Method for removing heavy metal elements from fly ash

Abstract

The present application relates to a method for removing heavy metal elements from fly ash, which comprises the following steps: sieving the fly ash to remove large particle impurities and unburned carbon particles; then mixing the undersize fly ash with water and centrifuging to obtain a centrifugal liquid and fly ash from which heavy metal elements have been removed. The method for removing heavy metal elements from fly ash provided by the present application is simple and easy to operate, has low removal cost, low energy consumption, and is easy to popularize and apply. Moreover, the fly ash from which heavy metal elements have been removed can reduce the impact on the environment in subsequent applications, and has good environmental and economic benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization and environmental protection, and particularly relates to a method for removing heavy metal elements from fly ash. BACKGROUND

[0002] Fly ash is a main solid waste produced after high-temperature combustion in coal-fired power plants, and is mainly from thermal power plants and city central heating boilers. Domestic and foreign researches have found that the large accumulation of fly ash has become an important pollution source, which has caused great threat to rivers, lakes and urban water sources. Especially the toxic heavy metal elements such as Hg, Cd, Cr and Pb in fly ash have caused serious harm to human body and environment, and have limited the application and popularization of high-value-added products prepared by using fly ash as raw materials. At present, there are few reports on the removal of heavy metal elements in fly ash in existing researches, and most researchers use acid treatment or alkali treatment for the treatment of fly ash. Therefore, a large amount of strong acid and strong alkali solution needs to be consumed in the reaction process, and the waste liquid after treatment is difficult to handle, which is easy to cause secondary pollution.

[0003] CN111871605A discloses a method for separating heavy metal elements from fly ash, which comprises the following steps: adding a dispersing agent to fly ash after removing iron by magnetic separation, stirring uniformly, then dispersing by vibration, and then performing electrostatic separation to obtain fly ash particles with a particle size of 0.1-20 μm; the fly ash particles with a particle size of 0.1-20 μm obtained by screening are introduced into a first classification chamber for primary centrifugal separation, large particles are settled in a second classification chamber, secondary air is introduced into the second classification chamber to make small particles in the second classification chamber float into the first classification chamber, and fly ash particles with an average particle size of <10 μm are screened out. After fly ash is sequentially subjected to iron removal, dispersion, electrostatic separation and centrifugal separation, the fine particle part is completely separated out, and a large amount of heavy metal elements are enriched in the fine particle part, so that the content of heavy metal elements in fly ash can be effectively reduced. However, the separation method needs high-temperature heating and high-voltage action, and has high treatment energy consumption and complex process.

[0004] CN109942114A discloses a method for simultaneously removing heavy metals in fly ash and industrial wastewater, comprising the following steps: crushing unburned carbon to obtain adsorbed carbon; adding tap water to the adsorbed carbon to prepare adsorbed carbon liquid, then adding kerosene, stirring uniformly, then floating, vacuum filtering after floating, then drying to obtain modified adsorbed carbon; adding modified adsorbed carbon into several connected adsorption tanks, and passing wastewater containing heavy metals through the adsorption tanks in sequence to adsorb heavy metals, and adding liquid precipitant to the modified adsorbed carbon adsorbing heavy metals to make heavy metals form precipitate, and then filtering and removing. The method is complex in operation, and a series of operations such as crushing, floating, adsorption, desorption and precipitation are required, and new solid waste is generated due to the addition of precipitant in the process.

[0005] In view of the deficiencies in the existing heavy metal element removal methods in fly ash, a simple and efficient treatment method is provided, which can effectively remove heavy metals from fly ash in an environmentally friendly manner, and is of great significance to environmental protection and industrial production. SUMMARY

[0006] In view of the above problems, the purpose of the present application is to provide a method for removing heavy metal elements in fly ash. Compared with the prior art, the removal method provided by the present application has high efficiency in removing heavy metals, is simple to operate, has low processing cost, low energy consumption, and can effectively improve the utilization rate of fly ash.

[0007] To achieve the purpose of the present application, the following technical solutions are adopted:

[0008] The present application provides a method for removing heavy metal elements in fly ash, which comprises the following steps:

[0009] (1) The fly ash raw material is sieved to obtain sieve particles and sieve fly ash;

[0010] (2) The sieve fly ash of step (1) is mixed with water and centrifuged to obtain a centrifugal liquid and fly ash with removed heavy metal elements.

[0011] The inventors have found that the unburned carbon particles in fly ash raw material have the characteristics of being loose and porous, and are easy to adsorb heavy metals, resulting in a high content of heavy metals in unburned carbon particles, and a high proportion of unburned carbon particles in fly ash large particles. Therefore, the method for removing heavy metal elements in fly ash first sieves the fly ash raw material, removes the large particle impurities therein, and separates the unburned carbon therein, which is beneficial to reducing the content of heavy metals in the fly ash raw material.

[0012] The high-precision analysis and detection devices such as a scanning electron microscope-energy spectrum and an inductively coupled plasma mass spectrometer are adopted, and based on the non-crystalline silicon dioxide coated inert crystalline mullite core-shell spherical structure characteristics of the fly ash with high reactivity, the undersize fly ash obtained after screening is subjected to chemical treatment by alkali method in steps, and after deep detection and analysis, it is found that most of the heavy metals in the fly ash have a content of 0.01-100 ppm, the particle size is less than 5 nm, and the heavy metal content gradually decreases from the surface to the inside in the radial direction of the fly ash spherical particles, which indicates that there are a large amount of heavy metal elements on the surface of the undersize fly ash, wherein 80%-90% of Hg exists in the form of heavy metal compounds on the surface of the undersize fly ash, 20%-40% of Cr, 10%-20% of Cd and about 10% of Pb exist in the form of compounds on the surface of the undersize fly ash. In order to better remove the heavy metal elements in the undersize fly ash, the undersize fly ash is mixed with water and subjected to centrifugal separation, compared with filtration separation, the centrifugal separation can make the heavy metals enriched on the surface of the fly ash particles separate from the surface of the fly ash under the multiple actions of water flow impact and centrifugal force, and most of the heavy metals enter the centrifugal liquid in the form of nano-sized small particles, the centrifugal process provides greater centrifugal force, which is more conducive to the full separation of the fly ash large particles and the heavy metal nano particles by the difference in centrifugal force, and the fly ash with the heavy metal elements removed is obtained. Moreover, the physical method for removing the heavy metals in the fly ash does not cause secondary pollution, the fly ash with the heavy metal elements removed has significantly reduced harm to the environment, is conducive to realizing high value-added utilization, and also solves the problem of environmental pollution caused by the large accumulation of fly ash.

[0013] Preferably, the screen size of the screening treatment in step (1) is 40-100 mesh, for example, it can be 40 mesh, 50 mesh, 60 mesh, 70 mesh, 90 mesh or 100 mesh, but is not limited to the listed values, and other values not listed in the value range are also applicable, and preferably, it is 60-80 mesh.

[0014] Preferably, the liquid-solid ratio of the undersize fly ash and water in step (2) is 1:3-1:40 g / mL, for example, it can be 1:3 g / mL, 1:5 g / mL, 1:10 g / mL, 1:15 g / mL, 1:20 g / mL, 1:25 g / mL, 1:30 g / mL, 1:35 g / mL or 1:40 g / mL, but is not limited to the listed values, and other values not listed in the value range are also applicable, and preferably, it is 1:5-1:25 g / mL.

[0015] The liquid-solid ratio of the undersize fly ash and water in step (2) is preferably 1:3-1:40 g / mL. If the liquid-solid ratio is too small, the slurry is too thick, which is not conducive to the separation of heavy metals from the fly ash and reduces the heavy metal removal effect. If the liquid-solid ratio is too large, the water consumption is too large, which increases the burden of the centrifugal separation equipment and causes unnecessary waste.

[0016] Preferably, the mixing time of the undersize fly ash and water in step (2) is 0.1-3 h, for example, 0.1 h, 0.3 h, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, but is not limited to the listed values, and other values not listed in the value range are also applicable, and preferably 0.5-1 h.

[0017] Preferably, the centrifugal separation speed in step (2) is 2000-8000 r / min, for example, 2000 r / min, 3000 r / min, 4000 r / min, 5000 r / min, 6000 r / min, 7000 r / min or 8000 r / min, but is not limited to the listed values, and other values not listed in the value range are also applicable, and preferably 4000-6000 r / min.

[0018] Preferably, the centrifugal separation time is 5-120 min, for example, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min, 100 min, 105 min, 110 min, 115 min or 120 min, but is not limited to the listed values, and other values not listed in the value range are also applicable, and preferably 20-60 min.

[0019] The centrifugal separation speed in step (2) is preferably 2000-8000 r / min, which can achieve efficient removal of heavy metals on the surface of fly ash and save energy consumption of the centrifugal separation treatment.

[0020] Preferably, the fly ash from which the heavy metal elements are removed in step (2) is subjected to drying treatment.

[0021] Preferably, the drying treatment temperature is 60-160℃, for example, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃ or 160℃, but is not limited to the listed values, and other values not listed in the value range are also applicable, and preferably 100-130℃.

[0022] Preferably, the drying treatment time is 0.5-8h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 4h, 5h, 6h, 7h or 8h, etc., but is not limited to the listed values, other values not listed in the value range are also applicable, preferably 2-4h.

[0023] As a preferred technical solution of the present application, the removal method comprises the following steps:

[0024] (1) The fly ash raw material is subjected to screening treatment through a sieve with a mesh size of 40-100 mesh to obtain fly ash particles on the sieve and fly ash under the sieve;

[0025] (2) The fly ash under the sieve in step (1) is mixed with water at a liquid-solid ratio of 1:3-1:40 g / mL for 0.1-4h, and then subjected to centrifugal separation at a rotation speed of 2000-8000r / min for 5-120min to obtain a centrifugal liquid and fly ash from which heavy metal elements are removed; the fly ash from which heavy metal elements are removed is subjected to drying treatment at a temperature of 60-160℃ for 0.5-8h.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] (1) The removal method of heavy metal elements in fly ash provided by the present application achieves a removal rate of 5%-80% for heavy metal elements Hg, Cd, Cr and Pb in fly ash, realizing the removal of heavy metal elements in fly ash;

[0028] (2) The removal method of heavy metal elements in fly ash provided by the present application is a physical method and does not produce secondary pollution, and the fly ash from which heavy metal elements are removed has significantly reduced harm to the environment, which is conducive to realizing high-value utilization, and also solves the problem of environmental pollution caused by large amounts of fly ash accumulation;

[0029] (3) The removal method of heavy metal elements in fly ash provided by the present application obtains fly ash particles on the sieve which are mainly unburned carbon and can be used for secondary utilization, improving economic efficiency. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0031] Example 1

[0032] The present embodiment provides a removal method of heavy metal elements in fly ash, which comprises the following steps:

[0033] (1) the fly ash raw material is screened by a screen with a mesh size of 100 meshes to obtain fly ash particles and fly ash below the screen;

[0034] (2) the fly ash below the screen in step (1) is mixed with deionized water according to a liquid-solid ratio of 1:25 g / mL for 0.5 h, centrifuged at a speed of 8000 r / min for 40 min to obtain a centrifugal liquid and fly ash from which heavy metal elements are removed; and the fly ash from which heavy metal elements are removed is dried at a temperature of 110 ℃ for 4 h.

[0035] Example 2

[0036] The embodiment provides a method for removing heavy metal elements from fly ash, and the method comprises the following steps:

[0037] (1) the fly ash raw material is screened by a screen with a mesh size of 60 meshes to obtain fly ash particles and fly ash below the screen;

[0038] (2) the fly ash below the screen in step (1) is mixed with distilled water according to a liquid-solid ratio of 1:20 g / mL for 0.6 h, centrifuged at a speed of 4000 r / min for 30 min to obtain a centrifugal liquid and fly ash from which heavy metal elements are removed; and the fly ash from which heavy metal elements are removed is dried at a temperature of 120 ℃ for 3 h.

[0039] Example 3

[0040] The embodiment provides a method for removing heavy metal elements from fly ash, and the method comprises the following steps:

[0041] (1) the fly ash raw material is screened by a screen with a mesh size of 40 meshes to obtain fly ash particles and fly ash below the screen;

[0042] (2) the fly ash below the screen in step (1) is mixed with pure water according to a liquid-solid ratio of 1:30 g / mL for 1 h, centrifuged at a speed of 6000 r / min for 10 min to obtain a centrifugal liquid and fly ash from which heavy metal elements are removed; and the fly ash from which heavy metal elements are removed is dried at a temperature of 105 ℃ for 5 h.

[0043] Example 4

[0044] The embodiment provides a method for removing heavy metal elements from fly ash, and the method comprises the following steps:

[0045] (1) the fly ash raw material is screened by a screen with a mesh size of 80 meshes to obtain fly ash particles and fly ash below the screen;

[0046] (2) mixing the undersize fly ash of step (1) with deionized water at a liquid-solid ratio of 1:35 g / mL for 0.8 h, centrifuging at a speed of 5000 r / min for 50 min to obtain a centrifugal liquid and fly ash from which heavy metal elements are removed; and drying the fly ash from which heavy metal elements are removed at a temperature of 115 ℃ for 6 h.

[0047] Example 5

[0048] This example provides a method for removing heavy metal elements from fly ash, which is the same as example 1 except that the liquid-solid ratio of the undersize fly ash to deionized water in step (2) is 1:1 g / mL.

[0049] Example 6

[0050] This example provides a method for removing heavy metal elements from fly ash, which is the same as example 1 except that the liquid-solid ratio of the undersize fly ash to deionized water in step (2) is 1:50 g / mL.

[0051] Example 7

[0052] This example provides a method for removing heavy metal elements from fly ash, which is the same as example 1 except that the speed of centrifugation in step (2) is 1000 r / min.

[0053] Example 8

[0054] This example provides a method for removing heavy metal elements from fly ash, which is the same as example 1 except that the speed of centrifugation in step (2) is 9000 r / min.

[0055] Comparative Example 1

[0056] This comparative example provides a method for removing heavy metal elements from fly ash, which is the same as example 1 except that step (1) is not performed.

[0057] Comparative Example 2

[0058] This comparative example provides a method for removing heavy metal elements from fly ash, which is the same as example 1 except that the centrifugation in step (2) is replaced by a filtration treatment.

[0059] The removal rates of heavy metal elements Hg, Cd, Cr and Pb in the above examples and comparative examples are shown in Table 1.

[0060] Table 1

[0061]

[0062]

[0063] (1) From the comprehensive examples 1-8, it can be seen that the method for removing heavy metal elements in fly ash provided by the application has certain removal effect on different heavy metal elements Cr, Cd, Hg and Pb, among which the removal effect of mercury is the best, and can reach more than 80%;

[0064] (2) From the comprehensive example 1 and examples 5-6, it can be seen that in the example 1, the liquid-solid ratio of the undersize fly ash to deionized water in step (2) is 1:25 g / mL, compared with the liquid-solid ratio of the undersize fly ash to deionized water in step (2) of examples 5 and 6, which are 1:1 g / mL and 1:50 g / mL respectively, the removal rate of Cr in example 1 is 20.0%, the removal rate of Cd is 12.0%, the removal rate of Hg is 89.1%, and the removal rate of Pb is 9.1%. In example 5, due to the too small liquid-solid ratio of the undersize fly ash to deionized water, the slurry is too thick, which is not conducive to the separation of heavy metals and fly ash, the removal rate of Cr is only 16.3%, the removal rate of Cd is only 7.6%, the removal rate of Hg is only 75.9%, and the removal rate of Pb is only 3.0%. In example 6, although the removal rates of heavy metal elements Cr, Cd, Hg and Pb are only slightly lower than those in example 1, the liquid-solid ratio of the undersize fly ash to deionized water is too large, which will lead to excessive water consumption, increase the burden of centrifugal separation equipment, and cause unnecessary waste. Therefore, the application limits the liquid-solid ratio of the undersize fly ash to deionized water within a certain range, which can not only ensure the removal effect of heavy metals in fly ash, but also reduce the waste of water resources;

[0065] (3) From the comprehensive example 1 and examples 7-8, it can be seen that in the example 1, the rotation speed of centrifugal separation in step (2) is 8000 r / min, compared with the rotation speed of centrifugal separation in step (2) of examples 7 and 8, which are 1000 r / min and 9000 r / min respectively, the removal rates of heavy metal elements Cr, Cd, Hg and Pb in example 1 are higher than those in examples 7 and 8. Therefore, the application limits the rotation speed of centrifugal separation within a certain range, which can not only realize efficient removal of heavy metals on the surface of fly ash, but also save the energy consumption of centrifugal separation treatment;

[0066] (4) From the comparison between Example 1 and Comparative Example 1, it can be seen that the removal method described in Example 1 carries out the screening treatment in step (1), compared with Comparative Example 1 which does not carry out step (1), the fly ash raw material of Comparative Example 1 has more unburned carbon particles, and a large amount of heavy metal elements are adsorbed on the surface, and although the same treatment steps as Example 1 are carried out subsequently, the removal effect of heavy metal elements is poor, the removal rate of Cr is only 12.6%, the removal rate of Cd is only 2.3%, the removal rate of Hg is only 75.8%, and the removal rate of Pb is only 2.6%; thus, it is shown that the fly ash raw material is first screened in the present application to remove the large particle impurities therein and separate the unburned carbon therein, which greatly reduces the content of heavy metals in the fly ash raw material and improves the removal rate of heavy metal elements;

[0067] (5) From the comparison between Example 1 and Comparative Example 2, it can be seen that the mixture of undersize fly ash and deionized water in step (2) of Example 1 is subjected to centrifugal separation, compared with the mixture of undersize fly ash and deionized water in Comparative Example 2 which is subjected to filtration treatment, the removal rate of heavy metal elements in Example 1 is much higher than that in Comparative Example 2; centrifugal separation can make the heavy metals enriched on the surface of fly ash particles separate from the surface of fly ash under the multiple actions of water flow impact and centrifugal force, and enter the centrifugal liquid, and the centrifugal process provides greater centrifugal force, which is more conducive to the full separation of fly ash and heavy metals by the difference in centrifugal force.

[0068] In summary, the removal method of heavy metal elements in fly ash provided by the present application realizes the removal of heavy metal elements in fly ash, only uses physical methods to treat fly ash, solves the harm of fly ash to the environment, and improves the additional utilization value thereof.

[0069] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for removing heavy metal elements nanoparticles from fly ash, characterized in that, The removing method comprises the following steps: (1) the fly ash raw material is subjected to screening treatment to obtain fly ash particles and fly ash below the screen; The unburned carbon is separated while the larger particle impurities are removed, which is beneficial to reduce the content of heavy metals in the fly ash raw material; (2) the fly ash below the screen in step (1) is mixed with water, and centrifugal separation is performed, so that the heavy metals enriched on the surface of the fly ash particles are separated from the surface of the fly ash under the multiple actions of water flow impact and centrifugal force, and most of the heavy metals enter the centrifugal liquid in the form of nano-sized small particles, and fly ash from which heavy metal elements are removed and a centrifugal liquid are obtained; the liquid-solid ratio of the fly ash below the screen and water is 1:10-1:40 g / mL; The rotating speed of the centrifugal separation in step (2) is 2000-8000 r / min.

2. The removal method according to claim 1, characterized in that, The screen size of the screening treatment in step (1) is 40-100 meshes.

3. The removal method according to claim 2, characterized in that, The screen size of the screening treatment in step (1) is 60-80 meshes.

4. The removal method of claim 1, wherein, The mixing time of the fly ash below the screen and water in step (2) is 0.1-3 h.

5. The removal method according to claim 4, characterized in that, The mixing time of the fly ash below the screen and water in step (2) is 0.5-1 h.

6. The removal method of claim 1, wherein, The rotating speed of the centrifugal separation in step (2) is 4000-6000 r / min.

7. The removal method of claim 1, wherein The centrifugal separation time is 5-120 min.

8. The removal method according to claim 7, characterized in that, The centrifugal separation time is 20-60 min.

9. The removal method of claim 1, wherein, The fly ash from which heavy metal elements are removed in step (2) is subjected to drying treatment.

10. The removal method according to claim 9, characterized in that, The drying treatment temperature is 60-160 ℃.

11. The removal method according to claim 10, characterized in that, The drying treatment temperature is 100-130 ℃.

12. The removal method of claim 9, wherein, The drying treatment time is 0.5-8 h.

13. The removal method of claim 12, wherein, The drying treatment time is 2-4 h.

14. The removal method of claim 1 wherein, The removing method comprises the following steps: (1) the fly ash raw material is subjected to screening treatment through a screen with a screen size of 60-80 meshes to obtain fly ash particles and fly ash below the screen; (2) the fly ash below the screen in step (1) is mixed with water at a liquid-solid ratio of 1:10-1:40 g / mL for 0.1-4 h, and centrifugal separation is performed at a rotating speed of 2000-8000 r / min for 5-120 min, so that a centrifugal liquid and fly ash from which heavy metal elements are removed are obtained; The fly ash from which heavy metal elements are removed is subjected to drying treatment at a temperature of 60-160 ℃ for 0.5-8 h.

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