Recovery of indium from etching wastewater using supercritical carbon dioxide extraction

This study presents supercritical carbon dioxide (scCO2) extraction as an inherently safer and cleaner method for the recovery of indium (In) from the real etching wastewater obtained from indium tin oxide (ITO) etching process. Efficient chelation-supercritical fluids extraction (SFE) from etching wastewater was obtained at 80 °C, a pressure of 20.7 MPa, and with 15 min static extractions followed by 15 min dynamic extraction. The extractions were performed using unmodified scCO2 in the presence of the fluorinated β-diketone chelating agent, 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (HFOD). Percentages of indium recovery from etching wastewater were between 90.8% and 100.3% (n = 6) with relative standard deviations of <10%. The accuracy of the procedure was confirmed by determining indium levels in a single element standard solution. The developed method was applied to the analysis of real etching wastewater samples as well as to a commercially available ITO etching reagent (ITO-06SD) with satisfactory results.