Phosphoric acid modified zeolite method based on pH feedback control and application of phosphoric acid modified zeolite in cement-based material

Abstract

The invention discloses a method for modifying zeolite through phosphoric acid based on pH feedback control and application of the zeolite in cement-based materials, and belongs to the technical field of building materials. The method comprises the following steps: S1, putting zeolite into a phosphoric acid solution for soaking reaction; s2, monitoring the pH value of a reaction system in real time; and S3, stopping the reaction when the change amount of the pH value in at least 30 minutes is less than 0.05, so as to obtain the phosphoric acid modified zeolite. According to the method, a traditional fixed time mode is abandoned, and precise control over the zeolite dealumination and pore structure optimization process is achieved. The specific surface area and the pore volume of the zeolite powder treated by the method disclosed by the invention are remarkably optimized, and when the zeolite powder serving as an auxiliary cementing material is doped into a cement-based material, the rheological property and the long-term hydration property of cement paste can be synergistically improved, which shows that the yield stress and the plastic viscosity are greatly reduced, and the shear thickening phenomenon under high doping amount is eliminated; meanwhile, the later-stage hydration promotion degree is improved, and the accumulated heat release is increased.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a method for modifying zeolite with phosphoric acid based on pH feedback control and its application in cement-based materials. Background Technology

[0002] Natural zeolite (especially clinoptilolite) has attracted widespread attention in cement-based materials as a low-cost and widely available auxiliary cementitious material. It not only possesses a certain degree of pozzolanic activity but also plays an internal curing role, thereby improving the durability of the material.

[0003] However, the high porosity and specific surface area of ​​natural zeolite give it a strong water absorption capacity. When incorporated into cement-based materials, it absorbs a large amount of mixing water, leading to a reduction in free water available for lubricating solid particles. This, in turn, causes a sharp increase in the yield stress and plastic viscosity of the freshly mixed slurry, resulting in a significant decrease in workability. This defect severely restricts the application of natural zeolite in practical engineering, especially in applications requiring high fluidity and pumpability.

[0004] To address this issue, existing technologies have proposed methods such as calcination pretreatment. However, the calcination process easily leads to the collapse of the zeolite structure, significantly reducing its pozzolanic activity. Some studies have also employed acid treatment to enhance zeolite activity, but these studies primarily focus on using hydrochloric acid, nitric acid, and acetic acid to increase chemical reactivity. In-depth exploration and effective solutions are still lacking regarding how acid treatment systematically regulates the physical structure (especially the pore structure) of zeolite, and the impact of such structural changes on the rheological properties of cement-based materials.

[0005] Therefore, developing a method that can significantly improve the rheological properties of cement-based materials after incorporation of zeolite while maintaining its activity has become a key problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention provides a method for modifying zeolite with phosphoric acid based on pH feedback control and its application in cement-based materials, aiming to solve the problems of the prior art.

[0007] The main objective of this invention is to provide a method for modifying zeolite with phosphoric acid based on pH feedback control. This method can monitor and dynamically regulate the reaction process in real time, thereby achieving precise control of zeolite phosphoric acid treatment. It can effectively improve the rheological properties of natural zeolite in cement-based materials, while maintaining or even enhancing its long-term hydration activity.

[0008] In addition, the present invention also provides a phosphoric acid modified zeolite prepared by the above method and its application in cement-based materials. The specific surface area of ​​the phosphoric acid modified zeolite is increased by about 25% compared with that of natural zeolite, the pore volume in the pore size range of 2-20 nm is significantly increased, and the total pore volume is increased by more than 30%.

[0009] To achieve the above objectives, this invention provides a method for modifying zeolite with phosphoric acid based on pH feedback control, comprising the following steps: S1. Soak the zeolite in a phosphoric acid solution to react; S2. Monitor the pH value of the reaction system in real time; S3. Stop the reaction when the pH change is less than 0.05 over at least 30 minutes to obtain phosphoric acid modified zeolite.

[0010] Specifically, the zeolite described in this invention is natural clinoptilolite.

[0011] Specifically, the preferred concentration of the phosphoric acid solution described in this invention is 0.5 mol / L.

[0012] This invention dynamically determines the reaction endpoint by real-time monitoring of the pH value of the reaction system: when the rate of change of pH value over time approaches zero, that is, the amount of pH change (ΔpH) per unit time (at least 30 minutes) is less than the set threshold (0.05), it is determined that the main reaction of zeolite dealumination and pore structure optimization has been basically completed. After the reaction endpoint is reached and the processing is completed, the performance-optimized phosphoric acid modified zeolite powder of this invention is obtained.

[0013] The present invention also provides phosphoric acid modified zeolite prepared by the above method.

[0014] Specifically, the specific surface area of ​​the phosphoric acid modified zeolite described in this invention is increased by about 25% compared with that of natural zeolite, and the total pore volume is increased by more than 30%.

[0015] Specifically, the pore volume of the phosphoric acid modified zeolite described in this invention is significantly increased in the pore size range of 2-20 nm.

[0016] The present invention also provides the application of the above-mentioned phosphate-modified zeolite in cement-based materials.

[0017] This invention provides a cement-based material as one of the applications described above, wherein the cement-based material incorporates the phosphate-modified zeolite described in this invention into cement.

[0018] Specifically, the amount of phosphate-modified zeolite incorporated in this invention is 10-40% of the volume of cement.

[0019] The beneficial effects of this invention are as follows: 1. Precise and controllable, consistent quality This invention is the first to use pH value as a real-time monitoring indicator of the reaction process and as a criterion for determining the endpoint. The reaction of phosphoric acid with zeolite (especially the dealumination process) continuously consumes H₂. + Ions cause the pH value of the system to rise. When the reaction is nearing completion, the rate of pH change decreases. By monitoring this change in real time, the optimal processing point for each batch of materials can be accurately captured, effectively overcoming the problem of insufficient or over-processing caused by differences in raw materials. This ensures that the modified zeolite products have high stability and repeatability in key properties such as pore structure and specific surface area.

[0020] 2. Improve efficiency and save costs Traditional fixed-time processes often set excessively long safety processing times to accommodate the "slowest reaction" batches. This invention, based on the principle of "stopping once the reaction is complete," avoids ineffective energy and time consumption, significantly improves production efficiency, and reduces overall processing costs.

[0021] 3. Synergistically improves rheological properties and hydration activity This invention achieves optimized control of the pore structure and surface properties of zeolite through modification with phosphoric acid at a specific concentration. When the treated zeolite powder is incorporated into cement-based materials, it can not only significantly reduce the yield stress of the slurry (up to 80.6%) and plastic viscosity (up to 50%), but also provide more nucleation sites in the later stages, promote hydration, and improve the degree of hydration and the cumulative heat release.

[0022] 4. Eliminate unfavorable rheological phenomena Zeolite treated by the method of this invention can effectively suppress or eliminate the shear thickening phenomenon that easily occurs in high-dosage zeolite cement slurry, making the slurry rheological behavior more stable and facilitating construction and pouring.

[0023] 5. The mechanism is clear and the effect is controllable. This invention clearly reveals that 0.5 mol / L of phosphoric acid is an optimal concentration window. At this concentration, phosphoric acid can effectively achieve dealumination, expand pore size (especially mesopores of 2-20 nm), and remove impurities, thereby significantly increasing specific surface area and pore volume, while avoiding severe collapse of the zeolite framework structure. Concentrations that are too low (e.g., <0.4 mol / L) have little effect, while concentrations that are too high (e.g., 1.0 mol / L) will lead to structural damage, which is detrimental to performance improvement.

[0024] 6. The process is simple and the cost is low. The processing method described in this invention is simple, requires no complex equipment, uses inexpensive phosphoric acid, and is easy to scale up for industrial production, thus opening up new avenues for the high-value utilization of natural zeolite. Attached Figure Description

[0025] Figure 1This is a flowchart of the method of the present invention.

[0026] Figure 2 The diagram shows the distribution and cumulative distribution of pore volume of zeolite under different treatment conditions.

[0027] Figure 3 Yield stress diagrams of cement materials prepared from zeolite in different treatment states under different volume fractions of water-reducing agent and different cement substitution rates; a: 10% volume substitution; b: 20% volume substitution; c: 30% volume substitution; d: 40% volume substitution.

[0028] Figure 4 Plastic viscosity diagrams of cement materials prepared from zeolite in different treatment states with 0.5% volume fraction water-reducing agent and different volume fraction cement substitution rates.

[0029] Figure 5 Exothermic curves of cement materials with different volume fractions prepared from zeolite under different treatment states; a: Comparative Example 3 (natural zeolite); b: Comparative Example 2 (pre-wetted zeolite); c: Example 1 (0.5 mol / L phosphoric acid treated zeolite); d: Comparative Example 1 (1 mol / L phosphoric acid treated zeolite).

[0030] Figure 6 Cumulative exothermic curves of cement materials with different volume fractions prepared from zeolite under different treatment states; a: Comparative Example 3 (natural zeolite); b: Comparative Example 2 (pre-wetted zeolite); c: Example 1 (0.5 mol / L phosphoric acid treated zeolite); d: Comparative Example 1 (1 mol / L phosphoric acid treated zeolite). Detailed Implementation

[0031] The present invention will now be described in detail with reference to specific embodiments.

[0032] As used herein, the terms “prepared from” and “comprising” are synonymous. The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0033] When a mass, concentration, temperature, time, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, it should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, the range 1-50 should be understood to include any number, combination of numbers, or subranges selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50, as well as all decimal values ​​between the integers mentioned above, such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, and 1.9. Regarding subranges, specifically consider "nested subranges" extending from any endpoint of the range. For example, nested sub-ranges of the exemplary range 1-50 may include 1-10, 1-20, 1-30 and 1-40 in one direction, or 50-40, 50-30, 50-20 and 50-10 in another direction.

[0034] The singular form includes the plural objects of discussion unless the context clearly indicates otherwise. "Optional" or "any one" means that the matter or event described thereafter may or may not occur, and the description includes both the possibility that the event occurs and the possibility that the event does not occur.

[0035] Approximate terms used in the specification and claims to modify quantities indicate that the invention is not limited to that specific quantity, but also includes acceptable modifications close to that quantity that do not alter the relevant essential function. Correspondingly, the use of "about," "approximately," etc., to modify a numerical value means that the invention is not limited to that precise value. In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In this application's specification and claims, scope definitions can be combined and / or interchanged, unless otherwise stated, these scopes include all subscopes contained therein.

[0036] Furthermore, the indefinite articles “a” and “an” preceding the elements or components of this invention do not impose any limitation on the quantity requirement (i.e., the number of times) of the elements or components. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers to the singular form.

[0037] Figure 1The flowchart of this invention shows the core process of pre-treating natural clinoptilolite (crushing and grinding) followed by treatment with a phosphoric acid solution. This invention successfully optimizes the pore structure of zeolite by precisely controlling the phosphoric acid solution concentration (0.5 mol / L is the ideal modification condition, while 1.0 mol / L easily leads to structural damage), increasing the pore volume by approximately 31% and the specific surface area by approximately 25%, resulting in a phosphoric acid-modified zeolite product with improved performance. Further rheological property verification showed that the modified product reduced the yield stress of freshly mixed slurry by at least 80.6% and the plastic viscosity by at least 50%; in hydration heat analysis, the degree of hydration in the later stages was significantly enhanced. The high-performance, multifunctional phosphoric acid-modified zeolite obtained by this invention exhibits significant effects as a cement additive in cement-based materials.

[0038] The present invention will be further described below with reference to specific embodiments. Example

[0039] This embodiment prepares a phosphoric acid-modified zeolite, and the specific steps are as follows: S1. The zeolite is immersed in a 0.5 mol / L phosphoric acid solution for reaction (the liquid-solid ratio is controlled appropriately to ensure that the zeolite is completely submerged); the zeolite is natural clinoptilolite ore from Tangshan, Hebei, China, and is mechanically crushed and ground to a fineness similar to that of cement; the reaction temperature is room temperature (25℃).

[0040] S2. Monitor the pH value of the reaction system in real time; The reaction was stopped when the pH change (ΔpH) was less than 0.05 over 30 minutes, yielding the phosphoric acid-modified zeolite of this embodiment.

[0041] Comparative Example 1: Comparative Example 1 prepared a phosphoric acid-modified zeolite, and the specific steps are as follows: S1. The zeolite is immersed in a 1 mol / L phosphoric acid solution for reaction (the liquid-solid ratio is controlled appropriately to ensure that the zeolite is completely submerged); the zeolite is natural clinoptilolite ore from Tangshan, Hebei, China, and is mechanically crushed and ground to a fineness similar to that of cement; the reaction temperature is room temperature (25°C).

[0042] S2. Monitor the pH value of the reaction system in real time; The reaction was stopped when the pH change (ΔpH) was less than 0.05 over 30 minutes, yielding the phosphoric acid-modified zeolite of this comparative example.

[0043] Comparative Example 2: Comparative Example 2 prepared a pre-wetted zeolite, and the specific steps are as follows: S1. Soak the zeolite in deionized water (the liquid-to-solid ratio is controlled appropriately to ensure that the zeolite is completely submerged); the zeolite is a natural clinoptilolite ore from Tangshan, Hebei, China, which is mechanically crushed and ground to a fineness similar to that of cement; the temperature is room temperature (25°C).

[0044] S2. The pre-wetted zeolite of this comparative example was obtained after complete wetting.

[0045] Comparative Example 3: Comparative Example 3 uses untreated zeolite, which comes from natural clinoptilolite ore from Tangshan, Hebei, China, and is mechanically crushed and ground to a fineness similar to that of cement.

[0046] The phosphoric acid treatment concentrations for the examples and comparative examples are shown in Table 1 below: Table 1

[0047] The performance of the zeolites described in Example 1 and Comparative Examples 1 and 3 was tested, and the results are as follows: Figure 2 As shown, compared with Comparative Examples 1 and 3, the zeolite treated with 0.5 mol / L phosphoric acid in Example 1 showed a significant increase in cumulative pore volume, with a distinct peak in the pore size range of 2-20 nm, indicating a substantial increase in mesopore volume. Furthermore, BET surface area testing showed that the specific surface area of ​​Example 1 increased from 20.64 m² / m³. 2 / g increased to 25.72m 2 / g.

[0048] The zeolite described in Example 1 and Comparative Examples 1-2 was used to replace cement at volume fractions of 10%, 20%, 30%, and 40%, respectively, and mixed with water and polycarboxylate superplasticizers at volume fractions of 0.3%, 0.5%, and 0.7% to prepare a series of cement pastes with a water-cement ratio of 0.5. The rheological properties of the above cement pastes were tested using an RST-CC coaxial cylindrical rheometer to measure their rheological parameters. The results are as follows: Figure 3-4 As shown, compared with other slurries incorporating pre-wetted zeolite, when replacing cement at a volume fraction of 20%, the yield stress of the phosphate-modified zeolite described in Example 1 decreased from 125.1 Pa to 122.7 Pa. Figure 3 The plastic viscosity also decreased from 0.34 Pa·s to 0.30 Pa·s. Figure 4 Meanwhile, at high dosages (30%, 40%) and high water-reducing agent dosages (0.7%), shear thickening was effectively eliminated.

[0049] The zeolite described in Example 1 and Comparative Examples 1-3 was used to replace cement at volume fractions of 10%, 20%, 30%, and 40%, respectively, to prepare a series of cement pastes with a water-cement ratio of 0.5. The heat of hydration of the above cement pastes was tested using a TAMAir isothermal calorimeter, and the hydration exothermic curves over 72 hours were measured. The results are as follows: Figure 5-6 As shown, the hydration acceleration peak of the slurry with 0.5 mol / L phosphoric acid modified zeolite was delayed, but the hydration exothermic rate after 30 hours was higher. Figure 5 ) and the cumulative heat release over 48 hours ( Figure 6 All of them exceeded the benchmark cement slurry without zeolite, proving that it has good long-term hydration activity.

[0050] It is understood that the above specific embodiments are all further illustrations of the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, all other modifications and refinements obtained without creative effort are within the scope of protection of the present invention.

Claims

1. A method for modifying zeolite with phosphoric acid based on pH feedback control, characterized in that, Includes the following steps: S1. Soak the zeolite in a phosphoric acid solution to react; S2. Monitor the pH value of the reaction system in real time; S3. Stop the reaction when the pH change is less than 0.05 over at least 30 minutes to obtain phosphoric acid modified zeolite.

2. The method for modifying zeolite with phosphoric acid based on pH feedback control according to claim 1, characterized in that, The zeolite is natural clinoptilolite.

3. The method for modifying zeolite with phosphoric acid based on pH feedback control according to claim 1, characterized in that, The concentration of the phosphoric acid solution is 0.5 mol / L.

4. A phosphoric acid-modified zeolite prepared by the method according to any one of claims 1-3.

5. The application of the phosphoric acid modified zeolite according to claim 4 in cement-based materials.

6. A cement-based material, characterized in that, The phosphate-modified zeolite of claim 4 is incorporated into cement.

7. The cement-based material according to claim 6, characterized in that, The amount of phosphate-modified zeolite added is 10-40% of the volume of cement.

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