Environ. Sci. Technol. 2008, 42, 8698–8702
Spatially Resolved Micro-Raman Observation on the Phase Separation of Effloresced Sea Salt Droplets HAN-SHUANG XIAO, JIN-LING DONG, LIANG-YU WANG,* LI-JUN ZHAO, FENG WANG, AND YUN-HONG ZHANG* The Institute of Chemical Physics, Beijing Institute of Technology, Beijing, China 100081
Received April 29, 2008. Revised manuscript received September 3, 2008. Accepted September 23, 2008.
We report on the investigation of the phase separation of individual seawater droplets in the efflorescence processes with the spatially resolved Raman system. Upon decreasing the relative humidity (RH), CaSO4 · 0.5H2O separated out foremost from the droplet at an unexpectedly high RH of ∼90%. Occasionally, CaSO4 · 2H2O substituted for CaSO4 · 0.5H2O crystallizing first at ∼78% RH. Relatively large NaCl solids followed to crystallize at ∼55% RH and led to the great loss of the solution. Then, the KMgCl3 · 6H2O crystallites separated out from the residual solutions,adjacenttoNaClat ∼44%RH.Moreover,ashellstructure of dried sea salt particle was found to form at low RHs, with the NaCl crystals in the core and minor supersaturated solutions covered with MgSO4 gel coating on the surface. Ultimately, the shielded solution partly effloresced into MgSO4 hydrates at very dry state (
