In this study, the evaporation and crystallization processes of the desulfurization wastewater droplet with different concentrations of main solutes were analyzed by TGA and DSC methods. The drying crystals were scanned by a scanning electron microscope. The supersolubilities were measured by the laser intensity detecting method. A mathematic model was built to investigate the relationship between the evaporation and crystallization rates and the species and concentrations of the solutes. The results show that, comparing SO4 2– with Cl–, the higher concentration of SO4 2– gives higher evaporation rate (4.75 min of 0.006 mol NaCl, 4.5 min 0.003 mol Na2SO4) and lower crystallization rate (2.2 min of 0.006 mol NaCl, 2.5 min of 0.003 mol Na2SO4). This is because the vapor pressure is higher and the supersolubility is lower when the concentration of SO4 2– is higher. Comparing Mg2+ with Na+, the changing concentration hardly affects the evaporation rate because of similar vapor pressure. The higher concentration of Mg2+ leads to higher crystallization rate (2.1 min of 0.003 mol MgCl2, 2.2 min of 0.006 mol NaCl) due to the lower supersolubility. In the measurements of Ca2+, Mg2+, and Na+, the evaporation durations (around 4.45 min) and crystallization durations (2–2.05 min) are almost the same because of the low concentration solutes. According to the SEM results, the crystallization rate order when adding different ions is Mg2+ > Ca2+ > Na+.

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