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Author: Subject: Getting rid of mineral oil in calcium samples
hodges
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[*] posted on 4-2-2022 at 14:51
Getting rid of mineral oil in calcium samples


I purchased some calcium metal (many small nuggets) from an online auction site. I didn't realize that it would be packed in mineral oil. In the past when I have purchased calcium nuggets, they were just packed in an airtight bottle.

I use calcium as a reagent for various purposes, and the mineral oil is definitely not good news. It affects the mass when I am weighing out the calcium, and contaminates reactions.

Is there an economical way, that does not involve trying to vaporize it, to get rid of the mineral oil? My first thought would be to decant off as much of the mineral oil as possible, then wash with an easily evaporated non-polar solvent to wash away the mineral oil. Acetone comes to mind. But my concern would be that store-bought acetone probably contains a non-negligible amount of water, which would likely react with the calcium. Any thoughts? I did not pay too much for the calcium, so perhaps it would be better to just order more from another supplier. But if there is an inexpensive way to clean it up I would rather do that.
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[*] posted on 4-2-2022 at 17:52


I was going to say, melt some in a test tube, then insert a wire and let it harden. But after reading the melting point of 842c, i see that isnt going to work.

Maybe a reflux with dioxane? I know it works with sodium, and i believe other group 1 metals.

Its easy enough to make inside of a few hours with the right equipment. Maybe try a very small sample to start with.




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Admagistr
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[*] posted on 4-2-2022 at 18:02


I recently offered high purity calcium here on the Forum that has never been stored under any oil....The offer still stands;)
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[*] posted on 4-2-2022 at 18:29


Otherwise, I was approached years ago by a friend who is a professional seller of high purity chemical elements asking for advice on how to degrease reactive metals stored under paraffin oil before fusing it in a glass ampoule under argon... Gasoline came to my mind... A few days later he wrote me enthusiastically that it was a great idea and he had managed to degrease this metals perfectly, using a cleaner of gasoline...
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[*] posted on 5-2-2022 at 00:16


Quote: Originally posted by Admagistr  
Gasoline came to my mind


Yep, that works great for degreasing reactive metals. Whenenver I use sodium I dump the freshly cut pieces into a small beaker with petrol ether before transferring them to the reaction flask.




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[*] posted on 5-2-2022 at 05:25


Petroleum ether works without leaving behind residual crap, as part of the production process is distilling.

Acetone from the store is usually dry. I don't know how it is produced, but the process ensures a dry product.

Just wash the calcium with some solvent. Adding mineral oil is common practice to many air/water sensitive chemicals, as washing away the oil is easy and leaves few traces as long as the solvent used to do so is clean.

I never worked with gasoline, but I wouldn't use it without distilling it as I don't know what high boiling stuff is in there.

Also, maybe not calcium, but e.g. with sodium, more complex aromatics might react with the metal, making complex mixtures like gasoline unsuitable.

[Edited on 5-2-2022 by Tsjerk]
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[*] posted on 5-2-2022 at 07:41


Hexane is a great solvent for washing alkali metals (and sodium hydride) of oil. But then be careful to put the used solvent in a place that is safe in case it catches fire. It sometimes gets a little material in it and that will spark in humidity. Two washes or rinses in hexanes, and your metal will be clean enough for most purposes.
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[*] posted on 6-2-2022 at 14:00


Thanks for the replies.

I bought some "100% acetone" (nail polish removed) and tried it with a small sample of the calcium. There was no reaction, so I decanted as much of the mineral oil as possible and then used the acetone to wash the calcium.

I found that the mineral oil and acetone are not miscible. However, the mineral oil is washed off by the acetone and can also be poured off. After several washes, I left the calcium to dry in open air for a bit, then put it back in its bottle. There is still a slight acetone smell, but the calcium is now clean and dry and shakes easily in the bottle. I am leaving the cap on loosely so the remaining acetone vapor can dissipate.
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