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Rust removal methods safe for cutting tools / precision parts?

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Tim Stevens02/12/2017 17:30:47
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1020 forum posts

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 Gibbs02/12/2017 17:32:26
738 forum posts

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 Dowing02/12/2017 17:50:17
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245 forum posts
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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 Dowing02/12/2017 18:05:14
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245 forum posts
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@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

Vic02/12/2017 18:46:15
2047 forum posts
10 photos
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 Fury02/12/2017 22:31:37
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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?wink 2

SillyOldDuffer03/12/2017 10:07:31
4316 forum posts
940 photos

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 M2Z03/12/2017 11:31:09
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732 forum posts
278 photos
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. wink

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 Fury03/12/2017 13:15:30
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320 forum posts
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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.

mark smith 2003/12/2017 14:13:48
566 forum posts
296 photos

**LINK**

Tim Stevens03/12/2017 15:16:52
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1020 forum posts

An interesting error in the Patent which Mark Smith has found - and thanks for that, very helpful:

The much higher free acid present in the solutions according to the invention allows much of the ion to exist in a ferrous state.

I am certain that the word 'ion' should be 'iron'. There will be ions in the mix, for sure, but there ain't no such animal as an ion in a ferrous state, when you start with citric acid and ammonia, and therefore you include no iron at all until the rust removal starts. I think what they actually meant was 'iron ions ... in a ferrous state'.

The intro does make it clear that the text has been prepared by OCR, so may include errors.

In conclusion, make up your ammoniated citric acid in concentrated form, and use it diluted. Once diluted it will go mouldy.

Regards, Tim

Edited By Tim Stevens on 03/12/2017 15:27:42

maurice bennie03/12/2017 15:51:53
164 forum posts
1 photos

hi Martin Thanks for the reply , I was ,many years ago ,a technician in a pharmaceutical co, know a bit of chemistry

that was a nice lesson ,now understand what happens .

Maurice.

Mark Rand03/12/2017 20:55:59
692 forum posts

As I noted above, you do get ferrous citrate produced with steel and citric acid. It's almost insoluble, so you get a thick layer of precipitate. You wouldn't get that with the other posited reaction.

 

PS:- I see nothing novel in that patent application. I hope it was denied...

Edited By Mark Rand on 03/12/2017 21:01:40

Martin Dowing03/12/2017 21:29:39
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245 forum posts
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@Fowlers Fury

Quote from your link regarding Copper citrate:

"H302 (100%): Harmful if swallowed [Warning Acute toxicity, oral]
H315 (11.43%): Causes skin irritation [Warning Skin corrosion/irritation]
H400 (77.14%): Very toxic to aquatic life [Warning Hazardous to the aquatic environment, acute hazard]
H410 (74.29%): Very toxic to aquatic life with long lasting effects [Warning Hazardous to the aquatic environment, long-term hazard]"

I cannot find here at all that it is causing serious eye damage and only 11.43% of reports (not 93.75% as you claim) are recording skin irritation.

My own impression about copper citrate is that it is relatively harmless compound, unless consumed deliberately in considerable quantities and will cause skin irritation and sometimes allergy in rather few particularly careless or sensitive individuals, though I would avoid breathing in dust of it.

Statements about toxicity to aquatic life are correct albeit I would call it "toxic", not "very toxic" because if it is "very toxic" then other common industrial chemicals like cyanides would be "very very very toxic". You could not call them "extremely toxic" either because if you do, then alcaloid pilocarpine would be "extremely extremely toxic" etc.

From my own long industrial experience as research chemist I have found that most of risks assesments are rather political/legal documents of very limited value in real life. Their production is a great time wasting exercise and it is sometimes actually endangering health of workers because they are first forced to produce this nonsense to satisfy legal requirements and then they still must complete planned tasks, often in hurry and therefore without proper attention, because much time already was wasted on writting risk assessments, getting them authorised etc.

Re: descaling of copper from copper oxide: I would use 10-20% hydrochloric acid but on copper, not on brass. You can remove copper oxide from copper or brass with disodium salt of EDTA (di-sodium ethylenediamiotetraacetate or di-sodium wersenate) at pH 7-8, eg essentially neutral conditions.

You can easily buy this reagent over Internet. It is used for lead battery reconditioning and many other things and rather cheap. It will not remove copper sulfide scale only copper oxide.

Martin

Fowlers Fury03/12/2017 22:32:41
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(1) "only 11.43% of reports (not 93.75% as you claim) are recording skin irritation."
I am not claiming that, it is reproduced from the literature.
(2) "R(risk) and S(safety) phrases are assigned to chemicals by concensus in an expert committee of the EU. The risk phrases are somewhat of a misnomer because they are hazard phrases but distinguishing between those 2 concepts is linguistically difficult elsewhere in Europe.You are of course free to make your personal assessment of risk with "My own impression about copper citrate is that it is relatively harmless compound".
(3) "From my own long industrial experience as research chemist I have found that most of risks assesments are rather political/legal documents of very limited value in real life".
From my long experience as a toxicologist in the chemical industry I have a different view.
(4) "Their [risk assessments] production is a great time wasting exercise and it is sometimes actually endangering health of workers because they are first forced to produce this nonsense to satisfy legal requirements"
As a past member of the HSE's Advisory Committee on Toxic Substances, I assure you the TUC, CBI and HSE members think otherwise.
(5) I also use dil HCl to remove Cu oxide.


Martin Dowing03/12/2017 22:36:42
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245 forum posts
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@ Silly Old Duffer

Reaction of citric acid with rust is discussed here:

"Chemistry and metallurgy" Second Revised and Enlarged Edition; A. Sherry; J. S. Beck; A. E. Cruddace; page 357;

It reads:

"Fe2O3 + 2 H3Citrate ----> 2 FeCitrate + 3 H2O

where citric acid is represented by H3Citrate to simplyfy formula."

Martin

Martin Dowing03/12/2017 23:02:54
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245 forum posts
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Posted by Fowlers Fury on 03/12/2017 22:32:41:

(1) "only 11.43% of reports (not 93.75% as you claim) are recording skin irritation."
I am not claiming that, it is reproduced from the literature.
(2) "R(risk) and S(safety) phrases are assigned to chemicals by concensus in an expert committee of the EU. The risk phrases are somewhat of a misnomer because they are hazard phrases but distinguishing between those 2 concepts is linguistically difficult elsewhere in Europe.You are of course free to make your personal assessment of risk with "My own impression about copper citrate is that it is relatively harmless compound".
(3) "From my own long industrial experience as research chemist I have found that most of risks assesments are rather political/legal documents of very limited value in real life".
From my long experience as a toxicologist in the chemical industry I have a different view.
(4) "Their [risk assessments] production is a great time wasting exercise and it is sometimes actually endangering health of workers because they are first forced to produce this nonsense to satisfy legal requirements"
As a past member of the HSE's Advisory Committee on Toxic Substances, I assure you the TUC, CBI and HSE members think otherwise.
(5) I also use dil HCl to remove Cu oxide.

"it is reproduced from literature"

Not really. Link specified by you is claiming explicitly "H315.(11.43%) causes skin irritation", *You* are claiming 93.75% contrary to link which you have submitted yourself. So perhaps read it again.

"R(risk) and S(safety) phrases are assigned to chemicals by concensus in an expert committee of the EU"

There are plenty of commities in the EU, unfortunately most of them entirely useless.

"As a past member of the HSE's Advisory Committee on Toxic Substances, I assure you the TUC, CBI and HSE members think otherwise."

Who cares what they think? Industry is moving production to China and elsewhere and they have nothing to say there. Bureaucrats you mention are one of many causes of pending economic ruin of West where everything is outsourced and only bankrupt banksters and hopelessly indebted public is left.

Martin

AdrianR19/05/2019 18:07:27
197 forum posts
12 photos

I have just tried citric acid to clean up some rusty tool makers clamps, very impressed with the result. Actually it was Ecover toilet cleaner 1:4 with hot water.

I after scrubbing I soaked them in a solution of sodium bicarbonate to neutralise any remaining acid and then a light oil.

Brian H20/05/2019 14:24:44
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1107 forum posts
85 photos

I can vouch for the Frosts rust remover. I foolishly did some major silver soldering in the workshop and all unprotected steels went rusty.

I soaked a couple of items in Frosts, wiped them with a tissue, washed them in water and immediately sprayed on some WD40.

The items cam out a matt grey colour but free of rust.

Brian

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