Fly ash heavy metal stabilization method based on mechanochemical activation and product

Abstract

The invention discloses a fly ash heavy metal stabilization method based on mechanochemical activation. The fly ash heavy metal stabilization method comprises the following steps: (1) drying fly ash containing heavy metals and grinding the fly ash until the particle size is less than or equal to 200 microns; (2) preparing a composite additive: mixing and grinding nano-scale NaH2PO4-CaO and bentonite according to a mass ratio of 1: (3-5), wherein the particle size of the NaH2PO4-CaO is 50-200nm; (3) the composite additive accounting for 5-20% of the mass of the fly ash is added into the fly ash, mechanochemical activation treatment is carried out under the inert atmosphere, the ball milling rotating speed is 300-500 rpm, the ball-to-material ratio is (10-15): 1, and the activation time is 1-3 hours; and (4) adding water to adjust the size until the liquid-solid ratio is (2-4): 1, adjusting the pH value to 10-11, reacting for 12-24 hours, and curing and molding. Synchronous stabilization of multiple heavy metals such as Pb, Cd, Cu, Zn and the like in the fly ash is realized under the condition of normal temperature; the resource feasibility is improved; the treated fly ash meets the requirements of safe landfill or building raw materials, and the treatment cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste treatment and resource utilization, and in particular to a fly ash heavy metal stabilization method based on mechanochemical activation and a product thereof. Background Art

[0002] With the acceleration of urbanization, the annual production of municipal sludge has exceeded 60 million tons. Co-incineration of sewage sludge in power plant boilers has become a mainstream disposal method due to its advantages in both volume reduction and energy recovery. However, the fly ash produced by this co-incineration is classified as hazardous waste due to its concentration of heavy metals such as lead (50-500 mg / kg), cadmium (5-50 mg / kg), and copper (200-1000 mg / kg). If improperly disposed of, the heavy metals in the fly ash can leach out in acidic environments or through long-term weathering, causing irreversible contamination of soil and groundwater.

[0003] Current fly ash treatment technology faces bottlenecks: Traditional solidification methods face limitations: cement solidification causes a 50%-100% volume expansion, increasing landfill costs; chemical stabilizers (such as sulfides and phosphates) have poor selectivity for Pb / Cd and insufficient long-term stability; high-temperature treatment is limited: melting methods require temperatures exceeding 1200°C, consume 800-1200 kWh / ton of energy, and pose a significant risk of secondary enrichment of volatile metals such as Hg; and mechanochemical methods face bottlenecks: conventional additives (such as calcium silicate and iron oxide) differ significantly from the multi-metal reaction kinetics, resulting in Cd fixation efficiencies generally below 70%. Existing technologies struggle to balance environmental and economic performance, necessitating the development of efficient, integrated stabilization and resource recovery technologies. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desired to provide a fly ash heavy metal stabilization method based on mechanochemical activation to solve the above-mentioned technical problems.

[0005] A method for stabilizing heavy metals in fly ash based on mechanochemical activation comprises the following steps:

[0006] (1) Dry and grind the fly ash containing heavy metals to a particle size of ≤200 μm;

[0007] (2) preparing a composite additive: mixing and grinding nano-sized NaH2PO4-CaO and bentonite in a mass ratio of 1:(3-5), wherein the particle size of the NaH2PO4-CaO is 50-200 nm;

[0008] (3) adding the composite additive to the fly ash at a rate of 5% to 20% of the fly ash mass, and subjecting the fly ash to a mechanochemical activation treatment under an inert atmosphere, with a ball milling speed of 300 to 500 rpm, a ball-to-material ratio of (10-15):1, and an activation time of 1 to 3 hours;

[0009] (4) Add water to adjust the slurry to a liquid-solid ratio of (2-4):1, adjust the pH to 10-11, and react for 12-24 hours before solidifying and forming.

[0010] Furthermore, the composite additive also includes at least one of steel slag or fly ash, and the mass ratio of the steel slag to NaH2PO4-CaO is (0.5-2):1. The steel slag is crushed to ≤2mm and magnetically separated to remove iron, and the SiO2+Al2O3 content in the fly ash is ≥75%.

[0011] Furthermore, the composite additive includes fly ash, and a dispersant is added during the mechanochemical activation in step (3), wherein the dispersant is triethanolamine, and the addition amount is 0.1%-1% of the fly ash mass.

[0012] Furthermore, the curing molding in step (4) adopts compression molding, the pressure is 10-20 MPa, and the curing conditions are: temperature 35-40° C., relative humidity ≥85%, and curing time 7-14 days.

[0013] Furthermore, the composition of the nano-scale NaH2PO4-CaO is 50wt% NaH2PO4 and 50wt% CaO.

[0014] Furthermore, the bentonite is sodium bentonite and has a cation exchange capacity of ≥80 mmol / 100 g.

[0015] Furthermore, when the fly ash contains dioxins, ultraviolet photolysis treatment is performed before step (3): 1%-3% of the fly ash mass of TiO2 / activated carbon composite catalyst is added and irradiated under ultraviolet light of wavelength 254nm for 4-8 hours.

[0016] Furthermore, when the fly ash contains arsenic, arsenic pre-stabilization is performed before step (3): 1%-5% of the fly ash mass of FeSO4 is added to As 5+ Restore to As 3+ .

[0017] Furthermore, a heavy metal stabilized fly ash product prepared by the above method is provided.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The method of the present invention achieves efficient and simultaneous stabilization of multiple metals and significantly reduces leaching toxicity: through the mechanochemical activation of the composite additive (NaH2PO4-CaO / bentonite), a dual mechanism of Ca-Pb phosphate and bentonite interlayer adsorption is formed to achieve the simultaneous fixation of multiple metals Pb, Cd, Cu, and Zn. The reduction rate of Pb and Cd in the fly ash after treatment is greater than 97%, and the proportion of residual state is ≥85%. The method of the present invention can also be used for the coordinated treatment of arsenic / dioxin: As is pre-reduced by FeSO4 5+Converted to As 3+ A Ca-As-Fe precipitate is generated, reducing the As leaching concentration to ≤0.1 mg / L. Through UV photolysis combined with a TiO2 / activated carbon catalyst, the dioxin toxicity equivalent degradation rate exceeds 95%. The introduction of steel slag or fly ash fully utilizes other waste materials, conserving resources. The method of the present invention achieves a processing cost of less than 200 yuan per ton: room-temperature mechanochemical activation replaces high-temperature melting, reducing energy consumption by over 70%. Steel slag / fly ash partially replaces SDP-CaO in the composite additive, further reducing costs by 55% compared to traditional cement curing. Flexible molding methods: Pressed molding can adapt to different building material requirements, such as roadbed bricks and cement admixtures.

[0020] It should be understood that the contents described in the summary of the invention are not intended to limit the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention.

[0022] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0023] Example 1

[0024] Raw materials: fly ash from municipal sewage sludge (5% moisture content) from a power plant, heavy metal content Pb = 1800 mg / kg, Cd = 120 mg / kg, ground to 200 mesh.

[0025] Preparation of composite additive: Nano-scale NaH2PO4-CaO (particle size 50-100 nm, mechanically mixed by 50 wt% NaH2PO4 and 50 wt% CaO) and sodium bentonite (CEC = 85 mmol / 100 g) were mixed and ground in a mass ratio of 1:4.

[0026] Adding composite additives (12% of fly ash mass) to fly ash;

[0027] The samples were activated by planetary milling under nitrogen atmosphere (rotation speed 350 rpm, zirconia balls, ball-to-material ratio 15:1, time 2 h);

[0028] Add water to prepare the slurry (liquid-solid ratio 3:1), adjust the pH to 10.5±0.3 (NaOH solution), and react for 24 hours;

[0029] After press molding (pressure 10 MPa), curing (40°C, humidity 85%, 7 days).

[0030] Results: Leaching concentration: Pb 0.85 mg / L (decreased 98.2%), Cd 0.06 mg / L (decreased 99.1%); residual proportion: Pb 87%, Cd 89%; 28-day compressive strength: 4.1 MPa; processing cost per ton: 98 yuan.

[0031] Example 2

[0032] Raw materials: Municipal sludge (water content 60%) is mixed with fly ash from a power plant. The heavy metal content in the fly ash is: Pb = 1800 mg / kg, Cd = 120 mg / kg.

[0033] Composite additive: NaH2PO4-CaO: bentonite: steel slag = 1:4:1 (steel slag is crushed to 1mm and iron is removed by magnetic separation).

[0034] Adding composite additives (15% of fly ash mass) to fly ash;

[0035] Planetary ball mill (rotation speed 350 rpm, zirconia ball milling medium), ball to material ratio: 15:1, activation time 2.5 h (extended 0.5 h to enhance the dispersibility of bentonite).

[0036] Slurry preparation stage: liquid-solid ratio 3:1, stirring speed 200 rpm, pH control: 10.5±0.3 (maintained by adding 0.1 mol / L NaOH), reaction time 24 h (constant temperature 25°C);

[0037] Compression molding: 10MPa compression molding (simulating the strength requirements of roadbed materials), curing conditions: 40℃ oven curing for 7 days, relative humidity ≥85%.

[0038] Results: Leaching concentration Pb 0.85mg / L, Cd 0.06mg / L, 28-day strength 4.1MPa, 1-ton treatment cost 98 yuan, bentonite (high proportion 4 parts) fixed Pb through interlayer adsorption 2 +, calcium silicate in steel slag reacts with SDP-CaO to form Ca-Pb phosphate (Ca 10 (Pb)(PO4)6(OH)2), while the microporous structure of steel slag physically encapsulates Cd pollutants.

[0039] Example 3

[0040] Raw materials: Industrial sludge is mixed with the power plant, and the fly ash contains Pb = 2100 mg / kg and Cd = 150 mg / kg.

[0041] Composite additive: NaH2PO4-CaO: bentonite: fly ash = 1:3:2 (steel slag crushed to 1mm, magnetic separation to remove iron).

[0042] Adding composite additives (18% of fly ash mass) to fly ash;

[0043] Planetary ball mill (rotation speed 350 rpm, zirconia ball milling medium), ball to material ratio: 15:1, activation time 3 h.

[0044] Slurry preparation stage: liquid-solid ratio 3:1, stirring speed 200 rpm, pH control: 10.5±0.3 (maintained by adding 0.1 mol / L NaOH), additional 0.5 wt% triethanolamine (TEA) was added as a dispersant to prevent fly ash agglomeration, reaction time 24 h (constant temperature 25°C);

[0045] Compression molding: 10MPa compression molding (simulating the strength requirements of roadbed materials), curing conditions: 40℃ oven curing for 7 days, relative humidity ≥85%.

[0046] Results: The leaching concentration of Pb was 1.2 mg / L, that of Cd was 0.08 mg / L, the strength after 28 days was 6.3 MPa, and the treatment cost was 105 yuan per ton. Fly ash replaced part of SDP-CaO, which not only reduced the cost but also improved the material strength through aluminosilicate gel, making it suitable for the treatment of high-chlorine fly ash.

[0047] Example 4

[0048] Raw materials: Sludge with high organic matter content of 60%, fly ash containing Pb (950mg / kg) and dioxin (8ng-TEQ / kg).

[0049] Dioxin degradation treatment: After adding 1% TiO2 / activated carbon catalyst and UV photolysis (wavelength 254nm, 6h), the dioxin toxicity equivalent dropped to 0.3ng-TEQ / kg (a decrease of 96%).

[0050] Composite additive: NaH2PO4-CaO: bentonite: steel slag = 1:4:1 (steel slag is crushed to 1mm and iron is removed by magnetic separation).

[0051] Adding composite additives (15% of fly ash mass) to fly ash;

[0052] Planetary ball mill (rotation speed 350 rpm, zirconia ball milling medium), ball to material ratio: 15:1, activation time 2.5 h (extended 0.5 h to enhance the dispersibility of bentonite).

[0053] Slurry preparation stage: liquid-solid ratio 3:1, stirring speed 200 rpm, pH control: 10.5±0.3 (maintained by adding 0.1 mol / L NaOH), reaction time 24 h (constant temperature 25°C);

[0054] Compression molding: 10MPa compression molding (simulating the strength requirements of roadbed materials), curing conditions: 40℃ oven curing for 7 days, relative humidity ≥85%.

[0055] Results: Leaching concentrations were 0.85 mg / L for Pb and 0.06 mg / L for Cd, and 4.1 MPa for 28 days. Bentonite (4 parts high) fixed Pb through interlayer adsorption. 2 +, calcium silicate in steel slag reacts with SDP-CaO to form Ca-Pb phosphate (Ca 10 (Pb)(PO4)6(OH)2), while the microporous structure of steel slag physically encapsulates Cd pollutants. Dioxin levels meet the incineration pollution control standards of GB 18485-2014. The cost of fly ash treatment is 130 yuan per ton, a 40% reduction compared to activated carbon adsorption.

[0056] Example 5

[0057] Raw materials: A power plant burns municipal sewage sludge fly ash containing Pb (1500 mg / kg), Cd (50 mg / kg), and As (120 mg / kg).

[0058] As is stabilized first: FeSO4 is used for pre-reduction: 3% Fe is added 2+ As 5+ Restore to As 3+ ;

[0059] Preparation of composite additive: Nano-scale NaH2PO4-CaO (particle size 50-100 nm, mechanically mixed by 50 wt% NaH2PO4 and 50 wt% CaO) and sodium bentonite (CEC = 85 mmol / 100 g) were mixed and ground in a mass ratio of 1:4.

[0060] Adding a composite additive (12% of the fly ash mass) to the fly ash produces a Ca-As-Fe composite precipitate (pH 7.5-8.5). Adding a sulfur-based additive: 0.8% Na2S·9H2O produces metal sulfides.

[0061] The samples were activated by planetary milling under nitrogen atmosphere (rotation speed 350 rpm, zirconia balls, ball-to-material ratio 15:1, time 2 h);

[0062] Add water to prepare the slurry (liquid-solid ratio 3:1), adjust the pH to 10.5±0.3 (NaOH solution), and react for 24 hours;

[0063] After press molding (pressure 10 MPa), curing (40°C, humidity 85%, 7 days).

[0064] Results: The proportion of As in residual form increased from 15% to 82%, and the proportion of Pb / Cd in sulfide form exceeded 90%. Leaching toxicity: As 0.08 mg / L (a decrease of 99.3%), and Pb 0.3 mg / L (a decrease of 98%). While reagent costs accounted for 60%, the total cost per ton of disposal remained below 200 yuan.

[0065] Throughout this specification, terms such as "one embodiment" or "some embodiments" mean that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0066] The above are merely preferred embodiments of the present application and are not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A fly ash heavy metal stabilization method based on mechanochemical activation, characterized in that: The following steps are involved: (1) Dry and grind the fly ash containing heavy metals to a particle size of ≤200 μm; (2) preparing a composite additive: mixing and grinding nano-sized NaH2PO4-CaO and bentonite in a mass ratio of 1:(3-5), wherein the particle size of the NaH2PO4-CaO is 50-200 nm; (3) adding the composite additive to the fly ash at a rate of 5% to 20% of the fly ash mass, and subjecting the fly ash to a mechanochemical activation treatment under an inert atmosphere, with a ball milling speed of 300 to 500 rpm, a ball-to-material ratio of (10-15):1, and an activation time of 1 to 3 hours; (4) Add water to adjust the slurry to a liquid-solid ratio of (2-4):1, adjust the pH to 10-11, and react for 12-24 hours before solidifying and forming.

2. The fly ash heavy metal stabilization method based on mechanochemical activation according to claim 1, characterized in that: The composite additive further comprises at least one of steel slag or fly ash, wherein the mass ratio of steel slag to NaH2PO4-CaO is (0.5-2):1, the steel slag is crushed to ≤2 mm and subjected to magnetic separation to remove iron, and the SiO2+Al2O3 content in the fly ash is ≥75%.

3. The fly ash heavy metal stabilization method based on mechanochemical activation according to claim 2, characterized in that: The composite additive comprises fly ash. A dispersant is added during the mechanochemical activation in step (3). The dispersant is triethanolamine, and the amount added is 0.1%-1% of the fly ash mass.

4. The fly ash heavy metal stabilization method based on mechanochemical activation according to any one of claims 1 to 3, characterized in that: In step (4), the curing molding is carried out by compression molding, the pressure is 10-20 MPa, and the curing conditions are: temperature 35-40° C., relative humidity ≥85%, and curing time 7-14 days.

5. The fly ash heavy metal stabilization method based on mechanochemical activation according to claim 4, characterized in that: The composition of the nano-scale NaH2PO4-CaO is 50wt% NaH2PO4 and 50wt% CaO.

6. The fly ash heavy metal stabilization method based on mechanochemical activation according to claim 5, characterized in that: The bentonite is sodium bentonite and has a cation exchange capacity of ≥80 mmol / 100 g.

7. The fly ash heavy metal stabilization method based on mechanochemical activation according to claim 6, characterized in that: When the fly ash contains dioxins, ultraviolet photolysis treatment is performed before step (3): 1%-3% of the fly ash mass of TiO2 / activated carbon composite catalyst is added and irradiated under ultraviolet light of wavelength 254nm for 4-8 hours.

8. The fly ash heavy metal stabilization method based on mechanochemical activation according to claim 6, characterized in that: When the fly ash contains arsenic, arsenic pre-stabilization is performed before step (3): 1%-5% of the fly ash mass of FeSO4 is added to stabilize the As 5+ Restore to As 3 + .

9. A heavy metal stabilized fly ash product prepared according to the method according to any one of claims 1 to 8.