Plate strip green phosphorus removal process using pulse current

Abstract

The invention relates to the technical field of plate and strip dephosphorization, in particular to a green plate and strip dephosphorization process using pulse current. The invention discloses a green dephosphorization process for a plate strip by using pulse current. The efficient stripping and resource utilization of oxide skin on the surface of the plate strip are realized through strip steel uncoiling pretreatment, ultrasonic cavitation presplitting, aerosol seed crystal activation, pulse current electrolysis, washing separation and drying recovery. According to the green plate and strip phosphorus removal process using the pulse current, the electrolytic load is greatly reduced through the synergistic effect of ultrasonic cavitation presplitting and aerosol seed crystal activation, oxide skin is stripped in the conduction period of the pulse current, iron and phosphorus in-situ precipitation is induced in the turn-off period, efficient phosphorus removal and iron phosphate byproduct recovery are synchronously achieved, and the method is suitable for industrial production. The industrial problems that a traditional electrolysis dephosphorization technology is high in energy consumption, electrolyte iron ion accumulation is fast, and by-products are low in value are systematically solved, and a new green dephosphorization strategy which is low in energy consumption, close to zero emission and high in yield is provided for steel surface treatment.

Description

Technical Field

[0001] This invention relates to the field of strip dephosphorization technology, and more specifically to a green strip dephosphorization process using pulsed current. Background Technology

[0002] In the contemporary steel metallurgy and processing industry, the efficient removal of dense oxide scale from the surface of hot-rolled strip is becoming a key bottleneck restricting the green transformation of high-quality steel surface treatment. Traditional chemical pickling for descaling relies on strong acids to chemically dissolve the oxide scale. This single-mode corrosion based on highly corrosive media has inherent flaws. Pickling not only generates large amounts of acid-containing waste liquid and hazardous sludge, causing serious environmental pollution and high treatment costs, but also poses a significant risk of over-corrosion and hydrogen embrittlement of the steel substrate, severely impacting product surface quality. Furthermore, the iron resources in the oxide scale are completely converted into low-value solid waste, resulting in persistently high overall production costs. Even more challenging is the fact that with increasingly stringent environmental policies, the survival space for pickling processes is being drastically reduced, excluding this traditional process from sustainable manufacturing solutions.

[0003] In recent years, researchers have attempted to introduce electrolytic dephosphorization technology into the field of plate and strip surface treatment, aiming to achieve acid-free and clean production. However, existing technical solutions are still limited to using DC electrolysis as the sole driving force, treating the electrolyte merely as a conductive medium, lacking pretreatment design to reduce the burden on the oxide scale structure, and lacking resource utilization pathways for dissolved iron ions. Under conditions of thick oxide scale and high-speed production lines, they suffer from core defects such as high energy consumption, low efficiency, and frequent discharge due to rapid accumulation of iron ions in the electrolyte. Therefore, how to construct a multi-field synergistic pretreatment-electrolysis coupling system to achieve in-situ precipitation and resource recovery of iron ions while efficiently removing oxide scale has become a core technical bottleneck that urgently needs to be overcome in the field of green dephosphorization in the steel industry.

[0004] To address the above problems, the present invention provides a solution. Summary of the Invention

[0005] The purpose of this invention is to provide a green dephosphorization process for strip using pulsed current, which can efficiently remove oxide scale from the surface of the strip.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A green dephosphorization process for strip steel using pulsed current is achieved through strip steel uncoiling pretreatment, ultrasonic cavitation pre-cracking, aerosol seed activation, pulsed current electrolysis, rinsing separation and drying recovery, thereby realizing the efficient removal and resource utilization of oxide scale on the surface of strip steel.

[0007] A green dephosphorization process for strip panels using pulsed current includes the following steps: S1: Strip steel uncoiling pretreatment: The strip steel coil is installed on the uncoiler and fed into the straightener after being uncoiled. The straightening speed is set to 10-20m / min, the number of straightening rollers is 6-9, and the diameter of the straightening rollers is 50-80mm. The strip steel is leveled. After straightening, the strip steel enters the alkaline washing tank and stays for 30-45min. The temperature of the alkaline washing tank is set to 55-60℃. A 10% sodium carbonate solution is filled into the alkaline washing tank, and the filling amount is 70% of the volume of the alkaline washing tank. After the strip steel has stayed, it enters the pre-rinsing tank and is rinsed three times in countercurrent with room temperature clean water at 5MPa pressure to remove residual sodium carbonate solution and obtain clean strip steel. S2: Ultrasonic Cavitation Pre-splitting: The clean steel strip is fed into a sealed ultrasonic cavitation chamber filled with water. A multi-frequency composite ultrasonic generator is turned on, and the ultrasonic frequency is set to a composite frequency of 20kHz, 40kHz, and 80kHz, with an ultrasonic power density of 4-5W / cm². 2 The pre-cracking treatment time is the running time of the strip through the cavity. The running speed of the strip is 0.2-0.5 m / s. The pre-treatment time is controlled to be 8-12 s by adjusting the strip speed. After the treatment is completed, pre-cracked strip is obtained. S3: Aerosol Seed Activation: The pre-cracked strip is fed into a sealed aerosol spray chamber. The aerosol activation liquid is evenly sprayed onto the strip surface in the form of droplets with a diameter of 20 μm using atomizing nozzles, forming an extremely thin activation liquid film. The spray flow rate is 100 ml / m. 2 The strip runs at a speed of 20 m / min, and activated strip is obtained after spraying. S4: Pulsed Current Electrolysis: The activated steel strip is continuously passed through two electrolytic cells connected in series. Each cell contains anode and cathode plates; the anode plate is made of titanium-coated lead dioxide, and the cathode plate is made of stainless steel. The plate spacing is set to 50-100 mm. The electrolytic cells contain electrolyte. The pulse power supply is then turned on, and the pulse current parameters are set to a current density of 30-40 A / dm³. 2 The pulse frequency is 600-800Hz, the duty cycle is 25-40%, the positive and negative pulses are adjustable, the single cell electrolysis time is 12-15s, the total electrolysis time is 24-30s, the strip steel running speed is 20-30m / min, the length of a single electrolytic cell is 8m, and after electrolysis, dephosphorized strip steel and electrolyte containing precipitates are obtained. S5: Washing and Separation: The dephosphorized steel strip is sent to a high-pressure water washing device and washed with 15MPa high-pressure water to thoroughly remove the oxide scale debris and residual precipitates on the surface of the steel strip. After washing, clean dephosphorized steel strip is obtained. The wastewater generated by high-pressure water washing and the electrolyte containing precipitates are combined, collected and transported to a hydrocyclone for solid-liquid separation. The hydrocyclone separation particle size is set to 8um. After separation, the supernatant and iron-phosphorus precipitate filter cake are obtained. S6: Drying and Recycling: The clean, dephosphorized steel strip is fed into a hot air dryer. The drying temperature is set at 80-120℃ and the air velocity is 10-15m / s. The surface moisture of the steel strip is removed by drying. The dried steel strip is then wound up by a coiler at a speed of 10-60m / min and a maximum winding diameter of 1800-2200mm to obtain the finished phosphorus-free steel strip. The supernatant obtained is supplemented with sodium sulfate to adjust the sodium sulfate concentration to 10%, and then returned to the electrolytic cell as an electrolyte for recycling. The iron-phosphorus precipitate filter cake is collected after sedimentation and separation to obtain iron phosphate powder, hydroxy iron phosphate powder, and iron oxide powder, which are packaged separately for later use.

[0008] Furthermore, the sedimentation separation and collection described in step S6 includes the following steps: A1: The obtained iron-phosphorus precipitate filter cake is transferred to a spray drying tower, the drying temperature is set to 150-200℃, and the drying time is 30 min. After drying, it is transferred to a grinder and ground for 15 min. After grinding, it is transferred to an air classifier, the classifier wheel speed is set to 1000 rpm, and the air source pressure is 0.5 MPa. The iron phosphate is separated and collected by the particle size difference. After being packaged in a vacuum packaging machine and moisture-proof aluminum foil bags, it is stored in the warehouse to obtain iron phosphate and the remaining coarse powder material. A2: Transfer the remaining coarse powder material to a gravity separator. The gravity separator is set with a vibration frequency of 30Hz and a wind speed of 2.5m / s. The hydroxy ferric phosphate is separated by the density difference to obtain hydroxy ferric phosphate and residual heavy material. A3: Transfer the residual heavy material to a wet electromagnetic separator, setting the magnetic field strength to 15,000 Gauss and the slurry flow rate to 0.5 m / s. 3 / h, iron oxide powder is obtained by separating it using magnetic differences, and then packaged in vacuum packaging machine and woven bags before being stored.

[0009] Furthermore, the preparation method of the aerosol activation liquid in step S3 includes the following steps: B1: Accurately weigh citric acid and place it in a stainless steel mixing tank. Add deionized water, turn on the mixing tank stirrer, set the speed to 300 rpm, and stir continuously for 15 minutes at room temperature to obtain an organic acid base liquid. B2: Add ferric hydroxyphosphate powder to a grinder, set the grinding particle size to 2 μm, grind for 15 min to obtain seed powder, add seed powder to organic acid base liquid, turn on the mixer of the mixing tank, adjust the speed to 400 rpm, and continuously stir and disperse at room temperature for 30 min to make the seed powder uniformly suspended in organic acid base liquid to obtain seed suspension. B3: Filter the seed crystal suspension through a 100-mesh filter to remove agglomerated particles, then transfer it to the storage tank of the aerosol generator. Store it in a sealed container for later use. Use a low-speed stirring device in the storage tank to maintain a speed of 100 rpm to prevent the seed crystals from settling during the standing process and to keep the suspension concentration uniform and stable, thus obtaining the aerosol activation solution.

[0010] Furthermore, the mass ratio of citric acid to deionized water in step B1 is 1:50; the mass ratio of seed powder to organic acid-based liquid in step B2 is 1:50. Furthermore, the method for preparing the electrolyte in step S4 includes the following steps: C1: Accurately weigh sodium sulfate and place it in a corrosion-resistant mixing tank. Add deionized water, turn on the mixing tank stirrer, set the speed to 300 rpm, and stir continuously for 20 minutes at room temperature until the sodium sulfate is completely dissolved and the solution is clear and transparent with no visible insoluble matter, thus obtaining a sodium sulfate solution. C2: Slowly add sodium dihydrogen phosphate to the sodium sulfate solution, turn on the stirrer, keep the speed at 300 rpm, and continue stirring for 10 minutes to completely dissolve the sodium dihydrogen phosphate and mix it thoroughly with the sodium sulfate solution to obtain the electrolyte base solution; C3: The electrolyte base solution is filtered through a 5µm precision filter to remove impurity particles. The filtered clarified electrolyte is then transported to the storage tank of the electrolytic cell circulation system, where it is mixed with the electrolyte circulating in the system. The electrolyte is continuously supplied to the electrolytic cell via a circulation pump. During the electrolyte circulation process, water will be lost due to electrolysis and evaporation. Deionized water and sodium sulfate and sodium dihydrogen phosphate need to be added daily to maintain the stability of the electrolyte composition and concentration.

[0011] Furthermore, the mass ratio of sodium sulfate to deionized water in step C1 is 1:10; the mass ratio of potassium dihydrogen phosphate to sodium sulfate solution in step C2 is 1:200. In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: 1. This invention creates a novel three-stage synergistic green phosphorus removal mode of ultrasonic cavitation, aerosol activation, and pulsed current electrolysis. The oxide layer is pre-cracked in an acid-free environment through the cavitation effect of multi-frequency composite ultrasound. The oxide layer is instantly softened and the reaction path is induced by the aerosol activation liquid containing biodegradable organic acid and hydroxy ferric phosphate seed crystals. Finally, the residual oxide layer is stripped off during the conduction period of the pulsed current and the iron and phosphorus are induced to precipitate in situ during the off period. This invention solves the key problems of high energy consumption, rapid accumulation of iron ions in the electrolyte, and low value of by-products in traditional electrolytic phosphorus removal processes. 2: This invention uses multi-frequency composite ultrasound, aerosol seed activation solution, and pulsed current electrolysis as the core to construct a multi-process integrated dephosphorization system. Ultrasound is responsible for pre-cracking and reducing the load on the oxide scale, aerosol is responsible for chemical softening and seed introduction, and pulsed electrolysis is responsible for residual stripping and in-situ precipitation. This multi-target, cascaded design achieves precise control of the entire process from oxide scale pre-cracking to iron and phosphorus resource recovery. The resulting phosphorus-free strips are significantly superior to traditional processes in terms of dephosphorization level, surface quality, and energy consumption. 3: This invention, through the innovative integration of pulsed current in-situ precipitation and by-product classification and separation technology, successfully converts dissolved iron ions during the dephosphorization process into high-value-added iron phosphate by-products, significantly improving the media recycling rate and providing a new green dephosphorization strategy with low energy consumption, near-zero emissions, and high returns for surface treatment in the steel industry. Detailed Implementation

[0012] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0013] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0014] Example 1 1. Accurately weigh 100g of citric acid and place it in a stainless steel mixing tank. Add 5kg of deionized water, turn on the mixing tank stirrer, set the speed to 300rpm, and stir continuously for 15min at room temperature to obtain 5kg of organic acid base liquid. 2: Add hydroxyferric phosphate powder to a grinder, set the grinding particle size to 2 μm, grind for 15 min to obtain seed powder, add 100 g of seed powder to 5 kg of organic acid base liquid, turn on the mixer of the mixing tank, adjust the speed to 400 rpm, and continuously stir and disperse at room temperature for 30 min to make the seed powder uniformly suspended in the organic acid base liquid to obtain seed suspension. 3: Filter the seed crystal suspension through a 100-mesh filter to remove agglomerated particles, then transfer it to the storage tank of the aerosol generator. Store it in a sealed container for later use. Use a low-speed stirring device in the storage tank to maintain a speed of 100 rpm to prevent the seed crystals from settling during the standing process and to keep the concentration of the suspension uniform and stable, thus obtaining the aerosol activation solution prepared in Example 1.

[0015] Example 2 1. Accurately weigh 500g of sodium sulfate and place it in a corrosion-resistant mixing tank. Add 5kg of deionized water, turn on the mixing tank stirrer, set the speed to 300rpm, and stir continuously for 20min at room temperature until the sodium sulfate is completely dissolved, the solution is clear and transparent with no visible insoluble matter, and you get 5kg of sodium sulfate solution. 2: Slowly add 25g of sodium dihydrogen phosphate to 5kg of sodium sulfate solution, turn on the stirrer, keep the speed at 300rpm, and continue stirring for 10min to completely dissolve the sodium dihydrogen phosphate and mix it thoroughly with the sodium sulfate solution to obtain the electrolyte base solution; 3: The electrolyte base solution is filtered through a 5µm precision filter to remove impurity particles. The filtered clarified electrolyte is then transported to the storage tank of the electrolytic cell circulation system to obtain the electrolyte prepared in Example 2.

[0016] Example 3 1. Strip steel uncoiling pretreatment: The strip steel coil is installed on the uncoiler and fed into the straightener after being uncoiled. The straightening speed is set to 10m / min, the number of straightening rollers is 6, and the diameter of the straightening rollers is 50mm. The strip steel is leveled. After straightening, the strip steel enters the alkaline washing tank and stays for 30min. The temperature of the alkaline washing tank is set to 55℃. A 10% sodium carbonate solution is filled into the alkaline washing tank, and the filling amount is 70% of the volume of the alkaline washing tank. After the strip steel has stayed, it enters the pre-rinsing tank and is rinsed three times in countercurrent with room temperature clean water at 5MPa pressure to remove residual sodium carbonate solution and obtain clean strip steel. 2. Ultrasonic Cavitation Pre-splitting: Clean steel strip is fed into a sealed ultrasonic cavitation chamber filled with water. A multi-frequency composite ultrasonic generator is activated, and the ultrasonic frequency is set to a composite frequency of 20kHz, 40kHz, and 80kHz, with an ultrasonic power density of 4W / cm². 2 The pre-cracking treatment time is the running time of the strip through the cavity. The running speed of the strip is 0.5 m / s. The pre-treatment time is controlled to be 8 s by adjusting the strip speed. After the treatment is completed, the pre-cracked strip is obtained. 3. Aerosol Seed Activation: The pre-cracked strip is fed into a sealed aerosol spray chamber. The aerosol activation solution prepared in Example 1 is uniformly sprayed onto the strip surface in the form of droplets with a diameter of 20 μm using an atomizing nozzle, forming an extremely thin activation solution film. The spray flow rate is 100 ml / m. 2 The strip runs at a speed of 20 m / min, and activated strip is obtained after spraying. 4. Pulsed Current Electrolysis: The activated steel strip is continuously passed through two electrolytic cells connected in series. Each cell contains anode and cathode plates; the anode plate is made of titanium-coated lead dioxide, and the cathode plate is made of stainless steel. The distance between the plates is 100 mm. The electrolyte prepared in Example 2 is used in the electrolytic cells. The pulse power supply is then turned on, and the pulse current parameters are set to a current density of 30 A / dm³. 2The pulse frequency is 600Hz, the duty cycle is 40%, the positive and negative pulses are adjustable, the single cell electrolysis time is 12s, the total electrolysis time is 24s, the strip steel running speed is 30m / min, the length of a single electrolysis cell is 8m, and after electrolysis, dephosphorized strip steel and electrolyte containing precipitates are obtained. 5. Washing and Separation: The dephosphorized steel strip is sent to a high-pressure water washing device and washed with 15MPa high-pressure water to thoroughly remove the oxide scale debris and residual precipitates on the surface of the steel strip. After washing, clean dephosphorized steel strip is obtained. The wastewater generated by high-pressure water washing and the electrolyte containing precipitates are combined, collected and transported to a hydrocyclone for solid-liquid separation. The hydrocyclone separation particle size is set to 8μm. After separation, supernatant and iron-phosphorus precipitate filter cake are obtained. 6. Drying and Recovery: The clean, dephosphorized steel strip is fed into a hot air dryer, with a drying temperature of 80℃ and an air velocity of 10m / s. The strip is dried to remove surface moisture. After drying, the strip is wound up by a coiler at a speed of 60m / min, with a maximum winding diameter of 1800mm, yielding the phosphorus-free steel strip product prepared in Example 3. The supernatant is replenished with sodium sulfate to adjust the sodium sulfate concentration to 10%, and then recycled back to the electrolytic cell as electrolyte. The resulting iron-phosphorus precipitate filter cake is transferred to a spray drying tower, with a drying temperature of 150℃ and a drying time of 30min. After drying, it is transferred to a grinder and ground for 15min. The mixture was transferred to an air classifier, where the classifying wheel speed was set to 1000 rpm and the air source pressure to 0.5 MPa. The ferric phosphate was separated and collected based on particle size differences. After being vacuum-packed and packaged in moisture-proof aluminum foil bags, it was stored, yielding the ferric phosphate prepared in Example 3 and the remaining coarse powder. The remaining coarse powder was then transferred to a gravity separator, where the vibration frequency was set to 30 Hz and the air velocity to 2.5 m / s. Hydroxyferric phosphate was separated based on density differences, yielding the hydroxyferric phosphate prepared in Example 3 and the remaining heavy material. The remaining heavy material was then transferred to a wet electromagnetic separator, where the magnetic field strength was set to 15,000 Gauss and the slurry flow rate to 0.5 m / s. 3 / h, using magnetic difference separation, the iron oxide powder prepared in Example 3 was obtained, and then packaged in a vacuum packaging machine and woven bags before being stored.

[0017] Example 4 1. Strip steel uncoiling pretreatment: The strip steel coil is installed on the uncoiler and fed into the straightener after being uncoiled. The straightening speed is set to 20m / min, the number of straightening rollers is 9, and the diameter of the straightening rollers is 80mm. The strip steel is leveled. After straightening, the strip steel enters the alkaline washing tank and stays for 45min. The temperature of the alkaline washing tank is set to 60℃. A 10% sodium carbonate solution is filled into the alkaline washing tank, and the filling amount is 70% of the volume of the alkaline washing tank. After the strip steel has stayed for 45min, it enters the pre-rinsing tank and is rinsed in three stages of countercurrent with room temperature clean water at 5MPa pressure to remove residual sodium carbonate solution and obtain clean strip steel. 2. Ultrasonic Cavitation Pre-splitting: Clean steel strip is fed into a sealed ultrasonic cavitation chamber filled with water. A multi-frequency composite ultrasonic generator is activated, and the ultrasonic frequency is set to a composite frequency of 20kHz, 40kHz, and 80kHz, with an ultrasonic power density of 5W / cm². 2 The pre-cracking treatment time is the running time of the strip through the cavity. The running speed of the strip is 0.2m / s. The pre-treatment time is controlled to be 12s by adjusting the strip speed. After the treatment is completed, the pre-cracked strip is obtained. 3. Aerosol Seed Activation: The pre-cracked strip is fed into a sealed aerosol spray chamber. The aerosol activation solution prepared in Example 1 is uniformly sprayed onto the strip surface in the form of droplets with a diameter of 20 μm using an atomizing nozzle, forming an extremely thin activation solution film. The spray flow rate is 100 ml / m. 2 The strip runs at a speed of 20 m / min, and activated strip is obtained after spraying. 4. Pulsed Current Electrolysis: The activated steel strip is continuously passed through two electrolytic cells connected in series. Each cell contains anode and cathode plates; the anode plate is made of titanium-coated lead dioxide, and the cathode plate is made of stainless steel. The distance between the plates is 50 mm. The electrolyte prepared in Example 2 is used in the electrolytic cells. The pulse power supply is then turned on, and the pulse current parameters are set to a current density of 40 A / dm³. 2 The pulse frequency is 800Hz, the duty cycle is 25%, the positive and negative pulses are adjustable, the single cell electrolysis time is 15s, the total electrolysis time is 30s, the strip steel running speed is 20m / min, the length of a single electrolysis cell is 8m, and after electrolysis, dephosphorized strip steel and electrolyte containing precipitates are obtained. 5. Washing and Separation: The dephosphorized steel strip is sent to a high-pressure water washing device and washed with 15MPa high-pressure water to thoroughly remove the oxide scale debris and residual precipitates on the surface of the steel strip. After washing, clean dephosphorized steel strip is obtained. The wastewater generated by high-pressure water washing and the electrolyte containing precipitates are combined, collected and transported to a hydrocyclone for solid-liquid separation. The hydrocyclone separation particle size is set to 8μm. After separation, supernatant and iron-phosphorus precipitate filter cake are obtained. 6. Drying and Recovery: The clean, dephosphorized steel strip is fed into a hot air dryer, with the drying temperature set at 120℃ and the air velocity at 15m / s. The strip is dried to remove surface moisture. After drying, the strip is wound up by a coiler at a speed of 10m / min, with a maximum winding diameter of 2200mm, yielding a phosphorus-free steel strip. The supernatant is replenished with sodium sulfate to adjust the sodium sulfate concentration to 10%, and then recycled back to the electrolytic cell as electrolyte. The resulting iron-phosphorus precipitate filter cake is transferred to a spray drying tower, with the drying temperature set at 200℃ for 30 minutes. After drying, it is transferred to a grinding mill and ground for 15 minutes. After grinding, it is transferred to… In an air classifier, the classifying wheel speed was set to 1000 rpm and the air source pressure to 0.5 MPa. Ferric phosphate was separated and collected based on particle size differences. After being packaged in vacuum packaging machines and moisture-proof aluminum foil bags, it was stored, yielding the ferric phosphate prepared in Example 4 and the remaining coarse powder. The remaining coarse powder was transferred to a gravity separator, with a vibration frequency of 30 Hz and an air velocity of 2.5 m / s. Hydroxyferric phosphate was separated based on density differences, yielding the hydroxyferric phosphate prepared in Example 4 and the remaining heavy material. The remaining heavy material was then transferred to a wet electromagnetic separator, with a magnetic field strength of 15,000 Gauss and a slurry flow rate of 0.5 m / s. 3 / h, using magnetic difference separation, the iron oxide powder prepared in Example 4 was obtained, and then packaged in a vacuum packaging machine and woven bags before being stored.

[0018] Comparative Example 1 1. Strip steel uncoiling pretreatment: The strip steel coil is installed on the uncoiler and fed into the straightener after being uncoiled. The straightening speed is set to 10m / min, the number of straightening rollers is 6, and the diameter of the straightening rollers is 50mm. The strip steel is leveled. After straightening, the strip steel enters the alkaline washing tank and stays for 30min. The temperature of the alkaline washing tank is set to 55℃. A 10% sodium carbonate solution is filled into the alkaline washing tank, and the filling amount is 70% of the volume of the alkaline washing tank. After the strip steel has stayed, it enters the pre-rinsing tank and is rinsed three times in countercurrent with room temperature clean water at 5MPa pressure to remove residual sodium carbonate solution and obtain clean strip steel. 2. Aerosol Seed Activation: Clean steel strip is fed into a sealed aerosol spray chamber. The aerosol activation solution prepared in Example 1 is uniformly sprayed onto the surface of the steel strip in the form of droplets with a diameter of 20 μm using an atomizing nozzle, forming an extremely thin activation solution film. The spray flow rate is 100 ml / m. 2 The strip runs at a speed of 20 m / min, and activated strip is obtained after spraying. 3. Pulsed Current Electrolysis: The activated steel strip is continuously passed through two electrolytic cells connected in series. Each cell contains anode and cathode plates; the anode plate is made of titanium-coated lead dioxide, and the cathode plate is made of stainless steel. The distance between the plates is 100 mm. The electrolyte prepared in Example 2 is used in the electrolytic cells. Then, the pulse power supply is turned on, and the pulse current parameters are set to a current density of 30 A / dm³. 2The pulse frequency is 600Hz, the duty cycle is 40%, the positive and negative pulses are adjustable, the single cell electrolysis time is 12s, the total electrolysis time is 24s, the strip steel running speed is 30m / min, the length of a single electrolysis cell is 8m, and after electrolysis, dephosphorized strip steel and electrolyte containing precipitates are obtained. 4. Washing and Separation: The dephosphorized steel strip is sent to a high-pressure water washing device and washed with 15MPa high-pressure water to thoroughly remove the oxide scale debris and residual precipitates on the surface of the steel strip. After washing, clean dephosphorized steel strip is obtained. The wastewater generated by high-pressure water washing and the electrolyte containing precipitates are combined, collected and transported to a hydrocyclone for solid-liquid separation. The hydrocyclone separation particle size is set to 8μm. After separation, the supernatant and iron-phosphorus precipitate filter cake are obtained. 5. Drying and Recovery: The clean, dephosphorized steel strip is fed into a hot air dryer, with a drying temperature of 80℃ and an air velocity of 10m / s. The strip is dried to remove surface moisture. After drying, the strip is wound up by a coiler at a speed of 60m / min, with a maximum winding diameter of 1800mm, yielding the phosphorus-free steel strip product prepared in Comparative Example 1. The supernatant is replenished with sodium sulfate to adjust the sodium sulfate concentration to 10%, and then recycled back to the electrolytic cell as electrolyte. The resulting iron-phosphorus precipitate filter cake is transferred to a spray drying tower, with a drying temperature of 150℃ and a drying time of 30min. After drying, it is transferred to a grinder and ground for 15min. The ferric phosphate was transferred to an air classifier, with the classifying wheel speed set at 1000 rpm and the air source pressure at 0.5 MPa. The ferric phosphate was separated and collected based on particle size differences. After being vacuum-packed and packaged in moisture-proof aluminum foil bags, it was stored, yielding the ferric phosphate prepared in Comparative Example 1 and the remaining coarse powder. The remaining coarse powder was then transferred to a gravity separator, with a vibration frequency set at 30 Hz and an air velocity of 2.5 m / s. Hydroxyferric phosphate was separated based on density differences, yielding the hydroxyferric phosphate prepared in Comparative Example 1 and the remaining heavy material. The remaining heavy material was then transferred to a wet electromagnetic separator, with a magnetic field strength set at 15,000 Gauss and a slurry flow rate of 0.5 m / s. 3 / h, using magnetic difference separation, the iron oxide powder prepared in Comparative Example 1 was obtained, and then packaged in vacuum packaging machine and woven bags before being put into storage.

[0019] Comparative Example 2 1. Strip steel uncoiling pretreatment: The strip steel coil is installed on the uncoiler and fed into the straightener after being uncoiled. The straightening speed is set to 10m / min, the number of straightening rollers is 6, and the diameter of the straightening rollers is 50mm. The strip steel is leveled. After straightening, the strip steel enters the alkaline washing tank and stays for 30min. The temperature of the alkaline washing tank is set to 55℃. A 10% sodium carbonate solution is filled into the alkaline washing tank, and the filling amount is 70% of the volume of the alkaline washing tank. After the strip steel has stayed, it enters the pre-rinsing tank and is rinsed three times in countercurrent with room temperature clean water at 5MPa pressure to remove residual sodium carbonate solution and obtain clean strip steel. 2. Ultrasonic Cavitation Pre-splitting: Clean steel strip is fed into a sealed ultrasonic cavitation chamber filled with water. A multi-frequency composite ultrasonic generator is activated, and the ultrasonic frequency is set to a composite frequency of 20kHz, 40kHz, and 80kHz, with an ultrasonic power density of 4W / cm². 2 The pre-cracking treatment time is the running time of the strip through the cavity. The running speed of the strip is 0.5 m / s. The pre-treatment time is controlled to be 8 s by adjusting the strip speed. After the treatment is completed, the pre-cracked strip is obtained. 3. Pulsed Current Electrolysis: The pre-cracked strip steel is continuously passed through two electrolytic cells connected in series. The electrolytic cells contain anode and cathode plates. The anode plate is made of titanium-coated lead dioxide, and the cathode plate is made of stainless steel. The distance between the plates is set to 100 mm. The electrolyte prepared in Example 2 is used in the electrolytic cells. Then, the pulse power supply is turned on, and the pulse current parameters are set to a current density of 30 A / dm³. 2 The pulse frequency is 600Hz, the duty cycle is 40%, the positive and negative pulses are adjustable, the single cell electrolysis time is 12s, the total electrolysis time is 24s, the strip steel running speed is 30m / min, the length of a single electrolysis cell is 8m, and after electrolysis, dephosphorized strip steel and electrolyte containing precipitates are obtained. 4. Washing and Separation: The dephosphorized steel strip is sent to a high-pressure water washing device and washed with 15MPa high-pressure water to thoroughly remove the oxide scale debris and residual precipitates on the surface of the steel strip. After washing, clean dephosphorized steel strip is obtained. The wastewater generated by high-pressure water washing and the electrolyte containing precipitates are combined, collected and transported to a hydrocyclone for solid-liquid separation. The hydrocyclone separation particle size is set to 8μm. After separation, the supernatant and iron-phosphorus precipitate filter cake are obtained. 5. Drying and Recovery: The clean, dephosphorized steel strip is fed into a hot air dryer, with a drying temperature of 80℃ and an air velocity of 10m / s. The strip is dried to remove surface moisture. After drying, the strip is wound up by a coiler at a speed of 60m / min, with a maximum winding diameter of 1800mm, yielding the phosphorus-free steel strip product prepared in Comparative Example 2. The supernatant is replenished with sodium sulfate to adjust the sodium sulfate concentration to 10%, and then recycled back to the electrolytic cell as electrolyte. The resulting iron-phosphorus precipitate filter cake is transferred to a spray drying tower, with a drying temperature of 150℃ and drying time of 30min. After drying, it is transferred to a grinder and ground for 15min. The ferric phosphate was transferred to an air classifier, where the classifying wheel speed was set to 1000 rpm and the air source pressure to 0.5 MPa. The ferric phosphate was separated and collected based on particle size differences. After being vacuum-packed and packaged in moisture-proof aluminum foil bags, it was stored, yielding the ferric phosphate prepared in Comparative Example 2 and the remaining coarse powder. The remaining coarse powder was then transferred to a gravity separator, where the vibration frequency was set to 30 Hz and the air velocity to 2.5 m / s. Hydroxyferric phosphate was separated based on density differences, yielding the hydroxyferric phosphate prepared in Comparative Example 2 and the remaining heavy material. The remaining heavy material was then transferred to a wet electromagnetic separator, where the magnetic field strength was set to 15,000 Gauss and the slurry flow rate to 0.5 m / s.3 / h, using magnetic difference separation, the iron oxide powder prepared in Comparative Example 2 was obtained, and then packaged in vacuum packaging machine and woven bags before being put into storage.

[0020] Dephosphorization effect and surface quality test Five sampling points were evenly taken along the length of the strip from the finished phosphorus-free strips prepared in Examples 3, 4, 1, and 2, respectively. A 50mm×50mm sample was cut using a cutting sampler, and the surface oxide scale residue rate, surface roughness and phosphorus removal grade were determined in sequence. The residual oxide scale rate was determined by the gravimetric method: the initial mass of the sample was weighed using an electronic balance, and after the residual oxide scale was electrolytically removed, it was weighed again to calculate the residual oxide scale rate. Surface roughness was tested using a surface roughness tester according to GB / T 1031-2009 standard; The phosphorus removal grade was evaluated by comparing it with the standard spectrum according to GB / T 8923.1-2011. Table 1. Results of phosphorus removal effect and surface quality test

[0021] Results analysis: The residual oxide scale rates in Examples 3 and 4 were both less than 1%, achieving phosphorus removal grades of Sa 2.5 and Sa 3.0, respectively, with surface roughness of 1.2 μm and 1.0 μm, respectively, indicating that the synergistic process of the present invention has good phosphorus removal effect and surface quality. Comparative Example 1 lacked ultrasonic cavitation pre-cracking, resulting in a residual oxide scale rate as high as 3.2%, a phosphorus removal grade of only Sa 2.0, and a surface roughness of 1.8 μm. This indicates that the lack of ultrasonic pre-cracking led to incomplete oxide scale removal, and the residual oxide scale affected the surface quality. Comparative Example 2 lacked aerosol seed activation, resulting in an oxide scale residue rate of 2.1%, a phosphorus removal grade of Sa 2.0, and a surface roughness of 1.5 μm. This indicates that the lack of aerosol activation led to insufficient oxide scale softening, increased electrolytic load, and decreased phosphorus removal efficiency.

[0022] Energy consumption and media consumption test The production lines of Example 3, Example 4, Comparative Example 1 and Comparative Example 2 were tested for continuous operation for 8 hours. The total power consumption of the production line, the amount of sodium sulfate added and the total mass of the processed strip steel were recorded. The power consumption per ton of steel and the amount of sodium sulfate added per ton of steel were calculated. The power consumption was measured by an electricity meter, the amount of sodium sulfate added was measured by a flow meter and a weighbridge, and the mass of the processed strip steel was measured by a weighbridge. Table 2. Test results of energy consumption and media consumption

[0023] Results analysis: The power consumption per ton of steel in Examples 3 and 4 were 28.5 kWh / t and 32.0 kWh / t, respectively, and the sodium sulfate replenishment amounts were 1.2 kg / t and 0.9 kg / t, respectively, which were significantly lower than those in the comparative example. The comparative example showed that the power consumption per ton of steel was as high as 38.5 kWh / t, which was 35.1% higher than that of Example 3. The sodium sulfate replenishment was 2.5 kg / t, which was 108.3% higher than that of Example 3. This indicates that the lack of ultrasonic pre-cracking led to a significant increase in electrolytic load and aggravated electrolyte loss. The comparative example of 2 tons of steel consumed 35.0 kWh / t of electricity, which is 22.8% higher than that of Example 3. The amount of sodium sulfate replenished was 1.8 kg / t, which is 50.0% higher than that of Example 3. This indicates that the lack of aerosol activation led to a decrease in electrolysis efficiency and an increase in media consumption.

[0024] By-product yield and purity testing The byproducts of ferric phosphate, hydroxyferric phosphate, and iron oxide powder prepared in Examples 3, 4, Comparative Example 1, and Comparative Example 2 were weighed using an electronic balance, and the yield of each byproduct relative to the mass of the processed strip steel was calculated. The purity of ferric phosphate and hydroxyferric phosphate was determined using X-ray fluorescence spectrometry (XRF), and each sample was tested three times and the average value was taken. Table 3. Results of by-product yield and purity tests

[0025] Results analysis: The iron phosphate yields in Examples 3 and 4 reached 9.8 kg / t and 11.2 kg / t, respectively, with purities of 96.5% and 97.2%, respectively, meeting the standards for battery-grade iron phosphate precursors; the yields of low-value iron oxide powder were only 1.2 kg / t and 0.8 kg / t, respectively, accounting for a relatively low proportion. Comparative Example 1 showed a ferric phosphate yield of only 6.5 kg / t, a decrease of 42.0% compared to Example 4, with a purity of only 88.5%, which could not meet battery-grade standards; the iron oxide powder yield was as high as 2.8 kg / t, with a significantly increased proportion, indicating that the absence of seed induction resulted in the precipitation products being mainly low-value iron oxide. Comparative Example 2 had a ferric phosphate yield of 8.0 kg / t, which was 28.6% lower than that of Example 4, and a purity of 92.0%. Although it was better than Comparative Example 1, it was still lower than the battery grade standard, indicating that the lack of aerosol seed crystals led to insufficient precipitation induction effect.

[0026] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A green dephosphorization process for strip panels using pulsed current, characterized in that, It achieves efficient removal and resource utilization of oxide scale on the surface of strip steel through strip uncoiling pretreatment, ultrasonic cavitation pre-cracking, aerosol seed activation, pulsed current electrolysis, rinsing separation and drying recovery.

2. The green dephosphorization process for strip using pulsed current according to claim 1, characterized in that, Includes the following steps: S1: Strip steel uncoiling pretreatment: The strip steel coil is installed on the uncoiler and fed into the straightener after being uncoiled. The straightening speed is set to 10-20m / min, the number of straightening rollers is 6-9, and the diameter of the straightening rollers is 50-80mm. The strip steel is leveled. After straightening, the strip steel enters the alkaline washing tank and stays for 30-45min. The temperature of the alkaline washing tank is set to 55-60℃. A 10% sodium carbonate solution is filled into the alkaline washing tank, and the filling amount is 70% of the volume of the alkaline washing tank. After the strip steel has stayed, it enters the pre-rinsing tank and is rinsed three times in countercurrent with room temperature clean water at 5MPa pressure to remove residual sodium carbonate solution and obtain clean strip steel. S2: Ultrasonic Cavitation Pre-splitting: The clean steel strip is fed into a sealed ultrasonic cavitation chamber filled with water. A multi-frequency composite ultrasonic generator is turned on, and the ultrasonic frequency is set to a composite frequency of 20kHz, 40kHz, and 80kHz, with an ultrasonic power density of 4-5W / cm². 2 The pre-cracking treatment time is the running time of the strip through the cavity. The running speed of the strip is 0.2-0.5 m / s. The pre-treatment time is controlled to be 8-12 s by adjusting the strip speed. After the treatment is completed, pre-cracked strip is obtained. S3: Aerosol Seed Activation: The pre-cracked strip is fed into a sealed aerosol spray chamber. The aerosol activation liquid is evenly sprayed onto the strip surface in the form of droplets with a diameter of 20 μm using atomizing nozzles, forming an extremely thin activation liquid film. The spray flow rate is 100 ml / m. 2 The strip runs at a speed of 20 m / min, and activated strip is obtained after spraying. S4: Pulsed Current Electrolysis: The activated steel strip is continuously passed through two electrolytic cells connected in series. Each cell contains anode and cathode plates; the anode plate is made of titanium-coated lead dioxide, and the cathode plate is made of stainless steel. The plate spacing is set to 50-100 mm. The electrolytic cells contain electrolyte. The pulse power supply is then turned on, and the pulse current parameters are set to a current density of 30-40 A / dm³. 2 The pulse frequency is 600-800Hz, the duty cycle is 25-40%, the positive and negative pulses are adjustable, the single cell electrolysis time is 12-15s, the total electrolysis time is 24-30s, the strip steel running speed is 20-30m / min, the length of a single electrolytic cell is 8m, and after electrolysis, dephosphorized strip steel and electrolyte containing precipitates are obtained. S5: Washing and Separation: The dephosphorized steel strip is sent to a high-pressure water washing device and washed with 15MPa high-pressure water to thoroughly remove the oxide scale debris and residual precipitates on the surface of the steel strip. After washing, clean dephosphorized steel strip is obtained. The wastewater generated by high-pressure water washing and the electrolyte containing precipitates are combined, collected and transported to a hydrocyclone for solid-liquid separation. The hydrocyclone separation particle size is set to 8um. After separation, the supernatant and iron-phosphorus precipitate filter cake are obtained. S6: Drying and Recycling: The clean, dephosphorized steel strip is fed into a hot air dryer. The drying temperature is set at 80-120℃ and the air velocity is 10-15m / s. The surface moisture of the steel strip is removed by drying. The dried steel strip is then wound up by a coiler at a speed of 10-60m / min and a maximum winding diameter of 1800-2200mm to obtain the finished phosphorus-free steel strip. The supernatant obtained is supplemented with sodium sulfate to adjust the sodium sulfate concentration to 10%, and then returned to the electrolytic cell as an electrolyte for recycling. The iron-phosphorus precipitate filter cake is collected after sedimentation and separation to obtain iron phosphate powder, hydroxy iron phosphate powder, and iron oxide powder, which are packaged separately for later use.

3. The green dephosphorization process for strip using pulsed current according to claim 2, characterized in that, The sedimentation separation and collection described in step S6 includes the following steps: A1: The obtained iron-phosphorus precipitate filter cake is transferred to a spray drying tower, the drying temperature is set to 150-200℃, and the drying time is 30 min. After drying, it is transferred to a grinder and ground for 15 min. After grinding, it is transferred to an air classifier, the classifier wheel speed is set to 1000 rpm, and the air source pressure is 0.5 MPa. The iron phosphate is separated and collected by the particle size difference. After being packaged in a vacuum packaging machine and moisture-proof aluminum foil bags, it is stored in the warehouse to obtain iron phosphate and the remaining coarse powder material. A2: Transfer the remaining coarse powder material to a gravity separator. The gravity separator is set with a vibration frequency of 30Hz and a wind speed of 2.5m / s. The hydroxy ferric phosphate is separated by the density difference to obtain hydroxy ferric phosphate and residual heavy material. A3: Transfer the residual heavy material to a wet electromagnetic separator, setting the magnetic field strength to 15,000 Gauss and the slurry flow rate to 0.5 m / s. 3 / h, iron oxide powder is obtained by separating it using magnetic differences, and then packaged in vacuum packaging machine and woven bags before being stored.

4. The green dephosphorization process for strip using pulsed current according to claim 2, characterized in that, The preparation method of the aerosol activation solution in step S3 includes the following steps: B1: Accurately weigh citric acid and place it in a stainless steel mixing tank. Add deionized water, turn on the mixing tank stirrer, set the speed to 300 rpm, and stir continuously for 15 minutes at room temperature to obtain an organic acid base liquid. B2: Add ferric hydroxyphosphate powder to a grinder, set the grinding particle size to 2 μm, grind for 15 min to obtain seed powder, add seed powder to organic acid base liquid, turn on the mixer of the mixing tank, adjust the speed to 400 rpm, and continuously stir and disperse at room temperature for 30 min to make the seed powder uniformly suspended in organic acid base liquid to obtain seed suspension. B3: Filter the seed crystal suspension through a 100-mesh filter to remove agglomerated particles, then transfer it to the storage tank of the aerosol generator. Store it in a sealed container for later use. Use a low-speed stirring device in the storage tank to maintain a speed of 100 rpm to prevent the seed crystals from settling during the standing process and to keep the suspension concentration uniform and stable, thus obtaining the aerosol activation solution.

5. A green dephosphorization process for strip using pulsed current according to claim 2, characterized in that, The method for preparing the electrolyte in step S4 includes the following steps: C1: Accurately weigh sodium sulfate and place it in a corrosion-resistant mixing tank. Add deionized water, turn on the mixing tank stirrer, set the speed to 300 rpm, and stir continuously for 20 minutes at room temperature until the sodium sulfate is completely dissolved and the solution is clear and transparent with no visible insoluble matter, thus obtaining a sodium sulfate solution. C2: Slowly add sodium dihydrogen phosphate to the sodium sulfate solution, turn on the stirrer, keep the speed at 300 rpm, and continue stirring for 10 minutes to completely dissolve the sodium dihydrogen phosphate and mix it thoroughly with the sodium sulfate solution to obtain the electrolyte base solution; C3: The electrolyte base solution is filtered through a 5µm precision filter to remove impurity particles. The filtered clarified electrolyte is then transported to the storage tank of the electrolytic cell circulation system, where it is mixed with the electrolyte circulating in the system. The electrolyte is continuously supplied to the electrolytic cell via a circulation pump. During the electrolyte circulation process, water will be lost due to electrolysis and evaporation. Deionized water and sodium sulfate and sodium dihydrogen phosphate need to be added daily to maintain the stability of the electrolyte composition and concentration.

6. The green dephosphorization process for strip using pulsed current according to claim 4, characterized in that, The mass ratio of citric acid to deionized water in step B1 is 1:

50.

7. The green dephosphorization process for strip using pulsed current according to claim 4, characterized in that, The mass ratio of the seed powder to the organic acid-based liquid in step B2 is 1:

50.

8. The green dephosphorization process for strip using pulsed current according to claim 5, characterized in that, The mass ratio of sodium sulfate to deionized water in step C1 is 1:

10.

9. The green dephosphorization process for strip using pulsed current according to claim 5, characterized in that, The mass ratio of potassium dihydrogen phosphate and sodium sulfate solution in step C2 is 1:200.

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