REACTION-MECHANISM OF CALCIUM-CATALYZED THERMAL REGENERATION OF SPENT GRANULAR ACTIVATED CARBON

Thermal regenerations were conducted on a spent granular activated carbon (GAC) that had served in a water treatment plant for about four years, and contained 1.8% calcium. Oxidation was conducted in steam, CO2, or steam plus CO2, at 650-950 degrees C. As described earlier, when steam and CO2 were employed together, the regenerated product's pore structure maintained greater micropore volume at high temperatures (>800 degrees C) than at low temperatures (<750 degrees C). The work herein has linked this distinction to differences in reaction rate limitations: at high temperatures, with both oxidants employed together, the water-gas shift reaction (H2O + CO = H-2 + CO2) limited overall rate, whereas at low temperatures, the C(O) gasification step limited overall rate. The CO2 created via the water gas shift reaction served as the primary oxidant. Although steam served only as a secondary oxidant, its presence also facilitated more extensive oxidant transfer to the carbon surface.