Method for immobilizing hazardous metals by fly ash-titanium-bearing blast furnace slag-based geopolymer

Abstract

The present application relates to a method for sealing harmful metals by fly ash-titanium-containing blast furnace slag geopolymer, and belongs to the technical field of harmful metal pollution treatment. The present application uses fly ash and titanium-containing blast furnace slag as main raw materials, and is prepared through steps of baking, mixing with activator, geopolymer pre-sealing and microwave sealing. The synthesized geopolymer has advantages of high temperature resistance, acid, alkali and salt corrosion resistance, small shrinkage rate in freeze-thaw cycle and low permeability coefficient, and is a new type of green building material, which has broad application prospects in sealing harmful metals. The present application realizes industrial production and application of geopolymer synthesized by fly ash and titanium-containing blast furnace slag. The present application uses industrial solid waste as main raw material to prepare new building materials, which can consume a large amount of solid waste containing active silicon and aluminum, and form a three-dimensional network structure geopolymer structure under low temperature and alkali activation conditions, and can seal toxic metal ions in the skeleton structure.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of harmful metal pollution treatment, and particularly relates to a method for solidifying harmful metals by using fly ash-titanium-containing blast furnace slag geopolymer. BACKGROUND

[0002] As a new type of silicate inorganic polymer cementitious material, geopolymer is formed by three-dimensional network structure, amorphous or semi-crystalline silicate cementitious material through alkali activation of active silicate raw materials. It has attracted high attention in many application fields due to its low greenhouse gas emission and excellent properties such as acid resistance and heat resistance. Among them, heavy metal solidification is one of the important application fields. Solidification of heavy metals with geopolymer not only reduces heavy metal pollution, but also the solidified body can be used for other purposes. Compared with traditional cement, lime and glass resin, geopolymer has irreplaceable advantages in energy saving and emission reduction.

[0003] Fly ash is a solid waste mainly collected in flue gas discharged from high-temperature coal-fired power generation, which is a byproduct generated during power generation. Large amounts of fly ash accumulated will slowly release toxic and harmful substances into water and soil. In the case of rain, fly ash will flow into rivers and lakes with rainwater, and also seep into soil with rainwater, causing secondary pollution. Moreover, it has a great impact on the ecological environment.

[0004] Titanium-containing blast furnace slag is a large amount of solid waste generated during the blast furnace ironmaking process. Due to its complex mineral phase structure and dissemination relationship, the titanium component grains dispersed in the slag are fine, which are difficult to recover and utilize by traditional beneficiation technology, resulting in large-scale stockpiling. Not only does it cause environmental pollution and destruction, but also occupies a large amount of land resources, and leads to serious waste of resources.

[0005] In the prior art, the patent application with the application publication number CN111574078A discloses a fly ash-red mud geopolymer activated by carbide slag. The compressive strength of the geopolymer is only 13 MPa, and if it is used to solidify harmful metals, the compressive strength will be greatly reduced, which is difficult to meet the requirements. SUMMARY

[0006] In view of the above problems, the present application aims to provide a method for solidifying harmful metals by using fly ash-titanium-containing blast furnace slag geopolymer. Fly ash and titanium-containing blast furnace slag are used as main raw materials, and the reaction activity is improved by ball milling and alkali activation for the preparation of geopolymer. The synthesized geopolymer has the advantages of high strength, high temperature resistance, acid and alkali salt corrosion resistance, small freeze-thaw cycle body shrinkage rate, low permeability coefficient and low cost.

[0007] In order to achieve the above object, the specific scheme adopted by the present application is:

[0008] A method for sealing harmful metals by fly ash-titanium-containing blast furnace slag geopolymer, taking fly ash and titanium-containing blast furnace slag as basic raw materials, mixing and stirring the fly ash and titanium-containing blast furnace slag uniformly to obtain a raw material mixture, taking the mixture of an alkaline solution and water glass as an activator, pouring the activator into the raw material mixture and stirring uniformly to obtain a mixture, adding a salt containing harmful metals to the mixture and stirring uniformly, pouring the uniform mixture into a mold, placing it on a vibration table to vibrate, and then placing it in a constant temperature and humidity curing box for curing, demolding to obtain a pre-solidified geopolymer, and finally microwave treating the pre-solidified geopolymer to promote the further geopolymerization process of the geopolymer, so that the harmful metal salt is embedded in the three-dimensional network structure of the geopolymer.

[0009] The above method specifically comprises the following steps:

[0010] Step one, drying the titanium-containing blast furnace slag and crushing it with a crusher after drying, and passing it through a 500-mesh sieve, and drying the fly ash and passing it through a 200-mesh sieve, and then preparing them for use;

[0011] Step two, weighing the sieved fly ash and titanium-containing blast furnace slag in step one according to the required mass ratio;

[0012] Step three, weighing the water glass and sodium hydroxide, dissolving the sodium hydroxide in the water glass to obtain an alkali activator;

[0013] Step four, adding the alkali activator to the matrix material and stirring to obtain a mixture;

[0014] Step five, adding a salt containing harmful metals to the mixture and stirring uniformly to obtain a mixture;

[0015] Step six, pouring the uniform mixture into a mold, placing it on a vibration table to vibrate, and then placing it in a constant temperature and humidity curing box for curing, demolding to obtain a pre-solidified geopolymer;

[0016] Step seven, microwave treating the pre-solidified geopolymer to promote the further geopolymerization process of the geopolymer, so that the harmful metal salt is embedded in the three-dimensional network structure of the geopolymer.

[0017] In step one, the drying temperature of the raw materials is 150℃, and the drying time is 8h.

[0018] In step two, the mass ratio of the fly ash and titanium-containing blast furnace slag is between 2:1 and 3:1.

[0019] The titanium blast furnace slag mainly comprises CaO 10-15%, SiO2 20-25%, Fe2O3 5-10%, Al2O3 15-20%, MgO 5-10%, TiO2 15-20% and MnO2 3-5%.

[0020] The fly ash mainly comprises CaO 3-8%, SiO2 45-50%, Fe2O3 5-10%, Al2O3 10-15%, Na2O 3-5%, K2O 2-4% and MgO 5-10%.

[0021] In the third step, the modulus of the water glass solution is 0.5-1.3.

[0022] In the fifth step, the mass of the salt of the harmful metal is 15-20% of the total mass of the fly ash and the titanium-containing blast furnace slag, and the harmful metal comprises one or more metal elements of Cu, Pb, Cd, Cr, Cs, Sr, As and Ni.

[0023] In the sixth step, the temperature of the constant-temperature and constant-humidity curing is 25-30 DEG C, and the time is 6-8 h.

[0024] In the seventh step, the power of the microwave treatment is 400-600 W, and the heating time is 5-8 min.

[0025] The principle of the present application is that the fly ash containing active silicon and aluminum is dissolved in the water glass solution under alkaline conditions to form [SiO(OH)] - , [SiO2(OH)] 2- , [SiO3(OH)] 3- , [Al(OH)4] - ions, and the ions are condensed to form a primary gel, and further condensed to form a three-dimensional network structure.

[0026] The present application has the following advantages: (1) the titanium-containing blast furnace slag can increase the calcareous component in the system, enhance the alkalinity of the system to promote the release of the siliceous and aluminous components, generate C-A-S-H and other hydration products, and with the continuous progress of the geopolymerization reaction, Na + in the alkali activator reacts with the siliceous and aluminous components to generate N-A-S-H gel, and the gel continuously increases and develops, so that the structure is more compact and the strength is improved.

[0027] (2) The present application can maximize the utilization rate of the fly ash and the titanium-containing blast furnace slag to 80%, which not only improves the utilization rate of industrial waste, but also saves energy in production and reduces production cost.

[0028] Since the particle size of the titanium-containing blast furnace slag in the application reaches the nanometer level, the titanium dioxide can accelerate the hydration in the early geopolymerization reaction, the titanium dioxide can refine the pore size of the polymer, has a filling effect in the fly ash pozzolanic reaction and forms a more uniform and solid interface transition zone, effectively reduces the cracks, generates a large amount of high-strength gel and makes the polymer more dense in the geopolymerization reaction. The 7, 28d compressive strength of the geopolymer prepared by using the application can reach 19.26, 30.23 MPa, and the solidification rate of the harmful metal reaches 95%. DETAILED DESCRIPTION

[0029] The application utilizes SiO2, Al2O3 and TiO2 in fly ash and titanium-containing blast furnace slag to cooperatively produce geopolymer, Al2O3 in the geopolymer synthesis process is coordinated with SiO2 and TiO2 to form [AlO4] tetrahedron, and the [AlO4] tetrahedron has a negative charge and an ability to adsorb positive charges, thereby solidifying the harmful metal. 3+ , which is of great significance to the development of circular economy, the maximization of resource value, the protection of ecological environment and the saving of precious land resources, the exertion of the advantages of characteristic resources and the realization of sustainable development.

[0030] The technical solutions of the application will be clearly and completely described below in combination with the embodiments of the application.

[0031] The reagents or raw materials used in the following embodiments are all conventional commercially available products if not specifically stated, and the operations used are all conventional technical means.

[0032] Embodiment 1

[0033] A method for solidifying harmful metal by using fly ash-titanium-containing blast furnace slag geopolymer, comprising the following steps:

[0034] Step one, dry the titanium-containing blast furnace slag at 150 DEG C for 8h, crush it by using a crusher and pass it through a 500-mesh sieve, dry the fly ash at 150 DEG C for 8h and then pass it through a 200-mesh sieve, and wait for use;

[0035] Step two, weigh the sieved fly ash and titanium-containing blast furnace slag in step one according to the required mass ratio of 2:1;

[0036] Step three, weigh the water glass and sodium hydroxide, dissolve the sodium hydroxide in the water glass to obtain an alkali activator with a modulus of 1.2;

[0037] Step four, add 25% of the total mass of the fly ash and titanium-containing blast furnace slag alkali activator into the matrix material and stir to obtain a mixture;

[0038] Step five, add 20% of the total mass of the fly ash and titanium-containing blast furnace slag Pb(NO3)2 into the mixture and mix uniformly;

[0039] Step six, pour the uniform mixture into the mold, placed on the vibration table vibration, curing at 30 ℃ for 8 h, demolding to get pre-solidified polymer;

[0040] Step seven, the pre-solidified polymer is treated with microwave under the condition of power 600 W for 6 min, and then cooled to room temperature to obtain the polymer product.

[0041] The titanium blast furnace slag mainly comprises CaO 10-15%, SiO2 20-25%, Fe2O3 5-10%, Al2O3 15-20%, MgO 5-10%, TiO2 15-20% and MnO2 3-5%.

[0042] The fly ash mainly comprises CaO 3-8%, SiO2 45-50%, Fe2O3 5-10%, Al2O3 10-15%, Na2O 3-5%, K2O 2-4% and MgO 5-10%.

[0043] Example 2

[0044] A method for sealing harmful metals by fly ash-titanium-containing blast furnace slag geopolymer, comprising the following steps:

[0045] Step one, dry the fly ash at 150 ℃ for 8 h, and then sieve through a 200 mesh sieve for use;

[0046] Step two, weigh the sieved fly ash in step one according to requirements;

[0047] Step three, weigh the water glass and sodium hydroxide, dissolve the sodium hydroxide in the water glass to obtain an alkali activator with a modulus of 1.2;

[0048] Step four, add 25% of the total mass of the fly ash alkali activator to the substrate material and stir to obtain a mixture;

[0049] Step five, add 20% of the total mass of the fly ash Pb(NO3)2 to the mixture and mix uniformly;

[0050] Step six, pour the uniform mixture into the mold, placed on the vibration table vibration, curing at 30 ℃ for 8 h, demolding to get geopolymer.

[0051] Example 3

[0052] Step one, dry the fly ash at 150 ℃ for 8 h, and then sieve through a 200 mesh sieve for use;

[0053] Step two, weigh the sieved fly ash in step one according to requirements;

[0054] Step three, weigh the water glass and sodium hydroxide, dissolve the sodium hydroxide in the water glass to obtain an alkali activator with a modulus of 1.2;

[0055] Step four, 25% of the total mass of fly ash alkali activator is added to the substrate material and stirred to obtain a mixture;

[0056] Step five, 5% of the total mass of fly ash Pb(NO3)2 is added to the mixture and mixed evenly

[0057] Step six, the uniform mixture is poured into a mold and placed on a vibration table for vibration, cured at 30°C for 8 h, and demolded to obtain a geopolymer.

[0058] Example 4

[0059] A method for solidifying hazardous metals using fly ash-titanium-containing blast furnace slag geopolymer, comprising the following steps:

[0060] Step one, the titanium-containing blast furnace slag is dried at 150°C for 8 h, crushed by a crusher, and sieved through a 500 mesh sieve, and the fly ash is dried at 150°C for 8 h and sieved through a 200 mesh sieve, ready for use;

[0061] Step two, the sieved fly ash and titanium-containing blast furnace slag in step one are weighed according to the required mass ratio of 2:1;

[0062] Step three, sodium hydroxide and water glass are weighed, the sodium hydroxide is dissolved in the water glass to obtain an alkali activator with a modulus of 1.2;

[0063] Step four, 25% of the total mass of fly ash and titanium-containing blast furnace slag alkali activator is added to the substrate material and stirred to obtain a mixture;

[0064] Step five, 18% of the total mass of fly ash and titanium-containing blast furnace slag Na3AsO4 is added to the mixture and mixed evenly;

[0065] Step six, the uniform mixture is poured into a mold and placed on a vibration table for vibration, cured at 30°C for 8 h, and demolded to obtain a pre-solidified geopolymer;

[0066] Step seven, the pre-solidified geopolymer is subjected to microwave treatment under the condition of power 600W for 6 min, and then cooled to room temperature to obtain a geopolymer product.

[0067] Table 1 Properties of geopolymer of examples 1-4.

[0068] Efficiency of encapsulation of harmful metals 7d compressive strength (MPa) 28d compressive strength (MPa) Example 1 95.4% 19.26 30.23 Example 2 61.6% 7.61 11.28 Example 3 93.2% 12.38 25.36 Example 4 95.6% 19.85 30.37

[0069] It can be seen from the comparison of Example 1 and Example 2 in Table 1 that the fly ash and the titanium-containing blast furnace slag are pre-sealed and then subjected to microwave treatment, so that the sealing rate and the compressive strength of the harmful metal Pb are effectively improved. It can be seen from the comparison of Example 2 and Example 3 that the fly ash is only pre-sealed, so that only about 5% of the harmful metal salts can be sealed, and the mechanical properties of the geopolymer are obviously decreased due to too much harmful metal salts. Example 4 shows that the fly ash and the titanium-containing blast furnace slag are pre-sealed and then subjected to microwave treatment, so that various harmful metal salts can be sealed.

[0070] The above examples are only used to illustrate the technical solutions of the present application but not to limit the present application. It should be understood by those skilled in the art that the specific embodiments of the present application can be modified or replaced equivalently with reference to the above examples, and any modification or equivalent replacement without departing from the spirit and scope of the present application is within the protection scope of the claims.

Claims

1. A method for solidifying harmful metals using fly ash-titanium-containing blast furnace slag-based polymers, characterized in that, Includes the following steps: Step 1: Pre-treat the fly ash and titanium-containing blast furnace slag separately, including drying, crushing, and sieving, for later use. The titanium-containing blast furnace slag comprises the following components by mass percentage: CaO 10-15%, SiO2 20-25%, Fe2O3 5-10%, Al2O3 15-20%, MgO 5-10%, TiO2 15-20%, and MnO2 3-5%. The fly ash comprises the following components by mass percentage: CaO 3-8%, SiO2 45-50%, Fe2O3 5-10%, Al2O3 10-15%, Na2O 3-5%, K2O 2-4%, and MgO 5-10%. The titanium-containing blast furnace slag is dried in a drying oven at 150℃ for 8 hours, then crushed and sieved through a 500-mesh sieve. The fly ash is dried in a drying oven at 150℃ for 8 hours, then crushed and sieved through a 200-mesh sieve. Step 2: Mix the pretreated fly ash from Step 1 with titanium-containing blast furnace slag and stir evenly to obtain Mixture I; the mass ratio of fly ash to titanium-containing blast furnace slag is between 2:1 and 3:

1. Step 3: Mix water glass and an alkaline substance to form a solution as an alkaline activator; the alkaline activator is a water glass solution with a modulus of 0.5~1.3; Step 4: Pour the alkali activator into the mixture I and stir evenly to obtain a mixture; the mass of the alkali activator is 20-35% of the total mass of the fly ash and titanium-containing blast furnace slag; Step 5: Add the salt containing harmful metals to the mixture and stir evenly to obtain mixture II; the mass of the salt containing harmful metals is 15-20% of the total mass of the fly ash and titanium-containing blast furnace slag; the harmful metals include one or more of the following metallic elements: Cu, Pb, Cd, Cr, Cs, Sr, As and Ni. Step 6: Pour the mixture II into a mold, place it on a vibration table and vibrate, then place it in a constant temperature and humidity curing chamber for curing at a temperature of 25~30℃ for 6~8 hours. Demold to obtain the pre-cured geopolymer. Step 7: Microwave treatment is performed on the pre-cured geopolymer to promote further geological polymerization of the geopolymer, so that the harmful metal salt is embedded in the three-dimensional network structure of the geopolymer. The microwave treatment power is 400~600W and the heating time is 5~8 minutes.