A glass solidification additive and method for inhibiting the volatilization of radioactive elements

Abstract

The application relates to a glass solidification additive for inhibiting the volatilization of radioactive elements and a glass solidification method, and belongs to the technical field of radioactive waste solidification treatment. The additive is composed of a natural mineral adsorbent and a glass forming agent, and specifically comprises 2-10 parts of a silicon-aluminum-based natural mineral, 1-5 parts of a titanium-based natural mineral, 40-60 parts of silicon dioxide, 15-25 parts of boric acid, 10-20 parts of sodium carbonate and 1-10 parts of calcium oxide; the natural mineral adsorbent with a porous structure can effectively adsorb the volatilized radioactive elements in the high-temperature heat treatment process of medium and low radioactive solid waste; and the application further provides a glass solidification method for inhibiting the volatilization of radioactive elements. The method adds a low-temperature pyrolysis step before heat treatment, effectively promotes the separate volatilization of chlorine elements in the waste, reduces the promotion effect of chlorine elements on the volatilization of radioactive elements in the high-temperature section, and thus inhibits the release of radioactive elements in the heat treatment and melting processes.

Description

TECHNICAL FIELD

[0001] The present application relates to a glass solidification additive for inhibiting the volatilization of radioactive elements and a glass solidification method, and belongs to the technical field of radioactive waste solidification treatment. BACKGROUND

[0002] The heat treatment technology has obvious volume reduction effect on the disposal of medium and low level radioactive solid waste, and mainly uses incineration and high temperature melting methods. The heat treatment technology volatilizes combustible substances, and the remaining ash is treated by glass solidification method to finally form a stable glass body. This method has great volume reduction ratio and stable final product, and is paid attention by the industry.

[0003] However, during the heat treatment process, some radioactive elements in the medium and low level radioactive solid waste will volatilize into gas. Taking cesium (Cs), cobalt (Co) and strontium (Sr) as examples, cesium is an extremely volatile element, cobalt has certain volatility at high temperature, and the chemical properties of strontium are relatively stable. In addition, the resins, rubber, plastic or wood chips contained in the medium and low level radioactive solid waste generally contain a certain amount of chlorine (Cl) element, which will form low-melting-point chlorides with radioactive elements, significantly promoting the volatilization of radioactive elements, especially cesium which belongs to alkali metal elements.

[0004] Patent application CN 104658627A discloses a preparation method of a solidification body for low and medium radioactive waste glass solidification treatment. The method uses components SiO2, H3BO3, Na2CO3 and CaO as raw materials, and after batching and mixing, it is melted at a temperature of 1250℃ for 2.5-3 hours, then poured into a mold preheated to 500℃ for forming, and placed at a temperature of 500℃ for 0.5-1 hours, and then cooled to room temperature at a cooling rate of 0.5-1℃ / min to obtain the product. The method directly heat-treats low and medium radioactive waste at high temperature, and at high temperature, part of the radioactive elements (such as cesium) have strong volatility, and the release of chlorine elements contained in the waste will also significantly promote the volatilization of radioactive elements. The volatilized radioactive elements are enriched in fine particles or ultra-fine particles, which are difficult to be captured by the filtration system, and then released into the external environment to cause serious pollution. Therefore, the problem of thermal volatilization of radioactive elements needs to be specially considered in the design of heat treatment process and glass solidification process. SUMMARY

[0005] In order to overcome the defects of the thermal volatilization of radioactive elements in the heat treatment process and glass solidification process of the prior art, one of the purposes of the present application is to provide a glass solidification additive for inhibiting the volatilization of radioactive elements;

[0006] The second object of the present application is to provide a glass solidification method for inhibiting the volatilization of radioactive elements; the method realizes the inhibition of the thermal volatilization of radioactive elements under the premise of ensuring the stability of the glass body by optimizing the glass solidification process and adding adsorbents while adding glass formers.

[0007] To achieve the object of the present application, the following technical solutions are provided.

[0008] A glass solidification additive for inhibiting the volatilization of radioactive elements, the additive is composed of a natural mineral adsorbent and a glass former, the natural mineral adsorbent is a silicon-aluminum-based natural mineral and a titanium-based natural mineral; the glass former is silicon dioxide, boric acid, sodium carbonate and calcium oxide; specifically, the weight parts of each component in the additive are as follows:

[0009]

[0010] The silicon-aluminum-based natural mineral is at least one of kaolin, diatomite, zeolite and vermiculite;

[0011] The titanium-based natural mineral is at least one of ilmenite, titanomagnetite, anatase and rutile;

[0012] A glass solidification method for inhibiting the volatilization of radioactive elements, the specific steps of the method are as follows:

[0013] (1) low-temperature pyrolysis of medium and low level radioactive solid waste under a protective atmosphere at 250-500°C for 5-60 min to obtain pyrolysis coke;

[0014] The medium and low level radioactive solid waste is combustible solid waste generated in the actual operation of a nuclear power plant, and the components and weight parts are as follows:

[0015] 5-70 parts of polyethylene plastic (PE), 1-5 parts of polyvinyl chloride plastic (PVC), 5-40 parts of cotton, 1-10 parts of rubber products, 5-30 parts of paper, 1-10 parts of wood chips, 0.1 parts of CsCO3, 0.1 parts of CoCO3 and 0.1 parts of SrCO3;

[0016] Preferably, the medium and low level radioactive solid waste is combustible solid waste generated in the actual operation of a nuclear power plant, and the components and weight parts are as follows: 20-60 parts of polyethylene plastic (PE), 1-2 parts of polyvinyl chloride plastic (PVC), 12.5-35 parts of cotton, 5-8.7 parts of rubber products, 10-30 parts of paper, 6.2-10 parts of wood chips, 0.1 parts of CsCO3, 0.1 parts of CoCO3 and 0.1 parts of SrCO3;

[0017] The protective atmosphere is at least one of air, nitrogen, argon, oxygen and carbon dioxide.

[0018] (2) pyrolytic coke obtained in step (1) is incinerated at 800-1400℃ until the sample is completely ashed to obtain incineration ash;

[0019] Preferably, the incineration equipment is a muffle furnace, a large-scale incinerator, a cold crucible furnace or a plasma melting furnace.

[0020] (3) a glass solidification additive for inhibiting the volatilization of radioactive elements is added to the incineration ash obtained in step (2), and the mixture is melted at a temperature of 1100-1400℃ for 1-3h; the mass ratio of the incineration ash to the additive is 0.5:1-0.8:1;

[0021] (4) the melted substance in step (3) is cast into a molding mold at 450-550℃, and then annealed at 450-550℃ for 1-2h to complete the annealing, and the glass solidification body is obtained after cooling to room temperature.

[0022] Advantages

[0023] (1) the present application provides a glass solidification additive for inhibiting the volatilization of radioactive elements, which comprises a natural mineral adsorbent as an active component in addition to a glass former, wherein the natural mineral adsorbent is a silicon-aluminum-based natural mineral and a titanium-based natural mineral; the porous structure of the natural mineral can effectively adsorb a large amount of volatilized radioactive elements (such as cesium) in the initial stage of combustion of medium and low level radioactive solid waste, and titanium is also a grid modifier element, which can promote the combination of cesium and non-metallic elements; in addition, other components in the natural mineral, such as iron or magnesium, can reduce the melting point of the glass melt, increase its fluidity, and make the properties of the cooled glass solidification body more stable.

[0024] (2) the present application provides a glass solidification additive for inhibiting the volatilization of radioactive elements, wherein the natural mineral adsorbent accounts for 3-15 parts by weight of the total additive; when the natural mineral adsorbent is too much, the aluminum and titanium in the mineral will significantly increase the melting point of the mixture, affecting the stability of the glass solidification body; when the natural mineral adsorbent is too little, it cannot significantly adsorb radioactive elements.

[0025] (3) The present application provides a glass solidification additive for inhibiting the volatilization of radioactive elements, which is suitable for a wide range of waste ratio sources. When the content of alkaline oxides in waste incineration ash is high and the content of acidic oxides is low, the proportion of SiO2 in the additive formula is increased to stabilize the properties of the final glass solidification body. On the contrary, when the content of alkaline oxides in waste incineration ash is low and the content of acidic oxides is high, the proportion of SiO2 in the additive formula is reduced. In addition, the active components of the additive, i.e. silicon-aluminum-based natural minerals and titanium-based natural mineral raw materials, have a wide range of sources and low prices. At the same time, the glass former formula can be adjusted according to the composition and addition amount of natural minerals to maintain good stability of the final glass solidification body while meeting the waste minimization disposal principle.

[0026] (4) The present application provides a glass solidification method for inhibiting the volatilization of radioactive elements, which performs low-temperature pyrolysis in the first step of the heat treatment process, effectively promotes the volatilization of chlorine elements in the waste alone, reduces the promoting effect of chlorine elements on the volatilization of radioactive elements in the high-temperature section, and thereby inhibits the release of radioactive elements in the heat treatment and melting processes. In addition, due to the early volatilization of chlorine, the generation of dioxins in the incineration process can be reduced to some extent. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Elemental release rates of Cs, Co and Sr in the glass solidification bodies prepared in Examples 1 to 3 and Comparative Examples 1 to 3 during heat treatment.

[0028] Figure 2 X-ray diffraction (XRD) patterns of the glass solidification bodies prepared in Examples 1 to 3. DETAILED DESCRIPTION

[0029] The present application will be described in detail below with reference to the accompanying drawings and specific examples, but is not limited to the patent.

[0030] In the following comparative examples and examples:

[0031] (1) Raw material information:

[0032] Polyethylene plastic, polyvinyl chloride plastic, cotton, rubber products, paper and wood chips are all conventional commercially available products. Among them, the purity of polyethylene plastic is not less than 98%, the purity of polyvinyl chloride plastic is not less than 99%, cotton is cotton, rubber products are rubber products produced with natural rubber and styrene-butadiene rubber as raw materials, and paper is absorbent paper.

[0033] The isotopes CsCO3, CoCO3, and SrCO3 are non-radioactive isotopes of cesium, cobalt, and strontium, respectively. The various substances in the glass solidification additive, as well as the diatomite, kaolin, zeolite, ilmenite, anatase, and rutile, are all purchased from Shanghai Aladdin Biochem Technology Co., Ltd.

[0034] (2) Instruments and test methods:

[0035] The density of the glass solidification body was tested according to the glass density buoyancy method (GB / T 5432-2008);

[0036] The compressive strength of the glass solidification body was tested using a pressure testing machine (Instron 6027);

[0037] The impact strength of the glass solidification body was determined according to the heavy hammer free-fall impact method (EJ1186-2005).

[0038] Example 1

[0039] A glass solidification additive for inhibiting the volatilization of radioactive elements, the various components and weight portions in the additive being as follows:

[0040]

[0041] A glass solidification method for inhibiting the volatilization of radioactive elements according to the present embodiment, the specific steps of the method being as follows:

[0042] (1) Preparation of simulated medium- and low-level radioactive solid waste: The total amount of the simulated solid waste sample was 50 g, including 40 parts by weight of PE, 1 part by weight of PVC, 35 parts by weight of cotton, 5 parts by weight of rubber products, 12.5 parts by weight of absorbent paper, 6.2 parts by weight of wood chips, 0.1 part by weight of the isotope CsCO3, 0.1 part by weight of the isotope CoCO3, and 0.1 part by weight of the isotope SrCO3, which were mixed uniformly using a grinder;

[0043] The simulated medium- and low-level radioactive solid waste was placed in a crucible and was subjected to low-temperature pyrolysis in a muffle furnace at 250°C under a nitrogen atmosphere for 60 min, to obtain pyrolysis coke;

[0044] (2) The pyrolysis coke obtained in step (1) was incinerated in a high-temperature incinerator at 1400°C under an air atmosphere until the sample was completely ashed, to obtain incineration ash; after the incineration ash was cooled, the mass of the incineration ash was measured to be 4.76 g.

[0045] (3) To the incineration ash obtained in step (2), 9.52 g of a glass solidification additive for inhibiting the volatilization of radioactive elements described in the present embodiment was added, mixed uniformly, and placed in a corundum crucible, and high-temperature melting was performed in a high-temperature tube furnace, the melting temperature was 1100°C, the time was 3 h, and the atmosphere was air; the mass ratio of the incineration ash to the additive was 0.5:1;

[0046] (4) The substance after melting in step (3) was cast into a molding mold which had been preheated to 450°C in advance, and then annealing was completed at 450°C for 2 h, and a glass solidification body was obtained after cooling to room temperature.

[0047] Example 2

[0048] A glass solidification additive for inhibiting the volatilization of radioactive elements, the components and weight parts in the additive are as follows:

[0049]

[0050]

[0051] A glass solidification method for inhibiting the volatilization of radioactive elements described in the present embodiment, the specific steps of the method are as follows:

[0052] (1) Configuration of simulated medium and low level radioactive solid waste: the total amount of the simulated medium and low level radioactive solid waste sample was 50 g, wherein 20 parts by weight of PE, 1 part by weight of PVC, 30 parts by weight of cotton, 8.7 parts by weight of rubber products, 30 parts by weight of paper, 10 parts by weight of wood chips, 0.1 parts by weight of nuclide CsCO3, 0.1 parts by weight of nuclide CoCO3 and 0.1 parts by weight of nuclide SrCO3; a grinding instrument was used for mixing uniformly;

[0053] The simulated medium and low level radioactive solid waste was loaded into a crucible, and low-temperature pyrolysis was performed in a muffle furnace at 500°C under a nitrogen atmosphere for 5 min, and pyrolysis coke was obtained;

[0054] (2) The pyrolysis coke obtained in step (1) was incinerated in a muffle furnace at 800°C under an air atmosphere until the sample was completely ashed, and incineration ash was obtained; after the incineration ash was cooled, the mass of the incineration ash was 5.98 g.

[0055] (3) To the incineration ash obtained in step (2), 7.48 g of a glass solidification additive for inhibiting the volatilization of radioactive elements described in the present embodiment was added, mixed uniformly, and placed in a corundum crucible, and high-temperature melting was performed in a high-temperature tube furnace, the melting temperature was 1400°C, the time was 1 h, and the atmosphere was nitrogen; the mass ratio of the incineration ash to the additive was 0.8:1;

[0056] (4) The molten substance of step (3) is cast into a molding mold preheated to 550°C, then annealed at 550°C for 1 h, and a glass solidified body is obtained after cooling to room temperature.

[0057] Example 3

[0058] An additive for inhibiting the volatilization of radioactive elements, wherein the components and weight parts are as follows:

[0059]

[0060]

[0061] A glass solidification process for inhibiting the volatilization of radioactive elements according to the present embodiment, wherein the specific steps are as follows:

[0062] (1) Prepare simulated medium and low level radioactive solid waste: the total amount of the simulated medium and low level radioactive solid waste sample is 50 g, wherein 60 parts by weight of PE, 2 parts by weight of PVC, 12.5 parts by weight of cotton, 8 parts by weight of rubber products, 10 parts by weight of paper, 7.2 parts by weight of wood chips, 0.1 parts by weight of nuclide CsCO3, 0.1 parts by weight of nuclide CoCO3 and 0.1 parts by weight of nuclide SrCO3 are uniformly mixed using a grinder;

[0063] The simulated medium and low level radioactive solid waste is placed in a crucible and put into a muffle furnace for low temperature pyrolysis at 400°C under a nitrogen atmosphere for 30 min to obtain pyrolysis coke;

[0064] (2) The pyrolysis coke obtained in step (1) is incinerated in a muffle furnace at 900°C under an air atmosphere until the sample is completely ashed to obtain incineration ash; after the incineration ash is cooled, the mass of the incineration ash is 3.92 g.

[0065] (3) 5.6 g of the glass solidification additive for inhibiting the volatilization of radioactive elements according to the present embodiment is added to the incineration ash obtained in step (2) and uniformly mixed and placed in a corundum crucible, and high temperature melting is carried out in a high temperature tube furnace, the melting temperature is 1200°C, the time is 2 h, and the atmosphere is nitrogen; the mass ratio of the incineration ash to the additive is 0.7:1;

[0066] (4) The molten substance of step (3) is cast into a molding mold preheated to 500°C, then annealed at 500°C for 1.5 h, and a glass solidified body is obtained after cooling to room temperature.

[0067] Comparative Example 1

[0068] Comparative Example 1 only removes the low temperature pyrolysis step in step (1) based on Example 3, and the remaining conditions are unchanged, and a glass solidified body is obtained.

[0069] Comparative Example 2

[0070] Comparative Example 2 is only based on Example 3, and the natural mineral adsorbent in the additive is removed, and the weight fractions of the remaining components in the additive are adjusted as follows: 55.6 parts of SiO2, 20 parts of H3BO3, 18.9 parts of Na2CO3 and 5.5 parts of CaO in normalized percentage, and the remaining conditions are unchanged, to obtain a glass solidified body.

[0071] Comparative Example 3

[0072] Comparative Example 3 is only based on Comparative Example 2, and the low-temperature pyrolysis step in step (1) is removed, and the remaining conditions are unchanged, to obtain a glass solidified body.

[0073] The glass solidified bodies obtained in Examples 1-3 and Comparative Examples 1-3 are tested as follows:

[0074] (1) Element composition ratio in incineration ash

[0075] The X-ray fluorescence spectrometer (XRF) is used to determine the element composition ratio of the medium and low level radioactive solid waste incineration ash. The normalized percentage of the oxides of other elements except for the nuclides Cs, Co and Sr is shown in Table 1:

[0076] Table 1 Element composition ratio in incineration ash of Examples 1-3 and Comparative Examples 1-3

[0077]

[0078] From the results, it can be seen that the composition of the incineration ash of Examples 1-3 is significantly different, which is due to the different component allocation ratios of the simulated medium and low level radioactive solid waste. When the content of alkaline oxides (such as oxides of Na, K, Ca and other elements) in the waste incineration ash is high, and the content of acidic oxides (such as oxides of Al, Si and other elements) is low, the proportion of SiO2 in the additive formulation range of the present application is appropriately increased to stabilize the properties of the final glass solidified body. On the contrary, when the content of alkaline oxides in the waste incineration ash is low, and the content of acidic oxides is high, the addition proportion of SiO2 in the additive formulation range of the present application is appropriately reduced. This shows that the additive formulation of the present application can be applied to waste proportioning sources with different contents, and the adaptation range is wide.

[0079] The component allocation ratios of the simulated medium and low level radioactive solid waste of Example 3 and Comparative Examples 1-3 are the same, but the chlorine element content of the incineration ash is different. This is because compared with Example 3 and Comparative Example 2, the low-temperature pyrolysis process in the first step is removed in Comparative Examples 1 and 3, which causes the chlorine element to be unable to be released in advance, and the chlorine will continue to volatilize in the subsequent high-temperature melting process, thereby promoting the release of radioactive elements.

[0080] (2) Element Volatilization Percentage

[0081] The tail gas generated in the process of heat treatment (pyrolysis, incineration and high temperature melting) is directly introduced into a gas washing bottle through the gas outlet of the device, the bottle is filled with 0.5 mol / L HNO3 solution, which is used to absorb the volatilized elements in the tail gas, and the concentration is determined by inductively coupled plasma mass spectrometry (ICP-MS) to obtain the volatilization amount of the element, and the ratio of the volatilization amount of the element to the initial addition amount is the element volatilization percentage.

[0082] The element release rates of Cs, Co and Sr of the medium and low level radioactive solid waste in Examples 1-3 and Comparative Examples 1-3 in the process of heat treatment are shown in Table 1. Figure 1 As can be seen from the table, when the low temperature pyrolysis step is not used and the natural mineral adsorbent is not contained in the additive in Comparative Example 3, the release amount of cesium is as high as 98.6%, and the release amount of cobalt is also a certain degree, which is 28.6%, while the property of strontium is stable and the release amount is very small; the natural mineral adsorbent is added in the additive in Comparative Example 1, and the low temperature pyrolysis step is added in Comparative Example 2, the release amounts of cesium and cobalt in Comparative Examples 1 and 2 are reduced compared with Comparative Example 3, but are still higher than the release amounts in Example 3. After the method described in the present application is used, according to the test results of Examples 1-3, the release amounts of cesium and cobalt are significantly reduced. This shows that the low temperature pyrolysis process in the method and the addition of the natural mineral adsorbent in the additive can effectively inhibit the release of typical radioactive elements, among which the inhibition effect on the release of Cs element is the most obvious.

[0083] (3) Crystal and Crystal Type Test

[0084] The X-ray diffraction patterns of the glass solidification bodies obtained in Examples 1-3 are determined by X-ray diffractometer (XRD), and whether there is crystal and the crystal type in the glass solidification body is analyzed according to the patterns. As can be seen from Table 2, the obtained glass solidification body has no obvious crystal diffraction peak, and is mainly amorphous substance, which shows that each component in the glass solidification body has been fully melted. Figure 2

[0085] (4) Physical Property Test

[0086] The physical properties of the glass solidification bodies prepared in Examples 1-3 are tested, and the results are shown in Table 2: the density of the glass solidification body is 2.6-2.8 g / cm 3 , which reaches the required density of the glass solidification body; the compressive strength is higher than 78 MPa, which has very strong compressive performance; the impact strength is 6.9-8.2 cm 2 / J, which meets the requirement of less than 12 cm 2 / J in EJ1186-2005.​

[0087] (5) Anti-nuclide leaching properties

[0088] According to the standard test method for chemical resistance of nuclear waste and mixed waste glass: product consistency test (ASTM C1285), the stability of the glass solidification body prepared in Examples 1-3 was evaluated (the standard stipulates that it should be less than 0.2 g / m 2 ); the sample was subjected to a 7-day immersion experiment, the ion concentration of the immersion liquid was determined by ICP-MS, and then the leaching value of the element was obtained. The results are shown in Table 2.

[0089] As can be seen from Table 2, the leaching rate of each nuclide of the glass solidification body prepared in Examples 1-3 is less than 10×10 -4 (g·m -2 ·d -1 ), which is much lower than the 0.2 g / m 2 stipulated by the ASTM C1285 standard, indicating that the glass solidification body prepared by the method has good anti-leaching performance and stable properties.

[0090] Table 2 Physical properties and anti-leaching properties of the glass solidification body prepared in Examples 1-3

[0091]

Claims

1. A method of glass solidification for inhibiting volatilization of a radioactive element, characterized by: The method comprises the following steps: (1) low-temperature pyrolysis of the medium and low level radioactive solid waste under a protective atmosphere at 250-500°C for 5-60 min to obtain pyrolysis coke; The medium and low level radioactive solid waste is combustible solid waste generated in the actual operation of a nuclear power plant, and each component and weight part is as follows: 5-70 parts of polyethylene plastic, 1-5 parts of polyvinyl chloride plastic, 5-40 parts of cotton, 1-10 parts of rubber products, 5-30 parts of paper, 1-10 parts of wood chips, 0.1 parts of CsCO3, 0.1 parts of CoCO3 and 0.1 parts of SrCO3; The protective atmosphere is at least one of air, nitrogen, argon, oxygen and carbon dioxide; (2) incineration of the pyrolysis coke at 800-1400°C until the sample is completely ashed to obtain incineration ash; (3) adding a glass solidification additive for inhibiting the volatilization of radioactive elements to the incineration ash, melting at a temperature of 1100-1400°C for 1-3 h; the mass ratio of the incineration ash to the additive is 0.5:1-0.8:1; (4) pouring the molten substance into a forming mold at 450-550°C, then annealing at 450-550°C for 1-2 h to complete annealing, and obtaining a glass solidification body after cooling to room temperature; Each component and weight part in the glass solidification additive for inhibiting the volatilization of radioactive elements is as follows: Silicon-aluminum-based natural mineral 2-10 parts; Titanium-based natural mineral 1-5 parts; Silicon dioxide 40-60 parts; Boric acid 15-25 parts; Sodium carbonate 10-20 parts; Calcium oxide 1-10 parts; The silicon-aluminum-based natural mineral is at least one of kaolin, diatomite, zeolite and vermiculite; The titanium-based natural mineral is at least one of ilmenite, titanomagnetite, anatase and rutile.

2. The glass solidification process for inhibiting volatilization of radioactive elements according to claim 1, characterized by: The medium and low level radioactive solid waste is combustible solid waste generated in the actual operation of a nuclear power plant, and each component and weight part is as follows: 20-60 parts of polyethylene plastic, 1-2 parts of polyvinyl chloride plastic, 12.5-35 parts of cotton, 5-8.7 parts of rubber products, 10-30 parts of paper, 6.2-10 parts of wood chips, 0.1 parts of CsCO3, 0.1 parts of CoCO3 and 0.1 parts of SrCO3.

3. A method of glass solidification to inhibit volatilization of a radioactive element according to claim 1 or 2, characterized in that: The incineration equipment is a muffle furnace, a large-scale incineration furnace, a cold crucible furnace or a plasma melting furnace.

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