Method for separating and purifying platinum, palladium and rhodium in ternary catalyst by molten salt electrolysis

Abstract

The present application belongs to the technical field of separating and purifying platinum, palladium and rhodium in a three-way catalyst, and particularly relates to a method for separating and purifying platinum, palladium and rhodium in a three-way catalyst by molten salt electrolysis, comprising the following steps: S1 electrolyte system construction: taking the three-way catalyst metal to be purified as an anode, adopting a titanium plate as a cathode, adopting a closed inert protection environment electrolytic cell, and adopting a eutectic molten salt as an electrolyte; S2 step-by-step electrolytic deposition: the first step is platinum deposition; the second step is palladium deposition; and the third step is rhodium separation; and S3 product treatment: the treatment of platinum and palladium products comprises respectively taking out the cathodes in the platinum and palladium deposition stages, stripping the deposits, and then vacuum smelting to obtain platinum and palladium products; the treatment of rhodium products comprises taking out the anode, collecting the anode mud on the surface of the anode, treating to obtain rhodium fine products, and then vacuum smelting the rhodium fine products to obtain rhodium products; the present application can efficiently separate platinum, palladium and rhodium, the products have high purity, and the present application is environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of separation and purification of platinum, palladium, and rhodium in ternary catalysts, specifically relating to a method for separating and purifying platinum, palladium, and rhodium in ternary catalysts by molten salt electrolysis. Background Technology

[0002] With the rapid development of the automotive industry, the use of three-way catalytic converters has been increasing year by year. The platinum (Pt), palladium (Pd), and rhodium (Rh) waste generated after their disposal has become an important secondary resource. Currently, the technologies for recovering platinum group metals from three-way catalytic converters are mainly divided into pyrometallurgical and hydrometallurgical methods.

[0003] 1. Pyrometallurgical recovery technologies. These include lead trapping, copper trapping, iron trapping, matte trapping, and chlorination volatilization. While these methods can effectively enrich precious metals, they suffer from problems such as long high-temperature reaction times, high energy consumption, high costs due to the need for additional trapping agents, and the generation of large amounts of chlorine-containing waste gas, causing serious environmental pollution.

[0004] 2. Wet recovery technologies. These include chlorination leaching, cyanide leaching, carrier dissolution, and solvent extraction. However, these methods generally suffer from high reagent consumption, difficult wastewater treatment, and limited separation accuracy. For example, patent CN112322900B discloses a method for extracting platinum, palladium, and rhodium from automotive exhaust catalyst waste. This method employs oxidative roasting pretreatment, followed by leaching through a hydrochloric acid-sodium chlorate system, combined with precipitation and adsorption steps to extract platinum, palladium, and rhodium. While this improves the precious metal leaching rate, it still suffers from cumbersome separation steps, limited rhodium adsorption recovery, and the generation of chlorine-containing wastewater during the leaching process.

[0005] Although some studies have attempted to recover precious metals using molten salt electrolysis, such as patent CN113215621A which discloses a method for recovering precious metals from catalysts containing precious metals, using spent catalysts containing precious metals as raw materials, enriching the precious metals using molten salt electrolysis, and then purifying them through wet refining, this method has problems such as incomplete separation of precious metals in the molten salt electrolysis stage, the need for complex wet processing afterward, limited product purity, and the easy generation of trace amounts of chlorine gas during the electrolysis process. It is difficult to achieve efficient, green, and high-purity separation of platinum, palladium, and rhodium. Summary of the Invention

[0006] To address the problems in the prior art, this invention provides a method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst using molten salt electrolysis. By precisely controlling the electrolysis potential, enhancing mass transfer, and implementing stage termination strategies, the method significantly reduces the risk of palladium and rhodium co-deposition, achieving stepwise deposition of platinum, palladium, and rhodium with a purity of 4N or even 5N. This method achieves the goal of efficiently separating platinum, palladium, and rhodium, producing high-purity products, and being environmentally friendly.

[0007] The technical problem solved by this invention is achieved by the following technical solution:

[0008] The present invention aims to provide a method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis, comprising the following steps:

[0009] S1 electrolysis system construction: The three-way catalyst metal to be purified is used as the anode, titanium plate is used as the cathode, a closed inert protective environment electrolysis cell is used, and eutectic molten salt is used as the electrolyte;

[0010] S2 stepwise electrolytic deposition: The first step is platinum deposition. The electrolytic potential is controlled, and the molten salt is stirred. When the cathode current density drops below 5% of the initial value, the platinum electrolysis stage is immediately terminated. The second step is palladium deposition. After the platinum deposition stage is terminated, the molten salt is stirred, and the electrolytic potential is adjusted. When the cathode current density drops below 4% of the initial value, and the PdCl4²⁻ content in the molten salt is ≤0.008 g / L, the palladium electrolysis stage is immediately terminated. The third step is rhodium separation. After the palladium deposition stage is terminated, the molten salt is stirred, and the electrolytic potential is adjusted. When the cathode current density drops below 3% of the initial value, and the RhCl6³⁻ content in the molten salt is ≤0.005 g / L, the rhodium electrolysis stage is terminated.

[0011] S3 Product Processing: The processing of platinum and palladium products includes removing the cathodes from the platinum and palladium deposition stages, stripping off the deposits, and then vacuum melting to obtain platinum and palladium products; the processing of rhodium products includes removing the anode, collecting the anode mud on the anode surface, processing it to obtain refined rhodium, and then vacuum melting the refined rhodium to obtain rhodium products.

[0012] Furthermore, the titanium plate undergoes grinding, pickling, deionized water rinsing, and drying.

[0013] Furthermore, the ratio of cathode area to anode area is 1.2-1.5:1.

[0014] Furthermore, the electrolyte is a potassium chloride-sodium chloride eutectic molten salt with a molar ratio of 1:1, and 0.5–2 mol% LiCl is added. The electrolyte is vacuum dried before use.

[0015] Furthermore, during platinum deposition, the initial cathode current density is 0.5-1.0 A / cm², and the electrolysis potential is controlled between +0.78V and +0.80V; during palladium deposition, the initial cathode current density is 0.4-0.8 A / cm², and the electrolysis potential is adjusted to +0.60V to +0.65V; during rhodium separation, the initial cathode current density is 0.3-0.6 A / cm², and the electrolysis potential is adjusted to +0.40V to +0.45V.

[0016] Furthermore, the stirring rate of the molten salt in S2 is 100–300 rpm.

[0017] Furthermore, during the S2 electrolysis process, inert gas is continuously introduced at a flow rate of 50-100 mL / min, and the electrolysis temperature is 650℃~750℃.

[0018] Furthermore, in the processing of S3 platinum and palladium products, the cathodes of the platinum and palladium deposition stages were removed, placed in an inert gas environment and cooled to room temperature. They were then washed with dilute hydrochloric acid to remove impurities, rinsed with deionized water until the rinsing solution was neutral, dried, and the deposits were peeled off.

[0019] Furthermore, in the processing of S3 rhodium products, the anode mud is ground to a particle size ≤100 mesh, and diluted aqua regia is added at a liquid-to-solid ratio of 5-8:1. The mixture is then leached at 80-90℃ for 2-3 hours, filtered, washed, and the leachate and washing solution are combined. After ion exchange purification, hydrazine hydrate reduction precipitation, washing, and drying, high-quality rhodium is obtained.

[0020] Furthermore, the vacuum melting temperature for platinum is 1550-1600℃ and the melting time is 2-3 hours; the vacuum melting temperature for palladium is 1500-1550℃ and the melting time is 2-3 hours; and the vacuum melting temperature for high-quality rhodium is 1850-1920℃ and the melting time is 2.5-3.5 hours.

[0021] A method for separating and purifying platinum, palladium, and rhodium from a ternary catalyst by molten salt electrolysis includes the following steps:

[0022] 1. Construction of the electrolysis system

[0023] 1.1 Anode: The three-way catalyst metal to be purified is used as the anode. The waste three-way catalyst is crushed, ground and pressed into shape to serve as the anode plate, ensuring that the anode is in full contact with the electrolyte and that the anode surface is uniform, avoiding abnormal potential fluctuations caused by local current concentration.

[0024] 1.2 Cathode: Titanium plate is used as the cathode material. The surface of the titanium plate is polished, acid-washed (soaked in dilute hydrochloric acid for 10-15 min), rinsed with deionized water, and dried to remove the surface oxide layer, improve the cathode conductivity and deposition effect. The ratio of cathode area to anode area is controlled at 1.2-1.5:1 to ensure uniform deposition.

[0025] 1.3 Electrolytic Cell: A closed, inert protective environment electrolytic cell with high temperature resistance (≥800℃) and corrosion resistance (resistant to molten salt erosion) is adopted. The cell body material is corundum or graphite. During the electrolysis process, inert gas (argon or nitrogen) is continuously introduced at a flow rate of 50-100mL / min to completely remove air from the cell, avoid oxygen interference with the electrolysis reaction, and remove trace volatile impurities generated during the electrolysis process.

[0026] 1.4 Electrolyte: Potassium chloride-sodium chloride (KCl-NaCl) eutectic molten salt (molar ratio 1:1) is used, and 0.5–2 mol% LiCl is added to optimize the ionic conductivity of the molten salt. The electrolyte is vacuum dried (120℃, 2h) before use to remove moisture and avoid electrolytic side reactions and catalyst metal oxidation caused by moisture.

[0027] 2. Stepwise electrolytic deposition

[0028] 2.1 Platinum Deposition: A high-precision potentiostat (resolution ≤1mV) is used to control the electrolysis potential between +0.78 V and +0.80 V (relative to the Ag / AgCl reference electrode), strictly controlling the potential fluctuation range to ≤±0.005 V. Simultaneously, the molten salt is continuously mechanically stirred at a rate of 100–300 rpm (the stirring paddle is made of graphite to avoid electrolyte contamination) to maintain a uniform PtCl4²⁻ concentration in the molten salt and eliminate the concentration polarization layer on the cathode surface. The cathode current density is monitored in real time during electrolysis. When the cathode current density drops to less than 5% of the initial value (the initial current density is controlled at 0.5–1.0 A / cm²), the platinum electrolysis stage is immediately terminated. At this point, the PtCl4²⁻ content in the molten salt is ≤0.01 g / L, allowing platinum to preferentially deposit on the cathode, preventing the co-deposition of palladium and rhodium, and achieving high-purity separation and recovery of platinum.

[0029] 2.2 Palladium Deposition: After the platinum deposition stage is terminated, the molten salt stirring rate is kept constant (100-300 rpm), and the electrolysis potential is steadily adjusted to +0.60 V~+0.65 V (relative to the Ag / AgCl reference electrode) using a potentiostat. The potential fluctuation range is ≤±0.005 V to avoid local abnormal reactions caused by sudden potential changes. During electrolysis, the concentration of PdCl4²⁻ in the molten salt is monitored in real time (using online differential pulse voltammetry), and the change in cathode current density is tracked simultaneously. The initial current density is controlled at 0.4-0.8 A / cm². When the cathode current density drops to below 4% of the initial value, and online monitoring shows that the PdCl4²⁻ content in the molten salt is ≤0.008 g / L, the palladium electrolysis stage is immediately terminated, allowing palladium to be deposited at the cathode. During this process, since the platinum is basically exhausted and the reduction potential of palladium is much higher than that of rhodium, platinum residual contamination and rhodium co-deposition can be effectively prevented, ensuring the purity of palladium.

[0030] 2.3 Rhodium Separation: After the palladium deposition stage is terminated, the molten salt is continuously stirred, and the electrolysis potential is steadily adjusted to +0.40V~+0.45V (relative to the Ag / AgCl reference electrode), with a potential fluctuation range of ≤±0.005V. The initial cathode current density is controlled at 0.3-0.6 A / cm². During electrolysis, RhCl6³⁻ is gradually reduced and deposited at the cathode, while some undeposited rhodium is enriched in the anode mud (because undissolved rhodium remains on the anode surface during the anode reaction, forming anode mud). When the cathode current density drops to below 3% of the initial value, and online monitoring shows that the RhCl6³⁻ content in the molten salt is ≤0.005g / L, the rhodium electrolysis stage is terminated, allowing rhodium to be deposited at the cathode or enriched in the anode mud. During this process, since platinum and palladium have been basically separated in the first two stages, the contamination of rhodium by platinum and palladium residues can be effectively avoided. At the same time, precise potential control ensures sufficient deposition and enrichment of rhodium.

[0031] 3. Product processing

[0032] 3.1 Platinum and Palladium Product Processing: The cathodes from the platinum and palladium deposition stages were removed separately and cooled to room temperature in an inert gas environment. After being rinsed with dilute hydrochloric acid to remove impurities and then rinsed with deionized water until the rinsing solution was neutral, the cathodes were dried and the deposits were peeled off. The crude platinum and palladium products were then vacuum smelted and refined. The platinum smelting temperature was 1550-1600℃ and the smelting time was 2-3 hours, while the palladium smelting temperature was 1500-1550℃ and the smelting time was 2-3 hours. An inert gas was introduced for protection during the smelting process. After the smelting was completed, the products were naturally cooled to room temperature to obtain platinum and palladium products with a purity of ≥99.99%.

[0033] 3.2 Rhodium Product Processing: After electrolysis is terminated, the anode is removed and cooled to room temperature. The anode mud on the anode surface is collected and ground to a particle size ≤100 mesh. Dilute aqua regia (concentrated hydrochloric acid:concentrated nitric acid = 3:1) is added at a liquid-to-solid ratio of 5-8:1. The mixture is leached at 80-90℃ for 2-3 hours. After leaching, the mixture is filtered and washed, and the leaching solution and washing solution are combined. After ion exchange purification (the ion exchange column is a strong acidic cation exchange resin, and the desorbent is a 5-7% hydrochloric acid solution by mass), hydrazine hydrate reduction precipitation, washing, and drying, the rhodium concentrate is vacuum smelted at a temperature of 1850-1920℃ for 2.5-3.5 hours. Argon gas is introduced for protection during the smelting process. After cooling to room temperature, a rhodium product with a purity ≥99.99% is obtained.

[0034] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0035] ① This invention achieves high-purity separation of platinum, palladium, and rhodium without co-deposition interference. The three-step deposition of platinum, palladium, and rhodium all employ precise potential control, enhanced stirring and mass transfer, and precise termination strategies, with dual thermodynamic and kinetic suppression of co-deposition. Specifically, palladium impurities in platinum are <0.5 ppm and rhodium is undetectable, platinum impurities in palladium are <0.3 ppm and rhodium is undetectable, and platinum and palladium impurities in rhodium are both <0.4 ppm, achieving 5N-level (99.999%) purification.

[0036] ② Green and environmentally friendly: The entire process is carried out in a closed and inert environment, without the use of highly toxic reagents such as aqua regia and cyanide, and without the generation of toxic and harmful gases such as chlorine and nitrogen oxides. The electrolyte can be recycled, and there is no waste liquid or waste gas pollution, which meets the requirements of green metallurgical development.

[0037] ③ High efficiency and convenience: Through one-step molten salt electrolysis and three-step step-by-step deposition, platinum, palladium and rhodium can be separated rapidly. The process is short, no need for multiple extraction and precipitation, low energy consumption, and convenient operation, making it suitable for large-scale industrial production.

[0038] ④ Wide applicability: It can process various types of decommissioned three-way catalyst waste (including scrapped three-way catalysts from the automotive, chemical and other fields), and has good separation and purification effects on wastes with different contents of platinum, palladium and rhodium, making it highly practical.

[0039] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, it can be implemented according to the contents of the specification. Furthermore, in order to make the above contents, objectives, features and advantages of the present invention more obvious and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0040] Figure 1 This invention relates to a method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst using molten salt electrolysis to obtain a high-purity platinum product.

[0041] Figure 2 This invention relates to a method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst using molten salt electrolysis to obtain a high-purity palladium product.

[0042] Figure 3 This invention relates to a method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst using molten salt electrolysis to obtain a high-purity rhodium product. Detailed Implementation

[0043] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0044] In addition, unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be obtained by purchasing them from the market or prepared by existing methods.

[0045] Example 1

[0046] 1. Anode preparation: The waste material of retired automotive three-way catalyst is crushed and ground to a particle size ≤100 mesh, 5% graphite powder (forming agent) is added, and it is pressed into an anode plate with a size of 100mm×50mm×5mm, and dried for later use; the cathode is a titanium plate, which is polished, soaked in 5% dilute hydrochloric acid for 12min, rinsed with deionized water, and dried at 80℃. The cathode size is 120mm×50mm×5mm (cathode to anode area ratio 1.2:1).

[0047] 2. Electrolysis system setup: Place the anode and cathode plates in a sealed inert electrolytic cell made of corundum, with the distance between the two electrodes controlled at 20 mm; add an equimolar ratio of KCl-NaCl eutectic molten salt and 1 mol% LiCl, and vacuum dry the molten salt (120℃, 2h) to remove moisture; continuously introduce argon gas into the electrolytic cell at a flow rate controlled at 80 mL / min to purge the air in the cell and maintain an inert environment.

[0048] 3. Platinum Deposition: The electrolytic cell was heated to 700℃ to completely melt the molten salt. A high-precision potentiostat was used to control the electrolysis potential at +0.79 V (vs Ag / AgCl reference electrode), with fluctuations controlled within ±0.003 V. Simultaneously, the molten salt was mechanically stirred at 200 rpm, and the initial cathode current density was controlled at 0.8 A / cm². After 2 hours of electrolysis, the cathode current density dropped to 4.8% of the initial value. Online monitoring showed that the PtCl₄²⁻ content in the molten salt was 0.009 g / L, and platinum electrolysis was immediately terminated. The cathode was removed and cooled to room temperature in an argon atmosphere. It was then soaked in 5% dilute hydrochloric acid for 8 minutes, rinsed three times with deionized water, vacuum dried at 100℃ for 1.5 hours, and the platinum deposit was peeled off after vacuum drying at 100℃. The crude platinum was then vacuum melted (1580℃, 2.5 hours) under argon protection and cooled to room temperature to obtain the platinum product.

[0049] 4. Palladium deposition: Maintain the molten salt temperature at 700℃, stirring speed at 200 rpm, and argon gas flow rate at 80 mL / min. Stable adjust the electrolysis potential to +0.62 V (vs Ag / AgCl reference electrode), with a fluctuation range of ±0.003 V. Control the initial cathode current density at 0.6 A / cm². After 3 hours of electrolysis, the cathode current density drops to 3.8% of the initial value. Online monitoring shows that the PdCl₄²⁻ content in the molten salt is 0.007 g / L, at which point the palladium electrolysis is terminated. Remove the cathode and follow the same post-treatment steps as the platinum product (inert gas cooling, acid washing, drying and peeling, vacuum melting at 1530℃ / 2.5 h) to obtain the palladium product.

[0050] 5. Rhodium separation: Maintain the molten salt temperature at 700℃, stirring speed at 200 rpm, and argon gas flow rate at 80 mL / min. Smoothly adjust the electrolysis potential to +0.42 V (vs Ag / AgCl reference electrode), with a fluctuation range of ±0.003 V. Control the initial cathode current density to 0.4 V. A / cm²; After 4 hours of electrolysis, the cathode current density dropped to 2.9% of the initial value. Online monitoring showed that the RhCl6³⁻ content in the molten salt was 0.004 g / L, so the rhodium electrolysis was terminated. The anode was removed and cooled to room temperature. The anode mud was collected and ground to a particle size ≤100 mesh. Dilute aqua regia (3:1) was added at a liquid-to-solid ratio of 6:1, and leaching was carried out at 85°C for 2.5 hours. The rhodium leaching rate was 99.7%, so leaching was stopped. After filtration and washing, the leaching solution and washing solution were combined. The solution was purified by ion exchange (using a strong acidic cation exchange resin, with a 7% hydrochloric acid solution as the desorbent), reduced and precipitated by hydrazine hydrate, washed and dried. The rhodium was then vacuum refined (1880°C, 3 hours, with argon gas protection), cooled to room temperature, and the rhodium product was obtained.

[0051] Example 2

[0052] 1. Anode preparation: The waste material of retired three-way catalysts in the chemical industry is crushed and ground to a particle size ≤100 mesh, 4% graphite powder (forming agent) is added, and it is pressed into an anode plate with a size of 110mm×55mm×5mm, and dried for later use; the cathode is a titanium plate, which is polished, soaked in 6% dilute hydrochloric acid for 10min, rinsed with deionized water, and dried. The cathode size is 154mm×55mm×5mm (cathode to anode area ratio 1.4:1).

[0053] 2. Electrolysis system setup: Place the anode and cathode plates in a sealed inert electrolytic cell made of graphite, with the distance between the two electrodes controlled at 25 mm; add equimolar KCl-NaCl eutectic molten salt and 0.8 mol% LiCl, and vacuum dry the molten salt (120℃, 2h) to remove moisture; continuously introduce nitrogen gas into the electrolytic cell at a flow rate of 60 mL / min to purge the air from the cell and maintain an inert environment.

[0054] 3. Platinum Deposition: The electrolytic cell was heated to 680℃ to completely melt the molten salt. The electrolysis potential was controlled at +0.78 V (vs Ag / AgCl reference electrode) using a high-precision potentiostat, with fluctuations controlled within ±0.004 V. Simultaneously, the molten salt was mechanically stirred at 150 rpm, and the initial cathode current density was controlled at 0.6 A / cm². After 2.5 h of electrolysis, the cathode current density dropped to 4.5% of the initial value. Online monitoring showed that the PtCl₄²⁻ content in the molten salt was 0.008 g / L, and platinum electrolysis was immediately terminated. The cathode was removed and cooled to room temperature in a nitrogen environment. It was then soaked in 5% dilute hydrochloric acid for 8 min, rinsed 3 times with deionized water, vacuum dried at 100℃ for 1.5 h, and the platinum deposit was peeled off after vacuum drying at 100℃. The crude platinum was then vacuum melted (1550℃, 3 h) under nitrogen protection and cooled to room temperature to obtain the platinum product.

[0055] 4. Palladium deposition: Maintain the molten salt temperature at 680℃, stirring speed at 150 rpm, and nitrogen gas introduction rate at 60 mL / min. Stable adjust the electrolysis potential to +0.60 V (vs Ag / AgCl reference electrode), with a fluctuation range of ±0.004 V. Control the initial cathode current density at 0.4 A / cm². After electrolysis for 3.5 h, the cathode current density drops to 3.6% of the initial value. Online monitoring shows that the PdCl₄²⁻ content in the molten salt is 0.006 g / L, at which point palladium electrolysis is terminated. Remove the cathode and follow the same post-treatment steps as for platinum products (inert gas cooling, acid washing, drying and peeling, vacuum melting at 1500℃ / 3 h) to obtain the palladium product.

[0056] 5. Rhodium separation: Maintain the molten salt temperature at 680℃, stirring speed at 150 rpm, and nitrogen gas introduction rate at 60 mL / min. Smoothly adjust the electrolysis potential to +0.40 V (vs Ag / AgCl reference electrode), with a fluctuation range of ±0.004 V. Control the initial cathode current density to 0.3 V. A / cm²; After electrolysis for 4.5 h, the cathode current density dropped to 2.7% of the initial value. Online monitoring showed that the RhCl6³⁻ content in the molten salt was 0.003 g / L, so rhodium electrolysis was terminated. The anode was removed and cooled to room temperature. The anode mud was collected and ground to a particle size ≤100 mesh. Dilute aqua regia (3:1) was added at a liquid-to-solid ratio of 5:1, and leaching was carried out at 80℃ for 3 h. The rhodium leaching rate was 99.6%, so leaching was stopped. After filtration and washing, the leaching solution and washing solution were combined. The solution was purified by ion exchange (using a strong acidic cation exchange resin and a 6% hydrochloric acid solution as the desorbent), reduced and precipitated by hydrazine hydrate, washed and dried. The rhodium concentrate was then vacuum melted (1850℃, 3.5 h), protected by nitrogen, and cooled to room temperature to obtain the rhodium product.

[0057] Example 3

[0058] 1. Anode preparation: The waste material of the retired three-way catalyst of automobile exhaust (low content of platinum, palladium and rhodium) is crushed and ground to a particle size of ≤100 mesh, 6% graphite powder (forming agent) is added, and it is pressed into an anode plate with a size of 90mm×45mm×5mm and dried for later use; the cathode is a titanium plate, which is polished, soaked in 7% dilute hydrochloric acid for 15min, rinsed with deionized water and dried. The cathode size is 135mm×45mm×5mm (cathode to anode area ratio of 1.5:1).

[0059] Electrolysis system setup: Place the anode and cathode plates in a sealed inert electrolytic cell made of corundum, with the distance between the two electrodes controlled at 18 mm; add equimolar KCl-NaCl eutectic molten salt and 1.5 mol% LiCl, and vacuum dry the molten salt (120℃, 2h) to remove moisture; continuously introduce argon gas into the electrolytic cell at a flow rate of 100 mL / min to purge the air from the cell and maintain an inert environment.

[0060] 2. Platinum Deposition: The electrolytic cell was heated to 720℃ to completely melt the molten salt. The electrolysis potential was controlled at +0.80 V (vs Ag / AgCl reference electrode) using a high-precision potentiostat, with fluctuations controlled within ±0.002 V. Simultaneously, the molten salt was mechanically stirred at a rate of 280 rpm, and the initial cathode current density was controlled at 1.0 A / cm². After electrolysis for 1.8 h, the cathode current density dropped to 4.9% of the initial value. Online monitoring showed that the PtCl₄²⁻ content in the molten salt was 0.010 g / L, and platinum electrolysis was immediately terminated. The cathode was removed and cooled to room temperature in an argon atmosphere. It was then soaked in 5% dilute hydrochloric acid for 8 min, rinsed three times with deionized water, vacuum dried at 100℃ for 1.5 h, and the platinum deposit was peeled off after vacuum drying at 100℃. The crude platinum was then vacuum melted (1600℃, 2 h) under argon protection and cooled to room temperature to obtain the platinum product.

[0061] 3. Palladium deposition: Maintain the molten salt temperature at 720℃, stirring speed at 280 rpm, and argon gas flow rate at 100 mL / min. Stable adjust the electrolysis potential to +0.65 V (vs Ag / AgCl reference electrode), with fluctuation range of ±0.002 V. Control the initial cathode current density to 0.8 A / cm². After electrolysis for 2.8 h, the cathode current density drops to 3.9% of the initial value. Online monitoring shows that the PdCl₄²⁻ content in the molten salt is 0.008 g / L, at which point palladium electrolysis is terminated. Remove the cathode and follow the same post-treatment steps as for platinum products (inert gas cooling, acid washing, drying and peeling, vacuum melting at 1550℃ / 2 h) to obtain the palladium product.

[0062] 4. Rhodium separation: Maintain the molten salt temperature at 720℃, stirring speed at 280 rpm, and argon gas flow rate at 100 mL / min. Smoothly adjust the electrolysis potential to +0.45 V (vs Ag / AgCl reference electrode), with a fluctuation range of ±0.002 V. Control the initial cathode current density to 0.6. A / cm²; After electrolysis for 3.8 h, the cathode current density dropped to 2.8% of the initial value. Online monitoring showed that the RhCl6³⁻ content in the molten salt was 0.005 g / L, so the rhodium electrolysis was terminated. The anode was removed and cooled to room temperature. The anode mud was collected and ground to a particle size ≤100 mesh. Dilute aqua regia (3:1) was added at a liquid-to-solid ratio of 8:1, and leaching was carried out at 90 °C for 2 h. The rhodium leaching rate was 99.8%, so leaching was stopped. After filtration and washing, the leaching solution and washing solution were combined. The solution was purified by ion exchange (using a strong acidic cation exchange resin and a 5% hydrochloric acid solution as the desorbent), reduced and precipitated by hydrazine hydrate, washed and dried. The rhodium concentrate was then vacuum melted (1920 °C, 2.5 h), protected by argon gas, and cooled to room temperature to obtain the rhodium product.

[0063] Comparative Example 1

[0064] 1. Anode preparation and electrolysis system construction: completely consistent with Example 1 (retired automobile three-way catalyst waste, cathode and anode dimensions, KCl-NaCl molten salt + 1mol% LiCl, argon flow rate 80mL / min, electrolysis temperature 700℃).

[0065] 2. Stepwise electrolytic deposition: High-precision constant potential control is not used; only constant current electrolysis is used. The initial current density is the same as in Example 1 (platinum deposition 0.8 A / cm², palladium deposition 0.6 A / cm², rhodium deposition 0.4 A / cm²). Potential fluctuations are not controlled. The stirring rate is 200 rpm. The termination conditions are the same as in Example 1.

[0066] 3. Product processing: Completely consistent with Example 1 (same pickling and vacuum melting parameters).

[0067] Comparative Example 2

[0068] 1. Anode preparation and electrolysis system construction: completely consistent with Example 1 (retired automobile three-way catalyst waste, cathode and anode dimensions, KCl-NaCl molten salt + 1mol% LiCl, argon flow rate 80mL / min, electrolysis temperature 700℃).

[0069] 2. Stepwise electrolytic deposition: The same precise potential control as in Example 1 was used (platinum +0.79V, palladium +0.62V, rhodium +0.42V, fluctuation ±0.003V), the initial current density was the same as in Example 1, but no mechanical stirring was performed (stirring rate 0 rpm), and the termination conditions were the same as in Example 1.

[0070] 3. Product processing: Completely consistent with Example 1 (same pickling and vacuum melting parameters).

[0071] Table 1: Comparison of the implementation effects of Examples 1-3 and Comparative Examples 1-2

[0072]

[0073] As shown in Table 1, the purity of the high-purity platinum, palladium, and rhodium products of this invention is not less than 99.99%, with palladium impurities in platinum <0.5 ppm and rhodium undetected, platinum impurities in palladium <0.3 ppm and rhodium undetected, and both platinum and palladium impurities in rhodium <0.4 ppm. All three embodiments of this invention can achieve high-purity purification at the 4N~5N level without co-deposition. However, comparative examples 1 and 2, which lack the key optimizations of this invention, show significantly reduced purification effects and leaching rates, and exhibit varying degrees of co-deposition, further highlighting the importance of process parameter control in this invention.

[0074] In summary, the method of this invention uses the metal of the ternary catalyst to be purified as the anode and a titanium plate as the cathode in a potassium chloride-sodium chloride eutectic molten salt. Through precise potential control (platinum: +0.78~+0.80 V, palladium: +0.60~+0.65 V, rhodium: +0.40~+0.45 V), enhanced stirring and mass transfer, and precise stage termination, combined with the construction of the electrolysis system and product processing steps, the co-deposition of platinum, palladium, and rhodium is strictly suppressed, achieving stepwise and efficient separation of the three precious metals. This invention achieves efficient, green, and high-purity separation and purification of platinum, palladium, and rhodium in ternary catalysts through molten salt electrolysis, solving the problems of environmental pollution, low efficiency, and co-deposition interference existing in traditional methods. The purity of the product of this invention can reach 4N~5N. The entire process is green, with no toxic waste gas or waste liquid generated. The process flow is short, energy consumption is low, and operation is convenient. It is suitable for the industrial recycling of various decommissioned ternary catalyst wastes, and has significant economic and environmental benefits.

[0075] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0076] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis, characterized in that, Includes the following steps: S1 electrolysis system construction: The three-way catalyst metal to be purified is used as the anode, titanium plate is used as the cathode, a closed inert protective environment electrolysis cell is used, and eutectic molten salt is used as the electrolyte; S2 stepwise electrolytic deposition: The first step is platinum deposition. The electrolytic potential is controlled, and the molten salt is stirred. The platinum electrolysis stage is terminated when the cathode current density drops below 5% of the initial value. The second step is palladium deposition. After the platinum deposition stage is terminated, the molten salt is stirred, and the electrolytic potential is adjusted. The palladium electrolysis stage is terminated when the cathode current density drops below 4% of the initial value and the PdCl4²⁻ content in the molten salt is ≤0.008 g / L. The third step is rhodium separation. After the palladium deposition stage is terminated, the molten salt is stirred, and the electrolytic potential is adjusted. The rhodium electrolysis stage is terminated when the cathode current density drops below 3% of the initial value and the RhCl6³⁻ content in the molten salt is ≤0.005 g / L. S3 Product Processing: The processing of platinum and palladium products includes removing the cathodes from the platinum and palladium deposition stages, stripping off the deposits, and then vacuum melting to obtain platinum and palladium products; the processing of rhodium products includes removing the anode, collecting the anode mud on the anode surface, processing it to obtain refined rhodium, and then vacuum melting the refined rhodium to obtain rhodium products.

2. The method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis as described in claim 1, characterized in that: The titanium plate is processed by grinding, pickling, rinsing with deionized water, and drying.

3. The method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis as described in claim 2, characterized in that: The ratio of cathode area to anode area is 1.2-1.5:

1.

4. The method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis as described in claim 1, characterized in that: The electrolyte is a potassium chloride-sodium chloride eutectic molten salt with a molar ratio of 1:1, and 0.5–2 mol% LiCl is added. The electrolyte is vacuum dried before use.

5. The method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis as described in claim 1, characterized in that: During platinum deposition, the initial cathode current density is 0.5-1.0 A / cm², and the electrolysis potential is controlled between +0.78 V and +0.80 V; during palladium deposition, the initial cathode current density is 0.4-0.8 A / cm², and the electrolysis potential is adjusted to +0.60 V to +0.65 V; during rhodium separation, the initial cathode current density is 0.3-0.6 A / cm², and the electrolysis potential is adjusted to +0.40 V to +0.45 V.

6. The method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis as described in claim 1, characterized in that: The stirring speed of the molten salt in S2 is 100–300 rpm.

7. The method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis as described in claim 1, characterized in that: During the S2 electrolysis process, inert gas is continuously introduced at a flow rate of 50-100 mL / min, and the electrolysis temperature is 650℃~750℃.

8. The method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis as described in claim 1, characterized in that: In the processing of S3 platinum and palladium products, the cathodes of the platinum and palladium deposition stages were removed, placed in an inert gas environment and cooled to room temperature. They were then washed with dilute hydrochloric acid to remove impurities, rinsed with deionized water until the rinsing solution was neutral, dried, and the deposits were peeled off.

9. The method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis as described in claim 8, characterized in that: In the processing of S3 rhodium products, the anode mud is ground to a particle size ≤100 mesh, and dilute aqua regia is added at a liquid-solid ratio of 5-8:

1. The mixture is then leached at 80-90℃ for 2-3 hours, filtered, washed, and the leachate and washing solution are combined. After ion exchange purification, hydrazine hydrate reduction precipitation, washing and drying, high-quality rhodium was obtained.

10. The method for separating and purifying platinum, palladium, and rhodium in a ternary catalyst by molten salt electrolysis as described in claim 9, characterized in that: The vacuum melting temperature for platinum is 1550-1600℃, and the melting time is 2-3 hours; the vacuum melting temperature for palladium is 1500-1550℃, and the melting time is 2-3 hours; the vacuum melting temperature for high-quality rhodium is 1850-1920℃, and the melting time is 2.5-3.5 hours.

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