Indium and its compounds have numerous industrial applications in the manufacture of liquid crystal displays and semiconductors. Indium compounds are considered hazardous materials that can be carcinogenic. Supercritical fluid extraction using carbon dioxide was utilized in this research as a sample pretreatment step for extraction of indium(III) ions from the synthetic etching wastewater of the semiconductor and optoelectronic industries. Several parameters, including various chelating agents, pH of solution, molar ratio of chelating agent to indium(III) ions, temperature and pressure were systematically investigated. Indium(M) ions were extracted by supercritical CO2 Combined with several various types of chelating agents including beta-diketone (AcAcH), fluorinated beta-diketone (TTAH), thiopyridine (PySH), and piperidinyldithiocarbamic acid (NCS2H) to extract the ions from acidic aqueous solution. The performance of the various chelating agents from different studies indicated that the extraction efficiency by the supercritical CO2 was in the order: NCS2H >= PySH > TTAH >> AcAcH. The optimum pH for supercritical CO2 extraction should fall in the range from 2.0 to 3.0. The optimum molar ratio of chelating agents to indium(III) ions was found to be a ratio of 10:1. It was also revealed that the optimal extraction pressure and temperature for the supercritical CO2 extraction of indium(III) with various chelating agents AcAcH, PySH and NCS2H were 70 degrees C 2000 psi, 60 degrees C 2000 psi, and 60 degrees C 2000 psi, respectively. (C) 2007 Elsevier B.V. All rights reserved.