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Hydraulic separator may hold key to better plastics recycling

06/01/2009

  • Recycling
  • Italy

The recycling of plastics has been hampered in the past by sorting difficulties, but with the advent of the Multidune hydraulic separator, a solution may have finally been found.

The recycling of plastics has been hampered in the past by sorting difficulties, but with the advent of the Multidune hydraulic separator, a solution may have finally been found.

Conservation of resources, energy concerns and over-reliance on landfill have increased the need for better plastics recycling. A recent innovation developed by Italian researchers could solve the taxing problem of sorting plastics of similar size and density, and so provide a means to improve recycling.

Plastics recycling has traditionally proven difficult as many types of plastic, each with different physical and chemical properties, may have very similar masses. In the past, recycling techniques focused on separating particles according to their physical characteristics, mass (weight), size or chemical properties. These processes are usually carried out on single types or mixtures of plastics after a selective collection.

Any of the established methods of industrial separation may be implemented in the recycling plant – for example, automatic sorting, electrostatic separation, gravity separation or flotation. However, all are prone to the same problems and difficulties regarding separating plastics that have a similar mass. For this reason, the recycling of plastics has needed a precise technology to sort plastics according to their exact individual mass.

The Multidune Separator contains a series of parallel semi-cylindrical transparent tubes. It has been specifically designed to pinpoint even the smallest differences in mass between plastic particles. This enables it to address the problem of separating plastic particles of a similar mass. Its high sensitivity allows the instrument to recognise plastic particles of an extremely small specific mass (1g/cm³). It functions by transporting a mixture of plastic particles and fluid through a network of pipes, using fluid dynamics to separate the plastics into outlets that correspond to their particular density.

More information:  
mailto:floriana.lamarca@uniroma1.it

De Sena, G. Nardi, C., Cenedese, A. et al. (2008). The hydraulic separator Multidune: Preliminary tests on fluid-dynamic features and plastic separation feasibility. Waste Management. 28(9)