Fly ash harmless treatment method and application thereof

Abstract

The application provides a fly ash harmless treatment method and application thereof, and comprises the following steps: S1. mixing fly ash, water, a heavy metal chelating agent and a foaming agent to obtain a heavy metal chelate, clean fly ash and waste liquid; wherein the foaming agent comprises a first foaming agent and a second foaming agent, and the heavy metal chelating agent comprises a first heavy metal chelating agent and a second heavy metal chelating agent; S2. adding a calcium-magnesium precipitant to the waste liquid, and then performing solid-liquid separation to obtain calcium-magnesium impurities and brine; and S3. evaporating the brine to obtain sodium chloride and potassium chloride. The application can comprehensively realize the harmless treatment and resource utilization of fly ash, has remarkable effects, and is worth promoting.

Description

Technical Field

[0001] This invention belongs to the technical field of harmless treatment and resource utilization of hazardous solid waste, specifically relating to a method for harmless treatment of fly ash and its application. Background Technology

[0002] Incineration of municipal solid waste offers advantages such as significant volume and weight reduction, high levels of harmlessness, and energy recovery and reuse. However, the incineration process generates a large amount of toxic fly ash, accounting for 3% to 5% of the total municipal solid waste. Furthermore, fly ash accumulates a large number of heavy metal ions during incineration, leading to increasingly prominent impacts on the quality of water, air, and soil.

[0003] Currently, fly ash utilization and disposal methods mainly include landfill and resource recovery. Landfill is the traditional method for fly ash disposal, while resource recovery is a newer treatment method developed in recent years. Among them, solidification / stabilization-landfill treatment technology is currently the main method for fly ash disposal in China. However, this technology consumes land resources; fly ash also contains a high mass fraction of heavy metals and dissolved salts, especially chlorides, which can reach 37.3% of the mass fraction. Such a high concentration of chlorides poses a risk of water pollution, soil salinization, and increased leaching of heavy metals and other pollutants during fly ash disposal, resulting in a high risk of secondary pollution.

[0004] With the widespread adoption of municipal solid waste incineration technology and the increasing prominence of landfill pollution risks, the resource utilization of waste incineration fly ash is urgently needed. However, the high concentrations of heavy metals and chlorine in fly ash severely hinder its resource utilization process. In particular, the high concentration of chlorine, with some waste incineration fly ash reaching over 20%, far exceeds the requirement of ≤0.06% chloride ion content in raw materials as stipulated in the "General Portland Cement" (GB175-2007) standard. The "Technical Specification for Environmental Protection of Solid Waste Co-processing in Cement Kilns" (HJ662-2013) requires a chloride ion content of ≤0.04% in the materials fed into the kiln. Therefore, pre-treatment with dechlorination is essential to reduce the chlorine content in the fly ash to less than 1%.

[0005] Commonly used technologies often employ water washing to remove heavy metals and chlorine from fly ash, but these technologies still suffer from low resource recovery rates and poor desalination and demineralization effects.

[0006] Therefore, in order to solve the technical problems of low resource recovery rate and poor desalination effect of incineration fly ash in commonly used technologies, it is necessary to provide a method for harmless treatment of fly ash and its application. Summary of the Invention

[0007] To address the aforementioned technical problems of low fly ash resource recovery rate and poor desalination and heavy metal removal effects, this invention provides a method for the harmless treatment of fly ash, comprising the following steps:

[0008] S1. Fly ash, water, heavy metal chelating agent and foaming agent are mixed and then floated to obtain heavy metal chelate, clean fly ash and waste liquid;

[0009] The foaming agent includes a first foaming agent and a second foaming agent, and the heavy metal chelating agent includes a first heavy metal chelating agent and a second heavy metal chelating agent.

[0010] S2. Add calcium and magnesium precipitant to the waste liquid, and after solid-liquid separation, obtain calcium and magnesium impurities and brine;

[0011] S3. Evaporate the brine to obtain sodium chloride and potassium chloride.

[0012] Furthermore, in step S1, the flotation of the mixture of fly ash, water, heavy metal chelating agent, and frother includes:

[0013] The fly ash, water, the first heavy metal chelating agent accounting for 1% to 3% of the mass of the fly ash, and the first foaming agent are mixed and stirred for 2 to 8 minutes to form a first slurry. The first slurry is then floated to obtain the first heavy metal chelate, the first clean fly ash, and the first waste liquid.

[0014] The first clean fly ash is mixed with water, the second heavy metal chelating agent accounting for 0.1% to 2% of the mass of the first clean fly ash, and the second foaming agent, and stirred for 2 to 8 minutes to form a second slurry. The second slurry is then floated to obtain a second metal chelate, a second clean fly ash, and a second waste liquid.

[0015] The first heavy metal chelate and the second heavy metal chelate are collected to obtain the heavy metal chelate; the second clean fly ash is collected to obtain the clean fly ash; the first waste liquid and the second waste liquid are collected to obtain the waste liquid.

[0016] Furthermore, the heavy metal chelating agent includes one or more of xanthate esters, dithiocarbamate derivatives, and phosphates.

[0017] Furthermore, the foaming agent includes one or more of basic pine oil, camphor oil, and eucalyptus oil.

[0018] Furthermore, the amount of the first frother added is 10-50 g / t fly ash, and the amount of the second frother added is 5-25 g / t first clean fly ash.

[0019] Furthermore, the heavy metal chelate is roasted to obtain a metallurgical raw material; wherein the roasting time is 1 to 2 hours and the roasting temperature is 850 to 1000°C.

[0020] Furthermore, the calcium and magnesium precipitant includes sodium carbonate and / or carbon dioxide, and the calcium and magnesium impurities include magnesium carbonate and / or calcium carbonate.

[0021] Furthermore, step S3 also includes adding hydrochloric acid to the brine to neutralize the sodium hydroxide in the brine into sodium chloride and water, thereby adjusting the pH of the brine to 7.5-8.5.

[0022] Furthermore, step S3 includes heating and evaporating the brine to obtain a saturated solution of sodium chloride and potassium chloride;

[0023] Step S3 further includes condensing and crystallizing the saturated potassium chloride solution to obtain potassium chloride.

[0024] The present invention also provides an application of the fly ash harmless treatment method described in any one of the preceding claims in fly ash treatment, characterized in that the fly ash includes municipal solid waste incineration fly ash.

[0025] Compared with the prior art, the present invention has at least the following advantages:

[0026] This invention applies flotation technology to the harmless treatment of fly ash, with the addition of frothers and heavy metal chelating agents. The fly ash is de-desalinated to produce tailings, heavy metal chelates, and waste liquid. On one hand, the addition of the heavy metal chelating agent flocculates the heavy metals in the fly ash into clusters. Utilizing mechanisms such as coordination chelation, netting, bridging, and double-layer compression, various heavy metals are rapidly captured, thereby increasing the hydrophobicity of the heavy metal chelate particles (i.e., heavy metal chelates, hereinafter the same), facilitating the separation of heavy metal chelates.

[0027] On the other hand, frothers are typically composed of amphoteric molecules with both hydrophilic and hydrophobic portions. This dual structure allows the frother to adsorb onto the interface of the slurry (i.e., fly ash, water, heavy metal chelating agents, and a mixture of frothers, hereinafter the same), reducing interparticle interfacial energy and thus adjusting slurry characteristics. This causes heavy metal chelate particles to adhere to air bubbles and rise to the air-liquid interface, further improving flotation separation efficiency. The combined effect of the heavy metal chelating agents and frothers produces a synergistic gain greater than the sum of its parts (1+1>2), which is beneficial for the effective separation of heavy metals from other substances in fly ash, significantly improving the removal efficiency of heavy metals such as lead, zinc, and cadmium in fly ash, thereby ensuring the subsequent resource utilization of fly ash tailings. In addition, flotation technology can also simultaneously remove dioxins and sulfides adsorbed on carbon after they agglomerate with heavy metal chelates, further achieving fly ash detoxification.

[0028] This invention enables the harmless treatment of fly ash, achieving the capture and recovery of heavy metals while allowing the sodium chloride and potassium chloride products obtained from the fly ash treatment to be applied in production and daily life and recycled. This makes the fly ash treatment resource-based, thorough, and environmentally friendly, achieving 95% utilization of fly ash and effectively unifying social, environmental, and economic benefits. Attached Figure Description

[0029] 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 the structures shown in these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the process for harmless treatment of fly ash in one embodiment of the present invention. Detailed Implementation

[0031] 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 a part of the embodiments of the present invention, and not all of them. 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.

[0032] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0033] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0034] This invention provides a method for harmlessly treating fly ash, comprising the following steps:

[0035] S1. Fly ash, water, heavy metal chelating agent and frother are mixed and then floated to obtain heavy metal chelate, tailings and waste liquid.

[0036] Fly ash, a byproduct of municipal solid waste incineration, is widely used in municipal solid waste treatment due to its superior effects on reducing volume and waste and facilitating recycling. This has directly led to a year-on-year increase in the amount of fly ash awaiting treatment, which can even reach 3-5% of the total municipal solid waste volume. However, fly ash typically accumulates harmful substances such as heavy metals, dioxins, and sulfides, and its impact on water, air, and soil is becoming increasingly prominent. Therefore, the resource-based, economical, and environmentally friendly development of fly ash is urgently needed.

[0037] Taking into account the characteristics of fly ash, such as small particle size and high alkalinity, this invention applies flotation technology to fly ash treatment.

[0038] Flotation was first applied in the mineral processing industry. It utilizes the difference in hydrophobicity of mineral surfaces and adjusts the characteristics of the slurry by adding flotation reagents. This allows hydrophobic particles to adhere to air bubbles and rise to the air-liquid interface, thereby achieving mineral separation.

[0039] In some embodiments, heavy metal chelating agents can be xanthate esters, dithiocarbamate derivatives (DTC chelating agents), or phosphates, all of which possess good selectivity for heavy metals in fly ash and the hydrophobic and floatable properties of the heavy metal chelates. Exemplarily, the chemical structure of the parent DTC heavy metal chelating agent is typically linear. In application, DTC heavy metal chelating agents exhibit excellent treatment effects for complex heavy metal wastewater. Essentially, they are nitrogen-containing organic sulfur chelating agents that chelate cations of sulfophilic heavy metal elements. The strength of the chelation corresponds to the sulfophilicity of the element. They are typically prepared by reacting amines, polyamines, or ethylenediamines, polyethylenepolyamines, and carbon disulfide in a strong alkali. As high-molecular-weight, multifunctional heavy metal chelating agents, their performance is significantly superior to low-molecular-weight, monofunctional heavy metal chelating agents.

[0040] The high-molecular-weight active chelating groups in DTC-type heavy metal chelating agents rapidly capture various heavy metals through mechanisms such as coordination chelation, entrapment, bridging, and double-layer compression, forming water-insoluble heavy metal chelates. The flocculation of these heavy metal chelate particles enhances their hydrophobicity, facilitating the effective separation of heavy metals from other substances in fly ash and achieving heavy metal removal from fly ash. This provides strong technical support for the subsequent resource-based treatment of fly ash. Furthermore, the heavy metal chelate particles coat dioxins adsorbed on carbon, further achieving the harmlessness of fly ash.

[0041] In some embodiments, the foaming agent may be one of the following: alkaline pine oil, camphor oil, or eucalyptus oil. The surfactant is composed of an amphoteric molecular structure with both hydrophilic and hydrophobic portions. This dual structure allows the surfactant to adsorb at the liquid-air interface and reduce the surface tension of the slurry, making it easier for air introduced into the water to disperse into bubbles and generate stable foam.

[0042] The frother selected in this invention has excellent pulp property adjustment performance. It can be adsorbed on the pulp interface and reduce the interfacial energy of particles, so that the heavy metal chelate particles are attached to the bubbles in the flotation process and rise to the air-liquid interface, effectively improving the separation effect of heavy metal chelates.

[0043] The frother, in synergy with the aforementioned heavy metal chelating agent, causes most heavy metal chelates and dioxins adsorbed on carbon to float to the surface, where they can be easily wiped off physically. Meanwhile, water-soluble chlorides, potassium salts, and calcium and magnesium ions are all released into the waste liquid and discharged from the flotation machine along with the tailings. After desalination, de-heavy metal removal, and detoxification, the fly ash can be landfilled or recycled without burdening the environment or posing a leaching risk.

[0044] In some embodiments, the mass ratio of fly ash to water can be 1:2 to 5, the mass of the heavy metal chelating agent can be 1% to 3% of the mass of the fly ash, and the mass of the foaming agent can be 10 to 50 g per ton of fly ash, so that the heavy metal chelates and the activated carbon used to adsorb dioxins float to the surface.

[0045] To further refine this, since the solubility of soluble heavy metals in a unit mass of fly ash is greatly affected by the difference in the amount of lime added during the front-end desulfurization process, the added mass of the heavy metal chelating agent can be 10 to 15 times the mass of heavy metals dissolved in the fly ash.

[0046] For example, the fly ash can be mixed evenly with the above flotation reagents (including water, heavy metal chelating agents and frothers, hereinafter the same) by stirring, thereby accelerating the reaction process.

[0047] In practical applications, froth flotation can be used to treat fly ash. The process includes the following steps: adding fly ash and water to a flotation machine and stirring; adding flotation reagents to the fly ash and stirring for 2-8 minutes to obtain a slurry. During this process, the flotation reagents interact with the fly ash particles to amplify the difference in floatability between different particles. The prepared slurry is then fed into a flotation cell, stirred, and aerated. Mineral particles in the slurry contact and collide with the air bubbles. Heavy metal chelates with good floatability selectively adhere to the air bubbles and are carried upwards to form a mineralized froth layer composed of a gas-liquid-solid three-phase structure. This layer is then mechanically scraped off or overflows from the slurry surface, followed by dehydration and drying to obtain heavy metal products. Fly ash that cannot float is discharged as tailings from the bottom of the flotation cell along with the waste liquid.

[0048] During the flotation process, soluble harmful substances in the fly ash are also dissolved into the wastewater, including chloride salts, potassium salts, and calcium and magnesium ions, thus initially achieving the desalination treatment of fly ash.

[0049] In some embodiments, the above-mentioned dehydrated and dried heavy metal products can be placed in a roasting furnace at 800-1000°C for 1-2 hours to obtain metallurgical raw materials, which can then be applied to the smelting process, turning waste into treasure and further realizing the resource utilization of fly ash.

[0050] During the roasting process, the sulfides, dioxins, carbon, and other substances adsorbed in the heavy metal chelates also decompose simultaneously. After roasting, the heavy metal chelates yield harmless decomposition gases and metallurgical raw materials, realizing the comprehensive and efficient resource utilization of fly ash.

[0051] In some specific embodiments, step S1, which involves mixing fly ash, water, heavy metal chelating agent, and frother before flotation, includes:

[0052] S11. The fly ash, water, the first heavy metal chelating agent accounting for 1% to 3% of the mass of the fly ash, and the first foaming agent are mixed and stirred for 2 to 8 minutes to form a first slurry. The first slurry is floated to obtain a first heavy metal chelate, a first clean fly ash, and a first waste liquid.

[0053] In some embodiments, the mass ratio of fly ash to water can be 1:2 to 5; for example, the mass ratio of fly ash to water can be 1:4 to 5; and for yet another example, the mass ratio of fly ash to water can be 1:3 to 4.

[0054] S12. The first clean fly ash is mixed with water, the second heavy metal chelating agent accounting for 0.1% to 2% of the mass of the first clean fly ash, and the second foaming agent, and stirred for 2 to 8 minutes to form a second slurry. The second slurry is then floated to obtain a second metal chelate, a second clean fly ash, and a second waste liquid.

[0055] In some embodiments, the mass ratio of fly ash to water can be 1:2 to 5; for example, the mass ratio of fly ash to water can be 1:4 to 5; and for yet another example, the mass ratio of fly ash to water can be 1:3 to 4.

[0056] S13. Collect the first heavy metal chelate and the second heavy metal chelate to obtain the heavy metal chelate; collect the second clean fly ash to obtain the clean fly ash; collect the first waste liquid and the second waste liquid to obtain the waste liquid.

[0057] The above steps, through multiple flotation of fly ash, leach out as much heavy metal chelate and soluble harmful substances (including chloride salts, potassium salts and calcium and magnesium ions, hereinafter the same) as possible from the fly ash, making the harmlessness and resource utilization of fly ash more thorough.

[0058] This invention, by limiting the dosage of heavy metal chelating agent in steps S11, S12, and S13 respectively, makes the heavy metal content more compatible with the heavy metal chelating agent content, while reducing costs and avoiding unnecessary losses, so that the heavy metals in fly ash can be thoroughly and efficiently flocculated into clumps and float on the water surface.

[0059] In some embodiments, such as Figure 1 As shown, step S12 may further include: mixing the second clean fly ash with water, a heavy metal chelating agent accounting for 0-1% of the mass of the second clean fly ash, and a foaming agent, and stirring for 2-8 minutes to form a third slurry; flotating the third slurry to obtain a third heavy metal chelate, a third clean fly ash, and a third waste liquid; step S13 may further include: collecting the first heavy metal chelate, the second heavy metal chelate, and the third metal chelate to obtain the heavy metal chelate; collecting the third clean fly ash to obtain the clean fly ash; and collecting the first waste liquid, the second waste liquid, and the third waste liquid to obtain the waste liquid.

[0060] Repeating the flotation step can further improve the harmlessness of fly ash, more thoroughly leach out heavy metals and soluble harmful substances in fly ash, efficiently remove heavy metals and toxins, and effectively improve the cleanliness of fly ash.

[0061] S2. Add calcium and magnesium precipitant to the waste liquid, and separate the solid and liquid to obtain calcium and magnesium impurities and brine.

[0062] In some embodiments, the calcium and magnesium precipitant can be sodium carbonate or carbon dioxide. The calcium and magnesium precipitant reacts fully with the calcium and magnesium ions, precipitates, and the solid and liquid are separated to obtain calcium and magnesium impurities and brine. The calcium and magnesium impurities can be magnesium carbonate and calcium carbonate precipitates.

[0063] For example, the amount of calcium-magnesium precipitant added can be 1:1, which is the ratio of calcium-magnesium content in the waste liquid to the molar ratio of calcium-magnesium precipitant.

[0064] In other embodiments, calcium and magnesium impurities can be co-processed and comprehensively utilized with tailings after desalination and demineralization to generate economic benefits. The comprehensive utilization method can be building material raw materials, including cement, bricks, boards, ceramics, etc.

[0065] S3 evaporates the brine to obtain sodium chloride and potassium chloride.

[0066] In some embodiments, hydrochloric acid can be added to the brine to neutralize the sodium hydroxide in the brine solution into sodium chloride and water, making the brine weakly alkaline with a pH between 7.5 and 8.5.

[0067] In some embodiments, the brine is heated and evaporated to obtain a saturated solution of sodium chloride and potassium chloride.

[0068] For example, brine can be placed in an MRV system for crystallization and evaporation to obtain a saturated solution of sodium chloride and potassium chloride; wherein the main components of the saturated potassium chloride solution are potassium chloride and water, and the distilled water can be recycled back to step S1.

[0069] In some embodiments, step S3 further includes condensing and crystallizing the potassium chloride saturated solution to obtain potassium chloride.

[0070] For example, a saturated potassium chloride solution can be placed at room temperature to condense and crystallize, yielding potassium chloride and fresh water; the fresh water can be recycled back to step S1, improving the cleanliness of the process.

[0071] The sodium chloride and potassium chloride can be further decomposed by centrifugation to remove the mother liquor, and then dried and packaged to obtain the finished sodium chloride and potassium chloride products. The filtrate can be returned to the flotation system for slurry preparation.

[0072] The method of separating sodium chloride and potassium chloride using different temperatures and solubilities allows for relatively relaxed quality requirements on the sodium chloride and potassium chloride mixture, reduces investment, and is easy to implement. Furthermore, the particle size of the sodium chloride and potassium chloride products is controllable, the products have high purity, and can operate stably and continuously for a long period.

[0073] The present invention, through a fly ash harmless treatment process, mainly yields the following substances: heavy metal chelates, clean fly ash (de-heavy, desalinated, and de-dioxin-removed fly ash), calcium and magnesium impurities, distilled water, sodium chloride, potassium chloride, and filtrate.

[0074] Among them, heavy metal chelates can be roasted to obtain metallurgical raw materials and harmless mixed gases; fly ash that has been de-heavy, dechlorinated and de-dioxined can be used in conjunction with calcium and magnesium impurities for comprehensive utilization; distilled water and filtrate can be returned to the flotation system to participate in slurry preparation; sodium chloride and potassium chloride can be used as products, creatively realizing the comprehensive harmless and resource-based treatment of fly ash.

[0075] This invention applies flotation technology to the harmless treatment of fly ash, with the addition of a frother and a heavy metal chelating agent, resulting in clean fly ash, heavy metal chelates, and waste liquid after de-heavyning, desalination, and dioxin removal from the fly ash. On one hand, the addition of the heavy metal chelating agent flocculates the heavy metals in the fly ash into clusters, utilizing mechanisms such as coordination chelation, netting, bridging, and double-layer compression to rapidly capture various heavy metals, thereby increasing the hydrophobicity of the heavy metal chelate particles (i.e., heavy metal chelates, hereinafter the same), facilitating the separation of heavy metal chelates.

[0076] On the other hand, frothers are typically composed of amphoteric molecules with both hydrophilic and hydrophobic portions. This dual structure allows the frother to adsorb onto the interface of the slurry (i.e., fly ash, water, heavy metal chelating agents, and a mixture of frothers, hereinafter the same), reducing interparticle interfacial energy and thus adjusting slurry characteristics. This causes heavy metal chelate particles to adhere to air bubbles and rise to the air-liquid interface, further improving flotation separation efficiency. The combined effect of the heavy metal chelating agents and frothers produces a synergistic gain greater than the sum of its parts (1+1>2), which is beneficial for the effective separation of heavy metals from other substances in fly ash, significantly improving the removal efficiency of heavy metals such as lead, zinc, and cadmium in fly ash, thereby ensuring the subsequent resource utilization of fly ash tailings. In addition, flotation technology can also simultaneously remove dioxins and sulfides adsorbed on carbon after they agglomerate with heavy metal chelates, further achieving fly ash detoxification.

[0077] This invention also applies flotation technology to concentrate treatment, resulting in sodium chloride and potassium chloride products with controllable particle size and high purity, suitable for direct application. This significantly improves the harmless treatment of fly ash while simplifying subsequent application processes for sodium chloride and potassium chloride products, avoiding damage to the equipment.

[0078] This invention enables the harmless treatment of fly ash, achieving the capture and recovery of heavy metals while simultaneously allowing the sodium chloride and potassium chloride products obtained from the fly ash treatment to be applied in production and daily life and recycled. This makes the fly ash treatment resource-based, thorough, and environmentally friendly, achieving 95% utilization of fly ash and effectively unifying social, environmental, and economic benefits.

[0079] The present invention also provides the application of the fly ash harmless treatment method described in any of the above-mentioned methods in fly ash treatment, wherein the fly ash may include municipal solid waste incineration fly ash.

[0080] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided:

[0081] Example 1

[0082] The fly ash was collected from Pingdu, Qingdao.

[0083] S1. Water and fly ash are mixed at a mass ratio of 4:1, and then a heavy metal chelating agent and a frother are added. The heavy metal chelating agent is a piperazine chelating agent, with a mass of 3% relative to the weight of the fly ash; the frother is pine oil, with a mass of 20g per ton of fly ash. After stirring for 5 minutes, a first slurry is obtained. The first slurry is added to a flotation machine and subjected to aeration flotation. Surface foam is mechanically scraped off to obtain the first heavy metal chelate. Solid-liquid separation yields the first clean fly ash and the first waste liquid.

[0084] The first clean fly ash was mixed with water again at a water-ash ratio of 4:1, and then a heavy metal chelating agent and a frother were added. The heavy metal chelating agent was piperazine chelating agent, with a mass of 1.5% of the first clean fly ash weight; the frother was pine oil, with a mass of 10g per ton of fly ash. After stirring for 5 minutes, a second slurry was obtained. The second slurry was added to a flotation machine and subjected to aeration flotation again. Surface foam was mechanically scraped off to obtain a second heavy metal chelate. Solid-liquid separation yielded a second clean fly ash and a second waste liquid.

[0085] Collect the first heavy metal chelate and the second heavy metal chelate to obtain a heavy metal chelate; collect the second clean fly ash to obtain fly ash that has been de-chlorinated and de-dioxined; collect the first waste liquid and the second waste liquid to obtain waste liquid.

[0086] S2, based on the calcium and magnesium content in the waste liquid, an appropriate amount of sodium carbonate is added to the waste liquid, and the mixture is stirred for 30 minutes to separate the solid and liquid phases, obtaining calcium and magnesium impurities and brine. The brine mainly consists of sodium chloride and potassium chloride, while the calcium and magnesium impurities mainly consist of calcium carbonate and magnesium carbonate. The calcium and magnesium impurities are then mixed with tailings for further comprehensive utilization.

[0087] S3, before the brine evaporates, hydrochloric acid is added to the brine to adjust the pH of the brine to about 8, which converts sodium hydroxide in the brine into sodium chloride and water.

[0088] S4. After heating and evaporating the brine, a saturated solution of sodium chloride and potassium chloride is obtained; after drying the sodium chloride, a sodium chloride product is obtained, which is industrial wet salt grade one (National Standard GB / T5462-2015).

[0089] The components were detected and are shown in the table below:

[0090] Table 1. Chloride content of raw fly ash

[0091] Proportion 15.21 33.08 51.21 0.5 Specific gravity of ash 8.04 17.49 30.24 0.26

[0092] Table 2. Analysis of main chemical components of fly ash before and after treatment.

[0093]

[0094]

[0095] Table 3. Heavy metal leaching concentrations in fly ash

[0096]

[0097] *Pollution Control Standard for Municipal Solid Waste Landfills - 2008

[0098] Table 4. Fly Ash Utilization Indicators for the Entire Process

[0099]

[0100]

[0101] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for harmlessly treating fly ash, characterized in that, Includes the following steps: S1. Fly ash, water, heavy metal chelating agent and foaming agent are mixed and then floated to obtain heavy metal chelate, clean fly ash and waste liquid; the mass of the heavy metal chelating agent added is 10 to 15 times the mass of heavy metals dissolved in the fly ash; The foaming agent includes a first foaming agent and a second foaming agent, and the heavy metal chelating agent includes a first heavy metal chelating agent and a second heavy metal chelating agent; the heavy metal chelating agent is a high-molecular-weight, multifunctional dithiocarbamate derivative; the foaming agent includes one or more of basic pine oil, camphor oil, and eucalyptus oil; the amount of the first foaming agent added is 10~50g / t fly ash; The heavy metal chelate is roasted to obtain metallurgical raw material, wherein the roasting time is 1 to 2 hours and the roasting temperature is 850 to 1000°C. In step S1, the flotation of the mixture of fly ash, water, heavy metal chelating agent, and frother includes: The fly ash, water, the first heavy metal chelating agent accounting for 1% to 3% of the mass of the fly ash, and the first foaming agent are mixed and stirred for 2 to 8 minutes to form a first slurry. The first slurry is then floated to obtain the first heavy metal chelate, the first clean fly ash, and the first waste liquid. The first clean fly ash is mixed with water, the second heavy metal chelating agent accounting for 0.1% to 2% of the mass of the first clean fly ash, and the second foaming agent, and stirred for 2 to 8 minutes to form a second slurry. The second slurry is then floated to obtain the second heavy metal chelate, the second clean fly ash, and the second waste liquid. Collect the first heavy metal chelate and the second heavy metal chelate to obtain the heavy metal chelate; collect the second clean fly ash to obtain the clean fly ash; collect the first waste liquid and the second waste liquid to obtain the waste liquid; S2. Add calcium and magnesium precipitant to the waste liquid, and after solid-liquid separation, obtain calcium and magnesium impurities and brine; S3. Evaporate the brine to obtain sodium chloride and potassium chloride.

2. The method for harmlessly treating fly ash according to claim 1, characterized in that, The amount of the second foaming agent added is 5~25g / t of the first cleaning fly ash.

3. The method for harmlessly treating fly ash according to claim 1, characterized in that, The calcium and magnesium precipitant includes sodium carbonate and / or carbon dioxide, and the calcium and magnesium impurities include magnesium carbonate and / or calcium carbonate.

4. The method for harmlessly treating fly ash according to claim 1, characterized in that, Step S3 further includes adding hydrochloric acid to the brine to neutralize the sodium hydroxide in the brine into sodium chloride and water, and adjusting the pH of the brine to 7.5~8.

5.

5. The method for harmlessly treating fly ash according to claim 4, characterized in that, Step S3 includes heating and evaporating the brine to obtain a saturated solution of sodium chloride and potassium chloride. Step S3 further includes condensing and crystallizing the saturated potassium chloride solution to obtain potassium chloride.

6. The application of the fly ash harmless treatment method according to any one of claims 1 to 5 in fly ash treatment, characterized in that, The fly ash includes fly ash from municipal solid waste incineration.

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