Where is the good K2SO4

Where is the good K2SO4? This is a strange thing for many people, and here's the introduction to it:

Potassium sulfate (K2SO4) is a salt composed of sulfate ions and potassium ions, usually colorless or white crystals, granules or powders. No smell, bitter taste. Qualitative hard. The chemistry is not lively. It's stable in the air. The density of 2.66 g/cm3. Melting point is 1069 ℃. The aqueous solution is neutral and the pH at normal temperature is about 7. 1g is soluble in 8.3 ml water, 4ml boiling water, 75ml glycerin, and insoluble in ethanol.

The main purpose is serum protein biochemistry test, kjeldahl nitrogen catalyst, preparation of other potassium salts, fertilizer, drugs, preparation of glass, alum and so on.