Method for recovering platinum group metal from waste catalyst

Abstract

The invention belongs to the technical field of platinum group metal recovery, and particularly relates to a method for recovering platinum group metal from a waste catalyst. The method comprises the following steps: recovering platinum group metals in the waste catalyst by adopting an active metal enrichment-iodine replacement method, melting the active metals and the waste catalyst to obtain an intermetallic compound enriched with platinum group metal elements, putting the intermetallic compound enriched with the platinum group metals into iodide molten salt, heating and decomposing the iodide molten salt to generate iodine vapor, and removing the iodine vapor from the waste catalyst. The iodine vapor and the intermetallic compound are subjected to a replacement reaction, platinum group metal in the intermetallic compound is oxidized into a metal simple substance, meanwhile, the active metal iodide fused salt is generated, no fused salt is consumed in the whole process, and the fused salt can be recycled.

Description

Technical Field

[0001] The invention belongs to the technical field of platinum group metal recovery, and in particular relates to a method for recovering platinum group metals from waste catalysts. Background Art

[0002] PGMs (platinum group metals) have excellent physical and chemical properties such as high stability, high temperature resistance and good catalytic activity. They are often used as catalysts in the fields of automobiles, petroleum, chemicals, aerospace, etc. The activity of catalysts containing platinum group metals will gradually decrease during use, affecting the effect of use. The most common one is automobile exhaust catalyst, which affects automobile exhaust emissions after deactivation. In industrial production, economic benefits can be improved by recovering platinum group metals from waste catalysts.

[0003] At present, the recovery methods of platinum group metals in automobile exhaust catalysts are mainly divided into pyrometallurgy and hydrometallurgy. Pyrometallurgy recovery usually uses high-temperature smelting to compound platinum group metals with base metals (iron, copper, lead, nickel, etc.), and then extracts platinum group metals from them through separation and refining. Hydrometallurgy recovery usually includes crushing, leaching, filtration and washing stages to extract platinum group metals from the filtrate. Hydrometallurgy recovery of platinum group metal elements has the disadvantages of small processing scale, long process flow, and high waste gas / liquid emissions; pyrometallurgy recovery has the advantages of short process and large processing scale, but it has high energy consumption and high cost, and still needs further improvement.

[0004] In summary, there is an urgent need to provide a platinum group metal recovery method with a short process flow, low energy consumption and no waste gas / liquid emissions. Summary of the invention

[0005] The purpose of the present invention is to provide a method for recovering platinum group metals from waste catalysts. The present invention uses an active metal enrichment-iodine replacement method to recover platinum group metals from waste catalysts. No iodide molten salt is consumed in the whole process, and the iodide molten salt can be reused. At the same time, the process is shortened, energy consumption is reduced, and there is no waste liquid / gas emission. It is an efficient and environmentally friendly recovery method.

[0006] The present invention provides a method for recovering platinum group metals from waste catalysts, comprising the following steps:

[0007] The spent catalyst is crushed and then melted with active metal to obtain an intermetallic compound enriched with platinum group metal elements;

[0008] placing the intermetallic compound in an iodide molten salt to carry out an iodine replacement reaction to obtain a platinum group metal;

[0009] The waste catalyst is a waste catalyst containing platinum group metal elements;

[0010] The active metal is one or more of alkali metals, alkaline earth metals, Al and Zn.

[0011] Preferably, the molar ratio of the platinum group metal to the active metal in the waste catalyst is 1:2 to 1:4;

[0012] The waste catalyst is an automobile exhaust waste catalyst.

[0013] Preferably, the alkali metal includes one or more of K, Li and Na; and the alkaline earth metal includes one or both of Ca and Mg.

[0014] Preferably, the iodide is KI, LiI, NaI, CaI 2 MgI 2 , A1 3 and ZnI 2 One or more of .

[0015] Preferably, the temperature of the iodine replacement reaction is 400-600°C, the insulation time is 0.5-2.5h, and the heating rate to the iodine replacement reaction is 5-25°C / min; the iodine replacement reaction is carried out under a protective atmosphere or vacuum conditions.

[0016] Preferably, before placing the intermetallic compound in the iodide molten salt, the iodide molten salt is further dehydrated; the dehydration temperature is 200 to 400° C., and the insulation time is 6 to 8 hours.

[0017] Preferably, the melting process is arc melting.

[0018] Preferably, the arc melting current is 50-60A and the time is 4-7 minutes.

[0019] Preferably, the arc melting current is a pulsed firing current, the pulse period of the pulsed firing current is 0.5 to 1.5 s, and the duty cycle is 40% to 60%.

[0020] Preferably, the vacuum degree of the arc melting is below 10 Pa.

[0021] Beneficial effects:

[0022] The present invention provides a method for recovering platinum group metals from waste catalysts, comprising the following steps: crushing the waste catalyst and then melting it with an active metal to obtain an intermetallic compound enriched with platinum group metal elements; placing the intermetallic compound in an iodide molten salt for iodine replacement reaction to obtain platinum group metals. The present invention uses an active metal enrichment-iodine replacement method to recover platinum group metals from waste catalysts. First, an intermetallic compound enriched with platinum group metal elements (RM intermetallic compound, R is an active metal, M is a platinum group metal) is obtained by melting the active metal and the waste catalyst, and then the intermetallic compound enriched with platinum group metal elements is placed in an iodide molten salt, and the iodide molten salt is heated and decomposed to generate iodine vapor, and the iodine vapor and the RM intermetallic compound undergo a replacement reaction, and the platinum group metal in the RM intermetallic compound is oxidized to a metal element, and an active metal iodide molten salt is generated at the same time, and there is no molten salt consumption throughout the process, and the molten salt can be reused. In summary, the method provided by the present invention is simple to operate, has no waste liquid or waste gas emissions, zero pollution, low energy consumption, can efficiently recover platinum group metals from waste catalysts, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below.

[0024] Figure 1 Schematic diagram of the device for recovering platinum group metals by iodine replacement in the embodiment; wherein: 1 is the air inlet; 2 is the air outlet; 3 is the inner crucible; 4 is the intermetallic compound; 5 is the iodide molten salt; 6 is the outer crucible; 7 is the stainless steel reactor;

[0025] Figure 2 is the XRD pattern of the metal palladium recovered in Example 1;

[0026] Figure 3 is a SEM image of the metal palladium recovered in Example 1;

[0027] Figure 4 This is the EDS graph of the metal palladium recovered in Example 1. DETAILED DESCRIPTION

[0028] The present invention provides a method for recovering platinum group metals from waste catalysts, comprising the following steps:

[0029] The spent catalyst is crushed and then melted with active metal to obtain an intermetallic compound enriched with platinum group metal elements;

[0030] placing the intermetallic compound in an iodide molten salt to carry out an iodine replacement reaction to obtain a platinum group metal;

[0031] The waste catalyst is a waste catalyst containing platinum group metal elements;

[0032] The active metal is one or more of alkali metals, alkaline earth metals, Al and Zn.

[0033] In the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0034] The present invention crushes the waste catalyst and then melts it with the active metal to obtain an intermetallic compound enriched with platinum group metal elements. In the present invention, the waste catalyst is preferably an automobile exhaust waste catalyst, and the platinum group metal elements in the waste catalyst preferably include one or more of rhodium, palladium and platinum, specifically a platinum-based catalyst, a palladium-based catalyst or a platinum-palladium-rhodium three-way catalyst; the crushed particle size is preferably 0.1 to 1 mm; the molar ratio of platinum group metals to active metals in the waste catalyst is preferably 1:2 to 1:4, specifically 1:3.

[0035] In the present invention, the active metal is one or more of alkali metal, alkaline earth metal, Al and Zn, the alkali metal preferably includes one or more of K, Li and Na; the alkaline earth metal preferably includes one or both of Ca and Mg. In a specific embodiment of the present invention, the active metal is preferably one or more of K, Li, Na, Ca, Mg, Al or Zn.

[0036] In the present invention, the melting treatment is preferably arc melting; the current of the arc melting is preferably 50-60A, specifically 53A, 55A or 57A; the time of the arc melting is preferably 4-7min, specifically 5min or 6min; the current of the arc melting is preferably a pulsed firing current; the pulse period of the pulsed firing current is preferably 0.5-1.5s, specifically 1s, and the duty cycle is preferably 40%-60%, specifically 50% or 55%.

[0037] In the present invention, the vacuum degree of the arc melting is preferably below 10Pa. In the present invention, the arc melting is preferably carried out in an arc furnace; before the arc melting, it is preferred to further include washing the arc furnace with a protective gas; the protective gas is preferably Ar gas, and the number of washings is preferably 2 to 3 times; the air is removed by washing to prevent the air from participating in the reaction during the arc melting process; after washing, the vacuum degree of the arc furnace is preferably reduced to below 10Pa.

[0038] After obtaining the intermetallic compound enriched with platinum group metal elements, the present invention places the intermetallic compound in an iodide molten salt to carry out an iodine substitution reaction to obtain a platinum group metal. In the present invention, the iodide is preferably KI, LiI, NaI, CaI 2 MgI 2, A1 3 and ZnI 2 In a specific embodiment of the present invention, the metal element in the iodide is the same as the active metal element.

[0039] In the present invention, the temperature of the iodine replacement reaction is preferably 400-600°C, specifically 450°C, 500°C or 550°C, the insulation time is preferably 0.5-2.5h, specifically 0.7h, 1h, 1.5h or 2h, the heating rate to the iodine replacement reaction is 5-25°C / min, specifically 10°C / min, 15°C / min or 20°C / min; the iodine replacement reaction is preferably carried out under a protective atmosphere or vacuum conditions; the protective atmosphere is preferably argon.

[0040] In the present invention, before placing the intermetallic compound in the iodide molten salt, it is preferred that the iodide molten salt is dehydrated; the dehydration temperature is preferably 200-400°C, specifically 300°C, and the insulation time is preferably 6-8h, specifically 7h; the dehydration is preferably carried out under protective gas or vacuum conditions; the protective gas is preferably argon.

[0041] In an embodiment of the present invention, the device used for the iodine replacement reaction preferably includes an air inlet pipe, an air outlet pipe, an inner crucible, an outer crucible and a stainless steel reactor; wherein the air inlet pipe and the air outlet pipe are connected to the stainless steel reactor, the outer crucible is placed inside the stainless steel reactor, the outer crucible is used to hold iodide molten salt, the inner crucible is placed in the outer crucible, and the inner crucible is used to hold intermetallic compounds; a hole is provided on the side wall of the inner crucible to facilitate the iodide molten salt in the outer crucible to enter the inner crucible. The structural schematic diagram of the iodine replacement reaction device described in the present invention is as follows Figure 1 shown.

[0042] In a specific embodiment of the present invention, the intermetallic compound is preferably placed in an inner crucible with holes punched on the side, and a high-temperature resistant connecting wire is connected to the inner crucible. The inner crucible containing the intermetallic compound is placed in an outer crucible containing iodide molten salt, ensuring that the punched portion of the inner crucible is completely immersed in the iodide molten salt, and the outer iodide molten salt can enter the inner crucible.

[0043] In a specific embodiment of the present invention, the high temperature resistant connecting wire is preferably a Mo wire, and the diameter of the Mo wire is preferably 0.5 mm; the inner crucible is preferably a BN crucible or an Al 2 O 3 Crucible; the outer crucible is preferably Al 2 O 3 Crucible; the iodine substitution reaction is preferably carried out in a resistance furnace.

[0044] After the iodine replacement reaction is completed, a platinum group metal block with an outer layer of iodide molten salt is obtained. In the present invention, the obtained platinum group metal block is preferably clamped out and then rinsed with water; the iodide molten salt on the surface is removed by water washing to obtain the platinum group metal. In the present invention, the intermetallic compound is composed of a platinum group metal and an active metal. After the iodine replacement reaction, the active metal is completely removed. In the iodine replacement reaction step, the recovery rate of the platinum group metal is 96% to 99%.

[0045] In order to further illustrate the present invention, a method for recovering platinum group metals from waste catalysts provided by the present invention is described in detail below in conjunction with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0046] Example 1

[0047] The Pd / C waste catalyst is crushed, 50g of the crushed Pd / C waste catalyst is mixed with 35g of active metal Al, and placed in an electric arc furnace. The furnace chamber is purged with Ar gas. After purging, the vacuum degree in the electric arc furnace is below 10Pa. The current is adjusted to 53A for melting treatment. The current is a pulsed firing current (pulse period 1s, duty cycle 40%), and the melting is continued for 4min to obtain Al-Pd intermetallic compounds enriched in platinum group metals.

[0048] Take 100g of AlI 3 Molten salt in Figure 1 In the outer crucible of the device shown, Ar gas is introduced, and the temperature is raised to 300°C in a resistance furnace, and the temperature is kept for 6 hours to remove water from the iodide molten salt; the Al-Pd intermetallic compound enriched with platinum group metals is placed in the inner crucible with holes punched on the side, and a high-temperature resistant connecting wire is connected to the inner crucible, and the inner crucible containing the intermetallic compound is placed in the outer crucible containing the iodide molten salt, ensuring that the punched part of the inner crucible is completely immersed in the iodide molten salt, and the outer iodide molten salt can enter the inner crucible. Then the iodide molten salt is heated to 500°C at a heating rate of 5°C / min, and kept at this temperature for 0.7 hours to recover metal Pd, and the recovery rate of metal palladium in the Pd / C crushed waste catalyst is close to 97%.

[0049] Figure 2 is the XRD pattern of the metal palladium recovered in Example 1; Figure 2 It can be seen that the present invention successfully recovers metallic palladium in the Pd / C catalyst.

[0050] Figure 3 is a SEM image of the metal palladium recovered in Example 1; Figure 3 It can be seen that metal palladium has a porous structure, which is convenient for secondary processing after crushing.

[0051] Figure 4This is the EDS graph of the metal palladium recovered in Example 1; the EDS detection result shows that the purity of the metal palladium is 98%.

[0052] Example 2

[0053] The Pt / C waste catalyst is crushed, 55g of the Pt / C catalyst is mixed with 25g of active metal Mg, and placed in an electric arc furnace. The furnace chamber is purged with Ar gas. After purging, the vacuum degree in the electric arc furnace is below 10Pa. The current is adjusted to 50A for melting treatment. The current is a pulsed firing current (pulse period 1s, duty cycle 55%), and melting is continued for 5min to obtain Mg-Pt intermetallic compounds enriched in platinum group metals.

[0054] Take 105g of MgI 2 Molten salt in Figure 1 In the outer crucible of the device shown, Ar gas is introduced, and the temperature is raised to 300°C in a resistance furnace, and the temperature is kept for 6 hours to remove water from the iodide molten salt; the Mg-Pt intermetallic compound enriched with platinum group metals is placed in the inner crucible with holes punched on the side, and a high-temperature resistant connecting wire is connected to the inner crucible. The inner crucible containing the intermetallic compound is placed in the outer crucible containing the iodide molten salt, ensuring that the punched part of the inner crucible is completely immersed in the iodide molten salt, and the outer iodide molten salt can enter the inner crucible. Then the iodide molten salt is heated to 600°C at a heating rate of 5°C / min, and kept at this temperature for 1 hour, and the metal Pt is recovered, and the recovery rate is close to 96%.

[0055] Example 3

[0056] The Pt-Pd-Rh ternary waste catalyst is crushed, 45g of the Pt-Pd-Rh waste catalyst is mixed with 15g of active metal Li, and placed in an electric arc furnace. The furnace cavity is purged with Ar gas. After purging, the vacuum degree in the electric arc furnace is below 10Pa. The current is adjusted to 55A for melting treatment. The current is a pulsed firing current (pulse period 1.5s, duty cycle 50%), and the melting is continued for 7min to obtain a Mg-Pt-Pd-Rh intermetallic compound enriched in platinum group metals.

[0057] Take 110g of LiI molten salt and place it in Figure 1In the outer crucible of the device shown, Ar gas is introduced, and the temperature is raised to 300°C in a resistance furnace, and the temperature is kept for 6 hours to remove water from the iodide molten salt; the Mg-Pt-Pd-Rh intermetallic compound enriched with platinum group metals is placed in the inner crucible with holes punched on the side, and a high-temperature resistant connecting wire is connected to the inner crucible, and the inner crucible containing the intermetallic compound is placed in the outer crucible containing the iodide molten salt, ensuring that the punched part of the inner crucible is completely immersed in the iodide molten salt, and the outer iodide molten salt can enter the inner crucible. Then the iodide molten salt is heated to 550°C at a heating rate of 5°C / min, and kept at this temperature for 1.5 hours, and metal Pt, Pd and Rh are recovered, and the recovery rate is close to 97%.

[0058] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for recovering platinum group metals from spent catalysts, characterized in that: The following steps are involved: The spent catalyst is crushed and then melted with active metal to obtain an intermetallic compound enriched with platinum group metal elements; placing the intermetallic compound in an iodide molten salt to carry out an iodine replacement reaction to obtain a platinum group metal; The waste catalyst is a waste catalyst containing platinum group metal elements; The active metal is one or more of alkali metals, alkaline earth metals, Al and Zn.

2. The method according to claim 1, characterized in that The molar ratio of the platinum group metal to the active metal in the waste catalyst is 1:2 to 1:4; The waste catalyst is automobile exhaust waste catalyst.

3. The method according to claim 1, characterized in that The alkali metal includes one or more of K, Li and Na; the alkaline earth metal includes one or both of Ca and Mg.

4. The method according to any one of claims 1 to 3, characterized in that: The iodide is one or more of KI, LiI, NaI, CaI2, MgI2, AlI3 and ZnI2.

5. The method according to claim 1, characterized in that The temperature of the iodine replacement reaction is 400-600° C., the insulation time is 0.5-2.5 hours, and the heating rate to the iodine replacement reaction is 5-25° C. / min; the iodine replacement reaction is carried out under a protective atmosphere or vacuum conditions.

6. The method according to claim 1, characterized in that Before placing the intermetallic compound in the iodide molten salt, the iodide molten salt is further dehydrated; the dehydration temperature is 200-400° C., and the insulation time is 6-8 hours.

7. The method according to claim 1, characterized in that The melting process is arc melting.

8. The method according to claim 7, characterized in that The arc melting has a current of 50 to 60 A and a melting time of 4 to 7 minutes.

9. The method according to claim 7 or 8, characterized in that: The arc melting current is a pulsed firing current, the pulse period of the pulsed firing current is 0.5 to 1.5 seconds, and the duty cycle is 40% to 60%.

10. The method according to claim 7, characterized in that The degree of vacuum during the arc melting is below 10 Pa.

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