Sciencemadness Discussion Board - Wood Ash + Water reaction

Wood Ash + Water reaction

Random - 7-5-2010 at 13:14

This is beginner question and it may have been answered before, but please answer now. I am trying to get potassium carbonate out of wood ash, or maybe even potassium hydroxide. I put wood ash on the sieve and took the finer powder of the ash. After that I mixed it with water wanting to separate the potassium carbonate from the remaining parts of the ash. The water solution started making bubbles so I can predict some gas has formed. Did this reaction happen?

K2CO3 + 2H2O --> H2CO3 + 2KOH

But if that happened, some of the CO2 must have been synthesized because of the gas bubbles (It could be H2CO3 which was decomposed).

What do I actually have now and what should I do to get K2CO3 or KOH out of this?

not_important - 7-5-2010 at 13:55

No.

KOH is a strong base, CO2 a weak acid. K2CO3 is a weak base and H2O a very weak acid. The reaction will go from right to left, not left to right, under conditions anywhere near STP. Elementary chemistry, maybe pick up some theory as well as recipes.

Wood ash is very porous and traps a lot of air, that's the bubbles you see.

If the fire was hot enough, and the ash was not exposed to air to long after it cooled, then there will be some CaO in the ash and you can get some KOH from the reaction between K2CO3 and Ca(OH)2 from the CaO plus water. Leave the extract exposed to air and it will pick up CO2 to give just K2CO3. Isolate that first, then if you want KOH make it from the K2CO3.

The potassium content of wood ash varies with the type and origin of the wood, as does the sodium content, Typically there's only a tenth as much sodium as potassium, but in some woods it can be a smaller ratio than that. If you want good purity of potassium salts, you've a long purification process ahead of you.

The PDF at http://www.fpl.fs.fed.us/documnts/pdf1993/misra93a.pdf could be of interest, as might be the UTFSE located https://www.sciencemadness.org/whisper/viewthread.php?tid=81...

Mr. Wizard - 7-5-2010 at 15:31

As not_important mentioned you will get K2CO3 on letting a solution of wood ash sit exposed to air. Potash was the main source of the material and is the root of the English name for Potassium, though the K used as it's symbol is from Kalium of Latin which is from an Arabic word for plant ashes.

If you are getting it from ashes, I can tell you it really makes a mess in a filter. The material will quickly plug a filter, and the solution will come through ever so slowly. I would recommend mixing the ash with water in large buckets, and stirring once, then letting the ash and solids settle to the bottom over a period of days. Use a siphon tube to remove the clear but usually yellow liquid from the upper portion. You might want to filter this portion and save it for drying , making KOH by addition of Lime or separation by crystallization. The remaining wet ash can be remixed with some clean water and left to settle again, with the supernatant being used as the liquid for a fresh batch of ash.

I tried to get it from some wood ash in my fireplace, and I can tell you it is a messy job, with many buckets sitting around, in various stages of purification. I was convinced to give it up when I realized I had been burning homemade paper logs, and the ash contained a lot of sodium. I was fighting a losing battle then. Next time I will save only wood ash.

Random - 7-5-2010 at 23:29

Thank you for the answers

I will try to let the ash settle at the bottom, but it looks I will need to add more water to dissolve the remaining salts. I saw that some small parts of the charcoal are at the bottom so I will take them out. After that I will dry the solution in the air and try to add some 9% vinegar to the results, if the K2CO3 is formed, I should get CO2 because of the acid-base reaction. The problem is that the ash was exposed to rain 2-3 weeks, it wasn't raining much though so I hope there is still some potash in it.

Mr. Wizard, I suggest you to try hard wood ash, I read on few places it's better to use it than the ash from softwood (though I am trying softwood ash because I have only that now). I'll try the fresh ash too and I'll tell you results

Sedit - 7-5-2010 at 23:33

Then why go thru the bullshit bucket crap when you could get a large bucket(or 55gal drum for better if your feeling frisky) and do like they did in the old days of placing a bunch of holes like a buchner funnle at the bottom of a barrel with cotton to act as a filter..........

Then let rain (or supply your own water(rain is cheep and distilled, AKA very soft)) and place a collection basin under the filter on a hot day to allow evaporation.

Fill this container with ash and what drips out the bottom is SEMI pure. Eliminating the use of many buckets and much mess.

Now I have never done this before because I don't need to but I still am pretty good at problem solving and this seems to be to be the start of the best way to go about performing the operation.

Random - 7-5-2010 at 23:42

Quote: Originally posted by Sedit

Then why go thru the bullshit bucket crap when you could get a large bucket(or 55gal drum for better if your feeling frisky) and do like they did in the old days of placing a bunch of holes like a buchner funnle at the bottom of a barrel with cotton to act as a filter..........

Then let rain (or supply your own water(rain is cheep and distilled, AKA very soft)) and place a collection basin under the filter on a hot day to allow evaporation.

Fill this container with ash and what drips out the bottom is SEMI pure. Eliminating the use of many buckets and much mess.

Now I have never done this before because I don't need to but I still am pretty good at problem solving and this seems to be to be the start of the best way to go about performing the operation.

This seems to be one of the more simple ways to do this, I will try that too and tell you the results.

Random - 8-5-2010 at 01:53

I dried some of the solution on the air which became white/very light gray. After that I added some 9% vinegar to it and it started bubbling. That means I am on the right way of getting the carbonates/bases from the ash, at least mix of them. But that white/light gray salt becomes gray when mixed with water. Is this potassium carbonate or something other?

[Edited on 8-5-2010 by Random]

Mr. Wizard - 8-5-2010 at 07:39

I would guess the gray is soot or charcoal that has passed through the filter.

not_important - 8-5-2010 at 08:03

Indeed, charcoal and possibly trace organics. The trick is to burn the wood so that the hot ash is well exposed to heated air, while at the same time keeping the ash under 900 C to reduce loss of potassium through vapourisation.

There are a number of filtration tricks that will clean the solution up, simply using a fine filter, adding something like diatomaceous earth and then filtering, filtering through a bed of diatomaceous earth, centrifuging...

Sedit - 8-5-2010 at 08:33

What about using an old microwave to rid the mixture of any trace organics present? IIRC charcoal can heat pretty well in a MW and nuking it for a few minute seems in theory atlest like it could burn off the organics and leave you with the ash from it at the same time.

My suggestion is to get a large funnel and pack the stem tightly with toilet paper, Prewet it or else it will suck the fine ash particals into the pores, and add the solution to the funnel and let it ever so slowly gravity filter itself. I have done simular operations to filter micro particals that resisted every other attempt at filtration but one has to be patiant because it can take quite abit of time indeed.

Random - 8-5-2010 at 11:15

It looks I am on the next step of purifying. After everything sedimented, I used a cotton rag as a filter, which i put on the jar. After that I added more water to the solution of ash, I stirred it and put it through the filter. I did that with all water which dissolved the salts. In the filter remained something like cement mixed with water, but the filtrate was pale yellow color mixed with gray. I let it sediment. After some time, in the sediment were the small particles of that cement-like color, but above that was water in the yellowish color. It looks this water has some K2CO3 in it. I will decant it and try to dry it to see what is actually dissolved in that water.

That filtering idea with toilet paper is good, if it will not be pure enough, I will tyr it, but as the ash particles sediment, It's not necessary now.

[Edited on 8-5-2010 by Random]

Sedit - 8-5-2010 at 13:34

It is definitly a last step as far as filtering is concerned because if there is much particulate left it will clog the toilet paper quickly and cause and already long process to take longer. But all in all the result is a solution that contains nothing more then materials dissolved in a true solution and no suspension of any kind.

Fractions/Assay/Analysis of ash-water solubles

Riventree - 1-7-2010 at 12:28

Strangely, I am also in the process of doing some wood-ash-water work. In my case, the fire is particularly hot, well over 1000°C, so I'm expecting my "lump charcoal" burndown to contain a lot more calcium, and less potassium.

Here's the thing: After leeching and drying, I have a fine crystalline powder, presumably containing CaO, CaCO3, K2O, and K2CO3, as well as other smaller fractions.

Please, experts, help me: How do I assay this powder and find out how much of what I have?

JohnWW - 4-7-2010 at 07:03

Before evaporating and crystallizing it, you could have analyzed for likely metals forming soluble hydroxides in the leachate solution, particularly Na, Mg, K, Ca (there may also be trace amounts of Li, Rb, Sr, Cs, depending on the local mineralogy) by means of atomic absorption spectroscopy, although the cost of an AA spectrometer is beyond most home chemists. Alkali metals, and also to some extent alkaline earth metals, can also be analyzed for on a flame photometer. There are also colorimetric and titrimetric methods for Mg and Ca, depending on their being complexed by organic chelating agents. In addition, the total alkalinity, and the "hardness" due to Ca and Mg, can be determined by tritrations. See "Standard Methods For The Analysis Of Water & Wastewater" (APHA/AWWA), which I have uploaded to rapidshare.com , and have posted the link for in the References section.

Jimmymajesty - 6-7-2010 at 08:47

When I was a child I was working with ash from a glazed tile stove. I took a large dish suspended the ash in water by stirring with a large wood rod, then allowed it to settle, after a couple of hours it was finished, then separated the remained ash mass, and the soution by simply pouring the latter out of the dish.
Then I made its ph~4-5 with nitric acid and dryed under the sun, mixed with sulphur bla bla.., it made a very nice powder for my cannon

IIRC it was not hygroscopic.