TheAlchemist
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Sodium nitrate separation
I have found a brand of caustic soda-based drain unblocker in my local supermarket. It is cheap, highly impure (full of EUSSR-approved adulterants,
which is highly undesirable for those who prefer pure reagents), and contained in a shiny black bottle with fancy, eye-catching graphics and a
hard-hitting marketing name of "Buster" (which fools the sheeple into buying it, I suppose).
After looking up the MSDS, I have found that the product contains of prills consisting of sodium hydroxide, aluminium turnings and sodium nitrate.
Interestingly, the majority of the 'active ingredient' is the sodium nitrate- 80-90%.
I was wondering: if I were to dissolve the prills in distilled water in order to extract the sodium nitrate, the nitrate anion would be reduced by the
aluminium under such basic conditions, giving ammonia gas.
How could I extract the nitrate without it being chemically reduced by the aluminium?
I was considering neutralising the sodium hydroxide (after the prills were ground to a fine powder) with an excess of a weak carboxylic acid, such as
aqueous acetic acid. Such a weak acid would not react with the aluminium to any appreciable extent.
The next step would be to filter the aluminium particles from the acidic solution by simple gravity filtration.
Then I would neutralise the excess acetic acid with sodium bicarbonate, until the pH is neutral (I can measure the pH with my digital pH meter).
The next step would be to evaporate off the excess water, thus concentrating the solution.
Separating the sodium acetate/sodium nitrate mixture would, theoretically, be a simple and straightforward procedure, but I have not yet looked up the
solubility-temperature curves for each salt.
Given that sodium hydroxide is a strong base and dilute aqueous acetic is a weak acid, I probably require a large volume of acetic acid in order to
fully neutralise the hydroxide.
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Neil
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As soon as you get the mixture damp, the NaOH is going to react with the Al producing H2 which will react with the NaNO3 to produce ammonia. Try
searching the forum for Drano.
Edit: why not try mechanical separation? Are they turning big enough or small enough that you can sieve out the salts and separate them from the
majority of the Al?
[Edited on 18-5-2011 by Neil]
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ScienceSquirrel
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I would take the stuff and chuck it in a slight excess of hydrochloric acid, this will attack the aluminium but who cares we will sort this in the
next step.
Filter off any particles of aluminium and then add Lo Salt or potassium chloride.
Cool and crystallise your potassium nitrate.
Sorted!
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TheAlchemist
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"Cool and crystallise your potassium nitrate."
You must be skilled at mind reading- how did you know that I wanted it for potassium nitrate synthesis?
Well potassium nitrate is one useful nitrate salt, but there are numerous others that I would like to make, including those of group 2 (the alkaline
earth) metals, transition metals, trivalent lanthanide Ln3+ metals and group 13/14 metals.
I am just looking for a convenient, cheap source of the nitrate anion. I do'nt care too much about the identity of the cation, since I can use my
chemical knowledge to make new nitrate compounds, be they inorganic, organic or very proton-rich (acidic) and oxidising!
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watson.fawkes
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He didn't. He knew that the high temperature variation in solubility of KNO3
as opposed to NaNO3 makes K better for crystallizing out the nitrate, separating it from the chloride.
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TheAlchemist
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"He didn't. He knew that the high temperature variation in solubility of KNO3 as opposed to NaNO3 makes K better for crystallizing out the nitrate,
separating it from the chloride."
That's true, and it is exactly what I now intend to do- perform a fractional crystalisation and isolate the potassium nitrate from the sodium
chloride.
I am going to look up the solubility curves.
One thing to consider: if I use dilute HCl to neutralise the NaOH, then would'nt that introduce Al3+ contamination from the hydrated aluminium choride
formed by reaction between the Al and HCl?
I suppose that it is possible to remove Al3+ by precipitating it out as the insoluble carbonate, which is not amphoteric (unlike the hydroxide).
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ScienceSquirrel
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That is the point of crystallising out the potassium nitrate, everything else including any aluminium that dissolves will will remain in solution.
Because of it's very steep solubility curve potassium nitrate can be crystallised in high yield and purity from all sorts of shit.
Add in the fact that it is not hygroscopic and it is easy to understand why it's use in gunpowder changed everything.
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