CN102731138A - Fly ash based high-strength and high-porosity foamed ceramic and preparation method thereof - Google Patents

Abstract

A fly ash-based high-strength and high-porosity foamed ceramics and its preparation method. The red mud and fly ash are mixed and ground with calcium carbonate, borax and polyvinyl alcohol adhesives after passing through a 300-mesh sieve to make batch materials. , and then pressed into a block-shaped green body; the formed block-shaped green body is placed in a sintering furnace for sintering, and uniformly distributed pores are formed during the sintering process, and industrial waste-based foam with high strength and high porosity is obtained after cooling to room temperature ceramics. The existence of a large number of pores in the foam ceramics endows it with excellent heat insulation (summer), heat preservation (winter) and sound insulation functions, and the chemical combination during the high temperature sintering process makes the foam ceramics have high strength and high temperature resistance. The preparation process of this foam ceramic is simple, the sintering temperature is low, and the production cost is low. The total amount of fly ash and red mud introduced reaches 70wt% or more, which can consume a large amount of fly ash and red mud industrial waste, and can be widely used. On the top floor of the building (heat insulation, thermal insulation), indoor non-load-bearing walls (heat insulation, thermal insulation, sound insulation) and indoor and outdoor walls (heat insulation, thermal insulation), no new industrial waste will be generated during use, and it is environmentally friendly and multifunctional building materials.

Description

A kind of fly ash-based high-strength and high-porosity foam ceramics and its preparation method

technical field

The invention relates to a fly ash-based high-strength and high-porosity foamed ceramics and a preparation method, belonging to resources (land, minerals), environmental protection (emission of toxic and harmful substances), energy (building energy saving and consumption reduction) and new materials. cross-technical fields.

technical background

Fly ash is a solid waste discharged from coal-fired power plants, and its pollution to the environment is multifaceted. During the disposal, processing and utilization of fly ash, the harmful elements enriched in it can invade the environment in various ways, endangering organisms and human health. Fly ash stored in the ash yard, once the water evaporates, the surface ash particles can be peeled off and discarded when encountering a wind force above level 4, and the ash height can reach 40-50m, which not only affects the visibility, but also affects the building in a humid environment. Corrosion on surfaces such as objects and outdoor sculptures. The pollution of fly ash to water bodies is mainly due to the direct discharge of ash from power plants to waters. Fly ash enters the water body, forming sediment, suspended matter, soluble matter and other substances, which will increase the turbidity of the water and deteriorate the water quality. Fly ash is stored and stacked in large quantities, which not only occupies cultivated land, pollutes the environment, but also endangers human health and the ecological environment. Therefore, it is necessary to study and pay attention to the comprehensive utilization of fly ash resources to build a resource-saving and environment-friendly society. It can be seen that the comprehensive utilization of fly ash has important environmental protection value and economic benefits.

Red mud is a solid waste produced during the process of refining alumina from bauxite, and it is an insoluble residue. According to different aluminum smelting methods, red mud can be divided into sintering method, Bayer method and combined method red mud. The main components of red mud are SiO ₂ , CaO, Al ₂ O ₃ and so on. Generally, red mud particles contain a large amount of strong alkaline substances, as well as fluorine, aluminum and other harmful substances. The main methods of refining alumina from bauxite in my country are sintering and combined methods. The red mud produced by these two processes has similar components, mainly dicalcium silicate and its hydrate. In foreign countries, it is mostly Bayer process red mud, which mainly contains hematite and sodium aluminosilicate hydrate. So far, most of the red mud has not been fully utilized and disposed of, and has been piled up in the red mud pool for a long time, which not only occupies a large amount of land, but also consumes more storage yard construction and maintenance management costs, and the alkali-containing waste liquid pollutes the surface and groundwater. sources, causing serious damage to the natural ecological environment and directly endangering people's health. Comprehensive treatment and utilization of red mud has become an urgent issue in the alumina industry. With the strengthening of environmental protection awareness, red mud utilization has attracted widespread attention at home and abroad. At present, many countries around the world are actively looking for countermeasures to obtain more effective red mud treatment technologies and methods. The use of red mud to prepare and produce new materials—red mud fly ash-based foam ceramics can greatly improve the utilization rate of red mud, and is a promising new way to solve the problem of red mud resource utilization.

The "Technical Policy Outline for Comprehensive Utilization of Resources in China" has made improving the level of waste recycling as a key promotion area for comprehensive utilization of resources during the "Twelfth Five-Year Plan" period, focusing on the bulk utilization of solid waste with large emissions, large stockpiles, and serious pollution and high value-added utilization. The building materials industry is the best choice for mass utilization of industrial waste. At present, there are domestic patents for comprehensive utilization of red mud fly ash, Chinese patent (application number: 200610128450.4) "red mud fly ash free brick", Chinese patent (application number: 200910092222.X) "a kind of red mud powder Coal ash non-combustion geopolymer material and its preparation method", in these two patents, industrial solid waste red mud and fly ash are used as raw materials, but the total amount of industrial waste added is limited, which is not enough for large-scale consumption waste residue. And at present, there is no patent on the comprehensive utilization of red mud fly ash as raw material to prepare foam ceramics at home and abroad, and this patent just makes up for this deficiency.

Contents of the invention

The purpose of the present invention is to provide a fly ash-based high-strength and high-porosity foamed ceramics and its preparation method to consume a large amount of industrial solid waste (mainly fly ash and red mud), and at the same time to develop high porosity, anti- It is a high value-added foam ceramic product with good compressive strength and bending strength and excellent mechanical properties, so as to make rational use of resources, turn waste into treasure, save land, reduce the maintenance cost of enterprise waste residue, and reduce the harmful effects of toxic and harmful substances in waste residue. It is possible to integrate the pollution of the environment and realize the energy saving and consumption reduction of buildings.

A fly ash-based high-strength and high-porosity foamed ceramics, comprising the following components by mass percentage:

Fly ash 20-40wt%,

Red mud 30-50wt%,

Calcium carbonate 10-25wt%,

Borax 5-20wt%.

A method for preparing a fly ash-based high-strength and high-porosity foamed ceramics of the present invention comprises the following steps:

The first step: ingredients, billet making

According to the designed proportion of foam ceramic components, take red mud, fly ash raw materials through a 300-mesh sieve, and chemically analyzed pure grade calcium carbonate and borax raw materials, and mix them evenly to make a mixture; The adhesive with a mass of 1-10wt% is uniformly stirred and pressed into a block blank;

Step Two: Firing

Heat the block-shaped billet prepared in the first step to 800-950°C at a heating rate of 3°C/min-5°C/min for sintering, keep it warm for 0.5-3h; cool down to room temperature with the furnace, and then produce pulverized coal Ash-based high-strength and high-porosity foam ceramics.

The invention discloses a method for preparing fly ash-based high-strength and high-porosity foamed ceramics, wherein the binder is polyvinyl alcohol.

The invention discloses a method for preparing fly ash-based high-strength and high-porosity foamed ceramics. The pressing pressure is 20MPa-25MPa.

The invention discloses a method for preparing fly ash-based high-strength and high-porosity foamed ceramics. The sintering adopts a box-type resistance furnace or a ceramic sintering furnace.

The invention discloses a method for preparing fly ash-based high-strength and high-porosity foamed ceramics. The prepared foamed ceramics have a porosity as high as 69%, a bending strength as high as 8.05 MPa, and a compressive strength as high as 11.04 MPa.

Because the present invention adopts the above-mentioned component distribution ratio and preparation process, calcium carbonate decomposes and releases carbon dioxide gas during the sintering process of the sample, and a large amount of gas forms pores in the matrix. During the sintering process of the sample, minerals such as peroritite and bluestone with high hardness are formed. Although their strength is greatly affected by pores, the flexural strength can still reach 8.05MPa, and the compressive strength can reach 11.04MPa. The porosity makes the material have certain heat insulation, sound insulation and sound insulation properties.

Compared with the prior art, the present invention is characterized in that:

1) The main components of fly ash are SiO ₂ and Al ₂ O ₃ , and the main component of red mud is CaO, which belongs to a kind of calcium oxide-rich slag. The two kinds of slag just complement each other in composition, forming CaO-Al ₂ O ₃ - SiO ₂ series ceramics. The former endows the sintered product with high strength and high chemical stability, and the latter endows the sintered product with a relatively low firing temperature.

2) The consumption of fly ash and red mud industrial waste residue in foam ceramics reaches 70wt%, and the waste residue consumption is large, which has great environmental benefits.

3) Foam ceramics contain a large number of pores, which endow them with excellent heat insulation (summer), heat preservation (winter) and sound insulation functions.

4) The ceramic foam has been sintered at high temperature, and the chemical combination between the components makes the ceramic foam have high strength and high temperature resistance; at the same time, the ceramic foam has high chemical stability during use and will not produce new secondary pollution.

5) The industrial waste slag-based high-strength and high-porosity foam ceramics involved in the present invention require simple preparation conditions, easy operation, and low cost, and are mainly prepared from fly ash and red mud discarded in factories The foam ceramic material has excellent comprehensive properties; it can not only consume a large amount of industrial solid waste, but also obtain high value-added and multi-functional products.

In summary, the present invention proposes a new approach for the comprehensive utilization of fly ash and red mud. The amount of fly ash and red mud waste introduced reaches 70wt% or more, which can consume a large amount of industrial solid waste, It can also realize the energy saving and consumption reduction of buildings. It has very important social significance and economic benefits for the rational use of resources, turning waste into treasure, saving land, reducing the maintenance cost of waste residue in enterprises, and reducing the pollution of toxic and harmful substances in waste residue to the environment. Suitable for industrial applications.

Description of drawings:

Accompanying drawing 1 is the SEM picture of the ceramic foam prepared in Example 1 of the present invention.

Accompanying drawing 2 is the SEM picture of the ceramic foam prepared in Example 2 of the present invention.

Accompanying drawing 3 is the SEM picture of the ceramic foam prepared in Example 3 of the present invention.

Accompanying drawing 4 is the XRD spectrum of the foamed ceramics prepared in Examples 1, 2 and 3 of the present invention.

Accompanying drawing 5 is the SEM picture of the ceramic foam prepared in Example 4 of the present invention.

Accompanying drawing 6 is the SEM picture of the ceramic foam prepared in Example 5 of the present invention.

Accompanying drawing 7 is the SEM picture of the ceramic foam prepared in Example 6 of the present invention.

Accompanying drawing 8 is the SEM photo of the ceramic foam prepared in Example 7 of the present invention.

Accompanying drawing 9 is the SEM picture of the ceramic foam prepared in Example 8 of the present invention.

Accompanying drawing 10 is the SEM picture of the ceramic foam prepared in Example 9 of the present invention.

As can be seen from Fig. 1, 2, 3, the relative content of fly ash and red mud in the ceramic foam prepared by the present invention has a great influence on the porosity of the product. At 20wt% of red mud and 50wt% of fly ash, the pores are relatively Large; when the red mud is 30wt%, and the fly ash is 40wt%, the pore distribution is relatively uniform, and the pore diameter is small, and the porosity is high; when the red mud is 40wt%, and the fly ash is 30wt%, the obtained product pore diameter Small, relatively low porosity.

It can be seen from Fig. 4 that the main crystal phases of the foamed ceramics prepared by the present invention are mainly andandrite (Ca ₃ Fe ₂ (SiO ₄ ) ₃ ) and blue sidelite (K _1.6 Ca _2.4 Na _4.32 (AlSiO ₄ ) 6 (SO ₄ ) ₃ ), in 20wt% red mud and 50wt% fly ash, anorthite (CaAl ₂ Si ₂ O ₈ ) appears; when red mud is 30wt%, fly ash is 40wt%, mainly anorthite and There are two crystal phases of blue siderite; when red mud is 40wt% and fly ash is 30wt%, the main crystal phases are still andandrite and blue siderite, but nepheline phase appears.

It can be seen from Figures 5, 6, and 7 that the foamed ceramics prepared in the present invention have a great influence on the size and distribution of pores when the red mud is 30wt% and fly ash is 40wt%. When the holding time is 0.5h, the diameter of the pores is relatively small; when the holding time is 1h, the diameter of the pores is relatively large and the distribution is relatively uniform; when the holding time is 3h, the diameter of the pores is relatively large.

As can be seen from Figures 8, 9, and 10, the relative content of borax and calcium carbonate in the foam ceramics prepared in the present invention has a great influence on the sample. When the borax content is low and the calcium carbonate content is high (Figure 8, A7), The sample is not easy to soften, and the gas decomposed by calcium carbonate is not easy to overflow, and some pores with relatively small pore diameters are formed inside. When the content of borax is high and the content of calcium carbonate is low (Fig. 10, A9), the softening temperature of the sample is obviously lowered, the gas is more likely to overflow the green body, and pores with relatively large pore diameters are formed inside.

Detailed ways

The present invention will be further described below in conjunction with embodiment, but should not limit protection scope of the present invention with this.

Example 1 (No. A1): Raw material ratio (mass ratio) is red mud 20wt%, fly ash 50wt%, borax 15wt%, calcium carbonate 15wt%, heating rate 3°C/min-5°C/min, sintering temperature 800°C, keep warm for 2h. The test results show that the porosity is 59%, the compressive strength is 12.09MPa, and the bending strength is 3.08MPa.

Example 2 (No. A2): Raw material ratio (mass ratio) is red mud 30wt%, fly ash 40wt%, borax 15wt%, calcium carbonate 15wt%, heating rate 3°C/min-5°C/min, sintering temperature 800°C, keep warm for 2h. The test results show that the porosity is 64%, the compressive strength is 13.21MPa, and the bending strength is 7.05MPa.

Example 3 (No. A3): Raw material ratio (mass ratio) is 40wt% red mud, 30wt% fly ash, 15wt% borax, 15wt% calcium carbonate, heating rate 3°C/min-5°C/min, sintering temperature 800°C, keep warm for 2h. The test results show that the porosity is 59%, the compressive strength is 16.01MPa, and the bending strength is 8.04MPa.

Example 4 (No. A4): Raw material ratio (mass ratio) is 30wt% red mud, 40wt% fly ash, 15wt% borax, 15wt% calcium carbonate, heating rate 3°C/min-5°C/min, sintering temperature 900°C, keep warm for 0.5h. The test results show that the porosity is 57%, the compressive strength is 13.5MPa, and the bending strength is 11.09MPa.

Example 5 (No. A5): Raw material ratio (mass ratio) is 30wt% red mud, 40wt% fly ash, 15wt% borax, 15wt% calcium carbonate, heating rate 3°C/min-5°C/min, sintering temperature 900°C, keep warm for 1h. The test results show that the porosity is 69%, the compressive strength is 11.04MPa, and the bending strength is 8.05MPa.

Example 6 (No. A6): Raw material ratio (mass ratio) is 30wt% red mud, 40wt% fly ash, 15wt% borax, 15wt% calcium carbonate, heating rate 3°C/min-5°C/min, sintering temperature 900°C, keep warm for 3h. The test results show that the porosity is 59%, the compressive strength is 13.45MPa, and the bending strength is 9.20MPa.

Example 7 (No. A7): Raw material ratio (mass ratio) is red mud 25wt%, fly ash 45wt%, borax 8wt%, calcium carbonate 22wt%, heating rate 3°C/min-5°C/min, sintering temperature 950°C, keep warm for 1h. The test results show that the porosity is 52%, the compressive strength is 13.5MPa, and the bending strength is 10.42MPa.

Example 8 (No. A8): Raw material ratio (mass ratio) is 25wt% red mud, 45wt% fly ash, 13wt% borax, 17wt% calcium carbonate, heating rate 3°C/min-5°C/min, sintering temperature 950°C, keep warm for 1h. The test results show that the porosity is 57%, the compressive strength is 12.86MPa, and the bending strength is 8.24MPa.

Example 9 (No. A9): Raw material ratio (mass ratio) is red mud 25wt%, fly ash 45wt%, borax 18wt%, calcium carbonate 12wt%, heating rate 3°C/min-5°C/min, sintering temperature 950°C, keep warm for 1h. The test results show that the porosity is 60%, the compressive strength is 12.41MPa, and the bending strength is 6.4MPa.

It can be seen from the above that the high-strength and high-porosity ceramic foam prepared by the present invention has a porosity of about 60%, a compressive strength of more than 10 MPa, and a bending strength of more than 8 MPa, and has excellent mechanical properties.

Claims (6)

1. A fly ash-based high-strength and high-porosity ceramic foam, comprising the following components, composed by mass percentage: Fly ash 20-40wt%, Red mud 30-50wt%, Calcium carbonate 10-25wt%, Borax 5-20wt%. 2. A preparation method of fly ash-based high-strength and high-porosity foamed ceramics, comprising the following steps: The first step: ingredients, billet making According to the designed proportion of foam ceramic components, take red mud, fly ash raw materials through a 300-mesh sieve, and chemically analyzed pure grade calcium carbonate and borax raw materials, and mix them evenly to make a mixture; The adhesive with a mass of 1-10wt% is uniformly stirred and pressed into a block blank; Step Two: Firing Heat the block-shaped billet prepared in the first step to 800-950°C at a heating rate of 3°C/min-5°C/min for sintering, keep it warm for 0.5-3h; cool down to room temperature with the furnace, and then produce pulverized coal Ash-based high-strength and high-porosity foam ceramics. 3. A method for preparing fly ash-based high-strength and high-porosity foamed ceramics according to claim 2, characterized in that: the adhesive is polyvinyl alcohol. 4. A method for preparing fly ash-based high-strength and high-porosity foamed ceramics according to claim 3, characterized in that the pressing pressure is 20MPa-25MPa. 5. A method for preparing fly ash-based high-strength and high-porosity foamed ceramics according to claim 4, characterized in that: the sintering adopts a box-type resistance furnace or a ceramic sintering furnace. 6. A method for preparing a fly ash-based high-strength and high-porosity foamed ceramic according to any one of claims 2-5, characterized in that: the prepared foamed ceramic has a porosity of up to 69% and a flexural strength of up to 8.05MPa, the compressive strength is as high as 11.04MPa.

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