A non-fired γ-C2S phosphogypsum lightweight aggregate and its preparation method

Abstract

The present invention discloses a non-fired γ-C2S phosphogypsum lightweight aggregate, and its components and their mass percentages are as follows: phosphogypsum 43-68%, γ-C2S 12-28%, fly ash 5-10%, mineral powder 5-10%, red mud powder 3-6%, sodium metaaluminate 1-3%, water 5-7%; First, the weighed phosphogypsum, γ-C2S, mineral powder, fly ash, red mud powder, sodium metaaluminate and water are stirred and mixed; Then, through step-by-step pressing, crushing, rounding treatment and screening, aggregate blanks are obtained; Finally, they are cured in saturated lime water to obtain the product. The γ-C2S phosphogypsum lightweight aggregate obtained by the present invention has a low self-weight and high strength, can realize the high-value resource utilization of industrial wastes such as phosphogypsum, and has significant environmental and economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a non-fired γ-C2S phosphogypsum lightweight aggregate and a preparation method thereof. Background Art

[0002] Phosphogypsum is a solid waste generated in the wet-process phosphoric acid process, and has characteristics such as high temperature resistance and chemical corrosion resistance. After being purified, calcined, and modified, phosphogypsum is mainly applied in fields such as agricultural building materials and industry. At present, except for a small amount used in the production of building materials products, most of the phosphogypsum is still mainly stored as waste residue, which has a huge impact on the ecological environment. Effectively utilizing phosphogypsum waste residue is of extremely important significance for saving resources, protecting the environment, improving economic benefits, promoting economic growth, and sustainable development.

[0003] Phosphogypsum is porous, easy to absorb water, and its hydration product calcium sulfate dihydrate is easily soluble in water, which easily leads to problems such as a significant reduction in the strength of phosphogypsum; when it is applied to the preparation of phosphogypsum-based aggregates, there are generally problems such as low cylinder compressive strength, high self-weight, and softening when encountering water, which limits its popularization and application. To address the above problems, it is usually necessary to further introduce improvement means such as cement to achieve its strengthening or waterproofing effects, etc., but the improvement effects involved are limited. Further exploring the efficient resource utilization of industrial waste such as phosphogypsum in aggregates has important environmental and industrial application significance. Summary of the Invention

[0004] The main purpose of the present invention is to provide a non-fired γ-C2S phosphogypsum lightweight aggregate aiming at the problems and deficiencies existing in the prior art. It has low self-weight, high strength, good water stability, can realize the high-value resource utilization of industrial waste such as phosphogypsum, has significant environmental and economic benefits, and is suitable for popularization and application.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A non-fired γ-C2S phosphogypsum lightweight aggregate, the components and their mass percentages include: 43-68% of phosphogypsum, 12-28% of γ-C2S, 5-10% of fly ash, 5-10% of mineral powder, 3-6% of red mud powder, 1-3% of sodium metaaluminate, and 5-7% of water.

[0007] In the above solution, the pH value of the phosphogypsum is greater than 3.0, and the main chemical components and their mass percentages include: 37-41 wt% of CaO, 40-43 wt% of SO3; the residue on a 80um sieve is not more than 20%.

[0008] In the above solution, the particle size of the γ-C2S is 1.5-45 μm, and the purity is higher than 99%.

[0009] In the above scheme, the sodium aluminate is a white powder with a purity higher than 99.2%.

[0010] In the above scheme, the mineral powder is S95 grade or above, with a loss on ignition of 0.6-1.0wt%, and a specific surface area of ​​400-450m 2 / kg, moisture 0.1-1.0wt%.

[0011] In the above scheme, the red mud powder is obtained by drying and grinding red mud (water content is 32-36%); its particle size is less than 100 μm, the content of fine particles less than 0.075 mm is ≥ 75.6%, and the content of sand particles greater than 0.075 mm is ≤ 24.4%; the main chemical components and their mass percentages include: Fe2O3 50-53%, Al2O3 21-24%.

[0012] In the above scheme, the fly ash is Class I or Class II fly ash.

[0013] The method for preparing the above-mentioned unburned γ-C2S phosphogypsum lightweight aggregate comprises the following steps:

[0014] 1) Put the phosphogypsum, γ-C2S, mineral powder, fly ash, red mud powder and sodium aluminate weighed according to the proportion into a mixer and mix them evenly, then add water and stir evenly to obtain a mixed raw material;

[0015] 2) placing the obtained mixed raw materials into a mold and performing step-by-step vibration pressing to obtain a block green body;

[0016] 3) Use a crusher to crush the block blank to form a coarse aggregate; then perform a rounding process to remove the edges and corners on the surface of the aggregate; and then perform screening to obtain coarse aggregates of different particle sizes;

[0017] 4) The obtained rough aggregate is placed in saturated lime water for curing to obtain the γ-C2S phosphogypsum unburned ceramsite lightweight aggregate.

[0018] In the above scheme, the phosphogypsum used is block-shaped original phosphogypsum, whose main component is calcium sulfate dihydrate, and it needs to be crushed to a fineness of 80um and a sieve residue of no more than 20% to ensure its activity.

[0019] In the above scheme, the target pressure is set to 270-320KN.

[0020] Furthermore, in the pressing process of step 2), a step-by-step vibration pressing process is adopted, and the pressing process is vibrated on a vibration table with a frequency of 2860-3000 times / min and an amplitude of 0.3-0.6 mm; the specific steps include:

[0021] 1) First, pressurize to 170-220kN and maintain pressure for 5-10 minutes;

[0022] 2) Then pressurize to 220 - 270 kN and hold the pressure for 5 - 10 min;

[0023] 3) Continue to pressurize to the target pressure value of 270 - 320 kN and hold the pressure for 5 - 10 min.

[0024] In the above - mentioned scheme, the stress rate of the pressurization step is 0.330 - 0.410 MPa / s.

[0025] In the above - mentioned scheme, the crushing particle size in step 3) is 5.5 - 20 mm.

[0026] In the above - mentioned scheme, the inclination angle of the rounding equipment used in the rounding step in step 3) is 48 - 65°.

[0027] In the above - mentioned scheme, the particle size after rounding treatment in step 3) is 4.5 - 19.5 mm, and then the obtained granular material is screened and classified and cured by grading.

[0028] Furthermore, the rough embryo sizes of the aggregate after screening and classification in step 3) are 4.5 - 9.5 mm, 9.5 - 16.0 mm and / or 16.0 - 19.5 mm.

[0029] In the above - mentioned scheme, the curing time in the saturated lime water is 21 - 28 d. Under the curing of saturated lime water, a large amount of CO₂ is adsorbed, and at the same time, it can promote the reaction process between γ - C₂S and phosphogypsum, generating a cementitious material that is insoluble in water on the surface, effectively improving the strength of phosphogypsum aggregate, etc.

[0030] The γ - C₂S phosphogypsum autoclaved lightweight aggregate prepared according to the above - mentioned scheme has a bulk density of 917 - 955 kg / m 3 , softening coefficient of 0.95 - 0.98, cylinder compressive strength ≥8.6 Mpa, water absorption rate ≥4.9%, crushing value ≤12.0%, porosity ≤14.25%, the size of micro - fine connected pores is 0.01 - 100 nm and accounts for more than 34% of the total porosity, and each ton can solidify 23 - 32 kg of CO₂.

[0031] The principle of the present invention is:

[0032] The present invention organically combines γ - C₂S with solid wastes such as phosphogypsum, fly ash, mineral powder, red mud, etc. to prepare high - strength lightweight aggregate: the strong alkaline condition provided by red mud can consume SO₄ in phosphogypsum 2- etc., and provide a weakly alkaline environment; under the weakly alkaline condition, the activities of mineral powder and fly ash are activated, and react with Ca in phosphogypsum 2+Reactions occur, generating a large amount of ettringite crystals that coat the surface of the phosphogypsum aggregate, which is beneficial for filling the tiny voids in the aggregate and making its structure denser. However, problems such as softening in water and low strength still exist in the phosphogypsum aggregate. The present invention further combines the saturated lime water curing process to promote the further carbonation reaction of γ-C2S to generate a dense and water-insoluble silica gel phase substance, calcite, aragonite, vaterite, etc., forming a waterproof film on the surface of the aggregate, which can effectively solve problems such as large water absorption and softening in water, and significantly improve the strength after hardening.

[0033] In addition, the calcium carbonate crystals and ettringite formed under saturated lime water curing can form a framework between the uncarbonated γ-C2S and phosphogypsum, and then the silica gel phase fills the framework voids, while wrapping the surface of the uncarbonated γ-C2S and phosphogypsum, further effectively improving the mechanical properties, water stability, durability, etc. of the obtained phosphogypsum-based aggregate.

[0034] The present invention further combines the step-by-step pressing process, and each component is closely packed under the extrusion action, reducing initial defects.

[0035] The saturated lime water curing process adopted by the present invention can effectively avoid the dissolution of calcium hydroxide generated by the hydration of γ-C2S during curing, which may lead to problems such as a decrease in the strength of the aggregate; at the same time, it is beneficial to improve the adsorption effect of CO2 and effectively activate the mineral activity of γ-C2S.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] 1) The present invention uses phosphogypsum as the main raw material, supplemented by industrial wastes such as fly ash, slag powder, and red mud to prepare non-fired ceramsite aggregate, and combines the step-by-step vibration pressing and saturated lime water curing processes. On the premise of reducing self-weight, it can significantly improve the strength of the phosphogypsum-based aggregate, optimize the pore structure of the phosphogypsum-based aggregate, and take into account good water absorption, etc.

[0038] 2) The present invention utilizes the synergistic effect of γ-C2S and phosphogypsum, which can greatly increase the strength and water stability of the phosphogypsum lightweight aggregate, obtain a high-strength and lightweight phosphogypsum lightweight aggregate that can be applied in large amounts, greatly improve production efficiency and reduce production costs, and effectively broaden its application scope as building products; it can provide a new idea for the preparation of high-performance phosphogypsum-based aggregate.

[0039] 3) Under the weak alkaline condition of the phosphogypsum-red mud-based cementitious system, the introduced sodium aluminate can generate a large amount of Al(OH)4 - , which is beneficial to promoting the rapid reaction and recrystallization of phosphogypsum and γ-C2S, and preferentially generating silica gel phase substances; and it can combine with Mg in phosphogypsum 2+ , CO3 in fly ash and slag powder 2-Hydroxides are generated, greatly enhancing the early strength of the aggregate, providing favorable conditions for subsequent grading and pressing, and its affinity for Cl - , which can further improve the durability performance of the aggregate concrete products, etc. Specific implementation manners

[0040] The present invention is not limited to the above implementation manners. For those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements 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.

[0041] In the following examples, the phosphogypsum used is provided by industrial waste residues in Yichang City, Hubei Province. The water content in the natural state is about 5%, the pH value is 3.2, and the residue on a sieve of 80μm fineness is ≤20%; the main chemical components CaO and SO3 contents are 40.98wt% and 42.11wt% respectively.

[0042] The red mud used is combined process red mud with a natural water content of 35.9%. The red mud is dried and ground to obtain red mud powder. Among them, the content of fine particles less than 0.075mm accounts for 75.6%, the content of sand particles greater than 0.075mm accounts for 24.4%, the main chemical components Fe2O3 and Al2O3 contents are 52.21wt% and 23.66wt% respectively, and the particle size is less than 100μm.

[0043] The γ-C2S used is provided by a chemical company in Yichang, with a particle size of 1.5 - 45μm and a purity higher than 99%.

[0044] The fly ash used is Class II fly ash with a particle size ≤200μm; the mineral powder is commercially available S95 grade mineral powder with a loss on ignition of 1.0wt%, a specific surface area of 430m 2 / kg, and a moisture content of 1.0wt%.

[0045] Example 1

[0046] A non-fired γ-C2S phosphogypsum lightweight aggregate, and its preparation method includes the following steps:

[0047] 1) Pretreatment of raw materials: Put the original phosphogypsum into a blast drying oven, set the temperature to 45°C, after blast drying for 12h, put it into a sealed bag for storage; γ-C2S, fly ash and mineral powder are treated with a 105°C blast dryer for 12h, and then put into a sealed bag for storage;

[0048] 2) Raw material mixing: According to the size of the pressed block and the expected dry density value, calculate the total mass of the dry material mixture required to press the block of this density and size. Then, weigh each raw material according to the ratio requirements of 55% phosphogypsum, 18% γ-C2S, 10% fly ash, 5% mineral powder, 2% sodium metaaluminate, 3% red mud powder, and 7% water.

[0049] 3) Pour the weighed phosphogypsum, fly ash, γ-C2S, mineral powder, and red mud powder into the mixing equipment respectively, stir the powder thoroughly for 5 minutes to mix evenly, and then add water and stir thoroughly for 8 minutes.

[0050] 4) Pour the obtained mixed raw materials into the mold in three portions. Then place the whole between the upper and lower platforms of the press, place the press on the vibrating table and vibrate it on the vibrating table with a frequency of 2860 times / minute and an amplitude of 0.3 mm. By adjusting the control handle of the press platform, adjust the height of the upper platform until it touches the pressed block. Then use the computer terminal to edit the pressure program. The program content is divided into three levels of pressurization, and the pressurization method increases in units of stress. Specifically, the first level pressurizes at a stress rate of 0.330 MPa / s to 170 kN and holds the pressure for 5 minutes; the second level pressurizes at a stress rate of 0.330 MPa / s to 220 kN and holds the pressure for 5 minutes; the third level continues to pressurize at a stress rate of 0.330 MPa / s to 270 kN and holds the pressure for 10 minutes.

[0051] 6) Demolding and crushing treatment: Demold the blocky green body obtained in step 5) with a jack, and put the demolded blocky green body into a crusher for crushing treatment. The blocky green body is crushed into small pieces to obtain coarse aggregate with a particle size of 5.5 - 20 mm.

[0052] 7) Chamfering and rounding: Pour the crushed coarse aggregate into the rounding machine. The rounding machine consists of a disc and a motor, and set the inclination angle of the equipment to 60°. Grind the edges and corners on the surface of the aggregate to make them smooth to achieve the rounding effect. The particle size after rounding treatment is 4.5 - 19.5 mm. Then screen and classify the obtained granular material and carry out classified curing.

[0053] 8) Aggregate curing: Then screen the aggregate with a particle size of 4.5 - 9.5 mm, and then soak it in saturated lime water for curing for 28 days to obtain the γ-C2S phosphogypsum non-fired ceramsite lightweight aggregate.

[0054] After testing, the bulk density of the γ-C2S phosphogypsum non-fired ceramsite lightweight aggregate obtained in this example reaches 925 kg / m 3 , the softening coefficient is 0.98, the cylinder compressive strength is 9.0 Mpa, the water absorption rate is 7.8%, the crushing value is 11.2%, the porosity is 14.0%, the size of the micro fine connected pores is 0.01 - 100 nm and only accounts for 39.5% of the total porosity, and each ton can solidify 29 kg of CO2.

[0055] Example 2

[0056] A non-fired γ-C2S phosphogypsum lightweight aggregate and its preparation method include the following steps:

[0057] 1) Pretreatment of raw materials: Put the as-received phosphogypsum into a forced-air drying oven, set the temperature to 55°C, after forced-air drying for 24 hours, put it into a sealed plastic bag for storage; γ-C2S, fly ash, mineral powder and cement are treated with a 100°C forced-air dryer for 24 hours as well, and then stored in a sealed bag;

[0058] 2) Mixing of raw materials: According to the size of the pressed block and the expected dry density value, calculate the total mass of the dry material mixture required to press the block of this density and size. Then, take each raw material according to the ratio requirements of 68% phosphogypsum, 12% γ-C2S, 5% fly ash, 5% mineral powder, 2% sodium metaaluminate, 3% red mud powder, and 5% water;

[0059] 3) Pour the weighed phosphogypsum, fly ash, γ-C2S, mineral powder and red mud powder into the mixing equipment respectively, stir the powder fully for 5 minutes to mix evenly, and then add water and stir fully for 8 minutes;

[0060] 4) Pour the above-mentioned mixed powder into the mold in two batches; then place the whole between the upper and lower platforms of the press, place the press on a vibrating table and vibrate it on the vibrating table at a frequency of 2860 times / minute and an amplitude of 0.3 mm. By adjusting the control handle of the press platform, adjust the height of the upper platform until it touches the pressed block, and then use the computer terminal to edit the pressure program. The program content is divided into three levels of pressurization. The first level is set at 190 kN, and then keep the pressure for 10 minutes. The pressurization method is to increase by stress, and the stress speed is set at 0.410 MPa / s; the second-level pressure target value is set at 250 kN, applied at a speed of 0.362 MPa / s, and keep the pressure for 5 minutes after reaching the target pressure; the third-level pressure target value is set at 310 kN, applied at a speed of 0.410 MPa / s, and keep the pressure for 5 minutes after reaching the target pressure;

[0061] 6) Demolding and crushing treatment: Demold the blocky green body obtained in step 5) with a jack, put the demolded block into a crusher for crushing treatment, and crush the blocky green body into small pieces to obtain coarse aggregate;

[0062] 7) Chamfering and rounding: Pour the crushed coarse aggregate into a rounding machine. The rounding machine consists of a disc and a motor, and the inclination angle of the equipment is 65°. Grind the edges and corners on the surface of the aggregate to make them smooth to achieve the rounding effect; the particle size after rounding treatment is 4.5 - 17.5 mm, and then screen and classify the obtained granular materials and carry out classified curing.

[0063] 8) Aggregate curing: Then, sieve the aggregates of different particle sizes, and then soak them in saturated lime water for 28 days of curing to obtain the γ-C2S phosphogypsum non-fired ceramsite lightweight aggregate.

[0064] After testing, the bulk density of the γ-C2S phosphogypsum non-fired ceramsite lightweight aggregate obtained in this example reaches 952 kg / m 3 , softening coefficient 0.95, cylinder compressive strength 8.6 Mpa, water absorption rate 5.6%, crushing value 9.2%, porosity 14.25%, the size of micro-fine connected pores is 0.01 - 100 nm, accounting for 40% of the total porosity, and each ton can solidify 30 kg of CO2.

[0065] Example 3

[0066] A non-fired γ-C2S phosphogypsum lightweight aggregate, and its preparation method includes the following steps:

[0067] 1) Raw material pretreatment: Put the original phosphogypsum into a blast drying oven, set the temperature to 100 °C, after blast drying for 24 hours, put it into a sealed bag for storage; γ-C2S, fly ash, mineral powder and cement are treated with a 55 °C blast dryer for 24 hours as well, and then put into a sealed bag for storage;

[0068] 2) Raw material mixing: According to the size of the pressed block and the expected dry density value, calculate the total mass of the dry material mixture required to press the block of this density and size, and then take each raw material according to the proportion requirements of 45% phosphogypsum, 22% γ-C2S, 10% fly ash, 10% mineral powder, 3% sodium metaaluminate, 5% red mud powder, and 5% water;

[0069] 3) Pour the weighed phosphogypsum, fly ash, γ-C2S, mineral powder, cement and red mud powder into the mixing equipment respectively, stir the powder fully for 5 minutes to mix evenly, and then add water and stir fully for 8 minutes;

[0070] 4) Pour the above mixed powder into the mold in two batches; then place the whole between the upper and lower platforms of the press, place the press on a vibrating table and vibrate it on a vibrating table with a frequency of 2860 times / minute and an amplitude of 0.3 mm. By adjusting the control handle of the press platform, adjust the height of the upper platform until it touches the pressed block, and then use the computer terminal to edit the pressure program. The program content is divided into three levels of pressurization. The first level is set at 190 kN, and then keep the pressure for 10 minutes. The pressurization method is to increase by stress, and the stress speed is set at 0.362 MPa / s; the second level of pressure target value is set at 230 kN, applied at a speed of 0.362 MPa / s, and keep the pressure for 10 minutes after reaching the target pressure; the third level of pressure target value is set at 320 kN, applied at a speed of 0.362 MPa / s, and keep the pressure for 10 minutes after reaching the target pressure;

[0071] 6) Post - demoulding crushing treatment: Demould the block - shaped green body obtained in step 5) with a jack, and put the demoulded block into a crusher for crushing treatment. The block - shaped green body is crushed into small pieces to obtain coarse aggregate.

[0072] 7) Chamfer removal and rounding: Pour the crushed coarse aggregate into a rounding machine. The rounding machine consists of a disc and a motor, and the inclination angle of the equipment is 60°. Grind the edges and corners on the surface of the aggregate to make them smooth, achieving the effect of rounding. The particle size after rounding treatment is 4.5 - 17.5 mm, and then screen the obtained granular material.

[0073] 8) Aggregate curing: Then screen the aggregates with different particle sizes, and then soak them in saturated lime water for curing for 21 days to obtain the γ - C2S phosphogypsum non - fired ceramsite lightweight aggregate.

[0074] After testing, the bulk density of the γ - C2S phosphogypsum non - fired ceramsite lightweight aggregate obtained in this example reaches 926 kg / m 3 , softening coefficient 0.98, cylinder compressive strength 11.0 Mpa, water absorption rate 7.3%, crushing value 11.0%, porosity 13.5%, the size of micro - fine connected pores is 0.01 - 100 nm, accounting for 42.9% of the total porosity, and 31 kg of CO2 can be solidified per ton.

[0075] Comparative Example 1

[0076] A phosphogypsum - based lightweight aggregate, whose preparation method is roughly the same as that of Example 1, except that P·O42.5 ordinary Portland cement is used to replace γ - C2S with the same mass.

[0077] After testing, the bulk density of the phosphogypsum lightweight aggregate prepared in this comparative example reaches 606 kg / m 3 , cylinder compressive strength 5.6 Mpa, softening coefficient 0.85, water absorption rate 6.2%, crushing value 16.9%, porosity 35.6%, the size of micro - fine connected pores is 0.01 - 100 nm and only accounts for 22.6% of the total porosity, and 10.9 kg of CO2 can be solidified per ton.

[0078] The main reasons for the lower cylinder compressive strength, higher crushing value and higher porosity in this comparative example are as follows: Needle - shaped ettringite is generated during the reaction of phosphogypsum aggregate, but ettringite can only partially coat the phosphogypsum aggregate, and there are still many pores exposed, which cannot completely improve the problems of water softening and low strength of phosphogypsum aggregate. In this comparative example, P·O42.5 ordinary Portland cement is used to replace γ - C2S with the same mass. The strength of the aggregate in the later stage of water absorption softening and hardening is not high, the pore connectivity is high, there are a large number of connected pores inside, and the overall structure is unstable.

[0079] Comparative Example 2

[0080] A phosphogypsum-based lightweight aggregate, its preparation method is substantially the same as that of Example 1, except that: the components and their mass percentages include: 43% phosphogypsum, 27% γ-C2S, 13% fly ash, 5% mineral powder, 7% water, 5% water glass (water glass replaces sodium metaaluminate and red mud powder in Example 1); each raw material is weighed according to the ratio requirements; among them, the modulus of the water glass used is 1.5, and its main chemical components and contents are 10wt% Na2O and 24wt% SiO2.

[0081] After testing, the bulk density of the phosphogypsum lightweight aggregate prepared in this comparative example reaches 625 kg / m 3 , the softening coefficient is 0.89, the cylinder compressive strength is 3.5 Mpa, the water absorption rate is 8.2%, the crushing value is 20.1%, the porosity is 39.1%, the size of the micro-connected pores is 0.01 - 100 nm and accounts for 36.6% of the total porosity, and each ton can solidify 29.6 kg of CO2.

[0082] In this comparative example, the traditional alkali activator water glass is used to replace sodium metaaluminate and red mud powder in Example 1, the hardening time of the slurry is longer, and the strength of the obtained aggregate is greatly reduced.

[0083] Comparative Example 3

[0084] A phosphogypsum-based lightweight aggregate, its preparation method is substantially the same as that of Example 1, except that it is set to be pressed in three stages during step-by-step pressing, and the vibration condition is cancelled.

[0085] After testing, the bulk density of the phosphogypsum lightweight aggregate prepared in this comparative example reaches 706 kg / m 3 , the cylinder compressive strength is 3.6 Mpa, the softening coefficient is 0.84, the water absorption rate is 7.2%, the crushing value is 18.9%, the porosity is 25.2%, the size of the micro-connected pores is 0.01 - 100 nm and accounts for 13.2% of the total porosity, and each ton can solidify 30 kg of CO2.

[0086] The reasons for the lower cylinder compressive strength, higher crushing value and higher porosity in this comparative example are that the components do not form the most compact packing, the pore connectivity is high, the pore structure is unstable, and there are more connected pores inside.

[0087] Comparative Example 4

[0088] A phosphogypsum-based lightweight aggregate, its preparation method is substantially the same as that of Example 1, except that in step 8), the curing steps and conditions adopted include: then the aggregate with a particle size of 4.5 - 9.5 mm is sieved and immersed in water for curing for 28 d.

[0089] After testing, the bulk density of the phosphogypsum lightweight aggregate prepared in this comparative example reaches 802 kg / m 3, the softening coefficient is 0.91, the cylinder compressive strength is 3.5 Mpa, the water absorption rate is 6.5%, the crushing value is 15.8%, the porosity is 18.6%, the size of the micro fine connected pores is 0.01 - 100 nm and only accounts for 16.0% of the total porosity, and 21 kg of CO2 can be solidified per ton.

[0090] The present invention is not limited to the above - mentioned 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 non-fired γ-C2S phosphogypsum lightweight aggregate, characterized in that, The components and their mass percentages are as follows: phosphogypsum 43 - 68%, γ-C2S 12 - 28%, fly ash 5 - 10%, mineral powder 5 - 10%, red mud powder 3 - 6%, sodium metaaluminate 1 - 3%, water 5 - 7%. The pH value of the phosphogypsum is greater than 3.0, and the residue on a 80um sieve is less than 20%; its main chemical components and their mass percentages are: CaO 37 - 41%, SO3 40 - 43%. The particle size of the γ-C2S is 1.5 - 45μm, and its purity is higher than 99%. The red mud powder is obtained by drying and grinding red mud; its particle size is less than 100μm, the content of fine particles less than 0.075mm is ≥75.6%, and the content of sand particles greater than 0.075mm is ≤24.4%; its main chemical components and their mass percentages are: Fe2O3 50 - 53%, Al2O3 21 - 24%.

2. The non-fired γ-C2S phosphogypsum lightweight aggregate according to claim 1, wherein The mineral powder is above S95 grade, and the specific surface area is 400 - 450 m 2 / kg; the fly ash is Class I or Class II fly ash.

3. The preparation method of the non-fired γ-C2S phosphogypsum lightweight aggregate according to any one of claims 1 to 2, characterized in that, It includes the following steps: 1) Stir and mix evenly the weighed phosphogypsum, γ-C2S, mineral powder, fly ash, red mud powder, sodium metaaluminate and water according to the ratio to obtain a mixed raw material; 2) Put the obtained mixed raw material into a mold and carry out step-by-step vibration pressing to obtain a block-shaped green body; 3) Crush the block-shaped green body to form aggregate coarse material; then carry out rounding treatment and screening to obtain aggregate rough embryos; 4) Cure the obtained aggregate rough embryos in saturated lime water to obtain the γ-C2S phosphogypsum non-fired ceramsite lightweight aggregate.

4. The preparation method according to claim 3, characterized in that, The target pressure used in the step-by-step vibration pressing step is 270 - 320kN.

5. The preparation method according to claim 4, characterized in that, The step-by-step vibration pressing step in step 2) adopts a three-step pressing process, and the specific steps include: vibrating on a vibrating table with a frequency of 2860 - 3000 times / min and an amplitude of 0.3 - 0.6mm; first pressurize to 170 - 220kN and hold the pressure for 5 - 10min; then pressurize to 220 - 270kN and hold the pressure for 5 - 10min; continue to pressurize to 270 - 320kN and hold the pressure for 5 - 10min.

6. The preparation method according to claim 3, wherein The crushing particle size in step 3) is 5.5 - 20mm; the particle size after rounding treatment is 4.5 - 19.5mm.

7. The preparation method according to claim 3, characterized in that, The curing time in the saturated lime water is 21 - 28d.