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In order to clarify the solvent extraction and separation behaviors of rare earths and impurity of Al during the extraction and enrichment of low-concentration leach solution of ion-adsorption rare earth ore, the extraction mechanism and separation behaviors of Nd3+ and Al3+ in the Nd2(SO4)3–Al2(SO4)3 mixed solution using P507 were studied in this work. The extraction of Nd3+ and Al3+ follows the cation exchange mechanism. With the increase of the equilibrium pH, βNd/Al in the extraction of the Nd2(SO4)3–Al2(SO4)3 mixed solution using P507 is always higher than that in the extraction of single Nd2(SO4)3 and Al2(SO4)3 solutions. It can be attributed to the fact that the extraction of Nd3+ using P507 is much faster than that of Al3+, and Al3+ is more prone to be hydrolyzed at lower pH. βNd/Al in the extraction of the Nd2(SO4)3–Al2(SO4)3 mixed solution decreases gradually with the increase of mixing time within the equilibrium pH range of 1.5–1.9. The extraction of Nd3+ using P507 is much faster than that of Al3+, but the stability of Al3+-loaded organic phase is better than that of Nd3+-loaded organic phase, thus Nd3+ in the Nd3+-loaded organic phase is gradually replaced by Al3+ in the aqueous phase with the increase of mixing time.

As the oxygen redox ability shows great effects on the catalytic performances of ceria-zirconia based materials, many strategies have been utilized to improve the oxygen storage capacity. Here in this study, we report a simple and facile approach to prepare a SO42–-modified La, Y-doped ceria-zirconia material (SO/CZLY-f) with high oxygen storage capacity. Due to the additional redox process between SO42− and S2−, oxygen storage capacity of SO/CZLY-f (745.3 μmol O2/g) is about 1.6 times higher than that of La, Y-doped ceria-zirconia material without SO42– modification. Moreover, the catalytic activities and stability of the corresponding Pd-only three-way catalyst were measured. Compared to that of Pd@CZLY-f, the operation window of CO, full conversion temperature of HC and NO over Pd@SO/CZLY-f are obviously widened and lowered, respectively. After aging treatment at 1100 °C for 4 h, the superiority of aged Pd-loading composite is still maintained.

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−

The leaching behaviors of calcium and magnesium in the rare earth tailings leached with magnesium sulfate using deionized water, CaCl2 solution and lime water were investigated. Experimental data indicated that magnesium in the tailings was easy to be leached out since most of the magnesium was in the form of water-soluble phase. Most of calcium in the lime water was electrostatically adsorbed on the clay mineral of the tailings, and the water-soluble magnesium was also gradually converted into exchangeable phase because of back-adsorption of Mg2+ on the clay mineral with increasing the pH values. When the liquid-to-solid ratio was 0.80, the contents of readily-available magnesium and calcium were 104.4−207.6 and 201.7−1426.3 mg/kg, respectively, which could meet the requirements for plants. These results suggest a promising route for the environmental remediation of ion-adsorption rare earth ore after in-situ leaching.

Numerous light rare earth elements (LREE) minerals containing Fe and P were processed by sulfuric acid roasting method, and the leaching solution mainly comprises LREE sulfate, Fe2(SO4)3, H3PO4, and H2SO4, however, the solubility data of LREE sulfates in this system is few. This work studies the solubility of LREE sulfates in independent LREE sulfate system RE2(SO4)3-Fe2(SO4)3-H3PO4-H2SO4 (RE = La, Ce, Pr or Nd) and mixed LREE sulfates system (La,Ce,Pr,Nd)2(SO4)3-Fe2(SO4)3-H3PO4-H2SO4 at different temperature (25–65 °C) and concentrations of Fe2(SO4)3 (Fe2O3, 0–50.13 g/L), H2SO4 (0.5 mol/L), and H3PO4 (P2O5, 20.34 g/L) based on the industrial operating condition at low liquid and solid ratio 2:1. The solubility of each LREE sulfate in the independent system (La2O3, 12.25–20.88 g/L; CeO2, 41.93–62.35 g/L; Pr6O11, 37.34–56.69 g/L; Nd2O3, 26.60–37.63 g/L) is much higher than that of the mixed system (La2O3, 6.95–11.03 g/L; CeO2, 10.63–21.51 g/L; Pr6O11, 11.56–20.36 g/L; Nd2O3, 12.36–19.79 g/L) under the same other conditions. The results also indicate that, in the two systems, both Fe and the temperature have negative effects on the solubility of LREE sulfates. That may occur due to the complication reactions between the complexes of RESO4+ and Fe(SO4)2–. However, the influence degree of temperature and iron concentration on the LREE sulfates solubility varies in the two systems and among different LREE species. This research is of theoretical significance for optimizing the conditions of the sulfuric acid process for recovering the LREE from the mixed LREE bearing minerals as well as the single LREE containing secondary rare earth scraps.

In acid treatment technology of Baotou mixed rare earth ore, large quantities of ammonia-nitrogen wastewater are produced in the step of ammonium bicarbonate precipitation to transform rare earth sulfate. In this paper, we adopted a green precipitant magnesium bicarbonate (Mg(HCO3)2) to substitute ammonium bicarbonate to eliminate ammonia-nitrogen pollution. The effects of n(HCO3−):n(RE3+), aging temperature and aging time on the crystallization using Mg(HCO3)2 precipitation method were investigated. The results indicate that the rare earths could be completely recovered when n(HCO3−):n(RE3+) is higher than 3.15:1. The crystal water content of rare earth carbonates is affected by the aging temperature. The precipitate has a bad filterability when the aging temperature is over 40 °C. This can be attributed to the less crystallized water molecules of the hydrated rare earth carbonate precipitation. The mixed rare earth carbonates are prone to be crystalline, and have a good filterability at aging temperatures below 40 °C. Meanwhile, the evolution mechanism of crystalline mixed rare earth carbonates is reasonably deduced, the amorphous rare earth carbonates are first dissolute and then recrystallized. Under the optimized aging conditions, the purity of the crystalline precipitate meets the requirements of the fine product standard (GB/T 16479-2008). The filtrated could be used to produce Mg(HCO3)2, thus to realize the recycling of magnesium sulfate.

Solid oxide fuel cell is a promising energy conversion system which converts chemical energy into electrical energy directly. Electrolyte is the key component and determines the working temperature. In this paper, ceria and scandia co-doped zirconia electrolytes sintered from 1300 to 1550 °C were chosen as research objects. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were performed to characterize the ceramic samples. The effects of grain size and grain boundary element segregation on the electrical conductivity were focused. Electrochemical impedance spectroscopy was used to calculate the bulk, grain boundary and specific grain boundary conductivity. Results show that the bulk and grain boundary ionic conductivity increases with the increasing grain size. However, the specific grain boundary conductivity decreases with the increasing grain size. This is explained by the fact that Sc3+ is segregated at the grain boundary, which leads to higher oxygen vacancy concentration when sintered at lower temperature.

Phosphate rock has been considered as one of the potential promising resources for rare earth elements (REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the further development of REEs recovery technologies. In order to explore a green process for the recovery of REEs from phosphate rock, this study investigates the effects of phosphoric acid concentration, liquid-to-solid ratio (L/S ratio), leaching time and temperature on the leaching efficiencies of the major components from phosphate rock. A REEs recovery of 94.3% and a phosphorus recovery of 95.3% are achieved under the optimal conditions of attacking phosphate rock using 30%P2O5 acid with an L/S ratio of 10:1 and a stirring speed of 250 r/min at 25 °C for 4 h. Then, the selective precipitation of REEs with 81.3% REEs recovery is realized by heating up the leaching solution from 25 to 90 °C and keeping for 4 h. Thereafter, more than 95% phosphoric acid is recovered by H2SO4 and high purity gypsum, more than 95% CaSO4 (tested by XRF), is also produced at the same time. Ultimately, a green process that leaches phosphate rock with H3PO4, selectively precipitates REEs from leaching solution by heating up, recovers H3PO4 with H2SO4 is proposed. Compared with REE recovery in traditional processes, this process owns the merits of simple operation, energy saving and minimum wastes.

In order to achieve deeper understanding of rare earth elements (REEs) behaviors during phosphate rock processing with H3PO4. The solubility of REEs in Ca(H2PO4)2 H3PO4 solutions with various concentrations of Ca(H2PO4)2 at different temperatures were tested. The results demonstrate that REEs solubility decreases sharply with the increasing concentration of Ca(H2PO4)2. Equations between [REE3+] and [H+], [H+] and [Ca2+] in Ca(H2PO4)2 H3PO4 solutions were built based on the precipitation-dissolution equilibrium of rare earth phosphates and the ionization equilibrium of H3PO4. According to the equations, the decreasing mechanism of REEs solubility caused by elevated concentration of Ca(H2PO4)2 was determined. The mechanism can be illustrated as that the elevated concentration of [H2PO4–] decreases the concentration of hydrogen ion by retarding the ionization process of H3PO4 and directly promotes the precipitation of rare earth phosphates. Furthermore, it can be easy deduced that similar effect would be caused by the other cation impurities (Fe3+, Al3+, etc.) on REEs solubility based on the mechanism. In addition, superimposed reduction effect on REEs solubility caused by the elevated concentration of Ca(H2PO4)2 and the elevated temperature is found. This superimposed effect leads to a super low solubility of REEs in Ca(H2PO4)2 H3PO4 solution. On the basis of the experimental study, outlooks and suggestions for further development of REEs recovery method are given.

Rare earths (REs) are of vital importance for the development of new materials and green energy. Magnesium bicarbonate is one of the most recyclable and environmental-friendly precipitant for REs recovery from leaching solutions. Nd2(CO3)3 has difficulties in industrial production. So in this study, the precipitation of neodymium from chloride solution by magnesium bicarbonate are investigated. The effects of feeding method, [ HC O 3 − ]/[Nd3+] mole ratio, feeding speed and reaction temperature on yield and impurity (magnesia) content are systematically studied. Results show that the impurity (magnesia) content decreases to 0.010 wt% with a yield approaching to 100% obtained under the conditions of [ HC O 3 − ]/[Nd3+] = 3.00 by parallel flow addition at 50 °C. The major impurity (magnesia) in rare earth carbonates mainly presents in the form of physical absorption, which can be easily removed by scrubbing. Therefore, it offers a promising green process that uses magnesium bicarbonate to produce neodymium carbonate due to its cycling of carbon dioxide, magnesium salt and waste water.

Magnesium bicarbonate solution is considered as an environmentally friendly extractant saponification agent for the solvent extraction of rare earth elements due to its advantage of minimum water pollution. In order to reveal the extraction regularity, optimize production-process and guide the use of this new extraction system, the extraction of Nd(Ⅲ) in chloride medium with HEH/EHP saponified by magnesium bicarbonate solution was investigated with the self-designed constant interfacial area cell. Besides, the effects of stirring rate, temperature, specific interfacial area and concentration of Mg-HEH/EHP on the extraction rate of Nd(Ⅲ) were systematically investigated. Results show that, the rate of extraction is governed by both diffusion and chemical reaction, and the extraction reaction takes place at the interface. The apparent activation energy of the extraction reaction is 16.88 kJ/mol. The corresponding rate equation is deduced. The mechanisms and rate-determining step are speculated based on interfacial reaction models, which is consistent with the experimental results.

In order to improve the application values of Ce element, in this paper, rare earth chloride solution was used as raw material, the pH value was controlled by inorganic alkali, the ceria powders with special physical properties were prepared by carbon dioxide carbonization method. According to characterization of SEM, XRD, and TG-DSC, Ce(OH)3 prepared at pH = 7.5 exhibits smaller particle size than that prepared at other conditions. CeO2 precursor obtained by direct carbonization of Ce(OH)3 shows smaller particle size and narrow size distribution, CeO2 precursor forms at first by carbonization of Ce(OH)3 with the continuous addition of CO2 gas, and the chemical component is indicated to be Ce2O(CO3)2·6H2O. Cubic phase CeO2 powders are obtained by calcined at 750 °C for 4 h. The mean particle size D50 is 0.941 μm, and particle size distribution is smaller than 1. The microscopic appearance is homogeneous, with a spherical-like shape and a grain size of 200–500 nm. The light quality characteristics of sedimentation volume and accumulation density are obviously better than those of carbonate precipitation products. The carbonization method can be used not only to obtain ultra-fine rare earth oxides with fine particle size, narrow distribution and high dispersion properties, but also to achieve the reuse of carbon dioxide greenhouse gas.

Rare earth elements (REEs) play a critical role in numerous high-tech applications owing to their unique magnetic, optical, and electrical properties. China is widely recognized by its abundant rare earth resources with the annual output of 100,000–150,000 tonnes, which accounts for over 90% of the world’s total production. Bastnaesite is one of the four rare earth minerals in China. With the rapid development of rare earth industry, resources and environmental issues have attracted more and more public attention around the world. The Chinese government, together with the Chinese researchers, have been devoted to establish a high standard by proactively addressing resources and environmental issues. This review gives an overview of the recent progresses in the environmentally friendly rare earth separation and industrial application of bastnaesite in China, including oxidation roasting-acid leaching process, sulfuric acid bake-water leaching process, caustic soda decomposition process, chlorination process, NH4Cl roasting technique, hyperlink extraction process, equilibrium acidity controlling technique, and some other improved processes. These progresses have exerted important impacts on the wolrd’s rare earth industry and futher pointed out the future directions for the technical development of the rare earth industry in China. Moreover, the recent policies on the cleaner production of rare earth industry issued by the Chinese government have been briefly discussed, which provides sufficient policy support for the generalization and application of the advanced cleaner production technologies in the rare earth industry.

Ion-adsorption rare earth element (REE) ores are strategic mineral resources, particularly for heavy REEs. To reduce the amount of nitrogen in the form of ammonia in waste waters and to increase the low recovery efficiency of the current extraction process for REEs, we developed a novel environmentally friendly stepwise solvent extraction method for the separation and enrichment of REEs. Based on their different extraction abilities and a cation-exchange mechanism, two acidic phosphorus extractants (HEH(EHP) and HDEHP) were selected to sequentially separate and enrich REEs. Using this novel technique, ammonia nitrogen emissions were completely avoided and the recovery efficiency of REEs was significantly improved. From the McCabe–Thiele plots, it was found that a three-stage HEH(EHP) extraction at VA/VO = 10/1 and two-stage HCl stripping at VA/VO = 1/16 were required to enrich heavy REEs, whereas a three-stage HDEHP extraction at VA/VO = 25/1 and three-stage HCl stripping at VA/VO = 1/20 were required to enrich light REEs. The total recovery efficiency realized for REEs was >99% and the heavy and light REE chloride concentrations in solution were up to 240 and 200 g L−1, respectively. These results suggest an efficient way of recovering REEs from a leaching solution with low concentrations.

To improve the electrical properties of an 8 mol% yttria-stabilized zirconia (8YSZ) electrolyte, nanocrystalline (10–100 nm) 8YSZ powders were synthesized via a hydrothermal method followed by heat treatment at temperatures ranging from 800 °C to 1200 °C. Note that all the powders maintained the single-cubic phase structure, as observed via the results of the XRD and Raman spectra. Moreover, the annealing procedure of the powders caused the yttrium concentration of the surface to slightly increase, as observed via X-ray photoelectron spectroscopy (XPS). Moreover, according to the morphology shown in the SEM images and the electrochemical impedance spectroscopy (EIS), the powder grain size had an effect on the microstructure of the electrolytes fabricated via the conventional sintering method. In addition, it further influenced the relative density and conductivity of the electrolytes, which both first increased and then decreased with the increase in the powder grain size in the range of 10–100 nm. This showed that the powders with 50–80 nm grain size exhibited the best performance since it was not easy to induce grain coarsening in ceramics. The electrolyte sintered by these powders showed uniform and hexagonal grains with a mean size of 0.97 μm and a relative density of over 99%. Because of a large sum of grain boundaries and point defects, the electrolyte had a good conductivity of 174.1 mS cm−1 at 1000 °C measured by the four-probe DC method. In addition, the activation energy (0.955 eV) is lower than that for other samples; this suggests that 8 mol% Y2O3-stabilized ZrO2 has more advantages at lower working temperatures for SOFCs.

Oriented attachment and Ostwald ripening are two aging mechanisms of precipitation particles which may result in different crystallization mechanism of precipitates during the aging process. In this work, the effects of different aging process on the structure and properties of cerium zirconium mixed oxides were investigated. The results indicated that the mixed structure of 11.48% CeO 2 phase and 88.52% Ce 0.26 Zr 0.62 (LaPr) 0.12 O 2 solid solution phase were obtained under oriented attachment aging process. The rod-like CeO 2 phase coexisted with spherical Ce 0.26 Zr 0.62 (LaPr) 0.12 O 2 solid solution phase, which improved the surface area (64 m 2 /g) and pore volume (0.32 mL/g) of cerium zirconium mixed oxides after 1000 °C 4 h thermal treatment. However, through controlling the aging process, the Ce 0.35 Zr 0.55 (LaPr) 0.10 O 2 solid solution with homogenous phase structure was generated by Ostwald ripening aging process, exhibiting higher oxygen storage capacity (501 µmol O 2 /g) and H 2 consumption per gram (1378.3 µmol H 2 /g).

The adsorption behaviors of rare earth elements on clay minerals would have great influence on the mineralization process and the leaching process of the ion-adsorption type rare earths ore. In this work, the adsorption thermodynamics of REEs on kaolin were investigated thoroughly and systematically. The experimental results showed that the adsorption characteristics of La, Nd, Y on kaolin did fit well with the Langmuir isotherm model and their saturated adsorption capacities were 1.731, 1.587 and 0.971 mg/g, respectively. The free energy change (ΔG) values were −16.91 kJ/mol (La), −16.05 kJ/mol (Nd) and −15.58 kJ/mol (Y), respectively. The negative values of ΔG demonstrated that the adsorption of rare earth on kaolin was a spontaneously physisorption process. The deposit characteristic of the volcanic ion-adsorption type rare earths ore and the behavior of the rare earth in the column leaching process were also developed here. With the increase of the ore body depth, the distribution of the LREEs decreased and the HREEs increased. And the slight differences in the adsorption ability of REEs on clay minerals led to the fractionation effect in the column leaching process. These developed more evidences and better understanding of metallogenic regularity, and provided a theoretical basis and scientific approach to separation of the HREEs and LREEs in the leaching process.

Ultrafine powders of scandia-stabilized zirconia (ScSZ) were prepared by the co-precipitation method, using ZrOCl2 and ScO2 as raw materials and NH3·H2O as a precipitant. In this paper, the optimum process parameters were investigated. The pH of the reaction solution directly impacted the precursor structure, which further affected the obtained crystal forming. Many experiment methods of thermogravimetric analysis and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy (Raman), and nitrogen adsorption were employed to characterize the ScSZ powder. The structure transition mechanism from cubic to rhombohedral was discussed. In addition, the electrical conductivity of the powders was also studied after dry-pressing and calcining. The results showed that the structure of ScSZ with complete crystal surface belonged to the cubic phase. The crystallite sizes of the powders prepared are about 60-80 nm, meet the conditions of (D90-D10)/2D50≤1, and exhibited the good flow properties. The electrical conductivity was more than 190 mS/cm in air measured at 850 °C.