A wet absorption of sulfur dioxide in a batch-type reactor was carried out, using three calcium compounds, namely, CaCO3, CaO, and Ca(OH)(2) as absorbents. Based on Fourier Transform Infrared, X-ray diffraction, and scanning electron microscopy analyses, the different absorbents resulted in the different reaction pathways and mechanisms of crystal formation at the early reaction stage. In particular, the CaSO3 . 1/2H(2)O produced from CaO and Ca(OH)(2) showed spherical aggregates consisting of small subparticles, rather than plate or needle-like crystals, of CaSO4 . 2H(2)O from CaCO3. This might be due to the different solubility of the absorbents in water.