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"Rare earth elements"
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The 15 lanthanides and the 15 actinides
An introduction to the elements lanthanides and actinides, taking an in-depth look at their properties and myriad uses.
Book
ICP-MS Measurement of Trace and Rare Earth Elements in Beach Placer-Deposit Soils of Odisha, East Coast of India, to Estimate Natural Enhancement of Elements in the Environment
Inductively coupled plasma mass spectrometry (ICP-MS) has been used to measure the concentration of trace and rare earth elements (REEs) in soils. Geochemical certified reference materials such as JLk-1, JB-1, and JB-3 were used for the validation of the analytical method. The measured values were in good agreement with the certified values for all the elements and were within 10% analytical error. Beach placer deposits of soils mainly from Odisha, on the east coast of India, have been selected to study selected trace and rare earth elements (REEs), to estimate enrichment factor (EF) and geoaccumulation index (Igeo) in the natural environment. Enrichment factor (EF) and geoaccumulation index (Igeo) results showed that Cr, Mn, Fe, Co, Zn, Y, Zr, Cd and U were significantly enriched, and Th was extremely enriched. The total content of REEs (ƩREEs) ranged from 101.3 to 12,911.3 µg g−1, with an average 2431.1 µg g−1 which was higher than the average crustal value of ΣREEs. A high concentration of Th and light REEs were strongly correlated, which confirmed soil enrichment with monazite minerals. High ratios of light REEs (LREEs)/heavy REEs (HREEs) with a strong negative Eu anomaly revealed a felsic origin. The comparison of the chondrite normalized REE patterns of soil with hinterland rocks such as granite, charnockite, khondalite and migmatite suggested that enhancement of trace and REEs are of natural origin.
Journal Article
Relationship between concentration of rare earth elements in soil and their distribution in plants growing near a frequented road
Rare earth elements (REEs) are a group of elements whose concentration in numerous environmental matrices continues to increase; therefore, the use of biological methods for their removal from soil would seem to be a safe and reasonable approach. The aim of this study was to estimate the phytoextraction efficiency and distribution of light and heavy (LREEs and HREEs) rare earth elements by three herbaceous plant species:
Artemisia vulgaris
L.,
Taraxacum officinale
F.H. Wigg. and
Trifolium repens
L., growing at a distance of 1, 10, and 25 m from the edge of a frequented road in Poland. The concentration of REEs in soil and plants was highly correlated (
r
> 0.9300), which indicates the high potential of the studied plant species to phytoextraction of these elements. The largest proportion of REEs was from the group of LREEs, whereas HREEs comprised only an inconsiderable portion of the REEs group. The dominant elements in the group of LREEs were Nd and Ce, while Er was dominant in the HREEs group. Differences in the amounts of these elements influenced the total concentration of LREEs, HREEs, and finally REEs and their quantities which decreased with distance from the road. According to the Friedman rank sum test, significant differences in REEs concentration, mainly between
A. vulgaris
L., and
T. repens
L. were observed for plants growing at all three distances from the road. The same relation between
A. vulgaris
L. and
T. officinale
was observed. The efficiency of LREEs and REEs phytoextraction in the whole biomass of plants growing at all distances from the road was
A. vulgaris
L. >
T. officinale
L. >
T. repens
L. For HREEs, the same relationship was recorded only for plants growing at the distance 1 m from the road. Bioconcentration factor (BCF) values for LREEs and HREEs were respectively higher and lower than 1 for all studied plant species regardless of the distance from the road. The studied herbaceous plant species were able to effectively phytoextract LREEs only (BCF > 1); therefore, these plants, which are commonly present near roads, could be a useful tool for removing this group of REEs from contaminated soil.
Journal Article
A New Concept for an Integrated Mapping of Rare‐Earth Elements using Laser–Induced Fluorescence and Reflectance Spectroscopy
Rare earth elements are increasingly seen as critical raw materials and are currently the subject of geopolitical interests. To boost mineral exploration and extraction, it is important to ensure the rapid identification and mapping of rare earth elements, and non‐invasive spectroscopy‐based technologies could offer suitable solutions. We therefore investigated the potential of an integrated sensor system that combines hyperspectral and laser‐induced fluorescence imaging as a non‐invasive alternative characterization technique to conventional time‐consuming and costly chemical analysis. To test the analytical procedure we used representative material from the Siilinjärvi mine (Finland) and from Lofdal (Namibia). Laser‐induced fluorescence mapping results document the successful identification and efficient mapping of several rare earth elements within complex mineral matrices. The variation in laser‐induced fluorescence excitation wavelength facilitates the selective mapping of specific rare earth elements, thereby enhancing their differentiation capabilities. The combination with hyperspectral imaging provides mineral maps and cross‐validation. The major benefit of the integrated optical sensor system lies in the rapid acquisition of spatially continuous information on the occurrence and type of rare earth elements without the need for sample preparation. The non‐destructive character and operation in line‐scan mode opens manifold possibilities for in‐line applications with continuous sample throughput. We introduce a new integrated line‐scan sensor system that combines hyperspectral and laser‐induced fluorescence imaging as a non‐invasive alternative characterization technique specifically suited for rare‐earth element (REE) mapping and identification. We investigate in detail the potential and limitations in comparison to state‐of‐the‐art approaches using bulk or spectroscopy point‐wise acquisition methods. To test the capabilities, we used representative material from the Siilinjärvi mine (Finland) and from Lofdal (Namibia). Laser induced fluorescence mapping enables an efficient mapping of several rare earth elements within complex mineral matrices. Three excitation wavelength provide additional potentials for the selective mapping of specific rare earth elements, thereby enhancing their differentiation capabilities. The combination with hyperspectral imaging provides mineral maps and cross‐validation. The major benefit of the integrated optical sensor system lies in the rapid acquisition of spatially continuous information on the occurrence and type of rare earth elements. The non‐destructive character and operation in line‐scan mode open manifold possibilities for in‐line applications with continuous sample throughput.
Journal Article
Transfer of La, Ce, Sm and Yb to alfalfa and ryegrass from spiked soil and the role of Funneliformis mosseae
Rare earth elements (REEs) are widely used in high-tech industries, and REE waste emissions have become a concern for ecosystems, food quality and human beings. Arbuscular mycorrhizal fungi (AMF) have repeatedly been reported to alleviate plant stress in metal-contaminated soils. To date, little information is available concerning the role of AMF in REE-contaminated soils. We recently showed that there was no transfer of Sm to alfalfa by Funneliformis mosseae, but only a single REE was examined, while light and heavy REEs are present in contaminated soils. To understand the role of AMF on the transfer of REEs to plants, we carried out an experiment using alfalfa (Medicago sativa) and ryegrass (Lolium perenne) in compartmented pots with separate bottom compartments that only were accessible by F. mosseae fungal hyphae. The bottom compartments contained a mixture of four REEs at equal concentrations (La, Ce, Sm and Yb). The concentration of REEs in plants was higher in roots than in shoots with higher REE soil–root than root–shoot transfer factors. Moreover, significantly higher light-REEs La and Ce were transferred to ryegrass shoots than Sm and the heavy-REE Yb, but this was not observed for alfalfa. Alfalfa dry weight was significantly increased by F. mosseae inoculation, but not ryegrass dry weight. For both plant species, there was significantly higher P uptake by the mycorrhizal plants than the nonmycorrhizal plants, but there was no significant transfer of La, Ce, Sm or Yb to alfalfa and ryegrass roots or shoots due to F. mosseae inoculation.
Journal Article
Rare Earth Elements Enrichment in the Upper Eocene Tošići-Dujići Bauxite Deposit, Croatia, and Relation to REE Mineralogy, Parent Material and Weathering Pattern
Tošići-Dujići bauxite deposit, situated in Dalmatian inlands, Croatia, contains minor remaining bauxite reserves. The deposit lies on Lower Eocene foraminiferal limestone and is covered by Upper Eocene Promina sediments. Bauxite samples were analyzed for textural, mineralogical, and geochemical features in order to determine absolute REE abundances and their relation to mineralogy, as well as to devise the origin of REE enrichment and to trace weathering and bauxitization paths of the parent material. The samples show total REE abundances up to 3500 mg/kg with significant HREE enrichment in some cases. All samples are gibbsitic with hematite and anatase as major phases. Kaolinite occurs in most of the samples, and goethite, böhmite, and nordstrandite are minor phases. Monazite-(Ce) and xenotime-(Y) were identified as detrital REE minerals as well as authigenic florencite-(Ce). In the REE most abundant sample, REE are most likely bound to Fe- and Ti-oxide phases as suggested by correlation analysis. Chemical weathering proxies show intensive weathering. Geochemical and textural data imply that the REE enrichment is influenced by intensive weathering (CIA 97.87–99.26) of detrital material, and also by possible deposition/redeposition of residual material potentially derived and mobilized from various sedimentary rocks of the area.
Journal Article
Two-Step Solvent Extraction of Radioactive Elements and Rare Earths from Estonian Phosphorite Ore Using Nitrated Aliquat 336 and Bis(2-ethylhexyl) Phosphate
Estonian phosphorite ore contains trace amounts of rare earth elements (REEs), many other d-metals, and some radioactive elements. Rare earth elements, Mo, V, etc. might be economically exploitable, while some radioactive and toxic elements should be removed before any other downstream processing for environmental and nutritional safety reasons. All untreated hazardous elements remain in landfilled waste in much higher concentration than they occur naturally. To resolve this problem U, Th, and Tl were removed from phosphorite ore at first using liquid extraction. In the next step, REE were isolated from raffinate. Nitrated Aliquat 336 (A336[NO3]) and Bis(2-ethylhexyl) Phosphate (D2EHPA) were used in liquid extraction for comparison. An improved method for exclusive separation of radioactive elements and REEs from phosphorite ore in 2-steps has been developed, exploiting liquid extraction at different pH values.
Journal Article
Crystal Chemistry and Stability of Hydrated Rare-Earth Phosphates Formed at Room Temperature
In order to understand the crystal chemical properties of hydrous rare-earth (RE) phosphates, REPO4,hyd, that form at ambient temperature, we have synthesized REPO4,hyd through the interaction of aqueous RE elements (REEs) with aqueous P at room temperature at pH < 6, where the precipitation of RE hydroxides does not occur, and performed rigorous solid characterization. The second experiment was designed identically except for using hydroxyapatite (HAP) crystals as the P source at pH constrained by the dissolved P. Hydrated RE phosphate that precipitated at pH 3 after 3 days was classified into three groups: LREPO4,hyd (La → Gd) containing each REE from La-Gd, MREPO4,hyd (Tb → Ho), and HREPO4,hyd (Er → Lu). The latter two groups included increasing fractions of an amorphous component with increasing ionic radius, which was associated with non-coordinated water. REallPO4,hyd that contains all lanthanides except Pm transformed to rhabdophane structure over 30 days of aging. In the experiments using HAP, light REEs were preferentially distributed into nano-crystals, which can potentially constrain initial RE distributions in aqueous phase. Consequently, the mineralogical properties of hydrous RE phosphates forming at ambient temperature depend on the aging, the pH of the solution, and the average ionic radii of REE, similarly to the well-crystalline RE phosphates.
Journal Article
The role of clay minerals in formation of the regolith-hosted heavy rare earth element deposits
Rare earth elements (REEs) have become increasingly important to our modern society due to their strategic significance and numerous high technological applications. Regolith-hosted heavy rare earth element (HREE) deposits in South China are currently the main source of the HREEs, but the ore-forming processes are poorly understood. In these deposits, the REEs are postulated to accumulate in regolith through adsorption on clay minerals. In the Zudong deposit, the world's largest regolith-hosted HREE deposit, clay minerals are dominated by short, stubby, nanometer-scale halloysite tubes (either 10 or 7 Å) and microcrystalline kaolinite in the saprolite and lower pedolith and micrometer-sized vermicular kaolinite in the humic layer and upper pedolith. A critical transformation of the clay minerals in the upper pedolith is coalescence and unrolling of halloysite to form vermicular kaolinite. Microcrystalline kaolinite also transformed to large, well-crystalline vermicular kaolinite. This transformation could result in significant changes in different physicochemical properties of the clay assemblages. Halloysite-abundant clay assemblages in the deep regolith have specific surface area and porosity significantly higher than the kaolinite-dominant clay assemblages in the shallow soils. The crystallinity of clay minerals also increased, exemplified by decrease in Fe contents of the kaolinite group minerals (from ∼1.2 wt% in the lower saprolite to ∼0.35 wt% in the upper pedolith), thereby indicative of less availability of various types of adsorption sites. Hence, halloysite-abundant clay minerals of high adsorption capacity in deep regolith could efficiently retain the REEs released from weathering of the parent granite. Reduction in adsorption capacity during the clay transformation in shallow depth partially leads to REE desorption, and the released REEs would be subsequently transported to and adsorbed at deeper part of the soil profile. Hence, the clay-adsorbed REE concentration in the lower pedolith and saprolite (∼2500 ppm on average) is much higher than the uppermost soils (∼400 ppm on average). Therefore, weathering environments that favor the release of the REEs in the shallow soils but preservation of halloysite in the deep regolith can continuously adsorb REEs in the clay minerals to form economically valuable deposits.
Journal Article
Rare and Rare Earth Elements in Lateritized Bauxites of the Chadobets Uplift (Siberian Platform)
AbstractThe mineral and chemical composition of bauxites from the Chadobets uplift of the Siberian Platform is the total product of laterites on aluminosilicate rocks (source of aluminum) and on alkaline rocks and carbonatites (source of rare earth elements (REEs), Nb, Ta, Th, U, etc.). The laterization of these rocks and subsequent denudation led to the formation of unique bauxite deposits with a high content of rare and REEs. Supergene minerals of the laterite weathering crust are in a dispersed microcrystalline and amorphous state, which complicates their study and the choice of methods for extracting useful components. Precision methods were used to establish the forms and compositions of the main supergene minerals, biomineral films, biomorphoses, and the distribution of rare and rare earth elements in them.
Journal Article