A method for pressure filtration drying treatment of copper tailings powder in pyrometallurgical steelmaking

Abstract

This invention discloses a method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking, belonging to the field of metallurgical solid waste resource utilization technology. First, an outer slurry without reducing carbon powder and an inner slurry containing reducing carbon powder and flux are prepared separately. These are fed into a filter press in an outer-inner-outer layer sequence to form a sandwich-structured composite filter cake. After shearing and staged drying, the cake is fed into the furnace. The outer layer is carbon-free and high-strength, preventing premature carbon powder burn-off and dust generation; the inner layer carries the functions of reduction, slag conditioning, and fluxing, resolving the contradiction between strength and activity in a single formulation. This invention employs wet slurry mixing and layered feeding pressure filtration, ensuring that the reducing carbon powder, slag conditioner, and flux are fully dispersed in the inner slurry, reducing refining fluctuations caused by insufficient reduction, insufficient or excessive slag conditioner in certain areas.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical solid waste resource utilization technology, and specifically relates to a method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking. Background Technology

[0002] Copper tailings slag is typically a fine-powdered industrial solid waste, characterized by its fine particle size, large specific surface area, and the presence of a certain proportion of total iron (TFe), ferrous oxide (FeO), silica, and other mineral components. Utilizing it as an auxiliary material or iron-containing resource in pyrometallurgical steelmaking can achieve solid waste resource recovery, reduce land occupation during stockpiling, and mitigate environmental risks.

[0003] However, when copper tailings slag powder is directly used in pyrometallurgical steelmaking, the following problems arise: 1. The material has a fine particle size and light weight. When it is added directly, it is easily carried away by the hot air flow, flue gas flow or rising air flow in the electric arc furnace, which will generate dust, cause material loss and reduce the recovery rate of iron components. 2. If the powder material contains reducing carbon powder or other reducing components, it is prone to premature combustion or surface burn-off when it approaches the high-temperature furnace mouth, which prevents it from fully entering the reaction zone of molten steel or slag to participate in the reduction reaction. 3. Powdered materials lack sufficient size and momentum, making it difficult to overcome the impact of hot airflow in the furnace and stably enter the molten steel mother liquor or molten slag layer, thus affecting the efficiency of metallurgical reaction. 4. If the powder material has a high moisture content, the moisture will vaporize rapidly after entering the furnace, which may easily lead to splashing of molten steel, explosion, or operational safety risks. Existing processing methods typically include pelletizing, briquetting, granulation, and filter press molding. Among these, filter press molding can achieve better component dispersion by mixing wet slurry, and obtain a filter cake of a certain thickness and strength through filter press dewatering. After crushing and drying, the cake is fed into the furnace as a block material.

[0004] However, ordinary single-formulation filter press blocks still have the following shortcomings: 1. If the proportion of carbon powder is increased in order to improve the reduction activity, the carbon powder is easily distributed on the surface of the block material, which leads to premature burning of the surface carbon powder in the high-temperature environment before conveying and entering the furnace; 2. If the binder is increased or the carbon powder ratio is reduced in order to improve the transport strength, the self-reduction ability of the block material after entering the furnace will be insufficient; 3. Ordinary filter press blocks are prone to problems such as rapid surface water loss and insufficient water migration in the inner layer during the drying process.

[0005] Existing technologies have proposed improved solutions to address this issue. For example, Chinese invention patent (CN115232962B) discloses a method for preparing double-layer pellets containing carbon dust. This method produces double-layer carbon-containing pellets, with the inner layer containing carbon dust and coke, and the outer layer containing a pore-forming agent and iron concentrate. The pore-forming agent creates pores within the outer layer of pellets during sintering. However, the pellets are susceptible to localized component segregation due to factors such as particle size, wettability, and rolling trajectory. This results in uneven carbon powder distribution, with some areas exhibiting low CaO / SiO2 ratios, high slag viscosity, and slow refining; while others show high CaO / SiO2 ratios, leading to uneven melting and inconsistent reaction of the pellets.

[0006] Based on the above reasons, a pressure filtration and drying method for copper tailings slag powder in pyrometallurgical steelmaking is proposed. Summary of the Invention

[0007] One object of the present invention is to provide a method for pressure filtration drying of copper tailings slag powder in pyrometallurgical steelmaking, comprising the following steps: Step 1: Mix copper tailings slag powder, water, binder and slag conditioner to prepare the outer slurry; Step 2: Mix copper tailings slag powder, water, reducing carbon powder, slag conditioner and flux to prepare inner layer slurry; Step 3: Feed the outer layer slurry and the inner layer slurry into the filter press in a preset order so that the filter cake forms an outer layer-inner layer-outer layer sandwich structure along the thickness direction. The slurry is dewatered by the filtration pressure to form a composite filter cake. Step 4: Cut the composite filter cake into composite blocks of a predetermined size.

[0008] Step 5: Dry the composite block material; Step 6: Transport the dried composite block material to the steelmaking furnace.

[0009] Preferably, in step one, the mass percentages of each raw material are: 65% to 82% copper tailings slag powder, 15% to 25% water, 0.5% to 3% binder, and 3% to 10% slag conditioner. No reduced carbon powder is added to the outer slurry to reduce the risk of carbon powder exposure and premature burn-off on the surface of the lumps. Preferably, in step one, the binder includes at least one of bentonite, modified starch, and carboxymethyl cellulose.

[0010] Preferably, in step two, the mass percentage of each raw material is: 62% to 72% copper tailings slag powder, 18% to 22% water, 6% to 12% reducing carbon powder, 4% to 10% slag conditioner, and 0.5% to 3% flux.

[0011] Preferably, in steps one and two, the slag conditioner includes at least one of limestone powder, lime powder, dolomite powder, and lightly calcined dolomite powder.

[0012] Preferably, in step two, the flux includes at least one of pre-melted refined slag powder, steel slag powder, rolled iron oxide scale, and borate flux.

[0013] Preferably, in step three, an outer layer slurry is first introduced into the filter chamber of the filter press to form a first outer layer slurry zone; then an inner layer slurry is introduced to form an inner layer slurry zone; finally, an outer layer slurry is introduced again to form a second outer layer slurry zone; then filter press dewatering is performed so that the three slurry zones are compacted together to form a sandwich structure composite filter cake.

[0014] Preferably, in step three, the thickness of the composite filter cake is 20 mm to 40 mm; more preferably, the thickness of the composite filter cake is 20 mm to 30 mm.

[0015] Preferably, in step three, the total thickness of the outer layer of the composite filter cake accounts for 10%-60% of the total thickness of the filter cake; more preferably, the total thickness of the outer layer of the composite filter cake accounts for 20%-40% of the total thickness of the filter cake.

[0016] Preferably, in step three, the filtration pressure is 0.5 MPa-4.0 MPa; more preferably, the filtration pressure is 0.7 MPa-2.5 MPa.

[0017] Preferably, in step three, the filtration time is 5 min to 40 min; more preferably, the filtration time is 10 min to 25 min.

[0018] Preferably, in step three, the moisture content of the composite filter cake is 12%-30%; more preferably, the moisture content of the composite filter cake is 15%-25%.

[0019] Preferably, in step four, the particle size of the composite block is 20mm-80mm; more preferably, the particle size of the composite block is 25mm-60mm.

[0020] Preferably, in step five, the composite block material is dried in stages. The first stage, with a drying temperature of 100℃-180℃, is used to allow moisture to slowly migrate from the surface and interlayer of the block material, preventing rapid surface cracking or hardening. The second stage involves drying at a temperature of 180℃-240℃. This stage is used to further reduce the overall moisture content of the block material and increase its hardness.

[0021] The third stage involves drying at a temperature of 240℃-280℃. This stage is used to reduce the moisture content in the center of the block material, so that the difference between the moisture content in the center and the surface reaches a preset range.

[0022] The temperature of the waste heat exhaust gas from the steelmaking furnace can be 300℃-600℃. The effective drying temperature inside the drying chamber can be controlled within the above range by mixing air and adjusting valves.

[0023] Preferably, in step five, the moisture content of the dried composite block is 2%-10%; more preferably, the moisture content of the dried composite block is 4%-8%.

[0024] Preferably, in step five, the Shore hardness of the dried composite block is 15-35; more preferably, the Shore hardness of the dried composite block is 18-25.

[0025] The present invention has the following beneficial effects: 1. This invention proposes a method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking. Through layered pressure filtration of outer and inner slurries, a composite filter cake is formed along its thickness, creating an outer-inner-outer layer sandwich structure. The inner layer contains reduced carbon powder, while the outer layer is a carbon-free, high-strength layer. This reduces the exposure of reduced carbon powder on the surface of the slurry, minimizing premature burn-off during conveying, drying, and before furnace loading due to the high-temperature airflow. This invention employs wet slurry mixing and layered feeding pressure filtration, ensuring sufficient dispersion of reduced carbon powder, slag conditioner, and flux in the inner slurry. This facilitates control of the C / FeO ratio and CaO / SiO2 ratio, reducing refining fluctuations caused by insufficient or excessive localized reduction or slag conditioner.

[0026] 2. The outer layer of slurry contains binders and slag conditioners, enabling it to resist pulverization and provide protection. The inner layer of slurry contains reducing carbon powder, slag conditioners, and fluxing agents, enabling it to perform FeO reduction, slag conditioning, and fluxing refining. This resolves the contradiction in ordinary single-formulation block materials where "high strength results in insufficient reactivity, while high reactivity results in decreased strength."

[0027] 3. This invention achieves controllability of the moisture migration path and drying process of the composite block material through staged drying. The first stage involves low-temperature dehumidification to prevent surface hardening, the second stage involves medium-temperature drying to reduce overall moisture content, and the third stage involves stable temperature uniformity to reduce core moisture content. As a result, the moisture content of the dried composite block material is controlled between 4% and 8%, reducing the risk of splashing caused by rapid vaporization of moisture upon entering the furnace. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Example 1

[0029] Copper tailings slag powder was used as raw material to prepare outer and inner slurries.

[0030] Preparation of outer layer slurry: Take 1000 kg of copper tailings slag powder, 60 kg of limestone powder, 12 kg of bentonite, and 5 kg of modified starch, add 270 kg of industrial water, and stir in a mixing tank to obtain the outer layer slurry. No reducing carbon powder is added to this outer layer slurry, which is used to form a low-carbon, high-strength outer layer.

[0031] Inner layer slurry preparation: Take 1000 kg of copper tailings slag powder, 100 kg of reduced carbon powder, 60 kg of limestone powder, 20 kg of lightly calcined dolomite powder, and 20 kg of pre-melted refined slag powder, add 300 kg of industrial water, and stir in another mixing tank to obtain the inner layer slurry.

[0032] 3. Connect the outer and inner slurry layers to the filter press feed pipe via independent delivery pumps.

[0033] First, the outer layer slurry is introduced into the filter chamber of the filter press to form the first outer layer slurry zone; then the valve is switched to introduce the inner layer slurry to form the inner layer slurry zone; finally, the outer layer slurry is introduced again to form the second outer layer slurry zone.

[0034] The target thicknesses of the first outer layer, the inner layer, and the second outer layer are controlled to be 5 mm, 20 mm, and 5 mm, respectively, so that the total thickness of the composite filter cake is 30 mm.

[0035] The filter cake was then dewatered by pressure filtration to obtain a composite filter cake with an outer-inner-outer layer sandwich structure. The moisture content of the composite filter cake after pressure filtration was approximately 20%.

[0036] 4. After the composite filter cake is discharged from the filter press, it is sheared by a shear grid; a high-tooth steel belt conveyor is installed below the shear grid. After shearing and secondary shaping, composite blocks with an equivalent particle size of 30 mm to 50 mm are obtained.

[0037] 5. The composite blocks are fed into a waste heat drying chamber for staged drying. The first stage is a low-temperature dehumidification section, with a drying temperature of 140℃ and a drying time of 6 minutes; the second stage is a medium-temperature drying section, with a drying temperature of 220℃ and a drying time of 12 minutes; the third stage is a temperature stabilization section, with a drying temperature of 240℃ and a drying time of 8 minutes. The temperature of the waste heat exhaust gas from the steelmaking furnace is 400℃ to 500℃, and the effective temperature inside the drying chamber is controlled within this range by using air mixing and pneumatic regulating valves.

[0038] The dried composite block has a moisture content of 6%, a Shore hardness of 20, and a moisture difference of no more than 3% between the center and the surface.

[0039] 6. The dried composite blocks are conveyed to the charging position of the steelmaking furnace via a baffle conveyor, allowing them to enter the molten steel mother liquor or molten slag layer for refining. The outer high-strength structure is used to reduce pulverization during conveying and prevent premature carbon powder burn-off, while the inner reducing carbon powder, slag conditioner, and fluxing agent are used to participate in FeO reduction, slag conditioning, and molten refining after entering the furnace. Example 2

[0040] This embodiment illustrates a composite filter press block material with a transition layer. This embodiment reduces the risk of interlayer cracking between the outer and inner layers due to differences in carbon content, shrinkage rate, and drying speed by setting a five-layer structure: outer layer - transition layer - inner layer - transition layer - outer layer.

[0041] 1. Preparation of outer layer slurry: Take 800 kg of copper tailings slag powder, 48 kg of limestone powder, 10 kg of bentonite, and 4 kg of modified starch, add 220 kg of industrial water, and stir in a mixing tank for 20 min at a stirring speed of 60 r / min to obtain the outer layer slurry.

[0042] The outer slurry does not contain reducing carbon powder and is used to form a low-carbon, high-strength outer layer.

[0043] 2. Preparation of transition layer slurry: Take 500 kg of copper tailings slag powder, 20 kg of reduced carbon powder, 30 kg of limestone powder, 4 kg of bentonite, and 2 kg of modified starch, add 145 kg of industrial water, and stir in a mixing tank for 20 min at a stirring speed of 60 r / min to obtain the transition layer slurry.

[0044] The transition layer slurry contains a small amount of reduced carbon powder to mitigate the compositional differences between the outer and inner layers and improve the interlayer bonding strength.

[0045] 3. Preparation of inner layer slurry: Take 1000 kg of copper tailings slag powder, 100 kg of reduced carbon powder, 60 kg of limestone powder, 20 kg of lightly calcined dolomite powder, and 15 kg of pre-melted refined slag powder, add 300 kg of industrial water, and stir in a mixing tank for 25 min at a stirring speed of 60 r / min to obtain the inner layer slurry.

[0046] Among them, the reduced carbon powder is used to participate in the reduction of FeO after entering the furnace; limestone powder and lightly calcined dolomite powder are used as slag conditioners; and pre-melted refined slag powder is used as a flux.

[0047] 4. Layered feeding filter press: The outer layer slurry, transition layer slurry and inner layer slurry are respectively connected to the filter press feed pipeline through independent delivery pumps.

[0048] Feed the filter chamber of the filter press in the following order: The first layer of outer slurry is applied to form the first outer layer, with a target thickness of 4 mm. The first input of transition layer slurry forms the first transition layer with a target thickness of 3 mm. Input the inner layer slurry to form the inner layer with a target thickness of 16 mm; The second input of transition layer slurry forms the second transition layer with a target thickness of 3 mm. The second layer of slurry is applied to form the second outer layer, with a target thickness of 4 mm.

[0049] The total thickness of the composite filter cake is 30 mm.

[0050] 5. Filtration and dewatering: The filtration pressure is controlled at 1.4 MPa and the filtration time is 20 min.

[0051] After filtration, a composite filter cake with a five-layer sandwich structure is obtained, and the moisture content of the composite filter cake after filtration is 20%.

[0052] 6. Shearing, crushing and shaping: After the composite filter cake is discharged from the filter press, it enters the shear grid.

[0053] The shear grid spacing is 60 mm, and the filter cake discharge drop height is 1.5 m.

[0054] A high-tooth steel belt conveyor is installed below the shearing grid. The steel belt tooth height is 30 mm and the tooth spacing is 100 mm.

[0055] After secondary shaping by shearing grid and high-tooth steel strip, composite blocks with an equivalent particle size of 25 mm to 60 mm are obtained.

[0056] 7. Waste heat staged drying: The composite block material is sent into a waste heat drying box and dried in three stages using the waste heat tail gas of the steelmaking furnace.

[0057] The first stage is the low-temperature dehumidification stage, with a drying temperature of 140℃ and a drying time of 6 minutes.

[0058] The second stage is the medium-temperature drying section, with a drying temperature of 220℃ and a drying time of 12 minutes.

[0059] The third stage is the temperature stabilization stage, with a drying temperature of 250℃ and a drying time of 8 minutes.

[0060] The waste heat source temperature of the steelmaking furnace is 450℃. The effective temperature inside the drying chamber is controlled within the above range by mixing air and pneumatic regulating valve.

[0061] 8. Finished product specifications: The moisture content of the dried composite block is 6%, the Shore hardness is 21, and the difference between the moisture content of the center and the surface is 2.5%.

[0062] The dried composite lumps are conveyed to the charging position of the steelmaking furnace via a baffle conveyor. In this embodiment, the outer layer is used to improve the lumps' resistance to pulverization, the transition layer is used to improve the interlayer bonding strength, and the inner layer is used to provide self-reduction and slag conditioning functions. Example 3

[0063] This embodiment illustrates a three-layer sandwich filter press block material with high outer layer strength and high inner layer reducing activity. This embodiment is suitable for applications involving long transportation distances, large transfer drops, and high requirements for the block material's resistance to pulverization.

[0064] 1. Preparation of outer layer slurry: Take 1000 kg of copper tailings slag powder, 50 kg of dolomite powder, 15 kg of bentonite, and 2 kg of sodium carboxymethyl cellulose, add 260 kg of industrial water, and stir in a mixing tank for 22 min at a stirring speed of 65 r / min to obtain the outer layer slurry.

[0065] The outer slurry does not contain reducing carbon powder. Dolomite powder is used to provide CaO and MgO as slag conditioning components; bentonite and sodium carboxymethyl cellulose are used to improve the outer layer strength and resistance to pulverization.

[0066] 2. Preparation of inner layer slurry: Take 1000 kg of copper tailings slag powder, 120 kg of reduced carbon powder, 50 kg of limestone powder, 30 kg of steel slag powder, and 20 kg of pre-melted refining slag powder, add 310 kg of industrial water, and stir in a mixing tank for 25 min at a stirring speed of 65 r / min to obtain the inner layer slurry.

[0067] Among them, reducing carbon powder is used to improve the self-reduction ability of the inner layer; limestone powder and steel slag powder are used as slag conditioning components; and pre-melted refining slag powder is used as a flux to promote the softening and refining of the lumps after entering the furnace.

[0068] 3. Layered feeding filter press: The outer layer slurry and the inner layer slurry are connected to the filter press through independent delivery pumps.

[0069] Feed the filter chamber of the filter press in the following order: The first layer of outer slurry is applied to form the first outer layer, with a target thickness of 6 mm. Input the inner layer slurry to form the inner layer with a target thickness of 18 mm; The second layer of slurry is applied to form the second outer layer, with a target thickness of 6 mm.

[0070] The total thickness of the composite filter cake is 30 mm. The outer layer has a total thickness of 12 mm, accounting for 40% of the total thickness of the composite filter cake.

[0071] 4. Filtration and dewatering: The filtration pressure is controlled at 1.6 MPa and the filtration time is 22 min.

[0072] After pressure filtration, a composite filter cake with a three-layer sandwich structure of outer layer-inner layer-outer layer is obtained, and the moisture content of the composite filter cake after pressure filtration is 18%.

[0073] 5. Shearing, crushing and shaping: After the composite filter cake is discharged from the filter press, it is sheared by a shear grid.

[0074] The spacing between the shear grids is 50 mm, and the discharge drop height of the filter cake is 1.2 m.

[0075] A high-tooth steel belt conveyor is installed below the shearing grid. The steel belt tooth height is 35 mm and the tooth spacing is 100 mm.

[0076] After shearing and secondary shaping, composite blocks with an equivalent particle size of 30 mm to 55 mm are obtained.

[0077] 6. Waste heat staged drying: The composite block material is sent into a waste heat drying box for three-stage drying.

[0078] The first stage is the low-temperature dehumidification stage, with a drying temperature of 130℃ and a drying time of 8 minutes.

[0079] The second stage is the medium-temperature drying section, with a drying temperature of 210℃ and a drying time of 14 minutes.

[0080] The third stage is the temperature stabilization stage, with a drying temperature of 260℃ and a drying time of 10 min.

[0081] The waste heat source temperature of the steelmaking furnace is 480℃, and the effective drying temperature in the drying chamber is controlled by mixing air and pneumatic regulating valves.

[0082] 7. Finished product specifications: The moisture content of the dried composite block is 5.5%, the Shore hardness is 22, and the difference between the moisture content of the center and the surface is 2%.

[0083] The dried composite blocks are transported to the feeding position of the steelmaking furnace via a baffle conveyor, so that they can enter the molten steel mother liquor or molten slag layer for refining.

[0084] In this embodiment, the thicker high-strength outer layer can reduce the risk of pulverization of the block material during conveying and feeding, and reduce the exposure of the inner layer reduced carbon powder before entering the furnace; the higher proportion of reduced carbon powder, slag conditioner and flux in the inner layer is used to improve the FeO reduction capacity and refining speed after entering the furnace.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for pressure filtration and drying copper tailings slag powder in pyrometallurgical steelmaking, characterized in that, Includes the following steps: Step 1: Mix copper tailings slag powder, water, binder and slag conditioner to prepare the outer slurry; Step 2: Mix copper tailings slag powder, water, reducing carbon powder, slag conditioner and flux to prepare inner layer slurry; Step 3: Feed the outer layer slurry and the inner layer slurry into the filter press in a preset order so that the filter cake forms a sandwich structure of outer layer slurry-inner layer slurry-outer layer slurry along the thickness direction. The slurry is dewatered by the filtration pressure to form a composite filter cake. Step 4: Cut the composite filter cake into composite blocks of a predetermined size; Step 5: Dry the composite block material; Step 6: Transport the dried composite block material to the steelmaking furnace.

2. The method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking as described in claim 1, characterized in that, In step one, the mass percentage of each raw material is as follows: 65% to 82% copper tailings slag powder, 15% to 25% water, 0.5% to 3% binder, and 3% to 10% slag conditioner.

3. The method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking as described in claim 1, characterized in that, The binder includes at least one of bentonite, modified starch, and carboxymethyl cellulose.

4. The method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking as described in claim 1, characterized in that, In step two, the mass percentages of each raw material are as follows: 62% to 72% copper tailings slag powder, 18% to 22% water, 6% to 12% reducing carbon powder, 4% to 10% slag conditioner, and 0.5% to 3% flux.

5. The method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking as described in claim 1, characterized in that, The slag conditioner includes at least one of limestone powder, lime powder, dolomite powder, and lightly calcined dolomite powder.

6. The method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking as described in claim 1, characterized in that, In step two, the flux includes at least one of pre-melted refined slag powder, steel slag powder, rolled iron oxide scale, and borate flux.

7. The method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking as described in claim 1, characterized in that, In step five, the composite block material is dried in stages. The first stage involves drying at a temperature of 100℃-180℃. The second stage involves drying at a temperature of 180℃-240℃. The third stage involves drying at a temperature of 240℃-280℃.

8. The method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking as described in claim 1, characterized in that, In step five, the moisture content of the dried composite block is 2%-10%.

9. The method for pressure filtration and drying of copper tailings slag powder in pyrometallurgical steelmaking as described in claim 1, characterized in that, In step five, the Shore hardness of the dried composite block is 15-35.