Composite ammonia-fixing agent for inhibiting ammonia release of fly ash filling body as well as preparation method and application of composite ammonia-fixing agent

Abstract

The invention discloses a composite ammonia fixing agent for inhibiting ammonia release of a fly ash filling body as well as a preparation method and application of the composite ammonia fixing agent, and belongs to the technical field of industrial waste resource comprehensive utilization and mine filling. The adsorbent consists of the following raw materials in parts by weight: 25-55 parts of a main adsorbent, 18-45 parts of a precipitant, 4-18 parts of a pH buffer and auxiliary precipitant, 8-25 parts of an auxiliary adsorbent and 2-10 parts of a dispersing agent. Aiming at a strong-alkalinity special environment of a fly ash-cement system, a local precipitation microenvironment is created through preferential adsorption of the main adsorbent, pH buffering and the auxiliary precipitator, multi-stage synergy of precipitation ions is provided, efficient and stable fixation of NH4 < + > is realized, and an ammonia gas generation path is fundamentally blocked. The composite ammonia fixing agent can adapt to a strong alkaline environment in a fly ash filling body, is high in ammonia fixing efficiency, and has no negative influence on the workability of filling slurry and the mechanical property of a hardened body.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of industrial waste resources and mine backfilling technology, and in particular to a composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill bodies, its preparation method and application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] With the widespread adoption of selective catalytic reduction (SCR) denitrification processes in coal-fired power plants, ammonium salts such as ammonium bisulfate and ammonium sulfate often remain in the fly ash produced. When this type of fly ash is used as backfill aggregate or admixture in mines, the ammonium salts decompose and release ammonia gas with a strong, pungent odor in the high pH (typically >12) environment created by the hydration of alkaline cementitious materials such as cement. This not only severely deteriorates the underground working environment and endangers personnel health, but may also affect the long-term durability of the backfill material due to the ammonia gas escaping and leaving pores within the backfill.

[0004] Currently, the technical approaches to solving this problem mainly fall into two categories: one is to pretreat fly ash, such as through slurry stripping, but this method requires specialized equipment, is complex, energy-intensive, and significantly increases operating costs; the other is to try adding solidification components to the filling material. However, existing solidification approaches mostly draw on heavy metal solidification or simple physical adsorption, failing to effectively fix ammonium ions (NH4+) in highly alkaline environments. + This core challenge is addressed in the design. For example, simply using physical adsorption materials (such as activated carbon) can easily lead to rapid saturation and failure in highly alkaline environments; while directly adding acidic substances to attempt to adjust the overall pH will severely interfere with the normal hydration process of cement, resulting in a loss of strength in the filling material. Therefore, developing a specialized ammonium-fixing agent that can work synergistically with cement-based filling systems, efficiently and stably solidify ammonium ions in highly alkaline environments without affecting the key properties of the filling material, has urgent engineering needs and significant environmental value. Summary of the Invention

[0005] In view of the above problems, this invention provides a composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill, its preparation method, and its application. Targeting the highly alkaline environment of the fly ash-cement system, this invention achieves multi-level synergistic effects on NH4+ by preferential adsorption by the main adsorbent, the creation of a local precipitation microenvironment through pH buffering and auxiliary precipitants, and the provision of precipitated ions. + Its high efficiency and stable fixation fundamentally block the ammonia generation pathway.

[0006] In a first aspect, the present invention provides a composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill, comprising the following raw materials in parts by weight: 25-55 parts of main adsorbent, 18-45 parts of precipitant, 4-18 parts of pH buffer and auxiliary precipitant, 8-25 parts of auxiliary adsorbent, and 2-10 parts of dispersant.

[0007] Preferably, the main adsorbent is a layered double metal hydroxide (LDH). LDH possesses a unique interlayer anion exchange structure, and compared to conventional adsorbent materials, it maintains stable adsorption performance even in strongly alkaline environments with pH > 12. It can preferentially and selectively adsorb and enrich ammonium ions released from fly ash, avoiding the defects of existing physical adsorbent materials that are prone to saturation and failure in strongly alkaline environments. Simultaneously, the layered structure of LDH can provide site support for subsequent precipitation reactions, improving reaction efficiency and further enhancing the ammonia fixation effect.

[0008] Preferably, the precipitant is selected from at least one of magnesium hydrogen phosphate and magnesium oxide. Magnesium hydrogen phosphate and magnesium oxide can provide magnesium ions or phosphate ions, which are present in subsequent reactions. 2+ ) and phosphate ions (PO4) 3- ) and enriched NH4 + The reaction produces a stable precipitate, magnesium ammonium phosphate, which further fixes the ammonium ions and prevents them from being converted into ammonia gas and released.

[0009] Preferably, the pH buffer and auxiliary precipitant is sodium dihydrogen phosphate. Sodium dihydrogen phosphate has excellent pH buffering properties. After dissolving, it can form a weakly acidic microenvironment with a local pH of 9-10.5 around the adsorption sites of the main adsorbent. This microenvironment is perfectly suited to the formation conditions of magnesium ammonium phosphate precipitate, while not changing the overall strong alkalinity of the filling grout, thus avoiding the problem of cement hydration being hindered by direct acid adjustment in existing technologies. In addition, sodium dihydrogen phosphate can also provide phosphate ions, which, together with the magnesium ions released by the precipitant, participate in the precipitation reaction of ammonium ions, further improving the ammonia fixation efficiency.

[0010] Preferably, the auxiliary adsorbent is selected from at least one of modified zeolite and biochar. Modified zeolite or biochar has a rich pore structure and can supplement the main adsorbent to perform secondary capture of free ammonia molecules that are not completely fixed, thereby further reducing the risk of ammonia release.

[0011] Preferably, the dispersant is a polycarboxylate superplasticizer. Polycarboxylate superplasticizers have high dispersing properties, effectively reducing the probability of agglomeration between functional powder components, ensuring uniform distribution of the main adsorbent, precipitant, and other components in the filling slurry, and allowing each component to fully perform its function. Simultaneously, it exhibits excellent compatibility with cement-based systems, not only not interfering with cement hydration but also improving the fluidity of the filling slurry and enhancing its workability, thus solving the problem of slurry agglomeration and decreased fluidity caused by the addition of multiple components.

[0012] Preferably, it is composed of the following raw materials in parts by weight: 30-50 parts of main adsorbent, 20-40 parts of precipitant, 5-15 parts of pH buffer and auxiliary precipitant, 10-20 parts of auxiliary adsorbent, and 3-8 parts of dispersant.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill, comprising: mixing the main adsorbent, precipitant, pH buffer, auxiliary precipitant, auxiliary adsorbent, and dispersant evenly.

[0014] Thirdly, the present invention provides the application of the above-mentioned composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill during fly ash backfilling.

[0015] Preferably, the composite ammonia-fixing agent is incorporated into the fly ash, and the amount incorporated is 1.5%-5% of the total mass of the fly ash.

[0016] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The composite ammonia fixation agent of this invention constructs an ammonia fixation system of adsorption enrichment-local acidification-stable precipitation through the synergistic effect of the main adsorbent, precipitant, pH buffer and auxiliary precipitant. It is highly targeted and has a high ammonia fixation efficiency. The main adsorbent, layered bimetallic hydroxide, preferentially adsorbs and enriches ammonium ions in a strongly alkaline environment, providing a basis for subsequent reactions. The pH buffer and auxiliary precipitant, sodium dihydrogen phosphate, construct a local microenvironment suitable for precipitation reaction around the adsorption site, avoiding interference of overall acidification on cement hydration, and also providing phosphate ions. The magnesium ions and phosphate ions released by the precipitant react with the enriched ammonium ions to jointly generate magnesium ammonium phosphate (MgNH4PO4·6H2O) crystal precipitate with extremely low solubility in water and extremely stable chemical properties, thereby permanently fixing the ammonium ions and fundamentally blocking their conversion to ammonia (NH3). The weight ratio of each component ensures the maximization of the synergistic effect, which can make the ammonia release inhibition rate reach a stable and efficient level, solving the core problem of not being able to efficiently and stably fix ammonia in fly ash in a strongly alkaline environment.

[0017] (2) This invention uses sodium dihydrogen phosphate as a pH buffer and auxiliary precipitant. Without interfering with the overall alkalinity of the backfill (ensuring normal cement hydration), it creates a suitable microenvironment for localized precipitation reactions at the reaction sites, overcoming the core technical obstacle of struvite formation under strong alkaline conditions. Polycarboxylate dispersants help improve slurry fluidity and have no negative impact on the setting time and strength at various ages of the backfill; in fact, they may even slightly increase strength due to improved microstructure.

[0018] (3) The preparation method of the present invention only requires simple mixing, without complex equipment and high energy consumption process, and the difficulty of large-scale production is low and the cost is controllable. The product is in dry powder form, and the usage method is extremely simple. It can be used immediately after mixing, without the need to modify the existing filling process. It is easy to operate and has strong promotion. Compared with the existing pretreatment technology, it greatly reduces the equipment investment and operating costs. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and comparative experiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0020] The specific effects of the present invention are illustrated below through examples and compared with comparative examples.

[0021] Example 1 A composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill, comprising, by weight, 35 parts of layered bimetallic hydroxide (LDH), 30 parts of magnesium hydrogen phosphate, 10 parts of sodium dihydrogen phosphate, 15 parts of modified zeolite, and 5 parts of polycarboxylate superplasticizer. The preparation method of the above-mentioned composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill includes the following steps: Layered bimetallic hydroxide (LDH), magnesium hydrogen phosphate, sodium dihydrogen phosphate, modified zeolite, and polycarboxylate superplasticizer are added to a three-dimensional motion mixer according to the set ratio. The mixture is stirred at 160 rpm for 5 minutes at room temperature until the powder of each component is evenly dispersed and there is no visible color difference or lumps. The dry powder composite ammonia solidifying agent is then obtained and sealed in packaging for later use.

[0022] Example 2 A composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill, comprising, by weight, 50 parts of layered bimetallic hydroxide (LDH), 20 parts of magnesium hydrogen phosphate, 5 parts of sodium dihydrogen phosphate, 20 parts of modified zeolite, and 3 parts of polycarboxylate superplasticizer. The preparation method of the above-mentioned composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill includes the following steps: Layered bimetallic hydroxide (LDH), magnesium hydrogen phosphate, sodium dihydrogen phosphate, modified zeolite, and polycarboxylate superplasticizer are added to a three-dimensional motion mixer according to the set ratio. The mixture is stirred at 160 rpm for 5 minutes at room temperature until the powder of each component is evenly dispersed and there is no visible color difference or lumps. The dry powder composite ammonia solidifying agent is then obtained and sealed in packaging for later use.

[0023] Example 3 A composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill, comprising, by weight, 25 parts of layered bimetallic hydroxide (LDH), 40 parts of magnesium hydrogen phosphate, 15 parts of sodium dihydrogen phosphate, 10 parts of modified zeolite, and 8 parts of polycarboxylate superplasticizer. The preparation method of the above-mentioned composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill includes the following steps: Layered bimetallic hydroxide (LDH), magnesium hydrogen phosphate, sodium dihydrogen phosphate, modified zeolite, and polycarboxylate superplasticizer are added to a three-dimensional motion mixer according to the set ratio. The mixture is stirred at 160 rpm for 5 minutes at room temperature until the powder of each component is evenly dispersed and there is no visible color difference or lumps. The dry powder composite ammonia solidifying agent is then obtained and sealed in packaging for later use.

[0024] Comparative Example 1 Compared with Example 1, the preparation method of this comparative example is basically the same as that of Example 1. The difference is that the composite ammonia-fixing agent of this comparative example does not contain layered bimetallic hydroxide (LDH).

[0025] Comparative Example 2 Compared with Example 1, the preparation method of this comparative example is basically the same as that of Example 1. The difference is that the composite ammonia-fixing agent of this comparative example does not contain sodium dihydrogen phosphate.

[0026] Comparative Example 3 Compared with Example 1, the preparation method of this comparative example is basically the same, except that the composite ammonia-fixing agent of this comparative example does not contain magnesium hydrogen phosphate.

[0027] Comparative Example 4 Compared with Example 1, the preparation method of this comparative example is basically the same as that of Example 1. The difference is that the solidifying agent of this comparative example is directly 100 parts of layered bimetallic hydroxide (LDH).

[0028] Comparative Example 5 Compared with Example 1, the preparation method of this comparative example is basically the same as that of Example 1. The difference is that the composite ammonia-fixing agent of this comparative example does not contain modified zeolite.

[0029] Test case Application method of composite ammonia-fixing agent: During cemented backfilling in mines, the prepared composite ammonia-fixing agent dry powder is added directly during the mixing process as a functional admixture. The dosage is 1.5% - 5.0% (mass fraction) of the total fly ash mass. The specific application process is as follows: (1) Weigh the cementitious material, ammonium salt fly ash, aggregate and water according to the filling ratio.

[0030] (2) Mix the composite ammonia-fixing agent with fly ash beforehand, or add it directly to the mixer along with other dry materials (cementing materials, aggregates).

[0031] (3) Add water and stir thoroughly for 3-5 minutes to form a uniform filling slurry.

[0032] (4) The slurry is transported to the underground goaf for filling.

[0033] To further verify the ammonia-fixing effect of the composite ammonia-fixing agent of the present invention for suppressing ammonia release from fly ash backfill, the composite ammonia-fixing agents prepared in Examples 1-3 and Comparative Examples 1-5 were added to standard backfill materials (cement:fly ash:tailings:water = 1:4:12:0.8) at a dosage of 3% for performance testing. The ammonia release inhibition rate, compressive strength, and initial fluidity of the slurry after addition were also tested. The blank group consisted of standard backfill materials without the addition of ammonia-fixing agent. The experimental values ​​are shown in Table 1 below.

[0034] Test method: Ammonia release inhibition rate determination: Following the method outlined in GB / T 14669-1993 "Determination of Ammonia in Air Quality - Ion Selective Electrode Method", fixed-size filled test blocks were prepared and placed in a sealed environment chamber. Gas samples were periodically extracted from the chamber to measure the ammonia concentration. The total ammonia release per unit mass of test block over a specific age period (e.g., 7 days) was calculated. The inhibition rate was then calculated by comparing the results with a blank control group without added ammonia-fixing agent.

[0035] Test of compressive strength of filling material: Refer to GB / T 17671-2021 Cement mortar strength test method (ISO method) to prepare standard test blocks, and test their compressive strength after curing to the specified age (e.g., 3 days, 7 days, 28 days).

[0036] Table 1 Performance test results of Examples 1-3 and Comparative Examples 1-5

[0037] As can be seen from Table 1, the composite ammonia-fixing agents prepared in Examples 1-3 of this invention exhibit excellent ammonia release inhibition effects (>92%), verifying the effectiveness of the adsorption-local acidification-precipitation synergistic mechanism. Simultaneously, due to the effect of the dispersant and reasonable microenvironment control, the fluidity of the filling slurry is improved, with no adverse effect on the 28-day compressive strength; in fact, it is slightly improved due to the optimized microstructure.

[0038] Comparing Example 1 and Comparative Example 1, it was found that without the primary adsorbent LDH, NH4 could not be effectively enriched under strong alkaline conditions. + This leads to low efficiency in subsequent precipitation reactions and a significant decrease in the ammonia fixation rate.

[0039] By comparing Example 1 and Comparative Example 2, the lack of sodium dihydrogen phosphate prevented the formation of a suitable local microenvironment (pH 9.0-10.5) at the adsorption site, severely hindering the formation of struvite (magnesium ammonium phosphate) precipitate. At the same time, the lack of buffering in the system led to poor component compatibility and affected flowability.

[0040] Comparing Example 1 and Comparative Example 3, the lack of a crucial magnesium ion source prevented the formation of magnesium ammonium phosphate precipitate. Adsorption by LDH alone may be reversible and has limited capacity, making long-term stable ammonia fixation impossible.

[0041] Comparing Example 1 and Comparative Example 4, it was found that using only LDH for physical adsorption resulted in rapid saturation of adsorption sites under high alkalinity and high ammonium ion concentrations, and it was unable to adsorb NH4+. + It transforms into a stable precipitate, resulting in a short-lived and limited effect in inhibiting ammonia release.

[0042] By comparing Example 1 and Comparative Example 5, although the auxiliary adsorbent was lacking in its ability to capture free ammonia, the core chemical fixation mechanism still functioned, and therefore the main performance was less affected.

[0043] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent transformations, reasonable adjustments to component ratios made based on the inventive concept of the present invention and the content of this specification, or direct or indirect applications to other related technical fields, should be included within the patent protection scope of the present invention.

Claims

1. A composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill, characterized in that, It is composed of the following raw materials in parts by weight: 25-55 parts of main adsorbent, 18-45 parts of precipitant, 4-18 parts of pH buffer and auxiliary precipitant, 8-25 parts of auxiliary adsorbent, and 2-10 parts of dispersant.

2. The composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill as described in claim 1, characterized in that, The main adsorbent is a layered bimetallic hydroxide.

3. The composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill as described in claim 1, characterized in that, The precipitant is selected from at least one of magnesium hydrogen phosphate and magnesium oxide.

4. The composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill as described in claim 1, characterized in that, The pH buffer and auxiliary precipitant is sodium dihydrogen phosphate.

5. The composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill as described in claim 1, characterized in that, The auxiliary adsorbent is selected from at least one of modified zeolite and biochar.

6. The composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill as described in claim 1, characterized in that, The dispersant is a polycarboxylate superplasticizer.

7. The composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill as described in claim 1, characterized in that, It is composed of the following raw materials in parts by weight: 30-50 parts of main adsorbent, 20-40 parts of precipitant, 5-15 parts of pH buffer and auxiliary precipitant, 10-20 parts of auxiliary adsorbent, and 3-8 parts of dispersant.

8. The method for preparing the composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill as described in any one of claims 1-7, characterized in that, include: Mix the main adsorbent, precipitant, pH buffer, auxiliary precipitant, auxiliary adsorbent, and dispersant evenly.

9. The application of the composite ammonia-fixing agent for inhibiting ammonia release from fly ash backfill as described in any one of claims 1-7 during fly ash backfilling.

10. The application as described in claim 9, characterized in that, The composite ammonia-fixing agent is added to the fly ash at a rate of 1.5%-5% of the total mass of the fly ash.

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