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This work extends investigations into the development and use of a kinetic model to simulate and improve the iron-catalyzed oxidation of organic compounds using Fenton`s reagent. While a number of recent studies have successfully modeled the kinetics and species behavior in simple Fenton systems, none have extended and applied the model to examine the effect of operating parameters such as pH on treatment performance. The purpose of this work is to investigate the effect of pH in Fenton-based oxidation systems and to use kinetic modeling to gain insight into the reaction mechanism and speciation of the iron catalyst. Laboratory experiments were conducted across a range of starting concentrations of Fe(II) and H2O2 at pHs of 2.5, 3.0, and 4.0, both in the presence and absence of a target organic,formic acid (HCOOH). With minor modifications, the model presented is capable of accurately describing changes in Fe(II) concentrations over a wide range of reaction conditions and, provided account is taken of additional hydroxyl radical scavenging pathways, also accounts for the oxidation of formic acid over extended reaction times at all pHs considered. The use of composite values for rate constants of reactions involving weakly acidic species is shown to be appropriate, and analysis of the model reveals the catalytic role iron plays in the oxidation process. Experimental and simulated data at the different pHs highlights the effect the catalytic redox cycling of iron has on the performance and oxidation capacity of the Fenton system.