Method for reducing content of heavy metals in waste incineration fly ash

Abstract

The invention relates to a method for reducing the content of heavy metals in waste incineration fly ash, and belongs to the technical field of environmental protection. The waste incineration fly ash is added into water to be mixed and stirred, solid-liquid separation is conducted, dechlorinated fly ash and chlorine-containing waste water are obtained, and the chlorine-containing waste water is discharged after being treated to reach the standard; feeding the dechlorinated fly ash into a multi-stage countercurrent pickling system, taking a thiourea-sulfuric acid mixed solution as an extracting agent, adding dimercaptopropanol, and carrying out three-stage pickling, so as to obtain a leaching solution containing various heavy metals and pickled fly ash; the leaching liquid is sequentially subjected to filtering, adsorption purification, precipitation, extraction, reverse extraction and electro-deposition technologies, and heavy metal is recycled; waste acid generated by multi-stage countercurrent pickling is neutralized, filtered and subjected to impurity removal, and then the waste acid is circularly returned to the multi-stage countercurrent pickling system; the thiourea-sulfuric acid mixed solution is prepared from thiourea, sulfuric acid and deionized water; the method can obviously improve the recovery rate of medium and heavy metals, and can realize high-value utilization.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental protection, and in particular to a method for reducing the content of heavy metals in waste incineration fly ash. BACKGROUND

[0002] With the acceleration of urbanization, the amount of garbage is increasing rapidly. Waste incineration has become one of the main ways of garbage disposal in China due to its high degree of reduction, harmlessness and resource utilization. However, a large amount of fly ash is produced during the process of waste incineration. The fly ash is rich in heavy metals such as lead, cadmium, zinc, chromium and copper, as well as dioxin persistent organic pollutants. According to the National Hazardous Waste List, it is clearly listed as hazardous waste. If not properly treated, it will cause serious pollution to the soil, water and atmosphere, and threaten human health.

[0003] Chinese patent CN117224888A relates to the field of solid waste treatment. The application discloses a process for stabilizing heavy metals in municipal solid waste incineration fly ash, which includes the following steps: S1, mixing fly ash, chelating agent and water and stirring to obtain chelating slurry; S2, shaping the chelating slurry in a mold and curing to complete the stabilization treatment of the fly ash. The chelating agent is composed of EDTA and silicon-phosphorus-sulfur inorganic chelating agent, and the weight ratio of EDTA to silicon-phosphorus-sulfur inorganic chelating agent is (2-5.5):1.

[0004] Chinese patent CN115368104B discloses a method for solidifying heavy metals in waste incineration fly ash. The method includes the following steps: providing waste incineration bottom ash and waste incineration fly ash; crushing, magnetic separation and ball milling the waste incineration bottom ash in sequence to obtain fine bottom ash; mixing the fine bottom ash and waste incineration fly ash, then adding sodium hydroxide and water for stirring to form a mixed slurry; adding water glass to the mixed slurry and stirring to obtain a gelled slurry; pouring and shaping the gelled slurry, and then curing to form a heavy metal solidified block.

[0005] Currently, the main treatment method for waste incineration fly ash is cement solidification and safe landfill. The fixation of heavy metals by cement solidification is not permanent, and under the action of environmental factors such as long-term rainwater leaching and groundwater infiltration, there is still a risk of heavy metal leaching, which may cause soil and groundwater pollution. More importantly, valuable heavy metals such as zinc, lead and copper with high content in fly ash cannot be recycled and utilized, resulting in serious resource waste and not meeting the current requirements of circular economy development. SUMMARY

[0006] To solve the above problems, the present application provides a method for reducing the content of heavy metals in waste incineration fly ash, which has the following operation steps, in terms of mass fraction: S1: 10-20 parts of waste incineration fly ash is added to 30-100 parts of water, mixed and stirred, and then subjected to solid-liquid separation to obtain dechlorinated fly ash and chlorine-containing wastewater, and the chlorine-containing wastewater is discharged after treatment; S2: The dechlorinated fly ash is sent to a multi-stage countercurrent pickling system, a thiourea-sulfuric acid mixed solution is used as the leaching agent, and 0.03-0.15 parts of dimercaprol is added; the first-stage pickling has a pH value of 1.0-1.5, a temperature of 40-50°C, and a time of 60-90 min, to realize the preferential leaching of zinc and copper; the second-stage pickling has a pH value of 2.0-2.5, a temperature of 50-60°C, and a time of 90-120 min, to realize the leaching of lead and cadmium; the third-stage pickling has a pH value of 3.0-3.5, a temperature of 60-70°C, and a time of 120-150 min, to realize the leaching of chromium; and finally, an leaching solution containing multiple heavy metals and pickled fly ash are obtained; S3: The leaching solution is sequentially subjected to filtration and adsorption purification treatment to obtain a purified leaching solution; the filtration removes suspended particulate matters in the leaching solution; and the adsorbent used in the adsorption purification treatment accounts for 1-3 wt% of the mass of the leaching solution; S4: 5-10 parts of the leaching solution after adsorption purification is first adjusted to a pH value of 4.0-4.5, 0.02-0.2 parts of sodium carbonate is added as a precipitant, and the mixture is precipitated at a stirring speed of 150-200 r / min and a temperature of 30-40°C for 40-60 min, to obtain zinc carbonate through filtration separation; the pH value of the filtrate after zinc separation is adjusted to 6.0-6.5, 0.01-0.05 parts of sodium sulfide is added as a precipitant, and the mixture is precipitated at a stirring speed of 150-200 r / min and a temperature of 35-45°C for 50-70 min, to obtain lead sulfide through filtration separation; LIX984N extractant is added to the filtrate after lead separation, to realize the extraction of copper; then, 10-20 wt% sulfuric acid solution is used as a back-extracting agent for back-extraction, to obtain a copper-containing solution, and copper is recovered through electrodeposition technology; S5: The waste acid generated in the multi-stage countercurrent pickling is subjected to neutralization and impurity removal through filtration, and then is recycled back to the multi-stage countercurrent pickling system.

[0007] In some embodiments of the present application, the stirring speed in S1 is 200-300 r / min, and the stirring time is 30-60 min.

[0008] In some embodiments of the present application, the liquid-solid ratio of the leaching agent to the dechlorinated fly ash in S2 is 4-8:1.

[0009] In some embodiments of the present application, the adsorbent in S3 is one of activated carbon, amino phosphonic acid type chelating resin, and imino diacetic acid type chelating resin.

[0010] In some embodiments of the present application, the adsorption time of the S3 adsorption purification treatment is 30-60 min, and the temperature is 25-35℃.

[0011] In some embodiments of the present application, the volume ratio of the S4 LIX984N extractant to the filtrate is 1:2-3, and the volume ratio of the back-extractant to the extraction solution is 1:1-2.

[0012] In some embodiments of the present application, the current density of the S4 electrodeposition recovery of copper is 200-300 A / m 2 , the temperature is 40-50℃, the electrolysis time is 2-4h, and the cell voltage is 2.0-2.5V.

[0013] In some embodiments of the present application, the S5 neutralization uses calcium hydroxide to adjust the pH value to 2.0-2.5, and the filtration uses a microporous filtration membrane with a pore size of 0.1-0.2μm.

[0014] In some embodiments of the present application, the preparation method of the thiourea-sulfuric acid mixed solution is as follows: According to mass fraction, 0.1-1 parts of thiourea, 3-5 parts of sulfuric acid, and 90-96 parts of deionized water are added to a reaction kettle, stirred and reacted, and then cooled to room temperature to obtain a thiourea-sulfuric acid mixed solution.

[0015] In some embodiments of the present application, the reaction temperature is 35-55℃, and the time is 30-70 minutes.

[0016] Reaction mechanism: Sulfuric acid can destroy the combined state structure of heavy metals and silicates or oxides in fly ash by providing H⁺, break the stable existence form of heavy metals in fly ash, and create basic conditions for the release of heavy metal ions; thiourea can quickly form stable complexes with dissolved heavy metal ions, reduce the concentration of free heavy metal ions in the system, promote the continuous forward progress of the leaching reaction according to the leaching equilibrium principle, and improve the leaching rate of heavy metals; the mercapto group in dimercaprol can form strong coordination bonds with heavy metals such as lead and cadmium that are difficult to dissolve in traditional leaching methods, further dissolving such difficult-to-dissolve heavy metal compounds, and the three form a synergistic effect, significantly enhancing the overall dissolution effect of heavy metals from the three dimensions of destroying the combined structure, moving the equilibrium, and dissolving the difficult-to-dissolve components.

[0017] Technical effects The synergistic leaching system improves the recovery efficiency of heavy metals: compared with traditional single leaching agents or non-synergistic leaching combinations, the synergistic leaching system of thiourea-sulfuric acid mixed solution and dimercaprol used in the present application can more accurately target different types of heavy metals such as zinc, lead, and copper in fly ash, destroy their stable structures, and promote dissolution, providing a source of high-concentration and high-purity heavy metals for subsequent recovery processes, and greatly improving the recovery efficiency of valuable heavy metals.

[0018] Waste acid recycling reduces cost and environmental impact: By neutralizing and filtering the waste acid generated by multi-stage countercurrent pickling, it is recycled back to the pickling system, reducing the purchase and consumption of fresh leaching agent, and reducing the raw material cost of hazardous waste treatment; At the same time, it reduces the discharge of waste acid, avoids the secondary pollution of waste acid discharge to soil and water, and takes into account the economy and environmental protection.

[0019] Adapt to large-scale application and realize resource high value: Thiourea is a common chemical raw material, which has the advantages of easy access and economic price. The preparation process of mixed leaching agent is simple and easy to operate, and the stable process of multi-stage countercurrent pickling can meet the industrialization demand of large-scale treatment of waste incineration fly ash; At the same time, through efficient recovery of valuable heavy metals in fly ash, the hazardous waste is converted into reusable resources, realizing "waste into treasure", which meets the requirements of circular economy development. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The raw material of example 1.

[0021] Figure 2 The raw material of example 2. DETAILED DESCRIPTION

[0022] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined purpose of the application, the following will be described in detail in combination with examples and comparative examples: The raw garbage incineration fly ash is Guangda (Chunan), and the specific components are as follows: Cl - ]] SO3 K2O Na2O SiO2 Al2O3 Fe2O3 CaO % % % % % % % % 18.72 5.86 4.47 12.75 2.97 0.70 0.40 43.99 MgO TiO2 P2O5 Br- As Cd Cr Cu % % % % ppm ppm ppm ppm 0.89 0.20 0.28 0.08 18.18 232.86 54.74 373.87 Mn Mo Ni Pb Sb Sn V Zn ppm ppm ppm ppm ppm ppm ppm ppm 153.33 48.00 22.00 1104.68 168.73 319.81 11.76 4989.11 Zinc, lead and copper recovery rate: the content of heavy metals in the sample is determined by inductively coupled plasma mass spectrometry; by respectively determining the "metal content in the initial fly ash" and "metal content in the recovered product", the metal recovery rate is calculated by the formula: metal recovery rate = metal content in recovered product / metal content in initial fly ash) × 100%. Example 1

[0023] A method for reducing the content of heavy metals in waste incineration fly ash, the operation steps are: S1: 10 kg of waste incineration fly ash is added to 30 kg of water, mixed and stirred, then solid-liquid separation is carried out to obtain dechlorinated fly ash and chlorine-containing wastewater, and the chlorine-containing wastewater is discharged after treatment. S2: send the dechlorination fly ash into a multi-stage countercurrent pickling system, take thiourea-sulfuric acid mixed solution as leaching agent, and add 0.03 kg of dimercaprol; the first stage pickling has a pH value of 1.0, a temperature of 40 DEG C, and a time of 60 min, thereby realizing the preferential leaching of zinc and copper; the second stage pickling has a pH value of 2.0, a temperature of 50 DEG C, and a time of 90 min, thereby realizing the leaching of lead and cadmium; the third stage pickling has a pH value of 3.0, a temperature of 60 DEG C, and a time of 120 min, thereby realizing the leaching of chromium; finally, the leaching solution containing multiple heavy metals and the fly ash after pickling are obtained; S3: sequentially pass the leaching solution through filtration and adsorption purification treatment, thereby obtaining the purified leaching solution; remove the suspended particulate matters in the leaching solution through filtration; the adsorbent used in the adsorption purification treatment has a dosage of 1 t% of the mass of the leaching solution; S4: adjust the pH value of 5 kg of the leaching solution after adsorption purification to 4.0, add 0.02 kg of sodium carbonate as precipitant, and precipitate under the condition of a stirring speed of 150 r / min and a temperature of 30 DEG C for 40 min, thereby obtaining zinc carbonate through filtration separation; adjust the pH value of the filtrate after zinc separation to 6.0, add 0.01 kg of sodium sulfide as precipitant, and precipitate under the condition of a stirring speed of 150 r / min and a temperature of 35 DEG C for 50 min, thereby obtaining lead sulfide through filtration separation; add LIX984N extractant to the filtrate after lead separation, thereby realizing the extraction of copper; then, use 10 wt% sulfuric acid solution as back-extracting agent to perform back-extraction, thereby obtaining a copper-containing solution, and then recover copper through electrodeposition technology; S5: after neutralization and impurity removal treatment, recycle the waste acid generated in the multi-stage countercurrent pickling system to the multi-stage countercurrent pickling system.

[0024] The stirring speed of S1 is 200 r / min, and the stirring time is 30 min.

[0025] The liquid-solid ratio of the leaching agent to the dechlorination fly ash in S2 is 4:1.

[0026] The adsorbent in S3 is activated carbon.

[0027] The adsorption time of the adsorption purification treatment in S3 is 30 min, and the temperature is 25 DEG C.

[0028] The volume ratio of the LIX984N extractant to the filtrate in S4 is 1:2, and the volume ratio of the back-extracting agent to the extractive solution is 1:1.

[0029] The current density of the electrodeposition recovery of copper in S4 is 200 A / m2, the temperature is 40 DEG C, the electrolysis time is 2 h, and the cell voltage is 2.0 V.

[0030] In S5, calcium hydroxide is used to adjust the pH value to 2.0 in the neutralization, and a microporous filtration membrane with a pore size of 0.1 μm is used in the filtration.

[0031] The preparation method of the thiourea-sulfuric acid mixed solution is as follows: 0.1 kg of thiourea, 3 kg of sulfuric acid and 90 kg of deionized water are added into a reaction kettle, and after stirring and reaction, the mixture is cooled to room temperature to obtain the thiourea-sulfuric acid mixed solution.

[0032] The reaction temperature is 35℃, and the reaction time is 30 minutes. Example 2

[0033] A method for reducing the content of heavy metals in waste incineration fly ash, the operation steps of which are as follows: S1: 13 kg of waste incineration fly ash is added into 50 kg of water and mixed and stirred, and then solid-liquid separation is performed to obtain dechlorinated fly ash and chlorine-containing wastewater, and the chlorine-containing wastewater is discharged after treatment; S2: The dechlorinated fly ash is sent into a multi-stage countercurrent acid washing system, and 0.08 kg of dimercaprol is added as the leaching agent; the first-stage acid washing is performed at a pH value of 1.1, a temperature of 45℃ and a time of 70 min to realize the preferential leaching of zinc and copper; the second-stage acid washing is performed at a pH value of 2.1, a temperature of 55℃ and a time of 100 min to realize the leaching of lead and cadmium; the third-stage acid washing is performed at a pH value of 3.1, a temperature of 65℃ and a time of 130 min to realize the leaching of chromium; and finally, a leaching solution containing multiple heavy metals and acid-washed fly ash are obtained; S3: The leaching solution is sequentially subjected to filtration and adsorption purification treatment to obtain a purified leaching solution; the filtration removes suspended particulate matters in the leaching solution; and the adsorbent used in the adsorption purification treatment accounts for 2wt% of the mass of the leaching solution; S4: 6 kg of the adsorption-purified leaching solution is first adjusted to a pH value of 4.1, and 0.1 kg of sodium carbonate is added as a precipitant, and the mixture is precipitated at a stirring speed of 160 r / min and a temperature of 35℃ for 45 min, and then filtered and separated to obtain zinc carbonate; the pH value of the filtrate after zinc separation is adjusted to 6.1, and 0.02 kg of sodium sulfide is added as a precipitant, and the mixture is precipitated at a stirring speed of 160 r / min and a temperature of 40℃ for 55 min, and then filtered and separated to obtain lead sulfide; LIX984N extractant is added into the filtrate after lead separation to realize the extraction of copper; then, 15wt% sulfuric acid solution is used as a back-extracting agent for back-extraction to obtain a copper-containing solution, and copper is recovered by electrodeposition technology; S5: The waste acid generated in the multi-stage countercurrent acid washing is subjected to neutralization and filtration impurity removal treatment, and then recycled back to the multi-stage countercurrent acid washing system.

[0034] The stirring speed of S1 is 250 r / min, and the stirring time is 40 min.

[0035] The liquid-solid ratio of the leaching agent to the dechlorinated fly ash in S2 is 5:1.

[0036] The adsorbent of S3 is an amino phosphonic acid type chelating resin.

[0037] The adsorption time of the adsorption and purification treatment of S3 is 40 min, and the temperature is 30℃.

[0038] The volume ratio of the S4 LIX984N extractant to the filtrate is 1:2.2, and the volume ratio of the stripping agent to the extraction liquid is 1:1.2.

[0039] The current density of the S4 electrodeposition recovery of copper is 250 A / m², the temperature is 45℃, the electrolysis time is 3h, and the cell voltage is 2.1V.

[0040] The S5 neutralization uses calcium hydroxide to adjust the pH value to 2.1, and the filtration uses a microporous filtration membrane with a pore size of 0.1μm.

[0041] The preparation method of the thiourea-sulfuric acid mixed solution is: 0.5kg of thiourea, 4kg of sulfuric acid, and 92kg of deionized water are added to a reaction kettle, stirred and reacted, cooled to room temperature, and a thiourea-sulfuric acid mixed solution is obtained.

[0042] The reaction temperature is 40℃, and the time is 40 minutes. Example 3

[0043] A method for reducing the content of heavy metals in waste incineration fly ash, the operation steps are: S1: 18kg of waste incineration fly ash is added to 80kg of water and mixed and stirred, then solid-liquid separation is performed to obtain dechlorinated fly ash and chlorine-containing wastewater, and the chlorine-containing wastewater is discharged after treatment; S2: The dechlorinated fly ash is sent to a multi-stage countercurrent pickling system, using a thiourea-sulfuric acid mixed solution as the leaching agent, and 0.12kg of dimercaprol is added; the first stage pickling has a pH value of 1.4, a temperature of 45℃, and a time of 80min, realizing the preferential leaching of zinc and copper; the second stage pickling has a pH value of 2.4, a temperature of 55℃, and a time of 110min, realizing the leaching of lead and cadmium; the third stage pickling has a pH value of 3.4, a temperature of 65℃, and a time of 140min, realizing the leaching of chromium; finally, a leaching solution containing multiple heavy metals and a pickled fly ash are obtained; S3: The leaching solution is sequentially subjected to filtration and adsorption and purification treatment to obtain a purified leaching solution; filtration is used to remove suspended particulate matter in the leaching solution; the adsorbent used in the adsorption and purification treatment accounts for 2wt% of the mass of the leaching solution. S4: 8 kg of the leaching solution after adsorption purification is first adjusted to pH 4.4, 0.15 kg of sodium carbonate is added as a precipitant, and the solution is precipitated at a stirring speed of 180 r / min and a temperature of 35℃ for 55 min, and then filtered to obtain zinc carbonate; the filtrate after separation of zinc is adjusted to pH 6.4, 0.04 kg of sodium sulfide is added as a precipitant, and the solution is precipitated at a stirring speed of 180 r / min and a temperature of 40℃ for 65 min, and then filtered to obtain lead sulfide; LIX984N extractant is added to the filtrate after separation of lead to realize extraction of copper; then 15wt% sulfuric acid solution is used as a stripping agent to strip, obtain a copper-containing solution, and then recover copper by electrodeposition technology; S5: the waste acid generated by the multi-stage countercurrent pickling is treated by neutralization and filtration to remove impurities, and then recycled back to the multi-stage countercurrent pickling system.

[0044] The stirring speed of S1 is 250 r / min, and the stirring time is 50 min.

[0045] The liquid-solid ratio of the leaching agent to the dechlorinated fly ash in S2 is 7:1.

[0046] The adsorbent of S3 is an amino phosphonic acid type chelating resin.

[0047] The adsorption time of the adsorption purification treatment of S3 is 50 min, and the temperature is 30℃.

[0048] The volume ratio of the LIX984N extractant to the filtrate in S4 is 1:2.5, and the volume ratio of the stripping agent to the extract solution is 1:1.6.

[0049] The current density for electrodeposition recovery of copper in S4 is 250 A / m², the temperature is 45℃, the electrolysis time is 3 h, and the cell voltage is 2.4 V.

[0050] In S5, calcium hydroxide is used to adjust the pH value to 2.4, and a microporous filtration membrane with a pore size of 0.2 μm is used for filtration.

[0051] The preparation method of the thiourea-sulfuric acid mixed solution is as follows: 0.8 kg of thiourea, 4 kg of sulfuric acid, and 94 kg of deionized water are added to a reaction kettle, stirred and reacted, cooled to room temperature, and then a thiourea-sulfuric acid mixed solution is obtained.

[0052] The reaction temperature is 50℃, and the time is 60 min. Example 4

[0053] A method for reducing the content of heavy metals in waste incineration fly ash, the operation steps of which are as follows: S1: 20 kg of waste incineration fly ash is added to 100 kg of water and mixed and stirred, then solid-liquid separation is performed to obtain dechlorinated fly ash and chlorine-containing wastewater, and the chlorine-containing wastewater is discharged after treatment to meet the standard; S2: The dechlorinated fly ash is sent to a multi-stage countercurrent pickling system, a thiourea-sulfuric acid mixed solution is used as the leaching agent, and 0.15 kg of dimercaprol is added; the first-stage pickling has a pH value of 1.5, a temperature of 50℃, and a time of 90 min, to realize the preferential leaching of zinc and copper; the second-stage pickling has a pH value of 2.5, a temperature of 60℃, and a time of 120 min, to realize the leaching of lead and cadmium; the third-stage pickling has a pH value of 3.5, a temperature of 70℃, and a time of 150 min, to realize the leaching of chromium; and finally, a leaching solution containing multiple heavy metals and pickled fly ash are obtained; S3: The leaching solution is sequentially subjected to filtration and adsorption purification treatment to obtain a purified leaching solution; the filtration removes suspended particulate matter in the leaching solution; and the adsorbent used in the adsorption purification treatment accounts for 3wt% of the mass of the leaching solution; S4: 10 kg of the adsorption-purified leaching solution is first adjusted to a pH value of 4.5, 0.2 kg of sodium carbonate is added as a precipitant, and precipitation is performed at a stirring speed of 200 r / min and a temperature of 40℃ for 60 min, to obtain zinc carbonate through filtration separation; the pH value of the filtrate after zinc separation is adjusted to 6.5, 0.05 kg of sodium sulfide is added as a precipitant, and precipitation is performed at a stirring speed of 200 r / min and a temperature of 45℃ for 70 min, to obtain lead sulfide through filtration separation; LIX984N extractant is added to the filtrate after lead separation to realize copper extraction; then, 20wt% sulfuric acid solution is used as a stripping agent for stripping to obtain a copper-containing solution, and copper is recovered through electrodeposition technology; S5: The waste acid generated in the multi-stage countercurrent pickling is subjected to neutralization and impurity removal treatment and then recycled back to the multi-stage countercurrent pickling system.

[0054] The stirring speed of S1 is 300 r / min, and the stirring time is 60 min.

[0055] The liquid-solid ratio of the leaching agent to the dechlorinated fly ash in S2 is 8:1.

[0056] The adsorbent in S3 is iminodiacetic acid type chelating resin.

[0057] The adsorption time of the adsorption purification treatment in S3 is 60 min, and the temperature is 35℃.

[0058] The volume ratio of the LIX984N extractant to the filtrate in S4 is 1:3, and the volume ratio of the stripping agent to the extract solution is 1:2.

[0059] The current density of the S4 electrodeposition recovery of copper is 300 A / m2, the temperature is 50 DEG C, the electrolysis time is 4h, and the cell voltage is 2.5V.

[0060] The S5 neutralization adopts calcium hydroxide to adjust the pH value to 2.5, and the filtration adopts a microporous filter membrane with a pore size of 0.2 μm.

[0061] The preparation method of the thiourea-sulfuric acid mixed solution is as follows: 1 kg of thiourea, 5 kg of sulfuric acid, and 96 kg of deionized water are added to a reaction kettle, and after stirring and reaction, the mixture is cooled to room temperature to obtain a thiourea-sulfuric acid mixed solution.

[0062] The reaction temperature is 55 DEG C, and the time is 70 minutes.

[0063] Comparative Example 1 A method for reducing the content of heavy metals in waste incineration fly ash, the operation steps are as follows: S1: 10 kg of waste incineration fly ash is added to 30 kg of water and mixed and stirred, and then solid-liquid separation is performed to obtain dechlorinated fly ash and chlorine-containing wastewater, and the chlorine-containing wastewater is discharged after treatment; S2: The dechlorinated fly ash is sent to a multi-stage countercurrent acid washing system, and 5wt% oxalic acid is used as the leaching agent; the first stage of acid washing has a pH value of 1.0, a temperature of 40 DEG C, and a time of 60 min, to realize the preferential leaching of zinc and copper; the second stage of acid washing has a pH value of 2.0, a temperature of 50 DEG C, and a time of 90 min, to realize the leaching of lead and cadmium; the third stage of acid washing has a pH value of 3.0, a temperature of 60 DEG C, and a time of 120 min, to realize the leaching of chromium; finally, a leaching solution containing multiple heavy metals and acid-washed fly ash are obtained; S3: The leaching solution is sequentially subjected to filtration and adsorption purification treatment to obtain a purified leaching solution; the filtration removes suspended particulate matter in the leaching solution; the adsorbent used in the adsorption purification treatment accounts for 1t% of the mass of the leaching solution; S4: 5 kg of the adsorption-purified leaching solution is first adjusted to a pH value of 4.0, 0.02 kg of sodium carbonate is added as a precipitant, and the mixture is precipitated at a stirring speed of 150 r / min and a temperature of 30 DEG C for 40 min, and then filtered to obtain zinc carbonate; the pH value of the filtrate after zinc separation is adjusted to 6.0, 0.01 kg of sodium sulfide is added as a precipitant, and the mixture is precipitated at a stirring speed of 150 r / min and a temperature of 35 DEG C for 50 min, and then filtered to obtain lead sulfide; LIX984N extractant is added to the filtrate after lead separation to realize the extraction of copper; then, 10wt% sulfuric acid solution is used as a stripping agent for stripping to obtain a copper-containing solution, which is then recovered by electrodeposition technology; S5: The waste acid generated in the multi-stage countercurrent acid washing is subjected to neutralization and filtration impurity removal treatment and then recycled back to the multi-stage countercurrent acid washing system.

[0064] The stirring speed of S1 is 200 r / min, and the stirring time is 30 min.

[0065] The liquid-solid ratio of the S2 leaching agent to the dechlorinated fly ash is 4:1.

[0066] The adsorbent of S3 is activated carbon.

[0067] The adsorption time of the S3 adsorption purification treatment is 30 min, and the temperature is 25°C.

[0068] The volume ratio of the S4 LIX984N extractant to the filtrate is 1:2, and the volume ratio of the stripping agent to the extraction liquid is 1:1.

[0069] The current density of the S4 electrodeposition recovery of copper is 200 A / m², the temperature is 40°C, the electrolysis time is 2 h, and the cell voltage is 2.0 V.

[0070] In the S5 neutralization, calcium hydroxide is used to adjust the pH value to 2.0, and a microporous filtration membrane with a pore size of 0.1 μm is used for filtration.

[0071] Comparative Example 2 A method for reducing the content of heavy metals in waste incineration fly ash, the operation steps of which are: S1: 10 kg of waste incineration fly ash is added to 30 kg of water and mixed and stirred, and then solid-liquid separation is performed to obtain dechlorinated fly ash and chlorine-containing wastewater, and the chlorine-containing wastewater is treated and discharged after reaching the standard; S2: The dechlorinated fly ash is sent to a multi-stage countercurrent acid washing system, 0.03 kg of dimercaprol is added as a leaching agent, the first stage of acid washing has a pH value of 1.0, a temperature of 40°C, and a time of 60 min to realize the preferential leaching of zinc and copper, the second stage of acid washing has a pH value of 2.0, a temperature of 50°C, and a time of 90 min to realize the leaching of lead and cadmium, and the third stage of acid washing has a pH value of 3.0, a temperature of 60°C, and a time of 120 min to realize the leaching of chromium, and finally a leaching solution containing multiple heavy metals and acid-washed fly ash are obtained; S3: The leaching solution is sequentially subjected to filtration and adsorption purification treatment to obtain a purified leaching solution; filtration is used to remove suspended particulate matter in the leaching solution; and the adsorbent used in the adsorption purification treatment accounts for 1 t% of the mass of the leaching solution; S4: 5 kg of the leaching solution after adsorption purification is first adjusted to pH 4.0, 0.02 kg of sodium carbonate is added as a precipitant, and the precipitation is carried out at a stirring speed of 150 r / min and a temperature of 30℃ for 40 min, and then zinc carbonate is obtained by filtration separation; the pH value of the filtrate after separation of zinc is adjusted to 6.0, 0.01 kg of sodium sulfide is added as a precipitant, and the precipitation is carried out at a stirring speed of 150 r / min and a temperature of 35℃ for 50 min, and then lead sulfide is obtained by filtration separation; LIX984N extractant is added to the filtrate after separation of lead to realize extraction of copper; then 10wt% sulfuric acid solution is used as a stripping agent for stripping to obtain a copper-containing solution, and then copper is recovered by electrodeposition technology; S5: the waste acid generated by the multi-stage countercurrent pickling is subjected to neutralization and impurity removal treatment by filtration and then recycled back to the multi-stage countercurrent pickling system.

[0072] The stirring speed of S1 is 200 r / min, and the stirring time is 30 min.

[0073] The liquid-solid ratio of the leaching agent to the dechlorination fly ash in S2 is 4:1.

[0074] The adsorbent of S3 is activated carbon.

[0075] The adsorption time of the adsorption purification treatment of S3 is 30 min, and the temperature is 25℃.

[0076] The volume ratio of the LIX984N extractant to the filtrate in S4 is 1:2, and the volume ratio of the stripping agent to the extract solution is 1:1.

[0077] The current density of the electrodeposition recovery of copper in S4 is 200 A / m², the temperature is 40℃, the electrolysis time is 2 h, and the cell voltage is 2.0 V.

[0078] In S5, calcium hydroxide is used to adjust the pH value to 2.0, and a microporous filtration membrane with a pore size of 0.1 μm is used for filtration.

[0079] Comparative Example 3 A method for reducing the content of heavy metals in waste incineration fly ash, the operation steps of which are as follows: S1: 10 kg of waste incineration fly ash is mixed and stirred in 30 kg of water, and then solid-liquid separation is performed to obtain dechlorination fly ash and chlorine-containing wastewater, and the chlorine-containing wastewater is discharged after treatment. S2: send the dechlorination fly ash into a multi-stage countercurrent pickling system, using a thiourea-sulfuric acid mixture as the leaching agent; the first stage pickling has a pH value of 1.0, a temperature of 40℃, and a time of 60 min, to realize the preferential leaching of zinc and copper; the second stage pickling has a pH value of 2.0, a temperature of 50℃, and a time of 90 min, to realize the leaching of lead and cadmium; the third stage pickling has a pH value of 3.0, a temperature of 60℃, and a time of 120 min, to realize the leaching of chromium; finally, an leaching solution containing multiple heavy metals and fly ash after pickling are obtained; S3: sequentially pass the leaching solution through filtration and adsorption purification treatment to obtain a purified leaching solution; remove suspended particulate matter in the leaching solution by filtration; the adsorbent used in the adsorption purification treatment has a dosage of 1t% of the mass of the leaching solution; S4: take 5kg of the leaching solution after adsorption purification, first adjust the pH value to 4.0, add 0.02kg of sodium carbonate as a precipitant, and precipitate under the conditions of a stirring speed of 150r / min and a temperature of 30℃ for 40 min, to obtain zinc carbonate by filtration separation; adjust the pH value of the filtrate after zinc separation to 6.0, add 0.01kg of sodium sulfide as a precipitant, and precipitate under the conditions of a stirring speed of 150r / min and a temperature of 35℃ for 50 min, to obtain lead sulfide by filtration separation; add LIX984N extractant to the filtrate after lead separation to realize the extraction of copper; then use 10wt% sulfuric acid solution as a back-extracting agent to perform back-extraction, to obtain a copper-containing solution, and then recover copper by electrodeposition technology; S5: after neutralization and impurity removal treatment, the waste acid generated in the multi-stage countercurrent pickling is recycled back to the multi-stage countercurrent pickling system.

[0080] The stirring speed of S1 is 200r / min, and the stirring time is 30min.

[0081] The liquid-solid ratio of the leaching agent to the dechlorination fly ash in S2 is 4:1.

[0082] The adsorbent of S3 is activated carbon.

[0083] The adsorption time of the adsorption purification treatment in S3 is 30min, and the temperature is 25℃.

[0084] The volume ratio of the LIX984N extractant to the filtrate in S4 is 1:2, and the volume ratio of the back-extracting agent to the extract solution is 1:1.

[0085] The current density for electrodeposition to recover copper in S4 is 200A / m², the temperature is 40℃, the electrolysis time is 2h, and the cell voltage is 2.0V.

[0086] In S5, calcium hydroxide is used to adjust the pH value to 2.0 for neutralization, and a microporous filtration membrane with a pore size of 0.1μm is used for filtration.

[0087] The preparation method of the thiourea-sulfuric acid mixed solution is as follows: 0.1 kg of thiourea, 3 kg of sulfuric acid and 90 kg of deionized water are added into a reaction kettle, and after stirring and reaction, the mixture is cooled to room temperature to obtain the thiourea-sulfuric acid mixed solution.

[0088] The reaction temperature is 35°C, and the time is 30 minutes.

[0089] Table 1: Test result data table of examples and comparative examples Zinc recovery (%) Lead recovery (%) Copper recovery (%) Example 1 97.38 92.66 94.23 Example 2 97.43 92.69 94.27 Example 3 97.51 92.75 94.32 Example 4 97.56 92.78 94.36 Comparative Example 1 78.62 71.22 74.12 Comparative Example 2 90.05 85.31 87.91 Comparative Example 3 90.72 85.92 88.53 As can be clearly seen from the test results of the examples and comparative examples, the recovery effect of the method of the present application on zinc, lead and copper, three core valuable heavy metals, is significantly better than that of the traditional leaching scheme. The heavy metal recovery rate of the comparative examples using the traditional oxalic acid leaching agent or only partially matching the synergistic components is much lower than that of the examples of the present application. This difference verifies the core role of the "thiourea-sulfuric acid-dimercaprol" synergistic leaching system in the present application - the system can effectively solve the problem of insufficient heavy metal dissolution in the traditional leaching technology, and at the same time, combined with the multi-stage countercurrent pickling and waste acid recycling process, further ensures the stability of the recovery efficiency. Overall, the data table results fully prove the reliability and superiority of the method of the present application in improving the heavy metal recovery rate in waste incineration fly ash and realizing high-value utilization of resources.

[0090] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present application. Any simplification, modification, equivalent change and modification of the above examples made according to the technical essence of the present application, as long as it does not deviate from the technical solution of the present application, still belongs to the scope of the technical solution of the present application.

Claims

1. A method for reducing the heavy metal content in fly ash from waste incineration, comprising the following steps, by weight: S1: Add 10-20 parts of waste incineration fly ash to 30-100 parts of water, mix and stir, and then perform solid-liquid separation to obtain dechlorinated fly ash and chlorine-containing wastewater. The chlorine-containing wastewater is discharged after being treated to meet the standards. S2: The dechlorinated fly ash is fed into a multi-stage countercurrent pickling system, using a thiourea-sulfuric acid mixture as the leaching agent, and 0.03-0.15 parts of dimercaprol are added. The first-stage pickling is carried out at a pH of 1.0-1.5, a temperature of 40-50℃, and a time of 60-90 min to achieve preferential leaching of zinc and copper. The second-stage pickling is carried out at a pH of 2.0-2.5, a temperature of 50-60℃, and a time of 90-120 min to achieve leaching of lead and cadmium. The third-stage pickling is carried out at a pH of 3.0-3.5, a temperature of 60-70℃, and a time of 120-150 min to achieve leaching of chromium. Finally, a leachate containing multiple heavy metals and pickled fly ash are obtained. S3: The leachate is sequentially purified by filtration and adsorption to obtain a purified leachate; filtration removes suspended particulate matter from the leachate; the amount of adsorbent used in the adsorption purification process is 1-3 wt% of the mass of the leachate. S4: Adjust the pH of 5-10 parts of the adsorption-purified leachate to 4.0-4.5, add 0.02-0.2 parts of sodium carbonate as a precipitant, and precipitate for 40-60 minutes under stirring speed of 150-200 r / min and temperature of 30-40℃. Filter to obtain zinc carbonate. Adjust the pH of the zinc-separated filtrate to 6.0-6.5, add 0.01-0.05 parts of sodium sulfide as a precipitant, and precipitate for 50-70 minutes under stirring speed of 150-200 r / min and temperature of 35-45℃. Filter to obtain lead sulfide. Add LIX984N extractant to the lead-separated filtrate to extract copper. Then, use 10-20 wt% sulfuric acid solution as a back-extraction agent to perform back-extraction to obtain a copper-containing solution, and then recover copper by electrodeposition technology. S5: After neutralizing and filtering the waste acid generated by multi-stage countercurrent pickling, it is recycled back to the multi-stage countercurrent pickling system.

2. The method for reducing the content of heavy metals in waste incineration fly ash according to claim 1, characterized in that: The stirring speed of S1 is 200-300 r / min, and the stirring time is 30-60 min.

3. The method for reducing the content of heavy metals in waste incineration fly ash according to claim 1, characterized in that: The liquid-to-solid ratio of the S2 extractant to the dechlorinated fly ash is 4-8:

1.

4. The method for reducing the content of heavy metals in waste incineration fly ash according to claim 1, characterized in that: The adsorbent for S3 is one of activated carbon, aminophosphonic acid chelating resin, or iminodiacetic acid chelating resin.

5. The method for reducing the content of heavy metals in waste incineration fly ash according to claim 1, characterized in that: The adsorption time for the S3 adsorption purification treatment is 30-60 min, and the temperature is 25-35℃.

6. The method of claim 1, wherein the method is characterized by: The volume ratio of the S4LIX984N extractant to the filtrate is 1:2-3, and the volume ratio of the back-extractant to the extract is 1:1-2.

7. The method of claim 1, wherein the method further comprises: The S4 electrodeposition method for recovering copper has a current density of 200-300 A / m², a temperature of 40-50℃, an electrolysis time of 2-4 h, and a cell voltage of 2.0-2.5 V.

8. The method of claim 1, wherein the method further comprises: The neutralization in S5 adopts calcium hydroxide to adjust pH value to 2.0-2.5, and the filtration adopts microporous filter membrane with pore size of 0.1-0.2 μm.

9. The method of claim 1, wherein the method further comprises: The preparation method of the thiourea-sulfuric acid mixed solution is as follows: According to mass fraction, 0.1-1 part of thiourea, 3-5 parts of sulfuric acid and 90-96 parts of deionized water are added into a reaction kettle, and after stirring reaction, the reaction kettle is cooled to room temperature to obtain the thiourea-sulfuric acid mixed solution.

10. The method of claim 9, wherein the method further comprises: The reaction temperature of the stirring reaction is 35-55 ℃, and the time is 30-70 minutes.

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