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Phosphoric acid


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I recently bought a bottle of rust remover/cleaner.. Its called Phosphoric Prep & Etch.. The only thing under contents says it contains phosphoric acid. It is a dark green liquid, a little oilly.


Any ideas on how to get the phosphoric acid out of this? Ive heard of green phophoric before but i have never seen it. I could boil it to get the water out, but phosphoric acid has a low boiling point doesnt it? Any ideas would really help thanks.

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Phosphoric acid does have a very high boiling point, and it also decomposes on heating, giving metaphosphoric acid and water. By heating, you will not get rid of the green impurity. The water will boil away, the acid will remain, together with all its impurities.


Unfortunately I see no real good way to get rid of the green stuff. The only thing which comes to mind is to add some active carbon and see whether this absorbs the green color.


Pure phosphoric acid (containing water only) is an oily colorless liquid, or when it is really pure (free of water), it is a white/transparent solid with very low melting point.

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  • 2 weeks later...

add some sulphuric acid, leaving sodium sulphate and phosphoric acid. heat until the Na2SO4 crystalises then filter them out when cold.

in order to know how much sulphuric to add you need to know if its mono/di/ or tri phosphate 1`st.

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