Thiodiphenol-Based n-Dialkylamino Extractants for Selective Platinum

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Thiodiphenol-Based n-Dialkylamino Extractants for Selective Platinum Group Metal Separation from Automotive Catalysts Manabu Yamada, Muniyappan Rajiv Gandhi, Yu Kaneta, Nozomi Kimura, and Hiroshi Katagiri Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b05009 • Publication Date (Web): 15 Jan 2018 Downloaded from http://pubs.acs.org on January 15, 2018

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Industrial & Engineering Chemistry Research

Thiodiphenol-Based n-Dialkylamino Extractants for Selective Platinum Group Metal Separation from Automotive Catalysts

Manabu Yamada,*a Muniyappan Rajiv Gandhi,b Yu Kaneta,c Nozomi Kimura,d and Hiroshi Katagirie

a

Research Center for Engineering Science, Graduate School of Engineering Science, Akita

University, 1-1 Tegatagakuen-machi, Akita 010-8502, Japan b

Graduate

School

of

International

Resource

Sciences,

Akita

University,

1-1

Tegatagakuen-machi, Akita 010-8502, Japan c

Department of Life Science, Graduate School of Engineering Science, Akita University, 1-1

Tegatagakuen-machi, Akita 010-8502, Japan d

Department of Life Science, Faculty of Engineering and Resource Science, Akita University,

1-1 Tegatagakuen-machi, Akita 010-8502, Japan e

Graduate School of Science and Engineering, Yamagata University, Jonan 4-3-16, Yonezawa

992-8510, Japan

*Corresponding author: Tel +81 18 889 3068; Fax: +81 18 889 3068; E-mail address: [email protected]

1

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Abstract: Five kinds of dialkylamino-modified thiodiphenols (2‒6) were synthesized to elucidate the extraction of Pd(II) and Pt(IV) in HCl media by thiodiphenol-based n-dialkylamino extractants. Although the synthesized species 2‒6 showed good solubility in hydrocarbon-based diluents such as kerosene, ShellSol D70, and ISOPER M, the addition of n-octanol to the platinum group metals (PGMs) extraction was needed to inhibit third layer formation. All the 2‒6 extract Pd(II) and Pt(IV) were much more effective than the commercial

extractants,

2-hydroxy-5-nonylacetophenone

oxime

(LIX84-I),

tri-n-butylphosphate (TBP), and tri-n-octylamine (TOA). Increasing the hydrophobicity of the extractants by increasing the alkyl chain length had an effect on the Pd(II), Pt(IV), and Rh(III) extractabilities, which increased in the order from 2 to 6. Extractant 6 could also be used for the selective extraction of Pd(II) and Pt(IV) (E% > 99%) from the leach liquors of automotive catalysts containing Pd(II), Pt(IV), Rh(III), La(III), Ce(III), Y(III), Zr(IV), Ba(II), and Al(III) in HCl media. The effective stripping of Pd(II) and Pt(IV) was achieved from an extracted organic phase containing 6 using 0.5 M thiourea in 1.0 M HCl. In addition, 6 was reusable and exhibited a high E% for Pd(II) and Pt(IV) (>96%) after five extraction cycles, indicating potential usefulness for the selective recovery of Pd(II) and Pt(IV) from leachates in platinum group metal refineries.

Keywords: Thiodiphenol derivatives; tertiary amine; palladium(II); platinum(IV); solvent extraction; automotive catalyst leach liquors

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1. INTRODUCTION Precious metals and rare metals are key elements and have great potential to improve the capability of many high-tech products. The demand for platinum group metals (PGMs = Pd, Pt, Rh, Ru, Ir, and Os) is ever-increasing because the metals are very important and exhibit high performance as automotive catalysts, electronics, and electric/hybrid.1-4 Although the development of alternative metals instead of PGMs has been implemented, the usage and price of PGMs is enormous and expensive.5 PGMs are only produced in a handful of countries including South Africa, Russia, North America, and Zimbabwe6. Therefore, recovery of PGMs from secondary resources such as spent automotive catalysts, industrial catalysts, and electronic scraps include PGMs is crucial for resource recycling and sustainable practices in many industries.7 PGM recycling from secondary resources reduces the environmental burden of mining and prevents environmental pollution. The recovery of PGMs from spent automotive catalysts is a good way to recirculate resources, since the content of PGMs in automotive catalysts is higher than in primary resources.8 The balance between supply and demand of three PGMs (Pd, Pt, and Rh) accounts for a high proportion in the manufacturing of automobile catalysts.5 Generally, separation and purification of PGMs from secondary resources are conducted by both pyrometallurgical and hydrometallurgical processes.1,9-11 Solvent extraction is one of the hydrometallurgical processes used to purify PGMs and is frequently employed.1,12 PGMs refineries, for example, Vale (Acton), Johnson Matthey, and Anglo American Platinum implement solvent extraction for PGM separation.1 Other hydrometallurgical processes of precipitation, electrolytic methods, adsorption, and ion-exchange processes for PGMs refining are also utilized.1,13 PGMs including concentrated primary and secondary resources are leached using HCl/Cl2 media.1 Similarly, leach liquors of automotive catalysts are prepared by leaching from HCl media, such as HCl/Cl2, HCl/H2O2, and, HCl/H2O2 with chloride salts,1,14,15 whereby the three PGMs Pd(II), Pt(IV),

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and Rh(III) exist as anionic chloro-complexes in the liquors.13 Currently, the separation and purification of the PGMs are carried out using commercial extractants, such as 2-hydroxy-5-nonylacetophenone oxime (LIX84-I), di-n-octyl sulfide (DOS) and tri-n-butyl phosphate (TBP).1,12 Although the above-mentioned commercial extractants for separation and purification of Pd(II) and Pt(IV) are well-known, their low selectivity, low stability in highly acidic media, and low extraction rate pose serious problems.1,12,16 To address the issues, development of new extractants has been the target of much research, and reports of PGM extractability using the developed extractants are continuously produced. We aimed to develop new extracting agents for the selective and efficient recovery of PGMs from the leach liquors of automotive catalysts. Among the developed extractants, PGM recovery from leach liquors of automotive catalysts as targeted secondary resources has been conducted using thiacalixarene,17−21 dithioether,22 and pincer ligands.23,24 Amide-based compounds, i.e., malonamide,25

sulfur-containing

monoamide,16

thioamide,26

thioglycolamide,27

dithioglycolamide,28 and succinamide,29 have been thoroughly investigated as advantageous extractants for the recovery of Pd(II) and Pt(IV). We

previously

reported

that

1,1'-bis[(dimethylthiocarbamoyl)oxy]-

2,2'-thiobis[4-t-butylbenzene], synthesized from 2,2'-thiobis[4-t-butylphenol] (1), showed potential for the rapid and selective extraction of Pd(II) from automotive catalyst leach liquors.30 The extractant skeleton of 1 has a linking sulfur, which improves PGM extractability based on the hard-soft-acid-base (HSAB) theory, easily introducing functional groups into two hydroxyl groups and/or o- and p-positions to enhance the selectivity and affinity for PGMs. Amine-based compounds, as well as TBP, are used for extraction of the PGM chloride anions.13,32 The cationic species produced by protonating the two extractants of amine-based compounds and TBP extracted the PGMs anionic chloride complexes via an ion-pair mechanism.12,13,31 Compared with the basicity of TBP, amine-based extractant of

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tri-n-octylamine (TOA) have a strong,13 and they can easily be protonated by contact with a weakly acidic solution. Recently, we demonstrated good extraction of Pt(IV) and/or Pd(II) using tertiary amino-modified thia- and calix[4]arenes.32,33 The objective of our research is to synthesize a thiodiphenol 1 based extractant utilizing tertiary amine groups. Furthermore, it is anticipated that the tertiary-amine-modified compound is a new candidate of PGM extractants, which has synergetic effects from both the structural and chemical properties of 1 and tertiary amine moieties. We report herein the extraction of three PGM (Pd(II), Pt(IV), Rh(III)) using five different 2,2'-bis[dialkylaminomethyl]-6,6'-thiobis[4-t-butylphenol] compounds with different alkyl chain lengths (Figure 1; alkyl = ethyl‒ n-hexyl: 2‒6). The introduction of amino groups with longer alkyl chains to thiodiphenol 1 improved the solubility of extractants in mixed hydrocarbon-based diluents and concomitantly led to good phase separation of the organic and aqueous phases during PGM extraction. The major advantages of the newly synthesized extractants (2‒6) exhibited a good solubility and clear phase separation after PGM extraction in hydrocarbon-based diluents, such as kerosene/n-octanol, ShellSol D70/n-octanol, and ISOPAR M/n-octanol. The extractive properties of extractants 2‒6 were compared with those of the commercial extractants LIX84-I, TBP, and TOA to explore the advantages of 2‒6. In addition, we discuss the crystal structure of 3, metal extraction of 2‒6 from single metal solutions containing Pd(II), Pt(IV), and Rh(III), selective Pd(II) and Pt(IV) extractions of 6 from mixed solution consisting of three PGMs, Pd(II) and Pt(IV) extractions of 6 from leach liquors of automotive catalysts, metal stripping from the organic phase, and reusability of the extractant 6. In the present study, our group reports novel tertiary amine extractants for PGM extraction in hydrocarbon-based diluents from leach liquors of automotive catalysts, which may be highly suitable for PGM refineries. - Figure 1-

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2. EXPERIMENTAL SECTION 2.1. Materials and methods Stock HCl solutions of Pd(II), Pt(IV), and Rh(III) were prepared using PdCl2 (Kanto Chemical Co., Inc.), PtCl4 (Acros Organics), and RhCl3·3H2O (Wako Pure Chemical Industries, Ltd.), respectively. 2,2-Thiobis(4-t-butylphenol), 1, was synthesized according to the procedure in the literature.34 Dialkylamine (ethyl ‒ n-hexyl), 37% formaldehyde solution, tetrahydrofuran (THF), acetic acid, and CHCl3 were also purchased from commercial sources and used without further purification. The commercial diluents, such as kerosene, ShellSol D70, and ISOPAR M, are obtained from Nacalai Tesque, Inc., Japan, Kremer Pigmente, GmbH & Co. KG, Germany, and Tonen General Petroleum Co., Ltd., Tokyo, respectively. 1,2-Dichlorobenzene, toluene, chloroform were obtained from Kanto Chemical Co., Inc. Japan and n-octanol was obtained from Tokyo Chemical Industry Co., Ltd. Japan. All the diluents were used without further purification. The concentration of each metal ion in its aqueous solution was determined using an inductively coupled plasma atomic emission spectrometer (ICP-AES) (SPS-3000, Seiko Instruments Inc. Japan). Fourier transform infrared (FT-IR) spectra were recorded at 4000–600 cm–1 by the attenuated total reflection (ATR) method using a Thermo Fisher Scientific Nicolet iS5 spectrophotometer (Thermo Fisher Scientific). The instrument used to record the nuclear magnetic resonance (NMR) data was a JEOL JNM-ECA500. The elemental analysis was performed on a Systems Engineering CE-440 M CHN/O/S elemental analyzer. 2.2. Synthesis of extractants 2-6 Extractant 2 was synthesized as follows: 1 (2.10 g, 6.06 mmol), THF (100 mL), diethylamine (2.20 g, 30.3 mmol), 37% formaldehyde solution (2.50 g, 30.8 mmol), and acetic acid (10 mL) were stirred at room temperature. After 24 h, the solvent was removed in vacuo. The resulting yellowish oily material was dissolved in chloroform (100 mL), and the 6


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organic layer was washed with water (100 mL), 10% K2CO3

aq

(100 mL), and more water

(100 mL), then dried over anhydrous Na2SO4. A yellowish oil was obtained via evaporation of the solvent under reduced pressure. Precipitation from n-hexane was used to yield the crude form of 2. Recrystallization from methanol (200 mL) yielded pure colorless crystals of 2 (2.80 g, 95.0%). 1H NMR (500 MHz, CDCl3, δ from TMS) 7.00 (s, 2H, ArH), 6.91 (s, 2H, ArH), 3.78 (s, 4H, Ar–CH2–N), 2.63 (q, 8H, –N–CH2–), 1.24 (s, 18H, tert-Bu), 1.12 (t, 12H, – CH2–CH3). 13C NMR (125 MHz, CDCl3, TMS) δ 154, 142, 128, 124, 121, 120, 59, 43, 31, 34, 16. FT-IR (v/cm): 2963, 2820, 1583, 1479, 1254. Calcd. for C30H48N2O2S·CH3OH = C31H52N2O3S: C, 69.88; H, 9.84; N, 5.26. Found: C, 61.81; H, 7.51; N, 5.56. Extractant 3 was synthesized following a similar procedure as described for 2, using di-n-propylamine. The yield of colorless crystals of 3 was 3.91 g (96.3%). 1H NMR (500 MHz, CDCl3, δ from TMS) 7.26 (s, 2H, ArH), 7.02 (s, 2H, ArH), 3.75 (s, 4H, Ar–CH2–N), 2.63 (q, 8H, –N–CH2–), 1.55 (q, 8H, –CH2– ), 1.16 (s, 18H, tert-Bu), 0.88 (t, 12H,–CH3). 13C NMR (125 MHz, CDCl3, δ from TMS) 155, 142, 128, 124, 121, 120, 58, 55, 34, 31, 19, 12. FT-IR (v/cm): 2960, 2821, 1585, 1479, 1254. Calcd. for C34H56N2O2S: C, 73.33; H, 10.14; N, 5.03. Found: C, 73.66; H, 10.42; N, 5.04. Extractant 4 was synthesized as follows: 1 (2.00 g, 6.06 mmol), THF (50 mL), di-n-butylamine (3.15 g, 30.3 mmol), 37% formaldehyde solution (2.01 g, 24.77 mmol), and acetic acid (5 mL) were stirred at room temperature. After 2 days, the solvent was removed in vacuo. The resulting yellowish oily material was dissolved in chloroform (50 mL), and the organic layer was washed with water (50 mL), 10% K2CO3

aq

(50 mL), 0.01 N HCl (50 mL

×3), and finally 10% K2CO3 aq (50 mL), then dried over anhydrous Na2SO4. After the solvent was removed in vacuo, a yellowish oil was obtained. The oil was dried under reduced pressure at 65 °C for several days. The yield of the brown oily product 4 was 3.75 g (92.6%). 1

H NMR (500 MHz, CDCl3, δ from TMS) 7.03 (s, 2H, ArH), 6.84 (s, 2H, ArH), 3.74 (s, 4H,

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Ar–CH2–N), 2.51 (q, 8H, –N–CH2–), 1.52 (t, 8H, –CH2–), 1.28 (t, 8H, –CH2–), 1.17 (s, 18H, tert-Bu), 0.88 (t, 12H, –CH3). 13C NMR (125 MHz, CDCl3, δ from TMS) 155, 142, 128, 124, 121, 120, 58, 53, 34, 31, 28, 21, 14. FT-IR (v/cm): 2957, 2870, 1599, 1479, 1253. Extractant 5 was synthesized following a similar procedure as described for 4, using di-n-amylamine. The yield of brown oily product 5 was 3.91 g (96.3%). 1H NMR (500 MHz, CDCl3, δ from TMS) 7.02 (s, 2H, ArH), 6.84 (s, 2H, ArH), 3.75 (s, 4H, Ar–CH2–N), 2.50 (q, 8H, –N–CH2–), 1.53 (t, 8H, –CH2–), 1.27 (m, 16H, –CH2–CH2–), 1.17 (s, 18H, tert-Bu), 0.87 (t, 12H, –CH3). 13C NMR (125 MHz, CDCl3, δ from TMS) 155, 142, 128, 124, 121, 120, 58, 53, 34, 31, 30, 26, 22, 14. FT-IR (v/cm): 2956, 2860, 1599, 1478, 1253. Extractant 6 was synthesized following a similar procedure as described for 4 and 5, using di-n-hexylamine. The yield of brown oily product 6 was 4.30 g (97.9%). 1H NMR (500 MHz, CDCl3, δ from TMS) 7.02 (s, 2H, ArH), 6.84 (s, 2H, ArH), 3.74 (s, 4H, Ar–CH2–N), 2.50 (q, 8H, –N–CH2–), 1.52 (t, 8H, –CH2–), 1.26 (m, 24H, –CH2–CH2–CH2–), 1.17 (s, 18H, tert-Bu), 0.87 (t, 12H, –CH3). 13C NMR (125 MHz, CDCl3, δ from TMS) 155, 142, 128, 124, 121, 120, 58, 53, 34, 32, 31, 27, 26, 22, 14. FT-IR (v/cm): 2955, 2858, 1587, 1464, 1252.

2.3. X-Ray crystallography of 3 Single crystals of 3 suitable for X-ray diffraction studies were grown from methanol by slow evaporation at room temperature. The crystals were extracted from the mother liquor with a glass pipette, and placed in Paratone-N oil. The single crystals coated with the oil were isolated on MicroMounts, and immediately placed in a cold nitrogen stream at 93 K. X-Ray diffraction data for 3 were collected on a Rigaku Saturn 724 CCD diffractometer with Mo-Kα radiation (λ = 0.71073 Å). The structures were solved by direct methods using SHELXT-2014,35 and refined using the full-matrix least-squares method on F2 using SHELXL-2014.36 All materials for publication were prepared by Yadokari-XG 2009

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software.37,38 All non-hydrogen atoms were refined anisotropically. The H atoms attached to O atoms were located by differential Fourier analysis and refined with Uiso(H) values of 1.5Ueq(O). The positions of other H atoms were calculated geometrically and refined as riding, with Uiso(H) values of 1.2Ueq(C). Crystal data for 3: C34H56N2O2S, Fw = 556.86, crystal dimensions = 0.40 × 0.40 × 0.20 mm, colorless, monoclinic, space group P21/c, a = 15.9714(3), b = 18.4729(4), c = 11.1685(2) Å, α = γ = 90º, β = 92.514(2)º, V = 3291.96(11) Å3, Z = 4, ρcalcd = 1.124 g cm–3. A total of 45098 reflections were collected, of which 24415 reflections were independent (Rint = 0.0535). The structure was refined to a final R = 0.0476 for 6581 data points [I > 2σ(I)] with 377 parameters, with wR = 0.1125 for all data, GOF = 1.032, and a residual electron density max/min = 0.479/–0.432 e Å–3. A propyl group showed disorder at two positions (A and B sites), which were refined anisotropically. The parts containing (C32A and C33A) and (C32B and C33B) were refined as the disordered propyl moiety, occupancy of which were fixed at 0.833 and 0.167, respectively. The supplementary crystallographic data for this paper can be found in CCDC entry 1573609; the data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

2.4. Solvent extraction studies Solvent extraction experiments were performed at 20 ± 1°C. The values of extractability (E%) obtained were reproducible to within ± 5%. In the typical extraction experiment, the mixture of organic and aqueous phases (each 10 mL) was shaken at a rate of 300 rpm for the required time, and the content of each metal ion in the aqueous phase was measured by ICP-AES. Effects of HCl concentration studies were carried out using single solutions containing 1 mM of Pd(II), Pt(IV), and Rh(III) with 10 mM of extractants 2‒6 or 20 mM of LIX84-I, TOA, and TBP in kerosene + 20 % n-octanol for 30 min. Effects of diluents were

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conducted using 1 mM of single solutions of Pd(II), Pt(IV), and Rh(III) 0.1 M in HCl media with 10 mM of 6 for 30 min. Effects of shaking time on the PGMs extraction were performed by varying contact time between 0-240 min with 1 mM of single solution of Pd(II), Pt(IV), and Rh(III) (10 mL) and 10 mM of 6 in kerosene + 20 % n-octanol. PGM extractions from three PGMs mixed solution were carried out using 100 mg/L of each Pd(II), Pt(IV), Rh(III) in 0.1‒8.0 M HCl media and 10 mM of 6 in kerosene + 20 % n-octanol. The distribution ratio for Pd(II) or Pt(IV) ions between the organic and aqueous phases was determined by varying the concentration of 6 from 5 × 10-5 to 8 × 10-4 M and the concentration of Pd(II) or Pt(IV) was 1.0 mM in 0.1 M HCl medium and the contact time was 30 min. Leach liquors of automotive catalysts were prepared using HCl (11.6 M)/H2O2 (1 vol%) according to the reported procedure14. The concentration of metal ions in the leached liquors of automotive catalysts was measured by ICP-AES. The metals exist as chloro complexes in concentrated HCl solution, which was diluted ten-fold with water before PGMs extraction studies. Metal concentration in the diluted leach liquors of automotive catalyst in mg/L is as follows (also see Table S1): Pd(II) = 46.1; Pt(IV) = 26.8; Rh(III) = 18.4; La(III) = 43.7; Ce(III) = 303.5; Y(III) = 1.8; Zr(IV) = 12.3; Ba(II) = 143.7; Al(III) = 159.4. Extraction of PGMs from acidic leach liquors of automotive catalyst was carried out using 10 mL of leach liquors (10 times diluted) and 10 mM of 6 in kerosene + 20% n-octanol solution (10 mL) over a period of 30 min at 300 rpm. The E% was calculated using Equations (1) and (2): E% = [M]org / [M]aq,init × 100

(1)

[M]org = ([M]aq,init – [M]aq)

(2)

where [M]aq,init and [M]aq are respectively the initial and final contents of the metal ions in the aqueous solution. After the PGM extraction from the diluted acidic leach liquors, the 10 mM organic

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phase of 6 (10 mL) was mixed with 10% (v/v) NH3 aqueous solution or 0.5 M thiourea in 1.0 M HCl (10 mL). The mixture was shaken at 300 rpm for 30 min (20 ± 1°C), and the concentration of the Pd(II) and Pt(IV) in the aqueous phase after stripping, [M]aq, was determined by ICP-AES. The stripping ability, S%, was calculated using the following Equation (3): S% = [M]aq/[M]org × 100

(3)

where [M]aq is the content of the Pd(II) and Pt(IV) in the aqueous solution after stripping, and [M]org is the content of the metal ions in the organic phase before stripping.

2.5 Stability studies of the extractants in HCl Media CHCl3 solutions (10.0 mM) of extractants 2‒6 (20 mL) were stirred with a 12 M HCl (20 mL) for 7 days. After 7 days, the CHCl3 layer was evaporated and dried at 40°C for 24 h. FT-IR spectra of extractants 2‒6 were measured.

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3. RESULTS and DISCUSSION 3.1. Crystal structure of 3 Single crystals of only 2,2'-bis[dipropylaminomethyl]-6,6'-thiobis[4-t-butylphenol] (3) suitable for single-crystal X-ray diffraction studies were obtained from methanol over several days, and the growth of single crystals of the other synthesized analogs 2 and 4‒6 was unsuccessful. The single X-ray crystal structure of 3 is illustrated in Figure 2. Crystals of 3 were obtained as colorless prisms that crystallized in the monoclinic space group P21/c. The asymmetric unit was composed of one thiodiphenol molecule, with no observed solvent incorporation. In the crystals, it was clear that there were two dipropylamino moieties at the o-positions of the thiodiphenol skeleton, which were immobilized by intramolecular interaction from the crystal structures. In fact, the 3 molecule was stabilized by the two intramolecular O-H···N hydrogen bonds between the two pendent phenolic hydroxyl groups of thiodiphenol and the nitrogen atoms of the tertiary amine moieties (O1-H23···N1 and O2-H24···N2 distances are 1.81(2) and 1.82(2) Å). In addition, the one phenolic moiety of the thiodiphenol is revolved perpendicularly at the sulfur atom axis (the C5-S1-C11-C12 torsion angle was 90.2(1)°), as compared with the adjacent base phenolic moiety. As mentioned above, we speculate that the other extractants 2 and 4‒6 adopt a structure close to that of 3, which is distinct from the alkyl chain length of the extractants. - Figure 2-

3.2. Comparison of extractants 2–6 with commercial extractants of Pd(II), Pt(IV), and Rh(III): extraction as a function of HCl concentration First, to determine the optimum HCl concentration for PGM extraction of extractants 2–6, liquid-liquid extraction from single solutions containing each of three Pd(II), Pt(IV), and Rh(III) were performed in the range 0.1 – 8.0 M HCl using 10 mM kerosene + 20% n-octanol solution containing 2–6 and 1 mM single metal solutions of each of three PGMs for 30 min. 12


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The E% of three Pd(II), Pt(IV), and Rh(III) in various HCl concentrations by 2–6 is illustrated in Figure 3. Figure 3a shows Pd(II) extraction using 2–6 and LIX84-I. Figures 3b and 3c show Pt(IV) and Rh(III) extraction using 2–6, TOA, and TBP, respectively. In all cases of 2–6, similar behavior for Pd(II) and Pt(IV) extractions was observed. The extractability of Pd(II) and Pt(IV) gradually decreased when increasing the HCl concentration from 0.1 – 8.0 M. A remarkable decrease of E% was observed for Pd(II) extraction from 2.0 – 6.0 M HCl, whereas the decrease of Pt(IV) E% was less than that of Pd(II) E%.

In contrast,

the Rh(III) E% remained virtually constant at concentrations varying from 0.1 – 8.0 M HCl (Rh(III) E% = ca. 40%) as shown in Figure 3c. The maximum E% of Pd(II) and Pt(IV) occurred at 0.1 M HCl (Pd(II) E% = 97.1 – 99.9% in 2–6, Pt(IV) E% = 94.6 – 98.9% in 2–6, and Rh(III) E% = 32.7 – 40.5% in 2–6), and the minimum E% of each reached the following values at 8.0 M HCl (Pd(II) E% = 11.8 – 17.5% in 2–6, Pt(IV) E% = 23.9 – 28.1% in 2–6, and Rh(III) E% = 31.7 – 35.6% by 2–6). The Pd(II) and Pt(IV) extractions are decreased with increasing the HCl concentrations from 0.1 M to 8.0 M may be due to the presence high concentration of Cl‒ ions and the co-extraction of Cl‒ together. In the highly acidic medium, there is heavy competition between Cl‒ ions and the PGMs. Therefore, the extraction percentage of Pd(II) and Pt(IV) decreased with increasing the HCl concentration. On the other hand, the three commercial extractants showed much worse extractability for the three PGMs than our developed extractants 2‒6 in this system, although the concentration of the commercial extractants was 20 mM (two times greater concentration as compared to that of 2–6). LIX84-I, used as an industrial Pd(II) extractant, was found to be the best for Pd(II) with an E% of 50.2% in 0.1 M HCl, as shown in Figure 3a. Thus, Pd(II) E% rapidly decreased at 1.0 M HCl and reached 21.0%. Then, Pd(II) extraction by LIX84-I gradually decreased and reached a Pd(II) E% value of 7.8% at 8.0 M HCl. The Pt(IV) extraction using TOA, which is utilized as a Pt(IV) extractant, was similar to the extractive behavior of the Pd(II) extraction

13



by LIX84-I as shown in Figure 3b. High Pt(IV) E% (= 92.3%) was observed at 0.1 M HCl, and then, a drastic decrease (E% = 11.0%) was observed in 1.0 M HCl. Furthermore, increasing the HCl concentration led to the non-extraction of Pt(IV) from the single Pt(IV) solution. By contrast, TOA was ineffective for Rh(III) extraction as is given in Figure 3c. TBP has no extractability for Pt(IV) and Rh(III) in all HCl concentration in Figures 3b and 3c. As shown by the results of the comparison, the extractants 2‒6 have a greater extractability than the above commercial extractants in the system at least. Interestingly, when increasing the alkyl chain lengths of the extractant, three PGM E% also increased. Thus, it seems that the hydrophobicity of the extractants has a significant influence on the extraction system. Hence, further studies of PGM extractive conditions were limited to the longest alkyl chain 6 because the extractant 6 had the best extractability in the results of this evaluation. - Figure 3-

3.3. Durability of extractants 2-6 in 12 M HCl media The stability of extractants in highly acidic media is very important for PGM refining in industrial operation with continuous usage. Acid durability of extractants 2‒6 (10 mM) in CHCl3 (20 mL) were carried out with a 12 M HCl (20 mL) for 7 days. Then, the CHCl3 layer was evaporated and the 12 M HCl-treated extractants were obtained. FT-IR spectra of the acid-treated extractants 2‒6 were measured in order to confirm any structural changes in the extractants. The FT-IR spectra of acid-treated 2‒6 exactly matched with corresponding native 2‒6, expect new peaks which appeared at 2650‒2500 cm-1 due to protonation of amino groups. The FT-IR spectra of native 6 and the acid-treated 6 are shown in the Figure S1. Therefore, significant structural changes in 2‒6 after the acid treatments were not observed, suggesting that 2‒6 are highly stable and suitable for metal extraction in HCl media.

14


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3.4. Effect of diluents for PGM extraction of 6 in HCl media In order to clarify the effect of diluents, nine diluents were selected for PGM extraction using 6 from single PGM solutions of Pd(II), Pt(IV), and Rh(III). The nine diluents were kerosene, ShellSol D70, ISOPAR M, 1,2-dichlorobenzene, toluene, chloroform, kerosene + n-octanol, ShellSol D70 + n-octanol, and ISOPAR M + n-octanol. The results of PGM extraction using these diluents are given in Table 1. Figure S2 shows a photograph of the Pd(II) extractions of 6 in kerosene, ShellSol D70, and ISOPAR M as hydrocarbon-based solvents. It is noteworthy that these three diluents are not better to use because they form a third layer (solid) on the Pd(II), Pt(IV), and Rh(III) during extraction. In contrast, the six other diluents showed clear phase separation during the PGM extractions. Good Pd(II) and Pt(IV) E% were obtained using 1,2-dichlorobenzene, toluene, and chloroform. In fact, although good Pd(II) and Pt(IV) E% were obtained using 1,2-dichlorobenzene, toluene, and chloroform, the use of the mixtures of commercial diluents such as kerosene + 20% n-octanol, ShellSol D70® + 20% n-octanol, or ISOPAR M + 20% n-octanol is preferable from an environmental point of view. Interestingly, 6 extracted Rh(III) chloride anions in the above mentioned the mixed diluents (Rh(III) E% < 30%) because the Rh(III) chloride complex is well-known as a non-active species in liquid-liquid extraction. Surprisingly, two-component mixed diluents of kerosene + 20% n-octanol, ShellSol D70 + 20% n-octanol, and ISOPAR M + 20% n-octanol, also exhibited good E% for the three PGM extractions. In the nine diluents, kerosene + 20% n-octanol had the best extractability for Pd(II), Pt(IV), and Rh(III). n-Octanol may act as a ‘phase modifier’ and inhibited third layer formation in the PGM extraction. Hence, kerosene + 20% n-octanol as an effective diluent for PGM extraction from three PGMs mixed solution and leach liquors of automotive catalysts. - Table 1-

15



3.5. Effect of shaking time The extraction from single PGM solutions (Pt, Pd, Rh) in HCl media were performed using various shaking times (0 – 240 min) to elucidate an extraction behavior of 6 depending on shaking time. Single metal extraction of PGMs were performed using 10 mM kerosene + 20% n-octanol solution of 6 and 1.0 mM of each of the three PGMs in 0.1 M HCl. Figure 4 shows the effect of shaking time on the Pd(II), Pt(IV), and Rh(III) extractions. The extraction of PGMs reached equilibrium within ~30 min. The E% was found to be 99.9% for Pd(II), 98.9% for Pt(IV), and 40.5% for Rh(III), respectively. As mentioned above, it might be suggested that the optimum conditions for high extraction of Pd(II), Pt(IV), and Rh(III) was found to be 30 min. - Figure 4-

3.6. Selectivity and extractability of 6 on extraction from PGM mixed solution Additionally, to clarify the selectivity and extractability of 6 toward a mixed system of three PGMs, the extraction of PGMs from a 100 mg/L mixed solution containing Pd(II), Pt(IV), and Rh(III) (10 mL) was conducted using a 10 mM kerosene + 20% n-octanol solution consisting of the extractant 6 in 0.1 ‒ 8.0 M HCl for 30 min. Results for the extraction of the mixed solution, in the range 0.1 – 8.0 M HCl, using 6, respectively, are given in Figure 5. The extraction behaviors of Pd(II) and Pt(IV) by 6 showed similar decreasing trends of extraction characteristics to those from single PGM solutions with increasing HCl concentration. In contrast, Rh(III) extractability differed from the single Rh(III) extraction. The Rh(III) E% from the mixed solution was lower than that of the single Rh(III) extraction (E% = ca. 10%). Among the three PGM mixed solutions, i.e., Pd(II), Pt(IV), and Rh(III), the extarctants showed high affinity towards Pd(II) and Pt(IV) during the extraction. The order of affinity is Pd(II) > Pt(IV) >> Rh(III). In the cases of the mixed metal solution, extractant 6 is fully saturated with Pd(II) and Pt(IV) in the initial stage and there is no free functional group to 16


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extract inert/labile [RhCl5(H2O)]2‒ or [RhCl6] 3‒. Thus, it may be suggested that 6 can extract Pd(II) and Pt(IV) together from a mixed system of the three PGMs and/or rare metals and base metals. As mentioned above, the best HCl concentration for the effective extraction of both Pt(IV) and Pd(II) was found to be 0.1 M HCl, being applicable for the separation of Pt(IV) and Pd(II) together from the mixed PGM solution. - Figure 53.7. Dependence of D of Pd(II) and Pt(IV) on the extractant 6 concentration and 1

H NMR analysis

As is clear from the results on the PGM extractions, extractant 6 showed high Pd(II) E%, and Pt(IV) E% from three-PGM mixed solution. Therefore, the dependence of D of Pd(II) and Pt(IV) from 0.1 M HCl on 6 concentration was investigated using log-log plots. Figure 6 illustrates two plots of log D vs. log [6] for two Pd(II) and Pt(IV) extractions. As given in the log-log plot for Pd(II) extraction in Figure 6a, the straight line closely corresponds to 1. The ratio of Pd(II) to 6 in the extracted species is probably 1:1 Pd(II):extractant in the system. Similarly, Figure 6b shows a log-log plot of Pt(IV) distribution, and 6 is nearly 1 and the Pt(IV)-extractant species for Pt(IV) extraction using 6 most likely had a 1:1 Pt(IV):extractant stoichiometry. Furthermore, in order to elucidate the protonation of 6 in 0.1 M HCl, native 6 and 0.1 M HCl-treated 6 were confirmed by means of 1H NMR and IR spectroscopies. Protonation of extractant 6 (10 mM) in CHCl3 (10 mL) was performed with a 0.1 M HCl (10 mL) for 30 min. 1H NMR spectra of the native 6 and the acid-treated 6 were obtained as given in Figure S3. After contact with 0.1 M HCl, especially protons of methylene groups directly bonded to nitrogen in 6 showed ca. 0.4 ppm downfield shift.39 The shift supports that extractant 6 was protonated after contacting with 0.1 M HCl by comparing the NMR spectra 17



of the native and the treated 6. In addition, IR spectrum of the treated 6 also supports the protonation of amino groups of 6. Comparison of FT-IR spectrum of 0.1 M HCl-treated 6 with those of native extractant 6 and 12 M HCl-treated 6 was given in Figure S4. In the case of 0.1 M HCl-treated 6 as well as 12 M HCl-treated 6, same broad and middle strength peak appeared at 2602 cm-1, which is a unique N-H stretching deriving from protonated quaternary amino moieties of 6. From the above-mentioned 1H NMR and IR spectral analysis and slope analysis of Pd(II) and Pt(IV) extractions by 6, the probable Pd(II) and Pt(IV) extraction mechanisms of 6 involve two quaternary amine groups of the cationic thiodiphenol, which extract one Pd(II) or one Pt(IV) chloride anion. First, the two amino moieties of 6 in kerosene + 20% n-octanol mixed diluent are fully protonated by contact with the HCl solution, followed by the extract species of the [PdCl4]2– and [PtCl6]2– via an ion-pair mechanism during Pd(II) or Pt(IV) extractions. - Figure 63.7. Pd(II) and Pt(IV) extractions from leach liquors of automotive catalysts Stock leach liquors of automotive catalysts were prepared previously according to literature.14 The concentration of total metal ions and the HCl in the original leach liquors obtained from our leaching process is 103.33 mM and ~1.0 M HCl, respectively. For PGMs extraction study from the leach liquors, the HCl concentration and the total metal concentration in the leach liquors is decreased to 0.1 M HCl and ~ 10.33 mM, respectively, by diluting 10 times with water. The metal concentrations in the diluted leach liquors were measured using ICP-AES. The leach liquors contained nine metal ions: Pd(II), Pt(IV), Rh(III), La(III), Ce(III), Y(III), Zr(IV), Ba(II), and Al(III). The concentration of PGMs, rare metals, and base metals in the diluted leach liquors used in the present study are given in Table S1. Extraction of PGMs was carried out using the leach liquors (10 mL) and a 10 mM kerosene +

18


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n-octanol solution of 6 (10 mL) over a period of 30 min at 300 rpm. Each E% value of nine metal ions included in the leach liquors is shown in Figure 7. The E% of 6 for Pd(II) and Pt(IV) was 99.5% and 99.3%. The E% of all other metal ions present in the leach liquors was found to be < 3%. In the case of the Pd(II) and Pt(IV) separation, di-n-hexylamino moieties of 6 play a very important role in the Pd(II) and Pt(IV) extraction from the leach liquors. - Figure 73.8. Stripping and reusability of 6 Stripping and reusability of 6 were investigated to confirm the major advantages of newly synthesized extractants 6. Additionally, the stripping efficiency of the extracted Pd(II) and Pt(IV) species from an organic phase and the reusability factor of 6 are very important for the successful establishment of an extraction system. The stripping of Pd(II) and Pt(IV) from the organic phase (10 mL) was carried out using two stripping reagents (10 mL): 10% (v/v) NH3 aqueous solution or 0.5 M thiourea in 1.0 M HCl solution, for 30 min at 300 rpm due to the selection of effective stripping reagent. A photographic example of the color change in organic and aqueous phases after stripping of Pd(II)/Pt(IV) using the two reagents is shown in Figure S5, and the stripping percentage (S%) on Pd(II) and Pd(IV) of each stripping reagent is listed in Table S2. The stripping using the two reagents indicate that 0.5 M thiourea/1.0 M HCl solution are very effective and almost stripped Pd(II) and Pt(IV) from the leach liquors extracted organic phase in the system, whereas 10% (v/v) NH3 aqueous solution did not. Hence, further studies of stripping and reusability of 6 were limited to 0.5 M thiourea/1.0 M HCl solution as a stripping reagent. The five extraction and stripping cycles of Pd(II) and Pt(IV) are illustrated in Figure 8. The S% of 6 during the first stripping cycle for Pd(II) and Pt(IV) was 99.3% and 98.7%, respectively. After, the first stripping cycle, an organic solution of 6 (10 mL) was washed with distilled water (20 mL) to remove thiourea from the organic phase and then the extraction of the leach liquors was repeated. The 19



second-cycle extraction and stripping of 6 indicated that the E% for Pd(II) and Pt(IV) was 98.8% and 96.6% and that the S% for Pd(II) and Pt(IV) was found to be 98.7% and 97.7%. Similarly, extraction and stripping were implemented for up to five cycles. Consequently, the third to fifth extractions and stripping by 6 were close to results of the first extraction and stripping cycle. The E% of Pd(II) and Pt(IV) after the final cycle was found to be 98.4% and 97.3%, and the S% toward Pd(II) and Pt(IV) was 98.1% and 96.7%. Finally, the extractant 6 can be used for more than five extraction and stripping cycles without loss of the E% and S% toward Pd(II) and Pt(IV) from these promising results, and therefore, it is anticipated that 6 can be a good PGM extractant for extraction of PGMs from secondary resources. - Figure 8-

4. CONCLUSIONS We

succeeded

in

synthesis

of

novel

five

2,2’-bis[dialkylaminomethyl]-

6,6’-thiobis[4-t-butylphenol]s (2‒6) for separation and purification of PGMs from leach liquors of automotive catalysts. Of the five extractants 2‒6, two di-n-hexylamino moieties having thiodiphenol (6) exhibited the high ability to effectively and selectively extract Pd(II) and Pt(IV) from single and three-PGM mixed solutions in HCl media. PGM extractability of 6 was in the order Pd(II) ≥ Pt(IV) >> Rh(III). The PGM extractions of 6 occur via an ion-pair extraction. In addition, the high selectively, extractability, and reusability of 6 for Pd(II) and Pt(IV) from the leach liquors of automotive catalysts as a secondary resource was observed, and the reused extractant 6 maintains the extractability for Pd(II) and Pt(IV) and can be used the extraction over five times. Mutual separation of Pd(II) and Pt(IV) may be achieved by combining

the

extractant

6

and

1,1'-bis[(dimethylthiocarbamoyl)oxy]-2,2'-

thiobis[4-t-butylbenzene]30 as a Pd(II) extractant via a multi-stage extraction from the leach liquors of automotive catalysts in the system. It is expected that the newly 20


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di-n-hexylamino-modified extractant 6 will be a new candidates for the separation of Pd(II) and Pt(IV) from various primary and secondary resources.

ASSOCIATED CONTENT Supporting Information Supporting Information is available free of charge on the ACS Publications website. The supplementary crystallographic data of 3 (CIF); the concentrations of metal ions in the leach liquors of automotive catalysts after 10 times dilution; Stripping of Pd(II) and Pt(IV) from the leach liquors extracted organic phase containing 6 by 10% (v/v) NH3 aqueous solution and 0.5 M thiourea/1.0 M HCl solution;; photograph of Pd(II) extraction by 6 which dissolved in kerosene, ISOPAR M, ShellSol D70, or kerosene + 20% n-octanol in HCl media; FT-IR spectra of native 6, and 12 M HCl-treated 6; 1H NMR and FT-IR spectra of native 6 and 0.1 M HCl-treated 6; Photograph of Pd(II)/Pt(IV) stripping from the leach liqueurs extracted organic phase containing 6 using 10% (v/v) NH3 aqueous solution and 0.5 M thioirea/1.0 M HCl solution.

AUTHOR INFORMATION Corresponding Author *M.

Yamada.

Tel:

+81

18

889

3068.

Fax:

+81

[email protected]. Notes The authors declare no competing financial interest.

21


18

889

3068.

E-mail:


ACKNOWLEDGEMENTS This work was supported by the “JSPS KAKENHI Grant Number 16K17941” and the “Program to Disseminate Tenure Tracking System”, MEXT, Japan. This work was also partially supported by“The Foundation for Japanese Chemical Research Grant Number 439(R)”.

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(39) Chamberlain, N. F. Producing NMR Data in the book: The Practice of NMR Spectroscopy with Spectra-Structure Correlations for Hydrogen-1, Chapter 2, pp. 15-43, Springer-Verlag, USA, 1974.

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Table and Figure Captions

Table 1 Effect of diluents for PGM extraction using 6.

Figure

1.

Structural

formula

of

2,2'-thiobis[4-t-butylphenol]

(1),

2,2'-bis(diethylaminomethyl)-6,6'-thiobis(4-t-butylphenol)

(2),

2,2'-bis(dipropylaminomethyl)-6,6'-thiobis(4-t-butylphenol)

(3),

2,2'-bis(dibutylaminomethyl)-6,6'-thiobis(4-t-butylphenol)

(4),

2,2'-bis(diamylaminomethyl)-6,6'-thiobis(4-t-butylphenol)

(5),

and

2,2'-bis(dihexylaminomethyl)-6,6'-thiobis(4-t-butylphenol) (6).

Figure 2 a) Stick diagram of 3 showing two O-H···N intramolecular hydrogen bonding (blue dotted lines) and b) space-filling representation of the molecular structure of 3. S = yellow, O = red, N = pale purple, C = dark grey, H = white.

Figure 3 Effects of HCl concentration on the extraction of single solutions containing each of three a) Pd(II), b) Pt(IV), and c) Rh(III) by the developed extractants 2‒6 and commercial extractants, LIX84-I, TOA, and TBP. Condition: [2‒6] = 10 mM; [LIX84-I], [TOA], and [TBP] = 20 mM; [Pd(II)] = 106.4 mg/L; [Pt(IV)] = 195.0 mg/L; [Rh(III)] = 102.9 mg/L in 0.1‒8.0 M HCl media, A/O= 1; shaking time = 30 min; shaking speed = 300 rpm; diluent = kerosene + 20 % n-octanol; temperature = 20 ± 1 °C.

Figure 4 Effect of shaking time on the extraction of three PGMs by 6. [6] = 10 mM; [Pd(II)] = 106.4 mg/L; [Pt(IV)] = 195.0 mg/L; [Rh(III)] = 102.9 mg/L; [HCl] =0.1 M; shaking time =

28


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0–240 min; shaking speed = 300 rpm; A/O= 1; diluent = kerosene + 20% n-octanol; temperature = 20 ± 1 °C.

Figure 5 PGM extractions from a mixed solution containing the three PGMs by 6 various HCl concentration. Condition: [6] = 10 mM; three PGMs (Pd(II), Pt(IV), Rh(III)) = each 100 mg/L in 0.1‒8.0 M HCl media; A/O= 1; shaking time = 30 min; shaking speed = 300 rpm; diluent = kerosene + 20 % n-octanol; temperature = 20 ± 1°C.

Figure 6 Effect of concentration of 6 on a) Pd(II) extraction and b) Pt(IV) extraction. Condition: a) [6] = 5 × 10-5 – 8 × 10-4 M; [Pd(II)] = 106.4 mg/L; [HCl] = 0.1 M; shaking time = 30 min; shaking speed = 300 rpm; diluent = kerosene + 20% n-octanol; temperature = 20 ± 1 °C and b) [6] = 5 × 10-5 – 8 × 10-4 M; [Pt(IV)] = 195.0 mg/L; [HCl] = 0.1 M; shaking time = 30 min; shaking speed = 300 rpm; diluent = kerosene + 20% n-octanol; temperature = 20 ± 1 °C.

Figure 7 Liquid–liquid extraction of metal ions from the diluted leach liquors (diluted 10 times) of by 6. [6] = 10 mM; shaking time = 30 min; shaking speed = 300 rpm; metal ions = Pd(II), Pt(IV), Rh(III), La(III), Ce(III), Y(III), Zr(IV), Ba(II), and Al(III); A/O = 1; temperature = 20 ± 1 °C.

Figure 8 E% and S% in extraction and stripping cycles of 6. Condition: shaking time = 30 min for extraction and stripping; shaking speed = 300 rpm for extraction and stripping; [6] = 10 mM, stripping reagent = 0.5 M thiourea/1.0 M HCl, A/O = 1 (10 mL × 10 mL) for extraction and stripping, A/O = 2 (20 mL × 10 mL) for washing with water; temperature = 20 ± 1 °C.

29



Page 30 of 40

Table 1 Effect of diluents for PGM extraction using 6 Pd(II)

Pt(IV)

Rh(III)

E%

E%

E%

Kerosene

-

-

-

Third layer formation

ShelSoll 70

-

-

-


ISOPAR M

-

-

-


1,2-Dichlorobenzene

99.9

89.8

28.0

Clear phase separation

Toluene

99.1

74.4

21.8


Chloroform

99.9

98.3

20.4


Kerosene + 20% n-Octanol

99.9

98.9

41.3


ShellSol D70 + 20% n-Octanol

99.8

98.9

31.2


ISOPAR M + 20% n-Octanol

99.8

99.2

33.5


Diluents

Remarks

[6] = 10 mM, A/O= 1; [Pd], [Pt], and [Rh] = 1 mM in 0.1 HCl media, time = 30 min, shaking speed = 300 rpm

30


Page 31 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure

1.

Structural

formula

of

2,2'-thiobis[4-t-butylphenol]

(1),

2,2'-bis(diethylaminomethyl)-6,6'-thiobis(4-t-butylphenol)

(2),

2,2'-bis(dipropylaminomethyl)-6,6'-thiobis(4-t-butylphenol)

(3),

2,2'-bis(dibutylaminomethyl)-6,6'-thiobis(4-t-butylphenol)

(4),

2,2'-bis(diamylaminomethyl)-6,6'-thiobis(4-t-butylphenol) 2,2'-bis(dihexylaminomethyl)-6,6'-thiobis(4-t-butylphenol) (6).

31


(5),

and


Figure 2 a) Stick diagram of 3 showing two O-H···N intramolecular hydrogen bonding (blue dotted lines) and b) space-filling representation of the molecular structure of 3. S = yellow, O = red, N = pale purple, C = dark grey, H = white.

32


Page 32 of 40

Page 33 of 40

a) 100 2 3

80

Pd(II) E%

4 5

60

6 LIX84-I

40 20 0 0

2

4

6

8

HCl concentration / M

b) 100 80

Pt(IV) E%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2

3

4

5

6

TOA

TBP

60 40 20 0 0

2

4

6

8

HCl concentration / M

(Figure 3: To be continued next page) 33



c)

100 80

Rh(III) E%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 40

2

3

4

5

6

TOA

TBP

60 40 20 0 0

2

4

6

8

HCl concentration / M Figure 3 Effects of HCl concentration on the extraction of single solutions containing each of three a) Pd(II), b) Pt(IV), and c) Rh(III) by the developed extractants 2‒6 and commercial extractants, LIX84-I, TOA, and TBP. Condition: [2‒6] = 10 mM; [LIX84-I], [TOA], and [TBP] = 20 mM; [Pd(II)] = 106.4 mg/L; [Pt(IV)] = 195.0 mg/L; [Rh(III)] = 102.9 mg/L in 0.1‒8.0 M HCl media, A/O= 1; shaking time = 30 min; shaking speed = 300 rpm; diluent = kerosene + 20 % n-octanol; temperature = 20 ± 1 °C.

34


Page 35 of 40

100 80

Pd(II) Pt(IV) Rh(III)

60

E%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40 20 0 0

50

100

150

200

250

Shaking time / min Figure 4 Effect of shaking time on the extraction of three PGMs by 6. [6] = 10 mM; [Pd(II)] = 106.4 mg/L; [Pt(IV)] = 195.0 mg/L; [Rh(III)] = 102.9 mg/L; [HCl] =0.1 M; shaking time = 0–240 min; shaking speed = 300 rpm; A/O= 1; diluent = kerosene + 20% n-octanol; temperature = 20 ± 1 °C.

35



100 Pd(II) Pt(IV)

80

Rh(III)

E%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 40

60 40 20 0 0

2

4

6

8

HCl concentration / M Figure 5 PGM extractions from mixed solution containing the three PGMs by 6 various HCl concentration. Condition: [6] = 10 mM; three PGMs (Pd(II), Pt(IV), Rh(III)) = each 100 mg/L in 0.1‒8.0 M HCl media; A/O= 1; shaking time = 30 min; shaking speed = 300 rpm; diluent = kerosene + 20 % n-octanol; temperature = 20 ± 1 °C.

36


Page 37 of 40

a) 1.0 0.6

Log D

y = 1.09x + 3.82 R² = 0.98

0.2 -0.2 -0.6 -1.0 -4.5

-4.1

-3.7

-3.3

Log [6]

b) 1.0 0.6 y = 1.03x + 3.55 R² = 0.97

Log D

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.2 -0.2 -0.6 -1.0 -4.5

-4.1

-3.7

-3.3

Log [6] Figure 6 Effect of concentration of 6 on a) Pd(II) extraction and b) Pt(IV) extraction. Condition: a) [6] = 5 × 10-5 – 8 × 10-4 M; [Pd(II)] = 106.4 mg/L; [HCl] = 0.1 M; shaking time = 30 min; shaking speed = 300 rpm; diluent = kerosene + 20% n-octanol; temperature = 20 ± 1 °C and b) [6] = 5 × 10-5 – 8 × 10-4 M; [Pt(IV)] = 195.0 mg/L; [HCl] = 0.1 M; shaking time = 30 min; shaking speed = 300 rpm; diluent = kerosene + 20% n-octanol; temperature = 20 ± 1 °C.

37



Figure 7 Liquid–liquid extraction of metal ions from the diluted leach liquors (diluted 10 times) of by 6. [6] = 10 mM; shaking time = 30 min; shaking speed = 300 rpm; metal ions = Pd(II), Pt(IV), Rh(III), La(III), Ce(III), Y(III), Zr(IV), Ba(II), and Al(III); A/O = 1; temperature = 20 ± 1 °C.

38


Page 38 of 40

Page 39 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8 E% and S% in extraction and stripping cycles of 6. Condition: shaking time = 30 min for extraction and stripping; shaking speed = 300 rpm for extraction and stripping; [6] = 10 mM, stripping reagent = 0.5 M thiourea/1.0 M HCl, A/O = 1 (10 mL × 10 mL) for extraction and stripping, A/O = 2 (20 mL × 10 mL) for washing with water; temperature = 20 ± 1 °C.

39



Liquid-Liquid Extraction 100

99.5 99.3

80 60

E%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Page 40 of 40

H

40 20 0

N OH

0.0

1.6

0.8

0.0

S

2.4

N

H

OH

0.9

0.9

Leach Liquors Automotive Catalysts ACS Paragon Plus Environment

Thiodiphenol-Based n-Dialkylamino Extractants for Selective Platinum

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