Mass Transfer and Chemical Oxidation of Naphthalene Particles with Zerovalent Iron Activated Persulfate

The usage of zerovalent iron (ZVI) activated persulfate to induce sulfate radical (SO4-center dot) oxidation of both aqueous and solid phase naphthalene (Nap) was investigated. It was determined that the removal of Nap particles occurred through an indirect route. Specifically, Nap released through dissolution from the pure Nap particles was subsequently oxidized in the aqueous phase by SO4-center dot. Rapid destruction of dissolved Nap created a greater concentration gradient between the solid and aqueous phases. This caused more Nap particles to be dissolved which were then available for the subsequent oxidative destruction of dissolved Nap. The rate constant (k(obs,Nap)) of ZVI activated persulfate degradation of dissolved Nap was determined to be 3.74 min(-1). The overall dissolution mass transfer coefficients (k(L)a) for the Nap particles were determined, 3.0 x 10(-2) min(-1) with initial 10 mg Nap in 40 mL water, and found to be proportional to the quantities of the Nap particles present. The results indicate that the k(obs,Nap) is much greater than the k(L)a. The net result of the dissolution of Nap particles and the destruction of dissolved Nap by oxidation was the removal of Nap particles. Sequential additions of ZVI at a lower concentration to slow down the formation of SO4-center dot can preventthe scavenging of SO4-center dot by ZVI and enhance the removal of Nap particles. The results of the mass balance analysis during the oxidized, aqueous and solid phases of Nap were consistent with experimental observations.