Method for precipitation separation and ceramic solidification of radioactive waste liquid divalent strontium and tetravalent uranium

Abstract

This invention discloses a method for precipitation separation and ceramic solidification of divalent strontium and tetravalent uranium in radioactive waste liquid, relating to the field of radioactive waste liquid treatment and disposal. U in high-level radioactive waste liquid is in the form of hexavalent uranyl (UO2). 2+ U exists in the form of hydrogenation catalytic reduction, and the present invention uses hydrogenation catalytic reduction to prepare U. 4+ Sr 2+ and U 4+ ionic radius and Ln 3+ Due to the significant differences, CePO4·0.667H2O cerium phosphate, which has a stronger nuclide-containing capacity, was selected as the co-precipitation enrichment agent for Sr. 2+ and U 4+ Separation precipitant. Inexpensive raw materials such as UO2(NO3)2·6H2O, Sr(C2H3O2)2, NH4H2PO4, and Ce(NO3)3·6H2O are selected. By controlling the Sr... 2+ :U 4+ Ion ratio, reaction time, temperature, pH, and preparation of well-developed Sr crystals 2+ / U 4+ The precipitate of cerium phosphate solid solution with high solid content is avoided by using spark plasma solid-state sintering technology to prevent grain agglomeration and adhesion during high-temperature dehydration and crystal transformation of cerium phosphate. Furthermore, pressure sintering can promote further growth of nanocrystals and promote U... 4+ and Sr 2+ Homogenization within the monazite ceramic solidified body enables a one-step preparation of monazite ceramic solidified body from a lanthanite solid solution.

Description

Technical Field

[0001] This invention belongs to the technical field of radioactive waste treatment and disposal, specifically relating to Sr 2+ and U 4+ Precipitation enrichment and separation of nuclides and their solidification treatment technology with monazite ceramics. Background Technology

[0002] High-level liquid waste (HLLW) mainly originates from the waste liquid generated during the PUREX (Plutonium Uranium Redox Extraction) process of spent fuel reprocessing. It contains more than 200 isotopes of more than 30 elements, including actinides and fissile nuclides, and contains more than 95% of the radioactivity in spent fuel.

[0003] The current challenges in high-level radioactive waste management research worldwide are as follows:

[0004] 1. Typical pressurized water reactor spent fuel contains approximately 95.5% [unclear - possibly referring to a specific component or component]. 238 U, 0.9% 239 Pu, 3.5% fission products, and 0.1% minor actinides. Among them, actinides (Np, Am, Cm, U, Pu, etc.) and Cs and Sr fission products are characterized by high toxicity, high radioactivity, and long half-life. Their processing and disposal technologies are complex, difficult, and expensive.

[0005] 2. The treatment of radioactive wastewater mainly includes evaporation and concentration, membrane separation, adsorption, chemical precipitation, and ion exchange.

[0006] (1) Evaporation concentration and membrane separation methods have advantages such as good decontamination and concentration effects and simple equipment. However, these treatment methods are highly dependent on water quality and equipment, have poor mobility, and are difficult to apply to nuclear accident leakage sites.

[0007] (2) The adsorption method has advantages such as simple operation and mature technology, but its adsorption capacity for nuclides is low and its binding force with nuclides is weak. Nuclides are prone to desorption and migration in the wastewater environment, which is not conducive to the safe and efficient removal of nuclides.

[0008] (3) For emergency treatment of radioactive wastewater, domestic and foreign research mainly focuses on ion exchange separation of materials such as aluminum silicon compounds, transition metal cyanides, and phosphomolybdates, as well as chemical precipitation enrichment of materials such as aluminum salts, iron salts, and carbonates. These materials have shown advantages in the enrichment and separation of nuclides, but because their chemical and irradiation stability is difficult to meet the requirements of high-level or long-lived nuclear waste for solidification substrates, they cannot be directly solidified. The enriched nuclides are prone to secondary pollution in subsequent treatment, which is not conducive to the safe treatment and disposal of nuclear waste.

[0009] Phosphates are readily and rapidly prepared in acidic and alkaline solutions. They exhibit excellent complexing ability with actinides, rare earth elements, and some heavy metal ions, and the complexed products possess superior chemical and radiation stability. Natural and synthetic phosphate crystals can solid-dissolve multivalent actinide nuclides, with divalent, trivalent, and tetravalent nuclides readily found in rabdophane (LnPO4·0.667H2O, Ln=La~Gd; a general term for hydrated phosphates of light lanthanides). Foreign researchers, in analyzing nuclear-contaminated soil, discovered that in addition to existing as oxides, Pu also forms Pu-rich rabdophane mineral phases, demonstrating its promising application prospects in the separation and enrichment of radioactive waste. Furthermore, lanthanum hydrophobicite is a precursor for the hydrothermal preparation of monazite (LnPO4). When the temperature exceeds 800℃, lanthanum hydrophobicite transforms into monoclinic monazite. Monazite has been proven to be the most promising ceramic curing substrate after vitrification. Therefore, using lanthanum hydrophobicite to precipitate and enrich actinide nuclides in HLLW is more conducive to the curing of actinide nuclides in monazite ceramics, effectively reducing the volume of HLLW. This simplifies and facilitates the process of ceramic curing actinide nuclides in HLLW, achieving complete lattice curing of actinide nuclides in monazite ceramic curing bodies and improving the long-term safety of actinide nuclides in deep geological treatment.

[0010] Domestic and international research mainly focuses on the precipitation enrichment of trivalent actinide nuclides in lanthanite, with no reports on its precipitation enrichment of divalent fissile nuclides. Considering the large amount of Sr contained in HLLW... 2+ (Long-lived fission element), therefore this invention uses Sr 2+ As a charge compensator, U in waste liquid is enriched by precipitating cerium phosphate (CePO4·0.667H2O), which has a stronger nuclide inclusion capacity, through the selection of solid solution substrate, formulation design, and control of precipitation reaction conditions. 4+ and Sr 2+ The solid solution precipitate was prepared by a one-step method of spark plasma sintering to obtain U. 4+ and Sr 2+ Co-doped monazite ceramic solidified bodies. Compared to traditional Ce-based ceramics prepared from oxide raw materials. 1-2x U x Sr x Compared to PO4 monazite ceramic solidification, this method solves the problem of difficult separation of highly radioactive nuclides, and uses inexpensive and clean raw materials, with a simple sintering process, avoiding secondary contamination of high-level radionuclides during separation and solidification; in addition, U is enriched by phyllite precipitation. 4+ and Sr 2+ The resulting nanocrystals have uneven composition; pressure sintering can effectively promote grain growth, making U... 4+ and Sr2+ Homogenization was performed within the monazite ceramic solidified body. The cerium phosphate solid solution designed using this method can simultaneously process tetravalent actinides and Sr. 2+ Fission elements are beneficial for achieving efficient volume reduction of high-level radioactive waste liquids, which is of great significance for the safe treatment and disposal of HLLW. Summary of the Invention

[0011] The safe handling and disposal of U and Sr nuclides, which are highly toxic and have long half-lives, in high-level radioactive waste has always been a challenge for the sustainable and clean development of the nuclear industry. This invention proposes an integrated precipitation-enrichment-solidification strategy to treat U in high-level radioactive waste. 4+ and Sr 2+ The purpose of this invention is to provide a novel method for treating radioactive nuclides, addressing the challenge of safely and cleanly handling long-lived nuclides in high-level radioactive waste. This invention facilitates efficient volume reduction of high-level radioactive waste, achieving complete lattice solidification of tetravalent and divalent actinides within monazite ceramic solidification bodies, thus improving the long-term safety of actinides in deep geological disposal. This method solves the problem of difficult separation of highly radioactive nuclides, and the selected sintering process is simple, avoiding secondary contamination of high-level radionuclides during separation and ceramic solidification, demonstrating excellent application prospects.

[0012] To achieve the technical effect of solving the above-mentioned technical problems, the present invention is implemented through the following technical solution:

[0013] The precipitation separation and ceramic solidification method for divalent strontium and tetravalent uranium in radioactive waste liquid comprises the following steps:

[0014] Step 1: Enriching hexavalent uranyl UO2 2+ Preparation of U by hydrogenation catalytic reduction in high-level radioactive waste liquid 4+ ;

[0015] Step 2: Add Ce(NO3)3·6H2O and Sr(C2H3O2)2 raw materials to U 4+ After magnetic stirring in the solution, the prepared NH4H2PO4 solution was slowly added dropwise, and the mixture was then transferred to an oven to stand and form Sr. 2+ and U 4+ Doped cerium phosphate solid solution;

[0016] Step 3: Centrifuge and dry the cerium phosphate solid solution into powder form;

[0017] Step 4: Prepare monazite ceramic solidified body by vacuum discharge plasma sintering of water-phosphorus cerium stone solid solution powder;

[0018] Furthermore, the hexavalent uranyl UO2 2+ Restore to U 4+The process is based on the reaction UO2(NO3)2 + H2 + 2HNO3 → U(NO3)4 + 2H2O;

[0019] Furthermore, the hexavalent uranyl UO2 2+ During the reduction process, a Pt-supported substrate was used as a catalyst, and UO2(NO3)2·6H2O and HNO3 were used as raw materials. The hydrogen pressure was controlled at 3–4 MPa, the temperature at approximately 25 °C, and the nitric acid concentration at 0.2–0.5 mol / L. After the reaction was completed, 0.3 mol / L hydrazine was added to the solution to prevent UO2 from being released into the atmosphere. 4+ Oxidation;

[0020] Furthermore, in step two, based on Sr 2+ :U 4+ =2:1, Ce 3+ :Sr 2+ ≥3:2, under an argon protective atmosphere at a temperature of approximately 25°C, Ce(NO3)3·6H2O and Sr(C2H3O2)2 raw materials are added to a tetravalent uranium solution and magnetically stirred for 3–5 minutes;

[0021] Further, in step two, after magnetic stirring for 3-5 minutes, a small amount of deionized water is taken to dissolve NH4H2PO4, based on PO4 3- :[Ce 3+ +Sr 2+ The prepared NH4H2PO4 solution was slowly added dropwise to the tetravalent uranium solution at a ratio of 1.03:1, and the mixture was magnetically stirred for 20 minutes. The mixture was then allowed to stand for 6 to 12 hours.

[0022] Furthermore, the mixed solution after settling in step two is transferred to a hydrothermal reactor and settling in an oven at 90°C for 14 to 28 days to produce Sr with well-developed grains. 2+ and U 4+ Doped cerium phosphate solid solution;

[0023] Furthermore, in step three, the supernatant is removed by filtration before centrifugation, and the remaining turbid solution is placed in a centrifuge tube. Then, a Hermle centrifuge is used to further separate the solid and liquid at a speed of 13,500 rpm. The prepared cerium phosphate solid solution is then dried in a constant temperature oven at 60°C for 24 hours.

[0024] Further, in step four, the dried cerium phosphate solid solution powder is placed in a graphite mold, and the graphite mold is fixed in a spark plasma sintering furnace. The temperature is then increased to 800°C at a heating rate of 100°C / min and held for 30 minutes. The temperature is then increased to 1100–1200°C at a heating rate of 50°C / min and sintered at 30–50 MPa for 15–30 minutes. During the cooling process, the temperature is reduced to 600°C at a rate of 25°C / min, and then allowed to cool naturally from 600°C to room temperature, ultimately yielding Sr. 2+ and U 4+ Uniformly distributed monazite ceramic solidified body.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention uses CePO4·0.667H2O hydrated cerium phosphate as Sr 2+ and U 4+ Precipitation enrichment and separation materials are used to separate Sr from high-level radioactive waste liquid through chemical precipitation. 2+ and U 4+ Monazite ceramic solidified bodies are prepared in a one-step process by separating and enriching cerium phosphate crystals within the lattice, followed by spark plasma sintering. This invention is beneficial for Sr... 2+ and U 4+ Highly efficient enrichment and separation enables efficient volume reduction of high-level radioactive waste liquid.

[0027] 2. Monazite ceramic solidified bodies were prepared by spark plasma sintering to achieve Sr 2+ and U 4+ Complete lattice solidification within the ceramic solidified body. The process of this invention is simple and easy to implement, avoiding secondary pollution caused by radionuclide extraction and separation, and atmospheric pressure solid-phase sintering processes. Furthermore, this invention solves the problem that ceramic solidification cannot directly treat high-level radioactive waste liquids, and its engineering application will greatly simplify the treatment of Sr in high-level radioactive waste. 2+ and U 4+ The processing technology flow. Attached Figure Description

[0028] Figure 1 Ce was prepared from a 0.5 mol / L HNO3 solution. 0.6 Sr 0.2 U 0.2 XRD pattern of the solid solution crystal grains of PO4·0.667H2O phosphate cerium precipitate;

[0029] Figure 2 It is Ce 0.6 Sr 0.2 U 0.2 XRD pattern of PO4 monazite grains;

[0030] Figure 3It is a 0.2 mol / L HNO3 solution containing Ce. 0.9 Sr 0.05 U 0.05 XRD pattern of the solid solution crystal grains of PO4·0.667H2O phosphate cerium precipitate;

[0031] Figure 4 (a) is a microscopic morphology diagram of hydrated phosphate, and (b) is a microscopic morphology diagram of newly formed heterogeneous phase. Detailed Implementation

[0032] Example 1

[0033] This embodiment provides specific steps for the precipitation separation and ceramic solidification method of divalent strontium and tetravalent uranium in radioactive waste liquid. First, using UO2(NO3)2·6H2O and HNO3 as raw materials, a 0.5 mol / L HNO3 solution is prepared, and a certain amount of UO2(NO3)2·6H2O is dissolved at approximately 25°C. Using a Pt-supported substrate as a catalyst, hydrogen gas at a pressure of 3–4 MPa is passed through the prepared solution to prepare a tetravalent uranium solution. After the reaction is complete, 0.3 mol / L hydrazine is added to the solution.

[0034] Using Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 as raw materials, according to Sr 2+ :U 4+ =2:1, Ce 3+ :Sr 2+ A 3:2 ratio of Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 were weighed. In a glove box under an argon protective atmosphere at approximately 25°C, the Ce(NO3)3·6H2O and Sr(C2H3O2)2 raw materials were added to the tetravalent uranium solution, and the mixture was magnetically stirred for 5 minutes. A small amount of deionized water was used to dissolve NH4H2PO4, based on the PO4... 3- :[Ce 3+ +Sr 2+ A 1.03:1 ratio of NH₄H₂PO₄ solution was prepared and slowly added dropwise to the above tetravalent uranium solution. The mixture was magnetically stirred for 20 minutes, then allowed to stand for 12 hours. The solution was then transferred to a hydrothermal reactor and dried in an oven at 90°C for 28 days to obtain well-developed Sr₂ crystals. 2+ and U 4+ Doped cerium phosphate solid solution. After the reaction, U was measured. 4+ and Sr 2+ The removal rates were 93.8% and 44.3%, respectively. The supernatant was removed by vacuum filtration, and the remaining turbid solution was placed in centrifuge tubes. Solid-liquid separation was further performed using a Hermle centrifuge at 13500 rpm to obtain Ce. 0.6Sr 0.2 U 0.2 The solid solution of PO4·0.667H2O phosphate cerium precipitate was dried in a constant temperature oven at 60℃ for 24 hours. The XRD of the solid solution is as follows: Figure 1 As shown.

[0035] The dried cerium hydrate solid solution powder was placed in a graphite mold, which was then fixed in a spark plasma sintering furnace. The temperature was increased to 800°C at a rate of 100°C / min and held for 30 minutes. The temperature was then increased to 1200°C at a rate of 50°C / min and sintered at 50 MPa for 30 minutes. During cooling, the temperature was reduced to 600°C at a rate of 25°C / min, and then allowed to cool naturally from 600°C to room temperature. Finally, the obtained Ce... 0.6 Sr 0.2 U 0.2 The density of PO4 monazite ceramic solidified body is approximately 99%. Figure 2 Its XRD pattern.

[0036] Example 2

[0037] This embodiment is based on Example 1, using UO2(NO3)2·6H2O and HNO3 as raw materials. A 0.2 mol / L HNO3 solution was prepared, and a certain amount of UO2(NO3)2·6H2O was dissolved at a temperature of approximately 25°C. Using a Pt-supported substrate as a catalyst, hydrogen gas at a pressure of 3–4 MPa was passed through the prepared solution to prepare a tetravalent uranium solution. After the reaction was completed, 0.3 mol / L hydrazine was added to the solution.

[0038] Using Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 as raw materials, according to Sr 2+ :U 4+ =2:1, Ce 3+ :Sr 2+ A 3:2 ratio of Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 were weighed. In a glove box under an argon protective atmosphere at approximately 25°C, the Ce(NO3)3·6H2O and Sr(C2H3O2)2 raw materials were added to the tetravalent uranium solution, and the mixture was magnetically stirred for 3 minutes. A small amount of deionized water was used to dissolve NH4H2PO4, based on the PO4... 3- :[Ce 3+ +Sr 2+ A 1.03:1 ratio of NH₄H₂PO₄ solution was prepared and slowly added dropwise to the above tetravalent uranium solution. The mixture was magnetically stirred for 20 minutes, then allowed to stand for 12 hours. The solution was then transferred to a hydrothermal reactor and dried in an oven at 90°C for 28 days to obtain well-developed Sr₂ crystals. 2+ and U4+ Doped cerium phosphate solid solution. After the reaction, U was measured. 4+ and Sr 2+ The removal rates were 94.9% and 45.2%, respectively. The supernatant was removed by vacuum filtration, and the remaining turbid solution was placed in centrifuge tubes. Solid-liquid separation was further performed using a Hermle centrifuge at 13500 rpm to obtain Ce. 0.6 Sr 0.2 U 0.2 The PO4·0.667H2O precipitate solid solution was dried in a constant temperature oven at 60°C for 24 hours. Compared with Example 1, the precipitate grains obtained in Example 2 were smaller, such as... Figure 3 As shown.

[0039] The dried cerium hydrate solid solution powder was placed in a graphite mold, which was then fixed in a spark plasma sintering furnace. The temperature was increased to 800°C at a rate of 100°C / min and held for 30 minutes. The temperature was then increased to 1200°C at a rate of 50°C / min and sintered at 50 MPa for 30 minutes. During cooling, the temperature was reduced to 600°C at a rate of 25°C / min, and then allowed to cool naturally from 600°C to room temperature. Finally, the obtained Ce... 0.6 Sr 0.2 U 0.2 The density of PO4 monazite ceramic solidified body is approximately 99%.

[0040] Example 3

[0041] This embodiment is based on Example 1, using UO2(NO3)2·6H2O and HNO3 as raw materials. A 0.5 mol / L HNO3 solution was prepared, and a certain amount of UO2(NO3)2·6H2O was dissolved at a temperature of approximately 25°C. Using a Pt-supported substrate as a catalyst, hydrogen gas at a pressure of 3–4 MPa was introduced into the prepared solution. Based on the reaction UO2(NO3)2 + H2 + 2HNO3 → U(NO3)4 + 2H2O, a tetravalent uranium solution was prepared. After the reaction was completed, 0.3 mol / L hydrazine was added to the solution.

[0042] Using Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 as raw materials, according to Sr 2+ :U 4+ =2:1, Ce 3+ :Sr 2+A 9:1 ratio of Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 were weighed. In a glove box under an argon protective atmosphere at approximately 25°C, the Ce(NO3)3·6H2O and Sr(C2H3O2)2 raw materials were added to the tetravalent uranium solution, and the mixture was magnetically stirred for 3 minutes. A small amount of deionized water was used to dissolve NH4H2PO4, based on the PO4... 3- :[Ce 3+ +Sr 2+ A 1.03:1 ratio of NH₄H₂PO₄ solution was prepared and slowly added dropwise to the above tetravalent uranium solution. The mixture was magnetically stirred for 20 minutes, then allowed to stand for 12 hours. The solution was then transferred to a hydrothermal reactor and dried in an oven at 90°C for 28 days to obtain well-developed Sr₂ crystals. 2+ and U 4+ Doped cerium phosphate solid solution. After the reaction, U was measured. 4+ and Sr 2+ The removal rates were 92.9% and 44.1%, respectively. The supernatant was removed by vacuum filtration, and the remaining turbid solution was placed in centrifuge tubes. Solid-liquid separation was further performed using a Hermle centrifuge at 13500 rpm to obtain Ce. 0.9 Sr 0.05 U 0.05 The precipitated solid solution of PO4·0.667H2O was dried in a constant temperature oven at 60℃ for 24 hours.

[0043] The dried cerium hydrate solid solution powder was placed in a graphite mold, which was then fixed in a spark plasma sintering furnace. The temperature was increased to 800°C at a rate of 100°C / min and held for 30 minutes. The temperature was then increased to 1200°C at a rate of 50°C / min and sintered at 50 MPa for 30 minutes. During cooling, the temperature was reduced to 600°C at a rate of 25°C / min, and then allowed to cool naturally from 600°C to room temperature. Finally, the obtained Ce... 0.9 Sr 0.05 U 0.05 The density of the solidified monazite ceramic body (PO4·0.667H2O) is approximately 99%.

[0044] Example 4

[0045] In this embodiment, UO2(NO3)2·6H2O and HNO3 were used as raw materials. A 0.5 mol / L HNO3 solution was prepared, and a certain amount of UO2(NO3)2·6H2O was dissolved at a temperature of approximately 25°C. Using a Pt-supported substrate as a catalyst, hydrogen gas at a pressure of 3–4 MPa was introduced into the prepared solution. Based on the reaction UO2(NO3)2 + H2 + 2HNO3 → U(NO3)4 + 2H2O, a tetravalent uranium solution was prepared. After the reaction was completed, 0.3 mol / L hydrazine was added to the solution.

[0046] Using Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 as raw materials, according to Sr 2+ :U 4+ =2:1, Ce 3+ :Sr 2+ A 9:1 ratio of Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 were weighed. In a glove box under an argon protective atmosphere at approximately 25°C, the Ce(NO3)3·6H2O and Sr(C2H3O2)2 raw materials were added to the tetravalent uranium solution, and the mixture was magnetically stirred for 3 minutes. A small amount of deionized water was used to dissolve NH4H2PO4, based on the PO4... 3- :[Ce 3+ +Sr 2+ A 1.03:1 ratio of NH₄H₂PO₄ solution was prepared and slowly added dropwise to the above tetravalent uranium solution. The mixture was magnetically stirred for 20 minutes, then allowed to stand for 12 hours. The solution was then transferred to a hydrothermal reactor and dried in an oven at 90°C for 28 days to obtain well-developed Sr₂ crystals. 2+ and U 4+ Doped cerium phosphate solid solution. After the reaction, U was measured. 4+ and Sr 2+ The removal rates were 92.9% and 44.1%, respectively. The supernatant was removed by vacuum filtration, and the remaining turbid solution was placed in centrifuge tubes. Solid-liquid separation was further performed using a Hermle centrifuge at 13500 rpm to obtain Ce. 0.9 Sr 0.05 U 0.05 The precipitated solid solution of PO4·0.667H2O was dried in a constant temperature oven at 60℃ for 24 hours.

[0047] The dried cerium hydrate solid solution powder was placed in a graphite mold, which was then fixed in a spark plasma sintering furnace. The temperature was increased to 800°C at a rate of 100°C / min and held for 30 minutes. The temperature was then increased to 1100°C at a rate of 50°C / min and sintered at 50 MPa for 30 minutes. During cooling, the temperature was reduced to 600°C at a rate of 25°C / min, and then allowed to cool naturally from 600°C to room temperature. Finally, the obtained Ce... 0.9 Sr 0.05 U 0.05 The density of the solidified monazite ceramic body is approximately 98%.

[0048] Example 5

[0049] In this embodiment, UO2(NO3)2·6H2O and HNO3 were used as raw materials. A 0.5 mol / L HNO3 solution was prepared, and a certain amount of UO2(NO3)2·6H2O was dissolved at a temperature of approximately 25°C. Using a Pt-supported substrate as a catalyst, hydrogen gas at a pressure of 3–4 MPa was introduced into the prepared solution. Based on the reaction UO2(NO3)2 + H2 + 2HNO3 → U(NO3)4 + 2H2O, a tetravalent uranium solution was prepared. After the reaction was completed, 0.3 mol / L hydrazine was added to the solution.

[0050] Using Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 as raw materials, according to Sr 2+ :U 4+ =2:1, Ce 3+ :Sr 2+ A 3:2 ratio of Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 were weighed. In a glove box under an argon protective atmosphere at approximately 25°C, the Ce(NO3)3·6H2O and Sr(C2H3O2)2 raw materials were added to the tetravalent uranium solution, and the mixture was magnetically stirred for 3 minutes. A small amount of deionized water was used to dissolve NH4H2PO4, based on the PO4... 3- :[Ce 3+ +Sr 2+ A 1.03:1 ratio of NH₄H₂PO₄ solution was prepared and slowly added dropwise to the above tetravalent uranium solution. The mixture was magnetically stirred for 20 minutes, then allowed to stand for 12 hours. The solution was then transferred to a hydrothermal reactor and dried in an oven at 90°C for 14 days to obtain Sr with smaller grain sizes. 2+ and U 4+ Doped cerium phosphate solid solution. After the reaction, U was detected. 4+ and Sr 2+The removal rates were 92.1% and 43.7%, respectively. The supernatant was removed by vacuum filtration, and the remaining turbid solution was placed in centrifuge tubes. Solid-liquid separation was further performed using a Hermle centrifuge at 13500 rpm to obtain Ce. 0.9 Sr 0.05 U 0.05 The precipitated solid solution of PO4·0.667H2O was dried in a constant temperature oven at 60℃ for 24 hours.

[0051] The dried cerium hydrate solid solution powder was placed in a graphite mold, which was then fixed in a spark plasma sintering furnace. The temperature was increased to 800°C at a rate of 100°C / min and held for 30 minutes. The temperature was then increased to 1200°C at a rate of 50°C / min and sintered at 50 MPa for 30 minutes. During cooling, the temperature was reduced to 600°C at a rate of 25°C / min, and then allowed to cool naturally from 600°C to room temperature. Finally, the obtained Ce... 0.9 Sr 0.05 U 0.05 The density of PO4 monazite ceramic solidified body is approximately 99%.

[0052] Example 6

[0053] In this embodiment, UO2(NO3)2·6H2O and HNO3 were used as raw materials. A 0.5 mol / L HNO3 solution was prepared, and a certain amount of UO2(NO3)2·6H2O was dissolved at a temperature of approximately 25°C. Using a Pt-supported substrate as a catalyst, hydrogen gas at a pressure of 3–4 MPa was introduced into the prepared solution. Based on the reaction UO2(NO3)2 + H2 + 2HNO3 → U(NO3)4 + 2H2O, a tetravalent uranium solution was prepared. After the reaction was completed, 0.3 mol / L hydrazine was added to the solution.

[0054] Using Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4 as raw materials, according to Sr 2+ :U 4+ =2:1, Ce 3+ :Sr 2+ A 1:1 ratio formula was prepared by weighing Ce(NO3)3·6H2O, Sr(C2H3O2)2, and NH4H2PO4. In a glove box under an argon protective atmosphere at approximately 25°C, the Ce(NO3)3·6H2O and Sr(C2H3O2)2 raw materials were added to the tetravalent uranium solution, and the mixture was magnetically stirred for 3 minutes. A small amount of deionized water was used to dissolve NH4H2PO4, based on the PO4... 3- :[Ce 3+ +Sr 2+A 1.03:1 ratio of NH₄H₂PO₄ solution was prepared and slowly added dropwise to the above tetravalent uranium solution. The mixture was magnetically stirred for 20 minutes, then allowed to stand for 12 hours. The solution was then transferred to a hydrothermal reactor and dried in an oven at 90°C for 28 days to obtain well-developed Sr₂ crystals. 2+ and U 4+ Doped cerium phosphate solid solution. After the reaction, U was measured. 4+ The removal rate was 80%, Sr 2+ The removal rate was 94%. The supernatant was removed by vacuum filtration, and the remaining turbid solution was placed in centrifuge tubes and further separated into solid and liquid phases using a Hermle centrifuge at 13500 rpm. The resulting precipitate solid solution was dried in a 60°C oven for 24 hours. Scanning electron microscopy revealed the formation of hydrated phosphates and a small amount of newly formed impurities. Figure 4 .

[0055] These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for precipitation separation and ceramic solidification of divalent strontium and tetravalent uranium in radioactive waste liquid, characterized in that, The specific steps are as follows: Step 1: Enriching hexavalent uranyl UO2 2+ Preparation of U by hydrogenation catalytic reduction in high-level radioactive waste liquid 4+ ; Step 2: Add Ce(NO3)3·6H2O and Sr(C2H3O2)2 raw materials to U 4+ After magnetic stirring in the solution, the prepared NH4H2PO4 solution was slowly added dropwise, and the mixture was then transferred to an oven to stand and form Sr. 2+ and U 4+ Doped cerium phosphate solid solution; based on Sr 2 + :U 4+ =2:1、Ce 3+ Sr 2+ ≥ 3:2, under an argon protective atmosphere at 25℃, Ce(NO3)3·6H2O and Sr(C2H3O2)2 raw materials are added to a tetravalent uranium solution and magnetically stirred for 3~5 minutes; Step 3: Centrifuge and dry the cerium phosphate solid solution into cerium phosphate solid solution powder; Step 4: Prepare monazite ceramic solidified body by vacuum discharge plasma sintering of water-phosphorus cerium stone solid solution powder; The hexavalent uranyl UO2 2+ Restore to U 4+ The process is based on the reaction UO2(NO3)2 + H2 + 2HNO3 → U(NO3)4 + 2H2O; The hexavalent uranyl UO2 2+ During the reduction process, a Pt-supported substrate was used as a catalyst, and UO2(NO3)2·6H2O and HNO3 were used as raw materials. The hydrogen pressure was controlled at 3-4 MPa, the temperature at 25℃, and the nitric acid concentration at 0.2-0.5 mol / L. After the reaction was completed, 0.3 mol / L hydrazine was added to the solution to prevent UO2 from being released into the atmosphere. 4+ Oxidation; After magnetic stirring for 3-5 minutes in step two, dissolve NH4H2PO4 in a small amount of deionized water, based on PO4. 3- :[Ce 3+ +Sr 2 + The prepared NH4H2PO4 solution was slowly added dropwise to the tetravalent uranium solution at a ratio of 1.03:1, and the mixture was magnetically stirred for 20 minutes. The mixture was then allowed to stand for 6 to 12 hours. In step four, the dried cerium phosphate solid solution powder is placed in a graphite mold, which is then fixed in a spark plasma sintering furnace. The furnace is heated to 800°C at a heating rate of 100°C / min and held for 30 minutes. The temperature is then increased to 1100-1200°C at a heating rate of 50°C / min and sintered at 30-50 MPa for 15-30 minutes. Finally, the temperature is reduced to 600°C at a rate of 25°C / min and allowed to cool naturally to room temperature to obtain Sr. 2+ and U 4+ Uniformly distributed monazite ceramic solidified body.

2. The method for precipitation separation and ceramic solidification of divalent strontium and tetravalent uranium in radioactive waste liquid according to claim 1, characterized in that, In step two, the mixed solution after settling is transferred to a hydrothermal reactor and placed in an oven at 90°C for 14 to 28 days to produce Sr. 2+ and U 4+ Doped cerium phosphate solid solution.

3. The method for precipitation separation and ceramic solidification of divalent strontium and tetravalent uranium in radioactive waste liquid according to claim 1, characterized in that, In step three, the supernatant is removed by vacuum filtration before centrifugation. The remaining turbid solution is placed in a centrifuge tube and the solid and liquid are separated by a Hermle centrifuge at a speed of 13,500 rpm. The resulting cerium phosphate solid solution is dried in a constant temperature oven at 60°C for 24 hours.

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