Method for recovering and purifying metal rhodium

Abstract

This application relates to the technical field of precious metal recovery and purification, and in particular to a method for recovering and purifying metallic rhodium, comprising the following steps: S1, adjusting the pH of the rhodium leaching solution, heating, adding a reducing agent, reacting and filtering to obtain a primary impurity-removed solution; S2, controlling the pH of the primary impurity-removed solution at 1.5-2, heating, adding thiodiglycolic acid and ammonium salt, reacting and separating the solid and liquid to obtain a primary rhodium-containing precipitate; S3, dispersing the primary rhodium-containing precipitate in an acidic solution, adding a strong oxidizing agent, heating and refluxing, adjusting the pH to 6-7 to obtain a secondary rhodium-containing precipitate; S4, dispersing the secondary rhodium-containing precipitate in a solution with a pH of 13-14 to form a slurry, adding a reducing agent, reducing the reaction at 90-100℃, separating the solid and liquid to obtain a tertiary rhodium-containing precipitate; S5, calcining the tertiary rhodium-containing precipitate and then reducing it with hydrogen to obtain metallic rhodium; this method has the advantages of improving rhodium recovery efficiency and reducing environmental impact.

Description

Technical Field

[0001] This application relates to the technical field of precious metal recycling and purification, and in particular to a method for recycling and purifying rhodium. Background Technology

[0002] Rhodium plays a vital role in industrial production, primarily used as an automotive exhaust catalyst, hydrogenation catalyst, thermocouple, and platinum-rhodium alloy. It is also used in gemstone polishing and electrical contact components, and as a coating for other metals. As a precious metal belonging to the platinum group, rhodium requires recycling and purification to obtain its pure form. Separating rhodium from other precious and base metals has always been a challenge in precious metal recycling and purification.

[0003] The commonly used purification method is the diethylenetriamine selective rhodium precipitation separation method. This method removes base metals such as sodium, potassium, aluminum, iron, and nickel by precipitating rhodium with diethylenetriamine. The resulting rhodium slag is dissolved in aqua regia, and then reduced to rhodium black through extraction with platinum and palladium and hydrazine hydrate. Metallic rhodium is then obtained through hydrogen reduction. However, the use of aqua regia presents significant pollution problems. The high complexation strength between diethylenetriamine and rhodium affects the reduction of rhodium, requiring multiple repetitions to obtain a high-purity rhodium product. Therefore, further research is needed on rhodium recovery. Summary of the Invention

[0004] In order to improve the efficiency of rhodium recovery and reduce the pressure on the environment, this application provides a method for recovering and purifying metallic rhodium.

[0005] In a first aspect, this application provides a method for recovering and purifying metallic rhodium, employing the following technical solution:

[0006] A method for recovering and purifying metallic rhodium, comprising the following steps:

[0007] S1. Adjust the pH of the rhodium leaching solution to 1-2 with alkali, heat it to 80-90℃, add excess reducing agent, stir the reaction and filter to obtain the first impurity removal solution and filter residue.

[0008] S2. Control the pH of the primary impurity removal solution at 1.5-2, heat it to 60-80℃, then add excess thiodiglycolic acid and ammonium salt, stir the reaction and cool, then separate the solid and liquid to obtain a primary rhodium-containing precipitate and filtrate.

[0009] S3. Disperse the primary rhodium-containing precipitate in an acidic solution with a pH ≤ 0.5, add an excess of strong oxidant, heat to 85-95℃ for reflux reaction, then adjust the pH to 6-7, cool, and separate the solid and liquid to obtain a secondary rhodium-containing precipitate.

[0010] S4. The secondary rhodium-containing precipitate is dispersed in sodium hydroxide or potassium hydroxide at pH 13-14 and slurried. Excess reducing agent is added, and the reduction reaction is carried out at 90-100℃. After cooling, the solid and liquid are separated, and the precipitate is washed to obtain the tertiary rhodium-containing precipitate.

[0011] S5. After calcining the three rhodium-containing precipitates at 600-700℃, reduce them with hydrogen at 650-750℃ to obtain metallic rhodium.

[0012] By adopting the above technical solution, firstly, by reducing with hydrazine hydrochloride under acidic conditions, impurities such as gold, silver, and tungsten in the rhodium leaching solution can be removed, thus removing the main obstacle to the subsequent deep purification of rhodium and avoiding interference from these impurities with the subsequent selective precipitation reaction. Secondly, by replacing the traditional sulfite with thiodiglycolic acid, the selective coordination to rhodium can be improved. Under acidic conditions, the thioether bond in thiodiglycolic acid acts as a soft base and has a very strong specific coordination ability to the soft acidic trivalent rhodium ion. In addition, a carboxylic acid group in its molecular structure can also participate in coordination, forming a stable five-membered ring chelate. The addition of ammonium salt for co-precipitation allows the ammonium salt to chelate with the TGA-Rh anion to form an insoluble salt, namely a stable (NH4)3[Rh(TGA)3] precipitate, which greatly improves the precipitation rate of rhodium and makes it excellent for separating from other metal impurities in the solution.

[0013] Then, under the oxidation of a strong oxidizing agent, the structure of (NH4)3[Rh(TGA)3] collapses. Firstly, this completely destroys the structure of its organic ligands, oxidizing them to sulfate, carbon dioxide, water, etc. Secondly, it oxidizes rhodium from trivalent to tetravalent. After adjusting the pH to near neutral, the tetravalent rhodium hydrolyzes to form hydrated rhodium dioxide. This step effectively removes metallic impurities with properties similar to rhodium. Furthermore, combining the dissolution and oxidation of this (NH4)3[Rh(TGA)3] precipitate into one step reduces the amount of acid used, lessens environmental impact, and improves the efficiency and cost of recovery and purification. Then, through calcination and reduction, a metallic rhodium product with a purity ≥99.95% and a direct recovery rate of 98.51% can be obtained.

[0014] Preferably, in step S2, the amount of thiodiglycolic acid and the ammonium salt added is 1.1-2 times the theoretical molar amount required for the reaction with rhodium ions in the rhodium leaching solution.

[0015] Preferably, in step S2, the amount of thiodiglycolic acid and the ammonium salt added is 1.1-1.5 times the theoretical molar amount required for the reaction of rhodium ions in the rhodium leaching solution.

[0016] By adopting the above technical solution and limiting the amount of thiodiglycolic acid and ammonium salt added, the full precipitation of rhodium can be ensured, guaranteeing a high direct recovery rate. Furthermore, limiting the amount to 1.1-1.5 times the theoretical amount can ensure a high rhodium recovery rate while saving raw material costs.

[0017] Preferably, the ammonium salt in S2 is one or both of ammonium sulfate and ammonium chloride.

[0018] By adopting the above technical solution, this type of ammonium salt, as a raw material, is inexpensive, readily available, stable, and highly water-soluble. It can effectively provide ammonium ions, promote precipitation, and ensure the stability and reliability of the process.

[0019] Preferably, in step S2, the stirring reaction time is 60-90 min.

[0020] By adopting the above technical solution, the reaction time of S2 is limited to 60-90 minutes, based on the optimization of the coordination precipitation reaction kinetics. Too short a time may result in incomplete reaction; too long a time is not beneficial for increasing production capacity. This time range ensures the reaction proceeds fully, balancing efficiency and effectiveness.

[0021] Preferably, the strong oxidant in S3 is sodium bromate.

[0022] Preferably, the amount of sodium bromate added is 1.1-1.4 times the theoretical amount.

[0023] By employing the above technical solution, sodium bromate, under acidic conditions, acts as a strong oxidizing agent, ensuring the complete oxidation of Rh(III) to Rh(IV) and the complete decomposition of TGA ligands. Compared to sodium chlorate, the reaction of sodium bromate is relatively easier to control, and its reduction product is sodium bromide, which has lower toxicity. Precise dosage control avoids equipment corrosion problems that may result from over-oxidation and also ensures the economic efficiency of the oxidation step.

[0024] Preferably, in step S3, the reflux reaction time is 2-3 hours.

[0025] By employing the above technical solution, a reflux time of 2-3 hours ensures the full progress of the oxidation and hydrolysis reactions. Under reflux conditions, this duration is sufficient to complete ligand decomposition, rhodium valence transformation, and the precipitation and growth of hydrated oxides, which is crucial for obtaining good purification results and precipitation properties.

[0026] Preferably, the reducing agent in S4 is hydrazine hydrate.

[0027] Preferably, the amount of hydrazine hydrate used is 1.5-2.5 times the theoretical amount.

[0028] By employing the above technical solution, hydrazine hydrate can efficiently reduce RhO2 to metallic rhodium black, with the oxidation products being nitrogen gas and water, without introducing new impurity ions into the system. Hydrazine hydrate reduction is a commonly used technique in precious metal refining, with a mature and reliable process; a suitable excess can ensure relatively complete reduction.

[0029] In summary, this application includes at least one of the following beneficial technical effects:

[0030] 1. This application first removes impurities such as gold, silver, and tungsten from the rhodium leaching solution by reduction with hydrazine hydrochloride under acidic conditions, thus removing a major obstacle to the subsequent deep purification of rhodium and avoiding interference from these impurities in the subsequent selective precipitation reaction. Then, by replacing the traditional sulfite with thiodiglycolic acid, the selective coordination to rhodium can be improved. Under acidic conditions, the thioether bond in thiodiglycolic acid acts as a soft base and has a very strong specific coordination ability to the soft acidic trivalent rhodium ion. In addition, a carboxylic acid group in its molecular structure can also participate in coordination, forming a stable five-membered ring chelate. The addition of ammonium salt for co-precipitation allows the ammonium salt to chelate with the TGA-Rh anion to form an insoluble salt, namely a stable (NH4)3[Rh(TGA)3] precipitate, which greatly improves the precipitation rate of rhodium and makes it excellent for separating from other metal impurities in the solution.

[0031] 2. Under the oxidation of strong oxidizing agents, the structure of (NH4)3[Rh(TGA)3] collapses. Firstly, it completely destroys the structure of its organic ligands, oxidizing them to sulfate, carbon dioxide, water, etc. Secondly, it oxidizes rhodium from trivalent to tetravalent. After adjusting the pH to near neutral, the tetravalent rhodium hydrolyzes to form hydrated rhodium dioxide. This step effectively removes metallic impurities with properties similar to rhodium. Furthermore, combining the dissolution and oxidation of this (NH4)3[Rh(TGA)3] precipitate into one step reduces the amount of acid used, lessens environmental impact, and improves the efficiency and cost of recovery and purification. Then, through calcination and reduction, a metallic rhodium product with a purity ≥99.95% and a direct recovery rate of 98.51% can be obtained. Detailed Implementation

[0032] The following provides a more detailed description of this application in conjunction with specific details.

[0033] raw material

[0034] All raw materials used in the embodiments of this application are common commercially available products. The main component contents of the rhodium leaching solution are shown in Table 1.

[0035] Table 1. Content of major components in rhodium leaching solution (g / L)

[0036] Example

[0037] Example 1

[0038] A method for recovering and purifying metallic rhodium, the specific steps of which are as follows:

[0039] S1. Take 500 mL of rhodium leaching solution, adjust the pH to 1.5 with alkaline solution (sodium hydroxide solution), heat to 85℃, add hydrazine hydrochloride, stir and react for 1.5 h, and separate the solid and liquid to obtain the first-stage purified solution and filter residue; the filter residue mainly contains impurities such as gold, silver, and tungsten.

[0040] The amount of hydrazine hydrochloride used is five times the theoretical molar amount of hydrazine hydrochloride required for the reduction of gold and silver ions in the rhodium leaching solution. This amount can remove impurities such as gold, silver, and tungsten to the maximum extent.

[0041] S2. The pH of the primary impurity removal solution was controlled to 2 by sodium hydroxide, the temperature was raised to 60℃, and then excess thiodiglycolic acid and ammonium chloride were added simultaneously. The mixture was stirred for 90 min, cooled, and the solid and liquid were separated to obtain a primary rhodium-containing precipitate and filtrate. The primary rhodium-containing precipitate was (NH4)3[Rh(TGA)3].

[0042] The amount of thiodiglycolic acid and ammonium chloride added is 1.5 times the theoretical molar amount required for complete rhodium precipitation;

[0043] S3. Disperse the primary rhodium-containing precipitate in a hydrochloric acid solution with a pH of 0.5 (solid-liquid mass ratio of 1:6), add sodium bromate, heat to 90℃ for reflux reaction, reflux reaction time is 3h, add sodium hydroxide dropwise to adjust pH to 6, cool to below 30℃, separate solid and liquid to obtain a secondary rhodium-containing precipitate, the secondary rhodium-containing precipitate is hydrated rhodium dioxide.

[0044] Among them, (NH4)3[Rh(TGA)3] is oxidized and decomposed by sodium bromate, and its ligands are oxidized to sulfate, carbon dioxide and water, and trivalent rhodium is oxidized to tetravalent rhodium; the amount of sodium bromate used is 1.4 times the theoretical amount.

[0045] S4. The secondary rhodium-containing precipitate was dispersed in a sodium hydroxide solution with a pH of 13.5 and slurried (solid-liquid mass ratio of 1:4). Excess hydrazine hydrate was added, and the mixture was reduced at 95°C for 3 hours. After cooling to 30°C, the solid and liquid were separated to obtain the precipitate. The precipitate was boiled and washed with hydrochloric acid solution with a pH of 3, and then washed with water until neutral to obtain the tertiary rhodium-containing precipitate (rhodium black).

[0046] Among them, hydrazine hydrate is twice the theoretical molar amount;

[0047] S5. The three rhodium-containing precipitates were calcined at 650℃ for 2 hours, and then reduced at 700℃ for 3 hours in a hydrogen reduction furnace (the hydrogen reduction furnace contains a mixture of hydrogen and nitrogen gas with a hydrogen content of 5%) to obtain metallic rhodium.

[0048] Example 2

[0049] A method for recovering and purifying metallic rhodium, the specific steps of which are as follows:

[0050] S1. Take 500 mL of rhodium leaching solution, adjust the pH to 1 with alkaline solution (sodium hydroxide solution), heat to 80℃, add hydrazine hydrochloride, stir and react for 2 hours, and separate the solid and liquid to obtain the first-stage impurity-removed solution and filter residue; the filter residue mainly contains impurities such as gold, silver, and tungsten.

[0051] The amount of hydrazine hydrochloride used is three times the theoretical molar amount of hydrazine hydrochloride required for the reduction of gold and silver ions in the rhodium leaching solution. This amount can remove impurities such as gold, silver, and tungsten to the maximum extent.

[0052] S2. The pH of the primary impurity removal solution was controlled to 1.5 using sodium hydroxide. The temperature was raised to 70°C, and then excess thiodiglycolic acid and ammonium chloride were added simultaneously. The mixture was stirred for 60 min, cooled, and the solid and liquid were separated to obtain a primary rhodium-containing precipitate and filtrate. The primary rhodium-containing precipitate was (NH4)3[Rh(TGA)3].

[0053] The amount of thiodiglycolic acid and ammonium chloride added is 1.1 times the theoretical molar amount required for complete rhodium precipitation;

[0054] S3. The primary rhodium-containing precipitate was dispersed in a hydrochloric acid solution with a pH of 0.4 (solid-liquid mass ratio of 1:5), sodium bromate was added, and the temperature was raised to 95°C for reflux reaction for 2.5 h. Sodium hydroxide was added dropwise to adjust the pH to 7, and the solution was cooled to below 30°C. The solid and liquid were separated to obtain a secondary rhodium-containing precipitate, which was hydrated rhodium dioxide.

[0055] Among them, (NH4)3[Rh(TGA)3] is oxidized and decomposed by sodium bromate, and its ligands are oxidized to sulfate, carbon dioxide and water, and trivalent rhodium is oxidized to tetravalent rhodium; the amount of sodium bromate used is 1.2 times the theoretical amount.

[0056] S4. The secondary rhodium-containing precipitate was dispersed in a sodium hydroxide solution with a pH of 13 and slurried (solid-liquid mass ratio of 1:5). Excess hydrazine hydrate was added, and the mixture was reduced at 90°C for 3.5 h. After cooling to 30°C, the solid and liquid were separated to obtain the precipitate. The precipitate was boiled and washed with hydrochloric acid solution with a pH of 2, and then washed with water until neutral to obtain the tertiary rhodium-containing precipitate (rhodium black).

[0057] The amount of hydrazine hydrate used was 1.5 times the theoretical molar amount.

[0058] S5. The three rhodium-containing precipitates were calcined at 670℃ for 2 hours, and then reduced at 750℃ for 2 hours in a hydrogen reduction furnace (the hydrogen reduction furnace contains a mixture of hydrogen and nitrogen gas with a hydrogen content of 5%) to obtain metallic rhodium.

[0059] Example 3

[0060] A method for recovering and purifying metallic rhodium, which differs from Example 1 in that ammonium chloride in step S2 is replaced with an equimolar amount of ammonium sulfate, while the remaining steps are the same as in Example 1.

[0061] Example 4

[0062] A method for recovering and purifying metallic rhodium differs from Example 1 in that, in step S2, the amount of thiodiglycolic acid and ammonium chloride added is twice the theoretical molar amount required for complete rhodium precipitation, while the remaining steps are the same as in Example 1.

[0063] Example 5

[0064] A method for recovering and purifying metallic rhodium, which differs from Example 1 in that the reaction temperature in S2 is 80°C, while the remaining steps are the same as in Example 1.

[0065] Example 6

[0066] A method for recovering and purifying metallic rhodium differs from Example 1 in that, in step S3, the amount of sodium bromate added is 1.6 times the theoretical amount, while the remaining steps are the same as in Example 1.

[0067] Comparative Example 1

[0068] A method for recovering and purifying metallic rhodium, which differs from Example 1 in that the reaction temperature in S2 is 50°C, while the remaining steps are the same as in Example 1.

[0069] Performance testing

[0070] Detection methods / test methods

[0071] Rhodium recovery was performed on the same rhodium leaching solution according to the methods of Rhodium recovery and purification in Examples 1-6 and Comparative Example 1, respectively. The obtained rhodium was tested, and its purity and direct recovery rate are shown in Table 2.

[0072] Table 2. Detection results of Examples 1-6 and Comparative Example 1

[0073]

[0074] As can be seen from the test data in Table 2, the purity of the rhodium products recovered by rhodium leaching solution in this application can reach 99.95-99.99%, and the direct recovery rate can reach 98.51-98.57%, which can simultaneously guarantee the purity and direct recovery rate of the rhodium products.

[0075] In conjunction with Examples 1 and 5 and Comparative Example 1, in S2, a lower reaction temperature is unfavorable for the coordination reaction of thiodiglycolic acid, ammonium salt, and rhodium ions. In conjunction with Example 2, thiodiglycolic acid, with its high selectivity for rhodium ions, has a wider range of process parameter requirements, making it suitable for actual production.

[0076] Combining Examples 1 and 3, ammonium sulfate and ammonium chloride are used as raw materials. They are inexpensive, readily available, stable, and water-soluble, effectively providing ammonium ions, promoting precipitation, and ensuring the stability and reliability of the process.

[0077] Combining Examples 1 and 4, the optimal addition amount of thiodiglycolic acid and ammonium chloride is 1.5 times the theoretical amount. Adding too much will not be conducive to its purity.

[0078] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for recovering and purifying metallic rhodium, characterized by: It comprises the following steps: S1, the rhodium leaching solution is adjusted to pH 1-2 by alkali, heated to 80-90℃, excess reducing agent is added, stirred and reacted, then filtered to obtain a first impurity removal liquid and filter residue; S2, the pH of the first impurity removal liquid is controlled at 1.5-2, heated to 60-80℃, then excess thiodiglycolic acid and ammonium salt are added, stirred and reacted, then cooled, solid-liquid separation is performed to obtain a first rhodium-containing precipitate and filtrate; S3, the first rhodium-containing precipitate is dispersed in an acid solution with pH ≤0.5, excess strong oxidizing agent is added, heated to 85-95℃ for reflux reaction, then the pH is adjusted to 6-7, cooled, solid-liquid separation is performed to obtain a second rhodium-containing precipitate; S4, the second rhodium-containing precipitate is dispersed in sodium hydroxide or potassium hydroxide with pH 13-14 for slurry, excess reducing agent is added, reduced at 90-100℃, cooled, solid-liquid separation is performed, the precipitate is washed to obtain a third rhodium-containing precipitate; S5, the third rhodium-containing precipitate is calcined at 600-700℃, then hydrogen reduced at 650-750℃ to obtain metallic rhodium.

2. The method for recovering and purifying metal rhodium according to claim 1, characterized by: In the S2, the addition amount of the thiodiglycolic acid and the ammonium salt is 1.1-2 times of the theoretical molar amount required for the reaction with rhodium ions in the rhodium leaching solution.

3. The method for recovering and purifying metal rhodium according to claim 2, characterized by: In the S2, the addition amount of the thiodiglycolic acid and the ammonium salt is 1.1-1.5 times of the theoretical molar amount required for the reaction with rhodium ions in the rhodium leaching solution.

4. The method for recovering and purifying metal rhodium according to claim 1, characterized by: In the S2, the ammonium salt is one or both of ammonium sulfate and ammonium chloride.

5. The method for recovering and purifying metal rhodium according to claim 1, characterized by: In the S2, the stirring reaction time is 60-90 min.

6. The method of recovering and purifying metal rhodium according to claim 1, characterized by: In the S3, the strong oxidizing agent is sodium bromate.

7. The method of recovering and purifying metal rhodium according to claim 6, characterized by: The addition amount of the sodium bromate is 1.1-1.4 times of the theoretical amount.

8. The method of claim 1, wherein: In the S3, the reflux reaction time is 2-3 h.

9. The method of claim 1, wherein: In the S4, the reducing agent is hydrazine hydrate.

10. The method for recovering and purifying a metal rhodium according to claim 9, characterized by: The amount of the hydrazine hydrate is 1.5-2.5 times of the theoretical amount.

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