Mineralization of sorbed and NAPL-phase hexadecane by catalyzed hydrogen peroxide

The oxidation and mineralization of hexadecane in silica sand slurries was investigated using aggressive Fenton-like reactions [high concentrations of hydrogen peroxide and an iron (II) catalyst]. When spiked with 0.1 mmol kg−1 hexadecane, 56% of the hydrocarbon was sorbed to the silica sand and most of the remaining hexadecane was found as nonaqueous phase liquid (NAPL). Gas-purge methodology documented that hexadecane desorption from the silica sand slurries was negligible over 72 h. Three process variables [hydrogen peroxide concentration, slurry volume and soluble iron (II) amendment] were studied to determine their effects on hexadecane oxidation. A central composite rotatable experimental design was used to determine the most effective oxidation conditions as well as possible interactions between variables. In addition to investigating the oxidation of the parent compound, parallel experiments were conducted using 14C-hexadecane to evaluate its mineralization. The recovery of 14C-CO2 confirmed that under the most effective conditions (high concentrations of hydrogen peroxide and low slurry volumes), 83% of the sorbed and NAPL-phase hexadecane was mineralized to CO2 and H2O. The iron (II) concentration had a negligible effect on parent compound degradation within the range investigated (5 to 25 mM) but was a significant variable in promoting the mineralization of hexadecane. The results show that under aggressive Fenton-like conditions, even a highly hydrophobic compound that is sorbed and in a NAPL-phase can be oxidized to its thermodynamic endpoints.