A bituminous coal and a coconut shell activated carbon were oxidized using nitric acid under conditions chosen to preserve their pore structures. The surface chemistry of the carbons was characterized using Boehm titration and thermal analysis. The carbons were then used as hydrogen sulfide adsorbents. The exhausted carbons were washed in order to remove the products of oxidation. The changes in the porous structure, surface pH, total sulfur content, and speciation of sulfur compounds were evaluated using sorption of nitrogen, thermal analysis, acid-base titrations, and ion chromatography. It was found that the presence of a trace amount of carbonates in coal-based carbon dramatically affects the mechanism of hydrogen sulfide immobilization. As a result of this, unreactive, insoluble, and bulky sulfur polymer which hinders the wash out of the deposits is formed. On the other hand, moderately oxidized samples; despite their lower H2S removal capacity, favor the formation of soluble sulfur oxides which are washed out as sulfuric acid. The H2S breakthrough capacity tests on regenerated samples revealed more than 30% recovery in their capability to effectively remove hydrogen sulfide.