In this video, I will be demonstrating how to obtain antimony metal from antimony trisulphide,
which can be bought cheaply and easily online.
It is used in pyrotechnics to generate particular effects.
Admittedly, it doesn't fit the objective of the video series of using a household material,
however, it is the most readily available highly concentrated form of the element (without
actually buying metallic antimony!)
It is used in flame retardants, however the concentration is extremely low.
It is also used in various metal alloys, the most accessible of these being in lead-acid
batteries (car batteries) and in bullets.
However, the concentrations here are no more than 5%, and it is worthwhile making the effort
to obtain the trisulphide if you wish to carry out a chemical reaction to obtain the metal
easily!
For those that wish to work from alloys with lead, however, this can be done by first dissolving
the metal in dilute nitric acid or acetic acid of any concentration.
Lead, tin, bismuth, and arsenic (whichever are present) will dissolve, leaving antimony
behind as a black precipitate.
If a white powder is also present, this is tin and/or lead arsenite.
The antimony can be separated by dissolving the precipitate in concentrated hydrochloric
acid, filtering off the undissolved material, and then diluting.
The antimony will separate as a white oxychloride, which can be reduced to the metal with aluminium
using the same method I show in this video.
If the white precipitate obtained from dissolving the metal in nitric acid does not dissolve,
it is lead arsenite, and should be treated with uttermost respect!
If it does, arsenious acid is present in the filtrate after dilution.
Assuming only a black precipitate is present after attack by nitric acid, this can be filtered
off and dried to yield pure antimony.
However, this is very difficult to melt into a lump, since it readily burns when finely
divided and a flame applied.
Anyway, after that slight diversion, I shall start proper with my video!
I have weighed here out 9 grams of antimonious sulphide powder, and 1 gram of aluminium powder.
These are then mixed together, and taken outside to be lit!
I have put a lump of magnesium powder on top of the pile to help ignite the mixture.
My magnesium powder has got damp somehow, hence the lump.
After the reaction has taken place, the resulting fused material is placed into some dilute
hydrochloric acid (this is about 1M) and allowed to react overnight.
Usefully, the slag and metal once cooled seems to reliably form a single plate, making this
step very easy.
The acid removes any reactants still present, and any byproducts.
Aluminium, aluminium antimonide and aluminium sulphide all dissolve in hydrochloric acid.
Admittedly, the antimony sulphide doesn't dissolve in dilute acid, (it does dissolve
in concentrated) but I was running out of hydrochloric, so I diluted some down and hoped
that any ureacted Sb2S3 had just burned away.
This step should be conducted in a fume hood or outside because hydrogen sulphide gas is
generated and is highly toxic.
The bubbling had ceased overnight, so the next day I set up for filtration, filtered
the antimony off, and washed with water.
The resultant black powder and lumps were then allowed to air dry.
The alternative way of making antimony is to generate a solution of an antimony salt,
and displace it with a more reactive metal.
Unfortunately, I had run out of concentrated hydrochloric acid and due to time constraints
was unable to obtain any more quickly enough for the video.
However, the procedure would be as follows: The antimony sulphide would be dissolved in
concentrated hydrochloric acid; sulphuric acid would not work.
Be aware that large volumes of hydrogen sulphide will be generated during this reaction, and
care must be taken to avoid this.
Conduct the reaction in a fume hood or outside.
Then aluminium or zinc powder would be carefully added to the acidic solution, taking care
not to add too much in case of a too violent reaction with the acid.
After all the aluminium has been added, filter the fine black precipitate off, and wash well
with distilled water.
The fine powder formed is more reactive than the bulk form, and is suitable for chemical
reactions requiring the metal.
Once more, bear in mind that the antimony generated by this process is impossible to
melt without an inert atmosphere, such as carbon dioxide, nitrogen or argon.
So, here we have the final product of the first reaction, 6.82g of antimony metal containing
some larger globules.
Unfortunately, this corresponds to a 109% yield, this likely due to a small contamination
of antimony sulphide, however, this can be removed by washing with concentrated hydrochloric
acid when I order some.
In my opinion, this first procedure is superior because it does not require handling volumes
of high concentration antimony salts, and there is no chance of a runaway reaction when
the residue is digested with acid.
Normally at this point I demonstrate a few of the properties of the element I have just
made, however, due to the fact that the soluble chemistry of antimony relies heavily on its
halides and oxides I was unable to show anything interesting.
Antimony does form a series of antimonites and antimonates, much like arsenic, on video
this would simply be two white powders reacting to give a third.
There are three allotropes of antimony, the first and the most stable being white or grey
antimony.
This is the one prepared earlier.
Another is explosive antimony prepared by electrolysis of a solution of antimony chloride.
I did attempt this, but I was unable to make any, and used some highly impure antimony
chloride I had made a couple of years ago.
The third allotrope is yellow antimony, prepared by condensing antimony vapour very quickly.
It is only stable below -90C, and converts back to the metallic form upon exposure to
light.
In this respect is is very similar to white phosphorous.
As you can imagine, I did not attempt the preparation of this allotrope...
Antimony does form an unstable hydride, stibine, which apparently has the odour of rotton eggs.
This is obviously highly toxic, and is unstable in the presence of metallic antimony.
It is probably formed in small amounts in the acid digestion step, but since safety
precautions are taken for hydrogen sulphide, it will likely not pose a hazard to the experimenter.
So, that's how antimony can be made from its sulphide.
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