Behavior Of Rare Earth Elements Research Articles

REE mineralogy and geochemistry of the Western Keivy peralkaline granite massif, Kola Peninsula, Russia

The authors have studied the geology, geochemistry, petrology and mineralogy of the rare earth elements (REE) occurring in the Western Keivy peralkaline granite massif (Kola Peninsula, NW Russia) aged 2674±6Ma. The massif hosts Zr- and REE-rich areas with economic potential (e.g. the Yumperuaiv and Large Pedestal Zr-REE deposits), where 25% of ΣREE are represented by heavy REE (HREE). The main REE minerals are: chevkinite-(Ce), britholite-(Y) and products of their metamict decay, bastnäsite-(Ce), allanite-(Ce), fergusonite-(Y), monazite-(Ce), and others. The areas contain also significant quantities of zircon reaching potentially economic levels. We have discovered that behavior of REE and Zr is controlled by alkalinity of melt/solution, which, in turn, is controlled by crystallization of alkaline pyroxenes (predominantly aegirine) and amphiboles (predominantly arfvedsonite) at a late magmatic stage. Crystallization of mafic minerals leads to a sharp increase of K2O content and decrease of SiO2 content that cause a decrease of melt viscosity and REE and Zr solubility in the liquid. Therefore, REE and zirconium immediately precipitate as zircon and REE-minerals. There are numerous pod- and lens-like granitic pegmatites within the massif. Pegmatites in the REE-rich areas are also enriched in REE, but HREE prevails over light REE (LREE), about 88% of REE sum.

Interaction of rare earth elements and components of the Horonobe deep groundwater

To better understand the migration behavior of minor actinides in deep groundwater, the interactions between doped rare earth elements (REEs) and components of Horonobe deep groundwater were investigated. Approximately 10 ppb of the REEs, i.e. Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, and Yb were doped into a groundwater sample collected from a packed section in a borehole drilled at 140 m depth in the experiment drift of Horonobe Underground Research Laboratory in Hokkaido, Japan. The groundwater sample was sequentially filtered with a 0.2 μm pore filter, and 10 kDa, 3 kDa and 1 kDa nominal molecular weight limit (NMWL) ultrafilters with conditions kept inert. Next, the filtrate solutions were analyzed with inductively coupled plasma mass spectrometry (ICP-MS) to determine the concentrations of the REEs retained in solution at each filtration step, while the used filters were analyzed through neutron activation analysis (NAA) and TOF-SIMS element mapping to determine the amounts and chemical species of the trapped fractions of REEs on each filter. A strong relationship between the ratios of REEs retained in the filtrate solutions and the ionic radii of the associated REEs was observed; i.e. smaller REEs occur in larger proportions dissolved in the solution phase under the conditions of the Horonobe groundwater. The NAA and TOF-SIMS analyses revealed that portions of the REEs were trapped by the 0.2 μm pore filter as REE phosphates, which correspond to the species predicted to be predominant by chemical equilibrium calculations for the conditions of the Horonobe groundwater. Additionally, small portions of colloidal REEs were trapped by the 10 kDa and 3 kDa NMWL ultrafilters. These results suggest that phosphate anions play an important role in the chemical behavior of REEs in saline (seawater-based) groundwater, which may be useful for predicting the migration behavior of trivalent actinides released from radioactive waste repositories in the far future.

Rare earth element behavior during groundwater–seawater mixing along the Kona Coast of Hawaii

Groundwater and seawater samples were collected from nearshore wells and offshore along the Kona Coast of the Big Island of Hawaii to investigate rare earth element (REE) behavior in local subterranean estuaries. Previous investigations showed that submarine groundwater discharge (SGD) is the predominant flux of terrestrial waters to the coastal ocean along the arid Kona Coast of Hawaii. Groundwater and seawater samples were filtered through 0.45μm and 0.02μm pore-size filters to evaluate the importance of colloidal and soluble (i.e., truly dissolved ionic species and/or low molecular weight [LMW] colloids) fractions of the REEs in the local subterranean estuaries. Mixing experiments using groundwater collected immediately down gradient from a wastewater treatment facility (WWTF) proximal to the Kaloko-Hanokohau National Historic Park, and more “pristine” groundwater from a well constructed in a lava tube at Kiholo Bay, were conducted with local seawater to study the effect of solution composition (i.e., pH, salinity) on the concentrations and fractionation behavior of the REEs as groundwater mixes with seawater in Kona Coast subterranean estuaries. The mixed waters were also filtered through 0.45 or 0.02μm filters to ascertain the behavior of colloidal and soluble fractions of the REEs across the salinity gradient in each mixing experiment. Concentrations of the REEs were statistically identical (two-tailed Student t-test, 95% confidence) between the sequentially filtered sample aliquots, indicating that the REEs occur as dissolved ionic species and/or LMW colloids in Kona Coast groundwaters. The mixing experiments revealed that the REEs are released to solution from suspended particles or colloids when Kona Coast groundwater waters mix with local seawater. The order of release that accompanies increasing pH and salinity follows light REE (LREE)>middle REE (MREE)>heavy REE (HREE). Release of REEs in the mixing experiments is driven by decreases in the free metal ion activity in solution and the concomitant increase in the amount of each REE that occurs in solution as dicarbonato complexes [i.e., Ln(CO3)2−] as pH increases across the salinity gradient. Input-normalized REE patterns of Kona Coast groundwater and coastal seawater are nearly identical and relatively flat compared to North Pacific seawater, indicating that SGD is the chief source of these trace elements to the ocean along the Kona Coast. Additionally, REE concentrations of the coastal seawater are between 10 and 50 times higher than previously reported open-ocean seawater values from the North Pacific, further demonstrating the importance of SGD fluxes of REEs to these coastal waters. Taken together, these observations indicate that large-scale removal of REEs, which characterizes the behavior of REEs in the low salinity reaches of many surface estuaries, is not a feature of the subterranean estuary along the Kona Coast. A large positive gadolinium (Gd) anomaly characterizes groundwater from the vicinity of the WWTF. The positive Gd anomaly can be traced to the coastal ocean, providing further evidence of the impact of SGD on the coastal waters. Estimates of the SGD fluxes of the REEs to the coastal ocean along the Kona Coast (i.e., 1.3–2.6mmolNdday−1) are similar to recent estimates of SGD fluxes of REEs along Florida’s east coast and to Rhode Island Sound, all of which points to the importance of SGD as significant flux of REEs to the coastal ocean.

Geochemical features of major and rare-earth element behavior in the Paratunka and Bol’shebannyi hydrothermal systems of Kamchatka

This paper presents original data on the content and distribution of major and rare-earth elements in the modern hydrothermal systems of the Paratunka and Bol’shebannyi thermal water deposits. In spite of the similar geochemical type of the waters, the individual sites of the hydrothermal systems differ in the major component composition, which is caused by the time of water–rock interaction, temperature control, and the possible influence of seawater intrusions. The REE concentrations in the studied thermal waters are extremely low (a few tenths of ppb). A distinctive feature of these thermal waters is the presence of a positive Eu anomaly. The possible reasons for its appearance are discussed. Calculation of REE speciation shows that the main parameters controlling the formation of the REE complexes in the Paratunka and Bol’shebannyi hydrothermal systems are their individual chemical properties, as well as pH, Eh, and temperature of the aqueous solution.

Time-resolved interaction of seawater with gabbro: An experimental study of rare-earth element behavior up to 475 °C, 100 MPa

High metal and rare-earth element (REE) concentrations with unusual (‘atypical’) normalized REE patterns are documented in fluids from active hydrothermal vent fields on the Mid-Atlantic Ridge, 5°S and the East Scotia Ridge. Those fluids show relative enrichment of middle heavy REEs and almost no Eu anomalies in chondrite-normalized patterns. To understand the processes that produce such atypical REE patterns we ran a series of experiments, in which natural bottom seawater or aqueous solutions (NaCl, NaCl–MgCl2, or NaCl–CaCl2) were reacted with gabbro and gabbro mineral assemblages from 300 to 475°C and 40 and 100MPa. These P–T conditions are representative for water–rock interactions in hydrothermal root and discharge zones. Fluid flux variability and kinetics were addressed in the experiments by varying the water-to-rock mass ratio (w/r) from 0.5–10 and using different run durations from 3–720h.Only seawater and synthetic MgCl2-bearing fluid mobilized significant amounts of REEs, Si, Ca, Fe, and Mn from gabbro, from clinopyroxene, and from plagioclase. At 425°C and 40MPa, fluids were initially acidic with pH (25°C) of ∼2 increasing to values between ∼4 and 7 upon progressing reactions. Rare earth element and Fe contents peaked within 3–6h after interaction with gabbroic mineral grains (125–500μm) at w/r of 5 (REEs) and 2–5 (Fe) but decreased with continuing reaction without strong REE fractionation. Most of the REEs that were leached from primary minerals and dissolved in the fluids early became redeposited into solid reaction products after 720h.Contents of dissolved SiO2 were pressure-dependent, being about twofold higher at 100MPa than at 40MPa (425°C) and were below quartz saturation with gabbro and clinopyroxene as solid starting material and close to quartz saturation with plagioclase reactant. However, Si in fluids from the rock-dominated experiments at 100MPa with gabbro (w/r 0.5–1) dropped to very low contents. A concomitant decrease in chlorinity suggests that these changes may be due to the breakdown of olivine and the formation of serpentine and Fe-hydroxy chlorides.Regardless of the starting solid reactants, fluid REE patterns were dominantly controlled by w/r. Atypical fluid REE patterns and high fluid REE contents were obtained at high w/r (⩾5). Whereas typical REE patterns known from many mid-ocean ridge vent fluids, showing relative enrichments of light REEs and a positive Eu anomaly, were obtained at low w/r of 0.5–1. Our results hence clearly show that REE contents and patterns of vent fluids are sensitive to variations in the w/r.

The behavior of rare-earth elements, zirconium and hafnium during magma evolution and their application in determining mineralized magmatic suites in subduction zones: Constraints from the Cenozoic belts of Iran

Processes, such as partial melting, differentiation, assimilation, magma mixing, and liquid immiscibility, together with partition coefficients between minerals and melt, solubility, and redox conditions, are the controlling parameters for element distribution and enrichment processes. These factors can be evaluated through the geochemical variation of trace elements, such as Rare Earth Elements (REEs) and High Field Strength Elements (HFSEs), specifically Zirconium (Zr) and Hafnium (Hf), in magmatic rocks. For this purpose, two well-mineralized Cenozoic subduction-related magmatic belts in Iran—the Arasbaran and the Urumieh-Dokhtar—were evaluated. The results of this study showed that, in subduction zones, the increase in crust thickness with arc maturity caused low partial melting and more differentiation, which left behind magmas with low Zr, Hf and HREEs. These factors can be used to evaluate the degree of differentiation, degree of partial melting, and the correlation of different magma pulses, from initiation to the end of the subduction processes. Using Zr-Hf or Hf-(Zr/Hf) diagrams, we concluded that low Zr and Hf contents with low Zr/Hf ratios without a Europium (Eu) negative anomaly, and with high LREE/HREE ratios, indicated the more evolved and mineralized magmatic suites, which occurred particularly in the mature arcs.

Negative cerium anomalies in manganese (hydr)oxide precipitates due to cerium oxidation in the presence of dissolved siderophores

We present experimental results on the sorption behavior of rare earth elements and yttrium (REY) on precipitating manganese (hydr)oxide in the presence of the biogenic siderophore desferrioxamine B (DFOB). In marked contrast to inorganic systems, where preferential adsorption of HREY and depletion of LREY is commonly observed in manganese (hydr)oxide precipitates, sorption of REY in presence of the DFOB siderophore leads to HREY-depleted and LREY-enriched patterns in the precipitates. Moreover, our data indicate that surface oxidation of Ce(III) to Ce(IV) during sorption onto manganese (hydr)oxides and the resulting development of a positive Ce anomaly, which are commonly observed in inorganic experiments, are prevented in the presence of DFOB. Instead, Ce(III) is oxidized to Ce(IV) but associated with the dissolved desferrioxamine B which forms complexes with Ce(IV), that are at least twenty orders of magnitude more stable than those with Ce(III) and REY(III). The overall result is the formation of a positive Ce anomaly in the solution and a negative Ce anomaly in the Mn (hydr)oxides. The distribution of the strictly trivalent REY and Eu(III) between the manganese (hydr)oxide phase and the remaining ambient solution mimics the distribution of published stability constants for complexes of REY(III) with DFOB, i.e. the heavy REY form more stable complexes with the ligand and hence are better shielded from sorption than the LREY. Surface complexation modeling corroborates our experimental results. Negative Ce anomalies in Mn precipitates have been described from biogenic Mn oxides. Our results provide experimental evidence for the development of negative Ce anomalies in abiogenic Mn (hydr)oxide precipitates and show that the presence of the widespread siderophore desferrioxamine B during mineral precipitation results in HREY-depleted Mn (hydr)oxides with negative Ce anomalies.

Acidic drainage drives anomalous rare earth element signatures in intertidal mangrove sediments

Sedimentary rare earth element (REE) signatures can provide powerful insights into nearshore biogeochemical processes and anthropogenic influences. Despite this, there is limited research investigating REE behaviour in sediments influenced by coastal acid sulfate soils (CASS). Here, we explore REE abundance and fractionation in intertidal mangrove sediments that received CASS drainage for ~15–20y within the Hastings Catchment in NSW, Australia. Sediments close to the CASS discharge point (<200m) were compared with those further downstream (1300–1600m), and at a nearby control site. Average ΣREE concentrations were highest near the CASS discharge point (148–186mg/kg), and decreased with distance downstream (111–146mg/kg) and in control sediments (70mg/kg). Reactive Fe concentrations (defined by 1M HCl extractability) were also significantly higher in surface sediments (0–6cm) near the CASS discharge point. Middle-REE (MREE) enrichments dominated fractionation patterns at all sites (>1.5), with a high proportion (63–100%) of REEs residing in the reactive (1M HCl extractable) sediment fraction. Interestingly, the degree of MREE enrichment was significantly correlated with Ce anomalies (r2=0.72, P<0.001) and the heavy-REE (HREE) to light-REE (LREE) ratios (HREE/LREE, r2=0.74, P<0.001) in the reactive sediment fraction, only in those sites situated closest to the CASS drainage. The observed high MREE enrichments, positive Ce anomalies (>1) and HREE/LREE ratios (>1) are consistent with reactive Fe(III) oxides/oxyhydroxides driving REE retention in these sediments. This study indicates that CASS drainage alters REE signatures in receiving sediments by (1) providing a source of REEs, thereby enhancing sedimentary REE concentrations, and (2) causing accumulation of reactive Fe(III) phases with a high affinity for REEs. Together, these two factors drive the development of distinctive REE signatures in CASS-impacted sediments. The recognition of such signatures may provide a promising tool for identifying coastal sediments receiving anthropogenic CASS drainage inputs.

Electrolytic Refining of Rare Earth Element from Neodymium Magnet Using Molten Salt

Introduction Neodymium magnets contain large amounts of neodymium, praseodymium, and dysprosium. Dysprosium, which is more expensive than neodymium and praseodymium, is added to neodymium magnets to increase their heat resistance. Neodymium magnets are used in numerous consumer electronics and electric- and hybrid-powered vehicles. Large amounts of neodymium are wasted each year when products that contain these magnets are discarded. Processes for the recovery of rare earth elements from neodymium magnets have been developed. Rare earth oxides are recovered from these processes, and these oxides are subsequently reduced to rare earth metals using molten salt electrolysis. We have reported a recovery process for rare earth elements from neodymium magnets using molten salt electrolysis, where these elements were recovered as alloys. In this study, we focus on the electrical behavior of rare earth elements in neodymium magnets during molten salt electrolysis. We use anodic polarization experiments to determine the optimal electric leaching conditions and observe the leaching behavior of rare earth elements. Materials and Methods The electrolysis potential was controlled using a potentiostat. The reactor was made of Pyrex glass and purged with Ar gas. A eutectic salt mixture of 59-mol% LiCl and 41-mol% KCl (melting point: 626 K), which melted at 723 K, was used in the electrolysis bath. The cathode electrode was a glassy carbon rod. The anode electrode was a neodymium magnet, a neodymium rod, a dysprosium rod, or an iron wire. The reference electrode was Ag/AgCl (0.1 N) in a eutectic composition of LiCl–KCl; this electrode was placed in a mullite tube. The electrolysis bath was maintained at 473 K for 24 h under a vacuum to eliminate water. Results and Discussion The scan rate of anodic polarization was 5 mV s−1. The oxidation current of neodymium and dysprosium is generated at approximately −2.2 V, and oxidation potential is the lowest among the elements in the neodymium magnet. The iron oxidation potential was the highest at −0.7 V. Iron is the main component of the neodymium magnet, and the leaching of iron must be avoided in the recovery process. The use of potentiostatic electrolysis enables the selective leaching of rare earth elements from the neodymium magnet, as reported in our previous research. Rare earth elements were leached from the neodymium magnets using potentiostatic electrolysis. The neodymium magnets were used as the anode, and a carbon rod served as the cathode. The electrolysis potential was −1.0 V, and the quantity of electricity was approximately 1200 C. the residual magnet and molten salt compositions were similar for all three neodymium magnets used in the experiments. The residual iron content increased, and the concentrations of the rare earth elements decreased. The rare earth elements were leached from the neodymium magnet into the molten salt, and the total rare earth content in the molten salt was greater than 99.0 mass%. Conclusion Rare earth elements were leached from neodymium magnets using electrolysis in a molten eutectic mixture of LiCl and KCl. The oxidation potential of all neodymium magnet was −1.0 V. The oxidation potential of dysprosium was similar to those for neodymium and praseodymium. The content of rare earth elements in the leaching component was greater than 99.0 mass%. Acknowledgement This work was supported by Environment Research and Technology Development Fund of the Ministry of the Environment, Japan 3K143005.

Fractionation characteristics of rare earth elements (REEs) linked with secondary Fe, Mn, and Al minerals in soils

Soil secondary minerals are important scavengers of rare earth elements (REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs (La to Lu and Y) associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La–Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs (LREEs) enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs (HREEs) was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs. The substantial fractions of REEs in soils extracted by oxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile (10 %–30 %), which were similar to the mass fraction of Fe (10 %–20 %). Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil formation from REE fractionation.

The profile of the rare earth elements in the Canada Basin, Arctic Ocean

AbstractWe analyzed the dissolved rare earth element (REE) content of three water column profiles (two shelf sites and one deep basin site) in the Canada Basin in order to better constrain the behavior of REEs in the Arctic Ocean. Dissolved concentrations of the REEs in the surface are 1.3–1.9 times higher than deep water (&gt;500 m) concentrations, which are constant with depth (La: 19–23 pM, Nd: 14–17 pM, Yb: 4.0–4.3 pM). The dominant source of REEs to the surface waters of the Canada Basin is most likely Pacific water flowing through the Bering Strait and Chukchi Sea and/or the Mackenzie River. Dissolved REEs in the intermediate and deep waters are constant and appear to behave conservatively, allowing us to investigate this aspect of REE behavior in the oceans. Calculated deep ocean residence times of the REEs in the Canada Basin range from 450 to 700 years and match the age of these waters. We postulate that these values are likely applicable to global deep ocean reservoirs and that observed deviations from this conservative value can help to constrain nonconservative processes acting on the REEs.

Behavior of rare earth elements and yttrium during simulation of arctic estuarine mixing between glacial-fed river waters and seawater and the impact of inorganic (nano-)particles

Rivers are the major source of many trace elements to the oceans. As a consequence of climate change, increasing volumes of glacial meltwater enter the oceans after being affected by estuarine processes. Although the behavior of high field strength elements such as the rare earth elements and yttrium (REY) has been intensively studied in tropical, temperate and boreal estuaries, little is known about arctic estuarine mixing of glacial-fed river waters that are poor in organic nanoparticles and colloids (NPCs), but rich in inorganic NPCs. Here we provide the first data set from estuarine mixing experiments with glacial-fed river waters and seawater. The glacial-fed river water endmembers originate from southern Iceland (sampled in 2010 and 2013) and from West Greenland (sampled in 2013); these endmembers are rich in NPCs and larger particles of (glassy) volcanic ash and of ultra-fine rock flour, respectively.For the mixing experiments, 0.2 μm-filtered glacial-fed river water was mixed with seawater in different ratios to cover the full range of estuarine low- to high-salinity conditions. All 2010 freshwater endmembers show higher concentrations of individual REY (due to their high NPC load) than the respective seawater endmember, whereas the 2013 freshwater endmembers have higher light REY, but lower heavy REY concentrations (due to significantly less NPCs). Admixture of minute amounts of seawater (5% and 10% seawater (SW) admixture, i.e. salinities of ~1.7 psu and of ~3.4 psu, respectively) already has a strong impact on REY concentrations and REY signatures. In all experiments, a large amount of REY (e.g., up to 98.2% of Nd and 98.2% of Yb) is removed at very low salinities. At intermediate to high salinities, however, remobilization of REY from aggregated NPCs occurs if NPC-rich river waters are used in the experiments, whereas if the endmember is poor in NPCs, the REY mix almost conservatively. The REY removal is dependent on the amount of NPCs present in the glacial-fed river waters; NPC-rich river water shows larger REY removal than NPC-poorer river water. After the initial drop in REY concentrations under low-salinity conditions, the experiment with glacial-fed river water from Greenland reveals that heavy REY mix almost conservatively, but light REY are again remobilized from aggregated NPCs. Our results suggest that aggregated NPCs composed of rock flour (Greenland) and volcanic ash (Iceland) may cause different trace element behavior during estuarine processes. However, all experiments show similar Y-Ho fractionation during estuarine mixing, indicating that the actual type of particle is not a major constraint on Y-Ho behavior, but rather the availability of particle surfaces. Estuarine processes may cause the development of negative Ce anomalies during remobilization of REY at higher salinity if Ce(IV) compounds of low solubility are present in the (nano-)particle load. However, if only Ce(III) is present, such as in fresh mafic volcanic ash, no fractionation of Ce from its trivalent REY neighbors occurs.

Decomposition of the mixed rare earth concentrate by microwave-assisted method

A novel process was proposed to strengthen the decomposition of the mixed rare earth concentrate by utilizing the microwave radiation. Mineralogical information on the mechanisms by which microwave heating improved the leaching behavior of rare earth elements (REEs), and an interpretation of the interrelationship between mineralogy, decomposition process, and leaching process were provided in this study. The influences of the temperature, time of microwave heating and contents of NaOH (mass ratio of NaOH to mixed rare earth concentrate) on the decomposition of mixed rare earth concentrate were investigated. The results revealed that the temperature was the main factor affecting the decomposition process. The recovery of REEs by hydrochloric acid leaching reached 93.28% under the microwave heating conditions: 140 °C, 30 min and 35.35% NaOH. The BET specific surface area and SEM analysis indicated that the particles of mixed rare earth concentrate were non-hole, while the particles presented a porous structure after heating the concentrate by microwave radiation. For the microwave treated sample after water leaching, the BET specific surface area was 11.04 m2/g, which was higher than the corresponding values (6.94 m2/g) for the mixed rare earth concentrate. This result could be attributed to the phase changes of bastnaesite and monazite, and a number of cracks induced by thermal stress. The increase of BET specific surface area resulted in an increase of the recovery of REEs by promoting interaction within the system of acid leaching.

Adsorption ability of rare earth elements on clay minerals and its practical performance

The adsorption behaviors of rare earth elements on clay minerals would have great influence on the mineralization process and the leaching process of the ion-adsorption type rare earths ore. In this work, the adsorption thermodynamics of REEs on kaolin were investigated thoroughly and systematically. The experimental results showed that the adsorption characteristics of La, Nd, Y on kaolin did fit well with the Langmuir isotherm model and their saturated adsorption capacities were 1.731, 1.587 and 0.971 mg/g, respectively. The free energy change (ΔG) values were −16.91 kJ/mol (La), −16.05 kJ/mol (Nd) and −15.58 kJ/mol (Y), respectively. The negative values of ΔG demonstrated that the adsorption of rare earth on kaolin was a spontaneously physisorption process. The deposit characteristic of the volcanic ion-adsorption type rare earths ore and the behavior of the rare earth in the column leaching process were also developed here. With the increase of the ore body depth, the distribution of the LREEs decreased and the HREEs increased. And the slight differences in the adsorption ability of REEs on clay minerals led to the fractionation effect in the column leaching process. These developed more evidences and better understanding of metallogenic regularity, and provided a theoretical basis and scientific approach to separation of the HREEs and LREEs in the leaching process.

HCl leaching behaviour of a bastnasite ore in terms of thorium and rare earth elements

Today, nuclear energy is considered as one of the most important energy sources. Thorium (Th) is also very important for nuclear energy because it can exist in nature spontaneously just as uranium (U) without depending on presence of another radioactive element. As plutonium and other trans-uranium elements are produced in lesser amounts compared to U in Th fuel cycle, Th is considered as the cleanest nuclear plant fuel. Bastnasite is one of the minerals which Th can be economically obtained. Bastnasite (Ce, La)FCO3, which is a rare earth fluorocarbonate, contains approximately 0.2–0.3% Th and 75% rare earth oxides. Within the scope of this study, dissolution behaviour of Th and rare earth element (REE) contents present in the bastnasite ores which is obtained from Eskisehir region of Turkey, with HCl leaching method was examined. In this context, the effects of different leaching parameters such as leaching time, HCl concentration and pulp temperature on Th and REE (Ce, Nd, La) dissolution efficiency and the best results have been obtained in the conditions of 5.48 M of HCl dosage, 220 min. of leach time and 70°C pulp temperature. In these optimum conditions, Th, Ce, Nd and La were obtained with dissolution efficiencies of 80.12, 77.12, 70.12 and 71.13%, respectively.

Zirconium–hafnium and rare earth element signatures discriminating the effect of atmospheric fallout from hydrothermal input in volcanic lake water

Geochemical behaviour of rare earth elements (REE), Zr, and Hf was investigated in CO2-rich waters circulating in Pantelleria Island also including ‘Specchio di Venere’ Lake within a calderic depression. A wide range of total dissolved REE concentrations was found (2.77–12.07nmolL−1), with the highest contents in the lake. The main REE complexes in the CO2-rich waters are [REE(CO3)2]− and [REECO3]+, showing changeable proportions as a function of pH. The REE normalized to post-Archean Australian Shale (PAAS) showed similar features with heavy REE (HREE) enrichments in CO2-rich waters collected from springs and wells, whereas a different REE pattern was found in the ‘Specchio di Venere’ Lake water with middle REE (MREE) enrichments. The PAAS normalized concentration ratios (LREE/HREE)N and (MREE/HREE)N in waters are <1, except for the lake water in which (MREE/HREE)N>1. Positive Eu anomalies were found in the investigated waters owing to water–rock interactions with less evolved host rocks. Ce anomalies as a function of Eh values were recognized, with the highest Ce anomaly occurring in the lake water with respect to the CO2-rich waters. The Y/Ho and Zr/Hf molar ratios are higher in the investigated waters (except for lake water) than that in the local rocks, with values ranging from 35.4 to 77.9 and from 76.3 to 299, respectively. The precipitation of authigenic phases was considered to be responsible for the increase in the Y/Ho and Zr/Hf ratios owing to enhanced Hf and Ho removal with respect to Zr and Y.The REE patterns in the lake water show a similar shape (MREE-enriched and a positive Ce anomaly) as those found in the settling dust and in the desert varnish coating of the rocks in arid environments, which mainly contain Fe- and Mn-oxyhydroxides and clay minerals. Similarly, Y/Ho and Zr/Hf ratios in the ‘Specchio di Venere’ Lake (35.4 and 76.3, respectively) show a desert varnish signature. These data, coupled with the presence of iron oxyhydroxides and phyllosilicates in the shallowest water layer of the ‘Specchio di Venere’ Lake, verify the aeolian input from the Sahara Desert.

Atmospheric deposition of rare earth elements in Albania studied by the moss biomonitoring technique, neutron activation analysis and GIS technology.

Rare earth elements (REEs) are typically conservative elements that are scarcely derived from anthropogenic sources. The mobilization of REEs in the environment requires the monitoring of these elements in environmental matrices, in which they are present at trace level. The determination of 11 REEs in carpet-forming moss species (Hypnum cupressiforme) collected from 44 sampling sites over the whole territory of the country were done by using epithermal neutron activation analysis (ENAA) at IBR-2 fast pulsed reactor in Dubna. This paper is focused on REEs (lanthanides) and Sc. Fe as typical consistent element and Th that appeared good correlations between the elements of lanthanides are included in this paper. Th, Sc, and REEs were never previously determined in the air deposition of Albania. Descriptive statistics were used for data treatment using MINITAB 17 software package. The median values of the elements under investigation were compared with those of the neighboring countries such as Bulgaria, Macedonia, Romania, and Serbia, as well as Norway which is selected as a clean area. Geographical distribution maps of the elements over the sampled territory were constructed using geographic information system (GIS) technology. Geochemical behavior of REEs in moss samples has been studied by using the ternary diagram of Sc-La-Th, Spider diagrams and multivariate analysis. It was revealed that the accumulation of REEs in current mosses is associated with the wind-blowing metal-enriched soils that is pointed out as the main emitting factor of the elements under investigation.

Anomalous abundance and redistribution patterns of rare earth elements in soils of a mining area in Inner Mongolia, China.

The Bayan Obo Mine, the largest rare earth element (REE) deposit ever found in the world, has been mined for nearly 60years for iron and rare earth elements. To assess the influences of mining activities on geochemical behavior of REEs in soils, 27 surface soil samples and three soil profile samples were collected from different directions in the vicinity of the mine area. The total concentrations of REEs in surface soils varied from 149.75 to 18,891.81mgkg(-1) with an average value of 1906.12mgkg(-1), which was apparently higher than the average values in China (181mgkg(-1)). The order of the average concentrations of individual REEs in surface soils was similar to that in Bayan Obo ores, which confirmed that the concentration and distribution of REEs in the soils was influenced by the mining activities. The concentrations of single REE in the soil profiles showed a similar trend with depth with an increase at 0-25cm section, then decreased and remained relatively stable in the deep part. The normalized curves inclined to the right side, showing the conspicuous fractionation between the light and heavy REEs, which supported by the North American Shale Composite (NASC) and Post-Archean Australian Shale (PAAS) normalized concentration ratios calculated for selected elements (La N /Yb N , La N /Sm N , Gd N /Yb N ). Slight positive Ce anomaly and negative Eu anomaly were also observed.

A geochemical modeling to predict the different concentrations of REE and their hidden patterns using several supervised learning methods: Choghart iron deposit, bafq, Iran

The Bafq mining district hosts some Kiruna-type iron oxide-apatite (IOA) deposits which are commonly formed as a result of the multistage interaction of hydrothermal-magmatic processes within the Early Cambrian volcano-sedimentary sequence. Rare earth elements (REEs) are potentially concentrated under different physicochemical conditions in IOA deposits. Choghart orebody is one of the main magnetite-apatite deposits in the region. A wide range of primary and secondary geological events have affected the Choghart deposit, causing the behavior of REEs to vary in different zones. This study proposes a suitable exploration technique using various classification methods to identify the different concentrations of REE and their hidden patterns. To provide the required data, a systematic lithogeochemical sampling was performed in the north and NE of the Choghart orebody. The REE contents of samples were transformed into discrete values as distinct classes based on the results of clustering analysis. All possible combinations of features, being the geographical location and the major oxide composition of samples, were selected as subsets of predictors in every classification method. For each REE, 455 prediction models were constructed using these predictors. The performances of the classification methods were evaluated by error criteria with regard to all cases. Having the least amount of errors, the decision tree method was selected as the most suitable method. Based on decision tree results, the best subsets of predictors were chosen for each element. The existence of a significant relationship between the distribution patterns of each REE and the related predictors was assessed by its prediction errors. The assessment illustrated that some REE are reasonably predictable, and others are too irregular to be modeled. The extracted classification rules describe the geochemical relationships among the most important factors influencing the different concentrations of REE in the Choghart orebody. These results can be extended to other similar deposits to predetermine some REE-enriched zones based on major elements analysis. Merely by employing such techniques in REE exploration projects, a great savings in time and cost will be affected.

Geochemical peculiarities of ores from the largest Natalka gold deposit in Northeastern Russia

This study of the behavior of trace and rare earth elements in ores from the Natalka gold deposit allows us to draw several conclusions. It is suggested that ore formation is related to the regional metamorphism of the host terrigenous carbonaceous rocks, which could be the major source for trace and rare earth elements. Minor enrichment of the Natalka ores in W is evidence of the contribution of magmatic fluid, which could be superimposed on early quartz veins, in ore formation. Our results support the metamorphic–magmatic model of formation of economic gold–quartz deposits of the Yana–Kolyma Belt. The similarity of metasomatites of the Natalka deposit with disseminated gold–sulfide refractory ores from the Nezhdaninskoe and Bakyrchik deposits points to the possible presence of such ores in the Natalka deposit. Our data are important for forecasting regional metallogenic reconstructions, search, and evaluation of gold deposits.