Citric acid and rust

[grannyknot]

Back in the summer there was a thread about a German product, a paste made of Citric acid and sawdust.  I can't find it at the moment but I have been playing around with Citric acid for a couple months now and it has become my go to rust remover.

I have found all the other acid rust removers have some drawbacks to them but Citric has the fewest so far.  It is very inexpensive especially the industrial grade,  I didn't want to purchase 50lbs until I knew it was worth it so bought 10lbs of food grade.  2 cups of dried powder in about a gallon of water makes a strong  solution. Your results may vary depending on the hardness of your water but it should be easy to repeat these results.

The test piece is from the KA24DE engine I'm using in the 510,  2 cups of Citric acid in a gallon of water, all I did was scrape the worst of the flaky rust off.  The shop is cold, just above freezing, when the water is room temp in the summer rust removal happens a lot faster.  If you splash some on your skin you just rinse it off, there is no drama, no burns.

These next 2 pics are after 20hrs soaking, took it out of the bucket and scrubbed it with an old wire brush and rinsed. The last 2 pics are after an additional 24hrs.

Now that might seem like a long time but I have lots of that so I'm good.  Muriatic acid is 10x faster for sure but I have never found a way to completely neutralize it, the rust always comes back under the paint,  so far that has hasn't happened with the Citric acid pieces.

 

[dutchzcarguy]

7 hours ago, grannyknot said:

scrubbed it with an old wire brush

Top tip...  Saw the first 1-2 inch off the brush.. you have a good brush again!  That piece of wood gets in the way with brushing.. now no longer! 

Use a steel saw..

Edited November 25, 2020 by dutchzcarguy

[AK260]

This is great!

Just to offer an alternative: I was frankly amazed how good this experiment went.

I bought 6 bottles of the cheapest / nastiest bottled lemon juice off the supermarket shelf.



Poured into an old ice creme tub and added lots of salt - no scientific measurement, just what felt right. If I had to quantity I would say 2 table spoons.

Degreased parts with thinners, then left them in the lemon juice and salt tub for 12 hours overnight.

See for yourself:

[Namerow]

44 minutes ago, AK260 said:

Poured into an old ice creme tub and added lots of salt - no scientific measurement, just what felt right. If I had to quantity I would say 2 table spoons.

Why did you add salt?

[AK260]

Why did you add salt?

I read somewhere that it speeds up the reaction. Interesting thing was that the garage / the solution smelled like sulphuric acid after the 12 hour soak. But I’m no chemist.

I reused the solution many times over and it worked well ...






Before this, I wasted way too much time with a wire wheel and drill achieving lesser results!

OK I’m gonna shut up now, I feel like I’m thread jacking!

[240260280]

Chris, I'd be careful using Acid of Citrus:

 

[AK260]

Chris, I'd be careful using Acid of Citrus:
 

Brilliant!

[Captain Obvious]

10 hours ago, grannyknot said:

I have been playing around with Citric acid for a couple months now and it has become my go to rust remover.

Brothers from a different mother, I tell ya.   I've gone through thirty pounds of the stuff in the past two months.

It's really hard to get a good picture of the results, but I tried. Here's a handful of misc hardware. Before:

I put the stuff in a wide mouth plastic container for a couple hours. When I first put the stuff in, it bubbles and becomes a little milky looking from all the tiny bubbles. I think that's the remaining yellow chromate and zinc plating being eaten off:

And then after a couple hours. They aren't sparkling perfect, but are a whole lot better than when I started:

Here's about the only good shot I have of before and after:

I've got parts out for professional plating right now. Should be done soon.....

[Captain Obvious]

44 minutes ago, Namerow said:

Why did you add salt?

That's a trick used with acetic acid to speed up the reaction. Apparently acetic acid works better than citric (but it stinks) and the addition of salt makes it work even faster. So fast, in fact, that they warn you not to put anything aluminum in the solution because it will be damaged. I don't know for positive sure if it has the same effect with citric, but like Granny, I did the same and added a little bit to my mix. I figured it wouldn't hurt, and may help.

From what I understand, the citric does not convert the rust to anything, but it is "chelated" instead. And my (quite limited) understanding of the whole thing goes like this...

Rust is not normally soluble in water, but additions of certain additives (like these mild acids) make it so that rust IS slightly soluble in the solution. I think that makes the acid additions to the water "chelating agents". So once you add citric acid to the water, rust becomes slightly soluble and "washes" off the parts. Doesn't happen quickly, but it happens.

So back to my very limited understanding... There are several different combinations of iron and oxygen that can be called "rust", and the addition of salt changes the ionic characteristics of the solution and makes a broader range of them soluble. So in other words, "a wider range of rust types are soluble".

[Muzez]

3 hours ago, Captain Obvious said:

I've got parts out for professional plating right now. Should be done soon.....

Does surface rusting restart once it is out of the solution? Or the chelating removes all of the rust particles and as long as the part is dry between removal and plating, it won't start to rust? 

[Mark Maras]

 I use Ospho which uses phosphoric acid as the active ingredient. It removes rust quite well and leaves a film of iron phosphate. When I'm ready to paint I wipe the area down with a little baking soda, and water on a sponge. Then a water rinse and a wipe down with lacquer thinner.

[AK260]

Does surface rusting restart once it is out of the solution? Or the chelating removes all of the rust particles and as long as the part is dry between removal and plating, it won't start to rust? 

So with my solution, I dropped the parts into clean water straight away to flush them. Then I would drop them into a container of Jenolite and ensure all surfaces were covered. This converts the surface into something that turns it purple and supposedly doesn’t rust.



The parts I didn’t Jenolite started to turn dull all too quickly as those pesky o2 atoms started to attach themselves!!!

After the allotted time and drying throughly, I just painted them; as at the time we were in serious lockdown and I couldn’t get to the plating place.