Cu modified low-calcium carbon sequestration cementing material and preparation method thereof

Abstract

The invention belongs to the field of building materials, and particularly relates to a Cu modified low-calcium carbon sequestration cementing material and a preparation method thereof. The raw materials of the material comprise a mixture of calcium carbonate, silicon dioxide and aluminum oxide and a Cu-containing modifier, the preparation method comprises the following steps: 1, mixing a mixture containing calcium carbonate, silicon dioxide and aluminum oxide with a Cu-containing modifier to obtain a mixed raw material; and 2, adding water into the mixed raw material obtained in the step 1, mixing, pressing into a cake-shaped wet blank, drying and multi-stage calcining the cake-shaped wet blank, quickly cooling to room temperature, and grinding into powder to obtain the Cu modified low-calcium carbon sequestration cementing material. According to the material, the hardening performance of LCCB is improved by doping Cu, copper ions enter crystals in a solid solution form, the leaching risk is small, and high environmental friendliness is achieved; according to the preparation method, the calcination temperature is lower than that of traditional cement, and the energy consumption and the production cost are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a Cu-modified low-calcium carbonation cementitious material and a preparation method thereof. Background Art

[0002] Due to the high-temperature decomposition of limestone and the mineral composition dominated by tricalcium silicate (C3S) in the current mainstream Portland cement system, the carbon emission intensity per ton of cement has been high for a long time, especially a large amount of CO2 is emitted during the clinker calcination process.

[0003] In recent years, new carbonation-hardening cementitious materials (Low Calcium Carbonatable Binber, LCCB) with low-calcium minerals such as calcium monosilicate (CS) and wollastonite (C3S2) as the core have shown significant emission reduction potential. Compared with traditional cement, this LCCB system reduces the carbon emissions in the raw material stage by more than 40% by reducing the amount of limestone used and the calcination temperature, and at the same time, utilizes the carbonation-hardening characteristics of the material to actively fix CO2 during the service life, forming a dual low-carbon effect of "process emission reduction + end carbon sequestration". However, although it has theoretically low carbon emission characteristics, in practical applications, it has exposed problems such as insufficient carbonation activity, low carbon sequestration efficiency, and poor mechanical properties after hardening. These problems seriously restrict the large-scale promotion and application of such materials.

[0004] The carbonation reaction activity is the root of the carbon sequestration performance. The methods to improve the reaction activity mainly include ion doping, adding external activators, adding crystal seeds, etc., but these are only external factors affecting the carbonation reaction and cannot fundamentally improve from the molecular level of the reaction activity.

[0005] Therefore, an improved technical solution is needed to address the above deficiencies in the prior art. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a Cu-modified low-calcium carbonation cementitious material and a preparation method thereof.

[0007] To achieve the above purpose, the present invention provides the following technical solution:

[0008] A Cu-modified low-calcium carbonation cementitious material is obtained by mixing, calcining, and grinding the following raw materials:

[0009] A mixture containing calcium carbonate, silicon dioxide, and aluminum oxide and a Cu modifier; the weight of Cu element in the Cu modifier is 0.09%-0.30% of the total weight of calcium carbonate, silicon dioxide, and aluminum oxide.

[0010] Furthermore, the mineral phases in the Cu-modified low-calcium carbonation cementitious material include α-CS, C3S2, and C2AS, and the mass ratio of α-CS, C3S2, and C2AS is 65:20:15; Cu ions enter α-CS, C3S2, and C2AS by substituting Ca ions.

[0011] Furthermore, the Cu-containing modifier is one or more of Cu2O, CuO, CuCl2, CuSO4, Cu(NO3)2, and Cu2(OH)2CO3. The Cu-containing modifier is CuO. Among other types of Cu-containing modifiers, Cl ions, SO4 2- ions, NO3 - , OH - , CO3 2- ions, etc. will enter the LCCB by ion substitution, thus affecting its carbonation activity. Cu2O is not suitable as the optimal choice due to its low solubility, low reactivity, and high cost.

[0012] Furthermore, in the mixture containing calcium carbonate, silicon dioxide, and aluminum oxide, the weight ratio of calcium carbonate, silicon dioxide, and aluminum oxide is (15.7 - 15.9):(8.0 - 8.2):1.

[0013] The present invention also provides a preparation method for the aforementioned Cu-modified low-calcium carbonation cementitious material, comprising the following steps:

[0014] Step 1: Mix the mixture containing calcium carbonate, silicon dioxide, and aluminum oxide with the Cu-containing modifier to obtain a mixed raw material.

[0015] Step 2: Add water to the mixed raw material obtained in Step 1 and press it into a cake-shaped wet blank. The cake-shaped wet blank is dried and calcined in multiple stages and then rapidly cooled to room temperature, and then ground to obtain the Cu-modified low-calcium carbonation cementitious material.

[0016] Furthermore, the cake-shaped wet blank is dried at 100 - 110 °C for 12 - 24 h to obtain a dry blank.

[0017] Further, in step two, the multi-stage calcination includes: the dry blank is heated from room temperature to 300 - 350 °C in 50 min, then heated to 900 - 950 °C in 60 min, and kept warm for 30 - 40 min after reaching the target temperature; then it is heated to 1250 - 1300 °C at a rate of 10 °C / min and kept warm for 2 - 3 h after reaching the target temperature. In the present invention, the calcination process is divided into stages because the raw materials of LCCB contain calcium carbonate, silica and alumina, and these three minerals react in different temperature ranges. The selection of the temperature and time in multiple stages is to ensure that the calcium carbonate, silica and alumina in the LCCB clinker system decompose and react completely.

[0018] Further, in step two, it is rapidly cooled to room temperature by direct blowing of a fan or cold air and passed through a 200-mesh sieve, and the cooling rate is not less than 450 - 550 °C / min; rapid cooling helps to fix the structure and properties of the material at high temperature and prevent unnecessary phase changes or reactions during the cooling process.

[0019] Further, in step two, 10% of the total mass of the mixed raw materials is added with clear water and mixed and pressed into a cake-shaped wet blank, and the thickness of the cake-shaped wet blank does not exceed 1.5 cm.

[0020] Further, in step two, the mixed raw materials are added with water and mixed and pressed into several cake-shaped wet blanks, and the weight of each cake-shaped wet blank is 200 ± 10 g, and the pressure for pressing the cake-shaped object is 300 - 350 KN.

[0021] When the Cu-modified low-calcium carbonation cementitious material of the present invention is used, it is generally used for making prefabricated products, such as bricks, plates, components, etc. It is necessary to mix the Cu-modified low-calcium carbonation cementitious material with water and press it into shape, and cure it in a carbon dioxide environment for more than 8 h.

[0022] The working principle of the present invention is that Cu ions tend to enter LCCB by replacing Ca ions, forming stable Cu - O bonds. The solid solution of Cu ions causes a tendency for parameters such as the distortion index and the average bond length to decrease, thereby inhibiting the dissolution of Ca ions and also prolonging the duration of the carbonation reaction. As the content of Cu ions increases, the crystal form of CaCO3 gradually changes from vaterite to calcite, becoming more stable and enhancing the hardening performance of LCCB; however, since Cu ions are solid-solved in C2AS without carbonation activity, resulting in an increase in its content, thereby reducing the contents of CS and C3S2, and further reducing the content of generated CaCO3, and finally showing a reduction in the content of CaCO3 (carbon sequestration amount).

[0023] The beneficial effects of the present invention are:

[0024] 1. Cu doping significantly reduces the carbonation reaction rate of LCCB, prolongs the reaction duration, and can avoid local stress concentration or cracking caused by too fast carbonation reaction, improving the durability and long-term stability of the material. This enables the Cu-modified LCCB material of the present invention to be used in scenarios requiring slow carbonation, such as large-volume components or complex environments, and reduces structural defects.

[0025] 2. Cu doping promotes the transformation of the carbonation product from vaterite to more stable calcite. The layered stacking and micro-mechanical bonding of calcite significantly enhance the micro-mechanical properties and improve the material density. The high elastic modulus of calcite contributes additional strength, and its stability can resist environmental erosion (such as humidity, acidic medium). This enables the material of the present invention to be used in the production of high-durability building materials, such as marine engineering or chemical plant facilities.

[0026] 3. The LF-NMR and SEM results show that Cu doping reduces the porosity and narrows the pore size distribution (the T2 relaxation time shortens), forming a denser structure. The lower porosity can inhibit the penetration of harmful substances, such as Cl- and SO4 2- . The penetration of SO4 improves the corrosion resistance, enabling the material of the present invention to be used in impermeable concrete or protective coatings.

[0027] 4. Cu ions stably exist in LCCB in a solid solution form, reducing the environmental risk of free heavy metals. At the same time, they can absorb and solidify CO2. Applying this method to practice can synergistically treat Cu-containing industrial waste and achieve waste resource utilization.

[0028] 5. The calcination temperature of the preparation method of the present invention is lower than the traditional cement firing temperature, reducing energy consumption, carbon emissions, and production costs. Brief Description of the Drawings

[0029] Figure 1 Shows the compressive strength and porosity of the test blocks of the examples and comparative examples of the present invention.

[0030] Figure 2 Shows the transverse relaxation time distribution curves of the test blocks of the examples and comparative examples of the present invention.

[0031] Figure 3 Shows the complete XRD spectra of the examples and comparative examples of the present invention after carbonation for 8 h.

[0032] Figure 4 Shows the mineral compositions of the examples and comparative examples of the present invention after carbonation for 8 h.

[0033] Figure 5 Shows the carbonation reaction heat curves of the examples and comparative examples of the present invention within 100 min.

[0034] Figure 6 Shows the compressive strength of the examples and comparative examples of the present invention after carbonation for 1 h.

[0035] Figure 7 SEM images of the embodiments and comparative examples of the present invention after 8 h of carbonization; among them, (a), (b), (c), and (d) are the microscopic morphologies of the specimens of the comparative example, Example 1, Example 2, and Example 3, respectively.

[0036] Figure 8 Mass loss curves of the embodiments and comparative examples of the present invention after 8 h of carbonization.

[0037] Figure 9 Mass loss derivative curves of the embodiments and comparative examples of the present invention after 8 h of carbonization.

[0038] Figure 10 FT-IR spectra of the embodiments and comparative examples of the present invention before and after carbonization; among them, (a) and (b) are the FT-IR spectra before and after carbonization, respectively.

[0039] Figure 11 Element distributions in the LCCB clinker of Example 4; among them, (a), (b), (c), and (d) are the element distributions of Ca, Si, Al, and Cu, respectively.

[0040] Figure 12 XRD patterns of the embodiments and comparative examples of the present invention; among them, (a) is the complete XRD pattern of the embodiments and comparative examples; (b) is a partial enlarged view of (a).

[0041] Figure 13 Bond order and bond length distributions of CS, C3S2, and C2AS after Cu doping; among them, (a), (b), and (c) are the BO-BL distributions of CS, C3S2, and C2AS after Cu ions replace cations at different sites, respectively.

[0042] Figure 14 Average bond lengths, polyhedral volumes, and effective coordination numbers before and after Cu substitution in the embodiments and comparative examples of the present invention. Detailed implementation manners

[0043] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0044] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments. For the purpose of laboratory research, CuO is used as the Cu modifier in the following examples and comparative examples; the grades of calcium carbonate, silica, alumina, etc. used are all of analytical purity, and the average particle size of the silica reagent is 500 mesh. The mineral phases in the low-calcium carbon-fixing cementitious materials in the examples and comparative examples include α-CS, C3S2, and C2AS, and the mass ratio of α-CS, C3S2, and C2AS is 65:20:15, which is the optimal ratio obtained from previous tests. In actual production, such low-calcium carbon-fixing cementitious materials can be fired from ores or solid wastes, etc.

[0045] Example 1

[0046] Example 1 is denoted as S1.

[0047] In this Example 1, a Cu-modified low-calcium carbon-fixing cementitious material has a raw material composition of: 126.66 g of calcium carbonate, 65.29 g of silica, 8.05 g of alumina, and 0.25 g of CuO. In this example, the weight of CuO is 0.125% of the total weight of calcium carbonate, silica, and alumina, and the weight of Cu accounts for 0.1% of the total weight of calcium carbonate, silica, and alumina.

[0048] A preparation method of a Cu-modified low-calcium carbon-fixing cementitious material includes the following steps:

[0049] Step 1: Mix the mixture containing calcium carbonate, silica, and alumina with CuO and grind for 30 min to ensure uniformity, obtaining a mixed raw material;

[0050] Step 2: Add water accounting for 10% of the total weight of the mixed raw material obtained in Step 1. After mixing evenly, press every 200 g of the mixture under a pressure of 320 KN into a cake-shaped wet blank with a thickness not exceeding 1.5 cm (the diameter of each cake-shaped wet blank is about 120 mm), and dry at 105 °C for 12 h; put the dried sample into a corundum crucible or furnace, first heat it to 300 °C in 50 min, then heat it to 900 °C in 60 min, and keep it for 30 min; subsequently, heat it at a rate of 10 °C / min to 1280 °C, keep it for 2 h, and then quickly cool it to room temperature. Grind the calcined sample to a 200-mesh sieve to obtain the Cu-modified low-calcium carbon-fixing cementitious material.

[0051] Specimen production: Add water accounting for 10% of the weight of the LCCB clinker to the LCCB clinker, press it into a 2 cm × 2 cm × 2 cm cube under a pressure of 4 MPa, and cure it under a CO2 pressure of 0.3 MPa for 8 h.

[0052] Example 2

[0053] Example 2 is denoted as S2. The difference between this Example 2 and Example 1 is only that the doping amount of the Cu modifier is 0.25%.

[0054] A Cu-modified low-calcium carbonation cementitious material, the raw material composition of which is: 126.66 g of calcium carbonate, 65.29 g of silica, 8.05 g of alumina and 0.5 g of CuO. In this example, the weight of CuO is 0.25% of the total weight of calcium carbonate, silica and alumina, and the weight of Cu accounts for 0.2% of the total weight of calcium carbonate, silica and alumina.

[0055] The test blocks were made in the same way as in Example 1.

[0056] Example 3

[0057] Example 3 is denoted as S3. The difference between this Example 3 and Example 1 is only that the doping amount of the Cu modifier is 0.375%.

[0058] A Cu-modified low-calcium carbonation cementitious material, the raw material composition of which is: 126.66 g of calcium carbonate, 65.29 g of silica, 8.05 g of alumina and 0.75 g of CuO. In this example, the weight of CuO is 0.375% of the total weight of calcium carbonate, silica and alumina, and the weight of Cu accounts for 0.3% of the total weight of calcium carbonate, silica and alumina.

[0059] The test blocks were made in the same way as in Example 1.

[0060] Comparative Example

[0061] The comparative example is denoted as S0.

[0062] The difference between this comparative example and Example 1 is that no Cu modifier is added to the mixed raw meal, and an ordinary low-calcium carbonation cementitious material is made.

[0063] The test blocks were made in the same way as in Example 1.

[0064] Verification Example

[0065] XRD, carbonation reaction heat analysis and SEM-EDS tests were carried out on the low-calcium carbonation cementitious materials (LCCB clinkers) in Examples 1-3 and the comparative example. And compressive strength, XRD, low-field nuclear magnetic resonance (LFNMR) test, FT-IR test, thermogravimetric analysis (TGA) and SEM observation were carried out on the test blocks or powders of the low-calcium carbonation cementitious materials after carbonation curing. The test methods and results are as follows:

[0066] 1. XRD:

[0067] The phase analysis was carried out using a Smart-lab X-ray diffractometer (produced by Rigaku Corporation, Japan) under the conditions of 150 mA and 40 kV. The data collection range was from 10° to 70°, the scanning speed was 5° / min, and the step size was 0.02°. Si powder was used as the internal standard, and the ratio of the sample to the standard was 3:1.

[0068] 2. SEM-EDS:

[0069] The calcined LCCB clinker was not ground into fine powder but broken into fragments of appropriate size. Part of it was used for SEM testing, and part was cured with epoxy resin for EDS testing. The elemental distribution was analyzed using a scanning electron microscope (model: Merlin Compact, produced by Carl Zeiss AG, Germany) and an energy dispersive spectrometer (manufactured by Oxford Instruments, UK), and the working voltage was 15 kV.

[0070] 3. FT-IR:

[0071] The powder samples before and after carbonization were passed through a 200-mesh sieve and analyzed using a fully automatic Fourier transform infrared spectrometer (FT-IR, model V70). The spectral analysis range was set to 400 - 4000 cm -1 , and each sample was scanned 16 times.

[0072] 4. Thermogravimetric analysis:

[0073] After the 200-mesh carbonized powder sample was prepared into a suitable size, thermogravimetric analysis (TGA) was carried out using a STA 8000 analyzer of PerkinElmer. The analysis temperature range was from 50°C to 1000°C, and the heating rate was 10°C / min.

[0074] 5. CO2 absorption capacity:

[0075] The CO2 absorption capacity of samples with different Cu ion doping concentrations was determined by the heating method. The decomposition process of calcium carbonate usually occurs in the temperature range of 500°C to 850°C. The CO2 absorption capacity was calculated according to the following formula:

[0076]

[0077] 6. Carbonization reaction heat:

[0078] The carbonization activity of LCCB was evaluated by monitoring the temperature change during the carbonization process. 7.5 g of LCCB clinker was mixed with 0.75 g of water and placed in a glass ampoule as a CO2 storage device. CO2 was continuously introduced into the ampoule through a thin tube to maintain the internal pressure at 0.3 MPa. The temperature change inside the ampoule within 1 h was recorded for analyzing the temperature fluctuation during the reaction process.

[0079] 7. Compressive strength:

[0080] The compressive strength of carbonized samples containing different Cu ion concentrations was measured using a WDW-200 electronic universal testing machine. The test was carried out at a constant loading rate of 0.5 mm / min. Each group of samples was measured independently three times, and the results were averaged.

[0081] 8. Low-field nuclear magnetic resonance (LF-NMR):

[0082] The porosity of carbonized specimens was measured using a MesoMR12–060V instrument from Suzhou Niumai Analytical Instruments Co., Ltd. through low-field nuclear magnetic resonance technology (LF-NMR). Before the test, the specimens were made into cylinders with a diameter of 20 mm, soaked in water in a vacuum oven for 24 h, and then weighed by volume. Subsequently, low-field NMR analysis was carried out to evaluate the pore characteristics of the specimens.

[0083] Table 1 Test results of specimens in examples and comparative examples

[0084]

[0085]

[0086] The compressive strength can reflect the effect of Cu ion doping on the hardening performance of LCCB. After carbonization for 8 h, the compressive strength of LCCB samples with different Cu ion doping amounts was tested, and the results are as Figure 1 shown. Compared with the comparative examples, the compressive strengths of the specimens in Examples 1-3 increased by 10.15%, 41.39%, and 37.14% respectively. Figure 1 The porosity corresponding to different Cu ion dopings is also shown, and it can be seen that with the increase of Cu ion content, the porosity shows a trend of first decreasing and then increasing, which corresponds to the change of strength. Figure 2 The transverse relaxation time (T2) distribution curves of S0, S1, S2, and S3 samples after carbonization for 8 h are shown. It can be seen that the micropore relaxation times corresponding to S2 and S3 are significantly shorter than those of S0 and S1, indicating that the pore diameters between the corresponding CaCO3 are smaller and the binding between the various matrices in the samples is tighter.

[0087] Through phase analysis testing, the changes in the constituent minerals of LCCB and the content of carbonization products can be seen to study the effect of Cu ions on the carbonization performance of LCCB. Figure 3 The complete XRD patterns of LCCB after carbonization for 8 h with different Cu ion doping amounts are shown. Compared with the samples before carbonization (the diffraction peaks are shown in Figure 12 (a)), the carbonized LCCB shows more diffraction peaks of calcite and vaterite, indicating that the calcium carbonate formed after carbonization of LCCB is mainly calcite and vaterite. Figure 4The results of quantitative analysis of the mineral composition of LCCB with different Cu ion doping amounts using the Rietveld method are shown, and Table 2 summarizes the quantitative results. Figure 4 It shows that with the increase of Cu ion content, the amount of calcium carbonate generated decreases, indicating that the doping of Cu ions inhibits the carbonation reaction of LCCB. Figure 4 Among them, the contents of CS and C3S2 with carbonation activity show a downward trend with the increase of Cu ion content, which can be attributed to the solid solution of Cu ions in C2AS without carbonation activity, resulting in an increase in its content, thus reducing the contents of CS and C3S2, and further reducing the content of generated CaCO3. With the increase of Cu ion content, the crystal form of CaCO3 gradually changes from vaterite to calcite and becomes more stable.

[0088] Table 2 Fitting quality of the Rietveld method

[0089] Group Weighted relative deviation factor Rwp Relative deviation factor Rp(%) <![CDATA[Comparative Example (S0)]]> 8.34 4.6 <![CDATA[Example 1 (S1)]]> 8.51 4.6 <![CDATA[Example 2 (S2)]]> 8.31 4.61 <![CDATA[Example 3 (S3)]]> 7.55 4.57

[0090] To clarify the relationship between the compressive strength and the carbonation reaction, the invention analyzed the heat of carbonation reaction. The carbonation reaction is an exothermic process, and the degree of heat release reflects the rate and depth of the carbonation reaction. Figure 5 It shows the curves of the heat of reaction varying with temperature within 1 h of carbonation under different Cu ion doping conditions. The peak temperatures of S0, S1, S2, and S3 are 57.5 °C, 61.7 °C, 55.2 °C, and 60.8 °C respectively. S0 reaches the peak temperature first, and the rate in the heating stage is S0 > S1 > S3 > S2. The differences in the carbonation reaction rates result in inconsistent peak time of the reaction temperature for each group of samples. The temperature drops to the peak because CO2 reacts preferentially on the mineral surface. When the surface carbonation is completed, the surface temperature drops, but since the reaction is still proceeding inside, the rate of its temperature drop is related to the change of the internal reaction. From Figure 5 It can be seen that the doping of Cu ions inhibits the carbonation reaction rate of LCCB. The time for the peak temperature of the reaction system of the samples doped with Cu ions to reach is later than that of the control group, and the internal temperature is always higher than that of the control group after 20 min, indicating that the doping of Cu ions prolongs the carbonation reaction process. Figure 6 It shows the compressive strength of LCCB after 1 h of carbonation under different Cu ion doping amounts. Among them, the compressive strength corresponding to S2 is the lowest, followed by S3 and S1, and the compressive strength corresponding to S0 is the highest. This indicates that the faster the carbonation reaction rate, the higher the early compressive strength. With the increase of carbonation time, the strength of the samples with a slower carbonation reaction rate increases, which can be attributed to the fact that the doping of Cu ions prolongs the carbonation reaction process.

[0091] Figure 7 It shows the microtopography of LCCB under different Cu ion doping amounts. At Figure 7In (a)-(b), the morphology of CaCO3 is mainly gravel-shaped, with a small amount being flaky of smaller size, and the overall structure is relatively loose. In Figure 7 (c)-(d), it can be observed that the structure is relatively dense, and a large number of rhombic substances with obvious structures appear. This indicates that with the increase in the content of Cu ions, a large amount of calcite is formed, which is consistent with Figure 4 the results. In Figure 7 (c)-(d), the calcite particles not only show a layered stacking pattern but also exhibit mechanical bonding, being restricted by other surrounding particles. This mechanical bonding generates a strong microscopic force, which, combined with the high elastic modulus of calcite itself, will make a significant contribution to the compressive strength of LCCB.

[0092] Figure 8 and Figure 9 are the thermogravimetric (TG) and derivative thermogravimetric (DTG) curves of the copper-doped LCCB samples after 8 h of carbonization, respectively. Figure 8 shows the mass loss curves corresponding to each sample after 8 h of carbonization. The mass loss below 150 °C can be attributed to free water and the dehydration of silica gel. The decomposition temperature range of calcium carbonate is 500 - 850 °C. The carbon fixation amounts (CO2 absorption amounts) of S0, S1, S2, and S3 are quantitatively calculated to be 14.46%, 12.11%, 10.84%, and 10.44%, respectively. This is consistent with the conclusion obtained from XRD, indicating that with the increase in the content of Cu ions, the carbonization reaction of LCCB is inhibited. Figure 9 In, multiple mass loss peaks appear after 500 °C, which can be attributed to the presence of vaterite. The decomposition temperatures of calcite corresponding to S0, S1, S2, and S3 are different, which may be related to the doping of Cu ions.

[0093] A preliminary analysis of the carbonization products of LCCB was carried out. Figure 10 shows the FT-IR spectra of the samples with different Cu doping levels before and after carbonization. The absorption band at 1070 cm -1 is the characteristic peak of C2AS mineral. The peaks near 985 cm -1 and 717 cm -1 are related to CS mineral, while the peaks near 925 cm -1 , 906 cm -1 , 846 cm -1 , 656 cm -1 and 559 cm -1 correspond to the specific absorption bands of C3S2 mineral. After 8 h of carbonization, new vibration bands at 1420 cm -1 , 1085 cm -1 , 875 cm -1 and 804 cm -1 appear. 1420 cm -1The broad peak nearby indicates the presence of calcite or amorphous calcium carbonate (ACC), which is caused by the asymmetric stretching vibration (v3) of CO3 2- . The peaks at 875 cm -1 and 805 cm -1 are related to aragonite and reflect the out-of-plane bending vibration of the C-O bond in calcite. In addition, the v3 vibration of the Si-O bond in the LCCB sample after carbonization shifts to a higher wavenumber of 1085 cm -1 , corresponding to Q4 (Q4 means that each silicon atom is connected to four other silicon atoms through four oxygen bridges, forming a completely polymerized network structure), indicating the formation of highly polymerized silica.

[0094] To explore the mechanism of action of Cu, we also carried out EDS tests. The LCCB clinker of Example 3 was polished and sputter-coated with gold before the EDS test. The obtained elemental distributions are as Figure 11 shown, where (a), (b), (c), and (d) are the elemental distributions of Ca, Si, Al, and Cu respectively, and the bright regions correspond to the high-content regions of the corresponding elements. The distribution regions of Ca and Si are brighter because all three minerals in LCCB contain Ca and Si elements. There are also enriched regions in the distribution of Al, representing the distribution region of C2AS. The distribution region of Cu element overlaps the most with that of Ca element, indicating that most Cu ions enter LCCB by substituting Ca ions.

[0095] To determine the specific substitution sites of Cu ions in LCCB, we carried out phase analysis. Figure 12 (a) shows the XRD patterns of different Cu ion doping levels, and the diffraction peaks of each mineral are marked with consistent symbols. As Figure 12 (a) shows, the XRD patterns of LCCB with different Cu ion concentrations are similar, and no peaks of Cu ion compounds are observed. Therefore, it is difficult to accurately locate the substitution sites of Cu ions in LCCB only through phase analysis. To solve this problem, Figure 12 (a) was magnified and localized, as Figure 12 (b) shows. It can be seen from Figure 12 (b) that as the Cu ion content increases, the diffraction peaks of CS, C3S2, and C2AS shift to the right. According to the ion substitution principle, this kind of shift occurs when smaller ions substitute larger ions. The ionic radii of Ca, Si, Al, and Cu are listed in Table 3, showing that Cu ions are smaller than Ca ions but larger than Al and Si ions. Based on the change in diffraction angle, phase analysis indicates that Cu ions substitute Ca ions in the LCCB structure.

[0096] Table 3 Ionic radii of Ca, Si, Al, and Cu

[0097]

[0098]

[0099] The bond order (BO) and bond length (BL) distributions provide information on the bonding efficiency at the atomic scale. The proximity of the BO and BL values before and after ion substitution indicates the likelihood of successful bonding. We analyzed the BO-BL distributions at different sites of the three minerals in LCCB after Cu substitution. As Figure 13 shown, the Al-O and Si-O bonds occupy regions with relatively high BO and BL values due to their covalent nature. Figure 6 The light blue region in shows that the Cu-O bond formed after Cu substitution for Ca is close to the distribution region of the Ca-O bond before substitution. The proximity of the BO and BL values indicates that Cu ions preferentially substitute for Ca ions in LCCB.

[0100] To study the effect of Cu ions on the carbonation reaction of LCCB, we also analyzed the structural changes of [CaOn] polyhedra in CS and C3S2 before and after Cu substitution (substituting for Ca). n- Figure 14 The average bond length, polyhedron volume, and effective coordination number before and after substitution were compared. An increase in the average bond length and polyhedron volume generally indicates the presence of more voids within the polyhedron, promoting ion migration and enhancing carbonation activity. For minerals with the same Ca / Si ratio, a higher Ca-O coordination number usually weakens the interatomic interaction, thus promoting the carbonation reaction. As Figure 14 shown, compared with the original [CaOn] n- polyhedron, Cu substitution decreased the average bond length, polyhedron volume, and effective coordination number in CS and C3S2. This decrease indicates that Cu doping inhibits the carbonation activity of LCCB, which is consistent with the results of XRD, TG, and carbonation reaction heat analysis.

[0101] The research on the modification mechanism of Cu in this invention shows that Cu ions tend to enter LCCB by substituting for Ca ions, which is attributed to the same orbital contribution and the approximation of bond order and bond length before and after substitution. Cu ions inhibit the carbonation activity of LCCB, which can be attributed to the decrease in average bond length, polyhedron volume, and effective coordination number. Compared with the comparative example, the strength of LCCB containing different Cu ions increased after 8 h of carbonation, which is attributed to the fact that the doping of Cu ions slowed down the carbonation reaction rate of LCCB, extended the carbonation reaction time, and at the same time, the increase in calcite content promoted the microscopic mechanical bonding and layered stacking between calcite particles, thus enhancing the hardening performance of LCCB.

[0102] In the present invention, by incorporating a Cu modifier into the LCCB system and in combination with the preparation method of the present invention, copper ions enter the low-calcium carbonated cementitious material (LCCB) in the form of a solid solution, replacing the position of calcium ions and forming a stable crystal structure. This solid solution structure can effectively reduce the leaching risk of copper, making this material highly environmentally friendly in applications. In addition, due to the incorporation of Cu, a large amount of calcite (CaCO3) is formed during the carbonation process of the LCCB material. These calcite particles further enhance the compactness of the material through microscopic mechanical bonding and layered packing, improving the compressive strength of the LCCB material. Moreover, even when the Cu element content is extremely low (0.09% - 0.3%), the strength of the LCBB material after carbonation can be significantly increased (the compressive strength is increased by 10.15% - 41.39%).

[0103] The present invention not only proposes a material and a preparation method for modifying LCCB with Cu, but also provides a theoretical basis for the large-scale application of LCCB in the cement industry, and provides a usable Cu-containing modifier and a modification method for the modification of LCCB.

[0104] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are within the scope of the claims of the present invention awaiting approval.

Claims

1. A Cu-modified low-calcium carbon-fixing cementitious material, characterized in that: It is obtained by mixing, calcining, and grinding the following raw materials: A mixture containing calcium carbonate, silicon dioxide, and alumina, and a Cu modifier; the weight of Cu element in the Cu modifier is 0.09%-0.30% of the total weight of calcium carbonate, silicon dioxide, and alumina.

2. The Cu-modified low-calcium carbonation cementitious material according to claim 1, characterized in that: The mineral phases in the Cu-modified low-calcium carbon-fixing cementitious material include α-CS, C3S2, and C2AS, and the mass ratio of α-CS, C3S2, and C2AS is 65:20:15; Cu ions enter α-CS, C3S2, and C2AS by substituting Ca ions.

3. The Cu-modified low-calcium carbonation cementitious material according to claim 1, characterized in that: The Cu modifier is one or more of Cu2O, CuO, CuCl2, CuSO4, Cu(NO3)2, and Cu2(OH)2CO3.

4. The Cu-modified low-calcium carbonation cementitious material according to claim 1, characterized in that: In the mixture containing calcium carbonate, silicon dioxide, and alumina, the weight ratio of calcium carbonate, silicon dioxide, and alumina is (15.7-15.9):(8.0-8.2):

1.

5. A preparation method of the Cu-modified low-calcium carbonation cementitious material according to any one of claims 1 to 4, characterized in that, It includes the following steps: Step 1: Mix the mixture containing calcium carbonate, silicon dioxide, and alumina with the Cu modifier to obtain a mixed raw material. Step 2: Add water to the mixed raw material obtained in Step 1 and press it into a cake-shaped wet blank. The cake-shaped wet blank is dried and multi-stage calcined and then quickly cooled to room temperature, and then ground to obtain the Cu-modified low-calcium carbon-fixing cementitious material.

6. The preparation method of the Cu-modified low-calcium carbonation cementitious material according to claim 5, characterized in that: The cake-shaped wet blank is dried at 100-110°C for 12-24 h to obtain a dry blank.

7. The preparation method of the Cu-modified low-calcium carbonation cementitious material according to claim 6, characterized in that: In Step 2, the multi-stage calcination includes: The dry blank is heated from room temperature to 300-350°C in 50 min, then heated to 900-950°C in 60 min, and kept at the target temperature for 30-40 min; then heated to 1250-1300°C at a rate of 10°C / min and kept at the target temperature for 2-3 h.

8. The preparation method of the Cu-modified low-calcium carbonation cementitious material according to claim 5, characterized in that: In Step 2, it is quickly cooled to room temperature by direct blowing of a fan or cold air and passed through a 200-mesh sieve, and the cooling rate is not less than 450-550°C / min.

9. The preparation method of the Cu-modified low-calcium carbonation cementitious material according to claim 5, characterized in that: In Step 2, add clean water accounting for 10% of the total mass of the mixed raw material and mix and press it into a cake-shaped wet blank. The thickness of the cake-shaped wet blank does not exceed 1.5 cm.

10. The preparation method of the Cu-modified low-calcium carbon-fixing cementitious material according to claim 5, characterized in that: In Step 2, the mixed raw material is added with water and mixed and pressed into several cake-shaped wet blanks. The weight of each cake-shaped wet blank is 200±10 g, and the pressure for pressing the cake is 300-350 KN.

Images