JP7423467B2 - Ruthenium recovery method - Google Patents

Description

The present invention relates to a method for recovering ruthenium from an acidic solution containing ruthenium and arsenic. It is particularly suitable for use in the slime treatment process generated in the electrolytic refining process of copper smelting.

In copper pyrometallurgy, copper concentrate is melted to produce blister copper with a purity of 99% or more in a converter or refining furnace, and then electrolytic copper with a purity of 99.99% or more is produced in an electrolytic refining process. In recent years, metal scraps containing precious metals derived from electronic components have been input into converters as recycled raw materials, and valuables other than copper are precipitated as slime during electrolytic refining.

This slime also concentrates precious metals, rare metals, and selenium and tellurium contained in copper concentrate. These elements are separately separated and recovered as copper smelting by-products.

A hydrometallurgical method is often applied to process this slime. 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 valuable materials are successively reduced and recovered using sulfur dioxide. . Patent Document 2 discloses a method in which gold and silver are recovered in a similar manner, then valuable materials are reduced and precipitated with sulfur dioxide, and only selenium is removed by distillation to concentrate precious metals.

The solution after recovering the precious metals contains rare metal ions, tellurium, and selenium, and it is necessary to further recover these valuables. As a recovery method, there are known methods such as recovering the precipitate generated by the reducing agent, and mixing the whole solution with copper concentrate, drying it with a dryer, and repeating it in the smelting furnace.

Japanese Patent Application Publication No. 2001-316735 Japanese Patent Application Publication No. 2016-160479 Japanese Patent Application Publication No. 2019-147990

The method shown in Patent Document 1 for recovering the precipitate produced by sulfur dioxide has many advantages in terms of cost and production scale. In addition, since each element is precipitated in sequence, it is effective for separation and purification.

In the method of recovering valuable substances using sulfur dioxide, the valuable substances can be sequentially reduced and recovered after dissolution. First, platinum and palladium precipitate. Next, selenium undergoes reduction. Iridium, ruthenium, and rhodium have relatively low redox potentials and are difficult to undergo reduction, so they remain in the solution until the end. Generally, ruthenium in a solution is oxidized with a strong oxidizing agent such as bromic acid, and then distilled to recover ruthenium dioxide.

Patent Document 3 discloses a method in which ruthenium remaining in the solution is cemented with metallic copper. By using copper as the metal used for cementation, it is possible to avoid coexisting arsenic from being generated as arsine gas.

In the method of distilling ruthenium, bromic acid, for example, can be used as an oxidizing agent during distillation, but it is expensive. Further, the ruthenium contained in the solution derived from the smelting precipitate process is usually about 100 to 300 mg/L, and the oxidation efficiency is low because the oxidizing agent reacts with other coexisting substances.

Additionally, the ruthenium oxide that is distilled is known to be a toxic compound. Multistage distillation is not preferred because it involves handling toxic substances at high concentrations and poses a safety problem. Furthermore, if impurities are mixed in during distillation, a repurification operation is required, but in distillation, azeotropic fractions are likely to be mixed in as impurities. Therefore, it is necessary to increase the purity of the raw material ruthenium (crude ruthenium) before it can be used for distillation.

In order to increase the purity of crude ruthenium, it is necessary to roughly separate and concentrate ruthenium in a harmless form. In the concentration operation, valuable substances in the solution are reduced and ruthenium and other elements are recovered as a precipitate. Other common elements include selenium, tellurium, and rhodium.

As disclosed in Patent Document 3, ruthenium can be recovered by cementation with copper. However, it is necessary to remove the copper from the recovered ruthenium-containing precipitate and it must be dissolved with sulfuric acid. Copper needs to be heated to dissolve in sulfuric acid, and the surface of unreacted copper is coated with substances such as selenium and tellurium precipitated by cementation, so the acid dissolution reaction is said to be efficient. I can't say that.

Furthermore, copper is a relatively expensive metal. When used for cementation, the cost cannot be ignored. However, typical base metals such as iron, zinc, and aluminum may react with coexisting arsenic under acidic conditions and generate arsine gas.

In view of such conventional circumstances, the present invention provides a method for selectively recovering ruthenium from an acidic solution containing ruthenium and arsenic. It is particularly suitable for a solution containing electrolytic precipitates generated in the electrolytic refining process in copper smelting.

As a result of extensive research to solve the above-mentioned problems, the inventors of the present invention have discovered a method for recovering ruthenium by cementing an acidic solution containing ruthenium and arsenic with iron. Embodiments of the invention are specified as follows.
(1) A method for recovering ruthenium from an acidic solution containing ruthenium and arsenic, comprising:
A method for recovering ruthenium, comprising adjusting the copper concentration of the acidic solution to 0.06 g/L or higher, bringing iron into contact with the solution at a temperature of 20° C. or higher, and recovering ruthenium by cementation.
(2) The method for recovering ruthenium according to (1), wherein the iron is 5 times or more by mass as much as the ruthenium.
(3) adjusting the copper concentration of the acidic solution by adding a water-soluble copper salt or a copper electrolyte;
Ruthenium according to (1) or (2), characterized in that the temperature of the acidic solution is maintained at 75° C. or lower and the copper concentration of the acidic solution is maintained at 0.03 g/L or higher until the end of the cementation. collection method.
(4) The method for recovering ruthenium according to any one of (1) to (3), characterized in that the copper concentration is adjusted to 1.5 g/L or more before adding iron to the acidic solution. .
(5) The average particle size of the iron is 1 mm or less, the amount of iron added is 30 to 300 times the mass of ruthenium contained in the acidic solution, and the concentration of copper is 1 mm or less than the amount of ruthenium contained in the acidic solution. The method for recovering ruthenium according to any one of (1) to (4), characterized in that the amount is adjusted to 2 times the mass or less.
(6) The iron is iron powder, and is added so that the mass ratio of copper/iron to the copper in the acidic solution is 0.5 to 2. The method for recovering ruthenium according to any one of the above.
(7) Before adding iron to the acidic solution, add sulfur dioxide, sulfite, or sulfite to the acidic solution to adjust the total concentration of gold, platinum, palladium, selenium, and tellurium to 300 mg/L or less. The method for recovering ruthenium according to any one of (1) to (6), characterized in that the method comprises:
(8) the acidic solution further contains copper and tellurium,
The iron is brought into contact with the acidic solution at a liquid temperature of 20° C. or higher and lower than 60° C. to precipitate copper on the surface of the iron, and then heated to 70° C. or higher to precipitate ruthenium and tellurium ( The method for recovering ruthenium according to any one of 1) to (7).
(9) Starting the cementation by adjusting the copper concentration of the acidic solution to 0.3 g/L or more, and maintaining the copper concentration of the acidic solution at 0.3 g/L or more until the end of the cementation. The method for recovering ruthenium according to (8), characterized in that:

According to embodiments of the present invention, a method for selectively recovering ruthenium from an acidic solution containing ruthenium and arsenic can be provided.

It is a graph showing the relationship between the mass ratio of copper and iron in the liquid and the amount of precipitated ruthenium, according to an experimental example. It is a graph showing the relationship between the mass ratio of copper and iron in a liquid and the amount of arsenic precipitated, according to an experimental example.

A method for recovering ruthenium according to an embodiment of the present invention is a method for recovering ruthenium from an acidic solution containing ruthenium and arsenic, in which the copper concentration of the acidic solution is adjusted to 0.06 g/L or more, and the liquid temperature is 20 ° C. The iron is brought into contact with the above, and ruthenium is recovered by cementation.

Electrolytic precipitates produced in the electrolytic refining process of nonferrous metal smelting, especially copper smelting, are enriched with platinum group elements, heavy metals, and toxic elements. Platinum group elements and toxic elements are not smelted alone, but are recovered as by-products of other metals or separated from recycled raw materials such as spent catalysts. Therefore, this method can also be applied to recycling from waste.

Hydrochloric acid and hydrogen peroxide can be added to dissolve the electrolytic precipitate, but the silver forms an insoluble silver chloride precipitate with chloride ions immediately after dissolution. A solution containing an oxidizing agent and chlorine, such as aqua regia or chlorinated water, can dissolve precious metals and separate silver as silver chloride. Since it is a chloride bath, platinum group elements, rare metal elements, chalcogen elements, arsenic, antimony, etc. are distributed in the leach liquid (PLS).

The leach liquid (PLS) is once cooled, and chlorides of base metals such as lead and antimony are precipitated and separated. The gold is then separated into an organic phase by solvent extraction. Dibutylcarbitol (DBC) is widely used as a gold extractant.

Valuables can be precipitated and recovered by reducing PLS after gold has been extracted, but since the redox potential differs depending on the element, the order of precipitation is naturally determined. First, gold, platinum, and palladium are precipitated, followed by chalcogens such as selenium and tellurium, and then inert precious metals such as ruthenium and iridium.

Reducing sulfur is used as the reducing agent in terms of cost and efficiency, and among these, sulfur dioxide is most suitable because it can be supplied in large quantities and at low cost by converter gas or roasting of sulfide ore. Inert noble metals have extremely slow reduction rates with sulfur dioxide and sulfites. The content of ruthenium in the copper electrolyte precipitate solution is not large in the first place, for example, about 150 to 300 mg/L. The current recovery rate of ruthenium using sulfur dioxide is about 30 to 50% in a reaction time of 6 to 8 hours, but it is expected that more than 10 hours will be required to achieve complete precipitation. This is too long to be a realistic reaction time.

Therefore, metal cementation is the most efficient way to recover ruthenium. It is known that ruthenium can be reduced to metallic ruthenium by metals that generate hydrogen with mineral acids, such as zinc, magnesium, and aluminum.

However, in an acidic solution containing arsenic, there is a risk that the above metal and arsenic will react and generate arsine gas. Therefore, cementation with base metals is not realistic. However, since cementation with iron does not have a fast reaction rate, it is possible to suppress the amount of arsine generated to a minimum. In an embodiment of the present invention, iron is brought into contact with the acidic solution at a temperature of 20° C. or higher, and ruthenium is recovered by cementation. When the temperature of the acidic solution is 20° C. or higher, cementation becomes good. Furthermore, the amount of arsine generated can be suppressed by maintaining the temperature of the acidic solution at 75° C. or lower until the end of cementation. More preferably, the temperature is 60°C or lower.

The amount of iron added is preferably 5 times or more the mass of ruthenium. If it is too small, ruthenium recovery will be insufficient. When using iron powder for cementation, if the amount added is too large, the amount of arsine generated will increase, so it is preferably 1000 times the mass of ruthenium or less. The amount of iron added is more preferably 300 to 1000 times the mass of ruthenium, and even more preferably 500 to 800 times the mass of ruthenium.

However, since some arsine is still generated, the effect of the present invention can be obtained as long as even a small amount of copper ions are present in the acidic solution to be treated before adding iron to the acidic solution. The concentration may be 0.06 g/L or more. Even if arsine is generated, it can react with copper ions and be trapped as copper arsenide. A more preferable copper concentration of the acidic solution before adding iron to the acidic solution is 1.5 g/L or more.

It is sufficient that the copper ions in the acidic solution are maintained even slightly until the end of cementation, and the specific copper concentration may be 0.03 g/L or more. According to such a configuration, generation of excessive hydrogen can be suppressed. Hydrogen in the nascent stage has a strong reducing power, and if a large amount of hydrogen comes into contact with the solution, the possibility of arsine generation cannot be excluded.

The copper concentration in the acidic solution can be adjusted with water-soluble copper salts such as copper(II) sulfate and copper(II) chloride. Alternatively, it may be adjusted by adding a copper electrolyte. Copper partially reacts with iron and precipitates, but this effect is small if the temperature of the acidic solution is 75° C. or lower.

When iron is added, it first reacts with copper ions and the surface of the iron is covered with copper. Ruthenium is also cemented in competition with copper ions. Copper deposited on the iron surface gradually dissolves and reacts with copper and ruthenium again. Depending on the temperature, it can also react with arsenic. Therefore, the efficiency of cementation is affected by the copper concentration and the ratio of added iron. It is preferable to add so that the mass ratio of copper/iron to copper in the acidic solution is 0.5 to 2, more preferably 0.5 to 1.5.

The recovered ruthenium is metallic ruthenium and can be processed using existing ruthenium purification processes. Generally, in cementation, an excess of substituent metal is added, but unreacted iron is dissolved by heating under acidic conditions. Alternatively, it is also possible to separate by magnetic force.

During cementation, the amount of iron used can be suppressed by removing metals with a high ionization tendency that react with iron, such as selenium and tellurium, using a reducing agent in advance. Specifically, during cementation, it is preferable to adjust the total concentration of gold, platinum, palladium, selenium, and tellurium in the acidic solution to 300 mg/L or less before adding iron to the acidic solution. The reducing agent at this time is preferably sulfur dioxide, which is inexpensive. Additionally, sulfurous acid or sulfite salts may be used.

The shape of the iron introduced in cementation may be plate-like, rod-like, shot, or iron powder. Instead of a tank-type reaction tank, iron may be charged into a packed tower or a circulation tank and the liquid to be treated may be passed therethrough. The contact method is determined by the allowable copper content in the recovered material, reaction efficiency, and equipment constraints. The higher the grade of iron used for cementation, the better, but iron with relatively low purity, such as iron scrap, is also used. Of course, iron having a large specific surface area, such as iron powder, is more preferable. The average particle size of iron may be 1 mm or less.

When introducing iron into a tank-type reaction vessel, it is preferable to introduce iron powder. Iron powder herein refers to iron particles having an average particle size P80 of 0.2 mm or less. Here, "P80" indicates the particle size at which 80% passes through a sieve. When chalcogens coexist in the solution, it is preferable to add more iron powder.

It is preferable to add the iron powder to the acidic solution in an amount of 30 to 300 times the mass of ruthenium contained in the acidic solution, and adjust the copper concentration to 1.2 times the mass of the iron powder or less. According to such a configuration, it is not necessary to add excessive iron powder. Adding too much iron powder causes problems such as excessive generation of hydrogen, increased cost, and contamination of unintended elements.

In the method for recovering ruthenium according to an embodiment of the present invention, the acidic solution further contains copper and tellurium, and the iron is brought into contact with the acidic solution at a liquid temperature of 20°C or higher and lower than 60°C to precipitate copper on the surface of the iron. After that, ruthenium and tellurium may be precipitated by heating to 70° C. or higher. In cementation with iron, the amount of arsine generated can be suppressed by coexisting copper ions in the acidic solution and adjusting the temperature to below 60°C. More preferably, the temperature is 50°C or lower.

Ruthenium, copper, and arsenic undergo cementation with iron immediately after they are added. Ruthenium reacts more easily, but because it has a high copper concentration, the iron surface exhibits a coppery color, as if covered with copper. By controlling the temperature at this time, reduction of arsenic is suppressed. Copper and ruthenium that cover the surface do not react with arsenic.

If the copper that covers the surface is heated gradually, it will gradually dissolve. At 50°C, the reaction is very slow, so heating to 70°C or higher is preferable. When copper dissolves and an iron surface appears, ruthenium cementation and copper precipitation occur again. Although an oxidizing substance is required to dissolve copper, it is preferable that sulfate ions be included in the solution due to cost and reactivity with other elements.

When the liquid temperature is 70° C. or higher, some arsenic becomes arsine, so the copper concentration of the solution is adjusted in advance to 0.3 g/L or higher. Even if arsine is generated, it can react with copper ions and be trapped as copper arsenide. A more preferable copper concentration is 1 g/L or more. Further, it is preferable to maintain the copper concentration of the acidic solution at 0.3 g/L or more until the end of cementation.

When the liquid temperature is high, copper deposited on the iron surface can directly cement ruthenium. Cementation of ruthenium with copper requires a liquid temperature of 70° C. or higher. Therefore, the temperature at the time of iron addition may be set to 50° C. or lower, and the temperature may be heated to 70° C. or higher after confirming that copper has precipitated on the iron surface.

Hereinafter, the present invention will be explained in more detail with reference to Examples. However, the present invention is not limited to these.

(Experiment example 1)
Sulfuric acid was added to the electrolytic precipitate recovered from the copper electrolytic refining process of copper smelting to remove copper. Next, concentrated hydrochloric acid and 60% hydrogen peroxide solution were added and dissolved, and solid-liquid separation was performed to obtain PLS (leaching liquid). The PLS was cooled to 6° C. to precipitate and remove base metals. Subsequently, the acid concentration was adjusted to 2N or higher, and DBC (dibutyl carbitol) and PLS were mixed to extract gold. After the gold extraction, the PLS was heated to 70°C, and a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20%) was blown into the PLS to reduce the precious metal and selenium and separate the solid and liquid. The selenium concentration of the liquid after selenium separation was 110 mg/L, the tellurium concentration was 85 mg/L, the ruthenium concentration was 82 mg/L, the copper concentration was 2.3 g/L, and the arsenic concentration was 1.4 g/L.

200 mL of the selenium separation solution (an acidic solution containing ruthenium and arsenic from which ruthenium is to be recovered) was weighed out, and 3 g of copper sulfate pentahydrate was added thereto. After heating, 1 g of iron powder having an average particle size P80 of 150 μm was added. The heating was carried out at the temperatures shown in Table 1, with samples carried out at 20 to 25 °C, samples carried out at 40 to 45 °C, samples carried out at 50 to 55 °C, samples carried out at 60 to 65 °C, and samples carried out at 70 to 65 °C. A total of 5 samples were prepared at 75°C. For these samples, samples for analysis were taken after 30 and 60 minutes, respectively. Further, the reaction was completed in 120 minutes. After the reaction was completed, the mixture was filtered and the residue was washed with water and rinsed with ethyl alcohol. It was dried at 50°C and its mass was measured.

2 mL of the test sample was taken and adjusted to 50 mL with dilute hydrochloric acid. The concentrations of ruthenium, arsenic, and copper in the solution were determined using ICP-OES (SPS3100 manufactured by Seiko). For analysis of the residue, approximately 0.1 g was weighed, dissolved in aqua regia, and the concentration was measured using ICP-OES to calculate the arsenic content. The results are shown in Table 1.

It can be seen that ruthenium was precipitated by iron cementation. Further, the arsenic concentration hardly changed below 60°C, indicating that the generation of arsine was suppressed. Further, at temperatures below 60°C, the content of arsenic in the precipitate was low, indicating that it did not react with iron and remained in the liquid.

When iron was added, it was visually confirmed that a copper-brown slurry was formed in the liquid. This indicates that copper was deposited on the iron surface. It is thought that the copper precipitation protected the iron surface, and as a result, the reaction with acids and arsenic was suppressed. Ruthenium was cemented directly with iron or by copper deposited on the iron surface.

Other compositions of the iron cementation precipitate were copper, selenium, and tellurium. If these elements are contained in the solution after selenium separation, they may precipitate on the surface of iron and inhibit the reaction. Since copper further reacts with ruthenium ions, there is no major problem, but it is preferable to adjust the total concentration of selenium and tellurium to 300 mg/L or less. More preferably, it is 200 mg/L or less.

(Experiment example 2)
200 mL of the same selenium-separated solution as in Experimental Example 1 was collected. The mixture was heated to 50°C, and copper sulfate pentahydrate and iron powder in the amounts shown in Table 2 were added and stirred. Since the solution after selenium separation contained about 2.3 g/L of copper, in the experimental example of "decrease" in the column of "copper sulfate" in Table 2, sodium thiosulfate 5 water was used to reduce the initial copper concentration. After adding 4 g of copper sulfide to precipitate copper as copper sulfide, iron powder was added without filtration. In the case of 0.5 g twice, 0.5 g of iron powder was added at the start of the reaction and after sample collection 60 minutes later. Samples for analysis were taken after 30 and 60 minutes. The reaction was completed in 120 minutes.
The analysis of the test sample was conducted in accordance with Experimental Example 1. The results are shown in Table 2.

Ruthenium cementation efficiency is low when copper concentration is high. This is thought to be due to the fact that copper precipitates and coats the iron surface, resulting in loss of reactive surface. Therefore, when iron is used as iron powder, the copper concentration is preferably 6 g/L or less as shown in Table 2. When iron becomes a metal lump or metal plate, this concentration ratio does not apply.

Furthermore, when the copper concentration is low, the arsenic concentration also decreases, and arsenic is mixed into the precipitate. Since the initial concentration of arsenic is about 1.4 g/L, about 280 mg of arsenic is contained in 200 ml. In Table 2, in the case of "reduction" where the most arsenic was precipitated, 40 mg of arsenic was distributed in the liquid and 210 mg was distributed in the precipitate based on the final arsenic concentration, and almost no arsenic gas leaked out of the system as highly toxic arsine gas. Therefore, the copper concentration needs to be 0.06 g/L or more. Furthermore, from the results in Table 2, it is necessary that the copper concentration be 1.5 g/L or more in order to leave most of the arsenic in the liquid.

Although it depends on the concentration of copper, when iron powder is added, the amount of iron to be added may be 30 to 300 times the mass of ruthenium. Since the concentration of ruthenium in the stock solution was 8 mg/L, the effect was seen even when 0.5 g was added, and it was significant when the amount of iron powder was 1 g or more.

(Experiment example 3)
200 mL of the same selenium-separated solution as in Experimental Example 1 was collected. The mixture was heated to 50°C to 70°C, and various amounts of copper sulfate pentahydrate and iron powder were added and stirred. The solution after selenium separation contained about 2.3 g/L of copper, so in some experiments, sodium thiosulfate pentahydrate was added to lower the initial copper concentration to precipitate the copper as copper sulfide. After that, iron powder was added without filtration. The reaction was completed in 120 minutes.
The analysis of the test sample was conducted in accordance with Experimental Example 1. The amounts of ruthenium and arsenic precipitated are shown in FIGS. 1 and 2, with the mass ratio of copper in the liquid and added iron powder plotted on the horizontal axis.

According to FIG. 1, in order to effectively precipitate ruthenium, it is preferable that the copper/iron mass ratio in the liquid is 2 or less. According to FIG. 2, in order to suppress precipitation of arsenic, it is preferable that the copper/iron mass ratio in the liquid is 0.5 or more.

(Experiment example 4)
200 mL of the same selenium-separated solution as in Experimental Example 1 was collected. Unless otherwise specified, the mixture was heated to 50° C., 3 g of copper sulfate pentahydrate and iron powder were added, and stirred. Samples for analysis were taken after 30 and 60 minutes. After 60 minutes, the sample was collected and the liquid temperature was raised to 70 to 75°C. The reaction was completed in 120 minutes. For comparison, the results of Experimental Example 1 at 50 to 55°C and 70 to 75°C are also shown.
2 mL of the test sample was collected and adjusted to 50 mL using the same procedure as in Experimental Example 1. The concentrations of ruthenium, arsenic, and copper in the solution were determined using ICP-OES (SPS3100 manufactured by Seiko). The results are shown in Table 3.

By adjusting the reaction temperature in two steps, cementation of ruthenium did not worsen. The required amount of iron addition remained unchanged in the two-step temperature reaction.

The final ruthenium and tellurium concentrations are somewhat higher than when the reaction is carried out at 70°C from beginning to end, but the reaction time at 70°C is different. This is more efficient compared to 50°C. Regarding these two valuable elements, it was more efficient than reacting at 50°C, but less effective than reacting at 70°C.

Arsenic is not a problem in the two-step temperature reaction, and the tendency is the same as that of ruthenium, but it is desirable to leave arsenic in the liquid without precipitating it. Therefore, arsenic separation is better than when the reaction is carried out at 70°C, but the selectivity is lower than when the reaction is carried out at 50°C. In a two-stage temperature reaction, the reaction time can be set depending on the arsenic content and ruthenium content of the liquid, since the reaction has properties intermediate between high temperature and medium temperature.

Claims (9)

A method for recovering ruthenium from an acidic solution containing ruthenium and arsenic, the method comprising:
A method for recovering ruthenium, comprising adjusting the copper concentration of the acidic solution to 0.06 g/L or higher, bringing iron into contact with the solution at a temperature of 20° C. or higher, and recovering ruthenium by cementation. 2. The method for recovering ruthenium according to claim 1, wherein the amount of iron is 5 times or more by mass as compared to ruthenium. Adjusting the copper concentration of the acidic solution by adding a water-soluble copper salt or a copper electrolyte,
Ruthenium recovery according to claim 1 or 2, characterized in that the temperature of the acidic solution is maintained at 75° C. or lower and the copper concentration of the acidic solution is maintained at 0.03 g/L or higher until the end of the cementation. Method. The method for recovering ruthenium according to any one of claims 1 to 3, characterized in that before adding iron to the acidic solution, the copper concentration is adjusted to 1.5 g/L or more. The average particle size of the iron is 1 mm or less, the amount of iron added is 30 to 300 times the mass of ruthenium contained in the acidic solution, and the concentration of copper is 1.2 mass times that of ruthenium contained in the acidic solution. The method for recovering ruthenium according to any one of claims 1 to 4, characterized in that the amount is adjusted to be less than twice as much. According to any one of claims 1 to 5, the iron is iron powder, and is added so that the mass ratio of copper/iron to the copper in the acidic solution is 0.5 to 2. The described method for recovering ruthenium. Before adding iron to the acidic solution, add sulfur dioxide, sulfite, or sulfite to the acidic solution to adjust the total concentration of gold, platinum, palladium, selenium, and tellurium to 300 mg/L or less. The method for recovering ruthenium according to any one of claims 1 to 6. The acidic solution further contains copper and tellurium,
A claim characterized in that the iron is brought into contact with the acidic solution at a liquid temperature of 20° C. or higher and lower than 60° C. to precipitate copper on the surface of the iron, and then heated to 70° C. or higher to precipitate ruthenium and tellurium. The method for recovering ruthenium according to any one of Items 1 to 7. The cementation is started by adjusting the copper concentration of the acidic solution to 0.3 g/L or more, and the copper concentration of the acidic solution is maintained at 0.3 g/L or more until the end of the cementation. The method for recovering ruthenium according to claim 8.