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Liquid–liquid extraction of yttrium using primene-JMT from acidic sulfate solutions
Hydrometallurgy 96 (2009) 313–317
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Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / h y d r o m e t
Liquid–liquid extraction of yttrium using primene-JMT from acidic sulfate solutions O.A. Desouky a,⁎, A.M. Daher a, Y.K. Abdel-Monem b, A.A. Galhoum a a b
Nuclear Materials Authority, P.O. Box 530, El-Maadi, Cairo, Egypt Chemistry Department, Faculty of Science, Minoufia University, Shabin El-Kom, Minoufia, Egypt
a r t i c l e
i n f o
Article history: Received 3 September 2008 Received in revised form 20 November 2008 Accepted 21 November 2008 Available online 6 December 2008 Keywords: Liquid–liquid extraction Yttrium Primene-JMT Extraction isotherm
a b s t r a c t The liquid–liquid extraction of yttrium(III) from sulfate medium using primene-JMT is investigated with regard to extractant concentration, diluent type, equilibrium pH and time, temperature, and extraction isotherm. Aliphatic kerosene diluents were preferred compared to aromatic diluents because of higher extraction, shorter equilibrium time and good phase separation. Increasing temperature had a negative effect on yttrium(III) extraction. Quantitative yttrium(III) extraction efficiency was achieved at room temperature within 5 min using three stages of extraction with 0.4 M primene-JMT from a synthetic yttrium solution at pH 1.5 (0.2 M H2SO4) at a phase ratio of 1:1. A mechanism for extraction is suggested. The proposed separation of yttrium(III) from rare earth concentrate obtained from alkaline leaching of Egyptian monazite is outlined. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Rare earths (yttrium, scandium, and lanthanides) are important elements in photo-electronic and metallurgical industries as well as in nuclear energy programs. The demand for rare earths and their alloys as structural materials, fluxes, radiation detectors, diluents of plutonium etc. in nuclear technology is steadily increasing. For a variety of uses in these specialized areas, high purity yttrium is often required (Zhou et al., 2007) but it is difficult to separate yttrium(III) from heavy rare earths (HRE) because of their similar physical and chemical properties (Wang et al., 2004). The solvent extraction of several rare earth ions from sulfate liquors has been extensively reported. Prominent extractants that have been employed are high molecular weight amines (Desai and Shinde, 1985), carboxylic acids (Singh et al., 2006), tri-n-butyl phosphate (TBP) (Mathur and Choppin, 1998) and di-(2-ethylhexyl) phosphoric acid (D2EHPA) (Panturu et al., 2000; Zhou et al., 2007). Primene-JMT (tri-alkyl-methylamine) is considered as a liquid anion-exchanger that requires the formation of ion-pairs or ion association to act as extractant. It was used extensively in the solvent extraction of lanthanum(III) (El-Yamani and Shabana, 1985), uranium (VI) (Shakir, 1980), zirconium and hafnium (El-Yamani et al., 1978). In the present preliminary laboratory investigation, emphasis is placed on the extraction of pure yttrium(III) from sulfuric acid solutions by primene-JMT in order to obtain a better understanding of the extraction behavior of individual elements as part of an overall ⁎ Corresponding author. E-mail addresses: [email protected] (O.A. Desouky), [email protected] (A.A. Galhoum). 0304-386X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2008.11.009
study on the separation of yttrium(III) from rare earth concentrate obtained from alkaline leaching of Egyptian monazite. 2. Experimental 2.1. Reagents and analysis The primene-JMT (tri-alkyl methylamine) was obtained from Rohm & Hass Co. Odorless kerosene (non-aromatic) was obtained from Misr Petroleum Co., Egypt. Stock solutions of yttrium were prepared from Y2O3 supplied by Fluka in concentrated sulfuric acid and diluted with distilled water. Arsenazo III (A.R grade) was obtained from Fluka and all other chemicals were Prolabo products and were used as received. Yttrium was determined spectrophotometrically using the colorimetric determination (Marczenko, 1976) and a “Metertech Inc” model SP-8001, UV–Visible spectrophotometer. 2.2. Procedure Batch experiments were carried out by equilibrating equal volumes of primene-JMT in kerosene with 8.86 × 10− 3 M yttrium(III) solution in stoppered glass bottles using a magnetic stirrer. After equilibration and phase separation, the yttrium concentration in the aqueous phase was determined spectrophotometrically whilst the concentration in the organic phase was obtained by mass balance. The percentage of extraction was calculated from Eq. ((1):
kE =
100×DðP Þ 1 + DðP Þ
ð1Þ
314
O.A. Desouky et al. / Hydrometallurgy 96 (2009) 313–317
Fig. 1. Plot of log D versus log [Primene JMT].
Fig. 2. Effect of equilibration time on yttrium(III) extraction.
where P is the phase volume ratio; D is the distribution coefficient. All experiments were carried out by equilibrating for 5 min at room temperature (25 ± 1 °C) and pH 1.5; except when the effect of time, pH and temperature on the distribution equilibria was studied. 3. Results and discussion
3.3. Effect of equilibration time The effect of equilibrium time (0.5–30 min) on the extraction of yttrium(III) was studied using 0.4 M primene-JMT in kerosene while other factors were kept constant. The results (±0.5%) shown in Fig. 2 clearly indicate that the extraction is fast and 5 min is quite adequate for efficient yttrium(III) extraction.
3.1. Effect of primene-JMT concentration 3.4. Extraction as a function of pH The effect of extractant concentrations on the extraction efficiency of yttrium(III) was studied in the range 0.1–0.5 M at pH 1.5. The extraction of yttrium(III) increased steadily from 70% to 97% with an increase in primene-JMT concentration up to 0.4 M and then plateaued. A plot of log D versus log [primene-JMT] is presented in Fig. 1 which shows a linear correlation with a slope ~2 indicating the requirement of two moles of primene-JMT for each mole of the yttrium(III). 3.2. Effect of diluents Diluents influence the extraction of metals by amines due to the aggregation of the amine in the organic phase (Ritcey and Ashbrook, 1984). Therefore, various aromatic and aliphatic solvents were tested as diluents for the extraction of yttrium(III) with 0.4 M primene-JMT (Table 1). The extraction of yttrium(III) was maximum with kerosene, chloroform and carbon tetrachloride as diluents but benzene, pxylene and toluene proved to be poor diluents. It is reported that there is sometimes a correlation between the effect of a diluent and its dielectric constant but no such correlation was found in our present study (Table 1). However, short equilibrium time and good phase separation was achieved when aliphatic diluents were used compared to aromatic diluents. Considering several factors like cost, environmental and safety aspects and maximum yttrium(III) extraction efficiency, aliphatic kerosene was preferred as the diluent for further studies.
The percentage extraction of yttrium(III) from aqueous sulfate medium was studied using 0.4 M primene-JMT within the initial pH range 0.5–2.33. As shown in Fig. 3, the extraction of yttrium(III) reached a maximum (97.8%) at equilibrium pH 1.56 where the formation of an ion-pair complex in sulfate media is favorable. With a further increase in pH to 2.33, yttrium(III) extraction decreased steadily to 93.1%. At higher pH, there is a possibility of hydrolysis of the Y(III) ion-pair complex. The lower values obtained at higher acid concentrations (pH b1) are due to competition between the extractable yttrium species and HSO−4 which predominates in sulfate media at low pH (El-Yamani and Shabana, 1985). 3.5. Effect of aqueous: organic phase ratio The aqueous:organic phase ratio has a significant effect on distribution coefficient and entrainment. This effect was studied by changing the aqueous:organic phase ratio from 1:1 to 1:4. The results
Table 1 Effect of diluents on the extraction of yttrium(III) by primene-JMT Diluents
Dielectric constant
Distribution coefficient
Extraction percent, [%]
Benzene Toluene P-Xylene Chloroform Carbon tetrachloride Kerosene
2.3 2.23 2.28 5.1 2.23 2
2.9 2.6 2.0 5.35 3.3 39.3
75 72 67 84 77 97.5
0.4 M Primene-JMT; Phase ratio A:O 1:1; time 10 min; room temperature.
Fig. 3. Effect of equilibrium pH on yttrium(III) extraction.
O.A. Desouky et al. / Hydrometallurgy 96 (2009) 313–317
315
Table 2 Effect of aqueous:organic phase ratio on the extraction process Phase ratio (Aq:Org)
Distribution coefficient
Extraction percent, [%]
1:1 2:1 3:1 4:1
43.6 6.3 2.6 1.9
97.8 86 72 66
0.4 M Primene-JMT; phase ratio A:O 1:1; room temperature; time 5 min.
presented in Table 2 clearly show that a phase ratio of 1:1 gives the best extraction of yttrium(III). At the 1:1 ratio, the rate of coalescence and re-dispersion of the dispersed phase is also enhanced. 3.6. Effect of temperature The extraction of a metal complex into an organic phase involves large changes in enthalpy (solvation processes) and in entropy (solvent orientation and restructuring), leading to considerable temperature effects. To study the effect of temperature on extraction of yttrium(III), experiments were carried in the range 298–333°K. The results obtained showed that the extraction of yttrium(III) decreased from 97.8% at 298°K to 88.9% at 333°K. This behavior is agrees with that reported by previous investigators (Mowafy and Aly, 2001). Fig. 4 plots Log D versus 1000/T, K− 1 which gives a straight line for the extraction of yttrium(III) by primene-JMT from 0.2 M H2SO4 solution. The ΔH value for yttrium(III) was −37 kJ/mol — as calculated from the slope using the Van't Hoff equation (Eq. (2)). Log D =
−ΔH +C 2:303 RT
Fig. 4. Plot of log DY against 1000/T, K− 1 for extraction of yttrium(III).
ð2Þ
where D is the distribution coefficient, ΔH the enthalpy change for the extraction reaction, R is the universal gas constant (8.314 J/mol k) and C is a constant for the system. This value of ΔH was used to obtain the corresponding free energy (ΔG = −9.4 kJ/mol) and entropy (ΔS = 47 J/ mol K) at 298°K using Eqs. (3) and (4), respectively: ΔG = −2:303RT log D
ð3Þ
ΔG = ΔH−TΔS:
ð4Þ
The negative value of ΔH indicates that the extraction of yttrium in this system is an exothermic process and the reaction becomes more favorable at room temperatures.
Fig. 5. McCabe–Thiele diagram for yttrium(III) extraction.
3 min equilibration time was sufficient. When higher organic:aqueous phase ratios were used the stripping efficiency decreased as shown in Table 3. However, it was found that when Y(III) was stripped from high organic phase ratios into 3 M HNO3 and 10% oxalic acid was added gradually to the Y-rich strip liquor, crystalline yttrium oxalates were obtained after 24 h. 4. Mechanism of extraction
3.7. Extraction isotherm The number of the theoretical stages was calculated by the McCabe–Thiele diagram which was constructed by standard procedures and is given in Fig. 5. In constructing this diagram, the extraction isotherm which represents the relationship between yttrium(III) concentration in raffinate and its concentration in the organic phase was first drawn. A vertical line is then drawn from the concentration of yttrium in the feed solution on the x-axis. The operating line is next inserted, the slope of which is equal to the phase ratio. This figure shows that three extraction stages are required at an A/O ratio of 2.4 for the extraction of yttrium.
The dissolution of yttrium oxide in sulfuric acid produces a chemically stable sulfate salt that forms anionic complex species in
3.8. Effect of stripping agents Stripping should be promoted by factors that affect extraction negatively such as low pH. Therefore yttrium stripping from the loaded organic solvent was investigated using various strong acids, such as HCl, H2SO4 and HNO3, in the range 0.5–9 M with an A:O ratio of 1:1. The results presented in Fig. 6 show that 3 M HNO3 and 3 M HCl are more effective than sulfuric acid for the quantitative stripping of yttrium(III) in two stages. Variation of the stripping time found that
Fig. 6. Effect of concentration of acid on stripping efficiency.
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solution which can pass into the organic phase (El-Yamani and Shabana, 1985). 3− Y3þ þ 3SO2− 4 →YðSO4 Þ3 ðaqÞ:
ð6Þ
The protonation of primary amines in sulfuric acid solutions gives sulfate or bisulfate ion-pairs, which can exchange with complex ions. 2RNH2ðorgÞ þ H2 SO4ðaq Þ↔ðRNH3 Þ2 SO4ðorgÞ
ð7Þ
ðRNH3 Þ2 SO4ðorgÞ þ H2 SO4ðaq Þ↔2RNH3 :HSO4ðorgÞ :
ð8Þ
With increasing concentration, the aggregation (dimerization) of bisulphate occurs and sometimes, excess acid extraction is described (Neková and Schrötterová, 2000). It is assumed that only amine sulfate reacts with the yttrium(III) species forming complexes in the organic phase (El-Yamani and Shabana, 1985). 2− 3ðRNH3 Þ2 SO4ðorgÞ þ 2YðSO4 Þ3− 3 ðaqÞ→2ðRNH3 Þ3 YðSO4 Þ3ðorgÞ þ 3SO4 ðaqÞ:
ð9Þ
The proposed mechanism of yttrium extraction is close agreement with experimental results shown in Fig. 1. The stripping and precipitation reaction of yttrium at ambient temperature gives a neutral salt Y2(C2O4)3.10H2O(s), according to the experimental conditions. Acidic salt YH(C2O4)2.3H2O(s) was also precipitated as follows (Combes et al., 1997): Y3þ þ 2H2 C2 O4 þ 3H2 O→YHðC2 O4 Þ2 :3H2 OðsÞ þ 3Hþ
ð10Þ
2Y3þ þ 3H2 C2 O4 þ 10H2 O→Y2 ðC2 O4 Þ3 :10H2 OðsÞ þ 6Hþ :
ð11Þ
5. Natural ore application A study of Egyptian monazite ore samples from Rosetta has been made by the Nuclear Material Authority of Egypt. Egyptian monazite (purity 97%) has been analyzed and was found to assay 5.9% ThO2, 0.44% U3O8, 26.55% Ce2O3, and 34.35% other rare earths (RE2O3) including yttrium (Osman, 1998). Commercially, both acid and alkaline leaching are commonly used, but alkaline leaching of monazite is most preferable and widely used due to economic reasons. By-product tri-sodium phosphate may be used in the fertilizer industry, and the alkaline method could be less complicated. The reaction of monazite with hot concentrated caustic soda can be represented by the following: 2REðPO4 Þ þ 6NaOH→RE2 O3 :3H2 O or REðOHÞ3 þ 2Na3 PO4
ð12Þ
Th3 ðPO4 Þ4 þ 12NaOH→3ThO2 :2H2 O or ThðOHÞ4 þ 4Na3 PO4 :
ð13Þ
diluted with water. The separation of thorium and uranium from lanthanides is carried out by selective neutralization of solutions with ammonia solution or alkali up to pH = 5.8–6. Osman (1998) separated uranium from thorium-uranium cake obtained from the hydrous oxide cake concentrate dissolved in concentrated H2SO4 solution by using solvent extraction. The present investigation is directed to develop a process to separate yttrium from the rare earth concentrate which also obtained by selective neutralization up to pH = 8. In the application studies, the extraction of yttrium was carried out from a rare earth hydrous oxide concentrate dissolved in sulfuric acid. In a typical experiment, 5 g rare earth concentrate was heated with 1 L 0.2 M sulfuric acid at ≈80 °C for 2 h to allow complete dissolution of all rare earth elements and then filtered. The filtrate contained all rare earth elements. Chemical analysis of rare earth concentrate was estimated by energy dispersive analysis with X-rays (EDAX). For this work, the REE concentrate contained (%) Y2O3 2.16, Gd2O3 1.89, Eu2O3 1.71, Sm2O3 2.81, Nd2O3 16.91, Pr2O3 5.38, Ce2O3 31.29, La2O3 12.42 and Na2O 24.81. Because the high percentage of Ce2O3 can affect the liquid–liquid extraction of yttrium, cerium should be removed using the method of separation illustrated by Morais et al. (2003). 5.1. Fractional separation of rare earths and solvent extraction of yttrium rich fraction Typically, the mother liquor is evaporated to such a consistency that it would solidify upon cooling. When it has cooled down considerably, but while still liquid, the mother liquor is poured off and evaporated further and the crystals well drained. In this way, the liquid and crystals are systematically fractionated by continuing the evaporating process for a long time; and the solution must be allowed to become alkaline gradually. Lanthanum separates in the first fraction, together with trace amount of non-separated cerium (IV). The second fraction contains praseodymium and neodymium, which are precipitated with trace amounts of samarium and gadolinium where praseodymium and neodymium occur together. After removal of cerium the mother liquor is evaporated and cooled many times to obtain fractions (III) and (IV) which are rich in yttrium — starting from 2.2% Y2O3 until the final fraction is 23.1% Y 2O 3 . The best source for yttrium is therefore found in fractions (III) and (IV) which are dissolved in 0.2 M sulfuric acid. Solvent extraction of yttrium from this sulfate liquor was carried out in three stages with a 0.4 M primene-JMT in kerosene followed by stripping in two stages with 3 M nitric acid at an aqueous:organic phase ratio of 1:1. Overall recovery of yttrium from the strip liquors was 92–93%. Yttrium was finally recovered from the nitrate solution as the oxalate and calcined to oxide. The final product contained 76.3% Y2O3 together with smaller amounts of 7.95% Gd2O3, 6.1% Eu2O3 and 9.6% Sm2O3. Our future work is directed towards increasing the purity of crude Y2O3 from 76.3% to high purity product. 6. Conclusions
The hydrous oxide concentrate obtained from alkaline processing of monazite is leached with hot hydrochloric acid at 80 °C, and then
Table 3 Effect of aqueous:organic phase ratio on the stripping efficiency Phase ratio (Aq:Org)
Stripping efficiency; [%]
1:1 1:2 1:3 1:4 1:5
92 85 74 72 70
3 M HNO3; room temperature; time 3 min.
The present study on the liquid–liquid extraction of yttrium(III) from sulfate solutions by primene-JMT has identified the following points: 1. Quantitative yttrium(III) extraction was achieved in 5 min with 0.4 M primene-JMT in kerosene in three stages at an aqueous: organic (A:O) phase ratio of 2.4:1 at equilibrium pH 1.56. 2. Aliphatic kerosene showed good results as a diluent for primeneJMT compared with other diluents used. 3. Temperature shows a negative effect on yttrium(III) extraction, when primene-JMT is used. The reaction is exothermic (ΔH = − 37 kJ/mol).
O.A. Desouky et al. / Hydrometallurgy 96 (2009) 313–317
4. Quantitative yttrium(III) stripping was achieved in two stages using 3 M HNO3 or 3 M HCl at an O:A ratio of 1:1 and contact time of 3 min. 5. Application of the bench scale results to the extraction of yttrium from a yttrium rich fraction of rare earth concentrate gave a crude yttrium oxide assaying ca. 76.3%. References Combes, E., Sella, C., Bauer, D., Sabot, J.L., 1997. Precipitation-stripping of yttrium oxalate powders from yttrium-loaded HDEHP organic solutions using an ultrasonic stirrer. Hydrometallurgy 46, 1–12. Desai, D.D., Shinde, V.M., 1985. Liquid anion-exchange extraction and separation of yttrium, neodymium and samarium. Anal. Chim. Acta. 167, 413–417. El-Yamani, I.S., Shabana, E.I., 1985. Solvent extraction of lanthanium(III) from sulfuric acid solutions by Primene-JMT. J. Less-Common Met. 105, 255–261. El-Yamani, I.S., Farah, M.Y., Abd El-Aleim, F.A., 1978. Co-extraction and separation of zirconium and hafnium by long-chain amines from sulphate media. Talanta 25, 523–525. Marczenko, Z., 1976. Spectrophotometric Determination of Elements. Ellis Harwood, Chichester, England, pp. 442–443. Mathur, J.N., Choppin, G.R., 1998. Paraffin wax as a diluent for extraction of actinides and lanthanides with TBP. Solvent Extr. Ion Exc 16, 459–469.
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Morais, C.A., Benedetto, J.S., Ciminelli, V.S.T., 2003. Recovery of cerium by oxidation/ hydrolysis with KMnO4–Na2CO3. Hydrometallurgy 2003 (Proc.5th Intl. Symp., Vancouver), TMS, Warrendale, vol. 2, pp. 1773–1782. Mowafy, E.A., Aly, H.F., 2001. Synthesis and characterization of N,N,N′,N′-tetrabytylsuccinamide as extractant for uranium(VI) ions from nitric acid solution. J. Radioanal. Nucl. Chem. 250, 199–203. Neková, P., Schrötterová, D., 2000. Extraction of V(V), Mo(VI) and W(VI) polynuclear species by Primene JMT. Chem. Eng. J. 79, 229–233. Osman, A., 1998. Solvent extraction study on uranium and thorium from sulfuric acid solution and its technological application; M.Sc. thesis, Zagazig University, Banha, Egypt. Panturu, E., Georgescu, D.P., Aurelian, F., Udrea, N., 2000. Selective separation of yttrium from chemical concentrate of rare earth. Dev. Miner. Process. 13, C6–84-C6-89. Ritcey, G.M., Ashbrook, A.W., 1984. Solvent Extraction: Principles and Applications to Process Metallurgy, Part I. Elsevier, p. 32. Shakir, K.A., 1980. Extraction of uranium(VI) from dilute phosphate solutions with neotridecanohydroxamic acid and amines. Hydrometallurgy 5, 191–206. Singh, D.K., Singh, H., Mathur, J.M., 2006. Extraction of rare earths and yttrium with high molecular weight carboxylic acids. Hydrometallurgy 81, 174–181. Wang, Y.G., Xiong, Y., Meng, S.L., Li, D.Q., 2004. Separation of yttrium from heavy lanthanide by CA-100 using the complexing agent. Talanta 63, 239–243. Zhou, J., Duan, W., Zhou, X., Zhang, C., 2007. Application of annular centrifugal contactors in the extraction flowsheet for producing high purity yttrium. Hydrometallurgy 85, 154–162.
Contents lists available at ScienceDirect
Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / h y d r o m e t
Liquid–liquid extraction of yttrium using primene-JMT from acidic sulfate solutions O.A. Desouky a,⁎, A.M. Daher a, Y.K. Abdel-Monem b, A.A. Galhoum a a b
Nuclear Materials Authority, P.O. Box 530, El-Maadi, Cairo, Egypt Chemistry Department, Faculty of Science, Minoufia University, Shabin El-Kom, Minoufia, Egypt
a r t i c l e
i n f o
Article history: Received 3 September 2008 Received in revised form 20 November 2008 Accepted 21 November 2008 Available online 6 December 2008 Keywords: Liquid–liquid extraction Yttrium Primene-JMT Extraction isotherm
a b s t r a c t The liquid–liquid extraction of yttrium(III) from sulfate medium using primene-JMT is investigated with regard to extractant concentration, diluent type, equilibrium pH and time, temperature, and extraction isotherm. Aliphatic kerosene diluents were preferred compared to aromatic diluents because of higher extraction, shorter equilibrium time and good phase separation. Increasing temperature had a negative effect on yttrium(III) extraction. Quantitative yttrium(III) extraction efficiency was achieved at room temperature within 5 min using three stages of extraction with 0.4 M primene-JMT from a synthetic yttrium solution at pH 1.5 (0.2 M H2SO4) at a phase ratio of 1:1. A mechanism for extraction is suggested. The proposed separation of yttrium(III) from rare earth concentrate obtained from alkaline leaching of Egyptian monazite is outlined. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Rare earths (yttrium, scandium, and lanthanides) are important elements in photo-electronic and metallurgical industries as well as in nuclear energy programs. The demand for rare earths and their alloys as structural materials, fluxes, radiation detectors, diluents of plutonium etc. in nuclear technology is steadily increasing. For a variety of uses in these specialized areas, high purity yttrium is often required (Zhou et al., 2007) but it is difficult to separate yttrium(III) from heavy rare earths (HRE) because of their similar physical and chemical properties (Wang et al., 2004). The solvent extraction of several rare earth ions from sulfate liquors has been extensively reported. Prominent extractants that have been employed are high molecular weight amines (Desai and Shinde, 1985), carboxylic acids (Singh et al., 2006), tri-n-butyl phosphate (TBP) (Mathur and Choppin, 1998) and di-(2-ethylhexyl) phosphoric acid (D2EHPA) (Panturu et al., 2000; Zhou et al., 2007). Primene-JMT (tri-alkyl-methylamine) is considered as a liquid anion-exchanger that requires the formation of ion-pairs or ion association to act as extractant. It was used extensively in the solvent extraction of lanthanum(III) (El-Yamani and Shabana, 1985), uranium (VI) (Shakir, 1980), zirconium and hafnium (El-Yamani et al., 1978). In the present preliminary laboratory investigation, emphasis is placed on the extraction of pure yttrium(III) from sulfuric acid solutions by primene-JMT in order to obtain a better understanding of the extraction behavior of individual elements as part of an overall ⁎ Corresponding author. E-mail addresses: [email protected] (O.A. Desouky), [email protected] (A.A. Galhoum). 0304-386X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2008.11.009
study on the separation of yttrium(III) from rare earth concentrate obtained from alkaline leaching of Egyptian monazite. 2. Experimental 2.1. Reagents and analysis The primene-JMT (tri-alkyl methylamine) was obtained from Rohm & Hass Co. Odorless kerosene (non-aromatic) was obtained from Misr Petroleum Co., Egypt. Stock solutions of yttrium were prepared from Y2O3 supplied by Fluka in concentrated sulfuric acid and diluted with distilled water. Arsenazo III (A.R grade) was obtained from Fluka and all other chemicals were Prolabo products and were used as received. Yttrium was determined spectrophotometrically using the colorimetric determination (Marczenko, 1976) and a “Metertech Inc” model SP-8001, UV–Visible spectrophotometer. 2.2. Procedure Batch experiments were carried out by equilibrating equal volumes of primene-JMT in kerosene with 8.86 × 10− 3 M yttrium(III) solution in stoppered glass bottles using a magnetic stirrer. After equilibration and phase separation, the yttrium concentration in the aqueous phase was determined spectrophotometrically whilst the concentration in the organic phase was obtained by mass balance. The percentage of extraction was calculated from Eq. ((1):
kE =
100×DðP Þ 1 + DðP Þ
ð1Þ
314
O.A. Desouky et al. / Hydrometallurgy 96 (2009) 313–317
Fig. 1. Plot of log D versus log [Primene JMT].
Fig. 2. Effect of equilibration time on yttrium(III) extraction.
where P is the phase volume ratio; D is the distribution coefficient. All experiments were carried out by equilibrating for 5 min at room temperature (25 ± 1 °C) and pH 1.5; except when the effect of time, pH and temperature on the distribution equilibria was studied. 3. Results and discussion
3.3. Effect of equilibration time The effect of equilibrium time (0.5–30 min) on the extraction of yttrium(III) was studied using 0.4 M primene-JMT in kerosene while other factors were kept constant. The results (±0.5%) shown in Fig. 2 clearly indicate that the extraction is fast and 5 min is quite adequate for efficient yttrium(III) extraction.
3.1. Effect of primene-JMT concentration 3.4. Extraction as a function of pH The effect of extractant concentrations on the extraction efficiency of yttrium(III) was studied in the range 0.1–0.5 M at pH 1.5. The extraction of yttrium(III) increased steadily from 70% to 97% with an increase in primene-JMT concentration up to 0.4 M and then plateaued. A plot of log D versus log [primene-JMT] is presented in Fig. 1 which shows a linear correlation with a slope ~2 indicating the requirement of two moles of primene-JMT for each mole of the yttrium(III). 3.2. Effect of diluents Diluents influence the extraction of metals by amines due to the aggregation of the amine in the organic phase (Ritcey and Ashbrook, 1984). Therefore, various aromatic and aliphatic solvents were tested as diluents for the extraction of yttrium(III) with 0.4 M primene-JMT (Table 1). The extraction of yttrium(III) was maximum with kerosene, chloroform and carbon tetrachloride as diluents but benzene, pxylene and toluene proved to be poor diluents. It is reported that there is sometimes a correlation between the effect of a diluent and its dielectric constant but no such correlation was found in our present study (Table 1). However, short equilibrium time and good phase separation was achieved when aliphatic diluents were used compared to aromatic diluents. Considering several factors like cost, environmental and safety aspects and maximum yttrium(III) extraction efficiency, aliphatic kerosene was preferred as the diluent for further studies.
The percentage extraction of yttrium(III) from aqueous sulfate medium was studied using 0.4 M primene-JMT within the initial pH range 0.5–2.33. As shown in Fig. 3, the extraction of yttrium(III) reached a maximum (97.8%) at equilibrium pH 1.56 where the formation of an ion-pair complex in sulfate media is favorable. With a further increase in pH to 2.33, yttrium(III) extraction decreased steadily to 93.1%. At higher pH, there is a possibility of hydrolysis of the Y(III) ion-pair complex. The lower values obtained at higher acid concentrations (pH b1) are due to competition between the extractable yttrium species and HSO−4 which predominates in sulfate media at low pH (El-Yamani and Shabana, 1985). 3.5. Effect of aqueous: organic phase ratio The aqueous:organic phase ratio has a significant effect on distribution coefficient and entrainment. This effect was studied by changing the aqueous:organic phase ratio from 1:1 to 1:4. The results
Table 1 Effect of diluents on the extraction of yttrium(III) by primene-JMT Diluents
Dielectric constant
Distribution coefficient
Extraction percent, [%]
Benzene Toluene P-Xylene Chloroform Carbon tetrachloride Kerosene
2.3 2.23 2.28 5.1 2.23 2
2.9 2.6 2.0 5.35 3.3 39.3
75 72 67 84 77 97.5
0.4 M Primene-JMT; Phase ratio A:O 1:1; time 10 min; room temperature.
Fig. 3. Effect of equilibrium pH on yttrium(III) extraction.
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315
Table 2 Effect of aqueous:organic phase ratio on the extraction process Phase ratio (Aq:Org)
Distribution coefficient
Extraction percent, [%]
1:1 2:1 3:1 4:1
43.6 6.3 2.6 1.9
97.8 86 72 66
0.4 M Primene-JMT; phase ratio A:O 1:1; room temperature; time 5 min.
presented in Table 2 clearly show that a phase ratio of 1:1 gives the best extraction of yttrium(III). At the 1:1 ratio, the rate of coalescence and re-dispersion of the dispersed phase is also enhanced. 3.6. Effect of temperature The extraction of a metal complex into an organic phase involves large changes in enthalpy (solvation processes) and in entropy (solvent orientation and restructuring), leading to considerable temperature effects. To study the effect of temperature on extraction of yttrium(III), experiments were carried in the range 298–333°K. The results obtained showed that the extraction of yttrium(III) decreased from 97.8% at 298°K to 88.9% at 333°K. This behavior is agrees with that reported by previous investigators (Mowafy and Aly, 2001). Fig. 4 plots Log D versus 1000/T, K− 1 which gives a straight line for the extraction of yttrium(III) by primene-JMT from 0.2 M H2SO4 solution. The ΔH value for yttrium(III) was −37 kJ/mol — as calculated from the slope using the Van't Hoff equation (Eq. (2)). Log D =
−ΔH +C 2:303 RT
Fig. 4. Plot of log DY against 1000/T, K− 1 for extraction of yttrium(III).
ð2Þ
where D is the distribution coefficient, ΔH the enthalpy change for the extraction reaction, R is the universal gas constant (8.314 J/mol k) and C is a constant for the system. This value of ΔH was used to obtain the corresponding free energy (ΔG = −9.4 kJ/mol) and entropy (ΔS = 47 J/ mol K) at 298°K using Eqs. (3) and (4), respectively: ΔG = −2:303RT log D
ð3Þ
ΔG = ΔH−TΔS:
ð4Þ
The negative value of ΔH indicates that the extraction of yttrium in this system is an exothermic process and the reaction becomes more favorable at room temperatures.
Fig. 5. McCabe–Thiele diagram for yttrium(III) extraction.
3 min equilibration time was sufficient. When higher organic:aqueous phase ratios were used the stripping efficiency decreased as shown in Table 3. However, it was found that when Y(III) was stripped from high organic phase ratios into 3 M HNO3 and 10% oxalic acid was added gradually to the Y-rich strip liquor, crystalline yttrium oxalates were obtained after 24 h. 4. Mechanism of extraction
3.7. Extraction isotherm The number of the theoretical stages was calculated by the McCabe–Thiele diagram which was constructed by standard procedures and is given in Fig. 5. In constructing this diagram, the extraction isotherm which represents the relationship between yttrium(III) concentration in raffinate and its concentration in the organic phase was first drawn. A vertical line is then drawn from the concentration of yttrium in the feed solution on the x-axis. The operating line is next inserted, the slope of which is equal to the phase ratio. This figure shows that three extraction stages are required at an A/O ratio of 2.4 for the extraction of yttrium.
The dissolution of yttrium oxide in sulfuric acid produces a chemically stable sulfate salt that forms anionic complex species in
3.8. Effect of stripping agents Stripping should be promoted by factors that affect extraction negatively such as low pH. Therefore yttrium stripping from the loaded organic solvent was investigated using various strong acids, such as HCl, H2SO4 and HNO3, in the range 0.5–9 M with an A:O ratio of 1:1. The results presented in Fig. 6 show that 3 M HNO3 and 3 M HCl are more effective than sulfuric acid for the quantitative stripping of yttrium(III) in two stages. Variation of the stripping time found that
Fig. 6. Effect of concentration of acid on stripping efficiency.
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solution which can pass into the organic phase (El-Yamani and Shabana, 1985). 3− Y3þ þ 3SO2− 4 →YðSO4 Þ3 ðaqÞ:
ð6Þ
The protonation of primary amines in sulfuric acid solutions gives sulfate or bisulfate ion-pairs, which can exchange with complex ions. 2RNH2ðorgÞ þ H2 SO4ðaq Þ↔ðRNH3 Þ2 SO4ðorgÞ
ð7Þ
ðRNH3 Þ2 SO4ðorgÞ þ H2 SO4ðaq Þ↔2RNH3 :HSO4ðorgÞ :
ð8Þ
With increasing concentration, the aggregation (dimerization) of bisulphate occurs and sometimes, excess acid extraction is described (Neková and Schrötterová, 2000). It is assumed that only amine sulfate reacts with the yttrium(III) species forming complexes in the organic phase (El-Yamani and Shabana, 1985). 2− 3ðRNH3 Þ2 SO4ðorgÞ þ 2YðSO4 Þ3− 3 ðaqÞ→2ðRNH3 Þ3 YðSO4 Þ3ðorgÞ þ 3SO4 ðaqÞ:
ð9Þ
The proposed mechanism of yttrium extraction is close agreement with experimental results shown in Fig. 1. The stripping and precipitation reaction of yttrium at ambient temperature gives a neutral salt Y2(C2O4)3.10H2O(s), according to the experimental conditions. Acidic salt YH(C2O4)2.3H2O(s) was also precipitated as follows (Combes et al., 1997): Y3þ þ 2H2 C2 O4 þ 3H2 O→YHðC2 O4 Þ2 :3H2 OðsÞ þ 3Hþ
ð10Þ
2Y3þ þ 3H2 C2 O4 þ 10H2 O→Y2 ðC2 O4 Þ3 :10H2 OðsÞ þ 6Hþ :
ð11Þ
5. Natural ore application A study of Egyptian monazite ore samples from Rosetta has been made by the Nuclear Material Authority of Egypt. Egyptian monazite (purity 97%) has been analyzed and was found to assay 5.9% ThO2, 0.44% U3O8, 26.55% Ce2O3, and 34.35% other rare earths (RE2O3) including yttrium (Osman, 1998). Commercially, both acid and alkaline leaching are commonly used, but alkaline leaching of monazite is most preferable and widely used due to economic reasons. By-product tri-sodium phosphate may be used in the fertilizer industry, and the alkaline method could be less complicated. The reaction of monazite with hot concentrated caustic soda can be represented by the following: 2REðPO4 Þ þ 6NaOH→RE2 O3 :3H2 O or REðOHÞ3 þ 2Na3 PO4
ð12Þ
Th3 ðPO4 Þ4 þ 12NaOH→3ThO2 :2H2 O or ThðOHÞ4 þ 4Na3 PO4 :
ð13Þ
diluted with water. The separation of thorium and uranium from lanthanides is carried out by selective neutralization of solutions with ammonia solution or alkali up to pH = 5.8–6. Osman (1998) separated uranium from thorium-uranium cake obtained from the hydrous oxide cake concentrate dissolved in concentrated H2SO4 solution by using solvent extraction. The present investigation is directed to develop a process to separate yttrium from the rare earth concentrate which also obtained by selective neutralization up to pH = 8. In the application studies, the extraction of yttrium was carried out from a rare earth hydrous oxide concentrate dissolved in sulfuric acid. In a typical experiment, 5 g rare earth concentrate was heated with 1 L 0.2 M sulfuric acid at ≈80 °C for 2 h to allow complete dissolution of all rare earth elements and then filtered. The filtrate contained all rare earth elements. Chemical analysis of rare earth concentrate was estimated by energy dispersive analysis with X-rays (EDAX). For this work, the REE concentrate contained (%) Y2O3 2.16, Gd2O3 1.89, Eu2O3 1.71, Sm2O3 2.81, Nd2O3 16.91, Pr2O3 5.38, Ce2O3 31.29, La2O3 12.42 and Na2O 24.81. Because the high percentage of Ce2O3 can affect the liquid–liquid extraction of yttrium, cerium should be removed using the method of separation illustrated by Morais et al. (2003). 5.1. Fractional separation of rare earths and solvent extraction of yttrium rich fraction Typically, the mother liquor is evaporated to such a consistency that it would solidify upon cooling. When it has cooled down considerably, but while still liquid, the mother liquor is poured off and evaporated further and the crystals well drained. In this way, the liquid and crystals are systematically fractionated by continuing the evaporating process for a long time; and the solution must be allowed to become alkaline gradually. Lanthanum separates in the first fraction, together with trace amount of non-separated cerium (IV). The second fraction contains praseodymium and neodymium, which are precipitated with trace amounts of samarium and gadolinium where praseodymium and neodymium occur together. After removal of cerium the mother liquor is evaporated and cooled many times to obtain fractions (III) and (IV) which are rich in yttrium — starting from 2.2% Y2O3 until the final fraction is 23.1% Y 2O 3 . The best source for yttrium is therefore found in fractions (III) and (IV) which are dissolved in 0.2 M sulfuric acid. Solvent extraction of yttrium from this sulfate liquor was carried out in three stages with a 0.4 M primene-JMT in kerosene followed by stripping in two stages with 3 M nitric acid at an aqueous:organic phase ratio of 1:1. Overall recovery of yttrium from the strip liquors was 92–93%. Yttrium was finally recovered from the nitrate solution as the oxalate and calcined to oxide. The final product contained 76.3% Y2O3 together with smaller amounts of 7.95% Gd2O3, 6.1% Eu2O3 and 9.6% Sm2O3. Our future work is directed towards increasing the purity of crude Y2O3 from 76.3% to high purity product. 6. Conclusions
The hydrous oxide concentrate obtained from alkaline processing of monazite is leached with hot hydrochloric acid at 80 °C, and then
Table 3 Effect of aqueous:organic phase ratio on the stripping efficiency Phase ratio (Aq:Org)
Stripping efficiency; [%]
1:1 1:2 1:3 1:4 1:5
92 85 74 72 70
3 M HNO3; room temperature; time 3 min.
The present study on the liquid–liquid extraction of yttrium(III) from sulfate solutions by primene-JMT has identified the following points: 1. Quantitative yttrium(III) extraction was achieved in 5 min with 0.4 M primene-JMT in kerosene in three stages at an aqueous: organic (A:O) phase ratio of 2.4:1 at equilibrium pH 1.56. 2. Aliphatic kerosene showed good results as a diluent for primeneJMT compared with other diluents used. 3. Temperature shows a negative effect on yttrium(III) extraction, when primene-JMT is used. The reaction is exothermic (ΔH = − 37 kJ/mol).
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4. Quantitative yttrium(III) stripping was achieved in two stages using 3 M HNO3 or 3 M HCl at an O:A ratio of 1:1 and contact time of 3 min. 5. Application of the bench scale results to the extraction of yttrium from a yttrium rich fraction of rare earth concentrate gave a crude yttrium oxide assaying ca. 76.3%. References Combes, E., Sella, C., Bauer, D., Sabot, J.L., 1997. Precipitation-stripping of yttrium oxalate powders from yttrium-loaded HDEHP organic solutions using an ultrasonic stirrer. Hydrometallurgy 46, 1–12. Desai, D.D., Shinde, V.M., 1985. Liquid anion-exchange extraction and separation of yttrium, neodymium and samarium. Anal. Chim. Acta. 167, 413–417. El-Yamani, I.S., Shabana, E.I., 1985. Solvent extraction of lanthanium(III) from sulfuric acid solutions by Primene-JMT. J. Less-Common Met. 105, 255–261. El-Yamani, I.S., Farah, M.Y., Abd El-Aleim, F.A., 1978. Co-extraction and separation of zirconium and hafnium by long-chain amines from sulphate media. Talanta 25, 523–525. Marczenko, Z., 1976. Spectrophotometric Determination of Elements. Ellis Harwood, Chichester, England, pp. 442–443. Mathur, J.N., Choppin, G.R., 1998. Paraffin wax as a diluent for extraction of actinides and lanthanides with TBP. Solvent Extr. Ion Exc 16, 459–469.
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