Method for efficiently separating and recovering metal palladium from waste Pd / Al2O3 leachate

Abstract

The invention belongs to the field of precious metal secondary resource recycling, particularly discloses a method for efficiently separating and recycling metal palladium from a waste Pd / Al2O3 leaching solution, and relates to separation, enrichment and purification of palladium in a leaching solution of an alumina carrier supported palladium-based sample such as waste palladium slag and palladium mud generated in the industrial production process of an inactivated Pd / Al2O3 catalyst and the Pd / Al2O3 catalyst. According to the method, the palladium in the leachate is separated and purified by adopting simple hydrazine hydrate induction-hydrogen reduction and dilute acid purification steps, the recovery rate is up to 99.9%, the purity is up to 99.95% or above, the problems of tedious steps, high energy consumption, serious pollution and the like in the prior art are avoided, the process is simple, efficient and environment-friendly, and the recovery cost of the precious metal palladium is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the field of precious metal secondary resource recycling, and in particular relates to a method for efficiently separating and recovering metal palladium from waste Pd / Al2O3 leaching solution. Background Art

[0002] The platinum group precious metal Pd is widely used in the fields of petrochemicals and fine chemicals such as oxidation, hydrogenation, dehydrogenation, and catalytic reforming due to its unique catalytic activity. It is known as an industrial vitamin and strategic reserve metal. Among them, the Pd / Al2O3 catalyst with broad application prospects is composed of high-strength molded porous alumina balls supporting a low-load of active component palladium (0.1~1 wt%). It is widely used in the enantioselective hydrogenation reaction of aromatic aldehydes, nitroaromatics and aniline compounds, olefin hydrogenation and refining, hydrocracking, isomerization, fluorine chemical industry, vinyl acetate industry, hydrogen peroxide production, and industrial tail gas and gas purification. In industrial production, a large number of waste Pd / Al2O3 catalysts that cannot be regenerated and recycled due to factors such as metal poisoning, loss, sintering or changes in the carrier structure need to be replaced every year.

[0003] The palladium leaching solution obtained by the wet process active component acid dissolution or acid chlorination method contains a large amount of aluminum ions and a large number of impurity metal ions such as iron, calcium, magnesium, and copper. 3+It is difficult to separate and recover a small amount of palladium from the leachate containing impurities such as metal ions and impurities, and the process is relatively complicated. Currently, the commonly used methods for separation and enrichment of palladium mainly include resin adsorption-dichlorodiamine palladium precipitation (CN111321307A; Hydrometallurgy, 2006, 25), metal replacement (CN108642300A), sulfide precipitation (CN106367611A) and other methods. Among them, the resin adsorption-dichlorodiamine palladium precipitation method can recover high purity sponge palladium, but it has the problems of high resin cost, low adsorption-desorption efficiency, difficult regeneration, complex process flow, large amount of acid and alkali, and large amount of wastewater. In addition, the dichlorodiamine palladium precipitation method is only applicable to the case where the palladium content is high and the aluminum ion is less. The low-concentration palladium-containing leachate has problems such as incomplete palladium precipitation and high aluminum hydroxide colloid content; the metal aluminum powder, zinc powder or iron plate replacement method can separate and enrich the palladium in the leachate to obtain a crude palladium with a palladium content of about 70-80%, but this method will cause the subsequent purification process to be more cumbersome on the one hand, and on the other hand, it will also generate high-concentration zinc chloride, ferric chloride and other strong acidic waste liquids, increasing the cost of waste liquid treatment; the sulfide precipitation method will produce hydrogen sulfide harmful gas, environmental pollution, and the precipitate will be difficult to separate from a large amount of aluminum hydroxide colloid under alkaline conditions, increasing the complexity and cost of the operation. In addition, the method has a large consumption of sodium sulfide, and the recovery rate and purity of palladium are low. In addition to the above method, patent CN108425014A also reports a butyl sodium xanthate palladium precipitation method, which causes a large amount of palladium ions to be adsorbed in aluminum hydroxide colloid and filtered out under alkaline conditions, resulting in a low palladium recovery rate. At the same time, the method needs to be reduced with H2 or CO at 500-900 ℃, which consumes a lot of energy. In addition, the process flow of the method is complicated, the cost is high, and a large amount of sodium butyl xanthate wastewater is generated. Based on this, the present invention provides a method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 catalyst leachate to overcome the above-mentioned shortcomings in the prior art. Summary of the invention

[0004] In view of the problems existing in the above-mentioned process, the present invention provides a method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 leachate, namely, separating and purifying metallic palladium by hydrogen reduction enrichment and dilute acid purification steps. The recovery process is simple, low in cost, with a recovery rate of up to 99.9% and a purity of up to 99.95%, and is suitable for large-scale industrial recovery of waste Pd / Al2O3 catalysts.

[0005] The present invention is achieved through the following technical solutions: A method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 leaching solution, using hydrogen enrichment and dilute acid purification, the specific steps are as follows: (1) After removing organic matter on the surface of the waste Pd / Al2O3 catalyst by high-temperature roasting, the waste Pd / Al2O3 catalyst is reduced by hydrazine hydrate, and then the reduced waste Pd / Al2O3 catalyst is subjected to acid leaching or acid chlorination leaching to obtain a palladium-containing leaching solution. After filtering and removing impurities, the filter residue is leached again by repeating the above steps. The palladium-containing solutions leached twice are mixed to obtain a palladium-containing leaching solution, hydrogen is introduced into the solution to reduce a small amount of palladium ions in the solution to metallic palladium, and crude palladium containing a small amount of aluminum ions and impurity metals is obtained after centrifugal washing.

[0006] (2) adding a dilute acid to the crude palladium obtained in step (1) and heating it under a reducing gas or inert gas atmosphere to prevent the palladium oxide formed by the oxidation of the metal palladium by air from being dissolved under acidic conditions; filtering, washing and vacuum drying the cooled suspension to obtain a sponge palladium with a high purity, thereby achieving the purpose of purifying the crude palladium.

[0007] In the step (1), the acid leaching solution is one of hydrochloric acid, nitric acid or aqua regia, and the acid chlorination leaching solution is a leaching solution formed by hydrochloric acid and one or more of the oxidants sodium chlorate, sodium hypochlorite and hydrogen peroxide.

[0008] In the step (1), the calcination temperature is 400-800 °C for 2-5 h, preferably 550 °C for 4 h.

[0009] In the step (1), a few drops of hydrazine hydrate are added during the hydrogen reduction process to induce the formation of PdCl4 under hydrogen conditions. 2- Quick restore.

[0010] In the step (1), the hydrogen reduction temperature is 60-150 °C, and the reduction time is 1-8 h, preferably 100-120 °C for 2-5 h.

[0011] In the step (2), the reducing gas or inert gas is a mixture of one or more of hydrogen, nitrogen, argon or helium.

[0012] In the step (2), the dilute acid used is one or both of sulfuric acid and hydrochloric acid, the concentration is 0.5-3 mol / L, the temperature is 60-120 °C, and the heating time is 1-5 h.

[0013] In the step (2), the temperature of the hot water used is 50-100 °C, and the filtrate is washed until there is no Cl in the filtrate after silver nitrate detection. - until.

[0014] In the step (2), the drying temperature is 60-80 °C, and the vacuum drying is performed for 12-24 h.

[0015] Beneficial effects of the present invention: This method can obtain high-recovery and high-purity sponge palladium by only two steps of hydrogen reduction enrichment and dilute acid purification. It is simpler than the dichlorodiammine palladium precipitation method, the sulfide precipitation method and the butyl sodium xanthate precipitation method, does not require resin enrichment and hydrochloric acid or ammonia water to adjust the pH, has low environmental pollution and low acid and alkali usage. The dilute acid washing liquid can also be used as the leaching liquid of the next waste Pd / Al2O3 catalyst, and produces less wastewater; compared with the metal replacement method or the electrodeposition method, this method has lower cost. Therefore, the present invention can solve the problems of high energy consumption, complex process and large amount of wastewater faced by the current palladium recovery technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through embodiments.

[0018] Example 1: Recovery and purification of palladium-containing leaching solution using aqua regia The waste Pd / Al2O3 catalyst was calcined at 550 °C for 4 h to remove the surface organic matter and then reduced with hydrazine hydrate. The reduced waste Pd / Al2O3 catalyst was then added with aqua regia and leached at 60 °C for 2 h and filtered. The remaining filter residue was calcined and reduced again and palladium was leached using the same method as above, and the two leached palladium solutions were mixed to obtain a solution containing a large amount of Al 3+ The palladium leaching solution was purified by centrifugation and washed with 1 mol / L dilute hydrochloric acid and heated to 100 °C in a hydrogen atmosphere for 2 h before being filtered and washed with hot water until free of Cl. - After vacuum drying at 60 °C overnight, sponge palladium was obtained, the palladium recovery rate could reach 98.6%, and the purity of sponge palladium was as high as 99.51%.

[0019] Example 2: Recovery and purification of palladium-containing leachate from hydrochloric acid-hydrogen peroxide leaching The spent Pd / Al2O3 catalyst after calcination at 550 °C and reduction with hydrazine hydrate was added to the hydrochloric acid and hydrogen peroxide leaching solution and leached at 60 °C for 2 h and filtered. The remaining filter residue was calcined and reduced again and palladium was leached using the same method as above, and the two leached palladium-containing solutions were mixed to obtain a solution containing a large amount of Al 3+Palladium leaching solution containing impurity metals such as Pd and Al2O3. In a single leaching process, the mass ratio of waste Pd / Al2O3 sample, HCl and H2O2 is 1:0.55:0.62, and the liquid-to-solid ratio is 2.5. The palladium-containing leaching solution is heated to 120 °C under hydrogen conditions, and a few drops of hydrazine hydrate are added to induce rapid reduction of palladium ions. After 2 h of reduction, the crude palladium is obtained by centrifugation and washing. The obtained crude palladium is placed in 1 mol / L dilute hydrochloric acid, heated to 100 °C in a hydrogen atmosphere for 2 h, filtered, and washed with hot water until there is no Cl - After vacuum drying at 60 °C overnight, sponge palladium was obtained, the palladium recovery rate could reach 98.9%, and the purity of sponge palladium was as high as 99.90%.

[0020] Example 3: Recovery and purification of palladium-containing leachate using hydrochloric acid-sodium hypochlorite leaching The spent Pd / Al2O3 catalyst after calcination at 550 °C and reduction with hydrazine hydrate was added to the sodium hypochlorite and hydrochloric acid leaching solution and leached at 60 °C for 2 h and filtered. The remaining filter residue was calcined and reduced again and palladium was leached using the same method as above, and the two leached palladium solutions were mixed to obtain a solution containing a large amount of Al 3+ The palladium leaching solution was purified by centrifugation and washed with 1 mol / L dilute hydrochloric acid and heated to 100 °C in a hydrogen atmosphere for 2 hours before reacting for 2 hours. The crude palladium was then filtered and washed with hot water until free of Cl. - After vacuum drying at 60 °C overnight, sponge palladium was obtained, the palladium recovery rate could reach 99.1%, and the purity of sponge palladium was as high as 99.92%.

[0021] Example 4: Recovery and purification of palladium-containing leachate using hydrochloric acid-sodium chlorate leaching The spent Pd / Al2O3 catalyst after calcination at 550 °C and reduction with hydrazine hydrate was added to sodium chlorate and hydrochloric acid leaching solution and leached at 60 °C for 2 h and filtered. The remaining filter residue was calcined and reduced again and palladium was leached using the same method as above, and the palladium solutions leached twice were mixed to obtain a solution containing a large amount of Al 3+The palladium leaching solution containing impurity metals such as Pd, HCl and NaClO3 was 1:0.55:0.62 in the single leaching process, and the liquid-solid ratio was 2.5. The palladium-containing leaching solution was heated to 120 °C under hydrogen conditions, and a few drops of hydrazine hydrate were added to induce rapid reduction of palladium ions. After 2 h of reduction, the crude palladium was obtained by centrifugation and washing. The obtained crude palladium was placed in 1 mol / L dilute hydrochloric acid, heated to 100 °C in a hydrogen atmosphere for 2 h, filtered, and washed with hot water until there was no Cl. - After vacuum drying at 60 °C overnight, sponge palladium was obtained, the palladium recovery rate could reach 99.5%, and the purity of sponge palladium was as high as 99.93%.

[0022] Example 5: Recovery and purification of palladium-containing leachate using hydrochloric acid-hydrogen peroxide-sodium chlorate leaching The palladium mud (Pd: 0.92 wt%) after calcination at 550 °C and reduction with hydrazine hydrate was added to the leaching solution containing hydrogen peroxide, sodium chlorate and hydrochloric acid and leached at 80 °C for 5 h and filtered. The remaining filter residue was calcined and reduced again and palladium was leached using the same method as above, and the two leached palladium solutions were mixed to obtain a large amount of Al 3+ The palladium leaching solution containing impurity metals such as palladium mud was obtained. The mass ratio of palladium mud: HCl: NaClO3: H2O2: H2O in the leaching process was 1: 2.44: 0.0228: 0.456: 3. The palladium-containing leaching solution was heated to 120 °C under hydrogen conditions, and a few drops of hydrazine hydrate were added to induce rapid reduction of palladium ions. After 2 h of reduction, the crude palladium was obtained by centrifugation and washing. The obtained crude palladium was placed in 1 mol / L dilute hydrochloric acid, heated to 100 °C in a hydrogen atmosphere for 2 h, filtered, and washed with hot water until there was no Cl. - After vacuum drying at 60 °C overnight, sponge palladium was obtained, the palladium recovery rate could reach 99.9%, and the purity of sponge palladium was as high as 99.95%.

[0023] Comparative Example 1: Recovery and purification of sponge palladium by hydrazine hydrate method under acidic conditions The palladium leaching solution obtained in Example 5 is directly added to hydrazine hydrate for heating and reduction to obtain crude palladium. Hydrazine hydrate is added in batches until the solution is free of bubbles. The mass ratio of hydrazine hydrate to palladium is about 20:1. The solution is cooled and filtered, and washed with hot water and hot dilute sulfuric acid for 3-4 times, and then washed with water until there is no SO4. 2- So far, sponge palladium was obtained after vacuum drying at 60 °C overnight, with a palladium recovery rate of only 90.3% and a sponge palladium purity of 85.71%.

[0024] Comparative Example 2: Recovery and purification of sponge palladium by hydrazine hydrate method under alkaline conditions The palladium leaching solution obtained in Example 5 was adjusted to pH 10-12 with ammonia water, and then hydrazine hydrate was added and heated for reduction. The molar ratio of hydrazine hydrate to palladium in the leaching solution was about 10:1. After cooling, centrifugation was performed to obtain crude palladium containing a large amount of aluminum hydroxide colloid. The crude palladium was placed in dilute hydrochloric acid and heated to 100°C for reaction for 2 h, and then filtered and washed. This was repeated three times (the hydrochloric acid concentrations were 2, 1, and 1 mol / L, respectively). The obtained powder was then vacuum dried at 60°C overnight to obtain sponge palladium. The palladium recovery rate was only 50.4%, and the purity of the sponge palladium was as high as 94.93%.

[0025] Comparative Example 3: Recovery and purification of palladium sponge by hydrogen reduction method without induction agent The palladium leaching solution obtained in Example 5 was heated at 120°C under hydrogen conditions, reduced for 2 h, and then centrifuged and washed to obtain crude palladium. The obtained crude palladium was placed in 1 mol / L dilute hydrochloric acid, heated to 100°C under hydrogen atmosphere for 2 h, filtered, and washed with hot water until there was no Cl - After vacuum drying at 60 °C overnight, sponge palladium was obtained, the palladium recovery rate was only 7.5%, and the purity of sponge palladium was as high as 99.93%.

[0026] Comparative Example 4: Recovery and purification of sponge palladium by hydrogen reduction at room temperature The palladium leaching solution obtained in Example 5 was reduced under hydrogen conditions at room temperature for 2 h and then centrifuged and washed to obtain crude palladium. The obtained crude palladium was placed in 1 mol / L dilute hydrochloric acid and reacted at room temperature for 2 h under hydrogen atmosphere, then filtered and washed with hot water until there was no Cl - After vacuum drying at 60 °C overnight, sponge palladium was obtained, and the palladium recovery rate was 0%.

[0027] Comparative Example 5: Recovery and purification of sponge palladium by iron powder replacement method The palladium leaching solution obtained in Example 5 was added with iron powder (Fe / Pd mass ratio of 5) under chlorine atmosphere for reaction for two hours and filtered to obtain crude palladium containing impurity metals such as Fe with a purity of only 70-80%. Then, dilute hydrochloric acid and dilute nitric acid were added for oxidation, and the pH was adjusted with ammonia water and filtered to obtain a dichlorotetraamminepalladium solution. Dilute hydrochloric acid was then added to convert it into a yellow dichlorodiamminepalladium precipitate. After calcination at 650°C for 2 hours, hydrogen was introduced for reduction to obtain sponge palladium. The palladium recovery rate was 98.5%, the purity of the sponge palladium was as high as 99.92%, and a large amount of acidic wastewater containing high concentration of FeCl3 was generated during the reaction.

[0028] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 leaching solution, characterized in that: The specific steps are as follows: (1) A palladium-containing leaching solution obtained by acid leaching or acid chlorination leaching of waste Pd / Al2O3 catalyst; (2) The palladium leaching solution is filtered to remove impurities to obtain a clear solution, hydrogen is introduced and heated for reduction, and crude palladium is obtained after centrifugation; (3) The crude palladium obtained in step (2) is placed in a dilute acid solution and heated under a reducing atmosphere or an inert atmosphere. After cooling, the solution is filtered and washed with hot water. After drying, a palladium sponge is obtained.

2. The method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 leaching solution according to claim 1, characterized in that: The acid leaching solution contains one of hydrochloric acid, nitric acid and aqua regia, and the acid chlorination leaching solution is a leaching solution formed by hydrochloric acid and one or more of the oxidants sodium chlorate, sodium hypochlorite and hydrogen peroxide.

3. The method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 leaching solution according to claim 1, characterized in that: In the step (2), hydrazine hydrate is added during the hydrogen reduction process to induce the Pd 2+ of restoration.

4. The method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 leaching solution according to claim 1, characterized in that: The heating time in step (2) is 1 to 8 h, preferably 2 to 5 h.

5. The method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 leaching solution according to claim 1, characterized in that: In the step (2), the heating temperature is 60-150°C, preferably 100-120°C.

6. The method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 leaching solution according to claim 1, characterized in that: In step (3), the reducing gas or inert gas is a mixture of one or more of hydrogen, nitrogen, argon or helium.

7. The method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 leaching solution according to claim 1, characterized in that: In the step (3), the dilute acid used is one or both of sulfuric acid and hydrochloric acid, the heating time is 1 to 5 h, the concentration is 0.5 to 3 mol / L, and the temperature is 60 to 120 °C.

8. The method for efficiently separating and recovering metallic palladium from waste Pd / Al2O3 leaching solution according to claim 1, characterized in that: In step (3), the hot water temperature is 50-100 °C, and the washing is performed until there is no Cl - until.

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