CN111704440A

CN111704440A - Lightweight porous aggregate and preparation process thereof

Info

Publication number: CN111704440A
Application number: CN202010546461.4A
Authority: CN
Inventors: 魏瀚; 袁林; 闫昕; 赵洪亮; 王俊涛; 尹超男; 徐如林; 徐琳琳
Original assignee: Ruitai Technology Co ltd
Current assignee: Ruitai Technology Co ltd
Priority date: 2020-06-16
Filing date: 2020-06-16
Publication date: 2020-09-25

Abstract

The invention discloses a method for pretreating bauxite powder by using low-grade diaspore ore as a main raw material according to the proportion of 40-70% and 5-35% of α -Al₂O₃5-30% of silica micropowder, 5-45% of soft clay, 0-20% of aluminum sol and 0-20% of silica sol; adding 3-5% of Al (OH) in the total mass fraction₃The light porous aggregate with good mechanical strength and low heat conductivity coefficient is prepared by preparing raw materials of micro powder, 10-20% of foaming agent, 0.03-0.5% of sodium polyphosphate and 0.01-0.06% of sodium carboxymethylcellulose and adopting a foaming method. The compressive strength of the lightweight aggregate is far greater than that of the traditional calcium silicate board material, the compressive strength of the lightweight aggregate is equivalent to that of the existing mullite heat-insulating material, and the heat-insulating capability of the lightweight aggregate is superior to that of the existing mullite heat-insulating material.

Description

Lightweight porous aggregate and preparation process thereof

Technical Field

The invention relates to a lightweight porous aggregate and a preparation process thereof, in particular to a lightweight refractory aggregate prepared by using bauxite as a main raw material, and particularly relates to a lightweight refractory aggregate with low heat conductivity coefficient and high aggregate strength.

Background

The light heat-insulating material is widely used outside a working layer of thermotechnical kiln equipment, and is used for reducing a large amount of heat emitted by the thermotechnical kiln to the outside, maintaining the internal temperature of a kiln body and stabilizing the working condition. At present, the widely used light heat-insulating material is mainly calcium silicate board, but after the use temperature exceeds 1000 ℃, the crystallization and aging phenomena appear at the material, the service life is rapidly reached, and the volume weight of the material is less than 1g/cm³The mechanical strength of the material is also low, and the material cannot bear large external force impact. When the heat emitted from the kiln to the outside is large, a light heat-insulating refractory material is required to replace a calcium silicate board material. At present, the light heat-insulating refractory material mainly adopts refractory aggregate with lower heat conductivity coefficient to improve the mechanical property, Chinese patent CN201611127147.2 discloses that the proportion of microporous mullite particles used in the high-performance mullite heat-insulating refractory castable reaches 60-70%, the porosity of the aggregate is 16-18%, and the volume density of the aggregate is still less than 1g/cm³Although the mechanical strength of the light heat-insulating refractory material can be improved by adding the aggregate, the heat conductivity coefficient of the material is influenced by the aggregate with stronger heat conductivity, the heat conductivity of the material is still larger (more than 0.4W/m.k), and the material cannot be compared with a calcium silicate plate (the heat conductivity of the calcium silicate plate is less than 0.1W/m.k), and the heat-insulating effect of the heat-insulating material on a kiln is limited. In order to solve the problem of high thermal conductivity of aggregate, chinese patent CN 102344290B proposes a method for producing lightweight refractory aggregate, in which alumina and zirconia raw materials are melted by electric melting, compressed air and water are sprayed onto the discharged melt from below the melt toward the front, and the melt is granulated to produce lightweight aggregate. Although the method prepares the lightweight refractory aggregate with low volume weight, the method still has some defects, 1. the raw material for preparing the aggregate has higher cost, and the alumina and the zirconium dioxide are both raw materials for preparing high-grade refractory material products, and the preparation of the lightweight aggregate by using the raw materials wastes non-renewable raw materials; 2. the light aggregate is prepared by melting the raw materials in an electric melting kiln, and the preparation processThe energy consumption is huge and is not beneficial to energy conservation and environmental protection; 3. although the formed hollow particles have a pore structure and play a certain role in thermal resistance, the thermal conductivity of zirconia in raw materials used for the aggregate is high (1000 ℃, 2.09W/(mK)), the aggregate has a low thermal conductivity coefficient limited by the performance of the zirconia material, and therefore the thermal conductivity coefficient of the lightweight aggregate at 1000 ℃ can only reach 0.37W/(m.k).

Therefore, the main technical problem of the preparation of the lightweight porous aggregate is how to reduce the cost of raw materials and the cost of a manufacturing process on the premise of reducing the heat conductivity coefficient, and the application economy of the lightweight porous aggregate is improved.

Disclosure of Invention

In order to solve the problems, the invention provides a lightweight porous aggregate adopting bauxite as a raw material and a preparation process thereof. The aggregate formula is as follows:

40-70% of pretreated bauxite powder (with the particle radius of 30-48 mu m)

α-Al₂O₃(particle radius of 40-160 μm) 5-35%

5 to 30 percent of silicon micropowder (with the particle radius of 5 to 20 mu m)

5-45% of soft clay (the particle radius is less than or equal to 35 mu m)

0 to 20 percent of aluminum sol (solute mass is 40 percent)

0 to 20 percent of silica sol (solute mass is 30 percent)

Adding the following components in percentage by mass:

10-20% of foaming agent

Sodium polyphosphate 0.03-0.5%

Sodium carboxymethylcellulose 0.01-0.06%

The pretreated bauxite powder is a pretreated raw material obtained after the process treatment of the monohydrate bauxite. Crushing and grinding the monohydrate bauxite until the granularity reaches a specified range, and removing iron from the treated powder. The boehmite ore used in the invention is boehmite-kaolinite subtype (D-K type) bauxite ore belonging to low-grade bauxite Al₂O₃52-63% of SiO2, 25-35% of Fe₂O₃5-6.5 percent of CaO, 1-2.2 percent of CaO and Na₂0.1 to 1% of O, K₂The content of O is 0.5-2.5%, and the loss on ignition is 10-13%. Mixing the pretreated bauxite powder and other raw materials according to the formula to prepare flowing slurry, adding a mixed solution of aluminum sol and silica sol, a coagulant and a foam stabilizer, and finally adding a foaming agent, wherein the foaming agent comprises a plurality of or one of cocamidopropyl betaine (CAB-35), octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate (TD-40) and FP-180 biological foaming agents which are mixed in any proportion, and after the foaming agent is added, rapidly stirring the foaming slurry at the stirring speed of 300-500 rad/min for 5-10 min. And pouring the stirred foamed slurry into a mold, then placing the mold into a drying kiln for drying, wherein the drying temperature is 200-350 ℃, the drying time is 10-24 hours, then demoulding, placing the mold into a tunnel kiln for firing, the maximum firing temperature point is 1200-1500 ℃, and the heat preservation time at the maximum temperature point is 3-24 hours. The burned lightweight aggregate can be used after being crushed again.

The innovation points of the invention are as follows:

firstly, low-grade bauxite is mainly adopted in the current market to prepare low-grade heat-insulating products, the product porosity is low, the heat-insulating property is poor, the product cannot be used in a high-temperature environment for a long time, the product prepared by adopting the raw material is not valued by the market, the profit margin is low, the raw material cannot be used as the main raw material for preparing the lightweight aggregate, the bauxite is changed into 'leftovers' and is discarded in large quantity, the bauxite resource is wasted in large quantity, and the discarded raw material can seriously pollute the environment. The invention adopts the low-grade bauxite raw material with the same quality in the current market, and after research and development personnel carry out a plurality of times of research and experiments, the lightweight aggregate with good thermal insulation performance, higher porosity and higher mechanical strength is obtained. The aggregate has the excellent performance mainly because an in-situ mullite phase is formed in the material after the formula is used, the attached drawings 1 and 2 show that the attached drawing 1 is an X-ray diffraction pattern of the pre-treated bauxite powder before preparation, no obvious mullite diffraction peak exists in the pattern, the main phase is alumina, after the process formula disclosed by the invention is used, the fired aggregate X-ray diffraction pattern is shown in the attached drawing 2, mullite phase characteristic peaks, alumina phase characteristic peaks and a sillimanite phase appear in the diffraction pattern, wherein the same characteristic peaks of the mullite appear in large quantity, the peak intensity is higher than that of the alumina phase, the fact that the secondary mullite crystal form is well developed is proved, the original alumina is consumed by the mullite formed in situ, and the characteristic peaks are reduced. FIG. 3 is an electron scanning micrograph of the aggregate from which the appearance of mullite crystals with a crisscross structure can be observed. As known in the common sense, mullite is a phase with low thermal conductivity and high strength in the existing non-metallic materials. Is the first choice raw material for preparing light heat insulation material. Generally, fire-resistant manufacturers can directly use mullite as a raw material of a heat insulation product, and the raw material cost of the product is high. The mullite phase heat-insulating material is directly synthesized by only utilizing the low-grade bauxite raw material through phase reaction without adding the mullite raw material, so that the low-grade bauxite resource is fully utilized, the non-renewable raw material is saved, and the production cost of the product is greatly reduced.

And secondly, the aluminum-silicon composite sol is used as a temporary bonding agent, so that the problems that the use temperature and the high-temperature strength of the material are reduced due to the fact that a large amount of liquid phase is generated in the aggregate due to more foreign impurities are avoided. The aluminum sol and the silica sol adopted by the invention can solidify a foaming blank body in a drying stage, so that the blank body has certain mechanical strength, and the demoulding and the subsequent sintering are convenient; meanwhile, in the high-temperature sintering stage, components formed in the material can participate in mullite reaction to form a high-temperature sintering product. According to the invention, the reasonable mass ratio of the two sols is finally determined by mixing the two sols for multiple times, wherein the mass ratio of the aluminum sol: silica sol = (0-2): (0-3).

Thirdly, the foaming treatment of the slurry is carried out by adopting a foaming mode, which is also a great characteristic of the invention. Before the invention, the inventor has published a research on a process for preparing mullite heat-insulating castable by a foaming method in a journal of China ceramic industry, and figure 4 shows that the foaming slurry is stirred and is directly added with a foaming agentTiny micro-bubbles exist inside the mullite thermal insulation material, the attached figure 5 is a microscopic picture of pores of the calcined lightweight aggregate, and the attached figure 6 is a picture of pores on the surface of a mullite thermal insulation material product prepared by a loss on ignition method. Comparing with fig. 5 and fig. 6, it can be found that the lightweight aggregate prepared by the foaming method has more micropores, and the mullite thermal insulation material prepared by the loss on ignition method has a main internal structure with big pores. The more pore structures are in the material with the same unit volume, the smaller the volume density of the material is, and the better the heat insulation performance of the material is. The volume density of the mullite heat-insulating material in the attached figure 5 is determined to be 1.05g/cm³Average thermal conductivity at 400 ℃ of 0.4W/(m.k), and volume density of the lightweight aggregate in figure 4 of 0.56g/cm³The average thermal conductivity at 400 ℃ is 0.08W/(m.k).

Fourthly, designing an internal pore structure of the aggregate. The adding proportion of the foaming agent is adjusted according to the test results of dozens of times, so that the foaming agent is added to form a micro-pore structure with the diameter less than or equal to 50 mu m in the foaming slurry, and the micro-pore structure is uniformly dispersed in the material. As a plurality of fine hole structures exist in the unit volume of the aggregate, the heat conduction path is lengthened, and the heat preservation and insulation capacity of the aggregate is improved.

Preparing a light refractory aggregate, firing the slurry after pore forming by a physical foaming method, wherein the fired and crushed light refractory aggregate has a lower bulk density of 0.50-0.89 g/cm³The thermal conductivity coefficient of the aggregate is 0.06-0.10W/(m.k), the strength of the aggregate after being fired at 1200 ℃ is 1.9-3.2 Mpa, and the high-temperature service temperature of the aggregate can reach 1400 ℃. In conclusion, the invention can utilize low-grade raw materials to prepare the lightweight porous aggregate with certain mechanical strength, lower bulk density and low thermal conductivity, and realizes the purpose of high-efficiency utilization of the low-grade raw materials.

Drawings

FIG. 1 is an XRD diffraction pattern of pretreated bauxite powder

FIG. 2 is a diffraction pattern of burned sample xrd;

wherein 1 is an alumina phase, 2 is a mullite phase, and 3 is a sillimanite phase;

FIG. 3 is a SEM microstructure photograph of a lightweight aggregate in which a criss-cross grown mullite phase structure may be seen;

FIG. 4 is a slurry of froth after agitation, wherein it can be seen that no macroscopic macro bubbles appear in the froth slurry;

FIG. 5 shows the surface porosity of the calcined lightweight aggregate;

fig. 6 shows the air holes on the surface of the mullite light insulating brick, wherein the holes visible on the surface of the material in fig. 5 are micropores, and the holes visible on the surface of the material in fig. 6 are macropores.

Detailed Description

Example 1:

40 percent of pretreated bauxite powder (the particle radius is 30 to 48 mu m)

α-Al₂O₃(particle radius of 40-160 μm) 15%

Silicon micropowder (particle radius 5-20 μm) 10%

15 percent of soft clay (the particle radius is less than or equal to 35 mu m)

Aluminum sol (40 percent of solution mass) 10 percent

Silica sol (30% by mass) 10%

Adding the following components in percentage by mass:

15 percent of foaming agent

Sodium polyphosphate 0.25%

The pretreated bauxite powder is a pretreated raw material obtained after the process treatment of the monohydrate bauxite. Crushing and grinding the monohydrate bauxite until the granularity reaches a specified range, and removing iron from the treated powder. Mixing the treated high-alumina bauxite raw material with other raw materials to prepare flowing slurry, adding a mixed solution of aluminum sol and silica sol, a coagulant and a foam stabilizer, and finally adding a foaming agent, wherein the foaming agent is a cocoamido propyl betaine (CAB-35) biological foaming agent, and rapidly stirring the foaming slurry after adding the foaming agent at the stirring speed of 320rad/min for 8 min. Pouring the stirred foamed slurry into a mold, then placing the mold into a drying kiln for drying, wherein the drying temperature is 250 ℃, demoulding is placed into a tunnel kiln for burning after the drying time is 14 hours, the maximum burning temperature point is 1380 ℃, and the heat preservation time is 6 hours at the maximum temperature point.

Example 2:

43 percent of pretreated bauxite powder (with the particle radius of 30-48 mu m)

α-Al₂O₃(particle radius of 40-160 μm) 15%

Silicon micropowder (particle radius 5-20 μm) 10%

15 percent of soft clay (the particle radius is less than or equal to 35 mu m)

Aluminum sol (40 percent of solution mass) 8 percent

Silica sol (30% by mass) 9%

Adding the following components in percentage by mass:

20 percent of foaming agent

Sodium polyphosphate 0.25%

Sodium carboxymethylcellulose 0.05%

Example 3:

40 percent of pretreated bauxite powder (the particle radius is 30 to 48 mu m)

α-Al₂O₃(particle radius of 40-160 μm) 15%

Silicon micropowder (particle radius 5-20 μm) 10%

15 percent of soft clay (the particle radius is less than or equal to 35 mu m)

Aluminum sol (40 percent of solution mass) 10 percent

Silica sol (solute content 30%) 10%

Adding the following components in percentage by mass:

20 percent of foaming agent

Sodium polyphosphate 0.25%

Sodium carboxymethylcellulose 0.05%

Example 4:

50 percent of pretreated bauxite powder (the particle radius is 30 to 48 mu m)

α-Al₂O₃(particle radius of 40-160 μm) 15%

Silicon micropowder (particle radius 5-20 μm) 10%

15 percent of soft clay (the particle radius is less than or equal to 35 mu m)

0 percent of aluminum sol (40 percent of solution mass)

Silica sol (solute content 30%) 10%

Adding the following components in percentage by mass:

foaming agent 5%

Sodium polyphosphate 0.25%

Sodium carboxymethylcellulose 0.05%

Example 5:

50 percent of pretreated bauxite powder (the particle radius is 30 to 48 mu m)

α-Al₂O₃(particle radius of 40-160 μm) 25%

Silicon micropowder (particle radius 5-20 μm) 10%

Soft clay (particle radius less than or equal to 35 μm) 5%

Aluminum sol (40 percent of solution mass) 10 percent

Silica sol (solute content 30%) 0%

Adding the following components in percentage by mass:

15 percent of foaming agent

Sodium polyphosphate 0.25%

Sodium carboxymethylcellulose 0.05%

Example 6:

48 percent of pretreated bauxite powder (the particle radius is 30-48 mu m)

α-Al₂O₃(particle radius of 40-160 μm) 25%

Silicon micropowder (particle radius 5-20 μm) 10%

Soft clay (particle radius less than or equal to 35 μm) 5%

Aluminum sol (40 percent of solution mass) 7 percent

Silica sol (40% of solution mass) 5%

Adding the following components in percentage by mass:

15 percent of foaming agent

Sodium polyphosphate 0.25%

Sodium carboxymethylcellulose 0.05%

Preparing a triple-mold sample (170 mm × 25mm × 25 mm) and a flat-plate heat-conducting sample mold (phi 160 × 10 mm) according to the above example formula, drying the triple-mold sample and the flat-plate heat-conducting sample mold for 12 hours in a drying box at 110 ℃, taking out the triple-mold sample and the flat-plate heat-conducting sample mold, firing the triple-mold sample in a high-temperature kiln at the firing temperature of 1100 ℃, preserving the heat for 3 hours, measuring the heat conductivity coefficient of a disc at 400 ℃ according to an experimental method for the heat conductivity coefficient of a YB/T4130-:

name of aggregate	Calcium silicate board	Mullite heat-insulating brick	Example 1 aggregate	Example 2 aggregate	Example 3 aggregate	Example 4 aggregate	Example 5 aggregate	Example 6 aggregate
									Bulk Density (g/cm)³）	0.23	1.05	0.64	0.58	0.65	0.63	0.72	0.74

The test results of the compressive strength of the sample strip and the heat-conducting disc sample prepared in each example are as follows:

name of sample	Compressive strength (MPa)	Plate thermal conductivity (W/(m.k))
			Calcium silicate board	0.35	0.071
Mullite brick	2.48	0.354
			Example 1 aggregate	2.01	0.076
Example 2 aggregate	2.00	0.069
			Example 3 aggregate	2.45	0.064
Example 4 aggregate	2.23	0.080
			Example 5 aggregate	2.69	0.082
Example 6 aggregate	2.54	0.091

Compared with mullite insulating bricks, the aggregate in the example has volume density far lower than that of the mullite insulating bricks, average heat conductivity coefficient at 400 ℃ far lower than that of the mullite insulating bricks, and compressive strength similar to that of the mullite insulating materials.

Claims

1. The lightweight porous aggregate is characterized by comprising 40-70% of pretreated bauxite powder and 5-35% of α -Al in percentage by mass₂O₃5-30% of silica micropowder, 5-45% of soft clay, 0-20% of aluminum sol and 0-20% of silica sol; 10-20% of foaming agent, 0.03-0.5% of sodium polyphosphate and 0.01-0.06% of sodium carboxymethylcellulose are added in the total mass fraction.

2. The lightweight porous aggregate according to claim 1, wherein the pretreatment powder is a pretreated raw material obtained by treating a diaspore ore which is a tri-class bauxite ore of diaspore-kaolinite subclass (D-K type), wherein the pretreatment powder is Al₂O₃52-63% of SiO2, 25-35% of Fe₂O₃5-6.5 percent of CaO, 1-2.2 percent of CaO and Na₂0.1 to 1% of O, K₂The content of O is 0.5-2.5%, and the loss on ignition is 10-13%.

3. The lightweight porous aggregate according to claim 1, characterized in that: the foaming agent is one or more of cocamidopropyl betaine (CAB-35), octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate (TD-40) and FP-180 biological foaming agent.

4. The lightweight porous aggregate according to claim 1, characterized in that: aluminum sol: silica sol = (0-2): (0-3);

the preparation process of the lightweight porous aggregate according to claims 1 to 4, comprising the steps of crushing bauxite, grinding, removing iron, mixing the treated high-alumina bauxite raw material with other raw materials according to the proportion of claims 1 to 4, preparing a flowing slurry, adding a mixed solution of alumina sol and silica sol, a coagulant and a foam stabilizer, adding the foaming agent, rapidly stirring the foaming slurry at a stirring speed of 300 to 500rad/min for 5 to 10min, pouring the stirred foaming slurry into a mold, drying the foaming slurry in a drying kiln at a drying temperature of 200 to 350 ℃, demoulding after drying for 410 to 24 hours, and firing in a tunnel kiln at a maximum firing temperature of 1200 to 1500 ℃ for 3 to 24 hours at the maximum temperature.