A method for adsorptive separation of palladium ions from an acidic aqueous phase

Abstract

The present application relates to the technical field of palladium separation, and discloses a method for adsorbing and separating palladium ions from an acidic aqueous phase. A nitrogen-containing soft ligand as shown in formula I is loaded on a macroporous resin carrier to obtain a binary composite material, wherein R1 is a phenyl group or a substituted phenyl group, and R2 is an alkyl group or an aromatic group of C 1‑10 The binary composite material is mixed with an acidic aqueous solution containing palladium ions and other metal ions, and palladium ions are efficiently adsorbed and separated therefrom. The composite material of the present application can adsorb and separate palladium ions from an aqueous phase containing various metal ions, has good selectivity, fast adsorption speed, an adsorption rate of more than 85% and up to 97.4%, good separation effect, and the method is simple and easy to industrialize.

Description

Technical Field

[0001] This invention relates to the field of palladium separation technology, and more specifically to a method for adsorbing and separating palladium ions from an acidic aqueous phase. Background Technology

[0002] Due to its unique physicochemical properties, palladium, a precious metal, holds an irreplaceable position in fields such as industrial catalysis, hydrogen storage, and energy storage. In addition to its excellent catalytic activity, palladium maintains chemical inertness over a wide temperature range and possesses characteristics such as high melting point, abrasion resistance, corrosion resistance, high ductility, and strong thermoelectric stability, making it widely used in various sectors of national industry.

[0003] However, palladium is present in extremely low amounts in the Earth's crust, far from meeting the needs of modern chemical industry. Currently, palladium metal is mainly sourced from the utilization of natural mineral resources and the recycling of palladium-containing secondary resources such as copper-nickel sulfide ore byproducts and palladium catalysts. However, with increasing palladium resource depletion, sustainable utilization of palladium resources is becoming increasingly difficult.

[0004] Nuclear power has seen rapid development in recent years due to its high energy density, low pollution, and lack of greenhouse gas emissions. However, spent fuel is inevitably generated during nuclear power plant operation. According to literature, each ton of spent fuel contains approximately 1-2 kg of palladium. High-level radioactive waste (HLLW) produced from spent fuel reprocessing is a highly acidic, highly radioactive, and multi-component strongly nitric acid aqueous solution, containing 10... 6 The content of Pd and its isotopes is approximately 165 mg / L, of which 10 6 Pd is a radioactive nuclide with a half-life of 6.5 × 10⁻⁶. 6 Palladium is approximately 17% of the total Pd isotope content. It has a long radioactive period, is highly hazardous, and has a high content. If the palladium resources contained in spent fuel can be separated, purified, and recycled, it will be of great significance for expanding the sources of palladium resources and increasing palladium resource reserves.

[0005] Compared to solvent extraction, chemical precipitation, and membrane separation, adsorption separation is a superior method for reprocessing spent fuel, characterized by low secondary waste generation, high separation efficiency, and environmental friendliness. Currently reported materials for the adsorption and separation of palladium from high-level radioactive waste include: crown ether-supported silica gel (F. Bai et al. / Separation and Purification Technology 106(2013)38–46), but its adsorption capacity for palladium is significantly reduced in high-acidity nitric acid (3-4M) solutions, and the alkaline earth metal Ba(II) significantly interferes with the adsorption of Pd(II), resulting in poor selectivity for Pd(II); 2-acetylpyridine-functionalized AP-XAD-16 (R. Ruhela et al. / Separation and Purification Technology 99(2012)36–43), but its weak adsorption capacity for Pd(II) and poor resistance to strong acid corrosion hinder its industrial application; other materials include activated carbon and nitrogen-containing soft ligand silica gel. Overall, the reported adsorbents have drawbacks such as low adsorption efficiency for Pd(II) under high acidity, poor selectivity, and poor acid and radiation resistance, making it difficult to realize their industrial application. Summary of the Invention

[0006] This invention addresses the problems of low palladium ion adsorption efficiency and low adsorption rate under high acidity in existing technologies by providing a method for adsorbing and separating palladium ions from an acidic aqueous phase. This method can efficiently adsorb palladium ions from an acidic aqueous phase, the adsorption material has high selectivity for elemental palladium, the method is simple to operate, has high separation efficiency, and is easy to industrialize.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for adsorbing and separating palladium ions from an acidic aqueous phase involves loading a nitrogen-containing soft ligand as shown in formula (I) onto a macroporous resin support to obtain a binary composite material, mixing the binary composite material with an acidic aqueous solution containing palladium ions and other metal ions, and adsorbing and separating palladium ions from the solution.

[0009]

[0010] Where R1 is a phenyl or substituted phenyl group, and R2 is a C group. 1-10 alkyl or aromatic groups;

[0011] The other metal ions include a variety of metal ions from alkali metals, alkaline earth metals, and transition metals.

[0012] Preferably, in formula (I), R1 is phenyl and R2 is phenyl or n-butyl;

[0013] More preferably, R1 is phenyl and R2 is n-butyl, and its specific structure is shown in formula (II):

[0014]

[0015] In the applicant's early research, it was discovered that the molecule structure shown in formula (I) could extract trivalent lanthanides and / or actinides from the aqueous phase. Since Pd(II) is a noble metal element with an oxidation state of +2 and a coordination number of generally 4, its electronic structure and physical and chemical properties are significantly different from those of actinides and rare earth elements Am(III), Cm(III), and Y(III). However, the applicant unexpectedly discovered that the macroporous resin material BuPh-PhenPO / XAD-7, supported by the nitrogen-containing soft ligand o-phenanthroline phosphorus oxide ligand shown in formula (II), could selectively adsorb palladium ions from highly acidic nitric acid aqueous solution, with a very high adsorption rate, reaching up to 97.4%; and the adsorption rate was fast, achieving an adsorption rate of over 80% in 10 minutes and over 90% after 30 minutes.

[0016] Pd(II), as a typical Lewis soft acid, readily coordinates with nitrogen-containing organic ligands containing Lewis soft bases to form stable complexes, according to the Lewis hard-soft acid-base theory. In this invention, the two nitrogen atoms on the o-phenanthroline ring of the o-phenanthroline phosphate ligand can coordinate with Pd(II) to form a stable complex. This is likely the fundamental reason why the BuPh-PhenPO / XAD-7 adsorbent material can selectively adsorb and separate palladium. Other metal ions, due to their different chemical properties from Pd(II) ions, are not adsorbed by the aforementioned material.

[0017] The palladium ions include isotopes of palladium. 104 Pd, 105 Pd, 106 Pd, 107 Pd, 108 Pd and 110 Any of Pd. Among them 107 Pd, as a radioactive isotope, has a half-life of 6.5 x 10⁻⁶. 6 Separating and recovering palladium from high-level radioactive waste is of great significance for both environmental protection and palladium resource recovery.

[0018] The macroporous resin carrier includes any one of the following: medium polarity resin XAD-7, highly cross-linked macro-network acrylic resin XAD-8, and styrene-divinylphenyl resin XAD-2010.

[0019] Preferably, the macroporous resin carrier is the moderately polar resin XAD-7, which is polymerized from methacrylic acid compounds. It possesses a large surface area and continuous pore size, exhibiting excellent physical and chemical stability, resistance to strong acid corrosion, and resistance to radiation decomposition. It is a novel inorganic / organic carrier with low synthesis costs and has already been industrially applied. Compared to other carrier materials such as silica gel, resins, zeolites, and activated carbon, this type of resin material has stronger chemical activity than silica gel and does not interact with adsorbates. It is more easily bonded to organic ligands through electrostatic interactions, hydrogen bonding, and chemical modification to prepare composite materials with special properties.

[0020] The mass ratio of the nitrogen-containing soft ligand to the macroporous resin carrier is 1:2-4, preferably 1:3.

[0021] The other metal ions include one or more of K(I), Rb(I), Cs(I), Sr(II), Zr(IV), Cu(II), Ba(II), Ni(II), Co(II), Fe(III), Ru(II), and Rh(II).

[0022] The acidic aqueous solution is a nitric acid aqueous solution, wherein the nitric acid concentration is 0.1-5.0 mol / L; preferably, the nitric acid concentration is 0.1-4 mol / L, as the adsorption and separation effect is better at low acidity. More preferably, the nitric acid concentration is 0.1-3 mol / L. Existing Pd(II) adsorption research has mostly focused on low acidity nitric acid concentrations less than 1.0 M. As acidity increases, the adsorption rate of Pd(II) decreases significantly. The composite material used in this patent application still exhibits an adsorption efficiency of over 94% for Pd(II) at a nitric acid concentration of 3.0 M, making it highly suitable for the direct adsorption and recovery of palladium and its isotopes from high-level radioactive waste liquids.

[0023] The mass concentration of palladium ions in the acidic aqueous solution is not less than 1 ppm. The method of the present invention can achieve palladium extraction when the concentration of palladium ions in the aqueous solution is only 1 ppm. However, if the concentration of other interfering metal ions is too high, it will be difficult to achieve effective adsorption of palladium. The mass concentration of other metal ions is not more than 20 times the mass concentration of palladium ions. When the concentration of interfering ions is more than 20 times the concentration of palladium ions, the adsorption rate of palladium ions will decrease. Preferably, the total mass concentration of other metal ions is not more than 15 times the mass concentration of palladium ions.

[0024] The mass-to-volume ratio of the binary composite material to the acidic aqueous solution is 0.5-1.5 g: 500 mL; preferably 1 g: 500 mL.

[0025] The mixing time is 1 minute or more, preferably 10 minutes or more, and more preferably 30 minutes or more. In some embodiments, the mixing time is 30-60 minutes. The adsorbent material can achieve an adsorption rate of more than 65% of palladium ions in an aqueous solution within 1 minute, an adsorption rate of more than 80% within 10 minutes, and an adsorption rate of more than 90% after 30 minutes. However, the increase in adsorption rate is not significant after 60 minutes.

[0026] The temperature during the mixing process is 10-50℃; preferably 15-45℃. As the adsorption temperature increases, the adsorption rate of Pd(II) by the material will decrease slightly. In order to reduce energy consumption, room temperature is the preferred adsorption temperature.

[0027] The method of the present invention achieves an adsorption rate of palladium ions of not less than 85%, preferably more than 90%; and an adsorption capacity of not less than 20 mg / g, preferably not less than 30 mg / g. The maximum adsorption capacity can reach 43 mg / g.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The composite material of this invention can adsorb and separate palladium ions from a variety of metal elements. When separating palladium from the aqueous phase, it exhibits good selectivity, fast adsorption rate, and an adsorption rate of over 85%, reaching up to 97.4%. The adsorption capacity can reach up to 43 mg / g, with good separation effect. The technology is simple and easy to implement, and the composite material used has low synthesis cost and is easy to industrialize. Attached Figure Description

[0030] Figure 1 The effect of nitric acid concentration on the palladium adsorption partition coefficient.

[0031] Figure 2 The effect of nitric acid concentration on palladium adsorption rate.

[0032] Figure 3 The graph shows the relationship between palladium ion concentration and adsorption efficiency.

[0033] Figure 4 This is a graph showing the relationship between adsorption mixing time and adsorption effect. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0035] The o-phenanthroline phosphorus oxide ligand BuPh-PhenPO involved in this patent was designed, developed, and synthesized in our laboratory. The macroporous resin XAD-7 used is a commercially available raw material that can be obtained inexpensively and on a large scale, enabling the material to be used in large-scale industrial applications. The structure and preparation method of BuPh-PhenPO are shown in CN 112458283 A.

[0036] Example 1

[0037] Step 1: Dissolve 0.5 g of BuPh-PhenPO compound in 35.0 ml of dichloromethane and mix thoroughly; add 1.5 g of activated macroporous resin material XAD-7 and stir thoroughly until most of the dichloromethane evaporates to a near-dry state. Then, vacuum dry the near-dry material at 60 °C for 24 h to obtain the binary composite material, named BuPh-XAD-7.

[0038] Step 2: Dissolve the metal salts KNO3, RbNO3, Sr(NO3)2, Zr(NO3)4, Cu(NO3)2, Ni(NO3)2, Co(NO3)2, Ba(NO3)2, Fe(NO3)3, and Pd(NO3)2 in water to prepare an aqueous solution. The concentration of each of the above metal salts in the aqueous solution is 5.0 × 10⁻⁶. -5 mol / L. Add HNO3 to adjust c(H) in the aqueous solution. + The concentrations of nitric acid were 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, and 5 mol / L, respectively. The resulting solutions with different acidities were then mixed with the aforementioned binary composite material at a solid-liquid ratio of 500 (i.e., 500 mL solution / 1.0 g composite material) in a container. After thorough mixing (in this example, 5.0 mL of aqueous phase + 0.01 g of solid phase), adsorption was performed using a TAITECMM-10 shaker. The shaking rate was 120 rpm, the operation was at room temperature, and the shaking time was 180 min to allow adsorption to reach equilibrium. The content of each element in the aqueous nitric acid phases before and after adsorption was then measured.

[0039] The partition coefficients and adsorption rates of each metal ion at different nitric acid concentrations are as follows: Figure 1 and 2 As shown in Table 1, the adsorption rate and partition coefficient of Pd(II) are listed in Table 1.

[0040] Existing research on Pd(II) adsorption mainly focuses on low acidity nitric acid concentrations below 1.0 M. As acidity increases, the adsorption rate of Pd(II) decreases significantly. Table 1 shows that the composite material used in this patent application exhibits excellent Pd(II) adsorption performance within an acidity range of 0.1-5 M, with adsorption rates mostly above 92%. Even at a nitric acid concentration of 3.0 M, its adsorption efficiency for Pd(II) remains above 94%, making it highly suitable for the direct adsorption and recovery of palladium and its isotopes from high-level radioactive waste. Furthermore, even at a nitric acid concentration of 5.0 M, the palladium adsorption rate reaches as high as 89.9%, demonstrating excellent performance. This composite material offers significant technical advantages compared to other acid-sensitive adsorbents.

[0041] from Figure 1 and Figure 2 It is evident that the composite material exhibits very high adsorption selectivity for Pd(II), effectively adsorbing it from a complex mixture of other metal ions, thus achieving efficient Pd(II) extraction and separation.

[0042] Table 1 Adsorption experimental results of Pd(II) at different nitric acid concentrations

[0043] Nitric acid concentration (mol / L) Pd(II) adsorption rate (%) Pd(II) partition coefficient (mL / g) 0.1 94.6 5495.1 0.5 97.4 5504.7 1.0 97.3 5379.9 2.0 96.2 5124.2 3.0 94.6 4937.1 4.0 92.2 4750.2 5.0 89.9 4536.1

[0044] Example 2

[0045] Following the process of Example 1, with a fixed nitric acid concentration of 3.0 M and an input mass of 10 mg of the binary composite material, only the concentration of palladium ions in the aqueous solution was changed, while other conditions remained constant. The resulting adsorption results are as follows: Figure 3 As shown in Table 2, it can be seen that as the concentration of palladium ions in the solution increases, the adsorption capacity at equilibrium first increases, reaches a maximum value, and then tends to stabilize, with a maximum adsorption capacity of 43 mg / g.

[0046] Table 2 Adsorption experimental results for different Pd(II) mass concentrations

[0047] Pd(II) mass concentration (mg / L) Pd(II) adsorption capacity (mg / g) 0.6977 5.14258 1.29736 10.94061 3.04923 21.82964 40.80288 40.01357 143.80925 37.44845 210.0046 40.24573 489.78865 42.62375

[0048] Example 3

[0049] Following the process of Example 1, with other parameters fixed and the nitric acid concentration at 3.0 M, only the contact time between the adsorbent and the reaction solution was changed, i.e., only the mixing time was changed. The resulting adsorption results are as follows: Figure 4 As shown in Table 3, it can be seen that with the increase of contact time, the partition coefficient of Pd(II) first increases, reaching 6000 mL / g at 60 min, and then fluctuates within a small range, indicating that the adsorption of Pd(II) by the BuPh-XAD-7 composite material can reach adsorption equilibrium at 60 min.

[0050] Table 3. Experimental results of adsorption time of Pd(II) on BuPh-XAD-7 composite material.

[0051] Contact time (min) Pd(II) adsorption rate (%) Pd(II) partition coefficient (mL / g) 1 65.4 943.4 5 78.3 1807.9 10 83.4 2512.7 30 91.2 5166.5 60 92.5 6170.3 90 92.1 5793.7 120 92.7 6351.8 180 91.9 5684.8

Claims

1. A method for adsorptive separation of palladium ions from an acidic aqueous phase, characterized in that, The nitrogen-containing soft ligand as shown in formula (I) is loaded on a macroporous resin carrier to obtain a binary composite material, and the binary composite material is mixed with an acidic aqueous solution containing palladium ions and other metal ions to adsorb and separate the palladium ions; the mixing time is 1-60 min; the adsorption rate of the method for the palladium ions is not less than 85%, and the adsorption capacity is not less than 20 mg / g. wherein R1is phenyl or substituted phenyl, R2is C 1-10 alkyl or aryl; The other metal ions include one or more metal ions of alkali metals, alkaline earth metals and transition metals.

2. The method for adsorptive separation of palladium ions from an acid aqueous phase according to claim 1, characterized in that, In formula (I), R1 is a phenyl group, and R2 is a phenyl group or a n-butyl group.

3. The method for adsorptive separation of palladium ions from an acidic aqueous phase according to claim 1, characterized in that, The macroporous resin carrier includes any one of medium-polar resin XAD-7, highly cross-linked macronet acrylic resin XAD-8 and styrene-divinylbenzene-based resin XAD-2010; the mass ratio of the nitrogen-containing soft ligand to the macroporous resin carrier is 1:2-4.

4. The method for adsorptive separation of palladium ions from an acidic aqueous phase according to claim 1, characterized in that, The palladium ion includes isotopes of palladium 104 Pd, 105 Pd, 106 Pd, 107 Pd, 108 Pd and 110 any of Pd.

5. The method for adsorptive separation of palladium ions from an acidic aqueous phase according to claim 1, characterized in that, The other metal ions include one or more of K(I), Rb(I), Cs(I), Sr(II), Zr(IV), Cu(II), Ba(II), Ni(II), Co(II), Fe(III), Ru(II) and Rh(II).

6. The method for adsorptive separation of palladium ions from an acidic aqueous phase according to claim 1, characterized in that, The acidic aqueous solution is an aqueous nitric acid solution, wherein the concentration of the nitric acid is 0.1-5.0 mol / L.

7. The method of claim 1, wherein the method is characterized by, The mass concentration of the palladium ions in the acidic aqueous solution is not less than 1 ppm, and the mass concentration of the other metal ions is not higher than 20 times of the mass concentration of the palladium ions.

8. The method of claim 1, wherein the method is characterized by, The mass-volume ratio of the binary composite material to the acidic aqueous solution is 0.5-1.5 g:500 mL.

9. The method of claim 1, wherein the method is characterized by, The temperature is 10-50°C.

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