Experimental Analysis of the Supercritical CO2-Based Circulation Type for the Remediation of Kilogram-Scale Soil Samples from Metal Ions

Supercritical carbon dioxide (sCO2) has been proposed as one new alternative separation medium for soil remediation due to its preferrable dissolution properties and environmentally friendly nature. This study is focused on the effects of operation parameters, such as separation pressure, temperature and processing time, on the extraction efficiency of inorganic contaminants (chromium; arsenic) from soil samples by using the newly established kilogram-scale prototype. The prototype system was operated with Cyanex 302 as a chelating agent and methanol as a co-solvent. The extraction efficiency (EE) of chromium (Cr) is experimentally identified to be 97.98% at 35 MPa and 75 °C (with 60 min processing time), while it is found to drop quickly at low temperature and pressure (only 40% under 20 MPa and 35 °C). The EE of arsenic (As) has been identified generally with high efficiency, over 95% for most cases. For chromium (Cr), 30 MPa and 55 °C or higher parameter ranges are recommended to maintain an efficiency over 90%.