In industrial gas cleaning, which adsorbent is most traditionally used to remove hydrogen sulfide (H2S) from a gaseous stream for odor control and sulfur capture?

Introduction / Context:
Hydrogen sulfide (H2S) is a toxic, corrosive gas with a characteristic rotten-egg odor. In gas purification and odor abatement, choosing the right solid medium for H2S removal is critical for safety, environmental compliance, and protection of downstream equipment.

Given Data / Assumptions:

• The feed is a gaseous stream containing H2S.
• Goal: remove H2S primarily by adsorption/chemisorption on a solid bed.
• Ambient or moderate temperatures typical of dry scrubbing are assumed.

Concept / Approach:
Classical “dry box” purification uses iron-oxide-impregnated media (often called bog iron or iron sponge). H2S reacts with hydrated iron oxides to form iron sulfide, which can be air-regenerated to elemental sulfur. This chemisorption route is robust, simple, and widely used for town gas, biogas polishing, and small natural-gas streams.

Step-by-Step Solution:
Identify removal mechanism: chemisorption of H2S on iron oxide is favored.Select medium: bog iron (iron oxide on wood chips or pellets) provides reactive sites.Reaction pathway (schematic): Fe2O3·H2O + H2S → Fe2S3 + H2O (followed by regeneration with air to form S).Confirm practicality: widely proven at scale with manageable pressure drop and regenerability.

Verification / Alternative check:
Activated carbon can remove H2S effectively when impregnated (e.g., with KOH or KI), but unimpregnated carbon is much less effective for sustained H2S loading. Silica gel and limestone powder are not standard dry H2S adsorbents for gas streams.

Why Other Options Are Wrong:
Silica gel: suited for moisture removal, poor H2S uptake.
Active carbon: effective mainly when chemically impregnated; generic carbon is inferior to bog iron for H2S.
Limestone powder: used in wet scrubbing (slurry) for SO2/H2S neutralization, not as a dry adsorbent.

Common Pitfalls:
Confusing dry chemisorption media with wet alkaline scrubbers; ignoring the need for impregnated grades when specifying activated carbon for H2S.

Final Answer:
bog iron (iron oxide on support)