Amounts Of Rare Earth Elements Research Articles

Electromagnetic wave absorption properties of cobalt-zinc ferrite nanoparticles doped with rare earth elements

Traditional ferrites are of poor electromagnetic wave (EMW) absorption while doping rare earth elements (REEs) can greatly enhance their permeability to improve the EMW loss performance. In this study, Co-Zn ferrite nanoparticles doped with various amounts of REEs (Gd3+, Nd3+ and Pr3+) were synthesized by a hydrothermal method, and their particle morphology and an EMW absorption performance were characterized by using transmission electron microscopy (TEM) and a Vector network analyzer (VNA). The results show that the initial spherical Co-Zn ferrite nanoparticles present an irregular quadrilateral structure after Gd3+ doping, and the average particle size of Co0.5Zn0.5−xGdxFe2O4 increases from 26 to 50 nm with x increasing from 0 to 0.35. At x of 0.25, the reflectivity absorbance achieves −27.94 dB at 18 GHz with the effective absorption bandwidth (EAB) of 4.08 GHz at a sample thickness of 2.5 mm. When Nd3+ doping amount reaches x = 0.3, the minimum reflection loss (RL) is −25.63 dB at 18 GHz and EAB is 3.91 GHz. Doping Pr3+ (x = 0.25) in the sample broadens EAB, and the minimum RL is −16.1 dB at 16.81 GHz and EAB is 7.31 GHz. This study shows that the magnetic moment produced by doping REES can form magnetic domains, which affects the incident EMW and improves the magnetic loss. It is expected that REEs-doped Co-Zn ferrite nanoparticles can be used as efficient electromagnetic shielding materials in aerospace.

Characterization of rare earth elements present in coal ash by sequential extraction

Although it has recently been reported that notable amounts of rare earth elements (REEs) are present in the residual coal ash, little is currently known regarding the association of these elements with the coal ash matrix, thereby limiting the potential for extraction of REEs from coal ash. In this study, we analyzed the binding characteristics of REEs within coal ash via sequential extraction and examined REE recovery during a coal ash recycling process. Major components of coal ash were found to be mineral oxides, mainly composed of Si, Fe, Al, and Ca, and residual carbons. Bottom and fly ashes were found to contain 185.8 mg/kg and 179.2 mg/kg of REEs, respectively. Tessier sequential extraction confirmed that 85 % of REEs are included in the residual fraction of both bottom and fly ashes. Furthermore, BCR sequential extraction revealed that 60–70 % of REEs are contained within the residual fraction, thereby indicating that REEs are strongly bound in both bottom and fly ashes and the use of very strong acids is required for the thorough extraction of REEs from coal ash. Additionally, it was found that 46.3 % of REEs can be recovered from the wastewaters produced during the process of coal ash-derived zeolite synthesis.

Coconversion of n-Dodecane and 2-Methylthiophene in the Presence of Dual-Zeolite Cracking Catalysts Containing Different Amounts of Rare-Earth Elements

The effect of the rare-earth element (REE) content in dual-zeolite cracking catalysts on the conversion of n-dodecane and an n-dodecane–2-methylthiophene mixture (5000 ppm S) has been studied. The catalysts have been synthesized using zeolites Y and ZSM-5 modified with REEs and phosphorus, respectively, as the active component. It has been shown that the presence of REE oxides in zeolite Y (at a constant SiO2/Al2O3 ratio) affects the catalytic activity of cracking catalysts based on this zeolite. The dependence of the light olefin yield on the REE oxide content in zeolite Y passes through a maximum at 2–3 wt %. The presence of a sulfur compound in an amount of 5000 ppm (in terms of sulfur) in the feedstock leads to a decrease in the model hydrocarbon conversion and the C2–C4 olefin yield. In the presence of a sulfur compound, the change in the C2–C4 olefin yield as a function of REE oxide content in zeolite Y is less pronounced than that in the case of individual n-dodecane cracking.

Assessing the transport of rare earth elements in runoff in a small watershed developed on a coarse-grained granite area in southern China

The transport of rare earth elements (REEs) in surface runoff could have adverse ecological and public health impacts in some regions. In this study, the transport of REEs in a small watershed developed on coarse-grained granite in southern China (the Zhuxi Watershed) was analyzed using a Soil and Water Assessment Tool (SWAT) model and an artificial rainfall experiment. The SWAT model was used to simulate the runoff and sediment generation in the Zhuxi Watershed. Moreover, an artificial rainfall experiment was conducted for determining the mass and distribution of REEs transported from the erosion of soils on a slope in the watershed. The results showed that the average annual runoff volume and amount of sediment in the Zhuxi Watershed from 2013 to 2017 were 4.793 × 1010 L and 1.037 × 107 kg, respectively. Additionally, the content of REEs in the runoff and sediment were 10.91 μg L−1 and 2.282 × 105 μg kg−1, respectively. The SWAT model indicated that the average annual amounts of REEs transported in runoff and sediment in the Zhuxi Watershed from 2013 to 2017 were 1554 ± 239 and 2367 ± 307 kg a−1. Further investigations should be conducted in the area to determine the most effective methods of reducing sediment export from the watershed to limit the potential for adverse environmental and public health impacts through exposure to REEs in areas receiving discharge.

Rare Earth Element Behavior in a Sandy Subterranean Estuary of the Southern North Sea

The use of rare earth elements (REEs) as tracers for oceanic processes requires knowledge and quantification of their sources and sinks. Submarine groundwater discharge (SGD) has been suggested to be a potentially important source of REEs and other trace elements to the ocean. To investigate the processes affecting REEs in a subterranean estuary (STE) of a sandy beach system and their contribution to coastal waters of the southern North Sea, we analyzed dissolved REE concentrations in beach pore waters, coastal seawater and fresh groundwater on the barrier island Spiekeroog, German North Sea. The pore waters show variable REE concentrations (Neodymium between 6 and 54 pmol/kg), generally increasing from the upper beach to the shoreline. At the upper beach, mixing of coastal pore water with rainwater and scavenging lead to lower REE concentrations than in coastal seawater and high heavy (HREE) over light (LREE) REE ratios. Close to the low water line, the REE concentrations increase, partly exceeding seawater concentrations and showing a positive deviation from conservative mixing, with shale-normalized light and middle REE-enriched patterns. This is due to the release of light and middle REEs from degrading particulate organic material and potentially dissolution of Fe/Mn-oxides under reducing conditions. Reducing conditions are further supported by the change from a negative Ce-anomaly at the upper beach to no anomaly close to the low water line. Net SGD fluxes of both fresh groundwater and recirculated seawater are a source of light, middle and heavy REEs to the ocean, with a higher contribution of LREEs than HREEs compared to seawater. However, the total amount of REEs added to the North Sea by SGD from the East Frisian Islands is still ~500 times smaller than input from nearby rivers. An anthropogenic Gd signal higher than previously reported is present throughout the pore waters and seawater, indicating increasing accumulation of anthropogenic Gd in the coastal marine environment.

Hydrometallurgical Recovery and Process Optimization of Rare Earth Fluorides from Recycled Magnets

Magnets containing substantial quantities of rare earth elements are currently one of the most sought-after commodities because of their strategic importance. Recycling these rare earth magnets after their life span has been identified to be a unique approach for mitigating environmental issues that originate from mining and also for sustaining natural resources. The approach is hydrometallurgical, with leaching and precipitation followed by separation and recovery of neodymium (Nd), praseodymium (Pr) and dysprosium (Dy) in the form of rare earth fluorides (REF) as the final product. The methodology is specifically comprised of sulfuric acid (H2SO4) leaching and ammonium hydroxide (NH4OH) precipitation followed by reacting the filtrate with ammonium bifluoride (NH4F·HF) to yield the REF. Additional filtering also produces ammonium sulfate ((NH4)2SO4) as a byproduct fertilizer. Quantitative and qualitative evaluations by means of XRD, ICP and TGA-DSC to determine decomposition of ammonium jarosite, which is an impurity in the recovery process were performed. Additionally, conditional and response variables were used in a surface-response model to optimize REF production from end-of-life magnets. A REF recovery of 56.2% with a REF purity of 62.4% was found to be optimal.

Geochemistry of Rare Earth Metals in the Ore Eudialyte Complex of the Lovozero Rare Earth Deposit

Rare earth elements belong to the category of strategic metals. The largest deposits of these strategic raw materials are associated with alkali-carbonatite formations. The largest alkali-carbonatite complexes of the world are located on the Kola Peninsula and in Polar Siberia. These complexes have great potential for strategic raw materials, including rare earths. The purpose of this work was to estimate the rare earth potential for ore eudialyte in the Lovozero deposit. Thus, 120 eudialyte grains from eudialyte ores were studied by inductively coupled plasma mass spectrometry. In the ore eudialyte-bearing complex, the average value of the total amount of rare earths in eudialytes is 12 566 g/t, which is significantly higher than the total amount of rare earths in apatite from five deposits of the Khibiny Massif. Considering the many millions of tons of nepheline syenites of the eudialyte-bearing complex and the almost linear trend of rare-earth spectra for eudialyte, it can be concluded that the eudialyte deposit of the Lovozero Massif is extremely valuable.

Synergistic effects of lanthanum and strontium to enhance the osteogenic activity of TiO2 nanotube biological interface

According to the clinician's experience, the main reason for the inefficiency of osseointegration between biometal and surrounding bone tissue is still caused by the biological inertness on the surface. Due to the osteogenic effects of its titanium dioxide nanotubes (TiO2) and strontium ions, strontium-containing TiO2 nanotube (STN) coatings have been widely used for titanium surface modification. Trace amounts of rare earth elements (such as lanthanum (La)) show some potential in the performance of repairing bone tissue. In this study, in order to shorten the osseointegration time of titanium implants, we first introduced lanthanum into the biological interface of SrTiO3 nanotubes (LSTN) to achieve the best osteogenesis effect. The AFM, SEM, EDS, FTIR, XPS analyses revealed that the nanocomposite structure of the LSTN was successfully fabricated. LSTN exhibits excellent hydrophilicity and protein adsorption capacity, which are essential for the adhesion of pre-osteoblasts to the surface of nanotubes. LSTN did not show any cytotoxicity in pro-osteoblast proliferation and differentiation experiments. Just the opposite, the cells stretched well on the surface of the LSTN, showing a large number of stress fibers and actin filaments. Furthermore, compared with La-free nanotubes, LSTN showed the potential to excellently up-regulate the expression of osteoblast-related genes such as OCN, ALP, Col-1, and RUNX2. Our results show that LSTN exhibits excellent osteogenic potential due to the osteogenic effect of lanthanum and strontium and the protein adsorption capacity of nanotubes, which provides the possibility for accelerating bone healing in patients with bone damage.

Experimental investigation on dry sliding wear resistance of recently developed hyper-duplex stainless steel

Abstract Duplex stainless steels (DSS) are used in a wide range of industries, predominantly because of the high strength and corrosion resistance they possess. ASTM A890 grade 7A is the newest addition to the family of duplex stainless steels with a unique composition having small amount of rare earth elements. This work is aimed at comparing the sliding wear behaviour of commercially used 5A, 6A and recently developed 7A grades of duplex stainless steel at high sliding velocities. The wear tests were conducted on pin-on-disk apparatus at varying load conditions. Three-dimensional surface analysis of the three grades were conducted using a 3D profilometer to study and compare the roughness of the worn surfaces. Weight loss method used to determine the material removal showed the highest weight loss for grade 5A followed by that of 6A and 7A grades. Grade 7A showed a large reduction in wear volume compared to the other grades. 3D profilometer studies of the worn surface at a load of 60N showed slight plastic deformation in all three grades. Grade 7A showed lower roughness also compared to previous grades

Selective flotation of phosphorus-bearing ores

This paper presents the results of the beneficiation of a phosphorus-bearing mineral through selective flotation process. The chemical examination showed that the sample contain a low content of P2O5 12.5 % and significant amounts of rare earth elements (REE), %: yttrium - 0.01, lanthanum - 0.06, cerium - 0.09, neodymium - 0.03. The particle size distribution of the sample was performed, and each separated fraction was chemically analyzed. A detailed examination of the mineralog ical characteristics was conducted using automated mineral liberation analyzer (MLA). It has been shown that the apatite particles are mostly liberated in all fraction sizes. The maximum percentage of apatite polymineral aggregate was recorded in the grain size of -0.5 + 0.2 mm, mainly with nepheline and pyroxenes. The maximum percentage of apatite binary aggregate was noted in the grain size of -0.16 + 0.071 and -0.071 + 0.045 mm. Based on the obtained results, the size of the flotation feed was predetermined, which allowing the complete liberation of phosphorusbearing mineral (apatite) and avoiding over-grinding of the ore.

Modelling and simulation of lanthanum (La) and neodymium (Nd) leaching from monazite ore using METSTM

Digestion and leaching are known as part of the main processing pre-treatment method in the extraction of rare earth elements (REEs). This work aims to carry out the sensitivity analysis of the liquid–solid (L/S) ratio, the type of acids as well as the number of reactors for the recovery of REEs, namely lanthanum (La) and neodymium (Nd) from monazite concentrate through the leaching process. A model was developed and simulated by using METSIM, a software for modelling metallurgical processes. The process was modelled as a two-step process; the first is the digestion, followed by the leaching process to produce monazite leachate. The results show that the optimum L/S ratio was 8:1 to recover the highest amount of REEs, with HCl was found to perform better as a solvent for the recovery of REEs compared to H2SO4. In addition, the optimum recovery of REEs was achieved by using three reactors, which is in the range of 70-95%.

Amorphous Silicate Decomposition from Non-Magnetic Coal Fly Ash using Sodium Hydroxide

In five years, from 2015 to 2020, the need of coal in Indonesia is doubled to 166.2 million tonnes and increasing up to 2050 as stated in the Indonesian Energy Mix policy. Generally, coal is used in the coal-fired power plan. After the combustion, there are some residual materials such as mineral matter, fly ash and bottom ash (FABA) listed as hazardous materials due to the toxicity and metal contents. Referring to the amount of coal consumption in 2020, the fly ash and bottom ash will be of about 19.92 million tonnes. The utilization of FABA is then become a must thing to do. One of the alternatives is rare earth element (REE) extraction. Indonesian coal contains sufficient amount of REE to extract that is concentrated in the FABA to the value of more than 400 ppm. Regarding to the REE mode of occurrence that is mostly concentrated in the glass form or amorphous silicate, this study was conducted in order to observe the effect of sodium hydroxide to breakage the amorphous silicate structure. In order to obtain the amorphous silicate, magnetic separator was applied. Based on the XRF analysis, the non-magnetic fly ash (amorphous silicate of glass form) contained major elements of SiO2, Al2O3, Fe2O3, CaO, MgO and the rest were minor and trace elements such as Na2O, K2O, Cr2O3, MnO, SrO and P2O5. The particle size of the amorphous silicate is less than < 38 μm (- 400 mesh). To run the experiments, sodium hydroxide was used as the reagent with varied concentrations of 6 M, 8 M and 10 M. Other variables were temperature of 28 0C (room temperature), 60 0C and 90 0C and residence time of 2, 4, and 6 hour. Based on the results analysis, the amorphous silicate was decomposed to the most of about 22 % at 90 0C of temperature, 10 M of sodium hydroxide concentration, and 6 hour of residence time.

Double-Front Crystallization in the Chapesvara Ultramafic Subvolcanic Complex, Serpentinite Belt, Kola Peninsula, Russia

Dunite–harzburgite–olivine-bearing orthopyroxenite successions in the subvolcanic Chapesvara-I and Chapesvara-II intrusions in the Serpentinite Belt, western Kola Peninsula, are notably magnesian. The mean Mg# value (whole-rock) is 86.6, and the olivine is Fo84−89. The upper contact facies (UCF) displays a lower Mg# (81.6). It consists of grains of Fo92 and abundant chromian spinel, implying rapid crystallization of an almost unfractionated melt. On average, the whole-rock Al2O3/TiO2 value is 22.45, close to 22.9 (UCF) and to the primitive mantle, ~22. The rise of primitive ultramafic magma presumably occurred in a special tectonic setting at the boundary of the Paleoproterozoic Lapland Granulite Terrane and the Belomorian Composite Terrane of Archean age. The Chapesvara suite resembles examples of the Al-undepleted komatiites in the Barberton Belt, South Africa, with magmas of up to 30–35% MgO. The UCF rock yields an anomalously low molar MgO/SiO2 value, close to that of dunitic rocks located at the center of the Chapesvara-II body. This rock is the most primitive, as indicated by the maximum Fo content of olivine, the lowest value of (Gd/Yb)N, 0.52, and the lowest abundances of middle to heavy rare-earth elements (REE) in the chondrite-normalized spectrum. The crystallization of the Chapesvara-II sill-like intrusion likely proceeded in two stages, which are evident from the olivine compositions varying from the maximum Fo92 (UCF) to Fo≤89.5 (the central dunite zone). At Stage 1, the UCF rock (Fo92) crystallized first, close to the upper contact. The area of crystallization then shifted to a central portion of the Chapesvara-II body, in which the dunitic zone (Fo89.5) formed in situ (Stage 2). The compositional variations in chromian spinel are consistent with this suggestion. Two crystallization trends were recognized. The type-1 trend displays a relative maximum or minimum close to the center, and then diverges into two linear subtrends directed upward and downward. This pattern is manifested in the variations of Mg# in olivine and chromian spinel, the whole-rock contents of Al and Ca, and in levels of incompatible elements: Ti, V, Zr, Y, and Hf. The type-2 trend decreases or increases uniformly from top to bottom. Variations in amount of Ni in olivine, the Fe3+# index in chromian spinel, and in values of Mg# (rocks), follow a type-2 trend. Variations in total amounts of REE, Nb, and Th, which gradually increase downward, are also related to a type-2 trend. Thus, a contrasting development and possible interference of the two types of evolutionary trends were observed in the crystallization history of the Chapesvara-II sill-like body. A double-front crystallization, hitherto unreported, involved two fronts moving upward and downward, respectively. The upward subtrend appeared to be of subordinate importance, whereas the extent of fractional crystallization of the downward front was much greater. Crystallization proceeded from the top to the bottom, presumably because of the preferential loss of heat at the roof. Variations in the Fe3+# index indicate that the level of fO2 also increased downward with progressive crystallization. Convection cells were presumably the key mechanism of accumulation of the crystallizing olivine grains to form the central dunite zone close to the center of the sill-like intrusion. The observed characteristics of the Chapesvara complex indicate the existence of a primitive-mantle source and imply a highly magnesian composition of intruding magma not only for Chapesvara, but also for the Pados-Tundra layered complex and associated suites of the Serpentinite Belt in the Kola Peninsula.

The composition design and properties investigation of Al-based amorphous powder

By adding different amounts of rare earth element Y and Gd in Al86Ni8Co1La5, aluminum amorphous ribbon samples were prepared using single roller melt-spinning under 2 different roller speeds. Then X-ray diffraction (XRD), transmission electron microscope (TEM) and differential scanning calorimetry (DSC) were adopted to study the effect of rare earth element Y and Gd additions on phase structure, forming ability and thermal stability of Al86Ni8Co1La5 alloy. The results show that the better chemical composite is Al86Ni8Co1La1Y2Gd2, which can form a whole amorphous strip when the roller speed is 3 m/s. After the better chemical composition is confirmed, the Al-based amorphous powder is produced using gas atomization and its properties are also validated using cold spray technique. The thickness, porosity and amorphous amount of coatings is about 600 μm, 0.5% and 80.2% (CS–C), respectively. These findings indicate that Al86Ni8Co1La1Y2Gd2 amorphous powder can be used as raw materials for cold spray technique.

Geochemical characteristics and geological significance of basalts in the Sangxiu formation, Rongbu area, southern Tibet

The Upper Jurassic–Lower Cretaceous Sangxiu Formation in the Rongbu area of Tibet is dominated by large–scale exposed basalts. This paper characterizes the geochemistry and magmatic activities of the Sangxiu Formation basalts in a geochemical analysis. The Sangxiu basalt has higher content of TiO2, TFeO and P2O5 (average content is 3.68%, 11.16% and 0.51%, respectively). The total amount of rare earth elements (REEs) in the Sangxiu Formation basalt is high and largely variable (ranging from 174.6 × 10−6 to 235.3 × 10−6). The light-to-heavy REE ratio ranges from 6.19 to 8.36. These characteristics and the REE fractionation degree of the samples indicate an origin from the same magma. The Zr/Nb ratio of the trace elements lies between 7.96 and 13.15, and the Hf/Th ratio is 1.73–6.67, similar to those of intraplate basalts. And the basalts have the characteristics of elements similar to OIB-type basalt. The magma experienced a large degree of separation and crystallization. During the low-level partial melting of the source material, the basaltic magma of the Sangxiu Formation were isolated and crystallized by olivine, clinopyroxene and other iron–magnesium minerals but were not contaminated by the crust during their evolution. After comparison, it is found that the Sangxiu basalts have similar trace elements and Sr–Nd isotopes with the T7090 diabase and the Laguila magnesite in the Jiangya–Kangma area. It is believed that the Sangxiu basalt is the early stage of the Kerguelen mantle. The hot spot is formed by mixing with the lithospheric mantle and quickly cascade to the edge of the passive continental rift.

Effect of rare earth elements on plasma electrolytic carbonitriding of Ti–6Al–4V alloy

ABSTRACTThe paper aims to research the effect of rare earth elements on the carbonitriding layer of titanium alloy by establishing a theoretical model between rare earth concentration and atomic diffusion efficiency. It shows that adding rare earth can not only refine the discharge holes, but also reduce surface cracks, which significantly improve the surface quality of the strengthening layer. It is also found that an appropriate amount of rare earth can greatly increase the growth rate of the carbonitriding layer and carbon content near the surface. Furthermore, compared with the conventional plasma electrolytic carbonitriding treatment, adding 2 g L−1 cerium oxide can effectively reduce the activation energy of carbon, so as to improve its diffusion ability.

Fault-controlled fluid evolution in the Xitian W–Sn–Pb–Zn–fluorite mineralization system (South China): Insights from fluorite texture, geochemistry and geochronology

Fluorite is one of the most common minerals in the granite-related hydrothermal systems, and widely distributed in the Xitan W–Sn polymetallic ore field (South China). It existed from the early W–Sn stage to the middle Pb–Zn stage and then to the late fluorite stage, thus responsible for the Xinggao and Guangming fluorite deposits in the region. In this research, textural, geochemical and geochronological analyses of fluorites were used to reconstruct the fluid evolutionary history and its bearings on fault activities in the ore field. The fluorites from the ore field yielded a Sm–Nd isochron age of 153.3 ± 8.0 Ma (initial 143Nd/144Nd = 0.511871 ± 0.000013, MSWD = 1.5) which is consistent to the timing of the W–Sn ore-forming stage within the error. This suggests that the fluorites were formed in the same time with the W–Sn ores. And the average value of εNd(t) is similar to those of the Jurassic granites (εNd(t) = −9.2 to −7.3) in the ore field. This indicates that fluorite mineralization is mainly related to the Jurassic granites, and the basement rocks could be the source for the ore-forming materials. From the early stage fluorites (coexisting with wolframite) to the late fluorite-only veins, the total amount of rare earth elements (∑REE) in the fluorites substantially decreases (average values vary from 174 to 37.2 ppm), especially the LREE (La/Lu values decrease from 80.0 to 16.6). In addition, the ore-forming elements (e.g., W, Sn, Mo) in the fluorites also decrease significantly with time. And the low δ18OH2O values (−4.30‰ to −3.90‰) and moderate δD values (−63.8‰ to −59.6‰) in the fluorites suggest that the late fluorite stage was contributed largely from meteoric water. Combined with previously reported fluid inclusion data in the ore field, we propose that the W–Sn mineralization was related to fluid boiling and mixing, the Pb–Zn ore was formed from the changing of the redox environment from oxidizing to reducing, and the fluorites were formed due to rapid cooling. The formation of the W–Sn, Pb–Zn, and fluorite ore-forming zones belong to a single magmatic-hydrothermal system but was controlled by the fault evolutionary processes from the early granite plutons intrusion to the large-scale crustal extension in the Xitian ore field.

The role of Al13-polymers in the recovery of rare earth elements from acid mine drainage through pH neutralization

Rare Earth Elements (REE) are crucial to the development of new technologies, given their strategic importance, a wide range of actions has been implemented to ensure sustainable and affordable supplies. Acid Mine Drainage (AMD) besides being one of the major environmental issues faced by the mining industry is a naturally occurring process involving a considerable amount of REE. The recovery of REE from AMD, which is considered a secondary source, has been investigated worldwide over the past few years aiming at sustainability. The current work seeks to provide an understanding of the geochemistry of the REE in an AMD system and also of its respective treatment through pH neutralization, as a contribution to the development of novel REE recovery technologies. The approach proposed herein employed acid mine water and sediment sampling, ICP-OES, XRD, SEM-EDS, TEM, 27Al MAS-NMR and XPS analysis, BCR sequential extraction and geochemical modelling by PHREEQC. The results showed that the REE content in the AMD investigated is very high being Ln3+, LnSO4+ and LnF2+ the dominant species in the impoundments at pH ± 3.5. The neutralization of the AMD with an alkali agent promoted a high REE recovery and produced an amorphous precipitate containing 14% of REE oxides. This precipitate contains Al13-polymers and accounts for the REE removal when the pH is raised to 8, thus promoting adsorption and entrapment simultaneously. Sequential extraction revealed that the REE could be efficiently leached with the use of acetic acid, thus supporting novel and promising recovery technologies through co-precipitation processes.

Extraction of Rare-Earth Elements(III) from Nitric Acid Solutions with Diethyl 2-[(Diphenylphosphoryl)methoxy]-5-ethylphenylphosphonate

Extraction of micro amounts of rare earth elements(III) (REE) from nitric acid solutions with diethyl 2-[(diphenylphosphoryl)methoxy]-5-ethylphenylphosphonate (I) in dichloroethane and ionic liquid, 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide has been studied. The stoichiometry of extracted complexes has been determined, the effect of HNO3 concentration in aqueous phase on the efficiency of metal ion recovery into organic phase has been considered. It has been found that compound I in dichloroethane extracts REE(III) less efficiently than its analogs with phenyl and butyl substituents at the phosphorus atom. It has been shown that the efficiency of REE(III) extraction with compound I from nitric acid solutions increases considerably in the presence of ionic liquid in organic phase.

Plasma dissociation of monazite

Monazite is a phosphate mineral which contains a significant amount of rare earth elements (REE) with thorium (Th) and a low concentration of uranium (U). The radioactive components of monazite, Th and U, make it an unattractive source of REE due to the added cost associated with radioactive waste handling. The mineral is also chemically inert requiring the use of corrosive reagents at elevated temperatures to effectively extract REEs. According to thermodynamic calculations, monazite dissociation into oxides of REE and phosphorus (P) is favourable at temperatures greater than 1000°C, while the reverse reaction occurs well below a 1000°C. Rapid cooling is required to prevent the reverse reaction. Achieving these high temperatures, with rapid heating and cooling, is possible by means of thermal plasma treatment such as a radio frequency plasma. This type of plasma system offers superior control of plasma/particle interaction, quenching rates and plasma gas composition. The objective of this study was to determine the parameters for dissociation of the monazite under various conditions to reduce its chemical inertness. Dark and grey powders were obtained under reducing conditions, while lighter powder formed in the presence of an oxygen plasma with increase particle circularity observed after plasma treatment. While SEM-EDS analysis indicated no notable change in powder composition after plasma treatment, dissolution tests proved that monazite was not only more reactive, but also more susceptible chemical reaction after treatment.