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Need some rough chemical/chemistry help, chelation of rust

M

MichVandal

Well-known member
So I'm in the process of putting an old Miata back on the road, and having to deal with some rusty nuts and bolts.

Long story short, I'm doing a chelation process by mixing citric acid and sodium bicarbonate- which results having sodium citrate in a water solution.

The sodium citrate protects the base metal, but attaches to the Fe+2 and Fe+3 ions found in rust, and then it somehow transitions to a chemical that dissolves in water. Which is quite dark.

What I don't know is what form is that iron now in? I know the sodium citrate is safe- but what in the world is that black stuff in solution? Fe*****?

edit- I've tried various google searches to tell me what it is, but other than saying the iron ions end up in the solution- nothing tells me what it is.
 
dxmnkd316 said:
Oh snap, it could be this. actually, it's very likely this

https://en.m.wikipedia.org/wiki/Schikorr_reaction
Click to expand...

glad I looked before replying to your first suggestion- but I can do both now...

This one makes sense- magnetite is black- which is what the solution is. Now I have to figure out if I can get it out of solution to keep using the liquid.

For the first post- it *might* be iron citrate- but it would be in very small amounts- as there's almost no orange, and (in theory) the citric acid was completely taken out with the sodium bicarbonate. Meaning the acid would be a very small part of what's going on (which is the point of the solution, since the acid would etch the base metal- a bad outcome).

If anyone cared- the commercial product that I'm not buying is called Evaporust, and someone deduced that it used a phosphorus salt for the chelation. I kind of like this one, as all of the ingredients are both commonly available, and pretty darned safe. The citric acid is stronger than orange juice, but it's not hydrochloric acid, or sulfuric acid. And sodium citrate (the output of the original reaction) is also quite safe and common.

Both this and Evaporust end up with the solution a dark black- which is the rust coming off the steel. And magnetite is pretty safe, too- being used for jewelry and all. For sure, the direction for evaporust is to dilute the black stuff and flush it- which I feel a lot better with my chemistry.
 
Evaporust works well, I've been restoring an old car and it will clean steel pretty well unless it has good paint on it. One thing you can try is Molasses, buy feed grade and it will remove rust also. Guys build plastic pools to remove rust from a frame, fill it with molasses diluted with I believe water. Let it set and then rinse. You would have to paint it with epoxy quickly before it rusted again though.
 
Thanks for the suggestions walrus. I do appreciate it, but I also know of all of those- remember my old alfablue name was half a car that is very well know for rust. So I have been part of a really cool car forum for a really long time (Grassroots Motorsports, if anyone cares). And rust has been an issue for a long time. The magazine even has Evaporust as an advertiser, which means they've tried it.

People there have tried all of your suggestions and add vinegar and electrolysis to that as other tries. But the simple way has always been using Evaporust and another commercial knock off.

I've hesitated to get it, as I'm cheap.

Then a video came up about an alternate chelation chemical to try, and as it so happened, I had all of the ingredients- water, sodium bicarbonate (baking soda), and citric acid. Which I happened to have from wine making a long time ago. So I tried it, and it worked REALLY well, just like the video. So I did some googling (I hesitate to call it research), and found that it was pretty safe, as the sodium citrate salt protects the base steel as well as dissolve the rust. Let alone, citric acid, baking soda, and the resulting sodium citrate are all safe chemicals to even ingest.

All I was left with was more solution and a bunch of black stuff suspended in the solution. I knew it was Fe something- and not something with Cl or S in it- since that's not part of the chemistry. Evpaorust tells it's customers that it can either dump it down the drain when it stops working or dilute it 10-1 and spray on your grass. I just wanted to make sure I could with the alternate chemistry. (and someone did do some deducing of Evaporust, and the concluded it uses some phosphorus salt to do the work).

Going forward, if I needed to, citric acid is cheap enough on the big river, and I can get sodium bicarbonate anywhere. Or sodium carbonate (washing soda). And it's considerably cheaper than Evaporust.

I'm trying to cheaply put my '99 Miata back on the road- so safely reusing everything is kind of important.
 
Jesus Christ. Stop putting chemicals on or in the ground. Like fuck. That's really terrible and awful advice. Never ever ever put something in the ground unless it's specifically labeled for it.

Especially when it hasn't been fully characterized.

edit: your best bet is to bring it to your local environmental center and explain what it is. They'll properly dispose of it.

If anyone ever tells you to put something that isn't labeled for ground use in the ground, they're wrong and you're breaking the law and possibly contaminating groundwater supplies.

Also, don't dump chemicals down the drain unless they're designed for it. It can damage the pipes and stress the wastewater treatment system. Just bring your chemicals to the environmental center. It's often free and it's the most responsible thing to do by about a parsec.
 
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The only thing I don’t know is the form of iron in solution. The rest of the inputs/outputs are known, and then form of iron is pretty limited in what it can be. There isn’t sulphur or chlorine to worry about an odd combo.

And other than the iron, all of the other inputs/outputs are able to go down the drain, since they are all used in food and health products.

which is why I’d like to know what the iron is. Mind you, my pipes are iron, so that specific chemical is probably showing up in the sewer anyway. We’ve sent plenty of lemon pieces down the disposal to clean things up in the same manner that it reacts with rust.
 
Right, and I get that. But it's still best to just take a day, clean up the garage of all the old oil bottles, weed killers, etc and make a trip to the environmental center. We usually do that once a quarter or so.

Chemicals that have undergone unknown reactions due to ill-controlled conditions can't be known to be safe or unsafe. And, even if safe, still need to be removed at a treatment center increasing costs for everyone. The chelation and flocculation they do at WWT plants take time and chemicals. Best to not need to do that in the first place.

Think about it like this, if everyone leaves an 8-W LED on for 8 hours a day at evenly spaced times, it's still roughly equivalent to 20% of a nuclear power plant before adding line losses in. Which is to say, turn off your lights and don't add what is seemingly an insignificant load to an entire system.
 
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