Amounts Of Rare Earth Elements Research Articles

Impact of Rare Earth Elements on CaCO3 Crystallization: Insights into Kinetics, Mechanisms, and Crystal Morphology.

This study investigated the crystallization kinetics and mechanisms of calcium carbonate (CaCO3) in the presence of rare earth elements (REEs) including lanthanum (La), neodymium (Nd), and dysprosium (Dy). Through a comprehensive approach utilizing UV-vis spectrophotometry, powder X-ray diffraction, and high-resolution electron microscopy, we examined the effects of REEs on CaCO3 growth from solution at varying concentrations and combinations of REEs. Our findings highlight that even trace amounts of REEs significantly decelerate the rate of CaCO3 crystallization, also leading to alterations in crystal morphology and mechanisms of growth. The impact of REEs becomes more pronounced at higher concentrations and atomic mass, although the potential formation of poorly ordered REEs carbonate precursor phases can result in a decrease in the REE3+/Ca2+ ratio, influencing the crystallization rate of CaCO3. Vaterite and calcite were identified as the main crystallized polymorphs, with vaterite exhibiting distinct growth defects and calcite developing complex morphologies at higher REEs concentrations and an internal architecture suggesting a nonclassical growth route. We propose that REEs ions selectively adsorb onto different calcite surfaces, impeding growth on specific sites and resulting in intricate morphologies.

Study of rotational dynamic recrystallization during warm compression of an Mg-Zn-Nd-Zr alloy

The dynamic recrystallized grains obtained by rotational dynamic recrystallization (RDRX) mechanism are finer and have fewer defects, which can effectively improve the performance of magnesium alloys. However, the impact of temperature and strain on RDRX is currently unclear. In this study, an extruded Mg-Zn-Nd-Zr alloy with trace amounts of rare earth elements and fine grain size was used as the raw material, and a warm deformation temperature interval was selected, which suppressed the large-angle migration, reduced the activity of twinning, and successfully ensured RDRX as the main recrystallization mechanism. The effects of temperature and strain on RDRX of magnesium alloys were systematically investigated, and it was found that the compression temperature and strain jointly affected the formation of RDRX. The RDRXed grains emerged during the dynamic softening stage and abundantly developed during the dynamic equilibrium stage. The percentage of the RDRXed grains increased with the increase of temperature for temperatures below 290 °C and decreased with the increase of temperature for temperatures above 290 °C at low strain levels (0.4). The percentage of RDRX monotonically increased with the increase of compression temperature at high strain (0.7). The size of the recrystallized grains increased with the increase of compression temperature. The formation of the RDRXed grains could effectively release the local strain and form a strain free region without distortion, resulting in strain softening.

In situ U-Pb isotopic dating method on titanite, and application to determine REE-Fe-Cu mineralization age of the Sin Quyen deposit, Lao Cai province

Titanite (CaTiSiO5) is an important common accessory mineral in hydrothermal deposits, with appreciable amounts of U and Th incorporated into their structures for age dating. Titanite crystals are usually larger than zircon and monazite and may have zoning in texture and geochemistry which represent different parageneses likely related to multiple hydrothermal or mineralization events. In line with the development of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) that has high sensitivity and spatial resolution, in-situ U-Pb isotopic dating method on titanite has become a powerful tool to investigate the ages of different zones from a mineral. Titanite typically accommodates a significant amount of Rare Earth Elements (REEs) and High Field Strength Elements (HFSEs) and the titanite generated from different origins exhibits distinct trace element geochemistry. Therefore, the trace element geochemistry of titanite can serve as an indicator of its formation environment. Titanite occurred in different mineralization stages of the Sin Quyen deposit, making it a suitable mineral for investigating the timing of mineralization. In this paper, we present the U-Pb age of titanite from different stages of the Sin Quyen deposit used to constrain the timing and origin of such events. The hydrothermal titanites are dated by in situ LA-ICP-MS technique and have U-Pb ages of 873±12 Ma and 844±12 Ma which indicate two mineralization/hydrothermal events at the same time, respectively. These ages from the Sin Quyen deposit are well correlated with regional tectono-thermal events during the long-lived Neoproterozoic subduction in the western Yangtze Block.

Rare earth elements in the red, brown, green algae and the seagrass from Kazachya Bay (Crimea, Black Sea)

The present study is focused on the first ever quantification of rare earth elements (REE) in four mass plants of the Black Sea coast of Crimea: the brown alga Gongolaria barbata, the green alga Ulva rigida, the red alga Ceramium ciliatum, and the seagrass Zostera noltei using inductively coupled plasma mass spectrometry. The REE contents in the macrophytes were found to be one to two orders of magnitude lower than in the sediments. In the plants, three groups of REE with similar levels have been identified. The first group included the most abundant elements Sc, Y, La and Ce; the second group consisted of Pr and Nd with the intermediate contents; and the third group contained the elements with the lowest contents: Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The contribution of light REE (Sc, Y, La, Ce, Pr, Nd) to the total REE content in the plants was 91–96%. The highest REE levels were found in the red alga and seagrass rhizomes. Higher translocation factors of Sc, Pr, La, Ce and Tb between seagrass rhizomes and leaves were noted. In terms of the REE content decrease, the marine plants are arranged in the following order: seagrass rhizomes > red alga > brown alga > seagrass leaves > green alga. Brown algae attached to the rocky seabed are widespread in the upper sublittoral, have a long lifespan, and accumulate relatively high amounts of REE. Therefore, they can be used as effective bioindicators of REE pollution in the marine environment.

First data on rare earth mineralization in acid rock varieties of the Shatak complex (Southern Urals)

Research subject. Acid rock varieties of the Shatak complex were studied. Materials and methods. The reseach object included the previously unknown abundant mineralization represented by rare earth minerals. The concentration of petrogenic oxides was determined by the X-ray fluorescence method at the IG UFRC RAS (Ufa) using a VRA-30 spectrometer (Carl Zeiss, Germany) with an X-ray tube with a W-anode (30 kV, 40 mA). The amount of rare earth elements in the rocks of the studied area was determined by the ICP-MS method at the Central Research Institute of VSEGEI (St. Petersburg). The mineralogy was studied using a Tescan Vega Compact scanning electron microscope equipped with an Xplorer Oxford Instruments energy-dispersive analyzer (IG UFRC RAS, Ufa). Results. The studied rocks were diverse in chemical composition, varying from alkaline varieties (trachydacites) to low-alkaline rhyolites. These rocks belong to a highalumina type characterized by potassium specialization and a low agpaitic coefficient. It is assumed that the felsic varieties are subvolcanic formations, and the term “rhyolites” in this case characterizes the chemical composition of the rocks, but not their genesis. The amount of rare earth elements in the studied rocks is subject to significant fluctuations, varying from 60.81 g/t to 1625.39 g/t; moreover, their distribution is characterized by significant differentiation. In general, the rocks belong to a contrasting basalt-rhyolitic series, and their genesis is due to the differentiation of magma in the intermediate chamber. Numerous rare-earth minerals were found in the rocks, inlcuding allanite-(Ce), monazite-(Ce), monazite-(La), nioboeshinit-(Y), aeschinite-(Y), talena-(Dy), talena-(Nd), synchisite-(Ce) and Ce–La–Fe oxide. Conclusions. The presence of paragenetic associations of rare-earth minerals, such as allanite-(Ce) + aeschinite-(Y) + nioboaeschinite-(Y) and allanite-(Ce) + talena-(Dy) + talena-(Nd), indicate the formation of rare-earth mineralization in the course of a single process. The described type of mineralization has no analogues on the western slope of the Southern Urals, which substantiates the need for further research.

Rare earth elements interaction with iron-organic matter colloids as a control of the REE environmental dissemination

Rare earth elements (REE) are highly sought after for advanced technology, in response concerns about their environmental impact have arisen. The mobility and transport of REEs are influenced by their binding to solid surfaces, particularly colloids. With the widespread occurrence of REEs and their potential increase due to climate change, there is growing interest in understanding colloids composed of organic matter (OM) and iron (Fe). The reactivity of these colloids depends on their structural organization and the availability of Fe phase and OM binding sites. The effect of pH on the binding and mobility of REEs in these colloids in response to structural modification of Fe-OM colloids was investigated. REEs are primarily bind to the OM component of Fe-OM colloids, and their mobility is controlled by the response of OM colloids and molecules to pH conditions. At pH 6, the solubilization of small organic colloids (<3 kDa) control the REE pattern and subsequent speciation and mobility. In contrast, at pH 4, Fe-OM colloids bind less amount of REE but aggregate to form a large network. While most REEs remain soluble, those bound to Fe-OM colloids are expected to be immobilized through settlement or trapping in soil and sediment pores.This study supports the idea that colloids control the REE speciation and subsequent dissemination. The findings are particularly relevant for assessing the fate and ecotoxicology of REE in response to changing environmental conditions and increasing REE concentration in natural systems.

Comparative electrochemical behavior of Prussian blue analogues as a host electrode for rare earth element recovery

In this paper, electrodeposited films belonging to the Prussian Blue Analogues (PBAs) family, namely, nickel-hexacyanoferrate (NiHCF) and copper-hexacyanoferrate (CuHCF), were employed as a host material for rare earth elements (REE), and the reported insertion/release study reveals a recovery capability for such valuable metals. The ion insertion/release was accomplished by adopting an electrochemically-driven process. A reversible intercalation was observed while considering both heavy and ligth rare earth elements. The amount of REEs inserted/released over the process and its kinetic evolution during the process were also studied by a chemometric approach. For CuHCF, it was seen that the intercalation of heavy rare earth elements occurs easily respect to the light ones, suggesting a possible selectivity among these ions.

Bioleaching of Rare Earth Elements: Perspectives from Mineral Characteristics and Microbial Species

Bioleaching exhibits high potential for the processing of low-grade complex mineral resources. With the development of the economy and an increase in demand, rare earth elements (REEs) in secondary resources, such as phosphogypsum, red mud and coal-related resources, are gaining more and more attention. In this review, the bioleaching performance of diverse microorganisms is summarized and compared for primary (mainly monazite) and secondary REE resources, based on publications from the past decade. The mineral characteristics of these REE resources are different, as they can be found in phosphate, sulfate, or silicate forms. Correspondingly, microbial species suitable for use in bioleaching differ. The most efficient bioleaching microbe for monazite is Paecilomyces sp., while Acidianus manzaensis is effective in processing red mud. Acidophilic sulfur oxidizers are suitable for processing acidic phosphogypsum. Acidithiobacillus thiooxidans could recover a significant amount of REEs from coal fly ash. In particular, monazite has a high REE content but extremely low bioleaching efficiency compared to that of secondary resources, supporting the understanding that bioleaching approaches are more competitive for minerals with low REE contents. Overall, great progress has been made over the last decade, as considerable REE recovery rates have been achieved, and the main metabolites of microbes were identified. However, numerous challenges still exist. Future efforts should focus on improving biorecovery efficiency, reducing the cost of cell-culture media, and exploring the interaction mechanism between cells and minerals, with an emphasis on mineralogical phase transformations and the molecular regulation mechanisms inside cells during the bioleaching process.

Analysis of element yield, bacterial community structure and the impact of carbon sources for bioleaching rare earth elements from high grade monazite

Rare earth element (REE) recovery from waste streams, mine tailings or recyclable components using bioleaching is gaining traction due to the shortage and security of REE supply as well as the environmental problems that occur from processing and refining. Four heterotrophic microbial species with known phosphate solubilizing capabilities were evaluated for their ability to leach REE from a high-grade monazite when provided with either galactose, fructose or maltose. Supplying fructose resulted in the greatest amount of REE leached from the ore due to the largest amount of organic acid produced. Gluconic acid was the dominant organic acid identified produced by the cultures, followed by acetic acid. The monazite proved difficult to leach with the different carbon sources, with preferential release of Ce over La, Nd and Pr.

LA–ICP–MS U–Pb geochronology and geological significance of two types of monazite in the Xinjiazui gold deposit, northwestern margin of Yangtze Block, China

The newly discovered Xinjiazui gold deposit situates on the northwestern margin of the Yangtze Block, China. Previously, the absolute age of gold metallogenesis in this area has yet to be well defined due to the lack of suitable dating minerals, significantly hindering the study of ore genesis and metallogenesis of gold deposits. This study presents high precision in-situ laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) U–Pb ages of monazite to address this issue. Two types of monazite have been found in this deposit, with Type 1 developed in the sedimentary diagenetic stage and Type 2 formed in the ore-forming stage. Type 1 monazite collected from carbonaceous slate is symbiotic with framboidal pyrite in a skeletal texture. It exhibits a high total amount of rare earth elements (REE) and low Y, Th, and U contents, indicating a low-grade metamorphic origin. In contrast, Type 2 monazite from the auriferous quartz vein is intergrown with hydrothermal mineral assemblages including free gold, Au-bearing pyrite and arsenopyrite, ankerite and sericite, suggesting a hydrothermal origin. The monazite (Type 1) LA–ICP–MS 206Pb/238U age is 460.8 ± 7.0 Ma, representing the sedimentary age of the host rock. A combination of lithologic associations and geochemical characteristics indicates that the Ordovician strata (O2ch) are important surrounding rocks in the Xinjiazui gold deposit. Additionally, the forming ages of monazite symbiotic with free gold in the auriferous quartz–sulfide veins range from 206.4 to 207.4 Ma, representing the gold mineralization age of the Xinjiazui deposit. Field geological observation shows that the vertical vein wall of columnar quartz crystals grows inward in the auriferous quartz–sulfide vein geodes and the euhedral granular sulfides develop in geodes. Therefore, this study proposes that the tectonic system changed from compression to extension in the late orogenic period with the closure of Paleo-Tethys and gold mineralization occurred in the Back-Longmenshan tectonic belt.

A Critical Review of the Enhanced Recovery of Rare Earth Elements from Phosphogypsum.

The increasing demand for rare earth elements (REEs), especially from new and innovative technology, has strained their supply, which makes the exploration of new REE sources necessary, for example, the recovery of REEs from phsophogypsum (PG). PG is a byproduct during the wet production of phosphoric acid, which is an attractive secondary resource for REEs due to a large amount of REEs locked in them. In most cases, REEs contained in PG are mainly encapsulated in the gypsum crystal, leading to a low leaching efficiency. Therefore, it is particularly important to use various methods to enhance the leaching of REEs from PG. In this review, we summarized and classified various enhanced leaching methods for the recovery of REEs from PG, and the advantages and disadvantages of different methods were compared. A joint method of recrystallization and RIL may be a promising enhanced leaching approach for the recovery of REEs from PG. Recrystallization could achieve both the complete REE release and simultaneous preparation of industrial materials with high value added, such as high-strength α-hemihydrate gypsum by phase transformation of PG, and the RIL technology could adsorb the releasing REEs and realize their efficient extraction. Such a combination appears to show significant advantages because of high REE recovery, as well as high value-added product preparation at low cost.

Analysis of enrichment, correlation, and leaching patterns of rare earth elements in coal fly ash assisted by statistical measures

Coal fly ash (CFA) is a typical industrial solid waste, which has recently been reported to contain rare earth elements (REEs). REEs are important materials in many industrial fields. Therefore, extracting REEs from CFA becomes a win-win strategy to both make full use of CFA and reclaim REEs. However, the stable crystalline structure of CFA is hard to break, which limits the extraction of REEs. The inter-correlation and the leaching patterns of the REEs in CFA also remain unclear. In this work, REEs were enriched by desilication, and the correlation and the influences of multiple acids of the leached REEs were investigated. It was found that desilication could increase the leachable amount of REEs from 137.37 ppm to 346.12 ppm. The light rare earth elements (LREEs) were less inter-correlated than heavy rare earth elements (HREEs) and desilication enhanced the leaching of LREEs more than that of HREEs. The ratio and type of the leaching acids both influenced the extraction of REEs from CFA: HCl and HF played important roles in the extraction from the untreated CFA while HNO3 and HF were more decisive for the desilicated CFA. In addition, we used statistical analysis to quantificationally confirm that desilication and acids both significantly influenced the extraction of REEs. This work provides evidence for the enrichment of REEs in CFA and acid choosing when leaching REEs from CFA.

Fluid-fluxed partial melting of the Buncheon granitic gneiss in the Yeongnam Massif, Korea: Protracted (ca. 1.86–1.84 Ga) reworking of the Paleoproterozoic Korean arc

The fluid-fluxed melting of igneous protoliths provides an opportunity to assess the role of fluid for the formation and modification of continental crust during high-temperature metamorphism. In order to investigate such an anatexis in the Buncheon granitic gneiss, Yeongnam Massif, we combined field, microstructural, and geochemical studies with the U-Pb and oxygen isotopic analyses of zircon and monazite. The granitic gneisses comprise metatexitic migmatites containing leucosomes, although neither melanosomes nor peritectic phases are associated with neosomes. These migmatites underwent syn-kinematic wet melting in the presence of ca. 0.9–1.4 wt% H2O (estimated from the pseudosection modeling) via the reaction, plagioclase + K-feldspar + quartz + H2O = melt, that took place at ∼650–750 °C and 4–6 kbar. The leucosomes differ in the degree of Eu anomalies and have variable amounts of rare earth elements, Zr, Y, and Th. Such variations are attributed to the segregation and migration of melts as well as the entrainment of residual phases. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages of zircon and monazite were determined from two granitic gneisses and three leucosomes together with an adjacent, undeformed Hongjesa granite. Zircon grains are oscillatory-zoned, except for homogeneous overgrowth rims rarely present in two leucosomes. Both zircon domains were dated at ca. 1.98–1.97 Ga and ca. 1.86 Ga, respectively, suggesting that igneous protoliths were partly recrystallized during the late Orosirian. Monazites from two gneiss samples contain submicroscopic polycrystalline inclusions of K-feldspar + quartz + apatite, reflecting the presence of former melts, and yielded a pooled 207Pb/206Pb age of 1859 ± 6 Ma (n = 30). In contrast, monazites from a leucosome are inclusion-free, and yielded the youngest age of 1840 ± 16 Ma (n = 6). This result is interpreted to represent the melt crystallization at ca. 1.84 Ga following the ca. 1.86 Ga anatexis. On the other hand, monazite from the Hongjesa granite, yielded a weighted mean 207Pb/206Pb age of 1878 ± 5 Ma (n = 11), most likely reflecting a prograde metamorphic growth. The δ18O values of ca. 1.98–1.97 Ga igneous zircon in granitic gneisses are 7.1–7.2 ‰, but those from the leucosome are reduced at 5.9–6.7 ‰. The latter is largely identical to 5.7–6.7 ‰ estimated from ca. 1.86 Ga domains of zircon in the leucosome and monazite in the granitic gneiss; in contrast, a slightly lower δ18O value of 5.46 ± 0.61 ‰ is recorded in the ca. 1.84 Ga monazite of leucosome. The relatively low δ18O values are most likely accounted for by an influx of fluid that has apparently triggered partial melting in the granitic gneiss, and the fluid itself is possibly linked to the crystallization of mafic magmas in an arc complex. Taken together, in contrast to the majority of zircons preserving the crystallization age of igneous protoliths, monazites are more susceptible to recrystallization during the fluid-present melting and permit us to decode a protracted (∼20 m.yr.) episode from partial melting to melt crystallization in the Yeongnam Massif. Such a longevity of melt-present system typifies the prolonged crustal reworking of Paleoproterozoic Korean arc situated at the eastern margin of the North China Craton.

Recovery of rare earth elements and sulfuric acid solution from phosphate byproducts via hydrofluoric acid conversion

The recovery of high-added value products from phosphate byproducts presents currently a great economic and environmental interests. Rare earth elements (REEs) are present in different byproducts of the fertilizer industry including phosphate tailings, phosphogypsum and phosphoric acid sludge (PAS). This latter contains significant amount of REEs, which could be regarded as a possible alternative resource of REEs. In this article, we addressed the enrichment of REEs in calcium fluoride (RE/CaF2) phase by a conversion reaction of calcium sulfate (RE/CaSO4) sourced from phosphoric acid sludge using hydrofluoric acid. The conversion rate and the enrichment factor of REEs were evaluated. It was demonstrated that the conversion rate reached over 97% with 100% transfer of REEs to CaF2 phase. The REEs were selectively enriched in CaF2 with an enrichment factor of over 42%. Characterizations using XRD, FTIR, TGA and SEM-EDS were conducted to confirm the obtained results. More importantly, the speciation and the conversion mechanisms of REEs were highly discussed. The leaching of REEs from CaF2 reached 48% by aqua regia solution, allowing the production of REEs solution for further precipitation of REEs products. Additionally, the process generates calcium fluoride and sulfuric acid solution as high-added value co-products.

Dynamics of trace and rare earth elements during long-term (over 4 years) decomposition in Scots pine and Norway spruce forest stands, Southern Sweden

The temporal dynamics of 33 major, trace, and rare earth elements (REEs) were studied in the litter samples containing Swedish Norway spruce (Picea abies) (NSL) and Scots pine (Pinus sylvestris) (SPL), with the aim to assess their release and accumulation dynamics. Litter bags (8 × 8 cm) were incubated in paired monoculture stands with both the species for up to 5 years from 1979 to 1984 according to a randomized block design comprising 25 blocks (1 × 1 m) within an area of 625 m2. The decomposition rate was slightly higher for Scots pine litter (k = 0.315) than for Norway spruce litter (k = 0.217). During litter decomposition, at ∼70% accumulated mass loss (AML), the concentration of trace elements increased by &amp;gt;50% in both litter types compared to initial concentrations. The concentration change took place in a non-linear pattern, and polynomial quadratic regression between concentration change and accumulated mass loss resulted in significant relationships (adj R2 = 0.20–0.97; p = 0.15–&amp;lt;0.0001). The changes in concentration and amount of trace elements resulted in two main types of dynamics: 1) both concentration and amount increased for Fe, Al, Ti, Cu, Mo, V, Zr, Sb, As, Cs, Pb, Th, and U; 2) concentration increased but amount decreased for Ni, Zn, Li, and Sr. The amount of REEs increased from ∼3-fold to 99-fold from the beginning to the end of incubation, suggesting accumulation during litter decomposition. The dynamics of different REEs were similar in their change patterns in the two litters. Different REEs had generally identical change patterns during incubation, which is reflected in the high correlations among them (r2 = &amp;gt;0.95). A general upward convexity in the dynamics suggests that if further incubated in the field, decomposing litter could have accumulated more REEs in the organic matter. The results of this study can be useful for future studies in other ecosystems including metal-contaminated sites or element-depleted sites. Plant litter accumulation, its decomposition, and build-up of humic substances in the decomposing organic matter can act as a sink for elements and can be used as a management tool for ecological amelioration of metal-contaminated sites as well as natural systems that are impoverished, especially recuperating sites. The study’s findings have implications beyond such sites and can be useful in any research that seeks to understand the patterns of accumulation and release related to decomposition in different ecosystems.

Pilot Scale Testing of Lignite Adsorption Capability and the Benefits for the Recovery of Rare Earth Elements from Dilute Leach Solutions

Naturally occurring organic materials containing humic acids show a strong affinity towards rare earth elements (REE) and other critical elements. Leaching experiments on lignite coal waste produced from construction sand production revealed that the contained REEs were associated with the organic matter. Furthermore, adsorption studies revealed that the lignite waste was capable of extracting REEs from a model solution and increased the REE content of the lignite waste by more than 100%. As such, this study aimed to utilize the lignite waste to adsorb REEs from pregnant leach solutions and acid mine drainage sources having low REE concentrations and subsequently leach the lignite material to produce pregnant leach solutions containing relatively high amounts of REEs, which benefits the performance and economic viability of downstream separation and purification processes. An integrated flowsheet was developed based on this concept and tested at a pilot scale. The pregnant leachate solution (PLS) was generated from a heap leach pad containing 2000 tons of Baker seam coarse refuse. The pilot scale circuit was comprised of aluminum precipitation, adsorption using the waste lignite, and rare earth-critical metal (RE-CM) precipitation stages in succession. The results indicated that the aluminum precipitation stage removed over 88% and 99% of the Al and Fe, respectively. The adsorption stage increased the REE content associated with the waste lignite from 457 ppm to 1065 ppm on a whole mass basis. Furthermore, the heavy REE (HREE) content in the feedstock increased by approximately 250%, which raised the percentage of HREE in the REE distribution by 19 absolute percentage points. In addition to the REEs, concentrations of other critical elements such as Mn, Ni, and Zn also improved by 75%, 37%, and 250%, respectively. Bench-scale tests revealed that increasing the solids concentration in the waste lignite and PLS mix from 1% to 20% by weight enhanced the adsorption efficiency from 32.0% to 99.5%, respectively. As such, a new flowsheet was proposed which provides significantly higher REE concentrations in the PLS that can be fed directly to solvent extraction and/or oxalic acid precipitation and, thereby, enhancing process efficiency and economics.

Effect of particle size analysis on the physicochemical characterization of Malaysian monazite

Rare earth elements (REEs) are the elements that have become extremely important to our world of technology owing to their unique physical and chemical properties, and widely used in advanced technology. Monazite is one of the mineral phosphate that contain a high amount of REEs including thorium and a small amount of uranium. In Malaysia, monazite is exist as by-product (‘amang’) from tin mining originated from Ipoh, Perak. The objective of this study is to determine the effects of the different particles size of raw and ground (milled) monazite on the physicochemical properties. The effectiveness of extraction and separation process of monazite was affected by the size of the particle. Based on the particle size distribution analysis, all the monazite samples were found to be present in the size range of 11-190 μm. The morphological and elemental composition of the monazite mineral have been characterized by field emission scanning electron microscope (FESEM) integrated with energy dispersive X-ray spectrometer (EDX). The FESEM micrographs of the monazite showed an irregular spherical structures with different sizes. The chemical composition and the mineral phases present in monazite were studied by wavelength-dispersive X-ray fluorescence spectrometer (WD-XRF) and X-ray diffraction (XRD). The XRF analysis confirmed the presence of the major REEs such as Ce, La and Nd elements in the mineral. XRD analysis also identified (Ce, La, Nd and Th)PO4 as the major phases along with quartz as minor phase. According to the FESEM-EDX and XRF analysis, smaller particle size of monazite gave higher content of REEs compare to raw monazite.

Leaching Kinetics of Y and Eu from Waste Phosphors under Microwave Irradiation

Waste fluorescent powder contains a large amount of rare earth elements, which have a high value for recovery and utilization. In order to achieve the rapid and efficient leaching of rare earth elements in these waste phosphors, microwave-assisted leaching of rare earth elements Y and Eu from the waste phosphor with hydrochloric acid was studied. The maximum leaching rates of Y (99.84%) and Eu (89.82%) were obtained at 600 W microwave power, 60 min microwave radiation time at 60 °C. The leaching kinetics showed that the microwave leaching process of Y and Eu conforms to the chemical reaction control model, and the apparent activation energy is 25.30 kJ/mol and 24.78 kJ/mol. Compared with the conventional heating method, the microwave leaching process can obviously reduce the reaction activation energy, shorten the reaction time, and achieve the rapid and efficient leaching of rare earth elements in the waste phosphors.

Monte Carlo simulation and study of REE/PET composites with wide γ-ray protection

In this paper, rare earth element (REE)/polyester composites were designed with lanthanum oxide, gadolinium oxide, and lutetium oxide as ray shielding agents, and polyethylene terephthalate (PET) as the base. Monte Carlo simulation was carried out using FLUKA software. We found that the radiation protection performance of the composite is affected by the type and amount of REE; a higher amount of REE equated to a better radiation protection performance of the composite. When the thickness of the composite and total thickness of the REE is constant, the number of superimposed layers inside the composite does not affect its shielding performance. Compared with a single-type REE/PET composite, a mixed-type REE/PET composite has a wider range of γ-ray absorption and better radiation protection performance. When the mass ratio of PET to REE is 2:8 and different types of REE are mixed with equal mass, several 0.2 cm-thick mixed-type REE/PET composites can shield >70% of 60 and 80 KeV γ-rays.

The behaviour of selected rare-earth elements during the conversion of phosphogypsum to calcium sulphide and residue

Phosphogypsum (PG) is a large hazardous waste from fertiliser and phosphoric acid industries from which useful products including rare-earth elements (REEs) can be recovered depending on the treatment process. Its conversion to calcium sulphide (CaS) which was achieved at 95% followed by the formation of S, CaCO3 and residue is one of the plausible treatment processes leading to economic and environmental benefits. This study aimed at monitoring selected REEs behaviour during the conversion of (PG) to (CaS). The concentrations of REEs in the raw PG, the produced CaS and the obtained residue were determined after digestion (microwave and traditional acid leaching) using ICP-OES. The effect of CO2 and H2S used in the process of forming CaCO3 and S from PG on the concentrations of REEs was also investigated. Microwave digestion proved to be more effective than traditional acid leaching in the recovery of REEs. Microwave digestion using 3 mL HNO3 + 1 mL HCl was more effective than 1 mL HNO3 + 3 mL in REEs recovery. CaS contained the highest amount of Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, La and Y with values of 2646, 476, 2255, 320, 60.5, 376, 79.8, 1.24, 476, 1185 and 318 µg/g respectively. Based on these findings, the residue could be further processed to recover REEs despite less than 40% decrease in concentration for the majority of REEs observed due to the use of H2S and CO2. CO2 was found to be more suitable as fewer REEs were leached as compared to H2S. All things considered, the obtained residue could be a good secondary source of REEs as it is easier to leach, retained good amount of REEs and lesser impurities.