Selected pairs of thermoplastic types are separated in a froth-flotation method that has been adapted to thermoplastics. The froth flotation process is capable of separating ABS and HIPS from the mixture in purities greater than 98 percent, according to Argonne. A demonstration of the process for separating ABS and HIPS has been conducted at Appliance Recycling Centers of America in Minneapolis. In the froth flotation process, ABS and HIPS, two plastics that are incompatible but have similar densities, are placed in an aqueous solution of a certain density, surface tension, and pH. The solution renders one of the plastics hydrophilic and the other hydrophobic. Air bubbles pass through the solution and adhere to the HIPS, carrying the HIPS to the surface.
ABS remains wetted and sinks to the bottom.
A similar strategy, incorporating solutions of different compositions, may be used to separate other pairs of plastics. These particles account for 30 to 60 percent of the residue's weight. We can concentrate the ferrous fraction, by sending it through a magnetic drum. The magnetic drum is capable of pulling out roughly 40 percent by weight. Ivan Vanherpe, project manager of Salyp's ELV Center, holds iron oxides, which have potential in cement manufacturing, he said.