Kinetic and mechanistic study of reaction between sulfide and sulfite in aqueous solution

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.