Supercritical CO₂ Extraction Of Polycyclic Aromatic Hydrocarbons And Cadmium From Soil With Co-solvents And Chelating Agent

In recent years,the compound pollution of polycyclic aromatic hydrocarbons(PAHs)and heavy metals in the soil had gradually attracted people’s attention.Supercritical CO2 extraction was environmentally friendly and efficient,and had good application prospects in the field of soil remediation.However,the ability of CO2 to extract PAHs and heavy metals from soil was limited by the lower solvating power of CO2.In order to improve the extraction efficiency of PAHs,the effects of temperature,pressure and CO2 flow rate on the extraction process were investigated.The results showed that the optimal temperature for extraction was 65℃;The extracted fraction of PAHs rose when the pressure increased from 16 MPa to 20 MPa;Increasing the CO2 flow rate had little effect on the extracted fraction of PAHs.Co-solvents were added to enhance the ability of supercritical CO2 to extract PAHs from soil.The results showed that the addition of dodecyl acetate(DAC)or benzyl acetate(BAC)could promote the dissolution of PAHs in supercritical CO2 and increase the extracted fraction of PAHs.A mathematical model for supercritical CO2 extraction of PAHs was established,and the average relative deviation between the experimental values and the calculated values were lower than 6.5%,indicating that the model could describe the extraction process well.In addition,the effects of temperature,pressure,concentration of chelating agent,and the combination of co-solvents and chelating agent on the extraction of PAHs and cadmium were investigated.The results showed that the co-solvents had significant effects on the extraction rate of PAHs and cadmium.With the chelating agent Cyanex302,the polar co-solvent ethanol and the non-polar co-solvent(DAC or BAC),more than 90%of PAHs and 70%of cadmium could be extracted from soil by supercritical CO2 extraction.