The solid−liquid equilibrium of the ternary MgBr 2 −MgSO 4 − H 2 O system at 348.15 K was explored by using the isothermal equilibrium method, intending to realize the comprehensive utilization of the basic magnesium bromide (MgBrOH) waste residue produced in maltol production. It was observed that the phase diagram was composed of four single-salt crystallization regions, four univariate solubility curves, three invariant points saturated with