How to remove plastic with gas floatation
David Owen
Treatchem Ltd
ynys.services@gmail.com
ECG Bulletin January 2020
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
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.
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.
