Abstract: According to the metastable phase diagram of K⁺，Na⁺，Mg²⁺∥Cl^-，SO₄^2--H₂O system at 15 ℃，the isothermal evaporation process of the brine of dissolution mining of the low grade solid potassium deposit from Mahai salt lake in Qinghai province was analyzed，and the enrichment behaviors and precipitation rules of salts from brine in process of evaporation were discovered.Results showed that a process of stage evaporation should be applied；and the compositions of mother liquor in each crystalline pond at terminal point were also given.This work provided theoretical foundation for the comprehensive utilization of Mahai salt lake brine in Qinghai province.

Key words: Mahai salt lake, dissolved brine, phase diagram analysis and computation