A method for treating fly ash from municipal solid waste incineration

Abstract

This invention provides a method for treating fly ash from municipal solid waste incineration, belonging to the field of solid waste treatment technology. The invention first employs water leaching for dechlorination, followed by acid leaching to dissolve calcium ions and separate calcium from heavy metals. The calcium-containing filtrate is then treated with an alkaline reagent to precipitate calcium. The resulting calcium sludge solid phase is combined with the residue and granulated. By controlling the pressing conditions and size of the solid particles, the subsequent thermal treatment process is facilitated to decompose dioxins while simultaneously stabilizing heavy metals, resulting in harmless products. The treatment method of this invention ensures that the concentrations of soluble chlorine, leached heavy metals, and dioxins in the treated product fully meet standards, achieving harmless, reduced-volume, and resource-based treatment of municipal solid waste incineration fly ash.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, and in particular to a method for treating fly ash from municipal solid waste incineration. Background Technology

[0002] Fly ash from municipal solid waste incineration is a harmful byproduct produced during the incineration process. It contains pollutants such as heavy metals (e.g., lead, cadmium, mercury), dioxins, and soluble salts. If not properly treated, it can cause serious harm to the environment and human health. Currently, fly ash treatment methods mainly include solidification and stabilization, co-processing in cement kilns, chemical stabilization, and high-temperature melting.

[0003] Solidification and stabilization technologies typically use materials such as cement and chelating agents to solidify fly ash to reduce the leaching toxicity of heavy metals. However, these technologies suffer from problems such as high volumetric efficiency and insufficient long-term stability. While co-processing in cement kilns can achieve resource utilization, it requires strict control over fly ash composition and may affect cement product quality. Chemical stabilization treatments are costly and have limited effectiveness in fixing certain heavy metals. High-temperature melting technology can effectively decompose dioxins and solidify heavy metals, but it is energy-intensive and requires significant equipment investment, making large-scale implementation difficult.

[0004] Therefore, there is an urgent need to develop an efficient, economical, and environmentally friendly technology for treating fly ash from municipal solid waste incineration, so as to achieve the harmless, reduced, and resource-based treatment of fly ash. Summary of the Invention

[0005] The purpose of this invention is to provide a method for treating fly ash from municipal solid waste incineration, which can achieve the harmless, reduced-volume, and resource-based treatment of fly ash from municipal solid waste incineration.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for treating fly ash from municipal solid waste incineration, comprising the following steps: The fly ash from waste incineration is mixed with water and then leached to obtain leachate and leaching residue. The leaching residue is mixed with an acid solution and acid leaching is carried out under pH conditions of 4-5 to obtain a calcium-containing filtrate and residue. The calcium-containing filtrate is mixed with an alkaline reagent to precipitate calcium, yielding calcium sludge and heavy metal residue; the heavy metal residue is then transported off-site for disposal. The calcium mud and residue are combined and then subjected to filter press granulation to obtain solid particles; the pressure of the filter press granulation is 2~3MPa and the diameter of the solid particles is 5~6cm. The solid particles are placed together with municipal solid waste in a waste incinerator for heat treatment to obtain harmless products.

[0007] Preferably, the mass ratio of the waste incineration fly ash to water is 1:5~10.

[0008] Preferably, the water immersion temperature is 20~60℃ and the time is 30~60 min.

[0009] Preferably, the acid in the acid solution includes acetic acid or citric acid; the concentration of the acid solution is 0.5~1.0 mol / L.

[0010] Preferably, the solid-liquid ratio of the leaching residue to the acid solution is 1g:(5~8)mL, the acid leaching temperature is 40~60℃, and the time is 1~2h.

[0011] Preferably, the alkaline reagent includes sodium carbonate or potassium carbonate; the molar ratio of calcium ions in the calcium-containing filtrate to carbonate ions in the alkaline reagent is 1:1 to 1.2.

[0012] Preferably, the temperature for calcium precipitation is 40~60℃, the time is 30~60 min, and the pH is 8~10.

[0013] Preferably, the heat treatment temperature is 500~750℃ and the time is 1~2h.

[0014] This invention provides a method for treating fly ash from municipal solid waste incineration. First, water leaching is used for dechlorination, followed by acid leaching to dissolve calcium ions and separate calcium from heavy metals. The calcium-containing filtrate is then treated with an alkaline reagent to precipitate calcium. The resulting calcium sludge solid phase is combined with the residue and granulated. By controlling the pressing conditions and size of the solid particles, the subsequent thermal treatment process is facilitated to decompose dioxins and stabilize heavy metals, resulting in harmless products. The treatment method of this invention ensures that the concentrations of soluble chlorine, leached heavy metals, and dioxins in the treated product fully meet standards, achieving harmless, reduced-volume, and resource-based treatment of municipal solid waste incineration fly ash. Detailed Implementation

[0015] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0016] This invention provides a method for treating fly ash from municipal solid waste incineration, comprising the following steps: The fly ash from waste incineration is mixed with water and then leached to obtain leachate and leaching residue. The leaching residue is mixed with an acid solution and acid leaching is carried out under pH conditions of 4-5 to obtain a calcium-containing filtrate and residue. The calcium-containing filtrate is mixed with an alkaline reagent to precipitate calcium, yielding calcium sludge and heavy metal residue; the heavy metal residue is then transported off-site for disposal. The calcium mud and residue are combined and then subjected to filter press granulation to obtain solid particles; the pressure of the filter press granulation is 2~3MPa and the diameter of the solid particles is 5~6cm. The solid particles are placed together with municipal solid waste in a waste incinerator for heat treatment to obtain harmless products.

[0017] This invention involves mixing fly ash from waste incineration with water and then leaching it to obtain leachate and leachate residue.

[0018] The present invention does not have any special limitation on the source of the waste incineration fly ash, which can be obtained from the waste incineration plant in a manner known in the art.

[0019] In this invention, the mass ratio of the waste incineration fly ash to water is preferably 1:5~10, more preferably 1:6~8.

[0020] In this invention, the water immersion temperature is preferably 20~60℃, more preferably 40~50℃, and the immersion time is preferably 30~60 min, more preferably 40~50 min.

[0021] After the water immersion is completed, the present invention preferably performs solid-liquid separation on the obtained product to obtain leachate and leaching residue; the present invention does not have any special limitation on the solid-liquid separation, and solid-liquid separation can be achieved in a manner known in the art.

[0022] This invention removes 85-90% of the chlorine from fly ash from waste incineration by water leaching; the leachate contains chloride salts, which can be crystallized to obtain industrial salt products.

[0023] After obtaining the leaching residue, the present invention mixes the leaching residue with an acid solution and performs acid leaching at a pH of 4-5 to obtain a calcium-containing filtrate and residue.

[0024] In this invention, the acid in the acid solution preferably includes acetic acid or citric acid; the concentration of the acid solution is preferably 0.5~1.0 mol / L, more preferably 0.6~0.8 mol / L.

[0025] In this invention, the solid-liquid ratio of the leaching residue to the acid solution is preferably 1g:(5~8)mL, more preferably 1g:(6~7)mL; the acid leaching temperature is preferably 40~60℃, more preferably 50℃; the leaching time is preferably 1~2 h, more preferably 1.5 h; and the pH is 4~5, more preferably 4.5~5.

[0026] After the acid leaching is completed, the present invention preferably performs solid-liquid separation on the obtained product to obtain calcium-containing filtrate and residue; the present invention does not have any special limitation on the solid-liquid separation, and solid-liquid separation can be achieved in a manner known in the art, and filtration is more preferred.

[0027] After obtaining the calcium-containing filtrate, the present invention mixes the calcium-containing filtrate with an alkaline reagent to precipitate calcium, thereby obtaining calcium mud and heavy metal residue; the heavy metal residue is transported off-site for disposal.

[0028] In this invention, the alkaline reagent preferably includes sodium carbonate or potassium carbonate; the molar ratio of calcium ions in the calcium-containing filtrate to carbonate ions in the alkaline reagent is preferably 1:1 to 1.2, more preferably 1:1.1.

[0029] In this invention, the temperature for calcium precipitation is preferably 40-60°C, more preferably 50°C, the time is preferably 30-60 min, more preferably 40-50 min, and the pH is preferably 8-10, more preferably 9.

[0030] After obtaining calcium mud, the present invention combines the calcium mud with the residue and then performs pressure filtration and granulation to obtain solid particles.

[0031] In this invention, the pressure of the filter press granulation is 2-3 MPa, and the diameter of the solid particles is 5-6 cm. This invention does not impose any special limitations on the length or shape of the solid particles. By controlling the pressure and diameter of the filter press granulation, this invention can improve the molding performance and mechanical strength of the mixture, avoid dust emission and breakage during subsequent remelting, and ensure the stable and continuous operation of the subsequent synergistic heat treatment process.

[0032] After obtaining solid particles, the present invention places the solid particles together with municipal solid waste in a waste incinerator for heat treatment to obtain harmless products.

[0033] In this invention, the heat treatment temperature is preferably 500~750℃, more preferably 600~700℃, and even more preferably 650℃, and the time is preferably 1~2h, more preferably 1.5h. This invention decomposes dioxins in solid particles through furnace heat treatment, while simultaneously stabilizing heavy metals.

[0034] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0035] Unless otherwise specified, the experimental and testing methods described below are conventional methods; unless otherwise specified, the reagents and raw materials described below are commercially available.

[0036] The fly ash used in the following examples comes from municipal solid waste incineration plants, and the content of each element is as follows: C 0.68%, O 32.49%, Na 6.24%, Mg 0.52%, Al 0.24%, Si 1.17%, S 3.18%, Cl23.35%, K 7.06%, Ca 25.07%; Metal content in fly ash from waste incineration: Mercury 8.85 mg / kg, copper 1290 mg / kg, zinc 6170 mg / kg, lead 531 mg / kg, cadmium 114 mg / kg, beryllium (ND), barium 392 mg / kg, nickel 63.1 mg / kg, arsenic 36.4 mg / kg, total chromium 107 mg / kg, hexavalent chromium 3.7 mg / kg, selenium 1.2 mg / kg.

[0037] Example 1

[0038] According to the mass ratio of waste incineration fly ash to water of 1:8, the waste incineration fly ash and water are mixed and soaked in water at 50°C for 50 min. The resulting product is filtered to obtain leachate and leach residue. The leaching residue was mixed with an acetic acid solution of 0.8 mol / L at a solid-liquid ratio of 1g:6mL, and then acid-leached for 1.5 h at pH 5 and temperature 50℃. After filtration, calcium-containing filtrate and residue were obtained. The calcium-containing filtrate was mixed with sodium carbonate at a molar ratio of 1:1.1 to calcium ions, and the mixture was subjected to calcium precipitation for 50 min at a temperature of 50°C and a pH of 9 to obtain calcium mud and heavy metal residue. The heavy metal residue was transported off-site for disposal. After the calcium mud and residue were combined, they were subjected to pressure filtration and granulation at a pressure of 2.5 MPa to obtain cylindrical solid particles with a diameter of 5 cm. The solid particles were placed together with municipal solid waste in a waste incinerator and heat-treated at 650°C for 1.5 hours to obtain harmless products.

[0039] Example 2

[0040] According to the mass ratio of waste incineration fly ash to water of 1:6, the waste incineration fly ash and water are mixed and soaked in water at 40°C for 40 min. The resulting product is filtered to obtain leachate and leach residue. The leaching residue was mixed with a 0.5 mol / L acetic acid solution at a solid-liquid ratio of 1 g: 5 mL, and acid leaching was carried out for 1 h at pH 5 and temperature 40 °C. After filtration, calcium-containing filtrate and residue were obtained. The calcium-containing filtrate was mixed with sodium carbonate at a molar ratio of 1:1.2 to calcium ions, and the mixture was subjected to calcium precipitation for 30 min at a temperature of 40°C and a pH of 8 to obtain calcium mud and heavy metal residue. The heavy metal residue was transported off-site for disposal. After the calcium mud and residue were combined, they were subjected to pressure filtration and granulation at a pressure of 3 MPa to obtain cylindrical solid particles with a diameter of 6 cm. The solid particles were placed together with municipal solid waste in a waste incinerator and heat-treated at 700°C for 1 hour to obtain harmless products.

[0041] Example 3

[0042] According to the mass ratio of waste incineration fly ash to water of 1:10, the waste incineration fly ash and water are mixed and soaked in water at 60°C for 60 min. The resulting product is filtered to obtain leachate and leach residue. The leaching residue was mixed with a 1.0 mol / L acetic acid solution at a solid-liquid ratio of 1g:8mL, and acid leaching was carried out for 2 hours at pH 5 and temperature 60℃. After filtration, calcium-containing filtrate and residue were obtained. The calcium-containing filtrate was mixed with sodium carbonate at a molar ratio of 1:1 to calcium ions, and calcium was precipitated for 60 min at a temperature of 60°C and a pH of 10 to obtain calcium mud and heavy metal residue. The heavy metal residue was transported off-site for disposal. After the calcium mud and residue were combined, they were subjected to pressure filtration and granulation at a pressure of 2 MPa to obtain cylindrical solid particles with a diameter of 5 cm. The solid particles were placed together with municipal solid waste in a waste incinerator and heat-treated at 600°C for 2 hours to obtain harmless products.

[0043] Performance testing

[0044] The content of harmful substances in the treated products obtained in Examples 1-3 was determined, and the results are shown in Table 1.

[0045] Table 1. Content of harmful substances (mg / L) in the treated products obtained in Examples 1-3

[0046] As shown in Table 1, after the method of the present invention treats the incineration fly ash, the leaching of soluble chlorine and heavy metals in the treated product meets the requirements of the "Technical Specification for Pollution Control of Municipal Solid Waste Incineration Fly Ash (Trial)" (HJ1134-2020), and the total concentration of dioxins does not exceed 50 ng-TEQ / kg (based on the dry weight of fly ash), which meets the requirements of HJ1134-2020.

[0047] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating fly ash from municipal solid waste incineration, characterized in that, Includes the following steps: The fly ash from waste incineration is mixed with water and then leached to obtain leachate and leaching residue. The leaching residue is mixed with an acid solution and acid leaching is carried out under pH conditions of 4-5 to obtain a calcium-containing filtrate and residue. The calcium-containing filtrate is mixed with an alkaline reagent to precipitate calcium, yielding calcium sludge and heavy metal residue; the heavy metal residue is then transported off-site for disposal. The calcium mud and residue are combined and then subjected to filter press granulation to obtain solid particles; the pressure of the filter press granulation is 2~3MPa and the diameter of the solid particles is 5~6cm. The solid particles are placed together with municipal solid waste in a waste incinerator for heat treatment to obtain harmless products.

2. The processing method according to claim 1, characterized in that, The mass ratio of the fly ash from the waste incineration to water is 1:5~10.

3. The processing method according to claim 2, characterized in that, The water immersion temperature is 20~60℃, and the time is 30~60 min.

4. The processing method according to claim 1, characterized in that, The acid in the acid solution includes acetic acid or citric acid; the concentration of the acid solution is 0.5~1.0 mol / L.

5. The processing method according to claim 4, characterized in that, The solid-liquid ratio of the leaching residue to the acid solution is 1g:(5~8)mL, and the acid leaching temperature is 40~60℃, and the time is 1~2h.

6. The processing method according to claim 1, characterized in that, The alkaline reagent includes sodium carbonate or potassium carbonate; the molar ratio of calcium ions in the calcium-containing filtrate to carbonate ions in the alkaline reagent is 1:1 to 1.

2.

7. The processing method according to claim 6, characterized in that, The calcium precipitation temperature is 40~60℃, the time is 30~60 min, and the pH is 8~10.

8. The processing method according to claim 1, characterized in that, The heat treatment is performed at a temperature of 500~750℃ for 1~2 hours.

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