Cleaning off rust with citric acid

This a before and after picture of leaving a tow hitch in food grade citric acid overnight
1 kg of crystals in about 5 gallons of water
Left overnight,then washed off in clean water with a rag
I have done whole petrol tanks this way with great success and no paint damage
Thought it might be useful to someone

Yup, it is a well known rust converter....not actually removing rust, but converting the iron oxide back to the non-oxidized form of iron (usually turns black). It will re-oxidize (re-rust) within a short time unless protected.

Phosphoric acid is the rust remover and converter, citric acid removes the rust but does not convert.

Phosphoric Acid:
Strong and fast-acting: Phosphoric acid is known for its ability to quickly and effectively convert rust into a protective layer.
Creates a protective layer: The iron phosphate layer it forms can help prevent future rusting.
Potent: It's a more powerful rust remover than citric acid, especially in higher concentrations.
Industrial applications: It's commonly used in industrial rust removers and converters.
Citric Acid:
Weaker and slower:
Citric acid is a weaker acid than phosphoric acid and may require more time and higher temperatures for effective rust removal.

As the conversion process can take place before all the rust layers are removed, the most effective method is first to use a rust remover like citric acid until all the rust is removed and then use the phosphoric acid as it will convert the top steel surface to iron phosphate. With no rust under it to then undermine the iron phosphate then it will a lot more effective.

If after the citric acid treatment you get a rust coloured bloom then the phosphoric acid will still convert this thin layer to iron phosphate and be effective.

Tornado said:

Yup, it is a well known rust converter....not actually removing rust, but converting the iron oxide back to the non-oxidized form of iron (usually turns black). It will re-oxidize (re-rust) within a short time unless protected.

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I was wondering about the re-oxidization as I've not noticed anything re rusting again when I've used this process
Whereas "shot" blasting can be really bad unless treated immediately in my experience
I first started using citric acid few years ago
Previous to this the firm I worked for had a tank of phosphoric acid that was brilliant

What kind blasting is that?
Must be Messy.....

MichaelB said:

What kind blasting is that?
Must be Messy.....

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I'd better edit that

I use the electrolysis method to loosen the surface rust then I brass wire brush it and repeat the process until all visible rust is removed. Then I brush it with phosphoric acid solution and leave it to form a white coating which I remove using the brass wire brush.

hybridracer said:

I use the electrolysis method to loosen the surface rust then I brass wire brush it and repeat the process until all visible rust is removed. Then I brush it with phosphoric acid solution and leave it to form a white coating which I remove using the brass wire brush.

Click to expand...

I only use clean water and a rag or a kitchen sponge to clean the rust off

I watched a fantastic restoration video on a '78 Honda ATC90, and noticed his use of Bilt-Hamber Deox-C. Pretty impressive stuff, looks like it's citric. I've done many rusty tanks using 30% vinegar (or even food-grade) for light rust, phosphoric (cheap muriatic pool cleaner), and electrolysis. Citic looks like a better solution than the last two, which are nasty and potentially paint-damaging solutions for 'worst case' tanks. I'm going to look for a cheap generic supply of crystals and try it out. Deox-C is expensive and not available except on eBay here.