My first go at citric acid rust removal

[JOEPRO]

Today I cut the top off a 25L drum and added water + about 1.5 cups of citric acid powder.

I dropped in a rusty vice just to try this out more than anything else the vice will end up getting wire wheeled and blasted in any case.

Do I leave it in for 24 hours and check or how long really can you safely leave something submerged?

 

[Onoff]

My first thought would be it's likely too dilute/ not hot enough. I follow the instructions for Deox-C, (see attached PDF), at either 4:1 or 19:1 (water : powder). Kept at 70 degrees C it fair rips the rust off. I also degrease and rinse any parts first.

If it's fizzing it's working. A rusty slick on the surface is good. Be VERY careful about leaving high carbon bits in there like hardened plane blades!

Periodically remove, wire brush, rinse and re-immerse.

 

[Ross365]

It does sound quite dilute; 25kg of water and 250g of citric (??), and you have no heating. All that said, I cannot recall the recommended concentration to use; I'll try dig it out.

A lot depends on what your are working on; sometimes you want it aggressive and sometimes much less so. I don't often use it at rates where you can see very many bubble comings off. As per post~2, periodic removal and wire brushing helps a lot.

 

[DanZac]

As above, I use a big yogurt pot of acid powder in a bucket full of water and just leave them in until they're done.

It works quicker hot, but I'm to tight and lazy to heat it up and I've just got a bucket full by the workshop door that I just dump stuff in.

I normally get it out every few days for a bit of a brush and scrape and see how it's doing, but even really rusty suspension bits etc come up clean if you leave them for a couple of weeks.

It's not a quick process on heavy rust, but it does work. It's worth decreasing and chipping off any loose rust first though.

 

[JOEPRO]

Thanks for the feedback - I have upped the dose of citric acid powder. The 25L tub now has about 3 cups of citric acid powder and 18L of water inside with the vice.

It is definitely bubbling continously so I guess that is a good sign.

I do have this little immersion heater which is not sketchy at all. Not. I only use it when I am in the garage and attending it of course but it does give a good does of heat into the bucket when I use it.

 

[Onoff]

I jury rigged this. TIG'd ali box with an element, can't remember out of what and key to it, an old cylinder stat set for 70 degC. Should work strapped to a plastic bucket too.

https://flic.kr/p/2mhBeJj

https://flic.kr/p/2h2szn2

Worked great:

https://flic.kr/p/2mhCvU5

Until it eventually ate through a weak spot.

 

[dieselsamurai]

I did all the wheels for my hilux in an old central heating tank a few weeks back was outside and would have froze but i wrapped a blanket round it , heating does help but not necessary if your not in a rush

I just pressure wash every now and then till the rust is gone

Lost count of the stuff Ive done with it now just got to dry it quick before it flash rusts or dip them in a tank of weak Phosphoric acid and then it stops it rusting too, Ive had the wheels for my Coot atv in storage for 4 years now and they've shown no sign of rusting

 

[Ross365]

I've just dug out an old technical paper about cleaning stuff in power stations. A concentration of 0.2% by weight and operation at 60'C was "good to work in short duration" in getting rust off carbon steel.

I do a lot of work on old radio equipment, and often throw small bits into a plastic beaker with citric and put it in the microwave to warm it up . With delicate stuff like that, I tend to err on the safe side, and keep an eye on it. Get some very pleasing results.

Always remember that citric at temperature can begin to dissolve the metal slowly; the commercial citric products have corrosion inhibitors in them so that they limit the process to just taking off rust with no attack on the metal. Previously in this forum, the idea of adding some Fernox to the mixture has been discussed, but I don't recall anybody actually trying that.

 

[Sergei Slovenija]

...the commercial citric products have corrosion inhibitors in them so that they limit the process to just taking off rust with no attack on the metal. Previously in this forum, the idea of adding some Fernox to the mixture has been discussed, but I don't recall anybody actually trying that.

I add 0.2% by weight, a tablet of dry fuel. Urotropin.

 

[Kram]

It is much more effective hot. A cold solution might take days or weeks, hot it will take half hour to couple hours.

Nothing flash rusts that I have done with citric. My weld bench has been outside for several years now and its got patchy spots all over but not enough to really bother treating yet. Would be rusted through if it was a flap disc finish.

Any inhibitors you add to it will reduce the effectiveness on rust, best just to keep an eye on it.

 

[Ross365]

Any inhibitors you add to it will reduce the effectiveness on rust, best just to keep an eye on it.

Reacting with the rust and the metal are different chemical reactions; do you have any supporting (non-anecdotal) info that corrosion inhibitor slows rust removal? However, I do usually try to plan things so I can keep an eye on things.

Re temperature, for really simple chemical reactions, it can be shown that raising the temperature by 10'C will double the rate of reaction. It may be a fair approximation for citric and rust. For many real-world situations (complex liquid mixtures and metal alloys), things are usually more complex.

 

[droopsnoot]

I've used citric acid to clean a lot of stuff, but I've never tried heating it up. I might have to dig out the fish tank heater that came with my plating kit and see what happens.

 

[rtcosic]

I've used citric acid to clean a lot of stuff, but I've never tried heating it up. I might have to dig out the fish tank heater that came with my plating kit and see what happens.

I just decant some of the solution into a jug and put it into the microwave. About 10 minutes for about 1 litre then pour the contents into the container. Repeat as necessary to get it as hot as you want.

For small parts I have recently found that periodically putting them in my little Lidl ultrasonic cleaner using hot general purpose cleaner does the same job as jet washing large components.

 

[angellonewolf]

as above if not in a rush leave it in there for a few days remove wire brush put back in rince repeat

 

[Onoff]

Citric acid has a smell all it's own once it gets going. Makes women complain when you do it in the kitchen for some reason.

 

[angellonewolf]

Citric acid has a smell all it's own once it gets going. Makes women complain when you do it in the kitchen for some reason.

no they complain about it as its the first thing that comes to mind remove that then they start on something else

 

[Barking Mat]

During confinement, I cleaned up aload of bits using citric, even well rinsed and dryed, it still wanted to revert to rust, so I mixed some bees wax, and oil (?) of some sort, that worked well.

 

[Ross365]

This thing about wanting to revert to rust, and even flash-rusting seems to be a very ill-defined issue, very variable, depends a lot on materials. There are lots of people who reach for the washing liquid to clean things, and there's so much chloride in there that rust will then come back.

I tend to just place small stuff in a tin can and spray with WD40 and leave as long as possible, then wipe dry before use. That seems to work.

 

[JimmyS]

I add 0.2% by weight, a tablet of dry fuel. Urotropin.

That's hexamine fuel tablets? I wonder how that works chemically?

 

[JOEPRO]

24 hrs later and wow what a difference. I picked up both of these no 4 vices at the weekend.

Before:



After- one on left below:





The rust has been 95% removed from the first one I am very pleased with that and that is far enough for it as I will be stripping and restoring it.

The second one is now back in the barrel with the same used mix. It is seized solid so I'm hoping the acid will do its thing and free it up.