UO2 dissolution in Boom Clay conditions

Stability constants of U(VI) and U(IV)-humic acid complexes

“…The U(IV) -HA value is particularly important because many possible far-field conditions, such as Boom Clay, are reducing. The solubility of crystalline UO 2 in Boom Clay conditions has been measured by Cachoir et al [4]. The solubility was found to vary between 3 x 10 -8 and 1.5 x 10 -6 mol dm -3 .…”

“…The solubility product approach involved three stages, (i) precipitation and ageing of amorphous U(OH) 4 ,…”

“…The yellow U(VI) solution was reduced to U(IV) and grey/brown amorphous U(OH) 4 precipitated. The precipitates were aged for 2 weeks.…”

“…shows that the dominant uranium(IV) species is U(OH) 4 ; which consequently dominates the A term. The A term was, therefore, calculated for the U 4+ + 4OH -= U(OH) 4 reaction equation using log β = 46, which was further adjusted to 48.5 to take account of the experimental ionic strength (I= 0.2).…”

“…The extract was concentrated using the diethyl-aminoethyl cellulose procedure of Miles et al [5]. The U(IV) constants were obtained by developing an approach based on the 'solubility product' of the solid phase precipitated under alkaline conditions and assumed to be U(OH) 4 (am). The U(VI) constants were obtained by employing the 'classical'…”