Process for comprehensive utilization of sulfuric acid pickling waste acid

Abstract

This invention discloses a comprehensive utilization process for sulfuric acid pickling waste acid, comprising: the pickling waste acid discharged from the cold rolling sulfuric acid pickling unit is discharged into a waste acid pit, then pumped to a pretreatment filtration system to remove a small amount of particulate matter; the pretreated permeate enters a pretreatment permeate tank; the pretreated permeate is pumped to an acid-resistant nanofiltration system, where scrap iron wire from the steel plant is placed in a packed tower, and the concentrated waste acid enters the scrap iron wire packed tower from the bottom, while the waste acid after dissolving the scrap iron wire flows out from the top; a ferrous sulfate solution is pumped to a primary reactor, where ozone is added for aeration and stirring; hydrogen peroxide is then added to oxidize it to ferric sulfate; the effluent is pumped into a secondary reactor; divinylbenzene and zeolite powder are added; polymerization and aging reactions are completed, and the effluent from the secondary reactor is polyferric sulfate coagulant. The purified sulfuric acid produced by nanofiltration can be returned to the unit for recycling, reducing acid consumption and emissions, while the concentrated liquid produced can be processed into a high-efficiency coagulant for wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a comprehensive utilization process for sulfuric acid pickling waste acid. Background Technology

[0002] Pickling is an indispensable process in cold rolling mills. During the production process, cold-rolled steel needs to be pickled to remove the iron oxide scale from the surface of the steel. Depending on the process requirements, pickling can be done with hydrochloric acid or sulfuric acid.

[0003] Hydrochloric acid pickling has a wide range of applications, and there are mature acid regeneration processes for the waste acid discharged during the pickling process, allowing for the recycling of the waste acid after treatment. Sulfuric acid pickling is mainly used in electroplating zinc, electroplating tin, and hot stretching and leveling of silicon steel. Compared with hydrochloric acid pickling, the amount of waste acid discharged is relatively small. Sulfuric acid pickling mostly does not have an acid regeneration process, and the high-concentration waste acid discharged is directly transported to a wastewater treatment plant for treatment.

[0004] The treatment processes for acidic wastewater from various cold rolling mills are basically the same, such as... Figure 1 As shown, acidic wastewater from different units first enters the equalization tank for water quality equilibration. Aeration also occurs in the equalization tank to prevent sedimentation and to remove some of the Fe from the wastewater. 2+ Oxidized to Fe 3+ Afterwards, the mixture enters the primary and secondary neutralization tanks, where lime is added to coarsely and finely adjust the pH, respectively. The pH in the secondary neutralization tank is controlled at around 8-9. Aeration continues in the neutralization tank to remove the remaining Fe. 2+ Oxidized to Fe 3+ After neutralization, the sludge enters a clarification tank for sludge-water separation. The effluent from the clarification tank then enters a final neutralization tank for fine-tuning based on the actual pH level by adding acid or alkali. Finally, it is filtered before being discharged. The sludge produced in the clarification tank is concentrated in a thickening tank and then dewatered by a sludge dewatering machine. The dewatered sludge is transported off-site for treatment. The supernatant from the thickening tank and the sludge dewatering machine is returned to the equalization tank for further treatment. See [link to relevant documentation]. Figure 1 .

[0005] Liu Qin et al. prepared polyferric chloride sulfate using sulfuric acid pickling waste liquid. Excess waste iron filings and a certain amount of hydrochloric acid waste liquid were added to a certain amount of sulfuric acid pickling waste liquid, and the mixture was heated in a 70℃ water bath for 3 hours. The mixture was then filtered to obtain a green, transparent liquid. The pH of the filtrate was measured to be between 3.2 and 4.0, and the iron content was measured to be between 90 and 130 g / L. Ferrous sulfate was added to the filtrate to adjust the iron ion concentration and the ratio of sulfate to chloride ions; a stabilizer and waste hydrochloric acid were added (to adjust the acidity); the mixture was heated to approximately 50℃ and stirred to fully dissolve the ferrous sulfate and stabilizer. An oxidant was added in batches over 0.5 hours, followed by a 1-hour reaction to obtain a reddish-brown composite polyferric chloride sulfate.

[0006] Wan Jinbao et al. from Nanchang University used a single-tube packed film rising film concentration and crystallization method to treat sulfuric acid pickling waste liquid. The waste acid content was: H₂SO₄ 5%–7%, FeSO₄ 200–230 g / L; the waste acid volume was 7000 m³. 3 / a; Inlet and outlet temperatures of chilled brine:

[0007] -15~-10℃; Concentrate content: H2SO4 7.24%, FeSO4 26.9%; Crystallization mother liquor content: H2SO4 12.5%, FeSO4 6.75%; Regenerated acid content: H2SO4 12%~15%, FeSO4 ≤6.75%; Ferrous sulfate content: FeSO4·7H2O ≥95%.

[0008] Zhang Tao et al. used diffusion dialysis to recover waste sulfuric acid generated during copper smelting. They typically controlled the flow ratio of the waste acid concentrate to water at 1:1. After diffusion dialysis, 80-90% of the sulfuric acid could be recovered and reused, while 10-20% remained in the waste liquid, which was generally neutralized. Using this process, the amount of waste liquid to be treated did not decrease, only the concentration decreased; the concentration of the recovered sulfuric acid was lower than that of the concentrate, requiring it to be mixed with fresh acid before recycling. Summary of the Invention

[0009] Therefore, the technical problem to be solved by the present invention is to provide a resource-based treatment method for waste sulfuric acid pickling waste liquid that is effective and low in cost.

[0010] The technical solution of this invention is a comprehensive utilization process for sulfuric acid washing waste acid, comprising the following steps:

[0011] a. The pickling waste acid discharged from the cold rolling sulfuric acid pickling unit is first discharged into the waste acid pit, and then the waste acid is lifted to the pretreatment filtration system by a primary lift pump to remove a small amount of particulate matter in the pickling waste acid. The filtration facilities and pipeline materials are made of acid corrosion resistant membrane materials. The pretreated product water enters the pretreatment product water tank.

[0012] b. The pretreated wastewater is then transferred to an acid-resistant nanofiltration system. The nanofiltration membrane used is an acid-resistant nanofiltration membrane, which allows monovalent H+ to be released. + Through, entering the product water side, divalent and trivalent Fe... 2+ Fe 3+ It is retained on the concentrate side; the flux of the acid-resistant nanofiltration membrane is controlled at 5–25 L / m. 2 ·h;

[0013] c. Place the scrap iron wire from the steel plant in the packed tower. The concentrated waste acid enters the waste iron wire packed tower from the bottom. The waste acid after dissolving the scrap iron wire flows out from the top. The iron ion concentration at the outlet of the waste iron wire packed tower reaches 1.5-5%, and the main component of the iron ion is ferrous sulfate.

[0014] d. The ferrous sulfate solution is transferred to the primary reactor, which is heated to 45-55°C. Ozone is added to the primary reactor for aeration and stirring. Hydrogen peroxide is then added at a concentration of 1%-3%. Under the combined oxidation of ozone and hydrogen peroxide, the ferrous sulfate is oxidized to ferric sulfate.

[0015] e. The effluent from the primary reactor is pumped into the secondary reactor. The temperature in the secondary reactor is maintained at 45-55℃. 100-500 mg / L of divinylbenzene is added, followed by 1-5% zeolite powder. The reaction time in the secondary reactor is 3-5 hours. The polymerization and maturation reactions are completed in the secondary reactor. The effluent from the secondary reactor is polyferric sulfate coagulant.

[0016] The addition ratio of divinylbenzene and zeolite powder refers to their proportion in the effluent.

[0017] In step b, the pretreated wastewater is pumped to an acid-resistant nanofiltration system by a high-pressure pump; the acid-resistant nanofiltration membrane only allows monovalent H+. + Through, entering the product water side, divalent and trivalent Fe... 2+ Fe 3+ Then it cannot pass through and is trapped on the concentrate side; to maintain charge balance, some divalent SO4... 2- It will pass through the nanofiltration membrane and enter the product water side. The flux of the nanofiltration membrane is controlled at 5–25 L / m. 2 • h, recovery rate controlled at 50-95%. SO4 in the permeate after nanofiltration treatment. 2- With a concentration of 3-10% and a TFe concentration of 0.1-1 g / L, the waste acid (SO4) can be recycled back to the pickling unit; the concentrated waste acid on the concentrate side... 2- Concentration 3-10%, TFe concentration 10-30 g / L.

[0018] In step c, the iron in the waste wire dissolves in the concentrated waste acid, consuming the hydrogen ions in the waste acid and increasing the ferrous ion content in the waste acid.

[0019] In step d, ozone decomposes into oxygen after oxidation, and hydrogen peroxide decomposes into water and oxygen, which will not affect the quality of ferric sulfate.

[0020] In step e, divinylbenzene, as a crosslinking agent, can enhance the adsorption bridging effect of the coagulant and improve the coagulation effect; zeolite has a microporous structure and a large specific surface area, which can act as a crystal nucleus to enhance the precipitation effect of the coagulant, and at the same time adsorb phosphorus, organic matter and other substances in wastewater.

[0021] According to a comprehensive utilization process for sulfuric acid pickling waste acid of the present invention, preferably, the water quality of the pickling waste acid discharged from the cold rolling sulfuric acid pickling unit is: SO42-. 2-3~10%, TFe 1~10g / L, pH 0~0.5.

[0022] According to a comprehensive utilization process for sulfuric acid washing waste acid of the present invention, preferably, the acid-resistant membrane material in step a is selected from inorganic ceramic membrane or sintered organic membrane.

[0023] Furthermore, the membrane pore size ranges from 20 to 200 nm; the circulation rate is 5 to 30 times the throughput; and the membrane flux is controlled at 50 to 300 L / m. 2 •h. Cross-flow filtration is used.

[0024] According to a comprehensive utilization process for sulfuric acid washing waste acid of the present invention, preferably, in step b, the acid-resistant nanofiltration membrane can operate stably for a long time under acid concentration conditions of less than 20%; the recovery rate of the nanofiltration membrane in step b is controlled at 50-95%.

[0025] Furthermore, the recovery rate of the nanofiltration membrane described in step b is controlled at 60-95%.

[0026] According to a comprehensive utilization process for sulfuric acid washing waste acid of the present invention, preferably, in step c, the concentration of ferrous sulfate at the outlet of the waste iron wire packed tower reaches 4% to 13.5%.

[0027] According to a comprehensive utilization process for sulfuric acid washing waste acid of the present invention, preferably, the ozone dosage in step d is 1-3 g / L; and the reaction time of the primary reactor in step d is 0.5-1 h.

[0028] According to a comprehensive utilization process for sulfuric acid washing waste acid of the present invention, preferably, the zeolite powder in step e has a particle size of 100-300 mesh.

[0029] Preferably, step e involves adding 1-3% zeolite powder.

[0030] Beneficial effects:

[0031] This invention provides a process for the resource utilization of sulfuric acid washing waste. After treatment by this invention, the purified sulfuric acid produced by nanofiltration can be returned to the unit for recycling, reducing acid consumption and emissions. Simultaneously, the resulting concentrate can be processed into a high-efficiency coagulant for wastewater treatment, and no waste is generated during the process. This invention has both economic and environmental benefits, demonstrating significant social and environmental advantages. Attached Figure Description

[0032] Figure 1 It is the existing technology for treating acidic wastewater.

[0033] Figure 2 This invention provides a process flow diagram for the resource utilization of sulfuric acid washing waste acid. Detailed Implementation

[0034] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the invention is not limited to the following embodiments.

[0035] Example 1

[0036] The waste acid water discharged from the cold rolling sulfuric acid pickling unit is SO4. 2- 6%, TFe 2g / L, pH 0.25.

[0037] A sintered organic membrane with a pore size of 100 nm is used. Cross-flow filtration is employed, with a circulation rate 20 times the treatment capacity, and the membrane flux is controlled at 200 L / m³. 2 • h, effluent sludge density index (SDI) 2.6. The pretreated permeate enters an acid-resistant nanofiltration system. Nanofiltration membrane flux 15 L / m³. 2 • h, recovery rate controlled at 90%. SO4 in the permeate after nanofiltration treatment. 2- With a concentration of 5.8% and a TFe concentration of 0.2 g / L, it can be returned to the pickling unit for recycling; the concentrated waste acid SO4 is concentrated on the concentrate side. 2- Concentration 6.1%, TFe concentration 18g / L.

[0038] Scrap iron wire from a steel plant was placed in a packed tower. The iron ion concentration at the outlet of the scrap iron wire tower was 1.62%, and the ferrous sulfate concentration was 4.4%.

[0039] The temperature of the primary reactor was 45℃, the ozone dosage was 3 g / L, the hydrogen peroxide dosage was 1%, and the reaction time in the primary reactor was 1 hour. In the secondary reactor, the temperature was kept constant, and divinylbenzene was added at a dosage of 100 mg / L; then zeolite powder ground to a particle size of 100 mesh was added at a dosage of 3%; the reaction time in the secondary reactor was 5 hours.

[0040] The coagulant produced in the secondary reactor is used to treat the concentrated brine of the cold-rolled reverse osmosis system. The COD of the biochemical effluent is 67 mg / L. After adding 1000 mg / L of coagulant, the COD of the treated effluent is 36 mg / L.

[0041] Example 2

[0042] The waste acid water discharged from the cold rolling sulfuric acid pickling unit is SO4. 2- 8%, TFe 10g / L, pH 0.14.

[0043] A sintered organic membrane with a pore size of 100 nm is used. Cross-flow filtration is employed, with a circulation rate five times the treatment capacity, and the membrane flux is controlled at 50 L / m³. 2• h, effluent sludge density index (SDI) 1.5. The pretreated permeate enters an acid-resistant nanofiltration system. Nanofiltration membrane flux 25 L / m³. 2 • h, recovery rate controlled at 50%. SO4 in the permeate after nanofiltration treatment. 2- With a concentration of 7.9% and a TFe concentration of 0.3 g / L, it can be returned to the pickling unit for recycling; the concentrated waste acid SO4 is concentrated on the concentrate side. 2 The concentration was 8.3%, and the TFe concentration was 19.3 g / L.

[0044] Scrap iron wire from a steel plant was placed in a packed tower. The iron ion concentration at the outlet of the scrap iron wire tower was 3.25%, and the ferrous sulfate concentration was 8.8%.

[0045] The temperature of the primary reactor was 50℃, the ozone dosage was 2 g / L, the hydrogen peroxide dosage was 2%, and the reaction time in the primary reactor was 0.75 h. In the secondary reactor, while maintaining a constant temperature, divinylbenzene was added at a dosage of 200 mg / L; then zeolite powder ground to a particle size of 200 mesh was added at a dosage of 2%; the reaction time in the secondary reactor was 4 h.

[0046] The coagulant produced in the secondary reactor is used to treat the biochemical effluent of cold rolling wastewater. The COD of the biochemical effluent is 35 mg / L. After adding 300 mg / L of coagulant, the COD of the treated effluent is 22 mg / L.

[0047] Example 3

[0048] The waste acid water discharged from the cold rolling sulfuric acid pickling unit is SO4. 2- 10%, TFe 1.6g / L, pH 0.3.

[0049] A sintered organic membrane with a pore size of 100 nm is used. Cross-flow filtration is employed, with a circulation rate 30 times the treatment capacity, and the membrane flux is controlled at 300 L / m³. 2 • h, effluent sludge density index (SDI) 3.2. The pretreated permeate enters an acid-resistant nanofiltration system. Nanofiltration membrane flux 5 L / m³. 2 • h, recovery rate controlled at 95%. SO4 in the product water after nanofiltration treatment. 2- The concentration is 4.5%, and the TFe concentration is 0.28 g / L. It can be returned to the pickling unit for recycling; the concentrated waste acid SO4 is concentrated on the concentrate side. 2- The concentration was 6.0%, and the TFe concentration was 28.9 g / L.

[0050] Scrap iron wire from a steel plant was placed in a packed tower. The iron ion concentration at the outlet of the scrap iron wire tower was 4.85%, and the ferrous sulfate concentration was 13%.

[0051] The temperature of the primary reactor was 55℃, the ozone dosage was 1 g / L, the hydrogen peroxide dosage was 3%, and the reaction time in the primary reactor was 0.5 h. In the secondary reactor, the temperature was kept constant, and divinylbenzene was added at a dosage of 500 mg / L; then zeolite powder ground to a particle size of 300 mesh was added at a dosage of 1%; the reaction time in the secondary reactor was 3 h.

[0052] The coagulant produced by the secondary reactor was used to treat phosphating wastewater from a phosphating unit. The biochemical effluent had a COD of 105 mg / L and a phosphate concentration of 8.8 mg / L. After adding 2000 mg / L of coagulant, the treated effluent had a COD of 48 mg / L and a total phosphorus concentration of 0.32 mg / L.

Claims

1. A comprehensive utilization process for sulfuric acid washing waste acid, characterized in that: Includes the following steps: a. The pickling waste acid discharged from the cold rolling sulfuric acid pickling unit is first discharged into the waste acid pit, and then the waste acid is lifted to the pretreatment filtration system by a primary lift pump to remove a small amount of particulate matter in the pickling waste acid. The filtration facilities and pipeline materials are made of acid corrosion resistant membrane materials. The pretreated product water enters the pretreatment product water tank. b. The pretreated wastewater is then transferred to an acid-resistant nanofiltration system. The nanofiltration membrane used is an acid-resistant nanofiltration membrane, which allows monovalent H+ to be released. + Through, entering the product water side, Fe 2+ Fe 3+ It is retained on the concentrate side; the flux of the acid-resistant nanofiltration membrane is controlled at 5–25 L / m. 2 ·h; c. Place the scrap iron wire from the steel plant in the packed tower. The concentrated waste acid enters the waste iron wire packed tower from the bottom. The waste acid after dissolving the scrap iron wire flows out from the top. The iron ion concentration at the outlet of the waste iron wire packed tower reaches 1.5-5%, and the main component of the iron ion is ferrous sulfate. d. The ferrous sulfate solution is transferred to the primary reactor, which is heated to 45-55°C. Ozone is added to the primary reactor for aeration and stirring. Hydrogen peroxide is then added at a concentration of 1%-3%. Under the combined oxidation of ozone and hydrogen peroxide, the ferrous sulfate is oxidized to ferric sulfate. e. The effluent from the primary reactor is pumped into the secondary reactor. The temperature in the secondary reactor is maintained at 45-55℃. 100-500 mg / L of divinylbenzene is added, followed by 1-5% zeolite powder. The reaction time in the secondary reactor is 3-5 hours. The polymerization and maturation reactions are completed in the secondary reactor. The effluent from the secondary reactor is polyferric sulfate coagulant.

2. The process for comprehensive utilization of sulfuric acid washing waste acid according to claim 1, characterized in that: The acid waste acid discharged from the cold rolling sulfuric acid pickling unit has the following characteristics: SO42- 2- 3~10%, TFe 1~10g / L, pH 0~0.

5.

3. The process for comprehensive utilization of sulfuric acid washing waste acid according to claim 1, characterized in that: The acid-resistant membrane material mentioned in step a is selected from either inorganic ceramic membranes or sintered organic membranes.

4. The process for comprehensive utilization of sulfuric acid washing waste acid according to claim 3, characterized in that: The membrane pore size range is 20–200 nm; the circulation rate is 5–30 times the throughput; and the membrane flux is controlled at 50–300 L / m. 2 ·h.

5. The process for comprehensive utilization of sulfuric acid washing waste acid according to claim 1, characterized in that: In step b, the acid-resistant nanofiltration membrane can operate stably for a long time under acid concentration conditions of up to 20%; the recovery rate of the nanofiltration membrane in step b is controlled at 50-95%.

6. The process for comprehensive utilization of sulfuric acid washing waste acid according to claim 5, characterized in that: The recovery rate of the nanofiltration membrane described in step b is controlled between 60% and 95%.

7. The process for comprehensive utilization of sulfuric acid washing waste acid according to claim 1, characterized in that: In step c, the concentration of ferrous sulfate at the outlet of the waste wire packed tower reaches 4% to 13.5%.

8. The process for comprehensive utilization of sulfuric acid washing waste acid according to claim 1, characterized in that: The ozone dosage in step d is 1-3 g / L; the reaction time in the primary reactor in step d is 0.5-1 h.

9. The process for comprehensive utilization of sulfuric acid washing waste acid according to claim 1, characterized in that: The zeolite powder in step e has a particle size of 100-300 mesh.

10. The process for comprehensive utilization of sulfuric acid washing waste acid according to claim 1, characterized in that: In step e, add 1-3% zeolite powder.

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