Solvent Extraction For Oil Removal From Heavily Contaminated Soils

Crude oil is an extremely complex mixture of hydrocarbons，and most oilcomponents have the potential risk to human health and environment. At present,Soils contamination with crude oil have been a global environment problem, and anumber of technologies have been developed for remediating soils contaminated withpetroleum hydrocarbons. Solvent extraction is a promising technology for soilsremediation. Such method can be efficient in removing hydrophobic organiccontaminants from polluted soils. Meanwhile, the contaminants can be recovered andrecycled.The soil samples used in this study were obtained from Gudong Oil ProductionPlant at the Shengli Oil Field located in Shandong Province, China. The oil contentwas98000mg·kg^-1and15priority polycyclic aromatic hydrocarbons weredeterminated. The four oil fractions analysis results showed that the total content ofheavy oil fractions （resins and asphaltenes） was more than50%in petroleumcontaminants.Based on Hansen solubility parameters （HSP） and the basic principle （“likedissolves like”） in solvent selection，the relations between HSP of solvent and theextraction efficiency in removing oil pollutants from soils were investigated. The HSPsphere of high-efficiency solvent was RM=3.2and the fractional parameters spherewas dispersion component fractional parameter （fd）62-85, polar component fractionalparameter （fp）2-20and hydrogen bonding component fractional parameter （fh）7-22.According to the HPS sphere, a series of mixed-solvents with character of low-toxic,acceptable cost, high efficiency and environmental friend were developed.The extraction process for oil contaminants removal from polluted soils wasinvestigated. The oil removal decreased with the increasing of the moisture content inthe polluted soils. The ratio between solvent and soil played a significant role insolvent extraction and results showed that the effciency would increase following thehigher solvent soil ratio. The desorption of oil from soils took place according to thelinear isotherm and the extraction efficiency was calculated as a function of thesolvent soil ratio. At the optimal conditions （solvent soil ratio6:1）, approx90%ofsaturates, aromatics, resins, and60%of asphaltenes were removed using the mixturesof hexane and acetone （25vol%）. The multistage crosscurrent and countercurrentextraction could obviously enhance the removal efficiency of oil pollutants. In order to reduce the solvent consuming, the multistage extraction with small solvent soilratio was necessary to achieve the high removal of oil.The application of water washing technology for removing and recycling thesolvent remained in soils after extraction was investigated. The residual oil pollutantsin soils played a significant role in water washing and could obviously decrease theremoval rate of solvent. With the lower interfacial tension and the solubilization ofsurfactant solution, surfactant enhanced washing could effectively increase theremoval rate of solvent remained in soils. After disposing，the content of solventwhich remained in soils dropped down to1%and the recovery rate of hydrophobicorganic solvent exceeded to95%. Meanwhile, the majority of surfactant solutioncould be recycled and reused in washing process.Base on the above experimental research, the technological process that usingsolvent extraction for heavy crude oil removal from contaminated soils has been built.The environment evaluation results showed that this technique could effectivelyreduce the risk of pollutants.