Cyanide breaking agent and method for treating alkaline cyanide-containing wastewater

Abstract

The invention provides a cyanide breaking agent and method for treating alkaline cyanide-containing wastewater. The cyanide breaking agent is a combination of an oxidizing agent, a Fe3O4 ZIF-8 core-shell magnetic catalyst and PDMS-hydrophobic silicon dioxide composite liquid. Through a catalytic oxidation-adsorption integrated method, the reaction path is shortened, efficient removal of cyanide is realized, the effluent is far lower than 0.5 mg / L specified by the national standard, a recyclable product is obtained, and the risk of secondary pollution caused by HCN or heavy metal precipitation is reduced; non-photocatalytic nanoscale Fe3O4-ZIF-8 core-shell magnetic catalyst particles are combined with PDMS-hydrophobic silicon dioxide composite liquid to cooperate with an oxidizing agent, the process that cyanide is converted into non-toxic products through integrated two-stage oxidation is promoted, and meanwhile the content of ammonia nitrogen in wastewater is further reduced by combining modified activated carbon.

Description

Technical Field

[0001] The present invention relates to the field of wastewater treatment, in particular to a cyanide-breaking agent and a method for treating alkaline cyanide-containing wastewater. Background Art

[0002] Cyanide-containing wastewater mainly refers to wastewater containing cyanide (CN - ) industrial wastewater. Cyanide-containing wastewater is characterized by high toxicity, high stability, complex composition, and large pH fluctuations. Cyanide is a highly toxic substance that is extremely harmful to humans and aquatic life. Even low concentrations of cyanide can cause poisoning, and in severe cases, it is life-threatening. Cyanide in wastewater usually exists in a complex state, is highly stable, and is difficult to degrade naturally. The country has strict standards for the discharge of cyanide-containing wastewater. For example, the "Comprehensive Sewage Discharge Standard" (GB 8978-1996) stipulates a maximum allowable discharge concentration of 0.5 mg / L. If cyanide-containing wastewater is not properly treated and discharged directly, it will cause harm to humans, animals, and the natural environment. Therefore, cyanide reaction wastewater must be decyanated before it can be discharged into the factory sewage system.

[0003] The treatment of cyanide-containing wastewater can be divided into cyanide recovery, cyanide transfer and cyanide destruction methods. Among them, the cyanide recovery method mainly involves acidification release-alkaline solution absorption. This method has high requirements for equipment corrosion protection and there is a risk of HCN leakage. After recovery, SO4 2- High levels still require advanced treatment. Currently, combined processes are often used, such as a cyanide destruction-cyanide transfer process, including a combination of adsorption, oxidation, and precipitation complexation. Patent CN104163518A discloses a method for treating cyanide-containing wastewater from printing and dyeing. After pre-adsorbing cyanide with an ion exchange resin, the cyanide is removed by graded oxidation complexation. During the reaction, the complexing agent fatty alcohol polyoxyethylene ether sodium sulfate and the catalysts copper sulfate and ferrous sulfate are added. The reaction produces a large amount of heavy metal-containing sludge (such as ferrocyanide complex), which is difficult to treat and dispose of.

[0004] At present, the combined process of cyanide transfer-cyanide destruction method includes a combination of advanced oxidation method-adsorption method. Patent CN104230059A discloses a comprehensive treatment method for cyanide wastewater ozone oxidation, which deeply treats cyanide wastewater by ultraviolet / ozone synergistic oxidation and ozone / activated carbon adsorption catalytic oxidation. This method requires ultraviolet catalysis to prevent low ozone utilization, complicated operation, high energy consumption, and difficult recovery of activated carbon. Patent CN106745961A discloses a method and system for deep treatment of coking wastewater for decarbonization, decolorization and decyanation, which uses Fenton oxidation method with hydrogen peroxide and ferrous sulfate, and deep oxidation and adsorption of sodium hypochlorite and activated carbon respectively, so that the effluent water quality meets the standard. Ferric hydroxide precipitate produced by flocculant precipitation is also added during the reaction process of this method, which increases the treatment cost and has a complicated process. It is necessary to accurately control the amount of hydrogen peroxide and ferrous sulfate to avoid reduced efficiency. Summary of the Invention

[0005] To address the generation of HCN or heavy metal precipitation during existing cyanide wastewater treatment processes, the present invention provides a cyanide-breaking agent and method for treating alkaline cyanide wastewater. Through an integrated two-stage oxidation process, the present invention produces a non-toxic, recyclable product, reducing the risk of secondary pollution from waste gas or hazardous waste.

[0006] Another object of the present invention is to solve the technical problems of complex operating procedures and high energy consumption. By integrating catalytic oxidation and adsorption, the reaction path is shortened, cyanide is efficiently removed while reducing the ammonia nitrogen content in the wastewater; and a recyclable non-photocatalytic magnetic catalyst is used to reduce operating costs.

[0007] The specific technical solutions of the present invention are:

[0008] In a first aspect, the present invention provides a cyanide-breaking agent for treating alkaline cyanide-containing wastewater, comprising 250-300 g / L of hydrogen peroxide, 80-120 g / L of sodium hypochlorite mass concentration, 0.6-1 g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst, and 0.02-0.05 g / L of PDMS-hydrophobic silica composite liquid.

[0009] As a preference, the hydrogen peroxide and CN in the cyanide-containing wastewater - The molar ratio is 5-5.5:1.

[0010] Preferably, the CN remaining after the initial oxidation of the sodium hypochlorite and the hydrogen peroxide - The molar ratio is 2.5-3:1.

[0011] The present invention shortens the reaction path and improves the oxidation efficiency by introducing Fe3O4@ZIF-8 core-shell magnetic catalyst. Unlike traditional photocatalysts or metal salt catalysts, it generates hydroxyl radicals by reacting divalent iron ions on the surface of the magnetic core Fe3O4 with hydrogen peroxide in a Fenton-like reaction. The shell ZIF-8 has a porous crystal structure and can selectively adsorb small molecular cyanide through the pore confinement effect. Cyanide is negatively charged under alkaline conditions. The imidazole nitrogen-containing group of ZIF-8 can adsorb cyanide through electrostatic action, forming local enrichment, thereby improving the contact between hydroxyl radicals and cyanide, and promoting the oxidation of remaining cyanide into resource-recoverable products (Na2CO3 and N2) by sodium hypochlorite. At the same time, the shell can block the poisoning effect of heavy metal ions on the magnetic core, allowing recycling and reuse while still maintaining activity.

[0012] Preferably, the Fe3O4@ZIF-8 core-shell magnetic catalyst is a nano-sized particle with a shell pore size of 0.3-0.5 nm and a specific surface area of ​​1300-1800 m 2 / g.

[0013] The present invention utilizes Fe3O4@ZIF-8 core-shell magnetic catalyst and amino-modified activated carbon to achieve efficient removal of cyanide through integrated catalytic oxidation-adsorption. The main cyanide in cyanide-containing wastewater, namely sodium cyanide, will produce NH3 under the action of hydrogen peroxide and Fe3O4@ZIF-8 core-shell magnetic catalyst. The lone pair electrons of the functional group NH2 of the amino-modified activated carbon and the hydrogen atoms of NH3 will form N-H...N hydrogen bonds, resulting in a stable structure with high binding energy. At the same time, the functional group NH2 of the amino-modified activated carbon can be protonated to form NH3. + , cyanide is adsorbed by electrostatic force.

[0014] As a preferred embodiment, a cyanide-breaking agent for treating alkaline cyanide-containing wastewater further comprises 1-3 g / L of amino-modified activated carbon, the micropores of which are 0.5-1 nm and the specific surface area is 1000-1500 m 2 / g.

[0015] The present invention utilizes a PDMS-hydrophobic silica composite liquid as a defoaming agent, and inserts hydrophobic silica nano-scale "microneedles" into the bubble liquid film to destroy its surface tension, causing the bubbles to merge and burst. Under alkaline conditions, the hydrophobicity of the silica surface is enhanced, making it easier to adsorb on the gas-liquid interface, thereby accelerating bubble breaking. Simultaneously, the PDMS molecules can spread on the bubble surface, reducing local surface tension and cooperating with the hydrophobic silica to cause the liquid film to be unevenly stressed and broken. The introduction of the PDMS-hydrophobic silica composite liquid does not cover the active sites of the Fe3O4@ZIF-8 core-shell magnetic catalyst to affect the reaction, because the Fe3O4@ZIF-8 core-shell magnetic catalyst repels the negatively charged PDMS molecules, thereby ensuring catalytic efficiency. Under the action of the defoaming agent, bubbles are reduced, and the contact efficiency between the cyanide-containing wastewater and the Fe3O4@ZIF-8 core-shell magnetic catalyst can also be improved, thereby promoting the generation of hydroxyl radicals and promoting the oxidation reaction.

[0016] In a second aspect, the present invention provides a method for using a cyanide-breaking agent for treating alkaline cyanide-containing wastewater, comprising the following steps:

[0017] S1: Add Fe3O4@ZIF-8 core-shell magnetic catalyst to cyanide-containing wastewater, stir, drop hydrogen peroxide, and add PDMS-hydrophobic silica composite liquid at the same time;

[0018] S2: Add sodium hypochlorite to oxidize the remaining CN - ;

[0019] S3: After magnetic adsorption of Fe3O4@ZIF-8 core-shell magnetic catalyst, amino-modified activated carbon was added for adsorption purification;

[0020] S4: Recycle and regenerate Fe3O4@ZIF-8 core-shell magnetic catalyst and amino-modified activated carbon for reuse.

[0021] The specific reaction of the present invention is as follows:

[0022] CN - +2·OH→CNO - +H2O;

[0023] CNO - +2H2O→HCO3-+NH3↑;

[0024] 2CN - +5ClO - +2OH - →2CO3 2- +N2↑+5Cl - +H2O;

[0025] Preferably, the reaction conditions of steps S1 and S2 are as follows: controlling the temperature at 30-55° C., stirring rate at 150-250 rpm, and total reaction time at 60-120 min.

[0026] Preferably, the reaction pH in step S1 is 9-11, and after the start of step S2, the reaction pH is controlled to naturally drop to 8-9.

[0027] Preferably, in step S3, the Fe3O4@ZIF-8 core-shell magnetic catalyst is adsorbed to the reactor wall by stopping stirring and applying an external magnetic field of 500-600 mT, and then the stirring rate is adjusted to 50-100 rpm. After the amino-modified activated carbon is adsorbed for 30-60 minutes, the mixture is allowed to stand for 20-40 minutes to separate the amino-modified activated carbon by sedimentation.

[0028] Preferably, in step S4, the Fe3O4@ZIF-8 core-shell magnetic catalyst is separated and then rinsed with deionized water, and the amino-modified activated carbon is pickled with 0.5-1M hydrochloric acid for 1.5-2.5h and then washed with water until neutrality, so as to be reused.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] The present invention achieves a cyanide removal rate of over 98% through integrated catalytic oxidation and adsorption, with effluent concentration below 0.1 mg / L, meeting national standards, and obtaining resource-recyclable products, thereby reducing the risk of secondary pollution. The present invention achieves efficient oxidative conversion of cyanide by adopting the synergistic effect of shell adsorption enrichment of the non-photocatalytic Fe3O4@ZIF-8 core-shell magnetic catalyst and catalytic activation of the magnetic core, and can be recycled through magnetic separation to reduce operating costs. The introduction of a PDMS-hydrophobic silica composite liquid as a defoaming agent can further promote contact between cyanide-containing wastewater and the Fe3O4@ZIF-8 core-shell magnetic catalyst, thereby increasing the generation efficiency of hydroxyl radicals and promoting the oxidation reaction. The -NH2 on the surface of the amino-modified activated carbon is used to selectively adsorb NH3 and cyanide, further ensuring that effluent pollutants meet standards. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the embodiments.

[0032] Overall embodiment

[0033] In a first aspect, the present invention provides a cyanide-breaking agent for treating alkaline cyanide-containing wastewater, comprising 250-300 g / L of hydrogen peroxide, 80-120 g / L of sodium hypochlorite mass concentration, 0.6-1 g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst, and 0.02-0.05 g / L of PDMS-hydrophobic silica composite liquid.

[0034] As a preference, the hydrogen peroxide and CN in the cyanide-containing wastewater - The molar ratio is 5-5.5:1.

[0035] Preferably, the CN remaining after the initial oxidation of the sodium hypochlorite and the hydrogen peroxide - The molar ratio is 2.5-3:1.

[0036] Preferably, the Fe3O4@ZIF-8 core-shell magnetic catalyst is a nano-sized particle with a shell pore size of 0.3-0.5 nm and a specific surface area of ​​1300-1800 m 2 / g.

[0037] As a preferred embodiment, a cyanide-breaking agent for treating alkaline cyanide-containing wastewater further comprises 1-3 g / L of amino-modified activated carbon, the micropores of which are 0.5-1 nm and the specific surface area is 1000-1500 m 2 / g.

[0038] In a second aspect, the present invention provides a method for using a cyanide-breaking agent for treating alkaline cyanide-containing wastewater, comprising the following steps:

[0039] S1: Add Fe3O4@ZIF-8 core-shell magnetic catalyst to cyanide-containing wastewater containing sodium cyanide and sodium hydroxide, stir, and drop hydrogen peroxide;

[0040] S2: When bubbles are generated in the reaction of step S1, sodium hypochlorite is added to oxidize the remaining CN - , sodium hydroxide solution was added dropwise to adjust the reaction pH;

[0041] S3: After magnetic adsorption of Fe3O4@ZIF-8 core-shell magnetic catalyst, amino-modified activated carbon was added for adsorption purification;

[0042] S4: Recycle and regenerate Fe3O4@ZIF-8 core-shell magnetic catalyst and amino-modified activated carbon for reuse.

[0043] The specific reaction of the present invention is as follows:

[0044] CN - +2·OH→CNO - +H2O;

[0045] CNO - +2H2O→HCO3-+NH3↑;

[0046] 2CN - +5ClO - +2OH - →2CO3 2- +N2↑+5Cl - +H2O;

[0047] Preferably, the reaction conditions of steps S1 and S2 are as follows: controlling the temperature at 30-55° C., stirring rate at 150-250 rpm, and total reaction time at 60-120 min.

[0048] Preferably, the reaction pH in step S1 is 9-11, and after the start of step S2, the reaction pH is controlled to naturally drop to 8-9.

[0049] Preferably, in step S3, the Fe3O4@ZIF-8 core-shell magnetic catalyst is adsorbed to the reactor wall by stopping stirring and applying an external magnetic field of 500-600 mT, and then the stirring rate is adjusted to 50-100 rpm. After the amino-modified activated carbon is adsorbed for 30-60 minutes, the mixture is allowed to stand for 20-40 minutes to separate the amino-modified activated carbon by sedimentation.

[0050] Preferably, in step S4, the Fe3O4@ZIF-8 core-shell magnetic catalyst is separated and then rinsed with deionized water, and the amino-modified activated carbon is pickled with 0.5-1M hydrochloric acid for 1.5-2.5h and then washed with water until neutrality, so as to be reused.

[0051] Example 1

[0052] The alkaline cyanide wastewater is treated by the following steps:

[0053] S1: Add 0.6 g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst to the cyanide-containing wastewater containing sodium cyanide and stir it thoroughly at a stirring rate of 150 rpm. Then, drop 300 g / L of hydrogen peroxide into the wastewater. - The molar ratio of 5:1 was set, and 0.03 g / L of PDMS-hydrophobic silica composite liquid was added at the same time. The reaction temperature was controlled at 50 ° C. The cyanide-containing wastewater contained sodium hydroxide and the pH was alkaline at 10. The pH was kept stable during the reaction.

[0054] S2: When bubbles are generated in step S1, add 100g / L sodium hypochlorite to oxidize the remaining CN - , the CN remaining after the initial oxidation of sodium hypochlorite and hydrogen peroxide - The molar ratio of 2.5:1 was 2.5:1, and sodium hydroxide solution was added dropwise to adjust the reaction pH. The pH was 10 at the beginning of the reaction and naturally decreased to pH 8 during the reaction. The reaction stirring rate was 150 rpm;

[0055] S3: After the reaction was carried out for 60 min, stirring was stopped, and an external magnetic field of 500 mT was applied to magnetically adsorb the Fe3O4@ZIF-8 core-shell magnetic catalyst to the reactor wall. The stirring rate was adjusted to 50 rpm, and 1.5 g / L amino-modified activated carbon was added for adsorption purification for 40 min. The mixture was allowed to stand for 30 min to separate the amino-modified activated carbon by sedimentation.

[0056] S4: After separating the Fe3O4@ZIF-8 core-shell magnetic catalyst, rinse it with deionized water 10 times; after separating the amino-modified activated carbon, wash it with 0.7M hydrochloric acid for 1.5h and then wash it with water until it is neutral, which can be recycled.

[0057] Example 2

[0058] The alkaline cyanide wastewater is treated by the following steps:

[0059] S1: Add 0.6 g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst to the cyanide-containing wastewater containing sodium cyanide and stir it thoroughly at a stirring rate of 150 rpm. Then, drop 250 g / L of hydrogen peroxide into the wastewater. - The molar ratio of 5:1 was set, and 0.03 g / L of PDMS-hydrophobic silica composite liquid was added at the same time. The reaction temperature was controlled at 50 ° C. The cyanide-containing wastewater contained sodium hydroxide and the pH was alkaline at 10. The pH was kept stable during the reaction.

[0060] S2: When bubbles are generated in the reaction of step S1, add 120g / L sodium hypochlorite to oxidize the remaining CN - , the CN remaining after the initial oxidation of sodium hypochlorite and hydrogen peroxide - The molar ratio of 3:1 was 3:1, and sodium hydroxide solution was added dropwise to adjust the reaction pH. The pH was 10 at the beginning of the reaction and naturally decreased to pH 8 during the reaction. The reaction stirring rate was 150 rpm;

[0061] S3: After the reaction was carried out for 90 min, stirring was stopped, and an external magnetic field of 500 mT was applied to magnetically adsorb the Fe3O4@ZIF-8 core-shell magnetic catalyst to the reactor wall. The stirring rate was adjusted to 50 rpm, and 2.5 g / L amino-modified activated carbon was added for adsorption purification for 40 min. The mixture was allowed to stand for 30 min to separate the amino-modified activated carbon by sedimentation.

[0062] S4: After separating the Fe3O4@ZIF-8 core-shell magnetic catalyst, rinse it with deionized water 10 times; after separating the amino-modified activated carbon, wash it with 0.8M hydrochloric acid for 2h and then wash it with water until it is neutral, which can be recycled.

[0063] Example 3

[0064] The alkaline cyanide wastewater is treated by the following steps:

[0065] S1: Add 1g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst to the cyanide-containing wastewater containing sodium cyanide and stir it thoroughly at a stirring rate of 200rpm. Then, drop 250g / L of hydrogen peroxide into the wastewater. - The molar ratio of 5.5:1 was set, and 0.03 g / L of PDMS-hydrophobic silica composite liquid was added at the same time. The reaction temperature was controlled at 50 ° C. The cyanide-containing wastewater contained sodium hydroxide and the pH was alkaline at 10. The pH was kept stable during the reaction.

[0066] S2: When bubbles are generated in step S1, add 100g / L sodium hypochlorite to oxidize the remaining CN - , the CN remaining after the initial oxidation of sodium hypochlorite and hydrogen peroxide - The molar ratio of 2.5:1 was 2.5:1, and sodium hydroxide solution was added dropwise to adjust the reaction pH. The pH was 10 at the beginning of the reaction and naturally decreased to pH 8 during the reaction. The reaction stirring rate was 200 rpm;

[0067] S3: After the reaction was carried out for 60 min, stirring was stopped, and an external magnetic field of 550 mT was applied to magnetically adsorb the Fe3O4@ZIF-8 core-shell magnetic catalyst to the reactor wall. The stirring rate was adjusted to 70 rpm, and 1 g / L amino-modified activated carbon was added for adsorption purification for 40 min. The mixture was allowed to stand for 30 min to separate the amino-modified activated carbon by sedimentation.

[0068] S4: After separating the Fe3O4@ZIF-8 core-shell magnetic catalyst, rinse it with deionized water 10 times; after separating the amino-modified activated carbon, wash it with 0.7M hydrochloric acid for 1.5h and then wash it with water until it is neutral, which can be recycled.

[0069] Example 4

[0070] The alkaline cyanide wastewater is treated by the following steps:

[0071] S1: Add 1g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst to the cyanide-containing wastewater containing sodium cyanide and stir it thoroughly at a stirring rate of 200rpm. Then, drop 300g / L of hydrogen peroxide into the wastewater. - The molar ratio of 5.5:1 was set, and 0.05 g / L of PDMS-hydrophobic silica composite liquid was added at the same time. The reaction temperature was controlled at 50 ° C. The cyanide-containing wastewater contained sodium hydroxide and the pH was alkaline at 10. The pH was kept stable during the reaction.

[0072] S2: When bubbles are generated in step S1, add 100g / L sodium hypochlorite to oxidize the remaining CN - , the CN remaining after the initial oxidation of sodium hypochlorite and hydrogen peroxide - The molar ratio of 2.5:1 was 2.5:1, and sodium hydroxide solution was added dropwise to adjust the reaction pH. The pH was 10 at the beginning of the reaction and naturally decreased to pH 8 during the reaction. The reaction stirring rate was 200 rpm;

[0073] S3: After the reaction was carried out for 90 min, stirring was stopped, and an external magnetic field of 500 mT was applied to magnetically adsorb the Fe3O4@ZIF-8 core-shell magnetic catalyst to the reactor wall. The stirring rate was adjusted to 50 rpm, and 1 g / L amino-modified activated carbon was added for adsorption purification for 40 min. The mixture was allowed to stand for 30 min to separate the amino-modified activated carbon by sedimentation.

[0074] S4: After separating the Fe3O4@ZIF-8 core-shell magnetic catalyst, rinse it with deionized water 10 times; after separating the amino-modified activated carbon, pickle it with 0.6M hydrochloric acid for 2.5h and then wash it with water until it is neutral, which can be recycled.

[0075] Example 5

[0076] The alkaline cyanide wastewater is treated by the following steps:

[0077] S1: Add 0.8 g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst to the cyanide-containing wastewater containing sodium cyanide and stir it thoroughly at a stirring rate of 150 rpm. Then, drop 260 g / L of hydrogen peroxide into the wastewater. -The molar ratio of 5.2:1 was set, and 0.03 g / L of PDMS-hydrophobic silica composite liquid was added at the same time. The reaction temperature was controlled at 30 ° C. The cyanide-containing wastewater contained sodium hydroxide and had a pH of 11, which was alkaline. The pH was controlled at 9 during the reaction.

[0078] S2: When bubbles are generated in step S1, add 100g / L sodium hypochlorite to oxidize the remaining CN - , the CN remaining after the initial oxidation of sodium hypochlorite and hydrogen peroxide - The molar ratio of 2.5:1 was 2.5:1, and sodium hydroxide solution was added dropwise to adjust the reaction pH to 9. The pH naturally dropped to 8 during the reaction. The reaction stirring rate was 150 rpm.

[0079] S3: After the reaction was carried out for 60 min, stirring was stopped, and an external magnetic field of 600 mT was applied to magnetically adsorb the Fe3O4@ZIF-8 core-shell magnetic catalyst to the reactor wall. The stirring rate was adjusted to 100 rpm, and 2 g / L amino-modified activated carbon was added for adsorption purification for 60 min. The mixture was allowed to stand for 40 min to separate the amino-modified activated carbon by sedimentation.

[0080] S4: After separating the Fe3O4@ZIF-8 core-shell magnetic catalyst, rinse it with deionized water 10 times; after separating the amino-modified activated carbon, wash it with 0.7M hydrochloric acid for 1.5h and then wash it with water until it is neutral, which can be recycled.

[0081] Example 6

[0082] The alkaline cyanide wastewater is treated by the following steps:

[0083] S1: Add 0.8 g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst to the cyanide-containing wastewater containing sodium cyanide and stir it thoroughly at a stirring rate of 150 rpm. Then, drop 280 g / L of hydrogen peroxide into the wastewater. - The molar ratio of 5.2:1 was set, and 0.04 g / L of PDMS-hydrophobic silica composite liquid was added at the same time. The reaction temperature was controlled at 30 ° C. The cyanide-containing wastewater contained sodium hydroxide and had a pH of 11, which was alkaline. The pH was controlled at 9 during the reaction.

[0084] S2: When bubbles are generated in step S1, add 80g / L sodium hypochlorite to oxidize the remaining CN - , the CN remaining after the initial oxidation of sodium hypochlorite and hydrogen peroxide - The molar ratio of 2.8:1 was 2.8:1, and sodium hydroxide solution was added dropwise to adjust the reaction pH. The pH was 9 at the beginning of the reaction and naturally decreased to pH 8 during the reaction. The reaction stirring rate was 150 rpm;

[0085] S3: After the reaction was carried out for 90 min, stirring was stopped, and an external magnetic field of 550 mT was applied to magnetically adsorb the Fe3O4@ZIF-8 core-shell magnetic catalyst to the reactor wall. The stirring rate was adjusted to 70 rpm, and 1.2 g / L amino-modified activated carbon was added for adsorption purification for 60 min. The mixture was allowed to stand for 40 min to separate the amino-modified activated carbon by sedimentation.

[0086] S4: After separating the Fe3O4@ZIF-8 core-shell magnetic catalyst, rinse it with deionized water 10 times; after separating the amino-modified activated carbon, wash it with 0.7M hydrochloric acid for 1.5h and then wash it with water until it is neutral, which can be recycled.

[0087] Example 7

[0088] The alkaline cyanide wastewater is treated by the following steps:

[0089] S1: Add 0.8 g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst to the cyanide-containing wastewater containing sodium cyanide and stir it thoroughly at a stirring rate of 200 rpm. Then, drop 280 g / L of hydrogen peroxide into the wastewater. - The molar ratio of PDMS to hydrophobic silica was 5.1:1, and 0.03 g / L of PDMS-hydrophobic silica composite liquid was added at the same time. The reaction temperature was controlled at 40°C. The cyanide-containing wastewater contained sodium hydroxide and had an alkaline pH of 11. The pH was controlled to remain stable during the reaction.

[0090] S2: When bubbles are generated in step S1, add 80g / L sodium hypochlorite to oxidize the remaining CN - , the CN remaining after the initial oxidation of sodium hypochlorite and hydrogen peroxide - The molar ratio of 2.8:1 was 2.8:1, and sodium hydroxide solution was added dropwise to adjust the reaction pH. The pH was 10 at the beginning of the reaction and naturally decreased to pH 8 during the reaction. The reaction stirring rate was 200 rpm;

[0091] S3: After the reaction was carried out for 60 min, stirring was stopped, and an external magnetic field of 500 mT was applied to magnetically adsorb the Fe3O4@ZIF-8 core-shell magnetic catalyst to the reactor wall. The stirring rate was adjusted to 50 rpm, and 1.2 g / L amino-modified activated carbon was added for adsorption purification for 40 min. The mixture was allowed to stand for 30 min to separate the amino-modified activated carbon by sedimentation.

[0092] S4: After separating the Fe3O4@ZIF-8 core-shell magnetic catalyst, rinse it with deionized water 10 times; after separating the amino-modified activated carbon, wash it with 0.7M hydrochloric acid for 1.5h and then wash it with water until it is neutral, which can be recycled.

[0093] Comparative Example 1

[0094] The only difference between this comparative example and Example 1 is that in step S1 , no PDMS-hydrophobic silica composite liquid is added.

[0095] Comparative Example 2

[0096] The only difference between this comparative example and Example 2 is that in step S1, no Fe3O4@ZIF-8 core-shell magnetic catalyst is added.

[0097] Comparative Example 3

[0098] The only difference between this comparative example and Example 3 is that in step S3, amino-modified activated carbon is not added.

[0099] Comparative Example 4

[0100] The only difference between this comparative example and Example 1 is that in step S1, the PDMS-hydrophobic silica composite liquid and the Fe3O4@ZIF-8 core-shell magnetic catalyst are not added; and in step S3, the amino-modified activated carbon is not added.

[0101] Comparative Example 5

[0102] The alkaline cyanide wastewater is treated by the following steps:

[0103] S1: Add 0.8g / L of ferrous sulfate to the cyanide-containing wastewater containing sodium cyanide, and stir it thoroughly at a stirring rate of 150rpm. Then, drop hydrogen peroxide with a mass concentration of 260g / L into the wastewater. - The molar ratio was 5.2:1, and 30ppm PDMS-hydrophobic silica composite liquid was added at the same time. The reaction temperature was controlled at 30°C. The cyanide-containing wastewater contained sodium hydroxide and had a pH of 11, which was alkaline. The pH was controlled at 9 during the reaction.

[0104] S2: When bubbles are generated in the reaction of step S1, sodium hypochlorite with a mass concentration of 100g / L is added to oxidize the remaining CN - , the CN remaining after the initial oxidation of sodium hypochlorite and hydrogen peroxide - The molar ratio of 2.5:1 was 2.5:1, and sodium hydroxide solution was added dropwise to adjust the reaction pH to 9. The pH naturally dropped to 8 during the reaction. The reaction stirring rate was 150 rpm.

[0105] S3: After the reaction was carried out for 60 minutes, the stirring rate was adjusted to 100 rpm, and 2 g / L amino-modified activated carbon was added for adsorption purification for 60 minutes. The mixture was allowed to stand for 40 minutes and the amino-modified activated carbon was separated by sedimentation.

[0106] Comparative Example 6

[0107] The alkaline cyanide wastewater is treated by the following steps:

[0108] S1: Add 0.8 g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst to the cyanide-containing wastewater containing sodium cyanide and stir it thoroughly at a stirring rate of 200 rpm. Then, drop 280 g / L of hydrogen peroxide into the wastewater. - The molar ratio of PDMS to hydrophobic silica was 5.1:1, and 30 ppm of PDMS-hydrophobic silica composite liquid was added at the same time. The reaction temperature was controlled at 40°C. The cyanide-containing wastewater contained sodium hydroxide and had an alkaline pH of 11. The pH was controlled to remain stable during the reaction.

[0109] S2: When bubbles are generated in the reaction of step S1, add 80g / L mass concentration of sodium hypochlorite to oxidize the remaining CN - , the CN remaining after the initial oxidation of sodium hypochlorite and hydrogen peroxide - The molar ratio of 2.8:1 was 2.8:1, and sodium hydroxide solution was added dropwise to adjust the reaction pH. The pH was 10 at the beginning of the reaction and naturally decreased to pH 8 during the reaction. The reaction stirring rate was 200 rpm;

[0110] S3: After the reaction was carried out for 60 min, stirring was stopped, and an external magnetic field of 500 mT was applied to magnetically adsorb the Fe3O4@ZIF-8 core-shell magnetic catalyst to the reactor wall. The stirring rate was adjusted to 50 rpm, and 1.2 g / L ion exchange resin was added for adsorption purification for 40 min. The reaction was allowed to stand for 30 min to allow sedimentation and separation of the ion exchange resin.

[0111] S4: After separating the Fe3O4@ZIF-8 core-shell magnetic catalyst, rinse it with deionized water 10 times; the ion exchange resin needs acid and alkali regeneration and recycling.

[0112] The test results are shown in Table 1.

[0113] Table 1

[0114] Analyzing the data in Table 1, we can see that:

[0115] Compared with Comparative Example 4, Examples 1-7 all achieved a cyanide removal rate of more than 98% in cyanide-containing wastewater, and the effluent content was far lower than the "Comprehensive Wastewater Discharge Standard" (GB 8978-1996) stipulates that the emission level is 0.5 mg / L, which is regulated by the regulations of 1996-1996. It shows that the Fe3O4@ZIF-8 core-shell magnetic catalyst can generate hydroxyl radicals through a Fenton-like reaction with hydrogen peroxide to improve the oxidation efficiency. Its shell ZIF-8 has a porous crystal structure. Through the pore confinement effect, it selectively adsorbs small molecular cyanide, forming local enrichment, shortening the reaction path, and promoting the contact between hydroxyl radicals and cyanide. Using PDMS-hydrophobic silica composite liquid as a defoaming agent can destroy the surface tension of the bubble liquid film, so that small bubbles can be combined into large bubbles, accelerating bubble breaking, and at the same time improving the contact efficiency between cyanide-containing wastewater and Fe3O4@ZIF-8 core-shell magnetic catalyst, promoting the generation of hydroxyl radicals. Under the action of hydrogen peroxide and Fe3O4@ZIF-8 core-shell magnetic catalyst, NH3 will be produced. The amino-modified activated carbon can adsorb NH3 and cyanide at the same time, further reducing the ammonia nitrogen content.

[0116] Compared with Comparative Example 1, Example 1 uses the PDMS-hydrophobic silica composite liquid as a defoaming agent, and destroys the surface tension of the liquid film through the hydrophobic end nano-particle silica, causing the bubbles to merge and burst, and the alkaline environment of the reaction can enhance the hydrophobicity of the silica surface, thereby accelerating the bubble breaking; the PDMS molecules can be wrapped on the surface of the bubbles, locally reducing the surface tension, and cooperating with the hydrophobic silica to cause the liquid film to be unevenly stressed and broken; under the action of the defoaming agent, the gas bubbles generated by the oxidation reaction under the action of the Fe3O4@ZIF-8 core-shell magnetic catalyst can be reduced, and the contact between the cyanide-containing wastewater and the Fe3O4@ZIF-8 core-shell magnetic catalyst can be increased to promote oxidation; at the same time, the bubbles will not carry the Fe3O4@ZIF-8 core-shell magnetic catalyst to float, resulting in a decrease in magnetic separation efficiency and causing losses; and the bubbles will not block the pore size of the amino-modified activated carbon, resulting in limited adsorption and reduced adsorption efficiency.

[0117] Compared with Comparative Example 2, Example 2 introduces a Fe3O4@ZIF-8 core-shell magnetic catalyst, in which the divalent iron ions on the surface of the magnetic core Fe3O4 can undergo a Fenton-like reaction with hydrogen peroxide, and generate hydroxyl radicals in contact with cyanide-containing wastewater; the shell ZIF-8 selectively adsorbs small molecular cyanide through its porous structure, forming local enrichment, thereby enhancing the contact between the hydroxyl radical domain and the cyanide, shortening the reaction path, and promoting the oxidation process; at the same time, the shell can block the poisoning effect of heavy metal ions on the magnetic core, can be recycled and reused, and after repeated use 10 times, it still maintains an activity of more than 90%; under the action of amino-modified activated carbon, the ammonia nitrogen content can be effectively reduced, and the amino-modified activated carbon will not be overloaded with cyanide adsorption prematurely, resulting in a significant reduction in its adsorption capacity.

[0118] Compared with Comparative Example 3, Example 3 improves the removal rate of cyanide and reduces the ammonia nitrogen content by integrating catalytic oxidation and adsorption; under the action of hydrogen peroxide and Fe3O4@ZIF-8 core-shell magnetic catalyst, NH3 is produced, and the lone pair electrons of -NH2 of the amino-modified activated carbon can form a stable hydrogen bond structure with high binding energy with the hydrogen atoms of NH3; at the same time, it can adsorb cyanide; and after being recycled and reused 5 times, its adsorption rate can still reach more than 85%.

[0119] Compared with Comparative Example 5, Example 5 can make the oxidation reaction more thorough. Unlike conventional ferrous sulfate catalysts, the Fe3O4@ZIF-8 core-shell magnetic catalyst does not deactivate in an alkaline environment, changing the catalytic pathway. The reaction is converted into ferric hydroxide precipitation, which adsorbs cyanide to form hazardous waste ferric cyanide mud, increasing treatment and disposal costs. Its porous shell can enrich cyanide, increase the reaction contact area, and promote more thorough oxidation of hydrogen peroxide and sodium hypochlorite in two stages. In addition, the Fe3O4@ZIF-8 core-shell magnetic catalyst can be magnetically separated and recovered, and after being reused 10 times, it still maintains an activity of more than 90%.

[0120] Compared with Comparative Example 6, Example 6 uses amino-modified activated carbon. Unlike conventional ion exchange resins, the selective adsorption of amino-modified activated carbon can further improve the removal rate of cyanide and reduce the ammonia nitrogen content; and after the amino-modified activated carbon is recycled and reused 5 times, its adsorption rate can still reach more than 85%, which is higher than that of ion exchange resin.

[0121] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0122] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A cyanide-breaking agent for treating alkaline cyanide-containing wastewater, characterized in that: The method comprises 250-300 g / L of hydrogen peroxide, 80-120 g / L of sodium hypochlorite mass concentration, 0.6-1 g / L of Fe3O4@ZIF-8 core-shell magnetic catalyst, and 0.02-0.05 g / L of PDMS-hydrophobic silica composite liquid.

2. A cyanide-breaking agent for treating alkaline cyanide-containing wastewater according to claim 1, characterized in that The hydrogen peroxide and CN in the cyanide-containing wastewater - The molar ratio is 5-5.5:

1.

3. A cyanide-breaking agent for treating alkaline cyanide-containing wastewater according to claim 1 or 2, characterized in that The CN remaining after the initial oxidation of the sodium hypochlorite and the hydrogen peroxide - The molar ratio is 2.5-3:

1.

4. A cyanide-breaking agent for treating alkaline cyanide-containing wastewater according to claim 1, characterized in that The Fe3O4@ZIF-8 core-shell magnetic catalyst is a nano-sized particle with a shell pore size of 0.3-0.5 nm and a specific surface area of ​​1300-1800 m 2 / g.

5. A cyanide-breaking agent for treating alkaline cyanide-containing wastewater according to claim 1, characterized in that It also includes 1-3g / L of amino-modified activated carbon, which has a micropore size of 0.5-1nm and a specific surface area of ​​1000-1500m 2 / g.

6. The method for using a cyanide-breaking agent for treating alkaline cyanide-containing wastewater according to any one of claims 1 to 5, wherein: The following steps are involved: S1: Add Fe3O4@ZIF-8 core-shell magnetic catalyst to cyanide-containing wastewater, stir, drop hydrogen peroxide, and add PDMS-hydrophobic silica composite liquid at the same time; S2: Add sodium hypochlorite to oxidize the remaining CN - ; S3: After magnetic adsorption of Fe3O4@ZIF-8 core-shell magnetic catalyst, amino-modified activated carbon was added for adsorption purification; S4: Recycle and regenerate Fe3O4@ZIF-8 core-shell magnetic catalyst and amino-modified activated carbon for reuse.

7. The method for using a cyanide-breaking agent for treating alkaline cyanide-containing wastewater according to claim 6, wherein: The reaction conditions of steps S1 and S2 are as follows: controlling the temperature at 30-55° C., stirring speed at 150-250 rpm, and total reaction time at 60-120 min.

8. The method for using a cyanide-breaking agent for treating alkaline cyanide-containing wastewater according to claim 7, wherein: The reaction pH in step S1 is 9-11, and after step S2 starts, the reaction pH is controlled to naturally drop to 8-9.

9. The method for using a cyanide-breaking agent for treating alkaline cyanide-containing wastewater according to claim 6, wherein: In step S3, the Fe3O4@ZIF-8 core-shell magnetic catalyst is adsorbed to the reactor wall by stopping stirring and applying an external magnetic field of 500-600 mT, and then the stirring rate is adjusted to 50-100 rpm. After the amino-modified activated carbon is adsorbed for 30-60 minutes, the mixture is allowed to stand for 20-40 minutes to separate the amino-modified activated carbon by sedimentation.

10. The method for using a cyanide-breaking agent for treating alkaline cyanide-containing wastewater according to claim 6, wherein: In step S4, the Fe3O4@ZIF-8 core-shell magnetic catalyst is separated and then rinsed with deionized water, and the amino-modified activated carbon is pickled with 0.5-1M hydrochloric acid for 1.5-2.5 hours and then washed with water until neutrality is achieved for reuse.

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