Materials derived from rice husk fly ash were tested as adsorbents of hydrogen sulphide, sulphur dioxide and nitrogen dioxide. Breakthrough experiments were carried out at ambient temperature either in dry or moist air. The second-stage waste obtained in the extraction of silica from fly ash using sodium hydroxide exhibits the better adsorption capacity compared with that of caustic-modified activated carbons. The high performance is related to the presence of residual sodium hydroxide and other metals such as calcium, which react with acidic gases forming corresponding salts. Moreover, a high dispersion of the alkali and alkaline earth metal sites in the mesopores renders the pH of the solution basic, aiding in the dissociation of hydrogen sulphide, thereby facilitating its oxidation. The oxidation of species is also catalyzed by the carbonaceous surface. While in the case of hydrogen sulphide and sulphur dioxide, water helps in acid-base reactions, the opposite effect is found for NO2. Because its reactivity with water is limited, reactive metal species present in small pores are likely screened by water adsorbed at pore entrances, and therefore the adsorption of NO2 on the surface is limited.
Utilization of third-stage waste from a rice production for removal of H2S, NO2 and SO2 from air
ARDESI, Rosario;BOSIO, Alberto;GIANONCELLI, Alessandra;DEPERO, Laura Eleonora
2013-01-01
Abstract
Materials derived from rice husk fly ash were tested as adsorbents of hydrogen sulphide, sulphur dioxide and nitrogen dioxide. Breakthrough experiments were carried out at ambient temperature either in dry or moist air. The second-stage waste obtained in the extraction of silica from fly ash using sodium hydroxide exhibits the better adsorption capacity compared with that of caustic-modified activated carbons. The high performance is related to the presence of residual sodium hydroxide and other metals such as calcium, which react with acidic gases forming corresponding salts. Moreover, a high dispersion of the alkali and alkaline earth metal sites in the mesopores renders the pH of the solution basic, aiding in the dissociation of hydrogen sulphide, thereby facilitating its oxidation. The oxidation of species is also catalyzed by the carbonaceous surface. While in the case of hydrogen sulphide and sulphur dioxide, water helps in acid-base reactions, the opposite effect is found for NO2. Because its reactivity with water is limited, reactive metal species present in small pores are likely screened by water adsorbed at pore entrances, and therefore the adsorption of NO2 on the surface is limited.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
