Metakaolin-based geopolymer material with function of slowly releasing alkali or acid and preparation method of metakaolin-based geopolymer material

Abstract

The invention discloses a metakaolin-based geopolymer material with an alkali or acid slow-release function and a preparation method, the metakaolin-based geopolymer material is prepared from the following raw materials in parts by weight: 100 parts of metakaolin, 0-27 parts of sodium metasilicate nonahydrate, an activator and 81-110 parts of water, the activator is an alkali activator or an acid activator, the alkali activator is 9-27 parts of sodium metasilicate nonahydrate, the acid activator is 8-12 parts of sodium metasilicate nonahydrate, and the water is 8-12 parts of sodium metasilicate nonahydrate. The acid activator is 12-36 parts of phosphoric acid solution with the concentration of 75%. Therefore, the acid-activated metakaolin geopolymer and the alkali-activated metakaolin geopolymer both show dual functions of slow release and buffering, and a geopolymer skeleton can gradually release acidic or alkaline species in water and continuously provide neutralizing ions, so that the stability of the pH of a system is maintained on a longer time scale.

Description

Technical Field

[0001] This invention relates to the field of geopolymer materials, and in particular to metakaolin-based geopolymer materials with slow-release alkali or acid functions. Background Technology

[0002] In recent years, solid acids and bases have shown broad application prospects in the fields of environmental protection, catalysis engineering and building materials due to their unique slow-release function, stability and controllable reaction characteristics in the field of modern materials science and engineering.

[0003] Geopolymers (hereinafter referred to as geopolymers) are inorganic polymeric materials based on silicon-aluminum compounds. They not only possess excellent mechanical properties and durability, but also, due to their unique porous structure and chemical activity, serve as an ideal matrix for solid alkali or acid slow-release carriers.

[0004] Metakaolin is widely recognized as the preferred material for preparing geopolymers, primarily because it is anhydrous aluminum silicate formed by dehydrating kaolin at high temperatures of 650–800 °C. This results in a metastable state, and the metakaolin particles themselves exhibit extremely high reactivity, with their surfaces almost entirely composed of potential "reaction sites." Metakaolin-based geopolymers with slow-release alkali or acid functions possess a highly cross-linked silica-alumina framework structure and tunable porosity. Their main advantages as solid alkali or acid matrices lie in their resistance to degradation, strong ion exchange capacity, tunable pore structure, and high specific surface area.

[0005] In the preparation of metakaolin-based geopolymers with slow-release alkali or acid functions, if the composition, structure, and release behavior of the acid and alkali materials can be precisely and quantitatively controlled, and the acid and alkali release effect over time can be quantified, the uniformity and efficiency problems of geopolymers in the acid and alkali activation process can be solved. Thus, by introducing a slow-release mechanism of solid acid and alkali, the application prospects of geopolymers in environmental remediation, fiber degradation, and functional materials can be significantly expanded, providing important support for achieving efficient resource utilization and sustainable environmental development. Summary of the Invention

[0006] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a metakaolin-based polymer material with slow-release alkali or acid functions.

[0007] According to an embodiment of the present invention, a metakaolin-based polymer material with slow-release alkali or acid functions comprises the following raw materials in parts by weight: 100 parts metakaolin, 0-27 parts sodium metasilicate nonahydrate, activator, and 81-110 parts water, wherein the activator is an alkali activator or an acid activator, the alkali activator is 9-27 parts sodium metasilicate nonahydrate, and the acid activator is 12-36 parts of a 75% phosphoric acid solution.

[0008] Specifically, the median particle size of the metakaolin is 3.03 μm, and the purity of the metakaolin is 98%.

[0009] This invention utilizes the combination of an alkaline activator and metakaolin to create a geopolymer with numerous alkaline sites. Under the influence of the alkaline activator, the silicon-oxygen tetrahedra (SiO4) and aluminum-oxygen tetrahedra (AlO4) in the metakaolin are partially depolymerized, forming silicate and aluminate ions. These depolymerized ions repolymerize under alkaline conditions, forming a three-dimensional geopolymer network structure with Si-O-Si and Si-O-Al as the main framework. The aluminum-oxygen tetrahedra in the network introduce negative charges, which balance the charges with cations (such as Na+ and K+), forming alkaline active sites.

[0010] The combination of acid activator and metakaolin results in a large number of acidic sites in the prepared geopolymer. Among them, phosphate (PO43-) coordinates with metal cations (such as Ca2+ and Al3+) in metakaolin in the framework structure to form acidic active sites.

[0011] Basic or acidic sites can adsorb specific ions through electrostatic interactions to achieve regulatory functions. Furthermore, acidic sites can act as proton donors, while basic sites can act as proton acceptors, providing or capturing H+ in catalytic reactions, thereby accelerating the reaction.

[0012] According to a second aspect of the present invention, a method for preparing a metakaolin-based polymer material with slow-release alkali or acid functions includes the following steps: Step 1: Weigh out the required concentration of alkaline or acidic activator and water, and fully dissolve them in water to prepare an activator solution of a specific concentration for later use; Step 2: Weigh the metakaolin and activator solution according to the water-cement ratio. Place the solution in a mixing pot first, then add the metakaolin and stir for 3-4 minutes until uniform. Step 3: Pour the mixed slurry into the mold, place it in a curing chamber at 60 degrees Celsius for wet curing for 48 hours, and then demold.

[0013] Beneficial effects

[0014] This invention introduces acidic or basic activators in varying amounts to form a multi-basic or acidic site structure with sustained-release function. This effectively regulates the release rate of the material's basic or acidic components, meeting the sustained-release performance requirements of different application scenarios. The resulting geopolymer not only exhibits excellent environmental adaptability but also maintains structural stability and long-term performance while slowly releasing acidic or basic active components.

[0015] Compared to traditional molecular buffers such as phosphates, acetates, or Tris, which rely on conjugate acid-base pairs in solution to resist pH fluctuations, their buffering capacity is often consumed in a short time and requires frequent replenishment. In contrast, the acid-activated and alkali-activated metakaolin geopolymers of this invention exhibit both slow-release and buffering functions. The geopolymer framework can gradually release acidic or basic species in water, continuously providing neutralizing ions, thereby maintaining the stability of the system's pH over a longer timescale.

[0016] This solid-state, long-lasting buffering mechanism can be modulated by the type of activator (acidic or basic), material composition, and pore structure, allowing for the designability of the buffering range and release kinetics. Furthermore, the geopolymer buffer of this invention is suitable for laboratory systems and can also be extended to complex environments such as water treatment, soil remediation, and metal corrosion inhibition. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the sustained-release capacity of alkali-activated geopolymer according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the sustained-release capacity of acid-activated geopolymer according to an embodiment of the present invention. Detailed Implementation

[0018] The embodiments of the present invention are described in detail below.

[0019] Example 1

[0020] This embodiment describes the preparation of a metakaolin polymer with an alkali activator, which consists of the following components and their weight parts: 4 parts metakaolin, 0.36 parts sodium metasilicate nonahydrate, and 4.4 parts water.

[0021] After mixing and stirring the above materials and letting them stand for 48 hours, the experimental steps for obtaining metakaolin-based polymer materials with alkali activator dosage, slow-release alkali or acid release functions are as follows: S1. Take 1g of 9% alkali activator mixed with metakaolin polymer and 50ml of water.

[0022] S2. Place the alkali activator-added metakaolin polymer in a beaker and add 50ml of water.

[0023] S3. Place the beaker on a magnetic stirrer, add the stir bar, and stir at an appropriate speed for 1 hour to ensure thorough mixing.

[0024] S4. After stirring, let the solution stand until it separates into layers. Take the clear upper layer and place it on a pH meter to measure the pH value.

[0025] Example 2

[0026] This embodiment describes the preparation of a metakaolin polymer with an alkali activator, which consists of the following components and their weight parts: 4 parts metakaolin, 0.56 parts sodium metasilicate nonahydrate, and 4.4 parts water.

[0027] After mixing and stirring the above materials and letting them stand for 48 hours, the experimental steps for obtaining metakaolin-based polymer materials with alkali activator dosage, slow-release alkali or acid release functions are as follows: S1. Take 1g of 13.5% alkaline activator mixed with metakaolin polymer and 50ml of water.

[0028] S2. Place the alkali activator-added metakaolin polymer in a beaker and add 50ml of water.

[0029] S3. Place the beaker on a magnetic stirrer, add the stir bar, and stir at an appropriate speed for 1 hour to ensure thorough mixing.

[0030] S4. After stirring, let the solution stand until it separates into layers. Take the clear upper layer and place it on a pH meter to measure the pH value.

[0031] Example 3

[0032] This embodiment describes the preparation of a metakaolin polymer with an alkali activator, which consists of the following components and their weight parts: 4 parts metakaolin, 0.72 parts sodium metasilicate nonahydrate, and 4.4 parts water.

[0033] After mixing and stirring the above materials and letting them stand for 48 hours, the experimental steps for obtaining metakaolin-based polymer materials with alkali activator dosage, slow-release alkali or acid release functions are as follows: S1. Take 1g of 18% alkaline activator mixed with metakaolin polymer and 50ml of water.

[0034] S2. Place the alkali activator-added metakaolin polymer in a beaker and add 50ml of water.

[0035] S3. Place the beaker on a magnetic stirrer, add the stir bar, and stir at an appropriate speed for 1 hour to ensure thorough mixing.

[0036] S4. After stirring, let the solution stand until it separates into layers. Take the clear upper layer and place it on a pH meter to measure the pH value.

[0037] Example 4

[0038] This embodiment describes the preparation of a metakaolin polymer with an alkali activator, which consists of the following components and their weight parts: 4 parts metakaolin, 0.9 parts sodium metasilicate nonahydrate, and 4.4 parts water.

[0039] After mixing and stirring the above materials and letting them stand for 48 hours, the experimental steps for obtaining metakaolin-based polymer materials with alkali activator dosage, slow-release alkali or acid release functions are as follows: S1. Take 1g of 22.5% alkaline activator mixed with metakaolin polymer and 50ml of water.

[0040] S2. Place the alkali activator-added metakaolin polymer in a beaker and add 50ml of water.

[0041] S3. Place the beaker on a magnetic stirrer, add the stir bar, and stir at an appropriate speed for 1 hour to ensure thorough mixing.

[0042] S4. After stirring, let the solution stand until it separates into layers. Take the clear upper layer and place it on a pH meter to measure the pH value.

[0043] Example 5

[0044] This embodiment describes the preparation of a metakaolin polymer with an alkali activator, which consists of the following components and their weight parts: 4 parts metakaolin, 1.08 parts sodium metasilicate nonahydrate, and 4.4 parts water.

[0045] After mixing and stirring the above materials and letting them stand for 48 hours, the experimental steps for obtaining metakaolin-based polymer materials with alkali activator dosage, slow-release alkali or acid release functions are as follows: S1. Take 1g of 27% alkaline activator mixed with metakaolin polymer and 50ml of water.

[0046] S2. Place the alkali activator-added metakaolin polymer in a beaker and add 50ml of water.

[0047] S3. Place the beaker on a magnetic stirrer, add the stir bar, and stir at an appropriate speed for 1 hour to ensure thorough mixing.

[0048] S4. After stirring, let the solution stand until it separates into layers. Take the clear upper layer and place it on a pH meter to measure the pH value.

[0049] Table 1. pH test results of kaolin polymers with different alkali activator dosages. .

[0050] Example 6

[0051] This embodiment describes the preparation of a metakaolin polymer with an acid activator, which consists of the following components and their weight parts: 4 parts metakaolin, 0.48 parts phosphoric acid, and 4.28 parts water.

[0052] After mixing and stirring the above materials and letting them stand for 48 hours, the experimental steps for obtaining metakaolin-based polymer materials with acid activator dosage, slow-release alkali or acid release functions are as follows: S1, Take 1g of 12% acid activator and add it to The amount of material is concentrated in kaolin soil, and 50ml of water is added.

[0053] S2. The acid activator dosage is too high. Place the soil aggregate in a beaker and add 50ml of water.

[0054] S3. Place the beaker on a magnetic stirrer, add the stir bar, and stir at an appropriate speed for 1 hour to ensure thorough mixing.

[0055] S4. After stirring, let the solution stand until it separates into layers. Take the clear upper layer and place it on a pH meter to measure the pH value.

[0056] Example 7

[0057] The preparation of metakaolin polymer with acid activator is composed of the following components and their weight parts: 4 parts metakaolin, 0.72 parts phosphoric acid, and 4.22 parts water.

[0058] After mixing and stirring the above materials and letting them stand for 48 hours, the experimental steps for obtaining metakaolin-based polymer materials with acid activator dosage, slow-release alkali or acid release functions are as follows: S1. Take 1g of 18% acid activator mixed with metakaolin polymer and 50ml of water.

[0059] S2. Place the acid activator-doped metakaolin polymer in a beaker and add 50ml of water.

[0060] S3. Place the beaker on a magnetic stirrer, add the stir bar, and stir at an appropriate speed for 1 hour to ensure thorough mixing.

[0061] S4. After stirring, let the solution stand until it separates into layers. Take the clear upper layer and place it on a pH meter to measure the pH value.

[0062] Example 8

[0063] The preparation of metakaolin polymer with acid activator is composed of the following components and their weight parts: 4 parts metakaolin, 0.96 parts phosphoric acid, and 4.16 parts water.

[0064] After mixing and stirring the above materials and letting them stand for 48 hours, the experimental steps for obtaining metakaolin-based polymer materials with acid activator dosage, slow-release alkali or acid release functions are as follows: S1. Take 1g of 24% acid activator mixed with metakaolin polymer and 50ml of water.

[0065] S2. Place the acid activator-doped metakaolin polymer in a beaker and add 50ml of water.

[0066] S3. Place the beaker on a magnetic stirrer, add the stir bar, and stir at an appropriate speed for 1 hour to ensure thorough mixing.

[0067] S4. After stirring, let the solution stand until it separates into layers. Take the clear upper layer and place it on a pH meter to measure the pH value.

[0068] Example 9

[0069] The preparation of metakaolin polymer with acid activator is composed of the following components and their weight parts: 4 parts metakaolin, 1.2 parts phosphoric acid, and 4.1 parts water.

[0070] After mixing and stirring the above materials and letting them stand for 48 hours, the experimental steps for obtaining metakaolin-based polymer materials with acid activator dosage, slow-release alkali or acid release functions are as follows: S1. Take 1g of 30% acid activator mixed with metakaolin polymer and 50ml of water.

[0071] S2. Place the acid activator-doped metakaolin polymer in a beaker and add 50ml of water.

[0072] S3. Place the beaker on a magnetic stirrer, add the stir bar, and stir at an appropriate speed for 1 hour to ensure thorough mixing.

[0073] S4. After stirring, let the solution stand until it separates into layers. Take the clear upper layer and place it on a pH meter to measure the pH value.

[0074] Example 10

[0075] The preparation of metakaolin polymer with acid activator is composed of the following components and their weight parts: 4 parts metakaolin, 1.44 parts phosphoric acid, and 4.04 parts water.

[0076] After mixing and stirring the above materials and letting them stand for 48 hours, the experimental steps for obtaining metakaolin-based polymer materials with acid activator dosage, slow-release alkali or acid release functions are as follows: S1. Take 1g of 36% acid activator mixed with metakaolin polymer and 50ml of water.

[0077] S2. Place the acid activator-doped metakaolin polymer in a beaker and add 50ml of water.

[0078] S3. Place the beaker on a magnetic stirrer, add the stir bar, and stir at an appropriate speed for 1 hour to ensure thorough mixing.

[0079] S4. After stirring, let the solution stand until it separates into layers. Take the clear upper layer and place it on a pH meter to measure the pH value.

[0080] Table 2. pH test results of kaolinite polymers with different acid activator dosages. ; Combining Table 1 and Figure 1According to the data, as the proportion of alkali activator gradually increases, the more OH- ions are released by the alkali-activated geopolymer in water, the higher the pH of the solution. When the ratio of alkali activator to high pH reaches 22.5%, the slow-release level of the alkali-activated geopolymer in the solution has reached the limit value of 10.76.

[0081] The sustained-release capacity of alkali-activated geopolymers tends to reach equilibrium within 96 hours. The pH of the alkali-activated geopolymer solution shows an upward trend within 6 hours, and gradually decreases after 6 hours. The pH of the alkali-activated geopolymer solution eventually stabilizes at around 8-9.

[0082] Combine Table 2 and Figure 2 The data showed that as the proportion of acid activator gradually increased, the more H+ released by the acid-activated geopolymer in water, and the lower the solution pH. Furthermore, even with a ratio of acid activator to high tertiary acid of 27%, the acidity limit achievable by the acid-activated geopolymer was not reached. The slow-release capacity of the acid-activated geopolymer tended to reach equilibrium within 96 hours, and the pH of the acid-activated geopolymer solution consistently decreased, eventually stabilizing at 5-6.

[0083] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0084] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A metakaolin-based polymeric material with slow release alkali or acid functionality characterised in that, The raw materials include the following components by weight: 100 parts of metakaolin, 0-27 parts of sodium metasilicate nonahydrate, an activator, 81-110 parts of water, wherein the activator is an alkali activator or an acid activator, the alkali activator is 9-27 parts of sodium metasilicate nonahydrate, and the acid activator is 12-36 parts of a 75% phosphoric acid solution.

2. A slow-release alkali or acid functional metakaolin-based polymeric material according to claim 1, characterised in that, The metakaolin has a median particle size of 3.03 μm.

3. A method of preparing a slow-release alkali or acid functional metakaolin-based polymer material according to claim 1 or 2, characterised in that, The metakaolin has a purity of 98 %.

4. A method of preparing a metakaolin-based polymeric material with slow release alkali or acid functionality, characterised in that, The preparation method includes the following steps: S1. weighing the activator and water, dissolving the activator in water to prepare an activator solution for use; S2. weighing the metakaolin and the activator solution, placing the solution in a stirring pot first, then adding the metakaolin, and uniformly stirring for 3-4 min; S3. pouring the stirred slurry into a mold, curing, and demolding to obtain a metakaolin-based polymer material with slow-release alkali or acid functions.

5. A method of preparing a slow-release alkali or acid functional metakaolin-based polymer material according to claim 4, characterised in that, The curing temperature in step S3 is 60 degrees.

6. The method of claim 4, wherein the method is characterized by, The curing time in step S3 is 48 hours.

Images