# Generation and Inhibition of SO\({}_{3}\) in Lead Smelting Flue Gas
## 3 Results and Discussion
### Generation of SO\({}_{3}\) in Experimentally Simulated Lead Smelting Flue Gas
#### 3.2.1 The Effect of Reaction Temperature on SO\({}_{3}\) Generation in Experimental Simulations  
Assuming a reaction range of 400-1000 \({}^{\circ}\)C, a total gas flow rate of 200 mL/min was maintained, and the gas-phase composition was set as follows: an O\({}_{2}\) content of 8%, an O\({}_{2}\) content of 15%, and a N\({}_{2}\) content of 77%. The experimental results are shown in Figure 4.  
Figure 4 demonstrates that gas-phase reactions alone yield minimal SO\({}_{3}\) conversion (<1%) across all temperatures. However, lead dust catalysis substantially enhances SO\({}_{3}\) generation, revealing catalytic activity in smelting particulates. Three thermal regimes govern SO\({}_{3}\) formation in lead smelting flue gas:  
1. High-Temperature Zone (>800 \({}^{\circ}\)C): Despite intense molecular collisions, SO\({}_{3}\) decomposition dominates due to unfavorable thermodynamics (\(\Delta\)G > 0). Conversion rates decline sharply above 800 \({}^{\circ}\)C.
2. Medium-Temperature Zone (600-800 \({}^{\circ}\)C): Peak SO\({}_{3}\) conversion occurs here (exceeding 15%), where thermodynamics (\(\Delta\)G < 0) and kinetics align. Catalysts reduce the activation energy, enabling efficient SO\({}_{2}\) oxidation.
3. Low-Temperature Zone (<600 \({}^{\circ}\)C): While thermodynamically favorable (\(\Delta\)G < 0), the low molecular kinetic energy restricts conversion to 4-5%.  
This behavior stems from competing thermodynamic and kinetic drivers. At high temperatures, SO\({}_{3}\) becomes unstable despite rapid molecular motions. Low temperatures maintain thermodynamic favorability but lack the activation energy. The medium-temperature \"window\" uniquely balances both factors.  
Operational variability (\(\pm\)50 \({}^{\circ}\)C) in temperature zones may occur due to the furnace design or feedstock differences. Practical mitigation strategies should focus on the following: (1) rapid gas cooling throughout the 600-800 \({}^{\circ}\)C range to limit SO\({}_{3}\) formation; (2) optimizing catalyst composition at lower effective activation temperatures; and (3) implementing real-time temperature monitoring to account for process fluctuations.  
These findings emphasize the critical role of thermal management in controlling SO\({}_{3}\) emissions. By targeting the medium-temperature regime through operational adjustments and catalytic optimizations, smelters can significantly reduce SO\({}_{3}\) generation while maintaining production efficiency.  
2.2 The Effect of Initial O\({}_{2}\) Content on SO\({}_{3}\) Generation in Experimental Simulations  
This study examined SO\({}_{3}\) formation at 600 \({}^{\circ}\)C with a fixed gas flow rate (200 mL/min) under varying oxygen concentrations (2-40%). Figure 5 reveals the distinct catalytic impacts: Under homogeneous conditions, SO\({}_{3}\) conversion remains minimal (<1%) despite oxygen concentration increases, confirming the limited gas-phase reactivity. Introducing lead dust catalysts dramatically enhances SO\({}_{3}\) yields. The catalytic effect is amplified with oxygen availability, suggesting O\({}_{2}\) participation in both SO\({}_{2}\) oxidation and catalyst activation [26; 27].  
Figure 4: Comparison of SO\({}_{3}\) conversion under homogeneous and heterogeneous conditions at different temperatures.  
Figure 5: SO\({}_{3}\) conversion under different oxygen contents in homogeneous and heterogeneous conditions.  
The two mechanistic regimes that emerge are as follows:  
Low O2 concentration (2-15%): rate limited by oxygen supply (a linear increase);  
High O2 concentration (>15%): plateauing kinetics due to SO2 depletion.  
The results highlight oxygen management as critical for optimizing the catalytic SO3 control. While higher O2 concentrations boost conversion, practical implementation requires balancing oxidation efficiency with operational costs and downstream corrosion risks.