kilowatt
Hazard to Others
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Registered: 11-10-2007
Location: Montana
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Mood: nitric
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Single Process for Ammonia, Lead Nitrate/Nitric Acid/Lead (II) Oxide, With Separation of Scrap Lead Alloys
By using DC electrolysis of scrap lead electrodes in an electrolyte of concentrated ammonium nitrate, I was able to prepare lead nitrate while
dissolving the anode at an alarming rate. Ammonia is given off at the cathode but not surprisingly only comes out at a somewhat low rate and high
cell temperature. Heating the cell is no problem; all you have to do is not cool it and let the electrolysis current do the work. Later I will
experiment with using membrane cells, AC electrolysis, or reversing the DC polarity every few minutes or so, and come up with a system to better
remove ammonia with a closed cell top and possibly vacuum. Anode removal exceeded 1/8" per hour with the cell at 3V in this experiment. This is tens
or hundreds of times faster than the electrode removal in my electrolytic sulfate production method. Spongy lead that collects at the cathode and
settles to the bottom of the cell may need recycled by melting/oxidizing (it oxidizes quite readily though which is nice), but this remains to be
seen. With AC electrolysis this problem may be more or less eliminated, but at the same time the ammonia may be oxidized. Some sort of trade-off may
be needed such as reversing the cell polarity repeatedly at a certain rate. A membrane cell would probably be even better, if it can minimize the
amount of lead that ends up in the cathode chamber. I will try that out too if I get around to setting up a suitable membrane cell, and eventually a
large battery of them.
The lead nitrate can then be separated by crystallization and decomposed at relatively low temperature (300-470°C according to online sources) to
yield nitric acid (4NO2 + O2 rather, just add water). By washing the remaining PbO in a conservative amount of sulfuric acid it should be easy to
then separate antimony and tin sulfates from the lead, as only they are soluble. I'm not sure if only enough acid to leech out the tin and antimony
will be needed, or if most of all of the lead oxide will be sulfated as well. In any case the lead sulfate or lead oxide can then be smelted, as well
as the other metal sulfates, to recover the pure metals and nitric acid.
It may also be quite practical to simply take the lead oxide left over from the nitrate decomposition step (after the lead has been purified and
re-cast to electrodes) and react it with ammonium nitrate with liberation of ammonia, to skip smelting and electrolysis from then on out. Reaction of
transition metal oxide with ammonium nitrate has been discussed in the nitric acid production thread (with copper oxide or carbonate more
specifically) and it is a slow reaction driven by the removal of ammonia. I did a small experiment last night with adding PbO to ammonium nitrate
solution and indeed it did give off some ammonia smell, but to be practical some external heating or possibly boiling would be required.
[Edited on 3-8-2008 by kilowatt]
The mind cannot decide the truth; it can only find the truth.
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Formatik
National Hazard
Posts: 927
Registered: 25-3-2008
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Mood: equilibrium
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NA from Pb(NO3)2
It’s a good idea if you have no other options, but Cu(NO3)2 (decomposition temperature 170°C) is more easily decomposed to nitrogen oxides than
Pb(NO3)2, and is less toxic.
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kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
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You wouldn't want to try the same process with copper, though. It forms TACN which will explode if you try to heat it to decomposition.
The mind cannot decide the truth; it can only find the truth.
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