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Concentrating sulfuric acid


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I have obtained about 2.5 litres of battery acid strength sulfuric acid which has been filtered. I tried to concentrate it by boiling it in a stainless steel pot outside. After about 5 minutes of heating the acid turned cloudy white and started producing noxious fumes which were not visible, the acid hadn't started to boil yet. The acid started to react with the metal pot and after about 10 mins it had changed from being cloudy white to a pale green/torquoise colour. The inside of the pot now has a black coating of somthing.


What I think happened is that when the acid was heated it reacted with the metal, maybe the chrome? But what I wish to know is what has formed in the acid and whether it can be removed. Next time I will use glass but I do not have any scientific equipment because I can't find anywhere that sells it retail.

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Nickel Chromiun and Iron are in stainless steel, it`s unlikely to be the Cr, but Every chance of Fe and Ni complexes.

as for getting the stuff out erm....

that`s going to be messy, you could try EDTA or making the acid Very concentrated and that should form crystals that can be filtered out with rockwool.

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The EDTA will be destroyed by the hot concentrated acid and you'll not remove the metal from the acid. I'm afraid, that you cannot easily get it out. The only way would be to distill the sulphuric acid, but that is VERY hot (over 300 C) and not something I would suggest you to do at home, unless you have the right equipment and experience.


You could concentrate the H2SO4 by boiling it for a while, and then you can use it for making nice and pure concentrated HCl by adding NaCl and leading the gas through distilled water.

The sulphuric acid also still is suitable for dehydrating purposes, and also for nitrations in combination with nitric acid.

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Where could I find some EDTA? And if I were to concentrate it to the point so it crystalises how would I do that without the acid boiling off? Just heat it gently?


no no, that`s 2 entirely different methods, you can use the EDTA when it`s dilute, you cannot concentrate it from this point though, it simply locks up the metal ions that renders them useless/inert to most simple reaction.



you can concentrate it (no EDTA) and then the crystals out the metal sulphates, although they will likely be amorphous as the water of crystalisation will have dehydrated out, at this point a good rockwool filter or even activated charcoal will shift most of the metal ions.


please note that in post #2 I said EDTA OR concentrate it :)

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Ok thanks for the replies YT and woelen, yeah I know that you said or I just wanted to know which would be the best line of action to pursue. But reading my post it does sound like I thought they were the same method.

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