How to collect iridium

Abstract

To provide a method for excellently separating and recovering iridium from a hydrochloric acid solution containing iridium, sulfur and at least one of copper, antimony, lead and arsenic.SOLUTION: A recovery method of iridium includes performing the following treatment steps (1)-(3) in this order on a hydrochloric acid solution containing iridium, sulfur and at least one of copper, antimony, lead and arsenic: (1) a precipitate recovery step of precipitating and recovering iridium by heating the hydrochloric acid solution to 40°C or more, and adding thiosulfate salt or a thiosulfate ion-containing solution; (2) a step of charging the precipitate recovered in step (1) into a sulfuric acid or hydrochloric acid solution of 0.5 N or more so as to dissolve and separate metal components; and (3) charging the precipitate from which metal components are separated in step (2) into an alkali solution containing sulfurous acids followed by heating to 20°C or more so as to dissolve and separate sulfur.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for recovering iridium, and more particularly to a method for recovering iridium from a hydrochloric acid solution containing iridium, sulfur, and one or more of copper, antimony, lead, and arsenic. [Background technology]

[0002] In copper pyrometallurgy, copper concentrate is melted and processed into crude copper of 99% purity or more in a converter and a refining furnace, after which electrolytic refining is carried out to produce electrolytic copper with a purity of, for example, 99.99% or more. In recent years, metal scrap containing precious metals from electronic components has been fed into converters as recycled raw materials, and valuable materials other than copper are precipitated as slime during electrolytic refining.

[0003] This slime also contains precious metals, rare metals, and the selenium and tellurium contained in copper concentrate. These elements are separated and recovered individually as by-products of copper smelting.

[0004] Hydrometallurgy is often used to treat this slime. For example, Patent Document 1 discloses a method in which silver is recovered from slime using hydrochloric acid and hydrogen peroxide, the dissolved gold is recovered by solvent extraction, and then other valuables are sequentially reduced and recovered using sulfur dioxide. Patent Document 2 discloses a method in which gold and silver are recovered using a similar method, and then the valuables are reduced and precipitated using sulfur dioxide, and only the selenium is removed by distillation to concentrate the precious metals.

[0005] The solution left after the precious metals have been recovered contains rare metal ions, tellurium, and selenium, and these valuable materials must be further recovered. Known recovery methods include recovering the precipitate formed by the reduction agent, or mixing the solution with copper concentrate, drying it in a dryer, and then returning it to the smelting furnace.

[0006] In particular, the method of recovering precipitates produced by sulfur dioxide, as shown in Patent Document 1, has many advantages in terms of cost and production scale. In addition, since each element precipitates sequentially, it is also effective for separation and purification.

[0007] In the method of recovering valuables using sulfur dioxide, valuables can be recovered by sequential reduction after dissolution. Platinum and palladium precipitate first. Selenium is then reduced. Iridium and ruthenium have relatively low redox potentials and are therefore less susceptible to reduction, remaining in the solution until the end. As for iridium, a widely known method is to separate it by solvent extraction, concentrate it, and then recover it by calcination, as described in Patent Document 3. Patent Document 4 also discloses a method of precipitating iridium by adding sodium thiosulfate to an aqueous solution containing iridium. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-316735 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-160479 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-332041 [Patent Document 4] Japanese Patent Publication No. 2022-135956 Summary of the Invention [Problem to be solved by the invention]

[0009] The precipitate obtained from a thiosulfate or thiosulfate ion-containing solution contains many impurities. Most of the impurities are elemental sulfur produced by the decomposition of thiosulfate ions and metal sulfides sulfurized by thiosulfate ions. Among these, iridium is generally contained in an amount of only about 0.5 to 3 mass%.

[0010] One method for refining iridium of this level of quality is to use solvent extraction after remelting, as shown in Patent Document 3. However, this method consumes a large amount of acid, increasing costs. In addition, because elemental sulfur does not dissolve, there are concerns about a decrease in the iridium recovery rate and an increase in the cost of processing elemental sulfur.

[0011] While it would be ideal if it could be introduced into existing iridium refining processes, there is the issue of removing elemental sulfur, which is generally achieved by roasting. However, roasting poses the problem of how to deal with sulfur dioxide gas derived from sulfur. Furthermore, elemental sulfur is classified as a hazardous material and is difficult to handle due to the risk of dust explosions.

[0012] In view of the above-described conventional circumstances, an embodiment of the present invention provides a method for effectively separating and recovering iridium from a hydrochloric acid solution containing iridium, sulfur, and one or more of copper, antimony, lead, and arsenic. The embodiment of the present invention is particularly suitable for separating and recovering iridium from a hydrochloric acid solution obtained by oxidatively dissolving electrolytic precipitate generated in an electrolytic refining step in copper smelting. [Means for solving the problem]

[0013] The above problems can be solved by the inventions specified below. [1] A method for recovering iridium, comprising subjecting a hydrochloric acid solution containing iridium, sulfur, and one or more of copper, antimony, lead, and arsenic to the following treatment steps (1) to (3) in this order: (1) a precipitation recovery step of heating the hydrochloric acid solution to 40°C or higher and adding a thiosulfate salt or a solution containing thiosulfate ions to precipitate and recover iridium; (2) A step of introducing the precipitate recovered in the step (1) into an acidic sulfuric acid or hydrochloric acid solution of 0.5N or more to dissolve and separate the metal components; (3) A step in which the precipitate obtained after separating the metal components in the step (2) is poured into an alkaline solution containing sulfites and heated to 20°C or higher to dissolve and separate the sulfur. [2] The method for recovering iridium according to [1] above, wherein in the step (1) above, a thiosulfate salt or a solution containing thiosulfate ions is added so that the concentration, calculated as sodium thiosulfate pentahydrate, is 10 g / L or more based on thiosulfate ions, thereby precipitating iridium. [3] The method for recovering iridium according to [1] above, wherein in the step (1), the hydrochloric acid solution contains ruthenium, and the ruthenium is precipitated and recovered simultaneously with iridium. [4] The method for recovering iridium according to [1] above, wherein in the step (2), the sulfuric acid or hydrochloric acid solution contains iron (III) ions in an amount of 0.05 times or more by mass of the iridium-containing precipitate. [5] The method for recovering iridium according to [1] above, wherein in the step (2), the precipitate recovered in the step (1) is added to the sulfuric acid or hydrochloric acid solution so that the slurry concentration is 150 g / L or less. [6] The method for recovering iridium according to [1] above, wherein in the step (3), the content of sulfites in the alkaline solution is equivalent to 1.5 times or more by mass, in terms of sodium sulfite, of the mass of the precipitate obtained in the step (1). [7] The method for recovering iridium according to [1] above, wherein the liquid obtained by dissolving and separating the sulfur in the step (3) is used as the thiosulfate ion-containing solution in the step (1) after adjusting the concentration of thiosulfate ions. [Effects of the Invention]

[0014] According to an embodiment of the present invention, it is possible to provide a method for effectively separating and recovering iridium from a hydrochloric acid solution containing iridium, sulfur, and one or more of copper, antimony, lead, and arsenic. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flowchart illustrating an example of a method for recovering iridium according to an embodiment of the present invention. [Figure 2] 10 is a graph showing the relationship between the amount of sodium sulfite added and the final residue mass in Experimental Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the method for recovering iridium of the present invention will be described, but the present invention should not be construed as being limited thereto, and various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art without departing from the scope of the present invention.

[0017] <Recovery of iridium by precipitation> The method for recovering iridium according to an embodiment of the present invention includes a step of precipitating and recovering iridium, a step of dissolving and separating metal components, and a step of dissolving and separating sulfur. Fig. 1 is a flowchart showing an example of the method for recovering iridium according to an embodiment of the present invention. The flowchart in Fig. 1 shows one example, and the method for recovering iridium according to an embodiment of the present invention is not limited to this.

[0018] In the method for recovering iridium according to an embodiment of the present invention, the hydrochloric acid solution containing iridium to be treated may be one obtained through any type of treatment, but a hydrochloric acid solution obtained by oxidatively dissolving electrolytic precipitate generated in the electrolytic refining step in copper smelting is particularly suitable as the hydrochloric acid solution containing iridium to be treated in the method for recovering iridium according to an embodiment of the present invention.

[0019] The hydrochloric acid solution to be treated in the iridium recovery method according to an embodiment of the present invention contains iridium (Ir), sulfur (S), and one or more of copper (Cu), antimony (Sb), lead (Pb), and arsenic (As). The hydrochloric acid solution to be treated may also contain alkali metals, alkaline earth metals, antimony (Sb), bismuth (Bi), etc. These do not react with the thiosulfate ions described below, so no special treatment is required. Furthermore, the hydrochloric acid solution to be treated may also contain selenium (Se), ruthenium (Ru), tellurium (Te), etc. However, since these are reduced by the thiosulfate ions, it is preferable to reduce the concentrations of these metals in advance, as described in detail below, to improve treatment efficiency.

[0020] Furthermore, since divalent iron (Fe) does not react with thiosulfate ions, it may be contained in the hydrochloric acid solution to be treated. On the other hand, trivalent iron (Fe) may also be contained in the hydrochloric acid solution to be treated, but since it reacts with thiosulfate ions, it is preferable to reduce it to divalent iron before adding thiosulfate ions.

[0021] As an example, we will show how to prepare a hydrochloric acid solution containing iridium from electrolytic sediment from the copper electrorefining process of copper smelting. First, copper is dissolved and removed from the electrolytic sediment from the copper electrorefining process using sulfuric acid. Next, concentrated hydrochloric acid and hydrogen peroxide are added to dissolve the precipitate, and the pregnant leach solution (PLS) is obtained by solid-liquid separation. Platinum group elements, rare metal elements, chalcogen elements, arsenic, antimony, etc. are distributed in the pregnant leach solution (PLS), which is a chloride bath.

[0022] The pregnant leach solution (PLS) is cooled once, and chlorides of base metals such as lead and antimony are precipitated and separated. Gold is then separated into an organic phase by solvent extraction. Dibutyl carbitol (DBC) is commonly used as the gold extractant. Next, sulfur dioxide is blown into the extract to reduce and remove precious metals such as platinum and palladium, as well as selenium and tellurium. Solid-liquid separation then produces a hydrochloric acid solution containing iridium.

[0023] The iridium concentration in this iridium-containing hydrochloric acid solution is approximately 10 to 100 mg / L, so further concentration is necessary. Precipitation separation using thiosulfate is a well-known concentration method, as described in Patent Document 4. The iridium-containing hydrochloric acid solution may also contain copper, antimony, lead, arsenic, ruthenium, and other elements that were not completely reduced by sulfur dioxide. Arsenic and copper can be selectively precipitated and separated by sulfurization treatment using hydrogen sulfide, sodium hydrosulfide, or sodium sulfide before precipitating and recovering iridium. This sulfurization treatment may also precipitate trace amounts of selenium and tellurium. Furthermore, ruthenium is often present in iridium refining raw materials, and since methods for separating them have been established, iridium and ruthenium can be simultaneously recovered by adding thiosulfate. In particular, a method of distillation using sodium bromate after acid dissolution is known.

[0024] (Iridium precipitation recovery process) In the iridium precipitation recovery process, a hydrochloric acid solution is heated to 40°C or higher, and a thiosulfate or thiosulfate ion-containing solution is added to precipitate and recover iridium. Adding a thiosulfate or thiosulfate ion-containing solution to a hydrochloric acid solution heated to 40°C or higher promotes the precipitation of iridium (also referred to as an iridium-containing precipitate). The hydrochloric acid solution is preferably heated to 60°C or higher, more preferably to 80°C or higher. Examples of thiosulfates to be added include sodium thiosulfate and its hydrates, and ammonium thiosulfate. Examples of thiosulfate ion-containing solutions to be added include a solution prepared by dissolving elemental sulfur in a sodium sulfite solution, and a solution prepared by suspending elemental sulfur in a sodium hydroxide solution and blowing sulfur dioxide into the solution.

[0025] In the iridium precipitation and recovery step, it is preferable to precipitate iridium by adding thiosulfate or a solution containing thiosulfate ions to a concentration of 10 g / L or more, calculated as sodium thiosulfate pentahydrate, based on thiosulfate ions. This configuration can promote the precipitation of iridium by thiosulfate ions.

[0026] (Metal component dissolution and separation process) In the metal component dissolution and separation step, the iridium-containing precipitate recovered in the iridium precipitation and recovery step is introduced into a 0.5N or higher sulfuric acid or hydrochloric acid solution to dissolve and separate the metal components. Here, the iridium-containing precipitate contains metal sulfides, which are decomposed and removed with the acid, enabling the metal components to be dissolved and separated. The acid used is preferably sulfuric acid or hydrochloric acid, which has an oxidizing power sufficient to prevent the precipitated iridium and ruthenium from redissolving. Furthermore, the iridium-containing precipitate recovered in the iridium precipitation and recovery step is in the form of a slurry. Adding the slurry to a sulfuric acid or hydrochloric acid solution so that the concentration of the slurry becomes 150 g / L or less is preferable, as this further promotes the dissolution and separation of the metal components.

[0027] If sulfuric acid is used as the acid, its oxidizing power may be insufficient. Therefore, it is preferable to add iron (III) ions to the sulfuric acid, as this will efficiently dissolve the metal sulfide. Specifically, it is preferable that the amount of iron (III) ions contained in the sulfuric acid or hydrochloric acid acid solution is 0.05 times or more by mass of the iridium-containing precipitate. Suitable iron (III) ion-containing solutions include solutions obtained by oxidizing iron (II) ion-containing solutions and ferric sulfate.

[0028] There is no particular temperature limit for the acid decomposition in the metal component dissolution and separation process, but a higher temperature is preferable because it shortens the treatment time. From this perspective, the acid decomposition is preferably carried out at 40°C or higher, more preferably at 60°C or higher, and even more preferably at 80°C or higher. Furthermore, the higher the concentration of the acid used in the acid decomposition, the more effective the decomposition becomes, so it is preferable. From this perspective, the acid concentration is preferably 0.5N or higher, more preferably 0.8N or higher, and even more preferably 1.0N or higher.

[0029] After acid decomposition in the metal component dissolution and separation step, the metal components are separated by solid-liquid separation, and at this time, the residue contains iridium, ruthenium, elemental sulfur, etc.

[0030] (Sulfur dissolution and separation process) In the sulfur dissolution and separation process, the precipitate (iridium-containing precipitate) obtained after separating the metal components in the metal component dissolution and separation process described above is placed in an alkaline solution containing sulfites, such as aqueous sodium hydroxide or aqueous ammonia, and heated to 20°C or higher to dissolve the sulfur (elementary sulfur), which is then separated by solid-liquid separation. At this time, the elemental sulfur is dissolved and removed as thiosulfate ions according to the following chemical formula (1), which increases the iridium concentration in the iridium-containing precipitate that remains after solid-liquid separation.

[0031] [ka]

[0032] The sulfite used here is preferably sodium sulfite, sodium hydrogen sulfite, or water that has been blown with and absorbed sulfur dioxide. However, the thiosulfate ion generated according to the above chemical formula (1) is unstable and decomposes under acidic conditions, so the reaction must be carried out while maintaining an alkaline environment.

[0033] Furthermore, the iridium-containing precipitate obtained after the dissolution and separation of the metal components may contain arsenic sulfide. Whether the arsenic is trivalent or pentavalent, arsenic sulfide is decomposed into sulfur and arsenic oxoanions by strong oxidizing agents such as nitric acid and hydrogen peroxide, but is stable in mineral acids. For this reason, it is preferable to prepare a solution containing sulfites as an alkaline solution with a pH of 10 or higher.

[0034] In the treatment with sulfites, the temperature of the reaction solution is preferably 20 to 70° C. If the temperature of the reaction solution is 20° C. or higher, the reaction rate increases, and if the temperature of the reaction solution is 70° C. or lower, decomposition of the sulfites can be suppressed. The temperature of the reaction solution is more preferably 30 to 50° C.

[0035] The amount of sulfite required to be added depends on the content of elemental sulfur and metal sulfides (referred to as non-sulfate sulfur) in the iridium-containing precipitate. For example, when 37% by mass of the iridium-containing precipitate is non-sulfate sulfur, the content of sulfite in the alkaline solution is preferably at least 1.5 times the mass of the iridium-containing precipitate recovered in the iridium precipitation recovery step, calculated as sodium sulfite. Since the iridium-containing precipitate is expected to contain 30 to 40% by mass of non-sulfate sulfur, it is preferable to add sulfite at a level equal to or greater than this amount. That is, it is preferable to add at least 1.5 times the mass of sulfite, calculated as sodium sulfite, of the iridium-containing precipitate, and more preferably at least 2 times the mass of sulfite. When the content of non-sulfate sulfur in the iridium-containing precipitate can be determined in advance, it is preferable to add sulfite so that the amount of sulfite ions is at least equimolar to the non-sulfate sulfur.

[0036] Furthermore, since the reaction follows the above chemical formula (1), if non-sulfate sulfur can be quantified, sulfites must be added in an amount four times or more by mass of non-sulfate sulfur, and it is more preferable to add sulfites in an amount five times or more by mass.

[0037] The method for quantifying non-sulfate sulfur is not particularly specified. For example, non-sulfate sulfur can be quantified by subtracting the sulfur content in sulfuric acid eluted with dilute hydrochloric acid of pH 1 to 2 from the total sulfur content in the iridium-containing precipitate. Another method involves adding nitric acid to the iridium-containing precipitate to decompose the metal sulfides, filtering the precipitate, measuring the mass of the residue, and then contacting the residue with a solution containing sulfite ions to calculate the non-sulfate sulfur content from the mass loss.

[0038] As shown in the above chemical formula (1), elemental sulfur dissolves as thiosulfate ions. Therefore, the liquid obtained by dissolving and separating sulfur can be reused as a thiosulfate ion-containing solution in the above-mentioned iridium precipitation recovery process after adjusting the thiosulfate ion concentration. If the thiosulfate ion concentration is insufficient, a thiosulfate salt such as sodium thiosulfate can be added to adjust the pH, and the solution can be reused. Alternatively, the liquid obtained by dissolving and separating sulfur can be cooled, and the precipitated sodium thiosulfate pentahydrate can be recovered and used in the above-mentioned iridium precipitation recovery process. [Example]

[0039] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0040] (Experimental Example 1) Copper was dissolved and removed from electrolytic sediment from the copper electrorefining process of copper smelting using sulfuric acid. Next, concentrated hydrochloric acid and 60% hydrogen peroxide solution were added to dissolve the material, and the material was subjected to solid-liquid separation to obtain PLS (pregnant leach solution). Next, the PLS was cooled to 6°C to precipitate and remove base metals, and then the acid concentration was adjusted to 2N or higher, and DBC (dibutyl carbitol) was added to extract gold. Next, the PLS after gold extraction was heated to 70°C, and sulfur dioxide was blown in to reduce and remove the precious metals, selenium, and tellurium. This was then subjected to solid-liquid separation to obtain a hydrochloric acid solution containing iridium. Next, a hydrochloric acid solution containing iridium was heated to 80°C, and sodium thiosulfate pentahydrate was added to a concentration of 10 g / L to obtain a slurry of iridium-containing precipitate. The components of the slurry of iridium-containing precipitate are shown in Table 1. Analysis of non-sulfate sulfur (S) was performed by heating 1 g of iridium-containing precipitate in nitric acid, measuring the mass of the undissolved portion, and then adding 2 g / 100 mL of sodium sulfite to dissolve the precipitate, and calculating the content from the difference in the mass of the residue. Furthermore, the "S" composition (48 mass%) in Table 1 represents the total amount of sulfated S (11 mass%) and non-sulfated S (37 mass%).

[0041] [Table 1]

[0042] Next, 2 g of the slurry of the iridium-containing precipitate was collected, and 200 mL of each of the acidic dissolving solutions shown in Table 2 was poured into it. Next, 2 g of ferric sulfate n-hydrate (iron content 20% by mass) was added as a source of iron (III) ions, and the mixture was heated to 60°C and stirred for 90 minutes. After the reaction, the mixture was filtered and diluted 25 times with dilute hydrochloric acid, and the element concentration in the solution was measured using an ICP-OES (Seiko SPS3100). The residue was washed with water and rinsed with alcohol, air-dried overnight, and then its mass was measured. 4 g of sodium sulfite was added to the residue, and 100 mL of water was poured into it, followed by stirring and heating at 60°C for 1 hour. After the reaction, the residue was filtered, washed with water and rinsed with alcohol, air-dried overnight, and then its mass was measured. The difference between the mass of the residue after acid decomposition and the mass of the residue after sodium sulfite treatment (final residue) was taken as the non-sulfated sulfur (S) content. If this value is significantly lower than expected (37%), it is considered that the decomposition of the metal sulfide is insufficient. All reagents used were of special grade manufactured by Wako Pure Chemical Industries, Ltd. The element concentrations in the solution were quantified by taking 2 mL of the solution, adjusting the volume to 50 mL, and then quantifying the concentrations using ICP-OES. The acid leaching rate (%) was calculated from the obtained concentrations. The evaluation results are shown in Table 2.

[0043] [Table 2]

[0044] The results in Table 2 show that with dissolving solutions other than nitric acid, it was possible to dissolve impurity elements while suppressing the loss of iridium and ruthenium. Furthermore, in systems in which iron (III) ions were added to hydrochloric acid and sulfuric acid, copper elution was also highly effective, and even cupric sulfide was eluted.

[0045] Furthermore, the results in Table 2 show that there is little dependence on the acid concentration for both hydrochloric acid and sulfuric acid. However, when the hydrochloric acid concentration increased to 6N, a significant loss of iridium was observed. It is questionable whether cupric sulfide could be eluted with 0.6N hydrochloric acid, and this problem can be solved by removing the copper through sulfurization treatment before obtaining the iridium-containing precipitate.

[0046] (Experimental Example 2) 2 g of the iridium-containing precipitate slurry obtained in Experimental Example 1 was weighed out, and 200 mL of 6.9 N sulfuric acid was poured into it, and 0.5 g to 6 g of ferric sulfate n-hydrate (iron content 20 mass%) was added as a source of iron (III) ions. Next, acid decomposition was carried out at the same temperature and time as in Experimental Example 1, followed by solid-liquid separation. The element concentrations in the solution after separation were quantified, and the acid leaching rate of each element was calculated, as in Experimental Example 1. The experimental conditions and evaluation results are shown in Table 3.

[0047] [Table 3]

[0048] The results in Table 3 show that adding 0.25 times or more by mass of iron (III) sulfate n-hydrate (iron content 20% by mass) to the iridium-containing precipitate, i.e., adding 0.5 g or more of iron (III) sulfate n-hydrate to 2 g of raw material, dissolves and removes the majority of impurities such as copper, arsenic, and tellurium. This amount, in terms of iron (III) ions, is 0.05 times the mass of the raw material precipitate.

[0049] More preferably, if more than 2 g of iron (III) sulfate n-hydrate is added, the amount of the final residue will be significantly reduced. This shows that although copper sulfide is relatively susceptible to oxidation by iron (III) ions, in order to oxidize and decompose other sulfides, such as lead sulfide, more than 2 g of iron (III) sulfate n-hydrate is required per 2 g of raw material.

[0050] The non-sulfate sulfur content of iridium-containing precipitate is 37% by mass, and iron (III) ions act on metal sulfides. The elemental sulfur content in iridium-containing precipitate varies depending on the lot, but as a rough guide, it is sufficient to add at least 0.6 times the mass of non-sulfate sulfur, which is iron (III) sulfate n-hydrate (iron content 20% by mass) for the 0.5 g addition condition in Table 3, and at least 0.13 times the mass of non-sulfate sulfur as iron (III) ions.

[0051] (Experimental Example 3) 2 g of the iridium-containing precipitate slurry obtained in Experimental Example 1 was weighed out, 200 mL of 3.2 N sulfuric acid was poured into it, and 2 g of ferric sulfate n-hydrate (iron content: 20% by mass) was added as a source of iron (III) ions. The mixture was heated to 60°C and stirred for 90 minutes. The ORP (oxidation-reduction electrode potential, reference electrode: Ag / AgCl) of the solution after the reaction was 530±5 mV. The reaction was carried out using the same acid decomposition procedure as in Experimental Example 1. The mass of the resulting residue was 0.83 g for 2 g of raw material. Next, 1 to 5 g of sodium sulfite was added, and 100 mL of water was added, followed by heating at 50°C for 1 hour. Next, elemental sulfur was dissolved and separated using the same procedure as in Experimental Example 1. Figure 2 shows a graph illustrating the relationship between the amount of sodium sulfite added and the final residue mass. According to the graph in Figure 2, the amount of residue decreases as the amount of sodium sulfite added increases, and once the amount reaches 3 g, the linearity decreases. Therefore, if only elemental sulfur is to be removed, it is sufficient to add sodium sulfite in an amount 1.5 times or more by mass relative to the iridium-containing precipitate used as the raw material.

[0052] There is no problem if sodium sulfite is further added, in which case the reverse reaction of the reaction shown in the above chemical formula (1) is suppressed, and the amount of residue gradually decreases.

[0053] (Experimental Example 4) For the sulfuric acid decomposition-sulfurous acid treatment, 5 g to 30 g of the slurry of the iridium-containing precipitate obtained in Experimental Example 1 was weighed out, 200 mL of 3.2 N sulfuric acid was poured into it, and 4 g of ferric sulfate n-hydrate (iron content: 20% by mass) was added. The mixture was heated to 60°C and stirred for 90 minutes. Next, the mass of the resulting residue was measured, and sodium sulfite was added in an amount twice the mass of the raw material iridium-containing precipitate, followed by 100 mL of water and heating at 50°C for 1 hour. Furthermore, under one set of conditions, 8 g of ferric sulfate n-hydrate (iron content: 20% by mass) was added for testing. In addition, for the hydrochloric acid decomposition-sulfurous acid treatment, 5 g to 30 g of the slurry of the iridium-containing precipitate obtained in Experimental Example 1 was weighed out, 200 mL of 2.8 N hydrochloric acid was poured into it, and the mixture was heated to 60°C and stirred for 90 minutes. Next, the mass of the resulting residue was measured, and sodium sulfite was added in an amount twice the mass of the raw material iridium-containing precipitate, followed by 100 mL of water and heating at 50°C for 1 hour. Furthermore, under one set of conditions, a test was conducted in which 4 g of ferric sulfate n-hydrate (iron content 20% by mass) was added. Next, elemental sulfur was dissolved and separated using the same procedure as in Experimental Example 1. The experimental conditions and evaluation results for sulfuric acid decomposition-sulfurous acid treatment are shown in Table 4. The experimental conditions and evaluation results for hydrochloric acid decomposition-sulfurous acid treatment are shown in Table 5. In Table 4, the amount of the residue from the 25 g / L slurry of iridium-containing precipitate was too small to be quantitatively analyzed.

[0054] [Table 4]

[0055] [Table 5]

[0056] Tables 4 and 5 show that the slurry concentration of the iridium-containing precipitate has a significant effect on the leaching rates of copper and sulfur. If the slurry concentration of the iridium-containing precipitate is 150 g / L or less, more than half of the copper and sulfur can be expected to be leached. Of course, it is not necessary to limit the acid decomposition to one time; it is also possible to increase the slurry concentration and treat with acid multiple times.

[0057] It can be seen that even when the slurry concentration of the iridium-containing precipitate is high, sulfuric acid leaching results in less loss of iridium and ruthenium than hydrochloric acid leaching. However, because the leaching rate of sulfur is low, leaching with hydrochloric acid may be used when the sulfur content is high.

Claims

1. A method for recovering iridium, comprising subjecting a hydrochloric acid solution containing iridium, sulfur, and one or more of copper, antimony, lead, and arsenic to the following treatment steps (1) to (3) in this order: (1) a precipitation and recovery step of heating the hydrochloric acid solution to 40°C or higher and adding a thiosulfate or a thiosulfate ion-containing solution to precipitate and recover iridium; (2) A step of introducing the precipitate recovered in the step (1) into an acidic sulfuric acid or hydrochloric acid solution of 0.5 N or more to dissolve and separate metal components; (3) A step of introducing the precipitate obtained after separating the metal components in the step (2) into an alkaline solution containing sulfites and heating it to 20°C or higher to dissolve and separate the sulfur.

2. A method for recovering iridium as described in claim 1, wherein in step (3), the precipitate obtained after separating the metal components in step (2) is poured into an alkaline solution containing sulfites and heated to 20 to 70°C to dissolve and separate the sulfur.

3. 2. The method for recovering iridium according to claim 1, wherein in the step (1), a thiosulfate or a solution containing thiosulfate ions is added so that the concentration of iridium is 10 g / L or more, calculated as sodium thiosulfate pentahydrate, based on thiosulfate ions, to precipitate iridium.

4. 2. The method for recovering iridium according to claim 1, wherein in the step (1), the hydrochloric acid solution contains ruthenium, and the ruthenium is precipitated and recovered simultaneously with iridium.

5. 2. The method for recovering iridium according to claim 1, wherein in the step (2), the sulfuric acid or hydrochloric acid solution contains iron (III) ions in an amount of at least 0.05 times by mass the amount of the iridium-containing precipitate.

6. 2. The method for recovering iridium according to claim 1, wherein in the step (2), the precipitate recovered in the step (1) is added to the sulfuric acid or hydrochloric acid solution so as to give a slurry concentration of 150 g / L or less.

7. 2. The method for recovering iridium according to claim 1, wherein in the step (3), the content of sulfites in the alkaline solution is equivalent to 1.5 times or more by mass, in terms of sodium sulfite, relative to the mass of the precipitate obtained in the step (1).

8. 2. The method for recovering iridium according to claim 1, wherein the liquid obtained by dissolving and separating the sulfur in the step (3) has a thiosulfate ion concentration adjusted, and is then used as the thiosulfate ion-containing solution in the step (1).

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