Depth of Fenton-Like Oxidation in Remediation of Surface Soil

A series of soil columns was used to investigate the depth of Fenton-like reactions provided by the surface application of catalyzed hydrogen peroxide. Initial experiments examined the effect of four stabilizers (monobasic potassium phosphate, dibasic potassium phosphate, sodium tripolyphosphate, and silicic acid) on H₂O₂ decomposition and the depth to which H₂O₂ could be detected. The H₂O₂ dynamics along the depth of the column showed that the addition of the most effective stabilizer, monobasic potassium phosphate, increased the depth of the detectable H₂O₂ in the soil by three times the depth in soil columns without stabilization. The oxidation of sorbed hexadecane, a highly hydrophobic compound (log K_ow= 9.07), by Fenton-like reactions focused on the process variables of H₂O₂ concentration, number of H₂O₂ applications, and pH. A single application of 15 M H₂O₂ with pH governed by the buffering of KH₂PO₄ provided maximum hexadecant oxidation. Minimal desorption (<10%) in the soil columns was found in control experiments using deionized water in place of H₂O₂, suggesting that hexadecane oxidation occurred in the sorbed phase. More detailed investigation of the process variables was conducted using central composite rotatable designs. The results showed that a KH₂PO₄ concentration greater than 30 mM provided increased hexadecane oxidation while maintaining minimal H₂O₂ decomposition relative to unstabilized H₂O₂. For higher KH₂PO₄ concentrations (60–75 mM), the central composite results documented greater than 90% hexadecane oxidation in the top 2 cm of the soil column and 20–40% oxidation in the 10–15 cm depths.