Abstract: To reveal the migration characteristics of key ions and heavy metals during flash evaporation concentration of desulfurization wastewater, a rotary evaporation experimental setup was employed. The variations in pH, total dissolved solids (TDS), Cl^-, NH⁺₄, Hg, and other key ions and heavy metals, as well as the characteristics of evaporated crystalline products, were investigated under different temperatures and concentration ratios. Results show that with the increasing concentration ratio, the pH of the concentrate decreases while TDS content increases at all evaporation temperatures. During evaporation and concentration, NH⁺₄ and Hg partially migrate to the gas phase, whereas Cl^- migration to the gas phase is negligible. After 10-fold concentration, Cl^- and NH⁺₄ remain predominantly enriched in the concentrate, while Hg is mainly enriched in the condensate. The crystalline products exhibit in sheet structure, with CaSO₄ as the main component and minor NaCl crystals.