Stepped closed-loop cyanide gas absorption treatment process

Abstract

The invention relates to the technical field of waste gas treatment, in particular to a stepped closed-loop cyanide gas absorption treatment process. The process comprises the following four core flows: firstly, cyanogen-containing waste gas is introduced into a filler absorption tower through a closed pipeline and reacts with a sodium hydroxide solution to generate sodium cyanide, toxicity fixation is realized, and the initial absorption efficiency is greater than or equal to 95%; secondly, sodium chloride is added into the absorption liquid to adjust the electrolyte concentration, then electrolysis is conducted, and a graphite anode oxidizes cyanide into cyanate till the concentration of CN <-> is lower than 0.5 ppm; thirdly, adding hydrogen peroxide, copper sulfate and other catalysts into the electrolyzed solution, and reacting at 60-85 DEG C to generate N2 and CO2; finally, condensate and supernate are filtered and then flow back to the absorption link, and state monitoring is achieved in cooperation with online detection. According to the technology, the HCN removal rate is larger than or equal to 99.7%, the emission concentration is smaller than or equal to 1.9 mg / m < 3 >, reagent consumption is reduced by 30% or above, the technology is suitable for multiple scenes such as gas chromatography and carbon fiber production, and safety and economical efficiency are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of waste gas treatment technology, specifically a stepped closed-loop cyanide gas absorption treatment process. Background Technology

[0002] Cyanide gases (represented by hydrogen cyanide) are extremely toxic, and emissions are widely required in industrial production and experimental analysis. The safety and thoroughness of their treatment directly affect the health of operators and environmental safety. In experimental scenarios such as gas chromatography sample introduction, cyanide-containing gases need to be purged for 1-2 minutes before injection. During this stage, the gas is often collected and discharged through a universal exhaust hood, which makes it difficult to completely prevent the diffusion of toxic gases, posing significant safety hazards.

[0003] Existing cyanide-containing waste gas treatment technologies suffer from limitations due to their reliance on a single approach, making it difficult to balance efficiency, safety, and economy. Some processes only use alkaline solutions to absorb and fix cyanide, which can convert gaseous HCN into non-volatile salts, but does not involve deep degradation, requiring the subsequent treatment of large amounts of cyanide-containing wastewater and increasing the risk of secondary pollution. Other processes use hydrogen peroxide catalytic oxidation, employing copper, cobalt, or iron salts as catalysts to oxidize HCN into non-toxic substances. While this can achieve harmlessness, it consumes a large amount of reagents when used alone and is not well-suited for low-concentration, dispersed waste gases.

[0004] Traditional processes generally lack closed-loop design, resulting in significant resource waste and secondary pollution. In scenarios such as alkali metal cyanide preparation, cyanide-containing vapor condensate generated during crystallization and cyanide-containing waste gas discharged from the absorption stage are often treated separately and then directly emitted, causing waste of water resources and reagents, and increasing environmental treatment costs. While processes such as electrolytic pretreatment can enhance cyanide removal, they do not form a synergistic treatment chain with front-end absorption and back-end deep oxidation, limiting their efficiency in treating high-concentration, multi-impurity cyanide-containing waste gas. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a stepped closed-loop cyanide gas absorption and treatment process, which achieves the interception of waste gas at the source through closed pipelines and pressure control, and the intermediate products are gradually reduced in toxicity through stepped transformation, eliminating the risk of HCN diffusion and solving the safety hazards of traditional exhaust hood collection.

[0006] This invention is achieved using the following technical solution: The aforementioned stepped closed-loop cyanide gas absorption and treatment process includes the following steps: (1) The cyanide-containing waste gas is introduced into the bottom of the packed absorption tower through a corrosion-resistant sealed pipeline and the gas inlet speed is controlled; sodium hydroxide solution is sprayed into the absorption tower. The HCN in the waste gas reacts with sodium hydroxide to generate sodium cyanide. After being absorbed by the packing layer, the liquid droplets are removed by the top wire mesh demister. (2) The sodium cyanide mixture at the bottom of the absorption tower is introduced into the electrolytic cell, sodium chloride is added to adjust the electrolyte concentration, and then the pH value is adjusted; electrolysis is carried out using graphite anode and titanium plate cathode, and the cyanide gas generated at the anode is collected and returned to the absorption tower until CN - Electrolysis should be stopped when the concentration is below 0.5 ppm. (3) The electrolyzed solution is introduced into the reactor, hydrogen peroxide solution is added at a volume ratio of 1:1, a catalyst is added, the temperature is controlled at 60-85℃ and the stirring rate is controlled, and the generated N2 and CO2 are discharged after drying. The HCN concentration before discharge is ≤1.9mg / m³. 3 ; (4) After filtering the condensate from the reactor and the supernatant from the electrolytic cell through a filter membrane, the condensate is returned to the sodium hydroxide absorption liquid storage tank; online cyanide ion detectors are installed at the outlets of the absorption tower, electrolytic cell, and reactor to monitor CN in real time. - concentration.

[0007] In step (1), the inlet velocity is 0.5-1.0 m / s, the system pressure is 0.1-0.12 MPa, the sodium hydroxide solution concentration is 4-6 mol / L, and the liquid-to-gas ratio is 15-20 L / m. 3 .

[0008] In step (2), the electrolyte concentration is 20-50 g / L, the pH is 7.6-8.0, the electrode spacing is 3.8-4.0 cm, and an application rate of 18-20 A / m is applied. 2 Current density and 3-3.2V voltage electrolysis.

[0009] In step (3), the concentration of hydrogen peroxide solution is 8 mol / L, the amount of catalyst added is 20-50 mg / L, the stirring rate is 200-300 r / min, and the reaction time is 40-60 min. In step (4), the filter membrane is 0.45 μm.

[0010] The corrosion-resistant sealing pipeline is made of polytetrafluoroethylene, and the packing material in the packed absorption tower is polypropylene stepped rings.

[0011] In step (2), the pH of the solution is adjusted by sodium hydroxide or hydrochloric acid, and the hydrogen gas generated at the cathode during electrolysis is collected and safely discharged.

[0012] In step (3), the catalyst is one or more of copper sulfate, cobalt sulfate, or ferrous sulfate.

[0013] In step (4), the effectiveness of sodium hydroxide is determined by observing the change in the transparency of the absorption liquid. When the CN⁻ concentration exceeds the standard or the reagent fails, an audible and visual alarm is triggered.

[0014] In step (1), the cyanide-containing waste gas originates from gas chromatography injection replacement, carbon fiber production carbonization, alkali metal cyanide preparation, or laboratory reaction scenarios.

[0015] In step (4), when treating the waste gas from the preparation of alkali metal cyanide, the cyanide vapor condensate generated in the crystallization step is filtered and mixed with the condensate from the reactor and returned to the absorption stage in step (1).

[0016] The steps of the aforementioned stepped closed-loop cyanide gas absorption and treatment process are as follows: Closed-loop collection and alkaline fixation: The cyanide-containing waste gas is introduced into the bottom of the packed absorption tower through a corrosion-resistant sealed pipeline, controlling the inlet velocity at 0.5-1.0 m / s and the system pressure at 0.1-0.12 MPa; a 4-6 mol / L sodium hydroxide solution is sprayed into the absorption tower, with a liquid-to-gas ratio of 15-20 L / m³. 3 The HCN in the exhaust gas reacts with sodium hydroxide to produce sodium cyanide, which is absorbed by the packing layer (4.5m high, 1.5m×3 sections) and then the liquid droplets are removed by the top wire mesh demister. Electrolytically enhanced cyanide removal: The sodium cyanide mixture at the bottom of the absorption tower is introduced into the electrolytic cell. Sodium chloride is added to adjust the electrolyte concentration to 20-50 g / L, and the pH is adjusted to 7.6-8.0. A graphite anode and titanium cathode are used, with an electrode spacing of 3.8-4.0 cm, and an A / m electrode is applied. 2 Electrolysis is performed at a current density of 3-3.2V. The cyanide gas generated at the anode is collected and refluxed back to the absorption tower until the CN⁻ concentration is below 0.5ppm, at which point electrolysis is stopped. Catalytic oxidation deep degradation: The electrolyzed solution is introduced into a reactor, and an 8 mol / L hydrogen peroxide solution is added at a volume ratio of 1:1. 20-50 mg / L catalyst is added, and the temperature is controlled at 60-85℃, with a stirring rate of 200-300 r / min. The reaction is carried out for 40-60 min. The generated N2 and CO2 are dried before emission. The HCN concentration before emission is ≤1.9 mg / m³. 3 ; Material circulation and monitoring: The condensate from the reactor and the supernatant from the electrolytic cell are filtered through a 0.45μm filter membrane and then returned to the sodium hydroxide absorbent storage tank; online cyanide ion detectors are installed at the outlets of the absorption tower, electrolytic cell, and reactor to monitor CN in real time. - concentration.

[0017] Compared with the prior art, the beneficial effects of the present invention are: (1) By using closed pipelines and pressure control, the source of exhaust gas is intercepted. The intermediate products are transformed in a stepwise manner to gradually reduce their toxicity. There is no risk of HCN diffusion, which solves the safety hazards of traditional exhaust hood collection.

[0018] (2) This invention integrates electrolysis and catalytic oxidation technologies, achieving an HCN removal rate of ≥99.7%, with final products being N2 and CO2, which meet environmental protection standards and avoids the problem of incomplete degradation by a single treatment technology.

[0019] (3) The closed-loop recycling of materials in this invention reduces the consumption of sodium hydroxide and water resources by more than 30%, and the amount of catalyst and oxidant used is greatly reduced after optimization, resulting in a 40% reduction in operating costs compared to existing processes.

[0020] (4) The process of the present invention can be adapted to laboratory small air volume and industrial large air volume scenarios. Online detection and visual observation dual monitoring ensure process stability and solve the problems of poor adaptability and difficulty in judging the status of traditional processes. Detailed Implementation

[0021] To make the objectives and technical solutions of this invention clearer, the invention will be further described in detail below.

[0022] Example 1 Treatment of low-concentration cyanide-containing waste gas by gas chromatography (copper sulfate as catalyst).

[0023] Exhaust gas parameters: Cyanide-containing exhaust gas generated by gas chromatography injection replacement, HCN concentration 50-80 mg / m³ 3 Air volume 100m 3 / h, temperature 25℃, humidity 40%.

[0024] A stepped closed-loop cyanide gas absorption and treatment process includes the following steps: (1) The sodium hydroxide solution concentration is 4 mol / L, and the liquid-to-gas ratio is 15 L / m³. 3 The absorber packing layer height is 3m (1.5m × 2 sections), and the system pressure is 0.1MPa; (2) Sodium chloride addition amount 20 g / L, pH adjusted to 7.6, current density 18 A / m 2 Voltage 3V, electrode spacing 3.8cm; (3) The volume ratio of hydrogen peroxide to reaction liquid is 1:1, the amount of copper sulfate catalyst added is 30 mg / L, the reaction temperature is 70℃, the stirring rate is 200 r / min, and the reaction time is 40 min; (4) The condensate is filtered and then directly returned to the absorbent storage tank.

[0025] Treatment effect: HCN concentration at the absorber outlet was 1.2-1.5 mg / m³. 3 After electrolysis, the CN⁻ concentration was 0.35 ppm, and HCN was not detected in the final emission gas, with a CN⁻ removal rate of 99.8%. The absorption liquid was recycled for 7 days, and the sodium hydroxide consumption was reduced by 35% compared with the traditional process.

[0026] Example 2: Treatment of high-concentration cyanide-containing waste gas during carbon fiber carbonization (copper sulfate as catalyst).

[0027] Exhaust gas parameters: HCN concentration 240-280 mg / m³ in the carbon fiber carbonization workshop. 3 NH3 concentration 20-40 mg / m³ 3 Air volume 12000m³ 3 / h, temperature 80℃, humidity 30%.

[0028] A stepped closed-loop cyanide gas absorption and treatment process includes the following steps: (1) The sodium hydroxide solution concentration is 6 mol / L, and the liquid-to-gas ratio is 20 L / m³. 3 The absorber packing layer height is 4.5m (1.5m × 3 sections), and the system pressure is 0.12MPa; (2) Sodium chloride addition amount 50g / L, pH adjusted to 8.0, current density 20A / m 2 Voltage 3.2V, electrode spacing 4.0cm; (3) The volume ratio of hydrogen peroxide to reaction liquid is 1:1, the amount of copper sulfate catalyst added is 50 mg / L, the reaction temperature is 85℃, the stirring rate is 300 r / min, and the reaction time is 60 min; (4) The condensate and the electrolytic supernatant are mixed, filtered, and then returned to replenish the loss of the absorbent.

[0029] Treatment effect: HCN concentration at the absorber outlet was 15-20 mg / m³. 3 After electrolysis, the CN⁻ concentration is 0.42 ppm, and the final emission gas HCN concentration is 0.2-0.4 mg / m³. 3 NH3 concentration 3-5 mg / m³ 3 The HCN removal rate was 99.9%; sodium hydroxide consumption was reduced by 40%; and there was no discharge of cyanide-containing wastewater.

[0030] Example 3: Treatment of cyanide-containing waste gas from alkali metal cyanide preparation (cobalt sulfate as catalyst) Waste gas parameters: Cyanide-containing waste gas generated during the absorption step of alkali metal cyanide preparation process, HCN concentration 180-220 mg / m³ 3 Air volume 8000m³ 3 / h, temperature 60℃, humidity 35%.

[0031] A stepped closed-loop cyanide gas absorption and treatment process includes the following steps: (1) The sodium hydroxide solution concentration is 5 mol / L, and the liquid-to-gas ratio is 18 L / m³. 3 The absorber packing layer height is 4.5m, and the system pressure is 0.11MPa; (2) Sodium chloride addition amount 35g / L, pH adjusted to 7.8, current density 19A / m 2 Voltage 3.1V, electrode spacing 3.9cm; (3) The volume ratio of hydrogen peroxide to reaction liquid is 1:1, the amount of cobalt sulfate catalyst added is 40 mg / L, the reaction temperature is 75℃, the stirring rate is 250 r / min, and the reaction time is 50 min; (4) After filtering the cyanide vapor condensate generated in the crystallization step, mix it with the condensate from the reactor and reflux it to the absorption stage.

[0032] Treatment effect: Final emission HCN concentration 0.3-0.5 mg / m³ 3 The HCN removal rate is 99.8%; material recycling enables 100% utilization of cyanide-containing condensate, eliminating the need for additional discharge treatment.

[0033] Example 4: Laboratory treatment of high-purity HCN waste gas (ferrous sulfate as catalyst) Exhaust gas parameters: High-purity HCN exhaust gas produced by laboratory synthesis reaction, HCN concentration 300-350 mg / m³ 3 Air volume 500m 3 / h, temperature 20℃, humidity 25%.

[0034] A stepped closed-loop cyanide gas absorption and treatment process includes the following steps: (1) The sodium hydroxide solution concentration is 6 mol / L, and the liquid-to-gas ratio is 20 L / m³. 3 The absorber packing layer height is 3m, and the system pressure is 0.1MPa; (2) Sodium chloride addition amount 50g / L, pH adjusted to 8.0, current density 20A / m 2 Voltage 3.2V, electrode spacing 4.0cm; (3) The volume ratio of hydrogen peroxide to reaction liquid is 1:1, the amount of ferrous sulfate catalyst added is 50 mg / L, the reaction temperature is 80℃, the stirring rate is 300 r / min, and the reaction time is 60 min. (4) The condensate is filtered twice (0.45μm+0.22μm) and then returned to ensure the purity of the absorbent.

[0035] Treatment effect: CN⁻ concentration after electrolysis is 0.38 ppm, and HCN concentration in the final emission gas is 0.1-0.3 mg / m³. 3 The removal rate was 99.9%; reagent consumption was reduced by 38% compared to the single catalytic oxidation method.

[0036] Example 5: Low-volume intermittent treatment of cyanide-containing waste gas (copper sulfate as catalyst) Exhaust gas parameters: Cyanide-containing waste gas generated by intermittent electroplating process, HCN concentration 80-120 mg / m³3 Air volume 2000m³ 3 / h, intermittent emission cycle 120min / time, temperature 30℃, humidity 50%.

[0037] A stepped closed-loop cyanide gas absorption and treatment process includes the following steps: (1) The sodium hydroxide solution concentration is 4.5 mol / L, and the liquid-to-gas ratio is 16 L / m³. 3 The absorber packing layer is 3m high, the system pressure is 0.1MPa, and the absorbent liquid is kept circulating when the waste gas enters intermittently. (2) Sodium chloride addition amount 25g / L, pH adjusted to 7.7, current density 18.5A / m 2 The voltage is 3.0V, the electrode spacing is 3.8cm, and the electrolysis is started and stopped synchronously with the intermittent cycle of exhaust gas. (3) The volume ratio of hydrogen peroxide to reaction liquid is 1:1, the amount of copper sulfate catalyst added is 35 mg / L, the reaction temperature is 65℃, the stirring rate is 220 r / min, and the reaction time is 45 min; (4) After a single treatment, the condensate is temporarily stored and then mixed and refluxed after a total of 3 treatments.

[0038] Treatment effect: After each treatment, the HCN concentration in the exhaust gas is 0.5-0.8 mg / m³. 3 The removal rate is 99.3%; there is no reagent waste under intermittent operation, and the operating cost is reduced by 25%.

[0039] Example 6: Treatment of high-humidity cyanide-containing waste gas (cobalt sulfate as catalyst) Exhaust gas parameters: Cyanide-containing waste gas generated from hydrometallurgy, HCN concentration 150-180 mg / m³ 3 Air volume 6000m³ 3 / h, temperature 40℃, humidity 70%.

[0040] A stepped closed-loop cyanide gas absorption and treatment process includes the following steps: (1) The sodium hydroxide solution concentration is 5.5 mol / L, and the liquid-to-gas ratio is 19 L / m³. 3 The absorption tower is equipped with a pre-dehumidification layer, the packing layer height is 4.5m, and the system pressure is 0.12MPa; (2) Sodium chloride addition amount 40g / L, pH adjusted to 7.9, current density 19.5A / m 2 Voltage 3.1V, electrode spacing 3.9cm; (3) The volume ratio of hydrogen peroxide to reaction liquid is 1:1, the amount of cobalt sulfate catalyst added is 45 mg / L, the reaction temperature is 70℃, the stirring rate is 280 r / min, and the reaction time is 55 min; (4) The condensate is returned after being desalinated and filtered to avoid electrolyte dilution caused by humidity.

[0041] Treatment effect: HCN concentration at the absorber outlet was 10-12 mg / m³. 3 The final HCN concentration in the exhaust gas is 0.4-0.6 mg / m³. 3 The removal rate is 99.7%; the process has good stability under high humidity conditions and there is no problem of decreased absorption efficiency.

[0042] Example 7: Treatment of cyanide-containing waste gas with impurities (CO, CO2) (ferrous sulfate as catalyst) Exhaust gas parameters: Cyanide-containing exhaust gas generated from industrial furnaces and kilns, HCN concentration 120-150 mg / m³ 3 Contains 500-600 mg / m³ of CO 3 CO2 10%-15%, air volume 10000m³ 3 / h, temperature 50℃, humidity 40%.

[0043] A stepped closed-loop cyanide gas absorption and treatment process includes the following steps: (1) The sodium hydroxide solution concentration is 5 mol / L, and the liquid-to-gas ratio is 17 L / m³. 3 The absorber packing layer is 4.5m high, the system pressure is 0.11MPa, and CO and CO2 do not participate in the absorption reaction and directly enter the subsequent stages. (2) Sodium chloride addition amount 30g / L, pH adjusted to 7.8, current density 19A / m 2 Voltage 3.1V, electrode spacing 3.9cm; (3) The volume ratio of hydrogen peroxide to reaction liquid is 1:1, the amount of ferrous sulfate catalyst added is 40 mg / L, the reaction temperature is 75℃, the stirring rate is 250 r / min, and the reaction time is 50 min; (4) The condensate is refluxed, and CO and CO2 are emitted along with the degradation products.

[0044] Treatment effect: Final emission HCN concentration 0.3-0.7 mg / m³ 3 CO concentration dropped to 100-120 mg / m³ 3 The HCN removal rate is 99.6%; impurity gases do not affect process stability and no additional pretreatment is required.

[0045] Example 8: Miniaturized portable cyanide-containing waste gas treatment (copper sulfate as catalyst) Exhaust gas parameters: A small amount of cyanide-containing exhaust gas was generated during on-site emergency testing, with an HCN concentration of 30-60 mg / m³. 3 Air volume 100m 3 / h, temperature 25℃, humidity 35%.

[0046] A stepped closed-loop cyanide gas absorption and treatment process includes the following steps: (1) The sodium hydroxide solution concentration is 4 mol / L, and the liquid-to-gas ratio is 15 L / m³. 3 Small packed absorption tower (diameter 150mm, packing layer height 1.5m), system pressure 0.1MPa; (2) Sodium chloride addition amount 20g / L, pH adjusted to 7.6, small electrolytic cell (volume 10L), current density 18A / m 2 Voltage 3.0V, electrode spacing 3.8cm; (3) The volume ratio of hydrogen peroxide to reaction liquid is 1:1, the amount of copper sulfate catalyst added is 30 mg / L, the small reaction vessel (volume 10 L), the reaction temperature is 70 °C, the stirring rate is 200 r / min, and the reaction time is 40 min; (4) After a small amount of condensate accumulates, manually return it to the absorbent storage tank.

[0047] Treatment effect: Final emission HCN concentration 0.2-0.5 mg / m³ 3 The removal rate is 99.2%; the equipment is small in size and easy to carry, suitable for emergency treatment scenarios, and can run continuously for 8 hours with a single reagent filling.

[0048] Comparative Example 1: The difference from Example 2 is that only the "electrolytic enhanced cyanide removal" step is removed, while the other parameters remain the same: the HCN concentration in the cyanide-containing waste gas is 240-280 mg / m³. 3 Air volume 12000m³ 3 / h; Step 1: Sodium hydroxide solution concentration 6 mol / L, liquid-to-gas ratio 20 L / m 3 Step 3: Directly introduce the absorbed sodium cyanide mixture into the reactor, add hydrogen peroxide and copper sulfate catalyst, react at 85℃, stir at 300r / min, and react for 60min; Step 4: reflux the condensate.

[0049] Treatment effect: The final emission gas HCN concentration was 8.2-10.5 mg / m³. 3 The HCN removal rate was 72%-78%; the CN⁻ concentration in the solution after the reaction was 12.3-15.6 ppm, which did not meet the emission requirements.

[0050] Comparative Example 2: The difference from Example 3 is that the "material recycling" step is removed, while the other parameters remain the same: the HCN concentration in the cyanide-containing waste gas is 180-220 mg / m³. 3 Air volume 8000m³ 3 / h; Steps 1-3 are alkaline absorption, electrolytic cyanide removal, and catalytic oxidation, respectively, with process parameters the same as in Example 3; Step 4 directly discharges the condensate from the reactor and the condensate from the crystallized cyanide vapor, without returning it to the absorption stage.

[0051] Treatment effect: Final emission HCN concentration 0.4-0.6 mg / m³ 3 The HCN removal rate was 99.7%; however, the sodium hydroxide consumption increased by 32% compared to Example 3, and the cyanide-containing condensate required an additional treatment device, increasing the treatment cost by 45%.

[0052] Comparative Example 3: The difference from Example 4 is that a single catalytic oxidation process is used instead of the "alkaline absorption-electrolytic cyanide removal-catalytic oxidation" stepwise process: the HCN concentration in the cyanide-containing waste gas is 300-350 mg / m³. 3 Air volume 500m 3 / h; The waste gas is directly introduced into the reactor, and 8 mol / L hydrogen peroxide solution (volume ratio of 1:1 with the absorbent liquid) and 50 mg / L ferrous sulfate catalyst are added. The reaction temperature is 80℃, the stirring rate is 300 r / min, and the reaction time is 60 min.

[0053] Treatment effect: Final emission HCN concentration 25.3-30.8 mg / m³ 3 The HCN removal rate was 90%-92%; the hydrogen peroxide consumption increased by 60% compared to Example 4; and the residual CN⁻ concentration in the solution after the reaction was 8.7-10.2 ppm.

[0054] The test data above show that, compared with Comparative Example 1, Example 2 demonstrates that the electrolytically enhanced cyanide-breaking step can initially oxidize cyanide ions into low-toxicity cyanate ions, significantly reducing the difficulty of subsequent catalytic oxidation. This is a core step in achieving deep degradation, and its absence would prevent compliance with environmental emission standards. The data from Example 3 and Comparative Example 2 indicate that the closed-loop design of returning the condensate and supernatant to the absorption stage achieves efficient resource utilization, significantly reduces reagent consumption and environmental treatment costs, and solves the resource waste problem of traditional processes. The comparison between Example 4 and Comparative Example 3 shows that the stepped treatment logic of "alkaline absorption - electrolytic cyanide-catalytic oxidation," by undertaking the detoxification task in stages, achieves both high removal rates and reduces the reagent load of individual stages, avoiding the shortcomings of low efficiency and high cost of single processes.

Claims

1. A stepped closed-loop cyanide gas absorption and treatment process, characterized in that, Includes the following steps: (1) The cyanide-containing waste gas is introduced into the bottom of the packed absorption tower through a corrosion-resistant sealed pipeline and the gas inlet speed is controlled; sodium hydroxide solution is sprayed into the absorption tower. The HCN in the waste gas reacts with sodium hydroxide to generate sodium cyanide. After being absorbed by the packing layer, the liquid droplets are removed by the top wire mesh demister. (2) The sodium cyanide mixture at the bottom of the absorption tower is introduced into the electrolytic cell, sodium chloride is added to adjust the electrolyte concentration, and then the pH value is adjusted; electrolysis is carried out using graphite anode and titanium plate cathode, and the cyanide gas generated at the anode is collected and returned to the absorption tower until CN - Electrolysis should be stopped when the concentration is below 0.5 ppm. (3) The electrolyzed solution is introduced into the reactor, hydrogen peroxide solution is added at a volume ratio of 1:1, a catalyst is added, the temperature is controlled at 60-85℃ and the stirring rate is controlled, and the generated N2 and CO2 are discharged after drying. The HCN concentration before discharge is ≤1.9mg / m³. 3 ; (4) The condensate from the reactor and the supernatant from the electrolytic cell are filtered through a filter membrane and then returned to the sodium hydroxide absorption liquid storage tank; online cyanide ion detectors are installed at the outlets of the absorption tower, electrolytic cell, and reactor to monitor CN in real time. - concentration.

2. The stepped closed-loop cyanide gas absorption and treatment process according to claim 1, characterized in that, In step (1), the inlet velocity is 0.5-1.0 m / s, the system pressure is 0.1-0.12 MPa, the sodium hydroxide solution concentration is 4-6 mol / L, and the liquid-to-gas ratio is 15-20 L / m. 3 .

3. The stepped closed-loop cyanide gas absorption and treatment process according to claim 1, characterized in that, In step (2), the electrolyte concentration is 20-50 g / L, the pH is 7.6-8.0, the electrode spacing is 3.8-4.0 cm, and an application rate of 18-20 A / m is applied. 2 Current density and 3-3.2V voltage electrolysis.

4. The stepped closed-loop cyanide gas absorption and treatment process according to claim 1, characterized in that, In step (3), the concentration of hydrogen peroxide solution is 8 mol / L, the amount of catalyst added is 20-50 mg / L, the stirring rate is 200-300 r / min, and the reaction time is 40-60 min. In step (4), the filter membrane is 0.45 μm.

5. The stepped closed-loop cyanide gas absorption and treatment process according to claim 1, characterized in that, The corrosion-resistant sealing pipeline is made of polytetrafluoroethylene, and the packing material in the packed absorption tower is polypropylene stepped rings.

6. The stepped closed-loop cyanide gas absorption and treatment process according to claim 1, characterized in that, In step (2), the pH of the solution is adjusted by sodium hydroxide or hydrochloric acid, and the hydrogen gas generated at the cathode during electrolysis is collected and safely discharged.

7. The stepped closed-loop cyanide gas absorption and treatment process according to claim 1, characterized in that, In step (3), the catalyst is one or more of copper sulfate, cobalt sulfate, or ferrous sulfate.

8. The stepped closed-loop cyanide gas absorption and treatment process according to claim 1, characterized in that, In step (4), the effectiveness of sodium hydroxide is determined by observing the change in the transparency of the absorption liquid. When the CN⁻ concentration exceeds the standard or the reagent fails, an audible and visual alarm is triggered.

9. The stepped closed-loop cyanide gas absorption and treatment process according to claim 1, characterized in that, In step (1), the cyanide-containing waste gas originates from gas chromatography injection replacement, carbon fiber production carbonization, alkali metal cyanide preparation, or laboratory reaction scenarios.