title: Removal of gallium (III) ions from acidic aqueous solution by supercritical carbon dioxide extraction in the green separation process.
abstract: Supercritical carbon dioxide extraction, which is a feasible "green" alternative, was applied in this study as a sample pretreatment step for the removal of gallium (III) ions from acidic aqueous solution. The effect of various process parameters, including various chelating agents, extraction pressure and temperature, dimensionless CO(2) volume, the concentration of the chelating agent, and the pH of the solution, governing the efficiency and throughput of the procedure were systematically investigated. The performance of the various chelating agents from different studies indicated that the extraction efficiency of supercritical CO(2) was in the order: thiopyridine (PySH)>thenoyltrifluoroacetone (TTAH)>acetylacetone (AcAcH). The optimal extraction pressure and temperature for the supercritical CO(2) extraction of gallium (III) with chelating agent PySH were found to be 70 degrees C and 3000psi, respectively. The optimum concentration of the chelating agent was found to be 50ppm. A value of 7.5 was selected as the optimum dimensionless CO(2) volume. The optimum pH of the solution for supercritical CO(2) extraction should fall in the range of 2.0-3.0.
authors.affiliation: Department of Industrial Safety & Health and Institute of Occupational Safety and Hazard Prevention, HungKuang University, Taichung, Taiwan. wlchou@sunrise.hk.edu.tw
authors.forename: Wei-Lung
authors.initials: WL
authors.lastname: Chou
authors.forename: Chih-Ta
authors.initials: CT
authors.lastname: Wang
authors.forename: Kai-Chiang
authors.initials: KC
authors.lastname: Yang
authors.forename: Yen-Hsiang
authors.initials: YH
authors.lastname: Huang
mesh_terms: D000143:Acids; D002245:Carbon Dioxide / Q000737:chemistry*; D002614:Chelating Agents / Q000737:chemistry; D025924:Chromatography, Supercritical Fluid / Q000379:methods*; D005708:Gallium / Q000737:chemistry* / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007659:Ketones / Q000737:chemistry; D011312:Pressure; D011725:Pyridines / Q000737:chemistry; D012996:Solutions; D013696:Temperature
chemical_list: D000143:Acids; D002614:Chelating Agents; D007202:Indicators and Reagents; D007659:Ketones; D011725:Pyridines; D012996:Solutions; D002245:Carbon Dioxide; D005708:Gallium