Preparation method of high-purity rhodium powder

Abstract

The invention relates to the technical field of precious metal refining, in particular to a preparation method of high-purity rhodium powder, which comprises the following steps: S1, mixing a raw material with rhodium content greater than or equal to 1% with caustic alkali and alkali metal peroxide, and carrying out alkali fusion treatment to obtain filter residues; s2, dissolving the filter residues with aqua regia to obtain filtrate. And S3, controlling the rhodium concentration and oxidation potential in the filtrate, adding ammonium chloride to obtain filtrate, and continuously adding sulfamic acid into the filtrate to obtain filtrate. And S4, dissolving the filter residue with an acid solution to obtain a filtrate. And S5, adding ammonium sulfite into the filtrate to obtain a new filtrate. S6, alkali liquor is continuously added, filter residues are obtained, the filter residues are dissolved, and new filtrate is obtained. And S7, adding ammonia water into the filtrate to obtain rhodium precipitate, and calcining and post-processing to obtain high-purity rhodium powder. The preparation method is generally suitable for low-grade and high-grade raw materials, the process is short, complex pretreatment is not needed, impurities such as ruthenium and iridium can be effectively removed, and the product purity is larger than or equal to 99.95%.

Description

Technical Field

[0001] This invention relates to the field of precious metal refining technology, specifically to a method for preparing high-purity rhodium powder. Background Technology

[0002] Rhodium (Rh), a key platinum group metal, holds an irreplaceable position in modern industry due to its outstanding catalytic activity, high-temperature stability, and excellent electrical properties. It is mainly used in automotive exhaust purification catalysts, high-end chemical catalysts, and precision electronic components. With increasingly stringent environmental standards and the rapid development of high-tech industries, the market demand for high-purity rhodium (≥99.95%) continues to rise. At the same time, the market is further imposing stricter requirements on physicochemical indicators such as rhodium burn-off rate and particle size.

[0003] In existing technologies, the production of high-purity rhodium metal mainly relies on traditional hydrometallurgical processes, such as dissolution-precipitation and extraction, to recover and purify rhodium from platinum group metal concentrates or rhodium-containing waste catalysts.

[0004] However, existing technologies still have the following problems:

[0005] First, existing processes have poor adaptability to raw materials, and processing low-grade materials is costly and cumbersome. The production of high-purity rhodium typically requires raw materials with a rhodium content exceeding 10%, or even approaching purity, to achieve efficient separation and enrichment. However, for low-grade, complex materials with a rhodium content of only 1%-10%, complex pretreatment and costly enrichment steps are necessary. Such pretreatment processes not only significantly extend the process cycle but also easily lead to rhodium loss.

[0006] Secondly, the existing preparation process for high-purity rhodium is lengthy and complex. To achieve the high purity requirements of rhodium, traditional processes often require multiple rounds of repeated dissolution, precipitation, and calcination, which not only increases energy consumption and cycle time but may also lead to reduced yield due to risks such as mechanical loss and dissolution residues. Furthermore, the process is difficult to operate.

[0007] Secondly, the deep removal of platinum group metal impurities is difficult. In complex materials, rhodium often coexists with other platinum group metals such as ruthenium, iridium, and platinum. These elements have similar chemical properties, making separation extremely difficult. Existing technologies mostly rely on expensive special reagents or multiple rounds of fine operations to remove platinum group metal impurities, which is not only costly but also prone to introducing new residues.

[0008] Therefore, there is an urgent need to provide a method for preparing high-purity rhodium that is more adaptable to low-grade raw materials, has a shorter and more efficient process, and can deeply remove impurities. Summary of the Invention

[0009] (a) Technical problems to be solved

[0010] To address the problems of poor raw material adaptability, long process, and difficulty in deep impurity removal in the production process of high-purity rhodium in the existing technology, the present invention provides a method for preparing high-purity rhodium powder.

[0011] (II) Technical Solution

[0012] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0013] A method for preparing high-purity rhodium powder includes the following steps:

[0014] S1: Mix raw materials with rhodium content ≥1% with caustic alkali and alkali metal peroxide, and perform alkali fusion treatment. The resulting alkali slag is filtered by water immersion to obtain the first filtrate and the first filter residue.

[0015] S2: Dissolve the first filter residue with aqua regia, filter, and obtain the second filtrate and the second filter residue;

[0016] S3: Maintain the rhodium concentration in the second filtrate at 1-15 g / L and the oxidation potential at 400-1000 mV, add ammonium chloride, filter to obtain the third filtrate and the third filter residue; add aminosulfonic acid to the third filtrate, react and filter to obtain the fourth filtrate and the fourth filter residue.

[0017] S4: Dissolve the fourth filter residue with acid to obtain the fifth filtrate and the fifth filter residue;

[0018] S5: Add ammonium sulfite to the fifth filtrate, and after the reaction, the sixth filtrate and the sixth filter residue are obtained;

[0019] S6: Add alkaline solution to the sixth filtrate to obtain the seventh filtrate and the seventh filter residue. Then dissolve the seventh filter residue with acid to obtain the eighth filtrate.

[0020] S7: Add ammonia to the eighth filtrate to obtain a rhodium precipitate. Calcine the rhodium precipitate and then perform post-treatment to obtain high-purity rhodium powder.

[0021] In the above-described method for preparing high-purity rhodium powder, preferably, in step S1, the caustic alkali is sodium hydroxide or potassium hydroxide, the alkali metal peroxide is sodium peroxide or potassium peroxide, the mass ratio of caustic alkali, alkali metal peroxide and raw materials is (3-5):(2-4):(1-3), the alkali fusion treatment temperature is 400-950℃, and the time is 0.5-4h.

[0022] In the preparation method of high-purity rhodium powder as described above, preferably, in step S2, aqua regia is added to the first filter residue, and after dissolving at 40-100℃ for 0.5-4h, the first filtrate and the first filter residue are obtained.

[0023] The volume-to-mass ratio of aqua regia to the first filter residue is (3-5) mL: 1 g.

[0024] In the above-described method for preparing high-purity rhodium powder, preferably, in step S3, water is added to the second filtrate to maintain the rhodium concentration at 1-15 g / L, and an oxidant is added to the second filtrate to maintain the oxidation potential at 400-1000 mV; after adding ammonium chloride, the concentration of ammonium chloride in the second filtrate is 60-100 g / L.

[0025] The oxidizing agent is nitric acid, sodium chlorate, or hydrogen peroxide.

[0026] In the preparation method of high-purity rhodium powder as described above, preferably, in step S3, after adding aminosulfonic acid to the third filtrate, it is reacted at 40-80℃ for 4-10 hours, and then filtered.

[0027] The mass ratio of aminosulfonic acid to rhodium in the third filtrate is 6-8:1.

[0028] In the method for preparing high-purity rhodium powder as described above, preferably, after step S3 and before step S4, the fourth filter residue is washed with hydrochloric acid at a pH of 4-6.

[0029] In the above-described method for preparing high-purity rhodium powder, preferably, in step S4, the fourth filter residue is added to the acid solution, and then a strong oxidizing agent is added dropwise until the filter residue no longer dissolves; the acid solution is hydrochloric acid, and the volume-to-mass ratio of the acid solution to the fourth filter residue is (3-5) mL:1g.

[0030] In the preparation method of high-purity rhodium powder as described above, preferably, in step S5, the rhodium concentration in the fifth filtrate is adjusted to 60-80 g / L with water, then the pH is adjusted to 1-2 with hydrochloric acid, and then ammonium sulfite is added and reacted at 40-100℃ for 1-3 h.

[0031] The molar ratio of ammonium sulfite to iridium in the fifth filtrate is 1:1 to 5:1.

[0032] In the method for preparing high-purity rhodium powder as described above, preferably, in step S6, a sodium hydroxide solution with a mass concentration of 15-25% is added to the sixth filtrate to make its pH 7-9, thereby obtaining a seventh filtrate and a seventh filter residue. Then, hydrochloric acid is added to the seventh filter residue to obtain an eighth filtrate.

[0033] In the above-described method for preparing high-purity rhodium powder, preferably, in step S7, the pH of the eighth filtrate is adjusted to 0.5-2 with hydrochloric acid, and then ammonia is added to the eighth filtrate at 60-80°C to obtain a rhodium precipitate. The rhodium precipitate is then calcined at 400-550°C for 2-4 hours under an inert atmosphere to obtain rhodium powder. After adding ammonia, the pH of the eighth filtrate is 6-8.

[0034] Rhodium powder is boiled and washed with a mixture of hydrochloric acid, nitric acid and hydrofluoric acid, then filtered, and the resulting filter residue is dried under vacuum to obtain high-purity rhodium powder.

[0035] (III) Beneficial Effects

[0036] First, the preparation method of the present invention is applicable to raw materials with a rhodium content ≥1%, which significantly broadens the applicable range of raw materials. In particular, it has a good processing effect on low-grade raw materials with a rhodium content between 1% and 10%, without relying on complex pretreatment processes such as high pressure, solvent extraction or multiple enrichment, and can directly and efficiently extract high-purity rhodium from low-grade raw materials.

[0037] Secondly, the process flow of this invention is concise and efficient, avoiding the lengthy operations of repeated dissolution, precipitation, and calcination in traditional technologies. By combining alkali fusion treatment with the synergistic effect of selective precipitation and dissolution, efficient connection between each process is achieved, significantly shortening the overall processing cycle, reducing mechanical losses and the risk of dissolution residues in intermediate links, improving the rhodium recovery rate, and making the operation simple and easy to achieve stable industrial operation.

[0038] Third, this invention can deeply remove platinum group metal impurities such as ruthenium and iridium that are difficult to separate, effectively reducing the content of iridium and ruthenium to below 0.01%, and the final rhodium powder has a stable purity of 99.95% or higher. At the same time, it has good particle size distribution and low burn-off rate, meeting the stringent requirements for high-purity metals in high-end catalysis, electronics and other application fields. Detailed Implementation

[0039] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0040] This invention provides a method for preparing high-purity rhodium powder, comprising the following steps:

[0041] S1: The raw material with a rhodium content ≥1% is mixed with caustic alkali and alkali metal peroxide, and then subjected to alkali fusion treatment. The resulting alkali slag is filtered by water immersion to obtain the first filtrate and the first filter residue.

[0042] S2: Dissolve the first filter residue with aqua regia, filter, and obtain the second filtrate and the second filter residue.

[0043] S3: Maintain the rhodium concentration in the second filtrate at 1-15 g / L and the oxidation potential at 400-1000 mV. Add ammonium chloride, filter, and obtain the third filtrate and the third filter residue. Then add aminosulfonic acid to the third filtrate, react, filter, and obtain the fourth filtrate and the fourth filter residue.

[0044] S4: Dissolve the fourth filter residue with acid to obtain the fifth filtrate and the fifth filter residue.

[0045] S5: Add ammonium sulfite to the fifth filtrate, and after the reaction, the sixth filtrate and the sixth filter residue are obtained.

[0046] S6: Add alkaline solution to the sixth filtrate to obtain the seventh filtrate and the seventh filter residue. Then dissolve the seventh filter residue with acid to obtain the eighth filtrate.

[0047] S7: Add ammonia to the eighth filtrate to obtain a rhodium precipitate. Calcine the rhodium precipitate and then perform post-treatment to obtain high-purity rhodium powder.

[0048] Rhodium in rhodium-containing raw materials is very stable and insoluble. In step S1 above, the alkali fusion treatment activates the raw material. During the alkali fusion treatment, alkali metal peroxides oxidize the rhodium in the solid rhodium-containing raw material to rhodium dioxide. Caustic alkali can form rhodium complex sodium salts or complex potassium salts with rhodium dioxide and other non-elemental rhodium. These complex sodium salts or complex potassium salts are insoluble. Simultaneously, ruthenium in the rhodium-containing raw material can also form complex salts during the alkali fusion treatment. However, ruthenium complex salts are soluble in water. Therefore, after the alkali fusion treatment, most of the impurity ruthenium can be removed by water leaching, allowing ruthenium to enter the first filtrate, while rhodium is enriched in the first filter residue.

[0049] The alkaline fusion treatment in this invention is particularly suitable for raw materials with a rhodium content (all rhodium content referred to in this invention is by mass fraction) of 1-10%, unlike other existing technologies that require high pressure and complex extraction to purify rhodium from low-grade raw materials.

[0050] In step S2 above, through the dissolving effect of aqua regia, all the rhodium in the first filter residue enters the second filtrate, while the second filter residue is an insoluble waste component, which can be collected for recycling.

[0051] In step S3 above, researchers of this invention, through long-term research and exploration, discovered that when the concentration of rhodium is 1-15 g / L and the oxidation potential is maintained at 400-1000 mV, adding ammonium chloride to the solution allows the rhodium in the solution to remain dissolved, but approximately 99% of the iridium in the solution will precipitate, thus achieving iridium removal. Subsequently, sulfamic acid combines with the rhodium in the third filtrate to form the fourth filter residue, which can be collected for the recovery of base metals and other platinum group metals.

[0052] In step S4 above, rhodium and residual iridium re-enter the solution, and the fifth filter residue can be collected for recycling.

[0053] In step S5 above, sodium sulfite can combine with the remaining iridium to form a precipitate, thus almost all of the iridium is removed, and rhodium is present in the sixth filtrate.

[0054] In step S6 above, adding alkaline solution to the sixth filtrate further removes other platinum group metal impurities. After adding the alkaline solution, rhodium precipitates, and other trace platinum group metal impurities also precipitate. However, research has shown that platinum has a higher precipitation rate than other platinum group metal impurities. Therefore, step S6 can further remove platinum group metals, resulting in a lower impurity content in the seventh filter residue. The absence of this step would affect the purity of the rhodium powder. Subsequently, the seventh filter residue redissolves, and rhodium re-enters the filtrate.

[0055] In step S7 above, ammonia water can react with rhodium to form a specific ammoniation precipitation, and after calcination, rhodium powder is obtained. The rhodium powder is then post-treated to obtain high-purity rhodium powder with a purity of 99.95% or higher.

[0056] The preparation method of the present invention has the following advantages:

[0057] The preparation method of the present invention is applicable to raw materials with a rhodium content ≥1%, which significantly broadens the applicable range of raw materials. In particular, it has a good processing effect on low-grade raw materials with a rhodium content between 1% and 10%. It does not require complex pretreatment processes such as high pressure, solvent extraction or multiple enrichment, and can directly and efficiently extract high-purity rhodium from low-grade raw materials.

[0058] This invention features a concise and efficient process, avoiding the lengthy operations of repeated dissolution, precipitation, and calcination in traditional technologies. By combining alkali fusion treatment with the synergistic effect of selective precipitation and dissolution, efficient connection between each step is achieved, significantly shortening the overall processing cycle, reducing mechanical losses and residual dissolution risks in intermediate stages, improving rhodium recovery rate, and facilitating stable industrial-scale operation.

[0059] This invention can deeply remove platinum group metal impurities such as ruthenium and iridium that are difficult to separate, effectively reducing the content of iridium and ruthenium to below 0.01%, and finally obtaining rhodium powder with a stable purity of 99.95% or higher. It also has good particle size distribution and low burn-off rate, meeting the stringent requirements for high-purity metals in high-end catalysis, electronics and other application fields.

[0060] Preferably, in step S1 above, the caustic alkali can be sodium hydroxide or potassium hydroxide, and the alkali metal peroxide can be sodium peroxide or potassium peroxide. The mass ratio of the caustic alkali, alkali metal peroxide, and raw materials is (3-5):(2-4):(1-3), the alkali fusion treatment temperature is 400-950℃, and the time is 0.5-4h.

[0061] In this invention, raw materials with a rhodium content ≥1% can be byproducts of copper-nickel smelting, or recycled waste obtained from the recovery of rhodium-containing catalysts or other rhodium-containing products. The main impurities in the raw materials are base metals such as copper, nickel, iron, and aluminum, as well as platinum group metals such as ruthenium and iridium. Among these, the separation of platinum group metals, especially iridium, from rhodium is particularly difficult.

[0062] Preferably, in step S2 above, aqua regia is added to the first filter residue, and after dissolving at 40-100℃ for 0.5-4 hours, a first filtrate and a first filter residue are obtained. The volume-to-mass ratio of aqua regia to the first filter residue is (3-5) mL:1 g.

[0063] Preferably, in step S3 above, water is added to the second filtrate to maintain the rhodium concentration at 1-15 g / L, and an oxidant is added to the second filtrate to maintain the oxidation potential at 400-1000 mV. Then, aminosulfonic acid is added to the third filtrate, and the mixture is reacted at 40-80°C for 4-10 hours, followed by filtration. Specifically, after adding ammonium chloride, the concentration of ammonium chloride in the second filtrate is 60-100 g / L, the oxidant is nitric acid, sodium chlorate, or hydrogen peroxide, and the mass ratio of aminosulfonic acid to rhodium in the third filtrate is 6-8:1.

[0064] More preferably, after step S3 and before step S4, the fourth filter residue is washed with hydrochloric acid at a pH of 4-6 to remove liquid impurities on its surface. The washing temperature is 25-35°C, and the washing is performed with stirring several times until the washing liquid is colorless. The resulting filtrate is collected for recycling.

[0065] Preferably, in step S4 above, the fourth filter residue is added to the acid solution, and then a strong oxidizing agent is added dropwise until the filter residue no longer dissolves. The acid solution used is hydrochloric acid, and the volume-to-mass ratio of the acid solution to the fourth filter residue is (3-5) mL:1 g. The strong oxidizing agent is nitric acid, sodium chlorate, or hydrogen peroxide.

[0066] Preferably, in step S5 above, the rhodium concentration in the fifth filtrate is adjusted to 60-80 g / L with water, then the pH is adjusted to 1-2 with hydrochloric acid, followed by the addition of ammonium sulfite. The reaction is carried out at 40-100°C for 1-3 hours, with the molar ratio of ammonium sulfite to iridium in the fifth filtrate being 1:1-5:1. In step S5, under the conditions of a rhodium concentration of 60-80 g / L and a pH of 1-2, sodium sulfite can combine with the remaining iridium to form a precipitate, while the rhodium remains in a dissolved state.

[0067] More preferably, in step S6 above, a sodium hydroxide solution with a mass concentration of 15-25% is added to the sixth filtrate to make its pH 7-9, thereby obtaining a seventh filtrate and a seventh filter residue. Then, hydrochloric acid is added to the seventh filter residue to obtain an eighth filtrate.

[0068] More preferably, in step S7 above, the pH of the eighth filtrate is adjusted to 0.5-2 with hydrochloric acid, and then ammonia is added to the eighth filtrate at 60-80°C to obtain a rhodium precipitate. The rhodium precipitate is calcined at 400-550°C for 2-4 hours under an inert atmosphere to obtain rhodium powder. After adding ammonia, the pH of the eighth filtrate is 6-8.

[0069] Calcination may introduce impurities such as silicon, which can lead to high burn-off in the rhodium powder product. Therefore, after obtaining rhodium powder through calcination, it is necessary to wash the rhodium powder with a mixture of hydrochloric acid, nitric acid, and hydrofluoric acid to remove impurities, followed by filtration. However, the filter residue obtained after washing still contains a certain amount of moisture, which can also cause high burn-off in the rhodium powder product. Therefore, the filter residue needs to be further dried under vacuum conditions to obtain high-purity rhodium powder with a burn-off rate of <0.1%.

[0070] The preferred mass ratio of hydrochloric acid, nitric acid, and hydrofluoric acid is 3:1:1.

[0071] In addition, the recovery rate of rhodium in existing technologies is generally 92-95%, while in the preparation method of the present invention, the recovery rate of rhodium can stably reach 98% or above.

[0072] Furthermore, to further reduce costs, rhodium can be enriched before step S1. Specifically, the rhodium-containing raw material can be oxidized and roasted before step S1 at a temperature of 400-500℃ for 2-3 hours, converting the rhodium in sulfide or hydroxide state into elemental or oxide form. Then, the roasted product is dissolved using 0.1-0.5M dilute sulfuric acid to remove most of the alkali metals. The rhodium content in the raw material obtained after oxidative roasting and acid leaching can be increased from 1% to around 50%.

[0073] To further clarify the present invention and its technological advancements, the following description is provided in conjunction with specific embodiments and technical effects.

[0074] Example 1

[0075] This embodiment provides a method for preparing high-purity rhodium powder, including the following steps:

[0076] A copper-nickel smelting byproduct with a rhodium content of 1% was subjected to oxidative roasting at 450℃ for 2.5 h. The roasted product was then dissolved in 0.3M dilute sulfuric acid, and the solution was filtered to obtain a pretreated raw material. The rhodium content in the pretreated raw material was 50.8%.

[0077] S1: The pretreated raw material is mixed with sodium hydroxide and sodium peroxide. The mass ratio of sodium hydroxide, sodium peroxide and raw material is 4:3:2. The mixture is alkali-fused at 700℃ for 2 hours. The resulting alkali-fused residue is filtered by water immersion to obtain the first filtrate and the first filter residue.

[0078] S2: Add aqua regia to the first filter residue, and dissolve it at 70℃ for 2 hours to obtain the first filtrate and the first filter residue. The volume-to-mass ratio of aqua regia to the first filter residue is 4 mL: 1 g.

[0079] S3: Water was added to the second filtrate to maintain the rhodium concentration at 6 g / L. Nitric acid was added to the second filtrate to maintain the oxidation potential at 700 mV. Ammonium chloride was then added, bringing the concentration in the second filtrate to 80 g / L. After filtration, a third filtrate and a third filter residue were obtained. Sulfamic acid was then added to the third filtrate, and the reaction was carried out at 60°C for 7 hours. After the reaction, the filtrate was filtered to obtain a fourth filtrate. The filter residue was washed with hydrochloric acid (pH 5) at 30°C until the washings became colorless, yielding the fourth filter residue. The mass ratio of sulfamic acid to rhodium in the third filtrate was 7:1.

[0080] S4: Add the fourth filter residue to hydrochloric acid, then add nitric acid dropwise until the residue no longer dissolves, yielding the fifth filtrate and the fifth filter residue. The volume-to-mass ratio of hydrochloric acid to the fourth filter residue is 4 mL: 1 g.

[0081] S5: Adjust the rhodium concentration in the fifth filtrate to 70 g / L with water, then adjust its pH to 1.5 with hydrochloric acid, and then add ammonium sulfite. React at 70°C for 2 hours to obtain the sixth filtrate and the sixth filter residue. The molar ratio of ammonium sulfite to iridium in the fifth filtrate is 3:1.

[0082] S6: Add a 20% sodium hydroxide solution to the sixth filtrate to make its pH 8, to obtain the seventh filtrate and the seventh filter residue. Then add hydrochloric acid to the seventh filter residue to obtain the eighth filtrate.

[0083] S7: Adjust the pH of the eighth filtrate to 1.2 with hydrochloric acid, then add ammonia to the eighth filtrate at 70°C to obtain a rhodium precipitate. Calcine the rhodium precipitate at 450°C for 3 hours under an inert atmosphere to obtain rhodium powder. Wash the rhodium powder with a mixture of hydrochloric acid, nitric acid, and hydrofluoric acid in a mass ratio of 3:1:1, filter, and then dry under vacuum to obtain high-purity rhodium powder. In this step, the pH of the eighth filtrate after adding ammonia is 7.

[0084] Example 2

[0085] This embodiment provides a method for preparing high-purity rhodium powder, including the following steps:

[0086] Rhodium-containing recycled waste with a rhodium content of 1% was subjected to oxidative roasting at 400℃ for 3 hours. The roasted product was then dissolved in 0.1M dilute sulfuric acid, and the mixture was filtered to obtain pretreated raw material. The rhodium content in the pretreated raw material was 53.4%.

[0087] S1: The pretreated raw material is mixed with potassium hydroxide and potassium peroxide. The mass ratio of potassium hydroxide, potassium peroxide and raw material is 3:2:1. The mixture is alkali-fused at 400℃ for 4 hours. The resulting alkali-fused residue is filtered by water immersion to obtain the first filtrate and the first filter residue.

[0088] S2: Add aqua regia to the first filter residue, and dissolve it at 40℃ for 4 hours to obtain the first filtrate and the first filter residue. The volume-to-mass ratio of aqua regia to the first filter residue is 3 mL: 1 g.

[0089] S3: Water was added to the second filtrate to maintain the rhodium concentration at 1 g / L. Hydrogen peroxide was added to the second filtrate to maintain the oxidation potential at 400 mV. Ammonium chloride was then added, bringing the concentration in the second filtrate to 60 g / L. After filtration, a third filtrate and a third filter residue were obtained. Sulfamic acid was then added to the third filtrate, and the mixture was reacted at 40°C for 10 hours. After the reaction, the mixture was filtered to obtain a fourth filtrate. The filter residue was washed with hydrochloric acid (pH 4) at 25°C until the washings became colorless, yielding the fourth filter residue. The mass ratio of sulfamic acid to rhodium in the third filtrate was 6:1.

[0090] S4: Add the fourth filter residue to hydrochloric acid, then add sodium chlorate dropwise until the residue no longer dissolves, obtaining the fifth filtrate and the fifth filter residue. The volume-to-mass ratio of hydrochloric acid to the fourth filter residue is 3 mL: 1 g.

[0091] S5: Adjust the rhodium concentration in the fifth filtrate to 60 g / L with water, then adjust its pH to 1 with hydrochloric acid, and then add ammonium sulfite. React at 40°C for 1 hour to obtain the sixth filtrate and the sixth filter residue. The molar ratio of ammonium sulfite to iridium in the fifth filtrate is 1:1.

[0092] S6: Add a 15% sodium hydroxide solution to the sixth filtrate to make its pH 7, to obtain the seventh filtrate and the seventh filter residue. Then add hydrochloric acid to the seventh filter residue to obtain the eighth filtrate.

[0093] S7: Adjust the pH of the eighth filtrate to 0.5 with hydrochloric acid, then add ammonia to the eighth filtrate at 60°C to obtain a rhodium precipitate. Calcine the rhodium precipitate at 400°C for 2 hours under an inert atmosphere to obtain rhodium powder. Wash the rhodium powder with a mixture of hydrochloric acid, nitric acid, and hydrofluoric acid in a mass ratio of 3:1:1, filter, and then dry under vacuum to obtain high-purity rhodium powder. In this step, the pH of the eighth filtrate after adding ammonia is 6.

[0094] Example 3

[0095] This embodiment provides a method for preparing high-purity rhodium powder, including the following steps:

[0096] A copper-nickel smelting byproduct with a rhodium content of 1% was subjected to oxidative roasting at 500℃ for 2 hours. The roasted product was then dissolved in 0.5M dilute sulfuric acid, and the solution was filtered to obtain a pretreated raw material. The rhodium content in the pretreated raw material was 48.6%.

[0097] S1: The pretreated raw material is mixed with sodium hydroxide and sodium peroxide. The mass ratio of sodium hydroxide, sodium peroxide and raw material is 5:4:3. The mixture is alkali-fused at 950℃ for 0.5h. The resulting alkali-fused residue is filtered by water immersion to obtain the first filtrate and the first filter residue.

[0098] S2: Add aqua regia to the first filter residue, and dissolve it at 100℃ for 0.5 h to obtain the first filtrate and the first filter residue. The volume-to-mass ratio of aqua regia to the first filter residue is 5 mL: 1 g.

[0099] S3: Water was added to the second filtrate to maintain the rhodium concentration at 15 g / L. Sodium chlorate was added to the second filtrate to maintain the oxidation potential at 1000 mV. Ammonium chloride was then added until the concentration in the second filtrate was 100 g / L. After filtration, a third filtrate and a third filter residue were obtained. Sulfamic acid was then added to the third filtrate and reacted at 80°C for 10 hours. After the reaction, the filtrate was filtered to obtain a fourth filtrate. The filter residue was washed with hydrochloric acid (pH 6) at 35°C until the washings were colorless, yielding the fourth filter residue. The mass ratio of sulfamic acid to rhodium in the third filtrate was 8:1.

[0100] S4: Add the fourth filter residue to hydrochloric acid, then add hydrogen peroxide dropwise until the residue no longer dissolves, obtaining the fifth filtrate and the fifth filter residue. The volume-to-mass ratio of hydrochloric acid to the fourth filter residue is 5 mL: 1 g.

[0101] S5: Adjust the rhodium concentration in the fifth filtrate to 80 g / L with water, then adjust its pH to 2 with hydrochloric acid, and then add ammonium sulfite. React at 100°C for 3 hours to obtain the sixth filtrate and the sixth filter residue. The molar ratio of ammonium sulfite to iridium in the fifth filtrate is 5:1.

[0102] S6: Add a 25% sodium hydroxide solution to the sixth filtrate to make its pH 9, to obtain the seventh filtrate and the seventh filter residue. Then add hydrochloric acid to the seventh filter residue to obtain the eighth filtrate.

[0103] S7: Adjust the pH of the eighth filtrate to 2 using hydrochloric acid, then add ammonia to the eighth filtrate at 80°C to obtain a rhodium precipitate. Calcine the rhodium precipitate at 550°C for 2 hours under an inert atmosphere to obtain rhodium powder. Wash the rhodium powder with a mixture of hydrochloric acid, nitric acid, and hydrofluoric acid in a mass ratio of 3:1:1, filter, and then dry under vacuum to obtain high-purity rhodium powder. In this step, the pH of the eighth filtrate after adding ammonia is 8.

[0104] Example 4

[0105] This embodiment provides a method for preparing high-purity rhodium powder, which differs from Embodiment 1 in that the copper-nickel smelting byproduct with a rhodium content of 5.4% is subjected to oxidative roasting.

[0106] Example 5

[0107] This embodiment provides a method for preparing high-purity rhodium powder, which differs from Embodiment 1 in that the copper-nickel smelting byproduct with a rhodium content of 12.7% is subjected to oxidative roasting.

[0108] Example 6

[0109] This embodiment provides a method for preparing high-purity rhodium powder. The difference from Embodiment 1 is that the rhodium-containing recycled waste with a rhodium content of 60.2% is subjected to oxidative roasting.

[0110] Example 7

[0111] This embodiment provides a method for preparing high-purity rhodium powder. The difference from Embodiment 1 is that the rhodium-containing recycled waste with a rhodium content of 82.4% is subjected to oxidative roasting.

[0112] Comparative Example 1

[0113] This comparative example provides a method for preparing rhodium powder, which differs from Example 1 in that no alkali fusion treatment is performed. This comparative method is not applicable to low-grade rhodium raw materials, especially for the recovery of rhodium from raw materials with a rhodium content of 1-10 wt%.

[0114] Comparative Example 2

[0115] This comparative example provides a method for preparing high-purity rhodium powder. The difference from Example 1 is that the concentration of rhodium was not adjusted in step S3, and the concentration of rhodium was found to be greater than 15 g / L.

[0116] Comparative Example 3

[0117] This comparative example provides a method for preparing high-purity rhodium powder. The difference from Example 1 is that the concentration of rhodium after adding water in step S3 is less than 1 g / L.

[0118] Comparative Example 4

[0119] This comparative example provides a method for preparing high-purity rhodium powder. The difference from Example 1 is that no oxidant is added in step S3 to adjust the oxidation potential.

[0120] Comparative Example 5

[0121] This comparative example provides a method for preparing high-purity rhodium powder. The difference from Example 1 is that the sixth filtrate obtained from S5 is processed according to S7 (i.e., step S6 is not performed).

[0122] The rhodium purity, ruthenium content, iridium content, and rhodium recovery rate of the products prepared in Examples 1-7 and Comparative Examples 1-5 were tested and the results are shown in Table 1.

[0123] Table 1. Statistics on rhodium purity, ruthenium content, iridium content, and rhodium recovery rate of the products prepared in Examples 1-7 and Comparative Examples 1-5.

[0124] Rhodium purity Ruthenium content Iridium content Rhodium recovery rate Example 1 99.97％ ＜0.01％ ＜0.01％ 98.4％ Example 2 99.95％ ＜0.01％ ＜0.01％ 98.2％ Example 3 99.95％ ＜0.01％ ＜0.01％ 98％ Example 4 99.98％ ＜0.01％ ＜0.01％ 98.1％ Example 5 99.99％ ＜0.01％ ＜0.01％ 98.9％ Example 6 99.97％ ＜0.01％ ＜0.01％ 98.7％ Example 7 99.97％ ＜0.01％ ＜0.01％ 98.2％ Comparative Example 1 / / / / Comparative Example 2 99.8％ 0.01％ 0.07％ 94.7％ Comparative Example 3 99.84％ 0.01％ 0.06％ 95.4％ Comparative Example 4 99.72％ 0.02％ 0.06％ 93.5％ Comparative Example 5 99.31％ 0.04％ 0.27％ 98.3％

[0125] As shown in Table 1, the rhodium powder prepared in Examples 1-7 consistently achieves a purity of 99.95% or higher, with ruthenium and iridium contents both below 0.01%, and a material recovery rate consistently above 98%. However, without alkali fusion treatment, rhodium could not be recovered in Comparative Example 1. Comparative Examples 2-4 demonstrate that in step S3, only by simultaneously adjusting the rhodium concentration and oxidation potential can good rhodium purity and recovery rate be ensured. Comparative Example 5 shows that adding alkali solution in step S6 further removes other platinum group metal impurities, improving product purity.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing high-purity rhodium powder, characterized in that, Includes the following steps: S1: Mix raw materials with rhodium content ≥1% with caustic alkali and alkali metal peroxide, and perform alkali fusion treatment. The resulting alkali slag is filtered by water immersion to obtain the first filtrate and the first filter residue. S2: Dissolve the first filter residue with aqua regia, filter, and obtain the second filtrate and the second filter residue; S3: Maintain the rhodium concentration in the second filtrate at 1-15 g / L and the oxidation potential at 400-1000 mV, add ammonium chloride, filter to obtain the third filtrate and the third filter residue; add aminosulfonic acid to the third filtrate, react and filter to obtain the fourth filtrate and the fourth filter residue. S4: Dissolve the fourth filter residue with acid to obtain the fifth filtrate and the fifth filter residue; S5: Add ammonium sulfite to the fifth filtrate, and after the reaction, the sixth filtrate and the sixth filter residue are obtained; S6: Add alkaline solution to the sixth filtrate to obtain the seventh filtrate and the seventh filter residue. Then dissolve the seventh filter residue with acid to obtain the eighth filtrate. S7: Add ammonia to the eighth filtrate to obtain a rhodium precipitate. Calcine the rhodium precipitate and then perform post-treatment to obtain high-purity rhodium powder.

2. The method for preparing high-purity rhodium powder according to claim 1, characterized in that, In step S1, the caustic alkali is sodium hydroxide or potassium hydroxide, the alkali metal peroxide is sodium peroxide or potassium peroxide, and the mass ratio of caustic alkali, alkali metal peroxide and raw materials is (3-5):(2-4):(1-3). The temperature of the alkali fusion treatment is 400-950℃ and the time is 0.5-4h.

3. The method for preparing high-purity rhodium powder according to claim 1, characterized in that, In step S2, aqua regia is added to the first filter residue, and after dissolving at 40-100℃ for 0.5-4 hours, the first filtrate and the first filter residue are obtained. The volume-to-mass ratio of aqua regia to the first filter residue is (3-5) mL: 1 g.

4. The method for preparing high-purity rhodium powder according to claim 1, characterized in that, In step S3, water is added to the second filtrate to maintain the rhodium concentration at 1-15 g / L, and an oxidant is added to the second filtrate to maintain the oxidation potential at 400-1000 mV; after adding ammonium chloride, the concentration of ammonium chloride in the second filtrate is 60-100 g / L. The oxidizing agent is nitric acid, sodium chlorate, or hydrogen peroxide.

5. The method for preparing high-purity rhodium powder according to claim 1, characterized in that, In step S3, aminosulfonic acid is added to the third filtrate and allowed to react at 40-80℃ for 4-10 hours, followed by filtration. The mass ratio of aminosulfonic acid to rhodium in the third filtrate is 6-8:

1.

6. The method for preparing high-purity rhodium powder according to claim 1, characterized in that, After step S3 and before step S4, the fourth filter residue is washed with hydrochloric acid at a pH of 4-6.

7. The method for preparing high-purity rhodium powder according to claim 1, characterized in that, In step S4, the fourth filter residue is added to the acid solution, and then a strong oxidizing agent is added dropwise until the filter residue no longer dissolves; the acid solution is hydrochloric acid, and the volume-to-mass ratio of the acid solution to the fourth filter residue is (3-5) mL:1g.

8. The method for preparing high-purity rhodium powder according to claim 1, characterized in that, In step S5, the rhodium concentration in the fifth filtrate is adjusted to 60-80 g / L with water, and then the pH is adjusted to 1-2 with hydrochloric acid. Ammonium sulfite is then added, and the reaction is carried out at 40-100℃ for 1-3 hours. The molar ratio of ammonium sulfite to iridium in the fifth filtrate is 1:1 to 5:

1.

9. The method for preparing high-purity rhodium powder according to claim 1, characterized in that, In step S6, a sodium hydroxide solution with a mass concentration of 15-25% is added to the sixth filtrate to adjust its pH to 7-9, resulting in a seventh filtrate and a seventh filter residue. Then, hydrochloric acid is added to the seventh filter residue to obtain an eighth filtrate.

10. The method for preparing high-purity rhodium powder according to claim 1, characterized in that, In step S7, the pH of the eighth filtrate is adjusted to 0.5-2 with hydrochloric acid, and then ammonia is added to the eighth filtrate at 60-80℃ to obtain rhodium precipitate. The rhodium precipitate is calcined at 400-550℃ for 2-4 hours under an inert atmosphere to obtain rhodium powder. After adding ammonia, the pH of the eighth filtrate is 6-8. Rhodium powder is boiled and washed with a mixture of hydrochloric acid, nitric acid and hydrofluoric acid, then filtered, and the resulting filter residue is dried under vacuum to obtain high-purity rhodium powder.