Repeated reductive and oxidative treatments of granular activated carbon

Fenton oxidation and reductive treatment solutions were applied to granular activated carbon (GAC) to chemically regenerate the adsorbent. No adsorbate was present on the GAC so physicochemical effects from chemically aggressive regeneration could be distinguished from the potential effects of accumulation of reaction byproducts. Fifteen sequential oxidation treatments with hydrogen peroxide (H_2O2) and fifteen sequential reduction/oxidation treatments with hydroxylamine and H_2O2 on Fe-amended GAC were evaluated. The GAC Iodine number, N₂ Brunauer-Emmett-Teller surface area, microporosity, and total porosity declined with sequential treatments, but meso- and macroporosity essentially remained unchanged. Similar changes in Iodine number, surface area, and pore volume distribution suggest that the effects of treatment are functionally dependent on oxidation and independent of hydroxylamine reduction. An inverse relationship was established between the number of chemical treatments and contaminant (methyl tert-butyl ether, 2-chlorophenol, trichloroethylene) adsorption. Loss in sorptive capacity was attributed to the combined and undifferentiated effects of reductions in microporosity and surface area, alterations in surface chemistry (overabundance of surface oxides), and to a lesser degree, micropore blockage by iron oxides.