In-situ high-strength gradient carbonized material and preparation method thereof

Abstract

The invention discloses an in-situ high-strength gradient carbonized material and the preparation method thereof. The in-situ high-strength gradient carbonized material includes a core structure composed of partially calcined calcium carbonate and a shell structure; the shell structure comprises calcium hydroxide and calcium carbonate and covers the outer layer of partially calcined limestone. The invention utilizes an in-situ carbonization reaction to recycle a large amount of low-grade limestone stored or discarded in industry, providing a new technological route for solid waste disposal and resource utilization; this method not only has a green and low-carbon process but also can be widely applied in carbon dioxide capture/collection technology, as well as the preparation of new low-carbon gel materials and concrete.

Claims

1. A preparation method of in-situ high-strength gradient carbonized material, including the following steps: crushing and grinding limestone, followed by partial calcination to a sample wherein partial calcination comprises calcining the sample in a rotatable calcination furnace at a speed of 6-10 r/min at a temperature of 900-1000 C., for a time of 5-30 min. and then rapidly cooling after calcination adding water and a sustained release agent to the sample, stirring evenly, and standing for 30-180 min to obtain a mixture; pressing the mixture into a body at a pressure of 1-2 MPa, and then perform CO.sub.2 curing on the body until it reaches the age to obtain the in-situ high-strength gradient carbonized material wherein the CO.sub.2 curing conditions comprise a CO.sub.2 concentration60%, CO.sub.2 pressure0.10 MPa; the air relative humidity during CO.sub.2 curing is 30%.

2. The preparation method of in-situ high-strength gradient carbonized material according to claim 1, wherein the limestone is low-grade limestone with an effective calcium carbonate content of 60.00%.

3. The preparation method of in-situ high-strength gradient carbonized material according to claim 1, wherein the sustained release agent is a flocculant or superplasticizer, and the addition amount of the sustained release agent is 2.00% by mass of the sample.

4. The preparation method of in-situ high-strength gradient carbonized material according to claim 2, wherein the flocculant is polyacrylamide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Accompanying drawings are for providing further understanding of embodiments of the disclosure. The drawings form a part of the disclosure and illustrate the principle of the embodiments of the disclosure along with the literal description. The drawings in the description below are merely some embodiments of the disclosure; a person skilled in the art can obtain other drawings according to these drawings without creative efforts. In the figures:

(2) FIG. 1 shows the comparison of compressive strength between Examples 1-3 and Comparative Examples 1-9;

(3) FIG. 2 shows the long-term compressive strength of the target product prepared in Example 2 under carbonization curing;

(4) FIG. 3 shows the TG-DTG curves of the target product (corresponding to TG-CO.sub.2 and DTG-CO.sub.2 in FIG. 3) and Ref prepared in Example 1;

(5) FIG. 4 is a microscopic schematic diagram of the target product prepared in Examples 1-3;

(6) FIG. 5 is an SEM image of the target product prepared in Example 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(7) The flocculant used in the following examples is polyacrylamide, sourced from Hubei Xijian New Materials Co., Ltd., with a solid content of 98%; polycarboxylate superplasticizer is produced by Guizhou Zhiqian Building Materials Co., Ltd., with a solid content of 45%.

(8) The source of limestone powder used in the following examples is waste limestone aggregate, obtained after grinding and crushing, and the effective percentage content of calcium carbonate is 91.96%. The chemical composition of the limestone used in the implementation example was determined by an X-ray fluorescence spectrometer (Zetium, Malvern Panalytics), and the test results are shown in Table 1.

(9) TABLE-US-00001 TABLE 1 chemical composition of the limestone Loss of SiO.sub.2, Al.sub.2O.sub.3, CaO, MgO, TiO.sub.2, Fe.sub.2O.sub.3, ignition, % % % % % % % 42.7 2.20 0.90 51.5 2.00 / 0.40

Example 1

(10) In this example, the preparation method of the in-situ high-strength gradient carbonized material includes the following steps:

(11) Selecting limestone raw materials, crushing and grinding them into powder with a particle size of 200 mesh, and then calcining the powder in a drum calciner at a temperature of 950 C. for 10 min. After calcination, rapidly cooling them to obtain a sample. Taking 20 g of the sample (with a calcium oxide content of 55.6 wt %) after rapidly cooling treatment, adding 7.57 g of water (in which 3.57 g of water is required to react with calcium oxide from CaO+H.sub.2O.fwdarw.Ca(OH).sub.2, and the remaining 4 g of water is used for material mixing) and 0.4 g of polycarboxylate superplasticizer. Stirring evenly and standing for 2 h to obtain the mixture. Press the mixture into a body under a pressure of 1.88 MPa, then place the body in a carbonization tank. Curing for 1 day at a CO.sub.2 concentration of 80% and a CO.sub.2 pressure of 0.2 MPa. The obtained product is recorded as CS1.

(12) The calcium oxide content in the sample after rapid cooling treatment in Example 1 is calculated as follows: 10 g of the sample after rapid cooling is taken and placed in a calciner for overburning (to decompose all calcium carbonate into calcium oxide). Then, its mass is weighed as 8.05 g, which is reacted by CaCO.sub.3.fwdarw.CaO+CO.sub.2. Through the loss of 1.95 g of carbon dioxide mass, (1.95 g/44)*100=4.44 g of calcium carbonate is decomposed in the sample. Therefore, the calcium oxide content in the sample is 10 g4.44 g=5.56 g, which is 55.6 wt % of calcium oxide content.

Example 2

(13) In this example, the preparation method of the in-situ high-strength gradient carbonized material includes the following steps:

(14) Selecting limestone raw materials, crushing and grinding them into powder with a particle size of 200 mesh, and then calcining the powder in a drum calciner at a temperature of 950 C. for 10 min. After calcination, rapidly cooling them to obtain a sample. Taking 20 g of the sample (with a calcium oxide content of 34.8 wt %) after rapidly cooling treatment, adding 5.24 g of water (in which 2.24 g of water is required to react with calcium oxide from CaO+H.sub.2O.fwdarw.Ca(OH).sub.2, and the remaining 3 g of water is used for material mixing) and 0.2 g of polycarboxylate superplasticizer. Stirring evenly and standing for 2 h to obtain the mixture. Press the mixture into a body under a pressure of 2 MPa, then place the body in a carbonization tank. Curing for 1 day at a CO.sub.2 concentration of 80% and a CO.sub.2 pressure of 0.2 MPa. The obtained product is recorded as CS2.

Example 3

(15) In this example, the preparation method of the in-situ high-strength gradient carbonized material includes the following steps:

(16) Selecting limestone raw materials, crushing and grinding them into powder with a particle size of 200 mesh, and then calcining the powder in a drum calciner at a temperature of 900 C. for 10 min. After calcination, rapidly cooling them to obtain a sample. Taking 20 g of the sample (with a calcium oxide content of 12.3 wt %) after rapidly cooling treatment, adding 4.19 g of water (in which 0.79 g of water is required to react with calcium oxide from CaO+H.sub.2O.fwdarw.Ca(OH).sub.2, and the remaining 3.4 g of water is used for material mixing) and 0.1 g of polycarboxylate superplasticizer. Stirring evenly and standing for 2 h to obtain the mixture. Press the mixture into a body under a pressure of 2 MPa, then place the body in a carbonization tank. Curing for 1 day at a CO.sub.2 concentration of 80% and a CO.sub.2 pressure of 0.2 MPa. The obtained product is recorded as CS3.

Comparative Example 1

(17) Selecting the calcined limestone powder of the same CaO quality as example 1 (the same limestone raw material source described in Example 1) and analytical reagent calcium carbonate powder of the same CaCO.sub.3 quality. Mixing the calcined limestone powder, analytical reagent calcium carbonate powder, and 7.57 g of deionized water, then adding 0.4 g of polycarboxylate superplasticizer and stirring evenly. After standing for 2 h, obtain the mixture. Press the mixture into a body under a pressure of 1.88 MPa, then place the body in a carbonization tank. Curing for 1 day at a CO.sub.2 concentration of 80% and a CO.sub.2 pressure of 0.2 MPa.

(18) After calculation, the mass of the calcined limestone powder in the comparative example 1 is 20 g55.6%=1.12 g. The quality of analytical reagent calcium carbonate powder is 20 g11.12 g=8.88 g. Based on CaO+H.sub.2O.fwdarw.Ca(OH).sub.2, 3.57 g of deionized water is required to react with calcium oxide. Based on the water-solid ratio, it can be inferred that an additional 20 g0.2=4 g of deionized water is required; so, take a total of 7.57 g of deionized water.

Comparative Example 2

(19) Selecting the analytical reagent CaO of the same CaO quality as example 1 and the analytical reagent calcium carbonate powder of the same CaCO.sub.3 quality. Mixing 11.12 g of the analytical reagent CaO, 8.88 g of the analytical reagent calcium carbonate powder, and 7.57 g of deionized water, then adding 0.4 g of polycarboxylate superplasticizer and stirring evenly. After standing for 2 h, obtaining the mixture. Press the mixture into a body under a pressure of 1.88 MPa, then place the body in a carbonization tank. Curing for 1 day at a CO.sub.2 concentration of 80% and a CO.sub.2 pressure of 0.2 MPa.

Comparative Example 3

(20) Except for not adding 0.4 g polycarboxylate superplasticizer, the other steps are the same as Example 1.

Comparative Example 4

(21) Selecting the calcined limestone powder of the same CaO quality as example 2 (the same limestone raw material source as described in Example 2) and analytical reagent calcium carbonate powder of the same CaCO.sub.3 quality. Mixing the calcined limestone powder, analytical reagent calcium carbonate powder, and 5.24 g of deionized water, then adding 0.2 g of polycarboxylate superplasticizer and stirring evenly. After standing for 2 h, obtaining the mixture. Press the mixture into a body under a pressure of 2 MPa, then place the body in a carbonization tank. Curing for 1 day at a CO.sub.2 concentration of 80% and a CO.sub.2 pressure of 0.2 MPa.

(22) After calculation, the mass of the calcined limestone powder in the comparative example 4 is 20 g34.8%=6.96 g. The quality of analytical reagent calcium carbonate powder is 20 g6.96 g=13.04 g. Based on CaO+H.sub.2O.fwdarw.Ca(OH).sub.2, 2.24 g of deionized water is required to react with calcium oxide. Based on the water-solid ratio, it can be inferred that an additional 20 g0.15=3 g of deionized water is required; so, take a total of 5.24 g of deionized water.

Comparative Example 5

(23) Selecting the analytical reagent CaO of the same CaO quality as example 2 and analytical reagent calcium carbonate powder of the same CaCO.sub.3 quality. Mixing 6.96 g of the analytical reagent CaO, 13.04 g of the analytical reagent calcium carbonate powder, and 5.24 g of deionized water, then adding 0.2 g of polycarboxylate superplasticizer and stirring evenly. After standing for 2 h, obtaining the mixture. Press the mixture into a body under a pressure of 2 MPa, then place the body in a carbonization tank. Curing for 1 day at a CO.sub.2 concentration of 80% and a CO.sub.2 pressure of 0.2 MPa.

Comparative Example 6

(24) Except for not adding 0.2 g polycarboxylate superplasticizer, the other steps are the same as Example 2.

Comparative Example 7

(25) Selecting the calcined limestone powder of the same CaO quality as example 3 (the same limestone raw material source as described in Example 3) and analytical reagent calcium carbonate powder of the same CaCO.sub.3 quality. Mixing the calcined limestone powder, analytical reagent calcium carbonate powder, and 4.19 g of deionized water, then adding 0.1 g of polycarboxylate superplasticizer and stirring evenly. After standing for 2 h, obtaining the mixture. Press the mixture into a body under a pressure of 2 MPa, then place the body in a carbonization tank. Curing for 1 day at a CO.sub.2 concentration of 80% and a CO.sub.2 pressure of 0.2 MPa.

(26) After calculation, the mass of the calcined limestone powder in the comparative example 7 is 20 g12.3%=2.46 g. The quality of analytical reagent calcium carbonate powder is 20 g2.46 g=17.54 g. Based on CaO+H.sub.2O.fwdarw.Ca(OH).sub.2, 0.79 g of deionized water is required to react with calcium oxide. Based on the water solid ratio, it can be inferred that an additional 20 g0.17=3.4 g of deionized water is required; so take a total of 4.19 g of deionized water.

Comparative Example 8

(27) Selecting the analytical reagent CaO of the same CaO quality as example 3 and analytical reagent calcium carbonate powder of the same CaCO.sub.3 quality. Mixing 2.46 g of the analytical reagent CaO, 17.54 g of the analytical reagent calcium carbonate powder, and 4.19 g of deionized water, then adding 0.1 g of polycarboxylate superplasticizer and stirring evenly. After standing for 2 h, obtaining the mixture. Press the mixture into a body under a pressure of 2 MPa, then place the body in a carbonization tank. Curing for 1 day at a CO.sub.2 concentration of 80% and a CO.sub.2 pressure of 0.2 MPa.

Comparative Example 9

(28) Except for not adding 0.1 g polycarboxylate superplasticizer, the other steps are the same as Example 3.

(29) Test and Analysis

(30) FIG. 1 shows a comparison of the compressive strength between Examples 1-3 and Comparative Examples 1-9 (wherein the thermal pretreatment corresponds to Examples 1-3; the calcined limestone corresponds to Comparative Examples 1, 4 and 7; the analytical reagent corresponds to Comparative Example 2, 5 and 8; no additives correspond to Comparative Example 3, 6 and 9). This figure shows their strength development patterns. It can be seen that the thermally pretreated limestone samples after carbonization curing have certain strength advantages at different calcination degrees (referring to different calcium oxide content). Compared with the addition of calcined limestone powder and analytical reagent calcium oxide separately, the strength of the three calcination systems has increased by 30%, 53%, 68%, 119%, 29.9% and 57.4%, indicating that the limestone powder after thermal pretreatment can effectively promote its strength development. In comparison with the absence of additives, it can be seen that additives can effectively improve the strength of the sample. This is because polycarboxylate superplasticizer can adsorb and aggregate dispersed colloidal particles, improving their body's strength; polycarboxylate superplasticizer improves the body's pore structure, allowing for deeper carbonization and higher strength.

(31) FIG. 2 shows the long-term compressive strength of the target product prepared in Example 2 under carbonization curing. It can be seen that the sample has already reached a relatively high level of strength in the early stage, and the strength growth is slow within 1-14 days. The final sample has reached a strength of nearly 50 Mpa, which has good development prospects.

(32) According to the preparation method described in Example 1, the prepared body was cured in the air for 1 day to obtain the target product (denoted as Ref).

(33) FIG. 3 shows the TG-DTG curves of the target product (corresponding to TG-CO.sub.2 and DTG-CO.sub.2 in FIG. 3) and Ref prepared in Example 1. From FIG. 3, it can be seen that the weight loss peak between 400 C. and 500 C. corresponds to the decomposition of Ca(OH).sub.2, while the weight loss peak between 600 C. and 800 C. corresponds to the decomposition of calcium carbonate. It can be seen that the weight loss peak of Ca(OH).sub.2 during carbonization curing is more minor, indicating a lower content of Ca(OH).sub.2. So, it indicates that more Ca(OH).sub.2 reacts with CO.sub.2 during carbonization curing to generate more calcium carbonate to support the strength of the body.

(34) FIG. 4 is a microscopic schematic diagram of the target product prepared in Examples 1-3. The figure shows that the dark gray part is calcium carbonate that has not been calcined after thermal pretreatment. In contrast, the light gray part in the secondary layer is a portion of calcium carbonate calcined and decomposed into calcium oxide. The outermost layer is based on the reaction of calcium oxide on limestone with water and carbon dioxide to generate flocculent Ca(OH).sub.2 and calcium carbonate with needle bar structure. It can be seen that the prepared carbonized material exhibits gradient changes from the inside out, specifically, CaCO.sub.3/CaO/Ca(OH).sub.2/CaCO.sub.3. Due to the reaction and growth of calcium oxide on limestone, the subsequent reactants are all based on limestone. Hence, the connections between these products are very tight, resulting in higher macroscopic strength.

(35) FIG. 5 is an SEM image of the target product prepared in Example 2. This figure shows that the distribution of small and granular calcium oxide on the surface of limestone is disorderly and numerous. It is precisely because of this large specific surface area of calcium oxide that its structure is very dense and has high carbonization activity.

(36) The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc., made within the spirit and principle of the present invention shall be included in the protection of the present invention.