Magnetic density separation technology is being advanced to improve plastic waste recycling by use of a ferrofluid that generates a vertical mass density gradient when in the presence of a magnetic field. Added plastic particles move to a height in the ferrofluid where the apparent mass density of the fluid is about the same as the mass density of the particles. Separated plastic can then be reused in higher-value products with this solution designed to increase the economic feasibility of recycling.

Limitations in this approach are associated with turbulence and particle collisions that can reduce separation efficiency. Researchers from Eindhoven University of Technology in the Netherlands sought to measure and analyze such turbulence by use of wind tunnels and to study particle collisions in a ferrofluid with a vertical mass density gradient in a magnetic field.

Schematic of the separation process. Source: Eindhoven University of Technology

After analyzing data documented by laser Doppler velocimetry, particle image velocimetry and particle tracking velocimetry, the researchers recommended use of a laminator to suppress turbulence during the separation process. This component should be designed with small, parallel square ducts and thin walls to help maintain a specific flow velocity.