Hf(SO4)2 + K2SO4 + 4H2O → K2[Hf(H2O)2(SO4)3]•2H2O
Hafnium(IV) sulfate react with potassium sulfate and water to produce potassium trisulfatodiaquahafnate(IV) dihydrate. This reaction takes place at a temperature near 0°C in the diluted solution sulfuric acid.