A lightweight particle and an autoclaved cement brick prepared by using the same

Abstract

The present invention discloses a kind of lightweight particles, and its preparation method comprises the following steps: 1) Mix quicklime and raw phosphogypsum evenly, and age them to obtain modified phosphogypsum; 2) Mix water, modified phosphogypsum, mine stripping soil dry powder and crystal conversion agent evenly, and granulate them to obtain spherical particles; 3) Mix carbonization raw materials, sodium silicate solution and thickening agent evenly to prepare a slurry; 4) Place the spherical particles prepared in step 2) into the slurry obtained in step 3), soak them and then take them out to obtain spherical core-shell particles; 5) Carry out carbonization curing on the obtained spherical core-shell particles to obtain the lightweight particles. The present invention uses phosphogypsum as the main raw material to prepare lightweight particles and applies them to autoclaved cement bricks. Without affecting the effective exertion of cement strength, it can effectively take into account the lightweight and high-strength properties of the obtained autoclaved cement bricks. Moreover, the involved preparation process is relatively simple, with high efficiency, convenient operation, low-carbon and environmental protection, and is suitable for popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a lightweight particle and an autoclaved cement brick prepared by using the same. Background Art

[0002] Sintered red brick products are gradually being replaced by more energy-saving and environmentally friendly autoclaved brick products. Compared with autoclaved products such as autoclaved lime-sand bricks and autoclaved fly ash bricks, autoclaved cement bricks have lower requirements for raw material quality and can dispose of a large amount of industrial solid waste. Autoclaved cement bricks are generally formed by static pressure molding and cured by high-temperature saturated steam. However, affected by the raw material density and the forming method, the product has a high bulk density, resulting in high transportation and construction costs.

[0003] Phosphogypsum is a waste discharged during the production of wet-process phosphoric acid. Using untreated powdered original phosphogypsum to prepare cement bricks can save raw material costs and reduce the bulk density, but there are currently three main problems: 1) The dissolution of SO4 2- and impurities such as soluble phosphorus and fluoride ions will reduce the rate of cement hydration reaction; 2) Phosphoric acid and sulfates in phosphogypsum will react with the cement hydration products, reducing the strength of the brick blank; 3) The incorporation of gypsum materials will reduce the water resistance of the brick blank. Usually, phosphogypsum needs to be modified to achieve effective application in cement bricks.

[0004] It has been reported that a core-shell structure phosphogypsum-based lightweight aggregate is prepared by coating cement and siliceous / calcareous materials on the surface of phosphogypsum and using the hydration reaction and silica-calcium reaction in a high-temperature and high-pressure steam environment. However, in the above modification process, phosphoric acid in the phosphogypsum core will react with calcium hydroxide in the shell, reducing the content of effective components in the shell structure and affecting the content of silica-calcium reaction products in the shell to a certain extent; in addition, SO4 2- in the gypsum core, soluble phosphorus, and fluoride ions migrate to the particle surface during the autoclave curing process, which will slow down the cement hydration rate in the shell and damage the cement hydration products, and is not conducive to ensuring the modified strength, etc. Further exploring phosphogypsum-based aggregates suitable for preparing autoclaved cement bricks has important research and application significance. Summary of the Invention

[0005] The main purpose of the present invention is to provide a lightweight particle mainly made of phosphogypsum in view of the problems and deficiencies existing in the prior art, and apply it to autoclaved cement bricks. Without affecting the effective exertion of cement strength, it can effectively take into account the advantages of light bulk density and high strength, and the involved preparation process is relatively simple, efficient, convenient to operate, low-carbon and environmentally friendly, providing a new idea for the resource utilization of industrial solid wastes such as phosphogypsum.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of a lightweight particle includes the following steps:

[0008] 1) By weight, mix 3 - 10 parts of quicklime with 80 - 100 parts of raw phosphogypsum evenly, and age for (1 - 3 h) to obtain modified phosphogypsum;

[0009] 2) By weight, mix 0 - 5 parts of water, 70 - 90 parts of modified phosphogypsum, 10 - 25 parts of dry powder of mine overburden soil, and 0.2 - 0.5 parts of crystal conversion agent evenly, and place them in a pair - roll extrusion granulator to prepare spherical particles with a diameter of 3 - 8 mm;

[0010] 3) By weight, mix 80 - 100 parts of carbonization raw material, 30 - 40 parts of sodium silicate solution, and 0.1 - 0.3 parts of thickening agent evenly to prepare a slurry;

[0011] 4) Place the spherical particles prepared in step 2) into the slurry obtained in step 3), soak and then take them out to obtain spherical core - shell particles with a diameter of 5 - 10 mm;

[0012] 5) Place the spherical core - shell particles obtained in step 4) in an environment with a temperature of 50 - 70 °C, a pressure of 0.3 - 0.6 MPa, a CO₂ concentration of 50 - 100 vol%, and a relative humidity of 70 - 90% for curing for 1 - 3 h to obtain lightweight particles.

[0013] In the above - mentioned scheme, the content of dihydrate gypsum in the raw phosphogypsum is greater than 90%, and the moisture content is 30 - 40%.

[0014] In the above - mentioned scheme, the moisture content of the modified phosphogypsum obtained in step 1) is 15 - 20%.

[0015] In the above - mentioned scheme, the content of clay minerals in the dry powder of mine overburden soil in step 2) is 14 - 30 wt%; its particle size is less than 350 um; the free swelling ratio is less than 20%.

[0016] In the above - mentioned scheme, the crystal conversion agent in step 2) is one or more of inorganic salt crystal conversion agents, organic acid crystal conversion agents, macromolecular crystal conversion agents, and surfactants.

[0017] Furthermore, the inorganic salt crystal conversion agent can be selected from one or more of sodium sulfate, potassium sulfate, aluminum sulfate, iron sulfate, etc.; the organic acid crystal conversion agent can be selected from one or more of sodium citrate, sodium isobutyrate, etc.; the macromolecular crystal conversion agent can be selected from one or more of gelatin, hyaluronic acid, etc.; the surfactant can be selected from one or more of sodium dodecyl sulfonate, stearic acid, fatty acid glyceride, etc.

[0018] Preferably, the crystal conversion agent is a compound admixture of an inorganic salt crystal conversion agent and an organic acid crystal conversion agent in a mass ratio of 1:1 - 3.

[0019] In the above solution, the carbonization raw material in step 3) consists of one or more of steel slag, washed desalted kiln ash, carbide slag, etc., and its particle size is less than 150 um.

[0020] Furthermore, the content of C2S in the steel slag is 40 - 50%; the content of calcium hydroxide in the washed desalted kiln ash is 30 - 50%; the content of calcium hydroxide in the carbide slag is greater than 90%.

[0021] Preferably, the carbonization raw material is compounded by steel slag, washed desalted kiln ash, and carbide slag according to a mass ratio of 1 - 3:5 - 7:2 - 4; its main mineral composition and the mass percentage it occupies include: C2S 10 - 25%, Ca(OH)2 30 - 50%.

[0022] In the above solution, the sodium silicate solution in step 3) is prepared by diluting water glass with a modulus of 2.0 - 3.5 and a solid content of 30 - 50% with water by 100 - 200 times.

[0023] In the above solution, the thickening agent is composed of one or several of cellulose ether, polyacrylamide, and polyvinyl alcohol.

[0024] Preferably, the thickening agent is one of methyl cellulose ether or hydroxypropyl methyl cellulose ether; its viscosity is 50,000 - 150,000.

[0025] In the above solution, the fluidity of the slurry obtained in step 3) is 90 - 110 mm.

[0026] In the above solution, in the soaking step in step 4), the time interval from immersion to removal is less than 30 s.

[0027] An autoclaved cement brick based on the above lightweight particles, each raw material and the weight parts it occupies include: 30 - 50 parts of lightweight particles, 8 - 12 parts of ordinary Portland cement, 40 - 55 parts of stone powder, and 5 - 8 parts of water.

[0028] Furthermore, the ordinary Portland cement is ordinary Portland cement with a strength grade not lower than 42.5; more than 90% of the total mineral composition in the stone powder is calcium carbonate, and its particle size is 100 - 300 mesh.

[0029] In the above solution, the autoclaved cement brick is obtained by mixing each raw material evenly to obtain a brick blank mixture; and then through molding and autoclave curing.

[0030] In the above solution, the molding step adopts a static pressure molding process, and its molding pressure is 8 - 12 MPa and the time is 2 - 5 s.

[0031] In the above solution, the steam temperature adopted in the autoclave curing process is 170 - 190 °C, the pressure is 0.6 - 1.3 MPa, and the constant temperature and constant pressure time is 4 - 6 h.

[0032] The apparent density of the lightweight unburned brick prepared according to the above scheme is 1750-1850 kg / m 3 The compressive strength meets the MU15 grade requirements and the softening coefficient is greater than 0.8.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1) The lightweight particles of the present invention use phosphogypsum as the main raw material. First, the phosphogypsum is modified using quicklime. After mixing with the original phosphogypsum, the quicklime is digested to generate Ca(OH)2, which can react with soluble phosphorus and soluble fluorine to generate insoluble calcium fluoride and calcium phosphate, which can effectively eliminate soluble harmful impurities in the lightweight particles. Then, the particles are mixed with dry powder of mine stripping soil, a crystallization agent, and water, and the stripping soil is plastically granulated to obtain phosphogypsum-based spherical particles (core). This is beneficial in promoting the conversion of dihydrate gypsum into α-hemihydrate gypsum in the crystallization agent and high-temperature and high-pressure water vapor environment during the subsequent brick autoclave curing process. After the autoclave curing is completed, the α-hemihydrate gypsum absorbs water and recrystallizes, thereby effectively improving the hardness of the obtained lightweight particles.

[0035] 2) The slurry is prepared with carbonized raw materials, sodium silicate solution and thickener as the main raw materials. The addition of thickener can ensure that raw materials with different densities do not bleed or separate in the slurry; after coating the phosphogypsum-based spherical particles and combining them with an optimized carbonization process (controlling CO2 concentration, curing temperature, etc.), it can promote the formation of chain calcium carbonate and cross-linked network structure of silica gel, which grows intertwinedly to form a denser shell, effectively avoiding SO4 in the modified phosphogypsum. 2- Soluble ions diffuse to the surface of cement particles to reduce the rate of cement hydration reaction in the brick and destroy the structural stability of the hydration products; by controlling the carbonization time, the density of lightweight particles is guaranteed to avoid excessive carbonation resulting in excessive carbonization weight gain; in addition, the introduced sodium silicate solution can react quickly with CO2 to generate silica gel, which fills the pores in the carbonized shell to form a "nested" structure, which can reduce the water absorption rate of lightweight particles and thus improve the water resistance of cement autoclaved bricks.

[0036] 3) The lightweight particles prepared by the present invention use raw materials with a variety of industrial solid wastes and a high dosage. The raw material cost is low and the preparation process efficiency is high, which can meet the needs of industrial production of cement brick products. With the advantage of the industrial production capacity of autoclaved cement bricks, waste can be turned into treasure and economic benefits can be created.

[0037] 4) The autoclaved cement bricks obtained by the present invention have the characteristics of low bulk density, high strength and good water resistance. At the same time, the bulk density of the bricks can be flexibly adjusted according to the dosage of lightweight particles, and the applicability is wide. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1Schematic diagram of the production process flow of the lightweight particles of the present invention and the autoclaved cement bricks prepared therefrom. Specific embodiments

[0039] The present invention will be further described in detail below in conjunction with embodiments, which is convenient for a clearer understanding of the present invention, but they do not constitute a limitation to the present invention.

[0040] In the following examples and comparative examples, the as-received phosphogypsum is from Xiangyun Phosphorus Chemical Industry in Wuxue City, Hubei Province; the quicklime is taken from Huaxin Cement (Lijiang) Co., Ltd.; the stripped soil dry powder is taken from Huaxin Cement (Yangxin) Co., Ltd., with an average particle size of 250 um, a plasticity index of 16.8, and a free swelling rate of 18%; one or more of aluminum sulfate, ferric sulfate (inorganic salts) and sodium citrate, sodium isobutyrate (organic acids) are used as crystal conversion agents, and the purity is industrial pure; the washed salt-removing kiln ash and steel slag are taken from Huaxin Cement (Wuxue) Co., Ltd., with a particle size of 100 um; the carbide slag is a commercially available product with a particle size of 50 um; the water glass solution is obtained by diluting the water glass stock solution with a solid content of 40% and a modulus of 3.3 produced by Hebei Litian Chemical Industry Co., Ltd. by 150 times; the thickener uses hydroxypropyl methyl cellulose ether with a viscosity of 150,000 produced by Jinan Xingwangda Chemical Industry Co., Ltd.

[0041] The cement used is PO42.5 cement produced by Huaxin Cement (Dao County) Co., Ltd.; the stone powder and the aggregate screen undersize produced by the Yangxin Aggregate Factory of Huaxin Cement are used.

[0042] The chemical compositions of each raw material are shown in Table 1.

[0043] Table 1 Chemical compositions of raw materials

[0044] Name <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[SO3 <!-- 3 -->]]> As-received phosphogypsum 6.51 0.70 0.51 29.49 0.24 41.44 Quicklime 4.75 2.28 0.24 86.70 0.99 0.27 Washed desalted kiln ash 14.64 4.32 2.11 49.58 2.72 3.11 Steel slag 11.46 5.41 22.15 42.68 10.18 1.00 Calcium carbide residue 2.37 0.91 0.19 95.90 0.11 0.39 Stripped soil 64.58 13.15 7.03 0.42 0.55 0.16 PO42.5 cement 20.99 5.98 3.03 59.57 1.83 3.04 Stone powder 4.57 1.06 0.51 48.86 2.84 0.72 Screened undersize 5.27 1.50 0.63 36.86 12.72 0.07

[0045] The mineral compositions of the raw materials are shown in Table 2

[0046] Table 2 Mineral compositions of raw materials

[0047]

[0048] Example 1

[0049] A kind of lightweight particles and autoclaved cement bricks prepared therefrom, and the preparation method thereof includes the following steps:

[0050] Preparation of lightweight particles;

[0051] 1) By weight, 6 parts of quicklime are mixed evenly with 100 parts of as-received phosphogypsum and aged for 1.5 h to obtain modified phosphogypsum (with a moisture content of 16%);

[0052] 2) Mix 75 parts of modified phosphogypsum, 4 parts of water, 25 parts of exfoliated soil dry powder, 0.1 part of ferric sulfate, and 0.2 part of sodium isobutyrate evenly by weight, and place them in a pair-roll extrusion granulator to prepare spherical particles with a diameter of 3 - 5 mm;

[0053] 3) Mix 25 parts of steel slag, 58 parts of washed desalted kiln ash, and 17 parts of carbide slag evenly by weight. Then, mix them evenly with 35 parts of sodium silicate solution and 0.2 part of hydroxypropyl methylcellulose to prepare a slurry with a fluidity of 95 mm;

[0054] 4) Immerse the spherical particles obtained in step 2) in the slurry obtained in step 3) for 10 s, and take them out to obtain core-shell particles with a diameter of 4 - 6 mm;

[0055] 5) Place the spherical core-shell particles obtained in step 4) in an environment with a temperature of 60 °C, a pressure of 0.4 MPa, a CO₂ concentration of 100%, and a relative humidity of 70 - 80% for 1 h to obtain lightweight particles.

[0056] Preparation of autoclaved cement bricks;

[0057] 6) Mix 40 parts of the obtained lightweight particles, 10 parts of PO42.5 cement, 50 parts of stone powder, and 7 parts of water evenly by weight to obtain a brick blank mixture;

[0058] 7) Press the brick blank mixture obtained in step 6) at a molding pressure of 10 MPa for 3 s to prepare a brick blank with a length of 240 * width of 115 * height of 53 mm; then, under the conditions of saturated steam at 180 °C and 1.00 MPa, maintain a constant temperature for 4 h to obtain autoclaved cement bricks.

[0059] Example 2

[0060] A kind of lightweight particles and autoclaved cement bricks prepared by using them, and its preparation method includes the following steps:

[0061] Preparation of lightweight particles;

[0062] 1) Mix 9 parts of quicklime and 100 parts of original phosphogypsum evenly by weight, and age for 3 h to obtain modified phosphogypsum (with a moisture content of 20%);

[0063] 2) Mix 65 parts of the modified phosphogypsum, 2 parts of water, 35 parts of exfoliated soil dry powder, 0.1 part of aluminum sulfate, and 0.3 part of sodium citrate evenly by weight, and place them in a pair-roll extrusion granulator to prepare spherical particles with a diameter of 3 - 6 mm;

[0064] 3) Mix 30 parts of steel slag, 50 parts of washed desalted kiln ash, and 20 parts of carbide slag evenly by weight. Then, mix them evenly with 42 parts of sodium silicate solution and 0.15 part of hydroxypropyl methylcellulose ether to prepare a slurry with a fluidity of 100 mm;

[0065] 4) Soak the spherical particles obtained in step 2) in the slurry obtained in step 3) for 15 s, and then take them out to obtain core-shell particles with a diameter of 4-8 mm;

[0066] 5) Place the spherical core-shell particles obtained in step 4) in an environment with a temperature of 50 °C, a pressure of 0.5 MPa, a CO₂ concentration of 60%, and a relative humidity of 70-90% for 2.5 h of environmental curing to obtain lightweight particles.

[0067] Preparation of autoclaved cement bricks;

[0068] 6) According to the parts by weight, mix 40 parts of the lightweight particles obtained in step 5), 12 parts of PO42.5 cement, 50 parts of stone powder, and 7 parts of water evenly to obtain a brick blank mixture;

[0069] 7) Press the brick blank mixture obtained in step 6) under a molding pressure of 12 MPa for 4 s to prepare a brick blank with a length of 240 * width of 115 * height of 53 mm; then, under the conditions of saturated steam at 170 °C and 0.80 MPa, carry out constant temperature curing for 6 h to obtain autoclaved cement bricks.

[0070] Comparative Example 1

[0071] A kind of lightweight particles and autoclaved cement bricks prepared by using the same, and the preparation method thereof includes the following steps:

[0072] 1) Mix 25 parts of steel slag, 58 parts of washed desalted kiln ash, and 17 parts of carbide slag evenly, and then mix them evenly with 35 parts of sodium silicate solution and 0.2 parts of hydroxypropyl methylcellulose to prepare a slurry with a fluidity of 95 mm;

[0073] 2) According to the parts by weight, mix 20 parts of the slurry obtained in step 1), 60 parts of modified phosphogypsum, 20 parts of exfoliated soil dry powder, 0.08 parts of ferric sulfate, and 0.16 parts of sodium isobutyrate evenly, and place them in a pair-roll extrusion granulator to prepare particles with a diameter of 4-6 mm

[0074] 3) According to the parts by weight, mix 40 parts of the lightweight particles obtained in step 2), 10 parts of PO42.5 cement, 50 parts of stone powder, and 7 parts of water evenly to obtain a brick blank mixture;

[0075] 4) Press the brick blank mixture obtained in step 3) under a molding pressure of 10 MPa to prepare a brick blank with a length of 240 * width of 115 * height of 53 mm, and then use saturated steam at 180 °C and 1.00 MPa for constant temperature curing for 4 h to obtain autoclaved cement bricks.

[0076] Comparative Example 2

[0077] This comparative example is the same as Example 1 in the preparation process except for step 7). The difference lies in that after preparing the brick blank in step 7), the maintenance regime of saturated steam at 180 °C and 1.00 MPa for 4 hours at a constant temperature is changed to maintenance at a humidity ≥ 90%, a temperature of 20 ± 2 °C for 28 days to obtain cement bricks.

[0078] Comparative Example 3

[0079] This comparative example is the same as Example 1 in the preparation process except for step 3). The difference lies in that 35 parts of the water glass solution in step 3) are replaced by 35 parts of water.

[0080] Comparative Example 4

[0081] This comparative example is the same as Example 2 in the preparation process except for step 3). The difference lies in that hydroxypropyl methyl cellulose ether is not incorporated into the slurry preparation in step 3).

[0082] Table 1 Performance test results of the lightweight particles obtained in Examples 1 - 2 and Comparative Examples 1 - 4

[0083]

[0084]

[0085] The autoclaved cement bricks obtained in the examples and comparative examples were respectively tested for performance according to the reference standard "Test Methods for Masonry Bricks - GB / T 2542 - 2012". The results are shown in Table 2.

[0086] Table 2 Performance test results of the autoclaved cement bricks obtained in Examples 1 - 2 and Comparative Examples 1 - 4

[0087] Number Strength / (MPa) <![CDATA[Unit weight / (Kg / m 3 )]]> Softening coefficient Example 1 16.8 1817 0.82 Example 2 18.4 1821 0.86 Comparative Example 1 12.5 1786 0.72 Comparative Example 2 13.5 1808 0.84 Comparative Example 3 16.8 1802 0.75 Comparative Example 4 14.7 1792 0.82

[0088] The present invention is not limited to the above embodiments. For those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches are also regarded as within the protection scope of the present invention. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

Claims

1. A lightweight particle, characterized in that: The preparation method comprises the following steps: 1) Mix quicklime and original phosphogypsum evenly and age them to obtain modified phosphogypsum; 2) Evenly mix water, modified phosphogypsum, dry powder of mine stripping soil and crystallization agent, and granulate to obtain spherical particles; 3) uniformly mixing the carbonized raw material, sodium silicate solution, and tackifier to prepare a slurry; 4) placing the spherical particles prepared in step 2) into the slurry obtained in step 3), soaking them, and then taking them out to obtain spherical core-shell particles; 5) carbonizing and curing the obtained spherical core-shell particles to obtain the lightweight particles; Step 3) the viscosity enhancer is one or more of cellulose ether, polyacrylamide, and polyvinyl alcohol; Step 5) The carbonization curing process includes: 50-70°C, pressure 0.3-0.6 MPa, CO2 concentration 50-100 vol%, relative humidity 70-90%; curing time 1-3 hours The raw materials in step 1) and their weight percentages include: 3-10 parts of quicklime and 80-100 parts of original phosphogypsum; The raw materials in step 2) and their weight proportions include: 0-5 parts of water, 70-90 parts of modified phosphogypsum, 10-25 parts of mine stripping soil dry powder, and 0.2-0.5 parts of crystallization agent; The raw materials in step 3) and their weight percentages include: 80-100 parts of carbonized raw material, 30-40 parts of sodium silicate solution, and 0.1-0.3 parts of viscosity enhancer; Step 3) The carbonization raw material is composed of one or more of steel slag, water-washed desalted kiln dust, and carbide slag, and its particle size is less than 150 μm.

2. The lightweight particles according to claim 1, characterized in that The dihydrate gypsum content in the original phosphogypsum is greater than 90%, and the water content is 30-40%.

3. The lightweight particles according to claim 1, characterized in that In step 2), the clay mineral content in the dry powder of the mine stripping soil is 14-30%; its particle size is less than 350 μm, and its free expansion rate is less than 20%.

4. An autoclaved cement brick based on the lightweight particles according to any one of claims 1 to 3, characterized in that: The raw materials and their weight proportions include: 30-50 parts of lightweight particles, 8-12 parts of ordinary Portland cement, 40-55 parts of stone powder, and 5-8 parts of water.

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