JP6882110B2 - Method for recovering precipitates containing platinum group elements - Google Patents

Description

The present invention relates to a method for precipitating and recovering from an acidic hydrochloric acid solution containing Se and one or more selected from the group consisting of Te, Ru, Pd, Pt and Rh. In particular, the present invention relates to a method for recovering a precipitate, which is applied to a slime treatment step generated in an electrolytic refining step of copper smelting.

In the copper pyrometallurgy, copper concentrate is melted to obtain 99% or more blister copper in a converter and a purification furnace, and then electrolytic copper having a purity of 99.99% or more is produced in the electrolytic refining process. In recent years, metal scraps containing precious metals derived from electronic parts have been introduced as recycling raw materials in converters, and valuable resources other than copper are precipitated as slime during electrolytic refining.

In addition to gold, silver, platinum and palladium, this slime also concentrates rare metals such as ruthenium, rhodium and iridium, and selenium and tellurium contained in copper concentrate. These elements are individually separated and recovered as copper smelting by-products.

A hydrometallurgy method is often applied to the treatment of this slime. For example, Patent Document 1 discloses a method in which silver is recovered from slime by hydrochloric acid-hydrogen peroxide, dissolved gold is recovered by solvent extraction, and then other valuable resources are sequentially reduced and recovered by sulfur dioxide. Patent Document 2 discloses a method of recovering gold and silver by the same method, reducing valuable resources with sulfur dioxide to precipitate them, and distilling and removing only selenium to concentrate precious metals.

The solution after recovering the noble metal contains rare metal ions, tellurium, and selenium, and it is necessary to recover these valuable resources. As a recovery method, a method of recovering the precipitate generated by the reducing agent and a method of mixing the solution with copper concentrate, drying it with a dryer, and repeating it in a smelting furnace are known.

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

Japanese Unexamined Patent Publication No. 2001-316735 Japanese Unexamined Patent Publication No. 2004-190134

In the method of recovering valuable resources using sulfur dioxide, the valuable resources are sequentially reduced and recovered after dissolution, but there are not a few valuable resources that finally remain in the liquid. However, if heating and sulfur dioxide supply are continued for a long time, all valuable resources can be recovered, but there are problems of production efficiency and energy cost per unit time.

If a stronger reducing agent such as hydrazine or zinc powder is added, most of the valuable resources can be recovered, but there are problems such as reagent cost and generation of various gases. In addition, the cost required for wastewater treatment will increase.

In particular, it is preferable to recover almost all of selenium and tellurium at the final stage of slime treatment. Emission standards are set for selenium and tellurium, and it is necessary to ensure that they are collected. In the wastewater treatment process, it is often treated by the coprecipitation method, and the valuable resources recovered by coprecipitation are sludge containing a coprecipitation agent and are treated as industrial waste. In this way, valuable resources are discarded, which is not preferable.

However, there are cases where selenium and tellurium are less likely to be reduced by sulfur dioxide at a certain frequency. The cause is unknown, but in this case sulfur dioxide is supplied for a long time, but the production efficiency decreases.

Further, when a compound having a ketone group is present in the liquid at a certain concentration or more, selenous acid is less likely to be reduced by sulfur dioxide. Ketones have the ability to reduce selenous acid, but excessive amounts rather suppress the precipitation of selenous acid, making it difficult to reduce it below a certain value. In this case as well, in order to satisfy the wastewater standards, it is necessary to take further measures such as removing organic substances by heating and diluting the liquid.

On the other hand, when ketones are added, ruthenium is easily reduced by sulfur dioxide. Ruthenium is relatively expensive, and it is important to recover it from the final solution so that it does not mix as impurities in other valuable resources. The addition of ketones is necessary from the viewpoint of ruthenium recovery, but the addition amount is preferably small.

Furthermore, when the target liquid contains valuable resources such as ruthenium and rhodium, these valuable metals are reduced and precipitated after the reduction of selenium and tellurium due to the redox potential (ORP). If selenium and tellurium are effectively reduced, the recovery of valuable metals will proceed smoothly. In particular, ruthenium has a high recovery efficiency when ketones are added.

In view of such conventional circumstances, the present invention is acidic containing Se generated in an electrolytic slime treatment step of copper smelting and one or more selected from the group consisting of Te, Ru, Pd, Pt and Rh. Provided is a method for satisfactorily separating and recovering one or more selected from the group consisting of Te, Ru, Pd, Pt and Rh from a liquid.

The present invention is specified as follows.
(1) In a method for recovering a precipitate from an acidic hydrochloric acid solution containing Se and one or more selected from the group consisting of Te, Ru, Pd, Pt and Rh.
The concentration of selenous acid in the hydrochloric acid acidic solution is adjusted in advance to 10 to 500 mg / L as the selenium concentration, and then ketones are added to the hydrochloric acid acidic solution, and then reducing sulfur is supplied to the hydrochloric acid acidic solution again. This is characterized by recovering a precipitate containing at least one selected from the group consisting of Te, Ru, Pd, Pt and Rh.
Method of collecting sediment.
(2) The method for recovering a precipitate according to (1), wherein the selenous acid concentration is adjusted by reducing and precipitating the selenous acid in the liquid with a reducing sulfur compound.
(3) To adjust the selenous acid concentration, the oxidation-reduction potential is reduced to less than 480 mV using a silver-silver chloride electrode as a reference electrode, and then a selenite or selenous acid-containing solution is added to the hydrochloric acid acidic solution. The method for recovering the precipitate according to (1) or (2).
(4) The oxidation-reducing potential is one or more of nitric acid, nitrate, hydrogen peroxide, Fe (III) compound, hypochlorite, hypochlorite, selenous acid, and selenate as an oxidizing agent. The method for recovering a precipitate according to (3), which is prepared by adding one or more of sulfur dioxide, sulfurous acid, and sulfite as a reducing agent.
(5) The method for recovering a precipitate according to any one of (1) to (4), wherein the amount of the ketones added is 5 mol times or more the amount of ruthenium.
(6) The method for recovering a precipitate according to any one of (1) to (5), wherein the ketone is any one of acetone, hydroxyacetone, and 2-butanone.
(7) The method for recovering a precipitate according to any one of (1) to (6), wherein the ketones are added and stirred for 5 minutes or more, and then sulfur dioxide is supplied as reducing sulfur.
(8) When reducing sulfur is supplied to the hydrochloric acid acidic liquid again after adding ketones to the hydrochloric acid acidic liquid, the temperature of the hydrochloric acid acidic liquid is 80 ° C. or higher (1). )-(7). The method for recovering the precipitate according to any one of (7).

According to the present invention, Te, Ru from an acidic liquid containing Se generated in an electrolytic slime treatment step of copper smelting and one or more selected from the group consisting of Te, Ru, Pd, Pt and Rh. , Pd, Pt and Rh can be provided as a method for satisfactorily separating and recovering one or more selected from the group.

It is a figure which shows the selenous acid concentration at the time of adding a ketone, the selenium concentration after 3 hours, and the ruthenium recovery rate. The horizontal axis of FIG. 1 is changed from the initial Se concentration to 0 to 1 g / L. It is a figure which shows the relationship between the selenium concentration and ORP when sulfur dioxide is blown. It is a figure which shows the time-dependent change of ruthenium when sulfur dioxide is supplied by changing the amount of acetone added.

The method for recovering the precipitate of the present invention is a method for recovering the precipitate from an acidic hydrochloric acid solution containing Se and one or more selected from the group consisting of Te, Ru, Pd, Pt and Rh. The concentration of selenium in the acidic solution is adjusted in advance to 10 to 500 mg / L as the selenium concentration, and then ketones are added to the hydrochloric acid acidic solution, and then reducing sulfur is supplied to the hydrochloric acid acidic solution again. It is characterized by recovering a precipitate containing one or more selected from the group consisting of Te, Ru, Pd, Pt and Rh.

In general, electrolytic slimes produced in the electrolytic refining process of non-ferrous metal smelting, especially copper smelting, are rich in chalcogen elements and precious metals. For example, gold is 10 to 30 kg / t, silver is 100 to 250 kg / t, palladium is 1 to 3 kg / t, platinum is 200 to 500 g / t, tellurium is 15 to 25 kg / t, and selenium is 5 to 15 wt%. Contains to some extent.

Hydrochloric acid and hydrogen peroxide are added to dissolve this electrolytic slime, but silver forms an insoluble silver chloride precipitate with chloride ions immediately after dissolution. In the case of a solution containing an oxidizing agent and chlorine, for example, aqua regia or chlorine water, precious metals can be dissolved and silver can be separated as silver chloride. Since it is a chloride bath, noble metal elements, rare metal elements, selenium, and tellurium are distributed in the leachate noble liquid (PLS).

The leached noble liquid (PLS) is cooled once to precipitate and separate chlorides of base metals such as lead and antimony. After that, the gold is separated into an organic phase by solvent extraction. Dibutyl carbitol (DBC) is widely used as a gold extractant.

Valuables can be precipitated and recovered by reducing PLS after extracting gold, but the order of precipitation is naturally determined because the redox potential differs depending on the element. First, precious metals, then chalcogens such as selenium and tellurium, and then the inert noble metals are precipitated.

After recovering the precious metals, the selenium in the liquid is reduced and solid-liquid separated to recover the selenium. Reducing sulfur is used as the reducing agent in terms of price and efficiency, and sulfur dioxide is most suitable because it can be supplied in large quantities and at low cost by roasting linz-Donaw gas or sulfide ore. From the viewpoint of recovering high-purity selenium, selenium is not completely recovered, and the liquid after recovering selenium contains 2 to 4 g / L of selenium. The liquid after selenium recovery also contains 200 to 1000 mg / L of tellurium and 50 to 300 mg / L of ruthenium and rhodium.

After recovering selenium, reducing sulfur is further blown into the liquid to recover valuable resources remaining in the liquid. At this time, valuable resources such as tellurium, ruthenium, and rhodium are also reduced and recovered at the same time. However, ruthenium is particularly susceptible to reduction by sulfur dioxide, so ketones are added for the following reasons.

Tetravalent selenium oxide, such as selenium dioxide and selenous acid, is known to have a selenoxide oxidation reaction that reacts with an allyl compound, and the same reaction occurs with ketones (Formula 1). Selenoxide oxidation refers to the electrophilic reaction of selenous acid or selenium dioxide to π electrons and the subsequent sigmatropic rearrangement.
H ₂ SeO ₃ + 2CH ₃ C (O) CH ₃ → 2CH ₃ C (O) CH ₂ OH + H ₂ O + Se ↓ (1)

The reaction product of this reaction is a multidentate ligand and replaces the chloride ion complex of a transition metal such as ruthenium. The complex after this substitution is relatively susceptible to reduction by sulfur dioxide, and it is expected that the recovery rate of ruthenium will be improved.

A small part of the ketone exists as an enol due to keto-enol tequation. As another mechanism, it is also considered that reduction occurs due to electron transfer from the π electron of the enol that occurs instantaneously. These two reaction mechanisms can proceed at the same time. Any of the ketones is effective, but the water-soluble ketones have high reaction efficiency, and a ketone group-containing substance having a low price is preferable. Specific examples thereof include acetone, hydroxyacetone and butanone.

This reducing effect is highly effective against soft acids, as is known as HSAB law. Typical soft acids are platinum group ions, and palladium, gold, platinum, and rhodium are known in addition to ruthenium.

However, as the amount of ketone added increases, selenium becomes less susceptible to reduction by sulfur dioxide. In particular, when 40 ml or more of ketones are added to 1 L of the target liquid, the reduction rate by sulfur dioxide significantly decreases from the time when the selenium concentration reaches about 150 to 200 mg / L or less. The reason for this is not clear, but it is hypothesized that in the selenoxide oxidation reaction of formula 1, if the intermediate generated when the electrophilic attack of selenium occurs does not cause dislocation, it remains stable in the solution.

Therefore, the minimum amount of ketones required should be added. This amount depends on the ruthenium concentration, but is about 5 mM with acetone when ruthenium is 300 mg / L. At that time, it is essential to generate the reaction of Equation 1.

According to Equation 1, the concentration of selenium cannot be set to 0 from the beginning. Therefore, the concentration of selenium should be lowered as much as possible before adding ketones and reducing with sulfur dioxide. The required concentration of selenium is 10 mg / L or more. From this viewpoint, the concentration of selenium is preferably 20 mg / L, more preferably 50 mg / L. On the other hand, if the concentration of selenium exceeds 500 mg / L, it becomes difficult to recover a part of selenium as a precipitate. When the selenium concentration is too low, if the ORP increases due to the addition of various oxidizing inorganic salts, the gradually precipitated selenium in the solution dissolves, so that the selenium concentration recovers.

The concentration of selenium can be adjusted by reducing and precipitating selenous acid in the liquid with a reducing sulfur compound. The precipitated selenium is separated by an appropriate method, and the liquid after recovery is transferred to the next step.

The reducing sulfur used in the present invention is an inorganic sulfur compound having a reducing ability, and examples thereof include sulfur dioxide, hydrogen sulfide, sodium sulfide, sodium hydrogen sulfide, sulfite, sodium hydrogen sulfite, sodium sulfite and sodium thiosulfate.

The concentration of selenous acid can be adjusted by reducing the ORP using a silver-silver chloride electrode as a reference electrode until it reaches less than 480 mV, and then adding a selenate or selenous acid-containing solution to the acidic hydrochloric acid solution. it can.

Sulfur dioxide, sulfurous acid and salts thereof are suitable for adjusting the ORP. If these reducing agents are added in excess, the effect of adding ketones is diminished, so it is necessary to decompose them. The oxidizing agent that decomposes is not specified as long as it can oxidize sulfur dioxide, but hydrogen peroxide, Fe (III) compounds, and hypochlorous acids are present in the system and do not affect wastewater treatment or other elements. , Selenous acids are suitable. It is sufficient that the ORP can be adjusted within a predetermined range regardless of which reagent is used. More specifically, ORP is any one or more of nitric acid, nitrate, hydrogen peroxide, Fe (III) compound, hypochlorite, hypochlorite, selenous acid, and selenate as an oxidizing agent. It can be adjusted by adding any one or more of sulfur dioxide, sulfurous acid, and sulfite as a reducing agent.

In the presence of sulfur dioxide, ketones have little improvement in ruthenium recovery. Therefore, ketones should be added after sufficient sulfur dioxide has been removed. When the selenium concentration is lowered by using sulfur dioxide in advance, there is no problem if the redox potential with the reference electrode as silver-silver chloride is higher than 480 mV. More preferably, it is 485 mV or more.

Even if sulfur dioxide is present in the liquid, sulfur dioxide may be oxidized by adding selenite or selenous acid. Alternatively, hydrogen peroxide, hypochlorous acids, and Fe (III) salts that effectively oxidize sulfur dioxide can also be applied. However, when As (III) or the like is contained like the electrolytic slime treatment liquid, the amount of the oxidizing agent added increases and the impurities in the recovered valuables increase, so that selenate or selenous acid is used. Is preferable.

After adding the ketones, the mixture is stirred at 70 ° C. or higher for 5 minutes or longer to accelerate the reaction of Formula 1. The reaction can be detected by the turbidity of the solution due to the precipitation of selenium. In some cases, the ruthenium and tellurium concentrations vary from lot to lot, so it is more preferable to stir for 15 minutes or more. If this stirring time is insufficient, the amount of ketones added will be insufficient.

In the case of acetone, the amount of ketones added is 0.5 ml / L of acetone with respect to 100 mg / L of ruthenium. This is about 6 times as much as ruthenium in terms of amount of substance. The effect is recognized even if it is about 4 times, but it is not so great. Therefore, the amount of ketones added should be 5 mol times or more that of ruthenium. On the contrary, when an amount exceeding 15 ml / L (150 mol times) of acetone is added, the reduction of selenium by sulfur dioxide is significantly inhibited.

Selenite or selenous acid is most suitable for the oxidative removal of sulfur dioxide by oxidizing inorganic salts. Selenium supply can be achieved at the same time by directly oxidizing sulfur dioxide with selenous acid. This is because the reaction time required for redissolving selenium can be significantly omitted as well as the increase in ORP. No problem occurs even if the undiluted solution is added to adjust the selenium concentration.

After adding the ketone and stirring thoroughly, the supply of sulfur dioxide as reducing sulfur is started. When the temperature of the liquid is 80 ° C. or higher, in addition to improving the reactivity of sulfur dioxide, the direct reducing effect from the ketone becomes remarkable. The supply rate and concentration of sulfur dioxide are not particularly limited.

The concentration of selenium is preferably 10 mg / L or less at the end of the reaction. More preferably, it is 1 mg / L or less. When the precipitate formed in the reaction is separated by an appropriate method, a valuable precipitate containing ruthenium and rhodium in addition to selenium and tellurium is obtained.

The upper limit of the total amount of substances of ruthenium and tellurium contained in the metal-containing hydrochloric acid acidic solution of acetone is not particularly limited. The greater the number, the better the reducing effect, but it should be adjusted in terms of cost and drainage.

The precipitate containing one or more selected from the group consisting of Te, Ru, Pd, Pt and Rh recovered by the method for recovering the precipitate of the present invention can be further used as a noble metal raw material for each of various elements as needed. Purified and separated.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

Copper was removed from the electrolytic slime recovered from copper smelting with sulfuric acid. Concentrated hydrochloric acid and 60% hydrogen peroxide solution were added and dissolved, and solid-liquid separation was obtained to obtain PLS. The PLS was cooled to 6 ° C. to precipitate and remove base metals. Gold was extracted by mixing DBC (dibutyl carbitol) and PLS.
The PLS after gold extraction was heated to 70 ° C., and exhaust gas from a copper smelting converter was blown in to reduce the noble metal and separate it into solid and liquid. The separated solution was heated again to 70 to 75 ° C. and the exhaust gas from the copper smelting converter was blown into it. Crude selenium was separated by solid-liquid separation, and a liquid was obtained after selenium separation.

(Experimental Example 1) Relationship between selenium concentration at the start of the reaction and the precipitation rate of valuable resources Sodium sulfite was added to 300 ml of the selenium separation solution (components are shown in Table 1) to prepare target solutions with various selenium concentrations. The mixture was heated to 70 to 75 ° C., 1 ml of acetone was added, and the mixture was stirred for 15 minutes, and it was confirmed that turbidity was generated. A mixed gas of sulfur dioxide and air (8 to 20 vol%) was blown at about 2 L / min and stirred. Samples were taken at regular intervals and diluted appropriately with hydrochloric acid. The concentrations of various elements were quantified by ICP-OES (SPS3100 manufactured by Seiko Corporation). The recovery rate was calculated from the residual concentration of ruthenium. The results are shown in FIGS. 1 and 2.

Since the ruthenium recovery rate when no ketones were added was 34%, improvement by adding ketones can be confirmed. However, if the selenium concentration is excessively low when the ketone is added, the effect is weak. On the contrary, if ketones are added and reduced while the selenium concentration is high, the selenium concentration after 3 hours becomes high. Normally, the reduction of selenium by sulfur dioxide when no ketone is added reaches 1 mg / L or less within 2 hours. From FIGS. 1 and 2, it can be understood that the optimum selenium concentration at the time of adding the ketone is 10 to 500 mg / L. In this example, all selenium forms were selenous acid.

(Experimental Example 2) Relationship between ORP and selenium concentration 200 ml of the same selenium-separated liquid as in Experimental Example 1 was taken. The mixture was heated to 70 to 75 ° C. and a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20%) was blown at 0.1 L / min. The ORP in the liquid was measured at predetermined time intervals, and 1 ml of a sample for quantitative analysis was taken. The sample was immediately transferred to a 50 ml volumetric flask containing 10 ml of 5 g / L iron chloride solution. As an internal standard, 2 ml of yttrium 50 mg / L solution was added for regulation. After filtration through 5C filter paper, the concentration was quantified by ICP-OES.

The concentration of selenium and the value of ORP with respect to the blowing time of sulfur dioxide are shown in FIG. The initial ORP was over 550 mV, but soon dropped to less than 500 mV due to the supply of sulfur dioxide. At the same time, the concentration of selenium also drops sharply. The ORP stabilizes for a while at around 490 mV, but it is presumed that the redox reaction of selenous acid mainly controls this potential.

With the disappearance of selenite, the ORP begins to decline again. The ORP at that time was about 470 mV. When sulfur dioxide is further supplied, the ORP reduction rate slows down near 400 mV and stabilizes at 350 mV. It is shown that some oxidized species remain in the liquid up to about 400 mV, and at 350 mV, the ORP-dominated species in the solution become sulfur dioxide and sulfurous acid.

The concentrations of ruthenium, tellurium and rhodium did not change until the end of the reaction. Therefore, it is considered that selenium in the liquid almost disappears when the ORP in the liquid reaches 480 mV or less. However, as described above, some selenic acid is required to generate the reaction of formula 1, and sulfur dioxide and sulfite ions diminish the effect of adding ketones, so a selenate or selenate ion-containing solution To adjust the ORP. As the selenite ion-containing liquid, a liquid after selenium separation can be used.

(Experimental Example 3)
Sodium sulfite was added to 300 ml of the selenium separation solution to adjust the selenium concentration. The mixture was heated to 70 to 75 ° C., 5 ml of various ketones was added, and the mixture was stirred for 15 minutes. Acetone, 2-butanone, hydroxyacetone, and pyruvic acid were selected as various ketones. Then, a mixed gas of sulfur dioxide and air (8 to 20 vol%) was blown at about 2 L / min and stirred. Samples were taken at regular intervals and diluted appropriately with hydrochloric acid. The concentrations of various elements were quantified by ICP-OES (SPS3100 manufactured by Seiko Corporation). Then, the amount of precipitation was calculated based on the concentration before the reaction, and used as the recovery rate. The results are shown in Table 2.

According to Table 2, although the recovery rate of selenium was different depending on the type of ketone, a high ruthenium recovery rate and tellurium recovery rate can be obtained regardless of the addition of any of the compounds having a ketone group. Moreover, the reaction was quick. Acetone, hydroxyacetone and 2-butanone can be said to be suitable additives for the recovery of ruthenium, tellurium and selenium.

(Experimental Example 4)
300 ml of another lot of selenium-separated solution prepared by the same operation as in Experimental Example 1 was taken. Table 3 shows the components of the liquid after selenium separation. It was heated to 70 ° C. and a mixed gas of sulfur dioxide and air (sulfur dioxide concentration 5 to 20%) was blown at 0.1 L / min. When the ORP of the solution reached 470 mV, the supply of gas was stopped and the undiluted solution after selenium separation was added until the ORP reached 490 mV or more. The amount added was about 10 to 30 ml. The mixture was heated to 80 to 83 ° C., 0 to 5 ml of acetone (special grade manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the mixture was stirred for 15 minutes. Then, a mixed gas of sulfur dioxide and air was blown in again, and 2 ml of a sample for quantitative analysis was taken at predetermined time intervals. The sample collected was adjusted to 50 ml by adding 1 ml of yttrium 50 mg / L solution as an internal standard.
The time course of the Ru concentration is shown in FIG. The change with time was observed with the time when the blowing of the sulfur dioxide and the air mixed gas was started after the addition of acetone as 0 hour.

Efficient ruthenium recovery can be achieved by adjusting the ORP to remove selenium, then adding a stock solution to adjust the selenium concentration, and then adding acetone. An effect was also observed when the amount of acetone added was 1.5 ml / L.

Claims (8)

In a method for recovering a precipitate from an acidic hydrochloric acid solution containing Se and one or more selected from the group consisting of Te, Ru, Pd, Pt and Rh.
The concentration of selenous acid in the hydrochloric acid acidic solution is adjusted in advance to 10 to 500 mg / L as the selenium concentration, and then ketones are added to the hydrochloric acid acidic solution, and then reducing sulfur is supplied to the hydrochloric acid acidic solution again. This is characterized by recovering a precipitate containing at least one selected from the group consisting of Te, Ru, Pd, Pt and Rh.
Method of collecting sediment. The method for recovering a precipitate according to claim 1, wherein the selenous acid concentration is adjusted by reducing and precipitating the selenous acid in the liquid with a reducing sulfur compound. The adjustment of the selenous acid concentration is carried out by reducing the oxidation-reduction potential using a silver-silver chloride electrode as a reference electrode until it reaches less than 480 mV, and then adding a selenite or selenous acid-containing solution to the hydrochloric acid acidic solution. The method for recovering a precipitate according to claim 1 or 2, wherein the deposit is collected. The oxidation-reduction potential is any one or more of nitric acid, nitrate, hydrogen peroxide, Fe (III) compound, hypochlorite, hypochlorite, selenous acid, and selenate as an oxidizing agent, as a reducing agent. The method for recovering a precipitate according to claim 3, wherein the preparation is made by adding any one or more of sulfur dioxide, sulfurous acid, and sulfite. The method for recovering a precipitate according to any one of claims 1 to 4, wherein the amount of the ketones added is 5 mol times or more the amount of ruthenium. The method for recovering a precipitate according to any one of claims 1 to 5, wherein the ketone is any one of acetone, hydroxyacetone, and 2-butanone. The method for recovering a precipitate according to any one of claims 1 to 6, wherein the ketones are added and stirred for 5 minutes or more, and then sulfur dioxide is supplied as reducing sulfur. Claims 1 to 7, wherein the temperature of the hydrochloric acid acidic liquid is 80 ° C. or higher when reducing sulfur is supplied to the hydrochloric acid acidic liquid again after adding ketones to the hydrochloric acid acidic liquid. The method for recovering the precipitate according to any one of the above.

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