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.
The current recovery technique of Sc was complicated and the chemical consumption was high,This was due to the low content of Sc in resources and the difficulty of stripping.In this research,the isooctanol was added into the 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester(P507)extraction system to reduce the extraction and improve the stripping of Sc.The maximum stripping ratio of Sc from loaded organic phase by sulfuric acid can increase from 10%(without isooctanol)to 99%(with 15 vol%isooctanol).In the extraction test of the simulated red mud leaching liquor,the separation factors between Sc and Zr,Sc and Ti are 36 and 350,separately.At the same time,other metals are almost not extracted.The high selectivity and stripping of Sc suggest that the P507 with isooctanol extraction system can be applied in the practical Sc recovery process.
Chuanying LiuLi ChenJi ChenDan ZouYuefeng DengDeqian Li
The separation method of changeable valence RE element of cerium （Ce） was reviewed in this paper. Solvent extraction is the most effective and efficient method to separate Ce（IV） from RE（III）, usually accompanied with fluorine （F） and phosphor （P） from bastnaesite and monazite etc. By roast or wet-air oxidation, Ce（III） of bastnaesite and monazite was oxidized into Ce（IV）, and Cyanex923 and [A336][P507] have been investigated to co-extract and recover Ce（IV）, F and P from H2SO4 leaching liquor, leading to favorable conditions for the subsequent separation of Th（IV） and RE（III）. The interaction of Ce（IV） and F and/or P enhances the roasting, leaching and extraction of Ce（IV） due to increasing of the stability of Ce（IV）, and the formation of CeF3 and CePO4 after reductive stripping will benefit the utilization of F and P. For dealing with RE ores of high-content Ce, the clean process of oxidation roasting and Ce（IV）-F separation for Sichuan bastnaesite highlights the advantages of Ce（IV） based clean technique, which firstly demonstrates the comprehensive utilization of Ce（IV）, Th（IV）, F and RE（III） and prevention of environmental pollution from fountainhead. A preliminary flowsheet of two-step oxidation and extraction of Ce（IV） for Bayan Obo mixed ores was further proposed to process the oxidation and extraction of Ce（IV） in presence of both F and P, indicating the possibility of similar effects with clean process of Sichuan bastnaesite. Ce（IV） separation chemistry and clean technique will open up new realms for light RE resources utilization, meeting“Emission Standards of Pollutants from Rare Earths Industry”promulgated by China’s Ministry of Environment Protection （MOP） in 2011.
The extraction kinetics of Ce（Ⅳ） and Ce（Ⅳ）-F^- mixture systems from sulfuric solutions to n-heptane solution containing Bif-ILE[A336][P204]（[trialkylmethylammonium][di-2-ethylhewanxylphosphinate]） with a constant interfacial area cell with laminar flow were studied,just to elucidate the extraction mechanism and the mass transfer models.The data were analyzed in terms of pseudo-first-order constants.The effects of stirring speed,specific interfacial area and temperature on the extraction rate in both systems were discussed,suggesting that the extractions were mixed bulk phases-interfacial control process.Supported by the experimental data,the corresponding rate equations for Ce（Ⅳ） extraction system and Ce（Ⅳ）-F^- mixture extraction system were obtained.The experimental results indicated the rate-controlling step.The kinetics model was deduced from the rate-controlling step and consistent with the rate equation.
N-methylimidazolium functionalized anion exchange resin in NO3 form （RNO3） was prepared and used for adsorption of Ce（Ⅳ） in nitric acid medimn. The adsorption amount increased with shaking time increasing and the adsorption equilibrium was obtained within 180 rain. Ce（Ⅳ） was partially reduced to Ce（Ⅲ） and the reduction percent of Ce（Ⅳ） increased with shaking time increasing. But RNO3 was more stable than other resins due to the high resistance to oxidation. A little increase of adsorption amount was found with concentration of HNO3 increasing. However, the reduction percent of Ce（Ⅳ） decreased with the increase of HNO3 concentration. The addition of NaNO3 decreased the adsorption amount of Ce（Ⅳ） on RNO3 due to the competitive anion exchange reaction. Ce（Ⅳ） was adsorbed on RNO3 in the form of Ce（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.
The extraction kinetics of La(III) from aqueous chloride solutions into n-heptane solutions of bifunctional ionic liquid extractant [A336][CA-12](tricaprylmethylammonium sec-octylphenoxy acetic acid) was investigated using a constant interfacial cell with laminar flow. The effects of stirring speed, temperature and specific interfacial area on the extraction rate were examined. The results indicate that mass transfer kinetics of La(III) is a mixed-controlled process influenced by interfacial reaction. On the basis of mass transfer kinetic results in the extraction of La(III) by [A336][CA-12], the extraction rate equation of La(III) is proposed in terms of pseudo-firstorder constants, which is supported by the measured thermodynamic equations. The mass-transfer kinetic model deduced from the rate controlling step is adequate to interpret the experimental data qualitatively.
A new kind of hydrophobic ionic liquids [1-alkyl-3-（1-carboxylpropyl）im][PF6] has been synthesized, and their extraction.properties for Y（III） in the nitric acid medium was also investigated. The effects of extractant concentration, equilibrium pH of aqueous phase, salt concentration, temperature etc. were discussed. The results show that this kind of Task-Specific Ionic Liquid （TSIL） needs to be saponified before being used for the Y（III） extraction, and the extraction is-acid dependent,-and the extraction efficiency increases with the aqueous phase acldity decreasing. Furthermore, the loaded organic phase is easy to be stripped; more than 95% Y（III） could be stripped from the loaded organic phase when the stripping acidity is higher than 0.07 mol-L-1. The slope analysis technique is used to investigate the extraction mechanism, and a possible cation-exchange extraction mechanism is proposed in the oresent extraction system.
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_(3)BO_(3)-H_(2)SO_(4)system using Cyanex 923.Extraction equilibrium process of different systems,including HF-H_(2)SO_(4),H_(3)BO_(3)-HF-H_(2)SO_(4),and Ce(Ⅳ)-HF-H_(2)SO_(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_(3)BO_(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_(2)SO_(4)was further determined.Besides,the effect of H_(3)BO_(3)on the extraction and stripping of Ce(Ⅳ)in complicated system was studied.Moreover,it shows that the addition of H_(3)BO_(3)has nothing to do with the purity of obtained CeF_(3)particle from bastneasite liquor in the practical system.Adding H_(3)BO_(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.
Knowledge of the solubilization behaviors of rare-earth-extractant complex is mandatory for full comprehension of interfacial phenomenon and intermediate state of rare earth（RE） ion transport from water to oil during solvent extraction. The lutetium with 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester（P507） extraction system was explored as a case study for the solubilization behaviors in this paper. With a quantitative analysis of a white crud obtained in the practical process, the results demonstrate that the insoluble REL3（L = the anion of P507） complex enriches at the oil/water interface and forms the network polymers. Besides, with the increase of RE loading ratios in the oil phase, the interfacial tension increases while the free ligand in the bulk phase decreases, which results in the flocculation of REL3 complex and the formation of polymers at the interface. Furthermore,the properties of the oil phase and the interface reveal that the free ligand can solubilize the REL3 complex along with the transfer of water from microemulsion to aqueous phase. In addition, the change of aqueous acidity can regulate the solubilization behaviors of the interfacial complex to improve RE extraction efficiency. These fundamental studies will hopefully provide new insights into the solubilization of metal-extractant complex and a technical guidance to the transfer of RE from water to oil.
Wenrou SuJi ChenYu JingChuanying LiuYuefeng DengMaohua Yang
