Star-shaped heavy metal chelator with melamine as core and preparation method and application thereof

Abstract

The present application discloses a star-shaped heavy metal chelator with melamine as the core, and a preparation method and application thereof. Melamine is first reacted with formaldehyde under weak alkaline conditions to generate hexamethylol melamine. Before the hexamethylol melamine is further dehydrated and polycondensed, polyethylene polyamine is added to condense the hydroxymethyl groups with the amino groups or imino groups on the polyethylene polyamine and connect the polyethylene polyamine to the melamine. Then, the product is reacted with carbon disulfide in the presence of alkali to connect the --CSS － groups to the polyethylene polyamine branches, forming a structure with melamine as the core and six polyethylene polyamine branches containing multiple --CSS － groups distributed in a star shape. The product of the present application binds heavy metal ions on the molecule through chelation, and then aggregates and grows into micro-flocs through the connection of the melamine core, thereby significantly improving the chelation binding capacity and flocculation and precipitation performance of the heavy metal ions. The process of the present application is simple, the reaction conditions are mild, the operation is easy to control, the process is environmentally friendly, and the industrial production can be easily realized.

Description

Technical Field

[0001] This invention relates to the fields of heavy metal wastewater treatment and heavy metal fixation in incineration fly ash, specifically to a star-shaped heavy metal chelating agent with melamine as its core, its preparation method, and its application. Background Technology

[0002] Heavy metals, whether essential or non-essential elements, can cause significant harm to organisms when their levels exceed certain limits. Due to their non-biodegradability, they easily accumulate in organisms and can ultimately enter the human body through the food chain, causing cumulative poisoning. Therefore, heavy metals not only severely damage the ecological environment but also pose a serious threat to human health. For example, Mn exceeding a certain concentration can affect the liver, blood vessels, immune system, and reproductive system; zinc exceeding a certain amount can lead to vomiting, diarrhea, gastric perforation, intestinal necrosis, and even shock and death; while Pb can damage the kidneys, liver, reproductive system, and nervous system. With the rapid development of industrial and agricultural production, the number of industries involving heavy metals is increasing, and the generation and discharge of heavy metal wastewater are becoming more abundant, with increasingly complex compositions, resulting in wider and more severe pollution and greater difficulty in prevention and control. Therefore, there is an urgent need to develop new and efficient treatment methods to address the increasingly serious heavy metal wastewater pollution.

[0003] To date, the main methods developed for treating heavy metal wastewater include traditional chemical precipitation, ion exchange, membrane filtration, electrochemical treatment, adsorption, and chelation flocculation (precipitation). These methods all have certain drawbacks, and few are universally applicable. In comparison, chelation flocculation (precipitation) utilizes the strong chelating ability of the chelating groups in chelating agents to bind heavy metal ions in wastewater, separating them from the main body of wastewater through flocculation or precipitation. Besides possessing the advantages of high efficiency, convenient treatment, and low energy consumption of traditional chemical precipitation, it produces less precipitate, making it easier for post-treatment and recycling. Therefore, it is a superior method for treating heavy metal wastewater, suitable for treating high-concentration and large-scale heavy metal wastewater. However, this method relies on highly efficient chelating agents or chelating flocculants. Structure determines performance; an excellent molecular structure determines the effectiveness of chelating agents or chelating flocculants in treating heavy metal ions in wastewater, while manufacturing cost is a crucial factor determining its widespread application. Therefore, developing chelating agents or chelating flocculants with excellent structure, superior performance, and low manufacturing cost has always been a direction that people have been striving to develop.

[0004] Melamine is a trimer of aminocyanide, a triazine-based nitrogen-containing heterocyclic organic compound with three amino groups evenly distributed on the triazine nitrogen heterocycle. However, due to its unique triazine nitrogen heterocycle structure, it is only slightly soluble in water, posing difficulties for further development, utilization, and modification. Although it has three amino groups evenly distributed on its molecule, the dithiocarbamate group (-CSS), which has a strong affinity for heavy metal ions, cannot be directly bonded to it.－ ) is attached to it. Because melamine is a relatively inexpensive raw material and possesses the aforementioned unique structure, if the strong chelating group—CSS—can be attached... － By attaching it to this, its structural and price advantages can be fully utilized, providing a new type of high-efficiency treatment agent for the efficient and low-cost treatment of heavy metal wastewater. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a star-shaped heavy metal chelating agent with melamine as its core, its preparation method, and its application.

[0006] The star-shaped heavy metal chelating agent with melamine as its core provided by this invention has the structure of its main components as shown in formula (Ⅰ):

[0007]

[0008] In equation (I), 2≤x≤4, 1≤y≤x, and x and y are both integers; when y<x, there are x-y N-connected H atoms; z is 0 or 1, when z is 0, the terminal N-connected H atoms.

[0009] The above-mentioned chelating agent uses melamine as its core, with six -CSS nucleotides grafted onto its three amino groups. － The polyethylene polyamine branches, substituted with functional groups, form a star-shaped structure. This is achieved through the -CSS groups on the six branches. － The functional group chelates and binds heavy metal ions from wastewater, and the melamine ring aggregates the chelated heavy metal ions bound by six branches, promoting the formation and growth of micro-flocs, making the flocs larger and denser, thus facilitating sedimentation and separation. Furthermore, this star-shaped heavy metal chelating agent also contains auxiliary components such as dithiocarbamate, xanthic acid, and NaOH, which work synergistically with the main components to not only enhance the chelation and binding capacity for heavy metals in wastewater but also significantly improve its flocculation and sedimentation separation performance.

[0010] The preparation method of the above-mentioned star-shaped heavy metal chelating agent with melamine core includes the following steps:

[0011] (1) Add formaldehyde solution to the reactor at a molar ratio of melamine to formaldehyde of 1:10-12, adjust the pH value to 8.3-9.2 with alkali or alkaline salt solution, and then add melamine; start the stirrer, heat to 75-85℃, and wait for the reaction mixture to change from turbid to clear, keep it at the temperature and continue the reaction for 20-60 minutes; then add distilled water preheated to 75-85℃ to the reactor at a volume ratio of distilled water to formaldehyde solution of 6-8:1, and stir thoroughly.

[0012] (2) Add polyethylene polyamine dropwise to the solution in step (1) at a molar ratio of 0.8 to 1.0:1, continue the reaction for 30 to 60 minutes, and then cool down to room temperature.

[0013] (3) Add NaOH to the solution obtained in step (2) according to the molar ratio of NaOH to n times the molar ratio of polyethylene polyamine, which is 0.24 to 1.2:1, where n represents the number of N atoms in the polyethylene polyamine molecule. After dissolving, continue the reaction for 30 to 60 minutes.

[0014] (4) Add carbon disulfide slowly dropwise to the solution obtained in step (3) at a molar ratio of carbon disulfide to sodium hydroxide of 1:1.1 to 1.2. Stir the reaction at room temperature for 4 to 5 hours until the bottom oil droplets disappear. Then heat the mixture to 50°C to 60°C and react for 1 to 2 hours. Then cool the mixture to room temperature to obtain the product, a star-shaped heavy metal chelating agent with melamine as the core.

[0015] Furthermore, in step (1), the melamine is a product with industrial grade or higher purity, and the formaldehyde is a product with a mass fraction of 37% to 40% and an industrial grade or higher purity.

[0016] Further, in step (1), the alkali or alkaline salt solution is a Na2CO3 solution with a mass fraction of 10% to 15% or a NaOH solution with a mass fraction of 20% to 30%.

[0017] Further, in step (2), the polyethylene polyamine is any one of diethylenetriamine, triethylenetetramine, or tetraethylenepentamine, preferably triethylenetetramine.

[0018] Furthermore, in step (3), the NaOH is a solid product with industrial-grade or higher purity.

[0019] Furthermore, in step (4), the carbon disulfide is a product of industrial grade or higher purity, and no further purification is required before use.

[0020] Furthermore, in step (4), the slow addition of carbon disulfide takes 30 to 60 minutes.

[0021] Furthermore, in step (1), the reactor is equipped with a mechanical stirrer, a dripping funnel, and a reflux condenser.

[0022] The above-mentioned chelating agents are applied to the treatment of heavy metals in various types of heavy metal wastewater or incineration fly ash, and the treatment effect is excellent.

[0023] This invention relates to a method for preparing a star-shaped heavy metal chelating agent with melamine as the core. First, melamine and formaldehyde undergo an addition reaction under weakly alkaline conditions to generate hexamethylol melamine. Then, before further dehydration and polycondensation, a polyethylene polyamine is added, causing the hydroxymethyl group to condense with the amino or imino group on the polyethylene polyamine, attaching it to the amino group of the melamine. Next, it reacts with carbon disulfide in the presence of NaOH, attaching -CSS to the grafted polyethylene polyamine branch chains. － Modifications are applied to the side chains, forming a structure with melamine as the parent nucleus, containing 6 chains with multiple —CSS － The star-shaped structure of the polyethylene polyamine branched chain. (via —CSS) － The chelation effect binds heavy metal ions in wastewater to molecules, and then the melamine core connects them to form micro-flocs and grows into larger flocs, significantly improving the chelation and binding capacity and flocculation and sedimentation performance of various heavy metal ions in water, thus achieving efficient removal of heavy metals from wastewater.

[0024] The advantages of this invention compared to the prior art are as follows:

[0025] (1) The product molecule of this invention has a melamine core grafted with 6 CSS-type nucleotides. － A star-shaped structure composed of branched polyethylene polyamine chains modified with functional groups. —CSS on the 6 branches. － The functional groups can chelate and bind heavy metal ions in wastewater over a wide range. Furthermore, the melamine rings aggregate the heavy metal ions bound by the six branched chains, promoting the formation and growth of micro-flocs, resulting in larger, denser flocs that facilitate sedimentation and separation. This superior structure of the product of this invention enhances the removal efficiency of heavy metal ions from wastewater.

[0026] (2) The method of the present invention involves diluting the generated hydroxymethyl melamine with water and adding polyethylene polyamine in a timely manner and maintaining an excess before further dehydration and condensation. This ensures that the hydroxymethyl group condenses with the polyethylene polyamine to form a relatively complete six-branched structure, and also acts as a blocker for the hydroxymethyl group, preventing the condensation polymerization between hydroxymethyl melamine groups. This overcomes the difficulty of directly attaching -CSS to melamine. － The difficulty in controlling the functional groups effectively prevented the problem of easy condensation polymerization of hydroxymethyl melamine, thus achieving effective control over the molecular structure.

[0027] (3) The product of this invention is safe and non-toxic, has multiple chelating active sites, and can rapidly react with most heavy metal ions in wastewater at room temperature to form stable, water-insoluble chelates, making it widely applicable. Due to —CSS －Distributed along the star-shaped branches centered on melamine, these branches can chelate and aggregate heavy metal ions around the melamine core over a wider area. Furthermore, the cooperation between multiple branches results in a greater number of chelated heavy metal ions, forming denser and more stable micro-flocs. This promotes further growth into larger flocs, accelerating sedimentation and separation. Therefore, it effectively improves the removal efficiency of heavy metal ions from wastewater.

[0028] (4) When the product of this invention is used to treat heavy metal wastewater, only a certain amount of the product of this invention needs to be added to the heavy metal wastewater and stirred thoroughly to quickly generate insoluble flocs, which can be separated by sedimentation and filtration. No complicated equipment and procedures are required, so the treatment process is simple.

[0029] (5) The preparation process of this invention is simple, the reaction conditions are mild, the operation and control are easy, the process is environmentally friendly, no special equipment is required, the investment is low, it is easy to realize industrial production, and it has broad application prospects.

[0030] This invention is suitable for the treatment of various heavy metal wastewaters and the fixation of heavy metals in incineration fly ash, and is especially suitable for removing heavy metal ions from industrial wastewater and domestic sewage, particularly complex wastewater containing multiple heavy metal ions. Attached Figure Description

[0031] Figure 1 This is a flowchart of the preparation method of the present invention.

[0032] Figure 2 The infrared spectrum of the star-shaped heavy metal chelating agent with melamine core (sample of Example 5) is a product of this invention. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0034] Examples 1-11 illustrate the preparation method of the star-shaped heavy metal chelating agent with melamine as the core of the present invention, and Examples 12-14 illustrate the application examples of the product of the present invention.

[0035] Example 1

[0036] (1) Take 37.0 mL of formaldehyde with a mass fraction of 37-40% and add it to a 500 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 10.00% Na2CO3 solution to adjust the pH of the formaldehyde solution to 8.3. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 75°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 20 min. Then add 222 mL of distilled water preheated to 75°C to the reactor and stir thoroughly.

[0037] (2) Take 43.6 mL of 99.00% diethylenetriamine and add it to the solution in step (1). Continue the reaction for 30 min and then cool it to room temperature.

[0038] (3) Weigh 21.00g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 30min;

[0039] (4) Take 25.9 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 30 min. Stir the reaction at room temperature for 4 h until the bottom oil droplets disappear. Then heat to 50℃ and react for 2 h. Then cool down to room temperature to obtain 388.8 mL of reddish-brown liquid, which is the star-shaped heavy metal chelating agent with melamine as the core.

[0040] Example 2

[0041] (1) Take 40.7 mL of formaldehyde with a mass fraction of 37-40% and add it to a 500 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 15.00% Na2CO3 solution to adjust the pH of the formaldehyde solution to 9.0. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 80°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 40 min. Then add 325 mL of distilled water preheated to 80°C to the reactor and stir thoroughly.

[0042] (2) Take 54.0 mL of 99.00% diethylenetriamine and add it to the solution in step (1). Continue the reaction for 40 min and then cool it to room temperature.

[0043] (3) Weigh 51.98g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 40min;

[0044] (4) Take 64.2 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 40 min. Stir the reaction at room temperature for 4.5 h until the bottom oil droplets disappear. Then heat to 55℃ and react for 1.5 h. Then cool down to room temperature to obtain 481.5 mL of reddish-brown liquid, which is the star-shaped heavy metal chelating agent with melamine as the core.

[0045] Example 3

[0046] (1) Take 44.4 mL of formaldehyde with a mass fraction of 37-40% and add it to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 20.00% NaOH solution to adjust the pH of the formaldehyde solution to 9.2. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 85°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 60 min. Then add 310.8 mL of distilled water preheated to 85°C to the reactor and stir thoroughly.

[0047] (2) Take 65.5 mL of 99.00% diethylenetriamine and add it to the solution in step (1). Continue the reaction for 60 min and then cool it to room temperature.

[0048] (3) Weigh 90.72g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 40min;

[0049] (4) Take 116.7 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 60 min. Stir the reaction at room temperature for 5 h until the bottom oil droplets disappear. Then heat to 60℃ and react for 1 h. Then cool to room temperature to obtain 552.9 mL of reddish-brown liquid, which is the star-shaped heavy metal chelating agent with melamine as the core.

[0050] Example 4

[0051] (1) Take 37.0 mL of formaldehyde with a mass fraction of 37-40% and add it to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 25.00% NaOH solution to adjust the pH of the formaldehyde solution to 8.5. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 75°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 40 min. Then add 296.0 mL of distilled water preheated to 75°C to the reactor and stir thoroughly.

[0052] (2) Take 78.4 mL of triethylenetetramine with a mass fraction of 95.00% and add it to the solution in step (1). Continue the reaction for 40 min and then cool it to room temperature.

[0053] (3) Weigh 52.50g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 50min;

[0054] (4) Take 64.8 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 40 min. Stir the reaction at room temperature for 4.5 h until the bottom oil droplets disappear. Then heat to 55℃ and react for 1.5 h. Then cool down to room temperature to obtain 489.5 mL of reddish-brown liquid, which is a star-shaped heavy metal chelating agent with melamine as the core.

[0055] Example 5

[0056] (1) Take 40.7 mL of formaldehyde with a mass fraction of 37-40% and add it to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 30.00% NaOH solution to adjust the pH value of the formaldehyde solution to 9.1. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 80°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 60 min. Then add 284.9 mL of distilled water preheated to 80°C to the reactor and stir thoroughly.

[0057] (2) Take 77.6 mL of triethylenetetramine with a mass fraction of 95.00% and add it to the solution in step (1). Continue the reaction for 50 min and then cool it to room temperature.

[0058] (3) Weigh 77.96g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 60min;

[0059] (4) Take 96.3 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 50 min. Stir the reaction at room temperature for 5 h until the bottom oil droplets disappear. Then heat to 60℃ and react for 2 h. Then cool down to room temperature to obtain 512.6 mL of reddish-brown liquid, which is a star-shaped heavy metal chelating agent with melamine core, denoted as MA-TETA-DTC.

[0060] The sodium dithiocarbamate chelating agent prepared using triethylenetetramine (TETA) as raw material and in the same ratio and reaction conditions as in this embodiment of triethylenetetramine, carbon disulfide and NaOH is denoted as TETA-DTC.

[0061] Example 6

[0062] (1) Take 44.4 mL of formaldehyde with a mass fraction of 37-40% and add it to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 25.00% NaOH solution to adjust the pH of the formaldehyde solution to 9.0. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 85°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 50 min. Then add 266.4 mL of distilled water preheated to 85°C to the reactor and stir thoroughly.

[0063] (2) Take 75.2 mL of triethylenetetramine with a mass fraction of 95.00% and add it to the solution in step (1). Continue the reaction for 60 min and then cool it to room temperature.

[0064] (3) Weigh 100.80g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 60min;

[0065] (4) Take 124.5 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 60 min. Stir the reaction at room temperature for 5 h until the bottom oil droplets disappear. Then heat to 60℃ and react for 2 h. Then cool down to room temperature to obtain 529.4 mL of reddish-brown liquid, which is the star-shaped heavy metal chelating agent with melamine as the core.

[0066] Example 7

[0067] (1) Take 40.7 mL of formaldehyde with a mass fraction of 37-40% and add it to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 15.00% Na2CO3 solution to adjust the pH of the formaldehyde solution to 8.8. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 80°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 40 min. Then add 325.6 mL of distilled water preheated to 80°C to the reactor and stir thoroughly.

[0068] (2) Take 86.2 mL of triethylenetetramine with a mass fraction of 95.00% and add it to the solution in step (1). Continue the reaction for 60 min and then cool it to room temperature.

[0069] (3) Weigh 28.88g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 50min;

[0070] (4) Take 35.7 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 30 min. Stir the reaction at room temperature for 4.5 h until the bottom oil droplets disappear. Then heat to 60 °C and react for 1.5 h. Then cool down to room temperature to obtain 499.6 mL of reddish-brown liquid, which is the star-shaped heavy metal chelating agent with melamine as the core.

[0071] Example 8

[0072] (1) Take 37.0 mL of formaldehyde with a mass fraction of 37-40% and add it to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 15.00% Na2CO3 solution to adjust the pH of the formaldehyde solution to 9.2. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 80°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 50 min. Then add 296.0 mL of distilled water preheated to 80°C to the reactor and stir thoroughly.

[0073] (2) Take 99.8 mL of tetraethylenepentamine with a mass fraction of 95.00% and add it to the solution in step (1). Continue the reaction for 40 min and then cool it to room temperature.

[0074] (3) Weigh 26.25g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 40min;

[0075] (4) Take 32.43 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 40 min. Stir the reaction at room temperature for 4 h until the bottom oil droplets disappear. Then heat to 55℃ and react for 1.5 h. Then cool down to room temperature to obtain 475.9 mL of orange-red liquid, which is the star-shaped heavy metal chelating agent with melamine as the core.

[0076] Example 9

[0077] (1) Take 40.7 mL of formaldehyde with a mass fraction of 37-40% and add it to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 20.00% NaOH solution to adjust the pH value of the formaldehyde solution to 9.1. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 85°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 60 min. Then add 284.9 mL of distilled water preheated to 80°C to the reactor and stir thoroughly.

[0078] (2) Take 98.8 mL of tetraethylenepentamine with a mass fraction of 95.00% and add it to the solution in step (1). Continue the reaction for 40 min and then cool it to room temperature.

[0079] (3) Weigh 51.98g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 50min;

[0080] (4) Take 64.2 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 50 min. Stir the reaction at room temperature for 5 h until the bottom oil droplets disappear. Then heat to 60℃ and react for 2 h. Then cool down to room temperature to obtain 505.8 mL of reddish-brown liquid, which is a star-shaped heavy metal chelating agent with melamine as the core.

[0081] Example 10

[0082] (1) Take 44.4 mL of formaldehyde with a mass fraction of 37-40% and add it to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 25.00% NaOH solution to adjust the pH of the formaldehyde solution to 8.5. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 85°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 60 min. Then add 310.8 mL of distilled water preheated to 85°C to the reactor and stir thoroughly.

[0083] (2) Take 95.8 mL of tetraethylenepentamine with a mass fraction of 95.00% and add it to the solution in step (1). Continue the reaction for 50 min and then cool it down to room temperature.

[0084] (3) Weigh 75.60g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 60min;

[0085] (4) Take 93.4 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 60 min. Stir the reaction at room temperature for 4.5 h until the bottom oil droplets disappear. Then heat to 60℃ and react for 1.5 h. Then cool down to room temperature to obtain 568.2 mL of orange-red liquid, which is the star-shaped heavy metal chelating agent with melamine as the core.

[0086] Example 11

[0087] (1) Take 37 mL of formaldehyde with a mass fraction of 37-40% and add it to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser. Add 30.00% NaOH solution to adjust the pH of the formaldehyde solution to 8.9. Then add 6.37 g of 99.00% melamine, start the stirrer and heat to 85°C. When the reaction mixture changes from turbid to clear, keep it at the temperature and continue the reaction for 60 min. Then add 296.0 mL of distilled water preheated to 85°C to the reactor and stir thoroughly.

[0088] (2) Take 99.8 mL of tetraethylenepentamine with a mass fraction of 95.00% and add it to the solution in step (1). Continue the reaction for 60 min and then cool it to room temperature.

[0089] (3) Weigh 105.00g of solid NaOH with a mass fraction of 96.00%, dissolve it, and continue the reaction for 60min;

[0090] (4) Take 129.7 mL of carbon disulfide with a mass fraction of 99.00% and slowly add it to the solution obtained in step (3) within 60 min. Stir the reaction at room temperature for 5 h until the bottom oil droplets disappear. Then heat to 60℃ and react for 2 h. Then cool down to room temperature to obtain 586.0 mL of orange-red liquid, which is the star-shaped heavy metal chelating agent with melamine as the core.

[0091] Infrared spectral analysis was performed on the melamine-based star-shaped heavy metal chelating agents obtained in Examples 1 to 11, and the results were basically consistent. The infrared spectral analysis results of the chelating agent obtained in Example 5 are as follows: Figure 2 As shown. Figure 2 The absorption peaks in the infrared spectrum can be assigned as follows: 3264.21 cm⁻¹ -1 These are the stretching vibration peaks of OH and -NH in the water content of the sample; at 2962.13 and 2854.61 cm⁻¹. -1 Asymmetric and symmetric stretching vibration peaks of -CH2- appear at 1342.21 cm⁻¹. -1 Its bending vibration peak appears at 1622.32cm. -1 The peak intensity represents the stretching vibration of the C=N group in the triazine ring of the melamine parent compound, and the bending vibration of the NH group in the -NH group and the OH group in the bound water molecule; 1427.07 cm⁻¹ -1 The strong peak at 879.38 cm⁻¹ is the in-plane stretching vibration peak of the triazine ring. -1 The medium-intensity peaks at these locations are out-of-plane vibrational peaks of the triazine ring; 1203.36, 1155.63, and 1107.90 cm⁻¹. -1 The weak peaks at 997.02 and 956.52 cm⁻¹ are the stretching vibration peaks of CO and CN in the molecule. -1 The weak peak at -CSS- The stretching vibration peaks of C=S and CS in the middle; 2492.54 cm. -1 This is the triazine ring deformation vibration peak; 699.55 cm⁻¹ -1 This is the out-of-plane bending vibration peak of the CH group in the -CH2- group of the molecule. Elemental analysis of the above sample showed that the S content was 37.49%, which, converted to -CSS... － On average, each heavy metal chelating agent molecule has 16.6 —CSS bonds attached. － The above results indicate that a star-shaped heavy metal chelating agent with melamine as its core has been successfully synthesized.

[0092] Example 12

[0093] This embodiment demonstrates the treatment effect of the sample from Example 5 on heavy metal wastewater.

[0094] The sample MA-TETA-DTC(—CSS) obtained in Example 5 was used respectively. — The chelating agent TETA-DTC (containing 6.388 mmol / g of CSS-) prepared by triethylenetetramine (TETA) under the same TETA to CS2 molar ratio and preparation conditions was used as a reagent to prepare 100 mg / L solutions containing Pb. 2+ Cd 2+ Ni 2+ Cu 2+ and Zn 2+ Simulated heavy metal water samples were used. Flocculation test conditions: 500 mL of simulated heavy metal water samples were taken, and the pH value was adjusted to approximately 6. The reagent was added to a MY3000-6G intelligent color screen coagulation test stirrer (Wuhan Meiyu Instrument Co., Ltd.). The mixture was stirred rapidly at 220 r / min for 5 min, then at 100 r / min for 10 min, followed by slow stirring at 60 r / min for 7 min. After standing for 20 min, the clear liquid at 2 cm below the surface was measured using an AA-7000 atomic absorption spectrophotometer (Shimadzu Corporation, Japan). The treatment results are shown in Table 1.

[0095] Table 1. Removal effect of the product of this invention on free heavy metal ions

[0096]

[0097] As shown in Table 1, under optimal conditions, the product MA-TETA-DTC of this invention has a better effect on free Pb than the control sample TETA-DTC. 2+ Cd 2+ Ni 2+ Cu 2+ and Zn 2+Plasma removal is highly effective, with residual ion concentrations far below the Class I standard of the "Integrated Wastewater Discharge Standard" (GB8978-1996), and it can even remove Pb. 2+ and Cd 2+ Completely removed.

[0098] Example 13

[0099] This example illustrates the settling velocity of flocs generated from the treatment of heavy metals in the MA-TETA-DTC chelated wastewater in Example 5.

[0100] Using the sample obtained in Example 5, MA-TETA-DTC (with a CSS content of 5.845 mmol / g) as the chelating agent, and TETA-DTC (with a CSS content of 5.845 mmol / g) as the chelating agent, respectively... — The sample containing 6.388 mmol / g was used as a comparison sample, and a sample containing 100 mg / L of Cu was used as a reference. 2+ Simulated wastewater was used as the test object. The experiment was first conducted according to the reagent addition amount and flocculation conditions in Example 12. After stirring was stopped, the test solution was quickly transferred into a 500mL graduated cylinder, and the timing was started to record the drop height of the clear and turbid interface at different times. The results are shown in Table 2.

[0101] Table 2. MA-TETA-DTC chelated Cu of the present invention. 2+ The settling velocity of the generated flocs

[0102]

[0103] As can be seen from the results in Table 2, the product of this invention, MA-TETA-DTC, is treated with Cu-containing... 2+ The flocs produced by MA-TETA-DTC settled significantly faster than those produced by TETA-DTC, and after 30 minutes of settling, the height of the clear liquid was greater than that of the TETA-DTC-treated liquid. During the experiment, it was clearly observed that the flocs produced by MA-TETA-DTC were larger and denser than those produced by TETA-DTC, with fewer small flocs, and the clear liquid had lower turbidity and was clearer. Therefore, MA-TETA-DTC prepared using the method of this invention exhibits superior chelation flocculation performance and floc settling performance.

[0104] Example 14

[0105] Using MA-TETA-DTC obtained in Example 5 as a chelating agent, the wastewater from a certain electroplating plant was used as the treatment target. The pollutant indicators of the wastewater were: Cu 2+ The concentration was 166.14 mg / L, Ni 2+ The concentration was 41.26 mg / L, the total Cr concentration was 16.64 mg / L, the pH value was 1.59, the turbidity was 345.1 NTU, it contained cyanide, and appeared as a grayish-white turbid substance.

[0106] The product MA-TETA-DTC obtained in Example 5, commercially available heavy metal chelating agents DTCR and TMT-18 were used as reagents. 200 mL of wastewater sample was taken, and the pH was first adjusted to approximately 6 with lime milk. Then, it was placed on a MY3000-6G intelligent color screen coagulation test stirrer (Wuhan Meiyu Instrument Co., Ltd.), and certain amounts of chelating agents such as MA-TETA-DTC, commercially available DTCR, and TMT-18 were added. The amount of chelating agent added was 1.2 times the stoichiometric ratio, where the stoichiometric ratio of MA-TETA-DTC and DTCR (i.e., the ratio of -CSS in MA-TETA-DTC or DTCR) was... － The molar ratios of TMT-18 to heavy metal ions were 1.97:1 and 2.01:1, respectively. The stoichiometric ratio of TMT-18 to metal ions was 2:3. When using DTCR as the reagent, FeCl3 needed to be added at a dosage of 200 mg / L. The chelating agent was added under stirring at 220 r / min for 5 min; then stirred at 100 r / min for 15 min (adding an appropriate amount of polyacrylamide PAM after stirring for 7 min), and then stirred at 60 r / min for 10 min. After standing for 20 min, samples were taken for analysis to determine the concentration of heavy metal ions in the treated water.

[0107] Table 3. Removal effect of the product of this invention on comprehensive wastewater from electroplating plants.

[0108]

[0109] The results in Table 3 show that the product MA-TETA-DTC of this invention has a better treatment effect on this comprehensive electroplating wastewater than the commonly used heavy metal capture agents DTCR and TMT-18 on the market. It requires less dosage, has lower turbidity in the treated water, and all pollutant indicators are lower than the limits specified in the "Electroplating Pollutant Discharge Standard" (GB21900-2008).

[0110] The results of Examples 12-14 show that the product MA-TETA-DTC of this invention has better removal efficiency for heavy metal ions in free heavy metal wastewater and complex electroplating wastewater than the comparative samples, and the resulting flocs settle faster. The reason is that MA-TETA-DTC has 6 star-shaped branches, each containing multiple -CSS- strong chelating groups, which easily chelate with heavy metal ions in water: (1) The 6 branches can contact heavy metal ions in water from multiple directions, and each branch has multiple -CSS- groups that can chelate with heavy metal ions, increasing the probability of contact and chelation with heavy metal ions, thereby increasing the reaction rate; (2) It can be two adjacent -CSS- groups in each branch, or two -CSS- groups in two adjacent branches, that chelate with heavy metal ions to form a water-insoluble disulfide-coordinated four-membered ring chelate; the formed chelate forms a denser micro-floc through the connection of the melamine parent ring; (3) Through two -CSS- groups from different MA-TETA-DTC molecules — The group chelates with the same heavy metal ion, connecting different molecules to form chelates that gradually grow into larger flocs, thereby improving the efficiency of chelating and binding heavy metal ions, the sedimentation performance of the flocs, and the stability of the chelates.

[0111] The above are merely preferred embodiments of the present invention. Based on the above concept of the present invention, those skilled in the art can make various modifications and variations. For example, within the range of proportions and process conditions given in the present invention, the proportions and process conditions can be combined and varied. Such variations and modifications are all within the scope of the present invention.

Claims

1. A star-shaped heavy metal chelating agent with melamine as its core, characterized in that, Its structure is shown in equation (Ⅰ): （Ⅰ）， In equation (I), 2≤x≤4, 1≤y≤x, and x and y are both integers; when y<x, there are x-y N-connected H atoms; z is 0 or 1, when z is 0, the terminal N-connected H atoms.

2. The star-shaped heavy metal chelating agent with melamine as its core according to claim 1, characterized in that, The chelating agent is an orange-red or reddish-brown liquid.

3. The method for preparing the star-shaped heavy metal chelating agent with melamine core as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Add formaldehyde solution to the reactor at a molar ratio of melamine to formaldehyde of 1:10~12, adjust the pH value to 8.3~9.2 with alkali or alkaline salt solution, wherein the alkali or alkaline salt solution is a 10%~15% Na2CO3 solution or a 20%~30% NaOH solution, and then add melamine; start the stirrer, heat to 75~85℃, wait for the reaction mixture to change from turbid to clear, keep the temperature and continue the reaction for 20~60min; then add distilled water preheated to 75~85℃ to the reactor at a volume ratio of distilled water to formaldehyde solution of 6~8:1, and stir thoroughly. (2) The molar ratio of polyethylene polyamine to formaldehyde is 0.8~1.0:1, wherein the polyethylene polyamine is any one of diethylenetriamine, triethylenetetramine or tetraethylenepentamine. The polyethylene polyamine is added dropwise to the solution in step (1), and the reaction continues for 30~60 min, and then cooled to room temperature. (3) Add NaOH to the solution obtained in step (2) according to the molar ratio of NaOH to n times the molar ratio of polyethylene polyamine, which is 0.24~1.2∶1, where n represents the number of N atoms in the polyethylene polyamine molecule. After dissolving, continue the reaction for 30~60 min. (4) Add carbon disulfide slowly dropwise to the solution obtained in step (3) according to the molar ratio of carbon disulfide to sodium hydroxide of 1:1.1~1.

2. Stir the reaction at room temperature for 4~5 hours until the bottom oil droplets disappear. Then heat to 50℃~60℃ and react for 1~2 hours. Then cool down to room temperature to obtain the product, a star-shaped heavy metal chelating agent with melamine core.

4. The method for preparing the star-shaped heavy metal chelating agent with melamine core according to claim 3, characterized in that, In step (1), the melamine is a product with a purity of industrial grade or above, and the formaldehyde is a product with a mass fraction of 37%~40% and a purity of industrial grade or above; the reactor is equipped with a mechanical stirrer, a drip funnel and a reflux condenser.

5. The method for preparing the star-shaped heavy metal chelating agent with melamine core according to claim 3, characterized in that, In step (3), the NaOH is a solid product with industrial grade or higher purity.

6. The method for preparing the star-shaped heavy metal chelating agent with melamine core according to claim 3, characterized in that, In step (4), the carbon disulfide is a product of industrial grade or higher purity and is not further purified before use.

7. The method for preparing the star-shaped heavy metal chelating agent with melamine core according to claim 3, characterized in that, In step (4), the slow addition of carbon disulfide takes 30 to 60 minutes.

8. The application of the melamine-core star-shaped heavy metal chelating agent obtained by the preparation method according to any one of claims 1 to 2 or any one of claims 3 to 7 in the treatment of heavy metals in heavy metal wastewater or incineration fly ash.

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