Method for preparing reduced iron powder using cold-rolled sludge

Abstract

This invention discloses a method for preparing reduced iron powder from cold-rolled sludge. The cold-rolled sludge is dried, crushed, and ball-milled to obtain cold-rolled sludge powder with a mesh size of less than 100 mesh. The obtained cold-rolled sludge powder is fed into a chain grate for preheating and then into a high-level silo 1 of a secondary reduction furnace, which is connected to a distributor 1. The preheated primary reduced iron powder is fed into a high-level silo 2 of the secondary reduction furnace, which is also connected to a distributor 2. In the distribution section of the secondary reduction furnace, a layer of cold-rolled sludge powder with a thickness of 1–3 mm is arranged on the steel strip of the secondary reduction furnace using the distributor 1. A layer of primary reduced iron powder with a thickness of 15–27 mm is then arranged on the cold-rolled sludge powder layer using the distributor 2 to obtain a mixed layer. The resulting mixed layer is fed into the reduction section of the secondary reduction furnace along with the steel strip, where it undergoes secondary fine reduction in an H2 atmosphere, and is then post-processed to obtain reduced iron powder.

Description

Technical Field

[0001] This invention pertains to the resource utilization of solid waste, specifically involving a method for preparing reduced iron powder using cold-rolled sludge. Background Technology

[0002] Cold-rolled sludge is a solid waste generated during the pickling process in cold-rolled sheet mills, requiring costly and environmentally friendly disposal. Research indicates that cold-rolled sludge primarily consists of three phases: solid, water, and oil, emulsified together. The solid phase, generated from friction between the steel sheet and rolls, is essentially micron-sized iron filings, representing a valuable ferrite resource. The oil phase is a plastic organic material. While outsourcing the environmental treatment of cold-rolled sludge solves the environmental problem, it is costly and represents a waste of high-quality resources.

[0003] CN 106281635A proposes a method for recovering and purifying sludge from cold-rolled silicon steel emulsion. The method involves pulping and demulsifying the sludge, removing silicon, separating, and extracting to obtain different products such as iron powder and rolling oil, which are then utilized. However, this method is lengthy, consumes large amounts of organic solvents, requires complex separation equipment, and has high costs for processing the sludge itself.

[0004] CN 104946893B proposes a method for extracting ultrafine iron from cold-rolled sludge. It is based on separation, oil replacement, and organic solvent extraction to separate and process cold-rolled sludge and obtain ultrafine iron powder. However, the separation and processing also suffers from problems such as high cost and long processing time.

[0005] CN 108558156A provides a method for the resource utilization of oil sludge produced in cold-rolled steel plants. The method involves heating and dehydrating the oil sludge, catalytically cracking it, and condensing it to obtain products such as light cracked oil, heavy cracked oil, and cracked dry residue. This method focuses on oil sludge cracking and is suitable for situations where the oil content in the oil sludge is high. The key point is the recovery of oil.

[0006] CN 108863426A proposes a method for preparing lightweight ceramsite from cold-rolled oil sludge. The method primarily involves mixing fly ash, bentonite, and cold-rolled oil sludge in a specific ratio, followed by granulation, drying, calcination, and cooling to obtain ultralight ceramsite. This method mainly focuses on the harmless disposal of oil sludge and does not realize the valuable utilization of the resources within the oil sludge. Summary of the Invention

[0007] Reduced iron powder is a high-grade raw material used in the powder metallurgy industry and is indispensable for manufacturing metal parts for automobiles and motorcycles. The two-step reduction method is a classic process for producing reduced iron powder. It involves subjecting high-purity iron ore powder or iron oxide scale to varying degrees of primary pre-reduction and secondary fine reduction, followed by magnetic separation purification to obtain qualified reduced iron powder. Reduced iron powder is relatively expensive in the market, mainly due to the difficulty in obtaining high-purity iron ore powder and iron oxide scale, as well as the high reduction cost. Cold-rolled sludge contains a large amount of high-purity micron-sized metallic iron filings, making it a potential candidate for the two-step reduced iron powder production process.

[0008] The purpose of this invention is to provide a method for preparing reduced iron powder using cold-rolled sludge. The cold-rolled sludge is treated and used in a secondary reduction process to replace conventional raw materials, which not only saves disposal costs but also realizes high-value-added resource utilization of steel solid waste.

[0009] To achieve the above objectives, the following technical solution is adopted:

[0010] A method for preparing reduced iron powder from cold-rolled sludge includes the following steps:

[0011] 1) After drying, the cold-rolled sludge is crushed and ball-milled to obtain cold-rolled sludge powder with a mesh size of less than 100.

[0012] 2) The obtained cold-rolled sludge powder is fed into a chain grate machine for preheating, and then fed into the high-level silo 1 of the secondary reduction furnace, which is connected to the material distributor 1.

[0013] 3) The preheated primary reduction iron powder is fed into the high-level silo 2 of the secondary reduction furnace, which is connected to the material distributor 2;

[0014] 4) In the charging section of the secondary reduction furnace, a layer of cold-rolled sludge powder with a thickness of 1-3 mm is arranged on the steel strip of the secondary reduction furnace by the charging device 1; and a layer of primary reduction iron powder with a thickness of 15-27 mm is further arranged on the cold-rolled sludge powder layer by the charging device 2 to obtain a mixed material layer.

[0015] 5) The resulting mixture layer is fed into the reduction section of the secondary reduction furnace along with the steel strip, where it undergoes secondary fine reduction in an H2 atmosphere, and is then processed to obtain reduced iron powder.

[0016] In the above scheme, the cold-rolled sludge in step 1) is a solid-water-oil three-phase mixture with a water content of 15% to 30%, an oil content of 5% to 20%, and a solid content of 60% to 80%. Its solid phase chemical composition is: TFe ≥ 92.0%, C ≤ 3.0%, O ≤ 5.0%; the balance is other alloying elements or unavoidable impurity elements; and the content of solid phase particles below 200 mesh is greater than 90%.

[0017] In the above scheme, the drying temperature in step 1) is 150-180℃ and the drying time is 60-90min.

[0018] In the above scheme, the preheating temperature in step 2) is 200-300℃, and the preheating time is 10-15 minutes.

[0019] In the above scheme, step 2) the preheating process of the chain grate machine is carried out in a N2 protective atmosphere, and the high-level material silo 1 of the secondary reduction furnace and its transfer channel with the chain grate machine are both in a N2 protective atmosphere; step 3) the high-level material silo 2 of the secondary reduction furnace and its transfer channel with the primary reduction iron powder are both in a N2 protective atmosphere.

[0020] In the above scheme, the primary reduced iron powder in step 3) is an intermediate product obtained by primary pre-reduction in the two-step reduced iron powder production process, wherein TFe≧90.0%, C≦5.0%, O≦5%, and the balance is other alloying elements or unavoidable impurity elements.

[0021] In the above scheme, the temperature of the primary reduced iron powder after preheating in step 3) is 500-700℃.

[0022] In the above scheme, the thickness of the mixture layer in step 4) shall not exceed 30 mm.

[0023] In the above scheme, the reduction temperature in step 5) is 900-1100℃ and the reduction time is 180-300min.

[0024] In the above scheme, the reduced iron powder obtained in step 5) has TFe≧98.0%, C≦1.0%, O≦0.5%, and the balance is other alloying elements or unavoidable impurity elements; the content of particles below 200 mesh is greater than 90%.

[0025] The cold-rolled sludge used in this invention has a three-phase structure of solid, water, and oil. The solid phase mainly originates from the friction between the rolls and the steel plate surface, producing metal shavings. Since both the rolls and the steel are made of steel, the chemical composition of the shavings is primarily steel and a small amount of iron oxides, with a particle size in the micrometer range. The oil phase mainly consists of the lubricating oil used in the rolling process. The oil undergoes condensation and other reactions at high temperatures, losing water and becoming thermosetting, thus transforming into a solid. This invention uses high-temperature drying to evaporate the moisture from the sludge, transforming the material into lumps. These lumps can then be further processed into powder using secondary crushing and grinding for reduction applications.

[0026] Due to the solid-phase physicochemical properties of oil sludge, its TFe content is higher than that of primary reduced iron powder, and its particle size is comparable to that of primary reduced iron powder. Therefore, it can be directly subjected to secondary fine reduction, eliminating the need for a pre-reduction process and saving a significant amount of energy consumption and costs.

[0027] Secondary reduction usually involves using hydrogen to further reduce and deoxidize the iron powder after the first pre-reduction, as shown in Formula 1 and Formula 2, followed by subsequent magnetic separation and other processes to remove impurities and obtain high-purity reduced iron powder.

[0028] Fe₂O₃ + 3H₂ = 2Fe + 3H₂O (Equation 1)

[0029] FeO + H2 = Fe + H2O Formula 2

[0030] This invention involves first laying an oily sludge layer on the strip using a material distributor, followed by laying a layer of primary reduced iron powder on top of the oily sludge layer. An electric heater is positioned between the support rollers in the reduction section. The strip first receives heat, which is then conducted to the oily sludge layer. Besides iron filings, the oily sludge contains oil. Under a non-oxidizing atmosphere, the oil decomposes at high temperature to produce hydrocarbons, which react with oxygen in the iron filings and primary reduced iron powder, as shown in Formulas 3 and 4. This process helps obtain high-quality reduced iron powder while simultaneously rendering the oil harmless.

[0031] Fe2O3 + C x H y = 2Fe + xCO2 + (y / 2)H2O Equation 3

[0032] FeO + C x H y = 2Fe + xCO2 + (y / 2)H2O Equation 4

[0033] H2 and hydrocarbons penetrate into the iron powder layer from the top and bottom directions respectively, ensuring the effectiveness and quality of the secondary reduction process.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] The method for preparing reduced iron powder from cold-rolled sludge described in this invention combines steel enterprise solid waste with the powder metallurgy industry. It fully utilizes the generation principle of cold-rolled sludge and its inherent characteristic of high solid metal iron content. By using cold-rolled sludge as a raw material, it not only solves the environmental protection problem of harmless disposal of solid waste and reduces disposal costs, but also reduces one reduction process compared to conventional raw materials such as iron oxide scale, saving energy consumption and costs, and realizing high-value utilization of solid waste.

[0036] This invention can be modified from existing reduced iron powder production lines, requiring minimal additional investment and demonstrating high technical and economic efficiency.

[0037] Oily substances in cold-rolled sludge are environmental pollutants in this type of solid waste. However, in the secondary reduction process involved in this invention, they are decomposed at high temperature to generate hydrocarbons, which have reducing properties. These hydrocarbons can be directly used in the iron powder reduction process, transforming the pollutants into useful reducing agents. After oxidation and decomposition, they are non-toxic and harmless, turning waste into treasure. Attached Figure Description

[0038] Figure 1 This invention utilizes a process flow diagram for preparing reduced iron powder from cold-rolled sludge.

[0039] Figure 2 : Schematic diagram of the secondary reduction furnace structure used in this invention. Detailed Implementation

[0040] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0041] A specific embodiment provides a cold-rolled sludge, which, after testing and analysis, has a water content of 18.3%, an oil content of 12.1%, and a solid content of 69.6%. Its solid phase chemical composition is: TFe 92.7%, C 2.5%, O 4.4%, with the balance being other alloying elements or unavoidable impurity elements; and its solid phase particle content below 200 mesh is 91.8%.

[0042] A specific embodiment provides a method for preparing reduced iron powder using cold-rolled sludge, as shown in the appendix. Figure 1 As shown:

[0043] 1) The cold-rolled sludge is fed into a dryer and dried at 150-180℃ for 60-90 minutes; the dried cold-rolled sludge is then fed into a jaw crusher and an impact crusher for two-stage crushing. After crushing, the material is screened. Material larger than 1.18mm is returned to the impact crusher for further crushing, while material smaller than 1.18mm is fed into a ball mill. The grinding time is 15-30 minutes. After grinding, the material is sieved. The portion larger than 100 mesh is returned to the ball mill for further grinding, while the portion smaller than 100 mesh is sent to the storage yard for later use.

[0044] 2) The cold-rolled sludge powder obtained in the previous step is fed into the chain grate machine for preheating. The preheating temperature is 200-300℃ and the preheating time is 10-15 minutes. After preheating, the material is immediately fed into the high-level silo 1 of the secondary reduction furnace, which is connected to the distributor 1.

[0045] 3) The preheated primary reduction iron powder is fed into the high-level silo 2 of the secondary reduction furnace, which is connected to the material distributor 2;

[0046] 4) In the secondary reduction furnace feeding section, the cold-rolled sludge powder layer is fed onto the steel strip of the secondary reduction furnace through the feeder 1. The thickness of the cold-rolled sludge powder layer is 1-3mm. The primary reduction iron powder layer is fed onto the cold-rolled sludge powder layer through the feeder 2. The thickness of the primary reduction iron powder layer is 15-27mm.

[0047] 5) The mixed material after feeding is fed into the reduction section of the secondary reduction furnace along with the steel belt, and undergoes secondary fine reduction in H2 atmosphere. The reduction temperature is 900-1100℃ and the reduction time is 180-300min.

[0048] 6) After secondary reduction, the material is cooled, sieved, magnetically separated, and packaged to produce reduced iron powder products.

[0049] Specifically, the primary reduced iron powder is an intermediate product obtained from the first pre-reduction stage in the two-step reduced iron powder production process, wherein TFe≧90.0%, C≦5.0%, O≦5%, and the balance is other alloying elements or unavoidable impurity elements. The temperature of the primary reduced iron powder after heating is 500~700℃.

[0050] Specifically, the embodiment provides an improved secondary reduction furnace, the structural schematic of which is shown in the attached diagram. Figure 2 As shown. The secondary reduction furnace is a belt reduction furnace, using a steel belt as the material transfer carrier, with the transfer power transmitted by the wheel head roller and support roller. The secondary reduction furnace is divided into a feeding section and a reduction section. The feeding section is equipped with feeder 1 and feeder 2, with a horizontal spacing of 0.4 to 0.8 m between feeder 1 and 2, and a horizontal spacing of 0.2 to 0.3 m between feeder 1 and the wheel head roller. The reduction section is equipped with a secondary reduction furnace hood, hydrogen supply pipelines, and other equipment. An electric radiant tube heater is installed between the support rollers of the reduction section.

[0051] Example 1

[0052] A method for preparing reduced iron powder from cold-rolled sludge includes the following steps:

[0053] 1) The cold-rolled sludge is fed into a dryer and dried at 155℃ for 65 minutes; the dried cold-rolled sludge is then fed into a jaw crusher and an impact crusher for two-stage crushing. After crushing, the material is screened. Material larger than 1.18mm is returned to the impact crusher for further crushing, while material smaller than 1.18mm is fed into a ball mill. The grinding time is 15 minutes. After grinding, the material is screened. The portion larger than 100 mesh is returned to the ball mill for further grinding, while the portion smaller than 100 mesh is sent to the storage yard for later use.

[0054] 2) The cold-rolled sludge powder obtained in the previous step is fed into the chain grate machine for preheating. The preheating temperature is 220℃ and the preheating time is 11min. After preheating, the material is immediately fed into the high-level silo 1 of the secondary reduction furnace. The silo is connected to the distributor 1.

[0055] 3) The preheated primary reduction iron powder is fed into the high-level silo 2 of the secondary reduction furnace, which is connected to the material distributor 2;

[0056] 4) In the secondary reduction furnace feeding section, the cold-rolled sludge powder layer is fed onto the steel strip of the secondary reduction furnace through the feeder 1. The thickness of the cold-rolled sludge powder layer is 0.5mm. The primary reduction iron powder layer is fed onto the cold-rolled sludge powder layer through the feeder 2. The thickness of the primary reduction iron powder layer is 18mm.

[0057] 5) The mixed material after feeding is fed into the reduction section of the secondary reduction furnace along with the steel belt, and undergoes secondary fine reduction in H2 atmosphere. The reduction temperature is 950℃ and the reduction time is 190min.

[0058] 6) After secondary reduction, the material is cooled, sieved, magnetically separated, and packaged to produce reduced iron powder products.

[0059] Example 2

[0060] A method for preparing reduced iron powder from cold-rolled sludge includes the following steps:

[0061] 1) The cold-rolled sludge is fed into a dryer and dried at 165℃ for 75 minutes; the dried cold-rolled sludge is then fed into a jaw crusher and an impact crusher for two-stage crushing. After crushing, the material is screened. Material larger than 1.18mm is returned to the impact crusher for further crushing, while material smaller than 1.18mm is fed into a ball mill. The grinding time is 20 minutes. After grinding, the material is screened. The portion larger than 100 mesh is returned to the ball mill for further grinding, while the portion smaller than 100 mesh is sent to the storage yard for later use.

[0062] 2) The cold-rolled sludge powder obtained in the previous step is fed into the chain grate machine for preheating. The preheating temperature is 250℃ and the preheating time is 12min. After preheating, the material is immediately fed into the high-level silo 1 of the secondary reduction furnace. The silo is connected to the material distributor 1.

[0063] 3) The preheated primary reduction iron powder is fed into the high-level silo 2 of the secondary reduction furnace, which is connected to the material distributor 2;

[0064] 4) In the secondary reduction furnace feeding section, the cold-rolled sludge powder layer is fed onto the steel strip of the secondary reduction furnace through the feeder 1. The thickness of the cold-rolled sludge powder layer is 1.5mm. The primary reduction iron powder layer is then fed onto the cold-rolled sludge powder layer through the feeder 2. The thickness of the primary reduction iron powder layer is 23mm.

[0065] 5) The mixed material after feeding is fed into the reduction section of the secondary reduction furnace along with the steel belt, and undergoes secondary fine reduction in H2 atmosphere. The reduction temperature is 1000℃ and the reduction time is 240min.

[0066] 6) After secondary reduction, the material is cooled, sieved, magnetically separated, and packaged to produce reduced iron powder products.

[0067] Example 3

[0068] A method for preparing reduced iron powder from cold-rolled sludge includes the following steps:

[0069] 1) The cold-rolled sludge is fed into a dryer and dried at 180℃ for 90 minutes; the dried cold-rolled sludge is then fed into a jaw crusher and an impact crusher for two-stage crushing. After crushing, the material is screened. Material larger than 1.18mm is returned to the impact crusher for further crushing, while material smaller than 1.18mm is fed into a ball mill. The grinding time is 30 minutes. After grinding, the material is screened. The portion larger than 100 mesh is returned to the ball mill for further grinding, while the portion smaller than 100 mesh is sent to the storage yard for later use.

[0070] 2) The cold-rolled sludge powder obtained in the previous step is fed into the chain grate machine for preheating. The preheating temperature is 290℃ and the preheating time is 15min. After preheating, the material is immediately fed into the high-level silo 1 of the secondary reduction furnace. The silo is connected to the distributor 1.

[0071] 3) The preheated primary reduction iron powder is fed into the high-level silo 2 of the secondary reduction furnace, which is connected to the material distributor 2;

[0072] 4) In the secondary reduction furnace feeding section, the material is fed onto the steel strip of the secondary reduction furnace through the material feeder 1. The thickness of the cold-rolled sludge powder layer is 3mm. The primary reduction iron powder is fed onto the cold-rolled sludge powder layer through the material feeder 2. The thickness of the primary reduction iron powder layer is 27mm.

[0073] 5) The mixed material after feeding is fed into the reduction section of the secondary reduction furnace along with the steel belt, and undergoes secondary fine reduction in H2 atmosphere. The reduction temperature is 1100℃ and the reduction time is 300min.

[0074] 6) After secondary reduction, the material is cooled, sieved, magnetically separated, and packaged to produce reduced iron powder products.

[0075] The performance of the reduced iron powder obtained in Examples 1, 2, and 3 is shown in Table 1, and it meets the product quality requirements.

[0076] Table 1

[0077] TFe C O Particle content below 200 mesh Example 1 98.5％ 0.7％ 0.3％ 94.6％ Example 2 98.8％ 0.5％ 0.3％ 93.8％ Example 3 99.2％ 0.4％ 0.2％ 95.5％ .

Claims

1. A method for preparing reduced iron powder from cold-rolled sludge, characterized in that... Includes the following steps: 1) Cold-rolled sludge is dried and then crushed and ball-milled to obtain cold-rolled sludge powder with a mesh size of less than 100. The cold-rolled sludge is a solid-water-oil three-phase mixture with a water content of 15%~30%, an oil content of 5~20%, and a solid content of 60~80%. Its solid phase chemical composition is: TFe≧92.0%, C≦3.0%, O≦5.0%; the balance is other alloying elements or unavoidable impurity elements; the content of solid phase particles with a mesh size of less than 200 is greater than 90%. 2) The obtained cold-rolled sludge powder is fed into a chain grate machine for preheating and then into the high-level silo 1 of the secondary reduction furnace. The high-level silo 1 is connected to the material distributor 1. The preheating process of the chain grate machine is carried out in a N2 protective atmosphere. The high-level silo 1 of the secondary reduction furnace and the transfer channel between it and the chain grate machine are both in a N2 protective atmosphere. 3) The preheated primary reduced iron powder is fed into the high-level silo 2 of the secondary reduction furnace, which is connected to the distributor 2; the primary reduced iron powder is an intermediate product obtained from the first pre-reduction in the two-step reduced iron powder production process, wherein TFe≧90.0%, C≦5.0%, O≦5%, and the balance is other alloying elements or unavoidable impurity elements; the high-level silo 2 of the secondary reduction furnace and its transfer channel with the primary reduced iron powder are both in a N2 protective atmosphere; 4) In the secondary reduction furnace feeding section, a layer of cold-rolled sludge powder with a thickness of 1~3 mm is arranged on the steel strip of the secondary reduction furnace by the feeder 1; a layer of primary reduction iron powder with a thickness of 15~27 mm is further arranged on the cold-rolled sludge powder layer by the feeder 2 to obtain a mixed material layer. 5) The resulting mixture layer is fed into the reduction section of the secondary reduction furnace along with the steel strip. It undergoes secondary fine reduction in an H2 atmosphere and is then processed to obtain reduced iron powder. Electric heaters are arranged between the support rollers in the reduction section. The steel strip first receives heat and conducts it to the cold-rolled oily mud powder layer. In addition to iron filings, the cold-rolled oily mud powder also contains oil. Under a non-oxidizing atmosphere, the oil decomposes at high temperature to produce hydrocarbons, which react with oxygen in the iron filings and the primary reduced iron powder. The reduction temperature is 900~1100℃ and the reduction time is 180~300 min.

2. The method for preparing reduced iron powder from cold-rolled sludge as described in claim 1, characterized in that... Step 1) The drying temperature is 150~180℃ and the drying time is 60~90 min.

3. The method for preparing reduced iron powder from cold-rolled sludge as described in claim 1, characterized in that... Step 2) The preheating temperature is 200~300℃ and the preheating time is 10~15 min.

4. The method for preparing reduced iron powder from cold-rolled sludge as described in claim 1, characterized in that... Step 3) The temperature of the primary reduced iron powder after preheating is 500~700℃.

5. The method for preparing reduced iron powder from cold-rolled sludge as described in claim 1, characterized in that... Step 5) The resulting reduced iron powder has TFe≧98.0%, C≦1.0%, O≦0.5%, with the balance being other alloying elements or unavoidable impurity elements; the content of particles below 200 mesh is greater than 90%.

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