Method for synergistically preparing magnesium ammonium phosphate by coupling steel slag-steel mill sintering desulfurization wastewater with CO2 in-situ sealing

Abstract

The invention discloses a method for synergistically preparing magnesium ammonium phosphate by coupling steel slag-steel mill sintering desulfurization wastewater with CO2 in-situ sealing. The method comprises the following steps: crushing, screening and drying steel slag; putting the pretreated steel slag into a reaction kettle, adding sintering desulfurization wastewater, raising the temperature, and introducing CO2 into the reaction kettle for reaction; after the reaction is finished, discharging gas in the kettle, cooling to room temperature, performing solid-liquid separation on a reaction product, and drying a solid; adding Na2HPO4 and MgCl2 into the filtrate to react, carrying out solid-liquid separation, and drying the solid to obtain magnesium ammonium phosphate; according to the method, comprehensive treatment and recycling of waste gas-waste residue-waste liquid in the field of steel smelting can be achieved, the carbon emission of a steel plant and the salt content of the waste water are reduced, meanwhile, the follow-up treatment difficulty of the sintering desulfurization waste water is reduced, products with added value are produced, and recycling of resources is fully achieved.

Description

Technical Field

[0001] The invention belongs to the field of wastewater treatment and fertilizer preparation, and specifically relates to a method for synergistically preparing magnesium ammonium phosphate by coupling steel slag-steel plant sintering desulfurization wastewater with CO2 in-situ storage. Background Art

[0002] Over the past two centuries, with the massive use of fossil fuels, the content of CO2 in the atmosphere has increased rapidly. Carbon dioxide can absorb long-wave radiation from the ground, causing the air temperature near the ground to rise. This is called the "greenhouse effect." According to a rough estimate, if the carbon dioxide content in the atmosphere increases by 25%, the temperature near the ground can increase by 0.5 to 2°C. If it increases by 100%, the temperature near the ground can increase by 1.5 to 6°C. Studies have shown that the global average temperature will rise by 1.4-5.8°C from 1900 to 2100. In addition, as a greenhouse gas, CO2 will also cause sea level rise, threatening the living environment of humans. Therefore, reducing CO2 emissions is already urgent for current environmental protection.

[0003] Steel slag is a by-product of the steelmaking industry. It contains abundant alkaline metal ions, which can react with CO2 to form insoluble carbonates, which can stabilize the CO2 storage. However, the current use of steel slag alone to capture CO2 is inefficient, so it is necessary to optimize the process to promote the leaching and activation of alkaline metal ions in steel slag and improve the reaction efficiency. Generally, aqueous solutions can promote the leaching of alkaline ions in steel slag, and the addition of weak acidic solutions and some leaching promoters (NH4 + , Cl - ) can further enhance the CO2 capture efficiency of steel slag, but the processing cost will also increase.

[0004] Sintering desulfurization wastewater is a weakly acidic wastewater produced in the steelmaking process of steel plants, which contains a variety of ions (NH4 + , Cl - , Ca 2+ ), the removal of these ions has always been a difficult problem in wastewater treatment. At present, the main method for treating desulfurization wastewater in China is to discharge it into domestic sewage treatment plants for final treatment after certain pretreatment including precipitation, adjustment, neutralization, biological treatment, osmosis and reverse osmosis. However, this method has strict requirements on the quality of influent water. It is necessary to carry out preliminary desalination before treatment to reduce the load of high ion concentration of influent water on the sewage treatment system, so the cost is relatively high.

[0005] Based on this, this method innovatively utilizes the waste slag, wastewater and waste gas generated in the steelmaking process to construct a steel slag sintering desulfurization wastewater coupled CO2 storage system. This method can not only capture CO2 in the flue gas of steel plants, but also effectively realize the integrated treatment of industrial wastewater, waste gas and waste slag. At the same time, it also produces magnesium ammonium phosphate, a value-added product that can be used to make fertilizers, providing strong support for the sustainable development of the steel industry. Summary of the invention

[0006] Based on the above background, the present invention provides a method for preparing magnesium ammonium phosphate by coupling steel slag-steel plant sintering desulfurization wastewater with CO2 in-situ storage, which aims to reduce CO2 emissions in steel plant flue gas while coordinating wastewater treatment and producing products with added value. The method of the present invention for preparing magnesium ammonium phosphate by coupling steel slag-steel plant sintering desulfurization wastewater with CO2 in-situ storage is as follows: 1. Crushing, screening, drying and cooling the steel slag; The particle size of the crushed slag is less than 500μm; 2. Put the steel slag from step 1 into the reactor, add the sintering desulfurization wastewater from the steel plant, and the volume mass ratio of sintering desulfurization wastewater to steel slag is L:Kg= (10-20):1; 3. Raise the temperature of the reactor to 90-110°C, and introduce CO2 into the reactor at the same time. When the pressure in the reactor reaches 0.1MPa, close the valve and start the reaction; 4. After 30-60 minutes of reaction, release the gas in the kettle, cool to room temperature, separate the reaction product into solid and liquid, dry the solid, and collect the filtrate for the next step of analysis. 5. Slowly add a certain amount of Na2HPO4×12H2O to the filtrate in step 4, stir and dissolve; add a certain amount of MgCl2×6H2O and stir to react, then adjust the pH value to 8-8.5 with a certain concentration of NaOH and HCl, let it stand, filter, and take the supernatant to determine NH4 + and PO4 3- The concentration of the precipitate is dried in a drying oven to obtain magnesium ammonium phosphate, wherein PO4 3- With NH4 + The molar ratio of Mg is 1-1.5:1. 2+ With NH4 + The molar ratio is 1.2-1.5:1.

[0007] The steel slag comprises the following components: CaO (30-40%), Fe3O4 (20-30%), SiO2 (10-20%), MgO (5-10%), Al2O3 (1-5%), TiO2 (1-5%), MnO (1-5%), Cr (0.1-0.5%), and V (0.5-1%).

[0008] The conductivity of steel plant sintering desulfurization wastewater is 35000-40000μS / cm, ammonia nitrogen is 2700-3200mg / L, suspended solids is 50-100mg / L, total hardness (CaCO3) is 40000-50000mg / L, chloride ion is 55000-65000mg / L, and pH (25℃) is 4.5-6.5.

[0009] The method of the present invention can realize the comprehensive treatment and resource utilization of waste gas, waste slag and waste liquid in the field of steel smelting. After the steel slag is added to the sintering desulfurization wastewater, CO2 is introduced into the reactor at the same time of heating; the reaction product is separated into solid and liquid. The solid product is the CO2 storage product, and the filtrate is the sintering desulfurization wastewater after the steel slag is carbonated; the harmful salt ions (Cl - , Ca 2+ , NH4 + ) is partially removed in the CO2 storage reaction. In order to further reduce the ion concentration of the wastewater and enhance the reusability of the wastewater, magnesium salts and phosphate salts will be further added to the water, the pH value will be adjusted and allowed to stand, and finally magnesium ammonium phosphate (MgNH4PO4·6H2O) will be precipitated to achieve NH4 + Magnesium ammonium phosphate is an important raw material for phosphate fertilizers and can be used as a resource. After the steel slag is carbonated, the emission of CO2 is greatly reduced, the salt content of the wastewater is greatly reduced, and the difficulty of subsequent treatment of sintering desulfurization wastewater is reduced. Not only is the discarded steel slag reused, but also products with added value are produced, fully realizing the recycling and reuse of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is the XRD spectrum of magnesium ammonium phosphate prepared by steel slag-steel plant sintering desulfurization wastewater coupling CO2 in-situ storage; Figure 2 This is the SEM image of magnesium ammonium phosphate prepared by coupling steel slag with steel plant sintering desulfurization wastewater and CO2 in-situ storage. DETAILED DESCRIPTION

[0011] The content of the present invention is further explained by the following examples, but these examples do not limit the protection scope of the present invention. The methods in the embodiments are conventional methods unless otherwise specified, and the reagents used are conventional reagents sold on the market unless otherwise specified; The composition of the steel slag in the following examples includes: CaO 39.038%, Fe3O4 21.745%, SiO2 14.964%, MgO 9.89%, Al2O3 3.243%, TiO2 4.689%, MnO 2.472%, Cr 0.221%, V 0.78%; The steel plant sintering desulfurization wastewater has a conductivity of 39250μS / cm, ammonia nitrogen of 3080.80mg / L, suspended solids of 94.40mg / L, total hardness (CaCO3) of 44435.50mg / L, chloride ions of 60520.20mg / L, and a pH (25°C) of 5.25; Example 1: Method for preparing magnesium ammonium phosphate fertilizer by coupling steel slag-steel plant sintering desulfurization wastewater with CO2 in-situ storage 1. Crushing and screening the steel slag to a particle size of less than 500 μm, drying at 105°C, and cooling to room temperature; 2. Put the treated steel slag into the reactor, add sintering desulfurization wastewater, and the volume mass ratio of wastewater to steel slag is L:Kg 20:1; raise the temperature of the reactor to 100°C, and introduce CO2 into the reactor at the same time. When the pressure in the reactor reaches 0.1MPa, close the valve and start the reaction. The reaction time is 60min; 3. After the reaction is completed, the gas in the kettle is released, and after cooling to room temperature, the slurry after the reaction is poured out and filtered. The filter residue is placed in a drying oven at 65°C and dried for 12 hours. The ion concentration of the filtrate is determined by ion chromatography; 4. Use a measuring cylinder to accurately measure the carbonated wastewater and pour it into a pre-prepared beaker. Place the beaker on a magnetic stirrer and press (PO4 3- ):(NH4 + ) Slowly add Na2HPO4×12H2O at a molar ratio of 1.1:1, stir thoroughly at a stirring speed of 100 r / min (until no crystals remain) and dissolve; 5. Then press (Mg 2+ ):(NH4 + ) MgCl2×6H2O was added in a molar ratio of 1.2:1, and the reaction was stirred for 10 min, and then the pH value was adjusted to 8-8.5 with a certain concentration of NaOH and HCl; 6. After the reaction is completed, the water sample is left to stand for 15 minutes, filtered, and the supernatant is taken to determine NH4 + and PO4 3- The precipitate was dried in an oven at 40 °C for 48 hours to obtain magnesium ammonium phosphate. Figure 1 , SEM images are shown in Figure 2 .

[0012] Through the above method, the carbonization rate of steel slag was finally measured to be 75%, and the Cl in the wastewater - The removal rate is 95%, NH4 + The removal rate of Ca is 75%. 2+ The removal efficiency was 50% and the residual concentration of phosphorus was 6.5 mg / L.

[0013] Example 2: Method for preparing magnesium ammonium phosphate by coupling steel slag-steel plant sintering desulfurization wastewater with CO2 in-situ storage 1. Crushing and screening the steel slag to a particle size of less than 500 μm, drying at 105 ° C, and then cooling to room temperature; 2. Put the treated steel slag into the reactor, add sintering desulfurization wastewater, and the volume mass ratio of wastewater to steel slag is L:Kg of 15:1; raise the temperature of the reactor to 100°C, and introduce CO2 into the reactor at the same time. When the pressure in the reactor reaches 0.1MPa, close the valve and start the reaction. The reaction time is 30min; 3. After the reaction is completed, the gas in the kettle is released, and after cooling to room temperature, the slurry after the reaction is poured out and filtered. The filter residue is placed in a drying oven at 65°C and dried for 12 hours. The ion concentration of the filtrate is determined by ion chromatography; 4. Use a measuring cylinder to accurately measure the carbonated wastewater and pour it into a pre-prepared beaker. Place the beaker on a magnetic stirrer and press (PO4 3- ):(NH4 + ) Slowly add Na2HPO4×12H2O at a molar ratio of 1:1, and stir thoroughly at a stirring speed of 100 r / min (until no crystals are left) and dissolve; 5. Then press (Mg 2+ ):(NH4 + ) MgCl2×6H2O was added in a molar ratio of 1.4:1, and the mixture was stirred for 20 min, and then the pH value was adjusted to 8-8.5 with a certain concentration of NaOH and HCl; 6. After the reaction is completed, the water sample is left to stand for 15 minutes, filtered, and the supernatant is taken to determine NH4 + and PO4 3- The resulting precipitate is dried in an oven at 40°C for 48 hours to obtain magnesium ammonium phosphate.

[0014] Through the above method, the carbonization rate of steel slag was finally measured to be 65%, and the Cl in the wastewater - The removal rate of NH4 + The removal rate of Ca was 73%. 2+ The removal efficiency was 50% and the residual concentration of phosphorus was 6.4 mg / L.

[0015] Example 3: Method for preparing magnesium ammonium phosphate by coupling steel slag-steel plant sintering desulfurization wastewater with CO2 in-situ storage 1. Crushing and screening the steel slag to a particle size of less than 500 μm, drying at 105 ° C, and then cooling to room temperature; 2. Put the treated steel slag into the reactor and add sintering desulfurization wastewater, the wastewater to steel slag volume mass ratio L:Kg is 10:1; raise the temperature of the reactor to 100°C, and introduce CO2 into the reactor at the same time. When the pressure in the reactor reaches 0.1MPa, close the valve and start the reaction. The reaction time is 30min; 3. After the reaction is completed, the gas in the kettle is released, and after cooling to room temperature, the slurry after the reaction is poured out and filtered. The filter residue is placed in a drying oven at 65°C and dried for 12 hours. The ion concentration of the filtrate is determined by ion chromatography; 4. Use a measuring cylinder to accurately measure the carbonated wastewater and pour it into a pre-prepared beaker. Place the beaker on a magnetic stirrer and press (PO4 3- ):(NH4 + ) Slowly add Na2HPO4×12H2O at a molar ratio of 1.2:1, and stir thoroughly at a stirring speed of 100 r / min (until no crystals are left) and dissolve; 5. Then press (Mg 2+ ):(NH4 + ) MgCl2×6H2O was added in a molar ratio of 1.3:1, and the mixture was stirred for 30 min, and then the pH value was adjusted to 8-8.5 with a certain concentration of NaOH and HCl; 6. After the reaction is completed, the water sample is left to stand for 15 minutes, filtered, and the supernatant is taken to determine NH4 + and PO4 3- The resulting precipitate is dried in an oven at 40°C for 48 hours to obtain magnesium ammonium phosphate.

[0016] Through the above method, the carbonization rate of steel slag was finally measured to be 50%, and the Cl in the wastewater was - The removal rate of NH4 + The removal rate of Ca is 65%. 2+ The removal efficiency was 40% and the residual concentration of phosphorus was 8 mg / L.

Claims

1. A method for preparing magnesium ammonium phosphate by coupling steel slag-steel plant sintering desulfurization wastewater with CO2 in-situ storage, characterized in that: Here are the steps: (1) Crushing, screening and drying the steel slag; placing the pretreated steel slag into a reactor, adding sintering desulfurization wastewater from the steel plant, heating it to 90-110°C, and introducing CO2 into the reactor at the same time. When the pressure in the reactor reaches 0.1MPa, close the valve and react for 30-60 minutes; (2) After the reaction is completed, the gas in the kettle is released, and the reaction mixture is cooled to room temperature. The reaction product is separated into solid and liquid, and the solid is dried. Na2HPO4 is added to the filtrate, and the mixture is stirred and mixed. MgCl2 is added and stirred for 10 minutes. The pH value is adjusted to 8-8.5, and the mixture is allowed to stand for solid-liquid separation. The solid is dried to obtain magnesium ammonium phosphate.

2. The method for preparing magnesium ammonium phosphate by coupling steel slag-steel plant sintering desulfurization wastewater with CO2 in-situ storage according to claim 1, characterized in that: Add 10-20L of steel plant sintering desulfurization wastewater for every kilogram of steel slag.

3. The method for preparing magnesium ammonium phosphate by coupling steel slag-steel plant sintering desulfurization wastewater with CO2 in-situ storage according to claim 1, characterized in that: PO4 in Na2HPO4×12H2O 3- With NH4 + The molar ratio is 1-1.5:

1.

4. The method for preparing magnesium ammonium phosphate by coupling steel slag-steel plant sintering desulfurization wastewater with CO2 in-situ storage according to claim 1, characterized in that: Mg 2+ With NH4 + The molar ratio is 1.2-1.5:1.

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