3 years ago

Radiolytic Dissolution of Calcite under Gamma and Helium Ion Irradiation

Radiolytic Dissolution of Calcite under Gamma and Helium Ion Irradiation
Guillaume Blain, Véronique Baty, Massoud Fattahi, Amaury Costagliola, Ferid Haddad, Johan Vandenborre
Samples of calcite have been irradiated using both the 60.7 MeV helium ion beam of the ARRONAX (Nantes, France) cyclotron and 661.7 keV gamma radiations. The irradiation of calcite pellets results mainly in radiolytically generated gas (H2, CO2). The presence of superficial water during the calcite irradiation in a humid atmosphere is a key factor for the production of radiolysis gases. Besides, the irradiation of calcite–water biphasic media was performed. The gas released after these irradiations is quantified. No significant amount of CO2 has been detected, whereas carbonate ions act as OH scavengers, thus inducing an increase of H2 production. The amount of hydrogen peroxide created confirms this scavenging mechanism. Finally, ionic chromatography experiments with irradiated solutions allow us to quantify the organic anions (formate HCOO, acetate CH3COO, propionate CH3-CH2COO, and oxalate C2O42–) formed by calcite and/or carbonate ion radiolysis and study the variation of calcium carbonate solubility under irradiation. Formate and acetate ions are formed at low irradiation doses, whereas oxalate is favored at high irradiation doses. The increase of calcium ions in solution during the irradiation of calcite–water media indicates that calcite is progressively dissolved during the irradiation. The main difference between calcite–water media and carbonate ion solutions is that calcite acts as a carbonate ion supply in the radiolysis mechanisms.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b07299

DOI: 10.1021/acs.jpcc.7b07299

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