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

This project further develops supercritical fluid extraction as an industri al remediation process for soil and other heavy-metal-cont,aminated solid m aterials. In this study, divalent metals such as Zn2+, Cu2+, Pb2+, Cd2+, an d 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 sele ctivity of organic ligands, a clean alternative to conventional liquid-liqu id and liquid-solid extraction is obtained. Extraction technologies are req uired, which not only remove the mobile or total fraction of metals but als o maintain the matrix's morphology and structure. In particular, the reuse of fly ash as construction or landfill material becomes possible with the a pplication of supercritical fluid technology. In a study with spiked sand s amples, the effect of pressure, the humidity of the contaminated material, and the use of methanol as the entrainer in CO2 on the extraction efficienc y 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 .