Sciencemadness Discussion Board

Making Relatively Pure Alumina

DFliyerz - 23-3-2015 at 12:54

I'm starting to take a bit of an interest in column chromatography, and decided that I wanted to find a way to make my own fairly pure alumina. My idea was to use sodium hydroxide to dissolve old aluminum cans with the labels scraped off, but I only have borosilicate glass beakers that I'd prefer not to destroy. Is there any way I can do this easily and hopefully without high temperatures (at least, not until I dehydrate the aluminum hydroxide :P)?

DraconicAcid - 23-3-2015 at 12:55

Pyrex glass is much more resistant to sodium hydroxide than aluminum is.

Milan - 23-3-2015 at 13:46

So you are trying to make Al(OH)3, am I right?
Wouldn't the reaction go like this:
2 Al + 2 NaOH + 2 H2O → 2 NaAlO2 + 3 H2
Here's a link to a Wikipedia article about it: http://en.wikipedia.org/wiki/Sodium_aluminate#Reaction_of_al...

One way I've tried to do this and know it works is when you react Al with alkali hydroxide (I used KOH, but NaOH can be used).
Then if your source of Al was not a pure strip of Aluminium, but a can or foil, filter off whatever is left (it's mostly some kind of polymer used for protection.
After that add H2SO4 and a white precipitate will form (this is Al(OH)3), continue adding acid until no more precipitate is forming. Note: Don't add too much acid or you'll start making alum.
Then just filter the precipitate.

Hope this helps you. :D

Edit: One more thing, if you are using foil or cans please don't use your beakers for this but a jar that you're ready to sacrifice, because the polymers will stick to the glass and it's really hard to get them off, I had learn this the hard way.

Edit:Oops, I just re-read your post. So you are trying to make Al2O3. You can still get it this way, though you have to calcine (heat strongly) the Al(OH)3 to decompose it. But you'll need to make a improvised furnace for this since Al(OH)3 starts calcining above 500 ºC and bellow 850 ºC. Here are a few articles about it:
http://en.wikipedia.org/wiki/Aluminium_oxide#Production
http://pubs.acs.org/doi/abs/10.1021/ie00090a015 this ones just a section about production of alumina and magnesia

[Edited on 23-3-2015 by Milan]

[Edited on 23-3-2015 by Milan]

morganbw - 23-3-2015 at 14:01

Is there a doable way for the home chemist to go from the hydroxide to the oxide/alumina?
The hydroxide is easy, the oxide?

Molecular Manipulations - 23-3-2015 at 14:10

The easiest way for me is to dissolve aluminum in hydrochloric acid. Then boil off the water to get solid hydrated aluminum chloride, then heat that very strongly to get hydroxide, then oxide. I'm not sure at what temperature aluminum hydroxide decomposes, but I usually go to about 650°C (Bunsen Burner).
Any well equipped home lab should have either a Bunsen or a propane torch at least, so I'd say this is very doable for a home chemist.

Milan - 23-3-2015 at 14:15

Quote:
The easiest way for me is to dissolve aluminum in hydrochloric acid. Then boil off the water to get solid hydrated aluminum chloride, then heat that very strongly to get hydroxide, then oxide.


Hmm, haven't tried it that way, the problem here is getting pure HCl, I can only get muriatic acid and that is really polluted.
Quote:
I'm not sure at what temperature aluminum hydroxide decomposes, but I usually go to about 650°C (Bunsen Burner).


Yup that's a good temperature, it's between 500 ºC and 850 ºC.

[Edited on 23-3-2015 by Milan]

morganbw - 23-3-2015 at 14:22

Quote: Originally posted by Molecular Manipulations  
The easiest way for me is to dissolve aluminum in hydrochloric acid. Then boil off the water to get solid hydrated aluminum chloride, then heat that very strongly to get hydroxide, then oxide. I'm not sure at what temperature aluminum hydroxide decomposes, but I usually go to about 650°C (Bunsen Burner).
Any well equipped home lab should have either a Bunsen or a propane torch at least, so I'd say this is very doable for a home chemist.


Thank you. I guess I should have done a little research but this is not an item I need to prepare. I simply asked, because I did not know and wanted red flags put out if this was not practical.
My initial thoughts were that this might not be simple/easy.

Mesa - 23-3-2015 at 14:30

If your interest is in chromatography grade alumina, the methods posted here are a long way off what you want.

Dr.Bob - 23-3-2015 at 17:35

You might be able to find aluminum oxide powder (alumina) through a ceramics supplier or on Ebay for cheaper than the cost of trying to make it. Not that I am against chemistry, but if you want to actually use it, I would start with a known quality. You might be able to find some locally or order it, but that will work to some degree. Other choices are to use a different material, like paper, cellulose or other materials to start experiments. Just depends on what you want to purify.

Sulaiman - 24-3-2015 at 05:58

Aluminium Oxide / alumina is a really common abrasive
look in your local hardware shop or eBay.
I got mine from here https://www.machinemart.co.uk/shop/product/details/7-5kg-80-...
use sieves to get the grade that you want, as supplied it has a wide range of particle sizes.

[Edited on 24-3-2015 by Sulaiman]

Milan - 24-3-2015 at 06:09

Hey, just had a thought, could you get Al(OH)3 by combining a salt of aluminium (like Al2(SO4)3) with NaHCO3, or would I get a carbonate of aluminium.

Dr.Bob - 24-3-2015 at 06:36

Most aluminum hydroxide salts are gelatinous goos, which are hard to filter, dry or work with. Anyone who has worked up a LAH reduction will have experience with that joy. When you mix Al salts with other salts, you will likely just get a mess. I have not tried to do that on purpose, but the few times I have worked with Al salts, I have hated them. Remember clay is an aluminum silicate complex, and think about how much fun it would be to filter or try to work with.

morganbw - 24-3-2015 at 14:00

Amateur astronomy stores offer it as an abrasive for grinding lens along with other oxides.
Just a thought.
Other oxides as well.

Magpie - 17-8-2015 at 19:46

Fisher A450 alumina is 80/200 mesh and sells for $140/500g:

https://www.fishersci.com/shop/products/alumina-80-200-mesh-...

Other than a defined particle size range and a huge price difference, what is the difference between A450 alumina and ceramics grade alumina?

If it is just a matter of washing, sizing, and heating in a furnace - well, I'm willing to do that myself.

careysub - 18-8-2015 at 05:11

Quote: Originally posted by Magpie  
Fisher A450 alumina is 80/200 mesh and sells for $140/500g:

https://www.fishersci.com/shop/products/alumina-80-200-mesh-...

Other than a defined particle size range and a huge price difference, what is the difference between A450 alumina and ceramics grade alumina?

If it is just a matter of washing, sizing, and heating in a furnace - well, I'm willing to do that myself.


If you are willing to take those steps my suspicion is that you can work with pottery grade alumina or alumina hydrate just fine.

Both stuffs are about $3-5 a pound (less in larger amounts). Axner lists their alumina as 325 mesh, and their alumina hydrate as 99.5% pure. Seattle Pottery and Aardvark Clay do no list such specs, but I expect their products are similar. Since alumina is used to make pure white glazes I expect purity is pretty good from any reputable source to avoid any discoloration.

Sigma-Aldrich has this to day about their chromatography alumina:
"When aluminum hydroxide is screened for particle size and heated in a carbon dioxide stream at about 900°C, it is converted to individual particles of aluminum oxide that are coated with a thin layer of aluminum oxycarbonate (with the
approximate formula: [Al2(OH)5]2CO3 H2O). The alumina particles are between 70-290 mesh (50-200 μm), and most are approximately 150 mesh.

Water content and alkalinity are then adjusted by washing with dilute acids.
Aluminas used for column chromatography or thin-layer chromatography are treated with acid or base to adjust the pH of a 10% slurry (w/v in water) to acidic, basic or neutral pH. These are designated by A, B or N, respectively. Acidic alumina has approximate pH 4.5, basic alumina has approximate pH 10.4"

and

"Alumina can be reactivated by dehydration at 360°C for five hours or overnight, then allowing the desired moisture content to be readsorbed."

https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/...

All of this sounds quite doable. You might want to start with a strong acid and a strong base wash to get your product as clean as possible upon receipt.

I also picked up some beer fining silica gel to try as chromatography media (TLC coating):

http://www.ebay.com/itm/1lb-0-455kg-of-Powdered-Silica-gel-f...

It says it has a 19 micron average particle size (the finest mesh size, 400, is 37 microns). Mesh sizes don't go below 400 (in particle size; above, numerical mesh value) since mesh sifting stops being practical at 400.


[Edited on 18-8-2015 by careysub]

JJay - 10-2-2016 at 00:02

I'm putting together an equipment and reagents list for analysis of Devil's Club (a relative of ginseng that reportedly contains no alkaloids - ???) via column chromatography and TLC this summer. Do you think I can get away with preparing my own alumina and TLC plates?

Pumukli - 10-2-2016 at 08:00

Depends on how deep you want to dive into the plant materials. Componenets in the low ppm range may easily slip through unnoticed with crude methods, but with at least the main components you have better chance of detection.

Think of the great discoveries in the 1800-s: the alkaloids and such. The "cutting edge" equipment of those days was probably not much better what an enthusiastic home-chemist (researcher) can make in a garage today.

(E.g. we chromatographed flower-petal extracts on simple blackboard chalks at school. Not really a high tech method, but worked. Before factory made UV sensitized TLC plates there was paper chromatography for decades too...)

Keep up and do things! :)

S.C. Wack - 10-2-2016 at 08:56

The starting point for answers IMHO is WTF exactly is the alumina sold for chromatographic purposes, how is it made, and which kind works best for you? We know at least of the activity and acidic, neutral, and basic grades, and mesh sizes, but not which one will work best with whatever you're doing. We know how to change the Brockmann activity of aluminas sold for chromatography, but is this really the same or similar to pottery alumina of the same mesh size, whatever the pH or alkali content is, for you, in this particular experiment?

As far as relatively pure alumina goes, a quick obvious guess is that the starting materials for making the isopropoxide could be impure and you could still come out with a pure hydroxide. But is that what you really want? What temperature do you heat that to, and for how long, to produce the best type of alumina and results for you? Which would you rather use instead of water to precipitate the hydroxide: NaOH, ammonia, carbon dioxide, or something else? Or does it matter at all?

Figuring all or some of this out would be an all-around excellent general chemistry lab exercise.

JJay - 10-2-2016 at 16:31

One often referenced method for grading alumina for chromatography is one by Brockmann and Schodder. I haven't found the original reference freely available online, but several summaries of their procedure are available. It looks like they originally used carbon tetrachloride as the eluant, but some have used a mixture of benzene and petroleum ether.

Armarego and Perrin's Purification of Laboratory Chemicals (fourth edition) discusses methods for preparing grade I activated alumina, as well as neutral alumina.


[Edited on 11-2-2016 by JJay]

S.C. Wack - 10-2-2016 at 22:10

Preparing in the sense of modifying the alumina for adsorption you already bought. The Brockmann article they mention and which I also found referred to elsewhere, actually looks vague on details to the not-German. It looks like the hydroxide was bought and was heated and that alumina was used for the experiments. I suppose if all alumina is made by the Bayer process then most alumina from wherever should be approximately adsorption grade basic alumina, after activation.

JJay - 10-2-2016 at 23:10

I believe that is correct. So it is likely that pottery grade alumina will work just fine for chromatography after activation, and it is easy enough to test it.