Removal of gallium (III) ions from acidic aqueous solution by supercritical carbon dioxide extraction in the green separation process

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 CO2 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 CO2 was in the order: thiopyridine (PySH) > thenoyltrifluoroacetone (TTAH) > acetylacetone (AcAcH). The optimal extraction pressure and temperature for the supercritical CO2 extraction of gallium (III) with chelating agent PySH were found to be 70 °C and 3000 psi, respectively. The optimum concentration of the chelating agent was found to be 50 ppm. A value of 7.5 was selected as the optimum dimensionless CO2 volume. The optimum pH of the solution for supercritical CO2 extraction should fall in the range of 2.0-3.0.