A process for the recovery and purification of chloroiridic acid from spent iridium-containing catalysts

Abstract

The application discloses a method for recovering and purifying chloroiridic acid from an iridium-containing waste catalyst, which comprises the following steps: firstly, mixing the iridium-containing waste catalyst with a reaction aid and a solid oxide, and then performing a melting reaction under the temperature condition of 250-400 DEG C to obtain an iridium oxide melt which is hardly soluble in water; secondly, adding water to the melt to remove impurities, and then filtering to obtain the iridium oxide; finally, adding acid to the iridium oxide to obtain a chloroiridic acid solution. The method for recovering and purifying chloroiridic acid from the iridium-containing waste catalyst can obtain the iridium oxide which is only soluble in acid but hardly soluble in water after the melting reaction under the temperature condition of 250-400 DEG C, and then the metal impurities and the catalyst carrier in the catalyst can be removed by simple water washing, and the chloroiridic acid can be obtained by acid leaching, so that the method is short in route, low in cost, and suitable for industrial application; in addition, the purity of the chloroiridic acid is high (more than 99.95%), and the recovery rate is also high (more than 98%).

Description

Technical Field

[0001] This invention belongs to the field of catalyst separation and recovery in battery MEA, and particularly relates to a method for recovering and purifying chloroiridium acid from iridium-containing waste catalyst. Background Technology

[0002] The membrane electrode assembly (MEA) in a proton exchange membrane fuel cell (PEMFC) typically consists of seven layers hot-pressed together: an anode diffusion layer, an anode porous carbon layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, a cathode porous carbon layer, and a cathode diffusion layer. The catalyst layer mainly consists of iridium oxide and a support, such as alumina, carbon, or titanium oxide. After operating within the fuel cell for a certain period, the MEA may become unusable due to external contamination or catalyst buildup. However, the physicochemical properties of precious metals such as platinum and iridium in the catalyst layer of the spent fuel cell remain unchanged; only the catalytic activity decreases. Therefore, the catalyst and proton exchange membrane can be separated to recover the precious metals from both.

[0003] Traditional iridium recovery methods include alkaline dissolution and acid dissolution. Alkaline fusion at high temperatures converts iridium into iridium oxides, but this method inevitably results in impurities in the iridium precipitate, increasing the difficulty of subsequent purification. While acid dissolution can dissolve most of the support, the iridium oxide in the catalyst is stable and highly corrosion-resistant due to its composition from iridium compounds and weak oxidants, making it difficult to dissolve with acid at room temperature and pressure, resulting in low iridium recovery rates. Furthermore, recovering iridium from the catalyst to elemental iridium typically requires high-temperature hydrogen reduction, which demands sophisticated equipment and processes. Elemental iridium also needs to be further processed into iridium compounds for the synthesis of iridium catalysts. Therefore, the optimal process is to directly recover iridium and prepare iridium compounds, bypassing the preparation of elemental iridium. To address the problems of these traditional recovery methods, current technology proposes high-temperature alkaline fusion followed by direct acid hydrolysis, and then resin extraction to obtain chloroiridic acid, thus improving the purity of iridium. Compared to traditional recycling methods, this method improves purity, but the longer process route leads to a decrease in iridium extraction rate. Furthermore, the acid hydrolysis after alkali fusion consumes a large amount of acid, resulting in higher costs and making it unsuitable for industrial application.

[0004] Therefore, shortening the recycling process and improving the iridium recovery rate to obtain high-purity chloroiridium acid are key control points in the iridium recycling and reuse cycle. Summary of the Invention

[0005] Objective of the invention: This invention provides a method for recovering and purifying chloroiridium acid from iridium-containing waste catalysts, aiming to shorten the recovery route, reduce costs, and obtain chloroiridium acid with high iridium recovery rate and high purity.

[0006] The present invention provides a method for recovering and purifying chloroiridium acid from iridium-containing spent catalysts, comprising the following steps:

[0007] (1) After thoroughly mixing the iridium-containing waste catalyst with the reaction aid and solid oxide, the mixture is melted and reacted at a temperature of 250-400℃ to obtain a water-insoluble iridium oxide melt.

[0008] (2) Add water to the melt and stir to wash it to remove impurities. After filtration, iridium oxide is obtained.

[0009] (3) Dissolve the oxide of iridium by adding acid to obtain a chloroiridium acid solution.

[0010] Furthermore, in step (1) of the recycling and purification method, the reaction aid is selected from sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfonate, and the mass ratio of the reaction aid to the iridium-containing waste catalyst is (2-3):1.

[0011] Furthermore, in step (1) of the recycling and purification method, the solid oxide is at least one of the alkali metal peroxides, the alkali metal element in the alkali metal peroxide is sodium or potassium, and the mass ratio of the alkali metal peroxide to the iridium-containing waste catalyst is (1-2):1.

[0012] Furthermore, in step (1) of the recycling and purification method, the melting reaction time is 4-8 hours.

[0013] Furthermore, in step (2) of the recycling and purification method, the mass ratio of water to molten material is (10-20):1, the stirring and washing time is 4-8 hours, and the washing temperature is maintained at 30-60℃.

[0014] Furthermore, in step (3) of the recycling and purification method, the acid used is hydrochloric acid with a mass fraction of 36-38%.

[0015] Furthermore, in step (3) of the recycling and purification method, the ratio of the amount of acid added to the mass of iridium in the iridium-containing waste catalyst is (15-25):1.

[0016] Beneficial effects: Compared with the prior art, the significant advantage of this invention is that the method for recovering and purifying chloroiridium acid from iridium-containing waste catalysts can obtain iridium oxides that are soluble in acid but not in water after a melt reaction at a temperature of only 250-400℃. Then, the metal impurities and catalyst support in the catalyst can be removed by simple water washing, and chloroiridium acid can be obtained by acid leaching. This method not only has a short route and can reduce the calcination temperature, but also has low cost and is suitable for industrial applications. Similarly, the purity of chloroiridium acid is high (reaching more than 99.95%) and the recovery rate is also high (reaching more than 98%). Detailed Implementation

[0017] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0018] It should be noted that the chemical reagents used in the embodiments and comparative examples of this invention, such as sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, and sodium peroxide, are preferably of analytical grade, and the mass fraction of hydrochloric acid is preferably 36%. Furthermore, the main components of the iridium-containing waste catalyst are shown in Table 1.

[0019] Table 1. Main components of iridium-containing spent catalysts

[0020]

[0021] Example 1

[0022] This Example 1 describes a method for recovering and purifying chloroiridium acid from iridium-containing spent catalysts, comprising the following steps:

[0023] (1) 10g of iridium-containing waste catalyst (containing 1g of iridium), 20g of sodium peroxide and 20g of sodium dodecylbenzenesulfonate were mixed evenly and reacted at 400℃ for 4h to obtain 45.2g of solid melt.

[0024] (2) Add 500g of water to the solid melt, stir and wash at 60°C for 4 hours, and filter to obtain iridium-containing insoluble matter.

[0025] (3) Add 20g of hydrochloric acid to the iridium-containing insoluble matter to dissolve it into a chloroiridium acid solution. Heat and concentrate until the mass fraction of iridium in the chloroiridium acid solution reaches 20%. The impurity index of the chloroiridium acid solution is shown in Table 2.

[0026] Example 2

[0027] Example 2 describes a method for recovering and purifying chloroiridium acid from iridium-containing spent catalyst, comprising the following steps:

[0028] (1) Add 15g of sodium peroxide and 30g of sodium dodecylbenzenesulfonate to 10g of iridium-containing waste catalyst (containing 1g of iridium), mix evenly, and melt at 300℃ for 4h to obtain 48.0g of solid melt.

[0029] (2) Add 500g of water to the solid melt, stir and wash at 60°C for 6 hours, and filter to obtain iridium-containing insoluble matter.

[0030] (3) Add 25g of hydrochloric acid to the iridium-containing insoluble matter to dissolve it into a chloroiridium acid solution; heat and concentrate until the mass fraction of iridium in the chloroiridium acid solution reaches 20%, and test the impurity index in the chloroiridium acid solution as shown in Table 2.

[0031] Example 3

[0032] Example 3 describes a method for recovering and purifying chloroiridium acid from iridium-containing spent catalysts, comprising the following steps:

[0033] (1) Add 10g of sodium peroxide and 20g of sodium dodecylbenzenesulfonate to 10g of iridium-containing waste catalyst (containing 1g of iridium), mix evenly, and melt at 250℃ for 4h to obtain 37.5g of solid melt.

[0034] (2) Add 500g of water to the solid melt, stir and wash at 30°C for 4 hours, and filter to obtain iridium-containing insoluble matter.

[0035] (3) Add 25g of hydrochloric acid to the iridium-containing insoluble matter to dissolve it into a chloroiridium acid solution; heat and concentrate until the mass fraction of iridium in the chloroiridium acid solution reaches 20%, and test the impurity index in the chloroiridium acid solution as shown in Table 2.

[0036] Example 4

[0037] Example 4 describes a method for recovering and purifying chloroiridium acid from iridium-containing spent catalysts, comprising the following steps:

[0038] (1) Add 20g of sodium peroxide and 30g of sodium dodecyl sulfonate to 10g of iridium-containing waste catalyst (containing 1g of iridium), mix evenly, and melt at 300℃ for 4h to obtain 52.8g of solid melt.

[0039] (2) Add 600g of water to the solid melt, stir and wash at 30°C for 4 hours, and filter to obtain iridium-containing insoluble matter.

[0040] (3) Add 20g of hydrochloric acid to the iridium-containing insoluble matter to dissolve it into a chloroiridium acid solution; heat and concentrate until the mass fraction of iridium in the chloroiridium acid solution reaches 20%, and test the impurity index in the chloroiridium acid solution as shown in Table 2.

[0041] Example 5

[0042] Example 5 describes a method for recovering and purifying chloroiridium acid from iridium-containing spent catalysts, comprising the following steps:

[0043] (1) Mix 10g of iridium-containing waste catalyst (containing 1g of iridium), 20g of sodium peroxide, 10g of sodium dodecylbenzenesulfonate and 10g of sodium dodecyl sulfonate evenly, and melt them at 400℃ for 4h to obtain 44.0g of solid melt.

[0044] (2) Add 500g of water to the solid melt, stir and wash at 60°C for 4 hours, and filter to obtain iridium-containing insoluble matter.

[0045] (3) Add 20g of hydrochloric acid to the iridium-containing insoluble matter to dissolve it into a chloroiridium acid solution. Heat and concentrate until the mass fraction of iridium in the chloroiridium acid solution reaches 20%. The impurity index of the chloroiridium acid solution is shown in Table 2.

[0046] Comparative Example 1

[0047] The method for recovering and purifying chloroiridic acid from iridium-containing spent catalyst in Comparative Example 1 is basically the same as that in Example 1, except that no reaction aid is used, and conventional alkali is used for alkali fusion, including the following steps:

[0048] (1) Add 20g of sodium peroxide and 20g of sodium hydroxide to 10g of iridium-containing waste catalyst (containing 1g of iridium), mix evenly, and melt at 400℃ for 4h to obtain 49.2g of solid melt.

[0049] (2) Add 600g of water to the solid melt, stir and wash at 60°C for 4 hours, and filter to obtain iridium-containing insoluble matter.

[0050] (3) Add 20g of hydrochloric acid to the iridium-containing insoluble matter to dissolve it into a chloroiridium acid solution; heat and concentrate until the mass fraction of iridium in the chloroiridium acid solution reaches 20%, and test the impurity index in the chloroiridium acid solution as shown in Table 2.

[0051] Comparative Example 2

[0052] The method for recovering and purifying chloroiridium acid from iridium-containing spent catalyst in Comparative Example 2 is basically the same as that in Example 1, except that no reaction aid is used, and conventional alkali is used with an increased alkali fusion temperature. The method includes the following steps:

[0053] (1) Add 20g of sodium peroxide and 20g of sodium hydroxide to 10g of iridium-containing waste catalyst (containing 1g of iridium), mix evenly, and melt at 650℃ for 4h to obtain 47.8g of solid melt.

[0054] (2) Add 600g of water to the solid melt, stir and wash at 60°C for 4 hours, and filter to obtain iridium-containing insoluble matter.

[0055] (3) Add 20g of hydrochloric acid to the iridium-containing insoluble matter to dissolve it into a chloroiridium acid solution; heat and concentrate until the mass fraction of iridium in the chloroiridium acid solution reaches 20%, and test the impurity index in the chloroiridium acid solution as shown in Table 2.

[0056] Comparative Example 3

[0057] The method for recovering and purifying chloroiridium acid from iridium-containing spent catalyst in Comparative Example 3 is basically the same as that in Example 1, except that no reaction aid is used, and conventional alkali is used with an increased alkali fusion temperature. The method includes the following steps:

[0058] (1) Add 20g of sodium peroxide and 20g of sodium hydroxide to 10g of iridium-containing waste catalyst (containing 1g of iridium), mix evenly, and melt at 550℃ for 4h to obtain 48.1g of solid melt.

[0059] (2) Add 600g of water to the solid melt, stir and wash at 60°C for 4 hours, and filter to obtain iridium-containing insoluble matter.

[0060] (3) Add 20g of hydrochloric acid to the iridium-containing insoluble matter to dissolve it into a chloroiridium acid solution; heat and concentrate until the mass fraction of iridium in the chloroiridium acid solution reaches 20%, and test the impurity index in the chloroiridium acid solution as shown in Table 2.

[0061] Table 2 Impurity Index in Chloroirilic Acid Solution

[0062]

[0063] Meanwhile, the iridium recovery rate was calculated according to the formula: iridium recovery rate = iridium content in chloroiridium acid / iridium content in catalyst. The iridium content in chloroiridium acid = iridium content in chloroiridium acid solution * iridium mass fraction in chloroiridium acid solution. The iridium recovery rates of the examples and comparative examples were calculated, and the results are shown in Table 3 below.

[0064] Table 3 Iridium recovery rate

[0065]

[0066] As shown in Table 2, the chloroiridium acid obtained using the recovery and purification methods of the embodiments and comparative examples of the present invention has high purity. However, further analysis of the data in Table 3 shows that the recovery and purification method of the embodiments of the present invention can achieve an iridium recovery rate of over 98% in iridium-containing waste catalysts.

[0067] The recovery and purification method used in Comparative Example 1 only achieved an iridium recovery rate of approximately 90%. Furthermore, as shown in Table 2, the chloroiridium acid obtained by the method in Comparative Example 1 has a low purity. This is because iridium binds to sodium under strongly alkaline conditions, making effective separation by water washing impossible. The recovery and purification method used in Comparative Example 2 achieved an even lower recovery rate of only about 88%. Table 3 shows that the recovery rates of Comparative Examples 1-3 indicate that at high temperatures, especially between 400-650℃, conventional methods form more soluble NaIrO. x Therefore, washing with water increases iridium loss and reduces the recovery rate. Furthermore, compared to Comparative Example 2, this embodiment of the invention achieves improved recovery rate under lower temperature conditions, effectively reducing production line costs.

[0068] Based on the above embodiments and comparative examples, and further mechanistic analysis, it can be seen that by using sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfonate to replace the traditional alkaline hydroxide during the melting reaction, the present invention can reduce the temperature required for melting activation, achieving sufficient enhancement of iridium activity at 250-400℃ to form iridium oxide IrO, which is easily soluble in acids. x It can also directionally form sodium iridium oxide (NaIrO) that is soluble only in acids, thus avoiding the formation of water-soluble sodium iridium oxide (NaIrO). xMetal impurities in iridium-containing waste catalysts can be removed simply by washing with water to obtain iridium oxides that are insoluble in water and highly active. Combined with acid leaching, high-purity chloroiridium acid can be obtained.

[0069] Furthermore, referring to the purity table in Table 2, it can be further seen that this invention, by using sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfonate to replace the traditional alkaline substance hydroxide during the melting reaction, can also effectively remove iridium-containing waste catalyst support, thereby obtaining high-purity chloroiridium acid. Based on this, combined with mechanism analysis, it can be seen that its effective removal is due to the introduction of sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfonate, which can provide metal ligands, reacting with the silicon-aluminum components in the waste catalyst under alkaline conditions to form water-soluble aluminosilicates, thus allowing for removal by direct water washing.

[0070] The recycling and purification process of this invention is not only short and simple, but also has high purity, high recovery rate, and low sintering temperature, resulting in reduced overall costs and increased efficiency.

[0071] In addition to the above embodiments, it should be noted that the technical effects claimed by the present invention can be achieved by using the eluent and the parameter range defined by the method of use of the present invention, and therefore, no further examples will be provided. For example, the reaction aid may also be sodium dodecyl sulfonate, or a compound of sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate. The solid oxide may also be potassium peroxide.

Claims

1. A method for recovering and purifying chloroiridium acid from iridium-containing waste catalyst, characterized in that, Includes the following steps: (1) After thoroughly mixing the iridium-containing waste catalyst with the reaction aid and solid oxide, the mixture is melted and reacted at a temperature of 250-400℃ to obtain a water-insoluble iridium oxide melt. (2) Add water to the melt and stir to wash it to remove impurities. After filtration, iridium oxide is obtained. (3) Dissolve the oxide of iridium by adding acid to obtain a chloroiridium acid solution.

2. The method for recovering and purifying chloroiridium acid from iridium-containing waste catalyst according to claim 1, characterized in that, In step (1), the reaction aid is selected from sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfonate, and the mass ratio of the reaction aid to the iridium-containing waste catalyst is (2-3):

1.

3. The method for recovering and purifying chloroiridium acid from iridium-containing waste catalyst according to claim 1, characterized in that, In step (1), the solid oxide is at least one of the alkali metal peroxides, the alkali metal element in the alkali metal peroxide is sodium or potassium, and the mass ratio of the alkali metal peroxide to the iridium-containing waste catalyst is (1-2):

1.

4. The method for recovering and purifying chloroiridium acid from iridium-containing waste catalyst according to claim 1, characterized in that, In step (1), the melting reaction takes 4-8 hours.

5. The method for recovering and purifying chloroiridium acid from iridium-containing spent catalyst according to claim 1, characterized in that, In step (2), the mass ratio of water to melt is (10-20):1, the stirring and cleaning time is 4-8 hours, and the cleaning temperature is maintained at 30-60℃.

6. The method for recovering and purifying chloroiridium acid from iridium-containing waste catalyst according to claim 1, characterized in that, In step (3), the acid used is hydrochloric acid with a mass fraction of 36-38%.

7. The method for recovering and purifying chloroiridium acid from iridium-containing spent catalyst according to claim 1, characterized in that, In step (3), the ratio of the amount of acid added to the mass of iridium in the iridium-containing waste catalyst is (15-25):1.

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