Uptake Of Rare Earth Elements Research Articles

Rare earth elements biomonitoring using the mussel Mytilus galloprovincialis in the Portuguese coast: Seasonal variations

Increased Rare earth elements (REE) usage culminates in discharges into the environment. Mussels have been chosen as models in biomonitoring, hence, REE concentrations in Mytilus galloprovincialis from six locations on the Portuguese coast were accessed to determine natural concentrations and possible linkage to local ecosystem characteristics and temporal variations, by determining them in distinct seasons (autumn and spring). Samples from Porto Brandão (located on the south bank of the Tagus estuary) exhibited the highest REE concentrations, while mussels from Aljezur (the southernmost point on the Portuguese coast) exhibited the lowest, in both seasons. Overall, ∑REE concentration was greater in the spring. LREE enrichment relative to HREE occurs and a negative Ce and Eu anomaly was observed. This study constitutes the first assessment of REE composition on this model species in the Portuguese coast, in two distinct seasons and contributes to a better understanding of REE uptake for future biomonitoring studies.

Adsorption of Uranium, Mercury, and Rare Earth Elements from Aqueous Solutions onto Magnetic Chitosan Adsorbents: A Review.

The compound of chitin is the second most important and abundant natural biopolymer in the world. The main extraction and exploitation sources of this natural polysaccharide polymer are mainly crustaceans species, such as shrimps and crabs. Chitosan (CS) (poly-β-(1 → 4)-2-amino-2-deoxy-d-glucose) can be derived from chitin and can be mentioned as a compound that has high value-added applications due to its wide variety of uses, including pharmaceutical, biomedical, and cosmetics applications, food etc. Furthermore, chitosan is a biopolymer that can be used for adsorption applications because it contains amino and hydroxyl groups in its chemical structure (molecules), resulting in possible interactions of adsorption between chitosan and pollutants (uranium, mercury, rare earth elements (REEs), phenols, etc.). However, adsorption is a very effective, fast, simple, and low-cost process. This review article places emphasis on recent demonstrated research papers (2014–2020) where the chemical modifications of CS are explained briefly (grafting, cross-linking etc.) for the uptake of uranium, mercury, and REEs in synthesized aqueous solutions. Finally, figures and tables from selected synthetic routes of CS are presented and the effects of pH and the best mathematical fitting of isotherm and kinetic equations are discussed. In addition, the adsorption mechanisms are discussed.

Arbuscular mycorrhizal fungi alter microbiome structure of rhizosphere soil to enhance maize tolerance to La

Rhizosphere microbes are essential partners for plant stress tolerance. Recent studies indicate that arbuscular mycorrhizal fungi (AMF) can facilitate the revegetation of soils contaminated by heavy metals though interacting with rhizosphere microbiome. However, it is unclear how AMF affect rhizosphere microbiome to improve the growth of plant under rare earth elements (REEs) stress. AMF (Claroideoglomus etunicatum) was inoculated to maize grown in soils spiked with Lanthanum (0 mg kg−1, La0; 10 mg kg−1, La10; 100 mg kg−1, La100; 500 mg kg−1, La500). Plant biomass, nutrient uptake, REE uptake and rhizosphere bacterial and fungal community were evaluated. The results indicated that La100 and La500 decreased significantly root colonization rates and nutrition uptake (K, P, Ca and Mg content). La500 decreased significantly α-diversity indexes of bacterial and fungal community. AMF enhanced significantly the shoot and root fresh and dry weight of maize in all La treatments (except for the root fresh and dry weight of La0 and La10 treatment). For La100 and La500 treatments, AMF increased significantly nutrition uptake (K, P, Ca and Mg content) in shoot of maize by 27.40–441.77%. For La500 treatment, AMF decreased significantly shoot La concentration by 51.53% in maize, but increased significantly root La concentration by 30.45%. In addition, AMF decreased bacterial and fungal Shannon index in La0 treatment, but increased bacterial Shannon index in La500 treatment. Both AMF and La500 affected significantly the bacterial and fungal community composition, and AMF led to more influence than La. AMF promoted the enrichment of bacteria, including Planomicrobium, Lysobacter, Saccharothrix, Agrococcus, Microbacterium, Streptomyces, Penicillium and other unclassified genus, and fungi (Penicillium) in La500, which showed the function for promoting plant growth and tolerance of heavy metal. The study revealed that AMF can regulate the rhizosphere bacterial and fungal composition and foster certain beneficial microbes to enhance the tolerance of maize under La stress. Phytoremediation assisted by AMF is an attractive approach to ameliorate REEs-contaminated soils.

Selective uptake of rare earth elements in marine systems as an indicator of and control on aerobic bacterial methanotrophy

Unicellular methanotrophs are a widespread, polyphyletic group of organisms that oxidize methane to assimilate carbon and obtain energy. Methanotrophs are of interest to astrobiologists given their prevalence in terrestrial environmental niches, like geothermal hot springs and hydrothermal vents, that are homologs for proposed extraterrestrial targets. Recent research demonstrates that light rare earth elements are required for the catalytic activity of the common xoxF isoform of methanol dehydrogenase, an enzyme in the aerobic methanotrophy pathway whose main isoform, mxa-MeDH, in contrast uses a calcium ion for catalysis. Although rare earth elements exist in picomolar concentrations in the ocean, the gene for xoxF is maintained in marine methanotrophs, pointing to a possible terrestrial origin for aerobic methanotrophy. Here we present a multi-season time series of rare earth element concentrations from autumn 2018 in the oligotrophic Sargasso Sea, and an initial analysis of molecular markers for aerobic methanotrophy in summer 2019. We observe a repeated depletion of light rare earth elements relative to heavy rare earth elements in the upper water column, between approximately 200 m and 500 m. This feature was collocated with observations of microbial growth on media with methanol as a sole carbon source, and detection of the xoxF5 gene. We aim to determine if aerobic methanotrophs generate a reproducible and identifiable signal through the selective uptake of light rare earth elements over heavier REEs that could be recorded in the geologic record indicating past aerobic methanotrophy.

Dielectrophoretic ultra-high-frequency characterization and in silico sorting on uptake of rare earth elements by Cupriavidus necator.

Rare earth elements (REEs) are widely used across different industries due to their exceptional magnetic and electrical properties. In this work, Cupriavidus necator is characterized using dielectrophoretic ultra-high-frequency measurements, typically in MHz range to quantify the properties of cytoplasm in C. necator for its metal uptake/bioaccumulation capacity. Cupriavidus necator, a Gram-negative bacteria strain is exposed to REEs like europium, samarium, and neodymium in this study. Dielectrophoretic crossover frequency experiments were performed on the native C. necator species pre- and post-exposure to the REEs at MHz frequency range. The net conductivity of native C. necator, Cupriavidus europium, Cupriavidus samarium, and Cupriavidus neodymium are 15.95 ± 0.029 μS/cm, 16.15 ± 0.028 μS/cm, 16.05 ± 0.029 μS/cm, 15.61 ± 0.005 μS/cm respectively. The estimated properties of the membrane published by our group are used to develop a microfluidic sorter by modeling and simulation to separate REE absorbed C. necator from the unabsorbed native C. necator species using COMSOL Multiphysics commercial software package v5.5.

Geochemical analyses suggest stratigraphic origin and late Miocene age of reworked vertebrate remains from Penanjong Beach in Brunei Darussalam (Borneo)

ABSTRACT We report on sporadic fossil vertebrates from Brunei Darussalam (Borneo). Most of these isolated remains are reworked and derive from Penanjong Beach known for former coastal cliffs used to be rich in marine molluscs. Previously, the only vertebrate remains reported were shark teeth. With new material, the fish fauna is now represented by six shark and a single ray taxa, while remains of three turtle families were discovered (Trionychidae, Cheloniidae, Geoemydidae). This fauna is compared to nearby upper Miocene fossiliferous beds from where remains of cheloniid and trionychid turtles were unearthed. To assess the origin of the reworked remains, rare earth element (REE) concentrations of the fossil bioapatite were compared between the reworked and the geographically closest in-situ Ambug Hill fauna. The obtained trend in REE variations are identical, revealing similar REE uptake mechanism and early diagenetic conditions. With the additional fact that the succession outcropping at Ambug Hill cuts the coastline imply that the majority of the reworked fossils derive from the local Miocene beds. This is supported by Sr-isotope ages from reworked calcite bivalve shells ranging from 9.74 to 6.62 Ma. These turtle remains thus represent the hitherto known first Neogene fossil tetrapods from Borneo.

Patterns of (trace) metals and microorganisms in the Rainbow hydrothermal vent plume at the Mid-Atlantic Ridge

Abstract. Hydrothermal vent fields found at mid-ocean ridges emit hydrothermal fluids that disperse as neutrally buoyant plumes. From these fluids seafloor massive sulfides (SMS) deposits are formed, which are being explored as possible new mining sites for (trace) metals and rare earth elements (REEs). It has been suggested that during mining activities large amounts of suspended matter will appear in the water column due to excavation processes and discharge of mining waste from the surface vessel. Understanding how hydrothermal plumes can be characterised by means of geochemistry and microbiology as they spread away from their source and how they affect their surrounding environment may help in characterising the behaviour of the dilute distal part of chemically enriched mining plumes. This study on the extensive Rainbow hydrothermal plume, observed up to 25 km downstream from the vent site, enabled us to investigate how microbial communities and (trace) metal composition change in a natural plume with distance. The (trace) metal and REE content of suspended particulate matter (SPM) was determined using sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) with high resolution (HR), and the microbial communities of the neutrally buoyant plume, above-plume, below-plume, and near-bottom water and sediment were characterised by using 16S rRNA amplicon sequencing methods. Both vertically in the water column and horizontally along the neutrally buoyant plume, geochemical and biological changes were evident, as the neutrally buoyant plume stood out by its enrichments in (trace) metals and REEs, as, for example, Fe, Cu, V, Mn and REEs were enriched by factors of up to ∼80, ∼90, ∼52, ∼2.5 and ∼40, respectively, compared to above-plume water samples taken at 1000 m water depth. The concentrations of these elements changed as the plume aged, shown by the decrease in element ∕ Fe molar ratios of chalcophile elements (Cu, Co, Zn), indicative of rapid removal from the hydrothermal plume or removal from the solid phase. Conversely, increasing REE ∕ Fe molar ratios imply uptake of REEs from the ambient seawater onto Fe-oxyhydroxides. This was also reflected in the background pelagic system, as Epsilonproteobacteria started to dominate and univariate microbial biodiversity declined with distance away from the Rainbow hydrothermal vent field. The Rainbow hydrothermal plume provides a geochemically enriched natural environment, which is a heterogeneous, dynamic habitat that is conducive to ecological changes in a short time span. This study of a hydrothermal plume provides a baseline study to characterise the natural plume before the interference of deep-sea mining.

A green method based on living macroalgae for the removal of rare-earth elements from contaminated waters

Low recycling rates of rare earth elements (REEs) are a consequence of inefficient, expensive and/or contaminating methods currently available for their extraction from solid wastes or from liquid wastes such as acid mine drainage or industrial wastewaters. The search for sustainable recovery alternatives was the motivation for this study. For the first time, the capabilities of 6 living macroalgae (Ulva lactuca, Ulva intestinalis, Fucus spiralis, Fucus vesiculosus, Osmundea pinnatifida and Gracilaria sp.) to remove REEs (Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy) from laboratory-prepared seawater spiked with REE solutions were evaluated. The assays lasted 72 h with REEs concentrations ranging from 10 to 500 μg L−1. The link between REEs uptake and algal metabolism, surface morphology and chemistry were addressed. Kinetics varied among the species, although most of the removal occurred in the first 24 h, with no equilibrium being reached. Lack of mortality reveal that the algae maintained their metabolism in the presence of the REEs. Green alga U. lactuca stood out as the only capable of efficiently removing at least 60% of all elements, reaching removals up to 90% in some cases. The high bioconcentration factors, derived from mass balance analysis (c.a. 2500) support that the REEs enriched algal biomass (up to 1295 μg g−1) may constitute an effective and environmentally friendly alternative source of REEs to conventional extraction from ores.

TRACKING AUTHIGENIC MINERAL CEMENTS IN FOSSIL BONES FROM THE UPPER CRETACEOUS (CAMPANIAN) TWO MEDICINE AND JUDITH RIVER FORMATIONS, MONTANA

ABSTRACT Previous studies have yielded mixed results as to whether authigenic mineral infill in fossilized bone tracks specific lithologies or depositional environments, with most suggesting weak to no correlation between infill composition and host lithofacies. This study documents infill patterns in a suite of fossil bones from the Upper Cretaceous Two Medicine and Judith River formations of Montana. The composition and distribution of void-filling materials, including authigenic mineral precipitates (e.g., calcite, chlorite, iron oxides/hydroxides, sulfides, and sulfates) and sedimentary detritus, were identified (petrography and SEM-EDS), imaged (photomicrographs, BSE maps), and quantified on false color maps using ImageJ. The authigenic cement content of fossil bone is distinct at the formation scale, with Two Medicine specimens characterized by pervasive calcite infill (non-ferroan followed by ferroan phase) and local chlorite infill. In contrast, Judith River specimens are characterized by abundant unfilled primary void space, with iron oxides and sulfides, along with rare sulfates, present in all bones, albeit in low abundance. Calcite infills are rare, chlorite is absent, and detrital infill is more abundant in Judith River specimens, presumably reflecting the rapid and more complete permineralization of Two Medicine bones. The sequencing of mineral cements in voids is generally consistent within formations, but is more complex in Two Medicine specimens. Authigenic cement content does not serve to effectively distinguish among facies or localities in either formation. This study compliments previous work on rare earth element (REE) content in the same general suite of fossil bones. In the previous study, patterns in REE uptake also served to readily distinguish fossils at the formation scale, and proved more effective than authigenic cements at differentiating fossils recovered from different facies.

Influence of toxic elements on the simultaneous uptake of rare earth elements from contaminated waters by estuarine macroalgae

The present study tested whether the presence of potentially toxic elements (PTEs) (Cd, Cr, Cu, Pb, Hg and Ni), commonly found in wastewaters, interferes with the ability of macroalgae (Ulva intestinalis, Ulva lactuca, Fucus spiralis, Fucus vesiculosus, Gracilaria sp. and Osmundea pinnatifida) to remove rare earth elements (REEs) (La, Ce, Pr, Nd, Eu, Gd, Tb, Dy and Y), which are key elements for most high technologies (e.g. electronics, aerospace, renewable energy). Results proved the high capacity of living macroalgae to remove REEs from multielement solutions, with the following sequence of bioconcentration factors being observed: U. intestinalis (2790) > Gracilaria sp. (2119) > O. pinnatifida (1742) > U. lactuca (1548) > F. vesiculosus (944) > F. spiralis (841). Competition among REEs to sorption sites on the six macroalgae was minor due to the chemical similarities between the elements. However, Ce and Y were the less removed while Gd, La and Eu the most removed among REEs. Ionic strength was an important factor in the sorption process, with salinity affecting differently the six macroalgae. Surprisingly, the presence of potential toxic elements in solution enhanced the removal of REEs. The most plausible explanation is the preferentially complexation of those elements by carbonates over REEs, which facilitates the binding of REEs cations onto the surface of macroalgae.

Sol-Gel Synthesis of NiO/CuO Nanocomposites for Uptake of Rare Earth Elements (Ho, Yb, and Sm) from Aqueous Solutions

NiO/CuO nanocomposites are synthesized successfully by sol-gel method and employed for the uptake of rare earth elements (Ho, Yb, and Sm) from aqueous solutions. NiO/CuO nanocomposites have been characterized by FT-IR, SEM-EDAX, and X-ray diffraction (XRD). Results of XRD analysis show the crystal structure of NiO/CuO with average sizes between 50–80 nm. The SEM photographs show granular and plate morphology of nanoparticles with high uniformity. FTIR spectra show a broad band at 480–486 cm–1, which are corresponded to the Cu–O bond in the CuO structure and a broad band in the range of 440–470 cm–1, this band is assigned to the Ni–O bond stretching vibrations. Various parameters including pH, contact time; initial concentration and temperature were optimized to achieve maximum adsorption capacity. The adsorption efficiency of Yb(III), Sm(III), and Ho(III) are 97, 96, and 96% on NiO/CuO-500 and 92, 94 and 93% on NiO/CuO-800, respectively, under room temperature, pH 5 and 300 min. The adsorption kinetics of Ho(III), Yb(III), and Sm(III) have been described by pseudo-first order mechanism. The thermodynamics studies confirm that the adsorption is exothermic. The results indicate that the nanocomposite is an efficient adsorbent with good adsorption capacity for Ho(III), Yb(III), and Sm(III).

Caught in the act: A case study on microscopic scale physicochemical effects of fossilization on stable isotopic composition of bone

Geochemical zoning in a partially fossilized Pleistocene artiodactyl metapodial was contrasted with a fully fossilized Cretaceous ceratopsian femur as distinct stages along the fossilization process to investigate the physicochemical effects of fossilization and fossilization mechanisms. Bone fragments were analyzed via laser ablation ICP-MS, FT-IR, and stable isotope microanalysis to determine zoning patterns in trace elements, relative carbonate content and collagen contents, and stable isotopes of both the CO3 and PO4 components (δ13CCO3, δ18OCO3, and δ18OPO4). The Pleistocene sample shows a pronounced step in U concentration from high values (up to 90 ppm) within 1 mm of the outer bone surface and inner medullary cavity to ppb-level concentrations typical of in-vivo bone in the interior (inner ∼6 mm). High U broadly coincides with reduced collagen, higher δ13CCO3, and lower δ18OCO3. Rare earth elements (REE), however, show typical exponential decreases from bone edges inward, and δ18OPO4 shows no clear trend. The Cretaceous bone shows high REE and U contents throughout, a complete absence of collagen, and relatively uniform isotope compositions. The Pleistocene data, especially U zoning, implicate a diffusion-reaction (DR) fossilization mechanism, in which collagen degradation facilitates a recrystallization front that propagates as a front towards the bone interior, reducing OH-site CO3 content, and shifting δ13CCO3, δ18OCO3, and δ18OPO4. Disequilibrium O-isotope partitioning between the CO3 and PO4 components in the interior of the Pleistocene bone suggests that both the CO3 and PO4 components have exchanged with diagenetic waters, likely through abiotic and microbially-induced exchange, respectively. Strong partitioning between apatite and soil water, coupled with uptake of REE in apatite from surrounding sediment matrix during fossilization, leads to exponential decreases in concentrations, which are passively recorded in apatite in the bone interior. The Cretaceous data do not implicate a unique fossilization mechanism but instead reflect the consequences of protracted fossilization and the final state that the Pleistocene bone might eventually have reached had the bone not been excavated. That is, the Cretaceous bone fossilization history resulted in no collagen, reduced or no OH-site CO3, and more uniform isotopic compositions. The multi-analytical methods employed in this study may benefit studies of diagenetic alteration of other apatitic tissues, e.g., tooth enamel.

Fractionation of Rare Earth Elements in Greisen and Hydrothermal Veins Related to A-Type Magmatism

This study focuses on concentrations and fractionation of rare earth elements (REE) in a variety of minerals and bulk materials of hydrothermal greisen and vein mineralization in Paleoproterozoic monzodiorite to granodiorite related to the intrusion of Mesoproterozoic alkali- and fluorine-rich granite. The greisen consists of coarse-grained quartz, muscovite, and fluorite, whereas the veins mainly contain quartz, calcite, epidote, chlorite, and fluorite in order of abundance. A temporal and thus genetic link between the granite and the greisen/veins is established via high spatial resolution in situ Rb-Sr dating, supported by several other isotopic signatures (δ34S, 87Sr/86Sr, δ18O, and δ13C). Fluid-inclusion microthermometry reveals that multiple pulses of moderately to highly saline aqueous to carbonic solutions caused greisenization and vein formation at temperatures above 200–250°C and up to 430°C at the early hydrothermal stage in the veins. Low calculated ∑REE concentration for bulk vein (15 ppm) compared to greisen (75 ppm), country rocks (173–224 ppm), and the intruding granite (320 ppm) points to overall low REE levels in the hydrothermal fluids emanating from the granite. This is explained by efficient REE retention in the granite via incorporation in accessory phosphates, zircon, and fluorite and unfavorable conditions for REE partitioning in fluids at the magmatic and early hydrothermal stages. A noteworthy feature is substantial heavy REE (HREE) enrichment of calcite in the vein system, in contrast to the relatively flat patterns of greisen calcite. The REE fractionation of the vein calcite is explained mainly by fractional crystallization, where the initially precipitated epidote in the veins preferentially incorporates most of the light REE (LREE) pool, leaving a residual fluid enriched in the HREE from which calcite precipitated. Fluorite occurs throughout the system and displays decreasing REE concentrations from granite towards greisen and veins and different fractionation patterns among all these three materials. Taken together, these features confirm efficient REE retention in the early stages of the system and minor control of the REE uptake by mineral-specific partitioning. REE-fractionation patterns and fluid-inclusion data suggest that chloride complexation dominated REE transport during greisenization, whereas carbonate complexation contributed to the HREE enrichment in vein calcite.

Are Clay Minerals the Primary Control on the Oceanic Rare Earth Element Budget?

The rare earth elements (REEs) are an important tool for understanding biogeochemical cycling and sedimentary processes in the global ocean. However, ambiguities in the marine REE budgets, including questions around the dominant source of REEs to the ocean, hinder the application of this tool. A bottom-up model for REE release into the ocean has recently been proposed, driven by early diagenetic processes such as sediment dissolution, with potentially significant implications for the interpretation of marine REE and Nd isotope paleo-records. Here, our goal is to identify the phase or phases that interact with the pore fluids to drive such a benthic flux. We use new pore water REE, microbeam imaging and mineralogical data in combination with published pore water REE data to evaluate potential sedimentary REE host phases. Mineralogical and direct imaging observations suggest that authigenic Fe or Mn oxyhydroxides, which are widely considered a dominant REE host phase, are not sufficiently abundant sediment components to account for the high Nd concentrations recovered in reductive leaches, and are unlikely to be the primary source of pore water REEs. Pore water REE signatures similar to river sourced clays indicate a detrital clay dissolution source, while the spread in heavy to light REE enrichment in pore fluids and bottom waters relative to this clay source is best explained by fractionation during authigenic clay uptake of REEs. We therefore conclude that clay mineral dissolution and authigenesis are likely the primary influences on the REE cycling near the seafloor. We propose that the balance between dissolution and authigenesis controls the concentration, ratio of heavy and light REE abundances, and the isotopic composition of the pore waters. We discuss the implications of this hypothesis on an oceanic REE budget controlled by a benthic flux from a sedimentary REE source, and the use of authigenic neodymium isotopes as a paleoproxy for shifts in ocean circulation.

Mechanism of Gd3+ uptake in gypsum (CaSO4·2H2O): Implications for EPR dating, REE recovery and REE behavior

Rare earth elements (REE) in gypsum have long attracted interest for geochemical applications from the reconstruction of paleoclimate, paleoenvironment and paleohydrology to the monitoring of volcanic and seismic activities. Resurgent interests in REE in gypsum stem from the potential recovery of these high-tech metals from gypsum-rich tailings. Development of new geochemical applications and invention of effective recovery technologies all require knowledge about the mechanism of REE uptake in gypsum. In this contribution, we have investigated Gd-doped gypsum from the gel diffusion technique at ambient conditions in the pH range from 6.5 to 9.5. Inductively coupled plasma mass spectrometry analyses of Gd-doped gypsum yielded 752 ppm Gd at pH = 6.5 down to 2.8 ppm Gd at pH = 9.5. Synchrotron Gd L3-edge X-ray absorption spectra show that Gd3+ has a local environment similar to that of Ca2+ in gypsum. Single-crystal electron paramagnetic resonance (EPR, also known as electron spin resonance or ESR) spectra reveal a dominant Gd3+ center with weak satellites. The dominant Gd3+ center arises from a substitutional Gd3+ ion at the Ca site retaining its C2 local symmetry, which is also confirmed by pulsed electron nuclear double resonance (ENDOR) data for proton hyperfine structures up to 5.2 Å away from Gd3+. The satellites are attributable to a Gd3+-Gd3+ pair (dimer) along the crystallographic a-axis with a dipolar coupling constant Dd/geβe = −13 G, which corresponds to a distance of 12.6 Å between the two Gd3+ ions and provides the first experimental confirmation for the substitution 2Gd3+ + □ = 3Ca2+ in gypsum. Hole trapping at cation vacancies associated with the incorporation of Gd3+ (and other trivalent REE) in gypsum offers a new class of radiation-induced paramagnetic defects in this mineral for EPR/ESR dating. These results also have implications for developing new technologies for effective recovery of REE from gypsum-rich tailings and for understanding the behavior of REE in evaporites and aqueous solutions.

Rare earth element uptake during olivine/water hydrothermal interaction

Ultramafic-hosted hydrothermal vent systems link the hydrosphere with the peridotitic mantle via serpentinization. Here, the fractionation and mobility of selected trace (Nd, Sm, Gd, Dy, Yb, Sr and Ba) and major cations (Si, Ca, Mg, Fe, Ni) during seawater-peridotite interaction was investigated through a series of experiments where natural olivine grains were reacted with an artificial seawater solution at a range of temperatures (15–90 °C) and grain size distributions. No evidence for any significant olivine dissolution or precipitation of carbonate and, Fe-oxy-hydroxide phases was observed in these experiments. Experimental data show a strong decoupling of REE (Nd, Sm, Gd, Dy, and Yb) from Sr and Ba under all experimental conditions, with Sr and Ba remaining quantitatively in solution. The REE were removed from the solution and were adsorbed onto olivine surface with kinetic rate constants (i.e. uptake over time) that increase with increasing temperature and increasing surface area (i.e. decreasing particle size). Dysprosium and Yb (heavy REE; HREE) were removed from solution with a faster rate than Nd and Sm (light REE; LREE). Gadolinium is decoupled from this trend, with a slower kinetic rate constant than Sm. The activation energies (Ea) of REE adsorption on olivine were higher for Nd and Sm than Dy and Yb. This suggests that the adsorbance of LREE is generally more dependent on temperature than the HREE. The Ea correlates well with the summed 1st, 2nd and 3rd ionization energies of REE suggesting a link between kinetic rates of element adsorption and electron configuration of the 4f-orbitals. Gadolinium has higher Ea than the other analyzed REE, consistent with the electron configuration of Gd3+ where all 4f-orbitals are filled with one electron each. These experimental data suggest that REE are adsorbed on the surface of olivine via inner sphere complexes under low-temperature hydrothermal conditions, when alteration processes are limited or extremely slow. Scavenging and fractionation of REE may occur within the recharge zone of peridotite-hosted hydrothermal systems at relatively low temperatures (<100 °C), leading to fluids with progressively higher LREE/HREE which could impose seawater-derived LREE enrichments in serpentinized peridotites during high temperature, high pressure water/rock interaction deeper in the oceanic lithosphere.

Use of rare-earth elements in the phyllosphere colonizer Methylobacterium extorquens PA1.

SummaryUntil recently, rare‐earth elements (REEs) had been thought to be biologically inactive. This view changed with the discovery of the methanol dehydrogenase XoxF that strictly relies on REEs for its activity. Some methylotrophs only contain xoxF, while others, including the model phyllosphere colonizer Methylobacterium extorquens PA1, harbor this gene in addition to mxaFI encoding a Ca2+‐dependent enzyme. Here we found that REEs induce the expression of xoxF in M. extorquens PA1, while repressing mxaFI, suggesting that XoxF is the preferred methanol dehydrogenase in the presence of sufficient amounts of REE. Using reporter assays and a suppressor screen, we found that lanthanum (La3+) is sensed both in a XoxF‐dependent and independent manner. Furthermore, we investigated the role of REEs during Arabidopsis thaliana colonization. Element analysis of the phyllosphere revealed the presence of several REEs at concentrations up to 10 μg per g dry weight. Complementary proteome analyses of M. extorquens PA1 identified XoxF as a top induced protein in planta and a core set of La3+‐regulated proteins under defined artificial media conditions. Among these was a REE‐binding protein that is encoded next to a gene for a TonB‐dependent transporter. The latter was essential for REE‐dependent growth on methanol indicating chelator‐assisted uptake of REEs.

Uptake of rare earth elements by citrus plants from phosphate fertilizers

Rare earth elements (REE) are a group of the periodic table formed by 17 chemical elements (lanthanoids plus yttrium and scandium). They have been used in different field applications. In agriculture, they can be found in some phosphate fertilizers at levels one or two orders of magnitude higher than those found in normal agricultural soils. Citrus plants are known to present high levels of REE when compared to most other species, however, there is little information about bioavailability of REE in phosphate fertilizers for citrus plants. This work focuses on the study of REE behavior by the application of increasing doses of single superphosphate fertilizer in Rangpur lime (Citrus limonia Osbeck) plants in a greenhouse study. The technique used was instrumental neutron activation analysis (INAA). The results showed that the fertilizer has caused significant increases in the content of REE in the citrus plant tissues, with higher concentrations in leaves than in branches. The highest substrate-leaf transfer factor was observed for La (0.0047), though the concentrations in the plants followed the same order found in the substrate, i.e. Ce > La > Sm > Eu > Sc. There was an increase of rare earth elements concentrations in Rangpur lime plants by superphosphate fertilizer application.

State of rare earth elements in the sediment and their bioaccumulation by mangroves: a case study in pristine islands of Indian Sundarban.

The mangrove ecosystems are known to efficiently sequester trace metals both in sediments and plant biomass. However, less is known about the chemistry of rare earth elements (REE) in the coastal environments, especially in the world's largest mangrove province, the Sundarban. Here, the concentration of REE in the sediment and plant organs of eight dominant mangrove species (mainly Avicennia sp.) in the Indian Sundarban was measured to assess REE sources, distribution, and bioaccumulation state. Results revealed that light REE (LREE) were more concentrated than the heavy REE (HREE) (128-144 mg kg-1 and 12-15 mg kg-1, respectively) in the mangrove sediments, with a relatively weak positive europium anomaly (Eu/Eu* = 1.03-1.14) with respect to North American shale composite. The primary source of REE was most likely linked to aluminosilicate weathering of crustal materials, and the resultant increase in LREE in the detritus. Vertical distribution of REE in one of the long cores from Lothian Island was altered by mangrove root activity and dependent on various physicochemical properties in the sediment (e.g., Eh, pH, organic carbon, and phosphate). REE uptake by plants was higher in the below-ground parts than in the above-ground plant tissues (root = 3.3 mg kg-1, leaf + wood = 1.7 mg kg-1); however, their total concentration was much lower than in the sediment (149.5 mg kg-1). Species-specific variability in bioaccumulation factor and translocation factor was observed indicating different REE partitioning and varying degree of mangrove uptake efficiency. Total REE stock in plant (above + live below ground) was estimated to be 168 g ha-1 with LREE contributing ~ 90% of the stock. This study highlighted the efficiency of using REE as a biological proxy in determining the degree of bioaccumulation within the mangrove environment.

Metal–organic complexes as a major sink for rare earth elements in soils

Environmental contextThe role of rare earth elements in soil–plant systems remains unclear. We use continuous-flow extraction, designed to mimic natural conditions while minimising artefacts, to study in vitro chemical fractionation of rare earth elements in soil. The study reveals a predominant association of rare earth elements and metal-organic complexes independent of soil type and contamination, and thereby provides valuable insights into the behaviour of these elements in soil–plant systems. AbstractThe role of rare earth elements (REEs) in soil–plant systems has attracted increasing attention but still remains somewhat unclear. Along invivo studies on the uptake of REEs by plants, invitro chemical fractionation of REEs in soil according to their physicochemical mobility can offer additional insights into the behaviour of REEs. In the present work, the fractionation of REEs was studied with the example of background, aerially and hydrogenically contaminated soil samples using dynamic (continuous flow) extraction, which allows natural conditions to be mimicked and artefacts to be minimised. The eluents applied addressed exchangeable, specifically sorbed, bound to Mn oxides, bound to metal–organic complexes, and bound to amorphous and poorly ordered Fe/Al oxides fractions extractable by 0.05M Ca(NO3)2, 0.43M CH3COOH, 0.1M NH2OH·HCl, 0.1M K4P2O7 at pH 11, and 0.1M (NH4)2C2O4 at pH 3.2 respectively. The distribution of trace metals (such as Pb, Cu, Zn, Ni) between separated fractions varies with sample and is dependent on the type of contamination. However, for all samples, the recoveries of REEs by pyrophosphate are surprisingly high, up to 40–45% of their total concentrations in background and anthropogenically transformed floodplain soils. As compared to metal–organic complexes, the contents of REEs bound to Fe/Al oxides are fairly low, no more than 12%. REEs in other fractions may be taken into consideration only for aerially contaminated soil. Such a predominant association of REEs and metal–organic complexes (i.e. humic and fulvic compounds) independent of the type of soil has not been reported before.