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

Abstract

The invention discloses a method for preparing a P-TiO2 photocatalyst and a method for recovering a waste Pd / Al2O3 catalyst. The P-TiO2 photocatalyst is prepared by a hydrothermal method. The invention provides a method for recycling a waste Pd / Al2O3 catalyst by using a photocatalysis technology. The method comprises the following steps: step A, obtaining a P-TiO2 photocatalyst; and B, mixing the waste Pd / Al2O3 catalyst with the P-TiO2 photocatalyst and a photocatalytic solvent, carrying out a photocatalytic reaction under the conditions of stirring and xenon lamp irradiation to dissolve Pd in the waste Pd / Al2O3 catalyst, after the reaction is sufficient, separating out an Al2O3 carrier, and then carrying out centrifugal separation on the residual solution to obtain a Pd-containing solution and the P-TiO2 photocatalyst. The recovery rate of Pd metal can be effectively increased, the whole process is environmentally friendly, and the cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of waste precious metal recovery, and in particular to a method for preparing a P-TiO2 photocatalyst and a method for recovering waste Pd / Al2O3 catalysts using photocatalytic technology. Background Art

[0002] Palladium (Pd) is a rare and expensive precious metal widely used in the field of catalysis, especially in the production of hydrogen peroxide. Pd / Al2O3 catalyst is a key material with high catalytic performance. However, the reserves of palladium are extremely limited, and the global mining volume is insufficient to meet the growing industrial demand. As the catalyst is discarded due to decreased activity or failure during use, the palladium resources contained in it need to be effectively recovered to achieve resource recycling.

[0003] Discarded Pd / Al2O3 catalysts still contain high-value palladium metal. If they are not recycled, it will not only cause a waste of resources, but also may pollute the environment due to the accumulation of waste. In addition, the price of palladium has continued to be high in recent years. Recycling palladium from waste catalysts can not only reduce the cost of raw materials for enterprises, but also alleviate external dependence on palladium resources, achieving a win-win situation in economic and environmental benefits. Therefore, the development of efficient and environmentally friendly recycling technology is of great significance for the resource recycling of waste Pd / Al2O3 catalysts. This is not only an important part of the sustainable development of precious metal resources, but also in line with the development goals of green chemical industry and circular economy.

[0004] At present, the main leaching methods for recovering palladium from spent catalysts containing palladium (Pd / Al2O3) are as follows: 1) Carrier leaching method: This method uses an acidic or alkaline leaching agent (such as HCl, H2SO4 or NaOH) to directly leach the Al2O3 carrier in the spent catalyst under certain temperature conditions, and then dissolves the Pd. 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.] The study showed that when 8.0 mol / L sulfuric acid was used, leaching was carried out at 100°C for 18 hours, and the slurry mass concentration was 220 g / L, the palladium leaching rate could 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 risk of long leaching time, high reagent consumption and palladium loss. It is usually necessary to perform pretreatment before leaching to reduce costs and improve the recovery rate of palladium. 2) Active component dissolution method: Li Qian et al. [Li Qian, Hu Long, Yang Yongbin, et al. Experimental study on the recovery of palladium from failed catalysts [J]. Hydrometallurgy, 2017, 36 (01): 41-45.] used a combination of oxidative roasting pretreatment, reduction and chlorination leaching to recover palladium from waste Pd / Al2O3 catalysts. The study showed that after roasting at 575°C for 2 hours, the palladium leaching rate could be increased to more than 98% using hydrazine hydrate (2.5 g / L) and sodium chlorate (3.0 g / L) and leaching under 5 mol / L HCl. This method is relatively simple, has a high palladium recovery rate, consumes less reagents, and has a low investment cost. However, if pretreatment is not performed, the leaching effect may not be ideal, the reagent consumption is large, and the palladium recovery is unstable. 3) Complete dissolution method: The palladium and Al2O3 carrier in the spent catalyst are completely dissolved by adding a leaching agent.The research of 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 the palladium leaching rate can reach 95% by adding spent Pd / Al2O3 catalyst to 6 mol / L HCl and 3 mol / L CuCl2 system and reacting at 80°C for 4 hours. Although the total dissolution method has a higher recovery rate than the other two methods, its leaching solution composition is more complex, which makes it difficult to recover palladium.

[0005] The existing recovery methods have the problems of environmental pollution and high reagent consumption. In addition, palladium will be lost during the carrier dissolution process, and the reaction time is long. The leachate obtained by the full dissolution method has a more complex composition, making subsequent enrichment of Pd more difficult. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems of low Pd metal recovery rate, large reagent consumption and environmental pollution in the existing waste catalyst Pd / Al2O3, and to provide a method for preparing P-TiO2 photocatalyst and a method for recycling waste Pd / Al2O3 using photocatalytic technology to improve the recovery rate of Pd metal. 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 a P-TiO2 photocatalyst by a hydrothermal method, comprising the following steps:

[0009] Step 1: Mix butyl titanate and deionized water, and stir to form a milky white uniform butyl titanate solution; prepare a diammonium hydrogen phosphate (NH4)2HPO4) aqueous solution;

[0010] Step 2: slowly drop the diammonium hydrogen phosphate aqueous solution into the butyl titanate solution under stirring to form a mixed solution; during the dropwise addition, the stirring speed is controlled to avoid excessive local concentration leading to particle agglomeration, and the pH value of the mixed solution is controlled between 5 and 7; the diammonium hydrogen phosphate aqueous solution and the butyl titanate solution are added in such a manner that the phosphorus content is 0.2-5%, wherein the phosphorus content = m P / m TiO2 ×100%,mP refers to the mass of P element contained in the diammonium hydrogen phosphate aqueous solution, m TiO2 It is the mass of TiO2 calculated based on the Ti element contained in the butyl titanate solution;

[0011] Step 3: Transfer the mixed solution obtained in step 2 to a high-pressure hydrothermal reactor, place it in an oven at 150°C to 200°C for 10 to 12 hours, and after the reaction is completed, allow the reactor to cool naturally to room temperature;

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

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

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

[0015] Furthermore, in step 4, the drying temperature is preferably 60° C. to 100° C., and the drying time is preferably 8 to 12 hours.

[0016] In a second aspect, the present invention provides a method for recycling waste Pd / Al2O3 catalyst using photocatalytic technology, wherein the size of the waste Pd / Al2O3 catalyst is above 2 mm, comprising the following steps:

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

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

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

[0020] Furthermore, in step B, the photocatalytic solvent is preferably at least one of a 5-20 wt% NaBr aqueous solution, a 5-20 wt% NH4Br aqueous solution, and a 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 1g: (5-20)mL.

[0022] Further, in step B, the photocatalytic reaction is carried out at a light power density of 0.01-2000 mW·cm -2 , preferably 100 to 500 mW·cm -2 The xenon lamp irradiation time is preferably 1 to 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 further comprises the following steps:

[0025] Step C: obtaining high isoelectric point activated carbon with an 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 sufficient enrichment, centrifuge to obtain a separation solution and palladium-enriched activated carbon; the palladium-enriched activated carbon is dried and then calcined in an air atmosphere to obtain Pd slag.

[0027] Furthermore, the step C is implemented as follows: take activated carbon, 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 to 1 mol / L, and the solid-liquid ratio of the activated carbon to the alkaline solution is 1 g: (10 to 25) mL; the obtained slurry containing activated carbon is stirred at 40 to 80° C. for 0.5 to 2 h, and then separated, washed, and dried to obtain a high isoelectric point activated carbon with an isoelectric point between 8 and 10.

[0028] Furthermore, in step D, the enrichment conditions are: after adding high isoelectric point activated carbon to the Pd-containing solution obtained in step B and mixing evenly, stirring 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°C-600°C, calcination in an air atmosphere in a muffle furnace for 1-2h, and a heating rate of 2-5°C / min.

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

[0031] The palladium slag obtained after calcination in step D of the present invention has a greatly reduced volume and mass, and is more convenient to handle. Since NaOH or KOH is used in the preparation process of high isoelectric point activated carbon, Na or K in the form of oxides and / or carbonates may remain in the palladium slag. When treating the palladium slag, Na or K can be removed first by utilizing the difference in acid solubility between Na, K and Pd, and then Pd can be further purified by the photocatalytic dissolution method of the present invention, or it can be purified by conventional methods such as aqua regia dissolution method.

[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 the present invention can efficiently dissolve Pd metal under a controllable light source, release palladium into the solution in the form of ions through oxidation, and dissolve more thoroughly compared to the P-TiO2 photocatalyst obtained by solid phase mixing modification reported in the prior art.

[0034] (2) The present invention uses high isoelectric point activated carbon to efficiently and selectively enrich palladium ions in the solution, is environmentally friendly, does not require strong acid reagents, reduces corrosion to equipment and environmental pollution, and reduces waste liquid treatment costs.

[0035] (3) In the present invention, the photocatalyst and the photocatalytic solvent can be recycled to perform photocatalytic dissolution of Pd multiple times, thereby reducing the processing cost. DETAILED DESCRIPTION

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

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

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

[0039] 1. Preparation of suspension:

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

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

[0042] 2. Select the titration solution:

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

[0044] 3. Measure 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] Slowly add the titration solution (acid or base) to the suspension, and measure the potential and pH value while adding. Record the potential and pH value every time you add a little 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. Draw the potential-pH curve:

[0050] Based on the experimental data, a curve of the relationship between potential and pH is drawn. Generally, the potential changes with the change of pH. Near the isoelectric point, the curve changes more dramatically. This is because the surface charge changes significantly at this time, resulting in a sharp fluctuation in potential.

[0051] 6. Determine the isoelectric point:

[0052] The isoelectric point usually appears where the potential changes most dramatically, usually showing as the turning point of the curve. This point is the isoelectric point pH (pHpzc) of activated carbon.

[0053] Example 1

[0054] Step 1: Preparation of P-TiO2 photocatalyst by hydrothermal method: In a beaker, add 50mL of deionized water, and slowly add 10mL of butyl titanate, stirring to form a milky white uniform solution; in another beaker, weigh diammonium hydrogen phosphate according to the solid-liquid ratio of 0.8 (g / mL) (diammonium hydrogen phosphate and butyl titanate) and dissolve it in 10mL of deionized water, stirring until completely dissolved, and slowly drop the diammonium hydrogen phosphate solution into the butyl titanate solution to form a mixed solution to achieve the target P content in titanium dioxide of 2wt%. During the dropwise addition, the stirring speed was maintained at 400rpm to avoid excessive local concentration leading to particle agglomeration; concentrated ammonia water was used to adjust the pH value of the mixed solution to 5 to ensure that the reaction conditions were suitable. After the dropwise addition was completed, the mixed solution was transferred to a 100mL high-pressure hydrothermal reactor. Place it in an oven and react at 150°C for 10h. After the reaction is completed, wait for the reactor to cool naturally to room temperature. Take out the reaction product and wash it repeatedly with deionized water until the washing liquid is neutral. The washed precipitate was placed in an oven at 60°C and dried for 8 hours to obtain 2 wt% P-TiO2 powder. The dried 2 wt% P-TiO2 powder was ground using a mortar and graded using a sieve to select 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, add an appropriate amount of 0.1mol / LNaOH solution, the solid-liquid ratio (g / mL) of activated carbon to NaOH solution is 1:10, and the activated carbon is completely immersed in the alkaline solution. Stir the activated carbon slurry on a magnetic stirrer and reflux at 40°C for 0.5h. After reflux heating, the obtained activated carbon is washed and then placed in a drying oven at 60°C for 12 hours to obtain high isoelectric point activated carbon, and the isoelectric point (pHpzc) is measured to be 8.

[0056] Step 3: The catalyst is used for photocatalytic dissolution of Pd and activated carbon enrichment of Pd:

[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 2wt% P-TiO2 photocatalyst to Pd in ​​0.3wt% waste Pd / Al2O3 catalyst is 1, the photocatalytic solvent is 5wt% NaBr aqueous solution, and the solid-liquid ratio (g / mL) of 2wt% P-TiO2 photocatalyst and 0.3wt% waste Pd / Al2O3 catalyst to photocatalytic solvent is 1:5. Put the above three substances into a round-bottom flask, connect a condenser and place it on a magnetic stirrer for stirring, use a light power density of 100mW·cm -2The xenon lamp was irradiated for 1 hour to dissolve the precious metal Pd. After the reaction was completed, the spherical Al2O3 carrier was separated first, and then centrifuged to separate the Pd solution and 2wt% P-TiO2 photocatalyst (powder). A portion of the obtained Pd solution was taken by ICP to measure the photocatalytic dissolution rate of Pd.

[0058] Weigh an appropriate amount of the prepared high isoelectric point activated carbon, add it to the above Pd solution, and perform ultrasonic treatment for 5 minutes to mix the solution and activated carbon evenly; then put the activated carbon slurry into a round-bottom flask, connect a condenser and place it on a magnetic stirrer for stirring, and heat it in a water bath at 30°C for 3 hours. After heating in a water bath, the obtained activated carbon slurry is centrifuged to obtain a separation solution and a carbon-Pd solid mixture. After drying, the carbon-Pd solid mixture is placed in an air atmosphere for calcination at 600°C for 3 hours to obtain Pd slag; a portion of the obtained separation solution is taken and the activated carbon enrichment rate of Pd is measured by ICP.

[0059] Example 2

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

[0061] Example 3

[0062] The operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the solid-to-liquid ratio (g / mL) of diammonium hydrogen phosphate to butyl titanate was selected to be 1.21 to achieve a target phosphorus content of 3 wt% 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 operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the solid-to-liquid ratio (g / mL) of diammonium hydrogen phosphate to butyl titanate was selected to be 1.61 to achieve a target phosphorus content of 4 wt% in titanium dioxide; in the second step of preparing high isoelectric point activated carbon, the concentration of the alkaline solution was selected to be 0.3 mol / L and the isoelectric point was 8.3.

[0065] Example 5

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

[0067] Example 6

[0068] The operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the stirring speed was 500 rpm when diammonium hydrogen phosphate was added; in the second step of preparing high isoelectric point activated carbon, 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 operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the stirring speed was 600 rpm when diammonium hydrogen phosphate was added; in the second step of preparing high isoelectric point activated carbon, 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 operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the pH was adjusted to 6; 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 operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the pH was adjusted to 7; 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 to be 1:15, and the isoelectric point was 8.9.

[0075] Example 10

[0076] The operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the hydrothermal reaction temperature was 160°C; 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 to be 1:20, and the isoelectric point was 9.5.

[0077] Embodiment 11

[0078] The operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the hydrothermal reaction temperature was 170°C; 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 to be 1:25, and the isoelectric point was 10.

[0079] Example 12

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

[0081] Embodiment 13

[0082] The operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, the hydrothermal reaction temperature was 190°C; in the second step of preparing high isoelectric point activated carbon, the water bath heating temperature was 60°C and the isoelectric point was 8.5.

[0083] Embodiment 14

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

[0085] Embodiment 15

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

[0087] Example 16

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

[0089] Embodiment 17

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

[0091] Embodiment 18

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

[0093] Embodiment 19

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

[0095] Embodiment 20

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

[0097] Embodiment 21

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

[0099] Embodiment 22

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

[0101] Embodiment 23

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

[0103] Embodiment 24

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

[0105] Embodiment 25

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

[0107] Embodiment 26

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

[0109] Embodiment 27

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

[0111] Embodiment 28

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

[0113] Embodiment 29

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

[0115] Embodiment 30

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

[0117] Embodiment 31

[0118] The operating steps of Example 1 are repeated, except that in the third step, when the catalyst is used for photocatalytic dissolution of Pd and activated carbon enrichment of Pd, the xenon lamp irradiation time is preferably 2 h and the water bath heating time is 5 h.

[0119] Embodiment 32

[0120] The operating steps of Example 1 are repeated, except that in the third step, when the catalyst is used for photocatalytic dissolution of Pd and activated carbon enrichment of Pd, the xenon lamp irradiation time is preferably 3 h and the water bath heating time is 6 h.

[0121] Embodiment 33

[0122] The operating steps of Example 1 were repeated, except that in the third step, when the catalyst was used for photocatalytic dissolution of Pd, the solid-to-liquid ratio (g / mL) of the P-TiO2 photocatalyst, the waste Pd / Al2O3 catalyst and the photocatalytic solvent was 1:10.

[0123] Embodiment 34

[0124] The operating steps of Example 1 were repeated, except that in the third step, when the catalyst was used for photocatalytic dissolution of Pd, the solid-to-liquid ratio (g / mL) of the P-TiO2 photocatalyst, the waste Pd / Al2O3 catalyst and the photocatalytic solvent was 1:15.

[0125] Embodiment 35

[0126] The operating steps of Example 1 were repeated, except that in the third step, when the catalyst was used for photocatalytic dissolution of Pd, the solid-to-liquid ratio (g / mL) of the P-TiO2 photocatalyst, the waste Pd / Al2O3 catalyst and the photocatalytic solvent was 1:20.

[0127] Embodiment 36

[0128] Repeat the experimental process of Example 4, and perform a cyclic dissolution experiment of waste Pd / Al2O3 with the separated P-TiO2 photocatalyst and the photocatalytic solvent after Pd enrichment by activated carbon. In each cyclic experiment, enough activated carbon is added to enrich Pd so that the enrichment rate reaches more than 99%.

[0129] Comparative Example 1

[0130] The operating steps of Example 1 were repeated, except that diammonium hydrogen phosphate was not added in the first step of the hydrothermal method to prepare the P-TiO2 photocatalyst, and the undoped P TiO2 powder was obtained to photocatalytically dissolve Pd. The specific experimental process is: in a beaker, add an appropriate amount of 50mL deionized water, and slowly add 10mL of butyl titanate, stir to form a milky uniform solution, and transfer the solution to a 100mL high-pressure hydrothermal reactor. Put it in an oven and react at 150°C for 10h. After the reaction is completed, wait for the reactor to cool naturally to room temperature. Take out the reaction product and wash it repeatedly with deionized water until the washing liquid is close to neutral. The washed precipitate is placed in a 60°C oven and dried for 8h to obtain TiO2 powder. The dried TiO2 powder is ground with a mortar and graded through a sieve to screen out nano titanium dioxide powder with a mesh size of 200-300.

[0131] Comparative Example 2

[0132] The operating steps of Example 1 were repeated, except that in the second step, high isoelectric point activated carbon was not prepared, and unmodified activated carbon was directly used to enrich Pd, and the isoelectric point of the activated carbon was 6.1.

[0133] Comparative Example 3

[0134] The operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst by hydrothermal method, TiO2 powder was first prepared, and the specific experimental steps for preparing the TiO2 powder were the same as those of Comparative Example 1; then it was mixed with diammonium hydrogen phosphate to prepare P-TiO2 by hydrothermal method, and the specific experimental steps were as follows: in another beaker, diammonium hydrogen phosphate was weighed and dissolved in 10mL of deionized water according to the solid-liquid ratio of 1:0.8 (g / mL) (diammonium hydrogen phosphate and butyl titanate), and stirred until completely dissolved to reach the target P content of 2wt% 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 400rpm to avoid excessive local concentration leading to particle agglomeration; concentrated ammonia water was used to adjust the pH value of the mixed solution to 5 to ensure that the reaction conditions were suitable. After the addition was completed, the mixed solution was transferred to a 100mL high-pressure hydrothermal reactor. It was placed in an oven and reacted at 150°C for 10h. After the reaction was completed, the reactor was cooled naturally to room temperature. The reaction product was taken out and repeatedly washed with deionized water until the washing liquid was neutral. The washed precipitate was placed in a 60°C oven and dried for 8 hours to obtain 2wt% P-TiO2 powder. The dried 2wt% P-TiO2 powder was ground using a mortar and graded through a sieve to screen out nano titanium dioxide powder with a mesh size of 200-300.

[0135] Comparative Example 4

[0136] The operating steps of Example 1 were repeated, except that potassium dihydrogen phosphate was added during the first step of preparing the P-TiO2 photocatalyst by the hydrothermal method to obtain P-doped TiO2 powder that photocatalytically dissolves Pd.

[0137] Comparative Example 5

[0138] The operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst, no hydrothermal reaction was performed, and P-TiO2 was formed by only stirring at room temperature.

[0139] Comparative Example 6

[0140] The operating steps of Example 1 were repeated, except that in the first step of preparing the P-TiO2 photocatalyst by the hydrothermal method, no ammonia water was used to adjust the pH value.

[0141] Comparative Example 7

[0142] The traditional aqua regia dissolution method was used to dissolve and recover Pd from the waste Pd / Al2O3 catalyst. The volume ratio (ml) of concentrated HCl:concentrated HNO3 was 9:3, the solid-liquid ratio of the waste Pd / Al2O3 catalyst to aqua regia was 1:7 (g / mL), the reaction temperature was 90°C, and the reaction time was 5h.

[0143] Table 1

[0144]

[0145]

[0146]

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

[0148] Table 2

[0149]

[0150] Table 3

[0151] Comparative Example Photocatalytic dissolution rate / % 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: Amount of activated carbon used when the Pd enrichment rate is above 99%.

Claims

1. A method for preparing P-TiO2 photocatalyst by hydrothermal method, characterized in that: The method comprises the following steps: Step 1: mixing butyl titanate with deionized water, stirring to form a milky white uniform butyl titanate solution; preparing a diammonium hydrogen phosphate aqueous solution; Step 2: slowly drop the diammonium hydrogen phosphate aqueous solution into the butyl titanate solution under stirring to form a mixed solution; during the dropwise addition, the stirring speed is controlled to avoid excessive local concentration leading to particle agglomeration, and the pH value of the mixed solution is controlled between 5 and 7; the diammonium hydrogen phosphate aqueous solution and the butyl titanate solution are added in such a manner that the phosphorus content is 0.2-5%, wherein the phosphorus content = m P / m TiO2 ×100%,m P refers to the mass of P element contained in the diammonium hydrogen phosphate aqueous solution, m TiO2 It is the mass of TiO2 calculated based on the Ti element contained in the butyl titanate solution; Step 3: Transfer the mixed solution obtained in step 2 to a high-pressure hydrothermal reactor, place it in an oven at 150°C to 200°C for 10 to 12 hours, and after the reaction is completed, allow the reactor to cool naturally to room temperature; Step 4: Take out the reaction product obtained in step 3 from the high-pressure hydrothermal reactor, wash it repeatedly with water until the washing liquid is neutral, and fully dry the washed precipitate to obtain P-TiO2 powder. After grinding the dried P-TiO2 powder, grade it through a sieve to screen out the powder with a mesh size of 200-300 to obtain the P-TiO2 photocatalyst.

2. The method according to claim 1, characterized in that: In step 2, the stirring speed is 400-600 rpm when the diammonium hydrogen phosphate aqueous solution is added dropwise.

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

4. A method for recovering waste Pd / Al2O3 catalyst using photocatalytic technology, characterized in that: The size of the waste Pd / Al2O3 catalyst is above 2 mm, and the method comprises the following steps: Step A: obtaining a P-TiO2 photocatalyst according to the method of any one of claims 1 to 3; Step B: Take the waste Pd / Al2O3 catalyst and mix it with the P-TiO2 photocatalyst and the photocatalytic solvent, and carry out a photocatalytic reaction under stirring and xenon lamp irradiation conditions to dissolve the Pd in ​​the waste Pd / Al2O3 catalyst. After sufficient reaction, first separate the Al2O3 carrier, and then centrifuge the remaining solution to obtain a Pd-containing solution and a P-TiO2 photocatalyst.

5. The method according to claim 4, characterized in that: In step B, the feed ratio of P-TiO2 photocatalyst to waste Pd / Al2O3 catalyst is 1-4 based on the molar ratio of P contained in P-TiO2 photocatalyst to Pd contained in waste Pd / Al2O3 catalyst; the total mass of the waste Pd / Al2O3 catalyst and P-TiO2 photocatalyst to the volume of the photocatalytic solvent is 1g:(5-20)mL; the photocatalytic solvent is at least one of 5-20wt% NaBr aqueous solution, 5-20wt% NH4Br aqueous solution, and 5-20wt% KBr aqueous solution; the photocatalytic reaction is carried out at a light power density of 0.01-2000mW·cm -2 , preferably 100 to 500 mW·cm -2 The xenon lamp irradiation time is 1 to 3 hours.

6. The method according to claim 4, characterized in that: The P-TiO2 photocatalyst recovered in step B is reused in the photocatalytic reaction of step B.

7. The method according to claim 4, characterized in that: The method further comprises the following steps: Step C: obtaining high isoelectric point activated carbon with an 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 sufficient enrichment, centrifuge to obtain a separation solution and palladium-enriched activated carbon; the palladium-enriched activated carbon is dried and then calcined in an air atmosphere to obtain Pd slag.

8. The method according to claim 7, characterized in that: The step C is implemented as follows: taking activated carbon, adding 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 to 1 mol / L, and the solid-liquid ratio of the activated carbon to the alkaline solution is 1 g: (10 to 25) mL; stirring the obtained slurry containing activated carbon at 40 to 80° C. for 0.5 to 2 h, and then separating, washing, and drying to obtain a high isoelectric point activated carbon with an isoelectric point between 8 and 10.

9. The method according to claim 4, 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 evenly, stirring at 30-50° C. for 3-6 hours to complete the enrichment of Pd ions.

10. The method according to claim 4, characterized in that: The separated solution obtained in step D is repeatedly used as a photocatalytic solvent for the photocatalytic reaction in step B.

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