Barium calcium sulphoaluminate cement clinker based on barium hydroxide sulfur fixation and preparation method thereof

Abstract

The invention relates to a barium calcium sulphoaluminate cement clinker based on barium hydroxide sulfur fixation and a preparation method thereof. The barium calcium sulphoaluminate cement clinker is obtained by firing a cement raw material containing sludge, and the cement raw material is prepared from the following components in parts by weight: 30 to 60 parts of dried sulfur-containing sludge, 20 to 50 parts of CaO, 5 to 25 parts of SiO2, 5 to 40 parts of Al2O3, 3 to 18 parts of Fe2O3 and 10 to 25 parts of Ba (OH) 2. The preparation method comprises the following steps: preparing a mixture of cement raw materials in parts by weight to obtain raw material powder; carrying out high-temperature calcination on the raw material powder until all minerals are completely formed, and cooling to room temperature in a quenching manner, so as to obtain the barium calcium sulphoaluminate cement clinker. Compared with the prior art, the method has the advantages that barium hydroxide is applied to the sulfur fixation process for preparing the cement clinker through sludge combustion co-treatment, accumulation of municipal sewage sludge can be reduced, the sulfur fixation rate can be increased, and high-value cyclic utilization of waste resources is promoted.

Description

Technical Field

[0001] This invention belongs to the field of cement preparation technology, and in particular relates to a barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation and its preparation method. Background Technology

[0002] Municipal sewage sludge (MSS) is an unavoidable byproduct of wastewater treatment, typically containing complex pollutants such as organic pollutants, microplastics, heavy metals, and pathogenic microorganisms. Improper treatment can pose a serious threat to the ecological environment. Among various municipal sewage sludge treatment methods, incinerating the sludge as a potential energy source can effectively reduce its volume and degrade most of the organic matter and toxic substances within it. However, the total sulfur content of the sludge is comparable to that of medium-sulfur coal, and organic sulfur typically accounts for over 70% of the total sulfur content. Direct combustion not only easily leads to the emission of toxic gaseous pollutants such as sulfur oxides but also indirectly wastes the sulfur resources in the sludge, reducing the degree of sulfur recycling.

[0003] Sulfoaluminate cement is a series of cements independently developed in my country. It is a hydraulic cementitious material with a series of excellent properties, including early strength, freeze-thaw resistance, corrosion resistance, impermeability, expansion resistance, and low alkali content. It can be widely used in marine engineering, nuclear power engineering, airport construction, emergency repairs, seepage prevention projects, and low-temperature construction projects. Compared to ordinary silicate cement, sulfoaluminate cement has lower production energy consumption, lower raw material costs, and higher profit margins, making it economically valuable. Its application scenarios and demand are rapidly increasing.

[0004] Sulfoaluminate cement clinker requires calcium, silica, aluminum, and sulfur raw materials during its preparation. Therefore, it has significant environmental benefits in the resource utilization of solid waste containing calcium, silicon, aluminum, and sulfur, and is an effective way to achieve high-value-added utilization of solid waste. Thus, using municipal sewage sludge as a raw material for cement clinker preparation is a treatment method that balances efficiency and economy. CN108046628A discloses a sulfoaluminate cement clinker, cement, and its preparation method. The cement clinker is mainly made from a first raw material, which includes electroplating sludge, limestone, and oilfield sludge. By mass percentage, the mineral composition of the cement clinker is: 38-44% C4A3S', 5-32% C2S, 0-34% C3S, and 8-9% C4AF. However, this method does not use municipal sewage sludge, thus failing to achieve the resource utilization of municipal sewage sludge; it also fails to achieve the effective solidification and utilization of sulfur-containing pollutants in the sludge.

[0005] Therefore, developing a new type of cement clinker and cement preparation technology that can make full use of municipal sewage sludge is crucial for further improving the resource utilization rate and environmental benefits of sludge. Summary of the Invention

[0006] The purpose of this invention is to overcome at least one of the defects in the existing technology, namely, the inability to realize the resource utilization of municipal sewage sludge and the inability to effectively solidify and utilize sulfur-containing pollutants in the sludge. The invention provides a barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation and its preparation method, so as to further improve the resource utilization of municipal sewage sludge.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] This invention first provides a barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation, obtained by calcining cement raw meal containing sludge, wherein the cement raw meal comprises the following components in parts by weight:

[0009] The dry sulfur-containing sludge contains 30-60 parts, CaO 20-50 parts, SiO2 5-25 parts, Al2O3 5-40 parts, Fe2O3 3-18 parts, and Ba(OH)2 10-25 parts.

[0010] Furthermore, the solid content of sulfur compounds in the dried sulfur-containing sludge is 3-5 wt%.

[0011] Furthermore, the dried sulfur-containing sludge is prepared by the following method: municipal sewage sludge is dried to constant weight, cooled to room temperature, ground, and sieved for later use.

[0012] Furthermore, the drying temperature is 90-110°C.

[0013] Furthermore, the grinding is carried out in a ball mill.

[0014] Furthermore, the mesh size of the sieve is 100-200 mesh.

[0015] Furthermore, the barium calcium sulfoaluminate cement clinker comprises the following mineral phase components by mass percentage:

[0016] 5-30% barium calcium sulfoaluminate, 15-40% C2S, 30-50% C3S, 5-10% C4AF, and 5-20% C3A.

[0017] Furthermore, the 3-day compressive strength of the barium calcium sulfoaluminate cement clinker is not less than 30 MPa, the 28-day compressive strength is not less than 55 MPa, and the sulfur fixation rate is not less than 70%.

[0018] This invention also provides a method for preparing barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation, the preparation method comprising the following steps:

[0019] The cement raw meal mixture is prepared according to the weight parts, and the residue on an 80μm square hole sieve is less than 10%, thus obtaining raw meal powder.

[0020] The raw meal powder is calcined at high temperature until all minerals are fully formed, and then cooled to room temperature by rapid cooling to obtain barium calcium sulfoaluminate cement clinker.

[0021] Furthermore, the high-temperature calcination temperature is 1250–1350°C, and the high-temperature calcination time is 1–2 hours.

[0022] Furthermore, fluorite is also added to the mixture.

[0023] Furthermore, the amount of fluorite added is 0.6-1.2 wt% of the total mass of cement raw materials.

[0024] The present invention also provides a cement made from barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) In the cement raw materials of the present invention, barium hydroxide is used as a sulfur-fixing agent, which reacts with SO2 converted from sludge burning process during combustion to generate barium sulfate that is not easily decomposed, thereby reducing sulfide emissions; at the same time, the generated barium sulfate will continue to react with other cement raw materials to generate cement clinker, and finally, barium sulfoaluminate cement clinker with excellent performance is successfully obtained.

[0027] (2) This invention uses municipal sewage sludge as the main raw material, maximizing the utilization of municipal sewage sludge in the process of preparing cement clinker. The amount of dried sludge in the raw material can exceed 50%, fully realizing the resource utilization of municipal sewage sludge. In addition, municipal sewage sludge has a high organic content and a high calorific value, which can replace part of the fossil fuel in the process of cement clinker preparation, saving the production cost of cement clinker, realizing the large-scale resource utilization of municipal sewage sludge, and effectively alleviating the resulting ecological and environmental pressure.

[0028] (3) This invention breaks through the limitations of traditional sulfur fixation technology in pre-combustion desulfurization, in-combustion desulfurization, and post-combustion desulfurization. It applies barium hydroxide to the sulfur fixation process in the co-processing of sludge combustion to prepare cement clinker. Sulfur-containing pollutants (such as SO2) generated during sludge combustion can be instantly solidified into barium sulfate with a high decomposition temperature. This barium-containing sulfur fixation product, along with sludge ash and other raw materials, is directly used to prepare cement clinker. This invention not only reduces the accumulation of municipal sewage sludge and lowers the production cost of cement clinker, but also effectively solidifies sulfur, increases the sulfur fixation rate, prevents its emission, and converts sulfur into usable components of cement minerals. Heavy metals in the sludge are also effectively solidified in the mineral structure of the cement clinker prepared by this invention, promoting the high-value recycling of waste resources and possessing significant environmental, social, and economic value.

[0029] (4) The barium sulfoaluminate cement clinker of the present invention has a firing temperature that is 50-100°C lower than that of ordinary silicate cement clinker, which is beneficial to reducing energy consumption and CO2 emissions. In addition, the sulfur fixation rate of the barium sulfoaluminate cement clinker of the present invention is not less than 70% and can be as high as 90%. Its setting performance and strength development law are similar to those of ordinary silicate cement clinker. The clinker has a significant increase in strength in the later stage, the initial setting time of the clinker is longer than 1 hour, and the 28-day compressive strength can exceed 50 MPa, which has excellent compressive strength. Attached Figure Description

[0030] Figure 1 This is the XRD pattern of the dried sludge used in this invention. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0032] The first aspect of this invention provides a barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation, which is obtained by firing cement raw meal containing sludge. The cement raw meal comprises the following components by weight: 30-60 parts of dried sulfur-containing sludge, 20-50 parts of CaO, 5-25 parts of SiO2, 5-40 parts of Al2O3, 3-18 parts of Fe2O3, and 10-25 parts of Ba(OH)2.

[0033] In some specific embodiments, the solid content of sulfur compounds in the dried sulfur-containing sludge is 3-5 wt%.

[0034] In some specific embodiments, fresh sludge is dried to facilitate mixing and processing of the raw materials. The dried sulfur-containing sludge is prepared by drying municipal sewage sludge to constant weight, cooling it to room temperature, grinding it, and sieving it for later use.

[0035] In some more specific embodiments, the drying temperature is 90-110°C.

[0036] In some more specific embodiments, the grinding is carried out in a ball mill.

[0037] In some more specific embodiments, the sieve mesh size is 100-200 mesh.

[0038] In some specific embodiments, the barium calcium sulfoaluminate cement clinker comprises the following mineral phase components by mass percentage: 5-30% barium calcium sulfoaluminate, 15-40% C2S, 30-50% C3S, 5-10% C4AF, and 5-20% C3A.

[0039] The abbreviations correspond to the following substances: calcium oxide (CaO), silicon dioxide (SiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3). C2S represents dicalcium silicate, C3S represents tricalcium silicate, and C4AF represents tetracalcium aluminoferrite. This represents calcium barium sulfoaluminate.

[0040] In some specific embodiments, the 3-day compressive strength of the barium calcium sulfoaluminate cement clinker is not less than 30 MPa, the 28-day compressive strength is not less than 55 MPa, and the sulfur fixation rate is not less than 80%.

[0041] The present invention provides a method for preparing barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation. The preparation method includes the following steps: preparing a mixture of cement raw meal according to the weight parts, and the residue of the powder on an 80μm square hole sieve is less than 10% to obtain raw meal powder; calcining the raw meal powder at high temperature until all minerals are completely formed, and cooling it to room temperature by rapid cooling to obtain barium calcium sulfoaluminate cement clinker.

[0042] In some more specific embodiments, the high-temperature calcination temperature is 1250–1350°C, and the high-temperature calcination time is 1–2 hours.

[0043] In some more specific embodiments, fluorite is also added to the mixture at an amount of 0.6-1.2 wt% of the total mass of the cement raw meal. Adding fluorite as a mineralizer to cement can improve the burnability of the raw meal, such as by disrupting the SiO2 crystal lattice and promoting the formation of dicalcium silicate and tricalcium silicate.

[0044] A third aspect of the present invention provides a cement made from barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation.

[0045] Each of the above embodiments can be implemented individually, or in any combination of two or more. The following detailed description of specific examples will further illustrate these embodiments.

[0046] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0047] In the following embodiments, the dried sulfur-containing sludge was prepared by the following method: municipal sewage sludge (taken from a sewage treatment plant in Shanghai) was dried at 100°C to constant weight, cooled to room temperature, ground in a ball mill, and then passed through a 200-mesh sieve for later use.

[0048] from Figure 1 As can be seen from the data, the main mineral phase in the dried sludge is SiO2. The main chemical components of the dried sulfur-containing sludge, as determined by XRF, are shown in Table 1.

[0049] Table 1. Content of each component (wt%) in dried sulfur-containing sludge

[0050] <![CDATA[Na2O]]> MgO <![CDATA[Al2O3]]> <![CDATA[SiO2]]> <![CDATA[P2O5]]> <![CDATA[SO3]]> <![CDATA[K2O]]> CaO <![CDATA[TiO2]]> <![CDATA[Fe2O3]]> ZnO 0.06 0.47 1.61 9.18 10.1 4.46 1.39 5.57 0.63 6.41 0.37

[0051] The cement clinker in the following examples and comparative examples was prepared according to the following method:

[0052] Prepare the cement raw meal mixture according to the weight proportions in Table 2, and add fluorite at 0.8% of the total raw meal mass. Powder the mixture and sieve it through an 80μm square-hole sieve until the residue is less than 10%, thus obtaining raw meal powder. Calcine the raw meal powder at high temperature using a silicon molybdenum rod electric furnace at 1300℃ for 2 hours until all minerals are fully formed. Then, rapidly cool the calcined cement clinker to room temperature using an indoor fan to obtain barium calcium sulfoaluminate cement clinker.

[0053] Table 2 Cement Raw Meal Batching Table (Unit: portions)

[0054]

[0055]

[0056] The present invention involves crushing and grinding cooled clinker, sieving it through a 200-mesh sieve, and then characterizing the sulfur content in the calcined cement clinker using an X-ray fluorescence spectrometer (XRF), and calculating the sulfur fixation rate using formula (1).

[0057] Y = C S / C×100%(1);

[0058] Where Y is the sulfur fixation rate (%), and C Sis the sulfur content in the clinker, and C is the sulfur content in the sludge.

[0059] In addition, according to the national standard GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the physical properties of cement clinker, such as compressive strength, standard consistency water requirement, setting time, and sulfur fixation rate, were measured. The specific results are shown in Table 3.

[0060] Table 3. Test Performance Results of Cement Clinker

[0061]

[0062] As shown in the table above, the present invention uses dried sulfur-containing sludge and barium hydroxide as the main cement raw materials. The barium calcium sulfoaluminate cement clinker produced through the co-treatment of sludge with barium hydroxide for sulfur fixation all exhibit a sulfur fixation rate of not less than 70%. Due to the rapid hydration rate of barium calcium sulfoaluminate, a higher content in the clinker leads to a shorter setting time and faster strength development. Compared with Comparative Example 1, it can be seen that without barium hydroxide, the sulfur fixation rate of the clinker is only 14%, and the initial and final setting times are extended to 96 min and 126 min, respectively, while the compressive strength also decreases. This comparison indicates that other raw materials also have a certain sulfur fixation capacity, but barium hydroxide's sulfur fixation capacity is more significant. Adding barium hydroxide to the raw materials not only significantly improves the sulfur fixation efficiency but also has a significant effect on improving the workability and mechanical properties of the cement clinker.

[0063] In summary, this invention utilizes municipal sewage sludge to prepare cement clinker. The amount of dried sludge in the raw materials can exceed 50%, fully realizing the resource utilization of municipal sewage sludge and saving on cement clinker production costs. Simultaneously, the sulfur dioxide generated during the cement clinker firing process is absorbed by barium hydroxide to generate barium sulfate, which has a decomposition temperature exceeding 1400℃. This solidifies the sulfur-containing gases from the thermal decomposition of the sludge, ultimately achieving the production of cement clinker containing barium aluminate sulfosulfate.

[0064] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation, obtained by calcining cement raw meal containing sludge, characterized in that, The cement raw meal comprises the following components in parts by weight: The dry sulfur-containing sludge contains 30-60 parts, CaO 20-50 parts, SiO2 5-25 parts, Al2O3 5-40 parts, Fe2O3 3-18 parts, and Ba(OH)2 10-25 parts.

2. The barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation according to claim 1, characterized in that, The solid content of sulfur compounds in the dried sulfur-containing sludge is 3-5 wt%.

3. The barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation according to claim 1, characterized in that, The dried sulfur-containing sludge is prepared by the following method: municipal sewage sludge is dried to constant weight, cooled to room temperature, ground, and sieved for later use.

4. The barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation according to claim 3, characterized in that, The drying temperature is 90-110℃; The grinding is carried out in a ball mill; The sieve mesh size is 100-200 mesh.

5. The barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation according to claim 1, characterized in that, The barium calcium sulfoaluminate cement clinker comprises the following mineral phase components by mass percentage: 5-30% barium calcium sulfoaluminate, 15-40% C2S, 30-50% C3S, 5-10% C4AF, and 5-20% C3A.

6. The barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation according to claim 1, characterized in that, The 3-day compressive strength of the barium calcium sulfoaluminate cement clinker is not less than 30 MPa, the 28-day compressive strength is not less than 55 MPa, and the sulfur fixation rate is not less than 70%.

7. A method for preparing barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: The cement raw meal mixture is prepared according to the weight parts, and the residue on an 80μm square hole sieve is less than 10%, thus obtaining raw meal powder. The raw meal powder is calcined at high temperature until all minerals are fully formed, and then cooled to room temperature by rapid cooling to obtain barium calcium sulfoaluminate cement clinker.

8. The method for preparing barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation according to claim 7, characterized in that, The high-temperature calcination temperature is 1250–1350℃, and the high-temperature calcination time is 1–2 hours.

9. The method for preparing barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation according to claim 7, characterized in that, Fluorite is also added to the mixture; The amount of fluorite added is 0.6-1.2 wt% of the total mass of cement raw materials.

10. A type of cement, characterized in that, It is prepared using the barium calcium sulfoaluminate cement clinker based on barium hydroxide sulfur fixation as described in any one of claims 1-6.

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