A method for dissolving rhodium powder

Abstract

The present application belongs to the technical field of noble metal, and discloses a rhodium powder dissolving method, which comprises the following steps: weighing rhodium powder and placing it in a ball mill jar for repeated ball milling; preparing heteroatom-doped carbon material through high-temperature annealing under N2 or Ar atmosphere in a tube furnace; fully grinding the prepared heteroatom-doped carbon material in an agate mortar, and then placing it in a ball mill jar containing rhodium powder, with the weight ratio of the heteroatom-doped carbon material to the rhodium powder being (8-40):1; starting the ball mill after setting the parameters of the ball mill to obtain fixed material; configuring a mixed solution according to the volume ratio of strong oxidant to strong acid being 1:1, placing the solid material and the mixed solution into a hydrothermal synthesis kettle, and placing the kettle into an oven after sealing to perform heating and dissolving. The present application adopts wet ball milling to give high energy, and uses carbon material carrier to assist noble metal dispersion, so that the particle size of the rhodium powder is successfully reduced to nanoscale, and then the rhodium powder is quickly dissolved through the method of one-step dissolving of strong acid and strong oxidant.

Description

Technical Field

[0001] This invention belongs to the field of precious metals technology, and specifically relates to a method for dissolving rhodium powder. Background Technology

[0002] Rhodium is the most valuable element among the six platinum group metals, widely used in ternary tail gas catalysts, chemical catalysts, and glass industry equipment. Rhodium compounds RhI3, Rh2(SO4)3, RhCl3, and Rh(OAc)x are important precursors for the preparation of these materials. Rhodium exhibits very stable physicochemical properties, with a boiling point of 3695.0℃ at normal pressure, and is almost insoluble in aqua regia.

[0003] Currently, the main technologies for dissolving rhodium include medium-temperature melting, high-temperature alloy fragmentation, electrochemical dissolution, and aqueous solution chlorination dissolution. However, these dissolution processes often lead to problems such as contamination by impurity metals, long processing cycles, equipment safety hazards, and low dissolution rates.

[0004] Patent CN200910073730.3 discloses a method for recovering platinum and rhodium from binary aqua regia insoluble residue, which uses barium peroxide melting to treat Pt-Rh binary network aqua regia insoluble residue. However, this process is particularly cumbersome and has low processing efficiency, and has been phased out.

[0005] Patent CN103341639A discloses a method for dissolving sparingly soluble rhodium powder, utilizing the redox reaction between chloroauric acid solution and rhodium powder under specific conditions. The rhodium powder is oxidized and dissolved to form an H3RhCl6 solution, while the chloroauric acid in the solution is reduced to form sponge gold powder. However, the raw material chloroauric acid used in this method is expensive and not suitable for large-scale application.

[0006] Patent CN106011495A discloses a method for dissolving rhodium powder, which involves mixing rhodium powder with base metal powder in a certain mass ratio; then using acid to dissolve the base metal and separating the solid and liquid phases to obtain rhodium material; finally, the obtained rhodium material is placed in an ultrasonic dissolving reactor and dissolved with aqua regia, achieving a rhodium powder dissolution rate of over 95%. This process is cumbersome, requires the introduction of base metal and aqua regia, and generates a significant amount of waste, leaving considerable room for improvement.

[0007] Patent CN111304457A discloses a highly efficient activation and dissolution method for rhodium powder. The method involves mixing rhodium powder with hydrochloric acid solution in a specific ratio and placing the mixture in a reactor. A certain amount of gold powder as an activator is added, and Cl2 is introduced at a controlled temperature of 60–112°C for 1–3 hours. The Cl2 is circulated during the dissolution process. After the Cl2 introduction is complete, the mixture is kept at a certain temperature for 10–90 minutes, then cooled to room temperature and filtered to obtain a rhodium chloride solution with a purity >99.95% and an Rh content >15%. The rhodium dissolution rate in this method is greater than 96%. However, this method requires chlorine gas as an oxidant, and the storage and use of chlorine gas pose safety hazards. Furthermore, the addition of gold powder as an activator reduces the purity of the gold powder after dissolving in the rhodium solution, resulting in a large amount of metallic impurities (gold) in the solution. This necessitates an additional gold removal process, making the process cumbersome and costly.

[0008] Patent CN114427036A discloses a method for dissolving rhodium powder and the resulting rhodium solution. The method involves pretreating the rhodium powder with concentrated sulfuric acid and concentrated nitric acid, followed by oxidizing the pretreated solution with a strong oxidizing agent to obtain a final rhodium solution. However, this method still requires a significant amount of strong acid and strong oxidizing agent, and the processing time is relatively long, thus having certain limitations.

[0009] In addition, microwave digestion involves placing precious metal materials and solvents in a sealed container and heating them with microwaves to dissolve the precious metal materials under high temperature and high pressure conditions. Its advantages include rapid heating rate, uniform heating of the material, and easy pressure control. However, this method has a small processing capacity and is not suitable for industrial production.

[0010] Therefore, it is essential to continue searching for a convenient, practical, simple, efficient, and environmentally friendly dissolution method. Summary of the Invention

[0011] Therefore, the purpose of this invention is to provide a method for dissolving rhodium powder, which uses wet ball milling and dispersion dissolution to achieve the purpose of rapidly dissolving refractory precious metals.

[0012] To achieve the aforementioned objectives, the technical solution adopted is as follows:

[0013] A method for dissolving rhodium powder includes the following steps:

[0014] S1. Weigh out rhodium powder

[0015] Weigh out the rhodium powder and place it in a ball mill jar for repeated ball milling; commercially available rhodium powder is repeatedly ground in a ball mill for short periods of time to reduce the particle size of the rhodium powder as much as possible.

[0016] S2. Preparation of heteroatom-doped carbon materials

[0017] Heteroatom-doped carbon materials are prepared by high-temperature annealing in a tube furnace under an atmosphere of N2 or Ar, wherein the temperature is controlled between 550℃ and 900℃; wherein heteroatoms refer to one or any combination of two of S, N, P, and I.

[0018] S3: Mix thoroughly and place in a ball mill jar

[0019] The heteroatom-doped carbon material obtained above was thoroughly ground in an agate mortar, and a small amount of high-boiling-point solvent was added to prevent the ball mill temperature from getting too high during operation. Then it was placed in a ball mill jar containing rhodium powder. The weight ratio of heteroatom-doped carbon material to rhodium powder was (8-40):1.

[0020] S4: Ball Mill

[0021] After setting the parameters of the ball mill, start the ball mill to obtain a fixed material through ball milling;

[0022] During ball milling, the coordination environment of Rh atoms also changes and the lattice is activated. When the particle size of noble metals can be controlled at the nanoscale, they can be dissolved in a sealed environment using a mixed solution of strong oxidant and strong acid.

[0023] By utilizing the mechanochemical energy provided by an enhanced planetary ball mill and the excellent coordination ability of elements such as S, N, P, and I with noble metals, Rh-Rh bonds are broken, transforming rhodium powder into noble metal nanoparticles dispersed on defects in a carbon support with coordination bonds of Rh-C, Rh-N, Rh-S, Rh-P, and Rh-I. In addition, the introduction of an inert gas at a certain pressure during the ball milling process can also prevent the oxidation of some rhodium powder due to the high temperature generated during the ball milling process (rhodium oxide is more stable and less soluble than rhodium powder). As the particle size of rhodium decreases from micrometers to nanometers under the action of mechanochemical energy, a carbon material with dispersed rhodium nanoparticles is finally obtained.

[0024] S5: Strong oxidant + strong acid for dissolution and solution preparation

[0025] Prepare a mixed solution with a volume ratio of strong oxidant and strong acid of 1:1, without dilution with water. Place the solid material obtained in step S4 and the mixed solution together into the polytetrafluoroethylene liner of the hydrothermal synthesis reactor, seal the reactor, and place it in an oven for heating and dissolution. The mixed solution of strong oxidant and strong acid can be dissolved in a sealed environment. The heating and dissolution temperature is 140-220℃, and the heating and dissolution time is 1-5 hours.

[0026] As a further improvement of the present invention, in step S2, the annealing temperature is 550℃~900℃, the heating rate is maintained at 5℃ / min, and the annealing time is 2~5h.

[0027] As a further improvement of the present invention, in step S2, the annealing temperature is 600-750°C and the annealing time is 2-3 hours.

[0028] As a further improvement of the present invention, in step S2, the carbon source in the heteroatom-doped carbon material is at least one of carbon nanotubes, graphene oxide, activated carbon, carbon black, carbon fiber, sucrose, cellulose, glucose, chitosan, and glucosamine hydrochloride.

[0029] As a further improvement of the present invention, in step S2, the heteroatoms in the heteroatom-doped carbon material are sourced from melamine, dicyandiamide, urea, sodium hypophosphite, triphenylphosphine, thiourea, allyl thiourea, pyrrole, thiophene, glycine, cysteine, ammonium chloride, ammonium iodide, p-phenylenediamine, and imidazole.

[0030] As a further improvement of the present invention, in step S1, 0.1g of rhodium powder is weighed and placed in a ball mill jar for repeated ball milling, and the rhodium powder has not been treated in any way after purchase.

[0031] As a further improvement of the present invention, in step S3, the weight ratio of heteroatom-doped carbon material to rhodium powder is (15-30):1.

[0032] As a further improvement of the present invention, in step S4, the rotational speed of the ball mill is selected from 100 to 1100 rpm, the rotational speed of the ball mill is selected from 200 to 2200 rpm, the material of the grinding tools inside the ball mill is one of zirconium oxide, hard stainless steel, hard alloy, and tungsten carbide, the size of the grinding balls is one of 0.5 mm, 1 mm, 3 mm, 5 mm, and 10 mm, the running time of the ball mill is 3 min to 15 min, after the set running time is completed, it needs to be paused for 30 minutes to dissipate the generated heat before it can be restarted, the number of times the ball mill is run can be selected from 5 to 40 times, the ball mill jar needs to be filled with inert gas, the filling amount of inert gas is 1 to 10 bar, the purity of the inert gas needs to reach 99.99%, and a small amount of deionized water is added in wet grinding to prevent high temperature damage to the machine.

[0033] As a further improvement of the present invention, in step S4, the rotational speed of the ball mill is selected from 500 to 750 rpm, the rotational speed of the ball mill is selected from 900 to 1400 rpm, the grinding tool inside the ball mill is made of tungsten carbide, and the size of the grinding ball is 3 mm.

[0034] As a further improvement of the present invention, in step S5, the heating and dissolving temperature is 200°C and the heating and dissolving time is 4 hours.

[0035] This invention utilizes the high-intensity energy generated during the revolution and rotation of a planetary ball mill to disrupt the original metallic bonds of noble metals and the excellent coordination and complexation capabilities of heteroatoms (S, N, P, I, etc.) on the noble metals. This ensures that the particle size of the noble metal powder is reduced and prevents it from re-aggregating into micron-sized powder. Furthermore, during the ball milling process, the coordination environment of Rh atoms also changes, and the crystal lattice is activated. When the particle size of the noble metal can be controlled at the nanometer level, it can be dissolved in a sealed environment using a mixture of a strong oxidant and a strong acid.

[0036] The beneficial effects of this invention are as follows: This invention innovatively adopts wet ball milling to impart high energy, carbon material carrier to assist in the dispersion of precious metals, so that the particle size of rhodium powder is successfully reduced to the nanoscale, and then the rhodium powder is successfully and rapidly dissolved by a one-step dissolution method of strong acid and enhanced oxidant. This invention has the following advantages: (1) The process is short, convenient and fast, and all work can be completed within 1 to 2 working days, reducing the workload and labor costs of personnel. At the same time, there is no introduction of base metal impurities and no repeated washing process of potassium ions, sodium ions, chloride ions and nitrogen oxides, which is in line with the social development goal of high efficiency, speed and cleanliness. It is applicable to a wide range of metals and has a good prospect for promotion and use; (2) The amount of strong acid used is greatly reduced, which is environmentally friendly; (3) There is no need to introduce base metals and heavy metals in the process, and there is no need to consider the reduction of precious metal purity caused by base metals. The pollution to water bodies is also small; (4) This invention has low requirements for the acid and corrosion resistance of equipment. Ball mills have been successfully applied in industry. The equipment is easy to purchase and has a good prospect for promotion. Attached Figure Description

[0037] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0038] Figure 1 This is a schematic diagram of the process of the present invention;

[0039] Figure 2 The relationship between the solubility of rhodium-loaded carbon materials and dissolution time is shown. Detailed Implementation

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0042] The first embodiment of this specification provides a method for dissolving rhodium powder, comprising the following steps:

[0043] S1. Weigh out rhodium powder

[0044] Weigh out the rhodium powder and place it in a ball mill jar for repeated ball milling; commercially available rhodium powder is repeatedly ground in a ball mill for short periods of time to reduce the particle size of the rhodium powder as much as possible.

[0045] S2. Preparation of heteroatom-doped carbon materials

[0046] Heteroatom-doped carbon materials are prepared by high-temperature annealing in a tube furnace under an atmosphere of N2 or Ar, wherein the temperature is controlled between 550℃ and 900℃; wherein heteroatoms refer to one or any combination of two of S, N, P, and I.

[0047] S3: Mix thoroughly and place in a ball mill jar

[0048] The heteroatom-doped carbon material obtained above was thoroughly ground in an agate mortar, and a small amount of high-boiling-point solvent was added to prevent the ball mill temperature from getting too high during operation. Then it was placed in a ball mill jar containing rhodium powder. The weight ratio of heteroatom-doped carbon material to rhodium powder was (8-40):1.

[0049] S4: Ball Mill

[0050] After setting the parameters of the ball mill, start the ball mill to obtain a fixed material through ball milling;

[0051] During ball milling, the coordination environment of Rh atoms also changes and the lattice is activated. When the particle size of noble metals can be controlled at the nanoscale, they can be dissolved in a sealed environment using a mixed solution of strong oxidant and strong acid.

[0052] By utilizing the mechanochemical energy provided by an enhanced planetary ball mill and the excellent coordination ability of elements such as S, N, P, and I with noble metals, Rh-Rh bonds are broken, transforming rhodium powder into noble metal nanoparticles dispersed on defects in a carbon support with coordination bonds of Rh-C, Rh-N, Rh-S, Rh-P, and Rh-I. In addition, the introduction of an inert gas at a certain pressure during the ball milling process can also prevent the oxidation of some rhodium powder due to the high temperature generated during the ball milling process (rhodium oxide is more stable and less soluble than rhodium powder). As the particle size of rhodium decreases from micrometers to nanometers under the action of mechanochemical energy, a carbon material with dispersed rhodium nanoparticles is finally obtained.

[0053] S5: Strong oxidant + strong acid for dissolution and solution preparation

[0054] Prepare a mixed solution with a volume ratio of strong oxidant and strong acid of 1:1, without dilution with water. Place the solid material obtained in step S4 and the mixed solution together into the polytetrafluoroethylene liner of the hydrothermal synthesis reactor, seal the reactor, and place it in an oven for heating and dissolution. The mixed solution of strong oxidant and strong acid can be dissolved in a sealed environment. The heating and dissolution temperature is 140-220℃, and the heating and dissolution time is 1-5 hours.

[0055] The second embodiment of this specification, based on the method for dissolving rhodium powder described in the first embodiment, involves an annealing temperature of 550℃~900℃ in step S2, a heating rate of 5℃ / min, and an annealing time of 2~5h.

[0056] According to the third embodiment of this specification, based on the second embodiment, a method for dissolving rhodium powder, in step S2, the annealing temperature is 600-750°C and the annealing time is 2-3 hours.

[0057] The fourth embodiment of this specification, according to the method for dissolving rhodium powder described in the first embodiment, in step S2, the carbon source in the heteroatom-doped carbon material is at least one of carbon nanotubes, graphene oxide, activated carbon, carbon black, carbon fiber, sucrose, cellulose, glucose, chitosan, and glucosamine hydrochloride.

[0058] According to the fifth embodiment of this specification, in the method for dissolving rhodium powder as described in the first embodiment, in step S2, the sources of heteroatoms in the heteroatom-doped carbon material are melamine, dicyandiamide, urea, sodium hypophosphite, triphenylphosphine, thiourea, allyl thiourea, pyrrole, thiophene, glycine, cysteine, ammonium chloride, ammonium iodide, p-phenylenediamine, and imidazole.

[0059] According to the sixth embodiment of this specification, based on the method for dissolving rhodium powder described in the first embodiment, in step S1, 0.1g of rhodium powder is weighed and placed in a ball mill jar for repeated ball milling, and the rhodium powder has not been treated in any way after purchase.

[0060] According to the seventh embodiment of this specification, in the method for dissolving rhodium powder as described in the first embodiment, in step S3, the weight ratio of heteroatom-doped carbon material to rhodium powder is (15-30):1.

[0061] According to the eighth embodiment of this specification, based on the first embodiment's method for dissolving rhodium powder, in step S4, the rotational speed of the ball mill is selected from 100 to 1100 rpm, the rotational speed is selected from 200 to 2200 rpm, the grinding tools inside the ball mill are made of one of zirconium oxide, hard stainless steel, hard alloy, or tungsten carbide, the size of the grinding balls is one of 0.5 mm, 1 mm, 3 mm, 5 mm, or 10 mm, the running time of the ball mill is 3 to 15 minutes, after the set running time is completed, it needs to be paused for 30 minutes to dissipate the generated heat before it can be restarted, the number of times the ball mill can be run is selected from 5 to 40 times, the grinding jar needs to be filled with inert gas, the filling amount of inert gas is 1 to 10 bar, the purity of the inert gas needs to reach 99.99%, and a small amount of deionized water is added in wet grinding to prevent high temperature damage to the machine.

[0062] According to the ninth embodiment of this specification, and the method for dissolving rhodium powder as described in the eighth embodiment, in step S4, the rotational speed of the ball mill is selected from 500 to 750 rpm, the rotational speed of the ball mill is selected from 900 to 1400 rpm, the grinding tool inside the ball mill is made of tungsten carbide, and the size of the grinding ball is 3 mm.

[0063] According to the tenth embodiment of this specification, in the method for dissolving rhodium powder as described in the first embodiment, in step S5, the heating and dissolving temperature is 200°C and the heating and dissolving time is 4 hours.

[0064] The technical solutions of the present invention described above will be further illustrated below with specific embodiments.

[0065] Example 1

[0066] S1. Weigh 0.1g of purchased Rh powder and ball mill it 3 times in a planetary ball mill for 5 minutes each time, then purge with 1 bar of nitrogen gas. Repeat this process 5 times.

[0067] S2. Using 2g of melamine, 2g of thiourea, and 5g of carbon black as precursors, mix them evenly in a mortar and spread them evenly on a quartz boat. Set the heating program and anneal at 700℃ for 3 hours in a tube furnace to obtain N and S co-doped carbon material.

[0068] S3. Weigh 3g of the heteroatom-doped carbon material prepared above, grind it thoroughly in an agate mortar, and then put it all into a ball mill jar. Put two 3mm tungsten carbide grinding balls into the jar and mix them with the rhodium powder in step 1) for ball milling.

[0069] S4. After sealing the ball mill jar, flush the inside of the jar five times with atmospheric pressure N2, and then introduce 5 bar of N2. Set the parameters: the revolution speed is set to 600 rpm, the rotation speed is set to 1000 rpm, and the running time is 5 minutes. After completion, pause for 30 minutes to allow heat dissipation, then restart the ball mill and repeat the above operation 20 times.

[0070] S5. Stop ball milling and allow the temperature to cool. Weigh 1g of the rhodium-containing carbon material obtained from ball milling and place it in a 200ml polytetrafluoroethylene-lined container. Add 30ml of concentrated sulfuric acid and 30ml of nitric acid successively. Heat in a rotary oven to 200℃ and remove after 2 hours. After filtration, washing, and weighing, 0.223g of solid residue was found. ICP testing showed that the Rh content in the solution was 4.07ppm.

[0071] Example 2

[0072] S1. Weigh 0.1g of purchased Rh powder and ball mill it 3 times in a planetary ball mill for 5 minutes each time, then purge with 1 bar of nitrogen gas. Repeat this process 5 times.

[0073] S2. Using 5g of carbon black as a precursor, mix it evenly in a mortar and spread it evenly on the right end of a quartz boat. Place 4g of ammonium iodide on the left end of the quartz boat. Prepare heteroatom-doped carbon material using chemical vapor deposition. Set the heating program and anneal at 700℃ for 3 hours in a tube furnace to obtain N and I co-doped carbon material.

[0074] S3. Weigh 3g of the heteroatom-doped carbon material prepared above, grind it thoroughly in an agate mortar, and then put it all into a ball mill jar. Put two 3mm tungsten carbide grinding balls into the jar and mix them with the rhodium powder in step 1) for ball milling.

[0075] S4. After sealing the ball mill jar, flush the inside of the jar five times with atmospheric pressure N2, and then introduce 5 bar of N2. Set the parameters: the revolution speed is set to 600 rpm, the rotation speed is set to 1000 rpm, and the running time is 5 minutes. After completion, pause for 30 minutes to allow heat dissipation, then restart the ball mill and repeat the above operation 20 times.

[0076] S5. Stop ball milling and allow the temperature to cool. Weigh 1g of the rhodium-containing carbon material obtained from ball milling and place it in a 200ml polytetrafluoroethylene-lined container. Add 30ml of concentrated sulfuric acid and 30ml of nitric acid successively. Heat in a rotary oven to 200℃ and remove after 2 hours. After filtration, washing, and weighing, 0.157g of solid residue was found. ICP testing showed that the Rh content in the solution was 4.54ppm.

[0077] Example 3

[0078] S1. Weigh 0.1g of purchased Rh powder and ball mill it 3 times in a planetary ball mill for 5 minutes each time, then purge with 1 bar of nitrogen gas. Repeat this process 5 times.

[0079] S2. Using 2g of cysteine ​​and 5g of carbon black as precursors, mix them evenly in a mortar and spread them evenly on the right end of a quartz boat. Place 2g of sodium hypophosphite on the left end of the quartz boat. Prepare heteroatom-doped carbon materials using chemical vapor deposition. Set the heating program and anneal at 700℃ for 3 hours in a tube furnace to obtain N and P co-doped carbon materials.

[0080] S3. Weigh 3g of the heteroatom-doped carbon material prepared above, grind it thoroughly in an agate mortar, and then put it all into a ball mill jar. Put two 3mm tungsten carbide grinding balls into the jar and mix them with the rhodium powder in step 1) for ball milling.

[0081] S4. After sealing the ball mill jar, flush the inside of the jar five times with atmospheric pressure N2, and then introduce 5 bar of N2. Set the parameters: the revolution speed is set to 600 rpm, the rotation speed is set to 1000 rpm, and the running time is 5 minutes. After completion, pause for 30 minutes to allow heat dissipation, then restart the ball mill and repeat the above operation 20 times.

[0082] S5. Stop ball milling and allow the temperature to cool. Weigh 1g of the rhodium-containing carbon material obtained from ball milling and place it in a 200ml polytetrafluoroethylene-lined container. Add 30ml of concentrated sulfuric acid and 30ml of nitric acid successively. Heat in a rotary oven to 200℃ and remove after 2 hours. After filtration, washing, and weighing, 0.181g of solid residue was found. ICP testing showed that the Rh content in the solution was 4.27ppm.

[0083] Comparative Example 1

[0084] S1. Weigh 0.1g of purchased Rh powder and ball mill it 3 times in a planetary ball mill for 5 minutes each time, then purge with 1 bar of nitrogen gas. Repeat this process 5 times.

[0085] S2. Place two 3mm tungsten carbide grinding balls into the grinding jar and mix them with the rhodium powder from step 1) and grind them together.

[0086] S3. After sealing the ball mill jar, flush the inside of the jar five times with atmospheric pressure N2, and then introduce 5 bar of N2. Set the parameters: the revolution speed is set to 600 rpm, the rotation speed is set to 1000 rpm, and the running time is 5 minutes. After completion, pause for 30 minutes to allow heat dissipation, then restart the ball mill and repeat the above operation 20 times.

[0087] S4. Stop ball milling and allow the temperature to cool. Weigh 1g of the rhodium-containing carbon material obtained from ball milling and place it in a 200ml polytetrafluoroethylene liner. Add 30ml of concentrated sulfuric acid and 30ml of nitric acid successively. Heat in a rotary oven to 200℃ and remove after 2 hours. After filtration, washing, and weighing, 1.006g of solid residue was found.

[0088] The solubility of rhodium powder in Examples 1-3 and Comparative Example 1 is shown in Table 1:

[0089] Table 1. Solubility of rhodium powder during ball milling under different coordination environments

[0090]

[0091] Examples 1-3 compared the coordination environment during the ball milling process of rhodium powder. As shown in Table 1, it was found that the solubility obtained by using I-doped carbon material as the dispersion matrix was higher. Since the coordination ability between Rh-I is stronger than that of other heteroatoms, the interaction ability is stronger and the dispersion effect is the best.

[0092] The comparison results of Comparative Example 1 and Examples 1-3 show that the method of using a carbon matrix to assist in the dispersion of rhodium powder during wet ball milling can reduce the particle size to the nanoscale. At the same time, the coordination environment of rhodium and the activation of the crystal lattice will also occur during high-energy ball milling. Rhodium powder treated by this method can be dissolved by using a conventional mixed solution method of strong oxidant and strong acid.

[0093] Using the N,I coordinated carbon material obtained in Example 2 as the dispersion matrix, the solubility of the ball-milled material was investigated after reacting in an oven for 0.5, 1, 2, 3, 4, and 5 hours. Specific results are as follows: Figure 2 As shown, as the reaction time increases to 4 or 5 hours, the dissolution efficiency can be maintained between 95% and 97%, therefore, the preferred dissolution time is 4 hours.

[0094] One of the key aspects of rhodium powder dissolution in this invention lies in reducing the particle size of rhodium powder from the micron level to the nanometer level and in the lattice activation of metallic rhodium during the physicochemical changes derived from different processing methods. The resulting rhodium powder sample can be dissolved without demanding equipment and reaction conditions. This invention innovatively utilizes a carbon matrix to assist in rhodium powder dispersion during wet ball milling to achieve the goal of reducing the particle size to the nanometer level. Simultaneously, changes in the coordination environment and lattice activation of rhodium also occur during high-energy ball milling. Rhodium powder treated by this method can then be dissolved using a conventional mixed solution method with a strong oxidant and a strong acid.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, component splitting or combination, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for dissolving rhodium powder, characterized in that, Includes the following steps: S1. Weigh out rhodium powder Weigh out the rhodium powder and place it in a ball mill jar for repeated ball milling; S2. Preparation of heteroatom-doped carbon materials Heteroatom-doped carbon materials are prepared by high-temperature annealing in a tube furnace under an atmosphere of N2 or Ar, wherein the temperature is controlled between 550℃ and 900℃; wherein heteroatoms refer to one or any combination of two of S, N, P, and I. S3: Mix thoroughly and place in a ball mill jar The heteroatom-doped carbon material obtained above was thoroughly ground in an agate mortar and then placed in a ball mill jar containing rhodium powder. The weight ratio of the heteroatom-doped carbon material to the rhodium powder was (8-40):

1. S4: Ball Mill After setting the parameters of the ball mill, start the ball mill to obtain a fixed material through ball milling; S5: Strong oxidant + strong acid for dissolution and solution preparation Prepare a mixed solution with a volume ratio of strong oxidant and strong acid of 1:1, without dilution with water. Place the solid material obtained in step S4 and the mixed solution together into the polytetrafluoroethylene liner of the hydrothermal synthesis kettle, seal the kettle, and place it in an oven for heating and dissolving. The heating and dissolving temperature is 140-220℃, and the heating and dissolving time is 1-5 hours.

2. The method for dissolving rhodium powder according to claim 1, characterized in that: In step S2, the annealing temperature is 550℃~900℃, the heating rate is maintained at 5℃ / min, and the annealing time is 2~5h.

3. The method for dissolving rhodium powder according to claim 2, characterized in that: In step S2, the annealing temperature is 600–750°C and the annealing time is 2–3 hours.

4. The method for dissolving rhodium powder according to claim 1, characterized in that: In step S2, the carbon source in the heteroatom-doped carbon material is at least one of carbon nanotubes, graphene oxide, activated carbon, carbon black, carbon fiber, sucrose, cellulose, glucose, chitosan, and glucosamine hydrochloride.

5. The method for dissolving rhodium powder according to claim 1, characterized in that: In step S2, the heteroatoms in the heteroatom-doped carbon material are sourced from melamine, dicyandiamide, urea, sodium hypophosphite, triphenylphosphine, thiourea, allyl thiourea, pyrrole, thiophene, glycine, cysteine, ammonium chloride, ammonium iodide, p-phenylenediamine, and imidazole.

6. The method for dissolving rhodium powder according to claim 1, characterized in that: In step S1, 0.1g of rhodium powder was weighed and placed in a ball mill jar for repeated ball milling. The rhodium powder was not processed after purchase.

7. The method for dissolving rhodium powder according to claim 1, characterized in that: In step S3, the weight ratio of heteroatom-doped carbon material to rhodium powder is (15-30):

1.

8. The method for dissolving rhodium powder according to claim 1, characterized in that: In step S4, the rotational speed of the ball mill is selected from 100 to 1100 rpm, and the rotational speed is selected from 200 to 2200 rpm. The grinding tools inside the ball mill are made of one of the following materials: zirconium oxide, hard stainless steel, hard alloy, or tungsten carbide. The size of the grinding balls is one of the following: 0.5 mm, 1 mm, 3 mm, 5 mm, or 10 mm. The running time of the ball mill is 3 to 15 minutes. After the set running time is completed, it needs to be paused for 30 minutes to dissipate the generated heat before it can be restarted. The number of times the ball mill can be run is selected from 5 to 40 times. The grinding jar needs to be filled with inert gas, with a filling amount of 1 to 10 bar and a purity of 99.99%. A small amount of deionized water is added during wet grinding to prevent high temperature damage to the machine.

9. The method for dissolving rhodium powder according to claim 8, characterized in that: In step S4, the rotational speed of the ball mill is selected from 500 to 750 rpm, the rotational speed of the ball mill is selected from 900 to 1400 rpm, the grinding tool inside the ball mill is made of tungsten carbide, and the size of the grinding ball is 3 mm.

10. The method for dissolving rhodium powder according to claim 1, characterized in that: In step S5, the heating and dissolving temperature is 200℃, and the heating and dissolving time is 4 hours.

Images