EP0261255B1 - Procédé de traitement d'une solution aqueuse d'acide phosphorique - Google Patents

Procédé de traitement d'une solution aqueuse d'acide phosphorique Download PDF

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Publication number
EP0261255B1
EP0261255B1 EP86112992A EP86112992A EP0261255B1 EP 0261255 B1 EP0261255 B1 EP 0261255B1 EP 86112992 A EP86112992 A EP 86112992A EP 86112992 A EP86112992 A EP 86112992A EP 0261255 B1 EP0261255 B1 EP 0261255B1
Authority
EP
European Patent Office
Prior art keywords
acid solution
phosphoric acid
iron
process according
oxalic acid
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP86112992A
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German (de)
English (en)
Other versions
EP0261255A1 (fr
Inventor
Norbert Dr. Ing. Eickelpasch
Manfried Dr. Rer. Nat. Lasch
Hans-Peter Mies
Wolfgang Stang
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kgb Kernkraftwerke Gundremmingen Betriebsgesellschaft MbH
Original Assignee
Kgb Kernkraftwerke Gundremmingen Betriebsgesellschaft MbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kgb Kernkraftwerke Gundremmingen Betriebsgesellschaft MbH filed Critical Kgb Kernkraftwerke Gundremmingen Betriebsgesellschaft MbH
Priority to EP86112992A priority Critical patent/EP0261255B1/fr
Priority to DE8686112992T priority patent/DE3662476D1/de
Priority to US07/090,958 priority patent/US4749455A/en
Priority to JP62228689A priority patent/JPS63145995A/ja
Priority to KR1019870010463A priority patent/KR920000291B1/ko
Publication of EP0261255A1 publication Critical patent/EP0261255A1/fr
Application granted granted Critical
Publication of EP0261255B1 publication Critical patent/EP0261255B1/fr
Expired legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/04—Treating liquids
    • G21F9/06—Processing

Definitions

  • the invention relates to a method for preparing a aqueous phosphoric acid solution which is used up in the course of chemical and / or electrochemical decontamination of parts of the system which are radioactively contaminated on its surface and is thereby substantially saturated with iron, with evaporation and the solids formed being conditioned for final storage.
  • Phosphoric acid electrolyte baths have been used for electrochemical decontamination for several years. After prolonged use, the iron content and activity in the electrolyte solution increase. With iron concentrations of over 100 g Fe / I, the use of the electrolyte becomes uneconomical because the decontamination does not succeed or the time and personnel expenditure is extremely high. That is why these electrolytes are discarded. Since they are radioactively contaminated, they must be disposed of and conditioned. The following two variants can be considered:
  • the electrolyte containing approx. 30-40% phosphoric acid is diluted 50-fold with water. This is necessary in order to avoid precipitation of the Na ⁇ PO4 ⁇ 12 H20 during the subsequent neutralization with sodium hydroxide solution.
  • a pH of 7 is adjusted with vigorous stirring with NaOH.
  • the previously dissolved iron phosphate precipitates out as a precipitate that can be decanted off.
  • the iron phosphate precipitation binds most of the radioactivity, so that the excess sodium phosphate solution is below the official exemption limit for radioactive waste water.
  • the water can also be subjected to a precipitation / flocculation process.
  • This method is advantageous because only about 1000 kg of iron phosphate remain for conditioning per 3000 l of electrolyte bath. It is disadvantageous that the radioactive waste water from a 3000 l electrolyte bath contains approx. 1800 kg NasP04, that is approx. 1500 kg PO ---. For reasons of environmental protection, this procedure is therefore only possible in special cases.
  • the usual technique today is evaporation of the electrolyte solution.
  • the acid must be neutralized (pH 10) in order to protect the evaporator and to maintain a solid product that can be stored for final storage.
  • Na ⁇ PO 4 ⁇ 12 H 2 0 and iron phosphate form as a mixture.
  • About 1000 kg of iron phosphate and 5200 kg of sodium orthophosphate with 12 H 2 O are formed per 3000 I batch of electrolyte bath, which are conditioned.
  • the high volume of waste is to be emphasized in this process, because both the sodium orthophosphate and the iron phosphate must be disposed of as radioactive waste.
  • Electrochemical decontamination is the most economical method of decontamination of large-area parts, whereas pickling in an acid bath is preferred for smaller parts and those with complicated geometries.
  • the suitability of a decontamination process depends on the fulfillment of several prerequisites: firstly, the radioactive contamination should be removed as completely as possible, but only as little inactive material as possible removed; Furthermore, a minimal amount of secondary wastes and a minimal release of radioactive substances via water and air are desirable, and finally the operating personnel dealing with the decontamination should be exposed to the lowest possible radiation exposure.
  • Processing the contaminated workpieces by pickling or electrochemical decontamination not only leads to a constant increase in activity in the acid baths, but also, due to the increase in the concentration of iron, to a gradual exhaustion of the baths.
  • the direct disposal of these iron-contaminated baths would contradict the requirement to minimize secondary waste; on the other hand, regeneration of the baths with the aim of reducing the iron content enables the operation to continue, which corresponds to the above requirement.
  • the invention has for its object to perform the method according to the preamble of claim 1 so that only relatively small amounts of radioactive waste have to be disposed of.
  • the solution to this problem according to the invention is that the spent phosphoric acid solution is combined with an aqueous oxalic acid solution, that the iron oxalate formed is separated off and conditioned after pyrolysis, and that the remaining phosphorus solution for reuse to a phosphoric acid content of 15 to 65% by weight. % is evaporated.
  • the invention is based on the consideration already indicated above that a minimization of the radioactive waste is only possible if the used phosphoric acid solution is processed in such a way that it is subsequently reusable and only the iron extracted from the solution is sent to the final storage.
  • the reduction treatment is carried out electrochemically in a stainless steel trough connected as a cathode with an immersed graphite anode surrounded by a diaphragm.
  • the reduction can also be brought about by using spent phosphoric acid solution as a decontamination solution (pickling) for a few days without electricity; this procedure is preferably used when many small parts have to be treated.
  • Optimal precipitation conditions for the iron oxalate result if the ver needed phosphoric acid solution is entered in a template of the cold oxalic acid solution.
  • an oxalic acid solution which has an oxalic acid content of 5 to 15% by weight, in particular 10% by weight.
  • the iron oxalate formed is expediently separated off by sedimentation and / or filtration. Furthermore, for reasons of energy saving, it is advisable to let the separated iron oxalate dry before pyrolysis.
  • the remaining phosphoric acid solution is best evaporated to a phosphoric acid content of about 40% by weight, because this phosphoric acid content enables both purely chemical decontamination (pickling) and electrochemical decontamination. Finally, for cost reasons, it is also advisable to condense the evaporated water and use it to prepare fresh oxalic acid solution.
  • the method according to the invention is described in more detail below: one begins with the selection of dismantled components for the subsequent decontamination process; it may be necessary to disassemble larger parts into workable pieces beforehand.
  • the chemical decontamination takes place either by pickling in an acid bath (approx. 40% phosphoric acid, approx. 60 ° C) or by electrochemical decontamination, because the workpiece connected as anode is also immersed in approx. 40% phosphoric acid; under the influence of a voltage of approximately 15 V, a current of approximately 1000 to several 1000 A flows between a stainless steel trough connected as a cathode and the workpiece, the strength of which increases with increasing temperature and decreases with increasing iron content.
  • the temperature must be stabilized to approx. 70 ° C with the help of the cooling water.
  • the attack of the acid dissolves the accessible metallic surface of the workpiece. This, as well as the effect of the resulting gaseous hydrogen (during pickling) or oxygen (during electrochemical decontamination) mechanically removes corrosion layers adhering to the surface.
  • the workpiece is removed from the bath and sprayed with deionized water. The cleaned workpiece is checked for any remaining activity and, if the measurements confirm that it falls below the exemption limit, is subjected to what is known as harmless recycling based on official approval.
  • the cycle of phosphoric acid begins with the previously described processes of pickling and electrochemical decontamination.
  • the electrolyte used for this absorbs considerable amounts of dissolved iron (up to over 100 g / l), which leads to a reduction in effectiveness.
  • the electrolyte is stored in a designated container and, if the proportion of divalent iron in the total iron is less than about 80%, filled into the stainless steel trough for reduction. A graphite anode surrounded by a diaphragm dips into this.
  • the electrolyte is poured into the reaction vessel, in which the same volume of cold oxalic acid solution has already been placed, and mixed intimately with the same while stirring.
  • the precipitation of iron oxalate, FeC 2 0 4 .2 H 2 0 begins within one minute; this precipitation is prevented by vigorous stirring.
  • the resulting suspension is pumped into a cylindrical plastic container, on the bottom of which there is a filter basket. The sedimentation of the precipitation that collects in the filter basket takes place in this container over the course of a few hours.
  • the supernatant clear solution is either added immediately to the phosphoric acid evaporator or, to remove remaining suspended solid particles, through a further filter basket into the filtrate collecting container, from where the pumping into the evaporator takes place.
  • the now low-iron electrolyte is heated in the evaporator until a sufficient amount of water has been distilled off at a boiling temperature of approximately 102 ° C. that the phosphoric acid content is approximately 40 to 65% by weight.
  • the electrolyte is then ready for use again and can be used again for pickling or for electrochemical decontamination, which closes the cycle.
  • the water also circulates in a closed cycle. All water supplied to the storage tank comes from the condenser of the evaporator system; It is used to spray the workpieces, to add oxalic acid solution and to wash the iron oxalate.
  • the spray water (contaminated by phosphoric acid and iron phosphate) is also used to produce oxalic acid solution.
  • the solid oxalic acid (oxalic acid dihydrate; H 2 C 2 0 4 .2 H 2 0) is mixed with such an amount of water at room temperature and stirred that an approximately 10% oxalic acid solution is formed. This is stored in a storage container and reacted with the reduced electrolyte if necessary.
  • the iron oxalate which is almost free of phosphoric acid after repeated washing, is first dried. Thermal decomposition of the iron oxalate at about 250 ° C. gives a mixture of iron oxides (FeO, Fe 2 0 3 and others), which are either filled as such in cast drums or, after mixing with cement and water, are filled into roller barrel drums and, after setting, are finally stored.
  • FeO, Fe 2 0 3 and others iron oxides
  • electrochemical decontamination plays the most important role, while pickling accounts for less than 10% of the total throughput of the iron.
  • a bath filling (3000 l regenerated electrolyte; 40% phosphoric acid with an iron concentration of 20 g / l) 24 t of material can be decontaminated in the course of about 6 to 7 weeks.
  • Pickling accounts for around 2 t (corresponding to a total consumption of 250 l phosphoric acid) and electrochemical decontamination approx. 22 t (corresponding to 2750 l phosphoric acid); for the latter process (assuming a current efficiency of 50%) a current consumption of 422000 Ah is required, which corresponds to a work of 6330 kWh at a voltage of 15 V on average.
  • the precipitation of the iron oxalate requires (assumptions: reduction in the amount of iron by 80%; complete conversion of the oxalic acid) 542 kg oxalic acid dihydrate (price per kg currently DM 2.92, totaling approximately DM 1600, -), which is dissolved in at least 4500 1 water ( Deionate or spray water) must be dissolved.
  • Iron oxalate (FeC 2 0 4 .2 H 2 0) produces 773 kg; the sedimentation vessels, which also hold 2 m3 and have to be filled 3 3/4 times, have to hold 206 kg of iron oxalate per fill, which collects in the filter basket.
  • the volumes of decantate / filtrate (7.5 m 3 ) and wash water (1 m 3 ), totaling 8.5 m3, are sufficient to fill the phosphoric acid evaporator eight times. Since the 8.5 m 3 have to be reduced to about 3 m 3 , i.e. 5.5 m3 have to be distilled off, a time requirement of at least 35 hours for the distillation can be assumed (the distillate decrease is approx. 158 I / h at maximum heating output). .

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Removal Of Specific Substances (AREA)
  • Chemical Treatment Of Metals (AREA)

Claims (10)

1. Procédé pour préparer une solution aqueuse d'acide phosphorique utilisée lors d'une décontamination chimique et/ou électrochimique de parties d'une installation ayant subi une pollution radioactive au niveau de leur surface, et sensiblement saturée par du fer, et selon lequel on purifie la solution d'acide phosphorique utilisée avec une solution aqueuse, on sépare les substances solides alors formées et on les conditionne, après les avoir déshydratées, en vue d'un stockage définitif, et selon lequel on récupère la solution d'acide phosphorique et on l'utilise pour une décontamination d'autres parties de l'installation, caractérisé en ce qu'on purifie la solution d'acide phosphorique utilisée avec une solution aqueuse d'acide oxalique, qu'on retire l'oxalate de fer alors formé et qu'on le conditionne après avoir mis en oeuvre une pyrolyse, et qu'on concentre par évaporation la solution restante d'acide phosphorique, en vue d'une nouvelle utilisation, de manière qu'elle présente une teneur en acide phosphorique de 15 à 65% en poids.
2. Procédé selon la revendication 1, caractérisé en ce qu'on soumet l'acide phosphorique utilisé, avant sa purification avec la solution d'acide oxalique, à un traitement de réduction jusqu'à ce qu'au moins 80% du fer soient présents sous forme bivalente.
3. Procédé selon la revendication 2, caractérisé en ce que le traitement de réduction est exécuté par voie électrochimique dans une cuve en acier spécial, branchée en tant que cathode, avec une anode en graphite immergée, entourée par un diaphragme.
4. Procédé selon l'une des revendications 1 à 3, caractérisé en ce qu'on introduit la solution d'acide phosphorique utilisée dans un récipient de la solution froide d'acide oxalique.
5. Procédé selon l'une des revendications 1 à 4, caractérisé en ce qu'on utilise la solution d'acide oxalique avec une teneur en acide oxalique comprise entre 5 et 15% en poids.
6. Procédé selon la revendication 5, caractérisé en ce qu'on utilise la solution d'acide oxalique possédant une teneur en acide oxalique égale à 10% en poids.
7. Procédé selon l'une des revendications 1 à 6, caractérisé en ce qu'on sépare par sédimentation et/ou filtration l'oxalate de fer formé.
8. Procédé selon l'une des revendications 1 à 7, caractérisé en ce qu'on exécute la dessication de l'oxalate de fer séparé, avant la pyrolyse.
9. Procédé selon l'une des revendications 1 à 8, caractérisé en ce qu'on concentre par évaporation la solution d'acide phosphorique subsistante de manière à obtenir une teneur d'acide phosphorique égale à environ 40% en poids.
10. Procédé selon l'une des revendications 1 à 9, caractérisé en ce qu'on condense l'eau évaporée et qu'on l'utilise pour préparer la solution d'acide oxalique.
EP86112992A 1986-09-20 1986-09-20 Procédé de traitement d'une solution aqueuse d'acide phosphorique Expired EP0261255B1 (fr)

Priority Applications (5)

Application Number Priority Date Filing Date Title
EP86112992A EP0261255B1 (fr) 1986-09-20 1986-09-20 Procédé de traitement d'une solution aqueuse d'acide phosphorique
DE8686112992T DE3662476D1 (en) 1986-09-20 1986-09-20 Process for working up an aqueous phosphoric-acid solution
US07/090,958 US4749455A (en) 1986-09-20 1987-08-28 Method of treating contaminated aqueous phosphoric acid solutions
JP62228689A JPS63145995A (ja) 1986-09-20 1987-09-14 燐酸水溶液の処理方法
KR1019870010463A KR920000291B1 (ko) 1986-09-20 1987-09-19 오염된 인산 수용액의 처리방법

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP86112992A EP0261255B1 (fr) 1986-09-20 1986-09-20 Procédé de traitement d'une solution aqueuse d'acide phosphorique

Publications (2)

Publication Number Publication Date
EP0261255A1 EP0261255A1 (fr) 1988-03-30
EP0261255B1 true EP0261255B1 (fr) 1989-03-15

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EP86112992A Expired EP0261255B1 (fr) 1986-09-20 1986-09-20 Procédé de traitement d'une solution aqueuse d'acide phosphorique

Country Status (5)

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US (1) US4749455A (fr)
EP (1) EP0261255B1 (fr)
JP (1) JPS63145995A (fr)
KR (1) KR920000291B1 (fr)
DE (1) DE3662476D1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012175098A1 (fr) 2011-06-23 2012-12-27 Babcock Noell Gmbh Procédé et installation de décontamination d'une solution d'acide phosphorique
KR101370573B1 (ko) * 2012-08-20 2014-03-06 한국원자력연구원 방사성 폐기물에 함유되어 있는 규제 핵종 Ｔｃ-99, Ｓｒ-90, Ｆｅ-55, Ｎｂ-94, 및 Ｎｉ-59(Ｎｉ-63)의 정량을 위한 분리 방법
JP5997579B2 (ja) * 2012-10-19 2016-09-28 日本碍子株式会社 放射性金属廃棄物の処理方法
WO2015162604A1 (fr) 2014-04-22 2015-10-29 Green Future Ltd. Procédé et formulations pour éliminer la rouille et le tartre de l'acier et pour régénérer la liqueur de décapage dans des procédés de galvanisation par immersion à chaud
TN2017000124A1 (en) 2014-10-30 2018-10-19 Jacobs Eng Group Inc Method for removing iron in the manufacture of phosphoric acid

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3008904A (en) * 1959-12-29 1961-11-14 Jr Benjamin M Johnson Processing of radioactive waste
US3582402A (en) * 1968-04-16 1971-06-01 Atcor Inc Technique for decontaminating metal surfaces in nuclear reactors
JPS5822381B2 (ja) * 1978-07-31 1983-05-09 日本車輌製造株式会社 ラツク併用式デイ−ゼル機関車
US4490336A (en) * 1981-05-27 1984-12-25 Prodeco, Inc. Process for stripping uranium from an alkyl pyrophosphoric acid
US4549985A (en) * 1982-06-07 1985-10-29 General Electric Company Waste disposal process
US4615776A (en) * 1983-10-21 1986-10-07 Shinko-Pfaudler Company Electrolytic decontamination process and process for reproducing decontaminating electrolyte by electrodeposition and apparatuses therefore
JPS60204900A (ja) * 1984-03-29 1985-10-16 Touden Kankyo Eng Kk 電解研磨液の再生法
US4701246A (en) * 1985-03-07 1987-10-20 Kabushiki Kaisha Toshiba Method for production of decontaminating liquid

Also Published As

Publication number Publication date
EP0261255A1 (fr) 1988-03-30
KR880004500A (ko) 1988-06-04
JPS63145995A (ja) 1988-06-18
US4749455A (en) 1988-06-07
DE3662476D1 (en) 1989-04-27
KR920000291B1 (ko) 1992-01-11

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