Lead Chamber Process - Chemistry

Chemistry

Sulfur dioxide is generated by burning elemental sulfur or by roasting pyritic ore in a current of air:

S8 + 8 O2 → 8 SO2
3 FeS2 + 8 O2 → Fe3O4 + 6 SO2

Nitrogen oxides are produced by decomposition of niter in the presence of sulfuric acid or hydrolysis of nitrosylsulfuric acid:

2 NaNO3 + H2SO4 → Na2SO4 + H2O + NO + NO2 + O2
2 NOHSO4 + H2O → 2 H2SO4 + NO + NO2

In the reaction chambers, sulfur dioxide and nitrogen dioxide dissolve in the reaction liquor. Nitrogen dioxide is hydrated to produce nitrous acid which then oxidizes the sulfur dioxide to sulfuric acid and nitric oxide. The reactions are not well characterized but it is known that nitrosylsulfuric acid is an intermediate in at least one pathway. The major overall reactions are:

2 NO2 + H2O → HNO2 + HNO3
SO2 (aq) + HNO3 → NOHSO4
NOHSO4 + HNO2 → H2SO4 + NO2 + NO
SO2 (aq) + 2 HNO2 → H2SO4 + 2 NO

Nitric oxide escapes from the reaction liquor and is subsequently reoxidized by molecular oxygen to nitrogen dioxide. This is the overall rate determining step in the process:

2 NO + O2 → 2 NO2

Nitrogen oxides are absorbed and regenerated in the process, and thus serve as a catalyst for the overall reaction:

2 SO2 + 2 H2O + O2 → 2 H2SO4

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