A method for solidifying secondary aluminum ash using desulfurized gypsum and a calcining device for desulfurized gypsum

Abstract

The invention discloses a method and a calcining device for solidifying secondary aluminum ash by utilizing desulfurized gypsum, comprising the following steps: S1. calcining desulfurized gypsum to obtain gypsum clinker; S2. mixing red mud, secondary aluminum ash, and water to obtain slurry A; S3. filtering slurry A and adding bottom ash to obtain slurry B; S4. mixing gypsum clinker and K2SO4 or Na2SO4, and adding the mixture to slurry B to obtain slurry C; S5. shaping slurry C into a solidified body. The desulfurization gypsum of the present application is calcined at high temperature to produce anhydrous gypsum, which has excellent strength, bonding and water resistance, and can firmly solidify the secondary aluminum ash together, reducing the erosion and penetration of external water on the aluminum ash; K2SO4 or Na2SO4 shortens the coagulation time of the slurry and increases its strength; after the red mud and aluminum ash are mixed in water, the alkaline substances released in the red mud can promote the hydrolysis of AlN and metallic Al in the secondary aluminum ash, thereby eliminating the water reactivity of the secondary aluminum ash, preventing the aluminum ash from spontaneously combusting and releasing harmful gases after landfill.

Description

Technical Field

[0001] The present invention relates to the technical field of harmless treatment of hazardous wastes, in particular to a method for solidifying secondary aluminum ash by utilizing desulfurized gypsum and a calcining device for desulfurized gypsum. Background Art

[0002] Aluminum ash refers to solid waste generated in the aluminum industry through the electrolysis, processing, and recycling of aluminum. It can be divided into primary and secondary aluminum ash based on its generation method and form. Secondary aluminum ash is black ash produced from the recycling and recasting of primary aluminum ash or other aluminum-containing metals, as well as from their processing. In recent years, aluminum ash production has increased due to the continuous increase in primary aluminum production. Typically, direct production of 1,000 tons of aluminum from aluminum ore produces 10 to 20 tons of aluminum ash, while secondary aluminum recycling generates 20 to 50 tons or even more of a more complex composition. It is estimated that China's annual aluminum ash production exceeds 3 million tons. The main components of aluminum ash include metallic aluminum, aluminum oxide, aluminum nitride, and chloride and fluoride salts. The presence of aluminum nitride in aluminum ash is one of the main reasons why it is listed as a toxic and flammable non-ferrous metal waste in the National List of Hazardous Wastes. Due to the lack of low-cost, scalable, and relatively mature treatment processes, solidification and landfilling remain the primary disposal method for secondary aluminum ash.

[0003] Typical solidification materials include cement, fly ash, red mud, and slag. Currently, aluminum ash is commonly treated with cement combined with chemical chelating agents. This treatment method is not only costly but also requires a high demand for cement, resulting in significant volume expansion and incompatible with sustainable development. Solidification materials like cement, red mud, and slag are alkaline. The aluminum ash and its compounds react with the alkaline solution to generate harmful gases, which can harm workers. The generated gases also cause the solidified material to expand, leading to secondary volume expansion.

[0004] The Chinese invention patent with publication number CN 114273382 A and publication date 2022.04.05 discloses a method for harmless treatment of secondary aluminum ash, comprising the following steps: (1) hydrolysis: adding secondary aluminum ash to a certain amount of water, adding calcium carbonate, and performing a hydrolysis reaction of aluminum nitride to obtain a secondary aluminum ash slurry; (2) acidification: adding dilute sulfuric acid to the secondary aluminum ash slurry of step (1) to perform an acidification reaction, and converting metallic aluminum and aluminum oxide into aluminum sulfate; (3) alkalization: after the acidification reaction is completed, adding slaked lime, using calcium ions to remove sulfate ions and fluoride ions to form insoluble calcium sulfate and calcium fluoride, and in an environment where the solution pH value is 9-11, the aluminum ions generated by acidification are formed into aluminum hydroxide precipitate to obtain solid waste; (4) solidification: taking a certain amount of cement to solidify the solid waste in step (3), and after curing and testing, landfill disposal. However, this treatment method, on the one hand, involves three steps of hydrolysis, acidification, and alkalization, which is a cumbersome process and has harsh reaction conditions; on the other hand, the addition of sodium carbonate, dilute sulfuric acid, and cement will lead to a significant increase in treatment costs. Summary of the Invention

[0005] In response to the deficiencies in the above-mentioned background technology, the present invention proposes a method for solidifying secondary aluminum ash using desulfurization gypsum and a calcination device for desulfurization gypsum, which can firmly solidify the secondary aluminum ash together, reduce the erosion and penetration of external water on the aluminum ash, and eliminate the water reactivity of the secondary aluminum ash, preventing the aluminum ash from spontaneously combusting and releasing harmful gases after landfill.

[0006] The technical solution of the present invention is achieved as follows:

[0007] A method for solidifying secondary aluminum ash using desulfurized gypsum comprises the following steps:

[0008] S1. The desulfurized gypsum is put into a calcining device and calcined to obtain gypsum clinker;

[0009] S2 red mud, secondary aluminum ash and water were mixed and stirred to prepare slurry A;

[0010] S3. The slurry A was filter pressed, and the bottom ash was added to the slurry A after the filter press, and stirred to obtain slurry B;

[0011] S4. The gypsum clinker obtained in step S1 was mixed with K2SO4 or Na2SO4 and added to slurry B and mixed again to obtain slurry C;

[0012] S5. The slurry C is fed into a mold to be formed into a solidified body.

[0013] Furthermore, the method further comprises the following steps:

[0014] S6. After removing the solidified slurry C from step S5 from the mold, place it in a sealed container for curing. The CO2 concentration in the container is >90%. The curing time is 10 to 85 hours and the curing temperature is 15 to 35°C.

[0015] Furthermore, the method further comprises the following steps:

[0016] S7. Evenly spray polymer mortar onto the surface of the solidified body cured in step S6, with a mortar layer thickness of 5 to 20 mm. Curing is then carried out for 1 to 3 days in an environment with a temperature of 10 to 30°C and a humidity of 30% to 60%. The landfill can then be performed. The polymer mortar has a 28-day compressive strength of 15 MPa to 20 MPa, a 7-day impermeability pressure of 0.6 MPa to 1.5 MPa, and a final setting time of 45 minutes to 8 hours.

[0017] Furthermore, the temperature in the calcination device is 550° C. to 850° C., and the calcination time is 20 min to 400 min.

[0018] Furthermore, in step S2, the red mud is 10 to 20 parts, the secondary aluminum ash is 30 to 60 parts, and the water is 50 to 120 parts; the red mud, secondary aluminum ash and water are stirred in a stirring container at a speed of 35 r / min to 95 r / min for 24 to 72 hours.

[0019] Furthermore, the Na2O content in the red mud is 7wt% to 10wt%, the SiO2 content in the red mud is 18wt% to 25wt%, the CaO content in the red mud is 15wt% to 20wt%, and the pH of the red mud is 11.5 to 12.8.

[0020] Furthermore, the slurry A described in step S3 is filtered in a filter press until the mass moisture content of the slurry A is 60% to 75%, and 15 to 25 parts of bottom ash are added to the slurry A after filtering; the SiO2 content in the bottom ash is 50wt% to 60wt%, and the specific surface area is 280m 2 / kg~430m 2 / kg.

[0021] Furthermore, in step S4, the gypsum clinker prepared in step S1 is 20 to 35 parts, and the K2SO4 or Na2SO4 is 0.3 to 0.8 parts.

[0022] A calcining device for desulfurized gypsum used in the method of solidifying secondary aluminum ash using desulfurized gypsum comprises a secondary combustion chamber and a rotary kiln arranged in the secondary combustion chamber, and the rotary kiln is arranged to rotate; the outlet end of the rotary kiln is connected to a discharge bin, and an exhaust pipe arranged on the top of the secondary combustion chamber is connected to the discharge bin.

[0023] Furthermore, a labyrinth sealing structure is provided between the rotary kiln, the secondary combustion chamber and the discharge bin, and the labyrinth sealing structure is filled with high-temperature resistant heat-conducting oil; the shell of the rotary kiln includes a heat-conducting layer and a heat-insulating layer arranged in the heat-conducting layer, the heat-conducting layer is made of graphite, and the heat-insulating layer is made of lightweight refractory material.

[0024] Beneficial effects of the present invention:

[0025] 1. The desulfurization gypsum of the present application is calcined at high temperature to produce anhydrous gypsum, which has more excellent strength, bonding and water resistance. The dihydrate gypsum generated by its hydration can firmly solidify the secondary aluminum ash together and reduce the erosion and penetration of external water on the aluminum ash; K2SO4 or Na2SO4 can shorten the setting time of the slurry and improve its strength.

[0026] 2. After the red mud of the present application is mixed with aluminum ash in water, the alkaline substances released in the red mud can promote the hydrolysis of AlN and metallic Al in the secondary aluminum ash, thereby eliminating the water reactivity of the secondary aluminum ash and preventing spontaneous combustion and the release of harmful gases after the aluminum ash is landfilled. In addition, red mud can act as a Si source and Fe source in the solidified body, which is conducive to the later hydration reaction to generate more gel phase, thereby increasing the strength of the solidified body. Most of the curing agents used in this application are solid waste, which can realize the resource utilization of solid waste and reduce the curing cost.

[0027] 3. Curing the solidified body in a CO2 atmosphere can form a hard and dense carbonate shell on the surface of the solidified body, thereby further improving the strength and impermeability of the solidified body; and realizing the storage of CO2, which is beneficial to reducing the content of greenhouse gases in the atmosphere; spraying polymer mortar on the outer surface of the solidified body can form a buffer layer between the stacked solidified bodies to avoid mutual squeezing and destruction of the solidified bodies. In addition, the dense hydrophobic shell formed by the polymer mortar can further prevent rainwater penetration and avoid the leaching of harmful components in the secondary aluminum ash.

[0028] 4. The rotary kiln separates the desulfurized gypsum from the secondary combustion chamber, preventing toxic gases from contaminating the desulfurized gypsum. The rotary kiln is constructed with a thermal insulation layer and a heat-conducting layer. Adjusting the layer thickness allows for temperature regulation within the rotary kiln, while adjusting the rotational speed allows for calcination time adjustment. A discharge hopper is installed, and the kiln discharge end is placed in a sealed container to prevent calcination exhaust gases from polluting the air during discharge. The calcination device utilizes waste heat from the hazardous waste incineration secondary combustion chamber to calcine the desulfurized gypsum, thereby utilizing waste heat and reducing curing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0030] Figure 1 It is a structural schematic diagram of the calcining device of the present invention;

[0031] Figure 2 This is the XRD pattern of the interior of the aluminum ash solidified body in specific embodiment 1 of the present invention;

[0032] Figure 3 This is a microscopic morphology of the interior of the aluminum ash solidified body prepared in specific embodiment 1 of the present invention after curing for one day. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0034] The present invention provides a method for solidifying secondary aluminum ash using desulfurized gypsum, comprising the following steps:

[0035] Step 1: Add desulfurization gypsum Figure 1 In the calcining device shown, the calcining temperature is controlled between 550° C. and 850° C., and the calcining time is controlled between 20 min and 400 min to produce gypsum clinker.

[0036] Step 2: Mix 10 to 20 parts of red mud, 30 to 60 parts of secondary aluminum ash, and 50 to 120 parts of water, and stir them in a closed container at a speed of 35 to 95 rpm for 24 to 72 hours to prepare slurry A. The gas generated during the stirring process is introduced into a hazardous waste incinerator for incineration disposal;

[0037] The red mud has a Na2O content of 7wt% to 10wt%, a SiO2 content of 18wt% to 25wt%, a CaO content of 15wt% to 20wt%, and a pH value of 11.5 to 12.8.

[0038] Step 3: The slurry A stirred in step 2 is fed into a filter press and filtered until the mass moisture content of the slurry A reaches 60% to 75%. Then, 15 to 25 parts of bottom ash are added to the filtered slurry A and stirred evenly to obtain slurry B.

[0039] The SiO2 content in the bottom ash is 50wt% to 60wt%, and the specific surface area is 280m 2 / kg~430m 2 / kg. The filter press equipment adopts the filter press equipment in the prior art.

[0040] Step 4: Mix 20 to 35 parts of gypsum clinker and 0.3 to 0.8 parts of K2SO4 or Na2SO4, add them to slurry B, and mix them again to obtain slurry C.

[0041] Step 5: Place slurry C into a curing mold, vibrate the mold until no more bubbles are generated in the slurry C, and place the mold in a room for curing for 5 to 68 hours at a temperature of 12 to 35°C and a humidity of 30% to 50%.

[0042] Wherein, the mold is a cube or a cuboid with a side length of 0.5 to 2 meters.

[0043] Step 6: After removing the solidified body of slurry C from step 5 from the mold, place it in a sealed container for further curing. The CO2 concentration in the container is greater than 90%. The curing time is 10h to 85h and the curing temperature is 15 to 35°C.

[0044] Step 7: Spray polymer mortar evenly on the surface of the solidified body cured in step 6, with a mortar layer thickness of 5 to 20 mm. Then place it in an environment with a temperature of 10 to 30°C and a humidity of 30% to 60% for curing for 1 to 3 days before landfilling.

[0045] The 28d compressive strength of the polymer mortar is 15MPa to 20MPa, the 7d anti-seepage pressure of the polymer mortar is 0.6MPa to 1.5MPa, and the final setting time is 45min to 8h.

[0046] Further, if Figure 1As shown, the calcination device described in step 1 is used for calcining desulfurized gypsum, and includes a secondary combustion chamber 1 and a rotary kiln 2 inserted into the secondary combustion chamber 1, and the rotary kiln 2 rotates in coordination with the secondary combustion chamber 1. A bracket is provided outside the secondary combustion chamber 1, and both ends of the rotary kiln 2 are rotatably mounted on the bracket. A reduction motor 4 is provided on the bracket, and a driving gear 5 is provided at the output end of the reduction motor 4. A rack 21 meshing with the driving gear 5 is provided on the outer periphery of one end of the rotary kiln 2. A rack 21 is also provided on the outer periphery of the end of the rotary kiln 2 away from the reduction motor 4, and a passive gear 6 meshing with the rack 21 is rotatably mounted on the bracket. A feed pipe 22 is provided at one end of the rotary kiln 2 and an outlet end is provided at the other end. The outlet end of the rotary kiln 2 is connected to a discharge bin 3, and a discharge port 31 is provided at the lower end of the discharge bin 3. The secondary combustion chamber 1 is provided with an exhaust pipe 11 at the top and a tapered section at the bottom. The lower end of the tapered section is connected to a slag discharge port 12. The side walls of the tapered section are provided with an air inlet 13 and an air supply port 14. The upper end of the silo 3 is connected to one side of the exhaust pipe 11 of the secondary combustion chamber 1.

[0047] Furthermore, a labyrinth-type sealing structure is installed between the rotary kiln 2, the secondary combustion chamber 1, and the discharge bin 3. This labyrinth-type sealing structure adopts the existing sealing structure. The labyrinth gaps are filled with high-temperature resistant heat transfer oil 7. The shell of the rotary kiln 2 includes a heat-conducting layer 23 and an insulation layer 22 disposed within the heat-conducting layer 23. The heat-conducting layer 23 is made of graphite, and the insulation layer 22 is made of lightweight refractory material. The rotary kiln temperature is controlled by adjusting the thickness of the insulation layer, and the calcination time is adjusted by adjusting the rotary kiln speed.

[0048] During operation, desulfurized gypsum raw material is fed through feed pipe 22 and calcined in rotary kiln 2 using waste heat from secondary combustion chamber 1. As rotary kiln 2 rotates, desulfurized gypsum clinker falls into discharge hopper 3 and is discharged through discharge port 31. The rotary kiln separates the desulfurized gypsum from the secondary combustion chamber, preventing toxic gases from contaminating the desulfurized gypsum. The discharge hopper also prevents air pollution from calcination exhaust gases during discharge. Utilizing waste heat from the secondary combustion chamber significantly reduces energy consumption.

[0049] Example 1

[0050] This embodiment provides a method for solidifying secondary aluminum ash using desulfurized gypsum. The desulfurized gypsum is placed in a calcining device, and the calcination temperature is controlled at 550°C and the calcination time is controlled at 400 minutes to produce gypsum clinker. 64 kg of red mud, 192 kg of secondary aluminum ash, and 320 kg of water are mixed and stirred in a closed container at 50 r / min for 48 hours to produce slurry A. The red mud has a Na2O content of 7 wt%, a SiO2 content of 18 wt%, a CaO content of 15%, and a pH of 11.5.

[0051] Then, the stirred slurry A was sent to the filter press equipment and filtered until the mass moisture content of slurry A was 60%. Then, 96 kg of bottom ash was added to the filtered slurry A and stirred evenly to obtain slurry B. The SiO2 content in the bottom ash was 50 wt% and the specific surface area was 280 m 2 / kg.

[0052] Afterwards, 128 kg of gypsum clinker was mixed evenly with 1.92 kg of K2SO4, added to Slurry B, and mixed evenly again to obtain Slurry C. Slurry C was placed in a mold for curing, and the mold was vibrated until no more bubbles were generated in Slurry C. The mold was then placed in a room for curing for 24 hours at a temperature of 25°C and a humidity of 48%. The mold was a cube with a side length of 0.5 m. After the solidified body of Slurry C was demolded, it was placed in a sealed container for further curing. The CO2 concentration in the container was >90%, and the curing time was 10 hours at a temperature of 28°C.

[0053] Finally, a polymer mortar layer was evenly sprayed onto the cured surface to a thickness of 10 mm. The material was then cured for one day at 30°C and 50% humidity before being landfilled. The polymer mortar exhibited a 28-day compressive strength of 15 MPa, a 7-day impermeability pressure of 0.6 MPa, and a final setting time of 45 minutes.

[0054] The obtained products were characterized as Figure 2 As shown by Figure 2 It can be seen that the main mineral components of the solidified body are dihydrate gypsum, alumina, calcium carbonate and katoite, among which dihydrate gypsum is produced by the hydration of gypsum clinker, calcium carbonate is produced by the carbonization of CO2, alumina is the unreacted component in aluminum ash, and katoite is the unreacted component in red mud.

[0055] The microscopic morphology after 28 days of curing is as follows Figure 3 As shown by Figure 3 It can be seen that the solidified body is hydrated to produce strip-shaped dihydrate gypsum and "cloud"-shaped condensation. The two types of products are intertwined and wrapped with each other, forming a higher strength.

[0056] Example 2

[0057] This embodiment provides a method for solidifying secondary aluminum ash using desulfurized gypsum. The desulfurized gypsum is placed in a calcining device, and the calcination temperature is controlled between 850°C and the calcination time is controlled within 20 minutes to produce gypsum clinker. 214 kg of red mud, 642 kg of secondary aluminum ash, and 1284 kg of water are mixed and stirred in a closed container at 35 r / min for 72 hours to produce slurry A. The red mud has a Na2O content of 10 wt%, a SiO2 content of 25 wt%, a CaO content of 20%, and a pH of 12.8.

[0058] Then, the stirred slurry A was sent to the filter press equipment and filtered until the mass moisture content of slurry A was 75%. Then, 267.5 kg of bottom ash was added to the filtered slurry A and stirred evenly to obtain slurry B; wherein the SiO2 content in the bottom ash was 60 wt% and the specific surface area was 430 m 2 / kg.

[0059] Afterwards, 374.5 kg of gypsum clinker was evenly mixed with 8.56 kg of K2SO4, added to slurry B, and mixed again to obtain slurry C. Slurry C was placed in a mold for curing, and the mold was vibrated until no more bubbles were generated in slurry C. The mold was placed in a room for curing for 68 hours at a temperature of 28°C and a humidity of 30%. The mold was a cube with a side length of 2 m. After the solidified body of slurry C was demolded, it was placed in a sealed container for further curing. The CO2 concentration in the container was >90%, the curing time was 85 hours, and the curing temperature was 15°C.

[0060] Finally, a 20mm thick polymer mortar layer was evenly sprayed onto the cured surface. The material was then cured for three days at 24°C and 60% humidity before being landfilled. The polymer mortar exhibited a 28-day compressive strength of 20 MPa, a 7-day impermeability pressure of 1.5 MPa, and a final setting time of 8 hours.

[0061] Example 3

[0062] This embodiment provides a method for solidifying secondary aluminum ash using desulfurized gypsum. The desulfurized gypsum is placed in a calcining device, and the calcination temperature is controlled between 650°C and the calcination time is controlled within 240 minutes to produce gypsum clinker. 127 kg of red mud, 383 kg of secondary aluminum ash, and 680 kg of water are mixed and stirred in a closed container at 75 rpm for 48 hours to produce slurry A. The red mud has a Na2O content of 8 wt%, a SiO2 content of 20 wt%, a CaO content of 18%, and a pH of 12.

[0063] Then, the stirred slurry A was sent to the filter press equipment and filtered until the mass moisture content of slurry A was 70%. Then, 170 kg of bottom ash was added to the filtered slurry A and stirred evenly to obtain slurry B; wherein the SiO2 content in the bottom ash was 55 wt% and the specific surface area was 380 m 2 / kg.

[0064] Next, 238 kg of gypsum clinker was mixed evenly with 5.1 kg of Na₂SO₄, added to Slurry B, and mixed again to produce Slurry C. Slurry C was placed in a curing mold and vibrated until no bubbles were generated. The mold was then placed in a room for curing for 48 hours at a temperature of 12-20°C and a humidity of 30%-40%. The mold was a cube with a side length of 1 meter. After the solidified Slurry C was demolded, it was placed in a sealed container for further curing. The CO₂ concentration in the container was >90%, and the curing time was 52 hours at a temperature of 15°C.

[0065] Finally, a polymer mortar layer was evenly sprayed onto the cured surface to a thickness of 5 mm. The material was then cured for three days at 12°C and 40% humidity before being landfilled. The polymer mortar exhibited a 28-day compressive strength of 18 MPa, a 7-day impermeability pressure of 1.2 MPa, and a final setting time of 5 hours.

[0066] Example 4

[0067] This embodiment provides a method for solidifying secondary aluminum ash using desulfurized gypsum. The desulfurized gypsum is placed in a calcining device, and the calcination temperature is controlled between 550°C and the calcination time is controlled within 200 minutes to produce gypsum clinker. 134 kg of red mud, 336 kg of secondary aluminum ash, and 672 kg of water are mixed and stirred in a closed container at 95 rpm for 24 hours to produce slurry A. The red mud has a Na2O content of 9 wt%, a SiO2 content of 22 wt%, a CaO content of 16%, and a pH of 12.

[0068] Then, the stirred slurry A was sent to the filter press equipment and filtered until the mass moisture content of slurry A was 60%. Then, 168 kg of bottom ash was added to the filtered slurry A and stirred evenly to obtain slurry B; wherein the SiO2 content in the bottom ash was 55 wt% and the specific surface area was 330 m 2 / kg.

[0069] Afterwards, 280 kg of gypsum clinker was evenly mixed with 5.6 kg of K2SO4, added to slurry B, and mixed again to obtain slurry C; slurry C was sent to a mold for curing, and the mold was vibrated until no more bubbles were generated in slurry C. The mold was placed in a room for curing for 5 hours, at a curing temperature of 12°C and a humidity of 30%. The mold was a rectangular parallelepiped with a side length of 1m and a length, width and height of 1*0.5*0.5. After the solidified body of the slurry C was demolded, it was placed in a sealed container for further curing. The CO2 concentration in the container was >90%, the curing time was 24 hours, and the curing temperature was 28°C.

[0070] Finally, a polymer mortar layer was evenly sprayed onto the cured surface to a thickness of 10 mm. The material was then cured for two days at 10°C and 30% humidity before being landfilled. The polymer mortar exhibited a 28-day compressive strength of 20 MPa, a 7-day impermeability pressure of 1.3 MPa, and a final setting time of 3 hours.

[0071] Example 5

[0072] This embodiment provides a method for solidifying secondary aluminum ash using desulfurized gypsum. The desulfurized gypsum is placed in a calcining device, and the calcination temperature is controlled between 680°C and the calcination time is controlled within 250 minutes to produce gypsum clinker. 244 kg of red mud, 732 kg of secondary aluminum ash, and 1220 kg of water are mixed and stirred in a closed container at 60 r / min for 60 hours to produce slurry A. The red mud has a Na2O content of 8 wt%, a SiO2 content of 20 wt%, a CaO content of 16%, and a pH of 11.8.

[0073] Then, the stirred slurry A was sent to the filter press equipment and filtered until the mass moisture content of slurry A was 68%. Then, 219 kg of bottom ash was added to the filtered slurry A and stirred evenly to obtain slurry B; wherein, the SiO2 content in the bottom ash was 55 wt% and the specific surface area was 320 m 2 / kg.

[0074] Next, 305 kg of gypsum clinker was mixed evenly with 3.7 kg of Na₂SO₄, added to Slurry B, and mixed again to produce Slurry C. Slurry C was placed in a curing mold and vibrated until no bubbles were generated. The mold was then placed in a room for curing for 24 hours at a temperature of 18°C ​​and a humidity of 30% to 35%. The mold was a cube with a side length of 1.2 m. After the solidified Slurry C was removed from the mold, it was placed in a sealed container for further curing. The CO₂ concentration in the container was >90%, and the curing time was 10 hours at a temperature of 50°C.

[0075] Finally, a polymer mortar layer was evenly sprayed onto the cured surface to a thickness of 5 mm. The material was then cured for one day in an environment with a temperature of 18°C ​​and a humidity of 60%, and then landfilled. The polymer mortar had a 28-day compressive strength of 15 MPa, a 7-day impermeability pressure of 0.8 MPa, and a final setting time of 2 hours.

[0076] Example 6

[0077] This embodiment provides a method for solidifying secondary aluminum ash using desulfurized gypsum. The desulfurized gypsum is placed in a calcining device, and the calcination temperature is controlled at 800°C and the calcination time is controlled at 80 minutes to produce gypsum clinker. 84 kg of red mud, 168 kg of secondary aluminum ash, and 378 kg of water are mixed and stirred in a closed container at 95 rpm for 32 hours to produce slurry A. The red mud has a Na2O content of 9 wt%, a SiO2 content of 20 wt%, a CaO content of 15%, and a pH of 12.

[0078] Then, the stirred slurry A was sent to the filter press equipment and filtered until the mass moisture content of slurry A was 75%. Then, 86.4 kg of bottom ash was added to the filtered slurry A and stirred evenly to obtain slurry B; wherein the SiO2 content in the bottom ash was 58 wt% and the specific surface area was 400 m 2 / kg.

[0079] Next, 105 kg of gypsum clinker was mixed evenly with 3.4 kg of Na₂SO₄, added to Slurry B, and mixed again to produce Slurry C. Slurry C was placed in a curing mold and vibrated until no bubbles were generated. The mold was then placed in a cubic container for 48 hours at a temperature of 24°C and a humidity of 30% to 35%. The mold was a cube with a side length of 0.8 m. After the solidified Slurry C was removed from the mold, it was placed in a sealed container for further curing at a CO₂ concentration of 90% for 10 hours at a temperature of 35°C.

[0080] Finally, a polymer mortar was evenly sprayed onto the cured surface, with a 5mm thick layer. The material was then cured for one day at 15°C and 45% humidity before being landfilled. The polymer mortar exhibited a 28-day compressive strength of 20 MPa, a 7-day impermeability pressure of 1.5 MPa, and a final setting time of 7 hours.

[0081] Comparative Example 1

[0082] A method for solidifying secondary aluminum ash using desulfurized gypsum is provided, which differs from Example 1 in that gypsum clinker is not added in step 4, and other contents remain unchanged.

[0083] Comparative Example 2

[0084] A method for solidifying secondary aluminum ash using desulfurized gypsum, which differs from Example 1 in that K2SO4 or Na2SO4 is not added in step 4, and other contents remain unchanged.

[0085] Comparative Example 3

[0086] A method for solidifying secondary aluminum ash using desulfurized gypsum is provided, which differs from Example 1 in that polymer mortar is not sprayed in step 7, and other contents remain unchanged.

[0087] Implementation effect:

[0088] Performance Testing

[0089] The solidified bodies prepared in step S6 of Examples 1-6 of the present invention and Comparative Examples 1-3 were tested for setting time, strength, and expansion rate. The solidified bodies prepared in step S7 were tested for ammonia nitrogen leaching and fluoride ion leaching. Setting time and strength were measured in accordance with national standard GB / T 9776-2022. The expansion rate was measured using a Φ100×150mm cement mortar expansion meter, and the result was calculated according to the formula: expansion rate = (height of slurry cured for 28 days - height of fresh slurry) × 100 / height of fresh slurry. A small cubic sample with a side length of 40 mm was prepared according to steps S1-S7. The sample was immersed in 1L of dilute sulfuric acid solution (pH = 3.2, temperature = 20°C) for 90 days. The ammonia nitrogen content in the solidified body leachate was measured in accordance with national standard GB 7479-87, and the fluoride ion concentration in the leachate was measured in accordance with national standard GB / T 34500.1-2017.

[0090] The results are as follows:

[0091] Table 1 Performance test results

[0092]

[0093] As shown in Examples 1-6, the solidified bodies exhibited a 2h strength range of 1.1 MPa to 2.6 MPa, enabling rapid consolidation to generate strength and landfill. The low expansion rate effectively minimized solidified body volume expansion, and both ammonia nitrogen and fluoride ion leaching remained within a low range. In Comparative Example 1, if gypsum clinker was not added, the solidified body would not solidify and develop strength. In Comparative Example 2, if K₂SO₄ or Na₂SO₄ were not added, the solidification time would be excessive, resulting in low construction efficiency. In Comparative Example 3, if polymer mortar was sprayed, both ammonia nitrogen and fluoride ion leaching exceeded standards.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for solidifying secondary aluminum ash using desulfurized gypsum, characterized in that: The steps include: S1. The desulfurized gypsum is put into a calcining device and calcined to obtain gypsum clinker; the calcining device has a temperature of 550 ℃ to 850 ℃ and a calcination time of 20min to 400min; S2. Red mud, secondary aluminum ash, and water are mixed and stirred to prepare slurry A; the red mud comprises 10-20 parts, the secondary aluminum ash comprises 30-60 parts, and the water comprises 50-120 parts; the red mud, secondary aluminum ash, and water are stirred in a stirring vessel at 35-95 rpm for 24-72 hours; the red mud has a Na2O content of 7-10 wt%; a SiO2 content of 18-25 wt%; a CaO content of 15-20 wt%; and a pH of 11.5-12.

8. S3. The slurry A is filtered, and the slurry A is filtered in a filter press until the mass moisture content of the slurry A is 60% to 75%. 15 to 25 parts of bottom ash are added to the slurry A after filtration. The SiO2 content in the bottom ash is 50wt% to 60wt%, and the specific surface area is 280m 2 / kg~430m 2 / kg; stir evenly to prepare slurry B; S4. The gypsum clinker obtained in step S1 is mixed with K2SO4 or Na2SO4 and added to slurry B and mixed again to obtain slurry C; 20 to 35 parts of gypsum clinker, and 0.3 to 0.8 parts of K2SO4 or Na2SO4; S5. The slurry C is fed into a mold to form a solidified body; S6. After the solidified slurry C in step S5 is demolded, it is placed in a closed container for curing; the CO2 concentration in the container is >90%, the curing time is 10h~85h, and the curing temperature is 15~35 ℃; S7. Evenly spray polymer mortar onto the surface of the solidified body cured in step S6, with a mortar layer thickness of 5 to 20 mm. Curing is then carried out for 1 to 3 days in an environment with a temperature of 10 to 30°C and a humidity of 30% to 60%. The landfill can then be performed. The polymer mortar has a 28-day compressive strength of 15 MPa to 20 MPa, a 7-day impermeability pressure of 0.6 MPa to 1.5 MPa, and a final setting time of 45 minutes to 8 hours.

2. A desulfurized gypsum calcining device used in the method of solidifying secondary aluminum ash using desulfurized gypsum according to claim 1, characterized in that: The rotary kiln (2) comprises a secondary combustion chamber (1) and a rotary kiln (2) passing through the secondary combustion chamber (1), wherein the rotary kiln (2) is arranged to rotate; the outlet end of the rotary kiln (2) is connected to a discharge bin (3), and an exhaust pipe (11) arranged at the top of the secondary combustion chamber (1) is communicated with the discharge bin (3); a labyrinth seal structure is provided between the rotary kiln (2), the secondary combustion chamber (1) and the discharge bin (3), and the labyrinth seal structure is filled with high-temperature resistant heat-conducting oil (7); the shell of the rotary kiln (2) comprises a heat-conducting layer (23) and a heat-insulating layer (22) arranged in the heat-conducting layer (23), wherein the heat-conducting layer (23) is made of graphite, and the heat-insulating layer (22) is made of a light refractory material.

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