A method for efficiently recovering iridium from organic coating fluid

Abstract

A method for efficiently recovering iridium from organic coating liquids involves first mixing the coating liquid with an alkaline solution, stirring and reacting at room temperature, followed by solid-liquid separation. The solid is dried and dehydrated for later use, while the liquid is the supernatant. The supernatant is heated, and an alkaline solution is added and stirred to react. After sufficient settling, solid-liquid separation is performed again. The solid is dried and dehydrated, then ground together with the previously dried and dehydrated solid into powder. The powder is then calcined in a muffle furnace to obtain iridium and tantalum oxide powders. HF is added to the oxide powders to remove impurities such as Ta2O5, and solid-liquid separation is performed again. The solid is washed with water until neutral, dried and dehydrated, dissolved in aqua regia, and concentrated by heating to obtain chloroiridium acid. The method provided by this invention has a simple synthesis process, the supernatant after precipitation is free of iridium, the iridium loss rate is low, effectively reducing iridium loss in the organic liquid evaporation and concentration steps, and the HF removes tantalum, allowing direct dissolution of IrO2 in aqua regia, improving efficiency and reducing iridium loss during the process.

Description

Technical Field

[0001] This invention relates to the field of precious metal recycling technology, specifically to a method for efficiently recovering iridium from organic coating solutions. Background Technology

[0002] Titanium-based iridium-tantalum coated electrodes are currently the most suitable anodes for oxygen evolution in the electrolytic industry, possessing advantages such as high current density carrying capacity, low oxygen evolution potential, excellent electrolytic durability, and good dimensional stability. In these electrodes, the titanium substrate acts as a framework and provides conductivity, while the iridium-tantalum oxide coating participates in catalyzing the anodic electrochemical reaction. Iridic acid and tantalum pentachloride are the main raw materials for these electrodes, and are mixed with solvents in a specific ratio to prepare a coating solution. This solution is then applied to the titanium substrate and sintered at high temperature to obtain the desired titanium-based iridium-tantalum coated electrode. However, prolonged exposure of the organic coating solution to air will cause compositional changes, rendering the solution ineffective and unusable. Furthermore, iridium is expensive, constituting a major cost component of coated titanium anodes. Therefore, recovering iridium from the ineffective coating solution is an important means of reducing production costs.

[0003] For the recovery of iridium from organic iridium catalysts, the organic components are mostly distilled. The distillation residue is then incinerated to remove residual organic matter, and iridium is converted into elemental form or oxides, remaining in the ash. After activation with activators and alkali melting, the iridium is transferred to a solution. During incineration, a small portion of iridium is lost with the flue gas. Incineration not only causes iridium loss but also makes it difficult to dissolve iridium or iridium oxides in the incineration residue.

[0004] The method for recovering iridium from organic waste liquid proposed by He Xiaotang et al. (Process for recovering iridium from organic waste liquid, Precious Metals, 2010, 31(2), P7) mainly includes steps such as aqua regia oxidation to destroy organic matter, hydrolysis to remove impurities, evaporation and concentration, calcination, and hydrogen reduction. First, the strong oxidizing properties of aqua regia are used to destroy the structure of organic matter in the waste liquid. After removing organic matter, the iridium-containing solution is denitrated with hydrochloric acid, diluted with deionized water, and then hydrolyzed to remove impurities and purified. The purified solution is concentrated and crystallized to obtain chloroiridic acid, which is then directly calcined at high temperature and reduced with hydrogen to obtain iridium powder. However, this method is not suitable for solutions containing a large number of other metal ions in the waste liquid, and the operation of aqua regia oxidation of organic matter has many safety risks.

[0005] Therefore, it is of great significance to research and develop a method to recover iridium from organic coating solutions, shorten the recovery cycle, increase operational safety, and convert it into chloroiridium acid. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for efficiently recovering iridium from organic coating liquids. The method involves stepwise precipitation of iridium, removal of tantalum by HF, and dissolution in aqua regia to prepare chloroiridic acid. This method has the advantages of simple recovery process, low iridium loss rate, significantly shortened recovery cycle, and high recovery efficiency.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for efficiently recovering iridium from organic coating solutions includes the following steps:

[0009] Step 1: Mix the organic coating liquid with the alkaline solution at a volume ratio of (1.5-2.5):1 and stir at room temperature until the reaction is complete;

[0010] Step 2: Separate the reaction products from Step 1 into solid and liquid phases. Dry and dehydrate the solid for later use, and keep the liquid as the supernatant for further processing.

[0011] Step 3: Heat the supernatant obtained from the solid-liquid separation in Step 2, and add an alkaline solution while stirring to carry out the reaction. The volume ratio of the supernatant to the alkaline solution is 1:(2-3.5).

[0012] Step 4: Cool the reaction product obtained in Step 3 and let it stand overnight to allow sufficient precipitation time;

[0013] Step 5: Separate the reaction product from Step 4 into solid and liquid phases. After drying and dehydrating the solid, grind it together with the dried and dehydrated solid from Step 2 into powder.

[0014] Step 6: Place the powder ground in step 5 into a muffle furnace and calcine it to obtain iridium and tantalum oxide powders;

[0015] Step 7: Add HF to the oxide powder obtained in step 6 to remove the impurity Ta2O5 from the oxide powder;

[0016] Step 8: Separate the reaction product from Step 7 into solid and liquid phases. Wash the solid with water until neutral and then dry it to remove water.

[0017] Step 9: Dissolve the solid from Step 8 in aqua regia and heat to concentrate it to obtain chloroiridic acid.

[0018] The alkaline solution mentioned in step 1 is an aqueous solution of alkali metal hydroxide, and the content of alkali metal hydroxide in the aqueous solution of alkali metal hydroxide is 1wt%-20wt%, preferably 2wt%-10wt%.

[0019] The alkali metal hydroxide includes at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0020] The organic coating solution is a mixed acidic solution prepared by mixing chloroiridic acid and tantalum pentachloride n-butanol solution in any ratio that is not zero.

[0021] The reaction that occurs in step 1 is as follows:

[0022] IrCl6 2- +4OH - →Ir(OH)4↓+6Cl - After stirring and reacting, the pH of the solution is 9-10.

[0023] The solid-liquid separation method described in step 2 is centrifugal separation or vacuum filtration, preferably centrifugal separation, with a centrifuge speed of 5000-11000 rpm, preferably 8000-10000 rpm.

[0024] In step 2, the solid drying temperature is 50-100℃, preferably 80-100℃.

[0025] The heating temperature in step 3 is 70-90℃, and the reaction time is 1-4h, preferably 1-2h.

[0026] The alkaline solution is an aqueous solution of an alkali metal hydroxide, which includes at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0027] The content of the alkaline solution is 1wt%-30wt%, preferably 5wt%-15wt%.

[0028] The reaction that occurs in step 3 is as follows:

[0029] 2IrCl6 2- +2OH - +Cl - →2IrCl6 3- +CIO - +H2O

[0030] IrCl6 3- +3OH - →Ir(OH)3↓+6Cl - After stirring and reacting, the pH value of the solution should not be less than 13.

[0031] The settling time mentioned in step 4 is 4-90 hours, preferably 4-40 hours.

[0032] The solid-liquid separation method described in step 5 is centrifugal separation or vacuum filtration, preferably centrifugal separation, with a centrifuge speed of 5000-11000 rpm, preferably 8000-10000 rpm.

[0033] The solid drying temperature is 50-100℃, preferably 80-100℃.

[0034] The calcination temperature in step 6 is 500-600℃, and the calcination time is 1.5-2.5h.

[0035] In step 7, the liquid-to-solid ratio of the oxide powder to HF is (8-10):1, and the unit of the liquid-to-solid ratio is mL / g.

[0036] The HF tantalum removal process takes 20-60 minutes.

[0037] The solid-liquid separation method described in step 8 is centrifugal separation or vacuum filtration, preferably centrifugal separation, with a centrifuge speed of 5000-11000 rpm, preferably 8000-10000 rpm.

[0038] The solid drying and dehydration temperature in step 8 is 50-100℃, preferably 80-100℃.

[0039] In step 9, the liquid-to-solid ratio of the solid powder to the aqua regia is (5-10):1, and the unit of the solid-to-solid ratio is ml / g.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] 1. This invention employs a stepwise iridium precipitation method by adjusting pH, which can accelerate the rapid enrichment of iridium in organic coating solutions, thereby improving recovery efficiency and reducing iridium loss.

[0042] 2. This invention uses HF to remove tantalum, which can quickly remove impurities from precipitates. It is simple to operate, easy to control, and saves time.

[0043] 3. This invention uses aqua regia to dissolve and prepare chloroiridic acid, which simplifies the preparation process and saves steps and reduces iridium loss during the process.

[0044] 4. In step 1 of this invention, an alkaline solution is used to recover iridium from the solution, which has the advantages of fast reaction, low cost and strong operability.

[0045] 5. In step 3 of this invention, a high-concentration alkaline solution is used to further recover residual iridium from the solution, which has the advantages of safe and reliable operation and minimal iridium loss.

[0046] 6. In step 3 of this invention, a reaction time of 1-2 hours is selected to allow sufficient contact time between the reactants and the alkaline solution, without causing excessively long reaction times that would lead to increased energy consumption and the occurrence of other side reactions.

[0047] 7. In step 3 of this invention, an alkaline solution of 5wt%-15wt% is selected. The appropriate concentration of alkaline solution makes the reaction phenomenon controllable and effectively shortens the precipitation time.

[0048] In summary, this invention uses HF to remove tantalum and aqua regia to dissolve and prepare chloroiridic acid. By adjusting the pH to precipitate iridium stepwise, it can accelerate the rapid enrichment of iridium in organic coating solutions, quickly remove impurities from precipitates, and simplify the preparation process of chloroiridic acid. It has the advantages of low cost, simple operation, easy control, time and process saving, while improving recovery efficiency and reducing iridium loss. Detailed Implementation

[0049] The present invention will be further explained and described below with reference to specific embodiments, but it should be understood that the scope of protection of the present invention is not limited thereto.

[0050] Example 1

[0051] Step 1: Add 16.7 ml of 7.2 wt% NaOH aqueous solution to 33.3 ml of organic coating solution at room temperature, and stir the mixture at room temperature for 30 min.

[0052] Step 2: Centrifugation is used to separate the reaction products from Step 1 into solid and liquid phases at 8000 rpm. The solid is dried and dehydrated at 80°C for later use, and the liquid is the supernatant for further processing.

[0053] Step 3: Take 50 ml of the supernatant obtained from the solid-liquid separation in Step 2, heat it to 70°C, add 100 ml of 2.3 wt% NaOH aqueous solution, stir continuously until pH = 14, and heat the reaction for 1 hour;

[0054] Step 4: Cool the reaction product obtained in Step 3 and let it stand overnight to allow the trivalent iridium in the solution to fully precipitate, thereby improving the recovery rate. Let it stand for a total of 42 hours to ensure complete precipitation.

[0055] Step 5: Using centrifugal separation, a centrifuge is used to separate the reaction product from Step 4 at a speed of 8000 rpm, and the precipitate is dried and dehydrated at 100℃ and then ground into powder.

[0056] Step 6: Place the powder from Step 5 in a muffle furnace and calcine at 500°C for 2.5 h to obtain iridium and tantalum oxide powders;

[0057] Step 7: Add 8 ml of HF to 1 g of the oxide powder obtained in Step 6 and treat at room temperature for 20 min;

[0058] Step 8: Using centrifugation, the reaction product from step 7 is separated by centrifugation at a speed of 9000 rpm. The solid is then washed with water at 90°C until neutral and dried.

[0059] Step 9: Dissolve 0.8g of the solid from Step 8 in 8ml of aqua regia and heat to concentrate to obtain chloroiridic acid.

[0060] Example 2

[0061] Step 1: Add 18 ml of 7.2 wt% NaOH aqueous solution to 27 ml of organic coating solution at room temperature, and stir at room temperature for 30 min.

[0062] Step 2: Centrifugation is used to separate the reaction products from Step 1 into solid and liquid phases at 8500 rpm. The solid is dried and dehydrated at 85°C for later use, and the liquid is the supernatant for further processing.

[0063] Step 3: Take 45 ml of the supernatant obtained from the solid-liquid separation in Step 2, heat it to 70°C, add 104 ml of 6.3 wt% NaOH aqueous solution, stir continuously until pH = 14, and heat the reaction for 1 h;

[0064] Step 4: Cool the reaction product obtained in Step 3 and let it stand overnight to allow the trivalent iridium in the solution to fully precipitate, thereby improving the recovery rate. Let it stand for a total of 89 hours until precipitation is complete.

[0065] Step 5: Using centrifugal separation, a centrifuge is used to separate the reaction product from Step 4 at a speed of 10,000 rpm, and the precipitate is dried and dehydrated at 90°C and then ground into powder.

[0066] Step 6: Place the powder from Step 5 into a muffle furnace and calcine at 550°C for 2 hours to obtain oxides of iridium and tantalum;

[0067] Step 7: Add 7.2 ml of HF to 0.8 g of the oxide powder obtained in Step 6 and treat at room temperature for 20 min;

[0068] Step 8: Using centrifugation, the reaction product from step 7 is separated by centrifugation at 10,000 rpm, and the solid is washed with water at 100°C until neutral and then dried.

[0069] Step 9: Dissolve 0.64g of the solid from Step 8 in 6ml of aqua regia and heat to concentrate to obtain chloroiridic acid.

[0070] Example 3

[0071] Step 1: Add 20 ml of 7.2 wt% NaOH aqueous solution to 50 ml of organic coating solution at room temperature, and stir the mixture at room temperature for 30 min.

[0072] Step 2: Using centrifugation, the reaction product from Step 1 is separated into solid and liquid components at a speed of 9000 rpm. The solid is dried and dehydrated at 90°C for later use, and the liquid is the supernatant for subsequent processing.

[0073] Step 3: Take 70 ml of the supernatant obtained from the solid-liquid separation in Step 2, heat it to 70°C, add 210 ml of 10.7 wt% NaOH aqueous solution, stir continuously until pH = 14, and heat to react for 1 h;

[0074] Step 4: Cool the reaction product obtained in Step 3 and let it stand overnight to allow the trivalent iridium in the solution to fully precipitate, thereby improving the recovery rate. Let it stand for a total of 4 hours to ensure complete precipitation.

[0075] Step 5: Using centrifugation, the reaction product from step 4 is separated into a precipitate by centrifugation at a speed of 9000 rpm, and then dried and dehydrated at 95°C before being ground into powder.

[0076] Step 6: Place the powder from Step 5 into a muffle furnace and calcine at 600°C for 1.5 h to obtain oxides of iridium and tantalum;

[0077] Step 7: Add 12 ml of HF to 1.5 g of the oxide powder obtained in Step 6 and treat at room temperature for 20 min;

[0078] Step 8: Using centrifugation, the reaction product from step 7 is separated by centrifugation at a speed of 9500 rpm. The solid is then washed with water at 95°C until neutral and dried.

[0079] Step 9: Dissolve 1.2g of the solid from Step 8 in 6ml of aqua regia and heat to concentrate to obtain chloroiridic acid.

[0080] Example 4

[0081] Step 1: Add 22 ml of 7.2 wt% NaOH aqueous solution to 26 ml of organic coating solution at room temperature, and stir at room temperature for 30 min;

[0082] Step 2: Centrifugation is used to separate the reaction products from Step 1 into solid and liquid phases at 10,000 rpm. The solid is dried and dehydrated at 100°C for later use, and the liquid is the supernatant for further processing.

[0083] Step 3: Take 48 ml of the supernatant obtained from the solid-liquid separation in Step 2, heat it to 70°C, add 168 ml of 20.2 wt% NaOH aqueous solution, stir continuously until pH = 14, and heat to react for 1 h;

[0084] Step 4: Cool the reaction product obtained in Step 3 and let it stand overnight to allow the trivalent iridium in the solution to precipitate fully and improve the recovery rate. After standing for 90 hours, the precipitation was still not complete.

[0085] Step 5: Using centrifugal separation, a centrifuge is used to separate the reaction product from Step 4 at a speed of 8500 rpm, and the precipitate is dried and dehydrated at 80℃ and then ground into powder.

[0086] Step 6: Place the powder from Step 5 into a muffle furnace and calcine at 580°C for 1.8 h to obtain oxides of iridium and tantalum;

[0087] Step 7: Add 5 ml of HF to 0.75 g of the oxide powder obtained in Step 6 and treat at room temperature for 20 min;

[0088] Step 8: Using centrifugation, the reaction product from step 7 is separated by centrifugation at 8000 rpm, and the solid is washed with water at 80°C until neutral and then dried.

[0089] Step 9: Dissolve 0.60g of the solid from Step 8 in 4.8ml of aqua regia and heat to concentrate to obtain chloroiridic acid.

[0090] Comparative Example

[0091] 33.3 ml of the coating solution was placed on a heating furnace, and aqua regia was added for oxidation. During the process, the reaction between the aqua regia and organic matter caused overflow. Then, 10 ml of hydrochloric acid was added to remove the nitrate and obtain an iridium hydrochloric acid solution. The nitrate removal process took 1 hour. Then, 10% NaOH solution was added to adjust the pH of the solution to 8-9, so that iridium precipitated in the form of Ir(OH)4 (IrO2·nH2O) and Ir(OH)3 (Ir2O3·nH2O). The precipitate was dissolved with hydrochloric acid, and impurities in the iridium solution were removed by ion exchange with a strong acid cation exchange resin. The exchange was performed twice, and then the resin was regenerated with 6 mol / L hydrochloric acid. The regenerated liquid had a large volume. Aqua regia was added to oxidize it and the solution was concentrated to obtain a chloroiridium acid solution.

[0092] In summary, comparing the operational procedures of Examples 1-4 with the comparative example, it can be seen that the present invention can quickly precipitate iridium in the organic coating solution by controlling the amount of alkali added, reducing the overflow phenomenon caused by aqua regia damaging organic matter. Furthermore, the subsequent use of hydrofluoric acid to remove single tantalum impurities is simpler and saves time compared to ion exchange. The overall fewer steps effectively reduce iridium loss during the process, and the shorter time consumption significantly improves recovery efficiency.

Claims

1. A method for efficiently recovering iridium from organic coating solutions, characterized in that, Includes the following steps: Step 1: Mix the organic coating solution with an alkali metal hydroxide aqueous solution at a volume ratio of (1.5-2.5):1, and stir at room temperature until the reaction is complete. After the reaction, the pH of the solution is 9-10. The content of alkali metal hydroxide in the aqueous solution of alkali metal hydroxide is 1wt%-20wt%; The alkali metal hydroxide includes at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide; The organic coating solution is a mixed acidic solution prepared by mixing chloroiridic acid and tantalum pentachloride n-butanol solution in any ratio that is not zero; Step 2: Separate the reaction products from Step 1 into solid and liquid phases. Dry and dehydrate the solid for later use, and keep the liquid as the supernatant for further processing. Step 3: Heat the supernatant obtained from solid-liquid separation in Step 2, and add alkaline solution and stir to react. After stirring and reacting, the pH value of the solution should not be less than 13, and the volume ratio of supernatant to alkaline solution should be 1:(2-3.5). The heating temperature is 70-90℃, and the reaction time is 1-4h; The alkaline solution is an aqueous solution of an alkali metal hydroxide, which includes at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide. The content of alkali metal hydroxide in the aqueous solution of alkali metal hydroxide is 1wt%-30wt%; Step 4: Cool the reaction product obtained in Step 3 and let it stand overnight to allow sufficient precipitation time; Step 5: Separate the reaction product from Step 4 into solid and liquid phases. After drying and dehydrating the solid, grind it together with the dried and dehydrated solid from Step 2 into powder. Step 6: Place the powder ground in step 5 into a muffle furnace and calcine it to obtain iridium and tantalum oxide powders; Step 7: Add HF solution to the oxide powder obtained in step 6 to remove the impurity Ta2O5 from the oxide powder; Step 8: Separate the reaction product from Step 7 into solid and liquid phases. Wash the solid with water until neutral and then dry it to remove water. Step 9: Dissolve the solid from Step 8 in aqua regia and heat to concentrate it to obtain chloroiridic acid.

2. The method for efficiently recovering iridium from organic coating solutions according to claim 1, characterized in that, In step 1, the content of alkali metal hydroxide in the aqueous solution of alkali metal hydroxide is 2wt%-10wt%.

3. The method for efficiently recovering iridium from organic coating solutions according to claim 1, characterized in that, The solid-liquid separation method described in step 2 is centrifugal separation or vacuum filtration. When the solid-liquid separation method is centrifugal separation, the centrifuge speed is 8000-10000 rpm. In step 2, the solid drying temperature is 80-100℃.

4. The method for efficiently recovering iridium from organic coating solutions according to claim 1, characterized in that, The heating reaction time in step 3 is 1-2 hours; The content of alkali metal hydroxide in the aqueous solution of alkali metal hydroxide is 5wt%-15wt%.

5. The method for efficiently recovering iridium from organic coating solutions according to claim 1, characterized in that, The solid-liquid separation method described in step 5 is centrifugal separation or vacuum filtration. When the solid-liquid separation method is centrifugal separation, the centrifuge speed is 8000-10000 rpm. The solid drying temperature is 80-100℃.

6. The method for efficiently recovering iridium from organic coating solutions according to claim 1, characterized in that, The calcination temperature in step 6 is 500-600℃, and the calcination time is 1.5-2.5h.

7. The method for efficiently recovering iridium from organic coating solutions according to claim 1, characterized in that, In step 7, the liquid-to-solid ratio of the HF solution to the oxide powder is (8-10):1, and the unit of the liquid-to-solid ratio is mL / g. The treatment time is 20 min-60 min.

8. The method for efficiently recovering iridium from organic coating solutions according to claim 1, characterized in that, The solid-liquid separation method described in step 8 is centrifugal separation or vacuum filtration. When the solid-liquid separation method is centrifugal separation, the centrifuge speed is 8000-10000 rpm. The drying and dehydration temperature described in step 8 is 80-100℃.

9. The method for efficiently recovering iridium from organic coating solutions according to claim 1, characterized in that, In step 9, the liquid-to-solid ratio of aqua regia to solid is (5-10):1, and the unit of the liquid-to-solid ratio is mL / g.