Method for recycling metallic palladium by using formate and preparing ultrafine palladium powder and application thereof

Abstract

The present invention discloses a method for recovering metallic palladium by using formate and preparing ultrafine palladium powder, and its application. The method comprises the steps of: (1) preparing a palladium-containing waste liquid with a pH greater than 1.5, adding formate thereto, reducing at normal temperature and pressure, dissolving the obtained solid with aqua regia, removing impurities with ammonia water, and then adding acid to obtain a palladium precipitate; (2) after the palladium precipitate is dissolved, reducing with formate at normal temperature and pressure to obtain ultrafine palladium powder with a specific surface area of more than 10 m 2 / g; in step (1) and step (2), the formate is independently selected from one or several mixtures of formate of 2-hydroxy-N,N,N-trimethyl-1-propanamine, cesium hydrogen phthalate, and ammonium dithiocarbamate. The above method can be used for recovering palladium from palladium-containing tailings, waste palladium catalysts or palladium-containing sewage in the production process of palladium salts, and can also be used for preparing high-purity ultrafine palladium powder by using palladium-containing waste liquid.

Description

Technical Field

[0001] The present invention relates to the technical field of palladium recycling, and particularly relates to a method for recycling metallic palladium by using formate and preparing ultrafine palladium powder, and its application. Background Art

[0002] As a platinum group precious metal element, palladium is widely used in fields such as chemical industry, medicine, aerospace, nuclear energy, and electronics due to its good plasticity, stability, and catalytic activity, and is an important strategic material. With the continuous progress of the industrial process, the demand for palladium is increasing day by day. The palladium resources are severely scarce and far from meeting the development needs of various industries. Therefore, it has become particularly important to recycle palladium from secondary resources.

[0003] At present, the recycling methods of palladium include precipitation method, ion exchange method, metal displacement method, molecular recognition method, etc. However, most of these methods are time-consuming, costly, low in separation efficiency, and not very universal, and are mostly applicable to the recycling of high-content palladium. Patent documents such as CN206199088U, CN108285978A, and CN1492062A report methods for directly reducing and recycling palladium by using hydrazine hydrate or formic acid. This direct reduction method has the advantages of short time consumption and high recovery rate, but it requires adjusting the pH of the solution to alkaline and heat treatment, which not only consumes high energy but also generates more hazardous wastes. Therefore, it is an urgent problem to be solved at present to develop a convenient, efficient, and low-cost palladium recycling method and prepare the recycled palladium into high-value-added products. The core of solving this problem is to select suitable reducing agents at different stages of the process. Summary of the Invention

[0004] In view of the above technical problems and the shortcomings in the art, the present invention provides a method for recovering metal palladium and preparing ultrafine palladium powder using formate. The present invention uses a direct reduction method. On the basis of reasonable design and screening of reducing agents, waste palladium materials can be prepared into high value-added electronic grade ultrafine palladium powder products through two-step normal temperature and pressure reduction. The first step of reduction is palladium recovery reduction. This step of reduction can recover waste palladium under acidic, normal temperature and pressure conditions, greatly reducing the recovery cost and operation complexity; in addition, the palladium element obtained by this step of reduction can be modified by the oxidation product of the reducing agent. The oxidation product not only reduces the surface tension of the palladium powder, accelerates the process of dissolving palladium in aqua regia, and improves the subsequent purification efficiency, but more importantly, it can greatly improve the palladium nucleation reaction rate in the preparation process of ultrafine palladium powder, ensuring the fine uniformity of ultrafine palladium powder particles. The second step of reduction is the preparation of ultrafine palladium powder. Due to the large Gibbs free energy on the surface of ultrafine palladium powder, palladium powder is easy to agglomerate and grow, so the reducing agent or the oxidation product of the reducing agent in this step needs to have a stabilizer function to stabilize the ultrafine palladium powder particles. The present invention uses the formate of 2-hydroxy-N,N,N-trimethyl-1-propylamine as a reducing agent for preparing ultrafine palladium powder, and the oxidation product N,N,N-trimethyl-2-acetone of the reducing agent can be adsorbed on the surface of palladium particles, thereby reducing the Gibbs free energy on the surface of the palladium particles and preventing the ultrafine palladium powder particles from agglomerating and growing. The present invention can realize the preparation of high-purity ultrafine palladium powder for use in the electronics industry from palladium-containing waste liquid.

[0005] A method for recovering metallic palladium and preparing ultrafine palladium powder using formate comprises the following steps:

[0006] (1) preparing a palladium-containing waste liquid with a pH greater than 1.5, adding formate thereto, reducing it at room temperature and pressure, dissolving the obtained solid with aqua regia, removing impurities with ammonia water, and then adding acid to obtain a palladium precipitate;

[0007] (2) After the palladium precipitate is dissolved, it is reduced using formate at room temperature and pressure to obtain a specific surface area of 10m 2 / g or more ultrafine palladium powder;

[0008] In step (1) and step (2), the formate salt is independently selected from the group consisting of formate salt of 2-hydroxy-N,N,N-trimethyl-1-propylamine, cesium hydrogen phthalate, and ammonium dithiocarbamate, or a mixture thereof.

[0009] The present invention is applicable to the recovery of palladium-containing tailings, waste palladium catalysts and palladium-containing wastewater in the production process of palladium salts and prepares them into high-value-added ultrafine palladium powder, and has a high recovery rate, strong universality and high economic value. When facing the recovery of solid palladium-containing waste, the solid waste needs to be pre-treated by liquid preparation, such as dissolving it with aqua regia.

[0010] In step (1) and step (2), the formate can be added in the form of one or more of an aqueous solution, an alcohol solution, and an acetone solution.

[0011] In step (1), if the pH of the palladium-containing waste liquid is already greater than 1.5, there is no need to adjust the pH. If the pH of the palladium-containing waste liquid is not greater than 1.5, an alkaline substance needs to be added to adjust the pH. The alkaline substance can be one or a mixture of several of KOH, NaOH, and ammonia water (such as 25wt% - 28wt% concentrated ammonia water).

[0012] In a preferred example, in step (2), the formate is the formate of 2-hydroxy-N,N,N-trimethyl-1-propanamine.

[0013] In step (1), the mass ratio of the added formate to the mass of palladium element in the palladium-containing waste liquid can be 0.1 - 100:1, preferably 1 - 10:1, and more preferably 3 - 5:1.

[0014] In step (2), the mass ratio of the used formate to the mass of palladium element in the palladium precipitate can be 0.1 - 100:1, preferably 1 - 10:1, and more preferably 3 - 5:1.

[0015] The upper limits of the above two mass ratios can be 3.5, 3.7, 3.9, 4.2, 4.5, or 5.0, and the lower limits can be 3.0, 3.2, 3.5, 3.6, 3.8, 4.1, 4.3, 4.6, or 4.8.

[0016] In steps (1) and (2), the reduction time can be independently selected from 0.5 - 200h. Preferably, the reduction time is independently selected from 4 - 20h. More preferably, the reduction time is independently selected from 12 - 16h.

[0017] The upper limits of the above two reduction times can be 12.5, 13, 13.5, 14.0, 14.5, 15.0, 15.5, or 16.0, and the lower limits can be 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, or 15.0.

[0018] Aqua regia is a mixture composed of 36wt% - 38wt% concentrated hydrochloric acid and 65wt% - 68wt% concentrated nitric acid in a volume ratio of 3:1.

[0019] In a preferred example, in step (1), the obtained solid is dissolved with an equal mass of aqua regia.

[0020] In a preferred example, in step (1), the dissolution temperature is 30 - 50°C.

[0021] In a preferred example, in step (1), a heating and nitrate-evaporation process is set between the aqua regia dissolution and ammonia water impurity removal processes. The nitrate-evaporation temperature is preferably 80 - 150°C. The nitrate-evaporation time is preferably 0.1 - 2h.

[0022] In step (1), during the impurity removal process with ammonia water, it is preferred to control the pH of the mixed solution to be not less than 10, and more preferably to control the pH of the mixed solution to be 11 - 14.

[0023] In a preferred example, in step (1), during the impurity removal process with ammonia water, the dropping rate of ammonia water is 1 - 5 drops / s, and the stirring rate of the mixed solution during the dropping process of ammonia water is 200 - 400 rpm.

[0024] In step (1), during the process of adding acid to obtain palladium precipitate, it is preferred to control the pH of the mixed solution to be not greater than 2, and more preferably to control the pH of the mixed solution to be 0 - 2.

[0025] In a preferred example, in step (1), during the process of adding acid to obtain palladium precipitate, the dropping rate of acid is 1 - 5 drops / s, and the stirring rate of the mixed solution during the dropping process of acid is 200 - 400 rpm.

[0026] In step (1), the acid added during the process of adding acid to obtain palladium precipitate can be one or several mixtures of nitric acid, acetic acid, sulfuric acid, iodic acid, citric acid, preferably one or several mixtures of acetic acid, sulfuric acid, citric acid, more preferably one or two mixtures of acetic acid and citric acid, and even more preferably citric acid.

[0027] The core of the method of the present invention is to select suitable reducing agents at different stages of the process; the process for recovering metallic palladium is simple in operation, without the need for heat treatment during the reduction process, nor the need to adjust the solution pH to neutral or even alkaline, and the amount of hazardous waste generated is small and easy to handle, and the recovery rate of metallic palladium can reach more than 99.6%; the purity of the ultrafine palladium powder obtained by the process for preparing ultrafine palladium is more than 99.96%, and the specific surface area of the palladium powder is more than 10 m 2 / g.

[0028] The present invention also provides the application of the described method in recovering palladium from palladium-containing tailings, waste palladium catalysts or palladium-containing sewage during the production process of palladium salts. The palladium-containing tailings during the production process of palladium salts can be tailings from the production of palladium diammine dichloride, palladium chloride, palladium sulfate, etc.

[0029] The present invention also provides the application of the described method in preparing high-purity ultrafine palladium powder from palladium-containing waste liquid. The method of the present invention can obtain high-purity ultrafine palladium powder with a purity of more than 99.96%.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. The palladium recovery and ultrafine palladium powder preparation process provided by the present invention can reduce palladium elements in waste palladium solution to elemental palladium through direct reduction with formate. On the one hand, heating is not required during the reduction process, reducing energy consumption. On the other hand, there is no need to adjust the solution pH to neutral or even alkaline, reducing the amount of alkali used. This recovery process not only has low recovery costs and low operation complexity, but also produces less hazardous waste and is easy to handle. It is an environmentally friendly recovery process with high economic value.

[0032] 2. The palladium recovery and ultrafine palladium powder preparation process provided by the present invention includes a purification process for the recovered palladium. The purity of the purified palladium can reach over 99.96%, and it can be directly used in the production of catalysts, palladium salts, etc.

[0033] 3. The palladium recovery and ultrafine palladium powder preparation process provided by the present invention can directly convert waste palladium materials into ultrafine palladium powder with a specific surface area of not less than 10 m 2 / g and high added value, which has high economic value.

[0034] 4. The palladium recovery and ultrafine palladium powder preparation process provided by the present invention is simple to operate, has strong universality, is easy to implement on a large scale industrially, and can be applied to the recovery of various palladium waste materials. Specific Embodiments

[0035] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The operating methods without specific conditions noted in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0036] Unless otherwise specified, the hydrochloric acid used in the following embodiments is concentrated hydrochloric acid with a concentration of 36 wt% - 38 wt%, nitric acid is concentrated nitric acid with a concentration of 65 wt% - 68 wt%, sulfuric acid is concentrated sulfuric acid with a concentration of 98 wt%, alkali is liquid alkali of 40 wt% KOH or NaOH, acetic acid is glacial acetic acid with a concentration of 98 wt%, citric acid is citric acid powder with a concentration of 99.5 wt%, iodic acid is iodic acid powder with a concentration of 99.5 wt%, and ammonia water is concentrated ammonia water with a concentration of 25 wt% - 28 wt%.

[0037] The formate of 2-hydroxy-N,N,N-trimethyl-1-propanamine and ammonium dithiocarbamate used in the examples were purchased from Invitrogen Biotechnology (Shanghai) Co., Ltd. Cesium hydrogen phthalate was prepared by the method reported in the master's thesis "Synthesis, Characterization and Thermodynamic Properties of Heavy Dilute Alkali Metal Cesium Compounds" by Geng Chunyu of Shaanxi Normal University.

[0038] The analysis methods in the embodiments of the present invention are as follows:

[0039] The determination of the main metal palladium content adopts the dimethylglyoxime precipitation EDTA complexometric titration method in "GB / T 23276-2009".

[0040] The pH value is measured using a PHS-3C pH meter from Sichuan Shuniu Company.

[0041] The determination of the impurity metal content adopts a NexIon 300Q inductively coupled plasma mass spectrometer (abbreviated as ICP-AES) from PerkinElmer, USA.

[0042] The characterization of the specific surface area and pore characteristics of ultrafine palladium powder adopts an ASAP2020M+C fully automatic physical adsorption instrument (abbreviated as BET) from Micromeritics, USA.

[0043] Example 1 Recovery of metallic palladium and preparation of ultrafine palladium powder from the tail liquid of palladium diammine dichloride production

[0044] The composition of the tail liquid from palladium diammine dichloride production is shown in Table 1.

[0045] Table 1 Composition of the tail liquid from palladium diammine dichloride production

[0046] Composition Palladium content <![CDATA[Chlorine content 1 > <![CDATA[Ammonia content 2 > <![CDATA[Total impurity content 3 > Content / wt 496 ppm 2.35％ 2.55％ 23 ppm

[0047] Note: 1. Including Cl - ; 2. Including NH3 and NH4 + ; 3. Including Fe, Pt, Au, Na, Cu, Pb, Sn, Al, Si, Mg, Ca, Bi, Sb and Ag, etc.

[0048] Take 10 Kg of the tail liquid from palladium diammine dichloride production in a 50 L autoclave quartz reactor, measure its pH with a pH meter, and the pH is 1.8 without the need to adjust the pH value by adding alkali. Add 50 g of a 10 wt% ethanol solution containing a 1:1 mass ratio of cesium hydrogen phthalate and ammonium dithiocarbamate to the tail liquid, and stir and react at room temperature (20 °C) for 12 h. After the reaction, black elemental palladium precipitates out. After filtration and weighing, 7.8 g (including water) of the precipitate is obtained. Next, enter the purification step: Transfer the precipitate to a beaker, add 7.8 g of aqua regia with a volume ratio of concentrated hydrochloric acid to concentrated nitric acid of 3:1, heat to 40 °C and dissolve for 30 min; after dissolution, heat to 120 °C to drive off the nitric acid for 30 min until no reddish-brown gas escapes; add ammonia water dropwise to the beaker until the pH value of the solution = 12, then add a mixed acid with a 1:1 mass ratio of sulfuric acid and citric acid until the pH value of the solution = 1, and filter to obtain a palladium-containing precipitate; transfer the precipitate to a beaker, add 20 mL of ammonia water to dissolve it; finally, add 50 g of a 10 wt% ethanol solution of 2-hydroxy-N,N,N-trimethyl-1-propanamine formate, stir and react at room temperature (20 °C) for 12 h, and after filtration and washing, high-purity ultrafine palladium powder can be obtained.

[0049] The weight of the ultrafine palladium powder was 4.95 g, and the calculated recovery rate was 99.8%. The specific surface area of the ultrafine palladium powder measured by BET was 12.2 m 2 / g. The impurity content of the ultrafine palladium powder is shown in Table 2.

[0050] Table 2 Impurity content of ultrafine palladium powder (wt%)

[0051] Pd 99.96 Cu 0.003 Mg 0.001 Fe 0.002 Pb 0.002 Ca 0.005 Pt 0.003 Sn 0.004 Bi 0.001 Au 0.005 Al 0.002 Sb 0.002 Na 0.004 Si 0.003 Ag 0.003

[0052] Example 2 Recovery of metallic palladium from the tail liquid of palladium chloride production and preparation of ultrafine palladium powder

[0053] The composition of the tail liquid from palladium chloride production is shown in Table 3.

[0054] Table 3 Composition of the tail liquid from palladium chloride production

[0055] Composition Palladium content <![CDATA[Chlorine content 1 > <![CDATA[Nitrate content 2 > <![CDATA[Total impurity content 3 > Content / wt 798 ppm 10.35％ 0.55％ 35 ppm

[0056] Note: 1. Including Cl - ; 2. Including NO3 - and NO2 - ; 3. Including Fe, Pt, Au, Na, Cu, Pb, Sn, Al, Si, Mg, Ca, Bi, Sb and Ag, etc.

[0057] 10 Kg of the tail liquid from palladium chloride production was placed in a 50 L autoclave quartz reactor. Its pH was measured with a pH meter to be -0.1, and liquid alkali was added to adjust the pH value to 1.9. 100 g of an ethanol solution containing 10 wt% of ammonium dithiocarbamate was added to the tail liquid, and the mixture was stirred at room temperature (20 °C) for 16 h. After the reaction ended, black elemental palladium precipitated out. After filtration, the precipitate weighed 10.6 g (containing water). The following is the purification step: The precipitate was transferred to a beaker, and 10.6 g of aqua regia with a volume ratio of concentrated hydrochloric acid to concentrated nitric acid of 3:1 was added, and it was heated to 40 °C and dissolved for 30 min; after dissolution, it was heated to 120 °C to remove nitrates for 30 min until no brownish-red gas escaped; ammonia water was added dropwise to the beaker until the pH value of the solution was 13, and then a mixed acid with a mass ratio of nitric acid to acetic acid of 1:1 was added until the pH value of the solution was 1, and a palladium-containing precipitate was obtained after filtration; the precipitate was transferred to a beaker and dissolved with 30 mL of ammonia water; finally, 20 g of an ethanol solution containing 10 wt% of the formate of 2-hydroxy-N,N,N-trimethyl-1-propanamine was added, and the mixture was stirred at room temperature (20 °C) for 16 h. After filtration and washing, high-purity ultrafine palladium powder could be obtained.

[0058] The weight of the ultrafine palladium powder was 7.96 g, and the calculated recovery rate was 99.7%. The specific surface area of the ultrafine palladium powder measured by BET was 12.5 m 2 / g. The impurity content of the ultrafine palladium powder is shown in Table 4.

[0059] Table 4 Impurity Content of Ultrafine Palladium Powder (wt%)

[0060] Pd 99.97 Cu 0.002 Mg 0.002 Fe 0.002 Pb 0.004 Ca 0.002 Pt 0.003 Sn 0.003 Bi 0.001 Au 0.002 Al 0.001 Sb 0.001 Na 0.001 Si 0.003 Ag 0.003

[0061] Example 3 Recovery of Metallic Palladium from the Spent Solution of Palladium Sulfate Production and Preparation of Ultrafine Palladium Powder

[0062] The composition of the spent solution of palladium sulfate production is shown in Table 5.

[0063] Table 5 Composition of the Spent Solution of Palladium Sulfate Production

[0064] Composition Palladium content <![CDATA[Chlorine content 1 > <![CDATA[Sulfur content 2 > <![CDATA[Total impurity content 3 > Content / wt 1568 ppm 0.15％ 28.55％ 49 ppm

[0065] Note: 1. Including Cl - ; 2. Including SO3 2- and SO4 2- ; 3. Including Fe, Pt, Au, Na, Cu, Pb, Sn, Al, Si, Mg, Ca, Bi, Sb and Ag, etc.

[0066] 10 Kg of the spent solution of palladium sulfate production was placed in a 50 L autoclave quartz reactor. The pH of the solution was measured with a pH meter to be 0.3, and the pH value was adjusted to 2.3 by adding liquid alkali. 150 g of a 10 wt% acetone solution of 2-hydroxy-N,N,N-trimethyl-1-propanamine formate was added to the spent solution, and the mixture was stirred at room temperature (20 °C) for 20 h. After the reaction, black elemental palladium was precipitated. After filtration, the precipitate was weighed to obtain 23.3 g (including water) of the precipitate. The following is the purification step: The precipitate was transferred to a beaker, and 23.3 g of aqua regia with a volume ratio of concentrated hydrochloric acid to concentrated nitric acid of 3:1 was added, and the mixture was heated to 40 °C and dissolved for 30 min; after the dissolution, it was heated to 120 °C to remove nitric acid for 30 min until no brown-red gas escaped; ammonia water was added dropwise to the beaker until the pH value of the solution was 12, and then a mixed acid with a mass ratio of nitric acid to sulfuric acid of 1:1 was added until the pH value of the solution was 1. After filtration, a palladium-containing precipitate was obtained; the precipitate was transferred to a beaker and dissolved with 50 mL of ammonia water; finally, 50 g of a 10 wt% acetone solution of 2-hydroxy-N,N,N-trimethyl-1-propanamine formate was added, and the mixture was stirred at room temperature (20 °C) for 20 h. After filtration and washing, high-purity ultrafine palladium powder was obtained.

[0067] The weight of the ultrafine palladium powder was 15.62 g, and the calculated recovery rate was 99.6%. The specific surface area of the ultrafine palladium powder was measured by BET to be 13.1 m 2 / g. The impurity content of the ultrafine palladium powder is shown in Table 6.

[0068] Table 6 Impurity Content of Ultrafine Palladium Powder (wt%)

[0069] Pd 99.96 Cu 0.003 Mg 0.005 Fe 0.004 Pb 0.001 Ca 0.003 Pt 0.002 Sn 0.003 Bi 0.001 Au 0.004 Al 0.001 Sb 0.001 Na 0.004 Si 0.005 Ag 0.003

[0070] Example 4 Recovery of Metallic Palladium from Spent Palladium-Carbon Catalyst and Preparation of Ultrafine Palladium Powder

[0071] Pretreatment of spent palladium-carbon catalyst: Weigh 100 g of the spent palladium-carbon catalyst, add 100 g of aqua regia with a volume ratio of concentrated hydrochloric acid to concentrated nitric acid of 3:1, heat to 50 °C and dissolve for 60 min, and filter to obtain a palladium-containing waste liquid.

[0072] The composition of the palladium-containing waste liquid is shown in Table 7.

[0073] Table 7 Composition of the Dissolution Liquid of Spent Palladium-Carbon Catalyst

[0074] Composition Palladium content <![CDATA[Chlorine content 1 > <![CDATA[Nitrate content 2 > <![CDATA[Total impurity content 3 > Content / wt 2.2％ 28.5％ 14.5％ 768 ppm

[0075] Note: 1. Including Cl - ; 2. Including NO3 - and NO2 - ; 3. Including Fe, Pt, Au, Na, Cu, Pb, Sn, Al, Si, Mg, Ca, Bi, Sb and Ag, etc.

[0076] Put 101.3 g of the dissolution liquid of the spent palladium-carbon catalyst in a beaker, measure its pH with a pH meter as -0.3, and adjust the pH value to 2.1 with ammonia water. Add 10 g of an aqueous solution of cesium hydrogen phthalate with a mass fraction of 10 wt% to the tail liquid, and stir and react at room temperature (20 °C) for 14 h. After the reaction, black elemental palladium precipitates. After filtration, weigh to obtain 4.2 g (containing water) of the precipitate. Next, enter the purification step: Transfer the precipitate to a beaker, add 4.2 g of aqua regia with a volume ratio of concentrated hydrochloric acid to concentrated nitric acid of 3:1, heat to 40 °C and dissolve for 30 min; after dissolution, heat to 120 °C to drive off nitric acid for 30 min until no brown-red gas escapes; add ammonia water dropwise to the beaker until the pH value of the solution is 12, and then add a mixed acid with a mass ratio of iodic acid to sulfuric acid of 1:1 until the pH value of the solution is 1, and filter to obtain a palladium-containing precipitate; transfer the precipitate to a beaker, add 15 mL of ammonia water to dissolve; finally, add 10 g of an aqueous solution of the formate of 2-hydroxy-N,N,N-trimethyl-1-propanamine with a mass fraction of 10 wt%, stir and react at room temperature (20 °C) for 14 h, and after filtration and washing, high-purity ultrafine palladium powder can be obtained.

[0077] The weight of the ultrafine palladium powder is 2.22 g, and the calculated recovery rate is 99.6%. The BET test shows that the specific surface area of the ultrafine palladium powder is 11.8 m 2 / g. The impurity content of the ultrafine palladium powder is shown in Table 8.

[0078] Table 8 Impurity Content (wt%) of Ultrafine Palladium Powder

[0079] Pd 99.96 Cu 0.006 Mg 0.002 Fe 0.004 Pb 0.001 Ca 0.002 Pt 0.004 Sn 0.006 Bi 0.001 Au 0.005 Al 0.001 Sb 0.001 Na 0.001 Si 0.005 Ag 0.001

[0080] Example 5 Recovery of Metallic Palladium from Palladium-Containing Sewage and Preparation of Ultrafine Palladium Powder

[0081] The composition of the palladium-containing sewage is shown in Table 9.

[0082] Table 9 Composition of Palladium-Containing Sewage

[0083] Composition Palladium content <![CDATA[Chlorine content 1 > <![CDATA[Nitrate content 2 > <![CDATA[Sulfur content 3 > <![CDATA[Total impurity content 4 > Content / wt 50 ppm 1.3％ 1.1％ 0.7％ 7214 ppm

[0084] Note: 1. Including Cl - ; 2. Including NO3 - and NO2 - ; 3. Including SO3 2- and SO4 2- ; 4. Including Fe, Pt, Au, Na, Cu, Pb, Sn, Al, Si, Mg, Ca, Bi, Sb and Ag, etc.

[0085] 30 Kg of palladium-containing sewage was placed in a 50 L autoclave quartz reactor. Its pH was measured with a pH meter to be 7.5, and there was no need to add liquid alkali to adjust the pH value. 100 g of an aqueous solution containing 10 wt% of cesium hydrogen phthalate was added to the sewage, and the mixture was stirred at room temperature (20 °C) for 24 h. After the reaction ended, black elemental palladium was precipitated. After filtration, the precipitate was weighed and 3.2 g (containing water) of the precipitate was obtained. Next, enter the purification step: The precipitate was transferred to a beaker, and 3.2 g of aqua regia with a volume ratio of concentrated hydrochloric acid to concentrated nitric acid of 3:1 was added, and it was heated to 40 °C and dissolved for 30 min; after the dissolution ended, it was heated to 120 °C to drive off the nitric acid for 30 min until no brownish-red gas escaped; ammonia water was added dropwise to the beaker until the pH value of the solution = 12, and then a mixed acid with a mass ratio of iodic acid to citric acid of 1:1 was added until the pH value of the solution = 1. After filtration, a palladium-containing precipitate was obtained; the precipitate was transferred to a beaker and dissolved with 10 mL of ammonia water; finally, 20 g of an aqueous solution containing 10 wt% of the formate of 2-hydroxy-N,N,N-trimethyl-1-propanamine was added, and the mixture was stirred at room temperature (20 °C) for 24 h. After filtration and washing, high-purity ultrafine palladium powder could be obtained.

[0086] The ultrafine palladium powder was weighed to be 1.496 g, and the recovery rate was calculated to be 99.7%. The specific surface area of the ultrafine palladium powder obtained by BET test was 12.9 m 2 / g. The impurity content of the ultrafine palladium powder is shown in Table 10.

[0087] Table 10 Impurity Content (wt%) of Ultrafine Palladium Powder

[0088] Pd 99.96 Cu 0.003 Mg 0.005 Fe 0.002 Pb 0.001 Ca 0.002 Pt 0.004 Sn 0.006 Bi 0.002 Au 0.005 Al 0.001 Sb 0.001 Na 0.002 Si 0.005 Ag 0.001

[0089] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for recovering metallic palladium and preparing ultrafine palladium powder by using formate, characterized in that, Including the steps: (1) Prepare a palladium-containing waste liquid with a pH greater than 1.5, add formate thereto, reduce at normal temperature and pressure, dissolve the obtained solid with aqua regia, remove impurities with ammonia water, and then add acid to obtain palladium precipitate; during the impurity removal process with ammonia water, control the pH of the mixed solution to be not less than 10; during the process of adding acid to obtain palladium precipitate, control the pH of the mixed solution to be not greater than 2; (2)After the palladium precipitate is dissolved, it is reduced with formate at room temperature and atmospheric pressure to obtain ultrafine palladium powder with a specific surface area of 10 m 2 / g or more; In step (1), the formate is selected from one or several mixtures of formate of 2-hydroxy-N,N,N-trimethyl-1-propanamine, cesium hydrogen phthalate, and ammonium dithiocarbamate; In step (2), the formate is formate of 2-hydroxy-N,N,N-trimethyl-1-propanamine.

2. The method according to claim 1, wherein In steps (1) and (2), the formate is added in the form of one or more of an aqueous solution, an alcohol solution, and an acetone solution.

3. The method according to claim 1, wherein In step (1): the mass ratio of the added formate to the mass of palladium element in the palladium-containing waste liquid is 3-5:1, and the reduction time is 12-16 h; In step (2): the mass ratio of the used formate to the mass of palladium element in the palladium precipitate is 3-5:1, and the reduction time is 12-16 h.

4. The method according to claim 1, wherein In step (1): The obtained solid is dissolved with an equal mass of aqua regia; The temperature of the dissolution is 30-50 °C.

5. The method according to claim 1, wherein In step (1), a heating and nitric acid removal process is set between the aqua regia dissolution and the ammonia water impurity removal processes, the nitric acid removal temperature is 80-150 °C, and the nitric acid removal time is 0.1-2 h.

6. The method according to claim 1, wherein In step (1), the dropping rate of ammonia water during the ammonia water impurity removal process is 1-5 drops / s, and the stirring rate of the mixed solution during the dropping process of ammonia water is 200-400 rpm.

7. The method according to claim 1, characterized in that In step (1), the dropping rate of acid during the process of adding acid to obtain palladium precipitate is 1-5 drops / s, the stirring rate of the mixed solution during the dropping process of acid is 200-400 rpm, and the acid added is one or several mixtures of nitric acid, acetic acid, sulfuric acid, iodic acid, and citric acid.

8. Application of the method according to any one of claims 1-7 in recovering palladium from palladium-containing tailings, waste palladium catalysts, or palladium-containing sewage during the production process of palladium salts.

9. Use of the method according to any one of claims 1 to 7 in the preparation of high-purity ultrafine palladium powder from palladium-containing waste liquid, characterized in that, The purity of the high-purity ultrafine palladium powder is above 99.96%.