Subcritical and supercritical fluid extraction of heavy metals from sand and sewage sludge

Demetalization of Pb, Ni, Zn, Cu and Cr heavy metal ions from sea sand and real samples of sewage sludge by subcritical water and supercritical carbon dioxide was investigated. Experimental parameters such as temperature, pressure, extraction time in the static and dynamic mode and sampling were optimized in order to determine the suitable conditions for high removal of metals. The best extraction efficiencies were obtained using acetyl acetonate as a chelating agent in both subcritical water and supercritical CO2 extractions for real and artificial samples. Samples collected from extraction system using both subcritical water and supercritical carbon dioxide were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The highest recoveries obtained from real samples for Cr, Cu, Ni, Pb and Zn were 77.25, 95.1, 84.82, 94.92 and 98.39 %, respectively, using the chelating agent in the subcritical water extraction.