Exploring flotation separation of polycarbonate from multi-microplastic mixtures via experiment and numerical simulation

Plastic recycling is a promising technology, as it can both contribute to circular economy goals and reducing plastic pollution; however, it faces significant challenges due to the lack of effective separation methods. Herein, we studied the flotation separation of polycarbonate (PC), a major component of plastic waste, from multi-plastic mixtures after hydrophilization by Fe(VI). First, the effect of Fe(VI) treatment on the surface properties of the plastics was studied. Fe(VI) induced hydrophilization of PC, with a decreased contact angle of about 19°; this was attributed to the introduction of hydrophilic moieties by surface oxidation and hydrolysis reactions. Then, the effect of operating conditions in both hydrophilization and flotation on the flotability of plastics was investigated. In both binary and multi-plastic mixtures, hydrophilization selectively suppressed the flotability of PC from 100% to about 0.0%. Numerical simulation was performed using the population balance model of computational fluid dynamics to determine the gas-liquid flows during flotation. It was found that the flow rate affected flotation of plastics via bubble formation rather than flow fields. Finally, the optimization of hydrophilization was performed using the Box Behnken design of response surface methodology. The results showed that PC was separated from multi-plastic mixtures with recovery and purity of 100.0% under the optimum conditions. These results would greatly facilitate the development of plastic recycling.