Reduction and resourceful treatment method for waste incineration fly ash

Abstract

The invention discloses a reduction and resourceful treatment method for waste incineration fly ash, which realizes reduction and innocent treatment of fly ash through a process of water washing, ammonium chloride washing and partial mother liquor evaporation, crystallization and salt separation, and comprises the following steps: firstly, washing out harmful substances chloride ions and soluble salt in the fly ash through water washing; the content of sodium chloride and potassium chloride impurities in the ammonium chloride solution is controlled in a reasonable range, the reduction of the fly ash is realized by generating calcium chloride through the reaction of ammonium chloride and calcium hydroxide in the fly ash, the reduction is about 40-50%, and the balance of the quality and the concentration of the ammonium chloride mother solution is ensured through partial evaporation, crystallization and salt separation subsequently; and long-term stable operation of the system is ensured. Besides, different calcium carbonate, including common calcium carbonate, light calcium carbonate and even nano-scale calcium carbonate, can be prepared by the method disclosed by the invention, so that a fly ash recycling byproduct calcium carbonate product line is enriched, the benefits of byproducts are increased, and the production cost is effectively reduced.

Description

A method for reducing and recycling fly ash from garbage incineration Technical Field

[0001] The present invention relates to environmental protection related fields, and in particular to a method for reducing and recycling fly ash from waste incineration. Background Art

[0002] In recent years, municipal waste emissions have increased rapidly. Incineration, due to its advantages in heat recovery for power generation and volume reduction, has led to rapid development in China's waste incineration industry. However, the incineration process produces large amounts of fly ash, which accumulates harmful substances such as dioxins and heavy metals and is classified as hazardous solid waste by the government. Landfilling fly ash requires significant land and poses potential long-term environmental risks. Therefore, its safe disposal and resource utilization have become new challenges for China's urban development.

[0003] Incineration fly ash refers to the incineration residue collected from the flue gas purification system of a waste incineration plant. Domestically, the amount of fly ash generated per ton of waste incineration ranges from 30 to 200 kg, with grate furnaces producing a lower amount (30-50 kg) and fluidized bed furnaces producing a higher amount (100-150 kg). Fly ash is widely considered a hazardous waste and poses a significant environmental threat because it contains highly toxic heavy metals, soluble salts, and organic chlorides (polychlorinated biphenyls and dioxins). Heavy metals accumulate on and within the ash, with Zn and Pb being the most abundant, with leaching concentrations reaching 35.84 mg / L and 5.98 mg / L, respectively. Direct landfilling of fly ash can seriously contaminate groundwater.

[0004] Patent document with publication number CN111408602B discloses a method for harmless resource treatment of fly ash from waste incineration, comprising mixing fly ash from waste incineration with 31% hydrochloric acid in a mass ratio of 1:1.3 and water or frozen mother liquor for neutralization reaction, dissolving calcium chloride synthesized from calcium oxide in the wastewater into the solution; liquid-solid separation of the mixture, removing the mother liquor from the separated waste liquor, and washing the remaining fly ash solids with two to ten times the amount of clean water in a countercurrent mixing manner two to five times, and finally filtering. The filtered wastewater is evaporated and crystallized to obtain crystalline salt mainly composed of sodium chloride; the mother liquor is first cooled and crystallized, and the crystalline salt is filtered to obtain a chloride salt mixture mainly composed of potassium chloride.

[0005] Patent document CN104070053B discloses a graded calcination and reduction treatment technology for waste incineration fly ash, including: adding a dechlorination flux to the waste incineration fly ash, stirring and mixing it evenly to form green body particles, using a small calcination device for primary rapid calcination with short calcination time and low energy consumption. Under the action of the dechlorination flux, dioxin pollutants are completely degraded, heavy metals and chloride salts are volatilized in large quantities, and secondary fly ash is captured to achieve the enrichment of heavy metals and chloride salts and the reduction of fly ash, with a reduction rate of 90-99%; after the primary calcination heavy metal leaching meets the standard, the primary calcination is sent to a waste incinerator for secondary continuous calcination. The slag formed can be used for ordinary landfill or as a building material raw material for resource utilization.

[0006] While existing technologies have explored fly ash reduction and harmless treatment, complete harmlessness is difficult to achieve with existing methods, and individual components are difficult to utilize. Furthermore, existing fly ash treatment methods are complex, resulting in poor equipment stability and operational economics. Therefore, it is crucial to develop a novel waste incineration fly ash reduction and resource utilization method to reduce the land resources occupied by fly ash solid waste storage and the risk of secondary pollution, achieve fly ash reduction and complete harmless treatment, and ensure long-term stable system operation.

[0007] Summary of the Invention

[0008] The object of the present invention is to provide a method for reducing and resource-recycling fly ash from waste incineration. The present invention adopts a process of water washing + ammonium chloride washing + evaporation and crystallization of part of the mother liquor to separate salts, thereby achieving fly ash reduction and harmless treatment, and ensuring the balance of the ammonium chloride solution, so that the system can operate stably for a long time.

[0009] A method for reducing and recycling fly ash from waste incineration comprises the following steps:

[0010] Step 1: washing the fly ash with water and filtering it to obtain a first filter cake and a first filtrate;

[0011] Step 2: placing the first filter cake obtained in step 1 in a reactor, adding ammonium chloride mother liquor into the reactor, and reacting until the pH at the reaction end point is 8-12.2 to obtain a reaction product;

[0012] Step 3: Filter the reaction product obtained in step 2 to obtain a second filter cake and a second filtrate, wash the second filter cake with water to obtain a first washing liquid, and mix the second filtrate with the first washing liquid to obtain a first mixed liquid;

[0013] Step 4: Using the first mixed solution obtained in step 3 as a raw material, reacting to prepare calcium carbonate;

[0014] Step 5: Filter the reaction product obtained in step 4 to obtain a third filtrate and a third filter cake, wash the third filter cake with water to obtain calcium carbonate and a second washing liquid, and mix the second washing liquid with the third filtrate to obtain a second mixed liquid;

[0015] Step 6: splitting the second mixed liquid, performing evaporation, crystallization and salt separation on a portion of the second mixed liquid to obtain ammonium chloride crystals, dissolving the ammonium chloride crystals in the remaining second mixed liquid to prepare an ammonium chloride solution, and controlling the amount of the second mixed liquid used for evaporation, crystallization and salt separation so that the concentration and quality of the prepared ammonium chloride solution are substantially the same as the concentration and quality of the ammonium chloride mother liquor added in step 2, and adding the prepared ammonium chloride solution to the reactor in step 2 for recycling.

[0016] The present invention adopts a process of water washing + ammonium chloride washing + evaporation crystallization and salt separation of part of the mother liquor to achieve the reduction and harmless treatment of fly ash. By washing the fly ash with water, most of the sodium chloride and potassium chloride in the fly ash are removed, ensuring that the sodium chloride and potassium chloride impurity content in the subsequently prepared ammonium chloride solution is controlled within a reasonable range, ensuring that salt separation and crystallization can be performed when the ammonium chloride solution is evaporated and crystallized, obtaining a high-purity ammonium chloride salt and a sodium chloride and potassium chloride mixed salt. By washing the first filter cake with ammonium chloride, the ammonium chloride reacts with the calcium hydroxide in the first filter cake to generate calcium chloride, thereby achieving fly ash reduction; by washing the second and third filter cakes, the ammonia in the filter cakes is fully recovered, and the chloride ion content of the second and third filter cakes is guaranteed to meet the design requirements. By evaporation crystallization and salt separation, the quality and concentration balance of the ammonium chloride mother liquor is guaranteed. Through the mutual cooperation of the above-mentioned steps, the present invention achieves the reduction and harmless treatment of fly ash, reduces the loss of ammonia, achieves ammonia balance, and enables the system to operate stably for a long time.

[0017] Preferably, in step 1, the mass fraction of calcium oxide in the fly ash is 20-50 wt%.

[0018] Preferably, in step one, in the washing step, the mass ratio of fly ash to water is 1:1 to 10. The water washing can be performed by one wash or 2-4 countercurrent washings. The present invention first washes the fly ash with water to wash out the harmful chloride ions and soluble salts in the fly ash, and controls the chloride ion content in the first filter cake to be lower than 3wt%, so as to ensure that the subsequent ammonium chloride mother liquor sodium chloride and potassium chloride impurity content is controlled within a reasonable range, and ensures that the ammonium chloride solution is evaporated and crystallized to obtain higher-purity ammonium chloride and sodium chloride and potassium chloride mixed salts. If the fly ash is not washed with water first, the ammonium chloride solution will be evaporated and crystallized to obtain a mixed salt of ammonium chloride, sodium chloride and potassium chloride, and it will be impossible to perform salt separation to obtain higher-purity ammonium chloride, which will eventually lead to the accumulation of miscellaneous salts in the ammonium chloride solution and the inability to discharge it, and the inability to establish a mass concentration balance system, resulting in the inability to achieve stable operation.

[0019] Preferably, in step one, the first filtrate is pretreated to remove calcium and magnesium ions to obtain a mixed solution in which the main components of the solute are sodium chloride and potassium chloride, and then evaporation crystallization and salt separation are performed to obtain sodium chloride crystals and potassium chloride crystals, respectively. Specifically, sodium carbonate or sodium sulfate can be added to the first filtrate for reaction and filtration, and after removing calcium and magnesium ions in the solution, the pretreated filtrate is added to a crystallization and salt separation device for evaporation and crystallization to obtain sodium chloride crystals that meet the standards, and then cooled and crystallized to obtain potassium chloride crystals that meet the standards.

[0020] Preferably, in step 2, the concentration of the ammonium chloride mother liquor is 1-30wt%, and the mass ratio of the first filter cake to the ammonium chloride solution is 1:2-20. More preferably, the mass fraction of the ammonium chloride mother liquor is 5-25%, and the mass ratio of the first filter cake to the ammonium chloride solution is 1:2-20. After the ammonium chloride mother liquor reacts with the first filter cake and is filtered, the leaching rate of calcium hydroxide exceeds 90%, and the obtained second filtrate is a solution of calcium chloride and ammonia, wherein the concentration of calcium chloride in the second filtrate is 3-17wt%, and the concentration of ammonia is 1.0-4.0wt%.

[0021] In this step, the first filter cake reacts with the ammonium chloride solution (ammonium chloride reacts with calcium oxide and calcium hydroxide in the first filter cake to generate calcium chloride and ammonia), and is filtered to obtain a second filter cake and a second filtrate. The main components of the second filter cake (fly ash residue) are calcium carbonate, calcium sulfate, silicon dioxide, iron, aluminum, etc., and the second filtrate is mainly a mixed solution of calcium chloride and ammonia.

[0022] Preferably, in step three, during the water washing step, the mass ratio of the second filter cake to water is 1:0.8-5. The water washing can be performed as a single wash or 2-4 countercurrent washes, or it can be performed within the filter. The chloride ion content in the fly ash residue obtained after washing is less than 1.0%. In this application, the second filter cake is washed, and the fly ash residue obtained after washing mainly contains calcium carbonate, calcium sulfate, silica, iron, and aluminum, achieving a fly ash reduction of approximately 40-50%. Washing reduces the chloride ion content in the fly ash residue to below 1.0%.

[0023] Preferably, the washed fly ash is post-processed using the following technical solutions:

[0024] Option 1: high-temperature sintering detoxification or low-temperature thermal detoxification;

[0025] Option 2: Co-processing in cement kilns for harmless treatment;

[0026] Option 3: First use hydrochloric acid reaction to remove calcium carbonate and heavy metal oxides in the fly ash, filter it, and the main components of the remaining filter cake are calcium sulfate dihydrate, silicon dioxide, some iron and aluminum, and a small amount of dioxins. Then send it to the cement kiln for co-treatment, high-temperature detoxification and harmlessness treatment, or hydrothermal detoxification and harmlessness treatment.

[0027] Preferably, in step 4, the first mixed solution obtained in step 3 is used as a raw material to react, and the technical solution for preparing calcium carbonate includes:

[0028] Option 1: directly introduce carbon dioxide into the first mixed solution to perform a carbonization reaction to generate calcium carbonate precipitation;

[0029] Option 2: stripping the first mixed liquid to remove ammonia to obtain aqueous ammonia and deammoniation mother liquor, and simultaneously introducing carbon dioxide and aqueous ammonia into the deammoniation mother liquor to react and generate calcium carbonate precipitate;

[0030] Option 3: stripping the first mixed liquid to remove ammonia to obtain aqueous ammonia and deammoniation mother liquor, carbonizing the aqueous ammonia to form an ammonium carbonate solution, and then subjecting the ammonium carbonate solution to a double decomposition reaction with the deammoniation mother liquor to generate calcium carbonate precipitate;

[0031] Option 4: 50% of the first mixed liquid is stripped to remove ammonia to obtain aqueous ammonia and a deaminated mother liquor. The aqueous ammonia is first carbonized to form an ammonium bicarbonate solution. The remaining first mixed liquid and the deaminated mother liquor are mixed and then subjected to a double decomposition reaction with the ammonium bicarbonate solution to generate calcium carbonate precipitation.

[0032] Option 5: The first mixed liquid is stripped and deaminated to obtain ammonia water and a deammoniation mother liquor. The ammonia water is first carbonized into an ammonium bicarbonate solution. The ammonium bicarbonate solution reacts with the deammoniation mother liquor to generate a calcium bicarbonate solution. The calcium bicarbonate solution is heated and decomposed or microwaved to prepare a calcium carbonate precipitate.

[0033] In step 4, the main component of the first mixed liquid is a mixture of calcium chloride and ammonia water. Through the above-mentioned different methods for preparing calcium carbonate, ordinary calcium carbonate, light calcium carbonate, and even nano-scale calcium carbonate can be obtained, thereby enriching the fly ash resource utilization by-product calcium carbonate product line, increasing the benefits of the by-product, and effectively reducing production costs.

[0034] Preferably, when using Scheme 1 to prepare calcium carbonate, the molar ratio of carbon dioxide introduced to calcium ions in solution is 1:1.0-1.1, the reaction temperature is 0-90°C, the reaction residence time exceeds 3 hours, and the stirred tank reaction speed is 60-600 rpm. One ton of fly ash yields over 400 kg of calcium carbonate, with a whiteness exceeding 92%, a purity exceeding 97%, and an average particle size of 15-25 microns.

[0035] Preferably, when using scheme 2 to prepare calcium carbonate, a solution of calcium chloride and ammonia is stripped and deaminated to obtain 10-20wt% ammonia water and a deaminated mother liquor, with a deammoniation rate exceeding 95%. Carbon dioxide and ammonia water are introduced into the deaminated mother liquor to undergo a carbonization reaction to produce calcium carbonate. The molar ratio of carbon dioxide introduced in the carbonization reaction to calcium ions in the solution is 1:1.0-1.1. The reactor is stirred at a speed of 60-600rpm, the reaction temperature is 0-90°C, and the reaction residence time is controlled at 30-120min. One ton of fly ash produces more than 400kg of calcium carbonate, with a whiteness exceeding 93%, a purity exceeding 98%, and an average particle size of 10-20 microns.

[0036] Preferably, when using Scheme 3 to prepare calcium carbonate, a solution of calcium chloride and ammonia is stripped and deaminated to obtain 10-20 wt% ammonia water and a deaminated mother liquor, with a deammoniation rate exceeding 95%. The ammonia water is carbonized with carbon dioxide to obtain an ammonium carbonate solution, which is then mixed with the deaminated mother liquor for a double decomposition reaction to prepare calcium carbonate. The molar ratio of ammonia water to carbon dioxide in the carbonization reaction is 1:2. The double decomposition reaction temperature is 0-90°C, the reaction residence time is controlled at 30-120 minutes, and the reactor stirring speed is 60-600 rpm. One ton of fly ash produces more than 400 kg of calcium carbonate, with a whiteness exceeding 93%, a purity exceeding 98%, and an average particle size of 3-15 microns.

[0037] Preferably, when using Scheme 4 to prepare calcium carbonate, 50% of the first mixed liquid is subjected to steam stripping and deammoniation to obtain 10-20wt% ammonia water and a deammoniation mother liquor, with a deammoniation rate exceeding 95%. The deammoniation mother liquor is mixed with the other 50% of the first mixed liquid to obtain a mixed solution, and the ammonia water obtained by steam stripping and deammoniation is carbonized with carbon dioxide to produce an ammonium bicarbonate solution. The molar ratio of ammonia water to carbon dioxide in the carbonization reaction is 1:1.0-1.1. The reaction temperature in the double decomposition reaction is 0-90°C, the reaction residence time is controlled at 30-120 minutes, and the stirring speed of the reactor is 60-600rpm. One ton of fly ash produces more than 400kg of calcium carbonate, with a whiteness exceeding 93%, a purity exceeding 98%, and an average particle size of 2-10 microns.

[0038] Preferably, when using scheme five to prepare calcium carbonate, the first mixed liquid is subjected to steam stripping and deammoniation to obtain 10-20 wt% ammonia water and a deammoniation mother liquor, with a deammoniation rate exceeding 95%. The ammonia water obtained by steam stripping and deammoniation is carbonized with carbon dioxide to produce an ammonium bicarbonate solution, wherein the molar ratio of ammonia water to carbon dioxide in the carbonization reaction is 1:1.0-1.1; the ammonium bicarbonate solution reacts with the deammoniation mother liquor to produce a calcium bicarbonate solution, the reaction temperature being controlled within 20°C, and then the calcium bicarbonate is decomposed by microwave or heat to obtain a calcium carbonate precipitate, the reaction temperature being controlled within 60-99°C, and the reactor stirring speed being 60-600 rpm. One ton of fly ash produces more than 400 kg of calcium carbonate, with a whiteness exceeding 93%, a purity exceeding 98%, and an average particle size of 0.1-5 microns.

[0039] Preferably, in step five, the second washing liquid is concentrated by membrane and then mixed with the third filtrate.

[0040] Preferably, the membrane concentration multiple is 2-20 times.

[0041] Preferably, in step 5, during the water washing step, the mass ratio of the third filter cake to water is 1:1-40. The water washing can be performed as a single wash or 2-4 countercurrent washes, or it can be washed in a filtration device. After the third filter cake is washed, the chloride ion content is less than 0.1%, and calcium carbonate meeting national standards is obtained. The obtained calcium carbonate is dried, packaged, and sold.

[0042] In step six, as the production proceeds, there are two changes in the ammonium chloride circulating mother liquor: (1) the ammonium chloride and potassium chloride in the fly ash enter the mother liquor, which will accumulate if not treated, thus affecting production; (2) the addition of washing liquid for fly ash residue and washing liquid for calcium carbonate increases the total amount of the mother liquor, and the increase in the quality of the mother liquor leads to imbalance. Therefore, the fly ash must first be washed with water to remove most of the sodium chloride and potassium chloride, and then part of the ammonium chloride mother liquor is evaporated and crystallized for salt separation. The purpose of washing the fly ash first is to ensure that the content of sodium chloride and potassium chloride impurities in the ammonium chloride solution is controlled within a reasonable range, and to avoid the ammonium chloride solution being evaporated and crystallized for salt separation to obtain a higher purity ammonium chloride and sodium chloride and potassium chloride mixed salt. By evaporating and crystallizing the salt, the quality and concentration of the ammonium chloride mother liquor are balanced, and the system can operate stably for a long time.

[0043] The loss rate of the ammonium chloride of the present invention does not exceed 2%. After the device has been running for a long time, ammonium bicarbonate or ammonium chloride can be appropriately supplemented according to the loss of ammonium chloride in the solution.

[0044] Preferably, in step six, the obtained mixed salt of sodium chloride and potassium chloride is mixed with the first filtrate pretreated in step one, and the mixture is evaporated and crystallized to separate the salt.

[0045] Compared with the prior art, the present invention has at least the following beneficial effects:

[0046] (1) The present invention realizes the reduction and harmless treatment of fly ash through the process of water washing + ammonium chloride washing + partial mother liquor evaporation crystallization salt separation. First, the harmful chloride ions and soluble salts in the fly ash are washed out by water to ensure that the impurity content of sodium chloride and potassium chloride in the ammonium chloride solution is controlled within a reasonable range. Then, ammonium chloride is reacted with calcium hydroxide in the fly ash to form calcium chloride to achieve the reduction of fly ash, with a reduction of about 40-50%. Subsequently, the balance of the quality and concentration of the ammonium chloride mother liquor is ensured by partial evaporation crystallization salt separation, so that the loss rate of ammonium chloride does not exceed 2%, ensuring that the system can operate stably for a long time.

[0047] (2) The present invention washes the fly ash residue after washing with ammonium chloride, reducing the chloride ion content in the fly ash residue to less than 1%, meeting the chloride ion requirements of subsequent treatment and achieving complete harmless treatment of the fly ash. The present invention also washes the calcium carbonate, reducing the chloride ion content of the washed calcium carbonate to less than 0.1%, thereby reducing impurities in the calcium carbonate and ensuring that the prepared calcium carbonate meets national standards. In addition, washing the fly ash residue and calcium carbonate fully recovers the ammonia entrained therein, reducing ammonia loss.

[0048] (3) The present invention adopts different methods for preparing calcium carbonate, which can obtain ordinary calcium carbonate, light calcium carbonate, and even nano-scale calcium carbonate, thereby enriching the fly ash resource by-product calcium carbonate product line, increasing the benefits of the by-product, and effectively reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0050] FIG1 is a process flow chart of the method for reducing and recycling fly ash from waste incineration in Example 1.

[0051] FIG2 is a particle size distribution diagram of the calcium carbonate prepared in Example 1.

[0052] FIG3 is a SEM image of the calcium carbonate prepared in Example 1.

[0053] FIG4 is a process flow chart of the waste incineration fly ash reduction and resource utilization treatment method in Example 2.

[0054] FIG5 is a particle size distribution diagram of the calcium carbonate prepared in Example 2.

[0055] FIG6 is a SEM image of the calcium carbonate prepared in Example 2.

[0056] FIG7 is a TEM image of the calcium carbonate prepared in Example 3. DETAILED DESCRIPTION

[0057] All features disclosed in this specification, or all steps in the disclosed methods or processes, except mutually exclusive features and / or steps, can be combined in any manner.

[0058] Example 1

[0059] The process flow chart of the waste incineration fly ash reduction and resource treatment method of this embodiment is shown in Figure 1, which specifically includes the following steps:

[0060] Step 1: 1 ton of fly ash (chloride ion content 16.4%, SiO2 4.45%, Al2O3 1.35%, Fe2O3 0.69%, CaO 39.67%, MgO 1.10%, sodium ion 5.46%, potassium ion: 3.88%, S content 1.94%, and other small amounts of zinc, copper, lead, nickel and other elements) and water are added to a first water washing and filtering device for slurry washing. After washing, the filter cake is filtered and washed with 2 tons of water to obtain approximately 1.16 tons of washed filter cake and 1.6 tons of first filtrate. The filter cake contains approximately 35% water and 1.5% chloride ion; the chloride ion content of the first filtrate is approximately 12.5%.

[0061] Step 2: The washed filter cake obtained in step 1 is reacted with 5 tons of 15% ammonium chloride solution. The reaction is carried out under normal pressure, at a temperature of 20-30°C, and at a stirring speed of 200 rpm. The reaction formula is as follows: Ca(OH)2+2NH4Cl——>CaCl2+2NH3↑+2H2O

[0062] The pH of the reaction endpoint is controlled to be between 8 and 12.2 to obtain a reaction product;

[0063] Step 3: Filter the reaction product obtained in step 2 to obtain a second filter cake and a second filtrate. The second filter cake weighs about 605 kg, has a moisture content of 33%, and contains about 3.0% chloride ions. After washing the second filter cake with 450 kg of water, the chloride ion content in the filter cake is 0.98%. The washing liquid is mixed with the second filtrate to obtain about 6 tons of a first mixed liquid.

[0064] Step 4: Add 220kg of carbon dioxide to the first mixed solution in step 3 to carry out carbonization reaction. The reaction is carried out under normal pressure, the reaction temperature is 30-35℃, the stirring speed is 300rpm, and the reaction time is about 5 hours. The reaction formula is as follows: CaCl2+2NH3+H2O+CO2——>CaCO3↓+2NH4Cl

[0065] Step 5: The reaction product obtained in step 4 is filtered to obtain a third filtrate and a third filter cake. The third filter cake weighs approximately 600 kg, has a moisture content of approximately 22%, and contains 2% chloride ions. The third filter cake is washed with 3.0 tons of water to obtain a calcium carbonate filter cake and a second washing liquid. The chloride ion content of the calcium carbonate filter cake is approximately 0.07%. The second washing liquid is membrane concentrated 12-fold, and 250 kg of the concentrated liquid is mixed with the third filtrate to obtain a second mixed liquid, which weighs approximately 5.84 tons. The calcium carbonate filter cake is dried, packaged, and sold.

[0066] Step 6: The second mixed liquid is split, wherein about 80% continues to go to the reactor in step 2 for further reaction, and about 20% is pre-treated and then evaporated and crystallized to obtain ammonium chloride crystals and sodium chloride and potassium chloride mixed salt crystals respectively;

[0067] Step 7: The ammonium chloride crystals obtained in Step 6 are dissolved in the remaining second mixed solution to prepare an ammonium chloride solution. The mass fraction of the ammonium chloride solution is now 15%, the mass is 4.989 tons, and the ammonium chloride loss is 1.1%. The prepared ammonium chloride solution is recycled back to the reactor in Step 2 to continue the reaction. The sodium chloride and potassium chloride mixed salt obtained in Step 6 is dissolved in the first filtrate obtained in Step 1.

[0068] Step 8: The second filter cake of step 3 is subjected to cement kiln co-disposal for harmless treatment;

[0069] Step 9: The first filtrate is added to a reaction device for pretreatment, sodium carbonate or sodium sulfate is added for reaction, and calcium and magnesium ions are removed from the first filtrate after filtering through the first water washing and filtering device. The remaining first filtrate is mainly composed of sodium chloride and potassium chloride, which serves as the pretreated filtrate. The pretreated filtrate is added to a crystallization and salt separation device for evaporation and crystallization to obtain 210kg of sodium chloride crystals (sodium chloride content is 95%) that meet the standards. It is then cooled and crystallized to obtain 100kg of potassium chloride crystals (potassium chloride content is 92%) that meet the standards.

[0070] The calcium carbonate obtained in this example has a purity of 98.07%, a whiteness of 93.6%, an average particle size of 20.3 μm, and a crystal form of calcite.

[0071] Example 2

[0072] Step 1: 1.2 tons of fly ash washed filter cake (chloride ion content 1.8%, SiO2 11.4%, Al2O3 4.1%, Fe2O3 2.87%, CaO 60.32%, MgO 1.6%, sodium ion 1.58%, potassium ion: 0.66%, S content 2.94%, and other elements such as small amounts of zinc, copper, lead, and nickel), of which the chloride ion content is 1.2%;

[0073] Step 2: The washed filter cake obtained in step 1 is reacted with 5 tons of 15% ammonium chloride solution. The reaction is carried out under normal pressure, the reaction temperature is 20-30°C, and the stirring speed is 260-300 rpm. The reaction formula is as follows: Ca(OH)2+2NH4Cl——>CaCl2+2NH3↑+2H2O

[0074] The reaction end point pH is between 8 and 12.2, and a reaction product is obtained;

[0075] Step 3: Filter the reaction product obtained in step 2 to obtain a second filter cake and a second filtrate. The second filter cake weighs about 610 kg, has a moisture content of 35%, and a chloride ion content of about 3.2%. After washing the second filter cake with 500 kg of water, the chloride ion content in the filter cake is 0.9%. After mixing the washing liquid with the second filtrate, about 6.1 tons of a first mixed liquid are obtained.

[0076] Step 4: 50% of the first mixed solution in step 3 is stripped and deaminated to obtain 780kg of 10% ammonia water and deaminated mother liquor. 200kg of carbon dioxide is added for carbonization to obtain 1080kg of ammonium bicarbonate solution. The ammonium bicarbonate solution is subjected to a double decomposition reaction with the deaminated mother liquor and the remaining first mixed solution to quickly generate calcium carbonate precipitate. The reaction is carried out under normal pressure, the reaction temperature is 30-40°C, and the stirring speed is 400-500rpm. The reaction formula is as follows: CaCl2+NH4HCO3+NH3——>CaCO3↓+2NH4Cl

[0077] Step 5: The slurry obtained in step 4 is filtered to obtain a third filtrate and a third filter cake. The third filter cake weighs approximately 620 kg, has a moisture content of 20%, and contains 2% chloride ions. The third filter cake is washed with 3.0 tons of water to obtain a calcium carbonate filter cake and a second washing liquid. The chloride ion content of the calcium carbonate filter cake is approximately 0.06%. The second washing liquid is membrane concentrated 10-fold, and the concentrate is mixed with the third filtrate to obtain a second mixed liquid. The mixed liquid weighs approximately 5.95 tons. The calcium carbonate filter cake is dried, packaged, and sold.

[0078] Step 6: The second mixed liquid is split, wherein about 80% continues to go to the reactor in step 2 for further reaction, and about 20% is pre-treated and then evaporated and crystallized to obtain ammonium chloride crystals and sodium chloride and potassium chloride mixed salt crystals respectively;

[0079] Step 7: The ammonium chloride crystals obtained in Step 6 are dissolved in the remaining second mixed solution to prepare an ammonium chloride solution. The mass fraction of the ammonium chloride solution is now 14.5%, the mass is 5.1 tons, and the ammonium chloride loss is 1.4%. The prepared ammonium chloride solution is circulated back to the reactor in Step 2 to continue the reaction. The sodium chloride and potassium chloride mixed salt obtained in Step 6 is dissolved in the first filtrate obtained in Step 1.

[0080] Step 8: The second filter cake from step 3 is first subjected to hydrochloric acid reaction to remove calcium carbonate and heavy metal oxides from the filter cake, and then filtered. The remaining filter cake mainly contains calcium sulfate dihydrate, silicon dioxide, some iron and aluminum, and a small amount of dioxins. It is then sent to a cement kiln for co-treatment, high-temperature detoxification, or hydrothermal detoxification.

[0081] The calcium carbonate obtained by this process has a purity of 98.27%, a whiteness of 93.1%, an average particle size of 7.16 μm, a sedimentation volume of 2.45 mL / g, and a crystal form of agglomerates of calcite and vaterite, meeting the quality requirements of light calcium carbonate.

[0082] Example 3

[0083] The waste incineration fly ash reduction and resource utilization treatment method of this embodiment specifically includes the following steps:

[0084] Step 1: 1 ton of fly ash (chloride ion content 17.45%, SiO2 4.56%, Al2O3 1.37%, Fe2O3 0.66%, CaO 36.37%, MgO 1.12%, sodium ion 7.3%, potassium ion: 4.95%, S content 1.76%, and other small amounts of zinc, copper, lead, nickel and other elements) and 2.4 tons of water are added to a first water washing and filtering device for slurry washing. After washing, the filter cake is filtered and washed with 2 tons of water to obtain a washed filter cake weighing about 1.2 tons and a first filtrate weighing 1.8 tons. The filter cake contains about 39% water and a chloride ion content of 1.1%. The chloride ion content of the first filtrate is about 12.5%.

[0085] Step 2: The washed filter cake obtained in step 1 is reacted with 5 tons of 15% ammonium chloride solution. The reaction is carried out under normal pressure, the reaction temperature is 20-30°C, and the stirring speed is 220 rpm. The reaction formula is as follows: Ca(OH)2+2NH4Cl——>CaCl2+2NH3↑+2H2O

[0086] The reaction end point pH is between 8 and 12.2, and a reaction product is obtained;

[0087] Step 3: Filtering the reaction product obtained in step 2 to obtain a second filter cake and a second filtrate, wherein the second filter cake weighs approximately 520 kg, has a moisture content of 30%, and contains approximately 2.9% chloride ions. After washing the second filter cake with 450 kg of water, the chloride ion content in the filter cake is 0.9%. The washing liquid is mixed with the second filtrate to obtain approximately 6.5 tons of a first mixed liquid;

[0088] Step 4: stripping and deammoniating the first mixed solution in step 3 to obtain 1600 kg of 10% ammonia water and deammoniated mother liquor, and introducing 440 kg of carbon dioxide into the ammonia water for carbonization to obtain 2040 kg of ammonium bicarbonate solution.

[0089] Ammonium bicarbonate solution reacts with deamination mother liquor to generate calcium bicarbonate solution. The reaction temperature is controlled within 20℃. The reaction formula is as follows: CaCl2+2NH4HCO3——>Ca(HCO3)2+2NH4Cl

[0090] Then microwave heating is performed. When the solution temperature exceeds 60 degrees, calcium carbonate precipitation begins to appear. The reaction is carried out under normal pressure, the reaction temperature is 70-80 degrees, and the stirring speed is 600-800 rpm. The specific reaction is as follows: Ca(HCO3)2-microwave heating->CaCO3↓+H2O+CO2↑

[0091] Step 5: The reaction product obtained in step 4 is filtered to obtain a third filtrate and a third filter cake. The third filter cake weighs approximately 660 kg, has a moisture content of approximately 25%, and contains 1.8% chloride ions. The third filter cake is washed with 3.0 tons of water to obtain a calcium carbonate filter cake and a second washing liquid. The chloride ion content of the calcium carbonate filter cake is approximately 0.08%. The second washing liquid is membrane concentrated 12-fold, and 250 kg of the concentrated liquid is mixed with the third filtrate to obtain a second mixed liquid. The mixed liquid weighs approximately 6.22 tons. The calcium carbonate filter cake is dried, packaged, and sold.

[0092] Step 6: The second mixed liquid is split, wherein about 80% continues to go to the reactor in step 2 for further reaction, and about 20% is pre-treated and then evaporated and crystallized to obtain ammonium chloride crystals and sodium chloride and potassium chloride mixed salt crystals respectively;

[0093] Step 7: The ammonium chloride crystals obtained in Step 6 are dissolved in the remaining second mixed solution to prepare an ammonium chloride solution. The mass fraction of the ammonium chloride solution is now 14.8%, the mass is 5.09 tons, and the ammonium chloride loss is 1.3%. The prepared ammonium chloride solution is circulated back to the reactor in Step 2 to continue the reaction. The sodium chloride and potassium chloride mixed salt obtained in Step 6 is dissolved in the first filtrate obtained in Step 1.

[0094] Step 8: subjecting the second filter cake from step 3 to high-temperature sintering to decompose dioxins and render them harmless;

[0095] Step 9: The first filtrate is added to a reaction device for pretreatment, sodium carbonate or sodium sulfate is added for reaction, and calcium and magnesium ions are removed from the first filtrate after filtering by the first water washing and filtering device. The remaining first filtrate is mainly composed of sodium chloride and potassium chloride, which serves as the pretreated filtrate. The pretreated filtrate is added to a crystallization and salt separation device for evaporation and crystallization to obtain 224kg of sodium chloride crystals that meet the standards (sodium chloride content is greater than 95%). It is then cooled and crystallized to obtain 102kg of potassium chloride crystals that meet the standards (potassium chloride content is greater than 92%).

[0096] Figure 7 is a TEM image of the calcium carbonate prepared in this example. The calcium carbonate in this example has a purity of 98.8%, a whiteness of 93.9%, and an average particle size of 0.16 μm.

Claims

1. A method for reducing and recycling fly ash from garbage incineration, characterized in that: The following steps are involved: Step 1, washing and filtering the fly ash to obtain a first filter cake and a first filtrate; Step 2, placing the first filter cake obtained in step 1 in a reactor, adding ammonium chloride mother solution into the reactor, reacting, the reaction end point pH is 8-12.2, and obtaining a reaction product; Step 3: Filter the reaction product obtained in step 2 to obtain a second filter cake and a second filtrate, wash the second filter cake with water to obtain a first washing liquid, and mix the second filtrate with the first washing liquid to obtain a first mixed liquid; Step 4: using the first mixed solution obtained in step 3 as a raw material, reacting to prepare calcium carbonate; Step 5: Filter the reaction product obtained in step 4 to obtain a third filtrate and a third filter cake, wash the third filter cake with water to obtain calcium carbonate and a second washing liquid, and mix the second washing liquid with the third filtrate to obtain a second mixed liquid; Step 6: split the second mixed solution, evaporate and crystallize a portion of the second mixed solution to obtain ammonium chloride crystals, dissolve the ammonium chloride crystals in the remaining second mixed solution to prepare an ammonium chloride solution, and control the amount of the second mixed solution used for evaporation, crystallization and salt separation so that the concentration and quality of the prepared ammonium chloride solution are substantially the same as the concentration and quality of the ammonium chloride mother liquor added in step 2, and add the prepared ammonium chloride solution to the reactor in step 2 for recycling.

2. The method for reducing and recycling fly ash from waste incineration according to claim 1 is characterized in that: In step 1, the mass fraction of calcium oxide in the fly ash is 20-50wt%, the mass ratio of fly ash to water is 1:1-10, and the chloride ion content in the first filter cake obtained after washing is less than 3wt%.

3. The method for reducing and recycling fly ash from waste incineration according to claim 1 or 2, characterized in that: In step 2, the concentration of the ammonium chloride mother solution is 1-30wt%, and the mass ratio of the first filter cake to the ammonium chloride solution is 1:2-20.

4. The method for reducing and recycling fly ash from waste incineration according to claim 1 or 2, characterized in that: In step 4, the first mixed solution obtained in step 3 is used as a raw material to react, and the technical solution used to prepare calcium carbonate includes: Solution 1: directly introducing carbon dioxide into the first mixed solution to perform a carbonization reaction to generate calcium carbonate precipitation; Scheme 2: stripping the first mixed liquid to remove ammonia to obtain aqueous ammonia and deammoniation mother liquor, and simultaneously introducing carbon dioxide and aqueous ammonia into the deammoniation mother liquor to react and generate calcium carbonate precipitate; Scheme 3: stripping and deammoniating the first mixed liquid to obtain aqueous ammonia and deammoniation mother liquor, wherein the aqueous ammonia is firstly carbonized into an ammonium carbonate solution, and the ammonium carbonate solution and the deammoniation mother liquor undergo a double decomposition reaction to generate calcium carbonate precipitation; Scheme 4: 50% of the first mixed liquid is stripped to remove ammonia to obtain ammonia water and deammoniation mother liquor, the ammonia water is first carbonized into ammonium bicarbonate solution, and the remaining first mixed liquid and deammoniation mother liquor are mixed and then subjected to double decomposition reaction with the ammonium bicarbonate solution to generate calcium carbonate precipitation; Scheme 5: The first mixed liquid is stripped and deaminated to obtain ammonia water and deammoniation mother liquor. The ammonia water is first carbonized into ammonium bicarbonate solution. The ammonium bicarbonate solution reacts with the deammoniation mother liquor to generate calcium bicarbonate solution. The calcium bicarbonate solution is heated or microwaved to decompose to prepare calcium carbonate precipitation.

5. The method for reducing and recycling fly ash from waste incineration according to claim 4 is characterized in that: When calcium carbonate is prepared by scheme 1, the molar ratio of the introduced carbon dioxide to the calcium ions in the solution is 1:1.0-1.1, the reaction temperature is 0-90°C, the reaction residence time is more than 3 hours, and the reaction speed of the stirred tank is 60-600rpm.

6. The method for reducing and recycling fly ash from waste incineration according to claim 4 is characterized in that: When calcium carbonate is prepared using scheme 2, the molar ratio of carbon dioxide introduced during the reaction to calcium ions in the solution is 1:1.0-1.1, the reaction temperature is 0-90°C, the reaction residence time is controlled at 30-180min, and the stirring speed of the reactor is 60-600rpm.

7. The method for reducing and recycling fly ash from waste incineration according to claim 4 is characterized in that: When calcium carbonate is prepared using scheme three, the molar ratio of ammonia water to carbon dioxide in the carbonization reaction is 1:2; the reaction temperature of the double decomposition reaction is 0-90°C, the reaction residence time is controlled at 30-120min, and the stirring speed of the reactor is 60-600rpm.

8. The method for reducing and recycling fly ash from waste incineration according to claim 4 is characterized in that: When calcium carbonate is prepared by scheme 4, the molar ratio of aqueous ammonia to carbon dioxide in the carbonization reaction is 1:1.0-1.1; the reaction temperature of the double decomposition reaction is 0-90°C, the reaction residence time is controlled at 30-180min, and the stirring speed of the reactor is 60-600rpm.

9. The method for reducing and recycling fly ash from waste incineration according to claim 4, characterized in that: When calcium carbonate is prepared by scheme five, the molar ratio of aqueous ammonia to carbon dioxide in the carbonization reaction is 1:1.0-1.1; the temperature of the reaction of the ammonium bicarbonate solution and the deammoniation mother liquor is controlled within 20°C; the reaction temperature of the heating decomposition or microwave decomposition is controlled at 60-99°C, and the stirring speed of the reactor is 60-600rpm.

10. The method for reducing and recycling fly ash from waste incineration according to any one of claims 5 to 9, characterized in that: The output of calcium carbonate produced from 1 ton of fly ash is more than 400 kg, the whiteness of calcium carbonate is more than 92%, the purity is more than 98%, and the average particle size is 0.1-25 microns.

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