Microwave Thermal Remediation Of Petroleum-Contaminated Soil Enhanced By Carbon Materials

Microwave thermal remediation enhanced by carbon materials(MTREC) was explored for decontamination of petroleum-contaminated soil.The advantage of rapid,selective and simultaneous heating of microwave heating technology was taken to clear up the soil rapidly and to recover the oil contaminant efficiently.The process was applied to the remediation of soils contaminated with different petroleum contaminants,such as diesel oil and crude oil,to investigate the possibility of its practical application.The following works were carried out in this dissertation:1.Microwave thermal remediation of the soil contaminated with 10.20 wt%diesel oil enhanced by granular activated carbon(GAC) was explored.The study on the microwave heaitng of soil and its enhancement of GAC were performmed,and the results revealed that soil could be heated to an appropriate temperature in microwave field when GAC was added. Some process parameters and oil recovery of the remediation were investigated.It was shown that,using the technics of protecting by inert gas(N₂),heating with microwave irradiation and condensation of gas products,when 5.0 wt%GAC mixed in,the soil could be heat to about 500℃within 10 min and that the contaminated soil could be remediated by this microwave thermal process such that more than 99%contaminant removal could be achieved.The analysis performed on the recovered oil indicated that up to 96.2%of diesel oil contaminant could be recovered during the remediation without changing obviously in chemical composition and physical properties,compared with the original oil.In addition,the experimental results showed that GAC could be reused in enhancing the microwave heating of soil with a little mass loss and that the remediation process did not destruct the soil significantly.2.Thermal remediation of the practical soil contaminated with about 8 wt%crude oil using microwave heating enhanced by GAC and carbon fiber(CF) was explored respectively. The results of GAC-enhanced microwave thermal remediation revealed that,using the technics of protecting by inert gas,heating with microwave irradiation,proper decompressing with vacuum and condensation of gas products,when 10.0 wt%GAC was mixed into the soil, more than 99%of the oil contaminant could be removed within 15 min,at the same time, about 91%crude oil in soil could be recovered. The experiment results of CF-enhanced microwave thermal remediation indicated that, when mixed into soil,CF,for its fiber shape and electric condutivity,could strongly increase the effective dielectric loss factor of the soil sample as terms of electrical conduction loss and Maxwell-Wagner loss,thereby,strongly enhancing microwave heating of soil more efficiently than other accepted microwave absorbers.When 0.10 wt%CF mixed in,the soil could be heated to approximately 700℃within 4 min using 800 W of microwave irradiation. And correspondingly,more than 99%removal efficiency of the oil contaminant could be obtained under some conditions.Investigation on the recovered oil of the process showed that the crude oil in the contaminated soil could also be removed and recovered without significant changes in chemical composition during the remediation and that the recovery efficiency could be more than 94%.3.Removal mechanisms of the contaminants during microwave thermal remediation of the contaminated soil enhanced by carbon materials were explored with different model contamiants of volatile,semi-volatile and non-volatile compounds.The experiment results showed that the removal mechanisms of the contaminant were relevant with its volatility and concentration in soil.For volatile and semi-volatile contaminant,no matter whether the concentration was low or high,the main removal mechanisms were the physical removal such as microwave-induced steam distillation(MISD),evaporation and thermal desoption without pyrolysis happenning.For non-volatile contaminant,when the concentration was low(e.g. about 1 wt%),pyrolysis played an important role in contaminant removal with some thermal desorption and a little MISD;when the concentration was reletivly high(e.g.about 10 wt%), however,evaporation and thermal desorption played an important role in contaminant removal with a little MISD and pyrolysis.4.MTREC was compared with other thermal remediation process on the decontamination of crude oil-contaminated soil.Comparing with MISD,MTREC could be used in a wider range.It could remove non-volatile contaminant in soil besides volatile and semi-volatile contaminant.Comparing with conventional thermal remediation of electric heating,MTREC could remediate the contaminated soil successfully with less energy comsuption and minor destruction of the contaminant,which may be good for the recovery of the oil contaminant.