Sciencemadness Discussion Board

Elemental Selenium

mrjeffy321 - 30-1-2008 at 12:05

I need a small amount of elemental Selenium, preferably a high purity powder but this is not a strict requirement.

I am exploring the possibility of scavenging the Selenium out of something (an old rectifier, for example), or extracting it from “Selenium Yeast” used as a dietary supplement. Does anyone know if these are feasible options?

If all else fails, I could get some as part of an element collection, but the unit price would likely be a little high in this case.

-jeffB - 30-1-2008 at 12:33

Quote:
Originally posted by mrjeffy321
I need a small amount of elemental Selenium, preferably a high purity powder but this is not a strict requirement.

I am exploring the possibility of scavenging the Selenium out of something (an old rectifier, for example), or extracting it from “Selenium Yeast” used as a dietary supplement. Does anyone know if these are feasible options?

If all else fails, I could get some as part of an element collection, but the unit price would likely be a little high in this case.


I'd think extracting it from yeast would be a non-starter, given the low initial concentration. Samples are available on eBay for US$20-40. How small is your "small amount"? What's your application?

microcosmicus - 30-1-2008 at 13:30

A while ago I too was looking for selenium (although I haven't yet gotten it, just
moved it to my wish list) --- I was interested in the fact that it has quite a high Seebeck
coefficient, so should be good for thermocouples. Anyway, I found that metallium
has selenium at about a dollar a gram --- the best bargain is their 80g chunk which
goes for $38.00:

http://www.elementsales.com/pl_element.htm#se

As for the dietary supplements, each pill contains 200 micrograms. That
means that to get your gram of selenium, you would need 5000 pills. Even if you
get the pills in a dollar store, that is going to cost way more than the price cited
above, never mind the cost of extracting the selenium.

As for rectifiers, that sounds a bit better because the selenium is
already in elemental form on the rectifier plates. The only question
here is how thick a coating of selenium they put on the plates --- I have
a sinking feeling that this might not be that much more than the pills.
Interestingly enough, there is still a company which still makes selenium
rectifiers.

http://www.cougarelectronics.com/selenium.htm

Also, selenium is used to make drums in photocopiers and laser
printers light-sensitive but, again, the amounts used may be miniscule.
Good luck looking for selenium, and if you find a better price than
the one cited above, please let me know as I might get some too.

[Edited on 30-1-2008 by microcosmicus]

mrjeffy321 - 30-1-2008 at 13:39

In terms of how much Selenium will actually be consumed in the reaction, I need quantities on the order of hundredths of a gram. But since it is incredibly impractical to buy such small amounts, something on the order of a few grams would be more than enough.

I did not hold much hope for the yeast method, but that is just the one readily available product I could find which contained Selenium.

I see listings on eBay for very pure elemental Selenium with prices ranging from $0.80 to upwards of $3.00 per gram and more. But they are not selling single grams of Selenium but rather nice, pretty, display pieces of varying masses well in excess of what I need.
But so far, I think this option is my best bet.

I intend to use the Selenium to produce Cadmium Selenide Quantum dots.

woelen - 30-1-2008 at 14:18

I have purchased elemental selenium from http://www.emovendo.net for $13 per 30 grams, plus $4 shipping cost. This is selenium in the form of small corpuscles, resembling the red blood cells:



Currently they don't have it in stock, but I would just contact the owner of this shop. He is a cooperative person and you make a good chance that he will help you with this.

chloric1 - 30-1-2008 at 14:28

The little corpusle looking things should work for your small quantity needs. Heck, if I where you, I would go ahead and buy 100 grams of selenium granules, take out 1 or 2 grams for yourself and resell them on ebay. Selenium should be a hot seller and you should get your money back or maybe a few dollars profit$$:D I have been doing this alot lately, That reminds me, I just received 5 lbs of nickel sulfate and 5 bs of manganese carbonate yesterday. Better get to ebay!

mrjeffy321 - 30-1-2008 at 15:02

Woelen, that is the best price per gram I have seen so far, and it is in a fairly reasonable quantity for my purposes so as to minimize excess.
I will try to get some of that if they have any in stock.

MagicJigPipe - 30-1-2008 at 15:35

Their silver was decently priced as well. Many things seem to be out of stock, though. That's no good as I wanted a few ounces of silver to keep around the lab. Pd isn't bad either. Can't wait 'til my tax return comes in.

Not that this will help at all but I noticed the other day that firearm "Cold Blue" contains selenious acid.

Also, I know that I used to have some selenium rectifiers from an old radio(?). If I find them (I will have to dig around in the mini-storage) I would be more than happy to let one of them go. I remember the reason I saved them at the time was because someone told me they were selenium and it was poisonous.

chloric1 - 30-1-2008 at 16:00

Quote:
Originally posted by MagicJigPipe
Not that this will help at all but I noticed the other day that firearm "Cold Blue" contains selenious acid.



This only 2% selenioud acid:(:( Its good for artistic steel coloring though. It blackens other metals to I believe.

Twospoons - 30-1-2008 at 18:25

Selenium is used as the photosensitive material on the print drums of some laser printers and photocopiers. Later technology uses organic photosensitive materials. So it may be you could aquire small amounts from junked laser printer cartridges. Though I'd have thought this a rather difficult and messy way to get selenium.

There is also selenium sulphide used in anti-dandruff shampoo - up to 1%.

12AX7 - 30-1-2008 at 19:44

I have a few scrapings of selenium recovered from a rectifier. I've had it soaking in acid for ages, which has succeeded in oxidizing some of it to a white goo. I don't know how much is left in solution. Starting with NaOH instead of HCl probably would've been a better idea.

As far as rectifiers go, it appears they coated one side of each aluminum vane with a thin layer of selenium. This can be chipped off (along with some paint) by bending the plate with pliers and scraping with a screwdriver. The aluminum could be dissolved chemically, but that's inviting H2Se, not a friendly compound.

Tim

not_important - 30-1-2008 at 20:11

Cadmium red paint is CdSe or a mixed selenosulfide, possibly with some BaSO4, TiO2, Al2O3, or similar white pigment. The strong saturated shades are less likely to have the white pigment mixed in, "dark cadmium red" is an example. The exact amount will vary with the manufacture, cheaper paint are more likely to have additional white pigment, but higher price paints are likely to be charging extra for the name. Read the label well, there are azo pigment replacements for cadmium pigments that may be sold with the same "colour name". In some countries you may not be able to buy cadmium based pigments, I believe this is true in the Netherlands.

The oil paints might be easier than acrylics to get the pigment from. Add the paint to several times its volume of a cheap organic solvent like paint thinner (surprise!) and mix very well. Put aside to settle for some time, pour off the solvent as well as you can, add fresh solvent and repeat. Do this several times, then switch to acetone for several washes, then let dry. Crush the pigment and dissolve in warm nitric acid. A white residue is the carrier like BaSO4, if the pigment was mixed selenosulfide then some pale yellow sulfur may be formed but bringing the acid to a gentle boil will oxidise it.

Metallic selenium could be precipitated from the acid solution by bubbling SO2 through it, but that may also reform some CdSe. Instead the acid solution can be made alkaline with NaOH solution, to a pH of about 11 or 12, to precipitate Cd(OH)2 or CdO. After filtering the filtrate can be made acidic with HNO3 or H2SO4, the reduced with SO2 to get elemental Se.

Water based paints might be more difficult because the binder often doesn't dissolve well. For watercolours you would want to steer away from gouache ( CaCO3, ZnO2, &ct added) unless there is no other choice. Gum arabic and polyols are the binders, water and alcohol can be used as solvents, hot HNO3 will oxidise the carrier to CO and water so separation may not be needed.

examples, without checking that they are truly CdSe based (check manufactures' sites)

http://www.artistcraftsman.com/servlet/the-24295/Georgian-Oi...

https://www.aswexpress.com/art-supply/catalogs/0055252000000

http://www.artmaterials.com.au/index.php?cPath=232_219_123

Ceramics and glass enameling supplies may stock cadmium red pigment without any binder, as in a reducing atmosphere or mixed in a glass it is stable to moderately high temperatures. This would easiest, as there is no binder to deal with and other (pigments are unlikely to be added.



[Edited on 31-1-2008 by not_important]

12AX7 - 30-1-2008 at 22:29

Quote:
Originally posted by not_important
Instead the acid solution can be made alkaline with NaOH solution, to a pH of about 11 or 12, to precipitate Cd(OH)2 or CdO.


Is Cd significantly amphoteric like Zn is? Na2CO3 or NaHCO3 might be a better candidate (or a titration with NaOH). I would guess pH as low as oh, 6 or so might be enough to precipitate the Cd cleanly.

Tim

not_important - 30-1-2008 at 23:30

Quote:
Originally posted by 12AX7

Is Cd significantly amphoteric like Zn is? Na2CO3 or NaHCO3 might be a better candidate (or a titration with NaOH). I would guess pH as low as oh, 6 or so might be enough to precipitate the Cd cleanly.

Tim


No, it takes very concentrated hydroxide to form the equivalent of zincates, the pH range given isn't that alkaline. And using hydroxide insures the SeO2 ends up as SeO3(2-), where it's less likely to interact with the cadmium.

YT2095 - 31-1-2008 at 06:24

Quote:
Originally posted by woelen
This is selenium in the form of small corpuscles, resembling the red blood cells:




an Interesting point with these Selenium "not quite finished Donuts" is that when you break one of them, the Inside is like black Glass almost Obsidian, and it Does conduct electricity also, the Tellurium (also very similar in appearance) does not conduct :)

this runs contrary to what you would think, Woelen was Kind enough to send me a sample of both of these from the same same batch featured in the pic a year or so ago, and of course I had to do some tests :D

it may or may not have been mentioned yet, but you have to be very careful with these elements, they`re Quite toxic and small amounts can kill you, and at best make you stink of Garlic for a few months!

another Idea that May help if you`re determined to extract your own, would be certain medicated anti-dandruff shampoos, like Selsun Blue for instance.

not_important - 31-1-2008 at 07:24

note:
Quote:
The active ingredient in Selsun Blue is selenium sulfide (1%). Selsun (not Selsun Blue) is a related product made by the same company and available over-the-counter (in some countries) which contains 2.5% selenium sulfide and sulphur.
Chattem announced that on November 1, 2005, they would introduce a new line of shampoos under the brand name Selsun Salon. These contained a different active ingredient as Selsun Blue, pyrithione zinc 1%, and are oriented toward the higher-end shampoo market.


Read the label carefully, as this seems to be a rather expensive source with the potential to not have any selenium in it.

mrjeffy321 - 31-1-2008 at 11:13

In my correspondence with http://www.emovendo.net I have been able to arrange to purchase 5 grams of Selenium shot (like the kind in woelen’s picture) for a little over $7. I got the impression that I am getting [nearly] the last of their stock.
When they eventually restock, the Selenium price will be higher to reflect the rising cost of metals.

Extracting Selenium can be a project for another day.

woelen - 31-1-2008 at 12:35

Yes, I have seen the price of selenium rising very much. I purchased one of those 30 gram lots from emovendo for only $8.99 a few years ago. Lateron, the price was going up to $12.99 and now, all selenium sources list the material for almost $1 per gram. If they restock, expect the price to be somewhere around $25 for 30 grams.

But, even at your $7 price, you had a fairly good purchase :). Extracting the element from nutrition tablets, shampoo or gun coating fluid is a real pain in the ass and the amounts you get are minute and probably very impure.

[Edited on 31-1-08 by woelen]

mrjeffy321 - 1-2-2008 at 19:28

This potter supply company,
https://protected.hypermart.net/uspigment/index2.html
Apparently sells “Selenium” for $40 per pound, which comes out to be a much cheaper unit price, by far, than anything else I have seen. But, of course, the Selenium’s form (powder, granules, …) and purity would be in question.

not_important - 1-2-2008 at 23:24

For ceramics and glass colouring, I suspect it will be fine shot a few mm in size or a coarse powder, 99 to 99,9 purity although it may be higher. Lower purity can cause problems with the colours formed, small shot and coarse powder are a tradeoff between being easy to measure out the correct amount and quickly react with the glass/glaze, and having a form that doesn't blow around too much or air oxidise during heatup.