# Generation and Inhibition of SO\({}_{3}\) in Lead Smelting Flue Gas
## 1 Introduction  
In China, the lead smelting industry mainly relies on the sintering-blast furnace process, followed by the closed-blast furnace smelting process. The smelting flue gas generated by these two processes contains a significant amount of sulfur oxides. In particular, the sintering-blast furnace process can produce approximately 0.5 t of SO\({}_{2}\) gas for every 1 t of crude lead produced [1]. The specific flue gas composition of some process furnace types is shown in Table 1[2]. In addition to the high emissions of sulfur oxides, lead smelting smoke exhibits a high dust concentration. The main components of lead smelting smoke are lead, elemental zinc and zinc compounds, and small amounts of Cd, Se, Te, Tl, Sb, Sn, In, Al, and other elements and compounds [3, 4]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Process**} & \multirow{2}{*}{**Num**} & \multicolumn{5}{c}{**Smoke Components, \%**} \\ \cline{3-6}  & & \(\mathbf{SO_{2}}\) & \(\mathbf{O_{2}}\) & \(\mathbf{CO_{2}}\) & \(\mathbf{CO}\) & \(\mathbf{H_{2}O}\) \\ \hline Direct lead smelting method & 1\# & 10 & 5 & 20 & & 33 \\  & 2\# & 7.5 & 8.4 & 8.4 & & 27.4 \\ \hline Sinter & 3\# & 4.10 & 10.38 & 2.0 & & 14.51 \\ \hline \multirow{2}{*}{ Blast furnace} & 4\# & 0.68 & 2.36 & 16.55 & 6.62 & 3.55 \\  & 5\# & \textless{}1 & 7.81 & 13.56 & 4.56 & \\ \hline \end{tabular}
\end{table} 
Table 1: Smoke composition of different furnace types in lead smelting. The pyrometallurgical processing of lead sulfide ores generates significant sulfur oxide emissions (SO\({}_{\rm x}\)), predominantly sulfur dioxide (SO\({}_{2}\)) with minor quantities of sulfur trioxide (SO\({}_{3}\)) [5; 6; 7]. These byproducts pose substantial operational and environmental challenges. Below the acid dew point temperature, SO\({}_{3}\) reacts with moisture to form corrosive acid mists and micro-droplets that degrade metal surfaces through low-temperature corrosion. Mitigation strategies include maintaining cold-end temperatures above the dew point or employing acid-resistant construction materials [8; 9]. A secondary corrosion mechanism involves SO\({}_{3}\) reacting with alkali metals and iron to form aggressive compounds such as alkali metal iron trisulfate, which contributes to furnace wall degradation [10; 11]. In the environment, unreacted SO\({}_{3}\) escapes as blue plume emissions through flue stacks, primarily through the formation of sulfuric acid (H\({}_{2}\)SO\({}_{4}\)) aerosols. The flue gas cooling profile (1100 \({}^{\circ}\)C to 300 \({}^{\circ}\)C) introduces complex technical constraints for SO\({}_{3}\) mitigation. Effective solutions must achieve three objectives: (1) substantial SO\({}_{3}\) reduction without disrupting smelting operations, (2) compatibility with existing gas treatment infrastructure, and (3) economic viability in construction and operation. Chemical inhibitors present a potential solution but require careful evaluation; they must demonstrate minimal process interference while enabling the recovery of valuable components from heterogeneous flue streams containing gas-phase species, particulate matter, and complex decomposition/oxidation products [12; 13]. Process simplicity and cost-effectiveness remain critical implementation criteria. Fundamentally, SO\({}_{3}\) generation in lead smelting originates from high-temperature oxidation reactions during sulfide ore processing [14; 15]. While SO\({}_{2}\) constitutes the primary sulfur oxide, catalytic conversion mechanisms (particularly in the presence of metal oxides and oxygen) enable partial SO\({}_{2}\) oxidation to SO\({}_{3}\). This conversion intensifies corrosion risks through two pathways: acid condensation below dew points (in the 250-150 \({}^{\circ}\)C range) and high-temperature sulfate salt formation. The resulting corrosion products--whether liquid acid films or solid alkali sulfates--progressively degrade refractory linings and metallic components [16; 17]. The current mitigation approaches present technical tradeoffs.