Coalescence Extraction System for Rapid Efficient and Selective

Jun 29, 2010 - The coalescence extraction system was developed for rapid, efficient, and selective separation of zirconium and hafnium from an aqueous...
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Coalescence Extraction System for Rapid Efficient and Selective Separation of Zirconium and Hafnium Majid Haji Hosseini and Naader Alizadeh* Department of Chemistry, Faculty of Science, Tarbiat Modares UniVersity, P.O. Box; 14115-175, Tehran, Iran

The coalescence extraction system was developed for rapid, efficient, and selective separation of zirconium and hafnium from an aqueous solution containing alkali, alkaline earth, and transition metal ions. Extraction was based on the coalescence properties of glutaronitrile in combination with the aqueous solution at elevated temperature from a homogeneous solution. In the next step, a significant temperature reduction (temperatureinduced phase separation) was used to enter the spinodal to form the two phase’s regions. The particle-size distribution at coalescence temperature was measured by a laser particle-size analyzer. Metal separation could be completed in a single operation lasting only 2 min with the extraction efficiency of more than 90%. The extractability in the coalescence extraction was comparable to that of traditional methods and was feasible for rapid separation of zirconium and hafnium. The mechanism of extraction was proposed depending on the hydrolysis and polymerization of these ions and the temperature of extraction. 1. Introduction Zirconium is used in the nuclear industry as a shielding material, in the manufacture of water-repellent textiles as a catalyst in organic reactions, and also in dye pigments and ceramics. Hafnium is used for alloying with iron, titanium, aluminum, and other metals. Hafnium is also used for nuclear control rods in an efficient “getter” for scavenging oxygen and nitrogen. Zirconium and hafnium coexist in nature but with opposite nuclear characteristics. Therefore, their separation prior to their transformation into pure metals is an essential task.1 On the other hand, zirconium is one of the most important fission products. High-level liquid waste (HLLW) arising from the spent nuclear fuel reprocessing process (PUREX process) contains zirconium with up to 1 g L-l concentration.2 The existence of zirconium will affect the solvent extraction process to recover actinides from HLLW. A survey of the literature shows that a number of extractants have been used for the extraction of zirconium and hafnium. Organophosphorus compounds, namely, TBP,3-7 D2EHPA,8-15 and Cyanex,16-20 have been extensively employed in solvent extraction of zirconium and hafnium. Amines, such as Aliquat 336 and alamine 33621 and trioctylamine,22,23 have been also used for the extraction. The use of other extractants such as dihexyl N,N-diethylmethylcarbamoyl phosphonate,24 isopropyl phosphonic acid mono(1-hexyl-4-ethyl) octyl ester (PT-2, HL),25 octyl (phenyl) N,N-diisobutylcarbamoyl methylphosphine oxide (CMPO),26 2-ethylhexyl phosphonic acid mono-2-ethyl hexyl ester (PC-88A),27 versatic acid 10,28 2-hydroxy-5-nonylacetophenoneoxime (LIX84-IC),29 DB18C6,30 and dibutyl butyl phosphonate (DBBP)31 have been also studied. Developing specific solvent extraction procedures for zirconium and hafnium, with the objective of making improvements in speed and efficiency, is desired by many workers. This calls for a novel extraction method for the separation of easily hydrolyzed and/or polymerized metal ions. A novel solvent extraction process developed by Ullmann et al.,32 called phase transition extraction (PTE) on the basis of the coalescence properties of solvents, in combination with the * Corresponding author. Fax +98-21-82883455. E-mail address: [email protected].

aqueous solution at elevated temperatures forms a homogeneous solution. In the next step, significantly reducing the temperature yields the separation of solution into two phases with the desired solute dissolved in the solvent phase. This process is called temperature-induced phase separation (TIPS). This technique, coalescence extraction, achieves extraction rates by approaching the theoretical limits and completely eliminates the limitations of diffusion and surface area that hamper other solvent extractions. At the same time, it avoids the problem of emulsion formation and eliminates the necessity of centrifuging. In this process, phase separation is very fast and completed within a few minutes. Lamb studied the phase transition extraction of Sr2+ and Pb2+ from solutions containing various nitrate salts by dicyclohexano-18-crown-6 as the chelating agent in a group of dinitrile solvents.33,34 In a previous work, we established the potential of this novel solvent system for the quantitative coalescence extraction of Ag+ from aqueous solution without any chelating agent.35 In this work, the coalescence extraction characteristics of Zr(IV) and Hf (IV) are experimentally examined using glutaronitrile from aqueous solutions without any chelating agent. Furthermore, the separation behaviors of these ions from alkali, alkaline earth, and transition metal ions solutions are also investigated. 2. Experimental Section 2.1. Materials. Glutaronitrile (GN) was procured from Merck Chemical Co. ZrOCl2 · 8H2O (Merck 98%) and HfOCl2 · 8H2O (Aldrich 98%) were used as the sources of Zr(IV), and Hf(IV), respectively. Stock solutions of Zr(IV) and Hf(IV) (200 mg L-1) were prepared by dissolving appropriate amounts of ZrOCl2 · 8H2O and HfOCl2 · 8H2O in doubly distilled water in a 100 mL volumetric flask. Dilute solutions were prepared by appropriate dilution of the stock solutions in water. Nitrate or chloride salts of other cations and chemicals were of reagent grade and used without further purification (all from Merck or Aldrich). 2.2. Equipment. A simultaneous inductively coupled plasmaoptical emission spectrometry (ICP-OES, Varian Vista-PRO, Springvale, Australia) with a radial torch coupled to a V-groove nebulizer and equipped with a charge-coupled detector (CCD)

10.1021/ie901729e  2010 American Chemical Society Published on Web 06/29/2010

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Table 1. Optimized Conditions for ICP Determination of the Zirconium and Hafnium Ions ICP-OES conditions (radial torch) rf generator power (kW) frequency of rf generator (MHz) plasma gas flow rate (L min-1) auxiliary gas flow rate (L min-1) nebulizer pressure (kPa) viewing hight (mm) pump rate (rpm) Hf wavelength (nm) Zr wavelength (nm)

1.65 40 15.0 1.5 240 9 15 263.872 343.823

was used for determination of the target elements. The argon gas with 99.999% purity for ICP-OES was purchased from Roham Gas Co., Tehran, Iran. Measurement was made in triplicate under the operating conditions listed in Table 1. The temperature of the solution in coalescence extraction was maintained at the desired value of (0.1 °C by circulating thermostat water through the jacketed glass cell, while the mixture solution was continuously stirred using a magnetic stirrer. Conductance measurements were carried out with a Metrohm 712 conductivity meter. A dip-type cell, made of platinum black, was used. The particle-size distribution of system in 50% (v/v) at coalescence temperature was measured with a laser particle-size analyze (Malvern Mastersizer, Malvern Instruments, Orsay, France). 2.3. Extraction Procedure. Coalescence extraction experiments were carried out by filling a glass vessel (constructed in the laboratory) with 2 mL of aqueous Zr(IV) and Hf(IV) solution (20 mg L-1) and an equal volume of GN. The vessel was then heated on a water bath-hot plate to the temperature of mutual miscibility (for GN-H2O 68.3 °C).35 The attainment of this temperature was accompanied by a suddenly visible change in the mixture from cloudy to clear. These temperatures were typically reached after less than 20 s of heating. Once complete miscibility was achieved, after 2 min in this condition, the solutions were immediately cooled by placing the vessel in a bath of cool water (for 2 min). After separation of the two phases, the analyte elements ions contained in the aqueous phase were quantified by ICP-OES measurements at the proper wavelength for each ion against the blank. The amount of Zr(IV) and Hf(IV) ions in aqueous solution were determined from the calibration curves and calculated extraction efficiency. A blank, submitted to the same procedure described above, was measured parallel to the samples and calibration solutions. The limit of detection, which was calculated as the concentration, gave a reading equal to 3 times the standard deviation of a series of the procedural blank signals, found to be 10 and 80 µg L-1 for Zr at 343.823 nm and for Hf at 263.872 nm, respectively. 3. Results and Discussion 3.1. Hydrolysis and Polymeric Reactions. The great tendencies of the Zr(IV) and Hf(IV) salts to be hydrolyzed are mainly due to the large charges and the small diameters of the zirconium and hafnium ions (rZr4+ ) 0.74 Å and rHf4+ ) 0.75 Å). Assuming no presence of the complex-forming ions, the hydrolysis of Zr and Hf (M) ions can be expressed by the following reaction.36 4+

mM(H2O)x

+ mnH2O T mM(OH)n(H2O)x-n

+ mnH3O+ (1)

(4-n)+

Throfimor and Stepanova found that the zirconium ions have a 4+ charge in 2 mol L-1 HNO3. Hydrolytic reactions decrease

Figure 1. Variation of conductivity and pH with time for 20 mg L-1 of Zr(IV) (O) and Hf(IV) (b) ions in the distilled water at room temperature.

the ion charge yielding a charge of 2+ in approximately 1 N HNO3.37 At the same time as the hydrolytic reactions in a solution of zirconium salts, a polymeric reaction may occur under certain conditions, that is, formation of ions and molecules containing more than one atom. Polymerization is frequently accompanied by formation of the colloids, which substantially complicates the behavior of zirconium and hafnium in aqueous solutions. In the 2 mol L-1 solution of HClO4 at a zirconium concentration of 20 mg L-1, this element is present in the form of simple ions with charges of 3+ and 4+. At higher concentrations or lower acidities, zirconium exists predominantly in the form of polymerized particles that may be formed according to eq 2.36 mM(OH)n(H2O)x-n(4-n)+ T Mm(OH)mn(H2O)m(x-n)m(4-n)+ (2) Previous studies on the formation of polymers reveal that the solution acidity substantially changes the diffusion coefficient of the zirconium ion, which can be more explained by polymerization at lower acidities. The results also indicate that the value of the diffusion coefficient is influenced by the time interval between the preparation of the solutions and the measurements. The results of cryoscopic measurements, the influence of outside parameters on the solution’s pH,38 the behavior of zirconium and hafnium, and other facts indicate the taking place of the polymerization. The study of the zirconium extraction by D2EHPA in kerosene12 revealed that the change of the polymerization factor is a function of the acid, zirconium and hafnium concentrations, the period of aging, and temperature of solution. According to eqs 1 and 2, hydrolysis and polymerization reactions of tetravalent zirconium and hafnium ions can be shown by the following equations Mm(OH)mn(H2O)m(x-n)m(4-n)+ T Mm(OH)nm+y(H2O)[m(x-n)]-y([m(4-n)]-y)+ + yH+ (3) mM(H2O)x4+ + mnH2O T Mm(OH)nm+y(H2O)[m(x-n)]-y([m(4-n)]-y)+ + (mn + y)H+ (4) Figure 1 shows the electrical conductivity and pH of 20 mg L-1 of zirconium and hafnium solutions vs time. The measurements are taken at room temperature under the same extraction

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Table 2. Variation of DGN/W with Temperature and Thermodynamic Data ∆H° (kJ mol-1) ∆S° (J mol-1) ∆G° (kJ mol-1)

DGN/W T (K) 298.0 323.0 341.0a 344.0 351.0 a

Zr

Hf

0.09 0.15 0.18 0.24 0.63 0.69 2.38 2.51 9.06 10.11

Zr

Hf

Zr

Hf

Zr

Hf

36.7 36.7 250.4 250.4 250.4

29.3 29.3 255.6 255.6 255.6

102.1 102.1 732.5 732.5 732.5

81.3 81.3 748.1 748.1 748.1

6.3 3.7 0.5 -1.7 -6.8

5.0 3.0 0.3 -1.9 -7.1

Coalascence temperature, Tc.

experimental conditions. The conductivity value rises significantly with time until reaching a maximum value in the range 80-200 min, but after 200 min, it increased slowly. As observed for the proton activity measurements, a time of about 400 min is necessary to obtain a stable conductivity value after hydrolysis and polymerization reactions of the metal ions, which indicates that the electrical conductivity measurement is more sensitive than the pH-metric. We find that during the polymerization reaction, the pH drops as the reaction proceeds (Figure 1). The polymer chain grows by the combination of monomer cations with oligomer cations followed by elimination of protons. This behavior can be in agreement with the variation of the conductivity and the pH of the solution according to eq 4. Further evidence for hydrolysis and polymerization reaction in the solution is exemplified in extraction of tetravalent zirconium and hafnium ions by glutaronitrile. Glutaronitrile is a dinitrile solvent [NC(CH2)3CN] containing two CN functional groups available for bonding with the metal ions. The coordination chemistry of dinitriles with ions39-41 and neutral molecules42 has been extensively investigated previously. The extraction efficiency with glutaronitrile for soft cations such as silver ion is quantitative because of the formation of complexes of ion and glutaronitrile.35 Some preliminary experiments show that coalescence extraction efficiency of glutaronitrile for 20 mg L-1 zirconium and hafnium ions in aqueous solution is 65% and 62.4% for hafnium and zirconium, respectively. On the other hand, glutaronitrile does not show any tendency for the extraction of zirconium and hafnium ions in the presence of 2 mol L-1 of HNO3. The results indicate that the zirconium and hafnium ions have the large charge (4+) in the 2 mol L-1 of HNO336 and glutaronitrile does not show any tendency for interaction with the metal ions. The hydrolysis and polymerization reactions are also carried out in the absence of HNO3 in solution.36,37 Therefore, to obtain quantitative extraction of Zr(IV) and Hf(IV) by glutaronitrile, the extraction procedure is optimized for various parameters affected in hydrolysis and polymerization such as temperature, acid concentration, and the period of aging of the solutions. The percent of extraction of Zr(IV) and Hf(IV) ions are calculated by the following equation: E% )

([M]tot - [M]aq) [M]org × 100 ) × 100 [M]tot [M]tot [M]tot ) [M]org + [M]aq

(5) (6)

where [M]org, [M]tot, and [M]aq are the metal ion concentration in organic phase after extraction, in aqueous phases before and after extraction, respectively. 3.2. Influence of Temperature and the Extraction Thermodynamic. To assess the temperature effect of the metal ions extraction by GN, a series of extraction experiments are performed in the range 25-78 °C and the obtained DGN/W values are listed in Table 2. The results indicate that the extraction

Figure 2. Influence of temperature on the DGN/W of Zr(IV) (O) and Hf(IV) (b). Extraction conditions: 20 mg L-1 of the ions in the distilled water; time of extraction, 2 min; cooling temperature, 0 °C; cooling time, 2 min; aging time, 48 h.

efficiency of the metal ions increases by increasing the temperature. From the viewpoint of thermodynamics, extraction of a metal ion into an organic phase from the aqueous phase can be regarded as a transfer process of an ion from the aqueous to the organic phase. The Gibbs free energy (∆G °T) of such transfer process at a given temperature can be calculated from the molar extraction equilibrium constant (Kex) using the following equation ∆G°T ) -RT ln Kex ) -RT ln DGN/W

(7)

where DGN/W and ∆H °T are the distribution ratio and transfer enthalpies, respectively. If the ∆H °T values for a given ion are assumed to be constant over the short temperature range of study, the values can be calculated from the linear relationships between log DGN/W and 1/T expressed as follows: + ∆S°/2.3R log DGN/W ) -∆H°/2.3RT T T

(8)

The transfer enthalpies and entropies for the zirconium and hafnium ions extraction processes are determined by the slopes and intercepts of the plots, respectively. The log DGN/W extraction of Zr(IV) and Hf(IV) at different temperatures is shown in Figure 2. A curve is obtained instead of a straight line with a single slope, and extraction of both of them increases as the temperature increases. The curves with different slopes indicate that extraction of zirconium and hafnium under these conditions is not a straightforward process but there are different extraction mechanisms. Clearly, there are two straight lines obtained by a transition around 68 °C (coalescence temperature ) TC). The different slopes of these lines indicate two ∆H °T values for two separate extraction mechanisms. In T g TC, dispersion and droplet coalescence phenomena are observed and the temperature dependency of the extraction of Zr(IV) and Hf(IV) is not distinct. The resultant ∆G °T, ∆H °T, and T∆S °T values are included in Table 2. It can be seen that all the values of ∆H °T and ∆S °T are positive whereas those of ∆G °T are negative or less positive. The negative values of ∆G °T indicate that the extraction processes in T > Tc are spontaneous. These thermodynamic data also suggest that all the extraction processes in T > Tc are driven by entropy terms, which is the characteristic of the desolvation of metal ions and the dispersion process. The interfacial surface area43 and diffusion are the predominant factors that control the extraction rate in most liquid-liquid

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Figure 3. Influence of H+ concentration on the precipitation (right scale) and coalescence extraction (left scale) of Zr(IV) and Hf(IV). Extraction conditions: 20 mg L-1 of the ions in the solution; time of extraction, 2 min, cooling temperature, 0 °C; cooling time, 2 min; agent time, 48 h; temperature of extraction, 76 °C.

extraction systems even when efficient stirring or shaking devices are employed. The coalescence extraction technique completely eliminates the limitation of diffusion and surface area hamper rather than other extraction systems. The surface area across which cation transfer can occur reaches its theoretical limit, and equilibrium is achieved almost instantaneously. At the coalescence temperature in the homogeneous phase, complexation of polymeric metal ion and GN is completed. On the other hand, the increase of temperature of the mixture increased the polymerization and, therefore, the percent of extraction to be increased. To investigate the phase separation between GN and water, the solution was cooled and each species partitioned into its appropriate phase. 3.3. Influence of pH. The pH of the solution plays an important role in the polymerization reaction (eqs 3 and 4), complex formation, and subsequent percent of extraction (Figure 3). In this case, the degree of polymerization and degree of hydrolysis (eqs 2 and 3) are decreased with an increase of [H+]; therefore, the percent of extraction is decreased. In the present work, the effect of [H+] on the complex formation of target ions is studied within HNO3 in the concentration range 10-5 to 10-1 mol L-1 and NaOH at concentrations of 10-3 and 10-4 mol L-1. The effect of pH on the precipitation of zirconium and hafnium ions from an aqueous solution without GN is first investigated. For all experiments described here, a contact time of 48 h and an initial concentration of 20 mg/L are used. Figure 3 shows variation of the emission intensities of ICP for zirconium and hafnium solutions at different values of the pH (right scale). As observed in Figure 3, the emission intensity remains constant at a pH ranging from 1.2 to 8. At pH below 8, zirconium and hafnium ions are in the form of the soluble hydrolyzed complexes. This would indicate that the zirconium and hafnium ions are not precipitating at pH < 8. For a pH above 8, the insoluble hydroxyl complexes become predominant and the emission intensity of the metal ions decreases. Also shown in Figure 3 is the effect of pH on the extraction of the zirconium and hafnium ion from an aqueous solution in the presence of GN (left scale). As shown in Figure 3, the percent of extraction is nearly constant in the pH range 3.4-7. Hence, neutral pH is used for the subsequent coalescence extraction of zirconium and hafnium ions. 3.4. Influence of Aging Period of the Solutions. A subsequent parameter that affected polymerization is the period of aging of the solutions. This factor is studied by variation of aging in the time range 90-3150 min. It can be noted that the percent of extraction is increased considerably with the allowed

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Figure 4. Influence of aging time on the coalescence extraction of Zr(IV) and Hf(IV). Extraction conditions: 20 mg L-1 of the ions in distilled water; time of extraction, 2 min; cooling temperature, 0 °C; cooling time, 2 min; temperature of extraction, 76 °C.

time for the aging time (E % is increased 5-fold when a freshly prepared solution is aged for 10 h). Figure 4 shows the percent of extraction vs aging time plots for both zirconium and hafnium ions. In both cases, E % is increased by increasing the aging time. Within 9 h, the variation is large, and then with further increase in aging time, the variation is slowed. The results presented in Figure 4 show that the aging time has a significant effect on the increase of the extraction efficiency, which is in agreement with the literature results, demonstrating that an increase of the period of aging is the reason for the increase of the degree of polymerization.12 3.5. Mechanism of Extraction. The probable mechanism of extraction can be summarized as follows: (I) Hydrolysis and polymerization of tetravalent zirconium and hafnium ions according to eqs 1-4: Mm(OH)nm+y(H2O)[m(x-n)]-y([m(4-n)]-y)+ ≡ P (P is polymeric cation)

If

(II) Phase transfer to critical solution (heating) organic phase + aqueous phase f critical phase Therefore GNorg T GNcritical

(9)

Paq T Pcritical

(10)

and

(III) Complex formation in critical phase takes place (PGN): Pcritical + GNcritical T PGNcritical

(11)

(IV) Phase transfer to organic phase (cooling) (PGN)critical T (PGN)org

(12)

where Paq is solvated hydrolyzed polymerized metal in aqueous before homogeneous mixture and (PGN)critical and (PGN)org are complexes of polymerized metal ions after heating (homogeneous solution) and organic phase after cooling, respectively. The overall reaction for the extraction of zirconium and hafnium for such solutions may be expressed by eq 13, and the extraction constant (Kex) can be written as follows:

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mM(H2O)xaq4+ + mnH2O + GNorg T (PGN)org + (mn + y)Haq+ (13) Kex )

[PGN]org[H+](mn+y) [M(H2O)x4+]aqm

(14)

It has been already mentioned that the hydrolysis and polymerization reactions are necessary for extraction of Zr(IV) and Hf(IV) ions by GN. The GN is known to form hydrogen bonds with the oxygen atoms of hydroxyl group in polymerized metal ion. Figure 5 shows the particle-size distributions of the coalescence extraction system in the critical temperature region where it can be seen that the particle-size distribution is broader at near coalescence temperature (Figure 5a). The broader particlesize distribution indicates that the coalescence of the particles has taken place to a greater extent. From Figure 5b, it can be seen that the particle size decreases with the increase of the temperature. This is due to the effect of increasing the temperature on reducing the unstable particle emulsion and then increasing the number of stabilized particles that yield the smaller particle size. The mean particle size in the critical phase is in the range 6.60-10.00 µm depending on the temperature used in the extraction process. 3.6. Interference Effect of Metal Ions. To investigate the selective extraction of Zr(IV) and Hf(IV) ions from their mixtures with diverse metal ions, 10 mL of a solution containing 20 mg L-1 of the Zr(IV) and Hf(IV) ions and foreign ions in different interference to the analyte ratios is considered in the extraction procedure. The obtained results (Table 3) indicate that under the specified conditions in the procedure, most of the examined cations and anions do not interfere with the extraction of the Zr(IV) and Hf(IV). Since the employed chloride and nitrate salts in this study are without any interference, their respective anions can pose no interference either. However, some of the tried species such as Al3+ and Fe3+ interfer with the extraction of Zr(IV) and Hf(IV) ions. Interference of Fe3+ is eliminated in the presence of 0.2 mol L-1 SCN- as masking agent, and interference of Al3+ is eliminated by extraction at pH above 9 (in the presence of 0.05 mol L-1 NaOH) where Al3+ is converted into the soluble tetrahydroxoaluminate(III).44 In this case, no interference is observed for Fe3+ and Al3+ up to 100 and 60 mg L-1, respectively. The reproducibility of the investigated ion extraction from four replicate measurements is found to be 93.4 ( 2.0 for Hf(IV) and 94.4 ( 3.7 for Zr(IV) in the presence of 1500 mg L-1 K+. 3.7. Loading Capacity and Stripping of the Glutaronitrile. The loading capacity of GN is tested by contacting repeatedly 3 mL of extractant with the same volume of aqueous containing 200 mg L-1 of Zr(IV) and Hf(IV). After coalescence extraction under the specified conditions in the procedure, the phases are separated and the zirconium and hafnium content in the aqueous phase are analyzed. The amount of zirconium and hafnium transferred into the organic phase in each contact is calculated by the difference in the cumulative concentrations of the ions in the organic phase after determining each stage of contact. After three contacts, the loaded extractant concentrations are 176.2 and 174.5 mg L-1 for Hf(IV) and Zr(IV), respectively, and they remain constant with further contacts. Stripping of metals from loading the organic phase by back-extraction is investigated using HCl in the range 1-5 mol L-1, and the results show that the best stripping agent is 1 mol L-1 HCl with >85% stripping.

Figure 5. Particle-size distributions of the coalescence extraction system in the critical temperature region: (a) 63 °C; (b) 68 °C. Table 3. Effect of Foreign Ions on the Recovery of 20 mg L-1 Zirconium and Hafnium in Aqueous Solution by Coalescence Extraction System recovery (%) foreign ion (mg L-1) +

K Li+ Na+ Mg2+ Ca2+ Ba2+ Ni2+ Co2+ Cd2+ Zn2+ Ce3+ La3+ Cu2+ Fe3+ Al3+

1500 1500 1500 1500 1500 1500 500 500 500 500 200 200 100 100b 60

Hf(IV) a

93 99 99 99 99 99 99 98 95 94 90 94 90 93 99

Zr(IV) 94 99 99 99 99 99 99 98 95 94 91 94 90 96 99

a Percent of extraction of target ions in the presence of the mentioned amount of the foreign ion. b Co extraction for Fe3+ is 25.63%.

4. Conclusion The zirconium and hafnium extraction efficiency of GN is quantitative (>90%) in the absence of chelating agents. The important features of the method described here comparing to the other previously published methods are summarized as follows: (i) Quantitative extraction is achieved from neutral media, so no added concentrated acid is required. (ii) GN is a solvent with a high boiling point and low upper critical solution temperature. This characteristic reduces the danger of losing the organic solvent to evaporation or the accumulation of toxic and flammable fumes during industrial and laboratory use. (iii) This method is very rapid. (iv) Phase separation is complete within a few minutes (v) with no emulsion formation at T > Tc. (vi) The surface area across which cation transfer can occur reaches its theoretical limit, and equilibrium is achieved almost instantaneously (particles size