Mixed Rare Earth Research Articles

Environmentally benign rare earth pigments: effect of calcium dopant and tuning of bandgaps for different color hues

PurposeAs there is a strong inducement to develop new colored inorganic materials to substitute the current industrial pigments that are based on toxic metals hazardous to health and the environment, the purpose of this paper is to invent environmentally benign rare earth-based colorants as viable alternatives to the traditional toxic pigment formulations. Herein, the authors developed a series of rare earth pigments having the general formula Ca0.1 Ln0.9 PO4 ( Ln = Y , Pr , mixed rare earth oxides, RE and Di). After studying all the optical properties, the authors have gone for some coloring application in plastic like PMMA.Design/methodology/approachThe designed pigments were synthesized by traditional solid-state method. Stoichiometric amounts of each reagent were mixed in an agate mortar and the mixtures were calcined at optimized temperature 1000 °C for 4 h in electric furnace followed by auto–cooling. The samples were characterized by X-ray diffraction diffraction, UV–vis spectroscopy, scanning electron microscope (SEM), particle size distribution, color coordinates determination, acid/alkali test, thermo gravimetric (TG) analysis and CIE–1976 L*a*b* color scales. Among the various lanthanide ions and calcium ion as dopant, the pigment composition shows various hues ranges from green to yellow. The designed pigments consist of non–toxic elements and were further found to possess high thermal and chemical stability. The pigments were also found to be appropriate candidates for the coloration of polymer substrates like PMMA.FindingsThe present investigations establish that various color hues can be achieved by the incorporation of suitable chromophore metal ions like calcium in various rare earth host lattice by tuning of the band gaps. The coloring mechanism is based on the strong absorption of the pigments in the blue and red regions due to electronic transitions of the micro states of rare earth ion. The pigment composition shows various hues ranges from green to yellow. The coloring mechanism is based on the tuning of band gap by the dopant like calcium in various rare earth host lattice. In addition, this pigment was chemically and thermally stable. Finally, it has applied in plastics like PMMA.Research limitations/implicationsMechanism of the color appearance using band calculations and on possible applications of rare earth phosphate powders as pigments in plastics and paints have not been explored much. However, the properties of the Ca-doped rare earth phosphate implies that this material has a potential to be applied as a satisfactory pigment for coating or coloring except for glaze, which may cause a side reaction at high temperatures, especially taking into consideration the economics and ecologies. The possibility of Ca2+ incorporation in CePO4 with monazite structure-type has been established.Practical implicationsThe designed pigments consist of non-toxic elements and were further found to possess high thermal and chemical stability. The pigments were also found to be appropriate candidates for the coloration of polymer substrates. Thus, the present environmental friendly pigment powders may find potential alternative to the classical toxic inorganic pigments for various applications.Social implicationsThere is a strong incentive to design new colorants based on inorganic materials to substitute for industrial pigments that are based on heavy elements hazardous to health and the environment. However, several industrial yellow pigments such as cadmium yellow (CdS), chrome yellow (PbCrO4) and nickel titanium yellow (TiO2-NiO-Sb2O3) contain the harmful elements (e.g. Cd, Pb, Cr and Sb) for the human body as well as the environment. The designed pigments consist of non-toxic elements and were further found to possess high thermal and chemical stability. The pigments were also found to be appropriate candidates for the coloration of polymer substrates. Thus, the present environmental friendly pigment powders may find potential alternative to the classical toxic inorganic pigments for various applications.Originality/valueThere is a strong incentive to design new colorants based on inorganic materials to substitute for industrial pigments that are based on heavy elements hazardous to health and the environment. However, several industrial yellow pigments such as cadmium yellow (CdS), chrome yellow (PbCrO4) and nickel titanium yellow (TiO2-NiO-Sb2O3) contain the harmful elements (e.g. Cd, Pb, Cr and Sb) for the human body as well as the environment. So, the authors have developed new class of inorganic pigments that are both non-toxic and environmentally unimpeachable, while preserving or even exceeding the optical, thermal and chemical characteristics of the existing commercial pigments. The developed colorants find practical applications in polymer matrix like PMMA.

Decomposition Process of Nonoxidative Microwave Radiation Roasting of a Mixed Rare Earth Concentrate with Sodium Carbonate.

This article introduces an efficient decomposition process that uses sodium carbonate (Na2CO3) and activated carbon (C) as additives to decompose Bayan Obo mixed rare earth concentrate (hereinafter to be referred to as RE concentrate) by nonoxidative microwave radiation roasting. The roasting temperature, holding time, and contents of Na2CO3 and activated carbon are investigated. The optimum process parameters for decomposition are 800 °C and 30 min. The ratio of m(Na2CO3)/m(RE concentrate) is 0.5, and the ratio of m(C)/m (ER concentrate and Na2CO3) is 0.2 based on experimental data. Under the above conditions, the decomposition rate (shortened to DR) of RE concentrate is 98.58%, and the removal rates (shortened to CRs) of fluorine (F) and phosphorus (P) reached 80.35 and 46.75%, respectively. These rates are higher than traditional oxidation roasting under the same conditions. The three reasons for the result are the unique microwave heating characteristics, the overall efficient reaction of the mixture (RE concentrate, Na2CO3, and activated carbon), and the high nonoxidation rate of cerium. For these reasons and large experimental data, the reaction rate of the mixture is improved, and the efficiency of dilute hydrochloric acid for leaching rare earth elements is enhanced. In this article, the valence of rare earth elements in the roasted ore is all in the form of trivalence. Importantly, this nonoxidative roasted product can avoid the generation of chlorine in hydrochloric acid leaching. Moreover, such a short holding time is scarce in traditional roasting. When the mixture was roasted by utilizing microwave heating, the sinter phenomenon of the roasted product was avoided at high-temperature roasting. Finally, the surface morphology of RE concentrate at different conditions was observed by scanning electron microscopy (SEM) analysis, which can be used to compare the specific differences of roasting methods. According to these results, this process is beneficial for the decomposition of RE concentrate in terms of Na2CO3 roasting and is helpful for improving the clean and green technology method of hydrometallurgy.

In-situ measurement of mineral phase transition and kinetics in roasting process of Bayan Obo mixed rare earth concentrate by sodium carbonate

In this study, the Bayan Obo rare earth concentrates mixed with Na2CO3 were used for roasting research. The phase change process of each firing stage was analyzed. The kinetic mechanism model of the continuous heating process was calculated. This study aims to recover valuable elements and optimize the production process to provide a certain theoretical basis. Using X-ray diffraction (XRD), Fourier infrared spectroscopy, scanning electron microscopy with energy dispersive spectrometry, the reaction process and the existence of mineral phases were analyzed. The variable temperature XRD and thermogravimetric method were used to calculate the roasting kinetics. The phase transition results show that carbonate-like substances first decompose into fine mineral particles, and CaO, MgO, and SiO2 react to form silicates, causing hardening. Further, REPO4 and NaF can directly generate CeF3 and CeF4 at high temperatures, and a part of CeF4 and NaF forms a solid solution substance Na3CeF7. Rare earth oxides calcined at a high temperature of 750 °C were separated to produce Ce0.6Nd0.4O1.8, Ce4O7, and LaPrO3+x. Then, BaSO4, Na2CO3, and Fe2O3 react to form barium ferrite BaFe12O19; the kinetic calculation results show that during the continuous heating process, the apparent activation energy E reaches the minimum in the entire reaction stage in the temperature range of 440–524 °C, and the reaction order n reaches the maximum, which indicates that the decomposition product REFO significantly impacts the reaction system and reduces the activation energy. The mechanism function is F(α) = [−ln (1−α)]1/3. The reaction order n reaches the minimum in the temperature range of 680–757 °C, and the apparent activation energy E is large. The difficulty of the reaction increases during the final stage. The reaction mechanism function is F(α) = [1−(1−α)1/3]2. Observing the entire reaction stage, the step of controlling the reaction rate changes from random nucleation to three-dimensional diffusion (spherical symmetry).

A novel, clean, closed-loop process for directional recovery of rare earth elements, fluorine, and phosphorus from mixed rare earth concentrate

The recycling of Bayan Obo rare earth has attracted widespread attention due to its potential environmental risks and the importance of key metal supplies. As a traditional technology, concentrated sulfuric acid roasting has led to the continuous deterioration of the local environment because of severe fluoride and sulfur dioxide emissions. Although it is difficult to achieve efficient recovery of rare-earth elements and their associated resources with this process, it is possible to eliminate pollutant emissions, and achieve a high recovery ratio of rare-earth elements using this technique. Fluorine and phosphorus from wastewater have been well controlled. Here, a novel, clean, closed-loop process is introduced to treat rare earth concentrates, which not only does not pollute the environment, but also generate more economic values. Through the oxidative roasting-hydrochloric acid leaching step, more than 98% of fluorine and phosphorus can be stably retained in the leaching residue. The leaching residue is then converted into rare earth hydroxides, sodium fluoride, and sodium phosphate in the sodium hydroxide sub-molten salt system. Moreover, most of the concentrated lye can be reused in the sub-molten salt decomposition step by filtration. The washed filter residue is then dissolved in the hydrochloric acid leachate to produce a rare earth chloride solution. Sodium fluoride and sodium phosphate can be recovered in the washing solution. In summary, this process can realize the internal circulation of concentrated lye and water while producing a rare earth chloride solution, sodium fluoride, and sodium phosphate. Finally, the rare earth concentration in the rare earth chloride solution reached 280 g L−1, 96.40% of fluorine was converted to sodium fluoride, and 99.82% of phosphorus was converted to sodium phosphate from the washing liquid. An environmentally-friendly, easy-to-implement strategy is proposed: the entire recycling process is highly selective, closed-loop and simplified, and can be used as an alternative method to recover different resources from the current Bayan Obo concentrate.

New Insights into Ion Adsorption Type Rare-Earths Mining—Bacterial Adsorption of Yttrium Integrated with Ammonia Nitrogen Removal by a Fungus

Ion adsorption-type heavy rare earths found in southern China are important ore resources, whose yttrium(Y)-group rare-earth elements account for 90% of the total mass of rare earths known on the planet. At present, ammonia-nitrogen wastewater from extraction of rare earths pose threats to the environment. A bacterial strain (Bacillus sp. ZD 1) isolated from the “Foot Cave” mining area was used for adsorption of Y3+. Its adsorption capacity reached 428 μmol/g when the initial concentration of Y3+ was 1.13 mM. Moreover, 50 mg of Bacillus sp. ZD 1 (converted to dry mass) could completely adsorb Y3+ in the mother solution of mixed rare earths from the rare-earth mining area. Ammonia nitrogen in the remaining solution after adsorption was removed through denitrification using a fungus named Galactomyces sp. ZD 27. The final concentration of ammonia nitrogen in wastewater was lower than Indirect Emission Standard of Pollutants for Rare-earth Industry (GB 26451-2011). Furthermore, the resulting fungal cells of Galactomyces sp. ZD 27 could be used to produce single cell proteins, whose content accounted for 70.75% of the dry mass of cells. This study offers a new idea for integrated environmentally-friendly extraction and ecological restoration of the mining area in southern China.

High-Velocity Impacts of Pyrophoric Alloy Fragments on Thin Armour Steel Plates.

The terminal ballistics effects of Intermetallic Reactive Materials (IRM) fragments have been the object of intense research in recent years. IRM fragments flying at velocities up to 2000 m/s represent a realistic threat in modern warfare scenarios as these materials are substituting conventional solutions in defense applications. The IRM add Impact Induced Energy Release (IIER) to the mechanical interaction with a target. Therefore, the necessity of investigations on IIER to quantify potential threats to existing protection systems. In this study, Mixed Rare Earths (MRE) fragments were used due to the mechanical and pyrophoric affinity with IRM, the commercial availability and cost-effectiveness. High-Velocity Impacts (HVI) of MRE were performed at velocities ranging from 800 to 1600 m/s and recorded using a high-speed camera. 70 MREs cylindrical fragments and 24 steel fragments were shot on armour steel plates with thicknesses ranging from 2 mm to 3 mm. The influence of the impact pitch angle (α) on HVI outcomes was assessed, defining a threshold value at α of 20°. The influence of the failure modes of MRE and steel fragments on the critical impact velocities (CIV) and critical kinetic energy () was evaluated. An energy-based model was developed and fitted with sufficient accuracy the Normalised () determined from the experiments. IIER was observed in all the experiments involving MRE. From the analyses, it was observed that the IIER spreads behind the targets with velocities comparable to the residual velocities of plugs and shattered fragment.

Effect of La-Ce on Microstructure and Properties of 30MnCrNiMo Alloy Steel

The 30MnCrNiMo alloy steel was modified by La-Ce mixed rare earth. The experiment used metallographic microscope, scanning electron microscope and energy spectrum to analyze the improvement behavior of rare earth on the as-cast structure of the alloy steel, the structure after heat treatment, and the morphology of inclusions; a thermal dilatometer was used to analyze the phase transition point, and a reasonable heat treatment process was developed; the effect of rare earth on the mechanical properties of alloy steel at room temperature, low temperature impact and tensile was analyzed. The results show that the 30MnCrNiMo alloy steel modified by rare earth has better refinement of the as-cast grains and the grains after heat treatment, and the size, morphology and distribution of inclusions have been improved. The addition of rare earths improves the impact toughness, especially the low-temperature impact. Compared with alloy steel without rare earth, the toughness can be increased by up to 38%, and the alloy strength has been improved to a certain extent.

Behavior of phase transformation of Baotou mixed rare earth concentrate during oxidation roasting

Based on the new process named “Combination Method” for metallurgy and separation of Baotou mixed rare earth concentrate (BMREC), the aim of this paper is to clearly elucidate the phase change behavior of BMREC without additives during oxidative roasting at 450–800 °C. The results indicate that the bastnaesite in BMREC is decomposed at 450–550 °C, the weight loss is about 10.3 wt%, and the activation energy (E) is 144 kJ/mol. The bastnaesite in BMREC is decomposed into rare earth fluoride, rare earth oxides (La2O3, Ce7O12, Pr6O11 and Nd2O3), and CO2, particularly, with the increase of roasting temperature, bastnaesite in BMREC is more completely decomposed into LaF3, which causes a decrease in leaching rate of La during the HCl leaching process. Additionally, the maximum cerium oxidation efficiency reaches about 60 wt% when the roasting temperature is equal to or above 500 °C, and the oxidation reaction rate of cerium increases with the increasing roasting temperature.

Deposition of REBCO with different rare earth elements on CeO2 buffered technical substrates by fluorine-free metal organic decomposition route

Pristine REBa2Cu3O7−δ (REBCO, RE with Yb, Y, Dy, Gd, Eu and Sm) superconducting films are deposited on CeO2 buffered technical substrates by fluorine-free metal organic decomposition (FF-MOD) method. The structure and superconductivity are comprehensively characterized and studied. Under the optimal conditions, all the films form good crystallinity and strong biaxial texture examined by XRD. A smooth and dense morphology is observed in the YBCO, GdBCO, EuBCO and SmBCO films. For all the films, Tconset values are lower than that in the corresponding bulk materials, implying a certain degree of microstructure defects (e.g., RE-Ba substitution, and/or oxygen vacancies). Among all the compositions, the GdBCO film shows a high Tconset value (>90 K), while the high Jc values are achieved at 77 K in broad field regime, also being with the largest maximum pinning force of 2.3 GN m−3. On the other hand, a high Jc value (at 77 K self-field) is obtained in the YBCO film, however, the rapid Jc decay with increase of the magnetic fields is found. These results reveal that defects in the YBCO film could only serve as weak pinning centers at least at 77 K. According to Dew-Hughes fitting models, we found that the primary pinning mechanism in all the REBCO films attributes to typical 2D non-superconducting phase i.e., Normal surface pinning. This work for the first time systemically demonstrates feasibility of deposition REBCO with various rare earth elements on technical substrates through the FF-MOD route, and provides a guideline for further growth of nano-composited and mixed rare earth REBCO films.

Behavior of sulfate in preparation of single light rare earth carbonate by Mg(HCO3)2 precipitation method

The precipitation of the water-leaching solution of Baotou mixed rare earth (RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate. To solve the serious problem of ammonia-nitrogen pollution, new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product (SO42−<1.8 wt% in RE carbonates products). In this paper, we studied the effects of feeding modes on the behavior of SO42− during the preparation of light RE carbonate (RE = La, Ce, Pr, Nd) from their sulfate solutions using Mg(HCO3)2 as a precipitant. The results indicate that the contents of SO42− in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La2(CO3)2.15(SO4)0.85·4H2O and Ce2(CO3)2.15(SO4)0.85·3H2O, while those of the Pr and Nd precipitates are 4 wt%–5 wt% since they exist in the form of n-carbonate. The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%–5 wt% of SO42− enclosed in the precipitation. The content of SO42− in the RE carbonate obtained using reverse feeding mode is the lowest. Among them, the content of SO42− in La precipitate is only 1.40 wt%. Both synchronous and reverse feeding modes can effectively reduce the content of SO42− in RE carbonate, which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO3)2 precipitation method.

Effect of La-Ce Mixed Rare Earth on High Temperature Deformation Behavior of 685 Armor Steel and Its Mathematical Model

A thermal simulation test machine was used to conduct high-temperature compression tests on two sets of 685 test steels with and without rare earths. Through linear fitting analysis and microstructure observation, the effect of rare earths on the high-temperature deformation behavior of 685 armored steel was studied. The results show that when the deformation temperature is 1000°C, La-Ce mixed rare earth can increase the deformation resistance of steel, and the influence varies with the amount of compression deformation, while at 1100°C, the rare earth has no obvious influence on the deformation resistance of steel. After adding rare earth, the recrystallization activation energy of steel is increased by 6.78%. Mixed rare earth (La-Ce) has an inhibitory effect on the recrystallization of steel. Using Origin8.0 software for regression analysis, a mathematical model of armored steel containing rare earths is established. The model has good curve fitting characteristics, and the calculated values are basically in agreement with the experimental values.

Research on the Effect of Rare Earth on the Structure and Impact Performance of Armor Steel

In order to study the impact performance of 685 armored steel with different mischmetal content, the impact performance of the steel at room temperature and -40°C was tested, and the impact fracture morphology and microstructure were observed and analyzed. The results show that the addition of mixed rare earth La-Ce to the test steel improves the tempered martensite structure and refines the austenite grains. At the same time, the inclusions in the steel are modified, and the elongated MnS inclusions are modified. It is a spherical composite rare earth inclusion, and the size of the inclusion is reduced from 6 μ m to 2 μ m. Compared with the test steel without rare earth, the room temperature impact performance of the mixed rare earth test steel and the -40 °C low temperature impact performance are improved. When the La-Ce content is 102 × 10−6, the room temperature impact energy of the protective steel increases by 24.5%, and the low temperature impact energy at -40 °C increases by 17. 4%. The results of the shooting test showed that the protection level of rare earth-containing armored steel reached NATO Level 2.

Microstructure and microhardness mechanism of selective laser melting Mg-Y-Sm-Zn-Zr alloy

Abstract In this study, a multi-element mixed rare earth magnesium alloy of Mg-3.4Y-3.6Sm-2.6Zn-0.8Zr (wt%) was selected to form selective laser melting (SLM). In addition, an investigation was conducted on the microstructure, precipitated phases and elements segregation of the experimental alloy deposited by SLM. Moreover, the microhardness and nanomechanical properties of the alloy were determined, with its mechanism summarized. As revealed from the results, there were refinement equiaxed grains in the center of the scanning tracks, and the grain size was 1–3 µm; the overlapping area primarily composed columnar crystals. Specific to the precipitated phases of the mentioned two regions, Mg matrix (hcp), eutectic phase ( Mg , Zn ) 3 (Y,Sm) (fcc) distributed in a network along the grain boundary, and the segregation of Y 2 O 3 and Zr elements were largely involved, noticeably inconsistent with the microstructure of as-cast. As corresponds to the mentioned, the microhardness mechanism of SLM deposited samples was mainly grain boundary hardening and solid solution hardening. The cross section exhibited the significantly greater microhardness (105 HV) than the as-cast (81.5 HV).

Boosting the extraction of rare earth elements from chloride medium by novel carboxylic acid based ionic liquids

Two novel carboxylic acid based ionic liquids (ILs), benzyltributylammonium myristic acetate ([N444Bn][MA]) and benzyltributylammonium dodecanedioic acetate ([N444Bn]2[DDA]), have been rationally designed and successfully synthesized for the extraction of yttrium (denoted as Y(III)) from a chloride aqueous solution and for the separation of mixed rare earth elements (REEs). Comparison studies of the extraction performances of [N444Bn][MA] and [N444Bn]2[DDA] were carefully investigated under different conditions (e.g., equilibrium time, solution acidity, salting-out agent concentration, and REEs concentration). The results indicated that the extraction efficiency of Y(III) reached 87.18% after 2 min using [N444Bn]2[DDA], whereas it required 10 min to reach an extraction efficiency of 47.37% using [N444Bn][MA], mainly due to the larger electronegativity of the incorporated dicarboxylates in the anions of [N444Bn]2[DDA], which enhanced its coordination with Y(III) compared to [N444Bn][MA]. However, [N444Bn][MA] illustrated better selective separation behavior than [N444Bn]2[DDA] in mixed REEs solutions (including La, Nd, Eu, Ho, Yb and Y), and the selective factors of Yb and La were 16.21 and 3.30, respectively. Furthermore, the ion association mechanism, evolved from the slope analysis and FT-IR results, contributed to avoiding the saponification procedures and resultant saponification wastewater during the extraction process. In addition, the back-extraction experiments indicated that ~97% Y(III) can be stripped from [N444Bn]2[DDA] and [N444Bn][MA] using 1.0 M and 0.4 M HCl, respectively, demonstrating that these ILs can be further used in large-scale applications for the separation and recovery of REEs.

Influence of rare earth particulate on the mechanical & tribological properties of Al-6063/SiC hybrid composites

Mechanical characteristics and tribological behavior of aluminum (Al6063) matrix composites (AMCs), fabricated using different compositions of SiC particles and mixed rare earth particulates (REP) were investigated. The hybrid composites samples were fabricated via bottom pouring casting route by varying 3, 6, and 9 wt.% of SiC and 1, 2, and 3 wt.% REP(CeO2+La2O3) mixture. Microstructural examination was conducted using electron back scattered diffraction (EBSD) and scanning electron microscope (SEM) analysis. Also the elemental composition of the samples was determined by using energy dispersive spectroscopy (EDS). The microstructural studies revealed uniform dispersion of REP (CeO2+La2O3) throughout the Al6063 matrix which promotes grain refinement. Mechanical properties such as micro-hardness, impact strength, ultimate tensile strength, percentage elongation, along with tribological properties such as wear rate were investigated on AMCs at room temperature. The outcomes concluded that incorporation of up to 2 wt.% of REP mixture resulted in superior hardness, impact strength, tensile strength and lower wear rate along with marginal improvement in percentage elongation. However, a decrement in mechanical properties and specific wear rate was observed on increasing the REP mixture to 3 wt.%.

Research on the formation process of selective laser melting Mg–Y–Sm–Zn–Zr alloy

Selective laser melting technology was proposed to form the multi-element mixed rare earth magnesium alloys of Mg–3.4Y–3.6Sm–2.6Zn–0.8Zr (wt-%). The formation process, relative density, evaporation, microstructure and microhardness of the deposited samples at different laser power and scanning speed were characterised. Under the experimental conditions with a laser power of 40 W and a scanning speed of 300 mm s−1, the maximum relative density of the sample is 98.6%. The evaporation of elements exists but is not serious under all process parameters. Compared with the as-cast process, the microstructure of the samples prepared by SLM is mainly composed of α-Mg matrix and (Mg, Zn)3(Y, Sm) eutectic phase, Mg12(Y, Sm)Zn eutectic phase and LPSO structure are not found.

Estimating the environmental cost of mixed rare earth production with willingness to pay: A case study in Baotou, China

Rare earths are important key metal minerals, but their exploitation, smelting and separation leads to the emission of environmental pollutants. China has taken a series of measures to control and govern the environmental pollution caused by mixed rare earth development in northern China, but currently, environmental pollution still exists. Environmental pollution affects the lives of local residents, and this impact can be measured by the nonuse value of the environmental pollution caused by rare earth development. Willingness to pay (WTP) is widely used to assess the nonuse value of environmental goods or services. By investigating residents' WTP for environmental improvement with respect to mixed rare earth development in northern China, we can better promote environmental governance and provide a decision-making basis for the government to propose quantitative and feasible environmental governance policies. Northern Chinese mixed rare earths are located mainly in Baotou in the Inner Mongolia Autonomous Region. In this study, we conducted a questionnaire survey of residents around the Baotou rare earth mine regarding their basic personal situation, environmental cognition of rare earth development and WTP for environmental pollution control. Based on our findings, we used a double-bounded dichotomous choice (DC) model to calculate the average amount that residents are willing to pay for the treatment of environmental pollution, and we obtained the estimated mean value of their WTP. From February to April 2019, we obtained 568 valid questionnaires in the Hondlon District and Bayan Obo Mining District of Baotou. The analysis results show that the average value of the respondents’ WTP under the double-bounded DC model is 153.63 CNY per year and that the total value of the respondents’ WTP for environmental improvement with respect to rare earth development in Baotou is 442 million CNY per year. In addition, regarding the direct influencing factors of WTP, gender, the degree of cognition of environmental pollution, the degree of perception of bodily influence and the degree of expectations regarding environmental remediation have a significant positive correlation with WTP; moreover, the perception of bodily influence is the most important factor. Regarding the factors indirectly influencing WTP, age and place of residence affect the respondents' environmental cognition, which, in turn, affect the respondents’ WTP. Based on these influencing factors, the government can implement distinct environmental governance policies for different groups to effectively support the implementation of environmental policies.

Thermochemical Preparation and Properties of Low-Cost Polylanthanide Manganite Materials of Ln(La, Ce, Nd, Pr)xCayMnO3-Type with Perovskite-Fluorite Structure

A physical and chemical investigation of ceramic materials based on manganites of mixed rare earth elements –

Environmentally friendly comprehensive hydrometallurgical method development for neodymium recovery from mixed rare earth aqueous solutions using organo-phosphorus derivatives

Rare earth elements (REEs) have obtained a greatest significant in human lives owing to their important roles in various high technology applications. The present method development was deal technology important REEs such as neodymium, terbium and dysprosium, selective extraction with possible separation and recovery studies, successfully. The chloride mediated mixed aqueous solution containing 1500 mg/L each of REEs such as Nd, Tb and Dy was subjected at selective separation of Nd from other associated REEs. Three organo-phosphorous based commercial extracting agents such as Cyanex 272, PC 88A and D2EHPA, were employed for the extraction, possible separation and recovery of rare earth elements. A comparative extraction behavior of all these three extractants as function of time, pH influence, extractant concentration, temperature and diluents were systematically investigated. The extraction tendency of organo-phosphorus reagents towards the extraction of either of the REEs follows of the sequence as: D2EHPA > PC 88A > Cyanex 272. The thermodynamic behavior of either of the extractants on liquid–liquid extraction processing of REEs was investigated and thermodynamic calculations were calculated and presented. Substantial recovery of neodymium oxalate followed by its calcined product as neodymium oxide was ascertained from XRD study and SEM–EDS analysis.

Analysis of structural phase stability and thermo-elastic properties of alloy of rare earth sulfides (LaxPr1-xS) under high pressure at room temperature

The high pressure structural behavior and associated properties of mixed rare earth sulfides (LaxPr1-xS) have been investigated by applying a Realistic Interaction Potential (RIP) model, including temperature effects. This model explains the inter-atomic interactions as it incorporates long range coulomb interaction; three body interaction (TBI), vdW (van der Waals) interaction, short range overlap repulsive interaction up to second neighbors and zero point energy effects including the temperature effects. We have predicted the high pressure structural phase transition from NaCl (B1 -type) to CsCl-type (B2-type) phase and associated volume drops for these compounds. The pressure induced phase transition is found to be a first order. Estimation of the elastic, thermal properties and Every’s parameters of these compounds has been performed during study. The results obtained are found to be in reasonable agreement with experimental and other theoretical data.