DE102022111440B3 - Process 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: 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 trapping solution contains an acid selected from sulfonic acids and carboxylic acids having at least two carboxy groups. It further describes the use of such an acid in the process and the use of the process in various fields.

Description

The invention relates to a method for recovering ruthenium.

Current methods for recovering ruthenium, e.g. from spent catalysts, are very complex and involve multiple pre-treatment and post-treatment steps. In the first step, the ruthenium-containing material is usually pretreated in order to obtain ruthenium oxide or metallic ruthenium powder.

Due to its limited availability and high demand, ruthenium is one of the most expensive metals from the platinum metal group. Ruthenium recycling is becoming increasingly important due to its importance in the manufacture of catalysts for the production of hydrogen as a zero-emission energy source. 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 due to the high temperature treatment required to separate ruthenium.

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

That in patent US4,002,470 The method described 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 forms ruthenium tetroxide. This oxidation occurs in the presence of an acid, starting at 1% to 90% (Step II). The ruthenium tetroxide is then collected in an absorbent solution. Here, ruthenium tetroxide is reduced at a temperature between 40 °C and 150 °C to form a halogenated ruthenic acid or a ruthenate, 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 elsewhere to reduce RuO ₄ using an aqueous acidic ethanol solution.

Out of US4,002,470 is also known to use the monocarboxylic acid acetic acid as a collecting solution. The disadvantage is that high losses occur when the ruthenium tetroxide is collected.

Ruthenium tetroxide corresponds to the formula RuO ₄ and the Ru is in 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 have to be carried out to obtain the ruthenium. The amount of peroxide, the temperature, pressure and time of treatment, and the strength of the acid solution must be carefully controlled, otherwise slow dissolution rate, prolonged oxidation time, and loss of ruthenium result. 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 in patent CN1872418A presented method involves the calcination of a carbon-loaded ruthenium catalyst at 600-1000 °C to remove the carbon support. This is followed by alkaline digestion with KOH and KNO ₃ 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 formed ruthenium tetroxide is treated with hydrochloric acid solution to obtain ruthenium halide. Hydrogen is used for the reduction to ruthenium. The process described is complicated and requires concentrated acids for volatilization (ie oxidation to ruthenium tetroxide) which are very corrosive. In addition, the long-term heating at high temperatures during the calcination and melting steps requires a large amount of energy.

At an in US2008/0287282A1 The proposed method for volatilizing Ru in one step to RuO ₄ 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% is obtained when using a ruthenium chloride oxide catalyst. 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 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 has to be melted beforehand, and this melting requires temperatures, preferably from 350 to 700° C., and is therefore relatively energy-intensive.

This in US2008/0293836A1 The process described consists of the reduction of ruthenium oxide to ruthenium metal with hydrogen vapor at elevated temperature, typically 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 about 100°C. The 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 lasts 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 obtain RuO ₄ . The metallic ruthenium is obtained after the oxidation and precipitation step and the subsequent reduction of the (NH ₄ ) ₂ RuCl ₆ powder in a hydrogen atmosphere at high temperature. The recovery process is lengthy and involves several pre-treatment steps before volatilization of Ru to RuO ₄ in an aggressive, oxidative atmosphere to finally recover Ru.

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

One in patent US8,454,914B2 The process described 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 instead by means of a reducing gas. The resulting solid is cooled and mixed with an oxidizing agent to solubilize the ruthenium. The disadvantage of this method is the use of high temperatures for ruthenium reduction and the safety issues of using hydrogen as the 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, the alkaline melting or the ruthenium distillation. Several methods 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 high energy investments and can lead to losses of ruthenium during thermal processing, since ruthenium is highly volatile in its highest oxidation state. Separation in an oxidizing atmosphere involves high consumption of corrosive gases such as ozone, oxygen, chlorine or a mixture of hydrochloric acid and oxygen. In the case of volatilization from the solution, due to the low oxidation potential of the proposed systems, high temperatures are also required for effective removal of ruthenium. Although some methods suggest 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, ruthenium can only be dissolved under aggressive conditions (e.g. with concentrated hydrochloric acid at a temperature of up to 150 °C), and mainly in autoclaves. At the same time, impurities can be introduced into 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 flexible enough that both solid and liquid ruthenium-containing materials can be used with the invention.

The 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 from electrolysers.

According to the invention, the object is achieved by the subject matter of the independent claims. Advantageous developments of the invention are specified in the dependent claims.

1. a) Zugabe eines Oxidationsmittels zu einem Ruthenium-haltigen Material,
2. b) Oxidation des Rutheniums eines Ruthenium-haltigen Materials zu Rutheniumtetroxid, und
3. c) Einleiten des gebildeten Rutheniumtetroxids in eine wässrige Auffanglösung,

dadurch gekennzeichnet, dass die wässrige Auffanglösung eine Säure ausgewählt aus Sulfonsäuren und Carbonsäuren mit mindestens zwei Carboxygruppen enthält.The invention relates to a method for recovering ruthenium from a ruthenium-containing material, with the steps:

1. a) addition of an oxidizing agent to a ruthenium-containing material,
2. b) oxidation of the ruthenium of a ruthenium-containing material to ruthenium tetroxide, and
3. c) introducing the ruthenium tetroxide formed into an aqueous collecting solution,

characterized in that the aqueous trapping solution contains an acid selected from sulfonic acids and carboxylic acids having 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 being introduced into the aqueous solution according to the invention, the sulfonic acid or the carboxylic acid in the aqueous capture solution being able to reduce the RuO ₄ , the RuO ₄ due to its oxidation power the sulfonic acid or the carboxylic acid oxidizes. Step c) is therefore a redox reaction between RuO ₄ and the acid. It is possible that the acids according to the invention complex the RuO ₄ very well, so that the redox pair, namely RuO ₄ and the reducing acid, are brought close to one another by complexing. When the ruthenium tetroxide is reduced, ruthenium compounds of different oxidation states are formed. In particular, compounds with ruthenium in the oxidation states Ru(III) and Ru(IV) are formed.

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

The term sulfonic acid includes aryl and alkyl sulfonic acid (where aryl = C5-C6 ring and where 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 the carboxy groups on an aromatic compound, and alkyl carboxylic acids, ie those with carboxy groups on an alkyl chain of length C1-C12 are included. The alkyl chain or the aromatic can also be substituted with small substituents such as NH ₂ (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 α-ketoglutaric acid). It also includes acids with more than two carboxylic acid groups. Dicarboxylic acids and tricarboxylic acids are preferred.

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

• - in der Edelmetallverarbeitung, -extraktion oder -raffination,
• - im Recycling von Elektrokatalysatoren, Autokatalysatoren, elektronischen Bauteilen,
• - im Recycling von Elektroden von Brennstoffzellen, von Leiterplatten oder von Elektrolyseuren,
• - bei der Aufarbeitung von bei der Elektrolyse anfallendem Anodenschlamm (wie bspw. bei der Cu-, Pb- oder Sn-Raffinerie), und/oder
• - zur Herstellung von halogenidfreien Ruthenium-Verbindungen.

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, autocatalysts, electronic components,
• - in the recycling of electrodes from fuel cells, printed circuit boards or electrolysers,
• - in the processing of anode sludge occurring during electrolysis (e.g. in the Cu, Pb or Sn refinery), and/or
• - for the production of halide-free ruthenium compounds.

A surprising advantage of the method according to the invention is that the sulfonic acid or carboxylic acid in the aqueous collecting solution lead to very high rates of collecting RuO ₄ . Apparently these acids are very good at complexing the ruthenium tetroxide well at the Ru atom and therefore bringing it together for reduction by these acids.

The process results in only minor losses of ruthenium, despite the volatility of the intermediate ruthenium tetroxide. The introduction and speedy reduction by the acids according to the invention in the aqueous collecting solution have proven to be advantageous. Considering the entire process, this combination leads to an extremely high recovery rate of ruthenium.

The application of the method according to the invention has a high potential for the field of hydrogen production and application, and for Improving the existing circular economy in the manufacture of electrocatalysts by allowing the process to reuse the recovered ruthenium.

It is advantageously a low-temperature process. In addition, 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, after the addition in step a), the persulfate is brought to a concentration of 0.5 to 6 mol/L with sulfuric acid, in particular to concentrations of, for example, 1 mol/L or 3 mol/L or 5 mol/L or 6 mol/L, particularly preferably to 1.5±0.5 mol/L, even 1.5-2 mol/L. Advantageously, this speeds up the distillation process for the RuO ₄ by adjusting the pH of the oxidizing solution and slowing 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 favorable for this adjustment of the concentration

In a preferred embodiment, the oxidizing agent in step a) is selected from persulfates, persulfate being known to denote, for example, peroxodisulfate compounds (counterion S ₂ O ₈ ^2- ) and peroxomonosulfate compounds (counter ion SO ₅ ^2- ).

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

It is also possible to dispense with melting the ruthenium-containing material.

Because with a strong oxidizing agent, such as persulfates, in steps a) and b), this strong oxidizing agent can oxidize all the ruthenium contained completely to RuO ₄ .

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

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

It is particularly preferred that potassium persulfate has the advantage that all of the RuO ₄ can be collected after only 1.5 hours of introduction into step c), so that a yield of 100% of the RuO ₄ formed in step b) can be collected .

In a preferred embodiment, the temperature in step b) 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 persulphate does not decompose and it is therefore not necessary to add it again.

In step b), stirring is preferably carried out for 2-3 hours, in particular 2.5 hours.

In one embodiment, the acid is a carboxylic acid having 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, α-ketoglutaric acid, oxaloacetic acid, ortho-phthalic acid, isophthalic acid, terephthalic acid, glutamic acid or aspartic acid. It is particularly preferably oxalic acid, tartaric acid or citric acid.

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

Preferably the sulfonic acid is 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 trapping solution contains oxalic acid in a Concentration of 0.5-2 mol/L, especially 1±0.2 mol/L.

In a preferred embodiment, the aqueous collecting solution is at room temperature when it is introduced into step c), 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 RuO ₄ formed is introduced. L

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 K ₂ PtCl ₆ complex, in the case of iridium it is probably the K ₂ IrCl ₆ complex.

This is very advantageous since various ruthenium-containing materials (such as electrocatalysts, for example) often contain platinum and/or iridium in addition to ruthenium, and these can be separated from the ruthenium at the same time as they are recovered.

Appropriately, a solid-liquid separation then 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.

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

1 Figure 12 shows recovery yields with the process of the invention versus the duration of the process.

exemplary embodiments

The invention is to be explained in more detail below on the basis of specific exemplary embodiments, without restricting the invention.

Comparative example 1: (Na persulfate, trapping solution with HCl, from solid Ru-containing material)

0.2 g of solid Rulr (Ru content 5.6 wt%) supported on antimony-doped tin oxide (ATC, Sb ₂ O ₅ /SnO ₂ ) was weighed into a 100 mL three-necked round flask . The persulfate salt, in the form of solid Na ₂ S ₂ O ₈ (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 set using 1.5 M sulfuric acid. The temperature of the resulting mixture was maintained at 60°C and stirred for 2.5 hours. The collecting solution, in which the formed ruthenium tetroxide is collected, consisted of 4 M hydrochloric acid solution with 5% by volume ethanol. The Ru yield was 85.5%.

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

10.72 g of Na ₂ S ₂ O ₈ 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. In the case of a hydrochloric acid-based solution of the metals, the additional absorption medium ammonium carbonate ((NH ₄ ) ₂ CO ₃ ) must be used to separate the chlorine gas as NH ₄ Cl. As a collecting solution for the ruthenium tetroxide formed, the same solution as in Example 1 was used. 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 wt%) on a carbon support was mixed with 10.72 g Na ₂ S ₂ O ₈ to reach a final concentration of 1 M persulfate salt in 45 mL solution , as described in example 1. The resulting mixture was heated to 60°C. The ruthenium content was measured in the receiving solution containing 1M oxalic acid. Under these conditions, 45.2% Ru recovery 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 containing 3.3 g/L Ru and 6.8 g/L Pt were mixed with 12.16 g potassium persulfate (K ₂ S ₂ O ₈ ) and dissolved in 40 mL 1.5 M dissolved 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 precipitated in the reaction flask in the form of potassium hexachloroplatinate(IV) (K ₂ PtCl ₆ ). A 2M hydrochloric acid solution containing 5% by volume of 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: (Collecting solution with sulfonic acids or various carboxylic acids with at least two carboxy groups)

Solid Ru-containing materials were used for the volatilization experiments. In each experiment, the peroxodisulfate salt (Na ₂ S ₂ O 8 , K ₂ S ₂ O ₈ , or (NH ₄ ) ₂ S ₂ O ₈ ) as a solid was placed in a 100 mL three-necked round bottom flask and diluted with deionized water to a concentration of Brought to 1 M, in a final volume of 45 mL. The addition of H ₂ SO ₄ (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 at 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 trapping solutions for the RuO ₄ capture (100 mL total volume).
The results are in 1 shown.

Comparative examples:

Attempts with the reducing agent ammonium chloride or acetylacetonate in step c) were unsuccessful.

Claims (12)

Method 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 that the aqueous trapping solution contains an acid selected from sulfonic acids and carboxylic acids having at least two carboxy groups on the carboxylic acid. procedure after claim 1 wherein the sulfonic acid is methanesulfonic acid or benzenesulfonic acid and the carboxylic acid is oxalic acid, tartaric acid or citric acid. Procedure according to 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. Procedure according to one of Claims 1 until 3 , wherein the oxidizing agent in step a) is selected from persulfates. procedure after claim 4 , the persulfate being brought to a concentration of 0.5 to 6 mol/L after the addition in step a) with sulfuric acid. Procedure according to one of Claims 4 or 5 , the persulfate being brought to a concentration of 1.5±0.5 mol/L with sulfuric acid after the addition in step a). Procedure according to one of Claims 1 until 6 , wherein the oxidizing agent is selected from sodium persulfate and potassium persulfate. procedure after claim 7 , where the oxidizing agent is potassium persulfate. Procedure according to one of Claims 1 until 8th , being heated to 50-90 ° C in step b). Procedure according to one of Claims 1 until 9 for separating ruthenium and platinum or iridium, where 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 or iridium is precipitated as a potassium complex. Use of an acid selected from sulfonic acids and carboxylic acids having at least two carboxy groups on the carboxylic acid in a process for recovering ruthenium from a ruthenium-containing material according to any one of Claims 1 until 10 . Use of the method according to one of Claims 1 until 10 : - in precious metal processing, extraction or refining, - in recycling of electrocatalysts, autocatalysts, electronic components, - in the recycling of electrodes from fuel cells, printed circuit boards or electrolysers, - in the processing of anode sludge produced during electrolysis, and/or - for the production of halide-free ruthenium compounds.

Images