Geochemical Behavior Of Rare Earth Elements Research Articles

Migration and controlling factors of rare earth elements in geothermal systems on the southern Tibetan Plateau

Rare earth elements (REE) serve as effective tracers of water-rock interactions, a crucial process in the evolution of geothermal systems. However, the geochemical behavior of REE during their migration within geothermal systems, particularly the fractionation mechanism, remains poorly understood. In this study, we focus on the geochemical characteristics of REE in hot springs, host rocks, and sinters from various hot spring systems in the Yadong-Gulu rift (YGR), the largest extensional rift in the southern Tibetan Plateau. The objective is to explore the factors that control REE concentrations in hot springs and elucidate the fractionation of REE during their migration. The concentrations of REE are significantly influenced by pH, Fe oxides (oxyhydroxides), and HCO3− concentrations in central and southern hot springs, whereas high reservoir temperatures contribute to higher ΣREE concentrations in northern hyperthermal springs. REE speciation calculations show that LnO2− and LnO2H are dominant complexes in northern alkaline hot springs, while carbonate complexes (LnCO3+ and Ln(CO3)2−) prevail in central and southern spring samples. Additionally, weakly acidic hot springs exhibit a prevalence of Ln3+, LnF2+, and LnSO4+ species. The chondrite-normalized REE patterns of all hot spring samples display enrichment in MREE, which is significantly distinct from the patterns observed in host rocks and sinters enriched in LREE. The fractionation of REE in the YGR hot spring systems is primarily controlled by the following processes: (1) Temperature, pH, and relative abundance of complexing agents influence the complexation of REE and further regulate their fractionation in hot springs; (2) During water-rock interaction, preferential leaching of HREE and MREE from host rocks can lead to their enrichment in alkaline hot springs. The dissolution of iron-rich sediments plays a significant role in generating the distinctive MREE bulge pattern in acid-neutral hot springs compared to host rocks; (3) The higher stability of MREE and HREE complexes in water, as well as the preferential coprecipitation of unstable LnCO3+ complexes formed by LREE with carbonates, are key factors responsible for LREE enrichment in sinters.

Geochemistry of Rare Earth Elements in Pahang River Sediment, Malaysia

Rare earth elements (REE) are a set of 17 chemically similar metallic elements including 15 lanthanides, scandium and yttrium. The current status of REE as a global strategic commodity has encouraged the identification of REE ore deposits. This research is carried out to identify the mining feasibility of fluvial sediment REE and to understand the sediment's physical and chemical characteristics and effects on the geochemical behaviour of REE in the longest river of Peninsular Malaysia namely Pahang River. Surface sediment samples were collected along Pahang River (n=44) in approximately 10 km distance intervals. The sediment samples were analyzed using XRF to determine the major oxide content. Meanwhile, REE content in the sediment samples was extracted using the Total Digestion method and analysed using ICP-MS. The results show the average value of ΣREE at surface sediments of the Pahang River is 42.58 ppm and can be considered too low to be economically mined. Each area shows higher fractionation of light REE than heavy REE with negative europium anomalies, suggesting sediments in this area were derived from felsic rocks. The concentration of REE in Pahang River surface sediments was controlled by the porosity and organic matter as showed by the correlation of ΣREE with porosity (R2=0.65) and organic matter content (R2=0.71). In conclusion, this research's findings are generally useful for further REE mineral exploration and fluvial sediment environmental monitoring.

Geochemical behaviors of rare earth elements in granite-hosted geothermal systems in SE China

Rare earth elements (REEs) are effective indicators in tracking water-rock interactions in the hydrothermal systems. Subject to multiple environmental effects, none a unified conclusion has been achieved to generalize the mechanism of diversifying the REEs in various thermal systems. Low-medium temperature hydrothermal systems occurring in fractured-granite exist widely in South China. However, geochemical behavior of REEs in geothermal water is not well studied though there are lots of REEs deposits. This study focuses on hydrogeochemical characteristics of REEs and constrains from salinity. Results show that the TDS (total dissolved solids) mutation due to transfer of sedimentary environments from coastal to relatively inland areas caused the great differentiation of REEs and their species. When TDS is greater than 1 g/L, Ln3+, LnOH2+, LnSO4+, and LnF2+ (Ln represents REEs) prevail and fractions of them except LnOH2+ are positively correlated with TDS. In contrast, when TDS is less than 1 g/L, LnCO3+ and Ln (CO3)2− constitute the most important part and mutually compete in fluids. A positive Eu anomaly is proved to originate primarily from the preferential dissolution of Eu-rich minerals and the seawater intrusion somewhat contributed to the negative Ce anomaly. This work first proposed the salinity effect on REEs by analysis of the in-situ sampling thermal waters that may have been neglected before and provided a new perspective to comprehensively understand the occurrence and migration mechanisms of REEs in different hydrothermal systems.

Origin and distribution of rare earth elements (REEs) in the soils of Meizhou City, southern China with high abundance of regolith-hosted REEs

Currently, regolith-hosted rare earth element (REE) deposits in South China are the major source of global REEs, particularly heavy REEs (HREEs). This type of REE resource contains abundant movable, bioavailable, and ion-exchangeable REEs and may act as an environmental hazard; however, little is known regarding REEs in soils from areas with abundant deposits. Here, we investigated the REEs in the soil, surface water and crops, collected from Meizhou City, Guangdong Province, South China, as a representative region with abundant regolith-hosted REEs. Mean REE concentration (ΣREE) in the soil (318 μg g−1) exceeded the local soil background (169 μg g−1). The LREE/HREE ratio ranged from 2.04 to 69.4 in soil samples, suggesting the enrichment of light REEs (LREEs) compared with HREEs. Most soil samples exhibited positive Ce anomalies and negative Eu anomalies. The highest ΣREE (1162 μg g−1) was detected in forest land, followed by garden land (793 μg g−1) and paddy field (519 μg g−1). According to the correlation analysis, pH as well as soil organic matter (SOM), Fe, and Mn content contributed to REE enrichment, while SOM and Mn content affected REE fractionation. REE enrichment in soil may be related to natural sources (e.g., parent materials) and anthropogenic activities (e.g., fertilizer application and coal combustion). The REE contamination of surface water was not serious. However, ΣREE in crops (7.08 μg g−1·dw) indicated that these elements migrate from soils to plants, producing potential adverse effects on crops and humans. These findings shed new light on the geochemical behavior of REEs in the environments with abundant regolith-hosted REEs and can serve as a reference to prevent and control REE contamination.

Geochemical fractionation pattern and environmental behaviour of rare earth elements (REEs) in mine wastes and mining contaminated sediments; Sarcheshmeh mine, SE of Iran

The geochemical fractionation pattern and environmental behaviour of rare earth elements (REEs) were investigated in the mining/processing wastes and contaminated sediments associated with the Sarcheshmeh mine, one of the largest Oligo-Miocene Cu-porphyry deposits in the world. For this purpose, the total concentration and the fractionation pattern of REEs were determined using microwave-assisted multi-acid digestion (HCl + HNO3 + HF) and BCR (Community Bureau of Reference, European Commission) sequential extraction methods, respectively. The normalizing patterns of the total concentration of REEs based on the world average shale (WAS) and average chondrite (AC) for the samples composed of primary lithogenic minerals have corresponded with the higher enrichment of LREEs than HREEs, a pattern that was similar to the Sarcheshmeh porphyry rocks. The BCR fractionation pattern of REEs in theses samples was mainly dominated by the residual fraction. By contrast, the normalizing patterns of the total concentration of REEs in the samples composed of secondary minerals or amorphous solid phases showed higher enrichment of HREEs than the LREEs. Surprisingly, depending on the mineralogy and environmental conditions, the BCR fractionation pattern of REEs in these samples was mainly associated with the both readily acid-soluble and reducible fractions. For example, the BCR fractionation pattern of REEs in the Sarcheshmeh mine pit sediments, which were enriched in amorphous Fe oxides, was mainly controlled by the reducible fraction (>46%), while these elements were mainly related to the acid-soluble fraction (>80%) in the sediment sample collected from the surface evaporative layer formed on top of the old weathered tailings. On the other hand, the BCR fractionation pattern of REEs was controlled by the both acid-soluble (>32%) and reducible fractions (>43%) in the samples collected from sediments and efflorescence salts formed along the waste rock drainages. These results showed that statement any general geochemical pattern and environmental behaviour for the REEs without considering the key environmental factors may lead to miss-understanding or even contrasting interpretations. This study emphasizes on the importance of the mineralogy, the conditions of weathering and oxidation reactions, and even the climate and topography on the BCR fractionation pattern and geochemical behaviour of REEs in the environment.

Spatial variability and geochemistry of rare earth elements in soils from the largest uranium-phosphate deposit of Brazil.

The Itataia uranium-phosphate deposit is the largest uranium reserve in Brazil. Rare earth elements (REEs) are commonly associated with phosphate deposits; however, there are no studies on the concentrations of REEs in soils of the Itataia deposit region. Thus, the objective of the research was to evaluate the concentration and spatial variability of REEs in topsoils of Itataia phosphate deposit region. In addition, the influence of soil properties on the geochemistry of REEs was investigated. Results showed that relatively high mean concentrations (mgkg-1) of heavy REEs (Gd 6.01; Tb 1.25; Ho 1.15; Er 4.05; Tm 0.64; Yb 4.61; Lu 0.65) were found in surface soils samples. Soil properties showed weak influence on the geochemical behavior of REEs in soils, except for the clay content. On the other hand, parent material characteristics, such as P and U, had strong influence on REEs concentrations. Spatial distribution patterns of REEs in soils are clearly associated with P and U contents. Therefore, geochemical surveys aiming at the delineation of ore-bearing zones in the region can benefit from our data. The results of this work reinforce the perspective for co-mining of P, U and REEs in this important P-U reserve.

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.

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.

Rare earth elements in French stream waters — Revisiting the geochemical continental cycle using FOREGS dataset

The geochemical behavior of rare earth elements (REEs) has been investigated mainly in geological systems where these elements represent the best proxies of processes involving the occurrence of an interface between different media. This behavior is assessed according to REE concentrations recorded along the REE series normalized with respect to upper continental crust. In this study based on a field approach, the geochemical behavior of REE was investigated in French stream waters. This study is based on FOREGS (Forum of European Geological Surveys) Geochemical dataset that consists on a sampling at regular mesh on all Europe. In France, 119 stream water samples were extracted in drainage basins <100km2. The aim of the study is that of describing the spatial variation of REEs and finding the hydro-topo-geochemical factors that affect their distribution by means of a Multivariate Factorial Kriging.On the basis of their atomic number and of the results of a preliminary Principal Component Analysis three REEs have been selected (La, Eu and Lu) and five physicochemical properties (pH, organic carbon, carbonates, Fe, Mn). A cokriging has been applied that shows a similar spatial organization of REEs: higher values are especially observed in the Aquitaine basin. In order to investigate more deeply on the different sources of variation acting in the study area, a factorial cokriging is applied. The first 2 regionalized factors have been estimated to give a synthetic description of the studied process at the different selected spatial scales. At higher spatial scales (250km) environmental parameters like Fe, carbonates, and pH, supposed to be ascribed to the rock's nature or to other geological larger scale processes (i.e., hydrographic network and topography), have shown to affect REE distribution. At short range, only Eu and Mn weigh more, which are ascribed to the process of liberation of Mn oxides in rivers that also release the REEs sorbed onto these oxides.

Rare earth element geochemistry of spring water, north western Bam, NE Iran

In this paper, based on the analysis of major ions and rare earth elements (REEs), spring water samples from the north western Bam area, central Iran were investigated for the hydrochemical processes, geochemical behavior of REEs and ion concentration background in the region . In the study area, the order of cation and anion abundance is Na+ > K+ > Mg2+ > Ca2+ and Cl− > SO 4 −2 > HCO3− > NO3−, and the dominated hydrochemical water are of Na–Cl type. The groundwater shows heavy REEs enrichment relative to light REEs. Depending on water types, REEs show different behaviors in study area. The increase in TDS and Fe contents in groundwater is accompanied by an increase in REE concentrations, while an increase in pH and Eh values is accompanied by a decrease in REE concentrations. Moreover, correlation analysis indicates that Eh–pH condition, TDS and Fe content, aquifer rock as well as their minerals play an important role in controlling the REE enrichment of groundwater.

Geochemical behavior of rare-earth elements and other major and minor elements in sound-producing and silent beach sands in Japan

The major element composition of sound-producing sand is reported together with rare-earth elements (REE) and other selected elements for the first time. Rare-earth element concentrations in beach sands from Miyagi and Tottori in Japan were determined by induction-coupled, argon-plasma spectrometry (ICP-MS) to characterize the REE of sound-producing and silent sands relative to the parental rocks. Sound-producing sand beaches are very common and all over in Japan: five beaches in Miyagi and 2 in Tottori are selected with other silent sand beaches in the areas. Both sound-producing sand and silent sand samples from Miyagi and Tottori contain more than 60wt% of SiO2 and are composed mainly of quartz and feldspar. Miyagi sand samples are characterized by light REE enrichment and flat chondrite-normalized patterns that are similar to those of local source sandstone. However, all sand samples from Miyatojima in Miyagi show positive Eu anomalies, a characteristic feature not shown in other sand samples from Miyagi. Tottori sand samples also are characterized by high REE contents and remarkable positive Eu anomalies. The sands containing lower REE contents are due to high quartz and feldspar contents. Miyatojima sand samples and Tottori sand samples have high REE contents and show remarkable positive Eu anomalies due to the presence of feldspar.

Determination of rare earth elements in carbonatites from the Kangankunde Mine, Malawi by instrumental neutron activation analysis

Nine rare earth elements (REEs) in African carbonatite samples were determined by instrumental neutron activation analysis (INAA). The geochemical behavior of REEs in carbonatites, especially REE pattern (chondrite-normalized), is studied in relation to carbonatite formation at the Kangankunde Mine, Malawi. REE-rich phosphate minerals, particularly monazite, and the other unusual minerals such as strontianite, are observed during the stages of carbonatite formation. Four kinds of carbonatites exhibit similar chondrite-normalized REE distribution patterns in spite of the marked difference of their REE contents. All these carbonatites are characterized by the strong fractionation between light and heavy REEs and by the very high La/Yb ratio (1000-2800).