Prediction of nickel mobility in a clayey formation requires accurate knowledge of the mineralogical assemblage

In the perspective of nuclear waste storage, 63 Ni is one of the radio-elements of primary concern. Modeling of its retention in clay formations is usually performed using modeling approaches which consider that only phyllosilicates participate to retention. However, isotopic exchange with stable nickel contained in phases (i.e. minerals and organic matter) from the clay formation may play a role. Thus, a sound understanding and prediction of Ni retention also requires detailed knowledge of Ni distribution amongst the different phases. Importance of such knowledge is reinforced by the fact that the distribution of stable Ni between solution and some reactive phases could be considered as representative of 63 Ni distribution after long-term interaction. The present study aimed at elucidating the relative contributions of fast reversible (e.g. sorption on phyllosilicates) and slowly reversible/irreversible (e.g. isotopic exchange) processes to Ni retention capacities of the CallovianOxfordian clay formation from Bure. To achieve this goal, we combined (i) short and long-term (up to 180 days) 63 Ni batch sorption experiments to determine the contribution of irreversible to total sorption and (ii) chemical and physical methods to determine Ni-bearing phases that may contribute to irreversible sorption through isotopic exchange.