Recovery of Perfluorinated Chemicals by Flotation-Development of New Collectors and New Flotation Process

Perfluorinated chemicals (PFCs), including perfluorooctanic acid (PFOA) and perfluorooctane sulfonate (PFOS) are persistent organic pollutants (POPs) and anionic surfactants. They have been widely used in semiconductor industry as a surface treatment agent in photolithography and other industries. The concentration of PFOS in semiconductor wastewater from photolithographic processes may be over 1000 mg/L. PFCs are difficult to decompose due to its strong C-F bonds (110 kcal/mol). Flotation is an effective method for surfactant removal or recovery. Lee and co-authors have successfully recovered PFCs by foam flotation with metal ion collectors (ferric ion). Both of the two PFCs can be effectively separate from water in 5 min and the recovery was over 80%. The process, however, needs to be conducted in acidic solution (pH = 2.3) to avoid the formation of ferric hydroxyl species. This study tries to modify the flotation method by using different types of collector such as cationic surfactants, nonionic surfactants, positively charged particles (CaF2) and mixtures of them to conduct the flotation in neutral solution in the first year. In the second year, a new flotation method, electrocoagulation flotation (ECF) will be used to recover PFCs with the new collectors or chelating agents. The effects of various operational parameters, such as type of electrodes, types and concentrations of the collectors and chelating agents, initial acidity, ion strength, current density and the initial concentration of PFCs will be investigated for the optimization of the PFCs recovery. Finally, the feasibility of the new recovery methods will be accessed by an indicator of energy consumption.