Extraction of heavy metals from fly ash and sand with ligands and supercritical carbon dioxide

This project further develops supercritical fluid extraction as an industrial remediation process for soil and other heavy-metal-cont,aminated solid materials. In this study, divalent metals such as Zn2+, Cu2+, Pb2+, Cd2+, and Cr3+ removed from sand and fly ash using CO2. When the solvating power of supercritical CO2 is combined with the metal ion complexing power and selectivity of organic ligands, a clean alternative to conventional liquid-liquid and liquid-solid extraction is obtained. Extraction technologies are required, which not only remove the mobile or total fraction of metals but also maintain the matrix's morphology and structure. In particular, the reuse of fly ash as construction or landfill material becomes possible with the application of supercritical fluid technology. In a study with spiked sand samples, the effect of pressure, the humidity of the contaminated material, and the use of methanol as the entrainer in CO2 on the extraction efficiency is investigated. Influences of the type of complexing ligands is studied with both fly ash and sand samples. It is shown that the use of methanol as the entrainer and the humidity have strong effects on the metal extraction.