A method for recovering iridium from a zirconium-iridium oxide-containing raw material

Abstract

The application relates to the field of noble metal recovery, and particularly discloses a method for recovering iridium from zirconium oxide-iridium mixed raw materials, which comprises the following steps: pretreating zirconium oxide-iridium mixed raw materials to a particle size less than 400 mesh and drying, then adding a hydrofluoric acid-based composite acid liquid to dissolve and remove impurities, so that zirconium oxide is dissolved and iridium is retained in the form of a solid, iridium-rich filter residue is obtained through filtration separation, and the iridium-rich filter residue is washed, dried or further dissolved and purified with aqua regia to obtain metallic iridium. Through a step-by-step targeted acid dissolution process, zirconium oxide is efficiently removed while the premature dissolution of iridium is effectively inhibited, unnecessary loss of iridium in the acid dissolution stage is avoided, the recovery rate and product purity of iridium are significantly improved, the operation is simple, the cost is controllable, and the method is suitable for processing fine-particle raw materials with low iridium content and high zirconium impurities.

Description

Technical Field

[0001] This invention belongs to the field of precious metal recycling, specifically relating to a method for recovering iridium from a zirconium oxide-iridium mixed raw material. Background Technology

[0002] Iridium, a platinum group metal, possesses an extremely high melting point, excellent chemical stability, and corrosion resistance, making it widely used in high-end fields such as aerospace high-temperature coatings, precision electrodes, and automotive exhaust catalysts. However, iridium is extremely rare in nature and often forms stable complexes with refractory oxides such as zirconium oxide and alumina, for example, the ZrO2-Ir coating in spent solid oxide fuel cells and the iridium-zirconium hybrid support in chemical catalysts. Recovering iridium from these zirconium oxide-containing raw materials typically requires first dissolving the zirconium oxide matrix and then further enriching the iridium. Due to the extremely stable chemical properties of zirconium oxide, conventional acids are difficult to dissolve it effectively; currently, the commonly used method is to use hydrofluoric acid as the main zirconium-dissolving agent.

[0003] However, in practice, while a single hydrofluoric acid system can dissolve zirconium oxide, it offers no protection for iridium. Some iridium enters the solution along with zirconium ions, leading to unnecessary loss of iridium during the acid dissolution stage and a significantly low recovery rate. Existing processes attempt to introduce other acids to form a composite system, but these often employ a one-step mixed acid dissolution method, failing to address the specific characteristics of fine-grained raw materials, high zirconium content, and low iridium content through stepwise targeted control. This makes it difficult to simultaneously achieve efficient removal of zirconium oxide and selective retention of iridium. Therefore, an acid dissolution process that can inhibit premature iridium dissolution and improve iridium recovery is needed. Summary of the Invention

[0004] This invention provides a method for recovering iridium from a zirconium oxide-iridium mixed raw material, thereby solving the problem of low recovery rate of iridium during the acid dissolution stage in the prior art.

[0005] This invention provides a method for recovering iridium from a zirconium oxide-iridium mixed feedstock, comprising the following steps:

[0006] (1) Raw material pretreatment: crush, grind and screen the zirconium oxide-iridium mixed raw material to a particle size of less than 400 mesh, and dry it at 50-60℃ to constant weight;

[0007] (2) Dissolution and impurity removal: Weigh 5g of the pretreated raw material, place it in an acid-resistant container, add the composite acid solution, and keep it at 80-100℃ for 4 hours to dissolve the zirconium oxide and retain the iridium in solid form;

[0008] (3) Filtration and separation: Cool the reaction mixture to room temperature, filter, collect the filter residue, wash the filter residue with 5%-8% dilute hydrochloric acid, filter again and dry in a vacuum drying oven at 50℃ to obtain metallic iridium;

[0009] The composite acid solution is any one of the following four combinations, and the concentrations of each reagent are as follows: hydrofluoric acid 40%, nitric acid 65%, concentrated hydrochloric acid 37%, and hydrogen peroxide 30%.

[0010] (a) Hydrofluoric acid and nitric acid, in a volume ratio of 3:1, with a dosage of 90 mL hydrofluoric acid and 30 mL nitric acid;

[0011] (b) Hydrofluoric acid, nitric acid and concentrated hydrochloric acid in a volume ratio of 6:1:2, with the following amounts: 60 mL hydrofluoric acid, 10 mL nitric acid and 20 mL concentrated hydrochloric acid.

[0012] (c) Hydrofluoric acid and concentrated hydrogen peroxide, in a volume ratio of 3:1, with 90 mL of hydrofluoric acid and 30 mL of hydrogen peroxide used.

[0013] (d) Hydrofluoric acid and concentrated hydrochloric acid, in a volume ratio of 3:1, with a dosage of 90 mL of hydrofluoric acid and 30 mL of concentrated hydrochloric acid.

[0014] Preferably, the drying time to constant weight in step (1) is 1-2 hours.

[0015] Preferably, the acid-resistant container in step (2) is a polytetrafluoroethylene beaker, and a polytetrafluoroethylene stirring rod is used for stirring, with stirring for 1 minute every 30 minutes during the reaction.

[0016] Preferably, the filtration in step (3) uses a Buchner funnel equipped with a 0.22 μm polytetrafluoroethylene filter membrane, and the amount of dilute hydrochloric acid used for each rinse is 20 mL, and the number of rinses is 3.

[0017] Preferably, the drying in step (3) is performed in a vacuum drying oven at a temperature of 50°C.

[0018] This invention provides a method for recovering iridium from a zirconium oxide-iridium mixed feedstock, comprising the following steps:

[0019] (1) Raw material pretreatment: crush, grind and screen the zirconium oxide-iridium mixed raw material to a particle size of less than 400 mesh, and dry it at 50-60℃ to constant weight;

[0020] (2) Dissolution and impurity removal: Weigh 5g of the pretreated raw material, place it in an acid-resistant container, add the composite acid solution, and keep it at 80-100℃ for 4 hours to dissolve the zirconium oxide and retain the iridium in solid form; the composite acid solution is a combination of hydrofluoric acid, concentrated hydrochloric acid and nitric acid, wherein 14mL of concentrated hydrochloric acid is added first to soak for 8 minutes, then 7mL of nitric acid is added, and finally 90mL of hydrofluoric acid is added; the concentration of hydrofluoric acid is 40%, the concentration of concentrated hydrochloric acid is 37%, and the concentration of nitric acid is 65%;

[0021] (3) Filtration and separation: Cool the reaction mixture to room temperature, filter, collect the filter residue, and rinse the filter residue with 5%-8% dilute hydrochloric acid;

[0022] (4) Deep dissolution and purification with aqua regia: Transfer the rinsed filter residue to an acid-resistant container, add aqua regia, keep it at 80-100℃ for 1.5-2.5 hours to dissolve the filter residue, wash with deionized water and dry to obtain metallic iridium; the aqua regia is a mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1, and the amount of aqua regia used is 8-12 times the mass of the filter residue.

[0023] Preferably, the acid-resistant container in step (2) is a polytetrafluoroethylene beaker, and a polytetrafluoroethylene stirring rod is used for stirring, with stirring for 1 minute every 30 minutes during the reaction.

[0024] Preferably, the filtration in step (3) uses a Buchner funnel equipped with a 0.22 μm polytetrafluoroethylene filter membrane, and the amount of dilute hydrochloric acid used for each rinse is 20 mL, and the number of rinses is 3.

[0025] Preferably, in step (4), the filter residue is stirred once every 20 minutes during the heat preservation period, the solubility rate of the filter residue in aqua regia is ≥95%, and the drying is carried out in a vacuum drying oven at a temperature of 50°C.

[0026] Preferably, the zirconium oxide-iridium mixed raw material has an iridium mass fraction of 8% and an overall iridium recovery rate of 86%.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] By employing a two-step acid dissolution process of "preliminary dissolution and impurity removal with composite acid solution + deep dissolution and purification with aqua regia", metallic iridium can be efficiently and selectively recovered from fine-particle zirconium oxide raw materials.

[0029] First, for zirconium oxide-iridium mixed raw materials with a particle size of less than 400 mesh, the targeted dissolution effect of hydrofluoric acid-based composite acid is utilized to rapidly destroy the dense structure of zirconium oxide under high temperature conditions, allowing zirconium to enter the solution in ionic form. Simultaneously, the oxidizing properties of nitric acid, hydrochloric acid, or hydrogen peroxide are used to effectively inhibit premature dissolution of iridium, ensuring that iridium remains in solid form in the filter residue, thus achieving preliminary separation of zirconium and iridium. This step overcomes the technical shortcomings of traditional single hydrofluoric acid systems, which easily lead to iridium loss, and single aqua regia systems, which are difficult to dissolve zirconium oxide.

[0030] Subsequently, the iridium-enriched filter residue was deeply dissolved in aqua regia. The strong oxidizing properties of aqua regia completely dissolved the residual iridium and its associated impurities. After washing and drying, high-purity metallic iridium was obtained. The entire process involves step-by-step targeted treatment, with clearly defined and controllable acid ratios and reaction conditions. This ensures efficient removal of zirconium oxide while avoiding unnecessary loss of iridium during the dissolution process. It also simplifies subsequent separation procedures, eliminating the need for multiple extractions and reducing operational difficulty and costs.

[0031] This invention is particularly suitable for ultrafine particulate raw materials with low iridium content and high zirconium impurities, significantly improving the recovery rate and product purity of iridium. It is safe to operate and has good reproducibility, providing a reliable technical solution for the green and efficient recovery of iridium from industrial by-products and spent catalysts. Attached Figure Description

[0032] Figure 1 It is a picture of a mixture of zirconium oxide and iridium.

[0033] Figure 2 This is a physical image of the iridium obtained in Example 5;

[0034] Figure 3 It is the XRD pattern obtained from the raw material;

[0035] Figure 4 This is the XRD pattern of iridium obtained in Example 5;

[0036] Figure 5 This is a scanning electron microscope image of iridium obtained in Example 5;

[0037] Figure 6 This is the EDS spectrum of iridium obtained in Example 5;

[0038] Figure 7 It is a process flow diagram. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available (including zirconium oxide-iridium mixed feedstock, which can be obtained from the dismantling of spent solid oxide fuel cells). Coating powder, iridium-zirconium mixed waste containing dense, transparent, insoluble zirconium oxide, physical image as shown. Figure 1As shown; hydrofluoric acid, nitric acid, concentrated hydrochloric acid, and hydrogen peroxide were all analytical grade. Unless otherwise specified in the examples, all procedures were performed in accordance with the techniques or conditions described in the literature or the product instructions. All operations were conducted in a fume hood, with operators wearing specialized hydrofluoric acid-resistant protective equipment. All containers used were made of polytetrafluoroethylene (PTFE) resistant to hydrofluoric acid corrosion.

[0041] Example 1: This example provides a specific process for recovering iridium from zirconium oxide-iridium raw materials. The specific steps are as follows:

[0042] I. Raw material pretreatment

[0043] Select zirconium oxide-iridium mixed raw materials with a particle size of less than 400 mesh after sieving (e.g.) Figure 1 As shown in the figure, spread it flat in a porcelain boat, place the porcelain boat in a drying oven, set the drying temperature to 50-60℃, and dry until the raw material reaches constant weight (about 2 hours). After drying, remove it and place it in a desiccator to cool to room temperature for later use.

[0044] II. Dissolving and Removing Impurities

[0045] Accurately weigh 5g of the pretreated zirconium oxide and iridium-containing raw material using an electronic balance and place it in a 500mL polytetrafluoroethylene (PTFE) beaker. Add 90mL of hydrofluoric acid (40% concentration) and 30mL of nitric acid (65% concentration) to the beaker, with a volume ratio of 3:1. Gently stir with a PTFE stirring rod for 5 minutes to ensure that the reagents and raw materials are mixed evenly. Place the PTFE beaker on a digital display heating plate, turn on the heating, and slowly raise the temperature to 80-100℃. After reaching the target temperature, maintain the temperature for 4 hours, stirring with a PTFE stirring rod for 1 minute every 30 minutes to ensure a uniform reaction.

[0046] III. Filtration and Separation

[0047] After the heat preservation period, the heating plate was turned off, and the reaction system in the beaker was allowed to cool to room temperature. A Buchner funnel (equipped with a 0.22 μm polytetrafluoroethylene filter membrane) was prepared, and a vacuum filtration device was connected. The reaction mixture (containing dissolved zirconium ion solution and iridium-containing solid residue) in the beaker was poured into the funnel, and vacuum filtration was started to separate the iridium-containing solid filter residue. A 5% concentration of dilute hydrochloric acid was prepared (5 mL of concentrated hydrochloric acid was added to 95 mL of deionized water and mixed thoroughly). The iridium-containing filter residue in the funnel was slowly rinsed with the dilute hydrochloric acid, using 20 mL each time, and the rinsing was repeated 3 times. After vacuum filtration, the mixture was placed in a vacuum drying oven at 50 °C to dry and obtain metallic iridium. In this example, the overall recovery rate of iridium was 73%.

[0048] Example 2: The difference between this example and Example 1 is the combination of acid solutions in the dissolution and impurity removal step.

[0049] I. Raw material pretreatment: Completely consistent with Example 1, the actual raw materials are as follows Figure 1 As shown.

[0050] II. Dissolving and Removing Impurities

[0051] Accurately weigh 5g of the pretreated zirconium oxide and iridium-containing raw material and place it in a 500mL polytetrafluoroethylene beaker. Add 60mL of hydrofluoric acid, 10mL of nitric acid, and 20mL of concentrated hydrochloric acid (37% concentration) to the beaker in a volume ratio of 6:1:2. Gently stir with a polytetrafluoroethylene stirring rod for 5 minutes to ensure uniform mixing. Place the beaker on a digital display heating plate and slowly heat it to 80-100℃. Keep it at this temperature for 4 hours, stirring for 1 minute every 30 minutes during the process.

[0052] III. Filtration and Separation: Consistent with Example 1, metallic iridium was finally obtained; the overall recovery rate of iridium in this example was 76%.

[0053] Example 3: This example uses a combination of hydrofluoric acid and hydrogen peroxide.

[0054] I. Raw material pretreatment: Same as in Example 1 (see raw materials) Figure 1 ).

[0055] II. Dissolving and Removing Impurities

[0056] Accurately weigh 5g of the pretreated zirconium oxide and iridium-containing raw material and place it in a 500mL polytetrafluoroethylene beaker. Add 90mL of hydrofluoric acid and 30mL of concentrated hydrogen peroxide (30% concentration) to the beaker, with a volume ratio of 3:1. Stir for 5 minutes. Place the beaker on a digital display heating plate and heat it to 80-100℃. Keep it at this temperature for 4 hours, stirring for 1 minute every 30 minutes during the process.

[0057] III. Filtration and Separation: Consistent with Example 1, metallic iridium was obtained. The overall recovery rate of iridium in this example was 64%.

[0058] Example 4: This example uses a combination of hydrofluoric acid and concentrated hydrochloric acid.

[0059] I. Raw material pretreatment: Same as in Example 1 (raw materials see...) Figure 1 ).

[0060] II. Dissolving and Removing Impurities

[0061] Accurately weigh 5g of the pretreated zirconium oxide and iridium-containing raw material and place it in a 500mL polytetrafluoroethylene beaker. Add 90mL of hydrofluoric acid and 30mL of concentrated hydrochloric acid (37% concentration) to the beaker at a volume ratio of 3:1 and stir for 5 minutes. Place the beaker on a digital display heating plate and heat it to 80-100℃. Keep it at this temperature for 4 hours, stirring for 1 minute every 30 minutes during the heating period.

[0062] III. Filtration and Separation: Consistent with Example 1, metallic iridium was obtained; the overall recovery rate of iridium in this example was 72%.

[0063] Example 5: This example uses a sequence of hydrofluoric acid-concentrated hydrochloric acid-nitric acid for initial impurity removal, combined with deep dissolution and purification using aqua regia. The process flow is as follows. Figure 7 The obtained metallic iridium physical specimens, such as Figure 2 As shown, structural and compositional analyses are provided. Figures 4 to 6 .

[0064] I. Raw material pretreatment

[0065] Consistent with Example 1, the XRD pattern of the raw material is as follows: Figure 3 As shown.

[0066] II. Dissolving and Removing Impurities

[0067] Accurately weigh 5g of the pretreated zirconium oxide and iridium-containing raw material using an electronic balance and place it in a 500mL polytetrafluoroethylene (PTFE) beaker. Add 14mL of concentrated hydrochloric acid (37%) to the beaker, stir well, and soak the sample for 8 minutes to allow the hydrochloric acid to fully penetrate the pores of the raw material and initially inhibit zirconium ion hydrolysis. Then slowly add 7mL of nitric acid (65%) and let it stand for 3 minutes. Subsequently, slowly add 90mL of hydrofluoric acid (40%), stirring continuously throughout the process. Place the PTFE beaker on a digital display heating plate and slowly heat it to 80-100℃, maintaining the temperature for 4 hours. During this period, stir with a PTFE stirring rod for 1 minute every 30 minutes to ensure uniform reaction.

[0068] III. Preliminary Filtration and Separation

[0069] Consistent with Example 1, iridium-containing filter residue was collected.

[0070] IV. Further dissolution and purification of aqua regia

[0071] Transfer all the rinsed iridium-containing filter residue to a 500mL PTFE beaker, add freshly prepared aqua regia solution (30mL concentrated hydrochloric acid + 10mL nitric acid, volume ratio 3:1), place the beaker on a digital display heating plate, turn on the heating, raise the temperature to 80-100℃, and maintain the temperature for 2 hours. During this period, stir with a PTFE stirring rod for 1 minute every 20 minutes to ensure that the filter residue is fully dissolved (dissolution rate ≥95%). After the holding time is completed, turn off the heating plate and allow it to cool naturally. After filtration, wash repeatedly with deionized water 3 times, and dry the iridium powder in a 50℃ vacuum drying oven to finally obtain metallic iridium (actual sample as shown). Figure 2 (as shown)

[0072] XRD analysis of this metallic iridium yielded the following spectrum: Figure 4 As shown; Scanning electron microscope image as follows Figure 5 As shown; EDS spectrum as shown Figure 6 As shown, it was confirmed to be high-purity metallic iridium; the overall recovery rate of iridium in this embodiment was 86%.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recovering iridium from a zirconium oxide-iridium mixed feedstock, characterized in that, Includes the following steps: (1) Raw material pretreatment: crush, grind and screen the zirconium oxide-iridium mixed raw material to a particle size of less than 400 mesh, and dry it at 50-60℃ to constant weight; (2) Dissolution and impurity removal: Weigh 5g of the pretreated raw material, place it in an acid-resistant container, add the composite acid solution, and keep it at 80-100℃ for 4 hours to dissolve the zirconium oxide and retain the iridium in solid form; (3) Filtration and separation: Cool the reaction mixture to room temperature, filter, collect the filter residue, wash the filter residue with 5%-8% dilute hydrochloric acid, filter again and dry in a vacuum drying oven at 50℃ to obtain metallic iridium; The composite acid solution is any one of the following four combinations, and the concentrations of each reagent are as follows: hydrofluoric acid 40%, nitric acid 65%, concentrated hydrochloric acid 37%, and hydrogen peroxide 30%. (a) Hydrofluoric acid and nitric acid, in a volume ratio of 3:1, with a dosage of 90 mL hydrofluoric acid and 30 mL nitric acid; (b) Hydrofluoric acid, nitric acid and concentrated hydrochloric acid in a volume ratio of 6:1:2, with the following amounts: 60 mL hydrofluoric acid, 10 mL nitric acid and 20 mL concentrated hydrochloric acid. (c) Hydrofluoric acid and concentrated hydrogen peroxide, in a volume ratio of 3:1, with 90 mL of hydrofluoric acid and 30 mL of hydrogen peroxide used. (d) Hydrofluoric acid and concentrated hydrochloric acid, in a volume ratio of 3:1, with a dosage of 90 mL of hydrofluoric acid and 30 mL of concentrated hydrochloric acid.

2. The method according to claim 1, characterized in that, The drying time to constant weight in step (1) is 1-2 hours.

3. The method according to claim 1, characterized in that, The acid-resistant container mentioned in step (2) is a polytetrafluoroethylene beaker, and a polytetrafluoroethylene stirring rod is used for stirring. During the reaction, the mixture is stirred for 1 minute every 30 minutes.

4. The method according to claim 1, characterized in that, The filtration in step (3) uses a Buchner funnel equipped with a 0.22 μm polytetrafluoroethylene filter membrane. The amount of dilute hydrochloric acid used for each rinse is 20 mL, and the number of rinses is 3.

5. The method according to claim 1, characterized in that, The drying process in step (3) uses a vacuum drying oven at a temperature of 50°C.

6. A method for recovering iridium from a zirconium oxide-iridium mixed feedstock, characterized in that, Includes the following steps: (1) Raw material pretreatment: crush, grind and screen the zirconium oxide-iridium mixed raw material to a particle size of less than 400 mesh, and dry it at 50-60℃ to constant weight; (2) Dissolution and impurity removal: Weigh 5g of the pretreated raw material, place it in an acid-resistant container, add the composite acid solution, and keep it at 80-100℃ for 4 hours to dissolve the zirconium oxide and retain the iridium in solid form; the composite acid solution is a combination of hydrofluoric acid, concentrated hydrochloric acid and nitric acid, wherein 14mL of concentrated hydrochloric acid is added first to soak for 8 minutes, then 7mL of nitric acid is added, and finally 90mL of hydrofluoric acid is added; the concentration of hydrofluoric acid is 40%, the concentration of concentrated hydrochloric acid is 37%, and the concentration of nitric acid is 65%; (3) Filtration and separation: Cool the reaction mixture to room temperature, filter, collect the filter residue, and rinse the filter residue with 5%-8% dilute hydrochloric acid; (4) Deep dissolution and purification with aqua regia: Transfer the rinsed filter residue to an acid-resistant container, add aqua regia, keep it at 80-100℃ for 1.5-2.5 hours to dissolve the filter residue, wash with deionized water and dry to obtain metallic iridium; the aqua regia is a mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1, and the amount of aqua regia used is 8-12 times the mass of the filter residue.

7. The method according to claim 6, characterized in that, The acid-resistant container mentioned in step (2) is a polytetrafluoroethylene beaker, and a polytetrafluoroethylene stirring rod is used for stirring. During the reaction, the mixture is stirred for 1 minute every 30 minutes.

8. The method according to claim 6, characterized in that, The filtration in step (3) uses a Buchner funnel equipped with a 0.22 μm polytetrafluoroethylene filter membrane. The amount of dilute hydrochloric acid used for each rinse is 20 mL, and the number of rinses is 3.

9. The method according to claim 6, characterized in that, In step (4), the filter residue is stirred once every 20 minutes during the heat preservation period. The solubility rate of the filter residue in aqua regia is ≥95%. The drying is carried out in a vacuum drying oven at a temperature of 50℃.

10. The method according to claim 6, characterized in that, The zirconium oxide-iridium mixed feedstock has an iridium mass fraction of 8% and an overall iridium recovery rate of 86%.

Images