Method for recovering platinum group metal palladium, ruthenium and rhodium from radioactive waste liquid

Abstract

The invention relates to a method for recovering platinum group metal palladium, ruthenium and rhodium from radioactive waste liquid. The method comprises the following steps: extracting palladium from the radioactive waste liquid through a palladium extraction agent, washing the obtained organic phase through a detergent, and carrying out reverse extraction on palladium through a palladium reverse extraction agent to obtain a product liquid of palladium; carrying out extraction removal on splitting element impurities in the extraction raffinate of the extracted palladium through a splitting extraction agent; adjusting the acidity of the impurity-removed raffinate of palladium through an acid adjusting agent, and carrying out coordination transformation on ruthenium and rhodium through a coordination transformation agent; and carrying out co-extraction on ruthenium and rhodium in the coordination-transformed palladium raffinate through a co-extractant, washing the obtained organic phase through a detergent, and carrying out reverse extraction on ruthenium and rhodium through ruthenium and rhodium reverse extractants with different concentrations to obtain ruthenium and rhodium product liquids. Compared with the prior art, palladium, ruthenium and rhodium can be respectively recovered from the radioactive waste liquid.

Description

Technical Field

[0001] The present invention belongs to the technical field of spent fuel reprocessing, and relates to a method for recovering platinum group metals palladium, ruthenium, and rhodium from radioactive waste liquid. Background Art

[0002] In nature, due to the very similar chemical and physical properties of platinum group metals, most of them coexist together. Platinum group metals are called precious metals because of their practical performance and scarce resources. The grade of platinum group metal raw ore is generally not high. With the rapid development of various industries, platinum group metals have been in short supply for a long time, and the contradiction between supply and demand is prominent.

[0003] Platinum group metals palladium (Pd), ruthenium (Ru), and rhodium (Rh) in high-level radioactive waste liquid account for about 15% of the total amount. From the perspective of reducing the total amount of radioactive waste, making full use of metal resources, and ensuring the smooth production of the entire spent fuel reprocessing process, platinum group metals should be separated from high-level radioactive waste liquid. In addition, it should be noted that most of the platinum group metals in high-level radioactive waste liquid belong to stable or short-lived nuclides. After several years of cooling period, they can be used in general industry. Research shows that among the various isotopes of ruthenium element, 103 Ru (T 1 / 2 is 39 days) and 106 Ru (T 1 / 2 is 368 days) are radioactive, but due to their short half-lives, the radioactivity basically disappears after several years of cooling; almost all of the isotopes of rhodium exist in the stable 103 Rh, and only 17% of the various isotopes of palladium are 107 Pd (T 1 / 2 is 6.5×10 6 years) is radioactive, but the radioactivity is relatively low. Thus, the weak radioactivity of platinum group metals in high-level radioactive waste liquid has little limitation on their later industrial applications. In addition, since the materials used in the nuclear industry itself have radioactivity or become radioactive after radiation and contamination, the platinum group metals extracted from high-level radioactive waste liquid can also have wide applications in the nuclear industry.

[0004] Currently, most of the recovery of platinum group metals is based on waste catalysts, and there are few studies on separating and recovering platinum group metals from high-level radioactive waste liquid. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for recovering platinum group metals palladium, ruthenium, and rhodium from radioactive waste liquid to overcome at least one defect existing in the above-mentioned prior art. The present invention can recover palladium, ruthenium, and rhodium from radioactive waste liquid respectively.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide a method for recovering platinum group metals palladium, ruthenium, and rhodium from radioactive waste liquid, and the method includes the following steps:

[0008] S1. Extract palladium (Pd) from the radioactive waste liquid with a palladium extractant, wash the obtained organic phase with a detergent to remove the impurity ions entrained in the organic phase, and back-extract palladium with a palladium stripping agent to obtain a product solution of palladium;

[0009] S2. Selectively extract and remove high-content fission product element impurities from the raffinate of palladium after extraction with a fission product extractant;

[0010] S3. In order to better adapt to the extraction acidity of subsequent ruthenium (Ru) and rhodium (Rh), adjust the acidity of the raffinate of palladium after removing impurities with an acid regulator, and carry out coordination transformation on ruthenium and rhodium with a coordination transformation agent to generate a complex more easily extractable;

[0011] S4. Co-extract ruthenium and rhodium from the raffinate of palladium after coordination transformation with a co-extractant, wash the obtained organic phase with a detergent to remove the impurity ions entrained in the organic phase, and back-extract ruthenium and rhodium with different concentrations of ruthenium-rhodium stripping agents according to the difference in the interaction force between the ruthenium-rhodium complex and the co-extractant to obtain product solutions of ruthenium and rhodium.

[0012] Further, in step S1, the palladium extractant is selected from one or more of phosphorus-containing extractants and sulfur-containing extractants. The phosphorus-containing extractant is selected from one or more of tri-n-octylphosphine oxide and trialkylphosphine oxide. The sulfur-containing extractant is selected from one or more of dihexyl sulfide, dibutyl sulfide, dioctyl sulfide, dodecyl sulfide, dibutyl sulfoxide, and dioctyl sulfoxide. The concentration of the palladium extractant is 0.04 - 0.15 mol / L.

[0013] As a preferred technical solution, the concentration of the palladium extractant in step S1 is 0.05 - 0.1 mol / L.

[0014] As a preferred technical solution, in step S1, the palladium extractant is dissolved in a diluent, and the diluent is selected from one or more of dodecane, toluene, xylene, trimethylbenzene, kerosene, dichloromethane, dichloroethane, n-octanol, and acetonitrile. The volume ratio of the palladium extractant and the diluent to the radioactive waste liquid is 1:(0.5 - 2).

[0015] Further, in step S1, the detergent is selected from one or more of nitric acid (HNO3), hydrochloric acid (HCl), and sulfuric acid (H2SO4). The concentration of the detergent is 0.1 - 1 mol / L.

[0016] As a preferred technical solution, in step S1, the detergent is dissolved in water, and the volume ratio of the organic phase after extraction to the detergent is (0.5 - 2):1.

[0017] Further, in step S1, thiourea is used as the palladium stripping agent, and the concentration of the palladium stripping agent is 0.1 - 0.5 mol / L.

[0018] As a preferred technical solution, in step S1, the palladium stripping agent is dissolved in water, and the volume ratio of the washed organic phase to the palladium stripping agent and water is (0.5 - 2):1.

[0019] As a preferred technical solution, in step S2, the high-content fission products are selected from one or more of cesium (Cs), strontium (Sr), barium (Ba), zirconium (Zr), molybdenum (Mo), rhenium (Re), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), and yttrium (Y).

[0020] Further, in step S2, the fission product extractant is selected from one or more of N,N,N',N'-tetraoctyl-3-oxapentanediamide (TODGA), N,N,N',N'-tetrahexyl-3-oxapentanediamide, N,N,N',N'-tetrapentyl-3-oxapentanediamide, and N,N,N',N'-tetraisooctyl-3-oxapentanediamide, and the concentration of the fission product extractant is 0.5 - 1.5 mol / L.

[0021] As a preferred technical solution, in step S2, the fission product extractant is dissolved in a diluent, the diluent is selected from one or more of dodecane, toluene, xylene, mesitylene, kerosene, dichloromethane, dichloroethane, n-octanol, and acetonitrile, and the volume ratio of the fission product extractant and the diluent to the raffinate of palladium after extraction is 1:(0.5 - 2).

[0022] Further, in step S3, the acid regulator is selected from one or more of sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonia water (NH3·H2O), and the acidity is adjusted to 0.1 - 0.5 mol / L.

[0023] Further, in step S3, the coordination transformation agent is selected from one or more nitrites such as sodium nitrite (NaNO2), potassium nitrite (KNO2), and ammonium nitrite (NH4NO2), and the concentration of the coordination transformation agent is 0.5 - 200 g / L.

[0024] As a preferred technical solution, in step S3, the concentration of the coordination transformation agent is 20 - 120 g / L.

[0025] As a preferred technical solution, in step S3, the coordination transformation agent is dissolved in water, and the volume ratio of the raffinate of palladium after acidity adjustment to the coordination transformation agent and water is (0.5 - 2):1.

[0026] As a preferred technical solution, the complex generated after coordination transformation in step S3 is selected from one or more of [RuNO(NO2)2(OH)(H2O)2], [RuNO(NO2)3(H2O)2], and [Rh(NO2)6]. 3- and the like.

[0027] Furthermore, the co - extractant in step S4 is selected from one of the amine extractants such as 4 - n - butylaniline, 4 - n - octylaniline, 4 - dodecylaniline, trioctylamine, triisooctylamine, methyltrioctylammonium chloride, methyltrioctylammonium nitrate, and methyltrioctylammonium iodide. The concentration of the co - extractant is 0.4 - 1.5 mol / L.

[0028] As a preferred technical solution, the concentration of the co - extractant in step S4 is 0.8 - 1.2 mol / L.

[0029] As a preferred technical solution, the co - extractant in step S4 is dissolved in a diluent. The diluent is selected from one or more of dodecane, toluene, xylene, mesitylene, kerosene, dichloromethane, dichloroethane, n - octanol, and acetonitrile. The volume ratio of the co - extractant and the diluent to the raffinate of palladium after coordination transformation is 1:(0.5 - 2).

[0030] Furthermore, the detergent in step S4 is selected from one or more of nitric acid, hydrochloric acid, and sulfuric acid. The concentration of the detergent is 0.1 - 1 mol / L.

[0031] As a preferred technical solution, the detergent in step S4 is dissolved in water. The volume ratio of the organic phase after co - extraction to the detergent is (0.5 - 2):1.

[0032] Furthermore, the ruthenium - rhodium stripping agent in step S4 is selected from one or more of nitric acid, hydrochloric acid, and sulfuric acid. When ruthenium is stripped, the concentration of the ruthenium - rhodium stripping agent is 6 - 10 mol / L, and when rhodium is stripped, the concentration of the ruthenium - rhodium stripping agent is 1 - 3 mol / L.

[0033] As a preferred technical solution, the ruthenium - rhodium stripping agent in step S4 is dissolved in water. The volume ratio of the washed organic phase to the ruthenium - rhodium stripping agent and water is (0.5 - 2):1.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention proposes a process route for the full - process recovery of platinum - group metals palladium, ruthenium, and rhodium from radioactive waste liquid, which can achieve the effect of separating and recovering palladium, ruthenium, and rhodium. Utilizing the "hard - soft acid - base theory", based on the fact that platinum - group metals are soft acids, appropriate soft - base extractants are screened, an efficient extraction model is established, and the extraction of each platinum - group metal in radioactive waste liquid is realized step by step.

[0036] (2) The separation method of the present invention is simple, fast, convenient, feasible and low-cost, meeting the requirements for the recovery of palladium, ruthenium and rhodium from radioactive waste liquid, and having broad industrial application prospects in the field of platinum group metal recovery from high-level radioactive waste liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic flow chart of the method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention will be described in detail below with reference to specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0039] Unless otherwise specified, the equipment used in the following embodiments is all conventional equipment in the art; unless otherwise specified, the reagents used are all commercially available products or prepared by conventional methods in the art. Those not described in detail in the following embodiments can be achieved by conventional experimental means in the art.

[0040] The simulated radioactive waste liquid feed solution contains 17 common fission products yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), cesium (Cs), strontium (Sr), barium (Ba), zirconium (Zr), molybdenum (Mo), rhenium (Re), ruthenium (Ru), rhodium (Rh), palladium (Pd), and the solvent is 3 mol / L nitric acid (HNO3).

[0041] Example 1:

[0042] A method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid, as Figure 1 shown, the specific steps are as follows:

[0043] S1. Extraction of palladium: Add a dodecane solution of 0.05 mol / L tri-n-octylphosphine oxide to the simulated radioactive waste liquid feed solution according to the volume ratio of the organic phase to the aqueous phase (simulated radioactive waste liquid feed solution) of 1:1, extract palladium, let it stand for phase separation, add an aqueous solution of 0.1 mol / L nitric acid to the obtained organic phase according to the volume ratio of the organic phase to the aqueous phase of 1:1 to wash once to remove the impurity ions entrained in the organic phase, let it stand for phase separation, add an aqueous solution of 0.1 mol / L thiourea according to the volume ratio of the organic phase to the aqueous phase of 1:1 to back-extract palladium, let it stand for phase separation, and obtain the product solution of palladium. The primary back-extraction rate of palladium is 85%, and most of the palladium can be separated.

[0044] S2. Removal of high-content fission products. Add a dodecane solution of 0.5 mol / L N,N,N',N'-tetraoctyl-3-oxapentanediamide (TODGA) to the raffinate of palladium after extraction in a volume ratio of the extractant phase to the feed liquid phase of 1:1 to selectively extract and remove common fission product element impurities, and then let it stand for liquid separation.

[0045] S3. Acidity adjustment and coordination transformation of ruthenium and rhodium. To better adapt to the extraction acidity of ruthenium and rhodium in the subsequent steps, add solid sodium hydroxide (NaOH) to the raffinate of palladium after removing impurities to adjust the acidity to 0.5 mol / L, and then add an aqueous solution of 20 g / L sodium nitrite (NaNO2) in a volume ratio of the feed liquid phase to the coordination transformation agent phase of 1:1, and let it stand overnight to allow ruthenium and rhodium to fully undergo a coordination reaction with nitrite ions to transform into more easily extractable complexes [RuNO(NO2)2(OH)(H2O)2], [RuNO(NO2)3(H2O)2], [Rh(NO2)6]. 3- ;

[0046] S4. Co-extraction and stripping of ruthenium and rhodium. Add a dodecane solution of 0.8 mol / L methyltrioctylammonium chloride to the raffinate of palladium after coordination transformation in a volume ratio of the co-extraction agent phase to the feed liquid phase of 1:1 to co-extract ruthenium and rhodium, and then let it stand for liquid separation. Add an aqueous solution of 0.1 mol / L nitric acid to the obtained organic phase in a volume ratio of the organic phase to the aqueous phase of 1:1 to wash once to remove impurity ions entrained in the organic phase, and then let it stand for liquid separation. According to the difference in the interaction force between the complex and the co-extraction agent, add an aqueous solution of 3 mol / L nitric acid to the organic phase in a volume ratio of the organic phase to the aqueous phase of 1:1 to strip rhodium, and then let it stand for liquid separation to obtain a product solution of rhodium. Add an aqueous solution of 7 mol / L nitric acid to the organic phase in a volume ratio of the organic phase to the aqueous phase of 1:1 to strip ruthenium, and then let it stand for liquid separation to obtain a product solution of ruthenium.

[0047] The compositions of the product solutions of rhodium and ruthenium in Example 1 are shown in Table 1.

[0048] Table 1 Compositions of the product solutions of rhodium and ruthenium in Example 1

[0049] Ru-Rh stripping agent Ru stripping rate (%) Rh stripping rate (%) 3 mol / L nitric acid 5 70 7 mol / L nitric acid 80 10

[0050] As shown in Table 1, most of the ruthenium and rhodium can be separated by nitric acid with different concentrations.

[0051] Example 2:

[0052] A method for recovering platinum group metals palladium, ruthenium, and rhodium from radioactive waste liquid is as Figure 1 shown, and the specific steps are as follows:

[0053] S1. Palladium extraction: Add a 0.1 mol / L solution of dihexyl sulfide in dodecane to the simulated radioactive waste liquid feed solution at a volume ratio of organic phase to aqueous phase (simulated radioactive waste liquid feed solution) of 1:1 for palladium extraction. Let it stand for phase separation. Then add an aqueous solution of 0.1 mol / L nitric acid to the obtained organic phase at a volume ratio of organic phase to aqueous phase of 1:1 for one - time washing to remove the impurity ions entrained in the organic phase. Let it stand for phase separation. Add an aqueous solution of 0.5 mol / L thiourea to the organic phase at a volume ratio of organic phase to aqueous phase of 1:1 for back - extraction of palladium. Let it stand for phase separation to obtain the product solution of palladium. The primary back - extraction rate of palladium is 88%, and most of the palladium can be separated.

[0054] S2. Removal of high - content fission products: Add a 1 mol / L solution of N,N,N',N'-tetraisooctyl - 3 - oxapentanediamide in dodecane to the raffinate of palladium after extraction at a volume ratio of extractant phase to feed liquid phase of 1:1 for selective extraction and removal of common fission product element impurities. Let it stand for phase separation.

[0055] S3. Acidity adjustment and coordination transformation of ruthenium and rhodium: To better adapt to the extraction acidity of ruthenium and rhodium in the subsequent steps, add solid sodium hydroxide to the raffinate of palladium after removing impurities to adjust the acidity to 0.1 mol / L. Then add an aqueous solution of 40 g / L sodium nitrite to the feed liquid phase at a volume ratio of feed liquid phase to coordination transformation agent phase of 1:1 and let it stand overnight to allow ruthenium and rhodium to fully carry out coordination reactions with nitrite ions, transforming into complexes [RuNO(NO2)2(OH)(H2O)2], [RuNO(NO2)3(H2O)2], [Rh(NO2)6] that are more easily extractable. 3- ;

[0056] S4. Co - extraction and back - extraction of ruthenium and rhodium: Add a 1 mol / L solution of methyltrioctylammonium chloride in dodecane to the raffinate of palladium after coordination transformation at a volume ratio of co - extractant phase to feed liquid phase of 1:1 for co - extraction of ruthenium and rhodium. Let it stand for phase separation. Then add an aqueous solution of 0.1 mol / L nitric acid to the obtained organic phase at a volume ratio of organic phase to aqueous phase of 1:1 for one - time washing to remove the impurity ions entrained in the organic phase. Let it stand for phase separation. According to the difference in the interaction force between the complex and the co - extractant, add an aqueous solution of 2 mol / L nitric acid to the organic phase at a volume ratio of organic phase to aqueous phase of 1:1 for back - extraction of rhodium. Let it stand for phase separation to obtain the product solution of rhodium. Add an aqueous solution of 8 mol / L nitric acid to the organic phase at a volume ratio of organic phase to aqueous phase of 1:1 for back - extraction of ruthenium. Let it stand for phase separation to obtain the product solution of ruthenium.

[0057] The compositions of the product solutions of rhodium and ruthenium in Example 2 are shown in Table 2.

[0058] Table 2 Compositions of the product solutions of rhodium and ruthenium in Example 2

[0059] Ru-Rh stripping agent Ru stripping rate (%) Rh stripping rate (%) 3 mol / L nitric acid 5 70 8 mol / L nitric acid 85 15

[0060] As shown in Table 2, the separation of most ruthenium and rhodium can be achieved through nitric acid with different concentrations.

[0061] Example 3:

[0062] A method for recovering platinum group metals palladium, ruthenium, and rhodium from radioactive waste liquid, as Figure 1 shown, the specific steps are as follows:

[0063] S1. Extraction of palladium: Add a 0.1 mol / L solution of dibutyl sulfoxide in dodecane to the simulated radioactive waste liquid feedstock in a volume ratio of organic phase to aqueous phase (simulated radioactive waste liquid feedstock) of 1:1 for palladium extraction. Let it stand for phase separation. Add an aqueous solution of 0.1 mol / L nitric acid to the obtained organic phase in a volume ratio of organic phase to aqueous phase of 1:1 for one-time washing to remove impurity ions entrained in the organic phase. Let it stand for phase separation. Add an aqueous solution of 0.3 mol / L thiourea to the organic phase in a volume ratio of organic phase to aqueous phase of 1:1 for back-extraction of palladium. Let it stand for phase separation to obtain the product liquid of palladium. The primary back-extraction rate of palladium is 86%, and the separation of most palladium can be achieved.

[0064] S2. Removal of high-content fission products: Add a 1.5 mol / L solution of N,N,N',N'-tetrapentyl-3-oxapentanediamide in dodecane to the raffinate of palladium after extraction in a volume ratio of extractant phase to feedstock phase of 1:1 for selective extraction and removal of common fission product impurities. Let it stand for phase separation.

[0065] S3. Acidity adjustment and coordination transformation of ruthenium and rhodium: To better adapt to the extraction acidity of subsequent ruthenium and rhodium, add solid sodium hydroxide to the raffinate of palladium after removing impurities to adjust the acidity to 0.5 mol / L. Add an aqueous solution of 80 g / L sodium nitrite to the feedstock phase in a volume ratio of feedstock phase to coordination transformation agent phase of 1:1 and let it stand overnight to allow ruthenium and rhodium to fully undergo coordination reaction with nitrite ions, transforming into complexes [RuNO(NO2)2(OH)(H2O)2], [RuNO(NO2)3(H2O)2], [Rh(NO2)6] that are more easily extractable. 3- ;

[0066] S4. Co-extraction and stripping of ruthenium and rhodium: Add a 1 mol / L solution of trioctylamine in dodecane to the raffinate of palladium after coordination transformation in a volume ratio of the co-extraction agent phase to the feed liquid phase of 1:1 for the co-extraction of ruthenium and rhodium. Let it stand for phase separation. Add an aqueous solution of 0.1 mol / L nitric acid to the obtained organic phase in a volume ratio of the organic phase to the aqueous phase of 1:1 for washing once to remove the impurity ions entrained in the organic phase. Let it stand for phase separation. According to the difference in the interaction force between the complex and the co-extraction agent, add an aqueous solution of 3 mol / L nitric acid to the organic phase in a volume ratio of the organic phase to the aqueous phase of 1:1 for the stripping of rhodium. Let it stand for phase separation to obtain the product liquid of rhodium. Add an aqueous solution of 10 mol / L nitric acid to the organic phase in a volume ratio of the organic phase to the aqueous phase of 1:1 for the stripping of ruthenium. Let it stand for phase separation to obtain the product liquid of ruthenium.

[0067] The compositions of the product liquids of rhodium and ruthenium in Example 3 are shown in Table 3.

[0068] Table 3 Compositions of the product liquids of rhodium and ruthenium in Example 3

[0069] Ru-Rh stripping agent Ru stripping rate (%) Rh stripping rate (%) 3 mol / L nitric acid 5 70 10 mol / L nitric acid 85 20

[0070] As shown in Table 3, most of the ruthenium and rhodium can be separated by nitric acid with different concentrations.

[0071] Example 4:

[0072] A method for recovering platinum group metals palladium, ruthenium, and rhodium from radioactive waste liquid, as Figure 1 shown, the specific steps are as follows:

[0073] S1. Extraction of palladium: Add a 0.1 mol / L solution of dioctyl sulfoxide in dodecane to the simulated radioactive waste liquid feedstock in a volume ratio of the organic phase to the aqueous phase (simulated radioactive waste liquid feedstock) of 1:1 for the extraction of palladium. Let it stand for phase separation. Add an aqueous solution of 0.1 mol / L nitric acid to the obtained organic phase in a volume ratio of the organic phase to the aqueous phase of 1:1 for washing once to remove the impurity ions entrained in the organic phase. Let it stand for phase separation. Add an aqueous solution of 0.1 mol / L thiourea to the organic phase in a volume ratio of the organic phase to the aqueous phase of 1:1 for the stripping of palladium. Let it stand for phase separation to obtain the product liquid of palladium. The primary stripping rate of palladium is 85%, and most of the palladium can be separated.

[0074] S2. Removal of high-content fission fragments: Add a 1.5 mol / L solution of N,N,N',N'-tetrahexyl-3-oxapentanediamide in dodecane to the raffinate of palladium after extraction in a volume ratio of the extractant phase to the feed liquid phase of 1:1 for the selective extraction and removal of common fission fragment element impurities. Let it stand for phase separation;

[0075] S3. Acid adjustment and coordination transformation of ruthenium and rhodium. To better adapt to the extraction acidity of subsequent ruthenium and rhodium, solid sodium hydroxide is added to the raffinate of palladium after removing impurities, and the acidity is adjusted to 0.3 mol / L. An aqueous solution of sodium nitrite at 120 g / L is added according to the volume ratio of the feed liquid phase to the coordination transformation agent phase of 1:1, and it is left overnight to allow ruthenium and rhodium to fully undergo a coordination reaction with nitrite ions, transforming into complexes [RuNO(NO2)2(OH)(H2O)2], [RuNO(NO2)3(H2O)2], and [Rh(NO2)6] that are more easily extractable. 3- ;

[0076] S4. Co-extraction and stripping of ruthenium and rhodium. To the raffinate of palladium after coordination transformation, a dodecane solution of triisooctylamine at 1.2 mol / L is added according to the volume ratio of the co-extraction agent phase to the feed liquid phase of 1:1 for the co-extraction of ruthenium and rhodium. After standing and separating layers, an aqueous solution of nitric acid at 0.1 mol / L is added to the obtained organic phase according to the volume ratio of the organic phase to the aqueous phase of 1:1 for washing once to remove impurity ions entrained in the organic phase. After standing and separating layers, according to the difference in the interaction force between the complex and the co-extraction agent, an aqueous solution of nitric acid at 1 mol / L is added to the organic phase according to the volume ratio of the organic phase to the aqueous phase of 1:1 for stripping rhodium. After standing and separating layers, a product liquid of rhodium is obtained. An aqueous solution of nitric acid at 9 mol / L is added to the organic phase according to the volume ratio of the organic phase to the aqueous phase of 1:1 for stripping ruthenium. After standing and separating layers, a product liquid of ruthenium is obtained.

[0077] The compositions of the product liquids of rhodium and ruthenium in Example 4 are shown in Table 4.

[0078] Table 4 Compositions of the product liquids of rhodium and ruthenium in Example 4

[0079] Ru-Rh stripping agent Ru stripping rate (%) Rh stripping rate (%) 1 mol / L nitric acid 2 60 9 mol / L nitric acid 80 15

[0080] As shown in Table 4, most of the ruthenium and rhodium can be separated through nitric acid of different concentrations.

[0081] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those familiar with the technology in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid, characterized in that: The method comprises the following steps: S1. Extracting palladium from the radioactive waste liquid by a palladium extractant, washing the obtained organic phase by a detergent, and stripping the palladium by a palladium stripping agent to obtain a palladium product solution; S2, extracting and removing the fragment element impurities from the palladium raffinate after extraction through a fragment extractant; S3, adjusting the acidity of the palladium raffinate after removing impurities by an acid adjusting agent, and performing coordination transformation on ruthenium and rhodium by a coordination transformation agent; S4. The raffinate of palladium after coordination transformation is used to co-extract ruthenium and rhodium through a co-extractant, the obtained organic phase is washed with a detergent, and ruthenium and rhodium are stripped by ruthenium-rhodium stripping agents of different concentrations to obtain a product solution of ruthenium and rhodium.

2. The method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid according to claim 1, characterized in that: In step S1, the palladium extractant is selected from one or more of a phosphorus-containing extractant and a sulfur-containing extractant, the phosphorus-containing extractant is selected from one or more of tri-n-octylphosphine oxide and trialkylphosphine oxide, the sulfur-containing extractant is selected from one or more of dihexyl sulfide, dibutyl sulfide, dioctyl sulfide, dodecyl sulfide, dibutyl sulfoxide, and dioctyl sulfoxide, and the concentration of the palladium extractant is 0.04-0.15 mol / L.

3. The method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid according to claim 1, characterized in that: In step S1, the detergent is selected from one or more of nitric acid, hydrochloric acid and sulfuric acid, and the concentration of the detergent is 0.1-1 mol / L.

4. The method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid according to claim 1, characterized in that: In step S1, thiourea is used as the palladium stripping agent, and the concentration of the palladium stripping agent is 0.1-0.5 mol / L.

5. The method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid according to claim 1, characterized in that: In step S2, the fragment extractant is selected from one or more of N,N,N',N'-tetraoctyl-3-oxoglutaramide, N,N,N',N'-tetrahexyl-3-oxoglutaramide, N,N,N',N'-tetrapentyl-3-oxoglutaramide, and N,N,N',N'-tetraisooctyl-3-oxoglutaramide, and the concentration of the fragment extractant is 0.5 to 1.5 mol / L.

6. The method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid according to claim 1, characterized in that: In step S3, the acid adjusting agent is selected from one or more of sodium hydroxide, potassium hydroxide and ammonia water, and the acidity is adjusted to 0.1-0.5 mol / L.

7. The method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid according to claim 1, characterized in that: In step S3, the coordination transformation agent is selected from one or more nitrites selected from sodium nitrite, potassium nitrite, and nitrosamines, and the concentration of the coordination transformation agent is 0.5-200 g / L.

8. The method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid according to claim 1, characterized in that: In step S4, the co-extractant is selected from an amine extractant selected from 4-n-butylaniline, 4-n-octylaniline, 4-dodecylaniline, trioctylamine, triisooctylamine, methyltrioctylammonium chloride, methyltrioctylammonium nitrate, and methyltrioctylammonium iodide, and the concentration of the co-extractant is 0.4-1.5 mol / L.

9. The method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid according to claim 1, characterized in that: In step S4, the detergent is selected from one or more of nitric acid, hydrochloric acid and sulfuric acid, and the concentration of the detergent is 0.1-1 mol / L.

10. The method for recovering platinum group metals palladium, ruthenium and rhodium from radioactive waste liquid according to claim 1, characterized in that: In step S4, the ruthenium-rhodium stripping agent is selected from one or more of nitric acid, hydrochloric acid and sulfuric acid. The concentration of the ruthenium-rhodium stripping agent is 6-10 mol / L during ruthenium stripping, and the concentration of the ruthenium-rhodium stripping agent is 1-3 mol / L during rhodium stripping.

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