Sciencemadness Discussion Board

Potassium metabisulfite to K2CO3 or KOH

Random - 24-7-2010 at 00:38

I have some potassium metabisulfite and it's my only available potassium salt so I want to turn it to my potassium source. I want KOH, K2CO3 or KHCO3 from it, is there an way to accomplish that?

[Edited on 24-7-2010 by Random]

not_important - 24-7-2010 at 14:28

Heat it quite hot to decompose it to SOx and K2O, you'll lose some K2O through vapourisation.

OR

Dissolve in water, bubble air through it to convert to K2SO4, react with Ca(OH)2 * to get CaSO4 (mostly solid) and KOH in solution. For K2CO3 treat with CO2, which will precipitate the small amount of CaSO4 in solution - fractionally crystalise to separate K2CO3 and small amount of K2SO4.

* Make Ca(OH)2 from CaO and water, make CaO by heating CaCO3 in a pottery kiln to 900 C or so. Note that 'blackboard chalk' and the powdered chalk used marking lines on sports fields generally are _not_ CaCO3.

entropy51 - 24-7-2010 at 15:11

Quote: Originally posted by Random  
I have some potassium metabisulfite and it's my only available potassium salt so I want to turn it to my potassium source. I want KOH, K2CO3 or KHCO3 from it, is there an way to accomplish that?

[Edited on 24-7-2010 by Random]
I think you can find lots of other potassium salts if you try.

For example, potassium bitartarate is sold in most grocery stores as Cream of Tartar (in the spice section). IIRC the bitartarate can be rather easily converted to K2CO3 by careful heating. Temperature control is probably important, but I think I have seen the procedure someplace. It might be worth Googling for it since it may be easier than starting with the metabisulfite. I think the procedure may be in some of the older chemistry textbooks.

I have also seen K2CO3 sold for something in the garden section of the local hardware store but I cannot recall what the product was. Try going to the hardware or garden store and reading labels. You may be amazed at the things you find.

Hydroponics suppliers also sell "pH Up" which is KOH or K2CO3 or a mixture of the two.

Random - 24-7-2010 at 23:09

Quote: Originally posted by not_important  
Heat it quite hot to decompose it to SOx and K2O, you'll lose some K2O through vapourisation.

OR

Dissolve in water, bubble air through it to convert to K2SO4, react with Ca(OH)2 * to get CaSO4 (mostly solid) and KOH in solution. For K2CO3 treat with CO2, which will precipitate the small amount of CaSO4 in solution - fractionally crystalise to separate K2CO3 and small amount of K2SO4.

* Make Ca(OH)2 from CaO and water, make CaO by heating CaCO3 in a pottery kiln to 900 C or so. Note that 'blackboard chalk' and the powdered chalk used marking lines on sports fields generally are _not_ CaCO3.



I will try this method, sounds good. Thanks :)

Random - 24-7-2010 at 23:12

Quote: Originally posted by entropy51  
Quote: Originally posted by Random  
I have some potassium metabisulfite and it's my only available potassium salt so I want to turn it to my potassium source. I want KOH, K2CO3 or KHCO3 from it, is there an way to accomplish that?

[Edited on 24-7-2010 by Random]
I think you can find lots of other potassium salts if you try.

For example, potassium bitartarate is sold in most grocery stores as Cream of Tartar (in the spice section). IIRC the bitartarate can be rather easily converted to K2CO3 by careful heating. Temperature control is probably important, but I think I have seen the procedure someplace. It might be worth Googling for it since it may be easier than starting with the metabisulfite. I think the procedure may be in some of the older chemistry textbooks.

I have also seen K2CO3 sold for something in the garden section of the local hardware store but I cannot recall what the product was. Try going to the hardware or garden store and reading labels. You may be amazed at the things you find.

Hydroponics suppliers also sell "pH Up" which is KOH or K2CO3 or a mixture of the two.


I think there is no cream of tartar in my country, but I will check. Thanks for the info.

Panache - 25-7-2010 at 08:26

Quote: Originally posted by Random  
Quote: Originally posted by not_important  
Heat it quite hot to decompose it to SOx and K2O, you'll lose some K2O through vapourisation.

OR

Dissolve in water, bubble air through it to convert to K2SO4, react with Ca(OH)2 * to get CaSO4 (mostly solid) and KOH in solution. For K2CO3 treat with CO2, which will precipitate the small amount of CaSO4 in solution - fractionally crystalise to separate K2CO3 and small amount of K2SO4.

* Make Ca(OH)2 from CaO and water, make CaO by heating CaCO3 in a pottery kiln to 900 C or so. Note that 'blackboard chalk' and the powdered chalk used marking lines on sports fields generally are _not_ CaCO3.



I will try this method, sounds good. Thanks :)



you will find when filtering the KOH solution from the CaSO4 that it takes a very long time, don't bother with suction or pressure, just find the coarsest filtering medium that produces a clear solution and leave it to filter for a day or so.
Bridal fabrics are good (like the fine veil materials etc)

Random - 25-7-2010 at 13:41

Quote: Originally posted by Panache  
Quote: Originally posted by Random  
Quote: Originally posted by not_important  
Heat it quite hot to decompose it to SOx and K2O, you'll lose some K2O through vapourisation.

OR

Dissolve in water, bubble air through it to convert to K2SO4, react with Ca(OH)2 * to get CaSO4 (mostly solid) and KOH in solution. For K2CO3 treat with CO2, which will precipitate the small amount of CaSO4 in solution - fractionally crystalise to separate K2CO3 and small amount of K2SO4.

* Make Ca(OH)2 from CaO and water, make CaO by heating CaCO3 in a pottery kiln to 900 C or so. Note that 'blackboard chalk' and the powdered chalk used marking lines on sports fields generally are _not_ CaCO3.



I will try this method, sounds good. Thanks :)



you will find when filtering the KOH solution from the CaSO4 that it takes a very long time, don't bother with suction or pressure, just find the coarsest filtering medium that produces a clear solution and leave it to filter for a day or so.
Bridal fabrics are good (like the fine veil materials etc)


Thanks for the suggestion, also I could decant it and filter what I decanted, it would take less time :)

I saw that I could make K2SO4, is there an easy way to make sulphuric acid from that?

densest - 26-7-2010 at 13:55

KCl is often sold as potassium-only fertilizer. Since plants absolutely require potassium, you must be able to buy it. In the US (and I believe EU as well) there are 3 numbers N-P-K (nitrogen, phosphorous, and potassium) on the package. KCl would be something like 0-0-60. Also sold is K2SO4 which is 0-0-62 (approximately). There is also "sul-po-mag" which has magnesium mixed in for 0-0-26 with sulfur.

"Muriate of potash" KCl is usually the cheapest potassium salt you can buy. It is mined from ancient lake beds (or from the Dead Sea), crushed, and bagged. It requires recrystallization to purify it for use in a lab.

The products I mentioned have no use for drug or explosive manufacturing. They should be easily purchased by anyone with no questions.

In most fertilizers, the potassium and nitrogen parts are the most soluble. In the US & EU, the components are listed with some more detail such as "nitrogen from nitrate 5%, urea 39%, ammonium salts 56%", etc. so you can work out what will dissolve easily.

Many fertilizers are mixed with oils, waxes, clays, or plastics to slow down the speed of dissolving in the soil. You might have to add boiling water and mix vigorously to dissolve the mess in that case then let the insoluble mess settle and decant the solutes to get useful chemicals. If possible, get the simplest and cheapest fertilizer for a farm or commercial gardener, not the ones designed for a home gardener which are mixed with dozens of useless additives.

If you have access to buckets of wood ashes you can make potash - potassium carbonate - by rinsing the ashes with water, collecting the liquid, decanting the clear liquid, and evaporating it. If the ashes are free, the potash costs you only the labor.


[Edited on 26-7-2010 by densest]

woelen - 28-7-2010 at 08:55

Quote: Originally posted by not_important  
Heat it quite hot to decompose it to SOx and K2O, you'll lose some K2O through vapourisation.

This is not true, you probably missed this recent thread:

http://www.sciencemadness.org/talk/viewthread.php?tid=14077

K2S2O5 does not decompose to K2O and SO2 when it is heated, unless you use really high temperatures and probably you will have lots of impurities as well when it is heated to very high temperatures.

[Edited on 28-7-10 by woelen]

not_important - 28-7-2010 at 13:43

Quote: Originally posted by woelen  
Quote: Originally posted by not_important  
Heat it quite hot to decompose it to SOx and K2O, you'll lose some K2O through vapourisation.

This is not true, you probably missed this recent thread:



Nope, I did say "quite hot" which given the context meant yellow heat or better. Often, but in this case I don't know, passing superheated steam over the compound being decomposed will increase the decomposition rate and/or lower the temperature needed. Be a decent research topic.

ScienceSquirrel - 28-7-2010 at 16:21

Potassium carbonate is easy to buy almost everywhere.
But if you really want to make potassium carbonate then take cream of tartar aka potassium hydrogen tartrate, as a common baking ingredient it must be available everywhere, and calcine it with a gas torch. The residual ash will be pure potassium carbonate.
Really easy!

densest - 28-7-2010 at 16:40

Another name for potassium carbonate is "pearl ash" which is available at potter's supply stores.

KCl is available as a no-sodium salt substitute. "No Salt" is a brand name in the US.

Melgar - 29-7-2010 at 20:08

KCl is also available as water softener salt for people on low-sodium diets, or who don't want sodium in their water for some other reason. In the US, I've seen 20-pound bags for around $20.

Random - 29-7-2010 at 23:11

I will check sometime if there is some KCl in the stores. :)