Method for recovering platinum group elements

Abstract

A method is provided for selectively adsorbing only platinum and palladium from an aqueous solution containing platinum, palladium and impurities in high yield, and completely eluting and recovering them from the adsorbent. [Solution] The method includes a reduction step in which a reducing agent is added to a platinum group element-containing solution containing platinum and palladium to perform a reduction treatment, and the oxidation-reduction potential of the platinum group element-containing solution after the reduction treatment is 100 to 600 mV using a silver / silver chloride electrode (saturated with potassium chloride) as a reference electrode; an adsorption step in which a cation exchange chelating resin having dithizone as a functional group is contacted with the platinum group element-containing solution after the reduction treatment to adsorb the platinum and palladium; a washing step in which the cation exchange chelating resin adsorbed in the adsorption step is washed with hydrochloric acid at a concentration of more than 0 mol / L and less than 1 mol / L; and an elution step in which a mixed solution of hydrochloric acid and thiourea is contacted with the cation exchange chelating resin washed in the washing step to elute the platinum and palladium into the mixed solution.

Description

[Technical Field]

[0001] The present invention relates to a method for recovering platinum group metals from ores, smelting intermediates, recycled raw materials, etc. containing platinum group metals. [Background technology]

[0002] Platinum group elements (PGM) generally refer to six elements: platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os). Even if the abundance of all six elements in the Earth's crust is added together, the purity of these PGMs is approximately 0.001 to 0.01 ppm, which is lower than the purity of gold. Furthermore, because they often coexist with iron group elements, which have similar chemical properties, and highly electronegative elements that tend to form anions, selective separation and enrichment of PGMs is difficult.

[0003] Industrially, the most common method is that disclosed in Non-Patent Document 1, in which a raw material containing platinum group metals is melted at high temperature to recover it into a matte consisting of sulfides and a metal phase, this matte is oxidized to remove coexisting elements, and then slowly cooled to precipitate a matte phase enriched in platinum group metals, which is then separated from the matte phase having a low platinum group metal content by crushing and magnetic separation, and impurities are further dissolved and removed with acid to obtain a concentrate containing only platinum group metals.

[0004] Alternatively, a widely adopted method is disclosed in Non-Patent Document 2, in which raw materials containing platinum group elements are processed in a dry copper, lead, or nickel smelting process to produce matte or alloys, which are then used as anodes for electrolytic refining, during which the platinum group elements are separated and concentrated in anode slime (anode mud).

[0005] For ores containing a large amount of platinum group metals, the method disclosed in the former Non-Patent Document 1 is the method of choice, while for recycling secondary raw materials containing platinum group elements generated in the market, the method disclosed in the latter Non-Patent Document 2 is the method of choice.

[0006] The platinum group metal content of the platinum group metal-containing material recovered using the above method is on the order of 0.n to n% for the six elements combined, making it difficult to separate and purify each platinum group element in its original state. For this reason, the material is usually chemically dissolved and further concentrated to only the platinum group elements, a process known as concentration separation.

[0007] Known methods for collecting and separating platinum group metals include a method of separating them as precipitates of selenides, tellurides, etc., as disclosed in Non-Patent Document 3, and a method of adsorbing them with an ion exchange resin, as disclosed in Patent Documents 1 to 6.

[0008] The ion exchange method has the advantage of having a high recovery rate for platinum group elements, allowing for continuous recovery, and eliminating the need for separate dry separation processes such as evaporation, distillation, and roasting of elements that tend to co-precipitate, such as selenium and tellurium. As the ion exchange resin used in the ion exchange method, anion exchange resins have been used exclusively because platinum group elements dissolve in chloride solutions as anions of chloro complexes.

[0009] For example, Patent Document 1 discloses the adsorption of platinum group elements by an anion exchanger in which nicotinamide is supported on activated carbon. Specifically, the present invention provides an adsorbent that can efficiently adsorb platinum-group precious metals with high selectivity even in systems in which other base metals and precious metals coexist in addition to the platinum-group precious metals, and that does not itself have a negative impact on the environment. The adsorbent adsorbs platinum-group precious metals from a solution containing the platinum-group precious metals using nicotinamide-supported activated carbon as an adsorbent.

[0010] Patent Document 2 discloses the adsorption of platinum group elements by a polyamine-type anion exchange resin. Specifically, the present invention provides a method for selectively adsorbing platinum group elements in the form of chlorides such as chloro complexes using an ion exchange resin, regardless of the type of platinum group elements, from a chloride solution containing platinum group elements at relatively low concentrations but coexisting with impurity elements at high concentrations, and then separating and recovering the eluted platinum group elements. The present invention also provides a method for recovering platinum group elements from a chloride solution containing platinum group elements and impurity elements, comprising a first step of contacting the chloride solution with a polyamine-type anion exchange resin to selectively adsorb the platinum group elements, a second step of washing the resin after adsorption, and a third step of eluting the platinum group elements from the washed resin.

[0011] Patent Document 3 discloses a method using an anion exchange resin made of a water-insoluble polymer alloy composed of a polymer containing an amino group and a polymer other than an amine group. Specifically, the present invention provides a method for separating and recovering platinum group elements, which allows for the elution of adsorbed platinum group elements at a high elution rate while maintaining the ability to selectively adsorb platinum group elements in an aqueous chloride solution at a high adsorption rate in the presence of high concentrations of impurity elements.The method for recovering platinum group elements from an acidic solution containing platinum group elements and impurity elements involves the following steps, in order: a first step of contacting the acidic solution with a resin made of a water-insoluble polymer alloy composed of a polymer containing an amino group and a polymer other than an amine, thereby adsorbing the platinum group elements contained in the acidic solution onto the resin; a second step of washing the resin after the adsorption; and a third step of eluting the platinum group elements from the washed resin.

[0012] Patent Document 4 discloses the adsorption of platinum group elements by a water-insoluble resin having a structure in which a polymer containing an amino group is chemically bonded to a hydrophilic polymer. Specifically, the present invention provides a physically and chemically stable method for adsorbing platinum group elements in an aqueous chloride solution in the presence of high concentrations of impurity elements with high selectivity and adsorption rate, and with a higher adsorption capacity than conventional resins, and eluting the adsorbed platinum group elements with a high elution rate, as described below. This method for recovering platinum group elements from an acidic solution containing platinum group elements and impurity elements is characterized by sequentially undergoing the following steps: (1) a first step of adsorption treatment in which the acidic solution is brought into contact with a water-insoluble resin having a structure in which a polymer containing an amino group is chemically bonded to a hydrophilic polymer, thereby causing the resin to adsorb the platinum group elements contained in the acidic solution; (2) a second step of washing the resin that has adsorbed the platinum group elements through the first step; and (3) a third step of contacting the resin that has been subjected to the second step with an aqueous solution containing thiourea at a liquid temperature of 60 to 90°C, thereby eluting the platinum group elements adsorbed on the resin.

[0013] Patent Document 5 discloses the adsorption of platinum group elements by an anion exchange resin in which a primary amine is introduced into the ion exchange group. Specifically, the present invention provides a method for separating and recovering platinum group elements from a chloride solution containing the platinum group elements, which is capable of efficiently recovering the platinum group elements and is stable and can be used for a long period of time, and a method for recovering the platinum group elements.The anion exchange resin converts the platinum group elements into chloro complexes in a solution containing chloride ions, and the chloro complexes of the platinum group elements are adsorbed onto the ion exchange groups by ion exchange, and the ion exchange groups have primary amines introduced therein.

[0014] With anion exchange resins, the type of anions that can be adsorbed and their binding strength can be controlled to some extent by varying the amino group series (primary to tertiary or quaternary ammonium), the type of other elements adjacent to the amino group, and the bonding state (presence or absence of double bonds, and aromatic or aliphatic). However, there is a problem in that elements in anionic form other than the element to be recovered are adsorbed to some extent.

[0015] In particular, impurity elements that often coexist with platinum group metals and have low basicity (high electronegativity) and easily form anions, such as tin, lead, arsenic, antimony, and bismuth, are strongly adsorbed like platinum group metals and are difficult to elute.Furthermore, they undergo secondary hydrolysis within the resin, precipitating inside and outside the resin in the form of hydroxides, basic salts, etc., causing problems such as clogging of the resin tower.

[0016] Chloro complexes of platinum group ions are represented by the formula [MCl6] 2- (where M represents a tetravalent platinum group element) is easily adsorbed by an anion exchange resin. However, in the aqueous solution in which the actual platinum group raw materials were treated, Cl - Part of the - , SO4 2- and so on, and some complexes of a form that is highly hydrophilic and cannot be adsorbed by anion exchange resins coexist.

[0017] In addition, due to the influence of organic solvents and reducing agents often used in the precious metal refining process, the valence of platinum group metals is often reduced to 2-3, making it difficult to adsorb the chloro complex form [MCl6]. 3- {M represents a trivalent platinum group element} or [MCl4] 2- {M represents a divalent platinum group element}. For these reasons, there is a limit to the complete separation of platinum group metals using anion exchange resins, resulting in economic losses.

[0018] Furthermore, [MCl6] 2- The binding force between the platinum group anion complex in the form of amine-type resin is strong, making it difficult to quantitatively elute and recover the platinum group metals. Therefore, the resin must be frequently roasted and pyrolyzed to recover the platinum group metals as metal powder. This requires the purchase of resin, the operation from resin extraction to pyrolysis, and the construction and maintenance of dedicated equipment. In addition to the associated economic losses, the decomposition inevitably generates harmful organic halides and carbon dioxide.

[0019] In addition, aqueous solutions containing platinum group elements often contain residual oxidizing agents that dissolve the platinum group elements. 2-The coexistence of an oxidizing agent is effective in stabilizing anions in the form of (I) in an aqueous solution, but the amino groups and ammonium salts of the anion exchange resin are susceptible to oxidation, leading to the elimination of alkyl groups, decomposition into amides, and ultimately the elimination of nitrogen, resulting in a complete loss of adsorption performance. Therefore, even if the accumulation of platinum group metals could be avoided, there was a limit to the lifespan of the resin itself.

[0020] Furthermore, Patent Document 6 discloses a technology for selectively separating and recovering platinum group metal (Pt, Pd) ions efficiently from low-concentration wastewater after recovering platinum group metals from high-concentration wastewater, thereby improving the recycling rate. Specifically, at least tetravalent platinum group metal ions, Pt 4+ ions and divalent platinum group metal ions, Pd 2+ The first dithizone-bonded resin column selectively separates and recovers divalent platinum group metal ions from acidic wastewater containing ions, and the second dithizone-bonded resin column selectively separates and recovers divalent platinum group metal ions from the treated wastewater. 4+ Ion reduction to Pt 2+ The system is equipped with a second dithizone-bonded resin column that selectively separates and recovers divalent platinum group metal ions from the reduction treatment wastewater, and Pt 2+ ions and Pd 2+ This system selectively separates and recovers each ion, and efficiently separates and recovers divalent Pt and Pd ions selectively from low-concentration wastewater after recovering platinum group metals from high-concentration wastewater.

[0021] However, the method of Patent Document 6 has a relatively complicated configuration, is laborious on an industrial scale, and has problems such as unclear elution of PGMs after adsorption onto the resin and separation of coexisting impurities. As such, it has not been easy to efficiently separate and recover PGMs on an industrial scale using conventional techniques. [Prior art documents] [Patent documents]

[0022] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-194450 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-131745 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-181393 [Patent Document 4] Japanese Patent Application Publication No. 2016-132782 [Patent Document 5] Japanese Patent Application Laid-Open No. 2017-189774 [Patent Document 6] Japanese Patent Publication No. 2020-066802 [Non-patent literature]

[0023] [Non-Patent Document 1] Bureau of mine report 1982 RI 8717(https: / / www.911metallurgist.com / recovery-platinum-group-metals-flotation-concentrates-matte-smelting-leaching / #Experimental-Procedure-and-Equipment) [Non-patent document 2] Journal of the Japanese Society for Material Cycles and Waste Management, Vol. 22, No. 1, pp. 50-57, 2011 (https: / / www.jstage.jst.go.jp / article / mcwmr / 22 / 1 / 22_50 / _pdf) [Non-patent document 3] New Revised Analytical Chemistry Volume 2, Nankodo (1976), p401 Summary of the Invention [Problem to be solved by the invention]

[0024] The present invention aims to provide a method for selectively and quantitatively recovering platinum group metals in the presence of a large excess of impurities, regardless of the form of the platinum group complex, while avoiding the effects of adsorbent decomposition by an oxidizing agent, and for eluting and recovering platinum group metals from an adsorbent without roasting the resin. [Means for solving the problem]

[0025] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by reducing an aqueous solution containing platinum and palladium, bringing the resulting solution into contact with an adsorbent containing dithizone as a functional group, thereby selectively and quantitatively recovering only platinum and palladium, and then eluting the recovered platinum and palladium using a mixed solution of this adsorbent, thiourea, and hydrochloric acid, thereby completing the present invention.

[0026] The first aspect of the present invention includes a reduction step in which a reducing agent is added to a platinum group element-containing solution containing platinum and palladium to perform reduction treatment, and the oxidation-reduction potential of the platinum group element-containing solution after the reduction treatment is 100 to 600 mV using a silver / silver chloride electrode (saturated with potassium chloride) as a reference electrode; an adsorption step in which a cation exchange chelating resin having dithizone as a functional group is brought into contact with the platinum group element-containing solution after the reduction treatment to adsorb platinum and palladium onto the cation exchange chelating resin; and an adsorption step in which the cations adsorbed in the adsorption step are adsorbed onto the cation exchange chelating resin. The method for recovering platinum group elements comprises: a washing step of washing an exchange chelating resin with hydrochloric acid having a concentration of more than 0 mol / L and less than 1 mol / L; and an elution step of contacting the cation exchange chelating resin washed in the washing step with a mixed solution of hydrochloric acid and thiourea to elute platinum and palladium into the mixed solution, wherein the cation exchange chelating resin is synthesized by the reaction of chloromethylstyrene resin with dithizone or the reaction of chloromethylstyrene resin with dihydrodithizone.

[0027] A second aspect of the present invention is a method for recovering platinum group elements according to the first aspect, characterized in that the reducing agent used in the reduction step is one or more of hydrazine, hydrazine salts, hydrazine hydrate, sulfur dioxide, sulfites, hydrogen sulfites, disulfites, dithionites, tin(II) chloride, thiourea, glue, surfactants, dibutyl carbitol, amines, hydrocarbons, oxalic acid, and urea.

[0028] A third aspect of the present invention is a method for recovering platinum group elements, characterized in that, in the first aspect, dimethylformamide having a water content of less than 1% is used as the solvent used in synthesizing the cation exchange chelating resin. [Effects of the Invention]

[0029] According to the present invention, platinum group metals can be selectively recovered in high yield from a platinum group-containing liquid having a high impurity content and a low platinum group content. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a flow chart of a synthesis process of an adsorbent containing dithizone according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] Specific embodiments of the present invention will be described below. Note that the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the present invention. The method according to the present embodiment is a method for recovering platinum, palladium, or both of these elements from an aqueous solution containing these elements.

[0032] The raw materials from which platinum and palladium are recovered include those containing these precious metal elements, such as the platinum group concentrate obtained through nickel matte, copper electrolytic slime, and natural platinum group-containing materials such as platinum group ores, as well as secondary raw materials containing platinum group elements, such as waste catalysts, waste electronic circuit boards, scrap alloys, and even spent nuclear fuel.

[0033] The raw material is a raw solution to be adsorbed, which is dissolved in hydrochloric acid or hydrochloric acid and an oxidizing agent. However, sulfuric acid is not preferred because it does not easily dissolve platinum even in the presence of an oxidizing agent, and nitric acid interferes with the reduction reaction in the reduction step described below. Hydrobromic acid can be used as a hydrohalic acid instead of hydrochloric acid, but hydrofluoric acid does not easily form a stable complex with platinum group metals, and hydroiodic acid is not preferred because palladium forms a precipitate of palladium(II) iodide. Instead of dissolving the solid platinum group metal raw materials described above, the raw liquid to be adsorbed may also be an aqueous solution containing platinum group metals, which is a by-product in the production of platinum group elements or their compounds, or in the process of using platinum group metals, such as in catalysts, or a process waste liquid. Such a stock solution also contains platinum and palladium in the form of divalent or tetravalent ions.

[0034] [Reduction process] In the reduction step according to this embodiment, a platinum-group-containing aqueous solution containing tetravalent platinum and palladium can be subjected to reduction treatment to convert both platinum and palladium into divalent cations.

[0035] Specifically, the oxidation-reduction potential of the platinum group-containing aqueous solution after reduction treatment, using a silver / silver chloride electrode (saturated with potassium chloride) as a reference electrode, is set to a range of 100 to 600 mV, preferably 120 to 500 mV, thereby converting both tetravalent platinum and palladium into divalent cations.

[0036] If the redox potential is lower than this range, platinum and palladium are reduced to their elemental metals and precipitate. If the redox potential is higher than this range, reduction to divalent metals is incomplete, leaving tetravalent chloro complexes, which reduces the adsorption rate.

[0037] The reduction treatment method can be specifically reduction using a reducing agent or electrochemical reduction at the cathode, but because platinum group metals are easily electrodeposited on the cathode as simple metals, it is preferable to reduce them using a reducing agent with weak reducing power. Specific examples include hydrazine, hydrazine salts, hydrazine hydrate, sulfur dioxide, sulfites, hydrogen sulfites, disulfites, dithionites, and tin(II) chloride. Considering factors such as preventing over-reduction, cost, and preventing contamination of the aqueous solution, sulfites are the most preferable. In addition to the reducing agents exemplified above, other substances that can be expected to have a similar reduction effect include, for example, reducing impurities present in precious metal raw materials, such as thiourea, glue, and surfactants, as well as organic solvents, ion exchange resins, and additives used in the intermediate treatment of precious metal raw materials, such as dibutyl carbitol, amines, hydrocarbons, oxalic acid, urea, and thiourea.

[0038] [Adsorption process and washing process] In the adsorption step according to this embodiment, a cation exchange chelating resin having dithizone as a functional group is used as an adsorbent. This resin can be synthesized by the reaction of chloromethylstyrene resin with dithizone, or by the reaction of chloromethylstyrene resin with dihydrodithizone, as shown in Figure 1.

[0039] Dimethylformamide (DMF) is used as the reaction solvent, but it is important to use a sufficiently dehydrated solvent because the presence of water reacts with the chloromethyl group to generate hydroxyl groups, which then adsorb copper(II) ions, reducing adsorption selectivity. The lower the water content, the better, but a water content of at least less than 1%, and even less than 0.01%, is more preferable. The water content of the DMF can be measured by a known method, such as the Karl Fischer method. By using sufficiently dehydrated DMF, the amount of dithizone groups introduced can be maximized, as shown in the examples below, and the amount of platinum and palladium adsorbed can also be maximized. After synthesis, the adsorbent is washed with water to remove DMF before use. Here, the methylstyrene resin to which dihydrodithizone is bonded, which is synthesized by the above synthesis process, is also referred to as "dithizone resin (oxidized type)." Then, the dithizone of the dithizone resin (oxidized form), which is an intermediate product (that is, a precursor), is further reduced with a reducing agent, whereby a resin having dithizone as a functional group can be synthesized. An example of the reducing agent is ascorbic acid.

[0040] A resin with dithizone as a functional group (hereinafter referred to as "this adsorbent") can selectively adsorb platinum and palladium by contacting it with an aqueous solution containing platinum group metals after the reduction treatment described above. Unlike anionic complexes, it is presumed to be in a single chemical form in the cationic state, and both platinum and palladium can be completely recovered down to <0.1 mg / L in an aqueous solution containing platinum group metals after reduction treatment.

[0041] As mentioned above, this adsorbent has high selectivity for platinum and palladium, but exhibits weak adsorption when copper(II) ions coexist. Therefore, it is desirable to remove copper(II) ions by performing a washing step to wash the platinum and palladium ions before elution. In the washing step, hydrochloric acid can be suitably used as the washing solution used in the washing treatment. When using hydrochloric acid as the washing solution, if the concentration is too high, elution of platinum group metals will begin, so the concentration is desirably more than 0 mol / L and less than 1 mol / L, preferably about 0.1 mol / L. As will be shown in the comparative example described later, when a polyamine-type resin is used as an adsorbent, impurity elements such as bismuth and antimony remain in the resin even after the washing process, and the content of these impurities is higher than that of the platinum and palladium to be recovered. Such polyamine-type resins cannot selectively recover platinum and palladium.

[0042] [Elution process] In the elution step according to this embodiment, a chelating agent (complexing agent) with stronger bonds than dithizone is used because platinum and palladium are adsorbed to the adsorbent by a cation exchange reaction and form chelates with the sulfur and nitrogen in dithizone, which tends to result in incomplete elution even when elution is performed with a concentrated strong acid.

[0043] There are no particular limitations on the type of compound that can be used as a chelating agent, as long as it can form a stable chelate (complex) with platinum and palladium. However, thiourea is the most suitable, considering that it can be mass-produced industrially, is inexpensive, and can easily separate platinum and palladium by decomposition.

[0044] The effect of thiourea is enhanced when used in combination with hydrochloric acid. Hydrochloric acid acts on cation exchange elution, while thiourea is thought to act to break the chelate bond between dithizone and platinum or palladium. Using an eluent that is a mixture of hydrochloric acid and thiourea makes it possible to keep the eluent concentration low. Note that a concentration of 0.1 mol / L or more of thiourea and hydrochloric acid is sufficient for both.

[0045] Furthermore, while elution with anion exchange resins often requires high temperatures, elution with this adsorbent is possible even at room temperature. The platinum and palladium in the aqueous solution after elution can be recovered as sulfide precipitates by known methods, for example, by decomposing them with an alkali. The series of steps of adsorption, washing and elution can be carried out by either a batch method or a continuous method using a column or the like. [Example]

[0046] The present invention will be described in detail below using examples. [Example]

[0047] [Creating adsorbent] This adsorbent was prepared by the following procedure. (Process 1: Raw materials) The functional groups, dithizone and chloromethylstyrene resin, were reagents manufactured by Tokyo Chemical Industry Co., Ltd. Chloroform, potassium hexacyanoferrate (III), and potassium carbonate were reagents manufactured by Kanto Chemical Co., Ltd. Dimethylformamide (ultra-dehydrated) was a reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. The moisture content of dimethylformamide was measured by the Karl Fischer method and was found to be 0.001%.

[0048] (Step 2: Synthesis) 25 g of dithizone was dissolved in 3600 mL of chloroform, and 1200 mL of an aqueous phase containing 81 g of potassium hexacyanoferrate (III) and 75 g of potassium carbonate was added thereto and stirred. In chloroform, most of the dithizone was converted to dihydrodithizone, and this was allowed to dry naturally at room temperature to obtain a dried product (see symbol (a) in Figure 1). This was then dissolved in 1000 mL of dimethylformamide, and 36 g of chloromethylstyrene resin was added. The mixture was then shaken at 25°C for 14 days to synthesize the precursor "dithizone resin (oxidized form)" (see symbol (b) in Figure 1), to which dihydrodithizone was bound. Next, the synthesized precursor "dithizone resin (oxidized form)" was filtered, and 500 mL of dimethylformamide, then 250 mL of DMF + 250 mL of water, 500 mL of water, and 500 mL of 1 mol / L hydrochloric acid were added in that order, and finally the resin was washed with 500 mL of water to obtain a washed resin. The washed resin was then placed in an aqueous solution containing 26 g of ascorbic acid and 7.2 g of sodium hydroxide, and stirred to rapidly reduce the dithizone (oxidized form), synthesizing an adsorbent with dithizone as a functional group (dithizone resin, see Figure 1(c)). This was washed with 150 mL of water, 200 mL of 0.01 mol / L sodium hydroxide solution, 150 mL of water, and 200 mL of 0.01 mol / L hydrochloric acid, and the washed dithizone resin was stored in 0.1 mol / L hydrochloric acid solution.

[0049] (adsorbent properties) The amount of resin recovered from the "washed dithizone resin" was approximately 50 g on a wet basis. The adsorption capacity of platinum or palladium was measured by a batch method in which the resin was placed in a beaker and the amount of adsorption was measured from the change in the platinum or palladium concentration in the solution, and by a column method in which the resin was packed in a column and the liquid was passed through the resin to calculate the difference in the amount of adsorption. In both cases, it was confirmed to be approximately 0.5 mol / kg-Resin.

[0050] [Reduction process] The raw solution from which platinum group elements were recovered was an aqueous solution containing platinum group elements, which was the residue obtained by subjecting valuable components including gold and platinum group elements to chlorine leaching using a known method, in which copper was electrolytically refined and the resulting copper electrolytic slime (raw sediment) was subjected to chlorine leaching using a known method. The gold was then extracted with dibutyl carbitol from the chlorine leachate. Here, the valence of platinum and palladium in the above-mentioned stock solution was divalent. This is because dibutyl carbitol is an extractant and also functions as a reducing agent for the above-mentioned platinum and palladium. In other words, the tetravalent forms of platinum and palladium are reduced to platinum and palladium in the form of divalent cations. The composition of the stock solution (i.e., aqueous solution) is shown in Table 1.

[0051] [Table 1]

[0052] [Adsorption process] To 1000 mL of the stock solution having the composition shown in Table 1, 80 g of the prepared adsorbent (hereinafter also simply referred to as "dithizone resin") was added, and the mixture was mixed for 1 hour while maintaining the temperature at 25°C, followed by solid-liquid separation to obtain a filtrate. The concentrations of platinum and palladium in the filtrate were both <0.1 mg / L, confirming that they were completely adsorbed.

[0053] [Cleaning process] The recovered dithizone resin was filtered by suction, washed repeatedly with 0.1 mol / L hydrochloric acid, and then repeatedly subjected to suction filtration and dehydration. When the amount of washing was 200 mL, the color of the washing liquid disappeared. The concentrations of platinum and palladium in the cleaning solution were both <0.1 mg / L, confirming that no elution occurred during cleaning. After cleaning, the resin was dehydrated and its components were quantitatively analyzed. The results are shown in Table 2.

[0054] [Table 2]

[0055] It was confirmed that the content of impurity elements such as bismuth and antimony, which are present in greater amounts than platinum and palladium, is lower than that of platinum and palladium, and that selectivity for the platinum group metals is high.

[0056] [Elution process] 50 g of the washed resin obtained above was mixed with 500 mL of a mixed solution of 0.1 mol / L hydrochloric acid and 0.1 mol / L thiourea at 25°C for 1 hour. The solution from which platinum and palladium had been eluted was then suction filtered and washed with 100 mL of water. The platinum and palladium contents, including the washings, were analyzed, and the elution rate (%) with the thiourea and hydrochloric acid mixed solution was calculated. The results are shown in Table 3. It was confirmed that all elements could be completely eluted at room temperature.

[0057] [Table 3]

[0058] (Comparative Example 1) The adsorption step, washing step, and elution step were carried out using the same stock solution as in Example 1, except that a commercially available polyamine-type resin (Purolite A830, manufactured by Purolite, an anion-exchange chelating resin, also simply referred to as "amine-type resin") was used as the adsorbent. The results are shown in Tables 2 and 3. In the adsorption process, platinum and palladium showed high adsorption rates similar to those of the adsorbent synthesized in the present invention (dithizone resin), but large amounts of the impurities bismuth and antimony were also adsorbed, confirming poor selectivity. Analysis of the post-adsorption liquid revealed trace amounts of platinum (0.5 mg / L) and palladium (0.2 mg / L) that had not been adsorbed. Furthermore, it was confirmed that the elution rate of platinum in particular was low.

Claims

1. a reduction step in which a reducing agent is added to a platinum group element-containing solution containing platinum and palladium to carry out a reduction treatment, and the oxidation-reduction potential of the platinum group element-containing solution after the reduction treatment is 100 to 600 mV using a silver / silver chloride electrode (saturated with potassium chloride) as a reference electrode; an adsorption step of contacting the platinum group element-containing solution after the reduction treatment with a cation exchange chelating resin having dithizone as a functional group to adsorb platinum and palladium onto the cation exchange chelating resin; a washing step of washing the cation exchange chelating resin adsorbed in the adsorption step with hydrochloric acid having a concentration of more than 0 mol / L and less than 1 mol / L; an elution step of contacting the cation exchange chelating resin washed in the washing step with a mixed solution of hydrochloric acid and thiourea to elute platinum and palladium into the mixed solution; Including, A method for recovering platinum group elements, characterized in that the cation exchange chelating resin is synthesized by the reaction of a chloromethylstyrene resin with dithizone or a chloromethylstyrene resin with dihydrodithizone.

2. 2. The method for recovering platinum group elements according to claim 1, wherein the reducing agent used in the reduction step is one or more of hydrazine, hydrazine salts, hydrazine hydrate, sulfur dioxide, sulfite, hydrogen sulfite, disulfite, dithionite, tin (II) chloride, thiourea, glue, surfactant, dibutyl carbitol, amines, hydrocarbons, oxalic acid, and urea.

3. 2. The method for recovering platinum group elements according to claim 1, wherein dimethylformamide having a water content of less than 1% is used as the solvent in synthesizing the cation exchange chelating resin.

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