A method for the collaborative utilization of by-products of steel desulfurization

Abstract

The present invention belongs to the technical field of resource utilization of solid waste, and discloses a method for co-utilizing by-products of steel desulfurization. The method comprises the following steps: 1) Mix calcium-based desulfurized ash and sodium-based desulfurized ash, control the molar ratio of NaHCO₃ in the sodium-based desulfurized ash to Ca(OH)₂ in the calcium-based desulfurized ash to be 2:1, add water and stir to form a suspension; 2) Under stirring conditions, introduce air into the suspension for reaction; 3) Perform solid-liquid separation on the reacted suspension, the obtained liquid product is a sodium salt solution, and the obtained solid product is a calcium-based product after drying. The present invention co-utilizes calcium-based desulfurized ash and sodium-based desulfurized ash, and prepares them into a sodium salt solution and a calcium-based product, which can be respectively recycled to the zero-discharge desalination system of the steel enterprise and the limestone-gypsum method desulfurization system, so as to solve the problem of disposal of desulfurization solid waste in the steel enterprise.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste resource utilization, and particularly relates to a method for co-utilizing by-products of steel desulfurization. Background Art

[0002] Sulfur is a harmful element in steel metallurgy. More than 85% of the sulfur in the whole steel production process is discharged into the atmosphere in the form of SO2. Flue gas desulfurization is an important environmental protection measure. The semi-dry desulfurization process is widely used because of its simple process, high desulfurization efficiency and low cost, and a large amount of difficult-to-utilize by-product desulfurization ash is generated, becoming an environmental protection problem for steel enterprises.

[0003] According to different working conditions, desulfurization processes, desulfurizing agents, etc., the semi-dry desulfurization ash is divided into calcium-based desulfurization ash and sodium-based desulfurization ash. The calcium-based desulfurization ash mainly contains substances such as Ca(OH)2, CaSO4, Ca2SO3, CaCO3, CaCl2, etc. The current utilization methods include cement retarder, co-disposal in limestone-gypsum desulfurization process, return to sintering for utilization, and use in tailings treatment, etc. The sodium-based desulfurization ash mainly contains substances such as Na2SO4, Na2SO3, NaHCO3, etc. There is less research on related utilization technologies, and there are also fewer reports on large-scale industrial application cases. There are reports in the literature on the use of similar materials for wastewater treatment, production of compound fertilizers and conversion utilization, etc. However, the existing utilization technologies generally have problems such as high disposal costs and insufficient application adaptability, and the problem of resource utilization of steel plant desulfurization by-products has not been completely solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for co-utilizing by-products of steel desulfurization in view of the deficiencies of the existing technology, which co-utilizes calcium-based desulfurization ash and sodium-based desulfurization ash to prepare raw materials that can be used in the processes of flue gas treatment and water treatment, and recycle them within steel enterprises to solve the problem of solid waste disposal in steel enterprises.

[0005] To solve the technical problems proposed by the present invention, the present invention provides a method for co-utilizing by-products of steel desulfurization, including the following steps:

[0006] 1) After mixing calcium-based desulfurization ash and sodium-based desulfurization ash, add water and stir to make a suspension;

[0007] 2) Under stirring conditions, introduce air into the suspension for reaction;

[0008] 3) Perform solid-liquid separation on the reacted suspension. The liquid product obtained is a sodium salt solution, and the solid product obtained is a calcium-based product after drying.

[0009] In the above solution, the calcium-based desulfurized ash comprises components with the following mass percentages: 25-40% of Ca(OH)₂, 25-40% of CaSO₃, 10-20% of CaSO₄, 5-15% of CaCO₃, 1.5-5% of CaCl₂, and the mass ratio of CaSO₃ to CaSO₄ > 2, with the balance being crystal water and other trace impurities.

[0010] In the above solution, more than 80% by mass of the particles in the calcium-based desulfurized ash have a particle size ≤ 75 μm.

[0011] In the above solution, the sodium-based desulfurized ash comprises components with the following mass percentages: 30-60% of Na₂SO₄, 10-20% of Na₂SO₃, 20-60% of NaHCO₃, and the mass ratio of Na₂SO₄ to Na₂SO₃ > 2, with the balance being crystal water and other trace impurities.

[0012] In the above solution, more than 90% by mass of the particles in the sodium-based desulfurized ash have a particle size ≤ 75 μm.

[0013] In the above solution, when the calcium-based desulfurized ash and the sodium-based desulfurized ash are mixed, the molar ratio of NaHCO₃ to Ca(OH)₂ is controlled to be 2:1.

[0014] In the above solution, the water is pure water, industrial water or intermediate water in steel enterprises.

[0015] In the above solution, the mass of the water is 6-12 times the mass of the sodium-based desulfurized ash.

[0016] Preferably, the mass of the water is 6-8 times the mass of the sodium-based desulfurized ash.

[0017] In the above solution, the stirring rate is 30-60 rpm.

[0018] In the above solution, the stirring time in step 1) is 5-10 min.

[0019] In the above solution, the ventilation air velocity in step 2) is 3.5-8 m / s, and the ventilation reaction time is 30-60 min.

[0020] Preferably, the ventilation reaction time in step 2) is 40-50 min.

[0021] In the above solution, the sodium salt solution comprises components with the following mass percentages: 5-15% of Na₂SO₄, 0-1% of Na₂CO₃, 0.05-0.5% of NaCl, with the balance being water and other impurities; the sodium salt solution can be recycled for the desalination system of zero wastewater discharge to produce solid Na₂SO₄ and crude NaCl.

[0022] In the above solution, the calcium-based product comprises components with the following mass percentages: 75-99.9% CaCO3, 0-25% CaSO3, and the balance being inevitable other impurities; the calcium-based product can be recycled and used in the limestone-gypsum flue gas desulfurization system to replace limestone.

[0023] The main chemical principles of the technical solution of the present invention are as follows:

[0024] Reaction 1: 2NaHCO3 + Ca(OH)2 = Na2CO3 + CaCO3↓ + 2H2O

[0025] Reaction 2: Na2CO3 + CaCl2 = 2NaCl + CaCO3↓

[0026] Reaction 3: Na2CO3 + CaSO4 = Na2SO4 + CaCO3↓

[0027] Reaction 4: Na2CO3 + CaSO3 = Na2SO3 + CaCO3↓

[0028] Reaction 5: 2Na2SO3 + O2 = 2Na2SO4

[0029] Reaction 6: 2CaSO3 + O2 = 2CaSO4

[0030] At room temperature, Ca(OH)2 in the calcium-based desulfurization ash reacts with NaHCO3 in the sodium-based desulfurization ash to undergo Reaction 1, generating soluble sodium salt Na2CO3 and insoluble CaCO3. After the reaction, Na2CO3 further reacts with various calcium salts in sequence to undergo Reactions 2-4, producing soluble sodium salts and insoluble CaCO3, thereby realizing the anion-cation exchange and spontaneous purification in the solid phase and liquid phase. CaCO3 is insoluble, CaSO3 is hardly soluble and mainly exists in the solid phase, while Na2SO4 and NaCl are soluble and exist in the solution.

[0031] Excess air is introduced into the water, and the oxygen in the air oxidizes Na2SO3 to Na2SO4 (Reaction 5), and a very small amount of CaSO3 may also be oxidized to CaSO4 (Reaction 6). The produced CaSO4 may exist in the water or in the solid, but it does not affect the further recycling and utilization of the obtained solid and liquid products. In addition, introducing air can also disturb the solution and has a certain effect of accelerating the reaction.

[0032] The solid product produced by the present invention is mainly CaCO3, or a mixture of CaCO3 and CaSO3, in a powdery form, which can be used as a calcium-based raw material to replace limestone in the limestone-gypsum flue gas desulfurization system. CaSO3 has good solubility in the limestone-gypsum slurry (pH 5-6), can be converted into CaSO4 with this process, and can be resourcefully utilized in the form of the by-product desulfurized gypsum of the limestone-gypsum method.

[0033] The liquid product generated by the present invention is mainly a mixed solution of Na2SO4 and NaCl, which can be recycled and used in the desalination system for zero discharge of steel mill wastewater to produce solid Na2SO4 and crude NaCl in this system, achieving high-value utilization. The solution may also contain Na2CO3, which does not affect the reuse of the aqueous solution in the zero-discharge desalination system. Such substances can be transformed in the desalination system and can be further converted into Na2SO4 by adding sulfuric acid.

[0034] In the invention, controlling the water addition amount can reasonably control the concentration of the solution product. According to the solubility of Na2SO4, water with a mass 6 to 12 times that of the sodium-based desulfurized ash can ensure its dissolution to form a concentrated solution, which is beneficial to reducing the operation cost of the desalination system. However, adding excessive water more than 12 times will dilute the solution and is not conducive to reducing the desalination cost.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] 1) The present invention co-disposes calcium-based desulfurized ash and sodium-based desulfurized ash, and reasonably converts them into solid and liquid products by utilizing the chemical composition and solubility characteristics of the two solid wastes, realizing waste treatment with waste. The two products obtained can be further recycled and utilized in the steel mill, solving the environmental protection problem of resource utilization of steel mill flue gas desulfurization solid waste and reducing solid waste emissions.

[0037] 2) The process equipment of the present invention is simple, easy to handle, has low energy consumption, treats waste with waste, has no raw material cost, can be produced on a large scale, is not restricted by other conditions, and has good economic performance and wide application potential for popularization. Description of the Drawings

[0038] Figure 1 It is the process flow chart of the embodiment of the present invention. Detailed Embodiments

[0039] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments. However, the content of the present invention is not limited to the following embodiments only.

[0040] Embodiment 1

[0041] A steel mill produces two by-products from steel desulfurization:

[0042] 1) Calcium-based desulfurized ash. After detection, its main chemical components are: Ca(OH)2 38.9%, CaSO3 36.2%, CaSO4 16.3%, CaCO3 5.9%, CaCl2 1.8%. The mass ratio of CaSO3 to CaSO4 is 2.22. It also contains a certain amount of crystal water and other trace impurities. The particle size is such that the particle diameter of more than 80% by mass is ≤75 μm;

[0043] 2) The sodium-based desulfurized ash, upon detection, mainly contains the following chemical components: 57.4% of Na2SO4, 19.2% of Na2SO3, 22.8% of NaHCO3. The mass ratio of Na2SO4 to Na2SO3 is 2.99. It also contains a certain amount of crystal water and other trace impurities. The particle size is such that the particle diameter of particles with a mass of more than 90% is ≤75 μm.

[0044] The following method is used for the collaborative utilization of the above two by-products, including the following steps:

[0045] 1) Mix the calcium-based desulfurized ash and the sodium-based desulfurized ash in an amount such that the molar ratio of NaHCO3 in the sodium-based desulfurized ash to Ca(OH)2 in the calcium-based desulfurized ash is 2:1. Then add pure water six times the mass of the sodium-based desulfurized ash and stir at 30 r / min for 9 min to make a suspension.

[0046] 2) Under the stirring condition of 30 r / min, pass air into the suspension for reaction. The ventilation air speed is 4 m / s, and the ventilation reaction time is 55 min.

[0047] 3) Filter the suspension after the reaction. The liquid product obtained is a sodium salt solution, and the solid product obtained is a calcium-based product after drying.

[0048] Upon detection, the obtained sodium salt solution is a mixed solution of Na2SO4, Na2CO3, and NaCl. Among them, the mass fraction of Na2SO4 is 13.58%, the mass fraction of Na2CO3 is 0.38%, and the mass fraction of NaCl is 0.08%. It can be recycled for the desalination system of zero discharge of steel plant wastewater to produce solid Na2SO4 and crude salt of NaCl. The main component of the obtained calcium-based product is CaCO3 with a mass fraction of 99.6%, and the balance is other inevitable impurities. It can be used as a substitute for limestone and recycled for the limestone-gypsum method desulfurization system of the steel plant.

[0049] Example 2

[0050] A steel plant produces two by-products during iron and steel desulfurization:

[0051] 1) The calcium-based desulfurized ash, upon detection, mainly contains the following chemical components: 26.3% of Ca(OH)2, 37.5% of CaSO3, 18.1% of CaSO4, 13.4% of CaCO3, 4.1% of CaCl2. The mass ratio of CaSO3 to CaSO4 is 2.07. It also contains a certain amount of crystal water and other trace impurities. The particle size is such that the particle diameter of particles with a mass of more than 80% is ≤75 μm.

[0052] 2) The sodium-based desulfurized ash, upon detection, mainly contains the following chemical components: 56.7% of Na2SO4, 14.8% of Na2SO3, 27.7% of NaHCO3. The mass ratio of Na2SO4 to Na2SO3 is 3.83. It also contains a certain amount of crystal water and other trace impurities. The particle size is such that the particle diameter of particles with a mass of more than 90% is ≤75 μm.

[0053] The following method is used for the collaborative utilization of the above two by-products, including the following steps:

[0054] 1) Mix the calcium-based desulfurized ash and the sodium-based desulfurized ash in an amount such that the molar ratio of NaHCO3 in the sodium-based desulfurized ash to Ca(OH)2 in the calcium-based desulfurized ash is 2:1. Then add industrial water nine times the mass of the sodium-based desulfurized ash and stir at 36 r / min for 7 min to make a suspension.

[0055] 2) Under the stirring condition of 36 r / min, pass air into the suspension for reaction. The ventilation air speed is 5 m / s, and the ventilation reaction time is 45 min.

[0056] 3) Filter the suspension after the reaction. The liquid product obtained is a sodium salt solution, and the solid product obtained is a calcium-based product after drying.

[0057] Upon detection, the obtained sodium salt solution is a mixed solution of Na2SO4 and NaCl. Among them, the mass fraction of Na2SO4 is 9.66%, and the mass fraction of NaCl is 0.22%. It can be recycled for the desalination system of zero wastewater discharge in the steel plant to produce solid Na2SO4 and crude salt of NaCl. The main components of the obtained calcium-based product are 81.5% of CaCO3 and 17.6% of CaSO3 by mass fraction, and the balance is other inevitable impurities. It can replace limestone and be recycled for the limestone-gypsum desulfurization system in the steel plant.

[0058] Example 3

[0059] A steel plant produces two by-products during steel desulfurization:

[0060] 1) The calcium-based desulfurized ash, upon detection, mainly contains the following chemical components: 39.2% of Ca(OH)2, 27.9% of CaSO3, 13.3% of CaSO4, 14.2% of CaCO3, 4.7% of CaCl2. The mass ratio of CaSO3 to CaSO4 is 2.10. It also contains a certain amount of crystal water and other trace impurities. The particle size is such that the particle diameter of particles with a mass of more than 80% is ≤75 μm.

[0061] 2) The sodium-based desulfurized ash, upon detection, mainly contains the following chemical components: 32.6% of Na2SO4, 12.3% of Na2SO3, 54.5% of NaHCO3. The mass ratio of Na2SO4 to Na2SO3 is 2.65. It also contains a certain amount of crystal water and other trace impurities. The particle size is such that the particle diameter of more than 90% by mass is ≤75 μm.

[0062] The following method is used for the collaborative utilization of the above two by-products, including the following steps:

[0063] 1) Mix the calcium-based desulfurized ash and the sodium-based desulfurized ash in an amount such that the molar ratio of NaHCO3 in the sodium-based desulfurized ash to Ca(OH)2 in the calcium-based desulfurized ash is 2:1. Then add 11 times the mass of the sodium-based desulfurized ash of steelmaking water, and stir at 45 r / min for 6 min to make a suspension.

[0064] 2) Under the stirring condition of 45 r / min, pass air into the suspension for reaction. The ventilation air speed is 6 m / s, and the ventilation reaction time is 40 min.

[0065] 3) Filter the reacted suspension. The liquid product obtained is a sodium salt solution, and the solid product obtained is a calcium-based product after drying.

[0066] Upon detection, the obtained sodium salt solution is a mixed solution of Na2SO4 and NaCl. Among them, the mass fraction of Na2SO4 is 5.73%, and the mass fraction of NaCl is 0.29%. It can be recycled for the zero-discharge desalination system of steel plant wastewater to produce solid Na2SO4 and crude salt of NaCl. The main components of the obtained calcium-based product are 84.6% of CaCO3 and 14.6% of CaSO3 by mass fraction, and the balance is other inevitable impurities. It can replace limestone and be recycled for the limestone-gypsum desulfurization system of the steel plant.

[0067] Example 4

[0068] A steel plant produces two by-products during steel desulfurization:

[0069] 1) The calcium-based desulfurized ash, upon detection, mainly contains the following chemical components: 25.9% of Ca(OH)2, 37.8% of CaSO3, 18.1% of CaSO4, 14.1% of CaCO3, 3.3% of CaCl2. The mass ratio of CaSO3 to CaSO4 is 2.09. It also contains a certain amount of crystal water and other trace impurities. The particle size is such that the particle diameter of more than 80% by mass is ≤75 μm.

[0070] 2) The sodium-based desulfurized ash, upon detection, mainly contains the following chemical components: Na2SO4 33.2%, Na2SO3 13.5%, NaHCO3 52.8%. The mass ratio of Na2SO4 to Na2SO3 is 2.46. It also contains a certain amount of crystal water and other trace impurities. The particle size is such that the particle diameter of particles with a mass of more than 90% is ≤75 μm.

[0071] The following method is used for the co-utilization of the above two by-products, including the following steps:

[0072] 1) Mix the calcium-based desulfurized ash and the sodium-based desulfurized ash in an amount such that the molar ratio of NaHCO3 in the sodium-based desulfurized ash to Ca(OH)2 in the calcium-based desulfurized ash is 2:1. Then add pure water 11 times the mass of the sodium-based desulfurized ash and stir at 50 r / min for 5 min to make a suspension.

[0073] 2) Under the condition of stirring at 50 r / min, pass air into the suspension for reaction. The ventilation air velocity is 7 m / s, and the ventilation reaction time is 35 min.

[0074] 3) Filter the suspension after the reaction. The liquid product obtained is a sodium salt solution, and the solid product obtained is a calcium-based product after drying.

[0075] Upon detection, the obtained sodium salt solution is a mixed solution of Na2SO4 and NaCl. Among them, the mass fraction of Na2SO4 is 7.73%, and the mass fraction of NaCl is 0.29%. It can be recycled for the desalination system of zero discharge of steel plant wastewater to produce solid Na2SO4 and crude salt of NaCl. The main components of the obtained calcium-based product are CaCO3 with a mass fraction of 81.3% and CaSO3 with a mass fraction of 17.9%. The balance is other inevitable impurities and can be used to replace limestone and recycled for the limestone-gypsum desulfurization system of the steel plant.

[0076] Example 5

[0077] A steel plant produces two by-products during steel desulfurization:

[0078] 1) The calcium-based desulfurized ash, upon detection, mainly contains the following chemical components: Ca(OH)2 33.4%, CaSO3 32.6%, CaSO4 15.7%, CaCO3 13.6%, CaCl2 4.3%. The mass ratio of CaSO3 to CaSO4 is 2.08. It also contains a certain amount of crystal water and other trace impurities. The particle size is such that the particle diameter of particles with a mass of more than 80% is ≤75 μm.

[0079] 2) The sodium-based desulfurized ash, upon detection, mainly contains the following chemical components: 45.5% of Na2SO4, 14.6% of Na2SO3, 39.2% of NaHCO3. The mass ratio of Na2SO4 to Na2SO3 is 3.12. It also contains a certain amount of crystal water and other trace impurities. The particle size is such that the particle diameter of more than 90% by mass is ≤75 μm.

[0080] The following method is used for the collaborative utilization of the above two by-products, including the following steps:

[0081] 1) Mix the calcium-based desulfurized ash and the sodium-based desulfurized ash in an amount such that the molar ratio of NaHCO3 in the sodium-based desulfurized ash to Ca(OH)2 in the calcium-based desulfurized ash is 2:1. Then add pure water eight times the mass of the sodium-based desulfurized ash and stir at 60 r / min for 7 min to make a suspension.

[0082] 2) Under the condition of stirring at 60 r / min, pass air into the suspension for reaction. The ventilation air velocity is 8 m / s, and the ventilation reaction time is 45 min.

[0083] 3) Filter the suspension after the reaction. The liquid product obtained is a sodium salt solution, and the solid product obtained is a calcium-based product after drying.

[0084] Upon detection, the obtained sodium salt solution is a mixed solution of Na2SO4, Na2CO3, and NaCl. Among them, the mass fraction of Na2SO4 is 10.37%, the mass fraction of Na2CO3 is 0.20%, and the mass fraction of NaCl is 0.33%. It can be recycled for the desalination system of zero discharge of steel plant wastewater to produce solid Na2SO4 and crude salt of NaCl. The main component of the obtained calcium-based product is CaCO3 with a mass fraction of 99.4%, and the balance is other inevitable impurities. It can replace limestone and be recycled for the limestone-gypsum method desulfurization system of the steel plant.

[0085] The above embodiments are merely examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Therefore, the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for the collaborative utilization of steel desulfurization by-products, characterized in that, It includes the following steps: 1) Mix calcium-based desulfurized ash and sodium-based desulfurized ash, control the molar ratio of NaHCO3 in the sodium-based desulfurized ash to Ca(OH)2 in the calcium-based desulfurized ash to be 2:1, add 6 - 12 times the mass of water of the sodium-based desulfurized ash and stir to make a suspension; 2) Under stirring conditions, pass air into the suspension for reaction, the ventilation speed is 3.5 - 8 m / s, and the ventilation reaction is carried out for 30 - 60 min; 3) Carry out solid-liquid separation on the reacted suspension, the obtained liquid product is a sodium salt solution, and the obtained solid product is a calcium-based product after drying; The calcium-based desulfurized ash includes the following components by mass percentage: Ca(OH)2 25 - 40%, CaSO3 25 - 40%, CaSO4 10 - 20%, CaCO3 5 - 15%, CaCl2 1.5 - 5%, and the balance is crystal water and other trace impurities; The sodium-based desulfurized ash includes the following components by mass percentage: Na2SO4 30 - 60%, Na2SO3 10 - 20%, NaHCO3 20 - 60%, and the balance is crystal water and other trace impurities.

2. The co-utilization method of the by-products of steel desulfurization according to claim 1, wherein In the calcium-based desulfurized ash, the mass ratio of CaSO3 to CaSO4 > 2; in the sodium-based desulfurized ash, the mass ratio of Na2SO4 to Na2SO3 > 2.

3. The co-utilization method of the by-products of steel desulfurization according to claim 1, wherein The sodium salt solution includes the following components by mass percentage: Na2SO4 5 - 15%, Na2CO3 0 - 1%, NaCl 0.05 - 0.5%, and the balance is water and other impurities.

4. The co-utilization method of the by-products of steel desulfurization according to claim 1, characterized in that The calcium-based product includes the following components by mass percentage: CaCO3 75 - 99.9%, CaSO3 0 - 25%, and the balance is other inevitable impurities.

5. The co-utilization method of the by-products of steel desulfurization according to claim 1, characterized in that The stirring rate is 30 - 60 rpm; the stirring time in step 1) is 5 - 10 min.

6. The co-utilization method of the by-products of steel desulfurization according to claim 1, characterized in that In the calcium-based desulfurized ash, more than 80% of the mass of the particles have a particle size ≤ 75 μm; in the sodium-based desulfurized ash, more than 90% of the mass of the particles have a particle size ≤ 75 μm.

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