Experimental Research On Catalytic Oxidation Of S(â…£) By Ferric And Thiobacillus Ferrooxidans In The Acid Solution

Acid rain caused by SO2 from the flue gas is one of the major environmental problems. The desulfurization by a acid solution with ferric and Thiobacillus ferrooxidans , which is a new technology to reduce the sulfur compound, utilizes the properties that T.f can oxidation Fe2+ and the catalytic oxidation of Fe3+. In this paper, the catalytic oxidation of S(Ⅳ) by Fe3+, the oxidation of sulfite by T.f and the desulfurization by the both of Fe3+ and T.f in the acid solution.are studied.Experimental investigations were carried out on the removal of simulated flue gas SO2 using acid ferric ion aqueous solution in a bubbling reactor. The results showed that the mechanism of the desulfrization reaction was supposed as the combination of complexation and catalytic oxidation and free radical reaction,and there was an optimal desulfuration effect when the total ferric ion concentration was 0.13 mol·L-1. The complex in solution was mainly the dimeric hydroxo-ferric ions when the total ferric ion concentration was relatively low (e.g., lower than 0.13 mol·L-1), and under this condition the formation and decomposition of the complex between ferric ion and sulfite was the step for controlling the reaction rate. On the other hand, when the concentration of ferric (Ⅲ) was more than 0.13 mol·L-1, a space baffle effect was formed by big groups when reacted with sulfite and resulted in a decrease in the reaction rate, because the formation of polynuclear complex, such as the poly-hydroxo-ferric (Ⅲ) complex and the sulfite complex of ferric (Ⅲ) iron, etc.Experimental investigations were carried out on oxidizing sulfite by Thiobacillus ferrooxidans without ferric ions. The result shows that Thiobacillus ferrooxidans can oxidize sulfite to form sulfate. And the experimental data fitting shows that the kinetic equation of the oxidation follows the form of Hill function. This is a cell reaction of substrate-inhibition, Ks depends on the concentration of metabolize substrate. The ph value influences the reaction notablely. When the value of pH closes to neutral the reaction faster and a small Ks is obtained. The experimental result may be an evidence for Thiobacillus ferrooxidans can use sulfite as a metabolic substrate of energy. It provides a theoretic base of the removal operation of SO2 from the flue gas with microorganism.According to the properties of the flue gas desulfrization by the solution with ferric and T.f, an airlift reactor of internal circulation was constructed and the major liquid dynamics including liquid circulation rate, liquid mixing time and volumetric oxygen mass transfer coefficient kLa were measured. The experimental results showed that liquid circulation rate, liquid mixing time, gas hold-up and gas-liquid mass transfer coefficient depended strongly on gas superficial velocity in the airlift reactor. In proper range, the increase of gas velocity can improve liquid circulation, mixing and mass transfer in the reactor. The key effect of desulfrization by the solution with ferric and T.f is the ferric ion, and the action of T.f is the oxidation of ferrous ion to ferric ion which has the catalytic oxidation activity. The efficiency of desulfrization is higher than the both of Fe3+ and T.f everyone.