Organic-inorganic acid-activated polygeomer and method for preparing the same

Abstract

The application discloses an organic-inorganic acid-activated geopolymer and a preparation method thereof, and belongs to the technical field of solid waste resource utilization. The raw materials of the organic-inorganic acid-activated geopolymer according to the application comprise, in parts by mass, 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 comprises inorganic acid and organic acid. The application overcomes the characteristics that a large amount of strong alkali or strong acid needs to be added when alkali activation and traditional inorganic acid activation of geopolymer are performed, and the safety hazards during on-site construction are relieved. The solid waste is treated by using low-risk organic acid to prepare geopolymer gel, which can not only prevent seepage and cracking, form a product with a more compact surface, but also avoid the weathering and efflorescence problems caused by the existence of Na and K in alkali activation, and has good application potential.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization, in particular to an organic-inorganic acid-activated geopolymer and a preparation method thereof. BACKGROUND

[0002] With the rapid development of economic society, the production of typical large industrial solid wastes such as coal gangue, fly ash, phosphogypsum, red mud and smelting slag is increasing worldwide. Among these typical large industrial solid wastes, a part of them has not been well utilized and the historical stockpiles are still increasing. Although positive results have been achieved in the resource utilization and safe disposal of typical large industrial solid wastes in recent years, there are still many problems and challenges to be solved, so it is urgent to explore a large-scale comprehensive utilization method for typical large industrial solid wastes.

[0003] Because the solid waste raw material often contains a large amount of silicon and aluminum elements, it has good potential value to prepare it into a geopolymer coating. The geopolymer coating is a new type of inorganic polymer coating, which is mainly composed of a three-dimensional network structure formed by splicing silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron units. The geopolymer coating has been widely used in concrete repair, building waterproofing, site closure repair, etc. due to its abundant source, low price, energy saving, simple process, environmental friendliness and other characteristics. At present, the main application in this field is alkali-activated geopolymer cementitious material, but this inorganic polymer often has the problems of easy shrinkage and cracking, and alkali-aggregate reaction, which affect the mechanical properties. On the contrary, acid-activated geopolymer can form a more compact surface to reduce the above problems and bring higher mechanical properties.

[0004] The existing patent CN114560640B discloses a method for preparing acid-activated fly ash geopolymer, which uses acid as an activator to initiate the reaction. By forming an acidic environment with sulfuric acid and phosphoric acid, hydrogen ions are immersed and destroy the Al-O layer, so that the layered structure of metakaolin is dissociated, Al in bauxite is dissolved to form [AlO4] monomers, which further contact with [PO4] monomers in the activator. When reaching a certain level, water glass is added, and a condensation reaction occurs between the monomers to form an inorganic polymer with a three-dimensional network structure of phosphoric acid groups. However, this method requires a reaction temperature of 70-80℃, while the preparation of field sprayed materials is usually carried out at room temperature, and there is a lack of high-temperature preparation and curing conditions, which can easily lead to slow reaction progress, failure to form effective strength support in time, and failure to meet the strength requirements.

[0005] CN118812194A discloses an acid-activated geopolymer and a preparation method thereof, which provides acid radical ions through a first activator, can promote the activation reaction inside the geopolymer, and makes the geopolymer have better chemical corrosion resistance in neutral or acidic application environment; the first metal ion with a dissolution rate higher than A1 2 under the environment with pH less than 7 is provided through an early strength agent, can preferentially react with the acidic first activator, generates a product with a gel phase structure, accelerates the geopolymer reaction, and improves the early strength development of the geopolymer; however, the method still essentially uses inorganic acid to activate the precursor material to form a spatial structure of Si-O-Al-O-P, and has no essential difference from the basic principle of CN114560640B, which only uses phosphoric acid to activate the precursor material, and the initial setting and final setting times are relatively long, and further improvement is still needed. SUMMARY

[0006] One of the purposes of the present application is to propose an organic-inorganic acid-activated geopolymer and a preparation method thereof to expand the disposal channels of solid waste materials in view of the current predicament of stockpiling of fly ash, steel slag, coal gangue and other bulk industrial solid waste, and to turn waste into resources, which has good application prospects in hydraulic structures, slope remediation and the like, and can achieve the purpose of protecting the environment and realizing social and economic benefits.

[0007] Another purpose of the present application is to use the preparation method of the organic-inorganic acid-activated geopolymer to prepare cementitious materials, which does not need the high-temperature calcination process in the preparation of traditional cement, and can reduce about 80% of carbon emissions in the preparation process of building materials, and realize the low-carbon goal of the building materials industry.

[0008] To achieve the above purpose, the present application provides the following technical solutions.

[0009] One of the technical solutions of the present application provides an organic-inorganic acid-activated geopolymer, the raw materials include, by mass fraction:

[0010] 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;

[0011] The mixed activator contains inorganic acid and organic acid.

[0012] Preferably, the inorganic acid is one or more of nitric acid, sulfuric acid, phosphoric acid and aluminum dihydrogen phosphate; and 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 application, the excitation effect of maleic acid is relatively too strong, which can cause the condensation before the complete polymerization; and the excitation effect of tartaric acid is relatively weak, and the polymerization degree is not high, so citric acid or oxalic acid is preferred.

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

[0016] Preferably, the pH value of the mixed excitation agent 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, the Fe content in the second solid waste accounts for <20% in terms of the mass ratio of Fe2O3.

[0019] More preferably, the Fe content in the second solid waste accounts for <5% in terms of the mass ratio of Fe2O3. Too high Fe content can reduce the mechanical strength of the coating.

[0020] Preferably, the fly ash is F-type fly ash.

[0021] Preferably, the SiO2 content in the metakaolin is <52% in terms of mass ratio.

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

[0023] Technical solution two of the present application: provide a preparation method of the organic-inorganic acid excited geopolymer, comprising the following steps:

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

[0025] Mixing the reaction precursor with the mixed excitation agent, stirring and reacting to obtain a silicon-aluminum slurry;

[0026] Mixing the second solid waste with the silicon-aluminum slurry to obtain an organic-inorganic acid excited geopolymer slurry, curing to obtain the organic-inorganic acid excited geopolymer.

[0027] More preferably, after mixing the fly ash and metakaolin, a crushing step is further included; the crushing mesh size is ≥800 mesh.

[0028] Preferably, the solid-liquid ratio of the reaction precursor and the mixed excitation agent is 1-2.5.

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

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

[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 uncertainty and large fluctuation of the second solid waste component can be avoided, so that the mechanical properties of the geopolymer coating are stable, and the problems of cracking, peeling and the like affecting the safety of the structure in use are avoided.

[0032] Preferably, the stirring reaction is stirring for 30 min at a temperature of 20-40 DEG C and a stirring speed of greater than or equal to 1000 rpm.

[0033] Preferably, after the stirring reaction is completed, the method further comprises the step of standing for 30 min.

[0034] After stirring, a large number of bubbles will be generated in the slurry, and standing can help to discharge the bubbles in the slurry, so as to prevent too many bubbles from affecting the strength of the test block.

[0035] More preferably, the temperature of the stirring reaction is 35-40 DEG C, and the stirring speed is greater than or equal to 1500 rpm. If the temperature is too low, the reaction process may be slow. Since the reaction system of the present application has high viscosity, the stirring speed should not be too low, otherwise the uniform distribution of particles will be affected, and agglomeration may occur, which affects the product effect.

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

[0037] During the stirring process, the raw material system loses plastic consistency and becomes liquid, which can effectively avoid the solidification of unused materials caused by long-time construction, prevent equipment damage and affect the spraying effect in the later stage.

[0038] Preferably, before the curing operation, the method further comprises the step of film curing the slurry at 20-40 DEG C for 60 min.

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

[0040] The application takes a composite acid activator of organic-inorganic acid as a core raw material, carries out acid activation polymerization on a multi-component solid waste base material mixed by fly ash, metakaolin and a second solid waste, replaces and dissolves Al in the base material by hydrogen protons of inorganic acid, increases the dissolution of Si by anion polarization reaction of organic acid, forms a multi-layer network structure by Si and Al recombination polycondensation function, has good toughness and adhesion, can be widely applied to water conservancy structures, slope consolidation and the like, and is a water conservancy material with great application potential.

[0041] The application overcomes the characteristics that a large amount of strong alkali or strong acid needs to be added in alkali activation and traditional inorganic acid activated geopolymer, and alleviates the safety hazards in on-site construction. The solid waste is treated by low-risk organic acid to prepare a geopolymer gel, which can not only prevent seepage and cracking and form a product with a more dense surface, but also avoid weathering and efflorescence problems caused by Na and K in alkali activation, and has great application potential.

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

[0043] (1) In the traditional acid activation system, an inorganic acid activation method is usually used for preparation. By the reaction between -Si-O- and [PO4] tetrahedron of phosphoric acid, Si-O-P bonds are formed in amorphous structure, and free-state aluminum ions exchanged by hydrogen protons react with PO4 3- to generate AlPO4 crystal phase, and then polycondense into amorphous structure, that is, new three-dimensional network is mainly formed by polycondensation of Al and P. However, the traditional inorganic acid activation system still has problems such as poor Si dissolution capacity, which may cause insufficient Si reactants in the polycondensation process in the later stage of geopolymerization reaction, and thus prolong the curing time of the coating. In the reaction system of the application, the added organic acid has more polar -COOH groups, and in addition to hydrogen proton exchange, the polarization of its anion can promote the dissolution of Si in minerals, thereby improving the dissolution capacity of the minerals; on the other hand, although the inorganic acid in the raw material of the application has good corrosion capacity for the metakaolin component in the solid waste base material, it mainly damages the layers in the transverse direction along the crystal diameter, but cannot completely dissolve the mullite converted from kaolinite, and after the addition of organic acid, the layers in the longitudinal direction along the crystal stacking height can be damaged, and thus the dissolution effect of mullite is better. Therefore, the solid waste material can be better deconstructed and complexed by using organic acid to form an acid activated geopolymer with better performance.

[0044] (2) The core component of the application is organic acid, which is widely available and easy to obtain, can reduce the safety risks caused by storage of inorganic strong acid on site, and is simple to operate without the need of high-temperature equipment, which is conducive to on-site construction implementation.

[0045] (3) In the preparation process of the present application, part of Ca in the second solid waste is dissolved out, which can form stable calcium phosphate hydrate, and through forming this typical linear chain structure, fiber or needle-like body can be generated, which enhances the toughness and strength of the product after solidification. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0047] Figure 1 Preparation process schematic diagram of organic-inorganic acid-activated geopolymer in Examples 1-6.

[0048] Figure 2 28d compressive strength comparison 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 coating in Examples 1-6 and Comparative Example 1.

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

[0051] Figure 5 Surface morphology SEM pattern of Examples 1-6 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0052] Now, various exemplary embodiments of the present application will be described in detail, which should not be considered as limiting the present application, but should be understood as a more detailed description of certain aspects, features and embodiments of the present application. It should be understood that the terms described in the present application are only for describing the particular embodiments, and are not intended to limit the present application.

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

[0054] Unless otherwise indicated, all technical and scientific terms have the same meaning as those one of ordinary skill in the art of the application would understand. Although preferred methods and materials are described, any method and material similar or equivalent to those described herein can be used in the practice or testing of the present application.

[0055] As used herein, the terms “comprises”, “comprising”, “includes”, “including”, “has”, “having” or the like are open-ended terms that are intended to mean including, but not limited to.

[0056] The fly ash used in the following examples and comparative examples of the present application is F-class fly ash in the ASTM C618 classification.

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

[0058] The Fe in the steel slag used in the present application accounts for 17.35% in terms of the mass ratio of Fe2O3.

[0059] Each raw material used in the following examples and comparative examples of the present application is a commercially available product.

[0060] Example 1 (Case 1)

[0061] An organic-inorganic acid-activated geopolymer, the raw materials are as follows in terms of mass fraction:

[0062] 33 parts of mixed activator (mass ratio of phosphoric acid to citric acid is 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) Take fly ash and metakaolin, mix and ball mill to 800 mesh to obtain a reaction precursor;

[0065] (2) Mix the reaction precursor in step (1) with the mixed activator, and mix well in the reaction kettle, control the solid-liquid ratio to be 1.2, stop after stirring at a temperature of 35℃ and a stirring speed of 1600 rpm for 30 min, and then stand for 30 min to obtain a high-activity silicon-aluminum slurry;

[0066] (3) Add steel slag to the high-activity silicon-aluminum slurry obtained in step (2), mix well at 40℃ to obtain an organic-inorganic acid-activated geopolymer coating;

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

[0068] (5) The compressive strength of the 40 mm cube shaped product at 28 days was measured using a mechanical testing instrument.

[0069] Example 2 (Case 2)

[0070] The difference from Example 1 is that phosphoric acid is replaced by equal mass of sulfuric acid.

[0071] Example 3 (Case 3)

[0072] The difference from Example 1 is that citric acid is replaced by equal mass of oxalic acid.

[0073] Example 4 (Case 4)

[0074] The difference from Example 1 is that citric acid is replaced by equal mass of tartaric acid.

[0075] Example 5 (Case 5)

[0076] The difference from Example 1 is that the pH value of the mixed activator is modified from 1.6 to 3 and the solid to liquid ratio is adjusted to 1.5.

[0077] Example 6 (Case 6)

[0078] The difference from Example 1 is that the pH value of the mixed activator is modified from 1.6 to 5 and the solid to liquid ratio is adjusted to 2.1.

[0079] Comparative Example 1 (Case 7)

[0080] The difference from Example 1 is that the addition of citric acid is omitted and equal mass of phosphoric acid is added.

[0081] Comparative Example 2 (Case 8)

[0082] The difference from Example 1 is that the addition of phosphoric acid is omitted and equal mass of citric acid is added.

[0083] Effect verification

[0084] Figure 1 The preparation flow chart of the organic-inorganic acid activated geopolymer in Examples 1-6.

[0085] Figure 2 The 28d compressive strength of the product of Examples 1-6 and Comparative Examples 1-2 (1-8 in the abscissa correspond to the geopolymer of Examples 1-6 and Comparative Examples 1-2 in turn).

[0086] Figure 3 The initial and final setting time of the organic-inorganic acid activated geopolymer coating in Examples 1-6 and Comparative Example 1 (1-7 in the abscissa correspond to the geopolymer of Examples 1-6 and Comparative Example 1 in turn).

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

[0088] Figure 5 Surface morphology SEM patterns of Examples 1-6 and Comparative Examples 1-2.

[0089] The compressive strength of the 40 mm cubic-shaped test blocks prepared in Examples 1-6 was analyzed. Figure 2 It can be found that the inorganic acid is phosphoric acid and the organic acid is citric acid, which has the best performance effect. This is mainly due to the difference in the dissolution capacity of different types of organic acids and inorganic acids for Si and Al in the reaction precursor and the second solid waste. Through research, it is found that with the passage of time, the Si and Al concentrations will increase with time, but 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 + with Si, and the Si dissolution capacity is poor; for oxalic acid, citric acid and tartaric acid, due to the strong polarization effect of the organic acid anion, the dissolution of Si in the silicate is not only dependent on the displacement of H + , but also on the polarization effect of the anion. Compared with oxalic acid and tartaric acid, citric acid has more polar-COOH groups, so its polarization effect and the ability to dissolve Si in silicate are stronger. But from the overall performance, as long as the pH value is adjusted within the appropriate range, the product after the geopolymerization reaction has good performance, and the compressive strength is more than 25 MPa, and similar conclusions can be drawn from the initial and final setting times Figure 3 of the coating, which is more conducive to on-site construction. Comparative Example 1 is a conventional aluminum phosphate geopolymer, and due to the reaction system only having phosphoric acid, the dissolution of fly ash is slowed down, which slows down the progress of the geopolymerization reaction, resulting in an increase in the initial and final setting times. The geopolymer gel prepared in Comparative Example 2 cannot be coagulated into shape and lacks strength, so the initial and final setting times cannot be counted.

[0090] But 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, the compressive strength of the test block and the final setting time of the coating are significantly changed. After the pH value is increased, the dissolution capacity of the activator for Si will be weakened, which will lead to insufficient Si and Al raw materials for the geopolymerization reaction, reduce the reaction rate, and thus reduce the product performance and increase the setting time. Therefore, when applying the organic-inorganic acid activated geopolymer coating in the present application, the pH value of the mixed activator should be strictly controlled to ensure the relative stability of the product performance.

[0091] Figure 4 The medium blue and red are the XRD patterns of Example 1 and Example 5, and there are obvious diffuse peaks at 25-30°, indicating that the geopolymer has been formed in the structure. While for Comparative Example 1 with only phosphoric acid, although the formation of a broad diffuse peak, but can be found that the quartz crystal phase peak is more obvious, indicating that the remaining quartz phase of the raw material is more, the reaction of Si is not complete, and the degree of peak shift is obviously lower than that of Example 1 and 5, and the degree and progress of geopolymerization is lower than that of Example 1 and 5.

[0092] From the above, it can be seen that the organic-inorganic acid-activated geopolymer has good mechanical properties and convenient construction. On the one hand, the application increases the disposal way of solid waste materials, and on the other hand, the preparation of the coating through the organic-inorganic acid-activated gel not only can achieve the effect of energy saving and emission reduction, but also can realize the application of the material in different scenes by adjusting the ratio, realize the function expansion, and has good application prospect. Figure 5

[0093] The above content shows that the organic-inorganic acid-activated geopolymer has good mechanical properties and convenient construction. On the one hand, the application increases the disposal way of solid waste materials, and on the other hand, the preparation of the coating through the organic-inorganic acid-activated gel not only can achieve the effect of energy saving and emission reduction, but also can realize the application of the material in different scenes by adjusting the ratio, realize the function expansion, and has good application prospect.

[0094] The above-described examples only describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.​

Claims

1. An organic-inorganic acid-activated geopolymer, characterized in that, The raw materials include, by mass fraction: 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 acid and organic acid; The inorganic acid is phosphoric acid, and the organic acid is citric acid or oxalic acid; The mass ratio of the inorganic acid to the organic acid is <0.2, and the pH value of the mixed activator is 1-2; The second solid waste is one or more of steel slag, red mud, calcined sediment, and coal gangue, and the Fe content in the second solid waste is <20% by mass fraction of Fe2O3; The preparation method of the organic-inorganic acid activated geopolymer includes the following steps: Mixing the fly ash and metakaolin to obtain a reaction precursor; Mixing the reaction precursor with the mixed activator, stirring and reacting to obtain a silicon-aluminum slurry; Mixing the second solid waste with the silicon-aluminum slurry to obtain an organic-inorganic acid activated geopolymer slurry, curing to obtain the organic-inorganic acid activated geopolymer.

2. The organic-inorganic acid-activated geopolymer according to claim 1, characterized in that, The fly ash is F-class fly ash.

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

4. The organic-inorganic acid-activated geopolymer of claim 1, wherein, 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.

5. The organic-inorganic acid-activated geopolymer according to claim 1, wherein, The stirring and reacting is stirring at a temperature of 20-40℃ and a stirring speed of ≥1000 rpm for 30 min.

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