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Extraction and stripping of rare earths using mixtures of acidic phosphorus-based reagents
JOURNAL OF RARE EARTHS, Vol. 29, No. 5, May 2011, P. 413
Extraction and stripping of rare earths using mixtures of acidic phosphorusbased reagents WANG Xianglan (⥟佭݄)1, LI Wei (ᴢ㭛)2, LI Deqian (ᴢᖋ䇺)3 (1. Department of Chemistry and Environmental Engineering, Wuhan Bioengineering Institute, Wuhan 430415, China; 2. School of Environmental and Bioengineering, Liaoning Shihua University, Fushun 113001, China; 3. State Key Lab of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China) Received 10 October 2010; revised 30 December 2010
Abstract: Studies were carried out on the extraction characters of trivalent rare earths from chloride solutions using organophosphorus acids 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (HEHEHP) combined with [di-(2-ethylhexyl)-phosphoric acid (HDEHP), isopropylphosphonic acid 1-hexyl-4-ethyloctyl ester (HHEOIPP), bis(2,4,4-trimethylpentyl)-phosphinic acid (Cyanex 272), bis(2,4,4-trimethypentyl)-monothiophosphinic acid (Cyanex 302) or bis(2,4,4-trimethypentyl)-dithiophosphinic acid (Cyanex 301)] as extractants. The effect of the equilibrium aqueous acidity on the extraction was studied. According to the corresponding separation factors for adjacent pairs of rare earths, it could be concluded that HEHEHP and Cyanex 272 could be employed for the separation of Tm(III), Yb(III), Lu(III) from the other rare earths. Taking Yb(III) as an example, based on the different stripping acid, the potential of the stripping was estimated. Keywords: extraction characters; trivalent rare earths; mixtures of acidic phosphorus-based reagents
With increasing demands for rare earths (REs) and their compounds, the separation and purification of them have gained considerable importance in recent years. The separation of the natural RE mixtures into the individual elements is very difficult to achieve due to the similar characters between the adjacent rare earths. Organophosphinic acids reagents have been used as extractants in this field for several years and attracted much attention[1–6]. Organophosphorus acids di-(2-ethylhexyl)-phosphoric acid (HDEHP) is one of the most extensively investigated extractants in the separation of rare earths. In recent years, studies have also been carried out with 2-ethylhexylphosphonic acid mono-(2ethylhexyl) ester (HEHEHP) in view of some of its advantages compared to DEHPA, such as higher separation factors and easier stripping[7]. Isopropylphosphonic acid 1-hexyl-4ethyloctyl ester (HHEOIPP) is a newly developed extractant with pKa value of 5.49, which has been used to extract transition metals and rare earths[8]. The extraction of REs with Cyanex extractants has attracted much attention[6,9–19]. Cyanex 302 exhibited favourable behavior in the extraction separation heavy lanthanids(Gd-Lu)[17,18]. The extraction of Sc(III), Th(IV), Fe(III) and Lu(III) with Cyanex 272 from sulphuric acid has been reported[19]. The practical application of these Cyanex reagents is strongly affected by their insufficient extractability and their low loading capacity for REs resulting from the low lipophilicity of the coordination compounds formed during ex-
traction. Growing attention is being paid to the development of new extraction systems for the separation of them as a group or from one another. This paper reported the extraction of rare earths from chloride solutions with organophosphorus reagents mixtures composed of two kinds of extractants such as HEHEHP and HDEHP, HEHEHP and HHEOIPP, HEHEHP and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272), HEHEHP and bis(2,4,4trimethypentyl)-monothiophosphinic acid (Cyanex 302), HEHEHP and bis(2,4,4-trimethypentyl)-dithiophosphinic acid (Cyanex 301)], which has not been reported so far. The possibility of separating REs with the mixing system was also discussed.
1 Experimental 1.1 Reagents and apparatus HDEHP and HEHEHP were obtained from Jiangxi Fengxin Chemistry Reagent Plant of China; HHEOIPP was provided by Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences; Cyanex 272, Cyanex 302 and Cyanex 301 were kindly supplied by CYTEC Canada Inc. All extractants were used without further purification and dissolved in heptane to the required concentration. The extraction experiments were measured at a ratio of HEHEHP to another extractant of 40 to 60.
Foundation item: Project supported by the Science and Technology Research Project of Hubei Provincial Department of Education (B20094007) and Wuhan Municipal Institutions of Scientific Project (2008K018) Corresponding author: LI Deqian (E-mail: [email protected]; Tel.: +86-431-85262036) DOI: 10.1016/S1002-0721(10)60470-X
414
JOURNAL OF RARE EARTHS, Vol. 29, No. 5, May 2011
Stock solutions of rare earths were prepared from their oxides (99.99%) by dissolving in concentrated hydrochloric acid and diluting with distilled water. The metal ions were analyzed by titration with a standard solution of EDTA with xylenol orange as indicator. NaCl (1.0 mol/L) was used to maintain the constant ionic strength. All the other chemicals used were of analytical grade. A PHS-3 digital pH meter (Shanghai Rex Instrument Factory) was used for pH measurements. 1.2 Solvent extraction procedures Distribution ratios were determined by shaking equal volumes of aqueous and organic phase for 30 min at 293±1 K, which was sufficient to attain equilibrium. After phases separation, the concentration of the rare earths in the aqueous phase was determined by titration with EDTA and that in the organic phase by difference. The concentration was used to obtain the distribution ratio D, where D =
[RE]o [RE]a
. The pH of
the aqueous phase at equilibrium was measured after phase separation.
2 Results and discussion 2.1 Extraction behavior The extraction behavior of rare earths (Dy3+, Ho3+, Y3+, Er , Tm3+, Yb3+, Lu3+) using HEHEHP and Cyanex 272 from hydrochloric acid solutions is shown in Fig. 1. The percentage extraction of rare earths decreases in the order: Lu3+>Yb3+>Tm3+>Er3+ >Y3+>Ho3+>Dy3+. It is clear that the extractabilities of these lanthanides increase with atomic number, presumably as a result of the increase in strength of the electrostatic interaction between the extractant anion and the lanthanide cation as the size of the latter decreases. The extraction of Y3+ lies between that of Ho3+ and Er3+, as would be expected on the basis of its cationic radii. A similar trend has been observed of rare earth from nitrate media with bis(2,4,4-trimethylpentyl)phosphinic acid in xylene as an extractant[6]. The order of extractability can also be explained 3+
by HSAB theory[3]. Rare earth ions are hard acids while HEHEHP is a hard base. The smaller the ionic radius, the harder the rare earth elements ion which results in the increasing extraction ability with decreasing ionic radius of the lanthanide ions. The extractability of HEHEHP/HHEOIPP system was between that of HEHEHP/HDEHP and HEHEHP/Cyanex 272 system, which was consistent with their order of increasing pKa: HDEHP
Fig. 1 Plots of the lgD for REs as a function of the aqueous phase pH ([HEHEHP]o+[Cyanex 272]o=1.5 mol/L, [RE3+]=0.2 mol/L) Dy3+ (R2=0.97); ŸHo3+(R2=0.98); δY3+(R2=0.99); ƹ Er3+ (R2=0.98); Ŷ Tm3+(R2=0.99);¨ Yb3+ (R2 = 0.99);—Lu3+(R2=0.99)
Ho/Dy
Y/Ho
Er/Y
Tm/Er
Yb/Tm
Lu/Yb
HEHEHP+Cyanex272 1.32
1.12
1.82
2.65
3.05
1.60
HEHEHP
1.77
1.65
1.53
1.33
2.50
1.17
Cyanex 272 [6]
2.23
1.61
1.20
2.66
2.40
1.32
WANG Lanxiang et al., Extraction and stripping of rare earths using mixtures of acidic phosphorus-based reagents
Fig. 2 Stripping behavior of Yb3+ from loaded mixtures of acidic phosphorus-based reagents as a function of aqueous HCl ([Yb3+]o=0.20 mol/L)
promising possibility to produce high purity rare earths from hydrochloric solutions.
3 Conclusions The extraction and stripping behavior of rare earths using mixtures of acidic phosphorus-based reagents were carried out. Extraction of metal ions increased with the increasing aqueous phase pH, which was discussed based on the HSAB theory. The addition of Cyanex 272 to HEHEHP extraction system provided better stripping performance in comparison with dividual extractant toward aqueous HCl.
References: [1] Peppard D F, Ferraro J R. The preparation and infra-red absorption spectra of several complexes of bis-(2-ethylhexyl)phosphoric acid. J. Inorg. Nucl. Chem., 1959, 10: 275. [2] Mason G W, Lewey S, Peppard D F. Extraction of metallic cations by mono-acidic orthophosphate esters in a monomerizing diluent. J. Inorg. Nucl. Chem., 1964, 26: 2271. [3] Li D Q, Wan X, Lin D Z, Xie Y F, Lin S X, Wang Z H, Li H, Ji E Y. Extraction separation of rare earth elements, scandium and thorium with 2-ethylhexyl-phosphonic acid mono-2ethylhexyl ester. Proc. ISEC'80 Liege Belgium, 1980, 3: 80. [4] Cyanex 272, Cyanex 302, Cyanex 301. Technical Brochures. Cytec Industries, Inc. West Paterson, New Jersey. [5] Komatsu Y, Freiser H. Extraction separation of tervalent lanthanide metals with bis(2,4,4-trimethylpentyl)phosphinic acid. Anal. Chim. Acta, 1989, 227: 397. [6] Zhang X F, Li D Q. Extraction of rare earth ions(III) with
415
bis(2,4,4-trimethylpentyl)phosphinic acid. Chin. J. Appl. Chem., 1993, 10(4): 72. [7] Xu G X. Rare earths: Vol. 1 (2nd Ed., in Chin.). Beijing: Metallurgy Industry Press, 1995. 525. [8] Lu J. Ph.D. Thesis, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 1998. [9] Wang X L, Li W, Meng S L, Li D Q. The extraction of rare earths using mixtures of acidic phosphorus-based reagents or their thio-analogues. J. Chem. Technol. Biotechnol., 2006, 81: 761. [10] Jensen M P, Bond A H. Influence of aggregation on the extraction of trivalent lanthanide and actinide cations by purified Cyanex272, Cyanex301, and Cyanex302. Radiochim. Acta, 2002, 90: 205. [11] Tian G X, Kimura T, Yoshida Z, Zhu Y J, Rao L F. Fluorescence and IR studies on the hydration state of lanthanides(III) and curium(III) in the complexes extracted with purifiedCyanex301, Cyanex302 and Cyanex272. Radiochim. Acta., 2004, 92: 495. [12] Peng Y B, Chen J. Extraction of Am3+ and Eu3+ from different aqueous media by bis(2,4,4-trimethyl) dithio phosphinic acid. J. Nucl. Radiochem., 2006, 28: 178. [13] Law J D, Peterman D R, Todd T A, Tillotson R D. Separation of trivalent actinides from lanthanides in an acetate buffer solution using Cyanex301. Radiochim. Acta, 2006, 94: 261. [14] Bhattacharyya A, Mohapatra P K, Ansari S A, Raut D R, Manchanda V K. Separation of trivalent actinides from lanthanides using hollow fiber supported liquid membrane containing Cyanex-301 as the carrier. J. Membr. Sci., 2008, 312: 1. [15] Bhattacharyya A, Mohapatra P K, Manchanda V K. Solvent extraction and extraction chromatographic separation of Am3+ and Eu3+ from nitrate medium using Cyanex (R) 301. Solven Extr. Ion Exch., 2007, 25: 27. [16] Jia Qiong, Tong Shanshan, Li Zhiying, Zhou Weihong, Li Hongfei, Meng Shulan. Solvent extraction of rare earth elements with mixtures of sec-octylphenoxy acetic acid and bis(2,4,4-trimethylpentyl) dithiophosphinic acidSeparation and Purification Technology, 2009, 64: 345. [17] Sole K C, Hiskey J B. Solvent extraction characteristic of thiosubstituted organophosphinic acid extractants. Hydrometallurgy, 1992, 30: 345. [18] Li D Q, Luo A Q, Wang C, Yuan M. Solvent extraction of trivalent lanthanides with Cyanex 302 from acidic aqueous chloride solutions, in Value Adding Through Solvent Extraction, Proc. ISEC’96. Shallcross D C, Paimin Rand Prvcic L M, Ed.. University of Melbourne, 1996, Vol. 1: 165. [19] Komatsu Y, Freiser H. Extraction separation of tervalent lanthanide metals with bis(2,4,4-trimethylpentyl)phosphinic acid. Anal. Chim. Acta, 1989, 227: 397.
Extraction and stripping of rare earths using mixtures of acidic phosphorusbased reagents WANG Xianglan (⥟佭݄)1, LI Wei (ᴢ㭛)2, LI Deqian (ᴢᖋ䇺)3 (1. Department of Chemistry and Environmental Engineering, Wuhan Bioengineering Institute, Wuhan 430415, China; 2. School of Environmental and Bioengineering, Liaoning Shihua University, Fushun 113001, China; 3. State Key Lab of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China) Received 10 October 2010; revised 30 December 2010
Abstract: Studies were carried out on the extraction characters of trivalent rare earths from chloride solutions using organophosphorus acids 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (HEHEHP) combined with [di-(2-ethylhexyl)-phosphoric acid (HDEHP), isopropylphosphonic acid 1-hexyl-4-ethyloctyl ester (HHEOIPP), bis(2,4,4-trimethylpentyl)-phosphinic acid (Cyanex 272), bis(2,4,4-trimethypentyl)-monothiophosphinic acid (Cyanex 302) or bis(2,4,4-trimethypentyl)-dithiophosphinic acid (Cyanex 301)] as extractants. The effect of the equilibrium aqueous acidity on the extraction was studied. According to the corresponding separation factors for adjacent pairs of rare earths, it could be concluded that HEHEHP and Cyanex 272 could be employed for the separation of Tm(III), Yb(III), Lu(III) from the other rare earths. Taking Yb(III) as an example, based on the different stripping acid, the potential of the stripping was estimated. Keywords: extraction characters; trivalent rare earths; mixtures of acidic phosphorus-based reagents
With increasing demands for rare earths (REs) and their compounds, the separation and purification of them have gained considerable importance in recent years. The separation of the natural RE mixtures into the individual elements is very difficult to achieve due to the similar characters between the adjacent rare earths. Organophosphinic acids reagents have been used as extractants in this field for several years and attracted much attention[1–6]. Organophosphorus acids di-(2-ethylhexyl)-phosphoric acid (HDEHP) is one of the most extensively investigated extractants in the separation of rare earths. In recent years, studies have also been carried out with 2-ethylhexylphosphonic acid mono-(2ethylhexyl) ester (HEHEHP) in view of some of its advantages compared to DEHPA, such as higher separation factors and easier stripping[7]. Isopropylphosphonic acid 1-hexyl-4ethyloctyl ester (HHEOIPP) is a newly developed extractant with pKa value of 5.49, which has been used to extract transition metals and rare earths[8]. The extraction of REs with Cyanex extractants has attracted much attention[6,9–19]. Cyanex 302 exhibited favourable behavior in the extraction separation heavy lanthanids(Gd-Lu)[17,18]. The extraction of Sc(III), Th(IV), Fe(III) and Lu(III) with Cyanex 272 from sulphuric acid has been reported[19]. The practical application of these Cyanex reagents is strongly affected by their insufficient extractability and their low loading capacity for REs resulting from the low lipophilicity of the coordination compounds formed during ex-
traction. Growing attention is being paid to the development of new extraction systems for the separation of them as a group or from one another. This paper reported the extraction of rare earths from chloride solutions with organophosphorus reagents mixtures composed of two kinds of extractants such as HEHEHP and HDEHP, HEHEHP and HHEOIPP, HEHEHP and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272), HEHEHP and bis(2,4,4trimethypentyl)-monothiophosphinic acid (Cyanex 302), HEHEHP and bis(2,4,4-trimethypentyl)-dithiophosphinic acid (Cyanex 301)], which has not been reported so far. The possibility of separating REs with the mixing system was also discussed.
1 Experimental 1.1 Reagents and apparatus HDEHP and HEHEHP were obtained from Jiangxi Fengxin Chemistry Reagent Plant of China; HHEOIPP was provided by Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences; Cyanex 272, Cyanex 302 and Cyanex 301 were kindly supplied by CYTEC Canada Inc. All extractants were used without further purification and dissolved in heptane to the required concentration. The extraction experiments were measured at a ratio of HEHEHP to another extractant of 40 to 60.
Foundation item: Project supported by the Science and Technology Research Project of Hubei Provincial Department of Education (B20094007) and Wuhan Municipal Institutions of Scientific Project (2008K018) Corresponding author: LI Deqian (E-mail: [email protected]; Tel.: +86-431-85262036) DOI: 10.1016/S1002-0721(10)60470-X
414
JOURNAL OF RARE EARTHS, Vol. 29, No. 5, May 2011
Stock solutions of rare earths were prepared from their oxides (99.99%) by dissolving in concentrated hydrochloric acid and diluting with distilled water. The metal ions were analyzed by titration with a standard solution of EDTA with xylenol orange as indicator. NaCl (1.0 mol/L) was used to maintain the constant ionic strength. All the other chemicals used were of analytical grade. A PHS-3 digital pH meter (Shanghai Rex Instrument Factory) was used for pH measurements. 1.2 Solvent extraction procedures Distribution ratios were determined by shaking equal volumes of aqueous and organic phase for 30 min at 293±1 K, which was sufficient to attain equilibrium. After phases separation, the concentration of the rare earths in the aqueous phase was determined by titration with EDTA and that in the organic phase by difference. The concentration was used to obtain the distribution ratio D, where D =
[RE]o [RE]a
. The pH of
the aqueous phase at equilibrium was measured after phase separation.
2 Results and discussion 2.1 Extraction behavior The extraction behavior of rare earths (Dy3+, Ho3+, Y3+, Er , Tm3+, Yb3+, Lu3+) using HEHEHP and Cyanex 272 from hydrochloric acid solutions is shown in Fig. 1. The percentage extraction of rare earths decreases in the order: Lu3+>Yb3+>Tm3+>Er3+ >Y3+>Ho3+>Dy3+. It is clear that the extractabilities of these lanthanides increase with atomic number, presumably as a result of the increase in strength of the electrostatic interaction between the extractant anion and the lanthanide cation as the size of the latter decreases. The extraction of Y3+ lies between that of Ho3+ and Er3+, as would be expected on the basis of its cationic radii. A similar trend has been observed of rare earth from nitrate media with bis(2,4,4-trimethylpentyl)phosphinic acid in xylene as an extractant[6]. The order of extractability can also be explained 3+
by HSAB theory[3]. Rare earth ions are hard acids while HEHEHP is a hard base. The smaller the ionic radius, the harder the rare earth elements ion which results in the increasing extraction ability with decreasing ionic radius of the lanthanide ions. The extractability of HEHEHP/HHEOIPP system was between that of HEHEHP/HDEHP and HEHEHP/Cyanex 272 system, which was consistent with their order of increasing pKa: HDEHP
Fig. 1 Plots of the lgD for REs as a function of the aqueous phase pH ([HEHEHP]o+[Cyanex 272]o=1.5 mol/L, [RE3+]=0.2 mol/L) Dy3+ (R2=0.97); ŸHo3+(R2=0.98); δY3+(R2=0.99); ƹ Er3+ (R2=0.98); Ŷ Tm3+(R2=0.99);¨ Yb3+ (R2 = 0.99);—Lu3+(R2=0.99)
Ho/Dy
Y/Ho
Er/Y
Tm/Er
Yb/Tm
Lu/Yb
HEHEHP+Cyanex272 1.32
1.12
1.82
2.65
3.05
1.60
HEHEHP
1.77
1.65
1.53
1.33
2.50
1.17
Cyanex 272 [6]
2.23
1.61
1.20
2.66
2.40
1.32
WANG Lanxiang et al., Extraction and stripping of rare earths using mixtures of acidic phosphorus-based reagents
Fig. 2 Stripping behavior of Yb3+ from loaded mixtures of acidic phosphorus-based reagents as a function of aqueous HCl ([Yb3+]o=0.20 mol/L)
promising possibility to produce high purity rare earths from hydrochloric solutions.
3 Conclusions The extraction and stripping behavior of rare earths using mixtures of acidic phosphorus-based reagents were carried out. Extraction of metal ions increased with the increasing aqueous phase pH, which was discussed based on the HSAB theory. The addition of Cyanex 272 to HEHEHP extraction system provided better stripping performance in comparison with dividual extractant toward aqueous HCl.
References: [1] Peppard D F, Ferraro J R. The preparation and infra-red absorption spectra of several complexes of bis-(2-ethylhexyl)phosphoric acid. J. Inorg. Nucl. Chem., 1959, 10: 275. [2] Mason G W, Lewey S, Peppard D F. Extraction of metallic cations by mono-acidic orthophosphate esters in a monomerizing diluent. J. Inorg. Nucl. Chem., 1964, 26: 2271. [3] Li D Q, Wan X, Lin D Z, Xie Y F, Lin S X, Wang Z H, Li H, Ji E Y. Extraction separation of rare earth elements, scandium and thorium with 2-ethylhexyl-phosphonic acid mono-2ethylhexyl ester. Proc. ISEC'80 Liege Belgium, 1980, 3: 80. [4] Cyanex 272, Cyanex 302, Cyanex 301. Technical Brochures. Cytec Industries, Inc. West Paterson, New Jersey. [5] Komatsu Y, Freiser H. Extraction separation of tervalent lanthanide metals with bis(2,4,4-trimethylpentyl)phosphinic acid. Anal. Chim. Acta, 1989, 227: 397. [6] Zhang X F, Li D Q. Extraction of rare earth ions(III) with
415
bis(2,4,4-trimethylpentyl)phosphinic acid. Chin. J. Appl. Chem., 1993, 10(4): 72. [7] Xu G X. Rare earths: Vol. 1 (2nd Ed., in Chin.). Beijing: Metallurgy Industry Press, 1995. 525. [8] Lu J. Ph.D. Thesis, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 1998. [9] Wang X L, Li W, Meng S L, Li D Q. The extraction of rare earths using mixtures of acidic phosphorus-based reagents or their thio-analogues. J. Chem. Technol. Biotechnol., 2006, 81: 761. [10] Jensen M P, Bond A H. Influence of aggregation on the extraction of trivalent lanthanide and actinide cations by purified Cyanex272, Cyanex301, and Cyanex302. Radiochim. Acta, 2002, 90: 205. [11] Tian G X, Kimura T, Yoshida Z, Zhu Y J, Rao L F. Fluorescence and IR studies on the hydration state of lanthanides(III) and curium(III) in the complexes extracted with purifiedCyanex301, Cyanex302 and Cyanex272. Radiochim. Acta., 2004, 92: 495. [12] Peng Y B, Chen J. Extraction of Am3+ and Eu3+ from different aqueous media by bis(2,4,4-trimethyl) dithio phosphinic acid. J. Nucl. Radiochem., 2006, 28: 178. [13] Law J D, Peterman D R, Todd T A, Tillotson R D. Separation of trivalent actinides from lanthanides in an acetate buffer solution using Cyanex301. Radiochim. Acta, 2006, 94: 261. [14] Bhattacharyya A, Mohapatra P K, Ansari S A, Raut D R, Manchanda V K. Separation of trivalent actinides from lanthanides using hollow fiber supported liquid membrane containing Cyanex-301 as the carrier. J. Membr. Sci., 2008, 312: 1. [15] Bhattacharyya A, Mohapatra P K, Manchanda V K. Solvent extraction and extraction chromatographic separation of Am3+ and Eu3+ from nitrate medium using Cyanex (R) 301. Solven Extr. Ion Exch., 2007, 25: 27. [16] Jia Qiong, Tong Shanshan, Li Zhiying, Zhou Weihong, Li Hongfei, Meng Shulan. Solvent extraction of rare earth elements with mixtures of sec-octylphenoxy acetic acid and bis(2,4,4-trimethylpentyl) dithiophosphinic acidSeparation and Purification Technology, 2009, 64: 345. [17] Sole K C, Hiskey J B. Solvent extraction characteristic of thiosubstituted organophosphinic acid extractants. Hydrometallurgy, 1992, 30: 345. [18] Li D Q, Luo A Q, Wang C, Yuan M. Solvent extraction of trivalent lanthanides with Cyanex 302 from acidic aqueous chloride solutions, in Value Adding Through Solvent Extraction, Proc. ISEC’96. Shallcross D C, Paimin Rand Prvcic L M, Ed.. University of Melbourne, 1996, Vol. 1: 165. [19] Komatsu Y, Freiser H. Extraction separation of tervalent lanthanide metals with bis(2,4,4-trimethylpentyl)phosphinic acid. Anal. Chim. Acta, 1989, 227: 397.