Method for recovering platinum from titanium-zirconium composite oxide platinum-loaded waste catalyst

Abstract

The invention relates to the technical field of catalyst recovery, and discloses a method for recovering platinum from a titanium-zirconium composite oxide platinum-loaded waste catalyst, which comprises the following steps: (1) roasting the platinum-loaded waste catalyst which takes TiO2-ZrO2 as a carrier, and crushing and grinding; (2) uniformly mixing the ground waste catalyst with disulfate, and carrying out roasting reaction to obtain a melt I; stirring and dissolving the melt I and an acid solution, and filtering to obtain filtrate and a filter cake I; (3) repeating the reaction in the step (2) on the filter cake I to obtain a filter cake II; (4) oxidizing and dissolving the filter cake II with hydrochloric acid and an oxidizing agent to obtain a platinum-containing solution; and (5) separating and purifying the platinum-containing solution to obtain metal platinum. According to the method, the carrier in the waste catalyst is decomposed by adopting the disulfate, and then the waste catalyst is oxidized and dissolved by adopting the hydrochloric acid and the oxidizing agent, so that the platinum recovery cost is reduced, the environmental pollution is reduced, the production efficiency is improved, and the cyclic utilization of resources is facilitated.

Description

Technical Field

[0001] This invention relates to the technical field of catalyst recovery, and in particular to a method for recovering platinum from spent catalysts supported on titanium-zirconium composite oxides. Background Technology

[0002] TiO2 supports possess excellent catalytic performance, resistance to carbon buildup and poisoning, and ZrO2 is the only compound with acidic, basic, oxidizing, and reducing properties. Furthermore, it exhibits good thermal stability and high mechanical strength. TiO2-ZrO2 composite oxides not only retain the unique properties of individual oxides but also possess a larger specific surface area, better thermal stability and mechanical strength, and stronger surface acidity and basicity. In recent years, they have attracted considerable attention and are widely used as catalyst supports in the production of chlorofluorocarbons and NO. x Reactions include catalytic elimination, photo-induced oxidation and reduction, hydrogenation, propylene epoxidation, cyclohexanone oxime gas-phase Beckmann rearrangement, particulate matter oxidation removal, hydrodesulfurization (denitrification), and catalytic reforming.

[0003] Platinum-supported catalysts based on TiO2-ZrO2 have been widely used in catalytic wet oxidation treatment of organic wastewater containing phenol, formaldehyde, acrylic acid, acetic acid, and glucose, achieving COD removal rates of over 99%. However, as these catalysts deactivate due to poisoning during use, large quantities need to be replaced. Since these spent catalysts contain valuable metals such as platinum, recycling them is of great significance.

[0004] Currently, the main methods for recovering platinum-loaded spent catalysts are pyrometallurgy and hydrometallurgy. The pyrometallurgical process for extracting platinum group metals involves melting the spent catalyst with a metal collector at high temperature, separating the alloy phase from the slag phase, dissolving and leaching the alloy phase with a strong acid, and then separating and purifying it to obtain pure platinum group metals. However, pyrometallurgical processes are complex, consume large amounts of energy and raw materials, require sophisticated equipment, and cause significant environmental pollution. Hydrometallurgical methods mainly include three types: carrier dissolution, total dissolution, and active component dissolution. Compared to pyrometallurgy, hydrometallurgy has advantages such as a shorter process and lower investment, but its metal recovery rate is lower.

[0005] There are numerous studies and patents both domestically and internationally on the recovery of platinum from spent catalysts. However, there are no reports on methods for recovering platinum from spent catalysts supported by titanium-zirconium composite oxides. If conventional pyrometallurgical processes are used to enrich platinum, a large amount of slag is required, resulting in high energy consumption and severe environmental pollution. If conventional wet dissolution separation is used, the titanium-zirconium composite oxide support contains a significant amount of platinum, leading to incomplete platinum separation and a low recovery rate. Patent application CN94118736.5 discloses a method for recovering platinum group metals from spent catalysts. After complete dissolution of the platinum group metals and the support, R410 resin is used to adsorb and recover platinum from the spent catalyst supported by alumina. The leaching and recovery rates of platinum are high, but liquid-solid separation is difficult after complete dissolution of the support, requiring multi-stage clarification of the leachate, resulting in a high total liquid-to-solid ratio. This reduces the processing capacity of the leaching equipment, increases the burden on adsorption and storage equipment, and also increases the pressure on wastewater treatment. The invention patent with application number CN201710383466.8 discloses a method for selectively dissolving and recovering platinum from aluminum-based platinum catalysts. Platinum is selectively dissolved by alumina transformation, which prevents it from being dissolved by sulfuric acid. However, it is only applicable to spent catalysts supported by alumina, and not to spent catalysts supported by titanium-zirconium composite oxides. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for recovering platinum from waste catalysts supported on titanium-zirconium composite oxides. The waste catalyst is first decomposed using bisulfate, and then dissolved by oxidation with hydrochloric acid and an oxidant. This method not only reduces the cost of platinum recovery and minimizes environmental pollution, but also significantly improves equipment utilization, increases production efficiency, and facilitates resource recycling.

[0007] The objective of this invention is achieved through the following technical solution: This invention provides a method for recovering platinum from a spent catalyst supported on a titanium-zirconium composite oxide, comprising the following steps: (1) The waste catalyst supported on TiO2-ZrO2 and loaded with platinum was roasted, then crushed and ground. (2) After grinding the waste catalyst and mixing it with hydrogen sulfate, the mixture is roasted to obtain molten material I; molten material I is stirred and dissolved with acid solution, and filtered to obtain filtrate and filter cake I; (3) Repeat the reaction in step (2) with filter cake I to obtain filter cake II; (4) Dissolve filter cake II by oxidizing it with hydrochloric acid and an oxidizing agent to obtain a platinum-containing solution; (5) The platinum-containing solution is separated and purified to obtain metallic platinum.

[0008] In this invention, the catalyst uses TiO2-ZrO2 as a support. If conventional wet dissolution and separation (acid + oxidant) is used, the titanium-zirconium composite oxide support contains a significant amount of platinum, preventing the metallic platinum from leaching and dissolving into the solution. This results in incomplete platinum separation and a low platinum recovery rate. Therefore, the spent catalyst is first roasted to remove organic impurities, and then mixed and roasted with bisulfate. The bisulfate decomposes the titanium-zirconium composite oxide support, exposing the metallic platinum, which can then be leached and purified using a conventional acid-oxidant method in subsequent processes, thus improving the platinum recovery rate.

[0009] Taking ammonium bisulfate as an example, the reaction equation for the reaction between bisulfate and the titanium-zirconium composite oxide support (TiO2-ZrO2) is as follows: 2NH4HSO4+ZrO2=Zr(SO4)2+2NH3(g)+2H2O; NH4HSO4+TiO2=TiOSO4+NH3+H2O.

[0010] After the spent catalyst is mixed and calcined with bisulfate, it is dissolved in an acid solution. The product of the reaction between the bisulfate and the titanium-zirconium composite oxide support reacts with the acid solution to obtain a filtrate containing titanium and zirconium, and a platinum-containing filter cake I. Filter cake I is calcined again with bisulfate because the initial solid-liquid melting reaction is inefficient. This second reaction allows the support to react fully, further improving the platinum recovery rate. The filter cake II obtained after the second reaction is dissolved by oxidation with hydrochloric acid and an oxidant. The platinum in the filter cake can leach and dissolve into the solution for subsequent separation and purification to obtain high-purity and high-yield metallic platinum.

[0011] Preferably, in step (1), the platinum content in the waste catalyst is 0.05-0.3% by mass.

[0012] Preferably, in step (1), the roasting temperature is 400-900℃ and the time is 1-6h; more preferably, the temperature is 600-700℃ and the time is 1-6h.

[0013] This roasting temperature helps ensure a high efficiency in removing organic impurities, resulting in a higher platinum recovery rate.

[0014] Preferably, in step (1), the particle size of the crushing and grinding is 50 to 400 mesh; more preferably, the particle size is 100 to 200 mesh.

[0015] If the particle size of the crushed and ground material is too large, it will not be conducive to the reaction with bisulfate, resulting in a low reaction efficiency; while if the particle size of the crushed and ground material is too small, it will also cause a small loss of platinum, and a trace amount of platinum will enter the filtrate and be lost.

[0016] Preferably, in step (2), the roasting temperature is 300-550°C and the time is 30 min-2 h; more preferably, the temperature is 400-500°C and the time is 30 min-2 h.

[0017] If the calcination temperature is too low, the platinum in the catalyst will not be completely passivated, resulting in a slight loss of platinum during the reaction of bisulfate with the support. If the calcination temperature is too high, the following side reactions will occur: TiOSO4 = SO3 + TiO2; Zr(SO4)2=2SO3(g)+ZrO2.

[0018] This can cause the reaction products to decompose into oxides that are insoluble in water and acid, resulting in these oxides remaining in the filter cake and affecting the platinum recovery rate.

[0019] Preferably, in step (2), the hydrogen sulfate is one or more of ammonium hydrogen sulfate, sodium hydrogen sulfate, potassium hydrogen sulfate, sodium pyrosulfate and potassium pyrosulfate; more preferably, the hydrogen sulfate is ammonium hydrogen sulfate.

[0020] Preferably, the total amount of bisulfate added in steps (2) and (3) is calculated based on the ratio of the total molar amount of zirconium and titanium in the waste catalyst to the molar amount of bisulfate being 1:3 to 15; more preferably, the ratio of the total molar amount of zirconium and titanium in the waste catalyst to the molar amount of bisulfate is 1:5 to 8.

[0021] Preferably, in step (2), the concentration of the acid solution is 0.5 to 6 mol / L; the acid is an inorganic acid, which is hydrochloric acid or sulfuric acid; more preferably, sulfuric acid is used.

[0022] The use of acid solution for dissolution is to prevent the titanium and zirconium in the molten material from hydrolyzing to form titanium dioxide and zirconium dioxide, which would remain in the filter cake and affect the platinum recovery rate. The filtrate after acid dissolution consists of titanium oxysulfate and zirconium sulfate, while the filter cake contains some unreacted carrier material and metallic platinum. This exposes the metallic platinum, which is beneficial for subsequent oxidation, dissolution, separation, and purification.

[0023] Preferably, in step (2), the temperature of stirring and dissolving is 30-90°C and the time is 2-5 hours.

[0024] Preferably, in step (4), the concentration of the hydrochloric acid is 2 to 8 mol / L; the amount of hydrochloric acid used is 4 to 10 times the mass of filter cake II.

[0025] Preferably, in step (4), the oxidant is sodium chlorate or nitric acid; more preferably, sodium chlorate is used; the amount of the oxidant is 5-15% of the mass of filter cake II.

[0026] Preferably, in step (4), the oxidation and dissolution temperature is 80-90°C and the time is 2-5 hours.

[0027] Oxidation and dissolution can be carried out multiple times, and the platinum in the filter cake can be completely dissolved into the solution through multiple dissolution and leaching processes.

[0028] Preferably, in step (5), the separation and purification method includes ammonium chloride precipitation or ion exchange resin adsorption.

[0029] Compared with the prior art, the present invention has the following beneficial effects: (1) The method of decomposing the carrier with hydrogen sulfate avoids the use of a large amount of strong acid to dissolve the leaching material in the traditional wet purification process. In addition, the titanium-zirconium composite oxide carrier will react with strong acid and dissolve in a small amount, causing filtration difficulties. This method can avoid a large amount of subsequent solid-liquid separation, improve production efficiency, and obtain a higher leaching rate, thus saving costs. (2) The amount of oxidant added is small, and it will not decompose to produce excess oxidizing gases (such as NO). x The process allows for the safe and effective separation and recycling of the precious metal platinum from spent catalysts (such as Cl2), avoiding the deterioration of the operating environment and reducing environmental pollution. Detailed Implementation

[0030] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] The method for recovering platinum from spent catalysts supported on titanium-zirconium composite oxides in this invention includes the following steps: (1) The waste catalyst is supported on TiO2-ZrO2 and loaded with platinum. The mass content of platinum in the waste catalyst is 0.05-0.3%. The waste catalyst is roasted at 400-900℃ for 1-6 hours to remove organic matter and other easily combustible impurities. After cooling, the roasting ash is collected. The roasting ash is crushed and ground to 50-400 mesh. (2) After grinding the waste catalyst, mix it with hydrogen sulfate and calcine it at 300-550℃ for 30 min-2 h to obtain melt I; Dissolve melt I with an acid solution with a concentration of 0.5-6 mol / L at 30-90℃ for 2-5 h, filter it to obtain filtrate I and filter cake I; Send filtrate I to the sewage treatment plant for treatment to meet the standards before discharge. (3) After washing and drying the filter cake I, mix it with bisulfate and calcine it again at 300-550℃ for 30 min-2 h to obtain melt II; mix melt II with an acid solution with a concentration of 0.5-6 mol / L at 30-90℃ for 2-5 h, filter it to obtain filtrate II and filter cake II; send filtrate II to the sewage treatment plant for treatment to meet the standards before discharge. (4) After washing and drying filter cake II, it is dissolved by oxidation with 2-8 mol / L hydrochloric acid and oxidant (sodium chlorate or 65 wt% nitric acid). The amount of hydrochloric acid is 4-10 times the mass of filter cake II, and the amount of oxidant is 5-15% of the mass of filter cake II. The reaction is carried out at 80-90℃ for 2-5 hours. After filtration, washing and drying, the obtained filter cake is leached again with 2-8 mol / L hydrochloric acid and oxidant. The leaching solution and washing solution obtained from the two repeated leachings are combined to obtain a platinum-containing solution. (5) The platinum-containing solution is separated and purified to obtain metallic platinum.

[0032] In a specific embodiment of the present invention, in steps (2) and (3), the hydrogen sulfate is one or more of ammonium hydrogen sulfate, sodium hydrogen sulfate, potassium hydrogen sulfate, sodium pyrosulfate and potassium pyrosulfate.

[0033] In a specific embodiment of the present invention, the total amount of hydrogen sulfate added in steps (2) and (3) is calculated based on the ratio of the total molar amount of zirconium and titanium elements in the waste catalyst to the molar amount of hydrogen sulfate being 1:3 to 15. More preferably, the amount of hydrogen sulfate added in step (2) is greater than the amount of hydrogen sulfate added in step (3).

[0034] In a specific embodiment of the present invention, in steps (2) and (3), the liquid-to-solid ratio of melt I to acid solution is 4-10 mL: 1 g, and the liquid-to-solid ratio of melt II to acid solution is 4-10 mL: 1 g. The acid in the acid solution is an inorganic acid, which is hydrochloric acid or sulfuric acid.

[0035] In a specific embodiment of the present invention, in steps (1), (2) and (3), the heating rate of calcination is 1-20℃ / min.

[0036] In a specific embodiment of the present invention, step (5) involves separation and purification using either ammonium chloride precipitation or ion exchange resin adsorption. The ammonium chloride precipitation method includes: adding ammonium chloride to a platinum-containing solution to selectively precipitate platinum metal while other metals do not precipitate; purifying and reducing the resulting ammonium chloroplatinate precipitate (after washing, calcining at 800°C or directly reducing with hydrazine hydrate) to obtain metallic platinum.

[0037] Example 1 The spent catalyst was supported on TiO2-ZrO2 with platinum loaded on it. By mass percentage, the spent catalyst contained 0.105% Pt, 54.32% TiO2, 25.39% ZrO2, and the remainder of impurities (moisture and organic matter).

[0038] (1) Take 10 kg of waste catalyst and put it into a roasting furnace. Heat it to 650°C at a heating rate of 10°C / min and keep the temperature for 2 hours to roast and remove organic matter and other easily combustible impurities. After cooling, collect the roasting ash. Crush and grind the roasting ash to 150 mesh. (2) Mix the waste catalyst obtained in step (2) with 45 kg of ammonium bisulfate and roast it to 480°C at a heating rate of 5°C / min for 4 hours to obtain melt I. After cooling, add melt I to a dilute sulfuric acid solution (100 kg of water and 20 kg of sulfuric acid) and stir the reaction at 70°C for 3 hours. After filtration, obtain filtrate I and filter cake I. Send filtrate I to the sewage treatment plant for treatment and discharge after reaching the standard. After washing and drying the filter cake I, the mass is 0.48 kg and the content of Pt is 2.178%. (3) After washing and drying, filter cake I and 2 kg of ammonium bisulfate are mixed and heated to 480°C at a heating rate of 5°C / min for 4 hours to obtain melt II. After cooling, melt II is added to dilute sulfuric acid solution (8 kg of water and 1.6 kg of sulfuric acid) and stirred at 70°C for 3 hours. After filtration, filtrate II and filter cake II are obtained. Filtrate II is sent to the sewage treatment plant for treatment and discharged after meeting the standards. After washing and drying, filter cake II has a mass of 0.07 kg and contains 14.86% Pt. (4) Add 400 mL of 6 mol / L hydrochloric acid to the washed and dried filter cake II, heat to 80°C, add 6 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; add 200 mL of 6 mol / L hydrochloric acid to the obtained filter cake, heat to 80°C, add 3 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; combine the leaching solution and washing solution obtained from the two repeated leachings to obtain a platinum-containing solution; (5) Add 90 g of ammonium chloride to the platinum-containing solution to precipitate platinum, and purify and reduce the obtained ammonium chloroplatinate to obtain metallic platinum.

[0039] Example 2 The spent catalyst was supported on TiO2-ZrO2 with platinum loaded on it. By mass percentage, the spent catalyst contained 0.094% Pt, 52.43% TiO2, 27.03% ZrO2, and the remainder of impurities (moisture and organic matter).

[0040] (1) Take 10 kg of waste catalyst and put it into the roasting furnace. Heat it to 600℃ at a heating rate of 10℃ / min and keep the temperature for 2.5 h. Roast to remove organic matter and other easily combustible impurities. After cooling, collect the roasting ash. Crush and grind the roasting ash to 200 mesh. (2) The waste catalyst obtained in step (2) was mixed with a mixture of 45 kg sodium bisulfate and ammonium bisulfate (the mass ratio of sodium bisulfate and ammonium bisulfate was 1:1), and then heated to 450 °C for 4 h at a heating rate of 5 °C / min to obtain melt I. After cooling, melt I was added to a dilute sulfuric acid solution (130 kg water and 30 kg sulfuric acid), and stirred at 60 °C for 3 h. After filtration, filtrate I and filter cake I were obtained. Filtrate I was sent to a sewage treatment plant for treatment and discharged after reaching the standard. After washing and drying, filter cake I had a mass of 0.64 kg and contained 1.465% Pt. (3) After washing and drying filter cake I, mix it with 2 kg of a mixture of sodium bisulfate and ammonium bisulfate (the mass ratio of sodium bisulfate to ammonium bisulfate is 1:1), heat it to 450℃ at a heating rate of 5℃ / min and calcine it for 4 hours to obtain melt II; after cooling, add melt II to dilute sulfuric acid solution (8 kg water, 2 kg sulfuric acid), stir and react at 60℃ for 3 hours, filter it to obtain filtrate II and filter cake II; send filtrate II to the sewage treatment plant for treatment to meet the standards and then discharge it; after washing and drying filter cake II, the mass is 0.09 kg and the content of Pt is 10.31%; (4) Add 500 mL of 6 mol / L hydrochloric acid to the washed and dried filter cake II, heat to 80°C, add 5.5 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; add 250 mL of 6 mol / L hydrochloric acid to the obtained filter cake, heat to 80°C, add 3 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; combine the leaching solution and washing solution obtained from the two repeated leachings to obtain a platinum-containing solution; (5) add 90 g of ammonium chloride to the platinum-containing solution to precipitate platinum, and purify and reduce the obtained ammonium chloroplatinate to obtain metallic platinum.

[0041] Example 3 The spent catalyst was supported on TiO2-ZrO2 with platinum loaded on it. By mass percentage, the spent catalyst contained 0.105% Pt, 54.32% TiO2, 25.39% ZrO2, and the remainder of impurities (moisture and organic matter).

[0042] (1) Take 10 kg of waste catalyst and put it into a roasting furnace. Heat it to 700°C at a rate of 10°C / min and keep the temperature for 2 hours to roast and remove organic matter and other easily combustible impurities. After cooling, collect the roasting ash. Crush and grind the roasting ash to 100 mesh. (2) Mix the waste catalyst obtained in step (2) with 45 kg of ammonium bisulfate and roast it to 500°C at a rate of 5°C / min for 4 hours to obtain melt I. After cooling, add melt I to a dilute sulfuric acid solution (100 kg of water and 20 kg of sulfuric acid) and stir the reaction at 70°C for 3 hours. After filtration, obtain filtrate I and filter cake I. Send filtrate I to the sewage treatment plant for treatment and discharge after reaching the standard. After washing and drying the filter cake I, the mass is 0.44 kg and the content of Pt is 2.357%. (3) After washing and drying, filter cake I and 2 kg of ammonium bisulfate are mixed and heated to 500°C at a heating rate of 5°C / min for 4 hours to obtain melt II. After cooling, melt II is added to dilute sulfuric acid solution (8 kg of water and 1.6 kg of sulfuric acid) and stirred at 70°C for 3 hours. After filtration, filtrate II and filter cake II are obtained. Filtrate II is sent to the sewage treatment plant for treatment and discharged after meeting the standards. After washing and drying, filter cake II has a mass of 0.067 kg and contains 14.41% Pt. (4) Add 400 mL of 6 mol / L hydrochloric acid to the washed and dried filter cake II, heat to 80°C, add 6 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; add 200 mL of 6 mol / L hydrochloric acid to the obtained filter cake, heat to 80°C, add 3 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; combine the leaching solution and washing solution obtained from the two repeated leachings to obtain a platinum-containing solution; (5) add 90 g of ammonium chloride to the platinum-containing solution to precipitate platinum, and purify and reduce the obtained ammonium chloroplatinate to obtain metallic platinum.

[0043] Example 4 This embodiment uses the same waste catalyst as in Example 1 to conduct three parallel experiments, the only difference being that different calcination temperatures are used in step (1).

[0044] (1) Take 10 kg of waste catalyst and put it into the roasting furnace. The temperature is increased at a rate of 10℃ / min. The temperature increases are 400℃, 650℃ and 800℃ respectively. The holding time is 2h. Roasting removes organic matter and other easily combustible impurities. After cooling, collect the roasting ash. Crush and grind the roasting ash to 150 mesh. (2) The waste catalyst obtained in step (2) is mixed with 45 kg of ammonium bisulfate and heated to 480 °C for 4 h at a heating rate of 5 °C / min to obtain melt I; after cooling, melt I is added to dilute sulfuric acid solution (100 kg water, 20 kg sulfuric acid) and stirred at 70 °C for 3 h. After filtration, filtrate I and filter cake I are obtained; filtrate I is sent to the sewage treatment plant for treatment to meet the standards before being discharged; filter cake I is washed and dried. (3) After washing and drying filter cake I, mix it with 2 kg of ammonium bisulfate and calcine it at 480°C for 4 h at a heating rate of 5°C / min to obtain melt II; after cooling, add melt II to dilute sulfuric acid solution (8 kg of water and 1.6 kg of sulfuric acid) and stir the reaction at 70°C for 3 h. After filtration, obtain filtrate II and filter cake II; send filtrate II to the sewage treatment plant for treatment to meet the standards before discharge; wash and dry filter cake II. (4) Add 400 mL of 6 mol / L hydrochloric acid to the washed and dried filter cake II, heat to 80°C, add 6 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; add 200 mL of 6 mol / L hydrochloric acid to the obtained filter cake, heat to 80°C, add 3 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; combine the leaching solution and washing solution obtained from the two repeated leachings to obtain a platinum-containing solution; (5) Add 90 g of ammonium chloride to the platinum-containing solution to precipitate platinum, and purify and reduce the obtained ammonium chloroplatinate to obtain metallic platinum.

[0045] Example 5 This embodiment uses the same waste catalyst as in Example 1 to conduct four parallel experiments, the only difference being that the roasting ash in step (1) is crushed and ground to different particle sizes.

[0046] (1) Take 10 kg of waste catalyst and put it into the roasting furnace. Heat it to 650°C at a heating rate of 10°C / min and keep the temperature for 2 hours to roast and remove organic matter and other easily combustible impurities. After cooling, collect the roasting ash. Crush and grind the roasting ash into 10 mesh, 50 mesh, 150 mesh and 300 mesh respectively. (2) The waste catalyst obtained in step (2) is mixed with 45 kg of ammonium bisulfate and heated to 480 °C for 4 h at a heating rate of 5 °C / min to obtain melt I; after cooling, melt I is added to dilute sulfuric acid solution (100 kg water, 20 kg sulfuric acid) and stirred at 70 °C for 3 h. After filtration, filtrate I and filter cake I are obtained; filtrate I is sent to the sewage treatment plant for treatment to meet the standards before being discharged; filter cake I is washed and dried. (3) After washing and drying filter cake I, mix it with 2 kg of ammonium bisulfate and calcine it at 480°C for 4 h at a heating rate of 5°C / min to obtain melt II; after cooling, add melt II to dilute sulfuric acid solution (8 kg of water and 1.6 kg of sulfuric acid) and stir the reaction at 70°C for 3 h. After filtration, obtain filtrate II and filter cake II; send filtrate II to the sewage treatment plant for treatment to meet the standards before discharge; wash and dry filter cake II. (4) Add 400 mL of 6 mol / L hydrochloric acid to the washed and dried filter cake II, heat to 80°C, add 6 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; add 200 mL of 6 mol / L hydrochloric acid to the obtained filter cake, heat to 80°C, add 3 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; combine the leaching solution and washing solution obtained from the two repeated leachings to obtain a platinum-containing solution; (5) Add 90 g of ammonium chloride to the platinum-containing solution to precipitate platinum, and purify and reduce the obtained ammonium chloroplatinate to obtain metallic platinum.

[0047] Example 6 This embodiment uses the same waste catalyst as in Example 1 to conduct 5 parallel experiments. The only difference is that steps (2) and (3) are calcined at different temperatures. In each parallel experiment, the calcination temperature used in steps (2) and (3) is the same.

[0048] (1) Take 10 kg of waste catalyst and put it into the roasting furnace. Heat it to 650°C at a heating rate of 10°C / min and keep the temperature for 2 hours to roast and remove organic matter and other easily combustible impurities. After cooling, collect the roasting ash. Crush and grind the roasting ash to 150 mesh. (2) The waste catalyst obtained in step (2) is mixed with 45 kg of ammonium bisulfate and heated at a rate of 5 °C / min to 300 °C, 400 °C, 480 °C, 600 °C and 700 °C respectively, and calcined for 4 h each time to obtain melt I; after cooling, melt I is added to dilute sulfuric acid solution (100 kg water and 20 kg sulfuric acid) and stirred at 70 °C for 3 h. After filtration, filtrate I and filter cake I are obtained; filtrate I is sent to the sewage treatment plant for treatment to meet the standards before being discharged; filter cake I is washed and dried. (3) After washing and drying, filter cake I and 2 kg of ammonium bisulfate are mixed and heated at a rate of 5 °C / min to 300 °C, 400 °C, 480 °C, 600 °C and 700 °C respectively, and calcined for 4 h each time to obtain melt II; after cooling, melt II is added to dilute sulfuric acid solution (8 kg water and 1.6 kg sulfuric acid), and stirred at 70 °C for 3 h. After filtration, filtrate II and filter cake II are obtained; filtrate II is sent to the sewage treatment plant for treatment to meet the standards before being discharged; filter cake II is washed and dried. (4) Add 400 mL of 6 mol / L hydrochloric acid to the washed and dried filter cake II, heat to 80°C, add 6 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; add 200 mL of 6 mol / L hydrochloric acid to the obtained filter cake, heat to 80°C, add 3 g of sodium chlorate in batches, react for 3 h, filter, wash and dry; combine the leaching solution and washing solution obtained from the two repeated leachings to obtain a platinum-containing solution; (5) Add 90 g of ammonium chloride to the platinum-containing solution to precipitate platinum, and purify and reduce the obtained ammonium chloroplatinate to obtain metallic platinum.

[0049] Comparative Example 1 This comparative example uses the spent catalyst from Example 1, the difference being that it employs conventional wet dissolution and separation.

[0050] Take 10 kg of waste catalyst, add 40 kg of 6 mol / L hydrochloric acid and 5 L of 65 wt% nitric acid, heat to 80 °C, react for 3 h, filter, wash and dry; add another 40 kg of 6 mol / L hydrochloric acid and 5 L of 65 wt% nitric acid to the obtained filter cake, heat to 80 °C, react for 3 h, filter, wash and dry; combine the leachate and washing solution obtained from the two repeated leachings, concentrate and remove nitrate, add ammonium chloride to the obtained solution to precipitate platinum, and purify and reduce the obtained ammonium chloroplatinate to obtain metallic platinum.

[0051] Comparative Example 2 This comparative example uses the waste catalyst and recovery method from Example 1, except that the waste catalyst is not mixed with ammonium bisulfate for roasting.

[0052] (1) Take 10 kg of waste catalyst and put it into a roasting furnace. Heat it to 650°C at a rate of 10°C / min and keep the temperature for 2 hours. Roast to remove organic matter and other easily combustible impurities. After cooling, collect the roasting ash. Crush and grind the roasting ash to 150 mesh. (2) Add 40 kg of 6 mol / L hydrochloric acid and 5 L of 65 wt% nitric acid to the waste catalyst obtained in step (2). React for 3 hours, filter, wash and dry. Add 40 kg of 6 mol / L hydrochloric acid and 5 L of 65 wt% nitric acid to the filter cake. Heat to 80°C and react for 3 hours. Filter, wash and dry. Combine the leaching solution and washing solution obtained from the two repeated leachings. Concentrate and remove nitrate. Add ammonium chloride to the resulting solution to precipitate platinum. Purify and reduce the obtained ammonium chloroplatinate to obtain metallic platinum.

[0053] Table 1 purity / % Platinum mass / g Platinum recovery rate / % Example 1 99.95 10.34 98.48 Example 2 99.95 9.22 98.09 Example 3 99.95 10.26 97.71 Comparative Example 1 99.95 6.08 57.9 Comparative Example 2 99.95 8.06 76.76 Table 2 The platinum recovery rate was calculated from the platinum obtained in the examples and comparative examples. The platinum recovery rate is the percentage of the mass of platinum in the spent catalyst, and the results are shown in Tables 1 and 2. Since the catalyst in this invention uses TiO2-ZrO2 as a support, and Comparative Example 1 uses conventional wet dissolution separation (acid + oxidant), the titanium-zirconium composite oxide support contains a large amount of platinum, preventing the platinum from leaching and dissolving into the solution. This results in incomplete platinum separation and a low platinum recovery rate. In Comparative Example 2, calcination is used to remove organic matter from the catalyst, which helps with subsequent wet dissolution separation. The platinum recovery rate is slightly higher than in Comparative Example 1, but because the leaching residue contains a large amount of platinum that cannot be leached into the solution, a significant amount of platinum is lost, resulting in a lower platinum recovery rate compared to Examples 1-3. Furthermore, the recovery process in Comparative Examples 1-2 requires a large amount of acid, and filtration and washing are difficult, generating a large amount of wastewater, resulting in high energy consumption and environmental pollution.

[0054] Therefore, in this invention, the spent catalyst is first roasted to remove organic impurities, and then mixed with bisulfate for roasting. The bisulfate can decompose the titanium-zirconium composite oxide support, thereby exposing the metallic platinum, which can be leached and purified in subsequent processes using ordinary acid and oxidant methods, ultimately achieving a high platinum recovery rate. Furthermore, Examples 4-6 show that the roasting temperature in step (1) affects the efficiency of organic impurity removal, which in turn affects the platinum recovery rate; the particle size of the roasting ash in step (1) affects the roasting efficiency of the catalyst and bisulfate, and if the particle size is too small, it will cause platinum loss, thus also affecting the platinum recovery rate; while the roasting temperature of the catalyst and bisulfate directly affects the roasting efficiency, and if the roasting reaction temperature is too high, side reactions will occur, resulting in a low platinum recovery rate.

[0055] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for recovering platinum from a spent catalyst of platinum supported on titanium-zirconium complex oxide, characterized by, The method comprises the following steps: (1) roasting and crushing a waste catalyst with TiO2-ZrO2 as carrier and loaded with platinum; (2) mixing the crushed waste catalyst with a hydrogen sulfate salt, roasting and reacting to obtain a melt I; stirring and dissolving the melt I with an acid solution, filtering to obtain a filtrate and a filter cake I; (3) repeating the reaction in step (2) with the filter cake I to obtain a filter cake II; (4) oxidizing and dissolving the filter cake II with hydrochloric acid and an oxidizing agent to obtain a platinum-containing solution; (5) separating and purifying the platinum-containing solution to obtain metallic platinum.

2. The process for recovering platinum from a spent catalyst of platinum supported on titanium-zirconium composite oxide according to claim 1, characterized by, In step (1), the mass content of platinum in the waste catalyst is 0.05-0.3%.

3. A process according to claim 1 or 2 for the recovery of platinum from spent platinum-on-titanium-zirconium composite oxide catalyst, characterized in that, In step (1), the roasting temperature is 400-900℃, and the time is 1-6h.

4. The method of recovering platinum from a spent catalyst of platinum on titanium-zirconium composite oxide according to claim 1, characterized by, In step (1), the particle size of the crushed and ground waste catalyst is 50-400 mesh.

5. The process for recovering platinum from a spent catalyst of platinum supported on titanium-zirconium complex oxide according to claim 1 or 4, characterized by, In step (2), the roasting temperature is 300-550℃, and the time is 30min-2h.

6. The method of recovering platinum from a spent catalyst of platinum on titanium-zirconium composite oxide according to claim 1, characterized by, In step (2), the hydrogen sulfate salt is one or more of ammonium bisulfate, sodium bisulfate, potassium bisulfate, sodium pyrosulfate and potassium pyrosulfate.

7. The process of recovering platinum from a spent catalyst of platinum supported on titanium-zirconium composite oxide according to claim 1 or 6, characterized by, In steps (2) and (3), the total amount of the hydrogen sulfate salt is calculated according to the ratio of the total moles of zirconium and titanium in the waste catalyst to the moles of the hydrogen sulfate salt, which is 1:3-15.

8. The process of recovering platinum from a spent catalyst of platinum supported on titanium-zirconium composite oxide according to claim 1 or 6, characterized by, In step (2), the concentration of the acid solution is 0.5-6mol / L; the stirring and dissolving temperature is 30-90℃, and the time is 2-5h.

9. The process of claim 1 for recovering platinum from a spent catalyst of platinum on titanium-zirconium composite oxide, characterized in that, In step (4), the concentration of the hydrochloric acid is 2-8mol / L.

10. The process for recovering platinum from a spent catalyst of platinum supported on titanium-zirconium composite oxide according to claim 1 or 9, characterized by, In step (4), the amount of the oxidizing agent is 5-15% of the mass of the filter cake II.

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