CN1241860C - Fly ash brightening method - Google Patents

Abstract

The invention discloses a method for whitening fly ash, which belongs to the technical field of solid waste recycling engineering of the discipline of environmental engineering. The specific method is to mix fly ash with calcium hydroxide solution, heat and stir to make the surface of fly ash well modified; remove the device. It has been determined that the final product not only maintains the characteristics of fly ash spherical particles that are easy to disperse, but its surface is modified by coated calcium silicate and other fine particles, which has a larger specific surface area and whiteness, and a more reasonable particle size distribution. This fly ash product is a potential high-quality filler with broad prospects for polymers such as plastics and rubber. The implementation of this technology can not only broaden the use of fly ash, improve the utilization rate, but also greatly reduce the accumulation of fly ash, reduce the serious pollution of solid waste to the environment, and turn harm into benefit.

Description

A method for whitening fly ash

technical field

The invention relates to a treatment method of fly ash, in particular to a treatment method of fly ash discharged outside by wet method. It belongs to the technical field of solid waste recycling engineering in the discipline of environmental engineering.

Background technique

Fly ash, also known as "fly ash", is thin and light, and it is inconvenient to collect, discharge, transport, and store, and it is even more difficult to manage and utilize it. In 2001, the national production of fly ash was 168 million tons, and the utilization rate was only 52%. If it is not developed and utilized, it will not only occupy a large amount of fertile land and increase the storage cost of fly ash, but also easily form public nuisance and pollute the environment. Since the 1950s, my country's building materials department has begun to try to use fly ash in the production of building materials and concrete. In the 1960s, a fly ash utilization pattern based on building materials has been formed. With the rapid increase of fly ash emissions, the utilization methods began to diversify, and the pattern of building materials utilization was broken. In recent years, as an important inorganic non-metallic resource, fly ash has been widely used in the fields of building materials, ceramics, chemicals, environmental protection, highways, large-scale water conservancy project construction, and polymer filling.

Fly ash is formed after the combustion of coal powder, and the inorganic components in it are formed under the thermodynamic conditions of high temperature and rapid cooling. The main components are Al ₂ O ₃ and SiO ₂ , most of which are spherical particles with fine particle size. Among them, the fine-grained sinking beads are round and smooth in shape, the aggregation force between particles is small, and the processing rheology is good. It is a potential excellent polymer filler.

In recent years, there have been reports on modified fly ash used as rubber filler. For example, Jin Lixun and other scholars use silane coupling agent to modify the surface of fly ash fine powder with an average particle size of less than 5 μm as rubber reinforcing agent. , its reinforcing performance is between semi-reinforcing carbon black and silicon-alumina carbon black (Jin Lixun. Zhu Xingwang. Zou Mingze. Li Kang, Ultrafine activation of fly ash and its application in rubber. Coal processing and comprehensive utilization , 1998, Issue 04: 48-50). Although silane coupling agents or surfactants can improve the surface properties of fly ash and increase the affinity with the polymer matrix to a certain extent, they cannot change the appearance color and surface morphology, which means that this method cannot improve the quality of fly ash. The whiteness and specific surface area of ash, so fly ash as a filler has not been widely promoted, and there are few related literatures.

Scholars such as Woolard used sodium hydroxide to etch the surface of fly ash by hydrothermal method to increase the roughness, and the specific surface area of fly ash after etching was increased by more than 8 times (Woolard, CD; Strong, J.; Erasmus, CREvaluation of the use of modified coal ash as a potential sorbent fororganic waste streams, Applied Geochemistry Volume: 17, Issue: 8, August, 2002, pp.1159-1164). Scholars such as Sarbak used chemical methods to etch the surface of fly ash with sodium hydroxide, sodium hydroxide/ammonium bicarbonate, ethylenediaminetetraacetic acid (EDTA) and hydrochloric acid, respectively. The specific surface of untreated fly ash is 3m ² /g, and the pore volume is 0.01cm ³ /g. After etching, the specific surface is increased to 59, 60, 60, ^{105m 2} /g; the pore volume is increased to 0.14, 0.13, 0.18, 0.10 cm ³ /g. (Sarbak, Z.; Kramer-Wachowiak, M. Porous structure of waste fly ashes and their chemical modifications, Powder Technology Volume: 123, Issue: 1, February 18, 2002, pp. 53-58). Although strong acid or strong alkali can roughen the surface of fly ash, it cannot improve the whiteness of fly ash, and the follow-up treatment is difficult, high cost, easy to cause secondary pollution, and is not suitable for large-scale promotion. According to literature reports, this method is still in the stage of laboratory research.

Contents of the invention

The purpose of the present invention is to provide a treatment method for improving the whiteness and surface area of fly ash. The implementation of this technology can not only broaden the utilization path of fly ash, improve the utilization rate, but also greatly reduce the accumulation of fly ash and reduce solid waste. Serious pollution of the environment by substances, turning harm into benefit.

The fly ash whitening method of the present invention is to use calcium hydroxide solution to carry out surface treatment on the fly ash. The specific method is to mix fly ash and calcium hydroxide at a weight percentage of 3 to 5:1, add water 5 to 20 times the solid mass, and heat and stir the slurry in the temperature range of 40 to 100°C to make the fly ash The surface is well modified; after cooling to the temperature range of 25-35°C, carbon dioxide is introduced to neutralize the residual calcium hydroxide; then the slurry is filtered, and finally the product is dried. This kind of fly ash product not only preserves the characteristics of easy dispersion of fly ash spherical particles, but also its surface is modified by coated calcium silicate particles, which increases the specific surface area of fly ash particles and improves whiteness; The nano-calcium carbonate particles generated by introducing carbon dioxide to neutralize the residual calcium hydroxide make the particle size distribution of the fly ash product more reasonable. The final product can be used as a filler for plastics, rubber and other polymers with high whiteness and good dispersibility.

For realizing the purpose of the present invention, specific embodiment has the following steps:

Prepare calcium hydroxide solution. In order to ensure the purity and quality of the product, calcium hydroxide solution after removing impurities should be selected.

Raw material pretreatment. (1) Grading. Fly ash has a wide particle size distribution range, and polymer fillers have certain restrictions and requirements on fineness, and those larger than 50 μm (300 mesh) are not suitable for fillers. The wet discharge fly ash is classified by a hydrocyclone, and the feed particle size is controlled to be less than 50 μm. (2) Purification. The test results show that the whitening effect of the fly ash product is more ideal if the content of residual carbon and magnetic substances in the fly ash is reduced before feeding.

The synthesis reaction is heated. In order to speed up the synthesis reaction and better improve the surface properties of fly ash, mix fly ash and calcium hydroxide in a ratio of 3 to 5:1, add water 5 to 20 times the solid mass, and stir well Start to heat the slurry to 40-100°C, control the heating rate to 1.5°C/min, and the reaction time is 1-8 hours. During the synthesis reaction, the calcium hydroxide crystal nuclei or crystal embryos react with the silicon dioxide in the fly ash to form calcium silicate particles, which are chemically combined on the surface of the fly ash particles to roughen the surface.

Carbon dioxide neutral. After the synthesis reaction is completed, there will be a small amount of residual calcium hydroxide solution in the slurry, and carbon dioxide gas is introduced to neutralize the unreacted calcium hydroxide solution until the pH value is in the range of 7 to 7.5, so that the slurry is neutral. And the nano-calcium carbonate particles generated by the reaction are uniformly mixed with the composite fly ash particles. In order to increase the reaction speed of carbon dioxide and calcium hydroxide, the slurry should be cooled to a temperature range of 25-35°C before introducing carbon dioxide.

Milling. After the neutralization reaction was completed, the solid particles were separated from the slurry by filtration and dried at 100° C. for 8 hours. It has been determined that the final product has good particle size distribution, dispersibility, high whiteness and specific surface area, and is an ideal filler for polymers such as plastics and rubber. Figures 1 and 2 show the electron micrographs of fly ash, in which Figure 1 is the topography of untreated fly ash particles, and Figure 2 is the topography of fly ash particles after treatment. From Figure 2, it can be clearly found that there are a large number of coated small particles on the surface of fly ash particles.

Explanatory drawings

Figure 1 is an electron microscope photo of untreated fly ash particles

Figure 2 is the electron microscope photo of fly ash particles after treatment

Detailed ways

Example 1:

200g of fly ash, 735ml of 9% Ca(OH) ₂ solution and 2750ml of tap water were fully mixed in the reactor. Heating at normal pressure and 100° C. for 1 hour with a stirring speed of 410 rpm. After the reaction is finished, cool the slurry to 30° C., and pass in carbon dioxide gas for neutralization, filtration, and drying. The whiteness of the final fly ash product is 68.66 (the whiteness of the raw material is 36.86), the specific surface area is 25.03m ² /g (the specific surface area of the raw material is 3.07m ² /g), and the bulk density is 0.38g/cm ³ (the bulk density of the raw material is 1.10 g/cm ³ ).

Example 2:

150g of fly ash, 735ml of 9% Ca(OH) ₂ solution and 1533ml of tap water were fully mixed in the reactor. Heating at normal pressure and 95° C. for 4 hours with a stirring speed of 320 rpm. After the reaction is finished, cool the slurry to 33° C., and pass in carbon dioxide gas for neutralization, filtration, and drying. The whiteness of the final fly ash product is 69.43 (the whiteness of the raw material is 35.99), the specific surface area is 23.95m ² /g (the specific surface area of the raw material is 3.07m ² /g), and the bulk density is 0.42g/cm ³ (the bulk density of the raw material is 1.10 g/cm ³ ).

Example 3:

200g fly ash, 833ml concentration of 8% Ca(OH) ₂ solution and 3700ml tap water were fully mixed in the reactor. Heating at normal pressure and 80° C. for 7 hours with a stirring speed of 470 rpm. After the reaction is finished, cool the slurry to 28° C., and pass in carbon dioxide gas for neutralization, filtration, and drying. The whiteness of the final fly ash product is 65.15 (the whiteness of the raw material is 33.54), the specific surface area is 34.83m ² /g (the specific surface area of the raw material is 3.07m ² /g), and the bulk density is 0.45g/cm ³ (the bulk density of the raw material is 1.10 g/cm ³ ).

Claims (1)

1. a method for fly ash whitening is characterized in that the fly ash is surface treated with calcium hydroxide solution, and the specific method is to mix the fly ash and calcium hydroxide in a weight percentage of 3～5:1 , add water 5 to 20 times the solid mass, heat and stir the slurry in the temperature range of 40 to 100 ° C, cool to the temperature range of 25 to 35 ° C, and then pass carbon dioxide to neutralize the residual calcium hydroxide; then the slurry Filtration is performed and the product is finally dried.

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