Separation and recovery method and system for metal resources in solid waste incineration fly ash

Abstract

The invention provides a separation and recovery method and system for metal resources in solid waste incineration fly ash. The separation and recovery method comprises the steps that S1, the solid waste incineration fly ash and an additive are mixed for pretreatment, and a mixture is obtained; s2, taking inorganic salt, placing the inorganic salt in a first-stage molten salt tank, heating the inorganic salt to a molten state, adding the mixture into the first-stage molten salt tank, adding an oxygen ion donor to extract K / Na salts, overflowing excessive molten salt in the first-stage molten salt tank into a second-stage molten salt tank along with the reaction, and discharging bottom residues into the second-stage molten salt tank; s3, an oxygen ion remover is added into the second-stage molten salt pond to extract heavy metal substances, excessive molten salt in the second-stage molten salt pond overflows to a molten salt bin, and a molten salt product is obtained; and S4, the molten salt product is cooled and then dissolved in water, the pH value of the solution is regulated and controlled, multi-metal mud sediment and salt-containing filtrate are obtained through filtering, and resource recycling is completed through reasonable treatment. On the basis of ensuring harmlessness of the fly ash, cascade directional separation is carried out on fly ash metal resources based on molten salt oxygen ion concentration regulation and control, and extraction and recovery of fly ash metal are achieved.

Description

Technical Field

[0001] This invention relates to the field of incineration fly ash resource recovery technology, and in particular to a method and system for separating and recovering metal resources from solid waste incineration fly ash. Background Technology

[0002] Solid waste incineration fly ash, due to its enrichment in heavy metals, high chloride content, and toxic dioxins (PCDD / Fs), poses a serious threat to ecological security and public health. It is listed as hazardous waste (HW18) in the National Hazardous Waste List and urgently requires harmless treatment. However, the metal resources in fly ash, such as sodium and potassium soluble chlorides (20–30 wt%) and heavy metals (Pb, Cd, Cu, Zn, Cr ≈ 2 wt%), also possess resource-related attributes and have the potential for high-value recycling. Therefore, the current treatment and disposal of solid waste incineration fly ash must consider both harmlessness and resource recovery.

[0003] Among existing fly ash treatment technologies, patent CN118122757A proposes a fly ash chelation and solidification treatment system and device, which achieves fly ash detoxification, but does not recover fly ash metal resources; patent CN113401923A proposes a method and system for the co-treatment of hazardous waste incineration wet deacidification and fly ash washing, which achieves the recovery of potassium and sodium salts, but cannot remove dioxin pollutants from the ash; patent CN113477668A proposes a centralized fly ash high-temperature melting vitrification utilization system and method, which, to some extent, simultaneously achieves the harmlessness and resource utilization of fly ash, but the required temperature is too high, the energy consumption is too large, the flue gas purification cost is high, and the phase change energy consumption of metal salt volatilization leads to a large energy cost, which does not conform to the principle of low consumption and energy saving, and needs to be improved.

[0004] As can be seen from the above, most existing technologies only focus on one aspect of the harmlessness or resource utilization of fly ash, or they incur high energy costs in order to achieve both aspects in a coordinated manner. Few inventions have disclosed fly ash disposal technologies that integrate the principles of harmlessness, resource utilization and energy conservation.

[0005] The inventors previously proposed a molten salt thermal treatment method for fly ash from waste incineration (patent CN106378352A), which initially proposed the concept and idea that molten salt can extract heavy metals from fly ash. However, since the reaction behavior between fly ash and molten salt is not yet clear, patent CN106378352A did not specify the specific control method for the dissolution of fly ash metals into molten salt, nor did it provide process steps for further recovery of metals dissolved in molten salt. Based on this, this patent application is filed. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art and provide a method and system for separating and recovering metal resources in solid waste incineration fly ash. On the basis of ensuring the harmlessness of fly ash, the invention uses the concentration regulation of oxygen ions in molten salt to perform tiered and directional separation of metal resources in fly ash, thereby realizing the extraction and recycling of metal resources in solid waste incineration fly ash.

[0007] This invention provides the following technical solution:

[0008] This invention provides a method for separating and recovering metal resources from solid waste incineration fly ash, comprising the following steps:

[0009] S1. Solid waste incineration fly ash and additives are mixed to obtain a first mixture, and the first mixture is pretreated to obtain a second mixture, wherein the additives are substances rich in silicon and aluminum components;

[0010] S2. Take inorganic salt and place it in the primary molten salt pool and heat it to a molten state. Continuously add the second mixture to the molten salt pool, and then add oxygen ion donor to extract K / Na salts from fly ash. As the reaction proceeds, excess molten salt in the primary molten salt pool overflows into the secondary molten salt pool, and the residue at the bottom of the primary molten salt pool is also discharged into the secondary molten salt pool.

[0011] S3. Add oxygen ion removal agent to the secondary molten salt tank to extract heavy metals from fly ash. As the reaction proceeds, excess molten salt in the secondary molten salt tank overflows into the molten salt chamber to obtain molten salt products. The residue at the bottom of the secondary molten salt tank is discharged and can be collected for building material utilization.

[0012] S4. After the molten salt product is cooled and crushed, it is dissolved, the pH value of the solution is adjusted to 9-11, and the polymetallic mud precipitate and salt filtrate are obtained by filtration, thus completing the resource recovery.

[0013] Furthermore, the additive comprises one or more combinations of waste incineration bottom ash, coal slag, fly ash, crushed glass, or granite; the additive accounts for 5% to 40% of the total mass of the first mixture.

[0014] Furthermore, the pretreatment steps include crushing and grinding, mixing and homogenizing, and dry granulation.

[0015] Furthermore, the mass of the added oxygen ion donor and oxygen ion remover is determined according to the quantitative criteria for metal resource separation and regulation.

[0016] Quantitative criteria for metal resource separation and control: A sample of the second mixture is taken for component analysis. The mass of the second mixture of solid waste incineration fly ash and additives is determined to be M. The mass concentrations of SiO2, Al2O3, CaO, Pb, Zn, Cu, Cd, and Cr are determined to be A, B, C, D, E, F, G, and H, respectively, and the molar concentrations are determined to be a, b, c, d, e, f, g, and h, respectively. The mass of added oxygen ion donor is set to X, and the molar concentration is set to x. Let the mass of the particle removal agent be Y, and its molar concentration be y. Calculations based on the molar concentration of the chemical reaction yield x = a + bc, therefore X = 56M(a + bc) = 56M(A / 60 + B / 102 - C / 56). Calculations based on the molar concentration of the chemical reaction yield y = 2(d + e + f + g + h), therefore Y = 53.5M × 2(d + e + f + g + h) = 107M(D / 207.2 + E / 65.4 + F / 63.5 + G / 112.4 + H / 52).

[0017] Furthermore, in inorganic salts, metal cations include Li + Na + K + Ca 2+ Mg 2+ Zn 2+ Pb 2+ Cu 2+ One or more of the following, wherein the anion contains Cl - It also includes SO4 2- CO3 2- OH - SO3 2- One or more of the following; the added mass m of the inorganic salt satisfies the condition that the height of the liquid molten salt surface does not exceed the height of the molten salt overflow port.

[0018] Furthermore, the temperature of the primary molten salt pool is 600–1300°C, and the temperature of the secondary molten salt pool is the same as that of the primary molten salt pool.

[0019] Furthermore, the oxygen ion donor is an alkaline earth metal oxide, and the oxygen ion donor is pretreated by one of the following methods before addition: high-energy ball milling, surfactant dispersion, or elemental doping to enhance the reactivity.

[0020] Furthermore, the oxygen ion remover is an HCl / Cl2 precursor, and the oxygen ion remover undergoes one of the following pretreatments before addition: pre-drying, mechanical crushing, sieving and grading, or spray granulation to enhance its reactivity.

[0021] Furthermore, in step S4, the ratio of the mass of the solution to the mass of the added molten salt product is (3-20):1.

[0022] This invention also provides a system for separating and recovering metal resources from fly ash in solid waste incineration used in the above method. The separation and recovery system includes a primary molten salt pool, a secondary molten salt pool, a molten salt chamber, a primary solution pool, a secondary solution pool, and a residue pool. The primary molten salt pool has a first overflow trough on its side wall and a first slag discharge port at its bottom. The first overflow trough and the first slag discharge port are respectively connected to the secondary molten salt pool through pipes. The secondary molten salt pool has a second overflow trough on its side wall and a second slag discharge port at its bottom. The second overflow trough is connected to the molten salt chamber through pipes. Each pipe is equipped with a heating device. The residue pool is located below the second slag discharge port. The primary solution pool and the secondary solution pool are arranged sequentially below the molten salt chamber.

[0023] The present invention has the following beneficial effects:

[0024] 1. This invention enables the recovery and utilization of various metal resources in fly ash by adding an oxygen ion donor to the primary molten salt pool to suppress the alkali metal K in the molten salt. + / Na + The fixed precipitation reaction makes K + / Na + The heavy metal oxides are fully incorporated into the molten salt for recovery. By adding an oxygen ion removal agent to the secondary molten salt tank, the equilibrium of the chlorination and dissolution reaction is shifted to the positive direction, promoting the transfer of heavy metals such as Pb / Zn / Cu / Cd / Cr from fly ash to the molten salt. The molten salt product, after treatment, yields polymetallic sludge precipitates containing heavy metals and potassium-containing... + / Na + The filtrate, after proper treatment, can enable the recovery and utilization of metal resources in fly ash.

[0025] 2. Based on the reaction characteristics of fly ash and molten salt, this invention creatively proposes a method for the directional separation of fly ash metal resources based on the regulation of oxygen ion concentration in molten salt. This method is a fly ash disposal method that integrates harmlessness, cascaded resource recovery and low energy consumption. This method can promote the dissolution of fly ash metal resources into molten salt to a great extent, and provides specific process steps for further recovery and full resource utilization of the metal resources dissolved in molten salt. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of the metal resource separation and recovery system in solid waste incineration fly ash of the present invention;

[0028] Figure 2 The reaction mechanism of K in fly ash in molten salt during the recycling process of this invention is as follows: (a) K after multiple treatments of fly ash with molten salt + (b) Content changes; (c) Content of insoluble K after the additive reacts with NaCl-KCl molten salt;

[0029] Figure 3 To illustrate the inhibitory effect of CaO on the potassium fixation reaction during the recovery process of this invention: (a) calculation of potassium content loss and benefits after adding CaO; (b) XRD pattern of the reaction slag after adding CaO;

[0030] Figure 4 The extraction effect of molten salt on heavy metals in fly ash during the recycling process of this invention is shown in the following figures: (a) changes in heavy metal content after multiple treatments of fly ash with molten salt; (b) extraction ratio of heavy metals from fly ash by molten salt.

[0031] Figure 5 The content distribution of heavy metals in slag and molten salt under different oxygen ion concentrations: (a) the distribution ratio of each heavy metal; (b) the average distribution ratio.

[0032] Figure 6 The following are SEM images (magnification 2000x) of the materials at each stage of the recycling process of this invention: (a) fly ash from waste incineration; (b) additives (fly ash); (c) molten slag after conventional molten salt heat treatment; (d) molten slag after conventional molten heat treatment. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention provides a method for separating and recovering metal resources from solid waste incineration fly ash, comprising the following steps:

[0035] S1. Solid waste incineration fly ash and additives are mixed to obtain a first mixture, and the first mixture is pretreated to obtain a second mixture, wherein the additives are substances rich in silicon and aluminum components;

[0036] S2. Take inorganic salt and place it in the primary molten salt pool and heat it to a molten state. Continuously add the second mixture to the molten salt pool, and then add oxygen ion donor to extract K / Na salts from fly ash. As the reaction proceeds, excess molten salt in the primary molten salt pool overflows into the secondary molten salt pool, and the residue at the bottom of the primary molten salt pool is also discharged into the secondary molten salt pool.

[0037] S3. Add oxygen ion removal agent to the secondary molten salt tank to extract heavy metals from fly ash. As the reaction proceeds, excess molten salt in the secondary molten salt tank overflows into the molten salt chamber to obtain molten salt products. The residue at the bottom of the secondary molten salt tank is discharged and can be collected for building material utilization.

[0038] S4. After the molten salt product is cooled and crushed, it is dissolved, the pH value of the solution is adjusted to 9-11, and the polymetallic mud precipitate and salt filtrate are obtained by filtration, thus completing the resource recovery.

[0039] The metallic elements in fly ash include major elements K and Na, as well as trace heavy metals such as Pb, Zn, Cu, Cd, and Cr. These metallic elements generally have high value, and it is necessary to separate and extract them to achieve the resource-based recycling of high-value components from fly ash.

[0040] In the process of fly ash molten salt heat treatment, this method regulates the oxygen ion concentration in the molten salt at different steps to separate metal resources from the fly ash and directionally migrate them to the molten salt phase in layers for further recovery.

[0041] Molten salt heat treatment allows organic pollutants such as dioxins in fly ash to undergo thermal decomposition, thus rendering the fly ash harmless. Furthermore, in a molten salt environment, alkali metal salts (such as chloride / sulfate salts containing K / Na) in the fly ash are extracted through direct dissolution, dissociating into cations and anions (K... + Na + Cl - (etc.) enter the molten salt, however, some of the K in the molten salt + / Na + The K / Na alkali metals in fly ash and additives are fixed as K / Na-Si-Al insolubles (such as KAlSi2O6, KAlSi3O8, etc.) and precipitate out as solid residues, causing unfavorable K / Na alkali metal loss. Therefore, it is necessary to add oxygen ion donors (such as CaO), which combine with the Si / Al components to form Ca-Si-Al insolubles (such as Ca2Al2SiO7, CaSiO3, CaAl2O4, etc.), thus inhibiting the K in the molten salt. + / Na + On the one hand, the fixed precipitation reaction occurs, and on the other hand, the reaction with the existing K / Na-Si-Al insoluble matter in the residue displaces the fixed potassium / sodium ions and releases them into the molten salt; in step S2, by adding an oxygen ion donor, the fixed loss reaction of potassium / sodium ions is suppressed, and the recovery of alkali metal resources in fly ash is promoted.

[0042] In the primary molten salt pool, the second mixture gradually settles to the bottom of the molten salt under the influence of density difference and gravity. Heavy metals (Pb / Zn / Cu / Cd / Cr, etc.) in the fly ash are discharged into the secondary molten salt pool along with the residue at the bottom of the primary pool. Heavy metals in fly ash mainly exist in the form of oxides and chlorides. In the molten chloride environment, heavy metal oxides are almost insoluble (forming precipitates), while heavy metal chlorides dissolve (dissociating into ions). Furthermore, heavy metal oxides and chlorides can interconvert: heavy metal oxides undergo chlorination under the direct or indirect action of molten chloride, becoming chlorides that dissolve in the molten salt; while heavy metal chlorides react with O in the molten salt. 2- Ions combine and transform into oxides that precipitate in the residue. The oxygen ion concentration in molten salt is an important parameter for measuring the degree of interconversion between the two types of compounds. The chlorination and precipitation reactions of heavy metals in molten salt reach equilibrium at a certain oxygen ion concentration. The lower the oxygen ion concentration, the less heavy metal oxide is formed, and the more heavy metal chloride is formed, meaning the higher the content of the heavy metal to be recovered in the molten salt phase. Therefore, adding an oxygen ion removal agent, which reacts with O... 2- The combination of these compounds into H2O volatilizes, reducing the oxygen ion concentration in the molten salt and shifting the equilibrium of the chlorination dissolution reaction of heavy metal oxides to the positive side, thereby promoting the transfer of heavy metals from fly ash to the molten salt.

[0043] This method achieves tiered and targeted separation of fly ash metal resources by controlling the oxygen ion concentration in molten salt, resulting in more complete recovery. The recovered molten salt product contains alkali metals K / Na and trace heavy metals Pb / Zn / Cu / Cd / Cr. After dissolving the molten salt product, the pH of the solution is adjusted to 9–11, converting the heavy metals in the molten salt product into precipitates that accumulate on small slag particles, forming a multi-metal sludge resource. Filtration captures this multi-metal sludge with a certain grade of resource recovery. The filtrate mainly consists of inorganic salts such as NaCl and KCl, which can be further utilized for resource recovery.

[0044] See Figure 1 The present invention also provides a separation and recovery system used in conjunction with a method for separating and recovering metal resources in fly ash from solid waste incineration. The system includes a primary molten salt pool, a secondary molten salt pool, a molten salt chamber, a primary solution pool, a secondary solution pool, and a residue pool. The primary molten salt pool has a first overflow trough on its side wall and a first slag discharge port at its bottom. The first overflow trough and the first slag discharge port are respectively connected to the secondary molten salt pool through pipes. The secondary molten salt pool has a second overflow trough on its side wall and a second slag discharge port at its bottom. The second overflow trough is connected to the molten salt chamber through pipes. Each pipe is equipped with a heating device. The residue pool is located below the second slag discharge port. The primary solution pool and the secondary solution pool are arranged sequentially below the molten salt chamber.

[0045] The present invention will be further illustrated below through specific embodiments:

[0046] Combination Figure 1 The apparatus shown is used in this embodiment for the separation and recovery of metal resources from solid waste incineration fly ash. The steps are as follows:

[0047] (1) Mix solid waste incineration fly ash with additives to obtain a first mixture, and perform pretreatment to obtain a second mixture;

[0048] Solid waste incineration fly ash can be one or more of the following substances: municipal solid waste incineration fly ash, hazardous waste (such as medical waste) incineration fly ash. Additives are additional substances added to aid in fly ash disposal, characterized by being rich in silica and aluminum components, and can be one or more of the following substances: waste incineration bottom ash, coal ash, fly ash, broken glass, granite, etc.; the additive's mass percentage of the total mixture can be 5% to 40%.

[0049] The purpose of pretreatment is to facilitate subsequent reaction with molten salt. The following methods can be used:

[0050] Mechanical crushing and grinding (increasing specific surface area): For blocky additives such as waste glass and granite, coarse crushing can be used first, employing a jaw crusher or hammer crusher to crush the blocky additives to a particle size ≤2mm. For fly ash and small-particle additives, fine grinding can be used, employing a dry ball mill or vertical roller mill to grind them to a particle size ≤50μm (approximately 300 mesh), with a ball milling time of approximately 2–3 hours and a rotation speed of approximately 200–350 rpm. If the average particle size of the fly ash and additives is already ≤50μm, this step is not necessary.

[0051] Homogenization (uniform distribution of components): Use mixing methods such as stirring, oscillation, and tumbling. For example, a double cone mixer or a three-dimensional motion mixer can be used. The mixing time is about 30 to 60 minutes, and the mixer speed is about 10 to 20 rpm. The uniformity of mixing is judged by the coefficient of variation (CV) (≤5%). 0.5% to 1% of nano-silica or fumed alumina can be added as a dispersant to improve particle dispersibility.

[0052] Dry granulation (easily sinks to the bottom of molten salt after molding): Considering the subsequent high-temperature environment and safety, an organic binder (such as carboxymethyl cellulose CMC, added at 0.5% to 1%) is used. Roller granulation (flake particles) or rolling granulation (spherical particles) is used to form 1 to 3 mm molded particles from the mixture of fly ash and additives, which is helpful for the subsequent molten salt reaction.

[0053] To determine the quality of the subsequently added oxygen ion donor and oxygen ion remover, the quality was determined according to the quantitative criteria for metal resource separation and control.

[0054] The quantitative criteria for metal resource separation and control are as follows: A sample of the second mixture is taken for component analysis. The mass of the second mixture of solid waste incineration fly ash and additives is determined to be M. The mass concentrations of SiO2, Al2O3, CaO, Pb, Zn, Cu, Cd, and Cr are determined to be A, B, C, D, E, F, G, and H, respectively, and the molar concentrations are determined to be a, b, c, d, e, f, g, and h, respectively. The mass of the added oxygen ion donor is set to X, and the molar concentration to be x. The mass of the added oxygen ion remover is set to Y, and the molar concentration to be y. X and Y are obtained through chemical reaction molar calculations.

[0055] The specific process is as follows: The methods for analyzing the elemental or component content of the mixture of fly ash and additives include: using X-ray fluorescence spectrometry (XRF) to analyze the elemental composition; or, after digestion, using inductively coupled plasma mass spectrometry (ICP-MS) or ion chromatography (IC) to analyze the specific component content.

[0056] ① Determine the mass of the mixture of solid waste incineration fly ash and additives as M, where the mass concentrations of SiO2, Al2O3, and CaO are A, B, and C, respectively, and the molar concentrations are a, b, and c, respectively. The K / Na content in the solid mixture and molten salt is significantly higher than the Si / Al content (i.e., the Si / Al component can react completely with K / Na under unimpeded conditions). The molar concentration and mass of CaO to be added to hinder the alkali metal fixation reaction are x. When CaO reacts with the Si / Al component, the complex Ca2Al2SiO7 (i.e., 2CaO·Al2O3·SiO2) is preferentially formed, followed by CaSiO3 (i.e., CaO·SiO2) or CaAl2O4 (i.e., CaO·Al2O3), etc. Through chemical reaction molar calculation, we get x = a + bc, therefore X = 56M(a + bc) = 56M(A / 60 + B / 102 - C / 56). If the amount of CaO added is greater than this value, more stable forms such as Ca2SiO4 and Ca3Al2O6 may be generated. If a+b≤c, then no additional oxygen ion donor such as CaO is needed. ② The mass of the mixture of fly ash and additives is M, where the mass concentrations of heavy metals Pb / Zn / Cu / Cd / Cr are D, E, F, G, and H, respectively, and the molar concentrations are d, e, f, g, and h, respectively. In the previous steps, most of the heavy metals in the fly ash are converted into oxides and precipitated in the residue under the action of oxygen ions in the molten salt. The molar concentration and mass of the oxygen ion removal agent NH4Cl to be added to promote chlorination are y. NH4Cl decomposes into NH3 and HCl in the high-temperature molten salt, which will promote the heavy metal oxides to undergo the following reaction (with Me representing the metal): MeO + 2HCl = MeCl2 + H2O. Based on the molar calculation of the chemical reaction, we can obtain y = 2(d + e + f + g + h), therefore Y = 53.5M·2(d + e + f + g + h) = 107M(D / 207.2 + E / 65.4 + F / 63.5 + G / 112.4 + H / 52).

[0057] During the reaction, the second mixture (containing fly ash) is continuously added, which enables material transfer from the primary to the secondary molten salt pool, as well as continuous feeding and discharging, thereby improving fly ash disposal efficiency. Since the reaction needs to be continuous, oxygen ion donors and oxygen ion removers are also continuously added. In the above calculation, M refers to the mass of the mixture added per unit time (which can be measured in seconds or minutes), and the calculated X and Y results are also the amount added per unit time.

[0058] (2) Feed the inorganic salt into the primary molten salt pool and heat it to a molten state. Add the second mixture into the primary molten salt pool and add oxygen ion donors to the primary molten salt pool.

[0059] In inorganic salts, metal cations may include one or more of the following ions: Li + Na +K + Ca 2+ Mg 2+ Zn 2 + Pb 2+ Cu 2+ Common cations; inorganic anions must contain chloride ions (Cl). - In addition, it may contain one or more of the following ions: SO42- 2- CO3 2- OH - SO3 2- Common anions, etc. The mass m of the added inorganic salt must meet the requirement that the liquid molten salt level does not exceed the height h of the molten salt overflow port, i.e., m / (ρ 熔盐 S 底 )≤h.

[0060] The feeding rate of the fly ash and additive mixture needs to be determined based on factors such as process scale and actual operating conditions. The average density of the mixture is approximately 2.3–2.8 g / cm³. 3 The average density of molten salt is approximately 1.5–1.8 g / cm³. 3 Therefore, due to density differences, the mixture generally settles at the bottom of the molten salt; however, a small portion of the ash with lower density remains suspended in the molten salt. During the heat treatment process, fly ash undergoes inorganic reactions such as salt dissolution, heavy metal separation and extraction, and potassium / sodium ion fixation and precipitation, as well as thermal decomposition reactions of organic pollutants such as dioxins, to achieve the harmlessness of fly ash. The dissolution of fly ash chlorides continuously replenishes the molten salt medium, eliminating the need for additional salt addition and achieving "self-sufficiency."

[0061] The heat treatment temperature of the primary molten salt pool can be 600–1300℃. The fly ash residue at the bottom will exhibit different reaction behaviors at different heat treatment temperatures: when subjected to mild heat treatment at 600–900℃, the fly ash residue is solid and can be rendered harmless, but the gaps between the residue particles are relatively large and the density is low; when subjected to sintering heat treatment at 900–1100℃, the fly ash residue is solid and can be rendered harmless, and its fine particles undergo sintering and agglomeration, increasing the density; when subjected to melting heat treatment at 1100–1300℃, the fly ash residue melts into a liquid state, can be rendered harmless, and forms a high-quality glassy body with a very high density.

[0062] The specific heat treatment temperature of the primary molten salt pool can be determined according to the actual process conditions. See 6(c) for mild molten salt heat treatment slag, where the molten salt pool temperature is 600-900℃. Although it achieves harmlessness, the residue particles have large gaps and low density, and can only be used for building materials such as cement and roadbeds. Figure 6(d) is the molten slag from heat treatment at a temperature of 1100 to 1300℃. At this temperature, the fly ash residue melts into a liquid state, forming a high-quality glass with a high degree of density, which is used in building materials such as microcrystalline glass, rock wool, and ceramics.

[0063] Oxygen ion donors can be alkaline earth metal oxides, specifically CaO or MgO, and under certain conditions, O2. The inhibitory effect of oxygen ion donors on the loss of alkali metal K / Na is mainly achieved through two aspects: firstly, they combine with Si / Al components to form insoluble substances, occupying reaction sites and inhibiting the loss of K in the molten salt. + / Na + On the one hand, it undergoes a fixed precipitation reaction; on the other hand, it reacts with the existing K / Na-Si-Al insoluble matter in the residue, thereby fixing the K... + / Na + The waste is displaced and released into the molten salt. Simultaneously, most of the heavy metal ions in the molten salt may combine with oxygen ions to form oxides that precipitate into the residue. In summary, the primary molten salt pool serves to detoxify and render harmless the fly ash, and to control the loss of alkali metal salts in the fly ash and to recover its resources.

[0064] See Figure 2 , Figure 3 : Figure 2 The data demonstrate two reaction behaviors of potassium salts in fly ash under molten salt conditions: dissolution and enrichment, and fixation and loss. Figure 2 (a) demonstrates that potassium salts in fly ash are extracted by molten salt through direct dissolution, dissociate into anions and cations that enter the molten salt, and continuously accumulate and increase in content. Figure 2 (b) explains the presence of K in the molten salt. + The K will be fixed as K-Si-Al insoluble matter by the Si / Al components in fly ash and additives, precipitating out as solid residue, resulting in adverse K loss.

[0065] Figure 3 The data show that after adding oxygen ion donor CaO for regulation, the K in the molten salt... + The phenomenon that the fixed precipitation reaction is significantly inhibited. Figure 3 (a) shows the amount of K that is fixed in the molten salt after adding different amounts of CaO, reflecting the inhibitory effect of different proportions of CaO on the reaction. The optimal value of economic benefits was briefly calculated. Figure 3 (b) is the XRD characterization diagram of the slag after adding CaO, which shows that CaO combines with the Si / Al components of the additive to form Ca-Si-Al insoluble substances, such as Ca2Al2SiO7, CaSiO3, CaAl2O4, etc.

[0066] In preferred embodiments, to increase the reaction area, improve reaction activity, and accelerate the reaction rate, oxygen ion donors such as CaO and MgO can be pretreated using processes such as high-energy ball milling, surfactant dispersion, and element doping (selectable as needed). 1. High-energy ball milling: The oxygen ion donor is mixed with grinding media (such as zirconia balls) and placed in a high-energy ball mill for 1–2 hours at a speed of 300–500 rpm. This reduces the particle size to the nanometer scale and significantly increases the specific surface area. 2. Surfactant dispersion: The ball-milled oxygen ion donor is placed in a cationic surfactant solution (such as hexadecyltrimethylammonium bromide CTAB, concentration 0.1–0.5 wt%) and ultrasonically treated for 0.5–1 hour to further enhance the reactivity of the metal oxide. 3. Element doping: Dopant elements (such as Al, Ni, etc., 0–5%) can be introduced into the oxygen ion donor through co-precipitation or hydrothermal methods to form composite oxides (such as CaO-Al2O3). Doping increases the lattice distortion and active sites. 4. The oxygen ion donor is collected and thoroughly dried.

[0067] (3) As the reaction proceeds, excess molten salt in the primary molten salt pool overflows into the secondary molten salt pool, and the residue at the bottom of the primary molten salt pool is also discharged into the secondary molten salt pool;

[0068] In the continuous fly ash treatment process, the residence time of fly ash material in the primary molten salt tank needs to be 10–120 minutes. After the treatment effect is achieved, the molten salt and residue need to be transferred to the secondary molten salt tank. Molten salt can be overflowed into the secondary molten salt tank through the side discharge channel. Precautions include: the discharge channel needs to be blocked during overflow; the discharge channel needs to be equipped with a heating device to ensure the channel temperature is above the melting point of the molten salt (600–800℃). Residue can be transferred using one of the following methods: the discharge channel is inclined downwards at a certain angle, and the residue enters the secondary molten salt tank by gravity; pressure is applied to the primary molten salt tank to push the residue into the secondary molten salt tank; the secondary molten salt tank uses a pump or other method to achieve a vacuum negative pressure and suck in the residue. Note that the discharge channel also needs to be equipped with a heating device to ensure the high temperature of the residue.

[0069] The overall pressure in the secondary molten salt tank should be lower than that in the primary molten salt tank, while the temperature should be consistent with that of the primary molten salt tank. This can be achieved by pressurizing the primary molten salt tank or by using a pump to depressurize the secondary molten salt tank, ensuring that the overall gas pressure in the secondary molten salt tank is lower than that in the primary molten salt tank. This helps prevent flue gas products from the secondary molten salt tank from entering the primary molten salt tank and affecting its treatment efficiency. Furthermore, the heat treatment temperature in the secondary molten salt tank should be consistent with that in the primary molten salt tank, ranging from 600 to 1300°C; the reaction behavior of the fly ash residue at the bottom should also be consistent with that in the primary molten salt tank.

[0070] (4) Add oxygen ion removal agent to the secondary molten salt tank. As the reaction proceeds, excess molten salt in the secondary molten salt tank overflows into the molten salt chamber to obtain molten salt products. The residue at the bottom of the secondary molten salt tank is discharged.

[0071] The oxygen ion remover is an HCl / Cl2 precursor (a raw material for generating the target product HCl / Cl2). The inorganic component of the HCl / Cl2 precursor is mainly NH4Cl, and the organic component is chlorinated organic compounds such as PVC. In specific embodiments, it can be one of the following substances: NH4Cl, chlorinated organic compound PVC, or HCl / Cl2. The oxygen ion remover can react with O... 2- The reaction generates H2O or O2 which volatilizes, reducing the oxygen ion concentration in the molten salt and shifting the equilibrium of the chlorination reaction of heavy metal oxides to the positive side. This results in heavy metal ions dissolving into the molten salt, thus promoting the resource recovery of heavy metals from fly ash.

[0072] See Figure 4 , Figure 5 : Figure 4 The data shows that molten salt can continuously dissolve and extract heavy metals (mainly chlorides) from fly ash during long-term processing, and a considerable portion of heavy metals migrate from fly ash to molten salt. Figure 4 (a) and Figure 4 (b) The extraction amount and extraction ratio of heavy metals from fly ash by molten salt are shown respectively. It can be seen that there is still room for improvement in the extraction effect of heavy metals by molten salt without regulation.

[0073] In a molten salt environment, heavy metal oxides will undergo a chlorination reaction and dissolve into the molten salt, while heavy metal chlorides will react with O. 2- The heavy metal oxides and chlorides in the molten salt combine and precipitate into the slag, meaning that the heavy metal oxides and chlorides in the molten salt can interconvert and form oxides in a certain O2O2 environment. 2- The concentration reached distribution equilibrium. Figure 5 The data shows the distribution ratio of various heavy metals in the slag (oxide state) and molten salt (chloride state) under different oxygen ion concentrations (C1>C2>C3). It can be seen that the lower the oxygen ion concentration in the molten salt, the lower the content of heavy metals (oxides) in the slag, and the higher the content of heavy metals (chlorides) in the molten salt. Therefore, there are more heavy metals to be recovered in the molten salt liquid phase. Thus, removing oxygen ions from the molten salt can promote the dissolution and extraction of heavy metals from fly ash.

[0074] In a preferred embodiment, to enhance the reactivity of the solid oxygen ion remover (using NH4Cl as an example), pretreatment processes such as pre-drying, mechanical pulverization, sieving and classification, and spray granulation can be employed (selected as appropriate). 1. Pre-drying: Place NH4Cl in an oven at 80–100°C to thoroughly remove moisture from the raw material. 2. Mechanical pulverization: An air jet mill (pressure 0.6–0.8 MPa) or a ball mill (200–300 rpm) can be used, controlling the pulverization time to 30–60 min. 3. Sieving and classification: A vibrating sieve can be used to obtain particles with a target particle size of 10–50 μm. 4. Spray granulation: NH4Cl can be dissolved in deionized water to form a 10–20 wt% solution, which is then atomized using a centrifugal spray dryer at an inlet temperature of 150–180°C and an outlet temperature of 80–100°C. The resulting porous microspheres are collected for subsequent reactions.

[0075] The residence time of fly ash residue in the secondary molten salt tank needs to be 10–120 minutes. After treatment in the primary and secondary molten salt tanks, the fly ash residue has been desalinated, detoxified, and rendered harmless, and is classified as general solid waste. Furthermore, based on the heat treatment temperature of the molten salt tank and the morphological characteristics of the residue (… Figure 6 c. Figure 6 d) can determine the specific type of fly ash residue: salt-containing slag, sintered slag, molten glass slag, so as to carry out corresponding building material utilization.

[0076] (5) The molten salt product is cooled and crushed in the molten salt chamber and added to the primary solution tank to dissolve the salt product. The pH value of the solution is adjusted to 9-11, and the heavy metals in the molten salt product are converted into precipitates and enriched on small particulate slag to form a resource-based product, polymetallic mud. The polymetallic mud and filtrate are obtained by filtration and separation.

[0077] The initial liquid in the primary solution tank can be pure water. The ratio of the solution mass to the mass of the added molten salt product is (3-20):1. During this process, one or more of the following measures can be used to accelerate the dissolution rate of the salt product: heating (30-80℃), stirring, shaking, ultrasonication, microwave treatment, etc.

[0078] During molten salt heat treatment, some alkaline components such as CaO in fly ash dissolve in the molten salt, resulting in an aqueous solution of the salt product that is generally strongly alkaline with a pH above 12. Under this strongly alkaline environment, amphoteric metals such as Pb and Zn do not precipitate but instead form Pb(OH)4. 2- ZnO2 2- The ions exist in solution in various forms. Therefore, it is necessary to adjust the pH of the solution to 9-11 to make it weakly alkaline, so as to promote the conversion of heavy metals in the salt product into precipitates, which are then easier to collect. Dilute HCl is generally used as the pH adjuster (the anions in the molten salt product are mainly Cl-). -(Mainly dilute acid), but dilute HNO3, dilute H2SO4, etc. can also be used; the pH of the dilute acid solution should be 0-2, and the volume added depends on the situation. The pH of the solution must be adjusted to 9-11. In addition, the molten salt product contains a small amount of small particulate slag, and various heavy metals that precipitate will be enriched on it, eventually forming a resource-based product, polymetallic mud.

[0079] The mixture in the primary solution tank was then separated into solid and liquid phases using a filtration method with a filter membrane size of ≤0.45μm. After solid-liquid separation, the solid polymetallic sludge captured and collected by the filter membrane was a resource-based product of a certain grade, while the filtrate required further treatment.

[0080] (6) After filtration, the filtrate is passed into a secondary solution tank and the filtrate is properly disposed of to achieve resource utilization;

[0081] After removing impurities such as heavy metals and small particulate residues, the main components of the filtrate are inorganic salts such as NaCl and KCl. One of the following methods can be adopted to realize the resource utilization of salts: ① Electrolyze the salt-containing filtrate to dechlorinate and produce hydrogen to produce alkali (to obtain products such as H2, Cl2 and NaOH / KOH); ② Use a salt separation crystallization process to extract high-purity inorganic salts such as NaCl and KCl.

[0082] (7) Repeat the above fly ash treatment process to continuously achieve the harmlessness and resource utilization of fly ash.

[0083] The fly ash treatment system is generally a continuous operation, meaning that fly ash is continuously fed in, and molten salt and residue are continuously or intermittently discharged. During the process, fly ash salts continuously dissolve into the molten salt, replenishing the reaction losses.

[0084] The present invention relates to a method and system for separating and recovering metal resources in solid waste incineration fly ash. This method can further extract and recover metal resources (K / Na / Pb / Zn / Cu / Cd / Cr, etc.) in fly ash while ensuring the harmlessness of fly ash. It innovatively proposes a step-by-step directional separation method for fly ash metal resources based on the control of oxygen ion concentration in molten salt, and explains the specific process steps of fly ash metal dissolution from molten salt and further recovery. It provides a new method and system for fly ash treatment and disposal that integrates harmlessness, resource recovery and low energy consumption.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for separating and recovering metal resources from fly ash of solid waste incineration, characterized in that, Includes the following steps: S1. Solid waste incineration fly ash and additives are mixed to obtain a first mixture, and the first mixture is pretreated to obtain a second mixture, wherein the additives are substances rich in silicon and aluminum components; S2. Take inorganic salt and place it in the primary molten salt pool and heat it to a molten state. Continuously add the second mixture to the molten salt pool, and then add oxygen ion donor to extract K / Na salts from fly ash. As the reaction proceeds, excess molten salt in the primary molten salt pool overflows into the secondary molten salt pool, and the residue at the bottom of the primary molten salt pool is also discharged into the secondary molten salt pool. S3. Add oxygen ion removal agent to the secondary molten salt tank to extract heavy metals from fly ash. As the reaction proceeds, excess molten salt in the secondary molten salt tank overflows into the molten salt chamber to obtain molten salt products. The residue at the bottom of the secondary molten salt tank is discharged and can be collected for building material utilization. S4. After the molten salt product is cooled and crushed, it is dissolved, the pH value of the solution is adjusted to 9-11, and the polymetallic mud precipitate and salt filtrate are obtained by filtration, thus completing the resource recovery.

2. The method for separating and recovering metal resources from solid waste incineration fly ash as described in claim 1, characterized in that: The additives include one or more combinations of waste incineration bottom ash, coal slag, fly ash, crushed glass, or granite; the additives account for 5% to 40% of the total mass of the first mixture.

3. The method for separating and recovering metal resources from solid waste incineration fly ash as described in claim 1, characterized in that: In step S1, the pretreatment step includes crushing and grinding, mixing and homogenizing, and dry granulation.

4. The method for separating and recovering metal resources from solid waste incineration fly ash as described in claim 1, characterized in that: The quality of the added oxygen ion donor and oxygen ion remover is determined according to the quantitative criteria for metal resource separation and regulation. The specific quantitative criteria for metal resource separation and control are as follows: A sample of the second mixture is taken for component analysis. The mass of the second mixture of solid waste incineration fly ash and additives is determined to be M. The component analysis determines the mass concentrations of SiO2, Al2O3, CaO, Pb, Zn, Cu, Cd, and Cr to be A, B, C, D, E, F, G, and H, respectively, and their molar concentrations to be a, b, c, d, e, f, g, and h, respectively. The mass of added oxygen ion donor is set to X, and its molar concentration is... Let x be the mass of the oxygen ion removal agent added, Y be the molar concentration, and y be the molar concentration. Based on the chemical reaction molar calculation, x = a + bc, therefore X = 56M(a + bc) = 56M(A / 60 + B / 102 - C / 56). Calculation yields y = 2(d + e + f + g + h), therefore Y = 53.5M × 2(d + e + f + g + h) = 107M(D / 207.2 + E / 65.4 + F / 63.5 + G / 112.4 + H / 52).

5. The method for separating and recovering metal resources from solid waste incineration fly ash as described in claim 1, characterized in that: The inorganic salt contains metal cations including Li. + Na + K + Ca 2+ Mg 2+ Zn 2+ Pb 2+ Cu 2+ One or more of the following, wherein the anion contains Cl - It also includes SO4 2- CO3 2- OH - SO3 2- One or more of the following; the added mass m of the inorganic salt satisfies the condition that the height of the liquid molten salt surface does not exceed the height of the molten salt overflow port.

6. The method for separating and recovering metal resources from solid waste incineration fly ash as described in claim 1, characterized in that: The temperature of the primary molten salt pool is 600–1300°C, and the temperature of the secondary molten salt pool is the same as that of the primary molten salt pool.

7. The method for separating and recovering metal resources from solid waste incineration fly ash as described in claim 1, characterized in that: The oxygen ion donor is an alkaline earth metal oxide. Before being added, the oxygen ion donor undergoes one of the following pretreatments: high-energy ball milling, surfactant dispersion, or elemental doping, to enhance its reactivity.

8. The method for separating and recovering metal resources from solid waste incineration fly ash as described in claim 1, characterized in that: The oxygen ion remover is an HCl / Cl2 precursor. Before being added, the oxygen ion remover undergoes one of the following pretreatments: pre-drying, mechanical crushing, sieving and grading, or spray granulation, to enhance its reactivity.

9. The method for separating and recovering metal resources from solid waste incineration fly ash as described in claim 1, characterized in that: In step S4, the ratio of the mass of the solution to the mass of the added molten salt product is (3-20):

1.

10. A system for separating and recovering metal resources from solid waste incineration fly ash, used in any one of the separation and recovery methods described in claims 1 to 9, characterized in that: The separation and recovery system includes a primary molten salt pool, a secondary molten salt pool, a molten salt chamber, a primary solution pool, a secondary solution pool, and a residue pool. The primary molten salt pool has a first overflow outlet on its side wall and a first slag discharge outlet at its bottom. The first overflow outlet and the first slag discharge outlet are connected to the secondary molten salt pool via pipes. The secondary molten salt pool has a second overflow outlet on its side wall and a second slag discharge outlet at its bottom. The second overflow outlet is connected to the molten salt chamber via pipes. Each pipe is equipped with a heating device. The residue pool is located below the second slag discharge outlet. The primary solution pool and the secondary solution pool are sequentially arranged below the molten salt chamber.

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