A method for extracting precious metals from cellulose-supported precious metal catalysts

Abstract

The present invention discloses a method for extracting precious metals from a cellulose-supported precious metal catalyst. The method mainly comprises the following steps: firstly hydrolyzing the failed cellulose-supported precious metal catalyst in a reactor, then calcining the hydrolyzed cellulose-supported precious metal catalyst in sections, then leaching in a solution containing sodium hypochlorite, sulfuric acid, FeCl3, and a nitrogen-containing organic reagent, and finally reducing the precious metal using a reducing agent. The present invention uses a method of hydrolyzing first and then calcining, which overcomes the problem of incomplete calcination of cellulose. The cellulose is hydrolyzed into small molecular compounds, and the calcination rate is greatly improved, so that subsequent leaching can be complete and the precious metal recovery rate is high; the present invention adopts the method of hydrolyzing first and then calcining to reduce the influence of the small molecular compounds after hydrolysis on the leaching process; the method for extracting precious metals from cellulose-supported precious metal catalysts of the present invention has a high extraction rate, which can reach more than 99.5%, greatly improving the recovery efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of noble metal regeneration, and in particular to a method for extracting noble metals from a cellulose-supported noble metal catalyst. Background Art

[0002] Catalysts play an irreplaceable and important role in the development of the chemical industry. However, as the catalyst is used for a longer time, the activity of the catalyst will decrease due to the growth of the active component grains or even sintering due to overheating, or it will partially or completely lose its activity due to poisoning by certain poisons. It will also reduce its activity due to the accumulation of pollutants on the active surface of the catalyst or the clogging of the catalyst pores, and eventually the catalyst has to be replaced. In the preparation process of the catalyst, in order to ensure its activity, selectivity, toxicity resistance, certain strength and life performance indicators, some precious metals are often selected as its main components. Although the morphology, structure and quantity of some components of the catalyst will change during use, the waste catalyst will still contain a considerable amount of non-ferrous metals or precious metals, and sometimes their content will be much higher than the content of the corresponding components in the lean ore. The global annual production of waste industrial catalysts is about 500,000 to 700,000 tons. Recycling them as secondary resources can obtain extremely high-grade precious metals. Recovering precious metals from waste industrial catalysts can not only achieve significant economic benefits, but also improve resource utilization and reduce environmental problems caused by catalysts.

[0003] Precious metals in waste catalysts are mainly from the platinum group. Catalysts containing precious metals are widely used in many industries to eliminate pollution, including chemicals, petrochemicals, plastics, paints, spraying and pharmaceuticals. Many companies use catalytic reaction technology to avoid the production of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). The catalysts used in these reactors contain single or combined precious metals, including platinum, palladium, rhodium, ruthenium, gold and silver. Depending on the different equipment and processes used, these precious metals are equipped with different carriers, such as flakes, particles and monolithic structures (substrates). After these catalysts lose their effectiveness, the precious metals in them must be recovered. According to data, about 800,000 tons of waste catalysts are discharged worldwide each year, and the replacement volume of China's petroleum and chemical catalysts exceeds 100,000 tons.

[0004] Common carriers for catalysts include inorganic carriers, synthetic organic polymer carriers and natural polymer carriers. Inorganic carriers, such as activated carbon, silica, and alumina, have the general advantages of traditional carriers, that is, they are easy to separate from the product and can be recycled and reused, but their preparation process often requires high-temperature calcination. Synthetic organic polymer carriers are usually some synthetic polymers, such as cross-linked polystyrene and polystyrene-polyethylene glycol, whose monomers are organic matter and are non-renewable energy. Typical natural polymer carriers include cellulose and chitosan. In recent years, with people's increasing attention to resource recycling and reuse, natural polymers, especially cellulose, have received great attention from researchers due to their abundant sources, non-toxicity, biodegradability and renewable properties. The large number of hydroxyl groups contained in the cellulose structure allows cellulose to participate in many reactions and has the excellent property of being derivatizable. Cellulose loading with metal catalysts is generally achieved in two ways: one is the direct complexation of metals or metal ions with the hydroxyl groups in the cellulose main chain structure; the other is to graft certain organic small molecule ligands containing lone pairs of electrons onto cellulose by chemical bonding, that is, functionalized cellulose, and then use it as a ligand to coordinate with metals or metal ions.

[0005] However, most of the spent catalysts are contaminated by organic substances in the reaction mixture. These organic substances are often toxic, so when recovering the precious metal components of the spent catalyst, the organic substances must first be removed from the carrier together with the carbon. In the previous recovery process, in order to remove the organic substances contained therein, the spent catalyst was burned, and then the residue was sampled and tested, and the precious metal oxides after the precious metal content was determined were chemically treated.

[0006] However, there is little research on the extraction of precious metals from cellulose-supported precious metal catalysts. After experiments, it was found that the traditional calcination method for extracting precious metals has a low extraction rate, high cost and long cycle. Therefore, it is necessary to develop an extraction process with high extraction rate, low cost and short cycle. Summary of the invention

[0007] Based on the above problems, the present invention provides a method for extracting precious metals from cellulose-supported precious metal catalysts. The method first decomposes cellulose, then calcines it, and then reduces it to obtain a precious metal catalyst. Through this method, the method greatly improves the recovery rate, the overall cycle is shorter, and the cost is saved. The details are as follows:

[0008] A method for extracting precious metals from a cellulose-supported precious metal catalyst comprises the following steps:

[0009] (1) Hydrolysis

[0010] The spent cellulose-supported noble metal catalyst is placed in an acidic FeCl3 aqueous solution in a reactor, rapidly heated to 300-350°C, and then naturally cooled to room temperature;

[0011] (2) Calcination

[0012] The solution after hydrolysis in step (1) is evaporated to dryness, calcined in a muffle furnace at 450-550° C. for 1-4 hours, and then the temperature is increased to 700-800° C. and calcined for another 2-4 hours to obtain a powder containing precious metals;

[0013] (3) Extraction

[0014] The precious metal-containing powder calcined in step (2) is added to a solution containing sodium hypochlorite, sulfuric acid, FeCl3, and a nitrogen-containing organic reagent for leaching;

[0015] (4) Restore

[0016] The pH value is adjusted to acidic, the precipitate is removed, and then adjusted to alkaline, the precipitate is removed, and then a reducing agent is used to reduce the precious metal.

[0017] Among them, step (1) is preferably:

[0018] The acid in the acidic FeCl3 aqueous solution is hydrochloric acid or sulfuric acid;

[0019] The pH value of acidic FeCl3 aqueous solution is 1-4;

[0020] The solid-liquid volume ratio is 1g:(1-10)ml;

[0021] The heating rate is 5-10℃ / s;

[0022] Keep at 300-350℃ for more than 10 minutes.

[0023] Step (2) preferably:

[0024] Calcine in a muffle furnace at 450-500°C for 2-3 hours, then raise the temperature to 750-800°C and calcine for another 2-3 hours;

[0025] Step (3) preferably:

[0026] The molar concentration of sodium hypochlorite is 0.1-10 mol / L, the molar concentration of sulfuric acid is 0.1-10 mol / L, the molar concentration of FeCl3 is 0.5-20 mol / L, and the molar concentration of nitrogen-containing organic reagent is 0.5-20 mol / L;

[0027] The nitrogen-containing organic reagent is pyridine, piperidine, imidazole or N,N-dimethylformamide;

[0028] Step (4) is preferably:

[0029] Adjust the pH value to 4-6 to acidic, remove the precipitate, then adjust it to 8-10 alkaline, remove the precipitate;

[0030] The reducing agent is hydrazine hydrate, formic acid or formate.

[0031] Beneficial effects of the present invention

[0032] (1) Direct calcination of cellulose loaded with precious metal catalysts will result in incomplete calcination of cellulose, which will lead to low precious metal leaching in the subsequent leaching. The present invention uses a method of hydrolyzing first and then calcining to overcome the problem of incomplete calcination of cellulose. The cellulose is hydrolyzed into small molecular compounds, and the calcination rate is greatly improved, so that the subsequent leaching can be complete and the precious metal recovery rate is high;

[0033] (2) After the cellulose-supported noble metal catalyst is hydrolyzed, if it is directly leached, the leaching rate of the noble metal is low. After a large number of experiments and research and analysis, the present invention finds that this is because the small molecular compounds after the cellulose hydrolysis react with the noble metals, so that the noble metals cannot be completely leached out. Therefore, the present invention adopts the method of hydrolysis first and then calcination to reduce the influence of the small molecular compounds after the hydrolysis on the leaching process;

[0034] (3) The present invention uses a combined leaching agent, which includes sodium hypochlorite and sulfuric acid for leaching precious metals, a capture agent FeCl3, and a complexing agent nitrogen-containing organic reagent, so that the leached precious metal ions can be more stable in the solution, greatly improving the recovery rate of precious metals;

[0035] (4) The method for extracting precious metals from cellulose-loaded precious metal catalysts of the present invention has a high extraction rate, which can reach more than 99.5%, and a short extraction cycle. The entire process can be completed within 8 hours, greatly improving the recovery efficiency. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below in conjunction with embodiments, but they are not intended to limit the present invention.

[0037] Embodiment 1:

[0038] A method for extracting precious metals from a cellulose-supported precious metal catalyst comprises the following steps:

[0039] (1) Hydrolysis

[0040] 1 kg of the spent cellulose-supported noble metal catalyst was placed in a reactor in 1000 ml of a hydrochloric acid FeCl3 aqueous solution with a pH of 1, and rapidly heated to 300°C at a heating rate of 5°C / s for 20 minutes, and then naturally cooled to room temperature;

[0041] (2) Calcination

[0042] The solution after hydrolysis in step (1) is evaporated to dryness, calcined in a muffle furnace at 500° C. for 2 hours, and then the temperature is increased to 750° C. and calcined for another 3 hours to obtain a powder containing precious metals;

[0043] (3) Extraction

[0044] The precious metal-containing powder calcined in step (2) is added to a solution containing sodium hypochlorite, sulfuric acid, FeCl3, and N,N-dimethylformamide for leaching; wherein the molar concentration of sodium hypochlorite is 5 mol / L, the molar concentration of sulfuric acid is 1 mol / L, the molar concentration of FeCl3 is 10 mol / L, and the molar concentration of N,N-dimethylformamide is 1 mol / L.

[0045] (4) Restore

[0046] The pH value is adjusted to 4, the precipitate is removed, the pH value is adjusted to 9, the precipitate is removed, and then the reducing agent hydrazine hydrate is used for reduction to obtain the precious metal.

[0047] After testing, the recovery rate of precious metals was 99.7%.

[0048] Embodiment 2:

[0049] A method for extracting precious metals from a cellulose-supported precious metal catalyst comprises the following steps:

[0050] (1) Hydrolysis

[0051] 1 kg of the spent cellulose-supported noble metal catalyst was placed in a reactor in 2000 ml of a hydrochloric acid FeCl3 aqueous solution with a pH of 2, and rapidly heated to 350°C at a heating rate of 10°C / s for 30 minutes, and then naturally cooled to room temperature;

[0052] (2) Calcination

[0053] The solution after hydrolysis in step (1) is evaporated to dryness, calcined in a muffle furnace at 450° C. for 2 hours, and then the temperature is increased to 800° C. and calcined for another 3 hours to obtain a powder containing precious metals;

[0054] (3) Extraction

[0055] The precious metal-containing powder calcined in step (2) is added to a solution containing sodium hypochlorite, sulfuric acid, FeCl3, and N,N-dimethylformamide for leaching; wherein the molar concentration of sodium hypochlorite is 10 mol / L, the molar concentration of sulfuric acid is 5 mol / L, the molar concentration of FeCl3 is 10 mol / L, and the molar concentration of N,N-dimethylformamide is 2 mol / L.

[0056] (4) Restore

[0057] The pH value is adjusted to 5, the precipitate is removed, the pH value is adjusted to 8, the precipitate is removed, and then the reducing agent formic acid is used for reduction to obtain the precious metal.

[0058] After testing, the recovery rate of precious metals was 99.8%.

[0059] Embodiment 3:

[0060] A method for extracting precious metals from a cellulose-supported precious metal catalyst comprises the following steps:

[0061] (1) Hydrolysis

[0062] 1 kg of the spent cellulose-supported noble metal catalyst was placed in 3000 ml of a hydrochloric acid FeCl3 aqueous solution with a pH of 3 in a reactor, and rapidly heated to 330°C at a heating rate of 10°C / s for 20 minutes, and then naturally cooled to room temperature;

[0063] (2) Calcination

[0064] The solution after hydrolysis in step (1) is evaporated to dryness, calcined in a muffle furnace at 480° C. for 3 hours, and then the temperature is increased to 800° C. and calcined for another 2 hours to obtain a powder containing precious metals;

[0065] (3) Extraction

[0066] The precious metal-containing powder calcined in step (2) is added to a solution containing sodium hypochlorite, sulfuric acid, FeCl3, and N,N-dimethylformamide for leaching; wherein the molar concentration of sodium hypochlorite is 8 mol / L, the molar concentration of sulfuric acid is 3 mol / L, the molar concentration of FeCl3 is 15 mol / L, and the molar concentration of N,N-dimethylformamide is 4 mol / L.

[0067] (4) Restore

[0068] The pH value is adjusted to 3, the precipitate is removed, the pH value is adjusted to 9, the precipitate is removed, and then the reducing agent sodium formate is used for reduction to obtain the precious metal.

[0069] After testing, the recovery rate of precious metals was 99.5%.

[0070] Embodiment 4:

[0071] A method for extracting precious metals from a cellulose-supported precious metal catalyst comprises the following steps:

[0072] (1) Hydrolysis

[0073] 1 kg of the spent cellulose-supported noble metal catalyst was placed in 3000 ml of a hydrochloric acid FeCl3 aqueous solution with a pH of 2 in a reactor, and rapidly heated to 350°C at a heating rate of 10°C / s, maintained for 10 min, and then naturally cooled to room temperature;

[0074] (2) Calcination

[0075] The solution after hydrolysis in step (1) is evaporated to dryness, calcined in a muffle furnace at 500° C. for 3 hours, and then the temperature is increased to 800° C. and calcined for another 3 hours to obtain a powder containing precious metals;

[0076] (3) Extraction

[0077] The precious metal-containing powder calcined in step (2) is added to a solution containing sodium hypochlorite, sulfuric acid, FeCl3, and N,N-dimethylformamide for leaching; wherein the molar concentration of sodium hypochlorite is 10 mol / L, the molar concentration of sulfuric acid is 5 mol / L, the molar concentration of FeCl3 is 10 mol / L, and the molar concentration of N,N-dimethylformamide is 2 mol / L.

[0078] (4) Restore

[0079] The pH value is adjusted to 4, the precipitate is removed, the pH value is adjusted to 9, the precipitate is removed, and then the reducing agent sodium formate is used for reduction to obtain the precious metal.

[0080] After testing, the recovery rate of precious metals was 99.8%.

[0081] Comparative Example 1:

[0082] A method for extracting precious metals from a cellulose-supported precious metal catalyst comprises the following steps:

[0083] (1) Calcination

[0084] 1 kg of the spent cellulose-supported noble metal catalyst was calcined in a muffle furnace at 500° C. for 2 hours, then the temperature was raised to 750° C. and calcined for another 3 hours to obtain a powder containing the noble metal;

[0085] (2) Extraction

[0086] The precious metal-containing powder calcined in step (1) is added to a solution containing sodium hypochlorite, sulfuric acid, FeCl3, and N,N-dimethylformamide for leaching; wherein the molar concentration of sodium hypochlorite is 5 mol / L, the molar concentration of sulfuric acid is 1 mol / L, the molar concentration of FeCl3 is 10 mol / L, and the molar concentration of N,N-dimethylformamide is 1 mol / L.

[0087] (3) Restore

[0088] The pH value is adjusted to 4, the precipitate is removed, the pH value is adjusted to 9, the precipitate is removed, and then the reducing agent hydrazine hydrate is used for reduction to obtain the precious metal.

[0089] After testing, the recovery rate of precious metals was 69.2%.

[0090] Comparative Example 2:

[0091] A method for extracting precious metals from a cellulose-supported precious metal catalyst comprises the following steps:

[0092] (1) Hydrolysis

[0093] 1 kg of the spent cellulose-supported noble metal catalyst was placed in 1000 ml of a hydrochloric acid FeCl3 aqueous solution with a pH of 2 in a reactor, and rapidly heated to 350°C at a heating rate of 10°C / s for 30 minutes, and then naturally cooled to room temperature;

[0094] (2) Extraction

[0095] The powder of step (1) is added to a solution containing sodium hypochlorite, sulfuric acid, FeCl3, and N,N-dimethylformamide for leaching; wherein the molar concentration of sodium hypochlorite is 10 mol / L, the molar concentration of sulfuric acid is 5 mol / L, the molar concentration of FeCl3 is 10 mol / L, and the molar concentration of N,N-dimethylformamide is 2 mol / L.

[0096] (3) Restore

[0097] The pH value is adjusted to 5, the precipitate is removed, the pH value is adjusted to 8, the precipitate is removed, and then the reducing agent formic acid is used for reduction to obtain the precious metal.

[0098] After testing, the recovery rate of precious metals was 82.6%.

[0099] It can be seen that after the four steps of hydrolysis, calcination, leaching and reduction of the present invention, the recovery rate of the noble metal in the cellulose-supported noble metal catalyst is greatly improved.

Claims

1. A method for extracting precious metals from a cellulose-supported precious metal catalyst, characterized in that: The method comprises the following steps: (1) Hydrolysis The spent cellulose-supported noble metal catalyst was placed in an acidic FeCl3 aqueous solution in a reactor, rapidly heated to 300-350°C, and then naturally cooled to room temperature; (2) Calcination The solution after hydrolysis in step (1) is evaporated to dryness, calcined in a muffle furnace at 450-550° C. for 1-4 hours, and then the temperature is increased to 700-800° C. and calcined for another 2-4 hours to obtain a powder containing precious metals; (3) Extraction adding the precious metal-containing powder calcined in step (2) into a solution containing sodium hypochlorite, sulfuric acid, FeCl3 and N,N-dimethylformamide for leaching; (4) Restore The pH value is adjusted to acidic, the precipitate is removed, and then adjusted to alkaline, the precipitate is removed, and then a reducing agent is used to reduce the precious metal.

2. The method for extracting precious metals from a cellulose-supported precious metal catalyst according to claim 1, characterized in that The acid in the acidic FeCl3 aqueous solution in step (1) is hydrochloric acid or sulfuric acid.

3. The method for extracting precious metals from cellulose-supported precious metal catalysts according to claim 1, characterized in that In step (1), the pH value of the acidic FeCl3 aqueous solution is 1-4; the solid-liquid volume ratio is 1g: (1-10) ml.

4. The method for extracting precious metals from cellulose-supported precious metal catalysts according to claim 1, characterized in that In step (1), the heating rate is 5-10°C / s; the temperature is maintained at 300-350°C for more than 10 minutes.

5. The method for extracting precious metals from cellulose-supported precious metal catalysts according to claim 1, characterized in that In step (2), the calcination is carried out at 450-500° C. in a muffle furnace for 2-3 hours, and then the temperature is increased to 750-800° C. and calcined for another 2-3 hours.

6. The method for extracting precious metals from a cellulose-supported precious metal catalyst according to claim 1, characterized in that In step (3), the molar concentration of sodium hypochlorite is 0.1-10 mol / L, the molar concentration of sulfuric acid is 0.1-10 mol / L, the molar concentration of FeCl3 is 0.5-20 mol / L, and the molar concentration of N,N-dimethylformamide is 0.5-20 mol / L.

7. The method for extracting precious metals from cellulose-supported precious metal catalysts according to claim 1, characterized in that In step (4), the pH value is adjusted to 4-6 to acidity, and the precipitate is removed, and then the pH is adjusted to 8-10 to alkalinity, and the precipitate is removed.