K[Sb(OH)6] + 4K2S → K3[SbS4] + 6KOH
Potassium hexahydroxoantimonate(V) react with potassium to sulfide produce potassium tetrathioantimonate(V) and potassium hydroxide. Potassium sulfide - saturated solution. This reaction takes place at a temperature near 0°C.