Clean separation technologies of rare earth resources in China

After a review on the conventional separation process of rare earths (RE), hyperlink extraction technology was introduced and a potential process was proposed for clean separation of RE. A great amount of acid, base and water was consumed in the conventional RE separation process which included the procedures of raw material dissolving, extraction separation and precipitation. Therefore hyperlink extraction technology had been developed, by which the repeated consumption of acid and base could be avoided during the extraction process. And based on the theory and successful applications of the hyperlink extraction technology, we proposed the integral hyperlink process in which the intermediate acid resulted in individual procedures would be recycled and reused after being treated. The proposed process would make it feasible to consume no chemicals except for oxalic acid, and so could be a promising clean separation technology with a significant reduction on consumption and emission.     

Investigations on mineralogical characteristics of rare earth minerals in Bayan Obo tailings during the roasting process

This paper focused on the investigation of the mineralogical characteristics of rare earth minerals from Bayan Obo tailings during the roasting process in the presence of coal,Ca(OH)_2 and NaOH.Roasting experiments and leaching experiments were carried out to study the decomposition of rare earth minerals.The results indicated that bastnaesite and monazite could be completely decomposed at 650 ℃ and the leaching ratio of rare earths could reach 89.78%.The reaction mechanisms of bastnaesite and monazite at 650 ℃were analyzed.For bastnaesite,both the outer layer decomposition and inner core decomposition occurred simultaneously during the roasting.However,monazite was decomposed in a spatial sequence starting from the outer layer and proceeding to the inner core.     

Impact of backmixing of the aqueous phase on two-component rare earth separation process

Solvent extraction based on mixer-settler is the major industrial method of rare earth (RE) separation. In the mixer-settler extraction process, due to the insufficient settling time in normal circumstances, backmixing of the aqueous phase could have significant impact on the process of RE extraction separation. Therefore on the basis of the extraction equilibrium and mass balance of the mixer-settler extraction process, here we developed a mathematic expression of the aqueous phase backmixing in a two-component separation process, and obtained a quantitative analysis of the backmixing effect on the purification process by the approximations according to certain hypotheses. Two extraction systems of La/Ce and Pr/Nd separation were chosen as the examples to analyze the backmixing effect, and the results showed that the aqueous backmixing had greater influence in the scrubbing segment than in the extraction segment, especially in the system with a high separation factor such as La/Ce separation. Therefore it was suggested that the aqueous backmixing effect should be well attended in the design and application of RE extraction separation.     

Thermodynamic and application study of complicated extraction system Ce(Ⅳ)-HF-H_3BO_3-H_2SO_4 using Cyanex 923

This article aims to reduce the environmental pollution while maximizing the recovery of REEs as well as associate resource-fluorine(F) from bastnaesite.This paper investigates the extraction equilibrium process and mechanism of Ce(Ⅳ)-HF-H_3BO_3-H_2SO_4 system using Cyanex 923.Extraction equilibrium process of different systems,including HF-H_2 SO_4,H_3BO_3-HF-H_2SO_4,and Ce(Ⅳ)-HF-H_2SO_4,were studied in detail and the corresponding extraction mechanisms were also determined.It is noteworthy that a synergistic effect between B-F and an antagonistic effect between Ce(Ⅳ)-F were discovered first in the extraction process by Cyanex 923.Besides,H_3BO_3 is found to be able to promote the extraction of F in quantitation by Cyanex 923.FTIR and ~(11)B and ~(19)F NMR were adopted to characterize the different loaded organic phase.Based on these results,the extraction mechanism of complicated system Ce(Ⅳ)-HF-H_3 BO_3-H_2SO_4 was further determined.Besides,the effect of H_3BO_3 on the extraction and stripping of Ce(Ⅳ) in complicated system was studied.Moreover,it shows that the addition of H_3BO_3 has nothing to do with the purity of obtained CeF_3 particle from bastneasite liquor in the practical system.Adding H_3BO_3 into bastnaesite leach liquor,on the one hand,will be beneficial for the recovery yield of Ce and F.On the other hand,it can avoid from environmental pollution caused by emission of F-containing waste water as well as reducing the waste residue.     

Separation of aluminum from rare earth by solvent extraction with4-octyloxybenzoic acid

Leaching method is usually used to extract rare earth(RE) elements from ion adsorbed RE ores.In the leaching process,some impurities such as aluminum(Al) enter the leaching solution.The separation of Al from RE by carboxylic acid extractant 4-octyloxybenzoic acid(POOA) was studied in this article.By changing the pH value,temperature,solvent,saponification degree and other parameters,the extraction and separation performance of POOA in chloride system was systematically studied.Through specific e...     

Adsorption of Ce（Ⅳ） in nitric acid medium by imidazolium anion exchange resin

N-methylimidazolium functionalized anion exchange resin in NO3-form(RNO3) was prepared and used for adsorption of Ce(IV)in nitric acid medium.The adsorption amount increased with shaking time increasing and the adsorption equilibrium was obtained within 180min.Ce(IV) was partially reduced to Ce(III) and the reduction percent of Ce(IV) increased with shaking time increasing.But RNO3 was morestable than other resins due to the high resistance to oxidation.A little increase of adsorption amount was found with concentration of HNO3increasing.However,the reduction percent of Ce(IV) decreased with the increase of HNO3 concentration.The addition of NaNO3 decreasedthe adsorption amount of Ce(IV) on RNO3 due to the competitive anion exchange reaction.Ce(IV) was adsorbed on RNO3 in the form ofCe(IV) anion nitrato-complex.RNO3 and Ce(IV)-loaded RNO3 were characterized by fourier transform infrared(FT-IR) and thermogravimeric analysis(TGA).Ce(IV) could be easily separated from RE(III) solution by RNO3.     

Phase change,micro-structure and reaction mechanism during high temperature roasting of high grade rare earth concentrate

The deposit of Bayan Obo in Inner Mongolia is the world's largest rare earth element(abbreviated as REE)resource.The exploration of the theory of mineral formation of Bayan Obo is an important foundation for mineralogical research,and is the scientific basis for mining,industrial beneficiation,smelting and extraction,and processing and utilization.With the rapid development of science and technology,the demand for the utilization of rare earth elements is increasing,and the separation process between rare earth elements needs to be developed.The purpose of this paper is to provide high temperature experimental information for the formation and application of rare earth minerals.To this end,the mineral evolution of high-grade rare earth concentrates with increasing temperature and the migration of rare earths at different stages and their reaction mechanisms were studied.According to thermogravimetric analysis and differential scanning calorimetry(TG-DSC),calcination was carried out at different temperature ranges,and the calcined products were characterized by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),scanning electron micro scope and energy dispers ive spectrometer(SEM-EDS)and other analytical techniques.The re sults are shown in this process,the ra re earth phase is first converted into rare earth oxide and rare earth oxyfluoride.As the temperature increases,Ca_5(PO_4)_3 F and a large number of self-shaped spherical Ca-RE-OF and Ca-RE-PO_4 particles are formed,and the separation of La and Ce elements is discovered.Acco rding to the phase diagram analysis,the production of Ca_5(PO_4)_3 F is due to the reaction of monazite and fluorite,and the phases CeF_2 and Ce F_3 are formed during the reaction.When it reaches 1500℃,barium ferrite is produced and a new substance containing Ba~(2+)is formed.     

Stepwise Chlorination-Chemical Vapor Transport Reactions for Bastnaesite Concentrate

Vapor phase extraction and mutual separation of rare earth (RE) elements from bastnaesite concentrate were investigated using stepwise chlorination-chemical vapor transport reactions mediated by vapor complexes LnAlnC13n 3(Ln = RE elements). The bastnaesite was heated to 800 K and chlorinated between 800- 1300 K with ,C C12 SiClr to remove CO2, SiF4 and high volatile chlorides. At the temperature of 1300 K for 6 h, the resulted RE chlorides were chemically transported and mutual separated with the vapor complexes while CaC12 and BaC12 were remained in the residues. Significantly different CVT characteristics were observed for gradually decreased and wave form temperature gradients.     

Adjacent stage impurity ratio in rare earth countercurrent extraction process

Impurity components decrease stage by stage in a cascade of rare earth (RE) extraction separation, and adjacent stage impurity ratio (ASIR) which is defined as the ratio of an impurity’s contents in the aqueous/organic phase of two adjacent stages can be used to evaluate the capacity of impurity removal for the two stages. On the basis of extraction equilibrium and mass balance, the ASIR in a two-component extraction separation was deducted and its simplified expressions were given for different process sections according to reasonable assumptions. The calculation simulation was then carried out to obtain the ASIR distribution in the cascade. The results showed that in both the extraction and scrubbing sections the ASIR principally increased with the decrease of the molar proportion of the impurity but along with a flat appearing in the purification zone located in the middle of the cascade. The ASIR intuitively exhibits the running status of RE extraction separation and purification, which could provide a theoretic guide for investigating the influence factors of RE extraction separation process in practical industry.     

Extraction and recovery of cerium(Ⅳ) and thorium(Ⅳ) from sulphate medium by an α-aminophosphonate extractant

In the present work, a novel α-aminophosphonate extractant(Cextrant 230) was synthesized for the extraction and recovery of cerium and thorium from sulphate medium. The introduction of amine group into the phosphate molecule would enhance the extraction of Ce(Ⅳ) and Th(Ⅳ). The effects of extractant concentration, H_2SO_4 concentration and temperature on the metal extraction were investigated in detail. It was found that the extraction of Ce(Ⅳ), Th(Ⅳ) and REs(La, Gd, Yb) in sulphate medium decreased in the following order: Ce(Ⅳ)Th(Ⅳ)REs(Ⅲ). A solvent extraction process to extract and recover cerium and thorium from bastnasite leaching was proposed, in which the purities of cerium and thorium products reached 99.9% and 99% with yield of 92% and 98%, respectively.     

Application of Ce(IV) in industrial wastewater treatment

At present,rare earth application in wastewater treatment has become more and more widely,according to the fact that the Ce(IV) has the strong oxidation ability under acid condition,we have studied the application of Ce(IV) in industrial wastewater treatment originally.Results showed that oxidation-reduction reaction occurred between Ce(IV) and the organic compounds or other reducing substances in industrial wastewater,thereby the colority and CODcr reduced effectively.Ce(IV) formed [Ce(OH)x·nH2O](4-x)+ after hydrolyzation and Ce(III) obtained after Ce(IV) reduction formed [Ce(OH)x·nH2O](3-x)+ after hydrolyzation,these hydrate had big specific surface area,could adsorb the suspension substances and removed toxic or harmful ions in industrial wastewater.After treatment by Ce(IV),the analytical results of industrial wastewater are as follows:The CODcr became 58 mg/L from 1646 mg/L,the total COD removal efficiency was more than 95.0%.Turbidity reduced to no more than 10NTU from 87NTU.The chroma became 6 degree from 26 degree,suspension substances content decreased to no more than 2 mg/L from 36 mg/L,and total arsenic and fluorion became <0.05 mg/L and <0.10 mg/L from 0.60 and 15.3 mg/L.Total cadmium reduced to 0.01 mg/L from the 0.58 mg/L.These all indicated that Ce(IV) was one kind of latent good water treatment chemical.     

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.     

MATLAB simulation of preparation of Sm-loaded extractant directly from HEH（EHP）

Computer simulation of the preparation process loading rare earth(RE)directly from acidic extractant and RE chloride was established using MATLAB software.The mechanism of the extraction reaction was assumed,and then an experiment was conducted to confirm the mechanism and the apparent equilibrium constant of the reaction was determined as well.Owing to the involvement of H+ ion in the reaction between acidic extractant and RE chloride,the computer simulation of the process was more complicated than that of the extraction only between different rare earths.In the present work,MATLAB software was therefore introduced to handle the resolution of the complicated processing equation,and the simulation was performed by varying some key parameters including feed composition and phase ratio,etc.Consequently this work presented a simple method to simulate the H+ ion involved countercurrent extraction process of rare earths and also provided the practical references for the relative process designing.     

Optimization of parameters for cerium(Ⅲ) biosorption onto biowaste materials of animal and plant origin using 5-level Box-Behnken design: Equilibrium,kinetic, thermodynamic and regeneration studies

Response surface methodology(RSM) employing 5-level Box-Behnken design was used to optimize the biosorption of cerium(Ⅲ) onto biowaste materials of animal and plant origin viz. prawn carapace(PC) and corn style(CS). Various process parameters viz. pH(A: 3.0–9.0), biomass dosage(B: 0.05–0.35 g/L), initial metal concentration(C: 50–350 mg/L), contact time(D: 2–6 h) and temperature(E: 20–60 °C) were chosen for optimization. A log transformation was suggested by the Box-Cox plot in the present case. A low p-value of 0.0001 validated the significance of the model. Maximum Ce(Ⅲ) uptake of 218.3 mg/g for PC and 180.2 mg/g for CS was noted under optimum conditions. Among the equilibrium isotherms, Freundlich model was found to be the best fitted one suggesting a heterogeneous mode of biosorption on PC whereas Langmuir model showed the best fit suggesting homogeneous mode of cerium biosorption on CS. This was further confirmed by scanning electron microscopy(SEM). Kinetic studies showed better applicability of pseudo-first order model suggesting physisorption as phenomena underlying the process. Film-diffusion was suggested by the non-linearity of the Boyd plot. Thermodynamic studies showed that the process was endothermic and spontaneous. FTIR analysis confirmed a major involvement of the participation of amide, amines, ketones and primary alcohol groups during Ce(Ⅲ) biosorption. EDAX analysis confirmed the major participation of carbon group during Ce(Ⅲ) biosorption. This was the first report on parameter optimization of Ce(Ⅲ) biosorption onto biowaste materials using 5-level Box-Behnken experimental design which might be helpful for the recovery of Ce(Ⅲ) from aqueous environment.     

Adsorption of Ce（ Ⅳ ） Anionic Nitrato Complexes onto Anion Exchangers and Its Application for Ce （Ⅳ） Separation from Rare Earths （ Ⅲ ）

Ceriumis one of the cheapest[1]and most abun-dant rare earths (RE) .However ,high purityis usual-ly required for its utilization in industry , where it isusedfor sulfur control insteels ,pyrophoric alloys ,ce-ramic ,catalyst support ,polishing powders ,etc .In its minerals ,as well as in the spent nuclearfuel ,ceriumis accompanied by other RE.They basi-cally exist in solution as stable RE(Ⅲ) species ,which makes their mutual separation rather difficult .In contrast to other RE, Ce(Ⅲ) can…     

A hydrometallurgical method of energy saving type for separation of rare earth elements from rare earth polishing powder wastes with middle fraction of ceria

This study described a hydrometallurgical method to investigate the separation of rare earth elements(REEs)from rare earth polishing powder wastes(REPPWs)containing large amounts of rare earth oxides with a major phase of CeO_2 and minor phases of La_2O_3,Pr_2O_3,and Nd_2O_3 using a process devised by the authors.The suggested approach consisted of five processes:the synthesis of NaR E(SO_4)_2·xH_2O from rare earth oxides in Na_2SO_4-H_2SO_4-H_2 O solutions(Process 1),the conversion of NaR E(SO_4)_2·xH_2O into RE(OH)_3 using NaO H(Process 2),and the oxidation of Ce(OH)_3 into Ce(OH)_4 using air with O_2 injection(Process 3),followed by Processes 4 and 5 for separation of REEs by acid leaching using HCl and H_2SO_4,respectively.To confirm the high yield of NaR E(SO_4)_2·xH_2O in Process 1,experiments were carried out under various Na_2SO_4 concentrations(0.4–2.5 mol/L),sulfuric acid concentrations(6–14 mol/L),and reaction temperatures(95–125 oC).In addition,the effect of the pH value on the separation of Ce(OH)_4 in HCl-H_2 O solutions with Ce(OH)_4,La-,Pr-,and Nd(OH)_3 in Process 4 was also investigated.On the basis of above results,the possibility of effective separation of REEs from REPPWs could be confirmed.     

Extraction mechanism of cerium（Ⅳ） in H2SO4/H3PO4 system using bifunctional ionic liquid extractants

The extraction of Ce（Ⅳ） in H2SO4/H3PO4 system was investigated systematically using bifunctional ionic liquid extractants（Bif-ILES） [A336][P507],[A336][P204] and [A336][C272] in n-heptane.The effects of H2SO4 concentration,extractant concentration and salting-out agent concentration were observed in detail.The extraction mechanism of Ce（Ⅳ） in H2SO4/H3PO4 system was obtained.The comparison with other extractants such as Cyanex923,TBP was also studied.Thermodynamic functions of the extraction reaction were calculated,showing that the extraction was an exothermic process.The separation of Ce（Ⅳ） from RE（Ⅲ） and Th（Ⅳ） was also investigated.The result indicated that Ce（Ⅳ） could be selectively extracted in this system.CePO4 nanoparticles were obtained in the process of stripping using H2O2 in H2SO4/H3PO4 system.X-ray diffraction（XRD）,scanning electron microscopy（SEM） and spectroscopy were adopted for the characterization of the sample.     

Solvent extraction and separation of light rare earth elements (La,Pr and Nd) in the presence of lactic acid as a complexing agent by Cyanex 272 in kerosene and the effect of citric acid,acetic acid and Titriplex Ⅲ as auxiliary agents

At present, the use of rare earth elements(REEs) has become an inevitable necessity in many modern industries. In general, liquid extraction is the best commercial method for extracting REEs due to its ability to control high volumes of liquids with electrical load. With the aim of improving a separation technology that would be superior to the existing extraction systems, the extraction behaviors of La(Ⅲ),Pr(Ⅲ), and Nd(Ⅲ) from an HCI medium with Cyanex 272 in the presence of the complexing agent lactic acid(HLac) and auxiliary agents citric acid(H_3 Cit), acetic acid(HAc), and Titriplex Ⅲ have been reported.The effect of pH and lactic acid concentration has been examined. The use of lactic acid as a complexing agent leading to a high extraction of REEs with Cyanex 272 at pH = 5 was compared with systems without lactic acid. The results show that the use of acetic acid along with lactic acid leads to an increase in the extraction percentage of LREEs. While use of citric acid and Titriplex Ⅲ reduces the extraction percentage of LREEs. Finally, the presence of Titriplex Ⅲ together with lactic acid could lead to an increase in the separation factor of Pr and Nd.     

Iron recovery and rare earths enrichment from Bayan Obo tailings using Coal-Ca(O H)2-NaO H roasting followed by magnetic separation

The recovery of iron and enrichment of rare earths from Bayan Obo tailings were investigated using CoalCa(OH)_2-NaOH roasting followed by magnetic separation.The influences of roasting temperature,roasting time,coal content,milling time,Ca(OH)_2 dosage and NaOH dosage on the iron and rare earths recovery were explored.The results showed that the magnetic concentrate containing 70.01 wt.% Fe with the iron recovery of 94.34% and the tailings of magnetic separation containing 11.46 wt.%rare earth oxides(REO)with the REO recovery of 98.19% were obtained under the optimum conditions(i.e.,roasting temperature of 650°C,roasting time of 60 min,coal content of 2.0%,milling time of 5 min,and NaOH dosage of 2.0%).The Ca(OH)_2 dosage had no effect on the separation of iron and rare earths.According to the mineralogical and morphologic analysis,the iron and rare earths of Bayan Obo tailings could be utilized in subsequent ironmaking process and hydrometallurgy process.     

Precipitation transformation of rare earth sulfate into chloride with p-dodecylphenoxy carboxylic acids

Methods for transforming rare earth(RE) sulfate into chloride mainly include extraction process with organophosphonic mono-acids or aliphatic acids and precipitation process with ammonium bicarbonate(NH_4 HCO_3).In this paper,alkylphenoxy carboxylic acids(HAs) ofp-dodecylphenoxy acetic acid(HA-Ⅰ),pdodecylphenoxypropanoic acid(HA-Ⅱ) and p-dodecylphenoxybutyric acid(HA-Ⅲ),which were liquid at room temperature were synthesized and characterized.The precipitation mechanisms of RE elements with the HAs were investigated and the HA/RE molar ratios of the solid complexes were determined as3:1 by equi-molar series method which accord with the principle of charge balance.Applicability of HAs for the transformation of RE sulfate from concentrated sulfuric acid roasted RE concentrate into chloride via precipitation method was discussed.100% HA-Ⅱ was selected as the liquid organic precipitant without dilution of volatile solvent soracceleration of phase separation by phase-modifiers.The RE sulfate solution can be precipitated by HA-Ⅱ after neutralization with liquid NaOH and stripped with concentrated HCl at room temperature.High concentration of RE chloride of 218.1 g/L with low residue of sulfate radical of 0.536 g/L was obtained.The residual organic precipitant in the raffinate solution was tested to be lower than 8 mg/L at 25℃and the chemical oxygen demand(COD) in wastewater was less than 50 mg/L.