Preparation method of palladium tetraammine sulfate

Abstract

The invention relates to the technical field of precious metal electroplating, in particular to a preparation method of palladium tetraammine sulfate, which comprises the following steps: palladium powder dissolution: adding palladium powder into concentrated nitric acid, heating to 60-70 DEG C, stirring and dissolving, and filtering to remove insoluble substances to obtain a palladium nitrate solution; preparing a palladium nitrate solid: heating the palladium nitrate solution to 70 DEG C, and concentrating into the palladium nitrate solid under a vacuum condition; preparing tetraamminepalladium nitrate: adding ammonia water into the palladium nitrate solid at normal temperature to react to generate a large amount of white precipitate, and filtering to obtain tetraamminepalladium nitrate; the method comprises the following steps: preparing tetraammine palladium sulfate: adding tetraammine palladium nitrate into a 6-8 mol / L sulfuric acid solution for dissolving, dropwise adding methanol at 90-100 DEG C, decomposing tetraammine palladium nitrate along with nitric acid to gradually generate tetraammine palladium sulfate, and concentrating the system to a solid state to obtain a tetraammine palladium sulfate crude product; purification of palladium tetramine sulfate: adding the palladium tetramine sulfate crude product into deionized water according to the mass ratio of 1: (8-10), stirring and dissolving at normal temperature, adding ammonium sulfate at one time to separate out white precipitate, filtering, transferring to a vacuum oven, and drying to obtain a palladium tetramine sulfate target product.

Description

Technical Field

[0001] This invention relates to the field of precious metal electroplating technology, specifically a method for preparing tetraamminepalladium sulfate. Background Technology

[0002] In the field of palladium-nickel alloy bonding or palladium plating of connectors, the palladium electroplating main salts used for many years have mostly been compounds containing halogens, sulfates, or nitrates, as disclosed in Chinese patents CN1420947A, CN1289716C, CN101709462A, and CN1249366A. The palladium-nickel electrolytes used for many years mostly contain chlorides, which can cause severe corrosion to electroplating equipment and substrates. A greater drawback is that chloride ions can cause fine cracks in the plated parts, seriously affecting the plating effect and quality. Because tetraamminepalladium sulfate has excellent water solubility and relatively stable solution chemical properties, it can not only serve as a precursor for palladium-supported catalysts but also as a novel main salt for electroplating. Due to its high plating efficiency, absence of halogens and nitrates, and clean and environmentally friendly nature, its application in palladium plating in the electronics industry is becoming increasingly widespread, gradually replacing traditional halogen-containing electroplating solutions.

[0003] Currently, the main methods for synthesizing tetraamminepalladium sulfate are as follows: Patent CN105836814A discloses a method for synthesizing tetraamminepalladium sulfate (II). This method uses potassium chloride palladiumate and ammonium acetate as raw materials to first synthesize cis-dichlorodiamminepalladium, then reacts it with ammonia to generate dichlorotetraamminepalladium, and then refluxes it with sulfuric acid to generate tetraamminepalladium sulfate. However, in this method, chloride ions are difficult to completely remove during reflux and concentration evaporation, resulting in excessive chloride ions in the product, and the yield is not high. Patent CN111732133A discloses a method for preparing tetraamminepalladium sulfate. This method involves dissolving palladium powder in a mixture of concentrated nitric acid and concentrated sulfuric acid under the action of an oxidant, and then removing the nitric acid to obtain palladium sulfate. US patent US634222B first converts palladium powder into palladium nitrate, then uses sulfuric acid to drive out the nitric acid in the palladium nitrate solution to obtain a palladium sulfate solution, and then complexes it with ammonia to obtain tetraamminepalladium sulfate. Both processes require large amounts of sulfuric acid to drive out nitric acid, which is difficult to completely remove. This results in high levels of nitrogen oxides and sulfuric acid mist, causing severe pollution. Excessive sulfuric acid leads to increased byproducts, and the ammonium sulfate produced during the complexation process mixes with tetraamminepalladium sulfate, making it difficult to control product yield and purity. Patent CN103395847A discloses a method for synthesizing tetraamminepalladium sulfate. This method involves dissolving palladium powder in aqua regia to obtain palladium chloride, then reacting it with sodium hydroxide to obtain palladium hydroxide. The palladium hydroxide then reacts with a stoichiometric amount of sulfuric acid to generate palladium sulfate, which in turn reacts with ammonia to generate tetraamminepalladium sulfate. However, in this method, palladium hydroxide is difficult to filter, and the chloride ions are difficult to remove completely, resulting in a yield below 87%. Patent CN102616869A discloses a method for synthesizing tetraamminepalladium sulfate. This method uses palladium chloride as a starting material, reacting it with ammonia to generate dichlorotetraamminepalladium, which then reacts with silver sulfate to generate tetraamminepalladium sulfate. However, silver sulfate has poor solubility, making its reaction with dichlorotetraamminepalladium difficult, resulting in a low yield (90%). Patent CN102786100A discloses another method for synthesizing tetraamminepalladium sulfate. This method uses palladium chloride as a starting material, reacting it with ammonia to generate dichlorotetraamminepalladium, then repeatedly exchanging it with an anion exchange resin to remove chloride ions. A measured amount of sulfuric acid is added to the exchange solution, and the solution is concentrated and crystallized to obtain tetraamminepalladium sulfate. The drawback of this method is that chloride ions are difficult to remove completely through resin exchange, requiring repeated resin exchange and regeneration, resulting in a large amount of waste liquid and a low product yield (87.6%). Patent CN108946829A discloses an electrodialysis preparation method for tetraamminepalladium sulfate. This method uses tetraamminepalladium dichloroethylene and sodium hydroxide as raw materials. Through electrodialysis, OH- ions replace Cl- to obtain palladium hydroxide, which is then reacted with sulfuric acid to obtain tetraamminepalladium sulfate. However, this method has a complex operation process and high operating costs, and is not suitable for large-scale production.Patent CN110482620A discloses a purification method for mass-producing tetraamminepalladium sulfate. This method uses rare palladium sulfate as its starting material. The crude tetraamminepalladium sulfate obtained by reacting with ammonia needs to be crystallized in alcoholic or ketone organic reagents. The palladium in the organic tailings is difficult to recover and is costly. Patent CN109609783B discloses a method for efficiently separating and purifying palladium and rhodium from an alloy sheet containing palladium and rhodium. This method uses dichlorodiamminepalladium as a raw material, which is slurried and then mixed with solid ammonium sulfate and ammonia to obtain tetraamminepalladium sulfate. However, in this method, chloride ions and ammonium sulfate are difficult to completely remove during the preparation process, resulting in low product purity. Patent CN112897600A discloses a method of dissolving dichlorodiamminepalladium(II) in dilute ammonia water to obtain a dichlorotetraamminepalladium(II) solution, which is then reacted sequentially with bicarbonate and sulfuric acid to generate a tetraamminepalladium(II) sulfate solution. After filtration, the solution is concentrated under reduced pressure, cooled to crystallize, and then the crystals are washed and dried to obtain tetraamminepalladium sulfate. However, this method uses dichlorodiamminepalladium as the starting material, which cannot avoid the problem of residual chloride ions.

[0004] In summary, most existing methods for preparing tetraamminepalladium sulfate cannot avoid the problem of residual chloride ions, or methods such as extraction cannot avoid the problem of residual organic matter. Both chloride ions and organic matter affect the preparation of electroplated layers from tetraamminepalladium sulfate. Therefore, the efficient preparation of chloride-free, high-purity tetraamminepalladium sulfate is of great significance. Summary of the Invention

[0005] The purpose of this invention is to address the technical problems existing in the prior art by proposing a method for preparing tetraamminepalladium sulfate, which does not involve the addition of any chloride ion-containing reagents and has a simple and stable production process.

[0006] The technical solution for achieving the objective of this invention is as follows: A method for preparing tetraamminepalladium sulfate, characterized by comprising the following steps: Step 1: Dissolving palladium powder: Add palladium powder to concentrated nitric acid, heat to 60-70℃ and stir to dissolve. Filter to remove insoluble matter to obtain palladium nitrate solution, wherein the mass ratio of palladium to concentrated nitric acid is 1:4. Step 2: Preparation of palladium nitrate solid: The palladium nitrate solution is heated to 70°C and concentrated under vacuum to obtain palladium nitrate solid; Step 3: Preparation of tetraamminepalladium nitrate: At room temperature, solid palladium nitrate is added to ammonia water to react and a large amount of white precipitate is produced. After filtration, tetraamminepalladium nitrate is obtained. The amount of ammonia water added is 6-8:1 molar ratio of ammonia to palladium. Step 4, Preparation of tetraamminepalladium sulfate: Add tetraamminepalladium nitrate to a 6-8 mol / L sulfuric acid solution with a sulfuric acid:palladium molar ratio of 2.4-3.2 to dissolve it. Add methanol dropwise at 90-100℃. As nitric acid decomposes tetraamminepalladium nitrate, tetraamminepalladium sulfate is gradually generated. After the system is concentrated to solid, crude tetraamminepalladium sulfate is obtained. Step 5: Purification of tetraamminepalladium sulfate: Add crude tetraamminepalladium sulfate to deionized water at a mass ratio of 1:8-10, stir and dissolve at room temperature, then add ammonium sulfate in one go to precipitate a white precipitate, filter, and transfer to a vacuum oven at 40°C to dry to obtain the target product of tetraamminepalladium sulfate. The chemical reaction processes involved in the above process are as follows: 3Pd+8HNO3→3Pd(NO3)2+2NO2↑+4H2O 4NH3·H2O+Pd(NO3)2→[Pd(NH3)4](NO3)2+4H2O 3[Pd(NH3)4](NO3)2+5CH3OH+3H2SO4→3Pd(NH3)4SO4+5CO2↑+3N2↑+13H2O.

[0007] Furthermore, in step one, the palladium powder is a black needle-like crystal with a palladium content >99.5%.

[0008] Furthermore, in step two, the vacuum level is -0.08 MPa.

[0009] Furthermore, in step three, the ammonia water is electronic grade ammonia water with a mass concentration of 28%.

[0010] Furthermore, in step four, methanol is a colorless and transparent liquid with a content >99.9%, and the amount added is the molar ratio of methanol to palladium: 2-3:1.

[0011] Furthermore, in step five, the conductivity of the deionized water should be <0.1 μS / cm; the ammonium sulfate should be of superior purity with a purity >99.5%, and the amount added should be the molar ratio of ammonium sulfate to palladium of 2-3:1.

[0012] The beneficial effects of this invention are: 1. No chloride ion-containing reagents are added during the preparation process. Tetraamminepalladium sulfate causes little corrosion to equipment during electroplating and has low maintenance costs.

[0013] 2. The production process is short, simple to operate, and stable; the direct recovery rate of tetraamminepalladium sulfate reaches over 95%, and the purity of tetraamminepalladium sulfate prepared using this invention is greater than 99.95%. Attached Figure Description

[0014] Figure 1 This is an appearance diagram of the tetraamminepalladium sulfate prepared according to the present invention.

[0015] Figure 2 This is a process flow diagram for preparing tetraamminepalladium sulfate according to the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1

[0018] A method for preparing tetraamminepalladium sulfate, such as Figure 2 As shown, it includes the following steps: (1) Dissolving palladium powder: Add 106.42 g of palladium powder to 425.68 g of concentrated nitric acid, heat the system to 60°C and stir to dissolve, filter to remove insoluble matter to obtain palladium nitrate solution.

[0019] (2) Preparation of palladium nitrate solid: After the palladium nitrate solution was transferred to a rotary evaporator and heated to 70°C, it was concentrated at -0.07 MPa to obtain 230.40 g of palladium nitrate solid.

[0020] (3) Preparation of tetraamminepalladium nitrate: 230.40g of palladium nitrate solid was added to 364.5g of ammonia water and reacted at room temperature, producing a large amount of white precipitate. After filtration, 298.32g of tetraamminepalladium nitrate was obtained.

[0021] (4) Preparation of tetraamminepalladium sulfate: 298.32g of tetraamminepalladium nitrate was dissolved in 400ml of 6mol / L sulfuric acid solution. 64g of methanol was added dropwise at 90℃. As nitrate ions decomposed, tetraamminepalladium nitrate was gradually converted into tetraamminepalladium sulfate. After the system was concentrated to solid state, 269.5g of crude tetraamminepalladium sulfate was obtained.

[0022] (5) Purification of tetraamminepalladium sulfate: 269.5 g of crude tetraamminepalladium sulfate was added to 1617 g of deionized water and stirred at room temperature to dissolve. Then 264 g of ammonium sulfate was added at once, and a white precipitate was instantly precipitated. After filtration, the precipitate was transferred to a vacuum oven at 40°C and dried to obtain 258.12 g of tetraamminepalladium sulfate. The product yield was 95.6%.

[0023] Example 2

[0024] A method for preparing tetraamminepalladium sulfate includes the following steps: (1) Dissolving palladium powder: Add 106.42 g of palladium powder to 425.68 g of concentrated nitric acid, heat the system to 63 °C and stir to dissolve, filter to remove insoluble matter to obtain palladium nitrate solution.

[0025] (2) Preparation of palladium nitrate solid: After the palladium nitrate solution was transferred to a rotary evaporator, it was heated to 70°C and concentrated at -0.07 MPa to obtain 230.38 g of palladium nitrate solid.

[0026] (3) Preparation of tetraamminepalladium nitrate: 230.38g of palladium nitrate solid was added to 398g of ammonia water and reacted at room temperature, producing a large amount of white precipitate. After filtration, 297.09g of tetraamminepalladium nitrate was obtained.

[0027] (4) Preparation of tetraamminepalladium sulfate: 297.09g of tetraamminepalladium nitrate was dissolved in 400ml of 6.5mol / L sulfuric acid solution, heated to 93℃ and 73g of methanol was added dropwise. As nitrate ions decomposed, tetraamminepalladium nitrate was gradually converted into tetraamminepalladium sulfate. After the system was concentrated to solid state, 269.3g of crude tetraamminepalladium sulfate was obtained.

[0028] (5) Purification of tetraamminepalladium sulfate: 269.3 g of crude tetraamminepalladium sulfate was added to 1800 g of deionized water and stirred at room temperature to dissolve. Then 300 g of ammonium sulfate was added at once, and a white precipitate was instantly precipitated. After filtration, the precipitate was transferred to a vacuum oven at 40°C and dried to obtain 257.31 g of tetraamminepalladium sulfate. The product yield was 95.3%.

[0029] The tetraamminepalladium sulfate prepared in Example 2 has the following appearance: Figure 1 As shown, the powder is a white crystalline powder with a uniform color, indicating that it has a higher purity than most commercially available yellow crystalline powders, meeting the appearance requirements of the electroplating industry.

[0030] Example 3

[0031] A method for preparing tetraamminepalladium sulfate includes the following steps: (1) Dissolving palladium powder: Add 106.42 g of palladium powder to 425.68 g of concentrated nitric acid, heat the system to 66 °C and stir to dissolve, filter to remove insoluble matter to obtain palladium nitrate solution.

[0032] (2) Preparation of palladium nitrate solid: After the palladium nitrate solution was transferred to a rotary evaporator and heated to 70°C, it was concentrated at -0.07 MPa to obtain 230.58 g of palladium nitrate solid.

[0033] (3) Preparation of tetraamminepalladium nitrate: 230.58g of palladium nitrate solid was added to 450g of ammonia water and reacted at room temperature, producing a large amount of white precipitate. After filtration, 297.13g of tetraamminepalladium nitrate was obtained.

[0034] (4) Preparation of tetraamminepalladium sulfate: 297.13 tetraamminepalladium nitrate was dissolved in 400 mL of 7 mol / L sulfuric acid solution, heated to 95 °C and 90 g of methanol was added dropwise. As nitrate ions decomposed, tetraamminepalladium nitrate was gradually converted into tetraamminepalladium sulfate. After the system was concentrated to solid state, 268.8 g of crude tetraamminepalladium sulfate was obtained.

[0035] (5) Purification of tetraammine palladium sulfate: 268.8 g of crude tetraammine palladium sulfate was added to 1900 g of deionized water and stirred at room temperature to dissolve. Then 360 g of ammonium sulfate was added at once, and a white precipitate was instantly precipitated. After filtration, the precipitate was transferred to a vacuum oven at 40°C and dried to obtain 259.41 g of tetraammine palladium sulfate. The product yield was 96.0%.

[0036] Example 4

[0037] A method for preparing tetraamminepalladium sulfate includes the following steps: (1) Dissolving palladium powder: Add 106.42 g of palladium powder to 425.68 g of concentrated nitric acid, heat the system to 65°C and stir to dissolve, filter to remove insoluble matter to obtain palladium nitrate solution.

[0038] (2) Preparation of palladium nitrate solid: After the palladium nitrate solution was transferred to a rotary evaporator and heated to 70°C, it was concentrated at -0.07 MPa to obtain 230.43 g of palladium nitrate solid.

[0039] (3) Preparation of tetraamminepalladium nitrate: 230.43g of palladium nitrate solid was added to 420g of ammonia water and reacted at room temperature, producing a large amount of white precipitate. After filtration, 298.34g of tetraamminepalladium nitrate was obtained.

[0040] (4) Preparation of tetraamminepalladium sulfate: 298.34g of tetraamminepalladium nitrate was dissolved in 400ml of 7.5mol / L sulfuric acid solution, heated to 97℃ and 80g of methanol was added dropwise. As nitrate ions decomposed, tetraamminepalladium nitrate was gradually converted into tetraamminepalladium sulfate. After the system was concentrated to solid state, 269.8g of crude tetraamminepalladium sulfate was obtained.

[0041] (5) Purification of tetraamminepalladium sulfate: 269.8 g of crude tetraamminepalladium sulfate was added to 1800 g of deionized water and stirred at room temperature to dissolve. Then 350 g of ammonium sulfate was added at once, and a white precipitate was instantly precipitated. After filtration, the precipitate was transferred to a vacuum oven at 40°C and dried to obtain 258.66 g of tetraamminepalladium sulfate. The product yield was 95.8%.

[0042] Example 5

[0043] A method for preparing tetraamminepalladium sulfate includes the following steps: (1) Dissolving palladium powder: Add 106.42 g of palladium powder to 425.68 g of concentrated nitric acid, heat the system to 70°C and stir to dissolve, filter to remove insoluble matter to obtain palladium nitrate solution.

[0044] (2) Preparation of palladium nitrate solid: After the palladium nitrate solution was transferred to a rotary evaporator and heated to 70°C, it was concentrated at -0.07 MPa to obtain 230.41 g of palladium nitrate solid.

[0045] (3) Preparation of tetraamminepalladium nitrate: 230.40g of palladium nitrate solid was added to 486g of ammonia water and reacted at room temperature, producing a large amount of white precipitate. After filtration, 297.15g of tetraamminepalladium nitrate was obtained.

[0046] (4) Preparation of tetraamminepalladium sulfate: 297.15g of tetraamminepalladium nitrate was dissolved in 400ml of 8mol / L sulfuric acid solution, heated to 100℃ and 96g of methanol was added dropwise. As nitrate ions decomposed, tetraamminepalladium nitrate was gradually converted into tetraamminepalladium sulfate. After the system was concentrated to solid state, 268.9g of crude tetraamminepalladium sulfate was obtained.

[0047] (5) Purification of tetraamminepalladium sulfate: 268.9 g of crude tetraamminepalladium sulfate was added to 2689 g of deionized water and stirred at room temperature to dissolve. Then, 396 g of ammonium sulfate was added at once, and a white precipitate was instantly precipitated. After filtration, the precipitate was transferred to a vacuum oven at 40°C and dried to obtain 256.77 g of tetraamminepalladium sulfate. The product yield was 95.1%.

[0048] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing tetraamminepalladium sulfate, characterized in that, Includes the following steps: Step 1: Dissolving palladium powder: Add palladium powder to concentrated nitric acid, heat and stir to dissolve, filter to remove insoluble matter to obtain palladium nitrate solution; Step 2: Preparation of palladium nitrate solid: The palladium nitrate solution is heated to 70°C and concentrated under vacuum to obtain palladium nitrate solid; Step 3, Preparation of tetraamminepalladium nitrate: At room temperature, palladium nitrate solid is added to ammonia water to react, producing a large amount of white precipitate, which is then filtered to obtain tetraamminepalladium nitrate. Step 4: Preparation of tetraamminepalladium sulfate: Add tetraamminepalladium nitrate to a sulfuric acid solution with a sulfuric acid:palladium molar ratio of 2.4-3.2 to dissolve it. Add methanol dropwise at 90-100℃. As nitric acid decomposes tetraamminepalladium nitrate, tetraamminepalladium sulfate is gradually generated. After the system is concentrated to solid state, crude tetraamminepalladium sulfate is obtained. Step 5: Purification of tetraamminepalladium sulfate: Add crude tetraamminepalladium sulfate to deionized water, stir and dissolve at room temperature, then add ammonium sulfate in one step to precipitate a white precipitate. After filtration, transfer to a vacuum oven and dry at 40°C to obtain the target product of tetraamminepalladium sulfate. The chemical reaction processes involved in the above process are as follows: 3Pd+8HNO3→3Pd(NO3)2+2NO2↑+4H2O 4NH3·H2O+Pd(NO3)2→[Pd(NH3)4](NO3)2+4H2O 3[Pd(NH3)4](NO3)2+5CH3OH+3H2SO4→3Pd(NH3)4SO4+5CO2↑+3N2↑+13H2O.

2. The method for preparing tetraamminepalladium sulfate according to claim 1, characterized in that: In step one, the palladium powder is a black needle-like crystal with a palladium content >99.5%.

3. The method for preparing tetraamminepalladium sulfate according to claim 1, characterized in that: In step one, the mass ratio of palladium powder to concentrated nitric acid is 1:

4.

4. The method for preparing tetraamminepalladium sulfate according to claim 1, characterized in that: In step one, the heating temperature is 60-70℃.

5. The method for preparing tetraamminepalladium sulfate according to claim 1, characterized in that: In step two, the vacuum level is -0.08 MPa.

6. The method for preparing tetraamminepalladium sulfate according to claim 1, characterized in that: In step three, the ammonia water is electronic grade ammonia water with a mass concentration of 28%, and the amount of ammonia water added is such that the molar ratio of ammonia to palladium is 6-8:

1.

7. The method for preparing tetraamminepalladium sulfate according to claim 1, characterized in that: In step four, the concentration of the sulfuric acid solution is 6-8 mol / L.

8. The method for preparing tetraamminepalladium sulfate according to claim 1, characterized in that: In step four, the methanol is a colorless and transparent liquid with a content >99.9%, and the amount added is the molar ratio of methanol to palladium: 2-3:

1.

9. The method for preparing tetraamminepalladium sulfate according to claim 1, characterized in that: In step five, the mass ratio of the crude tetraamminepalladium sulfate to deionized water is 1:8-10, and the conductivity of the deionized water should be <0.1μS / cm.

10. The method for preparing tetraamminepalladium sulfate according to claim 1, characterized in that: In step five, the ammonium sulfate is of superior purity with a purity >99.5%, and the amount added is such that the molar ratio of ammonium sulfate to palladium is 2-3:1.

Images