Palladium extractant and method for separating palladium

Abstract

To provide a palladium extractant, and a palladium separation method employing the extractant.SOLUTION: A palladium extractant comprises, as an active ingredient, a thiodibenzene comprising two thioether groups represented by general formula (1), where R1 and R2 may be identical to or different from each other, and each represent a group selected from linear or branched C1-12 chain hydrocarbon groups.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a palladium extractant and a method for separating palladium. [Background technology]

[0002] Many of the three platinum group metals, palladium, platinum, and rhodium, are used in automobile exhaust catalysts. Due to the worldwide spread of exhaust gas regulations and their strengthening, as well as the increasing demand for these three platinum group metals, they have become metal resources that are difficult to secure in a stable manner. As the demand increases, the amount of used automobile exhaust catalysts is also steadily increasing. Since these metals are expensive and valuable as resources, they are recovered and reused after use. In order to supply a constant amount of platinum group metals, it is very important to increase the efficiency of the metal refining process (primary resource) and the separation and purification of platinum group metals from used products (secondary resource).

[0003] For the purification in the separation process of platinum group metals, electrolytic deposition, ion exchange, and precipitation have been proposed, but solvent extraction is widely adopted from the viewpoints of selectivity, economy, and operability. Various extractants for use in this solvent extraction method have been developed and used. Dialkyl sulfide (DAS) is currently used as a known palladium extractant (e.g., Patent Documents 1 and 2), and the former is characterized by being able to be back-extracted with an aqueous ammonia solution. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 10-130744 [Patent Document 2] Patent Publication No. 2005-146326 Summary of the Invention [Problem to be solved by the invention]

[0005] In the actual process of separating and refining platinum group metals using solvent extraction, the components containing platinum group metals present in primary or secondary resources are leached into an acidic solution using hydrochloric acid / chlorine gas or aqua regia, and this acidic solution is then subjected to extraction treatment. When DAS is used under these conditions, palladium is selectively extracted from the acidic solution containing palladium, platinum, rhodium, and base metals, but a significant amount of undesired metals are also extracted, and there are problems with the extraction speed being slow.

[0006] As described above, the present invention aims to provide a palladium extractant that is (1) capable of selectively extracting palladium from a solution containing a mixture of platinum, rhodium, base metals, and the like, and (2) capable of extracting palladium in a short period of time, and a method for separating palladium using the extractant. [Means for solving the problem]

[0007] As a result of extensive investigations, the present inventors have found that the above problems can be solved by using a palladium extractant containing a specific pincer-type compound as an active ingredient.

[0008] The first invention relates to a palladium extractant comprising, as an active ingredient, thiodibenzene having two thioether groups represented by the following general formula (1):

[0009] [ka] (In formula (1), R 1 and R 2 may be the same or different and represent a group selected from linear or branched chain hydrocarbon groups having 1 to 12 carbon atoms.

[0010] The second invention of the present invention is a method for separating palladium, comprising contacting an aqueous phase consisting of an acidic aqueous solution in which palladium is present with an organic phase containing the palladium extractant of the first invention of the present invention, thereby extracting palladium into the organic phase.

[0011] In the second aspect of the present invention, the aqueous phase is preferably an acid leachate obtained by treating a waste material containing a variety of metals including at least palladium with an acid to turn it into an aqueous solution. Effect of the Invention

[0012] The palladium extractant of the present invention and the method for separating palladium using said extractant (1) make it possible to selectively extract palladium from a solution containing a mixture of platinum, rhodium, base metals, etc., and (2) make it possible to extract palladium in a short period of time. [Brief description of the drawings]

[0013] [Figure 1] 1 is a graph showing the extraction rate (E%) of Pd(II) versus shaking time in a palladium extraction experiment in the examples. [Diagram 2] 1 is a graph showing the results of an extraction experiment from a palladium only solution in a hydrochloric acid bath having different hydrochloric acid concentrations in an embodiment. [Diagram 3] 1 is a graph showing the results of an experiment on selective extraction of palladium from a simulated solution in an embodiment. [Figure 4] 2 is a graph showing the results of an experiment on selective extraction of palladium from a solution obtained by acid leaching an automobile exhaust catalyst according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] <Palladium Extractant> The palladium extractant of the present invention is characterized in that it contains, as an active ingredient, thiodibenzene having two thioether groups represented by the following general formula (1):

[0015] [ka] (In formula (1), R 1 and R 2 may be the same or different and represent a group selected from linear or branched chain hydrocarbon groups having 1 to 12 carbon atoms.

[0016] Pincer-type metal complexes have been used as catalysts (organic synthesis reactions), fluorescent materials, and electrode materials, but little research has been done on their use as extractants. The present inventors have discovered that the palladium extractant of the present invention, which has a specific pincer ligand structure, can exhibit excellent selectivity and rapidity as a palladium extractant by utilizing the pincer ligand's characteristic of "pincer ligands' ability to hold the metal in a crab-like grip."

[0017] The palladium extractant of the present invention contains as an active ingredient a specific thiodibenzene structure represented by formula (1). Here, "containing as an active ingredient" means that the palladium extractant may contain, in addition to the active ingredient, for example, a solvent or various additives.

[0018] The pincer-type extractant of the present invention can separate palladium at a high extraction rate from a solution containing the platinum group elements palladium, platinum, rhodium, and other base metals. The skeleton of the extractant is a compound in which thioether groups have been introduced at two locations on thiodibenzene, which has a sulfur element at the bridging site (formula (1)), and it is a new compound as a palladium extractant. This extractant is capable of extracting palladium by chelation. It has been demonstrated that the dithioether group-containing dibenzene extractant of the present invention can extract palladium from the leachate of used automobile exhaust catalysts with high selectivity, high efficiency, and rapidity.

[0019] In the general formula (1), R 1 , R 2 may be the same or different, but from the viewpoint of ease of synthesis, it is preferable that they are the same. 1 , R 2 is a hydrocarbon group having 1 to 12 carbon atoms which may be branched, preferably a linear or branched alkyl group having 1 to 12 carbon atoms, more preferably a linear or branched alkyl group having 6 to 10 carbon atoms, even more preferably a linear or branched alkyl group having 7 to 9 carbon atoms, and even more preferably a linear alkyl group having 7 to 9 carbon atoms.

[0020] <How to separate palladium> The method for separating palladium of the present invention includes the steps of preparing an organic phase containing the above-mentioned palladium extractant, preparing an aqueous phase consisting of an acidic aqueous solution in which palladium is present, and extracting palladium into the organic phase by contacting the aqueous phase with the organic phase.

[0021] (Organic phase containing palladium extractant) The solvent used for the organic phase containing the palladium extractant is a water-insoluble solvent, and two or more solvents may be used in combination. The water-insoluble solvent is not particularly limited as long as it can dissolve the thiodibenzene compound containing two thioether groups represented by the general formula (I), and includes mineral oils such as petroleum and kerosene; aliphatic hydrocarbons such as hexane, heptane, octane, and dodecane; aromatic hydrocarbons such as toluene and xylene; and halogenated solvents such as carbon tetrachloride, methylene chloride, chloroform, and ethylene chloride. Among them, dodecane, toluene, and kerosene are preferred from the viewpoint of solubility.

[0022] The concentration of the thiodibenzene compound containing two thioether groups represented by general formula (I) in the organic phase is not particularly limited except that the upper limit is determined by the solubility of the compound. However, if the concentration is too low, the palladium extraction effect cannot be obtained, so that the concentration is usually used in the range of 0.1 mM to 1 M.

[0023] (Aqueous phase consisting of an acidic aqueous solution containing palladium) The acid concentration in the acidic aqueous solution containing palladium, for example, the hydrochloric acid concentration, the nitric acid concentration, or the concentration of a hydrochloric acid-nitric acid mixed solution, is preferably 2M or less and 5M or more, more preferably 1M or less and 6M or more, even more preferably 0.5M or less and 7M or more, even more preferably 8M or more, and particularly preferably 0.1M or less and 9M or more.

[0024] The acid contained in the acidic aqueous solution is not particularly limited as long as it is water-soluble, and an inorganic acid can be used. Examples of inorganic acids include hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, sulfuric acid, nitric acid, phosphoric acid, and hydrogen peroxide. Two or more types of acids may be contained. From the viewpoint of metal solubility, hydrochloric acid, nitric acid, or a mixture thereof is preferred.

[0025] There is no particular limitation on the concentration of palladium in the acidic aqueous solution containing palladium, and it is usually about 50 to 1000 ppm.

[0026] In the method for separating palladium according to the present invention, the acidic aqueous solution containing palladium is preferably an acid leachate obtained by treating a waste material containing a mixture of various metals including at least palladium with an acid, and by using such an acid leachate as the target, it becomes possible to more effectively utilize the excellent recognition, selectivity, efficiency and rapidity of the palladium extractant according to the present invention. An example of the waste material containing a mixture of various metals including at least palladium is an automobile exhaust catalyst.

[0027] The metals other than palladium contained in the acid leaching solution are not particularly limited, and may include alkali metals, alkaline earth metals, transition metals, 3B metals, etc., and in particular, from the viewpoint of exhibiting the selectivity of the palladium extractant of the present invention, it is preferable to include at least one selected from platinum, rhodium, lanthanum, rare earths, zirconium, and base metals. This allows rare and useful palladium to be recycled. In addition, since the amount of palladium contained in the acid leaching solution after separation of palladium can be greatly reduced, it can also be used as an operation to remove palladium. Therefore, the present invention can also be used as a pretreatment when isolating useful metals other than palladium from the acid leaching solution obtained by treating waste with an acid to turn it into an aqueous solution.

[0028] (Extraction conditions) The extraction temperature is not particularly limited as long as it is equal to or lower than the boiling point of the solvent used, and is usually carried out at around room temperature. The extraction operation is carried out by bringing an organic phase containing a palladium extractant and an aqueous phase consisting of an acidic aqueous solution containing palladium into contact with each other by shaking, stirring, etc. Shaking is usually performed about 100 to 500 times per minute. The palladium extractant of the present invention can extract palladium in a short time, and the majority of palladium can be extracted with a shaking time of 30 minutes, and almost the entire amount can be extracted with a shaking time of about 1 hour. The shaking time can be adjusted appropriately depending on the conditions of the extractant and the acidic aqueous solution. The lower limit of the shaking time is preferably 5 minutes or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, and particularly preferably 1 hour or more, and the upper limit is preferably 3 hours or less, more preferably 2 hours or less. EXAMPLES

[0029] <Synthesis of thiodibenzene extractant having dioctylthioether group> (1) Synthesis of 1,1'-N,N-dimethylcarbamoylthio-2,2'-sulfanediyl-4,4'-tert-butylbenzene

[0030] [ka]

[0031] A 100 mL recovery flask was charged with 2,2-thiobis[4-tert-butyl-ON,N-dimethylthiocarbamoylbenzene] (1.26 g, 2.5 mmol) and diphenyl ether (60 mL) as a hot solvent, and the mixture was reacted at 235°C under a nitrogen atmosphere for 15 hours. After the reaction was completed, the diphenyl ether was removed by vacuum distillation. The resulting brown solid was purified by flash column chromatography using an eluent of hexane:ethyl acetate = 1:2 and a column packed with silica gel to obtain the target solid (yield: 69.5%). The structure of the target product was 1 This was confirmed by 1 H NMR measurement.

[0032] The analytical results of the obtained target substance were as follows. 1 H NMR (300 MHz, CDCl3, TMS) δ7.50 (d, 2H, ArH), 7.27 (dd, 2H, ArH), 7.22(d, 2H, ArH), 3.08 (s, 6H, -S-(C=O)-N-(CH3)2), 2.99 (s, 6H, -S-(C=O)-N-(CH3)2), 1.22(q, 18H, -CH3))

[0033] (2) Synthesis of 2,2'-sulfanediyl-4,4'-tert-butyldibenzenethiol

[0034] [ka]

[0035] Lithium aluminum hydride (0.75g, 19.8mmol) was weighed and placed in a 200mL flask, followed by the addition of dehydrated tetrahydrofuran (30mL). 1,1´-N,N-dimethylcarbamoylthio-2,2´-sulfanediyl-4,4´-tert-butylbenzene (1.0g, 1.98mmol) dissolved in dehydrated tetrahydrofuran (20mL) was slowly added dropwise in a dropping funnel and stirred, followed by stirring at room temperature under a nitrogen atmosphere for 1 hour. After the reaction was completed, 2N hydrochloric acid (140mL) was added in small portions in an ice bath to quench the reaction, followed by stirring overnight. The target component was extracted with ethyl acetate (20mL x 5), washed with water (20mL x 2) and saturated saline (20mL), and the organic layer was dehydrated with anhydrous sodium sulfate. The brown oily substance obtained by removing the ethyl acetate by vacuum distillation was purified by flash column chromatography using an eluent of hexane:ethyl acetate = 10:1 and a column packed with silica gel to obtain a colorless transparent oily substance (yield: 76.6%). The structure of the target product is 1 This was confirmed by 1 H NMR measurement.

[0036] The analytical results of the obtained target substance were as follows. 1H NMR (300 MHz, CDCl3, TMS) δ 7.33 (d, 2H, ArH), 7.18 (d, 2H, ArH), 7.12 (d, 2H, ArH), 3.99 (s, 2H, -SH), 1.19 (q, 18H, -CH3))

[0037] (3) Synthesis of 1,1'-octylsulfanyl-2,2'-sulfanediyl-4,4'-tert-butylbenzene (Compound 1)

[0038] [ka]

[0039] 2,2'-Sulfanediyl-4,4'-tert-butyldibenzenethiol (0.2g, 0.55mmol), potassium hydroxide (0.09g, 1.65mmol), and ethanol (30mL) were added to a 100mL two-neck flask, 1-bromooctane (0.29mL, 1.65mmol) was added dropwise, and the mixture was refluxed under nitrogen for 2 hours. The mixture was cooled in an ice bath and neutralized by adding 3N HCl (1mL). After distilling off the solvent, the reaction product was extracted with dichloroethane (10mL x 5), and the organic layer was dehydrated with anhydrous sodium sulfate. The target component was then purified by flash column chromatography using an eluent of hexane:acetone (100:1) and a column packed with silica gel to obtain the target product (compound 1) as a yellow transparent oil (yield 64.7%).

[0040] The obtained target product (compound 1) 1 The measurement results of 1 H NMR were as follows: 1H NMR (300 MHz, CDCl3, TMS) δ 7.28 (d, 2H, ArH), 7.20(dd, 2H, ArH), 7.05(d, 2H, ArH), 2.90 (t, 4H, -S-CH2), 1.64 (t, 4H, -S-CH2-CH2), 1.40 (t, 4H, -S-CH2-CH2-CH2), 1.26 (m, 16H, -S-CH2-CH2-CH2CH2CH2CH2-CH3), 1.19 (s, 18H, tert-butyl) ,0.87 (t, 18H, -S-CH2-CH2-CH2-CH2-CH2-CH2-CH3))

[0041] <Palladium extraction experiment> (1) Study of palladium extraction ability (evaluation of extraction time) In this example, an HCl solution (0.1M) containing Pd(II) (1mM) was prepared as the aqueous phase, and a solution in which the extractant (compound 1) (1mM) synthesized above was diluted with toluene was prepared as the organic phase. 10mL of each solution was collected in a centrifuge tube and shaken at 300 rpm for an arbitrary time. After shaking, the tube was centrifuged at 3500 rpm for 3 minutes, and the concentration of each metal in the solution was measured by ICP emission spectrometry to determine the extraction rate. The extraction rate (E%) was calculated using the following formulas I and II.

[0042] E%=[M] org / [M] aq,init ×100 (Formula I) [M] org =[M] aq,init -[M] aq (Formula II)

[0043] The definitions of each element in the above formula I and formula II are as follows: [M] aq,init : Metal concentration in the aqueous phase before extraction [M] aq : Metal concentration in the aqueous phase after extraction [M] org : Metal concentration in the organic phase after extraction

[0044] The change in the extraction rate (E%) of Pd(II) versus shaking time is shown in Figure 1. The vertical axis represents the extraction rate (E%) and the horizontal axis represents the shaking time (hours). As shown in Figure 1, the extraction rate was about 60% after 0.5 hours of shaking, and most of the Pd(II) was extracted after 1 hour. After 1 hour, the extraction rate was maintained at about 100%.

[0045] (2) Extraction experiment from palladium alone in hydrochloric acid baths with different hydrochloric acid concentrations (evaluation of the hydrochloric acid concentration at which a high extraction rate can be maintained) In this example, an extraction experiment was carried out from an acidic solution containing palladium alone with different hydrochloric acid concentrations. The extractant (compound 1) was dissolved in a diluent of toluene to make 1 mM, which was used as the organic phase. An equal volume of each palladium solution prepared to a concentration of 1 mM using 0.1M to 10.0M hydrochloric acid shown in FIG. 2 was added to 10 mL of the organic phase as the aqueous phase, and palladium was extracted into the organic phase by vigorously shaking (300 rpm) for 3 hours. Thereafter, centrifugation was carried out in the same manner as in (1) above, and the palladium concentration in the aqueous phase was analyzed by an ICP emission spectrometer, and the extraction rate (E%) was calculated based on the obtained results using the above formulas I and II.

[0046] Figure 2 shows the change in extraction rate when the hydrochloric acid concentration is changed. The vertical axis is the extraction rate (%) and the horizontal axis is the hydrochloric acid concentration (M). Although the extraction rate was low in the range of hydrochloric acid concentrations from 1.0 to 7.0M, the other hydrochloric acid concentrations showed extraction rates of 94% or more. From the above, it can be concluded that palladium can be effectively extracted by applying hydrochloric acid concentrations other than the above 1.0 to 7.0M. In addition, the values ​​(M) on the horizontal axis of each plot in FIG. 2 are 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0047] (3) Selective extraction of palladium from a simulated solution (containing 13 types of metals) prepared by selecting metals contained in automobile exhaust catalysts (evaluation of palladium selectivity) Thirteen types of metals contained in automobile exhaust catalysts were selected, and a 0.1M HCl solution (simulation solution) was prepared so that each metal was 100 ppm. 10 mL of the organic phase in which the extractant (compound 1) was dissolved in toluene to a concentration of 1 mM, and 10 mL of the above-mentioned simulation solution (aqueous phase) were weighed into a 50 mL centrifuge tube and shaken at 300 rpm for 6 hours. Then, centrifugation was performed in the same manner as in (1) above, and the concentration of each metal in the aqueous phase was analyzed with an ICP emission spectrometer, and the extraction rate (E%) was calculated based on the obtained results using the above formulas I and II.

[0048] The extraction rate (E%) of each metal is shown in Figure 3. The vertical axis shows the extraction rate (E%) and the horizontal axis shows each metal ion. As shown in Figure 3, palladium was extracted at 99%, and the extraction rates of other metal species were 5.0% or less, demonstrating high selectivity for palladium. This result shows that when a toluene solution containing 1 mM of the extractant (compound 1) is contacted with a simulated solution containing 13 metals, palladium can be extracted at 90% or more, enabling effective separation.

[0049] (4) Selective extraction of palladium from acid leached solutions of automobile exhaust catalysts (evaluation of palladium selectivity) The waste discharged from the factory contained at least palladium and many other metals. The leachate was made into an aqueous solution by acid treatment (the leachate was made by leaching powdered used automobile catalysts with 11.7 M hydrochloric acid and 1 vol% hydrogen peroxide). The raw solution (Al(III): 8720 ppm, Ca(II): 1000 ppm, Cr(III): 106 ppm, Cu(II): 61 ppm, Fe(III): 2147 ppm, Mg(II): 1960 ppm, Ni(II): 170 ppm, Pd(II ): 472 ppm, Pt(IV): 934 ppm, Rh(III): 71 ppm, La(III): 128 pm, Ce(III): 7160 ppm) (aqueous phase) was mixed with 10 mL of an organic phase in which the extractant (compound 1) was diluted with toluene to 4 mM, and the organic phase and aqueous phase were vigorously shaken (300 rpm) for 6 hours.Then, the concentration of each metal in the aqueous phase was analyzed using an ICP emission spectrometer, and the extraction rate (E%) was calculated based on the results obtained using the above formulas I and II.

[0050] The extraction rate (E%) of each metal is shown in Figure 4. The vertical axis shows the extraction rate (E%) and the horizontal axis shows each metal ion. As shown in Figure 4, palladium was selectively extracted at about 92%, with almost no other metal species being extracted, demonstrating high selectivity for palladium. This result shows that when a toluene solution containing 4 mM of the extractant (compound 1) is brought into contact with an acid leaching solution of an automobile exhaust catalyst, more than 90% of palladium can be extracted and effectively separated.

Claims

1. A palladium extractant comprising, as an active ingredient, thiodibenzene having two thioether groups represented by the following general formula (1): 【Chemistry 1】 (In formula (1), R １ and R ２ may be the same or different and represent a group selected from linear or branched chain hydrocarbon groups having 1 to 12 carbon atoms.

2. A method for separating palladium, comprising contacting an aqueous phase consisting of an acidic aqueous solution containing palladium with an organic phase containing the palladium extractant according to claim 1, thereby extracting palladium into the organic phase.

3. 3. The method for separating palladium according to claim 2, wherein the aqueous phase is an acid leachate obtained by treating a waste material containing a mixture of various metals including at least palladium with an acid to turn it into an aqueous solution.

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