A method for selectively recovering rhodium from a sodium-potassium-rhodium solution

Abstract

The application discloses a method for selectively recovering rhodium from a sodium-potassium-rhodium-containing solution, and belongs to the technical field of precious metal separation. The method comprises the following steps: concentrating and nitrate-removing treatment of the sodium-potassium-rhodium-containing solution; adding a high-selectivity reducing agent to perform a reduction reaction, so as to obtain rhodium black precipitation; and finally, washing, drying and hydrogen reduction are performed to obtain high-purity rhodium powder. Through the synergistic effect of pH regulation and the high-selectivity reducing agent, efficient separation of rhodium and impurity ions such as sodium and potassium is realized, and co-precipitation and physical inclusion are avoided. The method has the advantages of short process, simple operation, high recovery rate, high product purity and the like, can stably prepare high-purity rhodium powder from a complex sodium-potassium-containing system, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of precious metal separation technology, specifically relating to a method for selectively reducing and recovering rhodium from sodium-potassium-rhodium solutions. Background Technology

[0002] The recovery and purification of rhodium typically employs a complexation-precipitation-reduction process. For example, ammonium chloride or similar complexing agents react with rhodium to form ammonium chlororhodate precipitate, which is then reduced to obtain rhodium powder. However, in actual industrial production, the rhodium solution to be processed often has a complex composition, especially when it contains high concentrations of sodium and potassium ions, posing a significant challenge to the stability of the aforementioned traditional processes. Research has found that high concentrations of sodium and potassium ions compete with complexing agents to form slightly soluble or insoluble chloroacidates (such as potassium chloroplatinate precipitates). Simultaneously, their strong salting-out effect significantly reduces the solubility of the rhodium complex, leading to the formation of a large amount of non-targeted precipitates during the complexation stage. These precipitates not only physically encapsulate rhodium ions, causing loss, but also severely interfere with subsequent selective precipitation and reduction processes, causing the entire recovery process to fail and significantly reducing the direct recovery rate of rhodium. Therefore, how to efficiently and selectively recover rhodium from complex rhodium solutions with high sodium and potassium content has become a pressing technical challenge in this field.

[0003] The industry has proposed a number of improved methods for the recycling of rhodium-containing materials.

[0004] For example, patent application CN114346251A discloses a reduction method for pure hydrated rhodium trichloride raw materials, which uses a double-drop addition of reducing agent in a strong alkaline system to prepare rhodium powder. However, this method is only applicable if the raw material is highly pure. If used directly on crude rhodium solution containing a large amount of sodium and potassium impurities, the strong alkaline environment easily causes co-precipitation or physical inclusion of impurity ions, which are difficult to remove deeply by conventional water washing, and the purity of the final product cannot meet the high-purity requirements. Patent application CN121496188A discloses a method for recovering and purifying metallic rhodium, which selectively precipitates rhodium using thiodiglycolic acid and ammonium salt to form (NH4) + Rhodium is precipitated by oxidation, hydrolysis, and reduction. However, the core precipitation step of this method depends on the participation of ammonium ions. When dealing with high sodium and potassium systems, a large number of sodium and potassium ions in the solution will compete with ammonium ions to generate sodium or potassium salts with completely different solubilities, resulting in incomplete or even no rhodium precipitation, and the recovery rate of rhodium is difficult to guarantee.

[0005] For example, patent application CN112705727A provides a method for preparing high-purity rhodium powder from platinum-rhodium alloys. This method achieves platinum-rhodium separation by adjusting pH and adding a coordinating agent, supplemented by multiple washing purification steps. However, the main objective of this method is to remove impurities such as platinum and base metals. Its process also involves a coordination precipitation step. For highly soluble sodium and potassium ions that are difficult to remove by conventional washing, no specific removal mechanism is designed, and it also faces the risk of decreased precipitation efficiency and impurity entrainment in high-sodium-potassium environments. Patent application CN101658942B proposes a complex multi-step method for extracting rhodium powder from waste platinum mesh, which removes impurities through sodium nitrite complexation, precipitation conversion, and ion exchange. Although this process can tolerate a certain level of salinity, its process is lengthy and cumbersome, requiring multiple precipitation-dissolution conversions and ion exchanges to achieve effective sodium-potassium separation. This results in high industrialization costs and low efficiency, failing to meet the demand for simple and efficient recycling.

[0006] In summary, existing recovery technologies for treating rhodium solutions containing high concentrations of sodium and potassium either fail due to interference from sodium and potassium in the core precipitation step, are difficult to apply industrially due to complex processes and low efficiency, or are only suitable for pure raw materials and cannot handle complex crude solutions. Therefore, developing a method with a simple process, easy operation, and high efficiency for recovering high-purity rhodium from high-sodium and potassium systems is of significant practical importance. Summary of the Invention

[0007] The technical problem to be solved by the present invention is that existing rhodium recovery methods fail to achieve efficient recovery and high-purity preparation of rhodium when processing rhodium solutions containing high concentrations of sodium and potassium due to interference from sodium and potassium ions, resulting in failure of the complexation precipitation step or low impurity removal efficiency.

[0008] The purpose of this invention is to provide a method for selectively reducing and recovering rhodium from sodium-potassium-rhodium solutions, so as to overcome the interference of sodium and potassium ions on traditional complexation precipitation processes in the prior art, and achieve efficient recovery and high-purity preparation of rhodium.

[0009] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows.

[0010] This invention provides a method for selectively reducing and recovering rhodium from a sodium-potassium-rhodium solution, comprising the following steps: S1. Concentrate the rhodium solution containing sodium or potassium, and add hydrochloric acid to remove nitrate until no yellow fumes are produced; S2. Add alkali solution to the solution obtained in step S1 to adjust the pH of the system to 7-10; S3. Heat the solution obtained in step S2 to 80~110℃, add a reducing agent with high selectivity for rhodium to carry out a reduction reaction, and after the reaction is complete, separate the solid and liquid to obtain filtrate and rhodium black precipitate; The reducing agent is selected from at least one of hydrazine hydrate, hydrazine hydrochloride, and formic acid; S4. The rhodium black precipitate obtained in step S3 is washed, dried, and then reduced in a reducing atmosphere to obtain rhodium powder.

[0011] In step S1 of the above method, the sodium or potassium-containing rhodium solution contains not less than 0.6% sodium and / or not less than 0.6% potassium.

[0012] In step S1 of the above method, the concentration is achieved by boiling at 100°C.

[0013] In step S2 of the above method, the alkaline solution is at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, or ammonia solution.

[0014] In step S3 of the above method, the reducing agent is preferably hydrazine hydrochloride.

[0015] In step S3 of the above method, the reducing agent is added in excess until the reduction reaction is complete and the rhodium content in the resulting filtrate is less than 0.5 ppm.

[0016] In step S4 of the above method, the washing is performed by washing with hot pure water at 50~70℃ at least 10 times.

[0017] In step S4 of the above method, the drying temperature is 80~90℃.

[0018] In step S4 of the above method, the reducing atmosphere is hydrogen, the reduction temperature is 500~800℃, and the reduction time is 1~5h.

[0019] The rhodium powder prepared by the above method for selective reduction and recovery of rhodium from sodium-potassium-rhodium solution has a purity of ≥99.99%, a rhodium recovery rate of ≥99.9%, and a sodium and potassium content of ≤100ppm.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention addresses the technical problems of low recovery rates and susceptibility to interference in traditional complexation processes for rhodium solutions with high sodium and potassium content. It provides a selective reduction recovery method that is simple to operate, streamlined, and yields excellent results. This method achieves highly efficient separation of rhodium from impurity ions such as sodium and potassium through the synergistic effect of concentration and denitrification, pH adjustment, and a specific reducing agent.

[0021] The core principle of this invention lies in its elimination of the complexation and precipitation step, which is easily interfered with by sodium and potassium ions. Instead, it employs a reducing agent with high selectivity for rhodium to directly reduce rhodium ions to rhodium black within an optimized pH range (7-10) and reaction temperature (80-110℃). Under these conditions, the reducing agent can accurately identify and reduce rhodium ions, while sodium and potassium ions in the solution remain chemically stable and will not be reduced, thus effectively avoiding the problems of impurity co-precipitation or physical inclusions. Simultaneously, the concentration and denitrification step completely eliminates the oxidizing interference of nitrate ions, creating a clean system environment for subsequent selective reduction.

[0022] Thanks to the aforementioned synergistic effect, the method of this invention can achieve complete reduction of rhodium, with extremely low residual rhodium content in the filtrate after reduction, eliminating the need for secondary recovery treatment and significantly shortening the production cycle. The obtained rhodium black precipitate, after washing, drying, and hydrogen reduction, yields rhodium powder with high purity and low impurity content, consistently meeting the quality requirements for high-purity rhodium powder. The entire process is simple and efficient, significantly improving the economy and feasibility of recovering high-purity rhodium from complex sodium-potassium rhodium solutions. Attached Figure Description

[0023] Figure 1 A process flow diagram for the selective reduction and recovery of rhodium from sodium-potassium-rhodium solutions. Detailed Implementation

[0024] To make the technical problems, solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with the embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as understood by one of ordinary skill in the art.

[0025] This invention provides a method for selectively reducing and recovering rhodium from sodium-potassium-rhodium solutions. It aims to solve the technical problems of existing recovery processes when handling rhodium solutions containing high concentrations of sodium and potassium ions, where interference from sodium and potassium leads to failure of the complexation-precipitation step, low recovery rates, and substandard product purity. The overall concept of this invention is to abandon the traditional complexation-precipitation step, which is easily interfered with by sodium and potassium ions, and instead employ a reducing agent with high selectivity for rhodium. Under optimized pH and temperature conditions, rhodium ions are directly reduced from the complex system to rhodium black, thereby achieving efficient separation of rhodium from impurity ions such as sodium and potassium.

[0026] A schematic diagram of the process flow for the selective reduction and recovery of rhodium from a sodium-potassium-rhodium solution according to the present invention is shown below. Figure 1 As shown below, the technical solution of the present invention will be described in detail with reference to specific steps.

[0027] S1, Concentrated Nitrate Removal: The rhodium solution containing sodium or potassium is concentrated, and hydrochloric acid is added for denitrification treatment until no yellow fumes are produced. Preferably, the concentration is achieved by boiling at 100°C.

[0028] The purpose of this step is to remove nitrate ions from the rhodium solution, eliminating their oxidizing interference with subsequent reduction reactions. Sodium-potassium rhodium solutions typically originate from nitric acid systems (such as solutions obtained after dissolving precious metals in aqua regia), which contain a large amount of nitrate ions. If nitrate ions are not completely removed, the residual nitrate ions will undergo a violent redox reaction with the reducing agent (especially hydrazine-based reducing agents) in the subsequent heating reduction step. This not only consumes a large amount of reducing agent, leading to incomplete rhodium reduction, but may also pose safety risks due to runaway reactions. Simultaneously, the presence of nitrate ions also affects the reduction reaction potential, reducing the selectivity of the reducing agent for rhodium. This step involves adding hydrochloric acid and heating to boiling, causing nitrate ions to escape as nitrogen oxides such as NO and NO2 (manifested as the production of yellow fumes). The process continues until no more yellow fumes are produced, indicating that the nitrate ions have been largely removed, creating a clean system environment for subsequent selective reduction.

[0029] S2, Adjust pH: Add an alkaline solution to the solution obtained in step S1 to adjust the pH of the system to 7-10. Preferably, the alkaline solution is at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, or ammonia solution; adjust the pH of the system to 9.

[0030] The purpose of this step is to adjust the solution pH to a suitable range for the reduction reaction and to suppress the co-precipitation of impurity ions. Studies have found that when the pH is below 7, the driving force for the reduction reaction is insufficient, resulting in incomplete reduction of rhodium ions and a decrease in yield. Conversely, when the pH is above 10, the strongly alkaline environment may cause small amounts of residual base metal ions (such as iron and aluminum) and high concentrations of sodium and potassium ions in the solution to precipitate as hydroxides or basic salts. These precipitates become physically trapped in the subsequently generated rhodium black particles, making them difficult to remove through conventional washing and ultimately affecting product purity. Maintaining the pH within a neutral to slightly alkaline range of 7-10 ensures that the reducing agent has sufficient activity to completely reduce rhodium while effectively preventing the large-scale co-precipitation of impurity ions such as sodium and potassium due to drastic pH changes. This is a crucial prerequisite for achieving selective reduction.

[0031] S3, Selective Reduction The solution obtained in step S2 is heated to 80-110°C, and a reducing agent with high selectivity for rhodium is added to carry out a reduction reaction. After the reaction is complete, the solid and liquid are separated to obtain a filtrate and a rhodium black precipitate. The reducing agent is selected from at least one of hydrazine hydrate, hydrazine hydrochloride, and formic acid. Preferably, the reducing agent is hydrazine hydrochloride.

[0032] This step is the core of this invention for achieving efficient separation of rhodium from sodium and potassium. Its principle lies in utilizing the high selectivity of a specific reducing agent under optimized conditions. Under heating conditions of 80-110°C, the reducing activity of the reducing agent is fully activated, effectively attacking rhodium ions (typically in the form of Rh). 3+ It exists in its original form and is reduced to a metallic element (Rh). Sodium ions (Na) exist in this form and are reduced to their metallic form. + ) and potassium ions (K + The reduction potential of sodium ions is much lower than that of rhodium, making them extremely stable in this reaction system. They will not be reduced and thus remain in solution in ionic form. This reduction-separation mechanism fundamentally avoids the problems of sodium and potassium ions participating in the reaction to form precipitates or interfering with the complexation equilibrium, which are present in traditional complexation-precipitation processes.

[0033] The reducing agent is selected from hydrazine hydrate, hydrazine hydrochloride, and formic acid. These reducing agents share the characteristics of strong reducing power and "clean" reduction products (such as nitrogen, water, and carbon dioxide), which do not introduce new metallic impurities into the system. Among them, hydrazine hydrochloride is a more preferred reducing agent in this invention. Compared to alkaline hydrazine hydrate, hydrazine hydrochloride aqueous solution is acidic. When treating the solution to be reduced with a pH of 7-10, it will not cause a drastic increase in local pH, further reducing the risk of sodium and potassium ions co-precipitating in the form of hydroxide crystals. Furthermore, hydrazine hydrochloride is not a hazardous chemical, making its use and control safer and more convenient.

[0034] The amount of reducing agent added should be sufficient to ensure complete reduction of rhodium. In practice, the reducing agent can be continuously added until the reaction is complete (e.g., observe the reaction until no new bubbles are produced or the solution becomes clear and transparent), ensuring that the reducing agent is in excess. After the reduction reaction is complete, rhodium precipitates out as a black precipitate (rhodium black), while sodium and potassium ions remain in the liquid phase. Solid-liquid separation can then be performed to achieve efficient separation of rhodium from sodium and potassium impurities. Testing shows that after reduction using the method of this invention, the residual rhodium content in the filtrate can be less than 0.5 ppm, indicating that the reduction of rhodium is extremely thorough, eliminating the need for secondary recovery treatment of the filtrate and significantly shortening the production cycle.

[0035] S4. Post-processing: The rhodium black precipitate obtained in step S3 is washed, dried, and then reduced in a reducing atmosphere to obtain rhodium powder.

[0036] The purpose of this step is to further remove trace impurity ions that may be physically adsorbed on the surface of rhodium black, and to convert rhodium black into dense metallic rhodium powder. The specific operation is as follows: Washing: Wash the rhodium black precipitate at least 10 times with hot pure water at 50-70℃. Although the reduction step has separated most of the sodium and potassium ions into the liquid phase, a small amount of solution may adhere to the surface of the rhodium black particles or be trapped in the interparticle spaces. Washing with hot pure water can improve the solubility and diffusion rate of impurities. Multiple washes can thoroughly remove these physically adsorbed sodium and potassium salts and other soluble impurities, ensuring the purity of the final product.

[0037] Drying: The washed rhodium black is dried at 80~90℃ to remove moisture, which facilitates subsequent reduction treatment.

[0038] Hydrogen reduction: The dried rhodium black is reduced in a reducing atmosphere. Preferably, the reducing atmosphere is hydrogen, the reduction temperature is 500-800℃, and the reduction time is 1-5 hours. The purpose of this step is to completely reduce the rhodium black (which has high reactivity; in air, especially during drying, a small amount of rhodium black on the surface is easily oxidized by oxygen in the air, turning into metal oxides) to elemental rhodium. Simultaneously, high-temperature heat treatment causes the rhodium powder particles to grow appropriately, resulting in high-purity rhodium powder with a metallic luster that meets product specifications. This step is a conventional refining method in the art, but combined with the deep purification steps of this invention, it can ultimately yield a rhodium product that meets high-purity standards.

[0039] Through the synergistic combination of the above steps, the method of this invention can achieve efficient recovery and high-purity preparation of rhodium from complex rhodium solutions containing high concentrations of sodium and potassium. This method is concise and easy to operate, with a recovery rate exceeding 99.9% and a rhodium powder purity exceeding 99.99%. The content of impurities such as sodium and potassium can be effectively controlled at extremely low levels, demonstrating promising prospects for industrial application.

[0040] The following specific embodiments will be provided to explain the solution of the present invention. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0041] Example 1 The compositional analysis results of the sodium-potassium-rhodium solution used in this embodiment are as follows: sodium content is 0.6017%, potassium content is 0.6508%; the analysis results of other major impurities are shown in Table 1.

[0042] Table 1. Content of major impurity elements in sodium, potassium, and rhodium solutions (%)

[0043] The selective reduction and recovery of rhodium from the above-mentioned sodium-potassium-rhodium solution specifically includes the following steps: S1. Concentration and Nitrate Removal: Take the above-mentioned high sodium and potassium content rhodium solution, boil it at 100°C to concentrate it, and add hydrochloric acid to remove nitrate until no yellow fumes are produced in the solution.

[0044] S2. Adjust pH: Add saturated sodium hydroxide solution to the concentrated denitrification solution obtained in step S1 to adjust the pH value of the system to 9, and continue stirring until homogeneous.

[0045] S3. Selective Reduction: The solution obtained in step S2 is heated to 90°C under continuous stirring, and then excess hydrazine hydrochloride is added to carry out a reduction reaction, reducing rhodium ions in the rhodium solution to rhodium black precipitate. After the reaction is complete, solid-liquid separation is performed to obtain filtrate and rhodium black precipitate. Testing shows that the rhodium content in the filtrate is <0.5ppm, indicating that the rhodium reduction is extremely thorough. Therefore, no further recovery treatment of the filtrate is required, and it can be directly discharged, significantly shortening the production cycle.

[0046] S4. Washing and Drying: The rhodium black precipitate obtained in step S3 is washed 10 times with hot pure water at 60°C to remove any impurity ions that may be physically adsorbed. The washed rhodium black precipitate is then placed in an oven and dried at 85°C.

[0047] S5. Hydrogen Reduction: The dried rhodium black is transferred to a hydrogen reduction furnace and reduced with hydrogen at 550°C for 2 hours to obtain rhodium powder.

[0048] The rhodium powder prepared in this embodiment was tested and found to meet the purity requirements of 99.99% in GB / T 1421-2018 standard, with sodium and potassium contents both ≤100ppm; the analysis results of other major impurities are shown in Table 2.

[0049] Table 2. Content of major impurity elements in rhodium powder (%)

[0050] A comparison of Tables 1 and 2 shows that the method in this embodiment starts from a complex crude rhodium solution containing large amounts of sodium and potassium (0.6017% sodium, 0.6508% potassium) and other impurities (total impurities 0.35%). Through the synergistic combination of steps such as concentration and denitrification, pH adjustment, selective reduction with hydrazine hydrochloride, washing, and hydrogen reduction, high-purity rhodium powder with a purity of up to 99.99% was successfully prepared. The sodium and potassium content was reduced from thousands of ppm in the raw material to ≤100 ppm in the product, achieving a removal rate of over 98%. Other base metal impurities such as iron, nickel, aluminum, and lead were also deeply removed, and the content of all impurity elements in the product was far below the national standard limits. The results indicate that the method of this invention has extremely high selective separation capability for interfering impurities such as sodium and potassium, and can achieve efficient recovery and deep purification of rhodium from complex high-sodium-potassium systems, demonstrating significant industrial application value.

[0051] Comparative Example 1 This comparative example uses the exact same high-sodium, potassium, and rhodium solution as Example 1 (sodium content 0.6017%, potassium content 0.6508%, and other impurities are listed in Table 1). The only difference in the process flow compared to Example 1 is the pH value adjusted in step S2; all other operating steps are the same as in Example 1. The specific steps are as follows: S1. Concentration and Nitrate Removal: Take the above-mentioned high sodium and potassium content rhodium solution, boil it at 100°C to concentrate it, and add hydrochloric acid to remove nitrate until no yellow fumes are produced in the solution.

[0052] S2. Adjust pH: Add saturated sodium hydroxide solution to the concentrated denitrification solution obtained in step S1 to adjust the pH value of the system to 5, and continue to stir until homogeneous.

[0053] S3. Selective Reduction: The solution obtained in step S2 was heated to 90°C with continuous stirring, and hydrazine hydrochloride was added to initiate a reduction reaction. During the experiment, it was observed that the reduction reaction proceeded slowly, with the solution changing color from wine red to brown to dark green to black. The solution never became clear and transparent. Compared to Example 1, a much larger excess of reducing agent was required to complete the reaction, and the reaction time increased dramatically. After the reaction was complete, solid-liquid separation was performed, yielding a filtrate and a rhodium black precipitate.

[0054] S4. Washing and drying: Wash the rhodium black precipitate obtained in step S3 with hot pure water at 60°C 10 times, and dry it in an oven at 85°C.

[0055] S5, Hydrogen Reduction: The dried rhodium black is transferred to a hydrogen reduction furnace and reduced with hydrogen at 550°C for 2 hours to obtain rhodium powder product.

[0056] Testing revealed that the rhodium content in the filtrate obtained in this comparative example was approximately 185 ppm, indicating that the reduction of rhodium was incomplete. Some rhodium ions were not completely reduced to elemental metal and remained in the filtrate, requiring secondary recovery to meet emission standards. The final rhodium powder obtained had a purity of only 99.98%, with sodium and potassium contents both ≤100 ppm. The analysis results of other major impurities are shown in Table 3.

[0057] Table 3. Content of major impurity elements in rhodium powder (%)

[0058] The comparison results between this comparative example and Example 1 show that when the pH value is below the lower limit of the range required by this invention, the driving force of the reduction reaction is significantly insufficient. Specifically, the reaction rate decreases significantly, requiring excessive addition of reducing agent to carry out the reaction; incomplete reduction leads to an increase in the rhodium content in the filtrate, resulting in rhodium loss. Meanwhile, as shown in Table 3, the content of various impurity elements in the final rhodium powder exceeds the limit requirement of 99.99% grade in the GB / T 1421-2018 standard, and the product purity is 99.98%.

[0059] Comparative Example 2 This comparative example uses the exact same high-sodium, potassium, and rhodium solution as Example 1 (sodium content 0.6017%, potassium content 0.6508%, and other impurities are listed in Table 1). The only difference in the process flow compared to Example 1 is the pH value adjusted in step S2; all other operating steps are the same as in Example 1. The specific steps are as follows: S1. Concentration and Nitrate Removal: Take the above-mentioned high sodium and potassium content rhodium solution, boil it at 100°C to concentrate it, and add hydrochloric acid to remove nitrate until no yellow fumes are produced in the solution.

[0060] S2. Adjust pH: Add saturated sodium hydroxide solution to the concentrated denitrification solution obtained in step S1 to adjust the pH value of the system to 12, and continue to stir until homogeneous.

[0061] S3. Selective Reduction: The solution obtained in step S2 was heated to 90°C with continuous stirring, and hydrazine hydrochloride was added to initiate the reduction reaction. During the experiment, it was observed that the reaction proceeded vigorously, producing a large number of bubbles, posing a risk of overflow. After the reaction was complete, solid-liquid separation was performed, yielding a filtrate and a rhodium black precipitate.

[0062] S4. Washing and drying: Wash the rhodium black precipitate obtained in step S3 with hot pure water at 60°C 10 times, and dry it in an oven at 85°C.

[0063] S5, Hydrogen Reduction: The dried rhodium black is transferred to a hydrogen reduction furnace and reduced with hydrogen at 550°C for 2 hours to obtain rhodium powder product.

[0064] The rhodium content in the filtrate obtained from the initial filtration in this comparative example was approximately 0.1 ppm. The final rhodium powder had a purity of only 99.96%, with sodium content ≤480 ppm and potassium content ≤220 ppm; the analysis results of other major impurities are shown in Table 4.

[0065] Table 4. Content of major impurity elements in rhodium powder (%)

[0066] The comparison results between this comparative example and Example 1 show that when the pH value is higher than the upper limit of the range required by the present invention, the strong alkaline environment causes the reduction reaction to be too violent. During the formation of the rhodium black precipitate, a large amount of sodium and potassium ions in the solution are physically adsorbed and mixed, which ultimately leads to a serious over-standard sodium and potassium content in the product. At the same time, as shown in Table 4, the content of various impurity elements in the final rhodium powder is also significantly increased, and the product purity is only 99.96%, which fails to meet the quality requirements of high-purity rhodium powder.

Claims

1. A method for selectively reducing and recovering rhodium from a sodium-potassium-rhodium solution, characterized in that, Includes the following steps: S1. Concentrate the rhodium solution containing sodium or potassium, and add hydrochloric acid to remove nitrate until no yellow fumes are produced; S2. Add alkali solution to the solution obtained in step S1 to adjust the pH of the system to 7-10; S3. Heat the solution obtained in step S2 to 80~110℃, add a reducing agent with high selectivity for rhodium to carry out a reduction reaction, and after the reaction is complete, separate the solid and liquid to obtain filtrate and rhodium black precipitate; The reducing agent is selected from at least one of hydrazine hydrate, hydrazine hydrochloride, and formic acid; S4. The rhodium black precipitate obtained in step S3 is washed, dried, and then reduced in a reducing atmosphere to obtain rhodium powder.

2. The method according to claim 1, characterized in that: In step S1, the sodium or potassium-containing rhodium solution contains a sodium content of not less than 0.6% and a potassium content of not less than 0.6%.

3. The method according to claim 1, characterized in that: In step S1, the concentration is achieved by boiling at 100°C.

4. The method according to claim 1, characterized in that: In step S2, the alkaline solution is at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, or ammonia solution.

5. The method according to claim 1, characterized in that: In step S3, the reducing agent is hydrazine hydrochloride.

6. The method according to claim 1, characterized in that: In step S3, the reducing agent is added in excess until the reduction reaction is complete and the rhodium content in the resulting filtrate is less than 0.5 ppm.

7. The method according to claim 1, characterized in that: In step S4, the washing process involves washing with hot pure water at 50-70°C at least 10 times.

8. The method according to claim 1, characterized in that: In step S4, the drying temperature is 80~90℃.

9. The method according to claim 1, characterized in that: In step S4, the reducing atmosphere is hydrogen, the reduction temperature is 500~800℃, and the reduction time is 1~5h.

10. The method according to any one of claims 1 to 9, characterized in that: The rhodium powder prepared by the method has a purity of ≥99.99%, a rhodium recovery rate of ≥99.9%, and a sodium and potassium content of ≤100ppm.

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