Serpentine carbon sequestration foamed lightweight soil and preparation method thereof

Abstract

The disclosure belongs to the technical field of materials for civil construction engineering, and specifically relates to a green and low carbon emission foamed lightweight soil prepared by using serpentine, magnesium oxide and CO.sub.2 as raw materials. In the serpentine carbon sequestration foamed lightweight soil, the ingredients of raw material include: magnesium oxide, serpentine, a filler, CO.sub.2 bubbles and water.

Claims

1. A serpentine carbon sequestration foamed lightweight soil, wherein ingredients of raw materials per cubic meter comprise: 10 to 100 parts by weight of magnesium oxide, 10 to 100 parts by weight of a filler, 10 to 100 parts by weight of serpentine, 2 to 45 parts by weight of CO.sub.2 bubbles and 20 to 400 parts by weight of water, wherein a weight of the serpentine is 30% of a sum of a weight of the magnesium oxide and a weight of the filler, wherein a preparation method of the serpentine carbon sequestration foamed lightweight soil comprises following steps: S1, preparing the raw materials: weighing 10 to 100 parts by weight of the magnesium oxide, 10 to 100 parts by weight of the filler, 10 to 100 parts by weight of the serpentine, and 20 to 400 parts by weight of the water for use later; S2, preparing a slurry: placing the serpentine, the magnesium oxide, and the filler into a mixing device in proportion, and stirring at a speed of 100 r/min for 1 minute to 2 minutes to mix the serpentine, the magnesium oxide, and the filler uniformly to obtain a mixture, adding the water respectively to the mixture 2 times or 3 times, stirring for 1 minute to 2 minutes after each addition of the water, and keeping the mixture from sinking to the bottom or agglomerating to ensure that the slurry is uniform and has no sedimentation until all of the water is completely added, and obtaining the slurry; S3, preparing the CO.sub.2 bubbles: adopting a pre-foaming method to use high-pressure CO.sub.2 to produce the CO.sub.2 bubbles, wherein the adopted CO.sub.2 is industrial high-purity carbon dioxide or carbon dioxide purified from industrial waste gas; S4, mixing and stirring: adding 2 parts by weight to 45 parts by weight of the CO.sub.2 bubbles into the slurry obtained from the step S2 for stirring, and ensuring that the CO.sub.2 bubbles are evenly distributed and the slurry has no sedimentation, then a good mixture is obtained, wherein a stirring speed is 600 r/min to 900 r/min, a stirring time is 10 minutes to 12 minutes; and S5, preparing and curing a sample: pouring the blended mixture into a mold for sealing, and curing the mixture in a curing room at a constant temperature to obtain the carbon sequestration foamed lightweight soil.

2. The serpentine carbon sequestration foamed lightweight soil according to claim 1, wherein the serpentine is serpentine tailings or a serpentine ore, or a mixture of the two.

3. The serpentine carbon sequestration foamed lightweight soil according to claim 1, wherein the magnesium oxide is light magnesium oxide or heavy magnesium oxide or a mixture of the two.

4. The serpentine carbon sequestration foamed lightweight soil according to claim 1, wherein the filler is engineering waste soil, sandy soil, silt soil or clay soil.

5. The serpentine carbon sequestration foamed lightweight soil according to claim 1, wherein raw materials of the CO.sub.2 bubbles comprise 0.33 to 20 parts by weight of a foaming agent, 0.0033 to 2 parts by weight of a foam stabilizer and 0.0033 to 2 parts by weight of an active agent; the foaming agent is one of a rosin resin, a synthetic surfactant, protein, and a composite foaming agent or a mixture of the above; the foam stabilizer is magnesium acetate; the active agent is sodium cocoyl glycinate, potassium cocoyl glycinate, lauroyl glutamic acid or potassium cocoyl glutamate.

6. The serpentine carbon sequestration foamed lightweight soil according to claim 5, wherein in the step S3, the method of preparing the CO.sub.2 bubbles is as follows: diluting the foaming agent at a dilution factor of 20 times to 60 times, adding the active agent and the foam stabilizer, and mixing them to obtain a foaming liquid; then connecting to a CO.sub.2 cylinder through a trachea, opening a CO.sub.2 vent valve and adjusting a pressure to 400 kPa, after air in a foaming liquid pipeline is exhausted, and the foaming liquid completely enters a water pump, a foaming device is closed after the pressure is stable and a foaming rate is stable; and opening a foam outlet valve to control the pressure with a range from 100 kPa to 400 kPa, a water pump speed ratio from 20 to 80, and a corresponding water pump flow from 1 L/min to 4 L/min, to release fine and stable CO.sub.2 foam, and the preparation is complete, and a container is used to collect CO.sub.2 foam and set the CO.sub.2 foam aside for use.

7. The serpentine carbon sequestration foamed lightweight soil according to claim 1, wherein the sample prepared from step S5 must be completed within a half-life of the foaming agent to prevent the foam from bursting and causing the CO.sub.2 to leak.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a preparation method of a serpentine carbon sequestration foamed lightweight soil of the present disclosure.

(2) FIG. 2 shows a thermogravimetric analysis results of samples prepared in Examples and Comparative Examples.

DESCRIPTION OF THE EMBODIMENTS

(3) In order to facilitate understanding of the present disclosure, the content of the present disclosure will be further explained below in conjunction with the examples, but the present disclosure is not limited only to the following examples. It should be understood that the specific embodiments described here are only used to explain the present disclosure and are not intended to limit the present disclosure.

(4) In the following examples, the silty clay used was taken from a construction site in Nanjing. The basic indicators are shown in Table 1 and the basic properties are shown in Table 2. The active magnesium oxide used is low-active magnesium oxide produced by Hebei Meishen Technology Co., Ltd., wherein the iodine absorption value is 14, and the ingredients are shown in Table 2. The serpentine tailings used were taken from an experimental site of the Jiangsu Geological Survey Institute and ground by a ball mill, wherein the ingredients are shown in Table 2, and the particle size is <0.075 mm.

(5) TABLE-US-00001 TABLE 1 Basic property indicators of silty clay Test items Test value Natural density /(g .Math. cm.sup.3) 1.88 Natural moisture content, w/% 33.3 Maximum dry density/(g .Math. cm.sup.3) 1.71 Optimal moisture content/% 17.4 Liquid limit, w.sub.L (%) 35.5 Plastic limit, w.sub.p (%) 19.8 Specific gravity, G.sub.s 2.71

(6) TABLE-US-00002 TABLE 2 Main chemical ingredients of serpentine, magnesium oxide and silty clay Ingredients MgO Al.sub.2O.sub.3 CaO SiO.sub.2 Fe.sub.2O.sub.3 Na.sub.2O Serpentine 45.93 1.97 1.27 40.43 8.74 0.27 Magnesium 98.68 0.06 0.06 0.50 0.10 0.38 oxide Silty clay 3.032 16.99 3.43 65.85 5.11 1.47

Example 1

(7) In a serpentine carbon sequestration foamed lightweight soil, each cubic meter of the serpentine carbon sequestration foamed lightweight soil contains: 100 parts by weight of active magnesium oxide powder, 100 parts by weight of silty clay, 60 parts by weight of serpentine tailings powder, 15 parts by weight of CO.sub.2 bubbles and 170 parts by weight of water.

(8) The silty clay needs to be air-dried first and then pulverized and filtered through a 2 mm sieve. The water used is distilled water, including the water used in the CO.sub.2 bubbles.

(9) 0.375 parts by weight of sodium dodecyl sulfonate used as the foaming agent, 0.00375 parts by weight of magnesium acetate used as the foam stabilizer, and 0.00375 parts by weight of sodium cocoylglycinate used as the active agent were taken. The above ingredients were mixed and the foaming agent was diluted at a dilution factor of 40 to obtain 15 parts by weight of the foaming liquid whose foaming rate is 40 times and the half-life is 20 minutes to 40 minutes.

(10) The following steps are adopted to prepare serpentine carbon sequestration foamed lightweight soil.

(11) S1. Preparing raw materials: weighing 60 parts by weight of serpentine tailings powder, 100 parts by weight of active magnesium oxide powder, 100 parts by weight of silty clay for use later.

(12) S2. Preparing slurry: Placing the serpentine tailings powder, active magnesium oxide powder, and silty clay into a mixing device in proportion, and stirring at a speed of 100 r/min for 2 minutes to mix the serpentine tailings powder, active magnesium oxide powder, and silty clay uniformly to obtain the mixture, adding water respectively to the mixture 2 times or 3 times, stirring for 1 minute to 2 minutes after each addition of water, and keeping the powder from sinking to the bottom or agglomerating to ensure that the slurry was uniform and had no sedimentation until all of the water was completely added, and obtaining the slurry.

(13) S3. Preparing CO.sub.2 bubbles: Diluting the foaming agent by adding water at a dilution factor of 40 times, adding an active agent and a foam stabilizer, and mixing them to obtain a foaming liquid; then connecting to the CO.sub.2 cylinder through a trachea, opening the CO.sub.2 vent valve and adjusting the pressure to 400 kPa. After the air in the foaming liquid pipeline was exhausted, and the foaming liquid completely entered the water pump, the foaming device was closed after the pressure is stable and the foaming rate is stable. The foam outlet valve was opened. The selected pressure size was 400 kPa, the water pump speed ratio was 60, and the water pump flow rate was 3 L/min. Fine and stable CO.sub.2 foam was released, and a container was used to collect the CO.sub.2 foam and set aside for use.

(14) S4. Mixing and stirring: Adding 10 parts by weight of CO.sub.2 bubbles into the slurry for stirring. The stirring speed was 800 r/min. The stirring time was 10 minutes. Ensuring that the CO.sub.2 bubbles were evenly distributed and the slurry had no sedimentation, then a good mixture was obtained.

(15) S5. Preparing and curing sample: Immediately pouring the blended mixture into the mold for sealing, and curing the mixture in a curing room at a constant temperature for 7 days to obtain carbon sequestration foamed lightweight soil. The sample preparation from steps S4 to S5 must be completed within the half-life of the foaming agent to prevent the foam from bursting and causing CO.sub.2 to leak.

Example 2

(16) In a serpentine carbon sequestration foamed lightweight soil, each cubic meter of the serpentine carbon sequestration foamed lightweight soil contains: 60 parts by weight of serpentine tailings powder, 100 parts by weight of active magnesium oxide powder, 100 parts by weight of silty clay, 10 parts by weight of CO.sub.2 bubbles and 170 parts by weight of water. The same serpentine tailings powder, active magnesium oxide powder, silty clay, water and foaming agent used in Example 1 were used, and the treatment methods for various materials were also identical.

(17) The preparation method of the serpentine carbon sequestration foamed lightweight soil in Example 2 is the same as that in Example 1, but the curing time is 14 days.

Example 3

(18) In a serpentine carbon sequestration foamed lightweight soil, each cubic meter of the serpentine carbon sequestration foamed lightweight soil contains: 60 parts by weight of serpentine tailings powder, 100 parts by weight of active magnesium oxide powder, 100 parts by weight of silty clay, 10 parts by weight of CO.sub.2 bubbles and 170 parts by weight of water. The same serpentine tailings powder, active magnesium oxide powder, silty clay, water and foaming agent used in Example 1 were used, and the treatment methods for various materials were also identical.

(19) The preparation method of the serpentine carbon sequestration foamed lightweight soil in Example 3 is the same as that in Example 1, but the curing time is 28 days.

Comparative Example 1

(20) In a serpentine carbon sequestration foamed lightweight soil, each cubic meter of the serpentine carbon sequestration foamed lightweight soil contains: 20 parts by weight of serpentine tailings powder, 100 parts by weight of active magnesium oxide powder, 100 parts by weight of silty clay, 10 parts by weight of CO.sub.2 bubbles and 140 parts by weight of water. The same serpentine tailings powder, active magnesium oxide powder, silty clay, water and foaming agent used in Example 1 were used, and the treatment methods for various materials were also identical.

(21) The preparation method of the serpentine carbon sequestration foamed lightweight soil in Comparative Example 1 is the same as that in Example 1, and the curing time is 7 days.

Comparative Example 2

(22) In a serpentine carbon sequestration foamed lightweight soil, each cubic meter of the serpentine carbon sequestration foamed lightweight soil contains: 100 parts by weight of serpentine tailings powder, 100 parts by weight of active magnesium oxide powder, 100 parts by weight of silty clay, 10 parts by weight of CO.sub.2 bubbles and 200 parts by weight of water. The same serpentine tailings powder, active magnesium oxide powder, silty clay, water and foaming agent used in Example 1 were used, and the treatment methods for various materials were also identical.

(23) The preparation method of the serpentine carbon sequestration foamed lightweight soil in Comparative Example 2 is the same as that in Example 1, and the curing time is 7 days.

Comparative Example 3

(24) In a serpentine carbon sequestration foamed lightweight soil, each cubic meter of the serpentine carbon sequestration foamed lightweight soil contains: 100 parts by weight of active magnesium oxide powder, 100 parts by weight of silty clay, 10 parts by weight of CO.sub.2 bubbles and 130 parts by weight of water. The same active magnesium oxide powder, silty clay, water and foaming agent used in Example 1 were used, and the treatment methods for various materials were also identical. Comparative Example 3 was used as conventional carbon sequestration foamed lightweight soil without the serpentine powder.

(25) Next, the samples prepared in the above examples were subjected to unconfined strength test and thermogravimetric analysis test.

(26) 1. Unconfined Strength Test and Inspection

(27) For the samples prepared in Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3, the unconfined compressive strength test was conducted after 7 days of curing. The unconfined compressive strength test was conducted in accordance with the specification Highway Geotechnical Test Regulations JTG E40-2007 through the user of a CBR-2 load-carrying ratio tester.

(28) Unconfined Strength Test Results

(29) TABLE-US-00003 TABLE 3 Properties of serpentine carbon sequestration foamed lightweight soil Content Unconfined ratio of Curing compressive Sample Serpentine time strength (MPa) Example 1 30% 7 d 0.660 Example 2 30% 14 d 0.980 Example 3 30% 28 d 1.409 Comparative 10% 28 d 1.249 Example 1 Comparative 50% 28 d 0.845 Example 2 Comparative 0 28 d 1.500 Example 3
Strength Indicator

(30) It can be seen from Table 3 that: through the content ratio of serpentine 10%, 30%, and 50% (serpentine tailings powder/active magnesium oxide powder+silty clay) in Comparative Example 1, Example 1 and Comparative Example 2, the 7-day unconfined compressive strength is 0.574 MPa, 0.660 MPa, and 0.600 MPa respectively. By increasing the content ratio of serpentine, the strength of the serpentine carbon sequestration foamed lightweight soil will be first increased and then reduced. There is a critical value for this content ratio, and the reason behind that is the strength of the serpentine carbon sequestration foamed lightweight soil is derived from the skeleton supporting function served by the magnesium carbonate generated by the hydration carbon sequestration reaction of active magnesium oxide and the filler. The increase in the content ratio of serpentine reduces the content of active magnesium oxide and increases the content SiO.sub.2 in the mixture, making the strength of the sample increase when the content ratio of serpentine changes from 10% to 30%. The activity of MgO in serpentine tailings powder is lower than that in active magnesium oxide powder, which affects the formation of final magnesium carbonate, making the strength of the sample reduce when the content ratio of serpentine changes from 30% to 50%.

(31) Through Comparative Example 3, it can be seen that after adding 30% serpentine powder, compared with the carbonized foamed lightweight soil without serpentine powder, the strength is not significantly reduced, and the serpentine carbon sequestration foamed lightweight soil does not require secondary carbonization throughout the process, and may be cured under ambient conditions in the air. Compared with carbonized foamed lightweight soil, the curing conditions are simple, a large amount of serpentine tailings is consumed, and the materials used are more environmentally friendly and more suitable for the construction on site.

(32) Through Examples 1, 2, and 3, it can be seen that the unconfined compressive strength of the serpentine carbon sequestration foamed lightweight soil corresponding to 30% of content ratio of serpentine after 7 days, 14 days, and 28 days is 0.660 MPa, 0.980 MPa, and 1.409 MPa respectively. The strength of the serpentine carbon sequestration foamed lightweight soil increases with curing days, and the increase is significantly fast in the first 7 days, and the strength increases rapidly.

(33) 2. Thermogravimetric Analysis Test and Inspection

(34) The samples prepared in Examples 1, 2, 3 and Comparative Examples 1, 2, and 3 were subjected to thermogravimetric analysis tests using a TA-Q500 thermogravimetric analyzer. The temperature started from 30 C. and increased at a rate of 10 C./min to 1000 C.

(35) Generally, the decarburization process of magnesium carbonate starts at 450 C. to 550 C. Therefore, during this heating stage, the higher the decline rate of the curve, the greater the escape rate of CO.sub.2, and the stronger the carbon sequestration ability of the sample.

(36) As shown in FIG. 2, through the comparison of Examples 1, 2, and 3, it can be seen that as the curing age increases, the mass loss rate of the sample increases, indicating that the carbonization degree of the sample increases, which is basically consistent with the unconfined strength test results. Through comparison of Comparative Examples 1, 2, and 3, the carbonization degree of the sample without adding serpentine powder is relatively highest, indicating that the sample of Comparative Example 3 has the optimal carbon sequestration effect, but the cost is also the highest. Samples added with 10% and 50% of serpentine powder have relatively lower carbonization degree compared with the sample added with 30% of serpentine powder, the carbon sequestration effect is relatively poor, which is basically consistent with the unconfined strength test results.

(37) Finally, the method of this disclosure is only a preferred embodiment and is not used to limit the protection scope of this disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this disclosure shall be included in the protection scope of this disclosure.