JP7808528B2 - Method for recovering ruthenium and iridium - Google Patents

Description

The present invention relates to a method for recovering ruthenium and iridium.

In copper pyrometallurgy, copper concentrate is melted and processed into crude copper of 99% purity or more in a converter and refining furnace, after which electrolytic refining produces electrolytic copper with a purity of, for example, 99.99% or more. Valuable materials other than copper are precipitated as sediment during electrolytic refining.

This sediment also contains concentrated 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.

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-hydrogen peroxide, 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 distilled and removed to concentrate the precious metals.

The solution obtained 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 methods for recovering these valuable materials include recovering the precipitate formed by the use of a reducing agent, and mixing the solution with copper concentrate, drying it in a dryer, and then returning it to the smelting furnace.

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.

In methods for recovering valuables using sulfur dioxide, valuables can be recovered by sequentially reducing them after dissolution. Platinum and palladium precipitate first, followed by selenium, which is reduced. Iridium and ruthenium have relatively low redox potentials and are therefore less susceptible to reduction, remaining in the solution until the end. Regarding iridium, a widely known method, as described in Patent Document 3, involves separating it through solvent extraction, concentrating it, and then calcining it to recover it. Patent Document 4 also 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, reducing and precipitating the precious metal.

Japanese Patent Application Laid-Open No. 2001-316735 JP 2016-160479 A Japanese Patent Application Laid-Open No. 2004-332041 Japanese Patent Application Laid-Open No. 2002-115015

For example, the iridium concentration in an acidic solution containing dissolved copper electrolytic deposits is approximately 1 to 100 mg/L. Iridium is an expensive metal, but at such low concentrations, smelting using solvent extraction is not cost-effective. In addition, the efficiency of separation from other metals and stripping are not high.

On the other hand, to recover ruthenium by distillation, a strong oxidizing agent such as _NaBrO3 is used. 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 precipitate solutions, which have a ruthenium concentration of about 50 to 200 mg/L. Furthermore, ruthenium tetroxide is highly toxic, and there are safety issues with recovering it by distillation.

Cementation with base metals such as zinc is an effective method for recovering both iridium and ruthenium. However, it is difficult to separate and recover iridium and ruthenium using base metal cementation.

Furthermore, when cementing with 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. Furthermore, the reaction efficiency is low because other elements that undergo cementation are also present.

Iridium and ruthenium are known to precipitate as their hydroxides. However, both elements precipitate simultaneously in alkaline regions, making them impossible to recover separately. A more general 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 an excessive amount of alkali, these sparingly soluble sulfates are expected to deposit in the piping of manufacturing equipment, causing blockages.

It is desirable to recover both ruthenium and iridium while minimizing contamination with other metals. Copper contamination is a particular concern when copper electrolytic deposits are used as the raw material. If copper is present in amounts that are difficult to remove by oxidative leaching, a separate process to remove the copper is required. Furthermore, no inexpensive, efficient method is known for separating and precipitating low concentrations of iridium and ruthenium from a strongly acidic solution.

In consideration of these conventional circumstances, the present invention provides a method for efficiently separating and recovering ruthenium and iridium from an acidic solution containing ruthenium and iridium. In particular, an acidic solution obtained by oxidizing and dissolving electrolytic deposits generated in the electrolytic refining process in copper smelting is an ideal candidate for the acidic solution containing ruthenium and iridium of the present invention.

The above problems can be solved by the inventions specified below.
That is, the present invention includes the following inventions.
[1] A ruthenium recovery step in which an acidic solution containing ruthenium, iridium, and one or more elements selected from the group consisting of copper, arsenic, and antimony is adjusted to 60°C or less, and (1) metallic iron is added so that the amount becomes 0.5 to 4.0 g/L, or (2) metallic iron is added until the oxidation-reduction potential using a silver/silver chloride reference electrode reaches 150 mV or less, thereby precipitating ruthenium, followed by solid-liquid separation;
a sulfurization step in which the filtrate obtained by performing solid-liquid separation after precipitating the ruthenium is adjusted to 70°C or less, and one or more of hydrogen sulfide, sodium hydrosulfide, and sodium sulfide are added as a sulfurizing agent to precipitate one or more elements of copper, arsenic, and antimony;
an iridium recovery step of precipitating one or more elements selected from copper, arsenic, and antimony, followed by solid-liquid separation, adjusting the temperature of the resulting filtrate to 40°C or higher, and adding sodium thiosulfate or a solution containing thiosulfate ions to precipitate iridium;
A method for recovering ruthenium and iridium, comprising:
[2] a ruthenium recovery step in which an acidic solution containing ruthenium, iridium, and one or more elements selected from the group consisting of copper, arsenic, and antimony is adjusted to 40°C or higher, and (1) copper-coated iron powder is added as metallic iron so that the iron content is 0.5 to 4.0 g/L, or (2) copper-coated iron powder is added as metallic iron until the oxidation-reduction potential using a silver/silver chloride reference electrode reaches 150 mV or less, thereby precipitating ruthenium, followed by solid-liquid separation;
a sulfurization step in which the filtrate obtained by performing solid-liquid separation after precipitating the ruthenium is adjusted to 70°C or less, and one or more of hydrogen sulfide, sodium hydrosulfide, and sodium sulfide are added as a sulfurizing agent to precipitate one or more elements of copper, arsenic, and antimony;
an iridium recovery step of precipitating one or more elements selected from copper, arsenic, and antimony, followed by solid-liquid separation, adjusting the temperature of the resulting filtrate to 40°C or higher, and adding sodium thiosulfate or a solution containing thiosulfate ions to precipitate iridium;
A method for recovering ruthenium and iridium, comprising:
[3] The method for recovering ruthenium and iridium according to [1] or [2], wherein in the ruthenium recovery step, the acidic solution containing ruthenium, iridium, and one or more elements of copper, arsenic, and antimony is an acidic solution obtained by blowing sulfur dioxide or hydrogen sulfide into the acidic solution or adding an aldehyde reducing agent to precipitate platinum, gold, palladium, and selenium, thereby adjusting the elemental concentrations of platinum, gold, palladium, and selenium to 10 mg/L or less.
[4] The method for recovering ruthenium and iridium according to any one of [1] to [3], wherein in the ruthenium recovery step, the metallic iron is added in an amount 5 to 25 times by mass the amount of ruthenium in the acidic solution.
[5] The method for recovering ruthenium and iridium according to any one of [1] to [4], wherein in the sulfurization step, at least one of hydrogen sulfide, sodium hydrosulfide, and sodium sulfide is added as the sulfurizing agent in an amount 5 to 20 times by mass the copper concentration when converted into a sulfur content concentration.
[6] The method for recovering ruthenium and iridium according to any one of [1] to [5], wherein in the ruthenium recovery step, the acidic solution containing ruthenium, iridium, and one or more elements of copper, arsenic, and antimony 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 ruthenium recovery step is 100 mg/L or less, and the sodium thiosulfate salt or the thiosulfate ion-containing solution is added in the iridium recovery step so that the concentration is 5 g/L or more, calculated as sodium thiosulfate pentahydrate.

The present invention provides a method for efficiently separating and recovering ruthenium and iridium from an acidic solution containing ruthenium and iridium.

FIG. 1 is a flow diagram illustrating an embodiment of the present invention.

Next, we will explain in detail the modes for implementing the present invention. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes and improvements may be made based on the common knowledge of those skilled in the art, without departing from the spirit of the present invention.

Figure 1 shows a flow diagram that outlines one embodiment of the present invention. The flow diagram in Figure 1 lists specific examples of each step, and the present invention is not limited to this flow diagram alone. In one aspect, a method for recovering ruthenium and iridium according to an embodiment of the present invention includes a ruthenium recovery step in which an acidic solution containing ruthenium, iridium, and one or more elements selected from the group consisting of copper, arsenic, and antimony is adjusted to a temperature of 60°C or below, and either (1) metallic iron is added in an amount of 0.5 to 4.0 g/L, or (2) metallic iron is added until the oxidation-reduction potential (RED) using a silver/silver chloride reference electrode reaches 150 mV or less to precipitate ruthenium, followed by solid-liquid separation; a sulfurization step in which the filtrate obtained by precipitating ruthenium and performing solid-liquid separation is adjusted to a temperature of 70°C or below, and one or more of hydrogen sulfide, sodium hydrosulfide, and sodium sulfide are added as a sulfiding agent to precipitate one or more elements selected from the group consisting of copper, arsenic, and antimony; and an iridium recovery step in which the filtrate obtained by precipitating one or more elements selected from the group consisting of copper, arsenic, and antimony is subjected to solid-liquid separation after the filtrate is adjusted to a temperature of 40°C or above, and sodium thiosulfate or a solution containing thiosulfate ions is added to precipitate iridium.

In the ruthenium and iridium recovery method according to an embodiment of the present invention, the acidic solution containing ruthenium and iridium to be treated may be obtained through any process. However, an acidic solution obtained by oxidizing and dissolving electrolytic deposits generated in the electrolytic refining process of copper smelting is particularly suitable as the iridium-containing acidic solution of the present invention. Furthermore, electrolytic deposits generated in the electrolytic refining process of non-ferrous metal smelting, particularly copper smelting, are enriched with platinum group elements along with other rare elements. Rare elements are not smelted separately; rather, they are recovered as by-products of other metals or separated from recycled materials such as waste catalysts. Therefore, the ruthenium and iridium recovery method according to an embodiment of the present invention can also be applied to recycling from waste. In other words, the acidic solution containing ruthenium and iridium generated in the waste treatment process can be used.

In the method for recovering ruthenium and iridium according to an embodiment of the present invention, if the acidic solution containing ruthenium and iridium to be treated is a hydrochloric acid solution obtained through a specified process, it will contain various metal elements in addition to ruthenium (Ru) and iridium (Ir).

When replacing ruthenium with metallic iron, selenium (Se), platinum (Pt), palladium (Pd), gold (Au), silver (Ag), etc. are replaced preferentially over ruthenium. As will be explained in more detail later, it is necessary to reduce the concentrations of these elements beforehand.

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

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.

In a 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.

Valuable materials remaining in the acidic solution after the above-mentioned treatment include ruthenium, iridium, antimony, copper, etc. Of these, ruthenium and iridium have particularly high added value and are therefore preferably recovered. The post-reduction solution also contains arsenic at 0.5 to 3 g/L, but arsenic is relatively easy to separate from metals, and some contamination is acceptable when recovering valuable materials. It is also preferable to recover ruthenium and iridium separately.

Metal cementation is an effective way to recover ruthenium from the post-reduction solution. However, since the acidic solution contains arsenic, the metal must have an oxidation-reduction potential of -380 mV or higher using a silver/silver chloride reference electrode to suppress the generation of arsine. Metals that meet the conditions for cementation of ruthenium include iron, nickel, lead, and copper.

Of the metals used in ruthenium cementation, the following pose individual problems. Copper also precipitates significant amounts of arsenic as copper arsenide, lead contaminates the ruthenium as unreacted lead does not dissolve in the acid, and nickel is expensive. However, although metallic iron does have the problem of generating large amounts of hydrogen instantaneously during reaction, this is not a major issue if the temperature of the acid solution is adjusted to below 60°C, preferably between 30 and 60°C, and metallic iron is added so that the concentration in the acid solution is 0.5 to 4.0 g/L. Furthermore, adding metallic iron causes ruthenium to undergo cementation before copper and arsenic, making it possible to separate and recover it.

In addition, in the ruthenium recovery process, it is preferable to add metallic iron in an amount 5 to 25 times the mass of ruthenium in the acidic solution. If the amount of metallic iron added is less than 5 times the mass of ruthenium in the acidic solution, there is a risk that cementation of the ruthenium by the metallic iron will be insufficient. Furthermore, if the amount of metallic iron added is more than 25 times the mass of ruthenium in the acidic solution, it will be disadvantageous in terms of cost and there is a risk of impurities being mixed in.

As the metallic iron to be added, iron powder is preferred due to its high reactivity. There are no particular restrictions on the grade of metallic iron. As will be explained later, the metallic iron to be added should be reducible, and even iron powder with a portion of its surface coated with copper (copper-coated iron powder) will work. In this case, copper-coated iron powder is added as metallic iron so that the iron content is 0.5 to 4.0 g/L. The dissolved copper is precipitated and removed as sulfide after ruthenium recovery, so contamination does not pose a major problem. Furthermore, when using copper-coated iron powder, the temperature of the acidic solution should be adjusted to 40°C or higher, and the copper-coated iron powder should be added so that the iron content is 0.5 to 4.0 g/L.

When metallic iron comes into contact with an acidic solution, it generates hydrogen, which can be explosive. Furthermore, if iron powder is used as metallic iron, its large surface area can cause a large amount of hydrogen to be generated in a short period of time, causing the solution to boil over. Therefore, especially when using iron powder, it is best to add it in multiple batches rather than all at once.

If the redox potential (reference electrode: silver/silver chloride) is used as an indicator for ruthenium cementation, metallic iron can be added until the redox potential of the acidic solution reaches 150 mV or less. Below this potential, the ruthenium concentration drops significantly.

To avoid the risk of overflow or explosion due to hydrogen generation, it is possible to use iron powder whose surface is partially coated with copper (copper-coated iron powder). In principle, hydrogen generation is suppressed by limiting contact between metallic iron and the acidic solution. After the copper gradually dissolves, the iron that appears on the surface reacts with ruthenium. If the copper content is too high, contact efficiency may be reduced, so the copper content of the copper-coated iron powder is preferably 70% by mass or less, and more preferably 40% by mass or less.

After precipitating ruthenium, the ruthenium-containing material obtained by solid-liquid separation is separated from iridium and other impurities using known methods. For example, after oxidative dissolution, sodium bromate is added and ruthenium tetroxide is distilled and separated for recovery. Iridium is sufficiently concentrated in this oxidative dissolution liquid, and can also be recovered using known solvent extraction methods.

A sulfiding agent is added to the acidic liquid, which is the filtrate after cementation separation (solid-liquid separation) of ruthenium. Suitable sulfiding agents are hydrogen sulfide, sodium hydrosulfide, and sodium sulfide, and any one or more of these may be used. Sodium thiosulfate is also known as a sulfiding agent, but is unsuitable as it may cause some of the iridium to precipitate and be lost. The sulfiding agent precipitates copper, arsenic, antimony, and lead.

The temperature of the acidic solution during sulfurization using the sulfurizing agent should be adjusted to 70°C or below. If the temperature of the acidic solution is higher than 70°C, there is a risk that the precipitated copper sulfide will re-dissolve. In addition, the reducing sulfur that forms sulfides from the solution may volatilize as hydrogen sulfide, reducing the reaction efficiency.

The sulfurizing agent is preferably added in an amount 5 to 20 times the copper concentration, converted into sulfur content, by mass. More preferably, it is added in an amount 5 to 12 times the copper concentration. If the amount of sulfurizing agent added is less than 5 times the copper concentration by mass, there is a risk that an excessive amount of the element to be removed by sulfurization will remain. If the amount of sulfurizing agent added is more than 20 times the copper concentration by mass, there is a risk that the amount of precipitate produced in the next step of recovering iridium will be extremely small, making solid-liquid separation difficult. There is also a risk that reagent costs will increase.

The sulfide precipitate separated during the sulfurization process contains valuable materials such as copper and lead, so it can be recycled into the smelting furnace and reused as a valuable raw material.

After precipitating one or more elements of copper, arsenic, and antimony in the sulfurization process, solid-liquid separation is performed. The resulting filtrate is adjusted to 40°C or higher, preferably 60°C or higher, and sodium thiosulfate salt or a solution containing thiosulfate ions is added to precipitate iridium. Sodium thiosulfate salt or a solution containing thiosulfate ions is added to precipitate iridium at a concentration of 5 g/L or more, calculated as sodium thiosulfate pentahydrate. Iridium hardly precipitates with the sulfurizing agent used in the previous sulfurization process. In contrast, thiosulfate ions have coordination ability, so it is thought that reducing them after coordinating with iridium ions is effective in precipitating iridium.

A typical example of sodium thiosulfate salt is commercially available sodium thiosulfate pentahydrate. It may be added as a solid sodium thiosulfate salt, 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 solid salts are particularly advantageous in terms of cost and ease of handling. Sodium thiosulfate pentahydrate is particularly suitable due to its low toxicity.

Addition of sodium thiosulfate or a solution containing thiosulfate ions produces a precipitate containing arsenic, sulfur, and iridium. When the iridium concentration in the acidic solution in the ruthenium recovery process is dilute, at 100 mg/L or less, precipitating only iridium results in too little recovery, causing problems with solid-liquid separation. The presence of a moderate amount of impurities is not a problem.

When the iridium concentration in the acidic solution in the ruthenium recovery step is high, it is more efficient to recover it by precipitation with KCl or NH ₄ Cl, but when the iridium concentration is dilute, such as 100 mg/L or less, it is preferable to recover it by precipitation by adding sodium thiosulfate salt or a solution containing thiosulfate ions. In this case, sodium thiosulfate salt or a solution containing thiosulfate ions may be added so that the concentration, calculated as sodium thiosulfate pentahydrate, is 5 g/L or more, or may be added so that it is 5 to 20 g/L or more.

The precipitated iridium-containing material is subjected to solid-liquid separation, followed by separation of iridium from other impurities using known methods. For example, one method involves oxidative dissolution followed by separation and recovery of iridium using solvent extraction. The iridium recovered as a precipitate is sufficiently concentrated, and can be recovered using known solvent extraction methods.

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.

(Experimental Example 1)
Copper was dissolved and removed from electrolytic deposits derived from the copper electrorefining process of copper smelting using sulfuric acid. Concentrated hydrochloric acid and 60% hydrogen peroxide solution were added for dissolution, followed by solid-liquid separation to obtain PLS (pregnant leach solution). The PLS was cooled to 6°C to precipitate and remove base metals. The acid concentration was adjusted to 1 mol/L or more, and DBC (dibutyl carbitol) and the PLS were mixed to extract gold. After gold extraction, the PLS 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, 200 mL of the sulfur dioxide reduced solution was taken and heated to 60°C. The iridium concentration of the sulfur dioxide reduced solution was 25 mg/L and the ruthenium concentration was 77 mg/L. The sulfur dioxide reduced solution also contained, as other elements, 1.32 g/L of arsenic, 0.49 g/L of copper, and 230 mg/L of antimony. Iron powder (P80 = 150 to 200 μm) in the amount shown in Table 1 was added and stirred.
The reaction was stopped after a predetermined time, and the precipitate was separated into solid and liquid. After filtration, the ORP (oxidation-reduction potential) of the solution was measured, and the concentrations of various elements were quantified.
All reagents used were of special grade manufactured by Wako Pure Chemical Industries, Ltd. The element 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 (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.

It can be seen that adding 0.1g of iron powder to 200mL of raw material solution resulted in preferential cementation of ruthenium. Furthermore, it can be seen that adding 0.3g or more of iron powder resulted in sufficient recovery of ruthenium. However, excessive iron powder increases the amount of arsenic and copper contamination. Therefore, it is preferable to add 0.8g or less.

The ORP value dropped sharply when more than 0.3g of iron powder was added. This indicates that adding iron powder until the ORP falls below 150mV is sufficient to cement ruthenium.

(Experimental Example 2)
200 mL of the same iridium-containing liquid as in Experimental Example 1 was taken and heated to 40 to 80°C. 0.6 g of iron powder was added. After stirring for 1 hour, the reaction was stopped. The filtrate was filtered and the component elements were quantified. The quantification method 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.

The results in Table 2 show that iridium precipitates when the temperature exceeds 60°C, so temperatures below 60°C are ideal for preferentially cementing ruthenium with iron powder. Copper becomes mixed in at lower temperatures, but this can be controlled by adjusting the amount of iron powder added. It is also assumed that metallic copper produced by cementation will easily dissolve in acid. This is because, as Table 2 shows, the copper concentration increases as the temperature increases, and it is thought that cemented copper was produced once but then re-dissolved.

(Experimental Example 3)
200 mL of the same iridium-containing liquid as in Experimental Example 1 was taken and heated to 50°C. 1 g or 2 g of sodium hydrosulfide was added and stirred for 1 hour. The filtrate was filtered and the amount of each element in the filtrate was quantified. The quantification method was the same as in Experimental Example 1. The results are shown in Table 3.

The results in Table 3 show that the addition of sodium hydrosulfide (NaSH) causes almost no sulfide or reduction precipitates in ruthenium and iridium. In contrast, copper selectively produces sulfide precipitates.

It is widely known that copper can be converted to copper sulfide by sulfiding agents such as hydrogen sulfide and sodium sulfide, in addition to sodium hydrosulfide. The results of Experimental Example 3 showed that 1 g of sodium hydrosulfide per 200 mL of solution was effective. This corresponds to 5.8 times the sulfur concentration of sodium hydrosulfide by mass. 2 g corresponds to 11.6 times the sulfur concentration by mass. Therefore, the reducing sulfur contained in the sulfiding agent should be added in an amount 5 to 12 times the mass of copper.

(Experimental Example 4)
200 mL of the same iridium-containing liquid as in Experimental Example 1 was taken and heated to 60°C. 0.3 g of iron powder was added, and the mixture was stirred and cemented for 30 minutes. The filtrates after solid-liquid separation were each heated to 40 to 70°C, and 1 g of sodium hydrosulfide was added. The mixture was stirred for 1 hour and then filtered again. The concentrations of each element in the filtrate were quantified. The filtrates were heated to 70°C, and 2 g or 4 g of sodium thiosulfate pentahydrate was added. The mixture was stirred for 1 hour and filtered, and the contents of each element were quantified. The quantification method was the same as in Experimental Example 1. The results are shown in Table 4 (element concentrations after sulfurization) and Table 5 (element concentrations after addition of sodium thiosulfate).

The results in Tables 4 and 5 show that ruthenium can be cemented with iron powder, copper and antimony can be removed by sulfurization, and the remaining iridium can be recovered using sodium thiosulfate.

Sodium thiosulfate pentahydrate was effective in recovering iridium even when added at a rate of 2g per 200mL of the target liquid, but had almost no effect on antimony. It was effective on copper, but if it was removed beforehand by sulfurization, it would not contaminate the iridium. Although the concentration was not measured, lead sulfide does not dissolve in water, and its ionization tendency is intermediate between that of iron and copper, so it is certain that it will precipitate and be removed.

Although some arsenic is mixed in, the iridium concentration in the raw liquid is low, and the arsenic compounds that precipitate during solid-liquid separation act as a filter aid. Therefore, there is no need to thoroughly remove arsenic during the sulfurization process.

(Experimental Example 5)
Copper-coated iron powder was prepared as follows. Iron powder was contacted with a copper sulfate solution containing copper sulfate in an amount five times the mass of iron, and stirred for 20 seconds. Two copper contents were prepared: 30% and 70%. The 70% copper content was prepared at a reaction temperature of 60°C during contact with the copper sulfate solution.

200 mL of the same iridium-containing liquid as in Experimental Example 1 was heated to 60°C or 40°C. 0.4 g of copper-coated iron powder was added, stirred, and cemented for 30 minutes. The filtrate after solid-liquid separation was heated to 40°C, and sodium hydrosulfide was added and stirred for 1 hour. Taking copper concentration into consideration, 2 g of sodium hydrosulfide was added to the 30% copper powder and 3 g to the 70% copper powder, and the mixture was filtered again. The concentration of each element in the filtrate was quantified. The filtrate was heated to 70°C, and 4 g of sodium thiosulfate pentahydrate was added. The mixture was stirred for 1 hour, filtered, and the elemental components were quantified. The quantification method was the same as in Experimental Example 1. The results are shown in Table 6 (element concentration after cementation), Table 7 (element concentration after sulfurization), and Table 8 (element concentration after sodium thiosulfate addition). In Tables 7 and 8, "ND" indicates that the corresponding element was not detected.

The results in Table 6 show that it is possible to precipitate ruthenium even when using copper-coated iron powder. Furthermore, the amount of copper extracted was also confirmed, but as shown in Table 7, copper could be selectively removed by sulfurization. Furthermore, iridium could be finally recovered by adding sodium thiosulfate.

Claims (7)

a ruthenium recovery step of adjusting the temperature of an acidic solution containing ruthenium, iridium, and one or more elements selected from the group consisting of copper, arsenic, and antimony, to 60°C or below, (1) adding metallic iron to the solution so that the amount is 0.5 to 4.0 g/L, or (2) adding metallic iron until the oxidation-reduction potential using a silver/silver chloride reference electrode reaches 150 mV or less, thereby precipitating ruthenium, followed by solid-liquid separation;
a sulfurization step in which the filtrate obtained by performing solid-liquid separation after precipitating the ruthenium is adjusted to 70°C or less, and one or more of hydrogen sulfide, sodium hydrosulfide, and sodium sulfide are added as a sulfurizing agent to precipitate one or more elements of copper, arsenic, and antimony;
an iridium recovery step of precipitating one or more elements selected from copper, arsenic, and antimony, followed by solid-liquid separation, adjusting the temperature of the resulting filtrate to 40°C or higher, and adding sodium thiosulfate or a solution containing thiosulfate ions to precipitate iridium;
A method for recovering ruthenium and iridium, comprising: a ruthenium recovery step of adjusting the temperature of an acidic solution containing ruthenium, iridium, and one or more elements selected from the group consisting of copper, arsenic, and antimony, to 40°C or higher, (1) adding copper-coated iron powder as metallic iron so that the iron content is 0.5 to 4.0 g/L, or (2) adding copper-coated iron powder as metallic iron until the oxidation-reduction potential using a silver/silver chloride reference electrode reaches 150 mV or less, thereby precipitating ruthenium, and then performing solid-liquid separation;
a sulfurization step in which the filtrate obtained by performing solid-liquid separation after precipitating the ruthenium is adjusted to 70°C or less, and one or more of hydrogen sulfide, sodium hydrosulfide, and sodium sulfide are added as a sulfurizing agent to precipitate one or more elements of copper, arsenic, and antimony;
an iridium recovery step of precipitating one or more elements selected from copper, arsenic, and antimony, followed by solid-liquid separation, adjusting the temperature of the resulting filtrate to 40°C or higher, and adding sodium thiosulfate or a solution containing thiosulfate ions to precipitate iridium;
A method for recovering ruthenium and iridium, comprising: The method for recovering ruthenium and iridium described in claim 1 or 2, wherein in the ruthenium recovery step, the acidic solution containing ruthenium, iridium, and one or more elements selected from the group consisting of copper, arsenic, and antimony is an acidic solution obtained by blowing sulfur dioxide or hydrogen sulfide into the acidic solution or adding an aldehyde reducing agent to precipitate platinum, gold, palladium, and selenium, thereby adjusting the elemental concentrations of platinum, gold, palladium, and selenium to 10 mg/L or less. The method for recovering ruthenium and iridium according to claim 1 or 2, wherein the metallic iron is added in an amount 5 to 25 times the mass of the ruthenium in the acidic solution during the ruthenium recovery step. The method for recovering ruthenium and iridium according to claim 1 or 2, wherein in the sulfurization step, one or more of hydrogen sulfide, sodium hydrosulfide, and sodium sulfide are added as the sulfurizing agent in an amount 5 to 20 times the copper concentration by mass when converted into a sulfur content concentration. The method for recovering ruthenium and iridium according to claim 1 or 2, wherein in the ruthenium recovery step, the acidic solution containing ruthenium, iridium, and one or more elements selected from the group consisting of copper, arsenic, and antimony is the acidic solution obtained after dissolving metal electrolytic deposits. The method for recovering ruthenium and iridium according to claim 1 or 2, wherein the iridium concentration in the acidic solution in the ruthenium recovery step is 100 mg/L or less, and the sodium thiosulfate salt or thiosulfate ion-containing solution is added in the iridium recovery step so that the concentration, calculated as sodium thiosulfate pentahydrate, is 5 g/L or more.