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Cerium zirconium solid solution is a key washcoat material for automotive three-way catalysts (TWCs). However, improving the redox ability and high temperature thermal stability of cerium zirconium solid solution is still a challenge. In this paper, the cerium zirconium solid solution was prepared by a coprecipitation-hydrothermal method, and the effects of the ammonia concentration on their structures and redox properties were investigated. The results show that when the ammonia concentration is 0.8 mol/L, the aged sample (1100 °C/10 h) of cerium zirconium solid solution has the highest specific surface area of 23.01 m2/g. Additionally, the increase of ammonia concentration improves the uniformity of phase compositions and increases the oxygen vacancies. When the ammonia concentration reaches 0.4 mol/L, the cerium zirconium solid solution exhibits the best redox activity, with the lowest reduction temperature of 565 °C. Therefore, increasing ammonia concentration in the hydrothermal treatment is beneficial to the thermal stability and redox performance of cerium zirconium solid solution.

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.

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.

Coronary CT angiography (CTA) with the characteristics of noninvasive and simple operation is widely used in the diagnosis of coronary artery stenosis. The choice of contrast agent exerts an important impact on the imaging quality of CTA. Conventional iodine contrast agents are easily excreted by the kidneys, from which the imaging window is short, and the imaging quality is poor. Metal nanomaterials have unique optical properties and have broad application prospects in imaging. Our aim is to explore the value of gold nanorod contrast agent in the diagnosis of coronary heart disease. A gold nanorod suspension was first prepared, and the prepared gold nanorod was uniform and had good dispersibility. It can be seen from the light absorption curve that there are two obvious peaks on the UV absorption peak of the gold nanorods. The gold nanorods were cultured in different solutions, and it was found that the particle size of the gold nanorods did not change significantly within 72 hours, indicating that the prepared gold nanorods had good stability. When observing the damage degree of mouse kidney tissue, it was shown that the damage degree of gold nanorod contrast agent to mouse kidney tissue was less than that of iodine contrast agent. The above results indicate that the gold nanorod contrast agent has good stability and safety. Therefore, our study demonstrated that the gold nanorod contrast agent has high value in the diagnosis of coronary arteries and the analysis of plaque properties.

In order to provide practical fundamental data for rare-earth elements (REEs) recovery from phosphoric acid and to better understand REEs behavior during the phosphoric acid evaporation process, the solubilities of REEs in phosphoric acid with various concentrations of phosphorus at different temperatures were measured. A simple linear model between REEs solubility and phosphoric acid concentration is built and the experimental data are found to fit it very well (R2>0.94). Hydrogen-ion concentration is found to be the predominant factor controlling the solubility of REEs in phosphoric acid. In addition, the solubility of REEs in phosphoric acid is found to sharply decrease with increasing temperature, which can be attributed to the increase of the Gibbs energy of the REEPO4 dissolution reaction or the restraint of the disassociation of phosphoric acid molecules owing to the elevated temperature.

To clearly elucidate the oxidative roasting behaviors of the bastnaesite, the thermal decomposition and oxidation of the bastnaesite concentrate in inert and oxidative atmosphere have been investigated in detail. Experimental data indicated that the initial decomposition temperature of the concentrate under N2 atmosphere is 150 °C higher than that under O2 atmosphere, most likely because the oxidation of the cerium induces the decomposition of the concentrate. For the roasted samples under N2 atmosphere at 500 °C and above, the oxidation efficiency of the cerium is 19.8%–26.8% because of the fact that rare-earth fluorocarbonate is first decomposed to form rare-earth oxyfluoride and CO2, and the cerium oxyfluoride is then partially oxidized by the CO2 gas. The rest cerium in these samples can be further oxidized in air at room temperature, with the oxidation efficiency of the cerium gradually increasing to above 80% in 7 d. This can be attributed to the obvious changes in the inner morphology of the roasted samples under N2 atmosphere at high temperatures, which largely induce the diffusion of the air and improves the oxidation activity of CeOF, and further induces the oxidation of CeOF by the air. XRD and XPS techniques were used to further verify the significant differences in the thermal decomposition behaviors of the bastnaesite concentrate under N2 and O2 atmosphere. Moreover, no oxidation of Pr3+ to Pr4+ in the roasted samples under both N2 and O2 atmosphere is observed. This gives an overall understanding of the oxidative roasting of the bastnaesite concentrate without additives.

Generally, phosphate rock contains about 0.05 wt% rare earth elements (REEs) on average. And the world commercial phosphate rock production is estimated to be 250 million tons per year, that makes phosphate rock a potential new REEs resource. However, low content of REEs in phosphate rock leads to the technical challenges and cost overages, that hindered the commercial recovery of REEs. In this paper, an overview of achievements aiming at solving the challenges is given. Based on the decomposition processes of phosphate rock by H2SO4, HNO3, HCl, H3PO4, various REEs recovery processes via crystallization, precipitation, solvent extraction and ion exchange methods are systematically reviewed. In H2SO4 processes, REEs are recovered based on the removal of impurities from phosphoric acid and phosphogypsum since the main challenge is the diluted content of REEs in these products. In the case of HCl, HNO3 and H3PO4 processes, REEs entirely transfers into leaching solution and the recovery research are mainly focused on REEs extraction from leaching solutions. For REE extraction from high phosphorus content leaching solutions, crystallization, precipitation, and ion exchange methods are currently inconsiderable due to the high energy consumption, impurity involvement and low efficiency, respectively. Solvent extraction seems to be the potential promising method in terms of its good overall performance. Finally, recommendations to promote the development of REEs recovery technologies from phosphate rock are provided.

In most cases, wet-process phosphoric acid (WPA) contains trace amount of rare earth elements and uranium, which ultimately enter and accumulate in soil and may cause environmental damages. In order to remove and recover these elements, studies about solvent extraction of heavy rare earth elements (HREEs) and uranium (U) with D2EHPA, selective stripping of HREEs from U, and evaporation precipitation of light rare earth elements (LREEs) were investigated. Extraction efficiency of U from WPA was greatly enhanced, but HREEs extraction were significantly retarded when using the solvent mixture of di- (2-ethylhexyl) phosphoric acid (D2EHPA) and tri-butyl-phosphate (TBP) or tri-octyl-phosphine oxide (TOPO) compared with D2EHPA alone. 89.4% and 94.2% accumulative two-stage extraction efficiencies of HREEs and U, respectively, were achieved with 1.0 M D2EHPA alone. And more than 98.1% HREEs were selectively stripped from loaded D2EHPA with 6.0 M HCl via three stages. In addition, LREEs were enriched to 1204.3 μg/g in evaporation sludge during the concentration process of phosphoric acid from 30% to 50% P2O5, and the filtration performance was greatly improved. Based on the studies, an alternative process was developed to recover and group LREEs, HREEs and U during the phosphoric acid production.

In order to study the aqueous stability of rare earth and thorium elements and the reaction mechanism of hydrochloric acid leaching of roasted bastnaesite, E h –pH diagrams for La–, Nd–, Ce–, Th–(Cl)–(F)–H 2 O systems at 20 °C were depicted using HSC Chemistry 6.0 software. E h –pH diagrams of La–, Ce–, Nd– and Th–Cl–H 2 O systems show that trivalent rare earth would be leached into solution by adjusting the acidity of the leaching solution, while tetravalent cerium and thorium would be remained in the leaching residue. And in the case that the pH value of the leaching solution is lower than 2, tetravalent cerium would be partially reduced by chlorine ions (Cl − ), which is well agreed with the industrial production. It can be inferred from E h –pH diagrams for the systems La–, Nd–, Ce–, Th–F–H 2 O that the leached trivalent rare earth ions (RE 3+ ) and tetravalent thorium ions (Th 4+ ) are preferentially combined with fluorine ions (F − ) to form sediment during non-reductive acid leaching of roasted bastnaesite. However, when controlling the pH value of the leaching solution below 0, fluorine and tetravalent cerium in the roasted bastnaesite would be leached out in the form of soluble [CeF 3 ] + complex. That means the precipitation of REF 3 and ThF 4 ·2.5H 2 O can be avoided in the leaching step. According to E h –pH diagrams for the system Ce–F–Cl–H 2 O, [CeF 3 ] + in the leaching solution would be reduced to CeF 3 precipitate in the presence of Cl − , that is to say, tetravalent cerium and fluorine would be firstly leached out to form [CeF 3 ] + , which would then be reduced to CeF 3 precipitate by Cl − in the hydrochloric acid leaching process of roasted bastnaesite.

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.

This paper investigated the recovery of rare earth elements (REEs) and aluminum (Al) from the waste slag discharged by FCC catalyst factory (FCC waste slag) via acid leaching and selective precipitation. Analysis methods such as ICP-AES, XRF and XRD were applied to obtain experiment data. The maximum leaching efficiency of REEs and Al was achieved at pH value of 1 and with liquid to solid ratio of 4:1. Under such conditions, 91.01%, 92.24% and 94.77% of La, Ce and Al were extracted at 20 °C for 2 h from the FCC waste slag, respectively. The SiO2 content in the leaching residue was 88.3%, which can be used as an available silicon resource. The REEs can be precipitated in the form of REEs and sodium double sulfate (NaRE(SO4)2·xH2O) by adding Na2SO4 to the leaching solution, while Al remained in the solution. Afterwards, the pH value of the filtrate was adjusted to 4.5, and Al was precipitated as Al(OH)3. Finally, NaRE(SO4)2·xH2O and Al(OH)3 were converted into RECl3 and Al2(SO4)3 solution, respectively, which were recycled to manufacture zeolite. This process recovered REEs and Al from the FCC waste slag and reduced the emissions of waste slag simultaneously, which has an important economic and environment significance.

A stepwise leaching process was developed to recover rare earth elements (REEs) and aluminum (Al) from FCC catalysts manufacturing slag (FCC waste slag), with NaOH and HCl. The FCC waste slag was treated with 2.5 mol/L NaOH at 293 K for 0.5 h to convert 72.4% of Al into NaAlO2. Then, the caustic conversion residue was decompose using 3 mol/L HCl to control leaching pH at 1.5 under 293 K for 3 h. Leaching efficiencies of 94.2%, 98.6% and 98.8% for Al, La and Ce, respectively, were achieved. 98.7% purity of rare earths oxide (REO) product was obtained after further treatments including oxalic acid precipitation and calcination. The filter liquor of oxalic acid precipitation was recycled to acid leaching step to recover the remaining Al. 97.6% REEs and 98.4% Al were recovered in total. Furthermore, the polymerization of metal ions and silicates were found and confirmed by IR and XRD analysis.

During the industrial production of FCC catalyst, a large amount of FCC catalyst waste slag (FCC waste slag) containing rare earths and aluminum was generated. Landfill was commonly used to deal with the slag, which may cause serious environmental degradation and resources depletion. A novel hydrometallurgical process consisting of hydrochloric acid leaching and subsequent neutralization is proposed to recover rare earths and aluminum from the FCC waste slag. The effect of leaching temperature, hydrochloric acid concentration and leaching time on the metal extraction are studied. The leaching kinetics of aluminum and rare earths are also investigated. It is shown that 91.0% of La, 92.2% of Ce, and 94.2% of Al are extracted under optimum leaching conditions of hydrochloric acid concentration 9.00 mol/L, solid to liquid ratio (S/L ratio) 0.05 g/mL, leaching temperature 293 K and leaching time 30 min. The leaching behaviors of aluminum and rare earths follow a shrinking core model which can be expressed as 1 − 1 − x 1 3 = k ap t , and the overall leaching process is controlled by the surface chemical reaction. The activation energies for the leaching of Al, La, and Ce are 6.24, 9.71, and 9.10 kJ/mol, respectively. Zeolite Na-Y and FCC catalyst presented in the FCC waste slag is leached with HCl individually. Only the FCC catalyst has a negative effect on the leaching of rare earths and aluminum. Finally, selective precipitation is employed to produce Al(OH)3 and RE(OH)3, which can be reused for the industrial production of FCC catalyst.

High performance solid electrolytes have been widely used in many devices, such as intermediate temperature (650–850 °C) solid oxide fuel cells, oxygen sensors, super capacitors, etc. In order to solve the problem of phase stability and high grain boundary resistance during the working process, the novel core/shell structure ScSZ nanocomposites were successfully prepared by fractional-precipated method. Non core/shell composites were also prepared by co-precipitation at the same Sc/Zr ratio for comparison. high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman characterization were performed to identify the microstructure and phase configuration of the obtained composites. According to HRTEM, clear rich scandia shell layer of 2–4 nm existed at the edge of each core/shell particle. The HRTEM figures of non core/shell composites were homogeneous without the shell structure. XPS element analysis for core/shell composite indicated that scandium ratio increased and zirconium ratio decreased when heat treatment temperature fell. When the heating temperature fell down to 450 °C, scandium ratio reached nearly 35 mol.%. EIS and DC measurement were taken for both kinds of electrolytes to study the electrochemical properties. The ionic conductivity were 178.2 and 154.4 mS/cm at 850 °C for core/shell and non core/shell electrolytes, respectively. The mechanism of conductivity improvement was also studied. It was predicted that the core/shell interface could improve ionic conductivity by modifying the space-charge regions. This result outlines a novel and potential direction for high-end electrolytes to enhance ionic conductivity.

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.

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.

Solvent extraction has been the most widely used technique for rare earths separation. In this study, thermodynamics and kinetics of lutetium extraction with HEH (EHP) in hydrochloric acid medium were investigated. The extraction mechanism and the relevant parameters were determined by experiment research which can guide the practical extraction process. The data indicated that chloride ion had no effect on lutetium extraction, the rate constant increased when stirring speed was enhanced. Effects of temperature, HEH (EHP) concentration, acidity, and chloride concentration were also studied. Thickness of the diffusion film was also calculated to be 4.66×10 –3 cm at 150 r/min.

China is the global leader in rare earth (RE) production using hydrometallurgical processes. Advantageous extraction techniques of rare earths from Baotou mixed rare earth minerals, bastnaesite, and ion-adsorption clays of rare earth deposits have been developed in China. The separation and purification technologies have also achieved rapid development. The industrial application processes for rare earth hydrometallurgy were summarized in the present paper. With the large demands and rapid development of rare earths, the issues of resources and environment are more prominent. This review gives an overview of the main processes that were developed in the past toward greener hydrometallurgy of rare earths in China. Based on the development of the rare earth industry, comprehensive utilization and cleaner production should still be focused on in the future, to support the sustainable development.

The extraction of yttrium from chloride medium with a mixture of 2-ethylhexyl phosphonic acid mono-(2-ethylhexyl) ester (HEHEHP, H2A2) and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex272, H2B2) in kerosene has been studied. The extraction mechanism was determined by the methods of slope analysis and constant mole. The maximum synergistic enhancement factor of 2.94 was obtained at a HEHEHP/Cyanex272 molar ratio of 1:1. It was found that yttrium was extracted with the synergistic system in the form of Y(HB2)(HA2)2. It is very different from the extraction forms of YH2ClA4 and YH2ClB4 when extracted by HEHEHP and Cyanex272 alone system, respectively. The effects of chloride ion on the yttrium extraction were also studied and the extracted complexes in the organic solution were determined by the infrared spectrum method. It was confirmed that the extraction was via a cation exchange mechanism.

A new environment friendly approach for rare earth separation has been developed in this paper. The approach used rare earth carbonates to control the equilibrium acidity during the rare earth loading with HEH(EHP) in chloride system. The kinetics of rare earth pre-loading by the approach was investigated. High rare earth loading of 0.17 mol L −1 and fast kinetics with about 5 min for equilibrium were achieved, which is suitable to the application of conventional rare earth separation process. The approach is free from environmental pollution because no saponification reagent is introduced.

Nanosheet-assembled tungsten oxide microspheres have been synthesized using rapid sonochemistry followed by thermal treatment. Transient observation of controllable synthesis reveals that the morphological evolution of the product is highly dependent on the ultrasonication time. An assembly mechanism based on oriented attachment and reconstruction is proposed for the sonochemical formation of the nanosheet-assembled microspheres. The obtained samples possess intrinsic non-stoichiometry and a hierarchically porous nano/microstructure, which is beneficial for their utilization in sensing materials and for fast diffusion of gas molecules. The maximum response of the tungsten oxide hierarchical microspheres is 3 times higher than that of commercial nanoparticles for NO2 gas. The gas adsorption–desorption kinetics during the sensing process were mathematically simulated by a derivative method. The first-principles calculation reveals that the NO2 molecule is most likely adsorbed at the terminal O1c site of tungsten oxide, leading to the introduction of new surface states, which are responsible for the intrinsic NO2-sensing properties.

The purpose of this study was to overcome the disadvantages of ammonia-nitrogen wastewater pollution and high cost of sodium saponification in rare earth separation process. The study focused on the non-saponification extraction technology with magnesia. The influences of the content and particle size of magnesia, reaction time, reaction temperature, and O/A on cerium extraction rate were also discussed. The results showed that the hydrogen ions of extractant were exchanged by rare earth ions when organic extractant and rare earth solution were mixed with magnesia powder, and then the exchanged hydrogen dissolved magnesia to make the acidity of the system stable. The magnesium ions were not participated in the extraction reaction. Non-saponification extraction process of rare earth had been realized. The cerium extraction rate could reach up to 99% in single stage within the optimal reaction conditions.

Sulfuric acid leaching process was applied to extracting rare earth (RE) from roasted ore of Dechang bastnaesite in Sichuan, China. The effect of particle size, stirring speed, sulfuric acid concentration and leaching temperature on RE extraction efficiency was investigated, and the leaching kinetics of RE was analyzed. Under selected leaching conditions, including particle size (0.074–h0.100 mm), sulfuric acid concentration 1.50 mol/L, mass ratio of liquid to solid 8 and stirring speed 500 r/min, the leaching kinetics analysis shows that the reaction rate of leaching process is controlled by diffusion through the product/ash layer which can be described by the shrinking-core model, and the calculated activation energy of 9.977 kJ/mol is characteristic for a diffusion-controlled process.

This paper describes a novel process for conducting the extraction and recovery of cerium, fluorine, and thorium from a bastnaesite sulfuric leaching solution using HEH(EHP) (2-ethylhexylphosphonic mono-2-ethylhexyl ester) as the solvent, and investigates the effects of HEH(EHP) concentration, the stoichiometric quantity of H 2 O 2 , and H 2 SO 4 concentration in the Th(IV) stripping liquor on extraction quantity and purity. Analysis of the process shows that Ce(III) extraction capacity with HEH(EHP) is negligible, and extraction efficiency for the elements is in order of Ce(IV) > F(I) > Th(IV) ≫ Ce(III). After coordination scrubbing of F(I) with Al(III), Ce(IV) is reductively stripped with H 2 O 2 and HCl, allowing recovery of CeO 2 with a purity of 99.95%. Furthermore, this paper provides appropriate technical parameters for industrial application of the extraction system—confirmed by a multistage countercurrent extraction test—showing that this process provides a more environmentally sound integrated separation and recovery flow of rare earths from bastnaesite.

La-hexaaluminate catalyst for methane catalytic combustion was synthesized by a reverse microemulsion. Pseudo-ternary phase diagrams of a quaternary microemulsion system of sodium dodecyl sulfate (SDS), n-pentanol, n-octane, and water (or Al(NO3)3 solution) were presented. The effects of alcohol chain length, cosurfactant-to-surfactant ratio, and salt concentration on the formation and stability of the microemulsion system were studied. The phenomenon that the conductivity changed with water supported the phase behavior of the microemulsion system. La(Mnx/Fex)Al12−xO19−δ catalysts, applied in methane combustion and with high-temperature stability, were synthesized within the stable areas of the phase diagram of the microemulsion system, when SDS was chosen as surfactant, n-pentanol as cosurfactant, and n-octane as oil phase. The physical properties and structure of the catalysts were characterized by BET method, transmission electron microscope (TEM), and X-ray diffraction (XRD). A micro-fixed-bed reactor was used to measure the catalytic activity of hexaaluminates in methane combustion. The results show that the reverse microemulsions can be used to produce discrete La-hexaaluminate nanoparticles that display excellent methane combustion activity owing to their high surface area and high thermal stability.

Phosphorite ore is a potential resource of rare earths (RE) as well as phosphate; therefore, the recovery of RE from wet-process phosphoric acid (WPA) is promising. This study investigated the influence of rotational speed, extractant concentration, flow ratio and phase contact time on the centrifugal extraction of RE from WPA and the separation of RE from impurities. The results indicate that higher rotational speed, higher extractant concentration and larger flow ratio are beneficial to the extraction of RE and impurities from phosphoric acid. It is found that the phase contact time for efficiently extracting RE and that for iron are of great difference, which provides an effective method for separating RE from iron using the non-equilibrium extraction process in centrifugal contactors. Compared with equilibrium extraction, the separation factor βRE/Fe is enhanced from 0.07 to 17.6.

Phosphorite ores are a potential resource of rare earths (RE) as well as phosphate so the recovery of rare earths during the wet processing of phosphoric acid is important. This study investigates the influence of operating conditions and crystal modifiers on the leaching of RE and the solvent extraction of RE with organo-phosphorus reagents. The results indicate that lower temperature, higher concentration of phosphoric acid and larger liquid/solid ratio are beneficial to RE enrichment in the phosphoric acid. Surfactant additives which enhance the crystal growth of gypsum also enhanced RE leach recovery about 75% under optimized conditions. Studies on the solvent extraction of RE found that D2EHPA mixtures with neutral organo-phosphorus reagents were antagonistic and that Fe3+ competed strongly over RE. Higher D2EHPA concentration, larger phase ratio, lower temperature and lower phosphoric acid concentration increased the RE extraction efficiency. A negative enthalpy change was found indicating an exothermic extraction reaction.

The aim of this study is to synthesize the catalysts of Fe- and Mn-substituted hexaaluminate by reverse microemulsion medium for methane catalytic combustion application. Pseudo-ternary phase diagrams in quaternary microemulsion systems of cetyltrimethylammonium bromide (CTAB), n-butanol, n-octane, and water [or Al(NO3)3 solution] were presented. The effects of the alcohol chain length, ratio of sur-factant to cosurfactant, and salt concentration on the formation and stability of microemulsion systems were studied. The phase behavior of microemulsion systems was confirmed through the varying of the conductivity with the water content. The performance and structure of the catalysts, La(Mn x /Fe x )Al12−x − O19-δ synthesized with the optimal parameter in the phase diagrams of microemulsions systems were characterized by BET, TG-DTA, and XRD. The micro fix-bed reactor was used to measure the catalytic activities of catalysts to methane combustion. The results showed that this synthesis method could yield non-agglomerated and highly dispersed precursors that would undergo crystallization at the lower temperature of 950°C. When temperature was raised up to 1050°C, the complete crystalline La-hexaaluminate was shaped. The hexaaluminate substituted with Fe had high-catalytic activity and stability at high temperature, while the Mn-substituted had higher catalytic activity at lower temperature. When the cooperation of Fe and Mn occurred, i.e., LaFeMnAl10O19−δ exhibited a high surface area and catalytic activity to CH4 combustion, the CH4 light-off temperature was only 475°C and the complete combustion temperature was 660°C. This was attributed to the synergistic effect between Fe and Mn.

A metal–organic framework Al-MIL-53-NH2-derived Bronsted acid catalyst (Al-MIL-53-RSO3H) has been synthesized employing a post-synthetic modification strategy under mild conditions. The Al-MIL-53-RSO3H catalyst was successfully utilized in the nitro-Mannich reaction taking advantage of its strong Bronsted acidity. Good to excellent yields of Mannich adducts were achieved for a variety of acylimine substrates in the presence of 0.1 mol% Al-MIL-53-RSO3H. Furthermore, the Al-MIL-53-RSO3H catalyst can be recycled five times without decreasing the yield and selectivity of Mannich adducts.

This paper investigates the development of a new environment friendly approach for treatment of bastnasite. A new process was developed to recover fluorine from bastnasite as synthetic cryolite by-product. The conditions affecting the fluorine removal and recovery in the process, including contact time, acidity, Al 3+ concentration, Al/F molar ratio and different kinds of aluminum salts being used, were investigated. The results indicate that high acidity and large Al/F molar ratio were beneficial to fluoride removal, and that the reaction reached equilibrium after 15 min. The effect of the initial Al 3+ concentration at a certain total Al 3+ amount was slight. Aluminum nitrate was more efficient than aluminum sulfate for the removal of fluoride. Optimum operation parameters for synthesizing cryolite have been obtained and proposed for industrial applications.