A tin-containing clean water recovery system

Abstract

This invention provides a tin-containing clean water recovery system, belonging to the field of water recycling technology. It includes a collection unit, a concentration unit, a filter press recovery unit, and a control system. The collection unit includes a storage tank for collecting tin-containing clean water wash water. The concentration unit includes a unit membrane filtration device, whose inlet is connected to the outlet of the storage tank. The membrane module is made of polyamide composite material and has a polysulfone or polyethersulfone support layer and an interfacial polymerized polyamide functional separation layer. The membrane filtration device is connected to a cross-flow circulation loop. The filter press recovery unit includes a filter press device, whose inlet is connected to the concentrate outlet of the membrane filtration device. The control system is electrically connected to each transfer pump, circulation pump, and filter press pump. This invention uses a purely physical membrane separation process to concentrate, enrich, and recover low-concentration tin-containing clean water wash water via filter press filtration. No chemical reagents are required, resulting in a high tin recovery rate, low tin content in the effluent, and high metallic tin content in the produced tin sludge, achieving efficient tin resource recovery and wastewater reduction.

Description

Technical Field

[0001] This invention relates to the field of water recycling equipment technology, and specifically to a tin-containing clean water recycling system. Background Technology

[0002] Tin plating is one of the most widely used surface treatment processes in the electronics industry. In the production of printed circuit boards (PCBs), both the tin plating process on pattern plating lines and the tin stripping process after etching require large amounts of water to rinse the workpieces to remove residual plating and stripping solutions. This rinsing water is called tin-containing rinse water, and the concentration of tin is typically between 50 and 200 ppm. For example, a typical pattern plating line can generate a daily overflow of 28.8 tons of tin-plating rinse water, and a daily overflow of 7.2 tons of tin-removing rinse water. Based on this calculation, a single production line can discharge several tons of tin metal annually with the rinse water.

[0003] Currently, the industry's treatment of tin-containing wastewater is extremely rudimentary: it is directly discharged into the plant's wastewater treatment plant, where it is mixed with wastewater from other processes and then neutralized and precipitated. During this process, tin ions are converted into hydroxides that precipitate into the sludge. However, due to the extremely low tin concentration in the wastewater, the tin content in the sludge is far below the economically viable threshold for recovery, meaning that tin-containing sludge can only be disposed of as general solid waste or hazardous waste, failing to achieve the valuable recovery of tin resources. This not only results in a significant waste of tin, a strategic non-ferrous metal, but also increases the company's hazardous waste disposal costs and environmental management burden.

[0004] Existing technologies for the treatment and recycling of tin-containing wastewater are mainly divided into two categories: chemical precipitation and membrane separation.

[0005] Chemical precipitation typically involves adding alkaline agents such as sodium hydroxide and sodium carbonate to wastewater to form insoluble tin ions, followed by solid-liquid separation to recover the tin sludge. While this method is simple to operate, it has several significant drawbacks: First, chemical precipitation requires continuous addition of large amounts of reagents, resulting in high operating costs. Second, for low-concentration clean water with tin concentrations below 200 ppm, chemical precipitation alone has low removal rates and difficulties in solid-liquid separation, often requiring the addition of coagulants and flocculants to enhance the precipitation effect, further increasing reagent consumption and sludge production. Third, the generated sludge is large in volume and has a high water content, leading to high energy consumption and disposal costs for subsequent dewatering. Literature indicates that the low removal rate, difficult solid-liquid separation, and large sludge production of chemical precipitation increase the difficulty of subsequent treatment processes.

[0006] Membrane separation utilizes the selective permeation properties of membranes to concentrate and separate metal ions in wastewater, offering advantages such as high-quality effluent, stable operation, and ease of automation. Researchers have already explored the use of nanofiltration, reverse osmosis, or microfiltration membranes for treating tin-containing wastewater. For example, they have employed a combination of chemical precipitation and membrane separation to remove tin ions, or used multi-stage acid-resistant pressure membrane elements to progressively concentrate acidic tin-containing wastewater. However, most existing membrane separation solutions are designed for wastewater with high tin concentrations (such as tin stripping wastewater and working mother liquor), lacking specialized treatment processes for clean water wash water with tin concentrations of only 50–200 ppm. Directly applying membrane concentration solutions for high-concentration wastewater would result in problems such as excessively large membrane area, high system investment, and uneconomical energy consumption. Furthermore, existing membrane separation devices commonly suffer from membrane fouling and concentration polarization during long-term operation, leading to membrane flux decline, high cleaning frequency, and short membrane life, making long-term stable operation difficult.

[0007] In summary, existing technologies for the resource recovery of low-concentration tin-containing washing water suffer from significant membrane fouling and concentration polarization problems, leading to membrane flux decay, high cleaning frequency, and short membrane life, making it difficult to achieve long-term stable operation. Therefore, there is an urgent need to develop a tin recovery system specifically designed for low-concentration tin-containing washing water, with economical investment and operating costs, high recovery rate, good automation, and the ability to operate stably for a long time. Summary of the Invention

[0008] In view of this, the present invention provides a tin-containing clean water recovery system, which can solve the problems of tin resource waste caused by direct discharge of low-concentration tin-containing clean water in the prior art, large consumption of reagents and large amount of sludge in chemical precipitation method, and poor adaptability of existing membrane separation schemes to low-concentration clean water and serious membrane fouling.

[0009] To address the aforementioned technical problems, this invention provides a tin-containing clean water recovery system, comprising a collection unit, a concentration unit, a filter press recovery unit, and a control system. The collection unit includes at least one storage tank, the inlet of which is sealed to the tin-containing clean water discharge outlet of the electroplating production line via a collection pipeline, for collecting and temporarily storing tin-containing clean water from various washing processes of the electroplating production line. The concentration unit includes a unit membrane filtration device, the inlet of which is sealed to the outlet of the storage tank via a delivery pipeline. The unit membrane filtration device is used to concentrate the tin-containing clean water, retaining tin ions in the influent in the concentrate, while simultaneously discharging the permeate with a significantly reduced tin concentration. The filter press recovery unit includes a filter press device, the inlet of which is sealed to the concentrate outlet of the unit membrane filtration device via a concentrate pipeline. The filter press device is used to perform solid-liquid separation on the concentrate, producing tin dioxide sludge that can be directly sold or reused. The signal input terminals of the control system are electrically connected to the level sensors and pressure sensors installed in each unit, and the signal output terminals of the control system are electrically connected to the delivery pumps on each delivery pipeline, the circulation pumps of the unit membrane filtration devices, and the filter press pumps of the filter press devices, so as to realize the automated operation of the system.

[0010] Furthermore, the unit membrane filtration device includes a membrane housing and at least one set of membrane modules disposed inside the membrane housing. The membrane module is a spiral wound nanofiltration membrane module or a spiral wound reverse osmosis membrane module. The membrane housing has a feed inlet at the front end, a concentrate outlet at the rear end, and a permeate outlet on the side. The membrane sheet of the membrane module is made of polyamide composite material, with a porous support layer of polysulfone or polyethersulfone as the base membrane and an ultrathin polyamide functional separation layer formed by interfacial polymerization. This ultrathin polyamide functional separation layer has a negatively charged surface, exhibiting preferential adsorption and efficient retention of divalent tin ions.

[0011] Furthermore, the membrane housing is made of stainless steel through welding, and the inner wall is polished. The membrane module has a detachable installation structure, with sealing end caps at both ends. The sealing end caps are sealed to the inner wall of the membrane housing through O-rings. The O-rings are made of fluororubber through molding and vulcanization, and have excellent resistance to acid and alkali corrosion and aging.

[0012] Furthermore, the unit membrane filtration device is connected to a cross-flow circulation loop. The cross-flow circulation loop includes a circulation pump and circulation piping. One end of the circulation piping is connected to the concentrate outlet of the membrane housing, and the other end is connected to the feed inlet of the membrane housing, forming a closed circulation channel. The circulation pump is installed in series on the circulation piping. Tin-containing rinse water circulates multiple times across the surface of the membrane module in a cross-flow manner within the closed loop formed by the membrane housing and circulation piping. In each cycle, some water molecules permeate through the membrane module to form permeate, while tin ions are retained and returned to the circulation loop with the concentrate, achieving a gradual enrichment of tin concentration.

[0013] Furthermore, the circulating pump is a Grundfos CRN series vertical multistage centrifugal pump with a stainless steel pump body. The delivery pump installed on the delivery pipeline is a Southern Pump Industry Co., Ltd. CHL series lightweight horizontal multistage centrifugal pump with a stainless steel pump body.

[0014] Furthermore, the storage tank is made of high-density polyethylene using a rotational molding process, resulting in a smooth inner wall that is resistant to acid and alkali corrosion. A liquid level sensor, specifically an Omron E2K-L series capacitive liquid level sensor, is installed inside the tank to monitor the liquid level in real time. When the liquid level reaches the preset upper limit, the sensor sends a signal to the control system, which then activates the transfer pump to deliver the tin-containing rinse water to the unit membrane filter. When the liquid level drops to the preset lower limit, the control system stops the transfer pump.

[0015] Furthermore, the filter press is either a chamber filter press or a plate and frame filter press. The filter plates are made of polypropylene using injection molding, exhibiting resistance to acid and alkali corrosion and high mechanical strength. The filter cloth is made of polyester or polypropylene filament cloth, offering good air permeability and retention. The filter press pump is a pneumatic diaphragm pump, specifically an ARO series pneumatic double diaphragm pump manufactured by Ingersoll Rand, with a pump body made of polypropylene and a diaphragm made of polytetrafluoroethylene (PTFE).

[0016] Furthermore, the control system includes a programmable logic controller (PLC) and a touchscreen human-machine interface. The PLC is a Siemens SIMATIC S7-1200, with a CPU model of 1214CDC / DC / DC, and is equipped with digital input modules, digital output modules, and analog input modules. The touchscreen human-machine interface is a Siemens SIMATIC HMI KTP700 Basic color touchscreen, which exchanges data with the PLC via an Ethernet communication interface.

[0017] Furthermore, the system also includes an online monitoring unit. The online monitoring unit includes a conductivity sensor installed on the permeate line of the unit membrane filtration device and a pressure sensor installed on the concentrate line. The conductivity sensor is an InPro 7100 series conductivity sensor manufactured by Mettler Toledo, used to monitor changes in the conductivity of the permeate in real time, indirectly reflecting the concentration level of residual metal ions in the permeate. The pressure sensor is a Honeywell PX2 series heavy-duty pressure sensor, used to monitor the pressure value in the concentrate line in real time. Both the conductivity sensor and the pressure sensor are electrically connected to the analog input module of the control system.

[0018] Furthermore, the system also includes an alarm indication unit. The alarm indication unit includes an audible and visual alarm and status indicator lights fixedly installed on the control system's electrical control cabinet panel. The audible and visual alarm is a JD series integrated audible and visual alarm manufactured by Shanghai Tianyi Electric Co., Ltd., with a sound pressure level of not less than 90dB. The status indicator lights include a green indicator light to indicate the system's power-on status, a yellow indicator light to indicate the operating status of the concentration unit, and a red indicator light to indicate the operating status of the filter press recovery unit.

[0019] In summary, compared with the prior art, this application includes at least one of the following beneficial technical effects: 1. This invention employs a unit membrane filtration device to concentrate and enrich tin-containing washing water. Utilizing the high retention characteristics of nanofiltration or reverse osmosis membranes for divalent tin ions, it achieves effective recovery of trace amounts of tin ions from low-concentration tin-containing washing water. This technical solution fundamentally solves the problem of tin resource waste caused by the direct discharge of low-concentration tin-containing washing water in existing technologies.

[0020] 2. This invention employs a purely physical membrane separation process. The entire concentration and enrichment process requires no addition of any chemical precipitating agents, completely avoiding the problem of large-scale reagent consumption inherent in chemical precipitation methods. Compared to chemical precipitation methods, the system of this invention does not require continuous purchase and addition of chemical agents such as sodium hydroxide, sodium carbonate, and coagulants during long-term operation, significantly reducing operating costs. Simultaneously, because no additional chemical substances are introduced, the system only produces a small amount of high-concentration concentrate after membrane concentration, without generating low-value chemical sludge, greatly reducing solid waste generation and disposal costs. This technical solution solves the problems of high reagent consumption and large sludge volume in existing chemical precipitation methods.

[0021] 3. This invention, by setting up a cross-flow circulation loop, allows tin-containing rinse water to flow at high speed across the membrane module surface in a cross-flow manner. Utilizing fluid shear force, it continuously washes the membrane surface, effectively inhibiting the deposition of tin ions and other impurities, and the formation of a concentration polarization layer. This design significantly slows down the rate of membrane flux decay, extends the membrane cleaning cycle and service life, and reduces operating and maintenance costs. This technical solution solves the problems of severe membrane fouling and high cleaning frequency commonly found in existing membrane separation solutions.

[0022] 4. This invention further enhances the separation efficiency and stability of the system through the synergistic optimization design of membrane module materials and structure. The membrane module adopts a spiral wound structure, providing a large effective membrane area within a limited volume, increasing the processing capacity per unit volume, and significantly reducing the overall system footprint. The membrane surface uses an ultrathin functional separation layer of polyamide formed by interfacial polymerization. This separation layer has a negative charge on its surface, exhibiting both electrostatic adsorption and high-precision retention of divalent tin ions. The base membrane uses a porous support layer of polysulfone or polyethersulfone, providing excellent mechanical strength and chemical stability. This technical solution enables the system to maintain high tin enrichment capacity and stable long-term operating performance even under low-concentration feed water conditions.

[0023] 5. This invention employs an automated control system comprised of a programmable logic controller (PLC) and a touchscreen human-machine interface, coupled with an online monitoring unit consisting of a level sensor, conductivity sensor, and pressure sensor. This achieves fully automated operation of the entire process, from collection and concentration of tin-containing wastewater to pressure filtration and recovery. The system can automatically start and stop each unit and adjust its operating status according to preset process parameters, requiring no manual supervision. The conductivity sensor monitors the permeate quality in real time, and the pressure sensor monitors the pipeline pressure. In case of abnormalities, the system automatically triggers an audible and visual alarm. This technical solution significantly reduces the intensity of manual operation and labor costs, while improving the reliability and safety of system operation.

[0024] 6. This invention forms a complete "collection-concentration-filtration" process chain through the modular integrated design of the collection unit, concentration unit, and pressure filtration recovery unit. The units are connected via standardized pipeline and electrical interfaces, allowing them to be maintained, repaired, and replaced as independent modules, or operated collaboratively through unified scheduling by the control system. When the production line scales up, the system can be expanded by increasing the number of modules or by operating them in parallel, demonstrating excellent scalability. This modular structure facilitates daily maintenance and troubleshooting, extends the overall service life of the system, and reduces overall operating costs.

[0025] 7. The system of this invention has a small footprint and low energy consumption, making it suitable for deployment in idle spaces near existing electroplating production lines without requiring significant modifications to the original production layout. The entire system generates no secondary pollution, and the tin content in the wastewater is below 10 ppm, meeting environmental emission requirements and allowing for direct discharge into a wastewater treatment plant for subsequent routine treatment. This technical solution provides electroplating enterprises with an economical, practical, and environmentally friendly solution for the resource recovery of tin-containing clean water. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the tin-containing clean water recovery system of the present invention; Figure 2This is a schematic diagram of the unit membrane filtration device in the tin-containing clean water recovery system of the present invention; Figure 3 This is a schematic diagram of the cross-flow circulation loop in the tin-containing clean water recovery system of the present invention; Figure 4 This is a block diagram showing the connection relationship of the control system in the tin-containing clean water recovery system of the present invention; Figure 5 This is a schematic diagram of the filter press recovery unit in the tin-containing clean water recovery system of the present invention.

[0027] Explanation of reference numerals in the attached drawings: 101, Collection unit; 102, Storage tank; 103, Transfer pump; 104, Concentration unit; 105, Unit membrane filtration device; 106, Circulation pump; 107, Filtration recovery unit; 108, Filtration device; 109, Control system; 201, Membrane housing; 202, Membrane module; 203, Feed inlet; 204, Concentrate outlet; 205, Permeate outlet; 206, Sealing end cap; 207, O 301. O-ring seal; 302. Circulation pipeline; 303. Concentrate; 304. Permeate; 405. Programmable logic controller; 406. Touch screen human-machine interface; 407. Liquid level sensor; 408. Conductivity sensor; 409. Pressure sensor; 4000. Transfer pump; 401. Circulation pump; 402. Filter press pump; 403. Audible and visual alarm; 410. Status indicator light; 501. Filter plate; 502. Filter cloth; 503. Filter press pump; 504. Tin sludge collection container; 505. Concentrate inlet; 506. Filtrate outlet. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will be described in conjunction with the accompanying drawings of the embodiments of the present invention. Figure 1-5 The technical solutions of the embodiments of the present invention will be clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0029] Example 1 Please see Figures 1 to 5 This embodiment provides a tin-containing clean water recovery system.

[0030] like Figure 1 As shown, the tin-containing clean water recovery system includes a collection unit 101, a concentration unit 104, a filter press recovery unit 107, and a control system 109. The units are connected by pipelines and electrical lines to form a complete tin-containing clean water washing water recovery and treatment process chain.

[0031] The collection unit 101 includes a storage tank 102. The storage tank 102 is made of high-density polyethylene (HDPE) using a rotational molding process and has a volume of 1500 liters. HDPE has excellent acid and alkali corrosion resistance, good impact strength, and a long service life. Its smooth inner wall is not prone to scaling, making it suitable for long-term storage of tin-containing rinse water. The inlet of the storage tank 102 is sealed to the tin-containing rinse water discharge outlets of the tin plating and etching stripping processes via a collection pipeline. The collection pipeline uses polyvinyl chloride (PVC) tubing, and the pipe connections are sealed with acid and alkali resistant sealant to ensure no leakage throughout the process. A liquid level sensor 403 is installed inside the storage tank 102. The liquid level sensor 403 is an E2K-L series capacitive liquid level sensor manufactured by Omron. It measures the liquid level in real time by detecting the capacitance change between the liquid level in the storage tank 102 and the sensor probe, featuring non-contact measurement, unaffected by liquid conductivity, and a long service life. The signal output terminal of the liquid level sensor 403 is electrically connected to the analog input module of the control system 109 via a shielded signal line.

[0032] The outlet of storage tank 102 is sealed to the inlet of concentration unit 104 via a delivery pipeline. A delivery pump 406103 is installed in series on the delivery pipeline. The delivery pump 406103 is a CHL series lightweight horizontal multistage centrifugal pump manufactured by Southern Pump Industry Co., Ltd. The pump body and flow parts are made of stainless steel, and it features small size, low noise and stable operation.

[0033] The concentration unit 104 is the core component of the system, including the unit membrane filtration device 105 and its associated cross-flow circulation loop. For example... Figure 2 As shown, the unit membrane filtration device 105 includes a membrane housing 201 and two sets of membrane modules 202 disposed inside the membrane housing 201. The membrane housing 201 is made of stainless steel by argon arc welding, and the inner wall is mechanically polished to reduce fluid resistance and impurity adhesion. The front end of the membrane housing 201 is provided with a feed liquid inlet 203, the rear end is provided with a concentrate 302 outlet 204, and the side is provided with a permeate 303 outlet 205. The membrane modules 202 are spiral wound nanofiltration membrane modules 202, adopting standard industrial specifications, which can be easily installed and replaced.

[0034] Membrane module 202 adopts a spiral wound structure, internally formed by multiple layers of membrane sheets and spacer materials wound in a specific order onto a central permeate pipe. The membrane sheets of membrane module 202 are made of polyamide composite material, with the base membrane being a porous polysulfone support layer prepared via a phase inversion process. This layer possesses an asymmetric porous structure, providing excellent mechanical support and permeability channels. A thin polyamide functional separation layer is formed on the base membrane surface through an interfacial polymerization process. The specific process of this interfacial polymerization is as follows: first, the base membrane is immersed in an aqueous solution containing polyamine monomers, allowing the polyamine monomers to be fully adsorbed onto the base membrane surface; then, it is contacted with an organic phase solution containing polyacrylamide chloride monomers, resulting in an interfacial polymerization reaction on the base membrane surface, generating a polyamide functional separation layer with a thickness of only tens of nanometers. This polyamide functional separation layer carries a negative charge, exhibiting strong electrostatic adsorption and high-precision retention of divalent tin ions. Membrane module 202 has a molecular weight cutoff of 200 Daltons and a retention rate of no less than 98% for divalent and polyvalent metal ions.

[0035] The membrane module 202 has a detachable installation structure. Sealing end caps 206 are provided at both ends of the membrane module 202, and the sealing end caps 206 are sealed to the inner wall of the membrane housing 201 via O-rings. The O-rings are made of fluororubber material through molding and vulcanization. Fluororubber material has excellent resistance to acid and alkali corrosion, high-temperature aging, and compression set, and can maintain a good sealing effect under the weak acidity of tin-containing rinse water and long-term circulating operation conditions, preventing cross-contamination between the concentrate 302 and the permeate 303.

[0036] like Figure 3 As shown, the unit membrane filtration device 105 is connected to a cross-flow circulation loop. The cross-flow circulation loop includes a circulation pump 407106 and a circulation pipeline 301. One end of the circulation pipeline 301 is connected to the concentrate outlet 204 of the membrane housing 201 (302), and the other end is connected to the feed inlet 203 of the membrane housing 201, forming a closed circulation channel. The circulation pump 407106 is installed in series on the circulation pipeline 301. The circulation pump 407106 is a CRN series vertical multistage centrifugal pump manufactured by Grundfos, with the pump body and impeller made of stainless steel, featuring high efficiency, low energy consumption, and reliable operation.

[0037] The permeate outlet 205 of the unit membrane filtration device 105 is connected to a permeate 303 pipeline, on which a conductivity sensor 404 and a flow meter are installed. The conductivity sensor 404 is a Mettler Toledo InPro 7100 series conductivity sensor, employing a four-electrode measurement principle, featuring high measurement accuracy, strong anti-fouling capability, and comprehensive temperature compensation. The conductivity sensor 404 is used to monitor the conductivity value of the permeate 303 in real time, indirectly reflecting the concentration level of residual metal ions in the permeate 303 through changes in conductivity, thereby determining whether the retention performance of the membrane module 202 is normal. An electromagnetic flow meter is used to measure the real-time and cumulative flow of the permeate 303. A pressure sensor 405 is installed on the concentrate 302 pipeline. The pressure sensor 405 is a Honeywell PX2 series heavy-duty pressure sensor, featuring high accuracy, good stability, and resistance to vibration and shock. The signal output terminals of conductivity sensor 404 and pressure sensor 405 are electrically connected to the analog input module of control system 109 via shielded signal lines.

[0038] The filter press recovery unit 107 includes a filter press device 108. For example... Figure 5 As shown, the filter press 108 is a chamber filter press. The filter plates 501 are made of polypropylene material through injection molding, possessing good acid and alkali corrosion resistance and sufficient mechanical strength. The filter cloth 502 is made of polyester filament filter cloth, which has good air permeability, high retention accuracy, and excellent cake discharge performance. The feed inlet of the filter press 108 is sealed to the concentrate 302 outlet 204 of the unit membrane filtration device 105 through the concentrate 302 pipeline. A pneumatic diaphragm pump is installed on the concentrate 302 pipeline as the filter press pump 503408. The pneumatic diaphragm pump is an ARO series pneumatic double diaphragm pump manufactured by Ingersoll Rand, with a pump body made of polypropylene and a diaphragm made of polytetrafluoroethylene. The pneumatic diaphragm pump has advantages such as strong self-priming ability, ability to run dry, and ability to transport liquids containing solid particles, making it particularly suitable for the filter press feeding conditions of concentrate 302. A tin sludge collection container 504 is placed below the filter press 108 to collect the tin dioxide sludge filter cake discharged after the filter press.

[0039] The control system 109 includes a programmable logic controller (PLC) 401 and a touchscreen human-machine interface (HMI) 402. The PLC 401 is a Siemens SIMATIC S7-1200 PLC 401 with a CPU model of 1214C DC / DC / DC, equipped with 8 channels of analog input modules and 8 channels of digital output modules. The touchscreen HMI 402 is a Siemens SIMATIC HMI KTP700 Basic color touchscreen with a screen size of 7 inches and a resolution of 800×480 pixels, exchanging data with the PLC 401 via an Ethernet communication interface. The digital output terminals of the control system 109 are electrically connected to the contactors of the transfer pump 406103, the circulation pump 407106, and the solenoid valve of the pneumatic diaphragm pump, respectively. The analog input terminals of the control system 109 are electrically connected to the signal output terminals of the level sensor 403, the conductivity sensor 404, and the pressure sensor 405, respectively.

[0040] The control system 109 also includes an alarm indication unit. The alarm indication unit includes an audible and visual alarm 409 and status indicator lights 410, both fixedly mounted on the control cabinet panel of the control system 109. The audible and visual alarm 409 is a JD50A type integrated audible and visual alarm manufactured by Shanghai Tianyi Electric Co., Ltd., with a sound pressure level of not less than 90dB, a flashing frequency of 60 times / minute, and an operating voltage of DC24V. The status indicator lights 410 include green, yellow, and red indicator lights, all of which are XB4 series LED indicator lights manufactured by Schneider Electric, used to indicate the system's power-on status, the operating status of the concentration unit 104, and the operating status of the filter press recovery unit 107, respectively.

[0041] The working process of this embodiment is as follows: The system is installed at a designated location within the customer's factory, occupying an area of ​​approximately 18 square meters. Tin-containing rinse water from the tin plating process of the pattern plating line and the etching stripping process is collected via pipelines and temporarily stored in storage tank 102. The tin content of the tin plating rinse water from the pattern plating line is approximately 200 ppm, with a daily overflow of approximately 28.8 tons; the tin content of the tin rinse water after etching stripping is approximately 0.5 g / L, with a daily overflow of approximately 7.2 tons. After the two rinse waters are mixed in storage tank 102, the tin concentration is approximately 250–300 ppm.

[0042] Before system startup, the operator sets the concentration ratio to 8-10 times, the circulation time to 4-6 hours, and the maximum pressure for filtration to 0.6 MPa via the touchscreen human-machine interface 402. The level sensor 403 monitors the liquid level in the storage tank 102 in real time. When the liquid level reaches the preset upper limit, the control system 109 automatically starts the transfer pump 406103 to pump the tin-containing clean water wash to the unit membrane filtration device 105.

[0043] After the tin-containing rinse water enters the unit membrane filtration device 105, the circulation pump 407106 starts simultaneously. The tin-containing rinse water circulates at high speed in a cross-flow manner within the closed loop formed by the membrane housing 201 and the circulation pipeline 301. Under the driving pressure provided by the circulation pump 407106, water molecules permeate through the polyamide functional separation layer of the membrane module 202 under the action of pressure difference and enter the central product water pipe, forming permeate 303; tin ions are trapped by the polyamide functional separation layer due to size exclusion effect and electrostatic repulsion, and return to the circulation loop with the concentrate 302. In each cycle, some water molecules permeate through the membrane module 202 to form permeate 303, and the tin concentration in the concentrate 302 gradually increases. The permeate 303 is discharged into the wastewater station or collected for reuse through the permeate 303 pipeline, and the conductivity sensor 404 monitors the conductivity value of the permeate 303 in real time. When the conductivity of the permeate 303 remains stable at a low level, it indicates that the membrane module 202 has normal retention performance; if the conductivity value rises abnormally, the control system 109 triggers the audible and visual alarm 409 to issue an alarm signal.

[0044] When the circulation time reaches the preset duration or the concentration ratio reaches the preset value, the control system 109 shuts down the circulation pump 407106 and the transfer pump 406103, and opens the discharge valve on the concentrate 302 pipeline, allowing the enriched concentrate 302 to be transported to the filter press recovery unit 107 by gravity or the transfer pump 406103. The pneumatic diaphragm pump of the filter press 108 starts, pumping the concentrate 302 into the filter chamber of the filter press 108. Under the continuous pressure provided by the pneumatic diaphragm pump, the liquid in the concentrate 302 passes through the filter cloth 502 and is discharged from the filtrate outlet 506, while the tin dioxide solid particles are trapped in the filter chamber and gradually accumulate to form a dense filter cake. The pressure sensor 405 monitors the filter press pressure in real time. When the filter press pressure reaches the preset upper limit of 0.6 MPa, the control system 109 controls the pneumatic diaphragm pump to stop feeding, and the filter press process ends.

[0045] After filtration, the operator operates the plate-pulling mechanism of the filter press 108 to sequentially pull open the filter plates 501, allowing the tin dioxide sludge filter cake to fall into the tin sludge collection container 504 under gravity. Testing shows that the produced tin sludge contains more than 25% metallic tin (calculated as metallic tin), meeting the quality requirements for recycled tin dioxide products. The filtrate is returned to the storage tank 102 or directly discharged into the wastewater treatment plant. The system operates without manual intervention, and the tin sludge is collected every 1-3 months.

[0046] Throughout the operation, a constantly lit green indicator light indicates that the system is powered on normally; a lit yellow indicator light indicates that the concentration unit 104 is operating; and a lit red indicator light indicates that the pressure filtration and recovery unit 107 is operating. When the conductivity sensor 404 detects that the conductivity value of the permeate 303 exceeds the preset alarm threshold, or when the pressure sensor 405 detects an abnormal pipeline pressure, the control system 109 triggers the audible and visual alarm 409 to issue an audible and visual alarm signal. At the same time, the specific alarm information is displayed on the touch screen, prompting the operator to check and handle the situation.

[0047] Example 2 This embodiment is basically the same as Embodiment 1 in structure and operation, except that a spiral wound reverse osmosis membrane module 202 is used instead of a nanofiltration membrane module 202. The reverse osmosis membrane module 202 has a molecular weight cutoff of 100 Daltons and a tin ion rejection rate of over 99.5%. The reverse osmosis membrane module 202 is also made of polyamide composite material, with a polyethersulfone porous support layer as the base membrane and an ultra-thin polyamide functional separation layer formed by interfacial polymerization. Due to the higher rejection accuracy of the reverse osmosis membrane, this embodiment is particularly suitable for applications with extremely strict requirements on the tin content of the tailwater, which can be stably kept below 5 ppm. The reverse osmosis membrane module 202 requires a high operating pressure, and the circulation pump 407106 is a CRN series vertical multistage centrifugal pump manufactured by Grundfos. The remaining structure and operation are the same as in Embodiment 1, and will not be repeated here.

[0048] Example 3 This embodiment is basically the same as Embodiment 1 in structure and operation, except that there are two storage tanks 102 connected in parallel. Alternating water intake and material supply can be achieved by switching valves, ensuring continuous and uninterrupted system operation. When one storage tank 102 is supplying material to the concentration unit 104, the other storage tank 102 is receiving tin-containing washing water. This alternating switching improves the system's continuous processing capacity. The filter press 108 uses a plate and frame filter press instead of a chamber filter press. The filter plates 501 and filter frames of the plate and frame filter press are arranged alternately, and the filter cloth 502 covers the surface of the filter plates 501, providing a larger filtration area and better adaptability. The remaining structure and operation are the same as in Embodiment 1, and will not be repeated here.

[0049] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0050] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A tin-containing clean water recovery system, characterized in that, The system includes a collection unit (101), a concentration unit (104), a filter press recovery unit (107), and a control system (109). The collection unit (101) includes at least one storage tank (102), the inlet of which is connected to the outlet of the tin-containing clean water washing water. The concentration unit (104) includes a unit membrane filter (105), the inlet of which is connected to the outlet of the storage tank (102) via a conveying pipeline. The filter press recovery unit... The unit (107) includes a filter press (108), the inlet of which is connected to the outlet (204) of the concentrated liquid (302) of the unit membrane filter (105) via a concentrated liquid (302) pipeline; the signal output terminal of the control system (109) is electrically connected to the delivery pump (406)(103) on each delivery pipeline, the circulation pump (407)(106) of the unit membrane filter (105) and the filter press pump (503)(408) of the filter press (108).

2. The tin-containing clean water recovery system as described in claim 1, characterized in that: The unit membrane filtration device (105) includes a membrane housing (201) and at least one set of membrane modules (202) disposed inside the membrane housing (201). The membrane module (202) is a spiral wound nanofiltration membrane module (202) or a spiral wound reverse osmosis membrane module (202). The membrane sheet of the membrane module (202) is made of composite material, including a polysulfone or polyethersulfone porous support layer and a polyamide ultrathin functional separation layer formed on the surface of the support layer by an interfacial polymerization process.

3. The tin-containing clean water recovery system as described in claim 2, characterized in that: The unit membrane filtration device (105) is connected to a cross-flow circulation loop, which includes a circulation pump (407) (106) and a circulation pipeline (301). One end of the circulation pipeline (301) is connected to the concentrate (302) outlet (204) of the membrane housing (201), and the other end is connected to the raw liquid inlet (203) of the membrane housing (201), forming a closed circulation channel. The circulation pump (407) (106) is installed in series on the circulation pipeline (301).

4. The tin-containing clean water recovery system as described in claim 3, characterized in that: The membrane module (202) is provided with sealing end caps (206) at both ends. The sealing end caps (206) are sealed to the inner wall of the membrane housing (201) by means of O-rings.

5. The tin-containing clean water recovery system as described in claim 1, characterized in that: A liquid level sensor (403) is installed inside the storage tank (102), and the signal output terminal of the liquid level sensor (403) is electrically connected to the signal input terminal of the control system (109).

6. The tin-containing clean water recovery system as described in claim 1, characterized in that: The filter press (108) is a chamber filter press or a plate and frame filter press, and the filter plates (501) of the filter press (108) are made of polypropylene material.

7. The tin-containing clean water recovery system as described in claim 1, characterized in that: The control system (109) includes a programmable logic controller (401) and a touch screen human-machine interface (402). The programmable logic controller (401) is equipped with a digital input module, a digital output module and an analog input module.

8. The tin-containing clean water recovery system as described in claim 1, characterized in that: It also includes an online monitoring unit, which includes a conductivity sensor (404) installed on the permeate (303) pipeline of the unit membrane filtration device (105) and a pressure sensor (405) installed on the concentrate (302) pipeline. The conductivity sensor (404) and the pressure sensor (405) are electrically connected to the signal input terminal of the control system (109).

9. The tin-containing clean water recovery system as described in any one of claims 1-8, characterized in that: The control system (109) also includes an alarm indication unit, which includes an audible and visual alarm (409) and a status indicator (410).

10. The tin-containing clean water recovery system as described in claim 6, characterized in that: The filter press (503) and (408) are pneumatic diaphragm pumps, and the pump body of the pneumatic diaphragm pump is made of polypropylene and the diaphragm is made of polytetrafluoroethylene.

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