Salt and vinegar for rust removal

[Sandy]

On Wed, 19 May 2004 20:27:09 GMT, "Dan White" posted:

Nope, I merely interjected my question about the need for salt into an already existing thread. But I see what you mean.

Wiped away with a cloth? The salt may have been acting as a scourer? Copper is the other side of hydrogen in the electrochemical reactivity table, so perhaps there is some difference here with iron?

Except for what I said above.

Now this is perhaps the most important step and you have not elaborated. How did you clean these things? The salt crystals can act as a scourer, so if you wiped them with a rag....

Could be that more of the orange rust had dissolved leaving the black magnetite (Fe3O4), and the salt and vinegar dissolved less of this orange rust leaving it appearing lighter. Both my examples seem minutely more orange (lighter colour) than the non treated parts of the nails.

I would guess that they are the same colour, containing the same coloured ion Fe+++, but I'm not sure. I'm not even sure that this iron chloride complex exists, as my question as to what happens to all that excess Na+ was never answered.

My vinegar-only is definitely effervescing slightly more than the salt and vinegar as seen this morning by swirling the bubbles away and looking again in ten minutes for new bubbles to form. Previously, effervescence appeared roughly similar and quite slight.

My reading suggests that the salt-treated article will rust more, even if left dry. This is the problem, as the salt in the minute pits will attract atmospheric moisture and act as electrolyte in minute electrochemical cells. This will happen more in some alloys than others.

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My experiment was with very rusted nails.

The vinegar only solution is brown(orange) and the salt and vinegar is pale yellow. Effervescence is still going ever more strongly (though still quite weak) at 46 hours. There seems to be more black specks floating in the salted version. This may have been due to an original difference in the nails. Both have a few rust particles on the bottom of the tumblers. The nails are imperceptibly different from when I put them in the solutions -- slightly more yellow where the solutions have acted, but still very heavily rusted.

I found that salt perhaps inhibits the process slightly, (except, perhaps, as a scourer when the article is wiped with a rag?) I worry about that salt in the rust pits, and so personally would bever use salt on anything of mine that I valued.

My conclusion is that this procedure is useless for heavily rusted articles. And salt makes an insignificant difference.

A wire brush and/or electrolysis might be a better way to go.

Thanks for an interesting exchange, Dan.

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Dan:

Sandy:

Sandy:

[Sandy]

On Wed, 19 May 2004 17:36:16 -0400, "George" posted:

Although iron and copper straddle hydrogen, which is an important watershed. Very few sodium tools available :)

That would be acetic acid? H+ is surely what you need to dissolve insoluble carbonates/hydroxides/oxides? (Along with an anion that does not have insoluble salts with the iron)

BBbbbbut the topic was rust :)

[Dan White]

The salt could be a scouring agent, but I don't think this is the main benefit of salt. If you pour the salt on, you see small regions around each grain where the rust is dissolving, even before you touch the pot with a sponge.

Yes, for sure that could be it. I was hoping not to relearn every electronegativity etc etc. :)

I honestly don't think salt scouring had much to do with it. After I dumped out the acid I ran them under water and literally rubbed them with my fingers. It was really more of just brushing the black bits off the metal. I think all the salt had dissolved in the acid after 48 hours, anyway. Now, I next cleaned the weights with a brass brush, so that's where some scouring comes in. Even so, the vinegar/salt weight was cleaner, but I wouldn't say so conclusively. It really could just have been a difference in the two weights from the start. If there were any scouring other than the brass brush, it would probably be more from the bits of Fe2O3 or whatever it is that turns black.

snip

It is interesting, though, to note that in my experiment the vinegar/salt solution was pale orange, while the vinegar only was deep red. I'm interested to see how it ends up in your test. There is *definitely* something different going on in each case, and it would be interesting to know what that is. I wonder if the vinegar only is dissolving more Fe metal, and is somehow inhibited by the salt. Maybe this needs to be done in the absence of air, as the other poster suggested. Maybe the results would be different.

Ditto. You make a good point about salt corrosion. Good to know.

dwhite

[George]

Sodium salts are quite soluble versus iron, you know. You've had ion replacement going on as well as reduction.

[WillaimC]

Muriatic acid of the sort used for concrete work removes rust completely and in a fairly short order. I dropped some fine thread rusty bolts in this acid and left it overnight and the threads screwed into the correct size nut with no problem so the metal was not eaten away. The only posssible downside is that the metal is turned to an even light grey, possibly from very light etching

[Sandy]

On Thu, 20 May 2004 09:51:42 +0800, Sandy posted:

Final report on the great Salt and Vinegar test :)

Before I hoik it all out and consign the tumblers to the dishwasher, I thought I would describe conditions (About 75 hours, I think)

The salt-and-vinegar solution has just about NO colour to it; it has NO effervescence; and a black scum on the surface. The nails are no different from before treatment except that they have gone blacker. There is a an amount of rust flakes on the bottom.

The "vinegar-only" still has slight effervescence occurring, and is a strong orange/red colour. The nails are no different except a little more rusty coloured. There is a similar amount of rust flakes on the bottom.

As a final twist, I decanted some of the clear orange liquid from the vinegar-only solution and added excess salt. Lo and behold, a black precipitate occurred turning the solution almost chocolate brown and opaque. I will leave this to settle, coz what I'm trying to see is if this purported ferric chloride complex is less orange than the straight ferric ion. So far, half an hour, the red colour seems to be persisting, so unless there is a marked loss of colour, that ferric chloride complex has not been demonstrated. Although the lack of colour in the vinegar-salt test could be because no ferric ions have been formed at all, just black ?magnetite?

My conclusion is that although the vinegar and the salt-and-vinegar cause some of the loose rust to fall off the very rusty iron, the treated surface is by no means cleaned. The appearance is not even perceptibly changed. I can't determine if one works better than the other, but from the colours of the solution and the rust and the lesser effervescence, I would conclude the the salt impedes the dissolution process.

I will rinse these nails and stick them back out in the rain and see which ones fall apart quicker.

[charlie b]

(major snippage)

Sir:

You have WAY too much spare time on your hands.

Having said that The effervesence (sp?) may play an important role in rust removal , small bubbles forming in fine nooks and crannies of rust on the piece. As they get bigger they can mechanically, rather than chemically, loosen rust particles - similar to cavitation. However you get the rust off with an aqueous (sp?) solution, after rinsing and hand drying, wipe things down with a paper towel soaked with alcohol. Wipe things down again with a dry towel. The alcohol will grab any water left after the first "wiped dry".

charlie b

[Ken Muldrew]

That's a shame, but salt and vinegar is delicious on chips!

Ken Muldrew [e-mail] (remove all letters after y in the alphabet)

[Dan White]

Interesting, despite what the others say! Your test about jives with my results, the most notable difference being the nearly clear vinegar/salt solution and the dark red (in my case) vinegar only solution. I would say that the iron did come clean by using the vinegar solutions, but required some brushing to really get all the rust off. I think it came cleaner than it would have had I not used the vinegar, but maybe there are better mechanical ways of doing that, or using a little muriatic acid and being very quick to rinse it off.

dwhite