Valuable Rare Earth Research Articles

A Review of the Occurrence and Recovery of Rare Earth Elements from Electronic Waste.

Electronic waste (e-waste) contains valuable rare earth elements (REEs) essential for various high-tech applications, making their recovery crucial for sustainable resource management. This review provides an overview of the occurrence of REEs in e-waste and discusses both conventional and emerging green technologies for their recovery. Conventional methods include physical separation, hydrometallurgy, and pyrometallurgy, while innovative approaches such as bioleaching, supercritical fluid extraction, ionic liquid extraction, and lanmodulin-derived peptides offer improved environmental sustainability and efficiency. The article presents case studies on the extraction of REEs from waste permanent magnets and fluorescent powders, highlighting the specific processes involved. Future research should focus on developing eco-friendly leaching agents, separation materials, and process optimization to enhance the overall sustainability and efficiency of REE recovery from e-waste, addressing both resource recovery and environmental concerns effectively.

1, 3, 6, 8-pyrene sulfonic acid tetrasodium fluorescent pigment synthesis and security ink production

Colorants used in security inks are special pigments that radiate in the UV region or IR region. Obtained pigments can be from valuable rare earth elements or they can be organic based. Organic-based pigments are generally insoluble in water, which limits their use. For this purpose, an organic-based UV-radiating pigment was synthesized and made water-soluble by forming its salt. With the obtained salt-formed pigment, inkjet ink that can be used in counterfeiting was applied and its printability and resistance properties were determined. In this study, 1, 3, 6, 8-pyrene sulfonic acid tetrasodium salt was synthesized and water-based inkjet inks with hydroxy ethyl cellulose binder were produced. The prepared inks were printed on the paper surface. The color and gloss of the prints obtained were measured both in the visible region and in the UV region. Its optical properties were detected by UV spectroscopy. Strength properties such as light fastness, nitro resistance, alkali resistance, acid resistance, rub resistance, drying time, adhesion and dry film weight of the prints were determined. As a result; Inkjet ink with 1, 3, 6, 8-pyrene sulfonic acid tetrasodium salt was produced and it was concluded that it has good resistance properties.

Selective conversion of spent cracking catalyst to faujasite-structured zeolites

Current recycling strategies for spent catalyst in Fluid Catalytic Cracking (FCC) focus on valuable rare-earth elements (REE) and sometimes include a reuse of spent materials by down-cycling, which hinders a circular economy. Herein, a new procedure for the selective conversion of spent FCC catalysts to FAU-type zeolite without secondary crystalline phases such as sodalite, zeolite P or zeolite A is reported. The steps include a leaching process of REE, followed by thermal activation with sodium hydroxide and acid treatment to get an aluminum-rich feed. The synthesis of FAU-type zeolites with varying Si/Al ratios uses the aluminum-rich catalyst feed and commercial water glass. The experiments show that incorporation of silicate from water glass into the zeolite structure is limited to zeolite products with Si/Al ratio ≤ 2.0. It indicates a flocculation of silicates in higher concentration in competition to the crystallization process of FAU-type zeolites. This is reinforced by the resulting crystals, covered and surrounded with small particles with morphology of silica. Moreover, a clear differentiation between zeolite Y and zeolite X is possible from materials properties with the definite evidence of a mixed phase. The kinetics of feed dissolution and incorporation of impurities, alumina and silica are controlled by the pre-treatment temperature, duration and silicon source. This enables flexible adjustment of the aluminum re-use from spent FCC catalyst, the amount of foreign elements (Fe, Ni, V), phase purity, Si/Al ratio, specific surface area and thermal stability of the final zeolite product. Structural and textural data of the resulting zeolites reveals high crystallinity > 80 %, Si/Al ratios of 1.6–2.0, and specific surface areas up to 780 m2/g.

Application of Low-Pressure Nanofiltration Membranes NF90 and NTR-729HF for Treating Diverse Wastewater Streams for Irrigation Use

The application of low-pressure nanofiltration (NF) was investigated for three different applications: water reuse from acid mine drainage (AMD), surface water containing natural organic matter (NOM) and agricultural reuse of microfiltered biologically treated sewage effluent (MF-BTSE). AMD contains many valuable rare earth elements (REEs) and copper (Cu) that can be recovered with fresh water. The NF90 membrane was investigated for recovery of fresh water from synthetic AMD. A steady permeate flux of 15.5 ± 0.2 L/m2h was achieved for pretreated AMD with over 98% solute rejection. NF90 achieved a high dissolved organic carbon (DOC) rejection of 95% from surface water containing NOM where 80% of the organic fraction was hydrophilic, mainly humics. The NF process maintained a high permeate flux of 52 LMH at 4 bars. The MF-BTSE was treated by NTR-729HF for agricultural reuse. NTR-729HF membranes were capable of rejecting DOC and inorganics such as sulfates and divalent ions (SO42−, Ca2+ and Mg2+) from MF-BTSE, with less than 20% rejection of monovalent (Na+ and Cl−) ions. The sodium adsorption ratio (SAR) was significantly reduced from 39 to 14 after treatment through NTR-729HF at 4 bar. The resulting water was found to be suitable to irrigate salt-sensitive crops.

New hematite method: efficient and enhanced separation of rare earth and iron by alkaline regulation of pH in rare earth chloride solutions

Iron in RECl3 solutions is a detrimental impurity, adversely impacting both the purification efficiency of RECl3 and purity of rare earth compounds. RECl3 solutions employs the neutralization precipitation method for iron removal, leading to iron slag rich in valuable rare earth elements and radioactive thorium. This practice not only results in rare earth resource wastage but also poses significant ecological challenges. This study introduces an innovative hematite method for efficient and enhanced separation of rare earth and iron from RECl3 solutions. This method involves adjusting the solution's pH using alkali in a high-pressure reactor. Results indicate optimal conditions: a OH− to Fe3+ ratio of 1.5:1, temperature at 180°C, duration of 3 hours, and a Fe3+ (as Fe2O3) to Fe2O3 crystal seed molar ratio of 1:1. Under these conditions, the iron slag contains 1.3% REO and 63.69% TFe, with a rare earth loss rate of 0.35% and a TFe removal rate of 90.36%. Thermodynamic analysis reveals that at 25°C, ammonia water adjusts the pH of RECl3 solutions to 2-3, with the presence of Fe(OH)2+ and Fe(OH)2+ in the solution. The potential pH diagram of Ce-Fe-H2O at 180°C indicates that a pH range of -1.87 to 2.99 is crucial for Fe2O3 and Ce3+ formation. SEM analysis shows that the iron slag phase is a densely packed elliptical hematite sphere of approximately 1 micron and contains 0.36% thorium. This new hematite method using alkali-regulated high-temperature and high-pressure conditions for iron removal from RECl3 solutions not only minimizes rare earth loss but also mitigates iron slag's environmental impact. Furthermore, it offers a novel iron removal technique for the smelting industry.

Full-components utilization: Study on simultaneous preparation of sodalite and separation of yttrium from coal gangue by chlorination roasting process

Kaolinite-type coal gangue is a solid waste from coal mining that contains valuable rare earth elements (REE) and kaolinite. The simultaneous recovery of REE and synthesis of functional materials utilizing kaolinite from coal gangue presents an opportunity for full utilization. This study introduces synchronous chlorination volatilization of REE and preparation of sodalite from coal gangue. Thermodynamic analysis revealed xenotime reacts directly with NaCl to produce YCl3 for volatilization with the presence of O2. The effects of various factors on yttrium recovery and sodalite synthesis, including temperature, time, additives, and NaCl dosage, were investigated. Optimal conditions were identified as roasting coal gangue with 13.3 wt% NaCl and 41.7 wt% Na2CO3 at 1000 ℃, resulting in 93.4% yttrium volatilization and a 100% conversion efficiency of sodalite. The addition of Na2CO3 was found to accelerate the transition from aluminosilicate minerals to sodalite, thus achieving an outstanding sodalite conversion efficiency. This approach offers a theoretical and practical foundation for the efficient utilization of solid waste.

Extraction of scandium from bauxite residue by high-pressure leaching in sulfuric acid solution

Rare earth elements, such as yttrium, scandium, neodymium, and praseodymium, have been reported to be associated with minerals in bauxite and transferred to the refining residue when bauxite is refined to alumina (Al2O3) by Bayer Process. In terms of price, scandium is the most valuable rare-earth element in bauxite residue. This research discusses the effectiveness of scandium extraction from the bauxite residue through pressure leaching in sulfuric acid solution. The method was selected to obtain high scandium recovery and leaching selectivity to iron and aluminium. Series of leaching experiments were conducted under variations of H2SO4 concentration (0.5–1.5 M), leaching duration (1–4 h), leaching temperature (200–240 °C), and slurry density (10–30% (w/w)). Taguchi method with L9:34 orthogonal array was adopted to design the experiments. Analysis of Variance (ANOVA) was performed to determine the most influential variables of the extracted scandium. The experimental result and statistical analysis revealed that the optimum condition for scandium extraction was at 1.5 M H2SO4, a leaching duration of 1 h, a temperature of 200 °C, and a slurry density of 30% (w/w). The leaching experiment carried out at this optimum condition resulted in scandium extraction of 90.97% and co-extracted iron and aluminium of 32.44% and 75.23%, respectively. Analysis of Variance showed that solid/liquid ratio was the most influential variable with a contribution of 62%, followed by acid concentration (21.2%), temperature (16.4%), and leaching duration (0.3%).

Estimation of rare earth elements in Indian coal fly ashes for recovery feasibility as a secondary source

Huge amount of coal fly ash is being generated in India and the management of unutilized ash became an environmental issue due to its hazardous nature. Identification of new applications will increase its consumption which in turn reduces the environmental burden. Recently, fly ash was identified as potential secondary source to recover valuable rare earth elements. Considering this, the current study was initiated to quantify the rare earths in Indian coal fly ashes and the generated data was assessed for identifying suitable coal fly ash to recover rare earth elements. Accordingly, eight coal fly ash samples and two Indian coals were collected, acid digested and quantified for rare earths using Triple Quadruple-Inductively Coupled Plasma Mass Spectrometry. Chemical analysis results show that, Ce has highest abundance with concentration values ranging from 88±1.5 – 218±5.8 µg/g and the least concentration was observed for Lu with typical values ranging from 0.5 ± 0.02 – 0.8 ± 0.01 µg/g. Sum of all rare earth's content in analyzed samples was found in the range 234 µg/g to 533 µg/g. Coal fly ash samples, had critical REY content ≥30% (except few samples) and an outlook coefficient ≥0.7 which indicates that some samples can be used as secondary resource for rare earth elements extraction.

Analysis of the Adsorption-Release Isotherms of Pentaethylenehexamine-Modified Sorbents for Rare Earth Elements (Y, Nd, La).

Waste from electrical and electronic equipment (WEEE) is constantly increasing in quantity and becoming more and more heterogeneous as technology is rapidly advancing. The negative impacts it has on human and environment safety, and its richness in valuable rare earth elements (REEs), are accelerating the necessity of innovative methods for recycling and recovery processes. The aim of this work is to comprehend the adsorption and release mechanisms of two different solid sorbents, activated carbon (AC) and its pentaethylenehexamine (PEHA)-modified derivative (MAC), which were deemed adequate for the treatment of REEs deriving from WEEE. Experimental data from adsorption and release tests, performed on synthetic mono-ionic solutions of yttrium, neodymium, and lanthanum, were modelled via linear regression to understand the better prediction between the Langmuir and the Freundlich isotherms for each REE-sorbent couple. The parameters extrapolated from the mathematical modelling were useful to gain an a priori knowledge of the REEs-sorbents interactions. Intraparticle diffusion was the main adsorption mechanism for AC. PEHA contributed to adsorption by means of coordination on amino groups. Release was based on protons fostering both a cation exchange mechanism and protonation. The investigated materials confirmed their potential suitability to be employed in real processes on WEEE at the industrial level.

Sustainable Upcycling of Spent Electric Vehicle Anodes into Solution-Processable Graphene Nanomaterials.

A major transition to electric vehicles (EVs) is underway globally, as countries target reductions in greenhouse gas emissions from the transport sector. As this rapid growth continues, significant challenges remain around how to sustainably manage the accompanying large volumes of waste from end-of-life lithium-ion batteries that contain valuable rare earth and critical materials. Here, we show that high-shear exfoliation in aqueous surfactants can upcycle spent graphite anodes recovered from an EV into few-layer graphene dispersions. For the same hydrodynamic conditions, we report a process yield that is 37.5% higher when using spent graphite anodes as the precursor material over high-purity graphite flakes. When the surfactant concentration is increased, the average atomic layer number reduces in a similar way to that of high-purity precursors. We find that the electrical conductance of few-layer graphene produced using the graphite flake precursor is superior and identify the limitations when using aqueous surfactant solutions as the exfoliation medium for spent graphite anode material. Using these nontoxic solution-processable nanomaterial dispersions, functional paper-based electronic circuit boards were fabricated, illustrating the potential for end-to-end, environmentally sustainable upcycling of spent EV anodes into new technologies.

Recovery of rare earth elements from coal fly ash using enrichment by sodium hydroxide leaching and dissolution by hydrochloric acid

ABSTRACT The most common method to recover valuable rare earth elements from the potential resource coal fly ash is direct leaching in acidic solution. However, the extraction of rare earth elements using only acid leaching is not sufficiently effective due to the presence of Al-Si-based glasses. In the present work, pre-treatment using NaOH leaching was investigated to reduce the content of Al-Si-based phase before subjecting to acid leaching. The treatment at conditions NaOH 5 M, at 100 °C and for 120 min could dissolve 53% of the ash sample, and the rare earth contents were enriched from 267 mg/kg to 556 mg/kg. The NaOH leaching promote the further extraction of rare earth elements in all of acid medias (HCl, HNO3 and H2SO4), and HCl was the most effective leachant. More than 90% of rare earth elements was dissolved in 5 M HCl solution at 50°C after 120 min. The combination of NaOH treatment and HCl leaching presented an effective approach to extract rare earth elements from coal fly ash with enrichment of rare earth element contents, increase the leaching efficiency and avoidance of harmful impacts to the environment due to the conventional pre-treatment using alkaline roasting.

Enhancing rare earth element transfer from phosphate rock to phosphoric acid using an inexpensive fly ash additive

Adding active silica (SiO2) to reduce the free fluoride content is a known method to improve the filterability of phosphogypsum (PG) during wet phosphoric acid (WPA) processing of phosphate rock (PR). Besides, this process can also promote the transfer of valuable rare earth elements (REE) from the PR into the liquid phosphoric acid (PA) stream rather than into the solid PG matrix from which later economic recovery is more challenging. Khouribga PR, that shows total REE concentrations of 577 ppm (328 ppm heavy REE and 249 ppm light REE) of which yttrium (Y) with 240 ppm constitutes the major fraction, is processed at the Jorf Lasfar El-Jadida chemical complex in Morocco that is also home to the country’s largest coal power plant. Fly ash produced during thermal power production, 70% of which is stacked in the immediate vicinity, presently remains mostly unused and consists largely (48%) of silica. In this work the use of fly ash (34 kg per t PR) and pure silica (8.5 kg per t PR) on the transfer of REE from Khouribga PR into the PA and PG stream during dihydrate WPA production was examined. The inexpensive fly ash/silica additive increases the transfer of various REE to the PA stream. For Y an increase of 37% was measured that resulted in a concentration of 48 ppm in the PA stream prior to further concentration by evaporation.

Extraction of REEs (Ce, Tb, Y, Eu) from Phosphors Waste by a Combined Alkali Roasting–Acid Leaching Process

Rare Earth (RE) phosphors waste contains valuable rare Earth elements (REEs), such as cerium, terbium, yttrium, and europium. In industry, the process of NaOH roasting followed by acid leaching is usually used to extract the REEs from the waste in China. Using this process, the leaching efficiencies of cerium and terbium are clearly lower than those of other REEs, which results in uneven extraction of REEs in the waste and low total REE leaching efficiency. The key reason is that the trivalent cerium and terbium in the waste are oxidized into RE oxides during NaOH roasting, which are difficult to dissolve in acid solution. To solve this problem, an optimized process of controlling the oxygen concentration during NaOH roasting is proposed in this paper. The influences of the oxygen concentration, roasting temperature, roasting time, mass ratio of waste phosphor to NaOH, HCl solution concentration, acid leaching temperature, acid leaching time, and liquid–solid ratio on the REE leaching efficiency were investigated. Under the optimum conditions, the leaching efficiencies of cerium and terbium increased dramatically and the total REE leaching efficiency is 99.11%.

Investigation of technogenic deposits of phosphogypsum dumps

The article contains research materials on the storage of man-made deposits, including phosphogypsum dumps. The consequences of long-term operation of phosphogypsum dumps and their negative impact on the environment have been established. The quantitative content of microelements to the soil within the storage of technogenic phosphogypsum deposit was determined. Graphical dependences of phosphorus, manganese, fluorine, mobile sulfur, zinc, nickel content depending on the depth of sampling and distance from phosphogypsum dumps to settlements and the Goryn River are presented. The directions of processing and utilization of the given waste are offered. The elemental composition of phosphogypsum dumps of PJSC "Rivneazot" has been established, in particular, the presence of a group of valuable rare earth elements.

Исследование химического состава промышленных отходов Кадамжайского сурьмяного комбината

This article investigates the chemical composition of industrial waste (dump slag and flotation tailings). This study, in contrast to previous studies, was carried out by chemical, atomic emission, X-ray fluorescence methods. Valuable rare earth chemical elements (ytterbium, yttrium, lanthanum, scandium), valuable chemical elements (antimony, titanium, vanadium, tungsten, niobium, indium, germanium, gallium, tantalum, molybdenum, strontium, beryllium, zirconium, cobalt) and others have been determined. The oxides of elements (SiO2, Al2O3, MgO, CaO, Fe2O3, Na2O, K2O, S, FeO) have been investigated. Toxic elements (arsenic, cadmium, tin, lead). These studies were carried out with the aim of using man-made waste in various sectors of the national economy for the disposal of man-made waste and to improve the environmental situation in the region and reduce material costs for the production of new products.

Selective Biosorption of Valuable Rare Earth Elements Among Co-Occurring Lanthanides

To meet the increasing demand for rare earth elements (REEs) essential for low carbon-intensity energy technologies, new methods are needed for selective REE extraction from unconventional resource...

Sustainable management of spent fluid catalytic cracking catalyst from a circular economy approach

For sustainable growth, an economic model must tend toward a circular system, especially in the field of waste management. This work focuses on the valorization of spent fluid catalytic cracking catalyst from oil refineries, which generate 400,000 metric tons of spent catalyst per year worldwide, most of which is sent to landfills. A new alternative to landfilling is proposed for this waste, based on the combination of acid leaching for the recovery of lanthanum, a valuable rare earth, and the reuse of the leached solid residue as a cement substitute. A comparative life cycle assessment was made, including four environmental impact categories, i.e. global warming, fossil resource scarcity, mineral resource scarcity and water consumption, in order to quantify the potential environmental benefits of secondary lanthanum recovery from industrial waste with respect to primary lanthanum extraction from mineral resources. A maximum of 85.6% La recovery was achieved and 15 wt% of cement can be substituted with leached solid residue without changing the original cement classification. The waste management process presented in this paper promotes the sustainable management of the spent fluid catalytic cracking catalyst and contributes to the development of a new resource for a critical material such as lanthanum. The implementation of this novel waste management process could reduce global warming and mineral resource scarcity but would increase fossil resource scarcity and water consumption in comparison with primary La extraction.

Ultrafast and Stable Adsorption–Desorption Performance for Recovery of Valuable Rare-Earth Ions using High-Density Polyacrylic Acid Brush-Grafted Polypropylene Fibers Optimized by RSM Models

Polyelectrolytes with abundant ionizable groups always possess excellent adsorption capacity for metal ions. However, these polymer chains are limited for direct application, resulting from lacking...

Stable immobilized amine sorbents for heavy metal and REE removal from industrial wastewaters

Stable and immobilized amine sorbents can simultaneously remove/recover cationic and oxyanionic toxic metals plus valuable rare earth elements from industrial and mining effluents prior to discharging into environmental water systems.

D2EHPA is a potential extractant for extraction of europium and samarium from chloride medium

Europium and samarium, the most valuable rare earth metals are broadly used in different areas such as fluorescent, medical materials and samarium-cobalt permanent magnet in the industrial community. Solvent extraction is an extensively applied separation process for collection of high purity rare earth metal ions. Due to the congruent physical and chemical properties of rare earth metal ions, the separation of specific elements from the mixture is ambiguous. In such places solvent extraction process is most efficient because of their ease in terms of the equipment and conditions associated with them. Solvent extraction, using di-2-ethylhexylphosphoric acid (D2EHPA) is the most frequently used industrial extractant for the extraction and separation of rare earth metal ions compared with other extractants. Present report deal with the studies on solvent extraction of europium (III) and samarium (III) from chloride medium using D2EHPA diluted in kerosene. Utmost extraction such as 96.65% Eu(III) and 86% Sm(III) happened at 0.001 mol/L hydrogen ion concentration in the aqueous medium. 100% extraction of Eu (III) and Sm(III) has been noticed with 0.07 mol/L and 0.08 mol/L D2EHPA, respectively. The separation factors of Eu/Co and Sm/Co are 1844.44 and 1556, respectively.