Process for purifying crude palladium

Abstract

The application provides a purification method of crude palladium, and belongs to the technical field of precious metal purification. In the application, the precious metals such as palladium in the crude palladium are dissolved by aqua regia, then the palladium ions are oxidized into high-valence palladium by an oxidizing agent, and then the high-valence palladium is precipitated into palladium salt by a precipitating agent, so as to improve the purity; then the palladium salt is dissolved by an inorganic solvent, so as to remove the impurities such as platinum, copper, iron and silver, thereby improving the purity of the palladium; the palladium ions in the filtrate are complexed by a first complexing agent, so as to obtain a sub-palladium salt precipitate, thereby removing the impurities and improving the purity of the palladium; then the palladium ions are further complexed by a second complexing agent, thereby further improving the purity of the palladium; and then electro-deposition is adopted, so as to ensure that the palladium ions are fully reduced into palladium powder, thereby improving the purity of the palladium. The experimental results show that the purity of the palladium powder obtained by the purification method is greater than or equal to 99.95%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of noble metal purification, and particularly relates to a purification method of crude palladium. BACKGROUND

[0002] Palladium is a noble metal with high density, high melting point and elegant color value, which is silver-white, and high-purity palladium powder is gray-white. Palladium has good ductility and plasticity. At room temperature, 1 volume of sponge palladium can absorb 900 volumes of hydrogen, and hydrogen can freely pass through palladium, which has the ability to selectively permeate hydrogen. Palladium is an important material for hydrogen storage and hydrogen permeation, and is currently mainly used as a catalyst, especially a hydrogenation or dehydrogenation catalyst, and can also be used to make resistance wires and watch alloys.

[0003] At present, there are three methods for preparing fine palladium, namely, ammonium chloropalladate precipitation method, ammonia complexation method and combined method. The ammonium chloropalladate precipitation method has good base metal separation effect, but poor platinum group metal separation effect; the ammonia complexation method has good platinum group metal separation effect, but poor base metal separation effect; the combined method combines the two methods, so that the contents of base metals and platinum group in fine palladium powder can meet the corresponding standards. However, with the development of science and technology, the control of the purity of noble metals in the corresponding product standards is becoming more and more strict. Therefore, how to improve the purity of palladium has become a technical problem to be solved in the field. SUMMARY

[0004] The purpose of the present application is to provide a purification method of crude palladium. The purification method provided by the present application can significantly improve the purity of palladium.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0006] The present application provides a purification method of crude palladium, comprising the following steps:

[0007] (1) mixing crude palladium with aqua regia for digestion to obtain a palladium salt solution;

[0008] (2) mixing the palladium salt solution obtained in step (1) with an oxidizing agent for oxidation reaction to obtain a high-valence palladium salt solution;

[0009] (3) mixing the high-valence palladium salt solution obtained in step (2) with a precipitating agent for precipitation reaction to obtain a palladium salt;

[0010] (4) mixing the palladium salt obtained in step (3) with an inorganic solvent for impurity removal to obtain a filtrate;

[0011] (5) mixing the filtrate obtained in step (4) with a first complexing agent for first complexation reaction to obtain a palladous salt precipitate;

[0012] (6) mixing the sub-palladium salt obtained in step (5) with an inorganic solvent and a second complexing agent to perform a second complexing reaction to obtain a palladium salt complex solution;

[0013] (7) performing electrolysis using the palladium salt complex solution obtained in step (6) as an electrolyte to obtain palladium.

[0014] Preferably, the mass content of palladium in the crude palladium in step (1) is ≥ 90%.

[0015] Preferably, the mass-to-volume ratio of the crude palladium to aqua regia in step (1) is 1 g: (4-6) mL.

[0016] Preferably, the oxidizing agent in step (2) comprises hydrogen peroxide or sodium chlorate.

[0017] Preferably, the temperature of the oxidation reaction in step (2) is 60-80°C, and the time of the oxidation reaction is 1-2 h.

[0018] Preferably, the precipitant in step (3) comprises an ammonia chloride solution.

[0019] Preferably, the mass concentration of the ammonia chloride solution is 12-15%.

[0020] Preferably, the first complexing agent in step (5) and the second complexing agent in step (6) independently comprise ammonia water.

[0021] Preferably, the time of the first complexing reaction in step (5) and the second complexing reaction in step (6) is independently 0.5-1 h.

[0022] Preferably, the current density of the electrolysis in step (7) is 1-5 A / dm 2 , and the time of the electrolysis is 2-4 h.

[0023] The application provides a purification method of crude palladium, which comprises the following steps: mixing the crude palladium with aqua regia, performing digestion to obtain a palladium salt solution; mixing the palladium salt solution with an oxidizing agent, performing oxidation reaction to obtain a high-valence palladium salt solution; mixing the high-valence palladium salt solution with a precipitating agent, performing precipitation reaction to obtain a palladium salt; mixing the palladium salt with an inorganic solvent, performing impurity removal to obtain a filtrate; mixing the filtrate with a first complexing agent, performing first complexation reaction to obtain a sub-palladium salt precipitate; mixing the sub-palladium salt precipitate, the inorganic solvent and a second complexing agent, performing second complexation reaction to obtain a palladium salt complex solution; taking the palladium salt complex solution as an electrolyte, performing electrodeposition to obtain palladium. The palladium and other noble metals in the crude palladium are dissolved by aqua regia, then the palladium ions are oxidized into high-valence palladium by an oxidizing agent, and then the high-valence palladium is formed into a palladium salt precipitate by a precipitating agent, so that the purity is improved; then the palladium salt is dissolved by an inorganic solvent, and the platinum, copper, iron and silver impurities can be removed, so that the purity of the palladium is improved; the palladium ions in the filtrate are complexed by a first complexing agent, and the sub-palladium salt precipitate can be obtained, so that the platinum, copper and iron impurities can be further removed, and the purity of the palladium is further improved; then the palladium ions are further complexed by a second complexing agent, so that the purity of the palladium is further improved; and then the electrodeposition can ensure that the palladium ions are fully reduced into palladium powder, so that the purity of the palladium is improved. The experimental results show that the purity of the palladium powder obtained by the purification method is greater than or equal to 99.95%. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The process flow chart of the purification method of crude palladium provided by the application is shown. DETAILED DESCRIPTION

[0025] The application provides a purification method of crude palladium, which comprises the following steps:

[0026] (1) mixing the crude palladium with aqua regia, performing digestion to obtain a palladium salt solution;

[0027] (2) mixing the palladium salt solution obtained in the step (1) with an oxidizing agent, performing oxidation reaction to obtain a high-valence palladium salt solution;

[0028] (3) mixing the high-valence palladium salt solution obtained in the step (2) with a precipitating agent, performing precipitation reaction to obtain a palladium salt;

[0029] (4) mixing the palladium salt obtained in the step (3) with an inorganic solvent, performing impurity removal to obtain a filtrate;

[0030] (5) mixing the filtrate obtained in the step (4) with a first complexing agent, performing first complexation reaction to obtain a sub-palladium salt precipitate;

[0031] (6) mixing the sub-palladium salt precipitate obtained in the step (5), the inorganic solvent and a second complexing agent, performing second complexation reaction to obtain a palladium salt complex solution;

[0032] (7) Electrodepositing the palladium salt complex solution obtained in the step (6) to obtain palladium.

[0033] The present application does not have special limitation on the source of each raw material, and the commercially available products known to the skilled in the art can be used.

[0034] In the present application, the first and the second have no special meaning, and are only used to distinguish each raw material and step.

[0035] The purification method provided by the present application is suitable for crude palladium, preferably for crude palladium with mass content of palladium ≥ 90%.

[0036] In the present application, the crude palladium is mixed with aqua regia to perform digestion to obtain a palladium salt solution. The aqua regia used in the present application can dissolve the noble metals in the crude palladium.

[0037] In the present application, the mass-to-volume ratio of the crude palladium to the aqua regia is preferably 1 g: (4-6) mL, and more preferably 1 g: (4.5-5) mL. Limiting the mass-to-volume ratio of the crude palladium to the aqua regia in the above range can improve the dissolution rate of palladium and other noble metals, thereby further improving the yield of palladium.

[0038] The present application does not have special limitation on the operation of mixing the crude palladium with the aqua regia, and the technical solution for preparing a mixture known to the skilled in the art can be used.

[0039] In the present application, the temperature of the digestion is preferably room temperature, and the time of the digestion is preferably 2-4 h, and more preferably 3 h. Limiting the temperature and time of the digestion in the above range can make the palladium in the crude palladium fully dissolve.

[0040] After obtaining the palladium salt solution, the present application mixes the palladium salt solution with an oxidizing agent to perform oxidation reaction to obtain a high-valence palladium salt solution. The use of the oxidizing agent in the present application can oxidize the palladium ions to high-valence palladium.

[0041] In the present application, the oxidizing agent preferably includes hydrogen peroxide or sodium chlorate; the mass concentration of the hydrogen peroxide is preferably 25-30%, and more preferably 28-30%; and the purity of the sodium chlorate is preferably ≥ 98%.

[0042] The present application does not have special limitation on the amount of the oxidizing agent, as long as there is no divalent palladium in the palladium salt solution.

[0043] The present application does not have special limitation on the operation of mixing the palladium salt solution with the oxidizing agent, and the technical solution for preparing a mixture known to the skilled in the art can be used.

[0044] In the present application, the temperature of the oxidation reaction is preferably 60-80°C, more preferably 68-75°C; the time of the oxidation reaction is preferably 1-2h, more preferably 1.3-1.7h. The present application limits the temperature and time of the oxidation reaction in the above range to improve the degree of oxidation reaction.

[0045] After obtaining the high-valence palladium salt solution, the present application mixes the high-valence palladium salt solution and a precipitant to perform a precipitation reaction to obtain a palladium salt. The present application uses the precipitant to make the high-valence palladium form a palladium salt precipitate, thereby improving the purity.

[0046] In the present application, the precipitant preferably includes an ammonium chloride solution; the mass concentration of the ammonium chloride solution is preferably 12-15%, more preferably 12-14%. The present application does not have special limitation on the amount of the precipitant, until there is no new palladium salt precipitate.

[0047] The present application does not have special limitation on the operation of mixing the high-valence palladium salt solution and the precipitant, and the operation well known to those skilled in the art can be used.

[0048] The present application does not have special limitation on the temperature of the precipitation reaction, and the precipitation reaction can be performed at room temperature. The present application does not have special limitation on the time of the precipitation reaction, until there is no new palladium salt precipitate.

[0049] After the precipitation reaction is completed, the present application preferably filters the product obtained by the precipitation reaction to obtain a palladium salt. The present application does not have special limitation on the operation of filtering, and the operation well known to those skilled in the art can be used.

[0050] After obtaining the palladium salt, the present application mixes the palladium salt and an inorganic solvent to perform impurity removal to obtain a filtrate. The present application uses the inorganic solvent to dissolve the palladium salt, which can remove platinum, copper, iron and silver impurities.

[0051] In the present application, the inorganic solvent is preferably water; the mass ratio of the inorganic solvent to the palladium salt is preferably (4-6):1, more preferably 5:1. The present application limits the mass ratio of the inorganic solvent to the palladium salt in the above range to further improve the effect of impurity removal.

[0052] The present application does not have special limitation on the operation of mixing the palladium salt and the inorganic solvent, and the technical solution well known to those skilled in the art for preparing a mixture can be used.

[0053] In the present application, the impurity removal is preferably performed under boiling conditions. The present application performs the impurity removal under boiling conditions to further improve the effect of impurity removal.

[0054] After the impurity removal is completed, the present application preferably filters the product obtained by the impurity removal to obtain a filtrate.

[0055] The invention does not have special limitation on the operation of the filtering, and the operation known by those skilled in the art can be adopted.

[0056] After the filtrate is obtained, the invention mixes the filtrate and the first complexing agent to perform a first complexing reaction to obtain a sub-palladium salt precipitate. The invention adopts the complexing agent to complex the palladium ions in the filtrate, so that the sub-palladium salt precipitate is obtained, thereby further removing the platinum, copper and iron impurities, and further improving the purity of palladium.

[0057] In the invention, the first complexing agent preferably comprises ammonia water; the mass concentration of the ammonia water is preferably 20-25%, and more preferably 22.5-24%; the ratio of the volume of the first complexing agent to the mass of the crude palladium is (2-2.5) mL:1 g, and more preferably (2-2.45) mL:1 g.

[0058] The invention does not have special limitation on the operation of mixing the filtrate and the first complexing agent, and the technical solution for preparing a mixture known by those skilled in the art can be adopted.

[0059] In the invention, the temperature of the first complexing reaction is preferably normal temperature; and the time of the first complexing reaction is preferably 0.5-1 h, and more preferably 0.6-0.8 h. The invention limits the temperature and time of the first complexing reaction in the above range, so that the degree of the complexing reaction is improved, thereby improving the yield of palladium.

[0060] After the first complexing reaction is completed, the invention preferably performs precipitation and filtration on the product obtained by the first complexing reaction in sequence to obtain a sub-palladium salt precipitate.

[0061] In the invention, the precipitation is preferably performed under acidic conditions; the pH value of the acidic conditions is preferably 1-1.5; and the acidic conditions are preferably adjusted by hydrochloric acid. The invention does not have special limitation on the concentration of the hydrochloric acid, as long as the acidic conditions meet the requirement of the pH value. The solubility of palladium is lowest when the pH value is 1-1.5, so that the sub-palladium salt can be fully precipitated.

[0062] The invention does not have special limitation on the operation of the filtering, and the operation known by those skilled in the art can be adopted.

[0063] After the sub-palladium salt precipitate is obtained, the invention mixes the sub-palladium salt precipitate, an inorganic solvent and a second complexing agent to perform a second complexing reaction to obtain a palladium salt complexing solution. The invention adopts the second complexing agent to further complex the palladium ions, thereby further improving the purity of palladium.

[0064] In the invention, the inorganic solvent is preferably water; and the ratio of the mass of the sub-palladium salt precipitate to the inorganic solvent is preferably 1:(2-3), and more preferably 1:(2.2-2.8). The invention adopts the inorganic solvent for slurry.

[0065] In the present application, the second complexing agent preferably comprises ammonia water; the mass concentration of the ammonia water is preferably 20-25%, more preferably 22.5-24%; the ratio of the volume of the second complexing agent to the mass of the crude palladium is (2-2.5) mL:1 g, further preferably (2.15-2.45) mL:1 g, more preferably 2.30 mL:1 g.

[0066] In the present application, the mixing of the palladiumous salt precipitate, the inorganic solvent and the second complexing agent is preferably mixing the palladiumous salt precipitate and the inorganic solvent, and then adding the second complexing agent.

[0067] In the present application, the mixing of the palladiumous salt precipitate and the inorganic solvent is preferably carried out under stirring. The present application does not have special limitation on the operation of the stirring, as long as the palladiumous salt is sufficiently slurried.

[0068] The present application does not have special limitation on the operation of adding the second complexing agent, and a conventional operation can be used.

[0069] In the present application, the temperature of the second complexing reaction is preferably room temperature; the time of the second complexing reaction is preferably 0.5-1 h, more preferably 0.6-0.8 h. The present application limits the temperature and time of the second complexing reaction in the above range, which can improve the degree of complexing reaction, and ensure that the palladium salt is sufficiently complexed to form a stable palladium salt complex solution.

[0070] After obtaining the palladium salt complex solution, the present application uses the palladium salt complex solution as an electrolyte to carry out electrodeposition to obtain palladium. The present application uses electrodeposition to ensure that the palladium ions are sufficiently reduced to palladium powder, thereby improving the purity of palladium.

[0071] In the present application, the current density of the electrodeposition is preferably 1-5 A / dm 2 , more preferably 2.5-3.5 A / dm 2 ; the time of the electrodeposition is preferably 2-4 h, more preferably 2.5-3 h. The present application limits the current density and time of the electrodeposition in the above range, which can improve the degree of electrodeposition, thereby improving the yield of palladium.

[0072] In the present application, the electrodeposition preferably uses direct current; the cathode plate and the anode plate of the electrodeposition are independently preferably titanium. In the present application, the palladium is reduced on the cathode.

[0073] After the electrodeposition is completed, the present application preferably sequentially carries out powder scraping, washing and drying on the product obtained by the electrodeposition to obtain palladium.

[0074] The present application does not have special limitation on the operation of the powder scraping, and a conventional operation known to those skilled in the art can be used.

[0075] In the present application, the washing agent used in the washing is preferably deionized water. The present application does not have special limitation on the operation of the washing, and the palladium powder can be washed clean.

[0076] In the present application, the temperature of the drying is preferably 50-70℃; the time of the drying is preferably 1-3h; the drying is preferably carried out under vacuum condition; the vacuum degree of the vacuum condition is preferably -0.08 to -0.1MPa. The drying used in the present application can remove the solvent of the palladium powder.

[0077] The crude palladium with mass fraction of palladium ≥90% is dissolved by aqua regia at room temperature in the present application. After the crude palladium is completely dissolved, an oxidizing agent is added to the solution and heated to oxidize the palladium ions into high-valence palladium. A suitable precipitant is added at room temperature to form a palladium salt precipitate. Water is added and boiled until the palladium salt is dissolved. The solution is filtered to remove the impurity elements of platinum, copper, iron and silver. Then, ammonia is added to the filtrate at room temperature to complex and adjust the pH value to form a sub-palladium salt precipitate. The sub-palladium salt is stirred and slurried with water, and then ammonia is added to form a stable palladium salt complex solution. Finally, the palladium salt complex solution is placed in an electrolytic cell, and direct current is used for electrodeposition. After the electrodeposition process is completed, the palladium powder on the cathode is scraped off and cleaned with deionized water, and then dried under vacuum to obtain palladium powder with purity of 99.95% and above. The purification method provided by the present application is environmentally friendly and economical, and can efficiently electrodeposited and purify palladium powder from crude palladium. The operation is simple and easy to implement, meets the higher demand for the purity of palladium powder, and has broad industrial application prospects.

[0078] The purification method provided by the present application has a relatively simple whole process, greatly simplifies the operation process of the prior art, and improves the production efficiency. In the operation process of the present application, strong acid and strong base are reduced, thereby reducing the pollution to the environment, and the present application is more environmentally friendly than the prior art. Since the present application simplifies the operation process and improves the production efficiency, the production cost can be reduced, and the present application has more economic benefits than the prior art.

[0079] The process flow chart of the palladium purification method provided by the present application is shown in Figure 1 .

[0080] From Figure 1 it can be seen that the crude palladium is dissolved by aqua regia, and then a palladium salt is formed. Then, impurity separation, ammonia complexing, palladium powder electrodeposition and washing and drying are carried out to obtain palladium powder.

[0081] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0082] Example 1

[0083] The purification method of the crude palladium is as follows:

[0084] (1) Put 100 g of crude palladium with a palladium content of 90.5 wt% into a beaker, add aqua regia 400 mL, and digest at room temperature for 2 h to obtain a palladium salt solution;

[0085] (2) Add hydrogen peroxide with a mass concentration of 25% to the palladium salt solution obtained in step (1) and oxidize at 60°C for 1 h until no divalent palladium exists, to obtain a high-valence palladium salt solution;

[0086] (3) Add ammonia chloride solution with a mass concentration of 12% to the high-valence palladium salt solution obtained in step (2) to perform a precipitation reaction until no new palladium salt precipitates, and then filter to obtain a palladium salt;

[0087] (4) Add water 4 times the mass of the palladium salt obtained in step (3) to the palladium salt to boil and remove impurities, and then filter to obtain a filtrate;

[0088] (5) Add 200 mL of ammonia water with a mass concentration of 20% to the filtrate obtained in step (4) at room temperature to perform a complexation reaction for 0.5 h, then add hydrochloric acid to adjust the pH value to 1.5 to precipitate, and then filter to obtain a palladous salt precipitate;

[0089] (6) Add water 2.2 times the mass of the palladous salt precipitate to the palladous salt precipitate obtained in step (5) to stir and slurry, then add 200 mL of ammonia water with a mass concentration of 20% to perform a complexation reaction for 0.5 h to obtain a stable palladium salt complex solution;

[0090] (7) Put the palladium salt complex solution obtained in step (6) into an electrolytic cell, use titanium as the anode and cathode plates, and perform electrodeposition at a current density of 1 A / dm 2 under direct current for 4 h. After the electrodeposition is completed, the palladium powder on the cathode is scraped off, washed with 400 mL of deionized water, and then dried in a vacuum drying oven at 50°C for 3 h to obtain palladium powder with a purity of 99.95%. The vacuum degree is -0.08 MPa.

[0091] Example 2

[0092] The purification method of the crude palladium is as follows:

[0093] (1) Put 100 g of crude palladium with a palladium content of 92.3 wt% into a beaker, add aqua regia 450 mL, and digest at room temperature for 2.5 h to obtain a palladium salt solution;

[0094] (2) adding 30% mass concentration hydrogen peroxide to the palladium salt solution obtained in step (1) to oxidize at 68°C for 1.3 h until no divalent palladium exists, obtaining a high-valence palladium salt solution;

[0095] (3) adding 13.5% mass concentration ammonia chloride solution to the high-valence palladium salt solution obtained in step (2) to precipitate until no new palladium salt precipitates, and then filtering to obtain a palladium salt;

[0096] (4) adding 5 times the mass of the palladium salt to water to the palladium salt obtained in step (3) to boil off impurities, and then filtering to obtain a filtrate;

[0097] (5) adding 215 mL of 22.5% mass concentration ammonia water to the filtrate obtained in step (4) at room temperature to complex for 0.6 h, and then adding hydrochloric acid to adjust the pH value to 1.3 to precipitate, and filtering to obtain a palladous salt precipitate;

[0098] (6) adding 2.4 times the mass of the palladous salt precipitate to water to the palladous salt precipitate obtained in step (5) to stir and slurry, and then adding 215 mL of 22.5% mass concentration ammonia water to complex for 0.7 h, obtaining a stable palladium salt complex solution;

[0099] (7) placing the palladium salt complex solution obtained in step (6) into an electrolytic cell, using titanium as the cathode and anode plates, and using direct current to electrodeposit at a current density of 2.5 A / dm 2 for 3 h, scraping off the palladium powder on the cathode after the end of the electrodeposition, and washing with 450 mL of deionized water, and then drying in a vacuum drying oven at 55°C for 2 h, obtaining palladium powder with a purity of 99.96%; wherein the vacuum degree is -0.08 MPa.

[0100] Example 3

[0101] The purification method of the crude palladium is the following steps:

[0102] (1) placing 100 g of crude palladium with a palladium content of 94.6 wt% into a beaker, adding aqua regia 500 mL, and digesting at room temperature for 3 h to obtain a palladium salt solution;

[0103] (2) adding 98.5% purity sodium chlorate to the palladium salt solution obtained in step (1) to oxidize at 75°C for 1.7 h until no divalent palladium exists, obtaining a high-valence palladium salt solution;

[0104] (3) adding 14% mass concentration ammonia chloride solution to the high-valence palladium salt solution obtained in step (2) to precipitate until no new palladium salt precipitates, and then filtering to obtain a palladium salt;

[0105] (4) The palladium salt obtained in step (3) is added with water in an amount of 5.5 times the mass of the palladium salt, and impurities are removed by boiling, and then filtered to obtain a filtrate;

[0106] (5) The filtrate obtained in step (4) is added with 230 mL of ammonia water with a mass concentration of 24% at room temperature, and a complexing reaction is carried out for 0.8 h, then hydrochloric acid is added to adjust the pH value to 1.2 for precipitation, and after filtration, a pallous salt precipitate is obtained;

[0107] (6) The pallous salt precipitate obtained in step (5) is added with water in an amount of 2.8 times the mass of the pallous salt, and stirred to form a slurry, then 230 mL of ammonia water with a mass concentration of 20% is added, and a complexing reaction is carried out for 0.8 h to obtain a stable palladium salt complex solution;

[0108] (7) The palladium salt complex solution obtained in step (6) is placed in an electrolytic cell, titanium is used as the anode and cathode plates, and direct current is used to carry out electrodeposition at a current density of 3.5 A / dm 2 for 2.5 h, after the electrodeposition is completed, the palladium powder on the cathode is scraped off, and washed with 500 mL of deionized water, and then dried in a vacuum drying oven at 60°C for 1.5 h to obtain palladium powder with a purity of 99.97%; wherein the vacuum degree is -0.08 MPa.

[0109] Example 4

[0110] The purification method of the crude palladium is as follows:

[0111] (1) 100 g of crude palladium with a palladium content of 97.1 wt% is placed in a beaker, aqua regia 600 mL is added, and digestion is carried out at room temperature for 4 h to obtain a palladium salt solution;

[0112] (2) To the palladium salt solution obtained in step (1), sodium chlorate with a purity of 99% is added, and oxidation reaction is carried out at 80°C for 2 h until no divalent palladium exists, to obtain a high-valent palladium salt solution;

[0113] (3) To the high-valent palladium salt solution obtained in step (2), an ammonium chloride solution with a mass concentration of 15% is added for precipitation reaction until no new palladium salt precipitate is formed, and then filtered to obtain a palladium salt;

[0114] (4) The palladium salt obtained in step (3) is added with water in an amount of 6 times the mass of the palladium salt, and impurities are removed by boiling, and then filtered to obtain a filtrate;

[0115] (5) The filtrate obtained in step (4) is added with 245 mL of ammonia water with a mass concentration of 25% at room temperature, and a complexing reaction is carried out for 0.9 h, then hydrochloric acid is added to adjust the pH value to 1 for precipitation, and after filtration, a pallous salt precipitate is obtained;

[0116] (6) adding 3 times of water of the mass of the precipitated palladous salt obtained in step (5) to the precipitated palladous salt to form a slurry, then adding 245 mL of 20% ammonia water, and performing complexation reaction for 0.9 h to obtain a stable palladous salt complex solution;

[0117] (7) placing the palladous salt complex solution obtained in step (6) into an electrolytic cell, using titanium as the anode and cathode plates, and performing electrolysis for 1 h under the condition of a direct current with a current density of 5 A / dm 2 After the electrolysis is completed, the palladium powder on the cathode is scraped off, washed with 600 mL of deionized water, and then dried in a vacuum drying oven at 70°C for 1 h to obtain palladium powder with a purity of 99.99%; wherein the vacuum degree is -0.1 MPa.

[0118] As can be seen from the above examples, the purification method provided by the present application can significantly improve the purity of palladium.

[0119] The above only describes the preferred embodiments of the present application, and it should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for purifying crude palladium, comprising the following steps: (1) Mix crude palladium with aqua regia and digest it to obtain a palladium salt solution; (2) The palladium salt solution obtained in step (1) is mixed with an oxidant to carry out an oxidation reaction, thereby obtaining a high-valence palladium salt solution; (3) Mix the high-valent palladium salt solution obtained in step (2) with a precipitant to carry out a precipitation reaction. After the precipitation reaction is completed, filter the product obtained from the precipitation reaction to obtain palladium salt. (4) The palladium salt obtained in step (3) is mixed with an inorganic solvent to remove impurities. After the impurities are removed, the product obtained is filtered to obtain a filtrate. The inorganic solvent is water. The mass ratio of the inorganic solvent to the palladium salt is (4~6):

1. (5) The filtrate obtained in step (4) is mixed with the first complexing agent to carry out the first complexing reaction. After the first complexing reaction is completed, the product obtained from the first complexing reaction is precipitated and filtered in sequence to obtain palladium salt precipitate. The precipitation of the product obtained from the first complexing reaction is carried out under acidic conditions. The pH value of the acidic conditions is 1~1.

5. (6) The palladium salt precipitate obtained in step (5), the inorganic solvent, and the second complexing agent are mixed to carry out a second complexing reaction to obtain a palladium salt complexing solution, wherein the inorganic solvent is water; (7) Using the palladium salt complex solution obtained in step (6) as the electrolyte, perform electrowinning. After electrowinning, scrape off the product obtained by electrowinning, wash and dry it to obtain palladium. The oxidation reaction in step (2) is carried out at a temperature of 60-80°C for 1-2 hours. The impurity removal is carried out under boiling conditions; The temperature of the first complexation reaction is room temperature; The second complexation reaction occurs at room temperature; The oxidant in step (2) includes hydrogen peroxide or sodium chlorate; The precipitant in step (3) includes an ammonium chloride solution; The first complexing agent in step (5) and the second complexing agent in step (6) independently comprise ammonia.

2. The purification method according to claim 1, characterized in that, In step (1), the crude palladium contains ≥90% palladium by mass.

3. The purification method according to claim 1, characterized in that, In step (1), the mass ratio of crude palladium to the volume ratio of aqua regia is 1g:(4~6)mL.

4. The purification method according to claim 1, characterized in that, The mass concentration of the ammonium chloride solution is 12-15%.

5. The purification method according to claim 1, characterized in that, The time for the first complexation reaction in step (5) and the second complexation reaction in step (6) are independently 0.5~1h.

6. The purification method according to claim 1, characterized in that, The current density of the electrodeposition in step (7) is 1~5 A / dm. 2 The electrowinning time is 2-4 hours.

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