CN114712767B - Method for fixing chlorine and stabilizing heavy metal in fly ash - Google Patents
Method for fixing chlorine and stabilizing heavy metal in fly ash Download PDFInfo
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- A—HUMAN NECESSITIES
- A62—LIFE-SAVING; FIRE-FIGHTING
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- A62D3/00—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances
- A62D3/30—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents
- A62D3/33—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents by chemical fixing the harmful substance, e.g. by chelation or complexation
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- A—HUMAN NECESSITIES
- A62—LIFE-SAVING; FIRE-FIGHTING
- A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
- A62D2101/00—Harmful chemical substances made harmless, or less harmful, by effecting chemical change
- A62D2101/08—Toxic combustion residues, e.g. toxic substances contained in fly ash from waste incineration
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- A—HUMAN NECESSITIES
- A62—LIFE-SAVING; FIRE-FIGHTING
- A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
- A62D2101/00—Harmful chemical substances made harmless, or less harmful, by effecting chemical change
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- A62D2101/00—Harmful chemical substances made harmless, or less harmful, by effecting chemical change
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- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
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Abstract
The invention discloses a method for chlorine fixation and heavy metal stabilization of fly ash, belonging to the technical field of hazardous waste treatment. The method comprises the following steps: s1, mixing fly ash, red mud, steel slag powder, fly ash and limestone, then carrying out ball milling, adding water, and then carrying out sealed aging to obtain an aging mixture; s2, carrying out sectional roasting on the aged mixture obtained in the step S1, wherein the specific operation is as follows: keeping the temperature at 103-110 ℃ for 30-120 min, then quickly heating to above 650 ℃, continuously and slowly heating to 700-900 ℃, keeping the temperature for 1-3 h, and then cooling to room temperature to obtain a roasted mixture; and S3, adding water into the roasting mixture obtained in the step S2, and forming and curing to obtain a fly ash solidified body. The method can convert soluble chloride salt into various insoluble double salts, reduce the content of the soluble salt and simultaneously generate a chlorine-fixing product Kuzel's salt Ca 4 [Al(OH) 6 ] 2 Cl(SO 4 ) 0.5 ·6H 2 O can promote the solidification and stabilization of heavy metals, and realizes the high-efficiency stabilization of soluble salts and heavy metals in the fly ash.
Description
Technical Field
The invention belongs to the technical field of hazardous waste treatment, and particularly relates to a method for fixing chlorine and stabilizing heavy metals in fly ash.
Background
The fly ash refers to substances collected in a heat recycling system and a flue gas purification system after household garbage incineration, medical waste incineration and industrial production incineration. In the incineration process, volatile heavy metals and chlorides with lower melting points can be condensed and enriched on the surfaces of fly ash particles, and the condensed fly ash is enriched with a large amount of soluble chlorides, heavy metals and other substances. The fly ash belongs to dangerous waste, and is required to be subjected to harmless treatment according to technical code of pollution control of fly ash from incineration of household garbage (trial) (HJ 1134-2020). Leaching and solidification are common methods for the harmless disposal of fly ash. Soluble chlorine salt and heavy metal in the fly ash can be removed by leaching treatment, but the secondary pollution problem of leacheate can be generated; solidification stabilization can be carried out on heavy metals in fly ash through an organic chelating agent or an inorganic curing agent, but soluble chlorine salt in fly ash cannot be solidified, so that salting-out affects long-term stability of a solidified body.
At present, more than 1000 million tons of fly ash need to be treated every year in China, and a safe treatment technology with high efficiency and low cost needs to be found urgently. Chinese patent CN106377867A discloses a waste incineration fly ash heavy metal curing agent and a curing method thereof, wherein the curing agent comprises an aluminum-rich high-silicon material and an alkaline activator, calcium oxide, chloride and sulfide which are abundantly present in the waste incineration fly ash and the aluminum-rich high-silicon material are subjected to hydration reaction to generate calcium silicate hydrate (C-S-H), a calcium chloroaluminate (Friedel) phase and an ettringite (AFt) phase system, a solid solution is formed through ion exchange in the formation process of the mineral system, a new phase is formed through coprecipitation, and the heavy metal is strongly stably bound by physical adsorption and wrapping. However, the curing agent can only absorb stable heavy metals and cannot cure soluble chlorine salt in fly ash.
In addition, no document or patent technology discloses that the fly ash is subjected to chlorine fixing treatment by using mullite, and a characteristic chlorine fixing product (Kuzel's salt) is generated and regulated for solidification and stabilization of heavy metals. The present invention has been made in view of this point.
Disclosure of Invention
Aiming at the dual problem that soluble chloride and heavy metal in fly ash are difficult to fix, the invention aims to provide a method for stabilizing fly ash chloride and heavy metal 4 [Al(OH) 6 ] 2 Cl(SO 4 ) 0.5 ·6H 2 O can promote the solidification and stabilization of heavy metals, and realizes the high-efficiency stabilization of soluble salts and heavy metals in the fly ash.
In order to achieve the purpose, the specific technical scheme of the invention is as follows:
a method for stabilizing chlorine fixation and heavy metals of fly ash comprises the following steps:
s1, mixing fly ash, red mud, steel slag powder, fly ash and limestone, performing ball milling to obtain a solid-waste mixture, adding water, and performing sealed ageing to obtain an ageing mixture;
s2, carrying out sectional roasting on the aging mixture obtained in the step S1, wherein the operation is as follows: keeping the temperature at 103-110 ℃ for 30-120 min, then quickly heating to above 650 ℃, continuously and slowly heating to 700-900 ℃, keeping the temperature for 1-3 h, and then cooling to room temperature to obtain a roasted mixture;
and S3, adding water into the roasting mixture obtained in the step S2, and forming and curing to obtain a fly ash solidified body.
The fly ash is mixed and ground with the red mud, the steel slag powder, the fly ash and the limestone, then the mixture is roasted in sections, and finally water is added for molding and maintenance to obtain a fly ash solidified body. The method can convert soluble chloride salt into various insoluble double salts, reduce the content of the soluble salt and simultaneously generate a chlorine-fixing product Kuzel's salt Ca 4 [Al(OH) 6 ] 2 Cl(SO 4 ) 0.5 ·6H 2 O can promote the solidification and stabilization of heavy metals, and realizes the high-efficiency stabilization of soluble salts and heavy metals in the fly ash.
Wherein, the steel slag and the limestone provide an alkaline calcium source, and the red mud provides an alkaline and active aluminum source; alkaline calcium source and soluble chloride (NaCl or KCl) in fly ash form calcium hydroxychloride CaOHCl at about 105 ℃, see reactions (1) - (3); the mullite contained in the fly ash reacts with CaOHCl at the temperature of 650-900 ℃ to generate Wadalite phase Ca 6 Al 5 Si 2 O 16 Cl 3 And generating reducing gas HCl, see reaction (4); calcium carbonate in the solid waste can generate CaOHCl under the atmosphere of HCl, see reaction (5), and continuously reacts with mullite to generate Wadalite; wadalite is a stable water-insoluble mineral, and Cl is wrapped in [ SiO ] 4 ]And [ AlO 4 ]In the formed tetrahedron structure, the chlorine fixing effect is achieved, and the reaction principle in the whole process is as follows:
the steel slag, limestone and red mud are all alkaline materials, and the aging mixture discharges acidic gas CO after being roasted 2 The alkalinity of the system is enhanced, the hydration reaction of the roasted mixture can be promoted, and the calcium-aluminum activity of the roasted system is enhanced; by using the alkalinity of the roasting mixture and the active calcium-aluminum components, the hydration product Kuzel's salt Ca is generated under the action of hydration 4 [Al(OH) 6 ] 2 Cl(SO 4 ) 0.5 ·6H 2 O, the reaction principle is as follows:
3Ca(OH) 2 +Al 2 O 3 +0.5CaCl 2 +0.5CaSO 4 +3H 2 O→Ca 4 [Al(OH) 6 ] 2 Cl(SO 4 ) 0.5 ·6H 2 O (6)
the Kuzel's salt belongs to a bimetallic interlayer metal hydroxide, has low solubility product, can solidify heavy metal containing oxyanion, is a water-insoluble mineral, converts soluble chloride into the water-insoluble mineral and can also play a role in chlorine fixation. Kuzel's salts belong to the chlorothio solid solution, in contrast to the Friedel's salt Ca 4 [Al(OH) 6 ] 2 Cl 2 ·6H 2 O, the solubility product is lower, the stability is higher, the ion exchange capacity with heavy metal is stronger, and the solidification and stabilization of the heavy metal can be promoted. The ion exchange process of Kuzel's salts with heavy metals is as follows:
the reason why the process of the present invention is capable of producing Kuzel's salts is as follows:
the non-chlorine-fixed fly ash is solidified by the cementing material, because the solubility of the chlorine-containing mineral phase is much higher than that of the sulfate-containing mineral phase. Therefore, cl in the pore solution of the micro-area is in the hydration process - Concentration ratio of
Is higher than 1 order of magnitude, so that Cl is generated - Predominantly induces the production of Friedel's salt, and
an ettringite mineral phase is produced with the calcium-aluminum base.
But the hair is sentFirstly, the Wadalite phase is generated by roasting, so that the content of soluble chloride NaCl and KCl in fly ash is greatly reduced, and then Cl in pore liquid in the hydration process is coordinated and matched - And
induced to produce Kuzel's salt, but not Friedel's salt Ca 4 [Al(OH) 6 ] 2 Cl 2 ·6H 2 O。
Preferably, the fly ash, the red mud, the steel slag powder and the fly ash are in parts by weight as follows: 100 parts of fly ash, 5-15 parts of red mud, 5-15 parts of steel slag powder, 10-20 parts of fly ash and 10 parts of limestone.
Preferably, the contents of free calcium oxide and free magnesium oxide in the steel slag powder satisfy the following formula:
(w 1 +w 2 )×m 1 ≥1；
w 1 the content of free calcium oxide in the steel slag powder is percent; w is a 2 Is the content of free magnesium oxide in the steel slag powder percent; m is 1 Is the weight portion of the steel slag powder.
Preferably, the fly ash is F-grade fly ash, and SiO in the fly ash 2 、Al 2 O 3 And Fe 2 O 3 The total mass of the components is not less than 70 percent.
Preferably, in the step S1, the mass of the added water is 20-30% of the total mass of the fly ash, the red mud, the steel slag powder, the fly ash and the limestone; the sealing and aging time is 24h.
Preferably, in step S2, the heating rate is not lower than 10 ℃/min within the range of 500-650 ℃, and the heating rate is not higher than 2 ℃/min within the range of 700-900 ℃. Because the generated CaOHCl can generate side reaction at 500-550 ℃, and can be decomposed into CaCl 2 CaO, which is required to be rapidly heated at 500-650 ℃ in order to reduce the occurrence of side reactions; on the other hand, 700 to 900 ℃ is the main reaction zone of the reaction formulae (4) and (5), and therefore, the temperature needs to be raised slowly to allow the main reaction to proceed sufficiently.
Preferably, in step S2, the step of baking comprises the following specific operations: keeping the temperature at 105 ℃ for 30-120 min, then quickly heating to above 650 ℃, continuously and slowly heating to 900 ℃, keeping the temperature for 1-3 h, and then cooling to room temperature to obtain a roasted mixture.
Preferably, the specific operation of step S3 is as follows: and adding 31-35% by mass of water into the roasted mixture, and molding and curing for 3-7 days to obtain a fly ash solidified body.
Preferably, the specific operation of step S3 is as follows: adding 18-26% of water by mass into the roasted mixture, putting the mixture into a compaction grinding tool for compaction forming, wherein the pressure is more than 60kN, the pressing time is 15-30 s, and curing is carried out for 3-7 days to obtain a fly ash solidified body. High static pressure forming is adopted, so that the water consumption can be reduced, the porosity of a solidified body is reduced, and the strength is improved.
Compared with the prior art, the invention has the advantages that:
(1) The invention utilizes the alkaline calcium source and mullite in solid waste materials such as red mud, steel slag, fly ash and the like to react with soluble chloride salt in fly ash under the roasting action to generate Wadalite phase Ca 6 Al 5 Si 2 O 16 Cl 3 (ii) a The alkaline and activated calcium-aluminum components of the roasting mixture are continuously utilized to generate hydration products Kuzel's salt Ca under the action of hydration 4 [Al(OH) 6 ] 2 Cl 2 ·6H 2 O; the Wadalite phase and the Kuzel's salt are both water-insoluble minerals, and the soluble chloride is converted into the water-insoluble minerals, so that the content of the soluble chloride is reduced, and the chlorine fixing effect is achieved.
(2) The invention generates Wadalite phase by roasting, reduces the content of soluble chloride in fly ash, shortens ion diffusion distance by high hydrostatic pressure forming, and coordinates and matches Cl in pore liquid in hydration process - And
induced by Kuzel's salt, but not Friedel's salt Ca 4 [Al(OH) 6 ] 2 Cl 2 ·6H 2 O; kuzel's salt belongs to a chlorine-sulfur solid solution, and compared with Friedel's salt, the Kuzel's salt has the advantages of lower solubility product, higher stability and stronger ion exchange capacity with heavy metal.
(3) The raw materials adopted by the invention are the red mud, the steel slag and the fly ash which are solid wastes, and through reasonable component design and a specific process, the red mud, the steel slag and the fly ash are harmless, and the high-efficiency recycling of resources such as alkalinity, calcium, aluminum and the like in the wastes is realized;
(4) The method for removing the soluble chloride does not generate waste liquid and does not cause secondary pollution.
Drawings
FIG. 1 is a flow chart of the fly ash chlorine fixation and heavy metal stabilization method of the present invention;
FIG. 2 is a schematic diagram of the mechanism of the fly ash chlorine fixation and heavy metal stabilization method of the present invention;
FIG. 3 is SEM images of the solidified bodies of fly ash of examples 1 and 2 after soaking in water and without soaking in water; FIG. 3 (a) is a microscopic morphology of the solidified body of fly ash of example 1 magnified 10000 times; FIG. 3 (b) is a microstructure of the fired mixture of example 2 at 2000 times magnification; FIG. 3 (c) is a microscopic morphology of the fly ash of example 2 after solidifying the body bubble water, magnified 10000 times;
FIG. 4 shows the chloride ion concentration in the soaking solution of the solidified fly ash in the original fly ash, examples 1 to 7, and comparative examples 1 to 5;
FIG. 5 is an X-ray diffraction pattern and post-conditioning mineral constituent content of the calcined mixture of example 2;
FIG. 6 is an X-ray diffraction pattern and post-conditioning mineral component content of the calcined mixture of example 5;
FIG. 7 is an X-ray diffraction pattern and post-crystal modification mineral content of the calcined mixture of example 6.
Detailed Description
The technical solutions of the present invention will be described clearly and completely below, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
The embodiment provides a method for stabilizing chlorine fixation and heavy metals in fly ash, as shown in fig. 1, comprising the following steps:
s1, mixing 1000g of fly ash, 50g of red mud, 50g of steel slag powder, 100g of fly ash and 100g of limestone, and then sending the mixture into a planetary ball mill for ball milling for 40min to obtain a solid-waste mixture; adding 25% by mass of water into the solid waste mixture, and performing sealed ageing for 24 hours to obtain an aged mixture;
s2, carrying out sectional roasting on the aged mixture obtained in the step S1 according to the following steps: keeping the temperature at 105 ℃ for 30min; rapidly heating to 650 ℃, continuously and slowly heating to 700 ℃, keeping the temperature for 2 hours, and naturally cooling to room temperature to obtain a roasted mixture;
and S3, adding 18-26% of water by mass into the roasted mixture obtained in the step S2, putting the mixture into a compaction grinding tool for compaction forming under the pressure of 60kN for 15S, and curing for 3 days to obtain a fly ash solidified body.
The solidified body of fly ash obtained in example 1 was subjected to scanning electron microscopy to analyze the microscopic morphology, and the obtained SEM image is shown in fig. 3 (a). As can be seen from fig. 3 (a), a Kuzel's salt hydration product of hexagonal plate structure was produced in the solidified body of fly ash.
Crushing the fly ash solidified body for 5mm, sieving, taking 50g of the sieved sample, soaking in 1L of deionized water, and testing the chloride ion concentration in the soaking solution by adopting ion chromatography, wherein the obtained result is shown in figure 4. The concentration of chloride ions in the soaking solution is 492mg/L, and compared with the concentration of chloride ions in the original fly ash soaking solution, the concentration of soluble chloride is reduced from 97.74 percent to 8.01 percent.
Example 2
The embodiment 2 is basically the same as the embodiment 1, except that in the step S1, the steel slag is 150g, and the fly ash is 200g; step S2, carrying out sectional roasting according to the following steps: keeping the temperature at 103 ℃ for 120min, quickly heating to 650 ℃, continuously and slowly heating to 700 ℃, keeping the temperature for 2h, and naturally cooling to room temperature.
XRD mineral phase analysis was performed on the calcined mixture obtained in step S2, and the results obtained are shown in FIG. 5. As can be seen from FIG. 5, wadalite, a water-insoluble chloride, was produced in the mixture obtained by calcination at 700 ℃ in an amount of 4.52%.
The chloride ion concentration in the soaking solution is shown in fig. 4, the chloride ion concentration in the soaking solution is 77mg/L, and compared with the chloride ion concentration of the original fly ash soaking solution, the soluble chloride is reduced from 97.74% to 1.26%.
The fired mixture obtained in step S2 and the solidified body after being soaked in water were subjected to scanning electron microscopy to analyze the microscopic morphology, and SEM images obtained were respectively shown in fig. 3 (b) and 3 (c). As can be seen from FIG. 3 (b), wadalite phase is generated in the fired mixture; as can be seen from FIG. 3 (c), the fly ash solidified body still contains a large amount of Wadalite phase and Kuzel's salt after soaking, indicating that the two chlorine-containing mineral phases resist soaking and act as chlorine fixing.
Example 3
The embodiment 3 is basically the same as the embodiment 1, except that 150g of red mud and 200g of fly ash are used in the step S1; step S2, carrying out sectional roasting according to the following steps: keeping the temperature at 110 ℃ for 30min, quickly heating to 650 ℃, continuously and slowly heating to 700 ℃, keeping the temperature for 2h, and naturally cooling to room temperature.
The chloride ion concentration in the soaking solution is shown in fig. 4, the chloride ion concentration in the soaking solution is 82mg/L, and compared with the chloride ion concentration of the original fly ash soaking solution, the soluble chloride is reduced from 97.74% to 1.33%.
Example 4
Example 4 is substantially the same as example 1 except that 150g of red mud and 200g of steel slag powder are used in step S1.
The chloride ion concentration in the soaking solution is shown in fig. 4, the chloride ion concentration in the soaking solution is 299mg/L, and compared with the chloride ion concentration of the original fly ash soaking solution, the soluble chloride is reduced from 97.74% to 4.88%.
Example 5
Example 5 is substantially the same as example 2 except that the staged firing conditions in step S2 are as follows: keeping the temperature at 105 ℃ for 120min; rapidly heating to 650 ℃, continuously and slowly heating to 800 ℃, keeping the temperature for 2 hours, and then naturally cooling to room temperature to obtain a roasted mixture;
XRD mineral phase analysis was performed on the calcined mixture obtained in step S2, and the obtained results are shown in fig. 6. As can be seen from FIG. 6, wadalite, which is a water-insoluble chloride, was produced in the mixture obtained by firing at 800 ℃ and the diffraction peak of the product was stronger than that obtained by firing at 700 ℃, indicating that more Wadalite phases were produced, with a content of 13.28%. The content of Wadalite phase is higher than that of example 2, so that the chlorine fixing performance is better than that of example 2.
The chloride ion concentration in the soaking solution is shown in fig. 4, the chloride ion concentration in the soaking solution is 65mg/L, and compared with the chloride ion concentration of the original fly ash soaking solution, the soluble chloride is reduced from 97.74% to 1.06%.
Example 6
Example 6 is substantially the same as example 2 except that the staged firing conditions in step S2 are as follows: keeping the temperature at 105 ℃ for 120min; rapidly heating to 650 ℃, continuously and slowly heating to 900 ℃, keeping the temperature for 2 hours, and then naturally cooling to room temperature to obtain a roasted mixture;
XRD mineral phase analysis was performed on the calcined mixture obtained in step S2, and the results obtained are shown in FIG. 7. As can be seen from FIG. 7, wadalite, a water-insoluble chloride, was produced in the mixture obtained by calcination at 900 ℃ in an amount of 14.18%. The content of Wadalite phase is higher than that of example 2 and example 5, so that the chlorine fixing performance is better than that of example 5.
The chloride ion concentration in the soaking solution is shown in fig. 4, the chloride ion concentration in the soaking solution is 23mg/L, and compared with the chloride ion concentration of the original fly ash soaking solution, the soluble chloride is reduced from 97.74% to 0.38%.
Example 7
Example 7 is substantially the same as example 6 except that the specific operation of step S3 is as follows: and (3) adding 35% by mass of water into the roasted mixture obtained in the step (S2), and forming and curing for 7 days to obtain a fly ash solidified body.
The chloride ion concentration in the soaking solution is shown in fig. 4, the chloride ion concentration in the soaking solution is 31mg/L, and compared with the chloride ion concentration of the original fly ash soaking solution, the soluble chloride is reduced from 97.74% to 0.51%. The soluble chloride in this example was slightly higher than that in example 6, indicating that pressure molding was advantageous in dissolving out the chloride.
Comparative example 1
Comparative example 1 is essentially the same as example 7 except that step S1 is as follows: 1000g of fly ash is taken and sent into a planetary ball mill for ball milling, the ball milling time is 40min, then water with the mass ratio of 25% is added into the fly ash, and the aging fly ash is obtained after sealing and aging for 24h.
Compared with the embodiment 7, the red mud, the steel slag powder, the fly ash and the limestone are not added in the comparative example; the chloride ion concentration in the soaking solution is shown in fig. 4, the chloride ion concentration in the soaking solution is 5881mg/L, and the soluble chloride content is 95.83%. It is understood from this, in step S1 of this comparative example, no red mud, steel slag powder, fly ash and limestone were added, and since the alkali and mullite phases were lacking, the soluble chloride salt in fly ash could not react to form the Wadalite phase even by calcination, and the chlorine fixing effect could not be produced.
Comparative example 2
The method for stabilizing the chlorine fixation and heavy metals of the fly ash comprises the following steps:
s1, mixing 1000g of fly ash, 50g of red mud, 150g of steel slag powder, 200g of fly ash and 100g of limestone, and then sending the mixture into a planetary mill for ball milling for 40min to obtain a solid-waste mixture; adding 25% by mass of water into the solid waste mixture, and performing sealed ageing for 24 hours to obtain an aged mixture;
s2, adding 35% of water by mass into the aging mixture obtained in the step S1, and forming and maintaining for 7 days to obtain a fly ash solidified body.
That is, in comparison with example 7, this comparative example omits the calcination step; the chloride ion concentration in the soaking solution is as shown in fig. 4, the chloride ion concentration in the soaking solution is 5394mg/L, and the soluble chloride content is 87.89%. From this, it is understood that if the calcination treatment is not employed in step S2, the Wadalite phase is not generated even if the fly ash mixture of the red mud, the steel slag powder, the fly ash and the limestone is added, and the chlorine fixing action is not generated.
Comparative example 3
Comparative example 3 is substantially the same as example 7 except that no staged firing is used in step S2 and step S2 is as follows: roasting the aged mixture obtained in the step S1, rapidly heating to 650 ℃, continuously and slowly heating to 900 ℃, keeping the temperature for 2 hours, and then naturally cooling to room temperature to obtain a roasted mixture;
the chloride ion concentration in the soaking solution is shown in fig. 4, the chloride ion concentration in the soaking solution is 3736mg/L, and the soluble chloride accounts for 60.88%. From this fact, it is found that if the high-temperature baking is performed without first applying the heating treatment at 105 ℃ in step S2, caOHCl cannot be induced to be generated, and a sufficient Wadalite phase cannot be generated in the subsequent baking process, and the chlorine fixing effect is limited.
Comparative example 4
Mixing heavy metal chelating agent A (TMT 15 type, purchased from Alibab) and fly ash according to the weight ratio of 1;
the chloride ion concentration in the soaking solution is shown in fig. 4, the chloride ion concentration in the soaking solution is 5926mg/L, and the soluble chloride content is 96.57%. Therefore, the heavy metal chelating agent A cannot obviously reduce the content of soluble chloride in the fly ash.
Comparative example 5
Mixing heavy metal curing agent B (ionic compound type, obtained from Alibab) and fly ash uniformly according to the weight ratio of 1:5, and putting the mixture into a cylindrical mold with the diameter of 10 multiplied by 10cm to prepare a test block; naturally curing the prepared test block for 7 days;
the chloride ion concentration in the soaking solution is shown in FIG. 4, the chloride ion concentration in the soaking solution is 5722mg/L, and the soluble chloride content is 93.24%. It can be seen that the heavy metal chelating agent B cannot significantly reduce the soluble chloride content of the fly ash.
Test examples
The leaching concentrations of heavy metals of Pb, cr, zn and Cd in the solidified bodies of fly ashes obtained in examples 1 to 7 and comparative examples 1 to 5 were measured according to the regulations related to the "sulfuric-acid-nitric acid method for leaching toxicity of solid wastes" (HJ/T299-2007), and the results of the measurements are shown in Table 1.
TABLE 1 heavy metal leaching concentration
As can be seen from the data in Table 1, the leaching concentration of each heavy metal in the fly ash solidified bodies of examples 1 to 7 of the present invention satisfies the limit of the pollution concentration in the hazardous waste identification standard leaching toxicity identification (GB 5085.3-2007) and the domestic waste landfill control standard (GB 16889-2008). The leaching concentrations of heavy metals Pb, cd and Cr in comparative examples 1 and 2 exceed the requirement of pollution concentration limit in the domestic garbage landfill control Standard (GB 16889-2008). In the comparative example 1, since the red mud, the steel slag powder, the fly ash and the limestone are not added in the step S1, the fly ash cannot generate effective active ingredients, cannot generate hydration reaction to generate C-S-H and Kuzel' S salt, and has no obvious solidification effect on heavy metals; the red mud, the steel slag powder, the fly ash and the fly ash added in the comparative example 2 are not calcined at high temperature, and the solid waste activity is low, so the generated hydration products are limited, the curing effect of part of heavy metals does not reach the standard, and the curing efficiency of Cr is low because Kuzel's salt is not generated. The solid waste in the comparative example 3 can generate enough active ingredients after being calcined, and the active calcium, silicon and aluminum ingredients can generate hydration reaction to generate hydration products such as C-S-H, friedel 'S salt and the like and generate a certain amount of Kuzel' S salt, so that the leaching concentration of each heavy metal in the solidified body meets the requirement of pollution concentration limit values in hazardous waste identification standard leaching toxicity identification (GB 5085.3-2007) and domestic garbage landfill control standard (GB 16889-2008); but its ability to solidify metal is poor compared to example 7 due to less Kuzel's salt produced. The leaching concentration of heavy metal Cr in comparative examples 4 and 5 exceeds the requirement of the limit value of the pollution concentration in the control Standard for municipal solid waste landfill (GB 16889-2008). The heavy metal chelating agent A and the heavy metal curing agent B have good curing effects on cationic heavy metals Pb, zn and Cd, but have insufficient binding capacity on anionic heavy metal Cr (VI), so that the leaching of the heavy metal Cr (VI) exceeds the standard.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (8)
1. A method for stabilizing chlorine fixation and heavy metals of fly ash is characterized by comprising the following steps:
s1, mixing 100 parts of fly ash, 5-15 parts of red mud, 5-15 parts of steel slag powder, 10-20 parts of fly ash and 10 parts of limestone, ball-milling, adding water, and sealing and aging to obtain an aging mixture;
s2, carrying out sectional roasting on the aged mixture obtained in the step S1, wherein the specific operation is as follows: keeping the temperature at 103-110 ℃ for 30-120min, then quickly heating to over 650 ℃, continuously and slowly heating to 700-900 ℃, keeping the temperature for 1-3h, and then cooling to room temperature to obtain a baking mixture;
and S3, adding water into the roasting mixture obtained in the step S2, and forming and curing to obtain a fly ash solidified body.
2. The method of claim 1, wherein the contents of free calcium oxide and free magnesium oxide in the steel slag powder satisfy the following formula:
(w 1 +w 2 )×m 1 ≥1；
w 1 is the content of free calcium oxide in the steel slag powder percent; w is a 2 Is the content of free magnesium oxide in the steel slag powder percent; m is a unit of 1 Is the weight portion of the steel slag powder.
3. The method of claim 1, wherein the fly ash is class F fly ash, and SiO in the fly ash is SiO-containing fly ash 2 、Al 2 O 3 And Fe 2 O 3 The total mass of the components is not less than 70 percent.
4. The method for chlorine fixation and heavy metal stabilization of fly ash according to claim 1, wherein in the step S1, the mass of the added water is 20 to 30 percent of the total mass of the fly ash, the red mud, the steel slag powder, the fly ash and the limestone; the sealing and aging time is 24h.
5. The method for chlorine fixation and heavy metal stabilization of fly ash according to claim 1, wherein in step S2, the temperature rise rate is not lower than 10 ℃/min within an interval of 500 to 650 ℃, and the temperature rise rate is not higher than 2 ℃/min within an interval of 700 to 900 ℃.
6. The method for chlorine sequestration and heavy metal stabilization of fly ash according to claim 1, wherein in step S2, the specific operation of the staged roasting is as follows: keeping the temperature at 105 ℃ for 30-120min, then quickly heating to above 650 ℃, continuously and slowly heating to 900 ℃, keeping the temperature for 1-3h, and then cooling to room temperature to obtain a baking mixture.
7. The method for chlorine fixation and heavy metal stabilization of fly ash according to claim 1, wherein the specific operation of step S3 is as follows: and adding 31-35% by mass of water into the roasted mixture, and forming and curing for 3~7 days to obtain the fly ash solidified body.
8. The method for chlorine fixation and heavy metal stabilization of fly ash according to claim 1, wherein the specific operation of step S3 is as follows: adding water with the mass ratio of 18-26% into the roasted mixture, putting the mixture into a compaction grinding tool for compaction forming, wherein the pressure is greater than 60kN, the pressurization time is 15-30s, and curing for 3~7 days to obtain a fly ash solidified body.
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