The solubilities of the K2O-Nb2O5-H2O ternary salt-water system were studied at 30 ℃ and 80 ℃ by isothermal method
and the corresponding equilibrium diagram was plotted.These results might be used as the basis of crystallizing separation of potassium hexaniobate and KOH involved in the disposal of low-grade refractory niobium-tantalum ore by the KOH sub-molten method in the clean metallurgy process.