Low Rare Earth Element Contents Research Articles

Controlling factors and impacts of river-borne neodymium isotope signatures and rare earth element concentrations supplied to the Canadian Arctic Archipelago

Determining the factors controlling the neodymium (Nd) isotopic compositions (expressed as εNd) and rare earth element (REE) concentrations of rivers is imperative to improve our understanding of the distribution of these water mass tracers in the ocean. Here we present the first measurements of <0.45 μm-filtrate REE concentrations (i.e., the concentration of truly dissolved, nano-particulate and colloidal REEs passing through a 0.45 μm filter, hereafter referred to as dissolved) and εNd in rivers draining into the Canadian Arctic Archipelago (CAA). Results show a large variation in both REE concentrations (Nd=[8;37,260] pmol/kg) and εNd ([−32.1;−15.1]) in the thirteen rivers sampled. Dissolved REE concentrations increase with increasing fractions of metamorphic rocks and ice cover in the rivers' watersheds, while εNd and PAAS-normalized REE patterns are inherited from the watershed's bedrock lithology. The four rivers draining watersheds composed of Precambrian metamorphic rocks exhibit the highest REE concentrations, the least radiogenic εNd, and shale-normalized patterns enriched in light REEs. The remaining nine rivers drain mainly or exclusively sedimentary bedrock and have lower REE concentrations, more radiogenic εNd and generally show heavy REE enrichment, with variable negative cerium (Ce) anomalies. The presence of ice sheets in the drainage area, and the ionic strength, pH, and dissolved organic carbon concentration of river water are the main factors determining riverine dissolved REE concentrations by controlling the formation and stabilization of colloids. We estimate a flow of dissolved Nd transported by Arctic rivers discharging into the CAA equivalent to the Nd flux of seawater entering the CAA. Depending on the percentage of Nd removal during mixing with seawater, the impact of river water on the εNd of seawater exiting the CAA could be modest (if 90% removal) or more significant (if ≪90% removal). This riverine contribution could potentially impart a climate-sensitive εNd signature to the seawater reaching Baffin Bay, with possible implications for the use of εNd in paleoceanographic reconstructions of water mass distribution.

Grinding activation effect on the flotation recovery of unburned carbon and leachability of rare earth elements in coal fly ash

Coal fly ash (CFA) as a secondary resource has received a great deal of attention over the past few decades. Research on rare earth elements (REEs) and unburned carbon removal by flotation from CFA is burgeoning, respectively. It will be beneficial if REEs could be rich in the flotation product with the carbon removal. In this study, the optimization of flotation for the unburned carbon removal was investigated and near 100% removal came true with loss on ignition of 56% and the yield of 7.7%. The optimal conditions contain rotation speed of 600 rpm and time of 30 min using the collector of 1200 g/t, the frother of 140 g/t, and the density of 130 g/t for the flotation. The majority of REEs occurred in the tailing after the flotation due to the low yield and REEs contents of the concentrates. The difference of REEs distribution in the tailing and concentrate is more significant in the milled sample. The morphology was also observed to explain the microscale behavior of REEs during the flotation.

Subducted sediment contributions to REE deposits recorded by alkaline mafic dikes in the Lizhuang REE deposit, Panxi area, southwest China

Carbonatite-associated rare earth element (REE) deposits are the most important source of REEs worldwide. Recycled subducted sediments are critical for REE mineralization, but it remains unclear how the subducted sediments contribute to the REE mineralization. This study presents new whole-rock and apatite geochemical data for alkaline mafic dikes from the Lizhuang REE deposit, southwest China. These alkaline mafic dikes were emplaced at ca. 28.4 Ma (monazite U-Pb age), broadly coeval with the carbonatite–syenite complex and REE mineralization in the Lizhuang REE deposit. The alkaline mafic dikes have enriched Sr-Nd-Pb isotopic compositions, and variable Ba/Th and La/Sm ratios, demonstrate they were derived from an enriched mantle source, which had been modified by both slab-derived fluids and sediment melts. The apatite grains in the alkaline mafic dikes have distinctive geochemical features in their irregular cores (apatite A) and rim overgrowths (apatite B). Apatite A has low REE contents (18.6–161 ppm) and apatite B has high REE contents (1869–4288 ppm). The different REE contents in these apatites could have been caused by the addition of REE-rich carbonatitic melts at lower crustal depths. We propose that the REE-rich carbonatitic melts could be formed by melting of a sediment-rich mantle source, and that collision between India–Asia triggered the melting.

Rare Earth Elements Distribution in Weathered Volcanic Rock from Mamuju Area, West Sulawesi

The study on the distribution of rare earth elements (REE) was carried out from bedrock and its weathering profile at North Botteng Village, Simboro District and Kelapa Tujuh Village, Mamuju District, Mamuju Regency, West Sulawesi. This study aims to determine the potential and distribution of REE in the bedrock and its weathering profile and to identify the REE-bearing bedrock type. In addition, the relationship between REE and Zr element as one of REE associated elements is also discussed. The analytical method used include petrographic observations to identify the REE-bearing host rock and the ICP-MS (Inductively Coupled Plasma Mass Spectrometry) method to determine the REE content. Samples were taken from drilled hole samples in three different locations and classified into three groups, namely Group 1 (K-01 drill hole sample) and Group 2 (K-62 drill hole sample) from Kelapa Tujuh while Group 3 taken from the P-05 drill hole sample from North Botteng Village. Petrographic observations on the bedrock show that the REE are hosted by phonolitic leucitite composed of mainly leucite as phenocryst set in K-feldspar, plagioclase, pyroxene and opaque groundmass. REE content (expressed as TRE2O3 or total rare earth oxides) show a high concentration values ranging from 2000 - 6400 ppm and display variations enrichment in depth. The highest total REE content in Group 1 found in samples from 9 - 11 meters depth, which is 4600 ppm, while in Group 2 the highest concentration is from 4 - 5 meters depth with a total REE value of 2380 ppm and in Group 3 the highest value of REE content encountered at a depth of 6 - 7 meters, which is 6400 ppm. Zr content in Group 1 samples shows value range between 1780 - 2870 ppm whereas in Group 2 ranges from 1670 - 2380 ppm with the highest Zr concentration at a depth of 4 meters while in Group 3 the Zr content show values ranging from 2100 ppm - 4480 ppm with the highest concentration encountered a depth of 11 meters. The study results suggest that the relationship between REE and Zr element in Group 2 samples showed a positive relationship. Meanwhile, the Group 1 and 3 samples show a varied relationship. The REE concentration is controlled by elevation, in which areas with higher REE concentrations are encountered at elevations above 359 meter above sea level (masl) while low REE content concentrates in areas with elevations below 365 masl. REE enrichment is caused by weathering process that occurs on phonolitic leucite in the study area.

Geological implications of apatite within the granite-related Jiepai W–(Cu) deposit, Guangxi, South China

The Jiepai W–(Cu) deposit is one of the largest Caledonian granite-related W deposits in the Miaoershan–Yuechengling (MY) pluton of southern China. The deposit consists of skarn-type and altered granite-type mineralization along with an ore shoot hosted by altered arkose. This study presents new petrographic and geochemical data for apatite from fresh biotite granite (ApI), mineralized biotite granite (ApII), and ore shoot (ApIII) samples and uses these data to constrain the magmatic and hydrothermal processes that formed the deposit. ApI is associated with primary biotite and has core–rim textures or oscillatory zoning visible during backscattered electron (BSE) imaging, indicating that this apatite has a magmatic origin. ApII is associated with scheelite and secondary biotite and consists of BSE-bright cores (ApIIa) with oscillatory zoning and rare fluid inclusions surrounded by BSE-dark rims (ApIIb) free of fluid inclusions. These relationships suggest that ApIIa and ApIIb record the effects of slight and significant fluid metasomatism, respectively. ApIII appears homogenous during BSE imaging, is associated with abundant scheelite, sericite and quartz, and contains abundant fluid inclusions, indicative of a hydrothermal origin. ApI has increasing total rare earth elements (REE) (2959–14057 ppm) and Y (1598–9099 ppm) contents from cores to rims, high Na2O (0.05–0.2 wt%) and MnO (0.1–0.32 wt%) and low Sr (71.6–86.1 ppm) contents, and low LaN/YbN values (0.55–1.21). ApIIa contains similar REE and Y contents to ApI, but has higher Sr (194–258 ppm) and lower Na2O (<0.03 wt%) and MnO (0.04–0.11 wt%) contents. ApIIb contains similar Na2O, MnO, and Sr contents to ApIIa, but with much lower REE (1766–2021 ppm) and Y (1128–1512 ppm) contents. ApIII apatite has similar Na2O, MnO, REE, and Y contents to ApIIb, but with slightly lower Sr (103–173 ppm) contents and higher LaN/YbN values (0.92–3.28).The large increase in REE contents from core to rim within ApI is indicative of prolonged crystallization, generating W-enriched residual melts and eventually W mineralization. ApIIa and ApIIb contain similar Na, Mn, and Sr contents to ApIII, but have REE contents that are similar to ApI and ApIII, respectively. This suggests that Na, Mn, and Sr were affected by weak fluid metasomatism, whereas REE can only be mobilized by significant fluid metasomatism. The relatively low REE contents and high LaN/YbN values of ApIII reflect the presence of abundant co-precipitated scheelite. These data indicate that ApI, ApII, and ApIII all have different textural and geochemical (Na, Mn, Sr, Y, REE, and LaN/YbN) characteristics and fluid inclusion populations. All of this suggests that apatite is a potential indicator mineral in mineral exploration for granite-related W–(Cu) mineralization.

Identification of ca. 520 Ma mid-ocean-ridge–type ophiolite suite in the inner Cathaysia block, South China: Evidence from shearing-type oceanic plagiogranite

AbstractAn ophiolite suite, predominantly composed of residual mantle peridotites, mid-ocean-ridge basalt (MORB)–like ultramafic rocks, and oceanic plagiogranites, has been identified in the Zhenghe-Dapu fault zone, Cathaysia block, South China. The peridotites experienced strong serpentinization and are characterized by low 187Os/188Os ratios of 0.11621–0.12008 and very low 187Re/188Os values of 0.031–0.129, similar to those from highly refractory mantle residues. The meta-ultramafic rocks, mainly amphibolites, can be classified into two groups. Group I is characterized by high Ni and Cr and low K2O contents. Their spoon-like rare earth element (REE) patterns, along with lower concentrations of highly incompatible elements, indicate that the protolith was of cumulate origin. Group II displays depleted REE patterns and low Nb/Yb, Th/Yb, and Ti/V ratios, which are geochemically similar to normal (N) MORB. Both groups exhibit positive εNd(t) values (1.2–4.1) and relatively high (87Sr/86Sr)i ratios (0.7046–0.7096), suggesting their origin from partial melting of depleted mantle sources in a mid-ocean-ridge setting that experienced a greater extent of fluid-rock alteration. The meta-plagiogranites intercalated with the mylonitic amphibolites are characterized by low K2O (0.09–0.21 wt%) and total REE contents along with low K2O/Na2O and Rb/Sr ratios, which are consistent with those of typical oceanic plagiogranite. They exhibit strongly positive zircon εHf(t) values (+9.5 to +15.1) and positive whole-rock εNd(t) values (+2.8 to +3.6). Their extremely low MgO (0.6–1.65 wt%), Cr (0.22–6.26 ppm), and Ni (0.77–4.74 ppm) compositions and low Mg# (22.4–31.9) preclude their origination from mantle-derived primary magma but favor oceanic crust. Low zircon δ18O values (4.02‰–5.4‰) and decoupled Sr-Nd isotope features imply the involvement of high-temperature seawater alteration in their source region. The enriched light rare earth element (LREE) patterns with strongly positive Eu anomalies, similar to the East Karmøy–type plagiogranite in western Norway, imply that the plagiogranites were derived from anatexis of amphibolite in an active shear zone near the mid-ocean ridge. The magmatic and metamorphic zircons from the meta-plagiogranites yield nearly identical secondary ion mass spectrometry (SIMS) U-Pb ages ranging from 523 to 521 Ma and from 522 to 518 Ma, respectively. The simultaneous magmatism and metamorphism also signify an active high-temperature shear zone, where the plagiogranites were formed slightly later than the oceanic crust. The age of ca. 520 Ma represents the formation age of the oceanic crust rather than its emplacement age. The identification of the ca. 520 Ma ophiolite suite along the Zhenghe-Dapu fault zone indicates that the Cathaysia block consisted of at least two different terranes rather than a single tectonic unit in the Cambrian, and the final amalgamation of the eastern and western Cathaysia block may have occurred far later than ca. 520 Ma, most likely during the late early Paleozoic.

Phosphate Polymer Nanogel for Selective and Efficient Rare Earth Element Recovery.

Demand for rare earth elements (REEs) is increasing, and REE production from ores is energy-intensive. Recovering REEs from waste streams can provide a more sustainable approach to help meet REE demand but requires materials with high selectivity and capacity for REEs due to the low concentration of REEs and high competing ion concentrations. Here, we developed a phosphate polymer nanogel (PPN) to selectively recover REEs from low REE content waste streams, including leached fly ash. A high phosphorus content (16.2 wt % P as phosphate groups) in the PPN provides an abundance of coordination sites for REE binding. In model solutions, the distribution coefficient (Kd) for all REEs ranged from 1.3 × 105 to 3.1 × 105 mL g-1 at pH = 7, and the sorption capacity (qm) for Nd, Gd, and Ho were ∼300 mg g-1. The PPN was selective toward REEs, outcompeting cations (Ca, Mg, Fe, Al) at up to 1000-fold excess concentration. The PPN had a Kd of ∼105-106 mL g-1 for lanthanides in coal fly ash leachate (pH = 5), orders of magnitude higher than the Kd of major competing ions (∼103-104 mL g-1). REEs were recovered from the PPN using 3.5% HNO3, and the material remained effective over three sorption-elution cycles. The high REE capacity and selectivity and good durability in a real waste stream matrix suggest its potential to recover REEs from a broad range of secondary REE stocks.

Rare earth element distributions in salt marsh sediment cores reveal evidence of environmental lability during bioturbation and diagenetic processes

The distribution and accumulation of rare earth elements (REE) in the labile fraction of sediment cores collected from salt marshes in the Patos Lagoon estuary from southern Brazil were investigated. Sediment cores (ca. 40 cm) were obtained from three locations within the estuary to capture possible changes in REE content across the salinity gradient (i.e., where saline, brackish, and freshwater dominate). Salt marsh sediments from all three coring locations were enriched in the light REE (LREE) over the heavy REE (HREE) when normalized to the North American shale composite (NASC). Shale normalized values for the LREE of marsh sediments from sites M2 and M3 in the mid- and upper estuary commonly approximates unity indicating these sediments chiefly exhibit a terrigenous signature. In contrast, all 14 naturally occurring REE are depleted in the sediments from the M1 coring location in the lower estuary compared to shale. Sediments from the mid-estuary (M2 core location) where typical salinity values are ca. 10 practical salinity units, exhibit the greatest shale normalized LREE enrichments. The higher LREE contents of the M2 sediments likely reflect preferential removal of LREE from the water column owing to salt-induced coagulation of river-borne colloids that occurs during estuarine mixing processes. Sediments samples collected from the salt marsh in the lower estuary nearer the Atlantic Ocean (i.e., M1), have substantially lower REE contents than salt marsh sediments from sites M2 and M3 in the mid- and upper estuary, respectively. The more sand-rich lower estuary sediments are exposed to higher salinity water from the South Atlantic compared to the generally finer grained sediments from the mid- and upper estuary, which are dominated by brackish and freshwater conditions, respectively. Negative Ce-anomalies (i.e., Ce/Ce* < 1) in marsh sediments from depths generally greater than 27 cm support the occurrence of early diagenetic reactions consistent with suboxic to anoxic conditions whereby reductive dissolution of ferromanganese oxide/oxyhydroxide carrier phases, and/or Ce(IV) phases, release Ce(III) to the marsh pore waters. The negative Ce anomalies suggests that a suboxic or anoxic environment predominates to a depth of 9 cm, and then again below 27 cm depth in sediments from the M2 salt marsh core, and below a depth of 13 cm in the upper estuary marsh sediments (i.e., M3). In contrast, positive Ce anomalies (Ce/Ce* > 1) for much of the sediment from the M1 core, the mid depths of core M2 (i.e., 9 cm to 27 cm), and shallower than 13 cm in sediments from core M3 support oxic conditions where Ce is enriched in sediments from these depths by preferential scavenging from pore waters onto Fe/Mn oxides/oxyhydroxides. These trends in Ce/Ce* with depth in each sediment core are also consistent with known bioturbation that occurs within these marsh sediments. The relatively high REE contents of the sediments from location M3 are also related to the fact that these sediments are dominantly composed of clay-silt deposits that are enriched in organic matter. Finally, we find no conclusive evidence that the studied salt marsh sediments have been impacted by addition of REE from the local fertilizer manufacturing industry.

Quantitative estimation of rare earth element abundances in compositionally distinct carbonatites: Implications for proximal remote-sensing prospection of critical elements

Rare earth elements (REE) became a strategic raw material in the 21st century and carbonatite-related deposits frequently carry potentially economic levels of these critical metals. To determine concentrations of major and trace elements (including REE) conventional analysis of bulk rock geochemical samples by means of inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) is mostly applied. However, these analytical methods are labor-intensive, costly and time-consuming. In contrast, modern Remote Sensing (RS) – e.g. proximal remote sensing or imaging spectroscopy – has become a novel tool for detecting and quantifying geological materials as they offer an efficient, non-destructive and cost-effective way not only to identify different minerals and/or chemical elements but also model their abundances. In this study, we investigated whether Partial Least Squares Regression (PLSR) models linking the laboratory sample reflectance to mineral/geochemical property could be employed for quantitative predictions of bulk LREE and HREE concentrations. The suite included samples from four different geographic regions in India, East Africa and the USA. Our results showed that for such samples the quantitative approaches have some limitations.First, our models required to exclude samples with high modal abundance of hematite and samples with too low REE contents (LREE < 500 μg/g, HREE < 100 μg/g). Furthermore, it was revealed that the sample mineralogy has a significant impact on the PLSR predictions. To achieve reliable models the sample suite had to be divided into two datasets following their mineralogy and geochemistry. The first dataset comprised rocks with increased amounts of strontium (Sr, DatasetSr), where REE were predominantly bound in Sr-carbonates. On the other hand, REE mainly bound in Ca–REE-carbonates characterized the second dataset (DatasetOther). Following this division, we were able to construct valid prediction models for bulk LREE and HREE concentrations using PLSR. However, the detected spectral assignments associated with the REE presence indicated that the predictions were mainly indirect, based on the present mineral phases rather than direct absorptions related to LREE and HREE. This illustrates the difficulty and limitations for further model generalization and the ability to be further transferred to other lithologically diverse carbonatite sites.We posit that this topic requires future systematic investigations using the extended carbonatite datasets – samples having a wide range of REE abundances – collected from lithologically diverse regions. This would enable further validation and re-calibration of the constructed prediction models.

Efficient recovery and enrichment of rare earth elements by a continuous flow micro-extraction system

The excessive exploitation of rare earth elements (REEs) has caused major losses of non-renewable resources and damage to the ecosystem. The processes of mining and smelting produce massive amounts of wastewater with low concentrations of REEs. Consequently, the enrichment and recovery of low-concentration REEs from wastewater has significant economic and environmental value. For this purpose, operation under large phase ratios (the flow rate ratio between the aqueous phase and extractant) is more desirable and economically viable. However, the traditional REE extraction process suffers from the uneven dispersion of the extractant and the difficulty of phase separation, which leads to long extraction times and large consumption of extractants. Hence, there is an urgent need to develop a green and efficient technique to extract low concentrations of REEs from wastewater. In this work, a droplet-based microfluidic technique was used to continuously extract and recover low-concentration REEs at large phase ratios. Snowman-shaped magnetic Janus nanoparticles were added to the continuous phase as emulsifiers to facilitate uniform extractant dispersion and rapid phase separation. Several key factors affecting the extraction efficiency, including pH, residence time, and the amount of added Janus nanoparticles, were systematically investigated. Compared to batch extraction, droplet-based microfluidic extraction with the addition of Janus nanoparticles showed the advantages of a large specific surface area and fast phase separation during extraction. Meanwhile, the Janus nanoparticles exhibited good emulsification performance after three extraction cycles. In summary, the Janus nanoparticle-stabilized droplet generated by microfluidic methods provides a feasible path for the efficient enrichment and recovery of low-concentration REEs.

Rational assembly of GO-based heterocyclic sulfur- and nitrogen-containing aerogels and their adsorption properties toward rare earth elementals

An aromatic heterocyclic compound, 2-aminobenzothiazole (ABT), was used to decorate graphene oxide (GO) by a facile hydrothermal self-assembly procedure. The developed three-dimensional (3D) GO-ABT composite aerogels could be utilized as high-powered and sustainable adsorbents for the enrichment and recovery of low concentration rare earth elements (REEs) from aqueous solutions. The composition and microstructure of GO-ABT composites were explored various characterization methods. The enrichment properties of GO-ABT composites for REEs were investigated in detail, revealing the existence of S-, N- and –NH2 in ABT, as well as the carboxyl and hydroxyl groups of GO which might act as the major REE binding sites. The adsorption of GO-ABT composites for low concentration REEs could reach equilibrium in 30 min. Our investigations confirmed that the optimal pH value of GO-ABT composites for REEs was pH 4.0–5.0. For the adsorbent regeneration study, 50.0 mg of GO-ABT15:1/120 °C/6 h composite was used toward 20.0 mL of Er3+ solutions. After ten regeneration cycles, the adsorption rates of GO-ABT composites for Er3+ remained around 100%, and the desorption rates maintained over 90%. The long-term storage of the adsorbent did not affect its adsorption ability, while desorption rates increased, indicating it possessed relatively higher stability.

Garnet major and trace element evidence of the alteration and mineralizing processes associated with genesis of the Qiaomaishan skarn deposit, Xuancheng ore district, eastern China

The Qiaomaishan deposit is a skarn-type Cu–W deposit located within the Xuancheng ore district of the Middle–Lower Yangtze River Metallogenic Belt of eastern China. The mineralization within the deposit is predominantly located along the contact between a porphyritic granodiorite intrusion and surrounding Carboniferous limestone units. The deposit is associated with a well-developed and zoned skarn system that includes both endoskarn and exoskarn zones. This study presents new garnet major, trace, and rare earth element (REE) geochemical data for these skarn zones, discusses the factors (e.g., crystal chemistry, oxygen fugacity and water/rock interaction) that control the incorporation of trace elements into garnet, and constrains the formation of skarn within the Qiaomaishan deposit. Grossular (Adr21–70Grs29–78; type 1) garnet is generally located within the endoskarn and is light REE (LREE) enriched but heavy REE (HREE) depleted with weakly negative Eu anomalies and higher total REE contents than the exoskarn garnet in the study area. Type 1a grossular garnet is further split from type 1b grossular garnet by the presence of positive Pr and Nd anomalies and high LREE concentrations. Exoskarn garnet has pure andradite compositions and is split into type 2 and 3 garnets, where type 2 andradite garnet has variably positive Eu anomalies and variable total REE contents that are indicative of formation under transitional or oscillating conditions (e.g., pH, oxygen fugacity). In comparison, the type 3 andradite garnet has low total REE contents and positive Eu anomalies. Endoskarn garnet Al2O3 and total REE contents positively correlate, indicating that REE is incorporated into this garnet through coupled YAG-type substitution. The differences between the total REE contents of the type 2 exoskarn and endoskarn garnets may reflect host rock buffering as well as variations in the crystal chemistry of the two garnets present within the different parts of the skarn system (grossular and andradite). In comparison, the differences in the total REE contents of the two types of exoskarn garnet may reflect variations in water–rock ratios and crystal growth rates. The different Eu anomalies and U contents present within the different types of garnets record variations in the pH and oxygen fugacity of the hydrothermal fluid over time. These changes may have promoted the crystallization of magnetite and scheelite and the formation of the tungsten mineralization within the deposit. This study demonstrates the usefulness of garnet in tracking variations in mineralizing conditions and processes and confirms the validity of these minerals as vectors or indicator minerals that can be used in combination with traditional exploration approaches to determine whether a system is mineralized or not during the early stages of exploration.

How Feasible is Direct Determination of Rare Earth Elements in Seawater by ICP-MS?

With the increasingly wide industrial use of rare earth elements (REEs), their release into marine systems makes it important to understand in what quantities they occur and to what geochemical processes they contribute, preferably using direct analytical methodology. In this study, analytical performance of high-resolution ICP-MS was assessed with regard to quantification of REEs in seawater without matrix separation and analyte preconcentration. With optimized sample dilution, precise and interference-free quantifications of most of the REEs in samples taken from Kara Sea were obtained, with an accuracy of 3 to 9% (against the independently asserted values), repeatability of 3 to 5%, and intermediate precision and reproducibility, averaging 4 and 11%, respectively. The method was further validated by using a certified reference material for nearshore seawater. However, the limits of detection obtained (0.04 - 0.38 ng L-1), while not significantly inferior to those obtained after sample enrichment, appear to be not low enough to analyze high salinity sea samples (over 30 parts per thousand) or open-ocean water samples, which require higher dilution factors or contain (much) lower REE concentrations, respectively. Therefore, it was concluded that the direct determination of REEs is only possible from samples with moderate salinity such as estuarine or shallow-sea water. In the latter case, the longitudinal REE profiling assayed by ICP-MS allowed us to assume that the export of the contaminated material from land areas into estuaries and then to the sea by rivers may substantially contribute to the seawater pool of REEs.

Lanthanum Diffusion in Fluorapatite at 400 °C, 50 MPa and 4–16 wt %

Apatite is an important carrier of rare earth elements (REEs) and phosphorite is a potential REEs resource. However, the influence of hydrothermal fluids on the migration and enrichment of REE in apatite remains controversial. The experimental study of the interaction between REE-bearing fluid and apatite is one of the essential ways to understand the chemical behavior of rare earth elements in apatite. In this study, we conducted the fluid–mineral reaction experimental study (at 400 °C, 50 MPa and 4–16 wt %) between high lanthanum (La) content hydrothermal solution and low REE content to reveal the influence of different salinities on the diffusion of rare earth elements in fluorapatite. Based on in situ geochemical analyses of experimental products, we show that the diffusion coefficients of La in fluorapatite are between 3.24 × 10−15 and 5.88 × 10−15 m2/s. The salinity of the fluid has a great influence on the diffusion coefficient, with the increase of salinity, the diffusion coefficient increase.

A comparative study of the magnetic induction heating properties of rare earth (RE = Y, La, Ce, Pr, Nd, Gd and Yb)-substituted magnesium–zinc ferrites

Rare earth (RE)-substituted magnesium–zinc ferrite (Mg0.5Zn0.5RExFe2–xO4) nanoparticles with different RE elements (Y, La, Ce, Pr, Nd, Gd and Yb) and different RE contents (x = 0–0.1) were synthesized via coprecipitation of metal hydroxides as the precursor, followed by calcination. Their crystal structures were characterized by X-ray diffraction (XRD) analysis, confirming that the RE-substituted Mg–Zn ferrites had a single-phase spinel structure at low x values. However, the Ce-substituted ferrites contained CeO2 as a byproduct. Scanning electron microscopy (SEM) showed that the particle diameters of the samples decreased from approximately 100 to 20 nm as x was increased regardless of the RE elements. The magnetic induction heating properties were evaluated using the intrinsic loss power (ILP) determined from the temperature rise profiles in an alternating magnetic field and the amplitude and frequency of the magnetic field. By using various RE elements, it was found that the increase in the magnetic moment of RE ions can increase the magnetization of ferrites, resulting in improvements in the ILP at low RE contents, except for Gd substitutions. The increase in RE content decreased the ILP due to reductions in crystallinity. The results suggest that the RE elements and contents can precisely control the magnetic induction heating properties, and RE-substituted Mg–Zn ferrite nanoparticles are promising candidates for magnetic hyperthermia applications.

Industrial Ramie Growing on Reclaimed Ion-Adsorption Rare Earth Elements Mine Tailings in Southern China: Defibration and Fibers Quality

Ramie plants (Boehmeria nivea) have been cultivated on ion-adsorption rare earth elements (REEs) mine tailings and showed a low ability to accumulate REEs, especially in the stems (ΣREE = 24 ± 17 mg kg−1) with higher concentration in leaves and roots (ΣREE = 57 to 66 mg kg−1). Ramie individual fibers were isolated using three degumming processes: a traditional alkali treatment (AT), a steam explosion (SE) treatment after a neutral (SEN) or after a basic (SEB) impregnation. Cellulose-rich (> 80%) fine fibers with very low amounts of non-cellulosic sugars (< 5%), low REE concentrations (ΣREE ≈ 4–6 mg kg−1) and a high mechanical strength (tensile strength ≈ 260–540 cN/fiber, breaking point ≈ 20–50 cN/fiber) have been produced. However, SE degumming resulted in more degraded fibers with cracks slightly affecting their tensile properties.

Responses of ramie (Boehmeria nivea L.) to increasing rare earth element (REE) concentrations in a hydroponic system

A number of studies have focused on the effects of rare earth elements (REEs) on crop plants, while little attention has been paid on how tolerant plant species respond to increasing mixed REE concentrations. In this study, ramie (Boehmeria nivea L.) was exposed to a series of REE concentrations prepared with equimolar mixtures of 16 REEs (i.e. 0, 1.6, 8, 16, 80, 160, 400, 800 μmol/L) in order to explore REE accumulation and fractionation characteristics in ramie and the responses of this plant to mixed REEs. Results show that ramie root and shoot biomasses are unaffected under lower REE concentrations (1.6–80 μmol/L), while the growth of ramie and the uptake of nutrients especially Ca and Mn are largely inhibited under higher REE concentrations (160–800 μmol/L). The P and Mo concentrations in the roots increase with the increasing REE concentrations in the solution, suggestive of an involvement of P and Mo in dealing with the high concentrations of REEs in this plant. The preferential uptake of Ce and heavy REEs (HREEs) and the preferential transport of HREEs within the plant lead to a positive Ce anomaly and a HREE enrichment in ramie leaves. Our study suggests that ramie could be a good candidate for the phytoremediation of heavily REE-contaminated soils (e.g., REE mine tailings in southern China). Our results also shed light on points of taking into account phytoremediation management strategies of REE-contaminated soils (e.g., P and Mo fertilization).

Solubility of Monazite–Cheralite and Xenotime in Granitic Melts, and Experimental Evidence of Liquid–Liquid Immiscibility in Concentrating REE

Abstract We provide new experimental data on monazite, xenotime and U–Th-bearing cheralite solubility in slightly peralkaline to peraluminous granitic melts using dissolution and reverse (i.e. recrystallization after dissolution) experiments in water-saturated and flux-bearing (P + F + Li) granitic melts, at 800 °C and 200 MPa. Although a positive correlation between rare earth element (REE) solubility and melt peralkalinity is confirmed, monazite solubilities reported here are much lower than the values previously published. We suggest that the presence of elevated phosphorus concentrations in our melts depresses monazite solubility, principally because phosphorus complexes with Al and alkali, which normally depolymerize the melt through the formation of non-bridging oxygens. The new solubility data provide an explanation for the very low REE concentrations generally encountered in phosphorus-bearing peraluminous granites and pegmatites. This accounts for the compatibility of REE in peraluminous systems, as the early crystallization of REE-bearing minerals (mainly monazite and zircon) leads to progressive REE depletion during liquid differentiation. In addition, dissolution and reverse experiments on U–Th-bearing cheralite–monazite display liquid–liquid immiscibility processes in our slightly peralkaline glass. The immiscible liquid forms droplets up to 10 µm in diameter and hosts on average 35 wt% P2O5, 25–30 wt% F, 22 wt% Al2O3, 4 wt% CaO, 5 wt% Na2O, 2 wt% La2O3, and 12 wt% ThO2 + UO2. We believe that the droplets formed during the runs and may have coalesced to larger droplets during quenching. We suggest that liquid–liquid immiscibility is a possible mechanism of REE concentration in highly fluxed melts and should be considered in natural systems where REE are extremely concentrated (up to thousands of µg g–1) in magmatic rocks.

Boron isotope compositions establish the origin of marble from metamorphic complexes: Québec, New York, and Sri Lanka

Abstract The origin of an array of marble samples found in both the Grenville Province and southwestern Sri Lanka remains uncertain, whether magmatic, sedimentary, or mixed, due to their proximity to both carbonatite bodies and carbonate-rich metasedimentary rocks. This study reports boron and trace element abundances, in addition to carbon, oxygen, boron, and strontium isotopic compositions, to determine the petrogenesis of these carbonate-rich samples. Boron abundances for all of the samples are relatively high and variable (1.48–71.1 ppm) compared to those for carbonatites worldwide (≤1 ppm), and mostly overlap those documented for sedimentary sources (up to 54 ppm). The rare earth element (REE) abundances (0.5–1068 ppm) for the marbles studied are similar to those for local sedimentary units and thus contain, in general, lower REE contents than both the average worldwide calciocarbonatite and respective neighboring carbonatite bodies. The δ13CV-PDB and δ18OV-SMOW compositions for all of the samples range between –2.9 to +3.2 ± 0.1‰ and +14.3 to +25.8 ± 0.2‰, respectively, and are considerably heavier than those reported for magmatic or metamorphosed carbonatites. The 87Sr/86Sr ratios reported here range from 0.70417 to 0.70672, which are more radiogenic than the average 87Sr/86Sr (~0.70345) reported for carbonatites included for comparison in this study. Importantly, the boron isotopic compositions (δ11B‰) for samples from the Grenville Province range from +7.5 to +15.7 ± 0.5‰, which are consistent with those reported for biogenic carbonate (+4.9 to +35.1‰). In contrast, δ11B values for the samples of marble from Sri Lanka vary from –9.8 to –14.3 ± 0.5‰ overlapping with those estimated for average bulk continental crust (–9.1 ± 2.4‰). Together, the boron compositions, chemical data, stable (C, O), and radiogenic Sr isotopic data overwhelmingly point to a sedimentary origin for the marble samples examined here. Specifically, the samples from the Grenville Province represent marble formed during high-temperature regional metamorphism of limestone units. The Sri Lankan samples were formed from carbonate-rich and 11B-poor fluids derived from a crustal source. The boron isotopic compositions for the samples studied here are also compared to those reported for mantle-derived carbonate (i.e., carbonatites) worldwide, along with their associated δ13CV-PDB and 87Sr/86Sr values. This comparison results in defining three isotopically distinct fields; mantle-derived carbonates, sedimentary carbonates derived from heterogeneous limestone protoliths, and carbonates derived from meteoric water interacting with crustal material. This work establishes the effective use of boron isotopic compositions in determining the origin of carbonate-rich rocks of contentious petrogenesis.

U–Pb geochronology and trace-element composition of zircons from the Jinchang Au–Ni deposit, SW China, and their implications for tectonics

AbstractSituated between the South China Block and the Simao Block, the Ailaoshan Belt is a significant component of the Jinshajiang–Ailaoshan tectonic-magmatic-metallogenic belt of southwestern China. The formation of the Ailaoshan Belt is closely related to the evolution of the Palaeo-Tethys Ocean. In this study, we constrain ages of sedimentation in the Jinchang Au–Ni deposit in the Ailaoshan Belt, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb ages of the youngest populations of detrital zircons separated from a chert layer and two uncomfortably overlying meta-sandstones. The combined data of the meta-sandstone samples from the Yiwanshui Formation yielded a concordant age of 250.8 ± 0.6 Ma (mean square weighted deviation (MSWD), 2.8; n = 26). The chert sample from the Jinchangyan Formation yielded a concordant age of 347.0 ± 1.5 Ma (MSWD, 2.8; n = 16). Detrital zircons from the meta-sandstone are characterized by low rare earth element contents (∑REE) and low Y, and high U and U/Yb ratio, suggesting a continental crustal origin. Zircons in the meta-sandstones were derived mainly from pre-collision subduction zone magmatic rocks related to the closure of the Palaeo-Tethys Ocean. In contrast, detrital zircons from the chert contain relatively high ∑REE and Y, and low U and U/Yb ratio, suggesting an oceanic crust origin. Zircons in the chert bed were derived mainly from ophiolites related to seafloor spreading in a branch of the Palaeo-Tethys Ocean.