Separation of polyvinyl chloride from waste plastic mixtures by froth flotation after surface modification with sodium persulfate

Abstract

A new method of surface treatment based on advanced persulfate oxidation technology is proposed for separation of plastics by froth flotation. By means of sodium persulfate treatment, waste plastic mixtures, including polyvinyl chloride (PVC), polycarbonate (PC) and polystyrene (PS), were selectively modified to achieve effective flotation separation. After sodium persulfate treatment, flotation percentage of PS and PC decreased significantly, while flotation percentage of PVC was not affected. The mechanism of sodium persulfate treatment was examined by contact angle, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The flotability reduction of PS and PC was in virtue of the increase of surface hydrophily. FT-IR analysis and XPS analysis demonstrated the introduction of oxygen-containing functional groups on the surface of PS and PC. The optimum conditions for separating PVC from plastic mixtures were sodium persulfate (Na2S2O8) concentration 0.1 M, temperature 70 °C, pH 10.5, treatment time 30 min, frother concentration 15.8 mg/L and flotation time 4 min. The impacts of particle size, mass ratio and reusability of Na2S2O8 solution were also studied. The results demonstrated that under optimum conditions, PVC was efficiently separated from plastic mixtures. The purity and the recovery of PVC were up to 99.77% and 100%. The proposed method is a simple, environmentally friendly and efficient way to promote the separation of PVC from waste plastic mixtures.