Froth Flotation Techniques for Waste Plastics Separation
Summary
Froth flotation has emerged as a pivotal technology for the recovery and purification of secondary plastics from mixed waste streams. By exploiting differences in surface chemistry rather than density alone, flotation enables the selective adhesion of target polymers to air bubbles within an aqueous medium. The process typically comprises a pretreatment stage—often involving pH adjustment or chemical conditioning—followed by the addition of surfactants or collectors that enhance the hydrophobicity of specific plastics. Subsequent aeration generates a froth layer to which hydrophobic particles attach and rise, while hydrophilic or depressant-treated materials remain in the bulk. Continuous or batch flotation cells can be tailored to optimise residence time, air flow and froth stability, leading to high-purity concentrates suitable for mechanical or chemical recycling. Recent innovations focus on integrating flotation with upstream density-based sink–float methods, combining selective wetting agents and alkaline or acid pretreatments to broaden the range of separable polymers. Globally, these advances contribute directly to circular economy targets and resource efficiency, providing pathways for reclaiming high-value plastics such as PET, PS, PVC, ABS and HIPS from electronic, packaging and automotive wastes.
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Froth Flotation Techniques for Waste Plastics Separation publication trend
The graph below shows the total number of articles in froth flotation techniques for waste plastics separation across all publications each year (not limited to Nature Index journals).
Technical terms
Froth flotation: a process in which hydrophobic particles are separated from hydrophilic counterparts by attachment to rising air bubbles in an aqueous medium.
Wetting agent (collector/depressant): a chemical added to modify the surface tension of water and adjust particle wettability, promoting or inhibiting bubble–particle adhesion.
Contact angle: the angle where a liquid interface meets a solid surface, serving as a measure of wettability and influencing floatability.
Hydrophobicity: the characteristic of a surface that repels water, essential for enabling particle attachment to air bubbles.
Sink–float separation: a preliminary density-based technique in which particles are immersed in liquids of known densities to partition materials by buoyancy before flotation.
References
- Separation of plastic mixtures by sink-float combined with froth flotation. Polímeros (2023).
- Study on PET Recovery from Polymeric Mixtures, Using the Floatation Technique, and Valorization of the Collected Particles by Dyeing Them. Fibers and Polymers (2023).
- Selecting chemicals for separation of ABS and HIPS in WEEE by froth flotation. Polímeros (2019).
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