[jakfak]

Smee again with the lettuce.
I can get calcium nitrate (from China) extremely cheaply and have a large sack of potassium sulfate on hand.
Using potassium nitrate for hydroponics is much more efficient than other substances with spectator ions, especially when our tap water is so full of these already.
If I mix a saturated solution of calcium nitrate with one of potassium sulfate in a stoichiometric ratio, I will lose most of the calcium and sulfate ions in a precipitate of calcium sulfate.
Unfortunately, the potassium sulfate is not as soluble as I would like.
I'm wondering what would result if I ground up the amount of potassium sulfate required in a large pestle and mortar I have handy and added it to the saturated solution of calcium nitrate while giving it a good seeing to with a blender stick.
Regards,   Jak

[Borek]

Goan read about solubility product

[jakfak]

Goan read about solubility product

Thanks, Borek. I've done this. Not sure what your point is.
If I mix the two saturated solutions, I will get a solution of mostly potassium nitrate with a small amount of calcium sulfate in the large amount of solution (large because the potassium sulfate needs lots to dissolve in). I'm trying to end up with a lesser amount of water in the end mixture (just sufficient to dissolve to saturation the remaining potassium nitrate) so am wondering if a fine powder of potassium sulfate will react with vigorous mixing and not end up as undissolved potassium sulfate particles coated with a precipitate of calcium sulfate. I probably have to try this myself, but I thought I would ask -- someone might have experience here. Regards,   Jak

[Borek]

Do I understand correctly that you are mainly concerned about synthesis of potassium nitrate? I supose final concentration of the solution after calcium sulfate precipitate would be too large for a direct use. If so, I would not worry too much about amount of water used, as you may dry the solution out till you see first crystals of potassium nitrate. At this moment filtrate calcium sulfate and you should be left left with saturated solution of KNO₃. Dilute as required.

[jakfak]

Do I understand correctly that you are mainly concerned about synthesis of potassium nitrate? I supose final concentration of the solution after calcium sulfate precipitate would be too large for a direct use. If so, I would not worry too much about amount of water used, as you may dry the solution out till you see first crystals of potassium nitrate. At this moment filtrate calcium sulfate and you should be left left with saturated solution of KNO₃. Dilute as required.

Thanks again, Borek
Yes potassium nitrate is what I want. I could buy it directly, but it is three times the price for the nitrate ion, and nitric acid is four times $/kg nitrate. Having scads of potassium, and partial to a good brewup, I will buy some ultra cheap calcium nitrate tetra hydrate and condense the required ions as described. Potassium sulfate is however not very soluble, and many litres extra of water will be involved, and evaporation is such a tiresomely slow process.
But I guess this will be a more certain way of getting my potassium nitrate. I will be doing this process with hot water and when I cool the saturated potassium  nitrate, crystallisation will start. I need to know how much is in my nutrient solution, so weighing solids is much more convenient. Do you suspect my idea of adding finely powdered potassium sulfate to the saturated hot calcium nitrate solution will end in a precipitate of potassium sulfate particles with a coating of calcium sulfate on the outside?    Cheers,    Jak

[Borek]

I like the idea of using finely grinded potassium sulfate in not enough water, no idea what will be the outcome. But I doubt calcium sulfate would be tight enough to not allow water getting inside of the CaSO₄ covered crystals - so intuition tells me the process should continue till all potassium is in the solution. I can be wrong.

[jakfak]

I like the idea of using finely grinded potassium sulfate in not enough water, no idea what will be the outcome. But I doubt calcium sulfate would be tight enough to not allow water getting inside of the CaSO₄ covered crystals - so intuition tells me the process should continue till all potassium is in the solution. I can be wrong.

Thanks again, Borek, I will give it a try. I will use excess water only to the extent of using enough to give me a hot, saturated solution of the produced quantity of potassium nitrate. From my Rubber Bible, I see that potassium nitrate is nearly twenty times more soluble in hot water than cold, so cooling my resultant filtrate should get crystallisation well under way.  Cheers,    Jak