Chemical durability of uraninite precipitated on Navajo sandstone

Batch and sand column experiments were conducted with sandstone and ground water to investigate the oxidation of uraninite. Uraninite and mackinawite precipitated by indigenous bacteria in contaminated ground water from a former uranium mill tailings site near Tuba City, Arizona, USA. Leaching of a sand column containing uraninite and mackinawite by oxygen-saturated uncontaminated ground water from the same site showed that uraninite was slowly dissolved. U(VI) concentration in the effluent of column did not exceed 4μg.L-1. Batch experiments showed that most of the oxygen was consumed by mackinawite oxidation. Hence it is concluded that the oxidation of uraninite is insignificant in the presence of mackinawite. (authors)