water interfaces: implications for rare earth minerals separation

Hydration of surface ions gives rise to structural heterogeneity and variable exchange kinetics of water at complex mineral-water interfaces. Here, we employ ab initio molecular dynamics (AIMD) simulations and water adsorption calorimetry to examine the aqueous interfaces of xenotime, a phosphate mineral that contains predominantly Y3+ and heavy rare earth elements. Consistent with natural crystal morphology, xenotime is predicted to have a tetragonal prismatic shape, dominated by the {100} surface. Hydration of this surface induces multilayer interfacial water structures with distinct OH orientations, which agrees with recent crystal truncation rod measurements. The exchange kinetics between two adjacent water layers exhibits a wide range of underlying timescales (5-180 picoseconds), dictated by ion-water electrostatics. Adsorption of a bidentate hydroxamate ligand reveals that {100} xenotime surface can only accommodate monodentate coordination with water exchange kinetics strongly depending on specific ligand orientation, prompting us to reconsider traditional strategies for selective separation of rare-earth minerals.

Selective Recovery of Rare Earth Elements from a Wide Range of E-Waste and Process Scalability of Membrane Solvent Extraction

In this study, the scalability of the supported membrane solvent extraction (MSX) process for the recovery of rare earth elements (REEs) from scrap permanent magnets was demonstrated by processing larger quantities of different scrap magnet feedstocks with a membrane area of more than 1 m². The MSX process was successfully employed to recover high-purity REEs in their oxide form (REOs) from a wide range of end-of-life magnet feedstocks including hard disk drives (HDDs), MRI, cell phone, bonded, swarf, and hybrid car magnets. REEs with the purity of more than 99.5 wt %, recovery of more than 95%, and an extraction rate of as high as 9.3 g/(h m²) were recovered from feed solutions containing REEs of up to 46 000 mg/L. It was found that the extraction rate strongly depends on the initial REE concentration in the feed solution and to some extent on the composition of the scrap magnet source. The results demonstrated that MSX is a scalable and versatile process for the recovery of REEs from a wide range of electronic wastes.

Extraction of strategically important elements from brines: Constraints and opportunities

Strategically important elements are those that are vital to advanced manufacturing, low carbon technologies and other growing industries. Ongoing depletion and supply risks to these elements are a critical concern, and thus, recovery of these elements from low-grade ores and brines has generated significant interest worldwide. Among the strategically important elements, this paper focuses on rare earth elements (REEs), the platinum-group metals and lithium due to their wide application in the advanced industrial economics. We critically review the current methods such as precipitation, ion exchange and solvent extraction for extracting these elements from low-grade ores and brines and provide insight into the technical challenges to the practical realisation of metal extraction from these low-grade sources. The challenges include the low concentration of the target elements in brines and inadequate selectivity of the existing methods. This review also critically analyzes the potential applicability of an integrated clean water production and metal extraction process based on conventional pressure-driven membrane and emerging membrane technologies (e.g., membrane distillation). Such a process can first enrich the strategically important elements in solution for their subsequent recovery along with clean water production.

Prenatal exposure of rare earth elements cerium and ytterbium and neonatal thyroid stimulating hormone levels: Findings from a birth cohort study

BACKGROUND

Prior studies have suggested exposure to heavy metals and endocrine disrupting chemicals could disturb the homeostasis of thyroid stimulating hormone (TSH), but no epidemiology study concerning the influence of rare earth elements (REE) exposure during pregnancy on neonatal TSH levels. The present study aimed to investigate the relationships between prenatal REE exposure and neonatal TSH levels.

METHODS

A total of 7367 pregnant women were recruited from Wuhan Children's Hospital between September 2012 and October 2014 in Wuhan, China. Urinary concentrations of cerium (Ce), and ytterbium (Yb) were measured by inductively coupled plasma mass spectrometry (ICP-MS). Immunofluorescence assay was used to detect neonatal TSH levels. The associations between REE exposure and neonatal TSH levels were evaluated using multivariate linear regression models.

RESULTS

The geometric means of maternal urinary Ce and Yb concentrations were 0.060 μg/g creatinine and 0.025 μg/g creatinine, respectively. The results showed that per doubling of maternal urinary Ce and Yb were associated with 4.07% (95% CI: -5.80%, -2.31%), 5.13% (95% CI: -6.93%, -3.30%) decreased neonatal TSH levels respectively in the adjusted model. Sex stratified analysis demonstrated that the decreased neonatal TSH levels were observed both in male infants and female infants, and the decrease was greater in male infants in urinary Ce. There were no significant interactions between maternal urinary Ce, Yb and infant sex (Ce: P for interaction = 0.173, Yb: P for interaction = 0.967).

CONCLUSIONS

Our findings demonstrated that increased maternal urinary Ce and Yb were associated with decreased neonatal TSH levels. Further researches from different populations are warranted to verify the association and to explore the mechanisms.

Successful isolation of a tolerant co-flocculating microalgae towards highly efficient nitrogen removal in harsh rare earth element tailings (REEs) wastewater

Acidic rare earth element tailings (REEs) wastewater with high nitrogen and low COD is the most serious and yet unsolved environmental issue in the rare earth mining industry. The effective and cheap remediation of NH₄⁺-N and NO₃^--N from the REEs wastewater is still a huge challenge. This harsh wastewater environment results in the difficulty for common microbes and microalgae to be survived. In this work, a novel highly tolerant co-flocculating microalgae (the combination of Scenedesmus sp. and Parachlorella sp.) was successfully isolated from the rare earth mine effluent through three-year cultivation. The removal efficiency of total inorganic nitrogen (TIN) by the co-flocculating microalgae cultivation was as high as 90.9%, which is 1.9 times than the average removal efficiency (47.9%) of previously-reported microalgae species in the wastewater with COD/N ratio ranging from 0 to 1. Thus, the residual concentrations of NH₄⁺-N and TIN could reach the Emission Standards of Pollutants from Rare Earths Industry (GB 26451-2011). Along with the high N removal performance, other related characteristics of the co-flocculating microalgae were also revealed, such as high tolerance towards high NH₄⁺-N and strong acid, rapid growth and sedimentation, and simultaneous removal of NH₄⁺-N and NO₃^--N. These algae characteristics were ascribed to the specific co-flocculating community structure covered by extracellular polymeric substances.

Ultra-High Performance of Hyper-Crosslinked Phosphate-Based Polymer for Uranium and Rare Earth Element Adsorption in Aqueous Solution

In this work, a new type of hyper-crosslinked phosphate-based polymer (HCPP) polymerized by bis(2-methacryloxyethyl)phosphate has been developed for uranium and rare earth element (REE) extraction in an aqueous solution. The influence of the pH value, contact time, initial concentration, temperature, and competing ions on uranium adsorption of HCPP is investigated in detail. HCPP exhibits a maximum uranium adsorption capacity of up to 800 mg g^-1 at pH = 6.0 and excellent selectivity toward uranium adsorption over coexisting ions, because of the high affinity between HCPP and uranium ions and dense phosphate groups on the backbone. It also demonstrates high adsorption performance in both simulated seawater with a high salt concentration and a real nuclear industrial effluent. Besides, the crosslinked network structure of HCPP endows this polymer with high chemical stability and reusability. Furthermore, the adsorption mechanism is probed by energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared measurements. It is confirmed that the adsorption of uranium on the adsorbent originates from the interaction between phosphate groups and uranium ions. Meanwhile, HCPP also displays high REE adsorption capacities. This work indicates that the phosphate-based HCPP could be utilized as a promising adsorbent for the effective removal of uranium and REEs from aqueous solution.

Potentially toxic elements in solid waste streams: Fate and management approaches

Solid wastes containing potentially toxic elements (PTEs) are widely generated around the globe. Critical concerns have been raised over their impacts on human health and the environment, especially for the exposure to PTEs during the transfer and disposal of the wastes. It is important to devise highly-efficient and cost-effective treatment technologies for the removal or immobilisation of PTEs in solid wastes. However, there is an inadequate overview of the global flow of PTEs-contaminated solid wastes in terms of geographical distribution patterns, which is vital information for decision making in sustainable waste management. Moreover, in view of the scarcity of resources and the call for a circular economy, there is a pressing need to recover materials (e.g., precious metals and rare earth elements) from waste streams and this is a more sustainable and environmentally friendly practice compared with ore mining. Therefore, this article aims to give a thorough overview to the global flow of PTEs and the recovery of waste materials. This review first summarises PTEs content in various types of solid wastes; then, toxic metal(loid)s, radioactive elements, and rare earth elements are critically reviewed, with respect to their patterns of transport transformation and risks in the changing environment. Different treatments for the management of these contaminated solid wastes are discussed. Based on an improved understanding of the dynamics of metal(loid) fates and a review of existing management options, new scientific insights are provided for future research in the development of high-performance and sustainable treatment technologies for PTEs in solid wastes.

Automated SEM Mineral Liberation Analysis (MLA) with Generically Labelled EDX Spectra in the Mineral Processing of Rare Earth Element Ores

Many rare earth element (REE) deposits have experienced multistage geological enrichment processes resulting in REE bearing mineral assemblages of considerable complexity and variability. Automated scanning electron microscopy (SEM) mineral liberation analysis of such REE ores is confronted by the difficult assignment of energy-dispersive X-ray (EDX) spectra to REE mineral names. To overcome and bypass this problem, a generic and reliable labelling of EDX reference spectra obtained from REE-bearing minerals based on their contents of Si, Ca, F and P in a bulk normalised analysis is proposed. The labelled spectra are then combined into groups of REE-P (~monazite), REE-Ca-Si-P (~britholite), REE-Ca-F (~synchysite) and REE-F (~bastnaesite, parisite, fluocerite). Mixed spectra with low counts for REE from minute REE mineral grains are combined into a separate group. This classification scheme is applied to automated SEM mineral liberation analysis (MLA) data from beneficiation products by comminution and multistage flotation of REE carbonatite ores. Mineral modes, mineral grain size distribution, mineral liberation, mineral locking and mineral grade versus recovery curves based on the analysis of >200,000 particles in a sample can be recognised and interpreted in virtual grain size fractions. The approach as proposed here will allow future process mineralogical studies of REE deposits to be robust and comparable.

Zinc-Adeninate Metal-Organic Framework: A Versatile Photoluminescent Sensor for Rare Earth Elements in Aqueous Systems

Rare earth elements (REEs) are strategically important for national security and advanced technologies. Consequently, significant effort has been devoted towards increasing REE domestic production, including the extraction of REEs from coal, coal combustion byproducts, and their associated waste streams such as acid mine drainage. Analytical techniques for rapid quantification of REE content in aqueous phases can facilitate REE recovery through rapid identification of high-value waste streams. In this work, we show that BioMOF-100 can be used as a fluorescent-based sensitizer for emissive REE ion detection in water, providing rapid (<10 min) analysis times and sensitive detection (parts-per-billion detection limits) for terbium, dysprosium, samarium, europium, ytterbium, and neodymium, even in the presence of acids or secondary metals.

The effects of phytoremediation on soil bacterial communities in an abandoned mine site of rare earth elements

Overexploitation of rare earth elements (REEs) has caused serious desertification and environmental pollution. The ecological restoration of mining areas has attracted increasing attention in China. Soil microbiota is important for successful ecological remediation of abandoned mine land. In this study, soil samples were collected from a restored REE mine site, and the bacterial community composition and diversity were assessed by Illumina high-throughput sequencing targeting the V3-V4 region of the 16S rRNA gene. Microbiota significantly developed in the remediated land. A total of 663,781 effective 16S rRNA gene sequences were obtained, which were classified into 28 bacterial phyla and 3 archaeal phyla. The dominant phyla across all samples (>5% of total effective sequences) were Proteobacteria, Acidobacteria and Firmicutes. Bacterial diversity indices (OTU number, Shannon index and Chao1 index) of the restored soils were higher than those of the tailings and even surpassed those in the unmined site. Redundancy analysis indicated that soil nutrients (soil organic carbon, available phosphorus and total nitrogen) were the dominant factors, followed by soil pH, affecting bacterial community structure. In general, these results suggested that soil amendment and phytoremediation effectively improved the soil environment of the abandoned mine site, which also increased our understanding of the correlation between microbial variation and soil properties in restored REE mine soils.

Cryptic footprints of rare earth elements on natural resources and living organisms

BACKGROUND

Rare earth elements (REEs) are gaining attention due to rapid rise of modern industries and technological developments in their usage and residual fingerprinting. Cryptic entry of REEs in the natural resources and environment is significant; therefore, life on earth is prone to their nasty effects. Scientific sectors have expressed concerns over the entry of REEs into food chains, which ultimately influences their intake and metabolism in the living organisms.

OBJECTIVES

Extensive scientific collections and intensive look in to the latest explorations agglomerated in this document aim to depict the distribution of REEs in soil, sediments, surface waters and groundwater possibly around the globe. Furthermore, it draws attention towards potential risks of intensive industrialization and modern agriculture to the exposure of REEs, and their effects on living organisms. It also draws links of REEs usage and their footprints in natural resources with the major food chains involving plants, animals and humans.

METHODS

Scientific literature preferably spanning over the last five years was obtained online from the MEDLINE and other sources publishing the latest studies on REEs distribution, properties, usage, cycling and intrusion in the environment and food-chains. Distribution of REEs in agricultural soils, sediments, surface and ground water was drawn on the global map, together with transport pathways of REEs and their cycling in the natural resources.

RESULTS

Fourteen REEs (Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Tb, Th and Yb) were plighted in this study. Wide range of their concentrations has been detected in agricultural soils (<15.9-249.1 μg g^-1) and in groundwater (<3.1-146.2 μg L^-1) at various sites worldwide. They have strong tendency to accumulate in the human body, and thus associated with kidney stones. The REEs could also perturb the animal physiology, especially affecting the reproductive development in both terrestrial and aquatic animals. In plants, REEs might affect the germination, root and shoot development and flowering at concentration ranging from 0.4 to 150 mg kg^-1.

CONCLUSIONS

This review article precisely narrates the current status, sources, and potential effects of REEs on plants, animals, humans health. There are also a few examples where REEs have been used to benefit human health. However, still there is scarce information about threshold levels of REEs in the soil, aquatic, and terrestrial resources as well as living entities. Therefore, an aggressive effort is required for global action to generate more data on REEs. This implies we prescribe an urgent need for inter-disciplinary studies about REEs in order to identify their toxic effects on both ecosystems and organisms.

Recovery of Rare Earth Elements by Carbon-Based Nanomaterials-A Review

Modern societies depend strongly on electronic and electric equipment (EEE) which has a side effect result on the large production of electronic wastes (e-waste). This has been regarded as a worldwide issue, because of its environmental impact-namely due to non-adequate treatment and storage limitations. In particular, EEE is dependent on the availability of rare earth elements (REEs), considered as the "vitamins" of modern industry, due to their crucial role in the development of new cutting-edge technologies. High demand and limited resources of REEs in Europe, combined with potential environmental problems, enforce the development of innovative low-cost techniques and materials to recover these elements from e-waste and wastewaters. In this context, sorption methods have shown advantages to pre-concentrate REEs from wastewaters and several studies have reported the use of diverse nanomaterials for these purposes, although mostly describing the sorption of REEs from synthetic and mono-elemental solutions at unrealistic metal concentrations. This review is a one-stop-reference by bringing together recent research works in the scope of the application of carbon nanomaterials for the recovery of REEs from water.

Leaching Characteristics of Low Concentration Rare Earth Elements in Korean (Samcheok) CFBC Bottom Ash Samples

Coal-derived power comprises over 39% of the world’s power production. Therefore, a mass volume of coal combustion byproducts are generated and shifted the extra burden onto the economy and environment. Circulating fluidized bed combustion (CFBC) has been found to be a clean and ultimate technology for Korea’s coal-fired power plants to have effective power generation from low-grade imported coal with reduced emissions. Efforts have been made to broaden the utilization of CFBC coal ash, and to promote sustainable development of CFBC technology. Investigations provided numerous evidences for coal ash to be a potential deposit for rare earths reclamation. However, the basic characteristics and the methods of rare earth mining from the CFBC bottom ash lack detailed understanding and are poorly reported. This study highlighted an insight of the CBFC bottom ash with respect to REEs concentration. Moreover, agents were tested as a means for leaching REEs from Samcheok CFBC bottom ash. The leaching tests were performed in relation to variations in concentration, time and temperature. The results were applied to identify suitable processes to leach REEs from the ash and clarify the potential valuation of CFBC bottom ash. The leaching conditions attained by ANOVA analysis for hydrochloric concentration, temperature, and time of 2 mol L−1, 80 °C, and 12 h, were found to provide a maximum extraction of yttrium, neodymium and dysprosium of 62.1%, 55.5% and 65.2%, respectively.

Selective Recovery of Rare Earth Elements from Coal Fly Ash Leachates Using Liquid Membrane Processes

Coal combustion residues and other geological waste materials have been proposed as a resource for rare earth elements (REEs, herein defined as the 14 stable lanthanides, yttrium, and scandium). The extraction of REEs from residues often generate acidified leachates that require highly selective separation methods to recover the REEs from other major soluble ions in the leachates. Here, we studied two liquid membrane processes (liquid emulsion membranes, LEM, and supported liquid membranes, SLM) and compared them to standard solvent extraction techniques for selective recovery and concentration of REEs from a leachate of coal fly ash. All separation methods involved an organic solution of di(2-ethylhexyl)phosphoric acid dissolved in kerosene or mineral oil and an acid strippant solution of 5 M nitric acid for the liquid-based separations. The LEM configuration, which separated REEs by immersing an acid-in-oil emulsion in the ash leachate, resulted in similar recovery percentages of individual REEs as the conventional solvent extraction approach. The recovery of REEs in the SLM configuration, which involved the impregnation of the solvent in a hydrophobic membrane, was slower than the LEM process. However, the SLM process was notably more selective for the heavy (and higher value) REEs, while the conventional extraction and LEM processes were more selective for the light REEs. A flux-based model of the extraction processes suggested that recovery rates were limited by REE affinity for the solvent chelator in the SLM, while the rates of REEs separation via LEM were limited by diffusive mass transfer across the liquid membrane. Altogether, these results help to identify specific steps in the recovery process that future work should target in the development of scalable liquid membrane separations for REE recovery.

Ecological risk assessment of cerium for tropical agroecosystems

Cerium (Ce) is present in high technology materials and in mineral P fertilizers and the use and discharge of such resources may change the natural status of Ce in the soil environment. Brazilian soils in farming areas are significantly exposed to increased levels of unintentionally-added Ce through intensive input of phosphate fertilizers. The aims of this study were to evaluate the ecotoxicological risk to plants growing in tropical soils contaminated with Ce, as well as to create a database to support future legislation regulating the limits of this element in Brazilian and conceivably other tropical soils. Eight crop species (corn, sorghum, rice, wheat, soybeans, sunflower, radish, and beans) were exposed to a Ce concentration gradient in two typical tropical soils (Oxisol and Inceptsol), and an artificial soil. Our findings showed that among the endpoints measured, Ce phytotoxicity was more pronounced on shoot dry matter than on percent germination and germination speed index. Sensitivity of plants is species specific and our data showed that sunflower and radish exposed to Ce were the most sensitive crop species. Soil properties such as pH, cation exchange capacity, and organic carbon may have influenced the severity of Ce phytotoxicity. Because of that, the Oxisol contaminated with this element caused higher phytotoxicity than the other soils tested. Our risk assessment results (hazardous concentration, HC₅ = 281.6 mg Ce kg^-1) support the idea that unintentional Ce input through P fertilizers does not pose a risk to soils of Brazilian agroecosystems.

What Happens after the Rare Earth Crisis: A Systematic Literature Review

Rare earths (REs) play an important role in modern life, and have been the focus of global attention in recent years. As a result, the number of scientific publications has grown enormously, increasing the need for understanding the knowledge base of various research streams and their emerging branches. The economic analysis of REs has also augmented steadily. Nevertheless, the relevant literature is rather fragmented concerning the thematic topics. To respond to this, a systematic review in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and a bibliometric analysis were developed to offer a systematic and holistic literature review of the economic research on REs. This review incorporates studies of REs regarding aspects of supply, price, export policy, international trade, relationship with clean energy, and sustainability. The database of this review includes a set of 85 systemically selected state-of-the-art articles from five databases, including Web of Science, Science Direct, Springer, Proquest, and China National Knowledge Infrastructure (CNKI) that were published after the rare earth crisis, covering empirical and theory research conducted in different countries with different resource endowments. The results show that the majority of the economic research studies have been conducted in the past six years. Furthermore, among the six categories, the most popular research trend is sustainability. Some possible opportunities for future research are also illustrated in this paper.

Biomineralization and Bioaccumulation of Europium by a Thermophilic Metal Resistant Bacterium

Rare earth metals are widely used in the production of many modern technologies. However, there is concern that supply cannot meet the growing demand in the near future. The extraction from low-grade sources such as geothermal fluids could contribute to address the increasing demand for these compounds. Here we investigated the interaction and eventual bioaccumulation of europium (Eu) by a thermophilic bacterium, Thermus scotoductus SA-01. We demonstrated that this bacterial strain can survive in high levels (up to 1 mM) of Eu, which is hundred times higher than typical concentrations found in the environment. Furthermore, Eu seems to stimulate the growth of T. scotoductus SA-01 at low (0.01-0.1 mM) concentrations. We also found, using TEM-EDX analysis, that the bacterium can accumulate Eu both intracellularly and extracellularly. FT-IR results confirmed that carbonyl and carboxyl groups were involved in the biosorption of Eu. Infrared and HR-XPS analysis demonstrated that Eu can be biomineralized by T. scotoductus SA-01 as Eu2(CO3)3. This suggests that T. scotoductus SA-01 can potentially be used for the biorecovery of rare earth metals from geothermal fluids.

Pb speciation in rare earth minerals and use of entropy and fuzzy clustering methods to assess the migration capacity of Pb during mining activities

Ionic rare earth mining is of strategic importance in China; however, the heavy metal pollution it causes is of great concern, both at home and abroad. Data on Pb speciation at a rare earth mine were used to analyse the migration capacity of Pb during the process of ore leaching. The major factors thought to influence the migration capacity of Pb, including the clay mineral content, soil pH, oxidation-reduction potential, organic matter content, and cation exchange capacity (CEC), were quantified. Entropy and fuzzy clustering methods were used to identify the most predictive factors. The results showed that the clay mineral content of the soil exerts the strongest influence on the migration capacity of Pb in rare earth mines; the other factors demonstrated relatively weak influences on the transport processes. The results obtained from the classification of Pb per the potential migration index (PMI) approximated those obtained from fuzzy clustering, and the results of entropy analyses were consistent with those of fuzzy clustering. Thus, the methods upon which the proposed model is based are suitable for predicting the migration capacity of Pb in ore during the mining of ionic rare earth minerals.

Geochemistry and Mineralogy of Rare Earth Elements (REE) in Bauxitic Ores of the Catalan Coastal Range, NE Spain

Karst bauxite deposits are currently investigated as a new resource for rare earth elements (REE) in order to avoid present and future supply shortfalls of these critical metals. The present work focuses on the geochemistry and mineralogy of the REE in karst bauxite deposits of the Catalan Coastal Range (CCR), NE-Spain. It is revealed that the studied bauxitic ores have a dominant breccia and local ooido-pisoidic and pelitomorphic texture. The bauxitic ores are mostly composed of kaolinite and hematite, as well as of lesser amounts of boehmite, diaspore, rutile and calcite. The mineralogy and major element composition indicate incomplete bauxitization of an argillaceous precursor material possibly derived from the erosion of the Mesozoic Ebro massif paleo-high. The studied bauxites are characterized by ∑REE (including Sc, Y) between 286 and 820 ppm (av. 483 ppm) and light REE to heavy REE (LREE/HREE) ratios up to 10.6. REE are mainly concentrated in phosphate minerals, identified as monazite-(Ce) and xenotime-(Y) of detrital origin and unidentified REE-phosphates of a possible authigenic origin. REE remobilization presumably took place under acidic conditions, whereas REE entrapment in the form of precipitation of authigenic rare earth minerals from percolating solutions was related to neutral to slightly alkaline conditions. During the bauxitization process no significant REE fractionation took place and the REE distribution pattern of the bauxitic ores was governed by the REE budget of the precursor material. Finally, adsorption as a main REE scavenging mechanism in the studied CCR bauxite deposits should not be considered, since the presented data did not reveal significant REE contents in Fe-and Mn-oxyhydroxides and clay minerals.

Circumstances of La, Eu, Dy, and Yb Cations Intercalated via Ion Exchange in γ-Zirconium Phosphate

Both α- and γ-zirconium phosphate were examined for use as ion exchangers for recovery of rare earth elements. Trivalent rare earth elements can be partially substituted for protons in the interlayer space, and γ-zirconium phosphate shows a much better ion exchange competency than α-zirconium phosphate. The exchanged cation of the rare earth elements might be related to different amounts of oxygen from P-OH and H₂O, and these rare earth elements were thus positioned at a different separations from the zirconium phosphate layer. The radial structure function (RSF) curve from extended X-ray absorption fine structure data implied that the calibrated M-O distance and coordination number changed with the ionic radius. The calibrated M-O distances from RSF were 2.52, 2.42, 2.38, and 2.28 for La, Eu, Dy, and Yb, respectively. The coordination numbers of oxygen for Yb were approximately 7 and greater than 10 for La and Eu, respectively. These smaller coordination numbers for smaller cations may result from the strong interaction between the cations and the zirconium phosphate layer. The Debye-Waller factor also increased with an increase in the ionic radius. These factors show a strong relation to the coordination state of rare earth elements in the unit cell of the γ-zirconium phosphate and to the interaction strength.

Chelator-induced recovery of rare earths from end-of-life fluorescent lamps with the aid of mechano-chemical energy

Rare-earths (REs) are key components for the transition to a greener energy profile and low carbon society. The elements turn out to be of limited availability in the market, due to the supply-demand issues, exponential price rises, or geopolitics, which has led to a focus on the exploration of secondary sources for RE reclamation. End-of-life (EoL) nickel-metal hydride batteries, permanent magnets, and fluorescent lamps (FL) have been the primary sources for recyclable REs, while the recovery of REs in EoL FL (Ce, Eu, La, Tb, or Y) includes comparatively fewer processing steps than the other potential sources. In the current work, we proposed a simple, energy-efficient protocol for EoL FL processing, using chelators in combination with ball milling. The parameters for optimum chelator-assisted recovery (chelator concentration, solid-to-liquid ratio, solution pH), and milling variables (ball size, ball weight, milling speed, milling duration), were evaluated at room temperature (RT, 25 ± 2 °C). The dissolution of REs with ethylenediaminetetraacetic acid (EDTA), ethylenediaminedisuccinic acid, methylglycinediacetic Acid, or 3-hydroxy-2,2'-iminodisuccinic acid, was compared at RT, while EDTA was used as the reference chelator throughout. Increasing the system temperature from 25 to 135 °C achieved at least double Eu and Y recovery, relative to that at RT, whereas the recovery rate improvement for Ce, La or Tb was insignificant. Mechano-chemical treatment at RT, via wet milling of EoL FL, with chelators, yielded a five order of magnitude increase in Ce, La and Tb recovery, however, plus a two-order increase for Eu or Y, compared with non-abetted operating conditions. It was also found that higher impact energy achieved improved recovery over a reduced milling duration with this technique having the added advantage of minimal acid consumption and reduced effluent production.

A novel evaluation of the effect of lanthanum exposure on plant populations

The accumulation of rare earth elements (REEs) in the environment has recently become a new environmental problem. There have been many studies about the effects of REEs on plant at the individual, organ, cellular and genetic levels. Plants exist in populations under natural conditions, but little is known about the effects of REEs on plant populations. In this study, the effects of lanthanum (III) [La(III)] on the root module growth of soybean (Glycine max L) populations at different densities were investigated by simulating La(III) pollution. Results showed that at La(III) concentrations of 0.40 and 1.20 mM, both the root module growth parameters and leaf photosynthesis parameters were decreased, with 1.20 mM of La(III) causing a more significant decrease. In addition, the above parameters in low-density soybean populations decreased more significantly than those in high-density soybean populations. The above results show that the inhibitory effects of 0.40 and 1.20 mM of La(III) on the growth of root modules are closely related to the inhibition of photosynthesis in soybean population. Moreover, the inhibitory effect of La(III) on the growth of root modules of soybean population is enhanced as the La(III) concentration increases, while is weakened as plant population density increases. This study would provide a reference for the further research on the ecotoxicology of REEs, and show a new perspective and basis for the objective assessment of the environmental risks of REEs.

ONE SENTENCE SUMMARY

La(III) pollution affects the root module growth and photosynthesis in soybean populations, and the effects vary depending on soybean population densities.

Mesoporous SiO2 Nanoparticles: A Unique Platform Enabling Sensitive Detection of Rare Earth Ions with Smartphone Camera

Fast and sensitive detection of dilute rare earth species still represents a challenge for an on-site survey of new resources and evaluation of the economic value. In this work, a robust and low-cost protocol has been developed to analyze the concentration of rare earth ions using a smartphone camera. The success of this protocol relies on mesoporous silica nanoparticles (MSNs) with large-area negatively charged surfaces, on which the rare earth cations (e.g., Eu³⁺) are efficiently adsorbed through electrostatic attraction to enable a "concentrating effect". The initial adsorption rate is as fast as 4025 mg (g min)^-1, and the adsorption capacity of Eu³⁺ ions in the MSNs is as high as 4730 mg g^-1 (equivalent to ~ 41.2 M) at 70 °C. The concentrated Eu³⁺ ions in the MSNs can form a complex with a light sensitizer of 1,10-phenanthroline to significantly enhance the characteristic red emission of Eu³⁺ ions due to an "antenna effect" that relies on the efficient energy transfer from the light sensitizer to the Eu³⁺ ions. The positive synergy of "concentrating effect" and "antenna effect" in the MSNs enables the analysis of rare earth ions in a wide dynamic range and with a detection limit down to ~ 80 nM even using a smartphone camera. Our results highlight the promise of the protocol in fieldwork for exploring valuable rare earth resources.