The reaction kinetics of the Fe(H)-induced catalytic oxidation of S(IV) in a concentration range of 10(-6) M <= [Fe(II)] <= 1 M was studied. The S(IV) catalytic oxidation reaction order for O-2 and HSO3- was found to be 0 and 1 in this iron concentration range. The reaction order toward Fe(II) was 1 for 10(-6) M <= [Fe(II)] <= 10(-4) M, 0 for 10(-4) M < [Fe(II)] <= 10(-2)M, and -0.2 for 10(-2) M <= [Fe(II)] <= 1 M. At 30-50 degrees C the activation energy values were low but increased after an increase in the ionic strength. The ionic strength had a negative influence on the reaction rate constant in the iron concentration range. By analyzing the radical mechanisms and reaction kinetic results, a simplified model for the Fe(II)-induced catalytic oxidation of S(IV), which enables a better analysis and elucidation of the experimental results, is proposed.