The reaction between sulfide and sulfite in neutral to weak alkaline aqueou
s solutions was studied by following thiosulfate and sulfite concentrations
using ion chromatography. The thiosulfate formation rate from the reaction
2HS(-) + 4HSO(3)(-) --> 3S(2)O(3)(2-) + 3H(2)O at pH 8 to 9 was found to b
e d[S2O32-]/dt = k(A)[HS-][HSO3-](2), where k(A) = 1.1 x 10(12) exp(-48000/
RT) M-2 s(-1). A mechanism for this reaction has been proposed with disulfi
te (S2O52-) and HSO2- intermediates. The measured rate of sulfite disappear
ance was higher than that calculated from the stoichiometry of the above re
action. This phenomenon is attributed to other reactions, that consume sulf
ite and form other sulfur compounds such as polythionates, polysulfides, an
d elemental sulfur. These reactions mere treated as a single reaction, whos
e rate was found to be (-d[HSO3-]/dt)(B) = k(B)[H+](-0.6)[HS-](0.7)[HSO3-](
1.5), where k(B) = 5 x 10(-5) M-0.6 s(-1) at 20 degrees C. A kinetic model
was established on the basis of the kinetic data obtained in this and a pre
vious work. The experimental data at pH 7 agreed with the model prediction
in a satisfactory manner. The biphasic behavior of thiosulfate is considere
d to be critical in developing a new sulfur-producing flue gas desulfurizat
ion (SP-FGD) process based on sulfur dioxide absorption using sodium sulfid
e solution.