Hot-rolled stainless steel annealing sulfuric acid scrubbing wastewater treatment and sulfuric acid recovery process

Abstract

The invention discloses a hot-rolled stainless steel annealing sulfuric acid scrubbing wastewater treatment and sulfuric acid recovery process. Comprising the following steps: 1) carrying out homogeneous and average adjustment on wastewater; 2) after two-stage neutralization reaction, removing most of iron ions and heavy metals in the wastewater through a high-density sedimentation tank to obtain sedimentation tank produced water; (3) filtering the water produced by the sedimentation tank through a walnut shell filter to remove oil, and then carrying out microfiltration through a tubular membrane to obtain microfiltration permeate liquid; 4) performing reverse osmosis membrane treatment on the microfiltration permeate, and enabling reverse osmosis concentrated water to flow back to the microfiltration water producing tank; and 5) carrying out filtration treatment on the reverse osmosis concentrated water by using a nanofiltration membrane to obtain nanofiltration concentrated water, and deeply removing divalent or higher metal ions in the nanofiltration concentrated water by using chelating softening resin to obtain softened produced water. And 6) carrying out bipolar membrane treatment on the softened produced water to obtain recovered acid liquor and recovered alkali liquor. The method does not need an evaporator with high investment, does not generate waste water and waste salt, and has the advantages of economy, environmental protection, high resource utilization rate and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical wastewater treatment, and particularly relates to a process for treating hot-rolled stainless steel annealing sulfuric acid scrubbing wastewater and recovering sulfuric acid. Background Art

[0002] After being treated by hot rolling and the previous annealing process, a large amount of oxides exist on the surface of stainless steel. Usually, most of the scale on the surface needs to be removed by mechanical descaling (shot blasting), and then the remaining scale on the surface is removed by sulfuric acid pickling and mixed acid pickling, finally making the stainless steel present a smooth and corrosion-resistant surface state.

[0003] For the stainless steel after sulfuric acid pickling, there are partial sulfuric acid liquid and loose scale particles remaining on the surface. To avoid bringing them into the mixed acid pickling section, it needs to be removed through the sulfuric acid scrubbing section before entering the mixed acid pickling. The wastewater discharged from the scrubbing system has a lower acid concentration compared with the pickling waste liquid and cannot be discharged into the acid regeneration system. Usually, it needs to be pretreated by neutralization precipitation and then discharged into the production wastewater system or separately subjected to membrane concentration and then evaporation crystallization treatment. However, discharging into the production wastewater system cannot recover the sulfuric acid in the pickling wastewater, resulting in waste of resources, and will increase the salt content of the production wastewater system, increasing the difficulty of wastewater treatment. If evaporated and crystallized separately, the treatment cost is high, and the by-product sodium sulfate produced requires a separate disposal route. Summary of the Invention

[0004] To solve the above problems, the purpose of the present invention is to provide a process for treating hot-rolled stainless steel annealing sulfuric acid scrubbing wastewater and recovering sulfuric acid, so as to solve the problems of resource waste, high treatment difficulty, high treatment cost, etc. in the conventional treatment methods.

[0005] To achieve the above purpose, the present invention provides a process for treating hot-rolled stainless steel annealing sulfuric acid scrubbing wastewater and recovering sulfuric acid, including the following steps:

[0006] 1) The annealing sulfuric acid scrubbing wastewater is collected and enters the wastewater regulation tank for homogenization and equalization adjustment;

[0007] 2) The scrubbing wastewater after homogenization and equalization adjustment is first subjected to two-stage neutralization reaction, and then most of the iron ions and heavy metals in the wastewater are removed through a high-density sedimentation tank to obtain the sedimentation tank effluent;

[0008] 3) The sedimentation tank effluent is first filtered to remove oil through a walnut shell filter, and then further removes iron ions and heavy metals through tubular membrane microfiltration to obtain the microfiltration permeate;

[0009] 4) After the microfiltration permeate is treated by the first-stage reverse osmosis membrane, the first-stage reverse osmosis product water and the first-stage reverse osmosis concentrate are obtained; after the first-stage reverse osmosis product water is treated by the second-stage reverse osmosis membrane, the second-stage reverse osmosis product water and the second-stage reverse osmosis concentrate are obtained. The second-stage reverse osmosis product water is reused, and the second-stage reverse osmosis concentrate is refluxed to the microfiltration product water tank; the second-stage reverse osmosis product water and the nanofiltration product water are recycled and used as new industrial water in the steel plant.

[0010] 5) After the first-stage reverse osmosis concentrate is filtered by the nanofiltration membrane, the nanofiltration product water and the nanofiltration concentrate are obtained. The nanofiltration product water is reused, and the nanofiltration concentrate is further treated by chelating softening resin to deeply remove divalent and higher metal ions in the concentrate, obtaining softened product water. The material of the nanofiltration membrane is polyamide, the system recovery rate ≥ 50%, and the operating flux ≤ 10 L / m2·h.

[0011] Further, the following steps are also included:

[0012] 6) The softened product water is treated by a bipolar membrane to obtain recycled acid solution and recycled alkali solution.

[0013] Further, the following steps are also included: The recycled acid solution is used as the acid supplement solution for the annealing sulfuric acid pickling system, and the recycled alkali solution is used as the liquid alkali supplement solution for the neutralization process section.

[0014] Further, the annealing sulfuric acid scrubbing wastewater is the wastewater generated in the sulfuric acid scrubbing section after the stainless steel annealing process. After homogenization and equalization, the sulfuric acid concentration in the wastewater is 1 - 2%, and the divalent iron ion concentration is 3 - 5 g / L.

[0015] Further, the two-stage neutralization reaction time is not less than 30 min, and the divalent iron ions are oxidized to trivalent iron ions by means of air blowing aeration, with an air-water ratio of 10 - 15.

[0016] Further, the rapid mixing time of the high-density sedimentation tank is about 1 - 2 min, the flocculation time is about 10 - 20 min, the surface load of the clarification zone is about 2 - 3 (m3 / m2·h), and the suspended solid concentration of the sedimentation tank product water ≤ 20 mg / L; after the sludge discharged from the high-density sedimentation tank is plate-and-frame filtered, the filtrate is refluxed to the wastewater regulation tank, and the dry sludge can be sent to the pelletizing process section of the steel plant for treatment.

[0017] Further, the filtration speed of the walnut shell filter is 24 - 26 m / h, and the oil content of the effluent < 5 mg / L; the material of the tubular membrane microfiltration membrane is polyvinylidene fluoride (PVDF), the filtration accuracy is 0.05 um, the operating flux ≤ 320 L / m2·h, the working pressure is 0.3 - 0.4 MPa, and the SDI of the obtained microfiltration permeate ≤ 3, and the turbidity ≤ 0.2 NTU.

[0018] Further, the first-stage reverse osmosis uses a seawater desalination membrane with a polyamide membrane material, a system recovery rate ≥ 60%, and an operating flux ≤ 10 L / m2·h; the second-stage reverse osmosis uses a brackish water membrane with a polyamide membrane material, a system recovery rate ≥ 80%, and an operating flux ≤ 15 L / m2·h.

[0019] Further, the chelating softening resin adsorption hydraulic retention time ≥ 1 h, and the total sum of divalent and above metal ions in the produced water < 0.5 mg / L; the regeneration of the chelating resin includes the following steps: regenerate by passing 8 - 10% sulfuric acid through the resin layer at a flow rate of 1 - 2 BV / h, then perform slow washing and fast washing at flow rates of 1 - 2 BV / h and 5 - 10 BV / h respectively, and finally pass 3 - 4% liquid caustic soda solution through the resin layer at a flow rate of 1 - 2 BV / h and rinse with pure water to convert the resin into the sodium form. The regeneration liquid is refluxed to the secondary neutralization tank.

[0020] Further, the bipolar membrane process uses a bipolar membrane electrodialysis system, which consists of a bipolar membrane and cation exchange membranes and anion exchange membranes arranged alternately to form an electrodialysis membrane stack. Each membrane stack consists of multiple repeating units, and each repeating unit contains a salt chamber, an acid chamber, and a base chamber. Under the action of a direct current electric field, H+ and OH- are generated by the hydrolysis reaction at the bipolar membrane interface and enter the acid chamber and the base chamber respectively. SO42- in the salt chamber permeates through the anion exchange membrane into the acid chamber to obtain sulfuric acid, and Na+ permeates through the cation exchange membrane into the base chamber to obtain liquid caustic soda. The bipolar membrane uses a modified bipolar membrane prepared by the impregnation method, the ion exchange membrane uses a perfluorosulfonic acid membrane, the electrode solution uses the produced water of the second-stage reverse osmosis, the operating voltage of each pair of bipolar membranes is 1.8 - 2.5 V, and the current density is 20 - 50 mA / cm 2 , and the operating temperature is 25 - 40 °C.

[0021] Compared with the prior art, in the process of the present invention, after pretreatment such as neutralization precipitation, filtration, and concentration, through the bipolar membrane device, the sulfuric acid in the hot-rolled stainless steel annealing sulfuric acid brushing wastewater is fully recovered, reducing the sulfuric acid usage amount in the annealing pickling process. Therefore, it has the advantages of not requiring investment in expensive evaporators, no wastewater and waste salt generation, and high economic, environmental protection, and resource utilization rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the process flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The embodiments of the present invention will be described in detail below with reference to the drawings.

[0024] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0025] The terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0026] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] Example 1

[0028] A hot-rolled stainless steel annealing sulfuric acid brushing wastewater treatment and sulfuric acid recovery process includes the following steps:

[0029] 1) The brushing wastewater is collected and enters the wastewater regulation tank for homogenization regulation;

[0030] The brushing wastewater comes from the hot-rolled stainless steel annealing sulfuric acid brushing section. After homogenization, the sulfuric acid concentration of the waste liquid generated by different brushing machines is 1.5%, and the divalent iron ion concentration is 4 g / L;

[0031] 2) After the homogenization-regulated brushing wastewater is first subjected to two-stage neutralization reaction, most of the iron ions and heavy metals are removed by a high-density sedimentation tank to obtain the sedimentation tank effluent;

[0032] The reaction time of the first-stage neutralization tank is 40 min, and the reaction time of the second-stage neutralization tank is 30 min. The divalent iron ions are oxidized into trivalent iron ions by means of air blowing aeration, and the air-water ratio is 15;

[0033] The rapid mixing time of the high-density sedimentation tank is 2 min, the flocculation time is 20 min, the surface load of the clarification zone is 2 (m3 / m2·h), and the measured suspended solid concentration of the effluent is 13 mg / L;

[0034] 3) The water produced by the sedimentation tank is first deoiled by a walnut shell filter and then filtered through a tubular membrane microfiltration to obtain microfiltration permeate;

[0035] The walnut shell filter uses specially processed walnut shells as the filtering medium, with a filtration speed of 25 m / h and the measured oil content in the effluent being 0.8 mg / L;

[0036] The tubular membrane microfiltration membrane material is polyvinylidene fluoride (PVDF), with a filtration accuracy of 0.05 μm, an operating flux of 318 L / m2·h, a working pressure of 0.3 MPa, and the SDI of the obtained microfiltration permeate ≤ 3 and the turbidity ≤ 0.2 NTU;

[0037] 4) The microfiltration permeate is treated by a first-stage reverse osmosis membrane to obtain first-stage reverse osmosis product water and first-stage reverse osmosis concentrate; the first-stage reverse osmosis product water is treated by a second-stage reverse osmosis membrane to obtain second-stage reverse osmosis product water and second-stage reverse osmosis concentrate. The second-stage reverse osmosis product water is recycled, and the second-stage reverse osmosis concentrate is returned to the microfiltration product water tank;

[0038] The first-stage reverse osmosis uses a seawater desalination membrane with a membrane material of polyamide, a system recovery rate ≥ 60%, and an operating flux of 9.4 L / m2·h; the second-stage reverse osmosis uses a brackish water membrane with a membrane material of polyamide, a system recovery rate ≥ 80%, and an operating flux of 12.6 L / m2·h. The second-stage reverse osmosis product water is used as new industrial water in the steel plant;

[0039] 5) The first-stage reverse osmosis concentrate is filtered through a nanofiltration membrane to obtain nanofiltration product water and nanofiltration concentrate. The nanofiltration concentrate is further treated by chelating softening resin to deeply remove divalent and higher metal ions in the concentrate to obtain softened product water;

[0040] The nanofiltration membrane material is polyamide, with a system recovery rate ≥ 50% and an operating flux of 9.9 L / m2·h. The nanofiltration product water is used as new industrial water in the steel plant, and the sodium sulfate content in the nanofiltration concentrate is 12%;

[0041] The hydraulic retention time for the adsorption of chelating softening resin is 1 h, and the total sum of divalent and higher metal ions in the softened product water < 0.5 mg / L.

[0042] 6) The softened product water is treated by a bipolar membrane to obtain recycled acid solution and recycled alkali solution;

[0043] The bipolar membrane uses a modified bipolar membrane prepared by an impregnation method, the ion exchange membrane uses a perfluorosulfonic acid membrane, and the electrode solution uses the second-stage reverse osmosis product water. The obtained recycled acid solution has a sulfuric acid concentration of 9.8%, and the recycled alkali solution has a sodium hydroxide concentration of 8%. The recycled acid solution is used as the acid supplement solution for the annealing sulfuric acid pickling system, and the recycled alkali solution is used as the liquid alkali supplement solution for the neutralization process section.

[0044] In this embodiment, the recovery rate of sulfuric acid in the scrubbing wastewater is 98%. A small amount of loss is mainly caused by being carried by the water-containing sludge during the treatment of the sludge in the high-density tank.

[0045] Example 2

[0046] A process for treating hot-rolled stainless steel annealing sulfuric acid scrubbing wastewater and recovering sulfuric acid includes the following steps:

[0047] 1) The scrubbing wastewater is collected and enters the wastewater adjustment tank for homogenization adjustment;

[0048] The scrubbing wastewater comes from the hot-rolled stainless steel annealing sulfuric acid scrubbing section. After homogenization, the sulfuric acid concentration of the waste liquid generated by different scrubbing machines is 1.2%, and the divalent iron ion concentration is 3.4 g / L;

[0049] 2) After the scrubbing wastewater after homogenization adjustment undergoes two-stage neutralization reaction, most of the iron ions and heavy metals are removed through a high-density sedimentation tank to obtain the sedimentation tank effluent;

[0050] The reaction time of the first-stage neutralization tank is 30 min, and the reaction time of the second-stage neutralization tank is 30 min. The divalent iron ions are oxidized into trivalent iron ions by means of air blowing aeration, and the air-water ratio is 12;

[0051] The rapid mixing time of the high-density sedimentation tank is 1 min, the flocculation time is 10 min, the surface load of the clarification zone is 3 (m3 / m2·h), and the measured suspended solid concentration of the effluent is 15 mg / L;

[0052] 3) The sedimentation tank effluent is first deoiled through a walnut shell filter and then filtered through a tubular membrane microfiltration to obtain the microfiltration permeate;

[0053] The walnut shell filter uses specially processed walnut shells as the filtering medium, the filtering speed is 24 m / h, and the measured oil content of the effluent is 0.6 mg / L;

[0054] The tubular membrane microfiltration membrane material is polyvinylidene fluoride (PVDF), the filtration accuracy is 0.05 um, the operating flux is 313 L / m2·h, the working pressure is 0.3 MPa, and the SDI of the obtained microfiltration permeate ≤3, and the turbidity ≤0.2 NTU;

[0055] 4) The microfiltration permeate is treated through a first-stage reverse osmosis membrane to obtain the first-stage reverse osmosis effluent and the first-stage reverse osmosis concentrate; the first-stage reverse osmosis effluent is treated through a second-stage reverse osmosis membrane to obtain the second-stage reverse osmosis effluent and the second-stage reverse osmosis concentrate. The second-stage reverse osmosis effluent is recycled, and the second-stage reverse osmosis concentrate is refluxed to the microfiltration product water tank;

[0056] The first-stage reverse osmosis uses seawater desalination membranes with a polyamide membrane material. The system recovery rate is ≥60%, and the operating flux is 9.8 L / m2·h. The second-stage reverse osmosis uses brackish water membranes with a polyamide membrane material. The system recovery rate is ≥80%, and the operating flux is 14.5 L / m2·h. The water produced by the second-stage reverse osmosis is used as the new industrial water in the steel plant;

[0057] 5) After the concentrated water from the first-stage reverse osmosis is filtered by nanofiltration membranes, nanofiltration-produced water and nanofiltration-concentrated water are obtained. The nanofiltration-concentrated water is further treated by chelating softening resin to deeply remove divalent and higher metal ions in the concentrated water, obtaining softened-produced water;

[0058] The nanofiltration membrane material is polyamide. The system recovery rate is ≥50%, and the operating flux is 9.8 L / m2·h. The nanofiltration-produced water is used as the new industrial water in the steel plant, and the sodium sulfate content in the nanofiltration-concentrated water is 10%;

[0059] The hydraulic retention time for the adsorption of chelating softening resin is 1 h, and the total sum of divalent and higher metal ions in the softened-produced water is <0.5 mg / L.

[0060] 6) The softened-produced water is treated by bipolar membranes to obtain recovered acid solution and recovered alkali solution;

[0061] The bipolar membranes are modified bipolar membranes prepared by the impregnation method. The ion exchange membranes are perfluorosulfonic acid membranes, and the electrode solutions are the water produced by the second-stage reverse osmosis. The sulfuric acid concentration of the obtained recovered acid solution is 8.5%, and the sodium hydroxide concentration of the recovered alkali solution is 7%. The recovered acid solution is used as the acid replenishing solution for the annealing sulfuric acid pickling system, and the recovered alkali solution is used as the liquid alkali replenishing solution for the neutralization process section.

[0062] In this embodiment, the recovery rate of sulfuric acid in the scrubbing wastewater is 99%, and there is a small amount of loss mainly carried by the water-containing sludge during the treatment of the sludge in the high-density tank.

[0063] Example 3

[0064] An annealing sulfuric acid scrubbing wastewater treatment and sulfuric acid recovery system, including: connected in sequence through pipelines: a wastewater regulation tank, a neutralization tank, a high-density sedimentation tank, a walnut shell filter, a tubular membrane microfiltration device, a microfiltration-produced water tank, a reverse osmosis water treatment device, a nanofiltration water treatment device, a nanofiltration-concentrated water tank, a chelating resin softening device, a bipolar membrane electrodialysis device; where

[0065] The wastewater regulation tank is used to adjust the homogenization and equalization of the collected annealing sulfuric acid scrubbing wastewater;

[0066] The neutralization tank is used to carry out a neutralization reaction on the scrubbing wastewater after homogenization and equalization adjustment;

[0067] The high-density sedimentation tank is used to remove most of the iron ions and heavy metals in the neutralized wastewater, obtaining sedimentation tank-produced water;

[0068] A walnut shell filter for filtering and removing oil from the water produced by the sedimentation tank;

[0069] Tube-type membrane microfiltration is used to further remove iron ions and heavy metals from the wastewater after oil filtration to obtain microfiltration permeate; the microfiltration permeate enters the microfiltration product water tank;

[0070] A reverse osmosis water treatment device, and the microfiltration permeate is treated by a reverse osmosis membrane to obtain reverse osmosis product water;

[0071] A nanofiltration water treatment device for filtering and treating reverse osmosis concentrate to obtain nanofiltration concentrate, and the nanofiltration concentrate enters the nanofiltration concentrate water tank;

[0072] A chelating resin softening device for deeply removing divalent and above metal ions from the nanofiltration concentrate to obtain softened product water;

[0073] A bipolar membrane electrodialysis device, and the softened product water is treated by a bipolar membrane to obtain recovered acid solution and recovered alkali solution.

[0074] Among them, the above-mentioned various devices are all obtained by purchasing from the market:

[0075] The tube-type membrane microfiltration device, also known as the tube-type membrane complete set of equipment, such as the tube-type membrane complete set of equipment sold by Duraflow (Shanghai) Membrane Technology Co., Ltd. (https: / / www.duraflowllc.com / products.asp?classid=5);

[0076] The reverse osmosis water treatment device, such as the industrial reverse osmosis equipment sold by Chuanyi Water Treatment Company (http: / / www.chuanyiscl.com / product_article.asp?id=5770);

[0077] The nanofiltration water treatment device, such as the nanofiltration equipment sold by Chuanyi Water Treatment Company (http: / / www.chuanyiscl.com / product.asp?lei=562);

[0078] The bipolar membrane electrodialysis device (such as the bipolar membrane electrodialyzer sold by Hangzhou Create Environmental Energy Technology Co., Ltd. (https: / / www.createnviro.com / sjmdsxq)).

[0079] Chelating resin softening equipment is made by filling chelating resin in an ion exchanger. For example, the ion exchanger sold by Suzhou Bangze Purification Equipment Co., Ltd. (http: / / www.szbzjh.com / content / ?207.html) is filled with the chelating resin sold by Tianjin Yunkai Resin Technology Co., Ltd. (http: / / tjyunkai.com / index.php / arc / show / id / 49.html).

[0080] Walnut shell filter (such as the LF-SYS series walnut shell filter sold by Xinxiang Lifierte Filter Co., Ltd. https: / / isite.baidu.com / site / wjz4ibs7 / bc2053a7-960c-499b-ab8b-7a239ec4a85b?fid=rHRYn1RkrjR4PjDvPHf3PjRsP-tznWNxnf&ch=4&bd_vid=14516970795375264751&bd_bxst=EiaKv J8w0F-WTmH900DD05hrE0QDA060000000zlzt1iEtX4OTQQkET0000000000006f1-jrRm1 n1-KPDNan1 D4fHwjrj-DnjDdwbm4nH-jwDZa2W08TjW0b6c000adTKs2A6000jYY4LZo0000Ds0L00zlzt1 iEtX4OTQQkET68_EnYoOZ8xLaztULCUQ0SexAVEEnv2A1dQHPVerMEPc00000OOOO OOOOOOqaz7hM&wid=a399b8e06a954db0821a9aa5089b0e78_0_0&field=&orderBy=&categoryId=undefined&uniqId=604002309ede46a5a49c0d8ac00a4e75)

[0081] Among them, the bipolar membrane electrodialysis device consists of a bipolar membrane, a cation exchange membrane, and an anion exchange membrane arranged alternately to form an electrodialysis membrane stack. Each membrane stack is composed of multiple repeating units, and each repeating unit contains a salt chamber, an acid chamber, and a base chamber. Under the action of a direct current electric field, H⁺ and OH⁻ are generated by the hydrolysis reaction at the interface of the bipolar membrane and enter the acid chamber and the base chamber respectively. SO₄²⁻ in the salt chamber permeates through the anion exchange membrane into the acid chamber to obtain sulfuric acid, and Na⁺ permeates through the cation exchange membrane into the base chamber to obtain liquid caustic soda. The bipolar membrane used is a modified bipolar membrane prepared by the impregnation method, the ion exchange membrane used is a perfluorosulfonic acid membrane, and the electrode solution uses secondary reverse osmosis product water. The operating voltage of each pair of bipolar membranes is 1.8 - 2.5 V, and the current density is 20 - 50 mA / cm 2 , and the operating temperature is 25 - 40 °C. The recovered acid solution is used as the acid replenishing solution for the annealing sulfuric acid pickling system, and the recovered alkali solution is used as the liquid caustic soda replenishing solution for the neutralization process section.

[0082] The above has described the present invention in detail with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention. Many other changes and modifications made without departing from the concept and scope of the present invention should be regarded as within the protection scope of the present invention.

[0083] In the description of this specification, specific features, structures, materials, or characteristics can be combined in a suitable manner in any one or more embodiments or examples.

[0084] The above is only the specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A hot-rolled stainless steel annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery process, characterized in that: The following steps are involved: 1) Annealing sulfuric acid washing wastewater is collected and sent to the wastewater regulating tank for homogenization and equalization; 2) The washing wastewater after homogenization and equalization is first subjected to a two-stage neutralization reaction, and then passed through a high-density sedimentation tank to remove most of the iron ions and heavy metals in the wastewater to obtain sedimentation tank water; 3) The water produced from the sedimentation tank is first filtered through a walnut shell filter to remove oil, and then further filtered through a tubular membrane to remove iron ions and heavy metals to obtain a microfiltration permeate; 4) After the microfiltration permeate is treated by the primary reverse osmosis membrane, primary reverse osmosis produced water and primary reverse osmosis concentrated water are obtained; after the primary reverse osmosis produced water is treated by the secondary reverse osmosis membrane, secondary reverse osmosis produced water and secondary reverse osmosis concentrated water are obtained, the secondary reverse osmosis produced water is reused, and the secondary reverse osmosis concentrated water is returned to the microfiltration water production pool; 5) The primary reverse osmosis concentrated water is filtered through a nanofiltration membrane to obtain nanofiltration product water and nanofiltration concentrated water. The nanofiltration product water is reused, and the nanofiltration concentrated water is further filtered through a chelating softening resin to deeply remove divalent and higher metal ions in the concentrated water to obtain softened product water; 6) The softened produced water is treated by a bipolar membrane to obtain recovered acid solution and recovered alkali solution.

2. The hot-rolled stainless steel annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery process according to claim 1, characterized in that: The following steps are also included: The recovered acid solution is used as the acid replenishing solution for the annealing sulfuric acid pickling system, and the recovered alkali solution is used as the liquid alkali replenishing solution for the neutralization process section.

3. The hot-rolled stainless steel annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery process according to claim 1, characterized in that: The annealing sulfuric acid washing wastewater is wastewater generated in the sulfuric acid washing section after the stainless steel annealing process. After homogenization and equalization, the sulfuric acid concentration in the wastewater is 1-2%, and the divalent iron ion concentration is 3-5g / L.

4. The hot-rolled stainless steel annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery process according to claim 1, characterized in that: The two-stage neutralization reaction time is not less than 30 minutes, and the divalent iron ions are oxidized into trivalent iron ions by aeration, and the air-water ratio is 10-15.

5. The hot-rolled stainless steel annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery process according to claim 1, characterized in that: The high-density sedimentation tank has a rapid mixing time of about 1 to 2 minutes, a flocculation time of about 10 to 20 minutes, a surface load of the clarification zone of about 2 to 3 (m3 / m2·h), and a suspended solids concentration of the sedimentation tank water output of ≤20 mg / L; after the sludge discharged from the high-density sedimentation tank is filtered through a plate and frame filter, the filtrate is returned to the wastewater regulating tank, and the dry sludge can be sent to the pelletizing process section of the steel plant for treatment.

6. The hot-rolled stainless steel annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery process according to claim 1, characterized in that: The filtration speed of the walnut shell filter is 24-26 m / h, and the oil content of the effluent is <5 mg / L; the tubular membrane microfiltration membrane is made of polyvinylidene fluoride (PVDF), the filtration accuracy is 0.05 um, the operating flux is ≤320 L / m2·h, the working pressure is 0.3-0.4 MPa, and the obtained microfiltration permeate SDI is ≤3, and the turbidity is ≤0.2 NTU.

7. The hot-rolled stainless steel annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery process according to claim 1, characterized in that: The primary reverse osmosis adopts a seawater desalination membrane made of polyamide, with a system recovery rate of ≥60% and an operating flux of ≤10L / m2·h; the secondary reverse osmosis adopts a brackish water membrane made of polyamide, with a system recovery rate of ≥80% and an operating flux of ≤15L / m2·h.

8. The hot-rolled stainless steel annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery process according to claim 1, characterized in that: The chelate softening resin adsorption hydraulic retention time is ≥ 1h, and the total amount of divalent and above metal ions in the produced water is < 0.5mg / L; the chelate resin regeneration The process comprises the following steps: regenerating the resin layer with 8-10% sulfuric acid at a flow rate of 1-2 BV / h, then performing slow washing and fast washing at flow rates of 1-2 BV / h and 5-10 BV / h respectively, and finally passing the resin layer with 3-4% liquid alkali solution at a flow rate of 1-2 BV / h and eluting with pure water to convert the resin into sodium type. The regenerated liquid is returned to the secondary neutralization tank.

9. The hot-rolled stainless steel annealing sulfuric acid washing wastewater treatment and sulfuric acid recovery process according to claim 1, characterized in that: The bipolar membrane process adopts a bipolar membrane electrodialysis system, which is composed of an electrodialysis membrane stack composed of a bipolar membrane, a cation exchange membrane, and an anion exchange membrane arranged alternately. Each membrane stack is composed of multiple repeating units, and each repeating unit contains a salt chamber, an acid chamber, and an alkali chamber. Under the action of a DC electric field, H+ and OH- are produced by a hydrolysis reaction at the interface of the bipolar membrane and enter the acid chamber and the alkali chamber respectively. The SO42- in the salt chamber passes through the anion exchange membrane to enter the acid chamber to obtain sulfuric acid, and Na+ passes through the cation exchange membrane to enter the alkali chamber to obtain liquid alkali. The bipolar membrane is a modified bipolar membrane prepared by an impregnation method, the ion exchange membrane is a perfluorosulfonic acid membrane, the polar liquid is a secondary reverse osmosis water production, the bipolar membrane operating voltage is 1.8 to 2.5V per pair of membranes, and the current density is 20 to 50mA / cm 2 , the operating temperature is 25 ~ 40 ℃.

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