Fly ash-based white micropowder and preparation method thereof

Abstract

The present invention relates to the technical field of fly ash comprehensive utilization, and discloses a fly ash-based white micropowder and a preparation method thereof. The method comprises the following steps: (1) sieving fly ash to obtain coarse ash with a particle size of 45-500 μm; wherein the content of Fe2O3 in the fly ash is 1.5-5 wt%; (2) subjecting the coarse ash to medium magnetic separation and strong magnetic separation for iron removal to obtain iron-removed coarse ash; (3) grinding the iron-removed coarse ash to obtain fine ash; (4) acid-washing the fine ash to obtain purified fine ash; and (5) calcining the purified fine ash to obtain fly ash-based white micropowder. The fly ash-based white micropowder prepared by the present method has the advantages of high yield, good whiteness, and small particle size.

Description

Technical Field

[0001] The invention relates to the technical field of comprehensive utilization of fly ash, and in particular to a fly ash-based white micropowder and a preparation method thereof. Background Art

[0002] Fly ash is an industrial waste residue that creates dust and contributes to air pollution when released into the air. Discharge into rivers can easily clog rivers and harm aquatic life. Long-term unused storage wastes land resources. Turning fly ash into valuable resources and reusing it as a resource has become a research hotspot.

[0003] Fly ash, primarily composed of residual carbon, aluminum oxide, silicon dioxide, and iron oxide, resembles cement in appearance and ranges in color from gray to black. After being decarbonized and iron-removed and brightened, fly ash can be used as a filler in papermaking, rubber, plastics, or refractory materials.

[0004] CN105419406A discloses a modification method for improving the whiteness of fly ash. The method comprises: 1) screening the fly ash to obtain screened fly ash; 2) subjecting the screened fly ash to high-temperature decarbonization to obtain decarbonized fly ash; and 3) coating the decarbonized fly ash. This method can increase the whiteness of the fly ash from 32% ISO to 89.4% ISO. However, the coating layer used for whitening is prone to detachment, resulting in unstable filler properties.

[0005] To improve the whiteness of fly ash, it is necessary to remove as much iron oxide as possible. Because fly ash particles are relatively fine, physical iron removal methods can cause agglomeration and result in low yields. Furthermore, because the iron in fly ash is encapsulated by silica-alumina oxides during high-temperature calcination, direct chemical iron removal is also ineffective.

[0006] CN104772214A provides a method for efficiently removing iron from fly ash. The method involves sequentially subjecting the raw fly ash to reduction, magnetic separation, and hydrochloric acid leaching to produce fly ash with an Fe2O3 content of less than 0.02 wt%. This method has high iron removal efficiency and can reduce the Fe2O3 content in the fly ash to below 0.02 wt%. However, this method requires reducing the fly ash using pulverized coal, coke powder, carbon monoxide, coal gas, or hydrogen under nitrogen protection to facilitate magnetic separation, which is complex and environmentally unfriendly.

[0007] CN106315597A provides a method for the comprehensive treatment and utilization of fly ash, comprising the following steps: grinding the fly ash and then removing iron with a magnetic separator; treating the ground material with hot acid, washing, and dehydrating it for later use; adding a fluorine-containing acid solution and hydrochloric acid and / or nitric acid to a reactor under stirring, and placing the material into the reactor to react and generate silicon tetrafluoride gas, which is then carried into a cooling kettle under negative pressure along with the acidic gas and water vapor volatilized from the mixed acid solution; the mixed gas reacts in the cooling kettle to generate SiO2·nH2O, collecting the SiO2·nH2O in the cooling kettle to remove the residual acidic gas, and drying to obtain a fumed silica product. Although this method can produce high-value-added fumed silica from waste such as fly ash, it also removes aluminum from the fly ash while removing iron, resulting in a low comprehensive utilization rate of the fly ash.

[0008] Therefore, there is an urgent need to provide a method for preparing fly ash-based white micropowder with a simple production process, good whitening effect and high product yield. Summary of the Invention

[0009] The purpose of the present invention is to overcome the problems of unstable fly ash whitening effect, complex production process and low comprehensive utilization rate in the prior art, and to provide a fly ash-based white micropowder and a preparation method thereof. The method has the advantages of simple operation, good whitening effect and high product yield.

[0010] In order to achieve the above object, the first aspect of the present invention provides a method for preparing fly ash-based white powder, the method comprising the following steps:

[0011] (1) Sieving fly ash to obtain coarse ash with a particle size of 45-500 μm; wherein the content of Fe2O3 in the fly ash is 1.5-5 wt%;

[0012] (2) subjecting the coarse ash to medium magnetic separation and high-strength magnetic separation to remove iron, thereby obtaining deironed coarse ash;

[0013] (3) grinding the iron-removed coarse ash to obtain fine ash;

[0014] (4) acid washing the fine ash to obtain purified fine ash;

[0015] (5) calcining the purified fine ash to obtain fly ash-based white powder.

[0016] The second aspect of the present invention provides a fly ash-based white fine powder prepared by the preparation method described in the first aspect of the present invention.

[0017] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0018] 1) The method for preparing fly ash-based white micropowder provided by the present invention utilizes medium magnetic separation and high magnetic separation to remove iron from coarse ash with large particle size, thereby improving the iron removal effect and increasing the yield of the deironed coarse ash.

[0019] 2) The method for preparing fly ash-based white micropowder provided by the present invention can minimize the loss of Al2O3 while removing iron as much as possible by controlling the pickling conditions, thereby obtaining a fly ash-based white micropowder with high yield, good whiteness and good quality;

[0020] 3) The fly ash-based white micropowder provided by the present invention has the advantages of high yield, good whiteness, and small particle size, and is widely used and suitable for promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a scanning electron microscope image of the fly ash-based white powder prepared in Example 1 of the present invention;

[0022] Figure 2 This is a particle size analysis chart of the fly ash-based white micropowder prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0024] A first aspect of the present invention provides a method for preparing fly ash-based white micropowder, the method comprising the following steps:

[0025] (1) Sieving fly ash to obtain coarse ash with a particle size of 45-500 μm; wherein the content of Fe2O3 in the fly ash is 1.5-5 wt%;

[0026] (2) subjecting the coarse ash to medium magnetic separation and high-strength magnetic separation to remove iron, thereby obtaining deironed coarse ash;

[0027] (3) grinding the iron-removed coarse ash to obtain fine ash;

[0028] (4) acid washing the fine ash to obtain purified fine ash;

[0029] (5) calcining the purified fine ash to obtain fly ash-based white powder.

[0030] The inventors of the present invention have discovered that, compared with grinding fly ash before magnetic separation, increasing the particle size of coarse ash from medium and high-intensity magnetic separations can improve iron removal and increase the yield of iron-removed coarse ash. By controlling the pickling conditions, Al₂O₃ loss can be minimized while maximizing iron removal, further increasing the yield and whiteness of fly ash-based white micropowder.

[0031] In a preferred embodiment, the content of Fe2O3 in the fly ash is 1.5-3wt%, preferably 1.8-2.2wt%.

[0032] Among them, in the present invention, the Fe2O3 content in the fly ash directly affects the whiteness of the obtained fly ash-based white micropowder. When the Fe2O3 content in the selected fly ash is between 1.8-2.2wt%, the whiteness of the prepared fly ash-based white micropowder is optimal.

[0033] In a preferred embodiment, the particle size of the coarse ash is 100-500 μm, preferably 100-450 μm.

[0034] If the particle size of the coarse ash is too large, the magnetic separation effect will be poor, while if the particle size of the coarse ash is too small, it will easily agglomerate. When the particle size of the coarse ash is controlled within 45-500μm, especially within 100-450μm, the iron removal effect is better.

[0035] In a preferred embodiment, the magnetic field strength of the medium magnetic separation is greater than or equal to 2000 Gs and less than 6000 Gs; the magnetic field strength of the strong magnetic separation is greater than or equal to 6000 Gs and less than or equal to 15000 Gs. Further preferably, the magnetic field strength of the medium magnetic separation is greater than or equal to 4000 Gs and less than or equal to 5500 Gs; the magnetic field strength of the strong magnetic separation is greater than or equal to 10000 Gs and less than or equal to 12000 Gs.

[0036] Compared with magnetic separation with a single magnetic field strength, the present invention adopts medium magnetic separation and strong magnetic separation to remove iron, which can improve the iron removal effect and increase the iron removal coarse ash yield when the coarse ash particle size is relatively large.

[0037] In a preferred embodiment, the medium magnetic separation is performed at least once, preferably 1-3 times; the strong magnetic separation is performed at least once, preferably 1-3 times.

[0038] In a preferred embodiment, the medium magnetic separation is performed more times than the high intensity magnetic separation; for example, the medium magnetic separation is performed three times, and the high intensity magnetic separation is performed once.

[0039] In the present invention, by controlling the particle size of the coarse ash and subjecting it to two-stage magnetic separation, the Fe2O3 content in the deironed coarse ash can be reduced to below 1 wt%, and the yield of the deironed coarse ash can be as high as 90-98%. The yield of the deironed coarse ash refers to the ratio of the mass of the deironed coarse ash to the mass of the coarse ash.

[0040] In a preferred embodiment, the D90 of the fine ash is 2-300 μm, more preferably 2-20 μm, and further preferably 5-10 μm.

[0041] The present invention does not require coating and whitening of fly ash, and can produce fly ash-based white micropowder of any specifications according to market demand, especially fly ash-based white micropowder with D90 of 2-20 μm.

[0042] In a preferred embodiment, the pickling conditions include: an acid solution concentration of 1-36 wt %, a pickling time of 0.5-24 h, and a pickling temperature of 25-80° C. Further preferably, the pickling conditions include: an acid solution concentration of 20-30 wt %, a pickling time of 6-10 h, and a pickling temperature of 60-80° C.

[0043] In a preferred embodiment, the pickling conditions further include: the acid solution is selected from hydrochloric acid and / or sulfuric acid, preferably hydrochloric acid; the mass ratio of fine ash to acid solution is 1:0.3-2, preferably 1:0.5-1.

[0044] In the present invention, pickling further removes iron while also removing a portion of Al2O3. If the pickling process is improperly controlled, a relatively large amount of Al2O3 will be removed, which will not only reduce the yield of the fly ash-based white micropowder, increase the consumption of the pickling solution, generate a large amount of aluminum-containing wastewater, and increase the environmental burden, but will also reduce the quality of the fly ash-based white micropowder. When used as a papermaking filler, the powder will have poor gloss, poor wear resistance when used as a rubber filler, and poor fire resistance when used as a refractory filler. Using the pickling conditions defined in the present invention, the loss of Al2O3 can be minimized while removing iron as much as possible, resulting in a high-yield, high-quality fly ash-based white micropowder.

[0045] In a preferred embodiment, after the acid washing is completed, the ash is washed with water, preferably deionized water, for 3-5 times, and then dried and dispersed to obtain purified fine ash.

[0046] In a preferred embodiment, the calcination conditions include: a calcination temperature of 600-1500° C., and a calcination time of 2-8 hours. More preferably, the calcination conditions include: a calcination temperature of 800-1200° C., and a calcination time of 2-5 hours.

[0047] The second aspect of the present invention provides a fly ash-based white fine powder prepared by the preparation method described in the first aspect of the present invention.

[0048] In a preferred embodiment, the whiteness of the fly ash-based white powder is ≥90, preferably ≥95.

[0049] In a preferred embodiment, the particle size D90 of the fly ash-based white powder is 2-50 μm, preferably 2-20 μm; the true density is 2.6-2.8 g / cm 3 , preferably 2.7-2.75g / cm 3 .

[0050] In a preferred embodiment, the refractoriness of the fly ash-based white powder is ≥1800°C, preferably ≥1850°C.

[0051] The present invention is described in detail below through examples. The whiteness of the fly ash-based white powder in the examples and comparative examples was measured in accordance with GB / T 5950-1996, "Method for measuring whiteness of building materials and non-metallic mineral products." The particle size was measured using a Malvern laser particle size analyzer. The true density was measured in accordance with GB / T 5071-2013, and the refractoriness was measured in accordance with GB / T 7322-2017.

[0052] Among them, fly ash A comes from the Guohua Zhungeer Power Plant in Inner Mongolia, with a Fe2O3 content of 1.9wt%, an Al2O3 content of 48.4wt%, a SiO2 content of 43.8wt%, and the remainder being impurities; fly ash B comes from the Guohua Shouguang Power Plant in Shandong, with a Fe2O3 content of 5.7wt%, an Al2O3 content of 31.5wt%, a SiO2 content of 46.9wt%, and the remainder being impurities.

[0053] Example 1

[0054] (1) Sieving fly ash A to obtain coarse ash with a particle size of 100-450 μm;

[0055] (2) subjecting the coarse ash to three medium magnetic separations for iron removal, and then subjecting it to one high-strength magnetic separation for iron removal, to obtain iron-removed coarse ash; wherein the magnetic field strength of the medium magnetic separation is 4000 Gs, the magnetic field strength of the high-strength magnetic separation is 10000 Gs, the content of Fe2O3 in the iron-removed coarse ash is 0.85 wt%, and the yield of the iron-removed coarse ash is 90%;

[0056] (3) Grinding the above iron-removed coarse ash to obtain fine ash with D90 = 5 μm;

[0057] (4) mixing the above-mentioned fine ash with 20 wt% hydrochloric acid in a mass ratio of 1:1 and pickling at 70°C for 6 hours, then washing the pickled fine ash three times with deionized water, drying and breaking it up to obtain purified fine ash;

[0058] (5) The purified fine ash was calcined at 1000°C for 2 h in an air atmosphere and then naturally cooled to obtain fly ash-based white powder.

[0059] Example 2

[0060] (1) Sieving fly ash A to obtain coarse ash with a particle size of 150-400 μm;

[0061] (2) subjecting the coarse ash to three medium magnetic separations for iron removal and then to one high-strength magnetic separation for iron removal, thereby obtaining iron-removed coarse ash; wherein the magnetic field strength of the medium magnetic separation is 5500 Gs, the magnetic field strength of the high-strength magnetic separation is 12000 Gs, the content of Fe2O3 in the iron-removed coarse ash is 0.85 wt%, and the yield of the iron-removed coarse ash is 92%;

[0062] (3) Grinding the above iron-removed coarse ash to obtain fine ash with D90 = 10 μm;

[0063] (4) mixing the above-mentioned fine ash with 30 wt% hydrochloric acid in a mass ratio of 1:1 and then pickling at 80°C for 10 h. Then, the pickled fine ash was washed three times with deionized water, dried, and then dispersed to obtain purified fine ash;

[0064] (5) The purified fine ash was calcined at 1200°C for 3 h in an air atmosphere and then naturally cooled to obtain fly ash-based white powder.

[0065] Example 3

[0066] (1) Sieving fly ash A to obtain coarse ash with a particle size of 150-500 μm;

[0067] (2) subjecting the coarse ash to three medium magnetic separations for iron removal and then to one high-strength magnetic separation for iron removal, thereby obtaining iron-removed coarse ash; wherein the magnetic field strength of the medium magnetic separation is 2000 Gs, the magnetic field strength of the high-strength magnetic separation is 8000 Gs, the content of Fe2O3 in the iron-removed coarse ash is 0.97 wt%, and the yield of the iron-removed coarse ash is 92%;

[0068] (3) Grinding the above iron-removed coarse ash to obtain fine ash with D90 = 3 μm;

[0069] (4) The fine ash was mixed with 15 wt% hydrochloric acid in a mass ratio of 1:0.5 and then pickled at 60°C for 8 h. The pickled fine ash was then washed three times with deionized water, dried, and then dispersed to obtain purified fine ash.

[0070] (5) The purified fine ash was calcined at 1100°C for 1 hour in an air atmosphere and then naturally cooled to obtain fly ash-based white powder.

[0071] Example 4

[0072] Similar to Example 1, except that the concentration of hydrochloric acid in step (4) is 5 wt %, and the mass ratio of fine ash to hydrochloric acid is 1:2.

[0073] Example 5

[0074] Similar to Example 1, except that the concentration of hydrochloric acid in step (4) is 36 wt %, and the mass ratio of fine ash to hydrochloric acid is 1:0.5.

[0075] Comparative Example 1

[0076] Similar to Example 1, except that: the particle size of the coarse ash in step (1) is 0-45 μm;

[0077] The content of Fe2O3 in the iron-removing coarse ash obtained in step (2) is 2.1wt%, and the yield of the iron-removing coarse ash is 35%.

[0078] Comparative Example 2

[0079] Similar to Example 1, the difference is that in step (2), the above coarse ash is subjected to only three intermediate magnetic separations to remove iron, and the content of Fe2O3 in the obtained iron-removed coarse ash is 1.3wt%, and the yield of the iron-removed coarse ash is 96%.

[0080] Comparative Example 3

[0081] Similar to Example 1, except that: the fly ash in step (1) is fly ash B;

[0082] The Fe2O3 content in the iron-removed coarse ash obtained in step (2) is 5.4%, and the yield of the iron-removed coarse ash is 53%.

[0083] Test Example 1

[0084] The performance tests of the fly ash-based white powders prepared in Examples 1-5 and Comparative Examples 1-3 were conducted, and the results are shown in Table 1:

[0085] Table 1

[0086] Yield % Whiteness Particle size D90μm <![CDATA[True density g / cm 3 > Refractoriness Example 1 86 96.55 5 2.75 1850 Example 2 89 97.08 10 2.70 1850 Example 3 88 91.24 3 2.63 1800 Example 4 85 92.58 5 2.68 1800 Example 5 86 92.03 5 2.61 1800 Comparative Example 1 27 78.14 5 2.73 1700 Comparative Example 2 90 74.03 5 2.70 1650 Comparative Example 3 42 62.57 5 2.48 1200

[0087] Note: The yield in Table 1 is the yield of fly ash-based white micropowder.

[0088] Table 1 shows that the present invention can prepare fly ash-based white micropowder with a whiteness of more than 90 and a refractoriness of more than 1800° C., and the yield of fly ash-based white micropowder is as high as ≥85%, which is suitable for industrial promotion.

[0089] Test Example 2

[0090] The fly ash-based white powder prepared in Example 1 was characterized by scanning electron microscopy and particle size analysis. The results are as follows: Figure 1 and Figure 2 As shown:

[0091] Among them, Figure 1 and Figure 2 It can be seen that the fly ash-based white powder prepared by the method of the present invention has a microscopic morphology of irregular particles, a relatively narrow particle size distribution, and a uniform particle size.

[0092] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A fly ash-based white powder, characterized in that: The fly ash-based white powder has a whiteness of ≥90, a particle size D90 of 2-50 μm, and a true density of 2.6-2.8 g / cm 3 , refractoriness ≥ 1800°C; the preparation method of the fly ash-based white micropowder comprises the following steps: (1) Screening the fly ash to obtain coarse ash with a particle size of 45-500 μm; wherein the content of Fe2O3 in the fly ash is 1.5-3wt%; (2) subjecting the coarse ash to medium magnetic separation and high-strength magnetic separation to remove iron, thereby obtaining iron-removed coarse ash; (3) grinding the iron-removed coarse ash to obtain fine ash; (4) pickling the fine ash to obtain purified fine ash; wherein the pickling conditions include: an acid solution concentration of 20-30 wt% and a pickling time of 6-10 h; (5) calcining the purified fine ash to obtain fly ash-based white powder; The magnetic field strength of the medium magnetic separation is greater than or equal to 2000 Gs and less than 6000 Gs; the magnetic field strength of the strong magnetic separation is greater than or equal to 6000 Gs and less than or equal to 15000 Gs; The medium magnetic separation and iron removal are carried out 1-3 times, and the strong magnetic separation and iron removal are carried out 1-3 times; The D90 of the fine ash is 2-300 μm; The mass ratio of the fine ash to the acid solution is 1:0.3-2.

2. The fly ash-based white powder according to claim 1, wherein: The content of Fe2O3 in the fly ash is 1.8-2.2wt%.

3. The fly ash-based white powder according to claim 1, wherein: The particle size of the coarse ash is 100-500 μm.

4. The fly ash-based white powder according to claim 3, wherein: The particle size of the coarse ash is 100-450 μm.

5. The fly ash-based white powder according to claim 1, wherein: The magnetic field strength of the medium magnetic separation is greater than or equal to 4000Gs and less than or equal to 5500Gs; the magnetic field strength of the strong magnetic separation is greater than or equal to 10000Gs and less than or equal to 12000Gs.

6. The fly ash-based white powder according to claim 1, wherein: The medium magnetic separation is performed more times than the strong magnetic separation.

7. The fly ash-based white powder according to claim 6, wherein: The medium magnetic separation was performed three times, and the strong magnetic separation was performed once.

8. The fly ash-based white powder according to claim 1, wherein: The D90 of the fine ash is 2-20 μm.

9. The fly ash-based white powder according to claim 8, wherein: The D90 of the fine ash is 5-10 μm.

10. The fly ash-based white powder according to claim 1, wherein: The pickling conditions include: the pickling temperature is 60-80°C.

11. The fly ash-based white powder according to claim 1, wherein: The acid solution is selected from hydrochloric acid and / or sulfuric acid.

12. The fly ash-based white powder according to claim 1, wherein: The acid solution is hydrochloric acid; And / or, the mass ratio of the fine ash to the acid solution is 1:0.5-1.

13. The fly ash-based white powder according to claim 1, wherein: The calcination conditions include: a calcination temperature of 600-1500° C. and a calcination time of 2-8 hours.

14. The fly ash-based white powder according to claim 13, wherein: The calcination conditions include: a calcination temperature of 800-1200° C. and a calcination time of 2-5 hours.

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