CHEMICAL DURABILITY OF URANINITE PRECIPITATED ON NAVAJO SANDSTONE

Batch and sand column experiments were conducted with sandstone and gr ound water to investigate the oxidation of uraninite. Uraninite and ma ckinawite precipitated by indigenous bacteria in contaminated ground w ater from a former uranium mill tailings site near Tuba City, Arizona, USA. Leaching of a sand column containing uraninite and mackinawite b y oxygen-saturated uncontaminated ground water from the same site show ed that uraninite was slowly dissolved. U(VI) concentration in the eff luent of column did not exceed 4 mu g.L-1. Batch experiments showed th at most of the oxygen was consumed by mackinawite oxidation. Hence it is concluded that the oxidation of uraninite is insignificant in the p resence of mackinawite. (C) Academie des sciences/Elsevier, Paris.).