A method for resource utilization of sodium-based desulfurization ash

Abstract

The present application relates to the technical field of desulfurization ash recycling, and discloses a method for resource utilization of sodium-based desulfurization ash, comprising the following steps: S1, adding desulfurization ash into a mixing pool according to a ratio of 1:6-8 with water, and the water temperature is above 25 DEG C; S2, using a primary lifting pump to lift the mixed liquid into a primary pH adjusting pool, adding sodium hydroxide in the primary adjusting pool to adjust the pH to 11-11.5, using air stirring in the primary adjusting pool, and the reaction time is 30-90 min; S3, the effluent of the primary adjusting pool enters a primary coagulation and defluorination and precipitation process, and adding efficient defluorination agent and coagulant aid in the coagulation pool.The present application uses sulfuric acid pickling waste acid nanofiltration concentrate to adjust the pH in the acidification and nitrate reduction stage, and uses ferrous ions therein as a reducing agent to reduce nitrate, realizes the resource utilization of sulfuric acid pickling waste acid nanofiltration concentrate, and uses waste to treat waste, the present application has economic and environmental double effects, and has good social and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of desulfurization ash recycling technology, and more specifically to a method for the resource utilization of sodium-based desulfurization ash. Background Technology

[0002] Flue gas desulfurization has become an essential facility for flue gas treatment in sintering plants, power plants, and coke ovens. Desulfurization processes can be divided into wet, semi-dry, and dry methods. Dry and semi-dry desulfurization methods produce solid powder products and do not generate wastewater during the process, thus they are widely used. Sodium-based rotary spray drying (SDA) is a commonly used semi-dry desulfurization process. Its principle involves preparing a 20-25% Na2CO3 solution by adding water to Na2CO3. This solution is then atomized into droplets by a high-speed atomizer and sprayed into an absorption tower. The Na2CO3 solution droplets can rapidly absorb SO2 and other acidic pollutants in the flue gas, achieving the purpose of removing SO2 and other acidic gases. The main component of the desulfurization ash produced during the desulfurization process is Na2CO4, in addition to some unreacted Na2CO3, incompletely oxidized Na2CO3, and a small amount of Cl. - F - NO 3- Ca 2+ Mg 2+ And impurities such as Si.

[0003] Steel companies have sulfuric acid pickling units that regularly discharge waste sulfuric acid. This waste sulfuric acid mainly consists of sulfuric acid, but also contains a small amount of ferrous ions. Because there is no sulfuric acid regeneration process, most of the waste sulfuric acid is discharged into the wastewater treatment plant, resulting in waste. Recently, acid-resistant nanofiltration has emerged, which can trap ferrous ions in waste acid, allowing the purified sulfuric acid to be returned to the unit for recycling. However, the ferrous ions in the concentrate are concentrated several times over, requiring further treatment.

[0004] Furthermore, the desulfurization ash produced by sodium-based semi-dry desulfurization has a complex and unstable composition. For example, Na2CO3 ash will be oxidized to Na2CO4 in the air, and Na2CO3 will release CO2 when it encounters acidic components. Therefore, this desulfurization ash is difficult to utilize and can only be landfilled or piled up as waste. Summary of the Invention

[0005] The main technical problem solved by this invention is to provide a method for the resource utilization of sodium-based desulfurization ash, thereby solving the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, according to one aspect of the present invention, more specifically, a method for the resource utilization of sodium-based desulfurization ash, comprising the following steps:

[0007] S1. Add desulfurization ash and water to the mixing tank at a ratio of 1:6 to 8, with the water temperature above 25℃.

[0008] S2. Use a primary booster pump to lift the mixture to a primary pH adjustment tank. Add sodium hydroxide to the primary adjustment tank to adjust the pH to 11-11.5. Use air stirring in the primary pH adjustment tank and react for 30-90 minutes.

[0009] S3. The effluent from the primary pH adjustment tank enters the primary coagulation, defluoridation, and sedimentation process. High-efficiency defluoridating agent and coagulant aid are added to the coagulation tank.

[0010] S4. The permeate from the primary coagulation and sedimentation process enters the primary permeate tank. The primary permeate is then pumped to the secondary pH adjustment tank using a secondary lift pump. Sodium hydroxide is added to the secondary pH adjustment tank to adjust the pH to 12-13. Air stirring is used in the secondary pH adjustment tank, and the reaction time is 30-90 minutes.

[0011] S5. The effluent from the secondary pH adjustment tank enters the secondary coagulation and sedimentation process, and coagulants and coagulant aids are added to the coagulation tank.

[0012] The permeate from the S6 and secondary coagulation sedimentation processes enters the secondary permeate tank. The secondary permeate is then pumped to the acidification and reduction tank by a tertiary lift pump, where waste sulfuric acid nanofiltration concentrate from the cold rolling sulfuric acid pickling unit is added.

[0013] S7. The effluent from the acidification and reduction tank enters the three-stage pH adjustment tank, where sodium hydroxide is added for neutralization to adjust the pH to 6-7.

[0014] The effluent from the S8 and tertiary pH adjustment tanks enters the tertiary coagulation and sedimentation system, where polyacrylamide (PAM) is added as a coagulant aid to reduce unreacted Fe2+. 2+ It is oxidized to Fe under neutral conditions 3+ Fe produced by the reduction reaction 2 (SO4) 3 Together they act as coagulants.

[0015] Furthermore, in step S1, adding the desulfurization ash to the mixing tank allows the sodium sulfate, sodium sulfite, sodium carbonate, and other soluble components in the desulfurization ash to fully dissolve in the water.

[0016] Furthermore, the chemical reaction that occurs in step S2 is as follows:

[0017] 1) Ca dissolved in water in desulfurization ash 2+ Mg 2+ With desulfurization ash And the newly added OH -The reactions respectively form CaCO3, MgCO3 and Mg(OH)2 precipitates;

[0018] 2) Si in water at pH 11–11.5 is expressed as... Form exists, With Ca 2+ Mg 2+ CaSiO3 and MgSiO3 precipitates are formed;

[0019] 3) During stirring, oxygen in the air oxidizes Na2SO3 to Na2SO4, which can improve the purity of subsequent sodium sulfate crystallization.

[0020] Furthermore, in step S3, the high-efficiency defluorinating agent can also act as a coagulant, and the coagulant aid is polyacrylamide (PAM).

[0021] The ratio of high-efficiency defluoridant to fluoride ions is 10-15:1, and the dosage of PAM is 3-5 mg / L. The coagulation defluoridation process can efficiently remove fluoride ions from water.

[0022] Furthermore, in step S4, the Mg that was not completely precipitated in the first stage is... 2+ Further precipitation, Mg 2+ With OH - The reaction produces Mg(OH)2 precipitate.

[0023] Furthermore, in step S5, the coagulant used is polyferric sulfate, with a dosage of 500-1000 mg / L; the coagulant aid used is polyacrylamide (PAM), with a dosage of 3-5 mg / L.

[0024] Furthermore, in step S6, the concentration of sulfuric acid in the waste sulfuric acid nanofiltration concentrate is 5-8%, and Fe... 2+ The concentration is 1-2%, and the pH is adjusted to 3-3.5, while ensuring Fe... 2+ NO 3- Greater than 5.

[0025] Furthermore, in step S6, the reaction time is 60–120 min, and two reactions occur:

[0026] 1) Residual CO3 in water 2- Under acidic conditions, it is converted into CO2 and escapes from the water.

[0027] CO3 2- +H - →CO2↑+H2O;

[0028] 2) NO in water 3- Fe in waste sulfuric acid nanofiltration concentrate 2+Under acidic conditions, it is reduced to nitrogen gas, thus NO 3- It was removed:

[0029] 2NaNO3+10FeSO4+6H2SO4→N2↑+5Fe2(SO4)3+Na2SO4+6H2O.

[0030] Furthermore, the preparation process of the highly efficient defluorinating agent:

[0031] 1) Adjust the pH of pure water to 3.5-4.5 with sulfuric acid, then mix chitosan with the pH-adjusted water at a ratio of 1:20-30, heat in a water bath to 55-65℃, and keep at a constant temperature for 60-90 minutes to allow the chitosan to fully dissolve in the acidic water;

[0032] 2) After cooling to room temperature, add aluminum sulfate and ferric sulfate to the chitosan solution, wherein the molar ratio of aluminum sulfate to ferric sulfate is 1:1.5 to 1.5:1, and the mass ratio of chitosan to aluminum sulfate and ferric sulfate is 1:5 to 10.

[0033] 3) Place the mixture of aluminum sulfate, ferric sulfate and chitosan solution in an ultrasonic bath for 40-60 minutes to enhance mixing, and let it stand for 24-48 hours to complete the polymerization and obtain the defluorination coagulant.

[0034] The beneficial effects of the method for resource utilization of sodium-based desulfurization ash of the present invention are as follows:

[0035] 1. In this invention, sodium-based desulfurization ash is dissolved in water, and then subjected to a process of first-stage pH adjustment to remove calcium, magnesium, silicon and fluorine, second-stage pH adjustment to deeply remove magnesium, acidification to remove carbonate and reduction of nitrate. After these processes, all impurities in the desulfurization ash are removed, and the remaining substances are only sodium sulfate and sodium chloride, which can be entered into the plant's zero-discharge wastewater system for evaporation and crystallization.

[0036] 2. In the acidification and nitrate reduction stages, this invention utilizes the concentrated acid nanofiltration solution of sulfuric acid washing waste to adjust the pH, and at the same time uses the ferrous ions in it as a reducing agent to reduce nitrate, thus realizing the resource utilization of the concentrated acid nanofiltration solution of sulfuric acid washing waste and treating waste with waste. This invention has both economic and environmental benefits, and has good social and environmental benefits. Attached Figure Description

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and specific implementation methods.

[0038] Figure 1 This is a process flow diagram of the sodium-based desulfurization ash resource utilization method in this invention. Detailed Implementation

[0039] The present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the present application can be combined with each other.

[0040] like Figure 1 As shown, according to one aspect of the present invention, a method for the resource utilization of sodium-based desulfurization ash is provided.

[0041] In this embodiment, the desulfurization ash is added to the mixing tank at a ratio of 1:7 with water, so that the soluble components in the desulfurization ash are fully dissolved in the water. The composition of the solution after dissolution is as follows:

[0042]

[0043] Sodium hydroxide was added to the primary equalization tank to adjust the pH to 11.3. Air agitation was used in the primary pH equalization tank, and the reaction time was 60 minutes. The effluent from the primary pH equalization tank entered the primary coagulation, defluoridation, and sedimentation process. The ratio of high-efficiency defluoridating agent to fluoride ions was 12.5:1, and the dosage of coagulant aid PAM was 4 mg / L.

[0044] The permeate from the primary coagulation and sedimentation process enters the primary permeate tank. The primary permeate is then pumped to the secondary pH adjustment tank using a secondary lift pump. Sodium hydroxide is added to the secondary pH adjustment tank to adjust the pH to 12.5. Air stirring is used in the secondary pH adjustment tank, and the reaction time is 60 minutes.

[0045] The effluent from the secondary pH adjustment tank enters the secondary coagulation and sedimentation process. Coagulants and coagulant aids are added to the coagulation tank. The dosage of coagulant polyferric sulfate is 750 mg / L, and the dosage of PAM is 4 mg / L.

[0046] Waste sulfuric acid nanofiltration concentrate from the cold rolling sulfuric acid pickling unit is added to the permeate of the secondary coagulation sedimentation process. The concentration of sulfuric acid in the waste sulfuric acid nanofiltration concentrate is 6%, and the Fe content is... 2+ The concentration was 1.5%. The pH was adjusted to 3.3, and Fe... 2+ NO 3- The value is 6.6. The reaction time for this stage is 90 minutes.

[0047] The effluent from the acidification and reduction tank enters the three-stage pH adjustment tank, where sodium hydroxide is added for neutralization to adjust the pH to 6.5.

[0048] The effluent from the three-stage pH adjustment tank enters the three-stage coagulation and sedimentation system, where 4 mg / L of PAM is added.

[0049] Preparation process of high-efficiency defluoridating agent: The pH of pure water is adjusted to 4 with sulfuric acid. Then, chitosan and the pH-adjusted water are mixed at a ratio of 1:25. The mixture is heated to 60℃ in a water bath and held at this temperature for 75 minutes to ensure that the chitosan is fully dissolved in the acidic water. After cooling to room temperature, aluminum sulfate and ferric sulfate are added to the chitosan solution, with a molar ratio of aluminum sulfate to ferric sulfate of 1:1 and a mass ratio of chitosan to aluminum sulfate and ferric sulfate of 1:7.5. The mixture of aluminum sulfate, ferric sulfate, and chitosan solution is subjected to ultrasonic intensified mixing for 50 minutes and allowed to stand for 36 hours to complete polymerization, thus obtaining the defluoridating coagulant.

[0050] The composition of the treated solution is as follows:

[0051]

[0052] In this embodiment, the desulfurization ash is added to the mixing tank at a ratio of 1:6 with water, so that the soluble components in the desulfurization ash are fully dissolved in the water. The composition of the solution after dissolution is as follows:

[0053]

[0054] Sodium hydroxide was added to the primary equalization tank to adjust the pH to 11.5. Air agitation was used in the primary pH equalization tank, and the reaction time was 90 minutes. The effluent from the primary pH equalization tank entered the primary coagulation, defluoridation, and sedimentation process. The ratio of high-efficiency defluoridating agent to fluoride ions was 15:1, and the dosage of coagulant aid PAM was 3 mg / L.

[0055] The permeate from the primary coagulation and sedimentation process enters the primary permeate tank. The primary permeate is then pumped to the secondary pH adjustment tank using a secondary lift pump. Sodium hydroxide is added to the secondary pH adjustment tank to adjust the pH to 13. Air stirring is used in the secondary pH adjustment tank, and the reaction time is 90 minutes.

[0056] The effluent from the secondary pH adjustment tank enters the secondary coagulation and sedimentation process. Coagulants and coagulant aids are added to the coagulation tank. The dosage of coagulant polyferric sulfate is 1000 mg / L, and the dosage of PAM is 3 mg / L.

[0057] Waste sulfuric acid nanofiltration concentrate from the cold rolling sulfuric acid pickling unit was added to the permeate of the secondary coagulation and sedimentation process. The concentration of sulfuric acid in the waste sulfuric acid nanofiltration concentrate was 8%, and the concentration of Fe2+ was 2%. The pH was adjusted to 3.0, and Fe... 2+ NO 3- The value is 7.5. The reaction time for this stage is 60 minutes.

[0058] The effluent from the acidification and reduction tank enters the three-stage pH adjustment tank, where sodium hydroxide is added for neutralization to adjust the pH to 7.0.

[0059] The effluent from the three-stage pH adjustment tank enters the three-stage coagulation and sedimentation system, where 3 mg / L of PAM is added.

[0060] Preparation process of high-efficiency defluoridating agent: The pH of pure water is adjusted to 3 with sulfuric acid. Then, chitosan and the pH-adjusted water are mixed at a ratio of 1:20. The mixture is heated to 55°C in a water bath and held at that temperature for 90 minutes to ensure that the chitosan is fully dissolved in the acidic water. After cooling to room temperature, aluminum sulfate and ferric sulfate are added to the chitosan solution, with a molar ratio of aluminum sulfate to ferric sulfate of 1.5:1 and a mass ratio of chitosan to aluminum sulfate and ferric sulfate of 1:5. The mixture of aluminum sulfate, ferric sulfate, and chitosan solution is subjected to ultrasonic intensified mixing for 40 minutes and allowed to stand for 48 hours to complete polymerization, thus obtaining the defluoridating coagulant.

[0061] The composition of the treated solution is as follows:

[0062]

[0063] In this embodiment, desulfurization ash is added to a mixing tank at a ratio of 1:8 to water, so that the soluble components in the desulfurization ash are fully dissolved in the water. The composition of the solution after dissolution is as follows:

[0064]

[0065] Sodium hydroxide was added to the primary equalization tank to adjust the pH to 11. Air agitation was used in the primary pH equalization tank, and the reaction time was 30 minutes. The effluent from the primary pH equalization tank entered the primary coagulation, defluoridation, and sedimentation process. The ratio of high-efficiency defluoridating agent to fluoride ions was 10:1, and the dosage of coagulant aid PAM was 5 mg / L.

[0066] The permeate from the primary coagulation and sedimentation process enters the primary permeate tank. The primary permeate is then pumped to the secondary pH adjustment tank using a secondary lift pump. Sodium hydroxide is added to the secondary pH adjustment tank to adjust the pH to 12. Air stirring is used in the secondary pH adjustment tank, and the reaction time is 30 minutes.

[0067] The effluent from the secondary pH adjustment tank enters the secondary coagulation and sedimentation process. Coagulants and coagulant aids are added to the coagulation tank. The dosage of coagulant polyferric sulfate is 500 mg / L, and the dosage of PAM is 5 mg / L.

[0068] Waste sulfuric acid nanofiltration concentrate from the cold rolling sulfuric acid pickling unit is added to the permeate of the secondary coagulation sedimentation process. The concentration of sulfuric acid in the waste sulfuric acid nanofiltration concentrate is 5%, and the Fe content is... 2+ The concentration is 1%. Adjust the pH to 3.5, Fe... 2+ NO 3- The value is 5.6. The reaction time for this stage is 120 minutes.

[0069] The effluent from the acidification and reduction tank enters the three-stage pH adjustment tank, where sodium hydroxide is added for neutralization to adjust the pH to 6.0.

[0070] The effluent from the three-stage pH adjustment tank enters the three-stage coagulation and sedimentation system, where 5 mg / L of PAM is added.

[0071] Preparation process of high-efficiency defluoridating agent: The pH of pure water is adjusted to 4.5 with sulfuric acid. Then, chitosan and the pH-adjusted water are mixed at a ratio of 1:30. The mixture is heated to 65℃ in a water bath and held at that temperature for 60 minutes to ensure that the chitosan is fully dissolved in the acidic water. After cooling to room temperature, aluminum sulfate and ferric sulfate are added to the chitosan solution, with a molar ratio of aluminum sulfate to ferric sulfate of 1:1.5 and a mass ratio of chitosan to aluminum sulfate and ferric sulfate of 1:10. The mixture of aluminum sulfate, ferric sulfate, and chitosan solution is subjected to ultrasonic intensified mixing for 60 minutes and allowed to stand for 24 hours to complete polymerization, thus obtaining the defluoridating coagulant.

[0072] The composition of the treated solution is as follows:

[0073]

[0074] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention are also within the protection scope of the present invention.

Claims

1. A method for the resource utilization of sodium-based desulfurization ash, characterized in that, Includes the following steps: S1. Add desulfurization ash and water to the mixing tank at a ratio of 1:6 to 8, with the water temperature above 25℃. S2. Use a primary booster pump to lift the mixture to a primary pH adjustment tank. Add sodium hydroxide to the primary adjustment tank to adjust the pH to 11-11.

5. Use air stirring in the primary pH adjustment tank and react for 30-90 minutes. S3. The effluent from the primary pH adjustment tank enters the primary coagulation, defluoridation, and sedimentation process. High-efficiency defluoridating agent and coagulant aid are added to the coagulation tank. S4. The permeate from the primary coagulation and sedimentation process enters the primary permeate tank. The primary permeate is then pumped to the secondary pH adjustment tank using a secondary lift pump. Sodium hydroxide is added to the secondary pH adjustment tank to adjust the pH to 12-13. Air stirring is used in the secondary pH adjustment tank, and the reaction time is 30-90 minutes. S5. The effluent from the secondary pH adjustment tank enters the secondary coagulation and sedimentation process, and coagulants and coagulant aids are added to the coagulation tank. The permeate from the S6 and secondary coagulation sedimentation processes enters the secondary permeate tank. The secondary permeate is then pumped to the acidification and reduction tank by a tertiary lift pump, where waste sulfuric acid nanofiltration concentrate from the cold rolling sulfuric acid pickling unit is added. S7. The effluent from the acidification and reduction tank enters the three-stage pH adjustment tank, where sodium hydroxide is added for neutralization to adjust the pH to 6-7. The effluent from the S8 and tertiary pH adjustment tanks enters the tertiary coagulation and sedimentation system, where polyacrylamide (PAM) is added as a coagulant aid to reduce unreacted Fe2+. 2+ It is oxidized to Fe under neutral conditions 3+ Fe produced by the reduction reaction 2 (SO4) 3 Together they act as coagulants.

2. The method for resource utilization of sodium-based desulfurization ash according to claim 1, characterized in that: In step S1, adding desulfurization ash to the mixing tank allows the sodium sulfate, sodium sulfite, sodium carbonate, and other soluble components in the desulfurization ash to fully dissolve in the water.

3. The method for resource utilization of sodium-based desulfurization ash according to claim 1, characterized in that: The chemical reaction that occurs in step S2 is as follows: 1) Ca dissolved in water in desulfurization ash 2+ Mg 2+ CO3 in desulfurization ash 2- And the newly added OH - The reactions respectively form CaCO3, MgCO3 and Mg(OH)2 precipitates; 2) Si in water exists as SiO3 at pH 11–11.

5. 2- It exists in the form of SiO3 2- With Ca 2+ Mg 2+ CaSiO3 and MgSiO3 precipitates are formed; 3) During stirring, oxygen in the air oxidizes Na2SO3 to Na2SO4, which can improve the purity of subsequent sodium sulfate crystallization.

4. The method for resource utilization of sodium-based desulfurization ash according to claim 1, characterized in that: In step S3, the high-efficiency defluorinating agent can also act as a coagulant, and the coagulant aid is polyacrylamide (PAM). The ratio of high-efficiency defluoridant to fluoride ions is 10-15:1, and the dosage of PAM is 3-5 mg / L. The coagulation defluoridation process can efficiently remove fluoride ions from water.

5. The method for resource utilization of sodium-based desulfurization ash according to claim 1, characterized in that: In step S4, the Mg that was not completely precipitated in the first stage is removed. 2+ Further precipitation, Mg 2+ With OH - The reaction produces Mg(OH)2 precipitate.

6. The method for resource utilization of sodium-based desulfurization ash according to claim 1, characterized in that: In step S5, the coagulant used is polyferric sulfate, with a dosage of 500-1000 mg / L; the coagulant aid used is polyacrylamide (PAM), with a dosage of 3-5 mg / L.

7. The method for resource utilization of sodium-based desulfurization ash according to claim 1, characterized in that: In step S6, the concentration of sulfuric acid in the waste sulfuric acid nanofiltration concentrate is 5-8%, and Fe... 2+ The concentration is 1-2%, and the pH is adjusted to 3-3.5, while ensuring Fe... 2+ NO 3- Greater than 5.

8. The method for resource utilization of sodium-based desulfurization ash according to claim 7, characterized in that: In step S6, the reaction time is 60–120 min, and two reactions occur: 1) Residual CO3 in water 2- Under acidic conditions, it is converted into CO2 and escapes from the water. CO3 2- +H - →CO2↑+H2O; 2) NO in water 3- Fe in waste sulfuric acid nanofiltration concentrate 2+ Under acidic conditions, it is reduced to nitrogen gas, thus NO 3- It was removed: 2NaNO3+10FeSO4+6H2SO4→N2↑+5Fe2(SO4)3+Na2SO4+6H2O.

9. The method for resource utilization of sodium-based desulfurization ash according to any one of claims 1-8, characterized in that: The preparation process of the high-efficiency defluoridating agent: 1) Adjust the pH of pure water to 3.5-4.5 with sulfuric acid, then mix chitosan with the pH-adjusted water at a ratio of 1:20-30, heat in a water bath to 55-65℃, and keep at a constant temperature for 60-90 minutes to allow the chitosan to fully dissolve in the acidic water; 2) After cooling to room temperature, add aluminum sulfate and ferric sulfate to the chitosan solution, wherein the molar ratio of aluminum sulfate to ferric sulfate is 1:1.5 to 1.5:1, and the mass ratio of chitosan to aluminum sulfate and ferric sulfate is 1:5 to 10. 3) Place the mixture of aluminum sulfate, ferric sulfate and chitosan solution in an ultrasonic bath for 40-60 minutes to enhance mixing, and let it stand for 24-48 hours to complete the polymerization and obtain the defluorination coagulant.

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