Method for preparing baking soda by using desulfurized fly ash

Abstract

The present application specifically relates to the technical field of solid waste treatment. Disclosed is a method for preparing baking soda by using desulfurized fly ash. The method comprises: dissolution, coagulation-defluorination coupled precipitation defluorination, oxidative acidification, cooling crystallization, preparation of baking soda from sodium sulfate, reverse precipitation and preparation of baking soda from sodium chloride. In the present application, the industrial desulfurized fly ash is prepared into baking soda having a high added value by using an effective process, and the baking soda is reused in a desulfurization process, thereby achieving resource recycling of the industrial desulfurized fly ash. In addition, impurity ion COD, sulfite, carbonate, bicarbonate and fluorine ions, etc., in the desulfurized fly ash are comprehensively removed; and compared with a traditional process, the recycled baking soda has a higher purity and a higher recovery rate by means of process innovation.

Description

A method for preparing baking soda using desulfurization ash

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on November 13, 2023, with application number CN202311498165.1 and application name “A method for preparing baking soda using desulfurization ash”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of solid waste treatment, and in particular to a method for preparing baking soda using desulfurization ash. Background Art

[0003] Flue gas desulfurization ash (FGD) is a primary hazardous solid waste generated during the desulfurization process of coke oven flue gas, using sodium carbonate and sodium bicarbonate as desulfurizers. Its primary components are sodium carbonate, sodium bicarbonate, sodium sulfate, and sodium sulfite, along with a certain proportion of impurity ions. FGD ash is highly soluble in water and, when stored or landfilled, can seep into the soil through rainwater, causing serious contamination of the soil and groundwater.

[0004] Patent CN11207363A proposes a method for resource utilization of baking soda desulfurization ash. The desulfurization ash is dissolved in pure water, clarified and separated into solid and liquid, and baking soda crystals are added to the clarified liquid. The solution is evaporated and concentrated to obtain a baking soda product. However, the technology does not mention the removal technology of impurity ions in the desulfurization ash, and the purity of the obtained baking soda and sodium sulfate products cannot be guaranteed.

[0005] Patent CN109850922A proposes a method and apparatus for resource utilization of baking soda desulfurization ash. Based on the dissolution and filtration of the desulfurization ash, the method uses lime milk, carbon dioxide, and oxygen to convert carbonates in the solution into bicarbonates. This improves the purity of the baking soda and produces calcium sulfate as a byproduct. However, the added value of calcium sulfate is lower than that of baking soda. Furthermore, due to the presence of organic matter and fluoride ions in the desulfurization ash, the purity of the recovered calcium sulfate cannot be guaranteed.

[0006] Patent CN110697738A proposes a method for resource-based treatment of desulfurization ash using a baking soda dry process, which recycles the desulfurization ash into sodium sulfate and sodium chloride. However, the added value of sodium sulfate is lower than that of baking soda for enterprises and cannot be reused within the enterprise.

[0007] Summary of the Invention

[0008] To this end, the present application provides a method for preparing baking soda using desulfurization ash to solve the above-mentioned problems.

[0009] This application improves on the existing technology, optimizes and perfects the impurity removal process in the process of recovering baking soda from desulfurization ash, and then converts the sodium sulfate in the system into baking soda, reducing the amount of conversion agent used for converting sodium sulfate into baking soda, and fully realizing the resource reuse of desulfurization ash.

[0010] In order to achieve the above objectives, this application provides the following technical solutions:

[0011] A method for preparing baking soda using desulfurization ash, the method comprising:

[0012] ①Dissolution: dissolve the desulfurization ash in water to obtain a suspension containing black suspended matter;

[0013] ② Fluoride removal by coagulation-defluorination coupled precipitation: Add a defluorination agent to the suspension containing black suspended matter, adopt a chemical defluorination method, and use the coagulation-defluorination coupled precipitation principle to remove the suspended matter in the suspension containing black suspended matter and the precipitate formed by the defluorination agent and fluoride ions. Filter the supernatant after precipitation to obtain the defluorination filtrate;

[0014] ③ Oxidation and acidification: The defluorination filtrate is subjected to oxidation and acidification treatment; all the sodium sulfite in the solution is oxidized into sodium sulfate, and then concentrated sulfuric acid is added for acidification, and the pH is adjusted to 4.4, and all the carbonate and bicarbonate are converted into sulfate to obtain a sulfate mixture;

[0015] ④ Cooling crystallization: After cooling and crystallizing the sulfate mixture, sodium sulfate is precipitated in the form of Glauber's salt; a portion of the cooled mother liquor is replenished with water and heated up, and then returned to step ①, and the other portion of the mother liquor is used as the subsequent treatment liquid;

[0016] ⑤ Sodium sulfate to baking soda: Sodium sulfate is dissolved in hot water to obtain a sodium sulfate aqueous solution, and ammonium bicarbonate is added to the sodium sulfate aqueous solution to convert the sodium sulfate into sodium bicarbonate and ammonium sulfate. The sodium bicarbonate is supersaturated and precipitated. The sodium bicarbonate enters the drying system to prepare baking soda, and the ammonium sulfate is recovered;

[0017] ⑥ Reverse precipitation: adding calcium chloride to the subsequent treatment solution of step ④ to precipitate calcium sulfate precipitate and sodium chloride solution;

[0018] ⑦ Preparation of baking soda from sodium chloride: Add ammonium bicarbonate to the sodium chloride solution in step ⑥ to convert the sodium chloride into sodium bicarbonate and ammonium chloride. The sodium bicarbonate is supersaturated and precipitated, and the sodium bicarbonate enters the drying system to prepare baking soda; the ammonium chloride is recovered.

[0019] Furthermore, in step ①, the dissolution temperature is 35-40° C.; and the mass ratio of desulfurized ash to water is 1:1-1:5.

[0020] Furthermore, in step ②, the chemical defluorination method includes adding a defluorinating agent according to a molar ratio of defluorinating agent: fluoride ion = 1:1 to 2:1, stirring and reacting for 30 to 50 minutes, adding 200 to 1000 ppm of a coagulant and stirring for 5 to 10 minutes, settling for 1 to 2 hours, removing the precipitate, and filtering the supernatant to obtain a defluorinated filtrate.

[0021] Furthermore, in step ③, the oxidation method is one or a combination of pharmaceutical oxidation, wet oxidation, Fenton oxidation, ozone catalytic oxidation, photocatalytic oxidation, and electrochemical oxidation; and the pH is adjusted to 4.4 by acidification.

[0022] Furthermore, in step ④, the temperature of cooling crystallization is 5-15°C; and the temperature of heating is 35-40°C.

[0023] Furthermore, in step ⑤, the hot water temperature is 50-60° C., the concentration of the sodium sulfate solution is 31%, and the amount of ammonium bicarbonate added is such that the molar ratio of ammonium bicarbonate to sodium sulfate is 1:1-1:10.

[0024] Furthermore, in step ⑦, the amount of ammonium bicarbonate added is such that the molar ratio of ammonium bicarbonate to sodium chloride solution is 1:1 to 1:10.

[0025] Compared with the prior art, this application has at least the following beneficial effects:

[0026] 1) This application utilizes an efficient process to prepare high-value-added baking soda from industrial desulfurization ash, which is then reused in the desulfurization process, achieving resource recovery of industrial desulfurization ash. Impurity ions such as COD, sulfite, carbonate, bicarbonate, and fluoride ions are comprehensively removed from the desulfurization ash. Through this innovative process, the recovered baking soda is of higher purity and has a higher recovery rate than conventional processes.

[0027] 2) During the cooling crystallization process, the temperature is properly controlled according to the Na2SO4-NaCl-H2O ternary phase diagram to ensure that the precipitated Na2SO4 accounts for more than 85% of the total Na2SO4 content in the solution, and a mixture of anhydrous sodium sulfate and baking soda with a purity of more than 98% is obtained;

[0028] 3) Utilizing the difference in solubility between Na2SO4 and NaHCO3 at a certain temperature, when ammonium bicarbonate is added to convert all Na2SO4 into NaHCO3, NaHCO3 begins to precipitate, and the conversion rate reaches 90%, thereby obtaining two industrial products: baking soda solid and ammonium sulfate.

[0029] 4) Calcium chloride is added to the cooled crystallization mother liquor to obtain gypsum and sodium chloride solution. Compared with the process of producing sodium chloride solid by evaporation crystallization and then dissolving it into sodium chloride solution, this method greatly reduces energy consumption.

[0030] 5) Utilizing the difference in solubility between NaCl and NaHCO3 at a certain temperature, when ammonium bicarbonate is added to convert all NaCl into NaHCO3, NaHCO3 begins to precipitate, and the conversion rate reaches 90%, thereby obtaining two industrial products: baking soda solid and ammonium chloride. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To more intuitively illustrate the prior art and the present application, exemplary drawings are provided below. It should be understood that the specific shapes and structures shown in the drawings should not generally be considered as limiting conditions for implementing the present application; for example, based on the technical concepts disclosed in this application and the exemplary drawings, those skilled in the art are capable of easily making routine adjustments or further optimizations to the addition / reduction / attribution division, specific shapes, positional relationships, connection methods, dimensional ratios, etc. of certain units (components).

[0032] FIG1 is a process flow chart of preparing baking soda using desulfurization ash provided in this application. DETAILED DESCRIPTION

[0033] The following specific embodiments illustrate the implementation of this application. Those familiar with the art can easily understand the other advantages and functions of this application from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of this application, but not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0034] A method for preparing baking soda using desulfurization ash, the process flow is shown in Figure 1, comprising:

[0035] 1) Dissolution: Desulfurization ash is dissolved in water at a temperature of 35-40°C according to a mass ratio of desulfurization ash to water of 1:1-1:5. The water can be tap water, pure water, evaporation condensate, etc. More than 98% of the desulfurization ash is dissolved in water by mass, and the insoluble matter is in a black suspended state;

[0036] 2) Coagulation-defluorination coupled precipitation: Using a chemical defluorination method, the defluorinating agent is added at a molar ratio of defluorinating agent: fluoride ion = 1:1-2:1, and the mixture is stirred for 30-50 minutes. 200-1000 ppm of coagulant is added and stirred for 5-10 minutes. The mixture is allowed to settle for 1-2 hours. The insoluble matter dissolved in step 1 and the precipitate formed by the defluorinating agent and fluoride ion are removed together. The fluoride ion content in the effluent is reduced to below 10 mg / L. The supernatant after precipitation is filtered, and the filtrate is collected for further treatment;

[0037] 3) Oxidation and acidification: The oxidation process includes one or a combination of conventional chemical oxidation, wet oxidation, Fenton oxidation, ozone catalytic oxidation, photocatalytic oxidation, and electrochemical oxidation, which oxidizes all the sodium sulfite in the solution into sodium sulfate, with a significant decolorization effect on the solution and an organic matter removal rate of more than 90%. An appropriate amount of concentrated sulfuric acid is added to the oxidized solution for acidification, and the pH is adjusted to 4.4. The carbonate and bicarbonate are completely converted into sulfate.

[0038] 4) Cooling crystallization: The solution treated in step 3 is cooled to 5-15°C, at which point the sodium sulfate in the solution precipitates as Glauber's salt; 10%-20% of the mother liquor after cooling crystallization is mixed with make-up water, heated to 35-40°C via a heat exchanger, and refluxed to the dissolution unit; 80%-90% of the mother liquor is collected for further processing;

[0039] 5) Sodium sulfate to baking soda: The cooled crystallized Glauber's salt is dissolved in 50-60°C water to a Na2SO4 concentration of 31%. Ammonium bicarbonate is added at a molar ratio of ammonium bicarbonate to sodium sulfate of 3:1-2:1 to convert the sodium sulfate into sodium bicarbonate and ammonium sulfate. The recovery rate of the obtained sodium bicarbonate is >90%. The sodium bicarbonate is then fed into a drying system to prepare baking soda. The purity of the baking soda is above 95%. The ammonium sulfate can be used as a nitrogen fertilizer.

[0040] 6) Reaction precipitation: Add an appropriate amount of calcium chloride to the remaining mother liquor in step 4 to precipitate the remaining sulfate as calcium sulfate. The resulting gypsum can be used as a building material. At this point, the remaining solution is mainly composed of sodium chloride.

[0041] 7) Preparation of baking soda from sodium chloride: ammonium bicarbonate is added at a molar ratio of 1.5:1 to 1:1 to the sodium chloride solution obtained in step 6 to convert the sodium chloride into sodium bicarbonate and ammonium chloride. The recovery rate of the obtained sodium bicarbonate is greater than 90%. The sodium bicarbonate is mixed with the sodium bicarbonate precipitated in step 5 and fed into a drying system to prepare baking soda. The purity of the baking soda is greater than 95%. The ammonium chloride can be used as a nitrogen fertilizer.

[0042] Example 1

[0043] The composition analysis of desulfurization ash from a coal coking enterprise is shown in Table 1:

[0044] Table 1 Analysis results of desulfurization ash composition percentage

[0045] Method for preparing baking soda using the desulfurization ash shown in Table 1:

[0046] Step 1: Dissolve desulfurized ash in water at a ratio of 1:4 by mass at a constant temperature of 40°C. Black insoluble matter will be present in the solution.

[0047] Step 2: Defluorination agent according to the molar ratio: F- =1:1 Add defluoridant to the solution and stir for 30 minutes, then add 500ppm coagulant and stir for 8 minutes, then stop stirring and let it settle for 1 hour, filter the supernatant and detect F - The content is 8.35 mg / L, and the filtered liquid is yellow and transparent.

[0048] Step 3: The filtrate in step 2 is introduced with O3, with the dosage being 2:1. After oxidation, the solution changes from yellow to colorless and transparent, and the COD removal rate reaches 60%. Concentrated sulfuric acid is then added to adjust the pH to 4.4, and all carbonate and bicarbonate ions are converted into sulfate ions.

[0049] Step 4: The solution obtained in step 3 is cooled to 5°C, where a large amount of sodium sulfate is precipitated. The purity of sodium sulfate is 98.5%. 10% of the mother liquor after cooling and crystallization is mixed with supplementary water, heated to 35-40°C through a heat exchanger, and refluxed to the dissolution unit. 90% of the mother liquor is collected for the next step of treatment.

[0050] Step 5: The sodium sulfate obtained in step 4 was dissolved in water to a Na2SO4 concentration of 31%, and ammonium bicarbonate solid was added at a molar ratio of ammonium bicarbonate to sodium sulfate of 2:1 to obtain sodium bicarbonate and ammonium sulfate. The recovery rate of the obtained sodium bicarbonate was 89%.

[0051] Step 6: Add molar Ca to the cooled crystallization mother liquor in step 4. 2+ :SO4 2- Calcium chloride was added in a ratio of 1:1, reacted for 30 minutes, and filtered after precipitation for 1 hour to obtain sodium chloride solution and gypsum.

[0052] Step 7: solid ammonium bicarbonate was added to the sodium chloride solution obtained in step 6 at a molar ratio of ammonium bicarbonate to sodium chloride of 1.5:1 to obtain sodium bicarbonate and ammonium chloride. The recovery rate of the obtained sodium bicarbonate was 91%.

[0053] Example 2

[0054] The composition analysis of desulfurization ash from a coal coking enterprise is shown in Table 1. The method for preparing baking soda using the desulfurization ash shown in Table 1 is as follows:

[0055] Step 1: Dissolve desulfurized ash in water at a ratio of 1:3 by mass at a constant temperature of 38°C. Black insoluble matter will be present in the solution.

[0056] Step 2: Defluorination agent according to the molar ratio: F - =1.5:1, add defluoridation agent to the solution and stir for 40 minutes, then add 200ppm coagulant and stir for 5 minutes, then stop stirring and settle for 1.5 hours, filter the supernatant and detect F - The content is 5.12 mg / L, and the filtered liquid is yellow and transparent.

[0057] Step 3: The filtrate in step 2 is introduced with O3, with the dosage being 2:1. After oxidation, the solution changes from yellow to colorless and transparent, and the COD removal rate reaches 60%. Concentrated sulfuric acid is then added to adjust the pH to 4.4, and all carbonate and bicarbonate ions are converted into sulfate ions.

[0058] Step 4: The solution obtained in step 3 is cooled to 10°C, where a large amount of sodium sulfate is precipitated. The purity of the sodium sulfate is 98.5%. 20% of the mother liquor after cooling and crystallization is mixed with supplementary water, heated to 35-40°C through a heat exchanger, and refluxed to the dissolution unit. 80% of the mother liquor is collected for the next step of treatment.

[0059] Step 5: The sodium sulfate obtained in step 4 was dissolved in water to a Na2SO4 concentration of 31%, and ammonium bicarbonate solid was added at a molar ratio of ammonium bicarbonate to sodium sulfate of 2.5:1 to obtain sodium bicarbonate and ammonium sulfate. The recovery rate of the obtained sodium bicarbonate was 92%.

[0060] Step 6: Add molar Ca to the cooled crystallization mother liquor in step 4. 2+ :SO4 2 Calcium chloride was added in a ratio of -=1:1, reacted for 30 minutes, and filtered after precipitation for 1 hour to obtain sodium chloride solution and gypsum.

[0061] Step 7: solid ammonium bicarbonate was added to the sodium chloride solution obtained in step 6 at a molar ratio of ammonium bicarbonate to sodium sulfate of 1.2:1 to obtain sodium bicarbonate and ammonium chloride. The recovery rate of the obtained sodium bicarbonate was 95%.

[0062] Example 3

[0063] The composition analysis of desulfurization ash from a coal coking enterprise is shown in Table 1. The method for preparing baking soda using the desulfurization ash shown in Table 1 is as follows:

[0064] Step 1: Dissolve desulfurized ash in water at a ratio of 1:5 by mass at a constant temperature of 35°C. Black insoluble matter will be present in the solution.

[0065] Step 2: Defluorination agent according to the molar ratio: F - =2:1 Add defluoridation agent to the solution and stir for 50 minutes, then add 1000ppm coagulant and stir for 10 minutes, then stop stirring and settle for 2 hours, filter the supernatant and detect F - The content is 1.52 mg / L, and the filtered liquid is yellow and transparent.

[0066] Step 3: The filtrate in step 2 is introduced with O3, with the dosage being 2:1. After oxidation, the solution changes from yellow to colorless and transparent, and the COD removal rate reaches 60%. Concentrated sulfuric acid is then added to adjust the pH to 4.4, and all carbonate and bicarbonate ions are converted into sulfate ions.

[0067] Step 4: The solution obtained in step 3 is cooled to 15°C, where a large amount of thenardite is precipitated. The purity of the thenardite is 98.5%. 20% of the mother liquor after cooling and crystallization is mixed with make-up water, heated to 35-40°C through a heat exchanger, and refluxed to the dissolution unit. 80% of the mother liquor is collected for the next step of treatment.

[0068] Step 5: The sodium sulfate obtained in step 4 was dissolved in water to a Na2SO4 concentration of 31%, and solid ammonium bicarbonate was added at a molar ratio of ammonium bicarbonate to sodium sulfate of 3:1 to obtain sodium bicarbonate and ammonium sulfate. The recovery rate of the obtained sodium bicarbonate was 95%.

[0069] Step 6: Add molar Ca to the cooled crystallization mother liquor in step 4. 2+ :SO4 2- Calcium chloride was added in a ratio of 1:1, reacted for 30 minutes, and filtered after precipitation for 1 hour to obtain sodium chloride solution and gypsum.

[0070] Step 7: solid ammonium bicarbonate was added to the sodium chloride solution obtained in step 6 at a molar ratio of ammonium bicarbonate to sodium sulfate of 1:1 to obtain sodium bicarbonate and ammonium chloride. The recovery rate of the obtained sodium bicarbonate was 98%.

[0071] The technical features of the above embodiments can be combined arbitrarily (as long as there is no contradiction in the combination of these technical features). In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described; these embodiments that are not explicitly written should also be considered to be within the scope of this specification.

Claims

1. A method for preparing baking soda using desulfurization ash, characterized in that: The method comprises: ①Dissolution: dissolve the desulfurized ash in water to obtain a suspension containing black suspended matter; ② Defluorination by coagulation-defluorination coupled precipitation: Add defluorination agent to the suspension containing black suspended matter, adopt chemical defluorination method, utilize coagulation-defluorination coupled precipitation principle, remove suspended matter in the suspension containing black suspended matter and precipitate formed by defluorination agent and fluoride ions, filter the supernatant after precipitation to obtain defluorination filtrate; ③ Oxidation and acidification: The defluorination filtrate is subjected to oxidation and acidification treatment; all the sodium sulfite in the solution is oxidized into sodium sulfate, and then concentrated sulfuric acid is added for acidification, the pH is adjusted to 4.4, and all the carbonate and bicarbonate are converted into sulfate to obtain a sulfate mixed solution; ④ Cooling crystallization: After cooling and crystallization of the sulfate mixture, sodium sulfate precipitated in the form of mirabilite is obtained; a part of the cooled mother liquor is replenished with water and heated up and then returned to step ①, and the other part of the mother liquor is used as a subsequent treatment liquid; ⑤ Sodium sulfate to make baking soda: Sodium sulfate is dissolved in hot water to obtain a sodium sulfate aqueous solution, and ammonium bicarbonate is added to the sodium sulfate aqueous solution to convert the sodium sulfate into sodium bicarbonate and ammonium sulfate. Sodium bicarbonate is supersaturated and precipitated, and the sodium bicarbonate enters the drying system to prepare baking soda, and the ammonium sulfate is recovered; ⑥ Reverse precipitation: adding calcium chloride to the subsequent treatment solution of step ④ to precipitate calcium sulfate precipitate and sodium chloride solution; ⑦ Preparation of baking soda from sodium chloride: Add ammonium bicarbonate to the sodium chloride solution in step ⑥ to convert the sodium chloride into sodium bicarbonate and ammonium chloride. Sodium bicarbonate is supersaturated and precipitated, and the sodium bicarbonate enters the drying system to prepare baking soda; ammonium chloride is recovered.

2. A method for preparing baking soda using desulfurization ash according to claim 1, characterized in that: In the step ①, the dissolution temperature is 35-40° C.; the mass ratio of desulfurized ash: water is 1:1-1:

5.

3. A method for preparing baking soda using desulfurization ash according to claim 1, characterized in that: In step ②, the chemical defluorination method includes adding a defluorinating agent according to a molar ratio of defluorinating agent: fluoride ion = 1:1 to 2:1, stirring the reaction for 30 to 50 minutes, adding 200 to 1000 ppm of a coagulant and stirring for 5 to 10 minutes, precipitating for 1 to 2 hours, removing the precipitate, filtering the supernatant, and obtaining a defluorinated filtrate.

4. A method for preparing baking soda using desulfurization ash according to claim 1, characterized in that: In the step ③, the oxidation method is one or a combination of pharmaceutical oxidation, wet oxidation, Fenton oxidation, ozone catalytic oxidation, photocatalytic oxidation, and electrochemical oxidation; acidification is used to adjust the pH to 4.

4.

5. The method for preparing baking soda using desulfurization ash according to claim 1, characterized in that: In the step ④, the temperature of the cooling crystallization is 5-15°C; the temperature after heating is 35-40°C.

6. The method for preparing baking soda using desulfurization ash according to claim 1, characterized in that: In step ⑤, the hot water temperature is 50-60° C., the concentration of the sodium sulfate solution is 20-30%; and the amount of ammonium bicarbonate added is such that the molar ratio of ammonium bicarbonate to sodium sulfate is 1:1-1:

10.

7. The method for preparing baking soda using desulfurized ash according to claim 1, characterized in that: In step ⑦, the amount of ammonium bicarbonate added is such that the molar ratio of ammonium bicarbonate to sodium chloride solution is 1:1 to 1:10.

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