Purification method of crude palladium

Abstract

The invention provides a crude palladium purification method, and belongs to the technical field of precious metal purification. Palladium and other precious metals in crude palladium are dissolved by adopting aqua regia, then palladium ions are oxidized into high-valence palladium by adopting an oxidizing agent, and then the high-valence palladium forms palladium salt precipitation by adopting a precipitating agent, so that the purity is improved; then, palladium salt is dissolved with an inorganic solvent, platinum, copper, iron and silver impurities can be removed, and therefore the purity of palladium is improved; palladium ions in the filtrate are complexed by adopting a first complexing agent, and palladium salt precipitate can be obtained, so that impurities are removed, and the purity of palladium is improved; then, palladium ions are further complexed by adopting a second complexing agent, so that the purity of palladium is further improved; and then electrodeposition is adopted to ensure that palladium ions are fully reduced into palladium powder, so that the purity of palladium is improved. Experimental results show that the purity of the palladium powder obtained through the purification method is larger than or equal to 99.95%.

Description

Technical Field

[0001] The invention belongs to the technical field of precious metal purification, and in particular relates to a method for purifying crude palladium. Background Art

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

[0003] At present, there are three methods for preparing refined palladium, namely ammonium chloropalladate precipitation method, ammonia complex method, and combined method. Among them, ammonium chloropalladate precipitation method has good separation effect on base metals, but poor separation effect on platinum group metals; ammonia complex method has good separation effect on platinum group metals, but poor separation effect on base metals; combined method combines these two methods, so that the base metal and platinum group content in refined palladium powder can meet the corresponding standards, but with the development of science and technology, the corresponding product standards have become more and more stringent in the control of the purity of precious metals. Therefore, how to improve the purity of palladium has become a technical problem that needs to be solved urgently in this field. Summary of the invention

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

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

[0006] The present invention provides a method for purifying crude palladium, comprising the following steps:

[0007] (1) mixing crude palladium with aqua regia and digesting the mixture to obtain a palladium salt solution;

[0008] (2) mixing the palladium salt solution obtained in step (1) with an oxidant to carry out an oxidation reaction to obtain a high-valent palladium salt solution;

[0009] (3) mixing the high-valent palladium salt solution obtained in step (2) with a precipitant to perform a precipitation reaction to obtain a palladium salt;

[0010] (4) mixing the palladium salt obtained in step (3) with an inorganic solvent, removing impurities, and obtaining a filtrate;

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

[0012] (6) mixing the palladium salt precipitate obtained in step (5), an inorganic solvent and a second complexing agent, and performing a second complexing reaction to obtain a palladium salt complexing solution;

[0013] (7) Using the palladium salt complex solution obtained in step (6) as an electrolyte, electrolysis is performed to obtain palladium.

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

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

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

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

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

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

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

[0021] Preferably, the time for the first complexation reaction in step (5) and the second complexation reaction in step (6) is independently 0.5 to 1 h.

[0022] Preferably, the current density of the electroplating in step (7) is 1 to 5 A / dm 2 The electrolysis time is 2 to 4 hours.

[0023] The invention provides a method for purifying crude palladium, which comprises the following steps: mixing crude palladium with aqua regia, digesting the mixture, and obtaining a palladium salt solution; mixing the palladium salt solution with an oxidant, performing an oxidation reaction, and obtaining a high-valent palladium salt solution; mixing the high-valent palladium salt solution with a precipitant, performing a precipitation reaction, and obtaining a palladium salt; mixing the palladium salt with an inorganic solvent, removing impurities, and obtaining a filtrate; mixing the filtrate with a first complexing agent, performing a first complexing reaction, and obtaining a palladium salt precipitate; mixing the palladium salt precipitate, an inorganic solvent, and a second complexing agent, performing a second complexing reaction, and obtaining a palladium salt complex solution; and using the palladium salt complex solution as an electrolyte, performing electrolysis, and obtaining palladium. The present invention adopts aqua regia to dissolve the palladium and other precious metals in the crude palladium, then adopts an oxidant to oxidize the palladium ions into high-price palladium, and then adopts a precipitant to form a palladium salt precipitate from the high-price palladium, thereby improving the purity; then adopts an inorganic solvent to dissolve the palladium salt, which can remove platinum, copper, iron and silver impurities, thereby improving the purity of palladium; adopts a first complexing agent to complex the palladium ions in the filtrate, and can obtain a palladium salt precipitate, thereby further removing platinum, copper and iron impurities, thereby improving the purity of palladium; then adopts a second complexing agent to further complex the palladium ions, thereby further improving the purity of palladium; and then adopts electrolysis to ensure that the palladium ions are fully reduced to palladium powder, thereby improving the purity of palladium. Experimental results show that the purity of the palladium powder obtained by the purification method provided by the present invention is ≥99.95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention provides a process flow chart of the method for purifying crude palladium. DETAILED DESCRIPTION

[0025] The present invention provides a method for purifying crude palladium, comprising the following steps:

[0026] (1) mixing crude palladium with aqua regia and digesting the mixture to obtain a palladium salt solution;

[0027] (2) mixing the palladium salt solution obtained in step (1) with an oxidant to carry out an oxidation reaction to obtain a high-valent palladium salt solution;

[0028] (3) mixing the high-valent palladium salt solution obtained in step (2) with a precipitant to perform a precipitation reaction to obtain a palladium salt;

[0029] (4) mixing the palladium salt obtained in step (3) with an inorganic solvent, removing impurities, and obtaining a filtrate;

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

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

[0032] (7) Using the palladium salt complex solution obtained in step (6) as an electrolyte, electrolysis is performed to obtain palladium.

[0033] The present invention has no particular limitation on the sources of the raw materials, and commercially available products known to those skilled in the art may be used.

[0034] In the present invention, the first and the second have no special meanings and are only used to distinguish between various raw materials and steps.

[0035] The purification method provided by the present invention is applicable to crude palladium, preferably applicable to crude palladium with a palladium mass content of ≥90%.

[0036] The invention mixes crude palladium with aqua regia, digests the mixture, and obtains a palladium salt solution. The invention adopts aqua regia to dissolve the precious metal in the crude palladium.

[0037] In the present invention, the mass ratio of the crude palladium to the volume ratio of aqua regia is preferably 1 g: (4-6) mL, more preferably 1 g: (4.5-5) mL. The present invention limits the mass ratio of the crude palladium to the volume ratio of aqua regia within the above range to increase the dissolution rate of precious metals such as palladium, thereby further increasing the yield of palladium.

[0038] The present invention has no particular limitation on the operation of mixing the crude palladium and aqua regia, and a technical solution for preparing a mixed material well known to those skilled in the art may be used.

[0039] In the present invention, the digestion temperature is preferably room temperature; the digestion time is preferably 2 to 4 hours, more preferably 3 hours. The present invention limits the digestion temperature and time within the above ranges to enable the palladium in the crude palladium to be fully dissolved.

[0040] After obtaining the palladium salt solution, the present invention mixes the palladium salt solution with an oxidant to perform an oxidation reaction to obtain a high-valent palladium salt solution. The present invention uses an oxidant to oxidize palladium ions into high-valent palladium.

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

[0042] The present invention has no particular limitation on the amount of the oxidant, as long as no divalent palladium is present in the palladium salt solution.

[0043] The present invention has no special limitation on the operation of mixing the palladium salt solution and the oxidant, and the technical scheme for preparing the mixed material well known to those skilled in the art can be adopted.

[0044] In the present invention, 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 invention limits the temperature and time of the oxidation reaction to the above ranges to improve the degree of the oxidation reaction.

[0045] After obtaining the high-valent palladium salt solution, the present invention mixes the high-valent palladium salt solution with a precipitant to perform a precipitation reaction to obtain a palladium salt. The present invention uses a precipitant to precipitate the high-valent palladium into a palladium salt, thereby improving the purity.

[0046] In the present invention, the precipitant preferably includes an ammonium chloride solution; the mass concentration of the ammonium chloride solution is preferably 12 to 15%, more preferably 12 to 14%. The present invention has no particular limitation on the amount of the precipitant, as long as no new palladium salt is precipitated.

[0047] The present invention has no special limitation on the operation of mixing the high-valent palladium salt solution and the precipitant, and the operation well known to those skilled in the art can be adopted.

[0048] The present invention has no particular limitation on the temperature of the precipitation reaction, which can be carried out at room temperature. The present invention has no particular limitation on the time of the precipitation reaction, which can be carried out until no new palladium salt is precipitated.

[0049] After the precipitation reaction is completed, the present invention preferably filters the product obtained by the precipitation reaction to obtain the palladium salt. The present invention has no special limitation on the filtering operation, and the operation well known to those skilled in the art can be used.

[0050] After obtaining the palladium salt, the present invention mixes the palladium salt with an inorganic solvent, removes impurities, and obtains a filtrate. The present invention uses an inorganic solvent to dissolve the palladium salt, and can remove platinum, copper, iron and silver impurities.

[0051] In the present invention, 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. In the present invention, limiting the mass ratio of the inorganic solvent to the palladium salt to the above range can further improve the effect of impurity removal.

[0052] The present invention has no special limitation on the operation of mixing the palladium salt and the inorganic solvent, and the technical scheme for preparing the mixed material well known to those skilled in the art can be adopted.

[0053] In the present invention, the impurity removal is preferably carried out under boiling conditions. The impurity removal under boiling conditions can further improve the effect of impurity removal.

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

[0055] The present invention has no particular limitation on the filtering operation, and any operation well known to those skilled in the art may be used.

[0056] After obtaining the filtrate, the present invention mixes the filtrate with a first complexing agent, performs a first complexing reaction, and obtains a palladium salt precipitate. The present invention uses a complexing agent to complex palladium ions in the filtrate, and obtains a palladium salt precipitate, thereby further removing platinum, copper and iron impurities, thereby improving the purity of palladium.

[0057] In the present invention, the first complexing agent preferably includes 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 first complexing agent to the mass of crude palladium is (2-2.5) mL:1 g, more preferably (2-2.45) mL:1 g.

[0058] The present invention has no special limitation on the operation of mixing the filtrate and the first complexing agent, and the technical scheme for preparing the mixed material well known to those skilled in the art can be adopted.

[0059] In the present invention, the temperature of the first complex reaction is preferably room temperature; the time of the first complex reaction is preferably 0.5 to 1 hour, more preferably 0.6 to 0.8 hours. The present invention limits the temperature and time of the first complex reaction to the above ranges to improve the degree of complex reaction, thereby improving the yield of palladium.

[0060] After the first complex reaction is completed, the present invention preferably sequentially precipitates and filters the product obtained by the first complex reaction to obtain a palladium salt precipitate.

[0061] In the present invention, the precipitation is preferably carried out under acidic conditions; the pH value of the acidic conditions is preferably 1 to 1.5; the acidic conditions are preferably adjusted by hydrochloric acid. The present invention has no special limitation on the concentration of the hydrochloric acid, as long as the acidic conditions meet the pH value requirements. In the present invention, the solubility of palladium is the lowest in the pH range of 1 to 1.5, so that the palladium salt can be fully precipitated.

[0062] The present invention has no particular limitation on the filtering operation, and any operation well known to those skilled in the art may be used.

[0063] After obtaining the palladium salt precipitate, the present invention mixes the palladium salt precipitate, the inorganic solvent and the second complexing agent to perform a second complexing reaction to obtain a palladium salt complexing solution. The present invention uses the second complexing agent to further complex palladium ions, thereby further improving the purity of palladium.

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

[0065] In the present invention, the second complexing agent preferably includes 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 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 invention, the palladium salt precipitate, the inorganic solvent and the second complexing agent are preferably mixed by mixing the palladium salt precipitate and the inorganic solvent, and then adding the second complexing agent.

[0067] In the present invention, the mixing of the palladium salt precipitate and the inorganic solvent is preferably carried out under stirring conditions. The present invention has no particular limitation on the stirring operation, as long as the palladium salt is fully slurried.

[0068] The present invention has no special limitation on the operation of adding the second complexing agent, and conventional operation can be adopted.

[0069] In the present invention, the temperature of the second complex reaction is preferably room temperature; the time of the second complex reaction is preferably 0.5 to 1 hour, more preferably 0.6 to 0.8 hours. The present invention limits the temperature and time of the second complex reaction within the above range to improve the degree of complex reaction, ensure that the palladium salt is fully complexed, and form a stable palladium salt complex solution.

[0070] After obtaining the palladium salt complex solution, the present invention uses the palladium salt complex solution as an electrolyte to perform electrolysis to obtain palladium. The present invention uses electrolysis to ensure that palladium ions are fully reduced to palladium powder, thereby improving the purity of palladium.

[0071] In the present invention, the current density of the electroplating is preferably 1 to 5 A / dm 2 , more preferably 2.5 to 3.5 A / dm 2 The electrolytic deposition time is preferably 2 to 4 hours, more preferably 2.5 to 3 hours. The present invention limits the current density and time of electrolytic deposition within the above ranges to improve the degree of electrolytic deposition, thereby improving the yield of palladium.

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

[0073] After the electrowinning is completed, the present invention preferably performs scraping, washing and drying in sequence on the product obtained by the electrowinning to obtain palladium.

[0074] The present invention has no special limitation on the operation of scraping the powder, and the operation well known to those skilled in the art can be adopted.

[0075] In the present invention, the washing agent used in the washing is preferably deionized water. The present invention has no special limitation on the washing operation, and the palladium powder can be washed clean.

[0076] In the present invention, the drying temperature is preferably 50 to 70°C; the drying time is preferably 1 to 3 hours; the drying is preferably performed under vacuum conditions; the vacuum degree of the vacuum conditions is preferably -0.08 to -0.1 MPa. The present invention uses drying to remove the solvent of the palladium powder.

[0077] The invention dissolves crude palladium with a palladium mass fraction of ≥90% with aqua regia at room temperature, adds an oxidant to the solution after the crude palladium is completely dissolved, heats the solution to oxidize palladium ions into high-valent palladium, adds a suitable precipitant at room temperature to form a palladium salt precipitate with the high-valent palladium, adds water and boils until the palladium salt is dissolved, and removes platinum, copper, iron and silver impurity elements in the solution through filtration; then adds ammonia water to the filtrate at room temperature for complexation and adjusts the pH value to form a palladium salt precipitate, stirs the palladium salt with water to form a slurry, and then adds ammonia water to form a stable palladium salt complex solution; finally, puts the palladium salt complex solution into an electrolytic cell, uses direct current for electrolysis, scrapes off the palladium powder on the cathode after the electrolysis process is completed, cleans it with deionized water, and then dries it under vacuum to obtain palladium powder with a purity of 99.95% or more; the purification method provided by the invention is environmentally friendly and economical, can efficiently purify palladium powder from crude palladium by electrolysis, is simple and easy to operate, meets the higher requirements of palladium powder purity, and has broad industrial application prospects.

[0078] The whole process of the purification method provided by the present invention is relatively simple, which greatly simplifies the operation process of the prior art and improves the production efficiency. During the operation process, the present invention reduces the use of strong acids and strong bases, thereby reducing pollution to the environment, and is more environmentally friendly than the prior art. Since the present invention simplifies the operation process and improves the production efficiency, the production cost can be reduced, and it is more economical than the prior art.

[0079] The process flow chart of the method for purifying crude palladium provided by the present invention is as follows: Figure 1 shown.

[0080] from Figure 1 It can be seen that the crude palladium is dissolved in aqua regia to form palladium salt, followed by impurity separation, ammonia complexation, palladium powder electrolysis, washing and drying to obtain palladium powder.

[0081] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0082] Example 1

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

[0084] (1) 100 g of crude palladium with a palladium content of 90.5 wt % was placed in a beaker, 400 mL of aqua regia was added, and digested at room temperature for 2 h to obtain a palladium salt solution;

[0085] (2) adding hydrogen peroxide with a mass concentration of 25% to the palladium salt solution obtained in step (1), and performing an oxidation reaction at 60° C. for 1 hour until no divalent palladium is present, thereby obtaining a high-valent palladium salt solution;

[0086] (3) adding a 12% ammonium chloride solution to the high-valent palladium salt solution obtained in step (2) to carry out a precipitation reaction until no new palladium salt precipitates, and then filtering to obtain a palladium salt;

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

[0088] (5) adding 200 mL of 20% ammonia water to the filtrate obtained in step (4) at room temperature, carrying out complexation reaction for 0.5 h, then adding hydrochloric acid to adjust the pH value to 1.5 for precipitation, and filtering to obtain a palladium salt precipitate;

[0089] (6) adding 2.2 times the mass of the palladium salt precipitate of water to the palladium salt precipitate obtained in step (5) to stir and slurry the mixture, then adding 200 mL of 20% ammonia water to carry out complex reaction for 0.5 h to obtain a stable palladium salt complex solution;

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

[0091] Example 2

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

[0093] (1) 100 g of crude palladium with a palladium content of 92.3 wt % was placed in a beaker, 450 mL of aqua regia was added, and digested at room temperature for 2.5 h to obtain a palladium salt solution;

[0094] (2) adding hydrogen peroxide with a mass concentration of 30% to the palladium salt solution obtained in step (1), and performing an oxidation reaction at 68° C. for 1.3 h until no divalent palladium is present, thereby obtaining a high-valent palladium salt solution;

[0095] (3) adding a 13.5% ammonium chloride solution to the high-valent palladium salt solution obtained in step (2) to carry out a precipitation reaction until no new palladium salt precipitates, and then filtering to obtain a palladium salt;

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

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

[0098] (6) adding 2.4 times the mass of the palladium salt precipitate of water to the palladium salt precipitate obtained in step (5) to stir and slurry, then adding 215 mL of 22.5% ammonia water to carry out complex reaction for 0.7 h to obtain 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 anode and cathode plates, and applying direct current at a current density of 2.5 A / dm 2 Electrolysis was carried out under the conditions for 3 hours. After the electrolysis was completed, the palladium powder on the cathode was scraped off and washed with 450 mL of deionized water, and then dried in a vacuum drying oven at 55° C. for 2 hours to obtain palladium powder with a purity of 99.96%; wherein the vacuum degree was -0.08 MPa.

[0100] Example 3

[0101] The purification method of crude palladium is as follows:

[0102] (1) 100 g of crude palladium with a palladium content of 94.6 wt % was placed in a beaker, 500 mL of aqua regia was added, and digestion was performed at room temperature for 3 h to obtain a palladium salt solution;

[0103] (2) adding sodium chlorate with a purity of 98.5% to the palladium salt solution obtained in step (1), and performing an oxidation reaction at 75° C. for 1.7 hours until no divalent palladium is present, thereby obtaining a high-valent palladium salt solution;

[0104] (3) adding a 14% ammonium chloride solution to the high-valent palladium salt solution obtained in step (2) to carry out a precipitation reaction until no new palladium salt precipitates, and then filtering to obtain a palladium salt;

[0105] (4) adding water 5.5 times the mass of the palladium salt to the palladium salt obtained in step (3) to boil and remove impurities, and then filtering to obtain a filtrate;

[0106] (5) adding 230 mL of 24% ammonia water to the filtrate obtained in step (4) at room temperature, carrying out complexation reaction for 0.8 h, then adding hydrochloric acid to adjust the pH value to 1.2 for precipitation, and filtering to obtain a palladium salt precipitate;

[0107] (6) adding 2.8 times the mass of the palladium salt precipitate of water to the palladium salt precipitate obtained in step (5) to stir and slurry the mixture, then adding 230 mL of 20% ammonia water to carry out complex reaction for 0.8 h to obtain a stable palladium salt complex solution;

[0108] (7) placing the palladium salt complex solution obtained in step (6) into an electrolytic cell, using titanium as the anode and cathode plates, and applying direct current at a current density of 3.5 A / dm 2 Electrolysis was carried out under the conditions for 2.5 hours. After the electrolysis was completed, the palladium powder on the cathode was scraped off and washed with 500 mL of deionized water, and then dried in a vacuum drying oven at 60° C. for 1.5 hours to obtain palladium powder with a purity of 99.97%; wherein the vacuum degree was -0.08 MPa.

[0109] Example 4

[0110] The purification method of crude palladium is the following steps:

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

[0112] (2) adding sodium chlorate with a purity of 99% to the palladium salt solution obtained in step (1), and performing an oxidation reaction at 80° C. for 2 h until no divalent palladium is present, thereby obtaining a high-valent palladium salt solution;

[0113] (3) adding a 15% ammonium chloride solution to the high-valent palladium salt solution obtained in step (2) to carry out a precipitation reaction until no new palladium salt precipitates, and then filtering to obtain a palladium salt;

[0114] (4) adding water 6 times the mass of the palladium salt to the palladium salt obtained in step (3) to boil and remove impurities, and then filtering to obtain a filtrate;

[0115] (5) adding 245 mL of 25% ammonia water to the filtrate obtained in step (4) at room temperature, carrying out complexation reaction for 0.9 h, then adding hydrochloric acid to adjust the pH value to 1 for precipitation, and filtering to obtain a palladium salt precipitate;

[0116] (6) adding water in an amount of 3 times the mass of the palladium salt precipitate to the palladium salt precipitate obtained in step (5) to stir and slurry the mixture, then adding 245 mL of 20% ammonia water to carry out a complex reaction for 0.9 h to obtain a stable palladium salt complex solution;

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

[0118] It can be seen from the above examples that the purification method provided by the present invention can significantly improve the purity of palladium.

[0119] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for purifying crude palladium, comprising the following steps: (1) mixing crude palladium with aqua regia and digesting the mixture to obtain a palladium salt solution; (2) mixing the palladium salt solution obtained in step (1) with an oxidant to carry out an oxidation reaction to obtain a high-valent palladium salt solution; (3) mixing the high-valent palladium salt solution obtained in step (2) with a precipitant to perform a precipitation reaction to obtain a palladium salt; (4) mixing the palladium salt obtained in step (3) with an inorganic solvent, removing impurities, and obtaining a filtrate; (5) mixing the filtrate obtained in step (4) with a first complexing agent to perform a first complexing reaction to obtain a palladium salt precipitate; (6) mixing the palladium salt precipitate obtained in step (5), an inorganic solvent and a second complexing agent, and performing a second complexing reaction to obtain a palladium salt complexing solution; (7) Using the palladium salt complex solution obtained in step (6) as an electrolyte, electrolysis is performed to obtain palladium.

2. The purification method according to claim 1, characterized in that The mass content of palladium in the crude palladium in the step (1) is ≥90%.

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

4. The purification method according to claim 1, characterized in that The oxidant in step (2) includes hydrogen peroxide or sodium chlorate.

5. The purification method according to claim 1, characterized in that: The temperature of the oxidation reaction in step (2) is 60-80° C., and the time of the oxidation reaction is 1-2 hours.

6. The purification method according to claim 1, characterized in that: In the step (3), the precipitant comprises an ammonium chloride solution.

7. The purification method according to claim 6, characterized in that: The mass concentration of the ammonium chloride solution is 12-15%.

8. The purification method according to claim 1, characterized in that: The first complexing agent in step (5) and the second complexing agent in step (6) independently include aqueous ammonia.

9. The purification method according to claim 1, characterized in that: The time of the first complexation reaction in step (5) and the second complexation reaction in step (6) is independently 0.5 to 1 hour.

10. The purification method according to claim 1, characterized in that: The current density of the electroplating in step (7) is 1 to 5 A / dm 2 The electroplating time is 2 to 4 hours.

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