Wet carbon steel knife forgotten on rice cooker

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Carbon steel knife inadvertently left 'wet' on top of the white plastic lid of a rice cooker, overnight.
Brown rust stain has soaked into the plastic. Is there any chemical that might remove the stain please?
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Rust is mostly a hydrate of Fe(II) oxides and hydroxides (if memory serves right). Oxidizing the "rust" and chelating/complexing the Fe(III) ions should remove this. I'd recommend oxalic acid for all this. Soft water (as opposed to calcium containing "hard" water) is best. Calcium oxalate forms hard, sharp, needle-like crystals, which are mechanically poisonous (part of the green leafy parts of rhubarb that should NOT be eaten).
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Han
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john ryan wrote:

Any commercial rust remover like CLR.
Any acid like vinegar, lemon juice, etc. Concentrated sulfuric, nitric or hydrochloric not recommended.
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dadiOH
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Hydrochloric acid doesn't do the required oxidation, so, no, not recommended. Depending on the kind of plastic sulfuric or nitric acids should work fine. You likely only need a little bit and it doesn't need to be too concentrated, with a short time of exposure. Rinse well. Wear eye protection (DAMHIKT).
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Han
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john ryan wrote:

Oxalic acid, dilute hydrofluoric acid ("Whink"), or "Iron Out" (contains sodium hydrosulfite and bisulfite.)
-Bob
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IN A LAB WITH ALL THE REQUISITE SAFETY GEAR!!!!!
Graham
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graham wrote:

It's available in the laundry aisle at the supermarket in a little brown plastic squeeze bottle for removing rust stains. It's called "Whink". It's important to wear rubber gloves when using it cuz it will F! you up (in a bad way) if absorbed through the skin.
-Bob
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to the general public. I'm fully aware of the dangers having used it under lab conditions and having to develop procedures in the case of accidents. These days, my processing work is handled by a contract lab so I don't go near the stuff. Graham
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It's all in the dose. Moreover, HF is readily soluble in water, so it washes away easily. I am NOT recommending sniffing it or drinking it, or washing your hands in it. On the other hand, it is present in toothpastes in various forms as a minor, but active ingredient.
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On 18/05/2011 19:02, Han wrote:

But the stuff in toothpaste is NOT HF, it's NaF. About as dangerous as common table salt.
<fx googles> OK, so 5g may well kill you, it takes a bit more table salt. Whereas HF will kill you at 30ppm in the air...
Andy
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NaF or SnF2 would become HF when it gets acid (like in a stomach). And [H+] is always there in some concentration.
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d:

So wrong! There are fluorine compounds in toothpaste, but not hydrofluoric acid. Usually sodium or potassium fluoride. Check the label.
HF isn't basically more dangerous than HCl. It's primary claim to fame its ability to attack glass. Don't confuse it with HCN.
Jerry -- Engineering is the art of making what you want from things you can get.
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So wrong! There are fluorine compounds in toothpaste, but not hydrofluoric acid. Usually sodium or potassium fluoride. Check the label.
HF isn't basically more dangerous than HCl. It's primary claim to fame its ability to attack glass. Don't confuse it with HCN. ----------------------------------------------------------- It bloody well is more dangerous! Much more dangerous! I speak as one who has used it and managed a lab that used large quantities of it. Graham
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On 5/26/2011 8:38 PM, Jerry Avins wrote:

That's wrong. HF is not nearly as strong an acid as HCl, but it is much more poisonous, and it will easily penetrate the skin without causing any apparent damage at first.
Wear rubber gloves and try not to spill the stuff on yourself and the 2% isn't all *that* bad. I keep a bottle handy and use the stuff; usually a drop at a time. Handle a rag sopped with the stuff for very long without wearing rubber or plastic gloves and you just might need you hand amputated -- or worse.
-Bob
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The good ones use tin fluoride. ;-)

F is certainly worse than Cl, in almost every way.
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Jerry Avins wrote:

HF interferes with the body's calcium and potassium metabolism and can cause death by cardiac arrest.
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From skin contact? I suppose I've been lucky, then. To clean nitric- acid stains off my hands, I would go to the plating shop, dunk my hands in the bright dip to be sure there were no cuts, then rinse them in the cyanide bath. Plenty of running water after than.
Jerry -- Engineering is the art of making what you want from things you can get.
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Jerry Avins wrote:

Isn't that how the Iceman killed his targets, spraying them with cyanide or just spilling it on them as he went by?
nancy
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MSDS for this (Whink rust remover) doesn't mention HF at all, nor any fluorides. Mike
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docholliday wrote:

Did you actually look? http://www.whink.com/images/msds/Rust_Stain_Remover_10062008.pdf
And there are DANGER! warnings about hydrofluoric acid printed on the bottle. (not many consumer products use "DANGER" anymore, most say "Caution" or "Warning")
-Bob
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