Promotion effect of carbon on the oxidation of ferrous ions by oxygen in the presence of sodium nitrite

Abstract

The effect of carbons was studied on the course of ferrous sulfate oxidation with oxygen catalyzed by sodium nitrite. Activated coconut carbon AR2, pyrolytic carbon Sibunit and carbon black Elftex 285 were used for this purpose. An enhanced initial rate of oxidation was observed when sodium nitrite catalyst was used in combination with carbon. The Fe II conversion within 30 min was substantially increased by carbon in some cases and decreased in others. The carbon effect on the initial rate and Fe II conversion was controlled by three factors, namely, quantity, surface area and surface functionality of the carbon. Previously used samples showed a higher promotion effect than the original carbons. In agreement with experimental data, the process under study is described by a complex mechanism, in which at least three steps involve participation of carbon: (i) oxidation of the active catalyst in the rate-determining reaction of Fe II nitroso complexes with oxygen, (ii) oxidative transformation of the active catalyst to inactive nitrate ions, (iii) the catalyst regeneration from nitrate ions.