Recovery of plutonium from polymeric waste matrices using supercritical fluid extraction
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Abstract:
Polymers are widely used materials and are indispensable in handling radioactive materials in fumehoods, gloveboxes, etc. Supercritical fluid extraction (SFE) technique is widely employed for the removal of radioactive contaminants from various matrices using supercritical carbon dioxide (Sc-CO2) modified with suitable ligands as an extraction medium. In the present study, recovery of plutonium from various polymeric matrices, such as neoprene, polyvinyl chloride (PVC) and surgical gloves has been demonstrated using Sc-CO2 modified with n-octylphenyl N,N-diisobutyl carbamoylmethylphosphine oxide (CMPO) in methanol. The matrix was initially subjected to neat Sc-CO2 extraction to prevent co-extraction of organic compounds during SFE of plutonium; in the initial extraction with Sc-CO2, organic compounds added as additives to the polymeric matrix were extracted. In the initial studies, SFE method was developed for the complete recovery of plutonium from simulated polymeric waste matrices. Subsequently, the actual waste, i.e. plutonium present in PVC matrix was processed from a 0.1 L extraction vessel for its recovery. The plutonium recovery was found to be ∼97% from the actual PVC waste matrix. The technique was also demonstrated for the recovery of important actinides e.g. americium from simulated neoprene waste matrix. As the disposal of polymer waste is of major concern in nuclear waste management, the SFE technique developed in the present study offers a potential opportunity for the recovery of actinides with generation of minimum secondary waste.Keywords:
Supercritical fluid extraction
Supercritical water oxidation
The characteristics of supercritical water,the principles and advantages of supercritical water oxidation are introduced,the features of applications of supercritical water oxidation technique in waste water treatment and current situation application progress in industry are also reviewed.
Supercritical water oxidation
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Supercritical Water Oxidation (SCWO) employs water which exceeds supercritical conditions (374℃ at 22MPa). This method utilizes the strong reactive solvent characteristics of supercritical water and can completely decompose organic materials in supercritical water. As a hazardous and refractory chemicals, decomposition of PCBs by SCWO was demonstrated using the continuous reactor with pressure balancing. This reactor has been successfully operated to decompose both PCBs and dioxins completely under the conditions of 630℃ and 23.5MPa.
Supercritical water oxidation
Refractory (planetary science)
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The characteristics of homogeneous catalytic reactions in supercritical fluids and latest advances in its application in homogeneous catalytic reactions were reviewed, including homogeneous hydrogenation and hydroxylation in supercritical CO_2, and supercritical water oxidation (SCWO).
Supercritical water oxidation
Homogeneous Catalysis
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Supercritical water oxidation is a new technology that takes supercritical water as reaction medium and thoroughly destroys organic matter.The basic theory,process and research status of supercritical water oxidation are introduced.Some key issues in its applications and the measures of improving the technique are also analyzed.
Supercritical water oxidation
Environmentally Friendly
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The destruction of hazardous chemical wastes by oxidation in supercritical water is a promising new technology which has several advantages over conventional methods of toxic chemical waste disposal. Although the feasibility of the supercritical water oxidation process has been demonstrated, there is little kinetic information available on the underlying reaction mechanisms. We have recently determined the oxidation kinetics of several model compounds in supercritical water, and now report on our results of the oxidation of methanol, a common industrial solvent, in supercritical water. Global kinetic expressions are presented and our attempts to model the reaction using a free—radical mechanism with 56 elementary reactions are discussed. The inability of the elementary reaction model to represent oxidation in supercritical water is demonstrated and future model modifications are discussed.
Supercritical water oxidation
Elementary reaction
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Supercritical fluid extraction is the most effective and efficient way to extract valuable constituent botanicals. Supercritical Fluid Extraction (SFE) is the process of separating one component (the extractant) from another (the matrix) using supercritical fluids that is CO2 as the extracting solvent. CO2 is the king of extraction solvents for botanicals. Extraction conditions for supercritical CO2 are above the critical temperature of 31°C and critical pressure of 74 bar. Supercritical fluids are highly compressed gases, which have combined properties of gases and liquids in an intriguing manner. Supercritical fluids can lead to reactions, which are difficult or even impossible to achieve in conventional solvents. It is a fast process completed in 10 to 60 minutes. A supercritical fluid can be separated from analyte by simply releasing pressure, leaving almost no trace and yields a pure residue.
Supercritical fluid extraction
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Affecting factors and kinetics by catalytic supercritical water oxidation were summed up,and the importance of catalyst in the process of catalytic supercritical water oxidation was emphasised. In addition,general kinetic model for catalytic supercritical water oxidation was deduced. Kinetic parameters and reacting conditions of organic compounds including phenol ,acetic acid and pyridine are expounded. The performance of complex compounds by catalytic supercritical water oxidation was discussed based on the above results. All of which offers theoretical guidance for waste water treatment. In the end,some suggestions were proposed for scale-up and engineering utilization of catalytic supercritical water oxidation.
Supercritical water oxidation
Catalytic Oxidation
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Supercritical water oxidation of DDNP wastewater was performed in a batch reactor with oxygen as the oxidant at the temperature ranged from 703 to 823 K,the pressure of 24 MPa and residence time ranged from 10 s to 50 s.The simulated wastewater of DDNP in supercritical water oxidation was studied and the COD removal rate reaches 99%.The macro-kinetics with the COD removal rate of wastewater by supercritical water oxidation was established.The results show that supercritical water oxidation is efficient for the treatment of DDNP waste water.In supercritical conditions,the COD removal rate increases with the increase of temperature and residence time of the reaction.In the case of oxidant excess twice,the reaction of supercritical water oxidation of DDNP is 1.33 order in organics and 0.21 order in oxygen.The activation energy Ea is 30.7 kJ/mol and the frequency factor A 61.97 s-1.
Supercritical water oxidation
Batch reactor
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Characteristics of supercitical fluid is introduced. A review is given on the application of the superceritical fluid technology (supercritical fluid cleaner production, supercritical fluid extraction, supercritical fluid chromatography and supercritical water oxidation) in the environmental protection and pollution control in the paper.
Supercritical fluid extraction
Supercritical water oxidation
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