Rust removal methods safe for cutting tools / precision parts?

[Fowlers FuryParticipant @fowlersfury]

The "fizz of bubbles" consists of carbon monoxide and hydrogen.
"……….Every form of treatment has its eco downsides, it's up to us to ameliorate their impact on the environment, the alternative is to sit in a chair and do bugger all, personally I'll just get on with using my citric treatments, at least you can stick your hand in the stuff without them vanishing in front of your eyes."
<><><>
Wasn't my original intention to add anything about either hazard or risk of CO and H release from citric acid use.
The hazards of both gasses are evident but the risks are for an informed user to assess according to their particular circumstances and beliefs.
CO represents the greater hazard because of its explosive and health effects in a confined & unventilated space.
For simplicity: Risk = Hazard x Exposure.

[EugeneParticipant @eugene]

A warm solution of boric acid powder / crystals is a cheap and very effective rust remover.

It really penetrates the rust deposit and is safe to use. I've used it on cast iron plane bodies very successfully. The only drawback is the danger of after rusting; best to water rinse, WD40 spray big time, and then use a spray oil.

There is a potential for hydrogen embrittlement on hardened parts with the electrolytic method, but wether it actually occurs is moot. I spent a long time studying the phenomenon and knew no more at the finish than I did at the start; an unpredictable business.

Eug

[Geoff TheasbyParticipant @geofftheasby]

Several natural products re poisonous, Deadly Nightshade, several types of mushrooms, apricot stones, etc. Ethylene glycol metabolises to oxalic acid in the liver, and kidney stones are mostly oxalic acid. Aspartame (sweetener) metabolises to methanol in the liver, as do many other chemicals. That is the liver doing its job.

[Fowlers FuryParticipant @fowlersfury]

"I don't think (and haven't checked) that Citric Acid and Rust produce Carbon Monoxide."

C₆H₈O₇ + Fe₂O₃ = 2FeO + 6CO + 2H₂O + 2H₂

[maurice bennieParticipant @mauricebennie99556]

Hi all, This may sound crazy but it works, Had two iron rail track nails from U.S.A. .told to put them in water and add chopped up potato ,leave to soak .Left them for 4 weeks . (forgot them) they were covered in black powder ,washed off off with an old tooth brush . could not believe that they were rust free and shiny. Do not know how it works but it does .I think it may be malic acid . Care with cleaning the black powder is very clinging and a job to get off hands.

Best wishes Maurice.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Fowlers Fury on 01/12/2017 14:17:42:

"I don't think (and haven't checked) that Citric Acid and Rust produce Carbon Monoxide."

C₆H₈O₇ + Fe₂O₃ = 2FeO + 6CO + 2H₂O + 2H₂

I'm convinced! In future rust removal with Citric Acid is an outdoor job. It would be a shame to MacGyver myself with an innocent food grade chemical!

Thanks,

Dave

[RJWParticipant @rjw]

I'm convinced! In future rust removal with Citric Acid is an outdoor job. It would be a shame to MacGyver myself with an innocent food grade chemical!

Thanks,

Dave

Yes definitely an outdoor job, ditto electrolysis, any acids and anything to do with Horolene type products (ammonia based), I perhaps mistakenly assumed folks would be doing these jobs outdoors anyway.
If it's raining or generally crappy weather and doing a bit of electrolysis, I commandeer the wife's greenhouse for a while (very draughty), and yes, I do warn her to keep out until I've done, the citric acid jobby can just sit outside.

John.

[Jon GibbsParticipant @jongibbs59756]

I'm quite surprised to see the equation quoted above for citric acid action on rust. What's it's provenance?

It's a while since I did A-level chemistry but surely, one would expect at least some iron citrate created (C₆H₅FeO₇) with hyrogen and water only liberated.

Jon

[Carl Wilson 4Participant @carlwilson4]

I’ve used a product called Bilt Hamber De-ox C. Very effective.

[Mark RandParticipant @markrand96270]

Posted by Jon Gibbs on 01/12/2017 22:52:01:

I'm quite surprised to see the equation quoted above for citric acid action on rust. What's it's provenance?

It's a while since I did A-level chemistry but surely, one would expect at least some iron citrate created (C₆H₅FeO₇) with hyrogen and water only liberated.

Jon

 

 

You very definitely do get ferrous citrate produced! it's quite surprising when you've got the mixture simmering on the hob and all of a sudden a layer of white powder precipitates on the bottom of the casserole dish (cleaning up a days worth of vertical lap TIG welding practice pieces, so I could weld the other sides up on the following week's session )

 

There was no remaining FeO on the pieces!

Edited By Mark Rand on 02/12/2017 01:39:34

[john fletcher 1Participant @johnfletcher1]

I have a slightly related question. What is an environmentally friendly and safe way of disposing of exhausted battery acid ( Sulphuric Acid), which has been used for other purposes. John

[vintagengineerParticipant @vintagengineer]

CO is also flammable as well as being poisonous!

[Fowlers FuryParticipant @fowlersfury]

"I'm quite surprised to see the equation quoted above for citric acid action on rust. What's it's provenance?"

My fast-declining memory resurrected the CO/citric acid link from way back so I had to check b4 posting.
Its "provenance" is that several reputable websites confirmed the basic equation. But rust is actually a mixture of Fe(III)₂O₃ “iron oxide”, and Fe(III)(OH)₃ “iron hydroxide” so the quoted equation is only partially correct in that it relates to Fe₂O₃ and not Fe(OH)_3.
It appears that the equation for trivalent iron hydroxide is:-
C₆H₈O₇ + Fe₂O₃ = Fe₂C₃ + 4H₂O + 3CO₂
However, several sources list the sequential equations for rust formation:-

1. 2Fe(s) + 2H₂O(l) + O₂(g) 2Fe²⁺(aq) + 4OH^–(aq)
2. Fe²⁺(aq) + 2OH^–(aq) Fe(OH)₂(s)
3. Fe(OH)₂(s) =O₂=> Fe(OH)₃(s)
4. Fe(OH)₃(s) =dehydrates=> Fe₂O₃.nH₂O(s) or rust

So from this, Fe₂O₃ is the final product and the original equation would seem to be applicable.

[Fowlers FuryParticipant @fowlersfury]

1. 2Fe + 2H₂O + O₂ = 2Fe²⁺ + 4OH^–
2. Fe²⁺ + 2OH^– = Fe(OH)₂
3. Fe(OH)₂ in O₂ → Fe(OH)₃
4. Fe(OH)₃ → [dehydrates] → Fe₂O₃.nH₂O or rust

Apologies, despite those equations appearing to display as intended, returning to the site they show with weird characters. This time I'll try cut'n'paste from Word and hope they don't become mangled.

[Martin DowingParticipant @martindowing58466]

@Fowlers Fury,

Sorry for slightly unpolite comments but equations you are writting as reaction of citric acid with Iron oxide is an utter nonsense.

Fe2C3 does not exist and even if very recently something of such composition was produced, that would be done by some meddling with elements above 900*C or so. It *certainly* cannot be made in water solution from iron salts or oxides and citric acid even if someone have written such nonsense on the internet.

Existing Iron carbide has a formula Fe3C, it is known as cementite and is produced by rapid cooling of solution of carbon in iron. It is responsible for difficult machinability of *chilled cast iron*.

Reaction #1 in your second post is also messed up, that because Fe(OH)2 does not dissociate and its solubility in water is very low.

Correct statement would be:

2Fe + 2H2O +O2 —> 2Fe(OH)2

I doubt that CO is formed easily from citric acid and iron salts or oxides/hydroxides in water solution during pickling

I suspect that *smelting* citric acid with rust at temperatures of 130*C and more may produce some carbon monooxide.

It is known that carbon monoxide is formed by slight heating citric and conc sulfuric acid or better with oleum, which acts as dehydrating agent.

Reaction goes as follows:

CH2COOH-C(OH)COOH-CH2COOH —-> CH2COOH-CO-CH2COOH + H2O + CO

On the left side of equation is citric acid and on right one something known as acetonedicarboxylic acid.

Regarding toxicity of citric and oxalic acids. They are for all practical purpose harmless compounds, lethal dose killing about half of those affected is ~ 20-30g for oxalic acid and about 40-60g for citric acid. Soluble salts have comparable toxicity. To get poisoned by these deliberate consumption of considerable quantities is needed.

One may say that oxalic acid is about 10 times more toxic than kitchen salt.

Regarding rust removal, it is monopotassium salt of oxalic acid (COOH-COOK), which does job the best. It is commercial product.

Fosforic acid is also often used for derusting and it is more pleasant to work with than hydrochloric or sulfuric acids.

Martin

[maurice bennieParticipant @mauricebennie99556]

Hi Martin, Could you please tell me what the reaction is between what is in the potato and iron rust .I know that it removes rust but do not know why .I spoke to an old lady yesterday and she told me that just rubbing a potato peel on rust , the rust goes . This seems to be an old trick .

PS I am 87 and not heard of it .

thanks Maurice.

[Tim StevensParticipant @timstevens64731]

John Fletcher the first asks:

What is an environmentally friendly and safe way of disposing of exhausted battery acid ( Sulphuric Acid), which has been used for other purposes.?

Well, it all depends on what the other purposes were. The acid itself won't do the drain system much good, as it tends to eat the lime in mortar – so a simple way to make it safer is to mix it with limestone or chalk. This will fizz, giving off carbon dioxide, and turning the calcium carbonate into calcium sulphate. This is a natural product found in rocks, and used as blackboard chalk. Not harmful unless thrown by an irate teacher and it hits you in the eye.

If the acid has been used to clean steel, or concrete, much of its corrosive nature will have been used up, but without analysis you can't easily tell how much. Use for other purposes may add noxious stuff to the mix, so further advice depends on knowing what exactly the uses were. Cleaning brass or copper, for example, will mean that copper is dissolved in the acid (as copper sulphate, blue in colour) along with zinc, perhaps, and this is poisonous to various sorts of wildlife, so 'down the drain' is not a safe option. Nor is 'in the corner of the garden when no-one is looking'.

Cheers, Tim

[Jon GibbsParticipant @jongibbs59756]

This is all interesting stuff but I'm afraid FF that just because an equation that has been reproduced several times doesn't mean it's correct.

It's 39 years since my A-level chemistry but this is pretty basic stuff. A solution of anhydrous citric acid in water is just going to be a dissociated mixture of H+ ions (this is the definition of an acid) and citrate ions (C₆H₅O₇-). All acids will dissolve rust (and iron/steel) and this one is no different. It's a fairly weak acid but will naturally react with the rust reducing it to a mixture of Fe2+ and Fe 3+ ions and citrate ions, liberating water or hydrogen in the process. The iron citrate will then potentially precipitate out, depending upon the solubility of the iron (II or III) citrate (**LINK** and **LINK**), which are both only weakly soluble.

Citrate ions are stable, and so is iron citrate in both forms, and so I agree with Martin that it is highly unlikely that the citrate compounds will decompose and release carbon monoxide.

Jon

[Martin DowingParticipant @martindowing58466]

Hi Maurice,

Potatos contain small amount of oxalic acid, which is known to dissolve rust.

It goes like this:

FeO(OH) + 3 HC2O4^- —–> Fe(C2O4)^3- + 2H2O

So insoluble rust, FeO(OH), is reacting with 3 hydrogen oxalate anions and soluble trioxalatoferrate(III) is formed.

Martin

[Martin DowingParticipant @martindowing58466]

@Tim Stevens,

Waste sulfuric acid containing Fe^2+, Fe^3+, Cu^2+ and Zn^2+ is to be treated with limestone or lime to neutralize acid, then excess of limestone will produce zinc and copper carbonate (inoluble) together with also insoluble basic carbonates of iron and copper and hydrated oxides of iron. Bulk of solid is calcium sulphate (gypsum). All of these compounds are also ores of respective elements, so they are not unknown to Nature.

this cake goes to landfill.

Martin

[VicParticipant @vic]

Posted by Gordon A on 29/11/2017 21:51:25:

I find that electrolysis works for me on tools etc. Washing soda is dirt cheap and not much electricity is used. Search for electrolysis rust removal on the web, lots of information out there on the subject.

Gordon.

Yes, that’s what I use and it’s never failed yet. Don’t use Acid, even Citric, it will etch the surface.

[Fowlers FuryParticipant @fowlersfury]

Posted by Jon Gibbs on 02/12/2017 17:32:26:
This is all interesting stuff but I'm afraid FF that just because an equation that has been reproduced several times doesn't mean it's correct.
<><><><>
I agree entirely ! My original comment was to the effect that buried in the memory was a link between citric acid+iron+CO. In searching for confirmation, that equation was repeated very frequently, it balanced and so without adequate consideration, I reproduced it. (Energy factors alone should have rung warning bells). Not to justify the error but I've since spent several fruitless hours trying to track down the origin of that equation. It has only been queried once (other than here) in a Norwegian publication.
<><><><>
It's 39 years since my A-level chemistry but this is pretty basic stuff. A solution of anhydrous citric acid in water is just going to be a dissociated mixture of H+ ions (this is the definition of an acid) and citrate ions (C₆H₅O₇-). All acids will dissolve rust (and iron/steel) and this one is no different. It's a fairly weak acid but will naturally react with the rust reducing it to a mixture of Fe2+ and Fe 3+ ions and citrate ions, liberating water or hydrogen in the process. The iron citrate will then potentially precipitate out, depending upon the solubility of the iron (II or III) citrate (**LINK** and **LINK**), which are both only weakly soluble.
<><><><>
I thought perhaps your 2nd link to a Wikipedia article might be useful but the reference given to "or by action of citric acid on metallic iron.^[1]" is of no value, like so many refs on there.
<><><><>
Citrate ions are stable, and so is iron citrate in both forms, and so I agree with Martin that it is highly unlikely that the citrate compounds will decompose and release carbon monoxide.
Jon
<><><><>
As for Martin Dowing's specific comment "Fe2C3 does not exist…." ~ that error was due to my attempt to use sub and superscript for the equations on this site which has limited text modifiers. I had made the changes in Word and had copied (Ctrl+V) the text directly without checking it appeared correctly. I should have used the "Paste from Word" icon. I'll do that now from this hopefully authoritative source but won't know for sure until after pressing "Add Posting" !
Corrosion of iron to form a hydrated iron (III) oxide Fe₂O₃.xH₂O.
It is an electrochemical process in which different parts of the iron surface act as electrodes.
At the anode, iron atoms dissolve as Fe²⁺ ions:-
Fe(s) → Fe²⁺ (aq) + 2e
At the cathode, hydroxide ions are formed:
O₂ (aq) + 2H₂O (l) + 4e → 4OH^– (aq)
The Fe(OH)₂ in solution is oxidised to Fe₂O₃
(Oxford Univ Press: Dictionary of Chemistry. 2000)
<><><><>
Apologies to anyone still following this thread.
<><><><>
P.S. to Martin D. "fosforic acid"? Are you Romanian?

[SillyOldDufferModerator @sillyoldduffer]

Fowler's Fury has my sympathy. I spent an unhappy hour plus last night searching the internet for a reliable formula for the action of Citric Acid on rust. Most of what I found was poor quality, much of it written by amateurs or – in one case – a self-appointed expert specialising in 'not answering questions whilst pretending to be smart'. Very few web-pages address the underlying chemistry, and if they do there are enough mistakes to cast doubt on the whole. There's a strong hint that quite a lot of ignorant copying is going on, warts and all! Doesn't help that many websites mangle chemical and mathematical formula even when the author has it right on paper.

I found FF's Carbon Monoxide formula in several places. Only one mention had a reference link to the source. As the link is broken it's a dead end!

The alternative formula says that the usual acid reaction takes place to produce the salt. Iron Citrate and no Carbon Monoxide. This is in line with what I originally expected the reaction to be. But no quality references are given for this either! A number of practical people mention thick scale developing when items are left too long in the Acid; this must be yet another – as yet unexplained – reaction.

Grateful if anyone can identify a reliable reference to the Citric Acid de-rusting reaction – a proper Chemistry Book or scientific paper. Without that it's still in doubt. At the moment I'm thinking of experimenting with a Carbon Monoxide detector to see if I can detect anything nasty whilst de-rusting with Citric Acid.

I don't think de-rusting with Citric Acid is hazardous. Common-sense – don't breath the concentrated fumes, drink the solution, squirt it up your nose, or splash it in your eyes. Also, don't leave items in de-rusting solution for too long unless you want to replace rust with some other type of corrosion.

Dave

PS One useful discovery was the suggestion that Ammoniated Citric Acid can be used to passivate steel after treatment. After removing rust in the usual way, the pH of the solution is reduced to 3.5 by adding Household Ammonia and left for a couple of hours. This – it is claimed – slows future rusting. I've seen pH strips on sale in Garden Centres.

Edited By SillyOldDuffer on 03/12/2017 10:08:43

[Danny M2ZParticipant @dannym2z]

Posted by Neil Wyatt on 01/12/2017 13:56:09:

Posted by Matt Harrington on 01/12/2017 13:03:05:

Posted by Geoff Theasby on 01/12/2017 12:40:41:

Oxalic acid is very poisonous.

Geoff

Really, I thought it was found in plants. I suppose everything is poisonous in certain proportions.

Matt

That's why you shouldn't eat rhubarb leaves!

It causes gout among other things.

Simmering an old aluminium model diesel engine crankcase in a pot of rhubarb leaves is an excellent way to clean it up before a rebuild.

Don't use mum's best saucepan for this, don't even use it for food again but marvel at how shiny the inside of the saucepan is up to the liquid level.

* Danny M *

[Fowlers FuryParticipant @fowlersfury]

Some consolation for my failings in that Dave (aka S.O.D.) fared no better in tracking a source of the erroneous equation. Sufficient grey cells remain to remember that my original search and hence link to CO, was a consequence of using citric acid to remove black Cu oxide after silver-soldering a boiler. Even after washing & drying, the layer of copper citrate had to be removed by a soft wire brush. The particles thus generated proved an eye & nasal irritant, subsequently confirmed by reference to the trusted nih data-base viz:–

H315 (93.75%): Causes skin irritation [Warning Skin corrosion/irritation]
H318 (93.75%): Causes serious eye damage [Danger Serious eye damage/eye irritation]
**LINK**

At some point in that hazard searching, I encountered the dubious “Fe/Citric/CO” equation.

(Yes – I should have worn goggles and a face mask when brushing off that copper citrate residue but as in so many home workshop activities, a risk assessment was ignored).
Renewed apologies for this time deflecting the thread to copper and citric acid.

[Author]

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