Method for recovering precious metal from waste resistance paste

Abstract

The invention discloses a method for recovering precious metal from waste resistor slurry, which comprises the following steps: S1, degumming the waste resistor slurry, mixing the degummed waste resistor slurry with water and a reducing agent for reaction, and then filtering to obtain first filter residue and first filtrate; s2, mixing and reacting the first filter residue with hydrochloric acid and an oxidation cosolvent, and then filtering to obtain a second filter residue and a second filtrate; s3, recovering metal palladium from the second filtrate; and / or recovering metal silver and metal ruthenium from the second filter residue. According to the method, high-purity precious metal (palladium, silver and ruthenium) can be efficiently recycled from the waste resistance paste, specifically, the palladium recycling rate is larger than or equal to 99%, the silver recycling rate is larger than or equal to 99%, the ruthenium recycling rate is larger than or equal to 99.5%, the palladium purity is larger than or equal to 99.95%, the silver purity is larger than or equal to 99.99%, the ruthenium purity is larger than or equal to 99.95%, and the recycling rate and the purity are both high.

Description

Technical Field

[0001] This invention belongs to the field of metal recycling, specifically relating to a method for recovering precious metals from waste resistor slurry. Background Technology

[0002] The main conductive components in resistive slurries are elemental or compound forms of precious metals such as ruthenium, palladium, and silver. During the production and testing of resistive slurries, some unusable waste slurries (including scraps, test materials, cleaning equipment materials, and defective products) are inevitably generated. To improve resource utilization, protect the environment, and reduce costs, it is necessary to recover the precious metals from these waste resistive slurries. Currently, the extraction and recovery of precious metals from industrial solid waste mostly employs wet processes, using aqua regia or inorganic acid + chlorine as the leaching medium. These leaching methods are direct leaching, resulting in low leaching rates, high liquid consumption, high production costs, low recovery rates, and large discharges of wastewater containing heavy metals and aluminum salts, which easily cause environmental pollution. Summary of the Invention

[0003] In order to overcome at least one of the technical problems existing in the prior art, one of the objectives of the present invention is to provide a method for recovering precious metals from waste resistor slurry.

[0004] The second objective of this invention is to provide a method for recovering precious metals from waste resistor slurry, and its application in the field of precious metal recycling.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of the present invention provides a method for recovering precious metals from waste resistor slurry, comprising the following steps:

[0007] S1: After the waste resistor slurry is degummed, it is mixed with water and reducing agent to react, and then filtered to obtain the first filter residue and the first filtrate;

[0008] S2: The first filter residue is mixed with hydrochloric acid and an oxidizing co-solvent and then filtered to obtain the second filter residue and the second filtrate;

[0009] S3: Recover palladium from the second filtrate; and / or, recover silver and ruthenium from the second filter residue.

[0010] Preferably, step S1 is as follows: after the waste resistor slurry is degummed, it is crushed and sieved, then mixed and reacted with water and reducing agent, and filtered to obtain the first filter residue and the first filtrate.

[0011] Preferably, the crushing and sieving step involves crushing the waste resistivity slurry after glue removal and then sieving it through a 30-100 mesh screen.

[0012] Preferably, the reducing agent is selected from at least one of ascorbic acid, sodium ascorbate, hydrazine hydrate, sodium hypophosphite, and sodium borohydride.

[0013] Preferably, in step S1, the temperature of the mixing reaction is 70–95°C. Reacting at this temperature can improve the efficiency of palladium oxide reduction.

[0014] Preferably, in step S1, the mass ratio of waste resistor slurry, water, and reducing agent is 1:(2-5):(0.5-1.5). When the mass ratio of waste resistor slurry, water, and reducing agent meets the above range, the powdered waste resistor slurry can be evenly dispersed, and palladium oxide can be fully reduced to elemental palladium.

[0015] Preferably, the glue discharge temperature is 350–450°C.

[0016] Preferably, the glue removal time is 60 to 180 minutes.

[0017] Preferably, step S1 is as follows: after removing the glue from the waste resistor slurry, crush and sieve it to obtain powdered waste resistor slurry; mix the powdered waste resistor slurry with water to obtain solution A; raise the temperature of solution A to 70-95°C; then mix solution A with a reducing agent to react, filter and wash to obtain the first filter residue and the first filtrate.

[0018] Preferably, in step S2, the mass ratio of the first filter residue, hydrochloric acid, and oxidizing co-solvent is 1:(1-3):(0.5-2). When the mass ratio of the first filter residue, hydrochloric acid, and oxidizing co-solvent meets the above range, the palladium in the first filter residue can be fully dissolved without causing other side reactions.

[0019] Preferably, the oxidizing co-solvent is selected from at least one of chlorine, hypochlorous acid, sodium hypochlorite, sodium chlorate, and hydrogen peroxide.

[0020] Preferably, in step S2, the mixing reaction temperature is 70–95°C. Reacting at this temperature can significantly increase the palladium dissolution rate.

[0021] Preferably, step S2 is as follows: the first filter residue is mixed with hydrochloric acid to obtain solution B; the temperature of solution B is raised to 70-95°C, and then solution B is mixed with an oxidizing co-solvent for reaction, filtered and washed to obtain the second filter residue and the second filtrate.

[0022] Preferably, step S3, the step of recovering metallic silver and metallic ruthenium from the second filter residue, includes the following steps:

[0023] Step a: Mix the second filter residue with nitric acid and react, then filter to obtain the third filter residue and the third filtrate;

[0024] Step b: Recover metallic silver from the third filtrate; and / or, recover metallic ruthenium from the third filter residue.

[0025] Preferably, the step of recovering metallic silver from the third filtrate comprises: mixing the third filtrate with hydrochloric acid to obtain crude silver chloride; then purifying the crude silver chloride using a hydrochloric acid-ammonia water purification method, followed by reduction with hydrazine hydrate to obtain metallic silver. Dissolving silver in the slurry residue with hot nitric acid results in a complex composition of impurities in the leaching solution. By treating the filtrate with hydrochloric acid to precipitate the silver, and then repeatedly using the hydrochloric acid-ammonia water combined purification process, the purity of silver can be increased to over 99.99%.

[0026] Preferably, the step of recovering metallic ruthenium from the third filter residue is as follows: the third filter residue is melted and reacted with an alkali and an oxidant, cooled, and then mixed and reacted with water and a strong oxidant. The gaseous ruthenium tetroxide generated by the mixture is then adsorbed using hydrochloric acid to obtain ruthenium chloride. The slurry residue after palladium and silver extraction still contains impurities such as glass materials. Due to its unique chemical stability, the ruthenium metal compound is difficult to completely dissolve using conventional methods, with a dissolution rate typically less than 10%. This invention uses an alkali and oxidant to melt ruthenium at high temperature, achieving a ruthenium utilization rate close to 100%. After dissolution, an alkali and a strong oxidant are used to convert the ruthenium into gaseous ruthenium tetroxide, which is then absorbed by hydrochloric acid and directly converted into the material required for producing resistive slurry powder, meeting production requirements.

[0027] Preferably, the alkali is selected from sodium hydroxide, potassium hydroxide, or a combination thereof.

[0028] Preferably, the melting reaction temperature is 550–650°C, and the melting reaction time is 2–4 hours.

[0029] Preferably, the strong oxidant is selected from at least one of sodium hypochlorite, chlorine, and ozone.

[0030] Preferably, the oxidant is selected from at least one of sodium peroxide and potassium nitrate.

[0031] Preferably, the step of recovering palladium from the second filtrate is as follows: reacting the second filtrate with a palladium precipitant to obtain a crude palladium salt product, purifying the crude palladium salt product using the dichlorodiammonium palladium sulfide method, and then reacting it with hydrazine hydrate to obtain palladium.

[0032] Preferably, the palladium precipitant comprises ammonium chloride.

[0033] Palladium in waste resistor slurry partially transforms into palladium oxide after debinding, which has poor solubility and is difficult to completely dissolve even with hot nitric acid or aqua regia in a short time. This invention employs a wet chemical reduction method, using water and a reducing agent to convert palladium oxide in the waste resistor slurry into elemental palladium. Then, hydrochloric acid and an oxidizing co-solvent are used to dissolve the palladium in the first filter residue, significantly improving the palladium dissolution rate. Furthermore, since nitric acid is not used for palladium dissolution, the subsequent palladium precipitation process eliminates the need for denitrification and heating concentration, greatly simplifying the process. Subsequently, palladium is separated by adding a palladium precipitant to the second palladium-containing filtrate, and the separated crude palladium is purified using a dichlorodiammine-palladium sulfide purification method to remove impurities with similar properties, such as platinum. Finally, the recovery rate of metallic palladium is high (approximately 100%), and the purity reaches over 99.95%.

[0034] The second aspect of the present invention provides the application of the method provided in the first aspect of the present invention in the field of precious metal recycling.

[0035] The beneficial effects of this invention are: the method of this invention can efficiently recover high-purity precious metals (palladium, silver, and ruthenium) from waste resistor slurry, specifically: palladium recovery rate ≥99%, silver recovery rate ≥99%, ruthenium recovery rate ≥99.5%, palladium purity ≥99.95%, silver purity ≥99.99%, and ruthenium purity ≥99.95%. The recovery rate and purity are both high. Furthermore, the method of this invention is environmentally friendly, low-cost, and requires less solvent, making it suitable for large-scale application. Detailed Implementation

[0036] The following examples provide a more detailed description of the specific implementation of the present invention, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described below are methods that can be implemented or understood by those skilled in the art by referring to existing technology. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0037] The mass (S) of the waste resistor slurry used in Examples 1-4 and Comparative Example 1 of this invention is 1 kg, wherein the mass percentage (α1) of palladium is 1.4%, the mass percentage (α2) of silver is 3.3%, and the mass percentage (α3) of ruthenium is 13.9%.

[0038] Example 1

[0039] This example provides a method for recovering precious metals from waste resistor slurry, the specific steps of which are as follows:

[0040] a. The waste resistor slurry is heated and debinded at a temperature of 400℃ for 120 minutes; then it is crushed and sieved through a 60-mesh screen to obtain powdered waste resistor slurry residue.

[0041] b. Mix the powdered waste resistor slurry residue with water and stir to disperse it evenly to obtain solution A, and raise the temperature of solution A to 85℃; then add a reducing agent (i.e., hydrazine hydrate) to solution A, mix and stir to disperse it evenly to obtain the first mixed liquid; wherein, the mass ratio of powdered waste resistor slurry residue, water and reducing agent is 1:3:1.

[0042] c. Filter and wash the first mixture to obtain the first filter residue; mix and stir the first filter residue with hydrochloric acid to obtain solution B, and raise the temperature of solution B to 90°C; then add an oxidizing co-solvent (i.e., sodium hypochlorite) to solution B, mix and stir to obtain the second mixture; wherein, the mass ratio of the first filter residue, hydrochloric acid and oxidizing co-solvent is 1:2:1.5.

[0043] d. Filter and wash the second mixture to obtain the second filter residue and the second filtrate; add palladium precipitant (i.e. ammonium chloride) to the second filtrate to obtain crude palladium salt precipitate. The mass ratio of the second filtrate to the palladium precipitant is 1:0.1.

[0044] e. The crude palladium salt precipitate is purified by dichlorodiammonia-palladium sulfide to obtain pure palladium salt precipitate; then the pure palladium salt precipitate is reacted with hydrazine hydrate (the mass ratio of pure palladium salt precipitate to hydrazine hydrate is 1:0.06) to obtain metallic palladium.

[0045] f. Dissolve the second filter residue in nitric acid (mass ratio of second filter residue to nitric acid is 1:2.5), then filter and wash to obtain the third filter residue and the third filtrate; add hydrochloric acid to the third filtrate (mass ratio of third filter residue to hydrochloric acid is 1:0.32) to obtain silver chloride precipitate.

[0046] g. After purifying the silver chloride precipitate with a combined hydrochloric acid-ammonia water process, the purified silver chloride is reacted with hydrazine hydrate (the mass ratio of silver chloride to hydrazine hydrate is 1:0.13) to obtain metallic silver.

[0047] h. After drying and pulverizing the third filter residue, mix it with sodium hydroxide and sodium peroxide (the mass ratio of the third filter residue, sodium hydroxide, and sodium peroxide is 1:3.5:3). Then heat it in a furnace until it melts (temperature is 600℃, 3h) to obtain a melt. Dissolve the melt in pure water to form a melt solution, and then add an oxidant (sodium hypochlorite) to react. The mass ratio of the melt to pure water is 1:30, and the mass ratio of the melt solution to the oxidant is 1:20. This causes ruthenium to react and generate gaseous ruthenium tetroxide. Then, use hydrochloric acid to absorb the gaseous ruthenium tetroxide (the mass ratio of hydrochloric acid to ruthenium tetroxide is 1:35) to obtain ruthenium chloride.

[0048] In this example, the recovered palladium (K1) mass is 0.01397 kg; the recovered silver (K2) mass is 0.03283 kg; and the recovered ruthenium (converted to the mass of ruthenium chloride) mass (K3) mass is 0.13874 kg.

[0049] Example 2

[0050] This example provides a method for recovering precious metals from waste resistor slurry, which differs from the method in Example 1 in that:

[0051] In step a, the glue discharge temperature is 350℃, the time is 180min, and the mesh size of the stencil is 100 mesh.

[0052] In step b, solution A is heated to 70°C; the reducing agent is sodium ascorbate; the mass ratio of powdered waste resistor slurry residue, water, and reducing agent is 1:5:1.5.

[0053] In step c, solution B is heated to 95°C; the oxidation co-solvent is hydrogen peroxide; the mass ratio of the first filter residue, hydrochloric acid, and oxidation co-solvent is 1:1:0.5.

[0054] In step h, the alkali is potassium hydroxide, the oxidant is potassium nitrate, the melting temperature is 550℃, and the time is 4h; the strong oxidant is ozone.

[0055] In this example, the recovered palladium (K1) mass is 0.013941 kg; the recovered silver (K2) mass is 0.03276 kg; and the recovered ruthenium (converted to the mass of ruthenium chloride) mass (K3) mass is 0.13855 kg.

[0056] Example 3

[0057] This example provides a method for recovering precious metals from waste resistor slurry, which differs from the method in Example 1 in that:

[0058] In step a, the glue discharge temperature is 450℃ and the time is 60 minutes; the mesh size of the stencil is 30 mesh.

[0059] In step b, solution A is heated to 95°C; the reducing agent is sodium hypophosphite; the mass ratio of powdered waste resistor slurry residue, water, and reducing agent is 1:2:0.5.

[0060] In step c, solution B is heated to 70°C; the oxidizing agent is chlorine gas; the mass ratio of the first filter residue, hydrochloric acid, and oxidizing agent is 1:3:2.

[0061] In step h, the alkali is sodium hydroxide, the oxidant is potassium nitrate, the melting temperature is 650℃, and the time is 2h; the strong oxidant is chlorine gas.

[0062] In this example, the recovered palladium (K1) mass is 0.01393 kg; the recovered silver (K2) mass is 0.03291 kg; and the recovered ruthenium (converted to the mass of ruthenium chloride) mass (K3) mass is 0.13859 kg.

[0063] Example 4

[0064] This example provides a method for recovering precious metals from waste resistor slurry, which differs from the method in Example 1 in that:

[0065] In step b, the powdered waste resistor slurry residue, water, and hydrazine hydrate are first mixed and stirred, and then heated to 85°C.

[0066] In step c, the first filter residue, hydrochloric acid, and sodium hypochlorite are mixed and stirred before being heated to 90°C.

[0067] In this example, the recovered palladium (K1) mass is 0.013888 kg; the recovered silver (K2) mass is 0.03271 kg; and the recovered ruthenium (converted to the mass of ruthenium chloride) mass (K3) mass is 0.13818 kg.

[0068] Comparative Example 1

[0069] This example provides a method for recovering precious metals from waste resistor slurry. The specific steps are as follows:

[0070] a. The waste resistor slurry is heated and debinded at a temperature of 400℃ for 120 minutes; then it is crushed and sieved through a 60-mesh screen to obtain powdered waste resistor slurry residue.

[0071] b. Mix and stir the powdered waste resistor slurry residue with nitric acid to obtain solution A, and raise the temperature of solution A to 90℃; then add sodium hypochlorite to solution A, mix and stir to obtain the first mixture; wherein, the mass ratio of powdered waste resistor slurry residue, nitric acid and oxidizing flux is 1:2:1.5.

[0072] c. Filter and wash the first mixture to obtain the first filter residue and the first filtrate; add palladium precipitant ammonium chloride to the first filtrate to obtain crude palladium salt precipitate; the mass ratio of the first filtrate to the palladium precipitant is 1:0.1.

[0073] d. The crude palladium salt precipitate was purified by dichlorodiammonia-palladium sulfide to obtain pure palladium salt precipitate; then the pure palladium salt precipitate was reacted with hydrazine hydrate (the mass ratio of pure palladium salt precipitate to hydrazine hydrate was 1:0.06) to obtain metallic palladium.

[0074] e. Dissolve the first filter residue in nitric acid (the mass ratio of the first filter residue to nitric acid is 1:2.5), then filter and wash to obtain the second filter residue and the second filtrate; add hydrochloric acid to the second filtrate (the mass ratio of the second filter residue to hydrochloric acid is 1:0.32) to obtain silver chloride precipitate.

[0075] f. After the silver chloride precipitate is purified by a combined hydrochloric acid-ammonia process, the purified silver chloride is reacted with hydrazine hydrate (the mass ratio of silver chloride to hydrazine hydrate is 1:0.13) to obtain metallic silver.

[0076] g. After drying and pulverizing the second filter residue, mix it with sodium hydroxide and sodium peroxide (the mass ratio of the second filter residue, sodium hydroxide, and sodium peroxide is 1:3.5:3). Then heat it in a furnace until it melts (temperature is 600℃, 3h) to obtain a melt. Dissolve the melt in pure water to form a melt solution, and then add an oxidant (sodium hypochlorite) to react. The mass ratio of the melt to pure water is 1:30, and the mass ratio of the melt solution to the oxidant is 1:20, so that ruthenium reacts to generate gaseous ruthenium tetroxide. Then, use hydrochloric acid to absorb the gaseous ruthenium tetroxide (the mass ratio of hydrochloric acid to ruthenium tetroxide is 1:35) to obtain ruthenium chloride.

[0077] In this example, the recovered palladium (K1) mass is 0.013753 kg; the recovered silver (K2) mass is 0.032534 kg; and the recovered ruthenium (converted to the mass of ruthenium chloride) mass (K3) mass is 0.1377 kg.

[0078] Performance testing:

[0079] The recovery rates and purities of palladium, silver, and ruthenium recovered using the methods described in Examples 1-4 and Comparative Example 1 were tested respectively. In the recovery rate calculation, the percentage of precious metals in the waste resistor slurry was set as α, the weight of the waste resistor slurry to be recovered was S, and the weight of the recovered precious metals was K. The recovery rate β = K * 100% / (α * S). The recovery rate requirements were: palladium recovery rate ≥ 99%, silver recovery rate ≥ 99%, and ruthenium recovery rate ≥ 99.5%. Purity was tested using the ICP method, with the purity requirements being: palladium purity ≥ 99.95%, silver purity ≥ 99.99%, and ruthenium purity ≥ 99.95%. The test results obtained according to the above testing and calculation methods are shown in Table 1.

[0080] Table 1 shows the recovery rate and purity of the precious metals recovered by the recovery methods in Examples 1-4 and Comparative Example 1.

[0081]

[0082] As shown in Table 1, the recovery rates of palladium obtained by the recovery methods in Examples 1-4 of this invention are greater than 99.2%, silver greater than 99.1%, and ruthenium greater than 99.4%, and the purity of the recovered precious metals is all higher than 99.91%, which is higher than the recovery rate of Comparative Example 1. This indicates that the method for recovering precious metals in this invention can further improve the recovery rate and purity. Therefore, the method for recovering precious metals from waste resistor slurry provided by this invention meets the requirements for purity and recovery rate.

[0083] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for recovering precious metals from waste resistor slurry, characterized in that: Includes the following steps: S1: After the waste resistor slurry is degummed, it is mixed with water and reducing agent to react, and then filtered to obtain the first filter residue and the first filtrate; S2: The first filter residue is mixed with hydrochloric acid and an oxidizing co-solvent and then filtered to obtain the second filter residue and the second filtrate; S3: Recover palladium from the second filtrate; and / or, recover silver and ruthenium from the second filter residue.

2. The method for recovering precious metals from waste resistor slurry according to claim 1, characterized in that: The reducing agent is selected from at least one of ascorbic acid, sodium ascorbate, hydrazine hydrate, sodium hypophosphite, and sodium borohydride; And / or, the oxidizing co-solvent is selected from at least one of chlorine, hypochlorous acid, sodium hypochlorite, sodium chlorate, and hydrogen peroxide.

3. The method for recovering precious metals from waste resistor slurry according to claim 1, characterized in that: In step S1, the mass ratio of waste resistor slurry, water, and reducing agent is 1:(2-5):(0.5-1.5). And / or, in step S2, the mass ratio of the first filter residue, hydrochloric acid, and oxidizing co-solvent is 1:(1-3):(0.5-2).

4. The method for recovering precious metals from waste resistor slurry according to claim 1, characterized in that: In step S3, the step of recovering metallic silver and metallic ruthenium from the second filter residue includes the following steps: Step a: Mix the second filter residue with nitric acid and react, then filter to obtain the third filter residue and the third filtrate; Step b: Recover metallic silver from the third filtrate; and / or, recover metallic ruthenium from the third filter residue.

5. The method for recovering precious metals from waste resistor slurry according to claim 4, characterized in that: The step of recovering metallic silver from the third filtrate is as follows: the third filtrate is mixed with hydrochloric acid to obtain crude silver chloride; then the crude silver chloride is purified by hydrochloric acid-ammonia water purification method, and then reduced with hydrazine hydrate to obtain metallic silver.

6. The method for recovering precious metals from waste resistor slurry according to claim 4, characterized in that: The step of recovering metallic ruthenium from the third filter residue is as follows: the third filter residue is melted and reacted with alkali and oxidant, cooled, and then mixed and reacted with water and strong oxidant, and the gaseous ruthenium tetroxide generated by the mixed reaction is adsorbed by hydrochloric acid to obtain ruthenium chloride.

7. The method for recovering precious metals from waste resistor slurry according to claim 6, characterized in that: The melting reaction temperature is 550–650°C, and the melting reaction time is 2–4 hours.

8. The method for recovering precious metals from waste resistor slurry according to claim 6, characterized in that: The strong oxidant is selected from at least one of sodium hypochlorite, chlorine, and ozone; and / or, the oxidant is selected from at least one of sodium peroxide and potassium nitrate.

9. The method for recovering precious metals from waste resistor slurry according to claim 1, characterized in that: The step of recovering palladium from the second filtrate is as follows: reacting the second filtrate with a palladium precipitant to obtain a crude palladium salt product, purifying the crude palladium salt product using the dichlorodiammonium palladium sulfide method, and then reacting it with hydrazine hydrate to obtain palladium.

10. The application of the method according to any one of claims 1 to 9 in the field of precious metal recycling.

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