The influence of stable element inventory on the migration of radionuclides in the vicinity of a high level nuclear waste repository exemplified for 59 Ni

•Stable element inventory may reduce 59Ni retardation by two orders of magnitude in time.•Individual sorption competition processes do not sum up linearly.•Cu has a potential strong effect on the Ni(II) retardation.•Sorption competition results in reduced retardation of radioactive Ni(II) in bentonite and clay.