TWI760749B - Use of silicon-aluminum oxide composite as hardening agent of radioactive phosphoric acid decontamination waste liquid and method for processing radioactive phosphoric acid decontamination waste liquid - Google Patents

Abstract

The method for processing radioactive phosphoric acid decontamination waste liquid includes mixing radioactive phosphoric acid decontamination waste liquid with first water to form pre-treating slurry, wherein the solidified radioactive phosphoric acid waste is 100wt%, the radioactive phosphoric acid decontamination waste liquid is ≧ 60 wt%, the first water is ≦30wt%; mixing the pre-treating slurry with silicon-aluminum oxide composite for a first time to form hardening slurry, wherein the solidified radioactive phosphoric acid waste is 100wt%, the silicon-aluminum oxide composite is ≧ 30 wt%, the ratio of the weight of water in the pre-treating slurry to the weight of the silicon-aluminum oxide composite is 0.5-1, the ratio of the mole number of the phosphoric acid in the pre-treating slurry to the mole number of the silicon-aluminum oxide composite is 1-1.9; and standing the hardening slurry for a second time at a first temperature to form solidified radioactive phosphoric acid waste.

Description

Application of silico-alumino-oxygen compound as curing agent of radioactive phosphoric acid decontamination waste liquid and treatment method of radioactive phosphoric acid decontamination waste liquid

The present invention relates to the use of a silicon-alumina-oxygen compound as a curing agent for the radioactive phosphoric acid decontamination waste liquid and a method for treating the radioactive phosphoric acid decontamination waste liquid.

In addition to stainless steel being the bulk of radioactively contaminated metal waste, carbon steel is also a commonly used material for nuclear power plant construction; due to the replacement of radioactively contaminated metals and old pipe fittings in decommissioned nuclear facilities, a large amount of radioactive metal waste that needs to be decontaminated has to be deal with. In order to solve the above-mentioned problem of a large amount of radioactive metal waste, the application of chemical decontamination methods for different metal materials and decontamination technologies has received extensive attention from research institutions. Among them, for stainless steel, phosphoric acid, sulfuric acid and nitric acid can be used in the chemical decontamination method, which can reach the standard of extremely low radioactive waste after decontamination.

Phosphoric acid decontamination agent has a good decontamination effect on various radioactive metal wastes. Among them, the mixed solution of phosphoric acid and nitric acid is suitable for the decontamination of copper and aluminum metal wastes, and the mixed solution of phosphoric acid, sulfuric acid and nitric acid is suitable for the electrification of stainless steel metal wastes. Learn to decontaminate. During the decontamination process, metal ions gradually accumulate in the decontamination agent, and after reaching a certain saturation concentration, the precipitation of metal salts occurs, which affects the decontamination efficiency or is polluted by nuclear species and increases the radioactivity, and needs to be regenerated. Used phosphoric acid decontamination agent can use oxalic acid selective precipitation method, electrolytic recovery method and cation exchange method to remove metal ions and achieve the purpose of recycling and reuse of decontamination agent. After the phosphoric acid decontamination agent is recycled and reused several times and cannot be reused, it is the radioactive phosphoric acid decontamination waste liquid and is replaced.

Conventional radioactive phosphoric acid decontamination waste liquid post-treatment methods include selective precipitation, direct neutralization precipitation and cement solidification, etc. However, the above treatment technologies have disadvantages such as the use of a large amount of neutralizer to increase the volume of secondary waste, cement solidification. A large amount of heat is released during the process, and a large amount of waste liquid cannot be processed. Therefore, it is necessary to improve the above shortcomings to improve the treatment effect of radioactive phosphoric acid decontamination waste liquid.

The purpose of the present invention is to provide the use of a silicon-alumina-oxygen compound as a curing agent for the radioactive phosphoric acid decontamination waste liquid, which can improve the treatment effect of the radioactive phosphoric acid decontamination waste liquid.

Another object of the present invention is to provide a method for treating waste liquid of radioactive phosphoric acid decontamination, which can reduce the volume of waste.

The method for treating the radioactive phosphoric acid decontamination waste liquid of the present invention is for preparing the radioactive waste acid solidified body from the radioactive phosphoric acid decontamination waste liquid, comprising: mixing and stirring the radioactive phosphoric acid decontamination waste liquid and the first moisture to form a pre-slurry, The radioactive waste acid solidified body is 100 wt%, the radioactive phosphoric acid decontamination waste liquid is more than 60 wt%, and the first moisture is less than 30 wt%; the pre-slurry and the silicon-aluminum-oxygen compound are mixed and stirred for the first time to form a solidified slurry material, wherein the radioactive waste acid solidified body is 100wt%, the silicon-aluminum-oxygen compound is more than 30wt%, and the ratio between the weight of water in the pre-slurry and the weight of the silicon-alumina-oxygen compound is between 0.5 and 1. The ratio between the molar number of phosphoric acid in the slurry and the molar number of alumina in the silicon-alumina-oxygen composite is between 1 and 1.9; the solidified slurry is allowed to stand above the first temperature for a second time to form radioactive waste acid solidified body.

In the embodiment of the present invention, the content of phosphoric acid in the radioactive phosphoric acid decontamination waste liquid is more than 40wt%, and the content of water is less than 60wt%.

In an embodiment of the present invention, the silicon-alumina-oxygen composite is selected from the group comprising metakaolin, Al ₂ O ₄ ·SiO ₂ and combinations thereof.

In the embodiment of the present invention, the first time is more than 10 minutes.

In the embodiment of the present invention, the second time period is more than 7 days.

In the embodiment of the present invention, the first temperature is between 25 and 45°C.

In the embodiment of the present invention, the ratio between the volume of the solidified radioactive acid and the volume of the radioactive phosphoric acid decontamination waste liquid is 1.1 or less.

In the embodiment of the present invention, the strength of the solidified body of radioactive waste acid is 50 kgf/m ² or more.

The method for treating radioactive phosphoric acid decontamination waste liquid of the present invention is for preparing a radioactive waste acid solidified body from the radioactive phosphoric acid decontamination waste liquid. As shown in the schematic flowchart of the embodiment shown in FIG. 1 , the processing method includes, for example, the following steps.

In step 1000, the radioactive phosphoric acid decontamination waste liquid and the first moisture are mixed and stirred to form a pre-slurry, and this step may be referred to as a pre-slurry forming step. Wherein, the solidified body of radioactive waste acid is 100wt%, the radioactive phosphoric acid decontamination waste liquid is more than 60wt%, and the first moisture is less than 30wt%. Furthermore, if the radioactive phosphoric acid decontamination waste liquid is less than 60 wt%, the mechanical strength of the finally prepared radioactive waste acid solidified body will be greatly reduced. In a preferred embodiment, the content of phosphoric acid in the radioactive phosphoric acid decontamination waste liquid is more than 40wt%, and the content of water is less than 60wt%, so as to ensure the decontamination effect of the original phosphoric acid decontamination agent and the final preparation of the radioactive waste acid formed. The mechanical strength of the cured body. In addition, sulfuric acid, nitric acid, etc. can be added to the orthophosphoric acid decontamination agent as needed, so the radioactive phosphoric acid decontamination waste liquid may contain sulfuric acid, nitric acid, etc., and the content of sulfuric acid, nitric acid, etc. is preferably 5 wt% or less. On the other hand, in one embodiment, the first water content may be 0, that is, the first water content is not added, and the pre-slurry is formed by stirring the waste liquid of radioactive phosphoric acid decontamination.

In step 3000, the pre-slurry is mixed and stirred with the silicon-alumina-oxygen compound for a first time to form a cured slurry. This step may be referred to as a curing slurry forming step. In other words, the silica-alumina composite powder is added to the pre-slurry, and the appropriate water-cement ratio, phosphoric acid and alumina molar ratio are configured. , and the solidified slurry is formed after mixing chains for a period of time. Among them, the radioactive waste acid solidified body is 100wt%, the silicon-aluminum-oxygen compound is more than 30wt%, and the ratio of the weight of water in the pre-slurry to the weight of the silicon-alumina-oxygen compound is between 0.5 and 1, and the pre-process The ratio between the molar number of phosphoric acid in the slurry and the molar number of alumina in the silicon-alumina-oxygen composite is between 1 and 1.9, so as to ensure the mechanical strength of the finally prepared radioactive waste acid solidified body.

Furthermore, if the water-cement ratio is in the range of >0.5 and >1, the solidified body of radioactive acid is too high in viscosity, and the air cannot easily flow out. Mechanical strength. More specifically, in a preferred embodiment, the silicon-alumina-oxygen composite is selected from the group comprising metakaolin, Al ₂ O ₄ ·SiO ₂ and combinations thereof, and the first time is more than 10 minutes. Among them, if the first time is longer than 10 minutes, the phosphoric acid has not dissolved the alumina of the layered structure, resulting in the poor quality of the overall radioactive waste acid solidified body, and the mechanical strength is greatly reduced.

In step 5000, the solidified slurry is allowed to stand at a temperature above the first temperature for a second time to form a solidified body of radioactive waste acid. This step may be referred to as a solidified body growing step. More specifically, the aforementioned solidified slurry is placed in a mold, and dried to harden in a specific temperature range (first temperature) and time range (second time) to form a hardened solidified body. Wherein, the second time is preferably more than 7 days, and the first temperature is preferably between 25 and 45° C., so as to ensure the mechanical strength of the finally prepared solidified body of radioactive waste acid. The range of mechanical strength can reach above 50 kgf/m ² . Furthermore, if the temperature is higher than 25°C, the bonding and curing efficiency will be poor. If the temperature is higher than 45°C, the curing speed will be too fast, which will easily lead to the disintegration of the cured body, which will lead to a significant decrease in the subsequent mechanical strength. If the time is more than 7 days, the bonding and curing time will be too short, and the mechanical strength will also be greatly reduced.

Based on the above, the strength of the solidified body of radioactive acid prepared by the treatment method of radioactive phosphoric acid decontamination waste liquid of the present invention is more than 50kgf/m ² , and the ratio of the volume of the solidified body of radioactive acid to the volume of the waste liquid of radioactive phosphoric acid decontamination Below 1.1, that is, after the solidification treatment of radioactive phosphoric acid decontamination waste liquid, the volume increases within about 10%, and the mechanical strength is sufficient. In addition, due to the direct addition of silicon-alumina-oxygen composite powder curing agent, there is no temperature and rapid hardening during the stirring process. than lower. On the other hand, from a different perspective, the silicon-alumina-oxygen compound added in the treatment method is used as a curing agent for the radioactive phosphoric acid decontamination waste liquid.

The radioactive waste acid solidified body produced by the treatment method of the radioactive phosphoric acid decontamination waste liquid of the present invention is tested as follows.

Example 1: Different curing times (second time)

Take 3.9 kg of 50 w/w% phosphoric acid, 750 g of extra water and 3 kg of metakaolin, the water-cement ratio is 0.9, and the molar ratio of phosphoric acid and alumina is fixed at 1.52. After mixing and stirring all the above materials for 20 minutes (the first time), Pour into molds with a size of 50mm in diameter and 100mm in height, and fill 20 pieces respectively. 20 pieces were cured at 45°C, and 5 pieces of radioactive waste acid solidified body were taken out at 1, 2, 5, and 7 days (second time) respectively, and the mechanical strength was measured, and 5 pieces of radioactive waste acid were measured under each condition. Cured body, and take the average value, the measurement results are shown in Figure 2.

As shown in Fig. 2, the mechanical strengths of the radioactive waste acid cured products prepared with curing time (second time) of 1, 2, 5, and 7 days were 45 kgf/cm ² , 58 kgf/cm ² , and 62 kgf/cm 2 , respectively. cm ² and 68 kgf/cm ² , as the growing time increases, the mechanical strength will gradually increase, and the growing curing time can reach close to the maximum mechanical strength in about 7 days.

Example 2: Different water-cement ratios

Take 1040g of 50 wt% phosphoric acid and 800g of metakaolin, the above conditions are added in each batch of the first water to be 0, 81.26g, 201.26g, 281.3g respectively, the adjustable water-cement ratio is 0.65, 0.75, 0.90, 1, phosphoric acid and alumina The molar ratio is fixed at 1.52. After mixing and stirring all the above materials for 20 minutes, pour them into a mold with a size of 50mm in diameter and a height of 100mm, and fill 20 pieces respectively. Place 20 pieces to cure at 45°C, the cure time (second time) is 7 days, take out the solidified body of radioactive acid, measure the mechanical strength, measure 5 pieces of solidified body of radioactive acid for each condition, and take the average value , the measurement results are shown in Figure 3.

As shown in Figure 3, the mechanical strength of the radioactive waste acid solidified body will gradually decrease with the increase of the water-cement ratio, which are 85 kgf/cm ² , 77 kgf/cm ² , 68 kgf/cm ² , and 55 kgf/cm ² , respectively. Except for the water-cement ratio of 0.65, other solidified bodies can maintain a good solidified body when the growing temperature is 45 degrees, mainly when the water-cement ratio is 0.65, when there is less water, the growing temperature is higher, and the curing speed is faster, resulting in solidification There are cracks in the body, but the more water in the solid body as a whole, it will affect the coagulation speed of the solid body, and generate many pores in the solid body, resulting in a higher water-cement ratio and a decrease in mechanical strength.

Example 3: Different Phosphoric Acid to Alumina Molar Ratios

Adjust the molar ratio of phosphoric acid and alumina to 1.52, 1.65, 1.75, and 1.85, the water-cement ratio to 0.65 and 800g of metakaolin. After mixing and stirring all the above materials for 20 minutes, pour them into a mold with a size of 50mm in diameter and a height of 100mm, and fill them respectively. Pack 20. Place 20 pieces at 25°C for curing, the curing time (second time) is 7 days, take out the solidified body of radioactive waste acid, measure the mechanical strength, measure 5 pieces of solidified body of radioactive waste acid under each condition, and take the average value, The measurement results are shown in Figure 4.

As shown in Figure 4, the mechanical strength increases with the increase of the molar number of phosphate, and the mechanical strengths are 101 kgf/cm ² , 124 kgf/cm ² , 130 kgf/cm ² and 148 kgf/cm ² , respectively. The higher the overall concentration of the radioactive waste acid solidified body, the more effective it can dissolve the alumina in metakaolin, the more solidified body with higher mechanical strength can be effectively polymerized, and the amount of water is adjusted to a minimum, so phosphoric acid and alumina are used. High molar formula As a priority, the mechanical strength is higher.

Example 4: Different growing curing temperatures

Take 3.9 kg of 50 w/w% phosphoric acid, 750 g of the first moisture and 3 kg of metakaolin, the water-cement ratio is 0.9, and the molar ratio of phosphoric acid and alumina is fixed at 1.52. After mixing and stirring all the above materials for 20 minutes, pour the size diameter 50mm and 100mm high molds are filled with 20 pieces respectively. Every 5 pieces were placed at 35°C, 45°C, 65°C, and 75°C for curing, and the curing time (second time) was 7 days, and the radioactive waste acid cured body was taken out for observation. As shown in Figure 5, from left to right are the solidified radioactive acid solidified at 35 °C, 45 °C, 65 °C, and 75 °C, respectively. It can be clearly seen that the solidified radioactive acid solidified at >45 °C has obvious cracks .

Although the foregoing description and drawings have disclosed preferred embodiments of the present invention, it must be understood that various additions, numerous modifications and substitutions may be made to the preferred embodiments of the present invention without departing from the scope of the appended claims The spirit and scope of the principles of the present invention. Those of ordinary skill in the art to which this invention pertains will appreciate that the invention is capable of many modifications in form, structure, arrangement, proportions, materials, elements and assemblies. Therefore, the embodiments disclosed herein should be considered to illustrate the present invention, rather than to limit the present invention. The scope of the present invention shall be defined by the appended claims, including their legal equivalents, and not limited to the foregoing description.

(none)

FIG. 1 is a schematic flowchart of an embodiment of the method of the present invention.

FIG. 2 is the measurement result of the mechanical strength of the radioactive waste acid solidified body obtained by the method of the present invention with different curing times.

FIG. 3 is the measurement result of the mechanical strength of the solidified body of radioactive waste acid obtained by the method of the present invention with different water-cement ratios.

FIG. 4 is the measurement result of the mechanical strength of the solidified body of radioactive waste acid obtained by the method of the present invention with different molar ratios of phosphoric acid and alumina.

Figure 5 is a photograph of the solidified body of radioactive waste acid obtained by the method of the present invention at different curing temperatures.

(none)

Claims (10)

A use of a silicon-alumina-oxygen compound as a curing agent for radioactive phosphoric acid decontamination waste liquid, wherein the content of phosphoric acid in the radioactive phosphoric acid decontamination waste liquid is more than 40wt%, and the water content is less than 60wt%. The use as claimed in claim 1, wherein the silicon-alumina-oxygen composite is selected from the group comprising metakaolin, Al ₂ O ₄ ·SiO ₂ and combinations thereof. A method for treating radioactive phosphoric acid decontamination waste liquid, for preparing a radioactive waste acid solidified body from a radioactive phosphoric acid decontamination waste liquid, comprising: mixing and stirring the radioactive phosphoric acid decontamination waste liquid with a first moisture to form a Putting slurry, wherein the solidified body of radioactive waste acid is 100wt%, the radioactive phosphoric acid decontamination waste liquid is more than 60wt%, and the first moisture is less than 30wt%; the pre-slurry is mixed with a silicon-aluminum-oxygen compound Stir for a first time to form a solidified slurry, wherein the solidified body of the radioactive waste acid is 100wt%, the silicon-alumina-oxygen compound is more than 30wt%, and the weight of the water in the pre-slurry is equal to the silicon-alumina-oxygen The weight ratio of the composite is between 0.5 and 1, and the ratio of the molar number of phosphoric acid in the pre-slurry to the molar number of alumina in the silicon-alumina-oxygen composite is between 1 and 1.9; the curing The slurry is allowed to stand above a first temperature for a second time to form the solidified body of radioactive waste acid. The treatment method according to claim 3, wherein the content of phosphoric acid in the radioactive phosphoric acid decontamination waste liquid is more than 40wt%, and the content of water is less than 60wt%. The processing method of claim 3, wherein the silicon-alumina-oxygen composite is selected from the group consisting of metakaolin, Al ₂ O ₄ ·SiO ₂ and combinations thereof. The processing method according to claim 3, wherein the first time is more than 10 minutes. The processing method according to claim 3, wherein the first temperature is between 25°C and 45°C. The processing method according to claim 3, wherein the first temperature is 25°C, and the second time is more than 7 days. The treatment method according to claim 3, wherein the ratio of the volume of the solidified radioactive acid to the volume of the radioactive phosphoric acid decontamination waste liquid is 1.1 or less. The processing method according to claim 3, wherein the strength of the solidified body of radioactive waste acid is 50 kgf/m ² or more.

Images