JP2024031675A - Method of recovering ruthenium and iridium - Google Patents

Abstract

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

Description

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

In copper pyrometallurgy, copper concentrate is melted and converted into 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. Valuables other than copper precipitate as precipitates during electrolytic refining.

Precious metals, rare metals, and selenium, tellurium, and arsenic contained in copper concentrate are also concentrated in this deposit. These elements are separately separated and recovered as copper smelting by-products.

A hydrometallurgical method is often applied to treat this precipitate. For example, Patent Document 1 discloses a method in which silver is recovered from a precipitate using hydrochloric acid-hydrogen peroxide, dissolved gold is recovered by solvent extraction, and other valuables 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 distilled and removed 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.

In particular, the method shown in Patent Document 1 for recovering the precipitate caused 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 and ruthenium have a relatively low oxidation-reduction potential (ORP), so they are difficult to undergo reduction and remain in the solution until the end. Regarding iridium, as described in Patent Document 3, a widely known method is to recover iridium by separating it by solvent extraction, concentrating it, and then baking it. Further, Patent Document 4 discloses a method in which a base metal selected from magnesium, aluminum, zinc, iron, tin, and lead and a mineral acid are added to an organic solvent containing iridium to reduce and precipitate the noble metal.

Japanese Patent Application Publication No. 2001-316735 Japanese Patent Application Publication No. 2016-160479 Japanese Patent Application Publication No. 2004-332041 Japanese Patent Application Publication No. 2002-115015

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

On the other hand, to recover ruthenium by distillation, a strong oxidizing agent such as NaBrO ₃ is used. The reagent cost of the oxidizing agent is high, and this method is not suitable for recovering ruthenium from a dilute solution with a ruthenium concentration of about 50 to 200 mg/L and many impurities, such as a copper electrolyte solution. Furthermore, ruthenium tetroxide, which is a distillation fraction, is highly toxic and there are safety issues in recovering it by distillation.

Cementation with base metals such as zinc is effective for both iridium and ruthenium. However, for solutions derived from copper electrolytic precipitates, cementation with base metals is problematic because coexisting arsenic is reduced to highly toxic hydrogen arsenide. Furthermore, copper in the solution also undergoes cementation and gets mixed in, necessitating an additional separation step from the copper.

Cementation with base metals requires the use of large amounts of metal to increase the recovery rate. Under strong acid conditions, there is a problem that hydrogen is generated intensively in a short period of time and boils over, or hydrogen generated due to static electricity, etc., explodes. In addition, the reaction efficiency is low because other elements that undergo cementation are also present.

It is known that the hydroxides of iridium and ruthenium precipitate. However, as a general problem, if strong acids are to be neutralized, the cost of alkaline reagents is high. 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, it is expected that this poorly soluble sulfate will deposit in the piping of the manufacturing equipment and cause blockage.

Furthermore, there is no known method for recovering low-concentration iridium and ruthenium from a strongly acidic solution at low cost and efficiently.

In view of such conventional circumstances, the present invention provides a method for efficiently recovering ruthenium and iridium from an acidic liquid containing ruthenium and iridium. In particular, an acidic liquid containing ruthenium and iridium in which arsenic is dissolved as an impurity is suitable as the acidic liquid containing ruthenium and iridium of the present invention.

The above problem can be solved by the invention specified below.
That is, the present invention includes the following inventions.
[1] A water-soluble inorganic iodine compound or elemental iodine is added to an acidic liquid containing ruthenium, iridium, and arsenic, and sulfur dioxide or hydrogen sulfide is further blown into the acidic liquid, or an aldehyde reducing agent is added. an arsenic reduction process to reduce arsenic to trivalent,
The acidic solution obtained in the arsenic reduction step was adjusted to 70°C or lower, and hydrogen sulfide or sodium hydrogen sulfide was added until ORP (redox electrode potential, reference electrode Ag/AgCl) reached 150 mV or lower to precipitate sulfide. an impurity removal process that separates substances from solid to liquid;
After the impurity removal step, a ruthenium and iridium recovery step of adjusting the liquid temperature of the filtrate to 40° C. or higher and adding a sodium thiosulfate salt or a solution containing thiosulfate ions to precipitate ruthenium and iridium;
A method for recovering ruthenium and iridium, including
[2] In the impurity removal step, if a precipitate is generated in the arsenic reduction step, after solid-liquid separation, the temperature is adjusted to 70 ° C. or lower, and the hydrogen sulfide or sodium hydrogen sulfide is added until ORP reaches 150 mV or lower. The method for recovering ruthenium and iridium according to [1].
[3] Between the impurity removal step and the ruthenium and iridium recovery step, the temperature of the filtrate obtained in the impurity removal step is further adjusted to 70°C or less to add 0.5 to 5 g/g of metallic iron. The method for recovering ruthenium and iridium according to [1] or [2], which includes the step of selectively precipitating ruthenium by adding L such that ruthenium becomes L.
[4] The inorganic iodine compound is one or more of iodine, potassium iodide, sodium iodide, potassium iodate, and sodium iodate, and has a content of 0.05 g/L or more when converted to potassium iodide. The method for recovering ruthenium and iridium according to any one of [1] to [3].
[5] The inorganic iodine compound is one or more of potassium iodide, sodium iodide, potassium iodate, and sodium iodate, and when copper is dissolved in the acidic liquid, potassium iodide The method for recovering ruthenium and iridium according to any one of [1] to [4], wherein ruthenium and iridium are added in an amount of 0.05 to 4 times the mass of copper when converted.
[6] In the arsenic reduction step, the acidic liquid containing ruthenium and iridium and arsenic is an acidic liquid after dissolving a metal electrolytic precipitate, according to any one of [1] to [5]. Method for recovering ruthenium and iridium.
[7] The iridium concentration in the acidic solution in the arsenic reduction step is 100 mg/L or less, and in the ruthenium and iridium recovery step, the sodium thiosulfate salt or thiosulfate ion-containing solution is converted into sodium thiosulfate pentahydrate. The method for recovering ruthenium and iridium according to any one of [1] to [6], wherein the ruthenium and iridium are added in an amount of 5 g/L or more.

According to the present invention, it is possible to provide a method for efficiently recovering ruthenium and iridium from an acidic liquid containing ruthenium and iridium.

1 is a flow diagram schematically illustrating an embodiment of the present invention. FIG. It is a graph showing the relationship between ORP value and copper and arsenic concentration according to an example. It is a graph showing the relationship between ORP value and ruthenium concentration according to an example.

Next, a mode for carrying out the present invention will be described in detail. It is understood that the present invention is not limited to the following embodiments, and that design changes, improvements, etc. may be made as appropriate based on the common knowledge of those skilled in the art without departing from the spirit of the present invention. Should.

FIG. 1 shows a flow diagram schematically illustrating one embodiment of the invention. The flowchart in FIG. 1 gives specific examples for each step, and the present invention is not limited to the flowchart. A method for recovering ruthenium and iridium according to an embodiment of the present invention includes adding a water-soluble inorganic iodine compound or elemental iodine to an acidic liquid containing ruthenium and iridium and arsenic, and then blowing sulfur dioxide or hydrogen sulfide into the acidic liquid. Alternatively, an arsenic reduction step in which arsenic is reduced to trivalent by adding an aldehyde reducing agent, and the acidic liquid obtained in the arsenic reduction step is adjusted to 70°C or less, and hydrogen sulfide or sodium hydrogen sulfide is added. After the impurity removal step of solid-liquid separation of precipitated sulfide by adding until ORP (oxidation-reduction electrode potential, reference electrode Ag/AgCl) reaches 150 mV or less, and after the impurity removal step, the temperature of the filtrate is increased to 40°C or higher. and a ruthenium and iridium recovery step in which ruthenium and iridium are precipitated by adjusting the thiosulfate salt and adding a sodium thiosulfate salt or a thiosulfate ion-containing solution.

In the method for recovering ruthenium and iridium according to the embodiment of the present invention, the acidic liquid to be treated is effective when it contains arsenic, copper, and lead as impurities, and is particularly effective when the acidic liquid to be treated contains arsenic, copper, and lead as impurities. Acidic liquids obtained by oxidizing and dissolving substances are good targets. The method for recovering ruthenium and iridium according to the embodiment of the present invention can also be applied to recycling from waste. That is, the acidic liquid containing ruthenium and iridium generated in the waste treatment process can also be targeted.

In the method for recovering ruthenium and iridium according to the embodiment of the present invention, when the acidic liquid to be treated is a hydrochloric acid acidic liquid obtained through a predetermined process, various materials other than ruthenium (Ru) and iridium (Ir) can be used. Contains metallic elements.

When ruthenium and iridium are separated by reduction or addition of thiosulfates, selenium (Se), platinum (Pt), palladium (Pd), gold (Au), silver (Ag), etc. react preferentially than ruthenium. As will be described in detail later, it is necessary to reduce the concentration of these elements in advance.

As an example, a method for producing a hydrochloric acid acidic solution containing ruthenium and iridium from a metal electrolytic precipitate derived from a copper electrolytic refining process of copper smelting is shown. First, copper is dissolved and removed using sulfuric acid from metal electrolytic precipitates derived from the copper electrolytic refining process of copper smelting. Next, concentrated hydrochloric acid and hydrogen peroxide solution are added and dissolved, and solid-liquid separation is performed to obtain PLS (leaching liquid). Platinum group elements, rare metal elements, chalcogen elements, arsenic, antimony, etc. are distributed in the leaching solution (PLS), which is a chloride bath.

The leach liquid (PLS) is once cooled and chlorides of base metals such as lead and antimony are separated by precipitation. The gold is then separated into an organic phase by solvent extraction. Dibutylcarbitol (DBC) is widely used as a gold extractant. By blowing sulfur dioxide into the extract, precious metals such as platinum and palladium, selenium, and tellurium are reduced and removed, followed by solid-liquid separation to create a hydrochloric acid acidic solution containing ruthenium and iridium. .

In the method for recovering ruthenium and iridium according to an embodiment of the present invention, sulfur dioxide or hydrogen sulfide is blown into an acidic liquid containing ruthenium and iridium, or an aldehyde reducing agent is added to recover platinum and gold. It is preferable to adjust the concentration of impurity elements such as , palladium and selenium to 10 mg/L or less. Examples of the aldehydes include formaldehyde, methylglyoxal, and the like. Note that if the acidic liquid to be treated has a concentration of contaminant elements such as platinum, gold, palladium, and selenium of 10 mg/L or less, there is no need to blow or add the reducing agent.

When contaminant elements are precipitated by blowing in sulfur dioxide or hydrogen sulfide or by adding a reducing agent such as an aldehyde, an inorganic iodine compound or elemental iodine is added. Inorganic iodine compounds that undergo reduction in acidic solutions produce iodide ions. This iodide ion can effectively reduce tellurium and further reduce arsenic in the acidic liquid to trivalent (chemical formula 1). As a result, the resulting elemental iodine is immediately reduced to sulfur dioxide or aldehyde, and iodide ions are regenerated (chemical formula 2). Therefore, the substance added when precipitating the impurity elements as described above may be an inorganic iodine compound or simple iodine.
(Chemical formula 1): As(V)+2I ^- → As(III)+I ₂
(Chemical formula 2): I ₂ +SO ₂ +2H ₂ O → H ₂ SO ₄ +2I ^- +2H ⁺

Inorganic iodine compounds are compounds that generate iodide ions in an aqueous solution in the presence of a reducing agent, and specifically include potassium iodide, sodium iodide, potassium iodate, sodium iodate, potassium periodate, and periodic acid. Examples include sodium.

Since iodide ions act catalytically, an inorganic iodine compound or elemental iodine may be added in an amount of 0.05 g/L or more when converted to potassium iodide. Further, the amount of the inorganic iodine compound added is preferably 0.1 to 0.5 g/L when converted to potassium iodide. However, when containing ions such as copper that cause iodide precipitation, the acidic solution must maintain an acidity of 1 mol/L or more.

In addition, since iodide ions act catalytically, inorganic iodine compounds or elemental iodine should be added in an amount of 0.05 to 4 times the mass of copper when converted to potassium iodide when copper is dissolved in an acidic solution. It is preferable. However, when containing ions such as copper that cause iodide precipitation, the acidic solution must maintain an acidity of 1 mol/L or more.

Impurities such as selenium, tellurium, platinum, and palladium are precipitated by blowing in sulfur dioxide or hydrogen sulfide, or by adding an aldehyde reducing agent. The precipitate containing these valuable substances is separated into solid and liquid, and then input into a process for further separation and purification. The liquid after solid-liquid separation contains arsenic, copper, antimony, iridium, and ruthenium.

After solid-liquid separation, a sulfurizing agent is added to the liquid to sulfurize and precipitate arsenic and copper. Hydrogen sulfide, sodium sulfide or sodium bisulfide is used as the sulfiding agent. If the liquid temperature is high, the sulfurization efficiency decreases, so the acidic liquid is adjusted to 70° C. or lower for sulfurization. The temperature of the acidic liquid during sulfurization is more preferably 50°C or lower. In addition, if no precipitate is produced by blowing in sulfur dioxide or hydrogen sulfide as described above, or by adding an aldehyde reducing agent, solid-liquid separation is not necessary, and in this case, the acidic liquid can be directly used as described above. Sulfurization is carried out by adjusting the temperature to below 70°C.

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

The amount of sulfurizing agent added varies depending on the arsenic concentration and copper concentration, but it is added until the ORP (reference electrode Ag/AgCl) reaches 150 mV or less. However, some ruthenium precipitates due to the addition of an excessive amount of sulfiding agent. Furthermore, excessive amounts of sulfiding agents have a negative effect when recovering ruthenium and iridium produced in metal cementation. Therefore, it is preferable to add it to an extent that does not reach 0 mV or less.

By adding a sulfiding agent, if the oxidized form of arsenic is trivalent, it will precipitate quantitatively, but if the oxidized form of arsenic is pentavalent, it will precipitate incompletely. For this reason, it is preferable to sufficiently reduce pentavalent arsenic to trivalent arsenic according to Chemical Formula 1.

The sulfide precipitated after sulfurization is separated into solid and liquid. The solid-liquid separated sulfide also contains valuable materials such as copper and antimony, so after drying, it can be repeatedly sent to the smelting furnace and used as a raw material for valuable materials. Iridium and ruthenium remain in the liquid (filtrate) after solid-liquid separation.

After solid-liquid separation, adjust the temperature of the liquid (filtrate) to 40°C or higher, preferably 60°C or higher, and add sodium thiosulfate salt or a solution containing thiosulfate ions to precipitate and recover ruthenium and iridium. can do.

Before adding sodium thiosulfate salt or a solution containing thiosulfate ions, adjust the temperature of the liquid (filtrate) after solid-liquid separation to 70°C or less, and add metallic iron to a concentration of 0.5 to 5 g/L. Then, ruthenium may be selectively precipitated by cementation. Preferably, the metallic iron is iron powder. If the amount of metallic iron added is less than 0.5 g/L, there is a possibility that ruthenium will not undergo sufficient cementation. If the amount of metal iron added exceeds 5 g/L, there is a risk that a large amount of hydrogen gas will be generated. At this time, since arsenic is reduced by the sulfurization treatment, there is no concern that hydrogen arsenide will be generated. Since ruthenium is selectively cemented in this way, solid-liquid separation may be performed after cementation.

Ruthenium can be precipitated and recovered more effectively by metal cementation than by sodium thiosulfates. However, if the liquid contains arsenic, even if it is pentavalent arsenic, there is a non-zero possibility that hydrogen arsenide will be generated due to the nascent hydrogen. Therefore, as mentioned above, it is important to reduce arsenic to its trivalent form and perform sulfidation treatment to lower its concentration.

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

Sodium thiosulfate also acts as a sulfurizing agent for some transition metals such as silver and copper, but its ability is weak. Also, the decomposition rate is not fast even in acidic solutions. Unlike sulfide ions, thiosulfate ions have coordination ability, and once they coordinate with ruthenium ions and iridium ions, it is possible to precipitate these metals.

When the iridium concentration in the acidic solution in the arsenic reduction process is high, it is more efficient to recover it by precipitation with KCl or NH ₄ Cl, but when the iridium concentration is dilute at 100 mg/L or less, sodium thiosulfate is used. It is preferable to precipitate and recover by adding a salt or a solution containing thiosulfate ions. If the amount of the sodium thiosulfate salt or thiosulfate ion-containing solution added is too small, recovery will be insufficient, and if it is too large, the cost will increase. For this reason, it is preferable to add the sodium thiosulfate salt or thiosulfate ion-containing solution in an amount of 5 g/L or more in terms of sodium thiosulfate pentahydrate. Further, a sodium thiosulfate salt or a solution containing thiosulfate ions may be added in an amount of 5 to 20 g/L or more in terms of sodium thiosulfate pentahydrate. The resulting precipitate is separated into solid and liquid.

The solid-liquid separated precipitate is purified separately into ruthenium and iridium by a known method. For example, ruthenium can be oxidized and dissolved again, and then sodium bromate can be added to distill ruthenium tetroxide to separate and recover it. Iridium can be recovered by crystallizing it as an ammonia salt after solvent extraction.

EXAMPLES Hereinafter, examples will be illustrated to better understand the present invention and its advantages, but the present invention is not limited to the examples.

(Experiment example 1)
Copper was dissolved and removed using sulfuric acid from electrolytic precipitates derived from the copper electrolytic refining process of copper smelting. 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. The acid concentration was adjusted to 1 mol/L or more, and DBC (dibutyl carbitol) and PLS were mixed to extract gold. After gold extraction, the PLS was heated to 70° C., and sulfur dioxide was blown into the PLS to reduce and remove noble metals and selenium. This was subjected to solid-liquid separation to obtain a hydrochloric acid acidic solution to be tested. The iridium concentration of this hydrochloric acid acidic solution was 24 mg/L, and the ruthenium concentration was 120 mg/L. As other elements, it contained 1.82 g/L of arsenic, 1.11 g/L of copper, and 300 mg/L of antimony.

200 mL of the hydrochloric acid acidic solution to be tested was taken and heated to 70°C. In order to eliminate the influence of organic matter, 2 mL of hydrogen peroxide solution (30% by volume) was added and stirred for 1 hour. 0.1 g of potassium iodide was added and a mixture of sulfur dioxide and air (5-20% by volume) was blown into it. After 30 minutes, the reaction was stopped and solid-liquid separation was performed. As a comparative example, an experiment was also conducted in which potassium iodide was not added.
After the solid-liquid separation liquid was adjusted to 40°C, 2g of sodium hydrogen sulfide was added. After stirring for 30 minutes, the sulfide precipitate was separated into solid and liquid.
After solid-liquid separation, the liquid was heated to 70°C and 2g of sodium thiosulfate pentahydrate was added. Subsequently, after stirring for 1 hour, solid-liquid separation was performed (Example 1). Separately, the solution after sulfide precipitation was heated to 60° C., and 0.4 g of iron powder was added. After stirring for 45 minutes and solid-liquid separation again, the mixture was heated to 70° C. and 2 g of sodium thiosulfate pentahydrate was added (Example 2).
All reagents used were special grade manufactured by Wako Pure Chemical Industries, Ltd. Samples for analysis were collected each time solid-liquid separation was performed. The element concentration in the solution was determined by taking 2 mL of the solution, adjusting the volume to 50 mL, and then quantifying the concentration using ICP-OES (SPS3100, manufactured by Seiko Instruments Inc.). The concentration of the precipitate solution was determined by adjusting the volume to 100 mL. The results are shown in Table 1. "ND" in Table 1 indicates that the element was not detected. Although the concentration increased due to evaporation of the solution, water was not replenished.

It can be seen that the addition of potassium iodide significantly reduces the arsenic concentration in the sulfurization process. Most of the copper and antimony were also precipitated during sulfidation. After removing impurities, iron powder was added to perform iron substitution, and ruthenium and iridium were recovered by reacting with thiosulfate ions.

If potassium iodide is not added, arsenic cannot be removed by sulfidation. In this case, residual arsenic reacts with iron substitution and thiosulfate ions and precipitates, forming a mixture with ruthenium and iridium. No generation of hydrogen arsenide was confirmed.

Note that the solid-liquid separation operation after iron substitution is not essential, and if there are few impurities, it is also possible to remove unreacted iron by acid treatment and then introduce it into the ruthenium and iridium purification process. As seen in Example 2, the iron substitution improves the ruthenium recovery efficiency.

(Experiment example 2)
200 mL of the same experimental target hydrochloric acid solution as in Experimental Example 1 was collected and heated to 70°C. In order to eliminate the influence of organic matter, 2 ml of hydrogen peroxide solution (30 vol%) was added and stirred for 1 hour. 0.02 g or 0.1 g of potassium iodide was added and a mixture of sulfur dioxide and air (5 to 20% by volume) was blown into the solution. After 30 minutes, the reaction was stopped and solid-liquid separation was performed.
After the solid-liquid separation liquid was adjusted to 40°C, 2 g of sodium hydrogen sulfide was dissolved in water and added thereto. After stirring for 30 minutes, the sulfide precipitate was separated into solid and liquid. Samples for analysis were taken at the time of solid-liquid separation.
Analytical operations were conducted in accordance with Experimental Example 1. The results are shown in Table 2. "ND" in Table 2 indicates that the element was not detected.

The results in Table 2 show that even when the amount of potassium iodide added is 0.02 g, that is, 0.1 g/L, the catalytic cycle is functioning as shown in Chemical Formulas 1 and 2 above. When the amount of addition was 0.02g and 0.1g, the arsenic concentration after sulfidation was higher in the latter. However, this is an effect of the sulfur dioxide feed rate. The catalytic effect of iodine is also effective in the precipitation of tellurium in the presence of sulfur dioxide. Therefore, if the tellurium concentration decreases significantly after supplying sulfur dioxide, it indicates that there was sufficient supply of sulfur dioxide, and this is because the reaction of chemical formula 2 occurs quickly and the turnover of iodine in the catalyst is improved. .

However, iodide ions partially react with copper to precipitate copper(I) iodide. Therefore, it is preferable that the iodide ion is 5% by mass or more of the copper concentration in terms of potassium iodide.

(Experiment example 3)
200 mL of the same experimental target hydrochloric acid solution as in Experimental Example 1 was collected. In order to eliminate the influence of organic matter, 2 mL of hydrogen peroxide solution (30% by volume) was added and stirred for 1 hour. 0.1 g of potassium iodide was added and a mixture of sulfur dioxide and air (5-20% by volume) was blown into it. After 30 minutes, the reaction was stopped and solid-liquid separation was performed.
After solid-liquid separation, the liquid was heated to 40°C, and an aqueous sodium hydrogen sulfide solution (80 g/L) was gradually added. ORP was measured after adding an appropriate amount. At the same time, samples for quantitative analysis were also collected. The quantitative method is based on Experimental Example 1. Figure 2 shows the relationship between the ORP value and the copper and arsenic concentrations. Furthermore, the relationship between the ORP value and the ruthenium concentration is shown in FIG.

It can be seen that by adding sodium hydrogen sulfide, copper first formed a sulfide precipitate, followed by arsenic precipitate. When ORP reached 150 mV or less, most of both elements precipitated.

Note that the concentration of ruthenium was 110 mg/L when the ORP reached 136 mV. Since the ruthenium concentration of the stock solution was 120 mg/L, the loss was small.

(Experiment example 4)
200 mL of the same experimental target hydrochloric acid solution as in Experimental Example 1 was collected and heated to 70°C. In order to eliminate the influence of organic matter, 2 mL of hydrogen peroxide solution (30% by volume) was added and stirred for 1 hour. 0.1 g of potassium iodide was added and a mixture of sulfur dioxide and air (5-20% by volume) was blown into it. After 30 minutes, the reaction was stopped and solid-liquid separation was performed.
After the solid-liquid separation liquid was adjusted to 40°C, 2g of sodium hydrogen sulfide was added. After stirring for 30 minutes, the sulfide precipitate was separated into solid and liquid.
The liquid after solid-liquid separation of the sulfide precipitate was heated to 60° C., and 0.4 g or 1 g of iron powder was added. The mixture was stirred for 45 minutes and solid-liquid separation was performed again. The separated solution was heated to 70° C. and 2 g of sodium thiosulfate pentahydrate was added thereto. After stirring for 1 hour, the mixture was separated into solid and liquid.
Samples for analysis were taken during each solid-liquid separation operation. Analytical operations were conducted in accordance with Experimental Example 1. The results are shown in Table 3.

The total amount of ruthenium and iridium recovered was improved by adding iron powder. There was no significant difference whether the amount of iron powder added was 1 g or 0.4 g, but as the amount of iron powder added increased, the amount of substitution increased somewhat. If ruthenium and iridium are to be recovered separately, it is better to add a small amount of iron powder and perform solid-liquid separation once. The amount of iron powder used for cementation is preferably 0.5 to 5 g/L. If ruthenium and iridium are to be recovered separately, the amount of iron powder added is less than 2 g/L and solid-liquid separation is performed to recover ruthenium first.

Claims (7)

Arsenic is removed by adding a water-soluble inorganic iodine compound or elemental iodine to an acidic liquid containing ruthenium, iridium, and arsenic, and then blowing in sulfur dioxide or hydrogen sulfide, or adding an aldehyde reducing agent. an arsenic reduction process that reduces the arsenic to trivalent,
The acidic liquid obtained in the arsenic reduction step is adjusted to 70°C or lower, hydrogen sulfide or sodium hydrogen sulfide is added until ORP (reference electrode Ag/AgCl) reaches 150 mV or lower, and the precipitated sulfide is solid-liquid separated. an impurity removal process,
After the impurity removal step, a ruthenium and iridium recovery step of adjusting the liquid temperature of the filtrate to 40° C. or higher and adding a sodium thiosulfate salt or a solution containing thiosulfate ions to precipitate ruthenium and iridium;
A method for recovering ruthenium and iridium, including In the impurity removal step, if a precipitate is generated in the arsenic reduction step, after solid-liquid separation, the temperature is adjusted to 70 ° C. or lower, and the hydrogen sulfide or sodium hydrogen sulfide is added until ORP reaches 150 mV or lower. Item 1. The method for recovering ruthenium and iridium according to item 1. Between the impurity removal step and the ruthenium and iridium recovery step, the liquid temperature of the filtrate obtained in the impurity removal step is further adjusted to 70° C. or lower so that metallic iron becomes 0.5 to 5 g/L. 2. The method for recovering ruthenium and iridium according to claim 1, comprising the step of selectively precipitating ruthenium by adding the ruthenium as described above. The inorganic iodine compound is one or more of potassium iodide, sodium iodide, potassium iodate, and sodium iodate, and is added at least 0.05 g/L when converted to potassium iodide. 1. The method for recovering ruthenium and iridium according to 1. The inorganic iodine compound is one or more of potassium iodide, sodium iodide, potassium iodate, and sodium iodate, and when copper is dissolved in the acidic liquid, when converted to potassium iodide. The method for recovering ruthenium and iridium according to claim 1, wherein the ruthenium and iridium are added in an amount of 0.05 to 4 times the mass of copper. The method for recovering ruthenium and iridium according to claim 1, wherein in the arsenic reduction step, the acidic solution containing ruthenium, iridium, and arsenic is an acidic solution after dissolving a metal electrolytic precipitate. The iridium concentration in the acidic solution in the arsenic reduction step is 100 mg/L or less, and in the ruthenium and iridium recovery step, the sodium thiosulfate salt or thiosulfate ion-containing solution is converted to sodium thiosulfate pentahydrate. The method for recovering ruthenium and iridium according to any one of claims 1 to 6, wherein the ruthenium and iridium are added at a concentration of 5 g/L or more.