Desulfurization wastewater and coal-based solid waste coupling material, and preparation method and application thereof

Abstract

The application provides a desulfurization wastewater and coal-based solid waste coupling material, a preparation method and application thereof, and is based on the desulfurization wastewater and coal-based solid waste to prepare the coupling material, thereby providing a new solution path for the collaborative treatment and subsequent utilization of the desulfurization wastewater and coal-based solid waste. The preparation method comprises the following steps: 1) mixing and reacting 8-10 parts by weight of coal-based solid waste and 0.8-5.0 parts by weight of desulfurization wastewater; 2) mixing the mixture obtained in step 1) with 0.1-0.5 parts by weight of a modifier to obtain the coupling material; wherein the coal-based solid waste used in step 1) has a pH of the leaching solution of >9 and a Se content of 0.1-0.5 mg / L, and the desulfurization wastewater used has a pH of 4-9 and a Mg ion content of >50 mg / L; in step 2), based on the total mass of the modifier, the modifier comprises 2-10% of an inorganic acid and 90-98% of the soluble salt.

Description

Technical Field

[0001] This invention relates to desulfurization wastewater and coal-based solid waste treatment technologies, and particularly to a coupling material for desulfurization wastewater and coal-based solid waste, its preparation method, and its application. Background Technology

[0002] Coal contains sulfur, and sulfur dioxide is produced during coal combustion. Currently, wet desulfurization is mainly used to treat sulfur-containing pollutants in power plant flue gas, producing desulfurization gypsum and desulfurization wastewater. On the other hand, a large amount of fly ash is generated during coal combustion, with a comprehensive utilization rate of over 70% in central and eastern China. However, in western China, while fly ash production is enormous, utilization methods are limited. Due to the small market size of building materials and the lack of comprehensive utilization pathways for large quantities of coal-based solid waste, a large-scale market for fly ash disposal has not been formed, resulting in a significantly low comprehensive utilization rate of coal-based solid waste in western China, becoming a prominent problem restricting the development of the power industry. Ecological restoration applications such as backfilling and reclamation are effective ways to utilize large quantities of coal-based solid waste, especially given the current market situation in western China. However, the "GB18599-2020 Standard for Pollution Control of Storage and Landfill of General Industrial Solid Waste" stipulates that only Class I industrial solid waste can be directly used as raw materials for backfilling or filling of mined-out areas. Most fly ash, due to its high alkalinity (pH greater than 9), fails to meet the pH requirement of 6-9 and is therefore difficult to utilize.

[0003] Currently, technologies for the co-utilization of desulfurization wastewater and fly ash are still lacking. Power plants use a mixture of desulfurization wastewater and fly ash to replace water used to reduce dust during transportation, which is then disposed of in landfills. However, this method, due to the lack of harmless treatment, does not meet the requirements of the "GB18599-2020 Standard for Pollution Control of General Industrial Solid Waste Storage and Landfill," and poses potential risks. Evaporation or crystallization water treatment technologies are the safest and most reliable, but also the most expensive, producing small amounts of high-salinity water or concentrated liquid, which still falls under the category of hazardous waste and requires further resolution.

[0004] Therefore, it is still necessary to explore solutions for the coordinated treatment of desulfurization wastewater and coal-based solid waste to balance economic efficiency, safety and reliability.

[0005] Chinese patent application CN202010366294.5 provides a zero-discharge system for flue gas desulfurization wastewater, comprising a pretreatment unit, a concentration and reduction unit, an end-of-pipe solidification unit, and a control system. The end-of-pipe solidification unit mixes the precipitated sludge generated during the desulfurization wastewater treatment process with fly ash, quicklime, and silicate cement to form low-grade building materials. The mass percentage of precipitated sludge: fly ash: quicklime: silicate cement is 1:(0.12-0.25):(0.15-0.3):(0.6-0.9). This invention proposes a solution that is completely different from this one. Summary of the Invention

[0006] This invention provides a method for preparing a coupling material from desulfurization wastewater and coal-based solid waste, as well as the resulting coupling material and its applications. The method of this invention, based on desulfurization wastewater and coal-based solid waste, can solve the problem of coal-based solid waste's difficulty in utilization due to its pH > 9. Furthermore, compared to the initial coal-based solid waste and desulfurization wastewater, the resulting coupling material exhibits significantly lower heavy metal content in its leachate and a lower selenium content, providing a new solution for the synergistic treatment and subsequent utilization of desulfurization wastewater and coal-based solid waste. Moreover, the method provided by this invention has fewer process steps, is simpler, requires fewer reagents, and requires no additional water or heat resources, making it economical and environmentally friendly.

[0007] To achieve its objective, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing a coupling material for desulfurization wastewater and coal-based solid waste, the method comprising the following steps:

[0009] 1) Mix 8-10 parts by weight of coal-based solid waste and 0.8-5.0 parts by weight of desulfurization wastewater to obtain a mixture.

[0010] 2) Mix the mixture obtained in step 1) with 0.1-0.5 parts by weight of a modifier to obtain the coupling material;

[0011] In step 1), the leachate from the coal-based solid waste has a pH > 9 and a Se content of 0.1-0.5 mg / L.

[0012] The desulfurization wastewater used must meet the following requirements: pH 4-9, Mg ion content ≥50mg / L;

[0013] In step 2), based on the total mass of the modifier, the modifier comprises 2-10% inorganic acid and 90-98% soluble salt; the soluble salt is selected from one or more of soluble aluminum salt and soluble iron salt, preferably soluble iron salt.

[0014] In this invention, 8-10 parts by weight of the aforementioned coal-based solid waste and 0.8-5.0 parts by weight of the aforementioned desulfurization wastewater are first mixed and reacted. Then, 0.1-0.5 parts by weight of a modifier with a specific composition are mixed to prepare a coupling material. This process does not require a system containing a large amount of water. Through the above two-step reaction, the components interact, not only modifying the high-alkali coal-based solid waste to obtain a solid or semi-solid coupling material with a pH of 6-9 (measured from the leachate of the coupling material), but also synergistically removing heavy metal pollutants from the desulfurization wastewater. The leachate of the obtained coupling material shows a significant reduction in heavy metal content and a substantial reduction in Se content. The obtained coupling material can be used as a mine filling or backfill material, or as a soil reclamation or improvement material.

[0015] In this invention, the modifier used comprises 2-10% inorganic acid and 90-98% soluble salt, wherein the soluble salt is selected from soluble aluminum salts and / or soluble iron salts, and preferably, the inorganic acid is selected from at least one of sulfuric acid and hydrochloric acid. The inventors have discovered that by further contacting the mixture obtained from the reaction of the modifier with coal-based solid waste and desulfurization wastewater, the leachate of the resulting coupled material not only has a pH of 6-9, but also exhibits a significant decrease in heavy metal content and a low Se content.

[0016] In a preferred embodiment, the soluble salt used in the modifier is preferably a soluble iron salt. The inventors have found that using a soluble iron salt, compared to using a soluble aluminum salt, is beneficial for improving the treatment effect and for further reducing the content of heavy metal ions in the leachate of the coupling material.

[0017] In this invention, the soluble iron salt and soluble aluminum salt can be one or more of ferrous sulfate, ferric sulfate, ferric chloride, aluminum sulfate, aluminum chloride and their hydrates.

[0018] In this invention, if the soluble salt is a hydrate, its mass percentage in the modifier is 90-98% based solely on the non-hydrated salt form corresponding to the soluble salt. For example, aluminum sulfate octadecahydrate is used as an example, and its mass percentage in the modifier is calculated as aluminum sulfate. In this invention, the inorganic acid is preferably sulfuric acid or hydrochloric acid; the mass percentage of these two inorganic acids in the modifier is 2-10% based on H₂SO₄ in sulfuric acid and HCl in hydrochloric acid, respectively.

[0019] In this invention, there are no particular limitations on the coal-based solid waste used. Coal-based solid waste whose leachate, as determined by its leachate analysis, meets the following criteria: pH > 9 and Se content 0.1-0.5 mg / L. When used in conjunction with desulfurization wastewater to prepare a coupling material according to the preparation method of this invention, the resulting coupling material can better meet the requirements for reuse. For example, the pH of the leachate obtained from the coupling material can be reduced to 6-9, and it has a low Se content, with significant removal of heavy metals from the leachate. In some preferred embodiments, the coal-based solid waste mentioned in step 1) is selected from at least one of fly ash and bottom ash.

[0020] Using the method of this invention, desulfurization wastewater with pH 4-9 and Mg ion content ≥ 50 mg / L and the aforementioned coal-based solid waste are used to prepare a coupling material according to the preparation method of this invention. The heavy metal content in the leachate of the obtained coupling material can be significantly reduced, i.e., it has a high heavy metal removal rate. In this invention, there are no particular restrictions on the source of the desulfurization wastewater used. In some embodiments, the desulfurization wastewater is selected from at least one of the following: raw desulfurization wastewater, effluent from a three-stage desulfurization wastewater treatment tank, and concentrated desulfurization wastewater. In some embodiments, in step 1), the desulfurization wastewater used has a Cd content of 0.1-1 mg / L, a Cr content of 1.5-15 mg / L, a Cu content of 0.5-10 mg / L, a Ni content of 1-10 mg / L, and a Pb content of 1-10 mg / L.

[0021] In some preferred embodiments, the mixing reaction in step 1) includes: mixing the coal-based solid waste and desulfurization wastewater, and then allowing the mixture to stand for 8-24 hours; in step 2), the mixture is allowed to stand for 1-7 days. Steps 1) and 2) are carried out within the preferred time range mentioned above, which is conducive to the full interaction between the components, to promoting the pH of the leachate of the resulting coupling material to reach 6-9, and to reducing the content of heavy metals and Se.

[0022] The preparation method provided by this invention involves pre-mixing desulfurization wastewater and coal-based solid waste within a specific dosage range, followed by further interaction with a modifier of a specific composition within the same dosage range. This process transforms the high Mg ion content in desulfurization wastewater, a significant drawback, into an advantage, making it an effective ion for modifying high-alkali coal-based solid waste. Through synergistic precipitation and inhibition, high-alkali fly ash is modified, resulting in a coupling material whose leachate pH can be reduced to 6-9, and whose Se content is also significantly decreased. Simultaneously, utilizing the high alkali nature of coal-based solid waste, the above process, combined with the modifier, synergistically removes heavy metal pollutants from desulfurization wastewater. The modified coupling material exhibits significantly reduced heavy metal content in its leachate compared to the initial material, meeting the requirements of GB8978.

[0023] The preparation method of this invention can solve the problem that existing coal-based solid wastes (such as fly ash and bottom ash) do not meet the requirements of Class I industrial solid waste in GB 18599-2020 due to pH > 9 and Se > 0.1 mg / L, making them difficult to further utilize. It can also simultaneously transform the high Mg ion content in existing desulfurization wastewater into an advantage, and address the risk of excessive heavy metal content, providing a feasible technical route for zero discharge of desulfurization wastewater. The preparation method of this invention can synergistically treat desulfurization wastewater and coal-based solid waste, and easily prepare coupling materials for desulfurization wastewater and coal-based solid waste that meet the GB18599 standard.

[0024] Using the above preparation method of the present invention, the weight α3 of heavy metal elements in the leachate of the obtained coupling material satisfies the following relationship with the weight α1 of heavy metal elements in the leachate of the coal-based solid waste used in step 1) and the weight α2 of heavy metal elements in the desulfurization wastewater used in step 1):

[0025] 40%≤((α1+α2-α3) / (α1+α2))×100%≤100%;

[0026] That is, the removal rate of heavy metal elements can reach 40%-100%, including Cd, Cr, Cu, Ni and / or Pb.

[0027] In another aspect, this invention provides a coupling material for desulfurization wastewater and coal-based solid waste prepared according to the preparation method described above. The coupling material prepared using the method of this invention has a leachate with a pH of 6-9 and a Se content ≤0.1 mg / L.

[0028] In the context of this invention, the terms "leaching solution of coal-based solid waste" and "leaching solution of coupling material" used throughout refer to the leaching of coal-based solid waste or coupling material according to HJ 557-2010 ("Leaching Toxicity of Solid Waste - Horizontal Oscillation Method"). The preparation of the leaching solution of coal-based solid waste is solely for determining whether the coal-based solid waste used meets the requirements of this invention; that is, the coal-based solid waste used is the corresponding coal-based solid waste whose leaching solution prepared according to the method in HJ 557-2010 meets the requirements of pH > 9 and Se content of 0.1-0.5 mg / L; it does not mean that the leaching solution used in the preparation of the coupling material is the same.

[0029] In another aspect, the present invention provides a method for simultaneous treatment of desulfurization wastewater and coal-based solid waste, the method comprising: preparing the desulfurization wastewater and coal-based solid waste into a coupling material using the preparation method described above, thereby achieving simultaneous treatment of desulfurization wastewater and coal-based solid waste;

[0030] Preferably, the coupling material is used for mine filling or backfilling, soil remediation or reclamation or improvement, ecological restoration, road materials, aggregates, mining materials, and / or solidification of trace metal elements; more preferably, it is used for mine filling or backfilling, soil reclamation or improvement.

[0031] In another aspect, the present invention also provides the application of the coupling material for desulfurization wastewater and coal-based solid waste described above, wherein the coupling material is used in mine filling or backfilling, soil remediation or reclamation or improvement, ecological restoration, road materials, aggregates, mining materials, and / or solidification of trace metal elements; more preferably, it is used in mine filling or backfilling, soil reclamation or improvement.

[0032] The technical solution provided by this invention has the following beneficial effects:

[0033] The coupling material preparation method provided by this invention is simple and requires no additional water or heat energy. It can prepare desulfurization wastewater and coal-based solid waste into a coupling material that is easy to reuse. On the one hand, it can solve the problem that coal-based solid waste is difficult to use due to pH>9. On the other hand, compared with the initial coal-based solid waste and desulfurization wastewater, the leachate of the coupling material has a significantly lower heavy metal content and a lower Se content, providing a new solution for the synergistic treatment and subsequent utilization of desulfurization wastewater and coal-based solid waste. Detailed Implementation

[0034] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0035] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in this technical field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0036] In the following text, "coupling material for desulfurization wastewater and coal-based solid waste" and "coupling material" are the same concept, both referring to the coupling material for desulfurization wastewater and coal-based solid waste.

[0037] In the following embodiments or comparative examples:

[0038] The leachate for coal-based solid waste and the leachate for coupling materials were prepared in accordance with HJ 557-2010 ("Solid Waste Leaching Toxicity Leaching Method - Horizontal Oscillation Method").

[0039] The heavy metal and non-metal element content parameters were measured using the methods required by GB 8978-88 "Integrated Wastewater Discharge Standard".

[0040] The removal rates of each heavy metal element listed in Tables 1 and 2 are calculated using the following formulas:

[0041] ((α1+α2-α3) / (α1+α2))×100%

[0042] Wherein, α1 refers to the weight of heavy metal elements in the leachate of the coal-based solid waste used to prepare the coupling material, in mg; α2 refers to the weight of heavy metal elements in the desulfurization wastewater used to prepare the coupling material, in mg; and α3 refers to the weight of heavy metal elements in the leachate of the obtained coupling material, in mg.

[0043] To facilitate understanding of the calculation process for the removal rate of heavy metal elements, the following explanation uses the removal rate of Cr element in Example 1 as an example:

[0044] According to the formula of Example 1 (8 parts by weight of fly ash, 5.0 parts by weight of desulfurization wastewater, and 0.1 parts by weight of modifier), 100.00g of dry weight of fly ash corresponds to 62.50g of desulfurization wastewater (volume 62.50ml) and 1.25g of modifier; the final coupling material has a dry weight of 100.00g. A 100.00g dry weight of fly ash from the same batch as in Example 1 was used to prepare a leachate (volume 1L). The content of the heavy metal element Cr in the leachate was measured to be 0.10mg / L. Multiplying this content by the volume of the leachate, the weight of Cr in the coal-based solid waste used is 0.10mg (i.e., the α1 value in the formula). The heavy metal Cr content of the desulfurization wastewater from the same batch as in Example 1 was 15.00 mg / L. Multiplying this content by the volume of the desulfurization wastewater used in Example 1 (62.50 ml) yielded a Cr weight of 0.94 mg (i.e., α2 value). A leaching solution (1 L volume) was prepared from 100.00 g dry weight of the coupling material obtained in Example 1. The Cr content in this leaching solution was measured to be 0 mg / L. Multiplying this content by the leaching solution volume yielded a Cr weight of 0 mg (i.e., α3 value in the formula).

[0045] In Example 1, the removal rate of Cr element was calculated according to the following formula: ((α1+α2-α3) / (α1+α2))×100%. Substituting the values ​​of α1, α2, and α3 obtained above, we get ((0.1+0.94-0) / (0.1+0.94))×100%=100%. That is, in Example 1, the removal rate of Cr element is 100%.

[0046] The calculation of heavy metal content in the other embodiments and comparative examples follows the same process as described above, and will not be repeated here.

[0047] Raw material description:

[0048] The desulfurization wastewater used in the examples and comparative examples had a pH of 4-9 and a Mg ion content ≥50 mg / L. The wastewater contained 0.1-1 mg / L Cd, 1.5-15 mg / L Cr, 0.5-10 mg / L Cu, 1-10 mg / L Ni, and 1-10 mg / L Pb.

[0049] The fly ash used in the examples and comparative examples had a leachate pH > 9 and a Se content of 0.1-0.5 mg / L.

[0050] The bottom ash used in the examples has a leachate with a pH > 9 and a Se content of 0.1-0.5 mg / L.

[0051] Examples 1-6

[0052] Examples 1-6 all prepared desulfurization wastewater and coal-based solid waste coupling materials according to the following steps:

[0053] 1) Mix coal-based solid waste and desulfurization wastewater, and let them stand for a period of time (see Table 1 below for specific standing reaction time) to obtain a mixture.

[0054] 2) Mix the mixture obtained in step 1) with the modifier and let it stand for a period of time (see Table 1 below for the specific standing time) to obtain the coupling material.

[0055] The weight proportions of coal-based solid waste, desulfurization wastewater, and modifiers, as well as the composition of the modifiers used, are shown in Table 1.

[0056] Example 7

[0057] The procedure was carried out in accordance with Example 1, except that the soluble salt used was a soluble aluminum salt (aluminum sulfate octadecahydrate).

[0058] Comparative Example 1-1

[0059] The same procedure was followed as in Example 1, and the similarities will not be repeated here. The only difference is that the amount of modifier was adjusted to 1 part by weight.

[0060] Comparative Examples 1-2

[0061] The procedure was carried out in accordance with Example 1, and the similarities will not be repeated here. The only difference is that the amount of modifier was reduced to 0.05 parts by weight.

[0062] Comparative Example 2-1

[0063] The procedure was carried out in accordance with Example 1, except that the amount of fly ash was adjusted to 15 parts by weight.

[0064] Comparative Example 2-2

[0065] The procedure was carried out in accordance with Example 1, except that the amount of fly ash was adjusted to 5 parts by weight.

[0066] Comparative Example 3

[0067] The procedure was carried out in accordance with Example 1, except that desulfurization wastewater was not used in step 1).

[0068] Comparative Example 4

[0069] The process was carried out in accordance with Example 1, except that the proportion of inorganic acid in the modifier was 15 wt% and the proportion of soluble salt was 85 wt%.

[0070] Comparative Example 5

[0071] The process was carried out in accordance with Example 1, except that the proportion of inorganic acid in the modifier was 1.5 wt% and the proportion of soluble salt was 98.5 wt%.

[0072] Comparative Example 6

[0073] The process was carried out in accordance with Example 1, except that the coal-based solid waste, desulfurization wastewater and modifier were mixed simultaneously in one step and allowed to stand for 8 days.

[0074] Table 1

[0075]

[0076]

[0077] Table 2

[0078]

[0079]

[0080] As can be seen from the experimental results of Examples 1-7, the process of the present invention can be used to co-treat desulfurization wastewater and coal-based solid waste. The two materials are then processed into a coupling material through a two-step method. The leachate of the resulting coupling material meets the requirements of pH 6-9, and the heavy metal removal rate is significant, and the Se content is significantly reduced. This meets the requirements for subsequent use, such as as a mine filling, backfill material, soil reclamation material, or soil improvement material.

[0081] As can be seen from the experimental comparison of Examples 1-6 and Example 7, under the same conditions, the leachate of the coupling material obtained by using soluble iron salts has a lower Se content and a higher removal rate of heavy metal elements compared to using soluble aluminum salts.

[0082] Compared with the embodiments of the present invention, the various comparative examples did not use the process requirements of the present invention to prepare the coupling materials. As a result, the leachate of the resulting coupling materials could not meet the requirements of pH 6-9, and the Se content was significantly higher than that of the examples.

[0083] Based on the experimental comparisons of the embodiments and comparative examples of this application, the formulation system of this invention, used to prepare coupling materials based on coal-based solid waste and desulfurization wastewater, can effectively achieve the following effects: 1) the leachate of the resulting coupling material meets the pH requirement of 6-9; 2) the selenium content in the leachate is relatively low; and 3) the simultaneous removal effect of multiple heavy metal elements is good. In contrast, the comparative examples struggle to achieve the same level of effectiveness.

[0084] In Examples 1-7 of this invention, the leachate of the coupling materials obtained were tested and found to meet the GB18599 standard, and their heavy metal content met the requirements of GB8978.

[0085] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a coupling material for desulfurization wastewater and coal-based solid waste, characterized in that, The preparation method includes the following steps: 1) Mix 8-10 parts by weight of coal-based solid waste and 0.8-5.0 parts by weight of desulfurization wastewater to obtain a mixture. 2) Mix the mixture obtained in step 1) with 0.1-0.5 parts by weight of a modifier to obtain the coupling material; In step 1), the leachate from the coal-based solid waste has a pH > 9 and a Se content of 0.1-0.5 mg / L. The desulfurization wastewater used must meet the following requirements: pH 4-9, Mg ion content ≥50mg / L; In step 2), based on the total mass of the modifier, the modifier comprises 2-10% inorganic acid and 90-98% soluble salt; the soluble salt is selected from one or more of soluble aluminum salts and soluble iron salts.

2. The preparation method according to claim 1, characterized in that, The inorganic acid is selected from at least one of sulfuric acid and hydrochloric acid.

3. The preparation method according to claim 1, characterized in that, The coal-based solid waste mentioned in step 1) is selected from at least one of fly ash and bottom ash.

4. The preparation method according to claim 1, characterized in that, The desulfurization wastewater is selected from at least one of the following: raw desulfurization wastewater, effluent from the desulfurization wastewater triple tank, and concentrated desulfurization wastewater.

5. The preparation method according to any one of claims 1-4, characterized in that, In step 1), the desulfurization wastewater used contains Cd at 0.1-1 mg / L, Cr at 1.5-15 mg / L, Cu at 0.5-10 mg / L, Ni at 1-10 mg / L, and Pb at 1-10 mg / L.

6. The preparation method according to any one of claims 1-4, characterized in that, The mixing reaction described in step 1) includes: mixing the coal-based solid waste and the desulfurization wastewater, and then allowing the mixture to stand for 8-24 hours; in step 2), the mixture is allowed to stand for 1-7 days after mixing.

7. A coupling material for desulfurization wastewater and coal-based solid waste prepared by the preparation method according to any one of claims 1-6.

8. The desulfurization wastewater and coal-based solid waste coupling material according to claim 7, characterized in that, The leachate of the coupling material has a pH of 6-9 and a Se content ≤0.1 mg / L.

9. The application of the coupling material for desulfurization wastewater and coal-based solid waste as described in claim 8, characterized in that, The coupling material is used in mine filling or backfilling, soil remediation or reclamation or improvement, ecological restoration, road materials, aggregates, mining materials, and / or the solidification of trace metal elements.

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