Sciencemadness Discussion Board

Ash of coal: K2CO3 ?

chief - 30-10-2008 at 10:14

Now, in winter, I have a fireplace going, and a lot of ash, from brown_coal. Can from this ahs too some K2CO3 be extracted, or whats in it ?
After all it initially was organic substance (wood), that came into geological conditions and transformed to the coal.

The amount of ash will, over the time, be in the range of several 100 kg ...

watson.fawkes - 30-10-2008 at 11:02

Coal ash is full of all sorts of things, including not insignificant amounts of mercury and uranium. It may not be all inorganic, either; depending on what your combustion temperature is, you may have some high-MW organics. I'd start with various assaying techniques. See what comes out with steam distillation, for example.

Picric-A - 30-10-2008 at 14:56

The chances of you getting anything usefull form coal in any usefull quantities is slim.
If you wanted to get anything useufll from coal destructive distilltion then fractionation/purification ect...
But becuase you are using it as a heat generator your best bet would be use wood and extract the K2CO3 from the wood ash.

[Edited on 30-10-2008 by Picric-A]

kclo4 - 30-10-2008 at 14:58

Then you could purify the K2CO3 from the other chemicals via solubility and fractional crystallization.
Wood might work better, but honestly I don't know. I just know coal ash is more radioactive then wood ash. So that leads me to think that you'd have to purify it from other things as well as what would be in wood.

Heating the ash should help get rid of any remaining carbon, decompose some bicarbonates, get rid of organic material, etc.

watson.fawkes - 30-10-2008 at 16:36

This page has a pretty good basic exposition on the composition of fly ash. Note that the composition is listed in terms of oxides, but that's the assay value, not the actual compounds that might be present. Fly as is much like rocks, mostly-but-not-completely. Lignite (brown coal), particularly, has more trace metals, as a result of bioconcentration. Coal burning is the largest single source of environmental mercury release, for example.

S.C. Wack - 30-10-2008 at 16:54

Power plants sell massive amounts of ash, its composition is not unknown.
http://www.google.com/search?q=%22furnace+bottom+ash%22

not_important - 30-10-2008 at 18:10

Power plant ash usually has a high calcium content, from the limestone added to reduce SOx emissions, so it doesn't represent ash from a simple coal fire.
Quote:

Coal ash is made of three types of solids:
1) chemically water stable solids (SiO, FeO, AIO),
2) relatively water soluble solids (e.g., metalS04,
metal-BO3,), and
3) water reactive metal-oxides (e.g., CaO, MgO, K20, Na20, etc).
Ash varies from acidic to alkaline because of the chemical make-up of the source coal. Physical appearance varies depending on coal type and furnace.


http://www.mcrcc.osmre.gov/PDF/Forums/CCB/5-1.pdf (PDF)

Mostly silica, alumina, and iron oxides, in order of decreasing amount. The alkali and alkaline earth elements tend to have been leeched out. There are traces of some interesting elements, such as vanadium and gallium.

http://cat.inist.fr/?aModele=afficheN&cpsidt=16694736

Attachment: Coal Ash.pdf (92kB)
This file has been downloaded 1410 times

Ebao-lu - 30-10-2008 at 23:24

K2CO3 is soluble in water, if that ash is been there for months, the rains will wash out K2CO3 at least part of it

not_important - 31-10-2008 at 20:16

Quote:
Originally posted by Ebao-lu
K2CO3 is soluble in water, if that ash is been there for months, the rains will wash out K2CO3 at least part of it


While chief is not likely to find much K2CO3 in their coal ash, they did type
Quote:
I have a fireplace going, and a lot of ash,

and SFAIK must home fireplaces receive very little rain, even in Ireland.

MagicJigPipe - 20-12-2008 at 17:36

I just did a simple experiment "on the fly" with no real measurements or anything. I just wanted to check the yields (by eye) and the basic properties of the resulting substance. This was mostly because I'm not in a very good position to do a long and drawn out experiment.

Some wood ash (from various kinds of wood) with very little carbon was placed in a 1000mL beaker. Tap water was poured into the beaker until it completely covered the ash (about 500mL of ash and 500mL of water above it).

It was stirred and allowed to settle several times over the course of 2 hours. The water "on top" was decanted and placed in another beaker. More water was poured onto the ashes and the process was repeated. A light brown liquid was obtained on both occasions. Both extracts were combined and then poured through a piece of filter paper and a medium sintered glass filter funnel. A light yellow liquid was obtained.

The liquid and ~8 tablespoons of aquarium grade activated charcoal were placed in a stainless steel pot and then boiled for about 20 mins. The boiling mixture was filtered through 2 coffee filters and the sintered glass funnel. A clear liquid with a very slight (almost unnoticeable) yellow tint was obtained.

The SS pot was cleaned and the liquid was placed back in the pot and boiled until dry. A fine, white, free-flowing powder with a very slight, brown tinge was obtained (after scraping it off).

It was then scraped from the bottom of the pot (with much difficulty) and placed in a small jar. Yield by volume was about 60mL with no compression.

The powder reacted with evolution of CO2 (assumed) when mixed with acetic acid. The powder was assumed to be an alkali carbonate since no bicarbonate could've "survived" the high temperatures involved in the final minutes of drying.

One reason I think it might not be mostly K2CO3 is because I left some sitting out about 20 minutes ago and it doesn't appear to be absorbing moisture. Isn't it deliquescent? I suppose I'll find out in a couple of hours...

[Edited on 12-20-2008 by MagicJigPipe]

not_important - 20-12-2008 at 20:00

The alkali bicarbonates are stable enough to survive a few minutes of heating not too high above 100 C, for full decomposition you usually have to get to 200 C or so. You also might have a mix of carbonate with some sulfate, phosphate, and even traces of chloride.

I think carrying on the original boiling for long, enough to reduce the liquid volume by 50% or even more might do better. Bubble a little air through it at the same time to push any iron to the ferric state. After that let it cool an settle, then decant and filter the liquid.

Extraction by letting water flow through the ash is more effective. You could cut the bottom out of a large plastic beverage bottle, stick a stopper with a small hole in the neck, mount it neck down, drop a coffee filter or two into it to hold the ash, fill with ash, top it off with water and rig it so water drips into it as fast as it drips out.

Update

MagicJigPipe - 21-12-2008 at 00:43

It seems that it does contain a good percentage of K2CO3 because the sample is now a "mushy pool". Of course this could be other things but I think it is most likely caused by potassium carbonate.

I'm sure I can improve the yields by doing this properly (thanks for the info not_important, but remember, this was just a spur of the moment, "get it done quick" sort of thing) and if I can improve the purity then I wouldn't mind getting my K2CO3 by this method at all. It's hard to come by here (except internet, of course) and this is such an easy process. Just a little more complex than I2 from KI!

Anyway, it seems to work, but how well and to what extent is yet to be determined. I should be able to do a "proper" experiment within the next week. I'll post my results here.

P.S.

I think using the ashes themselves as a filter my make the boiling with activated charcoal step unnecessary. Or, like not_important said, I could try removing iron as ferric.

What do you think is mostly responsible for the light brown discoloration of the powder? An iron compound? A potpourri of compounds?

Also, of course this method is not likely to ever yield K2CO3 of high quality without superfluous sophistication but for reactions that don't require high purity this is perfect.

EDIT

I forgot to mention that I did try pouring some water through the ashes and 3 coffee filters. This resulted in a "suspension" that didn't seem to settle at all even after an hour. I'll look more into next time.

[Edited on 12-21-2008 by MagicJigPipe]

Formatik - 21-12-2008 at 06:05

Quote:
Originally posted by MagicJigPipe What do you think is mostly responsible for the light brown discoloration of the powder? An iron compound? A potpourri of compounds?


The brown color comes from organic compounds (see ref below) that need to be roasted off, e.g. heated to glowing to be combusted. But the resulting potash still has a lot of other stuff, soluble compounds like potassium sulfate, -chloride, -silicate, also sulfide and thiosulfate (from oxidation of sulfide). Then also some sodium salts. Traces of K2MnO4 can also be present (this can impart a bluish color, but is destroyed by organics). Some other compounds have been found too. There is a method of purifying in the Handbook of Chemistry, see under Cineres clavellati.

MagicJigPipe - 23-12-2008 at 21:04

Organic material? I hate to doubt you but these ashes came from embers that were glowing red hot at well over 700*C for hours (it was hot enough to melt glass because I used a blower). How many organic compounds could not be oxidized/vaporized in this environment?

And if that didn't get rid of the organic compounds, how much more roasting must I do? More than the original "roasting"?

Thanks for the information. I look forward to your reply.

Formatik - 24-12-2008 at 01:26

In the reference they heated the extracted ashes themselves. If it still has discoloration after that then I would attribute this to an inorganic.

not_important - 24-12-2008 at 07:41

I suspect iron, maybe manganese, and suspended carbon are behind the colouration; however organics seem to sneak through with large scale ignition processes so they might be there although it sounds doubtful in your case.

You don't want to " pour some water through the ashes", you want the ashes covered with water and a slow drip of extract out the bottom with a matching drip in the top (or a 'burp' type water feeder) Doing that both gives fuller extraction and gets some self-filtering by the ashes. Coffee filters are not very good filter paper, they're only meant to hold back fairly course material.

As for further purification, the concentration to the point K2SO4 crystalises out is a good start, if you can establish the proper concentration. After that you might try making a hot nearly saturated solution of the crude K2CO3, saturate that with CO2 under mild pressure (1 atmosphere), let it cool while keeping the CO2 pressure on. As KHCO3 is roughly three and a half times less soluble than K2CO3 at room temperature, KHCO3 should drop out of solution leaving sulfate, phosphate, and chloride behind. Any silicate would turn to hydrated silica from reacting with the CO2.

The KHCO3 and SiO2 would be filtered off, and possibly washed with a tiny amount of ice cold water. Heating in shallow layer to 150 C will convert the bicarbonate back to carbonate. For further purification you could repeat the process, filtering the K2CO3 solution to remove SiO2 before saturating with CO2.

You might work up the liquors from the KHCO3 formation to recover the remaining potassium, although you'll have to do a bit of titrating to find the proper amount, by adding the proper amount of Ca(OH)2 suspension to the left over K2CO3 mother liquor; the intent is to remove some of the phosphate and sulfate as calcium salts. Bring it to a boil for a few minutes, let it cool then settle for several days. After that add the solution to the next batch of ash and extract away.

Xenoid - 24-12-2008 at 12:31

Several years ago, when we moved into our current home, I discovered the open fireplace had an ash pit which was accessible from the basement below. I removed several large bags of ash with the thought of recovering the K2CO3. From the remains of charcoal, nails etc. I assumed a mix of pine and native logs and old building timber had been burned.

After much leaching, extracting and flaking skin on the palms of my hands, I ended up with several buckets of golden yellow liquid. Because of the amount of boiling down required, I never got around to recovering the K2CO3, But I have often wondered about the source of the yellow colouration. This colour was a distinct bright yellow, similar to a dilute dichromate solution. I initially thought it was perhaps dichromate, formed somehow from "chromium" treated timber. Another possibility was potassium ferrocyanide, due to the large amount of iron scrap in the timber. I did not think nitrogen from the air would be sufficient for this process however, I thought some form of nitrogenous waste was required.

The recent short thread in beginnings;

http://www.sciencemadness.org/talk/viewthread.php?tid=11615

on ferrocyanide/cyanide has alerted me to the possibility that ferrocyanide may indeed be formed in an open fire in the presence of nails, etc.

Anyone care to comment on this possibility?

Edit: Hmmm.. thinking about it a bit more. My recollection of potassium ferrocyanide is that it is a fairly pale-yellow compound, unlikely to produce the strong golden yellow of the observed ash solution, especially at the concentrations likely to have formed!

[Edited on 24-12-2008 by Xenoid]