Depth of Fenton-Like Oxidation in Remediation of Surface Soil

Abstract

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 Kow= 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.