WO2023217568A1 - Method for recovering ruthenium from a ruthenium-containing material - Google Patents

Abstract

The invention relates to a method for recovering ruthenium from a ruthenium-containing material, with the steps of: a) adding an oxidizing agent to a ruthenium-containing material, b) oxidizing the ruthenium to ruthenium tetroxide, and c) introducing the ruthenium tetroxide formed into an aqueous capture solution, characterized in that the aqueous capture solution comprises an acid selected from sulfonic acids and carboxylic acids having at least two carboxyl groups. It additionally describes the use of such an acid in the method and the use of the method in various sectors.

Description

Process for recovering ruthenium from a ruthenium-containing material

The invention relates to a process for recovering ruthenium.

Current processes for recovering ruthenium, for example from spent catalysts, are very complex and include several pre-treatment and post-treatment steps. In the first step, the ruthenium-containing material is usually pretreated to obtain ruthenium oxide or metallic ruthenium powder.

Ruthenium is one of the most expensive metals from the platinum metal group due to its limited availability and high demand. Due to its importance in the production of catalysts for producing hydrogen as an emission-free energy source, the importance of ruthenium recycling continues to increase. In order to ensure the long-term availability of this metal, a cost-effective and energy-efficient process for extracting ruthenium from primary raw materials and end-of-life materials must be developed.

Most ruthenium recovery processes require high energy consumption because high-temperature treatment is required to separate ruthenium.

Furthermore, they are very complex and involve several pre-treatment and post-treatment steps.

The process described in patent US4,002,470 involves the alkaline melting of ruthenium-containing material with inorganic peroxide in a temperature range of 250-750 °C within a time of 5-600 minutes. The melt is then dissolved in acid and treated by oxidizing distillation with oxidizing agents such as ammonium persulfate, potassium permanganate, potassium dichromate, sodium bismuthate, sodium peroxide, lead peroxide, cerium sulfate, sodium perchlorate or a mixture thereof at a temperature between 50 ° C and 90 ° C, so that gaseous ruthenium tetroxide is formed. This oxidation occurs in the presence of an acid, starting from 1% to 90% (Step II). The ruthenium tetroxide is then collected in an absorbent solution. Ruthenium tetroxide is reduced to a halogenated ruthenic acid or a ruthenate at a temperature between 40 °C and 150 °C, depending on the absorbent. This requires heating with alcohol (e.g. methyl alcohol, ethyl alcohol, propyl alcohol, n-butyl alcohol, isopropyl alcohol and isobutyl alcohol) so that the ruthenium tetroxide is reduced by the alcohol. It is also known to reduce RuCL using an aqueous acidic ethanol solution. It is also known from US 4,002,470 to use the monocarboxylic acid acetic acid as a collecting solution. The disadvantage is that high losses occur when collecting the ruthenium tetroxide.

Ruthenium tetroxide corresponds to the formula RuC>4 and the Ru is in the oxidation state VIII.

The final recovery step to obtain a solid Ru(III) complex is preferably carried out at a temperature between 200 and 400 ° C.

The disadvantage of the method described is the number and complexity of the steps that must be carried out to obtain the ruthenium. The amount of peroxide, the temperature, the pressure and the duration of the treatment as well as the strength of the acid solution must be carefully adjusted, otherwise a slow dissolution rate, prolonged oxidation time and ruthenium losses will occur. In addition, the prolonged treatment of the material at high temperatures mentioned in this method can lead to high energy costs of the recovery process.

One method presented in patent CN1872418A involves calcining a carbon-loaded ruthenium catalyst at 600-1000°C to remove the carbon support. The alkaline digestion then takes place with KOH and KNO3 at 300-950 °C. The resulting solid is dissolved in hot water at 50-90 °C. A mixture of perchlorate and sulfuric acid was used to volatilize the ruthenium to ruthenium tetroxide. In the next step, the ruthenium tetroxide formed is treated with hydrochloric acid solution to obtain ruthenium halide. Hydrogen is used to reduce it to ruthenium. The process described is complicated and requires concentrated acids for volatilization (i.e. oxidation to ruthenium tetroxide), which are very corrosive. In addition, the long heating at high temperatures during the calcination and melting steps requires a lot of energy.

A method proposed in US2008/0287282A1 for volatilizing Ru to RuÜ4 in one step uses a highly corrosive atmosphere containing oxygen and chlorine at a temperature of over 600 °C. Under these extreme conditions, a low Ru yield of only 7.2% was achieved when a ruthenium chloride oxide catalyst was used. In order to increase the Ru yield, some preliminary steps must be carried out, such as the reduction of Ru in a hydrogen-containing atmosphere and the decomposition with oxidizing agents such as nitrates, chlorates, perchlorates, persulfates, permanganates, peroxide chromates, dichromates of alkali or alkaline earth metals, especially alkali metals. Above all, the ruthenium-containing material must first be melted and This melting requires temperatures, preferably from 350 to 700 ° C, and is therefore relatively energy-intensive.

The process described in US 2008/0293836A1 consists of the reduction of ruthenium oxide to metallic ruthenium with hydrogen vapor at elevated temperature, usually from 50 °C to 600 °C. In the next step, the metallic ruthenium is dissolved in a hydrochloric acid solution in the presence of an oxygen-containing gas, preferably air, at a temperature of around 100 ° C. Leaching of the ruthenium oxide support material as well as the reactor material constituting the reactor in which the dissolution step takes place requires an additional step to separate the ruthenium species from impurities. In addition, the process is time-consuming since the oxidation step in the example takes 24 hours.

In EP2824201A1, the ruthenium recovery process involves first reducing the ruthenium-containing catalyst with hydrogen at 200°C - 400°C for 2-3 hours and then oxidizing it with a mixture of oxygen and ozone at 500°C - 750°C for 1-8 hours to get RuÜ4. The metallic ruthenium is recovered after the oxidation and precipitation step and the subsequent reduction of the (NH^RuCle powder in a hydrogen atmosphere at high temperature. The recovery process is lengthy and includes several pretreatment steps before the volatilization of Ru to RuÜ4 in an aggressive, oxidative atmosphere , to finally win Ru.

A recovery process described in patent US4,132,569 involves the use of a fluorine-containing stripping solution to separate an insoluble ruthenium-containing precipitate, which is then subjected to thermal treatment with an alkali hypochlorite solution to form ruthenium tetroxide. Gaseous ruthenium tetroxide is distilled and passed through concentrated hydrochloric acid, in which the ruthenium tetroxide is condensed and converted into ruthenium trichloride. The process described is problematic for the environment due to the fluorine-containing exhaust gases, and the system technology used requires appropriate handling.

A process described in patent US8,454,914B2 consists of several steps in which ruthenium is first reduced to metallic ruthenium in the temperature range of 200 ° C - 1000 ° C without contact with an oxidizing gas, but using a reducing gas. The resulting solid is cooled and mixed with an oxidizing agent to bring the ruthenium into solution. The disadvantage of this method is the use of high temperatures for ruthenium reduction and the safety issues of using hydrogen as a reducing gas. A particular disadvantage of these known methods is the complexity of the ruthenium recovery process and the associated high energy consumption due to the high process temperatures, which include the reduction of the ruthenium species to the metallic form, alkaline melting or ruthenium distillation. Several processes involve the thermal treatment of ruthenium-containing materials with oxidizing agents, often at a temperature above 550 °C, to obtain the solid ruthenium complex, which can then be dissolved. This requires large energy investments and can lead to losses of ruthenium during thermal treatment since ruthenium is highly volatile in its highest oxidation state. Separation in an oxidizing atmosphere involves a high consumption of corrosive gases such as ozone, oxygen, chlorine or hydrochloric acid/oxygen mixtures. In the case of volatilization from solution, high temperatures are also required for effective separation of ruthenium due to the low oxidation potential of the proposed systems. Although some methods propose the efficient dissolution of the ruthenium-containing catalyst after its reduction with hydrogen, further separation of the ruthenium solution from the support materials requires an additional purification step, which further increases the overall cost of the recovery process. In addition, dissolving ruthenium is only possible under aggressive conditions (e.g. with concentrated hydrochloric acid at a temperature of up to 150 °C), and mainly in an autoclave. At the same time, impurities can enter the ruthenium-containing solution due to corrosion of the reactor material.

The object of the invention is to provide an effective method for ruthenium recovery that is simple. It should be able to work with reduced energy consumption, in particular it should be a low-temperature process (below 100°C). It should be so flexible that both solid and liquid ruthenium-containing materials can be used with the invention.

Ruthenium recovery rates should be as high as possible. In addition, it should be usable for important industrial waste such as electrocatalysts from fuel cells and/or electrolyzers.

According to the invention the object is solved by the subject matter of the independent claims.

Advantageous embodiments of the invention are specified in the dependent claims. The invention relates to a method for recovering ruthenium from a ruthenium-containing material, comprising the steps: a) adding an oxidizing agent to a ruthenium-containing material, b) oxidizing the ruthenium of a ruthenium-containing material to ruthenium tetroxide, and c) initiating of the ruthenium tetroxide formed into an aqueous collecting solution, characterized in that the aqueous collecting solution contains an acid selected from sulfonic acids and carboxylic acids with at least two carboxy groups.

In step b), the ruthenium-containing material is oxidized to ruthenium tetroxide. An oxidizing agent from step a) is used for this. The ruthenium tetroxide formed is highly volatile and is captured in step c) by introducing it into the aqueous solution according to the invention, the sulfonic acid or the carboxylic acid in the aqueous collecting solution being able to reduce the RuÜ4, the RuÜ4 being the sulfonic acid due to its oxidation performance or the carboxylic acid oxidizes. Step c) is therefore a redox reaction between RuÜ4 and the acid. It is possible that the acids according to the invention complex the RuÜ4 very well, so that the redox couple, namely RuÜ4 and the reducing acid are brought close to one another through complexation. When ruthenium tetroxide is reduced, ruthenium compounds of various oxidation states are formed. In particular, compounds are formed with ruthenium of the oxidation states Ru(III) and Ru(IV).

The invention also includes that the aqueous collection solution contains more than one of the above-mentioned acids.

The term sulfonic acid includes aryl and alkyl sulfonic acid (with aryl = C5-C6 ring and with alkyl = C1-12). The term “carboxylic acids with at least two carboxy groups” includes acids with two or more carboxy groups (-COOH, also called carboxyl groups), where the substituent R can be aliphatic or aromatic. This means that both aromatic carboxylic acids, ie those with carboxy groups on an aromatic, and alkyl carboxylic acids, ie those with carboxy groups on an alkyl chain of length C1-C12 are included. The alkyl chain or aromatic can also be substituted with small substituents, such as NH2 (as in glutamic acid) or OH (as in malic acid), or the alkyl chain can also carry a carbonyl group in the chain (as in a-ketoglutaric acid, for example). There are also includes acids with more than two carboxylic acid groups, preferably dicarboxylic acids and tricarboxylic acids.

The invention also relates to the use of an acid, selected from sulfonic acids and carboxylic acids with at least two carboxy groups, for the process according to the invention for recovering ruthenium from a ruthenium-containing material.

The invention also relates to the use of the method according to the invention:

- in precious metal processing, extraction or refining,

- in the recycling of electrocatalysts, car catalytic converters, electronic components,

- in the recycling of electrodes from fuel cells, circuit boards or electrolysers,

- when processing anode sludge resulting from electrolysis (such as in the Cu, Pb or Sn refinery), and/or

- for the production of halide-free ruthenium compounds.

The surprising advantage of the method according to the invention is that the sulfonic acid or carboxylic acid in the aqueous collection solution leads to very high collection rates for RuÜ4. Apparently, these acids are very capable of complexing the ruthenium tetroxide at the Ru atom and therefore bringing it together for reduction by these acids.

The process leads to only small losses of ruthenium, despite the volatility of the intermediate ruthenium tetroxide. The introduction and rapid reduction by the acids according to the invention in the aqueous collection solution have proven to be advantageous. This combination leads to an extremely high recovery rate of ruthenium when viewed across the entire process.

The application of the process according to the invention has high potential for the area of hydrogen production and application, and for improving the existing circular economy in the production of electrocatalysts, in which the recovered ruthenium can be reused through the process.

It is advantageously a low-temperature process. Furthermore, the process is easy to use and requires a short time to achieve high Ru recovery rates. Preferred Embodiments

The oxidizing agent is preferably a peroxodisulfate.

In a preferred embodiment, in which the oxidizing agent is persulfate, the persulfate is brought to a concentration of 0.5 to 6 mol/L with sulfuric acid after the addition in step a), in particular to concentrations of, for example, 1 mol/L or 3 mol/L or 5 mol/L or 6 mol/L, particularly preferably 1.5±0.5 mol/L, even 1.5-2 mol/L. This advantageously accelerates the distillation process for the RuÜ4 by adjusting the pH of the oxidation solution and slowing down the thermal decomposition of persulfate. The use of a sulfuric acid with a concentration of >1.5 mol/L, in particular with 1.5 mol/L, is particularly advantageous for adjusting the concentration.

In a preferred embodiment, the oxidizing agent in step a) is selected from persulfates, with persulfate, as is known, denoting, for example, peroxodisulfate compounds (counterion S20s ² ') and peroxomonosulfate compounds (counterion SOs ² ').

The advantage of this is that the process makes it possible to recover ruthenium from solid catalysts (elementary Ru) or from Ru oxides (both are poorly or not at all soluble) without first having to convert them into soluble compounds. Similar processes as in US 4,002,470 can only oxidize the ruthenium starting from a soluble ruthenium salt (from step II there).

There is also no need to melt the ruthenium-containing material.

Because with a strong oxidizing agent, such as persulfates, in steps a) and b), this strong oxidizing agent can completely oxidize all the ruthenium contained to RuÜ4.

The advantage of the design with persulfates as the oxidizing agent is that the oxidation of the ruthenium from the ruthenium-containing material can also take place in the absence of an acid due to the oxidizing agent persulfate (in step a).

In the invention, the oxidizing agent is preferably selected from sodium persulfate and potassium persulfate.

Particularly preferred is potassium persulfate, with the advantage that all RuÜ4 can be collected within a time of 1.5 hours of introduction into step e), so that a yield of 100% of the RuÜ4 formed in step b) can be collected. In a preferred embodiment, in step b), the temperature is below 100 ° C, in particular 50-90 ° C, particularly preferably 55-65 ° C, in particular 60 ° C. The advantage of the low temperature is that the persulfate does not decompose and therefore no further addition is necessary.

Stirring is preferred in step b) for 2-3 hours, in particular 2.5 hours.

In one embodiment, the acid is a carboxylic acid with at least two carboxy groups, such as oxalic acid (ethanedioic acid), malonic acid (propanedioic acid), succinic acid (butanedioic acid), glutaric acid (pentanedioic acid), adipic acid (hexanedioic acid), pimelic acid (heptanedioic acid), suberic acid (suberic acid, octanedioic acid). ), azelaic acid (nonanedioic acid), sebacic acid (decanedioic acid), tartaric acid, malic acid, a-ketoglutaric acid, oxaloacetic acid, ortho-phthalic acid, isophthalic acid, terephthalic acid, glutamic acid or aspartic acid. Particularly preferred is oxalic acid, tartaric acid or citric acid.

Ruthenium can also be found in aqueous solutions of sulfonic acids, such as. B. alkyl and arylsulfonic acids can be reduced.

The sulfonic acid is preferably an aromatic sulfonic acid.

In another preferred embodiment, the sulfonic acid is methanesulfonic acid or benzenesulfonic acid.

In a particularly preferred embodiment of the invention, the sulfonic acid, methanesulfonic acid or benzenesulfonic acid (or mixtures thereof) and the carboxylic acid are oxalic acid, tartaric acid or citric acid (or mixtures thereof). Mixtures of sulfonic acid and carboxylic acid are also possible.

In a preferred embodiment, the aqueous collection solution contains oxalic acid in a concentration of 0.5-2 mol/L, in particular 1±0.2 mol/L.

In a preferred embodiment, the aqueous collecting solution when introduced into step c) is at room temperature, i.e. 20°C ± 7°C, in particular 25°C ± 2°C.

In the process, the sulfonic acid and/or carboxylic acid preferably has a concentration in the collecting solution of at least 0.5 mol/L, in particular 1±0.5 mol/L, particularly preferably 1 mol/L before the RuÜ4 formed is introduced .

In a preferred embodiment of the invention, the method according to the invention is also a method for separating ruthenium and platinum or iridium, wherein the ruthenium-containing material also contains platinum and/or iridium, and wherein the oxidizing agent in step a) is potassium persulfate, so that in step b) ruthenium is oxidized to ruthenium tetroxide and platinum and/or iridium is precipitated as a potassium complex. In the case of platinum this is presumably the K2PtCl6 complex, in the case of iridium it is probably the ^IrCle complex.

This is very advantageous because various ruthenium-containing materials (such as electrocatalysts) often contain platinum and/or iridium in addition to ruthenium and, in addition to recovering the ruthenium, these can also be separated from it at the same time.

A solid-liquid separation then expediently takes place.

In a preferred embodiment, the ruthenium-containing material includes solid Rulr.

In one embodiment, the Ru content of the Ru-containing material is at least 4%, in particular 5.6±0.5%.

The mass ratio of the amount of Ru-containing material used to persulfate is preferably 1:50.

The mass ratio of ruthenium (in the Ru-containing material used) to persulfate is preferably 1:730 to 1:2000, in particular 1:960 to 1:1600.

To implement the invention, it is also expedient to combine the above-described inventive configurations, embodiments and features of the claims with one another.

Fig. 1 shows recovery yields with the process according to the invention versus the duration of the process. Examples of embodiments

The invention will be explained in more detail below using specific exemplary embodiments without restricting the invention.

Comparative Example 1: (Na persulfate, collecting solution with HCl, made of solid Ru-containing material)

0.2 g of solid Rulr (Ru content 5.6 wt.%), which is on a support made of antimony-doped tin oxide (ATC, Sb20s/Sn02), was weighed into a 100 mL round three-necked flask. The persulfate salt, in the form of solid Na2S20s (10.72 g), was added to the flask to reach the concentration of 1 M (=1 mol/L) in the final volume of 45 mL. The target volume was adjusted using 1.5 M sulfuric acid. The temperature of the resulting mixture was maintained at 60 °C and stirred for 2.5 h. The collecting solution in which the ruthenium tetroxide formed was collected consisted of 4 M hydrochloric acid solution with 5 vol.% ethanol. The Ru yield was 85.5%.

Comparative example 2: (Na persulfate, collecting solution with HCl, from Ru-containing solution)

10.72 g of Na2S20s were dissolved in 45 mL of a solution containing various metals Ru, Ir, Sn and Sb in the concentrations of 0.15 g/L, 0.85 g/L, 1.75 g/L and 0. 02 g/L contains. In the case of a hydrochloric acid-based solution of the metals, the additional absorption medium ammonium carbonate ((NH^COa) must be used for the separation of the chlorine gas as NH4Cl. The same solution as in exemplary embodiment 1 was used as the collecting solution for the ruthenium tetroxide formed. At 60 ° C The yield of 93.7% for Ru was reached after 2.5 hours.

Example 3: (Na persulfate, collecting solution with oxalic acid, made of solid Ru-containing material)

0.1 g of the RuPt powder (Ru content 14.9% by weight) on a carbon support material was mixed with 10.72 g of Na2S2Ü8 to achieve a final concentration of 1 M persulfate salt in 45 mL solution, as in Example 1 described. The resulting mixture was heated to 60 °C. The ruthenium content was measured in the receiving solution containing 1 M oxalic acid. Under these conditions, a Ru recovery of 45.2% was achieved after 2.5 hours.

Comparative example 4: (K-persulfate, collecting solution with HCl, from Ru-containing solution)

5 mL of a RuPt-containing solution, which contains 3.3 g/L Ru and 6.8 g/L Pt, were mixed with 12.16 g potassium persulfate (K2S2O8) and dissolved in 40 mL 1.5 M sulfuric acid. In this case, Ru is separated in the form of ruthenium tetroxide and trapped by an acidic solution of HCl, while Pt is simultaneously in the form of potassium hexachloroplatinate(IV) (KaPtCle) in the reaction flask is canceled. A 2 M hydrochloric acid solution with 5 vol.% ethanol was used as a collecting solution for ruthenium tetroxide. The Ru recovery yield was 95.5% after 1 h at 60 °C.

Example 5: (collection solution with sulfonic acids or various carboxylic acids with at least two carboxy groups)

Solid Ru-containing materials were used for the volatilization tests. In each experiment, the peroxodisulfate salt (Na2S2O8, K2S2O8, or (NH4)2S20s) as a solid was added to a 100 mL three-necked round bottom flask and brought to a concentration of 1 M with deionized water, in a final volume of 45 mL. The addition of H2SO4 (3M) solution was tested to investigate its influence on the self-decomposition of peroxodisulfate salt. Thereafter, the temperature was maintained at 60°C and the stirring speed was set to 600 rpm. Next, the material was added once the desired temperature was reached. Several acidic solutions (methanesulfonic acid and benzenesulfonic acid, or oxalic acid, tartaric acid and citric acid) were tested as collection solutions for RuC>4 capture (100 mL total volume).

The results are shown in Figure 1.

Comparative examples:

Attempts with the reducing agent ammonium chloride or acetylacetonate in step c) were not successful.

Claims

Patent claims 1. Process for recovering ruthenium from a ruthenium-containing material, with the steps: a) adding an oxidizing agent to a ruthenium-containing material, b) oxidizing the ruthenium to ruthenium tetroxide, and c) introducing the ruthenium tetroxide formed into an aqueous collecting solution, characterized in that the aqueous collecting solution contains an acid selected from sulfonic acids and carboxylic acids with at least two carboxy groups on the carboxylic acid. 2. The method according to claim 1, wherein the sulfonic acid is methanesulfonic acid or benzenesulfonic acid and the carboxylic acid is oxalic acid, tartaric acid or citric acid. 3. The method according to any one of claims 1 or 2, wherein the sulfonic acid and/or carboxylic acid each has a concentration in the collecting solution of at least 1 mol/L. 4. The method according to any one of claims 1 to 3, wherein the oxidizing agent in step a) is selected from persulfates. 5. The method according to claim 4, wherein the persulfate is brought to a concentration of 0.5 to 6 mol/L with sulfuric acid after the addition in step a). 6. The method according to any one of claims 4 or 5, wherein the persulfate is brought to a concentration of 1.5 ± 0.5 mol/L with sulfuric acid after the addition in step a). 7. The method according to any one of claims 1 to 6, wherein the oxidizing agent is selected from sodium persulfate and potassium persulfate. 8. The method of claim 7, wherein the oxidizing agent is potassium persulfate. 9. The method according to any one of claims 1 to 8, wherein in step b) the temperature is adjusted to 50-90°C. 10. The method according to any one of claims 1 to 9 for the separation of ruthenium and platinum or iridium, wherein the ruthenium-containing material also contains platinum and / or iridium, and where the oxidizing agent in step a) is potassium persulfate, so that in step b) ruthenium is oxidized to ruthenium tetroxide and platinum and/or iridium is precipitated as a potassium complex. Use of an acid selected from sulfonic acids and carboxylic acids with at least two carboxy groups on the carboxylic acid for a process for recovering ruthenium from a ruthenium-containing material according to any one of claims 1 to 10. Use of the process according to any one of claims 1 to 10: in in precious metal processing, extraction or refining, in the recycling of electrocatalysts, autocatalysts, electronic components, in the recycling of electrodes from fuel cells, circuit boards or electrolysers, in the processing of anode sludge resulting from electrolysis, and/or for the production of halide-free ruthenium -Links.