Fire coal ash backfill material as well as preparation method and application thereof

Abstract

The invention provides a fire coal ash backfill material and a preparation method and application thereof, and belongs to the technical field of solid waste utilization. The fire coal ash backfill material is prepared from the following raw materials in parts by weight: 86-94 parts of fire coal ash, 1-5 parts of sodium thiosulfate, 5-9 parts of humic acid and 10-20 parts of deionized water. Wherein the pH value of the lixivium of the fire coal ash is larger than 9.0, the content of Ca ions is 50-1000 mg / L, and the content of Se elements is 0.1-0.5 mg / L. The solid backfill material containing certain moisture is formed by adopting the fire coal ash, the humic acid, the sodium thiosulfate and the water, the synergistic effect of the fire coal ash and the humic acid is utilized, the pH value of the high-alkali fire coal ash is modified to 6.0-9.0, Se is smaller than or equal to 0.1 mg / L, and the requirements of class I solid waste materials in GB18599-2020 are met.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste utilization, and specifically relates to a coal ash backfill material and a preparation method and application thereof. Background Art

[0002] GB18599-2020 "General Industrial Solid Waste Storage and Landfill Pollution Control Standards" stipulates that Class I general industrial solid waste is general industrial solid waste in which the concentration of any characteristic pollutant in the leachate obtained according to the method specified in HJ 557 does not exceed the maximum allowable emission concentration of GB 8978 (the maximum allowable emission concentration of Class II pollutants shall be implemented in accordance with the first-level standard), and the pH value is within the range of 6-9. Only Class I industrial solid waste can be directly used as raw material for backfilling or filling treatment of goafs. However, most coal ash slag fails to meet the pH requirement of 6-9 due to its high alkalinity (pH value greater than 9), and it is difficult to use it directly as backfill material. If coal ash slag is used directly for backfilling, it will also have an adverse effect on the later ecological restoration. Therefore, the problem of high alkalinity of coal ash slag needs to be solved urgently. At present, there is still a lack of practical methods for high-alkali modification of coal ash slag. The existing methods for high-alkali modification of coal ash generally adopt the solution of liquid acid washing, but this solution first faces the difficulty of solid-liquid separation of coal ash and water. Secondly, since coal ash is a large industrial solid waste with huge output, the liquid phase modification solution consumes a lot of water resources, resulting in water resource waste. In addition, the water treatment of the liquid after solid-liquid separation becomes a new difficulty. Therefore, it is urgent to develop solid-phase high-alkali coal ash modification technology.

[0003] Humic acid is a high molecular organic acid composed of aromatics and their various functional groups, and has good physiological activity, so it is widely used. For example, Chinese patent application document CN113683381A discloses a high humic acid soil solidifying agent and its preparation method, wherein the mass percentage of each substance in the solidifying agent is: steel slag 25%-40%, fly ash 15%-25%, quicklime 10%-15%, ordinary Portland cement 10%-20%, activator 6%-10%, ion replacement agent 1%-5%, water repellent 1%-3%, retarder 4%-6%, early strength agent 1%-2%, filler 1%-3%, stabilizer 1%-3%, air entraining agent 1%-2%, water reducer 0.5%-1%, humic acid modifier 0.5%-2%. This technical solution can effectively reduce the impact of humic acid on the soil, improve the shear strength, compressibility, and water-stable strength of the soil, reduce the pore size, compressibility, and permeability of the soil, and has good economic and environmental effects.

[0004] At present, there are no reports in existing research on the preparation of backfill materials using a formula of humic acid and coal ash, or on the preparation of Class I solid waste materials that comply with GB18599-2020. Summary of the invention

[0005] In view of this, the present invention provides a coal ash backfill material and a preparation method and application thereof. In the present invention, coal ash, humic acid, sodium thiosulfate and water are used to form a solid backfill material containing a certain amount of water, and the pH value of the high-alkali coal ash is modified to 6.0-9.0 to meet the requirements of the backfill material; at the same time, the problems of solid-liquid separation, waste of water resources and secondary water production treatment faced by the liquid phase modification of high-alkali coal ash are avoided.

[0006] An object of the present invention is to provide a method for preparing coal ash backfill material.

[0007] The coal ash backfill material is prepared by using raw materials including the following components in parts by weight: 86-94 parts of coal ash, 1-5 parts of sodium thiosulfate, 5-9 parts of humic acid, and 10-20 parts of deionized water;

[0008] The pH value of the coal ash leaching solution is greater than 9.0, the Ca ion content is 50-1000 mg / L, and the Se element content is 0.1-0.5 mg / L.

[0009] The inventors have found that the coal ash backfill material obtained by mixing high alkalinity and high Se content coal ash with sodium thiosulfate, humic acid and deionized water in a certain proportion meets the requirements of Class I solid waste materials in GB18599-2020. Since the source of the alkalinity of coal ash is mainly alkaline calcium, on the one hand, through the synergistic adsorption and precipitation of coal ash and humic acid, some cations (such as Pb, Cd, Mg, Fe) in the coal ash are synergistically precipitated, and the pH and Se content of the leaching solution of the coal ash are further reduced through the combined action of synergistic adsorption and precipitation. On the other hand, coal ash, sodium thiosulfate, humic acid and deionized water show a synergistic gelling effect. While reducing the alkaline calcium content of coal ash through gelling reaction, the precipitate is further solidified, further reducing the pH and Se content of the leaching solution of coal ash.

[0010] The coal ash leaching solution is prepared by the method specified in HJ 557-2010 "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method".

[0011] In some embodiments, the coal combustion ash is selected from one or both of fly ash and bottom ash.

[0012] In some embodiments, the humic acid is one or more of mineral-derived humic acid, biomass-derived humic acid, and fulvic acid.

[0013] In some preferred embodiments, the preparation method comprises the following steps:

[0014] 1) mixing coal ash and sodium thiosulfate to obtain a first mixture;

[0015] 2) mixing the first mixture with deionized water and allowing the mixture to stand to obtain a second mixture;

[0016] 3) Continue to mix the second mixture with humic acid, and after standing, obtain coal ash backfill material.

[0017] The inventors have found that the mixing order of the raw materials has an important influence on the performance of the coal ash backfill material. If the mixing order of the deionized water in step 2) and the humic acid in step 3) is swapped, the pH value of the obtained leachate of the coal ash backfill material cannot meet the pH requirement of 6.0-9.0, and its pH is still >9.0, which does not meet the requirements for Class I solid waste materials in GB18599-2020.

[0018] In some embodiments, in step 2), the standing time is 1-7 days; and / or,

[0019] In step 3), the standing time is 12-36 hours.

[0020] Another object of the present invention is to provide a coal ash backfill material prepared by any of the preparation methods described above.

[0021] In some embodiments, the pH value of the leachate of the coal ash backfill material is 6.0-9.0, and the Se content is ≤0.1 mg / L.

[0022] The leaching solution of the coal ash backfill material is prepared by the method specified in HJ 557-2010 "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method".

[0023] Another object of the present invention is to provide the coal ash backfill material described in any of the above items for use in goaf backfill, subsidence area backfill, mine filling, sewage treatment, soil remediation or soil improvement.

[0024] Another object of the present invention is to provide the use of the coal ash backfill material described in any of the above items in road materials, aggregates, aggregates or mining materials.

[0025] The last object of the present invention is to provide a method for recycling coal ash.

[0026] In some embodiments, the coal ash is processed according to any of the preparation methods described above to prepare the coal ash backfill material.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] In the present invention, coal ash, humic acid, sodium thiosulfate and water are used to form a solid backfill material containing a certain amount of water. The synergistic effect of coal ash and humic acid is utilized, and the pH value of the leachate of the solid backfill material obtained based on high-alkali coal ash reaches 6.0-9.0, Se≤0.1mg / L, which meets the requirements of Class I solid waste materials in GB18599-2020; the solid backfill material prepared by the present invention has simple components and is easy to prepare, so it has good application prospects in the field of solid waste utilization technology. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The experimental methods without specific conditions in the examples are usually carried out according to conventional conditions and conditions described in the manual, or according to conditions recommended by the manufacturer. The general equipment, materials, reagents, etc. used are all available from commercial channels unless otherwise specified.

[0031] Example 1

[0032] The coal ash backfill material, in parts by weight, comprises the following raw materials: 94 parts of fly ash, 5 parts of sodium thiosulfate, 5 parts of biomass humic acid and 10 parts of deionized water;

[0033] The pH value of the fly ash leaching solution used was 11.9, the Ca ion content was 482 mg / L, and the Se content was 0.36 mg / L.

[0034] The method for preparing coal ash backfill material comprises the following steps:

[0035] 1) mixing 94 parts of fly ash and 5 parts of sodium thiosulfate to obtain a first mixture;

[0036] 2) mixing the first mixture with 10 parts of deionized water and letting it stand for 5 days to obtain a second mixture;

[0037] 3) Continue to mix the second mixture with 5 parts of biomass humic acid, and let it stand for 24 hours to obtain a coal ash backfill material.

[0038] Example 2

[0039] The coal ash backfill material, in parts by weight, comprises the following raw materials: 45 parts of fly ash, 41 parts of bottom slag, 1 part of sodium thiosulfate, 9 parts of mineral source humic acid and 20 parts of deionized water;

[0040] The pH value of the leaching solution of the fly ash and bottom slag mixture used was 11.9, the Ca ion content was 531 mg / L, and the Se content was 0.28 mg / L.

[0041] The method for preparing the coal ash backfill material comprises the following steps:

[0042] 1) mixing 45 parts of fly ash, 41 parts of bottom slag and 1 part of sodium thiosulfate to obtain a first mixture;

[0043] 2) mixing the first mixture with 20 parts of deionized water and letting it stand for 5 days to obtain a second mixture;

[0044] 3) Continue to mix the second mixture with 9 parts of mineral source humic acid, and let it stand for 24 hours to obtain a coal ash backfill material.

[0045] Example 3

[0046] The coal ash backfill material, in parts by weight, comprises the following raw materials: 88 parts of furnace bottom ash, 4 parts of sodium thiosulfate, 8 parts of fulvic acid and 15 parts of deionized water;

[0047] The pH value of the bottom slag leaching solution used was 11.8, the Ca ion content was 237 mg / L, and the Se content was 0.5 mg / L.

[0048] The method for preparing the coal ash backfill material comprises the following steps:

[0049] 1) mixing 88 parts of bottom slag and 4 parts of sodium thiosulfate to obtain a first mixture;

[0050] 2) mixing the first mixture with 15 parts of deionized water and letting it stand for 5 days to obtain a second mixture;

[0051] 3) Continue to mix the second mixture with 8 parts of fulvic acid, and let it stand for 24 hours to obtain a coal ash backfill material.

[0052] Example 4

[0053] The coal ash backfill material, in parts by weight, comprises the following raw materials: 93 parts of fly ash, 2 parts of sodium thiosulfate, 5 parts of biomass humic acid and 10 parts of deionized water;

[0054] The pH value of the fly ash leaching solution used was 11.3, the Ca ion content was 382 mg / L, and the Se content was 0.19 mg / L.

[0055] The method for preparing the coal ash backfill material comprises the following steps:

[0056] 1) mixing 93 parts of fly ash and 2 parts of sodium thiosulfate to obtain a first mixture;

[0057] 2) mixing the first mixture with 10 parts of deionized water and letting it stand for 5 days to obtain a second mixture;

[0058] 3) Continue to mix the second mixture with 5 parts of biomass humic acid, and let it stand for 24 hours to obtain a coal ash backfill material.

[0059] Example 5

[0060] The coal ash backfill material, in parts by weight, comprises the following raw materials: 88 parts of fly ash, 3 parts of sodium thiosulfate, 9 parts of biomass humic acid and 10 parts of deionized water;

[0061] The pH value of the fly ash leaching solution used was 12.0, the Ca ion content was 1000 mg / L, and the Se content was 0.42 mg / L.

[0062] The method for preparing the coal ash backfill material comprises the following steps:

[0063] 1) mixing 88 parts of fly ash and 3 parts of sodium thiosulfate to obtain a first mixture;

[0064] 2) mixing the first mixture with 10 parts of deionized water and letting it stand for 5 days to obtain a second mixture;

[0065] 3) Continue to mix the second mixture with 9 parts of biomass humic acid, and let it stand for 24 hours to obtain a coal ash backfill material.

[0066] Example 6

[0067] The coal ash backfill material, in parts by weight, comprises the following raw materials: 90 parts of bottom ash, 2 parts of sodium thiosulfate, 8 parts of biomass humic acid and 10 parts of deionized water;

[0068] The pH value of the bottom slag leaching solution used was 10.6, the Ca ion content was 50 mg / L, and the Se content was 0.36 mg / L.

[0069] The method for preparing the coal ash backfill material comprises the following steps:

[0070] 1) mixing 90 parts of bottom slag and 2 parts of sodium thiosulfate to obtain a first mixture;

[0071] 2) mixing the first mixture with 10 parts of deionized water and letting it stand for 5 days to obtain a second mixture;

[0072] 3) Continue to mix the second mixture with 8 parts of biomass humic acid, and let it stand for 24 hours to obtain a coal ash backfill material.

[0073] Comparative Example 1

[0074] The formulation and preparation method of the coal ash backfill material are basically the same as those of Example 2, except that no mineral source humic acid is added.

[0075] Comparative Example 2

[0076] The formulation and preparation method of the coal ash backfill material are basically the same as those in Example 2, except that sodium thiosulfate is not added.

[0077] Comparative Example 3

[0078] The formulation and preparation method of the coal ash backfill material are basically the same as those in Example 2, except that no deionized water is added.

[0079] Comparative Example 4

[0080] The formulation and preparation method of the coal ash backfill material are basically the same as those of Example 2, except that the mineral source humic acid is replaced by hydrochloric acid containing an equal amount of hydrogen ions.

[0081] The amount of hydrochloric acid added is determined as follows: 9 parts of mineral source humic acid are dissolved in 20 parts of deionized water, the pH value of the mineral source humic acid solution is measured, and then hydrochloric acid is added dropwise to the 20 parts of deionized water so that the measured pH value is equal to the pH value of the mineral source humic acid solution. At this time, the amount of hydrochloric acid added dropwise is the amount of hydrochloric acid added.

[0082] Comparative Example 5

[0083] The formulation and preparation method of the coal ash backfill material are basically the same as those in Example 2, except that the deionized water adding step in step 2) and the mineral source humic acid adding step in step 3) are swapped, and the other steps remain unchanged.

[0084] The raw material proportions of the coal ash backfill materials prepared in Examples 1-6 and Comparative Examples 1-5 are shown in Table 1 below:

[0085] Table 1 Raw material ratio of coal ash backfill material

[0086]

[0087] Performance Testing

[0088] The coal ash backfill materials prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to performance tests, wherein the leaching solution of the raw coal ash and the leaching solution of the prepared coal ash backfill materials were prepared by the method specified in HJ 557-2010 "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method". The heavy metal element content was measured by the method required by GB 8978-1996 "Comprehensive Wastewater Discharge Standard". The results of the performance test are shown in Table 2 below:

[0089] Table 2 Performance test results

[0090]

[0091] It can be seen from the data in the table that in Examples 1-6, the pH of the leachate of the coal ash backfill material obtained by mixing high-alkalinity, high-Se content coal ash with sodium thiosulfate, humic acid and deionized water in a certain proportion is reduced to within 6.0-9.0, and the Se element content is ≤0.1 mg / L, which meets the requirements for Class I solid waste materials in GB18599-2020. The coal ash backfill material prepared in Example 1 does not add mineral humic acid, the coal ash backfill material prepared in Example 2 does not add sodium thiosulfate, the coal ash backfill material prepared in Example 3 does not add deionized water, and the coal ash backfill material prepared in Example 4 replaces the mineral humic acid with hydrochloric acid containing an equal amount of hydrogen ions. It is found that the pH of the leaching solution of the coal ash backfill material obtained has decreased to a certain extent, and the Se element content has also decreased to a certain extent, but does not meet the requirements of Class I solid waste materials in GB18599-2020. In Comparative Example 5, the order of adding deionized water in step 2) and the mineral humic acid in step 3) is reversed, and the other steps remain unchanged. It is found that the pH of the leaching solution of the coal ash backfill material obtained has decreased to a certain extent, but the pH value is greater than 9.0, which does not meet the requirements of Class I solid waste materials in GB18599-2020.

[0092] The above embodiments are only specific implementation methods of the present invention, which are used to illustrate the technical solutions of the present invention rather than to limit them. The protection scope of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the aforementioned embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the aforementioned embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the protection scope of the present invention.

Claims

1. A method for preparing coal ash backfill material, characterized in that: The coal ash backfill material is prepared by using raw materials including the following components in parts by weight: 86-94 parts of coal ash, 1-5 parts of sodium thiosulfate, 5-9 parts of humic acid, and 10-20 parts of deionized water; The pH value of the coal ash leaching solution is greater than 9.0, the Ca ion content is 50-1000 mg / L, and the Se element content is 0.1-0.5 mg / L.

2. The method for preparing the coal ash backfill material according to claim 1, characterized in that: The coal ash is selected from one or both of fly ash and bottom ash.

3. The method for preparing the coal ash backfill material according to claim 1, characterized in that: The humic acid is one or more of mineral-derived humic acid, biomass humic acid and fulvic acid.

4. The method for preparing the coal ash backfill material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: 1) mixing coal ash and sodium thiosulfate to obtain a first mixture; 2) mixing the first mixture with deionized water and allowing the mixture to stand to obtain a second mixture; 3) Continue to mix the second mixture with humic acid, and after standing, obtain coal ash backfill material.

5. The method for preparing the coal ash backfill material according to claim 4, characterized in that: In step 2), the standing time is 1-7 days; and / or, In step 3), the standing time is 12-36 hours.

6. A coal ash backfill material prepared by the preparation method according to any one of claims 1 to 5.

7. The coal ash backfill material according to claim 6, characterized in that: The pH value of the leaching solution of the coal ash backfill material is 6.0-9.0, and the Se element content is ≤0.1 mg / L.

8. The use of the coal ash backfill material according to claim 6 or 7, characterized in that: The coal ash backfill material is used in backfilling of goaf areas, backfilling of collapsed areas, mine filling, sewage treatment, soil restoration or soil improvement.

9. The use of the coal ash backfill material according to claim 6 or 7, characterized in that: The coal ash backfill material is used in road materials, aggregates, aggregates or mining materials.

10. A method for recycling coal ash, characterized in that: The coal ash is processed according to the preparation method according to any one of claims 1 to 5, and the coal ash is made into the coal ash backfill material.

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