CN116282988B - Method for preparing low-calcium solid carbon gel material by using phosphogypsum - Google Patents

Abstract

The invention provides a method for preparing a low-calcium solid carbon gel material by using phosphogypsum, belonging to the technical field of inorganic materials. The method for preparing the low-calcium solid carbon gel material by using phosphogypsum provided by the invention comprises the following steps: (1) Mixing phosphogypsum, a calcareous raw material, a siliceous raw material, an iron-aluminum correction material and a carbonaceous raw material to obtain a mixed raw material; (2) And (3) preheating, pre-decomposing, sintering and grinding the mixed raw material obtained in the step (1) in sequence to obtain the low-calcium solid-carbon gel material. The results of the examples show that the compressive strength of the low-calcium solid-carbon gel material provided by the invention is more than or equal to 45MPa after carbonization and maintenance for 2 hours, the compressive strength is more than or equal to 77MPa after 24h of carbonization and maintenance, the flexural strength is more than or equal to 11MPa after 2h of carbonization and maintenance, and the flexural strength is more than or equal to 19MPa after 24h of carbonization and maintenance.

Description

A method for preparing low-calcium carbon-fixing cementitious material using phosphogypsum

Technical Field

The invention relates to the technical field of inorganic materials, and in particular to a method for preparing a low-calcium carbon-fixing cementitious material by utilizing phosphogypsum.

Background Art

As an industrial product, phosphoric acid is in great demand in many fields, and a large amount of solid waste phosphogypsum is produced in the process of wet phosphoric acid production. The main component of phosphogypsum is hydrated calcium sulfate. The hydrated calcium phosphate content in the solid content of most phosphogypsum is greater than 90%. In addition, there is a small amount of silicon dioxide, a byproduct of the reaction of phosphate rock, and residual fluoride, organic matter, phosphoric acid and unreacted phosphate rock during the reaction. These components other than hydrated calcium sulfate greatly increase the harmfulness of phosphogypsum and significantly reduce its availability. At present, about 80 million tons of phosphogypsum are produced each year, and the total stockpile volume has exceeded 400 million tons. Large-scale resource utilization of phosphogypsum has become a major environmental problem that needs to be solved urgently.

Using phosphogypsum to prepare building materials is a reliable way to consume phosphogypsum on a large scale. Although there is a relatively mature technology for using phosphogypsum to produce cement, it still faces many problems. The most difficult problem to solve is that the sulfur element of phosphogypsum will inhibit the formation of tricalcium silicate (C ₃ S) mineral phase in the mineral phase of clinker, which ultimately leads to a significant reduction in the quality of cement clinker. Therefore, the existing technology has extremely high requirements for the desulfurization rate of phosphogypsum. The current technology is to increase the pre-decomposition temperature, or to set up a dual-atmosphere decomposition furnace by transforming the existing production line, and finally achieve a higher desulfurization rate. However, the above technical routes have extremely high energy consumption, large carbon emissions, and require the transformation of existing equipment and production lines, which has high costs and is difficult to achieve. However, low-calcium carbon-fixing cementitious materials have low carbon emissions during the production process due to their low calcium-silicon ratio. At the same time, they can obtain mechanical strength by consolidating carbon dioxide, and are a good environmentally friendly building material. If phosphogypsum can be used to produce low-calcium carbon-fixing cementitious materials, large-scale resource utilization of phosphogypsum and "carbon neutrality" of the building materials industry can be achieved at the same time. Therefore, there is an urgent need to develop a method for preparing low-calcium carbon-fixing cementitious materials using phosphogypsum with low energy consumption and low-calcium carbon-fixing cementitious materials having excellent mechanical properties.

Summary of the invention

The object of the present invention is to provide a method for preparing a low-calcium carbon-fixing cementitious material using phosphogypsum. The method provided by the present invention requires a low decomposition temperature and low energy consumption, and the prepared low-calcium carbon-fixing cementitious material has excellent compressive strength and flexural strength.

In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

The present invention provides a method for preparing a low-calcium carbon-fixing cementitious material by using phosphogypsum, comprising the following steps:

(1) mixing phosphogypsum, calcium raw materials, silicon raw materials, iron and aluminum corrective materials and carbon raw materials to obtain a mixed raw material;

(2) Preheating, pre-decomposing, calcining and grinding the mixed raw material obtained in step (1) in sequence to obtain a low-calcium carbon-fixing cementitious material.

Preferably, in step (1), the calcareous raw materials include one or more of limestone, slaked lime and carbide slag, the siliceous raw materials include one or more of sandstone, shale, silica, clay and quartz powder, the iron-aluminum corrective materials include one or more of iron powder, bauxite and red mud, and the carbonaceous raw materials include one or more of coal powder and coke powder.

Preferably, in step (1), the mass ratio of the calcareous raw material to the phosphogypsum is <0.5, the molar ratio of the total CaO _{in the phosphogypsum and the calcareous raw material to the SiO2 in the siliceous raw material is 1.4-1.8, the sum of Al2O3 and Fe2O3 in the iron} -aluminum corrected material accounts for 2%-10wt.% of the components of the mixed raw material after burnt loss and _SO3 removal, and the molar ratio of C in the carbonaceous raw material to _SO3 in the mixed raw material is <2.0.

Preferably, the average particle size of the mixed raw material in step (1) is less than 100 μm.

Preferably, the preheating temperature in step (2) is ≥ 750°C.

Preferably, the pre-decomposition temperature in step (2) is 750-1000°C.

Preferably, the calcination temperature in step (2) is 1150-1350° C., and the calcination time is 0.5-2 h.

Preferably, the average particle size of the low-calcium carbon-fixing cementitious material in step (3) is less than 150 μm.

The present invention provides a low-calcium carbon-fixing cementitious material prepared by the method described in the above technical solution.

Preferably, the composition of the low-calcium carbon-fixing cementitious material includes, by mass percentage: C ₃ S ₂ >40%, C ₅ S ₂ $<40%, and C ₂ AS<15%.

The present invention provides a method for preparing a low-calcium carbon-fixing cementitious material using phosphogypsum, comprising the following steps: (1) mixing phosphogypsum, a calcium raw material, a silicon raw material, an iron-aluminum corrective material and a carbon raw material to obtain a mixed raw material; (2) preheating, pre-decomposing, calcining and grinding the mixed raw material obtained in step (1) in sequence to obtain a low- _calcium carbon-fixing cementitious material. On the one hand, the present invention uses a reasonable raw material configuration to allow undecomposed _CaSO4 to form a _C5S2 $ mineral phase during the calcining process. The mineral phase has a certain hydration activity and does not affect the carbonization performance of the final carbon-fixing cementitious material. On the other hand, the raw materials are controlled so that the carbonizable components _C3S2 and _C2S in the mineral phase composition of the low- _calcium carbon-fixing cementitious material are not affected by _SO3 brought by the decomposition of _CaSO4 during the formation process, thereby greatly reducing the impact of CaSO4 in the phosphogypsum on the carbonization performance. ₄ decomposition rate requirement, so that the decomposition temperature is lower, the decomposition energy consumption is reduced, and the production cost is saved; the preparation process is simple, and the matching degree with the industrial production process of ordinary Portland cement is high. It only needs to modify the atmosphere control of the decomposition furnace to use the industrial equipment of ordinary Portland cement for production, and there is no need to transform the existing equipment and production line, which saves production costs, can realize the large-scale resource utilization of solid waste phosphogypsum, and because the calcium-silicon molar ratio is significantly lower than that of ordinary Portland cement, it can significantly reduce the amount of limestone used in the production process of carbon-fixing cementitious materials, thereby greatly reducing the carbon dioxide emissions in the production process, and has extremely high environmental value; the prepared low-calcium carbon-fixing cementitious material has good mechanical properties after carbonization curing, and has broad application prospects in the field of structural engineering. The results of the embodiment show that the low-calcium carbon-fixing cementitious material provided by the present invention has a compressive strength of ≥45MPa and a flexural strength of ≥11MPa after carbonization curing for 2h, and a compressive strength of ≥77MPa and a flexural strength of ≥19MPa after carbonization curing for 24h.

DETAILED DESCRIPTION

The present invention provides a method for preparing a low-calcium carbon-fixing cementitious material by using phosphogypsum, comprising the following steps:

(1) mixing phosphogypsum, calcium raw materials, silicon raw materials, iron and aluminum corrective materials and carbon raw materials to obtain a mixed raw material;

(2) Preheating, pre-decomposing, calcining and grinding the mixed raw material obtained in step (1) in sequence to obtain a low-calcium carbon-fixing cementitious material.

The invention obtains mixed raw material by mixing phosphogypsum, calcium raw material, silicon raw material, iron-aluminum correcting material and carbon raw material.

In the present invention, the phosphogypsum is preferably pretreated before use. In the present invention, the pretreatment preferably includes dehydration and crushing treatments performed in sequence. In the present invention, the dehydration temperature is preferably 100-105°C, more preferably 105°C; the weight loss of the phosphogypsum after dehydration is preferably <1wt.%. In the present invention, the particle size of the product after the crushing treatment is preferably <1mm. The present invention can remove bound water in the phosphogypsum by pretreating the phosphogypsum, and at the same time reduce the particle size of the phosphogypsum, which is beneficial for subsequent mixing with other raw materials.

In the present invention, the CaO content in the phosphogypsum is preferably >30wt.%; the calcareous raw material preferably includes one or more of limestone, slaked lime and carbide slag, more preferably limestone or slaked lime; the CaO content in the chemical composition of the calcareous raw material after burnout at 950°C is preferably >90wt.%; the siliceous raw material preferably includes one or more of sandstone, shale, silica, clay and quartz powder; the _SiO2 content in the chemical composition of the siliceous-calcium raw material after burnout at 950°C is preferably >75wt.%, and the MgO content is preferably <8wt.%; the iron-aluminum correcting material preferably includes one or more of iron powder, _bauxite and red mud; the total mass of _Al2O3 and _Fe2O3 in the chemical composition of the iron- _aluminum correcting material after burnout at 950°C is preferably >50wt.%; the carbonaceous raw material preferably includes one or more of coal powder and coke powder. The present invention has no particular limitation on the specific sources of the calcium raw material, silicon raw material, iron-aluminum corrected material and carbon raw material, and commercially available products known to those skilled in the art may be used.

In the present invention, the mass ratio of the calcareous raw material to phosphogypsum is preferably <0.5; the molar ratio of the total CaO in the phosphogypsum and calcareous raw materials to _SiO2 in the siliceous raw materials is preferably 1.4-1.8, more preferably 1.5-1.6; the sum of _Al2O3 and _Fe2O3 in the iron-aluminum corrective material preferably accounts for 2-10wt _. % of the components of the mixed raw meal after burnout and _SO3 removal; the molar ratio _of C in the carbonaceous raw material to _SO3 in the mixed raw meal is preferably <2.0. The present invention controls the dosage relationship of phosphogypsum, calcium raw materials, silicon raw materials, iron-aluminum correcting materials and carbon raw materials. On the one hand, the undecomposed _CaSO4 can form _{a C5S2} $ mineral phase during the sintering process. The mineral phase has a certain hydration activity and does not affect the carbonization performance of the final carbon-fixing cementitious material. On the other hand _, the carbonizable components _C3S2 and _C2S in the mineral phase composition of the low-calcium carbon-fixing cementitious material are not affected by _SO3 brought by the decomposition of _CaSO4 during the formation process, thereby greatly reducing the decomposition rate requirement of _CaSO4 in the phosphogypsum, lowering the decomposition temperature, reducing the decomposition energy consumption, and saving production costs.

In the present invention, the mixing method is preferably grinding. In the present invention, the average particle size of the mixed raw material is preferably <100 μm. The present invention has no special limitation on the specific operation of the grinding, as long as the particle size of the mixed raw material meets the requirements.

After obtaining the mixed raw material, the present invention sequentially preheats, pre-decomposes, burns and grinds the mixed raw material to obtain a low-calcium carbon-fixing cementitious material.

In the present invention, the preheating temperature is preferably ≥ 750° C. The present invention facilitates subsequent pre-decomposition treatment of the mixed raw material by preheating the mixed raw material.

In the present invention, the pre-decomposition temperature is preferably 750-1000°C, more preferably 800-1000°C, and further preferably 850-950°C; the pre-decomposition is preferably carried out in a reducing atmosphere; the volume fraction of _O2 in the pre-decomposition atmosphere is preferably <5vol%; the volume fraction of CO in the pre-decomposition atmosphere is preferably >3vol%, and more preferably 4-7vol%. In the present invention, the content of _SO3 in the pre-decomposition product is preferably <12wt.%. By controlling the pre-decomposition temperature and atmosphere, the present invention can decompose a part of _CaSO4 in phosphogypsum into CaO and _SO3 , thereby improving the quality of clinker, and at the same time, the decomposition temperature is low, which can reduce energy consumption.

In the present invention, the pre-decomposition is preferably carried out in a decomposition furnace. The present invention has no particular limitation on the specific model of the decomposition furnace, and commercial products well known to those skilled in the art can be used.

In the present invention, the calcination temperature is preferably 1150-1350°C, more preferably 1200-1300°C, and further preferably ₁₂₅₀ °C; the calcination time is preferably 0.5-2h, more preferably 1-1.5h. The present invention can further form _C5S2 $ mineral phase from undecomposed _CaSO4 during the calcination process by controlling the calcination parameters, thereby further improving the performance of the low-calcium carbon-fixing cementitious material.

In the present invention, the sintering is preferably carried out in a rotary kiln. The present invention has no particular limitation on the specific model of the rotary kiln, and commercial products well known to those skilled in the art can be used.

The present invention has no special limitation on the specific operation of the grinding, as long as the average particle size of the low-calcium carbon-fixing cementitious material meets the requirements. In the present invention, the average particle size of the low-calcium carbon-fixing cementitious material is preferably <150 μm. The present invention can further improve the mechanical properties of the low-calcium carbon-fixing cementitious material by controlling the particle size of the low-calcium carbon-fixing cementitious material.

The present invention, on the one hand, uses reasonable raw material configuration to make undecomposed CaSO ₄ form C ₅ S ₂ $ mineral phase during the sintering process. The mineral phase has a certain hydration activity and does not affect the carbonization performance of the final carbon-fixing cementitious material. On the other hand, the raw materials are controlled so that the carbonizable components C ₃ S ₂ and C ₂ S in the mineral phase composition of the low-calcium carbon-fixing cementitious material are not affected by SO ₃ brought by the decomposition of CaSO ₄ during the formation process, thereby greatly reducing the impact of CaSO 4 in phosphogypsum. The decomposition rate requirement of ₄ makes the decomposition temperature lower, the decomposition energy consumption is reduced, and the production cost is saved; the preparation process is simple and highly compatible with the industrial production process of ordinary Portland cement. It only needs to modify the atmosphere control of the decomposition furnace to use the industrial equipment of ordinary Portland cement for production. There is no need to transform the existing equipment and production line, which saves production costs and can realize large-scale resource utilization of solid waste phosphogypsum. Moreover, since the calcium-silicon molar ratio is significantly lower than that of ordinary Portland cement, the amount of limestone used in the production process of carbon-fixing cementitious materials can be significantly reduced, thereby greatly reducing carbon dioxide emissions in the production process, which has extremely high environmental value; the prepared low-calcium carbon-fixing cementitious material has good mechanical properties after carbonization curing, and has broad application prospects in the field of structural engineering.

The present invention provides a low-calcium carbon-fixing cementitious material prepared by the method described in the above technical solution.

In the present invention, the composition of the low calcium carbon-fixing cementitious material preferably includes, by mass percentage: C ₃ S ₂ >40%, C ₅ S ₂ $<40%, C ₂ AS<15%. The present invention controls the chemical composition of the low calcium carbon-fixing cementitious material and utilizes the combination of different mineral phases to make it have excellent mechanical properties.

The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Example 1

A method for preparing a low-calcium carbon-fixing cementitious material using phosphogypsum, comprising the following steps:

(1) Pre-treating phosphogypsum to obtain pre-treated phosphogypsum, and then mixing and grinding the pre-treated phosphogypsum with a calcium raw material, a silica raw material, an iron-aluminum corrective material and a carbon raw material to obtain a mixed raw material; the pre-treatment is a dehydration and a crushing treatment performed in sequence; the dehydration temperature is 105° C., and the weight loss of the phosphogypsum after dehydration is less than 1wt.%; the maximum particle size of the product after the crushing treatment is 0.87mm; the calcium raw material is limestone, the silica raw material is sandstone, the iron-aluminum corrective material is bauxite, and the carbon raw material is coal powder; the mass ratio of the pre-treated phosphogypsum, the calcium raw material, the silica raw material, the iron-aluminum corrective material and the carbon raw material is 72:6:19:3:8; the average particle size of the mixed raw material is less than 100μm;

(2) The mixed raw material obtained in step (1) is preheated to 750°C by a 4-stage cyclone, pre-decomposed in a decomposition furnace, then calcined in a rotary kiln, and finally ground when cooled to below 55°C to obtain a low-calcium carbon-fixing cementitious material; the pre-decomposition temperature is 850°C; the _O2 volume fraction in the pre-decomposition atmosphere is 4 vol%, and the CO volume fraction is controlled at 5 vol%; the _SO3 content in the pre-decomposition product is 11.7 wt.%; the calcination temperature is 1280°C, and the calcination time is 0.5 h; the average particle size of the low-calcium carbon-fixing cementitious material is 147 μm.

The main chemical compositions of the different raw materials in Example 1 were analyzed by XRF testing, and the results are shown in Table 1:

Table 1 Main chemical composition of different raw materials (wt.%)

The chemical composition of the mixed raw material obtained in step (1) of Example 1 is shown in Table 2:

Table 2 Chemical composition of the mixed raw material obtained in Example 1 (wt.%)

LOI CaO SiO ₂ Al ₂ O _{3 Fe2O3 ​} SO ₃ Mixed raw materials 5.801 31.392 18.301 3.795 0.900 35.372

The composition of the low-calcium carbon-fixing cementitious material prepared in Example 1 was analyzed by XRD full spectrum fitting quantitative analysis. The results are shown in Table 3, where f-CaO was determined according to the Chemical Analysis Methods for Cement (GB/T 176-2017):

Table 3 Composition of low calcium carbon-fixing cementitious material prepared in Example 1 (wt.%)

C ₂ S C ₃ S ₂ C ₅ S ₂ $ C ₂ AS Others f-CaO 8.93 40.58 32.46 9.74 8.29 0.3

Application Example 1

The low-calcium carbon-fixing cementitious material prepared in Example 1 and water were mixed at a mixing ratio of 0.15 and then carbonized and cured to obtain a sample, and the compressive strength and flexural strength of the sample were tested. The size of the compressive strength sample was a cylinder of Φ20mm*20mm, and the size of the flexural strength sample was a cuboid of 37.5*6.5*6.8mm. The carbonization curing atmosphere was: 99% CO ₂ , the air pressure was 0.3MPa, and the curing temperature was room temperature. The strength test loading rate was 200N/s. The test results are shown in Table 4:

Table 4 Physical properties of low calcium carbon-fixing cementitious materials

Example 2

A method for preparing a low-calcium carbon-fixing cementitious material using phosphogypsum, comprising the following steps:

(1) Pre-treating phosphogypsum to obtain pre-treated phosphogypsum, and then mixing and grinding the pre-treated phosphogypsum with a calcium raw material, a silica raw material, an iron-aluminum corrective material and a carbon raw material to obtain a mixed raw material; the pre-treatment is a dehydration and a crushing treatment performed in sequence; the dehydration temperature is 105° C., and the weight loss of the phosphogypsum after dehydration is less than 1wt.%; the maximum particle size of the product after the crushing treatment is 0.92mm; the calcium raw material is limestone, the silica raw material is sandstone, the iron-aluminum corrective material is bauxite, and the carbon raw material is coal powder; the mass ratio of the pre-treated phosphogypsum, the calcium raw material, the silica raw material, the iron-aluminum corrective material and the carbon raw material is 66:7:25:3:7; the average particle size of the mixed raw material is less than 100μm;

(2) The mixed raw material obtained in step (1) is preheated to 750°C by a 4-stage cyclone, pre-decomposed in a decomposition furnace, then calcined in a rotary kiln, and finally ground when cooled to below 55°C to obtain a low-calcium carbon-fixing cementitious material; the pre-decomposition temperature is 850°C; the _O2 volume fraction in the pre-decomposition atmosphere is 4 vol%, and the CO volume fraction is controlled at 4 vol%; the _SO3 content in the pre-decomposition product is 8 wt.%; the calcination temperature is 1280°C, and the calcination time is 0.5 h; the average particle size of the low-calcium carbon-fixing cementitious material is 147 μm.

The main chemical compositions of the different raw materials in Example 2 were analyzed by XRF testing, and the results are shown in Table 5:

Table 5 Main chemical composition of different raw materials (wt.%)

LOI CaO SiO ₂ Al ₂ O _{3 Fe2O3 ​} SO ₃ Pretreated phosphogypsum 3.285 37.550 4.921 0.556 0.543 48.812 limestone 41.800 50.501 2.210 0.762 0.397 0.105 sandstone 2.336 4.731 76.431 9.114 2.605 0.028 Iron and aluminum correction material 12.500 4.200 16.700 61.000 0.172 0.089

The chemical composition of the mixed raw material obtained in step (1) of Example 2 is shown in Table 6:

Table 6 Chemical composition of the mixed raw material obtained in Example 2 (wt.%)

LOI CaO SiO ₂ Al ₂ O _{3 Fe2O3 ​} SO ₃ Mixed raw materials 5.423 26.937 20.324 4.047 0.923 29.467

The composition of the low-calcium carbon-fixing cementitious material was analyzed, and the results are shown in Table 7, where f-CaO was determined according to the Chemical Analysis Methods for Cement (GB/T 176-2017):

Table 7 Composition of low calcium carbon-fixing cementitious material prepared in Example 2 (wt.%)

C ₂ S C ₃ S ₂ C ₅ S ₂ $ C ₂ AS Others f-CaO 22.93 45.86 15.29 7.64 10.09 Not detected

Application Example 2

The low-calcium carbon-fixing cementitious material prepared in Example 2 and water were mixed at a mixing ratio of 0.15 and then carbonized and cured to obtain a sample, and the compressive strength and flexural strength of the sample were tested. The size of the compressive strength sample was a cylinder of Φ20mm*20mm, and the size of the flexural strength sample was a cuboid of 37.5*6.5*6.8mm. The carbonization curing atmosphere was: 99% CO ₂ , the air pressure was 0.3MPa, and the curing temperature was room temperature. The strength test loading rate was 200N/s. The test results are shown in Table 8:

Table 8 Physical properties of low calcium carbon-fixing cementitious materials

Example 3

A method for preparing a low-calcium carbon-fixing cementitious material using phosphogypsum, comprising the following steps:

(1) Pre-treating phosphogypsum to obtain pre-treated phosphogypsum, and then mixing and grinding the pre-treated phosphogypsum with a calcium raw material, a silica raw material, an iron-aluminum corrective material and a carbon raw material to obtain a mixed raw material; the pre-treatment is a dehydration and a crushing treatment performed in sequence; the dehydration temperature is 105°C, and the weight loss of the phosphogypsum after dehydration is less than 1wt.%; the maximum particle size of the product after the crushing treatment is 0.87mm; the calcium raw material is limestone, the silica raw material is sandstone, the iron-aluminum corrective material is bauxite, and the carbon raw material is coal powder; the mass ratio of the pre-treated phosphogypsum, the calcium raw material, the silica raw material, the iron-aluminum corrective material and the carbon raw material is 62.5:4.5:18.7:2.7:10; the average particle size of the mixed raw material is less than 100μm;

(2) The mixed raw material obtained in step (1) is preheated to 750°C by a 4-stage cyclone, pre-decomposed in a decomposition furnace, then calcined in a rotary kiln, and finally ground when cooled to below 55°C to obtain a low-calcium carbon-fixing cementitious material; the pre-decomposition temperature is 850°C; the _O2 volume fraction in the pre-decomposition atmosphere is 4 vol%, and the CO volume fraction is controlled at 6 vol%; the _SO3 content in the pre-decomposition product is 10 wt.%; the calcination temperature is 1280°C, and the calcination time is 0.5 h; the average particle size of the low-calcium carbon-fixing cementitious material is 147 μm.

The main chemical compositions of the different raw materials in Example 3 were analyzed by XRF testing, and the results are shown in Table 9:

Table 9 Main chemical composition of different raw materials (wt.%)

LOI CaO SiO ₂ Al ₂ O _{3 Fe2O3 ​} SO ₃ Pretreated phosphogypsum 3.285 37.550 4.921 0.556 0.543 48.812 limestone 41.800 50.501 2.210 0.762 0.397 0.105 sandstone 2.336 4.731 76.431 9.114 2.605 0.028 Iron and aluminum correction material 12.500 4.200 16.700 61.000 0.172 0.089

The chemical composition of the mixed raw material obtained in step (1) of Example 3 is shown in Table 10:

Table 10 Chemical composition of the mixed raw material obtained in Example 3 (wt.%)

LOI CaO SiO ₂ Al ₂ O _{3 Fe2O3 ​} SO ₃ Mixed raw materials 3.060 27.098 18.146 3.748 0.864 33.934

The composition of the low-calcium carbon-fixing cementitious material was analyzed, and the results are shown in Table 11, where f-CaO was determined according to the Chemical Analysis Method for Cement (GB/T 176-2017):

Table 11 Composition of low calcium carbon-fixing cementitious material prepared in Example 3 (wt.%)

C ₂ S C ₃ S ₂ C ₅ S ₂ $ C ₂ AS Others f-CaO 3.00 44.96 14.99 14.99 12.40 Not detected

Application Example 3

The low-calcium carbon-fixing cementitious material prepared in Example 3 and water were mixed at a mixing ratio of 0.15 and then carbonized and cured to obtain a sample, and the compressive strength and flexural strength of the sample were tested. The size of the compressive strength sample was a cylinder of Φ20mm*20mm, and the size of the flexural strength sample was a cuboid of 37.5*6.5*6.8mm. The carbonization curing atmosphere was: 99% CO ₂ , the air pressure was 0.3MPa, and the curing temperature was room temperature. The strength test loading rate was 200N/s. The test results are shown in Table 12:

Table 12 Physical properties of low calcium carbon-fixing cementitious materials

It can be seen from Application Examples 1 to 3 that the samples obtained by the low-calcium carbon-fixing cementitious material prepared by the present invention have a compressive strength of ≥45MPa after carbonization curing for 2h, a compressive strength of ≥77MPa after carbonization curing for 24h, a flexural strength of ≥11MPa after carbonization curing for 2h, and a flexural strength of ≥19MPa after carbonization curing for 24h, and have excellent physical properties.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (9)

1. A method for preparing a low-calcium carbon-fixing cementitious material using phosphogypsum, comprising the following steps: (1) mixing phosphogypsum, calcium raw materials, silicon raw materials, iron and aluminum corrective materials and carbon raw materials to obtain a mixed raw material; (2) preheating, pre-decomposing, calcining and grinding the mixed raw material obtained in step (1) in sequence to obtain a low-calcium carbon-fixing cementitious material; In the step (1), the mass ratio of the calcium raw material to the phosphogypsum is less than 0.5, the molar ratio of the total CaO in the _{phosphogypsum} and the calcium raw material to the _SiO2 in the silicon raw material is 1.4-1.8, _{the sum of Al2O3 and Fe2O3 in the} iron-aluminum corrected material accounts for 2%-10wt.% of the components of the mixed raw material after burning and _SO3 removal, and the molar ratio of C in the carbonaceous raw material to _SO3 in the mixed raw material is less than 2.0; Calculated by mass percentage, the composition of the low-calcium carbon-fixing cementitious material includes: C ₃ S ₂ >40%, C ₅ S ₂ $<40%, and C ₂ AS<15%. 2. The method according to claim 1 is characterized in that in the step (1), the calcareous raw materials include one or more of limestone, slaked lime and carbide slag, the siliceous raw materials include one or more of sandstone, shale, silica, clay and quartz powder, the iron-aluminum corrective material includes one or more of iron powder, bauxite and red mud, and the carbonaceous raw materials include one or more of coal powder and coke powder. 3. The method according to claim 1, characterized in that the average particle size of the mixed raw material in step (1) is less than 100 μm. 4. The method according to claim 1, characterized in that the preheating temperature in step (2) is ≥ 750°C. 5. The method according to claim 1, characterized in that the temperature of the pre-decomposition in step (2) is 750-1000°C. 6. The method according to claim 1, characterized in that the sintering temperature in step (2) is 1150-1350°C and the sintering time is 0.5-2h. 7. The method according to claim 1, characterized in that the average particle size of the low-calcium carbon-fixing cementitious material in step (2) is less than 150 μm. 8. The low-calcium carbon-fixing cementitious material prepared by the method according to any one of claims 1 to 7. 9. The low-calcium carbon-fixing cementitious material according to claim 8, characterized in that, in terms of mass percentage, the composition of the low _- calcium carbon-fixing cementitious material comprises: _C3S2 >40%, _{C5S2 $} <40%, _{and C2AS} <15%.