Removing rust with citric acid...

[b5blue]

  Working off an story from Hemmings Sport & Exotic Car then checking Wikipedia for uses of citric acid I've confirmed it's use as an industrial rust treating/remover. I plan on experimenting with it as it is a safe and cheap alternative to very expensive and hazardous chemicals offered for sale. I've a strong hunch it's what many sell in a fancy ad touting their "non-toxic environmentally friendly" products.  (You may recall my removing oxidation from connectors with salt and vinegar topic that worked quite well.)
  I'll report my findings and put pics of what I do and results here in hopes it helps us in our never ending battle with rust! Please feel free to chime in and try some yourself, the stuff is readily available and cheap. It's added to food and drink as a flavor enhancer and preservative so it's also yummy for your tummy!     
 

[areibel]

The only thing I'd wonder about is concentration- I'd bet anything food grade is going to be relatively weak compared to what you'd need to cut rust on sheet matal?
There's a recipie on Moparts for a rust remover that works well on small stuff (anything you can soak), it uses vinegar salt and lemon juice.  I tried it and it took the rust off of sone tools and small parts I tried it on and left the paint and undercoating, so it's not real aggressive on anythign else.  And it was reusable, for less than $10 I mixed up over two hgallons and used it in a big plastic tub.  It got quite a bit of sludge in it ( I soaked a lot of stuff just to see).  It worked best if you use a cheap paint brush to clean off the sludge every so often, but nothing took more than 24 hours.  Next test will be seeing if I can figure out how to do something bigger by wrapping it in a rag and basting it with the solution every so often.

[jar1292]

 

[b5blue]

I ordered 2lb of 99.9 pure from DudaDiesel for 11.49 with free shipping.

[Dino]

We've used citric acid in bodyshops for years, works great!

[b5blue]

Any advise or suggestions like mix ratio or using purified water?   

[Dino]

Any advise or suggestions like mix ratio or using purified water?   

Hot water, no need for purified.  Start low, 2-3% acid, see how it goes.  I've used as much as 10% but that was really pushing it.

[b5blue]

So a cup of water with a cup of acid is a no no?  I read if you add baking soda you get "fizzes"! What fun!! Fizzy rust remover....

[b5blue]

C acid came in and the old camera is charging......

[Dino]

So a cup of water with a cup of acid is a no no?  I read if you add baking soda you get "fizzes"! What fun!! Fizzy rust remover....

C acid came in and the old camera is charging......

I'm sure you know this but wear gloves, goggles and have lots of water near you just in case.

[b5blue]

Will do Dino! 

[Dino]

Any progress?  Haven't heard from you, still got all your fingers?

[b5blue]

Not yet I'm still sandblasting stuff....

[b5blue]

  Hey this crap kills flash rust pronto!
At 15ml citric mixed with 300ml hot tap water a few minutes of wiping with a paintbrush and the rust is gone leaving clean clear steel. Using a green scrubby speeds up the action and starts getting into pits. 
Now I'm experimenting, I mixed a batch at 15ml to 75ml then dumped aluminum oxide sand blast media to form an abrasive paste. This holds the pitted rust wetter longer and by putting it on with the green scrubby and rubbing it breaks up the rust that is weakened.....kinda a focused attack on the rear window channel area. 
I still have 10 fingers to boot!

[Nacho-RT74]

I have to clean up from surface rust a cast crank damper but I was worried about acid use due the rubber ring can get damaged I guess

so Do I begin to



?


I have used lemon juice to clean up nicelly the sulfat from battery ends

[440]

Oxalic Acid also works well for smaller parts that can be soaked in a bath.

[b5blue]

Citric acid can be found a hardware stores and many places like for canning supply's. I bought a coffee can size bag of it for 11.49 shipped free. So far in testing it looks to be ideal for engine stuff as on of the web I saw it's used to clean cooling systems. 
  Today I'm soaking some studs that have nuts rust frozen to them. The areas treated yesterday look fine this morning. 

[b5blue]

Sorry, with no "Before" pics it's hard to tell but I've reduced what needs to be sandblasted by 1/2 to 2/3's. This treatment would be ideal for projects on the "slow burner" where multiple applications out of a garden sprayer or pail and brush over time could bite into deeper rust. I could see it slowly attacking the border between clean steel and rust. This MUST be what others sell as a "safe and environmentally friendly rust remover".     

[Dino]

Looking good Neal.   

So you're using a 5% mixture, that's pretty good.  You can ramp it up a bit for the ticker steel pieces but try it on a scrap piece first.

Also try covering an area with cling wrap after you brush it on.  This makes the process last longer, or better yet, holds the acid onto the metal for a longer period as it doesn't evaporate as fast.  Again try on a scrap piece first.

Nacho, lemon and orange juice are medium strength acids, leaning towards the stronger side, so they work great to clean up a lot of things.  Citric acid is nothing more than the concentrated powder form of such acids and will save you a bit of money if you need to do larger pieces but I've taken a lemon to certain things before because I needed it clean asap.   The wife never likes it when I raid the fridge to clean car parts though.   

[440]

Do you need to neutralize the acid once the metal is clean, like with a baking soda wash?

[Nacho-RT74]

Citric acid can be found a hardware stores and many places like for canning supply's. 

never have seen that locally

[b5blue]

Do you need to neutralize the acid once the metal is clean, like with a baking soda wash?

It's so mild I just wipe it off with a clean cloth wile still wet. After any "treatment" I sand the area well before epoxy prime.

I sand blasted the rest of the channel's rust today, this really helped reduce the effort. (I'm really sick of sandblasting!!  )

[b5blue]

Citric acid can be found a hardware stores and many places like for canning supply's.  

never have seen that locally

It's used to keep fruit from browning like peaches, tomatoes or bananas. Mine is 100% food grade, it just drys out your skin slightly even after hours of messing with it like yesterday. Look in food stores.

[b5blue]

Like this:   http://www.walmart.com/ip/Ball-Citric-Acid-Additive/20469602

[Nacho-RT74]

Citric acid can be found a hardware stores and many places like for canning supply's. 

never have seen that locally

It's used to keep fruit from browning like peaches, tomatoes or bananas.

we do that with lemon juice LOL

[b5blue]

OK now for testing, insert one rusty hunk of 70 Charger Dutchman panel into a glass pan with 5% citric acid and now we wait....... 

[b5blue]

  Well good results! Yesterday it looked like not much was going on so I poked my finger at a spot and flakes of rust freed themselves. I scratched around with my fingernail and saw bare steel. Today I lightly rubbed the flat end of a small pry-bar across the surface and the rust detached like small corn flakes.
  I ran some errands and came back about 2 hrs later, I pulled the sample and hit it with tap water and a well used green scrubby lightly scuffing the rust. With no real effort this is what resulted:
   

[b5blue]

  This mix does not so much dissolve the rust, it lifts or separates it off the steel. You can see the flakes left in the pan. 

[JB400]

 

[Dino]

Stuff works doesn't it?      

[b5blue]

YUP, I'm sold that was 43 years of real rusted Charger.

[jt66383]

Now you just need a really big tub..... or maybe a swimming pool.... fill it with the citric acid and dunk the car in.... leave it for a few days, pull it out and you have a "rust free" charger.  LOL

This might be a new industry for the Orange Belt.
Jeff

[b5blue]

I was thinking of making a shallow tank out of 2x6's on my carport floor, lined with a thick plastic sheet. I could soak my hood in there a few days then pressure wash the thing between the support frame and skin. Speed up drying with alcohol and spray Rust Bullet or Rust Encapsulator between the two assembly's, 2 coats of epoxy prime and then paint. 

[69_XS29L]

I'm not a chemist, but I believe the point of treating steel corrosion with phosphoric acid is the fact that the heavy oxidation is is not only removed, but the remaining corrosion is converted to iron phosphate which is itself a corrosion inhibitor, similar to the black oxide finish on bolts and small parts we are all familiar with.
Citric acid can remove the rust, but on heavily corroded pieces may not necessarily penetrate into the pitting cells where corrosion starts, but you would be media blasting the worst of the rust first right? Whether or not you can see it or believe it, that shiny metal is oxidizing as soon as you finish drying it.   Alternatively, if the part is small enough to bathe, a mild caustic solution could be used with a DC power source to convert the rust back to iron through electrolysis with the same minor limitation as citric acid, the surface begins to oxidize almost immediately. On heavily corroded pieces this would have the benefit of salvaging some of the bulk and detail otherwise lost through stripping.
By the way, we use food grade citric acid in the oilfield to treat cement contamination in drilling mud. If you can find a drilling mud supplier with it in stock, it comes in 50lb bags for a little over 2 USD per lb. They should also have the medium grade walnut hulls or soda ash you can run as a less abrasive media in your sand blaster. Good luck,Mike.