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Separation mechanism of polyvinyl chloride and copper components from swollen electric cables by mechanical agitation

Lu, Jiaqi, Xu, Jing, Kumagai, Shogo, Kameda, Tomohito, Saito, Yuko, Yoshioka, Toshiaki
Waste management 2019 v.93 pp. 54-62
agitation, blades, copper, fluid mechanics, hydrophobicity, mixing, poly(vinyl chloride), recycling, simulation models, solvents, wastes
In this study, a high-accuracy separation process is proposed for recycling pure polyvinyl chloride (PVC) and Cu from the thin electric cables of electrical, electronic, and automotive wastes by PVC swelling and mechanical agitation in hydrophobic organic solvent mixed with water. The high stirring speed and low blade height combined with proper blade type and reactor tank shape ensure a separation rate of over 98%. By conducting computational fluid dynamic and discrete element model simulations, quantitative force, fluid velocity, and data visualization analyses were performed. The obtained separation rate exhibited strong positive correlations with the resultant, drag, and centripetal forces at various stirring speeds and blade heights. Using the experimental and simulation data, a plausible separation mechanism was suggested. It was found that Cu pieces could slip out from swollen PVC covers under the action of external forces, while the stirring speed should be high enough to apply sufficient external forces to cables via either blade-to-cable collisions or fluid drag. Furthermore, the vertical motion of cables induced by the low blade height was essential because the rotation in the bottom reactor part inhibited the slipping of Cu pieces.