Development of Novel Extractants with Amino Acid Structure for

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Development of Novel Extractants with Amino Acid Structure for Efficient Separation of Nickel and Cobalt from Manganese Ions Yuzo Baba,† Fukiko Kubota,† Noriho Kamiya,†,‡ and Masahiro Goto*,†,‡ †

Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan Center for Future Chemistry, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan

‡

ABSTRACT: The solvent extraction separation of nickel and cobalt from manganese is an important issue to be resolved. Novel amic acid type extractants with the glycine or sarcosine moiety N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG) and N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]sarcosine (D2EHAS) were synthesized to achieve this separation. These extractants were prepared by a simple two-step reaction and were readily soluble in aliphatic organic solvents. The extraction behavior of Ni2+, Co2+, and Mn2+ with D2EHAG and D2EHAS in n-dodecane was investigated compared with that of conventional extractants. The novel extractants extracted Ni2+ and Co2+ preferentially with a high selectivity to Mn2+. The metal ions could be back-extracted quantitatively using 1 mol dm−3 sulfuric acid. The extraction mechanism of the three metal ions with D2EHAG and D2EHAS was investigated, and results suggest that one divalent metal ion is extracted with two extractant molecules. capable of extracting Co2+ and Ni2+ selectively over Mn2+. Because of its high affinity to metal ions, however, a high temperature (60 °C) and high acid concentration (5.7 M HCl) are required to strip the metal ions from the extracting phase. Recently, a synergistic extraction system of an alkyl monocarboxylic acid, Versatic 10 (2-methyl-2-ethylheptanoic acid) with aliphatic α-hydroxyoxime such as LIX 63 (5,8diethyl-7-hydroxydodecan-6-one oxime),23−25 which has been used as a synergistic reagent for transition metals, has been reported to display a significant synergistic effect toward some transition metals including Co2+ and Ni2+. This has enabled their separation from other metals such as Mn2+. However, the use of multiple extractants may complicate the solvent extraction process. Few extractants can therefore separate Ni2+ and Co2+ from Mn2+ effectively, and novel extractants to meet such a requirement are strongly desired. In this study, we have developed two new amic acid type extractants for the selective separation of Co2+ and Ni2+ from Mn2+. One is a glycine derivative, N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG) (Figure 1a), and the other is a sarcosine (N-methyl glycine) derivative, N-[N,N-di(2ethylhexyl)aminocarbonylmethyl]sarcosine (D2EHAS) (Figure 1b). These two extractants contain a carboxyl group and a nitrogen atom derived from an amino acid structure in the molecule. Furthermore, we have designed the new extractants without a phosphorus atom, because extractants containing Patoms often generate secondary wastes.6 In this work, we investigate the extraction behavior of D2EHAG and D2EHAS for Co2+, Ni2+, and Mn2+ compared with some typical commercial extractants, such as D2EHPA

1. INTRODUCTION There is growing demand for cobalt and nickel because of their increased application in high-technology industries such as batteries, alloys, magnetic materials, and catalysts.1−4 Their stable supply is of worldwide concern, and used products that contain cobalt or nickel have been highlighted as possible secondary resources1−3 as opposed to using natural resources.4 Therefore, the development of efficient techniques for the separation and recovery of these metals is a critical issue. Solvent extraction is used widely for the separation and purification of metal ions on an industrial scale. It displays a number of advantages compared with other competitive techniques such as ion-exchange, adsorption, and precipitation, such as its easy operation using simple equipment and small amounts of reagent and the ability to operate in a continuous mode and achieve high sample throughput. In the solvent extraction process, separation performance is influenced by the properties of the extracting reagent (extractant) used. However, many metal combinations exist that are difficult to separate from one another. A variety of extractants have been designed for the separation of critical metals such as rare earth metals,5−9 precious metals,10,11 and transition metals such as nickel (Ni2+), cobalt (Co2+), and so on. The selective extraction of Ni2+ and Co2+ from impurity metals such as zinc, magnesium, and calcium has been examined.12−16 However, difficulties still remain for their separation from manganese (Mn2+), which often coexists in large amounts in natural and secondary resources.17,18 Commercial organophosphorous extractants, such as 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC-88A),19 di-(2-ethylhexyl) phosphoric acid (D2EHPA),20 and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272),19,20 are typically used in hydrometallurgy; however, the separation of Ni2+ and Co2+ from Mn2+ using these extractants is difficult because they are selective for Mn2+. Among them, Cyanex 301 (bis-(2,4,4-trimethylpentyl)dithiophosphinic acid),21,22 which includes a sulfur atom, is the only extractant © 2013 American Chemical Society

Received: Revised: Accepted: Published: 812

June 15, 2013 December 20, 2013 December 25, 2013 December 25, 2013 dx.doi.org/10.1021/ie403524a | Ind. Eng. Chem. Res. 2014, 53, 812−818

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2.2. Synthesis of Novel Extractants D2EHAG and D2EHAS. D2EHAG and D2EHAS were synthesized by a twostep bimolecular nucleophilic substitution (SN2 reaction) according to the synthesis route in Figure 2. Nuclear magnetic resonance spectra (NMR; AVANCE II 300, Bruker, Germany) were recorded for 1H NMR (300 MHz) and 13C NMR (75.5 MHz) in deuterated chloroform (CDCl3), with tetramethylsilane as internal standard for identification of the final products. 2.2.1. Synthesis of 2-Chloro-N,N-di(2-ethylhexyl)acetamide (CDEHAA). 2-Chloro-N,N-di(2-ethylhexyl)acetamide (CDEHAA) was synthesized from di(2-ethylhexyl)amine and chloroacetyl chloride as described previously (Figure 2a).26−28 Chloroacetyl chloride (13.6 g, 0.12 mol) was added slowly to the dichloromethane solution of di(2-ethylhexyl)amine (24.1 g, 0.1 mol) and triethylamine (10.1 g, 0.1 mol), and the mixture solution was stirred for 3 h at room temperature (synthesis scheme in Figure 2a). The resulting mixture was washed with 0.1 M HCl to remove unreacted amine. The organic phase was washed with deionized water several times and dried with anhydrous sodium sulfate. After vacuum filtration to remove anhydrous sodium sulfate, the dichloromethane was removed in vacuo and 29.1 g of yellow liquid was obtained (yield: 92%). 2-Chloro-N,N-di(2ethylhexyl)acetamide (CDEHAA): 1H NMR (300 MHz, CDCl3) δ 4.08 (s, 2H, COCH2Cl), 3.47−3.11 (m, 4H, NCH2CHR1R2), 1.65 (m, 2H, NCH2CHR1R2), 1.27 (m, 16H, RCH2R), 0.89 (q, 12H, CH3). 13C NMR (75.5 MHz, CDCl3) δ 167.1, 51.7, 48.7, 41.6, 38.5, 36.8, 30.6, 30.4, 28.8, 28.7, 23.8, 23.1, 14.1, 10.9, 10.6. Anal. Calcd for C18H36Cl1N1O1: C, 68.00; H, 11.41; N, 4.41%. Found: C, 67.91; H, 11.36; N, 4.61%. 2.2.2. Synthesis of N-[N,N-Di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG). D2EHAG was synthesized by the substitution reaction28,29 of glycine and CDEHAA prepared above, as follows (Figure 2b): glycine (15.0 g, 0.2 mol) was added to a methanol solution with dissolved sodium hydroxide (8.0 g, 0.2 mol) as alkaline catalyst. CDEHAA (12.7 g, 0.04 mol) was added dropwise to the mixture solution, and the reactant was stirred for 15 h at 333 K. The solvent from the resulting solution was removed in vacuo. The residue was dissolved in dichloromethane and washed with 1.0 mol dm−3 H2SO4 immediately to remove the unreacted glycine and sodium hydroxide. The organic phase was washed with deionized water several times and then dried with anhydrous sodium sulfate. After vacuum filtration to remove anhydrous sodium sulfate, dichloromethane was removed in vacuo. The product obtained was a yellow viscous liquid (12.5 g, yield 87%). N-[N,N-Di(2-ethylhexyl)aminocarbonylmethyl]-

Figure 1. Molecular structures of extractants used. Novel amic acid type (a) N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG), (b) N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]sarcosine (D2EHAS); synthesized (c) N,N-dioctyldiglycol amic acid (DODGAA); commercial (d) di-(2-ethylhexyl) phosphoric acid (D2EHPA), (e) 2-methyl-2-ethylheptanoic acid (Versatic 10), (f) 5,8-diethyl-7-hydroxydodecan-6-one oxime (LIX 63).

and a mixture of Versatic 10 and LIX 63, and discuss the potential use of the novel extractants for the separation and recovery of Co2+ and Ni2+ from Mn-containing resources.

2. EXPERIMENTAL SECTION 2.1. Reagents. Di(2-ethylhexyl)amine (>98.0%) and chloroacetyl chloride (>98.0%) were obtained from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). Triethylamine (>99.0%) and sarcosine (>95.0%) were purchased from Wako Pure Chemical Industries (Osaka, Japan). Glycine (>99.0%) was from Kishida Chemical Co., Ltd. (Osaka, Japan). N,NDioctyldiglycol amic acid (DODGAA) used as an extractant was synthesized as described previously,5,6 and the commercial extractants D2EHPA (>95.0%), Versatic 10 (100%), and LIX 63 (>70%) were supplied by the Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan), Mitsubishi Chemical Co., (Tokyo, Japan), and Cognis Corp. (Arizona, USA), respectively. The structures of these extractants are shown in Figure 1 along with the new extractants. Cobalt(II)sulfate heptahydrate (>99.0%), nickel(II)sulfate hexahydrate (>99.0%), and manganese(II)sulfate pentahydrate (>99.0%) were also from Kishida Chemical Co., Ltd. Special grade n-dodecane was used as an organic solvent. All other reagents and solvents were analytical grade and were used as received.

Figure 2. Synthesis scheme of extractants: (a) synthesis of 2-chloro-N,N-di(2-ethylhexyl)acetamide (CDEHAA), (b) synthesis of novel extractants using CDEHAA; D2EHAG: R = H, D2EHAS: R = CH3. 813

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Figure 3. Extraction behavior of Ni2+, Co2+, Mn2+ and separation factor β with (a) 10 mmol dm−3 D2EHAG in n-dodecane (solid lines for D2EHAG are theoretical lines) and 100 mmol dm−3 DODGAA in n-dodecane with 5% v/v 1-octanol; (b) 10 mmol dm−3 D2EHAS in n-dodecane.

mmol dm−3 metal ions was prepared by dissolving their sulfates in 0.1 mol dm−3 H2SO4 or (NH4)2SO4. The aqueous feed solution pH was adjusted by mixing these aqueous solutions and/or adding 28 wt % ammonia solution. Equal volumes (5 cm3) of the aqueous and organic solutions were mixed in a sealed tube by vortex mixer and then shaken gently for more than 1 h to attain extraction equilibrium at 298 K. After phase separation, the metal ions in the organic phase were stripped using H2SO4 solution. The metal concentrations in the aqueous phase for the extraction and stripping tests were measured using an inductively coupled plasma-atomic emission spectrometer (ICP-AES, Optima 5300, Perkin-Elmer Co, Waltham, Ma, USA). The pH was measured using a pH meter (HM-30R, DKK-TOA Co, Tokyo, Japan). The extent of extraction and stripping of the metal ions and the extraction E [−] and stripping S [−] ratios were calculated using eqs 1 and 2:

glycine (D2EHAG): 1H NMR (300 MHz, CDCl3) δ 8.83 (br, 1H, COOH), 4.04 (s, 2H, NHCH2COOH), 3.74−2.80 (m, 6H, NCH 2 CHR 1 R 2 and NC(O)CH 2 NH), 1.60 (m, 2H, NCH2CHR1R2), 1.25 (m, 16H, RCH2R), 0.88 (m, 12H, CH3). 13C NMR (75.5 MHz, CDCl3) δ 170.4, 165.9, 50.1, 48.2, 47.6, 37.7, 36.6, 30.5, 28.8, 23.8, 23.4, 14.1, 11.0, 10.9. Anal. Calcd for C20H40N2O3·0.2H2O C, 66.70; H, 11.31; N, 7.78. Found: C, 66.71; H, 11.30; N, 7.49. 2.2.3. Synthesis of N-[N,N-Di(2-ethylhexyl)aminocarbonylmethyl]sarcosine (D2EHAS). D2EHAS was synthesized in a manner similar to D2EHAG by the substitution reaction of sarcosine (N-methyl glycine) and CDEHAA as shown in Figure 2b. A mixture of sarcosine (4.0 g, 0.045 mol) and sodium hydroxide (1.8 g, 0.045 mol) as alkaline catalyst dissolved in methanol was prepared. CDEHAA (12.7 g, 0.04 mol) was added dropwise to the mixture solution followed by stirring for 15 h at 333 K. By following the same procedure for the synthesis of D2EHAG as described in 2.2.2, a brown viscous liquid (12.3g) was obtained (yield 83%). N-[N,N-Di(2ethylhexyl)aminocarbonylmethyl]sarcosine (D2EHAS): 1H NMR (300 MHz, CDCl3) δ 9.53 (br, 1H, COOH), 4.03 (s, 2H, CH3NCH2COOH), 3.70 (d, 2H, NC(O)CH2NCH3), 3.46−3.01 (m, 4H, NCH2CHR1R2), 2.84 (d, 3H, CH2N(CH3)CH2), 1.59 (m, 2H, NCH2CHR1R2), 1.25 (m, 16H, RCH2R), 0.87 (m, 12H, CH3). 13C NMR (75.5 MHz, CDCl3) δ 170.5, 167.4, 58.6, 56.9, 50.5, 48.4, 42.3, 37.9, 36.7, 30.5, 28.8, 23.8, 23.0, 14.1, 11.0, 10.6. Anal. Calcd for C21H42N2O3·0.2H2O: C, 67.41; H, 11.42; N, 7.49. Found: C, 67.71; H, 11.37; N, 7.31. 2.3. Extraction Procedure. The extracting organic solution was prepared by dissolving D2EHAG or D2EHAS in ndodecane, which is similar in properties to that of the industrial solvent kerosene. An organic solution containing a commercial extractant such as D2EHPA or a mixture of Versatic 10 and LIX 63 was prepared for comparison with the novel extractants. 1Octanol (5 vol%) was added to n-dodecane as a solubilizer when DODGAA was used. An aqueous solution containing 0.1

E=

S=

[M2 +]org,eq [M2 +]aq,init

=

[M2 +]aq,init − [M2 +]aq,eq [M2 +]aq,init

(1)

[M2 +]aq,strip [M2 +]org,init

(2)

where [M2+] represents the concentration of metal ion, aq and org denote the aqueous and organic phases, respectively, init and eq are the initial and equilibrium states, respectively, and strip represents the stripping phase at equilibrium. The distribution ratio D[-] was calculated from eq 3: D= 814

[M2 +]org,eq [M2 +]aq,eq

=

[M2 +]aq,init − [M2 +]aq,eq [M2 +]aq,eq

(3)

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Figure 4. Extraction behavior of Co2+, Mn2+ and separation factor βCo/Mn with (a) 50 mmol dm−3 D2EHPA in n-dodecane; (b) 50 mmol dm−3 LIX 63 and 50 mmol dm−3 Versatic 10 mixture in n-dodecane and 100 mmol dm−3 Versatic 10 in n-dodecane.

The high selectivity for Ni2+ and Co2+ with D2EHAG may therefore be attributed to the amine structure (-NH-) in the center of the D2EHAG, because Ni2+ and Co2+, which are a soft acid compared with Mn2+, have a higher affinity to softer nitrogen than oxygen, according to the hard and soft acids and bases rule.34,35 Although the extraction ability of Versatic 10 for Ni2+ and Co2+ was low as described above, the addition of LIX 63, which contains a nitrogen atom that can interact with metal ions, enhanced the extraction and separation performance by a synergistic effect as shown in Figure 4b. However, the extraction ability was lower than that of D2EHAG, and the high extraction and separation performance of D2EHAG could be attributed to a chelate effect by the tridentate structure of the D2EHAG formed by the amide and amino acid groups. The separation factor, β, defined as the ratio of distribution ratio D for each metal, is also given in Figures 3 and 4. The novel extractants have a high selectivity for Co2+ over Mn2+ compared with that of the conventional extractants. In the extraction with D2EHAS, which introduced a methyl group to the nitrogen atom in the amine structure, the selectivity of Co2+ and Ni2+ toward Mn2+ was enhanced, although the selectivity between Ni2+ and Co2+ decreased compared with that of D2EHAG. The difference in pH1/2 (half-extraction pH values), ΔpH1/2, between Co2+ and Mn2+ with D2EHAG and D2EHAS was approximately 2 and that between Co2+ and Ni2+ with D2EHAG was over 0.5. Therefore, the novel extractants, D2EHAG and D2EHAS, can be applied for the recovery of Ni2+ and Co2+ from leach solution of electronic wastes such as lithium ion batteries, or of Mn-rich natural ore even in the presence of large amounts of Mn2+. The separation of Ni2+ and Co2+ was also possible using D2EHAG. In preliminary investigations, it was confirmed that 1 mol dm−3 D2EHAG was soluble in the aliphatic organic solvent n-dodecane and not only in aromatic organic solvents such as toluene. As described

3. RESULTS AND DISCUSSION 3.1. Extraction Behavior of Metal Ions with Novel Extractants. The extraction of Ni2+, Co2+, and Mn2+ from the aqueous feed phase containing the three metal ions, with D2EHAG or D2EHAS in n-dodecane is shown in Figure 3 as a function of aqueous phase equilibrium pH. As shown in Figure 3a, D2EHAG extracted the metal ions selectively in the following order: Ni2+ > Co2+ ≫ Mn2+. The former two metal ions could be extracted satisfactorily, and Ni2+ and Co2+ were separated from Mn2+ under acidic conditions. A similar extraction behavior was observed for D2EHAS as for D2EHAG, and the separation of Ni2+ and Co2+ from Mn2+ was achieved at lower pH compared with D2EHAG under the same experimental conditions, although the selectivity between Ni2+ and Co2+ was suppressed (Figure 3b). The extraction behavior of Co2+ and Mn2+ was compared with that of the conventional extractants. The organophosphorus extractant, D2EHPA, extracted Mn2+ preferentially over Co2+ as shown in Figure 4a, and similar results were also reported for PC-88A and Cyanex 272.19 The industrial monocarboxylic acid extractant, Versatic 10,30,31 extracted the three metal ions at around neutral pH, and a high selectivity among the metal ions was not observed (Figure 4b). A new extractant N,Ndioctyldiglycol amic acid (DODGAA) was developed recently for the selective extraction of rare earth metals.5−7,32,33 Although DODGAA is also a monocarboxylic acid like Versatic 10, it showed a significantly higher extraction ability and selectivity for the rare earth metal ions compared with Versatic 10,5 because of the tridentate molecular structure in the center of DODGAA. Although DODGAA has a molecular structure similar to D2EHAG, except for an oxygen atom at the center of the molecule instead of a nitrogen atom, this extractant did not show the high extraction and separation performance for Co2+ over Mn2+ as Versatic 10 did not show (see Figures 3a and 4b). 815

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To confirm the extraction stoichiometry in an organic phase, a loading test was conducted for Ni2+. Equal volumes of the ndodecane phase containing 4.5 mmol dm−3 D2EHAG and aqueous phases with varying Ni2+ concentrations were equilibrated at pH 8.3 where quantitative extraction was achieved. As shown in Figure 6, the molar ratio of the loaded

later, the extraction capacity of the metal ions is considered to be high enough for practical use. Therefore, these novel extractants show potential for use in industrial processes as a new extractant. To our knowledge, this is the first report discussing the achievement of the mutual separation of Ni2+, Co2+, and Mn2+ with high efficiency, especially for Co2+ and Ni2+ from Mn2+, by solvent extraction with a single extractant. 3.2. Extraction Mechanism. Slope analysis was conducted to clarify the extraction mechanism of the divalent metal ions, Ni2+, Co2+, and Mn2+ with the novel extractants. Figure 5a

Figure 6. Loading test for divalent metal ion (Ni2+) on D2EHAG in ndodecane, [D2EHAG]init = 4.5 mmol dm−3, pHeq = 8.3.

Ni2+ concentration to the initial D2EHAG concentration approached a constant value of 0.5 with increasing Ni2+ concentration in the aqueous phase. This result supports the idea that one divalent metal ion is extracted to the organic phase with two D2EHAG molecules. On the basis of the slope analysis and results from the loading test, the extraction equilibrium equation of the metal ions with D2EHAG is expressed by eq 4: 2+ Maq + (HR)2,org ↔ MR 2,org + 2H+

(4)

The equilibrium constant of eq 4, Kex, is defined by eq 5: Kex =

[MR 2]org [H+]2 [M2 +]aq [(HR 2)]org

(5)

Rewriting eq 5 using the definition of D (eq 3) yields eq 6 with logarithmic expression:

Figure 5. Slope analysis for extraction (a) effect of pH on distribution ratio of divalent metal ions with 10 mmol dm−3 D2EHAG, (b) effect of dimer concentration of extractant on distribution ratio of Ni2+ and Co2+ with D2EHAG at pHeq = 3.0 (solid lines are theoretical lines).

log D = log[(HR)2 ]org + 2pH + log Kex

(6)

⎛ [(HR)2 ]org ⎞ ⎟⎟ + log Kex log D = log⎜⎜ + 2 ⎝ [H ] ⎠

(7)

As shown in Figure 7, the plots of log D versus log ([(HR)2]org/[H+]2) show a linear correlation with slope of 1 for each metal ion. The extraction equilibrium constant values, Kex, with D2EHAG were determined from the plots in Figure 7 to be 3.24 × 10−4 for Ni2+, 1.70 × 10−5 for Co2+, and 3.70 × 10−10 for Mn2+ (mol dm−3). Separation factors, β, as the ratio of the Kex values were also evaluated for the three metal ions (with same extraction mechanism for D2EHAG), to be 8.8 × 105 for Ni2+/Mn2+, 4.6 × 104 for Co2+/Mn2+, and 19 for Ni2+/Co2+. D2EHAG provided a high selectivity for Co2+ and Ni2+ to Mn2+ compared with that of commercial extractant D2EHPA or a mixture of Versatic 10 and LIX 63 as shown in Figures 3 and 4. 3.3. Stripping Behavior. The stripping of metal ions from the extracting phase was also conducted. Figure 8a shows the stripping ratio, S, for the metal ions from the extracting phase

shows the effect of pH on the distribution ratio of the metal ions with 10 mmol dm−3 D2EHAG. A linear relationship with a slope of 2 was obtained from the plots for each metal ion, indicating that two protons are released into the aqueous feed phase during the extraction. Figure 5b shows the effect of concentration of the extractant dimers at pHeq 3 on the distribution ratio for the metal ions. Some alkyl monocarboxylic acids such as Versatic 10 exist as a dimer in aliphatic solvents;30 therefore, D2EHAG was considered to be in dimer form (HR)2,org in n-dodecane. A linear dependency with slope 1 was obtained from the plots of log D versus log(HR)2,org as shown in Figure 5b. These results suggest that one metal ion was extracted with two D2EHAG molecules into the organic phase. A similar correlation was also obtained for D2EHAS (data not shown) under the same experimental conditions. 816

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divalent cobalt (Co2+) to trivalent cobalt (Co3+) ions.36 The stripping profiles of Co2+ with D2EHAG were confirmed visually as shown in Figure 8b, where the Co2+ concentration was increased to a practical level to make it visible. The pink octahedral Co2+ complex that has been extracted into the organic phase disappeared, and the stripping phase changed to the light pink cobalt ion.

4. CONCLUSIONS Novel amic acid extractants D2EHAG and D2EHAS were developed for the challenging separation of Co2+ and Ni2+ from Mn2+. Several typical commercial extractants such as D2EHPA, PC-88A, and Cyanex 272 are selective for Mn2+ against Ni2+ and Co2+, whereas the newly developed extractants were found to extract Ni2+ and Co2+ preferentially with high selectivity over Mn2+ from a sulfuric acid solution. The high affinity of D2EHAG and D2EHAS for Co2+ and Ni2+ is considered to be because of the carboxyl and amine groups in their molecular structures. Quantitative stripping of Co2+ and Ni2+ from the extracting phase was achieved using 1 M H2SO4, despite the stripping of Co2+ often being difficult in conventional extraction systems. The target ions Ni2+ and Co2+ were separated satisfactorily from Mn2+ through the extraction and stripping steps. Thus, the novel extractants D2EHAG and D2EHAS are useful for the recovery of important metals such as Co2+ and Ni2+ from a Mn2+-rich solution derived from secondary as well as natural resources.

Figure 7. Logarithmic plots of distribution ratios of Ni2+ and Co2+ as a function of log ([(HR)2,org]/[H+]2) ([M2+]aq,init = 0.1 mmol dm−3; solid lines are theoretical lines).

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AUTHOR INFORMATION

Corresponding Author

*Tel: +81-92-802-2806; fax: +81-92-802-2810; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank Sumitomo Metal Mining (SMM) Co., Ltd. for their financial support of this research. Y.B. was supported by Research Fellowships of the Japan Society for the Promotion of Science (JSPS) for Young Scientists.

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REFERENCES

(1) Suzuki, T.; Nakamura, T.; Inoue, Y.; Niinae, M.; Shibata, J. A hydrometallurgical process for the separation of aluminum, cobalt, copper and lithium in acidic sulfate media. Sep. Purif. Technol. 2012, 98, 396−401. (2) Fernandes, A.; Afonso, J. C.; Dutra, A. J. B. Separation of nickel(II), cobalt(II) and lanthanides from spent Ni-MH batteries by hydrochloric acid leaching, solvent extraction and precipitation. Hydrometallurgy 2013, 133, 37−43. (3) Chen, L.; Tang, X.; Zhang, Y.; Li, L.; Zeng, Z.; Zhang, Y. Process for the recovery of cobalt oxalate from spent lithium-ion batteries. Hydrometallurgy 2011, 108, 80−86. (4) Williams, C.; Hawker, W.; Vaughan, J. W. Selective leaching of nickel from mixed nickel cobalt hydroxide precipitate. Hydrometallurgy 2013, 138, 84−92. (5) Naganawa, H.; Shimojo, K.; Mitamura, H.; Sugo, Y.; Noro, J.; Goto, M. A new “green” extractant of the diglycol amic acid type for lanthanides. Solvent Extr. Res. Dev., Jpn. 2007, 14, 151−159. (6) Shimojo, K.; Naganawa, H.; Noro, J.; Kubota, F.; Goto, M. Extraction behavior and separation of lanthanides with a diglycol amic acid derivative and a nitrogen-donor ligand. Anal. Sci. 2007, 23, 1427− 1430.

Figure 8. (a) Stripping ratio of metal ions from extracting phase obtained by extraction from aq feed phase (pH 4.35, [M]init = 0.1 mmol dm−3) [HR]org,init = 10 mmol dm−3, stripping phase 1 mol dm−3 H2SO4, (b) stripping profile of Co2+ from extracting phase to stripping phase ([Co]org,init = 10 mmol dm−3, [HR]org,init = 50 mmol dm−3, stripping phase 1 mol dm−3 H2SO4).

prepared by extraction at pHeq = 4.35, where only Ni2+ and Co2+ were extracted efficiently. As shown in Figure 8a, quantitative recovery and separation of Ni2+ and Co2+ from Mn2+ was achieved (Ni2+: 100%, Co2+: over 95%) using 1 mol dm−3 H2SO4. Mn2+ was not extracted in the pH range, and accordingly Ni2+ and Co2+ could be separated to the stripping phase. Here, it is noted that the stripping of Co2+ was possible, despite its stripping being difficult for the conventional systems using a commercial extractant such as 2-hydroxy-5-nonylacetophenone oxime (LIX 84I), because of the oxidation of 817

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dx.doi.org/10.1021/ie403524a | Ind. Eng. Chem. Res. 2014, 53, 812−818