Oxidation and/or reduction of manganese species by γ-ray and He2+ particle irradiation in highly concentrated carbonate media

The aim of this study is using He2+ (E=64.5 MeV) and γ radiolysis for initiating and controlling the oxidation/reduction mechanism of Mn in highly concentrated carbonate media (5 mol l−1). For obtaining the best experimental conditions, electrochemistry was performed firstly. Radiolysis was performed; first, reduction of Mn(VII) and second, oxidation of Mn(II), each part was performed under He2+ and γ-ray irradiation. Gγ(-Mn(VII))=1.07×10−7 mol J−1 and GHe2+(-Mn(VII))=3×10−8 mol J−1 that shows higher efficiency for γ radiolysis with dose rate 1000 times less than α one. Gγ(-Mn(VII))/GHe2+(-Mn(VII))=5.6 and Gγ(H2)/GHe2+(H2)=0.5 confirm radical mechanism for radio-oxidation/reduction. Heterogeneity of irradiation plays an important role on hydrolysis. Final product oxidation state was determined by XPS and SEM for Mn solid precipitated after the reduction and oxidation experiments.