Comment on "Inhibitory effect of dissolved silica on H2O2 decomposition by iron(III) and manganese(IV) oxides: implications for H2O2-based in situ chemical oxidation".
Résumé
The main disadvantage of using iron mineral in Fenton-like reactions is that the decomposition rate of organic contaminants is slower than in classic Fenton reaction using ferrous ions at acidic pH. In order to overcome these drawbacks of the Fenton process, chelating agents have been used in the investigation of Fenton heterogeneous reaction with some Fe-bearing minerals. In this work, the effect of new iron complexing agent, ethylenediamine-N,N'-disuccinic acid (EDDS), on heterogeneous Fenton and photo-Fenton system using goethite as an iron source was tested at circumneutral pH. Batch experiments including adsorption of EDDS and bisphenol A (BPA) on goethite, H(2)O(2) decomposition, dissolved iron measurement, and BPA degradation were conducted. The effects of pH, H(2)O(2) concentration, EDDS concentration, and goethite dose were studied, and the production of hydroxyl radical ((*)OH) was detected. The addition of EDDS inhibited the heterogeneous Fenton degradation of BPA but also the formation of (*)OH. The presence of EDDS decreases the reactivity of goethite toward H(2)O(2) because EDDS adsorbs strongly onto the goethite surface and alters catalytic sites. However, the addition of EDDS can improve the heterogeneous photo-Fenton degradation of BPA through the propagation into homogeneous reaction and formation of photochemically efficient Fe-EDDS complex. The overall effect of EDDS is dependent on the H(2)O(2) and EDDS concentrations and pH value. The high performance observed at pH 6.2 could be explained by the ability of O (2) (*-) to generate Fe(II) species from Fe(III) reduction. Low concentrations of H(2)O(2) (0.1 mM) and EDDS (0.1 mM) were required as optimal conditions for complete BPA removal. These findings regarding the capability of EDDS/goethite system to promote heterogeneous photo-Fenton oxidation have important practical implications for water treatment technologies.