EP0277422B1 - Traitement chimique de liqueurs - Google Patents

Traitement chimique de liqueurs Download PDF

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Publication number
EP0277422B1
EP0277422B1 EP19870310701 EP87310701A EP0277422B1 EP 0277422 B1 EP0277422 B1 EP 0277422B1 EP 19870310701 EP19870310701 EP 19870310701 EP 87310701 A EP87310701 A EP 87310701A EP 0277422 B1 EP0277422 B1 EP 0277422B1
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EP
European Patent Office
Prior art keywords
liquor
precipitate
mixing
pipeline
reagent
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 - Lifetime
Application number
EP19870310701
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German (de)
English (en)
Other versions
EP0277422A2 (fr
EP0277422A3 (en
Inventor
Michael Joseph Bowe
Lionel Houston Ford
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.)
UK Atomic Energy Authority
Original Assignee
UK Atomic Energy Authority
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Filing date
Publication date
Priority claimed from GB868629320A external-priority patent/GB8629320D0/en
Application filed by UK Atomic Energy Authority filed Critical UK Atomic Energy Authority
Publication of EP0277422A2 publication Critical patent/EP0277422A2/fr
Publication of EP0277422A3 publication Critical patent/EP0277422A3/en
Application granted granted Critical
Publication of EP0277422B1 publication Critical patent/EP0277422B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • 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
    • G21F9/10—Processing by flocculation

Definitions

  • This invention relates to chemical processes in which a bulk quantity of liquor is to be treated with one or more chemical reagents.
  • One form of treatment for which the invention has application is in the precipitation of solids from liquors such as waste liquors arising in the nuclear fuel reprocessing and water treatment industries.
  • a number of precipitation processes are employed by the nuclear industry as a means of decontaminating aqueous waste streams.
  • the main contaminants are fission products and actinides.
  • Similar processes are also employed by the water treatment industries for removal of heavy metal species.
  • the effectiveness of the precipitation process depends to a large extent on factors such as the type of chemical additive used to treat the waste liquor at the various pH stages, the degree of control employed during the pH conditioning of the liquor and the degree of mixing within the reaction zones.
  • the effectiveness of the process also depends upon the degree of the solid/ liquid separation after the precipitation process is completed.
  • the first stage separation of the solid precipitate from the aqueous phase is usually achieved by gravity settling in the same reaction vessel used to produce the precipitate.
  • Control of pH in such large precipitate formation vessels may be difficult to achieve because after initial neutralisation to pH 1-2 further small additions of caustic solution (the usual neutralisation agent employed) can produce large changes in pH. Because the pH system is so inherently sensitive to caustic addition it is not inconceivable that large local variations in pH may exist within such tanks.
  • apparatus for combining and mixing a bulk flow of liquor with at least one reagent for reaction with the liquor, said apparatus comprising a pipeline along which the liquor flows, at least one fluidic mixing device in the pipeline for combining the liquor with at least one reagent and thoroughly mixing the same, the combined liquor and reagent(s) thereafter continuing to flow along a pipeline section downstream of the or each fluidic device.
  • the pipeline section may be designed in terms of dimensions and flowrates to allow an appropriate reaction residence time before the bulk liquor flow encounters the next fluidic mixing device or enters a vessel for subsequent processing of the liquor.
  • liquor-processing apparatus comprising a pipeline for conducting a bulk flow of liquor, at least one fluidic mixing device in the pipeline for combining the liquor with at least a precipitation-promoting reagent and thoroughly mixing the same, the or each fluidic mixing device being followed by a pipeline section affording a reaction residence time as the liquor and reagent(s) continue flowing along the pipeline, and means for effecting separation of the precipitate from the liquor.
  • the apparatus comprises a cascade of at least two fluidic mixing devices forming mixing junctions at spaced positions along the pipeline.
  • At least one of the fluidic mixing devices may be designed to admit simultaneously at least two streams of reagent flow along with the bulk liquor flow.
  • a proportion of the precipitate derived in the course of separation by the separation means is recycled back to said pipeline for mixing with the bulk liquor flow via said fluidic mixing device or devices.
  • the separating means may comprise a settling or thickening vessel into which the mixed liquor and reagent(s), including any recycled precipitate, are fed from said pipeline whereby at least a proportion of the solids content tends to settle towards the base of the vessel, and the separating means preferably further comprises at least one centrifugal separator means (e.g. a hydrocyclone) for receiving from said settling vessel a proportion of the vessel contents to effect further separation of the solids and liquid phases, at least a fraction of the solids-bearing stream from the centrifugal separator means being recycled back to the pipeline as specified above.
  • the flow rate of the recycled stream may be variable according to requirements.
  • the flow of the bulk liquor may be continuous and the transfer of liquor from the settling vessel to the centrifugal separator means may also be continuous.
  • the sludge accumulating towards the base of the settling vessel may be intermittently or continuously withdrawn for subsequent processing, e.g. dewatering. In practice, intermittent withdrawal may be employed to enable the level of the vessel contents to be maintained between predetermined limits while liquor is continuously fed into the vessel from said pipeline and withdrawn from the vessel for transfer to the hydrocyclone(s).
  • the waste liquor to be treated will be delivered via pipeline 10 to a buffer tank 12.
  • the liquor within the buffer tank will then be transferred continuously along a pipeline 14 using a steam ejector 16 or a suitable fluidic pump unit (such as a double diode pump).
  • mixing units At a number of points on the pipeline (marked A, B, C and D on Figure 1) will be located mixing units.
  • the mixing units will each be followed by a downstream section of pipework whose volume is calculated to give an appropriate reaction residence time.
  • the system will approximate to a plug flow reactor with reactants being admitted at the mixing junctions.
  • Such an arrangement serves to limit the degree of backmixing in the system and allows some reduction in the proportion of colloidal sized particles normally to be anticipated for a system with significant backmixing (such as a stirred tank reactor).
  • a precipitation-promoting additive such as caustic solution, and/or other chemical reagents is introduced at each of the mixing units A, B, and D.
  • the reagent flows into the mixer units are controlled by closed loop systems 20 sensing at points 22, 24, 26 a parameter such as pH.
  • a single reagent stream or several reagent streams can converge at each mixing unit.
  • the mixing unit may comprise either a Vortex type device as shown in Figures 2 and 3 or an entrainment type device as shown in Figure 3.
  • the treated liquor stream containing the precipitate formed by the chemical conditioning is then directed from the pipeline 14 into a thickening tank 30.
  • the precipitate has an opportunity to settle to a thickened slurry.
  • a reverse flow diverter pump unit 32 Located at the base of the tank is a reverse flow diverter pump unit 32 connected to an air piston 34 elevated above the maximum liquor level 36 in the tank.
  • the RFD pump 32 delivers a metered volume of thickened slurry via pipeline 38 to the next stage in the process, for example, a de-watering stage employing an ultra filter unit.
  • a steam ejector or a suitable fluidic pump unit 40 located in the thickening vessel at an elevation above the thickening zone.
  • the pump 40 continuously delivers the precipitate-bearing solution to a hydrocyclone unit 42.
  • the hydrocyclone unit 42 may comprise either a single hydrocyclone element or a multiplicity of elements connected in series or parallel as required.
  • the underflow liquor from the hydrocyclone unit containing the majority of the precipitated solids is then recycled, via a breakpot 44 and line 46, back to the mixer cascade (i.e. at mixer C in Figure 1) in order that it may act as a precipitate seeding solution. Such an operation may reduce the number of colloidal sized particles in solution.
  • the seeding flow stream is desirably introduced at a liquor pH value corresponding to the onset of precipitate nucleation.
  • the overflow liquor from the hydrocyclone unit containing a reduced proportion of solid material is then transferred, via breakpot 48 and line 50, to the next stage in the process which could be a further chemical conditioning treatment using a cascade of fluidic mixers and hydrocyclone unit or it may be an ultrafiltration unit employed to polish the hydrocyclone overflow liquor before final discharge.
  • each mixer may be of the vortex type as shown in which the bulk liquor flow and the reagent(s) are fed tangentially via tangentially directed inlets 60 into a vortex chamber 62 in which they undergo thorough mixing before discharging as a mixture via centrally located outlet 64.
  • inlets 60 only two inlets 60 are illustrated there may be more than two depending on the number of reagents to be mixed with the bulk flow of liquor.
  • Figure 4 shows an entrainment-type mixer in which the bulk flow of liquor (fed in the direction 70) enters a Venturi-type constriction and the reagent or reagents to be mixed intensively with the bulk flow are introduced via inlets 72 which enter at the narrow waist section of the constriction where the flow velocity is increased thereby enhancing mixing of the reactants.
  • a floc forming metal in the form of a compound of iron is introduced by means of a fluidic mixing unit into the pipeline at a position (not shown) upstream of or at the mixing unit A, while a precipitate-promoting additive such as a caustic solution, and/or other chemical reagents, is introduced at each of the mixing units A, B and D to establish a well-controlled pH profile through the cascade in order to achieve uniform and repeatable co-precipitation conditions.
  • the reagent flows into the mixer units are controlled by closed loop systems 20 sensing at points 22, 24 and 26 the pH of the liquor in the pipeline 14 so that the required pH profile can be maintained.
  • the bulk of the caustic required for neutralisation is introduced at the first mixer A and further smaller additions of caustic are made at subsequent mixers so that the pH of the liquor can be progressively adjusted to the pH range in which the iron has minimum solubility.
  • the seeding flow stream is introduced at a liquor pH value corresponding to the onset of precipitate nucleation and the position of introduction is chosen so that introduction takes place at a position along the cascade and hence on the pH profile which meets this condition.
  • the pH profile established may be such that this condition obtains at mixer C.
  • Introduction of the seeding flow stream upstream of C, that is at a lower pH than that at which onset of precipitate nucleation takes place tends to cause dissolution of the seeds, while introduction at a position downstream of C, that is at a pH higher than that at which onset of precipitate nucleation occurs, has a reduced effect since self-nucleation will have taken place before introduction of the seeding stream.
  • the waste stream contains plutonium in a concentration in the range 10 ⁇ 6 to 10 ⁇ 7 mol dm ⁇ 3 and iron (III) is added at a concentration of about 100 ppm.
  • iron (III) is added at a concentration of about 100 ppm.
  • the reduction in solubility arising from an increase in pH tends to produce a colloidal or polymeric precipitate which is difficult to remove.
  • iron (III) the plutonium colloid produced behaves as a substrate on which the iron (present at a higher concentration) can precipitate so that the colloidal plutonium particles become trapped within a ferric floc crystalline matrix producing a much larger particle which can be more readily separated from the aqueous phase.
  • the precipitate comprising thickened floc can, as well as or instead of being recycled as a seeding agent, be recycled from the phase separator, e.g. a thickening vessel or hydrocyclone unit, back to the first mixer A where, because the pH is relatively low, it redissolves to enhance the local iron (III) concentration. In this way the concentrations of iron (III) can be enhanced significantly, e.g. up to 500%, without increasing the feed iron (III) introduction rate. Also, by recycling precipitate in this way a greater proportion of the plutonium is incorporated within the floc crystalline matrix which is advantageous since the volume of precipitate requiring subsequent storage is reduced in comparison with the case where no iron (III) is recycled. In general where the precipitate is recycled for seeding purposes and for increasing iron (III) concentration, the proportion recycled for the latter purpose will usually be much greater than that recycled for seeding purposes.
  • the floc produced can be dissolved and the species separated from the floc forming metal by conventional chemical processes, such as dissolution followed by solvent extraction.
  • the separated floc-forming metal can then be recycled.
  • the floc-forming agent such as iron (III)
  • the floc-forming agent precipitates concurrently with, or after, the precipitation of the species being separated so that the ferric hydroxide floc derived from the floc-forming agent traps the precipitate arising from the species being separated. Therefore, it may be advantageous to add further floc-forming agent at mixing units downstream of the initial upstream addition of the floc-forming agent.
  • the reagent or reagents added to the liquor via the mixing units may be in gaseous form and not necessarily liquid form only.
  • the process may employ reactions resulting from the admixture of gases and liquids for producing a uranyl or plutonyl or uranyl/plutonyl precipitate which can be used to produce an oxide nuclear fuel. More specifically such a process may involve the mixture, within a cascaded fluidic device mixing arrangement as previously described, of a uranyl/plutonyl nitrite solution with gaseous ammonia and carbon dioxide at a pH between 8 and 9.
  • the useful product of the reaction is a complex ammonium uranyl/plutonyl carbonate precipitate which can be readily calcined to produce an oxide which may be free flowing and readily pressable.
  • the invention has applications in the chemical industry in general where processing of a liquor is required.
  • the invention may be used in the pharmaceutical industry in the precipitation of proteins, antibiotics and the oxygenation of shear-sensitive cell cultures; in the paint industry in the precipitation of pigments; in the manufacture of ceramics such as superconductors; and liquid-liquid mixing systems for the production, by chemical reaction, of chemicals such as polymers.
  • the invention may be employed in the minerals-processing industries for the recovery of valuable metal ions existing at low concentrations or to limit the environment impact of toxic heavy metal discharges.
  • the system may be operated with ion exchange materials added at the mixing units with subsequent recovery, regeneration and recycle of the ion exchange materials.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Removal Of Specific Substances (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)

Claims (18)

  1. Procédé de traitement d'une liqueur, qui comprend les opérations consistant à faire passer une liqueur le long d'un pipe-line, à combiner et à mélanger de façon poussée un réactif, favorisant la formation d'un précipité, avec la liqueur en au moins une position le long du pipeline, à l'aide d'un dispositif de mélangeage fluidique, à laisser la liqueur s'écouler à travers un tronçon de pipeline disposé en aval de la ou de chaque position de mélangeage pour garantir un temps de séjour permettant la réaction, à séparer le précipité résultant d'avec la liqueur et à recycler vers la ou vers au moins l'une des positions une partie du précipité pour le mélanger avec le courant de liqueur circulant dans le pipe-line.
  2. Procédé selon la revendication 1, qui comprend l'agencement de plusieurs positions espacées le long du pipe-line en utilisant une cascade de dispositifs de mélangeage fluidique.
  3. Procédé selon la revendication 1 ou 2, qui comprend le passage de la liqueur en continu le long du pipe-line.
  4. Procédé selon la revendication 1, 2 ou 3, qui comprend l'introduction de la liqueur mélangée au réactif, y compris le précipité recyclé, dans un récipient de dépôt et de décantation dans lequel au moins une certaine proportion des solides contenus tend à se déposer vers la base du récipient, et l'introduction d'une partie du contenu que l'on envoie dans un moyen du type séparateur centrifuge.
  5. Procédé selon l'une quelconque des revendications 1 à 4, dans lequel le réactif favorisant la formation d'un précipité est constitué par ou comprend une solution caustique.
  6. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'introduction du réactif favorisant la formation d'un précipité ou d'un autre réactif dans le pipe-line est commandée selon le pH décelé au sein du pipe-line.
  7. Procédé selon l'une quelconque des revendications 1 à 6, dans lequel la liqueur contient des métaux lourds, et lesdits métaux lourds sont précipités de la liqueur par ledit réactif favorisant la formation d'un précipité.
  8. Procédé selon l'une quelconque des revendications 1 à 7, dans lequel une solution de nitrate d'uranyle/plutonyle est mélangée à de l'ammoniac gazeux et à du bioxyde de carbone gazeux, à un pH compris entre 8 et 9.
  9. Procédé selon la revendication 1, dans lequel il existe une cascade desdits dispositifs mélangeurs située en des positions espacées le long du pipe-line, et un réactif d'ajustement du pH est introduit en des positions choisies ou dans tous lesdits dispositifs mélangeurs pour établir un profil bien défini de pH le long de la cascade.
  10. Procédé selon la revendication 9, dans lequel la liqueur contient un agent formateur d'un floculat et un composé ou une espèce qui est à séparer de la liqueur à l'aide de l'agent formateur du floculat, ledit réactif d'ajustement du pH étant ajouté par étapes auxdits dispositifs de mélangeage pour créer des conditions de pH dans lesquelles l'agent formateur du floculat et ladite espèce précipitent, de sorte que le floculat résultant capture au moins une partie du précipité obtenu à partir de ladite espèce.
  11. Procédé selon la revendication 10, dans lequel le précipité comprenant ledit floc et ladite espèce est séparé de la liqueur et il est recyclé vers au moins une position de mélangeage faisant partie de la cascade.
  12. Procédé selon la revendication 11, dans lequel au moins une certaine proportion dudit précipité recyclé floculat/espèce est introduite en une position de mélangeage dans laquelle le pH régnant est tel que le précipité recyclé se redissout dans la liqueur pour augmenter la concentration dudit agent formateur d'un floc ou floculat.
  13. Procédé selon la revendication 11 ou 12, dans lequel au moins une certaine proportion du précipité recyclé floculat/espèce est introduite en une position de mélangeage où le pH régnant permet au précipité recyclé de jouer le rôle de germes pour favoriser une précipitation à partir de la liqueur.
  14. Appareillage pour la mise en oeuvre d'un procédé de traitement d'une liqueur selon la revendication 1, cet appareil comprenant un pipe-line (14) en au moins un point de mélangeage (A, B, C et D) duquel un réactif favorisant la formation d'un précipité peut être ajouté et mélangé de façon poussée à ladite liqueur, à l'aide d'un dispositif de mélangeage fluidique (60, 62 ou 70, 72), un moyen pour maintenir la liqueur et les réactifs en contact pendant une période de temps suffisante pour permettre une réaction entre la liqueur et le réactif, des moyens (30, 40, 42) pour séparer le précipité de la liqueur ainsi traitée et des moyens (44, 46) pour recycler une partie du précipité vers l'un des points comportant un dispositif de mélangeage en vue d'une incorporation à la liqueur.
  15. Appareillage selon la revendication 14, dans lequel le moyen pour séparer la matière précipitée d'avec la liqueur est constitué par ou comprend un récipient (30) de dépôt, une pompe (40) et un séparateur centrifuge (42).
  16. Appareillage selon la revendication 15, dans lequel le moyen pour recycler une partie du précipité et la faire revenir vers le point de mélangeage comprend un pot (44) de rupture de mousse ou d'émulsion à la sortie du séparateur centrifuge (42) et un conduit (46) reliant le pot (44) à un point de mélangeage (C).
  17. Appareillage selon l'une quelconque des revendications 14 à 16, comprenant plusieurs points de mélangeage (A, B, C et D) disposés en cascade.
  18. Appareillage selon la revendication 17, comprenant un moyen (20) pour déceler le pH de la liqueur en plusieurs positions le long du pipe-line (14) et un moyen pour fournir du réactif à des dispositifs mélangeurs en un ou plusieurs des points de mélangeage (A, B ou D) afin de maintenir un profil prédéterminé de pH dans la liqueur circulant dans le pipe-line (14).
EP19870310701 1986-12-08 1987-12-04 Traitement chimique de liqueurs Expired - Lifetime EP0277422B1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB868629320A GB8629320D0 (en) 1986-12-08 1986-12-08 Chemical treatment of liquors
GB8629320 1986-12-08
GB8706529 1987-03-19
GB878706529A GB8706529D0 (en) 1986-12-08 1987-03-19 Chemical treatment of liquids

Publications (3)

Publication Number Publication Date
EP0277422A2 EP0277422A2 (fr) 1988-08-10
EP0277422A3 EP0277422A3 (en) 1990-02-14
EP0277422B1 true EP0277422B1 (fr) 1994-11-09

Family

ID=26291666

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19870310701 Expired - Lifetime EP0277422B1 (fr) 1986-12-08 1987-12-04 Traitement chimique de liqueurs

Country Status (3)

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EP (1) EP0277422B1 (fr)
DE (1) DE3750747T2 (fr)
GB (1) GB2200574B (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB9007027D0 (en) * 1990-03-29 1990-05-30 Atomic Energy Authority Uk Precipitation apparatus and method
DE4307468B4 (de) * 1993-03-10 2007-09-20 Wismut Gmbh Verfahren zur Fällung von Schwermetallen, Uran und toxischen Metallen bei der Sanierung von bergbaulichen Anlagen, insbesondere aus kontaminierten Wässern
GB2341120B (en) * 1998-09-04 2002-04-17 Aea Technology Plc Controlling uniformity of crystalline precipitates

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1175514A (en) * 1966-03-11 1969-12-23 Kodak Ltd Process and Apparatus for Mixing or Reacting Fluids
GB1237229A (en) * 1968-12-30 1971-06-30 Swift & Co Improvements in or relating to fertilizers
JPS5238505B2 (fr) * 1973-02-02 1977-09-29
JPS5390219A (en) * 1977-01-17 1978-08-08 Kao Corp Sulfonation process and its apparatus
DE2719956C2 (de) * 1977-05-04 1982-12-02 Bayer Ag, 5090 Leverkusen Vorrichtung zum Mischen, Reagieren und Ausdampfen
CA1137076A (fr) * 1978-12-13 1982-12-07 John R. Bauer Systeme melangeur par vaporisation de liquides a reaction chimique reciproque

Also Published As

Publication number Publication date
GB2200574A (en) 1988-08-10
GB8728387D0 (en) 1988-02-10
DE3750747T2 (de) 1995-03-16
GB2200574B (en) 1990-11-28
EP0277422A2 (fr) 1988-08-10
DE3750747D1 (de) 1994-12-15
EP0277422A3 (en) 1990-02-14

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