Method for synergistically removing chloride ions and heavy metals in fly ash
By combining oxidative pickling and pretreatment process and electric field action, the chloride ions and heavy metals in fly ash are efficiently removed, and the problems of high energy consumption, high cost and environmental pollution in the prior art are solved, and the dechlorination effect with low cost, low energy consumption and environmental protection are achieved.
Patent Information
- Application Number
- CN202411771766.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-04
- Publication Date
- 2025-03-04
AI Technical Summary
The prior art is difficult to remove chloride ions and heavy metals from fly ash with low energy consumption, low cost and environmentally friendly, and subsequently water purification is required.
The oxidative pickling combined with pretreatment process is adopted, and under the action of an electric field, the chloride ions and heavy metals in the fly ash are efficiently removed, and the metal salt products are co-produced, and the waste liquid can be recycled.
It realizes efficient removal of chloride ions in fly ash, coordinates the removal of dissolved heavy metals, reduces subsequent dechlorination costs and energy consumption, and improves the economic and environmental protection of the process.
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Figure CN119548790A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of fly ash treatment, and in particular relates to a method for collaboratively removing chloride ions and heavy metals in fly ash. Background Art
[0003] At present, the common dechlorination technologies are dry dechlorination and wet dechlorination. Dry dechlorination mainly includes high-temperature heat treatment and low-temperature plasma treatment, while wet dechlorination mainly includes water washing and acid washing pretreatment.
[0004] High-temperature heat treatment utilizes the high chlorine and heavy metal content of fly ash to perform high-temperature heat treatment, which volatilizes heavy metals and chlorine into flue gas for capture, thus achieving the purpose of removing chlorine and heavy metals from fly ash. However, the system has high energy consumption and needs to be coordinated with other units.
[0005] Low temperature plasma treatment (such as patent CN111589042A) is a method of adding titanium dioxide and using its photogenerated holes to oxidize chloride ions into chlorine gas. This method has the advantages of low temperature and synergistic dechlorination and decomposition of dioxins, but the reaction requires the addition of titanium dioxide, and the high cost makes it difficult to apply it industrially.
[0006] In order to effectively reduce energy consumption and costs, the industry also uses a simple wet process to treat fly ash. For example, water washing pretreatment technology can effectively remove Cl, Na, K and Ca elements in fly ash, and is one of the common methods for fly ash dechlorination. After water washing, soluble chloride salts such as (KCl, NaCl) in fly ash are dissolved in water and removed in large quantities. The fly ash water washing process can effectively remove soluble chlorine in fly ash, but it is difficult to remove insoluble chlorine, and the wastewater contains a large amount of heavy metal ions and chloride ions.
[0007] The acid washing pretreatment process is to add a certain proportion of acid to the water washing process to convert insoluble chlorine into soluble chlorine and then remove it. The dechlorination effect is better than that of simple water washing. However, both the water washing and acid washing pretreatment processes inevitably cause heavy metals and other pollutants to migrate from the solid phase to the liquid phase. The wastewater contains a large amount of heavy metal ions and chloride ions, and water purification is required later.
[0008] In summary, the low-energy, low-cost and environmentally friendly removal of chloride ions from fly ash remains the technical bottleneck of this technology.
[0009] In view of this, this application is hereby filed. Summary of the invention
[0010] The purpose of the present invention is to provide a method for synergistically removing chloride ions and heavy metals from fly ash, which can remove chloride ions and heavy metals efficiently under the action of an electric field on the basis of an oxidation pickling combined with a pretreatment process, and obtain a metal salt product. The present invention can remove high-content chlorine in the fly ash efficiently, cheaply and greenly in the whole chain.
[0011] In order to achieve the above objectives, the present invention particularly adopts the following technical solutions:
[0012] The present invention provides a method for collaboratively removing chloride ions and heavy metals in fly ash, comprising the following steps:
[0013] Adding water to the fly ash to obtain slurry, adding acid and oxidant, stirring, and filtering to obtain a first filtrate;
[0014] adding an adsorbent to the first filtrate, stirring, and filtering to obtain a second filtrate;
[0015] adding a precipitant to the second filtrate, stirring, and filtering to obtain a third filtrate;
[0016] The third filtrate is heated, stirred, and filtered to obtain a fourth filtrate;
[0017] The acid is added to the fourth filtrate, and an electric field is applied to obtain a fifth filtrate.
[0018] Compared with the prior art, the present invention has the following beneficial effects:
[0019] The present invention combines oxidative pickling with a pretreatment process to reduce the cost and difficulty of subsequent dechlorination to the maximum extent. Subsequently, under the action of an electric field, chloride ions in the liquid phase are efficiently removed, and dissolved heavy metals are also synergistically removed.
[0020] The present invention removes a large amount of Cl in fly ash by gentle and simple means, and co-produces calcium salt, sodium chloride, potassium chloride, hydrogen chloride and other products in the process, and the waste liquid in the process can be recycled, which greatly improves the economy of fly ash dechlorination process. Compared with the high-temperature dechlorination process of cement kilns in traditional industry, the present invention greatly reduces the energy consumption of the treatment process, and the Cl content of the product easily reaches the national standard. Compared with the wet dechlorination process in traditional industry, the co-production of products in the present invention improves the process economy. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.
[0022] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION
[0023] The embodiments of the present invention will be described in detail below in conjunction with specific examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If specific conditions are not specified in the examples, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.
[0024] In the present invention, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.
[0025] It should be noted that in the following examples or comparative examples, if there is a mixture, if there is no description of the ratio of each component, it can be any ratio. The solution concentration of the substance not specified is the conventional standard concentration or any concentration.
[0026] The embodiment of the present invention provides a method for collaboratively removing chloride ions and heavy metals from fly ash, such as Figure 1 As shown, the following steps are included:
[0027] S01: adding water to the fly ash to obtain a slurry, then adding an acid and an oxidant, stirring, and filtering to obtain a first filtrate;
[0028] S02: adding an adsorbent to the first filtrate, stirring, and filtering to obtain a second filtrate;
[0029] S03: adding a precipitant to the second filtrate, stirring, and filtering to obtain a third filtrate;
[0030] S04: heating the third filtrate, stirring, and filtering to obtain a fourth filtrate;
[0031] S05: adding the acid to the fourth filtrate and applying an electric field to obtain a fifth filtrate.
[0032] In the above step S01, the mass ratio of the fly ash to water is 1:(2-5); the slurry making process is to obtain the slurry after stirring and slurrying for about 30 minutes at room temperature.
[0033] In an embodiment, the mass ratio of the acid, the oxidant and the slurry is (1-10):(1-10):150.
[0034] In an embodiment, the acid comprises a strong acid; in an optional embodiment, the strong acid comprises one or more of sulfuric acid, hydrochloric acid or nitric acid.
[0035] In an embodiment, the oxidizing agent comprises hydrogen peroxide.
[0036] The role of the strong acid and hydrogen peroxide is to leach insoluble Cl from the solid phase to the liquid phase. After the two are added, stirring is carried out at room temperature for about 1 hour and then filtered to obtain the first filtrate. The first filtrate is subsequently mainly subjected to dechlorination treatment.
[0037] In an embodiment, the pH value of the first filtrate is 1-4.
[0038] In the above step S02, the adsorbent includes one or more of activated carbon, zeolite or biochar. After adding the adsorbent, stirring at room temperature for about 1 hour for complete adsorption, filtering to obtain the second filtrate. The adsorbent is used to remove a small amount of Zn, Cd, Pb, Cr, Ba, Cu, etc. dissolved in the fly ash.
[0039] In an embodiment, the mass ratio of the adsorbent to the first filtrate is (1-10):125.
[0040] In an embodiment, the pH value of the second filtrate is 1-4.
[0041] In the above step S03, the precipitant includes a soluble carbonate. In some optional embodiments, the soluble carbonate includes one or more of sodium carbonate, potassium carbonate or sodium bicarbonate. The function of the soluble carbonate is to precipitate Ca, Mg, etc. dissolved in the fly ash.
[0042] In an embodiment, the mass ratio of the precipitant to the second filtrate is (1-5):30.
[0043] In an embodiment, the pH value of the third filtrate is 7-11.
[0044] After adding the precipitant, stirring was performed at room temperature for about 20 minutes, and then the precipitation was complete and filtered to obtain the third filtrate.
[0045] In the above step S04, the heating temperature is 50-100°C, the chloride salt is crystallized by stirring for about 20 minutes, and the fourth filtrate is obtained by filtering.
[0046] In an embodiment, the pH value of the fourth filtrate is 7-11.
[0047] This not only makes it easier to remove Cl in the liquid phase, but also produces salt products with added value.
[0048] In the above step S04, the mass ratio of the supplemented acid to the slurry is (1-10):30.
[0049] In an embodiment, the applied electric field is a uniform electric field applied around the filtrate through electrode plates.
[0050] Furthermore, the polarity switching frequency of the uniform electric field is 30-100 Hz.
[0051] Furthermore, the current density of the uniform electric field is 20-80 mA / cm 2 .
[0052] The role of the acid supplement is to combine with Cl to generate HCl, and the uniform electric field can promote the local enrichment of Cl ions, generate hot spots, and effectively enhance the escape of HCl.
[0053] In some preferred embodiments, during the process of supplementing the acid and applying the electric field, the filtrate temperature is maintained at 30-90°C.
[0054] In an embodiment, the fifth filtrate is recycled and used in the pulping process.
[0055] The present invention will be further described below by way of examples:
[0056] Example 1
[0057] A method for synergistically removing chloride ions and heavy metals from fly ash:
[0058] 1500g of water was added to 500g of grate furnace fly ash, and stirred at room temperature for 30min to form a slurry, wherein the mass fraction of Cl element in the grate furnace fly ash was 24.5%. 30g of concentrated hydrochloric acid and 30g of hydrogen peroxide were added to the slurry, stirred at room temperature for 1h and filtered, and the mass fraction of Cl element in the solid obtained after washing was 0.85%, the pH of the obtained filtrate was 1.4, and the Cl ion concentration of the obtained filtrate was 71200mg / L.
[0059] Add 30g of zeolite to the filtrate, stir at room temperature for 1h to completely adsorb the heavy metals, and filter to obtain a filtrate. At this time, the pH of the filtrate is 2.0. Continue to add 100g of potassium carbonate to the filtrate, stir at room temperature for 20min, precipitate Ca and Mg, and filter to obtain a filtrate. At this time, the pH of the filtrate is 9.3. Continue to heat the filtrate to 75℃ for crystallization, continue to stir at 75℃ for 20min, crystallize Na and K, and filter to obtain a filtrate. At this time, the pH of the filtrate is 8.2.
[0060] At 80°C, 100 g of sulfuric acid was added to the filtrate, and a uniform electric field was applied around the filtrate through the electrode plates. The polarity switching frequency of the uniform electric field was 50 Hz, and the current density was 50 mA / cm 2 The final solution Cl ion concentration was 6053 mg / L, and the Cl ion removal rate in the solution was 90.1%.
[0061] Finally, the above solution was used for the second fly ash dechlorination. The final Cl ion concentration of the solution in the second experiment was 6220 mg / L, and the Cl ion removal rate in the solution was 89.9%.
[0062] Example 2
[0063] A method for synergistically removing chloride ions and heavy metals from fly ash:
[0064] 1500g of water was added to 500g of grate furnace fly ash, and stirred at room temperature for 30min, wherein the mass fraction of Cl element in grate furnace fly ash was 24.5%. 20g of concentrated sulfuric acid and 20g of hydrogen peroxide were added to the slurry, stirred at room temperature for 1h and filtered, and the mass fraction of Cl element in the solid obtained after washing was 1.11%, the pH of the obtained filtrate was 1.9, and the Cl ion concentration of the obtained filtrate was 61000mg / L.
[0065] Add 30g of activated carbon to the filtrate, stir at room temperature for 1h to completely adsorb the heavy metals, and filter to obtain a filtrate. At this time, the pH of the filtrate is 2.1. Continue to add 80g of potassium carbonate to the filtrate, stir at room temperature for 20min, precipitate Ca and Mg, and filter to obtain a filtrate. At this time, the pH of the filtrate is 8.6. Continue to heat the filtrate to 95℃ for crystallization, continue to stir at 95℃ for 20min, crystallize Na and K, and filter to obtain a filtrate. At this time, the pH of the filtrate is 9.0.
[0066] At 90°C, 150 g of sulfuric acid was added to the filtrate, and a uniform electric field was applied around the filtrate through the electrode plates. The polarity switching frequency of the uniform electric field was 50 Hz, and the current density was 50 mA / cm 2 The final solution Cl ion concentration was 6122 mg / L, and the Cl ion removal rate in the solution was 90%.
[0067] Finally, the above solution was used for the second fly ash dechlorination. The final Cl ion concentration of the solution in the second experiment was 6258 mg / L, and the Cl ion removal rate in the solution was 89.8%.
[0068] Example 3
[0069] A method for synergistically removing chloride ions and heavy metals from fly ash:
[0070] 2000g of water was added to 500g of grate furnace fly ash, and stirred at room temperature for 30min, wherein the mass fraction of Cl element in grate furnace fly ash was 24.5%. 25g of concentrated sulfuric acid and 25g of hydrogen peroxide were added to the slurry, stirred at room temperature for 1h and filtered, and the mass fraction of Cl element in the solid obtained after washing was 0.91%, the pH of the obtained filtrate was 2.1, and the Cl ion concentration of the obtained filtrate was 45700mg / L.
[0071] Add 30g of zeolite to the filtrate, stir at room temperature for 1h to completely adsorb the heavy metals, and filter to obtain a filtrate. At this time, the pH of the filtrate is 2.0. Continue to add 100g of potassium carbonate to the filtrate, stir at room temperature for 20min, precipitate Ca and Mg, and filter to obtain a filtrate. At this time, the pH of the filtrate is 9.2. Continue to heat the filtrate to 80℃ for crystallization, continue to stir at 80℃ for 20min, crystallize Na and K, and filter to obtain a filtrate. At this time, the pH of the filtrate is 8.3.
[0072] At 80°C, 200 g of sulfuric acid was added to the filtrate, and a uniform electric field was applied around the filtrate through the electrode plates. The polarity switching frequency of the uniform electric field was 50 Hz, and the current density was 50 mA / cm 2 The Cl ion removal rate in the solution was 90.5%.
[0073] Finally, the above solution was used for the second fly ash dechlorination. The final Cl ion concentration of the solution in the second experiment was 4577 mg / L, and the Cl ion removal rate in the solution was 90.0%.
[0074] Example 4
[0075] A method for synergistically removing chloride ions and heavy metals from fly ash:
[0076] 2000g of water was added to 500g of grate furnace fly ash, and stirred at room temperature for 30min to form a slurry, wherein the mass fraction of Cl element in the grate furnace fly ash was 24.5%. 20g of concentrated sulfuric acid and 20g of hydrogen peroxide were added to the slurry, stirred at room temperature for 1h and filtered, and the mass fraction of Cl element in the solid obtained after washing was 0.98%, the pH of the obtained filtrate was 2.4, and the Cl ion concentration of the obtained filtrate was 44600mg / L.
[0077] Add 30g of zeolite to the filtrate, stir at room temperature for 1h to completely adsorb the heavy metals, and filter to obtain a filtrate. At this time, the pH of the filtrate is 2.0. Continue to add 100g of potassium carbonate to the filtrate, stir at room temperature for 20min, precipitate Ca and Mg, and filter to obtain a filtrate. At this time, the pH of the filtrate is 9.4. Continue to heat the filtrate to 80℃ for crystallization, continue to stir at 80℃ for 20min, crystallize Na and K, and filter to obtain a filtrate. At this time, the pH of the filtrate is 8.2.
[0078] At 80°C, 100 g of sulfuric acid was added to the filtrate, and a uniform electric field was applied around the filtrate through the electrode plates. The polarity switching frequency of the uniform electric field was 50 Hz, and the current density was 50 mA / cm 2 The removal rate of Cl ions in the solution was 93.2%.
[0079] Finally, the mixed solution was used for the second fly ash dechlorination. The final Cl ion concentration of the solution in the second experiment was 3127 mg / L, and the Cl ion removal rate in the solution was 93.0%.
[0080] Comparative Example 1
[0081] 1500g of water was added to 500g of grate furnace fly ash, and stirred at room temperature for 30min, wherein the mass fraction of Cl element in grate furnace fly ash was 24.5%. 50g of concentrated hydrochloric acid was added to the slurry, stirred at room temperature for 1h, and then filtered. After filtering and washing, the mass fraction of Cl element in the obtained solid was 0.65%, the pH of the obtained filtrate was 1.1, and the Cl ion concentration of the obtained filtrate was 72300mg / L.
[0082] Add 30g of zeolite to the filtrate, stir at room temperature for 1h to completely adsorb the heavy metals, and filter to obtain a filtrate. At this time, the pH of the filtrate is 2.0. Continue to add 100g of potassium carbonate to the filtrate, stir at room temperature for 20min, precipitate Ca and Mg, and filter to obtain a filtrate. At this time, the pH of the filtrate is 8.5. Continue to heat the filtrate to 75℃ for crystallization, continue to stir at 75℃ for 20min, crystallize Na and K, and filter to obtain a filtrate. At this time, the pH of the filtrate is 8.5.
[0083] At 80°C, 100 g of sulfuric acid was added to the filtrate, and a uniform electric field was applied around the filtrate through the electrode plates. The polarity switching frequency of the uniform electric field was 50 Hz, and the current density was 50 mA / cm 2 The removal rate of Cl ions in the solution was 68.8%.
[0084] Finally, the above solution was used for the second fly ash dechlorination. The final Cl ion concentration of the solution in the second experiment was 21033 mg / L, and the Cl ion removal rate in the solution was 65.6%.
[0085] Comparative Example 2
[0086] 1500g of water was added to 500g of grate furnace fly ash, and stirred at room temperature for 30min to form a slurry, wherein the mass fraction of Cl element in the grate furnace fly ash was 24.5%. 30g of concentrated hydrochloric acid and 30g of hydrogen peroxide were added to the slurry, stirred at room temperature for 1h and filtered, and the mass fraction of Cl element in the solid obtained after washing was 0.85%, the pH of the obtained filtrate was 1.4, and the Cl ion concentration of the obtained filtrate was 71200mg / L.
[0087] Add 30g of zeolite to the filtrate, stir at room temperature for 1h to completely adsorb the heavy metals, and filter to obtain a filtrate. At this time, the pH of the filtrate is 2.0. Continue to add 100g of potassium carbonate to the filtrate, stir at room temperature for 20min, precipitate Ca and Mg, and filter to obtain a filtrate. At this time, the pH of the filtrate is 9.3. Continue to heat the filtrate to 75℃ for crystallization, continue to stir at 75℃ for 20min, crystallize Na and K, and filter to obtain a filtrate. At this time, the pH of the filtrate is 8.2.
[0088] At room temperature, 100 g of sulfuric acid was added to the above filtrate, and a uniform electric field was applied around the filtrate through the electrode plates. The polarity switching frequency of the uniform electric field was 50 Hz, and the current density was 50 mA / cm 2 The Cl ion removal rate in the solution was 75.3%.
[0089] Finally, the above solution was used for the second fly ash dechlorination. The final Cl ion concentration of the solution in the second experiment was 21033 mg / L, and the Cl ion removal rate in the solution was 71.9%.
[0090] It can be seen that the Cl ion removal rate in the solution of the methods of Examples 1-4 is generally higher than 90%, and can reach up to 93.2%. The results of the secondary dechlorination experiment are also very close to 90%. In Comparative Example 1, only acid is added to the slurry without hydrogen peroxide, which not only affects the Cl ion removal effect in the subsequent steps, but also the final Cl ion removal rate shows a cliff-like decline. In addition, Comparative Example 2 does not heat up when supplementing acid and applying a uniform electric field, but is carried out at room temperature, and the Cl ion removal rate also shows a cliff-like decline.
[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
[0092] In addition, those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present invention and to form different embodiments. For example, in the above claims, any one of the claimed embodiments may be used in any combination. The information disclosed in this background technology section is intended only to deepen the understanding of the overall background technology of the present invention and should not be regarded as an admission or in any form of implication that the information constitutes prior art known to those skilled in the art.
Claims
1. A method for synergistically removing chloride ions and heavy metals from fly ash, characterized in that: The following steps are involved: Adding water to the fly ash to obtain slurry, adding acid and oxidant, stirring, and filtering to obtain a first filtrate; adding an adsorbent to the first filtrate, stirring, and filtering to obtain a second filtrate; adding a precipitant to the second filtrate, stirring, and filtering to obtain a third filtrate; The third filtrate is heated, stirred, and filtered to obtain a fourth filtrate; The acid is added to the fourth filtrate, and an electric field is applied to obtain a fifth filtrate.
2. The method according to claim 1, characterized in that The mass ratio of fly ash to water is 1:(2-5); And / or, the mass ratio of the acid, the oxidant and the slurry is (1-10):(1-10):
150.
3. The method according to claim 1, characterized in that The acid comprises a strong acid; and / or, the oxidant comprises hydrogen peroxide; And / or, the pH value of the first filtrate is 1-4; Preferably, the strong acid comprises one or more of sulfuric acid, hydrochloric acid or nitric acid.
4. The method according to claim 1, characterized in that: The adsorbent includes one or more of activated carbon, zeolite or biochar; and / or, the mass ratio of the adsorbent to the first filtrate is (1-10):125; And / or, the pH value of the second filtrate is 1-4.
5. The method according to claim 1, characterized in that The precipitant includes a soluble carbonate; and / or, the mass ratio of the precipitant to the second filtrate is (1-5):30; And / or, the pH value of the third filtrate is 7-11; Preferably, the soluble carbonate comprises one or more of sodium carbonate, potassium carbonate or sodium bicarbonate.
6. The method according to claim 1, characterized in that The heating temperature is 50-100°C; And / or, the pH value of the fourth filtrate is 7-11.
7. The method according to claim 1, characterized in that The mass ratio of the supplemented acid to the slurry is (1-10):30; And / or, the applied electric field is a uniform electric field applied around the filtrate through electrode plates.
8. The method according to claim 7, characterized in that The polarity switching frequency of the uniform electric field is 30-100 Hz; And / or, the current density of the uniform electric field is 20-80 mA / cm 2 .
9. The method according to claim 1, characterized in that: During the process of supplementing the acid and applying the electric field, the filtrate temperature is maintained at 30-90°C.
10. The method according to claim 1, characterized in that The fifth filtrate is recycled and used in the pulping process.