| With the rapid development of the industrialization,radioactive spent engine oils are inevitably produced in the nuclear fuel processing plants,nuclear research institutes,and nuclear power plants.These spent engine oils cannot be easily treated and are temporarily stored due to high radioactivity,oxidation resistance and poor biodegradability.Electrochemical advanced oxidation process presents great potential due to its high catalytic degradation activity,ease of automation and no secondary pollution.In this thesis,the self-made boron-doped diamond film(BDD)electrode was employed as electrochemical anode to degrade the simulated radioactive spent engine oils(hydraulic oil).This may provide new ideas for the disposal of radioactive spent engine oils.Considering the hydraulic oil is completely immiscible with water,it is not in contact with the BDD electrode and the strong oxidants produced by BDD anode at all during the electrochemical oxidation process,so that it is difficult to be oxidized.Therefore,in this thesis,firstly,in order to obtain a stable hydraulic oil emulsion,we needed to systematically carry out the emulsification pretreatment of hydraulic oil.Secondly,the self-made boron-doped diamond film electrode was employed as the electrochemical anode to degrade the hydraulic oils emulsion.During the electrochemical oxidation process,observing and analyzing the physical state changes and Chemical Oxygen Demand(COD)values of the hydraulic oil emulsion.At the same time,considering that hydraulic oil has extremely high oxidation resistance,the service life of the electrode material is also a problem in oxidizing environment that needs to be paid attention to in this thesis.So,we also studied the microstructure evolution behavior of BDD electrodes during electrochemical oxidation process.This will be important for us to develop high quality long-life BDD electrodes.A series of studies indicates:(1)In the process of emulsification of hydraulic oil using a single emulsifier,the AEO nonionic surfactant has an obvious better emulsification effect than other types of emulsifiers,and could obtain a uniform and stable emulsion when emulsifying hydraulic oil.Using BDD electrode to carry out electrochemical oxidation electrolysis of hydraulic oil emulsion emulsified by AEO emulsifier.The trend of COD values of electrolyte during the 30 h of electrolysis was not straight down,but increased to 1,064,500 mg/L from the initial 712,800mg/L after 20 h of electrolysis and then reduced to 916,000 mg/L,which indicates the amount of reducing substances that can be measured in the electrolyte first increased and then decreased.However,in the electrolysis process,the AEO emulsifier is degraded prior to the hydraulic oil,causing the electrolytic emulsion to break,indicating that the stability of electrolyte emulsified by a single emulsifier is not ideal in the electrolysis process.(2)In the process of electrochemical oxidation electrolysis,the BDD electrode interacted with the emulsion of hydraulic oil which is emulsified by the mutual combination of nonionic emulsifier(OE-2)and anionic emulsifier(sodium dodecyl sulfate).Under the condition of magnetic stirring,the COD values of the hydraulic oil emulsion increasedslightly with the increase of electrolysis time,from the initial 276,000 mg/L to 284,000 mg/L after 30 h of initial electrolysis;then the COD value of the emulsion decreased rapidly with the increase of electrolysis time.After 117 h of electrolysis,the COD value decreased to115,800 mg/L.Compared with the initial emulsion,the COD value removed by electrochemical oxidation treatment of BDD electrode was approximately 160,000 mg/L.Besides,the theoretical COD value of the intermixed emulsifier(sodium dodecyl sulfate and OE-2)is only 69,000 mg/L.So,the COD value of the organic matter removed by the experiment is significantly larger than that of the pure emulsifier,which indicates that a small portion of the hydraulic oil was electrochemically oxidative degraded in the experiment.At the same time,the experimental results can also indicate that the effect of emulsifier obtained after mating is significantly better than using a single emulsifier.In the electrolysis experiment under ultrasonic conditions,the COD value of the electrolyte also showed a small increase and then a rapid decline,and in similar electrolysis time,more hydraulic oil could be electrochemically oxidized under the condition of magnetic stirring than ultrasound.Under the condition of magnetic stirring,the change trend of the COD value of the electrolyte to which the intermixing emulsifier was intermittently added still showed a slight increase and then a downward trend.But unfortunately,the electrolyte still demulsified during the electrolysis process,failing to completely degrade the hydraulic oil.(3)With the increase of electrochemical oxidation time,diamond grains of BDD electrode would be transferred from the irregular octahedron into mesa structure,indicating strong(111)surface etching.At the same time,the film thickness is gradually thinned,and the film thickness is reduced by about 1.55 ?m after 240 h of electrolysis.The grain size gradually decreases,and the surface roughness also decreases from 80 nm to 23 nm.Furthermore,X-ray diffraction and Raman spectroscopy analysis indicate that the phase and chemical bond state of the BDD electrode have not changed significantly.Correspondingly,the BDD electrode still kept well electrochemical activity and good cyclic stability. |
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