Method for recovering rhodium

Abstract

To provide a method for effectively separating and recovering rhodium from an acidic aqueous solution containing platinum, palladium, and rhodium.SOLUTION: A method for recovering rhodium includes the steps for: adding dimethyl sulfoxide to an acidic aqueous solution containing platinum, palladium, and rhodium, followed by adding a reducing agent to the acidic aqueous solution for the precipitation of platinum and palladium, and then separating the solid and liquid phases to recover platinum and palladium; and recovering rhodium from the platinum and palladium post-recovery solution obtained in the platinum and palladium recovery step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recovering rhodium, and more particularly to a method for recovering rhodium from an acidic aqueous solution containing platinum, palladium and rhodium. [Background technology]

[0002] Platinum and palladium are precious metals, expensive metals used in catalysts and jewelry, and are refined using the electrolytic deposit (slime) of copper dry smelting as the raw material.

[0003] In addition to gold, silver, platinum, and palladium, rare metals such as rhodium, ruthenium, and iridium, as well as selenium and tellurium contained in copper concentrate, are concentrated in this slime. These elements are separated and recovered individually as by-products of copper smelting.

[0004] This slime is often treated by hydrometallurgy. For example, Patent Document 1 discloses a method in which the slime is treated with hydrochloric acid and hydrogen peroxide to recover silver, the dissolved gold is recovered by solvent extraction, and other valuables are subsequently reduced and recovered with sulfur dioxide.

[0005] As disclosed in Patent Document 1, the method of recovering precipitates produced by sulfur dioxide has many advantages in terms of cost and production scale. In addition, since each element precipitates sequentially, it is also effective in separation and purification.

[0006] The platinum and palladium precipitated with sulfur dioxide are oxidized and dissolved again, and purified by solvent extraction. During this solvent extraction, they are separated from other impurity elements and concentrated. After solvent extraction, the platinum and palladium are stripped and recovered as ammonium salts.

[0007] On the other hand, rare metals such as rhodium, ruthenium, and iridium are precipitated after or simultaneously with the recovery of selenium and tellurium with sulfur dioxide (Patent Document 2). According to Patent Document 3, selenium and tellurium can be dissolved and separated by alkali treatment, and the rare metals contained in the undissolved residue can be further input to a refining process and individually separated by an appropriate method. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2001-316735 A [Patent Document 2] JP 2005-240170 A [Patent Document 3] JP 2004-332041 A Summary of the Invention [Problem to be solved by the invention]

[0009] Platinum and palladium are recovered as by-products of copper smelting, and other elements are mixed in as impurities during reduction and recovery using sulfur dioxide or sulfite. Rhodium, in particular, is a member of the platinum group like platinum and palladium, and exhibits similar chemical behavior, so separation efficiency is not high.

[0010] Rhodium is known as a particularly expensive platinum group element. It is highly valuable as a catalyst and in jewelry. Therefore, in the process of reducing platinum and palladium and precipitating them in the above-mentioned method, it is necessary to minimize the inclusion of rhodium and to increase the yield of rhodium.

[0011] Therefore, it is important to suppress the amount of rhodium entering the process of precipitating platinum and palladium from the copper electrolytic precipitate intermediate, which also leads to an improvement in the purity of platinum and palladium.

[0012] In view of the above-mentioned conventional circumstances, the present invention provides a method for effectively separating and recovering rhodium from an acidic aqueous solution containing platinum, palladium and rhodium. [Means for solving the problem]

[0013] As a result of intensive research aimed at solving the above problems, the present inventors have found that it is possible to satisfactorily separate and recover rhodium from an acidic aqueous solution containing platinum, palladium, and rhodium by masking and reducing rhodium in the acidic aqueous solution with dimethyl sulfoxide (DMSO), thereby suppressing the inclusion of rhodium and allowing platinum and palladium to be preferentially precipitated and recovered. The present invention was completed based on this finding.

[0014] That is, the present invention includes the following inventions. (1) a step of adding dimethyl sulfoxide to an acidic aqueous solution containing platinum, palladium and rhodium, then adding a reducing agent to the acidic aqueous solution to precipitate platinum and palladium, and recovering platinum and palladium by solid-liquid separation; a step of recovering rhodium from the platinum and palladium recovery solution obtained in the step of recovering platinum and palladium; A method for recovering rhodium, comprising: (2) The method for recovering rhodium according to (1) above, wherein 1 to 20 mL of the dimethyl sulfoxide is added per 1 L of the acidic aqueous solution. (3) The method for recovering rhodium according to (1) or (2) above, wherein the reducing agent is sulfur dioxide or a sulfite. (4) The method for recovering rhodium according to any one of (1) to (3), wherein in the step of recovering platinum and palladium, the acidic aqueous solution contains selenious acid, and acetone is added to the acidic aqueous solution as the reducing agent and the solution is heated to 65°C or higher to precipitate platinum and palladium. (5) A method for recovering rhodium according to any one of (1) to (4) above, wherein in the step of recovering rhodium, dimethyl sulfoxide contained in the platinum and palladium recovery solution is oxidized, a reducing agent is added to precipitate rhodium, and the rhodium is recovered by solid-liquid separation. (6) A method for recovering rhodium according to (5) above, comprising oxidizing dimethyl sulfoxide contained in the platinum and palladium recovery solution, adding iron or iron the surface of which is coated with copper as a reducing agent to precipitate rhodium, and recovering the rhodium by solid-liquid separation. (7) The method for recovering rhodium according to (6) above, wherein the amount of the iron or the iron whose surface is coated with copper is 5 g / L or more. (8) The method for recovering rhodium according to (5) above, wherein the oxidizing agent for oxidizing dimethyl sulfoxide is hydrogen peroxide. (9) The method for recovering rhodium according to (8) above, wherein the amount of hydrogen peroxide added is 0.5 to 4 times the volume of the dimethyl sulfoxide added, calculated as a 30 mass% hydrogen peroxide solution. Effect of the Invention

[0015] According to the present invention, there is provided a method for satisfactorily separating and recovering rhodium from an acidic aqueous solution containing platinum, palladium and rhodium. [Brief description of the drawings]

[0016] [Figure 1] 1 is a flow chart showing an example of a method for recovering rhodium according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Next, the embodiments for carrying out the present invention will be described in detail. It should be understood that the present invention is not limited to the following embodiments, and that appropriate changes and improvements in the design may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0018] (How to recover rhodium) The method for recovering rhodium according to an embodiment of the present invention includes a step of adding dimethyl sulfoxide (DMSO) to an acidic aqueous solution containing platinum, palladium, and rhodium, then adding a reducing agent to the acidic aqueous solution to precipitate platinum and palladium, and recovering platinum and palladium by solid-liquid separation, and a step of recovering rhodium from the platinum and palladium post-recovery liquid obtained in the step of recovering platinum and palladium. Fig. 1 is a flow chart showing an example of the method for recovering rhodium according to an embodiment of the present invention. The flow chart in Fig. 1 shows an example, and the method for recovering rhodium according to an embodiment of the present invention is not limited thereto.

[0019] Electrolytic slime, which is generated during the electrolytic refining process of non-ferrous metal smelting, especially copper smelting, contains a lot of chalcogen elements and precious metals. For example, it contains 10-30 kg / t of gold, 20-50 g / t of rhodium, 1-3 kg / t of palladium, 200-500 g / t of platinum, and 5-15 mass% of selenium.

[0020] When hydrochloric acid and hydrogen peroxide are added to dissolve this electrolytic slime, a solution of copper electrolytic deposit is produced, but immediately after dissolution, silver forms an insoluble silver chloride precipitate with chloride ions. If a solution containing an oxidizing agent and chlorine, such as aqua regia or chlorine water, is used, the precious metals can be dissolved and the silver can be separated as silver chloride. In this case, since the treatment is performed in a chloride bath, the precious metal elements, rare metal elements, selenium, and tellurium are distributed in the pregnant leach solution (PLS). In an embodiment of the present invention, the pregnant leach solution is an acidic aqueous solution.

[0021] If necessary, the gold is subsequently extracted with a solvent and recovered. After that, each valuable element is recovered by precipitating it out using the difference in oxidation-reduction potential (ORP). Platinum and palladium complexes in acidic aqueous solutions have a relatively high oxidation-reduction potential, and are the first to precipitate when a reducing agent is added. The most common method of recovery is to use sulfur dioxide as the reducing agent. Sulfur dioxide can be obtained from smelting exhaust gases and is a suitable reducing agent.

[0022] However, when platinum and palladium are precipitated, rhodium is mixed in. This is because the redox potential of rhodium complexes is low, but the reduction with sulfur dioxide is poorly selective. The same problem occurs when a reducing agent with a lower redox potential than sulfur dioxide is used.

[0023] Therefore, in an embodiment of the present invention, dimethyl sulfoxide (DMSO) is added to the acidic aqueous solution and stirred in order to suppress the precipitation of rhodium. The unpaired electron of the sulfur atom in the molecular skeleton of DMSO interacts with rhodium (III), and its coordination bond strength is stronger than that of sulfite. After the sulfite ion coordinates with the rhodium complex, electrons are transferred to the rhodium complex, reducing the rhodium complex. When one or more molecules of DMSO are coordinated to the rhodium complex, the steric hindrance of the first coordination sphere becomes large, making it difficult for the sulfite ion, which is a reducing agent, to approach.

[0024] When the acidic aqueous solution to be treated is copper smelting liquor, if the approach of sulfite ions to the rhodium(III) complex is hindered, sulfite reacts with selenite present in large excess in the liquor. Even if the liquor does not contain selenite, under acidic conditions, an increased amount of sulfur dioxide gas will evaporate from the liquor. The masking mechanism of DMSO when the reducing agent is sulfur dioxide or sulfite ions is as described above, but even if other reducing agents are added, the rhodium complex coordinated with DMSO will reduce the reduction efficiency due to steric barriers.

[0025] Rhodium is known to behave similarly to platinum and palladium. Therefore, there is concern that the addition of DMSO may make platinum and palladium less susceptible to reduction. However, while platinum and palladium have a divalent oxidation state in an acidic aqueous solution, rhodium has a trivalent oxidation state. This makes it a harder acid according to the HASB rule, and it is presumed that this is the reason why rhodium is less susceptible to reduction than platinum and palladium.

[0026] Rhodium that has been masked and stabilized with DMSO is relatively stable against various reducing agents, which are substances that reduce platinum and palladium. Specifically, these are thiosulfate ions, water-soluble aldehydes, sulfite ions, sulfur dioxide, etc., which, as mentioned above, are reducing agents that carry a negative or partial negative charge.

[0027] It is preferable to add 1 to 20 mL of DMSO per 1 L of the acidic aqueous solution. When the amount of DMSO is 1 mL or more per 1 L of the acidic aqueous solution, the masking effect of rhodium is improved. When the amount of DMSO is 20 mL or less per 1 L of the acidic aqueous solution, it is possible to suppress an increase in COD (chemical oxygen demand) in the wastewater and the generation of odor from DMSO decomposition products. In addition, the rhodium masked with DMSO is finally recovered by cementation, and as the amount of DMSO added increases, the rhodium becomes less susceptible to cementation. From this viewpoint, it is preferable to add 20 mL or less of DMSO per 1 L of the acidic aqueous solution. It is more preferable to add 5 to 10 mL of DMSO per 1 L of the acidic aqueous solution.

[0028] In an embodiment of the present invention, as described above, DMSO is added to the acidic aqueous solution and stirred, and then a reducing agent is added to the acidic aqueous solution to precipitate platinum and palladium. As the reducing agent, sulfur dioxide or sulfites are preferably used from the viewpoint of preventing impurities from being mixed in after the reaction. Examples of sulfites include sodium sulfite, sodium hydrogen sulfite, and sulfurous acid. The reaction temperature is not particularly limited, but is preferably 50 to 75°C.

[0029] After platinum and palladium are precipitated by adding a reducing agent to the acidic aqueous solution, the platinum and palladium in the solid phase are recovered by solid-liquid separation using a filter press or the like.

[0030] As shown in the flow chart in Figure 1, if the acidic aqueous solution to be treated contains selenium (selenious acid) in addition to platinum, palladium, and rhodium, as described above, DMSO is added to the acidic aqueous solution and stirred, and then ketones are added to the acidic aqueous solution. The ketones are oxidized by the selenious acid to produce aldehydes. As a result, platinum and palladium can be selectively reduced and precipitated. In this reaction system, rhodium is also mixed into the precipitate, but by adding DMSO before reduction, the amount of rhodium mixed into the precipitate can be minimized by the masking effect.

[0031] In addition, compared to sulfur dioxide reduction, the addition of ketones has the advantage of suppressing selenium contamination. This is because platinum and palladium are preferentially reduced by aldehydes compared to selenious acid. Ketones that can be added include acetone, 2-butanone, and 1-hydroxyacetone, with acetone being the most suitable in terms of safety and cost.

[0032] In this way, when the acidic aqueous solution contains selenious acid, DMSO is added to the acidic aqueous solution, and then the acidic aqueous solution is heated to a liquid temperature of 65°C or higher, acetone is added to precipitate platinum and palladium, and the precipitated platinum and palladium are recovered by solid-liquid separation using a filter press or the like. It is known that when the temperature of the acidic aqueous solution is less than 65°C, selenium precipitates as red selenium or sticky amorphous selenium. Selenium in these forms must be dehydrated or adhered to peripheral equipment before distillation and then peeled off. In addition, when the liquid temperature is 65°C or higher, the reduction rate also increases.

[0033] When selenite is contained in the liquid phase obtained by solid-liquid separation after precipitating platinum and palladium, sulfur dioxide is added to precipitate the selenite as selenium. The masking effect of DMSO is also effective in this selenium precipitation process, and it is possible to suppress the contamination of rhodium with selenium.

[0034] Next, the DMSO contained in the platinum and palladium recovery solution is oxidized, and then a reducing agent is added to precipitate rhodium, which is then separated into solid and liquid to recover the rhodium. Since rhodium is masked with DMSO, it is necessary to reduce the rhodium after oxidative decomposition of this DMSO.

[0035] The oxidizing agent used for the oxidative decomposition of DMSO is not particularly limited as long as it is an oxidizing agent capable of oxidizing sulfur in the molecular skeleton of DMSO, i.e., has the oxidizing power to oxidize sulfur (IV) to sulfur (VI). Examples of the oxidizing agent include hydrogen peroxide, hypochlorous acid, nitric acid, dichromate, ozone, permanganate, and base metals. From the viewpoints of ease of handling and prevention of contamination by impurities, hydrogen peroxide is preferable as the oxidizing agent.

[0036] The reaction temperature during the oxidative decomposition of DMSO is 60° C. or higher, and more preferably 60° C. to 80° C. If the reaction temperature exceeds 80° C., hydrogen peroxide may be consumed by other substances such as chloride ions. If the liquid temperature is less than 60° C., the oxidative decomposition of DMSO may not proceed.

[0037] Furthermore, when hydrogen peroxide is used as the oxidizing agent, the appropriate amount of hydrogen peroxide to be added is 0.5 to 4 times the volume of the added DMSO, calculated as 30 mass % hydrogen peroxide.

[0038] After oxidative decomposition of DMSO, the liquid temperature is adjusted to 40°C or higher and a reducing agent is added to precipitate rhodium. The reducing agent can be any substance that can generally reduce rhodium ions, such as sulfur dioxide, sulfite, sodium thiosulfate, iron, iron products, base metals, copper, or hydrazine. In terms of cost and rhodium recovery efficiency, it is preferable to precipitate rhodium by cementation using iron or iron products. Iron is preferably iron powder, which is easy to handle. There is no particular grain size for the iron powder. In addition, iron products here refer to iron with a part of its surface coated with a noble metal to suppress hydrogen generation, and various iron alloys and high-quality scrap iron can also be used.

[0039] There is also concern that the instantaneous generation of hydrogen may have a detrimental effect on the reducing power of the nascent hydrogen when the solution is contaminated with toxic substances such as arsenic. To suppress the generation of hydrogen, iron powder whose surface is coated with copper (copper-coated iron powder) may be used. There is no particular method for coating with copper, but a treatment such as immersing the iron powder in a copper sulfate solution will suffice.

[0040] The amount of iron or copper-coated iron powder added to the solution to be treated is preferably 5 g / L or more, and more preferably 5 to 20 g / L. If the amount of iron or copper-coated iron powder added is too much, the protons will react with the iron powder, causing the instantaneous generation of hydrogen, and if the amount is too little, cementation may be insufficient.

[0041] As described above, a reducing agent is added to precipitate rhodium, and after the reduction is stopped, the precipitated rhodium is recovered. At this time, the rhodium-containing material precipitated after the reduction treatment is recovered by solid-liquid separation using a filter press or the like. Since the recovered rhodium still contains impurities, it can be input as a rhodium raw material to the refining process described in Patent Document 2. When evaluated as a rhodium raw material, it has the advantage of containing fewer impurities than the selenium distillation residue described in Patent Document 2. EXAMPLES

[0042] The following examples are provided to better understand the present invention and its advantages, but the present invention is not limited to these examples.

[0043] (Preparation of treatment target solution A (acidic aqueous solution containing platinum, palladium and rhodium)) Electrolytic slime recovered from copper smelting was leached with sulfuric acid to remove copper, and then concentrated hydrochloric acid and 60% by mass hydrogen peroxide were added to dissolve the slime. Pregnant leach liquor (PLS) was obtained by solid-liquid separation. Next, the composition of the post-gold extraction liquid (liquid A to be treated) in which gold was removed from PLS by solvent extraction was analyzed. The palladium concentration was 420 mg / L, the platinum concentration was 88 mg / L, the selenium concentration was 39 g / L, and the rhodium concentration was 7 mg / L.

[0044] Example 1 2 mL of DMSO was added to 200 mL of the liquid A to be treated and stirred for 30 minutes, after which 0.5 mL of acetone was added. The liquid temperature was kept at 70-75°C and reduction was continued for 30 minutes, resulting in a precipitate containing platinum and palladium. Next, a precipitate (solid phase) containing platinum and palladium was recovered by solid-liquid separation. The liquid phase obtained by solid-liquid separation was diluted 25 times with dilute hydrochloric acid, and the concentrations of various components were measured using ICP-OES (Seiko SPS-3100) with yttrium as an internal standard. To prevent the influence of evaporation of the liquid, the concentrations of various components were corrected by the copper concentration in the liquid phase. The test results are shown in Table 1.

[0045] Comparative Example 1 A solution A to be treated that did not contain DMSO was prepared. Acetone was added to the solution A to be treated under the same conditions as in Example 1 to generate a precipitate containing platinum and palladium. The concentrations of various components in the liquid phase after solid-liquid separation were measured under the same conditions as in Example 1. The test results are shown in Table 1. In Table 1, "ND" indicates a concentration below the detection limit.

[0046] [Table 1]

[0047] As shown in Table 1, in Example 1, in which DMSO was added before the reduction of platinum and palladium with a reducing agent, the precipitation of rhodium was effectively suppressed by the masking effect of DMSO. In contrast, in Comparative Example 1, in which DMSO was not added before the reduction of platinum and palladium, rhodium also precipitated during the reduction of platinum and palladium, and the concentration of rhodium in the liquid phase after solid-liquid separation was lower than in Example 1. In addition, a decrease in the selenium concentration in the liquid phase after solid-liquid separation is observed in Comparative Example 1 compared to Example 1, but this is the result of reaction with acetone to produce elemental selenium.

[0048] (Examples 2 to 8) 200 mL of the liquid A to be treated was taken, 0.6 to 2.0 mL of DMSO was added, and the mixture was stirred for 30 minutes. Next, the mixture was heated to 70 to 75°C, 0.3 mL of acetone was added, and the liquid temperature was kept at 70°C for 60 minutes of reduction, resulting in the formation of a precipitate containing platinum and palladium. Next, a precipitate (solid phase) containing platinum and palladium was recovered by solid-liquid separation. The rhodium concentration in the liquid phase (treatment liquid 1) obtained by solid-liquid separation was measured by ICP-OES (Seiko SPS-3100) under the same conditions as in Example 1. The test results are shown in Table 2. Next, the treatment liquid 1 was heated again and kept at 75 to 80°C, and a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20% by volume) was blown in at 0.1 L / min for 60 minutes to precipitate selenium. Next, the precipitate (solid phase) containing selenium was collected by solid-liquid separation, and 0 to 2 mL of 30 mass% hydrogen peroxide solution (oxidizer) was added to the liquid phase, which was heated to 75 to 80°C. Thereafter, the rhodium concentration in the liquid (treatment liquid 2) was measured by ICP-OES (Seiko SPS-3100) under the same conditions as in Example 1. The test results are shown in Table 2. Next, a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20% by volume) was blown into the treatment liquid 2 again for 60 minutes. Next, the resulting precipitate was separated into solid and liquid, and the resulting liquid phase was heated to 60°C, after which 1 g of iron powder was added and stirred for 30 minutes to perform cementation. The rhodium concentration in the post-cementation liquid (treatment liquid 3) obtained by filtering the resulting liquid was measured by ICP-OES (Seiko SPS-3100) under the same conditions as in Example 1. The test results are shown in Table 2. In Table 2, "ND" indicates a concentration below the detection limit.

[0049] [Table 2]

[0050] From Example 8, it can be said that DMSO is effective even when added at 0.6 mL to 200 mL of the treatment target solution A. It can be seen that the rhodium content is significantly smaller than the other elements, but it is effectively masked. Platinum and palladium are also somewhat affected by masking, but not to the extent that it becomes a problem.

[0051] In Example 8, in which 0.6 mL of DMSO was added to 200 mL of the treatment solution A, hydrogen peroxide functioned sufficiently, and rhodium precipitated until the liquid concentration reached 1 mg / L. In Examples 2, 3, and 5 to 7, in which 1.0 mL or more of DMSO was added to 200 mL of the treatment solution, some rhodium precipitated by the addition of hydrogen peroxide even before the addition of iron powder. In Example 7, in which 4.0 mL of hydrogen peroxide was added, some rhodium remained even after the addition of iron powder. This is due to the excess hydrogen peroxide consuming the iron powder. For this reason, the amount of hydrogen peroxide added is preferably 0.5 to 4 times the volume of the added DMSO, calculated as 30 mass% hydrogen peroxide water.

[0052] If rhodium is recovered by cementation with iron in a later process, the addition of hydrogen peroxide is not essential. The amount of iron or copper-coated iron required to be added varies depending on the concentrations of other coexisting elements. It is advisable to remove oxidizing substances with sulfur dioxide or sulfite in advance, and then add iron or copper-coated iron to the treatment solution so that the amount of iron in the treatment solution is 1 g / L or more, preferably 5 g / L or more.

[0053] When hydrogen peroxide was not added, the odor of dimethyl sulfide, which is generated when DMSO was reduced, was confirmed when iron powder was added. Dimethyl sulfide is known to be a peculiar odorous substance, so its generation should be suppressed. For this reason, the method of oxidizing and decomposing DMSO with hydrogen peroxide and then recovering rhodium with iron powder is preferable.

Claims

1. a step of adding dimethyl sulfoxide to an acidic aqueous solution containing platinum, palladium and rhodium, adding a reducing agent to the acidic aqueous solution to precipitate platinum and palladium, and recovering platinum and palladium by solid-liquid separation; a step of recovering rhodium from the platinum and palladium recovery solution obtained in the step of recovering platinum and palladium; A method for recovering rhodium, comprising:

2. 2. The method for recovering rhodium according to claim 1, wherein 1 to 20 mL of the dimethyl sulfoxide is added per 1 L of the acidic aqueous solution.

3. 2. The method for recovering rhodium according to claim 1, wherein the reducing agent is sulfur dioxide or a sulfite.

4. 2. The method for recovering rhodium according to claim 1, wherein in the step of recovering platinum and palladium, the acidic aqueous solution contains selenious acid, and acetone is added to the acidic aqueous solution as the reducing agent and the solution is heated to 65° C. or higher to precipitate platinum and palladium.

5. 5. The method for recovering rhodium according to claim 1, wherein in the step of recovering rhodium, dimethyl sulfoxide contained in the platinum and palladium recovery solution is oxidized, a reducing agent is added to precipitate rhodium, and rhodium is recovered by solid-liquid separation.

6. 6. The method for recovering rhodium according to claim 5, further comprising oxidizing dimethyl sulfoxide contained in the platinum and palladium recovery solution, adding iron or iron the surface of which is coated with copper as a reducing agent to precipitate rhodium, and recovering the rhodium by solid-liquid separation.

7. 7. The method for recovering rhodium according to claim 6, wherein the amount of the iron or the iron the surface of which is coated with copper is 5 g / L or more.

8. 6. The method for recovering rhodium according to claim 5, wherein the oxidizing agent for oxidizing the dimethyl sulfoxide is hydrogen peroxide.

9. 9. The method for recovering rhodium according to claim 8, wherein the amount of hydrogen peroxide added is 0.5 to 4 times the volume of the dimethyl sulfoxide added, calculated as a 30 mass% hydrogen peroxide solution.

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