Organic-inorganic acid excited geopolymer and preparation method thereof

Abstract

The invention discloses an organic-inorganic acid excited geopolymer and a preparation method thereof, and belongs to the technical field of solid waste resource utilization. The organic-inorganic acid excited geopolymer is prepared from the following raw materials in parts by mass: 30 to 40 parts of mixed exciting agent, 30 to 50 parts of fly ash, 10 to 30 parts of metakaolin and 20 to 60 parts of second solid waste, the mixed exciting agent contains inorganic acid and organic acid. According to the invention, the characteristic that a large amount of strong alkali or strong acid needs to be added during alkali excitation and traditional inorganic acid excitation of geopolymers is overcome, and the potential safety hazard during site construction is relieved. The geopolymer gel is prepared by using low-risk organic acid to treat the solid waste, so that seepage and cracking can be prevented, a product with a more compact surface can be formed, the problem of weathering and saltpetering caused by the existence of Na and K in alkali excitation can be avoided, and the geopolymer gel has good application potential.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization, and particularly to an organic-inorganic acid-activated geopolymer and a preparation method thereof. Background Art

[0002] With the rapid development of the economic society, the generation amount of typical bulk industrial solid wastes such as coal gangue, fly ash, phosphogypsum, red mud, and smelting slag is increasing continuously worldwide. Among these typical bulk industrial solid wastes, a part of them still has not been well comprehensively utilized, and the historical stockpile is still increasing continuously. Although positive results have been achieved in the resource utilization and safe disposal of typical bulk industrial solid wastes in recent years, there are still many problems and challenges that need to be solved. The stacking of a large amount of bulk industrial solid wastes not only damages the ecological environment, but also occupies a large amount of natural resources such as cultivated land, forest land, and grassland. Therefore, it is urgent to explore large-scale comprehensive utilization methods for typical bulk industrial solid wastes.

[0003] Since solid waste raw materials often contain a large amount of silicon and aluminum elements, it has good potential value to prepare geopolymer coatings therefrom. Geopolymer coatings are a new type of inorganic polymer coatings, mainly composed of a three-dimensional network structure formed by splicing silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron units. Geopolymer coatings have been widely used in concrete repair, building waterproofing, site closure repair, etc. due to their rich sources, low prices, energy conservation, simple processes, environmental friendliness, etc. At present, the mainly widely used in this field is alkali-activated geopolymer cementitious materials. However, this kind of inorganic polymer often has problems such as easy shrinkage and cracking, and alkali-aggregate reaction, which affect the mechanical properties. On the contrary, acid-activated geopolymer can reduce the occurrence of the above problems by forming a denser surface, thereby bringing higher mechanical properties.

[0004] The existing patent CN114560640B discloses a preparation method of an acid-activated fly ash geopolymer, which uses an acid as an activator to initiate a reaction, forms an acidic environment through sulfuric acid and phosphoric acid, enables hydrogen ions to penetrate and destroy the Al-O layer, thereby dissociating the layered structure of metakaolin, dissolving Al in bauxite to form [AlO4] monomers, further contacting with [PO4] monomers in the activator, and adding sodium silicate when reaching a certain level, and polycondensation reaction occurs between the monomers to form an inorganic polymer with a three-dimensional network structure containing phosphate groups. However, this method needs to react under the condition of 70-80°C, while the preparation and use of on-site spraying materials are usually carried out at normal temperature, lacking the conditions of high-temperature preparation and curing. Therefore, it is easy to cause the reaction process to be slow, unable to form effective strength support in time, and not meeting the strength requirements.

[0005] The existing patent CN118812194A discloses an acid-activated geopolymer and its preparation method. The acid radical ions are provided by the first activator to promote the activation reaction inside the geopolymer and make the geopolymer have better chemical corrosion resistance in a neutral or acidic application environment. The early strength agent is provided to provide an acid radical ion higher than A1 in an environment with a pH value less than 7. 2 The first metal ion with a low dissolution rate can preferentially react with the acidic first activator to generate a product with a gel phase structure, thereby accelerating the geopolymer reaction and improving the early strength development of the geopolymer. However, this method essentially still utilizes inorganic acid to activate the precursor material to form a Si-O-Al-OP spatial structure, which is essentially no different from the basic principle of CN114560640B. It only uses phosphoric acid to activate the precursor material, and the initial and final setting times are relatively long, which still needs further improvement. Summary of the invention

[0006] One of the purposes of the present invention is to propose an organic-inorganic acid-activated geopolymer and a preparation method thereof to address the current difficulties in the storage of large-scale industrial solid wastes such as fly ash, steel slag, and coal gangue, so as to expand the disposal channels of solid waste materials and turn waste into resources. It has good application prospects in hydraulic structures, slope regulation, etc., and can achieve the purpose of protecting the environment and realizing social and economic benefits.

[0007] Another object of the present invention is to prepare cementitious materials by using a method for preparing organic-inorganic acid-activated geopolymers, which does not require the high-temperature calcination process in traditional cement preparation, will reduce carbon emissions in the preparation process of building materials by about 80%, and achieve the low-carbon goal of the building materials industry.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] One of the technical solutions of the present invention is to provide an organic-inorganic acid-activated geopolymer, wherein the raw materials, calculated by weight, include:

[0010] Mix 30-40 parts of activator, 30-50 parts of fly ash, 10-30 parts of metakaolin and 20-60 parts of second solid waste;

[0011] The mixed activator comprises an inorganic acid and an organic acid.

[0012] Preferably, the inorganic acid is one or more of nitric acid, sulfuric acid, phosphoric acid and aluminum dihydrogen phosphate; the organic acid is one or more of citric acid, oxalic acid, tartaric acid and maleic acid.

[0013] More preferably, the inorganic acid is phosphoric acid, and the organic acid is citric acid or oxalic acid.

[0014] In the reaction system of the present invention, the excitation effect of maleic acid is relatively too strong, which will cause condensation before sufficient polymerization; while tartaric acid is relatively weak and the degree of polymerization is not high. Therefore, citric acid or oxalic acid is preferred.

[0015] More preferably, the mass ratio of the inorganic acid to the organic acid < 0.2.

[0016] Preferably, the pH value of the mixed activator is 1 - 2.

[0017] Preferably, the second solid waste is one or more of steel slag, red mud, calcined sediment, coal gangue and metallurgical slag.

[0018] Preferably, calculated by the mass ratio of Fe2O3, the proportion of Fe in the second solid waste < 20%.

[0019] More preferably, calculated by the mass ratio of Fe2O3, the proportion of Fe in the second solid waste < 5%. Too high Fe content may reduce the mechanical strength of the coating.

[0020] Preferably, the fly ash is Class F fly ash.

[0021] Preferably, the mass proportion of SiO2 in the metakaolin < 52%.

[0022] More preferably, the metakaolin is coal series metakaolin, 51% < SiO2 < 51.5%, 48.5% < Al2O3 < 49%.

[0023] The second technical solution of the present invention: Provide a preparation method of the above-mentioned organic-inorganic acid activated geopolymer, including the following steps:

[0024] Mix the fly ash and metakaolin to obtain a reaction precursor;

[0025] Mix the reaction precursor with the mixed activator, stir and react to obtain a silicon-aluminum slurry;

[0026] Mix the second solid waste with the silicon-aluminum slurry to obtain an organic-inorganic acid activated geopolymer slurry, cure to obtain the organic-inorganic acid activated geopolymer.

[0027] More preferably, after the fly ash and metakaolin are mixed, a crushing step is further included; the mesh number of the crushing ≥ 800 mesh.

[0028] Preferably, the solid-liquid ratio of the reaction precursor to the mixed activator is 1 - 2.5.

[0029] Preferably, the mass ratio of the second solid waste to the reaction precursor is 0.43 - 1.5.

[0030] More preferably, the solid-liquid ratio of the reaction precursor to the mixed activator is 1 to 1.25; the mass ratio of the second solid waste to the reaction precursor is 0.6 to 1.2.

[0031] By controlling the addition amount of the reaction precursor, the relative stability of the overall performance of the coating can be ensured, and the instability of the mechanical properties of the geopolymer coating caused by the uncertainty and large fluctuations of the second solid waste component can be avoided, thereby preventing problems such as cracking and peeling that affect the safe use of the structure.

[0032] Preferably, the stirring reaction is carried out for 30 min at a temperature of 20 - 40°C and a stirring speed of ≥1000 rpm.

[0033] Preferably, after the stirring reaction is completed, it further includes a step of standing for 30 min.

[0034] A large number of bubbles will be generated inside the slurry after stirring. Standing can help discharge the bubbles in the slurry and prevent excessive bubbles from affecting the strength of the test block.

[0035] More preferably, the temperature of the stirring reaction is 35 - 40°C and the stirring speed is ≥1500 rpm. Too low a temperature may lead to a slow reaction process. Since the reaction system of the present invention has a high viscosity, the rotation speed should not be too low, otherwise it will be unfavorable for the uniform distribution of particles and easily lead to the occurrence of agglomeration phenomena, affecting the product effect.

[0036] Preferably, the temperature of the mixing stage of the second solid waste and the silicon-aluminum slurry is 20 - 40°C and the stirring speed is ≥1000 rpm. More preferably, the temperature of the mixing stage of the second solid waste and the silicon-aluminum slurry is 30 - 35°C and the stirring speed is ≥1500 rpm.

[0037] During the stirring process, the raw material system will lose its plastic consistency and reach a liquid state, which can effectively avoid the solidification of unused materials caused by long-term construction, prevent equipment damage, and affect the subsequent spraying effect.

[0038] Preferably, before the curing operation, it further includes a step of curing the slurry with a film at 20 - 40°C for 60 min.

[0039] The technical principle of the present invention is as follows:

[0040] The present invention takes a composite acid activator of organic-inorganic acids as the core raw material, and carries out an acid-activated polymerization reaction on a multi-component solid waste base material composed of fly ash, metakaolin and a second solid waste. The hydrogen protons of the inorganic acid are used to displace and dissolve Al in the base material, and at the same time, the anion polarization reaction of the organic acid is utilized to increase the dissolution of Si. Through the recombination and polycondensation functions of Si and Al, a multi-layer network structure is formed, which has good toughness and adhesion ability, and can be widely applied to scenarios such as hydraulic structures and slope bank solidification. It is a hydraulic material with great application potential.

[0041] The present invention overcomes the characteristics of requiring the addition of a large amount of strong alkali or strong acid when alkali-activated and traditional inorganic acid-activated geopolymers, and alleviates the safety hazards during on-site construction. Using organic acids with low hazard to treat solid waste to prepare geopolymer gels can not only prevent seepage and cracking, form products with a denser surface, but also avoid the problem of weathering and efflorescence caused by the presence of Na and K in alkali activation, and has good application potential.

[0042] The beneficial technical effects of the present invention are as follows:

[0043] (1) In the traditional acid activation system, an inorganic acid activation method is usually adopted. Through the reaction between -Si-O- and the [PO4] tetrahedron of phosphoric acid, Si-O-P bonds are formed in the amorphous structure. In addition, the free aluminum ions exchanged by hydrogen protons react with PO4 3- to produce the crystal phase of AlPO4, and then polycondense into an amorphous structure, that is, mainly rely on the polycondensation of Al and P to form a new three-dimensional network. However, the traditional inorganic acid activation system still has problems such as poor Si dissolution ability, which is likely to lead to insufficient Si reactants during the polycondensation process in the later stage of the geopolymerization reaction, slowing down the reaction process, and further prolonging the coating curing time. In the reaction system of the present invention, since the added organic acid has more polarizing -COOH groups, in addition to hydrogen proton exchange, the polarization of its anions can promote the dissolution of Si in minerals, thereby improving its ability to dissolve minerals; on the other hand, although the inorganic acid in the raw materials of the present invention has good erosion ability for the metakaolin component in the solid waste-based material, mainly destroying the lamellae along the crystal diameter direction, i.e., horizontally, it cannot completely dissolve the mullite transformed from kaolinite. After adding the organic acid, it can destroy the lamellae along the crystal stacking height direction, i.e., longitudinally. Therefore, the dissolution effect on mullite is better. Therefore, the organic acid can better deconstruct and complex the solid waste material to form an acid-activated geopolymer with better performance.

[0044] (2) The core component of the present invention is an organic acid, which has a wide source and is easy to obtain. It can also reduce the safety risks brought by storing inorganic strong acids on site, and has simple operation and does not require the use of high-temperature equipment, which is beneficial to on-site construction implementation.

[0045] (3) During the preparation process of the present invention, partial Ca in the second solid waste dissolves out, which can form stable calcium phosphate hydrate. By forming this typical linear chain structure, fibers or needles can be generated, enhancing the toughness and strength of the product after solidification. Description of the Drawings

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0047] Figure 1 Schematic diagram of the preparation process of the organic-inorganic acid-activated geopolymer in Examples 1-6.

[0048] Figure 2 Comparison of the 28-day compressive strength of the products in Examples 1-6 and Comparative Examples 1-2.

[0049] Figure 3 Initial setting time and final setting time of the organic-inorganic acid-activated geopolymer coatings in Examples 1-6 and Comparative Example 1.

[0050] Figure 4 XRD patterns of Examples 1, 5 and Comparative Example 1.

[0051] Figure 5 SEM micrographs of the surface morphologies of Examples 1-6 and Comparative Examples 1-2. Detailed Embodiments

[0052] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention.

[0053] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0054] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention.

[0055] The words “include,” “including,” “have,” “contain,” etc. used in the present invention are open-ended terms, meaning including but not limited to.

[0056] The fly ash used in the following embodiments and comparative examples of the present invention is Class F fly ash in the ASTM C618 classification method.

[0057] The metakaolin used in the following embodiments and comparative examples of the present invention is coal-based metakaolin, in which the mass ratio of SiO2 is 49.08% and the mass ratio of Al2O3 is 44.14%.

[0058] Calculated by the mass ratio of Fe2O3, the Fe content in the steel slag used in the present invention is 17.35%.

[0059] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0060] Example 1 (Case 1)

[0061] An organic-inorganic acid activated geopolymer, the raw materials, calculated by weight, are:

[0062] Mix 33 parts of an activator (phosphoric acid and citric acid in a mass ratio of 1:6, pH=1.6), 30 parts of fly ash, 10 parts of metakaolin and 60 parts of steel slag.

[0063] The specific preparation steps are as follows:

[0064] (1) fly ash and metakaolin are mixed and ball-milled to 800 mesh to obtain a reaction precursor;

[0065] (2) Mixing the reaction precursor in step (1) with the mixed activator, and fully mixing in a reaction kettle, controlling the solid-liquid ratio to 1.2, stirring at a temperature of 35° C. and a stirring speed of 1600 rpm for 30 min, then stopping, and then standing for 30 min to obtain a high-activity silicon-aluminum slurry;

[0066] (3) adding steel slag to the high-activity silicon-alumina slurry obtained in step (2), and mixing thoroughly at 40° C. to obtain an organic-inorganic acid-activated geopolymer coating;

[0067] (4) According to ASTM C191-13 standard, the initial setting time and final setting time of organic-inorganic acid activated geopolymer slurry were measured using a Vicat apparatus;

[0068] (5) Measure the compressive strength of the product in the shape of a 40-mm cube on the 28th day using a mechanical testing instrument.

[0069] Example 2 (Case 2)

[0070] It is different from Example 1 only in that phosphoric acid is replaced with sulfuric acid of equal mass.

[0071] Example 3 (Case 3)

[0072] It is different from Example 1 only in that citric acid is replaced with oxalic acid of equal mass.

[0073] Example 4 (Case 4)

[0074] It is different from Example 1 only in that citric acid is replaced with tartaric acid of equal mass.

[0075] Example 5 (Case 5)

[0076] It is different from Example 1 only in that the pH value of the mixed activator is modified from 1.6 to 3, and the solid-liquid ratio is adjusted to 1.5.

[0077] Example 6 (Case 6)

[0078] It is different from Example 1 only in that the pH value of the mixed activator is modified from 1.6 to 5, and the solid-liquid ratio is adjusted to 2.1.

[0079] Comparative Example 1 (Case 7)

[0080] It is different from Example 1 only in that the addition of citric acid is omitted and phosphoric acid of equal mass is added.

[0081] Comparative Example 2 (Case 8)

[0082] It is different from Example 1 only in that the addition of phosphoric acid is omitted and citric acid of equal mass is added.

[0083] Effect verification

[0084] Figure 1 It is a schematic diagram of the preparation process of the organic-inorganic acid-activated geopolymer in Examples 1-6.

[0085] Figure 2 It is a comparison of the 28-day compressive strength of the products in Examples 1-6 and Comparative Examples 1-2 (the numbers 1 to 8 in the abscissa correspond to the geopolymers in Examples 1-6 and Comparative Examples 1-2 in sequence).

[0086] Figure 3 It is the initial setting time and final setting time of the organic-inorganic acid-activated geopolymer coatings in Examples 1-6 and Comparative Example 1 (the numbers 1 to 7 in the abscissa correspond to the geopolymers in Examples 1-6 and Comparative Example 1 in sequence).

[0087] Figure 4 XRD patterns of Example 1, Example 5 and Comparative Example 1.

[0088] Figure 5 SEM images of the surface morphologies of Examples 1-6 and Comparative Examples 1-2.

[0089] Analysis of the compressive strength ( Figure 2 ) of the 40-mm cube-shaped specimens prepared in Examples 1-6 reveals that the best performance is achieved when phosphoric acid is selected as the inorganic acid and citric acid is selected as the organic acid. This is mainly because different types of organic and inorganic acids have certain differences in the dissolution ability of the reaction precursors and silicon and aluminum in the second solid waste. Through research, it is found that over time, the concentrations of Si and Al both increase with time. However, for the dissolution rate of Si, citric acid > tartaric acid > oxalic acid > phosphoric acid, and for the dissolution rate of Al, phosphoric acid > oxalic acid > citric acid > tartaric acid. For aluminum dihydrogen phosphate and phosphoric acid, they only dissolve Si by exchanging H + and have poor Si dissolution ability; for oxalic acid, citric acid and tartaric acid, due to the strong polarization effect of the organic acid anions, the dissolution of Si in aluminosilicates by organic acids depends not only on the replacement effect of H + but also on the polarization effect of the anions. Compared with oxalic acid and tartaric acid, citric acid has more polarizing -COOH groups, so its polarization effect and the ability to dissolve Si in aluminosilicates are stronger. However, in terms of overall performance, no matter which organic acid is used as the core component of the activator, as long as the pH value is adjusted within a suitable range, the products after geopolimerization have good performance and the compressive strength is above 25 MPa. Similar conclusions can also be obtained from the initial setting time and final setting time ( Figure 3 ) of the coating, which is more conducive to on-site construction. Comparative Example 1 is a conventional aluminum phosphate geopolymer. Since there is only phosphoric acid in the reaction system, the dissolution of fly ash is slowed down, which slows down the process of the geopolymerization reaction and leads to an increase in the initial and final setting times. The geopolymer gel prepared in Comparative Example 2 cannot coagulate and form, lacks strength, and therefore the initial setting time and final setting time cannot be counted.

[0090] However, from Figure 2 and Figure 3 it is not difficult to find that with the gradual increase of the pH value of the mixed activator, both the compressive strength of the specimens and the final setting time of the coating change significantly. After the pH value increases, it will lead to a decrease in the dissolution ability of the activator for Si, resulting in insufficient Si and Al raw materials for the geopolymerization reaction, reducing the reaction rate, and thus reducing the product performance and increasing the setting time. Therefore, when applying the organic-inorganic acid activated geopolymer coating of the present invention, the pH value of the mixed activator should be strictly controlled to ensure relatively stable product performance.

[0091] Figure 4 In the figure, the blue and red ones are the XRD patterns of Example 1 and Example 5. There are obvious diffuse peaks at 25 - 30°, indicating that geopolymers have been formed in the structure. For Comparative Example 1 with only phosphoric acid, although there are also broad and diffuse peaks formed, it can be found that the crystal phase peaks of quartz are more obvious, indicating that there is more remaining quartz phase in the raw materials, the reaction of Si is incomplete, and the degree of peak shift is significantly lower than that of Example 1 and Example 5, and the degree and progress of the geopolymerization reaction are lower than those of Example 1 and Example 5.

[0092] From Figure 5 It can be found from the SEM micrographs of the surface morphologies of Examples 1 - 6 and Comparative Examples 1 - 2 that the strength of the test blocks is closely related to the compactness of the surface morphology. The order of the compactness of their surfaces is Example 1 > Example 5 > Example 3 > Example 4 > Example 2 > Comparative Example 1, while Comparative Example 2 is mainly still granular, with insufficient bonded gel, resulting in its inability to be molded and lack of strength.

[0093] The above content shows that the organic - inorganic acid - activated geopolymer of the present invention has good mechanical properties and construction convenience. On the one hand, the present invention increases the disposal ways of solid waste materials. On the other hand, the preparation of coatings by activating gels with organic - inorganic acids can not only achieve the effect of energy conservation and emission reduction, but also realize the application of this kind of material in different scenarios by adjusting the proportion, so as to achieve function expansion and has good application prospects.

[0094] The embodiments described above are only used to describe the preferred mode of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solution of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. An organic-inorganic acid-activated geopolymer, characterized in that, The raw materials, by mass parts, include: 30 - 40 parts of a mixed activator, 30 - 50 parts of fly ash, 10 - 30 parts of metakaolin, and 20 - 60 parts of a second solid waste; The mixed activator contains inorganic acids and organic acids.

2. The organic-inorganic acid-activated geopolymer according to claim 1, wherein The inorganic acid is one or more of nitric acid, sulfuric acid, phosphoric acid, and aluminum dihydrogen phosphate; the organic acid is one or more of citric acid, oxalic acid, tartaric acid, and maleic acid.

3. The organic-inorganic acid-activated geopolymer according to claim 2, wherein The mass ratio of the inorganic acid to the organic acid < 0.2; and / or, the pH value of the mixed activator is 1 - 2.

4. The organic-inorganic acid-activated geopolymer according to claim 1, wherein The second solid waste is one or more of steel slag, red mud, calcined sediment, coal gangue, and metallurgical slag; and / or, calculated by the mass ratio of Fe2O3, the proportion of Fe in the second solid waste < 20%.

5. The organic-inorganic acid-activated geopolymer according to claim 1, wherein The fly ash is class F fly ash.

6. The organic-inorganic acid-activated geopolymer according to claim 1, wherein The mass proportion of SiO2 in the metakaolin < 52%.

7. A preparation method of the organic-inorganic acid-activated geopolymer according to any one of claims 1-6, characterized in that, It includes the following steps: Mix the fly ash and metakaolin to obtain a reaction precursor; Mix the reaction precursor with the mixed activator, stir and react to obtain a silicon-aluminum slurry; Mix the second solid waste with the silicon-aluminum slurry to obtain an organic-inorganic acid-activated geopolymer slurry, and cure to obtain the organic-inorganic acid-activated geopolymer.

8. The preparation method according to claim 7, characterized in that, The solid-liquid ratio of the reaction precursor to the mixed activator is 1 - 2.5; and / or, the mass ratio of the second solid waste to the reaction precursor is 0.43 - 1.

5.

9. The preparation method according to claim 7, wherein The stirring reaction is to stir for 30 min at a temperature of 20 - 40°C and a stirring speed ≥ 1000 rpm.

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