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How to remove plastic with gas floatation

David Owen
Treatchem Ltd
ynys.services@gmail.com
ECG Bulletin January 2020
A demonstration of how pressurised gas dissolved in water can separate out low-density microplastics by floatation.

Theory
Low-density microplastics usually have a density greater than, but near to, that of water. By attaching bubbles to the plastics from pressurised gas dissolved in water, the microplastics can be made to float to the surface where they may be scraped off. Some microplastics may be more difficult to float if they contain heavy fillers such as magnetite (e.g. toner in photocopiers) or barium sulphate.

Typically, the gas (air or nitrogen) is pressurised to about 5 atmospheres. For this demonstration and in the interest of safety, carbon dioxide is used, as commercial ‘fizzy’ water is readily available as a source of compressed gas dissolved in water. Sometimes, when dealing with very small pieces of plastic, a modest amount of a chemical known as flocculant is added to make the particles agglomerate to trap the bubbles.

A similar process, known as induced air floatation, uses low-pressure gas bubbled into the water through a sinter or frit. This is less efficient but can work adequately dependent on the material to be floated.

Set up
Chop or grate several coloured straws as small as possible and put about half a gram of the pieces in a jam jar-sized container (e.g., a tall 500 mL beaker). The container may be glass or see through plastic. Add roughly 100 mL of water to thoroughly wet the plastic so that it sinks and is not supported by surface tension. Drain off as much water as possible leaving the wetted plastic behind.

Take a bottle of fresh supermarket fizzy water and, through a long-necked funnel, add approximately 500 mL to the container, ensuring is added to the bottom of the container via the funnel. Remove the funnel and gently swirl the water for 10 seconds to allow the dissolved gas to release around the plastic. Put down the container and observe. The plastic pieces will float up to the surface and leave the bottom layer clear.

A further experiment can show that by adding small amounts of flocculent solution, floatation occurs much faster.

Challenge
Float out the plastic.

Kit List
  • 2 litre bottle(s) of supermarket fizzy water
  • Coloured straws or nylon thread
  • Scissors/grater/ domestic blender
  • Jam jar or beaker
  • Long necked plastic funnel capable of reaching the bottom of the jar when filling
  • Solution of flocculent, if needed, along with small syringe to dose the water
  • Disposable plastic gloves if using flocculant
  • Roll of paper towel to dry up spillages

Exhibition Cost
<£50

Exhibition weight
The weight is largely dominated by the weight of the water bottles used.

Exhibition size
Would fit into a printer paper box.

Resources required
MSDS of flocculent.

Things to look out for
Ideally have a separate table at viewing height so that more than one viewer may see what is happening. It will take up to 3 minutes for floatation to occur without flocculent. Flocculent solutions of 0.1% are viscous and sticky, so have paper towels handy and use disposable gloves to avoid contact with skin.
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  • Home
  • About
    • Committee
    • Annual reports
  • Environmental Briefs
  • Distinguished Guest Lectures
    • 2022 Disposable Attitude: Electronics in the Environment >
      • Steve Cottle
      • Ian Williams
      • Fiona Dear
    • 2019 Radioactive Waste Disposal >
      • Juliet Long
    • 2018 Biopollution: Antimicrobial resistance in the environment >
      • Andrew Singer
      • Celia Manaia
    • 2017 Inside the Engine >
      • Frank Kelly
      • Claire Holman
      • Jacqui Hamilton
      • Simon Birkett
    • 2016 Geoengineering >
      • Alan Robock
      • Joanna Haigh
      • David Santillo
      • Mike Stephenson
    • 2015 Nanomaterials >
      • Eugenia Valsami-Jones
      • Debora F Rodrigues
      • David Spurgeon
    • 2014 Plastic debris in the ocean >
      • Richard Thompson
      • Norman Billingham
    • 2013 Rare earths and other scarce metals >
      • Thomas Graedel
      • David Merriman
      • Michael Pitts
      • Andrea Sella
      • Adrian Chapman
    • 2012 Energy, waste and resources >
      • RAFFAELLA VILLA
      • PAUL WILLIAMS
      • Kris Wadrop
    • 2011 The Nitrogen Cycle – in a fix?
    • 2010 Technology and the use of coal
    • 2009 The future of water >
      • J.A. (Tony) Allen
      • John W. Sawkins
    • 2008 The Science of Carbon Trading >
      • Jon Lovett
      • Matthew Owen
      • Terry barker
      • Nigel Mortimer
    • 2007 Environmental chemistry in the Polar Regions >
      • Eric Wolff
      • Tim JICKELLS
      • Anna Jones
    • 2006 The impact of climate change on air quality >
      • Michael Pilling
      • GUANG ZENG
    • 2005 DGL Metals in the environment: estimation, health impacts and toxicology
    • 2004 Environmental Chemistry from Space
  • Articles, reviews & updates
    • Articles
    • Reviews
    • Updates
  • Meetings
    • Upcoming meetings
    • Meeting reports
  • Resources
  • Professional Qualifications
  • Index