Method for recycling of uranium fluorination wastewater

Abstract

The present application relates to the technical field of nuclear fuel cycle, and particularly relates to a method for recycling uranium fluorination wastewater. The method is as follows: adjusting the concentration ratio of bicarbonate and carbonate in the uranium conversion leaching solution, carrying out decolorization and filtration treatment to obtain a filtrate; the filtrate is subjected to uranium adsorption through a resin, and the resin adsorbed with uranium is subjected to leaching; the adsorption tail liquid is added with magnesium hydroxide slurry to adjust the pH to above 11, and then filtered, and the filtrate is adsorbed by amidoamine-based adsorption fiber; the adsorption tail liquid is added with magnesium carbonate slurry to generate magnesium fluoride and carbonate ions, and then filtered to obtain a sediment and a filtrate respectively; the filtrate is returned as a leaching agent of fluorination tail gas or is discharged after treatment; the sediment is used together with new magnesium carbonate to participate in fluorine removal reaction again, and the unreacted magnesium carbonate is used again. The present application realizes efficient recovery of uranium in the leaching solution and recycling of the leaching solution, fully utilizes the residual alkali in the returned liquid, reduces the treatment cost of fluorination tail gas, controls the radioactivity of the waste residue, and realizes radioactivity exemption of the treated sediment.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel cycle technology, and in particular to a method for recycling uranium fluoride wastewater. Background Technology

[0002] In my country's uranium purification and conversion production line, the process of preparing uranium hexafluoride from uranium ore concentrate involves processes such as dissolution, extraction, denitrification, reduction, hydrofluorination, and fluorination. Among these processes, the fluorination process generates fluorine- and uranium-containing tail gas. Currently, charcoal adsorption and alkaline solution (carbonate) leaching technology is used to purify the harmful components in the fluorination tail gas during the uranium hexafluoride production process, so that the tail gas meets emission standards.

[0003] During the exhaust gas treatment process, fluorine reacts with alkaline solution to generate fluoride ions, which enter the scrubbing liquid. Uranium also enters the scrubbing liquid in the form of uranyl carbonate. Fine particles and a small amount of organic matter from the charcoal also enter the scrubbing liquid, ultimately forming alkaline uranium fluoride wastewater containing both fluorine and uranium. Currently, there is a lack of targeted treatment technology for this type of wastewater. It is usually treated by mixing it with other types of wastewater and then settling it. This not only generates a large amount of radioactive waste residue and discharged wastewater, but also prevents the reuse of residual alkali in the wastewater, which requires neutralization and removal, thus increasing treatment costs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for the reuse of uranium fluoride wastewater, so as to achieve efficient recovery of uranium in the leaching solution and reuse of the leaching solution, make full use of the residual alkali in the returned solution, reduce the cost of fluoride tail gas treatment, control the radioactivity of the waste residue, and achieve radioactivity exemption for the treatment of sludge.

[0005] This invention provides a method for reusing uranium fluoride wastewater, comprising the following steps:

[0006] Step S1: Adjust the concentration ratio of bicarbonate and carbonate in the uranium conversion eluent, and obtain the filtrate after decolorization and filtration; after countercurrent washing of the filter residue, the first wash water is added to the filtrate.

[0007] Step S2: The filtrate is passed through a resin for uranium adsorption, and the resin that has adsorbed uranium is leached to obtain a leaching solution and an adsorption tail liquid.

[0008] Step S3: The pH of the adsorption tail liquid is adjusted to above 11 by adding magnesium hydroxide slurry, filtered, and the filtrate is adsorbed by a amine oxime adsorption fiber; the uranium concentration breakthrough point of the adsorption tail liquid is controlled to be 1 mg / L.

[0009] Step S4: The adsorption tail liquid obtained in step S3 is added to magnesium carbonate slurry to generate magnesium fluoride and carbonate ions. After filtration, sludge and filtrate are obtained respectively. Part of the filtrate is returned to the uranium conversion process as a scrubbing agent for fluorination tail gas, and the other part of the filtrate is discharged after treatment. The sludge and new magnesium carbonate participate in the defluorination reaction again, and the unreacted magnesium carbonate is reused.

[0010] Preferably, in step S1, the mass concentration ratio of bicarbonate to carbonate is maintained between 1:1 and 1:5.

[0011] Preferably, in step S1, sodium hydroxide or potassium hydroxide is used to adjust the concentration ratio of bicarbonate and carbonate in the uranium conversion eluent.

[0012] Preferably, in step S1, activated carbon is added for adsorption and decolorization. The particle size of the activated carbon powder is no greater than 1 mm, and the amount used is 1% to 5% of the solution mass. The contact time is no less than 5 minutes. The decolorized solution is filtered, and the filter cloth is pre-coated with perlite to remove colloidal substances and carbon powder particles. The thickness of the perlite coating is 1 to 5 cm, and the turbidity after filtration is no higher than 100 NTU.

[0013] Preferably, in step S1, the filter residue is washed countercurrently with a sodium carbonate solution of 1-5 g / L.

[0014] Preferably, in step S2, the adsorption contact time is not less than 5 minutes, the adsorption method is multi-tower series adsorption, and the uranium concentration breakthrough point of the adsorption tail liquid is controlled to be 10-20 mg / L.

[0015] Preferably, in step S2, the resin is rinsed using a bottom-feed method, the rinsing agent is a soluble bicarbonate, the rinsing contact time is not less than 20 minutes, and the first one-third of the rinsing solution with uranium concentration is taken as qualified solution for precipitation to prepare uranium products. The remaining solution is returned as part of the rinsing agent for the next rinsing.

[0016] Preferably, in step S3, the adsorption contact time is not less than 5 minutes, and the adsorption method is multi-tower series adsorption.

[0017] Preferably, in step S3, the amylopyridine adsorption fiber is leached by a bottom-feed method, the leaching agent is bicarbonate, the leaching contact time is not less than 20 minutes, and the first one-third of the leaching solution with uranium concentration is taken as qualified solution and returned to step S1, while the remaining solution is returned as part of the leaching agent for the next leaching.

[0018] Preferably, in step S4, the magnesium carbonate is stirred thoroughly to react with fluoride ions, and the stirring reaction time is not less than 30 minutes; after the sludge is reused for 3 cycles, it is discharged according to the amount of newly generated sludge each time it is defluorinated.

[0019] Compared with existing technologies, the method for recycling uranium fluoride wastewater of this invention achieves a uranium recovery rate of over 99.6% in the uranium fluoride tail gas scrubbing liquid; a wastewater recycling rate of over 90%; and a reduction of over 90% in discharged wastewater volume. The sludge is all radioactive-exempt sludge, reducing the total sludge volume by over 60% compared to lime precipitation treatment. This method effectively reuses uranium fluoride wastewater while significantly reducing the amount of radioactive waste and lowering treatment costs. Attached Figure Description

[0020] Figure 1 A flowchart illustrating the method for reusing uranium fluoride wastewater. Detailed Implementation

[0021] To further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the present invention.

[0022] An embodiment of the present invention discloses a method for reusing uranium fluoride wastewater, such as... Figure 1 As shown, it includes the following steps:

[0023] Step S1: Adjust the concentration ratio of bicarbonate and carbonate in the uranium conversion eluent, and obtain the filtrate after decolorization and filtration; after countercurrent washing of the filter residue, the first wash water is added to the filtrate.

[0024] Step S2: The filtrate is passed through a resin for uranium adsorption, and the resin that has adsorbed uranium is leached to obtain a leaching solution and an adsorption tail liquid.

[0025] Step S3: The pH of the adsorption tail liquid is adjusted to above 11 by adding magnesium hydroxide slurry, filtered, and the filtrate is adsorbed by a amine oxime adsorption fiber; the uranium concentration breakthrough point of the adsorption tail liquid is controlled to be 1 mg / L.

[0026] Step S4: The adsorption tail liquid obtained in step S3 is added to magnesium carbonate slurry to generate magnesium fluoride and carbonate ions. After filtration, sludge and filtrate are obtained respectively. Part of the filtrate is returned to the uranium conversion process as a scrubbing agent for fluorination tail gas, and the other part of the filtrate is discharged after treatment. The sludge and new magnesium carbonate participate in the defluorination reaction again, and the unreacted magnesium carbonate is reused.

[0027] This invention addresses the characteristics of high uranium concentration, carbonate and bicarbonate content, and trace amounts of solid particles and organic matter in uranium fluoride tail gas scrubbing solutions. It focuses on pretreatment of the scrubbing solution to reduce bicarbonate content and remove organic matter and solid particles, creating favorable conditions for uranium recovery. First, a strong-base resin is used to initially recover most of the uranium from the scrubbing solution. Then, the pH is adjusted, and special adsorption fibers are used to further reduce the uranium content in the tail gas, improving the uranium recovery rate. For bicarbonate in the scrubbing solution, basic magnesium salts are used to convert it into carbonate, maintaining the alkalinity for return. Fluoride ions in the scrubbing solution are reacted with magnesium carbonate to form magnesium fluoride, which has a smaller solubility product. This removes fluoride ions while replenishing the carbonate ions consumed in the reaction with the fluoride tail gas, thus maintaining the alkalinity of the wastewater during return and meeting the requirements for scrubbing fluoride tail gas. During sludge treatment, a certain carbonate concentration is maintained. Utilizing the strong complexing ability of carbonate with uranium, the uranium is kept in solution, reducing the amount entering the sludge. For trace amounts of uranium that do enter the sludge, a carbonate solution is used for washing, thus ensuring the sludge's radioactivity exemption. Ultimately, this achieves the efficient reuse of uranium fluoride wastewater.

[0028] The following steps detail the method for recycling uranium fluoride wastewater according to the present invention.

[0029] Step S1: Adjust the concentration ratio of bicarbonate and carbonate in the uranium conversion eluent, and obtain the filtrate after decolorization and filtration; after countercurrent washing of the filter residue, the first wash water is added to the filtrate.

[0030] It is preferable to use sodium hydroxide or potassium hydroxide to adjust the concentration ratio of bicarbonate and carbonate in the uranium conversion eluent, and the mass concentration ratio of bicarbonate to carbonate is maintained between 1:1 and 1:5.

[0031] After adjusting the concentration ratio of bicarbonate and carbonate, activated carbon is added for adsorption and decolorization. The particle size of the activated carbon powder is no larger than 1 mm, and the amount used is 1% to 5% of the solution mass. The contact time is no less than 5 minutes, and the decolorized solution is filtered.

[0032] Filtration preferably uses a filter aid to improve filtration efficiency. It is preferable to pre-coat the filter cloth with perlite to remove colloidal substances and carbon particles. The perlite coating thickness is 1-5 cm, and the turbidity after filtration is not higher than 100 NTU.

[0033] The filter residue is washed countercurrently with a sodium carbonate solution of 1–5 g / L.

[0034] Step S2: The filtrate is passed through a resin for uranium adsorption, and the resin that has adsorbed uranium is leached to obtain a leaching solution and an adsorption tail liquid.

[0035] Adsorption can be carried out using a resin tower with an adsorption contact time of no less than 5 minutes. The adsorption method is multi-tower series adsorption, and the breakthrough point of uranium concentration in the adsorption tail liquid is controlled at 10-20 mg / L.

[0036] After adsorption is complete, the resin is leached using a bottom-feed method with bicarbonate as the leaching agent. The leaching contact time is no less than 20 minutes. The first third of the leaching solution with uranium concentration is taken as the qualified solution for precipitation to prepare uranium products. The remaining solution is returned as part of the leaching agent for the next leaching.

[0037] The resin used is a strong base anion exchange resin, including but not limited to D201×7 resin.

[0038] Step S3: The pH of the adsorption tail liquid is adjusted to above 11 by adding magnesium hydroxide slurry, filtered, and the filtrate is adsorbed by a amine oxime adsorption fiber; the uranium concentration breakthrough point of the adsorption tail liquid is controlled to be 1 mg / L.

[0039] After adjusting the pH value, filter the residue and wash it countercurrently with a 1-5 g / L sodium carbonate solution. The wash water is then added to the filtrate.

[0040] The filtrate can be passed through an adsorption tower equipped with a amine oxime adsorption fiber, with an adsorption contact time of no less than 5 minutes, and the adsorption method is multi-tower series adsorption.

[0041] After adsorption is complete, the amylopyridine adsorption fiber is leached by bottom-feeding. The leaching agent is bicarbonate, and the leaching contact time is not less than 20 minutes. The first third of the leaching solution with uranium concentration is taken as qualified solution and returned to step S1. The remaining solution is returned as part of the leaching agent for the next leaching.

[0042] Step S4: The adsorption tail liquid obtained in step S3 is added to magnesium carbonate slurry to generate magnesium fluoride and carbonate ions. After filtration, sludge and filtrate are obtained respectively. Part of the filtrate is returned to the uranium conversion process as a scrubbing agent for fluorination tail gas, and the other part of the filtrate is discharged after treatment. The sludge and new magnesium carbonate participate in the defluorination reaction again, and the unreacted magnesium carbonate is reused.

[0043] After adding magnesium carbonate slurry to the adsorption tail liquid obtained in step S3, stir thoroughly to allow magnesium carbonate to react with fluoride ions. The stirring reaction time shall not be less than 30 minutes. After the sludge is reused for 3 cycles, it shall be discharged according to the amount of newly generated sludge each time it is defluorinated.

[0044] 90% of the filtrate is returned to the uranium conversion process as a scrubbing agent for the fluorination tail gas, and 10% of the filtrate is discharged after treatment.

[0045] The amount of magnesium carbonate used is 100% to 150% of the theoretical amount.

[0046] The filter residue obtained in steps S1 and S3, and the sludge obtained in step S4, can be pressed and dewatered together, and then piled up.

[0047] To further understand the present invention, the method for recycling uranium fluoride wastewater provided by the present invention will be described in detail below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0048] Example 1

[0049] After adjusting the concentration ratio of bicarbonate and carbonate in the uranium conversion eluent, the carbonate concentration was 30 g / L, the bicarbonate concentration was 15 g / L, the uranium concentration was 0.288 g / L, and the COD value was 0.1 g / L.

[0050] (1) Add 1m particle size activated carbon, 2% activated carbon dosage, decolorization time 5 minutes, and pre-coat the decolorized solution with perlite as a filter aid, with a coating thickness of 1cm. (2) Adsorb the filtrate with 3 towers of 201×7 resin in series, adsorption contact time 10min, and uranium concentration of tail liquid 0.011g / L; (3) Adjust the pH to 11.5 with magnesium hydroxide adsorption of tail liquid by resin, adsorb with 3 towers of amine oxime adsorption fiber, adsorption contact time 10min, and uranium concentration of adsorbed tail liquid 0.5mg / L. ④ The amount of magnesium carbonate used for defluorination of adsorbed tail liquid is 120% of the theoretical amount, the stirring reaction time is 40min, and the sludge is recycled after 3 cycles. It is discharged according to the amount of newly generated sludge each time defluorination, and the radioactivity of the sludge is 0.4Bq / g; ⑤ 90% of the magnesium carbonate defluorination filtrate is returned as a uranium fluoride tail gas scrubbing agent.

[0051] The uranium recovery rate reached 99.7%; the wastewater reuse rate reached 90%, and the amount of wastewater discharged was reduced by 90%; the sludge was all radioactive exempt sludge, and the total sludge volume was reduced by 62% compared with lime precipitation treatment.

[0052] Example 2

[0053] After adjusting the concentration ratio of bicarbonate and carbonate in the uranium conversion eluent, the carbonate concentration was 15 g / L, the bicarbonate concentration was 30 g / L, the uranium concentration was 0.350 g / L, and the COD value was 0.22 g / L.

[0054] (1) Add sodium hydroxide to adjust the carbonate concentration to 22 g / L and the bicarbonate concentration to 23 g / L; then add -100 mesh activated carbon, 5% activated carbon, decolorize for 10 minutes, and pre-coat the solution with perlite as a filter aid after decolorization, with a coating thickness of 5 cm. (2) Adsorb the filtrate with 4 towers of 201×7 resin in series, with an adsorption contact time of 15 min and a uranium concentration of 0.01 g / L in the tail liquid; (3) Adjust the pH of the tail liquid to 11.6 with magnesium hydroxide adsorbed by resin, adsorb it with 4 towers of amine oxime adsorption fiber, with an adsorption contact time of 10 min and a uranium concentration of 0.4 mg / L in the adsorbed tail liquid; (4) Use 150% of the theoretical amount of magnesium carbonate for defluorination of the adsorbed tail liquid, stir for 35 min, and after 3 cycles of sludge reuse, discharge it according to the amount of new sludge generated each time, with a radioactivity of 0.35 Bq / g in the sludge; (5) 90% of the magnesium carbonate defluorination filtrate is returned as a uranium fluoride tail gas scrubbing agent.

[0055] The uranium recovery rate reached 99.6%; the wastewater reuse rate reached 91%, and the amount of wastewater discharged was reduced by 92%; the sludge was all radioactive exempt sludge, and the total sludge volume was reduced by 60% compared with lime precipitation treatment.

[0056] Example 3

[0057] After adjusting the concentration ratio of bicarbonate and carbonate in the uranium conversion eluent, the carbonate concentration was 5 g / L, the bicarbonate concentration was 30 g / L, the uranium concentration was 0.189 g / L, and the COD value was 0.12 g / L.

[0058] (1) Add potassium hydroxide to adjust the carbonate concentration to 29 g / L and the bicarbonate concentration to 5 g / L; then add -100 mesh activated carbon, 1% activated carbon, decolorize for 15 minutes, and pre-coat the solution with perlite as a filter aid after decolorization, with a coating thickness of 1 cm. (2) Adsorb the filtrate with two 201×7 resin towers in series, with an adsorption contact time of 20 min and a uranium concentration of 0.015 g / L in the tail liquid; (3) Adjust the pH of the tail liquid to 11.7 with magnesium hydroxide adsorbed by the resin, and adsorb it with two fiber towers with a amine oxime group adsorption, with an adsorption contact time of 20 min and a uranium concentration of 0.5 mg / L in the adsorbed tail liquid; (4) Use 130% of the theoretical amount of magnesium carbonate for defluorination of the adsorbed tail liquid, stir for 40 min, and after 3 cycles of sludge reuse, discharge it according to the amount of new sludge generated each time, with a radioactivity of 0.28 Bq / g in the sludge; (5) 90% of the magnesium carbonate defluorination filtrate is returned as a uranium fluoride tail gas scrubbing agent.

[0059] The uranium recovery rate reached 99.6%; the wastewater reuse rate reached 90%, and the amount of wastewater discharged was reduced by 90%; the sludge was all radioactive exempt sludge, and the total sludge volume was reduced by 60% compared with lime precipitation treatment.

[0060] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0061] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for reusing uranium fluoride wastewater, characterized in that, Includes the following steps: Step S1: Adjust the concentration ratio of bicarbonate and carbonate in the uranium conversion eluent, and obtain the filtrate after decolorization and filtration. After countercurrent washing of the filter residue, the first wash water is added to the filtrate. Activated carbon is added for adsorption and decolorization. The activated carbon powder particle size is no larger than 1 mm, and the amount used is 1% to 5% of the solution mass. The contact time is no less than 5 minutes. The decolorized solution is filtered. The filter cloth is pre-coated with perlite to remove colloidal substances and carbon particles. The perlite coating thickness is 1 to 5 cm. The turbidity after filtration is no higher than 100 NT. The mass concentration ratio of bicarbonate to carbonate is maintained between 1:1 and 1:

5. The concentration ratio of bicarbonate to carbonate in the uranium conversion leaching solution is adjusted using sodium hydroxide or potassium hydroxide. The filter residue is countercurrently washed with a 1 to 5 g / L sodium carbonate solution. Step S2: The filtrate is passed through resin for uranium adsorption. The resin with adsorbed uranium is then leached to obtain a leaching solution and an adsorption tail liquid. The resin is leached using a bottom-feed method with bicarbonate as the leaching agent. The leaching contact time is no less than 20 minutes. The first third of the leaching solution with the highest uranium concentration is taken as the qualified solution and used for precipitation to prepare uranium products. The remaining solution is returned as part of the leaching agent for the next leaching. The adsorption contact time is no less than 5 minutes, and the adsorption method is multi-tower series adsorption. The uranium concentration breakthrough point of the adsorption tail liquid is controlled at 10~20 mg / L. Step S3: The pH of the adsorption tail liquid is adjusted to above 11 by adding magnesium hydroxide slurry, filtered, and the filtrate is adsorbed by the amylopyroxime adsorption fiber; the uranium concentration breakthrough point of the adsorption tail liquid is controlled at 1 mg / L; the amylopyroxime adsorption fiber is leached by bottom-feeding, the leaching agent is soluble bicarbonate, the leaching contact time is not less than 20 minutes, and the leaching solution with the first third of the uranium concentration is taken as qualified solution and returned to step S1, and the remaining solution is returned as part of the leaching agent for the next leaching; Step S4: The adsorption tail liquid obtained in step S3 is added to magnesium carbonate slurry to generate magnesium fluoride and carbonate ions. After filtration, sludge and filtrate are obtained respectively. Part of the filtrate is returned to the uranium conversion process as a scrubbing agent for fluorination tail gas, and the other part of the filtrate is discharged after treatment. The sludge and new magnesium carbonate participate in the defluorination reaction again, and the unreacted magnesium carbonate is reused. Stir thoroughly to allow magnesium carbonate to react with fluoride ions, and the stirring reaction time should be no less than 30 minutes. After the sludge is reused for 3 cycles, it should be discharged according to the amount of new sludge generated each time it is defluorinated.

2. The method for reusing uranium fluoride wastewater according to claim 1, characterized in that, In step S3, the adsorption contact time is no less than 5 minutes, and the adsorption method is multi-tower series adsorption.

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