Method for preparing P-TiO2 photocatalyst and method for recycling waste Pd / Al2O3 catalyst

Abstract

This invention discloses a method for preparing P-TiO2 photocatalyst and a method for recycling waste Pd / Al2O3 catalyst. The P-TiO2 photocatalyst is prepared by a hydrothermal method. This invention provides a method for recycling waste Pd / Al2O3 catalyst using photocatalytic technology, comprising the following steps: Step A: Obtaining P-TiO2 photocatalyst; Step B: Mixing waste Pd / Al2O3 catalyst with P-TiO2 photocatalyst and a photocatalytic solvent, and carrying out a photocatalytic reaction under stirring and xenon lamp irradiation conditions to dissolve Pd in ​​the waste Pd / Al2O3 catalyst. After sufficient reaction, the Al2O3 support is first separated, and then the remaining solution is centrifuged to obtain a Pd-containing solution and P-TiO2 photocatalyst. This invention can effectively improve the recovery rate of Pd metal, and the entire process is green, environmentally friendly, and low-cost.

Description

Technical Field

[0001] This invention relates to the field of waste precious metal recycling technology, specifically to a method for preparing P-TiO2 photocatalysts and a method for recycling waste Pd / Al2O3 catalysts using photocatalysis technology. Background Art

[0002] Palladium (Pd) is a rare and expensive precious metal widely used in catalysis, particularly in hydrogen peroxide production, where Pd / Al₂O₃ catalysts serve as key materials with highly efficient catalytic performance. However, palladium reserves are extremely limited, and global mining output is insufficient to meet the growing industrial demand. As catalysts are discarded due to decreased activity or failure during use, the palladium resources they contain need to be effectively recovered to achieve resource recycling.

[0003] Waste Pd / Al2O3 catalysts still contain valuable palladium metal. Failure to recycle them not only wastes resources but also risks environmental pollution due to waste accumulation. Furthermore, with palladium prices remaining high in recent years, recovering palladium from waste catalysts can reduce raw material costs for enterprises and alleviate external dependence on palladium resources, achieving a win-win situation for both economic and environmental benefits. Therefore, developing efficient and environmentally friendly recycling technologies is of great significance for the resource regeneration and utilization of waste Pd / Al2O3 catalysts. This is not only a crucial link in the sustainable development of precious metal resources but also aligns with the development goals of green chemistry and a circular economy.

[0004] Currently, the main leaching methods for recovering palladium from spent petroleum catalysts (Pd / Al2O3) are as follows: 1) Support leaching method: This method uses acidic or alkaline leaching agents (such as HCl, H2SO4 or NaOH) to directly leach the Al2O3 support in the spent catalyst under certain temperature conditions, and then dissolves the Pd. The research of Kim et al. [KIM MS, KIM EY, EONG J, et al. Recovery of platinum and palladium from the spent petroleum catalysts by substrate dissolution in sulfuric acid[J]. Materials Transactions, 2010, 51(10): 1927-1933.] shows that when using sulfuric acid with a concentration of 8.0 mol / L, leaching at 100℃ for 18 hours, and the slurry mass concentration is 220 g / L, the palladium leaching rate can reach more than 90%. However, this process easily leads to palladium dispersion, so a reducing agent needs to be added to improve the recovery rate. The carrier leaching method has the risks of long leaching time, large reagent consumption, and palladium loss. Pretreatment is usually required before leaching to reduce costs and improve palladium recovery. 2) Active component dissolution method: Li Qian et al. [Li Qian, Hu Long, Yang Yongbin, et al. Experimental study on palladium recovery from spent catalysts [J]. Hydrometallurgy, 2017, 36(01):41-45.] used a combination of oxidative roasting pretreatment, reduction and chlorination leaching to recover palladium from spent Pd / Al2O3 catalyst. The study showed that after roasting at 575℃ for 2 hours, using hydrazine hydrate (2.5 g / L) and sodium chlorate (3.0 g / L), and leaching under 5 mol / L HCl conditions, the palladium leaching rate can be increased to over 98%. This method is relatively simple, has a high palladium recovery rate, low reagent consumption, and low investment cost. However, without pretreatment, the leaching effect may be unsatisfactory, and the reagent consumption is large, and palladium recovery is unstable. 3) Complete dissolution method: The palladium and Al2O3 support in the waste catalyst are completely dissolved by adding a leaching agent.Nogueira et al. [CANogueira, APPaiva, PCOliveira, et al. Oxidative leaching process with cupric ion in hydrochloric acid media for recovery of Pd and Rh from spent catalytic converters[J]. Journal of Hazardous Materials, 2014, 278: 82-90.] showed that adding spent Pd / Al2O3 catalyst to a system of 6 mol / L HCl and 3 mol / L CuCl2, and reacting at a constant temperature of 80 °C for 4 hours, can achieve a palladium leaching rate of 95%. Although the total dissolution method has a higher recovery rate than the other two methods, its leachate composition is more complex, making palladium difficult to recover.

[0005] Existing recovery methods suffer from environmental pollution and high reagent consumption. Furthermore, the carrier dissolution method results in palladium loss and a long reaction time; the leachate obtained by the total dissolution method has a complex composition, making subsequent enrichment of Pd more difficult. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low Pd metal recovery rate, large reagent consumption, and environmental pollution in existing waste catalysts Pd / Al2O3. It provides a method for preparing P-TiO2 photocatalyst and a method for recovering waste Pd / Al2O3 using photocatalysis technology, so as to improve the Pd metal recovery rate. The whole process is green, environmentally friendly, and low in cost.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing P-TiO2 photocatalysts via a hydrothermal method, comprising the following steps:

[0009] Step 1: Mix tetrabutyl titanate with deionized water and stir to form a milky white homogeneous tetrabutyl titanate solution; prepare an aqueous solution of diammonium hydrogen phosphate (NH4)2HPO4.

[0010] Step 2: Under stirring conditions, slowly add the diammonium hydrogen phosphate aqueous solution dropwise to the tetrabutyl titanate solution to form a mixed solution; during the dropwise addition, control the stirring speed to avoid excessively high local concentrations that could lead to particle agglomeration, and simultaneously control the pH value of the mixed solution between 5 and 7; the diammonium hydrogen phosphate aqueous solution and the tetrabutyl titanate solution are added to achieve a phosphorus content of 0.2-5%, where the phosphorus content = m P / m TiO2 ×100%, mP This refers to the mass of phosphorus (P) in the diammonium hydrogen phosphate aqueous solution, m TiO2 The mass of TiO2 is calculated based on the Ti element contained in the tetrabutyl titanate solution;

[0011] Step 3: Transfer the mixed solution obtained in Step 2 to a high-pressure hydrothermal reactor, place it in an oven and react at 150℃~200℃ for 10~12h. After the reaction is completed, allow the reactor to cool naturally to room temperature.

[0012] Step 4: Take the reaction product obtained in step 3 out of the high-pressure hydrothermal reactor, wash it repeatedly with water until the washing solution is neutral, and dry the washed precipitate thoroughly to obtain P-TiO2 powder. After grinding the dried P-TiO2 powder, classify it through a sieve and screen out the powder with a mesh size of 200-300 to obtain the P-TiO2 photocatalyst.

[0013] Furthermore, in step 2, the preferred stirring speed is 400-600 rpm when adding the diammonium hydrogen phosphate aqueous solution.

[0014] Furthermore, in step 2, the pH value of the mixed solution is controlled between 5 and 7 by adding ammonia.

[0015] Furthermore, in step 4, the drying temperature is preferably 60℃~100℃, and the drying time is preferably 8-12h.

[0016] Secondly, this invention provides a method for recovering waste Pd / Al2O3 catalyst using photocatalysis technology, wherein the waste Pd / Al2O3 catalyst has a size of 2 mm or more, comprising the following steps:

[0017] Step A: Obtain the P-TiO2 photocatalyst according to the method described in the first aspect;

[0018] Step B: Take the waste Pd / Al2O3 catalyst, mix it with the P-TiO2 photocatalyst and photocatalytic solvent, and carry out the photocatalytic reaction under stirring and xenon lamp irradiation to dissolve Pd in ​​the waste Pd / Al2O3 catalyst. After the reaction is complete, first separate the Al2O3 support, and then centrifuge the remaining solution to obtain the Pd-containing solution and the P-TiO2 photocatalyst.

[0019] Furthermore, in step B, the feed ratio of P-TiO2 photocatalyst to waste Pd / Al2O3 catalyst, calculated as the molar ratio of P contained in P-TiO2 photocatalyst to Pd contained in waste Pd / Al2O3 catalyst, is preferably 1 to 4.

[0020] Furthermore, in step B, the photocatalytic solvent is preferably at least one of 5-20 wt% NaBr aqueous solution, 5-20 wt% NH4Br aqueous solution, and 5-20 wt% KBr aqueous solution.

[0021] Furthermore, in step B, the ratio of the total mass of the waste Pd / Al2O3 catalyst and the P-TiO2 photocatalyst to the volume of the photocatalytic solvent is 1 g: (5-20) mL.

[0022] Furthermore, in step B, the photocatalytic reaction is carried out at a light power density of 0.01-2000 mW·cm⁻¹. -2 The preferred value is 100–500 mW·cm. -2 The process is carried out under light irradiation, with the xenon lamp irradiation time preferably being 1–3 hours.

[0023] Furthermore, the P-TiO2 photocatalyst recovered in step B is reused in the photocatalytic reaction of step B.

[0024] Furthermore, the method also includes the following steps:

[0025] Step C: Obtain activated carbon with a high isoelectric point between 8 and 10;

[0026] Step D: Take an appropriate amount of the high isoelectric point activated carbon obtained in step C, add it to the Pd-containing solution obtained in step B to enrich the Pd ions therein, and after full enrichment, centrifuge to separate the Pd ions and obtain the separation solution and the palladium-enriched activated carbon; after drying the palladium-enriched activated carbon, calcine it in an air atmosphere to obtain Pd slag.

[0027] Furthermore, step C is carried out as follows: Take activated carbon, add an appropriate amount of alkaline solution to completely immerse the activated carbon in the alkaline solution, wherein the alkaline solution is a NaOH or KOH aqueous solution with a concentration of 0.1-1 mol / L, and the solid-liquid ratio of the activated carbon to the alkaline solution is 1 g:(10-25) mL; stir the obtained slurry containing activated carbon at 40-80℃ for 0.5-2 h, and then separate, wash and dry to obtain high isoelectric point activated carbon with an isoelectric point between 8 and 10.

[0028] Furthermore, in step D, the enrichment conditions are as follows: after adding high isoelectric point activated carbon to the Pd-containing solution obtained in step B and mixing evenly, the mixture is stirred at 30–50°C for 3–6 hours to complete the enrichment of Pd ions.

[0029] Furthermore, in step D, the calcination conditions are: 400℃-600℃, calcination in an air atmosphere in a muffle furnace for 1-2 hours, with a heating rate of 2-5℃ / min.

[0030] Furthermore, the separation solution obtained in step D is reused as a photocatalytic solvent in the photocatalytic reaction of step B.

[0031] The palladium slag obtained after roasting in step D of this invention has a significantly reduced volume and mass, making it easier to process. Since NaOH or KOH is used in the preparation of high isoelectric point activated carbon, the palladium slag may contain residual Na or K in the form of oxides and / or carbonates. When processing the palladium slag, the difference in acid solubility between Na, K and Pd can be used to remove Na or K first. Then, the photocatalytic dissolution method of this invention can be used to further purify Pd, or conventional methods such as aqua regia dissolution can be used for purification.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The P-TiO2 photocatalyst prepared by the hydrothermal method in this invention can efficiently dissolve Pd metal under a controllable light source compared with the P-TiO2 photocatalyst obtained by solid-phase mixing modification reported in the prior art. It releases palladium into the solution in ionic form through oxidation, resulting in more thorough dissolution.

[0034] (2) The present invention uses high isoelectric point activated carbon to efficiently and selectively enrich palladium ions in solution. It is environmentally friendly, requires no strong acid reagents, reduces equipment corrosion and environmental pollution, and reduces waste liquid treatment costs.

[0035] (3) In this invention, the photocatalyst and photocatalytic solvent can be recycled to perform multiple photocatalytic dissolutions of Pd, thereby reducing the processing cost. Detailed Implementation

[0036] The embodiments listed in this invention will be described in detail below through specific examples, but the scope of protection of this invention is not limited to the following examples.

[0037] The waste Pd / Al2O3 catalyst used in the following examples was spherical particles with a particle size of 2-3 mm. ICP testing by the China Nonferrous Metals Industry Testing Center showed a Pd content of 0.3 wt%. The activated carbon was sourced from Nanjing Kaichi Carbon Industry Co., Ltd., model: NAC-90.

[0038] The isoelectric point of the activated carbon in the examples was tested according to the following steps:

[0039] 1. Preparation of suspension:

[0040] Select 0.1g of activated carbon sample, add it to deionized water, and stir thoroughly to obtain a uniform suspension.

[0041] Ensure that the activated carbon particles are well dispersed so that they can react with ions in the solution.

[0042] 2. Selecting the titration solution:

[0043] The acid is hydrochloric acid (HCl), and the base is sodium hydroxide (NaOH). The titration is performed with both acid and base solutions having a concentration of 0.01 M.

[0044] 3. Measure the initial pH and potential:

[0045] Before adding acid or alkali, measure the initial pH value of the activated carbon suspension with a pH meter.

[0046] 4. Stepwise titration:

[0047] The titrant (acid or base) is slowly added dropwise to the suspension, while simultaneously measuring the potential and pH value. The potential and pH value are recorded after each addition of a small amount of acid or base. (The potential is measured using a potentiometer and a reference electrode.)

[0048] During the titration process, the potential changes corresponding to different pH values ​​are recorded.

[0049] 5. Plot the potential-pH curve:

[0050] Based on experimental data, a curve showing the relationship between electrical potential and pH was plotted. Normally, electrical potential changes with pH. Near the isoelectric point, the curve shows more dramatic changes. This is because the surface charge changes significantly at this point, leading to sharp fluctuations in electrical potential.

[0051] 6. Determine the isoelectric point:

[0052] The isoelectric point usually appears where the potential change is most drastic, typically representing the inflection point on the curve. This point is the isoelectric point pH (pHpzc) of activated carbon.

[0053] Example 1

[0054] Step 1: Hydrothermal preparation of P-TiO2 photocatalyst: In a beaker, add 50 mL of deionized water and slowly add 10 mL of tetrabutyl titanate, stirring to form a milky white homogeneous solution. In another beaker, weigh diammonium hydrogen phosphate (diammonium phosphate) according to a solid-liquid ratio of 0.8 (g / mL) (diammonium hydrogen phosphate and tetrabutyl titanate), dissolve it in 10 mL of deionized water, and stir until completely dissolved. Slowly add the diammonium hydrogen phosphate solution dropwise to the tetrabutyl titanate solution to form a mixed solution, achieving a target P content of 2 wt% in titanium dioxide. During the dropwise addition, maintain a stirring speed of 400 rpm to avoid excessively high local concentrations that could lead to particle agglomeration. Adjust the pH of the mixed solution to 5 using concentrated ammonia to ensure suitable reaction conditions. After the dropwise addition is complete, transfer the mixed solution to a 100 mL high-pressure hydrothermal reactor. Place it in an oven and react at 150 °C for 10 h. After the reaction is complete, allow the reactor to cool naturally to room temperature. Remove the reaction product and wash it repeatedly with deionized water until the washings are neutral. The washed precipitate was dried in an oven at 60°C for 8 hours to obtain 2wt% P-TiO2 powder. The dried 2wt% P-TiO2 powder was ground in a mortar and sieved to obtain nano-titanium dioxide powder with a mesh size of 200-300.

[0055] Step 2: Preparation of high isoelectric point activated carbon: Weigh an appropriate amount of activated carbon and add an appropriate amount of 0.1 mol / L NaOH solution. The solid-liquid ratio (g / mL) of activated carbon to NaOH solution is 1:10, ensuring the activated carbon is completely submerged in the alkaline solution. Stir the activated carbon slurry on a magnetic stirrer and reflux at 40℃ for 0.5 h. After reflux heating, wash the obtained activated carbon and then dry it in a drying oven at 60℃ for 12 hours to obtain high isoelectric point activated carbon. The isoelectric point (pHpzc) was measured to be 8.

[0056] Step 3: The catalyst is applied to the photocatalytic dissolution of Pd and the enrichment of Pd by activated carbon.

[0057] Weigh a certain amount of 0.3wt% waste Pd / Al2O3 catalyst, add 2wt% P-TiO2 photocatalyst and photocatalytic solvent. The molar ratio of P in the 2wt% P-TiO2 photocatalyst to Pd in ​​the 0.3wt% waste Pd / Al2O3 catalyst is 1. The photocatalytic solvent is a 5wt% NaBr aqueous solution. The solid-liquid ratio (g / mL) of the 2wt% P-TiO2 photocatalyst and the 0.3wt% waste Pd / Al2O3 catalyst to the photocatalytic solvent is 1:5. Place the above three substances into a round-bottom flask, connect a condenser, and stir on a magnetic stirrer with a light power density of 100 mW·cm⁻¹. -2Xenon lamp irradiation for 1 hour was used to dissolve the noble metal Pd. After the reaction, the spherical Al2O3 support was separated and then centrifuged to obtain a Pd solution and 2 wt% P-TiO2 photocatalyst (powder). A portion of the obtained Pd solution was subjected to ICP to determine the photocatalytic solubility of Pd.

[0058] Weigh an appropriate amount of the prepared high isoelectric point activated carbon and add it to the above Pd solution. Sonicate the mixture for 5 minutes to ensure uniform mixing. Then, place the activated carbon slurry into a round-bottom flask, connect a condenser, and stir on a magnetic stirrer. Heat the flask in a water bath at 30°C for 3 hours. After water bath heating, centrifuge the resulting activated carbon slurry to obtain a separation solution and a carbon-Pd solid mixture. Dry the carbon-Pd solid mixture and then calcine it at 600°C for 3 hours in air to obtain Pd slag. A portion of the separation solution was analyzed by ICP to determine the Pd enrichment rate on the activated carbon.

[0059] Example 2

[0060] The operation steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the solid-liquid ratio (g / mL) of diammonium hydrogen phosphate to tetrabutyl titanate was selected to be 0.08, so as to achieve a target phosphorus content of 0.2wt% in titanium dioxide.

[0061] Example 3

[0062] The operation steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the solid-liquid ratio (g / mL) of diammonium hydrogen phosphate to tetrabutyl titanate was selected as 1.21 to achieve the target phosphorus content of 3wt% in titanium dioxide; in the second step of preparing high isoelectric point activated carbon, KOH was selected as the alkaline solution with an isoelectric point of 9.3.

[0063] Example 4

[0064] The operation steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the solid-liquid ratio (g / mL) of diammonium hydrogen phosphate to tetrabutyl titanate was selected to be 1.61 to achieve the target phosphorus content of 4wt% in titanium dioxide; in the second step of preparing high isoelectric point activated carbon, the concentration of alkaline solution was selected to be 0.3mol / L and the isoelectric point was 8.3.

[0065] Example 5

[0066] The operation steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the solid-liquid ratio (g / mL) of diammonium hydrogen phosphate to tetrabutyl titanate was selected to be 2.02 to achieve the target phosphorus content of 5wt% in titanium dioxide; in the second step of preparing high isoelectric point activated carbon, the concentration of alkaline solution was selected to be 0.5mol / L and the isoelectric point was 8.6.

[0067] Example 6

[0068] The operation steps of Example 1 were repeated, except that when preparing the P-TiO2 photocatalyst in the first step, the stirring speed was 500 rpm when adding diammonium hydrogen phosphate; and when preparing the high isoelectric point activated carbon in the second step, the concentration of the alkaline solution was selected to be 0.7 mol / L and the isoelectric point was 8.8.

[0069] Example 7

[0070] The operation steps of Example 1 were repeated, except that when preparing the P-TiO2 photocatalyst in the first step, the stirring speed was 600 rpm when adding diammonium hydrogen phosphate; and when preparing the high isoelectric point activated carbon in the second step, the concentration of the alkaline solution was selected to be 0.9 mol / L and the isoelectric point was 9.0.

[0071] Example 8

[0072] The operation steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the pH was adjusted to 6; and in the second step of preparing the high isoelectric point activated carbon, the concentration of the alkaline solution was selected to be 1 mol / L and the isoelectric point was 9.2.

[0073] Example 9

[0074] The operation steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the pH was adjusted to 7; and in the second step of preparing high isoelectric point activated carbon, the solid-liquid ratio (g / mL) of activated carbon to alkaline solution was selected as 1:15, and the isoelectric point was 8.9.

[0075] Example 10

[0076] The operation steps of Example 1 were repeated, except that the hydrothermal reaction temperature was 160℃ when preparing the P-TiO2 photocatalyst in the first step; and the solid-liquid ratio (g / mL) of activated carbon to alkaline solution was selected as 1:20 and the isoelectric point was 9.5 when preparing the high isoelectric point activated carbon in the second step.

[0077] Example 11

[0078] The operation steps of Example 1 were repeated, except that the hydrothermal reaction temperature was 170°C when preparing the P-TiO2 photocatalyst in the first step; and the solid-liquid ratio (g / mL) of activated carbon to alkaline solution was selected as 1:25 and the isoelectric point was 10 when preparing the high isoelectric point activated carbon in the second step.

[0079] Example 12

[0080] The operation steps of Example 1 were repeated, except that the hydrothermal reaction temperature was 180°C in the first step of preparing the P-TiO2 photocatalyst, and the water bath heating temperature was 50°C and the isoelectric point was 8.1 in the second step of preparing the high isoelectric point activated carbon.

[0081] Example 13

[0082] Repeat the steps of Example 1, except that in the first step of preparing the P-TiO2 photocatalyst, the hydrothermal reaction temperature is 190℃; and in the second step of preparing the high isoelectric point activated carbon, the water bath heating temperature is 60℃, and the isoelectric point is 8.5.

[0083] Example 14

[0084] The operation steps of Example 1 were repeated, except that the hydrothermal reaction temperature was 200°C in the first step of preparing the P-TiO2 photocatalyst, and the water bath heating temperature was 70°C and the isoelectric point was 8.7 in the second step of preparing the high isoelectric point activated carbon.

[0085] Example 15

[0086] The operation steps of Example 1 were repeated, except that the hydrothermal reaction time was 11 h when preparing the P-TiO2 photocatalyst in the first step; and the water bath heating temperature was 80 °C and the isoelectric point was 8.9 when preparing the high isoelectric point activated carbon in the second step.

[0087] Example 16

[0088] The operation steps of Example 1 were repeated, except that the hydrothermal reaction time was 12 h when preparing the P-TiO2 photocatalyst in the first step; and the water bath heating time was 1 h and the isoelectric point was 8.3 when preparing the high isoelectric point activated carbon in the second step.

[0089] Example 17

[0090] The operation steps of Example 1 were repeated, except that the drying temperature was 70°C when preparing the P-TiO2 photocatalyst in the first step; and the water bath heating time was 1.5 h and the isoelectric point was 8.5 when preparing the high isoelectric point activated carbon in the second step.

[0091] Example 18

[0092] The operation steps of Example 1 were repeated, except that the drying temperature was 80°C when preparing the P-TiO2 photocatalyst in the first step; and the water bath heating time was 2 hours and the isoelectric point was 8.7 when preparing the high isoelectric point activated carbon in the second step.

[0093] Example 19

[0094] The operation steps of Example 1 were repeated, except that the drying temperature was 100°C when preparing the P-TiO2 photocatalyst in the first step; and the molar ratio of P in the P-TiO2 photocatalyst to Pd in ​​the 3wt% waste Pd / Al2O3 catalyst was 2 when the catalyst was applied to photocatalytic dissolution of Pd and activated carbon enrichment of Pd in ​​the third step.

[0095] Example 20

[0096] The operation steps of Example 1 were repeated, except that the drying time was 9 hours when preparing the P-TiO2 photocatalyst in the first step; and the molar ratio of P in the P-TiO2 photocatalyst to Pd in ​​the 3wt% waste Pd / Al2O3 catalyst was 3 when the catalyst was applied to photocatalytic dissolution of Pd and activated carbon enrichment of Pd in ​​the third step.

[0097] Example 21

[0098] The operation steps of Example 1 were repeated, except that the drying time was 10 h when preparing the P-TiO2 photocatalyst in the first step; and the molar ratio of P in the P-TiO2 photocatalyst to Pd in ​​the 3 wt% waste Pd / Al2O3 catalyst was 4 when the catalyst was applied to photocatalytic dissolution of Pd and activated carbon enrichment of Pd in ​​the third step.

[0099] Example 22

[0100] The operation steps of Example 1 were repeated, except that the drying time was 11 hours when preparing the P-TiO2 photocatalyst in the first step; and the photocatalytic solvent was an aqueous solution of NH4Br when the catalyst was applied to the photocatalytic dissolution of Pd and the enrichment of Pd by activated carbon in the third step.

[0101] Example 23

[0102] The operation steps of Example 1 were repeated, except that the drying time was 12 hours when preparing the P-TiO2 photocatalyst in the first step; and the photocatalytic solvent was KBr aqueous solution when the catalyst was applied to the photocatalytic dissolution of Pd and the enrichment of Pd by activated carbon in the third step.

[0103] Example 24

[0104] The operation steps of Example 1 are repeated, except that when the catalyst is applied to the photocatalytic dissolution of Pd in ​​the third step, the concentration of the photocatalytic solvent is preferably 10 wt%.

[0105] Example 25

[0106] The operation steps of Example 1 are repeated, except that when the catalyst is applied to the photocatalytic dissolution of Pd in ​​the third step, the concentration of the photocatalytic solvent is preferably 15 wt%.

[0107] Example 26

[0108] The operation steps of Example 1 are repeated, except that when the catalyst is applied to the photocatalytic dissolution of Pd in ​​the third step, the concentration of the photocatalytic solvent is preferably 20 wt%.

[0109] Example 27

[0110] The operation steps of Example 1 were repeated, except that in the third step, when the catalyst was applied to the photocatalytic dissolution of Pd, the photocatalytic reaction was carried out at a light power density of 200 mW·cm⁻¹. -2 .

[0111] Example 28

[0112] The operation steps of Example 1 were repeated, except that in the third step, when the catalyst was applied to the photocatalytic dissolution of Pd and the enrichment of Pd by activated carbon, the photocatalytic reaction was carried out at a light power density of 300 mW·cm⁻¹. -2 The hydrothermal heating temperature is 40℃.

[0113] Example 29

[0114] The operation steps of Example 1 were repeated, except that in the third step, when the catalyst was applied to the photocatalytic dissolution of Pd and the enrichment of Pd by activated carbon, the photocatalytic reaction was carried out at a light power density of 400 mW·cm⁻¹. -2 The hydrothermal heating temperature is 50℃.

[0115] Example 30

[0116] The operation steps of Example 1 were repeated, except that in the third step, when the catalyst was applied to the photocatalytic dissolution of Pd and the enrichment of Pd by activated carbon, the photocatalytic reaction was carried out at a light power density of 500 mW·cm⁻¹. -2 The water bath heating time is 4 hours.

[0117] Example 31

[0118] Repeat the steps of Example 1, except that in the third step, when the catalyst is applied to the photocatalytic dissolution of Pd and the activated carbon enrichment of Pd, the xenon lamp irradiation time is preferably 2 hours and the water bath heating time is 5 hours.

[0119] Example 32

[0120] Repeat the steps of Example 1, except that in the third step, when the catalyst is applied to the photocatalytic dissolution of Pd and the activated carbon enrichment of Pd, the xenon lamp irradiation time is preferably 3 hours and the water bath heating time is 6 hours.

[0121] Example 33

[0122] Repeat the steps of Example 1, except that in the third step, when the catalyst is applied to the photocatalytic dissolution of Pd, the solid-liquid ratio (g / mL) of the P-TiO2 photocatalyst, the waste Pd / Al2O3 catalyst and the photocatalytic solvent is 1:10.

[0123] Example 34

[0124] Repeat the steps of Example 1, except that in the third step, when the catalyst is applied to the photocatalytic dissolution of Pd, the solid-liquid ratio (g / mL) of the P-TiO2 photocatalyst, the waste Pd / Al2O3 catalyst and the photocatalytic solvent is 1:15.

[0125] Example 35

[0126] Repeat the steps of Example 1, except that in the third step, when the catalyst is applied to the photocatalytic dissolution of Pd, the solid-liquid ratio (g / mL) of the P-TiO2 photocatalyst, the waste Pd / Al2O3 catalyst and the photocatalytic solvent is 1:20.

[0127] Example 36

[0128] The experimental procedure of Example 4 was repeated, and waste Pd / Al2O3 was dissolved in a cyclic process using the separated P-TiO2 photocatalyst and the photocatalytic solvent enriched with activated carbon. During each cycle of Pd enrichment, sufficient activated carbon was added to achieve an enrichment rate of over 99%.

[0129] Comparative Example 1

[0130] The procedures of Example 1 were repeated, except that diammonium hydrogen phosphate was not added during the first step of preparing the P-TiO2 photocatalyst via hydrothermal method, resulting in undoped TiO2 powder that photocatalytically dissolves Pd. The specific experimental procedure was as follows: 50 mL of deionized water was added to a beaker, followed by the slow addition of 10 mL of tetrabutyl titanate. The mixture was stirred to form a milky white, homogeneous solution, which was then transferred to a 100 mL high-pressure hydrothermal reactor. The reactor was placed in an oven and reacted at 150°C for 10 hours. After the reaction was complete, the reactor was allowed to cool naturally to room temperature. The reaction product was removed and repeatedly washed with deionized water until the washings were nearly neutral. The washed precipitate was dried in a 60°C oven for 8 hours to obtain TiO2 powder. The dried TiO2 powder was then ground in a mortar and pestle and graded using a sieve to obtain nano-titanium dioxide powder with a mesh size of 200-300.

[0131] Comparative Example 2

[0132] The operation steps of Example 1 are repeated, except that in the second step, high isoelectric point activated carbon is not prepared, and Pd is directly enriched using unmodified activated carbon with an isoelectric point of 6.1.

[0133] Comparative Example 3

[0134] The procedures of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst via hydrothermal method, TiO2 powder was prepared first, and the specific experimental steps for preparing the TiO2 powder were the same as those in Comparative Example 1. Then, it was mixed with diammonium hydrogen phosphate to prepare P-TiO2 via hydrothermal method. The specific experimental steps were as follows: In another beaker, diammonium hydrogen phosphate was weighed according to a solid-liquid ratio of 1:0.8 (g / mL) (diammonium hydrogen phosphate and tetrabutyl titanate) and dissolved in 10 mL of deionized water. The solution was stirred until completely dissolved, achieving a target P content of 2 wt% in titanium dioxide. The diammonium hydrogen phosphate solution was slowly added dropwise to the TiO2 powder to form a mixed solution. During the addition, the stirring speed was maintained at 400 rpm to avoid excessively high local concentrations that could lead to particle agglomeration. The pH of the mixed solution was adjusted to 5 using concentrated ammonia to ensure suitable reaction conditions. After the addition was complete, the mixed solution was transferred to a 100 mL high-pressure hydrothermal reactor. The reactor was placed in an oven and reacted at 150 °C for 10 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The reaction product was removed and washed repeatedly with deionized water until the washing solution was neutral. The washed precipitate was dried in a 60°C oven for 8 hours to obtain 2wt% P-TiO2 powder. The dried 2wt% P-TiO2 powder was ground in a mortar and sieved to obtain nano-titanium dioxide powder with a mesh size of 200-300.

[0135] Comparative Example 4

[0136] Repeat the steps of Example 1, except that potassium dihydrogen phosphate is added when preparing P-TiO2 photocatalyst by hydrothermal method in the first step to obtain P-doped TiO2 powder to photocatalyze the dissolution of Pd.

[0137] Comparative Example 5

[0138] Repeat the steps of Example 1, except that in the first step of preparing the P-TiO2 photocatalyst, no hydrothermal reaction is carried out, and P-TiO2 is formed by stirring at room temperature.

[0139] Comparative Example 6

[0140] Repeat the steps of Example 1, except that when preparing the P-TiO2 photocatalyst by hydrothermal method in the first step, ammonia is not used to adjust the pH value.

[0141] Comparative Example 7

[0142] The Pd in ​​the waste Pd / Al2O3 catalyst was recovered by dissolving it with a traditional aqua regia. The volume ratio of concentrated HCl to concentrated HNO3 was 9:3 (ml), the solid-liquid ratio of the waste Pd / Al2O3 catalyst to aqua regia was 1:7 (g / mL), the reaction temperature was 90℃, and the reaction time was 5h.

[0143] Table 1

[0144]

[0145]

[0146]

[0147] Note: Amount of activated carbon used for enrichment: The amount of activated carbon used when the Pd enrichment rate is above 99%.

[0148] Table 2

[0149]

[0150] Table 3

[0151] Comparative Example Photocatalytic solubility / % 1 54.78 3 76.59 4 68.29 5 62.34 6 79.53 7 83.59

[0152] Table 4

[0153] Comparative Example Enriched activated carbon usage (g) 2 2.28

[0154] Note: Amount of activated carbon used for enrichment: The amount of activated carbon used when the Pd enrichment rate is above 99%.

Claims

1. A method for recovering waste Pd / Al2O3 catalyst using photocatalytic technology, characterized in that: The waste Pd / Al2O3 catalyst has a size of 2 mm or more, and the method includes the following steps: Step A: Obtain the P-TiO2 photocatalyst according to the following method; the method includes the following steps: Step 1: Mix tetrabutyl titanate with deionized water and stir to form a milky white homogeneous tetrabutyl titanate solution; prepare an aqueous solution of diammonium hydrogen phosphate. Step 2: Under stirring conditions, slowly add the diammonium hydrogen phosphate aqueous solution dropwise to the tetrabutyl titanate solution to form a mixed solution; during the dropwise addition, control the stirring speed to avoid excessively high local concentrations that could lead to particle agglomeration, and simultaneously control the pH value of the mixed solution between 5 and 7; the diammonium hydrogen phosphate aqueous solution and the tetrabutyl titanate solution are added to achieve a phosphorus content of 0.2-5%, where the phosphorus content = m P / m TiO2 ×100%, m P This refers to the mass of phosphorus (P) in the diammonium hydrogen phosphate aqueous solution, m TiO2 The mass of TiO2 is calculated based on the Ti element contained in the tetrabutyl titanate solution; Step 3: Transfer the mixed solution obtained in Step 2 to a high-pressure hydrothermal reactor, place it in an oven and react at 150℃~200℃ for 10~12 h. After the reaction is completed, allow the reactor to cool naturally to room temperature. Step 4: Take the reaction product obtained in step 3 out of the high-pressure hydrothermal reactor, wash it repeatedly with water until the washing liquid is neutral, and dry the washed precipitate thoroughly to obtain P-TiO2 powder. After the dried P-TiO2 powder is ground, it is classified by sieve and the powder with a mesh size of 200-300 is selected to obtain P-TiO2 photocatalyst. Step B: Take the waste Pd / Al2O3 catalyst, mix it with the P-TiO2 photocatalyst and photocatalytic solvent, and carry out the photocatalytic reaction under stirring and xenon lamp irradiation to dissolve Pd in ​​the waste Pd / Al2O3 catalyst. After the reaction is complete, first separate the Al2O3 support, and then centrifuge the remaining solution to obtain the Pd-containing solution and the P-TiO2 photocatalyst.

2. The method as described in claim 1, characterized in that: In step 2, the stirring speed is 400-600 rpm when adding diammonium hydrogen phosphate aqueous solution.

3. The method as described in claim 1, characterized in that: In step 2, the pH of the mixed solution is controlled between 5 and 7 by adding ammonia.

4. The method as described in claim 1, characterized in that: In step B, the feed ratio of P-TiO2 photocatalyst to waste Pd / Al2O3 catalyst is 1-4, calculated as the molar ratio of P in the P-TiO2 photocatalyst to Pd in ​​the waste Pd / Al2O3 catalyst; the ratio of the total mass of the waste Pd / Al2O3 catalyst and the P-TiO2 photocatalyst to the volume of the photocatalytic solvent is 1 g: (5-20) mL; the photocatalytic solvent is at least one of 5-20 wt% NaBr aqueous solution, 5-20 wt% NH4Br aqueous solution, and 5-20 wt% KBr aqueous solution; the photocatalytic reaction is carried out at a light power density of 0.01 2000mW · cm -2 The process is carried out under light irradiation, with xenon lamp irradiation time ranging from 1 to 3 hours.

5. The method as described in claim 4, characterized in that: In step B, the optical power density is 100–500 mW·cm⁻¹. -2 .

6. The method as described in claim 1, characterized in that: The P-TiO2 photocatalyst recovered in step B is reused in the photocatalytic reaction of step B.

7. The method as described in claim 1, characterized in that: The method further includes the following steps: Step C: Obtain activated carbon with a high isoelectric point between 8 and 10; Step D: Take an appropriate amount of the high isoelectric point activated carbon obtained in step C, add it to the Pd-containing solution obtained in step B to enrich the Pd ions therein, and after full enrichment, centrifuge to separate the Pd ions and obtain the separation solution and the palladium-enriched activated carbon; after drying the palladium-enriched activated carbon, calcine it in an air atmosphere to obtain Pd slag.

8. The method as described in claim 7, characterized in that: Step C is carried out as follows: Take activated carbon and add an appropriate amount of alkaline solution to completely immerse the activated carbon in the alkaline solution. The alkaline solution is a NaOH or KOH aqueous solution with a concentration of 0.1~1 mol / L. The solid-liquid ratio of the activated carbon to the alkaline solution is 1g:(10~25)mL. Stir the obtained slurry containing activated carbon at 40~80℃ for 0.5~2 h. Then, after separation, washing, and drying, high isoelectric point activated carbon with an isoelectric point between 8 and 10 is obtained.

9. The method as described in claim 7, characterized in that: In step D, the enrichment conditions are as follows: after adding high isoelectric point activated carbon to the Pd-containing solution obtained in step B and mixing it evenly, the mixture is stirred at 30-50 °C for 3-6 h to complete the enrichment of Pd ions.

10. The method as described in claim 7, characterized in that: The separation solution obtained in step D is reused as a photocatalytic solvent in the photocatalytic reaction of step B.

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