elementcollector1

Potassium Hydroxide Separation

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I found a jug of Enforcer Maximum Strength Drain Opener gel in my garage, and would like to know if there is any method for separating the KOH from the rest. The MSDS gives me 1-10% KOH and <5% NaOCl, so I should get those two and maybe a few other things after boiling down the solution. (The liquid was very soapy when I looked at it, forming bubbles easily).

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Is it more likely that I'm questioning your ability to read or making you think about the ions present in a solution?

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It says on the label and MSDS "contains KOH". Or maybe you're referring to a double-displacement reaction, in which case I would have to come up with a new plan.

 

I imagine this will be a difficult separation unless you are okay with getting a mixture of Na and K hydroxides.

 

I don't have any experience with the separation of Group I hydroxides but I'm getting the feeling that you may need to try and obtain KOH from elsewhere.

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I would imagine that the solvation gradients are significantly different for KClO and NaClO (considering that other chlorates are similar in such a way)... so you could ppt one or the other and be left with either KOH or a mixture of NaOH and KOH. If KClO ppts you could always convert it to the hydroxide then seperate from the contaminant of KCl.

 

Edit: If you want a displacement reaction:

 

K2SO4 + Ca(OH)2 --> CaSO4 + 2KOH

 

The trick would be to get a large beaker of distilled water and stick it on a stirrer plate. Add sufficient calcium hydrodixe or oxide and let it stir for a few mins. Keep it on stirr and add saturated potassium sulfate slowly until stoichimetric ratio is reached. Calcium sulfate will precipitate out quickly and eventually replace the calcium oxide floating in the beaker.

Edited by Suxamethonium

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" If KClO ppts "

Then I will be very surprised indeed The stuff isn't very stable as a solid.

 

You could hope to precipitate the potassium selectively as the perchlorate or, probably more easily, as the hydrogen tartrate.

Why start with a mixture of two ions that are difficult to separate when you could, for example, leach bonfire ashes with water?

 

Calcium oxide reacts with water and gives out enough heat to boil the water - it's been known to start fires.

So the idea of "Calcium sulfate will precipitate out quickly and eventually replace the calcium oxide floating in the beaker. " lacks a certain something.

What will end to happen is that calcium sulphate will ppt out on the surface of the (fairly insoluble) Ca(OH)2 and stop any further reaction.

 

What are you actually hoping to achieve here?

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"What will end to happen is that calcium sulphate will ppt out on the surface of the (fairly insoluble) Ca(OH)2 and stop any further reaction."

That is why it is being continually stirred and sulfate added slowly- it's less likely to form a suitable enough coating to hinder the calcium hydroxides solvation- at the very least you would get SOME KOH which is much easier to seperate from the Calcium ions.

 

As for the heat released- add it slowly its not exactly rocket science- and there is sufficient water to absorb this heat without boiling so a fire is highly unlikely in even the worst case scenario- NB. have you never made limewater before?

 

Also leaching bon fire ashes with water is still going to contaminate your solution with other cations (including sodium) so I don't see how this is 'easier to separate' than the original mixture, except that the ions envolved aren't quite so interesting.

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I may flatter myself, but I think I'm quite a good chemist.

However I know that nature is a great deal batter at it than I am.

 

 

So, if I want to get KOH I will not start from a mixture of roughly equal measures of potassium and something difficult to remove from it.

 

I will let a plant do the job for me because I know it's much better at it.

There's a lot of variation in such things but here's an analysis of some plant matter.

https://www-s.nist.gov/srmors/view_detail.cfm?srm=1515

As you can see, there's a whole lot more potassium than sodium

1.6% rather than 25 ppm so, even if you don't recrystallise it or whatever, you start off with better than 99% K

And, since the leachate is a dilute solution of alkaline carbonate, most other metals won't be very soluble.

 

There's a hint about how to get hold of caustic potash in the name- you causticise ashes.

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"There's a hint about how to get hold of caustic potash in the name- you causticise ashes."

 

Well yeah, pre-industry. The process is messy- and the alternative of calcium hydroxide + potassium sulfate is cheap (hardwood is expensive and tedious to burn just to get ash). Also potash is potassium carbonate and (who would of thought) is converted to potassium hydroxide by metathesis reaction with calcium hydroxide- so really I have just shortened the entire method to just a metathesis reaction. If the metathesis reaction I proposed doesn't work for the reasons you implied, then why does it work for the method employed pre-industry? Even so, you can buy potassium carbonate easily enough to just employ the alternative metathesis reaction without the mess of ash.

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Anyone who wants to can collect the garden trimmings from my garden for free. It's not expensive.

The last time I had a bonfire it took a few hours and got through about 100Kg of waste vegetation. It's not slow (though it was a bit warm).

 

Precipitation of calcium sulphate is usually messy- it tends to form gels. That's why one of the "obvious" methods to get nitric acid (sulphuric acid with calcium nitrate fertiliser) isn't very successful.

 

So you shortened the metathesis reaction from

 

Ca(OH)2 + K2CO3 --> CaCO3 +2 KOH (which has been known since pre-industral days

to

Ca(OH)2 + K2SO4 --> CaSO4 +2 KOH (which doesn't work very well.)

So, I guess that's "shorter" in some technical sense that escapes me, especially since you would have to get the K2SO4 from the KOH which involves another step.

 

I'm still wondering why the OP wants KOH.

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Potassium sulfate is readily available from 500g to 25kg. It is a standard fertiliser- thats why its shorter- you don't have to burn crap to get it. I've never had a problem with calcium sulfate precipitates, but if it so concerns you you can buy the potassium carbonate, its just not nearly as easy to get as the sulfate.

 

The reason i said i simplified it was because in no way does this method require one to burn garden wastes indefinately to get any reagents- it starts from readily available agricultural chems (which i can even buy from the local super market).

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Which is all very well, but hasn't got a lot to do with the OP.

Compared to trying to sort out that mixture, the ashes look like a good idea.

Why not just buy KOH?

 

As I said, it depends on why you are doing all this.

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*rolls eyes*

Whatever

 

Indeed. I want to make KOH because I'd like to attempt reduction to potassium metal (even though whatever product KOH I get is bound to be severely hydrated). Other uses could be production of KMnO4, etc.

Now, when you said 'garden clippings', John, did you literally mean bits of grass and shrub? That's going to be *very* hard to find here in the Evergreen State...

Suxamethonium, I've never seen many potassium compounds at the local Safeway but for salt substitute. What are they sold as? I know sodium carbonate is washing soda, is potassium carbonate some sort of sodium-free version?

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Potassium carbonate is harder to find (probably because it can be significantly corrosive to plant roots if used wrong) but you could probably find it in agricultural areas. Potassium sulfate is the primary ingredient in most lawn fertilisers (but you can get formulations with >95% pottasium sulfate and will usually say potassium sulfate somewhere on it)- this can often be found in the gardening section in super markets.

 

Alternatively, you can buy KOH (caustic potash) in various places, but concentration and purity may be an issue unless you can find easy access to the pellets. There's been a few posts in the 'how to make sodium' threads about making potassium- these might be useful to you if you havent seen them already.

 

Oh, by the way- if you do go burning stuff- you'll get the best results with hardwood (but it's a bit of a hassle to find and then get it durning hot enough for the best ash, you can buy hardwood but it's quite expensive).

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Reduction of potassium hydroxide looks like a good root to the metal but, as you say, the material is going to be damp.

Even lab grade KOH is typically only about 87% KOH- the rest is water.

So 100 grams of it has about 1.6 moles of KOH and 0.72 moles of water.

That's a lot of extra stuff you need to reduce and a lot of hydrogen to get rid of.

 

Yes, I really do mean stuff like hedge trimmings.

All plants do a very good job of extracting potassium from the soil and they do a pretty good job of leaving any sodium behind.

I don't understand how anyone could think that it's difficult or expensive to get ash. You don't need to use hardwood- most of the stuff I used when I did this was

this stuff

http://en.wikipedia.org/wiki/Leyland_Cypress

which grows like a weed and burns well too.

Though I actually used that because I have to keep my hedge trimmed anyway, rather than because it's especially good.

If you are after permanganate I'm fairly sure you can use the carbonate rather than the hydroxide but the melting point is a lot higher.

It might be easier to make NaMnO4 and then ppt the K salt with K2CO3 or possibly even KCl (which is fairly easy to get from low sodium "salt").

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Reduction of potassium hydroxide looks like a good root to the metal but, as you say, the material is going to be damp.

Even lab grade KOH is typically only about 87% KOH- the rest is water.

So 100 grams of it has about 1.6 moles of KOH and 0.72 moles of water.

That's a lot of extra stuff you need to reduce and a lot of hydrogen to get rid of.

 

Yes, I really do mean stuff like hedge trimmings.

All plants do a very good job of extracting potassium from the soil and they do a pretty good job of leaving any sodium behind.

I don't understand how anyone could think that it's difficult or expensive to get ash. You don't need to use hardwood- most of the stuff I used when I did this was

this stuff

http://en.wikipedia....Leyland_Cypress

which grows like a weed and burns well too.

Though I actually used that because I have to keep my hedge trimmed anyway, rather than because it's especially good.

If you are after permanganate I'm fairly sure you can use the carbonate rather than the hydroxide but the melting point is a lot higher.

It might be easier to make NaMnO4 and then ppt the K salt with K2CO3 or possibly even KCl (which is fairly easy to get from low sodium "salt").

 

What about pine trees? They're plentiful here in Washington, it wouldn't be hard to get a couple pounds of trimmings from them.

I prefer the hydroxide for most applications because of low melting point and the high base properties.

Not so sure about the K metal anymore, found a source of ~3 grams for $12. Might try anyway.

On that note, what about rubidium extraction? I can get 10 grams of the carbonate, should I try converting to hydroxide and electrolysis under a high-boiling, inert solvent?

I'm beginning to love this old-school alchemy-style science.

Also, how do you 'causticize' the ashes? Calcium hydroxide is practically insoluble, so aqueous reactions don't seem likely.

Edited by elementcollector1

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"Calcium hydroxide is practically insoluble, so aqueous reactions don't seem likely."

 

It's actually partially soluble- wiki data says 0.173g/100ml at 20oC. This is significant enough for displacement reactions- CaO or Ca(OH)2 can be mixed with the ash and water drained through (Or you can try doing away with the ash and using bought potassium carbonate. Or try possibly potassium sulfate- but others seem to think that the physical chemistry is different in such a case making it impractical- I have had no such issues with "gel-like" CaSO4 ppts forming so maybe it's worth the try?).

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"Calcium hydroxide is practically insoluble, so aqueous reactions don't seem likely."

 

It's actually partially soluble- wiki data says 0.173g/100ml at 20oC. This is significant enough for displacement reactions- CaO or Ca(OH)2 can be mixed with the ash and water drained through (Or you can try doing away with the ash and using bought potassium carbonate. Or try possibly potassium sulfate- but others seem to think that the physical chemistry is different in such a case making it impractical- I have had no such issues with "gel-like" CaSO4 ppts forming so maybe it's worth the try?).

 

Still, 0.173 is rather small. What about electrolysis? Or is there a more soluble hydroxide that converts to an insoluble carbonate?

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The point of it is that more can dissolve once the sulfate or carbonate precipitates- thats why it is included as a solid and 'washed' with water. That is also why I proposed my initial procedure to try- its the same principle without the ash (using readily available suflate instead)- I still think its worth a try but its up to you. Kudos if you can be arsed to get the clippings and burn them.

 

Edit- sentence structure.

Edited by Suxamethonium

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http://en.wikipedia....arium_hydroxide

does better but it's rather toxic and much more difficult to get hold of.

 

Luckily for me, I have a baryte rose I can convert if necessary, but not a lot.

So, I think electrolysis is still the best route here (no possible contaminants except for K2CO3). So, what is the best setup for this? I have a 12V plug-in adapter for electricity (does that convert amps as well?) Should I use carbon electrodes (taken from zinc-carbon batteries, I also have titanium if necessary)? What kind of apparatus should I use? I've heard that I should use two beakers with a saltwater-soaked tissue between them, and a saturated solution of KCl in each. Is there a better way to maintain electron flow between the two half-cells (gold wire)?

Sorry for the barrage of questions, I've tried electrolysis of KCl before with not-so-good results (9V battery source).

 

 

EDIT: Trying this with a 6V cell (made of 4 of those fat Duracell's), gold anode, graphite cathode (14k gold corroded), and an aqueous solution of NaCl. Will measure pH when the thing stops bubbling.

Edited by elementcollector1

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On 2/23/2012 at 10:58 AM, Suxamethonium said:

I would imagine that the solvation gradients are significantly different for KClO and NaClO (considering that other chlorates are similar in such a way)... so you could ppt one or the other and be left with either KOH or a mixture of NaOH and KOH. If KClO ppts you could always convert it to the hydroxide then seperate from the contaminant of KCl.

 

Edit: If you want a displacement reaction:

 

K2SO4 + Ca(OH)2 --> CaSO4 + 2KOH

 

The trick would be to get a large beaker of distilled water and stick it on a stirrer plate. Add sufficient calcium hydrodixe or oxide and let it stir for a few mins. Keep it on stirr and add saturated potassium sulfate slowly until stoichimetric ratio is reached. Calcium sulfate will precipitate out quickly and eventually replace the calcium oxide floating in the beaker.

hi dear

please illustrate about below reation. I want to achieve Koh from K2So4 with this reaction but we could not achieve it

please help me

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16 hours ago, mohammadmazidi said:

hi dear

please illustrate about below reation. I want to achieve Koh from K2So4 with this reaction but we could not achieve it

please help me

 

The member you are responding to hasn't visited the forum for almost 7 years. You are unlikely to get a response. 

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