Making salt from seawater

Friday 4th September 2015

When I told a friend I was going to make salt, her reaction was 'why bother?'. True, it's pretty cheap but I was curious to see the point where it turns from being water to being salt. We had some friends staying and their kids were really interested to see the process, so maybe your kids would like to see it too.



I wanted to get some nice clean sea water, so we went out for a sail in St Austell Bay and collected 5 litres of water from a spot about quarter of a mile offshore.



When we got back, I left it to sit overnight so any big particles settled to the bottom, and then filtered it through a bunch of coffee filters. There were a few specks in the filters, but generally it was pretty clean.



Okay, so this isn't the most environmentally friendly way I could have done it, but waiting for it to evaporate in the UK would have taken weeks. As the water level went down it became more and more cloudy.If you're doing this at home, don't use steel pans! It went a bit rusty.

Eventually it became a white crystalline sludge, at which point we ran it through another coffee filter but this time we kept the solid material.



We spread the sludge onto a piece of baking paper and dried it in the oven at about 85°C for a couple of hours, until it was completely dry.



Once it was dry, the salt had caked into large lumps, so we pushed it through a sieve. Ta da!


In total we got 134g of salt from 5 litres of water. Average sea salinity is 3.5% so the maximum yield was 175g. There was a lot crusted onto the pan, and some of the salt will have evaporated with the water, so this is about right.


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