Production method and device for recycling hydrochloric acid pickling wastewater

Abstract

The invention relates to the technical field of hydrochloric acid pickling waste liquid recovery treatment, and particularly discloses a production method and device for recycling hydrochloric acid pickling waste water, and the production method comprises the steps of purification and impurity removal, filter pressing to remove tailings, neutralization reaction, iron red filtration, refining electrolysis to separate acid and alkali and the like. According to the production method, full-quantization high-value recovery of the hydrochloric acid pickling wastewater is achieved, remarkable economic, environmental and industrial application values are achieved, regenerated hydrochloric acid and liquid caustic soda can be directly recycled, closed-loop utilization of resources is achieved, meanwhile, a high-temperature roasting process is abandoned, energy consumption of each ton of waste liquid is reduced, purchased chemicals are reduced, and the production method is suitable for large-scale production of enterprises. The manganese ion removal rate is greater than or equal to 99% through graded impurity removal, and the product purity is high; and only a small amount of hazardous waste tailings are generated, secondary pollution is avoided, the triple targets of wastewater treatment, resource recovery and economic benefits are achieved, and technical support is provided for sustainable development of enterprises.

Description

Technical Field

[0001] This invention belongs to the field of hydrochloric acid pickling wastewater recycling and treatment technology, specifically relating to a production method and apparatus for the recycling and reuse of hydrochloric acid pickling wastewater. Background Technology

[0002] Hydrochloric acid pickling is a core surface treatment process in the processing of metal products such as steel, stainless steel, and carbon steel structural parts. It cleans the metal surface by chemically reacting hydrochloric acid with iron oxide scale and rust, a necessary prerequisite for the smooth operation of subsequent deep processing steps such as rolling, welding, and painting. With the rapid development of my country's metal processing industry towards large-scale and refined operations, the discharge of hydrochloric acid pickling wastewater has been increasing year by year. A single medium-sized metal processing enterprise can generate 50-200 m³ of hydrochloric acid pickling wastewater per day. This type of wastewater has a complex composition and significant characteristics. Its core components include ferrous chloride and free hydrochloric acid, along with inorganic impurities such as manganese and silicon, trace amounts of heavy metal ions such as copper, zinc, chromium, nickel, lead, and cadmium, and small amounts of organic corrosion inhibitors and surfactants. It is a typical highly polluting industrial wastewater characterized by strong acidity, high salinity, and a wide variety of impurities. However, it is also rich in valuable resources such as iron and chlorine, possessing high resource recovery value.

[0003] Currently, the treatment technologies for hydrochloric acid pickling wastewater in the market are mainly divided into two categories: traditional disposal and traditional recycling. Both types of technologies have insurmountable industry pain points and are no longer suitable for the national "dual carbon" strategy and the industry's development requirements of strict environmental regulations. They also fail to meet the core production needs of metal processing enterprises for cost reduction, efficiency improvement, and resource recycling. The specific technical defects are as follows:

[0004] Disposal-type processes, represented by neutralization precipitation, are currently the mainstream method for treating hydrochloric acid pickling wastewater in small and medium-sized metal processing enterprises. This process neutralizes acidic wastewater by adding alkaline agents such as lime and caustic soda, achieving compliant discharge. While it is characterized by simple operation and low initial equipment investment, it suffers from fatal problems such as severe resource waste, significant secondary pollution, and persistently high long-term disposal costs. On the one hand, the neutralization reaction generates a large amount of ferric hydroxide sludge with a water content ≥80%, which is difficult to dewater. The iron resources in the sludge have almost no utilization value, and chloride ions enter the water body in the form of soluble salts, leading to excessive salinity in the effluent. On the other hand, the comprehensive cost of subsequent hazardous waste disposal of sludge and deep desalination treatment of effluent can reach 80-150 yuan / m³, placing a heavy environmental cost burden on enterprises in the long term. At the same time, this process does not recover resources such as iron and chloride in the wastewater, which violates the national industrial policy of resource recycling.

[0005] Recycling-type processes, centered on high-temperature roasting, are the mainstream choice for large metal processing enterprises. This process separates and recovers ferrous chloride and hydrochloric acid from wastewater through high-temperature spray roasting at 600-800℃. However, in actual market applications, this process suffers from drawbacks such as extremely high energy consumption, stringent equipment requirements, high operational difficulty, and insufficient resource recovery: First, the process requires evaporating more than 90% of the water in the waste liquid, with energy consumption reaching 800-1200 kWh per ton of waste liquid, resulting in high operating costs; Second, it places stringent requirements on the temperature and acid resistance of equipment materials, requiring core equipment to use imported special alloys, making equipment procurement and subsequent maintenance costs 5-8 times that of conventional treatment equipment; Third, the process flow is complex, requiring high levels of professional technical skills from operators, and problems such as coking and pipe blockage are prone to occur when treating waste liquid containing organic matter, and inadequate exhaust gas treatment can lead to air pollution; Fourth, it can only achieve single recovery of hydrochloric acid and iron, and has no effective treatment method for impurities such as manganese and silicon in wastewater, failing to achieve full-scale resource recovery.

[0006] In recent years, although a few improved processes for hydrochloric acid pickling wastewater recovery have emerged in the industry, most of them are partial adjustments and optimizations to traditional treatment or recovery processes, failing to fundamentally solve the technical pain points. Some improved processes can only achieve efficient recovery of a single resource, while other valuable resources are still wasted; some processes, although slightly reducing energy consumption, have insufficient removal rates of impurities in the wastewater, resulting in low purity of the recovered products that cannot be directly reused; and some processes lack dedicated automated equipment, resulting in poor process stability and difficulty in adapting to the continuous, low-cost, and large-scale production needs of metal processing enterprises. Summary of the Invention

[0007] The purpose of this invention is to provide a production method and apparatus for recycling hydrochloric acid pickling wastewater, so as to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A production method for recycling hydrochloric acid pickling wastewater includes the following steps:

[0010] S1. Purification and impurity removal:

[0011] The hydrochloric acid pickling wastewater was sequentially treated to remove manganese, heavy metals, and silicon. During the manganese removal process, a manganese removal agent was added to the wastewater and the pH value was adjusted to 7-8 to achieve a manganese ion removal rate of over 99%.

[0012] S2. Filter press to remove tailings:

[0013] The mixture after purification and impurity removal by S1 is subjected to primary pressure filtration to obtain the first filter cake and the first filtrate. The first filter cake is tailings containing manganese, silicon and heavy metals, and the first filtrate is clean iron-containing liquid.

[0014] S3, neutralization reaction:

[0015] Sodium hydroxide is added to the first filtrate to complete the acid-base neutralization reaction in the neutralization reaction apparatus;

[0016] S4. Filter out iron oxide red:

[0017] The neutralized liquid is subjected to two-stage pressure filtration to obtain a second filter cake and a second filtrate. The second filter cake is dried and ground into high-purity iron red with a purity of over 99%, and the second filtrate is used in subsequent processes.

[0018] S5. Refined electrolytic separation of acids and bases:

[0019] ① The second filtrate enters the refining unit, where a refining agent is added to remove Ca²+, Mg²+, SO₄²-, Fe³+, Al³+, heavy metals, and suspended solids;

[0020] ②After purification, the feed solution enters the ion membrane electrolysis device, where a DC voltage is applied to form an electric field, causing cations to migrate to the cathode and anions to migrate to the anode, thus achieving acid-base separation through electrode reactions;

[0021] ③ The synthetic hydrochloric acid produced by electrolytic anode is directly returned to the pickling tank for reuse;

[0022] ④ The liquid alkali produced by the electrolytic cathode is concentrated to the concentration required for the neutralization reaction and then returned to the neutralization reaction device for reuse.

[0023] Preferably, the manganese removal agent in S1 is one or more of pure iron powder, ferric hydroxide, and ozone; during the manganese removal process, when ozone is used as the manganese removal agent, the pH of the wastewater needs to be adjusted to above 5 with ferric hydroxide first, and then metallic iron powder is added to reduce the FeCl3 generated in the reaction to FeCl2.

[0024] Preferably, in S1, the removal of heavy metals involves introducing H2S gas into the purified liquid after manganese removal, causing heavy metal ions such as copper, zinc, chromium, nickel, lead, and cadmium to precipitate as sulfides; the desiliconizing agent is one or more of polyferric silicate flocculants, modified polysilicic acid flocculants, and activated silica flocculants, which remove silicon impurities through flocculation and precipitation.

[0025] Preferably, the refining agent in S5 is one or more of barium chloride, barium hydroxide, sodium hydroxide, sodium carbonate, sodium sulfide, polyaluminum chloride, polyferric sulfate, and polyacrylamide, and is used in combination with a chelating resin.

[0026] A production device for recycling hydrochloric acid pickling wastewater includes, in sequence, the following components along the waste hydrochloric acid pickling wastewater recovery and treatment process: waste liquid storage tank, purification and impurity removal unit, primary filter press, neutralization reaction unit, secondary filter press, drying and grinding unit, refining unit, ion membrane electrolysis unit, and concentration unit. Each unit is connected to a delivery pump via pipelines, and the pipelines are equipped with flow regulating valves and detection instruments.

[0027] The purification and impurity removal unit is a series reactor structure, which includes a manganese removal reactor, a heavy metal removal reactor, and a silicon removal reactor in sequence.

[0028] The neutralization reaction unit is a reaction vessel with grinding and stirring functions, and is equipped with a precise liquid alkali dosing device.

[0029] The drying and grinding unit includes, in sequence, a closed belt hot air drying device and an airflow ultrafine grinding mill.

[0030] The refining unit includes a refining tower and a chelation tower;

[0031] The ion-exchange membrane electrolysis unit includes an electrolysis cell with an alkali chamber and an acid chamber;

[0032] The concentration unit is one of the following: triple-effect evaporator, quadruple-effect evaporator, multi-effect evaporator, falling film evaporator, rising film evaporator, forced circulation evaporator, or low-temperature evaporation device, and is equipped with an evaporator separator, condenser, vacuum pump, condensate tank, condensate pump, and non-condensable gas separator.

[0033] Preferably, the demanganese reactor is equipped with a demanganese removal agent dosing device and a pH adjustment device; the heavy metal removal reactor is equipped with an H2S gas inlet and a gas distributor; the desiliconization reactor is equipped with a desiliconization agent dosing device and a low-speed stirring device, and the demanganese reactor, the heavy metal removal reactor, and the desiliconization reactor are all equipped with online temperature and pH monitoring instruments.

[0034] Preferably, the primary filter press is a plate and frame filter press, the filter plates are equipped with anti-clogging filter screens and have high-pressure pressing function; the secondary filter press is a precision filter press, its filtration accuracy is higher than that of the primary filter press, the filtrate outlet is connected to the material pipe of the refining unit, and the filter cake outlet is connected to the drying and grinding unit.

[0035] Preferably, the waste liquid storage tank is equipped with a stirring device, a pH detection port, a level gauge and a bottom slag discharge port; the neutralization reaction vessel is equipped with a variable frequency grinding and stirring paddle, the vessel body is equipped with a temperature regulating jacket, the liquid alkali precise dosing device is a molar ratio metering pump, the closed belt hot air drying device, and the discharge end of the airflow ultrafine grinding mill is connected to a high-purity iron red finished product storage silo equipped with a moisture-proof and sealing device.

[0036] Preferably, it also includes an auxiliary control system, which consists of a PLC control cabinet and online monitoring instruments for each unit, used to realize the automatic control of wastewater flow rate, reagent dosage, pH value, reaction temperature, stirring speed and electrolysis parameters, and supports manual operation mode.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] This invention provides a production method and apparatus for recycling hydrochloric acid pickling wastewater, which solves the problems of high energy consumption, low efficiency, insufficient resource recovery, and easy secondary pollution in traditional hydrochloric acid pickling wastewater treatment methods. It achieves clean and efficient disposal of wastewater and full-scale high-value recovery of resources, and has significant economic, environmental, and industrial application value. The specific beneficial effects are as follows:

[0039] 1. High resource recycling efficiency, achieving full-scale, high-value utilization.

[0040] This invention achieves precise recovery and high-value conversion of valuable resources in hydrochloric acid pickling wastewater through a complete process of graded purification and impurity removal, neutralization and iron extraction, and refined electrolytic acid and alkali separation. The wastewater treatment rate reaches 100%, the iron resource recovery rate is ≥98.2%, and the chlorine resource recovery rate is ≥99.0%. It not only produces high-purity iron oxide (≥99%) (which can be directly sold as an industrial raw material), but also regenerates hydrochloric acid and liquid alkali required for the neutralization reaction, meeting the requirements of the pickling process. Furthermore, the regenerated acid and alkali can be directly reused in production processes, breaking through the limitations of traditional processes that can only recover single resources or have low resource utilization value. This achieves full-scale, closed-loop recycling of wastewater resources.

[0041] 2. Low energy consumption and controllable operating costs, suitable for large-scale enterprise production.

[0042] This invention abandons the high-temperature evaporation process of traditional high-temperature roasting methods, and instead utilizes ion-exchange membrane electrolysis technology to regenerate acids and alkalis. Compared to high-temperature roasting, energy consumption per ton of waste liquid is reduced by more than 60%, significantly reducing energy consumption. Simultaneously, the regenerated liquid alkali can be directly reused in neutralization reactions, reducing the consumption of purchased reagents by more than 95%, significantly lowering raw material procurement costs. Furthermore, each stage of the process is equipped with an automated control system, eliminating the need for frequent manual intervention, resulting in low operating costs. The overall operating cost is far lower than traditional disposal and recycling processes, making it suitable for the continuous and large-scale production needs of metal processing enterprises such as steel, stainless steel, and carbon steel structural components.

[0043] 3. Excellent impurity removal effect, resulting in high product quality.

[0044] Through a staged purification and impurity removal process involving manganese removal, heavy metal removal, and silicon removal, the manganese ion removal rate is ≥99%. Heavy metal ions such as copper, zinc, chromium, and nickel are efficiently removed via sulfide precipitation. Silicon impurities are thoroughly removed after flocculation and precipitation with a specialized flocculant. Subsequent refining processes further remove impurities such as Ca²⁺, Mg²⁺, and SO₄²⁻, ensuring the purity of the electrolytic products. The final high-purity iron oxide red has a total impurity content of ≤0.4%. The regenerated hydrochloric acid concentration is highly compatible with the raw material hydrochloric acid, with no interference from impurities, and can be directly reused in the pickling tank, solving the problem of low product purity and inability to be directly reused in traditional processes.

[0045] 4. No secondary pollution, significant environmental benefits.

[0046] This invention produces no unorganized emissions of wastewater, waste gas, or waste residue throughout the entire process. The only solid waste generated is filter cake containing manganese, silicon, and heavy metals, which can be centrally disposed of according to hazardous waste regulations. No large amounts of ferric hydroxide sludge are generated, completely solving the problems of large sludge volume and secondary pollution caused by traditional neutralization and precipitation methods. The heavy metal removal process uses an H2S gas distributor to achieve full gas-liquid contact, eliminating hydrogen sulfide emissions. The ion-exchange membrane electrolysis process produces no harmful gases, and the concentration unit is equipped with a complete condensation and vacuum system, eliminating wastewater discharge. At the same time, the recycling of regenerated acid and alkali significantly reduces the amount of fresh acid and alkali used by enterprises, lowering the total amount of pollutants emitted in the production process, which complies with the national "dual carbon" strategy and strict environmental protection regulations.

[0047] 5. The process and equipment are highly compatible, easy to operate, and highly stable.

[0048] The production apparatus of this invention is modularly designed according to the wastewater treatment process. Each unit is seamlessly connected to the others via pipelines and pumps. Equipped with flow regulating valves, online monitoring instruments, and a PLC automated control system, it enables precise control of process parameters such as wastewater flow rate, reagent dosage, pH value, reaction temperature, and electrolysis parameters, resulting in strong process stability. The core equipment employs a specialized structural design; for example, the precise dosing device in the manganese removal reactor, the grinding and stirring function in the neutralization reactor, and the combination of coarse and fine filtration in the two-stage filtration system are all custom-designed for the process, achieving a high degree of compatibility between the process and the apparatus. Furthermore, the process supports both manual and automatic operation modes, with a low operating threshold, requiring no highly specialized operators. This solves the problems of complex processes, high operational difficulty, and easy equipment clogging associated with traditional high-temperature roasting methods.

[0049] 6. The equipment is highly versatile, has low modification costs, and is widely applicable.

[0050] The production device of this invention features a modular structure, allowing for flexible adjustment of equipment specifications and process parameters based on the wastewater output and composition characteristics of different metal processing enterprises (cold-rolled steel plates, stainless steel pipe fittings, carbon steel structural components, etc.) without the need for overall reconstruction. Existing traditional pickling wastewater treatment equipment can be partially modified to integrate with this process, resulting in low modification costs and short cycles. The process can treat hydrochloric acid pickling wastewater of varying concentrations and impurity types, covering the entire metal processing industry's hydrochloric acid pickling wastewater treatment needs, thus solving the problem of poor adaptability and limited ability to treat only specific types of wastewater in existing improved processes.

[0051] 7. Diversified economic benefits, generating additional revenue for enterprises.

[0052] This invention not only significantly reduces wastewater treatment costs and acid / alkali raw material procurement costs for enterprises, but also generates additional economic benefits through the export of high-purity iron oxide red. Simultaneously, the resource recycling production model helps enterprises obtain national environmental protection subsidies and tax incentives, aligning with the industrial policy orientation of green manufacturing and the circular economy. Compared to traditional processes that only achieve the single goal of "meeting emission standards," this invention achieves the triple goals of "wastewater treatment + resource recovery + economic benefits," providing technical support for the sustainable development of enterprises. Attached Figure Description

[0053] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0054] 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 some embodiments of the present invention, and not all embodiments. 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.

[0055] refer to Figure 1 As shown:

[0056] A production method for recycling hydrochloric acid pickling wastewater includes the following steps:

[0057] 1.S1, Purification and Impurity Removal

[0058] 1) Manganese Removal: A manganese removal agent is added to the hydrochloric acid pickling wastewater to adjust the pH to 7-8. This converts manganese ions in the wastewater into manganese hydroxide or manganese trioxide precipitate, achieving a manganese ion removal rate of over 99%. The manganese removal agent can be one or more of pure iron powder, ferric hydroxide, and ozone. The corresponding core reaction formula is as follows:

[0059] Pure iron powder as a manganese removal agent:

[0060] Mn2+ +Fe + 2H₂O → Mn(OH)₂↓ + Fe 2+ +H2↑

[0061] Ferric hydroxide as a manganese-removing agent:

[0062] Mn 2+ +2Fe(OH)3→Mn(OH)2↓+2Fe(OH)2↓

[0063] When using ozone as a manganese remover, the pH value must first be adjusted to above 5 using ferric hydroxide.

[0064] Mn 2+ +O3+H2O→MnO2↓+O2+2H + ,6FeCl2+O3+3H2O→6FeCl3+6OH - Then add metallic iron powder to adjust FeCl3 back to Fe. 2+ The reaction is 2FeCl3 + Fe → 3FeCl2.

[0065] 2) Heavy metal removal: H2S gas is introduced into the purified liquid after manganese removal, causing heavy metal ions such as copper, zinc, chromium, nickel, lead, and cadmium to form sulfide precipitates. The core reaction formula is Cu 2+ +H₂S=CuS↓+2H + Zn 2+ +H₂S=ZnS↓+2H + 2Cr 3+ +3H₂S=Cr₂S₃↓+6H + Ni 2+ +H₂S=NiS↓+2H + Pb 2+ +H₂S=PbS↓+2H + Cd 2+ +H₂S=CdS↓+2H + .

[0066] 3) Desiliconization: Add a desiliconizing agent to the purified liquid after heavy metal removal. The desiliconizing agent is one or more of polyferric flocculant and polyferric agent to achieve flocculation and precipitation of silicon impurities in the wastewater.

[0067] 2.S2, Filter press to remove tailings

[0068] The mixture after purification and impurity removal by S1 is sent to a filter press for filter press 1 treatment. The filter cake is tailings containing manganese, silicon and heavy metals, which is disposed of in accordance with the hazardous waste regulations. The filtrate is a clean iron-containing liquid, which enters the subsequent process.

[0069] 3. S3, Neutralization reaction. Sodium hydroxide is added to filtrate 1 after pressure filtration 1 to cause acid-base neutralization in the neutralization reaction apparatus;

[0070] 4.S4, Filter out the iron oxide red. The liquid after the neutralization reaction is filtered again by pressure. The filter cake 2 from pressure filtration 2 is dried and ground into high-purity iron oxide red; the purity of the iron oxide red is above 99%.

[0071] 5.S5, Refined electrolytic separation of acids and bases.

[0072] 1) Filtrate 2 enters the purification unit, where a refining agent is added to remove Ca. 2+ Mg 2+ SO4 2- Fe 3+ Al 3+ Heavy metals and suspended solids, etc.

[0073] 2) After purification, the feed solution enters the ion-exchange membrane electrolysis device. A DC voltage is applied to form an electric field: cations migrate to the cathode and anions migrate to the anode, separating acids and bases through electrode reactions.

[0074] 2) The synthetic hydrochloric acid produced by electrolytic anode is returned to the pickling tank for reuse.

[0075] 3) The liquid alkali produced by electrolytic cathode is concentrated to the concentration required for neutralization reaction and then returned to the neutralization reaction device for reuse.

[0076] II. Supporting Equipment

[0077] This invention also discloses a production apparatus for preparing ferrous oxalate from hydrochloric acid pickling wastewater to achieve the above-mentioned process. The apparatus, arranged sequentially along the wastewater treatment flow, includes: a waste liquid storage tank, a purification and impurity removal unit, a primary filter press, a neutralization reaction unit, a secondary filter press, a drying and grinding unit, a refining unit, an ion-exchange membrane electrolysis unit, a concentration unit, and conveying and storage facilities. Each unit is connected to a conveying pump via pipelines. The pipelines are equipped with flow regulating valves and detection instruments to achieve precise control of process parameters. The specific structure is as follows:

[0078] 1. Waste liquid storage tank: Used to store collected hydrochloric acid pickling wastewater. The tank is equipped with a stirring device, pH detection port and liquid level gauge, and a slag discharge port at the bottom, which can realize the homogeneous storage of wastewater and the initial sedimentation of impurities.

[0079] 2. Purification and Impurity Removal Unit: This unit is a series reactor structure, consisting of a manganese removal reactor, a heavy metal removal reactor, and a silicon removal reactor. The manganese removal reactor is equipped with a manganese removal agent dosing device and a pH adjustment device, which can accurately add pure iron powder / ferric hydroxide / ozone and adjust the pH to 7-8. The heavy metal removal reactor is equipped with an H2S gas inlet and a gas distributor to ensure full contact between H2S and wastewater. The silicon removal reactor is equipped with a silicon removal agent dosing device and a low-speed stirring device to ensure that the flocculation reaction proceeds fully. Each reactor is equipped with online temperature and pH monitoring instruments.

[0080] 3. Primary filter press: A plate and frame filter press is used and connected to the discharge end of the purification and impurity removal unit. It is used to separate the tailing filter cake containing manganese, silicon and heavy metals. The filter plate is equipped with an anti-clogging filter screen and has a high-pressure pressing function to improve the solid-liquid separation efficiency.

[0081] 4. Neutralization Reaction Unit: The core is a neutralization reaction vessel with grinding and stirring functions. The vessel is equipped with a variable frequency grinding and stirring paddle, which can adjust the stirring speed. It is also equipped with a sodium hydroxide precision dosing device, which controls the amount of sodium hydroxide added through a molar ratio metering pump. The vessel body is equipped with a jacket, which can adjust the reaction temperature according to the needs to ensure the rate and purity of the neutralization reaction.

[0082] 5. Secondary filter press: A precision filter press is used, with a filtration accuracy higher than that of the primary filter press. It is used to separate the iron oxide filter cake from acid and alkali solutions. The filtrate outlet is connected to the material pipe of the refining unit, and the filter cake outlet is connected to the drying and grinding unit.

[0083] 6. Drying and grinding unit: It includes a hot air drying device and an ultrafine grinding mill in sequence; the hot air drying device is a closed belt dryer, which adopts low temperature hot air drying, and the moisture content of the material after drying is ≤0.5%; the ultrafine grinding mill is an airflow grinding equipment, which can grind the dried high-purity iron oxide to the particle size required by industry. The discharge end is equipped with a finished product storage silo, which is equipped with moisture-proof and sealing devices.

[0084] 7. Refining Unit: Includes refining tower and chelation tower; equipped with a metering and control system to precisely control the proportioning and addition of refining agents.

[0085] 8. Ion membrane electrolysis unit: including an electrolytic cell with an alkali chamber (cathode chamber) and an acid chamber (anode chamber).

[0086] 9. Concentration Unit: Includes one of the following: triple / quadruple / multi-effect evaporator, falling film evaporator, rising film evaporator, forced circulation evaporator, low temperature evaporation device, etc., and is equipped with an evaporator separator (gas-liquid separator), condenser / surface condenser, vacuum pump / vacuum system, condensate tank, condensate pump, and non-condensable gas separator.

[0087] 10. Conveying and storage facilities.

[0088] 11. Auxiliary control system: including PLC control cabinet and online monitoring instruments for each unit, which can realize the automatic control of parameters such as wastewater flow rate, reagent dosage, pH value, reaction temperature, and stirring speed, while also supporting manual operation to adapt to different working conditions.

[0089] The process apparatus of this invention is as follows: waste liquid storage tank → manganese removal reactor → heavy metal removal reactor → silicon removal reactor → primary plate and frame filter press → neutralization reactor with grinding and stirring → secondary precision filter press → closed belt hot air drying device → airflow ultrafine grinding mill → high-purity iron oxide red finished product silo. The filtrate is sent from the filtrate outlet of the secondary filter press to the refining device → ion membrane electrolysis cathode → synthesized HCl is sent to the pickling tank, ion membrane electrolysis anode → liquid alkali → concentration, and then returned to the neutralization reactor for recycling.

[0090] Application Example 1: Treatment of hydrochloric acid pickling wastewater from a cold-rolled steel plate plant

[0091] 1. Basic parameters of wastewater raw materials

[0092] 1000 kg of hydrochloric acid pickling wastewater from a cold-rolled steel plate plant was selected. The core components and contents of the wastewater are as follows: ferrous chloride (FeCl2) 11.2%, free hydrochloric acid (HCl) 6.2%, total chlorine (Cl⁻) 19.0%; it contains trace impurities such as manganese ions 0.35%, silicon impurities 0.21%, zinc ions (Zn²⁺) 0.09%, and chromium ions (Cr³⁺) 0.004%; it also contains suspended solids (SS) 1.6% and organic additive hexamethylenetetramine 0.23%. The wastewater is strongly acidic, has high salinity, and contains a variety of impurities.

[0093] 2. Process Operation Steps

[0094] 1) Purification and Impurity Removal: The wastewater is transported to a manganese removal reactor, where pure iron powder is added as a manganese removal agent. The pH value of the wastewater is precisely adjusted to 7.5 using a pH adjustment device. After the reaction, the manganese ion removal rate reaches 99.2%. The purified liquid after manganese removal is then transported to a heavy metal removal reactor, where H2S gas is introduced into the liquid through a gas distributor and the reaction continues for 30 minutes to allow heavy metal ions to fully precipitate as sulfides. The liquid is then transported to a silicon removal reactor, where polyferric silicate flocculant is added, and a low-speed stirring device is activated for 20 minutes to achieve complete removal of silicon impurities. 2) Primary Filtration: The purified and impurity-removed mixture is transported to a primary plate and frame filter press, where the high-pressure pressing function is activated for solid-liquid separation. 28.6 kg of filter cake containing manganese, silicon, and heavy metals is obtained. The filtrate is a clean iron-containing liquid, which is then transported to a neutralization reactor. 3) Neutralization reaction: Sodium hydroxide is added to the iron-containing liquid in the neutralization reactor at a molar ratio of acid:base = 1:1 via a molar ratio metering pump. The variable frequency grinding and stirring paddle is turned on, and the stirring speed is adjusted to 300 r / min. The reaction is continued for 60 min to complete the acid-base neutralization reaction. 4) Secondary pressure filtration: The neutralized liquid is sent to a secondary precision filter press for fine filtration, and 132.8 kg of iron oxide red filter cake (moisture content 23.6%) is obtained. The filtrate is sent to the refining unit. Barium chloride + sodium carbonate + chelating resin are added to the refining unit as a refining agent, and the reaction is carried out for 40 min to remove impurities such as Ca²+, Mg²+, and SO4²- from the liquid. The refined liquid is sent to an ion-exchange membrane electrolysis device. The electrolysis cell voltage is set to 3.2V and the current density to 2000A / m², and electrolysis is carried out continuously for 90 min. The liquid alkali obtained from the electrolytic cathode is sent to a triple-effect evaporator and concentrated to the 30% concentration commonly used for industrial neutralization. 5) Drying and Grinding: The iron oxide filter cake obtained from the secondary pressure filtration is conveyed to a closed belt hot air drying device for low-temperature hot air drying, and then sent to an airflow ultrafine grinding mill for grinding to 200 mesh to obtain high-purity iron oxide finished product, which is then conveyed to a finished product storage silo equipped with moisture-proof and sealing devices. 6) Recycling: The synthetic hydrochloric acid produced by ion-exchange membrane electrolytic anode is directly returned to the pickling tank of the cold-rolled steel plate plant for reuse, and the concentrated 30% liquid alkali is returned to the neutralization reactor for reuse.

[0095] 3. Processing Results

[0096] In this embodiment, the wastewater treatment rate reaches 100%; the regenerated hydrochloric acid concentration is 6.0%, and the reuse amount is 925 kg, which can be directly reused in the pickling process without interference from impurity ions; 69.8 kg of high-purity iron oxide red product is obtained, with an iron oxide red purity of 99.7% (200 mesh), and the total content of impurities such as manganese, silicon, and heavy metals is ≤0.3%; 263.5 kg of 50% liquid alkali is regenerated, with a liquid alkali reuse rate of 95%; the iron resource recovery rate is 98.9%, and the chlorine resource recovery rate is 99.0%; only 28.6 kg of hazardous waste tailings filter cake is generated, which can be centrally disposed of in accordance with hazardous waste regulations, without generating secondary pollution.

[0097] Application Example 2: Treatment of Hydrochloric Acid Pickling Wastewater from a Stainless Steel Pipe Fittings Factory

[0098] 1. Basic parameters of wastewater raw materials

[0099] 1000 kg of hydrochloric acid pickling wastewater generated by a stainless steel pipe fitting factory was selected. The core components and contents of the wastewater are as follows: ferrous chloride (FeCl2) 6.2%, free hydrochloric acid (HCl) 10.0%, total chlorine (Cl⁻) 19.1%; it contains trace impurities such as manganese ions 0.28%, silicon impurities 0.15%, chromium ions (Cr³⁺) 0.021%, and nickel ions (Ni²⁺) 0.014%; it also contains suspended solids (SS) 0.7% and organic additives and surfactants 0.21%. The wastewater has a high content of free hydrochloric acid and contains nickel and chromium impurities unique to stainless steel processing.

[0100] 2. Process Operation Steps

[0101] 1) Purification and Impurity Removal: Wastewater is transported to a manganese removal reactor. Ferric hydroxide is added to adjust the pH to 7.2, and ozone is then introduced as a manganese removal agent. After the reaction, the manganese ion removal rate reaches 99.5%. The purified liquid after manganese removal is then transported to a heavy metal removal reactor, where H2S gas is introduced and reacted for 25 minutes to precipitate copper, zinc, chromium, nickel, and other heavy metal ions as sulfides. The liquid is then transported to a silicon removal reactor, where polyferric silicate flocculant is added and stirred for 15 minutes to remove silicon impurities. 2) Primary Filtration: The purified and impurity-removed mixture is sent to a primary plate and frame filter press for solid-liquid separation, yielding 19.3 kg of tailings filter cake. The clean iron-containing filtrate is then transported to a neutralization reactor. 3) Neutralization Reaction: Sodium hydroxide is added to the neutralization reactor at a 1:1 acid-to-base molar ratio. The grinding and stirring function is activated at 300 rpm, and neutralization is completed after 60 minutes of reaction. 4) Secondary Filtration: The neutralized liquid is fed into a secondary precision filter press to separate 75.1 kg of iron oxide red filter cake (22.5% moisture content); the filtrate is sent to a refining unit, where barium hydroxide, sodium sulfide, and polyaluminum chloride are added as refining agents, and the reaction is carried out for 35 min; the refined liquid is then sent to an ion-exchange membrane electrolysis device, where the electrolysis cell voltage is set to 3.0V and the current density to 1800A / m², and electrolysis is carried out for 80 min; the liquid alkali obtained from the electrolytic cathode is sent to a falling film evaporator for concentration to 30%. 5) Drying and Grinding: The iron oxide red filter cake is dried by a closed belt hot air system and then ground to 200 mesh using an airflow ultrafine grinding mill to obtain high-purity iron oxide red finished product. 6) Recycling: The synthetic hydrochloric acid obtained from the electrolytic anode is returned to the pickling tank of the stainless steel pipe fittings plant for reuse, and the concentrated liquid alkali is returned to the neutralization reactor for reuse.

[0102] 3. Processing Results

[0103] In this embodiment, the wastewater treatment rate reaches 100%; the regenerated hydrochloric acid concentration is 9.8%, and the reuse amount is 938 kg, which can be directly reused in the pickling process of stainless steel pipe fittings; 39.0 kg of high-purity iron oxide red product is produced, with a purity of 99.6% (200 mesh), and the total content of impurities such as manganese, silicon, and heavy metals is ≤0.4%; 317.1 kg of 45% liquid alkali is regenerated, with a liquid alkali reuse rate of 96%; the iron resource recovery rate is 98.5%, and the chlorine resource recovery rate is 99.1%; only 19.3 kg of hazardous waste tailings filter cake is generated, and there is no unorganized emission of wastewater or waste gas, resulting in significant environmental benefits.

[0104] Application Example 3: Treatment of Hydrochloric Acid Pickling Wastewater from a Carbon Steel Structural Components Factory

[0105] 1. Basic parameters of wastewater raw materials

[0106] 1000 kg of hydrochloric acid pickling wastewater generated by a carbon steel structural parts factory was selected. The core components and contents of the wastewater are as follows: ferrous chloride (FeCl2) 16.4%, free hydrochloric acid (HCl) 3.2%, total chlorine (Cl⁻) 28.1%; it contains trace impurities such as manganese ions 0.42%, silicon impurities 0.28%, lead ions (Pb²+) 0.002%, and cadmium ions (Cd²+) 0.0001%; ​​it also contains suspended solids (SS) 3.7% and organic additive corrosion inhibitors 0.43%. The wastewater has high levels of ferrous chloride and suspended solids, and contains heavy metal impurities such as lead and cadmium.

[0107] 2. Process Operation Steps

[0108] 1) Purification and Impurity Removal: Wastewater is transported to a manganese removal reactor, where ferric hydroxide is added as a manganese removal agent, and the pH is adjusted to 7.8. After the reaction, the manganese ion removal rate reaches 99.1%. The purified liquid after manganese removal is then transported to a heavy metal removal reactor, where H2S gas is introduced and reacted for 35 minutes to remove heavy metal ions such as lead and cadmium. The liquid is then transported to a silicon removal reactor, where polyferric silicate flocculant, modified polysilicic acid flocculant, and activated silica flocculant are added and stirred for 25 minutes to achieve deep removal of silicon impurities. 2) Primary Filtration: The purified and impurity-removed mixture is sent to a primary plate and frame filter press to separate 41.2 kg of tail filter cake. The clean iron-containing filtrate is then transported to a neutralization reactor. 3) Neutralization Reaction: Sodium hydroxide is added to the neutralization reactor at a molar ratio of acid:base = 1:1. The grinding and stirring paddle is turned on at a speed of 300 r / min, and the reaction is completed in 60 minutes to achieve acid-base neutralization. 4) Secondary Filtration: The neutralized liquid is fed into a secondary precision filter press to separate 135.8 kg of iron oxide red filter cake (moisture content 24.1%). The filtrate is sent to a refining unit, where sodium carbonate, polyacrylamide, and chelating resin are added as a refining agent, and the reaction is carried out for 45 min. The refined liquid is then sent to an ion-exchange membrane electrolysis device, where the electrolysis cell voltage is set to 3.3V and the current density to 2200A / m², and electrolysis is carried out for 100 min. The liquid alkali obtained from the electrolysis cathode is sent to a forced circulation evaporator for concentration to 30%. 5) Drying and Grinding: The iron oxide red filter cake is dried by a closed belt hot air system and then ground to 200 mesh using an airflow ultrafine grinding mill to obtain high-purity iron oxide red finished product. 6) Recycling: The synthetic hydrochloric acid obtained from the electrolysis anode is returned to the pickling tank of the carbon steel structural parts factory for reuse, and the concentrated liquid alkali is returned to the neutralization reactor for reuse.

[0109] 3. Processing Results

[0110] In this embodiment, the wastewater treatment rate reached 100%; the regenerated hydrochloric acid concentration was 3.1%, with a reuse rate of 912 kg, which can be directly reused in the pickling process of carbon steel structural parts; 89.2 kg of high-purity iron oxide red product was obtained, with a purity of 99.8% (200 mesh), and the total content of impurities such as manganese, silicon, and heavy metals was ≤0.2%, making it a high-quality industrial iron oxide red raw material; 259.3 kg of 50% liquid alkali was regenerated, with a liquid alkali reuse rate of 94%; the iron resource recovery rate was 99.1%, and the chlorine resource recovery rate was 99.1%; only 41.2 kg of hazardous waste tailings filter cake was generated, achieving full-scale high-value resource recovery of wastewater.

[0111] It should be understood that numerous specific implementation decisions can be made during the development of any practical implementation, such as in any engineering or design project. Such development efforts may be complex and time-consuming, but for those skilled in the art who benefit from this disclosure, the development effort will be a routine work of design, manufacturing, and production without requiring much experimentation.

[0112] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A production method for recycling hydrochloric acid pickling wastewater, characterized in that, Includes the following steps: S1. Purification and impurity removal: The hydrochloric acid pickling wastewater was sequentially treated to remove manganese, heavy metals, and silicon. During the manganese removal process, a manganese removal agent was added to the wastewater and the pH value was adjusted to 7-8 to achieve a manganese ion removal rate of over 99%. S2. Filter press to remove tailings: The mixture after purification and impurity removal by S1 is subjected to primary pressure filtration to obtain the first filter cake and the first filtrate. The first filter cake is tailings containing manganese, silicon and heavy metals, and the first filtrate is clean iron-containing liquid. S3, neutralization reaction: Sodium hydroxide is added to the first filtrate to complete the acid-base neutralization reaction in the neutralization reaction apparatus; S4. Filter out iron oxide red: The neutralized liquid is subjected to two-stage pressure filtration to obtain a second filter cake and a second filtrate. The second filter cake is dried and ground into high-purity iron red with a purity of over 99%, and the second filtrate is used in subsequent processes. S5. Refined electrolytic separation of acids and alkalis: ① The second filtrate enters the refining unit, where a refining agent is added to remove Ca²+, Mg²+, SO₄²-, Fe³+, Al³+, heavy metals, and suspended solids; ②After purification, the feed solution enters the ion membrane electrolysis device, where a DC voltage is applied to form an electric field, causing cations to migrate to the cathode and anions to migrate to the anode, thus achieving acid-base separation through electrode reactions; ③ The synthetic hydrochloric acid produced by electrolytic anode is directly returned to the pickling tank for reuse; ④ The liquid alkali produced by the electrolytic cathode is concentrated to the concentration required for the neutralization reaction and then returned to the neutralization reaction device for reuse.

2. The production method according to claim 1, characterized in that, The manganese removal agent in S1 is one or more of pure iron powder, ferric hydroxide, and ozone. During the manganese removal process, when ozone is used as the manganese removal agent, the pH of the wastewater must first be adjusted to above 5 with ferric hydroxide, and then metallic iron powder is added to reduce the FeCl3 generated in the reaction to FeCl2.

3. The production method according to claim 1, characterized in that, In S1, the removal of heavy metals involves introducing H2S gas into the purified liquid after manganese removal, causing heavy metal ions such as copper, zinc, chromium, nickel, lead, and cadmium to precipitate as sulfides. The desiliconizing agent is one or more of polyferric silicate flocculants, modified polysilicic acid flocculants, and activated silica flocculants, which remove silicon impurities through flocculation and precipitation.

4. The production method according to claim 1, characterized in that, The refining agent in S5 is one or more of barium chloride, barium hydroxide, sodium hydroxide, sodium carbonate, sodium sulfide, polyaluminum chloride, polyferric sulfate, and polyacrylamide, and is used in combination with a chelating resin.

5. A production apparatus for recycling hydrochloric acid pickling wastewater according to any one of claims 1-4, characterized in that, The waste hydrochloric acid pickling waste liquid recycling and treatment process includes, in sequence: waste liquid storage tank, purification and impurity removal unit, primary filter press equipment, neutralization reaction unit, secondary filter press equipment, drying and grinding unit, refining unit, ion membrane electrolysis unit, and concentration unit. Each unit is connected to a transfer pump through pipelines, and the pipelines are equipped with flow regulating valves and detection instruments. The purification and impurity removal unit is a series reactor structure, which includes a manganese removal reactor, a heavy metal removal reactor, and a silicon removal reactor in sequence. The neutralization reaction unit is a reaction vessel with grinding and stirring functions, and is equipped with a precise liquid alkali dosing device. The drying and grinding unit includes, in sequence, a closed belt hot air drying device and an airflow ultrafine grinding mill. The refining unit includes a refining tower and a chelation tower; The ion-exchange membrane electrolysis unit includes an electrolysis cell with an alkali chamber and an acid chamber; The concentration unit is one of the following: triple-effect evaporator, quadruple-effect evaporator, multi-effect evaporator, falling film evaporator, rising film evaporator, forced circulation evaporator, or low-temperature evaporation device, and is equipped with an evaporator separator, condenser, vacuum pump, condensate tank, condensate pump, and non-condensable gas separator.

6. The production apparatus according to claim 5, characterized in that, The demanganese reactor is equipped with a demanganese removal agent dosing device and a pH adjustment device; the heavy metal removal reactor is equipped with an H2S gas inlet and a gas distributor; the desiliconization reactor is equipped with a desiliconization agent dosing device and a low-speed stirring device, and all three reactors are equipped with online temperature and pH monitoring instruments.

7. The production apparatus according to claim 5, characterized in that, The primary filter press is a plate and frame filter press, with filter plates equipped with anti-clogging filter screens and high-pressure pressing function; the secondary filter press is a precision filter press, with a filtration accuracy higher than that of the primary filter press, the filtrate outlet is connected to the material pipe of the refining unit, and the filter cake outlet is connected to the drying and grinding unit.

8. The production apparatus according to claim 5, characterized in that, The waste liquid storage tank is equipped with a stirring device, a pH detection port, a liquid level gauge, and a bottom slag discharge port; the neutralization reaction vessel is equipped with a variable frequency grinding and stirring paddle, the vessel body is equipped with a temperature regulating jacket, the liquid alkali precise dosing device is a molar ratio metering pump, the closed belt hot air drying device, and the discharge end of the airflow ultrafine grinding mill is connected to a high-purity iron red finished product storage silo equipped with a moisture-proof and sealing device.

9. The production apparatus according to claim 5, characterized in that, It also includes an auxiliary control system, which consists of a PLC control cabinet and online monitoring instruments for each unit. This system is used to automatically control wastewater flow rate, reagent dosage, pH value, reaction temperature, stirring speed, and electrolysis parameters, and also supports manual operation mode.

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