Evaluation of iron catalysts for the Fenton-like remediation of diesel-contaminated soils

The treatment of a diesel-contaminated soil with hydrogen peroxide catalyzed by six iron compounds and by naturally-occurring minerals in which the hydrogen peroxide is stabilized by phosphate was investigated using central composite rotatable experimental designs. Iron (III) perchlorate and iron (III) nitrate with 1.5 M hydrogen peroxide promoted > 99% oxidation of 1000 mg kg(-1) diesel in a Palouse loess soil. Other iron catalysts (iron (III) sulfate, iron (II) sulfate, iron (II) perchlorate) provided 70-80% diesel oxidation under similar reaction conditions. The oxidation reactions were complete within one hour and minimal desorption occurred over 90 h, suggesting that the diesel was oxidized, at least in part, in the sorbed phase. Iron (II) compounds were less effective catalysts than iron (III) species owing to the initial loss of hydrogen peroxide in oxidizing iron (II) to iron (III). The effectiveness of the iron catalysts also correlated with the lowest rates at which their anionic component quenches hydroxyl radicals. Monobasic potassium phosphate was also investigated as a mechanism to enhance the mineral-catalyzed Fenton-like remediation of diesel in the Palouse loess, but resulted in only 40% diesel loss. A central composite design used to investigate the effect of hydrogen peroxide volume on the Fenton-like remediation of the diesel-contaminated Palouse loess showed that a solution sufficient to saturate the soil (3.5 ml (5 g soil)(-1)) provided the optimum volume. Based on these optimization results, the estimated chemical cost for the remediation of 1000 mg kg(-1) diesel in the Palouse loess was $52 (907 kg)(-1) (ton).