Citric acid de-rust

[Tippie]

Those who have used citric acid to remove surface rust from in fuel tanks, what ratio do you mix powder citric acid with water?
Do you just rinse with clean water after? Won't surface rust immediately form again?

[Grant]

1kg can make up to 20 litres of solution.
I just add the crystals and stir until no more can dissolve.
Warm water allows the process to act faster.
Yes, it will start to rust again unless coated, but so would a standard uncoated steel tank.
That assumes a heavy moisture or water environment.
If filled with fuel then that would help ave it from rusting all over.

[Gerald]

A friend of mine has removed severe internal rust from motorcycle tanks with a solution of phosphoric acid and I believe water.
Tanks never rusted again on the inside after several years of use.

Gerald

[Paul Marx]

Use phosphoric acid once clean.

Paul

[Paul H]

I did my SF tank a while ago. Various acids were tried and all worked to an extent, but have to say the most effective method was electrolysis. A big fat nail hung down into the tank, 12v from a battery+charger worked a treat. Needs a good few days though.

I use citric acid a lot for things I can brush off occasional. i.e. external surfaces. The brushing really helps the rust removal progress, but that's not so easy on the inside of a tank.

[Tippie]

So it seems like citric acid, rinse, then phosphoric acid. I can get both on the net here (phosphoric from home brew suppliers!)
Not sure I´d try electrolysis. Was that a steel nail or a gal one?
There's no deep rust in this tank, but powdery surface rust. I tried rust converter after a net search "best results ever!", was a stinking mess from it, now dried out and gone and the powdery rust is still there.

[Paul H]

Re nail - any chunk of mild steel or iron will do - not coated.

I only used a nail because it was a decent sized piece of low carbon steel that I had to hand. The 'nail' is the anode and the tank itself the cathode.

[AndyW]

Molasses works just as well: probably better...

[dja982]

How many moles would I have to get for a Laverda triple tank? 

[laverdas]

Hi you should use an inhibitor with 5% citric acid. This is to protect the good base metal. So what you do make sure it has the inhibitor with it. Just my take
Regards Andy

[Tippie]

What do you mean by an inhibitor? Can you give an example.

[laverdas]

Inhibitors I use industrial brands like armohib 28 or cronox, if go get a pack off the shelf it will have some with it. It allows your acid to oxidised the iron sulphides or just plain rust to you and me but protects the good metal.

[AndyW]

Sulphides? What sulphides?? Rust is ferric iron oxide and the citric acid (a weak acid) etches and renders it soluble. Orthophosphoric acid is able to reduce soluble ferric (Fe3+) ions to non-soluble ferrous (Fe2+) ions and thereby passivate it (ie ‘cure’ the rust).

Not sure what your ‘inhibitor’ does: can only assume it’s to passivate the steel after the citric acid has done its job (dilute hydrochloric acid would do the job just as well though molasses would do a far better job than either). If using either acid, rinse out well with water, dry and re-rinse with a little meths to finish: simples.

[Dellortoman]

Sulphides? What sulphides??

I was thinking the same thing myself. I wouldn't have thought the sulphur content of fuel would be sufficient to cause any chemical interaction with the steel tank. 

[Piranha Brother 2]

Need more detail. How does the nail work?? Is it in a tank full of water? Citric Acid solution? Which electrode is + and which - ?

An molasses? Straight thick gooey molasses or a solution? After treating with something else?