Treatment of Contaminated Soils Using Catalyzed Hydrogen Peroxide

Abstract

The on site and in situ generation of strong oxidants is a potential mechanism for treating refractory organic contaminants in soils. One method of introducing oxidants into soils is the catalyzed decomposition of hydrogen peroxide by iron (II) to form hydroxyl radical, which is commonly known as Fenton’s reagent. Hydroxyl radical has over twice the oxidation potential of chlorine and is 25% stronger than ozone. It reacts with organic compounds in aqueous solutions with rate constants of 107 to 1010 M-1 sec-1. Hydroxyl radical is therefore a strong, nonspecific oxidant capable of widespread destruction of organic compounds. Pentachlorophenol (PCP) was used as a model contaminant in the Fenton’s reagent treatment of soils of varying complexity. Mineralization of PCP in a simple two-phase system (silica sand-Fenton’s reagent) was demonstrated by the removal of the parent compound (PCP) and the total organic carbon associated with the PCP. In addition, stoichiometric quantities of chloride were recovered at the end of the experiment, which also supports mineralization. Fenton’s reagent, when used to treat PCP in natural soils and silica sand, was most effective at pH 2-to-3. In soils of varied organic carbon content, no iron ammendment provided the most efficient reaction (i.e., the greatest ratio of the contaminant degradation rate to the peroxide consumption rate). The efficient reactions occurring with no iron addition in natural soils may have been due to the dissolution of iron minerals which promote catalyzed peroxide decomposition or Fenton-like heterogeneous catalysis occurring on the surfaces of iron minerals.