A heavy metal stabilizer for treating incineration fly ash

Abstract

The application discloses a heavy metal stabilizer for treating incineration fly ash, which comprises the following components in percentage by weight: phosphate 2-5%, carbamate 15-45%, hydroxide 5-15%, polyacrylamide 0.2% or less, and water 34-77%. The application uses carbamate and phosphate to provide ligands for heavy metal ions, and uses sodium hydroxide to adjust the acidity and alkalinity of fly ash, to enhance the chelation reaction of fly ash. Meanwhile, the detection of the acid neutralization capacity of fly ash when the heavy metal stabilizer is used is embedded, so as to ensure the applicability of the heavy metal stabilizer and effectively solidify the heavy metals in fly ash.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology and relates to a heavy metal stabilizer for treating incineration fly ash. Background Technology

[0002] Fly ash from waste incineration is fine particulate matter collected during the waste incineration process. It usually contains a variety of heavy metals and a small amount of dioxins, and is therefore listed in the "List of Hazardous Wastes" under the code HW18. Fly ash that has not been safely disposed of poses a risk of polluting the ecological environment. The most common disposal methods at home and abroad are as follows: after the fly ash is treated with heavy metal chelating agents and the solidified sample meets the requirements of the "Standard for Pollution Control of Municipal Solid Waste Landfills" (GB16889-2008) shown in Table 1, it is then landfilled.

[0003] Table 1. Leaching toxicity limits of fly ash chelates

[0004] Serial Number Pollution Projects Mass concentration limit (mg / L) 1 mercury 0.05 2 copper 40 3 Zinc 100 4 lead 0.25 5 cadmium 0.15 6 beryllium 0.02 7 barium 25 8 nickel 0.5 9 arsenic 0.3 10 Total Chromium 4.5 11 Hexavalent chromium 1.5 12 selenium 0.1

[0005] The instability of waste incineration feedstocks leads to significant fluctuations in fly ash composition. Currently available chelating agents have limited composition, failing to adequately consider the solidification stability of heavy metals during selection, thus hindering the achievement of stable and compliant fly ash solidification samples. According to the five-step extraction method, heavy metals exist in exchangeable ionic states, carbonate-bound states, iron-manganese oxide-bound states, sulfide and organic matter-bound states, and residue states. Table 2 shows that easily migrating heavy metals in fly ash exhibit empty orbitals in their outer electron structures (s, p, d layers), indicating they exist as exchangeable ions. Therefore, understanding the types and forms of heavy metal ions in fly ash is crucial for chelating agent selection.

[0006] Table 2. Structure of outer electrons of heavy metal ions that are prone to exceeding standards in fly ash.

[0007] element Belonging to the clan outer electronic structure Zinc, cadmium, mercury Zinc group <![CDATA[(n-1)d 10n s 2 ]]> copper Copper Subgroup <![CDATA[(n-1)d 10 ns 1 ]]> lead Group 1 carbon elements <![CDATA[6s 2 6p 2 ]]> nickel Iron elements <![CDATA[3d 8 4s 2 ]]> arsenic Nitrogen group elements <![CDATA[4s 2 4p 3 ]]>

[0008] Existing chelating agents include acetic acid-based, phosphate-based, hydroxyl-based, ammonium sulfate-based, and sodium sulfide-based agents. Different functional groups have different chelating effects on fly ash, as detailed in Table 3, which lists the types and characteristics of chelating agents. Chelating agents, as multivalent ligands, form chelates with heavy metal ions, which in turn form chelate rings. This results in more stable complexes than those formed by single ligands. Furthermore, the stability of the chelate is related to the number and size of the chelate rings; the more chelate rings formed, the more stable the chelate. In addition to the size of the chelate rings, stability is also affected, with five- and six-membered rings being the most stable.

[0009] Table 3. Types and characteristics of chelating agents

[0010]

[0011] Based on the existing technology, the factors affecting the chelation effect of heavy metals in fly ash are as follows: (1) the form of heavy metals; (2) the chelation effect of other anions in fly ash and chelating agents competing for chelation effect on heavy metal ions; and (3) the selection of chelating agents. Therefore, it can be seen that the form of heavy metals in fly ash and the physical properties of fly ash itself affect the chelation effect of heavy metals in fly ash.

[0012] In view of the above, the present invention starts from the formulation and application method of heavy metal stabilizers to ensure that the heavy metal stabilizers used are compatible with the physical properties of fly ash itself, so that chelation operations are no longer blind and promote the solidification of heavy metals in fly ash. Summary of the Invention

[0013] In view of the above-mentioned defects in the existing technology, the purpose of this invention is to provide a heavy metal stabilizer for treating incineration fly ash. It uses carbamate and phosphate to provide ligands for heavy metal ions, and uses sodium hydroxide to adjust the alkalinity of fly ash to enhance the fly ash chelation reaction. At the same time, the detection of the acid neutralization capacity of fly ash is incorporated when the heavy metal stabilizer is used, thereby ensuring the applicability of the heavy metal stabilizer and effectively solidifying the heavy metals in fly ash.

[0014] To achieve the above objectives, the present invention adopts the following technical solution:

[0015] The present invention provides a heavy metal stabilizer for treating incineration fly ash, comprising the following components by weight percentage: phosphate 2-5%, carbamate 15-45%, hydroxide 5-15%, polyacrylamide ≤0.2%, and water 34-77%.

[0016] Preferably, the content of the polyacrylamide is 0.1% to 0.2%.

[0017] Preferably, the phosphate is selected from one or more of sodium phosphate, potassium phosphate, and ammonium phosphate;

[0018] Preferably, the carbamate is selected from one or two of sodium N,N-dimethylcarbamate and sodium diethyldithiocarbamate.

[0019] Preferably, the hydroxide is sodium hydroxide or potassium hydroxide.

[0020] Preferably, the amount of the heavy metal stabilizer added to treat incineration fly ash is 1.0% to 3.0%.

[0021] The present invention has the following beneficial effects:

[0022] 1. This invention uses carbamates and phosphates as ligands for heavy metal ions to form a cyclic structure. This substance forms a stable chelate with lead ions, chromium ions and cadmium ions in fly ash. Sodium hydroxide is used to adjust the acidity and alkalinity of fly ash to enhance the chelation reaction of heavy metals in fly ash.

[0023] 2. This invention optimizes the chelation process of fly ash by incorporating the detection of fly ash acid neutralization capacity during use, thereby determining the applicability of the heavy metal stabilizer of this invention. This makes the chelation of heavy metals in fly ash no longer blind, and can effectively solidify the heavy metals in fly ash, thereby enhancing the chelation effect. Detailed Implementation

[0024] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with embodiments.

[0025] The stability of heavy metal chelation in fly ash depends not only on its formulation but also on the characteristics of the fly ash itself, such as its alkaline content (calcium oxide, calcium hydroxide) and the anions (OH-) provided by these alkaline substances. - OH can enhance the chelation effect of heavy metals because OH - It can fill the empty s, p, and d orbitals of heavy metals, achieving a chelation effect. However, excessive OH groups... - Further reaction with stable Pb(OH)₂ and Zn(OH)₂ produces easily migrating [Pb(OH)₂]. n ] 2-n [Zn(OH)] n ] 2-n Excessive amounts of calcium oxide and calcium hydroxide can also affect the chelation effect. Therefore, this invention improves the formulation and application method of the heavy metal stabilizer to enhance the targeted chelation effect of waste incineration fly ash.

[0026] The present invention provides a heavy metal stabilizer for treating incineration fly ash, comprising the following components by weight percentage: phosphate 2-5%, carbamate 15-45%, hydroxide 5-15%, polyacrylamide (PAM) ≤0.5%, and water 34-77%.

[0027] In a preferred embodiment, the content of polyacrylamide (PAM) is 0.2% to 0.3%.

[0028] In specific embodiments, the phosphate is selected from one or more of sodium phosphate, potassium phosphate, and ammonium phosphate.

[0029] In a specific embodiment, the carbamate is selected from one or two of sodium N,N-dimethylcarbamate and sodium diethyldithiocarbamate.

[0030] In specific embodiments, sodium hydroxide or potassium hydroxide is selected as the hydroxide.

[0031] In this process, the nitrogen and oxygen elements in carbamates primarily provide ligands for heavy metal ions, forming cyclic structures. This substance can form stable chelates with lead, chromium, and cadmium ions. Phosphate provides empty electron pairs, which can fill the d and f orbitals of heavy metal ions. Hydroxides adjust the alkaline conditions in fly ash, promoting the formation of chelates between carbamates and heavy metal ions. Polyacrylamide (PAM) promotes the rapid flocculation of heavy metal chelates.

[0032] In addition to configuring the components of the heavy metal stabilizer, this invention also optimizes the chelation process of fly ash. That is, before use, the acid neutralization capacity of the fly ash is used to understand and judge its physical properties (such as the content of alkaline substances in it), so as to determine whether to use the heavy metal stabilizer of this invention, thereby making the chelation process of fly ash no longer blind.

[0033] The method for using the heavy metal stabilizer for treating incineration fly ash of the present invention includes the following steps: The method involves testing the acid neutralization capacity of the fly ash and determining the suitability of the heavy metal stabilizer based on the test results.

[0034] S1, Detect the fly ash sample and obtain the acid neutralization capacity K of the fly ash, specifically including the following process:

[0035] S11, after drying 50-100g of fly ash sample, grind it to below 150 mesh;

[0036] Specifically, the moisture content of fly ash is first determined. 50–100 g of fly ash sample is placed in a petri dish and dried in an oven (temperature set at 105℃) until constant weight. The moisture content is recorded as w. 含水率 The dried fly ash was then ground into a fine powder using a ball mill to a mesh size of less than 150.

[0037] S12, the finely ground fly ash sample was added to the sucrose solution, reacted on a magnetic stirrer, phenolphthalein indicator was added, and then titrated with hydrochloric acid. The volume V of hydrochloric acid consumed was recorded. HCl The acid neutralization capacity K of fly ash was calculated.

[0038] Specifically, take 1 ± 0.05 g of finely ground fly ash sample and add it to a sucrose solution with a concentration of 30–35 g / L (10 ± 0.5 ml). Then, place the solution on a magnetic stirrer and react for 10 ± 1 minutes. Next, add 2–3 drops of phenolphthalein indicator to the solution, and then titrate with 0.1 mol / L hydrochloric acid, recording the volume of hydrochloric acid consumed, V. HCl .

[0039] Since the alkaline substances in fly ash are mainly potassium oxide and calcium hydroxide, these alkaline substances can provide anions (OH-). -OH can enhance the chelation effect of heavy metals because OH - It can fill the empty s, p, and d orbitals of heavy metals, achieving a chelation effect. However, excessive OH groups... - Further reaction with stable Pb(OH)₂ and Zn(OH)₂ produces easily migrating [Pb(OH)₂]. n ] 2-n [Zn(OH)] n ] 2-n Therefore, the use of the heavy metal stabilizer of this invention should be determined based on the alkaline substance content in fly ash. The alkaline substance content in fly ash can be characterized by the acid neutralization capacity K of fly ash, which is calculated as follows:

[0040] K = V HCl ×C HCl / m 飞灰

[0041] In the formula, K is the acid neutralization capacity of a unit mass of fly ash, and the unit is mmol / g;

[0042] V HCl The volume of hydrochloric acid consumed during titration, expressed in mL;

[0043] C HCl This represents the molar concentration of hydrochloric acid used in the titration, expressed in mol / L.

[0044] m 飞灰 The mass of the fly ash sample used in the reaction with the sucrose solution is expressed in grams.

[0045] S2, when the acid neutralization capacity K of fly ash is less than 5, the heavy metals in fly ash are solidified using the above-mentioned heavy metal stabilizer for treating incineration fly ash.

[0046] Specifically, the choice of whether to use the heavy metal stabilizer of the present invention is determined based on the acid neutralization capacity of the fly ash. When the acid neutralization capacity K of the fly ash is less than 5, the heavy metals in the fly ash are solidified using the above-mentioned heavy metal stabilizer for treating incineration fly ash. Otherwise, it is necessary to adjust the acidity or alkalinity of the fly ash and select other heavy metal stabilizers.

[0047] When using heavy metal stabilizers to treat incineration fly ash, the addition amount is 1.0 to 3.0% of the fly ash mass. Add phosphate, carbamate, and polyacrylamide to water in proportion, stir evenly, add to the waste incineration fly ash, mix thoroughly, and then cure for a period of time.

[0048] The chelated solidified samples obtained after the above curing were tested and analyzed. The heavy metal content in the leachate met the requirements of Table 1 "Pollution Control Standard for Municipal Solid Waste Landfills" GB16889-2008, and can be directly landfilled or treated by other methods.

[0049] The following section provides a specific example to further illustrate the heavy metal stabilizer for treating incineration fly ash according to the present invention and its application method.

[0050] Example 1

[0051] In this embodiment, the fly ash from the waste incineration plant in Shanghai has a moisture content of 3 wt%, and the heavy metal composition of its leachate is shown in Table 4 as SH-1-YY.

[0052] The heavy metal stabilizer used in this embodiment for treating incineration fly ash comprises 2% sodium phosphate, 5% sodium hydroxide, 15% sodium N,N-dimethylcarbamate, 0.2% polyacrylamide (PAM), and the balance being water, by weight percentage.

[0053] The method of using the above-mentioned heavy metal stabilizer for treating incineration fly ash is as follows:

[0054] (1) Take 50-100g of fly ash sample in a petri dish, place it in an oven (temperature set at 105℃) and dry it to constant weight, and record its moisture content as 3wt%; grind the dried fly ash sample to below 150 mesh using a ball mill:

[0055] (2) Take 1g of finely ground fly ash sample and react it with 10mL of 30g / L sucrose solution. Place the solution on a magnetic stirrer and react for 10 minutes. After 10 minutes, add 2-3 drops of phenolphthalein indicator to the solution, and then titrate with 0.1mol / L hydrochloric acid. Record the volume of hydrochloric acid consumed, V. HCl =40ml, and calculate the acid neutralization capacity of fly ash K=V HCl ×C HCl / m 飞灰 =0.1*40 / 1=4mmol / g.

[0056] (3) Since the acid neutralization capacity K of fly ash is less than 5, the heavy metals in fly ash are solidified by the heavy metal stabilizer for treating incineration fly ash in this embodiment. That is, 0.50%, 1.00%, 1.50% and 2.00% of the heavy metal stabilizer by mass are added to fly ash to obtain 4 chelated solidified samples. The heavy metal composition of their leachate is shown in Table 4 as SH-1-1, SH-1-2, SH-1-3 and SH-1-4.

[0057] Compared to SH-1-YY before chelation treatment, after the fly ash was treated with the heavy metal stabilizer in this embodiment, no Cu or Ni was found in the leachate, and the Pd, Cd, Zn, and Ba in the leachate decreased with the increase of the amount of heavy metal stabilizer.

[0058] The chelated solidified sample after treatment in this embodiment meets the requirements of Table 1, "Pollution Control Standard for Municipal Solid Waste Landfills" GB16889-2008, and can be directly landfilled or treated by other methods.

[0059] Table 4. Amount of heavy metal stabilizer added and content of heavy metals in leachate (wt%)

[0060]

[0061] Example 2

[0062] In this embodiment, the fly ash from the waste incineration plant in Guangdong Province has a moisture content of 2 wt%, and the heavy metal composition of its leachate is shown in Table 5 as GZ-1-YY.

[0063] The heavy metal stabilizer used in this embodiment for treating incineration fly ash includes 4% potassium phosphate, 10% potassium hydroxide, 30% sodium diethyldithiocarbamate, 0.1% polyacrylamide (PAM), and the balance being water, by weight percentage.

[0064] The method of using the above-mentioned heavy metal stabilizer for treating incineration fly ash is as follows:

[0065] (1) Take 50-100g of fly ash sample in a petri dish, place it in an oven (temperature set at 105℃) and dry it to constant weight, and record its moisture content as 2wt%; grind the dried fly ash sample to below 150 mesh using a ball mill:

[0066] (2) Take 1g of finely ground fly ash sample and react it with 10mL of 30g / L sucrose solution. Place the solution on a magnetic stirrer and react for 10 minutes. After 10 minutes, add 2-3 drops of phenolphthalein indicator to the solution, and then titrate with 0.1mol / L hydrochloric acid. Record the volume of hydrochloric acid consumed, V. HCl =20ml, and calculate the acid neutralization capacity of fly ash K=V HCl ×C HCl / m 飞灰 =0.1*20 / 1=2mmol / g.

[0067] (3) Since the acid neutralization capacity K of fly ash is less than 5, the heavy metals in fly ash are solidified by the heavy metal stabilizer used in this embodiment for treating incineration fly ash. That is, 1.50% and 2.00% of the heavy metal stabilizer by mass are added to fly ash to obtain two chelated solidified samples. The heavy metal composition of their leachate is shown in Table 5 as GZ-1-1 and GZ-1-2.

[0068] Compared to GZ-1-YY before chelation treatment, after the fly ash was treated with the heavy metal stabilizer in this embodiment, no Cd, Cu, or Ni were found in the leachate, while the Pb, Zn, Ba, and Cr in the leachate decreased with the increase of the amount of heavy metal stabilizer.

[0069] The chelated solidified sample after treatment in this embodiment meets the requirements of Table 1, "Pollution Control Standard for Municipal Solid Waste Landfills" GB16889-2008, and can be directly landfilled or treated by other methods.

[0070] Table 5. Dosage of heavy metal stabilizer and content of heavy metals in leachate (wt%)

[0071]

[0072] Example 3

[0073] In this embodiment, the fly ash from the waste incineration plant in Shanghai has a moisture content of 2 wt%, and the heavy metal composition of its leachate is shown in Table 6 as SH-2-YY.

[0074] The heavy metal stabilizer used in this embodiment for treating incineration fly ash includes 5% ammonium phosphate, 15% sodium hydroxide, 40% sodium N,N-dimethylcarbamate, 0.1% polyacrylamide (PAM), and the balance being water, by weight percentage.

[0075] The method of using the above-mentioned heavy metal stabilizer for treating incineration fly ash is as follows:

[0076] (1) Take 50-100g of fly ash sample in a petri dish, place it in an oven (temperature set at 105℃) and dry it to constant weight, and record its moisture content as 2wt%; grind the dried fly ash sample to below 150 mesh using a ball mill:

[0077] (2) Take 1g of finely ground fly ash sample and react it with 10mL of 30g / L sucrose solution. Place the solution on a magnetic stirrer and react for 10 minutes. After 10 minutes, add 2-3 drops of phenolphthalein indicator to the solution, and then titrate with 0.1mol / L hydrochloric acid. Record the volume of hydrochloric acid consumed, V. HCl =10ml, and calculate the acid neutralization capacity of fly ash K=V HCl ×C HCl / m 飞灰 =0.1*10 / 1=1mmol / g.

[0078] (3) Since the acid neutralization capacity of fly ash is K<5, the heavy metals in fly ash are solidified by the heavy metal stabilizer for treating incineration fly ash in this embodiment. That is, 0.50%, 1.00%, 1.50% and 2.00% and 2.5% of the heavy metal stabilizer by mass are added to fly ash to obtain 5 chelated solidification samples. The heavy metal composition of their leachate is shown in Table 6 as SH-2-1, SH-2-2, SH-2-3, SH-2-4 and SH-2-5.

[0079] Compared to SH-2-YY before chelation treatment, after the fly ash was treated with the heavy metal stabilizer in this embodiment, no Cu or Ni was found in the leachate, and the Pb, Cd, Zn, and Ba in the leachate decreased with the increase of the amount of heavy metal stabilizer.

[0080] The chelated solidified sample after treatment in this embodiment meets the requirements of Table 1, "Pollution Control Standard for Municipal Solid Waste Landfills" GB16889-2008, and can be directly landfilled or treated by other methods.

[0081] Table 6. Amount of heavy metal stabilizer added and content of heavy metals in leachate (wt%)

[0082]

[0083] As shown in Examples 1-3, this invention uses carbamates and phosphates to provide ligands for heavy metal ions, and utilizes sodium hydroxide to adjust the acidity and alkalinity of fly ash to enhance the fly ash chelation reaction. At the same time, the detection of the acid neutralization capacity of fly ash is incorporated when using heavy metal stabilizers, thereby ensuring the applicability of heavy metal stabilizers and effectively solidifying heavy metals in fly ash.

[0084] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for using a heavy metal stabilizer for treating incinerator fly ash, characterized in that, Heavy metal stabilizers for treating incinerator fly ash comprise the following components by weight percentage: phosphate 2–5%, carbamate 15–45%, hydroxide 5–15%, polyacrylamide ≤0.2%, and water 34–77%. The method of use involves detecting the neutralizing capacity of fly ash acid and determining the suitability of the heavy metal stabilizer based on the test results, and includes the following steps: S1, Detect the fly ash sample and obtain the acid neutralization capacity K of the fly ash, specifically including the following process: S11, after drying 50-100g of fly ash sample, grind it to below 150 mesh; Specifically: First, determine the moisture content of the fly ash. Take 50-100g of fly ash sample in a petri dish, place it in an oven set at 105℃ and dry it until constant weight. Record the moisture content as w. 含水率 The dried fly ash was then ground into a finer powder using a ball mill to a mesh size of less than 150. S12, the finely ground fly ash sample was added to the sucrose solution, reacted on a magnetic stirrer, phenolphthalein indicator was added, and then titrated with hydrochloric acid. The volume V of hydrochloric acid consumed was recorded. HCl The acid neutralization capacity K of fly ash was calculated. Specifically: Take 1±0.05g of finely ground fly ash sample and add it to a sucrose solution with a concentration of 30-35g / L (10±0.5ml). Then, place the solution on a magnetic stirrer and react for 10±1 minutes. Next, add 2-3 drops of phenolphthalein indicator to the solution, and then titrate with 0.1mol / L hydrochloric acid, recording the volume of hydrochloric acid consumed, V. HCl ; Whether to use the aforementioned heavy metal stabilizer is determined based on the alkaline substance content in fly ash. The alkaline substance content in fly ash is characterized by the acid neutralization capacity K of fly ash, and the calculation method is as follows: K=V HCl ×C HCl / m 飞灰 In the formula, K is the acid neutralization capacity per unit mass of fly ash, and the unit is mmol / g; V HCl The volume of hydrochloric acid consumed during titration, expressed in mL; C HCl This represents the molar concentration of hydrochloric acid used in the titration, expressed in mol / L. m 飞灰 The mass of the fly ash sample used in the reaction with sucrose solution is expressed in grams. S2, When the acid neutralization capacity K of fly ash is less than 5, the heavy metals in fly ash are solidified using the above-mentioned heavy metal stabilizer for treating incineration fly ash. Specifically, the choice of heavy metal stabilizer is determined based on the acid neutralization capacity of the fly ash. When the acid neutralization capacity K of the fly ash is less than 5, the heavy metals in the fly ash are solidified using the above-mentioned heavy metal stabilizer for treating incineration fly ash. Otherwise, the acidity or alkalinity of the fly ash needs to be adjusted, and other heavy metal stabilizers should be selected.

2. The method of using the heavy metal stabilizer for treating incinerator fly ash according to claim 1, characterized in that, The content of the polyacrylamide is 0.1-0.2%.

3. The method of using the heavy metal stabilizer for treating incinerator fly ash according to claim 1, characterized in that, The phosphate is selected from one or more of sodium phosphate, potassium phosphate, and ammonium phosphate.

4. The method of using the heavy metal stabilizer for treating incinerator fly ash according to claim 1, characterized in that, The carbamate is selected from one or two of sodium N,N-dimethylcarbamate and sodium diethyldithiocarbamate.

5. The method of using the heavy metal stabilizer for treating incinerator fly ash according to claim 1, characterized in that, The hydroxide is selected from sodium hydroxide or potassium hydroxide.

6. The method of using the heavy metal stabilizer for treating incineration fly ash according to any one of claims 1 to 5, characterized in that, The amount of the heavy metal stabilizer added when treating incineration fly ash is 1.0 to 3.0%.

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