Melamine-core star-shaped heavy metal chelating agent as well as preparation method and application thereof

Abstract

The invention discloses a star-shaped heavy metal chelating agent taking melamine as a core as well as a preparation method and application of the star-shaped heavy metal chelating agent. The preparation method comprises the following steps: firstly, reacting melamine with formaldehyde under a weakly alkaline condition to generate hexamethylol melamine, and adding polyethylene polyamine before further dehydration polycondensation, so that hydroxymethyl is condensed with amino or imino on the polyethylene polyamine to be connected to the melamine; and reacting with carbon disulfide in the presence of alkali, and grafting-CSS <-> to polyethylene polyamine branched chains to form a structure in which melamine is used as a mother nucleus and six polyethylene polyamine branched chains containing a plurality of-CSS <-> groups are distributed in a star shape. According to the product disclosed by the invention, heavy metal ions are bound on molecules through a chelation effect, and then the heavy metal ions are gathered through a melamine mother nucleus connection effect to form micro-flocs and further grow, so that the chelation binding capability and the flocculation precipitation performance on the heavy metal ions are remarkably improved. The method is simple in process, mild in reaction condition, easy to control operation, environment-friendly in process and easy to realize industrial production.

Description

Technical Field

[0001] The invention relates to the field of heavy metal wastewater treatment and heavy metal fixation in incineration fly ash, and in particular to a star-shaped heavy metal chelating agent with melamine as a core, and a preparation method and application thereof. Background Art

[0002] Heavy metals, whether essential or non-essential elements of organisms, will have significant harmful effects on organisms as long as they exceed a certain limit. Due to their non-biodegradability, they are easy to accumulate in organisms and easily enter the human body through the food chain to cause cumulative poisoning. Therefore, heavy metals not only seriously damage the ecological environment, but also pose a serious threat to human health. For example, if Mn exceeds a certain concentration, it can affect the liver, blood vessels, immune system, and reproductive system; if zinc exceeds a certain amount, it can cause vomiting, diarrhea, gastric perforation, intestinal necrosis, and even shock and death; and Pb can damage the kidneys, liver, reproductive, and brain nervous systems. With the rapid development of industrial and agricultural production, the number of industries involving heavy metals is increasing, and the amount of heavy metal wastewater generated and discharged is increasing. The composition is becoming more and more complex, causing a wider and more serious pollution, and it is more difficult to prevent and control. Therefore, it is urgent to develop new and efficient treatment methods to cope with the increasingly serious heavy metal wastewater pollution.

[0003] So far, the main methods for treating heavy metal wastewater that have been developed include traditional chemical precipitation, ion exchange, membrane filtration, electrochemical treatment, adsorption and chelating flocculation (precipitation) methods. These methods all have certain defects, and there are few universal methods. In comparison, the chelating flocculation (precipitation) method uses the strong chelating ability of the chelating group in the chelating agent molecule to chelate and bind the heavy metal ions in the wastewater, and separate them from the main body of the wastewater by flocculation or precipitation. In addition to the advantages of high efficiency, convenient treatment and low energy consumption of the traditional chemical precipitation method, the amount of precipitate produced is less than that of the traditional chemical precipitation method, which is easy to post-process and recycle. Therefore, it is a better method for treating heavy metal wastewater, suitable for high concentration and large-scale heavy metal wastewater treatment. However, this method relies on high-efficiency chelating agents or chelating flocculants. Structure determines performance. The excellent molecular structure determines the efficiency of chelating agents or chelating flocculants in treating heavy metal ions in wastewater, and the manufacturing cost is an important factor in determining whether it can be promoted and applied. Therefore, research and development of chelating agents or chelating flocculants with excellent structure, good performance and low manufacturing cost has always been the direction of people's efforts.

[0004] Melamine is a trimer of aminocyanide, a triazine nitrogen-containing heterocyclic organic compound with three amino groups evenly distributed on the triazine nitrogen heterocyclic ring. However, due to its special triazine nitrogen heterocyclic structure, it is only slightly soluble in water, which makes further development and modification difficult. Although there are three amino groups evenly distributed on its molecule, it is impossible to directly convert the dithiocarbamic acid group (—CSS) that has a strong affinity for heavy metal ions into－ ) is attached to it. Since melamine is a relatively cheap raw material and has the above-mentioned special structure, if the strong chelating group - CSS － By connecting it, its structural and price advantages can be fully utilized to provide a new type of high-efficiency treatment agent for the efficient and low-cost treatment of heavy metal wastewater. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a star-shaped heavy metal chelating agent with melamine as a core, and a preparation method and application thereof.

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

[0007]

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

[0009] The above chelating agent is based on melamine as the core, and six CSS- － The polyethylene polyamine branches substituted with groups form a star-shaped structure. － The group chelates and binds heavy metal ions from wastewater, and aggregates the 6 branched chelated heavy metal ions through the melamine ring, promoting the formation and growth of micro-flocculation, making the flocs thicker and denser, which is conducive to sedimentation and separation. In addition, the star-shaped heavy metal chelating agent also contains auxiliary ingredients such as dithiocarbamate, xanthogenic acid and NaOH, which work synergistically with the main ingredients, not only improving the chelation and binding ability of heavy metals in wastewater, but also significantly improving its flocculation sedimentation and separation performance.

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

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

[0012] (2) adding polyethylene polyamine dropwise to the solution of step (1) at a molar ratio of polyethylene polyamine to formaldehyde of 0.8 to 1.0:1, continuing the reaction for 30 to 60 minutes, and then cooling to room temperature;

[0013] (3) adding NaOH to the solution obtained in step (2) at a molar ratio of NaOH to n times the molar ratio of polyethylene polyamine of 0.24 to 1.2:1, wherein n represents the number of N atoms in the polyethylene polyamine molecule, and continuing the reaction for 30 to 60 minutes after dissolution;

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

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

[0016] Furthermore, 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] Furthermore, 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 a purity above industrial grade.

[0019] Furthermore, in step (4), the carbon disulfide is a product with a purity above industrial grade and is used without further purification.

[0020] Furthermore, in step (4), the time for slowly adding carbon disulfide is 30 to 60 minutes.

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

[0022] The above chelating agent is used to treat various heavy metal wastewaters or heavy metals in incineration fly ash, and the treatment effect is excellent.

[0023] The present invention relates to a method for preparing a star-shaped heavy metal chelating agent with melamine as the core. The method firstly reacts melamine with formaldehyde under weak alkaline conditions to generate hexahydroxymethyl melamine, then adds polyethylene polyamine before further dehydration and polycondensation, so that the hydroxymethyl group condenses with the amino group or imino group on the polyethylene polyamine to connect it to the amino group of melamine, and then reacts with carbon disulfide in the presence of NaOH to connect -CSS on the grafted polyethylene polyamine side chain. － Modified on the side chain, with melamine as the parent core, 6 containing multiple-CSS － The star-shaped structure of the polyethylene polyamine branched chain. － The chelating effect binds the heavy metal ions in the wastewater to the molecules, and then aggregates them through the connecting effect of the melamine mother core to form micro-flocs and grow into larger flocs, which significantly improves the chelating binding ability and flocculation sedimentation performance of various heavy metal ions in the water, and realizes the efficient removal of heavy metals in the wastewater.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The product molecule of the present invention has melamine as the core and 6 grafted strands with -CSS － The star-shaped structure is composed of polyethylene polyamine branches modified by groups. － The group can chelate and bind heavy metal ions in wastewater from a wide range, and then aggregate the heavy metal ions chelated and bound by the six side chains through the melamine ring, promote the formation and growth of micro-flocculation, make the floccules become thicker and denser, and facilitate sedimentation and separation. The excellent structure of the product of the present invention improves the removal efficiency of heavy metal ions in wastewater.

[0026] (2) The method of the present invention adopts the method of adding water to dilute the generated hydroxymethyl melamine before further dehydration condensation and timely adding polyethylene polyamine and maintaining its excess, so as to ensure that the hydroxymethyl group and polyethylene polyamine condense to form a relatively complete 6-branched structure, and play a sealing role on the hydroxymethyl group, thereby preventing the condensation between the hydroxymethyl melamine and the melamine, thus overcoming the difficulty of melamine to be directly connected to the CSS － The difficulty of the groups effectively prevents the easy condensation of hydroxymethyl melamine and realizes the effective regulation of the molecular structure.

[0027] (3) The product of the present invention is safe and non-toxic, has many chelating active sites, can react rapidly with most heavy metal ions in wastewater at room temperature to generate stable water-insoluble chelates, and has a wide range of applications. －Distributed on the star-shaped side chains with melamine as the core, heavy metal ions can be chelated and gathered around the melamine core from a wider range, and multiple side chains cooperate with each other to chelate more heavy metal ions, forming more compact and stable micro-flocculations, which is conducive to further growth to form larger flocs and accelerate sedimentation and separation. Therefore, the removal effect of heavy metal ions in wastewater is effectively improved.

[0028] (4) When the product of the present invention is used to treat heavy metal wastewater, it is only necessary to add a certain amount of the product of the present invention to the heavy metal wastewater and stir it sufficiently to quickly produce insoluble flocs, which can then be separated by sedimentation and filtered. No complicated equipment and procedures are required, so the treatment process is simple.

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

[0030] The invention is suitable for treating various heavy metal wastewaters and fixing heavy metals in incineration fly ash, and is particularly suitable for removing heavy metal ions in industrial wastewater and domestic sewage, especially complex wastewater containing multiple heavy metal ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The figure is a process flow chart of the preparation method of the present invention.

[0032] Figure 2 This is the infrared spectrum of the star-shaped heavy metal chelating agent with melamine as the core (the sample of Example 5), which is the product of the present invention. DETAILED DESCRIPTION

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

[0034] Examples 1 to 11 are methods for preparing the star-shaped heavy metal chelating agent with melamine as the core, and Examples 12 to 14 are application examples of the product of the present invention.

[0035] Example 1

[0036] (1) 37.0 mL of formaldehyde with a mass fraction of 37-40% was added to a 500 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 10.00% Na2CO3 solution was added dropwise to adjust the pH value of the formaldehyde solution to 8.3, and then 6.37 g of 99.00% melamine was added, the stirrer was started, and the temperature was raised to 75°C. When the reaction mixture turned from turbid to clear, the reaction was continued for 20 minutes at the same temperature; then 222 mL of distilled water preheated to 75°C was added to the reactor and stirred thoroughly;

[0037] (2) adding 43.6 mL of 99.00% by mass diethylenetriamine to the solution of step (1), continuing the reaction for 30 min, and then cooling to room temperature;

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

[0039] (4) 25.9 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 30 min, and the mixture was stirred at room temperature for 4 h until the bottom oil droplets disappeared, and then the mixture was heated to 50° C. for 2 h, and then cooled to room temperature to obtain 388.8 mL of a reddish brown liquid, i.e., the product was a star-shaped heavy metal chelating agent with melamine as the core.

[0040] Example 2

[0041] (1) 40.7 mL of formaldehyde with a mass fraction of 37-40% was added to a 500 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 15.00% Na2CO3 solution was added dropwise to adjust the pH value of the formaldehyde solution to 9.0, and then 6.37 g of 99.00% melamine was added, the stirrer was started, and the temperature was raised to 80°C. When the reaction mixture turned from turbid to clear, the reaction was continued for 40 minutes at the temperature; then 325 mL of distilled water preheated to 80°C was added to the reactor and stirred thoroughly;

[0042] (2) adding 54.0 mL of 99.00% by mass diethylenetriamine to the solution of step (1), continuing the reaction for 40 min, and then cooling to room temperature;

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

[0044] (4) 64.2 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 40 min, and the mixture was stirred at room temperature for 4.5 h until the bottom oil droplets disappeared, and then the mixture was heated to 55° C. for 1.5 h, and then cooled to room temperature to obtain 481.5 mL of a reddish brown liquid, i.e., a star-shaped heavy metal chelating agent with melamine as the core.

[0045] Example 3

[0046] (1) 44.4 mL of formaldehyde with a mass fraction of 37-40% was added to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 20.00% NaOH solution was added dropwise to adjust the pH value of the formaldehyde solution to 9.2, and then 6.37 g of 99.00% melamine was added, the stirrer was started, and the temperature was raised to 85° C., and the reaction mixture was kept warm until it turned clear from turbidity, and the reaction was continued for 60 min; then 310.8 mL of distilled water preheated to 85° C. was added to the reactor and stirred thoroughly;

[0047] (2) adding 65.5 mL of 99.00% by mass diethylenetriamine to the solution of step (1), continuing the reaction for 60 min, and then cooling to room temperature;

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

[0049] (4) 116.7 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 60 min, and the mixture was stirred at room temperature for 5 h until the bottom oil droplets disappeared, and then the mixture was heated to 60° C. for 1 h, and then cooled to room temperature to obtain 552.9 mL of a reddish brown liquid, i.e., a star-shaped heavy metal chelating agent with melamine as the core.

[0050] Example 4

[0051] (1) 37.0 mL of formaldehyde with a mass fraction of 37-40% was added to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 25.00% NaOH solution was added dropwise to adjust the pH value of the formaldehyde solution to 8.5, and then 6.37 g of 99.00% melamine was added, the stirrer was started, and the temperature was raised to 75° C., and the reaction mixture was kept warm until it turned clear from turbidity, and the reaction was continued for 40 minutes; then 296.0 mL of distilled water preheated to 75° C. was added to the reactor and stirred thoroughly;

[0052] (2) adding 78.4 mL of 95.00% triethylenetetramine to the solution of step (1), continuing the reaction for 40 min, and then cooling to room temperature;

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

[0054] (4) 64.8 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 40 min, and the mixture was stirred at room temperature for 4.5 h until the bottom oil droplets disappeared, and then the mixture was heated to 55° C. for 1.5 h, and then cooled to room temperature to obtain 489.5 mL of a reddish brown liquid, i.e., a star-shaped heavy metal chelating agent with melamine as the core.

[0055] Example 5

[0056] (1) 40.7 mL of formaldehyde with a mass fraction of 37-40% was added to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 30.00% NaOH solution was added dropwise to adjust the pH value of the formaldehyde solution to 9.1, and then 6.37 g of 99.00% melamine was added, the stirrer was started, the temperature was raised to 80° C., and the reaction mixture was kept warm until it turned clear from turbidity, and the reaction was continued for 60 min; then 284.9 mL of distilled water preheated to 80° C. was added to the reactor and stirred thoroughly;

[0057] (2) adding 77.6 mL of 95.00% triethylenetetramine to the solution of step (1), continuing the reaction for 50 min, and then cooling to room temperature;

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

[0059] (4) 96.3 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 50 min, and the mixture was stirred at room temperature for 5 h until the bottom oil droplets disappeared, and then the mixture was heated to 60° C. for 2 h, and then cooled to room temperature to obtain 512.6 mL of a reddish brown liquid, i.e., the product was a star-shaped heavy metal chelating agent with melamine as the core, denoted as MA-TETA-DTC.

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

[0061] Example 6

[0062] (1) 44.4 mL of formaldehyde with a mass fraction of 37-40% was added to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 25.00% NaOH solution was added dropwise to adjust the pH value of the formaldehyde solution to 9.0, and then 6.37 g of 99.00% melamine was added, the stirrer was started, and the temperature was raised to 85° C., and the reaction mixture was kept warm until it turned clear from turbidity, and the reaction was continued for 50 min; then 266.4 mL of distilled water preheated to 85° C. was added to the reactor and stirred thoroughly;

[0063] (2) adding 75.2 mL of 95.00% triethylenetetramine to the solution of step (1), continuing the reaction for 60 min, and then cooling to room temperature;

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

[0065] (4) 124.5 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 60 min, and the mixture was stirred at room temperature for 5 h until the bottom oil droplets disappeared, and then the mixture was heated to 60° C. for 2 h, and then cooled to room temperature to obtain 529.4 mL of a reddish brown liquid, i.e., a star-shaped heavy metal chelating agent with melamine as the core.

[0066] Example 7

[0067] (1) 40.7 mL of formaldehyde with a mass fraction of 37-40% was added to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 15.00% Na2CO3 solution was added dropwise to adjust the pH value of the formaldehyde solution to 8.8, and then 6.37 g of 99.00% melamine was added, the stirrer was started, the temperature was raised to 80°C, and the reaction mixture was kept warm until it turned clear from turbidity and continued to react for 40 minutes; then 325.6 mL of distilled water preheated to 80°C was added to the reactor and stirred thoroughly;

[0068] (2) adding 86.2 mL of 95.00% triethylenetetramine to the solution of step (1), continuing the reaction for 60 min, and then cooling to room temperature;

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

[0070] (4) 35.7 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 30 min, and the mixture was stirred at room temperature for 4.5 h until the bottom oil droplets disappeared, and then the mixture was heated to 60° C. for 1.5 h, and then cooled to room temperature to obtain 499.6 mL of a reddish brown liquid, i.e., a star-shaped heavy metal chelating agent with melamine as the core.

[0071] Example 8

[0072] (1) 37.0 mL of formaldehyde with a mass fraction of 37-40% was added to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 15.00% Na2CO3 solution was added dropwise to adjust the pH value of the formaldehyde solution to 9.2. Then, 6.37 g of 99.00% melamine was added, the stirrer was started, and the temperature was raised to 80°C. When the reaction mixture turned from turbid to clear, the reaction was continued for 50 min at the temperature; then, 296.0 mL of distilled water preheated to 80°C was added to the reactor and the mixture was stirred thoroughly;

[0073] (2) adding 99.8 mL of 95.00% tetraethylenepentamine to the solution of step (1), continuing the reaction for 40 min, and then cooling to room temperature;

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

[0075] (4) 32.43 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 40 min, and the mixture was stirred at room temperature for 4 h until the bottom oil droplets disappeared, and then the mixture was heated to 55° C. for 1.5 h, and then cooled to room temperature to obtain 475.9 mL of an orange-red liquid, i.e., a star-shaped heavy metal chelating agent with melamine as the core.

[0076] Example 9

[0077] (1) 40.7 mL of formaldehyde with a mass fraction of 37-40% was added to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 20.00% NaOH solution was added dropwise to adjust the pH value of the formaldehyde solution to 9.1, and then 6.37 g of 99.00% melamine was added, the stirrer was started, and the temperature was raised to 85° C., and the reaction mixture was kept warm until it turned clear from turbidity, and the reaction was continued for 60 min; then 284.9 mL of distilled water preheated to 80° C. was added to the reactor and stirred thoroughly;

[0078] (2) adding 98.8 mL of 95.00% tetraethylenepentamine to the solution of step (1), continuing the reaction for 40 min, and then cooling to room temperature;

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

[0080] (4) 64.2 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 50 min, and the mixture was stirred at room temperature for 5 h until the bottom oil droplets disappeared, and then the mixture was heated to 60° C. for 2 h, and then cooled to room temperature to obtain 505.8 mL of a reddish brown liquid, i.e., a star-shaped heavy metal chelating agent with melamine as the core.

[0081] Example 10

[0082] (1) 44.4 mL of formaldehyde with a mass fraction of 37-40% was added to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 25.00% NaOH solution was added dropwise to adjust the pH value of the formaldehyde solution to 8.5, and then 6.37 g of 99.00% melamine was added, the stirrer was started, and the temperature was raised to 85° C., and the reaction mixture was kept warm until it turned clear from turbidity and continued to react for 60 min; then 310.8 mL of distilled water preheated to 85° C. was added to the reactor and stirred thoroughly;

[0083] (2) adding 95.8 mL of 95.00% tetraethylenepentamine to the solution of step (1), continuing the reaction for 50 min, and then cooling to room temperature;

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

[0085] (4) 93.4 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 60 min, and the mixture was stirred at room temperature for 4.5 h until the bottom oil droplets disappeared, and then the mixture was heated to 60° C. for 1.5 h, and then cooled to room temperature to obtain 568.2 mL of an orange-red liquid, i.e., a star-shaped heavy metal chelating agent with melamine as the core.

[0086] Embodiment 11

[0087] (1) 37 mL of formaldehyde with a mass fraction of 37-40% was added to a 750 mL three-necked flask equipped with a mechanical stirrer, a dropping funnel and a reflux condenser, and a 30.00% NaOH solution was added dropwise to adjust the pH value of the formaldehyde solution to 8.9, and then 6.37 g of 99.00% melamine was added, the stirrer was started, and the temperature was raised to 85° C., and the reaction mixture was kept warm until it turned clear from turbidity, and the reaction was continued for 60 min; then 296.0 mL of distilled water preheated to 85° C. was added to the reactor and stirred thoroughly;

[0088] (2) adding 99.8 mL of 95.00% tetraethylenepentamine to the solution of step (1), continuing the reaction for 60 min, and then cooling to room temperature;

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

[0090] (4) 129.7 mL of carbon disulfide with a mass fraction of 99.00% was slowly added to the solution obtained in step (3) within 60 min, and the mixture was stirred at room temperature for 5 h until the bottom oil droplets disappeared, and then the mixture was heated to 60° C. for 2 h, and then cooled to room temperature to obtain 586.0 mL of an orange-red liquid, i.e., a star-shaped heavy metal chelating agent with melamine as the core.

[0091] The infrared spectroscopy analysis of the star-shaped heavy metal chelating agents with melamine as the core obtained in Examples 1 to 11 showed basically the same results. The infrared spectroscopy analysis results of the chelating agent obtained in Example 5 are as follows: Figure 2 shown. Figure 2 The absorption peaks in the infrared spectrum can be attributed as follows: 3264.21cm -1 The stretching vibration peaks of OH and -NH in the sample are at 2962.13 and 2854.61 cm -1 The asymmetric and symmetric stretching vibration peaks of -CH2- appear at 1342.21 cm -1 The bending vibration peak appears at 1622.32cm -1 It is the stretching vibration peak of C=N in the triazine ring in the melamine matrix, the bending vibration peak of NH in -NH and the bound water molecule OH; 1427.07cm -1 The strong peak at 879.38 cm is the in-plane stretching vibration peak of the triazine ring. -1 The medium-strong peaks at 1203.36, 1155.63 and 1107.90 cm are the out-of-plane vibration peaks of the triazine ring; -1 The weak peaks at 997.02 and 956.52 cm are the stretching vibration peaks of CO and CN in the molecule; -1 The weak peak at -CSS- Stretching vibration peak of C=S and CS; 2492.54cm -1 is the triazine ring deformation vibration peak; 699.55cm -1 It is the out-of-plane bending vibration peak of CH in the molecule -CH2-. The elemental analysis of the above samples shows that the S content is 37.49%, which is equivalent to -CSS － Each heavy metal chelator molecule has an average of 16.6 CSS － The above results show that the star-shaped heavy metal chelating agent with melamine as the core has been successfully synthesized.

[0092] Example 12

[0093] This example shows the treatment effect of the sample in Example 5 on heavy metal wastewater.

[0094] The samples MA-TETA-DTC (—CSS — The chelating agent TETA-DTC (the content of —CSS— is 6.388mmol / g) prepared by using triethylenetetramine (TETA) at the same TETA to CS2 molar ratio and preparation conditions was used as the reagent to prepare 100mg / L Pb-containing 2+ 、Cd 2+ 、Ni 2+ , Cu 2+ and Zn 2+ Simulated heavy metal water samples. Flocculation test conditions: Take 500mL simulated heavy metal water samples respectively, adjust the pH value to about 6, add the reagent on the MY3000-6G intelligent color screen coagulation test stirring instrument (Wuhan Meiyu Instrument Co., Ltd.), stir quickly at 220r / min for 5min, stir at 100r / min for 10min, and then stir slowly at 60r / min for 7min, let it stand for 20min, take the clear liquid 2cm below the liquid surface and measure it on the AA-7000 atomic absorption spectrophotometer (Japan, Shimadzu Corporation), and the treatment effect is shown in Table 1.

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

[0096]

[0097] It can be seen from Table 1 that under the optimal conditions, the product MA-TETA-DTC of the present invention has a higher affinity to free Pb than the comparative sample TETA-DTC. 2+ 、Cd 2+ 、Ni 2+ , Cu 2+ and Zn 2+The plasma removal effect is good, and the residual ion concentration is far lower than the first-level standard of the "Comprehensive Wastewater Discharge Standard" (GB8978-1996), and even Pb 2+ and Cd 2+ Completely remove.

[0098] Example 13

[0099] This example shows the sedimentation rate of flocs produced by heavy metal treatment in wastewater by MA-TETA-DTC chelation in Example 5.

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

[0101] Table 2 Product of the present invention MA-TETA-DTC chelated Cu 2+ The sedimentation rate of the generated flocs

[0102]

[0103] From the results in Table 2, it can be seen that the product MA-TETA-DTC of the present invention treats Cu 2+ The flocs produced by wastewater settle significantly faster than those produced by TETA-DTC, and the height of the clear liquid after standing for 30 minutes is greater than that of the clear liquid treated by TETA-DTC. In the experimental process, it can be clearly seen that the flocs produced by MA-TETA-DTC are coarser and denser than those produced by TETA-DTC, with fewer small flocs, and the clear liquid has lower turbidity and is clearer. Therefore, MA-TETA-DTC prepared by the method of the present invention has better chelating flocculation performance and floc sedimentation performance.

[0104] Embodiment 14

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

[0106] The product MA-TETA-DTC obtained in Example 5, the commercially available heavy metal scavenger DTCR and TMT-18 were used as reagents respectively. Take 200 mL of wastewater sample, adjust the pH to about 6 with lime milk, and then place it on the MY3000-6G intelligent color screen coagulation test stirring instrument (Wuhan Meiyu Instrument Co., Ltd.), and add a certain amount of MA-TETA-DTC, commercially available DTCR and TMT-18 chelating agents respectively. The amount of chelating agent added is 1.2 times the stoichiometric ratio, where the stoichiometric ratio of MA-TETA-DTC and DTCR (i.e., the -CSS in MA-TETA-DTC or DTCR) is 1.2 times the stoichiometric ratio of MA-TETA-DTC and DTCR. － The molar ratio of TMT-18 to heavy metal ions is 1.97:1 and 2.01:1 respectively. The stoichiometric ratio of TMT-18 is 2:3 of TMT-18 to metal ions. When DTCR is used as the reagent, FeCl3 needs to be added in an amount of 200 mg / L. The chelating agent is added under stirring at 220 r / min and stirred for 5 min; then stirred at 100 r / min for 15 min (add appropriate amount of polyacrylamide PAM when stirring for 7 min), and then stirred at 60 r / min for 10 min. After standing for 20 min, sampling and analysis are performed to determine the concentration of heavy metal ions in the treated water.

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

[0108]

[0109] The results in Table 3 show that the product MA-TETA-DTC of the present invention has better treatment effect on this comprehensive electroplating wastewater than the commonly used heavy metal scavengers DTCR and TMT-18 on the market, with less usage, low turbidity of treated water, and pollutant indicators are all lower than the limit values ​​specified in the "Emission Standard of Pollutants for Electroplating" (GB21900-2008).

[0110] The results of Examples 12 to 14 show that the product MA-TETA-DTC of the present invention has better removal efficiency for free heavy metal wastewater and heavy metal ions in complex electroplating wastewater than the comparative samples, and the generated flocs settle faster. The reason is that MA-TETA-DTC has six star-shaped branches, each of which contains multiple -CSS- strong chelating groups, which are easy to chelate with heavy metal ions in water: (1) The six branches can contact heavy metal ions in water from multiple directions, and each branch has multiple -CSS- that can chelate with heavy metal ions, which increases the probability of contact and chelation with heavy metal ions, thereby increasing the reaction rate; (2) Either two adjacent -CSS- groups in each branch or two -CSS- groups in two adjacent branches can chelate with heavy metal ions to form a water-insoluble disulfide coordinated four-membered ring structure chelate; the formed chelate forms a denser microflocculation through the connection of the melamine mother ring; (3) through the two -CSS- groups from different MA-TETA-DTC molecules, the heavy metal ions can be chelated to form a water-insoluble disulfide coordinated four-membered ring structure chelate; the chelate can be connected to the melamine mother ring to form a denser microflocculation; (4) — The groups chelate with the same heavy metal ion and connect the chelates formed by different molecules and gradually grow to form larger flocs, thereby improving the efficiency of chelating and binding heavy metal ions, the sedimentation performance of flocs and the stability of the chelate.

[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 also make various modifications and changes thereto. For example, within the range of the ratios and process conditions given in the present invention, the ratios and process conditions can be combined and changed. Similar changes and modifications belong to the essence of the present invention.

Claims

1. A star-shaped heavy metal chelating agent with melamine as the core and a preparation method thereof, characterized in that: The structure of its main component is shown in formula (I): In formula (I), 2≤x≤4, 1≤y≤x, and x and y are both integers; when y<x, x-y N are connected to H atoms; z is 0 or 1, and when z is 0, the terminal N is connected to the H atom.

2. The star-shaped heavy metal chelating agent with melamine as the core according to claim 1, characterized in that: The chelating agent further comprises auxiliary components such as dithiocarbamate, xanthogenic acid and NaOH; the appearance of the chelating agent is orange-red or reddish-brown liquid.

3. The method for preparing a star-shaped heavy metal chelating agent with melamine as the core according to claim 1 or 2, characterized in that: The following steps are involved: (1) Add formaldehyde solution into a reactor at a molar ratio of melamine to formaldehyde of 1:10-12, adjust the pH value to 8.3-9.2 with an alkali or alkaline salt solution, and then add melamine; start the stirrer, raise the temperature to 75-85°C, wait for the reaction mixture to turn from turbid to clear, and continue the reaction at this temperature for 20-60 minutes; then preheat distilled water to 75-85°C at a volume ratio of distilled water to formaldehyde solution of 6-8:1, add the distilled water to the reactor, and stir thoroughly; (2) adding polyethylene polyamine dropwise to the solution of step (1) at a molar ratio of polyethylene polyamine to formaldehyde of 0.8 to 1.0:1, continuing the reaction for 30 to 60 minutes, and then cooling to room temperature; (3) adding NaOH to the solution obtained in step (2) at a molar ratio of NaOH to n times the molar ratio of polyethylene polyamine of 0.24 to 1.2:1, wherein n represents the number of N atoms in the polyethylene polyamine molecule, and continuing the reaction for 30 to 60 minutes after dissolution; (4) Slowly drop carbon disulfide into the solution obtained in step (3) at a molar ratio of carbon disulfide to sodium hydroxide of 1:1.1-1.2, and stir the mixture at room temperature for 4-5 hours until the bottom oil droplets disappear, then heat the mixture to 50°C-60°C for 1-2 hours, and then cool the mixture to room temperature to obtain a star-shaped heavy metal chelating agent with melamine as the core.

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

5. The method for preparing a star-shaped heavy metal chelating agent with melamine as the core according to claim 3, characterized in that: 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%.

6. The method for preparing a star-shaped heavy metal chelating agent with melamine as the core according to claim 3, characterized in that: In step (2), the polyethylene polyamine is any one of diethylenetriamine, triethylenetetramine or tetraethylenepentamine.

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

8. The method for preparing a star-shaped heavy metal chelating agent with melamine as the core according to claim 3, characterized in that: In step (4), the carbon disulfide is a product with a purity above industrial grade and is used without further purification.

9. The method for preparing a star-shaped heavy metal chelating agent with melamine as the core according to claim 3, characterized in that: In step (4), the time for slowly adding carbon disulfide is 30 to 60 minutes.

10. Use of a star-shaped heavy metal chelating agent with melamine as the core obtained by the preparation method according to any one of claims 1 to 2 or any one of claims 3 to 9 in the treatment of heavy metals in heavy metal wastewater or incineration fly ash.

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