I bought some sulfate of potash fertiliser with the intention of putifying it to potassium sulfate by dissolving in water, filtering and drying.
I was intrigued to see on the packet that the contents are actually:
Potassium oxide K2O 52%
Sulphur trioxide SO3 48%
Now I understand that on adding water the K20 will produce KOH and the SO3 will produce H2SO4 and thus neutralise each other producing K2SO4.
It would be nice though if the SO3 could instead be isolated and H2SO4 be produced on it's own. I don't expect this is possible though. imidazole - 17-3-2025 at 09:25
I hate to say it, but those are just the "active components" listed for fertilizer stuff, In actuality it's most likely just K2SO4.
Fertilizer has an odd notation style where they list things as oxides, for instance it tries measuring phosphorus as P2O5, if I remember correctly. fx-991ex - 17-3-2025 at 11:40
instead of dissolving filter and drying why not recrystallize it?
like get a liter of water to boil add 240g till it dissolved completly, try filtering hot(if you see undissolved contams) and let cool down as much as
you can.
[Edited on 17-3-2025 by fx-991ex]
[Edited on 17-3-2025 by fx-991ex]Chemgineer - 17-3-2025 at 12:02
instead of dissolving filter and drying why not recrystallize it?
like get a liter of water to boil add 240g till it dissolved completly, try filtering hot(if you see undissolved contams) and let cool down as much as
you can.
[Edited on 17-3-2025 by fx-991ex]
[Edited on 17-3-2025 by fx-991ex]
I would but the solubility doesn't change that much with temperature for potassium sulfate.
100 deg C 24g / 0 deg C 7.4gfx-991ex - 17-3-2025 at 12:55
instead of dissolving filter and drying why not recrystallize it?
like get a liter of water to boil add 240g till it dissolved completly, try filtering hot(if you see undissolved contams) and let cool down as much as
you can.
[Edited on 17-3-2025 by fx-991ex]
[Edited on 17-3-2025 by fx-991ex]
I would but the solubility doesn't change that much with temperature for potassium sulfate.
100 deg C 24g / 0 deg C 7.4g
thats enough, remove crystals then just re-heat it and evap water till it start precipitating and let it cool you will get another crop, you can do
that repeatedly till almost nothing is left(but contams).
Make sure you cool it till it almost freeze(salt water freeze below 0C so you can probably get it to -10 to -20C, if it freeze just let it warm up a
bit for ice to melt then filter.)
Like let it cool to room temp, then in the refrigerator then into freezer to avoid cooling too fast.
[Edited on 17-3-2025 by fx-991ex]MrDoctor - 18-3-2025 at 00:36
as its totally insoluble in acetone, it might be possible to add acetone to a saturated solution to precipitate it rapidly without having to boil it
down, although idk how miscible acetone would be in this saturated water.
Also, the solubility data for 40% ethanol is less than 1g/100ml
You have an abundance of relatively low purity, cheap material though, so slow, small crops of crystals with wide margins of loss might be desireable
depending on the application.
at the cost of time, it may be possible to apply the hydrothermal method of crystal growth used for copper sulfate here. it amounts to having a tall
container where a saturated solution with excess solid in the bottom is heated, and it precipitates on a nucleation point, usually a crystal, in the
middle between the hot and cold region. solids dissolve and recrystalize slowly, forming huge clean mono-crystals, but i think you can speed the
process up somehow to get faster formation. Depends how pure you want them, and when, id probably do this if i was going to make a catalyst of sorts
but didnt need it for a month.Frodo - 22-5-2025 at 12:33
I have purified some "sulphate of potash" recently, just by dissolving with boiling water, hot filtration and evaporation. Not looking for purity,
just mostly K2SO4. I would like to ultimately end up with potassium metal, though the path to kick off the sulphate polyatomic anion seems obscure..
one intermediate method i read is reacting with heat and carbon in a reducing atmosphere, but the products are either a K carbonate or K sulphide..
depending on where i read! Any ideas..?Chemgineer - 23-5-2025 at 08:39
I suspect the easiest way would be to use a potassium salt with a lower melting point and do molten electrolysis on it.Precipitates - 25-5-2025 at 20:09
There are other possible routes to potassium from potassium salts, that are easier than molten electrolysis, at least typically for the home chemist.
But potassium sulphate is kind of a dead end compound, although members may be able to suggest some things to do with potassium sulphate e.g., perhaps
to produce concentrated sulphuric acid. MrDoctor - 26-5-2025 at 04:01
isnt there a way to electrolyze the bisulfate into the persulfate? im pretty sure i saw something about this as a route for regeneration of spent
oxone.
While no split cell would ever allow you to seperate the potassium and sulfate ions entirely, i think there is enough ionic force that could be
applied to electrolytically form bisulfate from sulfate. from there its usable as a bisulfate, or further electrolysis under different conditions,
persulfate i believe only forms in a stable manner because its insoluble in cold water. persulfate liberates SO2, SO3 and oxygen. at a large enough
scale with with appropriate steps, sulfuric acid could be acquired.
