As you can see in the image I collected the ash from wood briquettes, they are sort of compacted wood, not bar-b-q stuff, wood for an open fire. It
was soaked in water for 36 hours. The expected clear water half way up did not appear. Instead there was a golden yellow colour. A sample of this
water was filtered and collected for testing.
Results: each test tube had 4 mL sample
pH established at 8.3 (expected a little higher)
Fe3+ ions - negative, tested with few drops 1M thiocyanate
NaOH no precipitate at all, tested with few drops of 0.2M and then added more for excess, no precipitate.
HCl - no precipitate, no colour change. Few drops of 6M added and then to excess.
A 75 mL solution from this same sample was then boiled down to dryness: Results:
The first precipitate was a clean white accross the pan, this I would imagine to be K2CO3; the second and last precipiate was a
tiny bit of the solution (about 2-3 mL) turning into a very dark golden brown, syrupy, and then as the final droplets of water were evapourating,
brown round granules started popping out over the saucepan, sort of mini explosions if you like. Well I would imagine that potassium and sodium do
this, (I heated up salt and I get the same effect). So I am left with asking members of this forum what their verdict is and what tests I can do now?
This is the final precipitate from the saucepan 0.17 g from 75 mL.
Boffis - 21-1-2015 at 14:55
Hi Chris, I hate to pour cold water on your fire but....
I live in an old house with a huge open fire and we burn hard wood logs, we burn about half a ton of wood a years so naturally I had the same idea, I
would extract the potash before I disposed of the ash. Hmmm things did not go to plan. I leached the ash from one night's fire with cold water and
decanted it through a piece of cheese cloth to remove the "floaters" (mostly small charcoal bits) and then washed the insoluble residue again. I left
the liquor to settle for a couple of days and then filtered most of it, the last bit of sludge seemed to clog the filter paper so I rejected it. I
ended up with about one and a half gallons of clear liquor which I evaporated down to a small volume and let it cool. Like you I got a whitish ppt
which I filtered off and then continued to evaporate the still fairly clear liquid to a very small volume, then left it to cool. Meanwhile I
investigated the white sparingly soluble ppt, there is little doubt that it consists mostly of calcium sulphate and contains a little phosphate in
some form or other (leach and filter a portion with dilute nitric acid (2M) and then added ammonium molybdate; rapid yellow ppt =phosphate). The small
amount of aqueous residue finally produced a few colourless crystals but on investigation these appeared to be mainly sodium carbonate and sulphate
but I had difficult then in identifying K in the presence of much Na. I final acidified the egg-cup full of residual liquid with dilute nitric acid
and allowed it to evaporate slowly and obtained a small crop of potassium nitrate prisms. The remaining, about a dessert-spoon full, of liquid was
evaporation to dryness but the final residue appeared not to contain any more nitrate only a little sulphate. I can't remember the quantities more
accurately now but I recall that I estimated that from a whole year I could recover only about 50-60g of potassium nitrate from this source. Potassium
carbonate appears to be just too soluble to crystallize out by itself.
Sorry to disappoint but I hope my experience is helpful.CHRIS25 - 22-1-2015 at 01:23
Boffis, thanks for the reply. My object here was to see if the K. carbonate stories that I had read were true, it appears not then on such small
quantities though I am aware that one would need a Kilo of ash for just a gram probably. But my main purpose was to get a 'natural' potash solution,
any impurities would actually be welcome in this particular case. Obviously needed to estimate how much consisted of potassium and sodium carbonate
from this particular wood that we use at home. I guess then it would be better to burn the garden weeds and any plant material and collect that ash
instead, see what we get there. I have done a huge amount of patination over the years, but I came across an old recipe for a certain rainbow colour
that has eluded me for ages with modern chemistry and it included potash, using the ingredients of chemistry to prepare a modern potash has not
worked, so There is just one last thing to try - an old recipe where perhaps nature's mix would be a better choice in this instance. Trouble with
potash is that it is so ambiguous a definition, modern potash is probably too pure and unbalanced maybe.Boffis - 22-1-2015 at 15:02
Hi Chris, yes I appreciate that you we trying to get potash. I too had originally intended to produce potash but it proved very difficult to
crystallise, as I say all the crystals I got we something else so in the end I added the nitric acid because I knew that potassium nitrate
crystallises nicely. Now I would used excess tartaric acid because potassium hydrogen tartrate is sparingly soluble and once recovered can be calcined
to anhydrous potassium carbonate.
Incidentally, an important source of potash in old times was from tartar or argol which are the crystalline potassium hydrogen tartrate from wine
barrels. The crude tartar was dissolved in potash or soda and then partially acidified to precipitate the pure tartrate or heavily acidified to give
tartaric acid. But sometimes it was simply calcined until only the inorganic material was left and this is fairly pure potassium carbonate. You could
by-pass the extraction because cream of tartar as it is now known is readily available in most supermarkets as a raising agent. Potash from wood would
have been much less pure and probably contains some sulphate and phosphate in addition to sodium.
If you are considering ashing herbaceous plants then according to one of my gardening books the plant Borage accumulates potassium and is recommended
for addition to compost heaps to improve the potash content. Once dry this plant may be your best source because it burns away to very little (there
concentrated) ash and it is fairly common in the wild (at least around where I live).S.C. Wack - 22-1-2015 at 16:32
You should test another plan. I'd start with ashing your ash.
JCE 231 (1947): ...On the average charcoal ash contained 19 per cent, and tobacco ash 30 per cent potassium carbonate.
Preparation of potash. Extraction of the ash with cold water or in the Soxhlet apparatus gave poor results. Boiling of 50 g. of ash with 250 ml. of
water extracted 60 per cent of the potash, a second extraction yielded another 28 per cent, and a third one an additional 4 per cent, so that two or
three extractions with 250 ml. of boiling water each are recommended. The residue of the evaporation of these extracts should be dried at 110 to 120C
for the determination of the yield...CHRIS25 - 23-1-2015 at 10:55
@Boffs - bit confused here - you say that the potassium bitartrate was acidified a little to produce pure tartrate, what do you mean by pure tartrate?
and that would leave what? totally lost here. Doesn't make sense. Since I see no connection between the carbonate and the tartrate? Sorry.
@SCwack - Yep got it, thanks.
[Edited on 23-1-2015 by CHRIS25]
[Edited on 23-1-2015 by CHRIS25]Boffis - 24-1-2015 at 08:39
Very simple.
My investigation suggested wood ash contains sodium too. The only simple way I can think of to separate K from Na that is available to amateurs and
allows the ready recovery of the potassium as dry carbonate is to precipitate the K as it's hydrogen tartrate which is very sparingly soluble in the
cold. When calcined at dull red heat in contact with air you get potassium carbonate. Simple!
However, since potassium hydrogen tartrate is available as cream of tartar, a byproduct of the wine industry, for about 16 poundsGB/Kg why bother
extracting potash from wood from wood?
@SCwack That's interesting information about charcoal in the ash, our fire grate has about 10mm wide gaps so small particles of charcoal are abundant
in the ash. I think to re-burn the ash would be difficult.S.C. Wack - 24-1-2015 at 11:03
I was thinking blowtorch and a coffee can, with gradual addition of ash. Or a longer time at red heat in a furnace, or fireplace.
BTW if a coastal someone was really serious (except about emissions), it would be sensible to burn kelp for potassium and obtain iodine as a
byproduct, when available species are high in K and I.
[Edited on 24-1-2015 by S.C. Wack]CHRIS25 - 25-1-2015 at 07:26
@Boffs, calcining by definition has to be done in an Oxygen free atmosphere so I can't do that. Stepping back to my original reason why I posted.
With ash from normal wood and plant material I have had a clear solution when left for 24 hours. But this produced a yellow solution. This is why I
boiled down to dryness to see what would evaporate. This was my original question, I am not interested in aquiring K carbonate since I can do that by
other means. I was just hoping that someone might recognise this and say Ah..this is because, obviously something to do with the fact that this is
compressed wood and may well be treated I suppose.
Just a boiled down potash solution is all I need and will use plants to do that and normal wood. I was just curious by the colour that's all.blogfast25 - 26-1-2015 at 08:23
Hi Chris, I hate to pour cold water on your fire but....
blahdiblahdiblah... diblahdiblah.
diblahdiblah... blahdiblahdiblah.
Sorry to disappoint but I hope my experience is helpful.
Hard to know where to start rebutting such a massive turd of misinformation!
CaSO4 AND orthophosphate? That's an oxymoron!
I don't know what it was you were burning/leaching but I can assure you that leaching small amounts of potash (potassium carbonate) from wood ash is
perfectly possible. I did it when I was about 15. Yield is small and the product was yellowish to ocre. Impure K2CO3, perfectly crystallisable by the
way.
The potash leaching process was once the basis of a sizeable industry, before Leblanc/Solvay.
[Edited on 26-1-2015 by blogfast25]aga - 26-1-2015 at 12:28
Doh.
Now you've done it.
I seem to have a bucket full of water & wood ash now. blogfast25 - 26-1-2015 at 13:26
