Harmless treatment method of heavy metal sludge

Abstract

The invention relates to a heavy metal treatment technology, and discloses an innocent treatment method of heavy metal sludge, which comprises the following steps: conveying the heavy metal sludge with the water content of about 80% to a double-screw press, dewatering in cooperation with 0.5-1.0 g / kg of cationic polyacrylamide flocculant, and accurately regulating and controlling the water content to 92-95% of a slurry state by controlling the rotating speed (10-15rpm) of a screw in a variable frequency manner, a planetary mixer is adopted for homogenization treatment for 30 minutes at the rotating speed of 200 rpm, it is ensured that the heavy metal distribution uniformity coefficient is smaller than 5%, and a differential stabilization strategy is adopted according to different heavy metal characteristics. According to the harmless treatment method for the heavy metal sludge, high-purity valuable metal is effectively recycled, residues are converted into building ceramsite meeting the standard, safety landfill and ecological restoration measures ensure the environmental safety of final treatment, and long-term ecological risk quotients meet the requirements; the treatment targets of harmlessness, reduction and recycling of the heavy metal sludge are comprehensively achieved, and the sustainable development of the environmental protection industry is powerfully promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy metal treatment, in particular to a method for harmless treatment of heavy metal sludge. Background Art

[0002] Heavy metal sludge treatment refers to a series of operations to reduce, stabilize, decontaminate and recycle sludge containing high concentrations of heavy metals, such as lead, cadmium, mercury, chromium, etc. These heavy metals are very harmful to the environment and human health. Therefore, it is necessary to separate the heavy metals in the sludge through heat treatment, chemical precipitation, biological methods or solidification treatment, convert them into non-toxic compounds or immobilize them to reduce their pollution to the environment and ensure that the treated sludge will not cause harm to the environment and human health.

[0003] At present, the treatment of heavy metal sludge faces many severe challenges. With the rapid development of industrial production, the amount of heavy metal sludge generated is increasing. Its composition is complex and contains a large amount of toxic heavy metals such as lead and cadmium. If it is not handled properly, it is very easy to cause serious pollution to the ecological environment such as soil and water bodies, threatening human health. Traditional heavy metal sludge treatment methods, such as simple landfill or incineration, not only cannot achieve effective fixation of heavy metals, but may also cause secondary pollution. At the same time, the resource utilization rate is extremely low, resulting in a huge waste of resources. Although some existing treatment technologies can reduce heavy metal pollution to a certain extent, there are still obvious deficiencies in treatment effect, cost control, resource recycling and utilization, etc., which are difficult to meet the increasingly stringent environmental protection requirements and sustainable development needs. Therefore, there is an urgent need for a harmless treatment method for heavy metal sludge that can effectively reduce the toxicity of heavy metal leaching, improve the heavy metal fixation effect, achieve efficient resource recycling and utilization, and ensure environmental safety. Summary of the Invention

[0004] (1) Technical problems solved

[0005] In view of the shortcomings of the existing technology, the present invention provides a harmless treatment method for heavy metal sludge, which has the advantages of harmless treatment, reduction and resource utilization of metal sludge, and solves the problem of insufficient utilization of metal resources.

[0006] (2) Technical solution

[0007] In order to achieve the above-mentioned purpose of harmless treatment, reduction and resource utilization of metal sludge, the present invention provides the following technical solution: a method for harmless treatment of heavy metal sludge, comprising the following steps:

[0008] S1. Heavy metal sludge pretreatment and heavy metal stabilization

[0009] The heavy metal sludge with a moisture content of about 80% is transported to a twin-screw press and dehydrated with 0.5-1.0g / kg cationic polyacrylamide flocculant. The screw speed is controlled by frequency conversion (10-15rpm) to accurately adjust the moisture content to a slurry state of 92%-95%. A planetary mixer is used to homogenize the sludge at 200rpm for 30 minutes to ensure that the heavy metal distribution uniformity coefficient is less than 5%. Differentiated stabilization strategies are adopted for different heavy metal characteristics. Lead-contaminated sludge is added. A chelating agent consisting of disodium ethylenediaminetetraacetic acid (EDTA-2Na) and nano-zero-valent iron (nZVI) in a ratio of 1:2 was used, while a chitosan-sodium alginate composite flocculant was used for cadmium-contaminated sludge. The surface charge of the flocs was monitored in real time using a zeta potential meter. When the absolute potential value exceeded 30 mV, a stable floc structure was formed. Leaching toxicity was then tested using inductively coupled plasma mass spectrometry (ICP-MS). The leached concentrations of lead and cadmium were reduced by 65% ​​and 58%, respectively, laying the foundation for subsequent synergistic stabilization.

[0010] S2. Synergistic stabilization using bio-chemical methods

[0011] The sludge obtained in the above steps was transferred to a jacketed temperature-controlled reactor, and chitosan with a deacetylation degree ≥90%, 50-80 nm nanohydroxyapatite (nHA), and humic acid with a molecular weight >5000 Da were added in sequence. The speed was maintained at 300 rpm by a variable frequency speed-controlled stirrer. At 25±2°C, the amino groups of chitosan formed coordination bonds with heavy metal ions, the phosphate groups of nHA fixed the metals through surface complexation, and the carboxylic acid groups of humic acid provided additional chelating sites. The amide bonds (1650 cm -1 ) and phosphate (1040 cm -1 ) characteristic peak shift. When the chelation reaction reaches equilibrium, the lead and cadmium leaching concentrations drop to 0.12 mg / L and 0.03 mg / L, respectively, which are only 1 / 8 and 1 / 10 of the GB5085.3 standard. X-ray diffraction (XRD) analysis confirms the formation of hydroxyapatite solid solution (Ca 10 Composite structure of (PO4)6(OH)2) and humic acid-metal complex;

[0012] S3, magnetic separation-membrane separation coupled recovery

[0013] After the stabilized sludge was mixed with deionized water in a ratio of 1:5, it was dispersed for 30 minutes using a 300W ultrasonic processor to destroy the particle agglomeration structure. The HGMS system with a gradient magnetic field strength of 0.8-1.2T was used to achieve efficient separation of magnetic components by adjusting the drum speed (5-10rpm). The lead recovery rate reached 96.5%, and the purity of the iron-based magnetic particles was >98%. After separation, the filtrate passed through a PVDF membrane module with a molecular weight cutoff of 10kDa at a cross-flow velocity of 5m / s. The operating pressure was controlled at 0.15MPa, and the membrane flux was stabilized at 80L / (m 2 h), the concentrate is further enriched with heavy metals through reverse osmosis (RO) treatment. The freshwater quality meets the "Water Quality for Industrial Water Use in Municipal Wastewater Recycling" (GB / T19923) standard, with COD < 50mg / L. It can be recycled in the pretreatment stage, realizing closed-loop utilization of water resources.

[0014] S4. Microbial Leaching and Resource Utilization

[0015] The inoculation concentration of magnetic tailings is 1×10 6 CFU / mL of Thiobacillus ferrooxidans was cultured in 9K medium at pH 1.5 at 35°C for 7 days using a constant temperature shaker (180 rpm) and the Fe 2+ The concentration is 2-3g / L, and the ORP is stable at 450-500mV. After the leaching is completed, the mixed solution is placed in a high-pressure reactor and pyrolyzed at 200℃ for 15 minutes under nitrogen protection. The organic matter removal rate is greater than 99%, and the decomposition rate of dioxins is 99.99%. The leaching solution is subjected to pulse current electrodeposition technology (current density 200A / m 2 , duty cycle 50%), metals were recovered on titanium-based lead dioxide electrodes, copper purity was 99.95%, nickel purity was 99.92%, Ca(OH)2 was added to the remaining liquid to adjust the pH to 10, and after plate and frame filtration, the filter cake (water content 58%) was mixed with fly ash in a ratio of 1:3 and sintered at 1100°C for 2 hours to prepare ceramsite with a compressive strength of 22 MPa and a water absorption rate of <8%, which met the standard of "Light Aggregates and Their Test Methods" (GB / T17431.1);

[0016] S5. Safe landfill and ecological restoration

[0017] The treated sludge solid phase (total heavy metal content <50 mg / kg) was mixed with sodium bentonite (montmorillonite content 88%) and crushed straw (particle size <2 mm) in a ratio of 7:2:1. After being fully mixed by a double-shaft mixer (speed 50 rpm), the mixture was formed into 200 mm × 100 mm × 50 mm blocks using a brick press with a compressive strength >15 MPa. The landfill used a double-layer anti-seepage system of HDPE membrane (thickness 2.0 mm). When landfilling in different areas, 50 cm of sludge blocks were laid on each layer, and 10 cm of sandy clay (permeability coefficient <1×10 -7 The surface vegetation concrete is made of Portland cement, aggregate (particle size 5-10mm), and heavy metal-resistant reed extract (active ingredient 18%) in a ratio of 4:5:1. It is spray-cured to form a permeable structure with a porosity of 28%. A microelectrode array monitoring system is used to detect the concentrations of lead and cadmium ions in the soil around the landfill in real time. Combined with the risk assessment model (RAC method), the long-term ecological risk quotient is ensured to be less than 0.8, meeting the requirements of the "Technical Guidelines for Risk Assessment of Contaminated Sites" (HJ25.3).

[0018] Preferably, in step S1, before transporting the sludge to the twin-screw press, it is necessary to check whether the pipeline is damaged to ensure smooth transportation. When adding cationic polyacrylamide flocculant, it must be prepared and used immediately to prevent it from being ineffective due to long-term exposure. During the frequency conversion control of the screw speed, pay close attention to the equipment operation status to avoid abnormal jamming. When the planetary mixer is running, the sealing of the equipment must be ensured to prevent material overflow.

[0019] Preferably, in step S1, when using a zeta potential meter for monitoring, the instrument is calibrated regularly to ensure data accuracy. Before using ICP-MS to detect leaching toxicity, the instrument must be preheated and debugged to ensure that the test results are reliable, thereby laying a solid foundation for the smooth implementation of subsequent collaborative stabilization work.

[0020] Preferably, in step S2, before transferring the sludge into the jacketed temperature-controlled reactor, the sealing of the reactor and the operating status of the jacket temperature control system must be carefully checked to ensure that the temperature can be accurately maintained at 25±2°C. When adding chitosan, nano-hydroxyapatite and humic acid, they must be accurately weighed to prevent impurities from mixing into the reagents and affecting the reaction.

[0021] Preferably, in step S2, when using an in-situ FTIR spectrometer for monitoring, the instrument wavelength is calibrated in advance to ensure the accuracy of the characteristic peak displacement data. Before X-ray diffraction analysis, the sample must be fully ground and evenly spread to ensure that the analysis results can truly reflect the generated composite structure, thereby ensuring the efficient and accurate conduct of the entire synergistic stabilization reaction.

[0022] Preferably, in step S3, before the filtrate passes through the PVDF membrane assembly, the membrane assembly is checked for damage. During the operation, the pressure is strictly controlled at 0.15 MPa to prevent pressure fluctuations from damaging the membrane. When the concentrate is treated by reverse osmosis, the dirt on the surface of the RO membrane is regularly cleaned to ensure that the fresh water quality is stable and meets the standards. All operations are strictly standardized to ensure the smooth realization of closed-loop utilization of water resources.

[0023] Preferably, in step S4, before inoculating Thiobacillus ferrooxidans, it is necessary to ensure that the concentration of the bacterial solution is accurate and free of contamination by other bacteria, the 9K culture medium is configured according to the standard and strictly sterilized, the operating stability of the constant temperature shaker is checked before use, and the speed and temperature are accurate. When recovering metals by electrodeposition, impurities on the electrode surface are cleaned regularly, and when adjusting the pH of the remaining liquid, Ca(OH)2 is slowly added and monitored in real time. During the preparation of ceramsite, the sintering temperature and time are controlled, and each link is strictly controlled to ensure that the product meets the standards.

[0024] Preferably, in step S5, before mixing the sludge solid phase, sodium bentonite and crushed straw, it is necessary to carefully check whether the quality and particle size of each material meet the standards, and accurately weigh them in a strict 7:2:1 ratio. Before the twin-shaft mixer is operated, it is confirmed that the blades are not damaged and are firmly installed, and the speed is stable at 50 rpm.

[0025] (3) Beneficial effects

[0026] Compared with the prior art, the present invention provides a harmless treatment method for heavy metal sludge, which has the following beneficial effects:

[0027] 1. This harmless treatment method for heavy metal sludge effectively reduces the toxicity of heavy metal leaching by precisely controlling equipment parameters and using targeted agents, laying a solid foundation for subsequent treatment. The biological-chemical synergistic stabilization greatly improves the heavy metal fixation effect, making the lead and cadmium leaching concentrations far below the national standard. The magnetic separation-membrane separation coupled recovery realizes the efficient recovery of magnetic metals and the closed-loop utilization of water resources, improving resource utilization. The microbial leaching and resource utilization links not only effectively recover high-purity valuable metals, but also convert the residue into standard building expanded clay. Safe landfill and ecological restoration measures ensure the environmental safety of the final disposal. The long-term ecological risk quotient meets the requirements, and the treatment goals of harmlessness, reduction and resource utilization of heavy metal sludge are achieved in all aspects, which effectively promotes the sustainable development of the environmental protection industry.

[0028] 2. This harmless treatment method for heavy metal sludge effectively avoids problems such as agent failure, bacterial contamination, and substandard materials through strict management of agent storage, bacterial culture, and material mixing ratios. Comprehensive measures in product transfer, equipment cleaning, filter cloth cleaning, and data backup further ensure the efficiency, stability, and safety of the entire treatment process, reduce potential risks during the treatment process, and provide solid support for the industrial application of heavy metal sludge treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a flow chart of the preparation method of the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Example 1:

[0032] The harmless treatment method of heavy metal sludge comprises the following steps:

[0033] S1. Heavy metal sludge pretreatment and heavy metal stabilization

[0034] The heavy metal sludge with a moisture content of about 80% is transported to a twin-screw press and dehydrated with 0.5-1.0g / kg cationic polyacrylamide flocculant. The screw speed is controlled by frequency conversion (10-15rpm) to accurately adjust the moisture content to a slurry state of 92%-95%. A planetary mixer is used to homogenize the sludge at 200rpm for 30 minutes to ensure that the heavy metal distribution uniformity coefficient is less than 5%. Differentiated stabilization strategies are adopted for different heavy metal characteristics. Lead-contaminated sludge is added. A chelating agent consisting of disodium ethylenediaminetetraacetic acid (EDTA-2Na) and nano-zero-valent iron (nZVI) in a ratio of 1:2 was used, while a chitosan-sodium alginate composite flocculant was used for cadmium-contaminated sludge. The surface charge of the flocs was monitored in real time using a zeta potential meter. When the absolute potential value exceeded 30 mV, a stable floc structure was formed. Leaching toxicity was then tested using inductively coupled plasma mass spectrometry (ICP-MS). The leached concentrations of lead and cadmium were reduced by 65% ​​and 58%, respectively, laying the foundation for subsequent synergistic stabilization.

[0035] S2. Synergistic stabilization using bio-chemical methods

[0036] The sludge obtained in the above steps was transferred to a jacketed temperature-controlled reactor, and chitosan with a deacetylation degree ≥90%, 50-80 nm nanohydroxyapatite (nHA), and humic acid with a molecular weight >5000 Da were added in sequence. The speed was maintained at 300 rpm by a variable frequency speed-controlled stirrer. At 25±2°C, the amino groups of chitosan formed coordination bonds with heavy metal ions, the phosphate groups of nHA fixed the metals through surface complexation, and the carboxylic acid groups of humic acid provided additional chelating sites. The amide bonds (1650 cm -1 ) and phosphate (1040 cm -1 ) characteristic peak shift. When the chelation reaction reaches equilibrium, the lead and cadmium leaching concentrations drop to 0.12 mg / L and 0.03 mg / L, respectively, which are only 1 / 8 and 1 / 10 of the GB5085.3 standard. X-ray diffraction (XRD) analysis confirms the formation of hydroxyapatite solid solution (Ca 10 Composite structure of (PO4)6(OH)2) and humic acid-metal complex;

[0037] S3, magnetic separation-membrane separation coupled recovery

[0038] After the stabilized sludge was mixed with deionized water in a ratio of 1:5, it was dispersed for 30 minutes using a 300W ultrasonic processor to destroy the particle agglomeration structure. The HGMS system with a gradient magnetic field strength of 0.8-1.2T was used to achieve efficient separation of magnetic components by adjusting the drum speed (5-10rpm). The lead recovery rate reached 96.5%, and the purity of the iron-based magnetic particles was >98%. After separation, the filtrate passed through a PVDF membrane module with a molecular weight cutoff of 10kDa at a cross-flow velocity of 5m / s. The operating pressure was controlled at 0.15MPa, and the membrane flux was stabilized at 80L / (m 2 h), the concentrate is further enriched with heavy metals through reverse osmosis (RO) treatment. The freshwater quality meets the "Water Quality for Industrial Water Use in Municipal Wastewater Recycling" (GB / T19923) standard, with COD < 50mg / L. It can be recycled in the pretreatment stage, realizing closed-loop utilization of water resources.

[0039] S4. Microbial Leaching and Resource Utilization

[0040] The inoculation concentration of magnetic tailings is 1×10 6 CFU / mL of Thiobacillus ferrooxidans was cultured in 9K medium at pH 1.5 at 35°C for 7 days using a constant temperature shaker (180 rpm) and the Fe 2+The concentration is 2-3g / L, and the ORP is stable at 450-500mV. After the leaching is completed, the mixed solution is placed in a high-pressure reactor and pyrolyzed at 200℃ for 15 minutes under nitrogen protection. The organic matter removal rate is greater than 99%, and the decomposition rate of dioxins is 99.99%. The leaching solution is subjected to pulse current electrodeposition technology (current density 200A / m 2 , duty cycle 50%), metals were recovered on titanium-based lead dioxide electrodes, copper purity was 99.95%, nickel purity was 99.92%, Ca(OH)2 was added to the remaining liquid to adjust the pH to 10, and after plate and frame filtration, the filter cake (water content 58%) was mixed with fly ash in a ratio of 1:3 and sintered at 1100°C for 2 hours to prepare ceramsite with a compressive strength of 22 MPa and a water absorption rate of <8%, which met the standard of "Light Aggregates and Their Test Methods" (GB / T17431.1);

[0041] S5. Safe landfill and ecological restoration

[0042] The treated sludge solid phase (total heavy metal content <50 mg / kg) was mixed with sodium bentonite (montmorillonite content 88%) and crushed straw (particle size <2 mm) in a ratio of 7:2:1. After being fully mixed by a double-shaft mixer (speed 50 rpm), the mixture was formed into 200 mm × 100 mm × 50 mm blocks using a brick press with a compressive strength >15 MPa. The landfill used a double-layer anti-seepage system of HDPE membrane (thickness 2.0 mm). When landfilling in different areas, 50 cm of sludge blocks were laid on each layer, and 10 cm of sandy clay (permeability coefficient <1×10 -7 The surface vegetation concrete is made of Portland cement, aggregate (particle size 5-10mm), and heavy metal-resistant reed extract (active ingredient 18%) in a ratio of 4:5:1. It is spray-cured to form a permeable structure with a porosity of 28%. A microelectrode array monitoring system is used to detect the concentrations of lead and cadmium ions in the soil around the landfill in real time. Combined with the risk assessment model (RAC method), the long-term ecological risk quotient is ensured to be less than 0.8, meeting the requirements of the "Technical Guidelines for Risk Assessment of Contaminated Sites" (HJ25.3).

[0043] Example 2:

[0044] The harmless treatment method of heavy metal sludge comprises the following steps:

[0045] S1. Heavy metal sludge pretreatment and heavy metal stabilization

[0046] The heavy metal sludge with a moisture content of about 80% is transported to a twin-screw press and dehydrated with 0.5-1.0g / kg cationic polyacrylamide flocculant. The screw speed is controlled by frequency conversion (10-15rpm) to accurately adjust the moisture content to a slurry state of 92%-95%. A planetary mixer is used to homogenize the sludge at 200rpm for 30 minutes to ensure that the heavy metal distribution uniformity coefficient is less than 5%. Differentiated stabilization strategies are adopted for different heavy metal characteristics. Lead-contaminated sludge is added. A chelating agent consisting of disodium ethylenediaminetetraacetic acid (EDTA-2Na) and nano-zero-valent iron (nZVI) in a ratio of 1:2 was used, while a chitosan-sodium alginate composite flocculant was used for cadmium-contaminated sludge. The surface charge of the flocs was monitored in real time using a zeta potential meter. When the absolute potential value exceeded 30 mV, a stable floc structure was formed. Leaching toxicity was then tested using inductively coupled plasma mass spectrometry (ICP-MS). The leached concentrations of lead and cadmium were reduced by 65% ​​and 58%, respectively, laying the foundation for subsequent synergistic stabilization.

[0047] S2. Synergistic stabilization using bio-chemical methods

[0048] The sludge obtained in the above steps was transferred to a jacketed temperature-controlled reactor, and chitosan with a deacetylation degree ≥90%, 50-80 nm nanohydroxyapatite (nHA), and humic acid with a molecular weight >5000 Da were added in sequence. The speed was maintained at 300 rpm by a variable frequency speed-controlled stirrer. At 25±2°C, the amino groups of chitosan formed coordination bonds with heavy metal ions, the phosphate groups of nHA fixed the metals through surface complexation, and the carboxylic acid groups of humic acid provided additional chelating sites. The amide bonds (1650 cm -1 ) and phosphate (1040 cm -1 ) characteristic peak shift. When the chelation reaction reaches equilibrium, the lead and cadmium leaching concentrations drop to 0.12 mg / L and 0.03 mg / L, respectively, which are only 1 / 8 and 1 / 10 of the GB5085.3 standard. X-ray diffraction (XRD) analysis confirms the formation of hydroxyapatite solid solution (Ca 10 Composite structure of (PO4)6(OH)2) and humic acid-metal complex;

[0049] S3, magnetic separation-membrane separation coupled recovery

[0050] After the stabilized sludge was mixed with deionized water in a ratio of 1:5, it was dispersed for 30 minutes using a 300W ultrasonic processor to destroy the particle agglomeration structure. The HGMS system with a gradient magnetic field strength of 0.8-1.2T was used to achieve efficient separation of magnetic components by adjusting the drum speed (5-10rpm). The lead recovery rate reached 96.5%, and the purity of the iron-based magnetic particles was >98%. After separation, the filtrate passed through a PVDF membrane module with a molecular weight cutoff of 10kDa at a cross-flow velocity of 5m / s. The operating pressure was controlled at 0.15MPa, and the membrane flux was stabilized at 80L / (m 2 h), the concentrate is further enriched with heavy metals through reverse osmosis (RO) treatment. The freshwater quality meets the "Water Quality for Industrial Water Use in Municipal Wastewater Recycling" (GB / T19923) standard, with COD < 50mg / L. It can be recycled in the pretreatment stage, realizing closed-loop utilization of water resources.

[0051] S4. Microbial Leaching and Resource Utilization

[0052] The inoculation concentration of magnetic tailings is 1×10 6 CFU / mL of Thiobacillus ferrooxidans was cultured in 9K medium at pH 1.5 at 35°C for 7 days using a constant temperature shaker (180 rpm) and the Fe 2+ The concentration is 2-3g / L, and the ORP is stable at 450-500mV. After the leaching is completed, the mixed solution is placed in a high-pressure reactor and pyrolyzed at 200℃ for 15 minutes under nitrogen protection. The organic matter removal rate is greater than 99%, and the decomposition rate of dioxins is 99.99%. The leaching solution is subjected to pulse current electrodeposition technology (current density 200A / m 2 , duty cycle 50%), metals were recovered on titanium-based lead dioxide electrodes, copper purity was 99.95%, nickel purity was 99.92%, Ca(OH)2 was added to the remaining liquid to adjust the pH to 10, and after plate and frame filtration, the filter cake (water content 58%) was mixed with fly ash in a ratio of 1:3 and sintered at 1100°C for 2 hours to prepare ceramsite with a compressive strength of 22 MPa and a water absorption rate of <8%, which met the standard of "Light Aggregates and Their Test Methods" (GB / T17431.1);

[0053] S5. Safe landfill and ecological restoration

[0054] The treated sludge solid phase (total heavy metal content <50 mg / kg) was mixed with sodium bentonite (montmorillonite content 88%) and crushed straw (particle size <2 mm) in a ratio of 7:2:1. After being fully mixed by a double-shaft mixer (speed 50 rpm), the mixture was formed into 200 mm × 100 mm × 50 mm blocks using a brick press with a compressive strength >15 MPa. The landfill used a double-layer anti-seepage system of HDPE membrane (thickness 2.0 mm). When landfilling in different areas, 50 cm of sludge blocks were laid on each layer, and 10 cm of sandy clay (permeability coefficient <1×10 -7 The surface vegetation concrete is made of Portland cement, aggregate (particle size 5-10mm), and heavy metal-resistant reed extract (active ingredient 18%) in a ratio of 4:5:1. It is spray-cured to form a permeable structure with a porosity of 28%. A microelectrode array monitoring system is used to detect the concentrations of lead and cadmium ions in the soil around the landfill in real time. Combined with the risk assessment model (RAC method), the long-term ecological risk quotient is ensured to be less than 0.8, meeting the requirements of the "Technical Guidelines for Risk Assessment of Contaminated Sites" (HJ25.3).

[0055] Specifically, in step S1, before transporting the sludge to the twin-screw press, it is necessary to check whether the pipeline is damaged to ensure smooth transportation. When adding cationic polyacrylamide flocculant, it must be prepared and used immediately to prevent it from being ineffective due to long-term exposure. During the frequency conversion control of the screw speed, pay close attention to the equipment operation status to avoid abnormal jamming. When the planetary mixer is running, the sealing of the equipment must be ensured to prevent material overflow.

[0056] Specifically, in step S1, when using a zeta potential meter for monitoring, the instrument should be calibrated regularly to ensure data accuracy. Before using ICP-MS to detect leaching toxicity, the instrument should be preheated and debugged to ensure that the test results are reliable, thereby laying a solid foundation for the smooth implementation of subsequent collaborative stabilization work.

[0057] Specifically, in step S2, before transferring the sludge into the jacketed temperature-controlled reactor, be sure to carefully check the sealing of the reactor and the operating status of the jacket temperature control system to ensure that the temperature can be accurately maintained at 25±2°C. When adding chitosan, nanohydroxyapatite and humic acid, they must be accurately weighed to prevent impurities from mixing into the reagents and affecting the reaction.

[0058] Specifically, in step S2, when using an in-situ FTIR spectrometer for monitoring, the instrument wavelength is calibrated in advance to ensure the accuracy of the characteristic peak displacement data. Before X-ray diffraction analysis, the sample must be fully ground and evenly spread to ensure that the analysis results can truly reflect the generated composite structure, thereby ensuring the efficient and accurate progress of the entire synergistic stabilization reaction.

[0059] Specifically, in step S3, before the filtrate passes through the PVDF membrane assembly, check whether the membrane assembly is damaged. During the operation, the pressure is strictly controlled at 0.15 MPa to prevent pressure fluctuations from damaging the membrane. When the concentrate is treated by reverse osmosis, the dirt on the surface of the RO membrane is regularly cleaned to ensure that the fresh water quality is stable and meets the standards. All operations are strictly standardized to ensure the smooth realization of closed-loop utilization of water resources.

[0060] Specifically, in step S4, before inoculating Thiobacillus ferrooxidans, it is necessary to ensure that the concentration of the bacterial solution is accurate and free of contamination by other bacteria, the 9K culture medium is configured according to the standard and strictly sterilized, and the operating stability of the constant temperature shaker is checked before use to ensure the accuracy of the speed and temperature. When electroplating to recover metals, impurities on the electrode surface are cleaned regularly, and when adjusting the pH of the remaining liquid, Ca(OH)2 is slowly added and monitored in real time. During the preparation of ceramsite, the sintering temperature and time are controlled, and each link is strictly controlled to ensure that the product meets the standards.

[0061] Specifically, in step S5, before mixing the sludge solid phase, sodium bentonite and crushed straw, it is necessary to carefully check whether the quality and particle size of each material meet the standards, and accurately weigh them in a strict 7:2:1 ratio. Before the twin-shaft mixer is operated, confirm that the blades are not damaged and are firmly installed, and the speed is stable at 50 rpm.

[0062] For heavy metal sludge with different characteristics, the storage conditions of the reagents involved in the differentiated stabilization strategy need to be strictly controlled. For example, the chelating agent EDTA-2Na and nZVI should be sealed and stored in a cool and dry place to prevent it from deteriorating and affecting the stabilization effect. In step S2, after the reaction in the reactor is completed, care should be taken to avoid secondary contamination when transferring the product, and the interior of the reactor should be cleaned and maintained regularly to ensure the accuracy of subsequent batch reactions. In step S3, when the ultrasonic processor disperses the sludge, the wear of the ultrasonic probe needs to be checked regularly. If the wear is serious, it should be replaced in time to avoid affecting the dispersion effect. The HGMS system runs for a period of time. Finally, the magnetic field generator must be calibrated to ensure that the magnetic field strength is stable. In step S4, when gas chromatography-mass spectrometry (GC-MS) is used to detect organic matter, the chromatographic column must be replaced regularly to prevent the decline in column efficiency from affecting the detection results. When there is residual liquid in the plate and frame filter press, the filter cloth must be cleaned in time to ensure the filter press efficiency. In step S5, when laying HDPE membranes in the landfill, attention must be paid to the welding quality between the membranes to ensure the anti-seepage effect. When using a microelectrode array monitoring system, the monitoring data must be backed up regularly to prevent data loss from affecting the accuracy of the ecological risk assessment, and to comprehensively ensure that the harmless treatment method for heavy metal sludge is implemented efficiently, stably and safely.

[0063] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. The harmless treatment method of heavy metal sludge includes the following steps: S1. Heavy metal sludge pretreatment and heavy metal stabilization The heavy metal sludge with a moisture content of about 80% is transported to a twin-screw press and dehydrated with 0.5-1.0g / kg cationic polyacrylamide flocculant. The screw speed is controlled by frequency conversion (10-15rpm) to accurately adjust the moisture content to a slurry state of 92%-95%. A planetary mixer is used to homogenize the sludge at 200rpm for 30 minutes to ensure that the heavy metal distribution uniformity coefficient is less than 5%. Differentiated stabilization strategies are adopted for different heavy metal characteristics. Lead-contaminated sludge is added. A chelating agent consisting of disodium ethylenediaminetetraacetic acid (EDTA-2Na) and nano-zero-valent iron (nZVI) in a ratio of 1:2 was used, while a chitosan-sodium alginate composite flocculant was used for cadmium-contaminated sludge. The surface charge of the flocs was monitored in real time using a zeta potential meter. When the absolute potential value exceeded 30 mV, a stable floc structure was formed. Leaching toxicity was then tested using inductively coupled plasma mass spectrometry (ICP-MS). The leached concentrations of lead and cadmium were reduced by 65% ​​and 58%, respectively, laying the foundation for subsequent synergistic stabilization. S2. Synergistic stabilization using bio-chemical methods The sludge obtained in the above steps was transferred to a jacketed temperature-controlled reactor, and chitosan with a deacetylation degree ≥90%, 50-80 nm nanohydroxyapatite (nHA), and humic acid with a molecular weight >5000 Da were added in sequence. The speed was maintained at 300 rpm by a variable frequency speed-controlled stirrer. At 25±2°C, the amino groups of chitosan formed coordination bonds with heavy metal ions, the phosphate groups of nHA fixed the metals through surface complexation, and the carboxylic acid groups of humic acid provided additional chelating sites. The amide bonds (1650 cm -1 ) and phosphate (1040 cm -1 ) characteristic peak shift. When the chelation reaction reaches equilibrium, the lead and cadmium leaching concentrations drop to 0.12 mg / L and 0.03 mg / L, respectively, which are only 1 / 8 and 1 / 10 of the GB5085.3 standard. X-ray diffraction (XRD) analysis confirms the formation of hydroxyapatite solid solution (Ca 10 Composite structure of (PO4)6(OH)2) and humic acid-metal complex; S3, magnetic separation-membrane separation coupled recovery After the stabilized sludge was mixed with deionized water in a ratio of 1:5, it was dispersed for 30 minutes using a 300W ultrasonic processor to destroy the particle agglomeration structure. The HGMS system with a gradient magnetic field strength of 0.8-1.2T was used to achieve efficient separation of magnetic components by adjusting the drum speed (5-10rpm). The lead recovery rate reached 96.5%, and the purity of the iron-based magnetic particles was >98%. After separation, the filtrate passed through a PVDF membrane module with a molecular weight cutoff of 10kDa at a cross-flow velocity of 5m / s. The operating pressure was controlled at 0.15MPa, and the membrane flux was stabilized at 80L / (m 2 h), the concentrate is further enriched with heavy metals through reverse osmosis (RO) treatment. The freshwater quality meets the "Water Quality for Industrial Water Use in Municipal Wastewater Recycling" (GB / T19923) standard, with COD < 50mg / L. It can be recycled in the pretreatment stage, realizing closed-loop utilization of water resources. S4. Microbial Leaching and Resource Utilization The inoculation concentration of magnetic tailings is 1×10 6 CFU / mL of Thiobacillus ferrooxidans was cultured in 9K medium at pH 1.5 at 35°C for 7 days using a constant temperature shaker (180 rpm) and the Fe 2+ The concentration is 2-3g / L, and the ORP is stable at 450-500mV. After the leaching is completed, the mixed solution is placed in a high-pressure reactor and pyrolyzed at 200℃ for 15 minutes under nitrogen protection. The organic matter removal rate is greater than 99%, and the decomposition rate of dioxins is 99.99%. The leaching solution is subjected to pulse current electrodeposition technology (current density 200A / m 2 , duty cycle 50%), metals were recovered on titanium-based lead dioxide electrodes, copper purity was 99.95%, nickel purity was 99.92%, Ca(OH)2 was added to the remaining liquid to adjust the pH to 10, and after plate and frame filtration, the filter cake (water content 58%) was mixed with fly ash in a ratio of 1:3 and sintered at 1100°C for 2 hours to prepare ceramsite with a compressive strength of 22 MPa and a water absorption rate of <8%, which met the standard of "Light Aggregates and Their Test Methods" (GB / T17431.1); S5. Safe landfill and ecological restoration The treated sludge solid phase (total heavy metal content <50 mg / kg) was mixed with sodium bentonite (montmorillonite content 88%) and crushed straw (particle size <2 mm) in a ratio of 7:2:

1. After being fully mixed by a double-shaft mixer (speed 50 rpm), the mixture was formed into 200 mm × 100 mm × 50 mm blocks using a brick press with a compressive strength >15 MPa. The landfill used a double-layer anti-seepage system of HDPE membrane (thickness 2.0 mm). When landfilling in different areas, 50 cm of sludge blocks were laid on each layer, and 10 cm of sandy clay (permeability coefficient <1×10 - 7 The surface vegetation concrete is made of Portland cement, aggregate (particle size 5-10mm), and heavy metal-resistant reed extract (active ingredient 18%) in a ratio of 4:5:

1. It is spray-cured to form a permeable structure with a porosity of 28%. A microelectrode array monitoring system is used to detect the concentrations of lead and cadmium ions in the soil around the landfill in real time. Combined with the risk assessment model (RAC method), the long-term ecological risk quotient is ensured to be less than 0.8, meeting the requirements of the "Technical Guidelines for Risk Assessment of Contaminated Sites" (HJ25.3).

2. The method for harmless treatment of heavy metal sludge according to claim 1, characterized in that: In step S1, before transporting the sludge to the twin-screw press, it is necessary to check whether the pipeline is damaged to ensure smooth transportation. When adding cationic polyacrylamide flocculant, it must be prepared and used immediately to prevent it from being ineffective due to long-term exposure. During the frequency conversion control of the screw speed, close attention should be paid to the operating status of the equipment to avoid abnormal jamming. When the planetary mixer is running, the sealing of the equipment must be ensured to prevent material overflow.

3. The harmless treatment method for heavy metal sludge according to claim 1, characterized in that: In step S1, when using a zeta potential meter for monitoring, the instrument is calibrated regularly to ensure data accuracy. Before using ICP-MS to detect leaching toxicity, the instrument must be preheated and debugged to ensure that the test results are reliable, thereby laying a solid foundation for the smooth implementation of subsequent collaborative stabilization work.

4. The method for harmless treatment of heavy metal sludge according to claim 1, characterized in that: In step S2, before transferring the sludge into the jacketed temperature-controlled reactor, be sure to carefully check the sealing of the reactor and the operating status of the jacket temperature control system to ensure that the temperature can be accurately maintained at 25±2°C. When adding chitosan, nano-hydroxyapatite and humic acid, they must be accurately weighed to prevent impurities from mixing into the reagents and affecting the reaction.

5. The harmless treatment method for heavy metal sludge according to claim 1, characterized in that: In step S2, when using an in-situ FTIR spectrometer for monitoring, the instrument wavelength is calibrated in advance to ensure the accuracy of the characteristic peak displacement data. Before X-ray diffraction analysis, the sample must be fully ground and evenly spread to ensure that the analysis results can truly reflect the generated composite structure, thereby ensuring the efficient and accurate conduct of the entire synergistic stabilization reaction.

6. The harmless treatment method for heavy metal sludge according to claim 1, characterized in that: In step S3, before the filtrate passes through the PVDF membrane assembly, the membrane assembly is checked for damage. During operation, the pressure is strictly controlled at 0.15 MPa to prevent pressure fluctuations from damaging the membrane. When the concentrate is treated by reverse osmosis, dirt on the surface of the RO membrane is regularly cleaned to ensure that the fresh water quality is stable and meets the standards. All operations are strictly regulated to ensure the smooth implementation of closed-loop utilization of water resources.

7. The harmless treatment method for heavy metal sludge according to claim 1, characterized in that: In step S4, before inoculating Thiobacillus ferrooxidans, it is necessary to ensure that the concentration of the bacterial solution is accurate and free of contamination by other bacteria, the 9K culture medium is configured according to the standard and strictly sterilized, the operating stability of the constant temperature shaker is checked before use, and the speed and temperature are accurate. When electroplating to recover metals, impurities on the electrode surface are cleaned regularly, and when adjusting the pH of the remaining liquid, Ca(OH)2 is slowly added and monitored in real time. During the preparation of ceramsite, the sintering temperature and time are controlled, and each link is strictly controlled to ensure that the product meets the standards.

8. The harmless treatment method for heavy metal sludge according to claim 1, characterized in that: In step S5, before mixing the sludge solid phase, sodium bentonite and crushed straw, it is necessary to carefully check whether the quality and particle size of each material meet the standards and accurately weigh them in a strict 7:2:1 ratio. Before the twin-shaft mixer is operated, it is confirmed that the blades are not damaged and are firmly installed, and the speed is stable at 50 rpm.

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