Effect of iron and sulfur on thermal regeneration of GAC

Regeneration of spent granular activated carbon (GAC) can be affected by inorganics that have accumulated by ion exchange on specific GAC sites, precipitation, or adsorption of metal-organic complexes. The authors found iron (Fe) in several spent GAC samples. Sulfur (S) always appeared in these GAC samples as well. Although Fe catalyzes the gasification of GAC to oxides of carbon, Fe catalysis of GAC gasification experienced dramatic inhibition by S at concentrations as low as 100-300 mg S/kg GAC (0.01-0.03 percent). When S was reduced to 20 mg S/kg GAC, the Fe at I percent loading became a strong catalyst. Because S is usually present in spent GACs at concentrations that inhibit catalysis, thermal regenerations behaved essentially the same whether Fe was present or absent.