Method for recovering ruthenium

Abstract

To provide a method for effectively separating and recovering ruthenium from an acidic aqueous solution containing platinum, palladium, and ruthenium.SOLUTION: A method for recovering ruthenium includes the steps for: adding dimethyl sulfoxide to an acidic aqueous solution containing platinum, palladium, and ruthenium, 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 ruthenium 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 ruthenium, and more particularly to a method for recovering ruthenium from an acidic aqueous solution containing platinum, palladium and ruthenium. [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 ruthenium, rhodium, 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] Meanwhile, rare metals such as ruthenium, rhodium, 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. Typical impurities are ruthenium and selenium.

[0010] According to conventional technology, platinum and palladium can be separated from selenium by solvent extraction of platinum group metals. However, the same platinum group elements, especially ruthenium, are contained in large amounts and cannot be selectively separated by solvent extraction. In particular, ruthenium cannot be effectively separated in the platinum purification process, so platinum precipitates as an ammonium salt (platinum ammonium salt) in the purification process, but is mixed in as an impurity. Therefore, if the amount of ruthenium mixed in the platinum ammonium salt increases, a process of recrystallization to increase the purity is required.

[0011] Ruthenium itself is a valuable metal classified as a platinum group metal, and is recovered and refined separately. Therefore, it is important to suppress the amount of ruthenium that is mixed into the process of precipitating platinum and palladium from the copper electrolytic precipitate intermediate. This 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 ruthenium from an acidic aqueous solution containing platinum, palladium and ruthenium. [Means for solving the problem]

[0013] As a result of intensive research conducted by the present inventors to solve the above problems, it was found that ruthenium can be satisfactorily separated and recovered from an acidic aqueous solution containing platinum, palladium, and ruthenium by masking and reducing ruthenium in the acidic aqueous solution with dimethyl sulfoxide (DMSO), suppressing the inclusion of ruthenium, and preferentially precipitating and recovering platinum and palladium. 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 ruthenium, 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 ruthenium from the platinum and palladium recovery solution obtained in the step of recovering platinum and palladium; 2. A method for recovering ruthenium comprising the steps of: (2) The method for recovering ruthenium 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 ruthenium according to (1) or (2) above, wherein the reducing agent is sulfur dioxide or a sulfite. (4) The method for recovering ruthenium 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 heated to 65°C or higher to precipitate platinum and palladium. (5) The method for recovering ruthenium according to any one of (1) to (4), wherein in the step of recovering ruthenium, dimethyl sulfoxide contained in the platinum and palladium recovery solution is oxidized, a reducing agent is added to precipitate ruthenium, and ruthenium is recovered by solid-liquid separation. (6) The method for recovering ruthenium according to (5) above, in which dimethyl sulfoxide contained in the platinum and palladium recovery solution is oxidized, iron or iron the surface of which is coated with copper is added as a reducing agent to precipitate ruthenium, and ruthenium is recovered by solid-liquid separation. (7) The method for recovering ruthenium according to (6) above, wherein the amount of the iron or the iron whose surface is coated with copper added is 5 g / L or more. (8) The method for recovering ruthenium according to (5) above, wherein the oxidizing agent for oxidizing dimethyl sulfoxide is hydrogen peroxide. (9) The method for recovering ruthenium according to (8) above, wherein the amount of hydrogen peroxide added is 0.5 to 2 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, it is possible to provide a method for satisfactorily separating and recovering ruthenium from an acidic aqueous solution containing platinum, palladium and ruthenium. [Brief description of the drawings]

[0016] [Figure 1] 1 is a flowchart showing an example of a method for recovering ruthenium 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] (Ruthenium recovery method) The ruthenium recovery method according to the embodiment of the present invention includes the steps of adding dimethyl sulfoxide (DMSO) to an acidic aqueous solution containing platinum, palladium and ruthenium, 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 recovering ruthenium from the platinum and palladium recovery liquid obtained in the step of recovering platinum and palladium. Figure 1 is a flow chart showing an example of the ruthenium recovery method according to the embodiment of the present invention. The flow chart in Figure 1 shows an example, and the ruthenium recovery method according to the 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, 600-1500 g / t of ruthenium, 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 precipitate, ruthenium gets mixed in. This is because the redox potential of ruthenium complexes is low, but reduction with sulfur dioxide is poorly selective. The same problem occurs even when a reducing agent with a lower redox potential than sulfur dioxide is used. Although there are variations depending on the lot, the precipitate usually contains 2000 to 3000 g / t of ruthenium.

[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 ruthenium. The unpaired electron of the sulfur atom in the molecular skeleton of DMSO interacts with ruthenium (II), and its coordinate bond strength is stronger than that of sulfite. Furthermore, when DMSO coordinates to ruthenium, the steric hindrance of the first coordination sphere becomes large, making it difficult for reducing compounds such as sulfite ions and aldehydes to approach.

[0024] When the approach of reducing compounds to ruthenium (II) is hindered, in the case where the acidic aqueous solution is a copper smelting-derived solution, the reducing compounds are more likely to react with selenite, which is present in large excess, rather than with ruthenium. Even if the acidic aqueous solution is not a copper smelting-derived solution, under acidic conditions, the amount of reducing compounds that become sulfur dioxide gas and leave the solution increases. In particular, when the reducing compound is an aldehyde or the like, the inhibition of the approach of reducing compounds to the DMSO-coordinated ruthenium complex is significant. In this way, it is thought that a masking effect (reaction suppression effect) by DMSO appears. Due to a similar reaction mechanism, the masking effect of DMSO is also exerted on reducing compounds such as sulfur dioxide, sulfite ions, and thiosulfate ions.

[0025] On the other hand, platinum and palladium, which are also in the platinum group, are not as susceptible to the masking effect of DMSO as ruthenium. Platinum and palladium are planar tetracoordinate complexes, and the first coordination sphere is relatively less sterically crowded. This allows easy access for reducing compounds. In contrast, ruthenium(II) is hexacoordinate, which means it is more spatially crowded and susceptible to the masking effect of DMSO.

[0026] 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 ruthenium is improved. When the amount of DMSO is 20 mL or less per 1 L of the acidic aqueous solution, the increase in COD (chemical oxygen demand) in the wastewater and the generation of odor from DMSO decomposition products can be suppressed. In addition, the ruthenium masked with DMSO is finally recovered by cementation, and as the amount of DMSO added increases, the ruthenium 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.

[0027] 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.

[0028] 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.

[0029] 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 ruthenium, 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. Ruthenium also gets mixed into the precipitate in this reaction system, but by adding DMSO before reduction, the amount of ruthenium mixed into the precipitate can be minimized by the masking effect.

[0030] 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.

[0031] 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.

[0032] 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 ruthenium with selenium.

[0033] Next, the DMSO contained in the platinum and palladium recovery solution is oxidized, and then a reducing agent is added to precipitate ruthenium, which is then separated into solid and liquid to recover ruthenium. Since ruthenium is masked with DMSO, it is necessary to reduce ruthenium after oxidative decomposition of this DMSO.

[0034] 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, chlorine, hypochlorous acids, chromates, ozone, and permanganates. From the viewpoints of ease of handling and prevention of contamination by impurities, hydrogen peroxide is preferred as the oxidizing agent.

[0035] 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.

[0036] Furthermore, when hydrogen peroxide is used as the oxidizing agent, the appropriate amount of hydrogen peroxide to be added is 0.5 to 2 times the volume of the added DMSO, calculated as 30 mass % hydrogen peroxide.

[0037] After oxidative decomposition of DMSO, the liquid temperature is adjusted to 40°C or higher and a reducing agent is added to precipitate ruthenium. The reducing agent can be any substance that can generally reduce ruthenium ions, such as sulfur dioxide, sulfite, sodium thiosulfate, iron, iron products, base metals, copper, or hydrazine. In terms of cost and ruthenium recovery efficiency, it is preferable to precipitate ruthenium by cementation using iron or iron products. Iron is preferably iron powder, which is easy to handle. The particle size of the iron powder is not particularly specified. In addition, iron products here refer to iron with a part of the surface coated with a noble metal to suppress hydrogen generation, and various iron alloys and scrap iron with high iron quality can also be used.

[0038] 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.

[0039] 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.

[0040] As described above, a reducing agent is added to precipitate ruthenium, and after the reduction is stopped, the precipitated ruthenium is recovered. At this time, the ruthenium-containing material precipitated after the reduction treatment is recovered by solid-liquid separation using a filter press or the like. The purity of the recovered ruthenium can be increased by dissolving it in acid again and then distilling it further. EXAMPLES

[0041] The following examples are provided to better understand the present invention and its advantages, but the present invention is not limited to these examples.

[0042] (Preparation of treatment target solution A (acidic aqueous solution containing platinum, palladium and ruthenium)) 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, and the palladium concentration was 420 mg / L, the platinum concentration was 88 mg / L, the selenium concentration was 40 g / L, and the ruthenium concentration was 169 mg / L.

[0043] Example 1 2 mL of DMSO was added to 200 mL of the liquid A to be treated, and the mixture was stirred for 30 minutes, after which 0.5 mL of acetone was added. The liquid temperature was kept at 70°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 effects 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.

[0044] 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.

[0045] [Table 1]

[0046] As shown in Table 1, in Example 1, in which DMSO was added before reducing platinum and palladium with a reducing agent, precipitation of ruthenium was well suppressed by the masking effect of DMSO. In contrast, in Comparative Example 1, in which DMSO was not added before reducing platinum and palladium, ruthenium also precipitated during reduction of platinum and palladium, and the concentration of ruthenium 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.

[0047] (Examples 2 to 6) 200 mL of the liquid A to be treated was taken, and 0.6 mL, 1.0 mL, or 2.0 mL of DMSO was added and stirred for 30 minutes. Next, each was heated to 70 to 75 ° C., 0.3 mL of acetone was added, and the liquid temperature was kept at 70 ° 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 (treated liquid 1) 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. In order 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 2.

[0048] Next, the above-mentioned treatment liquid 1 was heated again and held at 70 to 75°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 the liquid phase was heated to 75 to 80°C after adding 0 to 2 mL of 30 mass% hydrogen peroxide water (oxidizer). Next, a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20% by volume) was blown in again for 30 minutes. Thereafter, the ruthenium concentration in the obtained liquid (treatment liquid 2) was measured by ICP-OES (Seiko SPS-3100) under the same conditions as above. The test results are shown in Table 2.

[0049] Next, 200 mL of the above treatment liquid 2 was heated to 60° C., 1 g of iron powder was added, and the mixture was stirred for 30 minutes to perform cementation. The ruthenium concentration in the liquid (treatment liquid 3) obtained after cementation by filtering the mixture was measured by ICP-OES (Seiko SPS-3100) under the same conditions as above. The test results are shown in Table 2.

[0050] [Table 2]

[0051] In Comparative Example 1 in Table 1, after the platinum and palladium precipitates were collected, the ruthenium concentration was reduced to 148 mg / L, and this value was used as the evaluation benchmark. From Example 6 in Table 2, it can be said that DMSO is effective even when added in an amount of 0.6 mL to 200 mL of the treatment target liquid A. From the results of Examples 4 and 5, it is considered that DMSO has a sufficient ruthenium masking effect (ruthenium precipitation suppression effect) when added in an amount of 1.0 mL to 200 mL of the treatment target liquid A. Furthermore, from the results of Examples 4 to 6, it can be seen that a ruthenium precipitation suppression effect of 5 mg / L can be expected by increasing the amount of DMSO added by at least 0.4 mL to 200 mL of the treatment target liquid A.

[0052] It is also clear that the masking effect of DMSO becomes noticeable after adding about 1 / 3 of 0.6 mL of DMSO to 200 mL of the treatment target solution A. This is because the benchmark for the ruthenium concentration after recovering the platinum and palladium precipitates is 148 mg / L, and the difference of 13 mg / L divided by 5 mg / L equals 2.6. That is, it is understood that the masking effect of ruthenium is further improved by adding DMSO to the treatment target solution A in an amount of 1.0 mL / L or more.

[0053] As shown in Example 5 of Table 2, even masked ruthenium without oxidatively decomposing DMSO can be recovered by cementing with iron powder. However, a comparison of Example 5 with Example 4 shows that more ruthenium can be recovered by cementing ruthenium with iron powder after oxidatively decomposing DMSO as in Example 4.

[0054] Comparing Examples 2, 4, and 6 in Table 2, it can be seen that as the amount of DMSO added increases, cementation becomes less likely to occur. Therefore, the amount of DMSO added is preferably 20 mL / L or less relative to the liquid A to be treated. On the other hand, as can be seen from comparing Examples 2 and 3, if the amount of hydrogen peroxide added is excessive relative to DMSO, iron may be wasted in the cementation treatment of iron powder, which may have a negative effect on ruthenium recovery. The recovery rate of ruthenium varies depending on the balance between the amount of DMSO added, the amount of oxidizing agent added, and the amount of iron powder added. Therefore, in order to eliminate the effects of excess hydrogen peroxide, for example, the amount of iron powder added may be increased, or the surface of the iron powder may be pre-coated with a noble metal, such as copper, or other processing may be performed.

[0055] Example 7 200 mL of the liquid A to be treated was taken, 2.0 mL of DMSO was added, and the mixture was stirred for 30 minutes. Next, the mixture was heated to 70-75°C, and a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5-20% by volume) was blown in at 0.1 L / min for 30 minutes. Next, a precipitate (solid phase) containing platinum and palladium was collected 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 3.

[0056] Comparative Example 2 A treatment target liquid A containing no DMSO was prepared. Treatment target liquid A was heated to 70-75°C under the same conditions as in Example 7, and a mixed gas of sulfur dioxide and air was blown into it to produce a precipitate containing platinum and palladium. 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 3. In Table 3, "ND" indicates a concentration below the detection limit.

[0057] [Table 3]

[0058] As shown in Table 3, even when sulfur dioxide was used as the reducing agent, the addition of DMSO prevented the precipitation of ruthenium when precipitating platinum and palladium.

Claims

1. a step of adding dimethyl sulfoxide to an acidic aqueous solution containing platinum, palladium and ruthenium, 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 ruthenium from the platinum and palladium recovery solution obtained in the step of recovering platinum and palladium; 2. A method for recovering ruthenium comprising the steps of:

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

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

4. 2. The method for recovering ruthenium 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 heated to 65° C. or higher to precipitate platinum and palladium.

5. The ruthenium recovery method according to any one of claims 1 to 4, wherein in the step of recovering ruthenium, dimethyl sulfoxide contained in the platinum and palladium recovery liquid is oxidized, and then a reducing agent is added to precipitate ruthenium, and ruthenium is recovered by solid-liquid separation.

6. The method for recovering ruthenium according to claim 5, wherein dimethyl sulfoxide contained in the platinum and palladium recovery solution is oxidized, and then iron or iron whose surface is coated with copper is added as a reducing agent to precipitate ruthenium, and ruthenium is recovered by solid-liquid separation.

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

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

9. The ruthenium recovery method according to claim 8, wherein the amount of hydrogen peroxide added is 0.5 to 2 times the volume of the added dimethyl sulfoxide in terms of 30 mass% hydrogen peroxide water.

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