Total Rare Earth Elements Content Research Articles

Correction to: Comparison of Single-Phase and Two-Phase Composite Thermal Barrier Coatings with Equal Total Rare-Earth Content

Correction to: Comparison of Single-Phase and Two-Phase Composite Thermal Barrier Coatings with Equal Total Rare-Earth Content

Carbon isotope and REE characteristics of the Paleocene–Eocene shallow marine Subathu formation from the NW Himalaya (India) and their paleo-environmental implications

Carbon isotope (δ13C) and rare earth element (REE) concentrations in representative samples of the shallow marine Subathu Formation, explored from the Neelkanth and Dogadda sections of Northwestern Himalaya (India) were determined to infer the palaeo-environmental condition during the late Paleocene and middle Eocene. δ13C values show variation of ∼5.0‰ with maximum excursion (−27.34‰) in calcareous sandstone at the basal part and minimum (−22‰) in red shale towards the terminal end. Total REE concentration varies (due to lithology) from 27.23 ppm to 564.35 ppm with an average of 187.60 ppm. The chondrite and PAAS normalized patterns exhibit positive Ce anomaly (0.95–4.45), enriched LREE, and depleted HREE, medium Y/Ho ratio (∼30–45) along with positive correlation between Y/Dy and Y/Ho ratio. In addition, calcite veins present in some shale samples indicate redox sensitive trace elements. The overall REE abundance and distribution suggests highly oxygenated environment under the shallow marine regressive phase of deposition. The depositional setting, biostratigraphical constrained age along with δ13C values and lower TOC suggested an intense warm period, that might be coeval with the Paleocene-Eocene Thermal Maxima event (PETM).

Effects of Sm content on microstructures and mechanical properties of casting Mg-Y-Nd-Sm-Zr alloys

The microstructures and mechanical properties of Mg-5Y-2Nd-xSm-0.5Zr (x = 0, 1, 3, 5) alloys were investigated. The results indicated that a new Mg41Sm5 phase was generated in the as-cast Sm-containing alloys. As the Sm content was increased, the grain of α-Mg matrix was refined and the amount of second phases at the grain boundary increased. After the solution and aging treatment, a large number of β′ phases precipitated, the alloys mainly consisted of α-Mg, Mg24Y5, Mg41Nd5 and Mg41Sm5. The grain size significantly reduces from 80 μm to 23 μm with the increasing of Sm content. Under all conditions in this paper, Mg-5Y-2Nd-3Sm-0.5Zr alloy had the best mechanical properties. The tensile strength and elongation of the aged Mg-5Y-2Nd-3Sm-0.5Zr alloy were 296.9 MPa, 4.78% room temperature and 279.4 MPa, 6.43% at 250 °C, respectively. The mechanical properties of this alloy is obviously superior to the commercial WE54 alloy with equivalent total rare earth content, which has excellent heat resistance and can be reliably applied below 250 °C. The improving of the mechanical properties is mainly due to grain refining strengthening, solid solution strengthening and precipitation strengthening of the β′-Mg41Sm5 phase.

Effects of roasting additives and leaching parameters on the extraction of rare earth elements from coal fly ash

Coal fly ash is a promising alternative source for rare earth elements (REE), which are critical materials in many technologies. REEs are entrained in the aluminosilicate glass of the fly ash particles, hindering their ability to solubilize during acid leaching. The purpose of this research was to test the effectiveness of roasting techniques to improve extraction of REEs from fly ash, determine key parameters controlling REE extraction, and understand trade-offs in reagent use. Representative coal ash samples from major U.S. coal basins (Appalachian, Illinois, and Powder River basins) were roasted using a variety of chemical additives (Na2O2, NaOH, CaO, Na2CO3, CaSO4, (NH4)2SO4). Further experiments investigated the effects of additive:ash ratio, roasting temperature, and leachate pH on REE extraction. We found that NaOH roasting often recovered >90% of total REE content, equivalent to the USGS-recommended method (Na2O2 sintering). Other additives tested recovered <50% of total REE content; the 450 °C sinter temperature, which was well below the melting points of these agents, may have been a contributing factor. Decreasing the NaOH-ash ratio did not significantly inhibit in REE recoveries, while increasing the leachate pH led to a sharp decline. There was a strong positive correlation between REE extraction and leachate H+ molarity. Recoveries of ~100% were observed for the Powder River Basin ash sample regardless of the roasting agent and additive:ash ratio used. This suggests that acid leaching alone is sufficient for recovering REEs from more soluble Powder River Basin ashes. For Appalachian and Illinois Basin ashes, the recommended roasting conditions for >70% REE extraction are a 1:1 NaOH-ash ratio and leaching with 1–2 mol/L HNO3.

The different sources and petrogenesis of Jurassic intrusive rocks in the southern Lhasa subterrane, Tibet: Evidence from the trace element compositions of zircon, apatite, and titanite

ABSTRACT The Jurassic magmatism distributed in the southern Lhasa subterrane (SLT) has been recognized as a record of the early-stage evolution of the Neo-Tethys ocean; however, the magma compositions and detailed crystallization histories remain an enigma. Zircon, apatite, and titanite in igneous rocks can serve as effective petrogenetic indicators. In this paper, we present the whole-rock geochemical, zircon U Pb data, zircon Hf isotopic analyses, and major and trace elemental compositions of zircon, apatite, and titanite from Baiga granite porphyry (EGP), Shanba granodiorite (EGD), Pengcuolin granodiorite porphyry (MGP), and Dazhuqu monzonite (LM) rocks in the SLT to constrain their source and petrogenesis. The results from this study show that a combination of zircon Ti, Th/U, Hf, and rare earth element (REE) contents, apatite halogen, REE and Sr contents, and titanite REEs can be used to track the detailed magmatic crystallization histories. Higher Sr contents are found in apatite (SrAp) from EGP (ca. 192 Ma) and EGD (ca. 176 Ma) than those in their host rocks (SrWR), indicating that their magma genesis may have involved some mafic magma. The magma genesis of LM (ca. 159 Ma) may have involved more reduced mafic (or least evolved) magma, as evidenced by the higher Th/U but lower Yb/Gd ratios, higher zircon saturation and Ti-in-zircon temperatures in zircon, highest SrAp/SrWR ratios, and large positive Eu anomalies in titanite from LM. The lower Cl contents and higher (La/Sm)N values in apatite from MGP (ca. 172 Ma) are inherited from the low-Cl melts. The MGP rocks have higher zircon Ce4+/Ce3+ and EuN/EuN* ratios, a greater apatite SO3 content, and a higher titanite total REE content, which indicates that MGP has a higher oxidation state than do EGP, EGD, and LM. The MGP also exhibits a higher H2O content (>11 wt%) dissolved in the melt, greater Ba/La and Nb/Ta ratios in whole rock, and higher Nb/Ta ratios in zircon. However, MGP demonstrates lower zircon saturation and Ti-in-zircon temperatures, which suggest that MGP was generated by fluid-fluxed melting below 750 °C. The low Ti-in-zircon temperatures but high La/Yb and Sr/Y ratios of MGP indicate that a local thickened crust likely existed in the Middle Jurassic period in the SLT due to mafic magma underplating during this time.

Syntrophic effect of indigenous and inoculated microorganisms in the leaching of rare earth elements from Western Australian monazite

The unique physiochemical properties exhibited by rare earth elements (REEs) and their increasing application in high-tech industries has created a demand for secure supply lines with established recovery procedures that create minimal environmental damage. Bioleaching experiments conducted on a non-sterile monazite concentrate with a known phosphate solubilising microorganism (PSM) resulted in greater mobilisation of REEs into solution in comparison to experiments conducted on sterile monazite. By combining the native consortia with an introduced PSM, a syntrophic effect between the populations effectively leached a greater amount of REEs than either a single PSM or the indigenous population alone. With sterile monazite, Penicillium sp.CF1 inoculated experiments released a total REE concentration of 12.32 mg L−1 after incubation for 8 days, whereas on non-sterile ore, double the soluble REE concentration was recorded (23.7 mg L−1). Comparable effects were recorded with Enterobacter aerogenes, Pantoea agglomerans and Pseudomonas putida. Alterations in the microbial populations during bioleaching of the monazite ore were determined by diversity profiling and demonstrated noticeable changes in community inhabitants over 14 days. The presence of native Firmicutes on the monazite appears to greatly contribute to the increased leaching recorded when using non-sterile monazite for REE recovery.

The role of magmatic and post-magmatic hydrothermal processes on rare-earth element mineralization: A study of the Bachu carbonatites from the Tarim Large Igneous Province, NW China

The contribution of magmatic and hydrothermal processes to rare earth element (REE) mineralization of carbonatites remains an area of considerable interest. With the aim of better understanding REE mineralization mechanisms, we conducted a detailed study on the petrology, mineralogy and C-O isotopes of the Bachu carbonatites, NW China. The Bachu carbonatites are composed predominantly of magnesiocarbonatite with minor calciocarbonatite. The two types of carbonatite have primarily holocrystalline textures dominated by dolomite and calcite, respectively. Monazite-(Ce) and bastnäsite-(Ce), the major REE minerals, occur as euhedral grains and interstitial phases in the carbonatites. Melt inclusions in the dolomite partially rehomogenize at temperatures above 800 °C, and those in apatite have homogenization temperatures (Th) ranging from 645 to 785 °C. Oxygen isotope ratios of the calciocarbonatite intrusions (δ18OV-SMOW = 6.4‰ to 8.3‰), similar to the magnesiocarbonatites, indicate the parental magma is mantle-derived, and that they may derive from a more evolved stage of carbonatite fractionation. The magnesiocarbonatites are slightly enriched in LREE whereas calciocarbonatites have higher HREE concentrations. Both dolomite and calcite have low total REE (TREE) contents ranging from 112 to 436 ppm and 88 to 336 ppm, respectively, much lower than the bulk rock composition of the carbonatites (371 to 36,965 ppm). Hence, the fractional crystallization of carbonates is expected to elevate REE concentrations in the residual magma.Rocks from the Bachu deposit with the highest TREE concentration (up to 20 wt%) occur as small size (2 mm to 3 cm) red rare earth-rich veins (RRV) with barite + celestine + fluorapatite + monazite–(Ce) associations. These rocks are interpreted to have a hydrothermal origin, confirmed by the fluid inclusions in barite with Th in the range 198–267 °C. Hydrothermal processes may also explain the existence of interstitial textures in the carbonatites with similar mineral assemblages. The C-O isotopic compositions of the RRV (δ13CV-PDB = −3.6 to −4.3‰, δ18OV-SMOW = 7.6 to 9.8‰) are consistent with an origin resulting from fluid exsolution at the end of the high temperature fractionation trend. A two-stage model involving fractional crystallization and hydrothermal fluids is proposed for the mineralization of the Bachu REE deposit.

Aqueous acid and alkaline extraction of rare earth elements from coal combustion ash

The recovery of rare earth elements (REEs) from coal combustion fly ash has recently gained attention as a possible beneficial reuse application that could provide an alternative, low-grade source of REEs in an unstable global supply market. To economically recover REEs, an efficient process needs to be developed to remove them from the ash. This study investigated different methods of leaching REEs from fly ash and other coal combustion ashes. Aqueous acid and alkaline leaching were employed on multiple types of coal fly ash samples (representing coals from three major U.S. coal basin sources) with variable leaching parameters that include extractant type (HCl, NaOH), extractant concentration, leachate-to-ash ratio, and addition of CaO during the leaching process. Acid leaching of high calcium-containing fly ashes such as samples derived from Powder River Basin coals had the highest recoveries of REEs (near 100% of total REE contents), while leaching efficiencies were much lower (<40%) for low calcium fly ashes from Appalachian and Illinois Basin coals. If the fly ashes were subjected to aqueous NaOH (to decompose alumunosilicates) and followed with dilute acid to maintain solubility of metal cations, recoveries of the REEs was up to 85% for Appalachian ashes. Overall, these results demonstrate that REEs in the Powder River Basin-based coal fly ashes are more easily leached into acidic solution than the other ashes tested. While the Appalachian Basin-based coal ashes contained the highest total REEs concentrations out of all regional coal ash sources, these ashes required more complex leaching methods that first decompose the aluminosilicate glassy matrix of the ash (e.g. alkaline digestion) prior to acid leaching.

Distribution, pollution, and ecological risks of rare earth elements in soil of the northeastern Qinghai–Tibet Plateau

ABSTRACTInformation on rare earth elements (REEs) in soils of the Qinghai–Tibet Plateau is very limited. Therefore, this study performed field sampling to explore the concentrations, contamination degree, and potential ecological risks of REEs in soil of the northeastern Qinghai–Tibet Plateau. Concentrations of total REEs (TREEs) ranged from 95.82 to 544.01 mg/kg with average value of 241.81 mg/kg. Light REEs accounted for 72.3%–84.2% of TREEs, whereas Ce was the dominant element. Four methods were employed to evaluate the pollution of soil REEs. About 45.7% of sampling sites exhibited uncontaminated to moderately contaminated levels based on geoaccumulation index values of TREEs. Over 95.7% of sampling sites exhibited deficiency to minimal enrichment based on enrichment factor values of TREEs. The pollution load index evaluation results illustrated that about 85.7% of sampling sites possessed moderate levels of pollution, more serious than those evaluated by modified degree of contamination method. The potential ecological risk indexes of soil REEs in study area ranged from 11.02 to 40.55, showing low risk levels. This study provided important information on REEs in soils of the northeastern Qinghai–Tibet Plateau for soil pollution prevention and control at the high-elevation areas.

Seasonal and spatial variations in rare earth elements and yttrium of dissolved load in the middle, lower reaches and estuary of the Minjiang River, southeastern China

With the aim of elucidating the spatial and seasonal behaviors of rare earth elements (REEs), we investigated the dissolved REE concentrations of surface water collected during four seasons from middle, lower reaches and estuary of the Minjiang River, southeastern China. The results display that the REE abundances in Minjiang River, ranging from 3.3–785.9 ng/L, were higher than those of many of the major global rivers. The total REE concentrations (ΣREE) were seasonally variable, averaging in 5 937.30, 863.79, 825.65 and 1 065.75 ng/L during second highest flow (SHF), normal flow (NF), low flow (LF) and high flow (HF) season, respectively. The R(L/M) and R(H/M) ratios reveal the spatial and temporal variations of REE patterns, and particularly vary apparently in the maximum turbidity zone and estuary. REE patterns of dissolved loads are characterized by progressing weaker LREEs-enrichment and stronger HREEsenrichment downstream from middle reaches to estuary during all four seasons. Comparing with NF and LF seasons, in which REE patterns are relatively flat, samples of SHF season have more LREE-enriched and HREE-depleted patterns that close to parent rocks, while samples of HF season are more LREEs-depleted and HREE-enriched. REE fractionations from the middle to lower reaches are stronger in the SHF and HF seasons than those in NF and LF seasons. Generally, spatial and seasonal variations in REE abundance and pattern are presumably due to several factors, such as chemical weathering, mixture with rainfall and groundwater, estuarine mixing, runoff, biological production and mountain river characters, such as strong hydrodynamic forces and steep slopes. The highest Gd/Gd * always occurs at north ports during all four seasons, where most of the large hospitals are located. This suggests Gd anomalies are depended on the density of modern medical facilities. Y/Ho ratios fluctuate and positively correlate to salinity in estuary, probably because of the geochemical behavior differences between Y and Ho.

Conception of an integrated flowsheet for rare earth elements recovery from coal coarse refuse

The majority of rare earth elements (REEs) existing in the feed to coal preparation plants report to the coarse refuse streams which are transported for permanent storage in contained piles. In this study, an integrated flowsheet was developed based on laboratory test data which combines physical separation, pyrite bio-oxidization, heap leaching, selective precipitation and solvent extraction processes. The test data was obtained from (1) characterization of a number of natural leachate and solid samples collected from different preparation plants which process coals from a number of coal seams and (2) laboratory acid leaching and selective precipitation tests results. The highly-valued critical REEs (i.e., Y, Nd, Eu, Tb and Dy) were selectively leached from the refuse samples in the natural environment due to the acid generated by pyrite oxidization. The leachate samples were evaporated to remove water and obtain residual solids (i.e., dissolved solids in the leachates). The total REE content in the dissolved solids from a given leachate sample was 380 ppm, which was higher than the REE content of the coarse refuse material that generated the leachate (322 ppm). Acid leaching tests recovered as much as 80% of the total REEs from the coarse refuse samples using a 1.2 M sulfuric acid solution. Afterwards, the pH of the leachate was increased in a step-wise fashion which resulted in the production of precipitates containing 0.3–1.1% total REEs. A significant amount of contaminants, such as Fe, Al, and Ca, were eliminated in the sequential precipitation process, which allowed further upgrading using oxalic acid precipitation and/or solvent extraction. In the proposed flowsheet, the coarse refuse is arranged in heap leach pads and the acid needed for REE leaching is primarily produced from pyrite bio-oxidization, which enhances the selectivity of REE recovery and significantly reduces the cost. The successful application of the flowsheet would result in significant benefits to both the coal and rare earth industries.

Mineralogical controls on mobility of rare earth elements in acid mine drainage environments

Rare earth elements (REE) were analyzed in river waters, acid mine waters, and extracts of secondary precipitates collected in the Iberian Pyrite Belt. The obtained concentrations of the REE in river water and mine waters (acid mine drainage - AMD) were in the range of 0.57 μg/L (Lu) and 2579 μg/L (Ce), which is higher than previously reported in surface waters from the Iberian Pyrite Belt, but are comparable with previous findings from AMD worldwide. Total REE concentrations in river waters were ranged between 297 μg/L (Cobica River) and 7032 μg/L (Trimpancho River) with an average of 2468 μg/L. NASC (North American Shale Composite) normalized REE patterns for river and acid mine waters show clear convex curvatures in middle−REE (MREE) with respect to light- and heavy−REE.During the dissolution experiments of AMD-precipitates, heavy−REE and middle−REE generate the most enriched patterns in the solution. A small number of precipitates did not display MREE enrichment (an index Gdn/Lun < 1.0) in NASC normalized pattern and produced relatively lower REE concentrations in extracts. Additionally, very few samples, which mainly contained aluminum sulfates, e.g., pickeringite and alunogen, displayed light−REE enrichment relative to heavy−REE (HREE). In general, the highest retention of REE occurs in samples enriched in magnesium (epsomite or hexahydrite) and aluminum sulfates, mainly pickeringite.

Rare earth elements in German soils - A review

Rare earth elements (REEs) are increasingly used in high-tech industry, agriculture, and healthcare technologies what leads to their release into soils and waters, and to the transfer into plants what may have negative impacts on human health and the environment. The toxicity and potential mobilization of REEs in soils can be assessed by their content and geochemical behavior along with soil properties. However, those interactions are so far not reviewed in German soils although such a review is important for a better understanding and prediction of the potential mobilization and toxicity. Therefore, this review summarizes the recent knowledge about REE contents and potential mobilization in different soil profiles in Germany. We found that the REE content tends to decrease in dependence on the parent material in the following order: Carbonatite > basalt > orthogneiss > clay slate > loess > sandstone > Pleistocene and Holocene sediments > organic material. Also, we used data of earlier studies, summarized and newly evaluated those data aiming to quantify the factors influencing the total REE content in German soil profiles. The contents of REEs in soil profiles of different parent material showed significant relations with content of clay, carbonate, organic matter, aluminium, iron, and manganese. Geochemical fractionation results suggest that the bioavailability of REEs is relatively low while the residual fraction is relatively high in German soils. In soils, where water fluctuations are important, the redox potential is a key factor controlling the mobilization of REEs also via related changes of pH.

Discovery of the Plagiogranites in the Diyanmiao Ophiolite, Southeastern Central Asian Orogenic Belt, Inner Mongolia, China and Its Tectonic Significance

AbstractIn this study, plagiogranites in the Diyanmiao ophiolite of the southeastern Central Asian Orogenic Belt (Altaids) were investigated for the first time. The plagiogranites are composed predominantly of albite and quartz, and occur as irregular intrusive veins in pillow basalts. The plagiogranites have high SiO2 (74.37–76.68wt%) and low Al2O3 (11.99–13.30wt%), and intensively high Na2O (4.52–5.49wt%) and low K2O (0.03–0.40wt%) resulting in high Na2O/K2O ratios (11.3–183). These rocks are classified as part of the low‐K tholeiitic series. The plagiogranites have low total rare earth element contents (ΣREE)(23.62–39.77ppm), small negative Eu anomalies (δEu=0.44–0.62), and flat to slightly LREE‐depleted chondrite‐normalized REE patterns ((La/Yb)N=0.68–0.76), similar to N‐MORB. The plagiogranites are also characterized by Th, U, Zr, and Hf enrichment, and Nb, P, and Ti depletion, have overall flat primitivemantle‐normalized trace element patterns. Field and petrological observations and geochemical data suggest that the plagiogranites in the Diyanmiao ophiolite are similar to fractionation‐type plagiogranites. Furthermore, the REE patterns of the plagiogranites are similar to those of the gabbros and pillow basalts in the ophiolite. In plots of SREE–SiO2, La–SiO2, and Yb–SiO2, the plagiogranites, pillow basalts, and gabbros show trends typical of crystal fractionation. As such, the plagiogranites are oceanic in origin, formed by crystal fractionation from basaltic magmas derived from depleted mantle, and are part of the Diyanmiao ophiolite. LA–ICP–MS U–Pb dating of zircons from the plagiogranites yielded ages of 328.6±2.1 and 327.1±2.1Ma, indicating an early Carboniferous age for the Diyanmiao ophiolite. These results provide petrological and geochronological evidence for the identification of the Erenhot–Hegenshan oceanic basin and Hegenshan suture of the Paleo‐Asian Ocean.

In-situ measurements of rare earth elements in deep sea sediments using nuclear methods

The prospecting activities for finding new rare earth elements (REE) sources have increased greatly in recent years. One of the main discoveries was announced in 2011 by Japanese researchers who found large quantities of REE on the ocean seafloor at the sea depths greater than 4,000 m. The classic approach to investigate REE in deep sea sediments is to obtain sediment samples by drilling that is followed by laborious laboratory analysis. This is very expensive, time consuming and not appropriate for exploring vast areas. In order to efficiently explore the ocean floor for REE deposits, the further development of affordable sensors is needed. Here, we propose two nuclear techniques for exploring REE in surface deep sea sediments: i) Passive measurement of lutetium-176 radioactivity, appropriate if long-term in-situ measurements are possible, and ii) The use of the neutron sensor attached to a remotely operated vehicle for rapid in-situ measurement of gadolinium by thermal neutron-capture. Since concentrations of lutetium and gadolinium show strong linear correlation to the total REE concentrations in deep sea sediments, it is possible to deduce the total REE content by measuring Lu or Gd concentrations only.

Comparison of Single-Phase and Two-Phase Composite Thermal Barrier Coatings with Equal Total Rare-Earth Content

Rare-earth zirconates have been the focus of advanced thermal barrier coating research for nearly two decades; however, their lack of toughness prevents a wide-scale adoption due to lack of erosion and thermal cyclic durability. There are generally two methods of improving toughness: intrinsic modification of the coating chemistry and extrinsic modification of the coating structure. This study compares the efficacy of these two methods for a similar overall rare-earth content via the air plasma spray process. The extrinsically toughened coatings were comprised of a two-phase composite containing 30 wt.% Gd2Zr2O7 (GZO) combined with 70 wt.% of a tougher t′ low-k material (ZrO2-2Y2O3-1Gd2O3-1Yb2O3; mol.%), while a single-phase fluorite with the overall rare-earth content equivalent to the two-phase composite (13 mol.% rare-earth) was utilized to explore intrinsically toughened concept. The coatings were then characterized via x-ray diffraction, energy-dispersive spectroscopy, and scanning electron microscopy, and their performance was evaluated via erosion, thermal conductivity, thermal annealing (500 h), and thermal cycling. It was shown that the extrinsic method provided an improved erosion and thermal conductivity response over the single phase, but at the expense of high-temperature stability and cyclic life.

Bioleaching of rare earth elements from bastnaesite-bearing rock by actinobacteria

Biological leaching of rare earth elements (REEs) from low-grade ores and mine tailings represents a potentially cost-effective green technology for REE recovery, yet the specific mechanisms of such biological process, especially by common rock-dwelling actinobacteria, remain unclear. In this study, we performed laboratory bioleaching experiments to understand the rates and mechanisms of REE bioleaching. Four actinobacterial strains, including two isolates from REE-rich rocks and two from surrounding red soil, were found to have the capability of bioleaching REEs from a bastnaesite-bearing rock and bastnaesite. Bastnaesite is one member of a REE mineral family REE(CO3)F, where REE is dominated by Ce, La or Y. In a nutrient-rich growth medium, bioleached total REE concentration ranged from 56 to 342 μg/L. In an oligotrophic medium, only one strain (Streptomyces sp.) grew in the presence of the bastnaesite-bearing rock and bastnaesite, and leached as much as 548 μg/L total REEs. The leaching efficiency of total REEs, defined as the amounts of leached REEs relative those present in the rock was 0.008–0.08%, which should be underestimated due to new REE-bearing mineral precipitation and/or sorption of leached REEs to residual rock and cell surfaces. These bioleached REE concentrations were higher than those leached by abiotic methods under a similar pH condition, suggesting that pH was not the only factor in REE bioleaching. Additional experiments demonstrated that these four actinobacterial strains secreted various organic acids, complexing ligands, and siderophores as dominant agents to extract REEs from bastnaesite-bearing rock. Some of the leached REEs were observed to accumulate on cell surfaces. Multiple lines of evidence suggest that REEs were leached primarily from primary REE mineral bastnaesite. Our results suggest that microorganisms have a potential to selectively bioleach and recover certain REEs from low-grade ores and mine tailings.

Geochemistry of high‐Nb basalt‐andesite in the Erguna Massif (NE China) and implications for the early Cretaceous back‐arc extension

This paper presents new zircon laser ablation–inductively coupled plasma–mass spectrometry U–Pb age and whole‐rock geochemical data for the high‐Nb basalts‐andesites (HNBs) from the Meiletu Formation in NE China. In comparison with common arc basalts and Nb‐enriched basalts, the Meiletu HNBs (140 Ma) show high TiO2 (1.7–3.2 wt.%), P2O5 (0.7–1.7 wt.%), Nb (14.6–34.0 ppm), and Zr (314–600 ppm) contents, and high (Nb/Th)PM (0.26–0.91), (Nb/La)PM (0.22–0.36), Nb/U (8.2–24.8) ratios. They show strongly light rare earth element (REE) enriched chondrite‐normalized REE patterns with unusually high total REE contents [(TREE)cn = 978–1802]. Unlike adakite‐associated HNBs derived from a mantle wedge metasomatized by adakites, the Meiletu HNBs were derived from low degree (&lt;2%) partial melting of the garnet peridotite at considerable depth (&gt;80 km). The Meiletu HNBs were generated in an intracontinental back‐arc extension setting. Combined with previous geological observations, it is argued that Early Cretaceous tectonics of the Erguna Massif is dominated by the Mongol–Okhotsk oceanic slab‐rollback and back‐arc extension.

Lithologically-related rare earth element variations the Mio-Pliocene Poznań Formation (Poland)

Concentrations of rare earth elements (REEs) were determined in 129 clay samples collected from the Mio-Pliocene Poznan Formation in Poland. The REEs occur in a relatively wide range from 58.2 to 1,709 mg/kg. Low North American Shale Composite (NASC)-normalized total REE contents with heavy rare earth element (HREE) depletion were noted in most of the samples analysed. Small variations were detected in the REE contents in the lithologies distinguished. Red clays are characterised by slightly lower REE concentrations relative to green and grey clays. All the Poznan Formation clays exhibit a negative Eu anomaly when normalized to the average of chondrites. Values increase according to the following sequence: grey clays grey clays > red clays. The variability of the REE contents of the Poznan Formation decreased from west to east.

Origin of dolomite in the Middle Devonian Guanwushan Formation of the western Sichuan Basin, western China

The carbonates in the Middle Devonian Guanwushan Formation (D2g) of the western Sichuan Basin are extensively dolomitized. Three types of replacement dolomite can be distinguished: (1) micritic-microcrystalline dolomite (<30μm) with some shale content (Type 1); (2) very fine crystalline dolomite (30–100μm) with anhedral-subhedral dolomite crystals (Type 2); and (3) fine crystalline dolomite (>100μm) with anhedral-subhedral dolomite crystals (Type 3). The anhedral to subhedral fine crystalline crystals in Type 3 dolomite are truncated by a stylolite, which indicates that the formation of Type 3 dolomite most likely occurred simultaneously or predated the stylolite formation. Stratigraphic, petrographic and geochemical data indicate that the 87Sr/86Sr ratios (0.70839 to 0.71117) of the D2g dolomites, which are higher than those of the contemporaneous seawater (0.70780–0.70830), were affected by the underlying siliciclastic rocks of the Jinbaoshi Formation (D2j), Pingyipu Formation (D1p) and Silurian strata. The dolomitizing fluids incorporated elemental Sr, which tends to be abundant in crustal fluids. The rare earth element (REE) compositions of the D2g dolomites are characterized by enrichment in light REEs and depletion in heavy REEs, Ce, and Eu, indicating that the dolomites of the D2g inherited the characteristics of the contemporaneous seawater and formed in a low-temperature, relatively oxic environment. The δ18O values of Type 1 and Type 2 dolomites (−6.3‰ to +0.43‰ and −7.2‰ to −1.69‰, respectively) are slightly higher than those of seawater-derived dolomite, suggesting that these dolomites may be related to the evaporation of seawater during the penecontemporaneous stage. The δ18O values of Type 3 dolomite (−8.32‰ to −0.83‰) are slightly lower than those of the seawater-derived dolomites, indicating that this dolomite may have formed at a higher temperature during shallow-moderate burial. Type 1 dolomite has higher δ18O values, Sr2+ concentrations and total REE (∑REE) concentrations and slightly lower Mn2+ concentrations than the other two types of dolomite, suggesting that Type 1 dolomite formed via capillary concentration dolomitization from evaporated seawater. Type 2 dolomite has lower δ18O values and ∑REE contents and slightly higher Mn2+ and Sr2+ concentrations than Type 1 dolomite, suggesting that Type 2 dolomite formed via the seepage-reflux process from denser seawater. Type 3 dolomite has a stylolite, lower δ18O values, Sr2+ concentrations and ∑REE concentrations and slightly higher Mn2+ concentrations and Mg/Ca values, suggesting that Type 3 dolomite formed during shallow-moderate burial.