Method for separating platinum and rhodium with high direct recovery rate

Abstract

The invention provides a method for separating platinum and rhodium with high direct recovery rate, which comprises the following steps: step 1, uniformly mixing a platinum-rhodium alloy, sulfuric acid and ammonium sulfate according to a mass ratio of 1: (3-6): (0.1-0.2) by taking a platinum-rhodium alloy waste material as a raw material, and after mixing, putting the mixture into a muffle furnace for sulfating roasting to obtain roasted slag containing platinum, rhodium sulfate and ash impurities of a small amount of non-metal oxides; 2, the roasting slag is put into alkaline leaching liquid to be subjected to alkaline leaching, and alkaline leaching slag only containing platinum and rhodium hydroxide precipitates is obtained through filtering; 3, the alkaline leaching residues are put into sulfuric acid pickle liquor, rhodium hydroxide is precipitated and neutralized to form rhodium sulfate which is left in the pickle liquor, platinum is left in the acid leaching residues, the acid leaching residues only containing platinum are obtained through filtering, and effective separation of platinum and rhodium in the platinum-rhodium alloy waste is achieved. Under the condition of process conditions, the theoretical direct recovery rate of rhodium is 87% or above, and the theoretical direct recovery rate of platinum is 90% or above.

Description

Technical Field

[0001] The present invention belongs to the technical field of noble metal separation, and particularly relates to a method for separating platinum and rhodium with high direct recovery rate. Background Art

[0002] Platinum and rhodium have extraordinary physical and chemical properties, such as high catalytic activity, good oxidation resistance, corrosion resistance, high melting point, high thermal stability, etc. Therefore, they are widely used in various sectors of modern industry. With the development of science and technology, platinum group metals play an increasingly important role in sectors such as petroleum, chemical industry, national defense, and scientific research. Platinum and rhodium belong to Group VIII elements in the periodic table, and their physical and chemical properties are relatively similar. It is difficult to separate platinum and rhodium from platinum-rhodium alloy waste. Whether it is platinum-rhodium alloy in industrial materials or platinum-rhodium alloy obtained in the platinum-rhodium production process, separating them has high technological value. The current separation methods are to first dissolve by electrolysis, pressurization, microwave, melting activation, etc., and then separate by extraction, ion exchange, hydrolysis, precipitation, etc. However, these methods have complex processes, low direct recovery rate, high cost, difficult process control, and incomplete separation. Summary of the Invention

[0003] In view of the above problems, the present invention aims to provide a method for separating platinum and rhodium with high direct recovery rate to effectively separate platinum and rhodium, improve the direct recovery rate, and simplify the process. This process method not only provides huge economic benefits but also makes outstanding contributions to the recycling of platinum and rhodium resources and to fields such as petrochemical industry and national defense scientific research.

[0004] To achieve the above object, a method for separating platinum and rhodium with high direct recovery rate of the present invention includes the following steps:

[0005] Step 1: Using platinum-rhodium alloy waste as raw material, uniformly mix platinum-rhodium alloy: sulfuric acid: ammonium sulfate in a mass ratio of 1:3 - 6:0.1 - 0.2. After mixing, put it into a muffle furnace for sulfation roasting. The roasting temperature is 250 - 400 °C, and the roasting time is 1 - 3 h. The platinum-rhodium alloy waste reacts with sulfuric acid under the joint action of ammonium sulfate to undergo a sulfation reaction, breaking the structure of the platinum-rhodium alloy to obtain rhodium sulfate. At the same time, the organic components in the platinum-rhodium alloy waste are removed in the form of gas after high-temperature roasting, and the obtained roasting slag contains platinum, rhodium sulfate, and ash impurities of a small amount of non-metallic oxides.

[0006] Step 2: Put the roasting slag into an immersion device for alkaline leaching and washing. In the alkaline leaching solution, the mass concentration of sodium hydroxide is controlled at 100 - 200 g / L, and alkaline leaching is carried out for 2 - 5 h. Rhodium sulfate hydrolyzes to form rhodium hydroxide precipitate, and the ash impurities of non-metallic oxides contained in the roasting slag dissolve in the alkaline leaching solution, removing the ash impurities of non-metallic oxides in the roasting slag. Filter to obtain an alkaline leaching residue containing only platinum and rhodium hydroxide precipitate.

[0007] Step 3: Put the alkali leaching residue into a leaching solution device for acid leaching with an acid leaching solution. In the acid leaching solution, the mass concentration of sulfuric acid is 10% - 20%, the acid leaching time is 3 - 6 h, rhodium hydroxide precipitate is neutralized to form rhodium sulfate and remains in the acid leaching solution, and platinum remains in the acid leaching residue. Filter to obtain an acid leaching residue containing only platinum.

[0008] In the present invention, through neutralization hydrolysis precipitation filtration of the acid leaching solution containing rhodium sulfate, and then through traditional refining such as reduction and calcination, high-purity rhodium powder can be extracted.

[0009] Preferably, in Step 1, the sulfuric acid is concentrated sulfuric acid with a concentration of 95% - 98%.

[0010] Preferably, in Step 2, the solid-liquid ratio (mass ratio) of the calcination residue to the sodium hydroxide solution in the alkali leaching solution is 1:15 - 20.

[0011] Preferably, in Step 2, the alkali leaching temperature is 60 - 100 °C.

[0012] Preferably, in Step 3, the solid-liquid ratio (mass ratio) of the alkali leaching residue to the acid leaching solution is 1:15 - 20.

[0013] Preferably, in Step 3, the acid leaching temperature is 60 - 100 °C.

[0014] Preferably, the leaching solution device includes a leaching tank. Two relatively arranged and movable ultrasonic vibrating plates are provided in the leaching tank. Each ultrasonic vibrating plate is inclined at an acute angle of θ = 30 - 60° with respect to the horizontal plane of the leaching tank, so that a cross-vibration propagation direction is formed between the two relatively ultrasonic vibrating plates. The ultrasonic vibrating plates perform cross-vibration on the alkali leaching solution or the acid leaching solution within a frequency range of 20 - 80 KHz.

[0015] Preferably, a connecting rod is provided on the ultrasonic vibrating plate. The connecting rod is adjustably fixed on the sliding block up and down through an adjusting screw. The sliding block is provided with a plurality of sliding wheels at the bottom. The leaching tank is provided with slide rails on both sides for the sliding block to slide. Slide grooves corresponding to the sliding wheels are opened on the slide rails, and the slide grooves are slidably matched with the sliding wheels. A cylinder is fixed at the end of the slide rail, and the telescopic rod of the cylinder is connected to the sliding block. By means of the cylinder, the sliding block slides on both sides of the slide rail, so that the two ultrasonic vibrating plates move away from or approach each other, and the two ultrasonic vibrating plates perform a cross-range variable vibration on the alkali leaching solution or the acid leaching solution.

[0016] Preferably, a magnetic stirring device is further provided at the bottom of the leaching solution device, and magnetic stirring forms a vortex inside the leaching solution with cross-vibration of the two relatively arranged ultrasonic vibrating plates.

[0017] The technical features of the present invention are as follows:

[0018] In the present invention, platinum-rhodium alloy reacts with sulfuric acid and ammonium sulfate at the roasting temperature to undergo a sulfation reaction, breaking the structure of the platinum-rhodium alloy to obtain rhodium sulfate. Then, trace impurities are removed by alkali leaching and hydrolysis of rhodium sulfate forms a precipitate. Rhodium sulfate is leached into the solution by acid leaching for efficient separation from platinum. Under the process conditions of the present invention, the theoretical direct recovery rate of rhodium is over 85% and that of platinum is over 90%.

[0019] The present invention can better ensure the leaching effect of roasted slag or alkali leached slag through cross ultrasonic oscillation. Since the rhodium sulfate formed after roasting covers the surface of platinum, and rhodium sulfate and platinum cover each other. During the alkali leaching process of the roasted slag, the rhodium sulfate hydrolyzes to form rhodium hydroxide precipitate which also covers the surface of platinum. Through cross ultrasonic oscillation, it is beneficial for the rhodium hydroxide precipitate covering the surface of platinum to quickly detach from the surface of platinum, facilitating further hydrolysis and separation of the rhodium sulfate covering the surface between platinum by the alkali leached slag to obtain an alkali leached slag containing only platinum and rhodium hydroxide precipitate. After the roasted slag is alkali leached, the obtained platinum separates from rhodium, resulting in sponge platinum with a porous structure. A large amount of rhodium hydroxide precipitate also adheres to the interior of the porous structure of the sponge platinum. Therefore, during the acid leaching process of the alkali leached slag, cross ultrasonic oscillation is used to react acid with rhodium hydroxide to form soluble rhodium sulfate and release the rhodium sulfate from the porous structure of the sponge platinum into the acid leaching solution.

[0020] In the present invention, two ultrasonic vibration plates move away from or close to each other, causing the two ultrasonic vibration plates to implement an oscillating with a changing cross range on the alkali leaching solution or acid leaching solution, which is beneficial for implementing cross ultrasonic oscillation on the roasted slag or alkali leached slag in different ranges in the leaching solution tank. Moreover, through the action of the ultrasonic vibration plates, the concentration exchange between the low-concentration area and the high-concentration area of the leaching solution tank can be well achieved, thereby improving the leaching effect.

[0021] Platinum or rhodium-containing substances in the roasted slag or alkali leached slag have a large density and are prone to quickly settling at the bottom of the leaching solution tank during the leaching process, causing deposition. Through the vortex formed by magnetic stirring, the roasted slag or alkali leached slag can be well stirred up to achieve the purpose of rapid leaching. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a process flow chart for separating platinum and rhodium of the present invention.

[0023] Figure 2 It is a schematic diagram of the leaching solution tank and the stirring structure.

[0024] Figure 3 It is a three-dimensional structure schematic diagram of the leaching solution tank.

[0025] Wherein: 1 - immersion liquid device, 11 - immersion liquid tank, 12 - ultrasonic vibration plate, 13 - sliding block, 14 - cylinder, 15 - connecting rod, 16 - sliding wheel, 17 - slide rail, 171 - chute, 18 - adjusting screw, 2 - magnetic stirring device, 21 - magnetic stirring blade, 22 - stirring motor, 3 - magnetic stirrer. Specific implementation manner

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the following further elaborates on the present invention in conjunction with the accompanying drawings and embodiments.

[0027] In this embodiment, a platinum-rhodium alloy waste for industrial catalysis is used. In the platinum-rhodium alloy waste, the platinum content is 89.38 wt%, the rhodium content is 9.93 wt%, and the impurities are about 0.69 wt%. The main components of the impurities are silicon dioxide, iron oxide and adsorbed and deposited organic compounds. During the implementation process, the above platinum-rhodium alloy waste is subjected to crushing and grinding pretreatment to facilitate the separation and treatment of the platinum-rhodium alloy waste.

[0028] Example 1

[0029] Take 41.40 g of the above platinum-rhodium alloy, and uniformly mix it with 248 g of sulfuric acid with a concentration of 98% and 8.30 g of ammonium sulfate. After mixing, put it into a muffle furnace for sulfation roasting. The roasting temperature is 200 °C and the roasting time is 3 h. The platinum-rhodium alloy waste reacts with sulfuric acid under the joint action of ammonium sulfate to undergo a sulfation reaction, breaking the structure of the platinum-rhodium alloy to obtain rhodium sulfate. At the same time, the organic components in the platinum-rhodium alloy waste are removed as gases after high-temperature roasting, and a roasted residue containing platinum, rhodium sulfate and a small amount of ash impurities of non-metallic oxides is obtained, and 42.08 g of roasted residue is obtained; put the prepared roasted residue into the alkali leaching solution in the immersion liquid device 1. The alkali leaching solution is 631.21 g, and the mass concentration of sodium hydroxide in the alkali leaching solution is 200 g / L. The alkali leaching temperature is 100 °C and the alkali leaching time is 5 h. Rhodium sulfate hydrolyzes to form rhodium hydroxide precipitate, and the ash impurities of non-metallic oxides contained in the roasted residue dissolve in the alkali leaching solution, and the ash impurities of non-metallic oxides in the roasted residue are removed. After filtration, an alkali leaching residue containing only platinum and rhodium hydroxide precipitate is obtained, which is 41.81 g; put the alkali leaching residue into the acid leaching solution in the immersion liquid device 1. The acid leaching solution is 627.10 g, and the mass concentration of sulfuric acid in the acid leaching solution is 10%. The acid leaching temperature is 60 °C and the acid leaching time is 6 h. The rhodium hydroxide precipitate is neutralized to form rhodium sulfate and remains in the acid leaching solution. 579 ml of acid leaching solution is collected, and platinum remains in the acid leaching residue. After filtration, the acid leaching residue W 酸浸渣 = 34.617 g.

[0030] Among them, in order to better ensure the leaching effect of roasted slag or alkali leaching residue, in the process steps of alkali leaching and acid leaching, an ultrasonic oscillation with a cross-range variation is applied to the alkali leaching solution and the acid leaching solution, and the application frequency range is 20 - 80 KHz.

[0031] The structure of the applied leaching solution device 1 can be referred to Figure 2 and Figure 3 the shown structure.

[0032] The leaching solution device 1 includes a leaching solution tank 11. Inside the leaching solution tank 11, there are two relatively arranged and movable ultrasonic vibration plates 12. Each ultrasonic vibration plate 12 is inclined at an acute angle of θ = 30 - 60° with respect to the horizontal plane of the leaching solution tank 11. Preferably, θ = 60°. The inclined setting enables a cross-vibration propagation direction to be formed between the two relatively ultrasonic vibration plates 12, thereby realizing the cross-oscillation of the ultrasonic vibration plates 12 on the alkali leaching solution or the acid leaching solution.

[0033] Moreover, the two relatively arranged ultrasonic vibration plates 12 are movably arranged, including being movably arranged in the up and down direction. Specifically, a connecting rod 15 is arranged on the ultrasonic vibration plate 12, and the connecting rod 15 is adjustably fixed on the sliding block 13 up and down through an adjusting screw 18. In this way, by adjusting the adjusting screw 18, it is convenient to adjust the depth of the ultrasonic vibration plate 12 extending into the leaching solution tank 11.

[0034] The ultrasonic vibration plate 12 is movably arranged, and also includes a movable setting of moving away from or approaching each other. Specifically, a plurality of sliding wheels 16 are arranged at the bottom of the sliding block 13, and sliding rails 17 for the sliding block 13 to slide are installed on both sides of the leaching solution tank 11. A sliding groove 171 corresponding to the sliding wheel 16 is opened on the sliding rail 17, and the sliding groove 171 is in sliding fit with the sliding wheel 16. A cylinder 14 is fixed at the end of the sliding rail 17, and the telescopic rod of the cylinder 14 is connected to the sliding block 13. By driving the cylinder 14, the sliding block 13 slides on both sides of the sliding rail 17, thereby controlling the two ultrasonic vibration plates 12 to move away from or approach each other, realizing the cross-range variation oscillation of the two ultrasonic vibration plates 12 on the alkali leaching solution or the acid leaching solution, which is beneficial to the cross-ultrasonic oscillation of the roasted slag or alkali leaching residue in different ranges in the leaching solution tank 11. Moreover, the moving ultrasonic vibration plate 12 can push the alkali leaching solution or the acid leaching solution, exchange the concentrations of the low-concentration area and the high-concentration area in the leaching solution tank 11, and play a role of "adding strength to what is already strong", thereby improving the leaching effect.

[0035] The immersion liquid device 1 is placed above the magnetic stirring device 2. In the process steps of alkali leaching and acid leaching, driven by the stirring motor 22 with the magnetic stirring blade 21, the magnetic stirrer 3 at the bottom of the placed immersion liquid tank 11 realizes magnetic stirring rotation. The magnetic stirring forms a vortex inside the immersion liquid with the cross oscillation of the two relatively arranged ultrasonic vibration plates 12, thus solving the problem that due to the large density of platinum or rhodium-containing substances, they are likely to quickly settle at the bottom of the immersion liquid tank 11 during the leaching process, causing deposition problems. Through the vortex formed by magnetic stirring, the calcined slag or alkali leaching slag can be well stirred up to achieve the purpose of rapid leaching.

[0036] For the acid leaching slag and acid leaching liquid obtained by the above implementation method, the inductively coupled plasma mass spectrometry (ICP-MS) method is used to detect the content of platinum and rhodium elements in the acid leaching liquid and the content of platinum in the acid leaching slag.

[0037] After detection, the rhodium ion content W Rh离子 = 6.541 g / L in the acid leaching liquid, and the platinum content W Pt离子 = 3.22 mg / L.

[0038] After calculation, the mass of rhodium ions in the acid leaching liquid: W Rh离子 = 6.541 g / L × 0.579 L = 3.787 g, the leaching rate (%) of rhodium: S Rh = W Rh离子 / (W 铂铑合金 × 9.93%) × 100% = 3.787 g / (41.40 g × 9.93%) × 100% = 92.12%, that is, the theoretical direct recovery rate of rhodium is 92.12%. The direct recovery rate (%) of platinum: S Pt = W 酸浸渣 / (W 铂铑合金 × 89.38%) × 100% = 34.617 g / (41.40 g × 89.38%) × 100% = 93.55%, that is, the theoretical direct recovery rate of platinum is 93.55%.

[0039] The implementation results are shown in Table 1.

[0040] For the subsequent treatment of the rhodium-containing acid leaching liquid, after neutralizing, hydrolyzing, precipitating, and filtering the acid leaching liquid containing rhodium sulfate, high-purity rhodium powder can be extracted through traditional refining such as reduction and calcination. Since it is not within the protection scope of the present invention, it will not be elaborated one by one in this embodiment.

[0041] Example 2

[0042] The method for separating platinum and rhodium is the same as that in Example 1, except that cross ultrasonic oscillation is not applied in the alkali leaching step. The implementation process conditions, the results after detection, and the results after calculation are shown in Table 1.

[0043] Example 3

[0044] The method for separating platinum-rhodium is the same as that in Example 1, except that cross ultrasonic oscillation is not applied in the acid leaching step. The implementation process conditions, the results after detection, and the calculated results are shown in Table 1.

[0045] Example 4

[0046] The method for separating platinum-rhodium is the same as that in Example 1, except that cross ultrasonic oscillation is not applied in both the alkali leaching step process and the acid leaching step process. The implementation process conditions, the results after detection, and the calculated results are shown in Table 1.

[0047] Comparative Example 1

[0048] The method for separating platinum-rhodium is the same as that in Example 4, except that ammonium sulfate catalyst is not added before roasting the platinum-rhodium alloy. The implementation process conditions, the results after detection, and the calculated results are shown in Table 1.

[0049] Table 1

[0050]

[0051]

[0052] In Table 1, W 铂铑合金 represents the weight of the platinum-rhodium alloy, which is T 焙烧 represents the roasting temperature, and t 焙烧 represents the roasting time.

[0053] C NaOH represents the mass concentration of sodium hydroxide in the alkali leaching solution, T 碱浸 represents the alkali leaching temperature, and t 碱浸 represents the alkali leaching time, C 硫酸 represents the sulfuric acid mass concentration in the acid leaching solution, T 酸浸 represents the acid leaching temperature, and t 酸浸 represents the acid leaching time, V 酸浸 represents the volume of the collected acid leaching solution, W 酸浸渣 represents the weight of the acid leaching residue, W Rh离子 represents the rhodium ion content in the acid leaching solution, W Pt离子 represents the platinum content in the acid leaching solution.

[0054] As can be seen from Table 1, in Examples 1 to 4, when the platinum-rhodium alloy waste is processed under the process conditions of the present invention, the theoretical direct recovery rate of rhodium is above 87%, and the theoretical direct recovery rate of platinum is above 90%. Compared with Comparative Example 1 where the platinum-rhodium alloy waste was calcined without using ammonium sulfate as a catalyst, the theoretical direct recovery rate of rhodium was only 75.89%, which is much lower than the theoretical direct recovery rate of rhodium in the inventive process. This shows that ammonium sulfate as a catalyst plays a crucial role in improving the theoretical direct recovery rate of rhodium in the calcination process. Ammonium sulfate catalyst decomposes at the calcination temperature to produce sulfuric acid and ammonia, which can well supplement the sulfuric acid consumption due to the sulfation reaction of sulfuric acid and rhodium at the calcination temperature, better destroy the structure of the platinum-rhodium alloy, and obtain rhodium sulfate. Therefore, using ammonium sulfate is beneficial to improving the sulfation reaction of rhodium, facilitating the leaching of rhodium in the subsequent acid leaching process, and thus improving the theoretical direct recovery rate of rhodium. During the calcination process, the excess sulfuric acid further decomposes into gas and is removed.

[0055] In Examples 1 and 2, in the alkali leaching process of Example 2, since cross ultrasonic oscillation was not applied, the theoretical direct recovery rate of rhodium decreased relatively. This shows that in the alkali leaching process, applying cross ultrasonic oscillation to the alkali leaching solution is beneficial to improving the theoretical direct recovery rate of rhodium. After calcination, the rhodium sulfate formed covers the surface of platinum, and rhodium sulfate and platinum cover each other. During the alkali leaching of the calcination slag, the rhodium sulfate hydrolyzes to form rhodium hydroxide precipitate, which also covers the surface of platinum. Through cross ultrasonic oscillation, it is beneficial for the rhodium hydroxide precipitate covering the surface of platinum to quickly detach from the surface of platinum, facilitating the further hydrolysis and separation of the rhodium sulfate covering the surface between platinum by the alkali leaching slag to obtain an alkali leaching slag containing only platinum and rhodium hydroxide precipitate. Moreover, applying cross ultrasonic oscillation is also beneficial to the removal of impurities in the calcination slag and the purity of platinum-rhodium recovery.

[0056] In Examples 1 and 3, in the acid leaching process of Example 3, since cross ultrasonic oscillation was not applied, the theoretical direct recovery rate of rhodium decreased relatively. This shows that in the acid leaching process, applying cross ultrasonic oscillation to the acid leaching solution is also beneficial to improving the theoretical direct recovery rate of rhodium. After the calcination slag is alkali leached, the obtained platinum separates from rhodium, and the resulting particles are sponge platinum with a porous structure. A large amount of rhodium hydroxide precipitate also adheres to the interior of the porous structure of the sponge platinum. Therefore, during the acid leaching of the alkali leaching slag, cross ultrasonic oscillation is used to react acid with rhodium hydroxide to form soluble rhodium sulfate, and the rhodium sulfate is released from the porous structure of the sponge platinum into the acid leaching solution.

[0057] In Examples 2 and 3, the difference in applying cross ultrasonic oscillation in the alkali leaching process or the acid leaching process shows that the theoretical direct recovery rate of rhodium is more favorable in the acid leaching process. This is because the acid leaching process can directly acidify rhodium sulfate more fully in the acid leaching solution.

[0058] Example 4. Under the condition that no cross ultrasonic oscillation is applied in the alkali leaching step process and the acid leaching step process, the theoretical direct recovery rate of rhodium and the recovery rate of platinum are significantly lowered. Further, it is shown that by applying cross ultrasonic oscillation under special conditions and simultaneously through the movable ultrasonic vibration plate 12, the alkali leaching solution or the acid leaching solution can be pushed, and the concentration exchange between the low-concentration area and the high-concentration area of the leaching solution tank 11 can be realized, playing a role of "adding fuel to the flames". By using the vortex formed by magnetic stirring, the problem that due to the large density of platinum or rhodium-containing substances, they are likely to quickly settle at the bottom of the leaching solution tank 11 during the leaching process, resulting in deposition, can be solved. The calcination slag or alkali leaching slag can be well stirred up to achieve the purpose of rapid leaching, which plays a crucial role in increasing the theoretical direct recovery rate of rhodium and the recovery rate of platinum. By using the above method, especially for the leaching of sponge platinum with a porous structure, obvious effects can be obtained.

[0059] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for separating platinum and rhodium with high direct yield, characterized in that: The following steps are involved: Step 1, using platinum-rhodium alloy waste as raw material, uniformly mixing platinum-rhodium alloy: sulfuric acid: ammonium sulfate = 1:3-6:0.1-0.2 by mass ratio, and after mixing, placing in a muffle furnace for sulfation roasting, the roasting temperature is 250-400° C., the roasting time is 1-3 hours, and the obtained roasting slag contains platinum, rhodium sulfate and a small amount of non-metallic oxide ash impurities; Step 2, placing the roasted slag in an leaching device and leaching with an alkaline leaching solution, wherein the mass concentration of sodium hydroxide in the alkaline leaching solution is controlled at 100-200 g / L, leaching for 2-5 hours, hydrolyzing rhodium sulfate to generate rhodium hydroxide precipitate, and filtering to obtain an alkaline leaching residue containing only platinum and rhodium hydroxide precipitate; Step 3, placing the alkaline leaching residue into an leaching device and leaching it with acid leaching solution, wherein the mass concentration of sulfuric acid in the acid leaching solution is 10% to 20%, the acid leaching time is 3 to 6 hours, rhodium hydroxide is precipitated and neutralized to form rhodium sulfate which remains in the acid leaching solution, and platinum remains in the acid leaching residue, and the acid leaching residue containing only platinum is filtered out.

2. A method for separating platinum and rhodium with high direct yield according to claim 1, characterized in that: In step 1, the sulfuric acid is concentrated sulfuric acid with a concentration of 95-98%.

3. A method for separating platinum and rhodium with high direct yield according to claim 1, characterized in that: In step 2, the solid ratio (mass ratio) of the roasted slag to the sodium hydroxide solution alkali leaching liquid is 1:15-20.

4. A method for separating platinum and rhodium with high direct yield according to claim 1, characterized in that: In step 2, the alkali leaching temperature is 60-100°C.

5. A method for separating platinum and rhodium with high direct yield according to claim 1, characterized in that: In step 3, the acid leaching liquid-to-solid ratio (mass ratio) is 1:15-20.

6. A method for separating platinum and rhodium with high direct yield according to claim 1, characterized in that: In step 3, the acid leaching temperature is 60-100°C.

7. A method for separating platinum and rhodium with high direct yield according to claim 1, characterized in that: The immersion device includes an immersion tank, in which two relatively arranged and movable ultrasonic vibration plates are provided. Each of the ultrasonic vibration plates is inclined at an acute angle of θ=30~60° to the horizontal plane of the immersion tank, so that a cross vibration propagation direction is formed between the two relatively ultrasonic vibration plates. The ultrasonic vibration plates implement cross oscillation in the frequency range of 20~80KHz on the alkaline immersion liquid or the acid immersion liquid.

8. A method for separating platinum and rhodium with high direct yield according to claim 7, characterized in that: A connecting rod is arranged on the ultrasonic vibration plate, and the connecting rod can be adjusted up and down and fixed on the sliding block by an adjusting screw. The sliding block is provided with a plurality of sliding wheels at the bottom, and the immersion tank is provided with sliding rails for the sliding block to slide on both sides. The sliding rail is provided with sliding grooves corresponding to the sliding wheels, and the sliding grooves are slidably matched with the sliding wheels. A cylinder is fixed at the end of the sliding rail, and the telescopic rod of the cylinder is connected to the sliding block. By means of the cylinder, the sliding block slides on both sides of the sliding rail, so that the two ultrasonic vibration plates move away from or close to each other, so that the two ultrasonic vibration plates perform a cross-range variation of oscillation on the alkaline immersion liquid or the acid immersion liquid.

9. A method for separating platinum and rhodium with high direct yield according to claim 7, characterized in that: A magnetic stirring device is also provided at the bottom of the immersion device, and the magnetic stirring causes a vortex to form inside the immersion liquid caused by the cross-vibration of two ultrasonic vibration plates arranged opposite to each other.

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