Adsorption and Desorption of Exogenous Rare Earth Elements in Soils:Ⅰ. Rate and Forms of Rare Earth Elements Sorbed

Adsorption and desorption of exogenous rare earth elements (REE) in soils were studied.Results showed that soils had strong adsorbability for REE and the rate of adsorption of REE was over 95% of the added REE in these tests.The characteristics of adsorption isotherms corresponded well with the both Freundlich and Temkin equations,but deviated from the Langmuir equation.The adsorption of REE tended to increase with the rising of soil pH.A sequential extraction method used for studing the desorption and distribution of REE sorbed in soils are also discussed.

The Characteristics of Adsorption and Desorption of Rare Earth Elements by the Main Types of Soils of China

The adsorption-desorption behavior of the mixed rare earth elements(RE)on the main types of soils of China,kaolinite and synthetic oxides was studied.The isothermal adsorption of RE was fitted to Langmuir.Freundlich and Temkin equations.The main factors determining the RE adsorption capacity of the soils are the type of clay mineral and the content of amorphous iron oxide in the soils.The above two fac- tors and the pH of soil determine the RE adsorption ability of the soils.The soil and synthetic iron,manga- nese oxides strongly adsorb RE specifically.

Effect of Anion on Adsorption of Rare Earth Elements on Kaolinite

For a better understanding the adsorption of rare earth elements(REEs) on minerals and its controlling factors, adsorption experiments were performed with kaolin in a matrix of various concentration of anion (Cl-, ClO4-, SO42-) in the pH 6.5. The adsorption of REEs onto the kaolin increase with increasing anion concentration, especially in the presence of SO42-, which is ascribe to the Na+ mass effect and anion complexation. furthermore, the heavy REEs are more adsorbed onto kaolin in presence of higher concentration of anion, especially for Cl-and SO42-, presumably due to the difference of anion complexation with light REE and heavy REEs.

The selective adsorption of rare earth elements by modified coal fly ash based SBA-15

Rare earth elements(REE)are strategic resources and the recycling of REE in alternative resources is urgent and gets increasingly attention.However,the separation of REE in these alternative resources is still a challenge due to the low concentration of REE and multi coexisted ions in acidic system.In this study,the species distribution of REE within the pH 0-8.0 was calculated.The SBA-15 originated from coal fly ash was modified by two steps with(3-aminopropyl)triethoxysilane(APTES)and diethylenetriaminepentaacetic dianhydride(DTPADA)to obtain DTPADA-SBA-15 adsorbent,which was applied to the selective adsorption of REE.The results showed that DTPADA-SBA-15 possessed excellent adsorption performance on the selective adsorption of REE,including Eu,Gd,Tb,Nd and Sm,in acidic solution(pH 2)with multi competing ions.The FT-IR and Zeta potential characterization verified that the chemical adsorption through the coordination of O in DTPADA-SBA-15 with REE was dominant at lower pH value.The study of adsorption kinetics indicated that the adsorption of rare earth metal ions followed pseudosecond-order kinetic,of which the adsorption process followed the Langmuir isotherm model.

Experimental Study on Adsorption of Rare Earth Elements on Kaolinite and Halloysite

1 Introduction The weathered crust rare earth deposits is one of the most significant rare earth deposits,which are mostly distributed in southern China,especially in the south of Jiangxi province(Chi et al.,2007).The compositions of these deposits,which are weathered from igneous rocks such as granite through biological,physical or chemical

STUDY OF ADSORPTION OF RARE EARTH ELEMENTSBY FERRIC OXIDE GEL

A new secondary ore of rare earth was discovered in the Southwest of China. It is a kind of product of the weathered mineral. The rare earth elements (REE) in it exist probably as ionic characteristic adsorption state in manganesian and ferric oxide colloid mineral, and one bearer of REE is amorphous ferric oxide gel. It is neessary to study the binding state of rare earth elements on manganesian and ferric oxide in order to utilize comprehensively the rare earth resources and avoid latent influence on the environment resulting from the fact that highcontent rare earth elements are carried into soil by the mineral efflorescence. A simulating adsorption test of rare earth ions in weak acid media is carried out with ferric oxide gel prepared by sol-gel method. The experimental results show that the characteristics of adsorption isotherm correspond well with the Flory-Huggins equation, but deviated from the Langmuir equation. The standard molar adsorption Gibbs function, standard molar adsorption entropy and standard molar adsorption enthaply are calculated. The measurements of the point of zero charge and isoelectric point show occurrence of the characteristic adsorption. It has been proved that the OH group on the skeleton of ferric oxide gel is the innate cause of the characteristic adsorption.

Adsorption experiment of water-soluble rare earth elements in atmospheric depositions and implications for source tracing in South China

The distribution patterns of rare earth elements(REEs)in fine-grained materials in various depositions were often found to be similar to those of the aeolian sediments deposited in the Loess Plateau in North China and the fine-grained materials were suggested to be derived from wind-blown dust.However,increasing evidence indicated that the REEs in the water-soluble portion of atmospheric depositions also displayed similar patterns to those of aeolian sediments.In this study,water-soluble REEs in three atmospheric depositions collected from different climatic zones in China were adsorbed with two adsorbents with distinct adsorption capacity,glass powder,and co-precipitated iron hydroxide.The results showed that the REEs adsorbed by the two adsorbents displayed patterns similar to those of the original atmospheric depositions.The typical characteristics of the REE patterns of atmospheric deposition can be well reproduced in the adsorbed REEs.The higher the REE concentrations in the atmospheric depositions,or the higher adsorption efficiency of the adsorbents,the better reproducibility of the REEs patterns.The results suggest that the REEs of the fine-grained materials in various sediments,which have a high adsorption capacity,especially those deposited in South China,may come from the water-soluble REEs in atmospheric deposition,and may not be appropriate tracers of wind-blown dust from North China.

Geochemical Characteristics of Rare Earth Elements in Guposhan Granite Complex and Their Petrogenetic Implication

In this paper the geochemical characteristics of rare earth elements in Guposhan granite complex in Nanling Area,South China,is systematically studied,and the balance of REE distribution in rock-forming minerals, which contain only 21.47～29.71 wt% of total REE in granites,is calculated.The petrogenetic relationship be- tween three different stages of the granites in the complex is discussed,and a geochemical model is suggested for the formation of granitic magma in early stage by partial melting of the crustal basement rocks containing more REE than that in the late stage.It shows that a ion-adsorption type of REE deposit could ocuur in the weath- ering crust on the early stage granite.Rb-Sr isotope isochron dating of the first stage medium-coarse-grained K-feldspar granite shows that its age is 146.5 Ma and initial ^(87)Sr/^(86)Sr ratio is 0.71198.

Simultaneous removal of critical rare earth elements and chalcogen oxyanions by anaerobic granular sludge

Conventional mining of economically and strategically important critical rare earth elements(REEs)(such as neodymium,lanthanum and dysprosium),and chalcogens(such as selenium and tellurium)are associated with a huge economic and environmental cost.Therefore,the need to recover REEs as well as chalcogens from different waste streams including wastewaters is becoming urgent.Batch assays on synthetic chalcogen/REE-laden wastewater showed that the presence of REEs significantly improved the tellurite removal rate(>80%)and enhanced selenate removal by 66%±10%.Three 3.9 L continuous upflow anaerobic granular sludge bed(UASB)reactors were operated at a hydraulic retention time of 24 h and 30℃.Selenate reduction was achieved with a removal efficiency of~98% with an influent p H of 4.0 for more than 28 days.The effect of REEs on tellurite removal in the UASB bioreactor could not be clearly established since a soluble tellurium removal efficiency of more than 98%was observed already before the addition of REEs at elevated tellurite concentrations.The complete REE removal in both batch assays and UASB reactors at higher pH(7.0±0.5)was attributed to precipitation,whereas chalcogen oxyanions removal was due to microbial reduction.However,at acidic p H,biosorption was responsible for REE's removal,and the Se-enriched sludge exhibited a superior REE's removal efficiency than the non-enriched and Te-enriched sludge.

Behavior and mechanism of graphene oxide-tris(4-aminophenyl)amine composites in adsorption of rare earth elements

Three-dimensional(3D)graphene oxide-tris(4-aminophenyl)amine(GO-TAPAx:y)composites with different GO-to-TAPA mass ratios(x:y)were prepared by a facile one-step ultrasonic treatment.GOTAPAx:y composites were characterized by scanning electron microscopy(SEM),nitrogen(N2)adsorption-desorption isotherms,Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and thermogravimetric analysis(TGA).Behavior and mechanism of GO-TAPAx:yco mposites for the adsorption of rare earth elements(REEs)were investigated.The adso rption capacities of GO-TAPA1;2 composite for Yb^3+,Er^3+,Nd^3+,La^3+and Y^3+are 30.88,26.52,20.60,11.24 and 10.52 mg/g,respectively.Effects of some important parameters including GO-to-TAPA mass ratios,contact time,reaction temperature and initial Yb^3+concentration on the adsorption were evaluated in detail.FTIR spectral and XPS analyses show that the metal complexations and ion exchanges between nitrogen/oxygen-containing species of the adsorbents and REEs are involved in the adsorption procedure besides the conventional adsorption based on specific surface area,indicating the introduction of specific molecules onto GO is beneficial to its adsorption ability.The convenient reusability and applicability of GO-TAPAx:y composites toward real samples also demonstrate their feasibility in the enrichment of REE ions.

Adsorption of rare earth elements on organic matter in coal

The occurrence modes of rare earth elements(lanthanide and yttrium,abbreviated as REY) in coal are impo rtant both for coal geochemistry studies and the application potential of REY as a by-product of coalbased resources.In this study,the adsorption behaviors of REY on organic matter in coal were investigated by leaching tests using REY solution and ultra-low ash coal samples.On this basis,the adsorption mechanism of REY on organic matter in coal was also studied by molecular simulation calculations.The leaching tests show that the organic matter in coal has a relatively strong adsorption capacity for REY,and that the average adsorption rate or the net adsorption amount of heavy rare earth elements(HREY:Gd,Tb,Y,Dy,Ho,Er,Tm,Yb and Lu) is always higher than that of the light rare earth elements(LREY:La,Ce,Pr,Nd,Sm and Eu).A molecular model of humic acid(HA) was constructed and the adsorption amount between REY and HA was calculated.The results show that the theoretical adsorption rate of HREY(84.88%) is higher than that of the LREY(84.00%).The analysis of the adsorption distances between REY atoms and various functional groups on HA molecules shows that the minimum adsorption distance of LREY is 0.372 nm on average,which is larger than that of HREY(0.368 nm),indicating that the adsorption capacity of the latter is stronger.In addition,a coal molecule(C_(18)H_(22)O) was also constructed to investigate the adsorption characteristics of various REY atoms on the molecule.As a result,it is found that the average binding ene rgy and bond length between the hydroxyl functional group and LREY atoms are 0.12469 Ha(Hartree,the unit of energy in the atomic unit system) and 0.1407 nm,respectively,while for HREY,0.12883 Ha and 0.1121 nm,respectively.This confirms that HREY is more stable than LREY in binding on organic matter in coal.To conclude,both leaching tests and molecular simulation calculations reveal that REY has a strong adsorption affinity for organic matter in coal,and in particular,HREY shows a stronger organic adsorption preference in coal than LREY,which is probably due to stronger chemical bonding between the former and the functional groups on the coal molecule.

Specific Adsorption and Its Mechanisms of Rare Earth Elements by Soils and Oxides

There have been many studies on the adsorption-desorption behavior of heavy metals such as Cu, Zn, Co, Ni, Cd and Pb by soils in China and abroad, and their adsorption mechanisms have also been sought. The above research has demonstrated that the synthetic or soil oxides like Fe, Mn and Al oxides adsorb heavy metals specifically and their specific adsorption is greatly affected by the ambient pH. The proposed mechanisms for explaining the above phenomena are as follows: ion hydrolysis-adsorption, outer or in-

Determination of rare earth elements in geological samples by adsorption and separation with P507 foam loaded plastic-neutron activation analysis

研究了P507负载泡塑萃取柱吸附、分离和富集稀土元素的条件,确定了地学样品中微量稀土元素的化学前处理方法和中子活化测量条件。方法的RSD在3.4%~10%之间,回收率大于92%。用国家标准物质进行分析验证,测定结果与推荐值相符。

Distributions of dissolved rare earth elements during estuarine mixing at the Changjiang River mouth

The first data on the concentrations of dissolved REE in surface waters collected from the north passage of the Changjiang Estuary where the salinity ranges from 0.15 to 19 mg/g were determined by ICP-MS after preconcentration with solvent extraction and back-extraction techniques. Relative to other estuaries, the river-water end-member concentrations of dissolved REE are very low, ranging from 11.963 (Y) to 0.098 ng/kg (Lu). Dissolved REE removed markedly from water in the Changjiang Estuary where salinity lies within the range of 0.15-1 mg/g, but the percent removal is low, ranging only from 47%(La) to 25%(Lu). Strong water-sediment interaction due to shallow water depth in the Changjiang Estuary leads to remarkable concentration peaks of dissolved REE in the location where the salinity varies from 1 to 8 mg/g. In the moderate and high salinity regions from 8 to 19 mg/g, the concentrations of dissolved REE gradually increase as a result of desorption or partial dissolution of particles.

Oxygen adsorption/desorption behavior of YBaCo4O7+δ and its application to oxygen removal from nitrogen

A new medium-temperature (200-400 °C) adsorbent material for oxygen removal and air separation, YBaCo4O7+δ, was prepared by the solid-state reaction method. This new adsorbent could adsorb a large quantity of oxygen in the temperature range of 200-370 °C. Adsorbed oxygen could be released by raising temperature over 400 °C or by switching the atmosphere from oxygen to nitrogen. This oxygen adsorption and desorption process had good reproducibility. Taking advantage of this unique oxygen intake/release behavior, a nitrogen purification process was investigated. The results showed that YBaCo4O7+δ material was a promising candidate for the oxygen sorption process and could be used to produce high-purity nitrogen or to remove trace oxygen from other gases.

Thermogravimetric Study on Oxygen Adsorption/Desorption Properties of Double Perovskite Structure Oxides REBaCo_2O_(5+δ)(RE= Pr,Gd,Y)

The oxygen adsorption/desorption properties of double perovskite structure oxides PrBaCo2O5＋δ,GdBaCo2O5＋δ,and YBaCo2O5＋δ were investigated by the thermogravimetry（TG）method in the temperature range of 400~900 ℃.The calculated oxygen adsorption/desorption surface reaction rate constants ka and kd of these double perovskite structure oxides were larger than the commonly used cubic perovskite oxides,such as Ba0.95Ca0.05Co0.8Fe0.2O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ,whereas,the oxygen permeation flux was comparable to that of the latter,which was attributed to the smaller difference of oxygen vacancy in oxygen and nitrogen atmosphere（Δδ/Vmol）in these double perovskite structure oxides.The large oxygen adsorption/desorption rate constants of GdBaCo2O5＋δ and PrBaCo2O5＋δ made them nice catalyst coating materials,on other membrane surfaces,to improve the oxygen permeability.

Specific Adsorption of Trivalent La, Ce and Y by Soils and Ferro-manganese Oxides and Its Mechanism

In this paper, the adsorption-desorption variations of trivalent La, Ce, Y and mixed rare earths are discussed. The curves of pH-rare earth element adsorption were very well fitted to the equation: InD =a+b pH. The selectivity of RE (rare earth element) ions by the samples decreased in the following order: Ce> RE> La> Y, but the sequences were: La> Ce> Y on kaolinite and Y> La on amorphous iron oxide. Since the trivalent RE ions existed in the form of RE(OH)2+ in the solutions from pH < 5.45 to 7.0, the ratio of H+ displaced to RE3+ adsorbed in micromole was proposed to be about 2. The specific adsorption mechanism for RE was proposed to be that the RE ions complexed with oxide surface and the ion-surface complex of Ce3+ promoted oxidization on Mn hydroxide.

Microstructure and Gd-rich phase evolution of as-cast AZ31-xGd magnesium alloys during semi-solid isothermal heat treatment

The microstructure and Gd-rich phase evolution of as-cast AZ31-xGd(x=0,1.5 wt.%,2.0 wt.%and 2.5 wt.%)magnesium alloys during semi-solid isothermal heat treatment were investigated deeply in the present work.Results showed that the lamellar(Mg,Al)3Gd phases transformed into the particle-like Al2Gd phases in AZ31 magnesium alloys with Gd addition during semi-solid isothermal heat treatment,leading to yielding more sphericalα-Mg grains.When Gd content is 2.0 wt.%,the size of semi-solid spherical grains reaches the minimum.The main mechanism of grain refinement lies in the remelting of dendritic branches as well as the auxiliary effect of a small number of Al2Gd particles as grain refining inoculants.Meanwhile,Al2Gd particles enriched at the solid-liquid interfaces can remarkably retard the growth rate ofα-Mg grains.A reduction of deformation resistance has been successfully achieved in AZ31-2.0Gd magnesium alloy after semi-solid isothermal heat treatment,which shows a moderate compressive deformation resistance(230 MPa),comparing to the as-cast AZ31 magnesium alloy(280 MPa)and semi-solid AZ31 magnesium alloy(209 MPa).

Evolution and distribution of Al_2Sm phase in as-extruded AZ61-xSm magnesium alloys during semi-solid isothermal heat-treatment

The evolution and distribution of Al2Sm phase in as-extruded AZ61-xSm（x=0, 1.5, 2.0 and 2.5, mass fraction, %） magnesium alloys during semi-solid isothermal heat treatment were investigated. The results showed that when as-extruded AZ61 magnesium alloys were modified with Sm, the smaller and rounder grains were obtained during semi-solid isothermal heat treatment. When the Sm content is 2.0%（mass fraction）, the average size of the globular grains reached the smallest value of 90 μm. Although a few Al2Sm particles existed in the α-Mg grains, most of Al2Sm particles solidified at the edge of the globular grains with the width of 20 μm. These phenomena are mainly attributed to the forces acting on Al2Sm particles in front of the solid-liquid interface, leading to Al2Sm particles accumulating at the solid-liquid interface and then solidifying at the edge of the globular grains in the quenching process.

Insight into leaching of rare earth and aluminum from ion adsorption type rare earth ore:Adsorption and desorption

Clay minerals are inferred to be the primary host materials for ion-exchangeable rare earth in ion adsorption type rare earth ore(IAREO).During the rare earth leaching process,the adsorption and desorption reactions of the cations controlling the leaching process continue to occur at the clay minerals-leaching agent solution interface.In order to understand the leaching mechanism and behavior of rare earth and co-leached aluminum,adsorption,competitive adsorption,and desorption experiments were carried out using kaolin as a typical clay mineral.The powerful electrostatic attraction and concentration driving forces facilitate the adsorption of cations.The adsorption ability and competitive adsorption ability of cations depend on their charge,hydration radius,and hydrolysis properties,and decrease in the order of La^(3+),Y^(3+),Al^(3+),Mg^(2+),and NH_(4)^(+).The desorption of rare earth and aluminum is positively affected by the concentration-driving force exerted by high concentrations of Mg^(2+) and NH_(4)^(+),with the order of the desorption ability being opposite to the adsorption ability.However,unspecified interactions between clay mineral particles enhanced by high-concentration desorbents,especially by Mg^(2+) than NH_(4)^(+),will adversely affect desorption reactions,which result in lower desorption efficiencies of rare earth and aluminum obtained with magnesium sulfate compared to those obtained with ammonium sulfate at high concentrations.Solid-phase Al(OH)_(3) generated at a high peak aluminum concentration leads to a considerably delayed aluminum efflux,thereby partially separating the rare earth from aluminum during the actual column leaching process.To advance the mining technology of IAREO by selectively improving the rare earth leaching efficiency with minimal leaching agent consumption,higher charged cations with concentrations limited to suitable levels should be preferred as leaching agents.