A method for extracting and separating palladium ions from acidic aqueous phase

Abstract

The present invention relates to the technical field of spent fuel reprocessing, and discloses a method for extracting and separating palladium ions from acidic aqueous phases, which includes the steps of: diluting a ligand as shown below to form an organic phase, and using an acidic aqueous solution containing palladium ions and multi-metal ions to extract and separate palladium ions, where R is a linear or branched alkyl substituent with C1-C 10 The method can exhibit high selectivity for palladium at high acidity, with an extraction efficiency of more than 92% for palladium ions in the acidity range of 0.1-6M. When the acidity concentration is 3.0-4.0M, the extraction efficiency of Pd(II) reaches more than 98%, and the extraction rate is extremely fast with an extraction equilibrium time of less than 2 minutes. At the same time, the extraction ability for other co-existing elements such as alkali metals, alkaline earth metals, Group VIII metals iron, cobalt, nickel, transition metal copper, and zirconium is relatively low, which has great technical advantages compared with other sulfur-containing extractants and previous nitrogen-containing extractants. #imgabs0#

Description

Technical Field

[0001] The present invention relates to the field of spent fuel reprocessing technology and precious metal resource recovery, and particularly relates to a method for extracting and separating palladium ions from acidic aqueous solutions. Background Art

[0002] The precious metal palladium has characteristics such as high melting point, wear resistance, corrosion resistance, strong ductility, and strong thermoelectric stability, and occupies an irreplaceable position in the fields of industrial catalysis, hydrogen storage, and energy storage. However, the content of palladium element in the earth's crust is extremely low. At present, the sources of palladium metal mainly come from the utilization of natural mineral resources and the recycling of palladium-containing secondary resources such as copper-nickel sulfide by-products and palladium catalysts. However, with the increase of palladium resource depletion, the sustainable utilization of palladium resources is becoming increasingly difficult to achieve.

[0003] It is reported in the literature that each ton of spent fuel generated during nuclear power operation contains about 1-2 kg of palladium, and among them 106 the content of Pd and its isotopes is about 165 mg / L. 106 Pd has a long radioactive period, great harm and high content. If the palladium resources contained in spent fuel can be separated and purified for recycling, it is of great significance for expanding the sources of palladium resources and increasing palladium resource reserves. However, the spent fuel dissolution solution is in a complex environment of high nitric acid acidity, high radiation field, and a large number of coexisting ions in excess. It is extremely difficult to separate Pd from it. Until now, the separation of precious metal palladium in high-level radioactive waste liquid is still in the research stage.

[0004] CN105002359A discloses a method for extracting palladium from an aqueous solution, using a diazamidohydrazone pyridine derivative as a ligand to separate palladium from alkali metals and alkaline earth metals. However, such ligands have the defects of complex synthesis routes and low extraction efficiency, so it is difficult to carry out further industrial applications.

[0005] CN106140112A discloses a method for simultaneously separating palladium, cesium, and strontium from acidic aqueous solutions. A quaternary composite material is mixed with a nitric acid aqueous solution, and palladium, cesium, and strontium in the nitric acid aqueous solution are adsorbed and separated by the quaternary composite material. The complex composition of the composite material, low adsorption capacity, and insufficient selectivity for palladium ions also limit its further practical popularization and application.

[0006] Due to the advantages of such o-phenanthroline phosphate esters ligands, such as resistance to strong acid hydrolysis, radiation resistance, and simple preparation process, they have broad application prospects in the separation and recovery of relevant precious metal palladium ions in industrial waste liquids, especially high-level radioactive waste liquids generated during the spent fuel reprocessing process. However, there are relatively few research attempts on using such extractants for the extraction and separation of precious metal palladium at present. Summary of the Invention

[0007] In view of the problem of difficult separation and extraction of palladium ions from spent fuel, the present invention provides a technical method for extracting and separating palladium ions from an aqueous phase containing multiple metal elements. This method can exhibit high selectivity for palladium under high acidity conditions, and has a low extraction ability for other co-existing alkali metals, alkaline earth metals, Group VIII metals iron, cobalt, nickel, transition metal copper, zirconium, and other elements, showing great technical advantages compared with other sulfur-containing extractants.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for extracting and separating palladium ions from an acidic aqueous phase, comprising the steps of: diluting a ligand as shown below to form an organic phase, and using an acidic aqueous solution containing palladium ions and multiple metal ions for extracting and separating palladium ions; the structure of the ligand is as follows:

[0010]

[0011] Wherein R is a linear or branched alkyl substituent of C1-C 10 of.

[0012] The present invention uses a ligand of o-phenanthroline phosphate ester with the advantages of being resistant to strong acid hydrolysis and radiation, etc., to rapidly extract and separate palladium ions with high selectivity from an aqueous solution containing multiple metal ions. Compared with traditional sulfur-containing extractants such as dialkyl disulfide, thiodiglycolamide, dialkyl sulfoxide (RSC Adv., 2014, 4, 24344-24350), etc., which have problems such as low extraction rate of palladium in a high nitric acid aqueous solution, being easily oxidized, and low extraction rate, this type of extractant has obvious technical advantages.

[0013] It should be emphasized that this patent has obvious differences from the previously applied use of this type of extractant for the separation of Pu(IV) in terms of principle and application scenarios. The separation of Pu(IV) mainly uses an O-containing extractant to recover and reuse a large amount of U(VI) and Pu(IV) in spent fuel at the front end of spent fuel reprocessing. The reason why this type of extractant can extract and separate Pu(IV) is mainly to utilize the selective complexation of Pu(IV) by the P=O group contained in the structure of this type of extractant; while the separation of Pd(II) by this type of extractant is mainly at the end of spent fuel reprocessing, to extract and separate Pd(II) in high-level radioactive waste under the condition of 3-4M nitric acid concentration, which mainly utilizes the selective complexation of Pd(II) by the N atoms on the o-phenanthroline ring contained in the structure of this type of extractant.

[0014] Preferably, R is any one of n-butyl, isobutyl, sec-butyl or tert-butyl, more preferably n-butyl or isobutyl. Compared with extractants with other substituents, these two structures have advantages such as better solubility in diluents commonly used in the reprocessing of spent nuclear fuel in the nuclear industry, such as kerosene and octanol, and stronger extraction ability.

[0015] Preferably, the ligand is diluted by dilution, and the diluent includes any one or more of 3-trifluoromethylnitrobenzene, octanol, chloroform, octanol, and kerosene.

[0016] The multi-metal ions include ions of one or more metal elements such as alkali metals, alkaline earth metals, iron, cobalt, nickel, copper, zirconium, lead, molybdenum, yttrium, and lutetium. It has been found through research that the o-phenanthroline phosphate ligands in the present invention have low extraction ability for alkali metals, alkaline earth metals, Group VIII metals iron, cobalt, nickel, transition metal copper, and zirconium, etc., while having high extraction selectivity and extraction rate for palladium. Traditional sulfur-containing extractants such as dialkyl disulfides, thiodiglycolamides, and dialkyl sulfoxides (RSC Adv., 2014, 4, 24344-24350) have problems such as low extraction rate for palladium in high nitric acid aqueous solutions, being easily oxidized, and low extraction rate, which further indicates that this type of extractant has great technical advantages compared with other sulfur-containing extractants.

[0017] Preferably, the multi-metal ions include one or more of K(I), Rb(I), Sr(II), Ba(II), Cu(II), Fe(III), Co(II), Ni(II), Zr(IV), Pb(II), Mo(VII), Lu(III), and Y(III).

[0018] Preferably, the concentration of palladium ions in the acidic aqueous solution is above 0.1 ppm, and the total concentration of multi-metal ions is not higher than 1000 times the concentration of palladium ions. In some embodiments, the concentration of palladium ions in the acidic aqueous solution is above 0.5 ppm, and the total concentration of multi-metal ions is not higher than 500 times the concentration of palladium ions, such as not higher than 400 times the concentration of palladium ions, not higher than 300 times, not higher than 200 times, not higher than 100 times, etc.

[0019] Preferably, it is an aqueous solution of nitric acid, hydrochloric acid or perchloric acid, where the concentration of H + is 0.1 - 6 mol / L. Such as 0.2 mol / L, 0.3 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, or any value between them.

[0020] Most of the Pd(II) extraction studies in the prior art remain at low acidity (acidity less than 1.0 M). When the acidity increases, the adsorption rate of Pd(II) decreases significantly. In the present invention, the extraction efficiency of the phenanthroline phosphate ligand for palladium ions is very high in the acidity range of 0.1 - 6 M, reaching more than 92%, and even higher when the acidity is higher. At an H + When the concentration is 3.0 - 4.0 M, the highest extraction effect on Pd(II) is more than 98%. Since the acidity in high-level radioactive waste liquid is extremely high itself, the method of the present invention is very suitable for directly adsorbing and recovering palladium and its isotopes from high-level radioactive waste liquid with a nitric acid concentration of 3.0 - 4.0 M.

[0021] Further preferably, the nitric acid concentration in the acidic aqueous solution is 2 - 4 mol / L. The palladium extraction rate is higher at this acidity.

[0022] Preferably, the temperature for extracting and separating palladium ions is 15 - 55 °C, and the extraction equilibrium time is more than 2 min. The research results show that the extraction rate of this type of ligand for palladium ions is extremely fast. After 2 min of extraction, the extraction equilibrium can be reached. Further preferably, the extraction equilibrium time is 2 - 30 min;

[0023] Preferably, the extraction rate of palladium ions is more than 90%, such as more than 92%, more than 95%, more than 96%, more than 98%, more than 99%, etc., and the distribution ratio is more than 10, such as more than 12, more than 15, more than 20, more than 30, more than 40, more than 50, more than 60, more than 80, more than 100.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention uses a phenanthroline phosphate extractant to achieve high-selectivity extraction of Pd(II) at high acidity. The extraction rate is more than 92%, and when the acidity is 3.0 - 4.0 M, the extraction rate shows a more excellent effect. The extraction rate is extremely fast and the extraction equilibrium can be reached within 2 min. It is very suitable for adsorbing and recovering the noble metal palladium and its isotopes from high-level radioactive waste liquid with a nitric acid concentration of 3.0 - 4.0 M.

[0026] (2) The phenanthroline phosphate ligand used in the present invention shows a very low extraction ability for alkali metals, alkaline earth metals, Group VIII metals, etc., enabling the method of the present invention to efficiently and highly selectively separate Pd(II) from various metal ions, which is important for the separate recovery of palladium elements.

[0027] (3) The phenanthroline phosphate ligand used in the present invention has the characteristics of being resistant to strong acid hydrolysis, radiation resistance, and simple preparation method, which is more conducive to the recovery of the noble metal palladium and its isotopes from high-level radioactive waste liquid in industrial production. Description of the Drawings

[0028] Figure 1 Performance of C4-POPhen in extracting Pd(II) under different acidity conditions in Example 1.

[0029] Figure 2 Performance of iBu-POPhen in extracting Pd(II) under different acidity conditions in Example 2.

[0030] Figure 3 Performance of C4-POPhen and iBu-POPhen in extracting Pd(II) under different contact time conditions in Example 3. Detailed implementation manners

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent replacements based on the understanding of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall all be covered within the protection scope of the present invention.

[0032] In the following detailed implementation manners, the two o-phenanthroline phosphate ligands in the raw materials are prepared with reference to the synthesis method in Synthesis 2012, 44, 3805-3810. The diethyl phosphite in the synthesis of compound 8 in the original text is replaced with n-butyl phosphite and isobutyl phosphite respectively. The structures of the obtained C4-POPhen and iBu-POPhen are as follows:

[0033]

[0034] Other raw materials are all purchased from the market. Among them, the distribution ratio D is the ratio of the metal ion content in the organic phase to the metal ion content in the equilibrium aqueous phase after the completion of a single extraction equilibrium (the metal ion content in the equilibrium aqueous phase is detected by ICP-OES, and then the metal ion content in the equilibrium organic phase is obtained by subtraction), that is

[0035] D = C org / C aq = (C’ aq - C aq ) / C aq (1)

[0036] In formula (1), C org represents the metal ion concentration in the organic phase after the completion of a single extraction equilibrium; C aq represents the metal ion concentration in the aqueous phase after the completion of a single extraction equilibrium; C’ aq represents the metal ion concentration in the aqueous phase before a single extraction.

[0037] The extraction rate E is the percentage of the amount of the substance to be extracted transferred from the aqueous phase to the organic phase during the extraction process in the total amount of the substance to be extracted in the original aqueous phase, that is:

[0038] E = 100% × (C’ aq - C aq ) / C’ aq (2)

[0039] In formula (2), C aq represents the concentration of metal ions in the equilibrium aqueous phase after one extraction; C’ aq represents the concentration of metal ions in the aqueous phase before one extraction.

[0040] Example 1

[0041] Extract and separate Pd(II) with the o-phenanthroline phosphate ligand C4-POPhen:

[0042] Step 1, Prepare the organic phase and the aqueous phase: The o-phenanthroline phosphate ligand C4-POPhen is dissolved in the 3-trifluoromethyl nitrobenzene solvent to obtain a 3-trifluoromethyl nitrobenzene organic phase with a ligand concentration of 10.0x10 -3 mol / L; KNO3, RbNO3, Sr(NO3)2, Ba(NO3)2, Cu(NO3)2, Fe(NO3)3, Co(NO3)2, Ni(NO3)2, Pd(NO3)2, Zr(NO3)4, Lu(NO3)3 and Y(NO3)3 are dissolved in the nitric acid aqueous solution to prepare the extraction aqueous phase, and the nitric acid concentrations are respectively 0.4, 1.0, 2.0, 3.0, 4.0 mol / L, and the concentration of each metal ion in the nitric acid aqueous solution is about 5.0×10 -4 mol / L.

[0043] Step 2, Extraction experiment process: Take an appropriate amount of the organic phase and pre-perform an acid balance experiment with an equal volume and equal concentration of nitric acid aqueous solution, and then mix the organic phase after nitric acid balance with an equal volume of the aqueous phase containing the above metal ions, and put it into a constant temperature shaking box at 298K for extraction experiment.

[0044] After reaching the extraction equilibrium, perform phase separation, take out the aqueous phase and dilute it, analyze and detect the metal ion concentration, and obtain the distribution ratio D and extraction rate E of each metal ion in the organic phase and the aqueous phase before and after extraction under different acidity conditions.

[0045] Example 2

[0046] Use iBu-POPhen as the extractant and test its extraction effect on Pd(II) according to the same method as in Example 1.

[0047] Example 3

[0048] Step 1, configure the organic phase and the aqueous phase: Dissolve the ligands of o-phenanthroline phosphate C4-POPhen and iBu-POPhen in 3-trifluoromethylnitrobenzene solvent respectively to obtain the 3-trifluoromethylnitrobenzene organic phase with the concentrations of C4-POPhen and iBu-POPhen being 10.0x10 -3 mol / L; Prepare the extraction aqueous phase by dissolving Pd(NO3)2 in 1.0M nitric acid aqueous solution. The concentration of Pd(II) ions in the nitric acid aqueous solution is about 5.0×10 -4 mol / L.

[0049] Step 2, according to the same extraction experiment steps in Example 1, at different time points, test the extraction effects of the two extractants on Pd(II) respectively.

[0050] The variation results of the distribution ratio D of C4-POPhen and iBu-POPhen for extracting metal ions with the nitric acid concentration in the aqueous phase and the extraction time are respectively as Figure 1 、 Figure 2 and Figure 3 shown. The extraction rates and distribution ratios of Pd(II) are shown in Table 1, Table 2 and Table 3.

[0051] Table 1 Experimental results of C4-POPhen extracting Pd(II) at different nitric acid concentrations

[0052] Nitric acid concentration (mol / L) Extraction rate of Pd(II) (%) Partition ratio D of Pd(II) 0.63 92.9 13.0 1.0 94.3 16.5 2.0 97.7 42.2 3.0 98.6 67.9 4.0 98.7 76.4

[0053] Most of the studies on Pd(II) extraction in the prior art stay at low acidity (acidity less than 1.0M). When the acidity increases, the adsorption rate of Pd(II) decreases significantly. It can be seen from Table 1 that the extractants used in this patent application have a very high extraction efficiency for Pd(II) in the acidity range of 0.6 - 4M. The extraction rate of C4-POPhen for Pd(II) is above 92%. When the nitric acid concentration is 3.0 - 4.0M, its extraction effect on Pd(II) is up to more than 98%, which is very suitable for directly adsorbing and recovering palladium and its isotopes from high-level radioactive waste liquid with a nitric acid concentration of 3.0 - 4.0M. At the same time, it is also found that the extraction ability of this type of extractant for other coexisting alkali metals, alkaline earth metals, Group VIII metals iron, cobalt and nickel, transition metal copper and zirconium and other elements is low, indicating that this type of extractant has a high extraction selectivity for palladium, and further shows that this type of extractant has great technical advantages compared with other sulfur-containing extractants.

[0054] Table 2 Experimental results of iBu-POPhen extracting Pd(II) at different nitric acid concentrations

[0055] Nitric acid concentration (mol / L) Extraction rate of Pd(II) (%) Partition ratio D of Pd(II) 0.63 91.1 10.3 1.0 93.8 15.2 2.0 97.8 44.7 3.0 98.8 80.4 4.0 99.1 106.1

[0056] As can be seen from Table 2, within the acidity range of 2.0-4M, the extractant iBu-POPhen has better extraction performance than C4-POPhen, and its extraction efficiency of Pd(II) is higher. When the nitric acid concentration is 4.0M, its single-stage extraction effect for Pd(II) is as high as more than 99%, which is very suitable for direct adsorption and recovery of palladium and its isotopes from high-level radioactive waste liquid with a nitric acid concentration of 3.0-4.0M. It is also found that this type of extractant has a low extraction capacity for other coexisting alkali metals, alkaline earth metals, Group VIII metals iron, cobalt, nickel, transition metal copper, and zirconium, indicating that this type of extractant has a high extraction selectivity for palladium.

[0057] Table 3 Experimental results of extraction of Pd(II) by C4-POPhen and iBu-POPhen at different extraction times

[0058]

[0059] As can be seen from Table 3, within the range of 1.0 M nitric acid concentration, the extractants iBu-POPhen and C4-POPhen both exhibited very excellent extraction kinetic behavior. Under the condition of an extraction time of only 2 min, the extraction rates of Pd(II) both exceeded 93%, showing an extremely fast extraction rate. The reduction in extraction time directly reduced the irradiation dose of the extractant under strong radiation conditions, thereby extending the service life of the extractant. The extractant is very suitable for adsorbing and recovering precious metal palladium and its isotopes directly from high-level radioactive waste liquid with a nitric acid concentration of 3.0-4.0 M under strong irradiation conditions.

[0060] The above results show that this type of o-phenanthroline phosphate extractant has a strong extraction ability for the precious metal Pd(II), an extremely fast extraction rate, and a high selectivity, and is a type of precious metal palladium special-effect extractant with great application prospects.

Claims

1. A method for extracting and separating palladium ions from acidic aqueous phase, characterized in that, It includes the steps of: forming an organic phase by diluting a ligand as shown below, and extracting and separating palladium ions from an acidic aqueous solution containing palladium ions and polymetallic ions; the structure of the ligand is as follows: wherein R is a straight-chain or branched-chain alkyl substituent having C1-C 10 ; The polymetallic ions include ions of one or more metal elements among alkali metals, alkaline earth metals, iron, cobalt, nickel, copper, zirconium, lead, molybdenum, yttrium, and lutetium.

2. The method for extracting and separating palladium ions from an acidic aqueous phase according to claim 1, characterized in that, R is any one of n-butyl, isobutyl, sec-butyl, or tert-butyl.

3. The method for extracting and separating palladium ions from acidic aqueous phase according to claim 1, wherein The ligand is diluted with a diluent, and the diluent includes any one or more of 3-trifluoromethylnitrobenzene, octanol, chloroform, and kerosene.

4. The method for extracting and separating palladium ions from an acidic aqueous phase according to claim 1, characterized in that, The polymetallic ions include one or more of K(I), Rb(I), Sr(II), Ba(II), Cu(II), Fe(III), Co(II), Ni(II), Zr(IV), Pb(II), Mo(VII), Lu(III), and Y(III).

5. The method for extracting and separating palladium ions from acidic aqueous phase according to claim 1, characterized in that, The concentration of palladium ions in the acidic aqueous solution is above 0.1 ppm, and the total concentration of polymetallic ions is not higher than 1000 times the concentration of palladium ions.

6. The method for extracting and separating palladium ions from acidic aqueous phase according to claim 1, characterized in that, The acidic aqueous solution is an aqueous solution of nitric acid, hydrochloric acid, perchloric acid or sulfuric acid, wherein the concentration of H + is 0.1 - 6 mol / L.

7. The method for extracting and separating palladium ions from acidic aqueous phase according to claim 1, characterized in that, The temperature for extracting and separating palladium ions is 15 - 55 °C, and the extraction equilibrium time is above 2 min.

8. The method for extracting and separating palladium ions from an acidic aqueous phase according to claim 1, characterized in that, The extraction rate of palladium ions is above 90%, and the distribution ratio is above 10.

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