Method for promoting dissolution and inhibiting calcium dissolution of waste incineration fly ash

Abstract

This invention relates to a method for promoting dechlorination and inhibiting calcium leaching from waste incineration fly ash, belonging to the field of municipal solid waste resource utilization technology. The method includes the following steps: 60-90% fly ash, 10-40% auxiliary materials, 0-5% additives, and 0-5% regulators are mixed evenly by mass percentage, then mixed with water at a solid-liquid ratio of 1:(2-3.5). The mixture is stirred hydrothermally at 120-200℃ and 0.5-1.5MPa for 1-5 hours. After cooling, solid-liquid separation is performed to obtain solid material and ash washing wastewater. This invention achieves complete leaching and separation of chloride salts in waste incineration fly ash. Simultaneously, the calcium in the fly ash reacts with the silicon and aluminum components in the auxiliary materials to form a calcium-silicon-aluminum mineral phase, thereby inhibiting the dissolution of calcium in the fly ash into the liquid phase and significantly reducing the treatment cost of fly ash desalination wastewater.

Description

Technical Field

[0001] This invention relates to waste incineration fly ash treatment technology, specifically to a method for promoting dechlorination and inhibiting calcium leaching from waste incineration fly ash, belonging to the field of municipal solid waste resource utilization technology. Background Technology

[0002] Fly ash from municipal solid waste incineration contains large amounts of harmful substances such as chloride salts, soluble heavy metals, and dioxins.

[0003] Currently, the most commonly used resource recovery technologies for waste incineration fly ash include cement kiln co-processing, high-temperature sintering ceramsite technology, high-temperature melting technology, and water washing-low-temperature pyrolysis technology. Among these, high-temperature sintering and high-temperature melting technologies require temperatures above 1300℃, resulting in excessive energy consumption and severe equipment corrosion. Furthermore, during high-temperature processing, heavy metals and chlorine in the fly ash typically form low-boiling-point heavy metal chloride salts, which volatilize in large quantities into the high-temperature flue gas and eventually accumulate in secondary fly ash. Currently, the primary method for treating secondary fly ash is wet extraction, which is not only costly but also prone to secondary pollution. On the other hand, the most widely used fly ash co-processing in cement kilns and the water washing-low-temperature pyrolysis technology, which have lower overall energy consumption, both require multi-stage water washing to remove chlorine and soluble heavy metals from the fly ash. Water washing is the most commonly used dechlorination method, but it faces significant technical bottlenecks in practical operation. (1) Fly ash usually contains a large amount of calcium components in the form of CaO, Ca(OH)2, CaCO3, etc., which are easily dissolved to form soluble calcium salts during the washing process, resulting in a significant increase in the concentration of calcium ions in the washing wastewater. This requires a large amount of reagents for subsequent calcium removal treatment, increasing the treatment cost and generating secondary sludge.

[0004] (2) Existing technologies generally assume that calcium dissolution is an unavoidable side effect during the water washing and dechlorination process, and lack effective means to simultaneously inhibit calcium dissolution during the dechlorination stage.

[0005] (3) Conventional wastewater treatment methods, such as adding precipitants to the aqueous phase to solidify calcium, only target dissolved Ca. 2+ This is a post-treatment measure after dechlorination and cannot resolve the contradiction between dechlorination and calcium dissolution at the source.

[0006] For example, Chinese patent CN113231446B discloses a system for treating and disposing of fly ash from municipal solid waste incineration. While reducing the chlorine content of the fly ash, it also washes away NaCl, KCl, CaCl2, and CaClOH, which have significantly different solubilities. Therefore, while this technology achieves fly ash dechlorination, it inevitably causes a large amount of calcium to dissolve, resulting in a significant increase in the calcium ion concentration in the washing wastewater. This necessitates a complex subsequent chemical calcium removal process, which not only increases wastewater treatment costs and system complexity but also easily generates secondary sludge, hindering the further promotion and application of this type of fly ash washing dechlorination technology.

[0007] Therefore, there is still a lack of technology that can simultaneously inhibit calcium leaching and facilitate the resource utilization of fly ash while ensuring the dechlorination efficiency of fly ash. Summary of the Invention

[0008] To address the technical problem that dechlorination in existing technologies inevitably involves the dissolution of large amounts of calcium, this invention provides a method for promoting dechlorination and inhibiting calcium dissolution in waste incineration fly ash. The core of this method lies in the fact that, under high temperature and high pressure hydrothermal conditions, calcium components in fly ash are preferentially fixed into a stable calcium-silicon-aluminum mineral phase through an in-situ mineralization reaction, thereby simultaneously inhibiting calcium dissolution during the dechlorination process.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash includes the following steps: By mass percentage, 60-90% fly ash, 10-40% auxiliary materials, 0-5% additives, and 0-5% regulators are mixed evenly and then mixed with water in a high-temperature and high-pressure reactor at a solid-liquid ratio of 1:(2-3.5). The mixture is then subjected to hydrothermal reaction at 120-200℃ and 0.5-1.5MPa for 1-5 hours. After cooling, solid-liquid separation is performed to obtain solid materials and hydrothermal reaction wastewater.

[0010] Preferably, the auxiliary material is a material containing silicon and aluminum, including but not limited to natural minerals / ores, soil, and various industrial solid by-products / solid wastes, such as aluminum ash, fly ash, quartz sand, silica powder, and mineral powders containing silicon and / or aluminum, or one or more combinations thereof. The mass ratio of silicon to aluminum in the auxiliary material is not strictly required; only that the silicon content is higher than the aluminum content is required. This helps to preferentially generate silicate-based mineral phases during the hydrothermal process, while simultaneously forming aluminosilicates and aluminates, thereby optimizing the mineral transformation process, improving the stabilization effect on harmful components in fly ash, and facilitating resource utilization.

[0011] Preferably, the additives include, but are not limited to, silicates, aluminates, silica sols, and alumina sols. The purpose of adding additives is to further provide components such as silicate ions, aluminate ions, highly reactive silica, and highly reactive alumina that react more readily with calcium. These components react with calcium more readily than the relatively stable silica / alumina in the excipients, thereby more effectively fixing calcium and inhibiting dissolution.

[0012] Preferably, the regulator includes, but is not limited to, alkaline regulators such as sodium hydroxide. The purpose of adding the regulator is to adjust the acidity or alkalinity of the mixed system. Maintaining the system under strongly alkaline conditions will help form the calcium-silicon-aluminum mineral phase, and at the same time, it can cause free calcium ions to form alkaline precipitates, inhibiting the dissolution of calcium in the aqueous phase.

[0013] Preferably, the mass ratio of fly ash to auxiliary materials is 7:3.

[0014] Preferably, the solid-liquid ratio is 1:(2-3).

[0015] Preferably, the hydrothermal reaction pressure is 0.6-1.1 MPa.

[0016] Preferably, the hydrothermal reaction temperature is 160-180℃; since 180℃ has high energy consumption, 160℃ is preferred.

[0017] Preferably, the hydrothermal reaction time is 1-2 hours.

[0018] This invention treats waste incineration fly ash under high temperature and high pressure hydrothermal conditions, achieving complete dissolution and separation of chloride salts in the fly ash, while effectively inhibiting the dissolution of calcium into the liquid phase, thus achieving simultaneous and synergistic dechlorination and calcium inhibition. Its beneficial effects are mainly manifested in: Through the above method, during the hydrothermal process of fly ash under specific temperature and pressure, the favorable trend of chloride solubility gradually increasing with increasing temperature and pressure, as well as the enhanced chloride ion diffusion and migration activity under high temperature and high pressure, are utilized to promote the full dissolution and release of chloride into the solution under high temperature and high pressure, thus achieving complete separation of chloride from the fly ash solid phase. Simultaneously, under high temperature and high pressure hydrothermal conditions, calcium in the fly ash reacts chemically with components such as silica, alumina, silicates, and aluminates in the additives and auxiliary materials. Before a large amount of calcium enters the aqueous phase, specific hydrothermal conditions induce a chemical reaction with these components at the solid-liquid interface, generating a low-solubility, high-stability calcium-silica-aluminate mineral phase (such as hydrated aluminum silicate, hydrated calcium aluminate, hydrated calcium aluminosilicate, etc.), achieving in-situ calcium fixation. Furthermore, adjusting the system pH (e.g., adding sodium hydroxide) accelerates the calcium mineralization reaction, allowing calcium to preferentially enter the solid phase without affecting chloride dissolution and migration, thus achieving simultaneous dechlorination and calcium inhibition.

[0019] Regarding the reaction mechanism, this invention achieves kinetic and thermodynamic coupling control of chloride salt entry into the liquid phase and preferential calcium solidification through comprehensive optimization of temperature, pressure, reaction time, and the ratio of excipients / additives. This solves the technical bottleneck in existing technologies where "dechlorination is inevitably accompanied by calcium dissolution," enabling simultaneous dechlorination and calcium inhibition. Under these specific conditions, the mineralization reaction rate is faster than the calcium dissolution rate, achieving kinetic control of calcium preferential entry into the mineral phase. Furthermore, by fixing calcium through in-situ mineralization, the calcium content in fly ash desalination wastewater is significantly reduced, decreasing subsequent wastewater treatment costs and secondary pollution. The hydrothermally generated calcium-silica-alumina mineral phase has a stable structure, with dense crystal or semi-crystalline structures and stable chemical bonds, exhibiting a strong inhibitory effect on water-soluble calcium ions. This ensures that calcium does not enter the aqueous phase in large quantities during hydrothermal dechlorination. Moreover, this calcium-silica-alumina mineral phase structure possesses cement-like cementitious properties, which is beneficial for the safe resource utilization of fly ash.

[0020] Therefore, this invention induces calcium and silicon-aluminum components in fly ash to form a low-solubility, high-stability mineral phase in situ under high-temperature and high-pressure hydrothermal conditions, thereby achieving preferential solidification of calcium during the dechlorination stage and solving the problem of high calcium in wastewater from the source. Detailed Implementation

[0021] The specific embodiments of the present invention will be described in further detail below with reference to the examples. These examples are used to illustrate the present invention but are not intended to limit its scope. The main parameters of the examples and comparative examples are shown in Table 1.

[0022] Example 1

[0023] The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash in this embodiment 1 includes the following steps: By mass percentage, 90% fly ash and 10% fly ash (58% silica, 31% alumina, and 11% other components) were mixed evenly and then mixed with water at a solid-liquid ratio of 1:2.5. The mixture was stirred hydrothermally at 180℃ and 1.1 MPa for 1.5 hours. After cooling, solid-liquid separation was performed to obtain solid material and ash washing wastewater. The wastewater contained 4.2% chlorine and had a calcium ion concentration of 6584 mg / L.

[0024] Example 2

[0025] The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash in this embodiment 2 includes the following steps: By mass percentage, 85% fly ash, 10% auxiliary materials (mineral powder, of which 53% silicon dioxide, 41% alumina, and 6% other impurities), and 5% additives (silica sol) were mixed evenly and then mixed with water at a solid-liquid ratio of 1:2.5. The mixture was stirred hydrothermally at 160℃ and 0.8MPa for 2.5 hours. After cooling, solid-liquid separation was performed to obtain solid material and ash washing wastewater. The chlorine content of the wastewater was 4.2%, and the calcium ion concentration was 6245 mg / L.

[0026] Example 3

[0027] The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash in this embodiment 3 includes the following steps: By mass percentage, 80% fly ash, 10% fly ash (58% silica, 31% alumina, and 11% other components), 5% additives (aluminum sol), and 5% regulator (sodium hydroxide) were mixed evenly and then mixed with water at a solid-liquid ratio of 1:3. The mixture was then hydrothermally stirred at 160℃ and 0.6 MPa for 3 hours. After cooling, solid-liquid separation was performed to obtain solid material and ash washing wastewater. The wastewater contained 4.1% chlorine and had a calcium ion concentration of 6075 mg / L.

[0028] Example 4

[0029] The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash in this embodiment 4 includes the following steps: By mass percentage, 80% fly ash and 20% fly ash (58% silica, 31% alumina, and 11% other components) were mixed evenly and then mixed with water at a solid-liquid ratio of 1:3.5. The mixture was stirred hydrothermally at 190℃ and 1.3MPa for 1 hour. After cooling, solid-liquid separation was performed to obtain solid material and ash washing wastewater. The wastewater contained 4.1% chlorine and had a calcium ion concentration of 6286 mg / L.

[0030] Example 5

[0031] By mass percentage, 75% fly ash, 20% fly ash (58% silica, 31% alumina, and 11% other components), and 5% additives (3% silica sol and 2% alumina sol) were mixed evenly and then mixed with water at a solid-liquid ratio of 1:3.5. The mixture was stirred hydrothermally at 200℃ and 1.5 MPa for 1 hour. After cooling, solid-liquid separation was performed to obtain solid material and ash washing wastewater. The wastewater contained 3.9% chlorine and had a calcium ion concentration of 6035 mg / L.

[0032] Example 6

[0033] By weight percentage, 70% fly ash, 20% auxiliary materials (mineral powder, of which 61% silicon dioxide, 30% alumina, and 9% other impurities), 5% additives (3% silica sol, 2% alumina sol), and 5% regulator (sodium hydroxide) were mixed evenly and then mixed with water at a solid-liquid ratio of 1:2.5. The mixture was then hydrothermally stirred at 130℃ and 0.6 MPa for 4 hours. After cooling, solid-liquid separation was performed to obtain solid material and ash washing wastewater. The wastewater contained 3.8% chlorine and had a calcium ion concentration of 8178 mg / L.

[0034] Example 7

[0035] By mass percentage, 70% fly ash and 30% fly ash (58% silica, 31% alumina, and 11% other components) were mixed evenly and then mixed with water at a solid-liquid ratio of 1:3. The mixture was stirred hydrothermally at 160℃ and 0.7MPa for 2.5 hours. After cooling, solid-liquid separation was performed to obtain solid material and ash washing wastewater. The wastewater contained 3.7% chlorine and had a calcium ion concentration of 7545 mg / L.

[0036] Example 8

[0037] By mass percentage, 70% fly ash, 30% fly ash (58% silica, 31% alumina, and 11% other components), and 5% additives (silica sol) were mixed evenly and then mixed with water at a solid-liquid ratio of 1:2. The mixture was then hydrothermally stirred at 160℃ and 0.7 MPa for 1 hour. After cooling, solid-liquid separation was performed to obtain solid material and ash washing wastewater. The wastewater contained 4.2% chlorine and had a calcium ion concentration of 5078 mg / L.

[0038] Example 9

[0039] By mass percentage, 70% fly ash, 30% auxiliary materials (60% silica powder, 40% aluminum slag), 5% additives (silica sol), and 5% regulator (sodium hydroxide) were mixed evenly and then mixed with water at a solid-liquid ratio of 1:2.5. The mixture was then hydrothermally stirred at 180℃ and 1.0 MPa for 1.5 hours. After cooling, solid-liquid separation was performed to obtain solid material and ash washing wastewater. The wastewater contained 4.2% chlorine and had a calcium ion concentration of 5061 mg / L.

[0040] Example 10

[0041] By mass percentage, 60% fly ash and 40% auxiliary materials (55% quartz sand and 45% aluminum ash) were mixed evenly, and then mixed with water at a solid-liquid ratio of 1:3. The mixture was stirred hydrothermally at 120℃ and 0.5MPa for 5 hours. After cooling, solid-liquid separation was performed to obtain solid material and ash washing wastewater. The chlorine content in the wastewater was 3.5%, and the calcium ion concentration was 8867 mg / L.

[0042] Comparative Example 1 The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash in Comparative Example 1 includes the following steps: This comparative example uses 100% fly ash as the raw material, without any other auxiliary materials, additives, or regulators. The hydrothermal method involves a solid-liquid ratio of 1:3 and stirring at room temperature and pressure for 2 hours. The wastewater contains 3.0% chlorine and has a calcium ion concentration of 18587 mg / L.

[0043] Comparative Example 2 The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash in this comparative example 2 includes the following steps: The material ratios for this comparative example are the same as those for Comparative Example 1, and the hydrothermal method is the same as that for Example 1. The chlorine content in the wastewater is 3.2%, and the calcium ion concentration is 17794 mg / L.

[0044] Comparative Example 3 The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash in Comparative Example 3 includes the following steps: The material ratios for this comparative example are the same as in Example 7, except that the hydrothermal method is conventional ambient temperature and pressure stirring hydrothermal. The chlorine content in the wastewater is 2.6%, and the calcium ion concentration is 15109 mg / L.

[0045] Comparative Example 4 The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash in Comparative Example 4 includes the following steps: The material ratio and hydrothermal conditions for this comparative example are the same as in Example 7, except that the hydrothermal temperature is reduced to 80°C and the pressure is approximately 0.1 MPa. The chlorine content in the wastewater is 2.9%, and the calcium ion concentration is 14896 mg / L.

[0046] Comparative Example 5 The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash in Comparative Example 5 includes the following steps: The material ratios for this comparative example are the same as in Example 9, except that the hydrothermal method is conventional ambient temperature and pressure stirring hydrothermal. The chlorine content in the wastewater is 2.6%, and the calcium ion concentration is 15873 mg / L.

[0047] Comparative Example 6 The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash in Comparative Example 6 includes the following steps: The material ratio and hydrothermal conditions for this comparative example are the same as in Example 9, except that the hydrothermal temperature is reduced to 80°C and the pressure is approximately 0.1 MPa. The chlorine content in the wastewater is 2.8%, and the calcium ion concentration is 16582 mg / L.

[0048] Table 1. Data from Examples and Comparative Examples

[0049] A comparison of data from Examples 1-10 and Comparative Examples 1-2 revealed that when the material consisted only of fly ash, the chlorine content in the wastewater from the ambient temperature stirring and washing and high-temperature, high-pressure hydrothermal processes was only about 3%, lower than the 3.5%-4.2% in the examples with auxiliary materials. However, the calcium concentration reached approximately 18,000 mg / L, far exceeding the 5,000-8,000 mg / L range of the examples. This indicates that not only was the chlorine leaching effect insufficient in the fly ash, but excessive calcium leaching also occurred.

[0050] A comparison of data from Examples 1-10 and Comparative Examples 3-6 revealed that when fly ash and auxiliary materials were combined, and the hydrothermal reaction temperature was between room temperature and 80°C, the chlorine content in the wastewater was less than 3%, indicating insufficient chlorine dissolution from the fly ash. Simultaneously, the calcium concentration in the wastewater reached 14896 mg / L-16582 mg / L, with a large amount of calcium dissolving into the liquid phase. This means that at insufficient temperatures, the calcium in the fly ash could not fully react with the silicon-aluminum components in the auxiliary materials, thus failing to effectively solidify free calcium in the production of hydrated calcium silicate and other mineral phases.

Claims

1. A method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash, characterized in that, Includes the following steps: By mass percentage, 60-90% fly ash, 10-40% auxiliary materials, 0-5% additives, and 0-5% regulators are mixed evenly and then mixed with water in a high-temperature and high-pressure reactor at a solid-liquid ratio of 1:(2-3.5). The mixture is then subjected to hydrothermal reaction at 120-200℃ and 0.5-1.5MPa for 1-5 hours. After cooling, solid-liquid separation is performed to obtain solid materials and hydrothermal reaction wastewater. The excipient is a material containing silicon and aluminum, wherein the mass of silicon is greater than the mass of aluminum. The additive is one or more of silicates, aluminates, silica sols, and aluminosilicates; The regulator is an alkaline regulator.

2. The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash as described in claim 1, characterized in that, The auxiliary materials are one or more combinations of aluminum ash, aluminum slag, fly ash, quartz sand, silica powder, and mineral powder containing silicon and / or aluminum.

3. The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash as described in claim 1, characterized in that, The alkalinity regulator is sodium hydroxide.

4. The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash as described in claim 1, characterized in that, The mass ratio of fly ash to auxiliary materials is 7:

3.

5. The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash as described in claim 1, characterized in that, The solid-liquid ratio is 1:(2-3).

6. The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash as described in claim 1, characterized in that, The hydrothermal reaction pressure is 0.6-1.1 MPa.

7. The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash as described in claim 1, characterized in that, The hydrothermal reaction temperature is 160-180℃.

8. The method for promoting dechlorination and inhibiting calcium leaching in waste incineration fly ash as described in claim 1, characterized in that, The hydrothermal reaction time is 1-2 hours.

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