Ionization by electron beam of aqueous solutions of naphthalenesulfonate, benzenesulfonate and by-products

This research belongs to the study of the ionization of aqueous solutions by electron beam (E.B.) as an advanced oxidation process for water treatment. The hydroxyl radical (^.OH) and hydrated electron (e_aq^-) are the two major active species produced from the ionization of aqueous solutions by high energy electron beam. It has been shown that the generation of additional radicals such as the sulfate radical (SO₄^.-) and hydroxyl radical from the reaction of persulfate ion (S₂O₈^--) or hydrogen peroxide (H₂O₂) with the hydrated electron, improved the efficiency of this process towards the degradation and mineralization of organic pollutants in aqueous solution. In the present work, the degradation and mineralization of naphthalenesulfonate, benzenesulfonate and gallic acid were studied by electron beam irradiation alone and coupled with oxidants (S₂O₈^--, H₂O₂). In the absence of oxidant, an absorbed dose of 1.5 kGy leads to total elimination of these pollutants. The presence of added oxidants usually reduces the radiation dose required. In addition, increasing oxidant concentration or applied dose had a beneficial effect towards the organic carbon removal. It was found that coupling E.B./S₂O₈^-- has more suitable than E.B./H₂O₂ even in the presence of inorganic constituents. The results also highlighted the importance of dissolved oxygen in the system when mineralization is aimed. For each of the molecules studied, oxidation by-products resulting from hydroxylation and aromatic ring opening were identified. (author)