Method for recovering platinum group noble metals in silicon carbide DPF catalyst

Abstract

A method for recovering platinum group precious metal in a silicon carbide DPF catalyst comprises the steps that S1, smelting treatment is conducted, specifically, the silicon carbide DPF catalyst is crushed and then mixed with a smelting agent in a layered mode, a smelting reaction is conducted at the high temperature, and the smelting agent is composed of sodium carbonate and sodium peroxide; s2, leaching and separation are conducted, specifically, after the smelting product obtained in the step S1 is cooled, acid leaching treatment is conducted through hydrochloric acid, leaching liquid containing platinum group precious metal and residues are obtained through filtering separation, the residues are washed, and washing liquid is added into main leaching liquid; and S3, precious metal enrichment is conducted, specifically, the leachate obtained in the step S2 is enriched through a chemical precipitation method, the obtained precipitate is dissolved with aqua regia, and a platinum-palladium chloride mixed solution is obtained. The method is high in recovery rate, and under the optimal condition, the recovery rate of platinum can reach 91% or above, and the recovery rate of palladium can reach 96% or above; the process is simple, the cost is controllable, the used smelting agent is a common chemical raw material, and the cost is low.

Description

Technical Field

[0001] This invention relates to the field of precious metal recovery technology, specifically a method for recovering platinum group precious metals from a silicon carbide DPF catalyst. Background Technology

[0002] Platinum group metals (such as platinum (Pt), palladium (Pd), and rhodium (Rh)) are widely used in automotive exhaust purification catalysts due to their excellent catalytic performance. With increasingly stringent environmental regulations, the demand for precious metals continues to grow. However, precious metal mineral resources are scarce, mining costs are high, and they cause significant environmental damage. Therefore, recovering precious metals from waste catalysts has become an important resource source.

[0003] Currently, most automotive exhaust purification catalyst carriers are made of cordierite, and the precious metal recovery technology for such carriers is relatively mature. However, silicon carbide (SiC) is increasingly used in high-performance diesel particulate filters (DPFs) due to its excellent thermal stability and thermal conductivity. SiC has extremely high chemical inertness and stability, which makes the platinum group precious metals in it firmly encapsulated. It is difficult to effectively release and recover them using traditional acid leaching or conventional roasting methods, and the recovery efficiency is generally low.

[0004] In the existing technology, a variety of technical routes have been developed for the recovery of platinum group metals (PGMs). However, when processing DPF catalysts supported on SiC, there are still obvious technical compatibility issues and process limitations.

[0005] First, some existing methods are based on the dissolution and destruction of the metal matrix. For example, Chinese patent CN118308601A (Dong Haigang et al.) discloses a process for enriching platinum group metals from ferrosilicon alloys. This process uses a multi-step combined process of sulfuric acid dissolution, alkali roasting, and water immersion to destroy the Fe-Si-C-PGM metal phase structure to achieve noble metal enrichment. However, this method is applicable to metal alloy systems, and its mechanism of action depends on the chemical dissolution of the metal matrix. SiC, as a ceramic material with strong covalent bonds, has extremely stable chemical properties and is difficult to effectively destroy its crystal structure through such wet-fire combined processes, thus failing to achieve efficient release of noble metals.

[0006] Other technologies focus on addressing the problem of carbonaceous residues in catalysts encapsulating precious metals. For example, Chinese patent CN119800081A (by Zhao Ming et al.) proposes oxidizing and removing organic carbon deposits through sodium carbonate calcination, thereby improving platinum recovery. This method primarily targets physical carbon coverage, while the binding of precious metals to the SiC support stems from its robust covalent lattice structure, fundamentally different from carbon encapsulation. Therefore, relying solely on oxidation for carbon removal cannot overcome the strong encapsulation of precious metals by the SiC lattice and is unsuitable for catalyst recovery scenarios using SiC as the support.

[0007] In addition, there are pyrometallurgical smelting processes specifically designed for SiC-containing materials internationally. For example, Chinese patent CN114901843A discloses a method for oxidizing SiC by adding iron oxides (such as Fe2O3) and smelting at high temperatures (approximately 1550°C) and then using the reduced iron phase to capture PGM. Although this method can achieve precious metal recovery to some extent, it still has several process defects: First, the amount of iron oxide added must strictly conform to the stoichiometric ratio (usually not less than 65%), otherwise it will lead to incomplete SiC conversion, increased slag viscosity, and consequently a significant decrease in PGM recovery rate (which can be lower than 70%); Second, the reaction must be carried out at high temperatures and under a precisely controlled reducing atmosphere, which places stringent requirements on equipment and consumes a lot of energy; Third, the large amount of iron-based lumps generated will dilute the precious metals, increasing the difficulty and cost of subsequent separation and refining.

[0008] In summary, existing technologies, whether based on metal dissolution, carbon removal, or iron oxide-assisted smelting, have failed to provide a complete solution that can efficiently, economically, and specifically destroy the SiC support structure and achieve stable recovery of platinum group metals. Therefore, developing a targeted, simple, and highly efficient method for recovering precious metals from silicon carbide DPF catalysts remains a pressing technical challenge in this field. Summary of the Invention

[0009] To address the aforementioned problems, the present invention aims to provide a method for recovering platinum group metals from silicon carbide DPF catalysts.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows: a method for recovering platinum group noble metals from a silicon carbide DPF catalyst, comprising the following steps: S1. Melting treatment: After crushing the silicon carbide DPF catalyst, it is mixed with the melting agent in layers and then melted at high temperature. The melting agent is composed of sodium carbonate and sodium peroxide. S2. Leaching and separation: After cooling the smelting product obtained in step S1, acid leaching is performed with hydrochloric acid. The product is then filtered and separated to obtain a leachate containing platinum group noble metals and a residue. The residue is washed and the washing liquid is incorporated into the main leachate. S3. Enrichment of precious metals: The leachate obtained in step S2 is enriched by chemical precipitation, and the precipitate is dissolved in aqua regia to obtain a mixed solution of platinum-palladium chloride.

[0011] Further, in step S1, the mass ratio of sodium carbonate to sodium peroxide in the smelting flux is 6-10:9-12.

[0012] Furthermore, the total mass ratio of silicon carbide DPF catalyst to smelting flux is 1:15 to 22.

[0013] Furthermore, in step S1, the layered mixing with the smelting agent refers to the order in which the reagents are placed from the bottom to the top of the crucible as follows: sodium carbonate, silicon carbide DPF catalyst powder + sodium peroxide, sodium peroxide, and sodium carbonate.

[0014] Furthermore, in step S1, the melting temperature is 750–870°C.

[0015] Furthermore, in step S1, the holding time for melting is 0.5 to 2 hours.

[0016] With the above settings, the beneficial effects of the present invention compared with the prior art are as follows: 1. Significantly Improved Recovery Rate and Complete Release of Precious Metals: Through the synergistic effect of sodium carbonate and sodium peroxide, the stable covalent lattice structure of silicon carbide is effectively disrupted during high-temperature smelting, fundamentally solving the problem of precious metals being firmly encapsulated, allowing for their full release and conversion. A specific layered mixing and feeding method effectively suppresses splashing that may be caused by the violent reaction of sodium peroxide, ensuring the safety and completeness of the reaction. Experimental verification shows that under optimized process conditions, the recovery rate of platinum can reach over 91%, and the recovery rate of palladium can reach over 96%. The recovery efficiency is significantly better than traditional acid leaching or conventional roasting methods, and it also overcomes the problem of a sharp drop in recovery rate (below 70%) caused by inaccurate batching or atmosphere control in iron oxide smelting methods.

[0017] 2. Unique Technical Approach, Precisely Solving the SiC Recovery Challenge: The "alkali fusion oxidation" approach employed in this invention is specifically designed to overcome the core obstacle of SiC's stable covalent bond structure. Its mechanism of action differs fundamentally from techniques for treating cordierite supports, and also from existing methods that only remove carbon coatings (e.g., CN119800081A) or are applicable to metal alloy systems (e.g., CN118308601A). This method directly targets the chemical inertness of SiC from the reaction principle perspective, providing an effective solution not previously fully revealed in published technologies, achieving highly efficient recovery of precious metals from specific supports.

[0018] 3. The synergistic effect of the flux is prominent, and the reaction mechanism is highly efficient: The combination of sodium carbonate and sodium peroxide plays a crucial synergistic role. Sodium carbonate, as both a flux and a reactant, not only lowers the melting temperature of the system, allowing the reaction to proceed at a relatively low temperature of 750–870°C, but also reacts with silicon carbide. Meanwhile, sodium peroxide, as a strong oxidant, can violently oxidize silicon carbide at high temperatures, strongly disrupting its crystal lattice. Comparative experiments show that the absence of either component leads to a sharp decrease in the recovery rate of precious metals. This synergistic mechanism is the core of achieving efficient recovery.

[0019] 4. Simple process flow and strong industrial feasibility: The core recovery step of this invention is a one-step smelting process. Subsequent acid leaching, filtration, and enrichment are all mature hydrometallurgical unit operations. The overall process is short, easy to operate, and easy to control and implement for large-scale industrial production. Compared with iron oxide smelting methods that require high temperatures (approximately 1550℃) and precise control of the reducing atmosphere (such as CN114901843A), this invention has relatively lower equipment requirements, lower energy consumption, a wider process window, and more advantageous operating costs.

[0020] 5. Simplified subsequent processing and high purity of enriched products: The products after smelting and destruction can be efficiently transferred to the solution by conventional hydrochloric acid leaching, achieving good separation from the residue. Subsequent enrichment is achieved through chemical precipitation, and finally, a mixed solution of platinum-palladium chlorides is obtained by dissolving in aqua regia. This solution has a relatively simple composition, laying a good foundation for subsequent refining and purification of precious metals, and avoiding the problems of difficult separation and high refining costs associated with the large amount of iron-based lumps containing precious metals produced by the iron oxide smelting method.

[0021] 6. Economical raw material costs and significant environmental benefits: The smelting agents used (sodium carbonate and sodium peroxide) are common and relatively low-cost chemical raw materials, avoiding the use of large amounts of expensive iron oxide additives, thus keeping overall material costs under control. This method achieves efficient recovery of scarce strategic resources from hazardous solid waste (used catalysts), reducing the environmental damage caused by traditional mining and meeting the requirements of green circular economy and sustainable development. Attached Figure Description

[0022] The present invention will now be further described with reference to the accompanying drawings.

[0023] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0024] Example 1: Core Formula Validation like Figure 1 As shown, a method for recovering platinum group noble metals from a silicon carbide DPF catalyst includes the following steps: S1. Melting treatment: After crushing the silicon carbide DPF catalyst, it is mixed with the melting agent in layers. That is, from the bottom to the top of the crucible, the order of reagent placement is sodium carbonate, silicon carbide DPF catalyst powder + sodium peroxide, sodium peroxide, sodium carbonate, etc. Melting reaction is carried out at high temperature. The melting temperature is 750-870℃, and the holding time is 0.5-2 hours. The melting agent is composed of sodium carbonate and sodium peroxide. The mass ratio of sodium carbonate to sodium peroxide in the melting agent is 6-10:9-12, and the total mass ratio of silicon carbide DPF catalyst to melting agent is 1:15-22. S2. Leaching and separation: After cooling the smelting product obtained in step S1, acid leaching is performed with hydrochloric acid. The product is then filtered and separated to obtain a leachate containing platinum group noble metals and a residue. The residue is washed and the washing liquid is incorporated into the main leachate. S3. Enrichment of precious metals: The leachate obtained in step S2 is enriched by chemical precipitation, and the precipitate is dissolved in aqua regia to obtain a mixed solution of platinum-palladium chloride.

[0025] Specifically, the following steps are included: S1. Melting treatment: Take 1g of crushed silicon carbide DPF catalyst powder (known to contain platinum and palladium), 10g of sodium peroxide, and 8g of sodium carbonate. Place them in a crucible in the following order: sodium carbonate (i.e., Na2CO3), silicon carbide DPF catalyst powder + sodium peroxide, sodium peroxide (i.e., Na2O2), and sodium carbonate. Then place the crucible in a box-type muffle furnace and heat it to 770℃. Keep it at this temperature for 1 hour for melting. After the reaction is completed, take out the crucible and let it cool naturally to room temperature. S2. Precious metal enrichment: After cooling, transfer the crucible to a beaker and add 5 to 10 times the volume of the smelting product in analytical grade hydrochloric acid (concentration of 1 to 3 mol / L) to ensure complete immersion of the crucible. Stir and leach at 100°C for 1 to 2 hours. Filter the reaction mixture through a Buchner funnel and wash the residue three times with hot water. Combine the filtrate and washing liquid and place them in a wide-mouth conical flask. S3. Precious metal enrichment: After sequentially adding appropriate amounts of 0.015 g / mL tellurium dioxide hydrochloric acid solution and 0.28 g / mL stannous chloride hydrochloric acid solution, a black precipitate appears. The solution is heated and kept at a gentle boil until the black precipitate is completely separated from the supernatant. Filter using a G4 funnel, then dissolve in aqua regia, and filter under vacuum to obtain a high-concentration mixed solution of platinum and palladium chlorides.

[0026] After adjusting the volume, the contents of platinum and palladium in the solution were determined by ICP-OES, and the recovery rate was calculated. The results showed that the recovery rate of platinum was 91.01% and the recovery rate of palladium was 96.97%.

[0027] Comparative Example 1: Lacking sodium peroxide Other conditions were the same as in Example 1, except that only 8g of sodium carbonate was used and sodium peroxide was not added. The results showed that the platinum recovery rate was only 29.9%, and the palladium recovery rate was only 29.5%. This demonstrates that the lack of the strong oxidant sodium peroxide is insufficient to effectively destroy the silicon carbide structure.

[0028] Comparative Example 2: Lack of sodium carbonate Other conditions were the same as in Example 1, except that only 10g of sodium peroxide was used and sodium carbonate was not added. In the specific layered mixing structure of this invention, sodium carbonate is located at the bottom and top layers, which is intended to melt first to form a stable molten salt medium and effectively encapsulate and buffer the violent reaction of sodium peroxide. Without sodium carbonate, this buffering and encapsulation mechanism completely fails, resulting in the direct and violent decomposition of sodium peroxide, causing serious splashing and loss of precious metals. Experimental results also show that the recovery rates of platinum and palladium are only 48.12% and 49.93%, respectively. This proves that sodium carbonate is not only a synergistic reactant that provides an alkaline environment and participates in the destruction of silicon carbide structure, but also an indispensable flux and buffer to maintain the physical stability of the reaction system. Its absence will cause the "layered mixing" design of this invention to fail.

[0029] Example 2: Experiment on Optimization of Fusing Flux Formulation To determine the optimal flux ratio, experiments were conducted by varying the ratio of sodium carbonate to sodium peroxide. The amount of silicon carbide DPF catalyst was fixed at 1 g, the melting temperature at 770℃, and the holding time at 1 hour. All other conditions were the same as in Example 1. The results are shown in the table below (the table below shows the experimental results of the flux formulation optimization):

[0030] As shown in Table 1, the flux ratio has a significant impact on the recovery rate, which profoundly reflects the synergistic mechanism of Na2CO3 and Na2O2 in the process of destroying the silicon carbide structure. 1. The experimental group (Na2CO3:Na2O2 = 8:10) achieved the best precious metal recovery effect. This ratio represents the optimal kinetic window for efficient smelting. Under this ratio, Na2CO3, acting as a flux, can first form a molten salt medium with suitable fluidity. This not only ensures the thermal uniformity of the reaction system but also provides an efficient mass transfer channel for the solid-liquid-gas multiphase reaction between Na2O2 and SiC. Simultaneously, sufficient Na2O2, acting as a strong oxidant, can continuously and intensely act on the SiC surface in this melt, oxidizing the Si in its lattice. 47 The process transforms the material into soluble silicates, thereby completely destroying its stable covalent bond structure and fully exposing the encapsulated platinum group metals. The two processes complement each other and are indispensable.

[0031] 2. The recovery rates of control groups 1 and 2 (with similar but slightly different ratios) decreased, but remained at a high level. This indicates that the synergistic mechanism remains effective within the ratio range of 6:9 to 10:12, and the system has a certain degree of tolerance. Although deviations from the optimal ratio may lead to slight changes in the physical properties of the molten salt (such as viscosity and mass transfer efficiency) or the absolute concentration of the oxidant, the core mechanism of "flux providing the reaction environment and oxidant performing the main destructive action" still holds true, thus maintaining a high recovery rate.

[0032] 3. The recovery rates of control groups 3 and 4 (severely unbalanced ratios) dropped sharply, which indirectly confirms the above mechanism. In control group 3 (insufficient Na2CO3), the excess Na2O2, lacking sufficient molten salt medium for buffering and dispersion, led to an overly violent and uncontrolled reaction, easily causing splashing losses. At the same time, the poor fluidity of the melt hindered reactant transfer and product diffusion, resulting in incomplete reaction. In control group 4 (insufficient Na2O2), the oxidant concentration was insufficient to completely destroy the hard SiC lattice, resulting in a large amount of precious metals remaining encased in the unreacted carrier and unable to be leached. These two sets of results jointly prove that the "melting and liquid-forming" effect of Na2CO3 and the "oxidative crystal-breaking" effect of Na2O2 must be precisely matched. If the function of either is weakened, the entire synergistic mechanism will fail.

[0033] In summary, a mass ratio of Na2CO3 to Na2O2 of 8:10 is the optimal flux formulation for achieving high recovery rates.

[0034] Example 3: Experiment on the Influence of Process Conditions

[0035] Based on Example 1, the melting temperature or time was changed, while the flux ratio (Na2CO3:Na2O2 = 8:10) was kept constant. Other conditions remained the same as in Example 1, and the effect of process conditions on the recovery rate was investigated. The table below shows the experimental results regarding the effect of process conditions:

[0036] As can be seen from the data in Table 2: 1. Temperature effect: The reaction is insufficient and the recovery rate is low at 670℃; the recovery rate is still relatively high at 870℃, but there is no significant improvement compared with 770℃ and the energy consumption is higher; 770℃ is the optimal temperature.

[0037] 2. Effect of heat preservation time: 0.5 hours of heat preservation time is insufficient and the reaction is incomplete; 2 hours of heat preservation slightly improves the recovery rate, but the improvement is not significant compared with 1 hour. Considering both efficiency and energy consumption, 1 hour is the optimal heat preservation time.

[0038] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for recovering platinum group noble metals in a silicon carbide DPF catalyst, characterized by, The method comprises the following steps: S1, smelting treatment, after crushing the silicon carbide DPF catalyst, the silicon carbide DPF catalyst is mixed with smelting agent in layers, and smelting reaction is carried out at high temperature, wherein the smelting agent is composed of sodium carbonate and sodium peroxide; S2, leaching and separation, after cooling the smelting product obtained in step S1, acid leaching treatment is carried out by using hydrochloric acid, and leaching liquid containing platinum group noble metal and residue are obtained by filtration and separation, and the residue is washed, and the washing liquid is incorporated into the main leaching liquid; S3, noble metal enrichment, the leaching liquid obtained in step S2 is enriched by using chemical precipitation method, and the obtained precipitate is dissolved by aqua regia to obtain platinum-palladium chloride mixed solution.

2. A method of recovering platinum group noble metals from a silicon carbide DPF catalyst according to claim 1, characterized in that: In step S1, the mass ratio of sodium carbonate to sodium peroxide in the smelting agent is 6-10:9-12.

3. A method for recovering platinum group noble metals from a silicon carbide DPF catalyst according to claim 2, characterized in that: The mass ratio of sodium carbonate to sodium peroxide in the smelting agent is 8:

10.

4. The method of claim 2, wherein the platinum group metal is recovered from the silicon carbide DPF catalyst by: The total mass ratio of the silicon carbide DPF catalyst to the smelting agent is 1:15-22.

5. The method of claim 1, wherein the platinum group metal is selected from the group consisting of platinum, palladium, rhodium, ruthenium, iridium, osmium, and combinations thereof. In step S1, the mixing with the smelting agent in layers means that, from the bottom of the crucible to the uppermost layer, the reagent placement order is sodium carbonate, silicon carbide DPF catalyst powder + sodium peroxide, sodium peroxide, and sodium carbonate.

6. The method of claim 1, wherein the platinum group metal is selected from the group consisting of platinum, palladium, rhodium, ruthenium, iridium, osmium, and combinations thereof. In step S1, the temperature of the smelting is 750-870 DEG C.

7. A method for recovering platinum group noble metals from a silicon carbide DPF catalyst according to claim 6, characterized in that: In step S1, the temperature of the smelting is 770 DEG C.

8. The method of claim 2, wherein the platinum group metal is recovered from the silicon carbide DPF catalyst by: In step S1, the holding time of the smelting is 0.5-2 hours.

9. The method of claim 8 wherein the platinum group metal is recovered from the silicon carbide DPF catalyst by: The holding time of the smelting is 1 hour.

10. The method of claim 2, wherein the platinum group metal is recovered from the silicon carbide DPF catalyst. The platinum group noble metal includes platinum and palladium.

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