Method for efficiently separating and recovering palladium and alumina powder from spent catalyst

Abstract

The invention relates to a method for efficiently separating and recycling palladium and alumina powder from a spent catalyst, and belongs to the technical field of comprehensive recycling of spent catalysts. The method comprises the following steps: adding spent catalyst powder into a sodium borohydride solution, and carrying out ultrasonic reinforcement in-situ reduction for 20-40 minutes at the temperature of 25-45 DEG C to obtain a pre-reduced spent catalyst; the method comprises the following steps: adding a pre-reduced invalid catalyst into a hydrochloric acid-sodium persulfate solution, carrying out ultrasonic activation selective leaching for 20-40 minutes at the temperature of 25-45 DEG C, and carrying out solid-liquid separation to obtain a palladium-enriched solution and alumina powder; according to the method, palladium oxide is subjected to in-situ reduction to form elemental palladium through ultrasonic-enhanced sodium borohydride in advance, then hydrochloric acid serves as a leaching agent, and palladium is selectively leached through ultrasonic-activated sodium persulfate, so that efficient palladium enrichment is achieved, and high-value aluminum oxide is synchronously recycled.

Description

Technical Field

[0001] The invention relates to a method for efficiently separating and recovering palladium and aluminum oxide powder from a spent catalyst, belonging to the technical field of comprehensive recovery and utilization of spent catalysts. Background Art

[0002] The dimethyl oxalate synthesis catalyst is based on alumina and loaded with about 0.3% elemental palladium as an active component. It is widely used in the field of coal-to-ethylene glycol. As the scale of the industry continues to grow, the demand for palladium is increasing year by year. At the same time, deactivated catalysts have long been a focus of attention due to their high palladium content. Catalysts that are deactivated for the first time are usually regenerated to extend their service life. However, the life of the regenerated catalyst is less than 1 / 3 of the original one, and it will soon need to be processed again. Therefore, the industry for recycling spent catalysts has developed rapidly.

[0003] The recovery and treatment process of spent catalysts is mainly based on wet combined pyrolysis. Due to the stability of α-Al2O3, the active component dissolution method is usually adopted to enrich palladium in the solution. However, the existing leaching conditions have problems such as high reaction temperature, high hydrochloric acid concentration, and high liquid-solid ratio. Supplementing chloride ions to accelerate the formation of palladium complexes is also one of the commonly used enrichment methods. This not only leads to additional material consumption, but also increases the processing cost. In addition, the existing recovery method only focuses on the enrichment of palladium and ignores the recovery of alumina. In order to pursue a high enrichment rate of palladium, the acid concentration is continuously increased, resulting in the physical dissolution of alumina. This is not only not conducive to the efficient recovery of alumina, but also causes the concentration of impurity ions in the leachate to increase, increasing the treatment cost of the leachate. In addition, incomplete reduction of palladium oxide is also one of the key factors leading to harsh reaction conditions and low purity of alumina powder. Existing reduction methods include gas phase reduction and non-gas phase reduction. Gas phase reduction refers to the introduction of reducing gases such as hydrogen and carbon monoxide to reduce palladium oxide at high temperature. However, this method has high requirements for equipment, and the maximum reduction temperature reaches more than 300°C, which poses great safety hazards. Non-gas phase reduction refers to the use of liquid or solid phase reducing agents for reduction, but the reduction reaction is usually carried out in solution. However, in order to pursue a high reduction rate, the temperature of the solution is generally 80°C. At the same time, salt or sodium hydroxide is added to increase the alkalinity of the solution to promote the reduction reaction.

[0004] Therefore, the existing methods for recovering palladium from deactivated catalysts have the problems of harsh reduction-leaching conditions, high energy consumption, low alumina recovery rate, and high impurity ion concentration in the enriched solution. Summary of the invention

[0005] In view of the problems that a method for recovering palladium from a deactivated catalyst has harsh reduction-leaching conditions, high energy consumption, low alumina recovery rate, high impurity ion concentration of the leaching solution, etc., the present invention proposes a method for efficiently separating and recovering palladium and alumina powder from a failed catalyst, that is, in advance, ultrasonically enhanced sodium borohydride is used to in-situ reduce palladium oxide to a palladium element, and then hydrochloric acid is used as a leaching agent, and ultrasonically activated sodium persulfate is used to selectively leach palladium to achieve efficient enrichment of palladium and simultaneous recovery of high-value alumina.

[0006] A method for efficiently separating and recovering palladium and alumina powder from a spent catalyst, the specific steps are as follows:

[0007] (1) crushing and grinding the spent catalyst to obtain spent catalyst powder;

[0008] (2) adding the spent catalyst powder into a sodium borohydride solution and performing in-situ reduction under ultrasonic enhancement at a temperature of 25 to 45° C. for 20 to 40 minutes to obtain a pre-reduced spent catalyst;

[0009] (3) adding the pre-reduced depleted catalyst into a hydrochloric acid-sodium persulfate solution, performing ultrasonic activation and selective leaching at a temperature of 25 to 45° C. for 20 to 40 minutes, and performing solid-liquid separation to obtain a palladium-enriched solution and alumina powder.

[0010] Preferably, the carrier of the spent catalyst in step (1) is Al2O3, and the palladium content is 1500-3500 g / t; the particle size of the spent catalyst powder is 10-200 μm.

[0011] Preferably, in step (2), the mass ratio of the spent catalyst powder to sodium borohydride is 25-100:1, the liquid-to-solid ratio of the sodium borohydride solution to the spent catalyst powder is 2-4:1 in mL:g, and the ultrasonic power is 100-300W.

[0012] Preferably, in the hydrochloric acid-sodium persulfate solution in step (3), the concentration of hydrochloric acid is 0.2-0.6 mol / L, and the concentration of sodium persulfate is 10-15 g / L.

[0013] More preferably, the liquid-to-solid ratio of the hydrochloric acid-sodium persulfate solution to the pre-reduced spent catalyst is 3 to 5:1 in mL:g, and the ultrasonic power is 100 to 300W.

[0014] The present invention utilizes the principle of ultrasonically enhanced sodium borohydride in-situ reduction of palladium oxide in the spent catalyst and ultrasonically activated sodium persulfate to selectively leach palladium: the ultrasonic effect dissociates the insoluble α-alumina inclusions, releasing the internal palladium oxide to the surface of the spent catalyst, thereby reducing the diffusion resistance; Figure 2As shown, ultrasound-enhanced sodium borohydride produces a large number of strong reducing hydrogen radicals (H·, redox potential of -2.3V) in a short time, accelerating the reduction rate of palladium oxide. During the leaching process, ultrasound-activated sodium persulfate produces strong oxidizing hydroxyl radicals (·OH, redox potential of 2.8V), which efficiently enrich palladium under normal temperature and low acid conditions and recover high-value alumina powder.

[0015] The beneficial effects of the present invention are:

[0016] (1) The present invention utilizes ultrasonic cavitation to dissociate insoluble alumina inclusions during the reduction process, accelerates the diffusion of palladium oxide, and strengthens sodium borohydride to generate a large number of strong reducing hydrogen radicals in situ in a short time in the reducing solution to reduce palladium oxide to elemental palladium in situ. Compared with the traditional reduction method, the reduction time is short, the reduction temperature is low, and no alkali is required;

[0017] (2) The present invention uses ultrasonic activation of sodium persulfate in the oxidative leaching solution to generate a large number of strongly oxidizing hydroxyl radicals, so that palladium can be efficiently enriched and alumina dissolution can be significantly reduced under mild conditions of low temperature, low acid and low chlorine to recover high-value alumina;

[0018] (3) The present invention improves the harsh conditions of palladium oxide reduction and palladium leaching reaction by introducing an external field and a new chemical reagent. The reaction conditions are mild, low-consumption and energy-saving, which reduces the processing cost and improves the high-value utilization of the spent catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a process flow chart of the present invention;

[0020] Figure 2 This is a diagram of hydrogen radicals (DMPO-H) generated in situ by ultrasound-enhanced sodium borohydride. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0022] Example 1: In this example, the carrier of the spent catalyst is Al2O3, and the palladium content is 2941 g / t;

[0023] A method for efficiently separating and recovering palladium and alumina powder from spent catalysts (see Figure 1 ), the specific steps are as follows:

[0024] (1) crushing and grinding the spent catalyst to obtain spent catalyst powder with a particle size of 13 to 75 μm;

[0025] (2) adding the spent catalyst powder to a sodium borohydride solution, and performing ultrasonic enhanced in-situ reduction for 20 min at an ultrasonic power of 100 W and a temperature of 30° C. to obtain a pre-reduced spent catalyst (elemental palladium accounts for 82% of the total palladium content); the mass ratio of the spent catalyst powder to sodium borohydride is 100:1, and the liquid-to-solid ratio of the sodium borohydride solution to the spent catalyst powder is 2:1 in mL:g;

[0026] (3) adding the pre-reduced spent catalyst to a hydrochloric acid-sodium persulfate solution (hydrochloric acid concentration 0.2 mol / L, sodium persulfate concentration 10 g / L), ultrasonically activating and selectively leaching for 20 min at an ultrasonic power of 100 W and a temperature of 30° C., and solid-liquid separation to obtain a palladium-enriched solution and an alumina powder; the liquid-solid ratio of the hydrochloric acid-sodium persulfate solution to the pre-reduced spent catalyst is 3:1 in mL:g;

[0027] The palladium leaching rate in this embodiment reaches 94.6%, and the concentration of Al(III) in the leaching solution is lower than 500 mg / L.

[0028] Example 2: A method for efficiently separating and recovering palladium and alumina powder from spent catalyst (see Figure 1 ), the specific steps are as follows:

[0029] (1) crushing and grinding the spent catalyst to obtain spent catalyst powder with a particle size of 75 to 150 μm;

[0030] (2) adding the spent catalyst powder to a sodium borohydride solution, and performing ultrasonic enhanced in-situ reduction for 30 min at an ultrasonic power of 200 W and a temperature of 25° C. to obtain a pre-reduced spent catalyst (elemental palladium accounts for 91% of the total palladium content); the mass ratio of the spent catalyst powder to sodium borohydride is 40:1, and the liquid-to-solid ratio of the sodium borohydride solution to the spent catalyst powder is 3:1 in mL:g;

[0031] (3) adding the pre-reduced spent catalyst to a hydrochloric acid-sodium persulfate solution (hydrochloric acid concentration 0.4 mol / L, sodium persulfate concentration 12.5 g / L), ultrasonically activating and selectively leaching for 30 min at an ultrasonic power of 200 W and a temperature of 25° C., and solid-liquid separation to obtain a palladium-enriched solution and an alumina powder; the liquid-solid ratio of the hydrochloric acid-sodium persulfate solution to the pre-reduced spent catalyst is 4:1 in mL:g;

[0032] The palladium leaching rate in this embodiment is up to 99.1%, and the concentration of Al(III) in the leaching solution is lower than 500 mg / L.

[0033] Example 3: A method for efficiently separating and recovering palladium and alumina powder from spent catalyst (see Figure 1 ), the specific steps are as follows:

[0034] (1) crushing and grinding the spent catalyst to obtain spent catalyst powder with a particle size of 75 to 150 μm;

[0035] (2) adding the spent catalyst powder to a sodium borohydride solution, and performing ultrasonic enhanced in-situ reduction for 40 min at an ultrasonic power of 300 W and a temperature of 40° C. to obtain a pre-reduced spent catalyst (with elemental palladium accounting for 95% of the total palladium content); the mass ratio of the spent catalyst powder to sodium borohydride is 25:1, and the liquid-to-solid ratio of the sodium borohydride solution to the spent catalyst powder is 4:1 in mL:g;

[0036] (3) adding the pre-reduced spent catalyst to a hydrochloric acid-sodium persulfate solution (hydrochloric acid concentration 0.6 mol / L, sodium persulfate concentration 15 g / L), ultrasonically activating and selectively leaching for 40 min at an ultrasonic power of 300 W and a temperature of 40° C., and solid-liquid separation to obtain a palladium-enriched solution and an alumina powder; the liquid-solid ratio of the hydrochloric acid-sodium persulfate solution to the pre-reduced spent catalyst is 5:1 in mL:g;

[0037] The palladium leaching rate of this embodiment reaches 99.3%, and the concentration of Al(III) in the leaching solution is lower than 500 mg / L.

[0038] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for efficiently separating and recovering palladium and alumina powder from spent catalysts, characterized in that: The specific steps are as follows: (1) crushing and grinding the spent catalyst to obtain spent catalyst powder; (2) adding the spent catalyst powder into a sodium borohydride solution and performing in-situ reduction under ultrasonic enhancement at a temperature of 25 to 45° C. for 20 to 40 minutes to obtain a pre-reduced spent catalyst; (3) adding the pre-reduced depleted catalyst into a hydrochloric acid-sodium persulfate solution, performing ultrasonic activation and selective leaching at a temperature of 25 to 45° C. for 20 to 40 minutes, and performing solid-liquid separation to obtain a palladium-enriched solution and alumina powder.

2. The method for efficiently separating and recovering palladium and alumina powder from spent catalyst according to claim 1, characterized in that: In step (1), the carrier of the spent catalyst is Al2O3, and the content of palladium is 1500-3500 g / t; the particle size of the spent catalyst powder is 10-200 μm.

3. The method for efficiently separating and recovering palladium and alumina powder from spent catalyst according to claim 1, characterized in that: In step (2), the mass ratio of the spent catalyst powder to sodium borohydride is 25-100:1, the liquid-solid ratio of the sodium borohydride solution to the spent catalyst powder is 2-4:1 in mL:g, and the ultrasonic power is 100-300W.

4. The method for efficiently separating and recovering palladium and alumina powder from spent catalyst according to claim 1, characterized in that: In step (3), the hydrochloric acid concentration in the hydrochloric acid-sodium persulfate solution is 0.2-0.6 mol / L, and the sodium persulfate concentration is 10-15 g / L.

5. The method for efficiently separating and recovering palladium and alumina powder from spent catalyst according to claim 4, characterized in that: The liquid-solid ratio of the hydrochloric acid-sodium persulfate solution to the pre-reduced spent catalyst is 3-5:1 in mL:g, and the ultrasonic power is 100-300W.

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