A method and equipment for preparing a deacidifying agent from municipal solid waste incineration fly ash

Abstract

The present invention relates to a method and equipment for preparing a deacidifying agent from municipal solid waste incineration fly ash. The method comprises the following steps: primary conversion, converting various types of minerals in the municipal solid waste incineration fly ash into metal carbonate minerals; secondary conversion, converting the obtained metal carbonate minerals into corresponding metal oxides to obtain a deacidifying agent with high alkalinity; and optionally, a tertiary conversion before deacidification application, hydrating the metal oxides to make them into a deacidifying agent with high activity; wherein the municipal solid waste incineration fly ash is generated by deacidifying the flue gas from municipal solid waste incineration; the primary conversion is carried out in an aqueous solution and the conversion reagent contains water-soluble carbonate and / or water-soluble bicarbonate; the secondary conversion is carried out at a temperature above 700 °C. The method of the present invention realizes the harmlessness, reduction and resource utilization of the municipal solid waste incineration fly ash, prevents the environmental release and ecological burden of toxic and harmful substances, and has good technical and economic feasibility.

Description

Technical Field

[0001] The present invention relates to the technical field of waste treatment, and particularly relates to a method and equipment for preparing a deacidifying agent from municipal solid waste incineration fly ash. Background Art

[0002] Municipal solid waste incineration fly ash is a secondary pollutant intercepted and settled during the purification of flue gas in a municipal solid waste incineration system, with a production volume accounting for about 3-5% of the total incinerated waste. It is easy to enrich high-concentration heavy metals, such as lead (Pb), chromium (Cr), mercury (Hg), cadmium (Cd), copper (Cu), etc., and the content exceeds 10-100 times the soil background. In addition, the salt content in the fly ash is as high as 20-30%. Fly ash is recognized as hazardous waste both in China and internationally, and its safe disposal has become a global problem. Currently, the treatment technologies for municipal solid waste incineration fly ash mainly include safe landfill after stabilization and solidification, co-disposal in cement kilns, and use as filling aggregates after sintering and vitrification.

[0003] As a pre-treatment for safe landfill, stabilization technologies mainly include chemical stabilization and physical thermal stabilization. Chemical stabilization technology aims to add stabilizers to reduce the toxicity of toxic substances in fly ash, making the leaching risk smaller, thereby reducing the environmental risk of toxic substances, especially heavy metals, in fly ash. Commonly used organic stabilizers include dithiocarbamate (DTC), mercapto polyamine, EDTA polymer, sulfurized polysaccharide, etc.; inorganic stabilizers include lime, sodium sulfide, sulfate, phosphate, carbonate, silicate, and iron oxide, etc. Thermal stabilization and thermal sintering involve heating fly ash to a temperature at which particle bonding occurs and reorganizing the chemical phases in the fly ash. Generally, the temperature of such thermal stabilization processes is between 1000 and 1200 °C and often stabilizers are added synergistically. The sintered product has reduced porosity and high strength and heavy metals are difficult to leach. The disadvantages of stabilization technology are reflected in that the stabilizers themselves may have slow decomposition and degradation behaviors in the environment, so long-term stability is unreliable; in ambient temperature stabilization / curing landfills, water-soluble salts can cause the cured body to crack and heavy metals will leach out.

[0004] The co-disposal technology in cement kilns is to add fly ash to cement raw materials and sinter them together (1200-1500 °C) during the cement production process to co-dispose of municipal solid waste incineration fly ash, which has significant social and environmental benefits, mature technology, and a perfect standard system. The disadvantage of the co-disposal technology in cement kilns is that toxic heavy metals are actually transferred to cement products and will be released into the environment again during the use and life cycle of cement. The co-disposal in cement kilns has strict restrictions on the chlorides in fly ash, and it is necessary to wash the fly ash deeply in advance.

[0005] The fly ash contains a large amount of valuable metals such as zinc, lead, and copper. Academics and industry have developed many extraction and leaching technologies for the above-mentioned valuable metals in municipal solid waste incineration fly ash. Chemical extraction technology aims to extract valuable metals by adding specific extractants for recycling purposes. Commonly used extractants include hydrochloric acid, nitric acid, sulfuric acid, sodium hydroxide, sodium carbonate, ammonia water, and chelating agents, etc. Among them, sulfuric acid, hydrochloric acid, and nitric acid can extract most metals; sodium hydroxide and sodium carbonate can selectively extract amphoteric metals such as Zn and Pb. However, the disadvantage of chemical extraction technology is that a large amount of acidic or alkaline extractants are required, and the regeneration of the extractants is also relatively difficult. Therefore, the industry has been seeking methods for environmentally friendly treatment of municipal solid waste incineration fly ash. Summary of the Invention

[0006] For this reason, on the one hand, the present invention provides a method for preparing a deacidifying agent from municipal solid waste incineration fly ash, which includes the following steps:

[0007] Primary conversion, converting various types of minerals in the municipal solid waste incineration fly ash into metal carbonate minerals;

[0008] Secondary conversion, converting the obtained metal carbonate minerals into corresponding metal oxides to obtain a high-alkalinity deacidifying agent; and

[0009] Optionally, a tertiary conversion before deacidification application, hydrating the metal oxide to make it have a high deacidification activity;

[0010] wherein the municipal solid waste incineration fly ash is generated by deacidifying municipal solid waste incineration flue gas;

[0011] The primary conversion is carried out in an aqueous solution and the conversion reagent contains water-soluble carbonate and / or water-soluble bicarbonate;

[0012] The secondary conversion is carried out at a temperature above 700 °C.

[0013] On the other hand, the present invention provides a method for preparing a deacidifying agent from municipal solid waste incineration fly ash, the method comprising:

[0014] Primary conversion, adding an aqueous solution of a water-soluble carbonate and / or water-soluble bicarbonate conversion reagent to the municipal solid waste incineration fly ash, stirring and reacting to convert various types of minerals in the municipal solid waste incineration fly ash into metal carbonate minerals;

[0015] Secondary conversion, after the primary conversion is completed and liquid-solid separation is carried out, the solid-phase powder of the obtained metal carbonate minerals is secondarily converted into metal oxides at a temperature > 700 °C to obtain a high-alkalinity deacidifying agent; and

[0016] Tertiary conversion before deacidification application, hydrating the metal oxide to make it have a high deacidification activity.

[0017] On the other hand, the present invention provides a method for preparing a deacidifying agent from municipal solid waste incineration fly ash, which comprises the following steps:

[0018] (1) Before the first-stage conversion, the municipal solid waste incineration fly ash is first washed with water to remove water-soluble components, especially metal salts and chlorine-containing salts, and the washed fly ash is obtained through liquid-solid separation;

[0019] (2) An aqueous solution of a water-soluble carbonate and / or water-soluble bicarbonate conversion reagent is added to the washed fly ash, stirred and reacted, and various types of minerals in the washed fly ash are converted into metal carbonate minerals through the first-stage conversion;

[0020] (3) After liquid-solid separation again, the solid-phase powder of the obtained metal carbonate minerals is secondarily converted into metal oxides at a temperature >700 °C to obtain a high-alkalinity deacidifying agent; and

[0021] (4) Tertiary conversion before deacidification application, hydrating the metal oxides to make them have high deacidification activity.

[0022] In a preferred embodiment, the conversion reagents used in the first-stage conversion include sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate solution or any combination thereof. Among them, the conversion solution of ammonium carbonate and / or ammonium bicarbonate can be prepared on-site by introducing carbon dioxide into an ammonia water solution.

[0023] In a preferred embodiment, the concentration range of the aqueous solution of the conversion reagent is 0.1 - 5.0 M; and / or, the liquid-solid ratio of the aqueous solution of the conversion reagent to the fly ash is (1 - 100):1; and / or, the temperature range in the first-stage conversion is 0 - 100 °C; and / or, the time of the first-stage conversion is 0.5 - 48 h;

[0024] Preferably, the concentration range of the aqueous solution of the conversion reagent in the first-stage conversion is 0.5 - 4.5 M, the liquid-solid ratio of the aqueous solution of the conversion reagent to the fly ash in the first-stage conversion is (2 - 20):1, and the time of the first-stage conversion is 1 - 24 h.

[0025] In a preferred embodiment, the conversion reagent further includes an auxiliary agent, and the auxiliary agent is carbon dioxide.

[0026] In a preferred embodiment, the conversion reagent of ammonium carbonate and / or ammonium bicarbonate is prepared on-site by introducing carbon dioxide into an ammonia water solution.

[0027] In a preferred embodiment, the municipal solid waste incineration fly ash is generated by treating the flue gas of municipal solid waste incineration fly ash by the lime method, and its flue gas treatment method includes at least one of wet method, semi-wet method and dry method, or the municipal solid waste incineration fly ash is untreated fly ash and / or aged fly ash.

[0028] Preferably, the content of silicon dioxide in the municipal solid waste incineration fly ash does not exceed 20% by weight, more preferably does not exceed 10% by weight.

[0029] In a preferred embodiment, before the secondary conversion after the primary conversion to generate metal carbonate minerals and liquid-solid separation, it is preferred to dry the metal carbonate minerals first, and the drying temperature is 40 - 300 °C.

[0030] In a preferred embodiment, the method of the present invention further comprises the following steps: recycling the obtained deacidifying agent for flue gas treatment of municipal solid waste incineration fly ash, and then cyclically performing the method of preparing the deacidifying agent from municipal solid waste incineration fly ash of the present invention.

[0031] Finally, the present invention also provides a device for preparing a deacidifying agent from municipal solid waste incineration fly ash, which comprises:

[0032] - A fly ash collection device for collecting municipal solid waste incineration fly ash;

[0033] - A reaction device for converting various types of minerals in the municipal solid waste incineration fly ash into metal carbonate minerals;

[0034] - A heat treatment device for converting the obtained metal carbonate minerals into corresponding metal oxides to obtain a high-alkalinity deacidifying agent; and

[0035] - Optionally, a hydration device for hydrating the metal oxides to make them have a high deacidifying activity.

[0036] In a preferred embodiment, the device further comprises a washing device, and the washing device is located between the fly ash collection device and the reaction device.

[0037] The method of the present invention realizes the harmlessness, reduction and resource utilization of the hazardous solid waste of municipal solid waste incineration fly ash, and well solves the environmental release and ecological burden of toxic and harmful substances in such hazardous wastes. The present invention prepares a high-alkalinity metal oxide deacidifying agent from municipal solid waste incineration fly ash through two-stage conversion, and then hydrates the metal oxides through three-stage conversion before deacidification application to make them have a high deacidifying activity. The technical and economic feasibility of the method of the present invention is very good, the treatment cost is only a few hundred yuan, a reusable deacidifying agent and zinc- and lead-rich materials are prepared, and a revenue surplus can be achieved by comparison. Description of the Drawings

[0038] Figure 1 Shows a process flow diagram of an embodiment according to the method of the present invention;

[0039] Figure 2 (a) Shows a scanning electron micrograph of the original fly ash (i.e., before water washing) in Example 1;

[0040] Figure 2 (b) shows the SEM image of the fly ash after water washing in Example 1;

[0041] Figure 2 (c) shows the SEM image of the fly ash after water washing / calcination in Example 1;

[0042] Figure 2 (d) shows the SEM image of the hydrated deacidifier obtained in Example 1;

[0043] Figure 3 (a) shows the XRD pattern of the original fly ash in Example 1;

[0044] Figure 3 (b) shows the XRD patterns of different solid-phase products during the transformation of the original fly ash in Example 1;

[0045] Figure 4 (a)-(d) show the effects of the liquid-solid ratio on the alkalinity of the deacidifiers obtained from the transformation of fly ashes A, B, C, and D in Example 3, respectively;

[0046] Figure 5 Shows the effect of the reaction time of the primary transformation on the alkalinity in Example 6.

[0047] Figure 6 (a)-(d) show the comparison of the alkalinity effects of the materials obtained from fly ashes A, B, C, and D under different transformation methods (where I, II, III, and IV represent the alkalinity effects of adding no transformation reagent, adding CaO, adding CaCO3, and the deacidifier obtained in Example 1 of the present invention, respectively). Detailed implementation manners

[0048] The following examples describe various features and advantages provided by aspects of the present disclosure and are in no way intended to limit the present disclosure and the accompanying claims.

[0049] In the present invention, unless otherwise specified, the operations are carried out at normal temperature (25 °C) and normal pressure (101 kPa).

[0050] In the present invention, if there is no special description, all embodiments and preferred embodiments of the present application can be combined with each other to form a new technical solution.

[0051] In the present invention, if there is no special description, all technical features and preferred technical features of the present application can be combined with each other to form a new technical solution.

[0052] The total treatment volume of municipal solid waste in China reaches 250 million tons, of which the incineration treatment volume is about 180 million tons. It is roughly estimated that about 10 million tons of fly ash are generated annually. The fly ash contains heavy metals with complex compositions, and at the same time, pollutants such as dioxins and chlorides are enriched. The leaching concentration exceeds the upper limit of the identification of hazardous waste, and it is defined as hazardous waste by countries around the world. Unreasonable treatment methods will cause serious damage to the environment. The present invention can prepare a high-alkalinity deacidifying agent by two-stage conversion of municipal solid waste incineration fly ash, and then hydrate the metal oxide through three-stage conversion before deacidification application to make it have a high deacidification activity. The composition of municipal solid waste incineration fly ash is very complex, mainly composed of water-soluble mixed salts and insoluble mixed minerals of various metal ions such as Ca, Mg, Zn, Pb, Fe, Al, etc. Its acidic anion ligands are mainly hydroxide, carbonate, sulfate, silicate, fluoride, chlorosilicate, etc. The above various metal ions and various anion ligands are randomly combined or coupled together, intersecting and containing each other, thus forming a highly complex and mixed salt and mineral mixture, which exists in the fly ash in the form of powder or colloid and is difficult to thermally decompose.

[0053] The inventors unexpectedly found that, first, by using water-soluble carbonate and / or water-soluble bicarbonate as the conversion reagent, various types of minerals in the municipal solid waste incineration fly ash are uniformly converted into metal carbonate minerals through a conversion reaction; the metal carbonate minerals are converted into metal oxides at a relatively low temperature (for example, 700-1000 °C), and a metal oxide deacidifying agent with extremely high total alkalinity and effective alkalinity is obtained; before deacidification application, the metal oxide deacidifying agent is hydrated to make it have a high deacidification activity. Second, the prepared deacidifying agent can be recycled and reused for the flue gas treatment of municipal solid waste incineration fly ash (such as used as a deacidifying agent in the deacidification treatment of fly ash), and high-value zinc and lead-enriched materials with high recovery value can be obtained through multiple cycles of reuse. Third, after the generated tail liquid is properly treated, it can be evaporated and concentrated to obtain water-soluble metal salts or discharged into sodium salt water bodies without any toxic impact on the environment. Fourth, the harmlessness, reduction and resource utilization of municipal solid waste incineration fly ash hazardous solid waste are realized, which well solves the environmental release and ecological burden of toxic and harmful substances in such hazardous waste, and also significantly reduces the carbon footprint. Finally, the technical and economic feasibility of preparing a high-alkalinity and high-activity deacidifying agent from municipal solid waste incineration fly ash through conversion in the present invention is very good, and the treatment cost is only a few hundred yuan. A reusable deacidifying agent and zinc and lead-rich materials are prepared, and a profit surplus can be achieved by comparing the two. Therefore, the method of the present invention can simultaneously achieve significant economic benefits.

[0054] In view of this, on the one hand, the present invention provides a method for preparing a deacidifying agent from municipal solid waste incineration fly ash, which includes the following steps:

[0055] Primary conversion, converting various types of minerals in the municipal solid waste incineration fly ash into metal carbonate minerals;

[0056] Secondary conversion, converting the obtained metal carbonate minerals into corresponding metal oxides to obtain a deacidifying agent with high alkalinity; and

[0057] Optionally, a tertiary conversion, where the metal oxide is hydrated before the deacidification application to make it have a high deacidification activity;

[0058] The municipal solid waste incineration fly ash is generated by deacidifying the flue gas from municipal solid waste incineration;

[0059] The primary conversion is carried out in an aqueous solution and the conversion reagent includes water-soluble carbonate and / or water-soluble bicarbonate;

[0060] The secondary conversion is carried out at a temperature above 700 °C;

[0061] Preferably, the deacidifying agent is recycled for the flue gas treatment of municipal solid waste incineration fly ash, for example, the deacidification treatment of the flue gas from municipal solid waste incineration.

[0062] Through the two-stage conversion of the present invention, the municipal solid waste incineration fly ash can be finally converted into a metal oxide deacidifying agent with a relatively high total alkalinity and effective alkalinity; the tertiary conversion before the deacidification application hydrates the metal oxide to make it have a high deacidification activity. This deacidifying agent can be recycled for the flue gas treatment of municipal solid waste incineration fly ash to form a closed loop of the treatment process.

[0063] In a preferred embodiment, the municipal solid waste incineration fly ash refers to the fly ash generated by deacidifying the flue gas from a municipal solid waste incineration power plant.

[0064] In a preferred embodiment, the deacidifying agent used in the deacidification treatment of the flue gas from municipal solid waste incineration is the deacidifying agent prepared by the method of the present invention.

[0065] On the other hand, the present invention provides a method for preparing a deacidifying agent from municipal solid waste incineration fly ash, the method comprising:

[0066] Primary conversion, adding an aqueous solution of a water-soluble carbonate and / or water-soluble bicarbonate conversion reagent to the municipal solid waste incineration fly ash, stirring and reacting to convert various types of minerals in the municipal solid waste incineration fly ash into metal carbonate minerals;

[0067] Secondary conversion, after the primary conversion is completed and liquid-solid separation is carried out, the solid-phase powder of the obtained metal carbonate minerals is secondarily converted into metal oxides at a temperature > 700 °C to obtain a deacidifying agent with high alkalinity; and

[0068] Tertiary conversion before the deacidification application, hydrating the metal oxide to make it have a high deacidification activity.

[0069] In the present invention, unless otherwise specified, the term "liquid-solid ratio" refers to the volume / mass ratio (L / kg) of the aqueous solution of the water-soluble carbonate and / or water-soluble bicarbonate conversion reagent to the fly ash. Here, it can be understood that when the fly ash is washed with water and dried, the term "liquid-solid ratio" refers to the volume / mass ratio (L / kg) of the aqueous solution of the water-soluble carbonate and / or water-soluble bicarbonate conversion reagent to the fly ash after washing with water (dried, i.e., water-free).

[0070] In the present invention, the term "mineral" should be understood to refer to the general term for various metals and their salts, oxides and hydroxides present in the fly ash.

[0071] In the present invention, liquid-solid separation can be carried out by using conventional separation methods in the art, such as filtration separation, centrifugal separation or gravity separation, etc.

[0072] In the present invention, the heating in the secondary conversion can be carried out in a conventional heating device in the art, such as a muffle furnace, etc., as long as the heating temperature of the present invention can be achieved (i.e., greater than 700 °C, for example, 700 °C - 1200 °C, preferably 750 - 1100 °C, for example, 800 - 1000 °C or 850 - 1000 °C).

[0073] In a preferred embodiment, in the secondary conversion, the heating time can be 0.5 to 10 hours, such as 1 to 8 hours, 2 to 4 hours.

[0074] In the present invention, hydration can be carried out by directly adding the obtained metal oxide into water, and the obtained deacidifying agent suspension can be directly applied to the deacidification treatment; liquid-solid separation can also be carried out and the obtained solid component can be dried to obtain a deacidifying agent powder for use in the deacidification treatment. During the hydration process, most of the metal oxides will be converted into metal hydroxides, and thus the base capacity (alkalinity) is activated to have a high deacidifying activity. The effective component of the highly active deacidifying agent obtained after hydration is a mixture of metal oxides and metal hydroxides, which is expressed as "metal (hydro)oxide" for the convenience of writing. Therefore, in the context of the invention, the deacidifying agent after hydration is also referred to as "metal (hydro)oxide deacidifying agent". The water used in the present invention can be municipal water or the water recovered from the method of the present invention.

[0075] On the other hand, the present invention provides a method for preparing a deacidifying agent from municipal solid waste incineration fly ash, which comprises the following steps:

[0076] (1) Before the primary conversion, the municipal solid waste incineration fly ash is first washed with water to remove water-soluble components, especially metal salts and chlorine-containing salts, and the fly ash after washing with water is obtained through liquid-solid separation;

[0077] (2) Add an aqueous solution of a water-soluble carbonate and / or a water-soluble bicarbonate conversion reagent to the washed fly ash, stir and react to convert various types of minerals in the washed fly ash into metal carbonate minerals through primary conversion;

[0078] (3) After liquid-solid separation again, convert the solid-phase powder of the obtained metal carbonate minerals into metal oxides at a temperature of >700 °C through secondary conversion to obtain a high-alkalinity deacidifying agent; and

[0079] (4) Tertiary conversion before deacidification application, hydrate the metal oxides to make them have high deacidification activity.

[0080] Washing is carried out before the primary conversion to remove the water-soluble components in the fly ash, especially metal salts and chlorine-containing salts, which can reduce the impact on the subsequent primary conversion.

[0081] In a preferred embodiment, the conversion reagent used in the primary conversion includes sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate or any combination; preferably, the concentration range of the aqueous solution of the conversion reagent is 0.1-5.0 M; and / or, the liquid-solid ratio of the aqueous solution of the conversion reagent to the fly ash is (1-100):1; and / or, the temperature range in the primary conversion is 0-100 °C, preferably 5-80 °C, more preferably 20-60 °C, still more preferably 30-50 °C.

[0082] In a preferred embodiment, the conversion reagent used in the primary conversion includes a mixture of sodium carbonate and sodium bicarbonate and its molar ratio can be (0.1-4):1, preferably (0.5-2):1.

[0083] The inventors of the present invention found that when the concentration of the primary conversion reagent exceeds 4.5 M, sintering occurs in the material obtained after the secondary conversion, thus destroying its original ultrafine powder structure and not being suitable for recycling as a deacidifying agent. Therefore, preferably, in the primary conversion, the concentration range of the aqueous solution of the conversion reagent can be 0.5-4.5 M, preferably 0.7-4.0 M, more preferably 1-3.5 M, still more preferably 2-3.5 M, and the liquid-solid ratio of the aqueous solution of the conversion reagent to the fly ash in the primary conversion is (2-20):1.

[0084] In a preferred embodiment, the liquid-solid ratio of the aqueous solution of the conversion reagent to the fly ash can be (2-16):1, preferably (3-12):1, more preferably (4-8):1, still more preferably (4-6):1.

[0085] In a preferred embodiment, the time of the primary conversion can be 0.5-48 h, preferably 1-40 h, more preferably 4-35 h, still more preferably 10-30 h, and further preferably 20-25 h.

[0086] In one embodiment, the conversion reagent used for the primary conversion is ammonium carbonate and / or ammonium bicarbonate. Using ammonium carbonate and / or ammonium bicarbonate as the conversion reagent has the advantage over sodium carbonate in that the former has a lower price and the residual filtrate produced after the primary conversion can be used as fertilizer after purification treatment.

[0087] In a preferred embodiment, the conversion reagent further includes an auxiliary agent, and the auxiliary agent is carbon dioxide. Although carbon dioxide itself cannot be used as the primary conversion reagent and using carbon dioxide alone cannot uniformly convert various phases in the fly ash into metal carbonate minerals, as an auxiliary agent, carbon dioxide can adjust the pH of the system to a certain extent, thereby reducing the alkaline dissolution of heavy metals during the primary conversion and saving the consumption of some conversion reagents at the same time.

[0088] In a preferred embodiment, the conversion reagent of ammonium carbonate and / or ammonium bicarbonate is prepared in-situ by introducing carbon dioxide into an ammonia aqueous solution.

[0089] In a preferred embodiment, the municipal solid waste incineration fly ash is produced by treating the flue gas of municipal solid waste incineration fly ash with the lime method, and the flue gas treatment method includes at least one of wet method, semi-wet method and dry method. Or, the municipal solid waste incineration fly ash is untreated fly ash and / or aged fly ash. Preferably, the content of silicon dioxide in the municipal solid waste incineration fly ash does not exceed 20% by weight, more preferably does not exceed 10% by weight, and still more preferably does not exceed 5% by weight. The side effect of silicon dioxide in the municipal solid waste incineration fly ash is that it easily reacts with metal oxides at high temperatures during the secondary conversion to form metal silicate minerals, thereby reducing the alkalinity of the deacidifying agent.

[0090] In a preferred embodiment, before the secondary conversion after the primary conversion to generate metal carbonate minerals and liquid-solid separation, it is preferred to first dry the metal carbonate minerals (for example, reduce their water content to a suitable range, such as usually 0 to 15% by weight, preferably 0 to 5% by weight), and the drying temperature can be 40 - 300°C. The drying time can be selected as needed and is not particularly limited here.

[0091] In a preferred embodiment, the primary conversion reaction can be achieved in a single-stage reactor or completed through two-stage or multi-stage operations. Here, the specific operation can be selected according to the processing capacity and the processing ability of the equipment.

[0092] In a preferred embodiment, the liquid phase obtained by liquid-solid separation can be recycled to the corresponding stage, discharged into the sodium salt water body after treatment, or concentrated and evaporated.

[0093] In the present invention, the liquid phase separated by liquid-solid separation contains soluble components, which can be partially recycled to the process, or can be concentrated and evaporated using the heat generated in the process, and the obtained salts can be used for commercial purposes.

[0094] As Figure 1 shown, in a preferred embodiment, fly ash (6) obtained from treating municipal solid waste incineration fly ash by the lime method is added to a washing device (1) for water washing to remove water-soluble components in the fly ash, and then liquid-solid separation is carried out. The obtained solid phase (12) is transported to a reaction device (2) for primary conversion. At the same time, a part (111) of the obtained liquid phase (11) is returned to the washing device (1), and the remaining part (112) is subjected to waste liquid treatment (7). In the reaction device (2), primary conversion is carried out by reacting the solid phase (12) with an aqueous sodium carbonate solution. After the reaction is completed, liquid-solid separation is carried out. The obtained solid phase (22) is transported to a heat treatment device (3) for heating for secondary conversion to obtain a high-alkalinity deacidifying agent. At the same time, a part (211) of the liquid phase (21) obtained by liquid-solid separation is returned to the reaction device (2), and the remaining part (212) is subjected to waste liquid treatment (7). After the secondary conversion is completed, the high-alkalinity deacidifying agent obtained in the heat treatment device (3) is transported to a hydration device (4) for tertiary conversion to hydrate it to obtain a metal (hydro) oxide (5) with high deacidification activity.

[0095] In addition, the method for preparing a deacidifying agent from municipal solid waste incineration fly ash according to the present invention further includes the following steps: The obtained deacidifying agent is reused for flue gas treatment of municipal solid waste incineration fly ash, and then the method for preparing a deacidifying agent from municipal solid waste incineration fly ash according to the present invention is cycled. During this cycling process, lead and / or zinc in the municipal solid waste incineration fly ash will be enriched. When the zinc content is not less than 1% by weight and / or the lead content is not less than 0.5% by weight, part of the materials can be sourced to smelting enterprises as raw materials for lead-zinc smelting. The zinc and lead contents in the recycling of the deacidifying agent can be measured according to the national standard HJ 781-2016 method. Specifically, 0.25 g of the fly ash sample is weighed and placed in a polytetrafluoroethylene digestion tube. Nitric acid (65-68%), hydrofluoric acid (40%), and perchloric acid (70-72%) are added in a ratio of 10 mL:10 mL:5 mL. It is digested in a graphite digestion instrument at 200 °C for 6 hours until the digestion solution remains about 1-2 mL. After digestion is completed, 2 mL of nitric acid is added to dissolve the residue. After cooling, it is fixed to 25 mL, and after filtration, the lead and zinc contents are analyzed by an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0096] The deacidifying agent obtained by the present invention is recycled for flue gas treatment of municipal solid waste incineration fly ash, and through multiple cycles of recycling, a zinc and lead enriched material with high recovery value is obtained. Generally, after the deacidifying agent is recycled four times, the zinc enrichment concentration in the fly ash and the deacidifying agent material can exceed 1%, and the lead enrichment concentration is about 0.5%. Such materials can be sold to lead-zinc smelting enterprises. Therefore, the present invention also provides a method for enriching lead and / or zinc in municipal solid waste incineration fly ash, which includes the following steps: First, perform the method for preparing a deacidifying agent from municipal solid waste incineration fly ash of the present invention, and then recycle the obtained deacidifying agent to the flue gas treatment of the municipal solid waste incineration fly ash.

[0097] Finally, the present invention also provides a device for preparing a deacidifying agent from municipal solid waste incineration fly ash, which includes:

[0098] - A fly ash collection device for collecting municipal solid waste incineration fly ash;

[0099] - A reaction device for converting various types of minerals in the municipal solid waste incineration fly ash into metal carbonate minerals;

[0100] - A heat treatment device for converting the obtained metal carbonate minerals into corresponding metal oxides to obtain a deacidifying agent with high alkalinity; and

[0101] - Optionally, a hydration device for hydrating the metal oxides before deacidification application to make it have high deacidification activity.

[0102] In a preferred embodiment, the device further includes a washing device, and the washing device is located between the fly ash collection device and the reaction device.

[0103] In a preferred embodiment, the washing device is used to wash the municipal solid waste incineration fly ash with water to remove the water-soluble components therein, and after liquid-solid separation, the solid component is transported to the reaction device for primary conversion.

[0104] After the municipal solid waste incineration fly ash is washed with water and liquid-solid separated, pre-drying treatment can also be performed. Therefore, in a preferred embodiment, there is also a heating device between the downstream of the washing device and the upstream of the reaction device, which is used to pre-dry the fly ash after being washed with water and liquid-solid separated (the drying temperature can be, for example, 40 - 300 °C, preferably 50 - 200 °C).

[0105] In a preferred embodiment, the reaction device can be a reaction kettle (tank) with a stirring device. In a preferred embodiment, the reaction device further includes a metering device for adding an aqueous solution of a conversion reagent. Preferably, the metering device and the corresponding pipeline are alkali-resistant.

[0106] In a preferred embodiment, the heat treatment device is used to convert the obtained metal carbonate minerals into corresponding metal oxides, and the heating temperature can be greater than 700 °C, such as 700 °C - 1200 °C, preferably 750 - 1100 °C, such as 800 - 1000 °C or 850 - 1000 °C. The heat treatment device can be a heating device commonly used in the art, such as a muffle furnace, etc. Preferably, the heat of the heating device comes from the heat generated by the incineration of domestic waste.

[0107] In a preferred embodiment, the hydration device is a hydration reaction device, such as a reaction kettle (tank), which is used to receive the metal oxide obtained by heating with the heat treatment device and carry out a hydration reaction with the water in the hydration device. To prevent the water temperature from being too high caused by hydration, the hydration device may further include a heat exchange device for heat exchange.

[0108] In a preferred embodiment, a drying device for drying the obtained hydrated product may also be included downstream of the hydration device.

[0109] In a preferred embodiment, a conveying device (such as a conveyor belt, etc.) is also provided between the heat treatment device and the hydration device, which is used to convey the metal oxide obtained by the heat treatment device to the hydration device for a hydration reaction.

[0110] In addition, the equipment for preparing the deacidifying agent from the fly ash of domestic waste incineration according to the present invention can also be directly combined with the domestic waste incineration equipment, especially combined with the fly ash treatment device used in the domestic waste incineration equipment. In this way, the recycling of fly ash can be realized and the enrichment of metals such as lead and / or zinc in the fly ash can be realized.

[0111] The method of the present invention realizes the harmlessness, reduction and resource utilization of the hazardous solid waste of the fly ash from domestic waste incineration, and well solves the environmental release and ecological burden of the toxic and harmful substances in such hazardous wastes. The present invention prepares a metal oxide deacidifying agent with high alkalinity by two-stage conversion of the fly ash from domestic waste incineration, and then hydrates the metal oxide by three-stage conversion before the deacidification application to make it have high deacidification activity. The method of the present invention has very good technical and economic feasibility, the treatment cost is only a few hundred yuan, and a reusable deacidifying agent and zinc- and lead-rich materials are prepared, and a profit surplus can be realized by comparing the two.

[0112] Examples

[0113] The following examples are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0114] In the present invention, the total alkalinity refers to the total amount of alkaline substances in an aqueous solution, including all substances that can consume acid and contribute to alkalinity in an aqueous solution with a titration end point of pH 3.0, such as hydroxides, carbonates, bicarbonates, etc.; the effective alkalinity refers to the substances that can consume acid and contribute to alkalinity in an aqueous solution with a titration end point of pH 8.0, mainly the content of hydroxides. The measurement methods for the total alkalinity and the effective alkalinity are as follows:

[0115] Place a certain amount of solid sample in a beaker, add deionized water, control the liquid-solid ratio (by weight) to be 10:1, stir magnetically, and titrate to acidity with 2M HNO3 solution at room temperature. The amount of acid consumed with a pH value of 3.0 as the titration end point is the total alkalinity; then use 2M NaOH solution to back-titrate to alkalinity with a pH value of 8.0 as the titration end point. The difference between the amount of acid consumed in the former and the amount of base consumed in the back-titration is the effective alkalinity. For the convenience of measurement and comparison with the control example, in all examples, the number of moles of nitric acid consumed by the deacidifier powder sample obtained from the secondary conversion per unit mass (instead of the deacidifier emulsion obtained after hydration for volume measurement) is used for alkalinity evaluation. The titration errors generally vary for different batches, but relatively consistent titration errors can occur in the same batch of experiments.

[0116] The four fly ash samples selected in the present invention are all municipal solid waste incineration fly ash generated by the lime method for deacidifying municipal solid waste incineration flue gas, and are respectively denoted as: fly ash A, fly ash B, fly ash C, and fly ash D.

[0117] Example 1

[0118] Weigh 500 g of municipal solid waste incineration fly ash (original fly ash A, B, C, and D) into a reaction vessel respectively, add deionized water, with the water-to-fly ash ratio (L / Kg) being 10:1, stir it in water for 2 h, filter to remove soluble salt components, and then dry it in an electrothermal blast drying oven at 60 °C for 24 h to obtain the first solid phase, namely the washed fly ash. Weigh 15 g of the above-mentioned washed fly ash (after drying, the same below) into a polyethylene bottle respectively, add a conversion reagent Na2CO3 solution with a concentration of 20% (equivalent to 1.89 M, the same below), with the liquid-to-solid ratio (L / Kg, the same below) being 4:1, react at room temperature for 12 h, separate the liquid and solid, and then wash the unreacted Na2CO3 on the solid surface with water, filter and dry to obtain the second solid phase, namely metal carbonate minerals. Subject the second solid phase to secondary conversion in a muffle furnace at 900 °C for 3 h to generate the third solid phase (i.e., metal oxides), and obtain a high-alkalinity deacidifying agent. Place the third solid phase in water for hydration to obtain a deacidifying agent emulsion, at this time the alkali capacity of the deacidifying agent is fully activated. Use 2M HNO3 solution and 2M NaOH solution to titrate the total alkalinity and effective alkalinity of the original fly ash and the obtained deacidifying agent emulsion respectively. Use the number of moles of nitric acid consumed by the original fly ash per unit mass and the deacidifying agent powder sample obtained by secondary conversion per unit mass for alkalinity evaluation.

[0119] The total alkalinity and effective alkalinity of the four original fly ashes and the obtained product metal (hydro)oxide deacidifying agents are shown in Table 1. The total alkalinity of the original fly ash A, B, C, and D are 8.00, 7.90, 9.05, and 8.35 mol / kg respectively, and the total alkalinity of the metal (hydro)oxide deacidifying agents are 29.99, 29.31,

[0120] 30.29, and 31.24 mol / kg respectively, and their total alkalinity are 3.75, 3.71, 3.35, and 3.74 times that of the corresponding original fly ash respectively. The effective alkalinity of the original fly ash A, B, C, D are 7.10, 7.12, 8.30, and 7.28 mol / kg respectively, and the effective alkalinity of the metal (hydro)oxide deacidifying agents are 27.42, 26.68, 27.59, and 28.69 mol / kg respectively. The effective alkalinity of the obtained product metal (hydro)oxide deacidifying agents are 3.86, 3.75, 3.32, and 3.94 times that of the corresponding original fly ash respectively. It shows that the obtained deacidifying agent products have high alkalinity and corresponding deacidifying activity.

[0121] Table 1 List of total alkalinity and effective alkalinity of four original fly ashes and the obtained metal (hydro)oxide deacidifying agent products

[0122]

[0123] Taking caustic soda, soda ash, lime or slaked lime commonly used in industry as references for comparison, as shown in Table 2. The total alkalinity of the deacidifying agent product obtained in the present invention is higher than that of caustic soda (NaOH) with a purity of 98.0%, and its alkali capacity is also significantly higher than that of soda ash (Na2CO3) with a purity of 99.2%. The effective alkalinity of the deacidifying agent product obtained in the present invention is comparable to that of lime (CaO) of Class II standard.

[0124] Table 2 Comparison of alkalinity between the metal (hydro)oxide deacidifying agent of the present invention and the alkalis commonly used in industry

[0125]

[0126] Taking fly ash C as an example, the morphological and particle size changes from the original fly ash to the converted metal (hydro)oxide deacidifying agent were characterized by scanning electron microscopy (see Figure 2 ). The original fly ash ( Figure 2 (a)) was bonded together in dense large particle clusters, showing a dense aggregated state. After the water washing treatment, the aggregated state was still relatively significant ( Figure 2 (b)), distributed in nearly spherical clusters. The water-washed / calcined fly ash ( Figure 2 (c)) had a more irregular structure compared with the water-washed fly ash, but the particle aggregation was still obvious, which might be due to the collapse of its near-spherical cluster structure caused by calcination. The metal (hydro)oxide deacidifying agent obtained in the present invention ( Figure 2 (d)) had significantly enhanced dispersibility and significantly reduced particle size compared with the original fly ash.

[0127] The XRD was used to characterize the changes in the crystalline phases of different solid-phase products during the process of converting fly ash C from the original fly ash to the metal (hydro)oxide deacidifying agent ( Figure 3)。The composition of municipal solid waste incineration fly ash is very complex. Its main components are water-soluble mixed salts of various metal ions such as Na, K, Ca, Mg, Zn, Pb, Fe, Al, etc. and poorly soluble mixed minerals. Its acidic anion ligands are mainly chloride ions, hydroxide ions, carbonate ions, sulfate ions, silicate ions, fluoride ions, chlorosilicate ions, etc. These various metal ions and various anion ligands are randomly combined or coupled together, intersecting and containing each other, thus forming a highly complex and heterogeneous mixture of salts, amorphous minerals or crystalline minerals, which exist in the fly ash in the form of powder or colloid. From the crystalline minerals presented in the original fly ash, characteristic diffraction peaks of chlorides (NaCl, KCl), carbonates (CaCO3), sulfates (CaSO4), zinc carbonate (ZnCO3), silicates (Mg2SiO4), sulfides (FeS2), oxides (Al2O3) and metallic elements (Cd) can be found. Using sodium carbonate as a conversion reagent, they are uniformly converted into metal carbonate minerals through a conversion reaction. The diffraction peaks attributed to carbonates in the primary conversion products are very strong. A strong diffraction peak attributed to CaCO3 appears, and a diffraction peak attributed to Pb3(CO3)2(OH)2 also appears, indicating that the main products of the primary conversion are carbonates. After the secondary conversion, the metal carbonate minerals are converted into metal oxides at relatively low temperatures. In the secondary conversion products, diffraction peaks attributed to metal oxides mainly appear, including diffraction peaks attributed to CaO, MgO and (CaO) 12 (Al2O3)7, indicating that various metal oxide components are mainly formed in the secondary conversion, and it has a very high total alkalinity and effective alkalinity. X-ray fluorescence analysis (XRF) also shows that the main components of the secondary conversion products are metal oxides of Ca, Mg, Fe, Al and Zn, and the proportion of various metal oxides can reach about 90% of the total substances. Through the tertiary conversion, that is, hydrating the metal oxide mixture to make it have a high deacidification activity. The main products of the tertiary conversion are diffraction peaks attributed to metal hydroxides and some metal oxides, such as diffraction peaks of Ca(OH)2 and MgO. It should be noted that XRD cannot show the change rules of amorphous mineral phases in different conversion stages, and the phase components with a content lower than 5% are sometimes difficult to detect. In the examples, only XRD is taken as an example to elaborate on the change rules of crystalline phase substances in different solid-phase products in different conversion stages from the original fly ash to the highly active metal (hydroxide) deacidifying agent.

[0128] Example 2

[0129] Repeat the first step in Example 1 to obtain the first solid phase, i.e., the fly ash after washing. Take 15 g of the above-mentioned fly ash after washing in a polyethylene bottle, and add Na2CO3 solutions with concentration gradients of 6%, 10%, 20%, 30%, and 40% respectively. The liquid-solid ratio is 4:1 for all cases. React at room temperature for 12 h, first perform liquid-solid separation, and then wash the unreacted Na2CO3 on the solid surface with water, filter and dry to obtain the second solid phase, i.e., metal carbonate minerals. Subject the second solid phase to secondary conversion in a muffle furnace at 900 °C for 3 h to generate the third solid phase, i.e., the metal oxide deacidifying agent. Place the third solid phase in water for hydration to obtain a deacidifying agent emulsion, and the alkalinity of the deacidifying agent is fully activated. The measurement and evaluation method of the alkalinity of the obtained deacidifying agent are the same as above. In this example, the data of the total alkalinity and effective alkalinity of the corresponding metal (hydro)oxide deacidifying agents obtained from the four fly ashes with the change of Na2CO3 concentration are shown in Table 3. In this example, the total alkalinity and effective alkalinity of the metal (hydro)oxide deacidifying agents obtained by the conversion of fly ashes A, B, C, and D generally show an increasing trend first with the increase of the concentration of the conversion reagent Na2CO3, and reach a saturated peak when increasing to a certain concentration later. When the Na2CO3 concentration is 6%, the total alkalinity of the corresponding metal (hydro)oxide deacidifying agents obtained by the conversion of fly ashes A, B, C, and D is 26.54 - 28.14 mol / kg, and the effective alkalinity is 24.03 - 25.81 mol / kg. When the Na2CO3 concentration increases to 10%, the total alkalinity of the corresponding metal (hydro)oxide deacidifying agents obtained by the conversion of fly ashes A, B, C, and D is 27.46 - 29.61 mol / kg, and the effective alkalinity is 25.81 - 27.15 mol / kg. When the Na2CO3 concentration reaches 20%, the total alkalinity of the corresponding metal (hydro)oxide deacidifying agents obtained by the conversion of fly ashes A, B, C, and D is 29.31 - 31.24 mol / kg, and the effective alkalinity is 26.68 - 28.69 mol / kg. Compared with the conversion concentration of 6%, when the Na2CO3 concentration reaches 20%, the total alkalinity of fly ashes A, B, C, and D increases by 13.00%, 9.61%, 7.64%, and 13.84% respectively, and the effective alkalinity increases by 14.11%, 8.19%, 6.90%, and 14.58% respectively. This shows that increasing the concentration of the conversion reagent Na2CO3 can enhance the effect of the first-stage conversion, thereby improving the deacidification capacity and activity of the final product. When the Na2CO3 concentration is further increased to 30%, the total alkalinity and effective alkalinity of the corresponding metal (hydro)oxide deacidifying agents obtained by the conversion of fly ashes A, B, C, and D only increase by 1% - 6% compared with the conversion reagent concentration of 20%, that is, the total alkalinity only increases by 0.77%, 2.49%, 5.77%, and 1.02% respectively, and the effective alkalinity only increases by 0.51%, 2.47%,

[0130] 6.13% and 1.92%. Similarly, when adding a Na2CO3 solution with a concentration of 40%, the total alkalinity and the effective alkalinity hardly change compared with those at a conversion reagent concentration of 30%, and the difference between the two is less than the error. This indicates that when a sufficient concentration of Na2CO3 is added, the conversion reagent concentration is no longer the determining factor for the increase in the total alkalinity and the effective alkalinity of the metal (hydro) oxide deacidifier of the final product. Moreover, when the concentration of Na2CO3 reaches or exceeds 4.5 M (equivalent to a concentration of 48%), sintering often occurs in the material obtained after the secondary conversion, destroying the original ultrafine powder structure and no longer being suitable for recycling as a deacidifier.

[0131] Table 3 List of alkalinity change data of the metal (hydro) oxide deacidifier obtained from fly ash conversion in Example 2

[0132]

[0133] Example 3

[0134] Repeat the first step in Example 1 to obtain the first solid phase, i.e., the fly ash after washing. Respectively take 15 g of the above-mentioned fly ash after washing and place them in polyethylene bottles. Add a Na2CO3 solution with a concentration of 20%, and the liquid-solid ratios are 2:1, 4:1, 6:1, 8:1, 12:1, and 16:1 respectively. React the above-mentioned fly ash at room temperature for 12 h. First, perform liquid-solid separation, and then wash the unreacted Na2CO3 on the solid surface with water, filter and dry to obtain the second solid phase, i.e., the metal carbonate minerals. Subject the second solid phase to secondary conversion in a muffle furnace at 900 °C for 3 h to generate the third solid phase, i.e., the metal oxide deacidifier. Place the third solid phase in water for sufficient hydration to obtain a deacidifier emulsion, and the alkalinity of the deacidifier is fully activated. The method for measuring and evaluating the alkalinity of the obtained deacidifier is the same as above.

[0135] In this example, the influence of the liquid-solid ratio on the total alkalinity and the effective alkalinity of the metal (hydro) oxide deacidifier obtained from fly ash conversion is as Figure 4As shown in the figure. When the liquid-solid ratio is 2:1, the total alkalinity of the corresponding metal (hydroxide) deacidifying agents obtained from the conversion of fly ashes A, B, C, and D is lower than 29 mol / kg, and the effective alkalinity is lower than 26 mol / kg. When the liquid-solid ratio is 4:1, the total alkalinity of the corresponding metal (hydroxide) deacidifying agents obtained from the conversion of the above four fly ashes is 29.19 - 30.17 mol / kg, and the effective alkalinity is 26.57 - 28.57 mol / kg. Compared with the case where the liquid-solid ratio is 2:1, the total alkalinity of the corresponding metal (hydroxide) deacidifying agents obtained from the conversion of fly ashes A, B, C, and D increased by 7.70%, 5.37%, 7.21%, and 9.54% respectively, and the effective alkalinity increased by 8.24%, 7.86%, 8.55%, and 12.67% respectively. When the liquid-solid ratio increased to 6:1, compared with the metal (hydroxide) deacidifying agent prepared under the condition of a liquid-solid ratio of 4:1, the changes in both the total alkalinity and the effective alkalinity were less than the error at this time. When the liquid-solid ratio continued to increase to 8:1, 12:1, and 16:1, the total alkalinity and the effective alkalinity of the corresponding metal (hydroxide) deacidifying agents obtained from the conversion of the four fly ashes no longer increased. This shows that the first-stage conversion can be effectively carried out when the liquid-solid ratio reaches 4:1.

[0136] Example 4

[0137] Repeat the first step in Example 1 to obtain the first solid phase, namely the fly ash after washing. Take 50 g of the above-mentioned fly ash after washing in a polyethylene bottle, add a Na2CO3 solution with a concentration of 20%, and the liquid-solid ratio is 4:1. React the above fly ash at room temperature for 12 h, first perform liquid-solid separation, and then wash away the unreacted Na2CO3 with water, and filter and dry to obtain the second solid phase, namely the metal carbonate minerals. Divide the above second solid phase into five equal parts, and perform secondary conversion in a muffle furnace at 700 °C, 800 °C, 850 °C, 900 °C, and 1000 °C for 3 h to generate the third solid phase, namely the metal oxide deacidifying agent. Place the third solid phase in water for sufficient hydration to obtain a deacidifying agent emulsion, and the alkalinity of the deacidifying agent is fully activated. The alkalinity measurement and evaluation method are the same as above.

[0138] In this embodiment, the data of the secondary conversion temperature change and the fly ash conversion effect are shown in Table 4. When the secondary conversion temperature is 700 °C, the total alkalinity of the corresponding metal (hydroxide) deacidifying agents obtained by the conversion of fly ashes A, B, C, and D is 24.76 - 26.50 mol / kg, and the effective alkalinity is 22.41 - 24.20 mol / kg, indicating that the secondary conversion is insufficient at this temperature and has not reached the saturation value. When the secondary conversion temperature is increased to 800 °C, the total alkalinity range of the corresponding metal (hydroxide) deacidifying agents obtained by the conversion of fly ashes A, B, C, and D is 27.99 - 29.29 mol / kg, and the effective alkalinity is 25.60 - 26.81 mol / kg. Compared with 800 °C, when the secondary conversion temperature is increased to 850 °C, both the total alkalinity and the effective alkalinity of the corresponding metal (hydroxide) deacidifying agents obtained by the conversion of fly ashes A, B, C, and D still have a small increase. The total alkalinity is increased by 3.87%, 5.86%, 4.85%, and 7.90% respectively, and the effective alkalinity is increased by 5.43%, 5.78%, 4.81%, and 6.81% respectively. When the secondary conversion temperature rises to 900 °C, the total alkalinity values and the effective alkalinity values of the corresponding metal (hydroxide) deacidifying agents obtained by the conversion of the four fly ashes are not much different from the corresponding values under the secondary conversion conditions at 850 °C, and are basically lower than their error values, indicating that the secondary conversion in the fly ash has been fully completed at this time, and the carbonate components of the primary conversion are completely decomposed and converted into the corresponding metal oxides.

[0139] Table 4 List of data on the alkalinity change of the metal (hydroxide) deacidifying agent obtained by the conversion of fly ash in Example 4

[0140]

[0141] Example 5

[0142] Take 10 g of municipal solid waste incineration fly ash (original fly ashes A, B, C, and D) in reaction vessels respectively, and conduct the following experimental designs: (1) Directly add Na2CO3 solutions with concentrations of 6% and 10% to the original fly ash, and the liquid-solid ratio is 2:1; (2) Directly add a 20% Na2CO3 solution to the original fly ash, and the liquid-solid ratios are 2:1 and 4:1 respectively. Then react at room temperature for 12 h and separate the liquid and solid, and then wash the unreacted Na2CO3 on the surface of the solid with water, filter and dry to obtain the first solid phase, and place it in a muffle furnace for high-temperature calcination at 900 °C for 3 h to obtain the second solid phase. Place the second solid phase in water for sufficient hydration to obtain a deacidifying agent emulsion. The alkalinity measurement and evaluation method are the same as above.

[0143] As shown in Table 5, when the concentration of the conversion reagent Na2CO3 is 6% (liquid-solid ratio 2:1), the total alkalinity of the obtained metal (hydro)oxide deacidifying agent is 17.83 - 21.53 mol / kg, and the effective alkalinity is 16.54 - 20.29 mol / kg. When the concentration of the conversion reagent is 10% (liquid-solid ratio 2:1), the total alkalinity of the obtained metal (hydro)oxide deacidifying agent varies from 20.95 to 24.95 mol / kg, and the effective alkalinity varies from 19.59 to 23.35 mol / kg. When the concentration of Na2CO3 is 20% (liquid-solid ratio 2:1), the total alkalinity of the metal (hydro)oxide deacidifying agent varies from 23.50 to 25.43 mol / kg, and the effective alkalinity is 22.12 - 24.16 mol / kg. When the concentration of Na2CO3 is 20% (liquid-solid ratio 4:1), the total alkalinity of the metal (hydro)oxide deacidifying agent varies from 24.70 to 27.15 mol / kg, and the effective alkalinity is 23.39 - 25.87 mol / kg. Compared with the first-stage conversion (same liquid-solid ratio) in Example 1 where desalination is carried out first, the total alkalinity and effective alkalinity of the directly converted metal (hydro)oxide deacidifying agent are 82.36% - 90.28% and 85.30% - 93.37% of the latter respectively. This is because the presence of a large amount of water-soluble salts in the original fly ash affects the efficiency of the first-stage conversion. The influence of water-soluble salts on the conversion is particularly significant especially at lower liquid-solid ratios and lower conversion reagent concentrations, but the influence weakens relatively when the liquid-solid ratio and the conversion reagent concentration are higher. Compared with Example 1 where water washing is carried out first to remove water-soluble salts and then first-stage conversion is carried out, the consumption of reagents increases during the direct conversion of the original fly ash, and the recyclability of the conversion reagent decreases.

[0144] Table 5 List of data on the alkalinity change of the metal (hydro)oxide deacidifying agent obtained from fly ash conversion in Example 5

[0145]

[0146] Example 6

[0147] Repeat the first step in Example 1 to obtain the first solid phase, i.e., the fly ash after water washing. Take 5 g of the fly ash C after water washing in 12 polyethylene bottles, add Na2CO3 solution with a concentration of 10% to all of them, with a liquid-solid ratio of 4:1 and a reaction temperature of 35°C. Then, measurements are carried out at intervals of 0.5, 1, 2, 3, 4, 6, 8, 10, 13, 24, 32, and 48 h respectively. After solid-liquid separation, the unreacted Na2CO3 is washed away with clear water, and the second solid phase is obtained by filtration and drying. The second solid phase is subjected to a second-stage conversion in a muffle furnace at 900°C for 3 h to obtain the third solid phase. The third solid phase is fully hydrated in clear water to obtain a suspension of the metal (hydro)oxide deacidifying agent. The alkalinity measurement and evaluation method are the same as above.

[0148] From Figure 5It can be seen that the time of the primary conversion reaction significantly affects the total alkalinity and effective alkalinity of the final deacidifying agent. For the primary conversion reaction for 0.5 h, the total alkalinity and effective alkalinity are respectively increased from the initial 21.47 and 19.78 mol / kg to 23.44 and 21.26 mol / kg; for the primary conversion reaction for 1 h, they are rapidly increased to 25.90 and 24.15 mol / kg; for the primary conversion for 4 h, the total alkalinity and effective alkalinity are increased to 27.11 and 25.35 mol / kg; for the primary conversion for 10 h, the total alkalinity and effective alkalinity are further increased to 28.83 and 26.6 mol / kg; after the primary conversion for 13 h, the total alkalinity and effective alkalinity reach 29.31 and 26.97 mol / kg, and the conversion is basically close to equilibrium; for the primary conversion for 24 h, the total alkalinity and effective alkalinity reach 29.47 and 27.17 mol / kg; in the range of 24 - 48 h for the primary conversion, the total alkalinity and effective alkalinity are respectively stabilized at 29.47 - 29.75 mol / kg and 27.17 - 27.55 mol / kg.

[0149] Example 7

[0150] Repeat the first step in Example 1 to obtain the first solid phase, i.e., the fly ash after washing. Respectively take 5 g of the fly ash C after washing and place them in polyethylene bottles, add an aqueous solution of Na2CO3 / NaHCO3 single or mixed solution with a total concentration of 1.5 M as the conversion reagent, and set the molar ratios to 1:0, 2:1, 1:1, 1:2, 0:1 respectively. The liquid-solid ratio of the aqueous solution of the conversion reagent to the fly ash after washing is 4:1. React at room temperature for 12 h, first perform liquid-solid separation, and then wash the unreacted mixed conversion liquid on the solid surface with water, filter and dry to obtain the second solid phase. Subject the second solid phase to secondary conversion in a muffle furnace at 900 °C for 3 h to obtain the third solid phase. Place the third solid phase in water for sufficient hydration to obtain a metal (hydro) oxide deacidifying agent emulsion.

[0151] The alkali capacities of the corresponding obtained metal (hydro) oxide deacidifying agents are shown in Table 6. The total alkalinity and effective alkalinity of the deacidifying agent obtained by using Na2CO3 alone for conversion are 28.95 and 27.25 mol / kg respectively. When using NaHCO3 alone as an auxiliary agent, the total alkalinity and effective alkalinity of the obtained deacidifying agent are 27.46 and 25.18 mol / kg respectively. When Na2CO3 and NaHCO3 are combined in two phases, when n(Na2CO3):n(NaHCO3) = 2:1, the total alkalinity and effective alkalinity of the obtained deacidifying agent are 27.26 and 25.10 mol / kg respectively. When n(Na2CO3):n(NaHCO3) = 1:1 and 1:2, the total alkalinities of the obtained deacidifying agents are 27.71 and 27.56 mol / kg respectively, and the effective alkalinities are 25.39 and 25.26 mol / kg respectively.

[0152] Table 6 Summary of the effects of the conversion agent compounding in Example 7

[0153]

[0154] Example 8

[0155] Repeat the first step in Example 1 to obtain the first solid phase, i.e., washed fly ash. Take 5 g of washed fly ash C in polyethylene bottles, add 1.5 M (NH4)2CO3 solution and NH4HCO3 solution, respectively, with a liquid-solid ratio of 4:1, react at room temperature for 12 hours, first separate the liquid and solid, then wash the unreacted mixed conversion liquid on the solid surface with water, filter and dry to obtain the second solid phase. The second solid phase is subjected to secondary conversion at 900°C in a muffle furnace for 3 hours to obtain the third solid phase. The third solid phase is placed in water for full hydration to obtain a metal (hydr)oxide deacidifying agent emulsion. The total alkalinity of the corresponding metal (hydro)oxide deacidifiers obtained from (NH4)2CO3 solution and NH4HCO3 solution are 27.34 and 26.81 mol / kg, respectively, and the effective alkalinity are 25.25 and 24.72 mol / kg, respectively; the advantage of using ammonium carbonate or ammonium bicarbonate as the conversion agent compared to sodium carbonate is that the former is cheaper and the residual filtrate produced after the first-level conversion can be used as fertilizer after purification.

[0156] Example 9

[0157] Repeat the first step in Example 1 to obtain the first solid phase, i.e., washed fly ash. Take 5 g of washed fly ash C in a polyethylene bottle, add a 10% Na2CO3 solution (liquid-to-solid ratio of 4:1), and then introduce CO2 gas under atmospheric pressure for 1 hour, then stop ventilation, and continue to react at room temperature for 12 hours. Liquid-solid separation, then wash the unreacted mixed conversion liquid on the solid surface with water, filter and dry to obtain the second solid phase. The second solid phase is converted in a muffle furnace at 900°C for 3 hours to obtain the third solid phase. The third solid phase is placed in water for full hydration to obtain a metal (hydroxide) deacidification agent emulsion. The total alkalinity and effective alkalinity of the corresponding metal (hydroxide) deacidification agent obtained are 28.15 and 26.46 mol / kg, respectively. Experiments show that carbon dioxide itself cannot be used as a primary conversion reagent, and the use of carbon dioxide alone cannot uniformly convert various phases in fly ash into metal carbonate minerals. Carbon dioxide as an auxiliary agent can adjust the pH of the system to a certain extent, thereby reducing the alkaline dissolution of heavy metals during the primary conversion.

[0158] Example 10

[0159] Repeat step 1 in Example 1 to obtain the first solid phase, namely the washed fly ash. A primary conversion system comprising conversion reagents (NH4)2CO3 and NH4HCO3 was prepared in situ according to the following two methods.

[0160] (1) Take 5 g of fly ash in a reaction tank, add an ammonia aqueous solution with a concentration of 5%, with a liquid-solid ratio of 6:1. Stir magnetically at room temperature and introduce CO2 gas. Stop ventilation when the pH value of the reaction system reaches 9.0 - 9.5. Continue magnetic stirring for 8 h, then filter and dry to obtain the second solid phase.

[0161] (2) Add an ammonia aqueous solution with a concentration of 5% to the reaction tank. Stir magnetically at room temperature and introduce CO2 to in-situ generate a conversion solution containing (NH4)2CO3 and NH4HCO3. Stop ventilation, then add 5 g of washed fly ash to the system, with a liquid-solid ratio of 6:1. Stir magnetically for 8 h, then filter and dry to obtain the second solid phase.

[0162] The second solid phase is subjected to secondary conversion at 900 °C for 3 h in a muffle furnace to obtain the third solid phase. The third solid phase is fully hydrated in deionized water to obtain a metal (hydro)oxide deacidifying agent suspension. The alkalinity determination and evaluation method are the same as above. The obtained total alkalinities are 27.40 mol / kg and 26.88 mol / kg respectively, and the effective alkalinities are 25.84 mol / kg and 25.08 mol / kg respectively.

[0163] Example 11

[0164] Measure the activity of the deacidifying agent obtained in the above typical examples, that is, the actual acid neutralization efficiency of the deacidifying agent within 10 min. The method is as follows: Take 1 g of the deacidifying agent prepared from fly ash C in a 50 mL conical flask, add deoxygenated deionized water (40 °C warm water) with a liquid-solid ratio of 40:1 and immediately isolate the air with a sealing film. After hydration for about 2 min, add 5 drops of phenolphthalein reagent. Titrate 4 M hydrochloric acid rapidly until it just turns colorless and maintain at this inflection point for 10 min. Record the consumption of acid. The molar mass of hydrochloric acid consumed per kilogram of deacidifying agent is the activity. As shown in Table 7, the activities of the original fly ash C without any treatment and the original fly ash C only after calcination are only 2.36 and 7.24 mol / kg; under the typical conversion parameters of Examples 1 - 10, the activity of the deacidifying agent prepared from fly ash C is as high as 21 - 23.4 mol / kg, which is 9 - 10 times that of the original fly ash, and has extremely high deacidification activity. The activity of the deacidifying agent is up to more than 80% of its total alkalinity of the deacidifying agent, indicating that most of the alkali capacity stored in the obtained deacidifying agent has actual deacidification activity.

[0165] Table 7 Activity of the deacidifying agent prepared from fly ash C under typical conversion parameters

[0166]

[0167] As can be seen from the above embodiments, the present invention provides a simple and effective fly ash resource utilization solution. Through a three-stage conversion process, the metal oxide and its corresponding hydroxide components are gradually enriched and purified, and finally a metal (hydro) oxide deacidifying agent with ultra-high alkalinity and corresponding activity is obtained, realizing the resource utilization of fly ash. The classified research on stage fly ash and comprehensive fly ash emphasizes the universality of the present invention for fly ash resource utilization applications. The method provided by the present invention is not only simple and efficient in process, but also has the prospect of large-scale industrial application. In terms of environmental impact, it can solve the problem of fly ash disposal; in terms of benefits, it can basically realize the self-circulation of the metal (hydro) oxide deacidifying agent in the waste incineration plant. The above-described embodiments are the preferred embodiments of the present invention. It should be noted that without departing from the conversion principle and purpose of the present invention, several improvements and refinements can be made, and these improvements and refinements should be regarded as the protection scope of the present invention.

[0168] Comparative Example 1

[0169] In this comparative example, the first solid-phase washed fly ash of fly ashes A, B, C, and D in the first step of Example 1 was directly treated in a muffle furnace at 900 °C for 3 h to obtain the washed-calcined fly ash without primary conversion. After being fully hydrated in water, the alkalinity was measured. From Figure 6 it can be seen (where I corresponds to the total alkalinity and effective alkalinity of this comparative example, and IV corresponds to the total alkalinity and effective alkalinity of the deacidifying agent product obtained in Example 1 of the present invention) that the total alkalinities of the corresponding third solid phases of the four fly ashes in this comparative example are 18.34, 20.54, 23.84, and 22.74 mol / kg respectively, and the effective alkalinities are only 17.24, 18.38, 22.14, and 21.44 mol / kg respectively. The alkalinity is too low to be used for deacidification. The total alkalinities of the deacidifying agents obtained by the present invention are 29.46, 28.93, 29.77, and 30.77 mol / kg respectively, and the effective alkalinities are 26.89, 26.32, 27.07, and 28.22 mol / kg respectively. The total alkalinity and effective alkalinity of the washed-calcined fly ash are only 62.25%, 71.00%, 80.08%, 73.90% and 64.11%, 69.83%, 81.79%, 75.97% of those of the metal (hydro) oxide deacidifying agent in the present invention respectively, far lower than the corresponding product metal (hydro) oxide deacidifying agent obtained.

[0170] Comparative Example 2

[0171] In this comparative example, 20% (wt%) of analytical pure CaO powder was added to the first solid phase (i.e., the washed fly ash) of fly ashes A, B, C, and D in the first step of Example 1 and mixed thoroughly to obtain the second solid phase; the second solid phase was treated in a muffle furnace at 900 °C for 3 h to obtain the fly ash conversion product with added CaO. After being fully hydrated in water, the alkalinity was measured. FromFigure 6 It can be seen that (where II corresponds to the total alkalinity and effective alkalinity of this comparative example, and IV corresponds to the total alkalinity and effective alkalinity of the deacidifying agent product obtained in Example 1 of the present invention), the total alkalinities of the products obtained from the four fly ashes in this comparative example are 21.21, 22.72, 24.79, and 23.83 mol / kg respectively, and the effective alkalinities are 20.21, 21.62, 23.39, and 22.53 mol / kg respectively. 20% (by weight) of analytical pure CaO was added to the four fly ashes in this comparative example. However, compared with the washed-calcined fly ash, the total alkalinity and effective alkalinity only increased by 10.20%, 10.61%, 3.98%, 4.79% and 17.23%, 17.63%, 5.65%, 5.08% respectively. The total alkalinity and effective alkalinity of the fly ash conversion product with added CaO in this comparative example are only 72.00%, 78.53%, 83.27%, 77.45% and 75.16%, 82.14%, 86.41%, 79.84% of those of the metal (hydro)oxide deacidifying agent of the present invention respectively, still far lower than the corresponding product metal (hydro)oxide deacidifying agent obtained. This is because even though a certain amount of CaO is added to the untransformed calcined fly ash, the activity of its alkaline substances is still low, resulting in the inability to fully release the effective alkalinity during acid-base titration.

[0172] Comparative Example 3

[0173] In this comparative example, 20% (by weight) of analytical pure CaCO3 powder was added to the first solid phase (i.e., the washed fly ash) of fly ashes A, B, C, and D in the first step of Example 1 and mixed thoroughly to obtain a second solid phase; the second solid phase was treated in a muffle furnace at 900 °C for 3 h to obtain washed-calcined fly ash with added CaCO3, and the alkalinity was measured after being fully hydrated in water. From Figure 6It can be seen that (where III corresponds to the total alkalinity and effective alkalinity of this comparative example, and IV corresponds to the total alkalinity and effective alkalinity of the deacidifying agent product obtained in Example 1 of the present invention). The total alkalinities of the corresponding third solids of the four fly ashes in this comparative example are 19.54 mol / kg, 20.36 mol / kg, 21.76 mol / kg, and 21.54 mol / kg respectively, and the effective alkalinities are 17.54 mol / kg, 18.56 mol / kg, 20.01 mol / kg, and 19.29 mol / kg respectively. 20% (wt%) of CaCO3 was added to the four fly ashes in this comparative example, but compared with the washed-calcined fly ash, the alkalinity decreased instead. The differences were 1.2%, -0.18%, -2.08%, -1.2% and 0.3%, 0.18%, -2.13%, -2.15% respectively. The total alkalinity and effective alkalinity of the fly ash conversion product added with CaCO3 in this comparative example are only 66.33%, 70.38%, 73.09%, 70.00% and 65.24%, 70.52%, 73.92%, 68.36% of those of the metal (hydro)oxide deacidifying agent in the present invention respectively, still far lower than the obtained corresponding product metal (hydro)oxide deacidifying agent. This is because for the untransformed calcined fly ash, even if an appropriate amount of CaCO3 is added, the activity of its alkaline substances is still low, resulting in insufficient release of the effective alkalinity.

[0174] In the above three comparative examples, the activity range of the product obtained from fly ash C is 16.5 - 17.2 mol / kg

[0175] (as shown in Table 8), far lower than the activity (21 - 23.4 mol / kg) of the deacidifying agent obtained from fly ash C in the examples.

[0176] Table 8 Activity of the product prepared from fly ash C in the above comparative examples

[0177]

Claims

1. A method for preparing a deacidifying agent from municipal solid waste incineration fly ash, which comprises the following steps: Primary conversion, converting various types of minerals in the municipal solid waste incineration fly ash into metal carbonate minerals; and Secondary conversion, converting the obtained metal carbonate minerals into corresponding metal oxides to obtain a deacidifying agent with high alkalinity; wherein the municipal solid waste incineration fly ash is generated by deacidifying the flue gas from municipal solid waste incineration; The primary conversion is carried out in an aqueous solution and the conversion reagent contains water-soluble carbonate and / or water-soluble bicarbonate; The secondary conversion is carried out at a temperature above 700 °C.

2. The method according to claim 1, further comprising: Tertiary conversion before deacidification application, hydrating the metal oxide to make it have high deacidification activity.

3. The method according to claim 1, wherein the method comprises the following steps: Primary conversion, adding an aqueous solution of a water-soluble carbonate and / or water-soluble bicarbonate conversion reagent to the municipal solid waste incineration fly ash, stirring and reacting to convert various types of minerals in the municipal solid waste incineration fly ash into metal carbonate minerals; Secondary conversion, after the primary conversion is completed and liquid-solid separation is carried out, converting the solid-phase powder of the obtained metal carbonate minerals into metal oxides at a temperature > 700 °C to obtain a deacidifying agent with high alkalinity; and Tertiary conversion before deacidification application, hydrating the metal oxide to make it have high deacidification activity.

4. The method according to claim 1, wherein the method comprises the following steps: (1) Before the primary conversion, washing the municipal solid waste incineration fly ash to remove water-soluble components, and obtaining washed fly ash through liquid-solid separation; (2) Adding an aqueous solution of a water-soluble carbonate and / or water-soluble bicarbonate conversion reagent to the washed fly ash, stirring and reacting, and converting various types of minerals in the washed fly ash into metal carbonate minerals through primary conversion; (3) After liquid-solid separation again, converting the solid-phase powder of the obtained metal carbonate minerals into metal oxides at a temperature > 700 °C to obtain a deacidifying agent with high alkalinity; and (4) Tertiary conversion before deacidification application, hydrating the metal oxide to make it have high deacidification activity.

5. The method according to claim 4, wherein in step (1), the water-soluble components are metal salts and chlorine-containing salts.

6. The method according to any one of claims 1-5, wherein the conversion reagent used in the primary conversion comprises sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate or any combination thereof.

7. The method according to claim 6, wherein the concentration range of the aqueous solution of the conversion reagent is 0.1-5.0 M; and / or, the liquid-solid ratio of the aqueous solution of the conversion reagent to the fly ash is (1-100):1; and / or, the temperature range in the primary conversion is 0-100 °C; and / or, the time of the primary conversion is 0.5-48 h.

8. The method according to claim 7, wherein the concentration range of the aqueous solution of the conversion reagent in the primary conversion is 0.5-4.5 M, the liquid-solid ratio of the aqueous solution of the conversion reagent to the fly ash in the primary conversion is (2-20):1, and the time of the primary conversion is 1-24 h.

9. The method according to any one of claims 1-5, wherein the conversion reagent further comprises an auxiliary agent, carbon dioxide.

10. The method according to any one of claims 1-5, wherein the municipal solid waste incineration fly ash is produced by treating the flue gas of municipal solid waste incineration fly ash by the lime method, and the flue gas treatment method comprises at least one of wet method, semi-wet method and dry method, or the municipal solid waste incineration fly ash is untreated fly ash and / or aged fly ash.

11. The method according to any one of claims 1-5, wherein the metal carbonate minerals are dried before the secondary conversion after the primary conversion to generate metal carbonate minerals and liquid-solid separation, and the drying temperature is 40-300 °C.

12. The method according to any one of claims 1-5 further comprises the following steps: The obtained deacidifying agent is reused for the flue gas treatment of municipal solid waste incineration fly ash, and then this method is cycled.

13. A device for preparing a deacidifying agent from municipal solid waste incineration fly ash, comprising: - A fly ash collection device for collecting municipal solid waste incineration fly ash; - A reaction device for converting various types of minerals in the municipal solid waste incineration fly ash into metal carbonate minerals; and - A heat treatment device for converting the obtained metal carbonate minerals into corresponding metal oxides to obtain a deacidifying agent with high alkalinity.

14. The device according to claim 13, further comprising a hydration device for hydrating the metal oxides to make them have high deacidifying activity.

15. The device according to claim 13 or 14, wherein the device further comprises a washing device, and the washing device is located between the fly ash collection device and the reaction device.

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