Method for improving carbonation performance of high-magnesia low-carbon clinker

Abstract

The application discloses a method for improving carbonization performance of high-magnesium low-carbon clinker, which comprises the following steps: (1) mixing high-magnesium low-carbon clinker, an acid activator and water, and pressing into a shape; wherein the acid activator comprises phosphogypsum and MgSO4; (2) drying the shaped sample, regulating the water content, carbonizing, and obtaining a carbonization product. The acid activator is prepared by taking phosphogypsum and MgSO4 as main raw materials, and is applied to the carbonization process of high-magnesium low-carbon clinker, so that the carbonization intensity and carbon fixation rate of the high-magnesium low-carbon clinker can be significantly improved, and high-value resource utilization of the high-magnesium limestone low-carbon clinker is realized; and the preparation method is relatively simple and convenient to operate, has good economic and environmental benefits, and is suitable for popularization and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building materials, and particularly relates to a method for improving carbonation performance of high-magnesium low-carbon clinker. BACKGROUND

[0002] The CO2 emission of cement manufacturing mainly comes from the CO2 released from the decomposition of limestone in the cement production process. Compared with silicate cement clinker, low-carbon cement clinker (low-calcium cement clinker) requires less limestone and has a lower calcination temperature, and can reduce CO2 emission by about 20% in the production process, and can absorb CO2 in the subsequent carbonation process, which has significant environmental benefits.

[0003] The CaO content in high-magnesium limestone is low and the MgO and SiO2 contents are high, which are difficult to be utilized. When high-magnesium limestone is used to produce silicate cement clinker, the calcination temperature of the clinker is high, the effective hydration active ingredient is reduced, and MgO usually exists in the form of low-activity over-fired MgO, which is difficult to meet the requirements of production and product standards. When high-magnesium limestone is used to produce low-carbon cement clinker, MgO will enter the low-calcium silicon ratio calcium silicate minerals C2S, C3S2 and CS to form C7MS4, C3MS2 and C2MS2 phases with lower activity, and since the relative molecular mass of MgO is significantly smaller than that of Al2O3, this makes MgO combine with more CaO and SiO2 to form C7MS4, C3MS2 and C2MS2 phases with lower activity, thereby significantly reducing the carbonation activity of the obtained low-carbon clinker.

[0004] How to improve and enhance the carbonation performance of high-magnesium low-carbon clinker so as to achieve effective utilization of high-magnesium limestone to produce low-carbon clinker has become a technical problem to be solved. SUMMARY

[0005] The main purpose of the present application is to provide a method for improving the carbonation performance of high-magnesium low-carbon clinker, which can improve the carbonation activity of high-magnesium low-carbon clinker, significantly increase the carbonation strength and carbon sequestration rate of high-magnesium low-carbon clinker, and realize high-value resource utilization of high-magnesium limestone to produce low-carbon clinker.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A method for improving the carbonation performance of high-magnesium low-carbon clinker, comprising the following steps:

[0008] (1) mixing high-magnesium low-carbon clinker, an acid activator and water, and pressing into a shape; wherein the acid activator comprises phosphogypsum and MgSO4;

[0009] (2) drying and adjusting the moisture content of the shaped sample, and performing carbonation to obtain a carbonation product.

[0010] According to the above scheme, the high-magnesium low-carbon clinker in step (1) is mainly composed of one or more of calcium magnesium silicate minerals C7MS4, C3MS2 and C2MS2.

[0011] Further, in the high-magnesium low-carbon clinker, the chemical components and the mass percentage of each component include: CaO 37-59%, SiO2 25-47%, Al2O3 0-10%, Fe2O3 0-10%, and MgO 5-15%.

[0012] Preferably, the lower the mass ratio of CaO to SiO2 in the chemical components of the high-magnesium low-carbon clinker, the higher the content of low-carbon active minerals C3MS2 and C2MS2, and the more obvious the modification effect of the acidic activator.

[0013] According to the above scheme, in the acidic activator in step (1), the amount of phosphogypsum is 5-20wt% of the amount of high-magnesium low-carbon clinker, and the amount of MgSO4 is 0.5-5wt% of the amount of high-magnesium low-carbon clinker.

[0014] Further, the phosphogypsum does not need to be subjected to acid modification treatment, and the pH value is 1-6.

[0015] According to the above scheme, the amount of water is 10-25wt% of the amount of high-magnesium low-carbon clinker.

[0016] According to the above scheme, in step (2), the controlled moisture content is 4-20wt%.

[0017] According to the above scheme, in step (2), the drying temperature is 20-50℃.

[0018] According to the above scheme, in step (2), the CO2 concentration used in the carbonization step is 15-100%, the temperature is 20-50℃, the humidity is 40-80%, the air pressure is 0-0.3MPa, and the carbonization time is 6-72h.

[0019] According to the above scheme, the carbonization strength of the carbonized product prepared can be increased by 30-80% compared with the condition without adding an acidic activator, and the carbon sequestration rate can be increased by 30-50%.

[0020] The principle of the present application is:

[0021] The essence of the carbonization reaction of low-carbon clinker is that the alkaline Ca(OH)2 or alkaline hydrated calcium silicate dissolved from the low-carbon clinker reacts with H2CO3 to generate CaCO3, which is easy to occur and is an exothermic reaction. By adding MgSO4 (as an example), the influence mechanism of MgSO4 on the carbonization of low-carbon clinker is the following reactions 1 to 4:

[0022] Reaction 1 is that MgSO4 promotes the dissolution of Ca(OH)2 in the low-carbon clinker2+ Dissolution of CaSO4·2H2O which is slightly soluble in water:

[0023] MgSO4+ CaO·xSiO2+yH2O → Mg(OH)2·xSiO2·(y-3)H2O + CaSO4·2H2O

[0024] Reaction 2 is the dissolution of CO2 in water:

[0025] CO2+ H2O → H2CO3

[0026] Reaction 3 is the carbonation of Mg(OH)2 to Mg(HCO3)2:

[0027] Mg(OH)2·xSiO2·(y-3)H2O + 2H2CO3 + H2O → Mg(HCO3)2 + xSiO2·yH2O

[0028] Reaction 4 is the carbonation of CaSO4·2H2O to CaCO3 and the reformation of MgSO4 by Mg(HCO3)2:

[0029] Mg(HCO3)2 + CaSO4·2H2O → CaCO3 + CO2 + 3H2O + MgSO4

[0030] High-magnesium low-carbon clinker is equivalent to replacing CaO·xSiO2 with CaO·zMgO·xSiO2.

[0031] (1) The present application adds MgSO4, which only plays a role of a reaction aid in carbonation, generates slightly soluble Mg(OH)2 silica gel complex and slightly soluble CaSO4·2H2O through reaction 1, can accelerate and continuously promote the dissolution of Ca 2+ in high-magnesium low-carbon clinker, and can carry out carbonation reaction through the generated Mg(HCO3)2 by reactions 2, 3, and 4, effectively improving the carbonatable amount of high-magnesium low-carbon clinker.

[0032] (2) The present application adds solid waste phosphogypsum, which can promote the dissolution of Mg 2+ in high-magnesium low-carbon clinker to improve carbonation activity; phosphogypsum is acidic, and the addition of phosphogypsum can make a part of Ca 2+ and Mg 2+ in high-magnesium low-carbon clinker become calcium and magnesium salts before carbonation, and the magnesium salt will make high-magnesium low-carbon clinker dissolve Ca 2+In the carbonization process, the Mg part of the MgO in the high-Mg low-C clinker and the MgSO4 directly introduced in the raw material are carbonized into CaCO3 and generate MgSO4 through reactions 1 to 4, and the CaSO4·2H2O and CaSO4·2H2O in the phosphogypsum are carbonized into CaCO3, and MgSO4 is generated, and the recycling of the MgSO4 excitation component is realized at the same time;

[0033] In addition, the CaSO4·2H2O in the phosphogypsum will induce the MgO in the high-Mg low-C clinker to react with the CaSO4·2H2O in the phosphogypsum to generate MgSO4, thereby promoting the dissolution of MgO in the high-Mg low-C clinker, further improving the carbonization activity of the high-Mg low-C clinker, and generating MgSO4 to further promote reactions 1 to 4; 2+

[0034] After the CaSO4·2H2O in the phosphogypsum is carbonized through reaction 4, water that is not used for pressing and molding is released, which enables the lost water to be gradually supplemented as the carbonization proceeds, thereby prolonging the effective carbonization time.

[0035] (3) MgSO4 changes the carbonization from an acid-base neutralization reaction to a non-acid-base neutralization double decomposition reaction through reactions 1 to 4, which not only promotes the dissolution of CaO in the high-Mg low-C clinker, but also reduces the alkalinity of the reaction system and the carbonization rate of the dissolved CaO, so that the CaO can be better transported with the water, and CaCO3 is generated in the pores on the surface of the high-Mg low-C clinker, secondly, the generation rate of CaCO3 is slow and the supersaturation degree is low, which further promotes the generation of long and large aragonite, which plays a more effective role in filling and connecting the pores, and is beneficial to the continuous carbonization of the high-Mg low-C clinker. 2+ 2+ 2+ Although only the addition of phosphogypsum can directly generate a certain amount of MgSO4 with Mg in the high-Mg low-C clinker through reaction 4, the CaSO4·2H2O in the phosphogypsum itself has low activity and slow reaction rate, so the effect of only using phosphogypsum is poor, and MgSO4 needs to be additionally added.

[0036] Compared with the prior art, the beneficial effects of the present application are:

[0037] 1) The present application first proposes to use phosphogypsum and MgSO4 as main raw materials to prepare an acid excitation agent, which is applied to the carbonization process of high-Mg low-C clinker, which can significantly improve the carbonization intensity and carbon sequestration rate of the high-Mg low-C clinker, and provides a new idea for the efficient resource utilization of the high-Mg low-C clinker;

[0038] 2) The preparation method involved in the present application is relatively simple and easy to operate, has good economic and environmental benefits, and is suitable for popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 ​​​SEM images of the carbonization product obtained in Example 1. DETAILED DESCRIPTION

[0040] The present application is not limited to the above-mentioned embodiments, and for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements are also considered to be within the scope of protection of the present application. The contents not described in detail in the specification belong to the prior art known to those skilled in the art.

[0041] The high-magnesium low-carbon clinker, phosphogypsum and MgSO4 used in the following specific examples are as follows:

[0042] Different types of high-magnesium low-carbon clinker (clinker 1, clinker 2 and clinker 3 respectively) were obtained, and the chemical composition and mineral composition of the high-magnesium low-carbon clinker used in the examples of the present application are shown in Table 1 and Table 2 respectively, and were ground to R45μm≤20%:

[0043] Table 1 Chemical composition of high-magnesium low-carbon clinker (%)

[0044]

[0045]

[0046] Table 2 Mineral composition of high-magnesium low-carbon clinker (%)

[0047] Name [Alpha]C2S [C7MS4] [C3MS2] [C2MS2] [C2AS] MgFe 0.6 Al 1.4 O4]]> MgO Clinker 1 32.4 56.5 0 0.7 0 6.0 4.3 Clinker 2 0 55.1 29.8 1.9 8.2 4.0 1.1 Clinker 3 0 41.8 41.2 7.2 9.8 0 0

[0048] In the following examples, the chemical composition of the phosphogypsum used is shown in Table 3, and was ground to R80μm≤20% before use, with a pH value of 3.4.

[0049] Table 3 Chemical composition of phosphogypsum (%)

[0050] Name Loss on ignition SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O Phosphogypsum 19.27 6.6 0.23 0.52 29.66 0.03 42.46 0.37 0.08

[0051] The chemical reagent used was analytical grade MgSO4.

[0052] Example 1

[0053] A method for improving the carbonization performance of high-magnesium low-carbon clinker, comprising the following steps:

[0054] 1. Proportioning

[0055] 100 parts of high-magnesium low-carbon clinker 1, 13 parts of phosphogypsum, 2 parts of analytical grade MgSO4, and 17 parts of water were weighed;

[0056] 2. Sample preparation

[0057] The weighed MgSO4 is first put into the weighed water to completely dissolve to obtain a MgSO4 solution, then the high-magnesium low-carbon clinker 1 and the phosphogypsum are put into a blender to stir for 3 min to mix uniformly into a powder, the MgSO4 solution is then added into the powder to stir for 1 min, and the stirred wet material is pressed into a cylindrical sample with a diameter of 2 cm and a height of 2 cm at a molding pressure of 10 MPa;

[0058] 3. Pre-drying and carbonization

[0059] The obtained sample is dried under natural conditions until the water content is 13% (the water content with the highest carbonization strength obtained according to the carbonization test after drying to different water contents), and finally carbonized for 20 h under the conditions of a carbon dioxide concentration of 99%, a temperature of 30 ℃, a humidity of 60%, and a gas pressure of 0.3 MPa (the pressure indication number is 0.3 MPa) to obtain a carbonized product.

[0060] Example 2

[0061] A method for improving the carbonization performance of a high-magnesium low-carbon clinker, comprising the following steps:

[0062] 1. Proportioning

[0063] 100 parts of high-magnesium low-carbon clinker 2, 15 parts of phosphogypsum, 2 parts of analytical pure MgSO4, and 19 parts of water are weighed;

[0064] 2. Sample preparation

[0065] The weighed MgSO4 is first put into the weighed water to completely dissolve to obtain a MgSO4 solution, then the high-magnesium low-carbon clinker 2 and the phosphogypsum are put into a blender to stir for 3 min to mix uniformly into a powder, the MgSO4 solution is then added into the powder to stir for 1 min, and the stirred wet material is pressed into a cylindrical sample with a diameter of 2 cm and a height of 2 cm at a molding pressure of 10 MPa;

[0066] 3. Pre-drying and carbonization

[0067] The obtained sample is dried under natural conditions until the water content is 13% (the water content with the highest carbonization strength obtained according to the carbonization test after drying to different water contents), and finally carbonized for 20 h under the conditions of a carbon dioxide concentration of 99%, a temperature of 30 ℃, a humidity of 60%, and a gas pressure of 0.3 MPa (the pressure indication number is 0.3 MPa) to obtain a carbonized product.

[0068] Example 3

[0069] A method for improving the carbonization performance of a high-magnesium low-carbon clinker, comprising the following steps:

[0070] 1. Proportioning

[0071] Take high-magnesium low-carbon clinker 3 100 parts, phosphogypsum 15 parts, and analytical pure MgSO4 2 parts, and water 20 parts;

[0072] 2. Sample preparation

[0073] First, put the weighed MgSO4 into the weighed water to completely dissolve and obtain a MgSO4 solution. Then, put the high-magnesium low-carbon clinker 3 and phosphogypsum into a blender and stir for 3 min to mix uniformly into a powder. Then, add the MgSO4 solution to the powder and stir for 1 min. Finally, press the stirred wet material into a cylindrical sample with a diameter of 2 cm and a height of 2 cm at a forming pressure of 10 MPa.

[0074] 3. Pre-drying and carbonization

[0075] Put the obtained sample in a natural condition to dry until the water content is 13% (according to the highest carbonization strength of the water content obtained after drying to different water contents for carbonization test). Finally, carbonize the sample under the conditions of a carbon dioxide concentration of 99%, a temperature of 30°C, a humidity of 60%, and a gas pressure of 0.3 MPa (pressure indication 0.3 MPa) for 20 h to obtain a carbonized product.

[0076] Comparative Example 1

[0077] A carbonization process for high-magnesium low-carbon clinker, which has a preparation method substantially the same as that of Example 1, except that no phosphogypsum and MgSO4 are added.

[0078] Comparative Example 2

[0079] A carbonization process for high-magnesium low-carbon clinker, which has a preparation method substantially the same as that of Example 1, except that no phosphogypsum is added.

[0080] Comparative Example 3

[0081] A carbonization process for high-magnesium low-carbon clinker, which has a preparation method substantially the same as that of Example 1, except that no MgSO4 is added.

[0082] Comparative Example 4

[0083] A carbonization process for high-magnesium low-carbon clinker, which has a preparation method substantially the same as that of Example 3, except that no phosphogypsum and MgSO4 are added.

[0084] Comparative Example 5

[0085] A carbonization process for high-magnesium low-carbon clinker, which has a preparation method substantially the same as that of Example 3, except that no phosphogypsum is added.

[0086] Comparative Example 6

[0087] A carbonization process for high-magnesium low-carbon clinker, which has a preparation method substantially the same as that of Example 3, except that no MgSO4 is added.

[0088] Comparative Example 7

[0089] A carbonation process of high-magnesium low-carbon clinker was prepared in the same way as Example 2, except that no phosphogypsum and MgSO4 were added.

[0090] The compressive strength of the sample after carbonation is the carbonation strength, and the carbonation strength and carbon fixation rate of each example and comparative example after carbonation are shown in Table 4.

[0091] Table 4 Carbonation strength and carbon fixation rate

[0092] Item Carbonation intensity / MPa Carbonation rate / % Example 1 136.75 21.34 Example 2 118.47 21.09 Example 3 109.64 20.33 Comparative Example 1 100.95 15.78 Comparative Example 2 119.22 19.96 Comparative Example 3 120.36 18.62 Comparative Example 4 63.21 14.82 Comparative Example 5 81.54 18.65 Comparative Example 6 84.33 18.31 Comparative Example 7 81.74 15.20

[0093] The main role of phosphogypsum is to induce the dissolution of Mg 2+ in high-magnesium low-carbon clinker, and through reactions 1 to 4, the CaSO4·2H2O of itself is carbonated to CaCO3 for filling the structure pores, and water is released during the carbonation process, which is not used for water pressing, to supplement the water system and prolong the effective carbonation time; the main role of MgSO4 is to promote the dissolution of Ca 2+ in high-magnesium low-carbon clinker, and through reactions 1 to 4, CaCO3 is formed, and the carbonation is changed from acid-base neutralization reaction to non-acid-base neutralization double decomposition reaction, which reduces the alkalinity of the reaction system and the carbonation rate of the dissolved Ca 2+ , so that this part of Ca 2+ can be better transported with water, and CaCO3 is generated in the pores on the surface of non-high-magnesium low-carbon clinker, secondly, the generation rate of CaCO3 is slow and the supersaturation degree is reduced, which promotes the generation of long and large aragonite, which plays a more effective role in filling and connecting pores, and is beneficial to the continuous carbonation of high-magnesium low-carbon clinker.

[0094] Although the addition of phosphogypsum can directly generate a certain amount of MgSO4 with Mg in high-magnesium low-carbon clinker through reaction 4, the activity of CaSO4·2H2O in phosphogypsum itself is low and the reaction rate is slow, so the effect of using only phosphogypsum is poor, and additional MgSO4 is needed.

[0095] Figure 1 The SEM image of the carbonation product obtained in Example 1 can be observed to generate aragonite with a length-diameter ratio obviously larger than that of calcite, and can be filled into pores farther away from high-magnesium low-carbon clinker particles.

[0096] In summary, compared with the comparative examples, the simultaneous addition of phosphogypsum and MgSO4 as acid activator of high-magnesium low-carbon clinker can more obviously improve its carbonation performance.

[0097] The above embodiments are only the preferred embodiments of the present application, and cannot be used to limit the protection scope of the present application, and any non-essential changes and replacements made by those skilled in the art on the basis of the present application shall fall within the protection scope of the present application.

Claims

1. A method for improving the carbonization performance of high-magnesium low-carbon clinker, characterized in that: The following steps are involved: (1) mixing high-magnesium low-carbon clinker, an acidic activator, and water, and pressing and molding; wherein the acidic activator comprises phosphogypsum and MgSO4; (2) Drying the molded sample and adjusting the moisture content, and carbonizing the sample to obtain a carbonized product.

2. The method according to claim 1, characterized in that The high-magnesium, low-carbon clinker is mainly composed of one or more of magnesium calcium silicate minerals C7MS4, C3MS2, and C2MS2.

3. The method according to claim 1, characterized in that The chemical components and their mass percentages in the high-magnesium low-carbon clinker include: CaO 37-59%, SiO2 25-47%, Al2O3 0-10%, Fe2O3 0-10%, and MgO 5-15%.

4. The method according to claim 1, wherein In the acidic activator in step (1), the amount of phosphogypsum is 5-20wt% of the amount of high-magnesium low-carbon clinker, and the amount of MgSO4 is 0.5-5wt% of the amount of high-magnesium low-carbon clinker.

5. The method according to claim 1, wherein The pH value of the phosphogypsum is 1-6.

6. The method according to claim 1, characterized in that The amount of water used is 10-25wt% of the amount of high-magnesium low-carbon clinker used.

7. The method according to claim 1, characterized in that In step (2), the moisture content is adjusted to be 4-20 wt%.

8. The method according to claim 1, characterized in that In step (2), the carbonization step adopts a CO2 concentration of 15-100%, a temperature of 20-50°C, a humidity of 40-80%, an air pressure of 0-0.3 MPa, and a carbonization time of 6-72 hours.

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