Kinetics study on the degradation of a model naphthenic acid by ethylenediamine-N,N'-disuccinic acid-modified Fenton process

Naphthenic acids (NAs) are reported to be the main species responsible for the oil sands process-affected water (OSPW) toxicity. In this study, the degradation of cyclohexanoic acid (CHA) as a model compound for NAs by an ethylenediamine-N,N'-disuccinic acid (EDDS)-modified Fenton process was investigated at pH 8. Optimum dose for Fe-EDDS (EDDS:Fe = 2:1) was 0.45 mM, and 2.94 mM for hydrogen peroxide (H2O2). The time profiles of the main species in the process were studied, including CHA, H2O2, Fe(II), total Fe, and Fe-EDDS (in the main form of FeIIIEDDS). The second-order rate constant between EDDS and hydroxyl radical (OH) at pH 8 was obtained as 2.48 ± 0.43 × 109 M−1 s−1. OH was proved to be the main species responsible for the CHA degradation, while superoxide radical (O2−) played a minor role. The consecutive addition of H2O2 and Fe-EDDS led to a higher removal of CHA compared to that achieved by adding the reagents at a time. The half-wave potential of FeIII/IIEDDS was measured at pH 7-9. The EDDS-modified Fenton process is a promising alternative to degrade NAs.