CN109987905B

CN109987905B - Composite gelled material for solidifying active metal-containing radioactive waste

Info

Publication number: CN109987905B
Application number: CN201711464287.3A
Authority: CN
Inventors: 不公告发明人
Original assignee: 63653 Troops of PLA
Current assignee: 63653 Troops of PLA
Priority date: 2017-12-29
Filing date: 2017-12-29
Publication date: 2021-11-09
Anticipated expiration: 2037-12-29
Also published as: CN109987905A

Abstract

The invention belongs to the field of building materials, and discloses a composite cementing material for solidifying radioactive wastes containing active metals, which is prepared from the following raw materials in parts by weight: is prepared from cement (40-70 wt. portions), slags (10-20), zeolite (5-20), metakaolin (5-20) and additive (0-12.5). The invention can reduce pH value and free water content, ensure strength, and has simple process and convenient application, and can be used as a matrix for packaging radioactive waste and a structural material of a storage and disposal facility, and the like.

Description

Composite gelled material for solidifying active metal-containing radioactive waste

Technical Field

The invention belongs to the field of building materials, relates to the acquisition of a composite cementing material for solidifying aluminum-containing radioactive wastes, provides a novel composite cementing material, and has important practical value.

Background

The high pH and free water portland cement systems are not suitable as solidification matrices for certain low-to-medium waste, which have corrosive effects on the active metals aluminum, magnesium, uranium, lead, etc. The corrosion of the reactive metal can cause the volume of the cured body to change and generate a large amount of hydrogen, resulting in internal stress in the cured body, causing cracking of the cement and deformation of the cured body, and ultimately failure of the waste bag. Meanwhile, the generation of hydrogen can bring fire hazard and even explosion risk. The pH value of the slurry is reduced, the free water content is limited, and the corrosion reaction of a gelling system to metal is reduced. At present, the cementing systems which are confirmed to be possible to replace ordinary portland cement at home and abroad are as follows: alkali-activated slag cement, aluminate cement, sulphoaluminate cement, magnesium phosphate cement, phosphate-modified calcium aluminate cement and the like. However, research on these alternative gelling systems has limited literature, particularly in the application of radioactive waste solidification. Generally, these cements are used to replace portland cement for high acidity, high sulfate concentration, high temperature environments, or where rapid hardening is required.

Literature search reveals: yanghui et al, 2007, 5: 513 Astro 515, a publication of 'study on adaptability of neutral salt-slag-fly ash cementing material to consolidation of nuclear waste', Na₂SO₄-slag-fly ash cementitious material, CaSO₄-slag-fly ash cement and Na₂SO₄-CaSO₄The slag-fly ash cementing material has the characteristics of pH value of 11.0-11.6, strength of about 10.0-22.0 MPa in 28-day age, weak corrosion to metal Al and low free water content, and can be used as a cementing material system for consolidating radioactive wastes. However, only the fresh slurry was filled in the polypropylene can containing the aluminum strips, and the test for corrosion of Al was conducted to observe the presence or absence of swelling and cracking, and the quantitative test for corrosion gas generation of the cementitious material and Al was not conducted. ②Zhangbo et al 2011, 5: 1-3, published in the publications cement: the article of the research on the pH value change of the pore liquid phase of the silicate and sulphoaluminate composite cement shows that the pH values of the pore solutions of the silicate and sulphoaluminate composite cement with different proportions are lower than 3 hours of hydration, most of the pH values are above 12.50 after 1 day, and the pH value reaches the highest value when the pore solutions of the silicate and sulphoaluminate composite cement are hydrated for 3 days. The pH value of the composite cement hydrated for about 3h will have a trough between 20% and 80% of SAC dosage, and the pH value is the lowest when the SAC dosage is 60%. ③ luhuaming et al, 2012, 11: 11 to 14, published in the publications of Cement: the article of 'influence of the pH value of the silica powder on the performance of the high-alumina low-cement casting material', namely the pH value of the silica powder can obviously influence the fluidity of the casting material, and the casting material can obtain good fluidity when the pH value of the silica powder is between 5.5 and 8.5. The hardening time of the casting material is shortened along with the increase of the pH value of the silicon micropowder, and when the pH value exceeds 8.5, the hardening of the casting material is accelerated. When the pH value of the silica micropowder is 7-8, the strength of the castable is the best, and the improvement of the strength of the castable is not facilitated when the pH value is too high or too low. (r.) fans after manipulating the string of alkali-activated slab Na. Na, published by Wang, S.D. et al, 1994, Vol.24, number 6, pp. 1033-₂SO₄In a slag exciting system, 5-10% of lime or cement clinker is added, so that the strength can be improved only, and the system is not suitable for solidifying medium and low-level waste containing active metals, because the pH value of the system is enough to cause metal corrosion. Paul David Swift researches The solidification research of Phosphate, fly ash and boric acid modified Calcium-aluminium Phosphate Cement on aluminium-containing Radioactive Waste in a doctor paper of 2013, 12, wherein The pH value is between 8 and 10, The corrosion rate of aluminium is low in The first 55 to 65 days, The gas production is about 0.07L/(h.m), and then The gas production is increased to 0.4 to 0.5L/(h.m) until The end of experimental monitoring. The corrosion of aluminum is greatly increased and even exceeds that of blast furnace slag modified portland cement and fly ash modified calcium aluminate cement materials. In summary, although the problem of corrosion of aluminum in cement has received a high degree of attention in the nuclear industry, the open research literature is still very muchAt present, no treatment strategy specially aiming at the active metal waste exists.

Disclosure of Invention

The purpose of the invention is as follows: aiming at the defects that free water and high-alkalinity pore solution in curing systems such as ordinary portland cement, composite portland cement and the like are easy to corrode and react with active metal aluminum in radioactive waste to generate a large amount of hydrogen and cause over-expansion and even damage of the system, the invention adopts low-alkalinity cement, adds slag, zeolite and metakaolin, prepares the composite gelled material by compounding the low water-cement ratio and the high-efficiency water reducing agent, obtains the composite gelled material with high fluidity, low alkalinity, low free water content and high strength, can be used as a matrix for packaging the radioactive waste and has special requirements on alkalinity, and can also be used as a structural material of storage and disposal facilities and the like.

The technical scheme is as follows: the raw materials are prepared according to parts by weight: is prepared from cement (40-70 wt. portions), slags (10-20), zeolite (5-20), metakaolin (5-20) and additive (0-12.5).

The invention adds powder materials in steps to stir and form: adding 20-40 parts of water into a planetary stirrer containing 2-5 parts of water reducing agent, starting a power supply, meeting the JC/T681 requirement, and stirring at a low speed for 2 minutes; then sequentially adding 10-17.5 parts of cement, 10-20 parts of slag, 5-20 parts of zeolite and 5-20 parts of metakaolin, adding 0-12.5 parts of additive, and stirring at low speed for 2 minutes; then adding 20-35 parts of cement, and stirring at low speed for 2 minutes; and finally, adding 10-17.5 parts of cement, and stirring at a high speed for 5 minutes, wherein the cement with more parts by weight is added in three parts and stirred, and the proportions of the three parts are respectively one quarter, one half and one quarter.

The water reducing agent is a naphthalene water reducing agent or a polycarboxylate water reducing agent;

the cement comprises slag cement, aluminate cement, low-alkalinity sulphoaluminate cement and composite sulphoaluminate cement. These cements contain little or no substance C₃S, after hydration, Ca (OH) is also generated₂However, Ca (OH)₂The content of the silicate cement is far less than that of the silicate cement, and the silicate cement belongs to green and environment-friendly cement.

The slag refers to S105-grade granulated blast furnace oreThe specific surface area of the slag is 460-500m²·kg^-1. The zeolite has a bulk volume of 1000-1150 kg.m^-3The specific surface area is 300-350m²·kg^-1. Metakaolin refers to a metastable substance formed after calcination, and the specific surface area is 3000-3400m²·㎏^-1The pozzolanic activity is determined by the Chapelle method to be 1g metakaolin absorbing more than 1000mgCa (OH)₂。

The additive is one or more of micro silicon powder, bentonite, calcium carbonate powder and dolomite powder, and is used for adjusting the grain composition and the fluidity of the mixture of the cementing material and reducing the content of the active cementing material.

Advantageous effects

The invention realizes the reduction of pH value and free water content and simultaneously ensures the strength. The method has simple process and convenient application, can be used as a matrix for packaging radioactive wastes and has special requirements on alkalinity, and can also be used as a structural material of storage and disposal facilities, and the like. The obtained net paste has the fluidity of 235 mm and no bleeding, the pH value is =10.63, the 3d compressive strength of the mortar sample reaches 40MPa, the 7d compressive strength reaches 53MPa, and the 28d compressive strength reaches 65 MPa. The corrosion of aluminum is greatly reduced and is far lower than that of blast furnace slag modified Portland cement and modified calcium aluminate cement materials.

Drawings

FIG. 1 is a schematic diagram of a test for measuring hydrogen generation using a water discharge experimental setup;

in fig. 1: 1-iron stand table; 2-500 volumetric flasks; 3-20 g of porous aluminum particles; 4-rubber connecting pipe; 5, measuring cylinder; 6, beaker; as shown in fig. 1: fixing the slurry 2 on the slurry 1, injecting the prepared slurry into the slurry 2 containing the slurry 3, connecting one end of the slurry 4 with the port 2, sealing with epoxy resin, placing the water-filled slurry 5 upside down in the water-filled slurry 6, inserting the other end of the slurry 4 into the slurry 5, and measuring the generation of hydrogen by a drainage method.

Fig. 2 is a schematic view of a sealing device simulation test.

In fig. 2: 1-leak detection hole; 2-built-in beaker, size d =185mm, h =274 mm; 3, an outer cylinder of the sealing device, wherein the size of d =220mm, and h =300 mm; 4-absolute pressure transmitter; 5-temperature test point; 6- (B)200g of porous aluminum block; 7-temperature sensor; 8-temperature and pressure test recorder; 9-gas flow meter; 10-rubber connecting pipe; 11-measuring cylinder; 12-gas flow recorder; 13-beaker; as shown in fig. 2: the sealing device adopts a nested structure consisting of 2 (inner layer) and 3 (outer steel die), the upper part of the device is designed with a 1 for detecting leakage before testing, and the leakage rate of the sealing device is detected to be 5.0 multiplied by 10 by a helium mass spectrum leakage detection method^-7Pa·m³And s. The prepared slurry is injected into a device containing 6, equipped with 4 (pressure) and 7 (temperature) measurement control interfaces, respectively connected with 8 and 12, to display and record temperature and pressure data, and simultaneously installed with 9, to record gas flow, then one end of 10 is connected with 9, and the other end is inserted into an inverted 11 filled with water, and the generation of hydrogen is measured by a drainage method.

Detailed Description

The invention is further illustrated by means of examples

Example 1:

adding 40 parts of water into a planetary stirrer containing 2 parts of naphthalene water reducing agent, starting a power supply, meeting the JC/T681 requirement, and stirring for 2 minutes at a low speed; then, 12.5 parts of 52.5-grade aluminate cement, 10 parts of slag, 20 parts of zeolite and 20 parts of metakaolin are sequentially added, and the mixture is stirred at a low speed for 2 minutes; then adding 25 parts of 52.5-grade aluminate cement, and stirring at a low speed for 2 minutes; finally, 12.5 parts of 52.5-grade aluminate cement is added, and the mixture is stirred at a high speed for 5 minutes. The obtained slurry is tested according to national standards GB/T8077-2012, JC/T2153-2012 and GB/T17671-1999, the net slurry fluidity is 250 mm, no bleeding exists, the pH =11.18, the 3d compressive strength is 22.0MPa, the 7d compressive strength is 34.6MPa, and the 28d compressive strength is 43.2 MPa; the gas production rate of the reaction with 20g of ground porous aluminum is tested according to the method shown in the attached figure 1, the gas production reaction is started after about 9h, the maximum value of 3.05 mL/h/g is reached after 22h, and the gas production is stopped after 190 h.

Example 2:

adding 35 parts of water into a planetary stirrer containing 2 parts of naphthalene water reducing agent, starting a power supply, meeting the JC/T681 requirement, and stirring for 2 minutes at a low speed; then sequentially adding 10 parts of 32.5-grade composite sulphoaluminate cement, 20 parts of slag, 10 parts of zeolite and 12.5 parts of metakaolin, and stirring at low speed for 2 minutes; then 25 parts of 32.5-grade composite sulphoaluminate cement and 2.5 parts of silica fume are added in sequence, and the mixture is stirred at low speed for 2 minutes; finally, 10 parts of 32.5-grade composite sulphoaluminate cement is added and stirred at high speed for 5 minutes. The obtained slurry is tested according to national standards GB/T8077-2012, JC/T2153-2012 and GB/T17671-1999, the net slurry fluidity is 240 mm, no bleeding exists, the pH =10.15, the 3d compressive strength is 18.8MPa, the 7d compressive strength is 26.2MPa, and the 28d compressive strength is 40.0 MPa; the gas production reaction is started after about 8 hours, the maximum value of 0.193 mL/h/g is reached after 22 hours, and the gas production is stopped after 100 hours according to the method shown in the attached figure 1.

Example 3:

adding 35 parts of water into a planetary stirrer containing 2 parts of naphthalene water reducing agent, starting a power supply, meeting the JC/T681 requirement, and stirring for 2 minutes at a low speed; then sequentially adding 10 parts of 32.5-grade low-alkalinity sulphoaluminate cement, 20 parts of slag, 20 parts of zeolite and 20 parts of metakaolin, and stirring at low speed for 2 minutes; then 30 parts of 10 parts of 32.5-grade low-alkalinity sulphoaluminate cement is added, and the mixture is stirred at a high speed for 5 minutes. The obtained slurry is tested according to national standards GB/T8077-2012, JC/T2153-2012 and GB/T17671-1999, the net slurry fluidity is 240 mm, no bleeding exists, the pH =10.15, the 3d compressive strength is 15.6MPa, the 7d compressive strength is 22.1MPa, and the 28d compressive strength is 35.6 MPa; the gas production rate of the reaction with 20g of ground porous aluminum is tested according to the method shown in the attached figure 1, the gas production reaction is started after about 10 hours, the maximum value of 0.189 mL/h/g is reached after 30 hours, and the gas production is stopped after 100 hours. The raw materials in the proportion are stirred by a 15L mortar stirrer, the highest temperature of 46.1 ℃ is reached when hydration is carried out for 5 hours by adopting a method shown in figure 2, the highest pressure is 94.4 KPa, the pressure is reduced to negative pressure after 15 hours, and the final pressure is 73KPa respectively.

Example 4:

adding 20 parts of water into a planetary stirrer containing 5 parts of polycarboxylate water reducing agent, starting a power supply, meeting the JC/T681 requirement, and stirring for 2 minutes at a low speed; then, 15 parts of 32.5-grade low-alkalinity sulphoaluminate cement, 20 parts of slag, 10 parts of zeolite and 10 parts of metakaolin are sequentially added, and the mixture is stirred at low speed for 2 minutes; then sequentially adding 30 parts of 32.5-grade low-alkalinity sulphoaluminate cement, and stirring at a low speed for 2 minutes; and finally, adding 15 parts of 32.5-grade low-alkalinity sulphoaluminate cement, and stirring at a high speed for 5 minutes. The obtained slurry is tested according to national standards GB/T8077-2012, JC/T2153-2012 and GB/T17671-1999, the net slurry fluidity is 235 mm, no bleeding exists, the pH =10.67, the 3d compressive strength is 30.1MPa, the 7d compressive strength is 38.9MPa, and the 28d compressive strength is 43.2 MPa; the gas production rate of the reaction with 20g of ground porous aluminum is tested according to the method shown in the attached figure 1, the gas production reaction is started within about 5.5h, the maximum value of 0.12 mL/h/g is reached within 7.5h, and the gas production is stopped after 96 h.

Example 5:

adding 22 parts of water into a planetary stirrer containing 5 parts of polycarboxylate water reducing agent, starting a power supply, meeting the JC/T681 requirement, and stirring for 2 minutes at a low speed; then, 17.5 parts of 32.5-grade low-alkalinity sulphoaluminate cement, 20 parts of slag, 5 parts of zeolite and 5 parts of metakaolin are sequentially added, and the mixture is stirred at low speed for 2 minutes; then, 35 parts of 32.5-grade low-alkalinity sulphoaluminate cement are sequentially added, and the mixture is stirred at a low speed for 2 minutes; finally, 17.5 parts of 32.5-grade low-alkalinity sulphoaluminate cement is added, and the mixture is stirred at a high speed for 5 minutes. The obtained slurry is tested according to national standards GB/T8077-2012, JC/T2153-2012 and GB/T17671-1999, the net slurry fluidity is 235 mm, no bleeding exists, the pH =10.63, the 3d compressive strength is 37.6MPa, the 7d compressive strength is 48.7MPa, and the 28d compressive strength is 55.6 MPa; the gas production rate of the reaction with 20g of ground porous aluminum was measured according to the method shown in FIG. 1, and the gas production reaction started after about 70h, with a reaction rate of 0.03 mL/h/g.

Example 6

Adding 22 parts of water into a planetary stirrer containing 5 parts of polycarboxylate water reducing agent, starting a power supply, meeting the JC/T681 requirement, and stirring for 2 minutes at a low speed; then, 15 parts of 42.5-grade low-alkalinity sulphoaluminate cement, 20 parts of slag, 10 parts of zeolite and 10 parts of metakaolin are sequentially added, and the mixture is stirred at low speed for 2 minutes; then, 30 parts of 42.5-grade low-alkalinity sulphoaluminate cement is added in sequence and stirred at low speed for 2 minutes; and finally, adding 15 parts of 42.5-grade low-alkalinity sulphoaluminate cement, and stirring at a high speed for 5 minutes. The obtained slurry is tested according to national standards GB/T8077-2012, JC/T2153-2012 and GB/T17671-1999, the net slurry fluidity is 240 mm, no bleeding exists, the pH =10.63, the 3d compressive strength is 41.0MPa, the 7d compressive strength is 49.4MPa, and the 28d compressive strength is 59.6 MPa; the test and 20g of ground porous aluminum were tested according to the method shown in FIG. 1, and the hydrogen evolution was not detected after 180 days of monitoring.

Claims

1. A preparation method of a composite cementing material for solidifying radioactive wastes containing active metals is characterized by comprising the following steps:

s1, constructing a simulation test sealing device of the composite cementitious material slurry, adopting a nested structure consisting of a built-in beaker (2) and a sealing device outer cylinder (3), designing a leakage detection hole (1) at the upper part of the simulation test sealing device for detecting leakage before testing, and detecting that the leakage rate of the sealing device is 5.0 multiplied by 10 by adopting a helium mass spectrometry leakage detection method^-7Pa·m³The temperature and pressure measuring device comprises a sealing device, a built-in beaker (2) and a rubber connecting pipe, wherein the built-in beaker (2) is internally provided with a porous aluminum block (6), an outer cylinder (3) of the sealing device is provided with an absolute pressure transmitter (4) and a temperature sensor (7), the absolute pressure transmitter (4) and the temperature sensor (7) are respectively and correspondingly connected with a temperature and pressure test recorder (8) and a gas flow recorder (12) so as to display and record temperature and pressure data, a gas flowmeter (9) is installed to record gas flow, one end of the rubber connecting pipe (10) is connected with the gas flowmeter (9), and the other end of the rubber connecting pipe is inserted into an inverted measuring cylinder (11) filled with water;

s2, preparing the following raw materials in parts by weight: the cement-based cement mortar consists of 40-70 parts of cement, 10-20 parts of slag, 5-20 parts of zeolite, 5-20 parts of metakaolin, 0-12.5 parts of additive and 2-5 parts of water reducing agent; adding powder materials in steps, stirring and forming: adding 20-40 parts of water into a planetary mixer containing 2-5 parts of water reducing agent, according with JC/T681 requirements, and stirring for 2 minutes at a low speed; then sequentially adding 10-17.5 parts of cement, 10-20 parts of slag, 5-20 parts of zeolite and 5-20 parts of metakaolin, adding 0-12.5 parts of additive, and stirring at low speed for 2 minutes; then adding 20-35 parts of cement, and stirring at low speed for 2 minutes; finally, 10-17.5 parts of cement is added, and the mixture is stirred at a high speed for 5 minutes to prepare composite cementitious material slurry, wherein the cement with more parts by weight is added in three parts and stirred, and the proportions of the three parts are respectively one quarter, one half and one quarter;

the cement comprises slag cement, aluminate cement, low-alkalinity sulphoaluminate cement and composite sulphoaluminate cement;

the slag refers to S105-grade granulated blast furnace slag, and the specific surface area is 460-500m² · kg^-1The zeolite is 1000-1150 kg.m with bulk volume^-3The specific surface area is 300-350m² · kg^-1Metakaolin refers to a metastable substance formed after calcination, and the specific surface area is 3000-3400m² · kg^-1The pozzolanic activity is determined by the Chapelle method to be that 1g of metakaolin absorbs more than 1000mg of Ca (OH)₂ ；

The additive is one or more of micro silicon powder, bentonite, calcium carbonate powder and dolomite powder;

s3, injecting the prepared composite gelled material slurry into a built-in beaker (2) containing a porous aluminum block (6) in a simulation test sealing device, then inserting the other end of a rubber connecting pipe (10) into an inverted measuring cylinder (11) filled with water, and measuring the generation of hydrogen by adopting a drainage method.