Method for recovering fluorine, chlorine and bromine from flue gas deacidification waste liquid

Abstract

The invention relates to a salt-containing wastewater resourceful treatment technology, in particular to a method for recovering fluorine, chlorine and bromine from flue gas deacidification waste liquid, which comprises the following steps: (1) preparing a calcium sulfate dissolving solution; (2) carrying out precipitation reaction on the dissolving solution and the flue gas deacidification waste liquid to obtain calcium fluoride and primary precipitation reaction mother liquor; (3) carrying out precipitation reaction on the primary precipitation reaction mother liquor and a calcium chloride solution, and separating to obtain calcium sulfate and secondary precipitation reaction mother liquor; (4) reacting the secondary precipitation reaction mother liquor with sodium carbonate to obtain calcium carbonate and calcium-removed mother liquor; (5) reacting the calcium-removed mother liquor with hydrochloric acid to obtain neutralized mother liquor; (6) performing evaporative crystallization on the neutralized mother liquor to obtain sodium chloride, evaporative crystallization mother liquor and condensed water; and (7) cooling and crystallizing the evaporative crystallization mother liquor to obtain sodium bromide crystals and cooling crystallization mother liquor. According to the method disclosed by the invention, fluorine and bromine can be separated and recovered from the flue gas deacidification waste liquid at low cost, and meanwhile, new wastewater or solid wastes are prevented from being generated.

Description

Technical Field

[0001] This invention relates to a technology for the resource-based treatment of saline wastewater, specifically a method for recovering fluorine, chlorine, and bromine from flue gas desulfurization wastewater. Background Technology

[0002] Flue gas deacidification refers to the process of removing acidic gases such as HCl, HF, HBr, and SO2 from flue gas during hazardous waste incineration or pyrometallurgical processes. Flue gas deacidification waste liquid refers to the waste liquid containing various salts such as chlorides, fluorides, sulfates, and bromides generated during the flue gas deacidification process. Smelting flue gas generated from the smelting of hazardous waste such as waste circuit boards or the incineration of other hazardous waste typically contains acidic gases such as HF, HBr, HCl, and SO2. Flue gas treatment often uses sodium hydroxide or sodium carbonate solutions to absorb the flue gas, resulting in flue gas deacidification waste liquid containing various salts such as sodium fluoride, sodium bromide, sodium chloride, and sodium sulfate. Flue gas deacidification waste liquid contains fluorides and is classified as hazardous waste, requiring proper disposal. Flue gas desulfurization wastewater has a complex composition and high salt content. Direct evaporation desalination yields a mixed salt composed of sodium fluoride, sodium chloride, and sodium bromide, which is difficult to reuse. This mixed salt contains soluble fluorides, posing a significant environmental hazard and necessitating landfill disposal as hazardous waste. Some studies have attempted to recover bromine from flue gas desulfurization wastewater by first removing fluoride and then evaporating to recover bromine salts; however, this method failed to recover fluoride. Furthermore, the import dependence on fluoride and bromine is relatively high. Therefore, fluoride and bromine in flue gas desulfurization wastewater are scarce resources, with concentrations of fluoride and bromide ions reaching approximately 10 g / L, indicating high recovery value. Efficient recovery of fluoride and bromine resources from flue gas desulfurization wastewater offers economic, environmental, and social benefits.

[0003] While direct evaporation can desalinate flue gas desulfurization wastewater, it fails to separate and recover different salts, resulting in a mixed salt solution. Reusing this mixed salt requires further purification, leading to a lengthy and costly process. Although fluoride removal and bromine recovery technologies can recover bromine from desulfurization wastewater, they fail to effectively recover fluorine, resulting in a waste of fluorine resources. Existing methods for treating flue gas desulfurization wastewater do not achieve the resource recovery of valuable components.

[0004] Chinese patent application CN108164071A discloses a method for recovering bromide salts from flue gas absorbent liquid in waste circuit board smelting, involving processes such as defluorination and evaporation. The fluoride content of the recovered bromide salts is less than 0.1%. This method first uses precipitation to remove fluoride from the flue gas absorbent liquid, and then uses evaporation to recover bromide salts. Chinese patent application CN112194296A discloses a treatment system and method for flue gas desulfurization wastewater from a hazardous waste incineration workshop, involving processes such as precipitation defluorination, metal ion removal, and evaporation desalination. However, the defluorination processes involved in the above two flue gas desulfurization wastewater treatment methods both generate fluoride-containing sludge, failing to achieve effective resource recovery and utilization of fluoride.

[0005] The inventor's prior Chinese patent application CN119370864A discloses a method for recovering sodium fluoride, sodium chloride, and sodium bromide from smelting flue gas absorbent. By taking advantage of the large differences in the solubility of different salts in the flue gas absorbent, the method uses multiple evaporation and crystallization to separate and recover sodium fluoride, sodium chloride, and sodium bromide. However, the sodium fluoride product recovered by this method has a low added value.

[0006] In summary, existing flue gas desulfurization wastewater treatment technologies have failed to achieve efficient separation and high-value resource recovery of components such as fluorine and bromine. Therefore, it is necessary to develop a method to efficiently recover valuable components such as fluorine and bromine from flue gas desulfurization wastewater without generating wastewater or new solid waste. Summary of the Invention

[0007] The purpose of this invention is to provide a method for treating flue gas desulfurization wastewater, so as to separate and recover fluorine and bromine from it, while avoiding the generation of new wastewater or solid waste.

[0008] To address the above problems, this invention provides a method for recovering fluorine, chlorine, and bromine from flue gas desulfurization wastewater, comprising the following steps: Dissolve the gypsum / calcium sulfate to obtain a solution; The solution is reacted with the flue gas desulfurization waste liquid to separate calcium fluoride product and primary precipitation reaction mother liquor; The mother liquor from the primary precipitation reaction is reacted with calcium chloride solution to precipitate calcium sulfate and the mother liquor from the secondary precipitation reaction are separated. The calcium sulfate is returned to step (1) to prepare a gypsum / calcium sulfate solution. The secondary precipitation reaction mother liquor is reacted with sodium carbonate to separate calcium carbonate and calcium removal mother liquor. Calcium carbonate is reacted with hydrochloric acid to obtain calcium chloride solution and returned to step (3). The obtained calcium removal mother liquor was reacted with hydrochloric acid to obtain a neutralization mother liquor; The obtained neutralized mother liquor is evaporated and crystallized to obtain sodium chloride, evaporated crystallization mother liquor and condensate. The condensate is returned to step (1) to dissolve gypsum / calcium sulfate. The mother liquor of evaporation and crystallization is cooled and crystallized to obtain sodium bromide crystals and cooled crystallization mother liquor. The cooled crystallization mother liquor is returned to step (6) and mixed with the neutralized mother liquor for evaporation again.

[0009] The active ingredient in the gypsum / calcium sulfate mentioned in this application is calcium sulfate, and gypsum is the hydrated form of calcium sulfate. In this application, the two usually coexist.

[0010] As a preferred embodiment, the flue gas desulfurization waste liquid in step (2) includes sodium fluoride, sodium chloride, sodium bromide, sodium sulfate and water, wherein the fluoride ion concentration is 0.1~20 g / L, the chloride ion concentration is 1~100 g / L and the bromide ion concentration is 1~100 g / L.

[0011] As a preferred embodiment, in step (1), the dissolution of gypsum / calcium sulfate is carried out in a packed tower reactor, with the gypsum / calcium sulfate serving as the packing material, thereby achieving efficient and stable preparation of the solution.

[0012] As a preferred embodiment, the sodium bromide content in the mother liquor for evaporation and crystallization in step (6) is 400~580 g / L.

[0013] Furthermore, the sodium bromide content in the mother liquor for evaporation and crystallization in step (6) is 480~520 g / L.

[0014] As a preferred option, the evaporation method is single-effect evaporation, multi-effect evaporation, or heat pump evaporation to reduce evaporation energy consumption.

[0015] The reaction mechanism of this application is as follows: First, gypsum / calcium sulfate is dissolved in a packed tower reactor to obtain a calcium sulfate solution. Second, the calcium sulfate solution undergoes a precipitation reaction with flue gas desulfurization wastewater to separate the product calcium fluoride and a primary precipitation reaction mother liquor, which mainly contains sodium sulfate, sodium chloride, and sodium bromide. Third, the primary precipitation reaction mother liquor undergoes a precipitation reaction with a calcium chloride solution to remove sulfate ions, yielding solid calcium sulfate and a secondary precipitation reaction mother liquor. The solid calcium sulfate is returned to the first step for dissolution and then reacted with the flue gas desulfurization wastewater. The secondary precipitation reaction mother liquor mainly contains sodium chloride, sodium bromide, and small amounts of calcium sulfate and calcium chloride. Fourth, the secondary precipitation reaction mother liquor is reacted with a sodium carbonate solution to remove calcium, yielding a calcium-removed mother liquor and calcium carbonate. Calcium carbonate reacts with hydrochloric acid to obtain calcium chloride, which is returned to the third step for a secondary precipitation reaction. Fifth, the calcium-removed mother liquor is neutralized with hydrochloric acid to remove small amounts of carbonate in the solution, yielding a neutralized mother liquor. In step six, the neutralized mother liquor obtained after calcium removal and neutralization from the secondary precipitation reaction mainly contains sodium chloride and sodium bromide. Taking advantage of the significant difference in solubility between sodium chloride and sodium bromide, the neutralized mother liquor is evaporated and crystallized to precipitate sodium chloride salt. Simultaneously, the sodium bromide in the solution is concentrated, resulting in a high-concentration sodium bromide solution. The condensate from the evaporation is returned to step one for dissolving calcium sulfate. In step seven, utilizing the characteristic that the solubility of sodium bromide decreases with decreasing temperature, the evaporated crystallization mother liquor is cooled and crystallized to precipitate sodium bromide crystals. The cooled crystallization mother liquor is returned to step six and mixed with the neutralized mother liquor for further evaporation and crystallization.

[0016] The technical solution provided by this invention has the following characteristics: (1) The method provided by the present invention can separate fluorine, chlorine and bromine in flue gas desulfurization waste liquid and recover calcium fluoride, sodium chloride and sodium bromide, thus realizing the resource recovery of fluorine and bromine; (2) The method provided by this invention recovers products with high purity, with calcium fluoride purity greater than 99% and sodium bromide salt purity greater than 98%; (3) The method provided by the present invention does not generate wastewater or solid waste, and the process belongs to green and clean technology. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention.

[0018] Figure 1 This is a flowchart illustrating a method for recovering fluorine, chlorine, and bromine from flue gas desulfurization waste liquid in this embodiment.

[0019] Figure 2 This is a schematic diagram of a system for recovering calcium fluoride, sodium chloride, and sodium bromide from flue gas deacidification waste liquid in this embodiment.

[0020] Includes: 1. First centrifugal pump; 2. Packed tower; 3. Dissolving liquid tank; 4. Second centrifugal pump; 5. Deacidification waste liquid stock tank; 6. Third centrifugal pump; 7. First stirred reactor; 8. First centrifuge; 9. Primary precipitation reaction mother liquor tank; 10. Fourth centrifugal pump; 11. Calcium chloride solution tank; 12. Fifth centrifugal pump; 13. Second stirred reactor; 14. Second centrifuge; 15. Secondary precipitation reaction mother liquor tank; 16. Sixth centrifugal pump; 17. Sodium carbonate solution tank; 18. Seventh centrifugal pump; 19. Third stirred reactor; 20. Third centrifuge; 21. Calcium removal mother liquor tank; 22. Eighth centrifugal pump; 23. Hydrochloric acid solution tank; 24. Ninth centrifugal pump; 25. Fourth stirred reactor; 26. Neutralization mother liquor tank; 27. Tenth centrifugal pump; 28. Evaporator crystallizer; 29. ​​Fourth centrifuge; 30. Evaporator mother liquor tank; 31. Eleventh centrifugal pump; 32. Cooling crystallizer; 33. Fifth centrifuge. Detailed Implementation

[0021] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed in accordance with the techniques or conditions described in the literature in the field, or in accordance with the product manual.

[0022] In the description of this invention, unless otherwise stated, the terms "upper" and "lower" indicate the orientation or state relationship based on the orientation or state relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0023] In the following embodiments, all instruments and equipment used, unless otherwise specified, are conventional products that can be purchased through legitimate channels. Unless otherwise stated, all methods described are conventional methods, and all raw materials are available from publicly available commercial sources.

[0024] Example 1 This embodiment provides a method for recovering fluorine, chlorine, and bromine from flue gas desulfurization wastewater. The treatment method includes the following steps: (1) Water or condensate enters the packed tower from the top of the packed tower filled with gypsum / calcium sulfate and flows out from the bottom of the packed tower. Taking advantage of the fact that calcium sulfate is a slightly soluble substance, the calcium sulfate / gypsum is dissolved by the fluid shear force of the water flow through the packed tower, which eliminates the stirring and solid-liquid separation process required by the traditional stirring tank for dissolution. (2) The solution is subjected to a primary precipitation reaction with the flue gas desulfurization waste liquid with a fluoride ion concentration of 20 g / L to separate calcium fluoride product and primary precipitation reaction mother liquor. Since the primary precipitation process is a precipitation reaction between calcium ions in the solution and fluoride ions in the flue gas desulfurization waste liquid, calcium chloride and calcium bromide are both easily soluble substances and will not precipitate. Therefore, the purity of the precipitation reaction product calcium fluoride can be effectively guaranteed. The purity of calcium fluoride can reach 99.22%. (3) The mother liquor from the primary precipitation reaction undergoes a secondary precipitation reaction with the calcium chloride solution to separate calcium sulfate and the mother liquor from the secondary precipitation reaction. The calcium sulfate is returned to the packed tower for dissolution and reuse. (4) The mother liquor of the secondary precipitation reaction reacts with sodium carbonate to remove calcium, resulting in calcium carbonate and calcium removal mother liquor. Calcium carbonate reacts with hydrochloric acid to obtain calcium chloride solution, and then returns to step (3) to carry out the secondary precipitation reaction mother liquor. (5) The calcium-free mother liquor is neutralized with hydrochloric acid to obtain a neutralized mother liquor; (6) The neutralized mother liquor is evaporated and crystallized to obtain sodium chloride salt and evaporated crystallization mother liquor. The concentration of sodium bromide in the solution is controlled to not reach supersaturation. In this embodiment, the sodium bromide content of the evaporated crystallization mother liquor is 520 g / L. (7) Evaporate the mother liquor and cool it to crystallize, to obtain sodium bromide and cooled crystallization mother liquor. Return the cooled crystallization mother liquor to step (6) for evaporation and crystallization, and repeat the cycle. The purity of sodium bromide reaches 98.52%, and sodium bromide contains a small amount of impurity sodium chloride.

[0025] Example 2 (1) Water or condensate enters the packed tower from the top of the packed tower filled with gypsum / calcium sulfate, and the solution of gypsum / calcium sulfate flows out from the bottom of the packed tower; (2) The solution was subjected to a primary precipitation reaction with flue gas desulfurization waste liquid with a fluoride ion concentration of 0.1 g / L to separate calcium fluoride product and primary precipitation reaction mother liquor. The purity of calcium fluoride was 99.18%. (3) The mother liquor from the primary precipitation reaction undergoes a secondary precipitation reaction with a calcium chloride solution to separate calcium sulfate and the secondary precipitation reaction mother liquor. The calcium sulfate is returned to the packed tower for dissolution and reuse. (4) The mother liquor from the secondary precipitation reaction reacts with sodium carbonate to remove calcium, yielding calcium carbonate and the mother liquor from the calcium removal reaction. Calcium carbonate reacts with hydrochloric acid to obtain a calcium chloride solution, which is then returned to step (3) for the secondary precipitation reaction mother liquor. (5) The calcium-free mother liquor is neutralized with hydrochloric acid to obtain a neutralized mother liquor; (6) The neutralized mother liquor was evaporated and crystallized to obtain sodium chloride salt and evaporation crystallization mother liquor. The sodium bromide content of the evaporation crystallization mother liquor was 505 g / L; (7) The mother liquor from the evaporated crystallization solution is cooled and crystallized to obtain sodium bromide and cooled crystallization mother liquor. The cooled crystallization mother liquor is returned to step (6) for evaporation and crystallization, and this cycle is repeated. The purity of the sodium bromide is 99.03%.

[0026] Example 3 (1) Water or condensate enters the packed tower from the top of the packed tower filled with gypsum / calcium sulfate, and the solution of gypsum / calcium sulfate flows out from the bottom of the packed tower; (2) The solution was subjected to a primary precipitation reaction with flue gas desulfurization waste liquid with a fluoride ion concentration of 8.2 g / L to separate calcium fluoride product and primary precipitation reaction mother liquor. The purity of calcium fluoride was 99.25%. (3) The mother liquor from the primary precipitation reaction undergoes a secondary precipitation reaction with a calcium chloride solution to separate calcium sulfate and the secondary precipitation reaction mother liquor. The calcium sulfate is returned to the packed tower for dissolution and reuse. (4) The mother liquor from the secondary precipitation reaction reacts with sodium carbonate to remove calcium, yielding calcium carbonate and the mother liquor from the calcium removal reaction. Calcium carbonate reacts with hydrochloric acid to obtain a calcium chloride solution, which is then returned to step (3) for the secondary precipitation reaction mother liquor. (5) The calcium-free mother liquor is neutralized with hydrochloric acid to obtain a neutralized mother liquor; (6) The neutralized mother liquor was evaporated and crystallized to obtain sodium chloride salt and evaporation crystallization mother liquor. The sodium bromide content of the evaporation crystallization mother liquor was 480 g / L; (7) The mother liquor from the evaporated crystallization solution is cooled and crystallized to obtain sodium bromide and cooled crystallization mother liquor. The cooled crystallization mother liquor is returned to step (6) for evaporation and crystallization, and this cycle is repeated. The purity of the sodium bromide reaches 99.34%.

[0027] To achieve the above process, the present invention also provides a system for recovering calcium fluoride and sodium bromide from flue gas desulfurization wastewater, comprising a calcium source dissolution unit, a primary precipitation reaction unit, a secondary precipitation reaction unit, a calcium removal reaction unit, a neutralization reaction unit, an evaporation crystallization unit, and a cooling crystallization unit connected in sequence, wherein: The calcium source dissolution unit, used to dissolve calcium sulfate, includes a first centrifugal pump 1, a packed tower 2, and a dissolution tank 3. The packed tower 2 uses calcium sulfate as packing material, and water / condensate enters from the top of the tower, while the dissolution liquid enters the dissolution tank 3.

[0028] The primary precipitation reaction unit, used to recover calcium fluoride, includes a second centrifugal pump 4, a deacidification waste liquid raw liquid tank 5, a third centrifugal pump 6, a first centrifuge 8, a first stirred reaction vessel 7, and a primary precipitation reaction mother liquor tank 9. The secondary precipitation reaction unit includes a fourth centrifugal pump 10, a calcium chloride solution tank 11, a fifth centrifugal pump 12, a second centrifuge 14, a second stirred reaction vessel 13, and a secondary precipitation reaction mother liquor tank 15, which is used to remove sodium sulfate. The calcium precipitation reaction unit includes a sixth centrifugal pump 16, a sodium carbonate solution tank 17, a seventh centrifugal pump 18, a third centrifuge 20, a third stirred reaction vessel 19, and a calcium removal mother liquor tank 21. The secondary precipitation reaction unit is used to remove calcium ions from the solution, and the calcium sulfate obtained from the secondary precipitation reaction unit is returned to the calcium source dissolution unit. The neutralization reaction unit, used to remove sodium carbonate from the solution, includes an eighth centrifugal pump 22, a hydrochloric acid solution tank 23, a ninth centrifugal pump 24, a fourth stirred reaction vessel 25, and a neutralization mother liquor tank 26. The evaporation crystallization unit, used to recover sodium chloride, includes a tenth centrifugal pump 27, an evaporator crystallizer 28, a fourth centrifuge 29, and an evaporation mother liquor tank 30. The condensate produced by the evaporation crystallization unit is returned to the calcium source dissolution unit. The cooling crystallization unit, used to recover sodium bromide, includes an eleventh centrifugal pump 31, a cooling crystallizer 32, and a fifth centrifuge 33. The cooling crystallization mother liquor generated by the cooling crystallization unit is returned to the neutralization mother liquor tank, and then enters the evaporation crystallization unit for circulating evaporation through the tenth centrifugal pump.

[0029] The recycling method provided by this invention does not generate wastewater or new solid waste. The process is a green process and effectively achieves the efficient separation and recovery of fluorine, chlorine and bromine in flue gas desulfurization wastewater. The fluorine recovery product is calcium fluoride, which has a high added value, and the bromine recovery product is sodium bromide with high purity.

[0030] The above descriptions are merely embodiments of the present invention. Commonly known structures, properties, and reactant ratios are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. For example, simply adjusting the parameter selection within or near a specified parameter range should also be considered within the scope of protection of the present invention, and these will not affect the effectiveness of the invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for recovering fluorine, chlorine, and bromine from flue gas desulfurization wastewater, characterized in that... It includes the following steps: Dissolve the gypsum / calcium sulfate to obtain a solution; The solution is reacted with the flue gas desulfurization waste liquid to separate calcium fluoride product and primary precipitation reaction mother liquor; The mother liquor from the primary precipitation reaction is reacted with calcium chloride solution to precipitate calcium sulfate and the mother liquor from the secondary precipitation reaction are separated. The calcium sulfate is returned to step (1) to prepare a gypsum / calcium sulfate solution. The secondary precipitation reaction mother liquor is reacted with sodium carbonate to separate calcium carbonate and calcium removal mother liquor. Calcium carbonate is reacted with hydrochloric acid to obtain calcium chloride solution and returned to step (3). The obtained calcium removal mother liquor was reacted with hydrochloric acid to obtain a neutralization mother liquor; The obtained neutralized mother liquor is evaporated and crystallized to obtain sodium chloride, evaporated crystallization mother liquor and condensate. The condensate is returned to step (1) to dissolve gypsum / calcium sulfate. The mother liquor of evaporation and crystallization is cooled and crystallized to obtain sodium bromide crystals and cooled crystallization mother liquor. The cooled crystallization mother liquor is returned to step (6) and mixed with the neutralized mother liquor before evaporation.

2. The method for recovering fluorine, chlorine, and bromine from flue gas desulfurization wastewater according to claim 1, characterized in that: The flue gas deacidification waste liquid in step (2) includes sodium fluoride, sodium chloride, sodium bromide, sodium sulfate and water.

3. The method for recovering fluorine, chlorine, and bromine from flue gas desulfurization wastewater according to claim 2, characterized in that: In step (2), the concentration of fluoride ions in the flue gas desulfurization waste liquid is 0.1~20 g / L, the concentration of chloride ions is 1~100 g / L, and the concentration of bromide ions is 1~100 g / L.

4. The method for recovering fluorine, chlorine, and bromine from flue gas desulfurization wastewater according to claim 1, characterized in that: In step (1), the dissolution of gypsum / calcium sulfate is carried out in a packed tower reactor, and the packing material is gypsum / calcium sulfate.

5. The method for recovering fluorine, chlorine, and bromine from flue gas desulfurization wastewater according to claim 1, characterized in that: In step (6), the sodium bromide content in the mother liquor for evaporation and crystallization is 400~580 g / L.

6. The method for recovering fluorine, chlorine, and bromine from flue gas desulfurization wastewater according to claim 5, characterized in that: In step (6), the sodium bromide content in the mother liquor for evaporation and crystallization is 480~520 g / L.

7. The method for recovering fluorine, chlorine, and bromine from flue gas desulfurization wastewater according to claim 1, characterized in that: The evaporation method is single-effect evaporation, multi-effect evaporation, or heat pump evaporation.

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