Method for recovering ruthenium and iridium

Abstract

To provide a method of efficiently recovering ruthenium and iridium from an acidic solution containing ruthenium and iridium.SOLUTION: A method of recovering ruthenium and iridium includes: an arsenic-reducing process of adding a water-soluble inorganic iodine compound or element iodine, further blowing sulfur dioxide or hydrogen sulfide, or adding a reductant such as aldehyde into an acidic solution containing ruthenium and iridium, and arsenic to reduce arsenic to trivalent; an impurity-removing process of subjecting a sulfide precipitated by adjusting a temperature of an acidic solution obtained by the arsenic-reducing process to 70°C or lower, and adding hydrogen sulfide or sodium hydrogensulfide until an ORP (a reference electrode Ag / AgCl) reaches 150 mV or lower to solid-liquid separation; and a ruthenium and iridium-recovering process of precipitating ruthenium and iridium by adjusting a liquid temperature of a filtrate to 40°C or higher after the impurity-removing process, and adding sodium thiosulfate or a thiosulfate ion-containing solution.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for recovering ruthenium and iridium. [Background technology]

[0002] In copper pyrometallurgy, copper concentrate is melted and refined in a converter and a refining furnace to produce crude copper of 99% purity or more. After that, electrolytic refining is carried out to produce electrolytic copper of 99.99% purity or more. Valuable materials other than copper are precipitated as sediment during electrolytic refining.

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

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

[0005] The solution left after the precious metals have been 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 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 oxidation-reduction potentials (ORP), so they are less susceptible to reduction and remain 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. Furthermore, Patent Document 4 discloses a method in which a base metal selected from magnesium, aluminum, zinc, iron, tin, and lead and a mineral acid are added to an organic solvent containing iridium, thereby reducing and precipitating the precious metal. [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 Application Laid-Open No. 2002-115015 Summary of the Invention [Problem to be solved by the invention]

[0009] The iridium concentration in the solution containing dissolved copper electrolytic deposits is approximately 1 to 100 mg / L. Iridium is an expensive metal, but at such low concentrations, smelting by solvent extraction is not cost-effective. Furthermore, the separation efficiency from other metals and stripping efficiency when applying adsorption or solvent extraction are not high.

[0010] On the other hand, distillation recovery of ruthenium requires the use of a strong oxidizing agent such as NaBrO3. The cost of the oxidizing agent is high, and this method is not suitable for recovering ruthenium from dilute solutions with high impurities, such as copper electrolytic precipitate solutions, which have a ruthenium concentration of around 50-200 mg / L. Furthermore, the ruthenium tetroxide that is the distillation fraction is highly toxic, making recovery by distillation a safety issue.

[0011] Cementation with base metals such as zinc is an effective method for both iridium and ruthenium. However, when using base metals for the solution derived from copper electrolytic deposits, the coexisting arsenic is reduced to highly toxic hydrogen arsenide, which is problematic. Furthermore, the copper in the solution is also contaminated by cementation, requiring an additional separation process.

[0012] In cementation using base metals, a large amount of metal is used to increase the recovery rate. Under strongly acidic conditions, hydrogen is generated in a concentrated manner in a short period of time, causing boiling over, or the hydrogen generated by static electricity can explode. In addition, the reaction efficiency is low because other elements that undergo cementation are also present.

[0013] It is known that iridium and ruthenium precipitate as their hydroxides. However, a common problem is the high cost of alkaline reagents when neutralizing strong acids. Furthermore, sodium ions and alkaline earth metal ions precipitate sulfates that are sparingly soluble in water even under acidic conditions. When neutralized with excessive amounts of alkali, these sparingly soluble sulfates are likely to deposit in the piping of manufacturing equipment, causing blockages.

[0014] Furthermore, there is no known method for recovering low concentrations of iridium and ruthenium from strongly acidic solutions at low cost and efficiently.

[0015] In view of the above-mentioned conventional circumstances, the present invention provides a method for efficiently recovering ruthenium and iridium from an acidic solution containing ruthenium and iridium. In particular, an acidic solution containing ruthenium and iridium in which arsenic is dissolved as an impurity is a suitable target for the acidic solution containing ruthenium and iridium of the present invention. [Means for solving the problem]

[0016] The above problems can be solved by the inventions specified below. That is, the present invention includes the following inventions. [1] an arsenic reduction step in which a water-soluble inorganic iodine compound or elemental iodine is added to an acidic solution containing ruthenium, iridium, and arsenic, and sulfur dioxide or hydrogen sulfide is blown in, or an aldehyde reducing agent is added, to reduce the arsenic to a trivalent state; an impurity removal step in which the acidic solution obtained in the arsenic reduction step is adjusted to 70°C or less, hydrogen sulfide or sodium hydrosulfide is added until the ORP (oxidation-reduction electrode potential, reference electrode Ag / AgCl) reaches 150mV or less, and the precipitated sulfide is subjected to solid-liquid separation; a ruthenium and iridium recovery step in which, after the impurity removal step, the temperature of the filtrate is adjusted to 40°C or higher, and sodium thiosulfate salt or a solution containing thiosulfate ions is added to precipitate ruthenium and iridium; A method for recovering ruthenium and iridium, comprising: [2] The method for recovering ruthenium and iridium according to [1], wherein, in the impurity removal step, if a precipitate is formed in the arsenic reduction step, after solid-liquid separation, the temperature is adjusted to 70°C or less, and the hydrogen sulfide or sodium hydrosulfide is added until the ORP reaches 150 mV or less. [3] The method for recovering ruthenium and iridium according to [1] or [2], further comprising, between the impurity removal step and the ruthenium and iridium recovery step, a step of adjusting the temperature of the filtrate obtained in the impurity removal step to 70°C or less and adding metallic iron to the filtrate so that the concentration of metallic iron becomes 0.5 to 5 g / L, thereby selectively precipitating ruthenium. [4] The method for recovering ruthenium and iridium according to any one of [1] to [3], wherein the inorganic iodine compound is one or more of iodine, potassium iodide, sodium iodide, potassium iodate, and sodium iodate, and is added in an amount of 0.05 g / L or more when converted to potassium iodide. [5] The method for recovering ruthenium and iridium according to any one of [1] to [4], wherein the inorganic iodine compound is one or more of potassium iodide, sodium iodide, potassium iodate, and sodium iodate, and when copper is dissolved in the acidic solution, 0.05 to 4 times the mass of copper, calculated as potassium iodide, is added. [6] The method for recovering ruthenium and iridium according to any one of [1] to [5], wherein in the arsenic reduction step, the acidic solution containing ruthenium, iridium, and arsenic is an acidic solution obtained after dissolving a metal electrolytic deposit. [7] The method for recovering ruthenium and iridium according to any one of [1] to [6], wherein the iridium concentration in the acidic solution in the arsenic reduction step is 100 mg / L or less, and the sodium thiosulfate salt or the thiosulfate ion-containing solution is added in the ruthenium and iridium recovery step so that the concentration, calculated as sodium thiosulfate pentahydrate, is 5 g / L or more. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a method for efficiently recovering ruthenium and iridium from an acidic solution containing ruthenium and iridium. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a flow diagram illustrating an embodiment of the present invention. [Figure 2] 1 is a graph showing the relationship between the ORP value and the copper and arsenic concentrations according to an example. [Figure 3] 1 is a graph showing the relationship between ORP value and ruthenium concentration according to an example. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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 design changes, improvements, etc. may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0020] Fig. 1 shows a flow diagram that schematically illustrates one embodiment of the present invention. The flow diagram in Fig. 1 lists specific examples of each step, and the present invention is not limited to this flow diagram. A method for recovering ruthenium and iridium according to an embodiment of the present invention includes an arsenic reduction step in which a water-soluble inorganic iodine compound or elemental iodine is added to an acidic solution containing ruthenium, iridium, and arsenic, and then sulfur dioxide or hydrogen sulfide is blown in, or an aldehyde reducing agent is added, to reduce arsenic to a trivalent state; an impurity removal step in which the acidic solution obtained in the arsenic reduction step is adjusted to 70°C or less, and hydrogen sulfide or sodium hydrosulfide is added until the ORP (oxidation-reduction electrode potential, reference electrode Ag / AgCl) reaches 150 mV or less, thereby performing solid-liquid separation of the precipitated sulfides; and a ruthenium and iridium recovery step in which the temperature of the filtrate obtained after the impurity removal step is adjusted to 40°C or more, and sodium thiosulfate salt or a thiosulfate ion-containing solution is added to precipitate ruthenium and iridium.

[0021] The method for recovering ruthenium and iridium according to the embodiment of the present invention is effective when the acidic solution to be treated contains arsenic, copper, and lead as impurities, and is particularly suitable for an acidic solution obtained by oxidizing and dissolving electrolytic deposits generated in the electrolytic refining process in copper smelting. The method for recovering ruthenium and iridium according to the embodiment of the present invention can also be applied to recycling from waste. In other words, it can also be used for an acidic solution containing ruthenium and iridium generated in the process of treating such waste.

[0022] In the method for recovering ruthenium and iridium according to an embodiment of the present invention, when the acidic solution to be treated is a hydrochloric acid solution obtained through a predetermined process, it contains various metal elements in addition to ruthenium (Ru) and iridium (Ir).

[0023] When ruthenium and iridium are separated by reduction or by adding thiosulfates, selenium (Se), platinum (Pt), palladium (Pd), gold (Au), silver (Ag), etc. react preferentially with ruthenium. As will be explained in detail later, the concentrations of these elements must be reduced beforehand.

[0024] As an example, we will show how to prepare a hydrochloric acid solution containing ruthenium and iridium from metal electrolytic deposits from the copper electrorefining process of copper smelting. First, copper is dissolved and removed from the metal electrolytic deposits from the copper electrorefining process using sulfuric acid. Next, concentrated hydrochloric acid and hydrogen peroxide are added to dissolve the precipitate, followed by solid-liquid separation to obtain the pregnant leach solution (PLS). Platinum group elements, rare metal elements, chalcogen elements, arsenic, antimony, and other metals are distributed in the pregnant leach solution (PLS), which is a chloride bath.

[0025] 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 the gold extractant. Sulfur dioxide is blown into the extract to reduce and remove precious metals such as platinum and palladium, as well as selenium and tellurium. Subsequent solid-liquid separation produces a hydrochloric acid solution containing ruthenium and iridium.

[0026] In the method for recovering ruthenium and iridium according to an embodiment of the present invention, it is preferable to adjust the concentration of impurity elements such as platinum, gold, palladium, and selenium to 10 mg / L or less by blowing sulfur dioxide or hydrogen sulfide into an acidic solution containing ruthenium and iridium, or by adding an aldehyde reducing agent. Examples of such aldehydes include formaldehyde and methylglyoxal. Note that if the concentration of impurity elements such as platinum, gold, palladium, and selenium in the acidic solution to be treated is 10 mg / L or less, blowing in or adding the reducing agent is not necessary.

[0027] When impurity elements are precipitated by injecting sulfur dioxide or hydrogen sulfide or by adding an aldehyde reducing agent, inorganic iodine compounds or elemental iodine are added. Inorganic iodine compounds undergo reduction in an acidic solution to produce iodide ions. These iodide ions effectively reduce tellurium and can further reduce arsenic in the acidic solution to its trivalent form (chemical formula 1). The resulting elemental iodine is then immediately reduced to sulfur dioxide or an aldehyde, regenerating iodide ions (chemical formula 2). Therefore, the substance added when precipitating impurity elements as described above can be either an inorganic iodine compound or elemental iodine. (Formula 1):As(V)+2I - → As(III)+I2 (Chemical formula 2):I2+SO2+2H2O → H2SO4+2I - +2H +

[0028] Inorganic iodine compounds are compounds that generate iodide ions in an aqueous solution in the presence of a reducing agent, and specific examples include potassium iodide, sodium iodide, potassium iodate, sodium iodate, potassium periodate, and sodium periodate.

[0029] Because iodide ions act as a catalyst, inorganic iodine compounds or elemental iodine should be added at a concentration of 0.05 g / L or more when converted to potassium iodide. The amount of inorganic iodine compound added is preferably 0.1 to 0.5 g / L when converted to potassium iodide. However, if the solution contains ions such as copper that cause iodide precipitation, the acidic solution must be maintained at an acidity of 1 mol / L or more.

[0030] In addition, since iodide ions act as a catalyst, when copper is dissolved in the acidic solution, it is preferable to add an inorganic iodine compound or elemental iodine in an amount of 0.05 to 4 times the mass of copper when converted to potassium iodide. However, when containing ions such as copper that cause iodide precipitation, the acidic solution must be maintained at an acidity of 1 mol / L or more.

[0031] By blowing in sulfur dioxide or hydrogen sulfide or adding an aldehyde reducing agent, the impurities selenium, tellurium, platinum, and palladium are precipitated. The precipitate containing these valuable elements is subjected to solid-liquid separation and then fed to a process for further separation and purification. The liquid after solid-liquid separation contains arsenic, copper, antimony, iridium, and ruthenium.

[0032] After solid-liquid separation, a sulfiding agent is added to the liquid to sulfide and precipitate the arsenic and copper. Hydrogen sulfide, sodium sulfide, or sodium hydrosulfide is used as the sulfiding agent. Since sulfiding efficiency decreases when the liquid temperature is high, the acidic liquid is adjusted to 70°C or less before sulfidation. It is more preferable that the temperature of the acidic liquid during sulfidation be 50°C or less. Note that if no precipitate is formed by injecting sulfur dioxide or hydrogen sulfide as described above, or by adding an aldehyde reducing agent, solid-liquid separation is not necessary. In this case, the acidic liquid is adjusted to 70°C or less as described above before sulfidation.

[0033] When sodium hydrosulfide or sodium sulfide is used, it is dissolved in water in advance and added as an aqueous solution to increase the reaction efficiency. The concentration of sodium hydrosulfide or sodium sulfide is not particularly limited.

[0034] The amount of sulfurizing agent added varies depending on the arsenic and copper concentrations, but should be added until the ORP (reference electrode Ag / AgCl) reaches 150 mV or less. However, adding an excessive amount of sulfurizing agent will cause some ruthenium to precipitate. Furthermore, excessive amounts of sulfurizing agent have a negative effect on the recovery of ruthenium and iridium produced by metal cementation. Therefore, it is preferable to add the agent only to the extent that the ORP does not reach 0 mV or less.

[0035] The addition of a sulfurizing agent quantitatively precipitates trivalent arsenic, but not pentavalent arsenic. Therefore, it is preferable to reduce pentavalent arsenic to trivalent arsenic in accordance with Chemical Equation 1.

[0036] After sulfurization, the precipitated sulfides are separated into solid and liquid. The separated sulfides contain valuable materials such as copper and antimony, so after drying, they can be recycled into the smelting furnace and reused as valuable raw materials. Iridium and ruthenium remain in the liquid (filtrate) after solid-liquid separation.

[0037] The temperature of the liquid (filtrate) after solid-liquid separation is adjusted to 40°C or higher, preferably 60°C or higher, and sodium thiosulfate or a solution containing thiosulfate ions is added, whereby ruthenium and iridium can be precipitated and recovered.

[0038] Before adding sodium thiosulfate or a thiosulfate ion-containing solution, the temperature of the liquid (filtrate) after solid-liquid separation may be adjusted to 70°C or below, and metallic iron may be added to a concentration of 0.5 to 5 g / L to selectively precipitate ruthenium by cementation. The metallic iron is preferably iron powder. If the amount of metallic iron added is less than 0.5 g / L, ruthenium may not be sufficiently cemented. If the amount of metallic iron added is more than 5 g / L, a large amount of hydrogen gas may be generated. In this case, arsenic is reduced by the sulfurization treatment, so there is no concern about the generation of hydrogen arsenide. Because ruthenium is selectively cemented in this way, solid-liquid separation may be performed after cementation.

[0039] Ruthenium can be recovered more effectively by precipitation using metal cementation than by sodium thiosulfate. However, if the solution contains arsenic, even pentavalent arsenic may produce hydrogen arsenide due to nascent hydrogen. Therefore, as mentioned above, it is important to reduce the arsenic to trivalent form and then sulfurize it to lower its concentration.

[0040] Sodium thiosulfates may be added as a solid or as a solution containing thiosulfate ions. Thiosulfate ions can also be obtained by heating sulfurous acid and elemental sulfur in an alkaline solution, but from the standpoint of cost and ease of handling, it is advantageous to supply them as a solid salt. In particular, sodium thiosulfate pentahydrate has low toxicity and is the most suitable thiosulfate salt.

[0041] Sodium thiosulfate also acts as a sulfiding agent for some transition metals, such as silver and copper, but its activity is weak. It also does not decompose quickly in acidic solutions. Unlike sulfide ions, thiosulfate ions have coordination properties, and once coordinated with ruthenium and iridium ions, they can precipitate these metals.

[0042] When the iridium concentration in the acidic solution in the arsenic reduction step is high, it is more efficient to recover the iridium by precipitation with KCl or NH4Cl. However, when the iridium concentration is low, at 100 mg / L or less, it is preferable to recover the iridium by precipitation by adding sodium thiosulfate salt or a thiosulfate ion-containing solution. Adding too little sodium thiosulfate salt or a thiosulfate ion-containing solution results in insufficient recovery, while adding too much increases costs. For this reason, it is preferable to add sodium thiosulfate salt or a thiosulfate ion-containing solution so that the concentration is 5 g / L or more, calculated as sodium thiosulfate pentahydrate. Alternatively, sodium thiosulfate salt or a thiosulfate ion-containing solution may be added so that the concentration is 5 to 20 g / L or more, calculated as sodium thiosulfate pentahydrate. The resulting precipitate is subjected to solid-liquid separation.

[0043] The precipitate obtained by solid-liquid separation is purified into ruthenium and iridium by known methods. For example, ruthenium can be separated and recovered by adding sodium bromate after re-oxidizing and dissolving, and then distilling the ruthenium tetroxide. Iridium can be recovered by crystallizing as an ammonia salt after solvent extraction. [Example]

[0044] The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[0045] (Experimental Example 1) Copper was dissolved and removed from electrolytic deposits from the copper electrorefining process of copper smelting using sulfuric acid. Concentrated hydrochloric acid and 60% hydrogen peroxide were added and dissolved, followed by solid-liquid separation to obtain pregnant leachate (PLS). The PLS was cooled to 6°C to precipitate and remove base metals. Gold was extracted by adjusting the acid concentration to over 1 mol / L and mixing the PLS with DBC (dibutyl carbitol). After gold extraction, the PLS was heated to 70°C and sulfur dioxide was injected to reduce and remove the precious metals and selenium. This was then subjected to solid-liquid separation to obtain the hydrochloric acid solution used in the experiment. The iridium concentration of this hydrochloric acid solution was 24 mg / L and the ruthenium concentration was 120 mg / L. Other elements included arsenic at 1.82 g / L, copper at 1.11 g / L, and antimony at 300 mg / L.

[0046] 200 mL of the hydrochloric acid solution to be tested was taken and heated to 70°C. To remove the influence of organic matter, 2 mL of hydrogen peroxide solution (30% by volume) was added and stirred for 1 hour. 0.1 g of potassium iodide was added, and a mixture of sulfur dioxide and air (5-20% by volume) was blown in. The reaction was stopped after 30 minutes, and solid-liquid separation was performed. As a comparative example, an experiment was also conducted without adding potassium iodide. After the solid-liquid separation, the liquid was adjusted to 40°C, and 2 g of sodium hydrosulfide was added. After stirring for 30 minutes, the sulfide precipitate was separated into solid and liquid. The liquid after solid-liquid separation was heated to 70°C, and 2 g of sodium thiosulfate pentahydrate was added. The mixture was then stirred for 1 hour, and solid-liquid separation was carried out (Example 1). Separately, the liquid after sulfide precipitation separation was heated to 60°C, and 0.4 g of iron powder was added. The mixture was stirred for 45 minutes, and solid-liquid separation was carried out again. Then, the mixture was heated to 70°C, and 2 g of sodium thiosulfate pentahydrate was added (Example 2). All reagents used were of special grade manufactured by Wako Pure Chemical Industries, Ltd. Analysis samples were taken each time solid-liquid separation was performed. 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 concentration using ICP-OES (SPS3100 manufactured by Seiko Instruments Inc.). The solution containing the precipitate was adjusted to 100 mL, and its concentration was determined. The results are shown in Table 1. "ND" in Table 1 indicates that the element in question was not detected. Although the concentration increased due to evaporation of the solution, water was not replenished.

[0047] [Table 1]

[0048] It can be seen that the addition of potassium iodide significantly reduced the arsenic concentration during the sulfurization process. Furthermore, most of the copper and antimony also precipitated during sulfurization. After removing the impurities, iron powder was added to replace the impurities, and ruthenium and iridium were recovered by reacting them with thiosulfate ions.

[0049] If potassium iodide is not added, arsenic cannot be removed by sulfurization. In this case, the remaining arsenic reacts with iron substitution or thiosulfate ions to precipitate, becoming a mixture with ruthenium and iridium. No generation of hydrogen arsenide was confirmed.

[0050] It should be noted that solid-liquid separation after iron substitution is not essential, and if the amount of impurities is small, it is possible to remove unreacted iron by acid treatment and then feed the resulting material to the ruthenium and iridium purification process. As shown in Example 2, iron substitution improves the recovery efficiency of ruthenium.

[0051] (Experimental Example 2) 200 mL of the same hydrochloric acid solution as in Experimental Example 1 was taken and heated to 70°C. To remove the influence of organic matter, 2 mL of hydrogen peroxide solution (30 vol%) was added and stirred for 1 hour. 0.02 g or 0.1 g of potassium iodide was added, and a mixture of sulfur dioxide and air (5 to 20 vol%) was blown in. After 30 minutes, the reaction was stopped and solid-liquid separation was performed. After the solid-liquid separation, the liquid was adjusted to 40°C, and 2 g of sodium hydrosulfide dissolved in water was added. After stirring for 30 minutes, the sulfide precipitate was separated into solid and liquid. At the time of solid-liquid separation, a sample for analysis was taken. The analytical procedure was the same as in Experimental Example 1. The results are shown in Table 2. "ND" in Table 2 indicates that the element in question was not detected.

[0052] [Table 2]

[0053] The results in Table 2 show that the catalytic cycle functions as shown in Equations 1 and 2 above, even when potassium iodide is added at a rate of 0.02 g, i.e., 0.1 g / L. The arsenic concentration after sulfurization is higher for the 0.02 g and 0.1 g additions. However, this is due to the influence of the amount of sulfur dioxide supplied. The catalytic effect of iodine also affects tellurium precipitation in the presence of sulfur dioxide. Therefore, if the tellurium concentration drops significantly after sulfur dioxide is added, this indicates that sufficient sulfur dioxide was supplied, and the reaction of Equation 2 proceeds rapidly, resulting in improved turnover of the iodine catalyst.

[0054] However, some of the iodide ions react with copper to precipitate copper(I) iodide, so the iodide ions are preferably at least 5 mass % of the copper concentration in terms of potassium iodide.

[0055] (Experimental Example 3) 200 mL of the same hydrochloric acid solution as in Experimental Example 1 was taken. To remove the influence of organic matter, 2 mL of hydrogen peroxide solution (30% by volume) was added and stirred for 1 hour. 0.1 g of potassium iodide was added, and a mixture of sulfur dioxide and air (5-20% by volume) was blown in. After 30 minutes, the reaction was stopped and solid-liquid separation was carried out. After solid-liquid separation, the liquid was heated to 40°C and an aqueous solution of sodium hydrosulfide (80 g / L) was gradually added. Once the appropriate amount had been added, the ORP was measured. At the same time, samples were taken for quantitative analysis. The quantification method was the same as in Experimental Example 1. Figure 2 shows the relationship between the ORP value and the copper and arsenic concentrations. Figure 3 shows the relationship between the ORP value and the ruthenium concentration.

[0056] It can be seen that the addition of sodium hydrosulfide first caused copper to form a sulfide precipitate, followed by arsenic. When the ORP reached 150 mV or less, most of the elements had precipitated.

[0057] The ruthenium concentration was 110 mg / L when the ORP reached 136 mV. Since the ruthenium concentration in the raw solution was 120 mg / L, the loss was minimal.

[0058] (Experimental Example 4) 200 mL of the same hydrochloric acid solution as in Experimental Example 1 was taken and heated to 70°C. To remove the influence of organic matter, 2 mL of hydrogen peroxide solution (30% by volume) was added and stirred for 1 hour. 0.1 g of potassium iodide was added, and a mixture of sulfur dioxide and air (5-20% by volume) was blown in. After 30 minutes, the reaction was stopped and solid-liquid separation was carried out. After the solid-liquid separation, the liquid was adjusted to 40°C, and then 2 g of sodium hydrosulfide was added. After stirring for 30 minutes, the sulfide precipitate was separated into solid and liquid. After solid-liquid separation of the sulfide precipitate, the liquid was heated to 60°C and 0.4g or 1g of iron powder was added. The mixture was stirred for 45 minutes and solid-liquid separation was carried out again. After separation, the liquid was heated to 70°C and 2g of sodium thiosulfate pentahydrate was added. After stirring for 1 hour, solid-liquid separation was carried out. Samples for analysis were taken during each solid-liquid separation operation. The analytical procedures were the same as in Experimental Example 1. The results are shown in Table 3.

[0059] [Table 3]

[0060] The addition of iron powder improved the total recovery amount of ruthenium and iridium. There was no significant difference between the amount of iron powder added, 1g and 0.4g, but the amount of substitution increased somewhat as the amount of iron powder added increased. If separate recovery of ruthenium and iridium is desired, it is best to add a small amount of iron powder and perform solid-liquid separation first. The amount of iron powder added for cementation is preferably 0.5 to 5g / L. If separate recovery of ruthenium and iridium is desired, the amount of iron powder added should be less than 2g / L, and solid-liquid separation should be performed to recover ruthenium first.

Claims

1. an arsenic reduction step in which a water-soluble inorganic iodine compound or elemental iodine is added to an acidic solution containing ruthenium, iridium, and arsenic, and sulfur dioxide or hydrogen sulfide is blown in, or an aldehyde reducing agent is added, to reduce the arsenic to a trivalent state; an impurity removal step of adjusting the temperature of the acidic solution obtained in the arsenic reduction step to 70°C or less, adding hydrogen sulfide or sodium hydrosulfide until the ORP (reference electrode Ag / AgCl) reaches 150 mV or less, and separating precipitated sulfides into solid and liquid; a ruthenium and iridium recovery step in which, after the impurity removal step, the temperature of the filtrate is adjusted to 40°C or higher, and sodium thiosulfate salt or a solution containing thiosulfate ions is added to precipitate ruthenium and iridium; A method for recovering ruthenium and iridium, comprising:

2. 2. The method for recovering ruthenium and iridium according to claim 1, wherein, when a precipitate is formed in the arsenic reduction step, the impurity removal step performs solid-liquid separation, adjusts the temperature to 70°C or less, and adds the hydrogen sulfide or sodium hydrosulfide until the ORP reaches 150 mV or less.

3. The method for recovering ruthenium and iridium according to claim 1, further comprising, between the impurity removal step and the ruthenium and iridium recovery step, a step of adjusting the liquid temperature of the filtrate obtained in the impurity removal step to 70°C or less and adding metallic iron to the filtrate so that the concentration of metallic iron becomes 0.5 to 5 g / L, thereby selectively precipitating ruthenium.

4. 2. The method for recovering ruthenium and iridium according to claim 1, wherein the inorganic iodine compound is one or more of potassium iodide, sodium iodide, potassium iodate, and sodium iodate, and is added in an amount of 0.05 g / L or more when converted to potassium iodide.

5. 2. The method for recovering ruthenium and iridium according to claim 1, wherein the inorganic iodine compound is one or more of potassium iodide, sodium iodide, potassium iodate, and sodium iodate, and when copper is dissolved in the acidic solution, the inorganic iodine compound is added in an amount of 0.05 to 4 times the mass of copper when converted into potassium iodide.

6. 2. The method for recovering ruthenium and iridium according to claim 1, wherein in the arsenic reduction step, the acidic solution containing ruthenium, iridium, and arsenic is an acidic solution obtained after dissolving a metal electrolytic deposit.

7. 7. The method for recovering ruthenium and iridium according to claim 1, wherein the iridium concentration in the acidic solution in the arsenic reduction step is 100 mg / L or less, and the sodium thiosulfate salt or thiosulfate ion-containing solution is added in the ruthenium and iridium recovery step so that the sodium thiosulfate salt or thiosulfate ion-containing solution is added in an amount equivalent to 5 g / L or more in terms of sodium thiosulfate pentahydrate.

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