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I bought potassium sulfate to be used as a fertilizer. The fertilizer comes in the form of small pebbles 1-2mm in diameter. Wikipedia states that the solubility is around 111g/liter at 20°C.

I tested several concentrations

100g / liter

50g / liter

25g / liter

at room temperature (22° C). After 2 hours there are still solids remaining in the solution. The water here is hard (EC= 0.6ms / cm) which hinders the dissolution. What can I do to improve the solubility of this fertilizer in water apart from heating, using reverse osmosis, grinding the pebbles or vigorous shaking of the solution (which worked) but is very tedious.

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  • $\begingroup$ Did you buy chemically pure (lab grade) potassium sulfate to use as a fertilizer, or did you buy it as fertilizer in the first place? A fertilizer often contains additives such as phosphates that may be less soluble in water. Also, have you tried to warm up the solution? $\endgroup$ – andselisk Dec 9 '19 at 17:33
  • $\begingroup$ The label says potassium sulfate. (K2SO4) I'm using it to blend my fertilizer. It's definitely not lab grade. Warming up the solution will probably work but is impractical as I want to dissolve a large amount. $\endgroup$ – CuriousIndeed Dec 9 '19 at 17:39
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    $\begingroup$ I would try to warm up a little portion to see whether the residue is soluble at all and it's not some stone dust. Also, it might help if you add a photo of the label: there might be some useful information regarding the composition of the fertilizer. $\endgroup$ – andselisk Dec 9 '19 at 17:42
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    $\begingroup$ Shaking does not increase the solubility, it merely speeds up the process of dissolution. $\endgroup$ – FusRoDah Dec 9 '19 at 18:36
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Since you're really asking about speeding dissolution, not increasing solubility, use a mixer; either:

The links are just as examples; you could devise your own mixer.

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    $\begingroup$ An ultrasound probe would help too, but would be expensive $\endgroup$ – Waylander Dec 9 '19 at 21:15
  • $\begingroup$ Actually, inexpensive ultrasonic humidifiers might help, except the beam is focused to a pinpoint. Would it be powerful enough to help if diffused? $\endgroup$ – DrMoishe Pippik Dec 10 '19 at 4:01

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