Fractionation and fixation of rare earth elements in soils: Effect of spiking with lanthanum,cerium, and neodymium chlorides

Industrial and agricultural activities lead to the release of rare earth elements(REEs)in wastewater and aquatic ecosystems,and their accumulation in soils.However,the behavior of REEs in soils remains somewhat unclear.In the present work the fractionation and fixation of REEs in soddy-podzolic and chernozem soils spiked with La,Ce,and Nd chlorides were studied using dynamic(continuous flow)extraction,which allows natural conditions to be mimicked and artefacts to be minimised.The eluents applied are aimed to dissolve 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 0.05 mol/L Ca(NO₃)2,0.43 mol/L CH₃COOH,0.1 mol/L NH₂OH·HCl,0.1 mol/L K₄P₂O₇ at pH 11,and 0.1 mol/L(NH4)₂C₂O₄ at pH 3.2,respectively.It is found that the fixations of added La,Ce,and Nd in the form of metal-organic complexes is predominant for both types of soils:35%-38%in soddy-podzolic soil and 50%-79%in chernozem.The fixation of added elements in the first three fractions(exchangeable,specifically sorbed,and bound to Mn oxides)is significant for soddy-podzolic soil(5%-25%).For chernozem,the relative contents of added Ce and Nd in these fractions are nearly negligible.Only the content of exchangeable La is notable,about 5%.Adding any of three elements(La,Ce,or Nd)at the level of100 mg/kg to an initial sample results in changing the fractionation and bioaccessibility of other REEs present in soil.Their contents increase in the first three fractions and decrease in fifth(oxalate extractable)fraction for both soddy-podzolic soil and chernozem.The main difference is the behavior of REEs in pyrophosphate extractable fraction.For soddy-podzolic soil,adding La,Ce,or Nd results in decreasing the contents of other REEs associated with organic matter.For chernozem,on the contrary,the contents of REEs in the form of metal-organic complexes slightly increase.These processes may be attributed to competitive binding of elements and soil properties;they must be taken into account when assessing the environmental risks of soil pollution with REEs.     

Rare earth element content in the SPM of Daliao river system and its comparison with that in the sediments, loess and soils in China

Content and distribution patterns of rare earth dements （REEs） in the suspended particulate material （SPM） of Daliao River system were investigated and compared with those in the fiver and sea sediments, loess, and soils of China. Twenty-seven samples of SPM were taken in Daliao River system and digested with various acids followed by ICP-MS analysis for REEs and ICP-OES analysis for Al, Fe, Mn, Ti, Mg, Ca, Na, and K, to measure the total concentrations of these elements. Results indicated that the spatial change in the content of REEs was great, with the coefficient of variance （CV） from 84% to 105%, while the contents of REEs were significantly correlated with each other. Chondrite-normalized patterns of REEs were characterized by higher enrichment of light REEs than heavy REEs, and a depletion of Eu in the SPM was generally found. The positive anomaly of Eu in the SPM of Xi River was due to anthropogenic source in Shenyang City. Furthermore, chondfite- and upper continent crust-normalized patterns of REEs in the SPM of Daliao River system, sediments of Yangtze River and Yellow River, sediments of Yellow Sea, East Sea, South Sea of China, and loess and soil of China, were very similar to one another. These demonstrated that the weathering and sedimentary processes resulted in constant REE distribution not only in the typical sedimentary rocks, but also in the modem riverine particle, sea sediments, loess, and soils.     

REEs fractionation and sedimentary implication in surface sediments from eastern South China Sea

To get features of rare earth elements(REEs)fractionation,106 surface sediment samples from eastern South China Sea were determined for REEs combined with major and trace elements by ICP-MS.The distribution pattern of REEs,strong correlation between REEs and Al,North American shale composite(NASC)normalization all suggest a dominant crustal source for REEs in the research area.However, distinct fractionation among REEs was observed in surface sediment from area with water depth over 2000 m,confirmed by the strong positive correlation among light rare earth elements(LREEs)and among heavy rare earth elements(HREEs)but weaker relationship between LREEs and HREEs.Eluviation by Cl – might be a key role on the fractionation of REEs,comparing with factors such as grain size,co-precipitation with Fe and Mn hydroxide,calcareous and siliceous biogenic precipitation.The fractionation among REEs could be used as index to illustrate the sedimentary environment in reverse.     

Responses of ramie (Boehmeria nivea L.) to increasing rare earth element (REE) concentrations in a hydroponic system

A number of studies have focused on the effects of rare earth elements (REEs) on crop plants, while little attention has been paid on how tolerant plant species respond to increasing mixed REE concentrations. In this study, ramie (Boehmeria nivea L.) was exposed to a series of REE concentrations prepared with equimolar mixtures of 16 REEs (i.e. 0, 1.6, 8, 16, 80, 160, 400, 800 μmol/L) in order to explore REE accumulation and fractionation characteristics in ramie and the responses of this plant to mixed REEs. Results show that ramie root and shoot biomasses are unaffected under lower REE concentrations (1.6–80 μmol/L), while the growth of ramie and the uptake of nutrients especially Ca and Mn are largely inhibited under higher REE concentrations (160–800 μmol/L). The P and Mo concentrations in the roots increase with the increasing REE concentrations in the solution, suggestive of an involvement of P and Mo in dealing with the high concentrations of REEs in this plant. The preferential uptake of Ce and heavy REEs (HREEs) and the preferential transport of HREEs within the plant lead to a positive Ce anomaly and a HREE enrichment in ramie leaves. Our study suggests that ramie could be a good candidate for the phytoremediation of heavily REE-contaminated soils (e.g., REE mine tailings in southern China). Our results also shed light on points of taking into account phytoremediation management strategies of REE-contaminated soils (e.g., P and Mo fertilization).     

Content of rare earth elements in Salvia miltiorrhiza bunge from different areas

Salvia miltiorrhiza bunge(SMB) has been widely used as a traditional Chinese medicine for a long time,and today more and more attention has been paid to the effective components in Chinese traditional medicine,especially to rare earth elements(REEs).14 kinds of REEs in SMB from different areas were analyzed by the methods of ICP-MS.The results showed that the total concentration of REEs(as REO,the same below) ranged from 8.43(as dry weight,the same below) to 37.30 mg/kg,and the concentrations of La,Ce and Nd were higher than 2 mg/kg except Nd in SMB from Beijing.So the total concentration of REEs in SMB was much higher than that in rice,corn and barley,which could be the mechanism of curative effect of SMB on cardiovascular cerebrovascular system,digestive system,respiratory system,countershock and antibiotic.The character of other elements and the content of REEs in soil from different areas should be responsible for the difference,but the allocation mechanism of REEs in SMB should be further studied.     

Geochemistry of rare earth elements in cobalt-rich crusts from the Mid-Pacific M seamount

Rare earth elements (REEs) and major elements of 25 cobalt-rich crusts obtained from different depths of Mid-Pacific M seamount were analyzed using inductively coupled plasma-atomic emission spectrometer and gravimetric method. The results showed that they were hydrogenous crusts with average ∑REE content of 2084.69 μg/g and the light REE (LREE)/heavy REE (HREE) ratio of 4.84. The shale-normalized REE patterns showed positive Ce anomalies. The total content of strictly trivalent REEs increased with water depth. The Ce content and LREE/HREE ratios in Fe-Mn crusts above 2000 m were lower than those below 2000 m. The change in REE with water depth could be explained by two processes: adsorptive scavenging by setting matters and behaviors of REE in seawater. However, the Ce abundance took no obvious correlation with water depth reflects the constant Ce flux. The Ce in crusts existed mainly as Ce(IV), implying that the oxidative-enriching process was controlled by kinetic factors.     

Enhancing low-temperature NH3-SCR performance of Fe–Mn/CeO2 catalyst by Al2O3 modification

In the work, supported catalysts of FeO_x and MnO_x co-supported on aluminum-modified CeO₂ was synthesized for low-temperature NH₃-selective catalytic reduction (NH₃-SCR) of NO. Impressively, the SCR activity of the obtained catalyst is markedly influenced by the adding amount of Al and the appropriate Ce/Al molar ratio is 1/2. The activity tests demonstrate that Fe–Mn/Ce1Al2 catalyst shows over 90% NO conversion at 75–250 °C and exhibits better SO₂ resistance compared to Fe–Mn/CeO₂. Fe–Mn/Ce1Al2 shows the expected physicochemical characters of the ideal catalyst including the larger surface and increased active reaction active sites by controlling the amount of Al doping. Also, the better catalytic activity is well correlated with the present advantaged surface adsorption oxygen species, Mn⁴⁺ species, Ce³⁺ species and the enhanced reducibility of Fe–Mn/Ce1Al2, which is superior to the Fe–Mn/CeO₂ catalyst. More importantly, we further demonstrate that the amount and strength of surface acid sites are improved by Al-doping and more active intermediates (monodentate nitrate) is generated during NH₃-SCR reaction. This work provides certain insight into the rational creation of simple and practical denitration catalyst environmental purification.     

Magnetocaloric effect and magnetic properties of La_（0.9）Ce_（0.1）（Fe_（0.99）Mn_（0.01））_（11.6）Si_（1.4）H_（1.6） compound

Magnetocaloric effect and magnetic properties of La0.9Ce0.1(Fe0.99Mn0.01)11.6Si1.4 and its hydride La0.9Ce0.1(Fe0.99Mn0.01)11.6Si1.4H1.6 were investigated. The Curie temperature of La0.9Ce0.1(Fe0.99Mn0.01)11.6Si1.4 was increased by hydrogen absorption. XRD patterns showed that the structure of La0.9Ce0.1(Fe0.99Mn0.01)11.6Si1.4H1.6 remained NaZn13-type. The Curie temperature (TC) of the sample was increased from 174 K to 331 K. The homogeneity of the hydrogen absorption for La0.9Ce0.1(Fe0.99Mn0.01)11.6Si1.4H1.6 was proven very well by the random measurement of DSC. The magnetic entropy △SM of La0.9Ce0.1(Fe0.99Mn0.01)11.6Si1.4H1.6 had peak at 326 K. The peak value of-△SM-was 12.3 and 7.8 J/(kg.K) under magnetic field change of 0-2 T and 0-1 T,respectively,which was comparable with Gd5Si2Ge2. The negative slope and inflection point of the Arrott curve indicated that the first-order magnetic transition of La0.9Ce0.1(Fe0.99Mn0.01)11.6Si1.4 was reserved after hydrogen absorption.     

A novel strategy to extract lunar mare KREEP-rich metal resources using a silicon collector

The lunar mare potassium(K)-,rare-earth elements(REEs)-and phosphorous(P)-rich(KREEP-rich) region is a unique late-stage product of magma crystallization,in which ilmenite and incompatible elements have high grades,thus forming a giant natural reservoir.The extraction and purification of the high-value metal resources in the KREEP-rich region not only meet the construction needs of the lunar base but also solve the problem of resource scarcity on Earth.In this study,photovoltaic elemental silico...     

Effects of the accumulation of the rare earth elements on soil macrofauna community

The accumulation of rare earth elements(REEs)in soil has occurred due to the pollution caused by the exploitation of rare earth resources and the wide rare earth fertilizers in agriculture.The accumulation of REEs has a toxic effect on the soil macrofauna community.12study samples were collected near a mine tailings dam with a large amount of REEs by distance gradient sample method.The total concentration of REEs was analyzed and the results were compared with that of the sample from a control site.The effects of the amount of REEs in the soil on the soil macrofauna community were also analyzed.The results showed that the accumulation of REEs in soil was significant in the study area and its concentration was strongly correlated with the distance from the pollution source.One-way ANOVA analysis indicated the significant differences in soil macrofauna communities among the different sites.The ordination obtained through the redundancy analysis demonstrated that the concentration of REEs and the total nitrogen,total potassium and pH,had affected the soil macrofauna community.A small amount of REEs in the soil can promote the diversity of soil macrofauna,but a large amount of REEs can reduce its diversity.The insect groups of Carabidae and Dermaptera were comparatively sensitive to the concentration of REEs in soil,and could be used as an indicator of soil pollution of REEs.However,the Formicidae and Stibaropus formosanus exhibited a high tolerance to REEs in soil.We believe that it is very important for the soil environment protection to strictly control the application of the rare earth fertilizers in agriculture in China.     

Magnetic Properties and Molecular Field Analysis of （ Ce, Nd） 2 （Fe, Si, Mn） 17 Compounds

The temperature-dependent magnetization of the ( Ce, Nd) 2 (Fe, Si, Mn) 17 intermetallic compounds were measured and analyzed by molecular field theory (MFr). The relationship between Tc and the intrasublattice coupling interactions was discussed. The two-sublattice MFT model can well describe the temperature dependence of the magnetization for all the compounds investigated. Ce ion in (Ce, Nd)2Fel7 compounds does not simply dilute the magnetic structure, but is likely present in a mixed-valence state. The substitution of Si for Fe strongly raises Tc and the mean Fe moment remains unchanged for Ce2(Si, Fe)17 compounds, and the 3d exchange coupling constant JFF increases linearly. Mn decreases Tc of Nd2(Mn, Fe)17 compound by reducing JFF。     

电感耦合等离子体原子发射光谱法测定钼铌合金中8种元素

采用5.0 mL氢氟酸和10.0 mL硝酸混合酸消解样品,选择Ce 407.570nm、Cu217.895nm、Fe 234.350nm、Er 390.631nm、Mg 383.829nm、Mn 257.610nm、Pb 283.305nm、Zn 213.857nm为分析线,使用电感耦合等离子体原子发射光谱法(ICP-AES)进行测定,从而建立了电感耦合等离子体原子发射光谱法测定钼铌合金中Ce、Cu、Fe、Er、Mg、Mn、Pb、Zn等8种元素的分析方法。考察了主要元素Mo、Nb和Al对待测元素的影响,结果表明,这些元素对待测元素基本无影响。各元素校准曲线的线性相关系数均大于0.999;方法中各元素检出限为5.4~63μg/g。按照实验方法测定钼铌合金样品中Ce、Cu、Fe、Er、Mg、Mn、Pb、Zn,结果的相对标准偏差(RSD,n=6)为0.89%~4.4%;回收率为98%~102%。按照实验方法测定钼铌合金样品中Cu、Fe、Er、Mg、Mn、Pb、Zn、Ce,并与电感耦合等离子体质谱法(ICPMS)的测定结果进行比对,二者基本一致。     

Coordination-reduction leaching process of ion-adsorption type rare earth ore with ascorbic acid

The magnesium sulfate(MgSO₄)-ascorbic acid(Vc) compound leaching technique can extract rare earth elements(REEs) existing in ion-exchangeable phase and colloidal phase from ion-adso rption type rare earth ore through the synergy effect of coordination and reduction,but its reaction process and mechanism remain unclear.In this paper,the coordination-reduction leaching mechanism was analyzed from the perspectives of leaching thermodynamics and kinetics,which provide theoretical guidance...     

Cerium toxicity, uptake and translocation in Arabidopsis thaliana seedlings

Arabidopsis thaliana seedlings were cultivated in 0-500μmol/L of extraneous cerium(Ce)for 7 d to investigate the toxicity,uptake and translocation of rare earth elements(REEs).The results showed that Ce could be largely absorbed by the roots of A.thaliana and translocated to the shoots.But the uptake rates of Ce by the roots were much higher than the translocation rates from roots to shoots.Ultra-structural analysis revealed that Ce was mainly distributed on the cell wall.At higher concentration,Ce could also enter cell,destroy the ultra-structure of cells and disturb the intrinsic balance of nutrient elements of A.thaliana.Addition of Ce(50-500μmol/L)to the culture medium significantly inhibited the elongation of primary roots,decreased chlorophyll content,rosette diameter and fresh mass of plants.The damage increased with the increase of Ce concentration in culture medium,although primary root elongation,chlorophyll content,and rosette diameter were stimulated by relatively low concentration(0.5μmol/L)of Ce.Thus,it is speculated that REEs may become a new type contamination if we don’t well control the release of REEs into the environment.     

Dissolved rare earth elements estimation of ion-absorption rare earth ores using reflectance spectroscopy in south Jiangxi province,China

Ion-absorption rare earth ores are an important mineral resource in China. Nowadays, the unauthorized mining has become a serious problem, resulting in severe water pollution and the wastage of rare earth elements (REEs). Being able to estimate the concentration of dissolved REEs in water bodies near mines is essential for tackling this environmental problem. Conventionally, quantitative analyses of the contents of dissolved REEs are performed using laboratory-based techniques, which can be time consuming and costly. Spectral reflectance is a rapid and cost-effective means of characterizing the chemical compositions of light-absorbing materials. In this study, reflectance spectroscopy was performed on dissolved REEs, and the correlation between their reflectance characteristics and REE content was determined. A total of 50 aqueous media samples collected in south Jiangxi Province and 25 laboratory-produced aqueous media samples were tested, and their reflectance spectra and REE contents were measured using reflectance spectroscopy and inductively coupled plasma mass spectrometry, respectively. Next, the reflectance, differential reflectance, and absorption depth were analysed based on the REE content. Six diagnostic absorption features related to REEs are recognised in the visible and near-infrared wavelength regions, along with several smaller peaks. It indicates that the results of the absorption depth analysis are in accordance with the absorption spectra characteristics of the REEs, with the R² value being higher than 0.97. The intensity of each of the six absorption bands exhibits a linear correlation to the total REE content. Therefore, linear regression models can be derived for estimating the total concentration of REEs in aqueous media samples. What's more, the detection limit for REEs is determined to be about 30 μg/L. Thus, it can be concluded that reflectance spectroscopy is a suitable technique for estimating the concentration of dissolved REEs.     

Experimental Investigation of the Ce-Mg-Mn Isothermal Section at 723 K (450 °C) via Diffusion Couples Technique

The isothermal section of the Ce-Mg-Mn phase diagram at 723 K (450 °C) was established experimentally by means of diffusion couples and key alloys. The phase relationships in the complete composition range were determined based on six solid–solid diffusion couples and twelve annealed key alloys. No ternary compounds were found in the Ce-Mg-Mn system at 723 K (450 °C). X-ray diffraction and energy-dispersive X-ray spectroscopy spot analyses were used for phase identification. EDS line-scans, across the diffusion layers, were performed to determine the binary and ternary homogeneity ranges. Mn was observed in the diffusion couples and key alloys microstructures as either a solute element in the Ce-Mg compounds or as a pure element, because it has no tendency to form intermetallic compounds with either Ce or Mg. The fast at. interdiffusion of Ce and Mg produces several binary compounds (Ce _x Mg _y ) during the diffusion process. Thus, the diffusion layers formed in the ternary diffusion couples were similar to those in the Ce-Mg binary diffusion couples, except that the ternary diffusion couples contain layers of Ce-Mg compounds that dissolve certain amount of Mn. Also, the ternary diffusion couples showed layers containing islands of pure Mn distributed in most diffusion zones. As a result, the phase boundary lines were pointing toward Mn-rich corner, which supports the tendency of Mn to be in equilibrium with all the phases in the system.     

枫香中稀土元素含量区间谱图的测绘与药性分析

应用ICP-MS测定了海南中部山区野生枫香中稀土元素的含量,讨论了其分布区间尺度,稀土元素总含量中占有最大比值的是Ce,为33.14%,其次是La\,Nd.绘制了含量区间谱图.枫香中稀土元素的含量区间位于4.5～7.0μg/g之间,波形平缓,波幅小,可推断其为辛味药性.     

Photocatalytic activity of cerium-doped mesoporous TiO2 coated Fe3O4 magnetic composite under UV and visible light

A novel kind of magnetically separable photocatalyst of cerrium-doped mesoporous titanium dioxide coated magnetite (Ce/MTiO2/ Fe3O4) was prepared and its activities under UV and visible light were reported. The catalysts with Ce/MTiO2 shell and Fe3O4 core were pre-pared by coating photoactive Ce/MTiO2 onto a magnetic Fe3O4 core through the hydrolysis of tetrabutyltitanate (Ti(OBu)4, TBT) with pre-cursors of ammonium ceric nitrate and TBT in the presence of Fe3O4 particles. The MTiO2 shell was for photocatalysis, the Fe3O4 core was for separation by the magnetic field and the doped Ce was used to enhance the photocatalytic activity of MTiO2. The morphological, struc-tural and optical properties of the prepared samples were characterized by Brunauer-Emmett-Teller (BET) surface area, transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-vis absorption spectroscopy. The effect of cerrium-doped content on the photocatalytic activity was studied and the result revealed that 0.5 mol.% Ce/MTiO2/Fe3O4 exhibited highest photoactivity. The photocatalytic activities of obtained photocatalysts under UV and visible light were estimated by measuring the degradation rate of methylene blue (MB, 50 mg/L) in an aqueous solution. The results showed that the prepared photocatalyst was activated by visible light and used as effective catalyst in photooxi-dation reactions. In addition, the possibility of cyclic usage of the prepared photocatalyst was also confirmed. Moreover, Ce/MTiO2 was tightly bound to Fe3O4 and could be easily recovered from the medium by an external magnetic filed. So, the photocatalyst can be reused without any mass loss. It can therefore be potentially applied for the treatment of water contaminated by organic pollutants.     

Ce–Ti catalysts modified with copper and vanadium to effectively remove slip NH3 and NOx from coal-fired plants

In this work, V/Ce–Ti catalysts were modified with different kinds of transition metals (Cu, Fe, Co, Mn) by sol–gel and impregnation methods. The NH₃ oxidation performance of them was tested to select the most active catalyst in NH₃-selective catalytic oxidation (NH₃–SCO). The effect of NO, SO₂ and H₂O was also investigated. The experimental results indicate that 1% Cu–V/Ce–Ti catalyst exhibits the most significant ability to remove slip ammonia discharged from coal-fired plants and its NH₃ conversion efficiency reaches 90% at 300 °C. In addition, 97% NO_x can be removed when NO is introduced in the gas. Cu–V/Ce–Ti catalyst also obtains good resistance to H₂O and SO₂. Based on the characterization experiment, the introduced Cu and V are highly dispersed on Ce–Ti catalyst and they can increase the redox properties and the number of acidic sites. Besides, the redox cycles among Cu, V and Ce species on Cu–V/Ce–Ti catalyst surface are conducive to generating more active oxygen and promoting the oxidation capacity of the catalyst.     

Geochemical Characteristics of Rare Earth Elements in Different Types of Soils in China

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