Sink-float tank applying gravity separation

Applying a sink-float tank is one of the most valuable separation techniques in recycling systems. We also see descriptions in the industry such as separation tank or float sink separator. The tank is filled with water and, depending on the materials to be separated, additives to alter the fluid’s density.

The mixed plastic stream is dosed into the tank where high-density materials will sink, and low-density materials will float. The separated particles will be recovered and conveyed for further processing.


The separation tank is ideal for PET bottle recycling. The PET flakes, for instance, will sink to the bottom. Other materials such as plastic wrappers and bottle cap flakes will float, as they are manufactured from a different kinds of plastics, mainly from PP and PE.

Another application is mixed plastics streams. For example rigid PP/PE or film. This has a lower density making the plastics float while contaminant particles such as metals, glass, soil, and sand will sink to the bottom to be discarded.


An innovative float-sink tank installation built by B+B offers advantages including:

  • applicable for multiple types of plastics, e.g. PET, PP/PE, and PS/ABS
  • high selectivity through basic principle of gravity separation
  • automatic level adjustment via pressure gauging
  • cost-effective thanks to low operational costs (low maintenance and wear) and low energy consumption

We have a number of tailor-made example applications to share with you. For more information, download the leaflet Sink-Float Tank or contact our sales department directly.

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