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+.