A method for selectively enriching and recovering metallic palladium from a palladium-containing waste liquid

Abstract

The application discloses a method for selectively enriching and recovering metal palladium in a palladium-containing waste liquid; the method is characterized in that: first, inexpensive PVC or waste containing PVC is used as a support skeleton, and then, in an alkaline environment, an imidazole functional group is grafted through nucleophilic substitution to synthesize an imidazole-based polymer ionic liquid with certain mechanical strength, and then, the synthesized imidazole-based polymer ionic liquid is used to adsorb palladium (II) in the palladium-containing waste liquid; the imidazole-based polymer ionic liquid has excellent adsorption on Pd (II), and can be recycled. The method has high selectivity in enriching and recovering the noble metal palladium in the palladium-containing waste liquid, and is economic, feasible and green.

Description

Technical Field

[0001] This invention belongs to the field of precious metal processing and recycling, and more specifically, relates to a method for selectively enriching and recovering palladium from palladium-containing waste liquid. Background Technology

[0002] Palladium is a precious metal with luster, high corrosion resistance, high stability, and other special properties, and is widely used in important fields such as high-end jewelry, aerospace, medicine, electronics, and various chemical processes. The demand for palladium is increasing with significant economic growth; however, palladium ore is scarce in natural resources, and its price is high. In various industrial activities, some palladium enters solvents and water bodies, forming palladium-containing waste liquids and wastewater. Therefore, enriching, recovering, and reusing palladium from waste liquids and wastewater is of great significance for addressing palladium resource shortages and reducing production costs.

[0003] Commonly used methods for treating palladium-containing wastewater include solvent extraction, chemical oxidation-reduction, and electrochemical methods. Traditional solvent extraction can effectively extract and separate palladium from the mixture, yielding high-purity products. However, back-extraction remains a challenge, limiting its industrial application. Chemical oxidation-reduction involves adding oxidants or reductants to the heavy metal-containing wastewater to induce a series of oxidation-reduction reactions, resulting in the separation of sparingly soluble substances. However, this process generates large amounts of toxic and harmful waste residue, increasing subsequent treatment costs. Electrochemical methods yield high-purity products, but they are energy-intensive, and electrode passivation after a period of treatment reduces efficiency. Summary of the Invention

[0004] To address the shortcomings of existing palladium enrichment and reuse processes in wastewater treatment, this invention aims to provide a method for selectively enriching and recovering palladium from palladium-containing wastewater using imidazole-based polymeric ionic liquids. This method utilizes modified imidazole-based polymeric ionic liquids to recover palladium from palladium-containing wastewater. The raw material for these liquids, polyvinyl chloride (PVC), is inexpensive. The modified imidazole-based polymeric ionic liquid is water-insoluble, possesses certain mechanical strength, and is an extractant with excellent selectivity. It is highly effective in enriching and recovering palladium, achieving high selectivity and efficiency in recovering low concentrations of palladium from aqueous solutions. This method has significant potential application value in the field of palladium recovery and utilization from palladium-containing wastewater in factories.

[0005] This invention uses inexpensive PVC (or PVC-containing waste) as a supporting framework and synthesizes a polymeric ionic liquid with certain mechanical strength by nucleophilic substitution grafting of imidazole functional groups under alkaline conditions. The synthesized imidazole-modified polymeric ionic liquid adsorbs metals from palladium-containing wastewater under low pH conditions, exhibiting excellent selective adsorption of Pd(II), and the synthesized imidazole-based polymeric ionic liquid can be recycled. The technical solution of this invention is described in detail below.

[0006] A method for selectively enriching and recovering palladium from palladium-containing wastewater includes the following steps:

[0007] 1) Add polyvinyl chloride (PVC) granules or waste granules containing PVC and alkaline catalyst to the solvent and stir until homogeneous;

[0008] 2) Dissolve the imidazole modifier in a solvent to obtain an imidazole modifier solution;

[0009] 3) Add the imidazole modifier solution dropwise to the solution obtained in step 1), and react under reflux after the addition is complete;

[0010] 4) After the reaction is complete, filter the obtained solid, wash it with deionized water until the washing liquid is neutral, and vacuum dry it to obtain the modified polymeric ionic liquid of imidazole grafted PVC.

[0011] 5) Adjust the pH of the palladium-containing waste liquid to between 0.1 and 3, add the imidazole-grafted PVC modified polymeric ionic liquid, and adsorb the precious metal palladium in the waste liquid at room temperature.

[0012] Preferably, in step 1), the alkaline catalyst is selected from one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, or magnesium hydroxide; the molar ratio of polyvinyl chloride (PVC) to the alkaline catalyst is 3:1 to 1:3, the solvent is acetonitrile, and the solid-liquid mass-volume ratio is 1:5 to 1:20 g / mL; more preferably, in step 1), the alkaline catalyst is sodium hydroxide, and the molar ratio of polyvinyl chloride (PVC) to the alkaline catalyst is 2:1 to 1:2.

[0013] Preferably, in step 2), the imidazole modifier is 1-(3-aminopropyl)imidazolium, the solvent is acetonitrile, and the mass-volume ratio of the imidazole modifier to the solvent is 1:1 to 1:5 g / mL.

[0014] Preferably, the molar ratio of polyvinyl chloride (PVC) to imidazole modifier is 3:1 to 1:2; more preferably, the molar ratio is 1:1 to 1:1.6.

[0015] Preferably, in step 3), the reflux reaction time is 12-72 h; more preferably, it is 20-60 h.

[0016] Preferably, in step 4), the vacuum drying temperature is 20-80℃ and the vacuum degree is -50kpa to -100kpa; more preferably, the vacuum drying temperature is 20-40℃ and the vacuum degree is -60kpa to -80kpa.

[0017] Preferably, in step 5), the palladium content in the palladium-containing waste liquid is between 10 and 500 mg / L; more preferably, the palladium content in the palladium-containing waste liquid is between 50 and 200 mg / L, and the pH value of the palladium-containing waste liquid is between 1.5 and 2.5.

[0018] Preferably, in step 5), the mass-to-volume ratio of the imidazole-grafted PVC modified polymeric ionic liquid to the waste liquid is 1:2-2:1 g / L, and the reaction time is 5 min-10 h; more preferably, the mass-to-volume ratio of the imidazole-grafted PVC modified polymeric ionic liquid to the waste liquid is 7:10-3:2 g / L, and the reaction time is 5 min-3 h.

[0019] The present invention provides an economical, feasible, environmentally friendly, and highly selective method for the enrichment and recovery of palladium from palladium-containing waste liquid based on an imidazole-based polymeric ionic liquid. Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1) Using inexpensive polyvinyl chloride (PVC) particles produced in the chlor-alkali industry as raw materials, imidazole was grafted onto the PVC chain through a simple nucleophilic substitution reaction to synthesize a novel functionalized polymeric ionic liquid for the enrichment and recovery of metals in waste liquid, with low cost.

[0021] 2) The functionalized polymeric ionic liquid used in this invention for metal enrichment and recovery from palladium-containing waste liquid exists in the form of a hydrophobic solid, has excellent mechanical strength, avoids the problem of strong water solubility of general small molecule ionic liquids, and the imidazole polymeric ionic liquid can be recycled and reused as an extractant, which is energy-saving and environmentally friendly.

[0022] 3) When the functionalized polymer ionic liquid of the present invention is used for the enrichment and recovery of palladium in palladium-containing waste liquid, an adsorption rate of more than 90% can be achieved in 5 minutes at room temperature, which is fast, energy-saving and environmentally friendly.

[0023] 4) Palladium-containing wastewater usually contains common metals such as copper, zinc, iron, calcium, and cobalt. This invention adjusts the pH of the wastewater to between 0.1 and 3 by using acid, thereby achieving highly selective adsorption of palladium and preventing the adsorption of other metals. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the actual operation of palladium metal in factory wastewater according to the present invention.

[0025] Figure 2This is a schematic diagram of the reaction flow for the synthesis of the imidazole-modified polymeric ionic liquid of the present invention.

[0026] Figure 3 The imidazole-modified polymeric ionic liquid [PVC-amino]Cl of this invention is an imidazole-modified polymeric ionic liquid.

[0027] Figure 4 shows the energy spectrum of the imidazole-modified polymeric ionic liquid [PVC-amino]Cl and the adsorption product [PVC-amino]Cl-Pd of the present invention.

[0028] Figure 5 shows SEM images of the raw material (PVC), the imidazole-modified polymeric ionic liquid [PVC-amino]Cl, and the adsorption product [PVC-amino]Cl-Pd of the present invention; (a) and (b) show the raw material (PVC) and the imidazole-modified polymeric ionic liquid [PVC-amino]Cl magnified 2000 times, respectively; (c) and (d) show the imidazole-modified polymeric ionic liquid [PVC-amino]Cl and the adsorption product [PVC-amino]Cl-Pd magnified 20000 times, respectively. Detailed Implementation

[0029] The following are specific embodiments of the present invention, which, together with the accompanying drawings, will further describe the technical solution of the present invention.

[0030] Figure 1 This is a flowchart illustrating the actual operation of palladium metal in factory wastewater according to the present invention.

[0031] Example 1

[0032] I. Synthesis of Imidazole-Modified Polymeric Ionic Liquids

[0033] like Figure 2 The diagram shows the process from raw material polyvinyl chloride (PVC) to the product imidazole-modified polymeric ionic liquid. That is, the synthesis process of [PVC-amino]Cl.

[0034] First, weigh 15.36 g of polyvinyl chloride granules, then weigh 12 g of sodium hydroxide and place them in a 500 mL three-necked flask. Place the flask in a dry environment and measure 200 mL of acetonitrile as the reaction solvent. Dissolve 25.2 g of 1-(3-aminopropyl)imidazolium in 50 mL of acetonitrile and transfer the solution to the three-necked flask. Heat under reflux for 46 h. Filter the product under reduced pressure, wash 2-3 times with anhydrous ethanol to remove surface impurities, and then wash with deionized water until the filtrate is neutral to obtain the target synthetic product, the imidazolium-modified polymeric ionic liquid [PVC-amino]Cl. Its physical properties are as follows: Figure 3 The imidazole-modified polymeric ionic liquid shown is not water-soluble and has a certain mechanical strength.

[0035] II. Enrichment and Recovery of Palladium from Palladium-Containing Waste Liquid

[0036] 25 ml of palladium-containing waste liquid from the factory was added to a 25 ml beaker. The palladium content in the waste liquid was measured to be 115 mg / L. The pH of the palladium waste liquid was adjusted to 2, and then 0.03 g of [PVC-amino]Cl was added. The mixture was stirred at 200 rpm for 7.5 h at room temperature. The mixture was then filtered under reduced pressure to obtain [PVC-amino]Cl-Pd.

[0037] By comparing the palladium content in the waste liquid before and after adsorption, the synthesized imidazole-modified polymeric ionic liquid achieved an adsorption rate of 99.969% for palladium.

[0038] XPS analysis was performed on the imidazole-modified polymeric ionic liquid [PVC-amino]Cl and the metal-loaded [PVC-amino]Cl-Pd. The results are shown in Figure 4(b). The full spectrum shows that the modified polymeric ionic liquid loaded with Pd showed a Pd 3d signal at 342.08 eV, indicating that Pd was adsorbed in the imidazole-modified polymeric ionic liquid [PVC-amino]Cl. At the same time, it can be seen that the adsorption product does not contain other metals.

[0039] Example 2

[0040] I. Synthesis of Imidazole-Modified Polymeric Ionic Liquids

[0041] The palladium content in the palladium-containing wastewater from the factory was measured to be 75 mg / L, with a pH value of 2. First, 11.52 g of polyvinyl chloride (PVC) and 9 g of sodium hydroxide were weighed and placed in a 500 mL three-necked flask. Under a dry environment, 200 mL of acetonitrile was measured as the reaction solvent. Then, 18.9 g of 1-(3-aminopropyl)imidazole was dissolved in 70 mL of acetonitrile and transferred to the three-necked flask. The oil bath temperature was set at 90℃, and the reaction was carried out for 48 hours. Figure 2 The diagram shows the synthesis process from raw materials to the target product [PVC-amino]Cl. The product is filtered under reduced pressure, washed 2-3 times with anhydrous ethanol to remove surface impurities, and then washed with deionized water until the filtrate is neutral.

[0042] II. Enrichment and Recovery of Palladium from Palladium-Containing Waste Liquid

[0043] Seven 25ml beakers, numbered 1, 2, 3, 4, 5, 6, and 7, were used to add 25ml of palladium-containing waste liquid from the factory to each beaker. The palladium content in the waste liquid was measured to be 75mg / L. The pH of the waste liquid was adjusted to 2, and then 0.02g of [PVC-amino]Cl was added. The reaction was carried out at room temperature with a magnetic stirrer at 200rpm. The reaction time was as follows: beaker 1: 5min; beaker 2: 12min; beaker 3: 0.5h; beaker 4: 1h; beaker 5: 2h; beaker 6: 3h; and beaker 7: 7.5h. By measuring the palladium content in the remaining waste liquid, it was found that the adsorption rate of [PVC-amino]Cl on palladium in the waste liquid was 91.6% at 5min, 96.42% at 12min, and reached saturation at 99.52% after 3h.

[0044] SEM analysis was performed on the raw material (PVC), the polymeric ionic liquid [PVC-amino]Cl, and the [PVC-amino]Cl-Pd loaded with metal Pd. As shown in Figures 5(a) and 5(b), when the raw material (PVC) and the synthesized product [PVC-amino]Cl are magnified 2000 times, the precursor PVC has a relatively smooth surface. After grafting 1-(3-aminopropyl)imidazolium, many tiny particles and irregular pores are formed, which increases the surface area of ​​the polymeric ionic liquid and thus improves the adsorption capacity for metal ions. As shown in Figures 5(c) and 5(d), when the synthesized product [PVC-amino]Cl and the adsorbed product [PVC-amino]Cl-Pd are magnified 20000 times, the SEM images of the palladium-loaded ionic liquid both show particle clusters. This is because when the metal enters the reaction site on the surface of the ionic liquid, it occupies the original pores with its own volume.

Claims

1. A method for selectively enriching and recovering palladium from palladium-containing wastewater, characterized in that, Includes the following steps: 1) Add polyvinyl chloride (PVC) granules or waste granules containing PVC and alkaline catalyst to the solvent and stir until homogeneous; 2) Dissolve the imidazole modifier in a solvent to obtain an imidazole modifier solution; 3) Add the imidazole modifier solution dropwise to the solution obtained in step 1), and react under reflux after the addition is complete; 4) After the reaction is complete, filter the obtained solid, wash it with deionized water until the washing liquid is neutral, and vacuum dry it to obtain the imidazole-grafted PVC modified polymeric ionic liquid. 5) Adjust the pH of the palladium-containing waste liquid to between 0.1 and 3, add imidazole-grafted PVC-modified polymeric ionic liquid, and adsorb the precious metal palladium in the waste liquid at room temperature; wherein: In step 5), the palladium content in the palladium-containing waste liquid is between 10 and 500 mg / L, and the palladium-containing waste liquid contains copper, zinc, iron, calcium, and cobalt; the mass-volume ratio of the imidazole-grafted PVC modified polymeric ionic liquid to the palladium-containing waste liquid is 1:2-2:1 g / L, and the reaction time is 5 min-10 h.

2. The method according to claim 1, characterized in that, In step 1), the alkaline catalyst is selected from any one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide or magnesium hydroxide; the molar ratio of polyvinyl chloride (PVC) to alkaline catalyst is 3:1-1:3, the solvent is acetonitrile, and the solid-liquid mass-volume ratio is 1:5~1:20 g / mL.

3. The method according to claim 1, characterized in that, In step 2), the imidazole modifier is 1-(3-aminopropyl)imidazolium, the solvent is acetonitrile, and the mass-volume ratio of the imidazole modifier to the solvent is 1:1 to 1:5 g / mL.

4. The method according to claim 1, characterized in that, The molar ratio of polyvinyl chloride (PVC) to imidazole modifier is 3:1 to 1:

2.

5. The method according to claim 1, characterized in that, In step 3), the reflux reaction time is 12-72 hours.

6. The method according to claim 1, characterized in that, In step 4), the vacuum drying temperature is 20-80℃ and the vacuum degree is -50kpa to -100kpa.

7. The method according to claim 1, characterized in that, The pH value of palladium-containing waste liquid is between 1.5 and 2.5.

Images