A method for preparing a fly ash-based hardness removal agent

Abstract

This invention discloses a method for preparing a fly ash-based hardening agent, comprising: 1) acid leaching to obtain an acid leaching solution, then washing the solid residue with deionized water until neutral, and drying at 110 ℃ for 2 h to obtain a dried sample; 2) alkali leaching: mixing and stirring the dried sample with an ammonia solution at room temperature, then vacuum filtering and separating, collecting the alkali filtrate, rinsing the filter with distilled water, collecting the washing liquid, and mixing the alkali filtrate and washing liquid to obtain an alkali leaching solution; 3) polymerization: adding the alkali leaching solution dropwise into the acid leaching solution while magnetically stirring until the pH value is 4.2, and aging to obtain a stable polysilicate; 4) preparing polysilicates with different (Al+Fe) / Si ratios, bathing in a 30 ℃ water bath for 24 h, then storing in a 4 ℃ refrigerator, and drying all samples in a -42 ℃ freeze dryer for 48 h to obtain the fly ash-based hardening agent. This invention's preparation method has high resource utilization, strong process synergy, controllable and adjustable products, environmental friendliness, and high hardening removal efficiency.

Description

Technical Field

[0001] This invention belongs to the technical field of hardness removal agents, specifically relating to a method for preparing a fly ash-based hardness removal agent. Background Technology

[0002] The main components of black water and ash water from coal gasification include suspended solids, hardness components, and acidic gases. Common suspended solids in black water and ash water include fine ash and slag, which mainly originate from the quench chamber, carbon washing tower, and slag pool in the high-pressure pulverized coal gasification process. In addition, black water and ash water also contain high levels of hardness components, primarily calcium (Ca). 2+ ), magnesium (Mg) 2+ divalent cations such as bicarbonate (HCO3-) 3- ), sulfate (SO4 2- ), silicate (H3SiO4) - ) and phosphate (HPO4) 2- These components exist in anionic forms such as ions, which not only affect the reuse of grey water, but also easily lead to scaling in pipes and equipment, increasing maintenance costs. Summary of the Invention

[0003] To address the problems existing in the prior art, the purpose of this invention is to provide a method for preparing a fly ash-based hardening agent, which is specifically achieved through the following technical solution:

[0004] A method for preparing a fly ash-based hardening agent, the method comprising the following steps:

[0005] 1) Acid leaching: Take fly ash, rinse it with water to remove soluble salts, transfer the precipitate to a beaker, add sulfuric acid to the beaker for acid leaching while stirring, then separate by vacuum filtration, collect the acid filtrate, rinse the filter with distilled water, collect the washing liquid, mix the acid filtrate and washing liquid to obtain acid leaching solution, then wash the solid residue with deionized water until neutral, dry at 110℃ for 2h to obtain a dry sample;

[0006] 2) Alkali leaching: The dried sample obtained in step 1) is mixed and stirred with an ammonia solution at room temperature, then separated by vacuum filtration, and the alkali filtrate is collected. The filtration device is then rinsed with distilled water and the washing liquid is collected. The alkali filtrate and the washing liquid are mixed to obtain the alkali leaching solution.

[0007] 3) Polymerization: The alkaline leaching solution is added dropwise to the acidic leaching solution while magnetically stirring until the pH value is 4.2. After aging, a stable polysilicate is obtained.

[0008] 4) Preparation of polysilicates with different (Al+Fe) / Si ratios: When the solution turns light blue, add different volumes of acid leaching solution to the polysilicate under stirring to obtain solutions with different silicon contents. Place the solutions in a 30°C water bath for 24 hours, and then store them in a 4°C refrigerator. All samples are dried in a -42°C freeze dryer for 48 hours to obtain fly ash-based hardening remover.

[0009] Furthermore, in step 1), the ratio of precipitate to sulfuric acid is 1g:6ml, and the concentration of sulfuric acid is 10%.

[0010] Furthermore, in step 1), the acid leaching temperature is 100℃ and the acid leaching time is 2h.

[0011] Furthermore, in step 2), the concentration of the ammonia solution is 10%, and the stirring time is 6 hours.

[0012] Furthermore, in step 3), the concentration of the acid leaching solution is 2 mol / L, and the aging time is 20 min.

[0013] Furthermore, in step 4), the molar ratio of polysilicates with different (Al+Fe) / Si ratios is 10-13:1.

[0014] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0015] 1) High resource utilization rate: The step-by-step acid leaching-alkali leaching process efficiently extracts active silicon, aluminum, iron and other components from fly ash, realizing the high-value utilization of solid waste;

[0016] 2) Strong process synergy: The acid leaching stage (100℃ sulfuric acid treatment) and the alkali leaching stage (room temperature ammonia treatment) complement each other: acid leaching preferentially dissolves aluminum and iron, while alkali leaching selectively extracts silicon. The filtrates from both processes are precisely polymerized (pH=4.2) to generate polysilicates, which solves the problem of incomplete separation of metals and silicon in traditional methods.

[0017] 3) Product controllability and adjustability: By dynamically adjusting the amount of acid leaching solution added, the (Al+Fe) / Si molar ratio can be precisely controlled within the range of 10-13:1, which is more adaptable than the existing fixed ratio process and can optimize the composition of hardening remover for different water hardness.

[0018] 4) Outstanding performance stability: Gradient temperature treatment (30℃ water bath → 4℃ refrigeration → -42℃ freeze drying) enables polysilicate to form a stable network structure, and the product does not exhibit gelation during storage;

[0019] 5) Significantly environmentally friendly: The final product is an inorganic polymer, with no risk of secondary pollution, which is superior to organophosphorus hardeners; the fly ash residue can meet the standards for building material raw materials after neutralization treatment, realizing the utilization of all components;

[0020] 6) Significant cost advantages: The energy consumption of the preparation process is reduced by 40%, the acid leaching time is shortened to 2 hours, and the alkali leaching does not require heating;

[0021] 7) Improved hardening efficiency: The prepared polysilicate has a better effect on Ca... 2+ Mg 2+ The complexing capacity is over 300 mg / g, and the formed flocs are easier to settle, requiring only 20 minutes of aging time. Attached Figure Description

[0022] Figure 1 The preparation process of the fly ash-based hardening agent of the present invention is as follows;

[0023] Figure 2 Infrared characterization spectra of the fly ash-based hardening agent prepared in this invention ((a) novel fly ash-based hardening agents with different (Al+Fe) / Si molar ratios, (b) hardening agents synthesized from precipitates with different (Al+Fe) / Si molar ratios, (c) precipitates after hardening).

[0024] Figure 3 XRD patterns of a novel fly ash-based hardening agent (denoted as PAFSiC) with different (Al+Fe) / Si molar ratios;

[0025] Figure 4 SEM images of the fly ash-based hardening agent prepared in this invention ((a), (b), (c), (d), and (e) are novel fly ash-based hardening agents with (Al+Fe) / Si molar ratios of 5:1, 7:1, 10:1, 13:1, and 15:1, respectively);

[0026] Figure 5 The experimental results of the fly ash-based hardening agent prepared according to this invention are shown in the figure.

[0027] Figure 6 The water quality indicators of ash water (water sample 1) after using the fly ash-based hardening agent of the present invention;

[0028] Figure 7 The water quality indicators of ash water (water sample 2) after using the fly ash-based hardening agent of the present invention;

[0029] Figure 8 The water quality indicators of ash water (water sample 3) after using the fly ash-based hardening agent of the present invention. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments in order to better understand the technical solution.

[0031] Example: Preparation of fly ash-based hardening agent

[0032] This fly ash-based hardening agent is prepared from fly ash as raw material, and the main components of the fly ash used are shown in Table 1.

[0033] Table 1: Main Components of Fly Ash

[0034]

[0035] The specific preparation steps are as follows:

[0036] Step 1, acid leaching: Take 50g of the precipitate from fly ash after rinsing with water to remove soluble salts (mainly chlorides, sodium salts, etc.), transfer it to a 500ml beaker, add 300ml of sulfuric acid (10% = 2.88mol / L), and leach at 100℃ for 2 hours while stirring. Then, separate by vacuum filtration, collect the acid filtrate, rinse the filter with distilled water, collect the washing liquid, mix the acid filtrate and washing liquid to obtain the acid leaching solution, then wash the solid residue with deionized water until neutral, and dry at 110℃ for 2 hours to obtain the dried sample.

[0037] The second step is alkaline leaching: The dried sample from the first step is leached with an ammonia solution (10%) at room temperature and stirred for 6 hours. Then, it is separated by vacuum filtration, and the alkaline filtrate is collected. The filtration device is then rinsed with distilled water, and the washing liquid is collected. The alkaline filtrate and washing liquid are mixed to obtain the alkaline leaching solution.

[0038] The third step is polymerization: the alkaline leaching solution is added dropwise to the 2 mol / L sulfur leaching solution while magnetically stirring until the pH reaches 4.2, and then aged for 20 minutes to obtain stable polysilicate.

[0039] Step 4: Preparation of polysilicates with different (Al+Fe) / Si ratios: When the solution turns pale blue, different volumes of acid leaching solution are added to the polysilicate under stirring to obtain solutions with different silicon contents. The solutions are then placed in a 30°C water bath for 24 hours, followed by storage in a 4°C refrigerator. All samples are dried in a -42°C freeze dryer for 48 hours to obtain the fly ash-based hardening remover. The preparation process is as follows: Figure 1 As shown.

[0040] The fly ash-based hardening agents prepared in the examples were characterized. Fly ash-based hardening agents were prepared according to (Al+Fe) / Si molar ratios of 5-15:1, and their infrared characterization spectra are shown below. Figure 2 As shown, by Figure 2 Possible chemical bonds can be identified, 3442 cm⁻¹ -1 and 1641cm -1 The two absorption peaks at 2346 cm⁻¹ are likely due to the stretching vibration of -OH and the bending vibration of adsorption, polymerization, and crystallization water in the coagulant. -1 The peak at that location is caused by carbon dioxide in the air. Figure 2 (a) 815cm -1The wavenumber absorption peak corresponds to the Si-O-Si symmetric stretching vibration, at 665 cm⁻¹. -1 The peak at that location can be attributed to the bending vibrations of the Si-O-Fe bonds, indicating the formation of a silicon-iron-oxygen polymer in the sample. Figure 1 (c) 1021cm -1 The presence of this substance can be attributed to Si-O-Al bonds, indicating that the precipitate also possesses the conditions to act as a hardening agent. Figure 2 (b) in the figure represents a hardening agent synthesized from precipitates, which is missing 815 cm. -1 The peak corresponds to Si-O-Si bonds, suggesting that the hardening agent synthesized from the precipitate may be ineffective. Figure 1 It can be seen that the new fly ash-based hardening agent is a complex compound formed by Fe, Al, and Si.

[0041] XRD patterns of fly ash-based hardening removers (denoted as PAFSiC) with different (Al+Fe) / Si molar ratios are shown below. Figure 3 As shown, by Figure 3 It can be seen that PAFSiC with different silicon contents has certain similarities. The peaks at 15° and 17° are attributed to AlCl3·6H2O, which is due to the presence of free Al. 3+ The crystals are formed. The peaks at 32° and 46° are attributed to NaCl, which is a byproduct formed during the drying process of the sample. Ca3Al2(SiO4)2(OH)4 (Hibschite) is a product formed during the synthesis of coagulants. It does not have much coagulation effect under neutral conditions, but under strongly alkaline conditions (such as pH≥12), it will release Ca. 2+ and Al(OH)4 - This also explains why the coagulation effect improved as the alkalinity increased during the experiment. The AlFeSiO4 corresponding to 27° also corresponds to the Si-O-Fe and Si-O-Al bonds in FT-IR. Therefore, it can be concluded that the fly ash-based hardening agent synthesized by the method of this invention is a mixture of various complex compounds.

[0042] The fly ash-based hardening remover (PAFSiC) prepared by the method of this invention is an amorphous polymer composite material. The morphology of PAFSiC with different silicon contents was observed by SEM, and the results are as follows. Figure 4As shown in the figure, the morphology of PAFSiC changes significantly with silicon content. At higher silicon contents ((Al+Fe) / Si molar ratios of 5:1 and 7:1), many irregular particles are observed on the surface, indicating a tendency for the agglomerator to aggregate. When the (Al+Fe) / Si molar ratio increases to 10:1 and 13:1, a three-dimensional chain network structure appears, exhibiting good entrapment and agglomeration effects. However, when the (Al+Fe) / Si molar ratio further increases to 15:1, this chain network structure begins to disappear, transforming into a plate-like structure. The results indicate that a certain amount of silicon content is required to form a well-developed three-dimensional chain network structure. However, excessive silicon leads to the formation of aggregates, resulting in a plate-like structure rather than a chain network. Therefore, the hardening remover synthesized with an (Al+Fe) / Si molar ratio of 10:1-13:1 should have the best effect.

[0043] The experimental results of fly ash-based hardening remover prepared by the method of this invention under different formulations are shown in the figure. Figure 5 As shown, by Figure 5 It can be seen that the water after hardness removal is relatively clear, and the sediment appears as aggregated flocculent matter. The flocculated sediment is yellow, presumably due to the presence of a small amount of Fe. 3+ lead to.

[0044] The main components and conventional indicators of the ash water from the second phase of the coal-to-gas project of Zhejiang Petrochemical Co., Ltd. were analyzed, and the results are shown in Tables 2 and 3. As can be seen from the tables, the ash water has a high content of inorganic ions. Among the inorganic ions, calcium (Ca) is particularly high. 2+ ), magnesium (Mg) 2+ divalent cations such as carbonate (HCO3-) - ), sulfate (SO4 2- ), silicate (H3SiO4) - The content of these ions is relatively high, and they are all ions that contribute to scaling, forming scaling components such as calcium carbonate (CaCO3), calcium sulfate (CaSO4), and magnesium silicate (MgSiO3).

[0045] Table 2

[0046]

[0047] Table 3

[0048]

[0049] During the production process, to ensure the stable operation of the grey water discharge and reuse system, key performance indicators were specified, primarily: pH 6-9 and hardness mg / L < 1000. To reduce the likelihood of scaling during grey water reuse, the most effective measure is to address the main scaling contributor – calcium (Ca). 2+ ), magnesium (Mg) 2+This will remove the wastewater and reduce the burden on external drainage treatment.

[0050] The fly ash-based hardening agent (PAFCS) prepared according to this invention was used to conduct hardening experiments on water samples 1-3, and various water indicators (total hardness, calcium hardness, magnesium hardness, silicon content, sodium ion content, alkalinity, turbidity, and total dissolved solids content) were further tested. Figures 6-8 The dosage of the new fly ash-based hardening agent is 0-200 ppm, and the dosage of PAM is 5 ppm.

[0051] In three tests on water samples, the fly ash-based hardening agent performed excellently; the main indicators all decreased significantly at a dosage of 100-200 ppm. The new fly ash-based hardening agent meets the requirements for hardening removal in ash-water applications, and requires a relatively small dosage.

Claims

1. A method for preparing a fly ash-based hardening agent, characterized in that, The method includes the following steps: 1) Acid leaching: Take fly ash, rinse it with water to remove soluble salts, transfer the precipitate to a beaker, add sulfuric acid to the beaker for acid leaching while stirring, then separate by vacuum filtration, collect the acid filtrate, rinse the filter with distilled water, collect the washing liquid, mix the acid filtrate and washing liquid to obtain acid leaching solution, then wash the solid residue with deionized water until neutral, dry at 110 ℃ for 2 h to obtain a dry sample; 2) Alkali leaching: The dried sample obtained in step 1) is mixed and stirred with an ammonia solution at room temperature, then separated by vacuum filtration, and the alkali filtrate is collected. The filtration device is then rinsed with distilled water and the washing liquid is collected. The alkali filtrate and the washing liquid are mixed to obtain the alkali leaching solution. 3) Polymerization: The alkaline leaching solution is added dropwise to the acidic leaching solution while magnetically stirring until the pH value is 4.

2. After aging, a stable polysilicate is obtained. 4) Preparation of polysilicates with different (Al+Fe) / Si ratios: When the polysilicate solution in step 3) turns light blue, different volumes of acid leaching solution are added to the polysilicate under stirring to obtain solutions with different silicon contents. In the polysilicates with different (Al+Fe) / Si ratios, the molar ratio of (Al+Fe) to Si is 10-13:

1. The solution is placed in a water bath at 30 ℃ for 24 h, and then stored in a refrigerator at 4 ℃. All samples are dried in a freeze dryer at -42 ℃ for 48 h to obtain fly ash-based hardening remover.

2. The preparation method of a fly ash-based hardening agent as described in claim 1, characterized in that... In step 1), the ratio of precipitate to sulfuric acid is 1g:6ml, and the concentration of sulfuric acid is 10%.

3. The preparation method of a fly ash-based hardening agent as described in claim 1, characterized in that... In step 1), the acid leaching temperature is 100℃ and the acid leaching time is 2 hours.

4. The preparation method of a fly ash-based hardening agent as described in claim 1, characterized in that... In step 2), the concentration of the ammonia solution is 10%, and the stirring time is 6 hours.

5. The preparation method of a fly ash-based hardening agent as described in claim 1, characterized in that... In step 3), the concentration of the acid leaching solution is 2 mol / L, and the aging time is 20 min.

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