Removal of SO 2 with oxygen in the presence of Fe(III)
- PDF / 862,749 Bytes
- 9 Pages / 603.28 x 783.28 pts Page_size
- 19 Downloads / 151 Views
I.
INTRODUCTION
O N E of the major sources of sulfur dioxide emission is smelting operations in nonferrous pyrometallurgical processes. Controlling the emission of this toxic gas has been a very important task for scientists and engineers for many years. The oxidation of sulfur dioxide with ferric ion is an important reaction which is utilized in one of the stack gas desulfurization processes known as the Chiyoda process.l Ferric ion is used as a catalyst for the oxidation of aqueous sulfur dioxide by oxygen in this process. The oxidation of SO2 with Fe(III) presents a very complex mechanism. Fe(III) is acting as a catalyst and is not merely entering into a simple redox reaction. Freiberg reviewed previous works of the oxidation and proposed a reaction mechanism on which his rate equation was based to explain the rate data of the previous studies. The mechanism he proposed involves a series of reactions in which the ferricsulfite complex is oxidized to sulfate by oxygen and reacts with ferric ion to produce ferrous and sulfate ions. Also, the mechanism involves an equilibrium in which the regeneration of ferric ion is possible. Freiberg z derived a rate equation showing that the reaction is second order with respect to SO2 but first order with respect to Fe 3+. Freiberg did not determine the individual rate constants of the reactions involved. The catalytic oxidation of SO2 with Fe 3§ inherently involves a reaction associated with Fe :§ in its mechanism. Tiwari, Kolbe, and Hayden 3 studied the oxidation of ferrous ion with an oxygen-sulfur dioxide mixture. They found that the oxidation proceeds according to the stoichiometric reaction: 2Fe 2§ + SO2 + 02 = 2Fe 3§ + SO42-
[1]
They also found that a maximum oxidation rate was obtained at a temperature between 341 and 345 K. These investigations attributed the reaction mechanism basically to that proposed by Karraker. 4 More recently, Schlitt et al. 5 conducted a study under a system where dissolved SO2 was
oxidized in the presence of 02 and Fe 2+. They found that the effects of temperature and 02 pressure on the oxidation rate of SO2 were such that the oxidation rate increased with increasing the parameters up to certain levels; however, further increases had no impact on the oxidation rate. They proposed the oxidation mechanism of SO2 with Fe 3+ in which SO2 is oxidized by two routes. One involves oxygenation that can be written as: 1
SO2 + HzO + -~-O2 Fe3+> S O 2- + 2H +
[2]
The other involves a ferric oxidation route which is: SO2 + 2Fe 3+ + 2H20 ~
S O ] - + 4H + + 2Fe 2+ [3]
There are many inherent difficulties in resolving the reaction mechanism of the oxidation of SO2 with Fe 3+. The primary difficulty is that since the oxidation is a multi-stage reaction system, a single reaction can not be isolated to verify its course. Another difficulty may be that well established analytical methods are not available to determine concentrations of the intermediate species such as thionate proposed by Karraker 4 and ferric-sulfite complex proposed by Freiberg. 2 Fu
Data Loading...
