JP7792876B2 - Method for recovering ruthenium and iridium - Google Patents

Description

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

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

This sediment also concentrates precious metals, rare metals, and the selenium, tellurium, and arsenic contained in copper concentrate. These elements are separated and recovered individually as by-products of copper smelting.

Hydrometallurgical methods are often used to treat this precipitate. For example, Patent Document 1 discloses a method in which silver is recovered from the precipitate using hydrochloric acid-hydrogen peroxide, dissolved gold is recovered by solvent extraction, and then other valuables are sequentially reduced and recovered using sulfur dioxide. Patent Document 2 discloses a method in which gold and silver are recovered using a similar method, and then the valuables are reduced and precipitated using sulfur dioxide, and only the selenium is distilled and removed to concentrate the precious metals.

The solution obtained after the precious metals have been recovered contains rare metal ions, tellurium, and selenium, and it is necessary to further recover these valuable materials. Known recovery methods include recovering the precipitate formed by the use of a reducing agent, or mixing the solution with copper concentrate, drying it in a dryer, and then returning it to the smelting furnace.

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

In methods for recovering valuables using sulfur dioxide, valuables can be recovered by sequentially reducing them after dissolution. Platinum and palladium precipitate first, followed by selenium, which is reduced. Iridium and ruthenium have relatively low oxidation-reduction potentials (ORP), so they are less susceptible to reduction and remain in the solution until the end. A widely known method for recovering iridium is by separating it through solvent extraction, concentrating it, and then calcining it, as described in Patent Document 3. Patent Document 4 also discloses a method in which a base metal selected from magnesium, aluminum, zinc, iron, tin, and lead, and a mineral acid are added to an organic solvent containing iridium, reducing and precipitating the precious metal.

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

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

On the other hand, to recover ruthenium by distillation, a strong oxidizing agent such as _NaBrO3 is used. The reagent cost of the oxidizing agent is high, and this method is not suitable for recovering ruthenium from dilute solutions with many impurities, such as copper electrolytic deposit solutions, which have a ruthenium concentration of about 50 to 200 mg/L. Furthermore, ruthenium tetroxide, which is the fraction of the distillation, is highly toxic, and there are safety issues with recovering it by distillation.

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

When using base metals for cementation, large amounts of metal are used to increase the recovery rate. Under strongly acidic conditions, hydrogen can be generated in large quantities in a short period of time, causing boiling over, or the hydrogen generated by static electricity can explode. Furthermore, the reaction efficiency is low because other elements that undergo cementation are also present.

Iridium and ruthenium are known to precipitate as their hydroxides. However, a general problem is that when neutralizing strong acids, the cost of alkaline reagents is high. Furthermore, sodium ions and alkaline earth metal ions precipitate sulfates that are poorly soluble in water, even under acidic conditions. When neutralizing with an excessive amount of alkali, these poorly soluble sulfates are expected to deposit in the piping of manufacturing equipment, causing blockages.

Furthermore, there is no known method for recovering low concentrations of iridium and ruthenium from strongly acidic solutions in an inexpensive and efficient manner.

In consideration of these conventional circumstances, the present invention provides a method for efficiently recovering ruthenium and iridium from an acidic solution containing ruthenium and iridium. In particular, an acidic solution containing ruthenium and iridium in which arsenic is dissolved as an impurity is an ideal candidate for the acidic solution containing ruthenium and iridium of the present invention.

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

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

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

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

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

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

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

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

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

The pregnant leach solution (PLS) is cooled once, and chlorides of base metals such as lead and antimony are precipitated and separated. Gold is then separated into an organic phase by solvent extraction. Dibutyl carbitol (DBC) is widely used as the gold extractant. Sulfur dioxide is blown into the extract to reduce and remove precious metals such as platinum and palladium, as well as selenium and tellurium. Subsequent solid-liquid separation produces a hydrochloric acid solution containing ruthenium and iridium.

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

When impurity elements are precipitated by injecting sulfur dioxide or hydrogen sulfide or by adding an aldehyde reducing agent, an inorganic iodine compound or elemental iodine is added. The inorganic iodine compound undergoes reduction in the acidic solution to produce iodide ions. These iodide ions effectively reduce tellurium and can further reduce arsenic in the acidic solution to trivalent arsenic (Chemical Formula 1). The resulting elemental iodine is immediately reduced to sulfur dioxide or an aldehyde, regenerating iodide ions (Chemical Formula 2). Therefore, the substance added when precipitating impurity elements as described above may be either an inorganic iodine compound or elemental 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 produce iodide ions in an aqueous solution in the presence of a reducing agent. Specific examples include potassium iodide, sodium iodide, potassium iodate, sodium iodate, potassium periodate, and sodium periodate.

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

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

By blowing in sulfur dioxide or hydrogen sulfide, or by adding an aldehyde reducing agent, the impurities selenium, tellurium, platinum, and palladium are precipitated. The precipitate containing these valuable elements is subjected to solid-liquid separation and then fed 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 sulfiding agent is added to the liquid to sulfide and precipitate the arsenic and copper. Hydrogen sulfide, sodium sulfide, or sodium hydrosulfide is used as the sulfiding agent. Since sulfiding efficiency decreases when the liquid temperature is high, sulfidation is carried out by adjusting the acidic liquid to 70°C or below. It is more preferable that the temperature of the acidic liquid during sulfidation be 50°C or below. If no precipitate is formed by injecting sulfur dioxide or hydrogen sulfide as described above, or by adding an aldehyde reducing agent, solid-liquid separation is not necessary. In this case, the acidic liquid is adjusted to 70°C or below as described above and sulfidation is carried out.

When using sodium hydrosulfide or sodium sulfide, dissolving it in water beforehand and adding it as an aqueous solution will increase the reaction efficiency. There are no particular restrictions on the concentration of sodium hydrosulfide or sodium sulfide.

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

When a sulfurizing agent is added, trivalent arsenic will precipitate quantitatively, but pentavalent arsenic will precipitate incompletely. For this reason, it is preferable to fully reduce pentavalent arsenic to trivalent arsenic according to Chemical Equation 1.

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

By adjusting the temperature of the liquid (filtrate) after solid-liquid separation to 40°C or higher, preferably 60°C or higher, and adding sodium thiosulfate salt or a solution containing thiosulfate ions, ruthenium and iridium can be precipitated and recovered.

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

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

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

Sodium thiosulfate also acts as a sulfiding agent for some transition metals such as silver and copper, but its ability is weak. Its decomposition rate is also slow, even in acidic solutions. Unlike sulfide ions, thiosulfate ions have coordination ability, and once coordinated with ruthenium ions or iridium ions, it is possible to precipitate these metals.

When the iridium concentration in the acidic solution in the arsenic reduction step is high, it is more efficient to recover the iridium by precipitation with KCl or NH ₄ Cl. However, when the iridium concentration is low, such as 100 mg/L or less, it is preferable to recover the iridium by precipitation by adding sodium thiosulfate salt or a thiosulfate ion-containing solution. Adding too little sodium thiosulfate salt or a thiosulfate ion-containing solution results in insufficient recovery, while adding too much increases costs. Therefore, it is preferable to add sodium thiosulfate salt or a thiosulfate ion-containing solution so that the concentration is 5 g/L or more, calculated as sodium thiosulfate pentahydrate. Alternatively, sodium thiosulfate salt or a thiosulfate ion-containing solution may be added so that the concentration is 5 to 20 g/L or more, calculated as sodium thiosulfate pentahydrate. The resulting precipitate is subjected to solid-liquid separation.

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

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

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

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

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

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

Note that solid-liquid separation after iron substitution is not essential; if the amount of impurities is small, it is possible to remove unreacted iron by acid treatment before feeding the material into the ruthenium and iridium purification process. As shown in Example 2, iron substitution improves the recovery efficiency of ruthenium.

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

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

However, some iodide ions react with copper to precipitate copper(I) iodide. Therefore, it is preferable that the iodide ions, converted into potassium iodide, be at least 5% by mass of the copper concentration.

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

It can be seen that the addition of sodium hydrosulfide first produced a sulfide precipitate of copper, followed by the precipitation of arsenic. When the ORP reached 150mV or below, most of both elements had precipitated.

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

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

The total amount of ruthenium and iridium recovered improved with the addition of iron powder. There was no significant difference between the amount of iron powder added, 1g and 0.4g, but the amount of substitution increased slightly as the amount of iron powder added increased. If you want to recover ruthenium and iridium separately, it is best to add a small amount of iron powder and perform solid-liquid separation first. The amount of iron powder used for cementation is preferably 0.5 to 5g/L. If you want to recover ruthenium and iridium separately, add less iron powder, and perform solid-liquid separation to recover ruthenium first.

Claims (7)

an arsenic reduction step in which a water-soluble inorganic iodine compound or elemental iodine is added to an acidic solution containing ruthenium, iridium, and arsenic, and sulfur dioxide or hydrogen sulfide is blown in, or an aldehyde reducing agent is added, to reduce the arsenic to a trivalent state;
an impurity removal step of adjusting the temperature of the acidic solution obtained in the arsenic reduction step to 70°C or less, adding hydrogen sulfide or sodium hydrosulfide until the ORP (reference electrode Ag/AgCl) reaches 150 mV or less, and separating precipitated sulfides into solid and liquid;
a ruthenium and iridium recovery step in which, after the impurity removal step, the temperature of the filtrate is adjusted to 40°C or higher, and sodium thiosulfate salt or a solution containing thiosulfate ions is added to precipitate ruthenium and iridium;
A method for recovering ruthenium and iridium, comprising: The method for recovering ruthenium and iridium described in claim 1, wherein if a precipitate forms in the arsenic reduction step during the impurity removal step, the temperature is adjusted to 70°C or less after solid-liquid separation, and hydrogen sulfide or sodium hydrosulfide is added until the ORP reaches 150 mV or less. The method for recovering ruthenium and iridium described in claim 1 further comprises, between the impurity removal step and the ruthenium and iridium recovery step, a step of adjusting the temperature of the filtrate obtained in the impurity removal step to 70°C or less and adding metallic iron to the filtrate to a concentration of 0.5 to 5 g/L, thereby selectively precipitating ruthenium. The method for recovering ruthenium and iridium described in claim 1, wherein the inorganic iodine compound is one or more of potassium iodide, sodium iodide, potassium iodate, and sodium iodate, and is added in an amount of 0.05 g/L or more when converted to potassium iodide. The method for recovering ruthenium and iridium described in claim 1, wherein the inorganic iodine compound is one or more of potassium iodide, sodium iodide, potassium iodate, and sodium iodate, and when copper is dissolved in the acidic solution, 0.05 to 4 times the mass of copper, converted into potassium iodide, is added. 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 the acidic solution obtained after dissolving metal electrolytic deposits. The method for recovering ruthenium and iridium described in any one of claims 1 to 6, wherein the iridium concentration in the acidic solution in the arsenic reduction step is 100 mg/L or less, and the sodium thiosulfate salt or thiosulfate ion-containing solution is added in the ruthenium and iridium recovery step so that the concentration, calculated as sodium thiosulfate pentahydrate, is 5 g/L or more.