A pollution-free method for the complete utilization of silicon steel pickling waste liquid

Abstract

This invention relates to a method for the complete and pollution-free utilization of silicon steel pickling wastewater. It is a novel waste acid treatment method that utilizes vacuum carbothermal reduction of silicon steel pickling sludge to prepare iron-silicon alloys, fully leveraging the value of the waste acid. The entire process includes four stages: waste acid filtration to separate SiO2, ammonia gas or ammonia water purging of the acid to prepare iron-containing precipitate, calcination of the iron-containing precipitate to prepare Fe2O3, and vacuum carbothermal reduction to prepare iron-silicon alloys. In this invention, the main components of silicon steel pickling wastewater—HCl, SiO2, FeCl2, and FeCl3—are all converted into iron-silicon alloys and ammonium chloride, which can be used as an industrial raw material, achieving effective resource utilization and pollution-free discharge.

Description

Technical Field

[0001] This invention relates to the field of waste treatment technology, specifically to a comprehensive utilization technology for pickling waste liquid from silicon steel production, which is particularly suitable for the treatment and resource recycling of pickling waste liquid generated during silicon steel production. Background Technology

[0002] Silicon steel is the core of various motors, generators, and transformers, and is an essential raw material for the power and home appliance industries. During the hot rolling process of silicon steel, due to the high temperature environment and air atmosphere, iron oxide scale will appear on the surface of the hot-rolled silicon steel sheet and strip. The main components of iron oxide scale are FeO, Fe2O3, Fe3O4, and SiO2. In the subsequent processing of silicon steel sheets, it is necessary to remove the iron oxide scale from the surface of the hot-rolled silicon steel. First, shot blasting removes rust: using the high-speed rotation of mechanical equipment, steel shot of a certain particle size is thrown out by the centrifugal force of the blasting head. The thrown steel shot violently collides with the components, thereby removing the rust from the steel surface. Then, pickling removes rust: using the acid in the pickling solution to chemically react with the metal oxides, dissolving the metal oxides and removing the rust and dirt from the steel surface.

[0003] Pickling and rust removal generate a large amount of pickling waste liquid, which contains hydrochloric acid, ferrous chloride, ferric chloride and silica mud (mainly composed of SiO2). Currently, the waste acid is usually treated by directly neutralizing it with a large amount of alkaline solution before being discharged. This treatment method ignores the value of silica mud and iron elements, and its treatment and disposal have problems such as increased economic costs, environmental pollution and waste of resources. Summary of the Invention

[0004] In view of the above-mentioned problems in the existing technology, the technical problem to be solved by the present invention is: how to make rational use of waste liquid and reduce resource waste and environmental pollution.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for the complete and pollution-free utilization of silicon steel pickling waste liquid, comprising the following steps:

[0006] S1: The pickling waste liquid of silicon steel is filtered to obtain precipitate 1 and filtrate 1 (precipitate 1 is silicon mud, whose main component is SiO2).

[0007] S2: Ammonia gas is introduced into filtrate 1 at a flow rate of 30–50 m / s. 3 / h, when the pH of the solution is 6.5 to 8.07, stop the ammonia gas flow and filter to obtain precipitate 2 and filtrate 2 (precipitate 2 is an iron-containing precipitate, filtrate 2 is a nitrogen-containing filtrate, and the main components of filtrate 2 are NH4Cl and NH3·H2O);

[0008] S3: Calcine precipitate 2 to prepare Fe2O3, wherein the calcination temperature is 700-850℃ and the calcination time is 2-4h.

[0009] S4: Coking coal powder was added to Fe2O3 obtained in S3 and precipitate 1 obtained in S1, and a vacuum carbothermic reduction was performed to obtain an iron-silicon alloy. The iron and silicon were mixed in a molar ratio of 1:1, and C was calculated based on the reduced CO with a C excess of 10%. The furnace was cleaned three times with high-purity argon (99.999%). The vacuum degree was maintained below 50 Pa during the experiment. The carbothermic reduction temperature was raised from room temperature to 1250-1350℃ and held for 3-5 hours, and then cooled to room temperature with the furnace.

[0010] Preferably, the optimal flow rate of ammonia gas introduced in S2 is 30 m / s. 3 The ammonia flow was stopped when the solution pH reached 7.5.

[0011] Preferably, the optimal calcination temperature in S3 is 750°C and the calcination time is 3 hours.

[0012] Preferably, the optimal carbothermic reduction reaction temperature in S4 is 1300°C, and the reaction time is 4 hours.

[0013] Preferably, in the S4 carbothermal reduction, the sludge powder is calculated as pure SiO2, the coking coal powder is calculated as 71% fixed carbon, the iron and silicon are mixed in a molar ratio of 1:1, the C is calculated as CO after reduction, and the C is in excess by 10%.

[0014] Compared with the prior art, the present invention has at least the following advantages:

[0015] In this invention, the waste liquid is first filtered, and the precipitate obtained is SiO2. Filtration can extract 99% of the SiO2 from the waste liquid. At this point, the main components of the filtered liquid are HCl, FeCl2, and FeCl3. Ammonia gas or ammonia water is introduced into the liquid, and Fe is converted into an iron-containing precipitate, while HCl is converted into NH4Cl. The iron-containing precipitate is calcined to prepare Fe2O3. Then, Fe2O3, SiO2, and carbon are mixed and subjected to vacuum carbothermic reduction to obtain an iron-silicon alloy. In this invention, the main components of the waste liquid—HCl, SiO2, FeCl2, and FeCl3—are all converted into an iron-silicon alloy and ammonium chloride, which can be used as an industrial raw material, achieving efficient resource utilization and zero-pollutant emissions. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the method of the present invention.

[0017] Figure 2 The XRD results are for silica mud.

[0018] Figure 3 The raw material briquettes are those used in Example 1.

[0019] Figure 4The morphology of the reduced sample in Example 1.

[0020] Figure 5 The XRD results are for the reduced sample. Detailed Implementation

[0021] The present invention will now be described in further detail.

[0022] See Figure 1 The pickling waste liquid from hot-rolled silicon steel coils is first filtered to obtain precipitate 1 and filtrate 1. After drying, precipitate 1 yields dried silica mud powder. Ammonia gas or ammonia water is passed through filtrate 1, and then filtered to obtain precipitate 2 and filtrate 2. Filtrate 2 can be used as a raw material for making nitrogen fertilizer. After calcining precipitate 2, iron oxide powder is obtained. The iron oxide powder, silica mud powder, and carbon powder are mixed in a certain proportion and then vacuum carbothermic reduction is performed to prepare iron-silicon alloy. In the entire process, silicon and iron elements can be utilized as resources and no waste is generated.

[0023] Example 1: A method for the complete and pollution-free utilization of silicon steel pickling waste liquid, comprising the following steps:

[0024] S1: Filter the waste liquid

[0025] The pickling waste liquid was filtered to obtain precipitate 1 and filtrate 1. After drying, precipitate 1 was weighed. The silica mud content in the waste liquid was 10-20 g / L. The main components of the silica mud are shown in Table 1. The main component of the silica mud is silicon dioxide. The hydrochloric acid concentration in the waste acid liquid was about 10%, and the iron concentration was 80-120 g / L.

[0026] The phase composition of silica mud was analyzed using XRD, and the results are as follows: Figure 2 As shown, the silica mud mainly exists as amorphous material, and XRF analysis shows that it consists of SiO2 and a small amount of Fe3O4.

[0027] Table 1 Chemical composition of pickling sludge (wt.%)

[0028]

[0029] S2: Ammonia gas is introduced into filtrate 1 at a flow rate of 30 m / s. 3 / h, when the solution pH is 7.5, stop the ammonia gas flow and filter to obtain precipitate 2 and filtrate 2. The main component of precipitate 2 is iron oxide and a small amount of chlorine.

[0030] Table 2 Chemical composition of precipitate 2 (wt.%) based on oxides

[0031]

[0032] S3: Calcine precipitate 2 to prepare Fe2O3, wherein the calcination temperature is 750℃ and the calcination time is 3h.

[0033] Table 3 Chemical composition of precipitate 2 after calcination (wt.%) (based on oxides)

[0034]

[0035] S4: Carbothermic reduction to prepare iron-silicon alloy. Coking coal powder is added to Fe2O3 obtained in S3 and precipitate I obtained in S1. The silica mud is calculated as pure SiO2, the coking coal powder is calculated as 71% fixed carbon, the iron and silicon are mixed in a molar ratio of 1:1, and C is calculated as CO after reduction. C is in excess by 10%. The specific composition is listed in Table 2.

[0036] Table 2 Raw material ratio for vacuum carbothermal reduction

[0037]

[0038] The raw materials are thoroughly ground in an agate mortar to ensure uniform mixing, and then pressed into blocks using a block press. Figure 3 As shown.

[0039] The raw materials were mixed evenly and pressed into blocks using a briquetting mold on a press. The blocks were placed in a corundum crucible and then placed in a vacuum high-temperature furnace for vacuum thermal reduction. Vacuum regime: The furnace was cleaned three times with high-purity argon (99.999%), and a vacuum was maintained below 50 Pa throughout the reaction. Temperature regime: The temperature was increased from room temperature to 1300℃ at a rate of 8℃ / min and held for 4 hours, then cooled to room temperature with the furnace. The results of the reduced sample test are as follows. Figure 2 As shown in the figure. The results indicate that the reduced sample mainly contains Fe. x Si y The main component is Fe. x Si y The content is 92.53%.

[0040] The morphology of the sample after reduction is as follows Figure 4 As shown, the XRD detection results are as follows: Figure 2 As shown in the figure. The results indicate that the reduced sample mainly consists of ferrosilicon alloy Fe. x Si y It is mainly composed of Fe and C.

[0041] Examples 2-5 follow the same process steps as Example 1, except for the selection of process parameters. For details on the selection of process parameters, please refer to Table 3.

[0042] Table 3 Implementation Cases

[0043]

[0044] As shown in Table 3, the amount of ammonia added in S2 determines the pH of the solution, which in turn determines the recovery rate of iron in the solution, but does not affect the content of iron-silicon alloy in the product. The higher the calcination temperature and the longer the calcination time in S3, the more complete the conversion of precipitate II to Fe2O3, which is beneficial to the synthesis of iron-silicon alloy. When the temperature is higher than 750℃, there is no significant change in the iron-silicon alloy content in the product. The higher the vacuum carbothermal reduction temperature in S4, the higher the iron-silicon alloy content in the product. When the temperature is higher than 1300℃, there is no significant change in the iron-silicon alloy content in the product.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for the complete and pollutant-free utilization of silicon steel pickling waste liquid, characterized in that, Includes the following steps: S1: The pickling waste liquid of silicon steel is filtered to obtain precipitate 1 and filtrate 1; the main components of the pickling waste liquid of silicon steel are HCl, SiO2, FeCl2 and FeCl3; S2: Ammonia gas is introduced into filtrate 1 to obtain NH4Cl, which is used as a nitrogen fertilizer raw material. The flow rate of ammonia gas introduced is 30-50 m / s. 3 / h, when the solution pH is 6.5 to 8.07, stop the ammonia gas flow and filter to obtain precipitate 2 and filtrate 2; S3: Calcine precipitate 2 to prepare Fe2O3, wherein the calcination temperature is 700-850℃ and the calcination time is 2-4h; S4: Coking coal powder is added to Fe2O3 obtained in S3 and precipitate 1 obtained in S1, and iron-silicon alloy is obtained by vacuum carbothermal reduction. The iron and silicon are mixed in a molar ratio of 1:1, and C is calculated as CO after reduction. The carbothermal reduction temperature is raised from room temperature to 1250-1350℃ and held for 3-5 hours, and then cooled to room temperature with the furnace.

2. The method for the complete and pollutant-free utilization of silicon steel pickling waste liquid as described in claim 1, characterized in that: The optimal flow rate for ammonia gas introduced into S2 is 30 m / s. 3 The ammonia flow was stopped when the solution pH reached 7.

5.

3. The method for the complete and pollutant-free utilization of silicon steel pickling waste liquid as described in claim 2, characterized in that: The optimal calcination temperature for S3 is 750℃, and the calcination time is 3h.

4. The method for the complete and pollutant-free utilization of silicon steel pickling waste liquid as described in claim 2, characterized in that: The optimal carbothermic reduction reaction temperature in S4 is 1300℃, and the reaction time is 4h.

5. The method for the complete and pollutant-free utilization of silicon steel pickling waste liquid as described in claim 2, characterized in that: In the S4 carbothermic reduction, the sludge powder is calculated as pure SiO2, the coking coal powder is calculated as 71% fixed carbon, the iron and silicon are mixed in a molar ratio of 1:1, the C is calculated as CO after reduction, and the C is in excess by 10%.

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