Surface treatment by the Fe(III)/sulfite system for flotation separation of hazardous chlorinated plastics from the mixed waste plastics

A novel advanced oxidation process by a combination of Fe(III) and sulfite for surface treatment of waste plastic mixtures is proposed. The Fe(III)/sulfite system has been found to enhance hydrophilicity of the mixed waste plastics, including acrylonitrile butadiene styrene (ABS), polystyrene (PS) and polycarbonate (PC), while it has little effect on hazardous polyvinyl chloride (PVC), thus promoting separation of PVC from the mixed waste plastics by flotation. Radical scavenging experiments indicate that sulfate radicals are the main reactive species. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) results imply the formation of C=O or C-O groups on the treated plastics surface except for PVC and a plausible mechanism for oxidizing plastics with sulfate radicals is proposed. PVC with 100.00% recovery and 99.84% purity is achieved under optimum surface treatment conditions of sodium sulfite concentration 10 mM, ferric sulfate concentration 0.4 mM, pH 6.0, temperature 25 degrees C and treatment time 15 min. Consequently, surface treatment by the Fe(III)/sulfite system is an effective technology for separating hazardous PVC from the mixed waste plastics by flotation.