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
  • G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
  • G21F9/002—Decontamination of the surface of objects with chemical or electrochemical processes
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
  • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
  • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
  • C02F1/467—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction
  • C02F1/4672—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction by electrooxydation
• • 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
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/42—Treatment of water, waste water, or sewage by ion-exchange
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/12—Halogens or halogen-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/30—Organic compounds
  • C02F2101/303—Complexing agents
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/34—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32
  • C02F2103/343—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32 from the pharmaceutical industry, e.g. containing antibiotics
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2201/00—Apparatus for treatment of water, waste water or sewage
  • C02F2201/46—Apparatus for electrochemical processes
  • C02F2201/461—Electrolysis apparatus
  • C02F2201/46105—Details relating to the electrolytic devices
  • C02F2201/46115—Electrolytic cell with membranes or diaphragms
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2201/00—Apparatus for treatment of water, waste water or sewage
  • C02F2201/46—Apparatus for electrochemical processes
  • C02F2201/461—Electrolysis apparatus
  • C02F2201/46105—Details relating to the electrolytic devices
  • C02F2201/4618—Supplying or removing reactants or electrolyte
  • C02F2201/46185—Recycling the cathodic or anodic feed

Definitions

• This invention relates to a novel system for the decontamination of surfaces and treatment of the resulting effluent. More specifically, the system provides a process which allows for the removal of contaminants with suitable decontaminating media and the subsequent treatment and safe disposal of the contaminants, decontaminating species and associated products.
• the present invention seeks to provide an integrated treatment system that couples decontamination with both treatment of the resulting effluent and, typically, subsequent reagent recycling, and thereby to permits the use of previously restricted or prohibited reagents through the removal of residual components which have previously proved to be problematic in terms of effluent handling and disposal.
• the invention seeks to address the problems associated with the handling of chloride from spent decontamination solutions and also considers the possibility of reagent recycling and the destruction of organic materials, including complexants.
• a method for the decontamination of a contaminated system comprising at least the steps of:
• Certain embodiments of the invention envisage an initial characterisation step, wherein the system is examined in order that the nature of the contaminant may be determined and evaluated so as to assist in optimising the selection of a decontaminating agent.
• a chemical dosing step may be employed between steps (c) and (d), prior to electrochemical treatment of the used decontaminating agent. This step may facilitate the precipitation of certain materials and thereby allow their removal by e.g. deposition or filtration.
• Further embodiments of the invention envisage a subsequent characterisation step, wherein the system is re-evaluated in order to determine whether the decontamination objectives have been successfully accomplished.
• the sequence of steps comprised in the method of the invention may be refined or repeated as many times as necessary in order to successfully complete the decontamination operation.
• Still further embodiments of the invention envisage a final step comprising post- treatment of the effluent remaining after the electrochemical treatment.
• Yet further embodiments of the invention provide for irradiation of the used decontaminating solution with ultra-violet radiation, wherein said irradiation treatment may be performed before, during or after said electrochemical treatment of said decontaminating solution.
• the method of the first aspect of the invention may comprise one, some or all of said optional additional steps.
• embodiments of the method according to the first aspect of the invention may comprise the following steps:
• the system which is to be treated comprises at least one contaminated surface.
• Contaminated surfaces may, for example comprise contaminated pipework.
• Said surfaces are typically concrete surfaces or metal surfaces formed of, for example, stainless steel.
• the disclosed method therefore provides a decontamination system coupled to an effluent treatment process and thereby facilitates the use of, for example, chloride bearing reagents such as HCI and NaCI, as well as nitric acid and complexants - and combinations thereof - for decontamination operations by virtue of the fact that it allows for the removal and destruction of problematic species such as chlorides and complexants from the waste solution whilst also facilitating the treatment of removed contamination.
• chloride bearing reagents such as HCI and NaCI
• the system which is provided permits the local treatment of effluent, e.g. using trolley based units, thereby in certain embodiments allowing decontamination operations to be decoupled from the central plant infrastructure.
• the system can be used as an addition to an existing centralised decontamination facility.
• the present inventors have established that the electrochemical treatment, chemical dosing and post-treatment steps of the method of the present invention are also applicable to the treatment of process liquors in order to remove chloride and organic materials which are present in process or environmental streams, as opposed to streams generated through decontamination operations.
• a second aspect of the present invention envisages a method for the removal of contaminants from a process or environmental stream which comprises the steps of:
• the method comprises at least one of steps (a) and (c).
• the methods of the invention are typically operated as batch procedures but may, if required be operated as continuous processes in certain embodiments.
• Figure 1 is a flow chart which provides an overview of the method according to the invention.
• Figure 2 is a flow chart which illustrates the process stapes associated with the electrochemical treatment of the used decontaminating agent.
• Figure 3 illustrates a typical electrochemical cell for use in a method according to the invention.
• Figure 4 illustrates graphically the efficiency of removal of chloride and organic carbon from a decontamination solution according to the method of the invention.
• the present invention provides a decontamination/local effluent treatment process which includes multiple steps and comprise at least the steps of:
• Embodiments of the invention include at least one additional step selected from the steps of:
• a system is characterised (Step 1) in order to facilitate selection of at least one suitable decontamination agent (Step 2).
• the process involves the delivery of decontamination agent(s) (Step 3) to remove surface contamination and/or remove contaminated surface (e.g. surfaces comprising stainless steel and concrete), following which the waste decontamination agent(s) is/are subjected to an electrochemical treatment (Step 4) in order to remove residual corrosive species and/or complexant species so as to make them compatible with downstream plant or the environment.
• the system may be re-characterised (Step 5) to determine if the decontamination objective has been achieved; if not, then steps 2, 3 and 4 may be repeated.
• the spent decontaminant is post-treated in order to remove the contaminants by, for example, precipitating the removed contamination/contaminated surface components.
• Characterisation of the system may be carried out by any of a number of techniques known to those skilled in the art. Characterisation may be carried out remotely where required - notably, for example, when the system comprises a hazardous environment. A knowledge of parameters such as the severity, type and location of the contaminant is important to an efficient decontamination process, so this step is typically included when one or more of these parameters is not known.
• Suitable characterisation techniques may, for example, include simply using an established knowledge of plant history, or may involve active methods such as radiation and chemical fingerprinting techniques, including the use of devices for the detection of elevated levels of radiation in remote locations, such as those described in WO-A- 201 1/018657 which comprise scintillators in combination with fibre optic cables, or methods such as Laser Induced Breakdown Spectroscopy (LIBS) or Raman Spectroscopy which may involve the collection and analysing of samples.
• LIBS Laser Induced Breakdown Spectroscopy
• Raman Spectroscopy Raman Spectroscopy
• aggressive decontaminants are utilised, typical examples of which may be selected from, for example, hydrochloric acid, nitric acid, sodium hydroxide, sodium chloride, hydrogen peroxide, or various complexants, or suitable mixtures of one or more of these components.
• this reagent is delivered to the system to be decontaminated. Delivery may be achieved via any convenient means. Thus, for example, delivery may simply involve flooding and draining the system and this may be carried out with the decontaminant in the form of, typically, a foam, gel, bulk liquid, mist, spray, an aerosol or an atomised reagent. In certain embodiments of the invention, delivery is by means of atomisation and misting, which allows the reagent volume to be kept to a minimum and thereby reduces the inventory in use and the amount of reagent to be prepared.
• HCI or NaCI
• HN0 3 may be deployed to (a) wash down the HCI (or NaCI), (b) provide passivation of the steel in order to prevent an unintentional breach of containment, and (c) optimise the postprocessing of the spent decontamination solution in an electrochemical cell.
• the dissolution rate of steel in high concentrations of HCI may vary from 0.07 micron h “1 under passivating conditions to more than 70 micron h "1 for the corrosion rate of bare steel.
• the dissolution rate was found to be 1.94 micron h "1
• the dissolution rate was 0.037 micron h "1
• 1 M NaCI +10M HN0 3 the dissolution rate was measured as 0.57 micron h "1 .
• the time taken to remove 10 micron of a steel surface using HCI or NaCI mixed with HN0 3 is in the range of 10 minutes to 5 hours, assuming that the decontaminating reagent is present in excess.
• atomised reagents having droplet sizes in the range of from 0.5-20 micron, more specifically from 1-10 micron, most specifically from 2-5 micron, which are useful in achieving high surface area distribution of the decontaminating reagent.
• the proportion of liquid to air in the atomised droplets may advantageously be increased to give droplet sizes in the region of 50 micron for the purpose of surface flooding and washing down of surfaces.
• the electrochemical treatment is carried out in at least one electrochemical cell.
• a single electrochemical cell is employed.
• a multiplicity of electrochemical cells may be used.
• the multiplicity of cells may comprise a cell stack comprising multiple repeat units.
• said multiplicity of cells may comprise a multiplicity of duplicate identical cells or a multiplicity of cells of different design, wherein each cell is optimised for a specific electrochemical process, for example the treatment of high or low chloride-containing process streams.
• a chemical dosing step may optionally be employed prior to treatment in the cell, this step facilitating the precipitation of certain materials and allowing their removal by e.g. deposition or filtration.
• chloride may be removed by electrolysis and liberated as chlorine gas which may then be treated in an off-gas scrubber prior to release of any remaining harmless gases to the atmosphere, whilst any complexants - typically organic compounds such as EDTA or citric acid - which are present in the stream are oxidised in the electrochemical cell.
• chloride ions may optionally be added to the electrolyte in order to enhance oxidation of organic materials through the generation of chlorine, or chlorine- containing ions, such as chlorate, hypochlorite or hypochlorate, on or in the vicinity of the anode.
• Suitable off-gas systems which may be used to scrub the liberated chlorine may, for example, use NaOH as the scrubbing agent. This would then produce NaCI, which may be re-used as a decontamination agent.
• solid state scrubbers can be employed.
• FIG. 3 A more detailed illustration of an electrochemical cell is seen in Figure 3, wherein there is shown a typical example of such a cell. This cell seeks to perform two electrochemical tasks:
• the cathode reaction is hydrogen evolution and it is generally beneficial to separate the anode and cathode reactions through the use of a separator or membrane (porous or ion selective) for the following reasons:
• the catholyte is typically nitric acid which prevents any problems from occurring as a consequence of cross-over from the anolyte (electrolyte in the anode circuit) and catholyte compartments.
• the catholyte will gradually accumulate cations, e.g. metal ions from the anolyte, but it could be re-used periodically as a make-up solution for the nitric acid based decontamination solution.
• Typical separators/membranes are polymeric in nature and may comprise any of a number of commercially available alternatives which would be apparent to a skilled person such as, for example, a Nafion ® (su!phonated tetrafluoroethylene based fluoropolymer copolymer) cationic selective membrane or a microporous polyethylene separator.
• Nafion ® su!phonated tetrafluoroethylene based fluoropolymer copolymer
• cationic selective membrane or a microporous polyethylene separator.
• Polymeric membrane lifetimes are likely to be reduced in environments with a high radiation dosage during use, which can lead to accelerated damage and/or embrittlement.
• replacement of the membranes/separators may not be possible so that, in certain embodiments of the invention, the use of radiation resistant materials, such as ceramics (for example porous silicon nitride or porous alumina) may be necessary.
• a cell such as that which is illustrated in Figure 3 for use in a method according to the invention is unlike a conventional electrochemical chlorine generator, in that the majority reaction changes during the treatment of a batch of effluent.
• the cell would normally operate in batch mode but could be operated in a continuous flow-through mode if required.
• the predominant reactions result in mainly chlorine evolution and oxidation of organic materials.
• the degree of oxygen evolution increases until the stage at which the chloride has almost been removed from the system, at which point more than 99% of the anodic current is utilised for oxygen evolution.
• Mechanisms for the enhancement of the mass transport are found to be beneficial to the system, and such mechanisms may include, for example, high fluid velocities, the use of 3D electrodes, and the incorporation of inert mesh turbulence promoters.
• a cell 1 which comprises an anode 2 and a cathode 3 with membrane 4 being placed between the anolyte circuit and the catholyte circuit.
• the cell additionally comprises anolyte tank 5 and catholyte tank 6, valves 7, 8, 9 and 10 and pumps 11 and 12.
• effluent flows through valve 7 into anolyte tank 5 through which it passes before being pumped by pump 11 into cell 1.
• the anolyte then flows out of cell 1 and returns to anolyte tank 5 from which it is discharged via valve 9 for optional further treatment, whilst purge gas (for example, nitrogen or air) enters the tank and liberated chlorine and oxygen is vented therefrom.
• purge gas for example, nitrogen or air
• the liberated gases may be extracted from the vessel under negative pressure and diluted at a different location.
• the catholyte then flows out of cell 1 and returns to catholyte tank 6 from which it is discharged via valve 10 for re-use in the decontamination solution, whilst purge gas enters the tank and liberated hydrogen is vented therefrom.
• the processes according to the invention are batchwise processes wherein the liquors in the anolyte and catholye circuits are recirculated throughout the process and only discharged from valves 9 and 10 following completion of the process.
• the components of the cell including the electrodes and fluid circuits are adapted to handle the gas evolution, such that the evolved gases may be disengaged from the fluid streams and then suitably post-treated.
• Effluent which is released from the cell following the electrochemical treatment may optionally be further characterised and/or post-treated as previously indicated.
• Such treatment of the waste stream may, for example, involve the destruction of organic materials which do not form complexes in chloride/radioactive waste streams.
• the anode material of the cell should show stability in the electrolyte and in the presence of complexants.
• the material should be suitable for both oxygen and chlorine evolution and demonstrate low wear rates for both reactions, as well as low overpotentials for the reactions which are comprised in the method of the invention - specifically, for example, chlorine evolution and the oxidation of organic materials.
• the anode material should show higher overpotentials for other reactions, such as oxygen evolution.
• Typical materials for use as anode materials include boron-doped diamond, coated titanium (coated with oxides of metals, e.g. iridium oxide, mixed iridium/ruthenium oxide, tin oxide and lead dioxide) and bulk platinum.
• the optional chemical dosing step prior to feeding to the electrochemical cell may, for example, be employed for the removal of a contaminant, such as chloride, via chemical precipitation.
• a contaminant such as chloride
• Such an approach could be valuable in situations wherein the off-gas management facilities are inadequate to handle and clean up toxic gas discharges. If necessary, further polishing of chloride may be achieved through precipitation with silver nitrate to form silver chloride.
• removed contaminant/contaminated surface dissolved in a spent decontaminant stream which comprises nitric acid may be precipitated through the addition of NaOH and, optionally, other reagents.
• streams which result from the treatment of stainless steel surfaces will typically contain iron, nickel and chromium, and will thereby produce an iron hydroxide floe on treatment with NaOH, thus allowing for the iron to be removed as a precipitate.
• Such treatments are also successfully used for the removal of actinides, heavy metals and other metals such as strontium, which may either be removed as co-precipitates or by means of sorption onto floes.
• Such chemical precipitation procedures may also be augmented by the addition of at least one ion exchange material which could be tailored to the fingerprint of the contamination; thus, for example, hexacyanoferrate ion-exchange material may be used in instances wherein the contaminant comprises Cs-137.
• delivery of the relevant precipitation/neutralisation reagent can be achieved via in-line mixing in order to achieve rapid mixing and good floe characteristics, and to reduce space demands in the equipment.
• Such an operation could also most conveniently be applied before the treatment in the electrochemical cell in order to remove Fe from the feed to the cell, which would then eliminate the requirement for the use of a membrane (by removing the Fe 2+ /Fe 3+ redox couple).
• the mixing of reagents at the optional chemical dosing step may be achieved using in-line mixing controlled by algorithm.
• the optional system re-characterisation procedure may be employed in order to establish if further treatment is required, and the techniques employed would typically be the same as those which are appropriate to the initial system characterisation step.
• the final stage of the procedure involves post-treatment of the effluent produced from the electrochemical cell, and an embodiment of this step may be gleaned from Figure 2, wherein the stream is further treated locally to precipitate additional waste solids and associated contaminants - including, for example, radionuclides or radioactive materials containing alpha- and/or beta- and/or gamma-radiation, chlorides, total organic carbon (TOC) and heavy metals - which are subsequently removed prior to discharge of the remaining liquid effluent.
• the effluent discharged from the cell may be bowsered to a centralised treatment facility where post- treatment of the material may be effected.
• the method of the first aspect of the invention may typically be applied to nuclear decontamination processes which involve the treatment of surfaces to remove contamination as part of routine operations and plant shut downs, post-operational clean- out (POCO) procedures, and decommissioning. They are also used for the cleaning of non-nuclear surfaces, in applications such as the treatment of stainless steel to remove contaminants e.g. surface treatment post fabrication.
• POCO post-operational clean- out
• the successful application of the method according to the first aspect of the invention may be gleaned from Figure 4 which illustrates the successful removal of organic carbon and chloride from a used decontamination solution. The Figure shows the reduction in total organic carbon content and chloride concentration against the electrolytic charge which is passed (in Farads).
• the starting solution was 0.75 I of 0.1 M HCI, 3M HN0 3 and 1 g/l of SGD3 (a commercial complexant mixture containing the chelators citric acid and EDTA).
• the applied current was 8A and a divided cell was used with boron doped diamond electrodes.
• both the chloride content and the TOC content initially dropped rapidly and then the rate of reduction reduced as their concentration dropped. Both TOC and chloride content continued to fall until the chloride content was reduced to around 5 ppm and the TOC content reduced to around 50 mg/l. It should be pointed out that the remaining organic carbon content is probably not the chemicals which were originally present but, rather, comprises degradation products without the complexing functionality.
• Methods according to the second aspect of the invention are applicable to a range of process effluent treatment operations where the effluent has become contaminated, and are particularly successfully applied to the destruction of organics (e.g. complexants), the destruction of organics from trade or pharmaceutical wastes, the removal of chloride from process effluent, and the removal of chloride from radioactive contaminated oils from drilling.
• organics e.g. complexants
• chloride e.g. complexants
• Methods according to the invention allow for the use of reagents to facilitate increases in decontamination rate/efficiency to minutes/hours compared with hours/weeks in the case of the methods of the prior art. Furthermore, the relative volumes of reagents which are employed is dramatically reduced to tens of litres compared with thousands of litres in the case of prior art methods. The processes also allow for reagents to be recycled.
• the electrochemical treatment may be carried out using cells which are portable, so that decommissioning activities may be decoupled from infrastructure and adapted to produce an effluent that is compatible with existing infrastructure.
• the method of the invention is, therefore, flexible and adaptable to the system to be treated.
• the method of the first aspect of the invention finds particular applicability in the treatment of substrates which are contaminated with radioactive contaminants and they bring together the ability to use nitric acid and chloride bearing reagents as decontamination agents in combination with complexants by facilitating the removal of components which have downstream processing implications and providing a post-treatment option to precipitate the stripped material and remove radioactivity.
• the method when the method is used in combination with low volume delivery of reagent (e.g. using an atomised reagent), the volume of reagent is substantially reduced when compared to the methods of the prior art, thereby allowing for fine tuning of decontamination and minimisation of effluent volume, and consequently limiting the size of treatment unit which is required.
• the method also provides the facility to deploy aggressive reagents in limited controlled quantities where plant integrity is of concern to such decontamination operations.

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