A method and system for recycling cold rolling alkaline washing waste liquid

Abstract

This invention provides a method and system for recycling cold rolling alkaline washing waste liquid, used for treating waste alkaline liquid with an alkaline concentration of 20-30 g / L, an oil concentration of 5-10 g / L, and a suspended solids concentration of 4-10 g / L. The method includes the following treatment steps: (1) the waste alkaline liquid is pre-filtered to remove 20-30 μm particles and some of the oil encapsulated by the particles; (2) the pre-filtered waste liquid is led to a high-efficiency oil removal filter with an upper inlet and a lower outlet for further oil-water separation, wherein the high-efficiency oil removal filter is filled with several layers of hydrophilic and oleophobic filter screens; (3) the effluent from the high-efficiency oil removal filter is connected to a microfiltration filter and then filtered through a filter membrane.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method and system for reusing cold rolling alkaline washing waste liquid. Background Technology

[0002] Cold-rolled strip steel surfaces are typically contaminated with rolling oil, machine oil, residual iron, and dust. If not thoroughly cleaned, these contaminants will turn into carbides after annealing, damaging both the appearance and the quality of the steel sheet. Alkaline washing is an effective method for removing these surface contaminants. The main components of alkaline washing solution are alkali and surfactants. The concentration of alkali varies depending on the requirements of the washing process, generally ranging from 1.5% to 5%. During alkaline washing, the alkali solution undergoes a complex chemical reaction with the rolling oil and machine oil on the steel sheet surface. Under the catalytic action of the high-temperature alkali, the grease hydrolyzes into glycerol and sodium fatty acids, which dissolve in the alkaline washing solution. After cooling, the solution forms soaps. Simultaneously, residual iron, dust, and other particulate matter from the dry sheet surface exist as suspended solids in the alkali solution or mix with the grease to form sludge. As the washing time increases, impurities accumulate in the solution, affecting the washing effect. In such cases, it is necessary to replace the alkaline washing solution or purify the impurities before recycling.

[0003] In the prior art, Chinese patent document with application number 200910047969.3 provides a method and equipment for purifying alkaline washing solution for silicon steel. The specific technical solution of the method for purifying alkaline washing solution for silicon steel is as follows: the alkaline washing solution from the bottom of the electrolytic cell enters the centrifugal separator, and the separated alkaline washing solution enters the settling chamber of the gravity settling tank. The solids remaining in the alkaline washing solution enter the clear liquid chamber after settling in the settling chamber and are then pumped back to the electrolytic cell. The solid particles precipitated in the tank are periodically fed into the centrifugal separator for filtration by a sewage pump.

[0004] Chinese patent application number 201210444928.X discloses a steel rolling alkali washing solution filtration and recovery system, comprising oil removal, coarse filtration, fine filtration, concentration, dehydration, and slag discharge. The key features are: the oil removal uses an inclined plate oil separator with a chain-type oil scraper at the top and a sedimentation cone at the bottom; the coarse filtration uses a self-cleaning filter to trap large particles of impurities, extending the backwashing cycle of the microfiltration unit; the fine filtration uses a microporous filter with a composite microporous filter element; the slag from the inclined plate oil separator, the wastewater from the self-cleaning filter, and the wastewater from the microfiltration unit are all collected in a waste alkali solution storage tank for secondary concentration; the concentrated waste residue in the waste alkali solution storage tank is dehydrated by a plate and frame filter press or a centrifugal dewatering machine and then transported off-site by slag truck.

[0005] Chinese patent application No. 201710490990.5 discloses an alkaline solution purification system. This system includes an alkaline solution filter, a cleaning water tank, an acid pickling solution tank, an alkaline washing solution tank, a surfactant tank, and a supply pump. The input end of a first pipe is connected to the bottom of an alkaline solution circulation tank or a pretreatment device; the input end of a second pipe is connected to the cleaning water tank; the input end of a third pipe is connected to the acid pickling solution tank; the input end of a fourth pipe is connected to the alkaline washing solution tank; the input end of a fifth pipe is connected to the surfactant tank; the input end of a sixth pipe is connected to the outlet of the supply pump, and its output end is connected to the bottom of the alkaline solution filter; the input end of a seventh pipe is connected to the top of the alkaline solution filter, and its output end is connected to the alkaline solution circulation tank; the input end of an eighth pipe is connected to the outlet of the supply pump; the input end of a ninth pipe is connected to the bottom of the alkaline solution filter; and the output end of a tenth pipe is connected to the alkaline washing solution tank. It has automatic filtration and backwashing functions, which can effectively remove sludge from the alkaline solution and greatly reduce the amount of sludge deposited in the alkaline solution circulation tank. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a method for reusing cold rolling alkaline washing waste liquid with both economic and environmental benefits.

[0007] The technical problem it aims to solve can be addressed through the following technical solutions.

[0008] A method for reusing cold rolling alkaline washing wastewater, used to treat waste alkaline solutions with an alkaline concentration of 20-30 g / L, an oil concentration of 5-10 g / L, and a suspended solids concentration of 4-10 g / L, is characterized by the following treatment steps:

[0009] (1) The waste alkaline solution is pre-filtered to remove particles of 20-30μm and some of the oil encapsulated in the particles.

[0010] (2) The pre-filtered waste liquid is directed to a high-efficiency oil removal filter with water inlet at the top and water outlet at the bottom for further oil-water separation. The high-efficiency oil removal filter is filled with several layers of hydrophilic and oleophobic filter screens.

[0011] (3) The water from the high-efficiency oil removal filter is connected to the microfiltration filter and then filtered through the filter membrane.

[0012] Furthermore, the pre-filtration process is carried out using vacuum negative pressure paper tape filtration; the vacuum pump controls the vacuum degree of the filtration chamber at 0 to -0.05 MPa, and the filter paper precision is 20 μm to 30 μm.

[0013] Preferably, in step (2), the interlayer spacing of the several layers of hydrophilic and oleophobic filter screen is 20-30cm; the number of filter screen layers is 4-6.

[0014] Furthermore, in step (2), the flow rate in the high-efficiency oil removal filter is controlled at 3 to 5 m / h.

[0015] Furthermore, step (2) also includes a backwashing process. During backwashing, a combined air-water backwash is used, with both air and water entering from the bottom and exiting from the top. The flow rate during backwashing is 30–50 m / h, and the compressed air volume is 20–30 L / m³. 2 •s, backwash time 10-15min.

[0016] Furthermore, the microfiltration in step (3) adopts a circulating microfiltration mode, and cross-flow filtration is used during microfiltration; the microfiltration membrane is a tubular microfiltration membrane.

[0017] Furthermore, in the circulating microfiltration mode, the circulation volume of the circulating microfiltration system is 10 to 30 times the water production volume, the microfiltration membrane filtration accuracy is 0.05 μm to 1 μm, and the flux is 50 to 200 L / m³. 2 •h, operating pressure 0.5~1.0MPa.

[0018] Furthermore, in step (2), the hydrophilic and oleophobic filter screen is obtained using the following preparation method:

[0019] 1) Select a stainless steel filter screen with a pore size of 50-100μm for ultrasonic cleaning;

[0020] 2) Place the cleaned stainless steel filter screen in a 3-5% NaOH solution, add 100-300 mg / L sodium dodecylbenzenesulfonate to the NaOH solution, control the temperature at 35-45℃, keep the temperature constant for 10-30 minutes, and then take it out and clean it with deionized water.

[0021] 3) Place the stainless steel filter screen, which has been cleaned with deionized water, into a mixed solution of 5-10% HNO3 and 0.5-1% HF, and keep the temperature at 35-45℃ for 10-30 minutes.

[0022] 4) Remove the stainless steel filter screen, rinse it with deionized water, and store it in anhydrous ethanol;

[0023] 5) Rinse the filter screen with pure water before use and dry it in an oven;

[0024] 6) The dried stainless steel filter screen is used to prepare a ZnO modified layer by electrodeposition; wherein the stainless steel filter screen is the anode and carbon is the cathode;

[0025] 7) After electrodeposition, rinse with pure water and dry in an oven to obtain the modified hydrophilic and oleophobic stainless steel filter screen.

[0026] Furthermore, in the preparation of the ZnO modified layer by electrodeposition, the electrodeposition solution composition is: 0.1–0.2 mol / L lead nitrate (Zn(NO3)2), 0.5–0.6 mol / L sulfamic acid (NH2SO3H), and 0.03–0.04 mol / L sodium dodecyl sulfate (C 12 H 25 (SO4Na); electrodeposition temperature 40–50℃, current density 5–10 A / dm³ 2 Electroplating time is 30-60 minutes.

[0027] Another technical problem to be solved by the present invention is to provide a system for implementing the aforementioned method for recycling cold rolling alkaline washing waste liquid, comprising, along the path through which the waste alkaline liquid passes:

[0028] 1) A primary booster pump, which is used to boost the waste alkaline solution to a pre-filtration site;

[0029] 2) Primary water pump and primary intermediate water tank, wherein the primary water pump pumps the pre-filtered water into the primary intermediate water tank;

[0030] 3) Secondary booster pump, which boosts the water output from the primary intermediate water tank to the high-efficiency oil removal filter;

[0031] 4) A circulating microfiltration system consisting of a circulating water tank, a circulating pump, and a tubular microfiltration membrane.

[0032] The method and system for recycling waste alkaline liquor from cold rolling mill washing, employing the above-mentioned technical solution, firstly removes large suspended solids and oil encapsulated in particulate matter using a vacuum paper belt filter. Then, a modified hydrophilic-oleophobic high-efficiency oil removal filter further removes oil from the waste alkaline liquor. Finally, a tubular microfiltration system is used for deep oil removal. After this process, the waste alkaline liquor can be returned to the unit for recycling. This invention has both economic and environmental benefits, demonstrating significant social and environmental advantages. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the method and system for recycling cold rolling alkaline washing waste liquid provided by the present invention. Detailed Implementation

[0034] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0035] This invention provides a method and system for reusing cold rolling alkaline washing waste liquid, as detailed below:

[0036] The composition of the waste alkaline solution is as follows: alkaline concentration 20-30 g / L, oil 5-10 g / L, suspended solids 4-10 g / L.

[0037] The waste alkaline solution discharged from the alkaline washing unit is poured into a mixing tank, and then lifted by a primary booster pump to a paper belt filter. The paper belt filter, as a pre-filtration process, can remove 20-30μm particles from the waste alkaline solution, and also remove some of the oil encapsulated in the particles. The paper belt filter uses vacuum negative pressure filtration, with a vacuum pump controlling the vacuum level in the filter chamber to 0 to -0.05 MPa, and the filter paper precision is 20μm-30μm. A primary product water pump pumps the filtered product water from the vacuum filtration chamber into a primary intermediate water tank.

[0038] Water from the primary intermediate water tank is pumped by the secondary booster pump to a high-efficiency oil-removing filter. The filter is filled with hydrophilic and oleophobic filter screens, spaced 20-30 cm apart. The filter uses a top-inlet and bottom-outlet design. The filter screen surface is hydrophilic and oleophobic; the aqueous phase in the alkaline solution passes through due to its hydrophilicity, while the oil phase is trapped by the filter media due to its hydrophobicity, gradually accumulating into large oil droplets around the media, thus achieving oil-water separation. The multi-layered filter screen arrangement enables multi-stage oil-water separation, improving the separation efficiency. The flow rate in the oil-removing filter is controlled at 3-5 m / h. Backwashing is performed when the effluent quality does not meet requirements. To enhance the backwashing effect, a combined air-water backwash is used. During backwashing, both air and water are introduced from the bottom and discharged from the top, with a flow rate of 30-50 m / h and a compressed air volume of 20-30 L / m³. 2 •s, backwash time 10-15min.

[0039] The effluent from the high-efficiency oil removal filter enters a microfiltration filter for further treatment. The microfiltration membrane has a small pore size and high filtration precision, effectively trapping tiny particles and further removing oil droplets formed in the filter. This improves the oil removal efficiency in the waste alkali solution, enhances the effluent quality, and meets the requirements for waste alkali solution reuse. The effluent from the filter flows into the microfiltration system's circulation tank, and is then pumped to the microfiltration membrane module. The microfiltration membrane is a tubular type, and cross-flow filtration is used to reduce membrane fouling. The circulation volume of the microfiltration system is 10–30 times the production water volume. The microfiltration membrane has a filtration precision of 0.05 μm–1 μm and a flux of 50–200 L / m³. 2 The operating pressure is 0.5-1.0 MPa. After microfiltration, the waste alkaline solution meets the subsequent requirements and is returned to the unit for recycling.

[0040] The preparation method of the hydrophilic and oleophobic filter screen is as follows: A stainless steel filter screen with a pore size of 50–100 μm is cleaned ultrasonically for 10–30 minutes. The cleaned stainless steel filter screen is then placed in a 3–5% (w / w) NaOH solution, with 100–300 mg / L of sodium dodecylbenzenesulfonate added. The temperature is controlled at 35–45°C and maintained for 10–30 minutes. After removal, it is rinsed with deionized water to remove oil stains from the surface of the stainless steel filter screen. Next, the cleaned stainless steel filter screen is placed in a mixed solution of 5–10% (w / w) HNO3 and 0.5–1% (w / w) HF, with the temperature controlled at 35–45°C and maintained for 10–30 minutes. This process further removes oxides from the surface of the stainless steel filter screen. The above process is called etching. After etching, the stainless steel filter screen has a grayish-brown surface, which increases its hydrophilicity and makes it bond more firmly to the coating. Finally, the etched stainless steel filter screen is removed, rinsed with deionized water, and stored in anhydrous ethanol. Before use, it is rinsed with pure water and dried in an oven at 105°C.

[0041] After drying, the stainless steel filter screen was modified with ZnO by electrodeposition. ZnO is polar and therefore has good hydrophilic properties. The modified layer was prepared by electrodeposition, with the stainless steel filter screen as the anode and carbon as the cathode. The electrodeposition solution consisted of: 0.1–0.2 mol / L lead nitrate (Zn(NO3)2), 0.5–0.6 mol / L sulfamic acid (NH2SO3H), and 0.03–0.04 mol / L sodium dodecyl sulfate (C). 12 H 25 (SO4Na). Electrodeposition temperature 40–50℃, current density 5–10 A / dm³ 2 Electroplating time is 30-60 minutes. After electrodeposition, rinse thoroughly with pure water and dry in an oven at 105℃ to obtain the modified hydrophilic and oleophobic stainless steel filter screen.

[0042] 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.

[0043] Example 1

[0044] The composition of the waste alkaline solution is as follows: alkali concentration 25g / L, oil 7.2g / L, suspended solids 6.5g / L.

[0045] Waste alkali solution enters a paper belt filter, and a vacuum pump is used to control the vacuum degree of the filter chamber at -0.03Mpa. After filtration by the paper belt filter, the alkali concentration is 24g / L, the oil concentration is 5.1g / L, and the suspended solids concentration is 1.2g / L.

[0046] The water effluent from the paper tape filter enters a high-efficiency oil filter. The filter is filled with hydrophilic and oleophobic filter screens, spaced 25cm apart, for a total of 5 layers. The filter uses a top-inlet and bottom-outlet design. The flow rate in the oil filter is controlled at 4m / h. The backwash flow rate is 40m / h, and the compressed air volume is 25L / m³. 2 •s, backwash time 13min. The effluent from the high-efficiency oil removal filter has an alkalinity concentration of 23g / L, an oil concentration of 1.2g / L, and a suspended solids concentration of 350mg / L.

[0047] The effluent from the high-efficiency oil removal filter enters the microfiltration filter. The circulation rate of the microfiltration system is 20 times the production water rate. The microfiltration membrane has a filtration accuracy of 0.5μm and a flux of 120L / m³. 2 The operating pressure is 0.8 MPa. After microfiltration, the concentration of the waste alkaline solution is 23 g / L, the oil concentration is 820 mg / L, and the suspended solids concentration is 15 mg / L, which meets the requirements for continued use. It is returned to the unit for recycling.

[0048] The preparation method of the hydrophilic and oleophobic filter screen is as follows: A stainless steel filter screen with a pore size of 75 μm is ultrasonically cleaned for 20 minutes. The cleaned stainless steel filter screen is then placed in a 4% (w / w) NaOH solution, with 200 mg / L sodium dodecylbenzenesulfonate added. The temperature is controlled at 40℃ and maintained for 20 minutes. After removal, it is rinsed with deionized water. Next, the cleaned stainless steel filter screen is placed in a mixed solution of 8% (w / w) HNO3 and 0.7% HF, and the temperature is controlled at 40℃ and maintained for 20 minutes. Finally, the etched stainless steel filter screen is removed, rinsed with deionized water, and stored in anhydrous ethanol. Before use, it is rinsed with pure water and dried in an oven at 105℃.

[0049] After drying, the stainless steel filter screen was used to prepare a ZnO modified layer using electrodeposition. The modified layer was prepared using electrodeposition, with the stainless steel filter screen as the anode and carbon as the cathode. The electrodeposition solution consisted of: 0.15 mol / L lead nitrate (Zn(NO3)2), 0.55 mol / L sulfamic acid (NH2SO3H), and 0.035 mol / L sodium dodecyl sulfate (C). 12 H 25 (SO4Na). Electrodeposition temperature 45℃, current density 7A / dm³ 2 Electroplating time was 40 minutes. After electrodeposition, the filter was rinsed with pure water and dried in an oven at 105°C to obtain the modified hydrophilic and oleophobic stainless steel filter screen.

[0050] Example 2

[0051] The composition of the waste alkaline solution is as follows: alkali concentration 21 g / L, oil 5.5 g / L, suspended solids 4.8 g / L.

[0052] Waste alkali solution enters a paper belt filter, and a vacuum pump is used to control the vacuum degree of the filter chamber at 0 MPa. After filtration by the paper belt filter, the alkali concentration is 20 g / L, the oil concentration is 3.6 g / L, and the suspended solids concentration is 1.1 g / L.

[0053] The water effluent from the paper tape filter enters a high-efficiency oil filter. The filter is filled with hydrophilic and oleophobic filter screens, spaced 30cm apart, for a total of four layers. The filter uses a top-inlet and bottom-outlet design. The flow rate in the oil filter is controlled at 5m / h. Backwashing flow rate is 30m / h, and compressed air volume is 20L / m³. 2 •s, backwash time 15min. The effluent from the high-efficiency oil removal filter has an alkalinity concentration of 19g / L, an oil concentration of 0.9g / L, and a suspended solids concentration of 300mg / L.

[0054] The effluent from the high-efficiency oil removal filter enters the microfiltration filter. The circulation rate of the microfiltration system is 20 times the production water rate. The microfiltration membrane has a filtration accuracy of 0.05μm and a flux of 50L / m³. 2 The operating pressure is 0.5 MPa. After microfiltration, the concentration of the waste alkaline solution is 19 g / L, the oil concentration is 650 mg / L, and the suspended solids concentration is 16 mg / L, which meets the requirements for continued use. It is returned to the unit for recycling.

[0055] The preparation method of the hydrophilic and oleophobic filter screen is as follows: A stainless steel filter screen with a pore size of 50 μm is ultrasonically cleaned for 10 minutes. The cleaned stainless steel filter screen is then placed in a 3% (w / w) NaOH solution, with 100 mg / L sodium dodecylbenzenesulfonate added. The temperature is controlled at 45℃ and maintained for 10 minutes. After removal, it is rinsed thoroughly with deionized water. Next, the cleaned stainless steel filter screen is placed in a mixed solution of 5% (w / w) HNO3 and 1% HF, and the temperature is controlled at 45℃ and maintained for 10 minutes. Finally, the etched stainless steel filter screen is removed, rinsed thoroughly with deionized water, and stored in anhydrous ethanol. Before use, it is rinsed with pure water and dried in an oven at 105℃.

[0056] After drying, the stainless steel filter screen was used to prepare a ZnO modified layer using electrodeposition. The modified layer was prepared using electrodeposition, with the stainless steel filter screen as the anode and carbon as the cathode. The electrodeposition solution consisted of: 0.1 mol / L lead nitrate (Zn(NO3)2), 0.6 mol / L sulfamic acid (NH2SO3H), and 0.03 mol / L sodium dodecyl sulfate (C). 12 H 25 (SO4Na). Electrodeposition temperature 50℃, current density 5A / dm³ 2 Electroplating time was 60 minutes. After electrodeposition, the filter was rinsed with pure water and dried in an oven at 105°C to obtain the modified hydrophilic and oleophobic stainless steel filter screen.

[0057] Example 3

[0058] The composition of the waste alkaline solution is as follows: alkali concentration 28 g / L, oil 8.8 g / L, suspended solids 8.6 g / L.

[0059] Waste alkali solution enters a paper belt filter, and a vacuum pump is used to control the vacuum degree of the filter chamber at -0.05Mpa. After filtration by the paper belt filter, the alkali concentration is 26g / L, the oil concentration is 6.8g / L, and the suspended solids concentration is 1.6g / L.

[0060] The water effluent from the paper tape filter enters a high-efficiency oil filter. This filter is filled with hydrophilic and oleophobic filter screens, spaced 20cm apart, for a total of 6 layers. The filter uses a top-inlet and bottom-outlet design. The flow rate in the oil filter is controlled at 3m / h. Backwashing flow rate is 50m / h, and compressed air volume is 30L / m³. 2 •s, backwash time 10min. The effluent from the high-efficiency oil removal filter has an alkalinity concentration of 25g / L, an oil concentration of 1.4g / L, and a suspended solids concentration of 450mg / L.

[0061] The effluent from the high-efficiency oil removal filter enters the microfiltration filter. The circulation volume of the microfiltration system is 30 times the production water volume. The microfiltration membrane has a filtration accuracy of 1μm and a flux of 200L / m³. 2 The operating pressure is 1 MPa. After microfiltration, the concentration of the waste alkaline solution is 25 g / L, the oil concentration is 860 mg / L, and the suspended solids concentration is 21 mg / L, which meets the requirements for continued use. It is returned to the unit for recycling.

[0062] The preparation method of the hydrophilic and oleophobic filter screen is as follows: A stainless steel filter screen with a pore size of 100 μm is ultrasonically cleaned for 30 minutes. The cleaned stainless steel filter screen is then placed in a 5% NaOH solution, with 300 mg / L sodium dodecylbenzenesulfonate added. The temperature is controlled at 35℃ and maintained for 30 minutes. After removal, it is rinsed with deionized water. Next, the cleaned stainless steel filter screen is placed in a mixed solution of 10% HNO3 and 0.5% HF, and the temperature is controlled at 35℃ and maintained for 30 minutes. Finally, the etched stainless steel filter screen is removed, rinsed with deionized water, and stored in anhydrous ethanol. Before use, it is rinsed with pure water and dried in an oven at 105℃.

[0063] After drying, the stainless steel filter screen was used to prepare a ZnO modified layer using electrodeposition. The modified layer was prepared by electrodeposition, with the stainless steel filter screen as the anode and carbon as the cathode. The electrodeposition solution consisted of: 0.2 mol / L lead nitrate (Zn(NO3)2), 0.5 mol / L sulfamic acid (NH2SO3H), and 0.04 mol / L sodium dodecyl sulfate (C). 12 H 25 (SO4Na). Electrodeposition temperature 40℃, current density 10A / dm³2 Electroplating time: 30 min. After electrodeposition, rinse thoroughly with pure water and dry in an oven at 105℃ to obtain the modified hydrophilic and oleophobic stainless steel filter screen.

Claims

1. A method for reusing cold rolling alkaline washing wastewater, used for treating waste alkaline solutions with an alkaline concentration of 20-30 g / L, an oil concentration of 5-10 g / L, and a suspended solids concentration of 4-10 g / L, characterized in that, The processing steps include the following: (1) The waste alkaline solution is pre-filtered to remove particles of 20-30μm and some of the oil encapsulated in the particles. (2) The pre-filtered waste liquid is directed to a high-efficiency oil removal filter with water inlet at the top and water outlet at the bottom for further oil-water separation. The high-efficiency oil removal filter is filled with several layers of hydrophilic and oleophobic filter screens. (3) The water from the high-efficiency oil removal filter is connected to the microfiltration filter and then filtered through the filter membrane.

2. The method for reusing cold rolling alkaline washing waste liquid according to claim 1, characterized in that, The pre-filtration process is carried out using vacuum negative pressure paper tape filtration; the vacuum pump controls the vacuum degree of the filtration chamber at 0 to -0.05 MPa, and the filter paper precision is 20 μm to 30 μm.

3. The method for reusing cold rolling alkaline washing wastewater according to claim 1, characterized in that, In step (2), the spacing between several layers of hydrophilic and oleophobic filter screens is 20-30cm; the number of filter screen layers is 4-6.

4. The method for reusing cold rolling alkaline washing waste liquid according to claim 1 or 3, characterized in that, In step (2), the flow rate in the high-efficiency oil removal filter is controlled at 3 to 5 m / h.

5. The method for reusing cold rolling alkaline washing waste liquid according to claim 1 or 3, characterized in that, Step (2) also includes a backwashing process. During backwashing, a combined air-water backwash is used, with both air and water entering from the bottom and exiting from the top. The flow rate during backwashing is 30–50 m / h, and the compressed air volume is 20–30 L / m³. 2 •s, backwash time 10-15min.

6. The method for reusing cold rolling alkaline washing waste liquid according to claim 1, characterized in that, The microfiltration in step (3) adopts the circulating microfiltration mode and cross-flow filtration is used during microfiltration; the microfiltration membrane is a tubular microfiltration membrane.

7. The method for reusing cold rolling alkaline washing waste liquid according to claim 6, characterized in that, In the circulating microfiltration mode, the circulation rate of the circulating microfiltration system is 10 to 30 times the water production rate, the microfiltration membrane filtration accuracy is 0.05 μm to 1 μm, and the flux is 50 to 200 L / m³. 2 •h, operating pressure 0.5~1.0MPa.

8. The method for reusing cold rolling alkaline washing waste liquid according to claim 1, characterized in that, In step (2), the hydrophilic and oleophobic filter screen is obtained using the following preparation method: 1) Select a stainless steel filter screen with a pore size of 50-100μm for ultrasonic cleaning; 2) Place the cleaned stainless steel filter screen in a 3-5% NaOH solution, add 100-300 mg / L sodium dodecylbenzenesulfonate to the NaOH solution, control the temperature at 35-45℃, keep the temperature constant for 10-30 minutes, and then take it out and clean it with deionized water. 3) Place the stainless steel filter screen, which has been cleaned with deionized water, into a mixed solution of 5-10% HNO3 and 0.5-1% HF, and keep the temperature at 35-45℃ for 10-30 minutes. 4) Remove the stainless steel filter screen, rinse it with deionized water, and store it in anhydrous ethanol; 5) Rinse the filter screen with pure water before use and dry it in an oven; 6) The dried stainless steel filter screen is used to prepare a ZnO modified layer by electrodeposition; wherein the stainless steel filter screen is the anode and carbon is the cathode; 7) After electrodeposition, rinse with pure water and dry in an oven to obtain the modified hydrophilic and oleophobic stainless steel filter screen.

9. The method for reusing cold rolling alkaline washing waste liquid according to claim 8, characterized in that, When preparing ZnO modified layers by electrodeposition, the electrodeposition solution composition is: 0.1–0.2 mol / L lead nitrate (Zn(NO3)2), 0.5–0.6 mol / L sulfamic acid (NH2SO3H), and 0.03–0.04 mol / L sodium dodecyl sulfate (C2SO3H2O). 12 H 25 (SO4Na); electrodeposition temperature 40–50℃, current density 5–10 A / dm³ 2 Electroplating time is 30-60 minutes.

10. A system for implementing the method for reusing cold rolling alkaline washing waste liquid according to any one of claims 1-9, characterized in that, Along the path of the waste alkali solution, the following are included in sequence: 1) A primary booster pump, which is used to boost the waste alkaline solution to a pre-filtration site; 2) Primary water pump and primary intermediate water tank, wherein the primary water pump pumps the pre-filtered water into the primary intermediate water tank; 3) Secondary booster pump, which boosts the water output from the primary intermediate water tank to the high-efficiency oil removal filter; 4) A circulating microfiltration system consisting of a circulating water tank, a circulating pump, and a tubular microfiltration membrane.

Images