The effects of metals on thermal regeneration of granular activated carbon

The goal of this research was to explore how accumulated metals on granular activated carbon (GAC) affected thermal regeneration, and to determine whether thermal regeneration could restore the spent GAC's virgin adsorption capacity, despite the metals.Calcium and iron accumulated in many of the spent GACs that the author evaluated. In order to isolate which of these metals catalytically accelerated the rate of GAC gasification, each metal was loaded individually onto GAC.Iron catalysis was dramatically inhibited by sulfur, even at sulfur concentrations as low as 300 mg/kg. However, when this sulfur was almost completely extracted to 10 mg/kg, the iron (at 1 percent loading) became a strong catalyst. Calcium, in comparison, catalytically accelerated the rate of GAC gasification dramatically, even in the presence of 0.7 percent sulfur.Thermal regenerations were conducted on a spent GAC that had served in a water treatment plant for about four years, and contained 2 percent calcium. Proper regeneration restored the spent GAC to the same pore structure and surface area as was exhibited by several virgin GACs.When calcium appeared inside the spent GAC, it caused micropores to be converted to small mesopores during thermal oxidation. If the calcium was leached out of the GAC with acid, thermal oxidation increased only the micropore volume. The larger micropores and smaller mesopores are probably the most important for adsorbing the organic compounds found in water supplies. Despite calcium's tendency toward widening micropores, these adverse effects could be overcome via proper control of calcium catalyzed regeneration.Kinetic and thermodynamic experiments of the spent GAC revealed that steam participated in the water-gas shift reaction (H$\sb2$O + CO = H$\sb2$ + CO$\sb2$). The CO$\sb2$ created by this reaction in turn served as the primary oxidant.When both steam and CO$\sb2$ were employed together, the water-gas shift step limited overall reaction rate at high temperatures. However, at low temperatures, the rate of converting solid CO groups to gaseous CO limited overall rate. With both oxidants together, the regenerated product's pore structure appeared better suited for water treatment applications when the water-gas shift reaction limited overall rate, than when the solid CO-to-gaseous CO step limited overall rate. (Abstract shortened by UMI.)U of I OnlyETDs are only available to UIUC Users without author permissio