阅读说明：本技术 一种固体螯合剂哌嗪-n,n-双二硫代氨基甲酸钠的合成方法 (Synthetic method of piperazine-N, N-bisdithiocarbamate serving as solid chelating agent ) 是由 杨书逸 杨飞 陶庆文 周英玖 石磊明 徐三善 周梅阳 于 2021-08-18 设计创作，主要内容包括：本发明提供了一种固体螯合剂哌嗪-N,N-双二硫代氨基甲酸钠的合成方法。该方法包括哌嗪的仲胺负离子化阶段、仲胺负离子与二硫化碳双重亲核反应阶段、结晶阶段和二次结晶阶段。本发明的合成方法的所用原材料种类少,合成步骤少,反应时间短,反应易控制,制备得到的固体产品纯度高,收率高,而且固体产品更有利于储存和运输。本发明提供的合成方法,操作简单,对设备要求低,生产成本低,且制备的哌嗪-N,N-双二硫代氨基甲酸钠固体产品稳定性好,货架期可达三年。哌嗪-N,N-双二硫代氨基甲酸钠固体产品对重金属离子的去除效果好,对飞灰无害化处理效果好,符合国家标准。(The invention provides a method for synthesizing piperazine-N, N-bis-dithiocarbamate serving as a solid chelating agent. The method comprises a secondary amine negative ionization stage of piperazine, a secondary amine negative ion and carbon disulfide double nucleophilic reaction stage, a crystallization stage and a secondary crystallization stage. The synthesis method has the advantages of less raw material types, less synthesis steps, short reaction time, easy reaction control, high purity of the prepared solid product, high yield and favorable storage and transportation of the solid product. The synthesis method provided by the invention is simple to operate, has low requirements on equipment and low production cost, and the prepared piperazine-N, N-bis-dithiocarbamate solid product has good stability and the shelf life of the product can reach three years. The piperazine-N, N-bis-dithiocarbamate solid product has good effect of removing heavy metal ions and good effect of harmless treatment of fly ash, and meets the national standard.)

1. A method for synthesizing piperazine-N, N-bis-dithiocarbamate serving as a solid chelating agent is characterized by comprising the following steps: the method comprises the following steps:

s1 negative ionization stage of secondary amine of piperazine

Dissolving anhydrous piperazine, tetramethylguanidine and sodium hydroxide solution in water, and heating for reaction for a period of time to obtain solution A;

s2, secondary amine negative ion and carbon disulfide double nucleophilic reaction stage

Dropwise adding carbon disulfide into the solution A obtained in the step S1, continuously heating and reacting to obtain a piperazine-N, N-bis-dithiocarbamate solution;

s3 crystallization stage

Crystallizing the solution of piperazine-N, N-sodium bisdithiocarbamate obtained in the step S2, performing solid-liquid separation, washing, drying and crushing to obtain powder crystalline solid of piperazine-N, N-sodium bisdithiocarbamate.

S4, secondary crystallization stage

And (4) adding the piperazine-N, N-sodium bisdithiocarbamate solution obtained in the step (S3) into a crystallization solvent, standing at a low temperature for secondary crystallization, performing solid-liquid separation, drying, and crushing to obtain a white crystal powder product of the piperazine-N, N-sodium bisdithiocarbamate.

2. The method for synthesizing the sodium piperazine-N, N-bisdithiocarbamate as a solid chelating agent according to claim 1, wherein the solid chelating agent comprises: in step S1, the mass concentration of the sodium hydroxide solution is: 40 to 45 percent.

3. The method for synthesizing the sodium piperazine-N, N-bisdithiocarbamate as a solid chelating agent according to claim 2, wherein the solid chelating agent comprises: in the step S1, the molar ratio of the added piperazine to the added NaOH is 1: 1.96-2.05; the molar ratio of the piperazine to the carbon disulfide is 1: 2.02-2.08; the molar ratio of the piperazine to the water is 1: 14.3-15.4.

4. The method for synthesizing the sodium piperazine-N, N-bisdithiocarbamate as a solid chelating agent according to claim 3, wherein the solid chelating agent comprises: in step S1, the amount of tetramethylguanidine is 0.3-0.8% of the weight of piperazine.

5. The method for synthesizing the sodium piperazine-N, N-bisdithiocarbamate as a solid chelating agent according to claim 4, wherein the solid chelating agent comprises: in the step S1, the heating temperature of the reaction is 20-42 ℃, and the reaction time is as follows: 15-20 min.

6. The method for synthesizing the sodium piperazine-N, N-bisdithiocarbamate as a solid chelating agent according to claim 1, wherein the solid chelating agent comprises: in the step S2, the reaction temperature is kept at 25-30 ℃ in the dropping process of the carbon disulfide, and the dropping time of the carbon disulfide is 10-15 min; and after the carbon disulfide is dripped, keeping the temperature for reacting for 20-30 min.

7. The method for synthesizing the sodium piperazine-N, N-bisdithiocarbamate as a solid chelating agent according to claim 1, wherein the solid chelating agent comprises: in step S3, the crystallization temperature is 0-35 ℃.

8. The method for synthesizing the sodium piperazine-N, N-bisdithiocarbamate as a solid chelating agent according to claim 7, wherein: in step S4, the crystallization solvent includes one or more of ethanol, acetone, ethyl acetate, and isopropyl acetate.

9. The method for synthesizing sodium piperazine-N, N-bisdithiocarbamate as solid chelating agent according to claim 8, wherein: in step S4, the secondary crystallization temperature is 0-5 ℃.

10. A piperazine-N, N-bis-sodium dithiocarbamate product prepared by the method of any one of claims 1 to 9.

Technical Field

The invention relates to the technical field of organic synthesis application, in particular to a method for synthesizing piperazine-N, N-bis-dithiocarbamate serving as a solid chelating agent.

Background

With the increasing amount of the waste incineration fly ash, it is important to develop a safe and effective fly ash chelating agent, improve the water solubility and stability of the chelating agent, optimize a synthesis process, reduce the cost and promote the commercialization of the novel chelating agent.

piperazine-N, N-bisdithiocarbamate (hereinafter referred to as BPD) is a heavy metal chelating agent also called heavy metal capturing agent, etc. The molecular weight is moderate, the molecular space structure is reasonable, and the chelating trapping efficiency and the sedimentation performance are good. The chelating agent can be used for stabilizing various waste incineration fly ash containing heavy metal ions, treating industrial wastewater, repairing heavy metal polluted soil and the like. The commercially available BPD chelating agent is mainly piperazine-N, N-bis-dithiocarbamate potassium solution (hereinafter referred to as BPD-K).

The existing BPD-K synthesis process still has the problems of long reaction time, difficult control of byproducts in the synthesis process, difficult preparation of solid products, inconvenient transportation and storage of obtained liquid products, high production cost and the like. Only the synthesis technology of piperazine-N, N-bis-dithiocarbamate (BPD-Na for short) is not accepted by the market because the used raw materials are complex, the mixture ratio is not accurate enough, the reaction process is not easy to control, the reaction time is long, the product yield is not ideal enough, and the production and use cost is higher than that of BPD-K and the like.

Disclosure of Invention

The invention aims to provide a method for synthesizing a solid chelating agent piperazine-N, N-bis-sodium dithiocarbamate, aiming at the defects of the prior art.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a method for synthesizing piperazine-N, N-bis-dithiocarbamate serving as a solid chelating agent, which comprises the following steps:

step S1, secondary amine negative ionization stage of piperazine:

dissolving anhydrous piperazine, tetramethylguanidine and sodium hydroxide solution in water, and heating for reaction for a period of time to obtain solution A;

step S2, secondary amine negative ionization stage of piperazine:

dropwise adding carbon disulfide into the solution A obtained in the step S1, keeping the temperature and reacting to obtain a piperazine-N, N-bis-dithiocarbamate solution;

step S3, crystallization stage:

crystallizing the sodium piperazine-N, N-bisdithiocarbamate solution obtained in the step S2 at normal temperature, carrying out solid-liquid separation, washing, drying and crushing to obtain a powdery crystalline solid of sodium piperazine-N, N-bisdithiocarbamate;

step S4, secondary crystallization stage:

and (4) adding the piperazine-N, N-sodium bisdithiocarbamate solution obtained in the step (S3) into a crystallization solvent, standing at a low temperature for secondary crystallization, performing solid-liquid separation, drying, and crushing to obtain a white crystal powder product of the piperazine-N, N-sodium bisdithiocarbamate.

Further, in step S1, the mass concentration of the sodium hydroxide solution is: 40 to 45 percent.

Further, in step S1, the molar ratio of the piperazine to 100% NaOH is 1: 1.96-2.05; the molar ratio of the piperazine to the carbon disulfide is 1: 2.02-2.08; the molar ratio of the piperazine to the water is 1: 14.3-15.4.

Further, in step S1, the amount of the tetramethylguanidine is 0.3% to 0.8% by weight of the piperazine.

Further, in step S1, the heating temperature of the reaction is 20 to 42 ℃, and the reaction time is: 15-20 min.

Further, in the step S2, the reaction temperature is kept at 25-30 ℃ in the dropping process of the carbon disulfide, and the dropping time of the carbon disulfide is 10-15 min; and after the carbon disulfide is dripped, continuing heating and reacting for 20-30 min.

Further, in step S3, the crystallization temperature is 0 to 35 ℃.

Further, in step S4, the crystallization solvent includes one or more of ethanol, acetone, ethyl acetate and isopropyl acetate.

Further, in step S4, the secondary crystallization temperature is 0 to 5 ℃.

The invention also provides a piperazine-N, N-bis-dithiocarbamate product.

The technical scheme provided by the invention has the beneficial effects that:

(1) the synthesis method of the solid chelating agent piperazine-N, N-bis-dithiocarbamate provided by the invention has the advantages of few raw material types, few synthesis steps, short reaction time, easy reaction control, high purity and high yield of the prepared solid product, and the solid product is more favorable for storage and transportation. The synthesis method adopts strong-alkaline organic compound tetramethylguanidine as a catalyst, and cooperates with sodium hydroxide and other operating conditions, so that the reaction speed of piperazine, sodium hydroxide and carbon disulfide is increased, and the reaction time is shortened. Due to reasonable temperature control, the reflux condensation operation and the absorption of escaped carbon disulfide are cancelled, the dropping time of the carbon disulfide is shortened, the operation steps are simplified, and the energy consumption is reduced. Although the potassium and sodium ions belong to the same alkali metal and have similar properties, the ionic radii of the potassium and sodium ions are different. Therefore, the structure formed by the sodium ions and the piperazine is easier to form crystals, and the purity of the crystal product is high. The method has the advantages of full reaction in the synthetic process, difficult generation of byproducts, transparent solution after the reaction is finished, no white precipitate or black fine particles, no detected impurity content in the product and nearly 100 percent of product purity. The prepared product is colorless crystals or white crystalline powder in appearance, so that the problems of storage and transportation caused by a liquid product prepared by the traditional BPD-K process are avoided, and the problem of instability of the liquid product caused by the hydrolysis tendency of dithiocarbamate is also avoided, so that the stability of the solid product is better.

(2) The synthesis method provided by the invention is simple to operate, has low requirements on equipment and low production cost, and the prepared piperazine-N, N-bis-dithiocarbamate solid product has good stability and shelf life of three years, and has market competitiveness.

(3) The piperazine-N, N-sodium dithiocarbamates solid product provided by the invention has good effect of removing heavy metal ions and good effect of harmless treatment of fly ash, and meets the national standard.

Drawings

FIG. 1 is a diagram of a solid chelating agent piperazine-N, N-bis-dithiocarbamate provided by the invention;

FIG. 2(a) is the NMR spectrum of the solid chelating agent piperazine-N, N-bis-sodium dithiocarbamate provided by the invention;

FIG. 2(b) is the nuclear magnetic resonance carbon spectrum of the solid chelating agent piperazine-N, N-bis-sodium dithiocarbamate provided by the invention;

FIG. 2(c) is the NMR spectrum of the solid chelating agent potassium piperazine-N, N-bis-dithiocarbamate provided by the invention;

FIG. 2(d) is the nuclear magnetic resonance carbon spectrum of the solid chelating agent potassium piperazine-N, N-bis-dithiocarbamate provided by the invention;

FIG. 3 is a crystallization diagram of sodium piperazine-N, N-bisdithiocarbamate as a solid chelating agent provided by the invention at room temperature;

FIG. 4 is a crystal diagram of the sodium piperazine-N, N-bisdithiocarbamate as a solid chelating agent provided by the present invention after being placed at 4 ℃ for 1 hour;

FIG. 5 is a crystal diagram of the sodium piperazine-N, N-bisdithiocarbamate as a solid chelating agent provided by the present invention after being left at 4 ℃ for 24 hours;

FIG. 6 is a comparative crystal diagram of BDP-Na (right) and BDP-K (left) solutions prepared in example 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be further described with reference to the accompanying drawings and examples.

The invention provides a method for synthesizing piperazine-N, N-bis-dithiocarbamate serving as a solid chelating agent, which comprises the following steps:

step S1, secondary amine negative ionization stage of piperazine:

adding anhydrous piperazine and tetramethylguanidine into water, stirring for dissolving, then adding a sodium hydroxide solution, and heating for reacting for a period of time to obtain a solution A;

step S2, double nucleophilic reaction stage of secondary amine negative ions and carbon disulfide:

dropwise adding carbon disulfide into the solution A obtained in the step S1, keeping the temperature and reacting to obtain a piperazine-N, N-bis-dithiocarbamate solution;

step S3, crystallization stage:

crystallizing the sodium piperazine-N, N-bisdithiocarbamate solution obtained in the step S2 at normal temperature, carrying out solid-liquid separation, washing, drying and crushing to obtain a sodium piperazine-N, N-bisdithiocarbamate crystalline solid;

step S4, secondary crystallization stage:

and (3) adding the solution of the piperazine-N, N-sodium dithiocarbamates obtained in the step (S3) into 10% ethanol (or other organic solvents), standing at a low temperature for secondary crystallization, performing solid-liquid separation, drying, and crushing to obtain white powder products of the piperazine-N, N-sodium dithiocarbamates.

The purpose of step S1 is to react the secondary amine of piperazine with hydroxide ions to generate secondary amine anions in a system of tetramethylguanidine, a strong organic base, and sodium hydroxide, a strong inorganic base.

The purpose of step S2 is to perform a double nucleophilic reaction between the secondary amine negative ions and carbon disulfide to form the target chelating agent piperazine-N, N-bisdithiocarbamate ions, and then coordinate with free sodium ions in water to obtain a BPD-Na solution.

The step S3 is to cool the BPD-Na solution to room temperature or lower to produce colorless needle crystal product, and to crush the crystal to obtain BPD-Na white powder product.

The purpose of step S4 is to lower the temperature, to promote the crystallization process by adding organic solvent, and to improve the product yield by secondary crystallization.

In order to improve the quality, reduce the production cost and win the market share, compared with the prior art, the invention simplifies the types of raw materials and optimizes the mixture ratio of the raw materials, and in the step S1, the mass concentration of the sodium hydroxide solution can be as follows: 40% -45%; the molar ratio of the piperazine to 100% of NaOH can be 1: 1.96-2.05; the molar ratio of the piperazine to the carbon disulfide can be 1: 2.02-2.08; the molar ratio of the piperazine to the water is 1: 14.3-15.4; the amount of the tetramethylguanidine is 0.3 to 0.8 percent of the weight of the piperazine; the heating temperature of the reaction is 20-42 ℃, and the reaction time is as follows: 15-20 min. The invention replaces potassium hydroxide with sodium hydroxide, reduces the corrosion resistance requirements on equipment and equipment, has easily obtained raw materials and reduces the cost of the raw materials; the use and the proportion of the raw materials are optimized, and the raw materials such as normal hexane (normal heptane), isopropanol, ether and the like are not needed; more importantly, the amount of carbon disulfide is reduced according to theoretical calculation, so that the production cost is lower.

In order to improve the yield and control the reaction more accurately, the temperature control is optimized, in step S2, the reaction temperature is kept at 25-30 ℃ in the carbon disulfide dropwise adding process, the carbon disulfide dropwise adding time is 10-15 min, and the temperature is kept for reacting for 20-30 min after the carbon disulfide dropwise adding is completed.

In order to prepare high-purity products, improve the yield and reduce the production cost, a fractional crystallization mode is adopted. The primary crystallization temperature is 0-35 ℃ at normal temperature; the temperature of the second crystallization is 0-5 ℃, and an organic solvent for promoting crystallization is added, wherein the crystallization solvent can be: one or more of ethanol, acetone, ethyl acetate and isopropyl acetate.

The method of the invention adds carbon disulfide dropwise under the condition of 30 ℃, which can effectively prevent the evaporation of carbon disulfide and the generation of white solid impurities (which should be a unilateral product of a synthesis byproduct), and the process does not need condensation and absorption of escaped carbon disulfide, thereby simplifying the operation steps and saving the energy consumption. In the prior reported process, carbon disulfide is dropwise added for reaction at 25-35 ℃ (synthesis of BPD-K) or 5-50 ℃ (synthesis of BPD-Na), steam is condensed, and escaped carbon disulfide gas is absorbed by alkali liquor. In actual operation, when the temperature during BPD-K synthesis exceeds 32 ℃, the reaction is out of control, a byproduct white solid is generated in advance, the content of the white solid in a final product is increased, raw materials are wasted, and the content of active ingredients in the product is low. This problem does not occur when BPD-Na is synthesized. And after the carbon disulfide is dripped, continuing heating for reaction, and stopping heating when the temperature exceeds 42 ℃ to finish the reaction.

The synthesis process time of the invention is 1.5-2 hours, which is shortened by 2-6 hours compared with the prior processes. The strong-alkaline organic compound tetramethylguanidine is used as a catalyst, and is cooperated with sodium hydroxide and other operation conditions, so that the reaction speed of piperazine, sodium hydroxide and carbon disulfide is increased, and the reaction time is shortened. Due to reasonable temperature control, the reflux condensation operation and the absorption of escaped carbon disulfide are cancelled, the dropping time of the carbon disulfide is shortened, the operation steps are simplified, and the energy consumption is reduced. The method has the advantages of full reaction in the synthetic process, difficult generation of byproducts, transparent solution after the reaction is finished, no white precipitate or black fine particles, no detected impurity content in the product and high product purity. The prepared product is colorless crystal or white powder in appearance, so that the problems of storage and transportation caused by a liquid product prepared by the traditional BPD-K process are avoided, and the problem of instability of the liquid product caused by the hydrolysis tendency of dithiocarbamate is also avoided, so that the stability of the solid product is better. Although the potassium and sodium ions belong to the same alkali metal and have similar properties, the ionic radii of the potassium and sodium ions are different. Therefore, the structure formed by the sodium ions and the piperazine is easier to form crystals. The purity of the crystal product is nearly 100%.

The following examples will explain the synthesis method of the solid chelating agent piperazine-N, N-bis-sodium dithiocarbamate (BPD-Na) and the effect of removing heavy metals of the solid chelating agent piperazine-N, N-bis-sodium dithiocarbamate provided by the present invention.

Example 1:

157.5g of deionized water, 49.5g of anhydrous piperazine and 0.32g of tetramethylguanidine were placed in a 500mL four-necked flask equipped with a thermometer, a dropping funnel and a reflux condenser, and stirring was started; stirring for 15-20 minutes, immediately adding 112.5g of 40% sodium hydroxide solution into the four-neck flask after piperazine is completely dissolved, and continuously stirring for 10 minutes; after the temperature of the solution is reduced to below 30 ℃ by using a water bath, 89.1g of carbon disulfide is dripped into the four-neck flask from the dropping funnel, the dripping time is 10-15 minutes, and the temperature is kept below 30 ℃ in the dripping process; after the carbon disulfide is dripped, heating the solution by using a water bath until the temperature of the solution reaches more than 42 ℃, removing the water bath for heating, and continuously stirring the solution for reaction for 10 minutes by using the residual temperature. After the reaction is finished, cooling the solution to room temperature to obtain a solid product through crystallization, washing, separating, drying and crushing the solid product to obtain the white crystal powder product of the piperazine-N, N-bis-dithiocarbamate. And adding 10% ethanol into the solution after the solid is separated at 0-5 ℃ for secondary crystallization, so that a solid crystal product can be continuously obtained, and the product yield is improved. The product is shown in figure 1.

The crystallization of the BPD-Na solution after the reaction is shown in FIGS. 3-5. The quality indexes of the prepared BPD-Na solid products are shown in the following table 1. The yield of the crystalline product is shown in table 2.

TABLE 1 quality index of the solid product

TABLE 2 yield of crystalline product

	Mass of solid product	Yield of product
			Primary crystallization at 25.5 deg.C	80 g	45.2％
Secondary crystallization at 4 deg.C	22 g	12.4％
			Remains in solution at 4 DEG C	75 g	42.4％
Total of	177 grams of	100％

As shown in FIGS. 2(a) and 2(b), the hydrogen spectrum and carbon spectrum of piperazine-N, N-bis-sodium dithiocarbamate shows that the purity of the product is nearly 100%. While the hydrogen and carbon spectra of our synthetic potassium piperazine-N, N-bisdithiocarbamate (BPD-K) shown in fig. 2(c) and 2(d) show that the product has impurity peaks, consistent with the tendency of the BPD-K solution product described in the literature to contain white precipitates and black fine particles.

As shown in Table 2 and FIGS. 3-5, the final BPD-Na solution (10 ml) was weighed to obtain a solution density of 1.1142g/ml, and rotary evaporated to obtain 2.7439g of solid, which was calculated to obtain a solution concentration of 24.63%. The molecular weight of BPD-Na is 282.38g/mol, corresponding to a yield of 0.57mol, and the theoretical yield should be 160.96 g. Since the solid product contained a portion of water of crystallization in a molar ratio of about 1:2.5, an amount of 151.35g of solid product was obtained as 94.26% of the total yield, which resulted in 90% or more of the product being converted to a solid by cooling to 4 ℃ for a second crystallization. The principle that BPD-Na solution is easy to obtain solid through crystallization is probably that the diameter of sodium ions is smaller than that of potassium ions and is also smaller than the S-S spacing of dithioformate, so that the BPD-Na solution can form a chain structure to generate a finer crystal structure, and the crystallinity of the solid is enhanced.

As shown in the left part of FIG. 6, BPD-K solution still has no obvious crystallization after being placed at 4 ℃ for more than 1 month, and the BPD-K solution can be converted into solid only by other means such as rotary evaporation, thermal evaporation and the like, special equipment is required, a large amount of energy is consumed, the cost is obviously increased, and the BPD-K solution is suitable for producing solution products.

The BPD-Na prepared in example 1 was used to dispose incineration fly ash.

1. The prepared BPD-Na solid product is used for treating the fly ash of a certain domestic garbage incineration plant in Zhejiang

When the prepared BPD-Na solid product is used for treating fly ash, the leaching concentration of lead (13.44mg/L) and cadmium (14.10mg/L) of the fly ash seriously exceeds the limit values (0.25 mg/L of lead and 0.15mg/L of cadmium) in the pollution control standard (GB16889-2008) of a household garbage landfill, and the fly ash can be landfilled after reaching the standard through stabilizing treatment. Cooling and converting the prepared liquid product into a solid powder product, and performing the following operations:

(1) controlling the final water content of the chelating system to be 30%, and respectively adding BPD-Na with the powder mass of 1%, 3%, 5%, 7% and 9% of the mass of the fly ash. After fully stirring and mixing, transferring the mixture into an aluminum tray, maintaining the mixture for 24 hours under natural conditions, then putting the sample into an oven at 105 ℃, drying the sample, grinding the sample by using a mortar, sieving the sample by using a 20-mesh fine sieve, and drying and storing the sieved substances for subsequent leaching toxicity test. Three replicates of each sample were run.

(2) Leaching the chelated product by adopting a solid waste leaching toxicity method acetic acid buffer solution method (HJ/T300-2007), filtering and collecting the leachate, and storing at 4 ℃.

(3) Meanwhile, a comparison test is carried out by adopting a BPD-K liquid product prepared by a laboratory so as to check the effect of the prepared BPD-Na solid product on removing heavy metals.

Table 3 shows that the BPD-Na and BPD-K products prepared in Table 3 have a comparative effect on removing lead and cadmium in certain fly ash in Zhejiang

Note: ND is lower than detection limit.

The concentrations of heavy metals in the fly ash and its chelate product leachate were analyzed by inductively coupled plasma mass spectrometry (ICP-MS), and the results are shown in table 3. It is known that the leaching concentration of lead and cadmium gradually decreases with the increase of the dosage. When the dosage of the two chelating agents is 5%, the leaching concentrations of lead and cadmium reach the standard; and the removal effect of BPD-K on cadmium is slightly lower than that of BPD-Na. BPD-Na has the same effect as BPD-K in removing heavy metal lead and cadmium.

In conclusion, the BPD-Na white crystalline powder provided by the invention is used as a new-form fly ash chelating agent applied to the fly ash harmless treatment technology, and can convert heavy metals in fly ash into a complex which is difficult to dissolve and migrate, so that heavy metal ions are fixed, and secondary pollution is avoided. Compared with the existing DTC chelating agents such as sodium ferbamate and the like and BPD-K, the BPD-Na white crystal powder has the advantages of no odor, low toxicity, safety, good chemical stability, convenience in transportation and use, low production cost, low requirement on equipment, market competitiveness and suitability for industrial production.

The features of the embodiments and embodiments described herein above may be combined with each other without conflict.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.