A method for recovering platinum from a spent platinum vanadia catalyst on a carbon support

Abstract

The present application relates to the technical field of precious metal secondary resource recovery, and specifically provides a method for recovering platinum from a failed platinum-vanadium catalyst with a carbon carrier, comprising the following steps: (1) temperature control roasting: adding water to the failed platinum-vanadium catalyst with a carbon carrier, then adding a combustion improver, and then roasting; during the roasting process, the temperature is raised in stages, first low-temperature roasting at room temperature-250 DEG C, and then medium-temperature roasting at 250-650 DEG C; (2) vanadium leaching with alkali: leaching the roasting product obtained in step (1) with a vanadium leaching agent and a reducing agent, then filtering, to obtain a vanadium-containing leaching solution and a vanadium-removed residue; (3) secondary roasting: roasting the vanadium-removed residue obtained in step (2); (4) low-acid platinum leaching: leaching platinum from the roasting product obtained in step (3) with an inorganic acid and an oxidizing agent, to obtain a platinum-containing solution, adding ammonium chloride to the platinum-containing solution to obtain ammonium chloroplatinate; (5) purification: roasting and purifying the ammonium chloroplatinate obtained in step (4), to obtain sponge platinum.

Description

Technical Field

[0001] This invention relates to the field of precious metal secondary resource recovery technology, specifically to a method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst. Background Technology

[0002] Pt-V / C catalysts are activated carbon-supported catalysts. As a mature and widely used catalytic material, they are extensively applied in petrochemical and pharmaceutical chemical industries, including the reduction of halonitro compounds, reductive alkylation reactions, and hydrogenation of halogenated compounds. After a period of use, the catalyst loses its activity due to factors such as high temperature and carbon buildup. The resulting spent catalyst typically contains over 95% carbon, 4%-5% vanadium, and 1‰-1% platinum, making it a very important secondary resource of platinum group metals.

[0003] For the recycling and disposal of Pt-V / C waste catalysts, the first step is to roast the activated carbon support to remove it. Only after removing the support can the roasted residue be used for platinum recovery. The commonly used method is the wet recovery method.

[0004] The roasted material mainly consists of vanadium and vanadium oxides. Two leaching processes with aqua regia are necessary to increase the leaching rate of platinum. The resulting platinum- and vanadium-containing leachate is then separated from the platinum using ammonium chloride precipitation. However, this method has the following main drawbacks:

[0005] (1) Before the aqua regia leachate is used for ammonium chloride precipitation of platinum, it must be denitrified, which is not feasible in large-scale production.

[0006] (2) Platinum and vanadium are separated by ammonium chloride precipitation. Platinum and vanadium have many similar chemical properties: they exist as complex anions in solution. When ammonium chloride is added to the solution, platinum precipitates as ammonium chloroplatinate, while vanadium is also affected by pH to produce different precipitates such as NH4VO3, ammonium decavanadate, and ammonium hexavanadate, making the separation and purification of platinum and vanadium difficult. The main problem during the purification process is that when crude platinum is roasted, the material agglomerates severely after roasting. During the dissolution and purification process of the roasted material, a large amount of yellow, insoluble yellow salt is produced, resulting in long platinum recovery time and difficult purification.

[0007] (3) Ammonium chloride precipitation of platinum cannot completely precipitate platinum, but can only precipitate about 95% of platinum. The remaining platinum in the solution must be replaced and recovered. However, vanadium is a variable valence element with five valence states. The replacement reaction cannot proceed due to the influence of vanadium ions in the solution with multiple valence states.

[0008] In addition, the research found that the presence of carbon has a significant impact on the leaching of platinum. In order to burn off as much carbon as possible, the roasting time and roasting temperature must be extended. At higher temperatures, a large amount of carbon is removed, and vanadium becomes the main element. The increase in vanadium content and high-temperature roasting lead to vanadium melting during the roasting process, forming an alloy, which ultimately makes the roasted material unrecoverable. Summary of the Invention

[0009] In view of the above situation and to overcome the shortcomings of the prior art, the present invention provides a method for recovering platinum from a degraded platinum-vanadium catalyst supported on a carbon substrate.

[0010] The technical solution adopted by this invention is as follows: This invention provides a method for recovering platinum from a degraded platinum-vanadium catalyst supported on a carbon base, comprising the following steps:

[0011] (1) Temperature-controlled calcination: Water is first added to the depleted platinum-vanadium catalyst on the carbon support so that the water content of the depleted platinum-vanadium catalyst on the carbon support is 10%-20%, then a combustion aid is added, and then calcination is carried out. During the calcination process, the temperature is raised in stages. First, low-temperature calcination is carried out at room temperature-250℃, and then the temperature is raised to 250-650℃ for medium-temperature calcination to obtain the calcined product.

[0012] (2) Alkali leaching of vanadium: The roasted material obtained in step (1) is leached with vanadium leaching agent and reducing agent, and then filtered to obtain vanadium-containing leachate and vanadium-removed slag.

[0013] The conditions for vanadium leaching are: leaching temperature of 70-95℃, leaching time of 1-3h, and liquid-solid ratio of 6-10:1.

[0014] (3) Secondary roasting: The vanadium-removed slag obtained in step (2) is subjected to secondary roasting to obtain roasted ash slag;

[0015] (4) Low acid platinum leaching: The calcined ash obtained in step (3) is leached with platinum using inorganic acid and oxidant to obtain a platinum-containing solution and leaching residue;

[0016] The conditions for leaching platinum are: leaching temperature of 70-95℃, leaching time of 1-3h, and liquid-to-solid ratio of 2-4:1.

[0017] (5) Purification: The platinum-containing solution obtained in step (4) is precipitated with ammonium chloride to obtain ammonium chloroplatinate. After calcination and purification, the ammonium chloroplatinate is used to obtain sponge platinum.

[0018] Furthermore, the amount of combustion improver used in step (1) is 5%-20% of the mass of the depleted platinum vanadium catalyst on the carbon support.

[0019] Furthermore, in step (1), the low-temperature roasting time is 2-3 hours, and the medium-temperature roasting time is 2-5 hours.

[0020] Furthermore, the vanadium impregnation agent in step (2) has a mass concentration of 10%-40%.

[0021] Furthermore, the reducing agent mentioned in step (2) is one or both of hydrogen peroxide and hydrazine hydrate.

[0022] Furthermore, the vanadium impregnation agent mentioned in step (2) is one or both of sodium hydroxide and sodium carbonate.

[0023] Furthermore, the temperature of the second roasting in step (3) is 750-800℃, and the time of the second roasting is 1-2h.

[0024] Furthermore, the inorganic acid mentioned in step (4) is one or both of hydrochloric acid and sulfuric acid.

[0025] Further, the oxidant mentioned in step (4) is one or more of hydrogen peroxide, sodium chlorate and sodium hypochlorite.

[0026] Furthermore, sufficient air needs to be blown in during both the low-temperature roasting and medium-temperature roasting processes in step (1).

[0027] The beneficial effects achieved by the present invention using the above structure are as follows:

[0028] This invention employs a two-stage roasting-alkali leaching for vanadium removal-secondary roasting-low-acid leaching for platinum recovery, effectively recovering platinum from a spent carbon-supported platinum-vanadium catalyst. First, the spent catalyst is mixed with a combustion aid and subjected to staged temperature control. Under low-temperature roasting conditions of room temperature to 250°C, sufficient air is blown in. This stage primarily aims to dry the material of moisture; blowing in air accelerates the escape of water vapor and reduces damage to the furnace. During roasting, vanadium is oxidized to its highest oxidation state, forming vanadium pentoxide. Vanadium pentoxide has a melting temperature of 690°C. The maximum roasting temperature in the medium-temperature roasting stage must be controlled below 650°C. During this stage, it is crucial to prevent vanadium from melting while maintaining the burn-off rate of the spent catalyst at 70-85% to ensure effective vanadium removal in subsequent stages. Therefore, under medium-temperature roasting conditions of 250-650°C, the roasting time is controlled at 2-5 hours, with sufficient air blown in to ensure the burn-off rate of the carbon support.

[0029] The obtained roasted material was subjected to alkaline leaching of vanadium. A 10%-40% alkaline solution was added at a liquid-to-solid ratio of 6-10:1, and the leaching temperature was controlled at 70-95℃. Since the roasted material mainly exists in the form of vanadium pentoxide, which has strong oxidizing properties, vanadium leaching was performed first. After leaching for 2 hours to allow more vanadium to enter the solution, a reducing agent was added. This is because some platinum also enters the solution during alkaline leaching of vanadium. To prevent platinum from dispersing, platinum leaching must be suppressed at this stage by adding a reducing agent to reduce the platinum in the solution to elemental form. This step also has another advantage: the reduced platinum particles are small and highly active, which is beneficial for subsequent platinum leaching. Furthermore, a small amount of reducing agent will not reduce vanadium to its elemental state, thus not affecting the vanadium leaching rate. This method ensures both the vanadium leaching rate and the absence of platinum loss, while also enhancing the activity of some platinum, which is beneficial for subsequent platinum leaching.

[0030] The filter residue after platinum leaching is fluffy and can be directly roasted. The temperature is raised directly to 750-800℃ and roasted for 1-2 hours to completely roast the remaining carbon. This method is time-efficient and cost-effective. The roasted product obtained after the second roasting is then leached with platinum using an inorganic acid + oxidant system to obtain a platinum-containing solution. The platinum content in this solution is generally 20-60 g / L, which can be directly precipitated with ammonium chloride without the need for enrichment, resulting in a short production cycle.

[0031] This method avoids the melting phenomenon of vanadium during roasting, reducing the risk of precious metal recovery. Furthermore, the alkaline leaching method for vanadium removal achieves a one-step leaching rate of over 99%, while ensuring no platinum dispersion, thus achieving one-step separation of platinum and vanadium. This avoids the problems associated with platinum recovery caused by the presence of vanadium, such as difficulty in leaching, displacement, and purification, and difficulty in handling the tailings, as well as the subsequent problems of long production cycles, intermittent production, severely impacting recycling operations and consuming significant amounts of time, reagents, equipment, and labor. Moreover, the vanadium-removed slag, after high-temperature roasting, can be directly leached with low-concentration acid, achieving a platinum leaching rate of over 99%. The resulting platinum leachate does not require enrichment and can be directly purified, saving acid consumption, being environmentally friendly, and reducing carbon emissions. Attached Figure Description

[0032] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0033] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments.

[0035] Example 1:

[0036] This invention discloses a method for recovering platinum from a degraded platinum-vanadium catalyst supported on a carbon base, comprising the following steps:

[0037] (1) Temperature-controlled roasting: Water is first added to the depleted platinum-vanadium catalyst on the carbon support so that the water content of the depleted platinum-vanadium catalyst on the carbon support is 10%. Then, a combustion aid is added, and the amount of combustion aid is 5% of the mass of the depleted platinum-vanadium catalyst on the carbon support. Then, roasting is carried out. During the roasting process, the temperature is raised in stages. First, low-temperature roasting is carried out for 2 hours at room temperature - 250℃, and then the temperature is raised to 650℃ for 2 hours of medium-temperature roasting to obtain the roasted product. The platinum content in the roasted product is 5.2864% and the vanadium content is 32.5899%. Sufficient air needs to be blown in during both the low-temperature roasting and medium-temperature roasting processes.

[0038] (2) Alkali leaching of vanadium: Take 50g of the roasted material obtained in step (1), leach vanadium with sodium hydroxide and hydrogen peroxide with a mass concentration of 40%, and then filter to obtain vanadium-containing leachate and 11.09g of vanadium-removed slag. The platinum content in the vanadium-removed slag is 23.8335%, the vanadium content is 2.4098%, the platinum leaching rate is only 0.0023%, the platinum is basically not leached, there is no loss of platinum, and the vanadium removal rate is 98.36%.

[0039] The conditions for vanadium leaching are: leaching temperature of 70℃, leaching time of 1h, and liquid-to-solid ratio of 6:1.

[0040] (3) Secondary roasting: The 11.09g vanadium-removed slag obtained in step (2) was roasted twice to obtain 7.54g roasted ash slag with a burn-off rate of 32.01%. The temperature of the secondary roasting was 750℃ and the time of the secondary roasting was 1h. The platinum content in the roasted ash slag was tested to be 35.0548%.

[0041] (4) Low acid leaching of platinum: The 7.54g of roasted ash obtained in step (3) was leached with hydrochloric acid and hydrogen peroxide to obtain a platinum-containing solution and 1.02g of leaching residue. The platinum content in the 1.02g leaching residue was 1666.7μg, and the platinum leaching rate was 99.94%.

[0042] The conditions for leaching platinum were: leaching temperature of 70℃, leaching time of 1 hour, and liquid-to-solid ratio of 2:1.

[0043] (5) Purification: The platinum-containing solution obtained in step (4) is precipitated with ammonium chloride to obtain ammonium chloroplatinate. After calcination and purification, the ammonium chloroplatinate is used to obtain sponge platinum.

[0044] Example 2:

[0045] This invention discloses a method for recovering platinum from a degraded platinum-vanadium catalyst supported on a carbon base, comprising the following steps:

[0046] (1) Temperature-controlled roasting: Water is first added to the depleted platinum-vanadium catalyst on the carbon support so that the water content of the depleted platinum-vanadium catalyst on the carbon support is 20%. Then, a combustion aid is added, and the amount of combustion aid is 20% of the mass of the depleted platinum-vanadium catalyst on the carbon support. Then, roasting is carried out. During the roasting process, the temperature is raised in stages. First, the low temperature roasting is carried out at 250℃ for 3 hours, and then the temperature is raised to 550℃ for 5 hours of medium temperature roasting to obtain the roasted product. The platinum content in the roasted product is 13.8245% and the vanadium content is 29.00%. Sufficient air needs to be blown in during both the low temperature roasting and medium temperature roasting processes.

[0047] (2) Alkali leaching of vanadium: Take 132.04g of the roasted material obtained in step (1), leach vanadium with sodium hydroxide and hydrazine hydrate with a mass concentration of 10%, and then filter to obtain vanadium-containing leachate and 52.24g of vanadium-removed slag. The platinum content in the vanadium-removed slag is 34.9422%, the vanadium content is 0.5479%, the platinum leaching rate is only 0.00045%, the platinum is basically not leached, there is no loss of platinum, and the vanadium removal rate is 99.25%.

[0048] The conditions for vanadium leaching are: leaching temperature of 95℃, leaching time of 3h, and liquid-to-solid ratio of 10:1.

[0049] (3) Secondary roasting: The 52.24g vanadium-removed slag obtained in step (2) was roasted twice to obtain 46.93g roasted ash slag with a burn-off rate of 10.16%. The temperature of the secondary roasting was 800℃ and the time of the secondary roasting was 2h. The platinum content in the roasted ash slag was tested to be 38.8958%.

[0050] (4) Low acid leaching of platinum: The 46.93g of roasted ash obtained in step (3) was leached with hydrochloric acid and hydrogen peroxide to obtain a platinum-containing solution and 8.58g of leaching residue. The platinum content in the 8.58g leaching residue was tested to be 6100.38μg, and the platinum leaching rate was 99.97%.

[0051] The conditions for leaching platinum were: leaching temperature of 95℃, leaching time of 3h, and liquid-to-solid ratio of 4:1.

[0052] (5) Purification: The platinum-containing solution obtained in step (4) is precipitated with ammonium chloride to obtain ammonium chloroplatinate. After calcination and purification, the ammonium chloroplatinate is used to obtain sponge platinum.

[0053] Example 3:

[0054] This invention discloses a method for recovering platinum from a degraded platinum-vanadium catalyst supported on a carbon base, comprising the following steps:

[0055] (1) Temperature-controlled calcination: Water is first added to the depleted platinum-vanadium catalyst on the carbon support so that the water content of the depleted platinum-vanadium catalyst on the carbon support is 15%. Then, a combustion aid is added, and the amount of combustion aid is 15% of the mass of the depleted platinum-vanadium catalyst on the carbon support. Then, calcination is carried out. During the calcination process, the temperature is increased in stages. First, the low temperature calcination is carried out at 150℃ for 1.5h, and then the temperature is increased to 450℃ for 3.5h for medium temperature calcination to obtain the calcined product. The platinum content in the calcined product is 3.22% and the vanadium content is 7.3%. Sufficient air needs to be blown in during both the low temperature calcination and the medium temperature calcination process.

[0056] (2) Alkali leaching of vanadium: Take 114.32g of the roasted material obtained in step (1), leach vanadium with sodium hydroxide and hydrogen peroxide with a mass concentration of 25%, and then filter to obtain vanadium-containing leachate and 95.37g of vanadium-removed slag. The content of platinum in the vanadium-removed slag is 3.8595%, the content of vanadium is 0.45%, the leaching rate of platinum is only 0.0081%, the platinum is basically not leached, there is no loss of platinum, and the vanadium removal rate is 94.86%.

[0057] The conditions for vanadium leaching are: leaching temperature of 80℃, leaching time of 2h, and liquid-to-solid ratio of 8:1.

[0058] (3) Secondary roasting: The 95.37g vanadium-removed slag obtained in step (2) was roasted twice to obtain 60.46g roasted ash slag with a burn-off rate of 36.60%. The temperature of the secondary roasting was 775℃ and the time of the secondary roasting was 1.5h. The platinum content in the roasted ash slag was found to be 6.0880%.

[0059] (4) Low acid leaching of platinum: The 60.46g of roasted ash obtained in step (3) was leached with hydrochloric acid and hydrogen peroxide to obtain a platinum-containing solution and 6.48g of leaching residue. The platinum content in the 6.48g leaching residue was 1367.28μg, and the platinum leaching rate was 99.96%.

[0060] The conditions for leaching platinum were: leaching temperature of 80℃, leaching time of 2h, and liquid-to-solid ratio of 3:1.

[0061] (5) Purification: The platinum-containing solution obtained in step (4) is precipitated with ammonium chloride to obtain ammonium chloroplatinate. After calcination and purification, the ammonium chloroplatinate is used to obtain sponge platinum.

[0062] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0063] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0064] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst, characterized in that, Includes the following steps: (1) Temperature-controlled calcination: Water is first added to the depleted platinum-vanadium catalyst on the carbon support so that the water content of the depleted platinum-vanadium catalyst on the carbon support is 10%-20%, then a combustion aid is added, and then calcination is carried out. During the calcination process, the temperature is raised in stages. First, low-temperature calcination is carried out at room temperature-250℃, and then the temperature is raised to 250-650℃ for medium-temperature calcination to obtain the calcined product. (2) Alkali leaching of vanadium: The roasted material obtained in step (1) is leached with vanadium leaching agent and reducing agent, and then filtered to obtain vanadium-containing leachate and vanadium-removed slag. The conditions for vanadium leaching are: leaching temperature of 70-95℃, leaching time of 1-3h, and liquid-solid ratio of 6-10:

1. (3) Secondary roasting: The vanadium-removed slag obtained in step (2) is subjected to secondary roasting to obtain roasted ash slag; (4) Low acid platinum leaching: The calcined ash obtained in step (3) is leached with platinum using inorganic acid and oxidant to obtain a platinum-containing solution and leaching residue; The conditions for leaching platinum are: leaching temperature of 70-95℃, leaching time of 1-3h, and liquid-to-solid ratio of 2-4:

1. (5) Purification: The platinum-containing solution obtained in step (4) is precipitated with ammonium chloride to obtain ammonium chloroplatinate. After calcination and purification, the ammonium chloroplatinate is used to obtain sponge platinum.

2. The method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst according to claim 1, characterized in that, The amount of combustion improver used in step (1) is 5%-20% of the mass of the depleted platinum vanadium catalyst on the carbon support.

3. The method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst according to claim 1, characterized in that, In step (1), the low-temperature roasting time is 2-3 hours, and the medium-temperature roasting time is 2-5 hours.

4. The method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst according to claim 1, characterized in that, The vanadium impregnation agent in step (2) has a mass concentration of 10%-40%.

5. The method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst according to claim 1, characterized in that, The reducing agent mentioned in step (2) is one or both of hydrogen peroxide and hydrazine hydrate.

6. The method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst according to claim 1, characterized in that, The vanadium impregnation agent mentioned in step (2) is one or both of sodium hydroxide and sodium carbonate.

7. The method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst according to claim 1, characterized in that, The temperature of the second roasting in step (3) is 750-800℃, and the time of the second roasting is 1-2h.

8. The method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst according to claim 1, characterized in that, The inorganic acid mentioned in step (4) is one or both of hydrochloric acid and sulfuric acid.

9. The method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst according to claim 1, characterized in that, The oxidant mentioned in step (4) is one or more of hydrogen peroxide, sodium chlorate and sodium hypochlorite.

10. The method for recovering platinum from a carbon-supported, degraded platinum-vanadium catalyst according to claim 1, characterized in that, Sufficient air needs to be blown in during both the low-temperature roasting and medium-temperature roasting processes in step (1).

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