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 C2O4
2–) 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.
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