Method for utilizing pickling line caustic wash waste liquor and waste liquor treatment device

Abstract

The application provides a utilization method of caustic washing waste liquid of an acid pickling line and a waste liquid treatment device. The utilization method comprises the following steps: performing primary neutralization on acid-containing waste water to obtain primary neutralized waste water; performing secondary neutralization on the primary neutralized waste water, and adding caustic washing waste liquid in the process of the secondary neutralization to obtain secondary neutralized waste water; adding polymeric ferric sulfate and polyacrylamide in the secondary neutralized waste water to perform clarification to obtain clarified waste liquid; and performing pH adjustment and filtration on the clarified waste liquid to obtain water to be concentrated and treated. The caustic washing waste liquid is added into a second neutralization tank, and the OH ‑ There is no significant decrease, and the silicic acid in the caustic washing waste liquid added in the secondary neutralization is in a monomer dispersed state. The silicic acid monomer in the caustic washing waste liquid acts as a coagulant aid and cooperates with the polymeric ferric sulfate and the polyacrylamide to perform clarification. The caustic washing waste liquid has a coagulant aid effect, realizes the effect of treating waste with waste, and makes the waste water treatment efficient, low in cost, and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and more particularly to a method for utilizing acid pickling line alkaline washing wastewater and a wastewater treatment device. Background Technology

[0002] To increase product added value, cold rolling pickling lines or pickling mill combined units are increasingly using high-silicon steel in their product mix. However, the silicic acid in the pickling solution can easily cause blockages in pipes, valves, graphite heaters, acid pumps, nozzles, etc., of the cold rolling pickling lines or pickling mill combined units.

[0003] Therefore, the acid pipeline system, including pipes, valves, graphite heaters, acid pumps, and nozzles, is periodically cleaned using an alkaline solution through circulation to remove the silica gel adhering to the pipes, restoring the actual flow diameter of the acid pipeline. The resulting waste alkaline solution is then mixed with acidic wastewater from the pickling line or pickling-rolling mill combined unit and acid regeneration in an acidic wastewater pit before being discharged into the cold rolling wastewater station. However, this treatment method is prone to clogging of the wastewater treatment pipelines in actual operation. Summary of the Invention

[0004] The main objective of this invention is to provide a method for utilizing acid washing line alkaline washing wastewater, in order to solve the technical problem that wastewater treatment pipelines are easily blocked in actual operation.

[0005] To achieve the above objectives, the present invention provides a method for utilizing acid pickling and alkaline washing waste liquid, comprising the following steps:

[0006] The acidic wastewater is subjected to primary neutralization to obtain primary neutralized wastewater. The acidic wastewater includes at least one of pickling wastewater and acid regeneration wastewater.

[0007] The primary neutralized wastewater is subjected to secondary neutralization, and alkaline washing waste liquid is added during the secondary neutralization process to obtain secondary neutralized wastewater. The alkaline washing waste liquid is the alkaline washing waste liquid from the acid washing line.

[0008] Polyferric sulfate and polyacrylamide were added to the secondary neutralized wastewater for clarification, resulting in clarified waste liquid.

[0009] The clarified waste liquid, after pH adjustment and filtration, yields water to be centrally treated.

[0010] According to the embodiments of this application, the amount of alkaline washing waste liquid added is such that the concentration of silicate ions in the secondary neutralized wastewater is 0.8-1.2 mg / L.

[0011] According to the embodiments of this application, the mass fraction of free NaOH in the alkaline washing waste liquid is 10-20%, and the concentration of silicate ions is 100-200 g / L.

[0012] According to an embodiment of this application, the pH value of the primary neutralized wastewater is 8-9. The pH value of the secondary neutralized wastewater is 9-10.

[0013] According to the embodiments of this application, the amount of polyferric sulfate added is such that the corresponding concentration in the secondary neutralized wastewater is 25-35 mg / L, and the amount of polyacrylamide added is such that the corresponding concentration in the secondary neutralized wastewater is 1.5-2.5 mg / L.

[0014] According to the embodiments of this application, the time for clarifying the secondary neutralized wastewater by adding polyferric sulfate and polyacrylamide is 2 to 4 hours.

[0015] According to the embodiments of this application, lime slurry is added for neutralization during the primary and secondary neutralization steps.

[0016] According to the embodiments of this application, the method also includes centrally treating the water to be centrally treated and then reusing it.

[0017] This application also provides a waste liquid treatment device, including an alkaline liquid collection tank, an acid-base wastewater equalization tank, a primary neutralization tank, a secondary neutralization tank, an acid-base clarification tank, a pH adjustment tank, a filter, and a discharge water tank connected in sequence.

[0018] The acid-base wastewater equalization tank is used to receive the acid-containing wastewater, which includes at least one of pickling wastewater and acid regeneration wastewater.

[0019] The primary neutralization tank is used to neutralize acidic wastewater in the first stage to obtain primary neutralized wastewater.

[0020] The secondary neutralization tank is used to perform secondary neutralization on the primary neutralized wastewater to obtain secondary neutralized wastewater.

[0021] The alkali collection tank is connected to the secondary neutralization tank and is used to introduce the alkali washing waste liquid into the secondary neutralization tank for secondary neutralization. The alkali washing waste liquid is the alkali washing waste liquid from the acid washing line.

[0022] The acid-base clarification tank is used to receive polyferric sulfate and polyacrylamide, and to clarify the secondary neutralized wastewater to obtain clarified waste liquid.

[0023] The pH adjustment tank and the filter are used to adjust the pH of the clarified waste liquid, filter it, and obtain water to be centrally treated and discharged into the discharge water tank.

[0024] According to an embodiment of this application, a metering pump is also included, which is connected between the alkali collection tank and the secondary neutralization tank.

[0025] In the above-mentioned method for utilizing pickling and alkaline washing wastewater, the alkaline washing wastewater is added to the second neutralization tank. On the one hand, this reduces the H2 content of the primary neutralization wastewater. + The OH content is lower compared to acidic wastewater, therefore, after adding alkaline washing wastewater, the OH content... - Without a significant decrease in concentration, and without the excessive precipitation of silica gel reducing the effectiveness of the monomeric silicic acid or clogging pipes, the system operates stably. Furthermore, the next step in the secondary neutralization wastewater treatment process is clarification. The silicic acid monomers in the alkaline washing wastewater act as coagulants, working synergistically with polyferric sulfate and polyacrylamide for clarification. The alkaline washing wastewater's coagulant effect achieves waste-to-waste treatment, resulting in efficient, low-cost, and environmentally friendly wastewater treatment. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 This is a flow chart of the existing technology for treating acid and alkaline washing waste liquid.

[0028] Figure 2 This is a flowchart of a method for utilizing acid pickling line alkaline washing waste liquid according to an embodiment of this application.

[0029] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings.

[0030] 100. Alkali collection tank; 110. Acid-base wastewater equalization tank; 120. Primary neutralization tank; 130. Secondary neutralization tank; 140. Acid-base clarification tank; 150. pH adjustment tank; 160. Filter; 170. Discharge tank; 180. Sludge thickening tank. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that all directional indicators (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0033] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0034] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0035] Generally, the alkaline washing process is as follows: Each time the pickling line or pickling rolling mill unit is shut down for maintenance, the acid in the pipeline system is emptied. Then, a large amount of alkaline solution is prepared in the alkaline solution circulation tank (30% concentration of caustic soda NaOH or 30% NaOH liquid alkali is added), heated to 70-85℃ with steam, and connected to the acid pump inlet. The existing acid pump is used to circulate the acid pipeline system, washing the pipes, valves, graphite heaters, acid pumps, nozzles, etc. of the acid pipeline system, washing away the silica gel adhering in the pipes, so that the actual flow diameter of the acid pipeline is restored. In fact, the hot alkaline solution can quickly dissolve the silica gel and restore the pickling ability. The reaction formula is: 2NaOH + H2SiO3 = Na2SiO3 + 2H2O.

[0036] Hot alkaline solutions can rapidly dissolve silica gel into monomeric silicic acid, and sodium silicate solutions can exist stably in high pH environments. However, once the monomeric silicic acid is exposed to decreasing pH and temperature, it tends to precipitate and combine to form silica gel, which then becomes ineffective in the flocculation and sedimentation process.

[0037] See Figure 1In related technologies, waste alkaline solution is mixed with acidic wastewater from pickling lines or pickling-rolling mills and acid regeneration in an acidic wastewater pit before being discharged into the cold rolling wastewater station. Studies have found that the wastewater pipeline from the acidic wastewater pit of the pickling line or pickling-rolling mill to the cold rolling wastewater station is quite long (exceeding 500 meters). Another issue is that the large amount of Na2SiO3 in the waste alkaline solution, due to its mixing with the acidic wastewater, causes a decrease in pH value. Combined with the temperature drop, silica gel forms in the wastewater pipeline, causing blockages in the discharge pipes (e.g., the pipeline between the acidic wastewater pit and the acid-base wastewater equalization tank, the pipeline between the acid-base wastewater equalization tank and the primary neutralization tank, and the pipeline between the primary and secondary neutralization tanks), resulting in poor drainage. Furthermore, because the silica gel has already reformed, it cannot act as a coagulant aid in synergistically with other clarifying agents to achieve clarification during the clarification process.

[0038] In other words, the waste alkaline solution containing a large amount of Na2SiO3 is actually a waste product, which only plays a role in neutralizing acidic wastewater in wastewater pits and in acid-base neutralization in acid-base wastewater treatment systems.

[0039] In addition, the pipeline between the acidic wastewater pit and the acid-base wastewater equalization tank is relatively long (that is, the length of the wastewater pipeline from the acidic wastewater pit to the cold rolling wastewater station is relatively long). Due to the blockage caused by the blockage, the drainage is not smooth, which can easily affect the production of pickling and pickling rolling. Specifically, the reason is that the acidic wastewater produced cannot be discharged normally, while normal production continuously produces acidic wastewater.

[0040] 1. The acid discharge pipeline is relatively long, and the blockage points caused by the mixed discharge of alkaline washing waste liquid are not easy to find, which brings trouble to the inspection and maintenance work.

[0041] 2. Due to the mixed discharge of alkaline washing waste liquid, silica gel continuously deposits inside the pipe wall, causing the overall pipe diameter to shrink. Maintenance work is often neglected, and repeated repairs are extremely troublesome.

[0042] 3. On-site acid discharge pipelines to wastewater treatment plants are often configured with dual pipelines (one in use and one on standby) to ensure normal acid discharge. If one pipeline becomes blocked, the other pipeline is activated. The blocked pipeline is then repaired, cleared, or even replaced entirely. This increases equipment maintenance costs and requires significant manpower, material resources, and financial investment.

[0043] The cause of the above problems is the blockage of pipelines caused by silica gel produced from the mixing and discharge of alkaline washing waste liquid and acidic wastewater.

[0044] This invention provides a method for utilizing waste liquid from acid washing lines and alkaline washing processes. (See attached image.) Figure 2 This includes the following steps:

[0045] S100: The acidic wastewater is neutralized in a primary stage to obtain primary neutralized wastewater. The acidic wastewater includes at least one of pickling wastewater and acid regeneration wastewater.

[0046] The purpose of neutralization is to add lime slurry to neutralize the acid in the acidic or alkaline wastewater. The wastewater after neutralization is weakly alkaline, which facilitates the subsequent clarification process.

[0047] In embodiments of this application, a two-stage neutralization process is performed, exemplarily in a primary neutralization tank 120 and a secondary neutralization tank 130. The primary neutralization tank 120 is used for coarse pH adjustment, and the secondary neutralization tank 130 for fine pH adjustment, ensuring that after aeration, ferric iron, along with oil, silicic acid, organic matter, and other metal ions, precipitates in the ferric hydroxide flocs entering the acid-base precipitation tank. Lime slurry is added for the neutralization reaction, exemplarily. To accelerate the mixing and reaction of lime slurry with the acidic and alkaline wastewater, in some embodiments, aeration is performed during the neutralization process.

[0048] The purpose of primary neutralization is to initially neutralize acidic wastewater and reduce H₂ levels. + The concentration increases the pH value of the primary neutralized wastewater. The specific primary neutralization method is not limited. The source of the acidic wastewater is also not specifically limited, and may include at least one of the following: pickling wastewater and acid regeneration wastewater.

[0049] S200: The primary neutralized wastewater is subjected to secondary neutralization, and alkaline washing waste liquid is added during the secondary neutralization process to obtain secondary neutralized wastewater. The alkaline washing waste liquid is the alkaline washing waste liquid from the acid washing line.

[0050] The alkaline washing wastewater actually contains a large amount of Na₂SiO₃. Adding it during the second-stage neutralization process shortens the flow path of the wastewater when it enters the clarification stage, reducing the impact of temperature drop on the precipitation of silicic acid. Simultaneously, the first-stage neutralization wastewater H... + The concentration has been reduced. This prevents premature contact between the alkaline washing wastewater and acidic wastewater, which could lead to neutralization and the generation of OH-. - There was no significant decrease in pH and the precipitation of silica gel. Thus, although the pH of the secondary neutralized wastewater was lower than that of the alkaline washing wastewater, it remained at a relatively high level, and the silicon element still existed in the form of Na2SiO3.

[0051] S300: Polyferric sulfate and polyacrylamide are added to the secondary neutralized wastewater for clarification to obtain clarified waste liquid.

[0052] In this step, the silica monomer of Na2SiO3 (SiO2·y(H2O2)) is used as a coagulant aid. The silica monomer SiO2·y(H2O2) undergoes a condensation reaction in solution due to hydroxyl and oxygen bridging. The inorganic polymer formed by condensation has tetrahedral anions, which can develop into filamentous, branched chain, or spherical particles. It only acts as a flocculator for negatively charged colloidal particles in water. Therefore, it is often used as a coagulant aid in combination with aluminum and iron salts. Even with a small dosage, it can significantly enhance the flocculation process, reduce the amount of coagulant needed, and improve coagulation performance under low temperature and low alkalinity conditions.

[0053] (1) Polyferric sulfate (PFS)

[0054] Polymerized flocculation (PFS) is an intermediate product in the hydrolysis of Fe2(SO4)3, which is gradually converted into Fe(OH)3. It polymerizes into an inorganic polymer through a hydroxyl-bridged reaction. PFS has two performance indicators: basicity and degree of polymerization. Basicity B = [OH] / 3 [Fe], representing the equivalent ratio of hydroxyl groups to iron in the compound. Generally, higher basicity indicates a greater number of low-charge, high-polymerization polynuclear complex ions, resulting in better flocculation and bonding properties. Conversely, lower basicity results in a majority of high-charge, low-polymerization inorganic polymers, leading to better colloidal destabilization through double-layer compression and charge neutralization. The basicity range of PFS is typically around 9%–16%. Using PFS alone cannot achieve optimal coagulation and flocculation results.

[0055] (2) Polyacrylamide (PAM)

[0056] PAM is a high molecular weight coagulant that disperses into a large number of linear chain polymers after dissolving in water. These large chain molecules can act as adhesives and bridges, while the charged groups on the molecules can compress the electric double layer and neutralize charges. Currently, anionic PAM is used, but the colloidal particles in wastewater are generally negatively charged. In such wastewater, anionic coagulants can only perform flocculation. PAM has a relatively narrow application range; excessive dosage can lead to colloidal protection, which increases the stability of the colloids and worsens the coagulation effect.

[0057] In this way, the combination of silicate monomer, polyferric sulfate, and polyacrylamide achieves the clarification effect. This eliminates the need to purchase additional silicate monomer, directly utilizing the high Na₂SiO₃ content in alkaline wastewater. The combined action of PAM (high molecular weight coagulant) and polyferric sulfate (PFS) effectively removes oil and COD from cold rolling acid and alkaline wastewater through flocculation and precipitation, turning waste into treasure and using waste-to-waste metallurgy. This allows for efficient, low-cost, and environmentally friendly operation of cold rolling wastewater treatment.

[0058] The sludge generated during the clarification process is treated separately, such as being pumped to the sludge thickening tank 180 at regular intervals, and then from the sludge thickening tank 180 to the filter press.

[0059] S400: The clarified waste liquid, after pH adjustment and filtration, yields water to be centrally treated.

[0060] For example, the clarified waste liquid is adjusted to pH value by adding reagents in pH adjustment tank, and then pumped to filter 160 for oil removal and filtration. The effluent flows by gravity to discharge pool 170 for subsequent centralized treatment.

[0061] Oil removal filtration can be achieved using a walnut shell filter, as its large surface area is effective for oil filtration. Taking a walnut shell filter as an example, clinoptilolite can be added. Zeolite is an aluminosilicate, and clinoptilolite is primarily used for removing ammonia nitrogen. Clinoptilolite has a sieving effect on ions in wastewater, as well as exchange adsorption effects, and is effective against NH4+. + It exhibits strong selectivity and can be used in exchange adsorption processes to remove ammonia nitrogen from water. It serves as the final step in removing ammonia nitrogen from cold rolling wastewater before it enters a centralized wastewater treatment plant.

[0062] The acidic wastewater and alkaline washing wastewater are now treated separately and discharged into the wastewater treatment plant. For example, the acidic wastewater enters the acid-base wastewater equalization tank; the alkaline washing wastewater enters the alkaline collection tank. This significantly reduces the possibility of silica gel clogging in the acid discharge pipes. Furthermore, the high concentration of free alkali in the alkaline washing wastewater, coupled with the good solubility of sodium silicate, allows the silicic acid to exist as active monomeric silicic acid within the wastewater, which is also beneficial for transportation and storage.

[0063] In the above-mentioned method for utilizing pickling and alkaline washing wastewater, the alkaline washing wastewater is added to the second neutralization tank. On the one hand, this reduces the H2 content of the primary neutralization wastewater. + The OH content is lower compared to acidic wastewater, therefore, after adding alkaline washing wastewater, the OH content... - Without a significant decrease in concentration, and without the excessive precipitation of silica gel reducing the effectiveness of the monomeric silicic acid or clogging pipes, the system operates stably. Furthermore, the next step in the secondary neutralization wastewater treatment process is clarification. The silicic acid monomers in the alkaline washing wastewater act as coagulants, working synergistically with polyferric sulfate and polyacrylamide for clarification. The alkaline washing wastewater's coagulant effect achieves waste-to-waste treatment, resulting in efficient, low-cost, and environmentally friendly wastewater treatment.

[0064] According to the embodiments of this application, the amount of alkaline washing waste liquid added is such that the concentration of silicate ions in the secondary neutralized wastewater is 0.8-1.2 mg / L.

[0065] The concentration of silicate ions in alkaline washing wastewater may fluctuate depending on the metal being treated. Therefore, the dosage needs to be adjusted accordingly, with the specific dosage based on a silicate ion concentration of 0.8-1.2 mg / L in the secondary neutralized wastewater. Under these conditions, the concentration requirements for silicate ions as a coagulant aid in the subsequent clarification process can be met.

[0066] The main components of secondary neutralized wastewater are hydroxides of iron and other metal ions, oil, organic matter, silica, chloride ions, phosphates, ammonium salts, amines, etc.

[0067] In some embodiments, the mass fraction of free NaOH in the alkaline washing waste liquid is 10-20%, and the concentration of silicate ions is 100-200 g / L.

[0068] In some embodiments, the pH value of the primary neutralized wastewater is 8-9. The pH value of the secondary neutralized wastewater is 9-10.

[0069] In some embodiments, the amount of polyferric sulfate added is such that the corresponding concentration in the secondary neutralized wastewater is 25-35 mg / L, and the amount of polyacrylamide added is such that the corresponding concentration in the secondary neutralized wastewater is 1.5-2.5 mg / L.

[0070] The inventors conducted a series of experiments, using combinations of different types and amounts of flocculants in the clarification step to clarify neutralized acidic and alkaline wastewater, and then tested the COD in the clarified liquid. Cr Oil content, calculate COD Cr The removal rates and oil removal rates are shown in Tables 1 and 2.

[0071] Table 1. Dosage and type of flocculant added (mg / L)

[0072]

[0073]

[0074] Table 2 COD and petroleum hydrocarbon removal rates

[0075] Experiment No. <![CDATA[COD in the clear liquid Cr > Oil content in clear liquid <![CDATA[COD Cr Removal rate Oil removal rate 1 80.6 52.2 72.2％ 77.7％ 2 100.6 79.3 65.3％ 66.1％ 3 75.4 54.0 74.0％ 76.9％ 4 101.2 78.8 65.1％ 66.3％ 5 112.2 86.1 61.3％ 63.2％

[0076] Among them, COD Cr Removal rate = (1 - COD in the supernatant) Cr COD of neutralized acidic and alkaline wastewater Cr Oil removal rate = (1 - oil content in clear liquid / oil content in neutralized acid and alkali wastewater) * 100%.

[0077] Taking into account the wastewater properties, treatment effectiveness, and cost, a suitable approach was to first add activated silica to the secondary neutralization tank, followed by the addition of PAM and PFS to the high-efficiency reaction clarification tank. The concentrations of activated silica (approximately 0.8-1.2 mg / L), PAM (approximately 1.5-2.5 mg / L), and PFS (approximately 25-35 mg / L) were used to achieve the expected treatment effect.

[0078] In some embodiments, the clarification time for adding polyferric sulfate and polyacrylamide to the secondary neutralized wastewater is 2 to 4 hours.

[0079] In some embodiments, the purpose of adding alkaline washing wastewater is to utilize the remaining free NaOH in the wastewater for neutralization. Additionally, after primary neutralization with lime slurry, the pH of the acidic or alkaline wastewater is 8-9; after secondary neutralization, the pH is adjusted to 9-10. The first stage of neutralization is a rapid, coarse pH adjustment; the second stage is a slow, fine pH adjustment. One benefit is reducing the amount of lime slurry needed. The free NaOH in the alkaline washing wastewater is alkaline and neutralizes acidic or acid-base wastewater; therefore, the wastewater replaces lime slurry for neutralization, reducing the amount of lime slurry required. Another benefit is the addition of monomeric silicic acid at a certain OH level. - At certain concentrations, the monomeric silicic acid, under the intense aeration and stirring action of the second-stage neutralization tank (which has twice the volume of the first-stage tank), results in a longer retention time of the acidic and alkaline wastewater. This allows for thorough contact between the monomeric silicic acid and the Fe(OH)3 flocs, metal ion hydroxides, oil, and organic matter in the wastewater, significantly promoting subsequent flocculation and sedimentation.

[0080] In some embodiments, see Figure 2 In the primary and secondary neutralization steps, lime slurry is added for neutralization. This method has a good neutralization effect and is relatively inexpensive.

[0081] In some embodiments, see Figure 2 This also includes the centralized treatment of water for reuse.

[0082] This application also provides a waste liquid treatment device, see [link to relevant documentation] Figure 2 It includes an alkaline collection tank 100, an acid-base wastewater equalization tank 110, a primary neutralization tank 120, a secondary neutralization tank 130, an acid-base clarification tank 140, a pH adjustment tank 150, a filter 160, and a discharge tank 170 connected in sequence.

[0083] The acid-base wastewater equalization tank 110 is used to receive the acid-containing wastewater, which includes at least one of pickling wastewater and acid regeneration wastewater.

[0084] The primary neutralization tank 120 is used to neutralize acidic wastewater in the first stage to obtain primary neutralized wastewater.

[0085] The secondary neutralization tank 130 is used to perform secondary neutralization on the primary neutralized wastewater to obtain secondary neutralized wastewater.

[0086] The alkali collection tank 100 is connected to the secondary neutralization tank 130 and is used to introduce the alkali washing waste liquid into the secondary neutralization tank 130 for secondary neutralization. The alkali washing waste liquid is the alkali washing waste liquid from the acid washing line.

[0087] The acid-base clarification tank 140 is used to receive polyferric sulfate and polyacrylamide, and to clarify the secondary neutralized wastewater to obtain clarified waste liquid.

[0088] The pH adjustment tank 150 and the filter 160 are used to adjust the pH of the clarified waste liquid and filter it to obtain water to be centrally treated and discharged into the discharge tank 170.

[0089] The above-mentioned device has the same technical effects as the above-mentioned method for utilizing the waste liquid from the acid washing line, and will not be described in detail here.

[0090] In some embodiments, a metering pump is also included, connected between the alkali collection tank 100 and the secondary neutralization tank 130.

[0091] The specific procedure is that the waste liquid in the alkali collection tank 100 liquid circulation tank is discharged into the alkali collection tank 100 by a newly added separate discharge pump, and the alkali solution containing sodium silicate monomer silicic acid is pumped into the secondary neutralization tank of the acid-alkali wastewater treatment system in proportion by a metering pump.

[0092] The alkali collection tank is used to collect the alkali solution generated during alkali cleaning in the pickling section of the pickling line and the pickling-rolling unit. Normally, it serves as a tank for preparing Na₂SiO₃. In some embodiments, to ensure continuous treatment of acid and alkali wastewater, monomeric activated silica is continuously added. When no alkali cleaning is performed in the pickling section of the pickling line and the pickling-rolling unit, Na₂SiO₃ is prepared to meet the required dosage.

[0093] In some specific embodiments, after primary neutralization with lime slurry, the pH of the acidic and alkaline wastewater is 8-9, and then adjusted to 9-10. The treatment capacity of the acidic and alkaline wastewater system is 100-150 cubic meters / hour. The concentration of silicate ions (i.e., monomeric activated silicic acid) in the secondary neutralized wastewater is 0.8-1.2 mg / L. When the concentration of silicate ions in the alkaline washing wastewater is 100 g / L, the metering pump continuously adds 800-1800 liters of alkaline washing wastewater to the secondary neutralization tank per hour; when the concentration of silicate ions in the alkaline washing wastewater is 200 g / L, the metering pump continuously adds 400-900 liters of alkaline washing wastewater to the secondary neutralization tank per hour.

[0094] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for utilizing waste liquid from an acid pickling line, characterized in that, Includes the following steps: The acidic wastewater is subjected to primary neutralization to obtain primary neutralized wastewater; the acidic wastewater includes at least one of pickling wastewater and acid regeneration wastewater. The primary neutralized wastewater is subjected to secondary neutralization, and alkaline washing waste liquid is added during the secondary neutralization process to obtain secondary neutralized wastewater; the alkaline washing waste liquid is the alkaline washing waste liquid from the acid washing line; the mass fraction of free NaOH in the alkaline washing waste liquid is 10-20%, and the concentration of silicate ions is 100-200 g / L; Polyferric sulfate and polyacrylamide were added to the secondary neutralized wastewater for clarification to obtain clarified waste liquid; The clarified waste liquid, after pH adjustment and filtration, yields water to be centrally treated.

2. The method for utilizing acid pickling line alkaline washing waste liquid according to claim 1, characterized in that, The amount of alkaline washing waste liquid added is such that the concentration of silicate ions in the secondary neutralized wastewater is 0.8-1.2 mg / L.

3. The method for utilizing acid pickling and alkaline washing waste liquid according to claim 1, characterized in that, The pH of the primary neutralized wastewater is 8-9; the pH of the secondary neutralized wastewater is 9-10.

4. The method for utilizing acid pickling and alkaline washing waste liquid according to claim 1, characterized in that, The amount of polyferric sulfate added is such that the corresponding concentration in the secondary neutralized wastewater is 25-35 mg / L, and the amount of polyacrylamide added is such that the corresponding concentration in the secondary neutralized wastewater is 1.5-2.5 mg / L.

5. The method for utilizing acid pickling line alkaline washing waste liquid according to claim 1, characterized in that, The clarification process involving the addition of polyferric sulfate and polyacrylamide to the secondary neutralized wastewater lasts for 2-4 hours.

6. The method for utilizing acid pickling line alkaline washing waste liquid according to claim 1, characterized in that, In the steps of primary neutralization and secondary neutralization, lime slurry is added for neutralization.

7. The method for utilizing the acid pickling and alkaline washing waste liquid according to any one of claims 1 to 6, characterized in that, This also includes the centralized treatment of water for reuse.

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