Water-resistant magnesium oxysulfate cement composite material for resource utilization of municipal sludge ash and preparation method of water-resistant magnesium oxysulfate cement composite material

Abstract

The invention relates to the technical field of civil engineering materials, and discloses a preparation method of a municipal sludge ash resource utilization water-resistant magnesium oxysulfate cement composite material, which is specifically implemented according to the following steps: step 1, weighing and preparing raw materials, and preparing the raw materials at room temperature; the preparation method comprises the following steps: respectively weighing the following raw materials in percentage by mass: 37.31%-47.94% of light calcined magnesia, 23.83%-23.84% of magnesium sulfate heptahydrate, 5.33%-15.99% of municipal sludge ash, 22.66%-22.68% of mixing water and 0.19%-0.24% of citric acid; the water-resistant magnesium oxysulfate cement composite material for resource utilization of municipal sludge ash can efficiently absorb a large amount of municipal sludge ash, and original waste sludge ash is converted into a material with practical value. Therefore, the land area possibly occupied by the municipal sludge ash is remarkably reduced, the problem of land resource shortage is effectively relieved, and a series of environmental risks caused by stacking of the sludge ash are greatly reduced. Meanwhile, the preparation process is simple, the production cost is low, the energy consumption is reduced, and environmental friendliness is really achieved.

Description

Technical Field

[0001] This invention relates to the field of civil engineering materials technology, specifically to a water-resistant magnesium oxysulfate cement composite material for the resource utilization of urban sludge ash and its preparation method. Background Technology

[0002] With the rapid urbanization in my country, the production of sewage sludge is also continuously increasing. Incineration, as an efficient sludge treatment method, is widely praised for its advantages in sterilization, deodorization, and energy recovery. However, the incineration of urban sewage sludge produces a byproduct—urban sewage ash—which is rich in various heavy metals. Currently, landfill is the main disposal method for urban sewage ash. However, this method allows heavy metals in the sludge ash to easily seep into the soil, posing a potential pollution risk to groundwater and threatening the safety of drinking water and the stability of the ecosystem. Therefore, finding an efficient and safe method for treating urban sewage ash has become an urgent environmental problem to be solved.

[0003] Magnesium oxysulfate cement, as a ternary air-hardening cementitious material, has attracted much attention in the building materials industry due to its advantages such as lightweight and wear-resistant properties, resistance to moisture absorption and efflorescence, and low carbon emissions and energy consumption. However, its poor water resistance has become a key factor limiting its widespread application and promotion. Existing research indicates that adding mineral admixtures is a feasible strategy to enhance the water resistance of magnesium oxysulfate cement. However, based on current experimental and application results, the existing improvement effect has not yet met expectations, and there is still room for improvement.

[0004] Reference 1, "The Influence of Silica Fume on the Mechanical and Water Resistance Properties of Magnesium Oxide Cement" (Jiang Wei, Liang Fenfen, Zhao Feng, et al. Jiangxi Building Materials, 2024, (04): 8-10.), discloses the influence of added silica fume on the mechanical and water resistance properties of magnesium oxysulfate cement. Adding silica fume can improve the mechanical and water resistance properties of magnesium oxysulfate cement. When the silica fume content is between 10% and 20%, the compressive strength and water resistance of magnesium oxysulfate cement gradually increase, but when the silica fume content exceeds 20%, the strength increase and water resistance gradually decrease. Even at the optimal content of 20%, the softening coefficient of magnesium oxysulfate cement only reaches 0.83. Reference 2, "The Influence of Flue Gas Desulfurization Gypsum and Tailings Powder Content on the Properties of Magnesium Oxide Cement" (Zhu Xiaojia, Zhu Qianqian, Zhu Yunxin, Zhu Yujie. Jiangsu Building Materials, 2021, (05): 16-20), discloses the influence of flue gas desulfurization gypsum and tailings powder content on the properties of magnesium oxysulfate cement. Reference 2 shows that the addition of flue gas desulfurization gypsum causes the softening coefficient of magnesium oxysulfate cement to first increase and then decrease, but even at the optimal dosage of 30%, the compressive softening coefficient of magnesium oxysulfate cement is only 0.83. Furthermore, the amount of tailings powder added will reduce the water resistance of magnesium oxysulfate cement regardless of the quantity.

[0005] Reference 3, "Study on the Influence of Mineral Admixtures on the Performance of Magnesium Oxide Sulfate Cement" (Xu Xun, Xu Yuanyuan. Building Science, 2018, 34(07)), discloses the influence of various mineral admixtures on the performance of magnesium oxysulfate cement. From the content disclosed in Reference 3, it can be seen that the addition of fly ash, light calcium carbonate powder, and quartz powder all reduce the water resistance of magnesium oxysulfate cement. Summary of the Invention

[0006] The purpose of this invention is to provide a water-resistant magnesium oxysulfate cement composite material for the resource utilization of urban sewage sludge and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a water-resistant magnesium oxysulfate cement composite material for the resource utilization of urban sewage sludge, specifically implemented according to the following steps: Step 1: Weigh and prepare raw materials Weigh the following raw materials by mass percentage at room temperature: The composition of the raw materials is as follows: lightly calcined magnesium oxide 37.31%-47.94%, magnesium sulfate heptahydrate 23.83%-23.84%, municipal sludge ash 5.33%-15.99%, mixing water 22.66%-22.68%, and citric acid 0.19%-0.24%. The sum of the mass percentages of the above raw materials is 100%. Step 2: Preparation of magnesium sulfate solution Dissolve the weighed magnesium sulfate heptahydrate and citric acid from step 1 in water, and stir rapidly for one minute in a planetary mixer to obtain a uniform magnesium sulfate solution. Step 3: Preparation of water-resistant magnesium oxysulfide cement composite material Pour the weighed lightly calcined magnesium oxide and municipal sludge ash from step 1 into a planetary mixer and stir slowly for 1 minute to ensure that the two are mixed evenly. Then, pour the magnesium sulfate solution prepared in step 2 into the mixer containing the mixed materials at a uniform speed, continue to stir slowly for 2 minutes, and then stir quickly for 2 minutes to finally obtain water-resistant magnesium oxide cement composite material.

[0008] Preferably, the stirring speed in step 2 is 120-150 rpm, the initial slow stirring speed in step 3 is 80-100 rpm, and the subsequent fast stirring speed is increased to 200-250 rpm.

[0009] Preferably, the planetary mixer is equipped with a temperature control system, and the temperature of the mixing drum is maintained at 25±5℃ during the mixing process.

[0010] Another technical problem to be solved by the present invention is to provide a water-resistant magnesium sulfate-oxygen cement composite material for the resource utilization of urban sewage sludge ash. It is prepared according to the above method and is composed of the following raw materials by mass percentage: 37.31%-47.94% light-burned magnesium oxide, 23.83%-23.84% magnesium sulfate heptahydrate, 5.33%-15.99% urban sewage sludge ash, 22.66%-22.68% mixing water, and 0.19%-0.24% citric acid. The sum of the mass percentages of the above raw materials is 100%.

[0011] Preferably, the lightly calcined magnesium oxide is a white powder obtained by calcining magnesite at 700-900℃, and the active magnesium oxide content is ≥65.5%.

[0012] Preferably, the magnesium sulfate heptahydrate is a colorless needle-like crystal with a purity > 99%.

[0013] Preferably, the urban sludge ash is a byproduct of urban domestic sludge incineration, containing various heavy metal components and exhibiting gelling activity; the incineration temperature of the urban sludge ash is controlled at 800-1000℃, and it needs to be dehydrated and dried before incineration.

[0014] Preferably, the mixing water is room temperature tap water; the citric acid is a white crystal with a purity > 99.5%.

[0015] This invention provides a water-resistant magnesium oxide cement composite material for the resource utilization of urban sewage sludge ash and its preparation method. It has the following beneficial effects: 1. The water-resistant magnesium sulfate cement composite material for the resource utilization of urban sewage sludge in this invention can efficiently and massively absorb urban sewage sludge, transforming the originally wasteful sludge into a material with practical value. This not only significantly reduces the land area that urban sewage sludge may occupy, effectively alleviating the problem of land resource scarcity, but also greatly reduces a series of environmental risks caused by sludge stockpiling. At the same time, its preparation process is simple, production costs are low, and energy consumption is reduced, truly achieving environmental friendliness.

[0016] 2. The water-resistant magnesium oxysulfate cement composite material for the resource utilization of urban sewage sludge of this invention has high strength and strong water resistance. The softening coefficient can reach up to 0.91, which is much greater than the industry standard of 0.85. This allows the material to maintain good physical properties in humid environments and can be widely used in various humid environments such as underground engineering and buildings in humid areas. Attached Figure Description

[0017] Figure 1 The diagram shows the comprehensive performance of the water-resistant magnesium oxide cement composite materials prepared in Examples 1-3 of this invention. Figure 2 This is a flowchart of the method steps of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0020] This invention relates to a water-resistant magnesium sulfate-oxygen cement composite material for the resource utilization of municipal sewage sludge ash. The material is composed of the following raw materials by mass percentage: 37.31%-47.94% light-burned magnesium oxide, 23.83%-23.84% magnesium sulfate heptahydrate, 5.33%-15.99% municipal sewage sludge ash, 22.66%-22.68% mixing water, and 0.19%-0.24% citric acid. The sum of the mass percentages of all the above raw materials is 100%.

[0021] Lightly calcined magnesium oxide is a white powdery material produced by calcining magnesium-containing ores such as magnesite at a relatively low temperature of 700-900℃, with an active magnesium oxide content of 65.5%.

[0022] Magnesium sulfate heptahydrate is a colorless needle-like crystal with a purity >99%.

[0023] Urban sludge ash is a byproduct of urban sludge incineration. It contains a variety of heavy metals but has potential gelling activity.

[0024] The mixing water is ordinary tap water at room temperature.

[0025] Citric acid is a white crystalline solid and an important organic acid with a purity >99.5%. The addition of citric acid can induce the formation of high-strength hydration products in magnesium oxysulfate cement, thereby improving its mechanical strength. Therefore, there is an optimal dosage of citric acid. When the dosage of citric acid is too low, the modification effect is not significant. This is because even with a small amount of citric acid added to magnesium oxysulfate cement, a large amount of loosely structured magnesium hydroxide will still be generated in the system. When the dosage of citric acid is too high, excessive citric acid may combine with a large number of ions in the cement, forming excessive complexes or precipitates. These complexes or precipitates may block the pore structure of the cement, affecting the hardening process and the distribution of hydration products.

[0026] The preparation method of the above-mentioned water-resistant magnesium oxide cement composite material for the resource utilization of urban sewage sludge ash is specifically implemented according to the following steps: Step 1: Weigh and prepare raw materials Weigh the following raw materials by mass percentage at room temperature: Lightly calcined magnesium oxide 37.31%-47.94%, magnesium sulfate heptahydrate 23.83%-23.84%, municipal sludge ash 5.33%-15.99%, mixing water 22.66%-22.68%, citric acid 0.19%-0.24%. The sum of the mass percentages of all the above raw materials is 100%. Step 2: Preparation of magnesium sulfate solution Dissolve the weighed magnesium sulfate heptahydrate and citric acid from step 1 in water, and stir in a planetary mixer for one minute to obtain a uniform magnesium sulfate solution. Step 3: Preparation of water-resistant magnesium oxysulfide cement composite material Pour the weighed lightly calcined magnesium oxide and municipal sludge ash from step 1 into a planetary mixer and stir slowly for 1 minute to ensure uniform mixing. Then, pour the magnesium sulfate solution prepared in step 2 into the mixer containing the mixed materials at a uniform speed. Continue stirring slowly for 2 minutes, then stir rapidly for 2 minutes to finally obtain the water-resistant magnesium sulfate-oxygen cement composite material.

[0027] Example 1: Step 1: Under room temperature conditions, weigh out the following components by mass percentage: 47.94% lightly calcined magnesium oxide, 23.83% magnesium sulfate heptahydrate, 5.33% municipal sludge ash, 22.66% mixing water, and 0.24% citric acid. Step 2: Dissolve the weighed magnesium sulfate heptahydrate and citric acid in water and stir in a planetary mixer for one minute to obtain a uniform magnesium sulfate solution. Step 3: Pour the weighed lightly calcined magnesium oxide and municipal sludge ash from Step 1 into a planetary mixer and stir slowly for 1 minute to ensure uniform mixing. Then, pour the magnesium sulfate solution prepared in Step 2 into the mixer containing the mixed materials at a uniform speed. Continue stirring slowly for 2 minutes, then stir rapidly for 2 minutes to finally obtain the water-resistant magnesium sulfate-oxygen cement composite material.

[0028] Example 2: Step 1: Under room temperature conditions, weigh out the following components by mass percentage: 42.63% lightly calcined magnesium oxide, 23.83% magnesium sulfate heptahydrate, 10.66% municipal sludge ash, 22.67% mixing water, and 0.21% citric acid. Step 2: Dissolve the weighed magnesium sulfate heptahydrate and citric acid in water and stir in a planetary mixer for one minute to obtain a uniform magnesium sulfate solution. Step 3: Pour the weighed lightly calcined magnesium oxide and municipal sludge ash from Step 1 into a planetary mixer and stir slowly for 1 minute to ensure uniform mixing. Then, pour the magnesium sulfate solution prepared in Step 2 into the mixer containing the mixed materials at a uniform speed. Continue stirring slowly for 2 minutes, then stir rapidly for 2 minutes to finally obtain the water-resistant magnesium sulfate-oxygen cement composite material.

[0029] Example 3: Step 1: Under room temperature conditions, weigh out the following components by mass percentage: 37.31% lightly calcined magnesium oxide, 23.84% magnesium sulfate heptahydrate, 15.99% municipal sludge ash, 22.68% mixing water, and 0.19% citric acid. Step 2: Dissolve the weighed magnesium sulfate heptahydrate and citric acid in water and stir in a planetary mixer for one minute to obtain a uniform magnesium sulfate solution. Step 3: Pour the weighed lightly calcined magnesium oxide and municipal sludge ash from Step 1 into a planetary mixer and stir slowly for 1 minute to ensure uniform mixing. Then, pour the magnesium sulfate solution prepared in Step 2 into the mixer containing the mixed materials at a uniform speed. Continue stirring slowly for 2 minutes, then stir rapidly for 2 minutes to finally obtain the water-resistant magnesium sulfate-oxygen cement composite material.

[0030] The comprehensive properties of the water-resistant magnesium oxysulfate cement composites prepared in Examples 1-3 are shown in Table 1. As can be seen from the table, the 3-day compressive strength of Example 1 is 72.9 MPa, the 7-day compressive strength is 79.5 MPa, and the 28-day compressive strength reaches 87.6 MPa. Examples 2 and 3 have different proportions than Example 1, but the strength test data shows that Examples 2 and 3 still have relatively high strengths. Furthermore, both examples exhibit better water resistance and can absorb more municipal sludge ash.

[0031] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0032] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a water-resistant magnesium oxysulfate cement composite material for the resource utilization of urban sewage sludge, specifically implemented according to the following steps: Step 1: Weigh and prepare raw materials Weigh the following raw materials by mass percentage at room temperature: The composition of the raw materials is as follows: lightly calcined magnesium oxide 37.31%-47.94%, magnesium sulfate heptahydrate 23.83%-23.84%, municipal sludge ash 5.33%-15.99%, mixing water 22.66%-22.68%, and citric acid 0.19%-0.24%. The sum of the mass percentages of the above raw materials is 100%. Step 2: Preparation of magnesium sulfate solution Dissolve the weighed magnesium sulfate heptahydrate and citric acid from step 1 in water, and stir rapidly for one minute in a planetary mixer to obtain a uniform magnesium sulfate solution. Step 3: Preparation of water-resistant magnesium oxysulfide cement composite material Pour the weighed lightly calcined magnesium oxide and municipal sludge ash from step 1 into a planetary mixer and stir slowly for 1 minute to ensure that the two are mixed evenly. Then, pour the magnesium sulfate solution prepared in step 2 into the mixer containing the mixed materials at a uniform speed, continue to stir slowly for 2 minutes, and then stir quickly for 2 minutes to finally obtain water-resistant magnesium oxide cement composite material.

2. The preparation method of a water-resistant magnesium oxide cement composite material for the resource utilization of urban sewage sludge as described in claim 1, characterized in that: In step 2, the stirring speed is 120-150 rpm. In step 3, the initial slow stirring speed is 80-100 rpm, and the subsequent fast stirring speed is increased to 200-250 rpm.

3. The preparation method of a water-resistant magnesium oxide cement composite material for the resource utilization of urban sewage sludge ash according to claim 1, characterized in that: The planetary mixer is equipped with a temperature control system, and the temperature of the mixing drum is maintained at 25±5℃ during the mixing process.

4. A water-resistant magnesium oxide cement composite material for the resource utilization of urban sewage sludge ash, characterized in that, The preparation according to any one of claims 1-3 comprises the following raw materials by mass percentage: 37.31%-47.94% light-burned magnesium oxide, 23.83%-23.84% magnesium sulfate heptahydrate, 5.33%-15.99% municipal sludge ash, 22.66%-22.68% mixing water, and 0.19%-0.24% citric acid, wherein the sum of the mass percentages of the above raw materials is 100%.

5. The water-resistant magnesium oxide cement composite material for the resource utilization of urban sewage sludge ash according to claim 4, characterized in that: The lightly calcined magnesium oxide is a white powder obtained by calcining magnesite at 700-900℃, with an active magnesium oxide content of ≥65.5%.

6. The water-resistant magnesium oxide cement composite material for the resource utilization of urban sewage sludge ash according to claim 4, characterized in that: The magnesium sulfate heptahydrate is a colorless needle-like crystal with a purity >99%.

7. The water-resistant magnesium oxide cement composite material for the resource utilization of urban sewage sludge ash according to claim 4, characterized in that: The urban sludge ash is a byproduct of urban domestic sewage sludge incineration, containing various heavy metal components and exhibiting gelling activity; the incineration temperature of the urban sludge ash is controlled at 800-1000℃, and it needs to be dehydrated and dried before incineration.

8. The water-resistant magnesium oxide cement composite material for the resource utilization of urban sewage sludge ash according to claim 4, characterized in that: The mixing water is room temperature tap water; the citric acid is a white crystal with a purity >99.5%.

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