Recovery method of 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 then processed into crude copper of 99% purity or more in a converter and a refining furnace, after which electrolytic refining process is carried out to produce electrolytic copper with a purity of, for example, 99.99% or more. In recent years, metal scraps containing precious metals from electronic parts have been input as recycled raw materials into converters, 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] This slime is often treated by hydrometallurgy. For example, Patent Document 1 discloses a method in which silver is recovered from slime using hydrochloric acid-hydrogen peroxide, dissolved gold is recovered by solvent extraction, and other valuables are subsequently 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 valuables are reduced and precipitated using sulfur dioxide, and only selenium is removed by distillation to concentrate precious metals.

[0005] The solution after the precious metals are recovered contains rare metal ions, tellurium, and selenium, and it is necessary to further recover these valuable materials. Known recovery methods include recovering the precipitate generated by the reduction agent, mixing the solution with copper concentrate, drying it with 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 in sequence, it is also effective in separation and purification.

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

[0008] [Patent Document 1] JP 2001-316735 A [Patent Document 2] JP 2016-160479 A [Patent Document 3] JP 2004-332041 A [Patent Document 4] JP 2022-135956 A Summary of the Invention [Problem to be solved by the invention]

[0009] The precipitate obtained from thiosulfate or a solution containing thiosulfate ions contains many impurities. Most of the impurities are elemental sulfur produced by the decomposition of thiosulfate ions, and metal sulfides sulfurized by thiosulfate ions. Generally, this contains only about 0.5 to 3 mass% of iridium.

[0010] Methods for refining iridium of this level of quality include remelting followed by solvent extraction as shown in Patent Document 3, but this consumes a large amount of acid, increasing costs, and since 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] It would be ideal if it could be put into the existing iridium refining process, but there is a problem with removing elemental sulfur, which is generally done by roasting. However, the roasting method poses a problem in treating sulfurous acid gas derived from sulfur. Furthermore, elemental sulfur is classified as a hazardous material and is difficult to handle due to the risk of dust explosion.

[0012] In view of the above-mentioned 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 oxidizing and dissolving electrolytic sediment 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 having a concentration of 0.5N or more to dissolve and separate metal components; (3) A process in which the precipitate obtained after separating the metal components in the above process (2) is introduced 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), 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 as to give a slurry concentration of 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 or more times the mass of the precipitate obtained in the step (1) in terms of sodium sulfite. [7] The method for recovering iridium according to [1] above, wherein in the step (3), a liquid obtained by dissolving and separating the sulfur is used as the thiosulfate ion-containing solution in the step (1) after adjusting the concentration of thiosulfate ions. Effect of the Invention

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

[0015] [Figure 1] 1 is a flowchart showing an example of a method for recovering iridium according to an embodiment of the present invention. [Diagram 2] 1 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 PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment 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] <Iridium precipitation recovery> The method for recovering iridium according to the embodiment of the present invention includes a process for precipitating and recovering iridium, a process for dissolving and separating metal components, and a process for dissolving and separating sulfur. Fig. 1 is a flow chart showing an example of the method for recovering iridium according to the embodiment of the present invention. The flow chart in Fig. 1 shows an example, and the method for recovering iridium according to the embodiment of the present invention is not limited thereto.

[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 in particular, a hydrochloric acid solution obtained by oxidizing and dissolving electrolytic precipitate generated in the electrolytic refining step in copper smelting is 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 the 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 thiosulfate ions, which will be described later, so no special treatment is required. Furthermore, the hydrochloric acid solution to be treated may contain selenium (Se), ruthenium (Ru), tellurium (Te), etc., but since these are reduced by thiosulfate ions, it is preferable to reduce the concentrations of these metals in advance, as will be described in detail later, in order to improve the treatment efficiency.

[0020] In addition, iron (Fe) may be contained in the hydrochloric acid solution to be treated since it does not react with thiosulfate ions if it is divalent. 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 make a hydrochloric acid solution containing iridium from electrolytic sediment from the copper electrolytic refining process of copper smelting. First, copper is dissolved and removed from the electrolytic sediment from the copper electrolytic refining process of copper smelting using sulfuric acid. Next, concentrated hydrochloric acid and hydrogen peroxide are added to dissolve the copper, 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 widely used as an extractant for gold. 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, and a hydrochloric acid solution containing iridium is produced by solid-liquid separation.

[0023] The iridium concentration of this iridium-containing hydrochloric acid solution is about 10 to 100 mg / L, so it needs to be further concentrated. As a method for this concentration, precipitation separation using thiosulfate is known as described in Patent Document 4. The hydrochloric acid solution containing iridium may also contain copper, antimony, lead, arsenic, ruthenium, etc. 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. In the sulfurization treatment, selenium, tellurium, etc. that remained in trace amounts may also precipitate. In addition, ruthenium is often mixed in the refining raw material of iridium, and a method for separating them from each other has been established, so iridium and ruthenium can be simultaneously recovered by adding thiosulfate. In particular, a method of distillation using sodium bromate after dissolving in acid is known.

[0024] (Iridium precipitation recovery process) In the iridium precipitation recovery process, the 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. The precipitation of iridium (also called iridium-containing precipitate) is promoted by adding a thiosulfate or thiosulfate ion-containing solution to the hydrochloric acid solution heated to 40°C or higher. The hydrochloric acid solution is preferably heated to 60°C or higher, and more preferably heated to 80°C or higher. Examples of the thiosulfate salt to be added include sodium thiosulfate and its hydrate, and ammonium thiosulfate. Examples of the thiosulfate ion-containing solution to be added include a solution prepared by dissolving elemental sulfur in sodium sulfite solution, and a solution obtained by suspending elemental sulfur in sodium hydroxide solution and blowing sulfur dioxide into the solution.

[0025] In the iridium precipitation recovery step, it is preferable to precipitate iridium by adding a thiosulfate salt 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 process, the iridium-containing precipitate recovered in the iridium precipitation and recovery process is put into a sulfuric acid or hydrochloric acid solution of 0.5N or more to dissolve and separate the metal components. Here, the iridium-containing precipitate contains metal sulfides, which are decomposed and removed with an acid, making it possible to dissolve and separate the metal components. The acid used is preferably sulfuric acid or hydrochloric acid, which has an oxidizing power that does not re-dissolve the precipitated iridium or ruthenium. In addition, the iridium-containing precipitate recovered in the iridium precipitation and recovery process is in the form of a slurry, and it is preferable to add the slurry to a sulfuric acid or hydrochloric acid solution so that the concentration of the slurry is 150g / L or less, since this promotes the dissolution and separation of the metal components.

[0027] If sulfuric acid is used as the acid, the oxidizing power may be insufficient. Therefore, it is preferable to add iron (III) ions to the sulfuric acid, since this will allow the dissolution of the metal sulfide to proceed efficiently. As for the specific amount, it is preferable that the sulfuric acid or hydrochloric acid solution contains iron (III) ions in an amount 0.05 times or more by mass of the iridium-containing precipitate. As the iron (III) ion-containing liquid, a liquid obtained by oxidizing an iron (II) ion-containing liquid, ferric sulfate, etc. are suitable.

[0028] In the acid decomposition in the metal component dissolution and separation process, there is no particular limit to the temperature, but a higher temperature is preferable because the treatment time is shorter. From this viewpoint, the acid decomposition is preferably performed at 40°C or higher, more preferably at 60°C or higher, and even more preferably at 80°C or higher. In addition, the higher the concentration of the acid used in the acid decomposition, the higher the decomposition effect is, so it is preferable. From this viewpoint, 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 is carried out 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) remaining after separation of the metal components in the above-mentioned metal component dissolution and separation process is placed in an alkaline solution containing sulfurous acid, such as an aqueous sodium hydroxide solution 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, when the elemental sulfur is dissolved and removed as thiosulfate ions according to the following chemical formula (1), the iridium concentration in the iridium-containing precipitate, which is the residue after solid-liquid separation, becomes high.

[0031] [ka]

[0032] The sulfite used in this case is preferably sodium sulfite, sodium hydrogen sulfite, or water into which sulfur dioxide has been blown and absorbed, etc. 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 state.

[0033] Furthermore, the iridium-containing precipitate after the above-mentioned metal components are dissolved and separated may contain arsenic sulfide. Although arsenic sulfide is decomposed into sulfur and arsenic oxoanion by nitric acid or hydrogen peroxide, which have strong oxidizing power, it is stable against mineral acids, regardless of whether the arsenic is trivalent or pentavalent. For this reason, it is preferable to prepare a solution containing sulfurous acid as an alkaline solution with a pH of 10 or more.

[0034] In the treatment with sulfites, the temperature of the reaction solution is preferably 20 to 70° C. When the temperature of the reaction solution is 20° C. or higher, the reaction rate is increased, and when 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 sulfurous acid required to be added depends on the content of elemental sulfur and metal sulfides (referred to as non-sulfuric sulfur) in the iridium-containing precipitate. For example, when 37% by mass of the iridium-containing precipitate is non-sulfuric sulfur, the content of sulfurous acid in the alkaline solution is preferably equivalent to 1.5 times or more by mass of the iridium-containing precipitate recovered in the iridium precipitation recovery step, calculated as sodium sulfite. Since it is expected that the iridium-containing precipitate contains 30 to 40% by mass of non-sulfuric sulfur, it is preferable to add sulfurous acid at a level equal to or greater than this. That is, it is preferable to add sulfurous acid at a level equal to or greater than 1.5 times by mass, calculated as sodium sulfite, relative to the mass of the iridium-containing precipitate, and more preferably to add sulfurous acid at a level equal to or greater than 2 times by mass. When the content of non-sulfuric sulfur in the iridium-containing precipitate can be known in advance, it is preferable to add sulfurous acid so that sulfite ions are added in an amount equal to or greater than the amount of non-sulfuric sulfur.

[0036] In addition, since the reaction follows the above chemical formula (1), when non-sulfuric sulfur can be quantified, sulfites are required in an amount four times or more by mass relative to the non-sulfuric sulfur, and it is more preferable to add five times or more by mass of sulfites.

[0037] The method for quantifying non-sulfuric sulfur is not particularly specified. For example, there is a method for quantifying non-sulfuric sulfur by subtracting the sulfur content in sulfuric acid dissolved with dilute hydrochloric acid of pH 1 to 2 from the total sulfur content contained in the iridium-containing precipitate. Another method is to add nitric acid to the iridium-containing precipitate to decompose the metal sulfide, measure the mass of the residue after filtering, and then contact the residue with a solution containing sulfite ions to calculate the amount of non-sulfuric sulfur from the weight 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 and recovery process after adjusting the thiosulfate ion concentration. If the thiosulfate ion concentration is insufficient, it can be reused by adding a thiosulfate salt such as sodium thiosulfate and adjusting the pH. 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 and recovery process. EXAMPLES

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

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

[0041] [Table 1]

[0042] Next, 2 g of the above-mentioned iridium-containing precipitate slurry was taken, and 200 mL of each of the acidic dissolving solutions shown in Table 2 was poured into the sample. Next, 2 g of ferric sulfate n-hydrate (iron content 20% by mass) was added as a source of iron (III) ions, heated to 60°C, and stirred for 90 minutes. After the reaction, the solution was filtered and diluted 25 times with dilute hydrochloric acid, and the element concentration in the solution was measured by ICP-OES (Seiko SPS3100). The residue was washed with water and rinsed with alcohol, air-dried overnight, and the mass was measured. 4 g of sodium sulfite was added to the residue, 100 mL of water was poured, and the mixture was heated and stirred at 60°C for 1 hour. After the reaction, the residue was filtered, washed with water and rinsed with alcohol, air-dried overnight, and the 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 elemental concentrations in the solutions 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] From the results in Table 2, it can be seen that in dissolving solutions other than nitric acid, it was possible to dissolve impurity elements while suppressing the loss of iridium and ruthenium. Furthermore, it can be seen that in systems in which iron (III) ions were added to hydrochloric acid and sulfuric acid, the dissolution of copper was also highly effective, and even cupric sulfide was able to be dissolved.

[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 was 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 copper through a 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, 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 performed at the same temperature and time as in Experimental Example 1, and solid-liquid separation was performed. 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] From the results in Table 3, it can be seen that adding 0.25 times or more by mass of iron (III) sulfate n-hydrate (iron content 20 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 of iron (III) ions is 0.05 times the mass of the raw material precipitate.

[0049] More preferably, the amount of the final residue is greatly reduced by adding more than 2 g of iron (III) sulfate n-hydrate. 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 the iridium-containing precipitate is 37% by mass, and iron (III) ions act on metal sulfides. The elemental sulfur in the 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 the non-sulfate sulfur, which is iron (III) sulfate n-hydrate (iron content 20% by mass) in the 0.5 g addition condition in Table 3, and at least 0.13 times the mass of the 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 in, 2 g of ferric sulfate n-hydrate (iron content 20 mass%) was added as a source of iron (III) ions, and 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 by the same acid decomposition procedure as in Experimental Example 1. The mass of the obtained residue was 0.83 g for 2 g of raw material. Next, 1 to 5 g of sodium sulfite was added, 100 mL of water was added, and the mixture was heated at 50° C. for 1 hour. Next, elemental sulfur was dissolved and separated using the same procedure as in Experimental Example 1. Figure 2 is a graph showing the relationship between the amount of sodium sulfite added and the final residue mass. According to the graph in Figure 2, as the amount of sodium sulfite added increases, the amount of residue decreases, and once the amount reaches 3g, the linearity decreases. Therefore, if only elemental sulfur is to be removed, it is sufficient to add 1.5 times the mass of sodium sulfite relative to the raw iridium-containing precipitate.

[0052] There is no problem if sodium sulfite is further added. In that 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) As the sulfuric acid decomposition-sulfurous acid treatment, 5g to 30g of the slurry of the iridium-containing precipitate obtained in Experimental Example 1 was weighed out, 200mL of 3.2N sulfuric acid was poured in, and 4g 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 obtained residue was measured, and sodium sulfite was added in an amount twice the mass of the iridium-containing precipitate as the raw material, and 100mL of water was added, followed by heating at 50°C for 1 hour. Furthermore, in one condition, a test was performed by adding 8g of ferric sulfate n-hydrate (iron content 20% by mass). As for the hydrochloric acid decomposition-sulfurous acid treatment, 5g to 30g of the slurry of the iridium-containing precipitate obtained in Experimental Example 1 was weighed out, 200mL of 2.8N 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, 100mL of water was added, and the mixture was heated at 50°C for 1 hour. Furthermore, in one condition, 4g of ferric sulfate n-hydrate (iron content 20% by mass) was added to test. Next, elemental sulfur was dissolved and separated by the same procedure as in Experimental Example 1. The experimental conditions and evaluation results of the sulfuric acid decomposition-sulfurous acid treatment are shown in Table 4. The experimental conditions and evaluation results of the hydrochloric acid decomposition-sulfurous acid treatment are shown in Table 5. In addition, 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] According to Tables 4 and 5, it can be seen that the slurry concentration of the iridium-containing precipitate has a large effect on the leaching rate 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, and 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, the loss of iridium and ruthenium is smaller when leaching with sulfuric acid than when leaching with hydrochloric acid. However, since 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 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 having a concentration 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 the solution to 20° C. or higher to dissolve and separate the sulfur.

2. 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, calculated as sodium thiosulfate pentahydrate, is 10 g / L or more based on thiosulfate ions to precipitate iridium.

3. 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.

4. 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 0.05 times or more by mass of the iridium-containing precipitate.

5. 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 that a slurry concentration is 150 g / L or less.

6. 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).

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

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