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REE behavior and influence factors during chemical weathering

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... By contrast, Eu is mainly controlled by lithology and is an important tracer for determining the source. It is reduced from Eu 3+ to Eu 2+ under strong reduction conditions and separated from REE (Ma et al., 2004). Therefore, REE are considered as sensitive agents in the water environment. ...
... The Eu/Eu*, Ce/Ce*, (La/Sm) N , (Gd/Yb) N and LREE/HREE are important geochemical parameters. Among them, Eu/Eu* and Ce/Ce* represent Eu and Ce anomalies, respectively, which can reflect the lithology and redox potential of the water environment, and have apparent regional distribution characteristics (Ma et al., 2004). (La/Sm) N and (Gd/Yb) N are indicators of LREE and HREE fractionation degree, respectively. ...
... As shown in Fig. 3, the LREE accounted for the largest proportion (87%-93%) of total REE in SPM at all sites. During the earth's supergene process, REE tend to lose three electrons and form complexion ions, and their complexion ability increases from La to Lu (Ma et al., 2004). REE with sulfates, carbonates, and fluoride are soluble in water; thus HREE tends to exist in the dissolved phase in the form of inorganic and organic complexes, while LREE is more likely to adsorb with solid phases such as clay minerals, organic matter, and Fe-Mn oxide (Liu et al., 2006;Ma et al., 2004). ...
Article
Rare earth elements (REE) are widely used as tracers for surface processes due to their zonal differences in composition and special geochemical indicators. In this study, we collected 30 glacial meltwater samples from a large area of the northeastern Tibetan Plateau region and analyzed the REE composition of suspended particulate matter (SPM, d > 0.45 μm) to explore the spatial distribution, origins and the influencing factors of REE in SPM. Results suggested that chondrite-normalized REE distribution patterns were characterized by steep LREE and relatively flat HREE, which is different from that of PAAS-normalized. The high (La/Sm)N ratio and low (Gd/Yb)N ratio indicated that the degree of LREE fractionation was higher than that of HREE. We found an obvious correlation between REE concentration and SPM concentration, indicating that REE concentration in glacial runoff was significantly affected by SPM contents. It was found that Ce/Ce* decreased first and then increased with the decrease of altitude in the glacial river basins, which may contribute to weathering, oxidation, and physicochemical property of the water environment in the study areas. At the glacier forefield, the degree of weathering is intense, resulting in the highest Ce/Ce* value in the altitude between 3200-4800 m. However, this was not obvious in non-glacial regions. Compared REE geochemical parameters (e.g., LREE/HREE, Eu/Eu*, LaN/SmN) of SPM in the glacier basin with those of Asian potential dust sources and long-range transport (LRT) dust deposited on the studied glaciers, we found that the SPM in the glacial river basins is affected by lithology of parent materials, the LRT dust from the surrounding deserts, the release of ice/snow dust, and the detrital material from local rock weathering. This study provides a new perspective on the composition, distribution and variation in the altitude of REE in the glacial river basin of the northeast TP, and thus is of significance to improve the understanding of the source and migration process of REE in SPM of glacial river basins.
... According to the high concentration of fluorine in the groundwater samples, Wu et al. (1990) suggested that REEs are transported by fluoride complexes. Among the lanthanides, HREEs could bond more strongly to both inorganic ligands (Byrne and Kim, 1990;Cantrell and Byrne, 1987;Chen and Wu, 1990;Tang and Johannesson, 2010b;Wood, 1990), like CO 3 2− , and organic ligands Johannesson et al., 2004;Ma et al., 2004;Tang and Johannesson, 2010b), leading to the preferential depletion of HREEs in regolith and corresponding enrichment in the groundwater (Duddy, 1980;Elderfield et al., 1990;Nesbitt, 1979), and furthermore, LREEs prefer to hydrolysis at shallower depth to form REE oxides/hydroxides while HREEs are mobilized and transported downward towards depth Shen, 1982, 1986). ...
... The ionic strength and pH of the soil solutions also affect greatly on REE adsorption. Lots of studies on regolith-hosted deposits show that adsorption would become stronger with increasing pH (Chen and Wu, 1990;Chi and Tian, 2007;Chi et al., 2012;Huang and Wang, 2002;Ma et al., 2004;Wu et al., 1990) as competition between REE 3+ and H + becomes less intense. The pH also affects the format of adsorption. ...
... However, for regolith-hosted REE deposits in South China, the importance of the secondary minerals and the residual primary minerals is regarded as minor or negligible (e.g. Bai et al., 1989;Bao and Zhao, 2008;Chi and Tian, 2007;Chi et al., 2012;Deng, 2013;Ma et al., 2004;Wu et al., 1990;Yang and Xiao, 2011;Zhang, 1990). Nevertheless, various secondary REE minerals have been discovered, including rhabdophane-(Ce), florencite-(Ce), and cerianite. ...
Article
Regolith-hosted rare earth element (REE) deposits, also called ion-adsorption or weathered crust elution-deposited REE deposits are distributed over Jiangxi, Guangdong, Fujian, Hunan, Guangxi and Yunnan provinces in South China. In general, these deposits can be categorized into the HREE-dominated, for example the famous Zudong deposit in southern Jiangxi province and the LREE-dominated type, such as the Heling and Dingnan deposits in southern Jiangxi province. Most of these deposits form from weathering of biotite and muscovite granites, syenites, monzogranites, granodiorites, granite porphyries, and rhyolitic tuffs. The parent rocks are generally peraluminous, siliceous, alkaline and contain a variety of REE-bearing minerals. Mostly, REE patterns of regolith are inherited from the parent rocks, and therefore, characteristics of the parent rocks impose a significant control on the ore formation. Data compilation shows that autometasomatism during the latest stage of granite crystallization is likely essential in forming the HREE-enriched granites, whereas LREE-enriched granites could form through magmatic differentiation. These deposits are normally two- to three-fold, but could be up to ten-fold enrichment in REE compared to the parent granites, where the maximum enrichment usually occurs in the middle part of the weathering profile from the lower B horizon to the upper C horizon. Ce shows different behavior with the other REEs. Strongly positive Ce anomalies are commonly at the upper part of weathering profiles, likely due to oxidation of Ce³⁺ to Ce⁴⁺ and removal of Ce from soil waters through precipitation of cerianite. Vertical pH and redox gradients in weathering crusts facilitate dissolution of REE-bearing minerals at shallow level and fixation of REE at depth through either adsorption on clay minerals or precipitation of secondary minerals. At the same time, mass removal of major elements plays an important role in concentrating REE in regolith. Combination of eluviation–illuviation dynamics and mass removal is the main mechanism for REE accumulation in weathering crusts. Favorable exogenetic factors facilitate the accumulation of REE in regolith and preservation of the ore bodies. These include quasi-equilibrium between denudation and exhumation at regional scales, local geomorphology dominated by low-lying gentle slopes, adequate rainfall, and favorable groundwater conditions. Continuous operation of the dynamic weathering system is essential in the formation of regolith-hosted REE deposits.
... The fine grain size may also contribute to the enrichment of the REE abundance in sediment samples. It has been demonstrated that the REE abundance in sediments may be significantly influenced by grain-size sorting (Li et al., 2006), because REE in weathering crust exists mainly in the form of the adsorption by clay minerals (Ma et al., 2004), and indeed clay minerals in sediments have a certain adsorption to REE (especially LREE), which results in an obvious increase of the REE contents (Ma et al., 2004;Wu et al., 1991). From the perspective of the REE distribution in PSA from the Horqin Sandy Land and Songnen Sandy Land (Table 1 and Fig. 2b), the REE content of the 11-30 μm size fraction is clearly lower than that of the b11 μm size fraction, which indicates that the REE content gradually increases with decreasing grain size. ...
... The fine grain size may also contribute to the enrichment of the REE abundance in sediment samples. It has been demonstrated that the REE abundance in sediments may be significantly influenced by grain-size sorting (Li et al., 2006), because REE in weathering crust exists mainly in the form of the adsorption by clay minerals (Ma et al., 2004), and indeed clay minerals in sediments have a certain adsorption to REE (especially LREE), which results in an obvious increase of the REE contents (Ma et al., 2004;Wu et al., 1991). From the perspective of the REE distribution in PSA from the Horqin Sandy Land and Songnen Sandy Land (Table 1 and Fig. 2b), the REE content of the 11-30 μm size fraction is clearly lower than that of the b11 μm size fraction, which indicates that the REE content gradually increases with decreasing grain size. ...
... Finally, the LREE and HREE are subjected to fractionation, resulting in the enrichment of LREE and the depletion of HREE relative to NASC (North American Shale Composite) (Nesbitt, 1979). The ∑ LREE/∑ HREE ratio increases with enhancement of weathering (Huang and Gong, 2000;Huang and Wang, 2002;Ma et al., 2004;Wang et al., 1990). As is the case with ∑REE, there is no significant correlation between the ∑ LREE/∑ HREE ratio of the sand-dust deposits and materials from the PSA and CIA. ...
Article
There has long been disagreement about the provenance of sandy dust deposits in Harbin city, Heilongjiang province, China. The present paper contributes to a better understanding of the source of sandy dust deposits in Harbin by the application of REE geochemistry. The REE composition of samples from sand–dust deposit events in Harbin was compared with that of three different grain size fractions (< 11 μm, 11–30 μm and 30–63 μm) of sandy soil samples from Horqin Sandy Land and Songnen Sandy Land. The results indicate that the REE distributions of all of the Harbin sand–dust samples are remarkably similar to each other, with distinct negative Eu anomalies and slightly negative Ce anomalies, indicating a stable provenance. Grain size exerts a significant influence on REE compositions, with a negative Eu-anomaly tending to develop with decreasing grain size. However, Ce is less influenced by grain size. The large lines of evidences, such as REE contents, distribution patterns, characteristic parameters, δEu (δEu = Eu anomalies values) vs. ΣREEs diagram, δEu vs. (LREE/HREE) diagram and (LREE/HREE) vs. LaN (subscript N represents chondrite normalized values) diagram, indicate that REE composition of dust deposits in Harbin is quite similar to that of samples from Horqin Sandy Land, especially in the case of the 11–30 μm grain size fraction. This indicates that the Harbin sand–dust deposits are derived from Horqin Sandy Land and not from Songnen Sandy Land, and that material contribution of Horqin Sandy Land to Harbin dust deposits was mainly 11–30 μm grain-size fraction. The importance of the Horqin Sandy Land as a major source of Harbin sand–dust weather is supported by meteorological records and meteorological data.
... In an oxidizing environment, Ce 3+ closely combines with Fe-Mn oxides to form clay minerals with Ce 4+ , which are then deposited in the surface soil (Laveuf and Cornu 2009). Ce has a stronger capacity to form complexes and is, therefore, more stable than other REEs (Ma Y et al. 2004). The negative anomaly of Eu in soil aggregates in our study was similar to those found by Aubert et al. (2001). ...
... Interestingly, the concentration of organic matter is known to affect the adsorption capacity of Ce (Ma et al. 2004). However, in the absence of organic matter, Ce 3+ combines with Fe-Mn oxides to form Ce 4+ via oxidation, which causes Ce to precipitate and accumulate on the soil surface (Laveuf and Cornu 2009). ...
Article
Full-text available
Rare earth elements (REEs) are widely applied in high-tech fields. However, their increasing presence in the food chain poses significant risks to human health. At present, little is known about the effects of organic matter on the distribution of ion-adsorbed REEs in soil aggregates during ecological restoration. Red soil derived from coarse-grained granite in Southern China is both prone to ecosystem degradation from soil erosion and rich in REEs. Understanding the distribution of REEs in soil aggregates undergoing ecological restoration is helpful to formulate effective measures for controlling the environmental migration of REEs. Four sites that had undergone different durations/degrees of ecological restoration were selected in the areas to analyze. REEs concentration of six different aggregates sizes (<0.25, 0.25−0.5, 0.5−1, 1−2, 2−5, and >5 mm) were analyzed and the enrichment coefficients were calculated in 4 sample sites of severe-degraded ecosystem in Changting County, Fujian Province, Southern China. The results showed that the total rare earth elements (TREEs) concentration in the aggregates increased from 213 mg kg−1 to 528 mg kg−1 with the extension of the ecological restoration time. At the initial stages of ecological restoration, there was no significant difference in the TREEs concentration among the six aggregates sizes. However, in the middle and late stages of restoration, the concentration of TREEs increased significantly with the decrease of aggregate size. The concentration of individual REEs showed three changing trends with sizes of aggregates during ecological restoration, respectively: 1) no obvious regular change (S1), 2) a V-shaped change trend (S2), and 3) increasing concentration with the decrease of aggregate size (S3 and S4). Ce and Eu showed a positive and negative anomaly in the soil aggregates, respectively. Moreover, the light rare earth elements (LREEs) were enriched, while the heavy rare earth elements (HREEs) were depleted during the initial stages, and the HREEs were enriched during the middle and late stages of restoration. The correlation coefficient between organic matter and REEs in aggregates was generally low; however, LREEs showed a stronger correlation with organic matter than that of HREEs during the initial stages of ecological restoration. The correlation between organic matter and HREEs gradually increased and even exceeded that of LREEs with on-going ecological restoration. The distribution of REEs concentration in degraded soil aggregates in Southern China showed obvious variability with the ecological restoration time.
... The hydrolytic strength and activity of REEs increase with the pH values [5,52]. The hydrolysis strength of LREEs is stronger than that of MREEs and HREEs, but their activities are opposite [85,86]. REEs tend to form stable complexes with HCO 3 − in alkaline environment because high pH would promote the activity of HCO 3 − [4]. ...
... Clay contents were negatively correlated with the contents of LREE, MREE in the T2 profile while only the negative correlation with the LREE contents was observed in the T1 profile, and the correlation between clay contents and REEs contents was not significant in the T3 profile ( Figure 5). The positive correlation between clay contents with REEs contents (especially the LREE contents) was widely reported in many studies [86,[88][89][90]. While the REEs contents were negatively correlated with clay mineral contents in the T1 and T2 profiles, it cannot completely explain the behaviors of REEs. ...
Article
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The geochemical characteristics of rare earth elements (REEs) can be employed to identify the anthropogenic and natural influence on the distributions of REEs in soils. A total of 47 soil samples from the three soil profiles of the secondary forest land, abandoned cropland, and shrubland in the Yinjiang county of Guizhou province, southwest China, were collected to determine the contents and distribution of REEs in the soil environment. The total REEs (ΣREE) contents in different soil profiles are in the following sequence: secondary forest land (mean: 204.59 mg·kg−1) > abandoned cropland (mean: 186.67 mg·kg−1) > shrubland (mean: 139.50 mg·kg−1). The ratios of (La/Gd)N and (Gd/Yb)N ranged from 0.62 to 1.00 and 1.18 to 2.16, which indicated that the enrichment of the medium rare earth elements (MREEs) was more obvious than that of the light rare earth elements (LREEs) and the heavy rare earth elements (HREEs). The phenomenon could be attributed to the preferential absorption of MREEs by fine particles and the substitution of Ca2+ by MREEs. Most soil samples were characterized by the negative Ce anomalies (anomalies values: 0.30–1.10) and positive Eu anomalies (anomalies values: 0.43–2.90). The contents of REEs in the profiles of secondary forest land and shrubland were mainly regulated by soil pH and Fe contents while clay content and agricultural activities were the main controlling factors in the soil profile of abandoned cropland. This study highlights the role of agricultural activities in affecting the distributions of REEs in karst soils, which could provide some insights for the protection of the soil environment.
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The Lenghu sandstone type uranium deposit as industrial value in the northern Qaidam Basin, Northwest China. This study analyzed the LA-ICP-MS U-Pb dating of detrital zircons, mineralogical features, electron probe, backscatter electron imaging and track etch of the altered minerals from uranium-bearing strata in the Xiaomeigou Formation of Lower Jurassic on the basis of field investigation in order to trace the source, parent rock lithology, geochronological age, uranium minerals, compositional characteristics, occurrences of uranium mineralization. The U-Pb ages of detrital zircons from the ore-bearing member are ranging from 117–270Ma and 370–480Ma, respectively, indicating that the provenance and uranium source were mainly derived from the Permian-Triassic intermediate-acid igneous rocks in the eastern Altyn Tagh and western Saishiteng Mountains, a small amount of them are from the Ordovician-Silurian intermediate-acid igneous rocks in the Xiaosaishiteng Mountains. Two types of ores in Xiaomigou Formation in Lenghu region are mainly composed of graywacke and carbonaceous sandstone with main uranium minerals are coffinite, pitchblende and trace amounts of lead selenite. They are closely associated with clay minerals, organics and pyrite, which lie in the intergranular space of quartz, feldspar and other altered lithic mineral grains or in cleavage joints of altered clay minerals that occur in fine columnar, gel-like or irregular sawtooth shape. It is inferred that the Fe²⁺ in feldspar and biotite reacts with H2S or S²⁻ bearing minerals participated in the formation of pyrite, where the U⁶⁺ was captured by late multiple fluid processes occurred reduction-precipitation-adsorption uranium mineralization in the reduction environment provided by Fe²⁺. Based on the analysis of the existence of high Y and low Y types of uranium minerals, alteration sequence and environmental characteristics, it is inferred that uranium in uranium minerals is the residual of original uranium minerals derived from the pre-enrichment of uranium-bearing detrital particles in sedimentary and diagenetic stages, and at the later stage, the high radioactivity abnormal geological bodies migrated to the inner basin through the multi-stage reformation of uranium-containing and oxygen-containing fluids without Y or at very low contents.
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The samples of urban road surface soils were collected from Harbin City of Heilongjiang Province and divided into different grain size fractions (bulk sample, > 63μ m, 63-30μ m, 30-11μ m and < 11μ m). These samples were analyzed to obtain the composition of trace elements and rare earth elements (REE). The results indicate that the variation degree of trace elements in different size fractions increases in order of Sr< Rb< Ga< Y< V< Zn< Nb< Cr< Zr< Cu< Ni, Sr and Rb are less affected by grain size, and Zr, Cu and Ni are severely affected by grain size. The volume of most trace elements such as V, Cr, Cu, Zn, Sr, Y, Zr and Nb tends to increase with decreasing grain size, while things are just opposite for Rb, and the relationship between Ni, Ga and grain size is unclear. Rb/Sr ratio is a chemical weathering index independent of grain-size sorting, Zr/Rb, Cu/Zn, V/Cr and Ni/V ratios are severely affected by grain size, Zr/Rb ratio obviously increases with decreasing grain size. It is shown that the distribution patterns and fluctuation ranges of all REE in different size fractions are highly consistent with each other, characterized by the enrichment of fine-grained material. The 8Eu value is obviously influenced by grain size, characterized by the variation of Eu from positive Eu anomalies to negative Eu anomalies with decreasing grain size. The variation of 8Ce in different size fractions was insignificant, indicating that 8Ce value was less influenced by grain size.
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The mining of rare earth ore leads to a series of environmental problems. To solve the problem of environmental monitoring of the ion-absorbed rare earth ore districts in southern China, the authors selected Xunwu area in south Jiangxi as the study area, and used IKONOS remote sensing data for investigation. For the two main kinds of environmental problems in the ion-absorbed rare earth ore mining, i.e., land desertification and water pollution, the spectral angle mapping classification method was chosen to extract the land desertification place in the study area, and ISODATA unsupervised classification algorithm was used to estimate the contamination of the river near the ion-absorbed rare earth ore district. An analysis of the results and field survey show that high spatial resolution remote sensing technology can provide a good means for environmental investigation of the ion-absorbed rare earth ore district.
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To understand the characteristics and evolution of REE during the process of the ultramafic laterization under different climate conditions, two outcrops Kolonodale in Indonesia and Yuanjiang in China are chosen for comparision. It is found that the contents of REE from the laterite crusts are higher than those from the bed rocks in both places (enrichment factor being 44.21 and 236.19 respectively). The indices of differentiation between the LREE and HREE decrease with profile downward toward, and the indice of Ce anomaly shows a shift from the positive Ce anomaly in the upper segment to negative Ce anomaly in the lower part. The difference between the two profiles lies in the distribution of the highest REE enriched segment. The laterite layer represent the most REE enriched for the Yuanjiang whereas the saprolite layer for the Kolonodale. The evaluation of the mass balance shows remarkable migration and differentiation of REE in the ultramafic laterization process, which were constrained effectively by the pH environmentand organic matter (O. M.). The results indicate that climate have had great influence on the geochemical evolution of REE during the ultramafic laterization. Under the rainforest climate condition, the REE from the Kolonodale originates mainly from the basal rocks and has experienced intensive redistribution during the laterization; whereas the REE from the Yuanjiang has a mixed source stemming from both the parent rock and aeolian sediment, and it has been through only slight redistribution during the laterization.
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To determine provenance of sand-dust fallouts in Harbin area, Heilongjiang Province, the sand-dust fallouts in Harbin and two different grain size fractions (<11 μm and 11-30 μm) of samples from the potential source areas, including Horqin sandy land and Songneng sandy land, are studied for rare earth element (REE) compositions. The results indicate that ΣREE for sand-dust fallouts in 2002 ranges from 179.07×10-6 to 200.92×10-6 with an average value of 189.67×10-6, ΣREE varied ranges from 166.70×10-6 to 184.44×10-6 with an average value of 175.57×10-6 for sand-dust fallouts in 2007, from 166.91×10-6 to 182.45×10-6 with an average value of 174.68×10-6 in 2008, ΣREE in 2011 is 181. 35×10-6. The REE distribution for all sand-dust fallouts focuses on very narrow scopes, which displays provenance for sand-dust fallouts in Harbin is very stable. The dust falls show very similar REE distribution patterns and characteristic parameters with distinct negative Eu anomalies (δEu value for dust falls in 2002, 2007, 2008 varied from 0.71 to 0.75, δEu value in 2011 was 0.92) and slightly negative Ce anomalies (δCe value was in the range from 0.89 to 0.92 with an average of 0.90). The relatively large amount of evidence, such as REE values and distribution patterns and characteristic parameters and δEu vs. ΣREEs diagram and δEu vs. (LREE/HREE) diagram and (LREE/HREE) vs. LaN diagram, indicate that REE compositions for dust falls in Harbin are quite similar to those of Horqin sandy land (specially 11-30 μm grain size fractions), showing sand-dust in Harbin stems from Horqin sandy land but not Songneng sandy land, and showing material contribution of Horqin sandy land to dust falls in Harbin is mainly 11-30 μm grain-size fractions. It is confirmed that dust falls in Harbin are from Horqin sandy land by relevant meteorological records and meteorological data.
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This paper approaches the vertical distribution and enrichment of the trace elements in an ion adsorption type REE deposit to understand the geochemical behavior of REEs. Based on the field geological works, the weathering crust of this deposit is divided into 4 layers. According to geochemical characteristics of the trace elements, the total amount of rare earth elements (ΣREE) in the weathered crust is higher than that in the parent rock. REE is distributed vertically in a parabolic form. Chondrite-normalized REE patterns are rich in LREE, with LREE/HREE decreasing vertically from the upper to the lower part of the profile. The REE distribution pattern of the weathering crust is similar to its original rocks. However, the differentiation of the trace elements is also very obvious. It occurs between some trace elements (such as Sr, etc.) and other trace elements, between LREE and HREE, and between Ce, Eu and other rare earth elements. The main effective factors of the mobility and fractionation of REE include the nature of REEs, the mineralogical assemblages of the weathering crust, the redox conditions, pH value, the microbial activities, and so on. The ion adsorption type rare earth elements deposit is a product of multistage and multiple metallogenetic processes in the open system.
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China has relatively abundant rare earth elements (REEs) reserves and will continue to be one of the major producers of REEs for the world market in the foreseeable future. However, due to the large scale of mining and refining activities, large amounts of REEs have been released to the surrounding environment and caused harmful effects on local residents. This paper summarizes the data about the contents and translocation of REEs in soils, waters, atmosphere, and plants in REE mining areas of China and discusses the characteristics of their forms, distribution, fractionation, and influencing factors. Obviously high concentrations of REEs with active and bioavailable forms are observed in all environmental media. The mobility and bioavailability of REEs are enhanced. The distribution patterns of REEs in soils and water bodies are all in line with their parent rocks. Significant fractionation phenomenon among individual members of REEs was found in soil-plant systems. However, limited knowledge was available for REEs in atmosphere. More studies focusing on the behavior of REEs in ambient air of REE mining areas in China are highly suggested. In addition, systematic study on the translocation and circulation of REEs in various media in REEs mining areas and their health risk assessment should be carried out. Standard analytical methods of REEs in environments need to be established, and more specific guideline values of REEs in foods should also be developed.
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The three kinds of soil formed by the weathering of the basalt in Yema village, Weining county of Guizhou province, the carbonate rock in Guiyang district and the phosphorite in the REE-bearing phosphate mining area in Zhijin county of Guizhou province were all rich in REE. The contents of LREE in these three soil were higher than that of HREE, which was caused by the different properties of LREE and HREE complexes. Since light REE could be easily absorbed by kaolinite grains, LREE was fully enriched in the process of desorption, migration and re-absorption, which formed a typical LREE soil. The chondrite normalized distribution models of those three types of REE-enriched soil are basically similar, which belong to the right deviation type, namely, rich in light rare earth element but short of heavy rare earth element, and showing Ce negative anomalies. Eu showed intense negative anomalies in the REE in the soil formed by the weathering of the sedimentary parent rocks (such as carbonate rock and phosphorite), while no pronounced Eu anomaly was found in the REE in the soil formed by the weathering of volcanic rocks (such as basalt). It is clear that though there were intense migration and enrichment of REE during the weathering process of rocks, no obvious differentiation of REE occurred and some features of the parent rocks were retained. That is why REE is of value in analyzing the source of materials.
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A new type of rare earth elements (REEs) deposit was discovered from the gaolinite mudstone in the weathering crust of Permian basalt, Bijie region, western Guizhou, China. It contained ΣRE2O3 0.065%–1.086%. This type of REEs deposit was widely distributed with steady horizon and thickness of 3–4 m. The ore-bearing weathering crust (kaolinite) of the three discovered REEs deposits belonged to the third episode of the Emeishan basalt eruption. The new type of REEs deposit was suggested that basalt (tuff) weathering could lead to the enrichment of the rare earth elements. Therefore, it is of important economic significance to explore REEs deposits in the weathering crust of basalt (tuffs) in Yunnan, Guizhou, and Sichuan Provinces.
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Preferential flow is a rapid movement of solution through pores caused by coarse ores. Macropore is the main factor for the preferential flow. Macropore can be defined from three aspects. Segregation of the ores during dumping was studied according to particle kinematics. Small ores become smaller under the effect of acid and weathering. Clay in the rainwater from the hillside precipitates in the dump. Segregation and fine ores are the main causes in macropore. The permeability in coarse ores is better than that in fine ores. The mechanism in the preferential flows was studied combining the fast conducting effect of the macropore. Experimental result shows that, at certain application rate, fine ore area is saturated while large volume of solution flows laterally to the coarse ore area and leaks out quickly through the macropores. Thus the mechanism of preferential solution flows is further illustrated.
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