Method for extracting heavy metal from waste incineration fly ash through multi-stage water washing

Abstract

The invention discloses a method for extracting heavy metals from waste incineration fly ash by multi-stage washing, which is characterized in that heavy metals in fly ash are dissolved step by step by multi-stage washing, so that more heavy metals are extracted, residues are reduced, and the total extraction rate is increased. Chemical agents are used in stages, a proper amount of agents are used in each step, waste is avoided, and cost is optimized. Impurities are removed through the steps of filtration, precipitation and the like after each stage of water washing, the concentration and purity of the heavy metal in the solution are gradually improved, and graded recovery is achieved. And waste liquid generated by step-by-step neutralization treatment is reduced, so that the pollution to the environment is reduced, and the finally discharged waste water is ensured to reach the environment-friendly standard. The washing conditions of each stage are adjustable to adapt to different fly ash components and flexibly cope with various conditions. Risks are decentralized, the washing process of each stage is monitored step by step, and operation safety is ensured. Energy is effectively utilized, unnecessary energy consumption is reduced, meanwhile, waste liquid and residues are recycled, and the resource utilization rate is increased.

Description

Technical Field

[0001] The invention relates to a waste incineration treatment technology, in particular to a method for extracting heavy metals from waste incineration fly ash by multi-stage water washing. Background Art

[0002] The method of fully burning garbage under oxygen supply conditions converts garbage into carbon dioxide, water and inert residues, and releases energy for power generation. The fly ash produced during the garbage incineration process contains high concentrations of heavy metals and other pollutants, which have a great impact on the environment. Existing technologies include: Chinese patent applications such as publication number CN117583362A propose a bioleaching process and equipment for removing heavy metals from fly ash from garbage incineration. In this patent, the raw ash is quickly mixed with the culture solution to make fly ash slurry, and the fly ash slurry and the highly active bioleaching engineering bacteria that have been fully regenerated in the regeneration tank are simultaneously introduced into the bioleaching tank, and the flow is reversed and pushed forward in the tank, and sulfur autotrophic bacteria nutrient fillers are added into the bioleaching tank. The bioleaching engineering bacteria use the sulfur autotrophic bacteria nutrient fillers to continuously reproduce, the pH in the system is continuously reduced, and the heavy metals in the fly ash are biologically leached.

[0003] Chinese patent applications such as publication number CN110607454A propose a method for extracting heavy metals from secondary fly ash from waste incineration. In this patent, secondary fly ash from waste incineration is mixed with activated carbon, sodium carbonate is added to water and dissolved completely to prepare a separation solvent, thereby improving the effective extraction rate of heavy metals.

[0004] However, fly ash contains many types of heavy metals, and it is difficult to completely extract the heavy metals therein by a single method. In view of this, the existing technology needs to be further improved. Summary of the invention

[0005] Based on the above technical problems, the present invention proposes a method for extracting heavy metals from waste incineration fly ash by multi-stage water washing, which uses multi-stage water washing to extract heavy metals from fly ash.

[0006] The technical solution of the present invention is achieved in this way: A method for extracting heavy metals from waste incineration fly ash by multi-stage water washing, characterized in that it comprises the following steps: Step 1: Mix the sieved fly ash and water at a solid-liquid ratio of 1:10 and stir thoroughly; Step 2: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 3: Filter using filter paper to obtain a primary water washing leachate and a primary water washing residue containing heavy metals; Step 4: Add 50-100 ml of sodium hydroxide solution to the first-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 5: Mix the primary washing residue with water at a solid-liquid ratio of 1:6 and stir thoroughly; Step 6: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 7: Filter using filter paper to obtain a secondary leaching solution and a secondary residue containing heavy metals; Step 8: Add 50-80 ml of hydrochloric acid solution to the second-stage water washing leachate to adjust the pH value to 8-9 to form an insoluble hydroxide precipitate; Step 9: Mix the secondary washing residue with water at a solid-liquid ratio of 1:8 and stir thoroughly; Step 10: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 11: Filter using filter paper to obtain a tertiary leaching solution and a tertiary residue containing heavy metals; Step 12: adding 40-60 ml of nitric acid solution to the second-stage water washing leachate, adjusting the pH value to 8-9, and forming an insoluble hydroxide precipitate; Step 13: combining the primary leachate, the secondary leachate and the tertiary leachate, adding a reducing agent to the combined leachate, adjusting the pH value to 8-9, and standing for 24 hours to allow the precipitate to settle completely; Step 14: Separating the precipitate and the supernatant by centrifugation or filtration; Step 15: Wash the precipitate at least three times with deionized water and dry at 105-200°C to a constant temperature.

[0007] As the present invention preferably, it comprises the following steps: Step 1: Mix the sieved fly ash and water in a solid-liquid ratio of 1:6 and stir thoroughly; Step 2: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 3: Filter using filter paper to obtain a primary water washing leachate and a primary water washing residue containing heavy metals; Step 4: Add 50-80 ml of hydrochloric acid solution to the first-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 5: Mix the primary washing residue with water at a solid-liquid ratio of 1:10 and stir thoroughly; Step 6: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 7: Filter using filter paper to obtain a secondary leaching solution and a secondary residue containing heavy metals; Step 8: Add 50-100 ml of sodium hydroxide solution to the second-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 9: Mix the secondary washing residue with water at a solid-liquid ratio of 1:8 and stir thoroughly; Step 10: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 11: Filter using filter paper to obtain a tertiary leaching solution and a tertiary residue containing heavy metals; Step 12: adding 40-60 ml of nitric acid solution to the second-stage water washing leachate, adjusting the pH value to 8-9, and forming an insoluble hydroxide precipitate; Step 13: combining the primary leachate, the secondary leachate and the tertiary leachate, adding a reducing agent to the combined leachate, adjusting the pH value to 8-9, and standing for 24 hours to allow the precipitate to settle completely; Step 14: Separating the precipitate and the supernatant by centrifugation or filtration; Step 15: Wash the precipitate at least three times with deionized water and dry at 105-200°C to a constant temperature.

[0008] As the present invention preferably, it comprises the following steps: Step 1: Mix the sieved fly ash and water at a solid-liquid ratio of 1:10 and stir thoroughly; Step 2: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 3: Filter using filter paper to obtain a primary water washing leachate and a primary water washing residue containing heavy metals; Step 4: Add 50-100 ml of sodium hydroxide solution to the first-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 5: Mix the primary washing residue with water at a solid-liquid ratio of 1:8 and stir thoroughly; Step 6: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 7: Filter using filter paper to obtain a secondary leaching solution and a secondary residue containing heavy metals; Step 8: Add 40-60 ml of nitric acid solution to the second-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 9: Mix the secondary washing residue with water at a solid-liquid ratio of 1:6 and stir well; Step 10: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 11: Filter using filter paper to obtain a tertiary leaching solution and a tertiary residue containing heavy metals; Step 12: Add 50-80 ml of hydrochloric acid solution to the third-stage water washing leachate to adjust the pH value to 8-9 to form an insoluble hydroxide precipitate; Step 13: combining the primary leachate, the secondary leachate and the tertiary leachate, adding a reducing agent to the combined leachate, adjusting the pH value to 8-9, and standing for 24 hours to allow the precipitate to settle completely; Step 14: Separating the precipitate and the supernatant by centrifugation or filtration; Step 15: Wash the precipitate at least three times with deionized water and dry at 105-200°C to a constant temperature.

[0009] The method for extracting heavy metals from waste incineration fly ash by multi-stage water washing according to the present invention has the following beneficial effects: The present invention dissolves heavy metals in fly ash step by step through multi-stage water washing, ensuring that more heavy metals are extracted, reducing residues and improving the total extraction rate. Chemical agents are used in stages, and appropriate amounts of agents are used in each step to avoid waste and optimize costs.

[0010] After each stage of water washing, impurities are removed through filtration, precipitation and other steps, gradually increasing the concentration and purity of heavy metals in the solution to achieve graded recovery. The waste liquid generated by the step-by-step neutralization treatment reduces pollution to the environment and ensures that the final discharged wastewater meets environmental protection standards. The water washing conditions (such as temperature, time, and reagent concentration) of each stage are adjustable to adapt to different fly ash components and flexibly respond to various situations. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a process diagram of the method for extracting heavy metals from waste incineration fly ash by multi-stage water washing according to the present invention; Figure 2 This is a process diagram of the method for extracting heavy metals from waste incineration fly ash by multi-stage water washing according to the present invention; Figure 3 This is a process diagram of the method for extracting heavy metals from waste incineration fly ash by multi-stage water washing according to the present invention; Figure 4 This is a process diagram of the method for extracting heavy metals from waste incineration fly ash by multi-stage water washing according to the present invention; Figure 5 This is a flowchart of the method for extracting heavy metals from waste incineration fly ash by multi-stage water washing according to the present invention; The reference numerals are represented as: garbage storage bin 1, driving grab bucket 2, boiler water treatment unit 3, gas separation bag 4, lime milk adding unit 5, activated carbon adding unit 6, bag filter 7, chimney 8, incinerator 100, hopper 101, feeding device 102, furnace 103, slag discharger 104, secondary combustion chamber 105, oil burner 106, first fan 107, waste heat boiler 108, flue gas preheater 109, air duct 110, steam preheater 111, second fan 112, neutralization reaction tower 113. DETAILED DESCRIPTION

[0012] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0013] Reference Figure 1 to Figure 2 As shown, in this embodiment, the garbage incineration process includes a garbage storage bin 1, a driving grab 2 and an incinerator 100. Domestic garbage is dumped into the garbage storage bin 1 by a truck and the liquid therein is separated, and then the driving grab 2 delivers the domestic garbage in the garbage storage bin 1 to the incinerator 100. A boiler water treatment unit 3 is connected to the top of the incinerator 100, and the boiler water treatment unit 3 injects denitrified soft water into the incinerator 100. Denitrified soft water refers to water that has been specially treated to remove most of the hardness ions (such as calcium and magnesium ions) and some or all of the nitrogen compounds (such as ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen) in the water. Denitrified soft water further reduces the corrosion of nitrogen compounds to the boiler system, prevents boiler scaling, extends the life of the boiler, and improves thermal efficiency. The steam discharged from the incinerator 100 passes through the gas distribution bag 4 to ensure that the gas flow entering each branch is uniform.

[0014] Furthermore, a lime milk adding unit 5 is connected to the top of the incinerator 100 to add lime milk to the incinerator 100. The lime milk can react chemically with heavy metal ions in water to generate insoluble hydroxide precipitates, thereby removing heavy metals.

[0015] Furthermore, an activated carbon adding unit 6 is connected to one side of the incinerator 100 to add activated carbon to the incinerator 100 for absorbing impurities such as organic matter, pigments, odors, heavy metal ions, etc. in the incinerator 100.

[0016] In this embodiment, the domestic garbage calcined by the incinerator 100 is discharged through the bag filter 7 and the chimney 8. The dust-containing gas enters the bag filter through the air inlet. The air inlet is usually designed with a guide plate to evenly distribute the gas and reduce local impact and wear. In some cases, the gas will pass through a pre-treatment device, such as a cyclone separator, before entering the bag filter to remove large particles of dust and reduce the burden on the bag. Subsequently, when the dust-containing gas passes through the filter bag, the dust particles are intercepted by the surface of the filter bag. The filter bag is usually made of porous materials, such as polyester, nylon, glass fiber, etc., which have a high filtration efficiency. As the filtration process proceeds, dust will gradually accumulate on the surface of the filter bag to form a layer of dust cake. The dust cake itself also has a filtering effect. The clean gas is discharged from the other side through the filter bag and then discharged through the chimney 8.

[0017] Refer again Figure 2 As shown, the incinerator 100 is composed of a hopper 101, a feeding device 102, a furnace 103, a slag discharger 104, a secondary combustion chamber 105, an oil burner 106, a first fan 107, a waste heat boiler 108, a flue gas preheater 109, an air duct 110, a steam preheater 111, a second fan 112, and a neutralization reaction tower 113.

[0018] Reference Figure 3 As shown in the figure, domestic waste undergoes oxidation combustion and reduction pyrolysis reactions at high temperatures, in which the more volatile heavy metal elements (such as As, Se, Cd, etc.) volatilize and exist in the flue gas in gaseous form, while the gaseous heavy metals react with Fe and Al oxides in the flue gas to transform into particles. A small number of less volatile elements (such as Cu, Cr, Ni, etc.) are entrained into the flue gas by the airflow after the waste is burned out, while most of the less volatile elements form oxides and remain in the bottom ash after burning out, so these elements have a higher concentration in the bottom ash (such as Cu). In addition, the silicon-aluminum compounds in domestic waste and added flame retardants react with heavy metals and their oxides at high temperatures to form aluminosilicates, thereby fixing the heavy metals in the bottom ash. In the flue gas condensation stage, the reduction in flue gas temperature causes some gaseous heavy metals to condense into submicron particles, which may be adsorbed by primary fly ash or agglomerated into coarser particles.

[0019] Due to their greater inertia, coarse particles collide with the pipe wall when the airflow turns and are removed from the flue gas to form economizer ash. The slaked lime slurry sprayed into the deacidification tower contacts the flue gas in the countercurrent flow, reacts and adsorbs the gaseous heavy metals in the flue gas, causing their phases to change. The granular heavy metals in the deacidification tower agglomerate into coarse particles under the action of liquid bridge force, and the coarse particles with larger mass settle under the action of inertia to form deacidification ash.

[0020] The activated carbon sprayed between the deacidification tower and the dust removal device further adsorbs the gaseous and fine-particle heavy metals in the flue gas, and is intercepted by the bag or adsorbed by the dust after entering the dust removal device. At the same time, the Ca(OH)2 escaping from the deacidification tower is adsorbed on the bag surface and further reacts with the gaseous heavy metals in the flue gas. There are differences in the concentration and mass distribution of heavy metals such as As and Se in the bag filter ash and deacidification ash, which is mainly caused by factors such as the properties of the heavy metals themselves and the combustion conditions; but they are mainly distributed in the fly ash, indicating that it has the best synergistic removal efficiency of heavy metals in waste incineration flue gas, especially the more volatile heavy metal elements. As the temperature of the flue gas decreases after passing through the economizer, the gaseous heavy metals condense on the particulate matter; and the reaction of the gaseous heavy metals with the deacidification agent, as well as the adsorption of the deacidification agent and the activated carbon, to a large extent, converts the gaseous heavy metals in the flue gas into particulate matter, effectively improving the synergistic removal effect of the flue gas heavy metals.

[0021] Reference Figure 4 As shown, heavy metals with low boiling points volatilize into the flue gas during the incineration process. As the flue gas temperature drops, part of the heavy metals condense and adhere to the fly ash particles; the other part is adsorbed by the injected activated carbon. The fly ash and activated carbon are captured by the flue gas dust removal equipment and mixed together to form bag fly ash. The fluidized bed incinerator has a fast airflow speed, a large fly ash output, and a serious particle entrainment phenomenon. Therefore, the content of heavy metals with higher boiling points in its fly ash is higher than that in the grate furnace fly ash. The boiling points of heavy metal compounds are shown in the following table: Metal Elemental state / ℃ Chlorinated state / ℃ Oxidation state / ℃ Pb 1740 950 885 Zn 905 733 2366 Cu 2585 632 1298 Cd 776 898 1452 Cr 2672 1295 2256 As 615 140 457 Se 685 130 325 Be 2970 515 3925 Hg 356 302 500 Ba 1595 1562 1956 Ni 2377 998 1975 Embodiment 1

[0022] On the basis of the above embodiment, this embodiment further proposes a method for extracting heavy metals from waste incineration fly ash by multi-stage water washing, comprising the following steps: Step 1: Mix the sieved fly ash and water at a solid-liquid ratio of 1:10 and stir thoroughly; Step 2: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 3: Filter using filter paper to obtain a primary water washing leachate and a primary water washing residue containing heavy metals; Step 4: Add 50-100 ml of sodium hydroxide solution to the first-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 5: Mix the primary washing residue with water at a solid-liquid ratio of 1:6 and stir thoroughly; Step 6: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 7: Filter using filter paper to obtain a secondary leachate and secondary residue containing heavy metals; Step 8: Add 50-80 ml of hydrochloric acid solution to the second-stage water washing leachate to adjust the pH value to 8-9 to form an insoluble hydroxide precipitate; Step 9: Mix the secondary washing residue with water at a solid-liquid ratio of 1:8 and stir thoroughly; Step 10: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 11: Filter using filter paper to obtain a tertiary leaching solution and a tertiary residue containing heavy metals; Step 12: adding 40-60 ml of nitric acid solution to the second-stage water washing leachate, adjusting the pH value to 8-9, and forming an insoluble hydroxide precipitate; Step 13: combining the primary leachate, the secondary leachate and the tertiary leachate, adding a reducing agent to the combined leachate, adjusting the pH value to 8-9, and standing for 24 hours to allow the precipitate to settle completely; Step 14: Separating the precipitate and the supernatant by centrifugation or filtration; Step 15: Wash the precipitate at least three times with deionized water and dry at 105-200°C to a constant temperature. Embodiment 2

[0023] On the basis of the above embodiment, this embodiment further proposes a method for extracting heavy metals from waste incineration fly ash by multi-stage water washing, comprising the following steps: Step 1: Mix the sieved fly ash and water in a solid-liquid ratio of 1:6 and stir thoroughly; Step 2: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 3: Filter using filter paper to obtain a primary water washing leachate and a primary water washing residue containing heavy metals; Step 4: Add 50-80 ml of hydrochloric acid solution to the first-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 5: Mix the primary washing residue with water at a solid-liquid ratio of 1:10 and stir thoroughly; Step 6: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 7: Filter using filter paper to obtain a secondary leachate and secondary residue containing heavy metals; Step 8: Add 50-100 ml of sodium hydroxide solution to the second-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 9: Mix the secondary washing residue with water at a solid-liquid ratio of 1:8 and stir thoroughly; Step 10: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 11: Filter using filter paper to obtain a tertiary leaching solution and a tertiary residue containing heavy metals; Step 12: adding 40-60 ml of nitric acid solution to the second-stage water washing leachate, adjusting the pH value to 8-9, and forming an insoluble hydroxide precipitate; Step 13: combining the primary leachate, the secondary leachate and the tertiary leachate, adding a reducing agent to the combined leachate, adjusting the pH value to 8-9, and standing for 24 hours to allow the precipitate to settle completely; Step 14: Separating the precipitate and the supernatant by centrifugation or filtration; Step 15: Wash the precipitate at least three times with deionized water and dry at 105-200°C to a constant temperature. Embodiment 3

[0024] On the basis of the above embodiment, this embodiment further proposes a method for extracting heavy metals from waste incineration fly ash by multi-stage water washing, comprising the following steps: Step 1: Mix the sieved fly ash and water at a solid-liquid ratio of 1:10 and stir thoroughly; Step 2: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 3: Filter using filter paper to obtain a primary water washing leachate and a primary water washing residue containing heavy metals; Step 4: Add 50-100 ml of sodium hydroxide solution to the first-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 5: Mix the primary washing residue with water at a solid-liquid ratio of 1:8 and stir thoroughly; Step 6: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 7: Filter using filter paper to obtain a secondary leachate and secondary residue containing heavy metals; Step 8: Add 40-60 ml of nitric acid solution to the second-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 9: Mix the secondary washing residue with water at a solid-liquid ratio of 1:6 and stir well; Step 10: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 11: Filter using filter paper to obtain a tertiary leaching solution and a tertiary residue containing heavy metals; Step 12: Add 50-80 ml of hydrochloric acid solution to the third-stage water washing leachate to adjust the pH value to 8-9 to form an insoluble hydroxide precipitate; Step 13: combining the primary leachate, the secondary leachate and the tertiary leachate, adding a reducing agent to the combined leachate, adjusting the pH value to 8-9, and standing for 24 hours to allow the precipitate to settle completely; Step 14: Separating the precipitate and the supernatant by centrifugation or filtration; Step 15: Wash the precipitate at least three times with deionized water and dry at 105-200°C to a constant temperature.

[0025] In this embodiment, different heavy metals have different solubility in water. For example, lead (Pb), zinc (Zn), copper (Cu), etc. are more soluble under acidic conditions. Some heavy metals may form stable compounds under certain conditions and are difficult to dissolve. The pH value of fly ash will affect the selection of chemical agents. Under acidic or alkaline conditions, fly ash may contain other impurities (such as organic matter, inorganic salts, etc.), which may affect the effect of the agent.

[0026] Hydrochloric acid (HCl): It can effectively dissolve most heavy metals, especially lead (Pb), zinc (Zn), copper (Cu), etc. It is suitable for fly ash containing more heavy metals that are easily soluble in acid.

[0027] Sulfuric acid (H2SO4): It can dissolve a variety of heavy metals, especially iron (Fe), aluminum (Al), etc. It is suitable for fly ash containing more heavy metals such as iron and aluminum.

[0028] Nitric acid (HNO3): It has strong oxidizing properties and can dissolve a variety of heavy metals, especially silver (Ag), copper (Cu), etc. It is suitable for heavy metals that need to be oxidized and dissolved.

[0029] Sodium hydroxide (NaOH): It is a strong alkaline substance and can form insoluble hydroxide precipitates with certain heavy metals, such as iron hydroxide (Fe(OH)3) and aluminum hydroxide (Al(OH)3). It is suitable for fly ash containing a large amount of heavy metals such as iron and aluminum.

[0030] Potassium Hydroxide (KOH): Strong base, similar to NaOH, but more soluble, suitable for alkaline conditions where high solubility is required.

[0031] Citric acid: It can form stable complexes with various heavy metals and improve solubility. It is suitable for situations where fly ash contains various heavy metals and the solubility needs to be improved.

[0032] Ethylenediaminetetraacetic acid (EDTA): A strong chelating agent that can form stable complexes with a variety of heavy metals and is suitable for the extraction of heavy metals that require a high degree of chelation.

[0033] Sodium sulfide (Na2S): It can form insoluble sulfide precipitates with certain heavy metals, such as lead sulfide (PbS), copper sulfide (CuS), etc. It is suitable for fly ash containing more heavy metals that are easy to form sulfides.

[0034] 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 and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for extracting heavy metals from waste incineration fly ash by multi-stage water washing, characterized in that: The steps include: Step 1: Mix the sieved fly ash and water at a solid-liquid ratio of 1:10 and stir thoroughly; Step 2: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 3: Filter using filter paper to obtain a primary water washing leachate and a primary water washing residue containing heavy metals; Step 4: Add 50-100 ml of sodium hydroxide solution to the first-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 5: Mix the primary washing residue with water at a solid-liquid ratio of 1:6 and stir thoroughly; Step 6: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 7: Filter using filter paper to obtain a secondary leaching solution and a secondary residue containing heavy metals; Step 8: Add 50-80 ml of hydrochloric acid solution to the second-stage water washing leachate to adjust the pH value to 8-9 to form an insoluble hydroxide precipitate; Step 9: Mix the secondary washing residue with water at a solid-liquid ratio of 1:8 and stir thoroughly; Step 10: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 11: Filter using filter paper to obtain a tertiary leaching solution and a tertiary residue containing heavy metals; Step 12: adding 40-60 ml of nitric acid solution to the second-stage water washing leachate, adjusting the pH value to 8-9, and forming an insoluble hydroxide precipitate; Step 13: combining the primary leachate, the secondary leachate and the tertiary leachate, adding a reducing agent to the combined leachate, adjusting the pH value to 8-9, and standing for 24 hours to allow the precipitate to settle completely; Step 14: Separating the precipitate and the supernatant by centrifugation or filtration; Step 15: Wash the precipitate at least three times with deionized water and dry at 105-200°C to a constant temperature.

2. A method for extracting heavy metals from waste incineration fly ash by multi-stage water washing, characterized in that: The steps include: Step 1: Mix the sieved fly ash and water in a solid-liquid ratio of 1:6 and stir thoroughly; Step 2: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 3: Filter using filter paper to obtain a primary water washing leachate and a primary water washing residue containing heavy metals; Step 4: Add 50-80 ml of hydrochloric acid solution to the first-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 5: Mix the primary washing residue with water at a solid-liquid ratio of 1:10 and stir thoroughly; Step 6: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 7: Filter using filter paper to obtain a secondary leaching solution and a secondary residue containing heavy metals; Step 8: Add 50-100 ml of sodium hydroxide solution to the second-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 9: Mix the secondary washing residue with water at a solid-liquid ratio of 1:8 and stir thoroughly; Step 10: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 11: Filter using filter paper to obtain a tertiary leaching solution and a tertiary residue containing heavy metals; Step 12: adding 40-60 ml of nitric acid solution to the second-stage water washing leachate, adjusting the pH value to 8-9, and forming an insoluble hydroxide precipitate; Step 13: combining the primary leachate, the secondary leachate and the tertiary leachate, adding a reducing agent to the combined leachate, adjusting the pH value to 8-9, and standing for 24 hours to allow the precipitate to settle completely; Step 14: Separating the precipitate and the supernatant by centrifugation or filtration; Step 15: Wash the precipitate at least three times with deionized water and dry at 105-200°C to a constant temperature.

3. A method for extracting heavy metals from waste incineration fly ash by multi-stage water washing, characterized in that: The steps include: Step 1: Mix the sieved fly ash and water at a solid-liquid ratio of 1:10 and stir thoroughly; Step 2: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 3: Filter using filter paper to obtain a primary water washing leachate and a primary water washing residue containing heavy metals; Step 4: Add 50-100 ml of sodium hydroxide solution to the first-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 5: Mix the primary washing residue with water at a solid-liquid ratio of 1:8 and stir thoroughly; Step 6: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 7: Filter using filter paper to obtain a secondary leaching solution and a secondary residue containing heavy metals; Step 8: Add 40-60 ml of nitric acid solution to the second-stage water washing leachate, adjust the pH value to 8-9, and form an insoluble hydroxide precipitate; Step 9: Mix the secondary washing residue with water at a solid-liquid ratio of 1:6 and stir well; Step 10: Place the mixture in a constant temperature water bath, react at 60-80°C for 2 hours, and stir until the heavy metal is dissolved; Step 11: Filter using filter paper to obtain a tertiary leaching solution and a tertiary residue containing heavy metals; Step 12: Add 50-80 ml of hydrochloric acid solution to the third-stage water washing leachate to adjust the pH value to 8-9 to form an insoluble hydroxide precipitate; Step 13: combining the primary leachate, the secondary leachate and the tertiary leachate, adding a reducing agent to the combined leachate, adjusting the pH value to 8-9, and standing for 24 hours to allow the precipitate to settle completely; Step 14: Separating the precipitate and the supernatant by centrifugation or filtration; Step 15: Wash the precipitate at least three times with deionized water and dry at 105-200°C to a constant temperature.

Images