Preparation Method and Application of a Polyoxometalate-Mediated Composite Flocculant Based on Coal Gasification Slag

Abstract

The present invention belongs to the technical field of resource utilization of solid waste, and relates to a preparation method and application of a polyacid-mediated coal gasification slag-based composite flocculant. The preparation method includes: taking coal gasification slag in a container, adding hydrochloric acid solution, and carrying out an acid leaching reaction. After the reaction is completed, suction filtration is carried out to obtain acid leaching filtrate A; taking coal gasification slag in a container, adding acetic acid solution, and carrying out an acid leaching reaction. After the reaction is completed, suction filtration is carried out to obtain acid leaching filtrate B; mixing acid leaching filtrate A and acid leaching filtrate B, heating and stirring for reaction. After the reaction is completed, standing at room temperature to completely ripen it to form a colloidal substance, and drying and grinding the colloidal substance evenly to obtain the polyacid-mediated coal gasification slag-based composite flocculant. The polyacid-mediated coal gasification slag-based composite flocculant of the present invention has excellent performance compared with the polyacid-mediated coal gasification slag-based composite flocculant prepared by single acid leaching, and greatly improves the removal rates of sewage turbidity, ammonia nitrogen, total phosphorus, and COD.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource utilization of solid waste, and relates to a preparation method and application of a polyacid-mediated coal gasification slag-based composite flocculant. Background Art

[0002] Coal gasification technology refers to a technology in which appropriately treated coal is fed into a reactor such as a gasifier, and at a certain temperature and pressure, it is converted into gas through an oxidant (air or oxygen and steam) in a certain flow mode (moving bed, fluidized bed or entrained bed) to obtain crude water gas, and refined carbon monoxide gas can be obtained through subsequent processes such as desulfurization and decarbonization. It is an important way and means for the clean utilization of coal resources. However, coal gasification technology will produce a large amount of coal gasification slag. At present, the utilization rate of coal gasification slag is relatively low, and its main treatment methods are stacking and landfilling. There is still a lack of key technologies for effective large-scale and high-value utilization. A large amount of coal gasification slag piled on the ground will not only cause a large amount of land waste, but also, due to the relatively small particle size of some coal gasification slag, dust will be generated during direct stacking, which is easily inhaled by animals and humans, and the heavy metal elements in the coal gasification slag will pose a serious threat to biological health. The coal gasification slag contains heavy metals such as Cu, Zn, Pb, Cr, Ni, and As. The coal gasification slag itself will not leach heavy metal substances, but under the action of acid rain leaching, river water scouring, or erosion by weak acidic landfill leachate in the landfill, the heavy metal components contained in it will gradually be released into the surrounding environment, causing water and soil pollution. Therefore, the disposal and efficient and clean utilization of coal gasification slag are imminent.

[0003] At present, the utilization of coal gasification slag mainly focuses on the following aspects:

[0004] (1) Preparation of building materials (such as wall materials, blended cement, aggregates, road base materials);

[0005] (2) Soil improvement (such as improving the microbial diversity of compost, soil improvers, improved planting sand);

[0006] (3) Water body restoration (such as zeolite, adsorbents, etc.);

[0007] (4) Other uses (such as plastic fillers, circulating co-combustion, hydrogen production, CO2 adsorption).

[0008] At present, flocculants are mainly prepared from chemical agents, and the cost is relatively high. Therefore, using solid waste to prepare polymer flocculants is an economical and environmentally friendly way. Moreover, as a solid waste rich in metal elements such as aluminum, iron, and calcium, coal gasification slag has the natural characteristic composition for preparing flocculants. Therefore, this study proposes a method for low-cost and high-value utilization of coal gasification slag, and prepares an environmentally friendly and highly efficient inorganic polymer flocculant for wastewater treatment. Summary of the Invention

[0009] To overcome the above problems, the present invention provides a preparation method and application of a polyacid-mediated coal gasification slag-based composite flocculant. Using the composite flocculant provided by the present invention, flocculation treatment is carried out on domestic wastewater, river water and aquaculture wastewater respectively. The highest turbidity removal rate of domestic sewage can reach 91.42%, the highest COD removal rate can reach 63.07%, and the highest total phosphorus removal rate can reach 80.25%. The highest turbidity removal rate of river water can reach 93.67%, the highest COD removal rate can reach 63.08%, and the highest total phosphorus removal rate can reach 75.02%. The highest turbidity removal rate of aquaculture wastewater can reach 78.69%, the highest COD removal rate can reach 47.36%, and the highest total phosphorus removal rate can reach 85.14%.

[0010] In the first aspect of the present invention, a preparation method of a polyacid-mediated coal gasification slag-based composite flocculant is provided, and the method includes:

[0011] (1) Take coal gasification slag in a container, add hydrochloric acid solution, stir under closed conditions for acid leaching reaction. After the reaction is completed, filter by suction, separate solid and liquid to obtain acid leaching filtrate A, and seal acid leaching filtrate A for later use;

[0012] (2) Take coal gasification slag in a container, add acetic acid solution, stir under closed conditions for acid leaching reaction. After the reaction is completed, filter by suction, separate solid and liquid to obtain acid leaching filtrate B, and seal acid leaching filtrate B for later use;

[0013] (3) Mix acid leaching filtrate A and acid leaching filtrate B, add NaOH solution, adjust the pH of the mixed solution, heat and stir for reaction. After the reaction is completed, let it stand at room temperature to thoroughly mature to form a colloidal substance. Dry the colloidal substance and grind it evenly to obtain the polyacid-mediated coal gasification slag-based composite flocculant.

[0014] In the second aspect of the present invention, a polyacid-mediated coal gasification slag-based composite flocculant prepared by the above preparation method is provided.

[0015] In the third aspect of the present invention, the application of the above polyacid-mediated coal gasification slag-based composite flocculant in wastewater treatment is provided.

[0016] The beneficial effects of the present invention are as follows:

[0017] (1) The preparation method of the polyacid-mediated coal gasification slag-based composite flocculant of the present invention not only realizes the resource utilization of coal gasification slag, but also has excellent performance compared with the coal gasification slag-based composite flocculant prepared by single acid leaching, improving the removal rates of sewage turbidity, total phosphorus and COD, and the prepared polyacid-mediated coal gasification slag-based composite flocculant can be used in various occasions such as sewage with low pollutant concentration or serious pollution, and has a wide application range.

[0018] (2) In this application, by adjusting the compounding ratio of the two acid leaching filtrates, the composition and polymerization degree of the synthesized flocculant are changed, and then the flocculation effect of the polyacid-mediated coal gasification slag-based composite flocculant is changed.

[0019] (3) The coal gasification slag mainly consists of residual carbon and inorganic components. The inorganic components mainly include metal oxides such as SiO2, Al2O3, Fe2O3, CaO, and MgO. Most of the metal oxides can be leached out by hydrochloric acid leaching, such as Al2O3, Fe2O3, CaO, and MgO. However, acetic acid does not react with Al2O3. Therefore, when acetic acid leaching is used, only metal oxides such as Fe2O3, CaO, and MgO are leached out. Using this property, the hydrochloric acid leaching solution and the acetic acid leaching solution can be mixed in a certain proportion to adjust the ratio of metal ions, and thus a polyacid-mediated coal gasification slag-based composite flocculant with more excellent performance can be obtained. It is found that a series of chemical changes occur in the solution system, mainly involving hydrolysis reaction and polymerization reaction. Fe 3+ and Al 3+ undergo hydrolysis in the system and combine with OH - in the system. This reaction is a reversible process. By heating, the Brownian motion of molecules is intensified, which promotes the rapid hydrolysis and polymerization of Fe 3+ and Al 3+ . Fe 3+ and Al 3+ combine with OH - to form compounds with different coordinations, but these compounds are extremely unstable. And metal ions such as Mg and Ca in the solution combine with this kind of substance to make it stable. By adjusting the ratio of the hydrochloric acid leaching solution to the acetic acid leaching solution, and then adjusting the ratio of metal ions in the solution, and the introduction of CH3COO - can effectively increase the molecular weight of the polyacid-mediated coal gasification slag-based composite flocculant, which is more conducive to improving its flocculation performance, and then changing the flocculation effect of the polyacid-mediated coal gasification slag-based composite flocculant. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0021] Figure 1 XRD diagrams of polyacid-mediated coal gasification slag-based composite flocculants with different compounding ratios prepared in Examples 1 to 5 of the present invention;

[0022] Figure 2 FT-IR diagrams of polyacid-mediated coal gasification slag-based composite flocculants with different compounding ratios prepared in Examples 1 to 5 of the present invention;

[0023] Figure 3 It is the effect diagram of treating domestic wastewater with polyoxometalate-mediated gasification slag-based composite flocculants with different compounding ratios in Experimental Example 1 of the present invention;

[0024] Figure 4 It is the effect diagram of treating domestic wastewater with the polyoxometalate-mediated gasification slag-based composite flocculant under the optimal preparation conditions in Experimental Example 2 of the present invention;

[0025] Figure 5 It is the effect diagram of treating river water with the polyoxometalate-mediated gasification slag-based composite flocculant under the optimal preparation conditions in Experimental Example 3 of the present invention;

[0026] Figure 6 It is the effect diagram of treating aquaculture wastewater with the polyoxometalate-mediated gasification slag-based composite flocculant under the optimal preparation conditions in Experimental Example 4 of the present invention;

[0027] Figure 7 It is the effect diagram of treating domestic wastewater with the polyoxometalate-mediated gasification slag-based composite flocculant prepared in Example 1 of the present application and the gasification slag-based composite flocculant prepared with a single acid leaching solution in Experimental Example 5 of the present invention;

[0028] Figure 8 It is the SEM diagram of the gasification slag-based composite flocculant prepared with the polyoxometalate-mediated gasification slag-based composite flocculant prepared in Example 1 of the present application and a single acid leaching solution in Experimental Example 5 of the present invention, where A and B are the SEM diagrams of Flocculant A prepared with hydrochloric acid leaching solution; C and D are the SEM diagrams of Flocculant B prepared with glacial acetic acid leaching solution; E and F are the SEM diagrams of the polyoxometalate-mediated gasification slag-based composite flocculant of the present invention;

[0029] Figure 9 It is the FT-IR diagram of the gasification slag-based composite flocculant prepared with the polyoxometalate-mediated gasification slag-based composite flocculant prepared in Example 1 of the present application and a single acid leaching solution in Experimental Example 5 of the present invention;

[0030] Figure 10 It is the XRD diagram of the gasification slag-based composite flocculant prepared with the polyoxometalate-mediated gasification slag-based composite flocculant prepared in Example 1 of the present application and a single acid leaching solution in Experimental Example 5 of the present invention. Detailed implementation manners

[0031] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0032] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] The first typical embodiment of the present invention is a method for preparing a polyoxometalate-mediated coal gasification slag-based composite flocculant, and the method includes:

[0034] (1) Take coal gasification slag in a container, add hydrochloric acid solution, stir under closed conditions for acid leaching reaction. After the reaction is completed, filter by suction to separate the solid and liquid, and obtain acid leaching filtrate A. Seal acid leaching filtrate A for later use;

[0035] (2) Take coal gasification slag in a container, add acetic acid solution, stir under closed conditions for acid leaching reaction. After the reaction is completed, filter by suction to separate the solid and liquid, and obtain acid leaching filtrate B. Seal acid leaching filtrate B for later use;

[0036] (3) Mix acid leaching filtrate A and acid leaching filtrate B, add NaOH solution, adjust the pH of the mixed solution, heat and stir for reaction. After the reaction is completed, let it stand at room temperature to thoroughly mature to form a colloidal substance. Dry the colloidal substance and grind it evenly to obtain the polyoxometalate-mediated coal gasification slag-based composite flocculant.

[0037] In one or more embodiments, in step (1), the dosage ratio (mass: volume) of coal gasification slag to hydrochloric acid solution is (1.0 - 10 g):(1.0 - 10 mL), preferably 1.0 g:10 mL.

[0038] In one or more embodiments, in step (1), the concentration of the hydrochloric acid solution is 2.0 - 5.0 mol / L, preferably 3.0 mol / L. When preparing the polyoxometalate-mediated coal gasification slag-based composite flocculant, due to the metal oxide properties contained in the used coal gasification slag, when using a hydrochloric acid solution with a concentration of 3.0 mol / L for acid leaching, the leaching effect of metal ions is the best. When the concentration of the hydrochloric acid solution is higher than 3.0 mol / L, the coal gasification slag is likely to form a colloid, which is not conducive to solid-liquid separation; the leaching rate of the hydrochloric acid solution with a concentration of 3.0 mol / L for metal oxides reaches the maximum, and the leaching rate of metal ions is lower when it is lower than 3.0 mol / L.

[0039] In one or more embodiments, in step (1), during the reaction process, the reaction temperature is 20 - 60 °C, preferably 40 °C.

[0040] In one or more embodiments, in step (1), the acid leaching time of the hydrochloric acid solution is 0.5 to 2.5 h, preferably 1.5 h. At this acid leaching time, the leaching rate of metal ions reaches the maximum value. Therefore, the hydrochloric acid leaching time is preferably 1.5 h.

[0041] In one or more embodiments, in step (2), the dosage ratio (mass: volume) of the coal gasification slag to the acetic acid solution is (1.0 - 10 g):(1.0 - 10 mL), preferably 1.0 g:10 mL.

[0042] In one or more embodiments, in step (2), the concentration of the acetic acid solution is 2.0 - 6.0 mol / L, preferably 5 mol / L. In the acid leaching experiment of the acetic acid solution on the coal gasification slag at this concentration, the leaching rate of metal ions in the coal gasification slag reaches the highest. Therefore, the acetic acid leaching concentration is preferably 5 mol / L.

[0043] In one or more embodiments, in step (2), during the reaction process, the reaction temperature is 20 - 60 °C, preferably 40 °C.

[0044] In one or more embodiments, in step (2), the acetic acid leaching time is 0.5 - 2.5 h, preferably 2.0 h. At this acid leaching time, the leaching rate of metal ions reaches the maximum value. Therefore, the acetic acid solution leaching time is preferably 2.0 h.

[0045] In one or more embodiments, in step (3), the volume ratio of the acid leaching filtrate A to the acid leaching filtrate B is 1 - 5:1 - 5, preferably 5:1, 3:1, 3:2, 1:1, 2:3, and further preferably 3:2. At this ratio, the removal efficiency of turbidity, total phosphorus and COD in the wastewater is the highest when preparing the polyacid-mediated coal gasification slag-based composite flocculant.

[0046] In one or more embodiments, in step (3), after the acid leaching solutions are mixed, the pH is adjusted to 2 - 5, preferably 3.5; the temperature of the heating and stirring reaction is 50 - 90 °C, preferably 70 °C; the time of the heating and stirring reaction is 1 - 5 h, preferably 3 h.

[0047] In one or more embodiments, in step (3), the time for standing at room temperature to completely ripen is 20 - 30 h, preferably 24 h.

[0048] In one or more embodiments, the preparation method further includes drying and storing the prepared polyacid-mediated coal gasification slag-based composite flocculant in a sealed manner.

[0049] Principle:

[0050] The main components of coal gasification slag are residual carbon and inorganic components. The inorganic components mainly include metal oxides such as SiO2, Al2O3, Fe2O3, CaO, and MgO. Most of the metal oxides can be leached out by hydrochloric acid acid leaching, such as Al2O3, Fe2O3, CaO, and MgO. However, acetic acid does not react with Al2O3. Therefore, when acetic acid acid leaching is used, only metal oxides such as Fe2O3, CaO, and MgO are leached out. Utilizing this property, the hydrochloric acid leaching solution and the acetic acid leaching solution can be mixed in a certain proportion to adjust the proportion of metal ions, and thus a polyacid-mediated coal gasification slag-based composite flocculant with more excellent performance can be obtained.

[0051] Research has found that a series of chemical changes occur in the solution system, mainly involving hydrolysis reactions and polymerization reactions. Fe 3+ and Al 3+ undergo hydrolysis in the system and combine with OH - in the system. This reaction is a reversible process. By heating, the Brownian motion of molecules is intensified, which promotes the rapid hydrolysis and polymerization of Fe 3+ and Al 3+ . Fe 3+ and Al 3+ combine with OH - to form compounds with different coordinations, but these compounds are extremely unstable. Ions such as Mg and Ca in the solution combine with these substances to make them stable. By adjusting the proportion of the hydrochloric acid leaching solution and the acetic acid leaching solution, and then adjusting the proportion of metal ions in the solution, and the introduction of CH3COO - can effectively increase the molecular weight of the polyacid-mediated coal gasification slag-based composite flocculant, which is more conducive to improving its flocculation performance, and thus changing the flocculation effect of the polyacid-mediated coal gasification slag-based composite flocculant.

[0052] The second typical embodiment of the present invention provides a polyacid-mediated coal gasification slag-based composite flocculant prepared by the above preparation method.

[0053] The third typical embodiment of the present invention provides the application of the above polyacid-mediated coal gasification slag-based composite flocculant in wastewater treatment.

[0054] In one or more embodiments, the wastewater includes domestic wastewater, river water, and aquaculture wastewater.

[0055] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with specific examples.

[0056] Example 1 Preparation of Polyacid-Mediated Coal Gasification Slag-Based Composite Flocculant

[0057] Accurately weigh 20.0 g of coal gasification slag and place it in a 250 mL beaker. Add 200 mL of hydrochloric acid solution (concentration of 3.0 mol / L) and place it in a constant temperature heating magnetic stirrer. Stir and acid leaching at 40 ° C for 1.5 h. After the acid leaching process is completed, use a vacuum filter to filter and separate the solid and liquid to obtain acid leaching filtrate A.

[0058] Accurately weigh 20.0 g of coal gasification slag and place it in a 250 mL beaker. Add 200 mL of acetic acid solution (concentration of 5.0 mol / L) and place it in a constant temperature heating magnetic stirrer. Stir and acid leaching at 40 ° C for 2 h. After the acid leaching process is completed, use a vacuum filter to filter and separate the solid and liquid to obtain acid leaching filtrate B.

[0059] Acid leaching filtrate A and acid leaching filtrate B were mixed uniformly in a volume ratio of 3:2. The pH of the mixed solution was adjusted to 3.5. The mixture was stirred and reacted at 70°C for 3 hours. Then, it was allowed to stand at room temperature for 24 hours to allow it to mature thoroughly. The resulting multi-acid-mediated coal gasification slag-based composite flocculant was then dried, fully ground, and sealed for storage.

[0060] The multi-acid mediated coal gasification slag-based composite flocculant prepared in this example was subjected to infrared spectroscopy analysis and X-ray diffraction test, and the obtained infrared spectrum is shown in FIG. Figure 1 , XRD pattern see Figure 2 .Depend on Figure 1 and Figure 2 Analysis shows that, from the molecular structure and crystal phase, a multi-acid mediated coal gasification slag-based composite flocculant is prepared using the method of the present invention.

[0061] Example 2 Preparation of Polyacid-Mediated Coal Gasification Slag-Based Composite Flocculant

[0062] The preparation methods of acid leaching filtrate A and acid leaching filtrate B are the same as those in Example 1.

[0063] Acid leaching filtrate A and acid leaching filtrate B were mixed uniformly in a volume ratio of 2:3. The pH of the mixed solution was adjusted to 3.5. The mixture was stirred and reacted at 70°C for 3 hours. Then, it was allowed to stand at room temperature for 24 hours to allow it to mature thoroughly. The obtained multi-acid-mediated coal gasification slag-based composite flocculant was then dried, fully ground, and sealed for storage.

[0064] Example 3 Preparation of Polyacid-Mediated Coal Gasification Slag-Based Composite Flocculant

[0065] The preparation methods of acid leaching filtrate A and acid leaching filtrate B are the same as those in Example 1.

[0066] Acid leaching filtrate A and acid leaching filtrate B were mixed uniformly in a volume ratio of 3:1. The pH of the mixed solution was adjusted to 3.5. The mixture was stirred and reacted at 70°C for 3 hours. Then, it was allowed to stand at room temperature for 24 hours to allow it to mature thoroughly. The resulting multi-acid-mediated coal gasification slag-based composite flocculant was then dried, fully ground, and sealed for storage.

[0067] Example 4 Preparation of Polyacid-Mediated Coal Gasification Slag-Based Composite Flocculant

[0068] The preparation methods of acid leaching filtrate A and acid leaching filtrate B are the same as those in Example 1.

[0069] Acid leaching filtrate A and acid leaching filtrate B were mixed uniformly in a volume ratio of 5:1. The pH of the mixed solution was adjusted to 3.5. The mixture was stirred and reacted at 70°C for 3 hours. Then, it was allowed to stand at room temperature for 24 hours to allow it to mature thoroughly. The resulting multi-acid-mediated coal gasification slag-based composite flocculant was then dried, thoroughly ground, and sealed for storage.

[0070] Example 5 Preparation of Polyacid-Mediated Coal Gasification Slag-Based Composite Flocculant

[0071] The preparation methods of acid leaching filtrate A and acid leaching filtrate B are the same as those in Example 1.

[0072] Acid leaching filtrate A and acid leaching filtrate B were mixed uniformly in a volume ratio of 1:1. The pH of the mixed solution was adjusted to 3.5. The mixture was stirred and reacted at 70°C for 3 hours. Then, it was allowed to stand at room temperature for 24 hours to allow it to mature thoroughly. The obtained multi-acid-mediated coal gasification slag-based composite flocculant was then dried, fully ground, and sealed for storage.

[0073] Figure 1 These are the XRD patterns of the multi-acid mediated coal gasification slag-based composite flocculants with different compounding ratios prepared in Examples 1 to 5. Figure 2 The FT-IR images of the multi-acid mediated coal gasification slag based composite flocculants with different compounding ratios prepared in Examples 1 to 5 are shown in FIG. Figure 1 It can be seen that the characteristic peaks of the material are not much different when the compounding ratio is from 5:1 to 3:2, and basically only the diffraction peak of NaCl is present, indicating that the degree of polymerization of the material is very good when the compounding ratio is from 5:1 to 3:2, and an amorphous composite flocculant is formed, rather than a simple mixture. With the further increase of glacial acetic acid acid leaching solution, when the compounding ratio reaches 1:1 and 2:3, the XRD pattern shows that some miscellaneous peaks appear in the range of 10° to 30°, which indicates that the addition of too much glacial acetic acid acid leaching solution leads to system instability and affects the polymerization of the flocculant, causing some crystal salts to precipitate, thereby reducing the flocculation efficiency of the flocculant, which is the same as the result of the subsequent experimental example 1. It is concluded that the appropriate compounding ratio is conducive to the formation of a stable, highly polymerized, amorphous multi-acid-mediated coal gasification slag-based composite flocculant. Figure 2The FT-IR spectra of multi-acid mediated coal gasification slag based composite flocculants with different compounding ratios are shown in Figure 3. -1 and 1628cm -1 The bands are all related to the vibration of -OH, at 3400cm -1 The stretching vibrations of Al-OH, Fe-OH and H-OH are superimposed at 1628 cm -1 The peak intensity here is the bending vibration of H-OH, and it reaches the maximum when the compounding ratio is 3:2. This shows that the coordinated water content of Al-Fe hydroxylated copolymer in the multi-acid mediated coal gasification slag-based composite flocculant reaches the highest and is relatively stable. After they are converted into structural water, the bonding effect between them and the central ion is the strongest. This is one of the reasons why the multi-acid mediated coal gasification slag-based composite flocculant achieves the best flocculation efficiency when the compounding ratio is 3:2. -1 A weak characteristic peak appears at 478cm, which may be the asymmetric stretching vibration of Fe-O-Fe and Al-O-Al. -1 ~515cm -1 The bands may be the bending vibrations of Fe-O and Al-O. -1 The characteristic peak at 1408cm-1 is probably caused by the asymmetric stretching of the carboxylate group (-COO-). With the increase of glacial acetic acid, the intensity of this peak is significantly enhanced compared with the compound ratio of 5:1 and 3:1, proving that it is related to -COO-. And when the ratio reaches 3:2 to 2:3, the peak at 1408cm-1 is significantly enhanced compared with the compound ratio of 5:1 and 3:1. -1 Characteristic peaks appeared, attributed to the coordination interactions between metal ions such as Al and Fe in the polyacid-mediated coal gasification slag-based composite flocculant and -COO- groups. Overall, when the blend ratio reached 3:2, the intensities of the characteristic peaks of the polyacid-mediated coal gasification slag-based composite flocculant were significantly stronger than those at other ratios. This suggests that a suitable blend ratio can increase the degree of polymerization of the polyacid-mediated coal gasification slag-based composite flocculant, allowing the -OH and -COO- groups in the system to be more effectively bound. Therefore, when the blend ratio was 3:2, the polyacid-mediated coal gasification slag-based composite flocculant had the highest degree of polymerization and flocculation efficiency, which is consistent with previous experimental results. These results indicate that the polyacid-mediated coal gasification slag-based composite flocculant formed by the blend is not a simple mixture, but rather a flocculant composed of metal elements such as Fe and Al, exhibiting properties such as Fe(III) and Al(III).

[0074] Comparative Example 1

[0075] The preparation method of acid leaching filtrate A is the same as that in Example 1.

[0076] The pH of the acid leaching filtrate A was adjusted to 3.5, stirred and reacted at 70°C for 3 hours, and then allowed to stand at room temperature for 24 hours to allow it to mature completely. The obtained flocculant was then dried, fully ground, and sealed for storage.

[0077] Comparative Example 2

[0078] The preparation method of acid leaching filtrate B is the same as that in Example 1.

[0079] The pH of the acid leaching filtrate B was adjusted to 3.5, stirred and reacted at 70°C for 3 hours, and then allowed to stand at room temperature for 24 hours to allow it to mature completely. The obtained flocculant was then dried, fully ground, and sealed for storage.

[0080] Experimental Example 1

[0081] Take 5 beakers, place 200 mL of domestic sewage in the beakers, add 250 mg / L of the multi-acid-mediated coal gasification slag-based composite flocculant prepared in Examples 1 to 5, respectively, and then stir rapidly at a speed of 250 r / min on a stirrer for 1 min to mix, then stir slowly at a speed of 60 r / min for 20 min. After standing for 20 min, the turbidity, total phosphorus, and COD of the sewage are measured, and the removal rate is calculated.

[0082] The test results are as follows Figure 3 As shown, it can be seen that the final flocculation effect is different when the ratio of acid leaching filtrate A to acid leaching filtrate B is different. When the ratio of acid leaching filtrate A to acid leaching filtrate B is 3:2, the flocculation effect is optimal.

[0083] Example 2

[0084] Take 6 beakers, place 200mL of domestic sewage in the beakers, add different doses of flocculants, namely 50, 100, 150, 200, 250, and 300mg / L respectively, then stir quickly at a speed of 250r / min on the stirrer for 1min to mix, then stir slowly at a speed of 60r / min for 20min, after standing for 20min, measure the turbidity, total phosphorus, and COD of the sewage, and calculate the removal rate.

[0085] Test results such as Figure 4 As shown in the figure, pollutant removal rates increase with increasing dosage, reaching their maximum at 300 mg / L. Turbidity removal rates reached a maximum of 91.42%, COD removal rates reached a maximum of 63.07%, and total phosphorus removal rates reached a maximum of 80.25%. However, increasing the dosage from 250 mg / L to 300 mg / L did not significantly improve the removal rate, so the flocculant dosage used for domestic wastewater treatment was 250 mg / L.

[0086] The test results demonstrate the reliability of the polyoxometalate-mediated gasification slag-based composite flocculant of the present invention. Moreover, the preparation method of the polyoxometalate-mediated gasification slag-based composite flocculant of the present invention is simple in operation. It can not only treat gasification slag on a large scale, but also the polyoxometalate-mediated gasification slag-based composite flocculant prepared from gasification slag can be applied to the treatment and disposal of sewage, making it suitable for large-scale promotion.

[0087] Experimental Example 3

[0088] Take 6 beakers, place 200 mL of river water in the beakers, and add flocculants at different dosages, namely 100, 150, 200, 250, 300, and 350 mg / L respectively. Then, quickly stir for 1 min at a speed of 250 r / min on a stirrer to mix evenly. Next, slowly stir for 20 min at a speed of 60 r / min. After standing for 20 min, measure the turbidity, total phosphorus, and COD of the sewage, and calculate the removal rate.

[0089] The test results are as Figure 5 shown. It can be seen that as the dosage increases, the removal rate of pollutants continuously increases and reaches the maximum at a dosage of 300 mg / L. The highest turbidity removal rate can reach 93.67%, the highest COD removal rate can reach 63.08%, and the highest total phosphorus removal rate can reach 75.02%.

[0090] Experimental Example 4

[0091] Take 5 beakers, place 200 mL of aquaculture wastewater in the beakers, and add flocculants at different dosages, namely 2.5, 5.0, 7.5, 10.0, and 12.5 g / L respectively. Then, quickly stir for 1 min at a speed of 250 r / min on a stirrer to mix evenly. Next, slowly stir for 20 min at a speed of 60 r / min. After standing for 20 min, measure the turbidity, total phosphorus, and COD of the sewage, and calculate the removal rate.

[0092] The test results are as Figure 6 shown. It can be seen that as the dosage increases, the removal rate of pollutants continuously increases and reaches the maximum at a dosage of 10 g / L. The highest turbidity removal rate can reach 78.69%, the highest COD removal rate can reach 47.36%, and the highest total phosphorus removal rate can reach 85.14%.

[0093] It can be seen from Experimental Examples 2 to 4 that the prepared polyoxometalate-mediated gasification slag-based composite flocculant has good removal efficiency for pollutants in domestic wastewater, river water, and aquaculture wastewater. This shows that the polyoxometalate-mediated gasification slag-based composite flocculant has excellent removal effects on wastewater with low pollutant concentrations and wastewater with high pollutant concentrations. Thus, it can be seen that the prepared polyoxometalate-mediated gasification slag-based composite flocculant can be applied to the sewage treatment in various aspects of reality.

[0094] Experimental Example 5

[0095] Flocculant A is the flocculant prepared in Experimental Example 2, Flocculant B is the flocculant prepared in Comparative Example 1, and Flocculant C is the flocculant prepared in Comparative Example 2.

[0096] Take 3 beakers, place 200 mL of domestic sewage in the beakers, and add 250 mg / L of Flocculants A, B, and C respectively. Then, mix well by rapidly stirring at a speed of 250 r / min on a stirrer for 1 min, and then slowly stir at a speed of 60 r / min for 20 min. After standing for 20 min, measure the turbidity, total phosphorus, and COD of the sewage, and calculate the removal rate.

[0097] The test results are as Figure 7 shown. It can be seen that the highest removal rate of domestic sewage turbidity by Flocculant A can reach 91.42%, the highest removal rate of COD can reach 63.07%, and the highest removal rate of total phosphorus can reach 80.25%; the highest removal rate of domestic sewage turbidity by Flocculant B can reach 87.63%, the highest removal rate of total phosphorus can reach 63.5%, and the highest removal rate of COD can reach 54.59%; the highest removal rate of domestic sewage turbidity by Flocculant C can reach 75.90%, the highest removal rate of total phosphorus can reach 58.97%, and the highest removal rate of COD can reach 32.35%.

[0098] Figure 8 SEM diagrams of Flocculants A, B, and C. Figure 8 A and B are SEM diagrams of Flocculant A prepared from hydrochloric acid leaching solution. It can be seen from the figure that Flocculant A has abundant pores and presents a porous structure, which is beneficial to the adsorption bridging effect of the flocculant on colloids and suspended solids. However, its relatively loose structure has certain limitations on the flocculation efficiency of the flocculant. Figure 8 C and D are SEM diagrams of Flocculant B prepared from glacial acetic acid leaching solution. It can be seen from the figure that the structure of Flocculant B presents a strip and branched chain morphology, and this structure can enhance the adsorption and net trapping ability and is conducive to the sedimentation of flocs. Figure 8 E and F are SEM diagrams of the polyacid-mediated coal gasification slag-based composite flocculant. It can be seen from the figure that it has a tight and complex gel network structure. At the same time, it has the pore structure of Flocculant A with tiny pores and the branched chain structure of Flocculant B with branched chain intersections, thus forming a tight and complex gel network structure of the polyacid-mediated coal gasification slag-based composite flocculant. The tight gel network structure is conducive to the flocculation of colloidal particles and the bridging between flocs. It also shows that it is not a simple mixture of two single acid flocculants, but a polymerized complex and tight flocculant.

[0099] Figure 9FT-IR diagrams of flocculants A, B, and C. It can be seen that the flocculants prepared with the mixed acid possess most of the functional groups of those prepared with single acids. The types of functional groups increase, and the flocculants become more complex. However, it can also be seen that this is not a simple mixture of the leaching solutions of two single acids. From the comparison between the mixed acid and single acids, it can be seen that after adding the acetic acid leaching solution, the characteristic peaks originally at 1565 cm -1 and 1425 cm -1 both shift. The shifted characteristic peaks appear at 1550 cm -1 and 1581 cm -1 as well as 1408 cm -1 and 1473 cm -1 . The appearance of these peaks is because metal ions such as Al and Fe in the polyacid-mediated coal gasification slag-based composite flocculant have a coordination interaction with the -COO- group, and -COO- is better utilized.

[0100] Figure 10 XRD diagrams of flocculants A, B, and C. It can be seen that the XRD characteristic peaks of the flocculant prepared with single hydrochloric acid are the same as those of the flocculant prepared with the mixed acid, and only the characteristic peaks of NaCl are shown. This indicates that the flocculants prepared with hydrochloric acid or the mixed acid have a good degree of polymerization and form amorphous flocculants. It can be seen from the XRD diagram of the flocculant prepared with single glacial acetic acid that there are many characteristic peaks in this flocculant at 5 - 30°. However, after mixing with the hydrochloric acid leaching solution, this characteristic does not appear in the XRD diagram of the polyacid-mediated coal gasification slag-based composite flocculant prepared with the mixed acid. This also shows that after adding the glacial acetic acid leaching solution to the hydrochloric acid leaching solution, the two solutions do not simply mix, but a polymerization reaction occurs, synthesizing a polyacid-mediated coal gasification slag-based composite flocculant with a good degree of polymerization.

[0101] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a polyoxometalate-mediated coal gasification slag-based composite flocculant, characterized in that, The method includes: (1) Take coal gasification slag in a container, add hydrochloric acid solution, stir under closed conditions for acid leaching reaction. After the reaction is completed, perform suction filtration to separate the solid and liquid, and obtain acid leaching filtrate A. Seal acid leaching filtrate A for later use. The dosage ratio (mass: volume) of coal gasification slag to hydrochloric acid solution is (1.0 - 10 g):(1.0 - 10 mL); the concentration of hydrochloric acid solution is 2.0 - 5.0 mol / L; (2) Take coal gasification slag in a container, add acetic acid solution, stir under closed conditions for acid leaching reaction. After the reaction is completed, perform suction filtration to separate the solid and liquid, and obtain acid leaching filtrate B. Seal acid leaching filtrate B for later use. The dosage ratio (mass: volume) of coal gasification slag to acetic acid solution is (1.0 - 10 g):(1.0 - 10 mL); the concentration of acetic acid solution is 2.0 - 6.0 mol / L; (3) Mix acid leaching filtrate A and acid leaching filtrate B, add NaOH solution, adjust the pH of the mixed solution, heat and stir for reaction. After the reaction is completed, let it stand at room temperature to thoroughly mature, form a colloidal substance, dry the colloidal substance and grind it evenly to obtain a multi - acid - mediated coal gasification slag - based composite flocculant.

2. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (1), the dosage ratio (mass: volume) of coal gasification slag to hydrochloric acid solution is 1.0 g:10 mL.

3. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (1), the concentration of hydrochloric acid solution is 3.0 mol / L.

4. The preparation method of the polyoxometalate-mediated gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (1), during the reaction, the reaction temperature is 20 - 60 °C; Or, in the step (1), the acid leaching time of hydrochloric acid solution is 0.5 - 2.5 h.

5. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that In the step (1), during the reaction, the reaction temperature is 40 °C.

6. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (1), the acid leaching time of hydrochloric acid solution is 1.5 h.

7. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (2), the dosage ratio (mass: volume) of coal gasification slag to acetic acid solution is 1.0 g:10 mL.

8. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, wherein, In the step (2), the concentration of acetic acid solution is 5 mol / L.

9. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, wherein, In the step (2), during the reaction, the reaction temperature is 20 - 60 °C; Or, in the step (2), the acid leaching time of acetic acid is 0.5 - 2.5 h.

10. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (2), during the reaction, the reaction temperature is 40 °C.

11. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (2), the acid leaching time of acetic acid is 2.0 h.

12. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (3), the volume ratio of acid leaching filtrate A to acid leaching filtrate B is 1 - 5:1 - 5; Or, in the step (3), after mixing the acid leaching solutions, adjust the pH to 2 - 5; the temperature of heating and stirring reaction is 50 - 90 °C; the time of heating and stirring reaction is 1 - 5 h; Or, in the step (3), the time for standing at room temperature to thoroughly mature is 20 - 30 h.

13. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (3), the volume ratio of acid leaching filtrate A to acid leaching filtrate B is 5:1, 3:1, 3:2, 1:1 or 2:

3.

14. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, wherein, In the step (3), the volume ratio of acid leaching filtrate A to acid leaching filtrate B is 3:

2.

15. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (3), after mixing the acid leaching solutions, adjust the pH to 3.

5.

16. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (3), the temperature of heating and stirring reaction is 70 °C.

17. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (3), the time for the heating and stirring reaction is 3 h.

18. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, In the step (3), the time for standing at room temperature to complete ripening is 24 h.

19. The preparation method of the polyoxometalate-mediated coal gasification slag-based composite flocculant according to claim 1, characterized in that, The preparation method further includes drying and storing the prepared polyacid-mediated coal gasification slag-based composite flocculant in a sealed manner.

20. A polyacid-mediated coal gasification slag-based composite flocculant prepared by the preparation method of the polyacid-mediated coal gasification slag-based composite flocculant according to any one of claims 1 to 19.

21. Use of the polyacid-mediated coal gasification slag-based composite flocculant according to claim 20 in wastewater treatment.

22. The application according to claim 21, wherein The wastewater includes domestic wastewater, river water and aquaculture wastewater.

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