Modified lignin heavy metal chelating agent, preparation method thereof and waste incineration fly ash stabilizing method
By developing a modified lignin-based heavy metal chelating agent, the problem of efficient and stable heavy metal chelation in municipal solid waste incineration fly ash was solved. This method achieves low-cost and environmentally friendly heavy metal capture and solidification, reduces heavy metal leaching toxicity, and improves environmental safety.
Patent Information
- Application Number
- CN202511159596.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-19
- Publication Date
- 2025-12-12
AI Technical Summary
In existing technologies, fly ash from municipal solid waste incineration contains highly toxic heavy metals. Traditional solidification methods are costly and pose a risk of secondary pollution. Natural lignin has limited chelating capacity, making it difficult to meet practical application needs.
By modifying the preparation method of lignin heavy metal chelating agents, including alkaline extraction, Mannich reaction and carbon disulfide crosslinking, multi-level chelating sites are constructed. Combined with biochar and water-soluble phosphate, a highly efficient chelating agent is formed to capture and stabilize heavy metals in fly ash.
It achieves a reduction in heavy metal leaching toxicity to below 50% of the standard limit, reduces curing costs by more than 30%, and maintains stability in strong acid and alkali environments, thus providing both environmental and economic benefits.
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of waste incineration fly ash treatment, and particularly relates to a modified lignin heavy metal chelating agent and a preparation method and a waste incineration fly ash stabilization method. BACKGROUND
[0002] The waste and other waste materials in China are produced in large quantities every year, and one of the disposal methods is incineration. However, incineration produces about 23% of bottom ash and 3-5% of fly ash of the total amount of waste. Among them, fly ash is produced by separating the flue gas generated by the incinerator through the reaction tower for neutralization and purification, mixing with a certain amount of adsorbent, and then separating by a high-efficiency dust separator.
[0003] The fly ash of domestic waste incineration contains a large amount of heavy metals such as lead, cadmium, mercury and chromium. These heavy metals have the characteristics of high toxicity, difficult degradation and easy migration, which pose a serious threat to the environment and human health.
[0004] The traditional fly ash solidification / stabilization method mainly relies on cement solidification and chemical agent stabilization technology, but has the problems of high cost and secondary pollution risk. Therefore, it is of great environmental and economic significance to develop an efficient, environmentally friendly and low-cost heavy metal chelating agent for the solidification / stabilization of fly ash of domestic waste incineration.
[0005] Lignin is an important component of plant cell walls and has rich functional groups (such as hydroxyl and carboxyl groups) that can complex with heavy metal ions. However, the chelating ability of natural lignin is limited and cannot meet the actual application requirements. Therefore, modification of lignin to improve its chelating performance has become a research hotspot. SUMMARY
[0006] The present application aims to solve the problems in the prior art and provides a modified lignin heavy metal chelating agent and a preparation method and a waste incineration fly ash stabilization method.
[0007] A preparation method of a modified lignin heavy metal chelating agent, comprising the following steps: dissolving lignin and polyethyleneimine in water, then adding formaldehyde, and reacting at 50-70℃ for 1-3h; then adding carbon disulfide, and reacting at 40-60℃ for 2-4h, and then dialyzing and drying.
[0008] Preferably, the mass ratio of lignin to polyethyleneimine is 1:0.5-2, the mass ratio of formaldehyde to lignin is 1-3:10, and the mass ratio of carbon disulfide to polyethyleneimine is 0.8-1.5:1.
[0009] Preferably, the lignin is prepared by the following steps: mixing rice husk with a strong alkali solution, reacting at 90-120℃ for 2-4h, centrifuging to obtain supernatant, acidifying to pH=2-3, and drying the precipitate.
[0010] Preferably, the molecular weight of polyethyleneimine is 600-10000 Da.
[0011] Preferably, after adding carbon disulfide and reacting for 2-4 hours, the pH of the system is adjusted to 9-10 to terminate the reaction.
[0012] A modified lignin heavy metal chelating agent is prepared by the above-mentioned preparation method of modified lignin heavy metal chelating agent.
[0013] Preferably, the functional groups contained therein include thiol, amino and hydroxyl groups; the thiol content is 0.8-1.5 mmol / g, the amino content is 1.2-2.0 mmol / g, and the hydroxyl content is 2.5-4.0 mmol / g.
[0014] A method for stabilizing fly ash from municipal solid waste incineration involves adding the aforementioned modified lignin heavy metal chelating agent to the fly ash, then adding water, stirring evenly, molding, and curing at room temperature for 3-7 days.
[0015] Preferably, the mass ratio of the modified lignin heavy metal chelating agent to the dry weight of fly ash is 3-8:100; water is added until the system moisture content is 15-25%.
[0016] Preferably, after curing, the material is soaked in acetic acid buffer for 72 hours, and the leaching concentration of lead is less than 0.1 mg / L and the leaching concentration of cadmium is less than 0.03 mg / L.
[0017] Preferably, after adding water, water-soluble phosphate and porous biochar are added and stirred evenly before molding.
[0018] More preferably, the mass ratio of the modified lignin heavy metal chelating agent, water-soluble phosphate, and porous biochar is 3-8:1-3:1-2.
[0019] More preferably, porous biochar is prepared by the following steps: the biochar is pulverized and sieved, added to hydrochloric acid and ultrasonically treated for 1-2 hours, filtered, washed, and vacuum dried; the product and dopamine hydrochloride are added to a tris(hydroxymethyl)aminomethane hydrochloride solution and ultrasonically treated for 0.5-2 hours, centrifuged, washed, and vacuum dried.
[0020] Specifically, the mass ratio of biochar to dopamine hydrochloride is 10-20:1-5.
[0021] Specifically, the hydrochloric acid concentration is 0.5-2 mol / L.
[0022] Specifically, the pH value of the tris(hydroxymethyl)aminomethane hydrochloride solution is 8-9.
[0023] Specifically, the ultrasonic frequency is 60-70kHz.
[0024] Beneficial effects:
[0025] This invention constructs multi-level chelation sites through a three-step reaction: (1) Alkali extraction: NaOH destroys the lignin-carbohydrate complex in rice husk to obtain high-purity lignin (>85%); (2) PEI-formaldehyde grafting: an amino group (-NH-CH2-PEI) is introduced into the lignin benzene ring through the Mannich reaction, the reaction formula is as follows: Lignin-OH+HCHO+H2N-PEI→Lignin-N(CH2-PEI)-CH2OH; (3) CS2 crosslinking: the primary amine in PEI reacts with CS2 to generate dithiocarbamate (-NH-CSS). - ), introducing high-affinity thiol groups.
[0026] This invention uses rice husks as raw material and extracts lignin using an alkaline method. Rice husk lignin contains more p-hydroxybenzene structures than coniferous lignin, making it more prone to electrophilic substitution. Then, it undergoes a Mannich reaction with polyethyleneimine (PEI) and formaldehyde. The long chain of PEI can provide a "chelation amplification effect," allowing a single molecule to bind multiple metal ions. Subsequently, carbon disulfide is used for cross-linking modification, making the resulting Lignin-PEI-CSS chelate stable in the pH range of 2-12 and preventing secondary dissolution.
[0027] The multifunctional heavy metal chelating agent obtained in this invention efficiently captures heavy metals such as Pb, Cd, Cr, and Zn from fly ash through the synergistic effect of thiol, amino, and hydroxyl groups. The chelated products are stable under strong acid and alkali environments. In application, the chelating agent is added at 3-8% of the fly ash mass, mixed with water, and cured for 3-7 days to reduce the leaching toxicity of the fly ash to below 50% of the limit specified in GB 16889-2024 "Pollution Control Standard for Municipal Solid Waste Landfills". This invention achieves resource utilization of agricultural and forestry waste, reduces solidification costs by more than 30%, and provides both environmental and economic benefits.
[0028] This invention loads a polydopamine layer onto the porous structure of biochar, further enhancing its adsorption and loading capacity for heavy metals. It also exhibits strong hydrophilicity and adhesion, allowing for the slow release of adsorbed water and promoting the formation of hydroxyapatite structures during curing. The stability of the chelated products is significantly enhanced under strong acid and alkali environments. Furthermore, this invention utilizes the obtained chelating agent, water-soluble phosphate, and porous biochar in combination to promote the formation of insoluble phosphates from heavy metals, leading to the formation of hydroxyapatite structures under alkaline curing conditions, thus significantly reducing the leaching toxicity of heavy metals. Detailed Implementation
[0029] The present invention will be further explained below with reference to specific embodiments.
[0030] Example 1: Preparation of chelating agents
[0031] 100g of rice husks were mixed with 1.2L of 1.5M NaOH solution and reacted at 105℃ for 3h. The filtrate was adjusted to pH=2.5 with 6M hydrochloric acid and centrifuged to obtain 22.3g of lignin. This lignin was dissolved in 500mL of water with 50g of PEI (MW=1800), and 15g of formaldehyde was added. The mixture was reacted at 65℃ for 2h. 45g of CS2 was added, and the mixture was reacted at 50℃ for 3h. The pH was then adjusted to 9.5, dialyzed, and lyophilized to obtain a brownish-black powder chelating agent (68g).
[0032] The chelating agent was detected using FT-IR: 2560 cm⁻¹ -1 (-SH), 1640cm -1 (C=N), 1040cm -1 (C = S).
[0033] Example 2: Application of fly ash curing
[0034] Fly ash from a waste-to-energy plant (containing 1200 mg / kg Pb and 85 mg / kg Cd) was mixed with 5% of the chelating agent obtained in Example 1, and the moisture content was adjusted to 20%. The mixture was then pressed into Φ50×50 mm cylinders. After 7 days of curing, the compressive strength reached 12.0 MPa. The leaching concentration of heavy metals was tested according to HJ / T300-2007 "Solid Waste Leaching Toxicity Leaching Method - Acetic Acid Buffer Solution Method". The leaching concentration of Pb was 0.070 mg / L, and the leaching concentration of Cd was 0.010 mg / L (80% below the standard limit).
[0035] Example 3: Application of fly ash curing
[0036] Fly ash from a waste-to-energy plant (containing 1200 mg / kg Pb and 85 mg / kg Cd) was mixed with 5% of the chelating agent obtained in Example 1, and the moisture content was adjusted to 20%. 2% water-soluble phosphate and 1.5% porous biochar were added and stirred evenly, and then pressed into a Φ50×50mm cylinder.
[0037] The porous biochar was prepared using the following steps: 15g of coconut shell charcoal was pulverized and passed through a 120-mesh sieve, added to 100g of 1mol / L hydrochloric acid and ultrasonically treated for 90min, filtered, washed, and vacuum dried; the product and 3g of dopamine hydrochloride were added to 50g of a tris(hydroxymethyl)aminomethane hydrochloride solution with a pH of 9, ultrasonically treated for 90min at a frequency of 65kHz, centrifuged, washed, and vacuum dried.
[0038] After 7 days of curing, the compressive strength reached 14.1 MPa. Referring to HJ / T 300-2007 "Solid Waste Leaching Toxicity Leaching Method Acetic Acid Buffer Solution Method", the leaching concentration of heavy metals was tested. The leaching concentration of Pb was 0.035 mg / L and the leaching concentration of Cd was 0.005 mg / L (80% lower than the standard limit).
[0039] Comparative Example 1
[0040] Fly ash from a waste-to-energy plant (containing 1200 mg / kg Pb and 85 mg / kg Cd) was mixed with 5% lignin obtained in Example 1, and the moisture content was adjusted to 20%. The mixture was then pressed into Φ50×50 mm cylinders. After 7 days of curing, the leaching concentration of heavy metals was tested according to HJ / T 300-2007 "Solid Waste Leaching Toxicity Leaching Method - Acetic Acid Buffer Solution Method". The leaching concentration of Pb was 1.800 mg / L (3.6 times the standard).
[0041] Comparative Example 2
[0042] Fly ash from a waste-to-energy plant (containing 1200 mg / kg Pb and 85 mg / kg Cd) was mixed with 8% commercially available DTC chelating agent, and the moisture content was adjusted to 20%. The mixture was then pressed into Φ50×50 mm cylinders. After 7 days of curing, the leaching concentration of heavy metals was tested according to HJ / T 300-2007 "Solid Waste Leaching Toxicity Leaching Method - Acetic Acid Buffer Solution Method". The leaching concentration of Pb was 0.050 mg / L. However, the cost was 3.2 times that of Example 2 and 1.4 times that of Example 3.
[0043] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for preparing a modified lignin heavy metal chelating agent, characterized in that, Includes the following steps: Lignin and polyethyleneimine are dissolved in water, then formaldehyde is added, and the mixture is reacted at 50-70℃ for 1-3 hours; then carbon disulfide is added, and the mixture is reacted at 40-60℃ for 2-4 hours, followed by dialysis and drying.
2. The preparation method of the modified lignin heavy metal chelating agent according to claim 1, characterized in that, The mass ratio of lignin to polyethyleneimine is 1:0.5-2, the mass ratio of formaldehyde to lignin is 1-3:10, and the mass ratio of carbon disulfide to polyethyleneimine is 0.8-1.5:
1.
3. The preparation method of the modified lignin heavy metal chelating agent according to claim 1, characterized in that, Lignin is prepared by the following steps: rice husks are mixed with a strong alkaline solution and reacted at 90-120℃ for 2-4 hours. The supernatant is collected by centrifugation, acid precipitation is performed until the pH of the system is 2-3, and the precipitate is dried.
4. A modified lignin heavy metal chelating agent, characterized in that, It is prepared by the method described in any one of claims 1-3 for the preparation of modified lignin heavy metal chelating agents.
5. The modified lignin heavy metal chelating agent according to claim 4, characterized in that, Its functional groups include thiol, amino and hydroxyl groups; the thiol content is 0.8-1.5 mmol / g, the amino content is 1.2-2.0 mmol / g, and the hydroxyl content is 2.5-4.0 mmol / g.
6. A method for stabilizing fly ash from municipal solid waste incineration, characterized in that, Add the modified lignin heavy metal chelating agent as described in claim 4 or 5 to the fly ash from municipal solid waste incineration, then add water and stir evenly, form into a mold, and cure at room temperature for 3-7 days.
7. The method for stabilizing fly ash from municipal solid waste incineration according to claim 6, characterized in that, The mass ratio of the modified lignin heavy metal chelating agent as described in claim 4 or 5 to the dry weight of fly ash is 3-8:100; water is added until the system moisture content is 15-25%.
8. The method for stabilizing fly ash from municipal solid waste incineration according to claim 6, characterized in that, After curing, the materials were soaked in acetic acid buffer for 72 hours, and the leaching concentration of lead was less than 0.1 mg / L and the leaching concentration of cadmium was less than 0.03 mg / L.
9. The method for stabilizing fly ash from municipal solid waste incineration according to claim 6, characterized in that, After adding water, add water-soluble phosphate and porous biochar, stir well, and then form the product. The mass ratio of the modified lignin heavy metal chelating agent, water-soluble phosphate, and porous biochar as described in claim 6 or 7 is 3-8:1-3:1-2.
10. The method for stabilizing fly ash from municipal solid waste incineration according to claim 9, characterized in that, Porous biochar is prepared by the following steps: the biochar is pulverized and sieved, added to hydrochloric acid and ultrasonically treated for 1-2 hours, filtered, washed, and vacuum dried; the product and dopamine hydrochloride are added to a tris(hydroxymethyl)aminomethane hydrochloride solution and ultrasonically treated for 0.5-2 hours, centrifuged, washed, and vacuum dried. The mass ratio of biochar to dopamine hydrochloride is 10-20:1-5.