Method for stripping surface heavy metal elements of fly ash

Abstract

This invention relates to a method for stripping heavy metals from the surface of fly ash. The method includes: first, magnetically separating the fly ash to obtain magnetic and non-magnetic fly ash; ball milling the obtained magnetic material; then mixing the stripping reagent, non-magnetic fly ash, and the ball-milled magnetic material; and finally, sequentially subjecting the mixture to magnetic separation and solid-liquid separation to obtain fly ash with surface heavy metals removed. The magnetic material is rich in Fe3O4, exhibiting excellent heavy metal adsorption performance and is easy to separate and recover. This method has the advantages of high stripping efficiency, simple operation, low processing cost, and low energy consumption, and can effectively improve the utilization rate of fly ash, solving the current problem of difficult removal of heavy metals from the surface of fly ash.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of solid waste and environmental protection technology, specifically to a method for stripping heavy metal elements from the surface of fly ash. Background Technology

[0002] Fly ash is a type of fine dust discharged from boilers in coal-fired power plants along with flue gas and collected by dust collectors. It is an industrial solid waste, primarily originating from thermal power plants. In recent years, the large-scale accumulation of fly ash has become a major source of solid waste pollution, posing a significant threat to the environment, soil, and water sources. In particular, the toxic heavy metals in fly ash, such as Hg, Cd, As, Cr, and Pb, can cause serious harm to human health. Furthermore, the heavy metals in fly ash limit and restrict the application and promotion of high-value-added products made from it.

[0003] Currently, there are few reports on the removal of heavy metals from fly ash, and most of the reports involve acid or alkali treatment. However, acid and alkali treatments produce acidic or alkaline waste liquids, which are difficult to treat and can easily cause secondary pollution.

[0004] For example, CN111871605A discloses a method for separating heavy metal elements in fly ash. This method uses a series of steps such as iron removal, dispersion, electrostatic separation and centrifugal separation to separate the fine particles enriched with a large number of heavy metal elements, thereby achieving the separation of heavy metal elements. However, this separation method requires high-temperature heating and high voltage, resulting in high energy consumption and a complex process.

[0005] CN112620295A discloses a method for removing mercury from fly ash. This method involves first mixing fly ash with water to obtain a slurry, and then performing liquid-solid separation on the slurry to achieve the separation of heavy metal elements. This method can separate some water-soluble and acid-soluble heavy metal elements, but it requires the addition of acid treatment, which will generate new acid wastewater pollution.

[0006] Therefore, in view of the shortcomings of existing methods for removing heavy metals from fly ash, this paper proposes a simple and efficient treatment method that can remove heavy metals from fly ash in an environmentally friendly and effective manner, which is of great significance to environmental protection and industrial production. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of this invention is to provide a method for stripping heavy metal elements from the surface of fly ash. This method has the advantages of high stripping efficiency, simple operation, low processing cost, and low energy consumption. It can also effectively improve the utilization rate of fly ash and solve the problem of the difficulty in stripping heavy metals from the surface of fly ash. Furthermore, this process does not remove the effective components in fly ash and has minimal impact on the subsequent utilization of fly ash.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for stripping heavy metal elements from the surface of fly ash, the method comprising:

[0010] First, fly ash is separated by magnetic separation to obtain magnetic and non-magnetic fly ash.

[0011] The obtained magnetic material was ball-milled, and then the stripping reagent, non-magnetic fly ash and the ball-milled magnetic material were mixed and treated. After that, the mixture was subjected to a second magnetic separation and solid-liquid separation to obtain fly ash with surface heavy metals removed.

[0012] The stripping agent includes one or a combination of at least two of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium n-hexadecyl sulfate, dodecyl dimethyl betaine, or dodecyl trimethylammonium bromide.

[0013] This invention employs an aqueous solution containing specific reagents and ball-milled magnetic material to stir fly ash (in which some heavy metals exist as insoluble or slightly soluble nanoparticles with a particle size of 0.5nm-100nm on the surface of fly ash particles). The solution containing specific reagents fully wets the surface of fly ash particles and heavy metal particles, and adsorbs them onto the surface through electrostatic interaction, forming a diffused double layer. This increases the electrostatic repulsion between particles, reduces the adsorption between heavy metal particles and fly ash on the fly ash surface, and separates the heavy metal elements from the fly ash under the stirring and impact of water flow. The magnetic material separated from fly ash by magnetic separation is rich in magnetic Fe3O4, which has strong magnetism. After grinding the magnetic material, it is co-treated with an aqueous solution containing a specific reagent to treat non-magnetic fly ash. On one hand, the specific reagent and the magnetic Fe3O4 particles have the same charge, causing the Fe3O4 particles to be uniformly dispersed in the slurry. This effectively adsorbs some of the magnetic heavy metal particles stripped from the fly ash surface, promoting the separation of heavy metals from non-magnetic fly ash. On the other hand, Fe3O4 particles can also adsorb dissolved heavy metal ions in the solution through ligand exchange complexation and electrostatic interactions. Furthermore, the specific reagent can form mixed micelles with Fe3O4, enhancing its adsorption capacity. This helps to disrupt the ion balance in the solution, further dissolving the slightly soluble heavy metals in the non-magnetic fly ash into the solution, thus further stripping heavy metals from the fly ash. After treatment, the Fe3O4 particles adsorbed with heavy metals can be easily separated by magnetic separation, achieving the purpose of heavy metal removal.

[0014] As a preferred embodiment of the present invention, the fly ash is the undersize product obtained by sieving. This is because fly ash contains a small amount of unburned carbon, which is loose and porous and has a strong ability to adsorb heavy metals. Its presence can affect the stripping of heavy metal elements from fly ash. Unburned carbon particles are generally large. The present invention uses sieving to pre-separate the large particles of unburned carbon from the oversize material, thereby improving the heavy metal stripping effect of fly ash.

[0015] Preferably, the size of the sieve opening in the sieving process is 60-140 mesh, for example, it can be 60 mesh, 70 mesh, 80 mesh, 90 mesh, 100 mesh, 110 mesh, 120 mesh, 130 mesh or 140 mesh, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 80 mesh-120 mesh.

[0016] As a preferred technical solution of the present invention, the first magnetic separation method is wet magnetic separation.

[0017] Preferably, the strength of the magnetic field in the first magnetic separation is 3000-12000 GS, for example, it can be 3000 GS, 3200 GS, 3400 GS, 3600 GS, 3800 GS, 4000 GS, 4200 GS, 4400 GS, 4600 GS, 4800 GS, 5000 GS, 5200 GS, 5400 GS, 5600 GS, 5800 GS, 6000 GS, 6200 GS, 6400 GS, 6600 GS, 6800 GS, 7000 GS, 7200 GS, 7400 GS, 7 600GS, 7800GS, 8000GS, 8200GS, 8400GS, 8600GS, 8800GS, 9000GS, 9200GS, 9400GS, 9600GS, 9800GS, 1000GS, 10200GS, 10400GS, 10600GS, 10800GS, 11000GS, 11200GS, 11400GS, 11600GS, 11800GS, or 12000GS, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0018] Preferably, the ball milling time is 5-240 min, for example, it can be 5 min, 20 min, 30 min, 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, 180 min, 200 min, 220 min, 240 min, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] As a preferred embodiment of the present invention, the concentration of the stripping reagent is 0.0001-0.005 g / mL, for example, it can be 0.0001 g / mL, 0.0002 g / mL, 0.0003 g / mL, 0.0004 g / mL, 0.0005 g / mL, 0.0006 g / mL, 0.0007 g / mL, 0.0008 g / mL, 0.0009 g / mL, 0.001 g / mL, 0.0012 g / mL, 0.0014 g / mL, 0.0016 g / mL, 0.0018 g / mL, 0.002 g / mL, 0.0014 g / mL, 0.0016 g / mL, 0.0018 g / mL, 0.002 g / mL, 0.0012 g / mL, 0.0014 g / mL, 0.0016 g / mL, 0.0018 g / mL, 0.0012 g / mL, 0.0014 g / mL, 0.0016 g / mL, 0.0018 g / mL, 0.0012 g / mL, 0.0014 g / mL, 0.0015 g / mL, 0.0016 g / mL, 0.0018 g / mL, 0.0012 ... The values ​​are 0.0022 g / mL, 0.0024 g / mL, 0.0026 g / mL, 0.0028 g / mL, 0.003 g / mL, 0.0032 g / mL, 0.0034 g / mL, 0.0036 g / mL, 0.0038 g / mL, 0.004 g / mL, 0.0042 g / mL, 0.0044 g / mL, 0.0046 g / mL, 0.0048 g / mL, or 0.005 g / mL, etc., but are not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 0.005-0.02 g / mL being preferred.

[0020] In this invention, it is preferable to control the concentration of the stripping reagent solution within a certain range to fully exert its function. When applying the stripping reagent, its hydrophilic properties are given priority to improve the removal efficiency of heavy metal elements.

[0021] In this invention, the solvent for the stripping agent can be water or other conventional solvents in the art, such as ethanol.

[0022] Preferably, the amount of magnetic material added after ball milling is 0.1%-5% of the mass of the non-magnetic fly ash, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0023] As a preferred technical solution of the present invention, the solid-liquid ratio (g / mL) of the non-magnetic fly ash and the stripping agent is 1:(3-20), for example, it can be 1:3g / mL, 1:4g / mL, 1:5g / mL, 1:1.8g / mL, 1:6g / mL, 1:7g / mL, 1:8g / mL, 1:9g / mL, 1:10g / mL, 1:11g / mL, 1:12g / mL, 1:13g / mL, 1:14g / mL, 1:15g / mL, 1:16g / mL, 1:17g / mL, 1:18g / mL, 1:19g / mL or 1:20g / mL, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 1:(5-10)g / mL.

[0024] In this invention, it is preferable to control the solid-liquid ratio of the stripping agent and fly ash within a specific range, which can promote mass transfer between substances, while saving the amount of stripping agent used and reducing cost burden.

[0025] As a preferred embodiment of the present invention, stirring is performed during the mixing process.

[0026] Preferably, the stirring speed is 10-400 r / min, for example, it can be 10 r / min, 20 r / min, 30 r / min, 40 r / min, 50 r / min, 60 r / min, 70 r / min, 80 r / min, 90 r / min, 100 r / min, 120 r / min, 140 r / min, 160 r / min, 180 r / min, 200 r / min, 220 r / min, 240 r / min, 260 r / min, 280 r / min, 300 r / min, 320 r / min, 340 r / min, 360 r / min, 380 r / min or 400 r / min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0027] As a preferred technical solution of the present invention, the mixing treatment time is 10-600 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 120 min, 140 min, 160 min, 180 min, 200 min, 240 min, 280 min, 320 min, 360 min, 400 min, 450 min, 500 min, 550 min, 600 min, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] As a preferred embodiment of the present invention, the second magnetic separation is a wet magnetic separation performed under a magnetic field strength of 3000-12000 GS, for example, 3000 GS, 3200 GS, 3400 GS, 3600 GS, 3800 GS, 4000 GS, 4200 GS, 4400 GS, 4600 GS, 4800 GS, 5000 GS, 5200 GS, 5400 GS, 5600 GS, 5800 GS, 6000 GS, 6200 GS, 6400 GS, 6600 GS, 6800 GS, 7000 GS, and 7200 GS. The range includes, but is not limited to, 7400GS, 7600GS, 7800GS, 8000GS, 8200GS, 8400GS, 8600GS, 8800GS, 9000GS, 9200GS, 9400GS, 9600GS, 9800GS, 1000GS, 10200GS, 10400GS, 10600GS, 10800GS, 11000GS, 11200GS, 11400GS, 11600GS, 11800GS, or 12000GS, etc. Other unlisted values ​​within this range also apply.

[0029] In this invention, since there is a significant accumulation of heavy metals in the magnetic material, this phase can be separated by magnetic separation, which can further reduce the heavy metal content in fly ash and improve the heavy metal stripping effect.

[0030] As a preferred technical solution of the present invention, the solid-liquid separation method includes sedimentation separation and / or centrifugal separation.

[0031] In this invention, some insoluble or slightly soluble heavy metals in fly ash have nanoscale particle sizes. After stripping, these heavy metals are separated from the fly ash particles and enter the slurry in the form of nanoparticles. Through sedimentation or centrifugation, the difference in gravity or centrifugal force between the large fly ash particles and the heavy metal nanoparticles can be used to achieve complete separation, resulting in fly ash free of heavy metal elements.

[0032] In this invention, sedimentation separation can be carried out in sedimentation tanks, such as horizontal flow sedimentation tanks and vertical flow sedimentation tanks.

[0033] In this invention, centrifugal separation can be carried out in centrifuges, hydrocyclones, or cyclone sedimentation tanks, etc.

[0034] Preferably, the sedimentation separation time is 0.5-5h, for example, it can be 0.5h, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h, 3.2h, 3.4h, 3.6h, 3.8h, 4h, 4.2h, 4.4h, 4.6h, 4.8h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1-3h.

[0035] As a preferred technical solution of the present invention, fly ash is first subjected to a first magnetic separation to obtain magnetic material and non-magnetic fly ash.

[0036] The obtained magnetic material was ball-milled, and then the stripping reagent, non-magnetic fly ash and the ball-milled magnetic material were mixed and treated. After that, the mixture was subjected to a second magnetic separation and solid-liquid separation to obtain fly ash with surface heavy metals removed.

[0037] The fly ash is the undersize product obtained by sieving; the size of the sieve holes in the sieving is 60-140 mesh.

[0038] The first magnetic separation method is wet magnetic separation; the magnetic field strength in the first magnetic separation is 3000-12000 GS;

[0039] The ball milling time is 5-240 min;

[0040] The stripping agent comprises one or a combination of at least two of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium n-hexadecyl sulfate, dodecyl dimethyl betaine, or dodecyl trimethylammonium bromide; the concentration of the stripping agent is 0.0001-0.005 g / mL;

[0041] The amount of magnetic material added after ball milling is 0.1%-5% of the mass of the non-magnetic fly ash; the solid-liquid ratio of the non-magnetic fly ash and the stripping agent is 1:(3-20) g / mL; stirring is carried out during the mixing process; the stirring speed is 10-400 r / min; the mixing time is 10-600 min;

[0042] The second magnetic separation is a wet magnetic separation performed under a magnetic field strength of 3000-12000 GS;

[0043] The solid-liquid separation method includes sedimentation separation and / or centrifugation separation; the sedimentation separation time is 0.5-5 hours.

[0044] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0045] (1) After being treated by the removal method of the present invention, the removal rate of heavy metal elements Hg, As, Cd, Cr and Pb in fly ash reaches 20%-85%, which realizes the removal of some heavy metal elements in fly ash, reduces its heavy metal content, and significantly reduces the harm to human body and environment. The fly ash after heavy metal removal can be used for high-value utilization such as agriculture and ecological restoration, and improve its comprehensive utilization rate.

[0046] (2) The entire removal process is a physical process with mild operating conditions, making it easy to implement. No strong acids or alkalis are used, and no acidic or alkaline waste liquid is generated. The entire process is clean, environmentally friendly, and low-cost, which is of great significance for solving the problem of large-scale fly ash storage and environmental pollution, and for realizing the high-value utilization of fly ash. Meanwhile, since other effective components in fly ash (SiO2, Al2O3, CaO, etc.) exist mostly in insoluble forms and will not react with the stripping reagent used in this invention, the stripping process will not remove the effective components. Specifically, after the heavy metal stripping process, the mass ratio of low-heavy-metal fly ash to the original fly ash is ≥93%. Detailed Implementation

[0047] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows:

[0048] In this invention, the fly ash being addressed contains toxic heavy metal elements such as Hg, Cd, As, Cr, and Pb, as well as other components. Specific contents may include Hg (0.36-1.56 ug / g), Cd (0.37-0.49 ug / g), As (18.43-43.25 ug / g), Cr (30.09-60 ug / g), Pb (31.78-41.68 ug / g), SiO2 (20-58.3%), Al2O3 (18.1-55%), CaO (2.6-14%), K2O (0.9-3%), Fe2O3 (2.2-7%), and MgO (0.5-2.5%).

[0049] Example 1

[0050] This embodiment provides a method for stripping heavy metal elements from the surface of fly ash, the method comprising:

[0051] (1) The fly ash was screened using an 80-mesh sieve to obtain large particles of unburned carbon and fly ash under the sieve. The fly ash under the sieve was subjected to 3000GS wet magnetic separation to obtain magnetic material and non-magnetic fly ash. The magnetic material after magnetic separation was then ball-milled for 40 minutes.

[0052] (2) Prepare a sodium hexadecyl sulfate solution with a concentration of 0.0001 g / mL as a stripping agent. Use the stripping agent and the ball-milled magnetic material to mix the non-magnetic fly ash. At the same time, stir at 100 r / min for 120 min. The solid-liquid ratio of non-magnetic fly ash and sodium hexadecyl sulfate solution is 1:3 g / mL. The amount of magnetic material added after ball milling is 1% of the mass of non-magnetic fly ash.

[0053] (3) The slurry processed in step (2) is first separated by magnetic separation, and then solid-liquid separation is carried out by sedimentation for 3 hours to remove the supernatant, thus obtaining fly ash after partial removal of heavy metals.

[0054] In this embodiment, the composition of the fly ash is as follows:

[0055] 19.7％ 58.3％ 5.1％ 2.3％ 5.9％ 0.8％

[0056] The heavy metal content is as follows: Cr 36.29 μg / g, As 20.06 μg / g, Cd 0.41 μg / g, Hg 0.36 μg / g, Pb 36.63 μg / g.

[0057] After processing, the final removal rate of heavy metal elements in fly ash is shown in Table 1.

[0058] Example 2

[0059] This embodiment provides a method for stripping heavy metal elements from the surface of fly ash, the stripping method comprising:

[0060] (1) The fly ash was screened with a 100-mesh sieve to obtain large particles of unburned carbon and fly ash under the sieve. The fly ash under the sieve was subjected to 9000GS wet magnetic separation to obtain magnetic material and non-magnetic fly ash. The magnetic material after magnetic separation was then ball-milled for 180 minutes.

[0061] (2) Prepare a sodium dodecyl sulfate solution with a concentration of 0.001 g / mL as a stripping agent. Use the stripping agent and the ball-milled magnetic material to mix the non-magnetic fly ash. Stir at 400 r / min for 180 min. The solid-liquid ratio of non-magnetic fly ash to sodium dodecyl sulfate solution is 1:20 g / mL. The amount of ball-milled magnetic material added is 2% of the mass of non-magnetic fly ash.

[0062] (3) The slurry processed in step (2) is first separated by magnetic separation, and then solid-liquid separation is carried out by sedimentation for 4 hours to remove the supernatant, thus obtaining fly ash after partial removal of heavy metals.

[0063] In this embodiment, the composition of the fly ash is as follows:

[0064] 18.1％ 55.3％ 9.6％ 2.5％ 6.1％ 0.8％

[0065] The heavy metal contents are: Cr 40.12 μg / g, As 18.43 μg / g, Cd 0.37 μg / g, Hg 0.58 μg / g, Pb 39.09 μg / g.

[0066] After processing, the final removal rate of heavy metal elements in fly ash is shown in Table 1.

[0067] Example 3

[0068] This embodiment provides a method for stripping heavy metal elements from the surface of fly ash, the stripping method comprising:

[0069] (1) The fly ash was screened using a 120-mesh sieve to obtain large particles of unburned carbon and fly ash under the sieve. The fly ash under the sieve was subjected to 6000GS wet magnetic separation to obtain magnetic material and non-magnetic fly ash. The magnetic material after magnetic separation was then ball-milled for 120 minutes.

[0070] (2) Prepare a sodium dodecylbenzenesulfonate solution with a concentration of 0.005 g / mL as a stripping agent. Use the stripping agent and the ball-milled magnetic material to mix the non-magnetic fly ash. Stir at 300 r / min for 240 min. The solid-liquid ratio of non-magnetic fly ash to sodium dodecylbenzenesulfonate solution is 1:12 g / mL. The amount of magnetic material added after ball milling is 0.5% of the mass of non-magnetic fly ash.

[0071] (3) The slurry processed in step (2) is first separated by magnetic separation, and then solid-liquid separation is carried out by sedimentation for 1 hour to remove the supernatant, thus obtaining fly ash after partial removal of heavy metals.

[0072] In this embodiment, the composition of the fly ash is as follows:

[0073] 47.4％ 40.6％ 2.6％ 0.9％ 2.2％ 0.5％

[0074] The heavy metal content is as follows: Cr 33.35 μg / g, As 22.12 μg / g, Cd 0.41 μg / g, Hg 1.56 μg / g, Pb 31.78 μg / g.

[0075] After processing, the final removal rate of heavy metal elements in fly ash is shown in Table 1.

[0076] Example 4

[0077] This embodiment provides a method for stripping heavy metal elements from the surface of fly ash, the stripping method comprising:

[0078] (1) The fly ash was screened with a 90-mesh sieve to obtain large particles of unburned carbon and fly ash under the sieve. The fly ash under the sieve was subjected to 11000GS wet magnetic separation to obtain magnetic material and non-magnetic fly ash. The magnetic material after magnetic separation was then ball-milled for 90 minutes.

[0079] (2) Prepare a dodecyl dimethyl betaine solution with a concentration of 0.0003 g / mL as a stripping agent. Use the stripping agent and the ball-milled magnetic material to mix the non-magnetic fly ash. Stir at 200 r / min for 300 min. The solid-liquid ratio of the non-magnetic fly ash and the dodecyl dimethyl betaine solution is 1:15 g / mL. The amount of magnetic material added after ball milling is 5% of the mass of the non-magnetic fly ash.

[0080] (3) The slurry processed in step (2) is first separated by magnetic separation, and then solid-liquid separation is carried out by settling for 4.5 hours to remove the supernatant, thus obtaining fly ash after partial removal of heavy metals.

[0081] In this embodiment, the composition of the fly ash is as follows:

[0082] 21.9％ 56.4％ 10.7％ 1.0％ 3.5％ 2.5％

[0083] The heavy metal contents are: Cr 36.18 μg / g, As 30.19 μg / g, Cd 0.47 μg / g, Hg 0.96 μg / g, Pb 36.98 μg / g.

[0084] After processing, the final removal rate of heavy metal elements in fly ash is shown in Table 1.

[0085] Example 5

[0086] This embodiment provides a method for stripping heavy metal elements from the surface of fly ash, the stripping method comprising:

[0087] (1) The fly ash was screened using a 60-mesh sieve to obtain large particles of unburned carbon and fly ash under the sieve. The fly ash under the sieve was subjected to 5000GS wet magnetic separation to obtain magnetic material and non-magnetic fly ash. The magnetic material after magnetic separation was then ball-milled for 200 minutes.

[0088] (2) Prepare a 0.002 g / mL dodecyltrimethylammonium bromide solution as a stripping agent. Use the stripping agent and the ball-milled magnetic material to mix the non-magnetic fly ash. Stir at 350 r / min for 60 min. The solid-liquid ratio of the non-magnetic fly ash and the dodecyltrimethylammonium bromide solution is 1:5 g / mL. The amount of magnetic material added after ball milling is 0.1% of the mass of the non-magnetic fly ash.

[0089] (3) The slurry processed in step (2) is first separated by magnetic separation, and then solid-liquid separation is carried out by sedimentation for 2.5 hours to remove the supernatant, thus obtaining fly ash after partial removal of heavy metals.

[0090] In this embodiment, the composition of the fly ash is as follows:

[0091] 39.5％ 35.0％ 14.1％ 0.6％ 2.8％ 1.6％

[0092] The heavy metal contents are: Cr 30.09 μg / g, As 43.25 μg / g, Cd 0.49 μg / g, Hg 0.41 μg / g, Pb 41.68 μg / g.

[0093] After processing, the final removal rate of heavy metal elements in fly ash is shown in Table 1.

[0094] Example 6

[0095] The difference from Example 2 is that the wet magnetic separation in step (1) is replaced with dry magnetic separation. The final removal rates of heavy metal elements in fly ash are shown in Table 1.

[0096] Example 7

[0097] The only difference from Example 2 is that the ball-milled magnetic material was not added during the mixing process; that is, only the stripping agent and non-magnetic fly ash were mixed. The final removal rates of heavy metals from the fly ash are shown in Table 1.

[0098] Example 8

[0099] The only difference from Example 2 is that the magnetic material separated by magnetic separation is not ball-milled. The final removal rates of heavy metal elements in fly ash are shown in Table 1.

[0100] Example 9

[0101] The difference from Example 2 is that step (1) is omitted, and only steps (2) and (3) are performed. The final removal rate of heavy metal elements in fly ash is shown in Table 1.

[0102] Example 10

[0103] The difference compared to Example 2 is that step (2) does not add sodium dodecyl sulfate solution, but uses an equal amount of water instead. Steps (1) and (3) are the same as in Example 2. The final removal rate of heavy metal elements in fly ash is shown in Table 1.

[0104] Example 11

[0105] The difference from Example 2 is that the sodium dodecyl sulfate solution was replaced with an equal amount of polyoxyethylene ether-10, molecular formula: C 49 H 89 O 15 Molecular weight: 917.

[0106] Table 1

[0107]

[0108]

[0109] In summary, the method provided by this invention can remove heavy metal elements from fly ash by using only physical methods, thus solving the environmental hazards caused by fly ash and improving its added value utilization.

[0110] The present invention is described in detail through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0111] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0112] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0113] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for stripping heavy metal elements from the surface of fly ash, characterized in that, The stripping method includes: First, the fly ash is subjected to a first magnetic separation to obtain magnetic and non-magnetic fly ash. The obtained magnetic material was ball-milled, and then the stripping reagent, non-magnetic fly ash and the ball-milled magnetic material were mixed and treated. After that, the mixture was subjected to a second magnetic separation and solid-liquid separation to obtain fly ash with surface heavy metals removed. The stripping agent includes one or a combination of at least two of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium n-hexadecyl sulfate, dodecyl dimethyl betaine, or dodecyl trimethylammonium bromide; The first magnetic separation method is wet magnetic separation; the amount of magnetic material added after ball milling is 0.1%-5% of the mass of non-magnetic fly ash; the solid-liquid ratio of non-magnetic fly ash and stripping reagent is 1:(3-20) g / mL.

2. The peeling method as described in claim 1, characterized in that, The fly ash is the undersize product obtained by screening.

3. The peeling method as described in claim 2, characterized in that, The sieve aperture size in the sieving process is 60-140 mesh.

4. The peeling method as described in claim 1, characterized in that, The strength of the magnetic field in the first magnetic separation is 3000-12000GS.

5. The peeling method as described in claim 1, characterized in that, The ball milling time is 5-240 min.

6. The peeling method as described in claim 1, characterized in that, The concentration of the stripping agent is 0.0001-0.005 g / mL.

7. The peeling method as described in claim 1, characterized in that, The mixing process involves stirring.

8. The peeling method as described in claim 7, characterized in that, The stirring speed is 10-400 r / min.

9. The peeling method as described in claim 1, characterized in that, The mixing process takes 10-600 minutes.

10. The peeling method as described in claim 1, characterized in that, The second magnetic separation is a wet magnetic separation performed under a magnetic field strength of 3000-12000GS.

11. The peeling method as described in claim 1, characterized in that, The solid-liquid separation methods include sedimentation separation and / or centrifugal separation.

12. The peeling method as described in claim 11, characterized in that, The sedimentation and separation time is 0.5-5 hours.

13. The peeling method according to any one of claims 1-12, characterized in that, The stripping method includes: First, the fly ash is subjected to a first magnetic separation to obtain magnetic and non-magnetic fly ash. The obtained magnetic material was ball-milled, and then the stripping reagent, non-magnetic fly ash and the ball-milled magnetic material were mixed and treated. After that, the mixture was subjected to a second magnetic separation and solid-liquid separation to obtain fly ash with surface heavy metals removed. The fly ash is the undersize product obtained by sieving; the size of the sieve holes in the sieving is 60-140 mesh. The first magnetic separation method is wet magnetic separation; the magnetic field strength in the first magnetic separation is 3000-12000 GS; The ball milling time is 5-240 min; The stripping agent comprises one or a combination of at least two of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium n-hexadecyl sulfate, dodecyl dimethyl betaine, or dodecyl trimethylammonium bromide; the concentration of the stripping agent is 0.0001-0.005 g / mL; The amount of magnetic material added after ball milling is 0.1%-5% of the mass of the non-magnetic fly ash; the solid-liquid ratio of the non-magnetic fly ash and the stripping agent is 1:(3-20) g / mL; stirring is carried out during the mixing process; the stirring speed is 10-400 r / min; the mixing time is 10-600 min; The second magnetic separation is a wet magnetic separation performed under a magnetic field strength of 3000-12000 GS; The solid-liquid separation method includes sedimentation separation and / or centrifugation separation; the sedimentation separation time is 0.5-5 hours.

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