Method for preparing artificial pozzolanic mixtures from contaminated soils using a cement kiln and its applications

Abstract

This invention relates to a method for preparing artificial volcanic ash composite materials using cement kiln treatment of contaminated soil and its application. The method includes the following steps: mixing contaminated soil with one of the following: coal gangue, fly ash, red mud, sulfur activator, or sulfur-alkali activator, ensuring the mixture contains ≥12% aluminum oxide and has an aluminum-silicon ratio ≥0.3; and feeding the mixture into the cement kiln from the kiln tail. The calcination temperature in the cement kiln is controlled at ≥650℃, and the calcination time is controlled at ≥30 min to obtain the volcanic ash composite material. The volcanic ash composite material is applied to masonry mortar or plastering mortar. This invention provides a solution and market outlet for the reuse of residues generated from the harmless treatment of contaminated soil in cement kilns. It is of great significance for broadening the utilization pathways of residues after contaminated soil treatment, increasing their reuse value, establishing a complete industrial chain for large-scale waste treatment in cement kilns, and promoting the construction of waste-free cities.

Description

Technical Field

[0001] This invention belongs to the field of volcanic ash materials technology, and in particular relates to a method for preparing artificial volcanic ash composite materials by disposing of contaminated soil in a cement kiln and its application. Background Technology

[0002] The closure or relocation of petroleum, chemical, and coking enterprises has left behind industrial waste and contaminated sites. Due to their hidden nature, volatility, cumulative effects, diversity, and toxicity, these sites not only seriously threaten the health and living environment of residents around them but also severely impact the safe reuse of the land. As a result, there is an increasing number of research and development efforts focused on remediation technologies and applications for contaminated soil.

[0003] Generally, one ton of contaminated soil, after undergoing thermal desorption, pyrolysis, and rapid cooling of flue gas in a cement kiln, will produce approximately 0.7 tons of residue. Currently, there are issues such as a low residue utilization rate, limited utilization pathways, and relatively low added value of the products. If dumped or stockpiled, it will cause secondary environmental pollution and hazards. Therefore, it is urgent to further address the issue of residue reuse.

[0004] Furthermore, in the building materials industry, such as mortar and concrete, the prices of mineral admixtures like fly ash and mineral powder are continuously rising due to environmental regulations, while their quality varies, leading to a constant increase in the cost of these products. There is an urgent need to develop a new type of active filler as a substitute to control product costs and enhance product competitiveness. Summary of the Invention

[0005] This invention addresses the problems existing in the prior art by proposing a method for preparing artificial pozzolanic composite materials using cement kilns to treat contaminated soil, and its application. This invention utilizes the harmless treatment of contaminated soil in cement kilns, and through a series of studies conducted at different calcination temperatures (450℃, 550℃, 650℃, 750℃, 850℃, 950℃) and calcination times, develops artificial pozzolanic composite materials. The pozzolanic properties meet the requirements of the standard "Pozzolanic Composite Materials for Cement" (GB / T 2847-2022), and the activity meets the requirements of the standard "Fly Ash for Cement and Concrete" (GB / T 1596-2017). This provides a solution and market outlet for the reuse of residues generated from the harmless treatment of contaminated soil in cement kilns, and is of great significance for broadening the utilization pathways of residues after contaminated soil treatment, increasing their reuse value, establishing a complete industrial chain for large-scale waste treatment in cement kilns, and promoting the construction of waste-free cities.

[0006] This invention is achieved by using a cement kiln to treat contaminated soil and prepare an artificial volcanic ash composite material, comprising the following steps:

[0007] The contaminated soil is mixed with one of the following: coal gangue, fly ash, red mud, sulfur activator, or sulfur-alkali activator, so that the aluminum oxide content in the mixture is ≥12% and the aluminum-silicon ratio is ≥0.3, and then fed into the cement kiln from the kiln tail.

[0008] By controlling the calcination temperature of the cement kiln to ≥650℃ and the calcination time to ≥30min, artificial volcanic ash composite material is obtained.

[0009] In the above technical solution, preferably, the calcination temperature is 650℃-750℃.

[0010] In the above technical solution, preferably, the sulfur activator is desulfurized gypsum, and the amount of desulfurized gypsum added accounts for 10% of the contaminated soil. The desulfurized gypsum contains 1.0-5.0% SiO2, 0.2-2.0% Al2O3, 0.1-0.5% Fe2O3, 30.0-40.0% CaO, 0.8-1.5% MgO, 0.2-0.4% R2O, 38.0-43.0% SO3, and Cl... - Content 0.03-0.06%, LOI content 12.0-17.0%.

[0011] In the above technical solution, preferably, the sulfur-alkali activator is desulfurized gypsum and quicklime, and the amount of desulfurized gypsum and quicklime added each accounts for 10% of the contaminated soil; the quicklime contains 85-90% CaO.

[0012] In the above technical solution, preferably, the coal gangue contains 30.72-48.33% SiO2, 16.27-24.10% Al2O3, 2.16-7.34% Fe2O3, 1.5-4.58% CaO, 0.61-1.99% MgO, 0.64-1.18% R2O, 0.46-1.97% SO3, and Cl... - Content 0.002-0.011%, LOI content 12.83-30.11%.

[0013] In the above technical solution, preferably, the fly ash contains 39.32-57.19% SiO2, 19.33-29.35% Al2O3, 5.11-9.93% Fe2O3, 3.94-15.81% CaO, 0.9-3.69% MgO, 0.89-1.57% R2O, 0.17-3.46% SO3, and Cl... - Content 0.011-0.3%, LOI 1.13-11.13%.

[0014] In the above technical solution, preferably, the red mud contains 4.18-46.78% SiO2, 3.17-18.26% Al2O3, 34.01-58.66% Fe2O3, 0.3-6.84% CaO, 0.12-1.7% MgO, 0.18-1.65% R2O, and Cl... - Content 0.004-0.083%, LOI content 3.71-13.89%.

[0015] In the above technical solution, preferably, the contaminated soil, coal gangue, fly ash, red mud, sulfur activator or sulfur-alkali activator are first subjected to grinding treatment before calcination.

[0016] Application of an artificial volcanic ash mixture, which is used in masonry mortar or plastering mortar.

[0017] In the above technical solution, preferably, when artificial volcanic ash mixture is used in masonry mortar, the amount of artificial volcanic ash mixture in the masonry mortar is ≤55‰.

[0018] In the above technical solution, preferably, when artificial volcanic ash mixture is used in plastering mortar, the amount of artificial volcanic ash mixture in the plastering mortar is ≤30‰.

[0019] The advantages and positive effects of this invention are:

[0020] 1. This invention utilizes a cement kiln to process contaminated soil containing coal gangue, fly ash, red mud, sulfur-activated soil, or sulfur-alkali-activated soil. The resulting material is a pozzolanic mixture that meets the requirements for activity and pozzolanic properties. It can be used as a mineral active admixture and can also be recycled and used in the mortar and other building materials industries.

[0021] 2. This invention utilizes the mineral activity of volcanic ash-based admixtures to replace expensive mineral admixtures such as fly ash and mineral powder in cement-based premixed mortar cementitious systems. This not only reduces the cost and increases the efficiency of premixed mortar products, but also consumes some ecological solid waste, giving full play to the solid waste resource utilization function of premixed mortar, and has significant economic, environmental and social benefits. Attached Figure Description

[0022] Figure 1 This is a schematic diagram showing the amount of volcanic ash mixed material added and the amount of water added to the masonry mortar provided in Embodiment 6 of the present invention;

[0023] Figure 2 This is a schematic diagram showing the relationship between the amount of volcanic ash mixed material added and the water retention rate of masonry mortar provided in Embodiment 6 of the present invention;

[0024] Figure 3This is a schematic diagram showing the relationship between the amount of volcanic ash mixed material added and the 2-hour consistency loss rate of masonry mortar provided in Embodiment 6 of the present invention;

[0025] Figure 4 This is a schematic diagram showing the relationship between the amount of volcanic ash mixed material added and the 28-day compressive strength of masonry mortar provided in Embodiment 6 of the present invention;

[0026] Figure 5 This is a schematic diagram showing the amount of volcanic ash mixed material added and the amount of water added to the plastering mortar provided in Embodiment 7 of the present invention;

[0027] Figure 6 This is a schematic diagram showing the relationship between the amount of volcanic ash mixed material added and the water retention rate of plastering mortar provided in Embodiment 7 of the present invention;

[0028] Figure 7 This is a schematic diagram showing the relationship between the amount of volcanic ash mixed material added and the 2-hour consistency loss rate of plastering mortar provided in Embodiment 7 of the present invention;

[0029] Figure 8 This is a schematic diagram showing the relationship between the amount of volcanic ash mixed material added and the 28-day compressive strength of plastering mortar provided in Embodiment 7 of the present invention. Detailed Implementation

[0030] To make the content of this invention easier to understand, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0031] The contaminated soil, coal gangue, fly ash, red mud, sulfur activator or sulfur-alkali activator used in the following examples were all tested after grinding and calcination.

[0032] Pozzolanic properties: Refer to GB / T 2847-2022 "Pozzolanic Blends for Cement" for pozzolanic performance testing.

[0033] Activity: The activity of artificial pozzolanic admixtures was tested in accordance with GB / T 1596-2017 "Fly Ash for Cement and Concrete".

[0034] In the examples, the chemical composition analysis of contaminated soil, coal gangue, fly ash, alumina red mud, and desulfurization gypsum is shown in Table 1 below:

[0035] Table 1 Analysis of Chemical Composition of Raw Materials

[0036]

[0037]

[0038] Example 1

[0039] Pozzolanic composite material was prepared by mixing contaminated soil and fly ash residue. Fly ash residue was added to adjust the composition of the contaminated soil. The mixture was then calcined at 650℃-750℃ (for 1 hour). The experimental data are shown in Table 2 below.

[0040] Table 2. Test data of contaminated soil calcined at 650℃-750℃

[0041]

[0042] As shown in Table 2, under the experimental conditions of calcination temperature ≥ 650℃, alumina content ≥ 12%, and aluminum-silicon ratio ≥ 0.3, the pozzolanic property qualification rate of the contaminated soil reached 100%. The activity at 28 days showed an increasing trend with increasing calcination temperature.

[0043] Example 2

[0044] A volcanic ash composite material was prepared by mixing contaminated soil and red mud. Red mud was added to adjust the composition of the contaminated soil. The material was then calcined at 650℃. The experimental data are shown in Table 3 below.

[0045] Table 3. Test data of contaminated soil calcined at 650℃

[0046] Sample <![CDATA[SiO2 / %]]> <![CDATA[Al2O3 / %]]> <![CDATA[Al2O3 / SiO2]]> 28-day strength / MPa 28-day activity % Volcanic ash 1 43.09 13.3 0.31 39.8 74.25 qualified 2 40.14 14.4 0.36 39.9 74.44 qualified 3 35.4 14.5 0.41 40.5 75.56 qualified 4 32.02 15.3 0.48 40.8 76.12 qualified

[0047] As shown in Table 3, under the experimental conditions of calcination temperature ≥ 650℃, aluminum oxide content ≥ 12%, and aluminum-silicon ratio ≥ 0.3, the pozzolanic property qualification rate of the contaminated soil reached 100%. At 650℃, the activity increased after 28 days with the increase of Al2O3 and Al2O3 / SiO2.

[0048] Example 3

[0049] A pozzolanic composite material was prepared by mixing contaminated soil and coal gangue. Coal gangue was added to adjust the composition of the contaminated soil. The mixture was then calcined at 650℃ and 750℃. The experimental data are shown in Table 4 below.

[0050] Table 4. Test data of contaminated soil at different calcination temperatures

[0051]

[0052] As can be seen from the data in Table 4, under the experimental conditions of calcination temperature of 750℃ and aluminum-silicon ratio of 0.39, the volcanic ash composite material has the highest strength, reaching 81.16%. The data analysis shows that the activity of the volcanic ash composite material increases with the increase of calcination temperature, aluminum content, and aluminum-silicon ratio.

[0053] By adjusting the aluminum oxide content and calcining at 650-750℃, the 28-day activity of the pozzolanic composite material can be effectively improved, and the pozzolanic properties are qualified.

[0054] Example 4

[0055] A pozzolanic composite material was prepared by mixing contaminated soil and desulfurized gypsum, and the effect of desulfurized gypsum activation on the activity of the pozzolanic composite material was investigated. Under calcination temperatures of 650℃ and 750℃ for 30 min, the 28-day strength of the composite material was compared to that of cement, which was 55.70 MPa. The experimental data are shown in Table 5 below.

[0056] Table 5 Test data of soil contaminated with desulfurized gypsum

[0057]

[0058] As shown in Table 5, under the experimental conditions of calcination temperatures of 650℃ and 750℃ for 30 minutes, the activity of the pozzolanic mixture initially increased and then decreased with increasing desulfurization gypsum content. Considering the control index of SO3 content in pozzolanic materials, a desulfurization gypsum content of 10% is recommended. Adding desulfurization gypsum promotes the formation of ettringite in the pozzolanic mixture. Eettringite, with its rod-like structure, is interspersed within the CHS gel, making the cement paste more compact and thus significantly improving the strength of the cement.

[0059] The activity test data after calcination at 650℃ and 750℃, with the addition of 10% desulfurized gypsum and 90% contaminated soil, and after calcination for 3 hours, are shown in Table 6 below:

[0060] Table 6. Test data of contaminated soil activated by desulfurized gypsum at different calcination temperatures.

[0061] Calcination temperature / °C 7-day intensity / MPa 28-day strength / MPa 7-day activity / % 28-day activity / % Volcanic ash 650 32.63 44.6 85.87 80.07 qualified 750 28.63 38.8 75.34 69.66 qualified

[0062] As can be seen from the data in Table 6, the activity after 7 days and 28 days gradually decreased as the calcination temperature increased. Desulfurized gypsum has a promoting effect on the activity of pozzolanic composite materials. The activity is highest at 650℃, with the activity reaching 85.87% after 7 days and 80.07% after 28 days.

[0063] Example 5

[0064] Pozzolanic composite material was prepared by mixing contaminated soil, desulfurized gypsum, and quicklime. The quicklime was produced by calcining limestone in a high-temperature furnace, with a calcium oxide content of 87%. After adding desulfurized gypsum and quicklime, the mixture was calcined at 850℃ for 30 minutes. The experimental data are shown in Table 7 below.

[0065] Table 7 Test data of contaminated soil activated by desulfurization gypsum and quicklime

[0066]

[0067] As can be seen from the data in Table 7, under the experimental conditions of calcination temperature of 850℃ and calcination time of 30 min, the activity after 7 days and 28 days showed a trend of first increasing and then decreasing with the increase of quicklime content. Under the condition that the content of desulfurized gypsum and quicklime was 10% each, the activity after 7 days reached 82.29% and the activity after 28 days reached 79.53%, which showed good results.

[0068] Under the action of sulfur-alkali activators in desulfurized gypsum and quicklime, a large amount of calcium hydroxide is generated. Since Ca(OH)₂ can rapidly provide Ca to the cementitious materials... 2+ and OH － ions, OH － Ions facilitate the leaching of active silicon and aluminum from the surface of pozzolanic composite particles, forming glassy crystals and gels, thus resulting in a rapid increase in compressive strength in the short term. However, with prolonged curing, OH groups... － Once the ion concentration reaches a certain value, the excess OH- in the alkali-activated cementitious material system... － Ions can dissolve and destroy the structure of the hydration product, aluminosilicate gel, thus reducing the strength of the cementitious material.

[0069] In summary, 1) under the conditions of calcination test temperature ≥650℃, aluminum oxide content ≥12%, and aluminum-silicon ratio ≥0.3, the prepared pozzolanic composite material has a high pozzolanic property qualification rate.

[0070] 2) As the calcination temperature increases, the activity of the pozzolanic mixture first increases and then decreases. The optimal calcination temperature is between 650℃ and 750℃. The activity of the pozzolanic mixture increases with the increase of calcination time. The activity of the pozzolanic mixture increases with the increase of calcination temperature, aluminum content, and aluminum-silicon ratio.

[0071] 3) Sulfur activation promotes the activity of pozzolanic composite materials. The activity is highest at calcination at 650℃, reaching 85.87% after 7 days and 80.07% after 28 days. As the calcination temperature increases, the activity of pozzolanic composite materials gradually decreases. With the increase of gypsum content, the activity of pozzolanic composite materials shows a trend of first increasing and then decreasing. The optimal proportion of gypsum content is 10%.

[0072] 4) Conduct sulfur-alkali composite activation. Adding 10% desulfurization gypsum and 10% quicklime to the contaminated soil at the same time has the best effect. The activity reaches 82.29% after 7 days and 79.53% after 28 days.

[0073] To ensure the stability of the pozzolanic mixture during subsequent use, it was ground to a certain fineness (control indicators before and after grinding are detailed in Table 8). The strength activity index was tested according to the test method in "Fly Ash for Cement and Concrete" (GB / T1596-20170). The results of the comparative test of the activity of the pozzolanic mixture (after grinding) and fly ash are shown in Table 9 below.

[0074] Table 8 Control Indicators for Volcanic Ash Blended Materials

[0075]

[0076] Table 9. Comparative test data of the activity of pozzolanic composites and fly ash.

[0077] Testing items 28-day flexural strength / MPa 28-day compressive strength / MPa Activity index / % Standard test mortar 8.4 54.3 / Class II fly ash 6.8 40.4 74.40 Volcanic ash mixture 7.0 40.8 75.14

[0078] The following is a more detailed explanation of the experimental research on pozzolanic composite materials in ordinary masonry mortar and ordinary plastering mortar:

[0079] Example 6

[0080] The admixture ratios of volcanic ash composite materials in ordinary masonry mortar are shown in Table 10 below:

[0081] Table 10 Experimental data on the admixture ratio of pozzolanic composite materials in ordinary masonry mortar.

[0082]

[0083] The experimental data on the relationship between the amount of volcanic ash admixture added and the amount of water added, water retention rate, 2-hour consistency loss rate, and 28-day compressive strength change are as follows: Figures 1-4 As shown. From Figures 1-4 It can be seen that with the increase of the amount of volcanic ash admixture, the water content of masonry mortar increases significantly; the water retention of masonry mortar increases first and then decreases, but the overall difference is not significant, and the decrease in the later stage is related to the increase of water content; with the increase of the amount of volcanic ash admixture, the 2-hour consistency loss rate of masonry mortar increases significantly, shortening the workable time for construction; the amount of volcanic ash admixture added has little effect on the 28-day compressive strength.

[0084] In summary, increasing the amount of pozzolanic admixture significantly increases the water demand and water retention rate of masonry mortar. However, it also leads to a substantial increase in the 2-hour consistency loss rate. This is because the internal layered structure of the pozzolanic admixture allows water molecules to penetrate, increasing its water retention rate. However, as the free water content decreases, the 2-hour consistency loss rate increases. When the pozzolanic admixture content reaches 65‰, the 2-hour consistency loss rate reaches 25%, severely affecting its workability. Therefore, it is recommended that the dosage of pozzolanic admixture in masonry mortar should be ≤55‰.

[0085] Example 7

[0086] The proportions of volcanic ash admixtures in ordinary plastering mortar are shown in Table 11 below:

[0087] Table 11 Experimental data on the admixture ratio of pozzolanic composite materials in ordinary plastering mortar.

[0088]

[0089] The experimental data on the relationship between the amount of volcanic ash admixture added and the amount of water added, water retention rate, 2-hour consistency loss rate, and 28-day compressive strength change are as follows: Figures 5-8 As shown. From Figures 5-8 It can be seen that with the increase of the amount of volcanic ash admixture, the water content of plastering mortar increases, but not significantly; the water retention rate increases slightly, but not significantly. With the increase of the amount of volcanic ash admixture, the 2-hour consistency loss rate of masonry mortar increases significantly, shortening the workable time; the amount of volcanic ash admixture added has a certain impact on the 28-day compressive strength, but it is not significant.

[0090] In summary, the mechanical properties of the pozzolanic composite are comparable to those of fly ash. The strength properties do not change significantly with increasing pozzolanic composite content, indicating that the 28-day activity of the pozzolanic composite is essentially equivalent to that of fly ash. However, with increasing pozzolanic composite content, its 2-hour consistency loss rate increases significantly, and its workability decreases. It is recommended that the content of pozzolanic composite in plastering mortar should not exceed 30‰.

[0091] Through the above series of experiments, this invention has verified the feasibility of the prepared pozzolanic composite material in ordinary masonry mortar and ordinary plastering mortar, and has formed a recommended mixing ratio, which can replace some of the active materials such as fly ash, and the effect is good.

[0092] This invention solves the problem of high-value reuse of residues after the treatment of contaminated soil, extends the environmental protection industry chain, achieves zero emissions after cement kiln treatment, protects the environment, and promotes the sustainable development of the ecological environment.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A method for producing an artificial pozzolanic material from contaminated soil using a cement kiln, characterized in that, It comprises the following steps: Mixing the contaminated soil with one of coal gangue, fly ash residue, and red mud, so that the mixture contains ≥12% of aluminum oxide and ≥0.3 of aluminum-silicon ratio, and the mixture is fed into a cement kiln from the kiln tail; Controlling the calcination temperature of the cement kiln to be 650-750℃, and the calcination time to be ≥30 min, to obtain the artificial pozzolan mixed material.

2. The method of preparing an artificial pozzolanaceous blended material from contaminated soil using a cement kiln according to claim 1, wherein, The coal gangue contains SiO2 30.72-48.33%, Al2O3 16.27-24.10%, Fe2O3 2.16-7.34%, CaO 1.5-4.58%, MgO 0.61-1.99%, R2O 0.64-1.18%, SO3 0.46-1.97%, Cl 0.002-0.011%, and LOI 12.83-30.11%. - The coal gangue contains SiO2 30.72-48.33%, Al2O3 16.27-24.10%, Fe2O3 2.16-7.34%, CaO 1.5-4.58%, MgO 0.61-1.99%, R2O 0.64-1.18%, SO3 0.46-1.97%, Cl 0.002-0.011%, and LOI 12.83-30.11%. - 3. The method of preparing an artificial pozzolanaceous blended material from contaminated soil using a cement kiln according to claim 1, wherein, The fly ash slag contains 39.32-57.19% of SiO2, 19.33-29.35% of Al2O3, 5.11-9.93% of Fe2O3, 3.94-15.81% of CaO, 0.9-3.69% of MgO, 0.89-1.57% of R2O, 0.17-3.46% of SO3, 0.011-0.3% of Cl and 1.13-11.13% of LOI. - The fly ash slag contains 39.32-57.19% of SiO2, 19.33-29.35% of Al2O3, 5.11-9.93% of Fe2O3, 3.94-15.81% of CaO, 0.9-3.69% of MgO, 0.89-1.57% of R2O, 0.17-3.46% of SO3, 0.011-0.3% of Cl and 1.13-11.13% of LOI.

4. The method of preparing an artificial pozzolanaceous blended material from contaminated soil using a cement kiln according to claim 1, wherein, The SiO2 content in the red mud is 4.18-46.78%, the Al2O3 content is 3.17-18.26%, the Fe2O3 content is 34.01-58.66%, the CaO content is 0.3-6.84%, the MgO content is 0.12-1.7%, the R2O content is 0.18-1.65%, the Cl content is 0.004-0.083%, and the LOI content is 3.71-13.89%. - The SiO2 content in the red mud is 4.18-46.78%, the Al2O3 content is 3.17-18.26%, the Fe2O3 content is 34.01-58.66%, the CaO content is 0.3-6.84%, the MgO content is 0.12-1.7%, the R2O content is 0.18-1.65%, the Cl content is 0.004-0.

5. The method for preparing an artificial pozzolanaceous blended material by disposing contaminated soil using a cement kiln according to claim 1, characterized in that, The contaminated soil, coal gangue, fly ash, and red mud are ground before calcination.

6. Use of the artificial pozzolanic mixture prepared according to any one of claims 1 to 5, characterized in that, The artificial pozzolan mixed material is applied in masonry mortar or plastering mortar.

7. Use of the artificial pozzolanic mixture material according to claim 6, characterized in that, When the artificial pozzolan mixed material is applied in masonry mortar, the amount of the artificial pozzolan mixed material in the masonry mortar is ≤55‰. When the artificial pozzolan mixed material is applied in plastering mortar, the amount of the artificial pozzolan mixed material in the plastering mortar is ≤30‰.

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