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.     

Rare earth recovery from fluoride molten-salt electrolytic slag by sodium carbonate roasting-hydrochloric acid leaching

Fluorinated rare earth molten-salt electrolytic slag contains a considerable amount of rare earth elements,as well as a variety of heavy metals and fluorides that cause environmental pollution.Therefore,it is of great importance to fully utilise this resource.In this study,the transformation mechanism of fluorinated rare earth molten-salt electrolytic slag roasted with sodium carbonate,and the regulation mechanism of rare earth leaching under different roasting conditions were investigated with ...     

稀土固体超强酸SO42-/SnO2- Nd2O3催化合成棕榈酸甲酯

采用溶胶-凝胶法制备稀土固体超强酸催化剂SO4-/SnO2- Nd2O3,以工业棕榈酸和甲醇为原料催化合成棕榈酸甲酯.考察了氧化钕添加量、焙烧温度、硫酸浓度、醇酸质量比、催化剂用量和反应时间对酯化反应的影响.结果表明,当氧化钕添加量为5％,以2.0 mol/L硫酸浸渍后,于550℃下焙烧3h制备的催化剂性能最好.正交实验结果表明,合成棕榈酸甲酯的优化条件为:醇酸质量比为15∶25,催化剂用量为棕榈酸质量的6.0％,反应时间5h.在此条件下,酯化率为90.1％.     

Ln2O3/MgO催化合成增塑剂IOP的研究

采用共沉淀-焙烧法制成了LnO3／MgO(Ln=Nd，Sm，Er)担载型催化剂。该型催化剂比表面大，分散性好。在催化合成IOP中效果明显，且使Ln2O3的用量减少80％左右。     

Hydrothermal synthesis of mixed rare earth-alkali metal or ammonium fluorides

The recent results on hydrothermal synthesis of mixed rare earth-alkali or ammonium fluorides were presented. The initial ratios of the starting materials, pH value and reaction temperature were the critical factors for obtaining the single-phase product. Four main types of complex rare earth fluorides, AREF4, A2REF5, ARE2F7 and ARE3F10 (A=Na+, K+, Rb+, NH4+), appeared in the primary hydrothermal reactions. The correlation between cation sizes and the formation of mixed rare earth fluorides under mild hydro...     

稀土固体超强酸Gd3+-SO2-4/ZrO2催化合成乙酸正丁醋

采用乙酸、正丁醇为原料,以固体超强酸Gd3+-SO24-/ZrO2作为催化剂,催化合成乙酸正丁酯。用固体超强酸Gd3+-SO42-/ZrO2和SO24-/ZrO2进行催化活性对比试验,考察浸渍硫酸浓度、浸渍时间、焙烧温度对催化剂活性的影响以及原料酸醇比、反应时间、催化剂用量对酯化率的影响,从而确定固体超强酸的最佳制备条件。试验结果表明:在反应温度105～110℃,催化剂用量1.5g,n(正丁醇)∶n(乙酸)=2.5∶1,反应时间2.5h条件下,酯化率可达98.86%;催化剂重复使用效果明显;加Gd3+的固体超强酸的催化活性明显增强。     

稀土改性膨润土的酯化催化活性

本文对用酸和稀土活化的玉山膨润土的酯化催化活性进行了表征。证明酸和稀土均能使膨润土的酯化催化活性得到大幅度的提高。稀土对催化作用的贡献不是独立的，而是与质子酸的催化共同存在，相互促进。     

Catalytic action of rare earth oxide (La2O3, CeO2, Pr6O11) on electrochemical oxidation of activated carbon in molten KOH–NaOH

The oxidation of anode carbon fuel directly affects the electrochemical performance of molten hydroxide direct carbon fuel cell (MHDCFC). In general, the anode carbon fuel can be oxidized at high temperature, thus the direct carbon fuel cell (DCFC) can show great electrochemical performance. In this study, rare earth oxides (La₂O₃, CeO₂, Pr₆O₁₁) were prepared by the method of precipitation. Activated carbon was prepared by pretreatment of lignite. Rare earth oxides and activated carbon were mixed as anode carbon fuel, and rare earth oxides were used to catalyze the electrochemical oxidation of anode carbon fuel. The results show that CeO₂ has better electrocatalytic activity compared with La₂O₃ and Pr₆O₁₁ in the MHDCFC. The electrochemical test results show that the current density (at 0.4 V) increases from 81.02 to 112.90 mA/cm² and the maximum power density increases from 34.78 to 47.05 mW/cm² at 450 °C, when the mass fraction of CeO₂ is increased from 0 to 40%. When the mass fraction of CeO₂ is 30%, the current density (82.55 mA/cm² at 0.4 V) at 400 °C is higher than that (81.02 mA/cm² at 0.4 V) without CeO₂ at 450 °C. The electrochemical oxidation mechanism of CeO₂ catalyzed anode carbon fuel is discussed.     

Extraction and separation of yttrium from other rare earths in chloride medium by phosphorylcarboxylic acids

Two phosphorylcarboxylic acids, 3-((bis(2-ethylhexyloxy))phosphoryl)propanoic acid (PPA) and 3-((bis(2-ethylhexyloxy))phosphoryl)-3-phenylpropanoic acid (PPPA), were synthesized for separating yttrium from other rare earths in the chloride feed of ion-adsorption type rare earth concentrate. The effect of the factors such as pH_1/2, temperature, saponification degree and phase modifiers was investigated. The separation efficiencies of PPA and PPPA are obviously better than the typical extractants such as sec-octylphenoxy acetic acid (CA-12) and naphthenic acid (NA). The extraction process of rare earths by PPA and PPPA is a cation exchanging reaction, which is similar to those of CA-12 and NA. The loaded rare earths in both PPA and PPPA systems can be effectively back-extracted by 0.5 mol/L HCl or higher concentration. A cascade extraction process for separating yttrium from other rare earths was developed using PPPA as the extractant. The yttrium product with the purity of 97.20 wt% was obtained by 35 stages of extraction and 12 stages of scrubbing.     

Rare earth extraction and separation from mixed bastnaesite-monazite concentrate by stepwise carbochlorination-chemical vapor transport

A stepwise carbochlorination-chemical vapor transport (SC-CVT) process is proposed for the rare earth extraction and separation from a mixed bastnaesite-monazite concentrate based on thermodynamic and kinetic analysis using carbon as reductant, chlorine gas as chlorination agent, SiCl₄ as defluorination agent, and AlCl₃ as vapor complex former. Between 500 °C and 800 °C, apparent activation energy of the carbochlorination within 2 hours changed from 22 to 16 kJ/mol roughly for the initial half hour and final 1 hour, respectively, in the absence of SiCl₄; but these values reduced to 15 and 2.1 kJ/mole under 2 kPa of SiCl₄ gas. The rare earth chloride yield for 2 hours was 56 to 88 mol pct in the absence of SiCl₄ and 92 to 99 mol pct in the presence of SiCl₄; but carbochlorination at above 1000 °C yielded a large amount of acid-insoluble residue. This, together with the negligible equilibrium vapor pressure of ThCl₄ at below 600 °C, suggests that carbochlorination of the mixed concentrate at temperatures as low as 500 °C in the (Cl₂ + SiCl₄) atmosphere is suitable for rare earth extraction and thorium-free volatile by-product release, which is different from the conventional Goldschmidt process at 1000 °C to 1200 °C. The CVT reaction of the carbochlorination product was performed at 800 °C for 0.5 hours in the (Cl₂ + SiCl₄ + AlCl₃) atmosphere and then at 1000 °C for 6 hours in the (Cl₂ + AlCl₃) atmosphere along different temperature gradients, leading to complete thorium removal and efficient rare earth separation, respectively. Their combination allows an efficient and environmentally conscious extraction and separation of rare earth elements from the mixed concentrate.     

Application of the Phase Transfer Catalysis in Rare Earth Solvent Extraction

ＡｐｐｌｉｃａｔｉｏｎｏｆｔｈｅＰｈａｓｅＴｒａｎｓｆｅｒＣａｔａｌｙｓｉｓｉｎＲａｒｅＥａｒｔｈＳｏｌｖｅｎｔＥｘｔｒａｃｔｉｏｎＹａｎＣｈｕｎｈｕａ（严纯华）；ＺｈａｎｇＹａｗｅｎ（张亚文）；ＬｉａｏＣｈｕｎｓｈｅｎｇ（廖春生）；ＪｉａＪｉａｎｇ...     

Decomposition of mixed rare earth concentrate by NaOH roasting and kinetics of hydrochloric acid leaching process

A new clean extraction technology for the decomposition of Bayan Obo mixed rare earth concentrate by NaOH roasting is proposed.The process mainly includes NaOH roasting to decompose rare earth concentrate and HCl leaching roasted ore.The effects of roasting temperature,roasting time,NaOH addition amount on the extraction of rare earth and factors such as HCl concentration,liquid-solid ratio,leaching temperature and leaching time on the dissolution kinetics of roasted ore were studied.The experimental results show that when the roasting temperature is 550℃ and the roasting time is 60 min,the mass ratio of NaOH:rare earth concentrate is 0.60:1,the concentration of HCl is 6.0 mol/L,the ratio of liquid to solid(L/S) 6.0:1.0,and the leaching temperature 90℃,leaching time 45 min,stirring speed 200 r/min,and the extraction of rare earth can reach 92.5%.The relevant experimental data show that the process of HCl leaching roasted ore conforms to the shrinking core model,but the control mechanism of the che mical reaction process is different when the leaching temperature is different.When the leaching temperature is between 40 and 70℃,the chemical reaction process is controlled by the diffusion of the product through the residual layer of the inert material.The average surface activation energy of the rare earth element is E_a=9.96 kJ/mol.When the leaching temperature is 75-90℃,the chemical reaction process is controlled by the interface transfer across the product layer(product layer interface mass transfer) and diffusion.The average surface activation energy of rare earth elements is E_a=41.65 kJ/mol.The results of this study have certain significance for the green extraction of mixed rare earth ore.     

稀土镧改性磷钨杂多酸盐催化油酸与甲醇酯化反应合成生物柴油活性研究

以H ₃PW ₁₂O ₄₀和La(NO ₃) ₃为原料,通过离子交换法制备一种稀土镧改性磷钨杂多酸盐催化剂.通过扫描电镜、红外光谱和X射线粉末衍射等表征方法,对合成的催化剂的物理及化学性能进行分析,进而通过以油酸和甲醇为反应物的酯化反应,对其催化活性进行研究.结果表明:稀土镧已经导入磷钨杂多酸的骨架结构,并与杂原子P形成配位键,有效提高磷钨杂多酸的比表面积和孔径;合成的催化剂具有完整的Keggin型结构;当反应温度为62 ℃,油酸与甲醇摩尔比为1∶6,反应时间为4.5 h,催化剂用量为反应物质量的2.5 %,油酸的转化率可达88.0 %.      

稀土固体超强酸催化剂S2O82-/ZrO2-SiO2-Sm2O3的制备

采用沉淀-浸渍法制备了负载稀土的固体超强酸S2O82-/ZrO2-SiO2催化剂,以乙酸丁酯的合成为探针反应进行了单因素测试,考察了制备条件对催化剂性能的影响.结果表明,载入不同稀土金属氧化物、不同硅锆原子量比以及预焙烧温度、焙烧温度和浸渍液浓度等因素对催化活性有显著影响.     

新型稀土固体超强酸催化剂的制备及乳酸丁酯的合成

制备了一系列稀土固体超强酸催化剂,以乙酸丁酯为探针反应,考察了催化剂最佳制备条件;以乳酸和丁醇为原料,以S2O82-/ZrO2-SiO2-Sm2O3(BR-3%-0.75-450)为催化剂合成乳酸丁酯,研究了对酯化反应的影响因素、催化剂稳定性。实验结果表明,该催化剂活性和稳定性均优于未改性的SO42-/ZrO2-SiO2。     

Study on Catalysts with Rhodium Loading on Different Cerium-Zirconium Mixed Oxides

The catalysts with Rh loading on different cerium-zirconium mixed oxides were characterized by BET, H2-TPR and OSC. The effects of different cerium-zirconium mixed oxides on catalytic performance and thermal stability of Rh loaded catalyst were studied. The results show that: (1) Rh can enhance cerium-zirconium mixed oxides OSC and catalytic reaction rates; (2) cerium-zirconium mixed oxides with high Ce contents and low Zr contents are more favorable to the stability of catalysts. Moreover, the contents of CeO2 have important effect on catalysts characteristics, and the addition of some rare earth components, such as La, Pr and Nd also have some influences.     

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 Ce_0.6Nd_0.4O_1.8, Ce₄O₇, and LaPrO_3+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).     

Effective rare earth extraction from Nd-Fe-B waste by liquid cuprum extraction method

Recovery of rare earth (RE) elements from Nd-Fe-B waste is one of the ways to solve the problem of so-called RE-crisis. An alternative approach of extracting RE elements from Nd-Fe-B waste by molten Cu extraction based on liquid-solid diffusion and reaction is reported in this paper. The extraction process, product microstructure and extraction efficiency were systematically studied. The results show that the extraction rate of RE at 1200 °C is about 20% higher than that at 1100 °C. The enhanced extraction efficiency at 1200 °C results from the fact that the liquid Fe and Fe₂B are not co-soluble with Cu. Reducing the mass ratio of Cu to waste and the size of the waste scraps is also beneficial to enhancing the separation of RE and Fe elements. In addition, the extraction time should be well controlled, for example, less than 2 h at 1100 °C, in order to avoid the increased Fe content in the extracted product. Based on optimized process, the RE elements can be almost fully extracted from the waste. This work thus provides an effective method to recover the RE elements.     

Migration behavior,separation and recycling of rare earth during thermal decomposition of Zhijin phosphorus ore

Zhijin phosphorus ore is a moderate and low-grade phosphorus rare-earth ore contained in mines. The separation and extraction of associated rare earth are important research topics. In this study,the migration behavior of rare earth during the thermal decomposition of Zhijin phosphorus ore and the separation and extraction of rare earth in phosphorus slag are discussed systematically. During the thermal decomposition process of phosphorus ore, almost all of the associated rare earth enters into the phosphorus slag phase but does not enter into the ferrophosphorus or gas phases. Amorphous calcium metasilicate and calcium fluosilicate are major components of phosphorus slag, and rare earth mainly exists as a calsil solid solution. Hydrochloric acid was used for acidolysis of the phosphorous slag.Under the following conditions, 96% of the rare earth in the phosphorous slag can be dissolved in the acidolysis solution: acid excess coefficient of 1.5, reaction time of 50 min and reaction temperature of 50℃. The rare earth in the acidolysis solution was separated and recycled using oxalic acid as a precipitator and NaOH as a pH modifier. At pH of 1.7, rare-earth-enriched matter with rare-earth content of 2.1 wt% was obtained, and the recovery of the rare earth was 88%.     

In-situ generation of platinum nanoparticles on LaCoO3 matrix for soot oxidation

The LaCo_0.94Pt_0.06O₃ catalyst is reduced under 5% H₂/Ar at different temperatures to get Pt/LaCoO₃ with high catalytic activity for soot oxidation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), X-ray photoelectron spectroscopy (XPS), H₂-temperature programmed reduction (H₂-TPR), O₂-temperature programmed desorption (O₂-TPD) and thermogravimetric analysis (TGA) were used to study the physicochemical properties of the catalyst. SEM and TEM results indicate that Pt nanoparticles (<10 nm) are grown homogeneously on the surface of the LaCoO₃ matrix after in-situ reduction. XRD shows that the reduced catalyst has a high symmetrical structure. TGA results indicate that all reduced catalysts exhibit an excellent activity, especially the catalyst reduced at 350 °C (T₁₀ = 338 °C, T₅₀ = 393 °C, T₉₀ = 427 °C). And perovskite is the primary active component. According to XPS study, the high symmetrical structure benefits the mobility of oxygen vacancy, and Pt nanoparticles induce the oxygen vacancy to move to its adjacent situation, resulting in more adsorbed oxygen on the surface of the reduced catalyst and increasing the activity. The possible reaction principle is also proposed.