Study on the chemical adsorption of gaseous As₂O₃ by ash

Arsenic (As) transformation during flue-gas cooling process determines terminal As emission. In this study, the dominant role of chemical adsorption in gaseous As transformed to ash was confirmed. Dynamic curves of As2O3 adsorption by ash at 500-900 degrees C were obtained. The adsorbed As amount increased linearly with time, far from reaching saturation, and the maximum amount was approximately 10 times the As content in ash collected from power plant dust collectors, indicating that the actual capacity of ash was far higher. Analysis of As form and elemental distribution directly proved that chemical adsorption by ash was mainly through the joint action of Ca and Fe, and its correlation with other components was weak. At 500-900 degrees C, as temperature increased, the amount of As adsorbed by CaO gradually increased, whereas that of Fe2O3 first increased and then decreased. The adsorption product of CaO was stable, whereas certain forms of products of Fe2O3 released at 800 degrees C. Therefore, as temperature increased, the amount of As adsorbed by ash with high Fe content first increased and then decreased, reaching a maximum at 800 degrees C degrees C, whereas that of ash with higher Ca content kept increasing. The strong adsorption capacity of ash with high Ca and Fe contents helps reduce terminal As emission.