Mercury vapor recovery and exhaust gas purification integrated device and method for mercury amalgam brazing

Abstract

This invention discloses an integrated device and method for mercury vapor recovery and waste gas purification in amalgam brazing, belonging to the field of electronic packaging brazing and hazardous gas treatment. The device comprises a brazing sealing enclosure, a condensation unit, an iodine solution absorption unit, a sulfur absorption unit, a zinc powder absorption unit, and a safety monitoring module, connected in series. During brazing, mercury-containing waste gas is collected by the enclosure and first enters the condensation unit for pre-cooling and recovery of liquid mercury; then it enters the iodine solution absorption unit, where it reacts with iodine to generate mercuric iodide precipitate and capture silver dust; next, the residual mercury is fixed as mercuric sulfide by the sulfur absorption unit; finally, trace mercury is adsorbed by the zinc powder absorption unit. The purified waste gas is monitored in real time by a mercury concentration sensor; if the concentration exceeds the standard, an alarm is triggered and the heating platform is automatically shut down. This invention achieves a mercury removal rate of over 99.5% through four-stage synergistic purification, with emission concentrations lower than the national standard of 0.01 mg / m³. 3 It has advantages such as high purification efficiency, safety and reliability, good material compatibility, and convenient maintenance.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging brazing and harmful gas treatment, specifically relating to an integrated device and method for mercury vapor recovery and waste gas purification for amalgam brazing. Background Technology

[0002] With the rapid development of the electronics and information industry, the application of high-power-density, high-heat-generating electronic devices (such as IGBTs, power MOSFETs, lasers, and electronic equipment) is becoming increasingly widespread, and their service environments are becoming increasingly demanding (such as high temperature, high humidity, strong vibration, and thermal cycling). This places unprecedented demands on electronic packaging technology, especially on the reliability of interconnections between dissimilar materials (such as metal substrates and semiconductor chips). As a key process for achieving this hermetically tight and high-strength interconnection, the performance of the core material—the solder—directly determines the performance, lifespan, and cost of the final product.

[0003] Currently, silver amalgam brazing filler metals (Hg-Ag alloys) have re-emerged in research due to their unique low-temperature properties: mercury and silver can form a paste-like alloy at room temperature, with a brazing temperature far lower than that of gold-tin brazing filler metals and traditional silver-based brazing filler metals. Furthermore, the silver layer remaining after mercury volatilization has high purity (≥99.5%), making it suitable for silver plating on other material surfaces, resulting in a coating with low resistivity (≤1.6×10⁻⁶). -8 Ω (m), fully adapted to the conductivity and reliability requirements of silver-plated brazing, while costing only 1 / 5 to 1 / 8 of gold-tin brazing filler metal, giving it a significant economic advantage.

[0004] However, the application of amalgam brazing filler metal faces severe environmental and safety challenges—the mercury volatilization rate during brazing is over 95%, and the generated mercury vapor is a highly toxic pollutant, with an occupational exposure limit (OEL) of only 0.025 mg / m³. 3 (GBZ2.1-2019 "Occupational Exposure Limits for Hazardous Factors in the Workplace Part 1: Chemical Hazardous Factors"), and it is easily inhaled, causing damage to the nervous system, digestive system, and kidneys; at the same time, if mercury vapor is directly emitted, it will cause persistent pollution to the atmosphere, soil, and water bodies, which does not meet the requirement of "mercury and its compounds emission concentration ≤ 0.01 mg / m³" in GB 16297-1996 "Integrated Emission Standard for Air Pollutants". 3 The mandatory requirement of "".

[0005] Existing mercury vapor purification technologies are ill-suited for the low-temperature brazing requirements of silver amalgam processes. This is because brazing exhaust gases contain trace amounts of silver dust, which, combined with mercury vapor, causes galvanic corrosion in ordinary stainless steel components, reducing equipment lifespan to less than three months. Single activated carbon or sulfur adsorption efficiencies are low (generally below 85%), and sulfur requires rapid reactions above 80°C, while exhaust gases only reach 40-60°C, resulting in a reaction efficiency of less than 50%. Safety is also a concern, as ordinary plastics and metals are easily permeated by mercury or form amalgams, leading to leaks. Furthermore, the lack of online monitoring and safety interlocks means that the heating plate cannot be automatically shut down when mercury concentrations exceed limits, posing a risk of poisoning. Purification units are mostly fixed structures, requiring disassembly of the entire unit for replacement, taking 1-2 hours and impacting production. Additionally, the absence of mercury recovery functionality means that spent adsorbents can only be disposed of as hazardous waste. Moreover, the single extraction mode results in insufficient natural airflow, high energy consumption at the terminal negative pressure, and a risk of displacement of the workpieces to be welded. Therefore, there is an urgent need to develop an efficient, safe, and integrated device adapted to brazing processes.

[0006] In summary, the electronic packaging industry urgently needs a "low-cost, low-melting-point" brazing solution. At the same time, it needs to develop an integrated device for mercury vapor recovery and waste gas purification that is "highly efficient, safe and reliable, material compatible, and easy to maintain" to solve the application bottleneck of silver amalgam brazing and promote its large-scale application in the electronic packaging field as a replacement for gold-tin brazing filler metal. Summary of the Invention

[0007] The technical problem to be solved: To overcome the shortcomings of existing technologies, this invention provides an integrated device and method for mercury vapor recovery and waste gas purification in amalgam brazing. The device connects a condensation unit, an iodine solution absorption unit, a sulfur absorption unit, and a zinc powder absorption unit in series. The condensation unit reduces the concentration of mercury vapor entering the iodine solution absorption unit to prevent precipitation blockage and rapid failure. The iodine solution absorption unit converts gaseous mercury into a further treatable intermediate product, improving the reaction efficiency of the subsequent sulfur absorption unit under low-temperature conditions. The sulfur absorption unit stabilizes and fixes residual mercury. The zinc powder absorption unit performs terminal capture of trace mercury in the exhaust gas. The units operate in a progressive recovery process, achieving low leakage rate, high purification efficiency, recyclability, and safety interlocking in the mercury vapor recovery and waste gas purification process through the coordination of each step.

[0008] The technical solution of this invention is: a method for mercury vapor recovery and waste gas purification for amalgam brazing, the specific steps of which are as follows: Step 1. Closed Collection and Atmosphere Control: Place the brazing sealing cover containing the workpiece to be brazed on the heating table, fasten the brazing sealing cover, introduce protective gas into it to form a local protective atmosphere, and exhaust the air inside the cover. Step 2. Staged heating and mercury vapor release: The heating platform is heated in stages. First, the temperature is raised to the first preset temperature and held to allow some of the mercury in the amalgam brazing filler to pre-evaporate. Then, the temperature is raised to the second preset temperature and held to allow the remaining mercury to completely evaporate and the silver layer to solidify, thus completing the brazing and forming mercury-containing vapor exhaust gas. Step 3. Condensation Pretreatment and Liquid Mercury Recovery: The mercury-containing vapor waste gas generated in step two is passed into the condensation unit and cooled to below the condensation point of mercury by a cooling medium, so that most of the gaseous mercury in the waste gas condenses into liquid mercury, which is then separated and recovered under the action of gravity. Step 4. Chemical absorption and conversion of iodine solution: The residual waste gas after step three is passed into the iodine solution in the iodine solution absorption unit. The waste gas generated after the reaction with the iodine solution then undergoes a reverse contact reaction with the atomized iodine solution in the iodine solution absorption unit, so that the remaining gaseous mercury in the waste gas reacts with the atomized iodine solution to generate solid mercuric iodide precipitate. At the same time, the silver dust carried in the waste gas is captured by the iodine solution and discharged with the precipitate. Step 5. Sulfur immobilization and adsorption: The waste gas treated in step four is passed into the sulfur absorption unit, whereby the trace amounts of residual mercury in the waste gas react with sulfur to form stable mercury sulfide, thereby achieving further fixation of mercury. Step Six. Deep Adsorption of Zinc Powder at the Terminal: The exhaust gas treated in step five is passed into the zinc powder absorption unit, where trace amounts of mercury vapor are adsorbed through the amalgamation reaction between zinc powder and mercury, while simultaneously intercepting solid particles entrained in the exhaust gas. Step 7. Emissions Monitoring and Safety Interlocks: The exhaust gas purified in step six is ​​monitored in real time by the exhaust gas detection unit. When the concentration of mercury at the outlet is lower than the preset safety threshold, it is discharged; when the concentration exceeds the preset safety threshold, an alarm is triggered and the heating station is shut down.

[0009] A further technical solution of the present invention is as follows: In step two, the first preset temperature is 180℃, the temperature is increased at a rate of 5℃ / min, and the holding time is 30 minutes; the second preset temperature is 240℃, the temperature is increased at a rate of 3℃ / min, and the holding time is 30 minutes; the protective gas is argon, and the gas inlet volume is adjustable within a range of 0.8m³. 3 / h.

[0010] A further technical solution of the present invention is as follows: In step three, the temperature of the cooling medium in the condensation unit is controlled at 20℃±2℃ to fully condense the mercury vapor. The condensed liquid mercury flows into the recovery unit through a one-way check valve. The recovery unit is equipped with a liquid level sensor, which issues an alarm when the liquid level reaches a preset value. A further technical solution of the present invention is as follows: In step four, the iodine solution is a 5% I2 aqueous solution, which is atomized through an atomizing nozzle with a particle size of 10-20 μm and then comes into countercurrent contact with the exhaust gas; in step five, the sulfur is granular sulfur with a diameter of 2-3 mm and a filling height of 8-10 cm; in step six, the zinc powder is granular zinc powder with a particle size of 10-100 micrometers. A further technical solution of the present invention is: in step seven, the preset safety threshold is 0.01 mg / m³. 3 When the concentration exceeds the threshold, in addition to triggering an alarm and shutting down the heating station, the cooling medium flow rate and exhaust volume of the condensing unit will be increased. If the concentration continues to exceed the threshold for 5 minutes, the unit will automatically shut down completely.

[0011] An integrated device for mercury vapor recovery and waste gas purification for amalgam brazing includes: A brazing sealing cover is installed above the heating table to seal and collect mercury-containing vapor waste gas generated during the brazing process. The brazing sealing cover has an air inlet and an air outlet. The air inlet is connected to a protective gas source, and the air outlet is connected to a waste gas purification unit. The condensation unit, whose inlet is connected to the outlet of the brazed sealing cover, is used to pre-condense the mercury-containing vapor waste gas to separate and recover part of the gaseous mercury in the waste gas; the liquid mercury formed by condensation flows into the liquid mercury recovery unit under the action of gravity to reduce the mercury load of subsequent units; The iodine absorption unit has its inlet connected to the gas outlet of the condensation unit. It is equipped with iodine absorption liquid and iodine atomizing spray device to allow the remaining gaseous mercury in the exhaust gas to react fully with the iodine liquid twice to generate solid mercuric iodide precipitate, and simultaneously capture silver dust in the exhaust gas. The sulfur absorption unit has its inlet connected to the gas outlet of the iodine solution absorption unit and contains granular sulfur packing material for fixing the trace amounts of mercury remaining after treatment by the iodine solution absorption unit. The zinc powder absorption unit has its inlet connected to the gas outlet of the sulfur absorption unit and contains granular zinc powder filler for terminal adsorption of trace mercury in the exhaust gas and interception of solid particles. The safety monitoring module is located at the gas outlet of the zinc powder absorption unit. It includes an exhaust gas detection unit and an alarm device and a heating platform control circuit that are electrically connected to the exhaust gas detection unit. It is used to monitor the exhaust gas concentration in real time and trigger a safety interlock when the concentration exceeds the standard. The condensation unit, iodine solution absorption unit, sulfur absorption unit, and zinc powder absorption unit are connected in series along the direction of exhaust gas flow to form an exhaust gas purification unit.

[0012] A further technical solution of the present invention is as follows: the brazed sealing cover is made of borosilicate glass, and the inner wall is provided with a 5mm thick aluminum silicate cotton insulation layer, and the inner wall is provided with a spiral groove to guide the flow of condensate; a fluororubber sealing ring is provided at the bottom of the cover where it fits with the heating table; the air outlet of the cover is connected to a corrosion-resistant pipe made of polytetrafluoroethylene, and the inner diameter of the pipe is 20-30mm. A further technical solution of the present invention is as follows: the condensation unit is provided with a microchannel heat exchange structure inside, and an inclined guide plate is provided at the bottom for guiding the liquid mercury formed by condensation into the liquid mercury recovery unit; the condensation unit is also connected to a closed water cooling circulation system, which includes a variable frequency circulating water pump, a liquid storage tank and inlet and outlet temperature sensors; a one-way check valve made of polytetrafluoroethylene is provided between the condensation unit and the liquid mercury recovery unit, and a liquid level sensor is provided in the recovery unit. A further technical solution of the present invention is as follows: the iodine absorption unit contains a 5% I2 aqueous solution, the nozzle of the iodine atomizing spray device has an atomization particle size of 10-20 μm, and the bottom of the tank is provided with a slag discharge port for periodically discharging mercuric iodide precipitate and the collected silver dust; the sulfur absorption unit contains granular sulfur with a diameter of 2-3 mm and a filling height of 8-10 cm, and both the upper and lower ends of the tank are provided with stainless steel sieve plates with a pore size of 1 mm; the zinc powder absorption unit contains granular zinc powder with a particle size of 10-100 micrometers.

[0013] A further technical solution of the present invention is that the exhaust gas detection unit of the safety monitoring module has a mercury concentration range of 0–0.1 mg / m³. 3 The accuracy is 0.001 mg / m 3 The alarm device activates when the concentration exceeds 0.01 mg / m³. 3 When the concentration exceeds the standard for 5 minutes, the control circuit will automatically shut down the heating function of the heating platform and increase the cooling medium flow and exhaust volume of the condensing unit. When the concentration exceeds the standard for 5 minutes, the control circuit will automatically shut down the machine completely. Beneficial effects The beneficial effects of this invention are as follows: By constructing a staged treatment method of "condensation-iodine solution absorption-sulfur fixation-zinc powder deep adsorption", this invention achieves stepwise load reduction and reaction path control of mercury vapor. The specific beneficial effects are as follows: (1) Implement graded load reduction to avoid rapid failure of the front-end absorption unit. This invention incorporates a condensation unit before the iodine solution absorption unit. By pre-cooling the high-temperature mercury-containing waste gas, some gaseous mercury is preferentially condensed and separated for recovery, thereby significantly reducing the mercury vapor concentration entering subsequent absorption units. This structure effectively avoids the problem of rapid formation and deposition of mercuric iodide, which clogs the spray system due to excessively high mercury concentrations during traditional iodine solution absorption. It delays the failure process of the absorption unit from the source and improves the system's operational stability.

[0014] (2) Construct a reaction pathway coupling mechanism to achieve purification and adaptation of the mercury-silver composite pollution system. This invention, through the sequential arrangement of an "iodine solution absorption unit—sulfur absorption unit," allows gaseous mercury to first be converted into a solid precipitate in the iodine solution, while also containing other particulate impurities in the waste gas, such as fine silver particles. Compared to directly using sulfur to absorb mercury vapor, this invention achieves preliminary purification of complex gases through a pre-conversion step, transforming a gas mixed with a large number of impurities into nearly pure mercury vapor. This significantly enhances the subsequent reactivity of sulfur with mercury and solves the problem of particulate impurities in the waste gas clogging the sulfur absorption unit in existing technologies.

[0015] (3) Achieve multi-level synergistic purification and avoid the problem of incomplete treatment by a single absorption unit. This invention adopts a multi-stage treatment structure of "condensation - iodine solution absorption - sulfur fixation - zinc powder terminal adsorption", and each treatment unit is functionally interconnected: the condensation unit reduces the load, the iodine solution unit achieves rapid capture, the sulfur unit achieves stable fixation, and the zinc powder unit performs tail gas bottom adsorption.

[0016] (4) Reduce equipment corrosion and operational risks in multi-contamination systems Addressing the characteristic of mercury vapor and metal particles (such as silver dust) simultaneously present in the exhaust gas during amalgam brazing, this invention effectively reduces the possibility of electrochemical reactions between mercury and other metal particles within the equipment through multi-stage separation and progressive treatment. Simultaneously, by combining corrosion-resistant materials and a tiered treatment structure, the risk of corrosion, scaling, and structural failure during long-term operation is reduced, thereby improving the lifespan and operational safety of the device.

[0017] The above-mentioned graded treatment mechanism effectively avoids the problems of incomplete absorption or exhaust gas leakage that exist in single treatment methods, and improves the overall reliability and safety of the system.

[0018] 1. Through a three-stage purification process involving iodine solution, sulfur, and zinc powder, the mercury vapor removal rate is ≥99.5%, and the final mercury concentration in the exhaust gas is ≤0.005mg / m³, far below the national standard of 0.01mg / m³. Simultaneously, it adsorbs silver / sulfur dust, preventing secondary pollution and enhancing the environmental friendliness of the equipment. High safety. For the brazing sealing cover, borosilicate glass is selected, which has excellent high-temperature resistance (suitable for brazing up to 240℃), meeting the requirements of amalgam brazing. It has no mercury permeability and allows for visual observation of the brazing process. PTFE pipes prevent leakage, concentration sensors provide real-time alarms, and mercury is recyclable, saving costs and preventing personnel poisoning and environmental pollution. The entire device employs safety interlocks; when the concentration exceeds the standard, the heating function of the hot plate is automatically shut down, while the water cooling flow and exhaust air volume are increased to achieve automatic emergency handling of the equipment, preventing continuous mercury vapor leakage / excessive emissions; if the concentration exceeds the standard for 5 minutes, the machine automatically shuts down, minimizing safety risks.

[0019] 2. Process Adaptation Segmented heating reduces thermal stress on the components to be soldered, is compatible with the packaging of thermistor electronic components, and the integrated device is easy to operate. It supports both natural pull-out and end negative pressure modes and can be applied in batches. Attached Figure Description Figure 1 This is a simplified schematic diagram of an integrated device for mercury vapor recovery and waste gas purification for amalgam brazing, as described in an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached drawings: 1. Heating platform, 2. Brazed sealing cover, 3. One-way valve, 4. Condensation unit, 5. Exhaust gas detection unit, 6. Zinc powder absorption unit, 7. Sulfur absorption unit, 8. Iodine solution atomizing spray device, 9. Iodine solution absorption unit, 10. Liquid mercury recovery unit, 11. Sample. Detailed Implementation

[0021] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0022] Existing mercury vapor purification technologies are ill-suited for the low-temperature brazing requirements of silver amalgam, mainly due to the following drawbacks: Poor material compatibility: During the treatment of amalgam brazing exhaust gas, trace amounts of silver dust (residual brazing filler metal powder from the brazing process) inevitably mix with mercury vapor and enter the purification unit. Existing purification units primarily use ordinary stainless steel for their core contact components. In humid, mercury-containing exhaust gas environments, stainless steel and silver dust readily form a galvanic cell effect, triggering electrochemical corrosion that continuously erodes the equipment's inner walls and pipelines. Furthermore, the system lacks a dedicated anti-corrosion and anti-alloying contact material design specifically for the characteristics of mercury-silver composite pollutants. The material's corrosion resistance and its compatibility with operating conditions are insufficient. Under the combined effects of corrosion and pollutant adhesion, the purification unit experiences accelerated wear and tear, resulting in a significantly shortened overall lifespan. The typical operating cycle is less than three months, increasing equipment replacement frequency and directly impacting the stability of exhaust gas treatment.

[0023] Lack of a pre-condensation unit: Most existing devices lack a pre-condensation and dehydration unit. High-concentration mercury vapor enters the absorbent tank directly without cooling, dehydration, or other recovery and pretreatment processes. The large amount of high-temperature mercury-containing flue gas carrying water vapor and impurities causes the absorbent to operate under overload conditions for extended periods. This not only significantly reduces the efficiency of reagent adsorption and reaction but also leads to rapid saturation and failure of the absorbent. The consumption rate of critical consumables such as filter cartridges and reagents far exceeds normal operating conditions, resulting in persistently high equipment operating loads and significantly increased maintenance costs.

[0024] Low purification efficiency: Existing devices mostly use single activated carbon adsorption or single sulfur adsorption technology. The adsorption capacity of activated carbon for mercury vapor is only 0.1-0.3g / g (25℃), and it is easily affected by humidity and temperature, leading to adsorption saturation. Sulfur adsorption requires high temperature (≥80℃) to react quickly, while the temperature of silver amalgam brazing exhaust gas is only 40-60℃, and the reaction efficiency is less than 50%. The mercury removal rate of single technologies is generally less than 85%, which cannot meet the emission requirements. Lack of safety protection: The existing equipment lacks effective leak prevention design. The contaminated contact parts (such as collection hoods and pipes) are mostly made of ordinary plastic or metal. Ordinary plastic is easily permeated by mercury, and metal materials (such as carbon steel) are prone to forming amalgams with mercury, leading to corrosion and leakage. At the same time, there is no online monitoring of mercury concentration and safety interlock mechanism. When the equipment malfunctions (such as adsorption saturation or pipe blockage) and the mercury concentration exceeds the limit, the brazing hot station cannot be shut down in time, which can easily lead to personnel poisoning accidents. Poor maintenance convenience: The purification units (such as the adsorbent packing box) mostly adopt a fixed structure. When replacing them, the entire device needs to be disassembled, which is complicated and time-consuming (1-2 hours for a single replacement). During this period, brazing production needs to be suspended, which affects production efficiency. At the same time, there is no mercury recovery function designed. The saturated waste adsorbent needs to be disposed of as hazardous waste, which increases environmental protection costs. Limited air extraction modes: Existing devices only support natural extraction (chimney effect) or only terminal negative pressure mode. Natural extraction is suitable for low air volume scenarios (≤0.5m³ / h), but when the number of brazing stations increases, insufficient air volume leads to incomplete mercury vapor collection. Although the terminal negative pressure mode can increase air volume, it has high energy consumption, and excessive negative pressure can easily cause the workpiece to be welded to shift, affecting the brazing accuracy.

[0025] To address the aforementioned problems, this invention proposes a method for mercury vapor recovery and waste gas purification in amalgam brazing, the specific steps of which are as follows: Step 1. Closed Collection and Atmosphere Control: Place the brazing sealing cover containing the workpiece to be brazed on the heating table, fasten the brazing sealing cover, introduce protective gas into it to form a local protective atmosphere, and exhaust the air inside the cover. Step 2. Staged heating and mercury vapor release: The heating platform is heated in stages. First, the temperature is raised to the first preset temperature and held to allow some of the mercury in the amalgam brazing filler to pre-evaporate. Then, the temperature is raised to the second preset temperature and held to allow the remaining mercury to completely evaporate and the silver layer to solidify, thus completing the brazing and forming mercury-containing vapor exhaust gas. Step 3. Condensation Pretreatment and Liquid Mercury Recovery: The mercury-containing vapor waste gas generated in step two is passed into the condensation unit and cooled to below the condensation point of mercury by a cooling medium, so that most of the gaseous mercury in the waste gas condenses into liquid mercury, which is then separated and recovered under the action of gravity. Step 4. Chemical absorption and conversion of iodine solution: The residual waste gas after step three is passed into the iodine solution in the iodine solution absorption unit. The waste gas generated after the reaction with the iodine solution then undergoes a reverse contact reaction with the atomized iodine solution in the iodine solution absorption unit, so that the remaining gaseous mercury in the waste gas reacts with the atomized iodine solution to generate solid mercuric iodide precipitate. At the same time, the silver dust carried in the waste gas is captured by the iodine solution and discharged with the precipitate. Step 5. Sulfur immobilization and adsorption: The waste gas treated in step four is passed into the sulfur absorption unit, whereby the trace amounts of residual mercury in the waste gas react with sulfur to form stable mercury sulfide, thereby achieving further fixation of mercury. Step Six. Deep Adsorption of Zinc Powder at the Terminal: The exhaust gas treated in step five is passed into the zinc powder absorption unit, where trace amounts of mercury vapor are adsorbed through the amalgamation reaction between zinc powder and mercury, while simultaneously intercepting solid particles entrained in the exhaust gas. Step 7. Emissions Monitoring and Safety Interlocks: The exhaust gas purified in step six is ​​monitored in real time by the exhaust gas detection unit. When the concentration of mercury at the outlet is lower than the preset safety threshold, it is discharged; when the concentration exceeds the preset safety threshold, an alarm is triggered and the heating station is shut down.

[0026] This invention also proposes an integrated device for mercury vapor recovery and waste gas purification for amalgam brazing, comprising: A brazing sealing cover is installed above the heating table to seal and collect mercury-containing vapor waste gas generated during the brazing process. The brazing sealing cover has an air inlet and an air outlet. The air inlet is connected to a protective gas source, and the air outlet is connected to a waste gas purification unit. The condensation unit, whose inlet is connected to the outlet of the brazed sealing cover, is used to pre-condense the mercury-containing vapor waste gas to separate and recover part of the gaseous mercury in the waste gas; the liquid mercury formed by condensation flows into the liquid mercury recovery unit under the action of gravity to reduce the mercury load of subsequent units; The iodine absorption unit has its inlet connected to the gas outlet of the condensation unit. It is equipped with iodine absorption liquid and iodine atomizing spray device to allow the remaining gaseous mercury in the exhaust gas to react fully with the iodine liquid twice to generate solid mercuric iodide precipitate, and simultaneously capture silver dust in the exhaust gas. The sulfur absorption unit has its inlet connected to the gas outlet of the iodine solution absorption unit and contains granular sulfur packing material for fixing the trace amounts of mercury remaining after treatment by the iodine solution absorption unit. The zinc powder absorption unit has its inlet connected to the gas outlet of the sulfur absorption unit and contains granular zinc powder filler for terminal adsorption of trace mercury in the exhaust gas and interception of solid particles. The safety monitoring module is located at the gas outlet of the zinc powder absorption unit. It includes an exhaust gas detection unit and an alarm device and a heating platform control circuit that are electrically connected to the exhaust gas detection unit. It is used to monitor the exhaust gas concentration in real time and trigger a safety interlock when the concentration exceeds the standard. The condensation unit, iodine solution absorption unit, sulfur absorption unit, and zinc powder absorption unit are connected in series along the direction of exhaust gas flow to form an exhaust gas purification unit.

[0027] In summary, this invention provides a mercury vapor recovery and waste gas purification device and method that combines low leakage rate, high purification efficiency, recyclability, and safety interlocking in the process of amalgam brazing and coating preparation.

[0028] The above technical solution will be further analyzed below with reference to the accompanying drawings and examples: In one embodiment, refer to Figure 1 As shown, the apparatus for implementing a mercury vapor recovery and exhaust gas purification method for amalgam brazing includes, in sequence: a brazing sealing cover 2, a condensation unit 4, a liquid mercury recovery unit 10, an iodine absorption unit 9, a sulfur absorption unit 7, a zinc powder absorption unit 6, and an exhaust gas detection unit, wherein the brazing sealing cover 2 is placed on a heating platform 1 as a heat source for the brazed sample 11.

[0029] I. Device Structure 1. Brazed sealing cover 2: Made of borosilicate glass, its inner wall has a 5mm thick aluminum silicate cotton insulation layer, and a spiral groove on the inner wall to guide the flow of condensed liquid mercury; its bottom connects to the groove of the heating platform 1 to recover the liquid mercury after initial condensation, and a fluororubber sealing ring is installed at the bottom of the brazed sealing cover 2 where it fits against the heating platform; the top of the brazed sealing cover 2 has an air inlet and an air outlet, wherein the air inlet is connected to a protective gas source, and the flow rate of the gas is adjusted by a one-way valve installed on the connecting pipeline, with an adjustment range of 0.5~1m. 3 / h; the exhaust port is connected to the exhaust gas purification unit through a corrosion-resistant pipe.

[0030] Preferably, the corrosion-resistant pipe is made of polytetrafluoroethylene and has an inner diameter of 20-30 mm.

[0031] 2. Exhaust gas purification unit: Connected sequentially along the exhaust gas flow direction: Condensation Unit: A heat exchange structure is adopted to initially condense high-temperature mercury vapor through water cooling. The heat exchange structure adopts a microchannel design to increase the contact area and improve the condensation efficiency. An inclined guide plate is set at the bottom of the condensation unit. The inlet of the heat exchange result is located at the top and is connected to the outlet of the brazed sealing cover, while the outlet is located at the bottom and is connected to the liquid mercury recovery unit 10. There is a spatial height difference between the inlet and the outlet so that the mercury-containing waste gas flows through the condensation unit from top to bottom, and the liquid mercury formed by condensation collects downward under the action of gravity.

[0032] The heat exchange structure is connected to an external closed-loop water cooling circulation system, which includes a variable frequency circulating water pump, a liquid storage tank, and inlet and outlet temperature sensors to ensure stable temperature / flow of the cooling medium and control the condensate temperature at 20℃ (below the mercury condensation point of 38.87℃) to ensure sufficient condensation of mercury vapor.

[0033] Liquid mercury recovery unit: A sealed container made of borosilicate glass. Its inlet is connected to the outlet of the condensation unit via a corrosion-resistant PTFE pipe, and a one-way check valve is installed on the pipe to prevent mercury vapor from the recovery unit from flowing back into the condensation unit. The sealed container of the liquid mercury recovery unit is equipped with a liquid level sensor. When the liquid level reaches 80%, an audible and visual alarm is triggered to prompt timely mercury recovery and prevent mercury accumulation from affecting condensation.

[0034] Iodine solution absorption unit: A sealed container made of borosilicate glass. Its inlet is connected to the outlet of the liquid mercury recovery unit via a corrosion-resistant polytetrafluoroethylene pipe, which in turn connects the sealed container of the liquid mercury recovery unit to the outlet of the condensation unit. It contains a 5% concentration of iodine solution (I₂ + H₂O), and an iodine solution atomizing spray device is installed at the top of the tank. The atomized particles sprayed from the nozzle of the atomizing spray device have a particle size of 10–20 μm.

[0035] The PTFE inlet pipe leads into the iodine solution, allowing the residual waste gas after condensation in the condensation unit to fully contact the iodine solution. High-concentration Hg rapidly precipitates as HgI2, forming mercuric iodide (HgI2, a stable solid). The waste gas produced after the reaction in the iodine solution then undergoes a reverse reaction with the atomized iodine solution, causing the remaining gaseous mercury in the waste gas to react with the atomized iodine solution, forming solid mercuric iodide precipitate. Simultaneously, silver dust entrained in the waste gas is captured by the iodine solution and discharged with the precipitate. A slag discharge port is located at the bottom of the sealed unit of the iodine solution absorption unit to periodically discharge the mercuric iodide precipitate. Furthermore, the liquid iodine solution absorption unit can further capture tiny silver particles in the mercury vapor, forming a precipitate that is discharged with the HgI2 precipitate, preventing subsequent blockage in the solid absorption unit.

[0036] Sulfur absorption unit: Its inlet is connected to the gas outlet of the iodine solution absorption unit through a corrosion-resistant polytetrafluoroethylene pipe. It is filled with granular sulfur (2-3 mm in diameter) to a height of 8-10 cm. Stainless steel sieves (1 mm aperture) are installed at the top and bottom of the tank to prevent sulfur particles from being lost. It is used to adsorb residual mercury that is not completely absorbed by the iodine solution (generating mercuric sulfide HgS).

[0037] Zinc powder absorption unit: Its inlet is connected to the gas outlet of the sulfur absorption unit through a corrosion-resistant polytetrafluoroethylene pipe, and it is filled with granular zinc powder (10-100 micrometers in diameter) to absorb unreacted mercury vapor, sulfur dust and organic impurities in the waste gas.

[0038] The condensation unit, iodine solution absorption unit, sulfur absorption unit, and zinc powder absorption unit are connected in series in the above order, and this order cannot be interchanged. The condensation unit is used to reduce the concentration of mercury vapor entering the iodine solution absorption unit to prevent precipitation blockage and rapid failure of the iodine solution absorption unit. The iodine solution absorption unit is used to convert gaseous mercury into intermediate products that can be further processed to improve the reaction efficiency of the subsequent sulfur absorption unit under low temperature conditions. The sulfur absorption unit is used to stabilize and fix residual mercury. The zinc powder absorption unit is used for terminal capture of trace mercury in the exhaust gas.

[0039] 3. Safety Monitoring Module: This includes an exhaust gas detection unit located at the outlet of the activated carbon filter tank, the exhaust gas detection unit, and an alarm device electrically connected to a mercury vapor concentration sensor. The exhaust gas detection unit is a mercury vapor concentration sensor with a range of 0–0.1 mg / m³ and an accuracy of 0.001 mg / m³. The alarm device activates when the concentration exceeds 0.01 mg / m³. 3 An audible and visual alarm will be triggered at any time.

[0040] II. Methods and Steps This embodiment uses a silver-plated substrate of an IGBT device to be brazed as an example to explain the method steps in detail.

[0041] Step 1: Pre-treatment and workpiece clamping; Take the silver-plated IGBT substrate (50mm×50mm×2mm) to be brazed, wipe the surface with anhydrous ethanol to remove surface oil and oxide impurities, and let it air dry. Stir the amalgam brazing filler metal (Hg-Ag alloy, mercury content 90wt%) into a paste at room temperature, and apply it evenly to the surface to be brazed, controlling the coating thickness to be 0.1–0.2mm. Place the workpiece coated with the brazing filler metal in the center of the heating table, adjusting its position to ensure good contact with the heating table.

[0042] Step 2: Closed collection and atmosphere control; The brazed sealing cover made of borosilicate glass is fastened onto the heating platform, and the fluororubber sealing ring at the bottom of the cover is pressed tightly against the surface of the heating platform to form an airtight seal. The one-way valve at the air inlet of the cover is opened to introduce high-purity argon gas, and the inlet flow rate is adjusted to 0.8 m³ / s. 3 At a rate of / h, argon gas is used to purge the air inside the enclosure from the outlet, continuously ventilating to reduce the oxygen volume fraction inside the enclosure below the required value, thus creating a localized protective atmosphere. The inlet flow rate is then adjusted to 0.5 m³ / h. 3 / h maintains a slight positive pressure.

[0043] Step 3: Segmented heating and mercury vapor release; The heating platform is started, and a segmented heating program is executed: First, the temperature is increased to 180℃ at a rate of 5℃ / min and held for 30 minutes. During this stage, some of the mercury in the amalgam brazing filler metal volatilizes due to heat, forming mercury-containing vapor exhaust gas. The exhaust gas rises under the influence of thermal convection within the hood and exits through the top outlet. After the holding period, the temperature is increased again to 240℃ at a rate of 3℃ / min and held for 30 minutes. At this temperature, the remaining mercury in the brazing filler metal completely volatilizes, producing a large amount of mercury vapor exhaust gas mixed with some silver particles carried out with the volatilization. The mercury vapor concentration is approximately 10 mg / m³. 3 After the mercury vapor has completely evaporated, the silver layer is sintered and solidified, completing the brazing process.

[0044] Step 4: The exhaust gas undergoes sequential treatment through the exhaust gas purification unit; The mercury-containing vapor generated during the heating process, under the combined effect of thermal pressure (chimney effect) and terminal exhaust, enters the condensation unit, iodine absorption unit, sulfur absorption unit and zinc powder absorption unit arranged in series through the air outlet at the top of the hood (connected to a polytetrafluoroethylene pipe with an inner diameter of 25mm).

[0045] 4.1 Condensation pretreatment and liquid mercury recovery; The exhaust gas first enters the condensation unit. The condensation unit is equipped with a multi-channel heat exchange assembly, using closed-loop circulating water as the cooling medium, driven by a variable frequency circulating water pump, with the temperature controlled at 20℃±2℃ (adjusted in real-time by inlet and outlet temperature sensors). The exhaust gas enters through the air inlet at the top of the condensation unit and flows downwards along multiple gas channels of the heat exchange assembly, fully exchanging heat with the channel walls. Since mercury's condensation point is 38.87℃, the exhaust gas temperature rapidly drops from approximately 180℃ to below 30℃, with most of the gaseous mercury condensing into liquid mercury. The condensed liquid mercury, under gravity, collects along the inner wall of the channel and the inclined guide plate, flowing into the liquid mercury recovery unit via a one-way check valve made of PTFE. The liquid mercury recovery unit is equipped with a level sensor; when the liquid level reaches 80% of the recovery unit's volume, an audible and visual alarm prompts the operator to recover the mercury promptly. The condensation unit removes nearly half of the mercury vapor, reducing the mercury vapor concentration to 5.0-6.0 mg / m³. 3 .

[0046] 4.2 Chemical absorption and conversion of iodine solution; The residual waste gas after condensation enters the iodine absorption unit through the outlet at the bottom of the condensation unit and the cavity above the liquid mercury recovery unit. The iodine absorption unit contains a 5% I₂ aqueous solution, and an atomizing nozzle (15μm atomization particle size) is installed at the top of the sealed cavity. The residual waste gas after condensation in the condensation unit is passed into the iodine solution in the sealed cavity for thorough contact. High-concentration Hg rapidly precipitates as HgI₂, forming mercuric iodide (HgI₂, a stable solid). The waste gas generated after the iodine reaction rises from the bottom and contacts the iodine solution sprayed from the top in the opposite direction. The gaseous mercury in the waste gas reacts chemically with iodine: Hg + I₂ → HgI₂↓, forming a stable solid mercuric iodide precipitate. Simultaneously, trace amounts of silver dust (1-10μm particle size) carried in the waste gas are wetted and captured by the iodine solution, settling together with the mercuric iodide precipitate to the bottom of the tank. A slag discharge port is located at the bottom of the tank, and the mixed precipitate of mercuric iodide and silver dust is discharged periodically every 15 days.

[0047] After treatment by the iodine absorption unit, the mercury vapor concentration can be further reduced to 0.5-1.0 mg / m³ due to the direct contact reaction of mercury vapor with the iodine solution and the reaction after spraying with the iodine solution. 3 .

[0048] 4.3 Sulfur immobilization and adsorption; The exhaust gas exiting from the top of the iodine absorption unit enters the sulfur absorption unit. The exhaust gas passes through the sulfur packing layer from bottom to top. The residual trace amounts of mercury vapor react with sulfur: Hg + S → HgS, forming stable mercury sulfide which is fixed on the surface of the sulfur particles. After further reaction with sulfur, the concentration of mercury vapor in the exhaust gas is further reduced to 0.06-0.08 mg / m³. 3 .

[0049] 4.4 Deep adsorption of zinc powder at the terminal; After being discharged from the top of the sulfur absorption unit, the exhaust gas enters the zinc powder absorption unit. As the exhaust gas passes through the zinc powder layer, trace amounts of mercury vapor react with the zinc powder to form a Zn-Hg solid solution, achieving ultimate adsorption and stabilizing the mercury vapor concentration in the exhaust gas at 0.005 mg / m³. 3 The zinc powder layer meets emission standards. Simultaneously, it can also intercept trace amounts of sulfur or silver dust that may be carried in the exhaust gas, preventing them from being released into the atmosphere.

[0050] Step 5: Emission monitoring and safety interlocks; The purified exhaust gas is discharged from the top outlet of the zinc powder absorption unit. A mercury concentration sensor is installed on the exhaust pipe to monitor the mercury concentration in the exhaust gas in real time. When the monitored value is ≤0.01mg / m³... 3At that time, the exhaust gas was discharged through the exhaust pipe in compliance with standards (far lower than the 0.01 mg / m³ specified in GB16297-1996). 3 (Limit). When the monitored value exceeds 0.01 mg / m³ 3 When the concentration exceeds the standard, the sensor signal is transmitted to the PLC controller, triggering an audible and visual alarm. Simultaneously, the heating power to the heating platform is automatically shut off, and the flow rate of the cooling water circulation pump in the condenser unit and the air volume of the terminal exhaust fan are increased. If the concentration exceeds the standard and remains above the standard for 5 minutes, the PLC controller automatically cuts off the power to the entire machine, forcing a shutdown to ensure personnel and environmental safety.

[0051] In one embodiment, application experiments and performance verification of the device of the present invention are conducted: This invention: An integrated device for mercury vapor recovery and waste gas purification; Control group 1: Single zinc powder adsorption mercury vapor purification device; Control group 2: Single sulfur adsorption mercury vapor purification device; Control group 3: A single iodine solution absorbs mercury vapor for purification; I. Experimental Preparation: 1. Experimental equipment: IGBT device silver-plated solderable parts (50mm×50mm×2mm); silver amalgam brazing filler (Hg-Ag alloy, mercury content 90wt%); anhydrous ethanol (analytical grade); argon gas (purity 99.999%); mercury vapor concentration detector (accuracy 0.001mg / m³, same specifications as the sensor matched with the device). 2. Experimental conditions: All four experiments were conducted in the same brazing workshop, with an ambient temperature of 25℃ and a humidity of 50% RH. The same amalgam brazing process parameters were used, and the pretreatment method of the workpieces to be brazed, the amount of brazing filler metal applied, and the heating regime were completely consistent. The experimental period was 30 days, with a total brazing operation time of 200 hours and an average of 80 IGBT workpieces to be brazed per day.

[0052] 3. Inspection indicators: Mercury concentration at the exhaust gas outlet (real-time monitoring, average value), adsorbent / absorbent replacement cycle, total mercury vapor removal rate, and performance of the finished silver layer (resistivity, bonding strength).

[0053] II. Operation steps of the present invention: Step 1: Pre-treat the silver-plated parts to be soldered by wiping the surface with ethanol to remove oil and impurities; Step 2: Apply the paste-like amalgam brazing filler evenly to the surface to be soldered (thickness 0.1-0.2 mm), and place the part to be soldered or the sample to be silvered in the center of the hot plate; Step 3: Secure the brazed sealing cover, open the one-way valve to introduce argon gas (adjust the gas inlet flow rate to 0.8m³). 3 / h), start the hot plate and perform segmented heating: first, heat up to 180℃ at 5℃ / min and hold for 30 minutes (to pre-evaporate some mercury and reduce subsequent load); then heat up to 240℃ at 3℃ / min and hold for 30 minutes (to completely evaporate the mercury and complete the brazing of the silver layer). Step 4: During the heating process, mercury vapor, along with hot air (chimney effect), enters the exhaust gas purification unit through the outlet. It undergoes sequential condensation, iodine absorption, sulfur absorption, and zinc powder absorption. After passing through exhaust gas detection sensors and meeting emission standards (concentration ≤ 0.01 mg / m³), it is released into the atmosphere. 3 ); Condensation Unit: The closed-loop water cooling circulation system stabilizes the condensate temperature at 20℃±2℃. After mercury vapor is condensed through the polytetrafluoroethylene microchannel, 92% of the gaseous mercury is converted into liquid mercury, which flows into the liquid mercury recovery unit along the inclined guide plate. Iodine solution absorption unit: After the 5% concentration iodine solution is fully in contact with the exhaust gas, the iodine solution is atomized by the atomizing nozzle (particle size 15μm) and then comes into contact with the exhaust gas in the opposite direction. The uncondensed trace amount of mercury vapor reacts with iodine to form mercuric iodide solid precipitate. Sulfur absorption unit: Exhaust gas passes through an 8cm high layer of 2-3mm granular sulfur, where trace amounts of residual mercury vapor are adsorbed to form mercury sulfide. Zinc powder absorption unit: Trace mercury vapor reacts with zinc powder via an amalgamation reaction to achieve ultimate adsorption, while simultaneously adsorbing trace amounts of silver dust and sulfur dust in the exhaust gas.

[0054] Step 5: After heating is complete, turn off the heating plate and wait for the temperature to drop to room temperature. Then, open the cover and remove the material. Periodically recover mercury through the drain valve of the liquid collection tank and collect mercuric iodide through the slag discharge port of the iodine solution tank.

[0055] During the experiment, the mercury concentration at the exhaust gas outlet was monitored in real time, and the equipment operating status was recorded daily. After the experiment, the corrosion of key components of the four sets of equipment was tested, and the performance of the silver layer of the brazed product was evaluated. Mercury was recovered periodically through the drain valve of the liquid mercury recovery unit, and mercuric iodide precipitate was collected through the slag discharge port of the iodine tank. The amount of mercury recovered was recorded.

[0056] III. Results Analysis The device of this invention: core performance quantification data; 1. Mercury vapor treatment performance: During the experimental period, the mercury concentration at the exhaust gas outlet remained stable at 0.004 mg / m³. 3 ±0.001mg / m 3 The total mercury vapor removal rate is 99.7%, the liquid mercury recovery efficiency is 86.5%, and a total of 1.2 kg of liquid mercury has been recovered, which can be recycled for the preparation of silver amalgam brazing filler metal.

[0057] 2. Performance of the finished silver layer: The purity of the residual silver layer after brazing is 99.6%, and the resistivity is 1.45×10⁻⁶.-8 The silver layer has a bonding strength of 22.5 MPa with the surface to be soldered, with no peeling, flaking, or oxidation, fully meeting the conductivity and interconnect reliability requirements of IGBT device electronic packaging.

[0058] 3. Equipment operation performance: The equipment operated without leaks or malfunctions throughout the experiment, and the performance of each purification unit showed no significant decline. The iodine solution replenishment cycle was 15 days, the sulfur replacement cycle was 30 days, and the zinc powder replacement cycle was 30 days. Key components showed no corrosion, and the equipment maintained good stability during continuous operation.

[0059] Control group: Quantitative data on core performance;

[0060] IV. Comparison Results Analysis 1. Waste gas purification efficiency: The mercury concentration at the outlet of the device of this invention is far lower than the national standard of 0.01 mg / m³. 3 The invention meets the mandatory requirements and is significantly better than the three control groups. The total mercury vapor removal rate is 17.4% higher than control group 1, 5.7% higher than control group 2, and 7.8% higher than control group 3. This is because the invention adopts a four-stage treatment process of "condensation recovery + three-stage deep purification", which realizes the step-by-step removal of mercury vapor and makes up for the efficiency shortcomings of single purification technology. 2. Consumable replacement and operating costs: The consumable replacement cycle of the device of the present invention is much longer than that of the control group. The zinc powder in control group 1 is prone to rapid saturation due to its low adsorption capacity (0.1~0.3g / g). The single iodine solution absorption in control group 3 requires continuous consumption of iodine solution and is prone to clogging of the nozzle due to mercuric iodide precipitation. However, the present invention significantly reduces the load of subsequent purification units through condensation recovery, reduces the consumption of adsorbent / absorbent, and significantly reduces operating costs.

[0061] 3. Equipment Corrosion and Stability: The device of this invention uses special materials such as polytetrafluoroethylene and 316L stainless steel, which are resistant to mercury, silver dust, and iodine solution corrosion. It also has a special contact structure designed for "mercury-silver" mixed pollutants, and there is no corrosion phenomenon. In contrast, control group 1 uses ordinary carbon steel, which is prone to forming amalgam with mercury, leading to corrosion and leakage. Control group 2 uses ordinary stainless steel for its iodine solution tank, which is susceptible to slight corrosion by iodine solution. Both control groups have a high equipment failure rate and cannot meet the needs of continuous industrial production.

[0062] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for mercury vapor recovery and waste gas purification in amalgam brazing, characterized in that... The specific steps are as follows: Step 1. Closed Collection and Atmosphere Control: Place the brazing sealing cover containing the workpiece to be brazed on the heating table, fasten the brazing sealing cover, introduce protective gas into it to form a local protective atmosphere, and exhaust the air inside the cover. Step 2. Staged heating and mercury vapor release: The heating platform is heated in stages. First, the temperature is raised to the first preset temperature and held to allow some of the mercury in the amalgam brazing filler to pre-evaporate. Then, the temperature is raised to the second preset temperature and held to allow the remaining mercury to completely evaporate and the silver layer to solidify, thus completing the brazing and forming mercury-containing vapor exhaust gas. Step 3. Condensation Pretreatment and Liquid Mercury Recovery: The mercury-containing vapor waste gas generated in step two is passed into the condensation unit and cooled to below the condensation point of mercury by a cooling medium, so that most of the gaseous mercury in the waste gas condenses into liquid mercury, which is then separated and recovered under the action of gravity. Step 4. Chemical absorption and conversion of iodine solution: The residual waste gas after step three is passed into the iodine solution in the iodine solution absorption unit. The waste gas generated after the reaction with the iodine solution then undergoes a reverse contact reaction with the atomized iodine solution in the iodine solution absorption unit, so that the remaining gaseous mercury in the waste gas reacts with the atomized iodine solution to generate solid mercuric iodide precipitate. At the same time, the silver dust carried in the waste gas is captured by the iodine solution and discharged with the precipitate. Step 5. Sulfur immobilization and adsorption: The waste gas treated in step four is passed into the sulfur absorption unit, whereby the trace amounts of residual mercury in the waste gas react with sulfur to form stable mercury sulfide, thereby achieving further fixation of mercury. Step Six. Deep Adsorption of Zinc Powder at the Terminal: The exhaust gas treated in step five is passed into the zinc powder absorption unit, where trace amounts of mercury vapor are adsorbed through the amalgamation reaction between zinc powder and mercury, while simultaneously intercepting solid particles entrained in the exhaust gas. Step 7. Emissions Monitoring and Safety Interlocks: The exhaust gas purified in step six is ​​monitored in real time by the exhaust gas detection unit. When the concentration of mercury at the outlet is lower than the preset safety threshold, it is discharged; when the concentration exceeds the preset safety threshold, an alarm is triggered and the heating station is shut down.

2. The method for mercury vapor recovery and waste gas purification for amalgam brazing according to claim 1, characterized in that: In step two, the first preset temperature is 180℃, with a heating rate of 5℃ / min and a holding time of 30 minutes; the second preset temperature is 240℃, with a heating rate of 3℃ / min and a holding time of 30 minutes; the protective gas is argon, and the gas inlet flow rate is adjustable within a range of 0.8m³. 3 / h.

3. The method for mercury vapor recovery and waste gas purification for amalgam brazing according to claim 1, characterized in that: In step three, the temperature of the cooling medium in the condensation unit is controlled at 20℃±2℃ to fully condense the mercury vapor. The condensed liquid mercury flows into the recovery unit through a one-way check valve. The recovery unit is equipped with a liquid level sensor, which issues an alarm when the liquid level reaches a preset value.

4. The method for mercury vapor recovery and waste gas purification for amalgam brazing according to claim 1, characterized in that: In step four, the iodine solution is a 5% I2 aqueous solution, which is atomized through an atomizing nozzle with a particle size of 10-20 μm and then comes into countercurrent contact with the exhaust gas; in step five, the sulfur is granular sulfur with a diameter of 2-3 mm and a filling height of 8-10 cm; in step six, the zinc powder is granular zinc powder with a particle size of 10-100 micrometers.

5. The method for mercury vapor recovery and waste gas purification for amalgam brazing according to claim 1, characterized in that: In step seven, the preset safety threshold is 0.01 mg / m³. 3 When the concentration exceeds the threshold, in addition to triggering an alarm and shutting down the heating platform, the cooling medium flow rate and exhaust volume of the condensing unit will be increased. If the concentration continues to exceed the threshold for 5 minutes, the unit will automatically shut down completely.

6. An integrated device for mercury vapor recovery and waste gas purification for amalgam brazing, implemented based on the method described in any one of claims 1-5; characterized in that, include: A brazing sealing cover is installed above the heating table to seal and collect mercury-containing vapor waste gas generated during the brazing process. The brazing sealing cover has an air inlet and an air outlet. The air inlet is connected to a protective gas source, and the air outlet is connected to a waste gas purification unit. The condensation unit, whose inlet is connected to the outlet of the brazed sealing cover, is used to pre-condense the mercury-containing vapor waste gas to separate and recover part of the gaseous mercury in the waste gas; the liquid mercury formed by condensation flows into the liquid mercury recovery unit under the action of gravity to reduce the mercury load of subsequent units; The iodine absorption unit has its inlet connected to the gas outlet of the condensation unit. It is equipped with iodine absorption liquid and iodine atomizing spray device to allow the remaining gaseous mercury in the exhaust gas to react fully with the iodine liquid twice to generate solid mercuric iodide precipitate, and simultaneously capture silver dust in the exhaust gas. The sulfur absorption unit has its inlet connected to the gas outlet of the iodine solution absorption unit and contains granular sulfur packing material for fixing the trace amounts of mercury remaining after treatment by the iodine solution absorption unit. The zinc powder absorption unit has its inlet connected to the gas outlet of the sulfur absorption unit and contains granular zinc powder filler for terminal adsorption of trace mercury in the exhaust gas and interception of solid particles. The safety monitoring module is located at the gas outlet of the zinc powder absorption unit. It includes an exhaust gas detection unit and an alarm device and a heating platform control circuit that are electrically connected to the exhaust gas detection unit. It is used to monitor the exhaust gas concentration in real time and trigger a safety interlock when the concentration exceeds the standard. The condensation unit, iodine solution absorption unit, sulfur absorption unit, and zinc powder absorption unit are connected in series along the direction of exhaust gas flow to form an exhaust gas purification unit.

7. The integrated device for mercury vapor recovery and waste gas purification for amalgam brazing according to claim 6, characterized in that: The brazed sealing cover is made of borosilicate glass, with a 5mm thick aluminum silicate cotton insulation layer on the inner wall, and a spiral groove on the inner wall to guide the flow of condensate; a fluororubber sealing ring is provided at the bottom of the cover where it fits against the heating table; the air outlet of the cover is connected to a corrosion-resistant pipe made of polytetrafluoroethylene, with an inner diameter of 20-30mm.

8. The integrated device for mercury vapor recovery and waste gas purification for amalgam brazing according to claim 6, characterized in that: The condensation unit is equipped with a microchannel heat exchange structure and an inclined guide plate at the bottom to guide the condensed liquid mercury into the liquid mercury recovery unit. The condensation unit is also connected to a closed-loop water cooling circulation system, which includes a variable frequency circulating water pump, a storage tank, and inlet and outlet temperature sensors. A one-way check valve made of polytetrafluoroethylene is installed between the condensation unit and the liquid mercury recovery unit, and a liquid level sensor is installed in the recovery unit.

9. The integrated device for mercury vapor recovery and waste gas purification for amalgam brazing according to claim 6, characterized in that: The iodine absorption unit contains a 5% I2 aqueous solution, and the nozzle of the iodine atomizing spray device atomizes particles with a diameter of 10-20 μm. A slag discharge port is provided at the bottom of the tank for periodically discharging mercuric iodide precipitate and collected silver dust. The sulfur absorption unit contains granular sulfur with a diameter of 2-3 mm and a filling height of 8-10 cm. Both the upper and lower ends of the tank are equipped with stainless steel sieves with a pore size of 1 mm. The zinc powder absorption unit contains granular zinc powder with a particle size of 10-100 micrometers.

10. The integrated device for mercury vapor recovery and waste gas purification for amalgam brazing according to claim 6, characterized in that: The exhaust gas detection unit of the safety monitoring module has a mercury concentration range of 0–0.1 mg / m³. 3 The accuracy is 0.001 mg / m 3 The alarm device activates when the concentration exceeds 0.01 mg / m³. 3 When the concentration exceeds the standard for 5 minutes, the control circuit will automatically shut down the heating function of the heating platform and increase the cooling medium flow and exhaust volume of the condensing unit. When the concentration exceeds the standard for 5 minutes, the control circuit will automatically shut down the machine completely.

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