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Salt: Separating Mixtures

Most of planet Earth is covered by water – but did you know that almost all of it is undrinkable? Seawater makes up 97.5% of all Earth’s water, but it contains so much salt that drinking it would actually dehydrate us: we need fresh water to survive. Scientists in Manchester have been working on a new way to make seawater drinkable, using a process called filtration with a chemical compound called graphene oxide (GO) to remove almost all of the dissolved salts.

Filtration is the separation of an insoluble solid from a liquid using a fine mesh called a filter. For example, you make filter coffee by stirring crushed coffee beans into hot water. The water takes on the coffee flavor, but the insoluble crushed beans don’t dissolve and stay floating in the liquid. To get rid of them, you pour the coffee through a paper filter that catches the crushed beans – letting you enjoy your coffee without bits.

To remove salt from seawater, the scientists use graphene oxide like a coffee filter, although on a far smaller scale. The seawater passes through unimaginably tiny holes in the graphene oxide just a nanometer in width – in comparison, a single human hair is about 75,000 nanometers wide! The graphene oxide filter traps almost all of the salt molecules and the water becomes safe to drink.

This is an important breakthrough in science, because many places in the world don’t have access to enough fresh clean water – essential for drinking, washing, watering crops and feeding farm animals. Current technologies used to remove salt from seawater rely on distillation – the water is evaporated away from the salt before being condensed as pure water. Although this is effective, and is used on ships and submarines, it uses a lot of energy, which makes it expensive.

The scientists developing the graphene oxide filter still need to work on reducing the costs of producing it on a large scale, but they’re making good progress so far. With so much seawater all around us, this incredible filter could provide a much-needed solution to some of the world’s worst water shortages!

Watch Salt: Separating Mixtures to learn about how we extract salt from water and rocks to use on our food.