Separation of mixed plastics for recycling involves successive flotation in water with pulsating air injection in a series of vessels

摘要

A mixture of different plastic materials is fed (1) to a flotation vessel (2) containing water, which is being agitated, e.g. by pulsating air (10). The heavier fraction sinks to a grid (16) from where it is transferred through a rotary lock (8) by an elevator (26) to a container (13). The suspension containing the lighter materials is passed to a succeeding vessel (2') where conditions are adjusted to separate the next lighter fraction. Separating conditions are set by a controller (17) that alters the slope of the grid (16) and the angle of the flaps (6) according to signals obtained from sensors (5). Pulsation in the liquid is preferably generated by compressed air through a bell-shaped distributor (11), but can also be generated by hydraulic, pneumatic, mechanical or electrical vibrators. The frequency and intensity of the pulsation are controlled to generate the required flotation effect with different densities in successive vessels.