METHOD FOR THE DESTRUCTION OF ORGANIC MATERIAL

Abstract

A method and apparatus for the electrochemically mediated oxidation of radioactive organic materials comprising the step of mixing aqueous phase that contains the oxidising agent with immiscible non-aqueous phase containing organic material that is to be destroyed in a chamber fitted with a contactor to integrate the aqueous phase with the organic material.

Claims

1. An electrochemically mediated method for the oxidation of organic material comprising the step of mixing aqueous phase that contains an electrochemically generated oxidising agent with immiscible non-aqueous phase containing organic material that is to be destroyed in a chamber fitted with a contactor to integrate the aqueous phase with the organic material.

2. The electrochemically mediated method for the oxidation of organic material according to claim wherein the non-aqueous phase is in the form of a liquid and the contactor comprises one or more mixing devices.

3. The electrochemically mediated method for the oxidation of organic material according to claim 1, wherein the non-aqueous phase is in the form of a liquid, the contactor comprises one or more mixing devices, and the one or more mixing devices comprise one or more mechanical stirrers, rotating shear mixers, shedder plates, static in pipe mixers, turbulent pipe flow eductors, and jet impingement devices.

4. The electrochemically mediated method for the oxidation of organic material according to claim 1, in which the non-aqueous phase is in the form of a liquid, the contactor comprises one or more mixing devices, and the non-aqueous phase containing the organic material is introduced into the aqueous phase immediately downstream of an electrochemical cell.

5. The electrochemically mediated method for the oxidation of organic material according to claim wherein the non-aqueous phase is in the form of a solid and in which the contactor comprises one or more of a fluidized bed, a fluidized bed with inert particulates, a fluidized bed with a spray nozzle, and a fluidized bed with a filter bed.

6. The electrochemically mediated method for the oxidation of organic material according to claim 1, in which the mixing is augmented by the application of gas sparges or ultrasound or sonic waves.

7. The electrochemically mediated method for the oxidation of organic material according to claim 1, in which ultrasound and sonic waves are applied to a mixing vessel and or in a flow pipe immediately downstream of an electrochemical cell.

8. The electrochemically mediated method for the oxidation of organic material according to claim 1, in which the organic material is dispersed into the aqueous phase to form a dispersion, and the degree of dispersion of the organic material into the aqueous phase is arranged to be intermediate between a coarse and a fine emulsion.

9. The electrochemically mediated method for the oxidation of organic material according to claim 1, in which a surface area of an interface between aqueous and non-aqueous phases is matched to both a concentration of the oxidising agent and to a rate of breakdown of the organic material.

10. The electrochemically mediated method for the oxidation of organic material according to claim 1, in which the electrochemically generated oxidising agent is generated in an electrochemical cell containing an electrolyte which includes one or more of the following elements, Ag, Cl, Br, Ce, and Co.

11. The electrochemically mediated method for the oxidation of organic material according to claim 1, in which a rate of addition of organic material is controlled by measuring a rate of evolution of gas.

12. The electrochemically mediated method for the oxidation of organic materials according to claim 1, further including an electrochemical cell generating or regenerating electrochemical aqueous oxidation material and a mixing chamber housing the contactor in which the aqueous oxidation material is mixed using the contactor with organic material to be mediated.

13. The electrochemically mediated method for the oxidation of organic materials according to claim 12, in which contact between the aqueous oxidation material and the organic material is immediately after introduction of the aqueous oxidation material into the mixing chamber.

14. The electrochemically mediated method for the oxidation of organic materials according to claim 12, further including a coalescer to promote at least partial separation of aqueous phase material from non-aqueous phase material.

15. The electrochemically mediated method for the oxidation of organic materials according to claim 12, further including a coalescer to promote at least partial separation of aqueous phase material from non-aqueous phase material, wherein the coalescer comprises a filter screen, mesh, foam coalescer, plate-coalescer, hydro-cyclone or separator tank.

16. The electrochemical mediation method for the oxidation of organic materials according to claim 12, in which the electrochemical cell comprises an ion exchange membrane in which an anolyte is the aqueous solution of an oxidising species and a catholyte is nitric acid.

17. The electrochemically mediated method for the oxidation of organic materials according to claim 12, further including a coalescer to promote at least partial separation of aqueous phase material from non-aqueous phase material, and wherein the contactor is combined in a single chamber with the coalescer.

18. The electrochemically mediated method for the oxidation of organic materials according to claim 12, further including a coalescer to promote at least partial separation of aqueous phase material from non-aqueous phase material, and wherein the contactor is combined in a single chamber with the coalescer, and the organic material is recirculated and destroyed within the single chamber.

19. The electrochemically mediated method for the oxidation of organic materials according to claim 12, in which of a rate of addition of organic material is controlled by measuring a rate of evolution of gas.

20. The electrochemically mediated method for the oxidation of organic materials according to claim 1, further including an electrochemical cell for generating or regenerating electrochemical aqueous oxidation material and a mixing chamber housing the contactor.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] The figures show two illustrative examples of apparatus employing the invention. However, the invention is not in any way limited to the configurations illustrated. In the figures:

[0024] FIG. 1 is a schematic drawing of one embodiment of the invention having a vertically orientated mixer-settler chamber; and

[0025] FIG. 2 is a schematic drawing of a second embodiment of the system with a horizontally orientated mixer-settler chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] In FIG. 1, vessel 1 which is the body of the vertically orientated mixer-settler chamber. A mixing chamber 2 is provided with a stirrer or other contactor device 3. Contaminated non-aqueous organic material is added by injection into pipe 11 or directly into the mixing chamber 2. An aqueous phase containing the oxidising species, nitric acid, is continuously added to the mixing chamber 2 through pipe 4. The mixed solution passes downwards through a coalescer unit 5. Non-aqueous phase is captured in the coalesce unit and floats upwards whilst the aqueous phase moves downwards and exits the vessel through pipe 6. Pump 7 draws the aqueous phase out and pumps it through a divided electrochemical cell 8 where the oxidation mediator is oxidised and then back into the mixing chamber 2 via pipe 11. The balancing catholyte solution passes through the other side of divided cell 8 and through a regeneration device 9 which replenishes the higher oxidation state catholyte. A gas extraction system 10 is provided to remove the off gases and allow the destruction rate to be monitored by measuring the amount of carbon dioxide produced.

[0027] A second embodiment of the system is shown in FIG. 2. A vessel 1 is the body of a horizontally orientated mixer-settler chamber. A mixing chamber 2 is agitated with a stirrer 3. Contaminated non-aqueous phase is added directly to the mixing chamber 2. An aqueous phase containing the oxidising species (nitric acid) is continuously added to the mixing chamber 2 through pipe 4. A mixture of both phases is drawn from the mixing chamber by pump 12 and pumped into a separate coalescer unit 5 which has a coalescer device 5A. The coalesce device 5A comprises a filter screen, mesh, foam or plate-coalescer device, hydro-cyclone or separator tank.

[0028] The heavy aqueous phase settles to the bottom of the settling chamber 5 and drawn out of the settling chamber through pipe 6 and pumped by pump 7 through one side of a divided electrochemical cell 8 and thence back into the mixing chamber through pipe 4. The separated light phase containing residual organic material flows over a weir 13 back into the mixing chamber 2. The balancing catholyte solution passes through the other side of divided cell 8 and through a regeneration device 9 which replenishes the higher oxidation state catholyte. A gas extraction system 10 is provided to the off gases and allow the destruction rate to be monitored by measuring the amount of carbon dioxide produced.

[0029] Other embodiments of the components of the system will be apparent to those skilled in the art.

EXAMPLES OF USE OF THE INVENTION

[0030] The following are examples of the destruction of organic materials using apparatus of the present invention.

Example 1 the Destruction of Contaminated Hydraulic Oil

[0031] Hydraulic oil was treated using a solution of silver nitrate in nitric acid in experiments to show the benefit of this invention. The oil was substantially oxidised to carbon dioxide using a solution of 0.2 mol % silver nitrate in 6 M nitric acid was used as the anolyte. The test was conducted with a 1 litre of electrolyte in both the anolyte and catholyte circuits of an electrochemical divided electrochemical cell the catholyte used contained 6 M nitric acid with no silver nitrate addition. The cell had a 25 square centimetre area electrode area and the separation membrane used is an ion exchange membrane. The cell was operated with a DC current and similar flow rates in both electrolyte streams, the current density used was 4000 A per square metre. Both electrolytes were heated to 333 K and known aliquots of oil were added to the anolyte solution. The anolyte was circulated through a reaction vessel where the return to the cell was at the base of the vessel. The analysis of the carbon dioxide quantities produced was converted into a current efficiency by matching the moles of Ag(II) generated with the carbon dioxide production.

[0032] Two experiments were conducted. In the first experiment a standard overhead lab stirrer was positioned at the interface between the oil and aqueous immiscible phases and the cell operated with the electrolyte feed entering the vessel into the aqueous phase below the oil phase. In this experiment run over 3 hours the cell voltage stabilised at 4 V and the overall current efficiency was 12% with the remaining species decaying in the aqueous phase. In the second experiment several changes were made to the experiment coalescence media was included at the base of the reaction vessel to remove oil prior to return to the electrochemical cell, the oil addition was made into the flow of anolyte exiting the electrochemical cell and subsequently passed through an inline static mixer before entering the reaction vessel and, the flow from the cell entered the reaction vessel above the liquid level and was distributed across the oil layer by means of a shedder plate set to generate the appropriate level of dispersion of the fluid. In this experiment operating over 3 hours the current efficiency was over 85% the voltage in the cell dropped to 2.6 V while maintaining the same current density. These results show the improvement achieved by controlling the mixing of the immiscible fluids and the reduction in voltage is due to reduction in organic species entering the electrochemical cell.

Example 2 the Destruction of Contaminated Ion Exchange Resin Beads

[0033] Ion exchange resin was treated using a solution of silver nitrate in nitric acid. The ion exchange resin was arranged as a fluidised bed, fluidised by the incoming stream of aqueous phase. Radioactive contamination was simulated using a trace non-radioactive metallic element present in a suitable form. The resin beads were substantially oxidised to carbon dioxide. The trace element was substantially transferred into the aqueous solution in a form suitable for subsequent treatment and recovery by means of conventional nuclear processing such as precipitation or solvent extraction.

Example 3 the Destruction of Contaminated Synthetic Glove Material

[0034] Shredded glove material was treated using a solution of silver nitrate in nitric acid. Radioactive contamination was simulated using a trace non-radioactive metallic element present in a suitable form. It was found that a relatively short treatment time gave a sufficient degree of decontamination for the reclassification of the waste material to a grade more easily disposed of. Longer treatment resulted in the glove material being substantially oxidised to carbon dioxide. The trace element was substantially transferred into the aqueous solution in a form suitable for subsequent treatment and recovery by means of conventional nuclear processing such as precipitation or solvent extraction.

Example 4 the Destruction of Contaminated Organic Matter Immobilised onto Inert Particles

[0035] For some contaminated material it may be advantageous to immobilise it onto solid particles of high surface area which are present in the contactor as a packed bed or fluidised bed. In this example an organic oil of high viscosity was distributed over the surface of silica beads. The beads were packed into a column through which the oxidising aqueous phase flowed. A non-radioactive metallic element present in a suitable chemical form was substantially transferred to the aqueous phase.

[0036] In the above examples a metallic non-radioactive marker was used as a substitute for a radioactive species. In live systems according to the invention, the radioactive species are indeed transferred into the aqueous (nitric acid) phase. They will remain in the aqueous phase and accumulate there until the aqueous phase is sent for conventional nuclear treatment.